Carbon nanotubes are of both single-walled and multi-walled. A single-walled carbon nanotube (SWNT) has a single grapheme cylinder, while a multi-walled carbon nanotube (MWNT) has several concentric grapheme cylinders.

Nanotubes have unusual properties due to strong covalent bonding, nanometer size and unique one-dimensional structure. The extraordinary properties include very high tensile strength, high resilience, electronic properties ranging from metallic to semi-conducting, the ability to sustain high current densities and high thermal conductivity. This makes carbon nanotubes a suitable material to be used as fillers in super-strong composite materials, as wires and components in nano-electronic devices, as tips of scanning probe microscopes and in flat panel displays and gas sensors.

In a single carbon nanotube, every atom is on two surfaces - the inside and the outside, and a single gram of nanotubes has over 2400 m2 of surface area. The nature of the carbon bonding gives the tubes their great tensile strength and electrical and thermal conductivity. The carbon nanotubes stiffness and toughness derives from their molecular perfection. In most materials the actual observed stiffness and toughness are degraded very substantially by the occurrence of defects in their structure. For example, high strength steel typically fails at about 1% of its theoretical breaking strength. Carbon nanotubes, however, achieve values very close to their theoretical limits because of their perfection of structure - there are no structural defects where mechanical failures can begin. It is, however, the tubular geometry of carbon nanotubes that gives them their most exotic properties.

An example of CNT typical properties:

Purity of CNTs90%, Content of SWNTs, 60%, Diameter 2 nm, Length 20 nm, Amorphous carbon 5%, Ash (catalyst residue) 3%, surface area 450 m2/g, Thermal conductivity 4000 W/m•k.

MWNTs were earlier prepared by the arc-discharge of graphite electrodes, but now, MWNTs are prepared in large quantities by the chemical vapor deposition process. High yields of SWNTs can be obtained by the following methods.

1.Arc-discharge of Ni-Y catalyzed graphite electrodes,

2.Laser ablation of Ni-Co catalyzed graphite targets and

3.Vapor phase paralysis of CO and Fe(CO)5 (HiPCO process).

Carbon nanotubes are always get contaminated with impurities like amorphous carbon, residual metal catalyst and graphitic nanoparticles during manufacture and handling and hence purification and chemical processing are vital steps in before any application of Carbon nanotubes.

• Electronical nanocomponents (diodes, transistors, nano-wires, etc.)

• Field emission

• Multi-functional composites(EMI shielding, thermal conducting, strengthen, conducting, etc.)

• Hydrogen storage

• Rechargeable lithium batteries

• Atomic force microscope (AFM) tips

• Electrode material of supercapacitors

• Biosensors

SWNTs prepared by the electric arc method with purity 40-60%, price $50/gram,

Processed AP-SWNTs containing lower carbonaceous and catalyst related impurities with purity 70-90%, price $ 400/gram,

Purified SWNTs with high carboxylic acid content 80-90%, price $ 400/gram,

Water soluble SWNTs functionalized with poly m-aminobenzene sulfonic acid (PABS) price $ 1500/gram

Coiled multi-walled carbon nanotubes with purity: > 60%, Outside diameter: 100-200 nm, Length: 1-10 um,SSA: > 50 m2/g, price $70/g

Multi-walled nanotubes Purity: 95+%, Amorphous carbon: <3%,>