Nanosecond Transient Absorption of Hydrated Electrons and Reduction of Linear Perfluoroalkyl Acids and Sulfonates

We report the rate constants (k_q) and activation energies (E_a) associated with the initial reduction of linear perfluoroalkyl carboxylates (PFxA, x = the number of carbons present in the surfactant) and perfluoroalkyl sulfonates (PFxS) by the hydrated electron (e_aq^–) as measured using temperature-dependent transient absorption spectroscopy. The reduction of PFxA and PFxS by e_aq^– displays a negligible dependence on the number of carbons present in the surfactant and occurs with an apparent k_q on the order of 10⁸ to 10⁹ M^–1 s^–1 with the k_q corresponding to PFxA reduction being on average two times smaller than those for PFxS. There are no significant differences in the E_a associated with PFxA or PFxS reduction; the magnitude of E_a (∼11 kJ mol^–1) is consistent with the reduction of PFxA and PFxS being a diffusion controlled process. These results are discussed within the framework of recent theoretical and experimental work on the degradation of PFxA and PFxS.