Showing papers on "Sol-gel published in 2005"

Solution-processed zinc oxide field-effect transistors based on self-assembly of colloidal nanorods.

Abstract: Colloidal zinc oxide (ZnO) nanocrystals are attractive candidates for a low-temperature and solution-processible semiconductor for high-performance thin-film field-effect transistors (TFTs). Here we show that by controlling the shape of the nanocrystals from spheres to rods the semiconducting properties of spin-coated ZnO films can be much improved as a result of increasing particle size and self-alignment of the nanorods along the substrate. Postdeposition hydrothermal growth in an aqueous zinc ion solution has been found to further enhance grain size and connectivity and improve device performance. TFT devices made from 65-nm-long and 10-nm-wide nanorods deposited by spin coating have been fabricated at moderate temperatures of 230 °C with mobilities of 0.61 cm2V-1s-1 and on/off ratios of 3 × 105 after postdeposition growth, which is comparable to the characteristics of TFTs fabricated by traditional sputtering methods.

Super-liquid-repellent surfaces prepared by colloidal silica nanoparticles covered with fluoroalkyl groups.

Abstract: A simple and easy method to prepare super-liquid-repellent surfaces is proposed Sol-gel films were prepared by hydrolysis and condensation of alkoxysilane compounds Both surface energy and roughness were controlled using colloidal silica particles and fluoroalkylsilane When the fractional amounts of both colloidal silica and fluoroalkylsilane were optimized in the films, the film surface exhibited repellency to both water and oil Finally, it was shown that the method proposed here would be applied to a simple one-pot coating for a uniform large area, and be useful for practical use

Chemical modification of titanium alkoxides for sol–gel processing

Abstract: The chemical modification of titanium alkoxides by alkoxy- and aminoalcohols, s-diketones, s-ketoesters, carboxylic and phosphonic acids, and related compounds, and the hydrolysis behavior of the organically modified precursors are reviewed Special focus is put on structural aspects and on the possibility to introduce functional organic groups Such precursors have a high potential for innovative materials syntheses because they permit control of the precursor reactivity in sol–gel processes and the preparation of titania-based inorganic–organic hybrid materials Coordination, solvation, aggregation and redistribution equilibria play an important role in the chemistry of the modified titanium alkoxides, and organic side reactions have to be taken into account

Sol‐Gel Synthesis of Amorphous Calcium Phosphate and Sintering into Microporous Hydroxyapatite Bioceramics

Abstract: A new route for preparing hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) bioceramic has been described. An amorphous, nanosized, and carbonate-containing calcium phosphate powder that had a Ca:P ratio of 1.67 was synthesized from calcium diethoxide and phosphoric acid in ethanol via a sol-gel method. The powder was pressed at 98 MPa into green specimens and then heated to a temperature range of 500°-1300°C. At 600°C, the powder crystallized to a carbonated hydroxyapatite and a trace of β-tricalcium phosphate before converting to hydroxyapatite at 900°C. The thermal crystallization was associated with grain growth, shrinkage, and active surface diffusion. The activation energy of grain growth was 37 ± 2 kJ/mol. After sintering at 1100°C, the decomposition of carbonated hydroxyapatite generated a microporous ceramic with an average pore size of 0.2 μm and an open porosity of 15.5%. This microporous bioceramic can be used as a bone filler.

Sol gel derived photocatalytic porous TiO2 thin films

Abstract: Transparent porous TiO 2 thin film was spin-coated on glass substrates from a sol gel solution containing titanium alkoxide as precursor. Polyethylene glycol (PEG), with different molecular weight, was added to the coating solution as a structure-directing agent, and the films thus prepared were transparent, crack free and nanoporous. The surface morphology of the films has been observed by field emission gun-scanning electron microscope (FEG-SEM), the crystal structure characterized by X-ray diffraction (XRD) and the photocatalytic activity of the TiO 2 thin films evaluated. All the films are hydrophilic. The decomposition of PEG during high temperature treating is considered to be responsible for the generation of porous structure in the films as compared with TiO 2 film without addition of the polymer, and higher molecular weight leads to larger pore size and specific surface area. XRD shows that all TiO 2 films display the characteristic diffraction peaks of a TiO 2 anatase structure at 550 'C. The photocatalytic activity of the TiO 2 thin films as evaluated by the decomposition of methyl orange was increased with the PEG molecular weight increased.

Nanostructuring titania by embossing with polymer molds made from anodic alumina templates.

Abstract: We demonstrate a method for embossing titania sol−gel precursor with poly(methyl methacrylate) (PMMA) molds to make thin films of titania that have dense arrays of 35−65 nm diameter pores, whose features are 1 order of magnitude smaller than those previously demonstrated for sol−gel molding. We show that the high modulus of PMMA is necessary to preserve small features with high aspect ratios on the mold for nanopatterning. The molds are prepared by thermally infiltrating PMMA into anodic alumina templates, whose pore dimensions and depths are adjustable by varying anodization conditions. The difficulties associated with mold release from a master are avoided by wet etching the template. These titania films, and others made with other semiconductors, could be useful for photovoltaic, photocatalytic, and sensing applications where nanostructuring of surfaces with controlled dimensions are essential.

Sol‐Gel Route to Ferroelectric Layer‐Structured Perovskite SrBi2Ta2O9 and SrBi2Nb2O9 Thin Films

Abstract: Precursors for layer-structured perovskite thin films of SrBi 2 Ta 2 O 9 (SBT) and SrBi 2 Nb 2 O 9 (SBN) were prepared by the reactions of a strontium-bismuth double methoxyethoxide and tantalum or niobium methoxyethoxide in methoxyethanol, followed by partial hydrolysis. Several spectroscopic techniques, such as 1 H-, 13 C-, and 93 Nb-NMR (nuclear magnetic resonance), and Fourier-transform infrared spectroscopy were used to analyze the arrangement of the metals and oxygen in the precursor molecules. The precursors contained Sr-O-M (where M is Ta or Nb) bonds (i.e., a strontium is connected to two MO 6 octahedra) and Sr-O-Bi bonds with a bismuth atom bonded to the oxygens of the MO 6 octahedron. The arrangement of metals and oxygens was considered to be similar to the layer-structured perovskite crystal sublattice. As a result, the sol-gel-derived SBT thin films crystallized, by rapid thermal annealing in an oxygen atmosphere below 550°C, and they exhibited preferred (115) orientation. The crystallinity improved and the crystallite size increased with temperature up to 700°C. In the case of SBN thin films, a low heating rate (2°C/min) was necessary for the control of the crystallographic (115) orientation, whereas a rate of 200°C/s (rapid thermal annealing) produced films that exhibited c-axis orientation. The (115) SBT thin film, heated to 700°C, exhibited improved ferroelectric properties.

Synthesis of TiO2 porous thin films by polyethylene glycol templating and chemistry of the process

Abstract: Titanium dioxide porous films have been deposited on glass slides by sol–gel technology. Tetrabutylorthotitanate and polyethylene glycol were used as a precursor and template, respectively. The chemical mechanism is discussed in relation to the sol–gel transition, which provides a possible theoretic explanation to the formation of TiO 2 porous films. The morphology of porous TiO 2 thin films strongly depends on the amount of water, the types of solvents and complexing agents, and the concentration and molecular weight of the template. It was shown that the diameter of pores is tunable in the range of 10–500 nm and the maximum of BET specific area of the films is 72 m 2 /g.

Preparation, characterization and photocatalytic properties of REFeO3 (RE = Sm, Eu, Gd)

Abstract: Nanometer materials of rare earth mixed oxides REFeO 3 (RE = Sm, Eu, Gd) with the structure of perovskite-type were synthesized by the sol–gel method in the citric acid system. The structure and crystal phase of the powders were characterized using an X-ray diffractometer. The shape and size were analyzed using a JEM-100X transmission electron microscopy. The perovskite-type oxides were spherical with the mean grain size of 28, 20 and 21 nm, respectively. Their crystal structures showed a certain amount of lattice distortion due to the decrease of grain size and the increase of surface area. The photocatalytic activities of these three materials were studied for the degradation of various water-soluble dyes. The effect of catalyst loading on the photocatalytic activity was also investigated. SmFeO 3 , EuFeO 3 , GdFeO 3 exhibited high photocatalytic activities and the increase in catalyst loading could improve their photocatalytic activities.

Organic–inorganic polymer hybrids prepared by the sol-gel method

Abstract: This review focuses on some aspects of organic-inorganic hybrid materials prepared by the sol-gel method. This field has been studied worldwide as one of the nanotechnologies, and is now of current interest for both organic and inorganic scientists. The elaboration of organic–inorganic polymer hybrid materials using the sol-gel process can be accomplished by various approaches. The simplest method is increasing the compatibility by using physical interactions, covalent bonding and compatibilizer between organic polymer and silica gel. Other novel approaches, such as an in-situ method, NHSG (Non- Hydrolysis Sol-Gel) process, and use of reactive polymer hybrids resulted in the preparation of novel transparent organic–inorganic polymer hybrid materials. Stimulus responsive polymer hybrids are also mentioned. Furthermore, nano-structured organic–inorganic polymer hybrids are created by using supermolecular and self-assembly of organic molecules or polymers recently. The obtained nano-structured hybrid materia...

Functional nanostructured chitosan–siloxane hybrids

Abstract: New organic–inorganic hybrids were prepared by a sol–gel method from the biopolymer chitosan and a silane coupling agent, 3-isocyanatopropyltriethoxysilane (ICPTES), in which covalent bridges, essentially composed of urea, bond the chitosan to the poly(siloxane) network. The structural characterization of the advanced chitosan–siloxane hybrids was performed by Fourier transform infrared spectroscopy, X-ray diffraction and 29Si and 13C nuclear magnetic resonance. The presence of siloxane nanodomains was detected by small angle X-ray diffraction. The chitosan–siloxane hybrids are bifunctional materials with interesting photoluminescent features and bioactive behaviour. The photoluminescence spectra display an additional high-energy band with longer lifetime, relatively to the characteristic emission of pure chitosan. This band is associated with electron–hole recombinations arising from silicon-related defects at the surface of the siliceous nanodomains. The bioactive behaviour of these materials was also evaluated; the apatite formation was shown to depend on the amount and arrangement of silanol groups.

Single Source Precursor Approach for the Sol−Gel Synthesis of Nanocrystalline ZnFe2O4 and Zinc−Iron Oxide Composites

Abstract: Nanostructured ZnFe2O4 and zinc oxide−iron oxide composites were obtained by sol−gel processing of a hetero-bimetallic alkoxide. For this purpose the novel molecular precursors Fe2Zn(OR)8 (R = tBu, iPr), fully characterized by spectroscopic and single-crystal diffraction techniques, have been synthesized and their applications in the sol−gel procedure were investigated. The obtained xerogels were annealed at very low temperatures (down to 200 °C) yielding crystalline phases with very small crystallite grain sizes. The phase compositions of the material strongly depend on the polarity of the solvents used in the hydrolysis reaction. When the hydrolysis was performed in the polar propan-2-ol, the spinel ZnFe2O4 (franklinite) formed at annealing temperature of 200 °C with a mean crystallite grain size Dvol of 2.24 nm. However, when using the less polar toluene as solvent in the sol−gel process, iron oxide and zinc oxide are formed together with the franklinite phase. This mixture of phases transforms to the ...

Preparation of Macroporous Titania Films by a Sol‐Gel Dip‐Coating Method from the System Containing Poly(ethylene glycol)

Abstract: Macroporous titania (TiO2) films have been prepared via a sol-gel dip-coating method from a titanium tetraisopropoxide solution that contains poly(ethylene glycol) (PEG). The macroporous morphology-i.e., the size, distribution, and shape of the macropores-is controlled by varying the content and molecular weight of PEG, the withdrawal speed, and the temperature of the dipping solution. The morphology of the TiO2 film is determined by competitive contributions of the following factors: (i) decrease in fluidity, because of the evaporation of solvent; (ii) network formation by polycondensation reactions; and (iii) domain formation during phase separation into gel phases and solvent phases.

General and Convenient Method for Making Highly Luminescent Sol−Gel Derived Silica and Alumina Films by Using LaF3 Nanoparticles Doped with Lanthanide Ions (Er3+, Nd3+, and Ho3+)

Abstract: Silica films with Ln3+-doped LaF3 nanoparticles were prepared by sol gel method and their luminescent properties were studied as a function of the temperature. Significant improvements in the luminescent properties, in terms of the lifetime for the 4I13/2 level of Er3+ (∼10.9 ms), 4F3/2 level of Nd3+ (∼171 μs), and 5F3 level of Ho3+ (∼6 μs), were obtained when corresponding nanoparticles are incorporated in silica films rather than the bare ions. In addition to the LaF3 as the low phonon energy matrix, the absence of lanthanide ion clustering, and the increased distance between the OH groups of the silica matrix and the lanthanide ions, are responsible for the observed improvements in the luminescent properties for nanoparticle incorporated silica films. Lifetime values could be further improved by incorporating core−shell nanoparticles (the doped LaF3 core surrounded by an undoped shell of LaF3) in the silica matrix, as a result of further reduction of the nonradiative pathways.

Handbook of sol-gel science and technology : processing, characterization and applications

Abstract: V1 -The Synthesis and Solution Stability of Alkoxide Precursors -Reactions of Alkoxides toward Nanostructured or Multi-Component Oxide Films -Sol-gel Processing of Thin Films with Metal salts -Chemistry and Applications of Polymeric Gel Precursors -Aqueous Precursors -Sol-Gel Formation of Bulk Glasses -Sol-Gel Derived Powders and Bulk Ceramics -Oxynitrides Glasses and Nitrides -Oxycarbide Glasses and Carbides -Sol-Gel Processing of Fluoride And Oxyfluoride Materials -Sol-Gel Processing of Sulfide Materials -Fundamental Issues on Sol-Gel Coatings: Stress Evolution, Cracking and Radiative Striations -Ultrasonic Pulverization of an Aerosol: A Versatile Tool for the Deposition of Sol-Gel Thin Films -Electrophoretic Sol-Gel Deposition -Low Temperature Processing of Sol-Gel Thin Films in the SiO2-TiO2 Binary System -Self-Standing Thick Films -Synthesis of Ferroelectric Thin Films with Preferred Orientation -Processing of Fibers -Processing of Monodisperse Particles -Entrapment of Organic Molecules -Encapsulation of Enzymes, Antibodies and Bacteria -Processing of High Performance Catalysts -Macroporous Morphology Control by Phase Separation -Formation of Ordered Mesoporous Thin Films through Templating -Aerogel Processing -Non-Hydrolytic Sol-Gel Technology -Ultraviolet (UV) Irradiation V2 -X-Ray and Neutron Diffraction Study of Xerogels and Gel-Derived Glasses -X-Ray Absorption Spectroscopy Studies on Materials Obtained by the Sol-Gel Route -Atomic Scale Structure of Gel Materials by Solid State NMR -Characterization of Sol-Gel Materials by Infrared Spectroscopy -Characterization of Sol-Gel Materials by Raman and Brillouin Spectroscopy -Surface Structure of Sol-Gel Derived Materials Using X-Ray Photoelectron Spectroscopy (XPS) - Structural Characterization of Hybrid Organic-Inorganic Materials -Small-Angle X-Ray Scattering by Nanostructured Materials -Porosity Measurement -Measurements of Gas Adsorption and Permeability of Sol-Gel Materials -Specific Behavior of Sol-Gel Materials in Mercury Porosimetry: Collapse and Intrusion -Viscosity and Spinnability of Gelling Solutions -Thermal Conductivity of Silica Aerogels -Mechanical Properties of Gels: From Alcogel and Aerogels to Glasses -Characterization of the Mechanical Properties of Sol-Gel Coatings -Mechanical Properties of Organic-Inorganic Hybrids -Characterization of Sol-Gel Thin Film Waveguides Ellipsometry of Sol-Gel Films -Active Sol-Gel Materials, Fluorescence Spectra and Lifetimes -Nonlinear Optical Properties of Materials Derived by Sol-Gel Technology -Molecule-to-Particle Charge Transfer in Sol-Gel Materials -Ferroelectric and Piezoelectric Properties V3 -The Outline of Applications of the Sol-Gel Method -Fabrication of Large Near Net Shapes of Fiber Optic Quality Silica -Monolithic Porous Silica for High Speed HPLC -Hydrophobic Silica Aerogels -Densification of Aerogels: From Optical Glasses to Nuclear Waste Confinement -Sol-Gel Derived Oxide Powders as Precursors for Sintered Ceramics -Sol-Gel Processed Membranes -Silica Spherical Microparticles Applied as Spacers -Sol-gel Abrasive Grains - History, Precursor Properties and Microstructural Control -Sol-Gel Prepared Glass and Ceramic Fibers -Sol-gel Processing for Spectral Hole-burning Materials -Sol-Gel Processed Lasers -Photonic Crystals Prepared by Using Sol-Gel -Colored Coatings with Organic Dyes and Pigments -Colored Coatings with Metal Colloids -Sol-Gel Micropatterning Process -Sol-Gel Prepared Reflective Coatings -Sol-Gel Prepared Antireflective Coatings -Sol-Gel Coatings Applied to Automotive Windows -Application of Transparent and Antiglare Conducting Coatings -Sol-Gel Coating of the Panel of Cathode Ray Tube for Improving the Quality of Display -Sol-Gel Coatings for Electrochromic Devices -Solar Cells Based on Sol Gel Films -Sol-Gel Processing for Battery and Fuel Cell Applications -Sol-gel Derived Silicate Based Composite Electrode -Sol-gel Processed Photocatalytic Titania Films -Coatings with Photocatalyst on Architectural Glass -Sol-Gel Protective Coatings for Metals -Inorganic Coating Materials for Buildings -Inorganic-Organic Polymers with Barrier Properties against Water Vapor, Oxygen and Migrating Monomers -Sol-Gel Materials for Art Conservation -Fullerene Nano-Composites Prepared via Soft-Chemistry Routes -Catalysis and Reactivity with Sol-Gel Entrapped Organic and Organometallic Chemicals -Inorganic-Organic Hybrids for Biomedical Applications -Hybrid Sol/Gels for DNA Arrays and other Lab-on-a-Chip Applications -Application of Sol-Gel Processing to Wood-Inorganic Composites

Method of synthesizing zirconium phosphate particles

Abstract: Zirconium phosphate particles are synthesized by providing a solution of zirconium oxychloride in an aqueous solvent, adding at least one oxygen-containing additive to the solution, the oxygen-containing additive being selected to form a complex with zirconium ions in the solution of zirconium oxychloride and thereby reduce hydration of the zirconium ions, and combining this solution with phosphoric acid or a phosphoric acid salt to obtain zirconium phosphate particles by sol gel precipitation.