Arsenite removal by using ZnAlFe mixed metal oxides derived from layered double hydroxides

Abstract

ZnAlFe mixed metal oxides (ZnAlFe-MMOs) were synthesized from layered double hydroxides (LDHs) preparedby the coprecipitation method at pH 9 using an initial weight composition of Zn2+ = 75%, Al3+ = 15% and Fe3+= 10%, with or without the addition of citric or oxalic acid. The solids were calcined at 400 ◦C to obtain the respective MMOs, which exhibited relatively high specific surface areas (165.3–63.8 m2 g− 1) and semiconductor properties active in the visible region (bandgap values (Eg) of 2.42–1.77 eV). The synthesized materials were tested for the removal of trivalent arsenic by adsorption and by photocatalysis under visible light irradiation (λ ≥ 420 nm). The best removal of As(III) by adsorption (65.9%) and by photocatalysis (99.9%) was obtained with the ZnAlFe-MMOs prepared in the absence of organic acids. The XPS results indicate the coexistence of As3+ and As5+ over ZnAlFe-MMOs after the photocatalytic reaction and also confirm the formation of Fe2+ sites on the hematite surface that enhances the removal of As(III). Raman measurements confirmed that, in the photo- catalytic experiments, As is largely retained as As(V) on ZnAlFe-MMOs, bound to Fe. The results of fluorescence of 7-hydroxycoumarin suggest that the photocatalyst produces HO•, which can be the main species for As(III) oxidation under UV–Vis irradiation. Moreover, ZnAlFe-MMOs exhibited a good reusability after regeneration making ZnAlFe-MMOs a promising material for arsenic decontamination in polluted water.