Liquid Phase Exfoliation of Graphite into Graphene Nanoplatelets using Graphene Oxide as Surfactant

Abstract

In this study, graphene nanoplatelets (GNP) are prepared using graphene oxide (GO), a derivative of graphene, as the dispersing agent in the liquid phase exfoliation of raw fake graphite. Graphene oxide has similar properties to that of graphene, however, it contains functional groups such as epoxides, hydroxyls and carboxyls. This added functionality makes GO amphiphilic and a suitable dispersing agent in water. In order to prepare stable GNP dispersions during exfoliation, the sheets need to overcome the van der Waals attractive forces and π-π interactions. Preliminary research shows that more widely stable GNP dispersions can be achieved by adjusting the pH of dispersions to 10. The major variables influencing the exfoliation of graphite are: the concentration of GO and graphite, along with shear rate, and time. Using dimensional reasoning and according to the factorial design of experiments, we obtain a correlation to optimize the GNP yield by a response surface methodology. The exfoliated GNP content in the dispersions is determined from UV-vis spectroscopy, via a GO/GNP standard calibration curve. Furthermore, the exfoliated GNP is characterized using, atomic force microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Finally, the GO/GNP dispersions are then concentrated and used to synthesize graphene hydrogels. The resulting hydrogels are used as an electrode material for making flexible supercapacitors and their performance is evaluated.