The Effect of SiO2 Addition on the Grain Size and Photocatalytic Activity of TiO2 Thin Films

The uniform transparent TiO₂/SiO₂ nanometer composite thin films were prepared via sol-gel method on the soda lime glass substrates, and were characterized by X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy, UV-VIS spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET surface areas. It was found that the addition of SiO₂ to TiO₂ thin films could suppress the grain growth of TiO₂ crystal and increase the hydroxyl content of the surface of TiO₂ films. The photocatalytic activity of the as-prepared TiO₂/SiO₂ composite thin films increases for SiO₂ content of less than 5 mol%.     

Nanorods of Various Oxides and Hierarchically Structured Mesoporous Silica by Sol-Gel Electrophoresis

In this paper, we report the template-based growth of nanorods of oxides and hierarchically structured mesoporous silica, formed by means of a combination of sol-gel processing and electrophoretic deposition. Both single metal oxides (TiO₂) and complex oxides (Pb(Zr_0.52Ti_0.48)O₃) have been grown by this method. This method has also been applied to the growth of nanorods of mesoporous silica having an ordered pore structure, where the pores are aligned parallel to the long axis of the nanorod. Uniformly sized nanorods of about 125–200 nm in diameter and 10 m in length were grown over large areas with near unidirectional alignment. Appropriate sol preparation yielded the desired stoichiometric chemical composition and crystal structure of the oxide nanorods, with a heat treatment (500–700°C for 15–30 min) for crystallization, densification and any necessary pyrolysis.     

Tris（2,2＇-bipyridyl） Ruthenium（Ⅱ） Doped Silica Film Modified Indium Tin Oxide Electrode and Its Electrochemiluminescent Properties

An approach was reported to synthesize silica hybridized ruthenium bipyridyl complex through amidation reaction by covalent attachment of bis（bipyridyl）-4,4＇-dicarboxy-2,2＇-bipyridyl-ruthenium to （3-aminopropyl）-triethoxysilane. The hybrid complex then was gelatinized through acid catalytic hydrolysis method and a sol-gel modified indium tin oxide electrode was prepared via spin coating technique. As prepared indium tin oxide electrode possesses good stability therein with excellent electrochemiluminescence behavior.     

Cobalt Ion Incorporation into Periodic Mesoporous Organosilica Materials Synthesized by Co-condensation of 1,2-Bistrimethoxysilylethane with 3-Glycidoxypropyltriethoxysilane

Bifunctional periodic mesoporous organosilica materials with and without cobalt ion incorporation were synthesized by co-condensation of 1,2-bistrimethoxysilylethane (BTME) with 3-glycidoxypropyltriethoxysilane (GPTS) in the presence of cetyltrimethylammonium bromide. Nitrogen gas adsorption on samples with varying ratios of BTME:GPTS revealed that increasing the amount of GPTS affects pore size, surface area and pore volume as well as shapes of the isotherms and hysteresis loops. The hysteresis loops of the Type IV isotherms obtained for GPTS-modified ethane silica materials (without cobalt ion) change from Type H3 to Type H4 with increasing GPTS content. There is a tendency for pore sizes to change from mesopore to micropore when the amount of GPTS is increased. Isotherms of cobalt ion incorporated GPTS-modified ethane silica materials change from Type IV to Type I with increasing GPTS content. The surface area, pore volume and pore diameter decrease with increasing loading of GPTS as well as after cobalt ion incorporation. Thermogravimetric analysis and differential thermal analysis show that the surfactant is removed by solvent extraction. Cobalt ion incorporation is confirmed by powder X-ray diffraction and Raman spectroscopy.     

Chemical Modification of Silica Gels

Highly porous pure and polyethyleneglycol (PEG)-doped silica gels have been prepared from tetraethyl orthosilicate (TEOS) in ethanol using NH₄OH base-catalysis. Addition of PEG to the SiO₂-system increases the average particle size and most frequent pore diameter of the resultant gels while their total surface area decreases. The viscosity of the sol increases with PEG concentration and passes through a maximum with increasing molecular weight at PEG 200. Results obtained indicate a definite interaction of the polymer with SiO₂ and that this interaction is not as a result of direct formation of Si– O– C linkage, but is more likely to be due to hydrogen bonding between the hydrated PEG and the Si– O– Si network. Structure-process correlations are considered.     

Preparation and Characteristics of Porous Silica Films by a Modified Base-Catalyzed Sol-Gel Process Containing PVA: II. Film Preparation

Porous SiO₂ films were successfully deposited on silicon substrates by a modified base-catalyzed Sol-Gel process (MBCP) containing polyvinyl alcohol (PVA). The process conditions, such as the gelation time, the synthesis temperature, the stabilizing agent of the precursor solution and the spin coating speed, the heat-treatment, the annealing temperature of the film on the microstructure and porosity of porous SiO₂ films were systematically investigated by SEM, XRD and ellipsometry techniques. This study provides a novel preparation technique for the porous SiO₂ film. Using this process, the resultant film can reach a thickness of 3.6 m for one layer, a porosity of 25–50%, a low thermal conductivity of 0.11 W/m·K. This film will be used as a low dielectric layer, an thermal-insulating layer and a low refractive index layer.     

Gas permeation of porous organic/inorganic hybrid membranes

Selective gas permeation of porous organic/inorganic hybrid membranes via sol-gel route and its thermal stability are described. Separation performance of the hybrid membrane was improved compared with porous membranes governed by the Knudsen flow, and gas permeability was still much higher than that through nonporous membranes. Additionally, it was shown that these membranes were applicable at higher temperatures than organic membranes.SEM observation demonstrated that the thin membrane was crack-free. Nitrogen physisorption isotherms showed the pore size was in the range of nanometers. Gas permeability through this membrane including phenyl group was in the range of 10^–8 [cc(STP) cm/(cm² s cmHg)] at 25°C. The ratios of O₂/N₂ and CO₂/N₂ were 1.5 and 6.0, respectively, showing the permeation was not governed by the Knudsen flow. The permeability decreased as the temperature increased. Furthermore, the specific affinity between gas molecules and surface was observed not only in the permeation data of the hybrid membranes but in the physisorption data. These results suggested that the gas permeation through the hybrid membrane was governed by the surface flow mechanism.Thermal analysis indicated that these functional groups were still stable at higher temperatures. The phenyl group especially remained undamaged even at 400°C.     

Effect of Niobium Modifications to PZT (53/47) Thin Films Made by a Sol-Gel Route

Niobium-modified lead zirconate titanate thin films (PNZT) with nominal compositions, Pb_(1–0.5x) (Zr_0.53 Ti_0.47)_1–x Nb _x O₃:x = 0.02–0.07, have been prepared using a diol based sol-gel route. Single-layer (0.5 m) films were fabricated on platinised silicon substrates by spin-coating. The effect of niobium additions with regard to phase development, microstructure, and ferroelectric and dielectric properties were investigated for different annealing temperatures. For comparison, unmodified PZT films were also prepared. Niobium substitution increased the crystallisation temperatures for perovskite PNZT phase formation. The values of remanent polarisation P _r and dielectric constant _r were found to decrease with the introduction of Nb. For example, in films heated at 700°C for 15 min, the P _r value of an unmodified PZT film was 31 C cm^–2, compared to 17 C cm^–2 for an x = 0.05 PNZT film, whilst respective relative permittivity values fell from 1190 to 600. The highest Nb concentration film, x = 0.07, did not display any switchable polarisation characteristics, which is consistent with high levels of intermediate pyrochlore phase.     

Investigation of the Crystallisation Behaviour of Lead Titanate (PT), Lead Zirconate (PZ) and Lead Zirconate Titanate (PZT) by EXAFS-Spectroscopy and X-Ray Diffraction

Two solid solutions of lead zirconium titanates PbZr _x Ti_{1 – x} O₃ (x = 0.1 and 0.35) as well as the reference compounds lead titanate and lead zirconate were prepared from zirconium and titanium n-propoxide, dissolved in 2-methoxyethanol, by sol-gel process. The amorphous products after pyrolysis of the dried gels and the crystalline phases were studied by EXAFS spectroscopy to monitor the structural changes from the amorphous oxide mixture to the crystalline ceramics after calcination. Additionally, the crystalline phases were identified by X-ray diffraction (XRD).It follows from the analysis of the EXAFS data that the local order of the amorphous phases seems to be completely different from that of the crystalline phase. There is no indication of a preformation of the local order of the perovskite structure. The analysis of our EXAFS spectra can be interpreted very consistently with the assumption that in the amorphous samples a segregation exists on molecular level and the low crystallisation temperatures are a consequence of very short diffusion paths.     

Alkoxide Derived SrBi2Ta2O9 Phase Pure Powder and Thin Films

Phase pure powder and thin films of the novel ferroelectric materials SrBi₂Ta₂O₉ (SBT) have been prepared using the organic precursors. The xero-gel formed was dried and characterized using TGA and DTA to determine the organic burn out and crystallization temperature of SBT. Powder X-ray diffraction was used systematically to check the crystallinity of SBT. Phase pure SBT powder was formed as low as 650°C and thin films at 600°C in comparison to other earlier reported work. SEM micrographs show a grain size of ≈0.1 μm and show crack free films with a film thickness of 2 μm.