Aqueous film-forming foam (AFFF) formulations have been used for decades to suppress hydrocarbon fuel-based fires at United States (US) military facilities. Per- and polyfluoroalkyl substances (PFASs) are key constituents of AFFFs and their occurrence in groundwater at many of these facilities has been widely reported. Developing cost-effective remediation strategies to remove PFASs from groundwater remains an important challenge. The goal of this project is to design, characterize, and evaluate the implementation of novel polymer adsorbents for the in situ or ex situ remediation of PFAS-contaminated groundwater. The research team will address some of the major deficiencies of contemporary adsorption-based processes including their insufficient affinity for shorter-chain and more hydrophilic PFASs, the propensity for fouling by natural organic matter and other matrix constituents, and costs associated with the regeneration of spent adsorbents. The research objectives of the project are to: (1) discover polymer adsorbents with high affinity, high capacity, and rapid kinetics for priority and environmentally relevant PFASs using a hypothesis-driven, rational design approach; (2) characterize the performance of each polymer under scenarios relevant to groundwater remediation to inform polymer development, elucidate adsorption mechanisms, and estimate parameters to be used for process design; and (3) transition toward the implementation of the new polymer adsorbents into in situ or ex situ remediation processes by optimizing synthesis pathways and evaluating adsorption process alternatives that maximize performance and minimize the life-cycle costs.

The project team recently developed a promising class of novel polymer adsorbents that can be rationally designed to target specific types of pollutants. These include the first mesoporous polymers of cyclodextrin, which exhibit rapid pollutant uptake, high pollutant capacity, and facile regeneration potential. The research team aims to design and characterize new cyclodextrin-based polymer adsorbents that specifically target PFASs and control polymer structure and morphology to enable their implementation into groundwater remediation processes. The project is structured around five scientific tasks: (1) develop new polymer adsorbents that maximize the adsorption kinetics, affinity, and capacity for priority PFASs using a hypothesis-driven, rational design approach; (2) characterize the uptake of diverse PFASs in both controlled laboratory experiments and from AFFF-impacted groundwater; (3) develop structure-activity relationships to understand and strengthen the non-covalent interactions by which promising polymer derivatives sequester PFASs; (4) optimize the synthesis of the most promising polymers to obtain useful morphologies and high yields to facilitate commercialization; and (5) evaluate alternatives for in situ or ex situ adsorption-based remediation strategies with consideration for adsorbent regeneration and the handling of ancillary waste streams.

This project will provide remediation project managers and the scientific community with alternative adsorbents to implement in remediation processes. These novel polymer adsorbents will have tailored affinity for various classes of PFASs, limited interactions with natural organic matter and other matrix constituents, and the potential for facile regeneration and reuse. These features will address the most important deficiencies of conventional adsorbents and lead to the development of more cost-effective adsorption-based remediation processes for AFFF-impacted groundwater. Anticipated deliverables of this project include: (a) the discovery of one or more polymer adsorbents that effectively remove PFASs, including those of varying chain length and degrees of hydrophilicity; (b) structure-activity relationships that predict the affinity of a polymer for PFASs based on molecular properties; and (c) guidelines to implement these novel polymers into adsorption-based groundwater remediation processes. (Anticipated Project Completion - 2023)

Ateia, M., D.E. Helbling, and W.R. Dichtel. 2020. Best Practices for Evaluating New Materials as Adsorbents for Water Treatment. ACS Materials Letters, 2(11):1532–1544. doi.org/10.1021/acsmaterialslett.0c00414.

Ching, C., Z. Lin, W.R. Dichtel, and D.E. Helbling. 2023. Evaluating the Performance of Novel Cyclodextrin Polymer Granules to Remove Perfluoroalkyl Acids (PFAAs) from Water. ACS ES&T Engineering. doi.org/10.1021/acsestengg.2c00379. 

Ching, C., M.J. Klemes, B. Trang, W.R. Dichtel, and D.E. Helbling. 2020. β-Cyclodextrin Polymers with Different Cross-Linkers and Ion-Exchange Resins Exhibit Variable Adsorption of Anionic, Zwitterionic, and Nonionic PFASs. Environmental Science and Technology, 54(19):12693–12702. doi.org/10.1021/acs.est.0c04028.

Ching, C., Y. Ling, B. Trang, M. Klemes, L. Xiao, A. Yang, G. Barin, W.R. Dichtel, and D.E. Helbling. 2022. Identifying the Physicochemical Properties of β-Cyclodextrin Polymers that Determine the Adsorption of Perfluoroalkyl Acids. Water Research, 209:117938. doi.org/10.1016/j.watres.2021.117938. 

Ji, W., L. Xiao, Y. Ling, C. Ching, M. Matsumoto, R.P. Bisbey, D.E. Helbling, and W.R. Dichtel. 2018. Removal of GenX and Perfluorinated Alkyl Substances from Water by Amine-Functionalized Covalent Organic Frameworks. Journal of the American Chemical Society, 140(40):12677−12681. doi.org/10.1021/jacs.8b06958.

Klemes, M.J., Y. Ling, C. Ching, C. Wu, L. Xiao, D.E. Helbling, and W.R. Dichtel. 2019. Reduction of a Tetrafluoroterephthalonitrile-β-Cyclodextrin Polymer to Remove Anionic Micropollutants and Perfluorinated Alkyl Substances from Water. Angewandte Chemie International Edition, 58(35):12049-12053. doi.org/10.1002/anie.201905142.

Klemes, M.J., L.P. Skala, M. Ateia, B. Trang, D.E. Helbling, and W.R. Dichtel. 2020. Polymerized Molecular Receptors as Adsorbents to Remove Micropollutants from Water. Accounts of Chemical Research, 53(10):2314–2324. doi.org/10.1021/acs.accounts.0c00426.

Wang, R., C. Ching, W.R. Dichtel, and D.E. Helbling. 2020. Evaluating the Removal of Per- and Polyfluoroalkyl Substances from Contaminated Groundwater with Different Adsorbents Using a Suspect Screening Approach. Environmental Science and Technology Letters, 7(12):954–960. doi.org/10.1021/acs.estlett.0c00736.

Wang, R., Z.W. Lin, M.J. Klemes, M. Ateia, B. Trang, J. Wang, C. Ching, D.E. Helbling, and W.R. Dichtel. 2022. A Tunable Porous β-Cyclodextrin Polymer Platform to Understand and Improve Anionic PFAS Removal. ACS Central Science, 8(5):663-669. doi.org/10.1021/acscentsci.2c00478.

Wu, C., M.J. Klemes, B. Trang, W.R. Dichtel, and D.E. Helbling. 2020. Exploring the Factors that Influence the Adsorption of Anionic PFAS on Conventional and Emerging Adsorbents in Aquatic Matrices. Water Research, 182:115950. doi.org/10.1016/j.watres.2020.115950.

Yang, A., C. Ching, M. Easler, D.E. Helbling, and W.R. Dichtel. 2020. Cyclodextrin Polymers with Nitrogen-Containing Tripodal Crosslinkers for Efficient PFAS Adsorption. ACS Materials Letters, 2(9):1240−1245. doi.org/10.1021/acsmaterialslett.0c00240.

Xiao, L., C. Ching, Y. Ling, M. Nasiri, M.J. Klemes, T.M. Reineke, D.E. Helbling, and W.R. Dichtel. 2019. Cross-linker Chemistry Determines the Uptake Potential of Perfluorinated Alkyl Substances by β-Cyclodextrin Polymers. Macromolecules, 52(10):3747-3752. doi.org/10.1021/acs.macromol.9b00417.