Purification of single-wall carbon nanotubes by ultrasonically assisted filtration

An efficient method for purification of single-wall carbon nanotubes (SWNT) synthesized by the laser-vaporization process has been developed. Amorphous and crystalline carbon impurities and metal particles are removed from SWNT samples by ultrasonically-assisted microfiltration. Sample sonication during the filtration prevents filter contamination and provides for a fine nanotube-nanoparticle suspension throughout the purification process. The process generates SWNT material with purity of more than 90% and yields of 30-70%, depending on the quality of the starting material. Nanotubes in purified samples are shorter than in pristine samples due to some sonication-induced nanotube cutting. Nanotube bundles in purified samples are also substantially thicker due to spontaneous nanotube alignment.