Simultaneous separation of high-purity semiconducting and metallic single-walled carbon nanotubes by surfactant concentration-controlled gel chromatography

Abstract

Gel chromatography methods have successfully achieved separation of metallic (M-) and/or semiconducting (S-) single-walled carbon nanotubes (SWNTs) from their mixtures with high purity. However, the optimum surfactant concentrations for gel chromatography methods are different for high-purity separation of S- and M-SWNTs; therefore, only one of S- or M-SWNTs can be obtained with high purity. In this work, we developed a new gel chromatography method for the simultaneous separation of both high-purity S-SWNTs and high-purity M-SWNTs, by adding steps to optimize surfactant concentrations of the SWNT solution prior to the separation of each SWNT. High-purity S-SWNT with a large diameter was obtained first with a high surfactant concentration (2 wt%), and then the remaining solution’s surfactant concentration was lowered to 1.5 wt% by dialysis or dilution to perform consecutive gel chromatography to separate the highly pure S-SWNT with a medium diameter. The remaining solution’s surfactant concentration was further lowered to 1 wt% to separate highly pure M-SWNTs. Through this study, we demonstrated that high purity M-SWNTs can be obtained only when all S-SWNTs are successfully separated first. Small-diameter S-SWNTs are least stable in a sodium dodecyl sulfate (SDS) dispersion among SWNTs and can be separated by a gel with a high surfactant concentration (2 wt%), while large-diameter S-SWNTs are more stable in SDS dispersions than small-diameter S-SWNTs and can therefore be separated by gel when the SDS concentration is low (1 wt%). M-SWNTs are most stable in SDS dispersions; therefore, they pass through all columns, are not adsorbed to gels, and can be collected at the end of the process. The optimum concentrations for high-purity separation of each kind of SWNTs were also investigated using their adsorption kinetics and experimental data.