Introduction
Depending on the number of tubes that are arranged concentrically, carbon nanotubes are classified into single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). SWCNTs are hollow, long cylinders with extremely large aspect ratios, made of one atomic sheet of carbon atoms in a honeycomb lattice. Their diameter typically lies in the nanometer range while their length often exceeds microns, sometimes centimeters, thus making them one-dimenstional structures.
Fig 1 A graphene sheet rolled up to form a SWNT
The electronic properties of SWCNTs are very sensitive to their microscopic atomic arrangements and symmetry, covering a wide spectrum of energy scales. Their electrical conductivity can show metallic or semiconducting behavior and their band gap can vary from zero to about 2 eV, which are not shared by the MWCNT variants. In addition, SWCNTs possess extraordinary thermal and mechanical properties, which are considered as one of the most promising nanomaterials for applications and basic researches.
Purification of single walled carbon nanotubes:
SWCNTs are commonly purified by competitive oxidation using mineral acids, which generates molecular debris. Then the mixture was washed with dilute aqueous base at room temperature to remove much of this debris, producing samples with increased purity. After that, the base groups of the molecule convert to their conjugate salts, therefore the partially oxidized organic debris can be soluble well in water and removed easily.
Applications
Photovoltaic industry: Because of low electron scattering and the suitable band gap, SWCNTs are attractive for transistor applications, especially suited for field effect transistor (FET) architectures. SWCNTs have achieved higher current densities and longer lifetime than the MWCNTs, which are widely applied in photovoltaic industry.
Electronics: SWCNTs are likely candidates for miniaturizing electronics. The most basic building block of these systems is the electric wire, and SWCNTs with diameters of an order of a nanometer can be excellent conductors.
Drug delivery: Anti-cancer drugs loaded SWCNTs can accumulate drugs at the cancer sites due to the improved penetration effect. Development of drug delivery based SWCNTs system could be effective to deliver anti-cancer drugs in the target tissue.
