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Showing papers on "Sol-gel published in 2003"


Journal ArticleDOI
TL;DR: In this paper, structural changes in sol-gel films with photo-irradiation were investigated using zinc oxide (ZnO) derived from zinc acetate, and the exposure of the films to an ultraviolet lamp induced hexagonal ZnO crystals in a relatively dense amorphous structure.
Abstract: Structural changes in sol-gel films with photo-irradiation were investigated using zinc oxide (ZnO) derived from zinc acetate. The exposure of the films to an ultraviolet lamp induced hexagonal ZnO crystals in a relatively dense amorphous structure. On the other hand, the formation of zinc metal was found in a porous gel film. The photo-induced crystallization and reduction are ascribed to the electronic excitation in the metastable non-crystalline states.

1,007 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of drying conditions and second-heat treatment on the structural, electrical and optical properties of ZnO thin films prepared by the sol-gel method was investigated.

630 citations


Journal ArticleDOI
TL;DR: In this article, a simple, rapid and generalizable aerosol decomposition (spray pyrolysis) process for the continuous synthesis of nanoparticles with adjustable sizes, narrow size distribution, high crystallinity and good stoichiometry is described.

556 citations


Journal ArticleDOI
TL;DR: It was found that silver ions were completely trapped in the silica matrix and their reduction could be achieved at 600 degrees C annealing temperature, and the coating films had an excellent antibacterial performance.

455 citations


Journal ArticleDOI
TL;DR: In this article, the effects of aluminum, indium and tin dopants on the microstructure and electrical properties of ZnO thin films prepared on silica glass substrates by the sol-gel method were investigated.

432 citations


Journal ArticleDOI
TL;DR: In this paper, a systematic study of the key parameters that influence the texture and preferential orientation of films deposited by sol-gel procedures (precursor, solvent and additive nature and concentration, coating and heat treatment conditions).

294 citations


Journal ArticleDOI
TL;DR: In this article, the Langmuir−Blodgett technique was used to control the sample thickness at the layer level whereas the overall crystal quality should be good enough for use in several applications.
Abstract: Colloidal crystals of various thicknesses were obtained using silica particles as basic units and the Langmuir−Blodgett technique as a tool for controlling the thickness. Submicronic silica particles are first synthesized via a sol−gel process and then functionalized with an appropriate coupling agent. After compression at the surface of a Langmuir trough to form a well-organized two-dimensional array, silica particles are transferred onto solid substrates. While repeating the transfer several times, we formed colloidal crystals that were characterized by scanning electron microscopy and UV−visible−NIR spectroscopies. Both techniques show that the sample thickness can be controlled at the layer level whereas the overall crystal quality should be good enough for use in several applications.

279 citations


Journal ArticleDOI
TL;DR: In this article, two mild chemical routes: complexation with citric acid and the sol-gel method were used to synthesize CeO2-ZrO2 mixed oxides, and the most stable solid solutions were obtained in the range 50 < Ce < 90% mol.
Abstract: CeO2-ZrO2 mixed oxides were synthesized by two mild chemical routes: complexation with citric acid and the sol-gel method. XRD and ESEM investigations revealed the appearance of a solid solution around 400degreesC , depending on the ratio between the two oxides and the preparation method. Solids obtained by the citrate method were more homogeneous on the whole range of composition. Solid-state investigations of the prepared materials did not show segregation of cerium or zirconium oxides, except in the high Ce ranges for samples prepared by the sol-gel method. The thermal stability of both oxides was enhanced by mutual substitution. The most stable solid solutions were obtained in the range 50 < Ce < 90% mol.

257 citations


Journal ArticleDOI
Muxin Yu1, J. Lin1, Junqing Fu1, Huiyin Zhang1, Yanchun Han1 
TL;DR: In this article, a Pechini sol-gel process combined with soft lithography on silicon and silica glass substrates was used to fabricate rare earth ion (Eu3+, Tb3+, Ce3+)-doped LaPO4 nanocrystalline thin films.
Abstract: Rare-earth ion (Eu3+, Tb3+, Ce3+)-doped LaPO4 nanocrystalline thin films and their patterning were fabricated by a Pechini sol–gel process combined with soft lithography on silicon and silica glass substrates. X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM), scanning electron microcopy (SEM), optical microscopy, absorption and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicate that the films begin to crystallize at 700 °C and the crystallinity increases with increasing annealing temperature. The morphology of the thin film depends on the annealing temperature and the number of coating layers. The 1000 °C annealed single layer film is transparent to the naked eye, uniform and crack-free with a thickness of about 200 nm and an average grain size of 100 nm. Patterned thin films with different strip widths (5–50 µm) were obtained by micromolding in capillaries (soft lithography). The doped rare earth ions show their characteristic emission in the nanocrystalline LaPO4 films, i.e., Eu3+5D0–7FJ (J = 1, 2, 3, 4), Tb3+5D3,4–7FJ (J = 6, 5, 4, 3, 2) and Ce3+ 5d–4f transition emissions, respectively. Both the lifetimes and the PL intensities of Eu3+ and Tb3+ increase with increasing annealing temperature, and the optimum concentrations for them were determined to be 5 mol% and 16 mol% of La3+ in LaPO4 thin films, respectively. An energy transfer phenomenon from Ce3+ to Tb3+ has been observed in LaPO4 nanocrystalline thin films, and the energy transfer efficiency depends on the doping concentration of Tb3+ if the concentration of Ce3+ is fixed.

241 citations


Journal ArticleDOI
TL;DR: In this paper, the formation of silica nanofibers using the sol-gel method and electrospinng technique was studied, and the result is the deposition of a thin polymer fiber on a substrate located above the counter electrode.
Abstract: The fabrication of materials with one-dimensional nanoscale structures is of great promise for the fundamental understanding of the roles of dimensionality and size in an optical, electrical, and mechanical properties with reference to applications in semiconductor mechanical and chemical industries. Polymer nanofibers are of considerable interest for various kinds of applications including filters, reinforcing agents, biomedical materials, and fiber templates to prepare nanotubes [1–6]. Recently, there has been a growing interest in one-dimensional, inorganic nanosized materials such as carbon nanotubes, carbide nanorods, silica and titania nanofibers/nanotubes [7–11]. These one-dimensional nanomaterials exhibit some novel physical and chemical properties due to their peculiar structure and size effect, and are of great importance in nanodevices and mesoscopic theoretical research. Electrospinning technique is an effective method to produce nanofibers [12–16]. The electrospinning process involves the application of a strong electrostatic field to a capillary connected with a reservoir containing a polymer solution or melt. Under the influence of the electrostatic field, a pendant droplet of the polymer solution at the capillary tip is deformed into a conical shape (Taylor cone). If the voltage surpasses a threshold value, electrostatic forces overcome the surface tension, and a fine charged jet is ejected. The jet moves towards a ground plate acting as counter electrode. Due to the extensional viscosity of the polymer solution and the presence of entanglements, the jet remains stable and does not transform into spherical droplets as expected for a liquid cylindrical thread. The solvent begins to evaporate immediately after the jet is formed. The result is the deposition of a thin polymer fiber on a substrate located above the counter electrode. The sol-gel method has widely been used as an alternative technology for the preparation of a wide variety of forms including monoliths, powders, coatings, and fibers [17–20]. The typical sol-gel method is hydrolysis and condensation of tetraethyl orthosilicate (TEOS), Si(OCH2CH3)4. In recent years, there have been efforts to synthesize metal oxide (silica or titania) nanofibers and nanotubes by the sol-gel template method [11, 21, 22]. Meanwhile, micron-scale silica fibers have been achieved by extruding the spinnable sol through an orifice [23–25]. In the present work, we study formation of silica nanofibers using the sol-gel method and electrospinng technique. We note that the TEOS solution used in this study does not contain any gelator or binder to help spinnability. Kobayashi and coworkers synthesized titania fibers via the sol-gel method from a physical gel of titanium tetraisopropoxide by a low molecular weight organogelator [10]. Zhang and coworkers synthesized silica and titania nanorods with the sol-gel method and anodic alumina template membrane [11, 21]. The silica sol was prepared from tetraethyl orthosilicate (TEOS), distilled water, ethanol, and HCl. The sol composition in molar ratio was 1:2:2:0.01 (TEOS:ethanol:water:HCl). First, TEOS was mixed with ethanol in a beaker. The HCl/water solution was then added drop by drop to the TEOS/ethanol solution under vigorous stirring. The solution was heated at 80 ◦C for 30 min and then cooled down to room temperature. The silica sol was placed in a pasteur pipet and the electrode was directly connected with the solution. A tubular shaped counter electrode with a diameter of 22 cm was located below the reservoir. The winding drum was rotated at speed of 10 rpm during the electrospinning. The fibers were collected on aluminum foil covered the tubular layer. The distance between the tip of the capillary and the counter electrode (tip-tocollector distance, TCD) was 10 cm and the applied voltages ranged from 10 kV to 16 kV. The morphology and diameter of silica fiber were measured with SEM (S-2350 of Hitachi). The composition of silica fiber was determined with FTIR (Travel IR of SensIR Technol.). The structure of silica fiber was analyzed with XRD (DMAX 2000 of Rigaku Denki). The thermal property was analyzed with a thermogravimetric analyzer of TGA 2050 of TA Instrument. TGA analysis was performed at 50–800 ◦C with 20 ◦C/min in air. It has been known that silica fibers obtained by the conventional technique through the sol-gel process are affected by composition of sol and ripening condition [20, 24]. In the current study, silica nanofibers were obtained successufully by electrospinning technique and

237 citations



Journal ArticleDOI
TL;DR: In this paper, thin films of titanium dioxide (TiO2) were deposited on a variety of substrates by a simple sol-gel dip coating technique, where the substrates were coated with titanium peroxide precursor solution of controlled viscosity at a constant pulling rate of 1mm s−1, air-dried and further heated at 400°C to obtain uniform films with good adhesion to the substrate.

Journal ArticleDOI
TL;DR: In this article, a simple sol−gel route was developed for the preparation of mesoporous and nanocrystalline anatase thin layers, and an anatase hydrosol was first synthesized at room temperature from acidic hydrolysis of titanium isopropoxide.
Abstract: A simple sol−gel route has been developed for the preparation of mesoporous and nanocrystalline anatase thin layers. An anatase hydrosol was first synthesized at room temperature from acidic hydrolysis of titanium isopropoxide. The optimization of the synthesis parameters, including titanium concentration, HCl/Ti and H2O/Ti ratios, temperature, and aging time, enabled us to produce a clear sol with a very low HCl/Ti ratio (equal to 1). As a function of the further thermal treatment conditions, it was then possible to control the size of the anatase crystallites (from 5 to >10 nm) and the O/Ti stoichiometry (from 1.9 to 2.0). Ordered mesoporosity was obtained by using a triblock copolymer as the templating agent. Preliminary experiments evidenced the photocatalytic activity of the prepared layers.

Journal ArticleDOI
TL;DR: In this paper, crack-free silica-calcia xerogel monoliths of various shapes and sizes of compositions expressed by the following formula xCaO·(1−x)SiO2 were prepared via the sol-gel technique, starting from tetraethyl orthosilicate and calcium nitrate, and were characterised using X-ray diffraction, infrared (FTIR) spectroscopy, energy dispersive scanning electron microscopy (SEM-EDS) as well as differential thermal analysis (DTA).
Abstract: The conventional method of preparing glasses is quenching a melt. However, as with many multicomponent glasses, only a certain range of CaO–SiO2 compositions can be melt derived. Sol–gel processing allows one to produce gel-glasses with compositions lying within the liquid–liquid immiscibility dome of the CaO–SiO2 system. Crack-free silica–calcia xerogel monoliths of various shapes and sizes of compositions expressed by the following formula xCaO·(1−x)SiO2, where 0⩽x⩽0.5 mole fraction, were prepared via the sol–gel technique, starting from tetraethyl orthosilicate and calcium nitrate. In this paper the processing technique is described. The materials produced were characterised using X-ray diffraction, infrared (FTIR) spectroscopy, energy dispersive scanning electron microscopy (SEM-EDS) as well as differential thermal analysis (DTA). The gel-glasses produced are confirmed to be amorphous even after stabilisation at 600 °C, with crystallisation temperatures above 850 °C. When sintered at 1000 °C they form crystalline phases in accordance to the CaO–SiO2 phase diagram. Acid digestion analysis confirms that the compositions of the gel-glasses are similar to that of the computed values. The gel-glasses are homogeneous throughout the monolith.

Journal ArticleDOI
TL;DR: In this article, several nanoparticle metal oxides were prepared and studied for the catalytic production of methanol from hydrogen and carbon dioxide, including ZnO, CuO, NiO, and a binary system CuO/ZnO.
Abstract: Several nanoparticle metal oxides were prepared and studied for the catalytic production of methanol from hydrogen and carbon dioxide. These catalysts include: ZnO, CuO, NiO, and a binary system CuO/ZnO. The catalysts were prepared through sol–gel synthesis and were found, via TEM and BET, to have high surface areas and small crystallite sizes. With this in mind, the catalytic production of methanol was studied at various temperatures in a flow reactor. The percent conversion and turnover numbers were calculated for each sample, and it was found that the nanoparticle ZnO, CuO/ZnO and NiO were much more active catalysts than the commercially available materials. The nanocrystalline CuO sample was found to rapidly reduce to Cu, where it lost all activity. The results suggest that the catalytic process is efficient for several nanoparticle metal oxide formulations, however, copper metal is not active, but small copper particles in a CuO/ZnO matrix is a very active combination.

Journal ArticleDOI
19 Feb 2003-Langmuir
TL;DR: In this article, a photo assisted sol−gel method was used to transform amorphous titania nanoparticles into crystalline anatase phase at lower calcination temperature compared to those prepared by a conventional sol-gel method, and the particle size distribution of anatase powder samples is also affected by UV illumination on the colloid.
Abstract: Titanium dioxide nanoparticles were prepared via a photoassisted sol−gel method in which ultraviolet light irradiation was used in the preparation process of TiO2 colloid. After characterization by X-ray diffraction, X-ray absorption near-edge structure (XANES) at the Ti K-edge, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, it was found that the amorphous titania nanoparticles prepared by a photoassisted sol−gel method can be transformed into crystalline anatase phase at lower calcination temperature compared to those prepared by a conventional sol−gel method. In addition, the particle size distribution of anatase powder samples is also affected by UV illumination on the colloid. It is suggested that UV illumination can induce the formation of oxygen vacancies on the colloid and this results in the accelerated phase transition from amorphous to anatase titania.

Journal ArticleDOI
TL;DR: In this article, a two-step method was used for electrodepositing sol-gel films, in which the monomer is first hydrolyzed in acidic solution and only then the negative potential is applied, which consumes protons and releases hydroxyl ions, thus enhancing the condensation.

Journal ArticleDOI
TL;DR: In this paper, a comparative study of the optical and electrochromic properties of different types of WO 3 thin films has been carried out by atomic force microscopy (AFM), optical studies and ATR-FTIR spectroscopy.

Journal ArticleDOI
TL;DR: By combining sol-gel processing with electrophoretic deposition, a new method for the growth of oxide nanorods was developed in this paper, where uniform sized nanorod 45-200 nm in diameter and 10 μm in length can be grown over large areas with near unidirectional alignment.
Abstract: By combining sol-gel processing with electrophoretic deposition, we have developed a new method for the growth of oxide nanorods. Both single metal oxides (TiO 2 , SiO 2 ) and complex - BaTiO 3 , Sr 2 Nb 2 O 7 , and Pb(Zr 0 . 5 2 Ti 0 . 4 8 )O 3 - have been grown by this method. Uniformly sized nanorods 45-200 nm in diameter and 10 μm in length can be grown over large areas with near unidirectional alignment. The nanorods have the desired stoichiometric chemical composition and crystal structure, after firing to 500-700°C for up to one hour.

Journal ArticleDOI
TL;DR: In this paper, the synthesis of composite polymeric organic−inorganic particles is described based on performing sol−gel polycondensation within a surfactant-stabilized emulsion of a solution of a polymer polystyrene of various molecular weights in tetraethoxysilane, with or without toluene, all dispersed in a basic ethanolic medium.
Abstract: We describe a convenient, one-step sol−gel route to composite polymeric organic−inorganic particles. The synthesis is based on performing the sol−gel polycondensation within a surfactant-stabilized emulsion of a solution of a polymer polystyrene of various molecular weights in tetraethoxysilane, with or without toluene, all dispersed in a basic ethanolic medium. The parameters that dictate the formation of the composite bicontinuous particles were explored and characterized by several methods including TEM, surface area and porosity measurements, high-resolution XPS, TGA, DSC, UV, and FTIR spectroscopies. The particles are obtained in monomodal distributions with diameters in the range of 200−500 nm, depending on the preparation conditions. The polystyrene phase is extractable, and when this extraction is carried out porous silica particles are obtained. Likewise, partial extraction leads to core−shell architecture. The particles were also found to be good carriers for entrapped dye molecules with no leac...

Journal ArticleDOI
TL;DR: In this paper, the thermal conductivity, electrical conductivity and Seebeck coefficient of hot-pressed Al 2 O 3 added ZnO ceramic samples were measured in dependence of temperature up to 600°C.
Abstract: Al 2 O 3 added ZnO powders were prepared via sol–gel processing, using zinc acetate, ammonia and Al 2 O 3 powders as starting materials. Scanning electron microscopy (SEM) observations indicated that the Al 2 O 3 added ZnO powders consisted of very fine particles (0.1–2 μm). The thermal conductivity, electrical conductivity and Seebeck coefficient of hot-pressed Al 2 O 3 added ZnO ceramic samples were measured in dependence of temperature up to 600 °C. The influence of Al 2 O 3 addition on the thermoelectric (TE) properties of ZnO ceramics is discussed.

Journal ArticleDOI
TL;DR: In this article, undoped ZnO films were post-annealed in hydrogen at 350°C for 3h after sol-gel spin-coating film fabrication followed by annealing from 500 to 575°C, and their electrical and optical properties were investigated.

Journal ArticleDOI
TL;DR: In this paper, the influence of the composition and thermal treatment on the in vitro bioactivity of glasses and glass ceramics obtained by the sol−gel method, to obtain bioactive glass Ceramics in a simpler system than those at present.
Abstract: The aim of this work was to study the influence of the composition and thermal treatment on the in vitro bioactivity of glasses and glass ceramics obtained by the sol−gel method, to obtain bioactive glass ceramics in a simpler system than those at present. For this purpose, gels in the systems SiO2−CaO (70S: 70/30) and SiO2−CaO− P2O5 (55S: 55/41/4) were heated at temperatures ranging between 700 and 1400 °C. The samples were characterized by DTA/TG, XRD, FTIR, SEM, and EDS and an in vitro bioactivity study in SBF was carried out. The results showed that all materials obtained (glasses or glass ceramics) were bioactive. The bioactivity was influenced by the initial gel composition, by the thermal treatment, and by the different phases present in the glass ceramics. In glasses the bioactivity decreased with the stabilization temperature. In the glass ceramics the bioactivity was favored by the presence of pseudo-wollastonite (most soluble phase of CaSiO3) and of tricalcium phosphate.

Journal ArticleDOI
TL;DR: In this article, a new route for the preparation of powdery metal, oxide and hydroxide materials is presented as a chimie douce alternative to the sol-gel method, which consists in the reduction or the hydrolysis of a metal salt dissolved and heated in polyol medium.
Abstract: A new route for the preparation of powdery metal, oxide and hydroxide materials is presented as a chimie douce alternative to the sol-gel method. It consists in the reduction or the hydrolysis of a metal salt dissolved and heated in a polyol medium. It appears through zinc and cobalt examples that the use of acetate precursors contrarily to chloride or sulfate ones leads to the precipitation of a solid (metal, oxide, hydroxide) whose nature depends on two main factors: the hydrolysis ratio, defined by the water to metal molar ratio, and the reaction temperature. As in the sol-gel method, acetate leads to the formation of intermediate alkoxyacetate complex. The absence of water favors metal formation while its presence favors oxide or hydroxyacetate formation.

Journal ArticleDOI
TL;DR: In this article, aqueous sol-gel method was used to produce thin films of vanadium dioxide (VO2) on glass substrates by adding small quantities of a water-soluble molybdenum compound to the sol.

Journal ArticleDOI
TL;DR: The electrodeposited films were found to be permeable to simple redox molecules, such as ruthenium(III) hexaammine and ferrocene methanol and to have a completely different surface structure and to be significantly rougher relative to spin-coated films.
Abstract: Sol−gel-derived silicate films were electrochemically deposited on conducting surfaces from a sol consisting of tetramethoxysilane (TMOS). In this method, a sufficiently negative potential is applied to the electrode surface to reduce oxygen to hydroxyl ions, which serves as the catalyst for the hydrolysis and condensation of TMOS. The electrodeposition process was followed by the electrochemical quartz crystal microbalance and cyclic voltammetry. The electrodeposited films were characterized for their surface morphology, porosity, and film thickness using atomic force microscopy, electrochemical probe techniques, surface area and pore size analysis, and profilometry. The electrodeposited films were found to have a completely different surface structure and to be significantly rougher relative to spin-coated films. This is likely due in part to the separation of the gelation and evaporation stages of film formation. The electrodeposited films were found to be permeable to simple redox molecules, such as r...

Journal ArticleDOI
TL;DR: In this article, the transmittance of the TiO 2 anatase thin films was found to be strongly dependent on the Li + inserted charge, and it was shown that the fully colorated state of the anatase films is Li 0.5 with a crystalline structure of Imma space group symmetry.

Journal ArticleDOI
TL;DR: In this article, a small roughness of about 20-50 nm was found on the surface of the Al2O3 gel films, which were then immersed in hot water at 60°C.
Abstract: Transparent, superhydrophobic coating films have been prepared on polymer substrates at low temperatures through the sol-gel method. Al2O3 gel films were prepared on poly(ethylene terephthalate) substrates from Al(O-sec-C4H9)3 chemically modified with ethyl acetoacetate. A small roughness of about 20–50 nm was found to form on the surface of the Al2O3 gel films dried at room temperature and then immersed in hot water at 60°C. The electron diffraction measurements have shown that this roughened surface consists of pseudoboehmite nanocrystals. The coating of hydrolyzed fluoroalkyltrimethoxysilane on the Al2O3 gel films with the small roughness produced transparent, superhydrophobic films with contact angle for water larger than 150°.

Journal ArticleDOI
TL;DR: In this paper, the authors described the preparation of novolac-type phenolic resin/silica hybrid organic-inorganic nanocomposite, with a sol-gel process.
Abstract: This article describes the preparation of novolac-type phenolic resin/silica hybrid organic-inorganic nanocomposite, with a sol- gel process. The coupling agent was used to improve the interface between the organic and inorganic phases. The effect of the structure of the nanocomposite on its physical and chemical properties is dis- cussed. The coupling agent reacts with the resin to form covalent bonds. The structure of the modified hybrid nanocomposites was identified with a Fourier transform infrared spectroscope. The silica network was characterized by nuclear magnetic resonance imaging ( 29 Si NMR). Results revealed that Q4 (tetrasubstituted) and T3 (trisubstituted) are the dominant microstructures. The size of the silica in the phenolic resin was characterized with a scanning electron microscope. The size of the particles of inorganic silica in the modified system was less than 100 nm. The nanocomposite exhibited good transparency. Moreover, the thermal and mechanical properties exhibited significant improvement. The modified hybrid composite exhibited favorable thermal properties. The temperature at which a weight loss of 5% occurred increased from 281 to 350 °C. The flexural strength increased by 6 -30%. The limiting oxygen index of the nanocom- posite reached 37, and the Underwriters Laboratory test was 94V-0. Consequently, these materials possess excellent flame-retardant properties. © 2003 Wiley Periodicals,

Journal ArticleDOI
Maolin Pang1, J. Lin1, Jipeng Fu1, Rubo Xing1, Chunxia Luo1, Yanchun Han1 
TL;DR: In this article, a Pechini sol-gel process combined with a soft lithography was used to obtain homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths.