Cataluminescence in Er-Substituted Perovskites.

Thermophotovoltaic devices have promising applications for energy conversion. However, current conversion efficiency of chemical energy to light is very low, limited by the competing process of heat dissipation released as black body radiation. From a fundamental point of view, the direct conversion of chemical energy into light without this detour is possible. This so called cataluminescence from methanol combustion over Er-substituted SrTiO3 with high efficiency is demonstrated. The catalytically active quaternary perovskites Er0.15 La0.15 Sr0.55 Ti0.95 Cu0.05 O3 - δ exsolute and reabsorb metallic Cu particles onto the surface in reducing and oxidizing conditions, respectively. Thus, it is able to manipulate the surface structure and investigate its influence on the catalytic as well as luminescent properties. The fuel to air ratio around the stoichiometry point changes the conditions from reducing to oxidizing and thereby alters the surface properties. This is evidenced by post mortem X-ray diffraction and X-ray photoemission as well as operando optical spectroscopy. Cataluminescence takes place under oxidizing conditions (lean fuel to air mixture) on the Er-perovskite oxide with a strong selective near infrared emission, while reducing conditions stimulate formation of plasmonic Cu-nanoparticles, which emit black body radiation.

Structural Reversibility and Nickel Particle stability in Lanthanum Iron Nickel Perovskite-Type Catalysts.

Perovskite-type oxides have shown the ability to reversibly segregate precious metals from their structure. This reversible segregation behavior was explored for a commonly used catalyst metal, Ni, to prevent Ni sintering, which is observed on most catalyst support materials. Temperature-programmed reduction, X-ray diffraction, X-ray absorption spectroscopy, electron microscopy, and catalytic activity tests were used to follow the extent of reversible Ni segregation. LaFe1-x Nix O3±Î´ (0≤x≤0.2) was synthesized using a citrate-based solution process. After reduction at 600 °C, metallic Ni particles were displayed on the perovskite surfaces, which were active towards the hydrogenation of CO2 . The overall Ni reducibility was proportional to the Ni content and increased from 35 % for x=0.05 to 50 % for x=0.2. Furthermore, Ni could be reincorporated reversibly into the perovskite lattice during reoxidation at 650 °C. This could be exploited for catalyst regeneration under conditions under which impregnated materials such as Ni/LaFeO3±Î´ and Ni/Al2 O3 suffer from sintering.

Effect of Nb doping on structural, optical and photocatalytic properties of flame-made TiO2 nanopowder.

TiO(2):Nb nanopowders within a dopant concentration in the range of 0.1-15 at.% were prepared by one-step flame spray synthesis. Effect of niobium doping on structural, optical and photocatalytic properties of titanium dioxide nanopowders was studied. Morphology and structure were investigated by means of Brunauer-Emmett-Teller isotherm, X-ray diffraction and transmission electron microscopy. Diffuse reflectance and the resulting band gap energy were determined by diffuse reflectance spectroscopy. Photocatalytic activity of the investigated nanopowders was revised for the photodecomposition of methylene blue (MB), methyl orange (MO) and 4-chlorophenol under UVA and VIS light irradiation. Commercial TiO(2)-P25 nanopowder was used as a reference. The specific surface area of the powders was ranging from 42.9 m(2)/g for TiO(2):0.1 at.% Nb to 90.0 m(2)/g for TiO(2):15 at.% Nb. TiO(2):Nb particles were nanosized, spherically shaped and polycrystalline. Anatase was the predominant phase in all samples. The anatase-related transition was at 3.31 eV and rutile-related one at 3.14 eV. TiO(2):Nb nanopowders exhibited additional absorption in the visible range. In comparison to TiO(2)-P25, improved photocatalytic activity of TiO(2):Nb was observed for the degradation of MB and MO under both UVA and VIS irradiation, where low doping level (Nb < 1 at.%) was the most effective. Niobium doping affected structural, optical and photocatalytic properties of TiO(2). Low dopant level enhanced photocatalytic performance under UVA and VIS irradiation. Therefore, TiO(2):Nb (Nb < 1 at.%) can be proposed as an efficient selective solar light photocatalyst.

One-step hydrothermal coating approach to photocatalytically active oxide composites.

Three-dimensional Bi(2)WO(6)/TiO(2) hierarchical heterostructures with secondary anatase TiO(2) nanoparticles grown on primary Bi(2)WO(6) microspheres have been successfully obtained by a low temperature hydrothermal method. The hierarchical Bi(2)WO(6)/TiO(2) structures displayed significantly enhanced visible-light-driven photocatalytic activity in comparison to isolated Bi(2)WO(6) microspheres and TiO(2) nanoparticles. Furthermore, this methodology is of general interest, because it can be used to fabricate other oxide heterostructures, such as BiVO(4)/TiO(2) and Bi(2)MoO(6)/TiO(2).