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＋.

Key words: Silver, Titanium dioxide, Photocatalytic reduction, Hexavalent chromium