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

High Resolution Image Download MS PowerPoint Slide The UV-sulfite reductive treatment using hydrated electrons ( e aq – ) is a promising technology for destroying perfluorocarboxylates (PFCAs, C n F 2n+1 COO – ) 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, C n F 2n+1 –CH 2 CH 2 –COO – ) and sulfonates (FTSAs, C n F 2n+1 –CH 2 CH 2 –SO 3 – ) 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, C n F 2n+1 –SO 3 – ), 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.