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Although most manufacturers stopped using long-chain per- and polyfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), short-chain PFASs are still widely employed. Short-chain PFASs are less known in terms of toxicity and have different adsorption behavior from long-chain PFASs. Previous studies have shown electrostatic interaction with the adsorbent to be the dominant mechanism for the removal of short-chain PFASs. In this study, we designed a high charge density cationic quaternized nanocellulose (QNC) to enhance the removal of both short- and long-chain PFASs from contaminated water. Systematic batch adsorption tests were conducted using the QNC adsorbent to compare its efficiency against PFASs with varying chain lengths and functional groups. From the kinetic study, PFBA (perfluorobutanoic acid), PFBS (perfluorobutanesulfonic acid) and PFOS showed rapid adsorption rates, which reached near equilibrium values (>95% of removal) between 1 min to 15 min, while PFOA required a relatively longer equilibration time of 2 h (it obtained 90% of removal within 15 min). According to the isotherm results, the maximum adsorption capacity ( Q m ) of the QNC adsorbent exhibited the following trend: PFOS ( Q m = 559 mg g −1 or 1.12 mmol g −1 ) > PFOA ( Q m = 405 mg g −1 or 0.98 mmol g −1 ) > PFBS ( Q m = 319 mg g −1 or 1.06 mmol g −1 ) > PFBA ( Q m = 121 mg g −1 or 0.57 mmol g −1 ). This adsorption order generally matches the hydrophobicity trend among four PFASs associated with both PFAS chain length and functional group. In competitive studies, pre-adsorbed short-chain PFASs were quickly desorbed by long-chain PFASs, suggesting that the hydrophobicity of the molecule played an important role in the adsorption process on to QNC. Finally, the developed QNC adsorbent was tested to treat PFAS-contaminated groundwater, which showed excellent removal efficiency (>95%) for long-chain PFASs (C7–C9) even at a low adsorbent dose of 32 mg L −1 . However, short-chain PFASs ( i.e. , PFBA and perfluoropentanoic acid (PFPeA)) were poorly removed by the QNC adsorbent (0% and 10% removal, respectively) due to competing constituents in the groundwater matrix. This was further confirmed by controlled experiments that revealed a drop in the performance of QNC to remove short-chain PFASs at elevated ionic strength (NaCl), but not for long-chain PFASs, likely due to charge neutralization of the anionic functional group of PFASs by inorganic cations. Overall, the QNC adsorbent featured improved PFAS adsorption capacity at almost two-fold of PFAS removal by granular activated carbons, especially for short-chain PFASs. We believe, QNC can complement the use of common treatment methods such as activated carbon or ionic exchange resin to remove a wide range of PFAS pollutants, heading towards the complete remediation of PFAS contamination.
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Characterization of a mixed mode fluorocarbon/weak anion exchange sorbent for the separation of perfluoroalkyl substances
The ubiquitous presence and persistence of per‐ and polyfluoroalkyl substances (PFAS) in the environment have raised concerns in the scientific community. Current research efforts are prioritizing effective PFAS remediation through novel sorbents with orthogonal interaction mechanisms. Recognized sorption mechanisms between PFAS and sorbents include hydrophobic, electrostatic, and fluorine‐fluorine interaction. The interplay of these mechanisms contributes significantly to improved sorption capacity and selectivity in PFAS separations. In this study, a primary/secondary amine‐functionalized polystyrene‐divinylbenzene (Sepra‐WAX) polymer was modified to create a fluorinated WAX resin (Sepra‐WAX‐KelF‐PEI). The synthesis intermediate (Sepra‐WAX‐KelF) was also tested to assess the improvement of the final product (Sepra‐WAX‐KelF‐PEI). The adsorption capacity of Sepra‐WAX, Sepra‐WAX‐KelF, and Sepra‐WAX‐KelF‐PEI, and their interactions with PFAS were evaluated. The effect of pH, ionic strength, and organic solvents on PFAS sorption in aqueous solution was also investigated. The sorbents showed varied adsorption capacities for perfluorooctanoic acid, perfluoropentanoic acid, perfluoro‐n‐decanoic acid, and hexafluoropropylene oxide dimer acid, with the average extraction capacity of the four analytes being Sepra‐WAX‐KelF‐PEI (523 mg/g) > Sepra‐WAX (353 mg/g) > Sepra‐WAX‐KelF (220 mg/g). Sepra‐WAX‐KelF‐PEI provided the highest adsorption capacity for all analytes tested, proving that the combination of electrostatic and hydrophobic/fluorophilic interactions is crucial for the effective preconcentration of PFAS and its future applications for PFAS remediation from aqueous solutions.
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- Award ID(s):
- 2432184
- PAR ID:
- 10643484
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Separation Science
- Volume:
- 47
- Issue:
- 16
- ISSN:
- 1615-9306
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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