William R. Dichtel of Northwestern University, Damian E. Helbling of Cornell University, and colleagues have developed an alternative adsorbent: a cross-linked cyclodextrin polymer with much higher affinity for PFOA than activated carbon. It also tends not to clog up with humic acid and can be regenerated with a methanol rinse.

β-Cyclodextrin—made of a ring of seven glucose molecules—has an inner hydrophobic pocket that is the right size to trap hydrophobic micropollutants such as pesticides and pharmaceuticals. Cyclodextrins have been studied as water purification agents and are used in the product Febreze to trap odor compounds.

At the moment, to remove perfluorinated chemicals from water, engineers primarily use granular activated carbon as an adsorbent. But the material has limitations. “Almost anything organic sticks to it,” including other pollutants and components of natural organic matter, such as humic acid, says Dichtel. Once that happens, the activated carbon usually needs to be replaced. And the material does not have particularly high affinity for PFOA, so it’s inefficient at trapping the pollutant. Other options for removing these compounds include reverse osmosis, which is much more expensive than activated carbon, and anion-exchange resins, which are still at the experimental stage for this application.

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