Ultrasonic-Assisted Production of Graphene with High Yield in Supercritical CO2 and Its High Electrical Conductivity Film

A simple, cost-effective approach is presented for producing exfoliated films of pure graphene or polymer–graphene composite with high yield, high conductivity, and processability. The approach combines supercritical CO 2 with ultrasonics. Characterization by Raman spectroscopy combined with atom force field microscopy demonstrates that the graphene sheets were obtained with 24% as monolayers, 44% as bilayers, and 26% as trilayers. The layer number and lateral size of graphene sheets can be controlled by adjusting the process parameters. The yield of graphene sheets with a lateral size of about 0.5–5.0 μm is about 16.7 wt % under optimum conditions, which can be easily raised to 40–50 wt % by repeated exfoliation of the sediment that remained in the reactor. The resultant pure graphene film made by filtration has a high electrical conductivity of 2.8 × 10 7 S/m. The electrical conductivity of the film of polyvinyl alcohol–graphene composite is 300 S/m.