Reactivity of carbon nanofibers with fluorine gas

The present study highlights the reactivity of carbon nanofibers (CNFs) with fluorine gas. Highly purified and graphitized CNFs were treated under a stream of fluorine gas for 16 h at temperatures ranging from 380 to 480 degrees C. Different fluorination temperature zones have been revealed by direct physicochemical analysis such as XRD, Raman spectroscopy, EPR, and solid-state NMR (C-13 and F-19). The comparison between various parameters such as covalence of C-F bond, T-1 spin-lattice nuclear relaxation time, density, and environment of the dangling bonds, among others, allows the fluorination mechanism to be determined, i.e., the formation of (C2F)(n) type graphite fluoride as the precursor of richer (CF)(n) compound. This is supported by TEM characterization as the fluorination proceeds from the external parts of the carbon nanofibers and then propagates through the core without a major structural change of the fluorinated parts. A low exfoliation of the sheets is necessary for extended fluorination and conversion into (CF)(n); this occurs for fluorination temperatures higher than 472 degrees C, with concomitant disappearance of the graphitic structure.