Degrading per- and polyfluoroalkyl substances (PFASs) is challenging because of the highly recalcitrant C–F bonds that comprise these molecules. Both oxidative and reductive chemistries have been used to address this issue with varying results. While the UV/sulfite system has been widely used to study the overall degradation of both perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs), significantly fewer studies exist on the transient kinetics of the initial reduction reaction. UV irradiation of an aqueous sulfite solution results in the formation of a hydrated electron which then reacts with other species in solution. Using nanosecond transient absorption spectroscopy to probe the hydrated electron in solutions of sulfite, we have found that on this timescale and at PFOA concentrations &lt; 1 mM, we did not observe any quenching of the electron by PFOA. This result was unexpected especially since we observed quenching of the electron with PFOS &lt; 1 mM in solutions of sulfite and quenching with both PFOS and PFOA in solutions of ferrocyanide. Additionally, it is well documented that the UV/sulfite system is able to effectively degrade PFOA over several hours. In this presentation, we will discuss our control experiments for ionic strength, using ferrocyanide as the hydrated electron precursor, using mixed ferrocyanide/sulfite solutions to generate hydrated electrons for PFOA reduction, and explore the effects of PFOA concentration on electron quenching. This work is important for understanding the initial reaction kinetics of PFOA reduction by hydrated electrons to better understand the overall degradation mechanism, which can be used to inform the design of safer, more efficient methods for treating PFAS contaminated water.

PFOA quenching of hydrated electrons in ferrocyanide and sulfite solutions

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