Self-sustaining reduction-oxidation coupling driven by hydrated electrons and reactive bromine species for synergistic PFAS defluorination and bromate detoxification in bromide-rich water under UV/sulfite

The persistent nature of per- and polyfluoroalkyl substances (PFAS) poses critical challenges for conventional water treatment technologies, particularly in bromide-rich matrices where coexisting bromates (e.g., coastal industrial wastewater or landfill leachate), a carcinogenic and mutagenic disinfection by-product amplifies remediation complexity. This study unveils a self-sustaining reduction-oxidation coupling (ROC) mechanism that synergistically harness hydrated electron (e aq − ) and reactive bromine species (RBS) to achieve simultaneous PFAS defluorination and bromate detoxification under UV/sulfite treatment. Through systematic experimentation and density functional theory (DFT) calculations, we demonstrate that bromate undergoes stepwise reduction to benign bromide ions while generating radical RBS (e.g., Br • and Br 2 •− ), which electrophilically attack intermediates of hydrogen-enriched fluorotelomer carboxylates (FTCAs) through hydrogen abstraction rather than directly targeting parent perfluorooctanoic acid (PFOA). This endogenous ROC process achieved 96 % defluorination of PFOA within 240 min at pH 10, outperforming conventional UV/sulfite treatment by 36.5 %. Notably, hydrogen-fluorine exchange strengthens adjacent C − F bonds with bond dissociation energy (BDE) up to 125 kcal mol −1 , rendering FTCAs resistant to e aq − but susceptible to bromine radicals, confirmed by Fukui function analysis. Meanwhile, this ROC process also works effectively in bromine-containing waters treated with UV/sulfite, highlighting its universal applicability in real-world water matrices. Across diverse water matrices (e.g., tap water or lake water), the system maintained >70 % defluorination efficiency. Additionally, this eₐ q ⁻/RBS-mediated ROC process demonstrated chain-length universality for C4-C8 perfluorocarboxylic acids and perfluorooctanesulfonic acid, while also detoxifying bromate to benign Br − , exemplifying its effectiveness in treating PFAS-contaminated waters with elevated bromide concentrations (e.g., seawater and brine), especially regions burdened with both PFASs and bromate contamination. By exploiting inherent water components as process catalysts, this work establishes a paradigm-shifting strategy for complex PFAS remediation without exogenous oxidant addition, offering dual environmental benefits through concurrent contaminant degradation and disinfection byproduct control.