ИСТИНА

Because of their unique features carbon nanomaterials are widely studied in numerous fields of applications. In order to adjust the properties of carbon materials the implementation of heteroatoms (e.g. oxygen, nitrogen, boron…) to carbon structure is commonly used. Among the fundamental bulk characteristics of materials are the heat of combustion and the standard enthalpy of formation. Both enthalpies are sensitive to the structure, number of graphene layers, presence of heteroatoms and their content1. The classic method of determination of combustion energy bomb calorimetry still has several disadvantages in carbon materials analysis application. Simultanious thermal analysis combining differential scanning calorimetry and thermogravymetry was chosen as fast and accurate technique2 to calculate the heat of combustion of carbon nanomaterials. Two series of nitrogen-doped carbon nanoflakes (N-CNF), which are promising materials for energy storage devices, were obtained by altering the duration of synthesis and the ratio of nitrogen containing precursor (CH3CN) to benzene. Enthalpies of combustion (cH0) were determined by differential scanning calorimetry method, enthalpies of formation (fH0) were calculated according to the elemental composition. All materials were characterized by elemental analysis, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy as well as liquid nitrogen adsorption. It was found that with the increase of the duration of synthesis the specific surface area of N-CNF decreased that can be caused by growth of graphene layers. The augmentation of the amount of graphene layers was also confirmed by TEM. For the time-dependent series of N-CNF nitrogen content identified by XPS and elemental analysis was constant and was estimated 121 wt.%. All (-cH0) values for N-CNF obtained from 15 to 90 min were found to be less than that of graphite and increased with the increase of the synthesis duration. Absolute values of heats of combustion grow gradually from 15 to 90 min and tend to approach to cH0(graphite) = -30.2 kJ/mol. It was also shown that the concentration of CH3CN in precursor mixture with benzene influenced the nitrogen content in N-CNF that varied from 0 to 12 wt.%. Calculated (-cH0) values decreased with the increase of nitrogen content.