Length-Dependent Enantioselectivity of Carbon Nanotubes by Gel Chromatography

High-purity enantiomer separation of chiral single-wall carbon nano tubes (SWCNTs) remains a challenge compared with electrical type and chirality separations due to the limited selectivities for both chirality and handedness, which is important for an exploration of their properties and practical applications. Here, we performed length fractionation for enantiomer-purified SWCNTs and found a phenomenon in which the enantioselectivities were higher for longer nanotubes than for shorter nanotubes due to length-dependent interactions with the gel medium, which provided an effective strategy of controlling nanotube length for high-purity enantiomer separation. Furthermore, we employed a gentler pulsed ultrasonication instead of traditional vigorous ultrasonication for preparation of a low-defect long SWCNT dispersion and achieved the enantiomer separation of single-chirality (6,5) SWCNTs with an ultrahigh enantiomeric purity of up to 98%, which was determined by using the linear relationship between the normalized circular dichroism intensity and the enantiomeric purity. Compared with all results reported previously, the present enantiomeric purity was significantly higher and reached the highest level reported to date. Due to the ultrahigh selectivity in both chirality and handedness, the two obtained enantiomers exhibited perfect symmetry in their circular dichroism spectra, which offers standardization for characterizations and evaluations of SWCNT enantiomers.

Automated summary

High-purity enantiomer separation of chiral SWCNTs remains a challenge, but the length-dependent interactions with the gel medium provided an effective strategy for controlling nanotube length and achieving high-purity separation. By using gentler pulsed ultrasonication and a low-defect long SWCNT dispersion, we achieved ultrahigh enantiomeric purity of up to 98%, the highest reported so far. The obtained enantiomers exhibited perfect symmetry in their circular dichroism spectra, enabling standardization for SWCNT enantiomer characterizations and evaluations.