Selective chemistry of single-walled nanotubes

These fluorine moieties can be removed from the nanotube by treatment in hydrazine and the spectroscopic properties of the SWNT can be restored completely.

Water-soluble diazonium salts react with carbon nanotubes via charge transfer in which they extract electrons from SWNT and form a stable covalent aryl bond.

This covalent aryl bond forms with extremely high affinity for electrons with energies near the Fermi level, Ef of the nanotube.

Metallic SWNT have a greater electron density near Ef resulting in their higher reactivity over semiconducting nanotubes.

The reactant forms a charge-transfer complex at the nanotube surface, where electron donation from the latter stabilizes the transition state and accelerates the forward rate.

Once the bond symmetry of the nanotube is disrupted by the formation of this defect, adjacent carbons increase in reactivity and initial selectivity for metallic SWNT is amplified.

Under carefully controlled conditions this behavior can be exploited to obtain highly selective functionalization of metallic nanotubes to the near exclusion of the semiconductors.

[3][4] Primary condition is addition of reactant molecules at a very small rate to SWNT solution for a sufficient long time.

However, if the entire diazonium solution is added all instantaneously then semiconducting SWNTs will also react due to presence of excess reactant.

These features are unique in carbon nanotubes and occur with the frequencies ωRBM between 120 and 350 cm−1 for SWNT in the diameter range (0.7 nm-2 nm).

They can be used to probe the SWNT diameter, electronic structure through their frequency and intensity (IRBM) respectively and hence perform an (n,m) assignment to their peaks.

The G-band frequency can be used (1) to distinguish between metallic and semiconducting SWNTs, and (2) to probe charge transfer arising from doping a SWNT.

First, the diazonium reagent adsorbs noncovalently to an empty site on the nanotube surface, forming a charge-transfer complex.

This is a fast, selective noncovalent adsorption and diazonium group in this complex partially dopes the nanotube, diminishing the tangential mode in the Raman spectrum.