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.
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