Towards High-Fidelity Single-Column Separation of Swcnts Using Agarose Gel

For their inclusion in novel electronic devices, the post synthesis separation of single walled carbon nanotubes (SWCNTs) is of great interest. While several methods have been utilized to achieve these separations with various levels in purity, one of the most promising techniques to produce large-scale separations is the selective adsorption of SWCNTs onto an agarose gel stationary phase. Recently, several researchers have reported successful modification to the process in order to achieve further separation of the semiconducting fractions by (n,m) type. While these changes are a significant step in SWCNT processing, they are difficult for development on an industrial scale due to the use of harsh chemical treatments (pH adjustments) and temperature gradients that may be difficult to control. In addition, many of these approaches require multiple (4 or more) columns in series, causing substantial dilution of the collected fractions, which increases the amount of surfactant required and may require the fractions to be concentrated before use. Here we report the mechanism of separation to the selective adsorption of semiconducting SWCNTs onto the agarose gels. The results indicate that the surfactant orientation on the SWCNT surface is an important parameter during separation and that the primary mode of attraction is ion-dipole interactions between SDS-SWCNTs and the agarose gel backbone. The selectivity of adsorption is then driven by the inherent differences in polarizability between the metallic and semiconducting species. Using our understanding of the mechanism behind selective adsorption of SWCNTs onto agarose, we have started to develop high-fidelity separations based on a single elution profile in a single column. The design of a simple, single-column technique to separate SWCNTs by (n,m) type is a major step in realizing their full potential.