Exploring the factors that influence the adsorption of anionic PFAS on conventional and emerging adsorbents in aquatic matrices.

Per and polyfluoroalkyl substances (PFASs) have raised great concern due to their ubiquity in aquatic environments, and adsorption technologies are among the most promising treatment solutions. This study investigated the key factors that influence the adsorption of anionic PFASs on conventional and emerging adsorbents. Batch adsorption experiments were conducted to evaluate the removal of 20 target PFASs at environmentally relevant concentrations by three different activated carbon (AC) materials and two different ß-cyclodextrin polymers (CDPs). Experiments were conducted in Milli-Q water and in groundwater. Major physical properties of the adsorbents were measured, along with general water chemistry parameters for each groundwater sample. Principal component analysis (PCA) was subsequently employed to extract the important associations from the multivariate dataset. The distinct performances of ACs and CDPs were attributed to their different surface chemistry and the distinct nature of their adsorption binding sites. Hydrophobic interactions dominated PFAS adsorption onto ACs while CDPs mostly attracted anionic PFASs via favorable electrostatic interactions. ACs of a smaller average particle size performed better, with our data pointing to an increased external specific surface area as the likely reason. pH and the concentration of cations were the primary contributors to adsorption inhibition in groundwater. Higher pH values limit anionic PFAS adsorption by deprotonating the functional groups on adsorbent surfaces. The elevated levels of cations in some groundwater samples limited the effects of attractive electrostatic interactions. Knowledge of PFAS adsorption mechanisms gained from this study can be used to design more efficient adsorbents and to predict their performance under a range of environmental scenarios.

Reduction of a Tetrafluoroterephthalonitrile-ß-Cyclodextrin Polymer to Remove Anionic Micropollutants and Perfluorinated Alkyl Substances from Water.

Organic micropollutants (MPs) are anthropogenic substances that contaminate water resources at trace concentrations. Many MPs, including per- and polyfluorinated alkyl substances (PFASs), have come under increased scrutiny because of their environmental persistence and association with various health problems. A ß-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, including anionic PFASs. To address this shortcoming, we reduced the nitrile groups in TFN-CDP to primary amines, which reverses its affinity towards charged MPs. TFN-CDP exhibits adsorption distribution coefficients (log KD values) of 2-3 for cationic MPs and -0.5-1.5 for anionic MPs, whereas the reduced TFN-CDP exhibits log KD values of -0.5-1.5 for cationic MPs and 2-4 for anionic MPs, with especially high affinity towards anionic PFASs. Kinetic studies of the removal of 10 anionic PFASs at environmentally relevant concentrations showed 80-98 % removal 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 a single polymerization and the promise of novel adsorbents constructed from molecular receptors.