Polyacylation for purifying nanotubes

Single-walled carbon nanotubes are notoriously difficult to purify, as they tend to aggregate in bundles and are therefore insoluble in common organic solvents. Teodor Silviu Balaban and coworkers at Karlsruhe Institute of Technology, in Germany, have now shown that polyacylation using Friedel-Crafts catalysts in nitrobenzene and other organic solvents can be used to attach acyl groups with long aliphatic chains or perfluorinated acyl residues to the nanotubes and render them soluble (Adv. Mater. 2006, 18, 2763). The polyacylated nanotubes were separated from impurities, such as metal catalyst nanoparticles, by size-exclusion chromatography. The polyacylation was also carried out under mild conditions in an AlCl₃/NaCl melt, which was subsequently separated from the polyacylated products by washing with water. Methanolysis or other defunctionalization methods restore the purified nanotubes by removing the acyl chains. The Karlsruhe team also showed that the nanotubes can be cross-linked to form Y-shaped structures by polyacylation with diacyl dichlorides.