Controllable preparation of nanosized TiO<Subscript>2</Subscript> thin film and relationship between structure of film and its photocatalytic activity

TiO₂ nano-crystalline film and fixed bed photocatalytic reactor were prepared by the sol-gel process using tetrabutylorthotitanate as a precursor and glass tube as the substrate. XRD, AFM, SEM and thickness analysis results indicate that the preparation of nano-crystalline film can be controlled by optimizing experiment process. Under the optimized process, the phase of TiO₂ in film is anatase, and the grain size is 3–4 nm. The size of particles, which is about 20-80 nm, can be controlled. The thickness of monolayer film is in nanometer grade. The thickness and particles size in films growing on nanometer film can also be controlled in nanometer grade. As a result, the crack of film can be effectively avoided. Rhodamine degradation results using UV-Vis spectrophotometer show that the activity of nano-crystalline film in the photocatalytic reactor has a good relation with the diameter of TiO₂ particles, that is, the film shows high activity when the size is 20 –30 nm and greatly reduced when the size is above 60 nm. The activity of film does not decrease with the increase of film thickness, and this result indicates that nano-crystalline film has no ill influence on the transmissivity of ultraviolet light.     

Influence of Temperature on Surface Morphology and Photoelectric Performance of CuAlO2 Thin Films

CuAlO₂ thin films were prepared on sapphire substrate by sol-gel method. The influences of annealing temperature, heating rates and annealing time on composition, morphology and photoelectric performance of film were investigated. The results of X-ray power diffraction, scanning electron microscope, transmissivity, and hall parameter tests showed that the CuAlO₂ phase was relatively pure when the annealing temperature was above 950 °C. The higher the temperature, the higher the peak position. Under the optimal conditions, CuAlO₂ film exhibited the best transmittance (90%) and the highest conductivity (1.23 S cm^?1). On this basis, increasing the heating rate and annealing time was in favor of enlarging the size of the particles and the film grain growth direction tended to be unified.     

Structural and Electrochemical Properties of Sol-Gel Derived Mo : CeO2, Si : Mo : CeO2 and Si : CeO2 Nanocrystalline Films for Electrochromic Devices

Mo:CeO₂, Si:CeO₂ and Mo:Si:CeO₂ films were made by the sol-gel dip-coating technique. XRD investigations of the analogously prepared powders revealed that particle grain size of CeO₂ with the addition of Mo, Si or both decreased. FT/IR spectra of the corresponding films showed that no separate Mo-oxide phase was formed while the Si containing CeO₂ films had nanocrystallites of ceria as well as amorphous silica. Electrochemical investigations (cyclic voltammetry, chronocoulometry) performed in protic (0.1M LiOH) and aprotic (1M LiClO₄/propylene carbonate(PC)) electrolytes showed that additions of Mo:, Si: and Mo: Si:-to ceria increased ion storage ability. The suitability of films as optically passive counter electrodes was demonstrated by making electrochromic cells with asymmetric and symmetric configurations using a Li⁺ doped ionic conductor (ormolyte^®) and an electrochromic tungstophosphoric acid (WPA)/TiO₂ gel film.     

Effect of alumina incorporation on restricting grain growth of nanocrystalline tin(IV) oxide

In this project, nanocrystalline SnO₂ powders were successfully prepared by (a) citrate sol-gel and (b) direct precipitation methods. Powders were characterized using thermal analysis techniques (DTA-TG-DSC), X-ray powder Diffraction (XRD), surface area (BET) and electrical conductivity measurements. XRD patterns showed the presence of the cassiterite structure. SnO₂ particles, prepared through sol-gel method exhibit crystallite sizes in the range from 3.1 to 22.3 nm when the gel is heat treated at different temperatures up to 900°C. SnO₂ nanocrystallites prepared by the precipitation method are comparatively larger in size. The higher specific surface area was obtained for the powder prepared using sol-gel method and the obtained average grain size (d) is relatively large compared with that of the average crystallite size. The powders show a semiconducting behavior with increasing temperature. The higher conductivity obtained for SnO₂ prepared by sol-gel method can be attributed to their smaller average crystallite size. XRD of alumina doped powder exhibits finer particles than pure SnO₂. TEM images showed that the particles are spherical in shape and consist of a core of SnO₂ surrounded by a coating of alumina. The calculated surface area was found to decrease with temperature increases. Due to the effective role of Al₂O₃ additive as a grain growth inhibitor for the matrix grains, the observed surface area for the coated materials are predominantly higher than for the uncoated materials.      

Land-ocean interaction in modern delta formation and development: A case study of the Pearl River delta,China

SnO₂ doped with La, Ce, Sm, Zn, Ca, Al and Sb was prepared by sol-gel technique and characterized by TEM, BET, XPS and XAES. The effect of the dopants on the grain sizes of SnO₂ was described and especially the effect of dopants on the distribution of the electronic state density (DESD) of Sn4d orbital was studied deeply by using X-ray-induced Auger electron spectroscopy (XAES). It was observed that the dopants could influence not only the grain sizes of SnO₂ but also electronic structure of SnO₂, as well as the stability of the doped SnO₂ samples. The experiment results indicated that the structure and stability of SnO₂ film could be improved by the chemical modification of the dopants.     

Land-ocean interaction in modern delta formation and development: A case study of the Pearl River delta,China

SnO₂ doped with La, Ce, Sm, Zn, Ca, Al and Sb was prepared by sol-gel technique and characterized by TEM, BET, XPS and XAES. The effect of the dopants on the grain sizes of SnO₂ was described and especially the effect of dopants on the distribution of the electronic state density (DESD) of Sn4d orbital was studied deeply by using X-ray-induced Auger electron spectroscopy (XAES). It was observed that the dopants could influence not only the grain sizes of SnO₂ but also electronic structure of SnO₂, as well as the stability of the doped SnO₂ samples. The experiment results indicated that the structure and stability of SnO₂ film could be improved by the chemical modification of the dopants.     

The diffusion of Pt in BST films on Pt/Ti/SiO2/Si substrate by sol-gel method

Barium strontium titanate (Ba_0.65Sr_0.35TiO₃) ferroelectric thin films have been prepared by sol-gel method on Pt/Ti/SiO₂/Si substrate. The X-ray diffraction (XRD) pattern indicated that the films were a polycrystalline perovskite structure and the atomic force microscope (AFM) image showed that the crystallite size and the root mean square roughness (RMS) were 90 nm and 3.6 nm, respectively. The X-ray photoelectron spectrum (XPS) images showed that Pt consisting in BST thin films was the metallic state, and the Auger electron spectroscopy (AES) analysed the Pt concentration in different depth profiles of BST thin films. The result displayed that the Pt diffusion in BST thin film is divided into two regions: near the BST/Pt interface, the diffusion type was volume diffusion, and far from the interface correspondingly, the diffusion type became grain boundary diffusion. In this paper, the previous researcher’s result was used to verify our conclusion.     

Study on the Superhydrophilicity of the SiO2-TiO2 Thin Films Prepared by Sol-Gel Method at Room Temperature

Nanoscale SiO₂-TiO₂ composite thin films with the thickness of about 100 nm were prepared by sol-gel method at room temperature in air. The chemical states of the elements on the surface and near the surface were measured by XPS. The results showed that the Ti on/near the surface of the thin films existed not only as TiO₂ but also as Ti₂O₃. Part of the TiO₂ was changed to Ti₂O₃ after UV irradiation. The crystalline structure of the TiO₂ in the SiO₂-TiO₂ thin films was anatase with the crystallite size of 14–20 nm. It was found that the thin film prepared at room temperature in air has good superhydrophilic property and has strong adherence to the substrate.     

Structure and properties of (1−x)(0.6Pb(Zn1/3Nb2/3)O3-0.4Pb (Mg1/3Nb2/3)O3)-xPbTiO3 thin films with perovskite phase promoted by polyethylene glycol

The preferential formation of a pyrochlore structure is a knotty problem in the preparation of Pb(Zn_1/3Nb_2/3)O₃ (PZN)-based thin film materials and its presence is significantly detrimental to the dielectric and piezoelectric properties. In this study, 40 mol% of PZN was replaced with Pb(Mg_1/3Nb_2/3)O₃ (PMN) for obtaining a perovskite composition around a morphotropic phase boundary (MPB), (1−x)(0.6PZN-0.4PMN)-xPT ((1−x)PZMN-xPT, PT: PbTiO₃) where x = 0.23. The thin films with this composition were prepared with a polyethylene glycol (PEG) modi-fied sol-gel method on LaAlO₃ substrates. The microstructural evolution of the films on heat treatment was examined with X-ray diffraction. With the aid of PEG, the formation of the pyrochlore phase was suppressed and the perovskite phase formed directly from the amorphous gel film. The multilayer films with a thickness around 0.25 μm showed a single perovskite phase without any detectable pyrochlore structure. Microscopic images showed uniform grain size of a few tens of nanometers. The role of the polymer dramatically promoting the perovskite phase was investigated with the aid of X-ray photoelectron spectroscopy and thermal analysis. The dielectric constant of the obtained film was 4160 at 1 kHz. The film demonstrated typical ferroelectric hysteresis loops and exhibited excellent piezoelectric performance.     

Sol-gel derived (LiCl)2-Al2O3-SiO2 thin film solid electrolyte

(LiCl)₂-Al₂O₃-SiO₂ thin film solid electrolyte was prepared by a sol-gel process with a spin coating technique. The thin film was studied by X-ray photoelectron spectroscopy (XPS) and ac impedance. The ionic conductivity of the solid electrolyte film is comparable to that of the bulk xerogel. The highest conductivity measured by ac impedance is 2.5×10^–4 S·cm^–1 at 300°C with E_a=0.75 eV.     

Structure and Optical Properties of 0.1BiFeO3-0.9SrBi2Nb2O9 Thin Films Using a Modified Sol-Gel Technique

Fe-doped SrBi₂Nb₂O₉ precursor solution was synthesized using bismuth nitrate Bi(NO₃)₃·5H₂O, strontium nitrate Sr(NO₃)₂, iron nitrate Fe(NO₃)₃·9H₂O, and niobium ethoxide Nb(OC₂H₅)₅ as starting materials, ethylene glycol monomethyl ether (C₃H₈O₂) as the solvent. 0.1BiFeO₃-0.9SrBi₂Nb₂O₉ thin films were prepared on fused quartz substrates using sol-gel processing. The surface morphology and crystal structure and optical properties of the thin films were investigated. The thin film annealing at 400°C were found to be amorphous, and the thin films crystallize to a perovskite structure after a post-deposition annealing at 600°C for 1 h in air. The grain of thin film was evenly distributed. The thin films exhibit the designed optical transmission, while the optical transition is indirect in nature. Their optical band gap is about 2.5 eV.     

The dependence of the conductivity of SiO2-γ-Fe2O3 film composites on air humidity

The influence of humidity on the electrophysical characteristics of SiO₂-γ-Fe₂O₃ film composites prepared by the sol-gel method was studied. The conductivity of the composites in air at room temperature was largely determined by the conductivity of a layer of adsorbed water. Conductivity changed by several orders of magnitude as air humidity increased from 40 to 98%. The time of the attainment of a stationary conductivity value did not exceed several dozen seconds. SiO₂-γ-Fe₂O₃ film composites could therefore be considered a promising material for high-sensitivity high-speed humidity sensors.     

TiO2 nanoparticles synthesized in an aprotic solvent and applied to prepare high-refractive-index TiO2-polyimide hybrid thin films

In this study, very small (2–5 nm) TiO₂ nanoparticles were synthesized in an aprotic solvent, N,N-dimethylacetamide, via hydrolysis and condensation of titanium alkoxide at room temperature. The synthesized TiO₂ sol showed 30 days of storage stability and could be used to prepare high-refractive-index TiO₂-polyimide hybrid thin films by an ex-situ method that involved a spin coating and multistep baking process. The field emission scanning electron microscope image showed a flat and uniform morphology of the hybrid thin film. TiO₂ domains were in the nanometer range, thus avoiding light scattering. The refractive index at 633 nm of the hybrid thin film reached 2.05, which suggested potential applications of the film to anti-reflective coatings and optical waveguides.     

Thin films of functionalized amorphous silica for immunosensors application

Within the framework of the development of an optical immunosensor, the sol-gel process has been used to prepare a thin film of amorphous silica, deposited by spin coating on a gold-coated glass slide, and possessing chemically active functional groups (SH, NH₂...). After activation of the sol-gel film in aqueous buffers by a bifunctional coupling agent, biological molecules such as antibodies could be covalently bonded on or inside the sol-gel film. Therefore, the behavior in aqueous solutions of the functionalized silica thin films has been analysed by Surface Plasmon Resonance (SPR) and guided wave propagation. Results show a modification of the thickness and of the refractive index of the silica film. Pore size range has been deduced by the infiltration of different molecular weight dextran molecules diluted in water into the sol-gel material. Immunosassays have demonstrated biological activity of antibodies which are covalently linked to or entraped in the sol-gel film.     

Effect of optical property of surfactant-treated TiO2 nanostructure on the performance of TiO2 photo-electrochemical cell

TiO₂ nanostructures have been treated using different kind of surfactant to modify its optical absorption and morphology. TiO₂ nanostructures were prepared via simple method on indium tin oxide (ITO) surface, namely, liquid-phase deposition technique (LPD) at 50°C. The TiO₂ nanostructures film with a thickness of about 236 nm was annealed at 400°C for 1 h in the air to enhance the interconnectivity of the particles. The dense and compact TiO₂ nanoparticle with different shape, particle size and surface morphology was used as a photovoltaic material in a photo-electrochemical cell of ITO/TiO₂/electrolyte/platinum. TiO₂ nanostructure films were treated with three different kinds of surfactants: cetyltrimethylammonium bromide (CTAB), hexamethylenetetramine (HMT) and polyvinylpyrrolidone (PVP). It was found that the film treated with HMT performed best, with a J _sc of 57.5 μA/cm². In conclusion, optical absorption, band gap and grain size of TiO₂ nanostructure influenced the performance of the cell.     

Preparation of TiO2 Thin Film Photocatalysts by Dip Coating Using a Highly Viscous Solvent

TiO₂ thin film photocatalysts coated onto soda lime glass were prepared by a dip coating process using a highly viscous solvent. The source of the TiO₂ was tetraisopropyl orthotitanate, and -terpineol was used as the solvent. Two types of thin film preparation procedures based on dip coating (a sol-gel system and thermal decomposition system) were used to prepare the samples. TiO₂ thin films were obtained after calcination at 450°C for 1 hour. The film thickness obtained with a single dipping was proportional to the viscosity of the dip coating solutions. The obtained thin films were transparent with a thickness of 1 m. The crystal form of the obtained photocatalyst films was anatase alone. The thin films were formed with aggregated nano-sized TiO₂ single crystals (7–15 nm). The photocatalytic activity of the TiO₂ thin films, as evaluated by the photooxidation of NO (1 ppm) in dry air, was as high as our previous TiO₂ thin films prepared by the sol-gel method.     

Effect of hexamethylenetetramines (HMT) surfactant concentration on the performance of TiO2 nanostructure photoelectrochemical cells

Hexamethylenetetramine (HMT) surfactant was used to modify the morphology of TiO₂ thin film nanostructure prepared by a simple technique, namely, liquid phase deposition (LPD) during its growth process. In order to obtain various surface morphologies of TiO₂ nanostructures, the concentration of HMT was varied from 10 to 100 mM. It was found that with an increase in concentration of HMT, the morphology of TiO₂ nanorod in term of its grain size decreases due to the particles agglomeration grown on the surface. The TiO₂ nanostructures with various grain sizes were utilized as photovoltaic materials in photoelectrochemical cell measurement. The highest performance of the cell in terms of the short-circuit current density, J _sc was 0.069 mA cm^?2. This result was achieved from the TiO₂ nanorod cell with the smallest grain size, 12 ± 2 nm. The J _sc of the cell increased with concentration of HMT. The cell utilizing the TiO₂ nanostructure with the smallest grain size possessed the best interfacial contact at the TiO₂/electrolyte containing iodide/triiodide redox couple. Thus, the redox reaction was optimised at this interface.     

Synthesis of SnO<Subscript>2</Subscript> nanopowders by a sol-gel process using propanol-isopropanol mixture

A simple sol-gel process is proposed for synthesizing SnO₂ nanopowders utilizing normal propanol and isopropanol mixture instead of just using normal alcohols such as ethanol, propanol or butanol for Sol preparation. No surfactant was used in this Sol preparation process. The structure of sol is studied by FT-IR-ATR technique. On altering propanol to isopropanol ratio, three different nanopowders were obtained. X-ray powder diffraction, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction pattern (SAED) and BET techniques were used to characterize prepared powders. Results show that smaller grain size was obtained via altering alcohols ratio. In addition, Merck commercial SnO₂ powder was also used as a reference material for comparing purposes; because it has nanometer scale (ca. 60 nm). HRTEM images show that obtained nanopowders were polycrystalline and their average diameters fall into the range of 6–80 nm. Finally, the effect of alkoxide ligand size through sol-gel synthesis on product particle size is discussed.      

染料敏化太阳能电池中大孔TiO2薄膜电极的制备及应用

采用溶胶-凝胶水热法制备了TiO₂纳晶薄膜电极，晶型为锐钛矿型。为了提高电极的光电性能，利用聚苯乙烯小球做造孔剂，制备了含有大孔隙的TiO₂纳晶薄膜电极，孔径约为200 nm，该电极具有较好的光漫反射性能，更重要的是球形大孔的存在，提高了凝胶电解质在TiO₂薄膜电极中的渗透和I₃^-离子的扩散性能，与不含大孔的TiO₂电极相比，电池的短路光电流提高约2 mA·cm^-2，光电转换效率提高0.6%。     

The evolution of morphology of ordered porous TiO2 films fabricated from sol-gel method assisted ZnO nanorod template

Ordered porous TiO₂ films, including TiO₂ nanotube arrays, are fabricated by a sol-gel dip-coating approach via ZnO nanorod templates obtained from aqueous solution approach. The results indicate that the morphologies of ordered porous TiO₂ films have been great affected by the sol-gel dip-coating cycle number. Open-ended TiO₂ nanotube arrays can be obtained in optimum dip-coating cycle numbers. The TiO₂ nanotubes with the inner diameter matching well with the diameters of ZnO nanorods, are well assembled and separate each other. When the cycle number is less than this optimum value, no intact porous TiO₂ film can be obtained. As the cycle number is larger than this optimum value, an ordered porous TiO₂ film with many throughout holes is formed. The evolutive mechanism of ordered porous TiO₂ films is proposed.