Perfluoroalkyl substances (PFASs), a large class of synthetic chemicals, are valued for their ability to withstand heat, water, and oil. These materials are used in the production of everyday as well as industrial items. PFAS molecules are made up of a chain of carbon and fluorine atoms linked together. The energy required to break the carbon–fluorine (C–F) bond is extremely high, making these compounds durable and highly resistant to biological degradation.
However, PFASs are also often called "forever chemicals," as they do not degrade easily. This persistence leads to ongoing pollution and bioaccumulation, raising global concerns about long-term exposure and contamination cycles for ecosystems and people. PFAS-defluorination is the process of removing fluorine atoms from the molecule, which makes it less stable and more susceptible to further breakdown. Traditional PFAS degradation techniques are challenging as they require harsh chemicals or high energy. The development of novel, sustainable, and energy-efficient methods is required to enable PFAS to be recycled and mitigate PFAS-associated environmental risks.
A new study, led by Professor Yoichi Kobayashi from Ritsumeikan University, Japan, with Mr. Shuhei Kanao also from the same university, explored the possibility of using zinc oxide (ZnO) nanocrystals (NCs) in the PFAS-defluorination process. NCs, known for their photocatalytic properties, can use light to generate reactive species that degrade organic pollutants. NCs capped with different ligands were used for their enhanced efficiency. "Perfluorooctanesulfonic acid or PFOS is a PFAS compound that was once widely used but is now strictly regulated, and we wanted to see if ligand-capped ZnO NCs can defluorinate it," mentioned Prof. Kobayashi. This study was published online in Chemical Science on November 5, 2025.
The study mainly focused on the defluorination efficiency of ZnO NCs, capped with acetic acid (AA–ZnO NCs) or 3-mercaptopropionic acid (MPA–ZnO NCs). Some other organic ligands were also used to cap the NCs for comparative analysis. The defluorination experiment was conducted using 365 nm LED light, as it mimics ambient lighting conditions. The defluorination effect of these ligand-capped NCs was also tested on a few other PFASs like trifluoroacetic acid and Nafion.
AA–ZnO NCs could efficiently defluorinate PFOS by irradiation with near-UV light under ambient conditions. The presence of acetic acid ligand proved to be far more efficient than 3-mercaptopropionic acid, as MPA–ZnO NCs achieved only 8.4% defluorination after 24 hours, while AA–ZnO NCs exhibited up to a 92% defluorination rate after 24 hours under optimized conditions.
To ensure the sustainability of these NCs, their durability and decrease in catalytic efficiency over time were also tested. The findings suggested that the decomposition reaction proceeded over multiple cycles, with a single ZnO NC able to break up to 8,250 C–F bonds, pointing towards its reusability.
ZnO NCs can be efficiently used in the defluorination process due to their unique properties. They are low-toxicity, inexpensive, and can be produced at scale, unlike many previous catalysts. "The reaction occurs at room temperature and does not require high-energy light sources, which can be costly, fragile, or hazardous," mentioned Mr. Shuhei Kanao.
This mild photodegradation system is capable of addressing the globally critical PFAS-recycling issue. It can be used to tackle industrial PFAS pollution and can be used in fluorochemical materials manufacturing units, semiconductor manufacturing units, the recycling industry, wastewater treatment facilities, and more. "PFAS pollution is a worldwide concern, and this simple NC-based technology could contribute significantly to tackling this issue," concluded Prof. Kobayashi.
