Breaking the bonds on PFAS

Two separate publications by chemists in China and the US in Nature have highlighted the discovery of photocatalytic means to break the C-F bonds integral to per- and polyfluoroalkyl substances (PFAS). These bonds are some of the strongest known in chemistry. 

Yan-Biao Kang’s group the University of Science & Technology of China in Hefei succeeded in degrading PFAS using a catalyst called KQGZ. This is described as twisted carbon-based organic molecule containing interconnected aromatic rings that can carry out reactions previously limited to precious metals such as ruthenium or iridium.

In purple LED light, KQGZ became a bright yellow-green colour, demonstrating that an electron had been excited to a high-energy state. In this stage, the catalyst can inject an electron into a C-F bond, making it unstable and ultimately breaking it. The reaction can take place in temperatures as low as 40°C.

This was demonstrated on polytetrafluoroethylene (PTFE)-coated stirring bars and could be applicable to other common polymeric PFAS, such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Kang said that the process removes “almost all the fluorine atoms” contained in the PFAS. 

Similarly, Garret Miyake’s team at Colorado State University developed an organic photoredox catalyst system based on a flat molecule called BPI. This also has interconnected aromatic rings and changes colour when excited. It was able break down PFAS including PFOA, though not PTFE, which did not dissolve in the reaction conditions they used. BPI can also transform C-F bonds to synthesise new molecules. 

“Important next steps include using these ideas in real-world settings, for example to develop catalysts that work in waste water or that can be used to clean up PFAS in contaminated soils,” Nature commented. “If a method can be adapted so that it is powered by sunlight, that would be of huge benefit.” 

Dubbed ‘forever chemicals’ because of their extremely prolonged persistence in the environment, PFAS have been linked to developmental problems, cancer, immune-system suppression and other serious health problems. They are under increasing regulatory pressure across the world.    

• - Nature 635, 524 (2024): doi: https://doi.org/10.1038/d41586-024-03753-z