New insights into ferric iron-facilitated UV254 photolytic defluorination of perfluorooctanoic acid (PFOA): Combined experimental and theoretical study

UV/Fe 3+ -facilitated PFOA defluorination was often reported and recognized to proceed through a “ligand-to-metal charge transfer (LMCT)” mechanism in the literatures. Sufficient Fe 3+ supply is important for sustaining the LMCT reaction pathway. In this study, an interesting “excessive defluorination” was observed, even the continuous Fe 3+ supply was cut off, implying a parallel mechanism strengthening PFOA defluorination . Based the results of intermediate products detection, 19 F NMR analysis, and exploration of electron density alternation, transition energy evolution, and bonds characteristics, remarkable electron density perturbation in [PFOA-Fe] 2+ was revealed. This effect was triggered by the complexation between PFOA anion and Fe 3+ , diminishing electron shielding on the perfluorinated carbon chain. Hence, the dissociation energy of C–C bonds was reduced by maximally 53% (C4-C5). Once attacked by high-flux UV 254 photons, the perfluorinated carbon chain underwent scission , and subsequent defluorination was achieved via hydrolysis reactions. This parallel mechanism cooperated with the LMCT mechanism, leading to the observed “excessive defluorination.” The degree of UV/Fe 3+ -synergized PFOA defluorination depended on UV 254 photon flux and Fe 3+ dosage. High UV 254 intensity guaranteed fast defluorination kinetics. A [Fe 3+ ]/[PFOA] molar ratio near 1 showed the best UV/Fe 3+ synergic effect on PFOA defluorination.