Synergistic photocatalysis of Cr(VI) reduction and 4-Chlorophenol degradation over hydroxylated α-Fe2O3 under visible light irradiation.

A series of Fe2O3 materials with hydroxyl are synthesized in different monohydric alcohol (C2-C5) solvents by solvothermal method and characterized by XRD, BET, XPS, TG and EA. The amount of hydroxyl is demonstrated to be emerged on the surface of the as-synthesized Fe2O3 particles and their contents are determined to be from 7.99 to 3.74 wt%. The Cr(VI) reduction experiments show that the hydroxyl content of Fe2O3 samples exacts great influence on the photocatalytic activity under visible light irradiation (λ>400 nm) and that the Fe2O3 sample synthesized in n-butyl alcohol exhibits the optimal photocatalytic activity. The synergistic photocatalysis for 4-Chlorophenol (4-CP) degradation and Cr(VI) reduction over above Fe2O3 sample is further investigated. The photocatalytic ratio of Cr(VI) reduction are enhanced from 24.8% to 70.2% while that of 4-CP oxidation are increased from 13.5% to 47.8% after 1 h visible light irradiation. The Fe2O3 sample keeps good degradation rates of mixed pollutants after 9 runs. The active oxygen intermediates O2(-)˙, ˙OH and H2O2 formed in the photoreaction process are discovered by ESR measurement and UV-vis test. The photocatalytic degradation mechanism is proposed accordingly.