National Institute Of Materials Physics - Romania

In this study, molybdenum doped iron cobaltite and cobalt ferrite catalysts were prepared by coprecipitation, and their structural, morphological, and optical, properties were evaluated by XRD, BET, SEM, FTIR, Raman, XPS and UV-VIS techniques. Their catalytic behavior evaluated in the malic acid oxidative decarboxylation reaction underlined the importance of the incorporation of Mo into the structure of iron cobaltite and cobalt ferrite catalysts. The catalysts with the highest molybdenum content forming cobaltite and iron molybdate phases showed better activity, with cobaltite-based catalysts being more active than ferrite-based ones.

Our study focuses on disclosing the mechanisms standing behind the improved photocatalytic performance of SrTiO3, where Al modification of the perovskite structure boosts the photocatalytic O2 evolution activity of the Al:SrTiO3 system. By adapting the synthesis method that produces well-crystallized materials with low defect density and employing surface modification techniques, we aim to enhance the photocatalytic efficiency of SrTiO3 via Al2O3 nanoceramic oxide doping at concentrations ranging from 0 to 10% and further examining of the relationship between doping process and the changes in the electronic and crystalline structure of SrTiO3. The prepared Al-based SrTiO3 perovskite samples (Al3%:SrTiO3, Al7%:SrTiO3, Al10%:SrTiO3) were thoroughly characterized to understand their structural, electronic, and morphological properties. Complementary X-ray techniques were employed to assess the stoichiometry (X-ray photoelectron spectroscopy - XPS), local environment, and chemical state (X-ray absorption spectroscopy - XAS in both total electron yield (TEY) and fluorescence yield (TFY). The comprehensive characterization enables us to understand the changes in the electronic properties and morphological features of the modified samples elucidating the surface formation mechanism while providing insights into the structural modifications induced by Al doping in the SrTiO3 perovskite lattice. Our findings give new perspectives for the development of Al-modified SrTiO3 perovskite materials with enhanced photocatalytic performance providing rich insights into the optimization of photocatalytic processes for applications in environmental remediation and sustainable energy production.

The European Fusion Reactor (DEMO, Demonstration Power Plant) relies significantly on joining technologies in its design. Current research within the EUROfusion framework focuses on developing materials for the first wall and divertor applications, emphasizing the need for suitable joining processes, particularly for tungsten. The electric field-assisted sintering technique (FAST) emerges as a promising alternative due to its high current density, enabling rapid heating and cooling rates for fast sintering or joining. In this study, FAST was employed to join tungsten and EUROFERE97 steel, the chosen materials for the first wall, using 50-mu m-thick Cu foils as interlayers. Three distinct joining conditions were tested at 980 degrees C for 2, 5, and 9 min at 41.97 MPa to optimize joint properties and assess FAST parameters influence. Hardness measurements revealed values around 450 HV0.1 for tungsten, 100 HV0.1 for copper, and 390 HV0.1 for EUROFER97 under all joining conditions. Increasing bonding time improved joint continuity along the EUROFER97/Cu and W/Cu interfaces. Notably, the 5 min bonding time resulted in the highest shear strength, while the 9 min sample exhibited reduced strength, possibly due to Kirkendall porosity accumulation at the EUROFER97/Cu interface. This porosity facilitated crack initiation and propagation, diminishing interfacial adhesion properties.

In this study, we report on the development of hydroxyapatite (HAp) and samarium-doped hydroxyapatite (SmHAp) nanoparticles using a cost-effective method and their biological effects on a bone-derived cell line MC3T3-E1. The physicochemical and biological features of HAp and SmHAp nanoparticles are explored. The X-ray diffraction (XRD) studies revealed that no additional peaks were observed after the integration of samarium (Sm) ions into the HAp structure. Valuable information regarding the molecular structure and morphological features of nanoparticles were obtained by using Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The elemental composition obtained by using energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of the HAp constituent elements, Ca, O, and P, as well as the presence and uniform distribution of Sm3+ ions. Both HAp and SmHAp nanoparticles demonstrated biocompatibility at concentrations below 25 mu g/mL and 50 mu g/mL, respectively, for up to 72 h of exposure. Cell membrane integrity was preserved following treatment with concentrations up to 100 mu g/mL HAp and 400 mu g/mL SmHAp, confirming the role of Sm3+ ions in enhancing the cytocompatibility of HAp. Furthermore, our findings reveal a positive, albeit limited, effect of SmHAp nanoparticles on the actin dynamics, osteogenesis, and cell migration compared to HAp nanoparticles. Importantly, the biological results highlight the potential role of Sm3+ ions in maintaining cellular balance by mitigating disruptions in Ca2+ homeostasis induced by HAp nanoparticles. Therefore, our study represents a significant contribution to the safety assessment of both HAp and SmHAp nanoparticles for biomedical applications focused on bone regeneration.

Curcumin, an important bioactive compound and natural photosensitizer, which exhibits various biological properties, was loaded into inorganic carriers MgAl/ZnAl layered double hydroxides (LDH). The supporting matrices were obtained by co-precipitation, and a surfactant was used for including the organic drug. The structural, morphological, and spectral properties of the obtained composites were followed by X-ray diffraction, FTIR, SEM, UV-Vis, and fluorescence spectroscopy in solid state and in different solvents. The prepared formulations, the curcumin-loaded carriers, were introduced in alcohol-aqueous mixtures and the effect of solvent on the spectral properties of the formulations was investigated. Interactions between the keto-enol group of the pigment and the metals in LDHs laminates as well as inter-molecular bonds between alcohols and curcumin were evidenced. As a consequence, it was concluded that the composition of the carrier as well as the nature of the solvent determine the structural changes of the formulations. MgAl-LDH in powder has better spectral characteristics in the low-energy range (UV-Vis and fluorescence) than ZnAl-LDH. Their spectra are altered when methanol and water are present in the solvent mixture. The released curcumin concentration is in the range for photosensitization applications. The results have potential utilizations in many fields such as food, pharmaceutical, and biology.

Recently, a smart strategy for two-dimensional (2D) materials synthesis has emerged, namely space-confined chemical vapor deposition (CVD). Its extreme case is the microreactor method, in which the growth substrate is face-to-face stacked on the source substrate. In order to grow 2D transition metal dichalcogenides by this method, transition metal oxides, dispersed in very small amounts on the source substrate, are used as source materials in most of the published reports. In this paper, a colloidal dispersion of MoS2 in saline solution is used and MoS2 nanosheets with various shapes, sizes (between 5 and 60 mu m) and thicknesses (2-4 layers) have been synthesized. Small MoS2 flakes (regular or defective) are present on the surface of the nanosheets. Catalytic sites, undercoordinated atoms located at the edges of MoS2 flakes and nanosheets, are produced in a high number by a layer-plus-island (Stranski-Krastanov) growth mechanism. Several double-resonance Raman bands (at 147, 177, 187, 225, 247, 375 cm(-1)) are assignable to single phonon processes in which the excited electron is elastically scattered on a defect. The narrow 247 cm(-1) peak is identified as a topological defect-activated peak. These findings highlight the potential of defect engineering in material property optimization, particularly for solar water splitting applications.

The study of granularity in superconducting films by using AC susceptibility has a crucial role in the development of and improvement in the ReBCO-coated conductors, which are a constantly evolving reality in the modern power applications of superconductivity. Specifically, the study of the granularity is essential because the ReBCO superconducting wires and tapes are far from the regularity of a single crystal while they often present an inter- and intragranular contribution to the critical current density. On the other hand, the AC susceptibility is a key part of the characterization of a granular sample because this technique is very sensitive to the presence of granularity in the superconductors and, moreover, the study of its first harmonic allows for determining pivotal properties such as the pinning energy as well as the dissipation processes acting in the sample. The pinning energy values and the granularity of an YBCO thin film have been studied by means of AC susceptibility measurements as a function of the AC amplitude, temperature, and DC field. In particular, the first harmonic imaginary component of the AC susceptibility chi 1 '' related to the dissipation processes of the sample has been studied. First, starting from the Brandt approach, the critical current density J(c) and the pinning energy U of the sample have been extracted at 77 K by using the chi 1 '' measurements as a function of the AC amplitude at different AC frequencies and DC fields. From these measurements, a first signal of granularity appears. In order to confirm it, the temperature dependence of the chi 1 '' at different DC fields has been studied and a contribution deriving from the inter- and intragranular part of the sample has emerged. By taking the temperature corresponding to the crossover between the two contributions at the different DC fields, the intergranular and intragranular response has been separated. Successively, the temperature has been fixed to 77 K, together with an AC frequency equal to 1597.9 Hz, and the chi 1 '' as a function of the DC field at different AC amplitudes has been analyzed showing a clear presence of granularity in all the curves. By drawing the contour plot of the chi 1 '' with the DC and AC values, it was possible to determine the best parameters to put at 77 K in order to exploit the material for applications.

The present study aims to describe the role of the grain size on the properties of submicron- and nano-structured Ba0.8Sr0.2TiO3 (BST) ceramics. Dense (1 - 2% porosity) ceramics with average grain sizes in the range of (77 234) nm were consolidated under different spark plasma sintering conditions starting from nanopowders with a mean particle size of 70 nm, synthesized via the acetate variant of the sol-gel method. The structural analysis based on XRD data revealed a mixture of cubic and tetragonal modifications at room temperature for the precursor powders and for all the investigated ceramics. The structural heterogeneity of the individual ceramic grains with coexistence of cubic and tetragonal polymorphs was confirmed by HR-TEM investigations. Accordingly, a "brick-wall" model with cubic grain boundary regions and tetragonal grain cores is proposed. By increasing the grain size, from 77 to 234 nm, a decrease of the phase transitions diffuseness accompanied by an increase of the permittivity maxima (from 650 to 4500) and dielectric losses (from 5 to 7.5%, at 100 Hz), was detected by broadband dielectric spectroscopy. No variation of the Curie temperature in the investigated Ba0.8Sr0.2TiO3 ceramics was detected, unlike typically reported for BaTiO3 ceramics with similar grain sizes. The Curie-Weiss temperature and the Curie constant decrease when grain size is diminished, indicating an overall reduction of the ferroelectric active volume, as a scaling effect. The ferroelectric switching was demonstrated for all the selected fine-grained BST ceramics, either at nanoscale or macroscopically, with an increased ferroelectric character for the coarser submicron-structured ceramics, with respect to the nanocrystalline one. The observed properties of the fine-grained Ba0.8Sr0.2TiO3 ceramics are explained in the frame of multiphase coexistence and ferroelectricity "dilution" due to the increasing role of non-ferroelectric grain boundaries when reducing grain size and complete the knowledge on the scale-dependent properties of dense fine-grained BaTiO3-based ceramics.

Visible light-mediated photodegradation offers a sustainable and environmentally friendly solution for removing emerging contaminants from water sources. Herein, we report on the synergy effect between adsorption and visible-light-driven photo-degradation of 17 fl - estradiol using (Au)TiO 2 nanotubes-graphene composites. The graphene structures (graphene oxide - GO or thermally reduced graphene oxide - trGO) provide a platform for strong adsorption of 17 fl -estradiol molecules and facilitate the charge transfer between plasmonic Au nanoparticles and TiO 2 , leading to an improvement of the overall degradation process. To better understand the effect of Au nanoparticles and TiO 2 separately, three different concentrations of Au (1 %, 2.5 %, and 5 %) were prepared and characterized. The estrogenic molecules preferred GO over trGO, suggesting that hydrogen bonds govern the interaction between GO and 17 fl -estradiol. Consequently, a higher photocatalytic efficiency of GOcontaining composites was observed when removing estrogenic molecules. The role of adsorption proved crucial for capturing and retaining more contaminant molecules on the composite surface, thus increasing the odds of surface reactions with the photogenerated carriers. A total removal of 17 fl -estradiol has been obtained for Au (1 %, 2.5 %, and 5 %) TiO 2 nanotubes-GO. The mechanism behind the adsorption and photo-degradation processes has been discussed.