Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management

This study investigates critical structure–reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While CnF2n+1–COO– with variable fluoroalkyl chain lengths (n = 2 to 10) exhibited a similar rate and extent of parent compound decay and defluorination, the reactions of telomeric CnF2n+1–CH2CH2–COO– and CnF2n+1–SO3– showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of experimental results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF3COO–, leads to the elucidation of new mechanistic insights into PFAS degradation. Theoretical calculations on the C–F bond dissociation energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluor...