Kondratiuk A. Mechanochemical preparation, structure, spectral and functional characteristics of modified graphenes, graphene-like carbon nitride and tungsten disulfide

The dissertation is devoted to the creation of methods for the mechanochemical production of graphene-like semiconductors C3N4 and WS2 and modified graphenes, using a set of complementary experimental methods to elucidate the influence of the preparation conditions of these materials on their structure, spectral, electrochemical properties, as well as on their behavior in the processes of electrochemical oxygen reduction, photochemical hydrogen evolution from water, electrochemical detection of biomolecules with close redox potential values and generation of photocurrent in nanocomposites with conductive polymers. The possibility of modifying graphene with functional groups and doping with nitrogen atoms or co-doping with nitrogen and fluorine atoms by means of the interaction of mechanochemically generated active centers in the mechanochemically obtained graphene structure with aliphatic alcohols, ammonia or products of thermal decomposition of ammonium fluoride, respectively, was established. It was found that nanoparticles of the obtained graphenes are characterized predominantly by monolayer morphology, and their lateral size depends on the nature of the exfoliating agent used. It was shown using Raman spectroscopy that modification of graphenes increases the ordering of their structure. It was found that graphene doped with nitrogen due to its structural features is characterized by higher electrocatalytic properties in the oxygen reduction reaction in comparison with graphene co-doped with nitrogen and fluorine (NF-GR). When used in electrochemical sensors, the presence of doping atoms in nanoparticles of the obtained graphenes leads to their high electrocatalytic activity and selectivity in determining the concentration of dopamine, ascorbic and uric acid biomolecules simultaneously present in an aqueous solution. The possibility of mechanochemical preparation of graphene-like semiconductor C3N4 and WS2 is shown. It was revealed that the predominantly monolayer morphology of graphene-like C3N4 provides a higher reduction potential, more efficient separation and transfer of photogenerated charges, which determines its high photocatalytic activity in the reaction of hydrogen evolution from water under the light irradiation. It has been found that significant quenching of the photoluminescence of substituted polyparaphenylenevinylenes (MEH-PPV or SuperYellow copolymer) and an increase in the photocurrent in their hybrid nanocomposites with mechanochemically prepared 2D materials are due to the transfer of photogenerated electrons from macromolecules of conductive polymers to nanoparticles of modified graphenes or MoS2 and WS2.