Researchers develop a new method for the technological use of 2D nanomaterials

To the human eye, layered crystals after osmotic swelling are visible only as unclear clumped structures. Credit: Chr. Wißler

Nanosheets are finely structured two-dimensional materials and have great potential for innovation. They are attached to each other in layered crystals, and must first be separated from each other so that they can be used, for example, to filter gas mixtures or for effective gas barriers. A research team from the University of Bayreuth has just developed a gentle and environmentally friendly process for this difficult delamination process, which can even be used on an industrial scale. This is the first time that a crystal from the technologically attractive group of zeolites has been made usable for a wide range of potential applications.

The delamination process developed in Bayreuth under the direction of Prof. Dr. Josef Breu is characterized by the fact that the structures of the nanosheets isolated from each other remain intact. It also has the advantage that it can be used at normal room temperature. The researchers present their findings in detail in Scientists progress.

The two-dimensional nanosheets, which sit on top of each other in layered crystals, are held together by electrostatic forces. For them to be used for technological applications, the electrostatic forces must be overcome and the nanosheets detached from each other. A particularly suitable method for this is osmotic swelling, in which the nanosheets are separated by water and the molecules and ions dissolved in them. So far, however, it has only been possible to apply it to a few types of crystals, including certain clay minerals, titanates and niobates. For the group of zeoliteshowever, whose nanosheets are very interesting for the production of functional membranes due to their fine silicate-containing structures, the mechanism of osmotic swelling has not yet been applicable.

Researchers develop a new method for the technological use of 2D nanomaterials

Study co-author Felix Uhlig M.Sc. in front of an X-ray diffractometer that was used to examine the nanosheets. Credit: Chr. Wißler

The Bayreuth research team has now, for the first time in an interdisciplinary collaboration, found a way to use osmotic swelling for the gentle separation of ilerite crystals, which belong to the group of zeolites. In the process, large sugar molecules are first inserted into the narrow spaces between the nanosheets. Then the nanosheets, which are stacked on top of each other and structurally aligned, are separated by water. In the process, their spacing becomes considerably larger. Now the nanosheets can be spread horizontally in different directions: during subsequent drying, a solid surface is created, consisting of many nanosheets. These are stacked like playing cards, overlapping only at the edges and leaving only a few gaps. The diameter of individual nanosheets is about 9,000 times greater than their thickness.

This now opens up the possibility of attaching more of these surfaces to each other and building new layered materials. The advantage of this process is that the nanostructures surfaces of the new material are offset from each other. Therefore, their gaps are not exactly superimposed, so that molecules, ions or even light signals cannot penetrate the new material directly. This labyrinthine overall structure allows for a wide range of potential applications, such as in packaging used to keep food fresh, in components for optoelectronics, and perhaps even in batteries.

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More information:
Patrick Loch et al, Nematic suspension of a microporous layered silicate obtained by forceless spontaneous delamination via repulsive osmotic swelling for casting high-barrier all-inorganic films, Scientists progress (2022). DOI: 10.1126/sciadv.abn9084

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