Purification strategies and purity visualization techniques for single-walled carbon nanotubes

Traditionally, SWNTs have been prepared by electric arc-discharge, laser ablation, or chemical vapor deposition (CVD) methods, yielding tubes of various diameter and length distributions. However, without exception, as-prepared SWNTs are contaminated with a number of impurities, decreasing the overall yield of usable material. Impurities include transition metal catalysts, such as Fe, Co, and Ni, which are necessary for the growth of SWNTs as well as carbonaceous species such as amorphous carbon, fullerenes, multishell carbon nanocapsules, and nanocrystalline graphite. In this Feature Article, we highlight the role of microscopy in designing and facilitating the interpretation of the success of strategies, including (a) oxidative methods including liquid and gas phase oxidation, (b) chemical functionalization protocols, (c) filtration and chromatography techniques, and (d) microwave heating methods, aimed at rationally purifying single-walled carbon nanotubes.