Crosslinked polymers containing β-cyclodextrin (β-CD) are promising adsorbents with demonstrated removal performances for per- and polyfluoroalkyl substances (PFASs) from contaminated water sources. Despite the promising performance of some β-CD-based adsorbents for PFAS removal, many of these materials are not amenable for rational performance improvement or addressing fundamental questions about the PFAS adsorption mechanisms. These ambiguities arise from the poorly defined structure of the crosslinked polymers, especially with respect to the random substitution patterns of the cyclodextrins, as well as side reactions that modify the structures of some crosslinkers. Here we report a new β-CD polymer platform in which styrene groups are covalently attached to β-CD to form a discrete monomer that is amenable to radical polymerization. A β-CD polymer copolymerized with a methacrylate bearing a cationic functional group achieved nearly 100% removal for eight anionic PFASs at an exceedingly low adsorbent loading of 1 mg L<sup>-1</sup>, which is at least an order of magnitude lower than that used in previous studies. Furthermore, when the adsorbents were studied in a challenging salt matrix, we observed that long-chain PFAS adsorption was controlled by a complementary interplay of hydrophobic and electrostatic interactions, whereas short-chain PFASs primarily relied on electrostatic interactions. These materials exhibit great promise for anionic PFAS removal, and we anticipate that new compositions will be tailored using the versatility of radical polymerization to simultaneously target PFAS and other classes of micropollutants in the future.

Using β-cyclodextrin polymers to remove perfluoroalkyl substances and trace organic contaminants

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ACS Fall 2022

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