Effect of Hydrogen Fluoride Addition and Synthesis Temperature on the Structure of Double-Walled Carbon Nanotubes Fluorinated by Molecular Fluorine

Double-walled carbon nanotubes (DWCNTs) have been fluorinated by pure molecular fluorine (F₂) at room temperature or 200 °C and a mixture of F₂ with hydrogen fluoride (HF) at 200 °C that resulted in products with compositions of CF_0.12, CF_0.39, and CF_0.53 as determined by X-ray photoelectron spectroscopy. The differences in the structures of three kinds of fluorinated DWCNTs were revealed using transmission electron microscopy, Raman scattering, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Quantum-chemical modeling of the NEXAFS F K-edge spectra detected a change in the fluorine pattern with the increase of the F₂ treatment temperature. The presence of HF in fluorine gas was found to accelerate the fluorination process and cause a partial destruction of outer shells of the DWCNTs.