*2.1.6.2 Purification of CNTs*

The synthesized CNTs can be separated from the amorphous carbon, carbon nanoparticles, residual catalyst and other impurities by various methods. The conventional methods of purification are not very successful but methods like gas phase, liquid phase and intercalation methods show good results.

**Gas phase purification of CNTs:** In this method the CNTs are subjected to a high temperature oxidation followed by repeated extractions with nitric acid and hydrochloric acid. This procedure makes the synthesized CNTs purer and high stability with fewer amounts of residual catalyst and other non CNTs forms.

**Liquid phase purification of CNTs**: A series of steps are followed in the liquid phase purification of synthesized CNTs. They are:


**33**

**Figure 5.** *Graphene to CNT.*

*Carbon Nanotubes: Synthesis, Properties and Applications*

• Chromatography to isolate multi-walled carbon nanotubes, single-walled

present are oxidized by metallic copper which acts as oxidation catalyst formed from the reduction of copper chloride added during the process. This process introduces intercalate residues and damage CNTs during oxidation process.

**Intercalation purification of CNTs:** In this method the nanoparticle impurities

There are numerous mechanisms available to build up structures occluded with

Based on wrapping mechanism, three different forms of SWCNTs include chiral, armchair, and zigzag pattern. The single walled structure is primarily characterized by a set of indices (n and m) which describes the vector mechanism of chiral and absolutely it impinges an impact on electrical tendency of both nanotubes **Figure 6**.

pattern of arrangement with weaker plane bonding of Vander Waals forces at the outside and strong forces at inner plane bounds. Few numbers of concentric cylinders were equipped with regular spacing of interlayers that are located around central hollow section and demonstrated as multi walled CNTs **Figure 5**. In general, the real time spacing of MWCNTs contain interlayer spacing in range of 0.35–0.40 nm. The inner diameter of multi-walled CNTs can even range from 0.40 nm to few nanometers [28]. Outer diameter can exist up to 25 nm. The tips on both sides were closed and protruding ends were capped using dome shaped half width fullerene molecules. Axial molecules can exist up to few centimeters. The primary function of half width fullerene molecules is to aid in shutting down the tubes at both the ends. Whereas SWCNT can exist up to 4 nm. Length is up to micrometer range. Such arrangement is organized in a hexagon shape so as to develop a crystal [29].

nature of carbon hybridization constructs a layered

*DOI: http://dx.doi.org/10.5772/intechopen.92995*

• Microfiltration.

carbon nanotubes, etc.

**2.2 Structure/properties of CNT**

various characteristics. The sp2

*2.2.1 Structure of SWCNT and MWCNT*

**Figure 4.** *Pulsed laser ablation method—Schematic representation.*

*Carbon Nanotubes: Synthesis, Properties and Applications DOI: http://dx.doi.org/10.5772/intechopen.92995*

• Microfiltration.

*21st Century Surface Science - a Handbook*

and calibrated.

*2.1.6.2 Purification of CNTs*

impurities).

further purified to get the pure form of CNTs.

*2.1.6.1 Procedure for pulsed laser deposition method*

nanotubes catalyst nanoparticles of Fe, Co, Ni are used. The obtained CNTs are

Pulsed Laser deposition is a thin film deposition technique in which the target material is vaporized by pulsed laser beam and vaporized target atoms are made to deposit on substrates **Figure 4**. The furnace contains a target at bottom and substrate mounted on the top. A pulsed laser beam from Nd:YAG laser source is made to strike the target to produce vaporized target atoms called the plume (plume is vaporized atoms at high temperature) [27]. The plume moves towards the substrate and it is deposited and grown as CNTs. Each shot of laser is directly related to the amount of material ablated, thus deposition rate can be controlled

The synthesized CNTs can be separated from the amorphous carbon, carbon nanoparticles, residual catalyst and other impurities by various methods. The conventional methods of purification are not very successful but methods like gas

**Gas phase purification of CNTs:** In this method the CNTs are subjected to a high temperature oxidation followed by repeated extractions with nitric acid and hydrochloric acid. This procedure makes the synthesized CNTs purer and high stability with fewer amounts of residual catalyst and other non CNTs forms.

**Liquid phase purification of CNTs**: A series of steps are followed in the liquid

• Dissolution in both organic solvents and concentrated acids to remove the

• Centrifugal separation of CNTs (Solid part) from the solution (containing

phase, liquid phase and intercalation methods show good results.

• Preliminary filtration to remove bulk graphite particles.

phase purification of synthesized CNTs. They are:

fullerenes and catalyst, respectively.

*Pulsed laser ablation method—Schematic representation.*

**32**

**Figure 4.**

• Chromatography to isolate multi-walled carbon nanotubes, single-walled carbon nanotubes, etc.

**Intercalation purification of CNTs:** In this method the nanoparticle impurities present are oxidized by metallic copper which acts as oxidation catalyst formed from the reduction of copper chloride added during the process. This process introduces intercalate residues and damage CNTs during oxidation process.
