Chemists in Würzburg have for the first time created a defect in graphene that allows ions to pass through. As they report in Nature, this could lead to new applications in water filtration or sensor technology.

Graphene is an extremely thin, flexible and resilient material made of pure carbon. It forms layers that consist of practically just a single layer of carbon atoms. To make graphene as thick as a human hair, you would have to stack thousands of such layers on top of each other.

Many researchers are studying graphene intensively. There is a good reason for this, because the material’s special properties promise new applications, for example in electronics or energy technology.

Making Graphene Permeable to Other Molecules

It is particularly interesting for science to be able to control the permeability of graphene for different substances: “So-called defects can be created in the carbon lattice of graphene. You can imagine these as small holes that make the lattice permeable to gases,” said chemistry professor Frank Würthner from the Julius Maximilian University (JMU) in Würzburg.

Permeability for other substances, such as ions such as fluoride, chloride or bromide, has not yet been observed. “But this would be of fundamental scientific interest for applications such as the desalination of water, the detection or purification of mixtures of substances,” explained the Würzburg professor.

Defect Allows Ions to Pass: Publication in Nature

For the first time, a team led by Frank Würthner has now created a model system with a defect that allows the halides fluoride, chloride and bromide to pass through, but not iodide.

This was achieved in a stable double layer consisting of two nanographenes that enclose a cavity. The halide ions that have penetrated are bound in this cavity, so that the time for entry could be measured. The results have been published in the journal Nature.

Chloride is a component of table salt, occurs in seawater and plays an important role in life processes in all organisms.

“The demonstration of high permeability for chloride through single-layer nanographene and selective binding of halides in a two-layer nanographene brings some applications closer,” said Dr. Kazutaka Shoyama, who initiated and led the project together with Frank Würthner. Such applications would include water filtration membranes as well as artificial receptors and chloride channels.

Larger Stacks of Nanographenes as the Next Goal

In the next step, the Würzburg chemists want to build larger stacks of their nanographenes. They want to use them to study the flow of ions – a process that also takes place in a similar form in biological ion channels.

This research was carried out at the Institute of Organic Chemistry and the Center for Nanosystems Chemistry at JMU. The work was funded by the German Research Foundation (DFG) as part of two research grants for the development of nanographenes equipped with imide groups.

Publication:
Bilayer nanographene reveals halide permeation through a benzene hole. MA Niyas, Kazutaka Shoyama, Matthias Grüne & Frank Würthner, Nature, January 15, 2025, DOI: 10.1038/s41586-024-08299-8, https://www.nature.com/articles/s41586-024-08299-8