Probing the Sorption of Perfluorooctanesulfonate Using Mesoporous Metal-Organic Frameworks from Aqueous Solutions

One approach to reduce increasing concentrations of toxic per- and polyfluoroalkyl substances (PFAS) 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 sorption. In this work, we demonstrate the excellent capture of perfluorooctanesulfonate (PFOS) using both the chromium and iron analogs of the MIL-101 framework. Experimental characterization of PFOS uptake reveals unique differences in sorption properties between these two analogs, providing key implications for future PFOS sorbent design. Specifically, STEM-EDS and IR spectroscopy show definitive proof of sorption. Furthermore, XPS analysis shows evidence of a strong interaction between sulfur atoms of the polar headgroup of PFOS and the metal center of the framework in addition to the fluorinated nonpolar tail. Additionally, in situ ¹⁹F NMR reveals higher PFOS affinity for Cr-MIL-101 versus Fe-MIL-101 based on sorption kinetics. Surprisingly, at these relatively high PFOS concentrations, activated acetylene black carbon is severely outperformed by both MOFs.