Preparing Highly Fluorinated Multiwall Carbon Nanotube by Direct Heating-Fluorination during the Elimination of Oxygen-Related Groups

Pristine and oxidized multiwalled carbon nanotubes (MWCNTs) were separately prepared and directly fluorinated with F₂ through two different routes: heating-fluorination and isothermal-fluorination. The amount of fluorine atoms (hereinafter referred to as “F-content”) bonding to the fluorinated samples was largely dependent on the modifing route and chemical bonding of MWCNTs. The F-content of heating-fluorinated pristine and oxidized MWCNTs was 3.2% and 9.2% respectively, which were about 8 times and 18 times that of the corresponding isothermal-fluorinated MWCNTs. According to structural analysis of samples before and after fluorination, it was found that thermal elimination of oxygen-related groups bonding to MWCNTs contributed to the formation of strongly covalent C–F bonds during heating-fluorination. It was considered that the oxygen-related groups provided reactive sites for the fluorination. The fluorination reaction took place at an sp³ carbon linking with the oxygen-related groups and did not increase the density of defect on MWCNTs. A radical-mediated mechanism is accepted for this reaction. Thus, MWCNTs could be first oxidized to increase the number of oxygen-related groups and then heating-fluorinated by F₂ directly to get highly fluorinated MWCNTs with stable C–F bonds.