Coupled Oxidation and Sequestration of Sb(III) via Oxygenation of Engineered FeS Nanoparticles: Dominant Role of Superoxide and Structural Incorporation

The oxidative transformation of highly toxic Sb(III) to less toxic Sb(V) is a critical detoxification pathway. While engineered carboxymethyl cellulose-stabilized FeS nanoparticles (CMC-FeS) have been traditionally applied for in situ remediation of water and soil under anoxic environments, information on coupled transformation of CMC-FeS and Sb(III) under oxic conditions has been limited. This study explored the oxidation and immobilization process and dynamic quantitative mechanisms of Sb(III) by CMC-FeS under oxic conditions. Experimental evidence integrated with density functional theory calculations revealed that structural Fe(II) activated adsorbed O2 via single-electron transfer. Crucially, superoxide radicals (•O2–) were identified as the dominant oxidant, contributing 77.5% to Sb(III) oxidation, significantly outperforming hydroxyl radicals (•OH, 22.5%). Concurrently, CMC-FeS was transformed into lepidocrocite, effectively sequestering the generated Sb(V) predominantly through structural incorporation into the Fe (oxyhydr)oxide lattice. At equilibrium, 73.6% of Sb(III) was adsorbed, of which 98.0% was oxidized to Sb(V), with 52.8% of the generated Sb(V) retained in the solid phase. The Sb(III) oxidation increased with increasing CMC-FeS dosage, and the highest oxidation was observed at neutral pH. These findings elucidate the oxidative capacity of FeS in oxic environments and underscore the previously overlooked roles of •O2– and Fe (oxyhydr)oxides, suggesting that coupling CMC-FeS with oxygen offers a sustainable strategy for remediating redox-active contaminants.