No abstract

Photochemical reactions on LaTiO 2 N, a perovskite-type oxynitride, were examined. Under visible-light irradiation (420 nm < λ < 600 nm), LaTiO 2 N reduced H + into H 2 and oxidized H 2 O into O 2 in the presence of a sacrificial electron donor (methanol) or acceptor (Ag + ) by the band gap transition (2.1 eV). Oxidation of water proceeded with little degradation of the oxynitride, whereas partial substitution of Ca 2+ for La 3+ of LaTiO 2 N and modification by IrO 2 colloid markedly suppressed degradation of the oxynitride and increased O 2 evolution efficiency.

LaTiO2N, a Ti-based oxynitride, was studied as a visible-light (420−600 nm)-driven photocatalyst. DFT calculation for LaTiO2N indicated that the top of the valence band consists predominantly of N 2p orbitals with a small contribution by O 2p orbitals, while the bottom of the conduction band is made up entirely of empty Ti 3d orbitals. LaTiO2N was synthesized from a La2Ti2O7 precursor at 1123 K under NH3 flow. The relationship between the preparation condition and the photocatalytic activities of H+ reduction to H2 and H2O oxidation to O2 was examined. It was found that the photocatalytic activity for O2 evolution increased with nitridation time, reaching a maximum at 72 h. Further treatment beyond 72 h lowered the rate of O2 evolution. The rate of H2 evolution was almost independent of nitridation time. The relationship between nitridation time and the rate of O2 evolution is discussed on the basis of X-ray photoelectron spectroscopy (XPS) analyses.