Water Splitting into H₂ and O₂ on New Sr₂M₂O₇ (M = Nb and Ta) Photocatalysts with Layered Perovskite Structures: Factors Affecting the Photocatalytic Activity

Sr₂Ta₂O₇ and Sr₂Nb₂O₇ with similar layered perovskite structure showed activities for water splitting into H₂ and O₂ in pure water without any additives under UV irradiation. The band gaps of Sr₂Ta₂O₇ and Sr₂Nb₂O₇ were 4.6 and 3.9 eV, respectively. Sr₂Ta₂O₇ gave H₂ and O₂ from pure water under UV irradiation even in the absence of a cocatalyst. The activity of Sr₂Ta₂O₇ was much increased by loading NiO as a cocatalyst even without pretreatment. The quantum yield of the NiO(0.15 wt %)/Sr₂Ta₂O₇ photocatalyst was 12% at 270 nm. On the other hand, native Sr₂Nb₂O₇ did not possess the activity. The high activity was obtained for the Sr₂Nb₂O₇ photocatalyst when NiO was loaded and pretreated. Factors affecting the photocatalytic activities were discussed by using the Sr₂Ta₂O₇ and Sr₂Nb₂O₇ powder with similar layered perovskite structure. A predominant factor affecting the photocatalytic behavior of Sr₂Ta₂O₇ and Sr₂Nb₂O₇ is the conduction band levels formed by Ta_5d and Nb_4d.