Reactivity of different kinds of carbon during oxidative purification of catalytically prepared carbon nanotubes

In the purification procedure of catalytically prepared carbon nanotube sam ples, the oxidative removal of amorphous carbon was investigated. Oxidation was carried out by KMnO4, H2O2, O-3 or HClO4. The selectivity of the amorp hous carbon burning reaction was studied as a function of the reaction temp erature by transmission electron microscopy. The advantages of the differen t methods are as follows: although oxidation by KMnO4 in an acidic suspensi on provides nanotubes free of amorphous carbon, and can easily be controlle d, it must be followed by filtration and cc HCl treatment in order to disso lve the MnO2 formed during the reaction. Oxidation with hydrogen peroxide d oes not give undissolved residue on the surface of the tubes. Ozone treatme nt produces gaseous by-products, but requires higher reaction temperature. This method is more difficult to control. During oxidation, competitive oxi dation always takes place: carbon nanotubes and amorphous carbon react simu ltaneously. While amorphous carbon can be attacked from any direction, carb on nanotubes can be oxidized only from the ends. (C) 2001 Elsevier Science B.V. All rights reserved.