The UV-sulfite reductive defluorination with hydrated electrons (eaq–) is a promising technology for destructing 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 treatment 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 groups. 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 cleaved 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.

Near-quantitative defluorination of perfluorinated and fluorotelomer carboxylates and sulfonates with integrated oxidation and reduction

ACS Fall 2021

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