Solid-State NMR Study of the Post-Fluorination of (C_2.5F)_n Fluorine−GIC

Abstract

The conversion of (C2.5F)n fluorine-graphite intercalation compounds (GIC) into covalent graphite fluoride during a post-treatment in pure F2 gas is studied by solid-state NMR. First, a careful characterization of the starting material is performed; in particular, for the first time for fluorinated carbons, two-dimensional 19F--> 13C cross-polarization wide-line separation (CP-WISE) experiments were carried out. This completes the classical NMR data such as 19F and 13C chemical shifts, quantitative 13C solid echo, and C-F bond length measurements, which were estimated by dipolar recoupling using inverse CP MAS. The data of the raw (C2.5F)n and of the samples post-fluorinated at 350, 450, and 550 degrees C were compared to investigate the C-F bonding as a function of the treatment temperature. The C-F bonding is discussed taking into account a hyperconjugation of the C-F bonds with neighboring unfluorinated carbon atoms.

Insights on the reactivity of ordered porous carbons exposed to different fluorinating agents and conditions

“…The 13 C chemical shift of sp 2 carbon atoms is expected at around 120 ppm [22,[51][52][53][54], the interaction with neighboring C-F bonds resulting in a shift towards high values, up to 145 ppm for highly Table 1 -Textural properties of carbonaceous materials before and after different fluorination treatments. fluorinated room temperature graphite fluoride [55][56][57].…”

“…The higher the interaction, the higher the chemical shift [51,56,57]; these carbon atoms are denoted as C-C-F on the NMR spectra. C-F bonds and CF 2 groups exhibit chemical shifts in the 80-90-ppm range and at 110 ppm, respectively [52][53][54][55][56][57].…”

“…C-F bonds and CF 2 groups exhibit chemical shifts in the 80-90-ppm range and at 110 ppm, respectively [52][53][54][55][56][57]. The integrated surface of the various components (sp 2 C, C-C-F, C-F, and CF 2 ), denoted as S C , S C-C-F , S C-F , and S CF2 , are used to estimate the chemical composition, that is, the fluorine content x in CF x .…”

3D microstructures of nuclear graphite: IG-110, NBG-18 and NG-CT-10

“…The fluorine compounds (ClF 3 , BrF 3 , LiF, etc.) in molten salts can react with graphite [5][6][7][8], and the pores in the nuclear graphite can accommodate the molten salt and fission products in normal operation condition [9]. Therefore, it is important to systematically analyze the pore structure characteristics of nuclear graphite in three-dimensional spaces.…”

New synthesis methods for fluorinated carbon nanofibres and applications

“…NMR lines are rather broad due to a strong homonuclear dipolar coupling but 19 F chemical shifts of CF and CF 2 covalent bonds differ sufficiently each from others (i.e. À170/À190 ppm and À120 ppm [12][13][14][15][16], respectively) to separate their lines. The relative amount of C-F and CF 2 will be discussed taking into account the intensities of these two lines.…”