Effective Nondestructive Purification of Single-Walled Carbon Nanotubes Based on High-Speed Centrifugation with a Photochemically Removable Dispersant

A purification method for raw single-walled carbon nanotubes (SWCNTs) without damage to their intrinsic structures has been desired in many applications. We investigated the purification of SWCNTs based on high-speed centrifugation of water-dispersed SWCNTs using the photoreactive dispersant we previously investigated. SWCNTs wrapped with the dispersant were separated from impurities, such as an amorphous carbon and metal particles by centrifugation, similarly to conventional physical purification using surfactants. In contrast to general surfactants that form micelles to disperse SWCNTs in aqueous solutions, the photoreactive dispersant did not form micelles. Therefore, an excess amount of the dispersant, which did not adsorb onto the SWCNT surfaces, was removable by dialysis of the supernatant. Since the amount of the dispersant was minimized by dialysis, we tuned the UV-irradiation time to eliminate the dispersibility of SWCNTs in water to as low a value as ∼2 h. The SWCNT precipitates were collected, and their chemical and structural purity were evaluated using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and resonance Raman spectroscopy. It was found that present methods combining high-speed centrifugation and photoreactive dispersant provided an effective procedure to purify SWCNTs without any apparent changes to their intrinsic properties.