Simple method destroys dangerous 'forever chemicals,' making water safe

There is some good news if you've been depressed by recent revelations that dangerous man-made chemicals known as PFAS, which may persist for thousands of years and make even rainfall unfit to drink, have completely invaded Earth's water supplies.

Chemists at UCLA and Northwestern University have created a straightforward method to degrade over a dozen different kinds of these "forever compounds" at relatively low temperatures without creating any negative consequences.

In a paper published today in the journal Science, the researchers demonstrate that in water heated to just 176 to 248 degrees Fahrenheit, common, inexpensive solvents and reagents severed some of the strongest known PFAS molecular bonds, starting a chemical reaction that "gradually nibbled away at the molecule" until it was gone, according to Kendall Houk, distinguished research professor at UCLA and co-corresponding author.

There is no upper limit to the amount of water that may be handled simultaneously due to the straightforward technology, the relatively low temperatures, and the absence of dangerous byproducts, according to Houk. In the future, the technology might make it simpler for water treatment facilities to remove PFAS from drinking water.

Around 12,000 synthetic compounds of the per- and polyfluoroalkyl substances (PFAS) class have been used in nonstick cookware, waterproof makeup, shampoos, electronics, food packaging, and a plethora of other items since the 1940s. Nothing in nature can sever the link between the atoms of fluorine and carbon found in them.

These substances enter the Earth's water cycle when they are released into the environment during production or product usage. Due to their strong carbon-fluorine link, PFAS have contaminated nearly every drop of water on Earth over the past 70 years and are utterly unaffected by the majority of water treatment technologies. Over time, they can build up in the tissues of people and animals and harm in ways that science is only now starting to fully comprehend. For instance, PFAS is linked to some malignancies and thyroid conditions.

These factors make the need for PFAS removal from water even more pressing. Numerous remediation solutions are being tested by scientists, but the most of them call for very high temperatures, specialized chemicals, or ultraviolet light. They also occasionally produce byproducts that are similarly toxic and necessitate extra processes to eliminate.

William Dichtel, a chemical professor at Northwestern, and PhD candidate Brittany Trang found that while PFAS molecules have a lengthy "tail" of resistant carbon-fluorine bonds, they also frequently have charged oxygen atoms in their "head" group, which strongly interacts with other molecules. By heating the PFAS in water with dimethyl sulfoxide, often known as DMSO, and sodium hydroxide, or lye, Dichtel's team created a chemical guillotine that chopped off the head and left an exposed, reactive tail.

It "started spitting out fluorine atoms from these compounds to generate fluoride, which is the safest form of fluorine" after all these reactions, according to Dichtel. Despite the fact that carbon-fluorine bonds are quite strong, the charged head group is the weak link.

The investigations, however, also turned up another surprise: The molecules didn't appear to be disintegrating in the manner predicted by conventional thinking.                                                                                                                 

Dichtel and Trang collaborated with Houk and Tianjin University student Yuli Li, who was working in Houk's group remotely from China during the pandemic, to unravel this mystery. In contrast to the researchers' expectations, Li and Houk's computer simulations of the PFAS molecules revealed that two or three carbon molecules peeled off the molecules simultaneously, just as Dichtel and Tang had observed experimentally.

The simulations also demonstrated that the only byproducts should be harmless formic acid, carbon dioxide, and fluoride, which is frequently added to water to prevent tooth decay. In additional studies, Dichtel and Trang found that these anticipated results were true.

Houk stated that the computations "proven to be an extremely difficult set that defied the most advanced quantum mechanical methods and fastest computers that we are now able to use." "Quantum mechanics is the mathematical technique that simulates all of chemistry, but it has only been in the last decade that we have been able to tackle large mechanistic problems like this, evaluating all the possibilities and determining which one can happen at the observed rate," says the author.

Li, according to Houk, is an expert in these computational techniques, and he collaborated remotely with Trang to find a solution to the basic but crucial issue.

Perfluoroalkyl ether carboxylic acids (PFECAs) and perfluoroalkyl carboxylic acids (PFCAs), including perfluorooctanoic acid, were degraded in the current investigation in ten different forms (PFOA). The researchers expect that this approach will help them find weak points in other classes of PFAS and that it will work for the majority of PFAS that contain carboxylic acids. They anticipate that these hopeful findings will spur additional investigation into strategies for removing the thousands of other PFAS species.

The National Science Foundation provided funding for the research, which was titled "Low-temperature mineralization of perfluorocarboxylic acids.

                                                                                                                       University of California - Los Angeles