Thermal Recovery Behavior of Fluorinated Single-Walled Carbon Nanotubes

Abstract

The thermal recovery behavior of fluorinated single-walled carbon nanotubes has been systematically examined by UV−vis−near-IR absorption spectroscopy, IR absorption spectroscopy and electric resistance measurements under different annealing temperatures. The decrease in the IR intensity of C−F stretch bands centered at about 1207 cm-1 and the reduced resistance of the nanotube samples with heat annealing indicates that pristine nanotubes are recovered by the removal of sidewall groups. After annealing at 100 °C in noble gases, the IR spectrum shows nanotube features of A2u mode at 867 cm-1 and E1u mode at 1579 cm-1. Correspondingly, in the UV−vis−near-IR spectrum, only a new feature at about 640 nm (1.9 eV) is observed. At higher annealing temperatures ≥150 °C, the intensity of the absorption features at 640 nm (1.9 eV) of metallic nanotubes, and 900 nm (1.4 eV) and 1630 nm (0.8 eV) of semiconducting nanotubes increases simultaneously. Generalized two-dimensional UV−vis−near-IR correlation spectroscopy has revealed that the thermal recovery behaviors of fluorinated metallic and semiconducting nanotubes are very similar at annealing temperatures between 150 and 350 °C, indicating that differentiation of these nanotubes for purification is difficult under those annealing conditions.