Preparation and photocatalytic H2-production on α-Fe2O3 prepared by sol-gel

In this work, the hematite α-Fe2O3 was synthesized by sol-gel method and characterized by X-ray diffraction and optical properties. The XRD patterns realized at different temperatures, show that pure hematite is obtained above 500 °C. The diffuse reflectance gives respectively direct and indirect optical transitions at 2.17 and 2.04 eV, in agreement with the red color. The capacitance measurement of α-Fe2O3 indicates p type behavior with a conduction band (−1.14 V vs. SCE), more cathodic than the H2 evolution (∼−0.8 V vs. SCE). The oxide was successfully tested for the hydrogen production under visible irradiation (29 mW cm−2). α-Fe2O3 is photo-electrochemically stable in alkaline medium by hole consumption reactions involving X2− (= SO32− and S2O32−) as hole scavengers. The best photocatalytic activity for H2 production was obtained on α-Fe2O3, calcined at 500 °C, in (Na2S2O3 0.025 M, pH ∼ 13), with an average evolution rate of 0.015 cm3 h−1 (mg catalyst)−1 and a quantum efficiency of 0.26%. The system shows a tendency toward saturation, due to the competitive reduction of end products with the water reduction and the cathodic shift of the H2 potential.