Anatase Content Research Articles

Temperature-dependent thermal stability and dispersibility of SiO2–TiO2 nanocomposites via a chemical vapor condensation method

Surface-modified TiO2 nanoparticles were prepared by a chemical vapor condensation method (CVC). The resultant nanocomposites were subjected to post-heat treatment with various temperatures. The sedimentation behavior of the surface-modified TiO2 nanoparticles in aqueous solution was investigated visually using a separation analyzer. The dispersion stabilities of the pure CVC-made TiO2 and the surface modified SiO2–TiO2 samples were enhanced due to low zeta potential values compared to a commercial TiO2 sample (P25). With increasing heat treatment temperature, the photocatalytic activity of the pure TiO2 samples (CVC–TiO2 and P25) suddenly dropped, which resulted from the increased particle size and the reduced anatase content. For the surface-modified TiO2 nanoparticles, the anatase-to-rutile phase transformation process did not occur even at 900°C. Although the surface-modified TiO2 nanoparticles formed using the chemical vapor condensation method were thermally treated with high temperature, the photocatalytic activity was higher than that of the pure TiO2 samples. This is probably due to the fact that the surface-modified TiO2 nanoparticles had increased thermal stability, and SiO2 provides better adsorption sites in the vicinity of the TiO2.

X-ray reflectivity analysis of titanium dioxide thin films grown by cathodic arc deposition.

TiO2 thin films deposited by a vacuum arc on a glass substrate were characterized by X-ray reflectivity (XRR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Several thin films with different amounts of deposited TiO2 mass and different deposition and annealing temperatures were studied. A qualitative analysis of the XRD patterns indicated the presence of the anatase and/or rutile crystalline phases in most of the studied samples. From the analysis of the experimental XRR curves--which exhibited a wide angular range of oscillatory behavior--the thickness, mass density and interface roughness were determined. All XRR patterns were well fitted by modeled curves that assume the presence of a single and homogeneous TiO2 layer over which a very thin H2O layer is adsorbed. The thickest H2O adsorption layers were developed in films with the highest anatase content. Our overall results of the XRR analyses are consistent with those derived from the imaging techniques (SEM and AFM).

The structures, electrochemical and cell performance of titania films formed on titanium by micro-arc oxidation

Through micro-arc oxidation, the titanium dioxide coatings were prepared on titanium at the different applied voltages (in the range of 100–200V) in an H2SO4/H3PO4 electrolyte. The morphologies, phase components, corrosion resistances, and biocompatibility of the coatings were investigated. The effect of the applied voltages on the characteristics and properties of the MAO treated coatings were also discussed. The titania coatings formed in acidic electrolyte is mainly composed of anatase phase and the anatase content increases with the applied voltage increasing. It is also found that the applied voltage plays an important role in the characteristics and properties of the composite coatings. With the increase of the applied voltage, the pore size, surface pore density and the roughness of the coatings increase, while the corrosion resistance decreases. Moreover, the MAO coatings treated at a higher voltage (180 and 200V) exhibited an effect on early osteoblast mineralization.

Industrial application of photocatalysts prepared by hydrothermal and sol–gel methods

TiO2-containing almond shell activated carbons (TiO2/ASAC) with high photocatalytic activity were prepared using hydrothermal and sol–gel methods. The prepared photocatalysts were characterized by different techniques. XRD study confirmed that TiO2 existed in a mixture of anatase and rutile phase. Nano-TiO2 particles were dispersed on the ASAC with the size of 18–24nm. The specific surface area of the samples decreased from 1398m2/g to 661m2/g indicating that the pores of activated carbon are blocked by TiO2. The photocatalyst obtained from the hydrothermal process is better than the other samples one in a comparison of the anatase content, and was also confirmed by the photocatalytic degradation of Total Organic Carbon (TOC) from industrial phosphoric acid solution under UV irradiation.

Fabrication of a Porous TiO2-Coated Silica Glass Tube and Its Application for a Handy Water Purification Unit

A simple, handy, reusable, and inexpensive water purification unit including a one-end sealed porous amorphous-silica (a-silica) tube coated with 2 μm of porous TiO2photocatalyst layers has been developed. Both TiO2and a-silica layers were formed through outside vapor deposition (OVD). Raman spectrum of the porous TiO2-coated a-silica glass tube indicated that the anatase content of the TiO2layers of the tube was estimated to be approximately 60 wt%. Developed porous TiO2-coated a-silica glass tube has been assayed for the tube filtering feature againstEscherichia coli(E. coli) solution used as one of the typical bacteria size species or Qβphage also used as typical virus size species and compared with the feature of porous a-silica tubes alone. The tubes removedE. colicompletely from the aqueous suspension which contained 106 CFU/mL ofE. coliwithout UV irradiation. The porous TiO2-coated a-silica glass tube with UV-C lamps successfully reduced the Qβphage amount in the suspension from 109to 103 PFU/mL.

Effect of TiO2 nanostructures on specific capacitance of Al2O3–TiO2 composite film on etched aluminum foil formed by the sol–gel and anodizing

Nano-thin TiO2 film on etched aluminum foil was prepared by the Sol–gel dip-coating method and annealing post-treatment at different temperatures; then, Al2O3–TiO2 composite oxide film on etched aluminum foil was fabricated by anodization in 13wt% ammonium adipate solution. Nanostructures of TiO2 film were characterized by means of X-ray Diffraction (XRD), Raman Spectroscopy (RS), and Atomic Force Microscope (AFM). TiO2 nanostructured films are composed of anatase nanopartilces in size of 5–12nm as annealed at 400°C and 500°C, and anatase-rutile complex nanopartilces in 5–15nm at 600°C. Compared with pure anodic aluminum oxide film, TiO2 nanostructures effectively improved specific capacitance of the Al2O3–TiO2 composite oxide film on etched aluminum foil, with an increment ratio of about 8.6%, 24.6%, and 33.3%, caused by anatase and rutile content increasing with annealing temperature from 400°C, 500°C to 600°C, respectively. The specific capacitance of dip-coated etched aluminum foil annealed at 500°C reached to a maximum after two dip-coating times with 28.3% enhancement.

Microstructure and Properties of Plasma-Sprayed Mixture of Cr2O3 and TiO2

Rutile TiO2 and Eskolaite Cr2O3 powders were mechanically mixed and fed into the plasma jet simultaneously. The influence of the ratio of components on behavior of the plasma-sprayed coatings was observed using two different compositions, both at two different feeding distances. The produced coatings were analyzed by XRD, SEM, XPS, and light microscopy. Electrical resistivity was measured at voltages from 1 to 100 V. Photocatalytic decomposition of butane on the coatings was studied using visible light together with a setup typically used for UV-light tests. For the coatings with high TiO2 content, besides rutile, low anatase content was identified. The coatings with predominant Cr2O3 exhibited lower porosity and higher hardness. All coatings are relatively efficient photocatalysts for butane decomposition. Moreover, they have good mechanical properties governed predominantly by Cr2O3 content as the harder component. It was proven that the spray process led to obtaining of robust photocatalytically active coatings.

Microwave induced degradation of parathion in the presence of supported anatase- and rutile-TiO2/AC and comparison of their catalytic activity

In this study, nano-sized anatase or rutile TiO2-supported activated carbon (A-TiO2/AC or R-TiO2/AC) was developed for the microwave (MW)-induced degradation of parathion as a model contaminant in aqueous solution. The effects of selected process parameters such as anatase or rutile TiO2 content, heat-treatment temperature and time, MW irradiation time, initial parathion concentration, catalyst dose, solution pH and MW power on the degradation were studied in details. The results showed that the anatase- and rutile-TiO2 supported on AC both significantly improved the MW/AC degradation effect and the supported A-TiO2/AC showed higher MW catalytic activity than R-TiO2/AC. Also, the supported A-TiO2 on AC can be excited leading to the production of more hydroxyl radicals (OH) than the supported R-TiO2 on AC in aqueous solution under MW irradiation. Comparatively, the supported A-TiO2/AC/MW process displayed many advantages such as high degradation rate, short irradiation time, no residual intermediates, and no secondary pollution. Therefore, the supported A-TiO2/AC/MW showed to be a promising technology for the removal of parathion in wastewater treatment applications.

Synthesis and modification of nano-sized TiO2 for photo-degradation process under visible light irradiation; a Placket–Burman experimental design

In this research, nitrogen and iron (III) co-doped nano TiO2 (N-Fe-TiO2) was prepared by sol-gel method using ammonium chloride and iron chloride solutions as nitrogen and iron sources, respectively. The effect of synthesis parameters (weight ratios of N/TiO2 and Fe/TiO2, synthesis temperature, calcination time and temperature) was simultaneously investigated on the quality of the N-Fe-TiO2 product by a two-level Placket–Burman experimental design. The synthesized powders were characterized by XRD, XPS and UV–Vis spectroscopy techniques. The mean crystal size and anatase content were determined and evaluated as the linear functions of so-called synthesis parameters by the statistical analysis and regression. The 2%N-1%Fe-TiO2 product by 11nm mean crystal size and 78% anatase content, synthesized at 35°C and calcined at 500°C during 2h, exhibited the most significant activity during the photo-degradation of acetaldehyde under visible light irradiation and its efficiency was obtained about four times more than photocatalytic activity of Degussa TiO2-P25.

Low‐Temperature Transformation of Titania Thin Films from Amorphous Nanowires to Crystallized Nanoflowers for Heterogeneous Photocatalysis

Titania thin films with ordered nanostructures are of general interest in fields of photocatalysis, gas sensors, energy storages, energy conversions, etc. In this study, we report a low‐temperature crystallization and the simultaneously occurred morphology change of titania thin films in a dilute H2SO4 solution. Amorphous titania nanowire arrays were fabricated by a Ti–H2O2 interaction, which transformed to crystallized nanoflower arrays through a dissolution–precipitation route during the subsequent acid treatments. The nanoflowers were doped with nitrogen and also incorporated with sulfate ions. An increasing H2SO4 concentration resulted in larger nanoflowers with higher anatase content; but the crystallinity reduced. The low‐temperature‐derived nanoflower arrays possessed high density of surface hydroxyl groups and defect VO‐Ti3+ sites, which contributed to a high absorption and enhanced photodegradation efficiency of rhodamine B in water under the illumination of UV–visible light during the first several runs of photocatalytic evaluations. The beneficial surface defects diminished gradually with increasing runs; however, the average reaction rate constants of the acid treated films are still superior to that of the calcinated one, which can be attributed to several structural parameters such as the nanoflower morphology, incorporation of sulfate ions, and the coexistence of anatase and rutile.

Synergy effect in photodegradation of contaminants from water using ordered mesoporous carbon-based titania catalyst

A synergy effect by carbon and anatase in the mesoporous C–TiO2 nanocomposites is reported here on the degradation of dye in contaminated water. The as-formed mesoporous C–TiO2 composites have ordered 2D hexagonal mesostructure, high surface area (384m2/g), uniform and large mesopores (4.5nm), large pore volume (0.31cm3/g), titania nanoparticles confined inside carbon frameworks, tunable TiO2 contents (40–87wt%), and dopant of element carbon into anatase lattice. The large mesopore space of carbon offers high capacity for the adsorption of dyes from water. Well-dispersed and carbon-doped anatase TiO2 nanoparticles are active for photocatalysis especially in visible light region. Once the dyes are involved inside mesopores by adsorption, they are easily accessible to anatase particles through the common interface between the two, and immediately fully oxidized. The immobilization of anatase particles in the carbon framework greatly improves the stability during its usage. The mesoporous C–TiO2 nanocomposite catalysts can be reused more than 20 times without obvious loss both in anatase content and processing ability of contaminated water.

Polymorphic phase transformation of Degussa P25 TiO2 by the chelation of diaminopyridine on TiO62− octahedron: Correlation of anatase to rutile phase ratio on the photocatalytic activity

A series of nitrogen-doped Degussa P25 photocatalysts were synthesized successfully by grinding and calcination method using 2,6-diaminopyridine (DAP) as a nitrogen precursor. The prepared samples were characterized by various analytical methods. The phase contents of anatase and rutile in the Degussa P25 powders have been altered by simply changing the proportion of DAP. A mechanism involving chelated DAP molecule on TiO62− octahedron is discussed. The enhanced activity is attributed to synergistic effect in the two phase solid material. Due to the low activation barrier, the effective inter particle electron transfer between the two polymorphs is quite efficient only when they are in close proximity with similar crystallite sizes. The transfer of electrons from the rutile phase to lattice/electron trapping sites of anatase and also to the Ti3+-Vo defect level created by the dopant favors effective charge separation and enhance the photocatalytic activity under solar illumination.

Heat treatment and substrate dependant properties of titania thin films with high copper loading

AbstractCopper‐doped titania thin films have been prepared on SiO2/Si(100), fused‐silica and soda‐lime glass substrates by using sol–gel deposition and subsequent annealing in air atmosphere at 200–900 °C. Several experimental techniques [X‐ray photoelectron spectroscopy (XPS), wavelength dispersive X‐ray fluorescence (WDXRF), Raman spectroscopy, atomic force microscopy (AFM), UV–Vis spectroscopy, energy dispersive X‐ray analysis (EDX), photocatalytic activity measurements and hydrophilicity measurements] have been applied to characterize these films. The results demonstrate that the films prepared on SiO2/Si(100) and fused‐silica substrates start to crystallize after annealing above 300 °C, then anatase phase is formed. At 700 °C anatase content starts to decrease and from 800 °C the films consist of rutile. Annealing causes a formation of regions with increased Cu concentration, in case of titania films prepared on SiO2/Si(100) substrates. On the other hand films prepared on soda‐lime glass substrates show large sodium diffusion into the films, the crystalline nature of the films decreases during annealing and outward segregation of copper compounds does not occur. However, the surface of copper‐doped titania films on soda‐lime glass appear to be naturally hydrophilic (i.e. surface is hydrophilic without UV irradiation), water droplet contact angles as low as 4.2° were achieved. Influence of annealing time and copper‐doping to the photocatalytic activity of thin titania films was also studied by using two organic dyes as model contaminants.

Influence of catalyst on structural and morphological properties of TiO2 nanostructured films prepared by sol–gel on glass

Transparent TiO2 thin films have been prepared by the sol–gel method using titanium alkoxides as precursors. Thin films were deposited on glass supports by the dip-coating technique. The TiO2 layer acts as a self-cleaning coating generated from its photocatalysis and photoinduced superhydrophilicity. The crystalline structure of TiO2 films was dominantly identified as the anatase phase, consisted of uniform spherical particles of about 14–50nm in size, which strongly depends upon catalyst-type and heat treatment temperature. Increasing heat treating temperature can lead to an increase in crystalline size. The results indicated that the sample S.S (sample derived from sol containing sulfuric acid as catalyst) exhibits superhydrophilic nature and better photocatalytic activity, which can be attributed to its higher anatase content and lower crystalline size. Morphological studies, carried out using Atomic Force Microscopy (AFM), confirm the presence of crystalline phase with such a grain size and low surface roughness. Thus, the applied films exhibiting high photocatalytic activity, superhydrophilic behavior, and low surface roughness can be used as an efficient self-cleaning coating on glass and other optical applications.

Low-temperature sol–gel synthesis of anatase nanoparticles modified by Au, Pd and Pt and activity of TiO2/Au, Pd, Pt photocatalysts in water splitting

Base catalyzed hydrolysis and condensation of Ti isopropoxide with water at ambient temperature and molar ratio H2O/Ti(i-PrOH)4 varied from 1 to 100 was studied. It was found that molar ratio H2O/Ti(i-PrOH)4 = 100 originated amorphous TiO2-precursor of summary composition TiO1.9(OH)0.2 with a specific surface area of 354 m2/g. Low-temperature crystallization of amorphous TiO2-precursor to nanostructured anatase at 80 °C in a slightly reducing environment of d-glucose was studied. It was found that the low-temperature nucleation and crystallization of anatase was initiated (activated) by combined effects of d-glucose and Au0, Pd0 and Pt0 nanoparticles, generated in situ by slow reduction of Au3+, Pd2+ and Pt4+ ions using d-glucose. Considerable photocatalytic activity of Ti-hydroxide-oxide/Au, Pd, Pt catalysts prepared at low-temperature was associated with high content of nanostructured anatase and low content of Au, Pd and Pt nanoparticles (0.02 wt.%) effectively deposited on the surface of titania particles. The maximum hydrogen evolution rates 3.4 μmol/min g at Ti-hydroxide-oxide/Au, 4.0 μmol/min g at Ti-hydroxide-oxide/Pd and 4.1 μmol/min g at Ti-hydroxide-oxide/Pt were found. The activity of all TiO2/Au, Pd and Pt catalysts increased by calcination at 600 °C from 50 to 100 %.

Effects of pH Value on Composite Structure of Poly-titanium-ion/Montmorillonite and Its TiO<SUB>2</SUB> Nano-particle

The montmorillonite composite structure samples were prepared using a hydrolysation-intercalation composite method with TiOSO4·2H2O as a precursor of TiO2 nano-particles and montmorillonite as substrate by controlling the pH value of the montmorillonite suspension. The changes of the structure, phase and crystal size of the samples were characterized by X-ray diffraction method. The results show that the pH value of montmorillonite suspension has a significant influence on the hydrolyzation of TiOSO4·2H2O, so the composite structure of hydratedtitanium-oxide/montmorillonite is affected. When the pH value of montmorillonite suspension is 0.5, the poly-titanium-ions are with the lower electrovalence and extent of polymerization and easily intercalate the interlayer space of montmorillonite, moreover, the structural layers of montmorillonite are separated best. The crystal size of anatase in the TiO2/montmorillonite composite samples calcinated at 700°C is smallest and reaches 13.4 nm. After calcination at 1100°C, the relative content of anatase in the composite structure reaches 35%. Compared with pure TiO2 nano-particle sample, TiO2/Montmorillonite composite sample has a higher phase transition temperature 第 12期 吕 霞, 等: pH值对聚合钛离子/蒙脱石复合结构及其 TiO2纳米粒子属性的影响研究 1295 from anatase phase to rutile phase and smaller crystal size of TiO2. Montmorillonite structure layer has a significant blocking effect on the TiO2 phase transformation and grain growth.

Improvement of the Visible‐Light Photocatalytic Performance of TiO2 by Carbon Mesostructures

An improvement in the photodegradation performance for dyes due to interaction between carbon and titania in a self-assembled mesoporous C-TiO(2) composite catalyst, even for the difficult degradation of azo dyes, is reported herein. The dye removal process involves adsorption of the dye from water by the mesoporous carbon-titania, followed by photodegradation on the separated dye-loaded solid. Such adsorption-catalysis cycles can be carried out more than 80 times without discernible loss of photocatalytic activity or the anatase content of the composite. In each run, about 120 mg dye per g catalyst can be degraded. The mesoporous carbon-titania catalyst also exhibits a high capacity for converting methyl orange in aqueous solution under visible light. Characterization by XRD, TEM, and N(2) sorption techniques has revealed that the self-assembled composite catalyst has an ordered mesostructure, uniform mesopores (4.3 nm), a large pore volume (0.30 cm(3) g(-1)), and a high surface area (348 m(2) g(-1)). The pore walls are composed of amorphous carbon and anatase nanoparticles of size 4.2 nm, which are well dispersed and confined. X-ray photoelectron spectroscopy (XPS), surface photovoltage spectroscopy (SPS), and UV/Vis absorption results indicate doping of carbon into the anatase lattice and a change in the bandgap of the semiconductor. The synergistic improvement in the composite catalyst can be attributed to the following features: (1) carbon doping of the anatase lattice modifies its bandgap and enhances its activity under visible light; (2) confinement within carbon pore walls prevents aggregation of tiny anatase nanoparticles, improving their activity and stability; (3) the mesopores provide a confined space for photocatalysis; and (4) the strong adsorption ability of porous carbon for organic substances ensures that large quantities can be processed and inhibits further diffusion of the adsorbed organic substances, thereby enhancing the mineralization on anatase.

Microstructure and photocatalytic activity of APS coatings obtained from different TIO2 nanopowders

In recent years, intense research has shown that thermal spray techniques, especially atmospheric plasma spraying (APS), can be used to obtain nanostructured TiO2 coatings with effective photocatalytic activity.This study compares the photocatalytic activity of APS coatings obtained from different powders: two nanostructured TiO2 powders produced by spray-drying of two TiO2 nanosuspensions with different solids contents, one spray-dried powder obtained from a suspension comprising a mixture of submicronic and nanometric TiO2 particles and finally one commercial, nanostructured, TiO2 spray-dried powder. All powders were characterised by XRD, FEG-ESEM, granule size distribution, and a flowability evaluation. Feedstock powders were then deposited on austenitic stainless steel coupons using APS. Hydrogen or helium was used as secondary plasma gas. Coating microstructure and phase composition were characterised using FEG-ESEM and XRD techniques; coating anatase content was quantified by the Rietveld method.A significant amount of anatase to rutile transformation was found to take place during the plasma spraying process. In general, the coatings had a bimodal microstructure characterised by the presence of completely fused areas in addition to non-molten areas consisting of agglomerates of anatase nanoparticles. Results also showed that anatase content and porosity of the coatings largely depend on the secondary plasma gas nature, as well as on the characteristics of the feedstock.Finally the photocatalytic activity of the coatings was determined by measuring the degradation of methylene blue dye in an aqueous solution. A reasonably good fit of a first-order kinetic model to the experimental data was found for all coatings. The values of the kinetic constant were related to feedstock characteristics as well as to plasma spraying conditions.

Effect of TiO2 crystalline composition on the dielectric properties of TiO2 /P(VDF-TrFE) composites

In order to study the effect of the TiO2 particle crystalline composition (with different proportions of rutile and anatase crystals) on the dielectric properties of the composite, titanium dioxide (TiO2) particles and TiO2/poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] composites were synthesized by a reflux method and the solution route, respectively. The results indicated that the optimum TiO2 particle crystalline composition is anatase content of 37% and rutile content of 63% for dielectric-constant modifier applications. Furthermore, a dielectric constant of 25.7 with dielectric loss of 0.17 at 100 Hz at room temperature were obtained in the composite with 40 wt% TiO2 particles. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tailored preparation of titania with controllable phases of anatase and brookite by an alkalescent hydrothermal route

Titanium dioxide (TiO2) with different ratio of anatase to brookite has been selectively synthesized by an alkalescent hydrothermal treatment of TiCl3 in the presence of different concentration of NaCl. The resulting powders have been characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) analysis, UV–vis diffuse reflectance spectra (DRS), and Brunauer–Emmett–Teller (BET) analysis. The contents of anatase and brookite have been successfully controlled by adjusting the NaCl concentration and NH4OH/H2O volume ratio. The photocatalytic activity of TiO2 has been assessed by the degradation of Rhodamine B in aqueous solution. The mixed-phase TiO2 exhibits higher activity than pure phase TiO2, and the product containing 53.4% brookite and 46.6% anatase shows the highest photocatalytic activity. This behavior is explained by the mixed-phase effect between anatase and brookite. A proposed formation process is discussed to interpret the evolution of the phases based on the effects of different NaCl concentration and NH4OH/H2O volume ratio.