Effect of annealing on the optical absorption spectra of single-walled carbon nanotubes

The thermal stability of initial and purified samples of single-walled carbon nanotubes prepared through gas-phase disproportionation of carbon monoxide CO in the presence of iron particles under high pressure (the HiPCO method) is investigated using optical absorption spectroscopy and thermogravimetry. An analysis of the optical absorption spectra demonstrates that thermal oxidation of the initial material proceeds rather rapidly and uniformly owing to the catalytic effect caused by the presence of iron particles in the sample. The destruction of the carbon nanotubes contained in the as-prepared and purified samples begins at temperatures of ∼250 and ∼300°C, respectively. It is shown that single-walled metallic nanotubes undergo faster oxidation as compared to the single-walled semiconducting nanotubes.