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NMR and EPR studies of room temperature highly fluorinated graphite heat-treated under fluorine atmosphere

par Dubois, Marc Alexandre;Guérin, Katia;Pinheiro, J.P.;Fawal, Ziad El;Masin, Francis ;Hamwi, André
Référence Carbon, 42, 10, page (1931-1940)
Publication Publié, 2004

Article révisé par les pairs

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Résumé :

Semi-ionic carbon fluoride obtained by reaction of graphite with a gaseous mixture of IF5, HF and F2 was modified by a post-fluorination at various temperatures in the range 100-680°C. The resulting materials were studied by 19F-NMR and EPR both at room temperature and at different experimental temperatures from 200 to 360 K and from 100 to 473 K for NMR and EPR experiments, respectively. 19F-NMR gives information about the residual intercalated iodine fluoride species (IF5, IF6- and IF7) such as the temperature of their removal from the host fluorocarbon matrix and their mobility into the interlayer space. The nature of the C-F bonding was investigated by 19F-NMR, MAS/13C-NMR, FT-IR spectroscopy and X-ray diffraction. The C-F bonding changes from semi-ionic to a mainly covalent character at a fluorination post-treatment temperature close to 450°C. This transformation coincides with the removal of the iodine fluoride species from the host structure. The densities of the paramagnetic dangling bonds were studied by EPR; this technique allows also to investigate the local environment of the dangling bonds in the fully fluorinated samples (obtained with fluorination post-treatment temperatures higher than 450°C). As a matter of fact, an hyperfine structure was observed for these samples; it results from interaction of the dangling bond electron with six neighboring fluorine nuclei. The role of the intercalated species (iodine fluoride compounds and HF) on the mechanisms of the extra-fluorination is also discussed. © 2004 Elsevier Ltd. All rights reserved.