Controllable Synthesis of Graphene in Aqueous Phase for Fabrication of Graphene-Based Composites

We report a facile, environment-friendly, and low-cost method for the synthesis of graphene in aqueous phase by the exfoliation of microwave-assisted expanded graphite with the assistance of surfactant cetyltrimethylammoniumbromide (CTAB). Scanning electron microscopy and transmission electron microscopy micrographs reveal that graphene sheets with adjustable number of layers were achieved. Raman and UV-Vis spectra further confirm this result and indicate that the as-prepared graphene sheets are of high quality with low defect density. By measuring the surface energy density of water with and without adding surfactant CTAB, a possible exfoliation mechanism through decreasing the surface energy of water induced by CTAB and subsequent intercalation of CTAB into graphite layers is proposed. By vacuum filtration, the generated graphene sheets can easily form conductive films. Because this method was carried out in aqueous phase, it is convenient to further fabricate the generated graphene sheets into controllable graphene-based composites for various applications, such as photocatalysts, supercpacitors, lithium ion batteries, etc.