Organic functionalization of graphene in dispersions.

Graphene is considered a promising material for a range of new applications from flexible electronics to functional nanodevices, such as biosensors or intelligent coatings. Therefore researchers need to develop protocols for the mass production of graphene. One possible method is the exfoliation of graphite to form stable dispersions in organic solvents or even water. In addition, researchers need to find effective ways to control defects and locally induced chemical changes. We expect that traditional organic chemistry can provide solutions to many of these challenges. In this Account, we describe our efforts toward the production of stable dispersions of graphene in a variety of solvents at relatively high concentrations and summarize representative examples of the organic reactions that we have carried out using these stable dispersions. The sonication procedures used to solubilize graphene can often damage these materials. To mitigate these effects, we developed a new methodology that uses mechanochemical activation by ball-milling to exfoliate graphite through interactions with melamine (2,4,6-triamine-1,3,5-triazine) under solid conditions. Alternatively, the addition of reducing agents during sonication leads to larger graphene layers in DMF. Interestingly, the treatment with ferrocene aldehyde, used as a radical trap, induces the formation of multiwalled carbon nanotubes. The resulting graphene sheets, stabilized by the interactions with the solvent, are suitable materials for performing organic reactions. Relatively few organic reactions have been performed in stable dispersions of graphene, but organic functionalization of these materials offers the opportunity to tune their properties. In addition, thermal treatments can remove the appended organic moieties, restoring the intrinsic properties of pristine graphene. We describe a few examples of organic functionalization reactions of graphene, including 1,3-dipolar cycloadditions, amide condensations, nitrene additions, and radical reactions. The design of novel protocols for further organic functionalization should increase our knowledge of the fundamental chemistry of graphene and spur the further development and application of these materials.