Separation of Carbon Nanotubes by their Properties

With the directed synthesis of individual species of carbon nanotubes remaining unfeasible in the foreseeable future, the available mixtures have to be separated for their components before any application requiring specific kinds of tubes. This task turned out rather complex, and a conclusive solution is still pending, but some partial successes have been achieved nevertheless. These at least allow for the enrichment of certain nano tubes. 

2 nm across, while at 514nm tubes with a diameter of 1.33 nm react. Closer investigation reveals that only semiconducting tubes are attacked by this oxidation, and that the energy of the irradiated light correlates to the S3-bandgap of the species preferably attacked. 

Other chemical transformations are suitable as well to discriminate between different types of tubes in a sample. The reaction with diazonium salts, for example, selectively functionalizes metallic nanotubes. Their solubility is enhanced by the surface modification so they may be separated from the unaltered, insoluble semiconducting tubes. Subsequent removal of the functional groups and annealing at elevated temperatures yield nanotubes with most of them being metallic conductors. As metallic nanotubes possess higher electron density close to the 

Noncovalent interactions with belt- or tube-like host molecules might also be suitable to a separation of carbon nanotubes by diameter. Cyclodextrines or beltshaped aromatic compounds could be named as examples here. They may not have proven their applicability as selective complexing agent yet, but considering their geometry reveals favorable dispositions for a discriminative interaction with certain nanotubes. Supramolecular arrangements with carbon nanotubes are also discussed in Section 3.5.7. 

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