| Abstract
| - The reversible protonation of carbon single-walled nanotubes (SWNTs) in sulfuric acid and Nafionwas investigated using solid-state nuclear magnetic resonance (NMR) and Raman spectroscopies. Magic-angle spinning (MAS) was used to obtain high-resolution 13C and 1H−13C cross polarization (CP) NMRspectra. The 13C NMR chemical shifts are reported for bulk SWNTs, H2SO4-treated SWNTs, SWNT−Nafionpolymer composites, SWNT−AQ55 polymer composites, and SWNTs in contact with water. Protonationoccurs without irreversible oxidation of the nanotube substrate via a charge-transfer process. This is thefirst report of a chemically induced change in a SWNT 13C resonance brought about by a reversibleinteraction with an acidic proton, providing additional evidence that carbon nanotubes behave as weakbases. Cross polarization was found to be a powerful technique for providing an additional contrastmechanism for studying nanotubes in contact with other chemical species. The CP studies confirmedpolarization transfer from nearby protons to nanotube carbon atoms. The CP technique was also appliedto investigate water adsorbed on carbon nanotube surfaces. Finally, the degree of bundling of the SWNTsin Nafion films was probed with the 1H−13C CP-MAS technique.
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