Photocatalytic removal of M2+ (=Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+) over new catalyst CuCrO2

The metal ions M2+ (Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+) are potentially toxic. Their electro deposition has been carried out in aqueous air-equilibrated CuCrO2 suspension upon visible illumination. The delafossite CuCrO2 is p-type semiconductor characterized by a low band gap (1.28 eV) and a long-term chemical stability. The corrosion rate is found to be 10(-2) mu mol m(-2) month(-1) in aqua regia. The oxide has been elaborated through nitrate route where the specific surface area is increased via the surface/bulk ratio. A correlation exists between the dark M2+ adsorption, the redox potential of M2+/0 couple and the conduction band of CuCrO2 positioned at -1.06 V-SCE.Ag+ cannot be photoreduced because of its positive potential located far above the valence hand. By contrast, Zn2+ is efficiently deposited due to the large driving force at the interface. The improved photoactivity of copper with a deposition percentage (90%) is attributed to the strong dark adsorption onto the surface catalyst. The results indicate a competitive effect with the water reduction; it has been observed that the M2+ deposition goes parallel with the hydrogen evolution. Such behavior is attributed to the low H-2 over voltage when ultra fine aggregate of M islands are photodeposited onto CuCrO2 substrate. (c) 2008 Elsevier B.V. All rights reserved.