PFAS Clear Victory Against Stubborn Chemicals: Effectively Removing PFAS from Water
As additives, PFAS are true all-rounders. Unfortunately, they are also a massive problem for the environment. This is because they cannot be degraded naturally. Polymer chemists from Saarland and the USA have now found a method to sustainably remove PFAS from water.
Per- and polyfluorinated chemicals, PFAS for short, are incredibly diverse substances. The fluorine-containing organic molecules ensure, among other things, that rain beads off outdoor jackets, they are in cardboard boxes in which food is packed, or they are a component of extinguishing agents and fireproof clothing. First used in the 1940s, these all-rounders began their triumphal march and now permeate our entire lives.
That is practical. And harmful for nature and humans. Because fluorinated chemicals are not degradable in nature. They have been detected all over the world — in water, soil, air, plants, animals and, at the end of the food chain, in humans. It is not yet clear exactly how harmful they are. However, initial studies in animal experiments show a reproductive hazard. What is certain, however, is that these compounds have no place in nature or in organisms, so it makes sense to keep their dose as low as possible.
But you can only get rid of organic molecules at great expense, which also pollutes the environment and the climate. Furthermore, you first have to detect these clever molecules. Even very low concentrations can have a very big effect in applications (e.g. as coatings). For example, PFAS can only be effectively filtered out of water with special membranes or with the much cheaper activated carbon. However, these must then be burned or exposed to relatively harsh conditions in order to finally destroy the substances, as it is no longer possible to dissolve the PFAS out of the filters.
Until now. Scientists led by Markus Gallei, Professor of Polymer Chemistry at Saarland University, and Xiao Su from Illinois, as well as their doctoral students Frank Hartmann (Saar University) and Paola Baldaguez (Illinois), have found a method to remove PFAS from water and then release them again immediately. In this way, the fluorinated substances can not only be collected, but also specifically examined and destroyed, without having to burn the filter straight away.
The secret behind this is an electrochemical method in which a certain group of metal-containing polymers, so-called metallocenes, play the main role. The oldest of these compounds, iron-based ferrocene, was discovered in 1951, followed by many other variants. Frank Hartmann, Markus Gallei and their international team have now been able to find out that electrodes made of ferrocene and — even more effectively — of a cobaltocene, which Frank Hartmann produced, can filter the PFAS molecules out of the water even in minute quantities.
The trick, however, is another one: if you “switch” ferro- or cobaltocene, i.e. apply an electrical voltage, they release the PFAS molecules again efficiently. “And cobalt can do this much better than iron,” Frank Hartmann was able to observe. “This means nothing other than that we have found a method of removing PFAS from the water on the one hand and, moreover, of releasing them again, so that the electrode can be used many times over. Unlike the activated carbon filter, which I have to destroy after the PFAS molecules get stuck in it, I can switch the metallocenes a thousand times if I want to,” Markus Gallei summarises the significance of the research work.
Frank Hartmann, Markus Gallei and their colleagues at the University of Illinois in the USA may thus have laid the foundation for further developments on a larger scale to be able to efficiently filter out the unwanted chemicals from the water of rivers and oceans.
Original Publication: Investigating the Electrochemically Driven Capture and Release of Long-Chain PFAS by Redox Metallopolymer Sorbents; Paola Baldaguez Medina, Valentina Ardila Contreras, Frank Hartmann, Deborah Schmitt, Angelique Klimek, Johannes Elbert, Markus Gallei, and Xiao Su
ACS Applied Materials & Interfaces 2023 15 (18), 22112-22122; DOI: 10.1021/acsami.3c01670, https://pubs.acs.org/doi/10.1021/acsami.3c01670