Crystal defects on multi-walled carbon nanotubes by cobalt oxide.

This paper reports a new method to make crystal defects on the surface of multi-walled carbon nanotubes (MWCNTs) using the cobalt oxide as the oxidant for breaking carbon surface. The air oxidation of cobalt oxide (CoO) deposited on MWCNTs created various kinds of defects on their surface. Transmission Electron Micrograph (TEM) images showed clear defects such as broken crystal lines and asymmetric wall after air oxidation. X-ray powder diffraction (XRD) data showed that CoO on MWCNTs changed into Co3O4 after air oxidation. After removing Co3O4 from MWCNTs by acid, defective MWCNTs were obtained and showed defects of a clear trace where cobalt oxide had existed. This resulted from the reaction of air oxidation of CoO and carbon reduction of Co3O4, leading to the crystallinity defect of MWCNTs.