Ag/AgBr/TiO2 visible light photocatalyst for destruction of azodyes and bacteria

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 (lambda > 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 Ago in the structure of all samples before and after reaction, and Ag-0 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)-O-center dot and O-2(center dot-) were formed in visible light irradiated aqueous Ag/AgBr/TiO2 suspension, while there was no reactive oxygen species in the visible light irradiated Ag-0/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.