Exploring the initial bond activations of PFAS on zero-valent iron

Abstract

Ever since appearing in our society nearly 80 years ago, per- and polyfluoroalkyl substances (PFAS) have become a staple chemical used in a variety of consumer medical products. Unfortunately, these chemicals have been shown to be linked to a variety of health issues, including but not limited to, cancers, low birth rates, and suppressed immune systems. New guidance from the United States Environmental Protection Agency (USEPA) have given public water systems until 2029 to bring down the concentrations of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), two major PFAS molecules, to concentrations below 4.0 parts per trillion. In order to meet these goals it is imperative to develop chemical means of degrading PFAS molecules, which is hampered by the high strength C–F bond found in these compounds. Heterogeneous catalysis offers an attractive route for the degradation of these bonds, however progress along these lines have been hampered by a lack of knowledge regarding PFAS interactions and reaction energetics on a variety of catalyst materials. In a recent study (Jenness and Shukla, Env. Sci. Adv., 2024, 3, 383) we explored a set of 27 transition metals in order to assess their ability to cleave the C–F bond and found iron (Fe) to be a promising candidate as a PFAS degradation catalyst. Consequently, in this study we focus on the (110) surface of Fe and explore how perfluorobutanoic acid (PFBA, a common PFAS molecule and stand-in for PFOA) can react with the catalytic surface sites using density functional theory (DFT). Through the calculation of the thermodynamics and kinetics of 10 reactions, we are able to build a simple kinetic model that demonstrates that while Fe(110) has the ability to degrade the C–F bonds in PFBA the primary reaction route is through the degradation of the carboxylic acid head group.