Ritsumeikan University finds new route to cleaning up ‘forever chemicals’

31 Jul 2024

Room-temperature LED-based method decomposes perfluorinated materials for recycling or removal.

Extensive use of perfluoroalkyl substances (PFASs) and fluorinated polymers (FPs) in a number of industrial processes has led to unwanted accumulation of the long-lasting and highly stable materials in the environment.

These chemicals can now be found in drinking water supplies, food and the soil, part of a picture of increasing contamination detected in the environment and many consumer products. Optical analysis methods have played their part in monitoring the spread of nanoparticles into brands of bottled water as well as into the global ocean.

For fluorine-containing materials, most current attempts at removal involve harsh chemical treatment or high temperatures, which present their own issues of safety and environmental impact. New decomposition methods under milder conditions are badly needed.

A project at Japan's Ritsumeikan University has now developed a promising new approach, based around visible LED light. The work was published in Angewandte Chemie.

The technique is a photocatalytic process, using visible light to break down PFAS and FPs at room temperature into fluorine ions. Using their method, the researchers achieved 100 percent defluorination of perfluorooctanesulfonate (PFOS) within just 8 hours of light exposure.

"The proposed methodology is promising for the effective decomposition of diverse perfluoroalkyl substances under gentle conditions, significantly contributing towards the establishment of a sustainable fluorine-recycling society," commented Yoichi Kobayashi of Ritsumeikan University.

In use, the technique involves introducing a solution of the PFAS and PF materials to semiconductor nanocrystal materials based around cadmium sulphide, and then irradiating the mixture with 405-nanometer LED light. This initiates a photochemical reaction, generating electrons that break down the strong carbon-fluorine bonds in the PFAS molecules.

Irradiation also modifies the surface chemistry of the particles in a way which creates space for the perfluoro molecules to attach to the nanocrystals, while careful control of the chemistry allows the lifetimes of the reactive electrons to be prolonged.

Towards fluorine recycling

In tests, the project found that both the amount of light irradiation and the chemistry of the process could be optimized to enhance the breakdown of the perfluorinated compounds. For PFAS, applying the LED irradiation for 1, 2 and 8 hours improved the efficiency of defluorination from 55 to 70 and then 100 percent.

The same approach allowed the researchers to achieve 81 percent defluorination of Nafion, widely used as an ion-exchange membrane in electrolysis and batteries, after 24 hours of LED irradiation.

In addition to treating troublesome pollutants, the process could also help promote a fluorine recycling ecosystem, according to the researchers. Fluorine is a critical component in industries from pharmaceuticals to clean energy technologies, so recovering fluorine from waste PFAS could reduce reliance on fluorine production and establish a more sustainable recycling process.

"This technique will contribute to the development of recycling technologies for fluorine elements, which are used in various industries and support our prosperous society," said Yoichi Kobayashi.