Web Release Date: October 12,
Effect of Mild Nitric Acid Oxidation on Dispersability, Size, and Structure of Single-Walled Carbon Nanotubes
and
Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, School of Chemical, Biological and Materials Engineering, University of Oklahoma, 100 East Boyd Street, Norman, Oklahoma 73019, E.R.C. Inc./NASA-Johnson Space Center, Mail Code ES4, 2101 NASA Parkway, Houston, Texas 77058
Received July 3, 2007
Revised Manuscript Received August 29, 2007
Abstract:
Oxidation of single-walled carbon nanotubes (SWNTs) with nitric acid increases their dispersability
in water, methanol, and N,N-dimethylformamide. Two oxidation protocols, sonication in 8 M HNO3 at
40 
C and reflux in 2.6 M HNO3, have been examined using SWNTs produced by the CoMoCat, HiPco,
and pulsed laser vaporization (PLV) methods. The dispersability of all types of nanotubes increased
substantially after 1 h of sonication and after 2-4 h of reflux. Longer treatments resulted in little further
improvement in dispersability and at reflux degraded the SWNTs. Stable dispersions of CoMoCat SWNTs
in DMF at concentrations as high as 0.4 g/L were achieved without the use of surfactants or polymers.
Raman spectroscopy showed greater covalent functionalization of the SWNTs by the reflux procedure
than by the sonication procedure. Concurrent with improved dispersability, oxidation resulted in smaller
diameters and shorter lengths as determined from AFM images, which show mostly bundles rather than
individual tubes. The lengths of SWNTs after oxidation decreased in the order PLV > HiPco > CoMoCat.
Recommendations for the method of conditioning of the various types of SWNTs depend on their intended
use.
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