ИСТИНА

The properties of graphene oxide (for example, high electrical conductivity and mobility of charge carriers after it reducing, a large specific surface area), as well as its comparative cheapness, initiate active searches for the application of this material in applied developments, as well as methods for its chemical modification. Graphene oxide is a promising compound for the production of composite materials. When assessing the possibility of using graphene oxide in this quality, it is necessary to take into account, in particular, the accessibility of areas that are close in composition to graphene and the chemical activity of oxygen-containing groups. The aim of this work was to determine the effect of heat treatment on the composition and structure of microwave exfoliated graphite oxide (MEGO). Heat treatment included stepwise heating samples of MEGO in a vacuum with mass-spectral monitoring of the composition of the emitted gases. The obtained samples were analyzed by XPS, XRD, IR and Raman spectroscopy, and electron microscopy (SEM and TEM). The complex of these methods made it possible to obtain heat treatment products from MEGO under controlled annealing conditions and determine its effect on various characteristics: morphology, total defectiveness, total oxygen concentration, types of oxygencontaining groups, and sizes of graphene crystallites. Annealing of MEGO at Tf = 573 K is accompanied by the release of H2O, CO, and CO2 molecules (no release of oxygen O2 and sulfur dioxide SO2 was detected), and does not lead to the complete removal of water and oxygen-containing groups from the sample. In the samples MEGO and MEGO /573 the total oxygen concentration is almost the same, and a similar set of oxygen-containing groups is found. The release of water molecules reaches a certain minimum level at a temperature of 773 K, and upon further heating changes slowly. Intensive emission of carbon oxides CO and CO2 at temperatures of 873–1073 K is completed by reducing their fluxes to a level beyond the sensitivity limits of the mass spectrometer. A 4,4 times decrease in oxygen concentration occurs during high-temperature (1073K) annealing of MEGO. The formation of MEGO/1073 is accompanied not only by the disappearance of quinone fragments and adsorption water, but also by a significant decrease in the content of oxygencontaining groups. The decrease in the content of carbonyl groups is estimated by a factor of 2, and hydroxyl and ether groups - by a factor of 3. During the high-temperature heat treatment of MEGO, deeper separation of particles occurs with the formation of highly deformed packs with a small number of layers, in which the same wrinkles, folds and twists are present. In addition to the morphological changes, there are numerous holes in the layer structure, which are formed in the areas of active oxygen removal in the form of CO and CO2 oxides. High-temperature annealing leads to an increase in the concentration of defects by ~20%; at the same time, the average distance between defects is reduced by ~17%. In conclusion, we note that the very small crystal areas distributed by volume, as well as twists, folds, and wrinkles in carbon layers are the “clips” that determine the stability of MEGO and keep them from decay.