High-Efficiency Production of Graphene by Supercritical CO2 Exfoliation with Rapid Expansion.

In this study, direct nonequilibrium molecular dynamics simulations based on the density-functional tight-binding potential were performed to investigate the mechanism of graphite exfoliation by supercritical CO2 in the depressurization process. We found that the graphite peeling rate and the graphene yield depended on the number of inserted CO2 molecules in our simulations, and the appropriate pressure or density of CO2 is a prerequisite to achieve graphite exfoliation. Our theoretical results proposed that the graphite peeling occurred till the pressure or the density of CO2 was larger than 12.2 MPa or 0.21 g/cm3. This is confirmed by the experimental observations. Furthermore, we declared that the essential effect of the pressure or density of CO2 was attributed to the competition between the van der Waals attraction in the graphite interlayer and repulsion of CO2 and graphite, which resulted from the steric hinder effect. The current theoretical observations provide potential scientific evidence to control graphite exfoliation by supercritical CO2.