A laser shines through a solution of still dissolving 2D nanomaterial, showing particles within the liquid (left). When a drop of the solution is dried, the still dissolving nanosheets stack into different tiled shapes (right). When left to fully dissolve, only single layer sheets are found. Images: Patrick Cullen et al.
A laser shines through a solution of still dissolving 2D nanomaterial, showing particles within the liquid (left). When a drop of the solution is dried, the still dissolving nanosheets stack into different tiled shapes (right). When left to fully dissolve, only single layer sheets are found. Images: Patrick Cullen et al.

A team led by researchers at University College London (UCL) in the UK has come up with a new way to produce two-dimensional (2D) nanomaterials by dissolving layered materials in liquids. These liquids can be used to apply the 2D nanomaterials over large areas and at low costs, potentially leading to a variety of important future applications.

With their remarkable physical properties, 2D nanomaterials such as graphene have the potential to revolutionize many technologies, but their translation into real world applications has been limited due to the challenges involved in making and manipulating 2D nanomaterials on an industrial scale.

The new approach, reported in a paper in Nature Chemistry, produced single layers of many 2D nanomaterials in a scalable way. The researchers applied the method to a wide variety of materials, including those with semiconductor and thermoelectric properties, to create 2D materials that could be used in solar cells or for turning wasted heat energy into electrical energy, for example.

"2D nanomaterials have outstanding properties and a unique size, which suggests they could be used in everything from computer displays to batteries to smart textiles," explained study director Chris Howard from UCL. "Many methods for making and applying 2D nanomaterials are difficult to scale or can damage the material, but we've successfully addressed some of these issues. Hopefully our new process will help us realize the potential of 2D nanomaterials in the future."

In the study, funded by the Royal Academy of Engineering and the UK Engineering and Physical Sciences Research Council, the scientists inserted positively-charged lithium and potassium ions between the layers of different 2D materials including bismuth telluride (Bi2Te3), molybdenum disulphide (MoS2) and titanium disulphide (TiS2). This gave each material layer a negative charge, creating a 'layered material salt'.

These layered material salts were then gently dissolved in selected solvents without using chemical reactions or stirring. This created solutions of 2D nanomaterial sheets with the same shape as the starting material but a negative charge.

Using atomic force microscopy and transmission electron microscopy, the scientists analyzed the contents of these solutions to investigate the structure and thickness of the 2D nanomaterials. They found that the layered materials dissolved to form tiny sheets of clean, undamaged, single layers.

The team, comprising researchers from UCL, the University of Bristol and the Cambridge Graphene Centre in the UK and the École Polytechnique Fédérale de Lausanne in France, was able to show that even 2D nanomaterial sheets comprising millions of atoms produced stable solutions rather than suspensions.

"We didn't expect such a range of 2D nanomaterials to form a solution when we simply added the solvent to the salt – the layered material salts are large but dissolve into liquid similar to table salt in water," said first author Patrick Cullen from UCL. "The fact that they form a liquid, along with their negative charge, makes them easy to manipulate and use on a large scale, which is scientifically intriguing but also relevant to many industries."

"We've shown they can be painted onto surfaces and, when left to dry, can arrange themselves into different tiled shapes, which hasn't been seen before," he continued. "They can also be electroplated onto surfaces in much the same way gold is used to plate metals. We're looking forward to making different 2D nanomaterials using our process and trying them out in different applications as the possibilities are near endless."

UCL Business, the technology commercialization company of UCL has patented this research and will be supporting the commercialization process.

This story is adapted from material from UCL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.