National Institute Of Materials Physics - Romania

In the present work, an essential advance in the preparation of novel nanocomposites based on functionalized V2O5 nanostructures with reduced graphene oxide by hydrothermal method, which has great potential for use in photocatalytic processes related to environmental remediation. XRD analysis confirmed V2O5 in an orthorhombic structure. SEM images showed transparent RGO layers well anchored onto the surface of the V2O5 with a homogeneous distribution. Raman spectroscopy further explained the hybridization and interaction between the components. The photocatalytic activity of Rhodamine-B in aqueous solutions has been studied upon irradiation with visible light. A high RhB degradation was obtained using the V2O5/RGO photocatalyst (82 %), compared to the degradation obtained with only V2O5 (60 %). First-principles Density Functional Theory (DFT) simulations reveal a strong interaction between V2O5 molecules and graphene surfaces, with an adsorption energy of -1.673 eV and a significant charge transfer of 0.367 e- to RGO. This interaction modifies the electronic structure, creating semi-metallic behavior near the Fermi level and enhancing catalytic activity through improved charge carrier dynamics and active sites for photocatalytic applications.

Synthetic bone graft substitutes, including calcium phosphates (CaP), bioactive glasses (BG), and their composites with biopolymer matrices are attracting interest for bone tissue repair and regeneration. A key challenge is accurately replicating the biological structure and functionality of natural bone and optimizing the porous structure to match trabecular bone. This has been addressed by doping CaPs with therapeutic ions and using scaffolding methods like polymeric sponge replication and different additive manufacturing techniques. Biomimetic approaches employing naturally occurring porous biominerals with pore sizes comparable to those of trabecular bone, offer promising alternatives. This work reviews the hydrothermal transformation of cuttlefish bone (CB) into CaP scaffolds, while preserving its original porous structure, producing hydroxyapatite (HA, Ca10(PO4)6(OH)2), tricalcium phosphate (TCP, Ca3(PO4)2), and biphasic CaPs, both undoped and therapeutic ion-doped, constructs. Coating such biomimetic scaffolds with sol-gel-derived BG and biopolymers produces multifunctional bone graft substitutes with enhanced mechanical and biological properties. Moreover, polymeric coatings can act as drug reservoirs, enabling controlled release of therapeutic agents. The review highlights that integrating biomimetic strategies with advanced coating solutions holds great promise for creating multifunctional scaffolds that mimic nature and improve therapeutic outcomes in bone tissue engineering.

Amyloid beta (A(3) peptide aggregates are well-established biomarkers for Alzheimer's disease, though the complete etiology of this disorder remains elusive. Developing biointerfaces to elucidate the physiological roles of these peptides is essential. This study investigates the aggregation, fibrillation, and interaction of A(3 peptides with conductive, biocompatible nanostructured materials designed for applications involving neuronal cells. Various conductive, rigid, and flexible surfaces, both functionalized and non-functionalized with A(340 fibrils, were fabricated. These included glass substrates and poly(methyl methacrylate) electrospun fiber networks coated with gold via magnetron sputtering. The substrates were also functionalized through physical adsorption with poly-L-lysine and collagen, known to support cell proliferation, as well as with the inverse-A(340 peptide and an Amyloid Protein Non-A(3 Component, and the results were compared. The scaffolds were characterized using scanning electron microscopy, X-ray diffraction, atomic force microscopy, contact angle and electrical measurements, while their biological interactions were assessed using MTS assays, fluorescence imaging, and scanning electron microscopy. Fibroblast L929 and neuroblastoma SH-SY5Y cell lines were used as models, with results indicating an elevated cell viability, comparable to the control. The developed nanostructured surfaces are highly promising for integration into advanced neuromorphic engineering devices, as they have proven capable of maintaining their structural integrity when exposed to proteases.

The present study investigates the influence of strontium (Sr) content on the intrinsic properties of barium strontium titanate (Ba1-xSrxTiO3, BST) which was successfully prepared by the conventional solid-state reaction with different concentrations of strontium (x = 0, 0.3, 0.5, 0.6, 0.7, 1). The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and diffuse reflectance spectroscopy, the dielectric properties being also investigated. Structural and vibrational analyses reveal a structural phase transition from tetragonal to cubic at x = 0.4, with a linear decline of the tetragonality ratio as well as a shrinkage in the unit cell volume that occur with increasing Sr content. The morphological study shows that the grain size decreases as the Sr content increases in the tetragonal phase. Yet, upon the phase transition from tetragonal to cubic, the grain size initially increases, followed by a subsequent decrease with further Sr addition. It has been found that the band gap shows a decrease as Sr content increases. The temperature dependence of the dielectric parameters reveals that the Curie temperature as well as the dielectric constant and the loss tangent are strongly affected by the addition of Sr. The activation energy derived from the dielectric response, was found to be in the range 0.685-1.065eV, suggesting the dominance of doubly ionized oxygen vacancy for conduction and relaxation mechanism. Ab initio calculations were done employing the Linear Combination of Atomic Orbitals (LCAO) method. The bandgap energy (Eg) and the structural parameters were calculated using various types of exchange-correlation functionals (PWGGA, PBE, B3LYP and PBE0). A good agreement with the experimental results is achieved using the PBE0 functional. This study contributes to a better understanding of the structure-property relationship in BaSrTiO3 and provides valuable insights for optimizing its performance in various technological applications.

The present research explores for the first time the intricate relationship between sulfurization temperature at unusual high temperatures (up to 700 degrees C) and the structural/optoelectronic properties of Cu-2(Zn,Cd)SnS4 (CZCTS) thin films, synthesized via a two-step sequential process involving the precursor film deposition using aprotic molecular ink followed by thermal treatment in sulfur atmosphere. X-ray diffraction patterns confirms the tetragonal structure. Scanning Electron Micrographs revealed significant grain growth, with grain sizes increasing from similar to 0.3 mu m at 620 degrees C to similar to 1.5 mu m at 680 degrees C, effectively reducing grain boundary recombination. Energy dispersive X-ray spectroscopy demonstrated a Cu-poor and Zn-rich composition, with a consistent Cd incorporation of similar to 3.7 at%. Raman spectroscopy showcases the homogeneity and purity of the CZCTS crystalline structure. Precise control of the sulfurization temperature plays a crucial role in determining the photovoltaic characteristics of CZCTS-based solar cells. By increasing the grain size and preventing the thermal decomposition of the CZTS phase, the photovoltaic performance peaked at a sulfurization temperature of 680 degrees C, achieving a power conversion efficiency (PCE) of 10.4%, with an open-circuit voltage of 0.701 V, a short-circuit current density of 24.3 mA/cm(2) and a fill factor of 60.8%. External quantum efficiency reached a maximum of 83.3% at 580 nm. The bandgap of the CZCTS absorber was determined to be 1.48 eV, optimal for photovoltaic applications. However, further increasing the sulfurization temperature to 700 degrees C resulted in a lower PCE of 8.5%, attributed to interface degradation and secondary phase formation. Temperature-dependent current-voltage measurements revealed a reduction in recombination losses, with an activation energy of 1.24 eV at the CZCTS/CdS interface, indicating effective defect passivation by Cd incorporation. The optimized films, sulfurized at 680 degrees C, displayed an absorber thickness of similar to 1.2 mu m after sulfurization, providing efficient light absorption and charge transport. The findings not only emphasize the critical role of sulfurization temperature in engineering CZCTS film and subsequently their functionality but also provide valuable insights for fine tuning their performance in the field of photovoltaic applications.

The present study investigates the influence of strontium (Sr) content on the intrinsic properties of barium strontium titanate (Ba1-xSrxTiO3, BST) which was successfully prepared by the conventional solid-state reaction with different concentrations of strontium (x = 0, 0.3, 0.5, 0.6, 0.7, 1). The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and diffuse reflectance spectroscopy, the dielectric properties being also investigated. Structural and vibrational analyses reveal a structural phase transition from tetragonal to cubic at x = 0.4, with a linear decline of the tetragonality ratio as well as a shrinkage in the unit cell volume that occur with increasing Sr content. The morphological study shows that the grain size decreases as the Sr content increases in the tetragonal phase. Yet, upon the phase transition from tetragonal to cubic, the grain size initially increases, followed by a subsequent decrease with further Sr addition. It has been found that the band gap shows a decrease as Sr content increases. The temperature dependence of the dielectric parameters reveals that the Curie temperature as well as the dielectric constant and the loss tangent are strongly affected by the addition of Sr. The activation energy derived from the dielectric response, was found to be in the range 0.685-1.065eV, suggesting the dominance of doubly ionized oxygen vacancy for conduction and relaxation mechanism. Ab initio calculations were done employing the Linear Combination of Atomic Orbitals (LCAO) method. The bandgap energy (Eg) and the structural parameters were calculated using various types of exchange-correlation functionals (PWGGA, PBE, B3LYP and PBE0). A good agreement with the experimental results is achieved using the PBE0 functional. This study contributes to a better understanding of the structure-property relationship in BaSrTiO3 and provides valuable insights for optimizing its performance in various technological applications.

This study presents an ultrasound-assisted synthesis of (3-cyclodextrin/hydroxyapatite composites to be used as green and safe auxiliaries in the tanning process. A combination of spectroscopic and non-spectroscopic techniques such as DLS (dynamic light scattering), ZP (zeta potential), XRD (X-ray diffraction), SEM (scanning electron microscopy) and ATR-FTIR (attenuated total reflectance-Fourier transform infrared spectroscopy) were used to thoroughly characterize the eight composites obtained by varying the ultrasound process parameters. While not cytotoxic, all composites had strong antibacterial action against Brevibacterium lines, Staphylococcus aureus, Escherichia coli, and Staphylococcus epidermis. All composites underwent lab-scale tanning tests, but only those exhibiting the most suitable set of tanning abilities underwent pilot-scale testing. The composites' interaction with the collagen matrix was assessed by micro-DSC (micro-differential scanning calorimetry), TG/DTG/ DTA (thermal analysis), 1H unilateral NMR (proton nuclear magnetic resonance), ATR-FTIR, in-situ temperature synchrotron-based XRD and standard tests (UNI EN ISO 3380: 2015, UNI EN ISO 2589: 2016, UNI EN ISO 105B02:2014). Thermal stability, dye penetration, thickness, colour fastness, surface appearance and microbiological protection were all improved for the leather treated with a small amount of composite added to the wet finish float. These findings demonstrate the benefits of (3-cyclodextrin/hydroxyapatite composites as safe and sustainable tanning additives.

Developing new glass electrolytes with the necessary room-temperature ionic conductivity (similar to 10(-3) Scm(-1)) for solid-state batteries, especially sodium-ion (Na+) batteries, has been impeded by the lack of a clear relationship between composition, structure, and conductivity in glass materials. This study highlights the impact of the mixed glass formers on the structure, Na+-ion dynamics, and glass conductivity. To this end, we substituted SiO2 for P2O5 in sodium alumino-phosphate glass while maintaining a constant molar concentration of Al2O3 and Na2O. A detailed analysis combining molecular simulations and experiments revealed that the glass containing 15 mol% SiO2 exhibited the highest DC ionic conductivity of similar to 9 x 10(-6) Scm(-1) at 473 K, followed by a decrease for 20 mol% SiO2. To understand this behavior, microscopic characteristic length such as critical hopping distance and Na+ diffusion coefficients were correlated with structural changes using AC conductivity analysis. Altogether, we elucidate the composition-dependent Na+ ion dynamics in the alumino-phosphate glass system, with factors like mobile charge carrier concentration, ion mobility, and coulombic forces influenced by the structure of different glass compositions.

Photoanodes based Ce-doped ZnO nanorods arrays were prepared by hydrothermal method in order to improve photoelectrochemical efficiency of ZnO photoanodes in water splitting process. Scanning electron microscopy investigation showed ZnO based nanorods with length of around 500 nm and different thicknesses and growth directions. Some morphological changes were noted following the thermal treatment. Energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy measurements proved the presence of cerium species both in bulk and on the surface of ZnO nanorods. A current density of 2.44 mA/cm(2) at 1.23 V against the reversible hydrogen electrode (0.265 V vs. Ag/AgCl) was obtained for Ce-doped ZnO sample, which is >162% increase over that of ZnO sample. The increased photocurrent value obtained for this sample was correlated with the passivation of surface defects evidenced by photoluminescence study and the increased concentration of Ce3+ on the surface. Also, the electrochemical impedance spectroscopy measurements suggested that Ce doping improves the charge transfer in bulk.

This article describes a new synthesis of nanoscaled Y2O3 that is bioinspired. It has been confirmed that Callistemon viminalis flower extract works well as a chelator when used to bioengineer high-shape anisotropy nanorods of single-phase Y2O3 . X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy and photoluminescence spectroscopy were used to analyse the structural, morphological, surface and optical features. The photoluminescent spectra of the bio-engineered nanorods show blue emissions. As the annealing temperature was increased from 300 to 500 degrees C, the blue colour purity values of the synthesized Y2O3 nanorods were 58.1, 80.7 and 77.0% at 300, 400 and 500 degrees C respectively. The chromaticity coordinates (0.2020, 0.1931), (0.1660, 0.1082) and (0.1714, 0.1226) from the photoluminescence spectra of the biosynthesized Y2O3 nanorods were used to determine these values. The CIE y-component coordinate values of the bioengineered blue-emitting nanophosphors suggest their potential for applications in display technology and white light-emitting diodes.