National Institute Of Materials Physics - Romania

This study explores how catalysts containing a low palladium loading (0.5 wt%) contribute to the selective hydrogenation of cinnamaldehyde. High specific surface area (SSA) mesoporous (2 wt%) TiO2 - SiO2 (UVM-7) materials were prepared by two different approaches: a one-step procedure, in which titania and silica precursors were added from the beginning to generate Ti2@UVM-7 support, and a two-step procedure, where TiO2 was deposited onto the UVM-7 silica surface via wet impregnation technique (Ti2/UVM-7). Both types of supports were decorated with Pd nanoparticles (NPs) through the deposition-precipitation technique. The obtained catalysts were thoroughly characterized by using different techniques, including XRD, N2 adsorption-desorption isotherms at liquid N2 temperature, ATR-FTIR, TEM-EDX, SEM-EDX, and XPS. Characterization data revealed that one-step procedure largely preserves the textural and structural properties of the support following the deposition-precipitation of the noble metal, whereas the two-step procedure slightly alters the UVM-7 morphology. Moreover, the preparation method of the supports impacts the Pd particle sizes and the metal-support interaction (MSI). The one-step procedure tends to promote the growth of larger Pd NPs, likely due to the TiO2 species being well embedded within the SiO2 matrix. In contrast, the two-step procedure yields well-dispersed Pd NPs smaller than 2 nm, due to the confinement of TiO2 nanodomains within the UVM-7 cavities, which enhances the MSI. Consequently, enhanced catalytic performance and stability were achieved with 0.5Pd/Ti2/UVM-7 (similar to 99% hydrocinnamaldehyde yield, TOF 4.81 s-1), due to the formation of very small Pd nanoparticles on the support that promote the MSI.

Rapidly solidified Fe-Pd-Ga ferromagnetic shape memory ribbons, containing 1 and 3 at. % Ga, were obtained, and annealed at 950 degrees C for 15 and 30 min. Gallium substitution destabilizes the cubic lattice but preserves ferromagnetic order; thereby, it modifies phase stability and magnetic sensitivity. The combined effects of composition and heat treatment on microstructure, martensitic transformation temperatures, transformation heat, kinetics, and magnetic-field-induced transformation shift are presented. Magnetic sensitivity is evaluated using thermomagnetic and magneto-elastic measurements, being further validated through Clausius-Clapeyron analysis. Short-time heat treatment enhances structural relaxation and significantly increases the transformation heat, whereas prolonged annealing promotes grain growth and precipitate formation without suppressing thermoelastic behavior. Increasing Ga content results in a pronounced linear increase of the martensitic transformation temperature with magnetic field, from approximately 0.6 K T-1 for 1 at. % Ga to about 1.45 K T-1 for 3 at. % Ga. The good agreement between thermomagnetic measurements and Clausius-Clapeyron analysis confirms that the transformation shift is primarily governed by intrinsic thermodynamic parameters. The smaller magneto-elastic response indicates that microstructure limits strain expression. Therefore, functional control requires tuning the balance between intrinsic thermodynamic driving forces and microstructure-dependent magneto-elastic effects through composition and heat treatment. This enables the design of thermally adaptive and magnetically programmable materials, where 3 at. % Ga composition is suitable for active magnetic control and that of 1 at. % Ga is optimized for enhanced thermal stability and precision sensing.

Co-/Cu-co-doped ZnO nanorods are synthesized by electrochemical deposition to investigate the effect of co-doping on their structural, optical, electronic, and electrochemical properties. XRD, Raman, SEM, and photoluminescence analyses reveal that Co/Cu incorporation modifies the ZnO lattice, increases defect-related states, and reduces the band gap from 3.11 to 2.15 eV. Density functional theory calculations further show that Co 3d and Cu 3d states appear near the Fermi level and contribute to the observed band-gap narrowing. Electrochemical measurements indicate that the co-doped nanorods exhibit the lowest charge-transfer resistance and the highest areal capacitance among the samples studied. Together, these results show that Co/Cu co-doping improves charge-transfer kinetics in ZnO nanorods and highlights co-doping as an effective strategy for tuning oxide electrodes for energy-storage applications.

This study reports on the physico-chemical and in vitro biological characterization of chromium-doped hydroxyapatite (10CrHAp, Cr3+, Ca10-xCrx(PO4)(6)(OH)(2), x(Cr) = 0.1) and chromium-doped hydroxyapatite in dextran matrix (10CrHAp-Dx) coatings, prepared for the first time via the spin coating technique. X-ray diffraction analysis and Rietveld refinement were used to characterize the materials. Fourier-transform infrared (FTIR) spectroscopy confirmed the presence of functional groups specific to hydroxyapatite. Scanning electron microscopy (SEM) observations revealed the presence of a conglomerate of nanoparticles distributed unevenly across the coatings surface. Atomic force microscopy (AFM) showed that both coatings presented continuous surfaces with uniform morphology. The in vitro biocompatibility of 10CrHAp and 10CrHAp-Dx coatings was evaluated using human osteoblast-like MG63 cell line and MTT assay. SEM and MM visualization assessed the cell adhesion and proliferation and morphological changes in the adhered cells. The antibacterial properties of the 10CrHAp and 10CrHAp-Dx coatings was assessed in vitro against two of the most common bacterial reference strains, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 25923. Overall, the coatings achieved log reductions up to similar to 9.35, corresponding to a bacterial kill rate (for S. aureus) exceeding 99.99%, with 10CrHAp-Dx showing slightly superior performance. Similar behavior (log reductions of similar to 8.6 and similar to 8.9, respectively, indicating a sustained antibacterial effect and >99.99% bacterial elimination) was observed and for Pseudomonas aeruginosa. AFM was used to evaluate the bacterial cells interaction with the coating's surfaces. The biological assays demonstrated that both coatings possess notable antibacterial activity, underscoring their potential in biomedical applications, particularly in the design of new antimicrobial devices.

Organic layers based on metal phthalocyanines (MPc acting as donor) and a perylene diimide derivative compound (PDI acting as acceptor) were deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on rigid and flexible substrates. Hence, blend films based on magnesium phthalocyanine (MgPc), copper phthalocyanine (CuPc), cobalt phthalocyanine (CoPc) or iron phthalocyanine (FePc) and N, N-bis-(1-dodecyl)perylene-3,4,9,10 tetracarboxylic diimide (AMC14) were obtained on indium tin oxide/glass (ITO/glass) and indium tin oxide/polyethylene terephthalate (ITO/PET) substrates. Although the investigated MPcs present low solubility in organic solvents, MAPLE technique enables their deposition as blend films. The organic layers reveal a globular morphology specific to the MAPLE process. The roughness of the blend films is related to the MPc molecular packing arrangement, the optical assessment disclosing the presence of MPc in the stable beta-form. The transmission spectra display the optical signature of both MPc and AMC14 components, their complementary absorption bands assuring the light harvesting over a wide part of the UV-Vis spectral range. The current-voltage characteristics recorded under illumination reveal the best electrical parameters for the structures based on FePc: AMC14 layer prepared on ITO/glass (V-OC=0.22 V, J(SC)=2 & times; 10(- 7) A/cm(2)) and on CuPc: AMC14 layer obtained on ITO/PET (V-OC=0.27 V, J(SC)=1.3 & times; 10(- 7) A/cm(2)). Thus, the properties of MAPLE-deposited MPc: AMC14 blend films on both rigid and flexible substrates endorse them as viable choice for applications in optoelectronic devices.

The glass/FTO/TiO2/Sb2S3-x/P3HT/Au solar cells were investigated, with a focus on identifying the origin of performance degradation after exposure to high relative humidity and to mild heat stress. Analyzing the photovoltaic output and Deep-Level Transient Spectroscopy (DLTS) results, we probed the evolution of defect states after thermal exposure and after long-term storage of Sb2S3-x-based devices. The DLTS analysis revealed that shallow hole traps govern the stability of the Sb2S3-x cells. Significantly, it was shown that this shallow defect is not related to chlorine in the absorber, indicating an intrinsic origin. In the broader context of Sb2S3-x photovoltaics, this study underlines the paramount importance of defect engineering towards achieving more stable and efficient Sb2S3-x solar cells.

Alloys (A) of crystalline Ge50Te50 and partially amorphous Ge20Te80 were added to MgB2 superconductor. Samples with composition (MgB2)A0.01 were ex situ spark plasma sintered (SPS) and characterized. Results are compared with pristine and Te ((MgB2)Te0.01) or Ge, ((MgB2)Ge0.01) added samples. Samples with Ge-Te alloys show the fastest densification rate of 3.4 to 5.2 times larger than for the other samples. Although there is a strong influence of Te, alloys synergistically contribute structural and microstructural development and superconducting properties as determined by magnetometry. The proposed methodology of densification curves analysis allows prediction of the final bulk density, MgO and MgB4 amounts, the amount of carbon substituting boron and critical temperature. The alloys addition promotes MgB4 formation and a slightly lower critical current density Jc for Ge50Te50. For Ge20Te80, Jc is approximately similar to pristine sample, while the highest Jc is for Te. Samples with Ge-Te have lower maximum pinning force values.

The present study, presents for the first time the development and characterization of innovative bioceramic samples based on magnesium doped hydroxyapatite (xMg = 0.015 and xMg = 0.05) obtained by a modified coprecipitation method and the lyophilization of the final precipitate (1.5MgHAp-LF and 5MgHAp-LF). The lyophilized powders were thoroughly investigated, obtaining valuable information regarding stability through non-destructive ultrasound measurements, structure, chemical composition, bonding states, surface properties and biological evaluations. The X-ray diffraction (XRD) patterns of the samples revealed peaks characteristic of pure hexagonal hydroxyapatite (P63/m). When calcium ions were substituted with magnesium ions, a reduction in peak intensity and a slight broadening of the peaks were observed as the magnesium concentration increased. Fourier transform infrared spectroscopy (FTIR) was used to investigate the structural and compositional characteristics of the studied samples. Information regarding the surface topography of 1.5MgHAp-LF and 5MgHApLF pellets was obtained using scanning electron microcopy (SEM) and atomic force microscopy (AFM) studies. Additionally, AFM topographies and SEM images provided useful insights into the roughness of the samples. A complementary analysis was performed on a larger surface area using a Scanning Acoustic Microscope (SAM). The biological performance of 1.5MgHAp-LF and 5MgHAp-LF pellets was evaluated using the MG63 osteoblastlike cell line. Surface analyses-including furrow morphology, texture orientation, fractal dimensionality, and frequency spectrum-revealed that increased magnesium content induces greater topographical order and complexity, enhancing the material's potential for osteoconductive applications. The cytotoxicity of the pellets was assessed by determining the cell viability through the MTT assay after an incubation period of 24 h. Also, fluorescence microscopy (FM) visualization was used to determine the cytotoxicity of the pellets. The results demonstrated that both 1.5MgHApLF and 5MgHApLF pellets exhibited good biocompatibility for both tested samples. Furthermore, the interaction of the MG63 cells with the surface of the 1.5MgHAp-LF and 5MgHAp-LF pellets was assessed by metallographic microscopy (MM) and atomic force microscopy (AFM). MM and AFM analyses revealed that the surface morphology of both materials effectively supported cellular attachment and growth. These findings suggest that both 1.5MgHAp-LF and 5MgHAp-LF pellets have a significant potential for being used in the development of advanced biomaterials for biomedical use.

Magnetic superconductor EuRbFe4As4 is a quite unique system in which macroscopic superconductivity and magnetic ordering coexist, with interesting interactions between Abrikosov vortices and Eu2+ spins that were investigated mostly by static (DC) magnetization measurements. Our aim is to study the dynamic interactions between the two sub-systems using AC susceptibility measurements in a wide range of temperatures and superimposed DC fields. In low DC fields, the magnetic transition at 15 K is clearly visible. We have observed very little difference between the AC susceptibility in different cooling regimes, but large difference for different field orientation. For field perpendicular to the superconducting planes, we have observed an anomalous dependence just below the critical temperature, which is absent in the parallel field orientation. We explained the anomaly by the interplay between the sample dimensions and the temperature dependence of the London penetration depth which may allow the paramagnetic Meissner-like response to be detected in the temperature dependence of the AC susceptibility. We stress that the newly reported phenomenon reflects an AC-susceptibility manifestation of a field-stabilized critical state rather than a thermodynamic phase. In addition, we have observed a paramagnetic AC response in the normal phase, in both field orientations, indicative of interactions between Eu2+ spins and flux lines.

This paper reports a method for separating the constituents of a cathode containing a composite of the type polydiphenylamine (PDPA)/multi-walled carbon nanotube grafted with carboxyl groups (PDPA/MWCNT-COOH-1) as active material in end-of-life rechargeable lithium-ion batteries (RLIB) and their reuse as active materials in the field of other energy storage devices. The materials recovered from lithium battery cathodes are characterized by FTIR spectroscopy, Raman scattering, surface-enhanced Raman scattering (SERS), and X-ray diffraction. The use of the PDPA/MWCNT-COOH-1 composite as active material in the development of new energy storage devices, such as symmetric supercapacitors, is also reported. The performance comparison of the recycled composite material (PDPA/MWCNT-COOH-1 and MWCNT-COOH) with the one synthesized from pure chemical compounds (PDPA/MWCNT-COOH-2) is shown. Values of the capacitance of symmetrical supercapacitors, having as electrode materials the composites of the type of a mixture of PDPA/MWCNT-COOH-1 and MWCNT-COOH, as well as PDPA/MWCNT-COOH-2, are equal to 136.6 mF cm-2 and 112.59 mF cm-2. Increasing the concentration of the PDPA/MWCNT-COOH-2 active material in the electrode mass from 80 wt% to 84 wt% led to variations in the capacitance values of the symmetrical supercapacitors from 112.59 mF cm-2 to 145.5 mF cm-2.