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) 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), 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, rendering FTCAs resistant to e 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⁻/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.

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