Photoreduction of Chromate Cr(VI) under Visible Light Using CuCr2O4/WO3 Hetero-system Photocatalyst

This work aims to develop a CuCr2O4 nanoparticle at 850°C in air, and WO3 nanoparticles by one-step hydrothermal method. The novel CuCr2O4/WO3 hetero-system is successfully used for the photoreduction of Cr(VI) (30 mg/l) under sunlight. Both materials are characterized by the structural, physical and electrochemical techniques. The energy of the spinel gap (CuCr2O4)(Eg = 1.78 eV) is determined by diffuse reflectance and corresponds to the solar spectrum. Capacitance measurements indicate p-type conduction with a flat band potential of 0.62VSCE. For WO3: a direct gap (Eg = 2.90 eV) with n-type behavior with an electron density (ND = 5.4 × 1016 cm–3) and a flat band potential of 0.25VSCE. Optimization of the experimental conditions of chromate photoreduction at pH ~4 (adipic acid = 5 × 10–1 mol /L, CuCr2O4/WO3 (1/1) and a dose of 1mg/L) led to a conversion of 92% of 30 mg/L of Cr (IV) in Cr(III) within 180 min under sunlight. The photocatalytic performance is due to the synergy of the p–n hetero-system whose electrons generated in the conduction band of CuCr2O4 excited by solar light are injected into CB-WO3). The role of adipic acid is essential; it improves the reduction of Cr(VI) under solar irradiation. The photoreduction kinetics follows a pseudo-first order model with a constant rate of 5.51 × 10–3 min–1.