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Photocatalytic low-temperature defluorination of PFASs

Nature volume 635, pages 610–617 (2024)Cite this article

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Abstract

Polyfluoroalkyl and perfluoroalkyl substances (PFASs) are found in many everyday consumer products, often because of their high thermal and chemical stabilities, as well as their hydrophobic and oleophobic properties1. However, the inert carbon–fluorine (C–F) bonds that give PFASs their properties also provide resistance to decomposition through defluorination, leading to long-term persistence in the environment, as well as in the human body, raising substantial safety and health concerns1,2,3,4,5. Despite recent advances in non-incineration approaches for the destruction of functionalized PFASs, processes for the recycling of perfluorocarbons (PFCs) as well as polymeric PFASs such as polytetrafluoroethylene (PTFE) are limited to methods that use either elevated temperatures or strong reducing reagents. Here we report the defluorination of PFASs with a highly twisted carbazole-cored super-photoreductant KQGZ. A series of PFASs could be defluorinated photocatalytically at 40–60 °C. PTFE gave amorphous carbon and fluoride salts as the major products. Oligomeric PFASs such as PFCs, perfluorooctane sulfonic acid (PFOS), polyfluorooctanoic acid (PFOA) and derivatives give carbonate, formate, oxalate and trifluoroacetate as the defluorinated products. This allows for the recycling of fluorine in PFASs as inorganic fluoride salt. The mechanistic investigation reveals the difference in reaction behaviour and product components for PTFE and oligomeric PFASs. This work opens a window for the low-temperature photoreductive defluorination of the ‘forever chemicals’ PFASs, especially for PTFE, as well as the discovery of new super-photoreductants.

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Fig. 1: Photocatalytic reductive defluorination of PTFE.
Fig. 2: Characterization and quantification of the PTFE defluorination products.
Fig. 3: Investigations on the defluorination of PFASs.
Fig. 4: Control experiments.
Fig. 5: Proposed mechanism.

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Data availability

All data are available in the main text or the supplementary materials.

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Acknowledgements

This paper is dedicated to Yong Tang at Shanghai institute of Organic Chemistry on the occasion of his 60th birthday. We appreciate the financial support from the National Key R&D Program of China (no. 2021YFA1500100) and the National Natural Science Foundation of China (22271268). We thank Q. Li at the University of Science and Technology of China for assistance with the X-ray photoelectron spectroscopy measurements and characterizations. We thank K. Gong at the University of Science and Technology of China for helpful discussions about solid-state magic-angle spinning nuclear magnetic resonance characterizations.

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Authors and Affiliations

  1. Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemistry, University of Science and Technology of China, Hefei, China

    Hao Zhang, Jin-Xiang Chen & Yan-Biao Kang

  2. Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing, China

    Jian-Ping Qu

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Contributions

H.Z. performed all experiments and analysed the data in the main text and supplementary information, with guidance from Y.-B.K. and J.-P.Q., unless otherwise stated. J.-X.C. assisted H.Z., synthesized the photocatalyst shown in Fig. 1 and performed the reactions in Fig. 4a,b and the analysis. Y.-B.K. and J.-P.Q. conceived the research, designed the experiments, supervised experiments and analyses, interpreted the data, generated figures and wrote the manuscript.

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Correspondence to Jian-Ping Qu or Yan-Biao Kang.

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A patent application has been filed by the University of Science and Technology of China on photocatalytic defluorination of polyfluoroalkyl and perfluoroalkyl substances.

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

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This file contains Supplementary Sections 1–16, including Supplementary Figs. 1–105, Supplementary Data and Supplementary References.

Supplementary Video 1

Combustion experiment of the defluorinated amorphous carbon product. The defluorinated amorphous carbon product sustains smouldering and stays red-hot without any flame when it is heated by an alcohol burner. The red-hot ember becomes a black solid when the alcohol burner is removed.

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Zhang, H., Chen, JX., Qu, JP. et al. Photocatalytic low-temperature defluorination of PFASs. Nature 635, 610–617 (2024). https://doi.org/10.1038/s41586-024-08179-1

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