Efficient solvent systems for improving production of few-layer graphene in liquid phase exfoliation

Liquid-phase exfoliation (LPE) of graphite is a promising method to produce few-layer graphene (FLG) in large quantities. Selection of the solvent or surfactant is the most important factor in determining the productivity of LPE and the stability of the liquid FLG dispersion. To find efficient solvent systems for improving the production of FLG, various approaches based on previous research, including addition of a surfactant and use of binary solvents, are investigated using a pressure homogenizer. Over the range of solvents and surfactants used in our study, we find that the greatest improvement in the production of FLG results from the addition of an alkaline aqueous solution (pH 11) into organic solvents. Moreover, we find that this approach works for the probe-sonication method of FLG production as well as for various types of natural graphite. Solvent molecular size and electrostatic repulsion of graphene in liquid play important roles in improving the production of FLG because they mitigate the restacking of FLG during exfoliation.