A review by Tohoku University researchers identifies key molecular features that could guide the development of more effective materials for removing PFAS from water.

Per- and polyfluoroalkyl substances (PFAS) are used in a wide range of industries, from semiconductor manufacturing and firefighting to textiles and food packaging. Their chemical stability and ability to repel water and oil make them useful in many applications. However, concerns about the potential health effects of some PFAS have increased the need for effective ways to remove these chemicals from water.

One promising approach is adsorption, in which PFAS molecules attach to the surface of a material called an adsorbent. By tailoring these materials to interact with specific PFAS molecules, researchers aim to improve their ability to capture these persistent chemicals from water.

A research team led by Kouki Oka, Associate Professor at Tohoku University's Institute of Multidisciplinary Research for Advanced Materials, reviewed current research and development in PFAS adsorption. The review examines well-studied compounds, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), alongside other PFAS covered by regulatory and monitoring frameworks in the European Union (EU) and Canada. The team identifies key principles for designing high-performance adsorbents that can target a wider range of PFAS.

A central finding is that effective adsorbent design requires understanding the different parts of a PFAS molecule. PFOS and PFOA, for example, each contain a fluorinated carbon chain and a terminal group that is typically charged in aqueous environments. These parts have different chemical properties and can interact with adsorbent materials in different ways.

By designing materials that interact strongly with these different structural features, researchers may be able to improve adsorption performance. Rather than treating a PFAS molecule as a single target, this approach considers its individual components to guide the selection and design of suitable adsorbents.

"As the range of PFAS subject to regulation continues to expand, we need adsorbents that can effectively target a wider variety of these compounds. By understanding how different parts of PFAS molecules interact with adsorbent materials, we can establish clearer design principles for developing more effective removal technologies," says Oka.

The need for such materials is growing as governments expand PFAS monitoring and regulation. In the EU, drinking water standards set a limit of 100 nanograms per liter (ng/L) for the combined concentration of 20 PFAS. The EU has also established environmental quality standards for 25 PFAS in surface waters, with an annual average limit of 4.4 ng/L expressed as PFOA equivalents to account for differences in toxicity. Canada has set an objective of 30 ng/L for the combined concentration of 25 PFAS.

As more PFAS come under regulatory scrutiny, removal technologies will need to address a broader range of molecular structures. The design principles outlined in this review provide a foundation for developing adsorbents tailored to different PFAS, potentially improving water treatment and helping industries manage these persistent chemicals.

The research team's next step is to apply these principles to the development of higher-performance adsorbents designed for specific PFAS.