Showing papers on "Sol-gel published in 1998"
TL;DR: In this article, a new route for the synthesis of a nanotube made of titanium oxide is presented, where needle-shaped TiO2 crystals (anatase phase) with a diameter of 8 nm and a length of 100 nm were obtained when sol−gel-derived fine TiO 2-based powders were treated chemically with a 5−10 M NaOH aqueous solution.
Abstract: Nanotubes composed of various materials such as carbon, boron nitride, and oxides have been studied recently. In this report, the discovery of a new route for the synthesis of a nanotube made of titanium oxide is presented. Needle-shaped TiO2 crystals (anatase phase) with a diameter of ≈8 nm and a length of ≈100 nm were obtained when sol−gel-derived fine TiO2-based powders were treated chemically (e.g., for 20 h at 110 °C) with a 5−10 M NaOH aqueous solution. It was found by observation using a transmission electron microscope that the needle-shaped products have a tube structure. The TiO2 nanotubes have a large specific surface area of ≈400 m2·g-1. TiO2 nanotubes obtained in the present work are anticipated to have great potential for use in the preparation of catalysts, adsorbants, and deodorants with high activities, because their specific surface area is greatly increased. If metallic-, inorganic-, or organic-based materials can be inserted into the TiO2 nanotubes, novel characteristics such as electr...
2,335 citations
TL;DR: Very fine cobalt oxide xerogel powders were prepared using a unique solution chemistry associated with the sol-gel process as mentioned in this paper, and the effect of thermal treatment on the surrace area, pore volume, crystallinity, particle structure, and corresponding electrochemical properties was investigated and found to have significant effects on all of these properties.
Abstract: Very fine cobalt oxide xerogel powders were prepared using a unique solution chemistry associated with the sol-gel process The effect of thermal treatment on the surrace area, pore volume, crystallinity, particle structure, and corresponding electrochemical properties of the resulting xerogels was investigated and found to have significant effects on all of these properties The xerogel remained amorphous as Co(OH) 2 up to 160°C, and exhibited maxima in both the surface area and pore volume at this temperature With an increase in the temperature above 200°C, both the surface area and pore volume decreased sharply, because the amorphous Co(OH) 2 decomposed to form CoO that was subsequently oxidized to form crystalline Co 3 O 4 In addition, the changes in the surface area, pore volume, crystallinity, and particle structure all had significant but coupled effects on the electrochemical properties of the xerogels A maximum capacitance of 291 F/g was obtained for an electrode prepared with the CoO x xerogel calcined at 150°C, which was consistent with the maxima exhibited in both the surface area and pore volume; this capacitance was attributed solely to a surface redox mechanism The cycle life of this electrode was also very stable for many thousands of cycles
441 citations
TL;DR: In this paper, the structure, optical and electrical properties of ZnO films were investigated, and the c-axis lattice constants of the thin films and the band gap were shown to be a little larger than those of the crystal. But the differences between the thin film and crystal might be attributable to the grain boundaries and imperfections in thin films.
361 citations
TL;DR: In this paper, X-ray analysis showed the anatase crystal phase of the nanocrystalline titanium dioxide colloids to be primarily the rodlike particle morphology after growth at lower temperatures and the formation of principally truncated tetragonal or tetrahydral bipyramidal nanocrystites following growth at higher temperatures.
Abstract: Nanocrystalline titanium dioxide colloids have been synthesized using a sol−gel technique followed by growth under hydrothermal conditions in a basic environment at temperatures between 190 and 270 °C. Thin films have been made from aqueous suspensions of these colloids. X-ray analysis showed the colloids to be primarily the anatase crystal phase. Scanning electron microscopy (SEM) revealed a predominantly rodlike particle morphology after growth at lower temperatures and the formation of principally truncated tetragonal or tetrahydral bipyramidal nanocrystallites following growth at higher temperatures. The rodlike particles self-organize into regular cubic arrays with the long axis of the rods aligned perpendicular to the film surface. This self-organization is dependent upon the base used in colloidal synthesis and also upon the dielectric constant of the medium used during film formation.
340 citations
TL;DR: The long-term quenching stability of DO sensing films was established over a period of 6 months, and the influence of water/precursor molar ratio, R, on the sol-gel film microstructure was investigated.
Abstract: Sol-gel-based optical sensors for both gas-phase and dissolved oxygen have been developed. Both sensors operate on the principle of fluorescence quenching of a ruthenium complex which has been entrapped in a porous sol-gel silica film. A comprehensive investigation was carried out in order to establish optimal film-processing parameters for the two sensing environments. Both tetraethoxysilane and organically modified sol-gel precursors such as methyltriethoxysilane and ethyltriethoxysilane were used. Film hydrophobicity increases as a function of modified precursor content, and this was correlated with enhanced dissolved oxygen (DO) sensor performance. Extending the aliphatic group of the modified precursor further improved DO sensitivity. The influence of water/precursor molar ratio, R, on the sol-gel film microstructure was investigated. R value tailoring of the microstructure and film surface hydrophobicity tailoring were correlated with oxygen diffusion behavior in the films via the Stern-Volmer constants for both gas phase and DO sensing. Excellent performance characteristics were measured for both gas-phase and DO oxygen sensors. The long-term quenching stability of DO sensing films was established over a period of 6 months.
284 citations
TL;DR: In this article, the X-ray absorption near edge structure (XANES) of the precipitate possesses a characteristic preedge that is dominated by a transition designated as A2 at 4970.7 eV, and assigned to five coordinate Ti.
Abstract: X-ray absorption spectroscopy (XAS) has been used to study the local Ti environment in titania xerogel samples containing nanoparticles of different sizes. The xerogels were prepared by hydrolysis of titanium isopropoxide followed by peptization with HNO3 and size control was achieved through calcination in air at different temperatures. An amorphous precipitate obtained by hydrolysis of titanium isopropoxide prior to peptization with HNO3 has also been studied. The X-ray absorption near edge structure (XANES) of the precipitate possesses a characteristic preedge that is dominated by a transition designated as A2 at 4970.7 eV, and assigned to five coordinate Ti. This A2 component is detected in all of the studied xerogels. Its intensity decreases as the surface-to-volume ratio of the titania particles decreases, suggesting that it is associated with surface layers of the anatase particles. Other changes observed in the XANES of the xerogels as a function of particle size include broadening of 1s → np tran...
224 citations
TL;DR: In this article, a review of extensive studies involving the in situ sol-gel reactions of the alkoxides of silicon, titanium, aluminum, zirconium and organoalkoxysilanes, as well as their mixtures and two step reactions involving these monomers are presented.
210 citations
TL;DR: Two approaches of the sol-gel process to prepare organic-inorganic hybrids are reviewed in this article, which is simple and involves mixing an organic polymer with a metal alkoxide such as tetraethoxysilane (TEOS).
200 citations
TL;DR: The photocatalytic reactivity of these catalysts was investigated as a function of the Ti content for the liquid-phase oxidation of 1-octanol to 1 -octanal, and it was dramatically enhanced in regions of lower Ti content as mentioned in this paper.
Abstract: Titanium−silicon (Ti/Si) binary oxides having different Ti contents were prepared by the sol−gel method and used as photocatalysts. The photocatalytic reactivity of these catalysts was investigated as a function of the Ti content for the liquid-phase oxidation of 1-octanol to 1-octanal, and it was found to be dramatically enhanced in regions of lower Ti content. In situ photoluminescence, UV−vis reflectance, FT-IR, ESR, XAFS, XRD, and XPS spectroscopic investigations of these Ti/Si binary oxides indicated that the titanium oxide species are highly dispersed in the SiO2 matrixes and exist in a tetrahedral coordination exhibiting a characteristic photoluminescence spectrum due to the radiative decay from the charge-transfer excited state of the tetrahedrally coordinated titanium oxide species. The good parallel relationship between the yield of the photoluminescence and the specific photocatalytic reactivity of the Ti/Si binary oxides as a function of the Ti content clearly indicates that the high photocata...
176 citations
TL;DR: In this paper, vanadium dioxide thin films have been obtained that exhibit both electrical and optical switching around 70°C and the switching temperature together with the shape of the hysteresis loop can be modified by doping VO2 films with foreign cations.
Abstract: Vanadium dioxide thin films have been deposited from vanadium alkoxides VO(OR)3. An amorphous film is formed that transforms into crystalline VO2 upon heating at 500°C under a reducing atmosphere. Optically transparent VO2 thin films are then obtained that exhibit both electrical and optical switching around 70°C. The switching temperature together with the shape of the hysteresis loop can be modified by doping VO2 films with foreign cations. Doped MxVO2 (M = W6+, Nb5+, Ti4+, Cr3+ or Al3+) thin films have been prepared under the same conditions by mixing the vanadium alkoxide and a metal salt in an alcoholic solution. The switching temperature decreases when the film is doped with high-valent cations (W6+) and increases with low-valent cations (Al3+, Cr3+). The transition temperature first decreases and then increases when TiIV is added to the VO2 film while the width of the hysteresis loop is significantly reduced.
153 citations
TL;DR: In this paper, a template-based approach was used to fabricate thin, porous, chemically selective silicate films using a template based approach that involves the formation of a cross-linked matrix around a specific reagent followed by removal of that reagent.
Abstract: Inorganic−organic hybrid sol−gel processing has been utilized to fabricate thin, porous, chemically selective silicate films. These materials have been fabricated using a template-based approach that involves the formation of a cross-linked matrix around a specific reagent followed by removal of that reagent. The silica sol consisted of a hybrid mixture of functionalized organosilicon precursors (phenyltrimethoxysilane and methyltrimethoxysilane), a network former (tetramethoxysilane), and the template molecule, dopamine (DA). Silicate thin films were prepared by spin casting an aliquot of the composite sol on the surface of a glassy carbon electrode. Dopamine was extracted from the dried film via soaking in phosphate buffer, and the affinity and selectivity of the DA-templated films were characterized using cyclic voltammetry. The results show that the DA-templated films have an increased affinity for dopamine over that of structurally related molecules including serotonin, epinephrine, and dihydroxynaph...
TL;DR: In this article, the effect of different processing parameters on the efficiency of entrapment of pH indicators in a sol-gel-derived silica film is reported, and an evanescent wave absorption approach is used to monitor dopant-leaching from these films.
Abstract: The effect of different processing parameters on the efficiency of entrapment of pH indicators in a sol–gel-derived silica film is reported. An evanescent wave absorption approach was used to monitor dopant-leaching from these films. The issues investigated include the effect on the rate of leaching of the water:alkoxide ratio, the pH of the leachant solution and the choice of silicon alkoxide. Results indicate that the most suitable sol–gel films in terms of leaching and response time are those prepared using tetraethoxysilane as precursor, acid catalysis and a water:alkoxide ratio of at least 4. Leaching is more pronounced for films used directly after preparation and varies for different pH environments. Implications of leaching for the long-term use of sol–gel based pH sensors are discussed.
TL;DR: In this paper, a nano-crystalline porous tin oxide thin film was successfully prepared by a sol-gel technique and evaluated for CO sensing and the surface morphology, electrical conductance and CO sensitivity of the thin films calcined at various temperatures (500-800°C) were studied and compared.
Abstract: Nano-crystalline porous tin oxide thin film was successfully prepared by a sol-gel technique and evaluated for CO sensing. The surface morphology, electrical conductance and CO sensitivity of the tin oxide thin films calcined at various temperatures (500–800°C) were studied and compared. The particles were in the diameter range of 7–15 nm and the pore diameters were about 1.6–9 nm. The tin oxide film calcined at 700°C deposited onto interdigitated electrodes showed high CO sensitivity with relatively fast response (∼ 4 min) and recovery time (∼ 1 min), respectively. The results indicate the advantages of using nano-crystalline porous materials for thin film sensor development.
TL;DR: Investigation of changes during aging of the sol and thermal gravimetric analysis employed to study the behavior of the xerogels as a function of temperature revealed that sols must be aged for at least 24 h to complete the reaction of the two reactants.
Abstract: Production of hydroxyapatite coatings using an alkoxide-based sol–gel route requires control of solution aging time and heating schedule. 31P nuclear magnetic resonance spectroscopy was used to investigate the changes during aging of the sol and thermal gravimetric analysis employed to study the behavior of the xerogels as a function of temperature, while final products were determined using X-ray diffraction. Results from 31P nuclear magnetic resonance spectroscopy and thermal analysis revealed that sols must be aged for at least 24 h to complete the reaction of the two reactants. Deposition of the sol for coating production will then yield monophasic hydroxyapatite. Coatings produced from sols aged for less than 24 h yielded calcium oxide in addition to hydroxyapatite. Prefiring is necessary to remove most of the residual organic materials. Final heating up to 800°C produces crystallization at 550°C and removal of the remaining organic constituents for the formation of a thin hydroxyapatite layer. © 1998 Kluwer Academic Publishers
TL;DR: In this article, solvent-free non-hydrolytic xerogels were characterized by chemical analysis, IR and 29Si NMR spectroscopy and thermogravimetric analysis.
Abstract: Silica was prepared by solvent-free non-hydrolytic condensation reactions from silicon tetrachloride with different oxygen donors: benzyl alcohol and tetrabenzyloxysilane (no catalysis), tetraethoxysilane, tetraisopropoxysilane, diethylether and diisopropylether (catalyzed by FeCl3, TiCl4, AlCl3 or ZrCl4). Highly condensed gels with a low hydroxyl content were obtained in high yields. A solution 29Si NMR study showed that in the presence of FeCl3 the condensation of SiCl4 with Si(OiPr)4 was accompanied by extensive redistribution of Si–Cl and Si–OiPr bonds, leading to increasingly complex mixtures. Non-hydrolytic silica xerogels were characterized by chemical analysis, IR and 29Si NMR spectroscopy and thermogravimetric analysis. Porosity and specific surface area were determined using nitrogen adsorption–desorption. Xerogels displayed a wide variety of textures depending on the nature of the oxygen donor and of the catalyst.
TL;DR: In this paper, the formation of hydroxyapatite (HA) from a sol-gel precursor was studied using X-ray diffraction (XRD), and it was found that at firing temperatures ranging from 300 to 1000°C, the dominant phase was HA with small amounts of calcium oxide and β-tricalcium phosphate (β-TCP).
TL;DR: In this article, a broad emission band was observed in the visible part of the electromagnetic spectrum and assigned to the intrinsic emission from the hybrid polymeric network, and Europium luminescent properties were used to study structural evolution during the sol-gel transition.
Abstract: Good optical quality Eu3+-doped silica-polyethyleneglycol hybrids were prepared by the sol-gel process. Thermomechanical analysis showed an increase of the glass transition temperature, due to the stiffness of the polymeric network, as the amount of Eu3+ increased. Europium luminescent properties were used to study structural evolution during the sol-gel transition. For lower doping concentrations dried gels present statistical distributions of Eu3+, typical of an amorphous environment, while for higher concentrations a crystalline-like environment of Eu3+ was observed. A broad emission band was observed in the visible part of the electromagnetic spectrum and assigned to the intrinsic emission from the hybrid polymeric network.
TL;DR: In this article, a silica-zirconia composite colloidal sol (molar ratio Si/Zr=9/1) was fabricated from a sol-gel process and the pore size and pore distribution were estimated based on the dynamic method of humid air permeation, and found to be from 1.0 to 2.9
TL;DR: The sol-gel process is based on the hydrolysis and condensation of molecular precursors as discussed by the authors, and the chemical design of these precursor provides an interesting tool to control condensation reactions and tailor the nanostructure of the oxide materials.
TL;DR: Hall effect measurements have been performed on tin-doped indium oxide thin films prepared by the dipping method and the apparent variation of electron mobility with carrier concentration in these films has been quantitatively interpreted in terms of scattering at charged and neutral impurities as discussed by the authors.
Abstract: Hall effect measurements have been performed on tin-doped indium oxide thin films prepared by the dipping method. The apparent variation of electron mobility with carrier concentration in these films has been quantitatively interpreted in terms of scattering at charged and neutral impurities. An electrical resistivity as low as 3.2×10−4 Ω cm was obtained for the films doped with about 6 at. % Sn. A further increase in the doping content lead to the formation of neutral defects without contributing carriers to the material.
TL;DR: In this article, a novel processing method was developed for preparing sol-gel derived Pb(Zr1−xTix)O3 (x=0.47) thin films on Pt/Ti/SiO2/Si substrates.
Abstract: A novel processing method is developed for preparing sol-gel derived Pb(Zr1−xTix)O3 (x=0.47) thin films on Pt/Ti/SiO2/Si substrates. Using a modified precursor solution and a rapid heat treatment without pyrolysis, it was possible to obtain highly (111) oriented PZT thin films with high perovskite content at a low annealing temperature of 550 °C. The low temperature processing was assisted by taking advantage of the heterogeneous nucleation of the PZT films, which reduces the activation energy for perovskite phase formation. Using this method, the PZT thin films exhibited better dielectric and ferroelectric properties at 550 °C than those reported by other methods. For example, the PZT films annealed at 550 °C showed a well-saturated hysteresis loop at an applied voltage of 5 V with Pr and Ec of 12 μC/cm2 and 38 kV/cm, and their dielectric constant and dissipation factor at a frequency of 100 kHz were 410 and 0.021, respectively. The leakage current density was lower than 10−8 at an applied electric field...
TL;DR: A series of Al 2 O 3 -ZrO 2 mixed oxides was prepared by the sol-gel method with variable amounts of ZrO2 2 between pure alumina and pure zirconia.
TL;DR: In this article, LiMn2O4 thin films are prepared by a sol-gel method using a spin coator. But they are not suitable for use as a cathode for thin-film microbatteries.
TL;DR: Using the hydrolysis of appropriate alkoxide mixtures in water-in-oil microemulsions, nanocrystalline BaTiO3 has been prepared in the form of nonaggregated, cube-shaped crystals at room temperature without any sintering process as demonstrated by means of x-ray diffractograms and transmission electron micrographs as discussed by the authors.
Abstract: Using the hydrolysis of appropriate alkoxide mixtures in water-in-oil microemulsions, nanocrystalline BaTiO3 has been prepared in the form of nonaggregated, cube-shaped crystals at room temperature without any sintering process as is demonstrated by means of x-ray diffractograms and transmission electron micrographs. By variation of the length of the hydrophilic part of the surfactant molecules, the diameter of the water droplets in the microemulsions could be tuned to values between 8 and 55 nm as determined by dynamic light scattering. The size of the resulting nano-BaTiO3 (6 nm ≤ 〈d〉vol ≤ 17 nm) was evaluated from the line broadening of x-ray reflections and correlates to the droplet size. The particle size distribution is very narrow, and in some cases nearly monodisperse.
TL;DR: In this article, the authors used 2,4-pentanedione as the complexing/templating agent to synthesize mixed-oxide supports using sol−gel techniques using 2 o3-, TiO2, SiO2-, and ZrO2-based mixedoxide supports.
Abstract: Al2O3-, TiO2-, SiO2-, and ZrO2-based mixed-oxide supports were synthesized by sol−gel techniques using 2,4-pentanedione as the complexing/templating agent. These materials have been investigated by employing nitrogen adsorption, 27Al, 29Si, and 1H solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), and Fourier transform laser Raman spectroscopy (FT-Raman). Nitrogen adsorption isotherms of the mixed oxides Al2O3−SiO2 and TiO2−SiO2 were of type IV, with hysteresis loops of type I, indicating well-defined pore structure, while other mixed oxides Al2O3−TiO2, Al2O3−ZrO2, TiO2−ZrO2, and ZrO2−SiO2 exhibited type II hysteresis loops, indicating pores of undefined nature. 27Al MAS NMR studies on the alumina-based mixed oxides showed the presence of four-, five-, and six-coordinated aluminum species, the number of four-coordinated framework aluminum sites being highest in the Al2O3−SiO2 mixed oxide. 29Si CP MAS NMR spectra of t...
TL;DR: In this paper, NAFION®/silicon oxide hybrid was prepared from solution by hydrolysis/polycondensation of alkoxy silanes and showed a lamellar structure by transmission electron microscopy.
TL;DR: In this article, a particulate sol-gel (PSG) process was developed for synthesizing LiNiO2 and LiNixCo1−xO2 powders, utilizing the reaction of lithium hydroxide with nickel acetate in a water-ethanol solvent system.
TL;DR: In this paper, the luminescence decay behavior of ruthenium(II)−tris-4,7-diphenyl-1,10-phenanthroline dichloride dissolved in different inorganic and organically modified silicate (ORMOSIL) sol−gel matrixes was investigated.
Abstract: The luminescence decay behavior of ruthenium(II)−tris-4,7-diphenyl-1,10-phenanthroline dichloride dissolved in different inorganic and organically modified silicate (ORMOSIL) sol−gel matrixes was investigated. Bulk xerogels and spin-coated thin films were synthesized from methyltrimethoxysilane (MTMS), tetraethyl orthosilicate (TEOS), and various molar ratios of the two precursors. Systematic changes in composition were conducted to examine the structural properties of sol−gel silicates for possible oxygen sensor supports. The luminescence behavior of the ruthenium complex quenched by oxygen was analyzed as a function of the sol−gel composition and processing technique. The Stern−Volmer ratio, indicative of the degree of luminescence quenching by oxygen, was found to increase with increasing additions of MTMS in the bulk xerogels. This improvement in oxygen sensitivity was attributed to the increased diffusivity in the less polar sol−gel matrix. Conversely, spin-coated thin films showed a decreasing Stern...