Separations of Metallic and Semiconducting Carbon Nanotubes by Using Sucrose as a Gradient Medium

The separation of metallic and semiconducting single-wall carbon nanotubes (SWCNTs) was achieved using sucrose as a gradient medium in density-gradient ultracentrifugations (sucrose-DGU). By lowering the temperature during sucrose-DGU and tuning the concentrations of the surfactants, metallic and semiconducting SWCNT samples were obtained in high purity. The purity of the metallic and the semiconducting SWCNTs obtained by the sucrose-DGU was estimated to be 69% and 95%, respectively, from their optical absorption spectra. It is well-known that the amounts and types of surfactants significantly influence the separations. However, the authors found that the temperature during centrifugation was also an important parameter that improved the metal-semiconductor separation capability.