The (n,m) population distribution of single-walled carbon nanotubes obtained on supported CoMo catalysts has been determined by photoluminescence and optical absorption. It has been found that the (n,m) distribution can be controlled by varying the gaseous feed composition, the reaction temperature, and the type of catalyst support used. When using CO as a feed over CoMo/SiO2 catalysts, increasing the synthesis temperature results in an increase in nanotube diameter, without a change in the chiral angle. By contrast, by changing the support from SiO2 to MgO, nanotubes with similar diameter but different chiral angles are obtained. Finally, keeping the same reaction conditions but varying the composition of the gaseous feed results in different (n,m) distribution. The clearly different distributions obtained when varying catalysts support and/or reaction conditions demonstrate that the (n,m) distribution is a result of differences in the growth kinetics, which in turn depends on the nanotube cap-metal cluster interaction.

Both fullerenes and single-walled carbon nanotubes (SWNTs) exhibit many advantageous properties. Despite the similarities between these two forms of carbon, there have been very few attempts to physically merge them. We have discovered a novel hybrid material that combines fullerenes and SWNTs into a single structure in which the fullerenes are covalently bonded to the outer surface of the SWNTs. These fullerene-functionalized SWNTs, which we have termed NanoBuds, were selectively synthesized in two different one-step continuous methods, during which fullerenes were formed on iron-catalyst particles together with SWNTs during CO disproportionation. The field-emission characteristics of NanoBuds suggest that they may possess advantageous properties compared with single-walled nanotubes or fullerenes alone, or in their non-bonded configurations.

Oxidation of single-walled carbon nanotubes (SWNTs) with nitric acid increases their dispersability in water, methanol, and N,N-dimethylformamide. Two oxidation protocols, sonication in 8 M HNO 3 at 40 °C and reflux in 2.6 M HNO 3 , have been examined using SWNTs produced by the CoMoCat, HiPco, and pulsed laser vaporization (PLV) methods. The dispersability of all types of nanotubes increased substantially after 1 h of sonication and after 2-4 h of reflux. Longer treatments resulted in little further improvement in dispersability and at reflux degraded the SWNTs. Stable dispersions of CoMoCat SWNTs in DMF at concentrations as high as 0.4 g/L were achieved without the use of surfactants or polymers. Raman spectroscopy showed greater covalent functionalization of the SWNTs by the reflux procedure than by the sonication procedure. Concurrent with improved dispersability, oxidation resulted in smaller diameters and shorter lengths as determined from AFM images, which show mostly bundles rather than individual tubes. The lengths of SWNTs after oxidation decreased in the order PLV > HiPco > CoMoCat. Recommendations for the method of conditioning of the various types of SWNTs depend on their intended use.