Chemists develop sustainable method to eliminate ‘chemicals forever’

PFAS is a very versatile chemical. These fluorine-containing organic molecules are the reason raindrops slide off their outdoor jackets. They are used in the grease-resistant coating of paper food packaging and are the main ingredient in fire-fighting foams and protective gear worn by firefighters. PFAS were first introduced in the 1940s and since then, the number of products and areas where they are used has grown rapidly.

And therein lies the problem. Because they are so inert and there are no natural pathways by which they can be broken down, these highly persistent chemicals accumulate in the natural environment – ​​creating problems for human health and the environment. PFAS are now detected all over the planet: in water, soil and air, in plants, animals and – at the end of the food chain – also in humans. How big a health risk this chemical poses is still unclear. Preliminary laboratory animal studies suggest that PFAS may interfere with reproductive health. What is clear is that these synthetic compounds are not included in the natural environment and are certainly not included in living organisms. It therefore makes sense to find ways to try and reduce the level of PFAS contamination in the environment.

But PFAS remediation is complex and challenging, and the process used alone can have devastating environmental and climate impacts. And before it can be removed, PFAS must be detected. Detection is not made easier by the fact that only small amounts of PFAS are required for large effects (eg ultra-thin coatings in food packaging). Conventionally, PFAS have been removed from water by filtration using special membranes or lower cost activated carbon absorbents. However, recovering PFAS from these filter systems so they can be permanently destroyed requires the use of harsh chemical conditions or incineration.

At least that’s what happened so far. A research team led by Markus Gallei, Professor of Polymer Chemistry at Saarland University, Professor Xiao Su of the University of Illinois Urbana-Champaign, and their doctoral students Frank Hartmann (Saarland) and Paola Baldaguez (Illinois) have developed a new electrochemical method that can remove materials PFAS chemicals from water and then release it back efficiently for destruction. This new PFAS remediation platform allows these fluorinated contaminants to be collected, identified and then destroyed without the need to burn filters.

In the method developed by the research team, the central role is played by metal-containing polymers known as metallocenes. Metallocene first appeared in 1951 with the discovery of the iron-containing molecule ferrocene. Since then, many other metallocenes have been reported. Frank Hartmann, Markus Gallei and their international team have found that electrodes functionalized with ferrocene or – even more effectively – with cobaltocene synthesized by Frank Hartmann, are able to remove even small amounts of PFAS molecules from water.

But the real key lies in the fact that if a voltage is applied to the ferrocene or cobaltocene metallopolymers, they can ‘switch’ their electrical state and release the previously captured PFAS molecules. “And cobalt is much better at doing this than iron,” says Frank Hartmann. ‘We have discovered a way by which PFAS can be efficiently removed from water and then released again, effectively regenerating the electrode for further use. Unlike activated carbon filters, which I have to destroy after becoming saturated with PFAS molecules, I can replace the metallocene thousands of times, if I want to,’ says Markus Gallei, summarizing the importance of the research work.

Having laid the foundations, Frank Hartmann, Markus Gallei and their colleagues at the University of Illinois are now looking for high-end developments to facilitate the removal of these highly persistent contaminants from our rivers and oceans.