Characterization of fractions from repeated functionalization reactions of carbon nanotubes

The fractionation of a purified pristine multiple-walled carbon nanotube (MWNT) sample was achieved via repeated functionalization reactions to produce several soluble nanotube fractions. The reactions were based on the esterification of the nanotube-bound carboxylic acids. The soluble nanotube fractions and the insoluble solid residue were characterized by using optical spectroscopy, electron microscopy, and other techniques. The results show that all of these soluble samples contain primarily functionalized MWNTs and that there is little difference among these soluble nanotube fractions, either in the degree of nanotube dispersion or in the nanotube length and diameter distributions. There are apparently no preferential solubilization of carbon nanoparticles or other carbon impurities present in the starting nanotube sample and also no selectivity in the solubilization of MWNTs of different sizes (lengths and diameters) in the functionalization reactions. Mechanistic implications of the results are discussed.