Titania on Silica. A Comparison of Sol-Gel Routes and Traditional Methods

Titania on silica samples have been prepared by: i) precipitation-deposition from a solution of TiCl₃ onto the surface of a commercial silica, and ii) base catalysed hydrolysis-condensation of TEOS followed by reaction with Ti isopropoxide. These samples were characterised by nitrogen and hydrogen adsorption, X-ray diffraction, FTIR, temperature programmed reduction, transmission electron microscopy and catalytic activity in butane-hydrogen conversion. The sol-gel preparation produced a better titania dispersion due to the formation of stabilising Ti-O-Si bonds. Upon these samples was then introduced Ir. Strong metal-support interactions between Ir and titania have been observed after high temperature reduction, causing a significantincrease in butane dehydrogenation activity relative to hydrogenolysis.It appears that using sol-gel chemistry useful supports for catalytic metals containing Si-O-Ti linkages can be produced and in future may be optimised for other metal-oxygen metal pairs.     

Sol-Gel Derived Macroporous Titania Films Prepared from the System Containing Poly(ethylene glycol) Together with Long-Chain Alcohols

The effect of alcohol-type on macroscopic morphology has been examined for the macroporous titania (TIO₂) films prepared by a sol-gel dip-coating method from the system containing poly(ethylene glycol) (PEG) and alcohols having larger alkyl groups than ethanol. The phase separation is enhanced by decreasing the compatibility between the solvent mixture and PEG as long as the polycondensation rate does not increase greatly. In the 1-butanol system, macroporous morphology appears clearly even at higher relative humidity as 70% RH due to the slower polycondensation. In contrast, the macroscopic domain formation is completely suppressed by the rapid polycondensation in the 2-propanol system.     

Scratch-Resistant Improvement of Sol-Gel Derived Nano-Porous Silica Films

Scratch-resistance of sol-gel derived nano porous silica films were studied. The thin films were prepared with a dip-coating method from both one-step and two-step catalyzed silica sols, and treated in a mixture gas of ammonia and water vapour afterwards. The thin films were characterized by using Atomic Force Microscope (AFM), ellipsometer, Fourier-transform Infrared Spectroscope (FTIR), respectively. Experimental results have shown that the two-step catalysis remarkably improves strength of the films, and abrasion-resistance and adhesion of the silica films were further increased after the mixture gas treatment. It is attributed to the cross-linking of silica particles in the sols by randomly branched or/and entangled linear chains and more Si–O–Si bonds formed by the mixture gas treatment.     

溶胶-凝胶法制备金属铂高分散的二氧化钛薄膜

Uniform and crack free TiO 2 thin films with highly dispersed platinum were prepared from i PrOH TTIP DEA H 2O system containing H 2PtCl 6·6H 2O as metal source by sol gel method. The microstructure and morphology of the films were characterized by TEM and XRD respectively. It was found that the Pt particles dispersed in the films and had a homogeneous distribution in the shape of sphere with an average size of about 5 nm. This study also showed that the doping with few percent of Pt resulted in the formation of pure rutile phase at a temperature as low as 550 ℃, whereas the same pure phase was formed at the temperature higher than 650 ℃ in TiO 2 or Au/TiO 2 thin films.     

Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(Ethylene Glycol). III. Effect of Chemical Additives

The variation of macroporous morphology has been studied for the titania (TIO₂) films prepared by a sol-gel dip-coating method from the system containing poly(ethylene glycol) (PEG) under the addition of various types of organic solvents. The influence of externally-added solvent is interpreted by considering the compatibility between PEG and the solvent mixture, the volatility of the solvent mixture, and the polycondensation rate of titania oligomers. The macroscopic domain formation is remarkable when the compatibility between the solvent mixture and PEG is relatively poor and the boiling point of external solvent is relatively low.     

Sol-Gel Preparation of Silica Films with Controlled Surface Morphology and Their Application to a Low Reflective Glass

Silica coating films with various surface morphologies, such as flat, porous (with deep pores), concave-convex (with hills and valleys), and convex (with hills on flat plane) structure were prepared from a mixture of two kinds of sols derived from polymerized tetraethoxy-silane (TEOS) and methyltriethoxysilane (MTES). Different surface morphologies were obtained by varying the molar ratio r = MTES/TEOS of the coating solution. The surface was flat for r less than 2.5, porous for 2.5 r < 5, concave-convex for 5 r < 7.5, convex for 7.5 r < 13, and again flat for r larger than 13. For 2.5 r < 5, the apparent refractive index of the silica film with porous morphology was decreased to 1.23 by selecting the solvent and by controlling the relative humidity of the coating atmosphere and the heat treatment temperature. Coating of glass with silica films of low refractive index of 1.23 led to the low reflective glasses with visible light reflectance Rvis of less than 0.2%.     

Preparation and Characterization of Porous Titania by Modified Sol-Gel Method

Mesoporous titania, especially anatase, is attractive due to its potential applications. A novel method to control pore structure of titania, surfactant- or polymer modification, is proposed. The wet gels and gel films, prepared from Ti(O-nC₄H₉)₄ were dried at 90°C and annealed at 500°C after immersion in surfactant or polymer solutions, and mesoporous anatase was obtained. The pore size, pore volume and specific surface area of the surfactant-modified bulk gels, estimated from N₂ absorption-desorption curves, are more than twice larger than those of the gels without modification. The pore size of the surfactant-modified gel films, observed by SEM, are similar to that of the bulk gels. The pore size obviously depended on the size of micelles. The pore size of the gels modified with hydrophilic polymers hardly increased, but the pore volume and the specific surface area increased.     

Bonding Strengths of Titania Sol-Gel Derived Coatings on Titanium

Bioactive ceramic coatings have had poor adhesion to substrate. In this study, the bond strength (tensile strength) of titania gel coating to titanium substrate was studied. In the experiments three different pretreatments were used, namely sodium hydroxide corroding, plasma cleaning and titanium nitride coating. Also the effects of heating temperature, heating in vacuum and titanium surface roughness were studied. The sol properties were altered with valeric acid addition. Samples were analysed by SEM-EDX, AES, AFM and tested by bond strength gauge. Those samples in which the titanium surface was precorroded one hour in sodium hydroxide, predeposited by titanium nitride or ground improved the bonding strengths of titania coatings to over 24 MPa. In these samples a fracture occurred at the glue-coating interface.     

Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol): Effects of Molecular Weight and Dipping Temperature

Macroporous morphology has been examined for the titania (TiO₂) films prepared by a sol-gel dip-coating method from the system containing poly(ethylene glycol) (PEG) under the variations of molecular weight of PEG and dipping temperature. The macroporous morphology is observed only within the limited range of molecular weight because the compatibility between PEG and the solvent mixture is quite sensitive to the molecular weight. The macroscopic domain formation is enhanced at higher withdrawal speed when the dipping temperature is raised, suggesting that the fluidity reduction and the phase separation are more accelerated than the polycondensation due to the enhanced solvent evaporation.     

Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(ethylene glycol). IV. General Principle of Morphology Formation and Effect of Heat Treatment

The variation of macroscopic morphology of the titania (TiO₂) films has been studied at various dipping conditions for a sol-gel dip-coating system containing poly(ethylene glycol) (PEG). The variation of macroscopic morphology is understood consistently by considering both the volume fraction of solvent phase during the phase separation and the water to alkoxide ratio in the sol film. The gel film shrinks and the average pore diameter increases concurrently with the thermal decomposition of PEG while the morphology depends less on the crystallization of titania gel.     

Structural Changes in Sol-Gel Derived SiO2 and TiO2 Films by Exposure to Water Vapor

Structural changes in sol-gel derived thin films by exposure to water vapor were investigated using Fourier transform infrared absorption spectroscopy, ellipsometry and x-ray diffraction. We found that SiO₂ gel films were densified with a decrease in OH groups by the exposure at 60°–180°C. The shrinkage and the peak frequency of ₄ (TO) for the exposed films were comparable to those heated in a dry atmosphere at temperatures above 500°C. However, OH groups in the films were not completely removed by the water exposure. A subsequent annealing above 300°C changed the structure of the water-exposed SiO₂ films with condensation of the remaining OH groups. Although the exposed SiO₂ gel films were amorphous, TiO₂ gel films were transformed to anatase with a decrease in OH groups by the treatments at 80°–180°C.     

Optical Sensing by Silica/Titania Thin Films Doped with Oxacarbocyanine Dye

Photocurrent responses of sol-gel films of silica/titania doped with oxacarbocyanine dye were investigated with a sandwich-type photocell constructed with polymer electrolyte membrane and indium-tin-oxide glass electrodes. At an equilibrium and positive bias voltages, a typical photocell exhibited negative and positive current peaks when the visible light illumination was on and off, respectively. The wavelength dependence of the photocurrent responses well matched to the absorption band of the doped dye. This differential photocurrent response was attributed to trapping of carriers photoexcited in the dye molecules at the defect states in the matrix film. At negative bias voltages, on the other hand, the cell exhibited constant, negative photoelectrochemical currents under illumination. These differential and linear photocurrent responses were affected by the SiO₂/TiO₂ matrix structures depending on the Si : Ti ratio.     

Selective Formation of Spinel Iron Oxide in Thin Films by Complexing Agent-Assisted Sol-Gel Processing

The structure of iron oxide was controlled by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands such as diols. Iron oxides were prepared by calcining the precursor polymers obtained from iron nitrate nonahydrate and diols. When the diols were 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol, α-Fe₂O₃ with corundum structure appeared exclusively or as the main crystalline phase, in spite of the amount of diol used and the calcination temperature. In the case of 1,2-decanediol and 1,2-dodecanediol, when five moles of the diols were used to one mole of iron nitrate and the calcination temperatures were below 400°C, ψ-Fe₂O₃ with spinel structure appeared as the main phase and, when less than five moles of the diols were used, α-Fe₂O₃ appeared exclusively or as the main phase, irrespective of the calcination temperature. This tendency was also observed in thin films. Thus, a transparent magnetic film composed of γ-Fe₂O₃ could be prepared by applying a benzene solution of the iron polymer, obtained with 5 equivalents of 1,2-decanediol, on quartz and calcining the gel film at 350°C.     

Study of Anatase to Rutile Phase Transition in Nanocrystalline Titania Films

Nanocrystalline titania films were prepared by a complexing agent-assisted sol-gel dip-coating process. The effect of acetylacetone, diethanolamine and polyethylene glycol on the structure of the heat-treated titania films was examined by Raman and FTIR spectroscopy and X-ray diffraction. The effect the complexing agents have on the anatase to rutile phase transition during the heat treatment process is studied. The understanding of this effect is expected to enhance our capacity to tailor the composition and morphology of films and thus their properties. The Raman and the infrared spectra of nanocrystalline titania films and the changes induced by the heat treatment were also investigated. We have also studied the size of the crystallites in TiO₂ films and its dependence on the type of complexing agent used.     

溶胶凝胶法制备超疏水二氧化硅涂膜及其表面润湿行为

采用溶胶-凝胶法以正硅酸乙酯(TEOS)和甲基三乙氧基硅烷(MTES)为前驱体制备超疏水SiO2涂层。红外光谱(FTIR)和热重分析(TGA)表征合成SiO2的化学组成,通过透射电镜(TEM)和扫描电镜(TEM)观察制备SiO2的结构形貌,扫描电镜(SEM)和原子力显微镜(AFM)观察SiO2涂膜的表面形貌,通过测试水接触角(WCA)讨论SiO2涂层的表面微观结构与其表面疏水性能的关系。结果表明以TEOS和MTES为共前驱体可以制备得到表面带-CH3基团的SiO2溶胶,SiO2溶胶在老化过程中纳米SiO2粒子由于自组装作用形成草莓状微米-纳米双微观结构,这种结构赋予SiO2涂膜表面不同等级的粗糙度,使得水滴与涂膜表面接触时能够形成高的空气捕捉率和较小的粗糙度因子,与SiO2表面疏水性的-CH3基团共同作用形成类荷叶超疏水结构。     

Macroporous Morphology of the Titania Films Prepared by a Sol-Gel Dip-Coating Method from the System Containing Poly(Ethylene Glycol). I. Effect of Humidity

The influence of humidity upon the macroporous morphology of the titania films has been studied for a sol-gel dip-coating system containing poly(ethylene glycol) (PEG). The water adsorption from the ambient atmosphere modifies the polycondensation rate of TiO2 oligomer and the phase separation rate between the TiO2-PEG complex and solvent mixture, and greatly varies the macroscopic morphology of the resultant TiO2 film.     

玻璃和石英基体上沉积的TiO2薄膜的光催化性能

采用直流磁控反应溅射法,在玻璃和石英基体上制备了TiO2薄膜.在氧气流速超过阈值的条件下溅射,能够得到均匀透明的TiO2薄膜.在玻璃和石英基体上制备的薄膜都由均匀的锐钛矿型氧化钛晶粒组成,在晶粒中间分布着微小的孔隙.尽管在整个光谱区域内石英基体的透射率都比玻璃基体高,但在两种基体上制备的TiO2薄膜的光谱吸收边沿基本相同.薄膜中的Ti都以Ti4 形式存在.两种TiO2薄膜光催化降解甲基橙的能力相差不大.     

CdS Thin Films Deposited by CBD Method on Glass

CdS thin films were prepared by chemical-bath-deposited method and the effect of tempera-ture and time on the properties of CdS thin films was studied. Independent of the deposited temperature, the growth was mainly controlled by the ion-by-ion growth mechanism at the beginning of the film deposition, then the cluster-by-cluster mechanism came to be domi-nant. The growth rate increased faster with the increasing of temperature until the thickness reached the limitation, then thickness instead become thinner. The scanning electron micro-scope results revealed that the morphology of the CdS film changed from pinholes to rough,inhomogeneous surface with increasing deposition time and deposition temperature. The X-ray diffraction results showed the film structure was a mixture of two phases: hexagonal and cubic, and it was very important to controll deposition time to the film's crystal phase. All films in depth of approximate 100 nm existed above 65% transmittance, the absorption edge became 〝red-shift〞 with temperature rising. At 60 and 70 oC, with 20 min deposited-time, the energy band gap was more than 2.42 eV and decreased with time, while at 80 and 90 oC, the energy band gap was less than 2.42 eV and increased little when the time changed from 10 min to 15 min at 80 oC.     

Microstructure and Porosity of Silica Xerogel Monoliths Prepared by the Fast Sol-Gel Method

An adaptation of the fast sol-gel method to the synthesis of xerogel monoliths using tetramethoxysilane (TMOS) as the alkoxide precursor is described in this paper. The procedure involves running the reaction at 70–80°C in an open vessel, which accelerates hydrolysis and condensation and reduces the amount of liquid by expelling excess methanol through outdistillation. This procedure yields crack-free monoliths. The porosity and microstructure of these xerogel monoliths were studied by using N₂ adsorption and desorption and scanning electron microscopy (SEM). The SEM data show that the solid skeletal phase has a globular morphology with particles, 20–40 nm in diameter, arranged into agglomerates a few hundred nm in diameter. The microstructure of the acid-catalyzed xerogel is a consolidation of these agglomerates. The isotherm data show these xerogels to be microporous. In contrast, the base-catalyzed xerogel has a hierarchical morphology with the clusters of agglomerates organized into larger clusters approaching 1 m in diameter. An analysis of the isotherm data shows these xerogels to be less microporous with a narrow distribution of mesopores having an average diameter of 50 Å.