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Separation of single-walled carbon nanotubes on silica gel. Materials morphology and Raman excitation wavelength affect data interpretation.

Journal of the American Chemical Society (2005-03-24)
Christopher A Dyke, Michael P Stewart, James M Tour
ABSTRACT

In this report, procedures are discussed for the enrichment of single-walled carbon nanotube (SWNT) types by simple filtration of the functionalized SWNTs through silica gel. This separation uses nanotube sidewall functionalization employing two different strategies. In the first approach, a crude mixture of metallic and semiconducting SWNTs was heavily functionalized with 4-tert-butylphenyl addends to impart solubility to the entire sample of SWNTs. Two major polarity fractions were rapidly filtered through silica gel, with the solvent being removed in vacuo, heated to 700 degrees C to remove the addends, and analyzed spectroscopically. The second approach uses two different aryldiazonium salts (one with a polar grafting group and one nonpolar), appended selectively onto the different SWNTs by means of titration and monitoring by UV analysis throughout the functionalization process. The different addends accentuate the polarity differences between the band-gap-based types permitting their partial separation on silica gel. Thermal treatment regenerated pristine SWNTs in enriched fractions. The processed samples were analyzed and characterized by Raman spectroscopy. A controlled functionalization method using 4-fluorophenyl and 4-iodophenyl addends was performed, and XPS analyses yielded data on the degree of functionalization needed to affect the van Hove singularities in the UV/vis/NIR spectra. Finally, we demonstrate that relative peak intensity changes in Raman spectra can be caused by morphological changes in SWNT bundling based on differing flocculation or deposition methods. Therefore a misleading impression of separations can result, underscoring the care needed in assessing efficacies in SWNT enrichment and the prerequisite use of multiple excitation wavelengths and similar flocculation or deposition methods in comparative analyses.

MATERIALS
Product Number
Brand
Product Description

Supelco
Silica gel, high-purity grade, average pore size 60 Å (52-73 Å), 70-230 mesh, 63-200 μm, for column chromatography
Supelco
Silica gel, high-purity grade, pore size 60 Å, 230-400 mesh particle size, 40-63 μm particle size, for flash chromatography
Supelco
Silica gel, high-purity grade (w/ Ca, ~0.1%), pore size 60 Å, 230-400 mesh particle size
Supelco
Silica gel, high-purity grade, pore size 60 Å, 220-440 mesh particle size, 35-75 μm particle size, for flash chromatography
Supelco
Silica gel, high-purity grade, 40, 35-70 mesh, for column chromatography
Supelco
Silica gel, high purity, 90Å, 35-70 mesh, for column chromatography
Supelco
Silica gel, high-purity grade, 60Å, 35-60 mesh particle size
Supelco
Silica gel, high-purity grade, 90Å, 15-25 μm, for column chromatography
Supelco
Silica gel, high-purity grade, 90Å, 70-230 mesh, for column chromatography
Supelco
Silica gel, high-purity grade (puriss), pore size 60 Å, 70-230 mesh, for column chromatography

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