Ultra Highly Selective Synthesis of Double-Walled Carbon Nanotubes

Double-walled carbon nanotubes were synthesized by a carbon arc discharge using Fe catalyst. Electron microscopy revealed that the dominant fraction of nanotubes appears in bundles and has outer diameters between 2.5 and 4.0 nm. The by-products (catalyst particles and amorphous carbon) were readily removed using diluted nitric acid. The success of the purification was tracked by electron microscopy and X-ray photoelectron spectroscopy. The surface of purified nanotubes was found to be covalently functionalized with carbonyl-containing groups, which were subsequently removed by thermal annealing. The developed synthesis route has high selectivity for double-walled carbon nanotubes and uses simple starting materials.