Researchers have developed a groundbreaking method to decompose perfluoroalkyl substances (PFASs), commonly known as “forever chemicals,” using visible LED light at room temperature. This innovative approach offers a promising solution for sustainable fluorine recycling and PFAS treatment.
PFASs, widely used since the invention of Teflon in 1938, are found in various applications such as cookware, clothing, and firefighting foam. Their stability and resistance to heat and water, while useful, pose significant environmental and health challenges. These chemicals do not break down easily and accumulate in water, soil, and animal bodies, causing carcinogenic effects and hormonal disruptions in humans. Traditionally, decomposing these chemicals requires temperatures exceeding 752°F (400°C), making the process difficult and energy-intensive.
The research team from Ritsumeikan University in Japan, led by Professor Yoichi Kobayashi, has developed a method to break down PFASs at room temperature using visible LED light. This technique achieved a 100% breakdown of perfluorooctanesulfonate (a type of PFAS) in just eight hours and an 81% breakdown of Nafion (a fluoropolymer) in 24 hours.
The new method involves a photocatalytic process using visible LED light to decompose PFAS and other fluorinated polymers (FPs) into fluorine ions at room temperature. The process works by irradiating cadmium sulfide (CdS) nanocrystals and copper-doped CdS (Cu-CdS) nanocrystals with surface ligands of mercaptopropionic acid (MPA) in a solution containing PFAS, FPs, and triethanolamine (TEOA).
When exposed to 405-nanometer LED light, these semiconductor nanocrystals generate electrons with high reduction potential, breaking down the strong carbon-fluorine bonds in PFAS molecules. The researchers added 0.8 mg of CdS nanocrystals, 0.65 mg of PFOS, and 20 mg of TEOA to 1.0 ml of water to initiate the photocatalytic reaction. The light excites the nanoparticles, generating electron-hole pairs and promoting the removal of MPA ligands, allowing PFOS molecules to adsorb onto the nanocrystal surface.
To prevent photoexcited electrons from recombining with holes, TEOA captures the holes, prolonging the lifetime of reactive electrons available for PFAS decomposition. These electrons undergo an Auger recombination process, creating highly excited electrons capable of breaking carbon-fluorine bonds in PFOS, resulting in the release of fluorine ions.
The defluorination efficiency depends on the amount of nanocrystals and TEOA used in the reaction and increases with the duration of light exposure. Laser flash photolysis measurements confirmed the presence of hydrated electrons generated by Auger recombination, identifying transient species based on the absorption spectrum upon laser pulse excitation.
“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,” said Professor Kobayashi. “This technique will aid the development of recycling technologies for fluorine elements, essential in various industries and supporting our prosperous society.”
By Impact Lab
