The contamination of groundwater by polyfluoroalkyl surfactants (PFASs) has garnered increased attention and concern due to their inherent toxicity and unusual stability owing to the bond energy associated with C-F bonds. To address remediation of PFASs from soil and groundwater photodetached hydrated electrons (eaq-) obtained from UV-irradiation of a variety of inorganic anions has been widely studied. Among these anions SO32- and Fe(CN)64- have served as prototypical sources of eaq-. Using transient absorption spectroscopy, nanosecond to microsecond dynamics of the eaq- generated by both SO32- and Fe(CN)64- as a function of pH (3 &lt; pH &lt; 11) and temperature (10 °C &lt; T &lt; 50°C) was explored. The pH-dependent deactivation of eaq- is shown to differ between SO32- and Fe(CN)64- . We find that eaq- quenching in SO32- involves a Brönsted acid catalysis mechanism mediated by HSO3- with a rate constant of 1.2x108 M-1 s-1, while eaq- quenching in Fe(CN)64- is primarily mediated by H+ with a rate constant of 3.3x109 M-1 s-1. As a result Fe(CN)64- as an eaq- source displays a larger functional pH range capable of degrading perfluorooctanesulfonate (PFOS) at pH as low as 4 (compared to ~7 for SO32-) before efficacy is significantly hindered. Interestingly, the bimolecular rate constant corresponding to the PFOS reduction reaction with eaq- is on the same order of magnitude whether SO32- or Fe(CN)64- (2.3x109 M-1 s-1 or 5.42x109 M-1 s-1, respectively) suggesting similar reductive mechanisms. Arrhenius parameters obtained for the reaction between eaq- and PFOS in solutions containing either SO32- or Fe(CN)64- are consistent with similar reductive mechanisms irrespective of eaq- source.

Na2SO3 versus K4Fe(CN)6 as photochemical sources of hydrated electrons for reduction of PFASs: pH and temperature effects

2019 Spring National Meeting

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