99.9% purity multi-walled carbon nanotubes by vacuum high-temperature annealing

Ultrahigh purity multi-walled carbon nanotubes (MWNTs) were obtained, which were produced by a catalytic chemical vapor deposition method and subsequently annealed at vacuum pressures between 10(-3) and 10 Pa and temperatures between 1500 and 2150 degreesC. Acid treatments were made for comparison. Scanning electron microscopy, transmission electron microscopy and energy dispersive spectra were used to characterize the specimens. Purities were characterized by thermogravimetric analysis. Raman spectra were also reported. The high-temperature vacuum process efficiently removed residual metal catalysts and metal oxide carriers and enhanced the graphitization of the MWNTs. The highest MWNT purity achieved is about 99.9%. This procedure presents a nondestructive, commercially viable purification method for carbon nanotubes. (C) 2003 Elsevier Ltd. All rights reserved.