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.