Per-and polyfluorinated alkyl substances (PFAS), such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and ammonium perfluoro-2-propoxypropionate (GenX), contaminate ground and surface waters throughout the world. The cost and performance limitations of current PFAS removal technologies motivate efforts to develop selective and high-affinity adsorbents. Covalent organic frameworks (COFs) are unexplored yet promising adsorbents because of their high surface area and tunable pore sizes. Here we show that imine-linked two-dimensional (2D) COFs bearing primary amines adsorb GenX rapidly at environmentally relevant concentrations. COFs with partial amine incorporation showed the highest capacity and fastest removal, suggesting that the synergistic combination of the polar group and hydrophobic surfaces are responsible for GenX binding. A COF with 28% amine loading also removed more than 90% of 12 out of 13 PFAS. These results demonstrate the promise of COFs for PFAS removal and suggest design criteria for maximizing adsorbent performance.

Organic micropollutants (MPs) are anthropogenic substances that contaminate water resources at trace concentrations.M any MPs,i ncluding per-a nd polyfluorinated alkyl substances (PFASs), have come under increased scrutiny because of their environmental persistence and association with various health problems.Ab-cyclodextrin polymer linked with tetrafluoroterephthalonitrile (TFN-CDP) has high affinity for cationic and many neutral MPs from contaminated water because of anionic groups incorporated during the polymerization. But TFN-CDP does not bind many anionic MPs strongly,i ncluding anionic PFASs.T oa ddress this shortcoming,w er educed the nitrile groups in TFN-CDP to primary amines,w hich reverses its affinity towards charged MPs.T FN-CDP exhibits adsorption distribution coefficients (log K D values) of 2-3 for cationic MPs and À0.5-1.5 for anionic MPs,w hereas the reduced TFN-CDP exhibits log K D values of À0.5-1.5 for cationic MPs and 2-4 for anionic MPs, with especially high affinity towards anionic PFASs.K inetic studies of the removal of 10 anionic PFASs at environmentally relevant concentrations showed 80-98 %r emoval of all contaminants after 30 min and was superior to commercial granular activated carbon. These findings demonstrate the scope and tunability of CD-based adsorbents derived from as ingle polymerization and the promise of novel adsorbents constructed from molecular receptors.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Per-and polyfluoroalkyl substances (PFAS) are widely used industrial chemicals that are of a great concern because of their pervasive presence in water resources and association with negative health effects. Crosslinked β-cyclodextrin-containing (β-CD) polymer adsorbents have shown promising performances for sequestering PFAS. Recently, installing amino groups into the crosslinkers of a β-CD polymer network improved the binding of many anionic PFAS, including short-chain and branched derivatives. However, the relative importance of the electrostatic interactions from the amino groups and the host-guest interactions within the cavity of the β-CD for PFAS binding are unclear. Herein, β-CD-based adsorbents crosslinked with tripodal crosslinkers containing three amino or amido groups are prepared with comparable physicochemical properties to investigate the respective roles of the crosslinker and β-CD in binding affinity and capacity for anionic PFAS. β-CD polymers containing amines showed superior removal for ten anionic PFAS compared to polymers containing amido groups. Both β-CD polymers have superior performance for perfluorooctanoic acid (PFOA) removal compared to activated carbons (ACs), consistent with β-CD:PFOA inclusion complexes playing an important role. Adsorbents containing amido groups showed low binding affinity and capacity for GenX, whereas the amine-functionalized polymer had outstanding affinity and capacity for GenX (K L = 8.8 × 10 4 M −1 , Q M = 222 mg g −1 ), underscoring the essential role of electrostatic interactions for removing short-chain and branched PFAS. The amine-containing β-CD polymer exhibited 100-fold higher affinity and twice the capacity (K L = 1.8 × 10 6 M −1 , Q M = 457 mg g −1 ) for PFOA compared to GenX, which are the highest reported values for β-CD polymers. These results highlight the synergistic effects of electrostatic interactions and host-guest interactions in β-CD polymers as important design criteria for efficient removal of anionic PFAS from water. This study further demonstrates broad tunability of crosslinked β-CD polymers and their promise as adsorbents for PFAS remediation.

Per-and polyfluoroalkyl substances (PFASs) occur in groundwater as mixtures of anionic, cationic, zwitterionic, and nonionic species, although few remediation technologies have been evaluated to assess the removal of different types of PFASs. In this study, we evaluated the performance of three β-cyclodextrin polymers (CDPs), an anion-exchange (AE) resin, and a cationexchange (CE) resin for the removal of anionic, zwitterionic, and nonionic PFASs from water. We found that a CDP with a negative surface charge rapidly removes all zwitterionic PFASs with log K D values ranging between 2.4 and 3.1, and the CE resin rapidly removes two zwitterionic PFASs with log K D values of 1.8 and 1.9. The CDPs with a positive surface charge rapidly remove all anionic PFASs with log K D values between 2.7 and 4.1, and the AE resin removes all anionic PFASs relatively slowly with log K D values between 2.0 and 2.3. All adsorbents exhibited variable removal of the nonionic PFASs and some adsorption inhibition at higher pH values and in the presence of groundwater matrix constituents. Our findings provide insight into how adsorbents can be combined to remediate groundwater contaminated with complex mixtures of different types of PFASs.

Per-and poly fluorinated alkyl substances (PFASs), notably perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid, contaminate many ground and surface water resources and are environmentally persistent. Furthermore, there are many other PFASs in use that are persistent and contaminate fresh water resources. A polymer consisting of β-cyclodextrin (β-CD) cross-linked with decafluorobiphenyl (DFB-CDP) has shown promise for sequestering PFOA at environmentally relevant concentrations, though its efficacy to remove other PFASs from water has not yet been explored. Additionally, although the DFB-CDP was designed to sequester PFASs on the basis of favorable fluorous interactions, the rationale for its relatively high affinity for PFOA compared to other previously synthesized β-CD polymers remains unknown. In this study, we explored cross-linker chemistry as a potential determinant of PFAS affinity for β-CD polymers. We synthesized three DFB-CDP derivatives with varying degrees of phenolation in the cross-linker (to evaluate effects of polymer surface charge) along with two β-CD polymers cross-linked by two other chemically distinct strategies, epichlorohydrin and 2isocyanatoethyl methacrylate. We measured the equilibrium removal of ten PFASs from water by each of the five polymers at environmentally relevant concentrations. We found that β-CD polymers cross-linked by perfluorinated aromatics with low degrees of phenolation are more favorable for PFAS adsorption. These findings provide insight into the mechanism of PFAS adsorption by β-CD-based polymers and will inspire modular designs of β-CD-based adsorbents to target other PFASs and micropollutants.