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Two purification methods of carbon nanotubes were conducted by means of different oxidation rate of various types of carbon in the cathode deposit produced by an arc plasma method. One was chemical method and the other physical method.
In the former method the catalytic reaction of copper to graphitic materials was used. Copper supported graphite was prepared in order for copper to be localized at the edge of graphitic materials by the intercalation of copper chloride into graphite interlayers, followed by the reduction of copper chloride to metal copper. Nanotubes were not intercalated by copper chloride because of the rigid tube structure. The catalytic reaction of copper to graphite could easily oxidize graphitic materials at such low temperature as 773 K. The temperature was 200 K lower than the oxidation temperature of coarse graphite, which enabled to separate nanotubes from various types graphitic materials from the cathode deposit. In the latter unit operations were used such as dispersion, comminution and filtration of a cathode deposit in ethanol to separate coarse graphitic materials from the deposit. The rate of weight loss by oxidation increased with the decrease of size of the graphitic materials. Nanotubes were found to be oxidized from the edges and expected to be oxidized more slowly than the other graphitic materials of the same size. This was the driving force to purify nanotubes.
Both could purify nanotubes from cathode deposits at their optimum operating conditions.