Advanced reduction processes (ARPs) in homogeneous and heterogeneous phases are an attractive and emerging method for destroying per- and polyfluoroalkyl substances (PFAS) that contain a wide variety of functional groups in aliphatic C-F chains. A number of experimental studies reported the second-order rate constants of homogeneous hydrated electrons with conventional organic compounds and the reaction mechanisms have been proposed. These include: (1) association with the π bond; (2) concerted dissociative cleavage; and, (3) stepwise dissociative cleavage. In order to understand the reaction between hydrated electrons and PFAS during ARPs, it is necessary to investigate and understand the reactivities of hydrated electrons with a wide variety of conventional organic compounds and PFAS. This will enhance our understandings of heterogenous reactivities of electrons with PFAS and enable predictions of the fate of PFAS destruction.  In this study, we used Density Functional Theory to calculate the one electron reduction potential of all possible reductive sites of three reaction mechanisms for 268 structurally diverse aliphatic compounds. We then determined the linear free energy relationships (LFERs) for each reaction mechanism between experimentally obtained literature-reported rate constants and the highest one electron reduction potential of each given compound. Finally, we determined the impact of neighboring functional groups on the reaction rate with the hydrated electron by investigating the effects of electron donating and electron withdrawing functional groups. The LFER determined for the stepwise mechanism of a C-F bond cleavage indicates the unique reactivity of hydrated electrons with PFAS. The investigation of the impacts of functional groups on reactivity sheds light onto the application of ARPs to the destruction of the large and structurally diverse class of PFAS compounds.

Reactivities of hydrated electrons with organic compounds and PFAS in aqueous-phase advanced reduction processes

ACS Spring Meeting 2021

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