Dr. Andreea-Alexandra NILA

Nanocomposites based on Fe3O4 and carbonaceous nanoparticles (CNPs), including carbon nanotubes (CNTs) and graphene derivatives (graphene oxide (GO) and reduced graphene oxide (RGO)), such as Fe3O4@GO, Fe3O4@RGO, and Fe3O4@CNT, have demonstrated considerable potential in a number of health applications, including tissue regeneration and innovative cancer treatments such as hyperthermia (HT). This is due to their ability to transport drugs and generate localized heat under the influence of an alternating magnetic field on Fe3O4. Despite the promising potential of CNTs and graphene derivatives as drug delivery systems, their use in biological applications is hindered by challenges related to dispersion in physiological media and particle agglomeration. Hence, a solid foundation has been established for the integration of various synthesis techniques for these nanocomposites, with the wet co-precipitation method being the most prevalent. Moreover, the dimensions and morphology of the composite nanoparticles are directly correlated with the value of magnetic saturation, thus influencing the efficiency of the composite in drug delivery and other significant biomedical applications. The current demand for this type of material is related to the loading of a larger quantity of drugs within the hybrid structure of the carrier, with the objective of releasing this amount into the tumor cells. A second demand refers to the biocompatibility of the drug carrier and its capacity to permeate cell membranes, as well as the processes occurring within the drug carriers. The main objective of this paper is to review the synthesis methods used to prepare hybrids based on Fe3O4 and CNPs, such as GO, RGO, and CNTs, and to examinate their role in the formation of hybrid nanoparticles and the correlation between their morphology, the dimensions, and optical/magnetic properties.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

We calculate the optical properties of atomic-sized core-shell graphene - boron nitride nanoflakes with triangular shaped cross-section using the density functional theory. The optical properties can be tuned by using different sizes and proportions of the core-shell materials. Anisotropic effects manifested in the absorption of unpolarized light with different orientations of the optical vector are pointed out.

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.

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.