A Technique To Pretreat Graphite Which Allows the Rapid Dispersion of Defect-Free Graphene in Solvents at High Concentration

We have demonstrated a simple method to pretreat graphite powder resulting in a significant reduction in the time required to produce dispersions of solvent-exfoliated graphene. Sonication of graphite in either stabilizing solvents such as NMP or nonstabilizing solvents such as water results in significant breakage of graphite flakes and considerable exfoliation to give graphene. As expected, much of the graphene produced is stable indefinitely in NMP. Surprisingly, however, in the water-based samples unaggregated graphene was observed up to 26 h after sonication with complete sedimentation only observed after 70-130 h. In both cases, removal of the solvent resulted in a powder consisting of broken graphite flakes and reaggregated graphene. For both water and NMP pretreatments, this powder could be very easily redispersed by sonication in NMP to give good quality, defect-free graphene nanosheets. However, the concentration achievable after a given resonication time depended strongly on the pretreatment solvent and time. Redispersion of NMP-pretreated powder occurred much faster with concentrations of 1 mg/mL achieved after only 1 min resonication. This pretreatment technique will facilitate both the storage and transportation of liquid exfoliated graphene.