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

Abstract In this work, the hematite α-Fe 2 O 3 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-Fe 2 O 3 indicates p type behavior with a conduction band (−1.14 V vs. SCE), more cathodic than the H 2 evolution (∼−0.8 V vs. SCE). The oxide was successfully tested for the hydrogen production under visible irradiation (29 mW cm −2 ). α-Fe 2 O 3 is photo-electrochemically stable in alkaline medium by hole consumption reactions involving X 2− (= SO 3 2− and S 2 O 3 2− ) as hole scavengers. The best photocatalytic activity for H 2 production was obtained on α-Fe 2 O 3 , calcined at 500 °C, in (Na 2 S 2 O 3 0.025 M, pH ∼ 13), with an average evolution rate of 0.015 cm 3  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 H 2 potential.