Manganese oxide (MnO2) with iron oxide was prepared for arsenite (As(III)) oxidation and subsequent arsenate (As(V)) electrosorption in a capacitive deionization system (CDI). The chemical properties of MnO2 polymorphs, precipitated on goethite (α-FeOOH) nanoparticles, were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and BET surface area. The voltammetry results showed that the redox couple of Mn(III)/Mn(IV) mediate the catalytic electron transfer with respect to As(III)/As(V) redox equilibrium. The Mn site contributed a high diffusive current to the redox reactivity, meanwhile the Fe site better provided the double-layer electrostatic capacity for arsenic species. Electrolysis of arsenite under constant anodic potential mode (+1.0 V vs. Ag/AgCl) enabled assess the performance of the electrodes. The consecutive reaction kinetics was derived to determine the effect of Mn to Fe molar ratio on the rate of electrochemical oxidation and adsorption of arsenic. Among the polymorphs, γ-Mn0.2Fe0.8O exhibited the best arsenic adsorption capacity of 48 mg-As g-1, compared to that of α-FeOOH NPs (15 mg-As g-1) and γ-MnO2 (7 mg-As g-1), based on multilayer Langmuir adsorption model.

Integrated electrocatalytic oxidation and electrosorption of arsenic (III) using nano-textured bimetal composite of iron oxyhydroxide and manganese dioxide polymorphs

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ACS Fall 2022

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