Surface Chemistry of Perovskite Oxynitride Photocatalysts: A Computational Perspective

Perovskite oxynitrides are an established class of photocatalyst materials for water splitting. Previous computational studies have primarily focused on their bulk properties and have drawn relevant conclusions on their light absorption and charge transport properties. The actual catalytic conversions, however, occur on their surfaces and a detailed knowledge of the atomic-scale structure and processes on oxynitride surfaces is indispensable to further improve these materials. In this contribution, we summarize recent progress made in the understanding of perovskite oxynitride surfaces, highlight key processes that set these materials apart from their pure oxide counterparts and discuss challenges and possible future directions for research on oxynitrides.

Copper Nitride Nanowire Arrays—Comparison of Synthetic Approaches

Copper nitride nanowire arrays were synthesized by an ammonolysis reaction of copper oxide precursors grown on copper surfaces in an ammonia solution. The starting Cu films were deposited on a silicon substrate using two different methods: thermal evaporation (30 nm thickness) and electroplating (2 μm thickness). The grown CuO or CuO/Cu(OH)2 architectures were studied in regard to morphology and size, using electron microscopy methods (SEM, TEM). The final shape and composition of the structures were mostly affected by the concentration of the ammonia solution and time of the immersion. Needle-shaped 2–3 μm long nanostructures were formed from the electrodeposited copper films placed in a 0.033 M NH3 solution for 48 h, whereas for the copper films obtained by physical vapor deposition (PVD), well-aligned nano-needles were obtained after 3 h. The phase composition of the films was studied by X-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis, indicating a presence of CuO and Cu(OH)2, as well as Cu residues. Therefore, in order to obtain a pure oxide film, the samples were thermally treated at 120–180 °C, after which the morphology of the structures remained unchanged. In the final stage of this study, Cu3N nanostructures were obtained by an ammonolysis reaction at 310 °C and studied by SEM, TEM, XRD, and spectroscopic methods. The fabricated PVD-derived coatings were also analyzed using a spectroscopic ellipsometry method, in order to calculate dielectric function, band gap and film thickness.

The Role of Fluorine on the Structure and SHG Property of inorganic Selenites and Tellurites

Fluorine, as the most electronegative element, can replace the oxygen ligands of functional groups under given conditions. These fluoride groups are more or less different from the pure oxide groups...

Phase Stability of Nanocrystalline Grains of Rare-Earth Oxides (Sm2O3 and Eu2O3) Confined in Magnesia (MgO) Matrix

Rare-earth (RE) oxides are important in myriad fields, including metallurgy, catalysis, and ceramics. However, the phase diagram of RE oxides in the nanoscale might differ from the phase diagrams for bulk, thus attracting attention nowadays. We suggest that grain size in the nanoscale also determines the obtained crystallographic phase along with temperature and pressure. For this purpose, nanoparticles of Sm2O3 and Eu2O3 were mixed in an inert MgO matrix via the sol-gel method. This preparation method allowed better isolation of the oxide particles, thus hindering the grain growth process associated with increasing the temperature. The mixed oxides were compared to pure oxides, which were heat-treated using two methods: gradual heating versus direct heating to the phase transition temperature. The cubic phase in pure oxides was preserved to a higher extent in the gradual heating treatment compared to the direct heating treatment. Additionally, in MgO, even a higher extent of the cubic phase was preserved at higher temperatures compared to the pure oxide, which transformed into the monoclinic phase at the same temperature in accordance with the phase diagram for bulk. This indicates that the cubic phase is the equilibrium phase for nanosized particles and is determined also by size.

Sensing Performance of Al and Sn Doped ZnO for Hydrogen Detection

Chemical gas sensors were studied long ago and nowadays, for the advantageous role they provide to the environment, health condition monitoring and protection. The recent studies focus on the semiconductors sensing abilities, especially of non toxic and low cost compounds. The present work describes the steps to elaborate and perform a chemical sensor using intrinsic and doped semiconductor zinc oxide. First, we synthesized pure oxide using zinc powder, then, two other samples were established where we introduced the same doping percentage of Al and Sn respectively. Using low cost spray pyrolysis, and respecting the same conditions of preparation. The obtained samples were then characterized by X Ray Diffraction (XRD) that revealed the hexagonal wurzite structure and higher crystallite density towards the direction (002), besides the appearance of the vibration modes related to zinc oxide, confirmed by Raman spectroscopy. SEM spectroscopy showed that the surface morphology is ideal for oxidizing/reduction reactions, due to the porous structure and the low grain sizes, especially observed for the sample Sn doped ZnO. The gas testing confirms these predictions showing that the highest response is related to Sn doped ZnO compared to ZnO and followed by Al doped ZnO. The films exhibited responses towards: CO, acetone, methanol, H2, ammonia and NO2. The concentrations were varied from 10 to 500 ppm and the working temperatures from 250 to 500°C, the optimal working temperatures were 350 and 400 °C. Sn doped ZnO showed a high response towards H2 gas target, with a sensitivity reaching 200 at 500 ppm, for 400 °C.

A first-principles study of stability of surface confined mixed metal oxides with corundum structure (Fe2O3, Cr2O3, V2O3)

Surface-confined mixed corundum metal oxides stability is shown to follow the stability trend of their similar pure oxide terminations.

DIÓXIDO DE ESTANHO MODIFICADO COM FERRO: CATALISADORES PARA REAÇÃO DE OXIDAÇÃO DE RODAMINA B

<p>Os descartes de efluentes industriais têm se tornado um grave problema ambiental, devido à sua composição diversificada e à toxicidade que dificulta sua remoção pelos processos convencionais de tratamento, em particular os rejeitos da indústria têxtil que, além de tóxicos, são caracterizados pela intensa coloração. Visando à remoção destes corantes, realizou-se, neste trabalho, uma dopagem do dióxido de estanho com 0,10%, 0,15% e 0,20% de ferro, com o objetivo de avaliar o potencial catalítico do óxido puro, em relação ao material dopado, na remoção de cor de soluções contendo o corante orgânico rodamina B como molécula modelo. Os materiais sintetizados foram caracterizados por meio de MEV-EDS, difração de raios X, fluorescência de raios X e reflectância difusa. As soluções contendo a molécula modelo foram acondicionadas em um fotorreator com iluminação ultravioleta e monitoradas em UV-Vis, a cada 30 minutos. Para verificar a condição ótima da reação, foram testadas quantidades diferentes de catalisadores, peróxido e concentrações de rodamina B. Foi observado que os materiais contendo 0,10% e 0,15% de ferro obtiveram resultados mais satisfatórios, removendo, aproximadamente, 60% da cor em 120 minutos de reação.</p><p>Abstract</p><p>The discharges of industrial waste have become a serious environmental problem because of its diverse composition and toxicity which hampers the removal by conventional treatment processes, in particular the waste from the textile industry that besides toxic, they are characterized by intense staining. Aimed at removing these dyes, was held in this study, a tin dioxide doping with 0.10%, 0.15% and 0.20% of iron in order to evaluate the catalytic potential of pure oxide, compared to doped materials, in the removal of color solutions containing the organic dye rhodamine B as template molecule. The synthesized materials were characterized by SEM –EDS, X-ray diffraction, X-ray fluorescence and diffuse reflectance. The solutions containing the template molecule were placed in a photoreactor with ultraviolet light and monitored by UV-Vis, every 30 minutes. To check the optimal reaction condition, were tested different amounts of catalysts, concentrations of peroxide and rhodamine B. It was observed that the material containing 0.10% to 0.15% iron obtained more satisfactory results, removing, approximately 60% of the color in 120 minutes of reaction.</p>