Investigation into the adhesion properties of PFAS on model surfaces

Perfluoroalkyl substances (PFAS) are a category of environmental contaminants of increasing global concern. Common treatments are adsorption, ion exchange and pressure-driven membrane processes, all of which are non-selective, demonstrate quick breakthrough, unsustainable regeneration, and require disposal of concentrates with high PFAS concentrations. The challenges presented by modern treatment practices to sustainably remove PFAS from water have led researchers to investigate alternative, economically viable PFAS remediation options such as development of novel sorbents. An integral step in developing novel PFAS removal matrices is material characterization; specifically pertaining to molecular interactions between adsorbent and adsorbate. To investigate this fundamental relationship, atomic force microscopy (AFM) was utilized to produce force profiles between two PFAS, perfluorooctanesulfonate (PFOS) and perfluorobutanesulfonate (PFBS), and surfaces in different conditions. Silicon wafers were surface modified with three silane molecules: aminopropyltriethoxysilane (APTES), triethoxy(octyl)silane, and trimethoxy(octdecyl)silane to observe the effect of surface polarity and hydrophobicity on PFAS adhesion. Force spectroscopy measurements taken with AFM were conducted in deionized water, sodium chloride, and magnesium chloride to examine the impact of ions on PFAS adhesion. The results of this study show that the force of PFAS adhesion onto surfaces is lowest in deionized water and increases in strength with addition of divalent cations. PFAS adhesion measured on siloxane films increased in divalent cation solutions compared to deionized water and monovalent salt solutions.