<i>Ab Initio</i> Investigation of Per- and\nPoly-fluoroalkyl Substance (PFAS) Adsorption on Zerovalent Iron (Fe<sup>0</sup>)

In this study, dispersion-corrected\ndensity functional theory (DFT)\ncalculations were employed to investigate the adsorption of per- and\npoly-fluoroalkyl substances (PFAS) onto zerovalent iron (Fe<sup>0</sup>). The main objective of this investigation was to shed light on\nthe adsorption properties, including adsorption energies, geometries,\nand charge transfer mechanisms, for four PFAS molecules, namely, perfluorooctanesulfonic\nacid (PFOS), perfluorobutanesulfonic acid (PFBS), perfluorooctanoic\nacid (PFOA), and perfluorobutanoic acid (PFBA), on the most thermodynamically\naccessible Fe<sup>0</sup> surface facets. Additionally, the DFT investigation\nexamined the role of PFAS chain length, functional group, protonation/deprotonation\nstate, and solvation in water in their adsorption to Fe<sup>0</sup>. Overall, the adsorption of the four PFAS molecules on various Fe<sup>0</sup> surfaces exhibited thermodynamically favorable energetics.\nNevertheless, solvation in water resulted in less exothermic adsorption\nenergies, and the presence of preadsorbed oxygen blocked the Fe<sup>0</sup> surface, preventing PFAS adsorption. Additionally, the inclusion\nof a monolayer of Ni on top of the Fe<sup>0</sup> surface reduced\nthe stability of PFAS adsorption compared to pristine Fe<sup>0</sup>. Results of the computational investigation were compared to experimental\nresults from the literature for qualitative validation.