Oxidation of carbon nanotubes by singlet O2

Chemisorption of singlet (1)Delta(g) O2 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 O2 is correctly treated. The process is initiated by the cycloaddition of a singlet O2 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.