TiO2, TiO2/Ag and TiO2/Au photocatalysts prepared by spray pyrolysis

TiO₂, TiO₂/Ag and TiO₂/Au photocatalysts exhibiting a hollow spherical morphology were prepared by spray pyrolysis of aqueous solutions of titanium citrate complex and titanium oxalate precursors in one-step. Effects of precursor concentration and spray pyrolysis temperature were investigated. By subsequent heat treatment, photocatalysts with phase compositions from 10 to 100% rutile and crystallite sizes from 12 to 120 nm were obtained. A correlation between precursor concentration and size of the hollow spherical agglomerates obtained during spray pyrolysis was established. The anatase to rutile transformation was enhanced with metal incorporations and increased precursor concentration. The photocatalytic activity was evaluated by oxidation of methylene blue under UV-irradiation. As-prepared TiO₂ particles with large amounts of amorphous phase and organic residuals showed similar photocatalytic activity as the commercial Degussa P25. The metal incorporated samples showed comparable photocatalytic activity to the pure TiO₂ photocatalysts.     

Study of the sulfation kinetics between SO2 and CaO catalyzed by TiO2 nano-particles

The catalytic activity of TiO₂ nano-particles, prepared by a sol-gel method, was studied when added in the reaction between SO₂ and CaO. The reaction products were analyzed by infrared spectrophotometry (IR) and specific surface area analysis and the kinetics and mechanisms of the sulfation catalyzed by the addition of TiO₂ are discussed. The results indicate that nano-TiO₂, which serves as an active catalytic center, enhances O₂ transfer and is helpful in the diffusion of SO₂ from the product layer to the inner unreacted CaO. As a result, the desulfurization efficiency increased. The results also suggest that the SO₂ and NO must both be removed simultaneously in order to keep the sulfation rate. The desulfurization reactions are first order for SO₂ concentration and zero order for O₂ concentration and include two zones, the surface reaction zone and the product layer diffusion zone, with later being the rate limiting step. The apparent activation energy of the desulfurization reaction decreased with the addition nano-TiO₂ as compared to that without. The unreacted shrinking reaction core model was used to investigate the reaction kinetics and was shown to describe the course of desulfurization. Lastly, the results obtained through calculation agree with the empirical data.     

Preparation of UO2/TiO2 composite ceramic fuel by sol gel-press forming method

This paper studies the preparation of UO₂/TiO₂ composite ceramic fuel through sol gel-press forming. The research shows that at 1200–1300 °C, UO₂/TiO₂ composite ceramic grains are small, uniform and compact. Among them, UO₂–0.5 wt%TiO₂ has the highest density and good mechanical strength at 1250 °C.     

Dispersion of TiO2 nanopowders to obtain homogeneous nanostructured granules by spray-drying

This work deals with the dispersion and stabilisation of nanosized TiO₂ particles in an aqueous medium as a first step in the preparation of spray-dried nanostructured powders.A colloidal route leading to the production of titania nanostructured feedstocks to obtain nanostructured powders was developed. The process was based on the production of homogeneous and concentrated TiO₂ nanosuspensions dispersed in deionised water with a suitable control of pH and the use of an appropriate anionic dispersant. Concentrated suspensions could be obtained by mixing with an ultrasounds probe at different times depending on the dispersing conditions.Homogeneous suspensions prepared were then reconstituted by spray drying into free-flowing powders with an adequate granule size distribution for diverse purposes, such as atmospheric plasma spraying coatings.     

Effect of TiO2 particle size on the photocatalytic reduction of CO2

Pure TiO₂ anatase particles with a crystallite diameters ranging from 4.5 to 29 nm were prepared by precipitation and sol–gel method, characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis and scanning electron microscopy (SEM) and tested in CO₂ photocatalytic reduction. Methane and methanol were the main reduction products. The optimum particle size corresponding to the highest yields of both products was 14 nm. The observed optimum particle size is a result of competing effects of specific surface area, charge–carrier dynamics and light absorption efficiency.     

Effect of Ag addition on the properties of Pd–Ag/TiO2 catalysts containing different TiO2 crystalline phases

Anatase and rutile TiO₂ were used for preparation of the TiO₂ supported Pd and Pd–Ag catalysts for selective hydrogenation of acetylene. It was found that Pd/TiO₂-anatase exhibited higher acetylene conversion and ethylene selectivity than rutile TiO₂ supported ones. However, addition of Ag to Pd/TiO₂-anatase catalyst resulted in lower ethylene selectivity while that of Pd/TiO₂-rutile increased. It is suggested that Ag addition suppressed the beneficial effect of the Ti³⁺ sites presented on the anatase TiO₂ during selective acetylene hydrogenation whereas without Ti³⁺, Ag promoted ethylene selectivity by blocking sites for over-hydrogenation of ethylene to ethane.     

Effect of TiO2 on phase evolution and microstructure of MgAl2O4 spinel in different atmospheres

The effect of TiO₂ on the formation and microstructure of magnesium aluminate spinel (MgAl₂O₄) at 1600 °C in air and reducing conditions were investigated. Under reducing conditions, stoichiometric MgAl₂O₄ spinel shifted toward alumina-rich types owing to volatilization of MgO, resulting in an increase in the porosity of fired samples. Addition of graphite to mixtures of MgO and Al₂O₃ intensified the reducing conditions and accelerated the formation of non-stoichiometric MgAl₂O₄. For TiO₂-containing samples on addition of MgAl₂O₄, magnesium aluminum titanium oxide (Mg_xAl_2(1−x)Ti_(1+x)O₅, x = 0.2 or 0.3) was detected as a minor phase. Under reducing conditions, XRD peak shifts were smaller for TiO₂-containing samples than for samples without TiO₂ owing to the formation of a solid solution of TiO₂ in MgAl₂O₄ and establishment of alumina-rich spinel, which have opposite effects on increasing the lattice parameter. In bauxite-containing samples, MgAl₂O₄ spinel, corundum, magnesium orthotitanate spinel (Mg₂TiO₄) and amorphous phases were identified. Mg₂TiO₄ spinel formed a complete solid solution with MgAl₂O₄ spinel but Mg₂TiO₄ remained as a distinct phase owing to the heterogeneous microstructure of bauxite-containing samples. Also dense microstructure established in air fired TiO₂ containing samples. The results are discussed with emphasis on the application and design of alumina-magnesia-carbon refractory materials, which are used in the steel industry.     

Synthesis of TiO2/PAA nanocomposite by RAFT polymerization

Due to the strong tendency of nanoparticles such as metal oxides to agglomerate, homogeneous dispersion of these materials in a polymeric matrix is extremely challenging. In order to overcome this problem and to enhance the filler-polymer interaction, this study focused on living polymerization that was initialized from the surface of titania nanofillers. A new method for synthesizing TiO₂/polymer nanocomposites was found with a good dispersion of the nanofillers by using the bifunctional RAFT agent, 2-{[(butylsulfanyl)carbonothioyl]sulfanyl}propanoic acid). This RAFT agent has an available carboxyl group to anchor onto TiO₂ nanoparticles, and an SC(SC₄H₉) moiety for subsequent RAFT polymerization of acrylic acid (AA) to form n-TiO₂/PAA nanocomposites. The functionalization of n-TiO₂ was determined by FTIR and partitioning studies, the livingness of the polymerization was verified using GPC and NMR, while the dispersion of the inorganic filler in the polymer was studied using electron microscopy, FTIR and thermal analysis.     

Effect of TiO2 supporting layer on Fe2O3 photoanode for efficient water splitting

For an electrochemical water splitting system, titanate nanotubular particles with a thickness of ∼700 nm produced by a hydrothermal process were repetitively coated on fluorine-doped tin oxide (FTO) glass via layer-by-layer self-assembly method. The obtained titanate/FTO films were dipped in aqueous Fe solution, followed by heat treatment for crystallization at 500 °C for 10 min in air. The UV–vis absorbance of the Fe-oxide/titanate/FTO film showed a red-shifted spectrum compared with the TiO₂/FTO coated film; this red shift was achieved by the formation of thin hematite-Fe₂O₃ and anatase-TiO₂ phases verified using X-ray diffraction and Raman results. The cyclic voltammetry results of the Fe₂O₃/TiO₂/FTO films showed distinct reversible cycle characteristics with large oxidation–reduction peaks with low onset voltage of I–V characteristics under UV–vis light illumination. The prepared Fe₂O₃/TiO₂/FTO film showed much higher photocurrent densities for more efficient water splitting under UV–vis light illumination than did the Fe₂O₃/FTO film. Its maximum photocurrent was almost 3.5 times higher than that obtained with Fe₂O₃/FTO film because of the easy electron collection in the current collector. The large current collection was due to the existence of a TiO₂ base layer beneath the Fe₂O₃ layer.     

Influence of TiO2 and CeO2 on the hydrogenation activity of bulk Ni2P

TiO₂- and CeO₂-promoted bulk Ni₂P catalysts were prepared by impregnation and in-situ H₂ temperature-programmed reduction method. The prepared catalysts were characterized by XRD and XPS. The hydrogenation activities of the catalysts were studied using 1.5 wt.% 1-heptene in toluene and 1.0 wt.% phenylacetylene in ethanol as the model feeds. The results indicate that bulk Ni₂P possesses low hydrogenation activity but is tunable by simply controlling the content of the additives (TiO₂ or CeO₂), suggesting that TiO₂ and CeO₂ are effective promoters to enhance the hydrogenation activity of Ni₂P.     

Preparation and characterization of CeO2/TiO2 nanoparticles by flame spray pyrolysis

Nanocrystalline TiO₂, CeO₂ and CeO₂-doped TiO₂ have been successfully prepared by one-step flame spray pyrolysis (FSP). Resulting powders were characterized with X-ray diffraction (XRD), N₂-physisorption, Transmission Electron Microscopy (TEM) and UV-Vis spectrophotometry. The TiO₂ and CeO₂-doped TiO₂ nanopowders were composed of single-crystalline spherical particles with as-prepared primary particle size of 10-13 nm for Ce doping concentrations of 5-50 at%, while square-shape particles with average size around 9 nm were only observed from flame-made CeO₂. The adsorption edge of resulting powder was shifted from 388 to 467 nm as the Ce content increased from 0 to 30 at% and there was an optimal Ce content in association with the maximum absorbance. This effect is due to the insertion of Ce^3+/4+ in the TiO₂ matrix, which generated an n-type impurity band.     

Structural colors from TiO2/SiO2 multilayer flakes prepared by sol-gel process

Preparation of TiO₂/SiO₂ multilayer flakes and their application to decorative powders were investigated. In contrast to conventional products prepared through the multicoating of core platelets, the coreless TiO₂/SiO₂ multilayer flakes were prepared by detaching multilayer films from their substrates. These flakes exhibited structural colors, when the optical path length of both the TiO₂ and SiO₂ layers are adjusted to be one fourth of the wavelength of visible light. A multicoating of more than five layers resulted in the propagation of cracks, which prevented the preparation of thick flakes. Paint films fabricated using the multilayer flakes and acrylic resins showed reflectance spectra that were comparable with those obtained for multicoatings on substrates.     

Investigation of surface modification of rutile TiO2 nanoparticles with SiO2/Al2O3 on the properties of polyacrylic composite coating

Surface modification and characterization of TiO₂ nanoparticles as an additive in a polyacrylic clear coating were investigated. For the improvement of nanoparticles dispersion and the decreasing of photocatalytic activity, the surface of nanoparticles was modified with binary SiO₂/Al₂O₃. The surface treatment of TiO₂ nanoparticles was characterized with FTIR. Microstructural analysis was done by AFM. The size, particle size distribution and zeta potential of TiO₂ nanoparticles in water dispersion was measured by DLS method. For the evaluation of particle size and the stability of nanoparticles in water dispersions with higher solid content the electroacoustic spectroscopy was made. To determine the applicability and evaluate the transmittance of the nano-TiO₂ composite coatings UV–VIS spectroscopy in the wavelength range of 200–800 nm was employed. The results showed that surface treatment of TiO₂ nanoparticles with SiO₂/Al₂O₃ improves nanoparticles dispersion and UV protection of the clear polyacrylic composite coating.     

Various TiO2 microcrystals: Controlled synthesis and enhanced photocatalytic activities

Titania microspheres with higher photocatalytic activity have been synthesized using TiCl₄ and FeCl₃ as the precursor in the presence of Span-80. The products were characterized with XRD, TEM and UV–vis DRS. XRD and TEM indicated that the microsphere was a mixture of rutile, brookite and anatase with a diameter of about 5–7 μm. The photocatalytic experiments revealed that the microspheres exhibited high photocatalytic activities under UV-light and solar irradiation. The degradation rate of methyl orange (MO) was 100% under UV-light irradiation for 3 h and 91% under solar irradiation for 6 h. In particular, the catalysts could be readily separated by sedimentation after the photocatalytic reaction.     

Electrochemical synthesis of self-organized TiO2 nanotubular structures using an ionic liquid (BMIM-BF4)

We show that an ionic liquid consisting of imidazolium salt with a BF₄ counter ion (BMIM-BF₄) can directly be used to grow well-defined layers of self-organized TiO₂ nanotubes. For this a Ti metal substrate is anodized in this electrolyte for potential range between 3 V_Ag/AgCl and 10 V_Ag/AgCl without addition of free fluoride species (fluorides are used in all previous tube growth procedures). Key factors that influence the morphology and geometry of the resulting nanotubular layer are the anodic potential, the anodization time and particularly the water content in the ionic liquid. The resulting nanotubes layers have thickness in the range of approximately 300-650 nm; with individual tubes that have diameters between 27 nm and 43 nm.     

基于WO3-MoO3和TiO2/CdS复合电极的光电致变色器件

电致变色广泛应用于智能窗领域,但电致变色材料仍需外部电源驱动,将太阳能电池与电致变色材料结合起来的光电致变色器件可实现无需外部供电的智能变色调控。性能优异的变色阴极和光阳极是当下光电致变色器件的研究热点。通过水热法制备WO₃-MoO₃薄膜,研究其电致变色性能;通过水热法结合连续离子层沉积法制备TiO₂/CdS复合薄膜,研究其光电转换性能。最后将WO₃-MoO₃薄膜和TiO₂/CdS复合薄膜分别作为光电致变色器件的变色阴极、光阳极构建WO₃/MoO₃-TiO₂/CdS光电致变色器件。WO₃/MoO₃-TiO₂/CdS光电致变色器件具有较大的光学调制范围(630nm处为41.99%)、更高的着色效率(35.787%),将其作为智能窗应用在现代建筑、通行工具等领域具有重要应用价值。     

The synthesis and morphology characteristic study of BAO-ODPA polyimide/TiO2 nano hybrid films

Hybrid nanocomposite films of titanium dioxide (TiO₂) in polyimide (PI) from 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (BAO) and 4,4′-oxydiphthalic anhydride (ODPA) have been successfully fabricated by an in situ sol-gel process. These nanocomposite films exhibit fair good optical transparency up to 40 wt% of TiO₂ content. X-ray diffraction spectroscopy shows three sharp peaks in pure BAO-ODPA PI. It results from the intermolecular regularity. However, the intermolecular regularity in the hybrid film is disrupted by the introduction of TiO₂ nanoparticles with no sharp peak in XRD spectra. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results confirm the formation of TiO₂ particles in PI matrix. The surface Ti content is much lower than the theoretical bulk content in all hybrid films. The ratio of the former to the latter increases with the TiO₂ content and levels off at TiO₂ wt%≥20. Transmission electron microscope (TEM) images show that the TiO₂ phase is well dispersed in the polymer matrix. The size of the TiO₂ phase increases from 10 to 40 nm when the TiO₂ content is 5-30 wt%, respectively.