Fig. 1.

(a) Schematic illustration of the fabrication of the nano-structure of graphene spheres (nano-rGO). (I) Surface modification of silica particles into a cationic surface by APTMS. (II) Surface coating of surface-modified silica by GO. (III) Self-assembly of GO-coated silica particles followed by reduction. (IV) Removal of particles. (V) Surface-treatment of silane. (b) Zeta-potential of aqueous solution of SiO2,GO,NH2–SiO2, and GO-coated NH2–SiO2measured at pH 7 [60]. Reproduced with permission from Royal society of Chemistry.