Mesoporous Anatase TiO2 Research Articles

Mesoporous anatase TiO 2 composite electrodes: Electrochemical characterization and high rate performances

A metal film of Cu or Sn was vacuum-deposited on the surface of mesoporous anatase TiO 2 electrodes, and the Li insertion/extraction behaviour was investigated by cyclic voltammetry and galvanostatic cycling. The morphological and structural characterization of metal-coated electrodes showed that the metallic layers do not alter the structure of anatase. The electrode surface modification made by thin-film deposition improves the kinetics of Li insertion/extraction and remarkably enhances the electrochemical performances in terms of capacity and stability, especially at high charge/discharge rates.

Electrochemical Performances of Mesoporous Anatase TiO2 Electrodes Modified by Vacuum Metal Deposition

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High temperature stable mesoporous anatase TiO2 photocatalyst achieved by silica addition

Abstract An aqueous sol–gel method was developed to synthesize a high temperature stable anatase titania photocatalyst by doping with silica. Doping was achieved in titania by the addition of silica sol prepared from tetra ethyl orthosilicate (TEOS). 1, 2, 5 and 15 mol% silica–titania mixed oxide were prepared and characterised by X-ray diffraction, Raman spectroscopy, surface area analysis and diffuse reflectance spectra. Fully anatase phase was obtained at 1000 °C by the addition of 15 mol% silica. The 15Si–Ti (15 denotes mol% of silica) had a specific surface area of 187.3 m 2 /g at 500 °C and it retains a value of 93.0 m 2 /g at 800 °C, whereas the undoped one shows 48.7 m 2 /g at 500 °C and zero value at 800 °C. Moreover, the 15Si–Ti composition retains the pore diameter in the mesoporous range (4.6 nm) at this high temperature of 800 °C. The photocatalytic analysis showed that the system with silica added possessed a higher activity than pure titania. The 15Si–Ti sample calcined at 800 °C decolourised the methylene blue dye within 30 min (rate constant 0.084 min −1 ), whereas the undoped sample decolourised the dye after 180 min (rate constant 0.018 min −1 ). The present method of preparation offers the advantages of inexpensive precursor, homogeneous distribution of the dopant over titania at nano-level and enables control over the powder characteristics of titania.

Mesoporous nanocrystalline TiO 2 electrode with ionic liquid-based solid polymer electrolyte for dye-sensitized solar cell application

Thick mesoporous TiO 2 films with excellent properties have been prepared for dye-sensitized solar cell application using doctor-blade method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) show the highly crystalline mesoporous anatase TiO 2 framework. On the other hand new solid electrolytes based on ionic liquid (IL) 1-methyl 3-propyl imidazolium iodide (PMII) and poly(ethylene oxide) (PEO) were prepared in film form and placed on porous-sensitized TiO 2 electrode following two-step casting technique. The doping of IL further provided large numbers of ions, resulting in the enhancement in conductivity and good solar cell performance.

Synthesis and Li-Ion Insertion Properties of Highly Crystalline Mesoporous Rutile TiO2

Mesoporous TiO2 has attracted great attention as a promising Li insertion electrode material with improved cycling life, rate capability, and high power density. Up to date, mesoporous anatase TiO2 has been investigated for Li insertion. Recent studies have shown that nanosized rutile could be an excellent candidate for anode materials for higher Li insertion capacity and improved stability. However, synthesis of highly crystalline mesoporous rutile has met with limited success so far. There has been no report on Li insertion of mesoporous rutile TiO2. In this paper, we report a new low-temperature solution growth of TiO2 nanocrystals within an anionic surfactant matrix to produce highly crystalline mesoporous rutile and investigate Li insertion properties of the mesoporous crystalline rutile. X-ray diffraction (XRD) patterns and N2 sorption isotherms reveal that mesoporous structure in the highly crystalline mesoporous TiO2 directly results from the anionic surfactant templating effects with high surface area (245−300 m2/g) and tunable mesopore diameter ranging from 2.2 to 3.8 nm after calcination. Transmission electron microscopy (TEM) measurements show that framework of the highly crystalline mesoporous TiO2 are composed of aligned rutile nanorod building blocks grown along [001] direction. The new mesoporous crystalline rutile can accommodate more than 0.7 Li (Li0.7TiO2, 235 mA h g−1) during the first discharge at a C/5 rate between 1 and 3 V versus Li+/Li, with a reversible capacity of 0.55 Li (Li0.55TiO2, 185 mA h g−1). The mesoporous crystalline rutile shows excellent capacity retention with less than 10% capacity loss after more than 100 cycles. XRD and TEM characterization on the electrochemically lithiated sample show that the rutile nanorods were transformed into cubic rocksalt LiTiO2 nanorods, but the mesostructures remained stable after the phase transformation and cycling. Furthermore, the crystalline mesoporous rutile may also have good potential for other applications such as stable catalyst supports.

Excellent antimicrobial properties of mesoporous anatase TiO 2 and Ag/TiO 2 composite films

Optically transparent, crack-free, mesoporous anatase TiO 2 thin films were fabricated. The Ag/TiO 2 composite films were prepared by incorporating Ag in the pores of TiO 2 films with an impregnation method via photoreduction. The as-prepared composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectronic spectra (XPS) and N 2 adsorption. The release behavior of silver ions in the mesoporous composite film was also studied. Moreover, the antimicrobial behaviors of the mesoporous film were also investigated by confocal laser scanning microscopy. The antibacterial activities of the composite films were studied by a fluorescence label method using Escherichia coli ( E. coli) as a model. The as-prepared mesoporous TiO 2 films showed much higher antimicrobial efficiency than that of glass and commercial P25 TiO 2 spinning film. The facts would result from the high surface area, small crystal size and more active sites for the mesoporous catalysis. After the doping of Ag, a significant improvement for the antimicrobial ability was obtained. To elucidate the roles of the membrane photocatalyst and the doped silver in the antimicrobial activity, cells from a silver-resistant E. coli were used. These results indicated that Ag nanoparticles in the mesoporous were not only an antimicrobial but also an intensifier for photocatalysis. The as-prepared mesoporous composite film is promising in application of photocatalysis, antimicrobial and self-clean technologies.

Synthesis and photocatalysis of mesoporous anatase TiO 2 powders incorporated Ag nanoparticles

Deposition of Ag nanoparticles on mesoporous anatase TiO 2 powders as well as on commercial TiO 2 powders via reduction of Ag + solution was performed and their photocatalytic activities were investigated. Photocatalytic activities of Ag/TiO 2 were evaluated by UV–vis test on degrading of methylene blue aqueous solution. For the synthesized mesoporous TiO 2 powders, the catalytic activity was found to be increased as the amount of Ag nanoparticles increased. However, for the commercial TiO 2 powders, the catalytic activity decreased as the amount of Ag increased. X-ray was employed to characterize the crystalline phase of synthesized Ag/TiO 2 powders. Particle sizes and morphologies of Ag/TiO 2 powders were investigated by transmission electron microscopy (TEM). Distribution of Ag in TiO 2 powders was revealed by element mapping under element dispersive X-ray analysis (EDAX). It is inferred that the Ag nanoparticles reduce the recombination of electron–hole pairs and therefore enhance the photocatalytic activity of the synthesized mesoporous TiO 2 powders. However, the Ag nanoparticles retard the photocatalytic activity of commercial TiO 2 powders by shielding their effective surface area (only 7.0 m 2/g) for accessing light.

Mesoporous Anatase TiO2Films: Use of Ti K XANES for the Quantification of the Nanocrystalline Character and Substrate Effects in the Photocatalysis Behavior

Mesoporous titania thin films with accessible porosity and anatase structure were synthesized on conductive glass or silicon substrates. Ti K-edge XANES was used to assess Ti local coordination. Analysis of the pre-edge region permitted accurate quantification of the degree of crystalline nature of the inorganic walls upon thermal treatment. The substrate has a marked effect: film crystallization takes places at temperatures 100 °C lower in the crystalline Si, with respect to conductive glass. Accordingly, remarkable photocatalytic properties are found in well-crystallized mesoporous titania deposited onto conductive silicon.

Effect of morphological properties of ionic liquid-templated mesoporous anatase TiO 2 on performance of PEMFC with Nafion/TiO 2 composite membrane at elevated temperature and low relative humidity

Three high-purity TiO 2 (anatase) powders (T PF6, T BF4, and T conventional) were prepared by the sol–gel method with/without ionic liquid as template and calcinations at 450 °C. These powders were, then, characterized to investigate their differences in morphological properties. Electrochemical performances of the H 2/O 2 PEMFCs employing the Nafion composite membranes with these three TiO 2 powders as fillers were studied over 80–120 °C under 50% and 95% relative humidity (RH). The result showed that the order of the fillers effect on the performance at 80 and 90 °C was the same as that of the TiO 2 filler's specific surface area (i.e. T PF6 > T conventional > T BF4 > P25, a commercially available nonporous TiO 2 powder). However, the order between T conventional and T BF4 was reversed at 110 and 120 °C under 50% RH. This indicates that the size and the amount of mesopores, which better confined the water molecules, were significant contributing factors to the performances at the higher temperatures. The best power density obtained under 50% RH at 120 °C and a voltage of 0.4 V was from the PEMFC with the T PF6-containing Nafion composite membrane. It was about 5.7 times higher than the value obtained from that with the recast Nafion membrane.

Study of preparation of mesoporous TiO 2-B nanofibers from mesoporous anatase TiO 2 and interaction between CH 3I and TiO 2-B

Anisotropically grown TiO 2-B with a textural porosity and a high specific surface area has been prepared, characterized, and used to catalyze the thermal and photochemical decomposition of CH 3I. The fibrous TiO 2-B is fabricated by the reaction of mesoporous anatase TiO 2 at 90 °C, followed by addition of 0.1 M HCl solution into the reaction precipitate to reach pH 1. Addition of 0.1 M HCl solution for other pH values of 6, 9, and 12 is also carried out to investigate the pH effect on the elemental composition and morphology of the reaction products, which provides some mechanistic clues for the formation of the TiO 2-B nanofibers. XRD patterns, Raman and reflectance UV–Vis spectra, and SEM and TEM images are used to characterize the material. The TiO 2-B fibers, ∼10 nm in width and several hundred nanometers in length, grow along the [ 1 2 0 1 ] direction of the monoclinic structure, as suggested by the observation of the (2 0 1) fringes which are normal to the axial direction and have a neighboring distance of 0.37 nm in the TEM images. The TiO 2-B nanofibers aggregate into cotton-like particles with a size similar to that of the original anatase particles, forming mesopores with an average diameter of 4.5 nm and a high BET area as much as ∼600 m 2/g which is much larger than those reported previously for titanates and TiO 2-B with morphologies of tube or fiber. The TiO 2-B material has an experimentally-determined bandgap energy of 3.3 eV. Its thermal and photochemical reactivities toward CH 3I decomposition are demonstrated by infrared spectroscopic investigation in a gas–solid system.

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO 2 nanopowders

Mesoporous anatase TiO 2 nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3–4 nm. The specific BET surface area of the as-synthesized sample was about 193 m 2/g. Mesoporous anatase TiO 2 nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO 2, nanofibers TiO 2 mesoporous TiO 2, and commercial TiO 2 nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency ( η) of the cell using the mesoporous anatase TiO 2 was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm 2, the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm 2, Voc of 0.704 V and ff of 0.649.

A novel approach to mesoporous anatase TiO 2: Oxidation of TiC by nitric acid

TiO 2 has been prepared by a novel, mild one-step reaction between TiC and aqueous HNO 3 at 70 °C. This material possesses an anatase crystal form and a narrow pore-size distribution of mesoporous channels. The BET surface area, average pore diameter, and total pore volume are 332.7 m 2/g, 3.28 nm, and 0.23 cm 3/g, respectively. Our method is a template-free synthesis process, distinct from sol–gel methods for mesoporous TiO 2 fabrication using structure-directing surfactants or polymers. TiO 2 is not generated from TiC reacting with other acids and oxidants, such as HCl, H 2SO 4, H 3PO 4, KMnO 4, K 2Cr 2O 7, Na 2S 2O 7, H 2O 2, and Na 2CrO 4, at a similar reaction condition. Since the average particle size of the mesoporous TiO 2 produced is much larger than that of the TiC starting material, the mechanism for the formation of the mesoporous TiO 2 is not via mesopore-etching of TiC particles and transformation of TiC pore walls into TiO 2 by HNO 3. It is likely that TiC is first transformed into Ti m X n species, followed by hydrolysis to form mesoporous TiO 2.

Preparation and photocatalytic activity of mesoporous anatase TiO 2 nanofibers by a hydrothermal method

Mesoporous anatase TiO 2 nanofibers were prepared by a simple hydrothermal post-treatment of titanate nanotubes. The as-prepared samples were characterized with transmission electron microscopy (TEM), thermogravimetry (TG), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and N 2 adsorption–desorption measurement. The photocatalytic activity of the mesoporous TiO 2 nanofibers was evaluated by photocatalytic oxidation of acetone in air. The effects of hydrothermal post-treatment time on the structures and photocatalytic activity of the mesoporous TiO 2 nanofibers were discussed. The results showed that the photocatalytic activity of the TiO 2 nanofibers prepared by this method exceeded that of Degussa P25 when the hydrothermal post-treatment time was kept at 200 °C for 3–24 h. This could be attributed to the fact that the former had smaller crystallite size, larger specific surface area, and higher pore volume.

Mesoporous TiO 2-based photocatalysts for UV and visible light gas-phase toluene degradation

UV and visible light photocatalytic removal of concentrated toluene (110 ppm) in the gas phase was performed in an annular flow-reactor on mesoporous anatase TiO 2 supported WO 3 photocatalysts. Depending on the template, hexagonal and cubic mesoporous TiO 2 thin layers were obtained by dip-coating of an anatase sol onto slides of soda lime–silica glass, which was then mechanically removed. The coupling of low contents of WO 3 (4 wt.%) with mesoporous anatase TiO 2 led to high photocatalytic efficiency both using UV and visible light activation. The highly positive effect of WO 3 on the toluene removal efficiency was attributed to a one-way and a two-way coupling phenomena depending on the photocatalyst nature and on the activation source. The hypothesis of a confinement effect of the reactants inside the mesoporous structure, based on an increase in their partial pressure on the active sites, was put forward to explain the high photocatalytic performances obtained under UV and visible light activation.

Li-intercalation property of mesoporous anatase-TiO2 synthesized by bicontinuous microemulsion-aided process

Mesoporous materials of anatase-TiO2 with different surface area and mesopore size were successfully synthesized by bicontinuous microemulsion-aided processes. The electrochemical lithium-intercalation into the mesoporous anatase-TiO2 was dependent on the surface area, crystallite size and mesopore size. The increase in surface area of mesoporous TiO2 resulted in an increase in the lithium-intercalation capacity. A mesoporous TiO2 with large mesopore size showed a relatively large lithium-intercalation capacity even at high charging rate.

Bicontinuous Microemulsion-aided Synthesis of Mesoporous TiO2

Abstract Mesoporous TiO2 with high surface area was synthesized via a sol–gel process in a bicontinuous microemulsion. The mesoporous structure was retained to some extent even if the anatase-TiO2 nanocrystallite produced in the mesophase with heating. The mesoporous anatase-TiO2 showed an effective Li-intercalation property.

A simple, template-free route for the synthesis of mesoporous titanium dioxide materials

Mesoporous titanium dioxide (TiO2) materials have been synthesized by a novel simple, template-free synthetic approach, which was carried out via nitric acid-catalyzed hydrolysis and polycondensation reactions of titanium(IV) n-butoxide. The as-prepared and calcinated mesoporous TiO2 materials are characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), and N2 adsorption/desorption measurements. The as-prepared amorphous TiO2 possesses a high BET surface area of 470 m2 g−1 and a pore volume of 0.28 cm3 g−1. After calcinations at 450 °C, anatase mesoporous TiO2 is formed with a BET surface area of 106 m2 g−1 and an average pore size of 4.8 nm. Avoidance of the structure-directing template during the synthesis of mesoporous TiO2 is of significant importance for application from both environmental and industrial points of view.

Preparation and characterization of mesoporous visible-light-active anatase

Mesoporous anatase TiO 2 was prepared for photocatalysis from TiOSO 4 solution. The samples were undoped or doped with chromium. The diffuse reflectance spectra of the samples and the morphology of the TiO 2 particles exhibited strong dependency on the preparation conditions. The mesoporous samples showed good photoactivity upon degradation of acetaldehyde in the visible range (>400 nm) and on degradation of methylene blue in aqueous solution in the UV range (366 nm). The catalyst activity demonstrated strong dependency on crystal size, on particle morphology and porosity, and on doping. Samples heated at 473 K were the most active in the gaseous phase and samples heated at 673 K in the aqueous phase. The pore size of the samples increased upon heating. The chromium-doped samples maintained activity at longer wavelengths (>420 nm) than the undoped samples.

Electrical and optical properties of TiO2 in accumulation and of lithium titanate Li0.5TiO2

Changes in the optical absorption and electrical conductivity of dense and mesoporous anatase TiO2 films were measured in situ as a function of electrode potential during electrochemical lithium intercalation. A special two-electrode geometry was used for the conductivity measurements, in which the contacts were separated by a small gap bridged by the TiO2. When electrons are injected, an accumulation layer is formed and the conductivity increases several orders of magnitude. A monotonic increase of the optical absorption with wavelength confirms the presence of (partially) delocalized electrons. Insertion of lithium ions results in the formation of the Li0.5TiO2 phase and a decrease of the overall conductance. The specific conductivity of the Li0.5TiO2 phase is (9.1±0.2) S/cm, significantly lower than that of Li-doped anatase TiO2. This is corroborated by the absorption spectrum of Li0.5TiO2, which shows two pronounced peaks around 440 and 725 nm and no characteristic free-electron features. At potentials below 1.7 V vs Li additional lithium could be inserted into Li0.5TiO2, and the conductance was found to increase again. The results are discussed in terms of possible changes in the electronic structure that are induced by the insertion of lithium ions.