The dissertation is dedicated to to the synthesis and investigation of titania based films co–modified with d–block metal ions and nitrogen. Chemical structure peculiarities of the photocatalysts’ surface affecting the photocatalytic conversion efficiency of the organic and inorganic contaminants under irradiation of solar light are determined.
The scientific results of the dissertation are to determine the optimal synthesis conditions of the photocatalytically active titania based films in the processes of antropogenic compounds’ removal and to establish the correlation between the nature of co–doped metal ions and the efficiency of nitrogen incorporation in semiconductive lattice. Co–modification with metal ions and nitrogen is shown to аffect the crystallization process. The transformation of the crystal lattice and the presence of the doping agents are accompanied by the change of the optical, structural and photocatalytic properties.
It is shown that the nature of co–doped metal ions influences the chemical state of nitrogen on the sol-gel film surface, as namely the co-modification with Pt2+ or Ru3+ ions leads to the formation of substitutional nitrogen along [–C=N–C] fragments that are also present on the surface of metal ions undoped and doped by Zn2+ або Zr4+ ions titania films. The formation of common bonds between titanium and metal ions [–Ті–О–М] affected the position of semiconductor energy levels and recognized as the surface active sites, are strictly determined by synthesis conditions, namely the hydrolysis rate of the metal precursors and organic components in the sols.
The mixture of pseudobrookite and landauite without individual oxide phases (titania and iron oxide) is obtained at relative low temperature (450 °С). It is shown that the crystallization rate and thermal stability of iron titanate phases are provided by nitrogen modification. The photoelectrochemical (band gap energy, the position of the conduction and valence bands) and XPS (the binding energy of the elements) characteristics of iron titanate phase are determined. The nitrogen atoms in the semiconductive structure are considered as the defective sites fixed by spectroelectrochemical methods and EPR. The formation of the active sites on the surface of the photocatalysts, that are responsible for high adsorption, results in the high efficiency of tetracycline hydrochloride degradation.
The mechanisms of urea thermolysis during the sol-gel film treatment are proposed. The formation of intermediates converted to the different nitrogen-containing fragments depending on the nature of co-doping metals is suggested. The formation of the complexes between metal ions and nitrogen atom of urea molecule is considered to be a key point for the formation of metalnitrogen bonds.
The results of the dissertation present the practical importance for the new materials’ synthesis with the controlled properties for a number of applied aims: as photocatalysts, electrocatalysts, sensors, self-cleaning surfaces, electronic techniques components and super hard materials. The photocatalysts in the form of thin films allows to decrease the costs of photocatalytic processes due to manifold application, simple and costless separation of a film from a liquid phase. The coating of different substrates including low melting materials (thermoplastics, aluminum substrates and membranes) without structure distortion and the relative low temperature of crystalline phase formation present important parameters for practical application. The low amount of used precursors and the simple route of the synthesis procedure provide the low-cost, fast and technologically available synthesis procedure.
Key words: photocatalytic activity, visible light, semiconductive films, titania, d–block metal, nitrogen, sol-gel synthesis, pulsed laser deposition, surface chemical composition, pseudobrookite, landauite.
