Purification of pulsed laser synthesized single wall carbon nanotubes by magnetic filtration

Great effort has been expended in the development of methods to purify raw nanotubes by chemical treatment, washing, mechanical filtration, or heat treatment in a vacuum or oxidative environment. These techniques are limited by incomplete removal of catalyst nanoparticles and by the damage to the nanotubes that often results. We have applied a new purification method using filtration in a magnetic field and oxidation and investigated the efficacy using magnetic filtration alone, or combined with chemical-based or annealing-based oxidative treatments. By applying magnetic filtration only, we reduce catalyst content from 11.7 to 3.7 wt %, which is a superior result to oxidation and/or chemical treated samples. By combining chemical and magnetic purification, metal catalyst content is reduced to as much as 0.3 wt %, which is the best result ever for SWNTs synthesized by the laser method. In addition to the reduction of catalyst content, the new purification method increased sample quality, confirmed by Raman spectroscopy and near-infrared absorption. Magnetic filtration is found to be very effective in removing metal catalysts, producing material with high quality and yields.