Liquid phase exfoliation

First demonstrated in 2008,[1] liquid-phase exfoliation (LPE) is a solution-processing method which is used to convert layered crystals into two-dimensional nanosheets in large quantities.

[3] According to IDTechEx, the family of exfoliation techniques which are directly or indirectly descended from LPE now make up over 60% of global graphene production capacity.

[4] This method involves adding powdered layered crystals, for example of graphite, to appropriate solvents and inserting energy, often by ultrasonication, although high-shear mixing[5] is often commonly used.

The addition of energy causes a combination of fragmentation and exfoliation resulting in the removal of small nanosheets from the layered crystals.

[7] In general, these nanosheets tend to be a few monolayers thick and of lateral sizes ranging from tens of nanometers to many microns.

Although this method was first applied to exfoliate graphite to yield graphene nanosheets, it has since been used to produce a wide range of 2D materials including molybdenum disulfide, tungsten diselenide, boron nitride, nickel(II) hydroxide, germanium monosulfide, SnP3, and black phosphorus.

[12] Liquid phase exfoliation was first described in detail in a paper by a research team in Ireland in 2008,[14] although a very short description of a similar process was published by the Manchester group around the same time.

[26] Recent work has shown that liquid phase exfoliation can be used to produce 2D-nanoplatelets from non-layered 3D-strongly bonded bulk materials.