Andri Vital

One-step flame synthesis of SnO2 / TiO2 composite nanoparticles for photocatalytic applications

SnO2 / TiO2 composite nanoparticles have been synthesized in a single-step by feeding evaporated precursor mixtures into an atmospheric pressure diffusion flame. Particles with controlled Ti: Sn ratios were produced at various flow rates of oxygen, and the resulting powders were characterized by BET surface area analysis, XRD, TEM, EDAX and UV-Vis spectroscopy. For the lowest concentration (3.4 mol %) of SnO2 employed in this study anatase phase of TiO2 is stabilized, while segregation of SnO2 is seen at medium (6.9 to 12.4 mol %) and high concentrations (20.3 mol %). Though the equilibrium phase diagram predicts complete solubility of one oxide in another at all compositions, segregation of SnO2 phase is observed which is explained by the usage of diffusion flame in the present study. The particle formation mechanism of SnO2 / TiO2 composites is proposed basing on the single component aerosol formation. Photocatalytic activity of the composite particles is tested for the degradation of methylene blue and is compared with pure TiO2 synthesized under similar conditions. Improved photocatalytic activity of the composite particles is attributed to the stabilized anatase phase and better charge separation due to the coupling of TiO2 and SnO2 within the composite nanoparticles.

Photocatalytic Activity of W-Doped TiO2 Nanopowders

Abstract Polycrystalline tungsten-doped titanium dioxide nanopowders within a dopant concentration of 0-1 at.% were prepared by a one-step flame spray synthesis (FSS). Mixtures of titanium tetra-isopropoxide dissolved in ethanol and tungsten hexacarbonyl solubilized in tetrahydrofuran were used as precursors. The specific surface area (SSA) of the powders was between 40 and 130 m2/g depending on the process parameters, namely the flame combustion stoichiometry and their chemical composition. Irrespective of their composition the powders consisted of spherical particles, as visible by transmission electron microscopy (TEM). They are highly crystallized with anatase as the predominant phase, according to X-ray diffraction (XRD). The band gap energy was determined by spectrophotometric measurement and was between 3.29 eV and 3.34 eV. The photocatalytic performance of the powders was studied by the degradation of methylene blue (MB) and methyl orange (MO) in aqueous suspensions under UV-A (365 nm) as well as visible (400-500 nm) irradiation. The catalytic activity was determined as a function of the tungsten concentration, the specific surface area and the flame combustion stoichiometry. It was found that the TiO2-0.7 at %W particles with high SSA have the highest photoactivity for degradation of MB and MO. This can be explained by the incorporation of the tungsten into the TiO2 crystal lattice as well as modification surface properties.

Synthesis of Spherical, Non-Aggregated Silica Nanoparticles

Commercially available SiO2 nanopowders synthesised by flame aerosol processes consist to a major part of large aggregates, formed by collision and sintering of primary particles during the process. These aggregates impair the physical and chemical benefits, which could be achieved from the properties of the primary, non-aggregated nanoparticles.