Australian researchers tested a new method for PFAS decontamination

Researchers at the University of New South Wales in Sydney have developed an effective technique to break down the strong carbon-fluorine bonds that make PFAS hard to break do

by Matteo Cavallito

 

Perfluoroalkylated substances or PFAS are known to be a serious threat to soils. Particularly persistent in soils, in fact, these compounds are difficult to remove to the point of being a real obstacle in environmental restoration. A group of researchers from the University of New South Wales in Sydney, however, may have found a solution to the problem.

The scientists, says a statement, have in fact designed a catalyst system capable of triggering a reaction to break down the most common branched PFAS. “Owing to its robust nature, simple application, and cost effectiveness, the new system we have developed shows successful remediation in the lab, which we hope to eventually test at a larger scale,” said Jun Sun, researcher and co-author of the study published in the journal Water Research. The new method, the scientists claim, would pave the way for more efficient and sustainable remediation in the future.

The characteristics of PFAS

Not surprisingly called forever chemicals because of their persistence in soils, PFAS “are both highly stable and useful in products designed to repel grease and water but it also means they do not readily biodegrade,” wrote the journal Scientific American. These compounds are typically found in fluorinated pesticides (i.e. those containing one or more fluorine atoms in their molecular structure) that are considered particularly effective in combating plant pests.

This efficacy derives precisely from the chemical stability that favours their prolonged action. A characteristic which brings with it the obvious downside: the difficulty of disposal.

According to some estimates, the half-life of some fluorinated products – that is, the time it takes for their presence in the environment to be halved after spraying – can be up to two and a half years. According to the EPA, the US Environmental Protection Agency, pollutants are defined as ‘persistent’ when they have a half-life of more than 60 days.

The solution? Zero-valent nano-metals

From a technical point of view, experts explain, the main problem with PFAS is the difficulty of breaking the strong carbon-fluorine bonds that characterise them at the molecular level. One of the most widely used remediation methods involves the use of activated carbon to absorb these substances. Another technique involves the use of a strong oxidising agent to separate the substance. However, both methods are challenging, not entirely effective and not very sustainable.

To solve these problems, the authors chose to focus on so-called zero-valent nano-metals (nZVMs).

These particular chemical agents, the study explains,”have been extensively utilized for decades in the reductive remediation of groundwater contaminated with chlorinated organic compounds, owing to their robust reducing capabilities, simple application, and cost-effectiveness.” However, “there remains a dearth of information regarding the efficient reductive defluorination of linear or branched per- and polyfluoroalkyl substances (PFASs) using nZVMs as reductants, largely due to the absence of appropriate catalysts.” And it is precisely on this aspect that the researchers’ work has focused.

A much more effective technique

Catalysts are all those substances that are capable of triggering a chemical reaction. These include vitamin B12, a popular compound capable of triggering the reaction between nano-metals and PFAS. Its use, however, does not appear satisfactory: the triggering process is slow and ineffective. Therefore, the researchers chose to synthesise a catalyst that mirrors the ring shape of B12: cobalt porphyrin.

The authors tested the method by measuring the amount of fluoride (the salt of hydrofluoric acid, ed.) released by breaking carbon-fluorine bonds.

They found that in the space of five hours, porphyrin caused 75% of the amount of the element to be released. At the same time, the amount released with B12 was no more than 8%. The effectiveness of the system, in short, is evident. And the hope of the researchers is that the method can be used in future remediation actions.