Vacuum-UV Radiation Capable of Catalyst-Free Decomposition of 6:2 FTSA: The Transformation Mechanism and Impacts of the Water Matrix

This study explores the potential of the vacuum-UV (VUV) process for remediating telomer-PFAS, a significant class of alternative per- and polyfluoroalkyl substances (PFAS). We assess (i) the degradability and transformation mechanism of 6:2 fluorotelomer sulfonic acid (6:2 FTSA), (ii) the impacts of background water constituents on the process, and (iii) the synergistic effects of VUV oxidative/reductive processes for enhancing the extent of 6:2 FTSA defluorination. In situ •OH formation upon VUV photolysis of water led to 6:2 FTSA transformation to a suite of intermediates where perfluorocarboxylic acids (PFCAs) were the major final byproducts of the process (68% of F-containing byproducts). Investigation of the effects of background water constituents showed marginal adverse impacts of ionic strength, while chloride, bicarbonate, and natural organic matter (NOM) exhibited notable inhibitory effects (NOM ∼ bicarbonate > chloride) owing to VUV radiation attenuation (Cl– and HCO3–) and/or •OH scavenging (HCO3– and NOM). Catalyst-free transformation of 6:2 FTSA to PFCAs in the VUV process integrated by the complementary contribution of a hydrated electron (eaq–) generated in the UV/VUV/sulfite process achieved 2.6 and 1.7 times greater degradation and defluorination efficiencies of 6:2 FTSA with the same energy/chemical consumption. These insights offer valuable solutions for addressing telomer-PFAS challenges.