Rapid As(III) removal by copper slag-derived oxygen vacancy-tailored amorphous Fe-Mn oxide: Interfacial oxygen activation and electron redistribution

Developing efficient and cost-effective processes for removing highly toxic As(III) from water is critical for environmental restoration. Herein, an amorphous Fe–Mn composite (A-CSM) rich in oxygen vacancies was synthesized via a one-pot process. Acid etching of a pretreated copper slag product created the chemical conditions that simultaneously enabled the in situ anchoring of MnO x clusters and induced a crystalline-to-amorphous transformation. The resulting strong Fe–O–Mn interfacial coupling drives interfacial electron redistribution, which upshifts the d-band center and thereby endows the material with unique capabilities for O 2 activation and arsenic adsorption. Leveraging abundant oxygen vacancies within the amorphous structure, A-CSM efficiently activates O 2 into •O 2 − radicals to drive spontaneous As(III) oxidation to As(V), while exposed unsaturated sites in amorphous FeO x domains provide rapid adsorption sites for As(V). Consequently, A‑CSM exhibits a broad pH range (3–9), rapid adsorption kinetics (achieving complete removal of 5 mg L −1 As(III) within 30 min, which is 24.7 times faster than its crystalline counterpart, CSM), the q max calculated by Langmuir model is 84 mg g −1 , and good reusability over five consecutive cycles. Mechanistic studies confirmed that the synergy between the acid etching‑induced amorphous structure and oxygen vacancies significantly reduces the O 2 adsorption energy while it upshifts the d‑band center. This effect lowers the energy barrier for As(III) oxidation/adsorption by approximately 48.9%, and substantially enhances •O 2 − generation. Adsorption primarily involves complexation, electrostatic interactions, and hydrogen bonding, which is consistent with a heterogeneous multilayer process as described by the Freundlich isotherm.