Konstantin S. Makarevich

Application of pyrolitic method of synthesis for preparation of calcium bismuthate based photocatalyst

The study describes use of pyrolytic synthesis method for preparation of visible light calcium bismuthate based photocatalyst. The advantage of the proposed method is that it allows obtaining single-phase, homogeneous samples with various types of crystal lattice and controlled defects. It is shown that it is possible to obtain crystalline calcium bismuthate with the same stoichiometry in the entire region of existence of the solid solution. Synthesized samples of calcium bismuthate have been characterized using the scanning electron microscopy and X-ray analysis. It was found that the scope and conditions of synthesis affect the degree of imperfection of both anionic and cationic sublattice of calcium bismuthate.

Photographic materials with direct blackening based on polymer-semiconductor compositions

Photographic properties of polyvinyl alcohol (PVA)-ZnO/TiO2 compositions sensitized by BiCl3 were investigated in a process with direct blackening. These properties in general are similar to those of earlier investigated compositions sensitized by lead acetate (PbAc). Direct blackening in system with BiCl3 is more resistant to moisture.

Hydrothermal synthesis of anatase nanocrystals

The hydrothermal synthesis of TiO2 (anatase) nanocrystals has been produced. The conditions of reproducible synthesis of anatase nanocrystals by thermal treatment of water solution of titanium isopropoxide and triethanolamine at T= 80-100°C by 48 h have been found. Phase composition of final product has been verified by TEM and XRD analysis. As it has been obtained, the dimensions of TiO2 particles varied in the range 10-100 nm with mean value of 45 nm.

Catalytic Activity of a Composition Based on Strontium Bismuthate and Bismuth Carbonate at the Exposure to the Light of the Visible Range

This paper presents the results pertaining to studying the properties of the photocatalytically active composition of strontium bismuthate SrBi2.70O5.05, SrBi2.90O5.35, and SrBi3.25O5.88 and bismuth carbonate (BiO)2CO3 in molar ratios 1/0.67, 1/0.56, and 1/0.37, respectively. These compositions are obtained through pyrolytic synthesis from organic precursor complexes of strontium and bismuth with sorbitol. It has been established that the synthesised powder materials absorb the light of the visible range up to 500 nm owing to the presence of a narrow-gap semiconductor strontium bismuthate. The presence of a wide-band semiconductor (BiO)2CO3 ensures an effective separation of electron-hole pairs. The diffuse reflection spectra (DRS) of compositions differ from the analogous spectra of a mechanical mixture of these semiconductor phases with the same composition, which allows one to assume the heterostructural structure of the semiconductor system. The same heterostructure is confirmed by the results of mapping. Catalytic particles that are synthesised at a temperature of 500°C containing 27 mass% (BiO)2CO3 (corresponding to SrBi2.9O5.35/(BiO)2CO3 = 1/0.56) have the greatest activity with respect to the photodecomposition of methylene blue (MB). The possibility of controlling the optical properties and photocatalytic activity of the composition is depicted due to the joint formation of the strontium bismuthate phase and the bismuth carbonate phase.

Optical characteristics of particles produced using electroerosion dispersion of titanium in hydrogen peroxide

Titanium oxide particles are produced using electric-discharge dispersion of titanium in aqueous solution of hydrogen peroxide. Electron vacuum microscopy, X-ray diffraction, and diffuse reflection spectroscopy are used to study the morphology, composition, and optical characteristics of the erosion particles. It has been demonstrated that the particles consist of titanium and titanium oxides with different valences. The edge of the optical absorption is located in the UV spectral range. The band gap is 3.35 eV for indirect transitions and 3.87 eV for direct allowed transitions. The band gap decreases due to the relatively long heating in air at a temperature of 480–550°C, so that powder oxide compositions can be obtained, the optical characteristics of which are similar to optical characteristics of anatase. The erosion products are completely oxidized to rutile after annealing in air at a temperature of 1000°C.

Hydrothermal synthesis of TiO2/WO3 compositions and their photocatalytic activity

Photocatalytic activity, optical properties, thermal stability, phase patterns and morphology of nano-size ТiО2/WO3 compositions obtained from organic precursors through hydrothermal synthesis have been studied. It has been shown that doping of anatase nanoparticles with tungsten W+6 results in particle diameter reduction from 35 to 10 nm; decrease in width of the band gap from 3.15 eV to 2.91 eV and increase in temperature of phase transition of anatase to rutile up to 980оС. Catalytic activity of ТiО2/WO3 (4 mol.%) composition under photochemical methylene blue (MB) oxidation by simulated solar light exceeds that of undoped anatase (obtained in the same way) 6-fold.