Trajectory of the selective dissolution of charged single-walled carbon nanotubes

© 2017 American Chemical Society. Single-walled carbon nanotubes (SWCNTs) are typically produced as a mixture of different lengths and electronic types. Methods for sorting these as-produced mixtures typically require damaging and unscalable techniques to first overcome the strong bundling forces between the nanotubes. Previously, it has been shown that negatively charging SWCNTs can lead to their thermodynamically driven, gentle dissolution in polar solvents, and moreover that this process can selectively dissolve different SWCNT species. However, there are several conflicting claims of selectivity that must be resolved before the full potential of this method for scalably postprocessing SWCNTs can be realized. Here we carefully investigate dissolution as a function of charge added to the as-produced SWCNT sample, using a range of complementary techniques. We uncover a far richer dependence on charge of SWCNT dissolution than previously imagined. At low values of charge added, amorphous carbons preferentially dissolve, followed sequentially by metallic, larger diameter (>9 Å) semiconducting SWCNTs, and finally smaller diameter semiconducting SWCNTs as more charge is added. At an optimal stoichiometry of NaC10, the dissolution yield is maximized across all species. However, at higher charge the larger diameter and metallic SWCNTs are so highly charged that they are no longer soluble, leaving smaller diameter SWCNTs in solution. Our results clearly demonstrate two interconnected mechanisms for dissolution: the sequential charging of the SWCNTs and their solution thermodynamics. This work reconciles conflicting reports in the literature, demonstrates that upon charge added the different SWCNTs behave like discrete molecular species, and points toward selective dissolution as a scalable method for SWCNT separation