Oxygen photoevolution on a tantalum oxynitride photocatalyst under visible-light irradiation: How does water photooxidation proceed on a metal-oxynitride surface?

Article abstract of DOI:10.1021/jp0501289

The mechanism of water photooxidation (oxygen photoevolution) on a TaON photocatalyst was studied on the basis of our previous studies on the mechanism of this reaction on TiO₂ and N-doped TiO₂. We have confirmed that photocatalytic O₂ evolution occurs from an aqueous TaON suspension in the presence of Fe³⁺, as reported. In-situ MIR-IR experiments have indicated that the TaON surface is slightly oxidized under visible-light irradiation, indicating that the oxygen photoevolution on TaON actually occurs on a thin Ta-oxide overlayer. The in-situ MIR-IR experiments have also shown that a certain surface peroxo species, tentatively assigned to adsorbed HOOH, is formed as an intermediate of the O₂ photoevolution reaction. Studies on the effect of addition of reductants to the electrolyte on the IPCE have shown that photogenerated holes at the TaON surface cannot oxidize reductants such as SCN^-, Br^-, methanol, ethanol, 2-propanol, and acetic acid, though they can oxidize H₂O into O ₂. Detailed considerations of these results have strongly suggested that the water photooxidation reaction on TaON proceeds by our recently proposed new mechanism, that is, the reaction is initiated by a nucleophilic attack of a water molecule (Lewis base) on a surface-trapped hole (Lewis acid). ? 2005 American Chemical Society.