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Photochemical degradation pathways and near-complete defluorination of chlorinated polyfluoroalkyl substances

Nature Water volume 1, pages 381–390 (2023)Cite this article

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Abstract

Chlorinated polyfluoroalkyl substances (Clx–PFAS) are an emerging class of pollutants worldwide. Here we demonstrate near-complete defluorination (that is, cleaving most C–F bonds) of diverse Clx–PFAS structures and the reaction mechanisms. First, we used ultraviolet/sulfite to degrade various carboxylic acids (n = 1, 2, 4 and 8 Cl–CnF2nCOO− and n = 1, 2 and 3 Cl–(CF2CFCl)nCF2COO−) and an ether sulfonic acid surfactant (F-53B, Cl–(CF2)6–O–(CF2)2SO3−). The initial reaction with a hydrated electron cleaved the C–Cl bond. The resulting fluorocarbon radicals (•CF2– on the terminal and –•CF– in the middle) yield C–H or C–SO3−, or form a dimer. In particular, we identified a novel reaction pathway with the unexpected HO• radical to cleave the C–C bond (for –•CF–) and yield –COO−. This pathway is critical for rapid and deep defluorination at 90–96% from carboxylic acids and 76% from F-53B. The following treatment with heat/persulfate at pH >12 achieved ~100% overall defluorination from carboxylic acids and 93% from F-53B without producing toxic ClO3− from Cl−. This study advances the understanding of PFAS transformation in engineering systems. It also suggests a synergy between molecular design and degradation technology towards sustainable management of fluorochemicals.

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Fig. 1: Structures, synthetic schemes and previously elucidated degradation pathways of Clx–PFAS.
Fig. 2: Degradability of ω-ClPFCAs and the comparison with PFCAs and ω-HPFCAs.
Fig. 3: Degradation pathways and transformation products of ω-ClPFCAs.
Fig. 4: Degradability, transformation products and reaction pathways of F-53B.
Fig. 5: Degradability of CTFEOAs and comparison with PFCAs.
Fig. 6: Transformation products and reaction pathways of CTFEOAs.

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Data availability

The data that support the findings of this study are available within the paper and its Supplementary Information. Source data for all graphs are provided with this paper. Mass spectrometry raw data are available from the corresponding author upon reasonable request.

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Acknowledgements

Financial support was provided by the Strategic Environmental Research and Development Program (ER18-1289 for J.G., Z.L. and J.L., and ER20-1541 for S.C. and Y.M.) and the National Science Foundation (CHE-1709719 for J.L.). S. Wang at Clarkson University provided helpful discussion on the background of F-53B. M. Elsner at the Technical University of Munich provided helpful discussion on the reaction mechanisms.

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Authors and Affiliations

  1. Department of Chemical & Environmental Engineering, University of California, Riverside, CA, USA

    Jinyu Gao, Zekun Liu, Dandan Rao, Shun Che, Yujie Men & Jinyong Liu

  2. State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, Nanjing University, Nanjing, Jiangsu, China

    Zhanghao Chen & Cheng Gu

  3. State Key Joint Laboratory of Environmental Simulation and Pollution Control (SKLESPC), Beijing Key Laboratory for Emerging Organic Contaminants Control (BKLEOC), Beijing Laboratory for Environmental Frontier Technologies (BLEFT), School of Environment, Tsinghua University, Beijing, China

    Jun Huang

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Contributions

J.G. conducted PFAS degradation experiments, analysed the data and drafted the manuscript; Z.L. conducted PFAS degradation experiments; Z.C., D.R. and C.G. measured and analysed electron paramagnetic resonance data; S.C. and Y.M. assisted in the liquid chromatography high-resolution tandem mass spectrometry analysis; J.H. provided F-53B and discussed the manuscript; J.L. designed and supervised the research, and revised the manuscript.

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Correspondence to Jinyong Liu.

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Nature Water thanks Zulin Zhang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–3, Tables 1–6 and detailed information on materials and methods, and coordinates of the calculated structures.

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Gao, J., Liu, Z., Chen, Z. et al. Photochemical degradation pathways and near-complete defluorination of chlorinated polyfluoroalkyl substances. Nat Water 1, 381–390 (2023). https://doi.org/10.1038/s44221-023-00046-z

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