Influence of TiO2 hollow sphere size on its photo-reduction activity for toxic Cr(VI) removal

After polystyrene@titanium dioxide (PS@TiO 2 ) composite with different size was calcined at designated temperature, TiO 2 hollow sphere with controllable size was obtained for high efficient photo-reduction of Cr(VI). The feature of the TiO 2 hollow sphere was investigated by SEM, TEM , XRD , UV–Vis, and photoluminescence . The photo-reduction of Cr(VI) were measured for the performance assessment of the TiO 2 hollow sphere, Cr(VI) was used as an electron acceptor . After irradiation for 2   h, the photo-reduction rate of Cr(VI) (pH   =   2.82) for TiO 2 (450   nm) was 96%, which exhibited an increase of 5% and 8% compared with TiO 2 (370   nm) and TiO 2 (600   nm). The absorption edges of TiO 2 hollow sphere (450   nm) was largest with the increasing of hollow sphere size from 370 to 600   nm. The optimal hollow sphere size of TiO 2 was 450   nm for the photo-reduction of Cr(VI), because the light-harvesting efficiency (the best of absorption edge) and photo-generated electron-hole separation rate (the best of photo-reduction rate) of TiO 2 hollow sphere were controlled by its hollow sphere size. In addition, we find that the behavior of the hydrogen production was inhibited by the coexistence Cr(VI) solution. This study can improve our understanding of the mechanism for the activity enhancement by the optimal hollow sphere size of TiO 2 .