First-Principles Study of the Interactions between Graphene Oxide and Amine-Functionalized Carbon Nanotube

We applied plane-wave density functional theory to study the effects of chemical functionalizations of graphene and carbon nanotube (CNT) on the properties of graphene–CNT complexes. The functionalizations of graphene and CNT were modeled by covalently attaching oxygen-containing groups and amines (NH2), respectively, to the surfaces of these carbon nanomaterials. Our results show that both dispersion energy and hydrogen bonding play crucial roles in the formation of complexes between graphene oxide (GO) and CNT–NH2. At a lesser degree of functionalization, the interaction energies between functionalized graphene and CNT were either unchanged or decreased, with respect to those without functionalization. Our study indicated that the gain or loss of interaction energy between graphene and CNT is a competition between two contributions: dispersion energy and hydrogen bonds. It was found that the heavy functionalization of graphene and CNT could be a promising route for enhancing the interaction energy between them. Specifically, the carboxyl-functionalized GO produced the greatest increase in the hydrogen bond strength relative to the dispersion energy loss. The influence of Stone–Wales defects in CNT on the computed interaction energies was also examined. The computed electron density difference maps revealed that the enhancement in the interaction energy is due to the formation of several hydrogen bonds between oxygen-containing groups of GO and NH2-groups of CNT. Our results show that Young's moduli of carbon nanomaterials decrease with the increasing concentration of functional groups. The moduli of GO–CNT–NH2 complexes were found to be the averages of the moduli of their constituents.