HCrO4- reduction on the novel heterosystem La2CuO4/SnO2 under solar light

The chromate reduction is successfully achieved over the new heterosystem La2CuO4/SnO2 under solar light. La2CuO4 is a narrow band gap semiconductor with a direct optical transition of 1.27 eV. Its photoelectrochemical characterization is undertaken to predict the electrons injection in SnO2, the latter acts as electrons bridge to adsorbed HCrO4-. The Mott-Schottky plot of La2CuO4 is characteristic of p-type conductivity with a flat band potential of -0.46 V-SCE. Hence, the conduction band (-1.62 V-SCE) is cathodic enough to reduce HCrO4- into Cr3+. The chrono-potentiometry shows that the adsorption is reached after approximate to 40 min. and averages 15% for an initial concentration of 30 mg/L at pH = 4. The photoactivity is strongly enhanced in presence of oxalic acid as holes scavenger, which hinders the recombination of electron/hole pairs. A complete reduction (30 mg/L) occurs in less than 2 h under solar irradiation. The kinetic of the chromate reduction is well described by the Langmuir-Hinshelwood model with an apparent rate constant of 0.23 mn(-1). The saturation beyond 75 min is due to the competitive water reduction which inhibits considerably the chromate reduction. The reutilization of the heterosystem shows a negligible deactivation effect and the heterosystem could be promising for the water depollution. (c) 2014 American Institute of Chemical Engineers Environ Prog, 2014 34: 744-750, 2015