Characterization of CuCo2O4 Prepared by Nitrate Route: Application to Ni2+ reduction under visible light

Abstract

Ni2+ was reduced by photo-catalysis on the hetero-system p-CuCo2O4 /n-TiO2 under visible light. The spinel CuCo2O4, elaborated by nitrate route, was characterized photo-electrochemically. A direct forbidden band of 1.44 eV was determined from the diffuse reflectance. It exhibits p-type behavior and a conduction band (- 1.11 VSCE) made up of Co3+: eg orbital, more cathodic than the Ni2+ level (-0.68 VSCE). The rate of Ni deposition increases with increasing the spinel dose and peaks for the optimal ratio CuCO2O4/TiO2 (50/50) with 60 % conversion (30 mg L−1) in less than 3 h. This occurred because TiO2 mediates the electron transfer to adsorbed Ni2+ ions. The decrease of the conversion rate on the system CuCo2O4/TiO2 over illumination time is due to the competitive water reduction onto deposited Ni clusters. The in situ photo-deposition of Ni-clusters forms hetero-system CuCo2O4/TiO2/Ni intimately contacted and the H2 formation is highly improved because of the low Ni over-potential. H2-evolution rate of 4.69 μmol min−1 g−1 and a quantum yield of 0.68 % were obtained under a light flux of 2.09 × 1019 photons s−1.