Photo-electrochemical Characterization of the Spinel CuFe2O4: Application to Ni2+ Removal under Solar Light

Abstract

The spinel CuFe2O4, prepared by nitrate route, is successfully tested for Ni2+ reduction under solar light. CuFe2O4 is a narrow band gap semiconductor with a direct optical transition at 1.66 eV. The electro-kinetic parameters indicate a good electrochemical stability with a high O2-over voltage. The energy diagram shows the feasibility of CuFe2O4 for Ni2+ deposition under illumination. At pH ~ 7, the conduction band (−1.22 VSCE) is located below the Ni2+ level (−0.60 VSCE), leading to a spontaneous nickel reduction under solar light. The charge transfer is mediated via TiO2. The photocatalytic performance is optimized with respect to the Ni2+ concentration and the catalyst dose. 72 % of Ni2+ (30 ppm) are reduced after ~5 h of exposure to sunlight (115 mW cm−2) on the hetero-system CuFe2O4/TiO2 (mass ratio = 1/1). The photochemical hydrogen evolution, an issue of energy concern, occurs competitively on ultra fine Ni aggregates. The improved performance {0.43 cm3 mn−1 (g catalyst)−1} is due to intimate contact of Ni/TiO2 and low over-voltage on nickel clusters.