The removal of encapsulated catalyst particles from carbon nanotubes using molten salts

A novel method, using molten salts, is described for the removal of encapsulated nickel catalyst particles from multi-walled carbon nanotubes. The multi-walled carbon nanotubes, synthesised by the decomposition of methane and hydrogen over a NiO/SiO2 aerogel catalyst, were treated in a LiCl-KCl eutectic molten salt and subsequently by hydrochloric acid to remove the nickel catalyst particles. The influence of the molten salt treatment on the microstructure of the carbon nanotubes was investigated by XRD, SEM and TEM analyses. The molten salt treatment promoted uncapping of the carbon capsules and the formation of strip-shaped carbon fragments. It was found that the hydrochloric acid treatment could then remove the nickel particles from the broken carbon capsules which was not possible prior to the molten salt treatment. The stability of carbon nanotubes in the molten salt is closely related to their ordered structure. (C) 2006 Elsevier Ltd. All rights reserved.