Photocatalytic degradation of methyl orange on TiO2 promoted by silver

The Ag-TiO2 photocatalyst was prepared by the sol-gel-hydrothermal method. The obtained powder has high surface area and small crystal size. The photocatalytic activity of Ag-TiO2 is enhanced by proper silver loading under UV and visible light irradiation. The optimum content of Ag is 0.15 %. However, the photocatalytic activity of Ag-TiO2 decreases with the excessive silver loading. The increment in activity of TiO2 powder enhanced by Ag under visible light irradiation is higher than that under UV light irradiation because of their different mechanisms. Under visible light irradiation, the photoexcited electrons are injected into the conduction band of TiO2 from the dye and then transformed to silver clusters rapidly. Ag clusters accelerate the photocatalytic process through promoting the separation of charges and depressing the recombination of electrons with dye radical cations. The results indicate that the key to improving the activity of dye-sensitized TiO2 system is to efficiently promote the separation of charges and accelerate the reaction of excited electrons and oxygen.