Control of valence band potential and photocatalytic properties of NaxLa1−xTaO1+2xN2−2x oxynitride solid solutions

Abstract

A series of oxynitride solid solutions, Na_xLa_1−xTaO_1+2xN_2−2x with x = 0.1, 0.2, 0.25, 0.3, 0.5, 0.75 and 0.85, was successfully synthesized by nitridation of amorphous oxide precursors under an NH₃ stream at 1273 K. The band gaps of the solid solutions increased with the Na content. Photoelectrochemical analysis was conducted to obtain information on the band potentials of the solid solutions. The valence band maxima of the solid solutions were at more positive potentials than that of LaTaON₂ (x = 0). Solid solutions of Na_xLa_1−xTaO_1+2xN_2−2x with x = 0.20–0.85 exhibited photocatalytic activity for both H₂ and O₂ evolution under visible light irradiation in the presence of sacrificial reagents, while LaTaON₂ had no activity for O₂ evolution. The achievement of O₂ evolution with these solid solutions is due to control of the valence band potential; therefore, control of the photocatalytic properties of LaTaON₂ was achieved by the formation of solid solutions.