Covalent Functionalization of Carbon Nanostructures

Covalent functionalization of carbon nanostructures, i.e., graphene, single- and multiwalled carbon nanotubes (SWCNTs and MWCNTs), fullerenes, carbon nanofibers (CNFs), etc., is the attachment of different chemicals onto their conjugated sp2 carbon scaffold. This reaction results in a transition from sp2 to sp3 hybridization and the simultaneous loss of conjugation. But, the reactivity of the carbon allotrope nanostructures is different from each other. Due to its planar, aromatic, sp2-linked carbon framework, graphene is chemically inert. Their level of reactivity can be raised by bending a flat graphene sheet into a two- or three-dimensional carbon framework. Therefore, fullerenes’ 3D curved π-surface can be functionalized more readily than the other carbon nanostructures. The main results of covalent functionalization are the change of the surface reactivity toward specific chemical species and better coupling with other substances. So, the functionalized carbon nanostructures exhibit improved properties concerning solubility and ease of dispersion, processability, and manipulation. Covalent functionalization is categorized based on the chemical involved and the type of reaction, such as chemical addition (nucleophilic, radical, etc.), cycloaddition (nitrene and 1,3-dipolar, etc.), hydrogenation, fluorination, etc. In the present chapter, the kind of covalent functionalization is reviewed.