Thermal Stability of Oxidized Single-Walled Carbon Nanotubes: Competitive Elimination and Decomposition Reaction Depending on the Degree of Functionalization.

The thermal stability of oxidized single-walled carbon nanotubes (SWNTs) with various degrees of oxidation was investigated. The oxidized SWNTs exhibited lower absorption and radial breathing mode (RBM) peaks and a higher intensity ratio of the D band to the G band (D/G) in their absorption and Raman spectra than those of the pristine SWNTs. After the thermal treatment, the D/G ratio of the oxidized SWNTs almost recovered its original intensity, regardless of the degree of oxidation. The absorption, photoluminescence (PL), and RBM peaks could not recover their original intensities when the oxidation degree was high. The results indicate that the elimination and decomposition reactions proceeded competitively depending on the degree of oxidation. In addition, a new PL peak was observed in the near-infrared region, and the PL peak intensity increased with the subsequent thermal treatment. The theoretical calculations provided an insight into the possible pathways for the decomposition of oxidized SWNTs, showing that the O2 elimination and CO/CO2 evolution proceed competitively during thermal treatment.