Efficient defluorination of perfluorooctanoic acid enabled by single-atom Cu/reduced graphene oxide electrocatalytic anode and peroxymonosulfate activation

In this study, an electrocatalytic system using reduced graphene oxide supported single-atom copper (SA-Cu/ rGO) anode was constructed for perfluorooctanoic acid (PFOA) defluorination. The successful doping of SA-Cu elevated the oxygen evolution potential and electrochemical active surface area of the anode and provided high electrocatalytic properties. Under optimum initial conditions with a peroxymonosulfate (PMS) concentra-tion of 10 mM, a current density of 15 mA & sdot;cm- 2, and an unadjusted pH of 7.75, the SA-Cu/rGO system achieved 98.8% removal ratio, 92.5% defluorination, and 94.4% mineralization of 20 mg & sdot;L-1 PFOA in 120 min. Kinetic studies indicate PFOA degradation following a pseudo-first-order model, with a rate constant of 4.7 x 10-2 min-1. The presence of PMS in the electrocatalytic system significantly improved the degradation rate and defluorination ratio. Radical trapping and quenching experiments confirmed that both & sdot;OH and & sdot;SO - 4 radicals contributed to PFOA degradation, with & sdot;SO4- playing a more important role in defluorination. The system show high flexibility in initial PFOA concentrations (0.2-20 mg & sdot;L-1) and environmental pH values (3.0-10.0), as well as good durability. The electrocatalytic degradation mechanism of PFOA was proposed through determination of intermediates and density functional theory (DFT) calculation. The total short-chain perfluorocarboxylic acids (PFCAs) intermediates generated throughout the degradation were far from sufficient recovery of the PFOA loss, indicating that apart from the & sdot;OH mediated decarboxylation-hydroxylation-elimination-hydrolysis (DHEH) pathway, the & sdot;SO4- mediated decarboxylation-hydroxylation-oxidation-decarbonyl fluoride (DHOD) pathway may play a significant role in the near-complete defluorination and mineralization of PFOA. Moreover, DFT calculations suggest that the DHOD pathway is energetically favorable over DHEH. This study provides a further understanding of the defluorination mechanism of PFOA in electrocatalytic systems and demonstrates that electrochemical degradation with single-atom copper catalyst is an promising method for PFOA remediation in aqueous environment.