Chromate reduction on the novel hetero-system LiMn2O4/SnO2 catalyst under solar light irradiation

In this work, the photocatalytic reduction of chromate ions was studied on a new hetero-system LiMn2O4/SnO2 under solar irradiation in the presence of salicylic acid as a hole scavenger. The nanocrystalline manganate (LiMn2O4) was synthesized by sol gel method and crystallizes in the spinel structure. The X-ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy and UV-Vis diffuse reflectance were used to characterize the as-prepared powder. The diffuse reflectance spectrum permits to determine a direct optical band gap (E-g) of 2.04 eV. The spinel LiMn2O4 exhibits n-type behavior, evidenced by the capacitance measurement. The detoxification of water containing Cr(VI) with the hetero-system LiMn2O4/SnO2 as photocatalyst was successful and completed under optimal conditions (initial concentration: 30 mg/L, pH similar to 4, catalyst dose: 1 mg/mL, T similar to 25 degrees C). The photocatalytic mechanism of the redox reaction taking place on the LiMn2O4/SnO2 surface was suggested.