Mesoporous Anatase TiO2 Research Articles

Microwave-assisted hydrothermal synthesis of mesoporous anatase TiO 2 via sol–gel process for dye-sensitized solar cells

Mesoporous titanium dioxide (TiO 2) with highly crystalline anatase phase and high surface area is a promising material for energy and environmental application. In this study, a novel and facile method for rapid synthesis of mesoporous TiO 2 via microwave-assisted hydrothermal route using stable and water-soluble titanium citrate complexes as the precursor was developed. The physicochemical properties of mesoporous TiO 2 in terms of morphology, crystallization, optical property, surface area, and thermal behaviour were characterized by SEM, TEM, XRD, UV–vis spectroscopy, BET surface area analysis, and TGA/DTA, respectively. Results showed that the synthesized TiO 2 contained mainly anatase phase with crystallite size of 5.0–8.6 nm at various hydrothermal temperatures and durations ranging from 150 to 180 °C and from 30 to 120 min, respectively. The specific surface areas of the TiO 2 nanocrystals were 217–323 m 2 g −1 with the pore diameter of 5.8–6.9 nm, clearly showing the mesoporous characteristics of the hydrothermal TiO 2 nanocrystals. The mesoporous nanocrystals synthesized at 180 °C were then used to prepare the TiO 2 photoelectrode using screen-printing deposition method. The MW180-120-based TiO 2 photoanode exhibited a good efficiency on photocurrent conversion and the conversion efficiency was in the range 4.8–7.1%, depending on active area and film thickness. In addition, the overall conversion efficiency of the DSSC with active area of 1 cm 2 and organic solvent electrolyte decreased slightly from 4.8% to 4.3% after being stored for more than 490 h, demonstrating the long-term stability of the DSSC used in this study.

Preparation Crystalline Mesoporous Titania at Mild Conditions with Inorganic Titanium Precursors

In order to avoid the damage on mesostructure by the high temperature treatment, inorganic titanium species were used as the precursors for the preparation of mesoporous TiO2 of crystalline framework at mild conditions. The influences of the precursor, additive, reaction pH and temperature on phase and textural structures of the products were investigated. The samples were characterized by XRD, N2 adsorption/desorption, FT-IR and SEM. The results show that anatase mesoporous TiO2 with large surface area could be obtained without calcination with Ti(SO4)2 as precursor or TiCl4 when SO42- was added. And the template could be completely removed by Soxhlet extraction.

Effects of templating surfactant concentrations on the mesostructure of ordered mesoporous anatase TiO 2 by an evaporation-induced self-assembly method

We prepared ordered hexagonal mesoporous TiO 2 by an evaporation-induced self-assembly (EISA) method using Pluronic P123 and tetrabutyl orthotitanate (Ti(OBu n ) 4, TBOT) as the templating agent and the titanium source, respectively. The main purpose of this study was to elucidate the effects of surfactant concentrations on the pore arrangement, pore size, specific surface area and structure of mesoporous TiO 2 by the EISA method. The mesostructures of mesoporous TiO 2 were characterized with X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, and transmission electron microscopy (TEM). By varying the concentration of the block copolymer, mesoporous TiO 2 of various pore sizes and pore ordering were prepared. Because the mesostructure is governed by the concentration of P123 surfactant at gelation of the solution, a higher P123/TBOT mole ratio favored the formation of highly ordered mesoporous TiO 2 with a maximum pore volume of 0.26 cm 3/g, a high specific surface area of 244 m 2/g, and a BJH average pore size of 4.7 nm.

Thermally stable SiO 2-doped mesoporous anatase TiO 2 with large surface area and excellent photocatalytic activity

A thermally stable SiO 2-doped mesoporous TiO 2 with high crystallinity was prepared by a templating method. The content of SiO 2 dopant was varied from 3% to 20%. The gels were characterized by TG-DTA analysis. And the resultant catalysts were investigated by various physicochemical techniques, such as WAXRD, Raman spectroscopy, N 2 adsorption–desorption, TEM, FT-IR, and XPS. The WAXRD, TEM, and Raman measurements suggest that the SiO 2 dopant can enhance the thermal stability of the anatase phase remarkably. Rutile phase did not present at all even at 1000 °C when the SiO 2 content was up to 15%. N 2 adsorption–desorption results show that the SiO 2-doped samples have uniform pore diameters and large specific surface area, which is beneficial for photocatalytic reaction. The photocatalytic activities of the samples were evaluated by degradation of Rhodamin-6G solution under UV irradiation. The results show that the SiO 2-doped mesoporous TiO 2 have better activity than commercial P25. Especially, the 15% SiO 2-doped mesoporous TiO 2 exhibited much higher photocatalytic activity than P25 in a large range of calcination temperatures, even at 900 °C. The excellent photocatalytic activity of the samples can be attributed to the high anatase crystallinity, large specific surface area, preserved surface hydroxyl groups and mesoporous channels.

Effect of ionic liquid-templated mesoporous anatase TiO2 on performance of dye-sensitized solar cell

In this study, the mesoporous anatase TiO2, TBF4, is synthesized by sol–gel polymerization using 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] as the template. The 450 °C-calcined TBF4 is found maintaining a mesoporous structure with a morphology that benefits dye adsorption and electrolyte diffusion. A series of dye-sensitized electrodes are prepared with a combination of the as-prepared TBF4 and P25, a commercial TiO2. It is found that the short-circuit photocurrent (Jsc) and open-circuit photovoltage (Voc) of the TBF4-containing electrodes are remarkably increased with the content of TBF4. The improvement is ascribed to an increase in the amount of dye molecules adsorbed and prolongation of the electron lifetimes (τeff). The highest light-to-electricity conversion efficiency (η) of the dye-sensitized solar cell is obtained from that prepared with the pure TBF4 electrode and is about 60% higher than that prepared with the pure P25 electrode under the same condition.

Effect of π–π stacking of water miscible ionic liquid template with different cation chain length and content on morphology of mesoporous TiO 2 prepared via sol–gel method and the applications

In this study, the imidazolium π–π stacking of two water miscible imidazolium ionic liquids (ILs) in the TiO 2 matrix formed during the sol–gel polymerization was studied by FT-IR, XRD, TEM and BET measurements. It was found that the mesoporous morphology, including surface area, average pore size and wormhole-like structure, and thermal stability of the as-prepared TiO 2 particle were varied with the imidazolium chain length and content of the IL used due to different extent of imidazolium π–π stacking. Besides, the wormhole-like mesoporous anatase TiO 2 particles with high surface area exhibited higher photodegradation efficiencies of methylene blue (MB) under 1 h UV irradiation, while those with large pore size used for the electrode materials showed higher efficiency in dye-sensitized solar cells.

Hard template synthesis of crystalline mesoporous anatase TiO2 for photocatalytic hydrogen evolution

Mesoporous crystalline anatase TiO2 has been synthesized by using the nanocasting method with mesoporous silica KIT-6 as the hard template and titanium alkoxide as the precursor. Three key synthetic parameters play important roles in the formation of crystalline porous materials. These are precursor/template ratios, calcination temperatures and immersion time (in 2 M NaOH to remove template). The synthesized materials are characterized with powder X-ray diffraction (XRD), N2 adsorption–desorption isotherm analysis and energy-dispersive X-ray spectroscopy (EDX) elemental analysis. Owing to the template confinement effect, mesoporous anatase TiO2 instead of rutile phase was obtained at the calcination temperature of 750 °C. Materials with a surface area as high as 207 m2 g−1 have been obtained. The photocatalytic activities of the as-prepared mesoporous TiO2 were studied with a loading of 0.5% Pt. The materials with higher surface areas showed higher H2 evolution activities. The H2 evolution activity of the mesoporous anatase sample prepared under optimal conditions was 5.5 times higher than that of bulk anatase TiO2. The work represents a step forward in the development of highly efficient photocatalysts based on crystalline high surface area porous materials and our results indicate that the hard template method may be an effective method to achieve this goal.

Synthesis of mesoporous anatase TiO2 with a combined template method and photocatalysis

Stable mesoporous anatase TiO2 with a large surface area has been prepared by removing the block coploymer template using photocatalysis.

Controlling synthesis of well-crystallized mesoporous TiO2 microspheres with ultrahigh surface area for high-performance dye-sensitized solar cells

In this study, well-crystallized mesoporous anatase TiO2 spheres were prepared by hydrothermal treatment of the titanium diglycolate precursors. These spheres are submicrometer-sized and consist of packed nanocrystallites with diameters of ∼8 nm, and possess a specific surface area of 193 m2 g−1 and main pore sizes of ∼5 nm. We demonstrated that due to the large particle diameters and ultrahigh specific surface areas, mesoporous TiO2 microspheres can enhance the light harvesting within the photoanodes for dye-sensitized solar cells (DSSCs), and meanwhile, their good crystallinity and better interparticle connections caused by partially oriented attachment of primary particles result in the effective charge transport through the film of mesoporous TiO2 spheres. A high light-to-electricity conversion of 8.20% has been achieved, indicating a 40% increase in the conversion efficiency compared to the standard Degussa P25 photoanode.

Synchronous role of coupled adsorption and photocatalytic oxidation on ordered mesoporous anatase TiO2–SiO2 nanocomposites generating excellent degradation activity of RhB dye

In this paper, we report a synchronous role of coupled adsorption and photocatalytic oxidation on ordered 2-D hexagonal mesoporous TiO2–SiO2 nanocomposites with large pore channels (>4.0nm) and high specific surface areas (>70m2g−1). These mesoporous frameworks consist of anatase TiO2 nanocrystals and amorphous SiO2 nanomatrixes, which link mutually, coexist to form unique composite-walls, providing unprecedented spaces for “the synchronous role of coupled adsorption and photocatalytic oxidation”. SiO2 nanomatrixes are excellent adsorbents, providing better adsorption centers and enriching organic pollutant molecules; while anatase nanocrystals behave as photocatalytic active sites to oxide the organic molecules pre-enriched by the surrounding SiO2 particles. Moreover, the high accessible surface areas can provide more adsorptive and photocatalytically active sites; and the large mesopore channels allow the reactive molecules to diffuse more easily both into and out of the inner surfaces before and after photocatalytic reactions, respectively. Our strategy realizes the synchronous role by adjusting Ti/Si ratios, the number of surface hydroxyls, the size and crystallinity of the anatase nanocrystals on the unique composite-frameworks. The cationic rhodamine-B (RhB) dye is used as the target pollutant to characterize the adsorption performance and photocatalytic activities. Our results show that the synchronous role results in excellent photocatalytic degradation activity (k=0.231min−1), which is much higher than that of Degussa commercial P25 photocatalyst (k=0.0671min−1).

Ultrafast Terahertz Conductivity Dynamics in Mesoporous TiO2: Influence of Dye Sensitization and Surface Treatment in Solid-State Dye-Sensitized Solar Cells

We have used optical-pump terahertz-probe spectroscopy to explore the photoinduced conductivity dynamics in mesoporous anatase TiO2 films, commonly employed as the electron-transporting electrode in dye-sensitized solar cells. We find an intrinsic mobility value of 0.1 cm2/(V s) and diffusion length of ∼20 nm for electron motion through the TiO2 matrix. The photoconductivity dynamics in TiO2 films, both before and after sensitization with a ruthenium bypyridyl complex termed Z907, were examined in order to study the charge injection, trapping, and recombination time scales. We observe a biphasic charge injection from Z907, with a fast sub-500 fs component, followed by a slower 70−200 ps component. This is followed by photoconductivity decay over the first few nanoseconds, predominantly reflecting charge carrier trapping. In addition, we have utilized terahertz spectroscopy to investigate the influence of treating the titania surface with TiCl4 on early-time charge dynamics. In the solar cells, surface tre...

Mesoporous Anatase TiO2 Electrodes Modified by Metal Deposition: Electrochemical Characterization and High Rate Performances

We propose the optimization of the electrochemical properties of mesoporous anatase electrodes for lithium-ion batteries by coating with thin Cu or Sn metal layers. The vacuum deposition of Cu or Sn causes no changes in the anatase structure. The metal/anatase composite electrodes show improved kinetics of Li insertion/extraction reactions and excellent electrochemical performances in terms of capacity, stability, and fast-cycling abilities. The higher electrochemical performances are ascribed to an enhanced lithium desolvation and wetting properties at the interface between electrode and electrolyte and to faster lithium diffusion into the anatase lattice. Due to the relatively easy modification procedure, the thin metal coating by physical vapor deposition appears to be a very promising optimization method for the development of high rate performance materials for lithium-ion batteries.

Study on highly visible light active Bi2O3 loaded ordered mesoporous titania

The well-defined two-dimensional (2D) hexagonal mesoporous nanocrystalline anatase TiO2 was synthesized by the nonhydrolytic evaporation-induced co-assembly (EISA) of non-ionic amphiphilic triblock-copolymer template, titanium tetrachloride and tetrabutyl titanate. The ordered mesoporous TiO2 (M-TiO2) was loaded with different % of Bi2O3 using the wet impregnation method. For comparison Degussa P25 impregnated with Bi2O3 was also prepared. The samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy, photoluminescence spectra (PLS), Fourier transform infrared spectra (FT-IR), N2 adsorption–desorption (BET) and X-ray photoelectron spectroscopy (XPS) techniques. XRD and Raman spectra showed the pore wall was composed of anatase. 1.0% Bi2O3 loaded M-TiO2 revealed the well-ordered mesostructure. UV–vis diffuse reflectance spectroscopy measurements showed an extension of light absorption into the visible region. PLS analysis indicated that the electron–hole recombination rate have been effectively inhibited when Bi2O3 was loaded with ordered M-TiO2. The photo oxidation efficiency was evaluated by methyl orange (MO) and 2,4-dichlorophenol (2,4-DCP) degradation under visible illumination. The samples loaded with different % of Bi2O3 showed higher photocatalytic activity than M-TiO2 and Bi2O3 loaded P25. The catalyst exhibited high activity due to the Bi2O3-photosensitization and well-ordered 2D pore structure. The ordered mesoporous channels facilitate mass transport of the organic pollutants. TiO2 could extend the spectral response from UV to visible region because of Bi2O3-photosensitization which make the Bi2O3 loaded M-TiO2 photocatalyst visible light responsive.

Transformation of microporous titanium glycolate nanorods into mesoporous anatase titania nanorods by hot water treatment

High surface area titanium glycolate microporous multi-faceted nanorods were synthesized from the reaction of titanium alkoxides (Ti(OEt)4, Ti(OiPr)4, or Ti(OnBu)4) with ethylene glycol, using a sol–gel reflux method. The specific surface area of the as-synthesized titanium glycolate nanorods obtained from Ti(OEt)4 is ~480 m2/g. A hot water treatment at 90 °C for 1 h transformed the titanium glycolate microporous nanorods into mesoporous anatase TiO2 nanorods. The shape of the nanorods was conserved after hot water treatment and the microporous to mesoporous transformation took place without significant change in the surface area (477 m2/g). Micro Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, solid state NMR, and nitrogen adsorption/desorption were used to characterize the samples. As a demonstration of potential applications, the thus formed mesoporous anatase TiO2 nanorods were tested for their photocatalytic efficiency in the degradation of crystal violet, and a photodegradation mechanism is proposed.

Mesoporous Anatase TiO2 with High Surface Area and Controllable Pore Size by F−-Ion Doping: Applications for High-Power Li-Ion Battery Anode

A pioneering effort has been made to develop F−-ion-doped anatase TiO2 with a spherical shape and mesoporous structure synthesized by a unique, low-temperature urea-assisted hydrothermal synthesis. The electrochemical anode performance of pristine TiO2 for lithium-ion batteries was improved significantly by utilizing F−-ion doping. TiO2 doped with 10 mol % fluorine ions achieved a reversible capacity of 157 mA h/g after 100 cycles. In addition, the rate capability of the F−-ion-doped TiO2 was encouraging, with a stabilized capacity of 144 mA h/g at 30C (C rating) of charge (Li extraction).

A simple method for producing mesoporous anatase TiO 2 nanocrystals with elevated photovoltaic performance

Mesoporous anatase TiO 2 nanocrystals with high crystallinity and large surface area were synthesized by an easy one-step method, combining hydrolysis and alcothermal processes, without the use of a templating agent. The photovoltaic performance of photoanodes for dye-sensitized solar cell under 1 sun (AM 1.5G) illumination gave a solar conversion efficiency as high as 6.06%, an enhancement of ∼20% with respect to that of a reference photoanode made of a commercial TiO 2 (Degussa, P25) powder.

Novel synthesis of high-surface-area ordered mesoporous TiO 2 with anatase framework for photocatalytic applications

Ordered mesoporous TiO 2 materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C 16TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S + and the negatively charged inorganic framework I − (S +I − type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO 2 materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO 2 possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum Brunauer–Emmett–Teller specific surface area of 284 m 2 g −1. This ordered mesoporous anatase TiO 2 also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.

Syntheses, Li Insertion, and Photoactivity of Mesoporous Crystalline TiO2

AbstractOrdered mesoporous rutile and anatase TiO2 samples are prepared using mesoporous silica SBA‐15 as template and freshly synthesized titanium nitrate and titanium chloride solutions as precursors. The rutile material formed from the nitrate solution is monocrystalline and contains minimal amounts of Si with a Si:Ti ratio of 0.031(4), whereas the anatase material formed from the chloride solution comprises nanocrystals and contains a higher content of Si with a Si:Ti ratio of 0.18(3). It is found that control of temperature and selection of Ti‐containing precursor play important roles in determining the crystal phase and crystallinity. A possible formation mechanism of porous crystalline TiO2 is suggested. Characterization of these porous materials is performed by XRD, HRTEM, and nitrogen adsorption/desorption. SBA‐15‐templated mesoporous rutile TiO2 exhibits a higher Li ion insertion capability than KIT‐6‐templated TiO2 due to its larger surface area. Likewise mesoporous anatase TiO2:SiO2 composite has a better photoactivity than bulk TiO2 or TiO2‐loaded SBA‐15 for bleaching methylene blue.

Mesoporous Anatase TiO2 Beads with High Surface Areas and Controllable Pore Sizes: A Superior Candidate for High‐Performance Dye‐Sensitized Solar Cells

Mesoporous Anatase TiO₂ Beads with High Surface Areas and Controllable Pore Sizes: A Superior Candidate for High‐Performance Dye‐Sensitized Solar Cells

Synthesis of mesoporous TiO 2 − xN x spheres by template free homogeneous co-precipitation method and their photo-catalytic activity under visible light illumination

The article presents preparation, characterization and catalytic activity evaluation of an efficient nitrogen doped mesoporous titania sphere photo-catalyst for degradation of methylene blue (MB) and methyl orange (MO) under visible light illumination. Nitrogen doped titania was prepared by soft chemical route i.e. template free, slow and controlled homogeneous co-precipitation from titanium oxysulfate sulfuric acid complex hydrate, urea, ethanol and water. The molar composition of TiOSO 4 to urea was varied to prepare different atomic % nitrogen doped titania. Mesoporous anatase TiO 2 − x N x spheres with average crystallite size of 10 nm and formation of titanium oxynitride center were confirmed from HRTEM, XRD and XPS study. UV–vis DRS showed a strong absorption in the range of 400–500 nm which supports its use in visible spectrum of light. Nitrogen adsorption–desorption study supports the porous nature of the doped material. All the TiO 2 − x N x samples showed higher photo-catalytic activity than Degussa P 25 and undoped mesoporous titania. Sample containing around one atomic % nitrogen showed highest activity among the TiO 2 − x N x samples.