Isolation of Adsorbent-Free Long Semiconducting Single-Walled Carbon Nanotubes Using a Hydrogen-Bonding Supramolecular Polymer

The separation/purification of semiconducting single-walled carbon nanotubes (sem-SWNTs) according to their chirality is one of the most important issues in the science and technology of carbon nanotubes[1-4]. We previously reported supramolecular coordination polymer systems [1] to achieve elimination of the sem-SWNT-extracting agents afterward, which was the first report to utilize a supramolecular system to selectively sort chemically purified sem-SWNTs not containing the used adsorbent.

The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only chiral- or chemical-purity with sacrificing sem-SWNT intrinsic structural identities by applying long-time ultrasonication and/or chemical modifications.

Toward the ultimate purification of the sem-SWNTs, we report a mild-conditioned extraction of the sem-SWNTs using removable hydrogen-bonding supramolecular polymers (HBPs) that are consisted of dicarboxilic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selectivity. Replacing conventional strong sonication to a simple shaking using HPBs was found to provide a very low D/G ratio of the extracted sem-SWNTs with long (>2.0 μm) tubes, which wad determined by an atomic force microscopy observation. The HBPs were readily removed from the nanotube surfaces by an outer stimuli, such as change of solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to provide a possible structure of the HBP-wrapped sem-SWNTs.

Such an efficient and easy extraction of the sem-SWNTs is a great advance in the chirality selective separation of SWNTs and the study is highly important since such advanced material is a promising nanomaterial in many applications. 

References

[1]     F. Toshimitsu, N. Nakashima, “Semiconducting Single-walled Carbon Nanotubes Sorting with a Removable Solubilizer Based on Dynamic Supramolecular Coordination Chemistry”, Nature Communications, 2014, 5, art no. 5041.

[2]     F. Toshimitsu, N. Nakashima, “Hybrids of Copolymers of Fluorene and C60-carrying-carbazole with Semiconducting Single-Walled Carbon Nanotubes”, Chem. Eur. J., 2015, 21, 3359-3366.

[3]     K. Akazaki, F. Toshimitsu, H. Ozawa, T. Fujigaya, N. Nakashima, “Recognition and One-pot Extraction of Right- and Left-handed Semiconducting Single-Walled Carbon Nanotube Enantiomers Using Fluorene-Binaphthol Chiral Copolymers", J. Am. Chem. Soc. 2012, 134, 12700-12707.

[4]     H. Ozawa, X. Yi, T. Fujigaya, Y. Niidome, T. Asano and N. Nakashima, “Supramolecular Hybrid of Gold Nanoparticles and Semiconducting Single-Walled Carbon Nanotubes Wrapped by a Porphyrin-Fluorene Copolymer”, J. Am. Chem. Soc., 133, 14771–14777(2011).