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Dr. Cristina BUCUR

Scientific Researcher

Laboratory of Surface and Interface Science

cristina[DOT]bucur[AT]infim[DOT]ro

Publications

1. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization
Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: FEB 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202205476

Pb(Zr,Ti)O-3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2Ti0.8)O-3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and LaxSrMn1-xO3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.
2. Experimental Band Structure of Pb(Zr,Ti)O-3: Mechanism of Ferroelectric Stabilization
Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: JAN 2023, ADVANCED SCIENCE, DOI: 10.1002/advs.202205476

Pb(Zr,Ti)O-3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2Ti0.8)O-3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and LaxSrMn1-xO3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.
3. Experimental Band Structure of Pb(Zr,Ti)O3: Mechanism of Ferroelectric Stabilization
Authors: Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN

Published: FEB 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202205476

Pb(Zr,Ti)O-3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2Ti0.8)O-3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and LaxSrMn1-xO3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.
4. Catalytic transformation of the marine polysaccharide ulvan into rare sugars, tartaric and succinic acids
Authors: Podolean, I; Coman, SM; Bucur, C; Teodorescu, C; Kikionis, S; Ioannou, E; Roussis, V; Primo, A; Garcia, H; Parvulescu, VI

Published: JAN 1 2022, CATALYSIS TODAY, 383, 357, DOI: 10.1016/j.cattod.2020.06.086

The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 degrees C renders a high percentage of rhamnose (78-79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 degrees C affords moderate amounts of tartaric acid (24-26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.
5. Doped microporous graphitic carbons as metal-free catalysts for the selective hydrogenation of alkynes to alkenes
Authors: Primo, A; Rendon-Patino, A; Bucur, C; Jurca, A; Cojocaru, B; Parvulescu, VI; Garcia, H

Published: JAN 2022, JOURNAL OF CATALYSIS, 405, DOI: 10.1016/j.jcat.2021.11.034

Microporous graphitic carbons obtained by pyrolysis of a-cyclodextrin have been conveniently doped with N and P elements by performing the thermal graphitization adding urea or phosphoric acid as source of these elements. Electron microscopy shows that doping does not influence the structure and dimensions of the micropores, while XPS reveals the distribution of these dopant elements in two main families corresponding to pyridinic and pryrrolic N atoms and to triphenylphosphine and triphenylphosphine oxide for P doping. Thermo-programmed desorption of H2, CO2 and NH3 indicates that the presence of dopant element is responsible for chemisorption of these gases and introduces basic and acid sites. These desorption measurements agree with the catalytic performance of the series of carbons for the chemo and stereo selective hydrogenation of internal aliphatic and aromatic alkynes to cis configured alkenes. N/P doped microporous carbons were found to be stable under the reaction conditions, according to the constant TOF values and XRD and XPS characterization of the materials after their use as catalysts. In addition microporosity appears to play a positive effect by comparing the activity of microporous carbons with the performance of analogous N/P-doped graphenes. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
6. Sonogashira Synthesis of New Porous Aromatic Framework-Entrapped Palladium Nanoparticles as Heterogeneous Catalysts for Suzuki-Miyaura Cross-Coupling
Authors: Cata, L; Terenti, N; Cociug, C; Hadade, ND; Grosu, I; Bucur, C; Cojocaru, B; Parvulescu, VI; Mazur, M; Cejka, J

Published: MAR 2 2022, ACS APPLIED MATERIALS & INTERFACES, 14, DOI: 10.1021/acsami.1c24429

Palladium nanoparticles entrapped in porous aromatic frameworks (PAFs) or covalent organic frameworks may promote heterogeneous catalytic reactions. However, preparing such materials as active nanocatalysts usually requires additional steps for palladium entrapment and reduction. This paper reports as a new approach, a simple procedure leading to the self-entrapment of Pd nanoparticles within the PAF structure. Thus, the selected Sonogashira synthesis affords PAF-entrapped Pd nanoparticles that can catalyze the C-C Suzuki-Miyaura cross-coupling reactions. Following this new concept, PAFs were synthesized via Sonogashira cross-coupling of the tetraiodurated derivative of tetraphenyl aLam an tan e or spiro-9,9'-bifluorene with 1,6-diethynylpyrene, then characterized them using powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, high-resolution scanning transmission electron microscopy, and textural properties (i.e., adsorption-desorption isotherms). The PAF-entrapped Pd nanocatalysts showed high catalytic activity in Suzuki-Miyaura coupling reactions (demonstrated by preserving the turnover frequency values) and stability (demonstrated by palladium leaching and recycling experiments). This new approach presents a new class of PAFs with unique structural, topological, and compositional complexities as entrapped metal nanocatalysts or for other diverse applications.
7. Sonogashira Synthesis of New Porous Aromatic Framework- Entrapped Palladium Nanoparticles as Heterogeneous Catalysts for Suzuki-Miyaura Cross-Coupling
Authors: Cata, L; Terenti, N; Cociug, C; Hadade, ND; Grosu, I; Bucur, C; Cojocaru, B; Parvulescu, VI; Mazur, M; Cejka, J

Published: FEB 2022, ACS APPLIED MATERIALS & INTERFACES, DOI: 10.1021/acsami.1c24429

Palladium nanoparticles entrapped in porous aromatic frameworks (PAFs) or covalent organic frameworks may promote heterogeneous catalytic reactions. However, preparing such materials as active nanocatalysts usually requires additional steps for palladium entrapment and reduction. This paper reports as a new approach, a simple procedure leading to the self-entrapment of Pd nanoparticles within the PAF structure. Thus, the selected Sonogashira synthesis affords PAF-entrapped Pd nanoparticles that can catalyze the C-C Suzuki-Miyaura cross-coupling reactions. Following this new concept, PAFs were synthesized via Sonogashira cross-coupling of the tetraiodurated derivative of tetraphenyladamantane or spiro-9,9 '-bifluorene with 1,6-diethynylpyrene, then characterized them using powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, high-resolution scanning transmission electron microscopy, and textural properties (i.e., adsorption-desorption isotherms). The PAF-entrapped Pd nanocatalysts showed high catalytic activity in Suzuki-Miyaura coupling reactions (demonstrated by preserving the turnover frequency values) and stability (demonstrated by palladium leaching and recycling experiments). This new approach presents a new class of PAFs with unique structural, topological, and compositional complexities as entrapped metal nanocatalysts or for other diverse applications.
8. From useless humins by-product to Nb@graphite-like carbon catalysts highly efficient in HMF synthesis
Authors: El Fergani, M; Candu, N; Tudorache, M; Bucur, C; Djelal, N; Granger, P; Coman, SM

Published: MAY 25 2021, APPLIED CATALYSIS A-GENERAL, 618, DOI: 10.1016/j.apcata.2021.118130

Highly dispersed supported NbOx species were prepared via a deposition precipitation-carbonization (DPC)-like method. As precursors for niobium species and carrier ammonium niobate(V) oxalate hydrate and humins were used. Characterization of the resulted catalysts indicated bi-functional acid-base niobium species anchored onto a highly hydrophobic graphite-like carbon structure. These catalysts were investigated in the one-pot conversion of glucose to 5-hydroxymethylfurfural (HMF) in a biphasic system consisting of a mixture of a 20 wt% NaCl aqueous solution phase and an organic extracting phase (methyl-isobutyl-ketone (MIBK), 2-tert-butylphenol (TBP) or 2sec-butylphenol (SBP)). The optimization conditions afforded the highest yield to HMF (96 %) for the GHNb1.2 catalyst (with 2.5 wt%Nb), the base/acid sites ratio of 1.76, in biphasic TBP/water system, at 180 ?C after 8 h.
9. New photoactive mesoporous Ce-modified TiO2 for simultaneous wastewater treatment and electric power generation
Authors: Mureseanu, M; Chivu, V; Osiac, M; Ciobanu, M; Bucur, C; Parvulescu, V; Cioatera, N

Published: APR 15 2021, CATALYSIS TODAY, 366, 176, DOI: 10.1016/j.cattod.2020.09.035

In the present paper is presented an efficient strategy for synthesis of mesoporous TiO2 modified with different Ce concentrations through a sol-gel process in the presence of triblock Pluronic P123 as structure directing agent, integrated with evaporation-induced self- assembly (EISA) approach. The nanocomposite consisted mostly of small crystallite of anatase. The presence of a new crystal phase corresponding to cerium titanate was evidenced in Ce-modified powder samples. All materials were characterized by SEM and TEM microscopies, UV-vis, XPS and N-2 adsorption-desorption isotherms in order to examine the textural and structural characteristics and the chemical nature of their surface. Furthermore, the photoelectrochemical characterization evidenced the effect of the TiO2 mesoporous structure, the amount of cerium and the oxidation state of Ti and Ce in the new photocatalysts on the enhanced photovoltaic performance. The photocatalytic activity of the as-synthesized materials was evaluated for phenol photodegradation in aqueous media and the reactive species involved in photocatalytic process were established by using some radical scavengers in the photodegradation experiments. Based on the obtained results, these new Ce-modified mesoporous TiO2 photocatalysts could be considered for degradation of organic compounds from wastewaters by advanced oxidation processes or for photoanodes construction for efficient photoelectrochemical fuel cell (PFC) systems.
10. Engineering hydrogenation active sites on graphene oxide and N-doped graphene by plasma treatment
Authors: Magureanu, M; Mandache, NB; Rizescu, C; Bucur, C; Cojocaru, B; Man, IC; Primo, A; Parvulescu, VI; Garcia, H

Published: JUN 15 2021, APPLIED CATALYSIS B-ENVIRONMENTAL, 287, DOI: 10.1016/j.apcatb.2021.119962

Graphene oxide (GO) and N-doped graphene [(N)G] graphenes were submitted to H-2 glow discharge under different discharge regimes, in both the negative glow and positive column plasma regions. The resulted catalysts were fully characterized using several techniques such as Raman, DRIFT and XPS spectroscopy, powder X-ray diffraction, H-2 pulse chemisorption and H-2-, CO2- and NH3-TPD experiments. Density functional theory calculations were performed taking a slab model of graphene sheet with an optimized C-C bond length (1.426 angstrom) and a 16 angstrom vacuum layer between sheets. An overview of these characterizations showed that the O/C atomic ratio of GO is influenced by the plasma regime, indicating the occurrence of O removal, as also predicted by DFT calculations. In the case of (N)G, the plasma treatment also removes pyridinic N with an increase of the C/N ratio. The efficiency of the plasma modification has been checked through catalytic tests in hydroisomerization of 1-octene and hydrogenation of alpha-methyl-styrene. Contrarily to classical thermal activation requiring high temperatures, the generation of the defects by treating with plasma occurs at voltages in the range of 2 5 kV. In consequence, the hydrogenation and isomerization of alkenes resulted with high yields and good selectivities. Graphene prepared from sodium alginate from brown algae was considered as reference in these investigations.
11. CO2 methanation catalyzed by oriented MoS2 nanoplatelets supported on few layers graphene
Authors: Primo, A; He, JB; Jurca, B; Cojocaru, B; Bucur, C; Parvulescu, VI; Garcia, H

Published: MAY 15 2019, APPLIED CATALYSIS B-ENVIRONMENTAL, 245, 359, DOI: 10.1016/j.apcatb.2018.12.034

Powders of molybdenum disulfide platelets strongly grafted on graphene have been prepared by pyrolysis of ammonium alginate containing adsorbed various proportions of (NH4)(2)MoS4. After pyrolysis, formation of MoS2 supported on graphene was determined by XRD and electron microscopy and spectroscopic techniques. MoS2/G exhibits catalytic activity for the methanation of CO2, the performance being optimal at intermediate loadings. The catalytic activity of sharply contrasts with that of bulk MoS2 that promotes the reverse water gas shift, affording CO as the main product. Characterization of the spent MoS2/G catalyst shows the partial conversion of external MoS2 into MoO3. Comparison of the catalytic activity of MoS2/G with that of MoO3/G shows that the latter is less efficient, but more selective for CO2 methanation.
12. N-Doped Defective Graphene from Biomass as Catalyst for CO2 Hydrogenation to Methane
Authors: Jurca, B; Bucur, C; Primo, A; Concepcion, P; Parvulescu, VI; Garcia, H

Published: FEB 6 2019, CHEMCATCHEM, 11, 990, DOI: 10.1002/cctc.201801984

N-doped, defective graphene obtained by pyrolysis of chitosan at 900 degrees C under Ar exhibits catalytic activity for the Sabatier hydrogenation of CO2 to CH4 at temperatures about 500 degrees C with estimated turnover frequencies and activation energy values of 73.17s(-1) and 24.3 kcal x mol(-1), respectively. It has been found that this enhanced catalytic activity compared to other related doped defective graphenes derives from the presence of pyridinic N atoms that adsorbs CO2 forming carbamate-type adsorbates.
13. Nitrogen-doped graphene as metal free basic catalyst for coupling reactions
Authors: Candu, N; Man, I; Simion, A; Cojocaru, B; Coman, SM; Bucur, C; Primo, A; Garcia, H; Parvulescu, VI

Published: AUG 2019, JOURNAL OF CATALYSIS, 376, 247, DOI: 10.1016/j.jcat.2019.07.011

N-doped defective graphene [(N)G] obtained by pyrolysis at 900 degrees C of chitosan contains about 3.7% of residual N atoms, distributed as pyridinic, pyrrolic and graphitic N atoms. It has been found that (N)G acts as basic catalyst promoting two classical C-C bond forming nucleophilic additions in organic chemistry, such as the Michael and the Henry additions. Computational calculations at DFT level of models corresponding to the various N atoms leads to the conclusion that N atoms are more stable at the periphery of the graphene sheets and that H adsorption on these sites is a suitable descriptor to correlate with the catalytic activity of the various sites. According to these calculations the most active sites are pyridinic N atoms at zig-zag edges of the sheets. In addition, N as dopant changes the reactivity of the neigh. bour C atoms. Water was found a suitable solvent to achieve high conversions in both reactions. In this solvent the initial distribution of N atoms is affected due to the easy protonation of the N-py to N-pyH sites. As an effect, C edge sites adjacent at N-PyH with an appropriate reactivity towards the alpha-C-H bond breaking are formed. The present results show the general activity of N-doped graphene as base catalysts and illustrate the potential of carbocatalysis to promote reactions of general interest in organic synthesis. (C) 2019 Elsevier Inc. All rights reserved.
14. The Influence of Heteroatom Dopants Nitrogen, Boron, Sulfur, and Phosphorus on Carbon Electrocatalysts for the Oxygen Reduction Reaction
Authors: Preuss, K; Siwoniku, AM; Bucur, CI; Titirici, MM

Published: MAY 2019, CHEMPLUSCHEM, 84, 464, DOI: 10.1002/cplu.201900083

A hard templating method, using SBA-15 in combination with glucose solution and different heteroatom precursors, has been employed to investigate the influence of the different heteroatom dopants nitrogen, boron, sulfur, and phosphorus on carbon electrocatalysts for the oxygen reduction reaction. Samples were synthesized under the same conditions and resulted in a similar morphology and surface areas around 1000 m(2)/g. Incorporating nitrogen into the carbon matrix was found to be easier than for boron or phosphorus, while sulfur doping proved problematic and only yielded 2 at% of sulfur or less. Different dopant concentrations as well as a combination of dopants suggested that nitrogen was the only heteroatom exerting an actual influence on the catalytic activity, resulting in higher electron transfer numbers. The other dopants exhibited a similar performance regardless of the dopant content, though slightly improved when compared to an undoped control sample. These findings indicate that incorporated nitrogen can act as catalytic sites, while boron, sulfur and phosphorus can enhance the catalytic activity by possibly creating defects in the carbon matrix.
15. Hydrogenolysis of lignin over Ru-based catalysts: The role of the ruthenium in a lignin fragmentation process
Authors: Verziu, M; Tirsoaga, A; Cojocaru, B; Bucur, C; Tudora, B; Richel, A; Aguedo, M; Samikannu, A; Mikkola, JP

Published: MAY 2018, MOLECULAR CATALYSIS, 450, 76, DOI: 10.1016/j.mcat.2018.03.004

The catalytic performances of two different classes of catalysts containing nickel or/and ruthenium as the active sites were studied in the depolymerisation of lignin isolated from Miscanthus x giganteus. The catalysts were prepared either by coprecipitation (ie, (RuNiMgAlO)x, (RuNiAlO)x, (NiAlO)x, (NiMgAlO)x) or by wet impregnation (ie, Ru/Al2O3) and characterized by nitrogen physisorption (BET), XRD, XPS, NH3-TPD, Raman and H-2-TPR techniques. The experimental results indicate that the presence of ruthenium led to dimers as dominant products.
16. Structural and optical properties of optimized amorphous GeTe films for memory applications
Authors: Galca, AC; Sava, F; Simandan, ID; Bucur, C; Dumitru, V; Porosnicu, C; Mihai, C; Velea, A

Published: NOV 1 2018, JOURNAL OF NON-CRYSTALLINE SOLIDS, 499, 7, DOI: 10.1016/j.jnoncrysol.2018.07.007

Chalcogenide amorphous materials, such as GeTe, are known to exhibit deposition dependent optical and structural properties. The formation of a single and homogeneous amorphous GeTe (a-GeTe) phase is questionable since the deposited films can be mixtures of monoelemental nanoclusters. In this work, we employed two deposition techniques, pulsed laser deposition from a polycrystalline GeTe target and co-sputtering from two distinct Ge and Te targets, respectively, to obtain a-GeTe films. To improve the homogeneity of the amorphous phase obtained by magnetron sputtering, the substrate temperature was varied from room temperature up to 180 degrees C. The samples were investigated by X-ray diffraction, X-ray reflectometry, X-ray photoelectron spectroscopy and spectroscopic ellipsometry. It was found that the film mass density, optical bandgap, refractive index and absolute reflectivity become progressively larger with increasing substrate temperature, due to the minimization of voids fraction and the number of dangling bonds in the amorphous structure. Moreover, X-ray photoelectron spectroscopy results prove the formation of Ge-Te bonds and therefore of the GeTe alloy at the optimal substrate temperature of 180 degrees C. This study reveals the importance of optimizing the deposition conditions for obtaining a specific amorphous phase, which enables the atomic rearrangements responsible for fast phase-change needed in memory applications.
17. Engineering active sites on reduced graphene oxide by hydrogen plasma irradiation: mimicking bifunctional metal/supported catalysts in hydrogenation reactions
Authors: Primo, A; Franconetti, A; Magureanu, M; Mandache, NB; Bucur, C; Rizescu, C; Cojocaru, B; Parvulescu, VI; Garcia, H

Published: JUN 7 2018, GREEN CHEMISTRY, 20, 2623, DOI: 10.1039/c7gc03397d

H2 plasma has been used to generate carbon vacancies on reduced graphene oxide to increase its catalytic activity as a hydrogenation catalyst. A relationship between the power of the plasma treatment and the exposure time with the activity of the material was observed for CvC double bond hydrogenation. The activity data in the case of 1-octene, showing skeletal isomerization besides hydrogenation, indicate that H2 plasma treatment can introduce hydrogenating and acid sites rendering a bifunctional catalyst that is reminiscent of the activity of noble metals supported on acid supports.
18. Insight on thermal behaviour of new complexes of Ni(II), Cu(II) and Zn(II) with a bismacrocyclic ligand developed as biologically active species
Authors: Badea, M; Bucur, C; Chifiriuc, MC; Bleotu, C; Grecu, MN; Lazar, V; Marinescu, D; Olar, R

Published: JAN 2017, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 127, 497, DOI: 10.1007/s10973-016-5502-y

A multi-component reaction involving metal ion, amines and formaldehyde has been used for a series of decaaza bismacrocyclic complexes M2L(CH3COO)(4)center dot nH(2)O [(1) M: Ni, n = 2.5; (2) M:Cu, n = 1; (3) M:Zn, n = 10; L:1,3-bis(N,N-1,3,6,9,12-pentaazacyclotridecane)-benzene] preparation. Elemental analyses, ESI-MS, IR, UV-Vis-NIR, NMR and EPR spectra, magnetic susceptibility at room temperature, molar conductivities, as well as thermogravimetric analysis, provided data concerning complexes features. The macrocyclic ligand behaves as bischelate, resulting in either a square planar or an octahedral stereochemistry. The in vitro screening of the antimicrobial activity was performed against both reference and clinical isolates multi-drug-resistant strains. The overall antimicrobial potency of complexes was enhanced in comparison with the free ligand, against both planktonic and biofilm-embedded pathogenic strains. Complexes exhibit no cytotoxicity on the HCT 8 tumour cells. Thermogravimetric curves (TG, DTG and DTA) evidenced in air processes as water elimination, acetate into carbonate transformation as well as oxidative degradation of the bismacrocyclic ligand. The powder X-ray diffraction data indicate MO (M: Ni, Cu, Zn) as final product.
19. N-Doped graphene as a metal-free catalyst for glucose oxidation to succinic acid
Authors: Rizescu, C; Podolean, I; Albero, J; Parvulescu, VI; Coman, SM; Bucur, C; Puche, M; Garcia, H

Published: APR 21 2017, GREEN CHEMISTRY, 19, 2005, DOI: 10.1039/c7gc00473g

N-Containing graphenes obtained either by simultaneous amination and reduction of graphene oxide or by pyrolysis of chitosan under an inert atmosphere have been found to act as catalysts for the selective wet oxidation of glucose to succinic acid. Selectivity values over 60% at complete glucose conversion have been achieved by performing the reaction at 160 degrees C and 18 atm O-2 pressure for 20 h. This activity has been attributed to graphenic-type N atoms on graphene. The active N-containing graphene catalysts were used four times without observing a decrease in conversion and selectivity of the process. A mechanism having tartaric and fumaric acids as key intermediates is proposed.
20. Studies on thermal, spectral, magnetic and biological properties of new Ni(II), Cu(II) and Zn(II) complexes with a bismacrocyclic ligand bearing an aromatic linker
Authors: Bucur, C; Badea, M; Chifiriuc, MC; Bleotu, C; Iorgulescu, EE; Badea, IA; Grecu, MN; Lazar, V; Patriciu, OI; Marinescu, D; Olar, R

Published: MAR 2014, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 115, 2189, DOI: 10.1007/s10973-013-3460-1

Novel complexes of M2LCl4 center dot nH(2)O type (M:Ni, n = 4; M:Cu, n = 3 and M:Zn, n = 0; L: ligand resulted from 1,4-phenylenediamine, 3,6-diazaoctane-1,8-diamine and formaldehyde one-pot condensation) were synthesized and characterised by microanalytical, ESI-MS, IR, UV-Vis, H-1 NMR and EPR spectra, magnetic data at room temperature and molar conductivities as well. The electrochemical behaviour of complexes was investigated by cyclic voltammetry. Simultaneous TG/DTA measurements were performed in order to evidence the thermal behaviour of the obtained complexes. Processes such as water elimination, fragmentation and oxidative degradation of the organic ligand as well as chloride elimination occurred during thermal decomposition. The antimicrobial assays demonstrate that the compounds exhibited good antibacterial activity, especially against S. aureus and E. coli strains, the most active being the copper(II) complex, which also exhibited the most prominent anti-biofilm effect, suggesting its potential use for the development of new antimicrobial agents. The biological activity was correlated with log P (ow) values. All complexes disrupt the membrane integrity of HCT 8 tumour cells.
21. Investigation of thermal stability, spectral, magnetic, and antimicrobial behavior for new complexes of Ni(II), Cu(II), and Zn(II) with a bismacrocyclic ligand
Authors: Bucur, C; Korosec, RC; Badea, M; Calu, L; Chifiriuc, MC; Grecu, N; Stanica, N; Marinescu, D; Olar, R

Published: SEP 2013, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 113, 1295, DOI: 10.1007/s10973-012-2912-3

Novel complexes of type M2LCl4 center dot nH(2)O (M: Ni, n = 4; M: Cu, n = 2.5 and M: Zn, n = 1.5; L: ligand resulted from 1,3-phenylenediamine, 3,6-diazaoctane-1,8-diamine, and formaldehyde one-pot condensation) were synthesized and characterized. The ligand was also isolated and characterized. The complexes features have been assigned from microanalytical, electrospray ionization tandem mass spectrometry, IR, UV-vis, H-1 NMR, and EPR spectra as well as magnetic data at room temperature. Simultaneous thermogravimetric/dynamic scanning calorimetry/evolved gas analysis measurements were performed to evidence the nature of the gaseous products formed in each step. Processes as water elimination, fragmentation, and oxidative degradation of the organic ligand as well as chloride elimination were observed during the thermal decomposition. The final product of decomposition was metal(II) oxide except for copper complex where CuCl remained also in the oxide network. The complexes exhibited an improved antibacterial activity in comparison with the ligand concerning both planktonic as well as biofilm-embedded cells.
22. Thermal behaviour of some new complexes with decaaza bismacrocyclic ligand as potential antimicrobial species
Authors: Bucur, C; Badea, M; Larisa, C; Marinescu, D; Grecu, MN; Stanica, N; Chifiriuc, MC; Olar, R

Published: OCT 2012, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 110, 241, DOI: 10.1007/s10973-012-2199-4

Novel complexes of type M2L(CH3COO)(4)center dot nH(2)O (M:Ni, n = 4; M:Cu, n = 2 and M:Zn, n = 0; L: ligand resulted in 1,2-phenylenediamine, 3,6-diazaoctane-1,8-diamine and formaldehyde template condensation) were synthesised and characterised. The features of complexes have been assigned from microanalytical, IR, UV-Vis, H-1 NMR, EPR as well as magnetic data at room temperature. Processes as water elimination as well as oxidative degradation of both organic components (bismacrocycle and acetate) were observed. The final product of decomposition was metal (II) oxide as powder X-ray diffraction indicates.
23. 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.
24. 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
25. 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.
26. Synthesis and optical properties of water-soluble poly(vinylpyrrolidone) - modified fullerene C-60
Authors: Rusen, E; Marculescu, B; Preda, N; Bucur, C; Mihut, L

Published: NOV 2008, POLYMER BULLETIN, 61, 592, DOI: 10.1007/s00289-008-0985-8

The effect of fullerene on the radical polymerization of N-vinylpyrrolidone with lauroyl peroxide in toluene was investigated kinetically. C-60 was found to act both as inhibitor and as retarder because the polymerization rate and the molecular weight of resulting poly(vinylpyrrolidone) is decreasing with the increase of the fullerene concentration (0-6.94 x 10(-4) mol l(-1)). The water-soluble poly(vinylpyrrolidone)-modified fullerene C-60 compound was characterized by differential scanning calorimetric, Infrared and Raman spectroscopy, UV absorption and photoluminescence. Based on the results obtained by optical measurements, it is argued that by the covalent attachment of the polymeric radicals to fullerene cage the extended electronic conjugation system of the C-60 is broken leading to the appearance of a polyene structure.
27. 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.
28. 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.
29. 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.
30. Radiological impact of C-14
Authors: Bucur, C; Olteanu, M; Olteanu, C; Pavelescu, M

Published: APR 2006, REVISTA DE CHIMIE, 57, 367, DOI:

Near surface disposal is considered a suitable option for the disposal of short-lived low and intermediate level waste (LILW) containing radionuclides which decay to insignificant radiation levels within a few decades or centuries. LILW containing limited concentrations of long-lived radionuclides may also be disposed of in near surface facilities. The main radionuclides in short lived LILW are Cs-137 and Sr-90 and therefore, a period of 300 years for the post-closure institutional controls would correspond to about ten half-lives of these radionuclides. The longer-lived radionuclides, such as C-14, I-129, Tc-99 will continue to be released even after that period due to the engineering barriers degradation. The paper presents the post closure radiological impact of LIL waste disposal due to the C-14, one of the long life radionuclides presented in the LILW generated at Cernavoda Nuclear Power Plant.
31. Nanocrystalline rhenium-doped TiO2: an efficient catalyst in the one-pot conversion of carbohydrates into levulinic acid. The synergistic effect between Bronsted and Lewis acid sites
Authors: Avramescu, S; Ene, CD; Ciobanu, M; Schnee, J; Devred, F; Bucur, C; Vasile, E; Colaciello, L; Richards, R; Gaigneaux, EM; Verziu, MN

Published: , CATALYSIS SCIENCE & TECHNOLOGY, DOI: 10.1039/d1cy01450a

Catalytic activity of TiO2, 2%Re-TiO2 and 10%Re-TiO2 in the conversion of carbohydrates into levulinic acid under autoclave conditions was evaluated. These materials were prepared by aerogel method, for the first time to the best of our knowledge, and characterized by XPS, SEM-EDX, DRIFTS, DR UV-vis, Raman, N-2 adsorption/desorption isotherms, TGA and XRD. Further, the surface acidity was probed by NH3-TPD and pyridine-FT-IR where it was observed that increasing the amount of rhenium doped into TiO2 led to an increase in the total number of acid sites (Lewis + Bronsted) but with an overall lower strength. The presence of both Bronsted and Lewis acid sites led to the hypothesis that these materials may be well suited for conversion of carbohydrates into levulinic acid. Indeed a levulinic acid yield of 57% was reached over 10%Re-TiO2 for a low mass ratio catalyst to glucose (1 : 5). Moreover, the 10%Re-TiO2 catalyst was reused in the conversion of glucose for four catalytic cycles without a significant loss of the catalytic activity.
32. Sonogashira Synthesis of New Porous Aromatic Framework- Entrapped Palladium Nanoparticles as Heterogeneous Catalysts for Suzuki-Miyaura Cross-Coupling
Authors: Cata, L; Terenti, N; Cociug, C; Hadade, ND; Grosu, I; Bucur, C; Cojocaru, B; Parvulescu, VI; Mazur, M; Cejka, J

Published: , ACS APPLIED MATERIALS & INTERFACES, DOI:

Palladium nanoparticles entrapped in porous aromatic frameworks (PAFs) or covalent organic frameworks may promote heterogeneous catalytic reactions. However, preparing such materials as active nanocatalysts usually requires additional steps for palladium entrapment and reduction. This paper reports as a new approach, a simple procedure leading to the self-entrapment of Pd nanoparticles within the PAF structure. Thus, the selected Sonogashira synthesis affords PAF-entrapped Pd nanoparticles that can catalyze the C-C Suzuki-Miyaura cross-coupling reactions. Following this new concept, PAFs were synthesized via Sonogashira cross-coupling of the tetraiodurated derivative of tetraphenyladamantane or spiro-9,9 '-bifluorene with 1,6-diethynylpyrene, then characterized them using powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, high-resolution scanning transmission electron microscopy, and textural properties (i.e., adsorption-desorption isotherms). The PAF-entrapped Pd nanocatalysts showed high catalytic activity in Suzuki-Miyaura coupling reactions (demonstrated by preserving the turnover frequency values) and stability (demonstrated by palladium leaching and recycling experiments). This new approach presents a new class of PAFs with unique structural, topological, and compositional complexities as entrapped metal nanocatalysts or for other diverse applications.
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