Efficient photocatalytic oxidation of arsenite from contaminated water by Fe2O3-Mn2O3 nanocomposite under UVA radiation and process optimization with experimental design

Abstract

The efficiency of photocatalytic oxidation process in arsenite (As(III)) removal from contaminated water by a new Fe₂O₃-Mn₂O₃ nanocomposite under UV_A radiation was investigated. The effect of nanocomposite dosage, pH and initial As(III) concentration on the photocatalytic oxidation of As(III) were studied by experimental design. The synthesized nanocomposite had a uniform and spherical morphological structure and contained 49.83% of Fe₂O₃ and 29.36% of Mn₂O₃. Based on the experimental design model, in photocatalytic oxidation process, the effect of pH was higher than other parameters. At nanocomposite concentrations of more than 12 mg L^-1, pH 4 to 6 and oxidation time of 30 min, photocatalytic oxidation efficiency was more than 95% for initial As(III) concentration of less than 500 μg L^-1. By decreasing pH and increasing the nanocomposite concentration, the photocatalytic oxidation efficiency was increased. Furthermore, by increasing the oxidation time from 10 to 240 min, in addition to oxidation of As(III) to arsenate (As(V)), the residual As(V) was adsorbed on the Fe₂O₃-Mn₂O₃ nanocomposite and total As concentration was decreased. Therefore, Fe₂O₃-Mn₂O₃ nanocomposite as a bimetal oxide, at low doses and short time, can enhance and improve the efficiency of the photocatalytic oxidation and adsorption of As(III) from contaminated water resources. Furthermore, the energy and material costs of the UV_A/Fe₂O₃-Mn₂O₃ system for photocatalytic oxidation of 1 mg L^-1 As(III) in the 1 L laboratory scale reactor was 0.0051 €.

Keywords: Arsenite; Contaminated water; Experimental design; Nanocomposite; Photocatalytic oxidation.