By employing honeycomb GO with large surface area as the starting materials and using elemental fluorine, we developed a novel, straightforward topotactic route toward highly fluorinated graphene in really large quantities at low temperature. The value of F/C molar ratio approaches to 1.02. Few-layer fluorinated graphene sheets are obtained, among which the yield of monolayered FG sheet is about 10% and the number of layers is mainly in the range of 2-5. Variations in morphology and chemical structure of fluorinated graphene were explored, and some physical properties were reported.
Sufficient amounts of fluorographene sheets with different sheet-size and fluorine/carbon ratio were synthesized for preparing of fluorographene/polyimide hybrids in order to explore the effect of fluorographene on the dielectric properties of hybrid materials. It is found that the fluorine/carbon ratio, width of band gap, and sheet-size of fluorographene play the important roles in determining the final dielectric properties of hybrids. The fluorographene with high fluorine/carbon ratio (F/C ≈ 1) presents broaden band gap, enhanced hydrophobicity, good dispersity and thermal stability, etc. Even at a very low filling, only 1 wt %, its polyimide hybrids exhibited drastically reduced dielectric constants as low as 2.1 without sacrificing thermal stability, improved mechanical properties obviously and decreased water absorption by about 120% to 1.0 wt %. This provides a novel route for improving the dielectric properties of materials and a new thought to carry out the application of fluorographene as an advanced material.
Pristine
and oxidized multiwalled carbon nanotubes (MWCNTs) were separately
prepared and directly fluorinated with F2 through two different
routes: heating-fluorination and isothermal-fluorination. The amount
of fluorine atoms (hereinafter referred to as “F-content”)
bonding to the fluorinated samples was largely dependent on the modifing
route and chemical bonding of MWCNTs. The F-content of heating-fluorinated
pristine and oxidized MWCNTs was 3.2% and 9.2% respectively, which
were about 8 times and 18 times that of the corresponding isothermal-fluorinated
MWCNTs. According to structural analysis of samples before and after
fluorination, it was found that thermal elimination of oxygen-related
groups bonding to MWCNTs contributed to the formation of strongly
covalent C–F bonds during heating-fluorination. It was considered
that the oxygen-related groups provided reactive sites for the fluorination.
The fluorination reaction took place at an sp3 carbon linking
with the oxygen-related groups and did not increase the density of
defect on MWCNTs. A radical-mediated mechanism is accepted for this
reaction. Thus, MWCNTs could be first oxidized to increase the number
of oxygen-related groups and then heating-fluorinated by F2 directly to get highly fluorinated MWCNTs with stable C–F
bonds.
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