Preparation,characterization and application of CuCrO_2/ZnO photocatalysts for the reduction of Cr(VI)

摘要

The delafossite CuCrO2 elaborated by sol-gel from 40nm diameter colloid is optically active in the visible region.It is characterized physically and photoelectrochemically.The microstructure is fairly homogenous with a mean crystallite size of ca.2μm.The optical gap(1.30eV),determined from the diffuse reflectance,is well suited to the sunlight spectrum.The Mott Schottky plot is characteristic of P-type conductivity with a flat band potential of-0.26VSCE.As application,the photoreduction of chromate is successfully achieved in air-equilibrated suspension CuCrO2/ZnO(1/1).CuCrO2 is photoactivated by visible light and the electrons in the conduction band(-1.34VSCE)are injected to ZnO.In the presence of salicylic acid,a conversion of Cr(VI)to Cr(III)of 57% is obtained under optimal conditions(pH3 at 25°C,5×10-4mol/L)because of the HCrO4 dark adsorption onto ZnO(4HCrO4-+3C7H6O3+18O2+16H+→4Cr3++21CO2+19H2O,△G0 =-557kcal/mol).Prolonged illumination is accompanied by a deceleration in the photoactivity owing to the competitive water reduction,an issue of energetic concern.The hetero-system exhibits self sensitization for hydrogen production with an evolution rate of 149μmol/(hr·g).