Linear perfluoroalkyl carboxylate reduction dynamics with solvated electrons from ferrocyanide and sulfite

Abstract

The initial reduction dynamics of perfluoroalkyl substances (PFASs) by the hydrated electron, e_aq⁻, is a topic of great interest and importance due to the pervasive environmental presence of PFAS in soil and waters and the need to remediate the contamination. Understanding how PFAS behaves in water, including the potential effect of aggregation on the apparent PFAS reduction rate constant (k_PFAS) is, therefore, of paramount importance. In this publication we re-examine the proposition that submicellar aggregation decreases the apparent k_PFAS for sodium perfluorocarboxylates of varying chain lengths (NaPFxA, x = number of carbons in the PFAS backbone, ranging from 4 to 8) using transient absorption spectroscopy. We compare the dynamics for e_aq⁻ quenching by NaPFxA in aqueous solutions of ferrocyanide, Fe(CN)₆⁴⁻, and sulfite, SO₃²⁻. The results demonstrate that the apparent rate constant depends on the choice of e_aq⁻ precursor. We demonstrate that the ionic strength of the solution and the counterion of the PFxA salt both affect the measured rate constant of PFAS reduction by e_aq⁻. The results presented here help to better understand PFAS degradation by advanced reduction processes.