Investigating the exfoliation behavior of MoS₂ and graphite in water: A comparative study

Liquid-phase exfoliation (LPE) offers a promising method for mass production of two-dimensional (2D) nanomaterials. Although numerous efforts have been made to improve the exfoliation efficiency, there is still a lack of understanding towards the exfoliation mechanism and process. Also, appropriate solvents for LPE are certain organic solvents, which are highly toxic, expensive and high boiling; residue surfactant molecules lead to degradation of intrinsic properties of 2D materials exfoliated in water/surfactant mixtures. Hence, exfoliation of 2D materials in a green and low boiling solvent is high demanded. In this paper, we perform a comparative study on the exfoliation behavior of MoS₂ and Graphite in water. It is found that bulk MoS₂ can be exfoliated into multilayer nanosheets, whereas graphite is hardly to be exfoliated into graphene. By applying a simple model and estimating the energy consumption from a microscopic view, we find that the main reason for different exfoliation behavior of MoS₂ and graphite can be attributed to their distinct fragmentation effect during sonication. This work provides new insights into exfoliation mechanism and process of 2D materials in solvents.