Mechanochemical, Sonochemical and Hydrothermal Activation of Niobium Pentoxide and its Catalytic Properties

Modification of niobium pentoxide with different dispersity via mechanochemical, ultrasound, hydrothermal and microwave treatments (MChT, UST, HTT, and MWT, respectively) has been studied. All types of treatment do not change of phase composition but leads to improvement (at HTT and MWT) or, on contrary, breaking of crystal structure (at MChT and UST) and variation of crystallite size and specific surface area. UV-Vis measurements display increase of absorption in visible region. As a result, modified samples show higher photocatalytic activity at degradation of rhodamine B under visible irradiation. Similarly, initial and modified Nb2O5 samples are catalysts for mechanochtmical and sonochemical destruction of the same dye. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3515

Effect of precursor and surfactant nature on geometrical characteristics of mesoporous silicas

Bimodal mesoporous silicas and materials MCM-41 type were synthesized with the use as a template cationic surfactants distinguished by a length of the alkyl chain. Fumed silica, tetraethyl orthosilicate as well as of mixture these compounds were applied as a silicate precursor. Obtained samples have been characterized by the powder X-ray diffraction technique and adsorption measurements. Specific surface area, pore diameter, pore size distribution was determined from nitrogen ad(de)sorption isotherms at 77 K for the silicas prepared. The products with bimodal pore distribution have not ordered structure and contain macropores and mesopores, whose sizes are typical for MCM-41 materials. Effect of surfactant and precursor nature on the geometrical features of the ordered structure of MCM-41 type and bimodal porous materials was studied

Synthesis and Photocatalytic Properties of Silver Niobate

The interaction between silver nitrate and niobium pentoxide has been studied under conventional thermal treatment (TT) as well as mechanochemical and sonochemical treatment (MChT and UST, respec-tively). The products of reaction have been investigated using XRD, DTA-TG, Raman spectroscopy, adsorp-tion of nitrogen. MChT and UST promote lowering the temperature of silver niobate (SN) formation. The formed SN possesses higher specific surface area and photocatalytic activity. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3527

High-pressure cryogelation of nanosilica and surface properties of cryosilicas

Silica cryogels (cryosilicas) in a powder state were synthesized with different concentrations of fumed silica A-300 (CA-300 = 5-20 wt.%), sonicated in aqueous suspension, then frozen at -14 oC at different pressures in a high-pressure stainless steel reactor (a freezing bomb), and dried in air at room temperature. To analyze the effects of low temperature and high pressure, samples were also prepared at -14 oC or room temperature and standard pressure. The structural and adsorption properties of the powder materials were studied using nitrogen adsorption, high-resolution transmission electron microscopy, infrared spectroscopy, thermogravimetry, low-temperature 1H NMR spectroscopy and thermally stimulated depolarization current. The structural, textural, adsorption and relaxation characteristics of high-pressure cryogel hydrogels and related dried powders are strongly dependent on the silica content in aqueous suspensions frozen at 1, 450 or 1000 atmospheres and then dried. The largest changes are found with CA-300 = 20 wt.% which are analyzed with respect to the interfacial behavior of nonpolar, weakly polar and polar adsorbates using low temperature 1H NMR spectroscopy

Controlled Gasification of Carbonaceous Materials in a Water Vapour Atmosphere. Part II. Effect of Ca and Fe Ions on the Gasification Kinetics

The catalytic activities of calcium(II) and iron(III) ions were studied in the controlled gasification of carbonaceous materials by means of water vapour. The Ca II ions were introduced into the carbonaceous materials by ionic exchange as well as by the classical impregnation method. Irrespective of the method of introduction, calcium ions are an effective catalyst for the process, decreasing the activation energy from 185 kJ/mol to 169–164 kJ/mol. Iron(III) ions are not an effective catalyst for gasification by means of water vapour. During the course of this reaction at high water vapour pressure, the Fe III ions change into a non-active form of the stable oxide and do not take part in the process