Correlation between the band positions of (SrTiO3)(1-x)center dot(LaTiO2N)(x) solid solutions and photocatalytic properties under visible light irradiation

N-doped SrTiO3 and (SrTiO3)(1-x)center dot(LaTiO2N)(x) samples were prepared by the thermal ammonolysis method. The photocatalytic activities of the samples were investigated in a water suspension system. Aqueous methanol solution (50 mL CH3OH + 220 mL H2O) for H-2 evolution and aqueous silver nitrate solution (270 mL, 0.01 mol L-1) for O-2 evolution were used as sacrificial reagents. The oxynitrides showed photocatalytic activities under visible light irradiation. The maximum rates of photocatalytic hydrogen and oxygen evolution under visible light irradiation (lambda > 420 nm) were 10 and 8 mu mol h(-1), respectively. The samples were characterized by X-ray diffractometry, UV-Vis spectrophotometry, Fourier transform infrared spectrometry, and laser Raman spectroscopy. The unit cell edge length of (SrTiO3)(1-x)center dot(LaTiO2N)(x) increased linearly and their band gaps reduced from 3.18 to 2.04 eV with increasing x from 0 to 0.30. Moreover, the calculation results of (SrTiO3)(0.75)center dot(LaTiO2N)(0.25) by density functional theory suggested that the band gap narrowing of the solid solutions came from the hybridization of N-2p and O-2p orbital. The band positions of the solid solutions were further investigated by Mott-Schottky and the onset potential method. The results suggested that the conduction band of the solid solution was lowered, which led to decrement of the hydrogen evolution rate.