Au-Ag-AgI nanoparticles (NPs) were uniformly dispersed onto mesoporous alumina by deposition-precipitation and photoreduction at low temperature. Compared with Ag-AgI/Al2O3, the catalyst showed higher photocatalytic activity under visible irradiation. In particular, the release of metal ions from the catalyst was significantly inhibited during photodegradation of pollutants. Electron spin resonance and cyclic voltammograms studies under a variety of experimental conditions verified that the coupling of Au and Ag NPs increased the efficiency of light energy conversion and accelerated interfacial electron transfer processes. The main active species involved in the photoreaction of Au-Ag-AgI/Al2O3 were O-2 (aEuro cent a') and excited h(+) on the metal NPs. The presence of several ubiquitous anions, including HCO3 (-), SO4 (2-), and NO3 (-) could act as electron donors trapping excited h(+) on the metal NPs to facilitate electron circulation. The results obtained herein indicated that coupled, noble, bimetal NPs exhibited high photosensitivity and photostability due to enhanced surface plasmon resonance and interfacial electron transfer. Addition of Au made Au-Ag-AgI nanoparticles (NPs) disperse more uniformly onto mesoporous Al2O3 and showed higher photocatalytic activity under visible irradiation.