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.