Question

It is not easy to control what kind of nanotube (metallic / semiconducting) you might obtain from a nanotube production process. However, if you want to incorporate it into electronic devices, you need to know whether you are working with metallic nanotubes or with semiconducting ones. Unfortunately, while their electric properties differ, their chemical properties do not differ much. Describe a process by which you could isolate batches of SWCNTs enriched for metallic or semiconducting tubes. For double points, explain what strategy might be more suitable: To develop a process to grow / produce nanotubes that have inherently purer populations or to purify desired nanotubes from a more or less heterogenous mixture of different kinds of nanotubes.

Answer 1

It is known that carbon nanotubes show desirable physical and chemical properties with a wide array of potential applications. Nonetheless, their potential has been hampered by the difficulties in acquiring high purity, chiral-specific tubes. Considerable advancement has been made in terms of the purification of carbon nanotubes, for instance chemical oxidation, physical separation, and myriad combinations of physical and chemical methods. The aqueous two-phase separation technique has recently been demonstrated to be able to sort carbon nanotubes based on their chirality. The technique requires low cost polymers and salt, and is able to sort the tubes based on their diameter as well as metallicity. In this review, we aim to provide a review that could stimulate innovative thought on the progress of a carbon nanotubes sorting method using the aqueous two-phase separation method, and present possible future work and an outlook that could enhance the methodology.

Nanotubes are members of the fullerene structural family. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene. These sheets are rolled at specific and discrete ("chiral") angles, and the combination of the rolling angle and radius decides the nanotube properties; for example, whether the individual nanotube shell is a metal or semiconductor. Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).

Chemical Vapour Deposition is a process.And  metallic nanotubes can carry an electric current density of 4 × 10⁹ A/cm², which is more than 1,000 times greater than those of metals such as copper.

When the SWCNTs were isolated with sodium dodecyl sulfate (SDS) and embedded in agarose gel, only the metallic SWCNTs separated from the starting gel by an electric field.After 20 min, almost all SWCNTs applied to gel electrophoresis were separated into two fractions, containing ~95% semiconducting and ~70% metallic nanotubes. The difference in the response to the electric field between metallic and semiconducting SWCNTs can be explained by the higher affinity of semiconducting SWCNTs to agarose than to SDS.