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 °C. Different fluorination temperature zones have been revealed by direct physicochemical analysis such as XRD, Raman spectroscopy, EPR, and solid-state NMR ( 13 C and 19 F). 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 (C 2 F) 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 °C, with concomitant disappearance of the graphitic structure.