Carbon Nanotubes

 

Schematic Molecular Representation of SWCNTs and MWCNTs

Carbon nanotubes are cylindrical structured wrapped graphene sheets. They may be single walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Since Iijima has been discovered carbon nanotubes (CNTs) in 1991, they have become main interest of scientists because of their excellent high mechanical strength, extremely bigger specific surface area, excellent chemical stability, extreme electrical conduction and well thermal stability. For researchers, the unique features of carbon nanotubes have become great advantage in terms of potential applications. If we put harness on the unique properties of carbon nanotubes, one technique is to exploit their composite structures and uses with other active substances such as metals, polymers and metal sulfides/oxides/phosphides/nitrides. The functional components coat the outer surface or fill cavities while carbon nanotubes usually act as matrix in these type of hybrid materials. There are many fields such as bioengineering, nanoscience and nanotechnology in which carbon nanotubes have been used.

In the revolution of nanotechnology carbon nanotubes (CNTs) considered the most important and attractive nanostructured material. Due to their excellent mechanical and remarkable electrical features great attention have been received by carbon nanomaterials with the continuous advancement of nanotechnology in material science and are used in tremendous research projects of engineering and scientific fields (Park et al., 2010). Nano electronic devices based on carbon nanomaterial such as carbon nanotubes have become more promising and recently received much attention. Now adays carbon nanotubes can be effectively employed in electrochemical sensors due to their excellent electrical, physical and chemical properties, such as better thermal conductivity, a very large surface-to-volume ratio and their enhanced electron transfer capability.

Classification of carbon nanotubes

Carbon nanotubes can be classified into types: Single walled carbon nanotubes (SWCNTs) and multi walled carbon nanotubes (MWCNTs). Comparison between these two types of carbon nanotubes given in table I.

Table I Comparison between SWCNTs and MWCNTs

SWCNTs	MWCNTs
Consist one layer of graphene	Consist multiple layers of graphene
Easy to evaluate and characterize	Consist of complex structure
Difficult to synthesize bulk amount	Easy to synthesize bulk amount.
Can be twisted easily and flexible.	Difficult to twist not much flexible.
Synthesis is not possible without catalyst.	Synthesis is possible without catalyst.
During functionalization chances of defects are high	Difficult to introduce defects on sidewalls by functionalization
Poor purity of product. 30–50wt% prepared by chemical vapour deposition (CVD) method. Maximum 80% reported by using arc discharge method.	High Purity of product. 35–90wt% prepared by chemical vapour deposition (CVD)