Chemists develop method to sustainably remove hazardous substances from water

New progress in the fight against PFAS

27-Jun-2023 - Germany

Graphical representation of a metal-containing polymer with ferrocene units used for reversible uptake of perfluorinated compounds.

Markus Gallei

PFAS - per- and polyfluorinated chemicals - are true all-rounders. The grease-, water- and dirt-repellent chemicals occur in thousands of varieties, for example in cookware, functional clothing, cosmetics and as fire extinguishing agents. 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. They have published their method in the scientific journal ACS Applied Materials & Interfaces.

PFASs are incredibly diverse substances. Among other things, the fluorine-containing organic molecules ensure that rain beads off outdoor jackets, they are in cardboard boxes in which food is packaged, 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's practical. And harmful to nature and people. Fluorinated chemicals are not degradable in nature. They are now found 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.

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But you can only get rid of organic molecules at great expense, which also pollutes the environment and the climate. Furthermore, these clever molecules first have to be detected. Even very low concentrations can have a very large effect in applications (e.g. as coatings). For example, PFAS can only be effectively filtered out of water using special membranes or the much cheaper activated carbon. However, one then has to burn these or expose them to relatively harsh conditions to finally destroy the substances, since one can no longer dissolve the PFAS out of the filters.

Until now. Because 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 for removing PFAS from water and then immediately releasing them again. In this way, the fluorinated substances can not only be collected, but also specifically examined and destroyed, without having to immediately burn the filter.

The secret behind this is an electrochemical method in which a certain group of metal-containing polymers, known as 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 from ferrocene and - even more effectively - from a cobaltocene that Frank Hartmann produced, can filter the PFAS molecules out of the water even in minute quantities.

The trick, however, is another: when ferro- or cobaltocene is "switched," i.e., an electrical voltage is applied, it efficiently releases the PFAS molecules again. "And cobalt can do this significantly 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, how to release 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," says Markus Gallei, summing up the significance of the research work.

Frank Hartmann, Markus Gallei and their colleagues at the University of Illinois in the U.S. may thus have laid the foundation for further developments on a larger scale to efficiently filter out the unwanted chemicals from the water of rivers and oceans.

Note: This article has been translated using a computer system without human intervention. LUMITOS offers these automatic translations to present a wider range of current news. Since this article has been translated with automatic translation, it is possible that it contains errors in vocabulary, syntax or grammar. The original article in German can be found here.

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

https://www.chemeurope.com/en/news/1180913/chemists-develop-method-to-sustainably-remove-hazardous-substances-from-water.html