Functionalization Methods of Carbon Nanotubes and its Applications

In 1991 Iijima [Iijima, 1991] presented transmission electron microscopy observations of elongated and concentric layered microtubules made of carbon atoms, nowadays which were called carbon nanotubes (CNTs). In order to understand the structure of a carbon nanotube, it can be first imagined as a rolled up sheet of graphene with planar-hexagonal arrangement of carbon atoms distributed in a honeycomb lattice. CNTs are classified into single-walled carbon nanotube, double-walled carbon nanotube, and multi-walled carbon nanotube according to the rolling layers of graphene sheets. Several techniques for producing CNTs have been established and all of them have advantages as well as disadvantages. Usually being applied methods are high temperature techniques, namely arc discharge [Bystrzejewski et al., 2008; Sun et al., 2007] and laser ablation [Rüummeli et al., 2007], as well as chemical vapor deposition (CVD) with its most common variants [Ayala et al., 2008; Nikolaev et al., 1999]. CNTs possess unique electronic, chemical, and mechanical properties that make them leading materials for a variety of potential applications. But the outer wall of pristine CNTs is, in principle, conceived as chemically inert. This is not always desirable for applications and for this reason. One of the most promising routes to overcome this difficulty is to functionalize CNT. Functionalization extends their properties and consequently their application potential. Hence understanding their functionalization is crucial for fully exploiting their potential. Researchers have developed some effective methods to functionalize CNT surfaces such as covalent modification or noncovalent approaches including polymer wrapping, biomolecule binding, and metal ion binding. Other functionalization routes which have been thought to make them chemically active in the past few years, including chemical and solid-phase or hydro-mechanochemical method will also be introuduced in details in the following contributions. The advantages and shortcomings of every functionalization method will be showed clearly. At the same time some characterization methods for CNTs will be also refered. In the last part of this chapter the applications of carbon nanotubes as functional materials in the fields of biosensing, fuel cells, medical treatment, and so on, especially in the field of thermal conductivity are summarized. It is our hope that all the content of this chapter can supply helps to the researchers in the study of carbon nanotubes.