Extraction of High-Purity Single-Chirality Single-Walled Carbon Nanotubes through Precise pH Control Using Carbon Dioxide Bubbling

The preparation of single-chirality single-walled carbon nanotubes (SWCNTs) is of great importance to comprehensively understand their physical properties and applications. The high-purity separation of single-chirality SWCNTs has been reported using gel chromatography with a mixed surfactant system, but further improvements are necessary to enhance the purity of the resulting single-chirality SWCNTs. In this study, we focused on using pH as a parameter to improve the separation purity and investigated its influence on mixed surfactant-based purification. The pH of the mixed surfactant solution was precisely controlled with carbon dioxide bubbling with an accuracy of approximately 0.1. Using this eluent with a series of different pH values, we achieved diameter-selective separation of the SWCNTs. Moreover, we found that the residual metallic SWCNTs could be completely removed under the proper pH condition. Finally, on the basis of these findings, we produced single-chirality SWCNTs with a purity of more than 99% without residual metallic SWCNTs.