Near-Quantitative Defluorination of Perfluorinated and Fluorotelomer Carboxylates and Sulfonates with Integrated Oxidation and Reduction

Abstract

The UV-sulfite reductive treatment using hydrated electrons (eaq-) is a promising technology for destroying perfluorocarboxylates (PFCAs, CnF2n+1COO-) in any chain length. However, the C-H bonds formed in the transformation products strengthen the residual C-F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-) and sulfonates (FTSAs, CnF2n+1-CH2CH2-SO3-) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidation (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixture of PFCAs. This process also cleaved 35-95% of C-F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent reduction (Red) with UV-sulfite achieved deep defluorination of the PFCA mixture for up to 90%. The following use of HO•to oxidize the H-rich residues led to the cleavage of the remaining C-F bonds. We examined the efficacy of integrated oxidative and reductive treatment of n = 1-8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, CnF2n+1-SO3-), n = 1-8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quantitative overall defluorination (97-103%), except for n = 7,8 fluorotelomers (85-89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technology design and water sample analysis.