Highly efficient activation of sulfite with robust Mn-MOF catalysts for arsenite oxidation: Formation and contribution of Mn(V)

Conventional manganese(II) (Mn(II))-activated sulfite (S(IV)) systems remain constrained by slow reaction kinetics and inefficient Mn redox cycling, limiting their application in water treatment. Although non-radical pathways have been reported in certain metal/S(IV) systems, the role of high-valent Mn species remains unresolved. To address this knowledge gap, this study engineered a Mn-based metal-organic framework (Mn-MOF, denoted MM) featuring unsaturated Mn(II)−OH sites to achieve efficient S(IV) activation and redirect the oxidation process toward a non-radical route. Arsenite (As(III)) was employed as a model contaminant to systematically evaluate the MM/S(IV) system through kinetic analysis, reactive species identification, and surface characterization. The MM/S(IV) system enabled rapid As(III) oxidation (99.3% within 5 min, 0.64 min −1 ) at pH 7.4. The catalyst exhibited excellent stability during sequential operation (0.04% Mn leaching) and could be nearly fully regenerated. Mechanistic investigation revealed an interfacial pathway initiated by an O 2 -assisted, ligand-bridged electron transfer that yielded SO 3 •− /SO 5 •− . SO 5 •− subsequently oxidized Mn(II) to Mn(III), which then underwent two-electron oxidation by HSO 5 − to form Mn(V) as the dominant oxidant. This work demonstrates how MOF coordination engineering can redirect S(IV) activation toward a non-radical Mn(V)-mediated route, advancing the design of metal-centered oxidation systems for water remediation.