Purification of SWNTs using high-speed centrifugation

For eventual commercial applications of singlewalled carbon nanotubes (SWNTs) in nanoscale devices, it will be very important to realize effective purification of SWNTs. We have developed a simple method to purify as-synthesized SWNTs by centrifugal force in an aqueous solution of sodium dodecyl sulfate (SDS). The method proposed in this paper can effectively remove impurities such as metal catalyst particles, graphitic nanoparticles and amorphous carbon. Our method takes advantage of the fact that more massive particles sediment faster than less massive particles. Through adjusting relative centrifugal force, we can respectively remove metal catalyst particles and carbon nanoparticles from SWNTs by centrifugation. SEM results indicate that the concentration of the SWNT solution decreased when the number of times of centrifugation is increased. Raman spectra suggest that the purity of the SWNT solution increased when the number of times of centrifugation is increased. These experimental results indicate that the centrifugal technique can provide a rapid and repeatable purification of SWNTs.