Highly stable Ag:AgBr/gamma-Al2O3 photo-catalyst was obtained by dispersing AgBr sol on hollow gamma-Al2O3 microsphere. Metallic Ag nanoparticles were in situ generated on AgBr crystals by a photo-reduction method. The activity of catalyst was characterized by MO and phenol decomposition. The light irradiation response, the life times of the photo-induced charges, and the charge separation and transition were determined by the UV-vis diffuse reflection spectra, open circuit voltage decay spectra and transient photocurrent responses. The as-prepared Ag:AgBr/gamma-Al2O3 catalyst can response to visible light irradiation. Charge separation was clarified to correlate with electrons transferring from Ag to AgBr surface and the consequent reaction with ads-O-2 to generate O-center dot(2)- species. It was found that the O-center dot(2)- rather than (OH)-O-center dot played a dominant role in the photocatalytic oxidation of MO and phenol in water. However, the electrons trended to transfer from AgBr to Ag intrinsically without light irradiation. Therefore, the electron transfer between Ag and AgBr reaching the dynamic equilibrium was the key factor for obtaining a high stable Ag/AgBr catalyst which can be obtained by optimizing the Ag:AgBr ratio. Loading amount of Ag:AgBr on gamma-Al2O3 was optimized to 30 wt.% and the metallic Ag content was stabilized at 9 wt.% of Ag:AgBr catalyst. (C) 2015 Elsevier B.V. All rights reserved.