Manganese doping of hematite enhancing oxidation and bidentate-binuclear complexation during As(III) remediation: Experiments and DFT calculation

Abstract

Iron and manganese oxides are commonly found in nature, such as hematite and pyrolusite, which strongly affect the migration and transformation of As(III). In this study, a series of hematite materials modified by MnO2 (Hm-Mn) were synthesized to achieve the adsorption-oxidation bifunctionality of hematite toward As(III). The maximal As(III) adsorption capacity of Hm-Mn (80.0 mg g−1) was nearly 3 times higher than that of pure hematite (28.5 mg g−1). The ratio of As(V) immobilized on Hm-Mn reached 71.5%, which was significantly higher than that of Hm (17.9%). The kinetic results indicated that chemisorption is the dominant adsorption behavior. Density functional theory (DFT) calculations revealed that manganese modification reduced the adsorption and oxidation energy of Hm-Mn, confirming that manganese modification was beneficial to both of the adsorption and oxidation of As(III). Bidentate-binuclear complex was the primary coordination type of arsenic binding on the Hm-Mn facets. Crystal orbital Hamilton population (COHP) analysis implied that the bonding of Hm-Mn with arsenic was stable. Specially, the bonding of Fe-O-As was stronger than that of Mn-O-As. Altogether, Hm-Mn provides a feasible solution for arsenic-contaminated water, and the fundamental theoretical data offer new perspective for understanding the remediation mechanisms of variable valence metal pollutants.