Sadova M. Modification of the energy state of a nanoporous bio-carbon for adsorbents and supercapacitors electric drives.

The dissertation investigates the structure, polarization and sorption properties of nanoporous bio-carbon, and modifies it by methods of ultrasonic influence in the pre-cavitation and cavitational regimes. It is shown on the basis of the analysis of X-ray diffraction data of the investigated materials, that all of them are characterized by a micro-heterogeneous structure, which is manifested in the formation of graphite-like and graphene nanocrystals distributed in the amorphous phase. It should be noted that the dominant contribution (from 75 to 82%) in the crystalline component is given by three-dimensional graphite-like crystallites. It has been established that ultrasound irradiation in precavitational and cavitational regimes of synthesized bio-carbons not only efficiently shreds carbon particles, but also reduces the total number of surface groups. At the same time there is an increase of hydrophilicity without significant changes in the porous structure. Such changes improve the coefficient of use of the active surface of carbon when it is used as an active material of electrodes of super-capacitors by increasing its specific capacity. An impedance analysis of activated carbon materials before and after ultrasound irradiation was performed, which shows a shift of the Fermi level to a region with a higher density of delocalized electronic states. This is the reason for the release of the Helmholtz layer capacity by increasing the capacity of the layer of the spatial charge region in a carbonaceous material. Such a redistribution of the values of the capacities forming the double electric layer, after the influence of ultrasound improves the characteristics of supercapacitors, and in particular, increases their specific capacity. For synthesized carbons, the presence of asymmetrization of the volt-farad dependencies with positive and negative polarizations has been established. At the same time, the strong growth of the specific capacity in the anode region of potentials up to 163 F/g, 172 F/g and 214 F/g, respectively, for activated charcoal grade BAU-A, and synthesized from beet pulp and corn stalks, provides them no alternative efficacy when used as the negative electrode asymmetric ultracapacitor. It has been established that ultrasound irradiation in cavitation mode increases the sorption ability of activated carbon to a wide range of petroleum products. Particularly this effect becomes noticeable in the absorption of diesel fuel with activated carbon from corn stems - absorption increases by 50% compared with the absorption with unmodified activated carbon. It has been established that the isotherms of adsorption of methylene blue from aqueous solutions for all investigated types of activated carbon can be described as isotherms of type ІІ. This type of isotherm is modeled by the Langmuir model. On the basis of modeling results, specific surface area was calculated based on the magnitude of the amount of absorbed dye. It is established that the method of determining the specific surface area of different types of coal by the absorption of methylene blue from aqueous solutions is in good agreement with the results obtained with the standard nitrogen adsorption method, taking into account the hydrophilic properties of the surface of activated carbon. This method can be proposed as a simple method for evaluating the surface area of carbon sorbents, since it does not require complex equipment and is fast enough.