Under visible light irradiation (lambda = 420-500 nm), a tantalum oxynitride, TaON, functions as a stable and very efficient photocatalyst for oxidation of water into O2 with a sacrificial electron acceptor (Ag+).

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.

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A transition metal nitride, Ta3N5, is a novel photocatalyst responding to visible light. Ta3N5 evolves H2 and O2 by visible light (λ&lt;600 nm) irradiation in the presence of sacrificial electron donor and acceptor, respectively without any noticeable photo-anodic or cathodic corrosion, representing a candidate for overall water splitting by visible light.