The dissertation is devoted to the study of nanostructured materials based on silicon carbide, optimization of their synthesis methods, chemical modification and regulation of physicochemical properties. Much attention was paid to elucidating the influence of chemical treatment conditions on the physicochemical properties and surface composition, as well as the development of simple and effective methods for their modification and functionalization. Prospects for the materials with controlled morphology based on nanostructured SiC were seen in the use as stable catalyst support, for the development of technologies of composites and biocompatible nanomaterials making, sensors elements and optical probes in biomedical research.
The method of controlled reduction of SiC nanoparticles’ (NPs) size from 17 to 9 nm by adjusting the calcination temperature in air in the range from 400 to 900 ˚C was presented. SiC NPs’ surface composition and strength of the acid-base sites depending on the selected oxide layer removal agent were determined. Among the approaches to the functionalization of the SiC NPs’ surface chemistry, the possibility of covalent grafting of 1-alkenes directly to the surface with the formation of hydrophobic SiC NPs, as well as the involvement of carboxyl surface groups (formed under oxidative etching in HF-HNO3 mixture) in modification of its lyophilic and electrokinetic properties were noted.
Conditions of thermochemical synthesis of mesoporous SiC from a polymer SiC-precursor (polycarbosilane, PCS) via method of “nanocasting” were optimized using SiO2 nanoparticles (from commercially available aqueous sol) as a template, which made it possible to obtain porous SiC with spherical mesopores of 12 and 22 nm. The comprehensive multiparametric study to determine the factors influencing the morphology and crystallinity of mesoporous SiC was performed. The study of the dependence of structural parameters of mesopores, size of the crystallites making up their walls on the synthesis temperature, the composition of PCS/SiO2 nanocomposite and the method of its production were presented. The resistance of the material to thermal oxidation depending on the selected synthesis temperature (1200, 1300 and 1400 ˚С) was also evaluated The study data of the influence of the additive amount of Ni (II) complex on SiC phase crystallinity and structure of the final material were presented and the recommendation on selection of the optimal thermochemical synthesis conditions for obtaining of the mesoporous SiC with morphological parameters and crystallinity best for a support for catalytically active metal nanoparticles was made.
The process of electrochemical dissolution (anodizing) of a compact polycrystalline SiC in HF solutions was considered and the elemental, phase composition and morphology of the products were determined. The influence of anodizing conditions (such as SiC plate resistivity, electrolyte composition, current density) on the yield of the products and their ratios was studied. For the first time, a detailed study of the chemical nature and physicochemical properties of the soluble product of SiC electrochemical dissolution (so-called “Carbon Fluorooxide", CFO) with a wide range of independent physical and chemical methods were performed. Some analogy was drawn between electrochemical dissolution of SiC as a result of anodic reaction in HF solutions and oxidative chemical etching of SiC under the action of HF – HNO3 mixture due to formation of organic matter of complex structure - CFO or its analogues. The physicochemical properties of the CFO were also compared to some natural (humic substances) and synthetic macromolecular compounds as well as graphene oxide in order to evaluate the structural analogy and differences.
The CFO’s functional groups composition was determined (-COO(H, Et), CAlk/Ar–(OH, F), and the structural model of this substance was proposed. Within the elemental analysis, the chemical state of Fluorine and its content in the CFO by chemical forms were made and also kinetics of its hydrolytic cleavage as a function of pH and alkalinity of the medium were studied. The strength of CFO’s acid groups was characterized and the methods of simple chemical modification and functionalization through reactions of carboxyl group with amines (ethylenediamine, diethanolamine and C18H37-NH2) were suggested.
The work represents detailed studies of the optical properties of CFO. It was shown that for CFO both one- and two-photon photoluminescence is characteristic. The possibility of using the detected photoluminescent properties of the CFO for biovisualization of living cells was shown. Electrocatalytic activity of the CFO in H2O2 reduction reaction was used to modify carbon planar electrodes (as a component of a composite film) in obtaining of more selective electrochemical sensor for hydrogen peroxide, which have high sensitivity and a wide linear range of detectable concentrations.
