Adsorption and desorption of an oxygen molecule on carbon nanotubes are investigated using density functional calculations. Several precursor states exist at the edge of armchair nanotubes, whereas an exothermic adsorption takes place at the edge of zigzag nanotubes. We also estimate desorption barriers of a CO molecule from nanotubes as well as fullerenes and amorphous phases. Our calculations suggest that carbon nanotubes can survive selectively during the oxidative etching process with a precise control of annealing temperature, in good agreement with experimental results of purification process of carbon nanotubes.

• Received 22 February 2000

DOI:https://doi.org/10.1103/PhysRevLett.85.2757