Photochemical degradation pathways and near-complete defluorination of chlorinated polyfluoroalkyl substances

Chlorinated polyfluoroalkyl substances (Cl x –PFAS) are an emerging class of pollutants worldwide. Here we demonstrate near-complete defluorination (that is, cleaving most C–F bonds) of diverse Cl x –PFAS structures and the reaction mechanisms. First, we used ultraviolet/sulfite to degrade various carboxylic acids ( n = 1, 2, 4 and 8 Cl–C n F 2 n COO − and n = 1, 2 and 3 Cl–(CF 2 CFCl) n CF 2 COO − ) and an ether sulfonic acid surfactant (F-53B, Cl–(CF 2 ) 6 –O–(CF 2 ) 2 SO 3 − ). The initial reaction with a hydrated electron cleaved the C–Cl bond. The resulting fluorocarbon radicals ( • CF 2 – on the terminal and – • CF– in the middle) yield C–H or C–SO 3 − , or form a dimer. In particular, we identified a novel reaction pathway with the unexpected HO • radical to cleave the C–C bond (for – • CF–) and yield –COO − . This pathway is critical for rapid and deep defluorination at 90–96% from carboxylic acids and 76% from F-53B. The following treatment with heat/persulfate at pH >12 achieved ~100% overall defluorination from carboxylic acids and 93% from F-53B without producing toxic ClO 3 − from Cl − . This study advances the understanding of PFAS transformation in engineering systems. It also suggests a synergy between molecular design and degradation technology towards sustainable management of fluorochemicals.