Diameter Selection of Single-Walled Carbon Nanotubes through Programmable Solvation in Binary Sulfonic Acid Mixtures
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- 作者：Sivarajan Ramesh ; Hongwei Shan ; Eric Haroz ; W. E. Billups ; Robert Hauge ; W. Wade Adams ; Richard E. Smalley
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：December 6, 2007
- 年：2007
- 卷：111
- 期：48
- 页码：17827 - 17834
- 全文大小：626K
- 年卷期：v.111,no.48(December 6, 2007)
- ISSN：1932-7455
文摘
Pristine carbon nanotubes (CNTs) dissolve as polycarbocations in superacids through direct protonation. Thesolvating power of a superacid is determined by the stability of the conjugate base anion that competes withthe CNTs for the dissociated proton. We have demonstrated that this equilibrium can be controlled in apredictable fashion, thus rendering the solvating power of a superacid system tunable. In this article, weshow that the solvating power of chlorosulfonic acid can be changed in a desired fashion by forming binarymixtures in different proportions with a non-superacid such as methane sulfonic acid. Thus, the successiveextraction of carbon nanotubes with binary acid mixtures of increasing solvating power leads to thedifferentiation of CNTs by their molecular geometry. We show that solvation by direct protonation is sensitiveto the geometric strain at the carbon atom and, hence, to the nanotube diameter. In this respect, the directprotonation method is distinct from surfactant-based or electrical-field-based methods that distinguish metallicCNTs from semiconducting types mainly on the existence of finite density of states or not at the Fermi level.We have employed solid-state Raman spectroscopic analysis of the CNT radial breathing modes and UV-vis absorption spectroscopy and a systematic mapping method to support our conclusions. We believe theconcept demonstrated in this paper holds the potential to be developed into a chemical tool kit useful in thescaleable separation of CNTs by their (n, m) types, thus paving the way for molecular carbon nanotechnology.