Photocatalytic reduction of Cr(VI) on nanosized Fe2O3 supported on natural Algerian clay: Characteristics, kinetic and thermodynamic study

Nanosized alpha-Fe2O3 (hematite) supported on Algerian clay (Fe2O3/clay), by impregnation is successfully used for the chromate reduction under visible light. The hetero-system is investigated by X-ray diffraction, FT-IR, scanning electron microscopy and energy dispersive spectroscopy (EDS) analysis. The microscopic observation shows that the supported hematite alpha-Fe2O3 is uniformly spread on the clay which consists mainly of similar to 80% illite. The BET measurement gives a specific surface area of 140 m(2) g(-1). The photo-electrochemical characterization is undertaken to assess the photoactivity. The sensitizer Fe2O3 has a conduction band (-0.76 V-SCE) more cathodic than the chromate level (similar to 0.1 V-SCE). As application. the reduction is optimized with respect to catalyst dosage. Cr(VI) concentration, pH and temperature. A remarkable performance is obtained in less than 3 h for a concentration of 50 ppm at pH similar to 2 with a dosage of 1 mg/mL. The chromate removal obeys to a pseudo first order kinetic with an apparent constant of 0.013 min(-1). The negative enthalpy and free energy indicate a spontaneous and exothermic process. Upon solar irradiation, the reduction of 100 ppm Cr(VI) solution is completed after only 50 min. (C) 2012 Elsevier B.V. All rights reserved.