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 °C, the system is mixed phases. When fired at 950 °C under nitrogen flow, the delafossite has been identified (CuO + CuFe2O4 → CuFeO2 + ½O2). 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 VSCE) is close to the flat band potential (+0.23 VSCE) 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 VSCE) 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 Cm (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.