Effects of synthesis temperatures on the photocatalytic activities of bismuth oxides for phenol and water oxidation under visible light

Abstract

Bismuth oxides with different crystal structures possess distinct photocatalytic properties. Herein, BiO2−x and Bi4O7 were prepared by a hydrothermal process done at varied synthesis temperatures (Ts), where BiO2−x was obtained at Ts = 25–180 °C and Bi4O7 was resulted at Ts = 200–220 °C. The samples (BiO-Ts) possessed increased crystallinity and decreased visible light absorption with the increment of Ts. They showed certain activities for phenol oxidation due to the oxygen species generated by tiny room light in the dark, which were much weaker than those under visible light irradiation, and all the reaction rates decreased with the increment of Ts. For water oxidation on a photoanode, BiO2−x and Bi4O7 showed an increased and decreased activity with Ts increasing, which agrees with the corresponding charge separation efficiencies. BiO2−x possesses an improved intrinsic photocatalytic activity with increased crystallinity, but its apparent activity is determined by the organics adsorbed thereon.