Papers by Keyword: Microwave Synthesis

Abstract: Microwave-assisted hydrothermal synthesis of TiO₂ nanofibers under various temperature and pressure conditions were done in this research. High quality TiO₂ nanofiber coatings where obtained when temperature was in range 240 – 245 °C and pressure was 27.3 – 29.1 bar. Obtained TiO₂ nanofiber coatings are with a specific surface area of ​​151.5 to 158.9 m²· g^-1 before calcination. Comparing with nanopowder photocatalysts nanofiber coatings photocatalysts can be much easier removed from solution after the photocatalysis process. Such coatings with relative large specific surface area are with higher potential application in industry.

Abstract: Sm₂O₃/ZnO nanoparticles were prepared via microwave-assisted hydrothermal and sol-gel combustion synthesis. Characteristics of obtained samples were compared in dependence of Sm₂O₃ content and calcination temperature. Prepared nanostructures were characterized with scanning electron microscopy and X-ray diffraction. Nanoparticles prepared via microwave-assisted hydrothermal and sol-gel method have flower-like and spherical shape respectively. The photocatalytic activity of samples under solar light simulated illumination was found to be affected by content of Sm₂O₃, calcination temperature and preparation method. The first-order rate constant of MB solution degradation of samples prepared via microwave-assisted hydrothermal method approximately three times exceeds that of sol-gel samples.

Abstract: In the present work formation of active TiO₂ nanofibers in microwave-assisted synthesis and their modification with Au, Pt, Pd and Ag nanoparticles were studied. Anatase nanopowder and 10M KOH solution were used as raw materials. Microwave-assisted synthesis permitted to obtain TiO₂ nanofibers and nanowires with a diameter of 10nm and a specific surface area 158.5m²/g. Chemical deposition method were used to modify TiO₂ nanofibers with precious metal nanoparticles. After modification, specific surface area decreased and were in range 73.1 – 74.7m²/g. Photocatalytic activity was determined by degradation of the methylene blue (MB) solution under visible light irradiation. High intensity LED lamp was used as light source. The obtained samples showed higher photocatalytic activity with respect to pure TiO₂ nanofibers. The doped TiO₂ nanofibers were appropriate for degradation of harmful organic compounds as well as for hydrogen production by water splitting.

Abstract: In this work we propose a new method for synthesis of ultrafine powders of tungsten, titanium and vanadium carbides combining two methods – liquid-phase precipitation on carbon substrate and low-temperature microwave heat treatment in argon stream. An entire spectrum of intermediates obtained by thermolysis, reduction and carbonization of precursors, as well as the final products has been presented. As a result of sample assessment, the phase composition, structure, morphology and particle size, as well as the size of specific surface areas have been determined.

Abstract: NiAl matrix composites reinforced with a-Al2O3 and TiB2 were fabricated by microwave synthesis from Al-TiO2-B-Ni system. The reaction process and microstructures were analyzed by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM).The results showed that the ignition temperatures of the reaction heating by microwave and conventional method were approximately 556°C and 592°C respectively. Furthermore, the fabrication time by microwave synthesis was about several minutes, which was much shorter than two hours spent usually in conventional heating method. The a-Al2O3 phase aggregated at the trigonal grain boundary of the NiAl matrix, and the TiB2 phase distributed uniformly in the NiAl matrix.

Abstract: Nanoflowers are desirable in light driven applications like Dye Sensitized Solar Cells (DSSCs) due to their large surface area and greater light absorption capabilities. An instant, simple, cheap and environment friendly method of preparing titanium dioxide nanoflowers is presented. The nanoflowers are produced in a time as short as 5 minutes in aqueous conditions without the use of hazardous hydrofluoric acid or organic surfactants at 1 atm. pressure and low temperature of 100°C. Titanium dioxide commercial nanopowders are treated with microwaves in an aqueous sodium hydroxide solution for small durations. The resulting powders are annealed at 450°C in air and characterization is performed using XRD, SEM and Raman spectroscopy.

Abstract: A new method in situ for producing of biocompatible composites based on hydroxyapatite and oligomers of lactic and glycolic acid is described. Their thermo-mechanical, physical-chemical and biological properties are studied as well. The formation of bonds between hydroxyapatite with lactic and glycolic oligomers in composites are confirmed by IR spectroscopy of the samples, including those obtained in the Soxhlet apparatus. The formation of calcium-phosphate layer on the composite's surface containing hydroxyapatite was shown by SBF-investigation. The scaffolds based on lactic acid oligomer do not stimulate formation of a calcium-phosphate layer and they are subjected to destruction by the way of hydrolysis.

Abstract: Cerium vanadate nanocrystalline was prepared by cerium nitrate, vanadium (V) oxide as raw materials and sodium dodecyl sulfate as surfactant under microwave irradiation. The sample was characterized by X-ray diffraction (XRD) and scanning electron micrograph (SEM). The XRD show that the as-prepared sample calcined at 773 K is tetragonal zircon, and the SEM graph show that the as-prepared CeVO₄ nanocrystalline is layer structure formated of small particles aggregation. We studied the photocatalytic activity of the as-prepared samples by using degradation of methyl orange in visible light. It shows that the photocatalytic activity of Cerium vanadate nanocrystalline was very well. The effects of different factors such as calcination temperature and the concentration of methyl orange on the characterization of CeVO₄ are discussed. It found that when the catalyst calcined at 873 K was 0.10 g, and 0.3 mL hydrogen peroxide joined as well as, pH was 2.0, the degradation ratio of CeVO₄ for methylene orange of 100 mL 20 mg/L reached 87% in 80 min.

Abstract: In this paper, the reaction mechanism of inorganic carbon and titanium dioxide synthesis of titanium carbide thermodynamic were explored, and a thermodynamic basis date for the microwave heating was provided. Through analyzing the experimental results for the thermal stability of titanium carbide, we could obtain the theoretical parameters for the actual synthesis process.

Abstract: In this work a new method of nanoand ultrafine powder of tungsten oxide and carbide synthesis by means of combinating carbon carrier supported classic liquid-phase precipitation and low-temperature microwave treatment was offered. The full range of intermediate substances obtained during thermolysis, reduction and carbidization precursors to final products were presented. The thermolysis of tungstic acid with the formation of tungsten oxide and carbide ultrafine particles of different modifications were studied. It was shown, that cooling ammonium tungstate solution to 4 °C, and use of carbon carrier on the precipitation stage can increase specific surface area from 20 to 100 m²g^-1. With the use of SEM precursors particles size were examined (∼200 nm) and the morphology of initial, intermediate and final products was shown.