Graphene Oxide-Assisted Dispersion of Pristine Multiwalled Carbon Nanotubes in Aqueous Media

Graphene oxide (GO) sheets, considered as soft two-dimensional macromolecules containing multiple aromatic regions and hydrophilic oxygen groups, can adsorb the pristine multiwalled carbon nanotubes (MWNTs) through the pi-stacking interaction, thus causing pristine MWNTs to stably disperse and fractionate in aqueous media. The water-soluble and insoluble complexes can be obtained by changing the initial proportion of MWNTs to GO sheets, which are important for noncovalent approaches toward solubilizing CNTs and open a new way for GO applications in colloidal chemistry. Solubility results indicate that the GO sheets are prone to stabilize MWNTs with larger diameters. When the diameters of CNTs decrease to a critical value, the pi-stacking interactions are weakened by large surface energy among CNTs themselves; the CNTs are inclined to form bundles or twisted structures instead of CNT-GO complexes. This can be probably developed into a practical method to fractionate MWNTs with different outer diameters in water.