Experimental research and numerical simulation of graphene preparation by supercritical CO₂

In this paper, the experimental research and numerical simulation of graphene preparation by supercritical carbon dioxide were carried out using flake graphite as raw material. The process of supercritical CO₂ preparation of graphene was carried out, and the concentration of graphene prepared under the pressure of 8–9 MPa did not increase significantly, and the concentration increased significantly after the pressure exceeded 10 MPa. When the pressure is 8–9 MPa, the graphite flake layer does not see obvious peeling, and the flake layer is very thick with a large radius by the SEM and Raman spectroscopy. The flake layer is thinned after the pressure exceeds 10 MPa, and the surface morphology appears to be wrinkled indicating that the graphene has been prepared. When the pressure reaches 12 MPa, monolayer graphene is observed by TEM and AFM. Furthermore, based on the first principle molecular dynamics method, the model of CO₂ molecules exfoliating the graphite layer is established, the different density effect of CO₂ molecules between graphite layers is realized by changing the size of graphite flake layer, and the critical pressure and density of peeling graphene are calculated to be 9.73 MPa and 0.16 g/cm³, respectively, to analyze the mechanism of the CO₂ molecules’ action on graphite layer in the process of pressure relief peeling. As the pressure increases, the exfoliation rate of the graphite layer increases, which in turn causes an increase in the concentration of graphene and a decrease in the number of graphene layers. This also explains the slow exfoliation of graphite into graphene when the pressure reaches 10 MPa in the experiments.