Production of high purity multi-walled carbon nanotubes produced from catalytic decomposition of methane

Abstract

Removing all the impurities in the carbon nanotubes is essential due to the unique characteristic of purified carbon nanotubes applications such as electronic devices, hydrogen storage, tools in nanotechnology, polymer reinforcement, fuel cells, sensors and actuators. However, the removal of some catalysts is very difficult. Carbon nanotubes, which were used for purification, were synthesized using Ni/TiO2 catalyst. The main impurity of the assynthesized carbon nanotubes that needs to be removed was the catalyst used to synthesized carbon nanotubes. In order to purify this carbon nanotube, nitric acid treatment followed by oxidation either chemical or thermal method has been used and the results have been compared. Acid treatment followed by thermal oxidation was more effective than acid treatment followed by chemical oxidation. The process again was compared with thermal oxidation followed by acid treatment. It was found that the thermal oxidation followed by acid treatment gave better result than acid treatment followed by thermal oxidation. The efficiency of oxidation followed by nitric or sulfuric acid treatment followed by re-oxidation also were tested and found that this method has successfully removed most of the impurities. The purity of the oxidation followed by sulfuric acid treatment then re-oxidation gave carbon nanotube with purity as high as 99.9 wt%. The percentage of the carbon nanotubes purity was obtained from Thermal Gravimetric Analysis (TGA) while the structure and morphology of carbon nanotubes were characterized using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). TEM and SEM showed that the structure of the carbon nanotubes was not damage after purification using oxidation followed by sulfuric acid treatment and then re-oxidation.