Effect of Ti(III) Surface Defects on the Process of Photocatalytic Reduction of Hexavalent Chromium

In this paper, the process of photocatalytic reduction of hexavalent chromium was investigated over Ti3+-modified TiO2 photocatalysts. The Ti3+ surface defects were repaired by annealing as-prepared sample at different temperatures to control the amount of Ti3+ sites. The samples were characterized by SEM, XRD, BET, UV-vis absorption, EPR and XPS. The results showed Ti3+ defects were successfully doped in TiO2. The surface selective adsorption of hexavalent chromium [Cr2O72- (Cr(VI))] and the desorption of trivalent chromium [Cr3+ (Cr(III))] were investigated during the process of photocatalytic reduction. Zeta potential results presented that the increased positive charges due to more Ti3+ defects on the surface show a significant improvement for adsorption of Cr(VI). Accordingly, the surface positive charges controlled by the Ti3+ defects play important roles in the photocatalytic reduction of Cr(VI).