Flavin analogues are dispersants of carbon nanotubes. We report the finding that riboflavin, which is a nutrient that is much less expensive than a flavin mononucleotide, is a good SWNT dispersant in water. We carried out a temperature dependence test of the solubilization of SWNTs, and propose a possible solubilization mechanism based on a regression analysis. We assume that the linear and lognormal components for the solubilized SWNTs can be explained by nonspecific and specific interactions between the riboflavin and the SWNTs, respectively. We also carried out computational calculations (molecular dynamics simulations) on this SWNT solubilization by which we proposed a suitable complex structure of the SWNT that provided the number of adsorbed flavin molecules via hydrogen bonding on the tubes.

The development of a facile method to sort semiconducting single-walled carbon nanotubes (s-SWCNTs) and their enantiomer recognition are still great challenges. We here describe a finding that a commercially available, safe, and cost-effective hydrophobic riboflavin analogue (riboflavin tetrabutyrate; RTB) efficiently sorts only s-SWCNTs by a one-pot method (bath-type sonication for 30 min followed by ultracentrifugation) and recognizes their enantiomers (left- and right-handed s-SWCNTs). The solubilization behavior of the SWCNTs strongly depends on the concentration of RTB; namely, with the decrease in the concentration of RTB, the s-SWCNT (n,m)-chiral selective sorting efficiency is enhanced. When using RTB = ∼0.4 mM (SWCNTs = 1 mg/3 mL toluene), two (n,m) chiralities of the s-SWCNTs with (n,m) = (8,6) and (8,7) were efficiently sorted. Furthermore, when using RTB = 0.5–1 mM, the SWCNT enantiomer recognition was observed. In addition, the X-ray photoelectron spectroscopic study revealed that the adsorbed RTB molecules on the s-SWCNTs were readily removed by simple rinsing with acetone to provide adsorbent-free pure s-SWCNTs. On the basis of the experimentally obtained data using Raman, photoluminescence, and visible–near-IR absorption spectroscopy techniques and computational density functional theory (DFT) approaches, we have revealed a possible mechanism for this unique s-SWCNT selective sorting and their enantiomer recognition. The supramolecular orientation of RTB into the helical superlattice with its own chirality provides a mechanism for chirality recognition. The study demonstrates one-pot sorting of s-SWCNTs and their enantiomer recognition using a cost-effective, safe molecule. Such a study is important for s-SWCNT separation science and its application in nanoscience and engineering areas.

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