Characterization of coupled NiO/TiO 2 photocatalyst for the photocatalytic reduction of Cr(VI) in aqueous solution

NiO/TiO2 coupled photocatalysts were fabricated by sol–gel process in this study. The coupled catalyst exhibited higher response of surface photovoltage than pure TiO2 indicating that the recombination of photogenerated electron–hole pairs was retarded by the inner electric field caused by p–n junction region. Photocatalytic reduction of hexavalent chromium in aqueous solution was studied using these NiO/TiO2 coupled photocatalysts prepared with various NiO loadings and calcined temperatures. The coupling of NiO strongly affects the performance of coupled photocatalysts, including the retard of phase transformation of TiO2, the decrement of particle size and the enhancement of separation efficiency of photogenerated electron–hole pairs. The addition of ethanol as a sacrificial agent significantly increased the photocatalytic activity of hexavalent chromium reduction using these NiO/TiO2 coupled photocatalysts.