ABSTRACT
Carbon nanotubes (CNTs) were discovered by a Japanese physicist, Sumio Iijima, in 1991. Since then, a number of studies investigating the properties and applications of CNTs have been reported. CNTs are apparently elongated fullerenes having either single or multiple hexagonal rolled-up sheets of carbon atoms (graphene) making up the walls with capped ends (Xie et al., 2005). Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) are commonly known as the common types of CNTs. Specifically, SWCNTs have only a single layer of graphene-sheet wall located around a central hollow core (tube) On the other hand, MWCNTs 62are generally composed of more than one graphene shell coaxially located along the tube. The diameters of the nanotubes are in the range of 1–10 s nm, depending on the number of walls, with high length-to-diameter ratio (generally more than 1000). CNTs are traditionally produced by thermal degradation of a carbon source in the presence of a metal catalyst using laser ablation or an arc discharge approach. The limitations of these methods are widely reported; specifically, laser ablation is not applicable for large-scale production while CNTs produced by the arc discharge process contain high-level contaminations of carbonaceous impurities as well as metal catalysts (Meyyappan et al., 2003).
