Synergies of hydrated electron, carbon dioxide anions radicals and hydroxyl radicals for enhancing the decomposition and defluorination of perfluorohexanesulfonate

Abstract

Removal of perfluorinated compounds (PFCs) from water remains a critical challenge in water treatment. This study introduces an ionizing radiation system coupled with formate (IR/HCOO^–) for the efficient defluorination and degradation of perfluorohexane sulfonate (PFHxS). These results demonstrate that the degradation and defluorination rates of PFHxS increase with higher absorbed doses and HCOO^– concentrations. At an initial PFHxS concentration of 5 mg/L, HCOO^– concentration of 10 mM, and absorbed dose of 20 kGy, the decomposition and defluorination efficiencies reached 24.8 % and 18.9 %, respectively. High-resolution mass spectrometry revealed that PFHxS degradation primarily occurred through H/F exchange, hydroxylation, desulfurization, and carbon dioxide addition. Mechanistic analysis identified hydrated electrons as the key species initiating PFHxS desorption, with subsequent synergistic contributions from hydrated electrons, hydroxyl radicals, and carbon dioxide radicals, driving deep defluorination and decomposition. The IR/HCOO^– system was effective over a pH range of 5–11 and demonstrated strong resistance to interference from inorganic anions. This study is the first to elucidate the synergistic roles of hydrated electrons, hydroxyl radicals, and carbon dioxide radicals in PFHxS defluorination and degradation and provides a promising approach for removing PFCs from water.