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 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mesoporous titanium dioxide nanosized powder with high specific surface area and anatase wall was synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as surfactant-directing agent and pore-forming agent. The resulting materials were characterized by XRD, nitrogen adsorption, FESEM, TEM, and FT-IR spectroscopy. The as-synthesized mesoporous TiO2 nanoparticles have mean diameter of 17.6 nm with mean pore size of 2.1 nm. The specific surface area of the as-synthesized mesoporous nanosized TiO2 exceeded 430 m2/g and that of the samples after calcination at 600 degrees C still have 221.9 m2/g. The mesoporous TiO2 nanoparticles show significant activities on the oxidation of Rhodamine B (RB). The large surface area, small crystalline size, and well-crystallized anatase mesostructure can explain the high photocatalytic activity of mesoporous TiO2 nanoparticles calcined at 400 degrees C.
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PMID:Synthesis of titanium dioxide nanoparticles with mesoporous anatase wall and high photocatalytic activity. 1686 52

TiO(2) nanospherical and fibered structures were obtained via a one-step sol-gel method in supercritical carbon dioxide (scCO(2)) involving polycondensation of the alkoxide monomers titanium isopropoxide (TIP) and titanium butoxide (TBO) with acetic acid (HAc). The resulting materials were characterized by means of electron microscopy (SEM and TEM), X-ray diffraction (XRD), thermal analysis (TGA), and attenuated total reflection Fourier transmission infrared (ATR-FTIR) analysis. Depending on the experimental conditions, TiO(2) anatase nanospheres with a diameter of 20 nm or TiO(2) anatase/rutile nanofibers with a diameter of 10-100 nm were obtained. Fiber formation was enhanced by a higher HAc/Ti ratio and the use of the titanium isopropoxide (TIP) monomer. The mechanism of the microstructure formation was studied using in situ FTIR analysis in scCO(2). The FTIR results indicated that the formation of nanofibers was favored by a titanium hexamer that leads to one-dimensional condensation, while nanospheres were favored by a hexamer that permits three-dimensional condensation.
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PMID:FTIR study on the formation of TiO2 nanostructures in supercritical CO2. 1691 45

Titanium carbide (TiC) nanoparticles are readily deposited onto tin-doped indium oxide (ITO) electrodes in the form of thin porous films. The nanoparticle deposits are electrically highly conducting and electrochemically active. In aqueous media (at pH 7) and at applied potentials positive of 0.3 V vs. SCE partial anodic surface oxidation and formation (at least in part) of novel core-shell TiC-TiO2 nanoparticles is observed. Significant thermal oxidation of TiC nanoparticles by heating in air occurs at a temperature of 250 degrees C and leads first to core-shell TiC-TiO2 nanoparticles, next at ca. 350 degrees C to TiO2 (anatase), and finally at temperatures higher than 750 degrees C to TiO2 (rutile). Electrochemically and thermally partially oxidized TiC nanoparticles still remain very active and for some redox systems electrocatalytically active. Scanning and transmission electron microscopy (SEM and TEM), temperature dependent XRD, quartz crystal microbalance, and voltammetric measurements are reported. The electrocatalytic properties of the core-shell TiC-TiO2 nanoparticulate films are surveyed for the oxidation of hydroquinone, ascorbic acid, and dopamine in aqueous buffer media. In TiC-TiO2 core-shell nanoparticle films TiO2 surface reactivity can be combined with TiC conductivity.
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PMID:Electrochemical properties of core-shell TiC-TiO2 nanoparticle films immobilized at ITO electrode surfaces. 1711 52

The present study describes the photocatalytic degradation of toluene in gas phase on different porous manganese oxide doped titanium dioxide. As synthesized birnessite and cryptomelane type porous manganese oxide were doped with titania and tested for photocatalytic decomposition of toluene in gas phase. The effects of the inlet concentration of toluene, flow rate (retention time) were examined and the relative humidity was maintained constantly. Thermal and textural characterization of manganese oxide doped titania materials were characterized by X-ray diffraction (XRD), thermogravemetry (TG), BET and TEM-EDAX studies. The aim of the present study is to synthesize the porous manganese oxide doped titania and to study its photocatalytic activity for toluene degradation in gas phase. Cryptomelane doped titania catalyst prepared in water medium [K-OMS-2 (W)] is shown the good toluene degradation with lower catalysts loading compared to commercial bulk titania in annular type photo reactor. The higher photocatalytic activity due to various factors such as catalyst preparation method, experimental conditions, catalyst loading, surface area, etc. In the present study manganese oxide OMS doped titania materials prepared by both aqueous and non-aqueous medium, aqueous medium prepared catalyst shows the good efficiency due to the presence of OH bonded groups on the surface of catalyst. The linear forms of different kinetic equations were applied to the adsorption data and their goodness of fit was evaluated based on the R2 and standard error. The goodness to the linear fit was observed for Elovich model with high R2 (>or=0.9477) value.
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PMID:Synthesis, characterization and photocatalytic activity of porous manganese oxide doped titania for toluene decomposition. 1732 73

Highly oriented hydroxyapatite coatings (HACs) were obtained on titanium substrates through a radio-frequency thermal plasma spraying (TPS) method. XRD patterns showed that the HACs had crystallites with [001] preferred orientation vertical to the coating's surface. XRD results also indicated that tetracalcium phosphate crystallites in the as-sprayed HAC were oriented in the (100) direction. XRD peaks corresponding to tetracalcium phosphate, tricalcium phosphate and calcium oxide were absent after heat and hydrothermal treatment. The orientation degree of the HAC was influenced little by such post-heat treatments. Considering the crystallographic relationship between the tetracalcium phosphate in the as-sprayed HAC and the HA crystallites formed in the heat-treated HAC, these XRD results indicate that the tetracalcium phosphate in the as-prepared coatings transformed topotaxially into HA during the post-heat treatment. TEM and SEM analyses of the highly oriented HAC were conducted. The characteristic lamellar structure of TPS deposits was observed in cross-sections of the HAC. A prismatic texture was also observed in magnified SEM images. TEM observation showed that 200-800-nm-wide prismatic crystallites were formed in HA splats, and their longitudinal axis was oriented vertically to the coating's surface. SAD patterns showed that the longitudinal axis of the prismatic crystallites corresponded to the [001] zone axis of the HA crystal.
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PMID:Phase transformation of plasma-sprayed hydroxyapatite coating with preferred crystalline orientation. 1740 Feb 90

In an endeavor to synthesize tetragonal nanocrystallites of BaTiO3 at much reduced reaction time, we explored the possibility of performing microwave assisted semi-solvothermal reaction by using Ba(OH)2 . 8H2O and amorphous titanium hydrous gel as precursors and 1,4-butanediol and water as solvent. Typically, such a microwave assisted reaction was accomplished within 2 hrs at 220 degrees C as against 12 hrs required in conventional approach. The crystallized BaTiO3 powders (microwave assisted as well as conventionally processed for reference) were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. We have detected metastable cubic phase by XRD while locally symmetric tetragonal phase by Raman spectroscopy in case of conventional semi-solvothermal processing. On the contrary, we could detect co-existence of tetragonal and cubic phases by XRD and only tetragonal phase by Raman spectroscopy in case of microwave assisted semi-solvothermal processing. The TEM analysis indicates typical particle size distribution in the range of approximately 20 to 80 nm for conventionally processed powder while that in the range of approximately 20 to 50 nm for microwave processed powder. HRTEM images evince the distortion from an ideal cubic structure in case of microwave processed powder which can be correlated with anisotropic lattice contraction during the microwave induced heating. AFM analysis exhibited relatively less aggregation of nanoparticles for microwave assisted process.
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PMID:Microwave assisted semi-solvothermal synthesis of nanocrystalline barium titanate. 1745 Aug 58

This work reports the synthesis of multiwalled carbon nanotubes (MWCNTs) on nanoporous titanium dioxide (TiO2) templates. TiO2 nanotubular templates for MWCNTs are produced by anodization of titanium followed by pulsed electrodeposition (PED) of cobalt inside the TiO2 nanotubes. Cobalt acts as a catalyst for the growth of MWCNTs using chemical vapor deposition (CVD) technique. The cobalt catalyst initiates the growth of well graphitized MWCNTs inside the titania pores as well as beyond the titania pores. These materials have been characterized by SEM, EDS, GXRD, XPS, TEM, and ED techniques. The MWCNTs were about 10 mu in length and 80-120 nm in diameter.
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PMID:Growth of carbon nanotubes on nanoporous titania templates. 1768 78

Biomimetic apatite coatings were obtained by soaking chemically treated titanium in SBF with different HCO(3)(-) concentration. XRD, FTIR and Raman analyses were used to characterize phase composition and degree of carbonate substitution. The microstructure, elemental composition and preferred alignment of biomimetically precipitated crystallites were characterized by cross-sectional TEM analyses. According to XRD, the phase composition of precipitated coatings on chemically pre-treated titanium after exposure to SBF was identified as hydroxy carbonated apatite (HCA). A preferred c-axis orientation of the deposited crystals can be supposed due to the high relative peak intensities of the (002) diffraction line at 2theta=26 degrees compared to the 100% intensity peak of the (211) plane at 2theta=32 degrees . The crystallite size in direction of the c-axis of HCA decreased from 26 nm in SBF5 with a HCO(3)(-) concentration of 5 mmol/l to 19 nm in SBF27 with a HCO(3)(-) concentration of 27 mmol/l. Cross-sectional TEM analyses revealed that all distances correspond exactly to the hexagonal structure of hydroxyapatite. The HCO(3)(-) content in SBF also influences the composition of precipitated calcium phosphates. Biomimetic apatites were shown to have a general formula of Ca(10-x-y)Mg(y)(HPO(4))(x-z)(CO(3))(z)(PO(4))(6-x)(OH)(2-x-w)(CO(3))(w/2). According to FTIR and Raman analyses, it can be supposed that as long as the HCO(3)(-) concentration in the testing solutions is below 20 mmol/l, only B-type HCA (0<z<1; w=0) precipitates. At higher HCO(3)(-) concentration, it can be assumed that AB-type HCA (z=1;0<w<1) is formed.
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PMID:Biomimetic apatite coatings--carbonate substitution and preferred growth orientation. 1785 64

The phase transformation of mesostructured titanium phosphate (TiPO) from hexagonal to lamellar structure was observed in a simply hydrothermal treatment, accompanied by drastically morphological changes in the micrometer-sized particles. XRD pattern revealed that different mesostructures were obtained by simply varying hydrothermal temperature or treatment duration. SEM and TEM observations showed the morphological evolution from individual particles to interconnected nanoplatelets. A significant blue shift in UV-vis spectra was observed for lamellar mesostructured material, which may be associated with the different coordinated Ti-sites in the hexagonal and lamellar mesostructures. FT-IR spectra and detailed (31)P MAS NMR studies indicated that additional POH groups were presented in the lamellar structure, which might play a key role in the structural and morphological transformations of mesostructures.
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PMID:Structural and morphological transformations of mesostructured titanium phosphate through hydrothermal treatment. 1788 92

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


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