A purification method for multi-walled carbon nanotubes (MWCNTs) has been developed to remove almost all (>98%) residual metal catalyst without introducing a significant amount of surface functionality. The process involves alternating mild acid oxidation and thermal oxidation in an iterative fashion with progressively higher temperatures for thermal treatment, in accordance with the increasing thermal stability. Thermogravimetric analysis and inductively coupled plasma mass spectrometry were employed to assess thermal stability and residual catalyst content, respectively, throughout the process. Transmission electron microscopy confirms the integrity of the nanotubes, and the degree of acid functionalization introduced by the acid oxidation is minimal, as determined by titration analysis.Key words: multi-walled carbon nanotube, purification, ICP-MS, TGA, FTIR.
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