Shining light through nanocrystals helps break down PFAS without the need for extreme heat or pressure.
Some “forever chemicals” – so named because of how difficult they are to break down – can be destroyed using light shining through quantum dots. This method could require less energy than other techniques to destroy the contaminants.
 |
| The carbon-fluorine bonds in “forever chemicals” make them hard to destroy Yurchanka Siarhei/Shutterstock |
“The major advantage of our approach is that it enables degradation using simple and versatile visible-light LEDs,” says Yoichi Kobayashi at Ritsumeikan University in Japan.
Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a class of thousands of chemicals containing carbon-fluorine bonds. These tough bonds make them useful materials, but have also made them a source of persistent environmental contamination, some of which has negative health effects for people. Efforts to clean up PFAS contamination are under way, but most methods of destroying the molecules require extreme heat or pressure, or incineration.
Kobayashi and his colleagues tested a method using visible light from an LED at room temperature and pressure. They used separate solutions containing two different PFAS: perfluorooctanesulfonate (PFOS), a widespread and difficult-to-degrade compound used in firefighting foam and non-stick pans, and Nafion, which is used in industrial membranes. Then they added quantum dots, or semiconductor nanocrystals, made of cadmium sulphide and copper. The electrons in quantum dots absorb specific wavelengths of light, which raises them to a more excited state, giving them greater potential to break the strong bonds found in PFAS.
After 8 hours under the LED light, all of the carbon-fluorine bonds in the PFOS broke down. After 24 hours, just over 80 per cent of such bonds were broken in Nafion.
According to the researchers, this breakdown occurs when free electrons from the quantum dots transfer to PFAS on or in the immediate vicinity of the nanocrystals. These free electrons then destroy the carbon-fluorine bond via a reduction reaction.
Michael Wong at Rice University in Texas says the study is the first to use quantum dots to break down PFAS, and that the team’s proposal for the mechanism involved adds “new twists” to what is known about the chemistry of degrading PFAS. However, practical use of the method to break down PFAS contamination is far off, he says.
Questions remain about how well it would work with the lower concentrations of PFAS found in the environment, and whether the reaction would work as well at larger scales and with other types of PFAS.
Journal reference:
Angewandte Chemie International Edition DOI: 10.1002/anie.202408687
0 Comments