Per- and polyfluoroalkyl substances (PFAS) are often called “forever chemicals” because their ultra-strong carbon–fluorine bonds make them stubbornly resistant to breakdown in the environment. They’re prized in industry for repelling water, oil and heat, but that same durability means they persist in soil, water and living tissue long after use. Now, a Yale Engineering doctoral student has developed a novel approach that doesn’t just capture PFAS, it chemically re-engineers them. By reacting certain PFAS molecules with octanol, the method roughly doubles their size, causing them to drop out of water and become far easier to destroy, according tozz Yale’s official announcement of the research from Professor John Fortner’s lab.Why PFAS are so hard to removePFAS are a large family of synthetic chemicals used in everything from nonstick cookware and stain-resistant fabrics to semiconductor manufacturing and firefighting foams. Their defining feature is a chain of carbon atoms heavily bonded to fluorine. The carbon–fluorine bond is one of the strongest in organic chemistry, which makes PFAS incredibly stable and useful, but also extremely difficult to break down once released.Conventional treatment methods mostly try to “catch” PFAS rather than destroy them. Activated carbon filters adsorb the chemicals, and reverse osmosis membranes physically separate them from water. Both approaches are expensive, generate PFAS-laden waste that still needs disposal, and don’t eliminate the underlying problem: the molecules themselves remain intact and potentially harmful.The Yale breakthrough: make PFAS too big to hideSusanna Maisto, a fifth-year Ph.D. student in Yale’s Department of Chemical & Environmental Engineering, took a different tack. Instead of treating PFAS as something to be filtered out, she asked whether the molecules could be chemically altered so they no longer behaved like typical PFAS in water.Her method uses a reaction with octanol, a chemical related to ordinary alcohol, that attaches to certain PFAS molecules—specifically perfluorocarboxylic acids (PFCAs), a common subclass. This esterification reaction effectively doubles the size of the PFAS molecule. The larger, modified molecule is no longer soluble in water, so it naturally separates out, forming a distinct phase that can be skimmed or settled.Crucially, the same chemical change that makes the molecule insoluble also makes it much easier to destroy. What used to require two separate treatment steps—removal and then destruction—becomes a more integrated process.Making organic chemistry work in waterOne of the biggest hurdles was getting an organic reaction to occur in an aqueous environment. Organic chemistry reactions typically struggle in water, which tends to interfere with or shut down the desired transformations.Maisto adapted a technique first described by chemists at the University of Tokyo in 2004. The method emulsifies the PFAS into tiny droplets suspended in the water phase. These droplets act as microreactors, creating tiny pockets where octanol and PFAS can meet and react in conditions that ordinary open water wouldn’t allow. This emulsion-based approach is central to making the chemistry work in real-world, water-based waste streams.Performance across different water typesThe Yale team tested the method across a broad range of PFAS chemistries, including newer replacement compounds that have proven especially resistant to existing treatment technologies. The reaction held up in dirty water loaded with organic matter, demonstrating that it isn’t easily thrown off by complex, real-world matrices.It also worked in salt water, though with a modest drop in efficiency as salt content increased. Given that the reaction is occurring in water at all, a significant achievement in itself—this trade-off is considered acceptable, especially for the types of concentrated industrial waste streams where the method is intended to be used.The full process takes about 24 hours and performs best in concentrated waste streams. Interestingly, the more PFAS-laden the water already is, the fewer additional additives the reaction requires, which could improve cost-effectiveness at industrial sites with high PFAS loads.Designed for point-source treatment, not municipal cleanupMaisto is clear about where this technology fits: at the source. Her method is a point-source treatment designed to act the moment PFAS exits an industrial process, such as a semiconductor fabrication plant or manufacturing facility—before it ever reaches a community’s water supply.It is not intended to replace municipal-scale cleanup of already-diluted contamination in drinking water systems. Instead, it aims to prevent that contamination from happening in the first place by treating concentrated industrial effluents where PFAS levels are highest and the chemistry is most favourable.This focus aligns with growing regulatory and industry interest in stopping PFAS at the source, rather than relying solely on end-of-pipe solutions or downstream remediation.From library reading to lab breakthroughMaisto’s path to the discovery was partly serendipitous. At the end of her first year at Yale, Professor John Fortner encouraged her to read about carboxylic acid reactions—the chemical class that includes many PFAS—in the library. That reading sparked the idea of using esterification, a well-known organic reaction, in a completely new context: PFAS treatment.What followed was three years of troubleshooting. For a long stretch, the reaction seemed to depend heavily on concentration, working reliably at high PFAS levels but stalling at low ones. Maisto had to systematically work through the chemistry to understand and overcome this limitation before she could reliably drive both the modification and destruction steps. She counts her first successful summer of experiments, and later cracking the destruction chemistry, as among the most rewarding periods of her Ph.D.What’s next for PFAS destructionAfter completing her doctorate at Yale, Maisto will continue working on PFAS destruction as a postdoctoral researcher at Columbia University, where she plans to explore plasma reactors as another route to break the notoriously stubborn carbon–fluorine bond.Her Yale work, titled Esterification as a Novel Treatment Paradigm for Aqueous Perfluorocarboxylic Acids, represents a shift in how engineers think about PFAS remediation: not just capturing forever chemicals, but chemically transforming them into something that can no longer hide in water and is far easier to eliminate.If scaled and integrated into industrial processes, this approach could significantly reduce the amount of PFAS entering the environment in the first place, complementing existing filtration technologies and emerging destruction methods.Why this matters for industry and regulatorsFor industries that use or produce PFAS, the Yale method offers a potential pathway to meet tightening regulations while managing waste more effectively. For regulators, it adds a new tool to the PFAS toolkit—one that targets concentrated sources before they become widespread contamination problems.While the technology is still in the research stage, its ability to work in complex, real-world water conditions and across multiple PFAS chemistries makes it a promising candidate for further development and pilot testing.
