Photocatalytic reduction of cadmium over CuFeO2 synthesized by sol-gel

The Cd2+ photo-electrodeposition was successfully carried out in air-equilibrated aqueous CuFeO2 suspension. The delafossite CuFeO2 is p-type semiconductor characterized by a low optical gap, properly matched to the sun spectrum, and a long term chemical stability in neutral solution. It has been elaborated by the sol-gel technique where the specific surface area is increased via the surface/bulk ratio. The TG/DSC plots and IR spectra show that the solid phases are formed only at temperatures exceeding 400 and at 700 degrees C, the system is mixed phases. When fired at 950 degrees C under nitrogen flow, the delafossite has been identified (CuO + CuFe2O4 -> CuFeO2 + 1/2O(2)). All the XRD lines index in a hexagonal unit cell with the lattice constants a = 284.2 and c = 169.4 pm. The photocurrent onset potential (+0.35 V-SCE) is close to the flat band potential (+0.23 V-SCE) determined from the capacitance measurement. CuFeO2/Cd2+ solution is a self photo-driven system. the absorption of light promotes electrons into CuFeO2-CB with a potential (-0.93 V-SCE) sufficient to reduce Cd2+. This occurs because of the dark Cd2+ adsorption on the surface powder. The system was optimized with respect to the following physical parameters: pH 6.8, Cd2+ (100 ppm) and a mass concentration C-m (1 mg catalyst/ml solution). The hetero-system CuFeO2/TiO2 has been also reported for a comparative purpose. Prolonged irradiation (>50 min) was accompanied by a pronounced decrease in the rate of Cd-deposition owing to the competitive water reduction. Indeed, the generated bi-functional CuFeO2/Cd particles account for the low over-potential of hydrogen and favour its evolution in aqueous solution. (C) 2008 Elsevier B.V. All rights reserved.