HCrO_4~- Reduction on the Novel Heterosystem La_2CuO_4/SnO_2 Under Solar Light

摘要

The chromate reduction is successfully achieved over the new heterosystem La_2CuO_4/SnO_2 under solar light. La_2CuO_4 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 SnO_2, the latter acts as electrons bridge to adsorbed HCrO_4~-. The Mott-Schottky plot of La_2CuO_4 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 HCrO_4~- into Cr~(3+). The chrono-potentiometry shows that the adsorption is reached after ～ 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.