In August 2008, a paper was published describing a new method to produce defect-free graphene nanosheets from graphite. Sometimes referred to as liquid phase exfoliation (LPE), this method uses ultrasonic energy to separate few-layer graphene nanosheets from their parent crystal in certain stabilising liquids. The resultant dispersions can then be used for further study or processed for applications. Over the subsequent decade, LPE has been extended beyond graphene to produce nanosheets from a host of layered compounds including MoS2, BN, MoO3, Ni(OH)2, phosphorene and many other 2D materials. The nanosheets produced by this method tend to be ~100-1000 nm wide, a few monolayers thick and relatively defect free. Using centrifugation, the dispersions can be easily size selected, solvent exchanged and concentrated to ~10 mg/ml. By using high-shear mixing instead of sonication, the process can be massively upscaled. A number of printing processes can be used to form these dispersions into nanosheet networks. Such networks are of use in electrochemical devices such as supercapacitors, battery electrodes or electrocatalysts, especially when combined with carbon nanotubes to form nano:nano composites. In particular, composite films fabricated from combinations of Co(OH)2 nanosheet and carbon nanotube networks perform as state of the art oxygen evolution catalysts. When graphene nanosheet networks are combined with soft polymers, the resultant composite becomes an extremely sensitive electromechanical sensor. When mounted next to the skin, such sensors can detect pulse and even measure blood pressure. Alternatively graphene networks can be printed to act as electrodes. When combined in the correct architecture with networks of semiconducting (eg MoS2) and insulating (eg BN) nanosheets it is possible to produce all-printed, all-nanosheet field effect transistors.

Ten years of liquid phase exfoliation: Making nanosheets for applications in energy, sensing and electronics

256th National Meeting (2018)

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