(346f) Dispersion of Functionalized Graphene Sheets in Nonpolar Solvents

The dispersion of reduced graphene oxide (RGO) as single- and few-layer sheets in aqueous and in polar organic solvents is well-established. Successful approaches for example include the use of surfactants or the careful selection of the solvent depending on its cohesive energy density (compatible Hansen Solubility Parameters – HSP values – between the solvent and the sheets). The dispersion of RGO in nonpolar organic solvents such as toluene or alkanes is more challenging and the sheets typically form large flocs within a few minutes. We developed a 2-steps one-pot technique to covalently attach alkyl chains to RGO using the residual oxygen-containing functional groups present of the surface of the sheets as anchoring points. The synthesized alkyl-chain-grafted RGO readily dispersed in a variety of polar and nonpolar organic solvents. By studying the stability of the suspensions, we found that the grafted alkyl groups increased the range of compatible HSP values, meaning that the synthesized material disperse in a broader variety of organic solvents, including methanol, ethanol, toluene and heptane. ATR-FTIR, UV-Vis and Raman spectroscopy showed that the grafting reaction did not significantly alter the structure and defect density of the sheets. Furthermore, TG-MS data indicated that most groups were stable below 300 °C. This technique is particularly interesting to design nanostructured heterogeneous catalysts for liquid phase reactions. In addition, we believe it could be particularly useful for the further processing of defect-engineered graphene sheets, to achieve particular electronic or optical properties.