ИСТИНА

Herein the transformation of structure, morphology and porosity observed during graphite chemical or electrochemical intercalation in nitric and sulfuric acids and further exfoliation was studied by scanning electron microscopy, contact angel measurements, X-ray diffraction, Raman spectroscopy, nitrogen adsorption etc. Natural graphite flakes was taken as a parent substance. Chemical intercalation was carried out in 98 % nitric and 96 % sulfuric acid to synthesize graphite nitrate and graphite bisulfate of different stages. Further chemical oxidation was conducted in the presence of oxidizer excess for 24-72 hours. Electrochemical intercalation was carried out by graphite anodic polarization in both concentrated and diluted (50 and 30 %) nitric and sulfuric acids at a constant current of 100 mA and specific quantity of electricity of 1000 – 3000 C/g. All the prepared samples were studied by XRD and then hydrolyzed to prepare expandable graphite. Expanded graphite was produced by the expandable graphite exfoliation at a temperature of 300 and 900 oC in air. According to the XRD data and using Scherer equation, the graphite crystalline size along “c” axis was estimated for all the samples. The reduction of crystalline size from 120 nm for natural graphite to 40-60 and 10 nm during graphite intercalation was shown. The significant change was observed for electrochemically prepared samples especially in diluted nitric acid. Moreover, deeply oxidized sample are characterized with the lowering of the order between crystallines that is reflecting in the decreasing of the peaks intensity on XRD patterns and D-line appearance in Raman spectra. Exfoliation was shown not to affect the crystalline size. Contact angel measurements shown that free surface energy for expanded graphite samples prepared by long-term chemical or electrochemical treatment is less than that for chemically prepared samples. Electrochemical samples demonstrate hydrophilic properties and could be wetted with polar liquids whereas chemically prepared samples are wetted only by non-polar liquids. The sorption capacity to water and octane was determined for the expanded graphite compacted to the pellets with a density of 0.3 g/cm3. The sorption rate along and perpendicular to the compacting axis was determined. Specific surface area of expanded graphite samples varies from 20 m2/g to 160 m2/g. Porous structure of expanded graphite consists mostly of micropores and mesopores although in electrochemically prepared samples micropores was observed as well. The pore volume and pore size distribution was determined for all investigated samples.