Aqueous Cr(VI) photo-reduction catalyzed by TiO2 and sulfated TiO2

TiO2 and sulfated TiO2 (SO42−/TiO2) catalysts with different textural properties were prepared under different calcination temperatures and the photo-reduction of Cr(VI) to Cr(III) catalyzed by these catalysts was investigated. For the photocatalytic reduction of Cr(VI), the photocatalytic activities of the TiO2 samples were found to be strongly dependent of the calcination temperature and TiO2 calcined at 400 °C showed a higher catalytic activity compared to other TiO2 catalysts. In contrast, sulfation of TiO2 stabilized the catalytic activities of SO42−/TiO2 catalysts. At low calcination temperature, SO42−/TiO2 catalysts exhibited catalytic activities almost comparable with that of TiO2 and the catalytic activities of SO42−/TiO2 catalysts were markedly higher than TiO2 under high calcination temperature. In addition, the removal of surface SO42− of SO42−/TiO2 catalyst led to a marked decrease of the catalytic activity for Cr(VI) photo-reduction, suggesting that the presence of surface SO42− provided an acid environment over the catalyst surface and favored the photo-reduction of Cr(VI).