PNNL

Abstract

To reduce increasing concentrations of toxic per- and polyfluoroalkyl substances (PFAS), one approach involves the capture of PFAS from aqueous media using porous materials. The use of highly porous, tunable metal organic framework (MOF) materials is appealing for targeted liquid phase adsorption. In this work, for the first time, we demonstrate the excellent capture potential of perfluorooctane sulfonate (PFOS) using both the chromium and iron analogs of the MIL-101 structure. Experimental characterization of PFOS uptake reveals unique differences in adsorption properties between these two analogs providing key implications for future PFOS sorbent design. Specifically, STEM-EDS and IR spectroscopy show definitive proof of adsorption. Furthermore, XPS analysis shows evidence of a strong interaction between sulfur atoms of the polar head group of PFOS and the metal center of the framework in addition to the fluorinated non-polar tail. Additionally, in-situ 19F NMR reveals higher PFOS affinity for Cr-MIL-101 versus Fe-MIL-101 based on adsorption kinetics. Surprisingly, at these relatively high PFOS concentrations, activated acetylene black carbon is severely outperformed by both MOFs.