Stability of fluorinated double-walled carbon nanotubes produced by different fluorination techniques

Double-walled carbon nanotubes (DWCNTs) have been fluorinated using (1) gaseous F2 at 200 °C, (2) a mixture of BrF3 and Br2 at room temperature, and (3) radio frequency CF4 plasma. The stability of the resultant samples was examined by thermogravimetric analysis in an inert atmosphere and by comparing the X-ray photoelectron spectra of the pristine samples with those after heating in vacuum at either 70 °C for 10 h or 120 °C for 20 h. The DWCNTs fluorinated by F2 showed the highest stability (the temperature of decomposition is around 396 °C), while the BrF3 and plasma-fluorinated DWCNTs lose fluorine from 150 °C. Prolonged annealing of the fluorinated DWCNTs in vacuum at a temperature below 150 °C also resulted in the defluorination of the samples. Fluorine atoms leave the DWCNT surface together with carbon atoms leading to defects in the graphitic network. These defects are likely to be centers for later functionalization by oxygen-containing groups during DWCNT storage