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)-O-center dot 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 similar to bicarbonate > chloride) owing to VUV radiation attenuation (Cl- and HCO3-) and/or (OH)-O-center dot 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 (e(aq)(-)) 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.