Adsorption of per- and poly-fluoroalkyl substances (PFAS) on Ni: A DFT investigation

Electrocatalytic destruction of per- and polyfluoroalkyl substances (PFAS) is an emerging approach for treatment of PFAS-contaminated water. In this study, a systematic ab initio investigation of PFAS adsorption on Ni, a widely used electrocatalyst, was conducted by means of dispersion-corrected Density Functional Theory (DFT) calculations. The objective of this investigation was to elucidate the adsorption characteristics and charge transfer mechanisms of different PFAS molecules on Ni surfaces. PFAS adsorption on three of the most thermodynamically favorable Ni surface facets, namely (001), (110), and (111), was investigated. Additionally, the role of PFAS chain length and functional group was studied by comparing the adsorption characteristics of different PFAS compounds, namely perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorobutanesulfonic acid (PFBS), and perfluorobutanoic acid (PFBA). For each PFAS molecule-surface facet pair, different adsorption configurations were considered. Further calculations were carried out to reveal the effect of solvation, pre-adsorbed atomic hydrogen (H), and surface defects on the adsorption energy. Overall, the results revealed that the adsorption of PFAS on Ni surfaces is energetically favorable, and that the adsorption is primarily driven by the functional groups. The presence of preadsorbed H and the inclusion of solvation produced less exothermic adsorption energies, while surface vacancy defects showed mixed effects on PFAS adsorption. Taken together, the results of this study suggest that Ni is a promising electrocatalyst for PFAS adsorption and destruction, and that proper control for the exposed facets could enhance the adsorption stability.