Inner- and outer-wall sorting of double-walled carbon nanotubes

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Double-walled carbon nanotubes (DWCNTs) consist of two coaxially aligned single-walled carbon nanotubes (SWCNTs), and previous sorting methods only achieved outer-wall electronic-type selectivity. Here, a separation technique capable of sorting DWCNTs by semiconducting (S) or metallic (M) inner- and outer-wall electronic type is presented. Electronic coupling between the inner and outer wall is used to alter the surfactant coating around each of the DWCNT types, and aqueous gel permeation is used to separate them. Aqueous methods are used to remove SWCNT species from the raw material and prepare enriched DWCNT fractions. The enriched DWCNT fractions are then transferred into either chlorobenzene or toluene using the copolymer PFO–BPy to yield the four inner@outer combinations of M@M, M@S, S@M and S@S. The high purity of the resulting fractions is verified by absorption measurements, transmission electron microscopy, atomic force microscopy, resonance Raman mapping and high-density field-effect transistor devices.

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The authors acknowledge the experimental assistance of J. Zaumseil and S. Grimm and thank K. Moore and A. Blanch for discussions. B.S.F. acknowledges support from the Deutsche Forschungsgemeinschaft (DFG, under grants nos. FL 834/1-1 and FL 834/2-1). R.K. acknowledges funding by the DFG under INST 163/354-1 FUGG. R.K. and F.H. acknowledge support by the Helmholtz Association through the STN programme. G.G. and S.R. acknowledge the German Research Foundation (DFG, via SFB 658, subproject A6) and Focus Area NanoScale of the Freie Universität Berlin for nancial support.

Author information


  1. Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany

    • Han Li
    • , Venkata Sai Kiran Chakravadhanula
    • , Shyam Kumar Chethala Neelakandhan
    • , Frank Hennrich
    • , Ralph Krupke
    •  & Benjamin Scott Flavel
  2. Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany

    • Georgy Gordeev
    • , Sören Wasserroth
    •  & Stephanie Reich
  3. Helmholtz Institute Ulm Electrochemical Energy Storage, 89081 Ulm, Germany

    • Venkata Sai Kiran Chakravadhanula
  4. Institute of Materials Science, Technische Universität Darmstadt, 64287 Darmstadt, Germany

    • Shyam Kumar Chethala Neelakandhan
    • , Ralph Krupke
    •  & Benjamin Scott Flavel
  5. Department of Physics, Federal University of Minas Gerais, Belo Horizonte, Brazil

    • Ado Jorio


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B.S.F., H.L. and F.H. devised and performed the DWCNT separation. G.G., S.W., A.J., R.K., S.R., H.L. and B.S.F. performed and analysed the resonance Raman maps. TEM measurements were performed by V.S.K.C., S.K.C.N., H.L. and B.S.F. All authors contributed to the preparation of the final manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Han Li or Benjamin Scott Flavel.

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