Making PFAS too big to hide
A Yale Engineering doctoral student found a way to react "forever chemicals," doubling their size so they're too big to slip past, and easy to destroy.
Written by Natalie Haase '27
Ask a chemist to name the strongest single bond in organic chemistry, and they'll likely say carbon-fluorine. It's that bond, repeated dozens of times over, that gives per- and polyfluoroalkyl substances (PFAS) their nickname: forever chemicals. Manufacturers prize PFAS for the same reason regulators dread them. The bonds barely break down, which is exactly why the compounds are so good at repelling water, oil, and heat in everything from semiconductor fabrication to nonstick cookware. This is also why PFAS persist in soil, water, and living tissue long after serving their industrial purpose.
Susanna Maisto, a fifth-year Ph.D. student in Prof. John Fortner's lab in the Department of Chemical & Environmental Engineering, has spent her doctorate – titled Esterification as a Novel Treatment Paradigm for Aqueous Perfluorocarboxylic Acids - finding a way to remove PFAS at their source, called point-source treatment, by re-engineering the molecules themselves.
Bigger, and suddenly solvable
Most industrial approaches to PFAS treat the pollutant as something to be caught: activated carbon adsorbs it, and reverse osmosis filters it out. Both methods pose considerable expense and neither actually destroys PFAS. Maisto's approach instead changes the chemistry of the molecule itself. Her method uses a reaction with octanol (a chemical cousin of ordinary alcohol) that latches onto a PFAS molecule and roughly doubles its size. The larger molecule is no longer soluble in water, so it separates out on its own. And the same reaction that makes it insoluble also makes it dramatically easier to destroy, turning what used to be two separate treatment problems into one.
The trick lies in getting an organic reaction to happen in water at all, something organic chemistry generally can't do. Maisto adapted a technique first described by chemists at the University of Tokyo in 2004, which emulsifies the PFAS into tiny droplets suspended in the aqueous phase. Those droplets effectively act as microreactors, giving the octanol and PFAS a place to react that ordinary open water wouldn't allow.
Image depicting the emulsions that act as microreactors for the PFAS and octanol, which normally wouldn't react in water – a technique central to Maisto's thesis.
The approach works across a broad range of PFAS chemistries, including newer replacement compounds that have proven especially resistant to existing treatment methods. It holds up in dirty water loaded with organic matter, and in salt water too, though salt content costs the reaction some efficiency. Maisto's data shows a dip in performance in salt water, a modest tradeoff given that the reaction is happening in water in the first place. The full process takes about 24 hours and performs best in concentrated waste streams, meaning it requires fewer additives the more PFAS-laden the water already is.
Concentration dependence points to where Maisto sees her technology fitting in: at the source. Maisto’s method is a point-source treatment for the moment PFAS exits an industrial process, like a semiconductor fab or manufacturing plant, before reaching a community's water supply. It is not designed to replace municipal-scale cleanup of already-diluted contamination; it's meant to prevent that contamination from happening at all.
An idea from the library
Maisto found her way to the discovery almost by accident, at the end of her first year at Yale, after a nudge from Prof. Fortner to read about carboxylic acid reactions (the chemical class that covers many PFAS) in the library. Three years of troubleshooting followed. For a long stretch, the reaction seemed to depend heavily on concentration, working reliably at high levels of PFAS but stalling at low ones, a puzzle Maisto had to work through before she could reliably force the destruction step. She counts that first successful summer, and later, cracking the destruction chemistry, among the most rewarding stretches of her Ph.D.
Next year, Maisto will take the underlying problem with her to a postdoc at Columbia, where she'll pursue PFAS destruction using plasma reactors in a continued attempt to break that famously stubborn carbon-fluorine bond.
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Published Date
Jul 30, 2026
