Multi-step purification of carbon nanotubes

An efficient purification procedure for multi-walled carbon nanotubes (MWNTs) synthesized by the floating catalyst method was discussed. The process involves ultra-sonication, heat treatment in hot water, bromination, oxidation and acid treatment. Most of amorphous carbon, multishell carbon nanocapsules as well as metal particles were successfully removed from the MWNT product. With this procedure, MWNTs with purity of more than 94% were obtained and the yield could approach 50%. It was found that bromination took an important role in the purification of MWNTs. Transmission electron microscopy, XPS and thermo-gravimetric analysis were used to evaluate the purification process of MWNTs. The mechanism of bromination on purification of the MWNTs was also discussed.