Structural and optical properties of TiO2:SnO2 thin films prepared by sol gel method

ABSTRACT

TiO₂:SnO₂ thin films were deposited on glass substrates, by using sol gel spin coating method with different ratio (3%, 5% and 7%) at 3200 rpm, to study their effect on different properties of TiO₂: SnO₂ thin films. The structural and optical properties of films have studied for different ratio. These deposited films have been characterized by various methods such as X-Ray Diffraction (XRD), Ultra Visible spectroscopy. The (XRD) can be used to identify crystal structure of as deposited films. The Transmission spectra have shown the transparent and opaque parts in the visible and UV wavelengths.     

Preparation of TiO2–Na2O glass by sol–gel method and structural characterization

The applicability of sol–gel process in glass formation of binary system, (100 − x)TiO₂–xNa₂O (x = 10, 20, 30), was investigated and the glasses were prepared successfully by the sol–gel process for the first time. The process of glass formation was checked by using X-ray diffraction measurement and DTA–TG analysis. In the baking step, a DTA peak related to the crystallization of gel was found. The short-range structure of glassified samples was studied by neutron scattering measurement. It is found from the results of neutron scattering measurement that the coordination number of O atom around Ti atom is about 4, and the O atoms around Ti atom form a planer square rather than a regular tetrahedron.     

Structural and conductivity study of Y and Rb co-doped TiO2 synthesized by the sol–gel method

Nanoparticles of titanium dioxide co-doped with Y³⁺ and Rb⁺ were prepared using the sol–gel method and were characterized by thermogravimetric-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. Y³⁺ and Rb⁺ co-doped TiO₂ powder calcined at 800 °C shows a synergistic effect, which shifted the transformation anatase–rutile to higher temperature. X-ray diffraction and XPS analysis revealed that Y³⁺ and Rb⁺ did not enter into the crystal lattices of TiO₂ and are uniformly dispersed onto TiO₂ particles. In this study, the conductivity measurements were performed under ambient atmosphere on undoped and co-doped TiO₂ in order to investigate the defect chemistry by identifying the predominant charge carriers. An increase in the conductivity σ of nano-TiO₂ is shown when the samples were co-doped with Y³⁺ and Rb⁺.     

Synthesis and characterization of V2O5–SiO2 xerogel composites prepared by base catalysed sol–gel method

In this report, the base-catalyzed sol–gel synthesis and electrochemical properties of homogeneous mixed oxide xerogel composite composed of vanadium pentoxide xerogel dispersed in a silica matrix are described. It was verified that the immobilization of vanadium pentoxide xerogel in a silica matrix does not affect its lamellar structure or its electrochemical properties. The silica matrix provides an improvement of the electrochemical properties, mainly in relation to the lithium electroinsertion into the oxide matrix with little decrease in the total charge during successive redox cycles. Moreover, the voltammetric behavior is dependent on the support electrolyte solution with varying cationic species. The effects of different catalysts were investigated.     

Structural and optical properties of TiO2 thin films derived by sol–gel dip coating process

Nanocrystalline thin films of titanium dioxide have been fabricated on glass and silica substrates from partially hydrolyzed precursor solution. These films were subjected to heat treatment for 1 h at temperatures 100, 200, 300, 400, 500, 600, 700, 800 and 900 °C and characterized by XRD, SEM, XPS and optical techniques. As deposited films are found to be amorphous and also contain hydroxyl and organic functional groups. Films heat treated above 100 °C do not contain hydroxyl and organic functional groups. Microcrystalline behavior is observed in the films heat treated above 300 °C. Crystallite size increases from ∼5 to 50 nm as sintering temperature is increased from 300 to 700 °C. Formation of anatase phase with c-axis length 7.03 Å is observed in the films annealed up to 700 °C. These films peel off from the substrate beyond 700 °C annealing temperature. Density as well as refractive index of the films increases with increase in annealing temperature up to 700 °C. Refractive index is found to show Cauchys behavior. Transmission better than 70% is observed in the visible range. There is a strong absorption around 370 nm, which is attributed to band gap absorption of the material.     

Ag/TiO2的制备及光催化性能研究

以钛酸丁酯为钛源,采用溶胶-凝胶法制备了Ag掺杂纳米TiO2,结合XRD、TEM、Uv-vis等测试手段,对样品的结构和性能进行了表征.以甲基橙溶液为目标降解物,探讨了Ag掺杂纳米TiO2的光催化活性,分析了Ag掺杂纳米TiO2提高光催化性能的机理.结果表明,Ag掺杂使TiO2晶粒减小,拓展了TiO2的光谱响应范围,降低了光生电子和空穴的复合几率;Ag掺杂后,TiO2光催化剂的吸收光谱向可见光区发生红移.Ag掺杂量为n(Ag)∶n(TiO2)=0.08;,紫外光下240 min,Ag掺杂纳米TiO2前后材料对甲基橙溶液去除率由60.3;提高到83.1;.     

Intense luminescence of amorphous Eu2O3 prepared by aqueous sol–gel method

Amorphous Eu₂O₃ was prepared by an aqueous sol–gel method. Emission due to the ⁵D₀ → ⁷F_J (J = 0, 1, 2) transitions of Eu³⁺ ions were observed. The dominant transition was the ⁵D₀ → ⁷F₂ red emission of Eu³⁺. The properties of the as-prepared samples were different with changes in the annealing temperature. To investigate the luminescence properties of the amorphous Eu₂O₃, the temperature-dependent photoluminescence (PL) spectra of samples annealed at 600 °C were measured in the temperature range 77–300 K. PL peak positions were unchanged with the change of temperature.     

Synthesis of Fe-doped nanosized SnO2 powders by chemical co-precipitation method

Fe-doped nanosized SnO₂ powders were prepared by chemical co-precipitation technique using SnCl₄ and FeCl₃ as starting materials and water as a carrier. Experimental results show that the grain size of Fe-doped SnO₂ crystallites is smaller than 5 nm, and the particle size is smaller than 15 nm. When the calcination temperature is below 650 °C, the SnO₂ crystal has tetragonal lattice structure. At higher temperature the particles become a two-phase mixture of tetragonal SnO₂ and hexagonal Fe₂O₃ crystallites. Fe doping can obviously prevent the growth of nanosized SnO₂ crystallites, and a higher Fe-doping concentration is more effective to prevent the growth of nanosized SnO₂ particles when the calcination temperature is below 550 °C.     

Synthesis by precipitation method and investigation of SnO2 nanoparticles

In this paper the synthesis of SnO₂ nanoparticles with average particle size up to about 70 nm using SnCl₂2H₂O and NH₄OH in 1‐botanol solution by the precipitation method is reported and the inhibition of sodium dodecyl sulphate (SDS) on the SnO₂ particle growth is investigated by soaking SnO₂precursor in the SDS solution for 24 h. The as‐prepared SnO₂and SDS modified‐SnO₂ powders, then, were calcined at different temperatures and the X‐ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FT‐IR) were used to characterize the output samples. The XRD results reveal that the structure of tin‐dioxide is tetragonal rutile and the as‐prepared SnO₂ nanoparticles grow with increasing the annealing temperature, while the SDS treatment prevents the particle growth under the same condition. Furthermore, the FT‐IR results indicate the formation of tin‐hydroxyl group which are then converted into tin‐dioxide with heat treatment. Further characterization of the samples by the transmission electron microscopy (TEM) and the photoluminescence (PL) spectroscopy was carried out. The room temperature PL spectra of SnO₂exhibits broad and strong peak attributed to the surface defects such as oxygen vacancies and intensity of which decreases with the increase in particle size. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimization of parameters for deposition of ZnO films by sol gel using Taguchi method

ABSTRACT

ZnO transparent conductive films were deposited on glass substrates by sol-gel spin coating method. Taguchi method was used to find the optimal deposition parameters, three influential parameters were selected in this experiment, Concentration of zinc (II) ions. Zn²⁺, annealing temperature T_r and pre-annealing temperature T_P. By employing the analysis of variance, we found that the annealing temperature T_r and the precursor Zn²⁺ are the most influencing parameters on the properties of ZnO films. Under the optimized deposition conditions, the ZnO films showed high crystal quality, and high transmittance of 90% in the visible region.     

Electrical conductivity and photoconductivity studies of TiO2 sol–gel thin films and the effect of N-doping

Several sol–gel TiO₂ thin films, N-doped and undoped, were prepared using the dip-coating technique. Dark conductivity in vacuum and in air gives information on the role of the adsorbed oxygen or water and the influence of nitrogen. Transient photoconductivity in vacuum and in air was studied with illumination time for various light intensities and found to be very sensitive to the environment. The rise and decay are much faster in air than in vacuum, suggesting the predominant mechanism of conduction in each case. The role of the presence of nitrogen is also discussed.     

Synthesis of TiO2 nanorings and nanorods on TCO substrate by potentiostatic anodization of titanium powder

Various TiO₂ nanostructures, such as nanorings, nanorods were synthesized via potentiostatic anodization of titanium powder under different conditions. The morphology of the obtained TiO₂ nanostructures can be easily tuned by varying applied voltage. The crystal structure, compositional information and morphological structures were characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectra (XPS) and field emission scanning electronic microscopy (FESEM). XRD and XPS analysis confirmed the anodization products were TiO₂. A possible formation mechanism was suggested on the basis of the shape evolution of TiO₂ nanostructures observed by FESEM. The results revealed that the applied voltage played an important role in the formation of various nanostructures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical characterization of bioresorbable sol–gel derived SiO2 matrices prepared at protein-compatible pH

Sol–gel derived SiO₂ have been shown to be biocompatible and bioresorbable and they have potential use in living tissue, e.g., in bone regeneration and controlled drug delivery. Bioresorbable SiO₂ is a potential alternative for the controlled delivery of large biologically active agents, such as proteins and peptides. The aim was to prepare SiO₂ matrices with varying bioresorption rate at protein-compatible conditions and to characterize the chemical features of the matrices. SiO₂ was prepared in two morphologies, monoliths by casting and microparticles by spray drying. A model protein was encapsulated into the SiO₂ matrices. Materials were carefully characterized with FTIR- and Raman spectroscopy, TGA-FTIR, solid state ²⁹Si MAS NMR, SEM and matrix dissolution was measured in simulated physiological conditions. It is shown that both fast and slowly dissolving SiO₂ matrices could be prepared at protein-compatible conditions. Fast-dissolving SiO₂ microparticles contained a high proportion of Q³ and a low portion of Q⁴ indicating poor cross-linking of SiO₂ species and an increased amount of hydrolysable terminal groups. Spectroscopic techniques and TGA-FTIR show that organic residues and moisture are left in the matrices. The amount of organic residues is larger in the fast-dissolving SiO₂ matrices, but it does not significantly affect the bioresorption rate.     

Synthesis of fluorine doped silica gel and its properties at high temperature

Fluorine doped silica gels were synthesized by using the sol-gel processes of (A) SiF₄(g) and H₂O(1) and (B) the mixed solution of Si(OC₂H₅)₄, C₂H₅OH, H₂O and H₂SiF₆. By the former process we obtained a gel of relatively high fluorine content (8–12 at.%F), while we could synthesize the gel of 0–12 at.% F by adjusting the F/Si ratio of the starting solution mixtures by the latter process.

The defluorination behavior and the structural change of these gels at high temperature were studied by heating-mass spectrometry, IR and ESR measurements. The results revealed the following: (1) defluorination by liberation of SiF₄(g) was admitted from temperatures at about 400°C and was controlled by the diffusion of fluorine in the gel bulk. (2) The peak separation analysis for the IR band of 1300-900 cm⁻¹, where the stretching vibrations of Si---O and Si---F appear, showed that the change of the band shape resulted from the increase or the decrease of the Si---F bonds and the change of the bond angle of Si---O---Si as well as the change of the force constant accompanied by fluorination or defluorination. (3) The defects of the Si E′ center were induced by X-ray irradiation depending on the degree of the defluorination, and were reduced by the heat treatment. However, with the heat treatment at temperatures higher than 1000°C, the E′ center increased again. The IR spectra suggest that this behavior might correspond to the gel-glass trasition.     

Synthesis and structural characterization of P2O5–CaO–Na2O sol–gel materials

Ternary phosphate-based glasses in the system P₂O₅–CaO–Na₂O were synthesized using the sol–gel approach. Glasses in this system have the potential for use as bioactive materials. A mixture of mono- and dialkyl phosphate PO(OH)_3−x(OC₂H₅)_x (x = 1, 2) and alkoxides of sodium and calcium in an ethylene glycol solution were used as precursors. One of the compositions has also been synthesized by sonocatalysis (application of ultrasonic vibration to the sol). The systems synthesized, which remain fully amorphous even after calcination at 400 °C given the appropriate composition, have been characterized using X-ray diffraction (XRD). Thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The structure of the phosphate network has been studied as a function of composition using Fourier transform infrared spectroscopy (FT-IR) and ³¹P MAS NMR.     

Zirconia foams prepared by integration of the sol–gel method and dual soft template techniques

This paper presents a new method to produce basic zirconium sulfate foams showing hierarchic porosity, based on a dual pores templating process by oil drops and gas bubbles dispersed into a hydrosol, followed by its fast gelation to form the porous patterned inorganic network. As revealed by mercury porosimetry, the hierarchical structures of final inorganic foams are composed by large gas bubble templated macro-pores (modal size 7–33 μm) and emulsion-templated supermeso-pores of modal size tunable around 3 and 0.4 μm. The relative population and modal pore size of each family and the overall porosity of the final inorganic foam can be varied by adjusting the emulsification and air–liquid foaming stirring speed, and the oil/sol ratio.     

A catalyst-free method to silicon nanowires at relative low temperature

Well-crystallized straight Si nanowires (SiNWs) were successfully prepared in large scale via a facile reaction between NaN₃ and Na₂SiF₆ at 600 °C without using any catalyst. Characterization by X-ray powder diffraction and transmission electron microscopy demonstrates that the as-obtained product is pure-phase cubic SiNWs with diameters of 40 nm or so, and lengths of several micrometers. And the SiNWs with spherical tips can be obtained at a temperature as low as 300 °C. Heating temperature and holding time have crucial influence on the synthesis and morphology of the SiNWs. An oxide-assisted growth mechanism is responsible for the formation of the SiNWs.     

Synthesis by sol–gel process,characterization and catalytic activity of vanadia–silica mixed oxides

This paper describes a new route for the preparation of V₂O₅–SiO₂ mixed oxides with high vanadium content and high surface area by the sol–gel processing method. Dry samples were characterized by powder X-ray diffraction, electron paramagnetic resonance, Fourier-transform infrared, and energy dispersive X-ray spectrometry. Our results show that the incorporation of vanadium pentoxide into the silica matrix was obtained by intimate mixing of the two different inorganic polymers (Si–O and V–O based polymers), and the overall structure is held together by a Si–O–Si network interpenetrated with V–O–V polymeric chains. The catalytic activity of the V₂O₅–SiO₂ mixed oxides was evaluated in the oxidation of the cyclooctene and styrene in liquid phase.     

Influence of TiO2 on proton conductivity in fuel cell electrolytes based on sol–gel derived P2O5–SiO2 glasses

P₂O₅–TiO₂–SiO₂ based glasses have been prepared by a sol–gel process. The glasses were characterized by structural, thermal, nitrogen adsorption–desorption and conductivity measurements. The structural formation has been confirmed by the FTIR and NMR analysis. The proton conductivity of the glasses increased linearly with increase in temperature. Glasses with an average pore size less than 2 nm showed higher values of proton conductivity in humid atmosphere. The conductivity value increased from 6.47 × 10⁻⁴ S/cm to 3.04 × 10⁻² S/cm at 70% RH in the temperature range 30–90 °C. We observed in fuel cell measurements that the performance of the E1 electrode is superior to that of the other electrodes at the same operating condition. The power density shows a similar pattern to current density.     

Time evolution of a sol–gel process monitored by Mn2+ EPR spectroscopy

The time evolution of the tetraethoxysilane (TEOS)-based sol–gel process was investigated by EPR spectroscopy of a Mn²⁺ spin probe. Analysis of the EPR spectra recorded at room temperature (RT) and liquid nitrogen temperature (77 K) showed that the values of the g-factor (for the central Mn²⁺ sextet) were found to be, within experimental error, identical during the sol–gel process evolution. However, the peak-to-peak half width, ΔB_pp, of the spectral lines recorded at RT, the splitting of the forbidden hyperfine lines (and thus the zero-field splitting parameter, D) recorded at 77 K, and the averaged hyperfine splitting constant, A_av, at both temperatures, were found to change significantly during the various stages of the sol–gel process. These EPR spectral parameters allow us to monitor changes in the TEOS-based sol–gel reaction mixture during the liquid-to-solid-state transition. It was clearly demonstrated that the sol-to-gel transition as well as the hydration and dehydration process of gels could be successfully studied by Mn²⁺ EPR spectroscopy.