Isolation of graphene and graphite by supercritical CO₂ elutriation technique: CFD simulation and experimental

Exfoliation of graphite has become a popular top-down method of producing graphene. However, it is still a challenging issue to prepare purified graphene because the exfoliated graphene was usually mixed with the un-exfoliated graphite. In this work, we investigated the isolation of the graphene and graphite by using supercritical CO₂ through Computational Fluid Dynamics (CFD)simulation and experimental. The Eulerian multiphase and standard k–ε turbulence models for CFD simulation were used to explore the influences of the pressure and the velocity of supercritical CO₂, the geometry of the separation column, and the feeding amount of the mixture on the distribution of the graphene and graphite in the column. The isolation experiments were carried out based on the CFD simulation results, and the isolated graphene was characterized by Raman spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy. The results indicate that the purified graphene sheets can be obtained by supercritical CO₂ elutriation approach and the optimal experimental conditions were consistent with that obtained by CFD simulation. The graphene was isolated with graphite completely when the volume fraction of the mixture of the graphene and graphite was <20%, the pressure and the flow rate of supercritical CO₂ were 8 MPa and 0.2 m/s, respectively. The obtained graphene sheets mainly consisted of 3–5 layers. The CFD simulation is helpful in scale-up production of purified graphene by supercritical CO₂ elutriation technique_.