Dear friend Bo Yong

Exfoliating bulk materials to obtain 2D nanosheets can be challenging, especially for materials that do not exhibit strong van der Waals forces between layers. However, there are several techniques that can be employed to exfoliate such materials:

1. Liquid-phase exfoliation: This method involves dispersing the bulk material in a suitable solvent and applying external forces to break down the material into nanosheets. Techniques such as sonication, high-shear mixing, or ball milling can be used to create shear forces and induce exfoliation. The choice of solvent and optimization of process parameters are crucial for successful exfoliation.

2. Chemical exfoliation: Chemical treatments can be employed to weaken the interlayer bonds and promote exfoliation. Functionalization with chemical agents or intercalation of molecules between the layers can facilitate the separation of layers. Acidic or basic treatments, oxidative treatments, or intercalation with specific ions or molecules can be utilized based on the specific material properties.

3. Mechanical exfoliation: While non-van der Waals materials may be more challenging to mechanically exfoliate; it is still possible to obtain nanosheets through techniques like scotch-tape exfoliation. In this method, repeated peeling and pressing of the material with adhesive tape can lead to the detachment of thin layers.

It's important to note that the exfoliation process may require optimization based on the specific bulk material and desired nanosheet properties. Furthermore, the selection of appropriate methods depends on the chemical and structural properties of the material being exfoliated.

Novoselov, K. S., Fal′ ko, V. I., Colombo, L., Gellert, P. R., Schwab, M. G., & Kim, K. (2012). A roadmap for graphene. Nature, 490(7419), 192-200.