Cyclodextrin Polymers with Nitrogen-Containing Tripodal Crosslinkers for Efficient PFAS Adsorption

Abstract

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.

Functionalized bio‐adsorbents for removal of perfluoroalkyl substances: A perspective

“…They found that the CDP1 with amino groups outperformed the amidefunctionalized polymer CDP2 with amido groups for the removal testing of 10 anionic PFAS (C4-C10). It was confirmed that the high loading of amino groups in CDP1 was mainly responsible for the superior removal PFAS performance, while amido groups in CDP2 cannot be protonated, underscoring the importance of electrostatic interactions to sequester PFAS (Yang et al, 2020). As the result, CDP1 exhibited the highest affinity and adsorption capacity among CD-based sorbents for GenX (222 mg/g) and PFOA (457 mg/g).…”

“…With this reduced polymer, anionic PFAS with C4-C10 were indiscriminately removed at high efficiency (80%-95% after 30 min), which outperformed GAC and PAC, especially for short-chain PFAS (PFBA removal >80%, while GAC and PAC have the removal of 40%-50%) (Klemes et al, 2019). To better understand the effect of the amino groups on the interactions between β-CD polymer and anionic PFAS, Yang et al (2020) selected two different tripodal crosslinkers containing amino or amido groups, respectively. They found that the CDP1 with amino groups outperformed the amidefunctionalized polymer CDP2 with amido groups for the removal testing of 10 anionic PFAS (C4-C10).…”

“…As a result, the adsorption capacity from various papers may not be compared directly due to huge difference of PFAS adsorption condition (e.g., initial concentration range). Based on the existing data of above summarized bio-adsorbents, the short-chain PFAS adsorption capacity is 363.9 mg/g for PFBA (Deng et al, 2013) and 222 mg/g for GenX (Yang et al, 2020), and the average removal range for long-chain PFAS is from 457 to 2751 mg/g. Unfortunately, we cannot provide more data about bio-adsorbents for short-chain PFAS due to limited number of relevant publications.…”

Advances and Classification of Cyclodextrin-Based Polymers for Food-Related Issues

“…In a study, Yang et al compared different β-CD polymers. The results demonstrated that the affinity of the polymers containing amine groups for removal of anionic PFAS was higher than that of amido polymers [ 83 ].…”

Passive sampler designed for per‐ and polyfluoroalkyl substances using polymer‐modified organosilica adsorbent

“…Alternative designs using thin films hosting adsorbent resins have also shown promise (Challis, 2018). New types of PFAS-specific adsorbents, including sol-gel derived media with ionic sites, have demonstrated that adsorption can be tailored (Wang et al, 2017;Yang et al, 2020).…”