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Long TiO2 hollow fibers with mesoporous walls have been fabricated with the sol-gel combined two-capillary spinneret electrospinning technique using a triblock copolymer (Pluronic, P123, (H(C2H5O)20(C3H7O)70 (C2H5O)20OH) as a pore-directing agent. The as-prepared hollow fibers were as long as 30 cm with an outer diameter of 0.1-4 microm and wall thickness of 60-500 nm. The diameters and wall thicknesses of the hollow fibers could be tuned by adjusting the electrospinning parameters. The fiber walls were composed of mesopores 6.7 nm in diameter as calculated from the N2 adsorption/desorption isotherm. The high-resolution TEM (HR-TEM) images exhibited that the mesopores were hexagonally aligned with a low order because of the curving of the pores. When comparing with other nanostructured TiO2 materials such as commercial TiO2 nanoparticles (P25, Degussa) and mesoporous TiO2 powders, the hollow fibers exhibited higher photocatalytic activities toward degradation of methylene blue and gaseous formaldehyde.
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PMID:Long TiO2 hollow fibers with mesoporous walls: sol-gel combined electrospun fabrication and photocatalytic properties. 1677 84

Nanosized anatase (< or = 10 nm), rutile (< or = 10 nm), and brookite (approximately 70 nm) titania particles have been successfully synthesized via sonication and hydrothermal methods. Gold was deposited with high dispersion onto the surfaces of anatase, rutile, brookite, and commercial titania (P25) supports through a deposition-precipitation (D-P) process. All catalysts were exposed to an identical sequence of treatment and measurements of catalytic CO oxidation activity. The as-synthesized catalysts have high activity with concomitant Au reduction upon exposure to the reactant stream. Mild reduction at 423 K produces comparably high activity catalysts for every support. Deactivation of the four catalysts was observed following a sequence of treatments at temperatures up to 573 K. The brookite-supported gold catalyst sustains the highest catalytic activity after all treatments. XRD and TEM results indicate that the gold particles supported on brookite are smaller than those on the other supports following the reaction and pretreatment sequences.
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PMID:Preparation and comparison of supported gold nanocatalysts on anatase, brookite, rutile, and P25 polymorphs of TiO2 for catalytic oxidation of CO. 1685 96

A porous beta-Ga2O3 photocatalyst has been successfully prepared. The photocatalyst was characterized by XRD, N2 adsorption-desorption, TEM, UV/vis, and FTIR techniques. The photocatalytic activity of the sample was evaluated by the decomposition of benzene in air under UV light illumination and was compared with that of the commercial titania (Degussa P25) and Pt/P25. Results revealed that the synthesized Ga2O3 was porous beta-Ga2O3 and was highly photoactive for mineralizing benzene and its derivatives (e.g., toluene and ethylbenzene) to CO2 under ambient conditions. The photocatalytic conversion of benzene over beta-Ga2O3 was about 1 order of magnitude higher than that over P25, and no obvious deactivation of beta-Ga2O3 was observed during the prolonged operation of 80 h. The high activity and long-term stability of the Ga2O3 have been ascribed to its stronger oxidative capability and higher specific surface area in comparison with P25.
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PMID:Efficient decomposition of benzene over a beta-Ga2O3 photocatalyst under ambient conditions. 1700 43

Porous TiO2 hollow aggregates have been synthesized on a large scale by means of a simple hydrothermal method without using any templates. The as-prepared products were characterized by means of field emission scanning electron microscopy, XRD, TEM, nitrogen adsorption, UV/Vis diffuse reflectance spectroscopy, and FTIR spectroscopy. The photocatalytic activity of the aggregates was demonstrated through the photocatalytic degradation of Rhodamine B. Structural characterization indicates that the porous TiO2 aggregates are 500-800 nm in diameter and display mesoporous structure. The average pore sizes and BET surface areas of the aggregates are 12 nm and 168 m2 g-1, respectively. Optical adsorption investigations show that the aggregates possess an optical band-gap energy of 3.36 eV. The as-prepared products were substantially more effective photocatalysts than the commercially available photocatalyst P25. The dye degradation rate of the porous TiO2 hollow aggregates is more than twice that of P25. The high photoactivities of the aggregates can be attributed to the combined effects of several factors, namely, large surface areas, the existence of mesopores, and the high band-gap energy. In addition, the as-prepared products can be easily recycled.
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PMID:One-step fabrication and high photocatalytic activity of porous TiO2 hollow aggregates by using a low-temperature hydrothermal method without templates. 1713 39

Mesoporous titania nanorod/titanate nanotube composites were prepared using TiF4 and H(3)BO(3) as the precursors. The prepared samples were characterized with TEM, SEM, XRD, HRTEM, and nitrogen adsorption-desorption isotherms. The photocatalytic activities were evaluated by photocatalytic oxidation of acetone in a gas phase and photocatalytic discolorization of methyl orange aqueous solution in an aqueous phase, respectively. The results indicated that the photocatalytic activity of the mesoporous titania nanorod/titanate nanotube composites exceeded that of P25 by a factor of about 2.5 times for the photocatalytic oxidation of acetone. This could be attributed to the fact that the former had a larger specific surface area and a higher pore volume. Moreover, the mesoporous titania nanorod/titanate nanotube composites, which could be readily separated after photocatalytic reaction in an aqueous phase, exhibited highly photocatalytic activity for the degradation of methyl orange aqueous solution.
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PMID:Synthesis, characterization and photocatalytic activity of mesoporous titania nanorod/titanate nanotube composites. 1729 35

In this article, we report a controllable and reproducible approach to prepare highly ordered 2-D hexagonal mesoporous crystalline TiO2-SiO2 nanocomposites with variable Ti/Si ratios (0 to infinity). XRD, TEM, and N2 sorption techniques have been used to systematically investigate the pore wall structure, and thermal stability functioned with the synthetic conditions. The resultant materials are ultra highly stable (over 900 degrees C), have large uniform pore diameters (approximately 6.8 nm), and have high Brunauer-Emmett-Teller specific surface areas (approximately 290 m2/g). These mesostructured TiO2-SiO2 composites were obtained using titanium isopropoxide (TIPO) and tetraethyl orthosilicate (TEOS) as precursors and triblock copolymer P123 as a template based on the solvent evaporation-induced co-self-assembly process under a large amount of HCl. Our strategy was the synchronous assembly of titanate and silicate oligomers with triblock copolymer P123 by finely tuning the relative humidity of the surrounding atmosphere and evaporation temperature according to the Ti/Si ratio. We added a large amount of acidity to lower condensation and polymerization rates of TIPO and accelerate the rates for TEOS molecules. TEM and XRD measurements clearly show that the titania is made of highly crystalline anatase nanoparticles, which are uniformly embedded in the pore walls to form the "bricked-mortar" frameworks. The amorphous silica acts as a glue linking the TiO2 nanocrystals and improves the thermal stability. As the silica contents increase, the thermal stability of the resulting mesoporous TiO2-SiO2 nanocomposites increases and the size of anatase nanocrystals decreases. Our results show that the unique composite frameworks make the mesostructures overwhelmingly stable; even with high Ti/Si ratios (> or =80/20) the stability of the composites is higher than 900 degrees C. The mesoporous TiO2-SiO2 nanocomposites exhibit excellent photocatalytic activities (which are higher than that for commercial catalyst P25) for the degradation of rhodamine B in aqueous suspension. The excellent photocatalytic activities are ascribed to the bifunctional effect of highly crystallized anatase nanoparticles and high porosity.
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PMID:Controllable and repeatable synthesis of thermally stable anatase nanocrystal-silica composites with highly ordered hexagonal mesostructures. 1794 37

Nanoscaled zinc oxide (ZnO) particles with different amounts are coated on titanate nanotubes (TNTs) by a facile chemical method at room temperature. The characterizations of XPS, TEM, XRD and UV-vis spectra confirm that pure hexagonal wurtzite ZnO nanoparticles with an average size of about 9nm are distributed on the surfaces of TNTs evenly and attached strongly. The photocatalytic activities of the ZnO-TNTs nanocomposite are superior to those of P25, ZnO, TNTs and ZnO-anatase TiO2 (TNP) nanocomposite in the oxidation of rhodamine B under UV light irradiation. A comparison of the photocatalytic activities between different catalysts is discussed. Furthermore, we also find that the ZnO-TNT nanocomposite shows very favorable recycle use potential, because they have a high sedimentation rate and their photocatalytic activity is only slightly decreased even after five times of repeated uses.
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PMID:Synthesis, characterization, and photocatalytic activities of titanate nanotubes surface-decorated by zinc oxide nanoparticles. 1845 2

Metal Fe or Cu doped P25 titania was prepared using the photodeposition method and characterized by TEM, ICP, XRD and UV-Vis, further tested for photocatalytic nitrate reduction and TN removal, under 20 W UV lamp irradiation. The influencing factors such as the pH values of solution, stirring gas, metal loadings, hole scavenger formic acid amount and co-doped Ag-Cu/TiO2 are investigated and discussed in detail. The experimental results after 2 h reaction indicated that with the increase of Cu loadings, nitrate conversion increases too, while a loading of 0.5% is optimal for highest N2 selectivity and TN (total nitrogen) removal. Using N2 as stirring gas and under acidic conditions, the N2 selectivity is lower (62%), but the highest conversion of nitrate and removal of TN can reach 36.9% and 23.2% respectively. Using CO2 as stirring gas, the highest selectivity for nitrogen 88.4% is obtained with 0.5% Cu/TiO2, 0.06 mol/L formic acid. Under the same conditions, using the prepared bimetallic titania (1%, 1:1 Ag/Cu), the conversion of nitrate and removal of TN are 48.1%, 34.2%, and N2 selectivity is 72.2%.
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PMID:[Photocatalytic reduction of nitrate using metal-doped titania]. 1906 39

Photocatalytic degradation of phenol was investigated using the supported nano-TiO(2)/ZSM-5/silica gel (SNTZS) as a photocatalyst in a batch reactor. The prepared photocatalyst was characterized using XRD, TEM, FT-IR and BET surface area analysis. The synthesized photocatalyst composition was developed using nano-TiO(2) as the photoactive component and zeolite (ZSM-5) as the adsorbents, all supported on silica gel using colloidal silica gel binder. The optimum formulation of SNTZS catalyst was observed to be (nano-TiO(2):ZSM-5:silica gel:colloidal silica gel=1:0.6:0.6:1) which giving about 90% degradation of 50mg/L phenol solution in 180 min. The SNTZS exhibited higher photocatalytic activity than that of the commercial Degussa P25 which only gave 67% degradation. Its high photocatalytic activity was due to its large specific surface area (275.7 m(2)/g), small particle size (8.1 nm), high crystalline quality of the synthesized catalyst and low electron-hole pairs recombination rate as ZSM-5 adsorbent was used. The SNTZS photocatalyst synthesized in this study also has been proven to have an excellent adhesion and reusability.
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PMID:Characteristics of supported nano-TiO2/ZSM-5/silica gel (SNTZS): photocatalytic degradation of phenol. 1981 56

F-Si-co-modified TiO(2) (FST) samples with different ratios of fluorine to titanium (R(F)) and silica to titanium (R(x)), were successfully synthesized by ultrasound-assisted hydrolysis. The structure and properties of the as-prepared codoped titania were characterized by means of XRD, TEM, XPS, BET, UV-Vis diffuse reflectance spectra and ESR. XRD analysis showed that Si and F atoms prevented phase transition of anatase to rutile and suppressed the growth of titania crystalline. ESR results showed that the concentration of the active species (.OH) on 1%-FST(R(x)=10%) was higher than that on other FST samples and P25 titania. The improvement in photocatalytic activity relative to titania can be achieved by co-modifying fluorine and silica to fabricate FST composite material. The photocatalytic activity of FST powders for decomposition of methyl orange was affected by the content of fluorine and the content of silica. When the ratios of R(F) and R(x) were 1 and 10%, respectively, 1%-FST(R(x)=10%) shows the best among photocatalytic activity, which is much superior to P25 under UV-Vis irradiation. The possible reasons for the high photocatalytic activity of the FST powders were proposed in the paper. In addition, the stability of the FST powders in photocatalytic process was confirmed based on the XPS analysis.
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PMID:Enhanced photocatalytic activity for titanium dioxide by co-modifying with silica and fluorine. 1986 60


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