Investigating the Exfoliation Behavior of MoS2 and Graphite in Water: A Comparative Study

Abstract 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.