Sang Won Bae

Photocatalytic Water Splitting over La2Ti2O7 Synthesized by the Polymerizable Complex Method

Highly donor-doped (110) layered perovskite materials, La2Ti2O7, with high surface areas were synthesized by the polymerizable complex (PC) method. Relative to La2Ti2O7 prepared by the solid state reaction (SSR) method, PC catalysts showed higher surface areas, crystallization at lower temperatures, higher phase purity, more uniform morphology and better-distributed nickel on the outer surface of La2Ti2O7. All these factors led to higher photocatalytic activity for overall water splitting under UV irradiation. The quantum yield of the reaction over La2Ti2O7 prepared by the PC method was as high as 27%, which was about twofold greater than that over La2Ti2O7 prepared by the SSR method.

Photocatalytic hydrogen production from water-methanol mixtures using N-doped Sr2Nb2O7 under visible light irradiation: effects of catalyst structure.

Nitrogen-doped perovskite type materials, Sr2Nb2O7-xNx (0, 1.5 < x < 2.8), have been studied as visible light-active photocatalysts for hydrogen production from methanol-water mixtures. Nitrogen doping in Sr2Nb2O7 red-shifted the light absorption edge into the visible light range and induced visible light photocatalytic activity. There existed an optimum amount of nitrogen doping that showed the maximum rate of hydrogen production. Among the potential variables that might cause this activity variation, the crystal structure appeared to be the most important. Thus, as the extent of N-doping increased, the original orthorhombic structure of the layered perovskite was transformed into an unlayered cubic oxynitride structure. The most active catalytic phase was an intermediate phase still maintaining the original layered perovskite structure, but with a part of its oxygen replaced by nitrogen and oxygen vacancy to adjust the charge difference between oxygen and doped nitrogen. These experimental observations were explained by density functional theory calculations. Thus, in Sr2Nb2O7-xNx, N2p orbital was the main contributor to the top of the valence band, causing band gap narrowing while the bottom of conduction band due to Nb 4d orbital remained almost unchanged.

Dopant dependent band gap tailoring of hydrothermally prepared cubic SrTixM1−xO3 (M=Ru,Rh,Ir,Pt,Pd) nanoparticles as visible light photocatalysts

Nanostructured cubic SrTiO3 particles were hydrothermally synthesized and studied experimentally/theoretically for photoreduction of water. The particles were doped with metal atoms (M=Ru,Rh,Ir,Pt,Pd), which acquired high cyrstallinity after thermal treatment. SrTiO3:Rh showed the highest rate of H2 evolution under λ>420nm photons. The density functional theory calculations of SrTixM1−xO3 (M=Ru,Rh,Ir,Pt) implied that the photocatalytic activity of SrTixRh1−xO3 was due to its suitable band energetics, and the induced hybridized Ti∕Rh orbitals in the bandgap of SrTiO3.

Effect of precursors on the morphology and the photocatalytic water-splitting activity of layered perovskite La2Ti2O7

A [110] layered perovskite, La2Ti2O7, was a good photocatalyst under ultraviolet light in water splitting reaction. The material was synthesized with La2O3 and TiO2 as precursors by solid-state transformation. The morphology and photocatalytic activity of La2Ti2O7 depended on the preparation methods, as well as purity and morphology of the precursors. Wet-grinding of precursors in ethanol gave a product with higher crystallinity and phase purity, and thus higher photocatalytic activity, than dry-grinding without solvent. It was important to reduce the particle size of La2O3, as it usually had larger initial particle sizes than TiO2. Thus, the particle size of La2O3 had a strong effect on the crystallinity and surface area of the product La2Ti2O7. On the other hand, a severe chemical purity control was required for TiO2, while the effect of morphology was relatively small. In all cases, a high degree of crystallinity and purity of the prepared La2Ti2O7 was critical to show a high photocatalytic water-splitting activity.

Nickel-loaded La2Ti2O7 as a bifunctional photocatalyst

Nickel-loaded La2Ti2O7, one of the highly donor-doped (110) layered perovskite materials, has been found to be an efficient photocatalyst for simultaneous H2 production from water splitting and decomposition of tetramethylammonium hydroxide (TMAH) under UV irradiation.

Formation of La2Ti2O7 Crystals from Amorphous La2O3-TiO2 Powders Synthesized by the Polymerized Complex Method

Amorphous La2O-TiO2 powders were synthesized by the polymerized complex (PC) method. The activation energies for crystallization and grain growth of La2Ti2O7 from these precursors were determined from results of XRD and DTA and compared with those for La2Ti2O7 precursors by the conventional solid-state reaction (SSR). Activation energy of grain growth of La2Ti2O7 in PC-sample was determined to be 7.1 kJ/mol while that of SSR sample was 14.8 kJ/mol. The energy required for the phase transformation from amorphous PC sample to layered perovskite was 432 kJ/mol, while the SSR sample did not show this transition below 900‡C. It was clearly demonstrated that the La2Ti2O7 crystals were formed at a lower temperature and they grew in size faster in the sample prepared by the PC method relative to the sample prepared by the SSR method. Mixing of elements in molecular level in PC preparation appeared responsible for these differences.