Direct dynamics simulations of the oxidation of a single wall carbon nanotube

Classical dynamics simulations, coupled directly with semiempirical molecular orbital theory, reveal some of the important oxidation chemistry occurring in single wall carbon nanotubes. Two chemisorption reactions, 1,2 and 1,4-cycloaddition with ¹O₂, are observed from the simulations, the latter determined as the kinetically favored adsorption pathway and confirmed with ab initio HF/6-31g total energy calculations. Opening of the nanotube is found to occur by the decomposition of a cyclic 1,2-peroxide-like addition product, which can be formed directly through a symmetric concerted addition reaction or by diffusion of the O₂ moiety from the 1,4-addition product. The oxygen induced degradation of the nanotube is initiated by tube opening followed by a two-step mechanism involving desorption of CO. The presence of a highly strained four-membered ring in the cap, following elimination of CO, is observed in the simulations. Consistent with experimental observation, the nanotube cap is oxidized substantially faster than is the cylindrical base of the tube. This suggests, as has previous work, that oxidation will initially occur preferentially at the cap and selectively with the pentagons. A likely product of cap removal consists of an open end oxygen-terminated nanotube.