Diameter Controllable Separation of Single-Walled Carbon Nanotubes by Simply Changing the Metal in Phenanthroline-Based Supramolecular Polymers

Graphical Abstract

We discover a novel approach for diameter-selective separation of single-walled carbon nanotubes (SWNTs) using metal-coordinating supramolecular polymers (M-PNB) consisting of phenanthroline-based nanobrackets (PNB) and metal ions (M). Due to notable disparity in the dihedral angle of the metal-phenanthroline complex (M(phen)₂), Pd- and Co-PNB preferentially extract smaller (0.90–0.92 nm) and larger (0.97–1.10 nm) diameter ranges, respectively. Moreover, the combinations of these separations (Pd-PNB/Co-PNB and Pd/Co-PNB) are found to enhance the selectivity.

Abstract

Carbon nanotubes (CNTs) possess unique electronic and optical properties that are highly dependent on their structures. Therefore, diameter-selective synthesis and separation are meaningful for a wide range of their applications. Although various methods have been developed for CNT separations, challenges still remain in more efficient discrimination for diameters and removal of dispersants. Here, we present a novel approach for size-tunable diameter separation of single-walled carbon nanotubes (SWNTs) using metal-coordinating supramolecular polymers (M-PNB) consisting of phenanthroline-based nanobrackets (PNB) and metal ions (M). The helical wrapping of SWNTs with M-PNB is confirmed by transmission electron microscopy (TEM) analysis. Interestingly, Pd(II) and Co(II) ions with PNB show the large difference in diameter preference to the smaller (0.90 – 0.92 nm) and the larger (0.97 – 1.10 nm) diameters, respectively. Moreover, the combination of these two metal ions in M-PNB is found to enhance the selectivity to the specific (n,m)-SWNTs. This method offers not only size-tunable diameter selectivity but also significant improvements in extraction efficiency and the facile and thorough removal of the host molecules as compared to previous techniques.