Mechanochemical synthesis and physical–chemical properties of carbon–fluorocarbon nanocomposition materials. A review

There are the described novel class of porous carbon–fluorocarbon nanocomposition materials “C–CF_1+x”, prepared via the mechanochemical activation (MA) in the heterogeneous mixed systems “nano-C–nano-CF_1+x”, having an atomic ratio C:F as 1.14–4.0. As nano-C it was used thermally expanded graphite TEG and mesoporous carbon material NUMS (free porosity 45–95% and specific area 25–400 m²/g). As nano-CF_1+x these were used a superstoichiometric fluorocarbons FS and FT (CF_1.18–1.25) having the coherent diffraction area (CDA) ∼20–25 Å, free porosity 60–70%, sum O + H₂O in mixtures ∼0.1–0.5 wt.%, and metals sum <0.01 wt.%.Prepared nanocomposites “C–CF_1+x” were studied by FTIR, Raman, XPS C1s, O1s, F1s, X-ray diffraction and by chemical C, H, F-analyses. It was shown, that decrease of weight in systems “C–CF_1+x” does not exceed 0.5 wt.% and stated two main features of the temporary dynamics in changes for all MA-products. These are monotonous changes in bulk properties, such as decrease of C-nanophase relative amounts, confirmed with XRD. Simultaneously, a decrease of sp³-C–F and sp³-CF₂-groups at 1200 and 1320 cm⁻¹ and an origination of sp³-C–F-groups at 1080–1120 cm⁻¹, typical for C₂F-like structures are observed. Decrease of specific surface is corresponding to decrease in CDA sizes and dencity for all MA-products.O-containing admixtures in starting materials have a key influence to interactions in nano-“C–CF_1+x” systems during MA-processing, despite to their low content. The main O-contained participant is H₂O and it is interaction with sp³-C–F–bonds is leading to primary hydrolytic substitution of F onto OH with the origin of surface sp³-C–OH-bonds and their subsequent transformations into edged sp²>CO or/and into ester bridges C–O–C among basal and edged nano-C and nano-fluorocarbon blocks. The presence of basal sp³-C–OH and edged sp²>CO (sp²>COOH)-groups is confirmed by FTIR and XPS C1s and O1s spectra for all MA-nanocomposites in “C–CF_1+x” systems. Changes in the surface properties of prepared MA-“C–CF_1+x” nanocomposites are corresponded to the origin of extrema in properties for MA-time 6–10 min, such as content of surface C-nanophases and surface F with the simultaneous appearance of extrema in the specific electro conductivities and capacitances. The nature of observed phenomena is explained by the origin of chemical carbon nanosized contacts on particle surface and it is possible to use for practical applications. The main difference among MA-“C–CF_1+x” nanocomposites is that the “FS–TEG” systems are dominated by sp²-C–sp³-C–F electroconductive bridges, whereas in “NUMS–FT” systems the character of conductivity is determined by contribution of ester bridges C–O–C.