Supramolecular surface modification and dispersion of graphene in water and organic solvents

Graphene sheets have been dispersed in water and organic solvents by noncovalent surface modification with the assistance of bifunctional molecule pyrene-adamantane (Py-Ad) carrying a pyrene moiety. Lipophilic graphene sheets have been obtained in the form of graphene-Py-Ad in a wide variety of organic solvents, such as dimethyl sulfoxide, N-methyl-2-pyrrolidone, N,N'-dimethylformamide, and tetrahydrofuran, in which the adamantane moieties served as the three-dimensional steric groups keeping the graphene sheets from stacking. Supramolecular complexes were employed as the dispersing agent for graphene formed through in situ reduction by hydrazine or hydroquinone. Water-dispersible graphene sheets have been obtained in the form of graphene-Py-Ad-bMCD (methylated beta-cyclodextrin, bMCD), in which the pyrene moiety attached to graphene by pi-pi stacking interaction and hydrophobic effect, and the adamantane group formed complex with bMCD, yielding a supramolecular system that made graphene sheets dissolved in water through the formed hydrophilic cyclodextrin shell. The resulting supramolecular complexes were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermal gravimetric analysis, transmission electron microscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, and Raman spectroscopy.