Ag/AgBr/TiO2 Visible Light Photocatalyst for Destruction of Azodyes and Bacteria

Abstract

Ag/AgBr/TiO₂ was prepared by the deposition−precipitation method and was found to be a novel visible light driven photocatalyst. The catalyst showed high efficiency for the degradation of nonbiodegradable azodyes and the killing of Escherichia coli under visible light irradiation (λ > 420 nm). The catalyst activity was maintained effectively after successive cyclic experiments under UV or visible light irradiation without the destruction of AgBr. On the basis of the characterization of X-ray diffraction, X-ray photoelectron spectroscopy, and Auger electron spectroscopy, the surface Ag species mainly exist as Ag⁰ in the structure of all samples before and after reaction, and Ag⁰ species scavenged h_VB⁺ and then trapped e_CB^- in the process of photocatalytic reaction, inhibiting the decomposition of AgBr. The studies of ESR and H₂O₂ formation revealed that ^•OH and O₂^•- were formed in visible light irradiated aqueous Ag/AgBr/TiO₂ suspension, while there was no reactive oxygen species in the visible light irradiated Ag⁰/TiO₂ system. The results indicate that AgBr is the main photoactive species for the destruction of azodyes and bacteria under visible light. In addition, the bactericidal efficiency and killing mechanism of Ag/AgBr/TiO₂ under visible light irradiation are illustrated and discussed.