Reduction' of chromium (VI) on the hetero-system CuBi2O4/TiO2 under solar light

The CuBi2O4/TiO2 heterojunction was tested with success for the photo-catalytic reduction of chromate ions under sunlight. CuBi2O4, prepared by nitrate process, was characterised photo-electrochemically. The oxide is stable against photo corrosion by consumption of holes in presence of oxalic acid. The light absorption promotes electrons in the conduction band of the sensitizer (CuBi2O4) with a very negative potential (-1.74 V-SCE) to participate in the exchange of the electron with HCrO4-. The enhanced activity is due to electron injection of activated CuBi2O4 into TiO2-CB (-0.97 V-sca). The band gap of the semiconductor is 1.50 eV with a direct optical transition. This compound is a p-type semiconductor with a flat band potential of -0.39 V-SCE and activation energy of 0.18 eV. The electrochemical impedance spectroscopy was undertaken to study the semiconductor/electrolyte interfacial phenomena. The photoactivity on the heterojunction is strongly enhanced. A CuBi2O4 remarkable performance is obtained in less than 4 h for a concentration of 30 mg in (Cr (VI)) at pH similar to 4 and a dose of 1 mg/mL; a 98% reduction has been obtained. The kinetic of chromate photoreduction is well described by the Langmuir-Hinshelwood model. The chromate elimination obeys to a pseudo-first order kinetic with an apparent rate constant of 0.014 min(-1).