Crystallization and Photoactivity of Tio2 Films Formed on Soda Lime Glass by a Sol-Gel Dip-Coating Process

Transparent nanophase TiO₂ thin films on soda lime glass were prepared from titanium tetraisopropoxide (TTIP) by a sol-gel dip-coating method. The TiO₂ films had amorphous phase up to 400°C and anatase phase at 500°C. The amorphous TiO₂ films obtained at 300–400°C showed considerable photoactivity for the degradation of formic acid. The photoactivity of the TiO₂ films was enhanced with increasing calcination temperature from 300° to 500°C. The crystallinity of the anatase films at 500°C was improved with increasing calcination time up to 2 h and reduced with a further increase in calcination time to 4 h due to the significant formation of sodium titanate phase as a result of sodium diffusion. The four-time-dipping anatase films at 500°C exhibited the greatest photoactivity at the calcination time of 2 h. Sodium diffusion into TiO₂ films was retarded by a SiO₂ underlayer of 50 nm in thickness.     

Preparation and characterization of TiO2–SiO2 nano-composite thin films

TiO₂ nanocrystalline particles dispersed in SiO₂ have been prepared by the sol-gel method using titanium- and silicon-alkoxides as precursors. Nano-composite thin films were formed on the glass substrates by dip-coating technique and heat treated at temperatures up to 500 °C for 1 h. The size of the TiO₂ nanocrystalline particles in the TiO₂–SiO₂ solution ranged from 5 to 8 nm. The crystalline structure of TiO₂ powders was identified as the anatase phase. As the content of SiO₂ increased, the anatase phase tended to be stabilized to higher temperature. TEM results revealed the presence of spherical TiO₂ particles dispersed in a disk-shaped glassy matrix. Photocatalytic activity of the TiO₂–SiO₂ (1:1) thin films showed decomposition of 95% of methylene blue solution in 2 h and a contact angle of 10°. The photocatalytic decomposition of methylene blue increased and the contact angle decreased with the content of TiO₂ phase. TiO₂–SiO₂ with the molar ratio of 1:1 showed a reasonable combination of adhesion, film strength, and the photocatalytic activity.     

Photocatalytic activity and OH radical formation on TiO2 in the relation to crystallinity

Two types of TiO₂ samples, ST-01 (Ishihara-Sangyo, Japan) and A11 precursor (Police, Poland), were heat-treated at 400–1000 °C and characterized by the phase composition, crystallite size and lattice strain. These TiO₂ samples were tested for methylene blue (MB) decomposition and OH radical formation. Through heating TiO₂ up to 700 °C for 1 h the single anatase phase was remained, which had improved crystallinity, large crystallite size and very small lattice strain. By extending the calcination time up to 2–5 h, the anatase phase partially transformed to rutile phase, much faster by A11 precursor than by ST-01. Transformation of anatase phase to rutile reduced the rate of methylene blue decomposition, although OH radical formation was the highest in the samples having around 9 mass% of rutile. However, methylene blue decomposition not only depended on OH radical formation on TiO₂ particles, but also the content of even small amount of rutile in TiO₂ reduces markedly the rate of methylene blue decomposition.     

Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity

Ag–TiO₂ multiphase nanocomposite thin films were prepared on quartz substrates by the liquid phase deposition (LPD) method from a mixed aqueous solution of ammonium hexafluouotitanate, silver nitrate and boric acid under ambient temperature and atmosphere followed by calcination at 500 °C for 1 h. The grain growth of anatase was depressed upon Ag⁺ doping. However, silver ions not only promoted (or catalyzed) the formation of brookite phase but also reduced the phase transformation temperature of anatase to rutile. With increasing AgNO₃ concentration, the transmittance and band gap of the composite thin films decreased; however, the intensity of surface plasmon absorption (SPA) peaks increased and their peak position shifted to a longer wavelength range. When AgNO₃ concentration was higher than 0.03 M, the prepared samples consisted of anatase, brookite, rutile and metal silver nanocrystal particles, and their grain size ranges were 5–30 nm. The photocatalytic activity of the Ag–TiO₂ multiphase nanocrystal composite thin films prepared by this method exceeded that of pure TiO₂ thin films by a factor of more than 6.3 when AgNO₃ concentration was kept in the range of 0.03–0.05. This was attributed to the fact that there were many hetero-junctions, such as anatase/rutile, anatase/brookite, Ag/anatase, Ag/rutile and so on, existed in the Ag–TiO₂ multiphase nanocomposite films.     

Local structure and photocatalytic activity of B2O3–SiO2/TiO2 ternary mixed oxides prepared by sol–gel method

The local structure and the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides (SiO₂ content was fixed as 30 at.% with respect to TiO₂) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing Ti---O---Si with Si---O---B or Ti---O---B bonds. Also, paramagnetic species such as O⁻ and Ti³⁺ defects were formed by the boron incorporation. In SiO₂/TiO₂ mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B₂O₃–SiO₂/TiO₂ samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900 °C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (g moles/min l) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (g moles/m² l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti³⁺ sites are responsible for the deterioration in the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase.     

Synthesis of nanosized TiO2/SiO2 particles in the microemulsion and their photocatalytic activity on the decomposition of p-nitrophenol

Nanosized pure TiO₂ particles were prepared by hydrolysis of TTIP in the sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles. TiO₂/SiO₂ nanoparticles were also prepared from TEOS as a silicon source and TTIP as a titanium source. These particles were characterized by TEM, XRD, FT-IR, BET, TGA and DTA. From thermal analysis and XRD analysis, the anatase structure of pure titania appeared in the 300–600 °C calcination temperature range and the rutile structure was showed above 700 °C. However, no rutile phase was observed for the TiO₂/SiO₂ particles up to 800 °C. The crystallite size decreased and the surface area of TiO₂/SiO₂ particles monotonically increased with an increase of the silica content. From FT-IR analysis, the band for Ti–O–Si vibration was observed and the band intensity for Si–O–Si vibration increased with an increase of the silica content. The micrographs of TEM showed that the TiO₂/SiO₂ nanoparticles had a spherical and a narrow size distribution. In addition, TiO₂/SiO₂ particles showed higher photocatalytic activity than pure TiO₂ and the TiO₂/SiO₂ (90/10) particles showed the highest activity on the photocatalytic decomposition of p-nitrophenol.     

Hydrothermal synthesis of titanium dioxides from peroxotitanate solution using different amine group-containing organics and their photocatalytic activity

Nanosized TiO₂ particles were prepared by hydrothermal method of the amorphous powders which were precipitated in an aqueous peroxotitanate solution using different amine group-containing organics. The physical properties of prepared nanosized TiO₂ particles were investigated. We also examined the activity of TiO₂ particles as a photocatalyst for the decomposition of orange II. The TiO₂ particles calcined at 400 °C were shown to have a stable anatase phase which has no organic compounds. The particles size of titania particles decreased from 15 to 10 nm as the carbon chain length increased. The titania nanoparticles were shown to have a polygonal shape prepared using NH₄OH and tetramethylammonium hydroxide (TMAOH) as additives, however, the micrographs showed the spherical and narrow size distribution prepared using tetraethyl-ammonium hydroxide (TEAOH) and tetrabutylammonium hydroxide (TBAOH). The titania particles prepared using TEAOH as an amine group-containing organic showed the highest activity on the photocatalytic decomposition of orange II. In addition, the titania particles calcined at 500 °C showed the highest activity on the photocatalytic decomposition of orange II.     

Effect of sulfate ions for sol–gel synthesis of titania photocatalyst

We have found that the use of sulfuric acid in the peptization process of sol–gel method produced SO₄²⁻-incorporated TiO₂ which is mechanically strong by firing at low temperature such as 200°C. The synthesized TiO₂ has larger specific surface area and retards the phase transition from anatase to rutile compared with that prepared from the peptization with nitric acid. The S-content of the TiO₂ fired at 200°C was 1.52 wt.%; the value has a maximum of 2.74 wt.% at 400°C. The XPS measurements indicate that S exists mainly as SO₄²⁻. The TiO₂ fired at 400°C showed the highest photocatalytic activity for ethylene degradation. Especially, we would like to emphasize the TiO₂ sintered at 200°C because they are extremely hard in spite of such a low sintering temperature. This photocatalyst may provide a great opportunity for extensive applications as self-supporting membranes.     

Synthesis of TiO2 particles by reverse microemulsion method using nonionic surfactants with different hydrophilic and hydrophobic group and their photocatalytic activity

TiO₂ nanoparticles were prepared using hydrolysis of titanium tetraisopropoxide in W/O microemulsions consisting of water, nonionic Brij series surfactants with different hydrophilic and Tween series surfactants with different hydrophobic group, and cyclohexane. The properties of these particles were characterized by TEM, XRD, FT-IR, TGA and DTA. The photocatalytic degradation of p-nitrophenol has been studied in order to compare the photocatalytic activity of prepared nanosized titania. TiO₂ particles calcined at 500 °C have a stable anatase phase which has no organic surfactants and the product completely transforms into the anatase phase above 300 °C and the rutile phase begins to appear at 600 °C regardless of surfactants. The particles are shown to have a spherical shape and have an uniform size distribution but the shape becomes distorted with a decrease of hydrophilic group chain length according to rapid hydrolysis of water and titanium alkoxide. In addition, the crystallite size and crystallinity increase with a decrease of hydrophilic and hydrophobic group chain length and an increase of calcination temperature. The photocatalytic activity increases with an increase of hydrophilic and hydrophobic group length and the titania calcined at 500 °C shows the highest activity on the photocatalytic degradation of p-nitrophenol regardless of surfactants.     

Hydrogen sorption of magnesium hydride doped with nano-sized TiO2

Various phases of TiO₂ such as anatase, rutile and commercial P25 were added to magnesium hydride by high-energy ball milling in order to improve the hydriding properties of the magnesium. After 1 h milling, the sample containing nano-size rutile powder (200–400 nm) showed uniform distribution, while other shapes of TiO₂ added samples did in separate phase. The effect of the rutile concentrations (3, 5, 7 and 10 mol%) on the hydrogen sorption property of MgH₂ has been investigated and found that the sample containing 5 mol% rutile had the highest hydrogen capacity of 4.40 wt.% at 300 °C and 3.54 wt.% at 250 °C. This amount of hydrogen absorption is still lower than the pure magnesium requires a long activation time, however, its kinetics of hydrogen sorption was greatly enhanced. Moreover, hydrogen absorption capacity was slightly increased with the increase in number of cycles. The mechanism of catalytic effect of uniformly distributed TiO₂ and TiO₂ dispersed as discrete particles in magnesium matrix has been discussed based on microstructural observations.     

INFLUENCE OF CALCINATION ON MICROSTRUCTURES AND PHOTOACTIVITIES OF ALKOXIDE-DERIVED TiO2 NANOPARTICLES PREPARED IN W/O MICROEMULSIONS

Ultrafine titania particles were synthesized by hydrolysis of titanium tetraisoproxide (TTIP) in the nanodroplets of water/NP-5/cyclohexane microemulsions. The as-prepared particles were amorphous, transformed into the anatase phase at 450°C, and completely into the rutile phase at 700°C. The amorphous-to-anatase phase transition temperature decreased with increasing water/surfactant molar ratio. With increasing temperature from 500 to 900°C, the crystallite size increased about twice from 11.7 to 24.4 nm, while the size of the secondary particles, agglomerates of the primary panicles, increased by a factor of about 10. The particles grew largely by intra-agglomerate densification below 700°C, whereas they grew by interagglomerate densification above 700°C. The anatase phase formed at 500-600°C showed considerable photoactivity for the degradation of phenol, whereas both the amorphous phase at 300°C and the rutile phase at 700°C were almost inactive for this reaction.     

Dielectric behavior of Nb2O5-doped TiO2/epoxy thick films

TiO₂/epoxy composite thick films containing the TiO₂ powders doped with 4 and 10 vol% Nb₂O₅ heat treated under vacuum at 1050 and 1150 °C, were prepared by the screen printing and curing steps. The Nb₂O₅-doped TiO₂ ceramic bulks demonstrated a higher effective dielectric constant at different densification environments, as compared with pure TiO₂. The dielectric properties of the TiO₂/epoxy thick films were improved if the heat-treated 4 vol% Nb₂O₅-doped TiO₂ powder was incorporated instead of the un-doped and heat-treated 10 vol% Nb₂O₅-doped TiO₂ powders. The disadvantage of the doped TiO₂ having higher dielectric loss tangent could be minimized after its powder was properly treated and mixed with epoxy to form the TiO₂/epoxy composite. A best result with the dielectric constant of 23 and the loss tangent of 0.046 was obtained for the 40 vol% TiO₂/epoxy composite thick films, where the TiO₂ powder was doped with 4 vol% Nb₂O₅ followed by calcination at 1000 °C in air and heat treatment at 1150 °C under vacuum.     

Molybdenum and tungsten dioxides, XO2 (X=Mo,W), as reforming catalysts for hydrocarbon compounds

The reforming catalytic properties of tungsten and molybdenum dioxides have been interpreted in terms of a bifunctional mechanism. A stable XO₂ (X=W,Mo) has been obtained following the reduction of XO₃ by hydrogen for 4 h at 400°C for Mo and 460°C for W. A relatively high selectivity up to 100% in isomerization products for the hexanes were obtained at reaction temperatures of 280°C in the case of MoO₂ and at 300°C for WO₂. Titanium dioxide, TiO₂, was chosen as the appropriate support on the basis of its electronic structure which enables to avoid a strong metal–support interaction with the active XO₂ phase.     

Characterization and photocatalytic activity of N-doped TiO2 prepared by thermal decomposition of Ti–melamine complex

Nitrogen doped spherical TiO₂ has been prepared by thermal decomposition of Ti–melamine complex in air atmosphere. A clear shift in the onset light absorption from UV region (<400) to visible region (>520 nm) has been observed for the N-doped samples. It has been deduced from the optical absorption spectra that the higher calcination temperature results in the decrease in the amount of N-doping. The XRD results revealed the phase transition of TiO₂ from anatase to rutile crystalline phase, starting at calcination temperature ≥600 °C. The electron microscopic images reveal the formation of spherical and flakes of TiO₂ nanocrystals (25 nm). The chemical nature of N in the N-TiO₂ has been evolved through X-ray photoelectron spectroscopy. The presence of different types of N species have been observed corresponding to different oxidation states and the presence of Ti–N and O–Ti–N have been confirmed from the observed binding energy values. Photocatalytic decomposition of methylene blue has been carried out both in the visible region and UV + visible region. In the visible region, N-TiO₂ showed higher activity compared to the undoped commercial TiO₂ (Degussa P25).     

Formation of niobium double oxides by the glycothermal method

Thermal reaction of niobium alkoxide in organic media at 300°C yielded amorphous niobia, which maintained a surface area above 130 m²/g after calcination at 500°C. Niobium double oxides (LiNbO₃, Zr₆Nb₂O₁₇, CaNb₂O₆, CrNbO₄, FeNbO₄, ZnNb₂O₆ and R₃NbO₇ (R; rare earth)) were directly obtained by the reaction of niobium alkoxide with the corresponding metal alkoxide, acetate or acetylacetonate in 1,4-butanediol at 300°C. In some cases, amorphous product was obtained; however, double oxides (SrNb₂O₆, Co₄Nb₂O₉, etc.) crystallized from the products at low temperatures.     

铋及钴掺杂TiO2陶瓷负载膜的制备及光催化性能

以钛酸四丁酯为钛源,Bi(NO₃)₃·5H₂O为铋源,Co(NO₃)₂·6H₂O为钴源,采用溶胶-凝胶法在陶瓷基片上分别制备了应用于固定式光催化反应器的Bi-TiO₂复合膜及Co-TiO₂复合膜。研究了涂膜方式及煅烧升温速率对膜表面形态的影响,并以甲基橙溶液为目标降解物,对比了旋涂法及浸渍提拉法制备的薄膜在不同升温速率下的光催化活性。通过热分析仪(TG-DSC)、X射线衍射仪(XRD)和扫描电镜(SEM)等测试手段分析了掺杂薄膜的结构。结果表明,采用旋涂法制备的薄膜与陶瓷基体结合较为紧密,而浸渍提拉法制备的薄膜催化活性较高。当煅烧温度为500 ℃,升温速率为10 ℃/min时,其对甲基橙的降解率较高。当摩尔比为0.010时Bi-TiO₂复合膜的催化活性较佳,100 min光降解甲基橙比率达到8.10%。钴或铋掺杂TiO₂均可提高TiO₂催化剂的光催化活性,Bi-TiO₂膜的催化活性优于Co-TiO₂膜。     

Preparation, structural and optical characterization of BaWO4 and PbWO4 thin films prepared by a chemical route

Polycrystalline BaWO₄ and PbWO₄ thin films having a tetragonal scheelite structure were prepared at different temperatures. Soluble precursors such as barium carbonate, lead acetate trihydrate and tungstic acid, as starting materials, were mixed in aqueous solution. The thin films were deposited on silicon, platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure of the thin films were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, and specular reflectance infrared Fourier transform spectroscopy, respectively. Nucleation stages and surface morphology evolution of thin films on silicon substrates have been studied by atomic force microscopy. XRD characterization of these films showed that BaWO₄ and PbWO₄ phase crystallize at 500 °C from an inorganic amorphous phase. FTIR spectra revealed the complete decomposition of the organic ligands at 500 °C and the appearance of two sharp and intense bands between 1000 and 600 cm⁻¹ assigned to vibrations of the antisymmetric stretches resulting from the high crystallinity of both thin films. The optical properties were also studied. It was found that BaWO₄ and PbWO₄ thin films have Eg=5.78 eV and 4.20 eV, respectively, of a direct transition nature. The excellent microstructural quality and chemical homogeneity results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of BaWO₄ and PbWO₄ thin films.     

Effect of HCl concentration and reaction time on the change in the crystalline state of TiO2 prepared from aqueous TiCl4 solution by precipitation

TiO₂ powder with 50% by volume or more of brookite phase was obtained by heating aqueous TiCl₄ solution, whose final concentration of HCl after reaction was kept between 4.9 and 6.4 M, at 80 °C for 15 h. Rutile-type TiO₂ was obtained at 5 h of reaction time, a mixture of predominant brookite and rutile at 10–15 h while rutile phase was formed at 25 h. Brookite phase was transformed directly to rutile phase with increase of reaction time but to rutile via anatase phase through heat treatment.     

煅烧温度对Mo-Mn/TiO2催化剂脱硝脱汞活性的影响

研究了浸渍法制备Mo-Mn/TiO₂（MMT）催化剂过程中煅烧温度（300℃、450℃、600℃、750℃）对Mo-Mn/TiO₂（MMT）催化剂协同脱硝脱汞活性的影响。结果表明,较低的煅烧温度更有利于MMT催化剂的协同脱硝脱汞性能,同时可有效降低SO₂对催化剂活性的抑制作用,最佳煅烧温度为300℃。利用BET、XRD、H₂-TPR、FTIR和XPS等表征手段对催化剂的理化性质进行了表征,结果表明较低的煅烧温度有利于提高催化剂中活性成分所占的比例,增加金属氧化物在TiO₂载体表面的分散度,提高催化剂的低温还原性能。随着煅烧温度的升高,催化剂的比表面积和孔容均逐渐减小,平均孔径先增大后减小,且在高温下发生烧结;MnO₂逐渐向Mn₂O₃转变,锐钛矿型TiO₂逐渐向金红石型转变,同时MoO₃由非晶态逐渐向晶态的转化,致使催化剂的协同脱硝脱汞活性下降。     

A PVB-based rheological phase approach to nano-LiFePO4/C composite cathodes

Nano-LiFePO₄/C cathode materials were synthesized by a PVB-based rheological phase method, followed by calcination at 550 °C for 10 h in argon. Simultaneous thermogravimetric-differential scanning calorimetry analysis indicates that the crystallization temperature of LiFePO₄ is about 436 °C. In the process of heat treatment, the decomposition of polyvinylbutyral coats carbon on the synthesized LiFePO₄ particles in situ. The resulting LiFePO₄ powders with fine particle sizes and homogeneous carbon network connection were observed by using scanning electron microscopy and transmission electron microscopy. Electrochemical measurements show that the LiFePO₄/C composite cathode delivers a large discharge capacity of 162.3 mAh·g^− 1 at the 0.1 C rate, and exhibits a favorable capacity cycling maintenance at lower charge and discharge rate such as 0.5 C rate.