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 10(8) to 10(9) 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 (similar to 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.

Automated summary

This study investigates the rate constants and activation energies associated with the reduction of linear perfluoroalkyl carboxylates and perfluoroalkyl sulfonates by hydrated electrons. The results show that the reduction process is diffusion-controlled with no significant differences in activation energies between the two surfactants, despite slightly different rate constants observed.