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

Abstract

Advanced reduction processes (ARPs) that generate reactive electrons in homogeneous solution and heterogeneous electrochemical or catalytic processes are effective in degrading oxidized forms of organic and inorganic contaminants. However, the detailed mechanisms of compounds with multiple functional groups and the effect of those functional groups on the reactivities of these compounds toward electrons have not been elucidated. In this study, we use density functional theory to calculate the aqueous-phase one electron reduction potential of 251 conventional organic compounds containing a wide variety of functional groups. We investigate three possible elementary reaction mechanisms, namely, the associative, concerted and stepwise cleavage mechanisms, at all possible reactive sites and determine the linear free energy relationships (LFERs) between the experimentally measured rate constants of hydrated electrons (e_aq⁻) and the values. In addition, we use the 75 priority per- and polyfluoroalkyl substance (PFAS) subsets from the United States Environmental Protection Agency (U.S. EPA) to calculate the values of all possible elementary reactions of each PFAS to determine their dominant reaction mechanisms and reactive sites. LFERs of conventional organic compounds are used to predict the reactivities of e_aq⁻ with PFASs, which can be used as a screening tool to evaluate the electron-induced degradability of thousands of PFASs for both homogeneous and heterogeneous reduction processes. Finally, we develop a kinetic model to investigate the impact of an accurate rate constant prediction on the fate of an environmentally relevant organic compound induced by e_aq⁻ in a homogeneous aqueous-phase ARP.