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

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.