Oxidation of Carbon Nanotubes by Singlet ${\mathrm{O}}_2$

Chemisorption of singlet ${}^1\Delta _g$ ${\mathrm{O}}_2$ on single-walled carbon nanotubes is reexamined by first principles calculations, and the reaction barrier is substantially lower than previously reported when the spin on ${\mathrm{O}}_2$ is correctly treated. The process is initiated by the cycloaddition of a singlet ${\mathrm{O}}_2$ on top of a C-C bond and ended with an epoxy structure with each of the two oxygen atoms occupying a bridge position. The overall process is exothermic, with an activation barrier as low as 0.61 eV for the (8, 0) tube. Our results raise the possibility that carbon nanotubes with small diameters could be degraded after exposure to air and sunlight, similar to the degradation of natural rubber and synthetic plastics.

Figure 1

Relative energy along the reaction path for the chemisorption of a singlet ${\mathrm{O}}_2$ on an (8, 0) single-walled carbon nanotube, with average C-O distance taken as the reaction coordinate.