Abstract
The direct F2 gas fluorination of a mesoporous silica gel has been shown to be a unique method leading to very high levels of fluorination (up to 13 wt % F in the bulk). The final powders are homogeneous with a controlled amount of grafted fluorine. In this study, various conditions of fluorination were tested, such as duration, temperature, F2 gas concentration of the fluorinating gas, or an annealing pretreatment. The content of grafted fluorine on silica was quantified by XPS and by the Seel method. Infrared spectroscopy measurements accounted for the consumption of different types of hydroxyl groups, that is, isolated (3740 cm−1), terminal (3715 cm−1), and bound (3520 cm−1), and also for the presence of unreacted internal hydroxyl groups inaccessible to D2O molecules and so to F2. Results showed that an F/OH substitution occurs during the fluorination process and that the grafted amount depends on the F2 concentration of the fluorinating gas and on the concentration of surface hydroxyl groups and phys...
Published Version
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