Purification of MWNTs produced by arc-discharge techniques can be done by using oxidation techniques which can take apart MWNTs from polyhedral graphite-like particles [10]. The main disadvantages of this method are low purity, high destroying rate of starting materials (95%), as well as high reactivity

of the remaining nanotubes at end GS-9973 chemical structure of process due to existence of dangling bonds (an unsatisfied valence) [36] and for elimination of such dangling bonds is necessary to use high-temperature annealing (2,800 ± C). The nondestructive methods for separating CNTs couple well-dispersed colloidal suspensions of tubes/particles with materials which prevent aggregation such as surfactants, polymers, or other colloidal particles [37]. The other method as aim of size exclusion nanotubes uses size exclusion chromatography and porous filters [37] as well as ultrasonically assisted microfiltration which purifies SWNTs selleck chemical from amorphous carbon and catalytic particles [38]. Studies have

shown the boiling of SWNTs in nitric acid [39] or hydrofluoric acid [40] aqueous solutions for purification of SWNTs and removing amorphous carbon and metal particles as an efficient and simple technique. For the purification of carbon tubules, scientist prefers to use sonication of nanotube in different media and afterward thermal many oxidation of SWNT material (at 470°C) as well as hydrochloric acid treatments [41]. Another way for oxidizing unsatisfied carbonaceous particles is use of gold clusters (OD 20 nm) together with the thermal oxidation of SWNTs at 350°C [42]. Huang et al. introduce a new way for separation of semiconducting and metallic SWNTs by using of size exclusion chromatography (SEC) of DNA-dispersed

carbon nanotubes (DNA-SWNT), which have the highest resolution length sorting [43]. The density-gradient ultracentrifugation has been used for separation of SWNT based on diameter [44]. Combination of ion-exchange chromatography (IEC) and DNA-SWNT (IEC-DNA-SWNT) has also been used for purification of individual chiralities. In this process, specific short DNA oligomers can be used to separate individual SWNT chiralities. Scientists have used fluorination and bromination processes as well as acid treatments of MWNT and SWNT material with the aims of purifying, cutting, and suspending the materials uniformly in certain organic solvents [45, 46]. As discussed above, depending on nanotube synthesis way, there are many different methods for purification of carbon nanotubes, and therefore, existence of methods which are single-step processes and unaffected on properties of carbon nanotube products is essential for producing clean nanotubes and should be targeted in the future.