Water splitting into H2 and O2 over niobate and titanate photocatalysts with (111) plane-type layered perovskite structure

Abstract

Photophysical and photocatalytic properties of A₅Nb₄O₁₅ (A = Sr and Ba), Ba₃LaNb₃O₁₂, ALa₄Ti₄O₁₅ (A = Ca, Sr, and Ba), and La₄Ti₃O₁₂ with layered perovskite structures, in which a plane in parallel with (111) of a simple perovskite structure was exposed at interlayer, were investigated. These oxides were obtained by a polymerizable complex method at 973–1473 K though only A₅Nb₄O₁₅ (A = Sr and Ba) were prepared by a solid state reaction even at 1673 K. The shapes of these complex metal oxides were plate-like derived from the perovskite layered structure. These band gaps were estimated to be 3.7–4.1 eV from the onsets of diffuse reflection spectra. These oxides showed photoluminescence at 77 K. These oxides loaded with NiO cocatalysts showed activities for water splitting under UV irradiation. NiO_x/BaLa₄Ti₄O₁₅ and NiO_x/Ba₅Nb₄O₁₅ showed the highest activities among the titanates and niobates tested in the present study. NiO_x/BaLa₄Ti₄O₁₅ and NiO_x/Ba₅Nb₄O₁₅ gave 15% and 17% of quantum yields at 270 nm, respectively. Photocatalytic activities of ALa₄Ti₄O₁₅ (A = Ca, Sr, and Ba) strongly depended on the alkaline earth metal ion. Pt, Au, Ni, and PbO₂ were selectively photodeposited on basal or edge plane of the BaLa₄Ti₄O₁₅ plate-like powder while these were randomly loaded on CaLa₄Ti₄O₁₅. It was suggested that this difference in the surface property was the one of the important factors affecting photocatalytic ability for ALa₄Ti₄O₁₅ (A = Ca, Sr, and Ba).