Northwestern University chemists have found a way to destroy two major classes of PFAS compounds to fall apart.
According to the university's press release, this involves using "low temperatures and inexpensive, common reagents...leaving behind only benign end products."
“PFAS has become a major societal problem,” said Northwestern’s William Dichtel, who led the study, reported the university. “Even just a tiny, tiny amount of PFAS causes negative health effects, and it does not break down. We can’t just wait out this problem. We wanted to use chemistry to address this problem and create a solution that the world can use. It’s exciting because of how simple — yet unrecognized — our solution is.”
Dichtel is the Robert L. Letsinger Professor of Chemistry in Northwestern’s Weinberg College of Arts and Sciences. Brittany Trang conducted the project as a part of her completed doctoral thesis in Dichtel’s laboratory and is the paper’s co-first author.
“In New York state, a plant claiming to incinerate PFAS was found to be releasing some of these compounds into the air,” Dichtel said, reported the university. “The compounds were emitted from the smokestacks and into the local community. Another failed strategy has been to bury the compounds in landfills. When you do that, you are basically just guaranteeing that you will have a problem 30 years from now because it’s going to slowly leach out. You didn’t solve the problem. You just kicked the can down the road.”
According to Dichtel, PFAS chemical bonds are the key, as PFAS contain many carbon-fluorine bonds. So, fluorine wants electrons, but carbon is more willing to give up its electrons.
Though PFAS contains a long tail of carbon-fluorine bonds, on one end of the molecule, there is a charged group that often contains charged oxygen atoms. The team targeted this head by heating the PFAS in dimethyl sulfoxide with sodium hydroxide, a common reagent, which "decapitated the head group, leaving behind a reactive tail."
“That triggered all these reactions, and it started spitting out fluorine atoms from these compounds to form fluoride, which is the safest form of fluorine,” Dichtel said. “Although carbon-fluorine bonds are super strong, that charged head group is the Achilles’ heel.”
According to collaborators Ken Houk at UCLA and Yuli Li, a student at Tianjin University, PFAS falls apart by more complex processes, and a simulation showed that PFAS falls apart two or three carbons at a time.
“This proved to be a very complex set of calculations that challenged the most modern quantum mechanical methods and fastest computers available to us,” said Houk, a research professor in organic chemistry. “Quantum mechanics is the mathematical method that simulates all of chemistry, but only in the last decade have we been able to take on large mechanistic problems like this, evaluating all the possibilities and determining which one can happen at the observed rate. Yuli has mastered these computational methods and worked with Brittany long distance to solve this fundamental but practically significant problem.”
Dichtel’s team will soon test the effectiveness of its new strategy on other types of PFAS. The current study successfully degraded 10 perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl ether carboxylic acids (PFECAs), including perfluorooctanoic acid (PFOA) and GenX, reported the university.
The study, titled, “Low-temperature mineralization of perfluorocarboxylic acids,” was supported by the National Science Foundation.
