Carbon nanofibres fluorinated using TbF4 as fluorinating agent. Part I: Structural properties

Fluorination of carbon nanofibres (CNFs) under fluorine gas at 480 °C leads to high fluorine content but also to some partial exfoliation. In order to avoid such phenomenon, an alternative route has been performed at temperatures ranged between 420 and 500 °C using a fluorinating agent, i.e. terbium tetrafluoride. The structural properties of the fluorinated CNFs are discussed taking into account the data of 13C solid state NMR, Raman spectroscopy, SEM, TEM and XRD. Whatever the fluorination temperature, a fluorinated phase of (CF)n structural type, is formed contrary to the direct process using F2 gas for which a (C2F)n-type fluorinated phase appeared for fluorination temperatures lower than 450 °C. The progressive release of fluorine atoms from the thermal decomposition of TbF4 allows an homogenous distribution of the fluorinated part into the CNFs matrix and the formation of a unique (CF)n type structure. Moreover, for high fluorination temperatures (480 and 500 °C), the fluorination leads to some nanofibres breaking but in no way to exfoliation.