Mechanism of silver modification for the enhanced photocatalytic activity of Cr(VI) reduction on TiO2 photocatalyst

Abstract

Under the condition that negative effects of proton starvation and photo-generated electron-hole recombination to the Cr6+ photocatalytic reduction process were minimized for the photocatalytic activities of TiO2 and Ag/TiO2 for Cr6+ reduction were comparatively investigated. Combined with the results of EPR, the mechanism of silver modification for the enhanced photocatalytic reduction of Cr6+ on TiO2 was discussed. The result revealed that Cr6+ reduction by the UV-Ag/TiO2 process was more effective than the UV-TiO2 process under the same conditions. Electron transfer from surface Ti3+ to Cr6+ was the key step for Cr6+ reduction. Cr6+ photocatalytic reduction by directly capturing photo-generated electrons is possible, but it occurs mainly indirectly by getting electrons from surface Ti3+. The higher reduction activity of Ag/TiO2 photocatalyst came mainly from the higher number of surface Ti3+.