Sulfite activation by FeCo-MOF/gelatin aerogel for efficient As(III) removal from water: A singlet oxygen–dominated nonradical pathway

Transition metal-based sulfite activation systems are generally governed by radical pathways, whereas singlet oxygen-dominated nonradical routes for As(III) oxidation remain largely unexplored. In this study, a FeCo-MOF/gelatin aerogel (FCGA)–sulfite [S(IV)] synergistic system was constructed via a facile synthesis strategy for the efficient removal of As(III) from water. The system achieved nearly 100% removal of As(III) within 4 h at an initial concentration of 1086 μg/L, with an adsorption capacity of 111.71 mg/g (per g of FeCo-MOF in FCGA). The cyclic experiment showed that the removal efficiency of the FCGA/S(IV) system decreased by only ~15% after five runs, and negligible Fe/Co leaching was detected, confirming excellent stability and regeneration. Furthermore, the FCGA-packed column treated As(III) influent (>200 μg/L) up to ~6.2 L before exceeding the drinking water limit (10 μg/L), with an adsorption density of 0.37 mg/g, over twice that of commercial HFO@D201. Mechanistic investigations revealed that Co sites served as the critical centers for S(IV) activation, while Fe sites primarily provided stable adsorption sites for As(V). Notably, multiple characterization techniques combined with density functional theory (DFT) calculations verified that the system predominantly generated singlet oxygen (¹O₂) as the primary oxide species, while the contributions of SO₅^⋅−, SO₄^⋅−, and ^⋅OH were limited. This nonradical-dominated activation pathway expands the conventional understanding that S(IV) activation is mainly radical-driven. Overall, this work not only provides new ideas for constructing an S(IV) synergistic system dominated by nonradical oxidation but also offers theoretical and practical support for the development of efficient and environmentally friendly arsenic-contaminated water remediation technology.