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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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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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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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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DOI: https://doi.org/10.1038/s44221-023-00046-z
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