Würzburg University researchers have created a defect in graphene that allows ions to pass through, which could lead to new applications in water filtration or sensor technology.
The Würzburg model system consisting of two nanographene layers that can absorb and bind chloride ions (green) through a defect in the crystal lattice. (Image: Kazutaka Shoyama / Universität Würzburg)
Defects that allow scientists to control the permeability of graphene for different substances can be very useful: ‘So-called defects can be created in the carbon lattice of graphene. These can be thought of as small holes that make the lattice permeable to gases,’ says chemistry professor Frank Würthner from Julius-Maximilians-Universität (JMU) Würzburg in Germany.
Permeability to other substances, such as ions like fluoride, chloride or bromide, has not yet been observed. ‘However, this would be of fundamental scientific interest for applications such as the desalination of water, the detection or purification of mixtures of substances,’ explains the Würzburg professor.
For the first time, a team led by Frank Würthner has 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 encloses a cavity. The penetrated halide ions are bound in this cavity so that the time required for entry could be measured. The results have been published in the journal Nature.
Chloride is a component of common salt, is found in seawater and plays an important role in life processes in all organisms. ‘The proof of a high permeability for chloride by single-layer nanographene and a selective binding of halides in a double-layer nanographene brings some applications closer,’ says Dr. Kazutaka Shoyama, who initiated and led the project together with Frank Würthner. Such applications include water filtration membranes, artificial receptors and chloride channels.
As a next step, the Würzburg chemists want to build larger stacks of their nanographenes. They want to use them to investigate the flow of ions – and thus a process that also takes place in a similar form in biological ion channels.
