HCrO 4 − reduction on the novel heterosystem La 2 CuO 4 /SnO 2 under solar light

The chromate reduction is successfully achieved over the new heterosystem La 2 CuO 4 /SnO 2 under solar light. La 2 CuO 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 adsorbedHCrO 4 − . The Mott‐Schottky plot of La 2 CuO 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 reduceHCrO 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. © 2014 American Institute of Chemical Engineers Environ Prog, 2014 34: 744–750, 2015