NIMP| Mihaela BAIBARAC, Author at NIMP

Expertize

Raman scattering, surface enhanced Raman scattering, photoluminescence, IR spectroscopy, surface enhanced IR absorption spectroscopy, polymers, composites, carbon nanoparticles, 2D materials

Projects

1. Recycling of the cathodes, based on carbon nanotubes and conducting polymers, from spent rechargeable Li batteries

Project Type: , Start Date: 2024-03-01 End Date: 2026-02-28

2. Nanocomposites based on recycled cellulose and carbon nanotubes for construction materials with improved fire resistance

Project Type: PED, Start Date: 2022-05-01 End Date: 2024-06-01

3. The development of integrated diagnostic methods for the rapid detection of liver diseases

Project Type: POC 2014-2020, Start Date: 2020-10-11 End Date: 2023-12-31

4. Physico-chemical analysis, nanostructured materials and devices for applications in the pharmaceutical field and medical in Romania

Project Type: POC 2014-2020, Start Date: 2016-09-05 End Date: 2021-09-04

5. 4D printed energy harvesting devices based on innovative printable conductive elastomers

Project Type: MANUNET, Start Date: 2019-06-01 End Date: 2021-05-30

6. Composite materials with graphene oxide to improve performance at the fire action of the elements of constructions and installations for the purpose life protection in case of fire

Project Type: PCCDI, Start Date: 2018-01-01 End Date: 2020-01-01

7. Interinstitutional program for the development of advanced solutions based on econ-nanotechnologies for multifunctional treatments of textile and leather materials

Project Type: PCCDI, Start Date: 2018-01-01 End Date: 2020-01-01

8. Optical properties of SWNTs highly separated in metallic (98%) and semiconducting (99%) functionalized with conjugated polymers

Project Type: HUMBERT CURIEN-BRANCUSI, Start Date: 2015-01-01 End Date: 2016-12-31

9. One-dimensional composites based on carbon nanotubes and conjugated polymers for applications in energy storage and optoelectronic devices field

Project Type: IDEAS, Start Date: 2011-10-01 End Date: 2016-10-01

10. Implementation in East Europe of new methods of synthesis and functionalization of carbon nanotubes for applications in the energy storage and sensors field

Project Type: SCOPES, Start Date: 2012-01-01 End Date: 2015-03-31

11. Hybrid materials based on carbon nanotubes, heteropolyacids and conducting polymers for applications in energy storage field

Project Type: PNII, Start Date: 2008-10-01 End Date: 2011-11-01

12. Optical and electrochemical properties of the carbn nanotubes/polyoxometalates/conducting polymers nanocomposites

Project Type: IDEAS, Start Date: 2007-09-01 End Date: 2010-09-01

13. Organic/inorganic type hybrid nanocomposites, with carbon nanotubes and inorganic semiconductor nanoparticles, for applications in the field of optoelectronics, supercapacitors and sensors.

Project Type: CEEX, Start Date: 2006-12-10 End Date: 2008-12-15

14. Optical and electrical processes in hybrid nano- structured materials produced by the intercalation of the bi-dimensional crystalline structures

Project Type: CEEX, Start Date: 2006-12-10 End Date: 2008-11-30

15. Nano-structured composites of poly N-vinyl carbazole/carbon nanotube for applications in optoelectronics and rechargeable lithium batteries: synthesis, optical, electrical and electrochemical characterisation and applicative demonstrations.

Project Type: CEEX, Start Date: 2005-12-10 End Date: 2008-10-03

16. Nanostructured materials for aplications in sensors and optoelectronic technology

Project Type: , Start Date: 2005-01-01 End Date: 2008-01-01

17. Photoconductivity and photoluminescence processes in poly para-phenylene vinylene/ carbon nanotubes and poly para-phenylene vinylene/oxide nanoparticles type composites

Project Type: CeEx, Start Date: 2005-12-01 End Date: 2007-12-01

Publications

1. Functionalization of Carbon Nanotubes and Graphene Derivatives with Conducting Polymers and Their Applications in Dye-Sensitized Solar Cells and Supercapacitors

Authors: Vaduva, M; Burlanescu, T; Baibarac, M

Published: JAN 2024, POLYMERS, 16, 53, DOI: 10.3390/polym16010053

Recent progress concerning the development of counter electrode material (CE) from the dye-sensitized solar cells (DSSCs) and the electrode material (EM) within supercapacitors is reviewed. From composites based on carbon nanotubes (CNTs) and conducting polymers (CPs) to their biggest competitor, namely composites based on graphene or graphene derivate (GD) and CPs, there are many methods of synthesis that influence the morphology and the functionalization inside the composite, making them valuable candidates for EM both inside DSSCs and in supercapacitors devices. From the combination of CPs with carbon-based materials, such as CNT and graphene or GD, the perfect network is created, and so the charge transfer takes place faster and more easily. Inside composites, between the functional groups of the components, different functionalizations are formed, namely covalent or non-covalent, which further provide the so-called synergic effect. Inside CPs/CNTs, CNTs could play the role of template but could also be wrapped in a CP film due to pi-pi coupling enhancing the composite conductivity. Active in regenerating the redox couple I-/I3-, the weakly bound electrons play a key role inside CPs/GD composites.

2. The influence of the functionalization of polystyrene and graphene oxide composites on the flammability characteristics: modeling with artificial intelligence tools

Authors: Anghel, I; Lisa, C; Curteanu, S; Preda, DM; Sofran, IE; Baia, M; Stroe, M; Paraschiv, M; Baibarac, M; Danciu, V; Cotet, LC; Baia, L

Published: 2024 FEB 3 2024, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, DOI: 10.1007/s10973-023-12869-9

This paper tackles the influence of the functionalization of polystyrene and graphene oxide (GO) composites on the flammability characteristics. A microscale combustion calorimeter (MCC) was used to experimentally determine the heat release capacity (HRC), the specific heat release rate (HRR) and the total heat released (THR). Neural models were designed that correlate the THR with a number of parameters related to the composition and type of flame retardant used, the heating rate, the amount of residue, the HRC, the peak heat release rate (PHRR), the temperature at the peak pyrolysis rate (TPHRR) and the time elapsed until the occurrence of the peak heat release rate (Time). The best results in the training, validation and testing stages were achieved with the neural model with 9 neurons in the input layer, 40 neurons in the hidden layer and one neuron in the output layer. This model was incorporated into an optimization procedure, based on a genetic algorithm, to establish the values of the input parameters used in the training of the neural networks, in order to generate a minimum THR value, which is the output parameter. Since the synthesis of polystyrene particles with different GO concentrations is costly, this research helps to reduce the number of experimental tests and allows to determine the best GO concentration by means of neural models and genetic algorithms.

3. Structural and flame retardancy properties of GO-DOPO-HAK composite

Authors: Mihis, AG; Cotet, LC; Cadar, C; Pop, LC; Todea, M; Rusu, MM; Vulpoi, A; Székely, I; Salagean, CA; Magyari, K; Muresan-Pop, M; Cadar, O; Baia, M; Sofran, IE; Lisa, G; Anghel, I; Baibarac, M; Danciu, V; Baia, L

Published: APR 2023, JOURNAL OF MATERIALS SCIENCE, 58, DOI: 10.1007/s10853-023-08456-w

In the view of the advantages of using P, N, Si and graphene oxide (GO) for the development of flame retardants materials, a multi-structure synergistic composite was synthesized by grafting a novel nitrogen-containing polyhedral oligomeric silsesquioxane (HAK) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) on the surface of GO nanosheet. In the first step, 2-hydroxyethyl acrylate was selectively reacted, and then, HAK was synthetized by the condensation of the aza-Michael addition product with 3-(methacryloyloxy)propyltrimethoxysilane. Finally, the GO obtained by an innovative variant of Marcano-Tour improved exfoliation method was functionalized, first with DOPO, and then with HAK. The structural, morphological and surface properties of GO and GO-DOPO-HAK were investigated by means of XRD, TEM-EDX, FT-IR, Raman, zeta potential and XPS techniques, and it was evidenced the functionalization of GO with DOPO, and then with HAK. The performed microscale combustion calorimetry (MCC) and TG measurements indicated a great potential of the GO-DOPO-HAK as flame retardant material as the obtained residual weight for this sample was found to be the highest one compared to the other investigated samples. MCC analyses further revealed a major decrease in heat release capacity (HRC) and a significant increase in char yield, results that confirm the great potential of GO-DOPO-HAK as flame retardancy material. [GRAPHICS] .

4. Surface species of the nematic mixture E7 obtained by electrochemical insertion of Li+ ions

Authors: Baibarac, M; Zgura, I; Ganea, CP; Frunza, L

Published: APR 2023, EUROPEAN PHYSICAL JOURNAL E, 46, 26, DOI: 10.1140/epje/s10189-023-00280-z

We studied here the influence of Li+ ions on the benzene rings of nematic mixture E7, which is electrochemically adsorbed onto gold electrode surface, to highlight the ability of this mixture for the applications in the field of the rechargeable Li+-ion batteries. Raman spectra support the changes observed in electrochemical analyses while contact angle measurements show that wetting properties of E7 layer were modified after deposition of this mixture onto gold support and the doping with Li+ ions.

5. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO2 Nanowires

Authors: Stroe, M; Burlanescu, T; Paraschiv, M; Lorinczi, A; Matei, E; Ciobanu, R; Baibarac, M

Published: FEB 2023, MATERIALS, 16, 1742, DOI: 10.3390/ma16041742

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO2 nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO2 NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 degrees C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO2 NW sample contains TiO2 tetragonal anatase (A), cubic Ti0.91O (C), and orthorhombic Ti2O3 (OR), as well as monoclinic H2Ti3O7 (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4 degrees and 48 degrees belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4 degrees is explained to be a consequence of the interaction of TiO2 NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765-771 cm(-1) and 3304-3315 cm(-1) from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO2 NW composites, respectively, with TiO2 NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO2 NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm(-1) and 635 cm(-1), which were assigned to the vibrational modes E-g in TiO2 A and E-g in H2Ti3O7 (ITiO2-A/I-H2Ti3O7), respectively, from 3.45 in TiO2 NWs to 0.94-0.96 in the TPU-TiO2 NW composites, which indicates that the adsorption of TPU onto TiO2 NWs involves an exchange reaction of TPU in the presence of TiO2 NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of TixO2x-mn, Ti2O3, and Ti0.91O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380-650 nm, in the presence of TiO2 NW. After increasing the TiO2 NW concentration in the TPU-TiO2 NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the TiO2 NW surface from 12.6 degrees to 32 degrees and 45.9 degrees, respectively, took place.

6. Photocatalytic Activity of the Blends Based on TiO2 Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

Authors: Daescu, M; Chivu, M; Matei, E; Negrila, C; Cramariuc, O; Baibarac, M

Published: JUN 4 2023, MOLECULES, 28, 4546, DOI: 10.3390/molecules28114546

The aim of this work is to highlight the influence of blends based on TiO2 nanoparticles and reduced graphene oxide (RGO) on the photodegradation of acetaminophen (AC). To this end, the catalysts of TiO2/RGO blends with RGO sheet concentrations equal 5, 10, and 20 wt. % were prepared by the solid-state interaction of the two constituents. The preferential adsorption of TiO2 particles onto the RGO sheets' surfaces via the water molecules on the TiO2 particle surface was demonstrated by FTIR spectroscopy. This adsorption process induced an increase in the disordered state of the RGO sheets in the presence of the TiO2 particles, as highlighted by Raman scattering and scanning electron microscopy (SEM). The novelty of this work lies in the demonstration that TiO2/RGO mixtures, obtained by the solid-phase interaction of the two constituents, allow an acetaminophen removal of up to 95.18% after 100 min of UV irradiation. This TiO2/RGO catalyst induced a higher photodegradation efficiency of AC than TiO2 due to the presence of RGO sheets, which acted as a capture agent for the photogenerated electrons of TiO2, hindering the electron-hole recombination. The reaction kinetics of AC aqueous solutions containing TiO2/RGO blends followed a complex first-order kinetic model. Another novelty of this work is the demonstration of the ability of PVC membranes modified with Au nanoparticles to act both as filters for the removal of TiO2/RGO blends after AC photodegradation and as potential SERS supports, which illustrate the vibrational properties of the reused catalyst. The reuse of the TiO2/RGO blends after the first cycle of AC photodegradation indicated their suitable stability during the five cycles of pharmaceutical compound photodegradation.

7. Surface species of the nematic mixture E7 obtained by electrochemical insertion of Li⁺ ions

Authors: Baibarac, M; Zgura, I; Ganea, CP; Frunza, L

Published: APR 2023, EUROPEAN PHYSICAL JOURNAL E, 46, 26, DOI: 10.1140/epje/s10189-023-00280-z

8. Functionalization of Graphene Derivatives with Conducting Polymers and Their Applications in Uric Acid Detection

Authors: Vaduva, M; Baibarac, M; Cramariuc, O

Published: JAN 2023, MOLECULES, 28, 135, DOI: 10.3390/molecules28010135

In this article, we review recent progress concerning the development of sensorial platforms based on graphene derivatives and conducting polymers (CPs), alternatively deposited or co-deposited on the working electrode (usually a glassy carbon electrode; GCE) using a simple potentiostatic method (often cyclic voltammetry; CV), possibly followed by the deposition of metallic nanoparticles (NPs) on the electrode surface (ES). These materials have been successfully used to detect an extended range of biomolecules of clinical interest, such as uric acid (UA), dopamine (DA), ascorbic acid (AA), adenine, guanine, and others. The most common method is electrochemical synthesis. In the composites, which are often combined with metallic NPs, the interaction between the graphene derivatives-including graphene oxide (GO), reduced graphene oxide (RGO), or graphene quantum dots (GQDs)-and the CPs is usually governed by non-covalent functionalization through pi-pi interactions, hydrogen bonds, and van der Waals (VW) forces. The functionalization of GO, RGO, or GQDs with CPs has been shown to speed up electron transfer during the oxidation process, thus improving the electrochemical response of the resulting sensor. The oxidation mechanism behind the electrochemical response of the sensor seems to involve a partial charge transfer (CT) from the analytes to graphene derivatives, due to the overlapping of pi orbitals.

9. Photocatalytic Activity of the Blends Based on TiO₂ Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

Authors: Daescu, M; Chivu, M; Matei, E; Negrila, C; Cramariuc, O; Baibarac, M

Published: JUN 4 2023, MOLECULES, 28, 4546, DOI: 10.3390/molecules28114546

10. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO₂ Nanowires

Authors: Stroe, M; Burlanescu, T; Paraschiv, M; Lorinczi, A; Matei, E; Ciobanu, R; Baibarac, M

Published: FEB 2023, MATERIALS, 16, 1742, DOI: 10.3390/ma16041742

11. Nanohybrid Composites Based on TiO₂ and Single-Walled Carbon Nanohorns as Promising Catalysts for Photodegradation of Amoxicillin

Authors: Cercel, R; Androne, A; Florica, CS; Lorinczi, A; Serbschi, C; Baibarac, M

Published: OCT 2023, MOLECULES, 28, 6958, DOI: 10.3390/molecules28196958

In this work, applications of nanohybrid composites based on titanium dioxide (TiO2) with anatase crystallin phase and single-walled carbon nanohorns (SWCNHs) as promising catalysts for the photodegradation of amoxicillin (AMOX) are reported. In this order, TiO2/SWCNH composites were prepared by the solid-state interaction of the two chemical compounds. The increase in the SWCNH concentration in the TiO2/SWCNH composite mass, from 1 wt.% to 5 wt.% and 10 wt.% induces (i) a change in the relative intensity ratio of the Raman lines located at 145 and 1595 cm(-1), which are attributed to the E-g(1) vibrational mode of TiO2 and the graphitic structure of SWCNHs; and (ii) a gradual increase in the IR band absorbance at 1735 cm(-1) because of the formation of new carboxylic groups on the SWCNHs' surface. The best photocatalytic properties were obtained for the TiO2/SWCNH composite with a SWCNH concentration of 5 wt.%, when approx. 92.4% of AMOX removal was achieved after 90 min of UV irradiation. The TiO2/SWCNH composite is a more efficient catalyst in AMOX photodegradation than TiO2 as a consequence of the SWCNHs' presence, which acts as a capture agent for the photogenerated electrons of TiO2 hindering the electron-hole recombination. The high stability of the TiO2/SWCNH composite with a SWCNH concentration of 5 wt.% is proved by the reusing of the catalyst in six photodegradation cycles of the 98.5 mu M AMOX solution, when the efficiency decreases from 92.4% up to 78%.

12. Three-Dimensional Printable Flexible Piezoelectric Composites with Energy Harvesting Features

Authors: Aradoaei, M; Ciobanu, RC; Schreiner, C; Paulet, M; Caramitu, AR; Pintea, J; Baibarac, M

Published: MAY 31 2023, POLYMERS, 15, 2548, DOI: 10.3390/polym15112548

The purpose of this work was to obtain an elastic composite material from polymer powders (polyurethane and polypropylene) with the addition of BaTiO3 until 35% with tailored dielectric and piezoelectric features. The filament extruded from the composite material was very elastic but had good features to be used for 3D printing applications. It was technically demonstrated that the 3D thermal deposition of composite filament with 35% BaTiO3 was a convenient process for achieving tailored architectures to be used as devices with functionality as piezoelectric sensors. Finally, the functionality of such 3D printable flexible piezoelectric devices with energy harvesting features was demonstrated, which can be used in various biomedical devices (as wearable electronics or intelligent prosthesis), generating enough energy to make such devices completely autonomous only by exploiting body movements at variable low frequencies.

13. Complex Spectroscopy Studies of Nifedipine Photodegradation

Authors: Paraschiv, M; Daescu, M; Bartha, C; Chiricuta, B; Baibarac, M; Ioele, G

Published: NOV 2023, PHARMACEUTICS, 15, 2613, DOI: 10.3390/pharmaceutics15112613

The aim of this work is to highlight the influence of UV light on the hydrolysis reaction of nifedipine (NIF) in the presence of alkaline solutions. In this context, the photodegradation of NIF in the absence of alkaline solutions caused (a) a change in the ratio between the absorbances of three bands in the UV-VIS spectra localized at 224-240 nm, 272-276 nm and 310-340 nm, assigned to the electronic transitions of -COOCH3 groups, -NO2 groups and a heterocycle with six atoms; (b) a red-shift of the photoluminescence (PL) band from 458 nm to 477 nm, simultaneous with an increase in its intensity; (c) a decrease in the ratio of the Raman line intensities, which peaked at 1224 cm-1 and 1649 cm-1, associated with the vibrational modes of -C-C-O in the ester group and C=C stretching; and (d) a decrease in the ratio between the absorbances of the IR bands, which peaked at 1493 cm-1 and 1223 cm-1, associated with the vibrational modes of the -NO2 group and C-N stretching. These changes were explained considering the NIF photodegradation reaction, which leads to the generation of the compound 4-(2-nitrosophenyl)-2.6-dimethyl-3.5-dimethoxy carbonyl pyridine. The interaction of NIF with NaOH in the absence of UV light was demonstrated to induce changes in the vibrational mode of the -C-C-O bond in the ester group. The photodegradation of NIF after its reaction with NaOH induces significant changes highlighted in its (a) UV-VIS spectra, by the shift of the absorption band at 238 nm; (b) PL spectra, by the supraunitary value of the ratio between the emission band intensities at 394-396 nm and 450 nm; (c) Raman spectra, by the change in the ratio between the intensities of the lines that peaked at 1224 cm-1 and 1649 cm-1 from 0.61 to 0.49; and (d) FTIR spectra, by the lowered absorbance of the IR band at 1493 cm-1 assigned to the vibrational mode of the -NO2 group as a result of the generation of the nitroso compound. These changes were explained considering the hydrolysis reaction products of NIF, as the nitroso compound is converted to a lactam-type compound. The photodegradation reaction rate constants of NIF and NIF after interaction with NaOH were also reported. The decrease in thermal stability of NIF samples after interaction with NaOH, as well as of NIF after exposure to UV light compared to NIF prior to exposure to UV light, was demonstrated by thermogravimetry, and the key fragments were confirmed by mass spectrometry.

14. From interface to interphase

Authors: Chipara, M; Baibarac, M; Compagnini, G; Gao, JW

Published: NOV 2023, SURFACES AND INTERFACES, 42, 103435, DOI: 10.1016/j.surfin.2023.103435

A critical brief review of the evolution of the ideas describing the matter, with emphasis on concepts relevant to the journal's goals: surfaces, interfaces, and interphases is presented. The complex relationship between interphase and interface, including the role of the submicron confinement on the physical and chemical properties of matter are analyzed from both theoretical and experimental standpoints. The most important consequences triggered by the recognition of interphases are briefly discussed. Most matter (at a macroscopic scale) is dominated by bulk behavior. The rapid advances in materials and especially the accelerated progress in the synthesis and characterization of submicron materials and associated technologies, labeled as the "nano revolution", revived the research on interfaces and interphases at atomic and molecular scales. It is suggested that interphase ignites a new kind of material, whose "bulk physical features" have been distorted by the submicron confinement. Such an "interphase surface" (for example a drop of gold with a diameter smaller than a few nanometers, or a few layers of graphene), may exist free standing and be stable. These materials, which no more exhibit the bulk properties will be tentatively referred to as "Sutter" ("Sutter" defines an abbreviation that involves both surface and matter concepts). Sutter is characterized by the fact that its physical and chemical properties are controlled by the interphase. It is concluded that Sutter is essentially a submicron phase of the matter, that exhibits size-dependent features. Sutter materials may be embedded in various materials (such as polymers, metals, and alloys) as nanocomposites, thus projecting specific features at the macroscopic scale. Most free standing interphases may be considered as Sutter materials or phases. The interface does not qualify as a Sutter material.

15. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development

Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: FEB 2022, DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, DOI: 10.1080/03639045.2022.2032131

The physico-chemical properties of two anhydrous AZA forms and their interaction with typical pharmaceutical excipients were assessed by applying various methods (such as PXRD, HPLC, TG/DSC, IR, Raman, PL or UV-Vis) in order to highlight new directions for drug formulation. The stability assessment of AZA anhydrous forms I and II was performed in order to determine the risk of degradation of the active ingredient by accidental exposure to nonstandard conditions in the industrial environment, under different storage, transport or processing conditions. The benefits of form II include increased resistance to chemical degradation over a wide range of pH, but further control of storage and processing conditions is necessary to avoid polymorphic transformation into form I. The solubility assessment on the AZA solid forms in different environments that simulate the conditions of the gastrointestinal tract has the advantage of a significantly increased solubility of form II compared with the commercial form I due to the modification of the crystalline structure. In the case of capsules compared to AZA form I or II as powder, an improvement in their solubility was observed, promoted by the presence of one or more excipients in the formulation mixture.

16. The Photoluminescence and Vibrational Properties of Black Phosphorous Sheets Chemically/Electrochemically Functionalized in the Presence of Diphenylamine

Authors: Baibarac, M., Burlanescu, T., Stroe, M., Smaranda, I., & Negrila, C.

Published: NOV 2022, Polymers, 21, 4479, DOI: 10.3390/polym14214479

In this work, new information concerning the optical properties of black phosphorus (BP) sheets chemically/electrochemically functionalized with diphenyl amine (DPA) and its macromolecular compound (poly(diphenylamine) (PDPA)) in the absence/presence of phosphotungstic acid (PTA) is reported. Raman scattering and FTIR spectroscopy studies indicate that the interaction of BP with PTA leads to the elimination of the PxOy layer onto the surface of the BP sheets. In the case of the chemical interaction of BP with DPA, the reaction product corresponds to DPA chemically functionalized BP sheets having an imino-phosphorane (IP) structure. The electrochemical oxidation of BP sheets chemically functionalized with DPA in the presence of PTA leads to an increase in the weight of P-N bonds as a consequence of the generation of PDPA doped with the PTA heteropolyanions, as shown by FTIR spectroscopy and Raman scattering. This process is evidenced by a shift of the Raman line from 362 cm(-1) to 378 cm(-1), assigned to the A(1g) mode. This change was explained by taking into account the compression of the layers containing P atoms, which is induced by PDPA macromolecular chains. The decrease in the intensity of the PL spectra of DPA as well as PDPA, in the presence of BP, indicates that BP acts as a PL quenching agent for these compounds. A preferential orientation of the PDPA doped with the PTA heteropolyanions on the surface of BP sheets is highlighted by the variation of the binding angle of the PDPA on the surface of BP sheets from 44.7 degrees to 39.9 degrees.

17. Degradation of Losartan Potassium Highlighted by Correlated Studies of Photoluminescence, Infrared Absorption Spectroscopy and Dielectric Spectroscopy

Authors: Paraschiv, M; Smaranda, I; Zgura, I; Ganea, P; Chivu, M; Chiricuta, B; Baibarac, M

Published: NOV 2022, PHARMACEUTICS , 14, 2419, DOI: 10.3390/pharmaceutics14112419

In this paper, new results on the degradation of losartan potassium (LP, (1)), in the absence and presence of excipients, which was induced by UV light, the acid character of phosphate buffer solution (PBS) and alkaline medium, respectively, are reported through correlated studies of FTIR spectroscopy, photoluminescence and dielectric spectroscopy. The photoluminescence (PL) spectra of LP and the drug marked under the name Lorista (LO) are characterized by intense emission bands, peaking at 378 nm and 380 nm, respectively, accompanied by low intensity bands with a maximum at similar to 450-460 nm. Photodegradation of LO in a solid state is evidenced by a decrease in the intensity of the PL band at 380 nm, a variation that originates both in the adsorption of water vapors from the air and in the interaction of LP with excipients such as cornstarch, silicon dioxide and cellulose. The LP-water interaction is described, taking into account the main electrical parameters, i.e., complex dielectric permittivity and electrical conductivity. Photodegradation of LP and LO also induces an increase in the intensity of the emission band, at similar to 450-460 nm. The influence of acid and alkaline medium on the LO degradation is analyzed using phosphate buffer (PBS) and NaOH solutions, respectively. In both cases, a decrease in the intensity of the PL band, at 380 nm, is reported. The intensity diminution of the PL spectra of NaOH-reacted LP and LO is the result of the formation of the photodegradation product N-methanolamide-{[2\'-(1H-tetrazol-5-yl)(1,1\'-biphenyl)-4-yl]methyl} (2). This compound was proven by the studies of FTIR spectroscopy achieved on LP and NaOH-reacted LP. The appearance of the IR band at 1740 cm(-1) and the increase in the absorbance in the IR band at 1423 cm(-1) indicate that the photodegradation product (2) contains the C=O and C-OH functional groups.

18. Correlated studies of photoluminescence, vibrational spectroscopy and mass spectrometry concerning the pantoprazole sodium photodegradation

Authors: Baibarac, M; Paraschiv, M; Cercel, R; Smaranda, I; Bartha, C; Trandabat, A

Published: JUN 9 2022, SCIENTIFIC REPORTS, 12, 9515, DOI: 10.1038/s41598-022-13648-6

In this work, new optical evidences concerning the changes induced of the UV light on pantoprazole sodium (PS), in solid state and as aqueous solution, are reported by UV-VIS spectroscopy, photoluminescence (PL), Raman scattering and FTIR spectroscopy. New evidences concerning the products of the PS photodegradation pathways are reported by the correlated studies of thermogravimetry and mass spectrometry. The influence of the excipients and alkaline medium on the PS photodegradation is also studied. New aspects regarding the chemical mechanism of the PS photodegradation in the presence of the water vapor and oxygen form air and the alkaline medium are shown. Our results confirm that the PS photodegradation induced of the water vapors and oxygen from air leads to the generation of 5-difluoromethoxy-3H-benzimidazole-2-thione sodium, 5-difluoromethoxy-3H-benzimidazole sodium, 2-thiol methyl-3, 4-dimethoxypyridine and 2-hydroxymethyl-3, 4-dimethoxypyridine, while in the alkaline medium, compounds of the type of the 2-oxymethyl-3,4-dimethoxypyridine sodium salts are resulted.

19. Photodegradation of Azathioprine in the Presence of Sodium Thiosulfate

Authors: Toulbe, N; Smaranda, I; Negrila, C; Bartha, C; Manta, CM; Baibarac, M

Published: APR 2022, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 23, 3975, DOI: 10.3390/ijms23073975

The effect of sodium thiosulfate (ST) on the photodegradation of azathioprine (AZA) was analyzed by UV-VIS spectroscopy, photoluminescence (PL), FTIR spectroscopy, Raman scattering, X-ray photoelectron (XPS) spectroscopy, thermogravimetry (TG) and mass spectrometry (MS). The PL studies highlighted that as the ST concentration increased from 25 wt.% to 75 wt.% in the AZA:ST mixture, the emission band of AZA gradual downshifted to 553, 542 and 530 nm. The photodegradation process of AZA:ST induced: (i) the emergence of a new band in the 320-400 nm range in the UV-VIS spectra of AZA and (ii) a change in the intensity ratio of the photoluminescence excitation (PLE) bands in the 280-335 and 335-430 nm spectral ranges. These changes suggest the emergence of new compounds during the photo-oxidation reaction of AZA with ST. The invoked photodegradation compounds were confirmed by studies of the Raman scattering, the FTIR spectroscopy and XPS spectroscopy through: (i) the downshift of the IR band of AZA from 1336 cm(-1) to 1331 cm(-1), attributed to N-C-N deformation in the purine ring; (ii) the change in the intensity ratio of the Raman lines peaking at 1305 cm(-1) and 1330 cm(-1) from 3.45 to 4.57, as the weight of ST in the AZA:ST mixture mass increased; and (iii) the emergence of a new band in the XPS O1s spectrum peaking at 531 eV, which was associated with the C=O bond. Through correlated studies of TG-MS, the main key fragments of ST-reacted AZA are reported.

20. New Aspects Concerning the Ampicillin Photodegradation

Authors: Cercel, R; Paraschiv, M; Florica, CS; Daescu, M; Udrescu, A; Ciobanu, RC; Schreiner, C; Baibarac, M

Published: APR 2022, PHARMACEUTICALS, 15, 415, DOI: 10.3390/ph15040415

New aspects concerning the photodegradation (PD) of ampicillin are reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. The exposure of ampicillin in the absence (AM) and in the presence of the excipient (AMP) to UV light leads to an intensity diminution of the photoluminescence excitation (PLE) and photoluminescence (PL) spectra and the emergence of a new IR band at 3450 cm(-1). The photoluminescence studies demonstrate that the AM PD is amplified in the presence of excipients and an alkaline medium. In this last case, the PD process of AM involves the emergence of new compounds, whose presence is highlighted by: (i) the emergence of the isosbestic point at 300 nm in the UV-VIS spectra; (ii) a change in the ratio between the absorbance of IR bands situated in the spectral ranges 1200-1660 and 3250-3450 cm(-1); and (iii) a change in the ratio between the intensities of the Raman lines localized in the spectral ranges 1050-1800 and 2750-3100 cm(-1). A chemical mechanism of the PD processes of AM in an alkaline medium is proposed.

21. Pyrolysis and combustion of polystyrene composites based on graphene oxide functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane

Authors: Anghel, I; Lisa, G; Sofran, IE; Mitroi-Symeonidis, FC; Rusu, MM; Baia, M; Baia, L; Magyari, K; Danciu, V; Cotet, LC; Stroe, M; Baibarac, M

Published: 2021, JOURNAL OF POLYMER ENGINEERING, 41, 626, DOI: 10.1515/polyeng-2021-0071

In this study, polystyrene composites (PS-GO(f)) with variable concentration (0.5; 1; 2; 3; 4; and 5 wt%) of GO(f) were obtained through the in-situ polymerisation of the styrene in the presence of benzoyl peroxide and graphene oxide(GO) functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane(gamma-MPTS). For determining the morphological and structural particularities of polymeric composites transmission electron microscopy (TEM) measurements were performed. The influence of functionalized GO on thermal and combustion properties of polystyrene (PS)-based composite materials was determined through several methods: Thermogravimetry (TGA); derived thermogravimetry (DTG); microscale combustion calorimetry analysis (MCC); and chemical kinetic studies through TGA and MCC determinations at similar heating rates.

22. Optical, Structural, and Dielectric Properties of Composites Based on Thermoplastic Polymers of the Polyolefin and Polyurethane Type and BaTiO3 Nanoparticles

Authors: Baibarac, M; Nila, A; Smaranda, I; Stroe, M; Stingescu, L; Cristea, M; Cercel, RC; Lorinczi, A; Ganea, P; Mercioniu, I; Ciobanu, R; Schreiner, C; Garcia, RG; Bartha, C

Published: FEB 2021, MATERIALS, 14, DOI: 10.3390/ma14040753

In this work, new films containing composite materials based on blends of thermoplastic polymers of the polyurethane (TPU) and polyolefin (TPO) type, in the absence and presence of BaTiO3 nanoparticles (NPs) with the size smaller 100 nm, were prepared. The vibrational properties of the free films depending on the weight ratio of the two thermoplastic polymers were studied. Our results demonstrate that these films are optically active, with strong, broad, and adjustable photoluminescence by varying the amount of TPU. The crystalline structure of BaTiO3 and the influence of thermoplastic polymers on the crystallization process of these inorganic NPs were determined by X-ray diffraction (XRD) studies. The vibrational changes induced in the thermoplastic polymer's matrix of the BaTiO3 NPs were showcased by Raman scattering and FTIR spectroscopy. The incorporation of BaTiO3 NPs in the matrix of thermoplastic elastomers revealed the shift dependence of the photoluminescence (PL) band depending on the BaTiO3 NP concentration, which was capable of covering a wide visible spectral range. The dependencies of the dielectric relaxation phenomena with the weight of BaTiO3 NPs in thermoplastic polymers blends were also demonstrated.

23. Optical Evidence for the Assembly of Sensors Based on Reduced Graphene Oxide and Polydiphenylamine for the Detection of Epidermal Growth Factor Receptor

Authors: Baibarac, M; Daescu, M; Fejer, SN

Published: FEB 2021, COATINGS, 11, DOI: 10.3390/coatings11020258

Using Raman scattering and FTIR spectroscopy, new optical evidence for the assembly of sensors based on reduced graphene oxide (RGO) and polydiphenylamine (PDPA) for the electrochemical detection of the epidermal growth factor receptor (EGFR) are reported. The assembly process of the RGO sheets electrochemical functionalized with PDPA involves the chemical adsorption of 1,4-phenylene diisothiocyanate (PDITC), followed by an incubation with protein G in phosphate buffer (PB) solution and after that the interaction with EGFR antibodies solution. Taking into account the changes reported by Raman scattering and FTIR spectroscopy, a chemical mechanism of the assembling process for this sensor is proposed. The preliminary testing of the electrochemical activity of the sensors based on RGO and PDPA was reported by cyclic voltammetry.

24. Optical Properties of Composites Based on Poly(o-phenylenediamine), Poly(vinylenefluoride) and Double-Wall Carbon Nanotubes

Authors: Baibarac, M; Daescu, M; Matei, E; Nastac, D; Cramariuc, O

Published: AUG 2021, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 22, DOI: 10.3390/ijms22158260

In this work, synthesis and optical properties of a new composite based on poly(o-phenylenediamine) (POPD) fiber like structures, poly(vinylidene fluoride) (PVDF) spheres and double-walled carbon nanotubes (DWNTs) are reported. As increasing the PVDF weight in the mixture of the chemical polymerization reaction of o-phenylenediamine, the presence of the PVDF spheres onto the POPD fibers surface is highlighted by scanning electron microscopy (SEM). The down-shift of the Raman line from 1421 cm(-1) to 1415 cm(-1) proves the covalent functionalization of DWNTs with the POPD-PVDF blends. The changes in the absorbance of the IR bands peaked around 840, 881, 1240 and 1402 cm(-1) indicate hindrance steric effects induced of DWNTs to the POPD fiber like structures and the PVDF spheres, as a consequence of the functionalization process of carbon nanotubes with macromolecular compounds. The presence of the PVDF spheres onto the POPD fiber like structures surface induces a POPD photoluminescence (PL) quenching process. An additional PL quenching process of the POPD-PVDF blends is reported to be induced in the presence of DWNTs. The studies of anisotropic PL highlight a change of the angle of the binding of the PVDF spheres onto the POPD fiber like structures surface from 50.2 degrees to 38 degrees when the carbon nanotubes concentration increases in the POPD-PVDF/DWNTs composites mass up to 2 wt.%.

25. A Special Section on Carbonaceous-Containing Nanomaterials for Multi-Functional Applications

Authors: Baia, M; Baibarac, MA; Valentini, L; Baia, L

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18977

26. Gypsum Composite Boards Incorporating Phase Change Materials: A Review

Authors: Pop, LC; Baibarac, M; Anghel, I; Baia, L

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18957

The purpose of this review is to provide an overview of the available gypsum based composite including various phase change materials employed to increase the thermal energy storage capacity of building materials. A wide range of materials such as n-alkane, saturated fatty acid, fatty acid esters etc are used as phase change materials. Adding carbonaceous material (carbon nanofibers, activated nanocarbon, graphite nanosheets etc.) to augment some properties is also a common practice. In addition, there are presented the methods of obtaining the nano/macro-composites together with some thermal characteristics of the newly prepared materials.

27. Azathioprine Electrochemical Adsorption onto the Reduced Graphene Oxide Sheets in Absence and in the Presence of Polyaniline

Authors: Udrescu, A; Toulbe, N; Matei, E; Baibarac, M

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18974

The azathioprine (AZA) electrochemical adsorption onto the screen-printed carbon electrodes (SPCE) modified with the reduced graphene oxide (RGO) sheets in the absence and in the presence of polyaniline-emeraldine salt (PANI-ES) is reported in this work. Using cyclic voltammetry(CV), in the case of the SPCE modified with the RGO sheets non-functionalized and functionalized with PANI-ES, respectively, an irreversible process at the electrode/electrolyte interface is highlighted to take place. In the case of the SPCE modified with the non-functionalized RGO sheets(SPCE-RGO), the oxidation-reduction processes induce an up-shift of the AZA Raman lines from 856 and 1011 cm(-1) to 863 and 1020 cm(-1), respectively. These variations indicate an AZA adsorption onto the surface of the SPCE modified with the RGO sheets that takes place throughtthe imidazole and pyrimidine cycles of mercaptopurine, when the generation of the pi-pi(*) bonds between the mercaptopurine structure and hexagonal carbon cycles of RGO occurs. The electrochemical functionalization of the RGO sheets with PANI-ES is proved bythe appearance of the Raman lines at 1165, 1332-1371, 1496 and 1585 and 1616 cm(-1). The oxidation-reduction processes induced at the interface of the SPCE modified with PANI-ES functionalized RGO sheets and the electrolyte consisting into a phosphate buffer (PB) and AZA lead to thegeneration of new positive charges onto the PANI macromolecular chain and the adsorption of the drug on the working electrode surface that takes place via the pi-pi(*) bonds established between the benzene/quinoide rings of PANI and the imidazole/ purine cyclesof AZA. These results indicate that the SPCE modified with the PANI-ES functionalized RGO sheets shows potential applications in the field of sensors for AZA detection.

28. The Influence of the Ceramic Nanoparticles on the Thermoplastic Polymers Matrix: Their Structural, Optical, and Conductive Properties

Authors: Smaranda, I; Nila, A; Ganea, P; Daescu, M; Zgura, I; Ciobanu, RC; Trandabat, A; Baibarac, M

Published: AUG 2021, POLYMERS, 13, DOI: 10.3390/polym13162773

This paper prepared composites under the free membranes form that are based on thermoplastic polymers of the type of polyurethane (TPU) and polyolefin (TPO), which are blended in the weight ratio of 2:1, and ceramic nanoparticles (CNs) such as BaSrTiO3 and SrTiO3. The structural, optical, and conductive properties of these new composite materials are reported. The X-ray diffraction studies highlight a cubic crystalline structure of these CNs. The main variations in the vibrational properties of the TPU:TPO blend induced by CNs consist of the following: (i) the increase in the intensity of the Raman line of 1616 cm(-1); (ii) the down-shift of the IR band from 800 to 791 cm(-1); (iii) the change of the ratio between the absorbance of IR bands localized in the spectral range 950-1200 cm(-1); and (iv) the decrease in the absorbance of the IR band from 1221 cm(-1). All these variations were correlated with a preferential adsorption of thermoplastic polymers on the CNs surface. A photoluminescence (PL) quenching process of thermoplastic polymers is demonstrated to occur in the presence of CNs. The anisotropic PL measurements have highlighted a change in the angle of the binding of the TPU:TPO blend, which varies from 23.7 degrees to approximate to 49.3 degrees and approximate to 53.4 degrees, when the concentration of BaSrTiO3 and SrTiO3 CNs, respectively, is changed from 0 to 25 wt. %. Using dielectric spectroscopy, two mechanisms are invoked to take place in the case of the composites based on TPU:TPO blends and CNs, i.e., one regarding the type of the electrical conduction and another specifying the dielectric-dipolar relaxation processes.

29. Mixture of Graphene Oxide/Phosphoric Acid/Melamine as Coating for Improved Fire Protective Performance and Enhancement of Surface Electrical Properties on Wood Chipboard

Authors: Cotet, LC; Cadar, C; Mihis, A; Magyari, K; Muresan-Pop, M; Pop, LC; Mihaila, A; Szekely, I; Dragan, S; Dudescu, M; Zgura, I; Matei, E; Baia, M; Baibarac, M; Anghel, I; Baia, L

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18959

Looking for multifunctional materials, an assessment of the performances both as fire retardant and generator of electrically conductive surfaces for a three component mixture of graphene oxide, phosphoric acid and melamine applied on wood chipboard was performed. A simple approach was used to investigate the intumescent char formation and quantify the loss mass during vertical burning tests, in which the prepared samples were exposed for a certain time interval to a flame generated by an ethanol lamp in ambient conditions. Moreover, mass loss evolution and structural changes that occur during the burning process were more comprehensive investigated by differential thermal and thermogravimetric (DTA/TGA) techniques. By comparing the performances between the wood chipboard samples without any coverage and those covered with one or multiple component mixture, an increase of protection against the fire action was noticed when the three component mixture was used. Also, an improvement of the electrical properties was observed, after flame exposure of the samples covered with multiple layers (i.e., two and three), when the three component mixture was used. Morphological and structural investigations by microscopy (optical and electronic-SEMEDX), X-ray diffraction (XRD) and spectral (Raman, FTIR) methods are described. An assessment of market potential is also discussed.

30. Vibrational and Photoluminescence Properties of Composites Based on Double-Walled Carbon Nanotubes, Poly(o-phenylenediamine) and Poly(ethylene oxide)

Authors: Daescu, M; Oprica, M; Smaranda, I; Matei, E; Nastac, D; Cramariuc, O; Cramariuc, B; Baibarac, M

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18975

Chemical polymerization of o-phenylenediamine (OPD) in the presence of poly(ethylene oxide), double-wall carbon nanotubes (DWNTs) and ferric chloride is carried out in order to obtain composites based on the poly(o-phenylenediamine)-poly(ethylene oxide) (POPD-PEO) fibres covered and interconnected with DWNTs. Vibrational and photoluminescence properties of these composite materials as well as their morphologies are shown by infrared (IR) spectroscopy, Raman scattering, photoluminescence (PL) and scanning electron microscopy (SEM). An adsorption of DWNTs onto the POPD rods surface in the absence and in the presence of. PEO is highlighted by SEM. The vibrational changes reported by Raman scattering and IR spectroscopy prove a covalent functionalization of DWNTs with the macromolecular compound POPD which is doped with FeCl4- T ions. New hydrogen bonds are generated between POPD covalently functionalized DWNTs and hydroxyl groups of PEO according to IR spectroscopic studies. The two macromolecular compounds, POPD and POPD-PEO, show a complex emission band with maxima at 572 and 566 nm, having a shoulder at 667 nm. A significant change in the profile of the PL bands of POPD and POPD-PEO is induced in the DWNTs presence. We show that DWNTs induce (i) a diminution in the POPD PL band intensity peaked between 525-600 nm simultaneous with the increase in the intensity of the PL band situated in the 600-800 nm spectral range and (ii) an enhancement process of the emission band localized in the 475-800 nm spectral range in the case of POPD-PEO.

31. Screen-Printed Carbon Electrodes Modified with Double-Walled Carbon Nanotubes Functionalized with Polypyrrole and Their Electrochemical Processes in the Presence of Folic Acid

Authors: Daescu, M; Baibarac, M; Enculescu, M; Serbschi, C

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18973

In this work, the electrochemical polymerization of pyrrole in the presence of H3PMo12O40 onto the screen-printed carbon electrodes (SPCE) modified with double-walled carbon nanotubes (DWNTs) is reported. The influence of the pyrrole and H3PMo12O40 concentration as well as a scan rate used to recording of cyclic voltammograms that describe the electrochemical synthesis of polypyrrole (PPY) onto the DWNTs surface is assessed. Using scanning electron microscopy (SEM) we demonstrate that the electrosynthesis of PPY doped with H3PMo12O40 heteropolyanions (PPY-PMo12) results in the generation of a globular morphology. Considering the variations induced of DWNTs in the IR and Raman spectra of PPY doped with H3PMo12O40 heteropolyanions, a functionalization process of carbon nanotubes with macromolecular compound is invoked. According to SEM investigations, DWNTs allow the realization of connections between the globular structures of the macromolecular compound. The changes induced of folic acid (FA) during the oxidation-reduction processes at the interface of the DWNTs functionalized with PPY doped with H3PMo12O40 heteropolyanions (SPCE-DWNT/PPY-PMo12) with electrolyte solution are reported.

32. Carbon Xerogel Nanostructures with Integrated Bi and Fe Components for Hydrogen Peroxide and Heavy Metal Detection

Authors: Fort, CI; Rusu, MM; Cotet, LC; Vulpoi, A; Florea, I; Tuseau-Nenez, S; Baia, M; Baibarac, M; Baia, L

Published: JAN 2021, MOLECULES, 26, DOI: 10.3390/molecules26010117

Multifunctional Bi- and Fe-modified carbon xerogel composites (CXBiFe), with different Fe concentrations, were obtained by a resorcinol-formaldehyde sol-gel method, followed by drying in ambient conditions and pyrolysis treatment. The morphological and structural characterization performed by X-ray diffraction (XRD), Raman spectroscopy, N-2 adsorption/desorption porosimetry, scanning electron microscopy (SEM) and scanning/transmission electron microscopy (STEM) analyses, indicates the formation of carbon-based nanocomposites with integrated Bi and Fe oxide nanoparticles. At higher Fe concentrations, Bi-Fe-O interactions lead to the formation of hybrid nanostructures and off-stoichiometric Bi2Fe4O9 mullite-like structures together with an excess of iron oxide nanoparticles. To examine the effect of the Fe content on the electrochemical performance of the CXBiFe composites, the obtained powders were initially dispersed in a chitosan solution and applied on the surface of glassy carbon electrodes. Then, the multifunctional character of the CXBiFe systems is assessed by involving the obtained modified electrodes for the detection of different analytes, such as biomarkers (hydrogen peroxide) and heavy metal ions (i.e., Pb2+). The achieved results indicate a drop in the detection limit for H2O2 as Fe content increases. Even though the current results suggest that the surface modifications of the Bi phase with Fe and O impurities lower Pb2+ detection efficiencies, Pb2+ sensing well below the admitted concentrations for drinkable water is also noticed.

33. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development

Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: OCT 3 2021, DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, 47, DOI: 10.1080/03639045.2022.2032131

34. Anisotropic Photoluminescence of Poly(3-hexyl thiophene) and Their Composites with Single-Walled Carbon Nanotubes Highly Separated in Metallic and Semiconducting Tubes

Authors: Baibarac, M; Arzumanyan, G; Daescu, M; Udrescu, A; Mamatkulov, K

Published: JAN 2021, MOLECULES, 26, DOI: 10.3390/molecules26020294

In this work, the effect of the single-walled carbon nanotubes (SWNTs) as the mixtures of metallic and semiconducting tubes (M + S-SWNTs) as well as highly separated semiconducting (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of poly(3-hexyl thiophene) (P3HT) was reported. Two methods were used to prepare such composites, that is, the chemical interaction of the two constituents and the electrochemical polymerization of the 3-hexyl thiophene onto the rough Au supports modified with carbon nanotubes (CNTs). The measurements of the anisotropic PL of these composites have highlighted a significant diminution of the angle of the binding of the P3HT films electrochemical synthetized onto Au electrodes covered with M + S-SWNTs. This change was attributed to metallic tubes, as was demonstrated using the anisotropic PL measurements carried out on the P3HT/M-SWNTs and P3HT/S-SWNTs composites. Small variations in the angle of the binding were reported in the case of the composites prepared by chemical interaction of the two constituents. The proposed mechanism to explain this behavior took into account the functionalization process of CNTs with P3HT. The experimental arguments of the functionalization process of CNTs with P3HT were shown by the UV-VIS-NIR and FTIR spectroscopy as well as surface-enhanced Raman scattering (SERS). A PL quenching process of P3HT induced both in the presence of S-SWNTs and M-SWNTs was reported, too. This process origins in the various de-excitation pathways which can be developed considering the energy levels diagram of the two constituents of each studied composite.

35. The Influence of UV Light on Photodegradation of Acetylsalicylic Acid

Authors: Daescu, M; Iota, M; Serbschi, C; Ion, AC; Baibarac, M

Published: APR 2021, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 22, DOI: 10.3390/ijms22084046

Photodegradation of the aqueous solutions of acetylsalicylic acid, in the absence (ASA) and the presence of excipients (ASE), is demonstrated by the photoluminescence (PL). A shift of the PL bands from 342 and 338 nm to 358 and 361-397 nm for ASA and ASE in solid state and as aqueous solutions was reported. By exposure of the solution of ASA 0.3 M to UV light, a decrease in the PL band intensity was highlighted. This behavior was revealed for ASA in the presence of phosphate buffer (PB) having the pH equal to 6.4, 7, and 8 or by the interaction with NaOH 0.3 M. A different behavior was reported in the case of ASE. In the presence of PB, an increase in the intensity of the PL band of ASE simultaneously with a change of the ratio between the intensities of the bands at 361-364 and 394-397 nm was highlighted. The differences between PL spectra of ASA and ASE have their origin in the presence of salicylic acid (SAL). The interaction of ASE with NaOH induces a shift of the PL band at 405-407 nm. Arguments for the reaction of ASA with NaOH are shown by Raman scattering and FTIR spectroscopy.

36. Rhodamine B Photodegradation in Aqueous Solutions Containing Nitrogen Doped TiO2 and Carbon Nanotubes Composites

Authors: Udrescu, A; Florica, S; Chivu, M; Mercioniu, I; Matei, E; Baibarac, M

Published: DEC 2021, MOLECULES, 26, DOI: 10.3390/molecules26237237

In this work, new results concerning the potential of mixtures based on nitrogen doped titanium dioxide (TiO2:N) and carbon nanotubes (CNTs) as possible catalyst candidates for the rhodamine B (RhB) UV photodegradation are reported. The RhB photodegradation was evaluated by UV-VIS absorption spectroscopy using samples of TiO2:N and CNTs of the type of single-walled carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs), multi-wall carbon nanotubes (MWNTs), and single-walled carbon nanotubes functionalized with carboxyl groups (SWNT-COOH) having various concentrations of CNTs. The best photocatalytic performance was obtained for sample containing TiO2:N and 2.5 wt.% SWNTs-COOH, when approx. 85% of dye removal was achieved after 300 min. of UV irradiation. The reaction kinetics of RhB aqueous solutions containing TiO2:N/CNT mixtures followed a complex first-order kinetic model. The TiO2:N/CNTs catalyst induced higher photodegradation efficiency of RhB than TiO2:N due to the presence of CNTs, which act as adsorbent and dispersing agent and capture the photogenerated electrons of TiO2:N hindering the electron-hole recombination.

37. Spectroscopic studies on photodegradation of atorvastatin calcium

Authors: Oprica, M; Iota, M; Daescu, M; Fejer, SN; Negrila, C; Baibarac, M

Published: JUL 28 2021, SCIENTIFIC REPORTS, 11, DOI: 10.1038/s41598-021-94693-5

In this work, the photodegradation process of atorvastatin calcium (ATC) is reported as depending on: (1) the presence and the absence of excipients in the solid state; (2) the chemical interaction of ATC with phosphate buffer (PB) having pH equal to 7 and 8; and (3) hydrolysis reaction of ATC in the presence of aqueous solution of NaOH. The novelty of this work consists in the monitoring of the ATC photodegradation by photoluminescence (PL). The exposure of ATC in solid state to UV light induces the photo-oxygenation reactions in the presence of water vapors and oxygen from air. According to the X-ray photoelectron spectroscopic studies, we demonstrate that the photo-oxygenation reaction leads to photodegradation compounds having a high share of C=O bonds compared to ATC before exposure to UV light. Both in the presence of PB and NaOH, the photodegradation process of ATC is highlighted by a significant decrease in the intensity of the PL and photoluminescence excitation (PLE) spectra. According to PLE spectra, the exposure of ATC in the presence of NaOH to UV light leads to the appearance of a new band in the spectral range 340-370 nm, this belonging to the photodegradation products. Arguments concerning the chemical compounds, that resulted in this last case, are shown by Raman scattering and FTIR spectroscopy.

38. Poly(Vinyl Chloride) Spheres Coated with Graphene Oxide Sheets: From Synthesis to Optical Properties and Their Applications as Flame-Retardant Agents

Authors: Baibarac, M; Stingescu, L; Stroe, M; Negrila, C; Matei, E; Cotet, LC; Anghel, I; Sofran, IE; Baia, L

Published: FEB 2021, POLYMERS, 13, DOI: 10.3390/polym13040565

A new method to obtain poly(vinyl chloride) (PVC) spheres, which consists of an interaction between commercial PVC grains and hexyl ethyl cellulose and lauroyl peroxide at a temperature of 60 degrees C, is reported. The addition of the graphene oxide (GO) sheets dispersed in dimethylformamide to the reaction mixture leads to the generation of composites made of PVC spheres coated with GO sheets. Scanning electron microscopy studies have demonstrated that this method allows for the transformation of PVC grains with sizes between 75 and 227 mu m into spheres with sizes varying from 0.7 to 3.5 mu m when the GO concentration in the PVC/GO composite mass increases from 0.5 to 5 wt.%. Our studies of Raman scattering and FTIR spectroscopy highlight a series of changes that indicate the appearance of ClCH=CH-, CH2=CCl-, and/or -CH=CCl- units as a result of PVC partial dehydrogenation. New -COO- and C-OH bonds on the GO sheet surfaces are induced during the preparation of PVC spheres coated with GO sheets. A photoluminescence (PL) band with a maximum at 325 nm is reported to characterize the PVC spheres. A PVC PL quenching process is demonstrated to be induced by the increase in the concentration of the GO sheets in the PVC/GO composite mass. The perspectives regarding the use of this composite as a flame-retardant material are also reported.

39. Photoluminescence as a Complementary Tool for UV-VIS Spectroscopy to Highlight the Photodegradation of Drugs: A Case Study on Melatonin

Authors: Daescu, M; Toulbe, N; Baibarac, M; Mogos, A; Lorinczi, A; Logofatu, C

Published: SEP 2020, MOLECULES, 25, DOI: 10.3390/molecules25173820

In this work, a complementary ultraviolet-visible (UV-VIS) spectroscopy and photoluminescence (PL) study on melatonin (MEL) hydrolysis in the presence of alkaline aqueous solutions and the photodegradation of MEL is reported. The UV-VIS spectrum of MEL is characterized by an absorption band with a peak at 278 nm. This peak shifts to 272 nm simultaneously with an increase in the band absorbance at 329 nm in the presence of an NaOH solution. The isosbestic point localized at 308 nm indicates the generation of some chemical compounds in addition to MEL and NaOH. The MEL PL spectrum is characterized by a band at 365 nm. There is a gradual decrease in the MEL PL intensity as the alkaline solution concentration added at the drug solution is increased. In the case of the MEL samples interacting with an alkaline solution, a new photoluminescence excitation (PLE) band at 335 nm appears when the exposure time to UV light reaches 310 min. A down-shift in the MEL PLE band, from 321 to 311 nm, as a consequence of the presence of excipients, is also shown. These changes are explained in reference to the MEL hydrolytic products.

40. Oxidation of chalcopyrite in air-equilibrated acidic solution: Inhibition with phenacyl derivatives

Authors: Chirita, P; Duinea, MI; Sarbu, LG; Birsa, LM; Baibarac, M; Sava, F; Matei, E

Published: JUL 2020, TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 30, 1942, DOI: 10.1016/S1003-6326(20)65351-1

The effects of 4-(2-hydroxyphenyl)-2-(morpholin-4-yl)-1,3-thiazole (Pr02), 1-(3,5-dibromo-2-hydroxyphenyl)-1-oxoethan-2-yl-N,N-diethyldithiocarbamate (Pr04) and 1-(5-bromo-2-hydroxy-3-methylphenyl)-1-oxoethan-2-yl-O- ethyl xanthate (Pr06) on the aqueous oxidation of chalcopyrite (CuFeS2) in air-equilibrated solution at a temperature of 25 degrees C and a pH of 2.5 were studied. The effects were investigated by using potentiodynamic polarization, electro-chemical impedance spectroscopy (EIS), scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, aqueous batch experiments, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. It is found that the anodic current densities decrease in the order of EtOH Pr02 > Pr04 > Pr06. These results, along with those of the EIS measurements, show that Pr02, Pr04 and Pr06 are effective anodic inhibitors of chalcopyrite aqueous oxidation. Both Raman scattering and FTIR spectroscopy indicate that the elemental sulfur, polysulfide and ferric oxyhydroxides that form on the surface of the mineral are not responsible when it comes to the aqueous oxidation inhibition of chalcopyrite. Quantum chemical calculations show that the adsorption of the tested compounds on the chalcopyrite surface is energetically favorable and so, it can explain the inhibiting effects that were observed.

41. Stimulated Raman scattering and defect-based photoconductivity in mixtures of CdS/TiO2

Authors: Nila, A; Baibarac, M

Published: DEC 14 2020, JOURNAL OF APPLIED PHYSICS, 128, DOI: 10.1063/5.0030301

Stimulated Raman scattering (SRS) is studied in polycrystalline CdS/TiO2 mixtures based on laser power and temperature dependences in Raman investigation. Our Raman analysis reveals several features of nonlinear behavior, such as nonlinear laser power dependencies or high enhancement of Raman lines at a low temperature due to the intrinsic nonlinear nature of CdS, a high light scattering inside the matter, and a trap-based diffusive medium in a grain-boundary system. In particular, building up experimental evidence of conductivity at various temperatures, it is shown that the samples exhibit thermally activated conductivity due to potential local barriers revealed by a considerable fraction of the grain-boundaries in a diffusive medium. Taking into account the defect-based conductivity, a double Poole-Frenkel barrier is established within the grain-boundaries of CdS/TiO2 mixtures, and their barrier energies are investigated considering the temperature-dependent dark current of the grain-boundary model. We thus demonstrate that diffusive medium-based defects in a grain-boundary model makes CdS/TiO2 mixtures behave efficiently in nonlinear processes such as SRS. These features are of particular interest for optical communication technology, and the fundamental application of the SRS effect is semiconductor optical amplifiers.

42. Reusable on-plate immunoprecipitation method with covalently immobilized antibodies on a protein G covered microtiter plate

Authors: Korodi, M; Rakosi, K; Baibarac, M; Fejer, SN

Published: AUG 2020, JOURNAL OF IMMUNOLOGICAL METHODS, 483, DOI: 10.1016/j.jim.2020.112812

Covalent immobilization of antibodies to protein G beads is a basic molecular biology method, although the beads present poor recovery results. Our aim was to reuse the immobilized antibody-protein G complex on a very small scale, therefore we optimized the crosslinking procedure to be used on the wells of a standard 96-well microplate. The method used involves the affinity binding of the antibody to the protein G surface, followed by the immobilization step using different crosslinking reagents, DMP and BS3, quenching the crosslinking reaction, and binding the antibody-specific antigen. By scaling down the procedure, we were able to reuse the anti-EGFR crosslinked wells more than 20 times. This method can be used to perform assays on a wide range of solid supports containing the protein G in an immobilized form, including functionalized nanosensors, for immunoprecipitation, protein and cell lysate purification, target protein enrichment.

43. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of alpha-Lipoic Acid in the Presence of Ag and Au Nanoparticles

Authors: Toulbe, N; Stroe, MS; Daescu, M; Cercel, R; Mogos, A; Dragoman, D; Socol, M; Mercioniu, I; Baibarac, M

Published: NOV 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10112238

The influence of Ag and Au nanoparticles and reduced graphene oxide (RGO) sheets on the photodegradation of alpha-lipoic acid (ALA) was determined by UV-VIS spectroscopy. The ALA photodegradation was explained by considering the affinity of thiol groups for the metallic nanoparticles synthesized in the presence of trisodium citrate. The presence of excipients did not induce further changes when ALA interacts with Ag and Au nanoparticles with sizes of 5 and 10 nm by exposure to UV light. Compared to the Raman spectrum of ALA powder, changes in Raman lines' position and relative intensities when ALA has interacted with films obtained from Au nanoparticles with sizes between 5 and 50 nm were significant. These changes were explained by considering the chemical mechanism of surface-enhanced Raman scattering (SERS) spectroscopy. The photodegradation of ALA that had interacted with metallic nanoparticles was inhibited in the presence of RGO sheets.

44. UV Light Effect on Cationic Photopolymerization of the SU8 Photoresist and Its Composites with Carbon Nanotubes: New Evidence Shown by Photoluminescence Studies

Authors: Baibarac, M; Radu, A.; Cristea, M; Cercel, R; Smaranda, I

Published: APR 2 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 7476, DOI: 10.1021/acs.jpcc.9b11925

The effect of UV light on the cationic photopolymerization of the SU8 negative photoresist is shown by photoluminescence (PL) studies. Our results demonstrate that the cationic photopolymerization reaction of the SU8 photoresist takes place predominantly under the influence of the UVA light. Using UVA light, the influence of carbon nanotubes [of the types single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), multiwalled carbon nanotubes (MWNTs), and SWNTs functionalized with carboxyl groups (SWNTs-COOH)] on the cationic photopolymerization process of the SU8 photoresist is shown by PL studies. The cationic photopolymerization of the SU8 photoresist is monitored by the variations of the two emission bands with maxima at similar to 400-429 nm and 523-556 nm. The increase in the relative intensity of the PL band at similar to 523-556 nm is dependent on (i) the carbon nanotube concentration in the SU8 photoresist matrix; (ii) the type of carbon nanotubes, i.e., SWNTs, DWNTs, and MWNTs; and (iii) the nonfunctionalized and functionalized state of SWNTs. The results reported in this work demonstrate that PL can be used as a complementary method to Raman scattering and IR spectroscopy in the investigation of the cationic photopolymerization reaction of the SU8 negative photoresist. A decrease in the wrapping angle of carbon nanotubes with the SU8 photoresist is highlighted by anisotropic PL studies.

45. Influence of Reduced Graphene Oxide on the Electropolymerization of 5-Amino-1-naphthol and the Interaction of 1,4-Phenylene Diisothiocyanate with the Poly(5-Amino-1-naphtol)/Reduced Graphene Oxide Composite

Authors: Baibarac, M; Daescu, M; Socol, M; Bartha, C; Negrila, C; Fejer, SN

Published: JUN 2020, POLYMERS, 12, DOI: 10.3390/polym12061299

A new composite base on reduced graphene oxide (RGO) and poly(5-amino-1-naphthol) (P5A1N) was synthesized by the electrochemical polymerization of 5-amino-1-naphthol (5A1N) in the presence of HClO(4)and H(4)SiW(12)O(40)onto the surface of Au electrode covered with the RGO sheets. The linear dependence of the current densities of the anodic and cathodic peaks with the scan rate of the potential range (0; 0.8) V vs. SCE, reported during electropolymerization of 5A1N, indicates an electron transfer that is controlled by diffusion. A covalent functionalization of the RGO sheets with P5A1N is argued by: (i) the simultaneous disappearance of the IR band at 1584 cm(-1)and the appearance of the new IR bands at 812, 976 and 3744 cm(-1), and (ii) the appearance of two Raman lines at 738 and 1428 cm(-1). An application of the RGO sheets covalently functionalized with P5A1N is demonstrated to support 1,4-phenylene diisothiocyanate (PDITC), a compound used as a cross-linking agent for various biological applications. The chemical adsorption of PDITC onto the RGO sheets covalently functionalized with P5A1N, which involves the appearance of new functional groups of the type thiourea, was proven by Raman scattering and IR spectroscopy.

46. Photoluminescence as a Valuable Tool in the Optical Characterization of Acetaminophen and the Monitoring of Its Photodegradation Reactions

Authors: Daescu, Monica; Matea, Adelina; Negrila, Catalin; Serbschi, Constantin; Ion, Alina C; Baibarac, Mihaela

Published: Oct 07 2020 , , DOI: 10.3390/molecules25194571

47. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of alpha-Lipoic Acid in the Presence of Ag and Au Nanoparticles

Authors: Toulbe, N'ghaya; Stroe, Malvina S; Daescu, Monica; Cercel, Radu; Mogos, Alin; Dragoman, Daniela; Socol, Marcela; Mercioniu, Ionel; Baibarac, Mihaela

Published: Nov 11 2020, , DOI: 10.3390/nano10112238

48. Optical Properties of Composites Based on Graphene Oxide and Polystyrene

Authors: Stroe, M; Cristea, M; Matei, E; Galatanu, A; Cotet, LC; Pop, LC; Baia, M; Danciu, V; Anghel, I; Baia, L; Baibarac, MA

Published: MAY 2020, MOLECULES, 25, DOI: 10.3390/molecules25102419

In this work, new optical properties of composites based on polystyrene (PS) microspheres and graphene oxide (GO) are reported. The radical polymerization of styrene in the presence of benzoyl peroxide, pentane and GO induces the appearance of new ester groups in the PS macromolecular chains remarked through an increase in the absorbance of the infrared (IR) band at 1743 cm(-1). The decrease in the GO concentration in the PS/GO composites mass from 5 wt.% to 0.5 wt.% induces a diminution in the intensities of the D and G Raman bands of GO simultaneous with a down-shift of the D band from 1351 to 1322 cm(-1). These variations correlated with the covalent functionalization of the GO layers with PS. For the first time, the photoluminescent (PL) properties of PS/GO composites are reported. The PS microspheres are characterized by a PL band at 397 nm. Through increasing the GO sheets' concentration in the PS/GO composite mass from 0.5 wt.% to 5 wt.%, a PS PL quenching process is reported. In addition, in the presence of ultraviolet A (UVA) light, a photo-degradation process of the PS/GO composite having the GO concentration equal to 5 wt.% is demonstrated by the PL studies.

49. Influence of boric acid concentration on the properties of electrodeposited CZTS absorber layers

Authors: Zaki, MY; Nouneh, K; Touhami, ME; Matei, E; Badica, P; Burdusel, M; Negrila, CC; Baibarac, M; Pintilie, L; Galca, AC

Published: MAY 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab6afd

This work involves the synthesis and characterization of Cu2ZnSnS4 (CZTS) layers. The films were prepared on Mo/glass substrates by single-step electrodeposition method followed by sulfurization at 500 degrees C under argon flow. The effect of boric acid concentration on the crystallographic structure, compositional and morphological properties of CZTS films was investigated, with the objective to understand the growth behavior and to enhance the film properties. Cyclic Voltammetry was used in order to estimate the adequate deposition potential for the CZT alloy. The x-ray diffraction analysis showed the formation of the kesterite phase in all the samples. The Raman and x-ray photoelectron spectroscopy studies confirmed the existence of the CZTS phase. The scanning electron microscopy was employed to inspect the films structure. The results indicated that increasing the concentration of boric acid affects the physico-chemical properties of the films.

50. Morphological and structural investigation of the poly(Vinyl chloride) / graphene oxide composites

Authors: Stingescu, L., Cadar, C., Cotet, L.C., Baia, L., Saszet, K., Magyari, K., Mihis, A.G., Fort, C.I., Stroe, M., Matei, E., Nila, A., Anghel, I., Baia, M., Baibarac, M., Danciu, V.

Published: 2020, , DOI: 10.24193/subbchem.2020.3.19

The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 µm to 227 µm. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman glines situated in the spectral ranges 600- 650 and 2850-3000 cm-1 (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp2 to sp3. An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24° to 26° when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed. © 2020, Universitatea Babes-Bolyai, Catedra de Filosofie Sistematica. All rights reserved.

51. Photoluminescence as a Valuable Tool in the Optical Characterization of Acetaminophen and the Monitoring of Its Photodegradation Reactions

Authors: Daescu, M; Matea, A; Negrila, C; Serbschi, C; Ion, AC; Baibarac, M

Published: OCT 2020, MOLECULES, 25, DOI: 10.3390/molecules25194571

In this work, new evidence for the photodegradation reactions of acetaminophen (AC) is reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. Under excitation wavelength of 320 nm, AC shows a PL band in the spectral range of 340-550 nm, whose intensity decreases by exposure to UV light. The chemical interaction of AC with the NaOH solutions, having the concentration ranging between 0.001 and 0.3 M, induces a gradual enhancement of the photoluminescence excitation (PLE) and PL spectra, when the exposure time of samples at the UV light increases until 140 min, as a result of the formation of p-aminophenol and sodium acetate. This behavior is not influenced by the excipients or other active compounds in pharmaceutical products as demonstrated by PLE and PL studies. Experimental arguments for the obtaining of p-aminophenol and sodium acetate, when AC has interacted with NaOH, are shown by Raman scattering and FTIR spectroscopy.

52. MORPHOLOGICAL AND STRUCTURAL INVESTIGATION OF THE POLY(VINYL CHLORIDE)/GRAPHENE OXIDE COMPOSITES

Authors: Stingescu, L; Cadar, C; Cotet, LC; Baia, L; Saszet, K; Magyari, K; Mihis, AG; Fort, CI; Stroe, M; Matei, E; Nila, A; Anghel, I; Baia, M; Baibarac, M; Danciu, V

Published: 2020, STUDIA UNIVERSITATIS BABES-BOLYAI CHEMIA, 65, 258, DOI: 10.24193/subbchem.2020.3.19

The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 mu m to 227 mu m. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman lines situated in the spectral ranges 600-650 and 2850-3000 cm(-1) (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp(2) to sp(3). An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24 degrees to 26 degrees when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed.

53. Nanostructures based detection of pharmaceuticals and other contaminants of emerging concern

Authors: Baibarac, M; Toulbe, N

Published: 2020, ADVANCED NANOSTRUCTURES FOR ENVIRONMENTAL HEALTH, 114, DOI: 10.1016/B978-0-12-815882-1.00003-3

54. The influence of UV light on the azathioprine photodegradation: New evidences by photoluminescence

Authors: Smaranda, I; Nila, A; Manta, CM; Samohvalov, D; Gherca, D; Baibarac, M

Published: SEP 2019, RESULTS IN PHYSICS, 14, DOI: 10.1016/j.rinp.2019.102443

In this work, we report a photodegradation process of azathioprine (AZA) highlighted by correlated studies of photoluminescence (PL) and the UV-VIS and IR absorption spectroscopy. The photodegradation process of AZA is observed by the gradual increasing in the intensity of the PL spectrum recorded under the excitation wavelength of 300 nm. This behaviour is accompanied, in the photoluminescence excitation (PLE) spectra, by a gradual intensity decreasing of the PLE band situated in the 250-320 nm spectral range simultaneous with the intensity increasing of the PLE band localized in the 325-425 nm spectral range. Regardless if the immunosuppressive compound is in the state of powder, tablet or solution, the PL and UV-VIS absorption spectroscopy studies have demonstrated that a photodegradation process under UV light takes place. According to the PL studies carried out in ambient and vacuum condition, the photodegradation process of AZA was demonstrated to be influenced by the oxygen from air. The presence of a new IR band with maximum at 1745 cm(-1) confirms the AZA photodegradation pathway proposed in this work.

55. Novel anhydrous solid-state form of Azathioprine: The assessing of crystal structure by powder X-Ray diffraction, Infrared Absorption Spectroscopy and Raman scattering

Authors: Covaci, OI; Samohvalov, D; Manta, CM; Buhalteanu, L; Barbatu, A; Baibarac, M; Daescu, M; Matea, A; Gherca, D

Published: FEB 15 2019, JOURNAL OF MOLECULAR STRUCTURE, 1178, 710, DOI: 10.1016/j.molstruc.2018.10.065

Azathioprine (Imuran), one of the oldest immunosuppressants, having been used in transplantation since the early 1960's, is known to have only two crystal forms: an anhydrous form and a dihydrate phase. We report the crystal structure of a new anhydrous solid-state form of Azathioprine, determined directly form powder X-Ray diffraction data, employing the direct-space genetic algorithm technique for structure solution, followed by Rietveld refinement. The new anhydrous polymorph is accessible only by a solid-state dehydration process of the readily obtained monohydrate form of Azathioprine, the form for which a crystal structure has not previously been reported. The IR and Raman spectra confirmed the results obtained from X-Ray diffraction indicating the presence of all functional groups involved in intermolecular hydrogen bonding which dictates different arrangement of molecules in the structural packing. (C) 2018 Elsevier B.V. All rights reserved.

56. Properties of textile and leather materials treated with new hybrid SiO2/TiO2/poly(2,2 '-bithiophene) nanocomposites

Authors: Chirila, L; Gaidau, C; Stroe, M; Baibarac, M; Stanca, M; Radulescu, DM; Radulescu, DE; Alexe, CA

Published: 2019, , DOI: 10.35530/IT.070.03.1634

The aim of this study was to investigate the influence of new hybrid composites of TiO2 or SiO2 nanoparticles with poly(2,2'-bithiophene) on 50% cotton/50% polyester fabric and sheep skin leather surface properties. The dispersion-based newly made nanocomposites were analyzed to determine conductivity, particle size, polydispersity and Zeta potential. The finished textile and leather materials were characterized in terms of functionalization treatments performance by: surface resistivity, water contact behaviour, physical-mechanical characteristics and photocatalytic properties. SEM analysis was used to investigate the distribution of nanoparticles on the textile and leather materials surface. Textile materials treated with SiO2/poly(2,2'-bithiophene) nanocomposite with concentration 98 wt% nanoparticles of SiO2 and leather treated with poly SiO2/poly(2,2'-bithiophene) nanocomposite with concentration of 95 wt% nanoparticles of SiO2 showed lower resistivity values, confirming the conductive properties of silica. The higher photodegradation efficiency of functionalized materials has been obtained for textile material treated with poly TiO2/(2,2'-bithiophene) with concentration of 95 wt% nanoparticles of TiO2 and for leather material treated with TiO2/poly(2,2'-bithiophene) with concentration of 98 wt% nanoparticles of TiO2, respectively.

57. Photoluminescence and structural properties of the nitrogen doped TiO2 and the influence of SiO2 and Ag nanoparticles

Authors: Nila, A; Baibarac, M; Udrescu, A; Smaranda, I; Mateescu, A; Mateescu, G; Mereuta, P; Negrila, CC

Published: SEP 18 2019, JOURNAL OF PHYSICS-CONDENSED MATTER, 31, DOI: 10.1088/1361-648X/ab2692

Mixtures of nitrogen-doped titanium dioxide (TiO2:N) with different concentrations of Ag and/or SiO2 particles (0.5, 1 and 2 wt.%) were prepared in solid state by mechanico-chemical interactions. Using UV-VIS spectroscopy, Raman scattering, photoluminescence (PL) and photoluminescence excitation (PLE), the influence of the particles on the host material is evaluated. UV-VIS spectroscopy studies indicate a TiO2:N band gap shift to the UV range with increasing concentrations of SiO2 and Ag particles. PL intensities decrease with increasing concentrations of Ag and/or SiO2 particles in the TiO2:N host matrix, which in turn could effectively restrict the electron and hole recombination. To explain these processes, the different de-excitation ways will be advanced, taking into account the energy levels diagram of TiO2:N/Ag, TiO2:N/SiO2 and TiO2:N/Ag/SiO2 systems. PLE spectra show a gradual decrease in their relative intensities after 165 min of continuous irradiation due to photosensitivity of TiO2:N. The plasmonic effect of Ag particles in the TiO2:N/Ag system is highlighted for the first time by PLE studies.

58. Adsorption of 1,4-phenylene diisothiocyanate onto the graphene oxide sheets functionalized with polydiphenylamine in doped state

Authors: Baibarac, M; Daescu, M; Fejer, SN

Published: AUG 19 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-48314-x

Adsorption processes of 1,4-phenylene diisothiocyanate (PDITC) on two new platforms of the type graphene oxide (GO) sheets and GO layers functionalization with polydiphenylamine (PDPA) are studied by Raman scattering and photoluminescence (PL). An interaction in solid state phase of the two constituents, i.e. PDITC and GO sheets, and a deposition of PDITC onto the PDPA functionalized GO layers, respectively, by the drop casting method, were performed. In the first case, it is shown that interaction in solid state phase of GO with PDITC leads to an intercalation of the organic compound between GO sheets simultaneously with the appearance of the o-thiocarbamate groups, that induces: (i) an enhancement of the PDITC Raman lines situated in the 400-800 and 1000-1300 cm(-1) spectral ranges, (ii) a change in the ratio between the relative intensities of the two Raman lines peaked at 1585 and 1602 cm(-1) accompanied by an up-shift in the case of the second line and (iii) a down-shift of the PDTIC PL band from 502 to 491 nm. Using cyclic voltammetry, an electrochemical functionalization of the GO layers with PDPA doped with H3PMo12O40 heteropolyanions takes place, as demonstrated by Raman scattering and FTIR spectroscopy. The presence of the amine groups in the molecular structure of the doped PDPA functionalized GO layers induces a chemical adsorption of PDITC on this platform, when the thiourea groups appear simultaneously with o-thiocarbamate groups. A chemical mechanism is proposed to take place at the interface of the GO sheets and the doped PDPA functionalized GO layers, respectively, with PDITC.

59. Vibrational and photoluminescence properties of polydiphenylamine doped with silicotungstic acid heteropolyanions and their composites with reduced graphene oxide

Authors: Baibarac, M; Stroe, M; Fejer, SN

Published: MAY 15 2019, JOURNAL OF MOLECULAR STRUCTURE, 1184, 35, DOI: 10.1016/j.molstruc.2019.02.014

In this work, the influence of silicotungstic acid concentration on the diphenylamine (DPA) electro-polymerization in the absence and the presence of reduced graphene oxide (RGO) is studied. The optical properties of the composites based on polydiphenylamine (PDPA) doped with the H4SiW12O40 heteropolyanions and RGO are investigated by Raman scattering, IR absorption spectroscopy and photoluminescence (PL). The presence of RGO induces an up-shift of the oxidation maximum of the DPA, as a result of a covalent functionalization process of graphene sheets with the polymer in the doped state. The deposition of PDPA onto RGO sheets surface is confirmed by the Raman scattering studies. Regardless of the H4SiW12O40 concentration, an up-shift of the IR bands from 910 to 1014 cm(-1) to similar to 920 and 1022 cm(-1) is reported as a consequence of the compensation of positive charges of PDPA macromolecular chains with of the H4SiW12O40 heteropolyanions. An enhancement in the absorbance of the IR bands situated in the spectral range 750-1050 cm(-1) accompanied of a decrease in the relative intensity of the PL bands of PDPA and their composites with RGO, as increasing the H4SiW12O40 concentration, is reported. In the presence of RGO, a change in the PDPA PL spectra profile is also highlighted. (C) 2019 The Authors. Published by Elsevier B.V.

60. Optical properties of folic acid in phosphate buffer solutions: the influence of pH and UV irradiation on the UV-VIS absorption spectra and photoluminescence

Authors: Baibarac, M; Smaranda, I; Nila, A; Serbschi, C

Published: OCT 3 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-50721-z

Using UV-VIS absorption spectroscopy, photoluminescence (PL) and photoluminescence excitation (PLE), the photodegradation reactions of folic acid (FA) in phosphate buffer (PB) solutions were studied. Regardless of the PB solution's pH, the UV-VIS spectra showed a gradual decrease in absorbance at 284 nm simultaneous with an increase in the absorbance of another band in the spectral range of 320-380 nm, which was downshifted under UV irradiation. The relative intensity of the FA PL band, situated in the spectral range 375-600 nm, was dependent on the pH of the PB solution. The FA PL intensity increased as increasing UV irradiation time up to 281 min. in PB solutions with pH values of 6.4 and 5.4. Under an emission wavelength of 500 nm, the position of the FA PLE spectrum changed as the PB solution pH varied from 7 to 5.4 and the irradiation time increased to 317 min. These changes were correlated with the formation of two photodegradation products, namely, pterine-6-carboxylic acid and p-amino-benzoyl-L-glutamic acid. According to UV-VIS spectroscopy and PL and PLE studies, the presence of various excipients in commercial pharmaceutical tablets does not affect the photodegradation of FA in PB solutions. Using IR spectroscopy, new evidences for the formation of the two photodegradation products of FA in PB solutions are shown.

61. Photoconductive Behavior of the PPV/RGO Composites: Insights of Charge Transfer Process

Authors: Ilie, M; Dragoman, D; Baibarac, M

Published: JUL 2019, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 256, DOI: 10.1002/pssb.201800392

The paper deals with a study of composites based on poly(p-phenylenevinylene) (PPV) and reduced graphene oxide (RGO) in terms of photoconductivity and photocurrent (PC) dynamics in charge-discharge cyclic processes. The explanation for the photoconductive behavior is built with the support of DeVore and Onsager theories. Scanning samples in both directions involves charge transport, to and from, available energy states called defect centers. The existence of these centers is confirmed by a decrease in the composite bandgap caused by the RGO localized states which are situated slightly above the first HOMO level in the PPV bandgap. The contribution of RGO to the photoconductive properties of PPV is revealed through a photocurrent value with two orders of magnitude higher than for PPV.

62. Effects of a surfactant on the morphology and photocatalytic properties of polycrystalline Fe-doped ZnO powders

Authors: Diamandescu, L; Cernea, M; Trusca, R; Enculescu, M; Tanase, L; Baibarac, M; Feder, M; Nicoara, AI; Popescu, T

Published: OCT 2018, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 121, 328, DOI: 10.1016/j.jpcs.2018.05.041

In this study, we compared the structural, morphological, and optical properties of a series of Zn1-xFexO (x = 0.00, 0.01, and 0.03) powders synthesized via a hydrothermal route with and without cetyltrimethylammonium bromide as a cationic surfactant. Our results highlighted the critical effects of the surfactant and the iron concentration on the structure, morphology, and optical properties of ZnO. X-ray diffraction, Mossbauer spectroscopy, and X-ray photoelectron spectroscopy analyses indicated the presence of a single phase comprising ZnO with a hexagonal wurtzite structure in all samples and a single oxidation state (+3) for the iron (Fe3+) that replaced Zn2+ in the ZnO structure. Morphological investigations by scanning electron microscopy showed that the surfactant and Fe3+ dopant greatly affected the shape of the ZnO grains, which varied between sheets and rod-like flowers. We found that the morphological and photocatalytic properties of the two series of samples comprising iron-doped ZnO with and without the surfactant were in opposition. We propose a possible growth mechanism for the ZnO polycrystalline grains in the presence of the Fe dopant and/or surfactant. The photocatalytic properties increased for the samples prepared with surfactant as the iron content increased, which was confirmed by ultraviolet-visible reflection measurements. The photocatalytic activities of the samples prepared without surfactant decreased in both the ultraviolet and visible spectral regions as the iron content increased in the samples.

63. Electrochemical Synthesis of the Composites Based on Multi-Wall Carbon Nanotubes and Polypyrrole Doped with Phosphomolybdic Acid Heteropolyanions and Their Vibrational Properties

Authors: Baibarac, M; Serbschi, C; Stroe, M

Published: NOV 2018, INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE, 13, 10526, DOI: 10.20964/2018.11.07

Using cyclic voltammetry, Raman scattering and infrared (IR) spectroscopy, new findings concerning the electrochemical synthesis of composites based on multi-wall carbon nanotubes (MWNTs) and polypyrrole (PPY) doped with H3PMo12O40 heteropolyanions are described in this report. To better understand the electrochemical mechanism behind the synthesis of these composites, the influence of the concentrations of pyrrole and the electrolytes of H3PMo12O40 and H2SO4 on the cyclic voltammogram profile is studied. The formation of PPY doped with H3PMo12O40 heteropolyanions onto the MWNT surface is demonstrated by complementary studies of Raman scattering and IR spectroscopy.

64. Inhibitory effect of three phenacyl derivatives on the oxidation of sphalerite (ZnS) in air-equilibrated acidic solution

Authors: Chirita, P; Duinea, MI; Sandu, AM; Birsa, LM; Sarbu, LG; Baibarac, M; Sava, F; Popescu, M; Matei, E

Published: JUL 1 2018, CORROSION SCIENCE, 138, 162, DOI: 10.1016/j.corsci.2018.04.017

Three phenacyl derivatives have been investigated as potential inhibitors for the aqueous oxidation of sphalerite (ZnS) in air-equilibrated solutions of HCl (pH 2.5 and 25 degrees C) using potentyodynamic polarization, aqueous batch experiments, scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. Findings show that the studied phenacyl derivatives are inhibitors of sphalerite aqueous oxidation. Quantum chemical calculations indicate that the adsorption of phenacyl derivatives on ZnS is energetically favorable and accounts for the observed inhibiting effects.

65. Investigation of the interactions of PVDF shell films with Ni core submicron wires and AAO matrix

Authors: Sima, M; Baibarac, M; Vasile, E; Sima, M; Schinteie, GA; Kuncser, V

Published: SEP 15 2018, PHYSICA B-CONDENSED MATTER, 545, 509, DOI: 10.1016/j.physb.2018.07.015

Arrays of Ni submicron wires surrounded by poly (vinylidene fluoride) (PVDF) submicron tubes were prepared via solution-processed polymer and Ni electrodeposition into anodic aluminum oxide template. The PVDF solution was filtered in vacuum through the template and the resulting dried structure was used for the electrodeposition of Ni wires. The obtained core-shell submicron wire structure consists of a metallic magnetic nanowire core of about 50 mu m in length and about 300 nm diameter surrounded by a polymer tube shell with thickness less than 10 nm. The specific ferroelectric beta-phase of the polymer was obtained whereas the magnetic behavior of the Ni-cores was proven to be specific to an array of ferromagnetic Ni cylindrical wires (about 0.62 mu(B)/Ni atom) with magnetization reversal mechanisms dominated by dipolar interactions and domain wall displacements. No significant differences of the magnetization reversal mechanism were observed in case of Ni submicron wires surrounded by PVDF tubes and similar Ni wires without PVDF shell, suggesting that magneto-coupling effects in such systems might be observed only by measuring the perturbation of the electric state of the polymer shell under a magnetic excitation of the Ni cores.

66. Polyaniline photoluminescence quenching induced by single-walled carbon nanotubes enriched in metallic and semiconducting tubes

Authors: Baibarac, M; Matea, A; Daescu, M; Mercioniu, I; Quillard, S; Mevellec, JY; Lefrant, S

Published: JUN 22 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-27769-4

The influence of single-walled carbon nanotubes enriched in semiconductor (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of polyaniline (PANI), electrosynthesized in the presence of the H2SO4 and HCl solutions, is reported. The emission bands peaked at 407-418 and 440-520 nm indicate that the electropolymerization of aniline (ANI) leads to the formation of short and longer macromolecular chains (MCs), respectively. We demonstrate that the reaction product consists of ANI tetramers (TT) and trimers (TR) as well as PANI-salt. Using Raman scattering and IR absorption spectroscopy, a covalent functionalization of SWNTs with shorter and longer MCs of PANI-salt is demonstrated. The presence of S-SWNTs and M-SWNTs induces a decrease in ANI TT weight in the reaction product mass consisting in S-SWNTs and M-SWNTs covalently functionalized with PANI-emeraldine salt (ES) and PANI-leucoemeraldine salt (LS), respectively. A PANI PL quenching is reported to be induced of the S-SWNTs and M-SWNTs. A de-excitation mechanism is proposed to explain PANI PL quenching.

67. Networked mesoporous SnO2 nanostructures templated by Brij (R) 35 with enhanced H2S selective performance

Authors: Stanoiu, A; Simion, CE; Sackmann, A; Baibarac, M; Florea, OG; Osiceanu, P; Teodorescu, VS; Somacescu, S

Published: NOV 1 2018, MICROPOROUS AND MESOPOROUS MATERIALS, 270, 101, DOI: 10.1016/j.micromeso.2018.05.008

Sensors based networked mesoporous SnO2 nanostructures templated by non-ionic surfactant - Brij (R) 35 were prepared via hydrothermal chemistry route. Specific patterns of the structure, morphology, surface chemistry and sensing properties were obtained by pH and autogenous pressure tuning. Consequently, the as-obtained SnO2 powders were subjected to extensive BET, Raman, TEM, HRTEM and XPS complementary investigations. The sensitive films were obtained by screen printing deposition of the powders onto commercial Al2O3 substrates. The gas sensing properties were assessed towards different hazardous gas species: CO, CH4, NH3, NO2, SO2 and H2S over a wide range of operating temperatures. Our particular SnO2 HP sensor synthesized at high autogenous pressure showed the highest selective-sensitivity to H2S (< 5 ppm) under 50% relative humidity (RH). The enhancement in the H2S sensitivity at low operating temperature under infield conditions was found to be closely connected to the morphological aspects and surface chemistry, peculiarities that can be assessed as consequences of the chemical tuning.

68. Effect of mixing complexing agents on the properties of electrodeposited CZTS thin films

Authors: Zaki, MY; Nouneh, K; Touhami, ME; Belakhmima, RA; Galca, AC; Pintilie, L; Enculescu, M; Baibarac, M; Taibi, M

Published: SEP 2018, OPTICAL MATERIALS, 83, 256, DOI: 10.1016/j.optmat.2018.06.030

This work involves the synthesis and characterization of Cu2ZnSnS4 (CZTS) layers. The films were prepared on ITO/glass substrate by ecofriendly and simple single-step electrodeposition method followed by sulfurization and annealing at 500 degrees C under Argon flow. By using two different complexing agents, the electrodeposition process can give better results. Therefore, the effect of combining the trisodium citrate - TC to multiple cornplexing agents (cetyl trimethyl ammonium bromide - CTAB, ethylene diamine tetra acetic acid - EDTA, Boric Acid - BA, Glutamic Acid - GA and Tartaric Acid - TA) is investigated. The characterization of the absorber films was done by X-ray diffraction (XRD) analysis, Raman spectroscopy, Scanning Electron Microscopy and Diffuse Reflectivity. The combination of TC and CTAB is suggested to be the best pair of complexing agents within the combinations used in this work.

69. Development and Biocompatibility Evaluation of Photocatalytic TiO2/Reduced Graphene Oxide-Based Nanoparticles Designed for Self-Cleaning Purposes

Authors: Nica, IC; Stan, MS; Popa, M; Chifiriuc, MC; Pircalabioru, GG; Lazar, V; Dumitrescu, I; Diamandescu, L; Feder, M; Baibarac, M; Cernea, M; Maraloiu, VA; Popescu, T; Dinischiotu, A

Published: SEP 2017, NANOMATERIALS, 7, DOI: 10.3390/nano7090279

Graphene is widely used in nanotechnologies to amplify the photocatalytic activity of TiO2, but the development of TiO2/graphene composites imposes the assessment of their risk to human and environmental health. Therefore, reduced graphene oxide was decorated with two types of TiO2 particles co-doped with 1% iron and nitrogen, one of them being obtained by a simultaneous precipitation of Ti3+ and Fe3+ ions to achieve their uniform distribution, and the other one after a sequential precipitation of these two cations for a higher concentration of iron on the surface. Physico-chemical characterization, photocatalytic efficiency evaluation, antimicrobial analysis and biocompatibility assessment were performed for these TiO2-based composites. The best photocatalytic efficiency was found for the sample with iron atoms localized at the sample surface. A very good anti-inhibitory activity was obtained for both samples against biofilms of Gram-positive and Gram-negative strains. Exposure of human skin and lung fibroblasts to photocatalysts did not significantly affect cell viability, but analysis of oxidative stress showed increased levels of carbonyl groups and advanced oxidation protein products for both cell lines after 48 h of incubation. Our findings are of major importance by providing useful knowledge for future photocatalytic self-cleaning and biomedical applications of graphene-based materials.

70. The influence of single-walled carbon nanotubes on optical properties of the poly[(2,5-bisoctyloy)-1, 4-phenylenevinylene] evidenced by infrared spectroscopy and anti-Stokes photoluminescence

Authors: Baibarac, M; Smaranda, I; Baltog, I; Lefrant, S; Mevellec, JY

Published: MAY 2017, OPTICAL MATERIALS, 67, 58, DOI: 10.1016/j.optmat.2017.03.039

Significant differences are reported for the IR spectra of poly[(2,5-bisoctyloy)-1, 4-phenylenevinylene] (BO-PPV) recorded onto the KBr, Ag and Au supports. In this work, a decrease in the absorbance of the IR spectra of the BO-PPV films deposited onto Au and Ag supports as increasing the macromolecular compound film thickness is reported. A preferential orientation of the BO-PPV molecules and its composite with single-walled carbon nanotubes (SWNTs) versus metallic supports of Ag and Au is assessed using the IR absorption spectroscopy under s and p polarized light. An anti-Stokes photoluminescence (ASPL) is reported to characterize the BO-PPV macromolecular compound. The BO-PPV ASPL spectra intensity dependent both of the thickness of the macromolecular compound layer deposited onto the metallic supports and the SWNTs weight in the BO-PPV/SWNTs composite mass. (C) 2017 Elsevier B.V. All rights reserved.

71. The exciton-phonon interaction as stimulated Raman scattering effect supported by the excitonic photoluminescence in BiI3 layered crystal structure

Authors: Nila, A; Matea, A; Baibarac, M; Baltog, I

Published: FEB 2017, JOURNAL OF LUMINESCENCE, 182, 171, DOI: 10.1016/j.jlumin.2016.10.028

Raman enhancement in a layered structure of Bib was studied under optical excitation near the edge of the fundamental absorption band. This phenomenon simultaneously appears at a low temperature with the generation of the excitonic photoluminescence (PL) band, unequally across the Raman spectrum, i.e. in the Stokes and anti-Stokes Raman branches, being dependent on the superposition of the excitation laser line to the excitonic emission band. Performed with the use of different resonant laser light excitations, this effect is regarded as a signature of the exciton-phonon interaction, which is interpreted in terms of a stimulated Raman scattering process (SRS), resulting from the mixing inside of the sample to two optical fields, the pump laser light and the excitonic PL light. (C) 2016 Elsevier B.V. All rights reserved.

72. Exciton-phonon interactions in the Cs3Bi2I9 crystal structure revealed by Raman spectroscopic studies

Authors: Nila, A; Baibarac, M; Matea, A; Mitran, R; Baltog, I

Published: APR 2017, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 254, DOI: 10.1002/pssb.201552805

The enhancement of the Raman scattering in Cs3Bi2I9 is evaluated by the ratio I-T/I-300K between the relative intensities of the Raman line peaked at 146cm(-1), when the spectra are recorded in the temperature range of 88-300K, as a signature of exciton-phonon interactions. In the resonant and nonresonant conditions, excitation wavelengths 476, 561, and 660nm, respectively, are used in order to overlap with great accuracy the bands disclosed by diffuse reflection, photoconductivity (PC), photoluminescence (PL), and photoluminescence excitation (PLE) spectra. Based on the experimental analyses, the strength of exciton-phonon interaction is dependent on the defects in the crystal and the type-range interaction of the excitations in an independent Bi2I93- cluster. The noticeable PL band, attributed to excitons trapped on different stacking faults, manifests some defects in crystal that diminish the movement of excitons. This effect significantly decreases the overlaps of excitons with the phonons, resulting in a reduced exciton-phonon coupling.

73. Influence of single-walled carbon nanotubes enriched in semiconducting and metallic tubes on the electropolymerization of tetrabromo ortho-xylene: Insights on the synthesis mechanism of poly(ortho-phenylenevinylene)

Authors: Baibarac, M; Nila, A; Baltog, I; Lefrant, S; Mevellec, JY; Quillard, S; Humbert, B

Published: MAR 2017, EUROPEAN POLYMER JOURNAL, 88, 125, DOI: 10.1016/j.eurpolymj.2017.01.015

New composite materials based on single-walled carbon nanotubes effectively separated into semiconducting (S-SWNTs) and metallic tubes (M-SWNTs) and poly(ortho-phenylenevinylene) (POPV) were synthesized by the electrochemical polymerization of the alpha,alpha,alpha',alpha',-tetrabromo-o-xylene monomer onto the surface of Au supports covered with carbon nanotubes films. Using FTIR spectroscopy, an increase of the quinoid structure weight is highlighted when a charge transfer is induced to take place between the two constituents of the POPV/S-SWNT composite material. In addition, a down-shift of the Raman line belonging to POPV (from 530 cm-(1) to 515 cm(-1)), which was accoinpanied by an increase in relative peak intensity, is reported as a result of steric hindrance effects induced by the covalent bonding of POPV onto the S-SWNT surface. The non-covalent functionalization of M-SWNTs with POPV is demonstrated to occur by Raman scattering and FTIR spectroscopy. The photoluminescence (PL) spectrum of POPV exhibits two bands at 2.82 and 2.25 eV, which were assigned to the electronic emission transitions of macromolecular chains having 3 and 7-10 repeating units, respectively. We demonstrate that POPV photoluminescence quenching in the presence of M + S-SWNTs, M-SWNTs and S-SWNTs is achieved by tubes with chirality (14,7), (12,10) and (11,9), respectively. (C) 2017 Elsevier Ltd. All rights reserved.

74. Aging phenomena and wettability control of plasma deposited carbon nanowall layers

Authors: Vizireanu, S; Ionita, MD; Ionita, ER; Stoica, SD; Teodorescu, CM; Husanu, MA; Apostol, NG; Baibarac, M; Panaitescu, D; Dinescu, G

Published: NOV 2017, PLASMA PROCESSES AND POLYMERS, 14, DOI: 10.1002/ppap.201700023

This paper reports on the aging of carbon nanowalls (CNW) and modification of their wettability by the storage time, growth conditions, and post-fabrication plasma treatments. The as-deposited CNW initially exhibit marked hydrophilic behavior (fresh CNW), but within a few days they become highly hydrophobic (aged CNW). Their final hydrophobicity is closely related to their topography which is controlled by the deposition parameters. In addition, subsequent fluorinated plasma treatments result in super-hydrophobic CNW layers, irrespective of the hydrophilic or hydrophobic character of the pre-treated samples. To explain this, we show that the CNW edges contain many defects initially, but such defects become passivated in time. As a result, the surfaces become highly hydrophobic after aging or fluorination, having inert stable terminations.

75. Optical properties of single-walled carbon nanotubes highly separated in semiconducting and metallic tubes functionalized with poly(vinylidene fluoride)

Authors: Matea, A; Baibarac, M; Baltog, I

Published: FEB 15 2017, JOURNAL OF MOLECULAR STRUCTURE, 1130, 45, DOI: 10.1016/j.molstruc.2016.10.017

In this paper, the interaction of poly(vinylidene fluoride) (PVDF) with single-walled carbon nanotubes (SWNTs) highly separated in metallic (M) and semiconducting (S) tubes is studied by resonant Raman scattering and FTIR spectroscopy. In this order, the PVDF/SWNTs membranes were prepared by the evaporation of dimethylformamide (DMF) from PVDF solutions containing i) the as-prepared SWNTs samples, i.e., as mixtures of metallic (33%) and semiconducting (66%) tubes (M + S-SWNTs), ii) SWNTs highly separated in metallic tubes (98%, M-SWNTs), and iii) SWNTs highly separated in semiconducting tubes (99%, S-SWNTs). An increase in the PVDF beta phase weight, highlighted by the increase in the absorbance of IR band at 843 cm(-1), is reported to take place in the presence of M + S-SWNTs and S-SWNTs. An increase of the PVDF gamma crystalline phase weight is reported for the PVDF/M + S-SWNTs, PVDF/M-SWNTs and PVDF/S-SWNTs membranes. Using Raman scattering, a donor-acceptor interaction is invoked to take place at the interface PVDF/M + S-SWNTs and PVDF/S-SWNTs. In the case of the membranes based on PVDF and M-SWNTs, the changes reported in Raman spectra of the two constituents are explained on the base induction-interaction forces between the permanent dipole of PVDF and induced dipole of M-SWNTs. (C) 2016 Elsevier B.V. All rights reserved.

76. The spectrochemical behavior of composites based on poly (para-phenylenevinylene), reduced graphene oxide and pyrene

Authors: Ilie, M; Baibarac, M

Published: OCT 2017, OPTICAL MATERIALS, 72, 146, DOI: 10.1016/j.optmat.2017.06.002

A new composite material based on poly (para-phenylenevinylene) (PPV), pyrene (Py) and reduced graphene oxide (RGO) is synthesized using thermal conversion route. The properties of this material are investigated by Raman scattering, photoluminescence (PL), infrared (IR) and ultraviolet visible (UV-Vis) spectroscopy. Adding Py at PPV precursor solution (PPV PS) containing RGO, yields to important modifications in both vibrational and electronic properties of these composites. The presence of Py into PPV matrix determines a blue shift of PPV PL. According to Raman and IR studies, PPV is non-covalently functionalized with Py which interacts forward with RGO through pi-pi interactions causing an important modification into the polymer chains conjugation length. (C) 2017 Elsevier B.V. All rights reserved.

77. Electrochemical characterization of the Poly(2, 2 '-Bithiophene-co-Pyrene) Functionalized Single-Walled Carbon Nanotubes Films and Their Applications in Supercapacitors Field

Authors: Baibarac, M; Baltog, I; Daescu, M

Published: MAR 2017, INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE, 12, 2025, DOI: 10.20964/2017.03.60

The performance of the poly(2, 2'-bithiophene-co-pyrene) copolymer doped with bis(2-ethyl hexyl) sulfosuccinate sodium (AOT) anions [(PBTh-Py)(+)AOT(-)] and its composite with single-walled carbon nanotubes (SWNTs) [(PBTh-Py)(+)AOT(-)/SWNTs] as active materials for the electrodes of symmetrical supercapacitors is demonstrated in this work. Using cyclic voltammetry, the influence of the electrolyte concentration and the different cations on the oxidation and reduction processes at the electrolyte/electrode interface is reported. Using charge-discharge galvanostatic measurements in the case of the symmetrical-supercapacitors having as electrode active materials, the (PBTh-Py)(+)AOT(-) copolymer and the (PBTh-Py)(+)AOT(-)/SWNTs composite, values of the specific capacitance equal with 11.5 and 59 F g(-1), respectively, for current densities of 100 mA g(-1), were reported.

78. Infrared dichroism studies and anisotropic photoluminescence properties of poly(para-phenylene vinylene) functionalized reduced graphene oxide

Authors: Baibarac, M; Ilie, M; Baltog, I; Lefrant, S; Humbert, B

Published: 2017, RSC ADVANCES, 7, 6942, DOI: 10.1039/c6ra26445j

Two methods were used for the synthesis of composites based on reduced graphene oxide (RGO) and poly(para-phenylene vinylene) (PPV) in un-doped and doped state, respectively, i.e. the annealing conversion (AC) of the PPV precursor solution (PS) at 300 degrees C and the electropolymerization (E) of alpha, alpha, alpha', alpha'-tetrabromo-p-xylene. In the case of the E method, a decrease in the distyrylbenzene (DSB) weight onto the RGO sheet surface in favor of PPV in doped state is demonstrated by the s and p polarized IR spectroscopy. The change of the orientation angle of the transition dipole moment vector for the IR bands at 835 and 964 cm(-1), in the case of the AC of the PPV PS, is a result of the p-p* interactions between the phenyl groups of PPV and the RGO sheets. The photoluminescence (PL) bands at 2.42 and 2.26 eV indicate the formation of PPV macromolecular chains (MCs) with lengths of 5 and 710 repeating units (RUs), respectively. The anisotropic PL studies performed on the composites RGO/PPV in un-doped and doped state, respectively, highlight an increase of the wrapping angle of RGO sheets with PPV MCs with lengths of 5 RUs, when graphene concentration increases.

79. Influence of TiO2 and Si on the exciton-phonon interaction in PbI2 and CdS semiconductors evidenced by Raman spectroscopy

Authors: Nila, A; Baltog, I; Dragoman, D; Baibarac, M; Mercioniu, I

Published: SEP 13 2017, JOURNAL OF PHYSICS-CONDENSED MATTER, 29, DOI: 10.1088/1361-648X/aa7cb3

The exciton-phonon interaction, considered as a stimulated Raman scattering process, is studied in different semiconductor mixtures: PbI2/TiO2, PbI2/Si and CdS/Si. Raman spectra recorded at excitation wavelengths of 514.5 and 488 nm for PbI2 and CdS, respectively, reveal a strong enhancement of the Raman lines peaked at 97 and 305 cm(-1), evaluated by the ratio I-TK/I-300 (K) between the relative intensities of the spectra recorded in the temperature range of 88-300 K. It is found that PbI2 and CdS exhibit a decrease in the Raman intensity modes with decreasing temperature, while in TiO2 and Si an increase in the Raman lines intensities peaked at 138 and 520 cm(-1) is observed. This behavior can be explained by an energy transfer process from PbI2 or CdS towards TiO2 and Si. This explanation is supported by the schematic potential energy levels diagram obtained from the density of states, which is calculated using the density functional theory. According to this energy levels diagram, the electrons are expected to migrate directly from the conduction band (CB) energetic levels of the PbI2 and CdS towards the CB levels of TiO2 and Si.

80. Mechanism of the cathodic process coupled to the oxidation of iron monosulfide by dissolved oxygen

Authors: Duinea, MI; Costas, A; Baibarac, M; Chirita, P

Published: APR 1 2016, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 467, 59, DOI: 10.1016/j.jcis.2016.01.010

This study investigated the mechanism of iron monosulfide (FeS) oxidation by dissolved oxygen (O-2(aq)). Synthetic FeS was reacted with O-2(aq) for 6 days and at 25 degrees C. We have characterized the initial and reacted FeS surface using Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) analysis, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). It was found that during the aqueous oxidation of FeS new solid phases (disulfide, polysulfide, elemental sulfur, ferric oxyhydroxides and Fe3O4) develop on the mineral surface. The results of potentiodynamic polarization experiments show that after 2 days of FeS electrode immersion in oxygen bearing solution (OBS) at initial pH 5.1 and 25 degrees C the modulus of cathodic Tafel slopes dramatically decreases, from 393 mV/dec to 86 mV/dec. This decrease is ascribed to the change of the mechanism of electron transfer from cathodic sites to O-2 (mechanism of cathodic process). The oxidation current densities (j(ox)) indicate that mineral oxidative dissolution is not inhibited by pH increase up to 6.7. Another conclusion, which emerges from the analysis of j(ox), is that the dissolved Fe3+ does not intermediate the aqueous oxidation of FeS. The results of electrochemical impedance spectroscopy (EIS) show that after 2 days of contact between electrode and OBS the properties of FeS/water interface change. From the analysis of the EIS, FTIR spectroscopy, Raman spectroscopy and SEM/EDX data we can conclude that the change of FeS/water interface properties accompanies the formation of new solid phases on the mineral surface. The new characteristics of the surface layer and FeS/water interface do not cause the inhibition of mineral oxidation. (C) 2016 Elsevier Inc. All rights reserved.

81. Optical properties of single-walled carbon nanotubes functionalized with copolymer poly(3,4-ethylenedioxythiophene-co-pyrene)

Authors: Baltog, I; Baibarac, M; Smaranda, I; Matea, A; Ilie, M; Mevellec, JY; Lefrant, S

Published: DEC 2016, OPTICAL MATERIALS, 62, 611, DOI: 10.1016/j.optmat.2016.11.005

Optical properties are reported for composites based on single-walled carbon nanotubes (SWNT5) and copolymer poly(3,4-ethylenedioxythiophene-co-pyrene) (PEDOT-Py) prepared by chemical polymerization of two monomers in the presence of carbon nanotubes. A charge transfer between SWNT5 and the PEDOT-Py copolymer was demonstrated by Raman scattering. The increase in the relative intensity of the Raman lines peaked at 440-577 cm(-1), which were assigned to the ethylenedioxy ring vibrational modes, indicated a significant hindrance steric in the case of the composites based on the PEDOT-Py copolymer and metallic SWNTs. The increase in the absorbance of IR band peaked at 984 cm(-1) occurred simultaneously with the disappearance of the IR band at 1639 cm(-1). This finding was a consequence of the formation of new covalent bonds between SWNTs and the thiophene and benzene rings of the repeating units of the PEDOT-Py copolymer. The photoluminescence (PL) quenching process of the PEDOT-Py copolymer was induced by semiconducting SWNTs. The PL quenching of PEDOT-Py copolymer in the presence of SWNT5 was. demonstrated based on the energy level diagrams of the two constituents of the PEDOT-Py/SWNTs composite material. (C) 2016 Elsevier B.V. All rights reserved.

82. Polarized Raman spectra of phosphorene in edge and top view measuring configurations

Authors: Baibarac, M; Nila, A; Baltog, I

Published: 2016, RSC ADVANCES, 6, 58009, DOI: 10.1039/c6ra09682d

We demonstrate the anisotropic features of the A(1g), B-2g and A(2g) vibrational Raman modes of phosphorene by performing for the first time a comparison of two orthogonal polarized Raman scattering studies in edge and top view measuring configurations. Despite the orthogonality between the vibration modes of A(1g) and A(2g), they exhibit intense and very weak Raman intensities under light polarized along and transverse to the armchair edge, respectively, while the B-2g mode is virtually non-existent. The B-2g mode significantly appears only in the top view configuration. The studies performed under different intensities of excited light in the top view configuration are detailed for the sample rotated at 0 degrees, 40 degrees, 80 degrees and 130 degrees about the incident laser beam. The studies reveal a quadratic opposite behavior of the A(2g) and B-2g modes and an unusual angle dependence of the A(1g) vibrational mode. An unexpected behavior of the A(2g) Raman mode at higher intensities, which still persists for the A(1g) mode, is shown. The anomalous behavior of the A(1g) mode from the edge and top view and the A(2g) mode in the top view configuration is explained in terms of the layer stacking structures of phosphorene.

83. Exciton-phonon interaction in CdS of different morphological forms manifested as stimulated Raman scattering

Authors: Baibarac, M; Nila, A; Baltog, I

Published: JUN 1 2016, OPTICAL MATERIALS EXPRESS, 6, 1895, DOI: 10.1364/OME.6.001881

Raman studies performed on different morphologies of CdS samples indicate an exciton-phonon interaction (EPI) that manifests at low temperatures by different enhancements in intensity of the Raman spectra in the Stokes and anti-Stokes branches. This effect, interpreted as stimulated Raman effect, is conditioned on the appearance and strength by the degree of overlap of the excitation laser light with the excitonic photoluminescence band. EPI is greatest in samples characterized by high light diffusing power, which means a long path of light into the sample and a great overlapping of the two optical fields, i.e., the pump laser and excitonic light. (C) 2016 Optical Society of America

84. Optical evidence for chemical interaction of the polyaniline/fullerene composites with N-methyl-2-pyrrolidinone

Authors: Baibarac, M; Baltog, I; Daescu, M; Lefrant, S; Chirita, P

Published: DEC 5 2016, JOURNAL OF MOLECULAR STRUCTURE, 1125, 349, DOI: 10.1016/j.molstruc.2016.07.001

Surface enhanced Raman scattering (SERS) spectroscopic studies reveal a particular chemical interaction of the polyaniline/fullerene (PANI/C-60) composite with N-methyl-2-pyrrolidinone (NMP). The chemical polymerization of aniline in the presence of sulfuric acid, potassium dichromate and fullerene has been used for the preparation of the PANI/C-60 composite. The polymerization reaction involves a doping of PANI with C-60 anion radicals. The interaction of the composite with NMP leads to a de-doping of PANI that involves a transformation of leucoemeraldine salt (LS) repeating units into leucoemeraldine base (LB). Additionally, a gradual increasing in the intensity of the Raman line at 1452 cm(-1) associated to the A(g)(2) pentagonal pinch mode of fullerene and a decrease in the intensity of the Raman lines of PANI are reported. This change arises from the formation of a charge-transfer complex C-60-NMP. The subsequent chemical treatment of PANI-LB with FeCl3 leads to the formation PANI-emeraldine salt. An inhibition of the transformation of PANI doped with C-60 anion radicals into a PANI-LB and the C-60-NMP charge transfer complex in the presence of CdS particles dispersed in NMP is demonstrated by SERS spectroscopy. (C) 2016 Elsevier B.V. All rights reserved.

85. Influence of Single-Walled Carbon Nanotubes Enriched in Semiconducting and Metallic Tubes on the Vibrational and Photoluminescence Properties of Poly(para-phenylenevinylene)

Authors: Baibarac, M; Baltog, I; Ilie, M; Humbert, B; Lefrant, S; Negrila, C

Published: MAR 17 2016, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 5705, DOI: 10.1021/acs.jpcc.5b11198

A new synthesis method based on the electrochemical reduction of alpha,alpha,alpha',alpha'-tetrabromo-p-xylene in the presence of single-walled carbon nanotubes (SWNTs) is used to obtain composites of carbon nanotubes (CNTs) functionalized with poly(para-phenyl-enevinylene) (PPV). To separate the effects of metallic and semiconducting CNTs on their interaction with PPV, the experiments are carried out with SWNTs enriched in semiconducting (S, 99%) and metallic (M, 98%) tubes. Significant changes in the relative intensity and shift of the radial breathing vibrational mode are reported in the Raman spectra of the as-prepared SWNTs samples, i.e., as mixtures of metallic (33%) and semiconducting (66%) entities and SWNTs enriched in M tubes (98%) that result from the electrofunctionalization with PPV. This different behavior originates in the noncovalent and covalent functionalization of SWNTs enriched in M and S SWNTs tubes with PPV, respectively. A gradual decrease in the absorption of the infrared (IR) bands of PPV situated in the spectral range of 750-1000 cm(-1) as a result of the increase of the polymer weight on the blank Au support is reported. The electrofunctionalization of the as-prepared SWNTs induces position changes of the PPV IR absorption bands. In the presence of S-enriched SWNTs, a significant increase in the absorbance of the two IR bands peaked at 1452 and 1471 cm(-1), which are assigned to the vibrational modes of the phenyl ring stretching and the quinoid structure of the PPV, respectively, is reported. This results from the covalent bonding of the PPV macromolecular chains onto the surface of the SWNTs enriched in S tubes. Our results also demonstrate that the photoluminescence quenching effect reported for the PPV/SWNTs composites is due to the metallic nanotubes.

86. Anti-Stokes Raman spectroscopy as a method to identify metallic and mixed metallic/semiconducting configurations of multi-walled carbon nanotubes

Authors: Baibarac, M; Matea, A; Ilie, M; Baltog, I; Magrez, A

Published: 2015, ANALYTICAL METHODS, 7, 6230, DOI: 10.1039/c5ay01281c

SERS studies were performed on films of two families of multi-wall carbon nanotubes (MWCNTs) under an excitation light of 514.5 nm and 647.1 nm. These included Aldrich-MWCNTs, which alternate semiconducting and metallic tubes and M-MWCNTs that contain only metallic tubes obtained by water assisted catalytic chemical vapour deposition (CCVD). The two families of MWCNTs reveal similar spectra in the Stokes branch, which feature an increasing Raman intensity when the glass substrate is replaced with an Au or Ag substrate, indicating a (surface enhanced Raman scattering) SERS mechanism. In the anti-Stokes branch, despite an enhancement of approximately 100 times compared to the predictions of the Boltzmann law, only Aldrich-MWCNTs exhibit a Raman spectrum with an intensity that increases as a result of the change in the glass substrate to Au or Ag, a fact that is revealed by the signature of the SERS process. The invariance of the Raman intensity in the anti-Stokes branch as a result of the change of the substrate is characteristic of M-MWCNTs and results from a Raman light scattering process that takes place only within the skin depth of the metallic structure.

87. Photochemical processes developed in composite based on highly separated metallic and semiconducting SWCNTs functionalized with polydiphenylamine

Authors: Baibarac, M; Baltog, I; Smaranda, I; Magrez, A

Published: JAN 2015, CARBON, 81, 438, DOI: 10.1016/j.carbon.2014.09.075

The electrochemical polymerization of diphenylamine (DPA) onto electrodes of Pt coated with highly separated metallic (98%) or semiconducting (99%) single-walled carbon nanotubes (SWCNTs) in the presence of H3PW12O40 was performed by cyclic voltammetry in order to obtain composite materials based on polydiphenylamine (PDPA) doped with heteropolyanions of H3PW12O40 and carbon nanotubes. Our data demonstrate that the photoluminescence quenching effect of the PDPA doped with H3PW12O40 heteropolyanions in the presence of SWCNTs is due to the metallic component. Under UV irradiation of SWCNTs highly separated in metallic and semiconducting tubes functionalized with PDPA doped with heteropolyanions of H3PW12O40 new photochemical reactions are evidenced by photoluminescence studies. These reactions lead to a shortening of the macromolecular chain of PDPA. The photochemical process is more intense in the case semiconducting SWCNTs functionalized with PDPA doped with heteropolyanions in comparison to metallic SWCNTs functionalized with PDPA in doped state, it being a consequence of an additional chemical interaction between the DPA dimer doped with H3PW12O40 heteropolyanions and semiconducting SWCNTs. (C) 2014 Elsevier Ltd. All rights reserved.

88. Fabrication and Raman scattering of a core-shell structure based on Mn doped ZnO and barium titanate

Authors: Sima, M; Baibarac, M; Vasile, E; Sima, M; Mihut, L

Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 1062, DOI: 10.1016/j.apsusc.2015.07.191

A combination of chemical and thermal annealing techniques was used to prepare an array of ZnO/Zn1-xMNxO/BaTiO3 nanorods. ZnO nanorod arrays were obtained by hydrothermal-electrochemical processes. The precursors for Zn1-xMnxO and BaTiO3, prepared by sol-gel technique were deposited by spin coating on the surface of ZnO nanorods. Each deposition stage was accompanied by thermal treatment stages. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence spectroscopy reveal the presence of a film of Zn1-xMnxO with wurtzite structure on the surface of ZnO nanorods. Transmission electron microscopy images demonstrate that a layer of BaTiO3 is deposited on the surface of each ZnO/Zn1-xMnxO core shell nanorod. BaTiO3 film onto the ZnO/Zn1-xMnxO core shell nanorods is also evidenced in Raman scattering by broadening of the Raman band situated in the spectral range 500-750 cm(-1). (C) 2015 Elsevier B.V. All rights reserved.

89. Optical Properties of Single-Walled Carbon Nanotubes Functionalized with Poly(2,2 '-bithiophene-co-pyrene) Copolymer

Authors: Smaranda, I; Baibarac, M; Ilie, M; Matea, A; Baltog, I; Lefrant, S

Published: 2015, CURRENT ORGANIC CHEMISTRY, 19, 661, DOI: 10.2174/1385272819666150311231454

The photoluminescent (PL) properties of composites based on single-walled carbon nanotubes (SWNTs) and poly(2,2'-bithiophene-co-pyrene) (PBTh-Py), prepared by in situ chemical polymerization of the two monomers in the presence of carbon nanotubes, are reported. We demonstrate that the functionalization of SWNTs with PBTh-Py copolymer is revealed through a gradual quenching process of PL with the increase of SWNT content (semiconducting component) in the composite mass. FTIR spectroscopy indicates the existence of several steric hindrance effects that originate in the covalent functionalization of SWNTs with PBTh-Py copolymer. The film deposition of PBTh-Py copolymer and PBTh-Py/SWNTs composite onto rough Au supports induces changes in the FTIR spectrum, which originate in an adsorption mechanism caused by the preferential orientation of molecules on the metallic support. Surface-enhanced Raman scattering (SERS) spectroscopy reveals the side-wall functionalization of SWNTs with PBTh-Py copolymer by changes in the shapes, peak position and relative intensities of different Raman lines.

90. Anti-Stokes Raman spectroscopy as amethod to identify the metallic and semiconducting configurations of double-walled carbon nanotubes

Authors: Baibarac, M; Baltog, I; Matea, A; Mihut, L; Lefrant, S

Published: JAN 2015, JOURNAL OF RAMAN SPECTROSCOPY, 46, 38, DOI: 10.1002/jrs.4597

Although Raman spectra reveal, as a signature of double-walled carbon nanotubes (DWCNTs), two radial breathing mode (RBM) lines associated with the inner and outer tubes, the specification of their nature as metallic or semiconducting remains a topic for debate. Investigating the spectral range of the RBM lines, we present a new procedure of the indexing of the semiconducting or metallic nature of the inner and outer shell that forms the DWCNT. The procedure exploits the difference between the intensities of recorded anti-Stokes Raman spectrum and the anti-Stokes spectrum calculated by applying the Boltzmann formulae to the recorded Stokes spectrum. The results indicate that the two spectra do not coincide with what should happen in a normal Raman process, namely, that there are RBM lines of the same intensity in both spectra, as well as RBM lines of higher intensity that are observed in the calculated spectrum. This discrepancy results from the surface-enhanced Raman scattering mechanism that operates differently on metallic or semiconducting nanotubes. In this context, the analysis of the RBM spectrum can reveal pairs of lines associated with the inner/outer shell structure of DWCNT, and when the intensities between the recorded and calculated spectra coincide, the nanotube is metallic; otherwise, the nanotube is semiconducting. Copyright (c) 2014 John Wiley & Sons, Ltd.

91. Exciton-phonon interaction in PbI2 revealed by Raman and photoluminescence studies using excitation light overlapping the fundamental absorption edge

Authors: Baibarac, M; Smaranda, I; Scocioreanu, M; Mitran, RA; Enculescu, M; Galatanu, M; Baltog, I

Published: OCT 2015, MATERIALS RESEARCH BULLETIN, 70, 772, DOI: 10.1016/j.materresbull.2015.06.012

Enhancement at low temperatures of the Raman scattering excited by laser light situated near the edge of the fundamental absorption band is often encountered when studying nanoscale structures. Theory devoted to this phenomenon has established that it originates in an exciton-phonon interaction process, known as the Frohlich interaction, Such a phenomenon was observed in PbI2. The experimental data conclude that the enhancement of the Raman emission results from: (i) an optical excitation near edge of fundamental absorption band; (ii) it is conditioned by the existence of excitonic PL; (iii) its occurrence is different over stokes and anti-stokes Raman branches as result of the different overlapping of the Raman spectral range and the excitonic PL band profile; and (iv) it appears more intense in micrometric powders or in bulk crystalline material. These data are interpreted as stimulated Raman effect resulting from the mixing of the pump laser light and the excitonic light. (C) 2015 Elsevier Ltd. All rights reserved.

92. Raman scattering and photoluminescence studies of ZnO nanowhiskers assembled as flowers in the presence of fullerene

Authors: Baibarac, M; Baltog, I; Matea, A; Lefrant, S

Published: JUN 1 2015, JOURNAL OF CRYSTAL GROWTH, 419, 164, DOI: 10.1016/j.jcrysgro.2015.03.028

In this work, the architecture of ZnO particles was found to be changed from nano-whiskers to flowers via the addition of fullerenes in the reaction mixture consisting of zinc chloride, sodium hydroxide and sodium dodecyl sulfate. The change in the morphological structure of ZnO particles is accompanied by a decrease in the photoluminescence (PL) intensity and the appearance of a new Raman line at 1594 cm(-1) that indicates the formation of the compound ZnC60. The growth of the ZnO flower-like particles occurs simultaneously with an aggregation process of C-60 in highly ordered structures, as evidenced in the Raman spectrum by a line at 2934 cm I. A mechanism for the growth of the ZnO flower-like particles is proposed in this work. (C) 2015 Elsevier B.V. All rights reserved.

93. 1D-polyaniline starting from self-assembled systems

Authors: Donescu, D; Ghiurea, M; Spataru, CI; StIng, G; Anghel, D; Baibarac, M; Baltog, I

Published: SEP 2015, COLLOID AND POLYMER SCIENCE, 293, 2524, DOI: 10.1007/s00396-015-3645-1

The radical polymerization of aniline hydrochloride (ANIHCl) in the presence of ammonium persulfate was studied. 1D-Polyaniline (PANI) with fibrillar morphologies was obtained in the presence of anionic surfactants. The changes of the PANI-template structures in aqueous solution were studied using static fluorescence measurements. The dispersed PANI nanoparticles were characterized using dynamic light scattering, scanning electron microscopy (SEM), and Raman and Fourier transform infrared spectroscopies. The thermal analysis and the electrical conductivity of the dried samples were also performed. The fluorescence measurements indicated that nanocrystals of ANIHCl form in water complexes with the anionic surfactants at smaller concentrations than the critical micellar concentration. The same method revealed that other organic complexes with sulfonate groups do not induce an increase of the hydrophobic region due to short hydrocarbon tails. The SEM micrographs and Raman spectra revealed that the PANI nanofibers are compact and different compared to the nanoparticles prepared without surfactants.

94. Abnormal anti-Stokes Raman scattering and surface-enhanced infrared absorption spectroscopy studies of carbon nanotubes electrochemically functionalized with poly(2,2 '-bithiophene-co-pyrene)

Authors: Baibarac, M; Baltog, I; Smaranda, I; Scocioreanu, M; Mevellec, JY; Lefrant, S

Published: AUG 1 2014, APPLIED SURFACE SCIENCE, 309, 21, DOI: 10.1016/j.apsusc.2014.04.114

A new composite material was synthesized via the electrochemical oxidation of 2,2'-bithiophene (BTh) and pyrene (Py) monomers dissolved in a solution of LiC1O(4) in CH3CN onto a working electrode of Au coated with a film of single-walled carbon nanotubes (SWNTs). The interaction of the poly(2,2'-bithiophene-co-pyrene) (PBTh-Py) with the SWNTs and the orientation of the copolymer on the working electrode were studied by anti-Stokes and Stokes Raman scattering and FTIR spectroscopy in the grazing-incidence angle reflection geometry. The Raman lines at 1464 and 1435 cm(-1), attributed to the symmetric stretching modes of the C=C bond in the quinoid and aromatic rings of the PBTh-Py copolymer, were observed when the working electrode is either a blank Au film or a Au support coated with a SWNT film. In the latter case, charge transfer occurs at the interface of the two constituents. This charge transfer leads to functionalization of the carbon nanotubes with the copolymer molecules. The presence of enhanced anti-Stokes Raman lines at -1461, -1435 and -1187 cm(-1) indicates a resonant optical excitation process of the PBTh-Py/SWNT composite. The FTIR spectra acquired under polarized light for the PBTh-Py copolymer electrosynthesized on a bare Au support reveal significant changes in the absorption bands situated in the spectral ranges of 1000-1150 and 1550-1650 cm(-1) that originate in the surface-enhanced IR absorption (SEIRA) processes. The functionalization of the SWNTs with the PBTh-Py copolymer is evidenced by the enhancement of the absorption of the FTIR bands at 793 and 846 cm(-1), which are assigned to the C S C deformation vibrational mode and the substituted benzene ring, respectively, due to the effects of steric hindrance that are induced for the copolymer molecules by the binding of carbon nanotubes. (C) 2014 Elsevier B.V. All rights reserved.

95. Synthesis and Raman scattering of multiferroic Fe-Pb(Zr0.2Ti0.8)O-3 core-shell wire arrays

Authors: Baibarac, M; Sima, M; Matei, E; Pasuk, I; Mihut, L

Published: JAN 2014, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 211, 205, DOI: 10.1002/pssa.201330062

A new method to fabricate an Fe-PZT core-shell wire arrays developed in three steps is reported in this paper. This involves the electrochemical growth of an iron wire array by template method, deposition by spin coating of the PZT precursor prepared by sol-gel technique on the iron wires surface and annealing treatment to obtain Fe-PZT core-shell structures. The structure of the Fe-PZT core-shell wire array was characterized by scanning electron microscopy (SEM) and Raman scattering. Raman lines situated at 372 and 575cm(-1) indicate the formation of the FeO particles on the Fe wires surface as a result of the use of an aqueous solution for electrochemical synthesis. An upshift of Raman lines of Fe decorated with FeO wires was observed after formation of Fe-PZT core-shell structure. The annealing treatment of this structure involves a partial transformation of the FeO into Fe2O3 particles both with structure rhombohedral and cubic that were evidenced by Raman lines peaked at 243 and 497cm(-1), respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

96. Electrochemical Grafting of Reduced Graphene Oxide with Polydiphenylamine Doped with Heteropolyanions and Its Optical Properties

Authors: Smaranda, I; Benito, AM; Maser, WK; Baltog, I; Baibarac, M

Published: NOV 6 2014, JOURNAL OF PHYSICAL CHEMISTRY C, 118, 25717, DOI: 10.1021/jp507324r

Electropolymerization of diphenylamine (DPA) onto a reduced graphene oxide (RGO) film was carried out to obtain a corresponding RGO/polydiphenylamie (PDPA) composite doped with phosphotungstic acid (H3PW12O40) heteropolyanions (PT). The synthesis was performed in the absence of light, since UVvis spectroscopy and photoluminescence (PL) studies on RGO/DPA blends irradiated by UV light revealed a partial transformation of the DPA monomer into oligomers of PDPA. Raman scattering demonstrates that the electropolymerization of DPA in the presence of H3PW12O40 (PTA) and RGO leads to the formation of PDPA covalently bonded to the RGO sheets (RGO/PDPA:PT). The presence of heteropolyanions in the PDPA matrix (PDPA:PT) is detected by FTIR spectroscopy. Comparing the PL excitation spectra of PDPA:PT and the RGO/PDPA:PT composite highlights an upshift of the band gap that is accompanied by a change in the composition of the PL spectrum in the spectral range of 2.253.54 eV. These changes originate in a charge transfer that takes place at the interface of nongrafted RGO and PDPA:PT. The gradual increase of the PL intensity of RGO covalently grafted with PDPA:PT reveals photochemical reactions under UV irradiation. These involve the CC stretching vibrational mode in the benzene ring of PDPA and indicate the transformation of an RGO/PDPA:PT composite containing HPW12O402 anions into an RGO/PDPA:PT composite stabilized by PW12O403 anions. These results not only provide important insights on the interactions between RGO, conjugated polymers, and stabilizing dopant ions but also impact on the synthesis conditions.

97. New features in the anti-Stokes and Stokes Raman spectra of single-walled carbon nanotubes that are highly separated into their semiconducting and metallic nanotube components

Authors: Baibarac, M; Baltog, I; Mihut, L; Lefrant, S

Published: MAY 2014, JOURNAL OF RAMAN SPECTROSCOPY, 45, 331, DOI: 10.1002/jrs.4473

Surface-enhanced Raman scattering studies were performed using nonresonant (514.5 nm) and resonant (676.4 nm) optical excitations on single-walled carbon nanotubes thoroughly separated into semiconducting (pure 99%) and metallic (pure 98%) components. Regardless of the support (Au or Ag), the metallic nanotubes do not present an anomalous anti-Stokes Raman emission. Regardless of whether an on-resonant or off-resonant optical excitation is used, only the semiconducting nanotubes produce an abnormal anti-Stokes Raman emission that grows when increasing the excitation light intensity or temperature. The Raman studies under light polarized relative to the main nanotube axis demonstrate that only semiconducting nanotubes are sensitive toward changes in the polarization of the excitation light. Copyright (c) 2014 John Wiley & Sons, Ltd.

98. Abnormal anti-Stokes Raman scattering and coherent backscattering as manifestation of Anderson localization of light in nonlinear mesoscopic materials

Authors: Smaranda, I; Mihut, L; Baibarac, M; Baltog, I; Lefrant, S

Published: SEP 2014, OPTICAL ENGINEERING, 53, DOI: 10.1117/1.OE.53.9.097109

We demonstrate that under continuous single-beam excitation, one can generate an abnormal antiStokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering. The effect has been observed in mesoscopic materials, which possess intrinsically nonlinear properties [lithium niobate (LiNbO3), bismuth germanium oxide (Bi12GeO20; BGO), bismuth silicon oxide (Bi12GeO20; BSO)], which have a nonzero electric susceptibility of the third order, chi((3)) not equal 0. Corroborated Raman and coherent backscattering studies demonstrate that the occurrence of both effects is conditioned by the existence of a mesoscopic morphology of the sample, which is able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, both AASRE and coherent backscattering effects are because of the Anderson localization of the light. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

99. Spectroelectrochemical properties of the poly[(2,5-bisoctyloxy)-1,4-phenylenevinylene]/single-walled carbon nanotube composite

Authors: Baibarac, M; Baltog, I; Srnaranda, I; Ilie, M; Scocioreanu, M; Mevellec, JY; Lefrant, S

Published: SEP 2014, SYNTHETIC METALS, 195, 285, DOI: 10.1016/j.synthmet.2014.06.010

Using surface-enhanced Raman scattering (SERS) and photoluminescence (PL) studies, new data concerning the electrochemical oxidation both of poly[(2,5-bisoctyloxy)-1,4-phenylene-vinylene] (BO-PPV) and the BO-PPV/HIPCO single-walled carbon nanotubes (SWNTs) composite are presented in this paper. The SERS studies performed at the excitation wavelengths of 752 nm and 532 nm of the BO-PPV/SWNTs composite that ensure the resonant excitation of the semiconductor and metallic nanotubes, respectively, reveal that the mixing of the two constituents results, on the one hand, in an isolation of semiconducting nanotubes from the bundles containing both metallic and semiconducting tubes and, on the other hand, in a functionalization of metallic SWNTs with BO-PPV. The isolation of semiconducting SWNTs is demonstrated by the narrowing of the G band and the change of the ratio between the intensities of the Raman lines situated in the low-frequency range that are assigned to the radial breathing vibrational modes. An additional isolation of the semiconducting nanotubes from the SWNTs bundles is reported when an electro-oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2) V vs. Ag/AgCl. According to the Fourier transformed infra-red (FTIR) spectra and the SERS studies performed at an excitation wavelength of 1064 nm, the chemical interaction of BO-PPV with HIPCO SWNTs reveals a charge transfer between the two constituents that leads to the formation of BO-PPV covalently functionalized SWNTs. The BO-PPV luminescence quenching effect induced by the presence of SWNTs that consists of a change in the relative intensities of the three PL bands of the polymer peaked at 1.73 eV, 1.9 eV and 2.07 eV is due to the metallic tubes. The appearance of a new emission band at 2.32 eV was regularly observed when electrochemical oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2) V. The PL band at 2.32 eV corresponds to ClO4- ions, which compensates the positive charges of BO-PPV generated during the electrochemical doping process. (C) 2014 Elsevier B.V. All rights reserved.

100. Influence of 2,2 '-bipyridine on oxidative dissolution of iron monosulfide

Authors: Chirita, P; Badica, CE; Constantin, CA; Birsa, LM; Matei, E; Baibarac, M

Published: OCT-NOV 2014, SURFACE AND INTERFACE ANALYSIS, 46, 846, DOI: 10.1002/sia.5459

The 2,2'-bipyridine effects on iron monosulfide (FeS) oxidative dissolution rates have been examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The adsorption of 2,2'-bipyridine to synthetic FeS was investigated by batch adsorption experiments, SEM, energy-dispersive X-ray analysis and Raman spectroscopy. The experiments were performed in air-saturated solutions at pH 5, 25 degrees C and an ionic strength of I = 0.004 M NaCl. Correlation between oxidative dissolution rates and 2,2'-bipyridine adsorption suggests that FeS oxidative dissolution is the result of two antagonistic processes: (i) the inhibiting adsorption of 2,2'-bipyridine on mineral surface and (ii) the promoting effect of 2,2'-bipyridine on the iron dissolution from FeS surface. Copyright (C) 2014 John Wiley & Sons, Ltd.

101. Nonlinear features of surface-enhanced Raman scattering revealed under non-resonant and resonant optical excitation

Authors: Baibarac, M; Baltog, I; Mihut, L; Matea, A; Lefrant, S

Published: MAR 2014, JOURNAL OF OPTICS, 16, DOI: 10.1088/2040-8978/16/3/035003

By performing comparative Raman studies on nanometric thin films (9.5, 39, 88 and 185 nm) of copper phthalocyanine (CuPc) deposited on glass, Au and Ag supports, we demonstrate that the mechanism of the surface-enhanced Raman scattering (SERS) generated on Au and Ag substrates differs in the Stokes and anti-Stokes Raman branches depending on whether non-resonant (515.5 nm) or resonant (647.1 nm) optical excitation is applied. The evaluation of the SERS effect via the I-aS/I-S ratio reveals that this ratio is smaller or larger than that predicted by the Boltzmann law for non-resonant or resonant optical excitation, respectively. In the former case, the enhancement of the Stokes Raman emission is similar to a stimulated Raman process resulting from the plasmon coupling associated with the incident excitation light and spontaneous Stokes Raman emission. For the latter case, the amplification of the anti-Stokes Raman emission results from a wave-mixing process reminiscent of a single-beam CARS effect.

102. Photoluminescence decay time studies on ZnS in cubic and hexagonal phase and its mechanico-chemical interaction with polyaniline

Authors: Scocioreanu, M; Mihut, L; Baibarac, M; Baltog, I

Published: JUL 2013, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 250, 1431, DOI: 10.1002/pssb.201248234

We report new photoluminescence (PL) data generated by pulsed optical excitation on the composites achieved by a mechanico-chemical reaction between ZnS in the cubic (c) and wurtzite (w) phases and polyaniline-emeraldine base (PANI-EB). Under continuous and pulsed optical excitation, powders of the (w)ZnS and (w)ZnS/PANI-EB composites display PL with different spectral compositions. Contrary to expectations, the (c)ZnS and the (c)ZnS/PANI-EB composite displayed weak PL and decay time in the range of nanoseconds. This results from the great involvement of the surface states in nanometric powders which creates efficient channels for the non-radiative recombination of the carriers. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

103. Spectroelectrochemical properties of the single walled carbon nanotubes functionalized with polydiphenylamine doped with heteropolyanions

Authors: Smaranda, I; Baibarac, M; Baltog, I; Mevellec, JY; Lefrant, S

Published: JAN 2013, JOURNAL OF SOLID STATE CHEMISTRY, 197, 360, DOI: 10.1016/j.jssc.2012.08.015

A combined chemical-electrochemical method was used for covalent functionalization of single-walled carbon nanotube (SWNT) with polydiphenylamine (PDPA) doped with heteropolyanions of H3PMo12O40 center dot xH(2)O. The functionalization process induces in Raman spectra of SWNTs the following changes: (i) an increase in relative intensity of the D band, accompanied a gradual up-shift of the G band in the case of the semiconducting tubes and a decrease in the relative intensity of band peaked at 1540 cm(-1) is remarked in the case of the metallic tubes; (ii) in the anti-Stokes Raman spectrum an increase in the relative intensity of Raman line of metallic tubes peaked at -1560 cm(-1) is remarked when the cycles number increases. The additional down-shift of the FTIR bands belonging to H3PMo12O40 heteropolyanions (at 881, 943 and 1055 cm(-1)) and PDPA (at 688, 736 and 1016 cm(-1)) originates in hindrance steric effects induced the covalent functionalization of SWNTs with polymer molecules. Using Raman scattering and FTIR spectroscopy we demonstrate that chemical polymerization of diphenylamine in the presence of H3PMo12O40 center dot xH(2)O and SWNTs results in a composite of the type blend based on PDPA in un-doped state and SWNTs doped with H3PMo12O40 heteropolyanions. (C) 2012 Elsevier Inc. All rights reserved.

104. Stability of carbon nanowalls against chemical attack with acid solutions

Authors: Vizireanu, S; Dinescu, G; Nistor, LC; Baibarac, M; Ruxanda, G; Stancu, M; Ciuparu, D

Published: JAN 2013, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 47, 65, DOI: 10.1016/j.physe.2012.09.027

In this paper we report on the stability of CNW layers, synthesized by a radiofrequency plasma jet, against the chemical attack with different acid solutions (sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid). We present the changes of the morphology and structure of the CNW caused by the post-growth chemical treatments. We demonstrate that self-sustaining and transferable CNW layers can be obtained, by chemically dissolving the substrates, while the initial characteristics of the material are well preserved. (C) 2012 Elsevier B.V. All rights reserved.

105. Single-walled carbon nanotubes functionalized with polydiphenylamine as active materials for applications in the supercapacitors field

Authors: Baibarac, M; Baltog, I; Frunza, S; Magrez, A; Schur, D; Zaginaichenko, SY

Published: FEB 2013, DIAMOND AND RELATED MATERIALS, 32, 82, DOI: 10.1016/j.diamond.2012.12.006

Composites based on polydiphenylamine (PDPA) doped with heteropolyanions of H3PW12O40 and single-walled carbon nanotubes (SWNTs) were prepared by electrochemical polymerization of diphenylamine (DPA) on carbon nanotube films deposited onto Pt electrodes. HRTEM studies reveal that the electrochemical polymerization leads to the filling the spaces between tubes which compose the bundles, creating a monolithic film on the Pt electrode. The resulting composites were tested as active materials in supercapacitors. Resonant Raman scattering studies showed that the electropolymerization of DPA in the presence of H3PW12O40 and SWNTs leads to the covalent functionalization of SWNTs with doped PDPA. The covalent functionalization of SWNTs with PDPA doped with H3PW12O40 heteropolyanions was revealed by FTIR spectroscopy, based on the changes in the vibrational features of PDPA and H3PW12O40. These changes included i) a down-shift of the PDPA IR bands, which was attributed to the C-H bending vibrational mode of benzene (B), C-aromatic-N, C-C stretching (B) + C-H bending (B) and C-C stretching vibrations of the B ring, from 1174, 1321, 1495 and 1603 cm(-1) to 1165, 1313, 1487 and 1599 cm-1, respectively; ii) a change in the peak positions of IR bands associated with the W = O and P-O-W vibration modes of H3PW12O40; and iii) a down-shift of the IR band situated in the spectral range 650-725 cm(-1), which was assigned to the inter-ring deformation vibration mode. The characterization of symmetric solid-state supercapacitors was performed for electrodes prepared from i) SWNTs functionalized with PDPA doped with H3PW12O40 heteropolyanions, ii) SWNTs electrochemically decorated with H3PW12O40 heteropolyanions, and iii). PDPA doped with H3PW12O40 heteropolyanions. Preliminary results indicate high discharge capacitance values of up to 157.2 mF/cm(2) for SWNTs functionalized with PDPA doped with H3PW12O40 heteropolyanions. The discharge capacitance of this material is superior to those recorded for SWNTs electrochemically decorated with H3PW12O40 heteropolyanions (similar to 18.2 mF/cm(2)) and PDPA doped with H3PW12O40 heteropolyanions (similar to 62.1 mF/cm(2)). (c) 2012 Elsevier B.V. All rights reserved.

106. Effect of tritiation on the superconducting properties of MgB2

Authors: Sandu, V; Aldica, G; Baibarac, M; Enachescu, M; Sandu, E; Chee, CY

Published: APR 2013, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 26, DOI: 10.1088/0953-2048/26/4/045014

We investigated the effect of tritium upload in the dense, polycrystalline MgB2 superconductor for 2 and 216 h. One basic property, the critical temperature T-c, slowly changes in time but is independent of the duration of tritium uptake. Immediately after tritiation, T-c shows a slight increase to 39.1 K but decreases to the critical temperature of the untritiated (pristine) sample, T-c = 38.8 K, after 370 days. The critical current density is strongly dependent on the tritium upload time, mainly at high magnetic fields. The underlying physics is discussed. This behaviour makes the use of MgB2 based conductors advantageous in tritium environments like fusion reactors.

107. Casimir effect demonstrated by Raman spectroscopy on trilayer graphene intercalated into stiff layered structures of surfactant

Authors: Baibarac, M; Baltog, I; Mihut, L; Pasuk, I; Lefrant, S

Published: JAN 2013, CARBON, 51, 142, DOI: 10.1016/j.carbon.2012.08.021

Polarized Raman scattering studies on stiff layered structure of surfactant intercalated with trilayer graphene were performed at different intensities and excitation wavelengths. The D and 2D Raman bands reach the highest and lowest intensity when the polarization of laser excitation light is oriented along and perpendicular on the edges. The 2D band discloses two lorentzian components, separated by similar to 40 cm(-1), which result from the action of interplanar forces, of Casimir nature. The value of similar to 40 cm(-1) is close to the energy value associated with E-2g interplanar layer shear mode evidenced so far only by neutron spectrometry. A new result regards the opposite variation of the intensities of D and 2D bands with the increase of the wavelength of the excitation light. This originates in the different origin of the D and 2D bands; the former is dependent on disorder including also the graphene edges while the latter, results from in a double resonant mechanism combined with a Casimir effect. One demonstrates that the magnitude of Casimir force, which activates interlayer vibration modes, depends on the carrier density on the graphene sheets which can be varied both by the intensity and the wavelength of the excitation laser light. (C) 2012 Elsevier Ltd. All rights reserved.

108. Raman scattering and anti-Stokes luminescence in poly-paraphenylene vinylene/carbon nanotubes composites

Authors: Baibarac, M; Massuyeau, F; Wery, J; Baltog, I; Lefrant, S

Published: APR 15 2012, JOURNAL OF APPLIED PHYSICS, 111, DOI: 10.1063/1.4705403

In this paper, we present Raman scattering and luminescence of poly-paraphenylene vinylene/single-walled carbon nanotubes composites, focused on data recorded in the anti-Stokes branch. We demonstrate that, when the excitation energy is in the long wavelength tail of the fundamental absorption edge, an anti-Stokes signal is generated, whose origin is a photon absorption accompanied by a phonon process from lower to upper vibronic states. The efficiency of this anti-Stokes photo-luminescence is increased when composites films are deposited onto an Au rough surface acting as a surface enhanced Raman scattering substrate. This mechanism is explained by a coherent anti-Stokes Raman scattering-like process, as observed in other nano-structured materials. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4705403]

109. Anti-Stokes Raman Scattering and Luminescence in Carbon Nanotube Nanostructures

Authors: Lefrant, S; Buisson, JP; Mevellec, JY; Massuyeau, F; Wery, J; Baibarac, M; Baltog, I

Published: 2012, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 554, 118, DOI: 10.1080/15421406.2012.633816

In this paper, we present recent results obtained on single-walled carbon nanotubes (SWNTs) and carbon nanotube/conjugated polymer composites by using resonant Raman scattering and Surface Enhanced Raman Scattering (SERS). Besides the characterization of these materials, we report on peculiar properties observed in the anti-Stokes Raman branch of the Raman spectra. They consist in an abnormal anti-Stokes Raman emission which is explained by a mechanism reminiscent of a Coherent anti-Stokes Raman Scattering (CARS) emission. It results from a wave mixing process between the incident laser light and Stokes Raman light, generated by the SERS mechanism. In a parallel way, we have investigated in details the resonance effects which also induce anomalies in the anti-Stokes/Stokes intensity ratios, as a function of several parameters including the observation temperature, the environmental conditions, the dilution in solvents, etc. Studies extended to composites based on carbon nanotubes and conjugated polymers reveal also interesting properties. In the case of poly(bithiophene) (PBTh), one observes a strong amplification of the 1450 cm(-1) Raman line in the anti-Stokes branch, generated by the plasmon excitation of metallic tubes. This phenomenon occurs in several other conjugated polymers such as PEDOT and PPV for modes located around 1500 cm(-1). The role of metallic SWNTs is discussed. Finally, an anti-Stokes luminescence excited in the low energy tail of the absorption band of PPV and PPV/SWNTs composites has even been observed for the first time, explained through a phonon-energy up-conversion mechanism.

110. NONLINEAR OPTICAL PROCESSES MANIFESTING AS ANDERSON LOCALIZATION OF LIGHT IN MESOSCOPIC MATERIALS

Authors: Baltog, I; Baibarac, M; Mihut, L; Smaranda, I; Lefrant, S

Published: APR-JUN 2012, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 13, 117, DOI:

Abnormal anti-Stokes Raman emission (AASRE) is defined by an anti-Stokes/Stokes intensity ratio much greater than expected on the basis of the equilibrium population of excited vibration states provided by the Boltzmann law. AASRE can be observed both in materials with intrinsic nonlinear optical properties as LiNbO3 or materials in which the nonlinear optical properties are induced by resonant optical excitation, as carbon nanotubes. Using a surface enhanced Raman scattering (SERS) device, consisting from single wall carbon nanotubes deposited on a rough Au or Ag support and LiNbO3 in form of powder, we demonstrate that under continuous single beam excitation they present AASRE whose properties are similar to a single beam pumped Coherent Anti-Stokes Raman Scattering. AASRE is usually accompanied by a coherent backscattering, it can be considered as Anderson localization of light that results from a wave-mixing mechanism of the incident laser light with a Stokes shifted Raman light produced by a spontaneous Raman light scattering process. The transport of the light inside of sample, giving rise to AASRE and coherent backscattering, is done by an elastic light scattering mechanism.

111. Photoluminescence and Raman evidence for mechanico-chemical interaction of polyaniline-emeraldine base with ZnS in cubic and hexagonal phase

Authors: Scocioreanu, M; Baibarac, M; Baltog, I; Pasuk, I; Velula, T

Published: FEB 2012, JOURNAL OF SOLID STATE CHEMISTRY, 186, 223, DOI: 10.1016/j.jssc.2011.12.012

The mechanico-chemical interaction of a polyaniline-emeraldine base (PANI-EB) with ZnS in the cubic and wurtzite phases is studied by Raman spectroscopy and photoluminescence (PL). The results demonstrate that such an interaction leads to the formation of a PANI-salt and metallic Zn. Regardless of the structural form of the ZnS, the formation PANI-salt is indicated by a band in the Raman spectrum that shifts from 1162 to 1176 cm(-1) and the appearance of a new band at 1330 cm(-1) that indicates the protonated structure of a PANI-salt. The presence of the second product is determined by comparative PL studies performed on ZnS that has interacted mechanico-chemically with PANI-EB and metallic Zn powder. The variations of the PL spectra and their associated excitation spectra are explained as resulting from the charge collection processes that occur in the composite materials produced by the mechanico-chemical interaction between ZnS and PANI-EB or metallic Zn. (C) 2011 Elsevier Inc. All rights reserved.

112. Abnormal Anti-Stokes Raman Emission and Infrared Dichroism Studies on Poly(p-phenylenevinylene)/Single-Walled Carbon Nanotube Composites

Authors: Baibarac, M; Baltog, I; Wery, J; Lefrant, S; Mevellec, JY

Published: DEC 6 2012, JOURNAL OF PHYSICAL CHEMISTRY C, 116, 25545, DOI: 10.1021/jp3070008

Using surface-enhanced Raman scattering (SERS) and Fourier transform infrared spectroscopy (FTIR) in the grazing angle incident reflection geometry, new data concerning the abnormal anti-Stokes Raman emission (AASRE) and the molecular orientation of poly(p-phenylenevinylene) (PPV) deposited on metallic supports of Ag and Au are reported. The particular dependencies of the anti-Stokes Raman intensity on the Raman shift, the sample thickness, and the incident pump intensity are highlighted in this paper. In the spectral range of 800-1000 cm(-1), the FTIR spectra of PPV films deposited on Ag and Au supports show a dichroism similar to that reported for the free-standing PPV film. Significant differences are reported in the spectral range of 1400-1700 cm(-1) for the s- and p-polarized FTIR spectra of PPV films deposited on Au and Ag supports. The annealing treatment at 110 degrees C of the PPV precursor solution in the presence of single-walled carbon nanotubes (SWNTs) induces a noncovalent functionalization of carbon nanotubes with the polymer molecules, as evidenced by a decrease of the radial breathing mode intensity and a decrease in the strength of AASRE. The process of noncovalent functionalization of SWNTs with PPV induces a change of the orientation angle of the transition dipole moment vector for the absorption band at 835 cm(-1). This fact is explained on the basis of the pi-pi* interaction between the phenyl group of PPV and the sidewall of the nanotubes.

113. Post-synthesis Carbon Nanowalls Transformation under Hydrogen, Oxygen, Nitrogen, Tetrafluoroethane and Sulfur Hexafluoride Plasma Treatments

Authors: Vizireanu, S; Ionita, MD; Dinescu, G; Enculescu, I; Baibarac, M; Baltog, I

Published: APR 2012, PLASMA PROCESSES AND POLYMERS, 9, 370, DOI: 10.1002/ppap.201100153

Carbon nanowalls (CNWs) functionalization allows the tailoring of some of their properties after they have been synthesized. Herewith we report on post-synthesis CNWs functionalization by plasma treatments. Radiofrequency plasmas generated in hydrogen, oxygen, nitrogen, tetrafluoroethane, and sulfur hexafluoride admixed to argon, were used. The changes of morphology, structure, chemical composition were determined by SEM, FTIR, Raman Spectroscopy, specifically for each gas mixture. The results point out to the surface erosion, the functional groups attachment, or to thin film coverage of CNWs material. Such processes strongly influence the material properties, as exemplified by the wettability: superhydrophilic or superhydrophobic surfaces are obtained starting from the same base CNWs material.

114. Recent Progress in Synthesis, Vibrational Characterization and Applications Trend of Conjugated Polymers/Carbon Nanotubes Composites

Authors: Baibarac, M; Baltog, I; Lefrant, S

Published: APR 2011, CURRENT ORGANIC CHEMISTRY, 15, 1196, DOI: 10.2174/138527211795203022

This review deals with recent progress on the development of composite materials based on cojugated polymers (CPs) and carbon nanotubes (CNTs), both from fundamental and applied point of view. In the first part of the manuscript, we present the different types of composites, the new protocols used in their synthesis as well as their vibrational properties reported in the last five years. A brief review of the contribution of Raman light scattering and FTIR spectroscopy to establish the type of interaction between the two constituents is discussed for different cases, i.e. bi-layers of polymers and carbon nanotubes, CPs doped with CNTs and CNTs functionalized with CPs. Recently, anti-Stokes resonant Raman studies have appeared as fruithful tools in the evaluation of functionalization process of CNTs with CPs. The review provides also information on CPs/CNTs composite properties specific to applications in the field of energy storage, optical limiting and electron field emission devices, transistors, conducting textiles, sensors, rewritable devices, biomedical and food domains as well as how these materials have been optimized to generate exploitable properties.

115. Polydiphenylamine/carbon nanotube composites for applications in rechargeable lithium batteries

Authors: Baibarac, M; Baltog, I; Lefrant, S; Gomez-Romero, P

Published: FEB 15 2011, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 176, 120, DOI: 10.1016/j.mseb.2010.10.008

Polydiphenylamine/single walled carbon nanotube (PDPA/SWNT) composites were synthesized electrochemically aiming at their application as active electrode materials for rechargeable lithium batteries. The electrochemical polymerization of diphenylamine (DPA) on a SWNT film immersed in a 1 M HCl solution was studied by cyclic voltammetry. Comparing cyclic voltammograms recorded on a blank Pt electrode with those obtained for a SWNT film deposited on Pt electrode one observes in the latter case a decrease of the DPA reduction potential. To elucidate electrochemical polymerization mechanism, photoluminescence studies on DPA/SWNT and PDPA/SWNT systems were carried out. Additional information concerning the functionalization process of SWNT with PDPA was obtained by Raman and IR spectroscopy. Using the PDPA/SWNT composite as active material for the positive electrode of a rechargeable lithium cell (LiPF(6) electrolyte), the charge-discharge tests show a specific discharge capacity of ca. 245 mA h g(-1), much higher than the 35 mA h g(-1) for pure PDPA. (C) 2010 Elsevier B.V. All rights reserved.

116. Hybrid organic-inorganic materials based on poly(o-phenylenediamine) and polyoxometallate functionalized carbon nanotubes

Authors: Baibarac, M; Baltog, I; Smaranda, I; Scocioreanu, M; Lefrant, S

Published: JAN 31 2011, JOURNAL OF MOLECULAR STRUCTURE, 985, 218, DOI: 10.1016/j.molstruc.2010.10.044

The chemical polymerization of o-phenylenediamine (OPD) on single-walled carbon nanotubes (SWCNTs) in the presence of phosphomolybdic acid (H3PMo12O40 xH(2)O) has been studied by surface enhanced resonant Raman scattering (SERRS) spectroscopy. One demonstrates that an organic-inorganic hybrid composite of the type poly(o-phenylenediamine)/polyoxometallate-functionalized SWCNTs is produced by the chemical interaction between polyoxometallate-functionalized SWCNTs and poly(o-phenylenediamine) (POPD) doped with [H2PMo12O40](-) ions. According to TEM investigations, a result of the chemical interaction of SWCNT with H3PMo12O40 xH(2)O is the formation into the composite mass of tube fragments of shorter length, which behave like closed shell fullerenes since Raman fingerprint is given by lines situated at 240-275 and 1450-1472 cm(-1). The chemical polymerization of OPD on SWCNTs achieved in the absence of H3PMo12O40 xH(2)O leads to a covalent functionalization of the wall side of the tubes, which is revealed in Raman spectra, recorded at the excitation wavelength of 514 nm, by an enhancement of the lines associated with the tangential vibrational modes of SWCNTs. Using FTIR spectroscopy, significant hindrance steric effects are evidenced in the POPD/polyoxometallate-functionalized SWCNT composite. (c) 2010 Elsevier B.V. All rights reserved.

117. One-dimensional composites based on single walled carbon nanotubes and poly(o-phenylenediamine)

Authors: Baibarac, M; Baltog, I; Scocioreanu, M; Ballesteros, B; Mevellec, JY; Lefrant, S

Published: NOV-DEC 2011, SYNTHETIC METALS, 161, 2354, DOI: 10.1016/j.synthmet.2011.09.001

The direct mixing of aqueous ferric chloride and o-phenylenediamine (OPD) solution at room temperature in the absence and presence of carbon nanotubes (CNTs) has been used to prepare poly(o-phenylenediamine) (POPD) micro-fibers and composites of the type CNTs/POPD having nanotubes incorporated in polymer fiber mass. Using surface enhanced infrared absorption (SEIRA) spectroscopy significant modifications in the low frequency range of the polymer spectrum are revealed when Au is used as metallic support. Similar variations are reported for the POPD samples prepared by the electropolymerization of OPD onto rough Au electrode. A covalent functionalization of CNTs with POPD and a doping process of POPD with radical anions of CNTs is proved by surface enhanced resonant Raman scattering and SEIRA spectroscopy. The X-ray diffraction (XRD) studies indicate a high crystallinity both for POPD and CNTs/POPD composites prepared by chemical or electrochemical methods. (C) 2011 Elsevier B.V. All rights reserved.

118. Sensitive detection of endocrine disrupters using ionic liquid - Single walled carbon nanotubes modified screen-printed based biosensors

Authors: Gurban, AM; Rotariu, L; Baibarac, M; Baltog, I; Bala, C

Published: SEP 30 2011, TALANTA, 85, 2013, DOI: 10.1016/j.talanta.2011.07.045

Simple and low cost biosensor based on screen-printed electrode for sensitive detection of some alkylphenols was developed, by entrapment of HRP in a nanocomposite gel based on single-walled carbon nanotubes (SWCNTs) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid. Raman and FTIR spectroscopy, CV and EIS studies demonstrate the interaction between SWCNTs and ionic liquid. The nanocomposite gel, SWCNT-[BMIM][PF6] provides to the modified sensor a considerable enhanced electrocatalytic activity toward hydrogen peroxide reduction. The HRP based biosensor exhibits high sensitivity and good stability, allowing a detection of the alkylphenols at an applied potential of -0.2 V vs. Ag/AgCl, in linear range from 5.5 to 97.7 mu M 4 for 4-t-octylphenol and respectively, between 5.5 and 140 mu M for 4-n-nonylphenol, with a response time of about 5s. The detection limit was 1.1 mu M for 4-t-octylphenol, and respectively 0.4 mu M for 4-n-nonylphenol (S/N = 3). (C) 2011 Elsevier B.V. All rights reserved.

119. Abnormal anti-Stokes Raman emission as single beam coherent anti-Stokes Raman scattering like process in LiNbO(3) and CdS powder

Authors: Baibarac, M; Baltog, I; Lefrant, S

Published: SEP 1 2011, JOURNAL OF APPLIED PHYSICS, 110, DOI: 10.1063/1.3633936

Abnormal anti-Stokes Raman emission (AASRE) is defined by an anti-Stokes/Stokes intensity ratio much greater than expected on the basis of the equilibrium population of excited vibration states provided by the Boltzmann law. Using nonlinear optical materials such as LiNbO(3) and CdS in powder form, we demonstrate that under continuous single beam excitation it presents AASRE whose properties are similar to a single beam pumped Coherent Anti-Stokes Raman Scattering. We explain AASRE as resulting from a wave-mixing mechanism of the incident laser light with a Stokes shifted Raman light produced by a spontaneous Raman light scattering process, both strongly scattered inside the sample. (C) 2011 American Institute of Physics. [doi:10.1063/1.3633936]

120. Electrochemical functionalisation of SWNTs with poly(3,4-ethylenedioxythiophene) evidenced by anti-Stokes/Stokes Raman spectroscopy

Authors: Baltog, I; Baibarac, M; Lefrant, S; Mevellec, JY

Published: MAR 2011, JOURNAL OF RAMAN SPECTROSCOPY, 42, 312, DOI: 10.1002/jrs.2705

The capability of anti-Stokes/Stokes Raman spectroscopy to evaluate chemical interactions at the interface of a conducting polymer/carbon nanotubes is demonstrated. Electrochemical polymerisation of the monomer 3,4-ethylenedioxythiophene (EDOT) on a Au support covered with a single-walled carbon nanotube (SWNT) film immersed in a LiClO4/CH3CN solution was carried out. At the resonant optical excitation, which occurs when the energy of the exciting light coincides with the energy of an electronic transition, poly(3,4-ethylenedioxythiophene) (PEDOT) deposited electrochemically as a thin film of nanometric thickness on a rough Au support presents an abnormally intense anti-Stokes Raman spectrum. The additional increase in Raman intensity in the anti-Stokes branch observed when PEDOT is deposited on SWNTs is interpreted as resulting from the excitation of plasmons in the metallic nanotubes. A covalent functionalisation of SWNTs with PEDOT both in un-doped and doped states takes place when the electropolymerisation of EDOT, with stopping at +1.6 V versus Ag/Ag+, is performed on a SWNT film deposited on a Au plate. The presence of PEDOT covalently functionalised SWNTs is rationalised by (1) a downshift by a few wavenumbers of the polymer Raman line associated with the symmetric C-C stretching mode and (2) an upshift of the radial breathing modes of SWNTs, both variations revealing an interaction between SWNTs and the conjugated polymer. Raman studies performed at different excitation wavelengths indicate that the resonant optical excitation is the key condition to observe the abnormal anti-Stokes Raman effect. Copyright (C) 2010 John Wiley & Sons, Ltd.

121. Abnormal anti-Stokes Raman emission as a coherent anti-Stokes Raman scattering-like process in disordered media

Authors: Baltog, I; Baibarac, M; Smaranda, I; Lefrant, S

Published: MAY 14 2011, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 44, DOI: 10.1088/0953-4075/44/9/095401

In this paper, we demonstrate that, by continuous single beam excitation, one can generate an abnormal anti-Stokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering (CARS). The effect has been observed in materials which possess intrinsically nonlinear properties (LiNbO(3) and CdS), which have the electric susceptibility of third order different from zero, chi((3)) not equal 0, as well as in materials that become nonlinear under resonant optical excitation. In the latter case, we used poly-3,4-ethylendioxythiophene (PEDOT) in its undoped state deposited electrochemically on Au support. Raman studies corroborated with images of optical microscopy demonstrate that the production of AASRE is conditioned by the existence of a particular morphology of the sample able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, it was found that LiNbO3 and CdS in powder form as well as the PEDOT films layered on a rough Au substrate are suitable morphological forms. We explain AASRE as resulting from a wave-mixing mechanism of the incident laser light omega(l) with a Stokes-shifted Raman light omega(S) produced by a spontaneous Raman light scattering process, both strongly scattered inside the sample. As a CARS process, AASRE is conditioned by the achievement of phase-matching requirements, which makes the difference between the wave vectors of mixing light close to zero, Delta k = /2k(l) - k(S) - k(CARS) /approximate to 0. In condensed media, the small dispersion of the refractive index makes Delta k approximate to 0 so that the formation of a favourable phase-matching geometry may be accomplished even at a crossing angle. of travelling scattered light omega(l) and omega(S). For tightly focused beams, the requirement of phase matching relaxes; it is no longer sensitive to the Raman shift, so that a wide intense anti-Stokes Raman spectrum is observed at an angle larger than the Stokes Raman spectrum.

122. Structural and thermoluminescence properties of undoped and Fe-doped-TiO2 nanopowders processed by sol-gel method

Authors: Cernea, M; Secu, M; Secu, CE; Baibarac, M; Vasile, BS

Published: JAN 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 85, DOI: 10.1007/s11051-010-0002-7

In this study, we report on the nanocrystalline powders of TiO2 and Fe-doped TiO2 (anatase and rutile phases) prepared by sol-gel method. The X-ray diffraction and Raman spectroscopy measurements indicated the presence of anatase or rutile phase in nanopowders. TEM micrographs showed 10 and 112 nm average particle sizes for anatase and rutile, respectively. Furthermore, their thermoluminescence properties were analyzed.

123. Non-linear and resonance effects in carbon nanotube structures

Authors: Lefrant, S; Buisson, JP; Mevellec, JY; Baibarac, M; Baltog, I

Published: JUL 2011, OPTICAL MATERIALS, 33, 1414, DOI: 10.1016/j.optmat.2011.03.014

In this paper, we report on Raman scattering and Surface Enhanced Raman Scattering (SERS) studies of single walled carbon nanotubes (SWNTs) and carbon nanotube/conjugated polymers composites. We demonstrate that under SERS conditions we induce an abnormal anti-Stokes Raman emission, that can be interpreted as being due to a "single-beam pumped" Coherent Anti-Stokes Raman Scattering (CARS) effect. We also investigate in detail the anti-Stokes/Stokes (aS/S) intensity ratios of the radial breathing modes (RBMs) of SWNTs as a function of several parameters. From calculations, we show that resonance phenomena mostly explain the aS/S intensity ratio anomalies, but only at low frequencies. In addition, we describe results obtained with polymers like poly(bithiophene) (PBTh) polymerized on carbon nanotube thin films which exhibit also an amplification of its high frequency Raman modes in the anti-Stokes branch, generated by the plasmon excitation of metallic tubes. This phenomenon occurs in several other materials such as composites based on SWNTs and conjugated polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) and polyparaphenylene-vinylene (PPV) for modes located around 1500 cm(-1). (C) 2011 Elsevier B.V. All rights reserved.

124. Photoluminescence and Raman studies on tin dioxide powder and tin dioxide/single-walled carbon-nanotube composites

Authors: Gontia, II; Baibarac, M; Baltog, I

Published: JUN 2011, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 248, 1498, DOI: 10.1002/pssb.201046569

Photoluminescence (PL) and Raman spectroscopy were used to characterize the tin dioxide (SnO(2)) powder and the SnO(2)/single-walled carbon-nanotube (SWCNT) composites. The SnO(2) powder shows a strong PL broad band centered at 1.95 eV (635 nm) under excitation at 280 nm (4.43 eV) and four PL bands peaking at: 1.95 eV (635 nm), 2.67 eV (464 nm), 2.82 eV (439 nm), and 2.98 eV (416 nm) under excitation at 350 nm (3.54 eV). PL decay-time measurements of the SnO(2) powder indicates a PL lifetime of about 1.53 ns. In the SnO(2)/SWCNT composites, prepared mechanicochemically, a quenching of PL is observed as the concentration of SWCNT increases. The Raman spectra were recorded at two excitation wavelengths: 514.5 and 676.4 nm. At the excitation wavelength of 676.4 nm (1.83 eV), the Raman spectrum shows a narrowed asymmetric profile of the G band (similar to 1585 cm similar to 1), which indicates that in the SnO(2)/SWCNT composite there is an interaction between SnO(2) and metallic SWCNTs. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

125. Photoluminescence of poly (N vinylcarbazole)/carbon nanotubes composites

Authors: Gontia, II; Baibarac, M; Baltog, I

Published: MAY-JUN 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 582, DOI:

The photoluminescence (PL) of two types of poly (N-vinyl-carbazole)(PVK)/carbon nanotubes (CN) composites, prepared by chemical and electrochemical method, has been investigated. In comparison with the pure PVK, the chemically prepared PVK/NC sample shows a significant PL quenching and a shorter decay time. For the samples prepared electrochemically, PL increases in intensity, red shifts and gets longer decay time with the increase of voltammetric cycles number. In addition, the latter shows a change in emission from high-energy excimer to low-energy excimer after a treatment with NH(4)OH.

126. Films and crystalline powder of BiI3 intercalated with ammonia

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I; Pandele, J; Andronescu, C; Fruth, V

Published: JAN 2010, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 30, 479, DOI: 10.1016/j.jeurceramsoc.2009.05.046

Intercalation, i.e. the insertion of guest species in a crystalline layered structure, is an efficient route for generating new materials with novel properties. Thin films and crystalline powder of BiI3 layered semiconductor were intercalated by exposure to ammonia vapors at room temperature. The intercalated compound was studied by thermo-gravimetric analysis, differential scanning calorimetry, X-ray diffraction, UV-vis optical absorption, FTIR spectroscopy and Raman scattering. After exposure of BiI3 to ammonia the formation of a new phase, BiI3(NH3)(3.83), was evidenced by thermal analysis. The intercalation process leads to a blue shift of the BiI3 Optical absorption edge by 0.5 eV. The appearance of new Raman lines at 135 and 353 cm(-1) in the Raman spectrum of intercalated BiI3 is considered as an evidence of the chemical interaction between the ammonia molecules and BiI3 lattice. (C) 2009 Elsevier Ltd. All rights reserved.

127. NON-LINEAR RAMAN SCATTERING EFFECTS GENERATED BY THE SURFACE PLASMONS EXCITATION

Authors: Baltog, I; Baibarac, M; Mihut, L; Smaranda, I

Published: 2010, ROMANIAN REPORTS IN PHYSICS, 62, 593, DOI:

An inciting and much debated subject in the surface enhanced Raman (SERS) studies is an unusual anti-Stokes Raman spectrum distinguished by an abnormal intensity, increasing with the vibrational wavenumber and some discrepancies with regard to the Stokes spectrum. We demonstrate that the abnormal anti-Stokes Raman emission on single walled carbon nanotubes and poly(3,4-ethylenedioxy thiophene) synthtetized electrochemically appears as a consequence of two corroborating effects: resonance, which occurs when the energy of the excitation light is near or coincident with the energy of an electronically allowed transition, and the SERS effect achieved by the excitation of surface plasmons. An abnormal intense Raman emission in the Stokes branch, reminiscent to a stimulated Raman effect, which increases exponentially with the intensity of exciting light is reported for the first time in the case of SWNTs.

128. Linear and Non-Linear Optical Properties of Carbon Nanotubes

Authors: Lefrant, S; Buisson, JP; Mevellec, JY; Baibarac, M; Baltog, I

Published: 2010, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 522, 479, DOI: 10.1080/15421401003719910

Carbon nanotubes are attractive materials with numerous possibilities of applications in various domains. Nevertheless, pertinent characterization studies are required in order to insure reproducibility in preparation, handling and incorporation in devices. Several spectroscopic tools have been developed so far, such as transmission electron microscopy and near-field electrical microscopy. Optical techniques have also been improved with the use of Raman Scattering, Surface Enhanced Raman Scattering (SERS) and near-field optical spectroscopy (SNOM). These non-destructive techniques have been used for nanotubes after synthesis and exploited to follow the modifications of their spectroscopic features when they are functionalized or embedded in host matrices. In this paper, we show that, by using SERS conditions, a new effect is observed: a "single-beam pumped'' Coherent anti-Stokes Raman Scattering (CARS). We demonstrate that under a tight-focusing of the excitation light, this emission, resulting from a wave mixing process between the incident laser light (omega(l)) and Stokes Raman light (omega(s)), is generated by a Surface Enhanced Raman Scattering (SERS) mechanism. Since abnormal anti-Stokes/Stokes intensity ratios are also observed for carbon nanotubes in powders, we have investigated in details their behaviour as a function of several parameters which include the excitation wavelengths, the laser power, the sample support, as well as the presence of nanotubes in isolated or in bundled form. It appears that resonance phenomena explain the anti-Stokes/Stokes intensity ratios in the case of powders and that CARS is only observed when SERS conditions are used. In addition, we have investigated other materials in which anomalies are also observed. This is the case of poly(bithiophene) (PBTh) electrochemically polymerized on carbon nanotubes for which its main Raman line at 1450 cm(-1) is enhanced, this enhancement being presumably generated by the plasmon excitation of metallic tubes. In the case of PEDOT, the analysis of the anti-Stokes branch provides additional information on the functionalization of carbon nanotubes with this polymer.

129. Photoluminescence and Raman spectroscopy studies on polyaniline/PbI2 composite

Authors: Baibarac, M; Baltog, I; Lefrant, S

Published: APR 2009, JOURNAL OF SOLID STATE CHEMISTRY, 182, 835, DOI: 10.1016/j.jssc.2009.01.007

Functionalization of PbI2 with conjugated polymers (polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES)) is demonstrated by Raman and luminescence studies. PbI2/PANI hybrid material was prepared by electrochemical polymerization of aniline onto the PbI2 modified Pt electrode and mechanico-chemical reaction between the two constituents. PANI interacting with the PbI2 gives rise to new Raman bands at 80,144 and 170 cm(-1). First line reveals the formation of "stacking faults" that disrupt the I-Pb-I layers stacking along the c axis by the insertion of polymer molecules. The bands at 144 and 170 cm(-1) are attributed to the vibrational mode associated with Pb-NHR ''(2) (R '' = C6H4) bond. The functionalization of PbI2 with PANI-EB brings forth the PANI-ES form. Depending on the semiconducting (PANI-EB) or conducting (PANI-ES) properties of the polymer in the PbI2/PANI intercalated material, a partial or total collection of the charges generated under band to band irradiation is revealed by photoluminescence studies. (C) 2009 Elsevier Inc. All rights reserved.

130. Carbon nanotubes from ethanol on Fe-Co/MgO catalysts and related interface phenomena

Authors: Lupu, D; Biris, AR; Baltog, I; Baibarac, M; Kuncser, V; Schinteie, G; Valeanu, M; Lefrant, S; Biris, AS; Misan, I; Filoti, G

Published: MAR 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 347, DOI:

Mossbauer spectroscopy studies of Fe-Co/MgO catalysts proved that a high dispersion degree of Fe may be achieved for catalysts containing Fe/Co in a ratio close to 1. During materials processing. the presence of hydrogen at high temperatures, even for short time, induced an increased particle size of the catalytic Fe. The evaluation of various iron species from their areas in the Mossbauer spectra revealed the dependence of the nanotube amount on (FeCo alloy + Fe2+) content in the catalyst, in good agreement with literature mechanisms. The Raman spectra show that carbon nanotubes synthesized from ethanol in argon flow on 4.5%Fe:4.5%Co/MgO are richer in low diameter (0.7-1.0nm) tubes than those obtained at low ethanol pressure, in agreement with the effects of hydrogen reported in literature. The close similarity with the Raman spectra of Aldrich double-walled carbon nanotubes and from literature, recommends the syntheses in argon flow as better conditions for double-walled carbon nanotube growth.

131. Raman spectroscopic evidence for interfacial interactions in poly(bithiophene)/single-walled carbon nanotube composites

Authors: Baibarac, M; Baltog, I; Lefrant, S

Published: APR 2009, CARBON, 47, 1398, DOI: 10.1016/j.carbon.2009.01.031

Electrochemical polymerization of 2,2'-bithiophene (BTh) on single-walled carbon nanotube (SWCNT) films has been studied by Raman scattering and infrared absorption spectroscopy. Covalent functionalization of SWCNTs with poly(bithiophene) (PBTh) in its un-doped and doped states is demonstrated. The occurrence of a charge transfer process at the interface of PBTh and SWCNTs, is shown by: (i) an up-shift of the Raman lines associated with the radial breathing modes of SWCNTs that reveals both a doping process and an additional twisting together as a rope with the conducting polymer as binding agent; (ii) a new Raman band in the range 1430-1450 cm(-1) indicating the functionalization of SWCNTs with PBTh in doped and un-doped states; (iii) strong absorption bands situated in the interval 600-800 cm(-1) resulting from steric hindrance produced by the nanotube binding to the polymeric chain. Treatment of the PBTh/SWCNT composite with aqueous NH4OH Solution forms un-doped PBTh covalently functionalized SWCNTs. At the resonant excitation of the metallic tubes, an additionally enhanced Raman process is generated by plasmon excitation in the metallic nanotubes. It is evidenced by a particular behavior in the Stokes and anti-Stokes branch of the PBTh Raman line at 1450 cm(-1). (C) 2009 Elsevier Ltd. All rights reserved.

132. Intercalation of Layered Metal Iodides with Pyridine Evidenced by Raman Spectroscopy

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I

Published: JUL 2009, ACTA PHYSICA POLONICA A, 116, 83, DOI: 10.12693/APhysPolA.116.81

PbI2, BiI3, CdI2 and AgI crystalline samples intercalated with pyridine have been studied by Raman spectroscopy. Comparing the Raman spectra of pristine metal iodides with those of intercalated samples we have shown the coexistence, in the host crystalline lattice, of two adsorbed forms: a physisorbed one, featured by weak forces of van der Waals type and a chemisorbed one, involving stronger forces related to an electrostatic interaction. The physisorbed form is consistent with the molecules inserted into the interlayer spaces while the chemisorbed form is represented by the molecules forming coordination complexes with the crystalline lattice cations. The crucial role in the formation of such complexes is played by the lone pair of nitrogen atom belonging to the molecules.

133. ZnO particles of wurtzite structure as a component in ZnO/carbon nanotube composite

Authors: Baibarac, M; Baltog, I; Velula, T; Pasuk, I; Lefrant, S; Gautier, N

Published: NOV 4 2009, JOURNAL OF PHYSICS-CONDENSED MATTER, 21, DOI: 10.1088/0953-8984/21/44/445801

Composites based on carbon nanotubes and ZnO particles with needle shapes were prepared for applications in energy storage. Depending on the temperature (85 or 25 degrees C) at which the reaction between NaOH and ZnCl(2) was carried out, particles with two different morphologies: needle-shaped (NS) and double-pyramid-shaped (DPS), respectively, are obtained. Scanning electron microscopy, photoluminescence, UV-Vis absorption spectroscopy, x-ray diffraction and Raman light scattering studies reveal that the NS and DPS particles belong to ZnO with wurtzite (WZ) structure and epsilon-Zn(OH)(2) as precursors of ZnO, respectively. Using the ZnO/carbon nanotube composite as a negative electrode and an electrolytic solution containing LiPF(6), the charge-discharge characteristics of rechargeable lithium ions cells were determined. Additional information concerning the electrochemical reactions at the interface of the two electrodes was obtained by cyclic voltammetry.

134. Optical advanced spectroscopic techniques for the study of nano-structured materials: Applications to carbon nanotubes

Authors: Lefrant, S; Baltog, I; Baibarac, M

Published: NOV 2009, SYNTHETIC METALS, 159, 2176, DOI: 10.1016/j.synthmet.2009.08.029

In this paper, we present the anti-Stokes Raman scattering as a technique allowing investigations of materials at a nanoscale level. When the energy of the excitation light coincides with the energy of an electronic transition, a strong anti-Stokes Raman spectrum with respect to the prediction of the Maxwell-Boltzman (MB) law is regularly observed. Under a tight-focusing of the excitation light, the anti-Stokes Raman emission is reminiscent of Coherent anti-Stokes Raman Scattering (CARS). It has been detected on carbon nanotubes (CNTs), prototypes of nanometric materials, as well as on other compounds such as copper phthalocyanine (CuPc), poly(bithiophene) (PBTh), poly(3,4-ethylene dioxythiophene) (PEDOT), polyparaphenylene vinylene (PPV) layered as thin films on a metallic support in which are generated surface plasmons. We demonstrate that nanostructures by themselves can be of importance by generating non-linear phenomena that can be exploited for studying such materials and in particular carbon nanotubes. (C) 2009 Elsevier B.V. All rights reserved.

135. ABSORPTION AND LUMINESCENCE PROPERTIES OF C-70 AGGREGATES IN SOLVENT MIXTURES

Authors: Husanu, AM; Baltog, I; Baibarac, M; Preda, N; Mihut, L; Velula, T; Bucur, C

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 538, DOI:

We report the formation of stable C-70 aggregate forms in o-dichlorobenzene/N-methyl-2-pyrrolidinone (DCB/NMP) and o-dichlorobenzene/acetonitrile (DCB/ACN) mixtures and their characterization by UV-VIS absorption spectroscopy and photoluminescence. As NMP acts on C-70 both as a solvent and reactant due to the unpaired electrons of the amidic nitrogen atom, molecular complexes (C-70/NMP) that aggregate slowly are formed by the binding of the NMP molecule to the fullerene cage. This interaction is seen in the UV-VIS absorption spectra of C-70 in DCB/NMP solvent mixtures by a gradual modification of the absorption spectra when increasing the NMP concentration. On the other hand, DCB and ACN combined form it typical solvent/non-solvent mixture favoring an intense aggregation of fullerenes. This yields to the C-70 clusters formations, having different size, similar to a precipitation process. Their characteristic is an abrupt variation in the absorbance appearing when the ACN is used in a greater extent. This different behavior of C-70 aggregation in DCB/NMP and DCB/ACN mixtures is also seen in their luminescence spectra recorded at different excitation wavelengths. While the PL spectra of C-70 solvated in DCB/NMP solution keeps almost the same modified shape irrespective the NMP concentration, the luminescence spectra Of C-70 in DCB/ACN mixture partially regains the powder C-70 PL signature as the ACN concentration is increased.

136. THE INTERCALATION OF PbI2 WITH 2,2 '-BIPYRIDINE EVIDENCED BY PHOTOLUMINESCENCE. FT-IR AND RAMAN SPECTROSCOPY

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I; Husanu, M; Bucur, C; Velula, T

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 675, DOI:

Hybrid material based on PbI2 intercalated with 2,2'-bypiridine (BIPY) was investigated by correlated studies of photoluminescence. infrared absorption and Raman spectroscopy. The PbI2(BIPY) intercalated compound has been synthesized by the chemical reaction of K1 and Pb(NO3)(2) in aqueous BIPY solution The optical studies reveal different properties for the hybrid material in comparison with those of pure PbI2 and BIPY. In the photoluminescence spectrum of the intercalated compound. recorded at liquid nitrogen temperature a new intense hand emission with maximum at 2 07 eV is observed. The excitation spectrum reveals it broad hand featured by several maxima at 2.77, 3.34 and 3 70 eV. New absorption bands at about 1589, 1489, 1435, 1312, 1009 cm(-1) are observed in the IR spectrum of PbI2(BIPY). The Raman spectrum of intercalated compound discloses new lines at 67, 83, 127 cm(-1) and the shift of two Raman lines from 994 cm(-1) to 1010 cm(-1) and from 1045 cm(-1) to 1060 cm(-1). A charge transfer process, leading to the formation of lead-BIPY coordination complexes. is considered its responsible for the strong host-guest interaction revealed by almost all experimental data

137. Surface Enhanced Raman Scattering Studies on Poly(3,4-ethylene dioxythiophene)/Single-Walled Carbon Nanotubes Composites and Their Application to Rechargeable Lithium Batteries

Authors: Baltog, I; Baibarac, M; Lefrant, S; Gomez-Romero, P

Published: OCT 2009, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 9, 6209, DOI: 10.1166/jnn.2009.1548

In this paper, surface enhanced Raman scattering (SERS) studies on the chemical polymerization of 3,4-ethylene dioxythiophene (EDOT) in the presence of single-walled carbon nanotubes (SWNTs) are reported. Both a non-covalent and covalent functionalization of SWNTs with poly(3,4-ethylene dioxythiophene) (PEDOT) is invoked as a result of the following variations induced in the SERS spectra of PEDOT and SWNTs: (i) the appearance of a Raman line at 140 cm(-1) indicating the formation of a new covalent bond between PEDOT and SWNTs; (ii) an increase in the intensity of the Raman line at 705 cm(-1), associated with the deformation vibration mode of C-S-C bond, the result of a steric hindrance effect induced by the bonding of PEDOT on SWNTs; and (iii) the enhancement of the Raman band with maximum at 1540 cm(-1) (G(-) component) in SWNTs when the PEDOT weight in the PEDOT/SWNTs composite increases. Using the PEDOT/SWNTs composite as a positive electrode and an electrolytic solution containing LiPF6, the charge-discharge characteristics of the rechargeable lithium cells are determined. High specific discharge capacity are reported for the PEDOT/SWNTs composite (ca. 218 mAh g(-1)) in comparison with PEDOT doped with FeCl4- ions (ca. 25 mAh g(-1)).

138. Optical Advanced Spectroscopic Techniques for the Study of Nano-Structured Materials Such as Carbon Nanotubes

Authors: Lefrant, S; Baltog, I; Baibarac, M

Published: AUG 2009, JOURNAL OF NANOELECTRONICS AND OPTOELECTRONICS, 4, 206, DOI: 10.1166/jno.2009.1022

Optical techniques allowing observations and spectroscopic investigations of materials at a nanoscale have been recently developed and applied to carbon nanotubes. They are briefly presented, including Scanning near-field optical microscopy, together with the Surface Enhanced or Tip Enhanced Raman Scattering. Even if new physical properties are difficult to extract from observed data, we show that nanostructures can generate non linear phenomena that can be exploited for studying nano-materials and in particular carbon nanotubes. By measuring the anti-Stokes/Stokes ratios of the Raman bands which present strong anomalies with respect to the prediction of the Maxwell-Boltzman law, one can distinguish between semi-conducting and metallic tubes on one hand and between isolated and bundled nanotubes on the other hand.

139. Quantum well effect in bulk PbI2 crystals revealed by the anisotropy of photoluminescence and Raman spectra

Authors: Baltog, I; Baibarac, M; Lefrant, S

Published: JAN 14 2009, JOURNAL OF PHYSICS-CONDENSED MATTER, 21, DOI: 10.1088/0953-8984/21/2/025507

On subjecting a bulk 2H-PbI2 crystal to vacuum annealing at 500 K followed by a sudden cooling at liquid nitrogen temperature stacking faults are generated that separate distinct layers of nanometric thickness in which different numbers of I-Pb-I atomic layers are bundled together. Such structures, containing two, three, four, five etc I-Pb-I atomic layers, behave as quantum wells of different widths. The signature of such a transformation is given by a shift towards higher energies of the fundamental absorption edge, which is experimentally revealed by specific anisotropies in the photoluminescence and Raman spectra. The quantum confining effect is made visible by specific variations of a wide extra-excitonic band (G) at 2.06 eV that originates in the radiative recombination of carriers (electrons and holes), trapped on the surface defects. The excitation spectrum of the G band, with p polarized exciting light, reveals a fine structure comprised of narrow bands at 2.75, 2.64, 2.59 and 2.56 eV, which are associated with the PbI2 quantum wells formed from two, three, four and five I-Pb-I atomic layers of 0.7 nm thickness. Regardless of the polarization state of the laser exciting light of 514.5 nm (2.41 eV), which is close to the band gap energy of PbI2 (2.52 eV), the Raman scattering on bulk as-grown PbI2 crystals has the character of a resonant process. For p polarized exciting light, the Raman scattering process on vacuum annealed PbI2 becomes non-resonant. This originates from the quantum well structures generated inside the crystal, whose band gap energies are higher than the energy of the exciting light.

140. VIBRATIONAL PROPERTIES OF POLYANILINE FUNCTIONALIZED PbI2

Authors: Baltog, I; Baibarac, M; Mihut, L; Preda, N; Velula, T; Bucur, C; Husanu, M

Published: 2009, ROMANIAN JOURNAL OF PHYSICS, 54, 688, DOI:

Functionalization of PbI2 with polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES) is demonstrated by Raman spectroscopy. Two functionalization methods were used: electrochemical polymerization of aniline onto the PbI2 modified Pt electrode and the mechanico-chemical reaction between PANI and PbI2. The functionalization induces changes in the Raman spectrum of PbI2 that consist in the appearance of new Raman lines with the peaks at 80, 144 and 170 cm(-1) The first line is the signature of the "stacking faults" that disrupt the stacking sequence of layers I-Pb-I atomic layers along the c crystalline axis by the intercalation of polymer molecules The bands at 144 and 170 cm(-1) are attributed to a vibrational mode associated to the Pb-NHR"(2) (R" = C6H4) bond.

141. Raman and FTIR spectroscopy as valuable tools for the characterization of polymer and carbon nanotube based composites

Authors: Lefrant, S; Baibarac, M; Baltog, I

Published: 2009, JOURNAL OF MATERIALS CHEMISTRY, 19, 5704, DOI: 10.1039/b821136a

The combination of the unique properties of carbon nanotubes (CNTs) with conjugated polymers makes their combined composite materials interesting as multifunctional systems with great potential. Supercapacitors, lithium rechargeable batteries, sensors, photovoltaic cells and photodiodes, optical limiting devices, solar cells, high-resolution printable conductors, electromagnetic absorbers and advanced transistors are among the most promising applications. Knowledge of the molecular structure of such compounds is essential for a better use, and for that reason vibrational spectroscopies are fruitful techniques. Therefore, this feature article presents recent progress in the characterization of composites based on conjugated polymers and carbon nanotubes. The contribution of Raman scattering and FTIR spectroscopy to establish the type of interaction between the two constituents will be discussed for different cases, i.e. bi-layers of polymers and carbon nanotubes, doped conjugated polymers with carbon nanotubes and covalently functionalized carbon nanotubes with conjugated polymers. In addition, surface enhanced Raman scattering (SERS) has also proven to be a suitable technique for characterization by providing signal enhancements, allowing for instance the detection of reactions at interfaces or the exploitation of properties associated with nanostructures. As an example, an extra increase of the Raman signal of a polymer deposited on a carbon nanotube thin film demonstrates the generation of surface plasmons in metallic tubes.

142. Vibrational properties of the electrochemically synthesized polyindole/single-walled carbon nanotubes composite

Authors: Baibarac, M; Baltog, I; Scocioreanu, M; Lefrant, S; Mevellec, JY

Published: DEC 2009, SYNTHETIC METALS, 159, 2555, DOI: 10.1016/j.synthmet.2009.09.010

Electrochemical polymerization of indole in a LiClO4/CH3CN solution on a single-walled carbon nanotubes (SWNTs) film was studied by cyclic voltammetry, Raman scattering and FTIR spectroscopy. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when carbon nanotubes films were previously deposited onto the Pt electrode, a down-shift of the indole reduction peak potential in the latter case was observed. Raman spectroscopy studies indicate that the electrochemical deposition of polyindole (PIN) onto the SWNT film results in a breaking of SWNT bundles into individual tubes. A covalent functionalization of SWNTs with PIN in the doped state is demonstrated by FTIR spectroscopy, when an increase in the intensity of the absorption band at 1045 cm(-1) is observed. Besides, Raman and FTIR studies performed on samples electrochemically prepared and thereafter post-chemically reacted with an NH4OH solution, indicate both a roping process of individual tubes with PIN as a binding agent and a strong steric hindrance effect. (C) 2009 Elsevier B.V. All rights reserved.

143. Electropolymerization of N-Ethylcarbazole on Single Walled Carbon Nanotubes-Cyclic Voltammetry, Raman and FTIR Studies

Authors: Baibarac, M; Baltog, I; Mihut, L; Mevellec, JY; Lefrant, S

Published: OCT 2009, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 9, 6203, DOI: 10.1166/jnn.2009.1547

The electrochemical polymerization of N-ethyl carbazole (EK) on carbon nanotubes (CNs) films immersed in a LiClO4/acetonitrile solution was studied by cyclic voltammetry. Cyclic voltammo-grams recorded on a blank Pt electrode were compared with those obtained when CNs films were deposited on a Pt plate. In the latter case, the oxidation maximum is not clearly observed. Using the Raman scattering studies, oligomers of poly(N-ethyl carbazole) (PEK) on CNs are shown to be formed. A covalent functionalization of CNs with the PEK oligomers is demonstrated by FTIR spectroscopy studies. The formation of new C-C covalent bonds between CNs and the benzene ring of PEK induces steric hindrance effects that are shown in FTIR spectra by the increase in the intensity of the absorption band at 1072 cm(-1) attributed to the vibration of C-H in plane deformation of aromatic ring. The influence of the monomer and the supporting electrolyte concentration as well as the sweep rate on the polymerization conditions in the case of the composites based on the PEK oligomers and CNs were also investigated.

144. Films and crystalline powder of PbI2 intercalated with ammonia and pyridine

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I; Ramer, R; Pandele, J; Andronescu, C; Fruth, V

Published: JAN 2009, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 20, 470, DOI: 10.1007/s10854-008-9681-6

Thin films and crystalline powder of PbI2 intercalated with ammonia or pyridine have been studied by optical absorption, Raman scattering, photoluminescence, FTIR spectroscopy and thermo-gravimetric analysis. Ammonia intercalated PbI2 shows an increased optical band gap, of about 0.6 eV, with an intense broad emission band peaking at about 2.3 eV as signature in the photoluminescence spectrum. The intercalation of PbI2 with ammonia is noticed in the Raman spectrum by the appearance of new lines situated in low frequency range. The D-3d coordination geometry of Pb2+ in the PbI2 crystal is reduced by compression to orthorhombic one, the distribution of the electronic states in valence band is also changed. Thus, the top of the valence band undergo a deformation inducing a weakness of the interaction between the lead and iodine ions within a layer. Also the PbI2 intercalated with pyridine is featured by optical and vibration properties different that of pure crystalline powder. Finally, the intercalation of PbI2 with different molecules changes the basic semiconducting properties of the crystal. Thermal analyses and infrared absorption spectra have been used to study the desorption of guests species from PbI2 in order to evaluate the stability range and morphological changes with temperature.

145. Synthesis of narrow diameter distribution carbon nanotubes on ZnO supported catalysts

Authors: Lupu, D; Biris, AR; Watanabe, F; Li, ZR; Dervishi, E; Saini, V; Xu, Y; Biris, AS; Baibarac, M; Baltog, I

Published: MAY 12 2009, CHEMICAL PHYSICS LETTERS, 473, 304, DOI: 10.1016/j.cplett.2009.03.069

Multiwall carbon nanotubes, as indicated by electron microscopy and spectroscopy, were grown over a novel Co(5 wt.%)/ZnO catalyst by using a cold wall radio-frequency catalytic chemical vapor deposition method. The nanotubes were found to have a rather narrow diameter distribution, which can be explained by the formation over the ZnO support particles of uniform Co clusters, as shown by high resolution transmission electron microscopy studies. The growth of carbon nanotubes over such a support could represent a fast and reliable method to develop in one step 3D ZnO-CNTs heterogeneous composites of any size or shape, for use in advanced applications. (c) 2009 Elsevier B.V. All rights reserved.

146. Photoluminescence properties of composites based on zinc oxyde and single-walled carbon nanotubes

Authors: Baibarac, M; Baltog, I; Husanu, M; Velula, T; Bucur, C; Mihut, L; Preda, N

Published: FEB 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 293, DOI:

Photoluminescence (PL) properties of the composites based on zinc oxide (ZnO) and single-walled carbon nanotubes (SWNTs) prepared by hydrothermal synthesis are studied in this paper. The emission and excitation spectra of nanometric ZnO powder are dramatically influenced by the adsorption of different molecules coming from the environment. Therefore, a special attention is given to reveal the influences of adsorption/de-sorption process on photoluminescence properties of zinc oxide nanoparticles. A quenching effect of the intrinsic PL is observed regularly when the ZnO is synthesized in the presence of SWNTs, i.e. when a ZnO/SWNTs composite is formed. A distinct feature of the ZnO/SWNTs composite, is an emission band with a maximum at 405-450 nm.

147. Particular signature of isolated and bundled carbon nanotubes in their Raman spectra

Authors: Husanu, M; Baibarac, M; Baltog, I

Published: 2008, ROMANIAN REPORTS IN PHYSICS, 60, 699, DOI:

The efficiency of different surfactants (anionic, cationic, neutral) as chemical agents favoring in the unbinding of nanotube bundles in isolated entities is investigated by Raman and UV-VIS-NIR spectroscopy. ne neutral surfactants Tween 20 - polyoxyethylene sorbitan monolaurate (T-20-PSM) and Tween 80 - polyoxyethylene (80) sorbitan monooleate (T-80-PSM) have been found the most efficient. The isolated single walled carbon nanotubes (SWNTs) nanotubes are apprised at lambda(exc) = 1064 nm by two simultaneous modifications of the Raman spectra: i) narrowing of the band associated to the transversal vibration modes, i.e., G band (similar to 1592 cm(-1)); ii) change of shape of the complex band associated to the radial vibration modes (RBM) consequent on the decrease of the intensity of the components associated with the bundled nanotubes. The individualization of nanotubes is evidenced also in the UV-VIS-NIR absorption spectra by the appearance of a fine structure in the wide absorption band (similar to 1400-1750 nm) that is associated with the transitions E-S(11) of semiconducting SWNTs. The fine structure grows gradually with the separation degree in isolated nanotubes entities.

148. Single-beam pumped coherent anti-Stokes Raman scattering on carbon nanotubes thin films excited through surface plasmons

Authors: Baltog, I; Baibarac, M; Lefrant, S

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2385, DOI: 10.1016/j.physe.2007.07.022

In this paper, we propose an interpretation for an abnormal anti-Stokes Raman emission observed on nanometric thin films of different materials and in particular carbon nanotubes. We demonstrate that under a tight-focusing of the excitation light, a coherent anti-stokes Raman scattering (CARS) emission is produced, resulting from a wave mixing process between the incident laser light (omega(1)) and Stokes Raman light (omega(s)) generated by a surface enhanced Raman scattering (SERS) mechanism. Although the Stokes/anti-Stokes intensity ratio has been explained differently, we present here the results which corroborate the CARS emission. They can be summarized as follows: (i) a square relationship between the CARS signal intensity and the film thickness; (ii) a square relationship between the CARS signal intensity and the exciting laser intensity; (iii) a dependence of the CARS intensity on the numerical aperture (NA) of the microscope objective used for the detection of the anti-Stokes emission. Such effects are not specific to carbon nanotubes and have been observed with other materials accommodated in similar conditions on rough metallic surfaces acting as SERS supports. (c) 2007 Elsevier B.V. All rights reserved.

149. Non-covalent functionalization of carbon nanotubes: Experimental evidence for isolated and bundled tubes

Authors: Husanu, M; Baibarac, M; Baltog, I

Published: OCT 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 41, 69, DOI: 10.1016/j.physe.2008.06.001

Single-walled carbon nanotubes (SWNTs) may be used in technological applications as individual entities instead of bundled tubes. The Raman signature of these two forms is still a controversial subject. The profile, peak position and relative intensity of the Raman band associated with the tangential vibration modes (G band similar to 1600cm(-1)) and radial vibration modes (RBM similar to 100-200cm(-1)) are the main parameters which can reveal the dispersion state of nanotubes. Resonant Raman scattering and absorption spectroscopy on SWNTs furnish complementary information concerning the efficiency of the nanotube dispersion in individual entities. (C) 2008 Elsevier B.V. All rights reserved.

150. Optical cooling of single-walled carbon nanotubes as revealed by their anti-Stokes Raman spectra

Authors: Baltog, I; Baibarac, M; Lefrant, S

Published: JUL 9 2008, JOURNAL OF PHYSICS-CONDENSED MATTER, 20, DOI: 10.1088/0953-8984/20/27/275215

Semiconducting single-walled carbon nanotubes resonantly excited by the interband E-22(S) electronic transitions (at 1064 nm) display for the two components of the radial Raman band-one associated with the isolated tubes and the other associated with the bundled tubes-an anti-Stokes/Stokes Raman intensity ratio (I-aS/I-S) which deviates oppositely from the predictions of the Maxwell-Boltzmann formula. A cooling and heating vibration process, evidenced by an enhancement and diminishment of (I-aS/I-S), appears in the isolated and bundled nanotubes, respectively. Here we confirm a cooling process, observed only for semiconducting nanotubes, which emerges from the relaxation of the E-22(S) excited state by the electronic relaxation from E-22(S) to E-11(S) that precedes the spontaneous luminescence emission at E-11(S). Metallic nanotubes do not exhibit luminescence and no cooling effect is observed. Both semiconducting and metallic nanotubes show for the bundled component of the radial Raman band an enhancement of (I-aS/I-S) such as is frequently observed in a coherent anti-Stokes Raman scattering process.

151. Single-beam pumped coherent anti-Stokes Raman scattering on carbon nanotubes

Authors: Lefrant, S; Buisson, JP; Mevellec, JY; Baltog, I; Baibarac, M

Published: OCT 2008, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 245, 2224, DOI: 10.1002/pssb.200879567

Giant optical fields locally generated in nanoscale metal structures through the local excitation of surface plasmons underlie a variety of nonlinear optical processes. Using silver and gold rough metallic films, reproducible enhancements of the Raman signal on various materials including carbon nano-tubes have been demonstrated. In addition, an abnormal anti-Stokes Raman emission, reminiscent of Coherent anti-Stokes Raman Scattering (CARS), is accurately observed on nano-metric thin films. We demonstrate that under a tight focusing of the excitation light, a CARS-type emission, resulting from a wave mixing process between the incident laser light and Stokes Raman light generated by a SERS mechanism, is produced. The results which corroborate the CARS emission are the following: a square relation between the CARS signal intensity and the film thickness; a square relationship between the CARS signal intensity and the exciting laser intensity; a dependence of the CARS intensity on the numerical aperture (NA) of the microscope objective used for the detection of the anti-Stokes signal; a polarization ratio in the anti-Stokes side always greater in comparison with that measured for an usual Stokes Raman signal. We demonstrate also that this mechanism may contribute to a clear identification of the state of the observed nanotubes, i.e. in isolated or bundled forms, even when tubes are in powders. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

152. Vibrational and photoluminescence properties of composites based on zinc oxide and single-walled carbon nanotubes

Authors: Baibarac, M; Baltog, I; Lefrant, S; Mevellec, JY; Husanu, M

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2564, DOI: 10.1016/j.physe.2007.09.034

Composites based on zinc oxide (ZnO) nanoparticles and single-walled carbon nanotubes (SWNTs) were investigated by photoluminescence (PL) and Raman scattering. The room temperature PL spectrum of ZnO at the excitation wavelength of 335 nm displays a narrow excitonic band, peaking at 368 nm (3.36eV), and a wide one, disclosing two components with maxima at about 444 nm (2.79eV) and 560 nm (2.21eV) which are associated to the local oxygen vacancies and oxygen excess, respectively. Regardless the preparation method of the ZnO/SWNTs compound (electrochemical, mechanicochemical and hydrothermal synthesis), PL spectra reveal an increased quenching tendency with the concentration of nanotubes in the composite mass. As distinct feature in the PL spectra of ZnO/SWNTs composites are two bands, one at 450 nm (2.75 nm) and another one attributed to the formation of a donor-acceptor complex at 680 nm (1.82eV). The role of the dispersion of carbon nanotubes in the ZnO/SWNTs composite is observed by Raman scattering with the excitation wavelength of 676 nm. (C) 2007 Elsevier B.V. All rights reserved.

153. Vibrational and photoluminescence properties of the polystyrene functionalized single-walled carbon nanotubes

Authors: Baibarac, M; Baltog, I; Lefrant, S; Mevellec, JY; Bucur, C

Published: JUL-OCT 2008, DIAMOND AND RELATED MATERIALS, 17, 1388, DOI: 10.1016/j.diamond.2008.01.061

Using surface enhanced Raman scattering (SERS) and FTIR spectroscopy, a covalent functionalization of single wall carbon nanotubes (SWNTs) with polystyrene (PST) is demonstrated. For this, two types PST/SWNTs composites were used: one resulting from the radical polymerization reaction of styrene achieved at 90 degrees C in the presence of benzene and benzoyl peroxide, latter being the initiator and another obtained by mixing the two constituents. These compounds reveal different SERS and photoluminescence spectra. The main experimental facts supporting the covalent functionalization of SWNTs with PST are provided by FTIR spectroscopy. In this frame significant is the increase of the intensities of absorption bands at 1270 and 1721 cm(-1), which are associated with the tangential C-H bending+C-O stretching and C=O stretching vibration modes, respectively. The presence of these absorption bands in the FTIR spectra of the PST/C-60 composites proves the formation of a compound with a similar molecular structure. in the case of polystyrene functionalized SWNTs, the appearance of a new FTIR band at ca. 1635 cm(-1) attributed to the C-C in cyclic hydrocarbons ring di-substituted vibration mode indicates the formation of an additional reaction product. (C) 2008 Elsevier B.V. All rights reserved.

154. Raman and photoluminescence studies on intercalated lead iodide with pyridine and iodine

Authors: Preda, N; Mihut, L; Baibarac, M; Husanu, M; Bucur, C; Baltog, I

Published: FEB 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 322, DOI:

Intercalated PbI2 compounds were prepared by exposing crystalline films and crystalline powders of lead iodide to pyridine or iodine vapor at room temperature. Correlated studies of optical absorption, Raman scattering and low temperature photoluminescence (PL) reveal different properties in comparison with those of pure crystalline PbI2 powder. Depending of the nature of intercalated molecules (organic or inorganic) the basic semiconducting properties of PbI2 are dramatically modified. The main signature of iodine intercalated PbI2 consists in a luminescence band peaking at 2.24 eV appearing at 77 K under 350 nm excitation light. In the case of pyridine intercalated PbI2 a new intense band at about 3.3 eV in the absorption spectrum is observed. The the PL spectra of pyridine intercalated PbI2 at 77 K change substantially when the excitation wavelength. The Raman spectra confirm the presence of pyridine between the PbI2 layers.

155. Raman and FTIR studies on electro-reduction of single-walled carbon nanotube films in the presence of Li salts

Authors: Baltog, I; Baibarac, M; Lefrant, S; Mevellec, JY

Published: JUL-OCT 2008, DIAMOND AND RELATED MATERIALS, 17, 1564, DOI: 10.1016/j.diamond.2008.01.041

Electrochemical reduction of single-walled carbon nanotube (SWNT) films in the presence of Li salts dissolved ill acetonitrile (AN), as an anhydrous medium, was investigated by Raman scattering, FTIR spectroscopy and TEM studies. Differences between the in-situ and ex-situ Raman spectra recorded on the SWNT films immersed in the Li salt/AN solution consist in the fort-nation of two reaction products with different stability in air. One corresponds to SWNTs doped with Li+ ions, a compound that is instable in air. The other, stable in air, exhibits in the Raman spectrum recorded at excitation wavelengths of 676 and 1064 nm an enhanced D band, a disappearance of the Breit-Wigner-Fano component and a significant decrease in the radial breaching mode intensity. Besides, in FTIR spectra, one observes: i) a down-shift of the absorption bands from 1456 and 1540 cm(-1) to 1440 and 15 10 cm(-1), respectively accompanied by an increase of their intensities and ii) an up-shift of the IR band from 1170 to 1192 cm(-1). The influence of the applied reduction potential and cycle voltammograms number on the vibrational features of the second product is shown, too. A recovery of the initial vibrational features of SWNTs is achieved by a subsequent treatment with an aqueous HCl 1M solution. (C) 2008 Elsevier B.V. All rights reserved.

156. Resonant Raman scattering and absorption spectroscopy studies on individual carbon nanotubes in surfactant solutions

Authors: Husanu, M; Baibarac, M; Preda, N; Baltog, I

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1726, DOI:

Carbon Nanotubes are exotic low-dimensional systems, and due to their remarkable properties, are promising components for technological applications. The electronic and vibrational signatures raising from their existence as individual entities or associated in bundles, is still a controversed subject. A careful analysis of the G (similar to 1600 cm(-1)) and RBM (100-200 cm(-1)) band features as: profile, peak position and intensity in the Raman spectra may be a valuable indication about their dispersion state. The UV-VIS-NIR absorption spectrum comes to support this assumption. Observing the absorption spectra associated to resonant excitation of semiconducting and metallic nanotubes, may reveal complementary informations concerning the individualization procedure efficiency.

157. Abnormal anti-Stokes Raman spectra of single walled carbon nanotubes raised from coherent anti-Stokes Raman scattering and optical cooling processes

Authors: Baltog, I; Baibarac, M; Mihut, L; Lefrant, S

Published: MAR 2007, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 2, 198, DOI:

For the single-walled carbon nanotubes, the higher values of anti-Stokes/Stokes Raman intensity ratio (I(as)/I(s)) then the predictions of the Maxwell-Bolzmann formula indicates a CARS emission resulting from a wave mixing process between the incident laser light (omega(l)) and Stokes Raman light (omega(s)) generated by a SERS mechanism. The weaker value of (I(as)/Is) observed at resonant excitation of semiconducting nanotubes in the E(22)(S) van Hove state, relates a quantum cooling process occurred during the relaxation of the E22S excited state in two steps-by phonon emission from E(22)(S) to E(11)(S) followed by a spontaneous luminescence emission at E(11)(S).

158. Poly(N-vinyl carbazole) and carbon nanotubes based composites and their application to rechargeable lithium batteries

Authors: Baibarac, M; Lira-Cantu, M; Sol, JO; Baltog, I; Casan-Pastor, N; Gomez-Romero, P

Published: SEP 2007, COMPOSITES SCIENCE AND TECHNOLOGY, 67, 2563, DOI: 10.1016/j.compscitech.2006.12.008

In order to prepare poly(N-vinyl carbazole) (PVK) and carbon nanotube (CNs) based composites, electrochemical polymerization of N-vinyl carbazole (NVK) was studied by cyclic voltammetry (CV) in LiClO4/acetonitrile solutions. Cyclic voltammograms recorded on a blank Pt electrode and those obtained when single or multi-walled carbon nanotubes (SWNTs or MWNTs) films were previously deposited onto the Pt electrode show a down-shift of the VK reduction peak potential in the latter case. The influence of monomer concentration and supporting electrolyte on the polymerization conditions and electrochemical properties of these composite materials were also investigated. Morphologic aspects as well as the photoluminescence properties of the PVK/CNs composite were also investigated. A covalent functionalization of carbon nanotubes with PVK is suggested on the basis of infrared (IR) spectroscopic studies. Using the PVK/CN composite as a positive electrode and an electrolytic solution containing LiPF6, a higher specific discharge capacity of the rechargeable lithium cells, similar to 45 and 115 mA h g(-1), are reported for PVK functionalized SWNTs and MWNTs, respectively. (c) 2007 Elsevier Ltd. All rights reserved.

159. Raman and SERS studies of single-walled carbon nanotubes and Nanotubes/Conjugated polymers composites

Authors: Lefrant, S; Buisson, JP; Mevellec, JY; Baibarac, M; Baltog, I

Published: 2007, FUNDAMENTAL AND APPLIED SPECTROSCOPY, 935, +, DOI:

In this paper, we recall the main characteristics of Raman spectra of single-walled carbon nanotubes. We illustrate our studies by results obtained on HiPCO samples on one hand, and "arc electric" samples on the other hand by using two different excitation wavelengths. We focus on the peculiarity of observing separately semi-conducting and metallic tubes. We emphasize also the role played by the radial breathing modes whose frequency depends on the tube diameter and on the need to take into account the interactions between tubes when they are in bundles in order to determine accurately the tube diameter distribution. Finally we demonstrate briefly the evidence of using the SERB (surface enhanced Raman scattering) spectroscopy to study reactions at interfaces or between components in nanotubes/conjugated polymers composites.

160. Raman and photoluminescence studies on low-dimensional PbI2 particles embedded in polymer matrix

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1361, DOI:

Pbl(2) crystallite incorporated in optically transparent polyacrylamide and poly (vinyl alcohol) matrix have been studied by Raman scattering, photoluminescence (PL) at low temperature and Scanning Electron Microscopy (SEM). The small particles of Pbl(2) embedded in different host matrix were prepared by: i) cooling to the room temperature a boiling saturated aqueous Pbl(2) solution containing polyacrylamide or poly (vinyl alcohol) and ii) by chemical reaction of KI and Pb(NO3)2 in aqueous polyacrylamide solution. In all cases, were identified hexagonal platelets of Pbl(2) and rods like particles. The rods are featured by a similar Raman spectrum and a specific green emission (cca 550 nm). Modification of the Raman and PL spectra results from a compressing effect produced by the penetration between the Pbl(2) layers of different molecular species. By compression the hybridized electronic level situated at the top of valence band, formed by the contribution.of the 6s and 5p states of Pb2+ and l ions, undergo a deformation that induces a weakness of the interaction between the lead ion and iodine electron within a layer so that the photoluminescence of intercalated Pbl(2) acquires the characteristics of Pb2+ emission when it is dissolved in an alkali halide crystal.

161. Spectroscopic evidence for the bulk polymerization of N-vinyl carbazole in the presence of single-walled carbon nanotubes

Authors: Baibarac, M; Baltog, I; Lefrant, S; Gomez-Romero, P

Published: AUG 24 2007, POLYMER, 48, 5288, DOI: 10.1016/j.polymer.2007.07.008

The bulk polymerization reaction of N-vinylcarbazole (VK) at 70 degrees C in the presence of single-walled carbon nanotubes (SWNTs) leads to a new composite, whose optical properties were studied by photoluminescence (PL), surface enhanced Raman scattering (SERS) and Fourier transform infrared (FTIR) spectroscopies. A dramatic reduction of the poly(N-vinylcarbazole) (PVK) PL efficiency and a change in the vibrational structure of the PL spectrum of this polymer were observed by adding SWNTs to the synthesis mixture. Steric hindrance effects were evidenced both in SERS spectra of the VK when it interacts mechanico-chemically with SWNTs and in FTIR spectra of the un-doped PVK/SWNTs' composites. Cyclic voltammetry was used to demonstrate the doping process of PVK in PVK/SWNTs' composite. (c) 2007 Elsevier Ltd. All rights reserved.

162. Electrosynthesis of the poly(N-vinyl carbazole)/carbon nanotubes composite for applications in the supercapacitors field

Authors: Baibarac, M; Gomez-Romero, P; Lira-Cantu, M; Casan-Pastor, N; Mestres, N; Lefrant, S

Published: OCT 2006, EUROPEAN POLYMER JOURNAL, 42, 2312, DOI: 10.1016/j.eurpolymj.2006.05.019

Electrochemical polymerization of N-vinyl carbazole (VK) on carbon nanotube (CN) films was studied by cyclic voltammetry in LiClO4/acetonitrile solutions. Cyclic voltammograms recorded on a blank Pt electrode were compared with those obtained when single or multi-walled CN films were deposited on the Pt electrode; in the latter case, a down-shift of the VK reduction peak potential was observed. Functionalization of CNs with poly(N-vinyl carbazole) (PVK) was invoked by Raman scattering and UV-VIS-NIR spectroscopic studies. The influence of sweep rate on the electrochemical properties of the PVK/CN nanocomposite and the performance of supercapacitors constructed using PVK-functionalized single-walled carbon nanotube electrodes were also evaluated. (c) 2006 Elsevier Ltd. All rights reserved.

163. Spectroscopic studies on nanocomposites obtained by functionalization of carbon nanotubes with conducting polymers

Authors: Lefrant, S; Baibarac, M; Baltog, I

Published: 2006, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 447, 403, DOI: 10.1080/15421400500385332

Vibrational properties of composites based on single-walled carbon nanotubes (SWNTs) and conducting polymers of the type polyaniline (PANI) and poly (3,4-ethylene dioxythiophene) (PEDOT) are reported. For PANI-functionalized SWNTs, the intensity increase of the Raman band at 178 cm(-1) , associated with radial breathing modes of SWNTs bundles, indicates an additional roping of nanotubes due to the presence of the polymer. The interaction of this composite with NH4OH solution involves an internal redox reaction between PANI and SWNTs. Thus, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. The functionalization of SWNT side walls with PEDOT is invoked as well.

164. Mechanico-chemical interaction of SWNTs with different host matrices evidenced by SERS spectroscopy

Authors: Lefrant, S; Baibarac, M; Mihut, L; Baltog, I

Published: NOV 2006, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 243, 3439, DOI: 10.1002/pssb.200669184

Surface enhanced Raman scattering (SERS) performed with 676.4 and 1064 nm excitations were used to investigate single-walled carbon nanotubes (SWNTs) thin films prepared from platelets obtained by nonhydrostatic compression at 0.58 GPa. SWNTs were compressed alone or dispersed into chemical reactive and non-reactive host matrices. SERS spectra indicate that by compression, SWNTs break into fragments of different sizes, which in turn can react or not with the host matrix. In inorganic hosts (KI, Ag) donor-acceptor complexes are formed. The appearance of short fragments of SWNTs with a closed-shell fullerenes behaviour is revealed in SERS spectra. This typical signature appears in the Raman spectrum as a line at ca. 1460 cm(-1) associated with a pentagonal pinch mode. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

165. A distinctive signature in the Raman and photoluminescence spectra of intercalated PbI2

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I; Lefrant, S

Published: OCT 4 2006, JOURNAL OF PHYSICS-CONDENSED MATTER, 18, 8912, DOI: 10.1088/0953-8984/18/39/020

Through correlated studies using scanning electron microscopy (SEM), Raman spectroscopy and low-temperature photoluminescence (PL) we have demonstrated that the intercalated PbI2 with ammonia, poly (vinyl alcohol) and polyacrylamide are characterized by a distinctive signature in the Raman and photoluminescence spectra. After intercalation, the Raman spectrum of PbI2 reveals an orthorhombic structure, identical with that observed on the micrometric scale, of KPbI3 rod-like particles resulting from the reaction between Pb(NO3)(2) and KI, carried out in liquid media such as ethanol and acetonitrile. The rods and the intercalated PbI2 are characterized by a new and strong emission band at 2.23 eV (about 550 nm) that appears at 77 K under an excitation wavelength of about 340 nm. Modification of the Raman and PL spectra results from a compressing effect produced by the penetration between the PbI2 layers of different molecular species. The compression acting primarily on the iodine layers has the result of lowering the contribution of the 5p states of I- ions to the constitution of the electronic level situated at the top of valence band of PbI2, so that the photoluminescence of intercalated PbI2 acquires the characteristics of Pb2+ emission when it is dissolved in an alkali halide crystal.

166. Electrochemically functionalized carbon nanotubes and their application to rechargeable lithium batteries

Authors: Baibarac, M; Lira-Cantu, M; Oro-Sole, J; Casan-Pastor, N; Gomez-Romero, P

Published: AUG 2006, SMALL, 2, 1082, DOI: 10.1002/smll.200600148

Electrochemical polymerization of N-vinyl carbazole (VC) on carbon nanotube (CNT) films was studied by cyclic voltammetry (CV) in LiClO4/acetonitrile solutions. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when single- or multi-walled carbon nanotube (SWNT or MWNT) films were previously deposited onto the Pt electrode, a downshift of the VC reduction peak potential is observed in the latter case. The influences of monomer concentration, type of solvent, and supporting electrolyte on the polymerization conditions and electrochemical properties of these composite materials are also investigated. The morphological aspects of poly(N-vinyl carbazole) (PVC)-functionalized CNTs are revealed by transmission electron microscopy (TEM) studies. A covalent functionalization of carbon nanotubes with PVC is invoked as a result of attenuated total reflection infrared (ATR-IR) spectroscopic studies. Using PVC-functionalized CNTs as a positive electrode and an electrolytic solution containing LiPF6, the charge-discharge characteristics of the rechargeable lithium cells are determined. High specific discharge capacity (approximate to 45 and 115 mA h g(-1)) is reported for PVC-functionalized single- and multi-walled carbon nanotubes, respectively.

167. Functionalization of single-walled carbon nanotubes with conducting polymers evidenced by Raman and FTIR spectroscopy

Authors: Lefrant, S; Baibarac, M; Baltog, I; Mevellec, JY; Godon, C; Chauvet, O

Published: MAR-JUL 2005, DIAMOND AND RELATED MATERIALS, 14, 872, DOI: 10.1016/j.diamond.2004.11.035

Using Raman scattering and Fourier transform infrared (FTIR) spectroscopy, we show that the vibrational properties of single-walled carbon nanotubes (SWNTs) functionalized with conducting polymers (CPs), such as polyaniline (PANI) and poly (3, 4-ethylenedioxythiophene) (PEDOT), are different depending on the synthesis method. In the case of SWNTs electrochemically functionalized with PANT, the increase in intensity of the Raman band at 178 cm(-1), associated with radial breathing modes of bundled SWNTs, indicates that an additional roping of nanotubes with PANT takes place. Besides, the functionalization of SWNTs with PANT induces strong steric hindrance effects observed in FTIR spectra by the enhancement of bands at ca. 740-750 and 772 cm(-1) associated to the deformation vibrations of the benzoid and quinoid ring, respectively. Raman spectra recorded after the electropolymerization of 3, 4-ethylenedioxythiophene (EDOT) on the SWNTs film reveal that a side-wall functionalization takes place. (c) 2005 Elsevier B.V. All rights reserved.

168. SERS, FT-IR and photoluminescence studies on single-walled carbon nanotubes/conducting polymers composites

Authors: Lefrant, S; Baibarac, M; Baltog, I; Godon, C; Mevellec, JY; Wery, J; Faulques, E; Mihut, L; Aarab, H; Chauvet, O

Published: DEC 15 2005, SYNTHETIC METALS, 155, 669, DOI: 10.1016/j.synthmet.2005.08.026

Surface-enhanced Raman scattering (SERS), Fourier transform infrared (FT-IR) and photoluminescence (PL) spectroscopies were used to investigate composites based on single-walled carbon nanotubes (SWNTs) and different conducting polymers like polyaniline (PANI), polyparaphenylene vinylene (PPV) and poly 3-hexylthiophene (3-PHT). In the case of SWNTs/PANI, different composites are obtained by adding dispersed SWNTs powder to the polymer solutions and by chemical polymerization of aniline in presence of SWNTs. The difference originates in the irreversible chemical transformation of SWNTs in the polymerization medium. The synthesis medium used for the preparation of PANI transforms SWNTs in fragments of shorter length like closed-shell fullerenes. This explains the similarity of SERS and FT-IR spectra of the composites PANI/SWNTs and PANI/C-60, chemically synthesized. Electrochemical polymerization of aniline in an HCl solution on a SWNT film leads to a covalent functionalization of SWNTs with PANI. In this case, Raman scattering data suggest an additional nanombes roping with PANI as a binding agent. A post treatment with the NH4OH solution of polymer-functionalized SWNTs involves an internal redox reaction between PANI and carbon nanotubes. As a result, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. In the case of PPV and 3-PHT, the effect of the concentration of SWNTs on the photoluminescence properties will be described and compared, as probes of interaction. (C) 2005 Elsevier B.V. All rights reserved.

169. Electrochemical and vibrational properties of single-walled carbon nanotubes in hydrochloric acid solutions

Authors: Lefrant, S; Baibarac, M; Baltog, I; Velula, T; Mevellec, JY; Chauvet, O

Published: MAR-JUL 2005, DIAMOND AND RELATED MATERIALS, 14, 880, DOI: 10.1016/j.diamond.2004.12.016

Raman spectroscopy and cyclic voltammetry (CV) are used for the investigation of the oxidation-reduction processes of single-wall carbon nanotubes (SWNTs) films in an HCl 0.5 M solution. In the potential ranges (+100; +800) and (0; +1500) mV vs. saturated calomel electrode (SCE), the oxidation-reduction reactions of SWNT films, in both aqueous and semi-aqueous HCl 0.5 M solutions, are reversible and irreversible, respectively. At potentials higher than +1000 mV vs. SCE, SWNTs break in fragments of different sizes. A post-treatment with an alkaline solution results in a partial restoration of the SWNTs. The functionalization of SWNTs with polydipherylamine (PDPA) is presented as an application of the reversible oxidation-reduction reactions of nanotubes in an HCl 0.5 M solution. In order to differentiate between a deposition of successive layers of the polymer and a functionalization process, a spectroelectrochemical study of the deposition of polypyrrole (PPY) on SWNT films was carried out, too. (c) 2004 Elsevier B.V. All rights reserved.

170. Coherent anti-Stokes Raman scattering on single-walled carbon nanotubes and copper phthalocyanine thin films excited through surface plasmons

Authors: Baltog, I; Baibarac, M; Lefrant, S

Published: NOV 2005, JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS, 7, 639, DOI: 10.1088/1464-4258/7/11/003

Experimental data indicating an anti-Stokes Raman emission, reminiscent of coherent anti-Stokes Raman scattering (CARS), that originates in a wave-mixing process between the incident laser light (omega(1)) and Stokes Raman light (omega(s)) generated by a surface enhanced Raman scattering (SERS) mechanism are reported. The variation of anti-Stokes SERS spectra of single-walled carbon nanotubes (SWNTs) and copper phthalocyanine (CuPc) as a function of the film thickness, laser excitation intensity and numerical aperture of the microscopic objective used for collecting the scattered light are presented as experimental arguments.

171. Surface enhanced Raman scattering and photoluminescence studies on single-walled carbon nanotubes submitted to non-hydrostatic compression

Authors: Baibarac, M; Baltog, I; Mihut, L; Preda, N; Velula, T; Godon, C; Mevellec, JY; Wery, J; Lefrant, S

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2181, DOI:

Single-walled carbon nanotubes (SWNTs) under a moderate non-hydrostatic pressure, of 0.58 GPa, undergo a non-reversible transformation. Due to the plastic deformations, structural defects and carbon nanotube fragments of different size are produced. Short fragments of spherical or ellipsoidal form, behaving as closed-shell fullerenes are observed both by Raman spectroscopy and photoluminescence (PL). The main vibrational indicative of the fragments of shorter length is the band at similar to 1458 cm(-1) that is regularly observed in the Raman spectra of fullerene. Similar to fullerenes self assemblies, the interaction between the nanotube fragments is noticed in the Raman spectrum by the band at similar to 94 cm(-1) that reveals an inter-particle vibration mode. When the nanotubes are dispersed into host matrix, as aromatic hydrocarbons (AHs) with isolated or condensed phenyl rings, supplementary mechanico-chemical reactions take place. For AHs with isolated phenyl rings, like biphenyl or p-terphenyl, a chemical functionalization of SWNT fragments is demonstrated by the appearance of a new Raman band at 1160 cm(-1). In PL spectra, the interaction of SWNTs with AHs, is noticed by a detailed vibronic structure appearing in the high energy side of the emission spectrum, that increase with the weight of SWNTs in the AHs/SWNTs mixtures.

172. Coherent anti-Stokes Raman scattering on single-walled carbon nanotube thin films excited through surface plasmons

Authors: Baltog, I; Baibarac, M; Lefrant, S

Published: DEC 2005, PHYSICAL REVIEW B, 72, DOI: 10.1103/PhysRevB.72.245402

We report experimental data that indicate an anti-Stokes Raman emission, reminiscent of coherent anti-Stokes raman scattering. It originates from a wave mixing process between the incident laser light (omega(l)) and Stokes Raman light (omega(s)) generated by a surface enhanced Raman scattering (SERS) mechanism. The variation of anti-Stokes SERS spectra of single-walled carbon nanotubes, copper phthalocyanine, and poly(bithiophene) as a function of the film thickness, the laser excitation intensity, and the numerical aperture of the microscopic objective used for collecting the scattered light demonstrate the described phenomenon.

173. Mechanico-chemical interaction of single-walled carbon nanotubes with different host matrices evidenced by SERS spectroscopy

Authors: Baibarac, M; Baltog, I; Lefrant, S; Godon, C; Mevellec, JY

Published: APR 23 2005, CHEMICAL PHYSICS LETTERS, 406, 227, DOI: 10.1016/j.cplett.2005.02.113

Surface enhanced Raman scattering with 676.4 and 1064 nm excitations was used to investigate single-walled carbon nanotubes (SWNTs) compressed non-hydro statically at 0.58 GPa, alone or dispersed into chemical reactive and non-reactive host matrices. By compression, SWNTs break in fragments of different size. Between SWNTs fragments and the host matrix various mechanico-chemical reactions take place. In matrices such KI and Ag, donor-acceptor complexes are formed. In aromatic hydrocarbons like biphenyl or p-terphenyl, an ionic and covalent functionalization of SWNTs fragments is demonstrated by new bands at 1160 and 1458 cm(-1), the latter being associated to an A(g)(2) pentagonal pinch mode. (c) 2005 Elsevier B.V. All rights reserved.

174. Surface-enhanced Raman scattering studies on C-60 fullerene self-assemblies

Authors: Baibarac, M; Mihut, L; Preda, N; Baltog, I; Mevellec, JY; Lefrant, S

Published: 2005, CARBON, 43, 9, DOI: 10.1016/j.carbon.2004.08.020

Surface-enhanced Raman scattering (SERS) was used to investigate C-60 self-assembling in solvents like pyrrolidine (Py) and Nmethyl-2-pyrrolidinone (NMP) as well as in binary mixtures of o-dichlorobenzene (DCB)/acetonitrile (ACN) and DCB/NMP. For a correct evaluation of the modifications of Raman spectra induced by the C-60 aggregation, we have also presented the variations due to the measuring method, i.e., the signal dependence of the metallic support type and the surface roughness. The interaction between C-60 and the Au substrate, appearing as a chemical component in SERS generation, is mainly evidenced by a band at similar to342cm(-1). In the aggregated phase, the intermolecular interactions lead to a reduction in the parent I-h C-60 symmetry as observed by a modified phonon spectrum. As a general feature, the spectral range below 800cm(-1) is the most diagnostic for the aggregate assignment, the main indicative being the disappearance of the Raman bands associated to the radial vibration modes. SERS measurements have revealed two stages in the self-assembling of C-60 in NMP. In the beginning, charge-transfer molecular complexes that associate slowly in stable aggregates are formed by the binding of an NMP molecule to the C-60 cage. These complexes are noticed in the SERS spectrum by the replacement of the original H-g(l) band at similar to269cm(-1) with two others at similar to255 and similar to246cm(-1). In the aggregated phase, when using NMP and P as a solvent, the Raman spectrum reveals new bands that appear around 94 and 110-118cm(-1), which are associated with the interball interactions. In a DCB/ACN solvent mixture, the self-assembling process is driven by weak van der Waals type forces and resembles a precipitation, yielding C60 clusters of different size. (C) 2004 Published by Elsevier Ltd.

175. Surface-enhanced Raman scattering, photoluminescence and viscosity studies on C-60 aggregates in N-metryl-2-pyrrolidinone

Authors: Baltog, I; Mihut, L; Baibarac, M; Preda, N; Velula, T; Lefrant, S

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2172, DOI:

Correlated studies of Surface Enhanced Raman Scattering (SERS) spectroscopy, photoluminescence (PL) and viscosity on aggregation of C-60 fullerene in N-methyl-2-pyrrolidinone (NMP) solutions were performed. The aggregation is a result of storing of the solutions at the room temperature for different periods of time. The modified phonon spectrum in the aggregate phase is a consequence of the intermolecular interactions that lead to a large reduction in parent I-h C-60 symmetry. The Raman range below 800 cm(-1) is the most diagnostic for aggregate assignment. Substitution of the original of H, (1) band from similar to 269 cm(-1) with a new one at similar to 255 cm(-1) relates the formation of (C-60, NMP) complexes. In the second stage of aggregation, this band shifts at similar to 246 cm(-1) and a new band, associate to the interball interaction, is formed at similar to 94 cm(-1). PL emission of the C-60 solutes in NMP presents two components, one in red (1.92-2.00 eV) and another in green (2.18-2.3 eV), which originate in two successive processes. Their weights depend on C-60 concentration and on storage time. In the beginning are formed quickly molecular complexes (C-60, NMP) by charge transfer, which on associate slowly in stable aggregates. A dependence of specific viscosity on C-60 solution concentration is observed too.

176. Surface-enhanced Raman scattering studies on chemically transformed carbon nanotube thin films

Authors: Lefrant, S; Baltog, I; Baibarac, M

Published: JUN-JUL 2005, JOURNAL OF RAMAN SPECTROSCOPY, 36, 698, DOI: 10.1002/jrs.1351

We review our experimental data obtained by Raman spectroscopy on single-walled carbon nanotubes (SWNTs) using surface-enhanced Raman scattering (SERS). We focused on the study of the dependence of the SERS spectra of SWNTs on both the rough metallic substrate type and the film thickness. In particular, we show that degradation of the nanotubes, mainly metallic, occurs for very thin films with the formation of graphitic, fullerene-like or amorphous carbon particles. We show also that SWNTs reacting with H2SO4 form a salt of the hydrogensulfate type similar to that resulting from graphite-H2SO4 interaction. SWNTs exhibit a complicated spectroelectrochemical behavior in aqueous and non-aqueous H2SO4 solutions that depends also on the sweep potential range. We demonstrate that the oxidation-reduction processes have a quasi-reversible or irreversible character. Finally, SERS studies on compressed SWNTs in different host matrices, inorganic and organic, reveal nanotube breaking and that tube fragments may react or not with the host matrix used. Copyright (c) 2005 John Wiley & Sons, Ltd.

177. Covalent functionalization of single-walled carbon nanotubes by aniline electrochemical polymerization

Authors: Baibarac, M; Baltog, I; Godon, C; Lefrant, S; Chauvet, O

Published: 2004, CARBON, 42, 3152, DOI: 10.1016/j.carbon.2004.07.030

Electrochemical polymerization of aniline in an HCl solution on a single-walled carbon nanotubes (SWNTs) film has been studied by Raman and FTIR spectroscopy. It is shown that this method leads to a covalent functionalization of SWNTs with polyaniline (PANI). A careful study in Raman scattering shows that the increase in the intensity of the band at 178cm(-1) associated with radial breathing modes of SWNTs bundles suggests an additional nanotubes roping with PANI as a binding agent. A post chemical treatment with the NH4OH solution of polymer-functionalized SWNTs involves an internal redox reaction between PANI and carbon nanotubes. As a result, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. (C) 2004 Elsevier Ltd. All rights reserved.

178. SERS spectroscopy studies on the electrochemical oxidation of single-walled carbon nanotubes in sulfuric acid solutions

Authors: Lefrant, S; Baibarac, M; Baltog, I; Mevellec, JY; Mihut, L; Chauvet, O

Published: JUL 22 2004, SYNTHETIC METALS, 144, 142, DOI: 10.1016/j.synthmet.2004.02.010

Surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV) were used to investigate oxidation-reduction processes of single-wall carbon nanotube (SWNT) films deposited on Au supports in 0.5 M H2SO4 solutions. In the potential range (0; +1000) and (0; +1500)mV versus saturated calomel electrode (SCE), the oxidation-reduction reactions of SWNT films are quasi-reversible and irreversible, respectively. Anodic polarization of SWNT films until +1000 mV versus SCE produced compounds similar to the bisulfate intercalated graphite. Regardless of excitation wavelength, i.e. 1064 or 676.4 nm, variation in the Raman spectra exhibited a decrease in the intensity of the bands associated with the radial breathing mode (RBM) situated in the 120-240 cm(-1) spectral range. Also an increase in the intensity of the D band is accompanied an up-shift of this band. A gradual decrease of the Breit-Wigner-Fano component was observed at lambda(exc) = 676.4 mn. Partial restoration of the Raman spectra was achieved by a subsequent alkaline solution treatment. Potentials higher than +1000 mV versus SCE resulted in SWNTs breakage and fragments of different length were formed such as closed-shell fullerene. This was observed in the SERS spectrum by: (i) the disappearance of the RBM band, (ii) the increased D-band shifted to ca. 1330 cm(-1) and (iii) the appearance of a new band at 1494 cm(-1), frequently observed also in the Raman spectrum of fullerenes on the type C-70, C-84, C-119, as well as in its derivative compounds (e.g. C60O, clathrates, etc.). Appearance and increase in the intensity of the Raman band at 1494 cm(-1) as result of an anodic polarization of the SWNT film in solution of H2SO4 0.5 M in 1-butanol is a further evidence of the nanotubes breakage. (C) 2004 Elsevier B.V. All rights reserved.

179. C-60 aggregates in pyrrolidine and N-methyl-2-pyrrolidinone evidenced by surface-enhanced Raman scaterring spectra

Authors: Baibarac, M; Preda, N; Mihut, L; Velula, T; Baltog, I; Mevellec, JY; Lefrant, S

Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 417, 587, DOI: 10.1080/15421400490478434

At room temperature, soluted C-60 in pyrrolidine and N-methyl-2-pyrrolidinone associates slowly in stable aggregates. The process originates in the charge transfer from the solvent molecules as electron donors towards fullerene. In the aggregate phase the intermolecular interactions lead to a large reduction in parent I-h C-60 symmetry such that a modified phonon spectrum is observed. Using the surface-enhanced Raman scattering we demonstrate that the Raman range below 800 cm(-1) is most diagnostic for aggregate assignment. In particular, the strong decrease of the radial breathing mode and appearance of new bands at 110 and 93 cm(-1) due to the interball interactions must be noticed.

180. Sers spectra of polyaniline/carbon nanotubes and polyaniline/fullerene composites

Authors: Baibarac, M; Baltog, I; Lefrant, S; Mevellec, JY; Chauvet, O

Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 415, 155, DOI: 10.1080/15421400490481269

SERS and FTIR spectra of M and S composites, provided by adding of single-walled carbon nanotubes (SWNTs) to the polyaniline (PANI) solution and chemical polymerization of aniline, respectively are different. The difference originates in the irreversible transformation of SWNTs in the polymerization medium. This explains the similarity of SERS and FTIR spectra of PANI/SWNTs and PANI/C-60 composites, chemically synthesized. For M composites, strong hindrance effects are evidenced by band at 773-755 cm(-1) associated to the vibration of deformation of the benzene and quinoid ring. The charge transfer is illustrated for all compounds by absorption band at 1144 cm(-1).

181. Photoluminescence studies on [C60] fullerene solutions in N-methyl-2-pyrrolidinone and pyrrolidine

Authors: Mihut, L; Preda, N; Baibarac, M; Baltog, I; Lefrant, S; Wery, J

Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 415, 21, DOI: 10.1080/15421400490478209

Photoluminescence (PL) spectra of C-60 solutions in N-methyl-2-pyrrolidinone (NMP) show a drastic increase of the PL intensity if the solutions are stored longer periods of time. Two distinct spectral components, one in the red (1.92-2.00 eV) and another in the green (2.18-2.3 eV) were identified in the whole PL emission. Their weights depend on C-60 concentration and on storage time. The two emissions come from two successive processes running with different kinetics. Charge transfer, leading to (C-60, NMP) loose molecular complexes and a slow aggregation process of these entities seems to originate the red and green emission, respectively. Similar PL properties are found when pyrrolidine (P) is used as solvent.

182. On the optical properties of micro- and nanometric size PbI2 particles

Authors: Baibarac, M; Preda, N; Mihut, L; Baltog, I; Lefrant, S; Mevellec, JY

Published: APR 7 2004, JOURNAL OF PHYSICS-CONDENSED MATTER, 16, 2356, DOI: 10.1088/0953-8984/16/13/014

Scanning electron microscopy, Raman scattering, UV-VIS absorption spectroscopy and low temperature photoluminescence (PL) were used to examine small particles produced by the chemical reaction between Pb(NO3)(2) and KI in different liquid media: water, methanol, ethanol and acetonitrile. By stoichiometric changes in the synthesis reaction, platelets of PbI2 and rods probably of KPbI3 are produced. Regardless of shape and size, these particles exhibit almost the same PL, which consists of two intense bands centred around the 2.5 (E band) and 2.0 eV (G band), in turn similar to that of a crystalline slide or a micrometric powder, both prepared from a PbI2 single-crystal grown from the melt. Crystalline PbI2 platelets exhibit an E band with two components, at 2.49 (E-F band) and 2.47 eV (E-T band), originating in the recombination of the free and trapped excitons produced by inter-band irradiation. A close relation between the enhancement of the E-T and G band reveals that they are linked to the surface defects. For the rod-like particles, the PL spectrum is somewhat similar to that of a Pb2+ ion introduced into an alkaline halide lattice, which as for any ns(2) ion displays two emission bands, A(T) and A(X), whose correspondents are E and G bands.

183. Raman studies of carbon nanotubes and polymer nanotube composites

Authors: Lefrant, S; Buisson, JP; Schreiber, J; Chauvet, O; Baibarac, M; Baltog, I

Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 415, 132, DOI: 10.1080/15421400490482844

In this paper, we present Raman studies of different carbon nanotubes systems like single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs) or composites prepared with different conjugated or non-conjugated polymers. We have focused our studies on the interactions that can take place in these systems and in general modify the characteristics of individual tubes. By introducing Van der Waals interactions between tubes, we are able to interpret experimental Raman spectra. In the case of SWNTs, we have put in evidence the so-called "bundle'' effect that consists of an upshift of the frequency of the RBM of 10 to 16 cm(-1), depending on the size of the bundles. In MWNTs, one can calculate the low frequency Raman modes observed experimentally. We found that they originate from the radial breathing modes of isolated tubes with an upshift that depends on the number of shells constituting the tube and we were then able to calculate the intensity of such modes. Finally, in polymer/nanotubes composites, we demonstrate that interactions take place between the two constituents in two different cases: PPV/SWNTs and PANI/SWNTs. The role of the method of preparation of composites is particularly put in evidence.

184. Study of interactions in carbon nanotubes systems by using Raman and SERS spectroscopy

Authors: Lefrant, S; Buisson, JP; Schreiber, J; Chauvet, O; Baibarac, M; Baltog, I

Published: OCT 9 2003, SYNTHETIC METALS, 139, 785, DOI: 10.1016/S0379-6779(03)00264-9

We present results obtained on carbon nanotube systems by means of Raman scattering and surface enhanced Raman scattering (SERS). Such systems consist of single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), or polymer/nanotubes composites. In particular, we have focused our studies on the interactions taking place in these compounds which lead to an upshift of the radial breathing mode (RBM) in the case of SWNTs, either when they are arranged in bundles or embedded in polymers. Similar calculations has allowed us to interpret the low frequency Raman modes observed in purified MWNTs. We show that they come from the RBM of individual tubes. From intensity calculations performed to simulate Raman spectra, we demonstrate the importance of two experimental parameters, namely the diameter of internal tubes and the number of shells which constitute the MWNTs, such parameters being extracted experimentally from high resolution transmission electron microscopy images. (C) 2003 Elsevier Science B.V. All rights reserved.

185. Polyaniline and carbon nanotubes based composites containing whole units and fragments of nanotubes

Authors: Baibarac, M; Baltog, I; Lefrant, S; Mevellec, JY; Chauvet, O

Published: OCT 21 2003, CHEMISTRY OF MATERIALS, 15, 4156, DOI: 10.1021/cm021287x

Using surface-enhanced Raman scattering (SERS) and Fourier transform infrared (FTIR) spectroscopy, we show that composites based on polyaniline (PANI) and single-walled carbon nanotubes (SWNTs) are different when they are prepared by two different methods: (1) by adding dispersed SWNTs to the polymer solutions and (2) by chemical polymerization of aniline in the presence of SWNTs. The difference originates from the irreversible chemical transformation of SWNTs in the polymerization medium. The synthesis medium used for the preparation of PANI transforms SWNTs into fragments of shorter length like closed-shell fullerenes. This explains the similarity of SERS and FTIR spectra of the composites PANI/SWNTs and PANI/C-60 chemically prepared. All compounds exhibit an absorption band at 1144 cm(-1) in their FTIR spectra, increasing with the carbon nanoparticules content, as a signature of a charge transfer between the constituents. Besides, the FTIR spectrum of the compounds obtained by adding SWNTs to the polymer solution display an intense absorption band with two components at 773 and 755 cm(-1), which are associated with the vibration of deformation of the benzene and the quinoid ring, respectively. This indicates a strong hindrance effect produced by the binding on the polymer chain of voluminous carbon particles as nanotubes and large fragments of nanotubes.

186. SERS studies on single-walled carbon nanotubes submitted to chemical transformation with sulfuric acid

Authors: Lefrant, S; Baltog, I; Baibarac, M; Mevellec, JY; Chauvet, O

Published: 2002, CARBON, 40, 2211, DOI: 10.1016/S0008-6223(02)00089-1

Surface-enhanced Raman scattering (SERS) at 676.44 nm and 1064 nm excitation wavelengths was used to investigate chemical transformation of single-walled carbon nanotubes (SWNTs) deposited on a gold support. Sulfuric acid was used as the chemical reagent. Special attention was paid to the changes in the Raman bands associated to radial and tangential vibration modes. Partial restoration of the Raman spectra by a Subsequent alkaline treatment indicates a transformation with a certain degree of reversibility. The recovery reaction achieved with a 0.5 M KOH solution showed that the variations of tangential and radial band groups are not correlated. The intensity changes of the radial bands is a principal indicator for the chemical transformation of the SWNTs. Particular attention was paid to radial bands at 164 and 176 cm(-1), observed with 1064 nm and 676.44 nm excitation wavelength, respectively, and their 14 cm(-1) up-shifted replicas i.e. the bands at 178 and 190 cm(-1). A different behavior of these bands in the anti-Stokes side was observed. (C) 2002 Elsevier Science Ltd. All rights reserved.

187. Modification of surface-enhanced Raman scattering spectra of single-walled carbon nanotubes as a function of nanotube film thickness

Authors: Lefrant, S; Baltog, I; Baibarac, M; Schreiber, J; Chauvet, O

Published: JUN 15 2002, PHYSICAL REVIEW B, 65, DOI: 10.1103/PhysRevB.65.235401

In this paper we report modifications of the surface enhanced Raman scattering (SERS) spectra with film thickness of carbon single-walled nanotubes (SWNTs). The decrease of film thickness reveals an increased degree of disorder, which is interpreted in terms of degradation of the single-walled nanotubes and the formation of particles similar to highly oriented pyrolytic graphite (HOPG), C-60 and amorphous carbon. The degradation of the nanotubes, dependent on the metal substrate type and its morphology, is explained on the basis of interactions between the nanotubes and the metal substrate. The D band, which is an indicator of the degree of disorder, increases its intensity when the film thickness is decreased. SERS spectra recorded at different excitation wavelengths reveal that metallic nanotubes are primarily affected. A mutual correlation was found between the variations in the relative intensity of the D band and the Breit-Wigner-Fano component due to metallic tubes displayed by Raman bands situated in the 1500-1600 cm(-1) range. A direct interaction between C-60 and nanotubes is revealed by comparative SERS spectra on SWNTs and (SWNTs+C-60) films. At lambda(exc)=676.4 nm the narrowing in the lower energy side of the broad band associated to tangential vibration modes indicates that the metallic tubes are involved in the formation of a [(SWNT)C-+(60)-] complex type.

188. Raman and SERS studies of carbon nanotubes

Authors: Lefrant, S; Baibarac, M; Baltog, I; Buisson, JP; Chauvet, O

Published: 2002, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 374, 334, DOI: 10.1080/10587250210472

Since the discovery of carbon nanotubes, Raman Scattering Spectroscopy and transmission Electron Microscopy have been proved to be powerful for a detailed investigation of their properties. In TEM, a direct observation can be made, whereas Raman Scattering is used extensively to probe the different samples via their vibrational properties. In this paper, we report on recent results obtained in both single-walled carbon nanotubes (SWNTs), multiwalled-carbon nanotubes (MWNTs) and PMMA/nanotubes composites. In addition, in the case of SWNTs, we present studies carried out in Raman scattering when SERS (Surface Enhanced Raman Scattering) conditions are used. In particular, we put in evidence an increased state of disorder at the interface nanotubes/metallic support when the nanotube film thickness is decreased. Strong degradations can be observed primarily on metallic tubes with a concomitant formation of C-60-like molecules. In the case of MWNTs, calculations of interactions between concentric tubes lead to the occurrence of low frequency vibrational modes, in good agreement with experiments.

189. C-60-polymer nanocomposites: evidence for interface interaction

Authors: Giusca, C; Baibarac, M; Lefrant, S; Chauvet, O; Baltog, I; Devenyi, A; Manaila, R

Published: 2002, CARBON, 40, 1574, DOI: 10.1016/S0008-6223(02)00024-6

Polyaniline-fullerene (PA-C-60) composites have been studied by Surface Enhanced Raman scattering (SERS) spectroscopy and X-ray diffraction. They were obtained by mixing solutions of polyaniline-emeraldine base (PA-EB) and C-60, as well as by chemical synthesis from aniline, sulfuric acid and potassium dichromate, with addition of C-60. The Raman bands peaking at 1330-1370 cm(-1). associated with a protonated structure Were used as indicative for changes of the PA-EB phonon spectrum resulting from C-60 doping. The two types of compounds show different SERS spectra, also dependent on the metallic support used (An or Ag). Variation of the SERS spectra with the type of metallic support is related to a chemical interface interaction between composite and metal. In mixture samples, a doped polymeric chain (with ionically attached C-60(-)) was evidenced by an increased fraction of quinoid rings. The SERS spectra of the chemically synthesized PA-C-60 reveals the existence of two polymeric structures: a doped PA (doped with C-60(-) ions) and an undoped one, the latter with a structure of 'pendant chain' type. Structural (XRD) data reveal the presence of C-60 nano-zones, with a lattice parameter increase of 0.3-0.6%, attributed to slight oxidation. Detailed analysis of the fcc(111) line asymmetry suggests, in mixture samples, a boundary zone with an 'expanded' lattice. induced by ionic interface effects. (C) 2002 Elsevier Science Ltd. All rights reserved.

190. SERS studies on disordered carbon nanotube thin films

Authors: Baibarac, M; Benoit, JM; Lefrant, S; Baltog, I; Schreiber, J; Bernier, P; Chauvet, O

Published: MAR 15 2001, SYNTHETIC METALS, 121, 1200, DOI: 10.1016/S0379-6779(00)00735-9

The SERS technique has been proved to be successful to study Single-Walled Carbon Nanotubes (SWNT's), with the observation of peculiar features. In this study, we present more specifically the Raman features which are strongly dependent on the morphology of the nanotube thin films, their thickness, the interfacial effects between films and support, the effect of solvent used to disperse the nanotubes onto the metallic surface.

191. Luminescence of oxidized porous silicon: Surface-induced emissions from disordered silica micro- to nanotextures

Authors: Fritsch, E; Mihut, L; Baibarac, M; Baltog, I; Ostrooumov, M; Lefrant, S; Wery, J

Published: NOV 1 2001, JOURNAL OF APPLIED PHYSICS, 90, 4782, DOI: 10.1063/1.1410887

The luminescence spectra of fully oxidized porous silicon show two broad bands and one vibronic structure between 2 and 3.3 eV, all excited at 340 or 275 nm (3.65 and 4.51 eV). Two of these structures have not been described previously. Interestingly, these emissions are found in other forms of amorphous or disordered silica with high specific surfaces: frosted silica glass, silica gel, even various natural opals. These emissions disappear when the surface is passivated. They are, therefore, attributed to surface-related defects. The vibronic structure involves a nearly free SiO4 tetrahedron. Another vibronic structure found only in some opals is attributed to the uranyl group. (C) 2001 American Institute of Physics.

192. C-60-polymer nanocomposites: Evidence for interface interaction

Authors: Giusca, C; Alexe, G; Baibarac, M; Baltog, I; Manaila, R; Devenyi, A

Published: 2001, EPDIC 7: EUROPEAN POWDER DIFFRACTION, PTS 1 AND 2, 378-3, 388, DOI: 10.4028/www.scientific.net/MSF.378-381.383

Structure of polyaniline (PAN)-C-60 nanocomposites was investigated by X-ray diffraction. Raman Spectroscopy was also used in order to find evidence for the C-60 - polymer interface interaction.

193. Doping and metallic-support effect evidenced on SERS spectra of polyaniline thin films

Authors: Baibarac, M; Mihut, L; Louarn, G; Lefrant, S; Baltog, I

Published: OCT 1 2000, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 38, 2609, DOI: 10.1002/1099-0488(20001001)38:19<2599::AID-POLB120>3.0.CO;2-Y

Surface-enhanced Raman scattering (SERS) is a process with origins, electromagnetic and chemical. The electromagnetic enhancement consists of the excitation of surface plasmons in the metallic support of the thin film. With only the electromagnetic enhancement mechanism, the surface spectra should not differ from volume Raman spectra. However, between SERS and volume Raman spectra, there are differences resulting from the chemical reactions taking place at the polymer/metal interface, intermediated by solvent molecules, that finally depend on the types of polymers and metallic supports. Polyaniline (PAN) is an excellent material to emphasize the chemical component of SERS. This is due to its particular structure with a repeating unit that contains two entities at different weights-a reduced state and an oxidized state-that, in turn, react differently with a metallic substrate. SERS spectra depend on the oxidizing properties of the metal surface, which involves an intermediate compound of the types Ag2O and Au2O3 when N-methyl-2-pyrrolidinone is used as the solvent. This article presents new results concerning the surface chemical effects that produce variations of the PAN SERS spectra. The SERS spectra of the PAN emeraldine base (PAN-EB) layered on Au support are characterized by a semiquinoid structure that we believe is induced on the intermediate compound Au2O3. In the presence of H2SO4, the SERS spectra change gradually as the degree of acid protonation doping increases. The SERS spectra of the fully protonated PAN-EB are identical to those obtained on PAN emeraldine salt (PAN-ES) synthesized by cyclic voltammetry in an acid medium and are invariable with the type of metallic support. The SERS spectra show that the emeraldine salt can be partially or totally deprotonated with water or NH4OH. The deprotonation is complete for the Ag support and partial for the Au support. The SERS spectra of the fully protonated PAN-EB are characterized by a double band with maxima at about 1330 and 1370 cm(-1). Although the generation process of positive charge on the macromolecular chain of PAN-EB doped in the presence of (C4H9)(4)NBF4 is similar to that due to protonic acid doping, involving cation addition (C4H9+ or H+ ions, respectively) in SERS spectra, the complex band situated at about 1330-1370 cm(-1) no longer appears. The doping of PAN-EB with FeCl3 produces two polymer cm forms: a salt type characterized by a protonated structure similar to that found for PAN-ES and a base type similar to the leucoemeraldine form. (C) 2000 John Wiley & Sons, Inc.

194. SERS spectra of mono and bisphthalocyanine complexes deposited on Ag and Au supports

Authors: Faulques, E; Baibarac, M; Galmiche, L; L'Her, M; Pondaven, A; Baltog, I

Published: 2000, SPECTROSCOPY LETTERS, 33, 631, DOI: 10.1080/00387010009350144

In this letter, we present a study of surface-enhanced Raman spectra of thin layers of phthalocyanine (Pc) complexes deposited on Ag and Au rough surfaces. The materials of this work are MgPc (monophthalocyanine) and the asymmetrical lutetium bisphthalocyanine (tBu)(4)PcLuPcCl8 (Pc'LuPc ") under three oxidation states. Enhancement of specific bands is observed depending on the surface and the oxidation state. SERS signatures of neutral, oxidised and reduced Pc'LuPc " are identified.

195. The inhibition of the corrosion of Armco iron in HCl solutions in the presence of surfactants of the type of N-alkyl quaternary ammonium salts

Authors: Branzoi, V; Branzoi, F; Baibarac, M

Published: AUG 15 2000, MATERIALS CHEMISTRY AND PHYSICS, 65, 297, DOI: 10.1016/S0254-0584(00)00260-1

The polarization behaviour of Armco iron in aqueous solutions of HCl with and without inhibitors has been studied by the potentiostatic method. At lower overvoltage values, the dissolution process is controlled by activation, while at higher overvoltage values, the dissolution process is controlled by diffusion. The inhibition of this metal corrosion in the aqueous solutions of HCl has been studied using four surfactants. Under the critical micelle concentration (CMC), the inhibition of these four surfactants is negligible. At a concentration higher than the CMC, the inhibiting action of tetradecyl trimethyl ammonium iodide (TTAI), tetradecyl trimethyl ammonium bromide (TTAB), hexadecyl trimethyl ammonium bromide (HTAB) and dodecyl trimethyl ammonium bromide (DTAB) increases rapidly. The process of inhibition was attributed to the formation of adsorbed film on the metal surface, that protects the metal against corrosive agents. Protection efficiency improved when the inhibitor concentration and the length of the alkyl chain were increased. The four quaternary ammonium salts tested were adsorbed on the Armco iron surface according to a Langmuir isotherm. (C) 2000 Elsevier Science S.A. All rights reserved.

196. Interfacial chemical effect evidenced on SERS spectra of polyaniline thin films deposited on rough metallic supports

Authors: Baibarac, M; Mihut, L; Louarn, G; Mevellec, JY; Wery, J; Lefrant, S; Baltog, I

Published: DEC 1999, JOURNAL OF RAMAN SPECTROSCOPY, 30, 1113, DOI: 10.1002/(SICI)1097-4555(199912)30:12<1105::AID-JRS507>3.0.CO;2-3

Surface-enhanced Raman scattering (SERS) has proved to be an effective technique for studying the structural properties of conducting polymer thin films. The enhancement process has a twofold origin, electromagnetic and chemical, The electromagnetic enhancement, which is the dominant mechanism in SERS generation, consists in the excitation of localized and delocalized surface plasmons (SPs) in the metallic support of the thin film, The Raman emission of the adsorbed molecules on the metal surface (the most efficient being Ag, Au and Cu) is due to the intense evanescent electromagnetic field located at the interface between the metal and the surrounding medium. The second enhancing mechanism for SERS is of chemical origin, involving the formation of new chemical bonds between the molecules and the metal surface, with the polarizability thus becoming considerably higher than that of the free molecules. This mechanism is as a rule accompanied by a metal-molecule or molecule-metal charge transfer, which partly accounts for the success of the SERS studies on conducting polymers. Unfortunately, these studies have revealed that the chemical effects at the polymer-metal interface varied substantially depending on the various types of polymer and metallic support. In this context, polyaniline containing two different entities (a reduced and an oxidized state) in its repeating units exhibits specific alterations in its SERS spectra depending on the type of metallic support. This paper presents new results concerning the structure of emeraldine-base and emeraldine-salt polyaniline thin films deposited on rough Ag and Au supports. The effect on the SERS spectra of the polymer-metal and polymer-ambient interface chemical reactions is also described. The presence of an interface compound depending on the oxidizing properties of the metallic support has a strong influence on the SERS spectra, no matter how the PAN films were deposited on the support (whether by solvent evaporation or by an electrochemical process, i.e. cyclic voltammetry). When an emeraldine base is doped with HSO4- ions, it turns into an emeraldine salt, which exhibits a disordered state in its macromolecular chain, leading to a modified profile of the similar to 1162 cm(-1) Raman line which is associated with the C-H bond of the quinoid ring. The Lorentzian profile is altered by the addition of a Gaussian profile component. For a rough Ag support, the SERS spectra show that the transformation of emeraldine base films into emeraldine salt films is a reversible process, Copyright (C) 1999 John Wiley & Sons, Ltd.

197. Studies by SERS spectroscopy of the structural properties of conducting polymers and carbon nanotubes

Authors: Lefrant, S; Baltog, I; de la Chapelle, ML; Baibarac, M; Louarn, G; Journet, C; Bernier, P

Published: MAY 1999, SYNTHETIC METALS, 101, 187, DOI: 10.1016/S0379-6779(98)00307-5

After being dispersed in liquid solvents (Ethanol, CHCl3), conducting polymers and singlewalled nanotubes have been deposited on ruguous substrats (Au, Ag, Cu). With FT Raman technique (laser excitation : 1064 nm), we have obtained SERS signal of both conductiong polymers and singlewalled nanotubes. The Raman signals change with substrat and/or solvent, which could be correlated with the size of clusters formed at the surface and then to the deposition mechanism. The main advantage of the >SERS technique will be emphasized in terms of enhancement as a powerful technique to study nanoparticles.

198. Structural properties of some conducting polymers and carbon nanotubes investigated by SERS spectroscopy

Authors: Lefrant, S; Baltog, I; de la Chapelle, ML; Baibarac, M; Louarn, G; Journet, C; Bernier, P

Published: MAR 26 1999, SYNTHETIC METALS, 100, 27, DOI: 10.1016/S0379-6779(98)00175-1

In this paper, we present Surface Enhanced Raman Scattering (SERS) experiments performed successfully on some conducting polymers and carbon nanotubes deposited in thin films on rough metallic surfaces. The enhancement mechanism in SERS has a twofold origin: electromagnetic and chemical. The electromagnetic enhancement is, however, the dominant mechanism and consists in the excitation of localized and delocalized surface plasmons (SP). The second enhancing mechanism for SERS, not yet convincingly supported by experimental data, is of chemical origin. This mechanism is due to the increase of the polarizability of the molecules on the metal surface under the action of the incident radiation, leading to the formation of new chemical bonds between the molecules and the metal surface. Unfortunately, the experimental data available to argue the presence of a chemical process are scarce and scattered. In this paper, we try to present some details regarding this aspect. In order to do so, we studied poly 3-hexylthiophene (3-PHT) and polyaniline (PAN) as a function of the type of the rough metallic support (Ag, Au or Cu), the oxidization state and thickness of the polymer layer. We studied also carbon single walled nanotubes. Our experiments reveal the existence of a chemical surface effect. The results obtained for 3-PHT show that SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds. The SERS measurements reported here reveal an increase of the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. We observe for the first time by SERS spectroscopy that doping of 3-PHT with FeCl3 leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. The type of the rough metallic support can modify SERS spectra and such an effect is clearly shown for the polyaniline case. No such dependence on metallic support type is observed on the SERS spectra of carbon nanotubes. (C) 1999 Published by Elsevier Science S.A. All rights reserved.

199. SERS spectra of poly(3-hexylthiophene) in oxidized and unoxidized states

Authors: Baibarac, M; Lapkowski, M; Pron, A; Lefrant, S; Baltog, I

Published: SEP 1998, JOURNAL OF RAMAN SPECTROSCOPY, 29, 832, DOI: 10.1002/(SICI)1097-4555(199809)29:9<825::AID-JRS309>3.3.CO;2-U

Surface enhanced Raman scattering (SERS) is being increasingly used for the study of the structural properties of conducting polymer thin films. It is generally accepted that the enhancement process has an electromagnetic origin, arising from the excitation of surface plasmons in the metal support on which the polymer film is deposited. However, the electromagnetic enhancement is also accompanied by a chemical process, for which available experimental data are scarce. The chemical process originates from the increase in the polarizability of the molecules at the metal surface under the action of the incident radiation, which leads to the formation of new chemical bonds with the atoms of the metal support. The present work was devoted to the study of the SERS spectra of poly(3-hexylthiophene) deposited on rough Ag and Au supports by evaporating the solvent from a solution of known concentration. The experiments revealed the existence of a chemical surface effect. The results obtained show that the SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds of the type MeX (Me = Ag or Au, X = Cl or O). The SERS measurements reported here reveal an increase in the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. It was observed for the first time by SERS spectroscopy that the doping of 3-PHT with FeCl3 leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. (C) 1998 John Whey & Sons, Ltd.

200. On the photoluminescence decay in porous silicon films

Authors: Baltog, I; Ciurea, ML; Pavelescu, G; Mihut, L; Baibarac, M

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 626, DOI: 10.1117/12.312818

The photoluminescence (PL) decay measurements were performed on porous silicon films. It was observed that the two components of FL, one of them fast (ns) and the other slow (mu s or ms sometimes) have different contributions to PL signal, depending on the wavelength of the excitation light. The slow component of PL was in details investigated. Time decay cures for different excitation (337.1 nm, 470 nm and 550nm) and emission (550, 650, 700, 800 and 860 nm) wavelengths and also for different excitation intensities were taken. All decay curves were fitted with a stretched exponential. The slow component of PL was proposed to be attributed to the radiative recombination on surfaces.

201. The inhibition of the corrosion of Armco iron in hydrochloric acid solutions by organic surfactants

Authors: Branzoi, V; Branzoi, F; Baibarac, M; Popa, MV

Published: JUN 1998, REVUE ROUMAINE DE CHIMIE, 43, 513, DOI:

The polarization behaviour of Armco iron in solutions of HCl with and without inhibitors has been studied by potentiostatic method. At lower overvoltage values the dissolution process is controlled by activation, while at higher overvoltage values the dissolution process is controlled by diffusion. The inhibition of this metal corrosion in the aqueous solutions of HCl has been studied using three surfactants. Under the critical micelle concentration the inhibition of those three surfactants is negligible. At a concentration higher than critical micelle concentration, the inhibiting action of surfactants increases rapidly. The process of inhibition was attributed to the formation of the adsorbed film on the metal surface, that protects the metal against the corrosive agents.

202. SERS spectra of polyaniline thin films deposited on rough Ag, Au and Cu. Polymer film thickness and roughness parameter dependence of SERS spectra

Authors: Baibarac, M; Cochet, M; Lapkowski, M; Mihut, L; Lefrant, S; Baltog, I

Published: JUL 15 1998, SYNTHETIC METALS, 96, 70, DOI: 10.1016/S0379-6779(98)00065-4

Surface-enhanced Raman scattering (SERS) has lately proved to be an effective technique which has led to its increasing application for studying the structural properties of conducting polymer thin films. It is generally accepted that the enhancement process has an electromagnetic origin arising from the excitation of surface plasmons (SPs) in the metal support on which the polymer film is deposited. However, the electromagnetic enhancement is also accompanied by a chemical process, on which only scarce experimental data are available at present. The chemical process originates in an increased polarizability of the molecules at the metal surface under the action of an incident radiation, as a result of which new chemical bonds are formed with the atoms of the metal support. This paper is devoted to the study of the SERS spectra under 1064 nm excitation for two forms of polyaniline, one of the emeraldine base type and the other of the emeraldine salt type. Our purpose has been to identify the chemical effects at the polymer/metal interface that are involved in specific modifications of the SERS spectra. The following results concerning SERS spectrum variation with metal support type (AE, Au and Cu) have been obtained. An oxidation of emeraldine base taking place at the polymer/metal interface has been revealed. In the case of emeraldine salt, an oxidized form of polyaniline, the SERS spectra remain unchanged regardless of the changes in the metal support, which proves the stability of this form. A new result has been obtained as SERS spectroscopy revealed an electron delocalization process taking place in the emeraldine salt molecule as a result of an electron transfer from metal to the polymer molecule occurring on the level of quinoid rings. The concept of a rough Raman-active surface has been clarified by using a parameter Wa, similar to the grating groove depth/grating periodicity ratio which occurs when a diffraction grating is used as optic coupler. (C) 1998 Elsevier Science S.A. All rights reserved.

203. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development

Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: , DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, DOI:

204. Textile Materials Treatment With Mixture of TiO2:N and SiO(2)Nanoparticles for Improvement of Their Self-Cleaning Properties

Authors: Mateescu, AO; Mateescu, G; Burducea, I; Mereuta, P; Chirila, L; Popescu, A; Stroe, M; Nila, A; Baibarac, M

Published: SEP 2020 , JOURNAL OF NATURAL FIBERS, DOI: 10.1080/15440478.2020.1818349

This study addresses the deposition with improved adhesion of TiO2:N/SiO(2)mixture, with different concentrations of the nano-powders (NPs) (1:0,5; 1:1 and 1:1,5) on 100% cotton fabrics. The characteristics of the deposited thin films were investigated by scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), Raman scattering, FTIR, and UV-VIS absorption spectroscopy. To improve the treatment durability to the external factors, the different crosslinking methods were used. Photocatalytic activity of functionalized textile fabrics was evaluated by determining the photodegradation efficiency of the methylene blue (MB) dye and forest juice, measuring the color difference of the irradiated samples compared with non-irradiated samples. Washing durability of the samples was achieved qualitatively by determining the photocatalytic activity remaining on the textile fabrics after 1 and 5 washing cycles. The samples treated with the mixture of TiO2:N/SiO(2)have demonstrated improved self-cleaning properties, the highest photocatalytic activity being obtained for the highest value of TiO2:N/SiO(2)NPs molar concentrations equal to 1:1.

205. Pyrolysis and combustion of polystyrene composites based on graphene oxide functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane

Authors: Anghel, I; Lisa, G; Sofran, IE; Mitroi-Symeonidis, FC; Rusu, MM; Baia, M; Baia, L; Magyari, K; Danciu, V; Cotet, LC; Stroe, M; Baibarac, M

Published: , JOURNAL OF POLYMER ENGINEERING, 2021, 626, DOI:

206. Textile Materials Treatment With Mixture of TiO2:N and SiO(2)Nanoparticles for Improvement of Their Self-Cleaning Properties

Authors: Mateescu, AO; Mateescu, G; Burducea, I; Mereuta, P; Chirila, L; Popescu, A; Stroe, M; Nila, A; Baibarac, M

Published: , JOURNAL OF NATURAL FIBERS, DOI: 10.1080/15440478.2020.1818349

Dr. Mihaela BAIBARAC

Scientific Researcher I

Expertize

Projects

1. Recycling of the cathodes, based on carbon nanotubes and conducting polymers, from spent rechargeable Li batteries

2. Nanocomposites based on recycled cellulose and carbon nanotubes for construction materials with improved fire resistance

3. The development of integrated diagnostic methods for the rapid detection of liver diseases

4. Physico-chemical analysis, nanostructured materials and devices for applications in the pharmaceutical field and medical in Romania

5. 4D printed energy harvesting devices based on innovative printable conductive elastomers

6. Composite materials with graphene oxide to improve performance at the fire action of the elements of constructions and installations for the purpose life protection in case of fire

7. Interinstitutional program for the development of advanced solutions based on econ-nanotechnologies for multifunctional treatments of textile and leather materials

8. Optical properties of SWNTs highly separated in metallic (98%) and semiconducting (99%) functionalized with conjugated polymers

9. One-dimensional composites based on carbon nanotubes and conjugated polymers for applications in energy storage and optoelectronic devices field

10. Implementation in East Europe of new methods of synthesis and functionalization of carbon nanotubes for applications in the energy storage and sensors field

11. Hybrid materials based on carbon nanotubes, heteropolyacids and conducting polymers for applications in energy storage field

12. Optical and electrochemical properties of the carbn nanotubes/polyoxometalates/conducting polymers nanocomposites

13. Organic/inorganic type hybrid nanocomposites, with carbon nanotubes and inorganic semiconductor nanoparticles, for applications in the field of optoelectronics, supercapacitors and sensors.

14. Optical and electrical processes in hybrid nano- structured materials produced by the intercalation of the bi-dimensional crystalline structures

15. Nano-structured composites of poly N-vinyl carbazole/carbon nanotube for applications in optoelectronics and rechargeable lithium batteries: synthesis, optical, electrical and electrochemical characterisation and applicative demonstrations.

16. Nanostructured materials for aplications in sensors and optoelectronic technology

17. Photoconductivity and photoluminescence processes in poly para-phenylene vinylene/ carbon nanotubes and poly para-phenylene vinylene/oxide nanoparticles type composites

Publications

1. Functionalization of Carbon Nanotubes and Graphene Derivatives with Conducting Polymers and Their Applications in Dye-Sensitized Solar Cells and Supercapacitors

2. The influence of the functionalization of polystyrene and graphene oxide composites on the flammability characteristics: modeling with artificial intelligence tools

3. Structural and flame retardancy properties of GO-DOPO-HAK composite

4. Surface species of the nematic mixture E7 obtained by electrochemical insertion of Li+ ions

5. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO2 Nanowires

6. Photocatalytic Activity of the Blends Based on TiO2 Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

7. Surface species of the nematic mixture E7 obtained by electrochemical insertion of Li+ ions

8. Functionalization of Graphene Derivatives with Conducting Polymers and Their Applications in Uric Acid Detection

9. Photocatalytic Activity of the Blends Based on TiO2 Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

10. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO2 Nanowires

11. Nanohybrid Composites Based on TiO2 and Single-Walled Carbon Nanohorns as Promising Catalysts for Photodegradation of Amoxicillin

12. Three-Dimensional Printable Flexible Piezoelectric Composites with Energy Harvesting Features

13. Complex Spectroscopy Studies of Nifedipine Photodegradation

14. From interface to interphase

15. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development

16. The Photoluminescence and Vibrational Properties of Black Phosphorous Sheets Chemically/Electrochemically Functionalized in the Presence of Diphenylamine

17. Degradation of Losartan Potassium Highlighted by Correlated Studies of Photoluminescence, Infrared Absorption Spectroscopy and Dielectric Spectroscopy

18. Correlated studies of photoluminescence, vibrational spectroscopy and mass spectrometry concerning the pantoprazole sodium photodegradation

19. Photodegradation of Azathioprine in the Presence of Sodium Thiosulfate

20. New Aspects Concerning the Ampicillin Photodegradation

21. Pyrolysis and combustion of polystyrene composites based on graphene oxide functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane

22. Optical, Structural, and Dielectric Properties of Composites Based on Thermoplastic Polymers of the Polyolefin and Polyurethane Type and BaTiO3 Nanoparticles

23. Optical Evidence for the Assembly of Sensors Based on Reduced Graphene Oxide and Polydiphenylamine for the Detection of Epidermal Growth Factor Receptor

24. Optical Properties of Composites Based on Poly(o-phenylenediamine), Poly(vinylenefluoride) and Double-Wall Carbon Nanotubes

25. A Special Section on Carbonaceous-Containing Nanomaterials for Multi-Functional Applications

26. Gypsum Composite Boards Incorporating Phase Change Materials: A Review

27. Azathioprine Electrochemical Adsorption onto the Reduced Graphene Oxide Sheets in Absence and in the Presence of Polyaniline

28. The Influence of the Ceramic Nanoparticles on the Thermoplastic Polymers Matrix: Their Structural, Optical, and Conductive Properties

29. Mixture of Graphene Oxide/Phosphoric Acid/Melamine as Coating for Improved Fire Protective Performance and Enhancement of Surface Electrical Properties on Wood Chipboard

30. Vibrational and Photoluminescence Properties of Composites Based on Double-Walled Carbon Nanotubes, Poly(o-phenylenediamine) and Poly(ethylene oxide)

31. Screen-Printed Carbon Electrodes Modified with Double-Walled Carbon Nanotubes Functionalized with Polypyrrole and Their Electrochemical Processes in the Presence of Folic Acid

32. Carbon Xerogel Nanostructures with Integrated Bi and Fe Components for Hydrogen Peroxide and Heavy Metal Detection

33. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development

34. Anisotropic Photoluminescence of Poly(3-hexyl thiophene) and Their Composites with Single-Walled Carbon Nanotubes Highly Separated in Metallic and Semiconducting Tubes

35. The Influence of UV Light on Photodegradation of Acetylsalicylic Acid

36. Rhodamine B Photodegradation in Aqueous Solutions Containing Nitrogen Doped TiO2 and Carbon Nanotubes Composites

37. Spectroscopic studies on photodegradation of atorvastatin calcium

38. Poly(Vinyl Chloride) Spheres Coated with Graphene Oxide Sheets: From Synthesis to Optical Properties and Their Applications as Flame-Retardant Agents

39. Photoluminescence as a Complementary Tool for UV-VIS Spectroscopy to Highlight the Photodegradation of Drugs: A Case Study on Melatonin

40. Oxidation of chalcopyrite in air-equilibrated acidic solution: Inhibition with phenacyl derivatives

41. Stimulated Raman scattering and defect-based photoconductivity in mixtures of CdS/TiO2

42. Reusable on-plate immunoprecipitation method with covalently immobilized antibodies on a protein G covered microtiter plate

43. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of alpha-Lipoic Acid in the Presence of Ag and Au Nanoparticles

44. UV Light Effect on Cationic Photopolymerization of the SU8 Photoresist and Its Composites with Carbon Nanotubes: New Evidence Shown by Photoluminescence Studies

45. Influence of Reduced Graphene Oxide on the Electropolymerization of 5-Amino-1-naphthol and the Interaction of 1,4-Phenylene Diisothiocyanate with the Poly(5-Amino-1-naphtol)/Reduced Graphene Oxide Composite

46. Photoluminescence as a Valuable Tool in the Optical Characterization of Acetaminophen and the Monitoring of Its Photodegradation Reactions

47. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of alpha-Lipoic Acid in the Presence of Ag and Au Nanoparticles

48. Optical Properties of Composites Based on Graphene Oxide and Polystyrene

49. Influence of boric acid concentration on the properties of electrodeposited CZTS absorber layers

50. Morphological and structural investigation of the poly(Vinyl chloride) / graphene oxide composites

51. Photoluminescence as a Valuable Tool in the Optical Characterization of Acetaminophen and the Monitoring of Its Photodegradation Reactions

52. MORPHOLOGICAL AND STRUCTURAL INVESTIGATION OF THE POLY(VINYL CHLORIDE)/GRAPHENE OXIDE COMPOSITES

53. Nanostructures based detection of pharmaceuticals and other contaminants of emerging concern

54. The influence of UV light on the azathioprine photodegradation: New evidences by photoluminescence

55. Novel anhydrous solid-state form of Azathioprine: The assessing of crystal structure by powder X-Ray diffraction, Infrared Absorption Spectroscopy and Raman scattering

56. Properties of textile and leather materials treated with new hybrid SiO2/TiO2/poly(2,2 '-bithiophene) nanocomposites

57. Photoluminescence and structural properties of the nitrogen doped TiO2 and the influence of SiO2 and Ag nanoparticles

58. Adsorption of 1,4-phenylene diisothiocyanate onto the graphene oxide sheets functionalized with polydiphenylamine in doped state

7. Surface species of the nematic mixture E7 obtained by electrochemical insertion of Li⁺ ions

9. Photocatalytic Activity of the Blends Based on TiO₂ Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

10. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO₂ Nanowires

11. Nanohybrid Composites Based on TiO₂ and Single-Walled Carbon Nanohorns as Promising Catalysts for Photodegradation of Amoxicillin