Showing papers on "Sol-gel published in 2004"
TL;DR: LiFePO4/carbon composite cathode materials were synthesized by a sol-gel process as discussed by the authors, where the citric acid in the developed sol−gel process plays the role not only as a complexing agent but also as a carbon source, which improves the conductivity of the composites and hinders the growth of the particles.
Abstract: LiFePO4/carbon composite cathode materials were synthesized by a sol–gel process. The citric acid in the developed sol–gel process plays the role not only as a complexing agent but also as a carbon source, which improves the conductivity of the composites and hinders the growth of LiFePO4 particles. Nano-sized LiFePO4 particles without the impurity phase were successfully synthesized. The grain size of LiFePO4 particles in the range of 20–30 nm is obtained at calcined temperatures from 450 to 850 °C. Increasing the calcination temperature leads to a decrease in the carbon content but an increase in the conductivity of the composites in the range of 400–850 °C. However, the conductivity slightly decreases if the calcination temperature further increases to 950 °C. The LiFePO4/carbon composite synthesized at 850 °C shows the highest conductivity (10−3 S cm−1), the highest specific capacity, and the best rate capability among the synthesized materials. It is worthy to note that the cell performance of the LiFePO4 depends on the electrochemical cycling procedure employed.
356 citations
TL;DR: In this article, the authors synthesize SnO2 particles by a sol-gel method from the very simple starting material granulated tin, where citric acid is introduced to stabilize the precursor solution and slow down the hydrolysis and condensation processes.
276 citations
TL;DR: The effect of SiO2 addition on anatase-to-rutile phase transition was investigated by DTA, XRD, FTIR, and XPS as mentioned in this paper.
Abstract: The effect of SiO2 addition on the anatase-to-rutile phase transition was investigated by DTA, XRD, FTIR, and XPS. TiO2 xerogels containing SiO2 up to 20 mol% were prepared by mixing and hydrolyzing titanium tetraisopropoxide (TTIP) and tetraethylorthosilicate (TEOS) with HNO3 as a catalyst. With increased amounts of SiO2 in the xerogels, the following results were obtained: (1) the crystallization temperature of anatase increased from 415°C in pure TiO2 to 609°C in 20-mol%-SiO2-containing xerogel in the DTA curves; (2) the formation temperature of rutile, according to quantitative XRD analysis, increased with increased SiO2 content up to 5 mol% SiO2 but became constant at higher SiO2 contents; (3) the crystallinity of anatase became lower; and (4) the lattice parameter a of the anatase decreased slightly, but the parameter c decreased greatly up to 20 mol% SiO2. Although the added silicon atoms were considered from these results to be incorporated into the amorphous TiO2 and anatase structures, the 29Si MAS NMR spectra of the xerogels containing 10 mol% SiO2 showed only tetrahedral silicon, with no indication of silicon in octahedral coordination. When calcined at higher temperatures, the xerogel showed polymerization of the SiO4 tetrahedra in the NMR spectra and the Si–O–Si vibration in the FTIR spectra. The chemical composition of the xerogel surfaces, measured using XPS, showed increased SiO2 content with increased calcining temperature, indicating the expulsion of silicon from inside the particles to form an amorphous SiO2 surface layer. The formation of this amorphous SiO2 surface layer was considered to be important in retarding the anatase-to-rutile phase transition by suppressing diffusion between anatase particles in direct contact and limiting their ability to act as surface nucleation sites for rutile. These effects of silicon additions were similar to those observed in the γ-Al2O3- to-α-Al2O3 transition.
247 citations
TL;DR: In this article, the surface structure of the thin films of iron (Fe) doped titanium dioxide (FeO2) were modified by adding different concentrations of polyethylene glycol (PEG) into the TiO2 sol.
246 citations
TL;DR: In this paper, the effect of dopant concentration, heating treatment and annealing in reducing atmosphere on the microstructure as well as on the electrical and optical properties of the thin films is discussed.
Abstract: Transparent and conductive high preferential c-axis oriented ZnO thin films doped with Al have been prepared by sol–gel method using zinc acetate and aluminium chloride as cations source, 2-methoxiethanol as solvent and monoethanolamine as sol stabilizer. Film deposition was performed by dip-coating technique at a withdrawal rate of 1.5 cm min−1 on Corning 1737 glass substrate. The effect of dopant concentration, heating treatment and annealing in reducing atmosphere on the microstructure as well as on the electrical and optical properties of the thin films is discussed. The optical transmittance spectra of the films showed a very good transmittance, between 85 and 95%, within the visible wavelength region. The minimum resistivity of 1.3×10−3 Ω cm was obtained for the film doped with 2 wt.% Al, preheated at 400 °C and post-heated at 600 °C, after annealing under a reduced atmosphere of forming gas.
236 citations
TL;DR: In this article, the photocatalytic activity of the formed layers was studied by means of their antibacterial property, and the UV blocking effect of titania coatings was also studied.
Abstract: Transparent thin film coatings of sol-gel derived titanium dioxide were produced on cotton fabrics at a low temperature of 150°C. The photocatalytic activity of the formed layers was studied by means of their antibacterial property. SEM images show the formation of continuous layers of titanium dioxide with grains of about 20 nm in diameter. The UV-blocking effect of titania coatings was also studied. XRD patterns revealed the existence of anatase phase in a small scale within the titania layers.
228 citations
TL;DR: In this article, a method based on the use of coordination chemistry is presented for stabilizing Ag + and Au 3+ ions in sol-gel systems, and the results are discussed with regard to the embedding matrix, the temperature and the atmosphere of the heat treatment, and it is concluded that crystallization of TiO 2 and ZrO 2 may hinder the growth of Ag and Au particles.
Abstract: Silver and gold nanoparticles were synthesized by the sol-gel process in SiO 2 , TiO 2 , and ZrO 2 thin films. A versatile method, based on the use of coordination chemistry, is presented for stabilizing Ag + and Au 3+ ions in sol-gel systems. Various ligands of the metal ions were tested, and for each system it was possible to find a suitable ligand capable of stabilizing the metal ions and preventing gold precipitation onto the film surface. Thin films were prepared by spin-coating onto glass or fused silica substrates and then heat-treated at various temperatures in air or H 2 . atmosphere for nucleating the metal nanoparticles. The Ag particle size was about 10 nm after heating the SiO 2 film at 600°C and the TiO 2 and ZrO 2 films at 500°C. After heat treatment at 500°C, the Au particle size was 13 and 17 nm in the TiO 2 and ZrO 2 films, respectively. The films were characterized by UV-vis optical absorption spectroscopy and X-ray diffraction, for studying the nucleation and the growth of the metal nanoparticles. The results are discussed with regard to the embedding matrix, the temperature, and the atmosphere of the heat treatment, and it is concluded that crystallization of TiO 2 and ZrO 2 films may hinder the growth of Ag and Au particles.
220 citations
TL;DR: In this article, high specific surface areas (77-244m 2 /g) were obtained for Titania-zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 ¼ ) by the sol-gel method.
Abstract: Titania–zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 wt.%) were prepared by the sol–gel method. High specific surface areas (77–244 m 2 /g) were obtained. Acidity determined by NH 3 -TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 μmol NH 3 /g for TiO 2 to 1226–1456 μmol NH 3 /g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO 2 adsorption, suggesting the formation of mixed oxides with acid–basic properties. XRD spectra identified anatase in the TiO 2 rich region, amorphous material in the mixed oxide 50–50 TiO 2 –ZrO 2 and tetragonal and monoclinic crystalline phases in the ZrO 2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid–basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density.
210 citations
TL;DR: In this paper, copper(II) oxide thin films were prepared by a sol-gel-like method on microscope glass substrates, and they were observed to crystallize to tenorite structure after heat treatment at 600°C for 30min.
202 citations
TL;DR: In this article, a multilayered system for delaying corrosion advance in metals requires that both the alteration mechanisms of the metal and the behaviour and properties of the protective coatings be known.
184 citations
TL;DR: It was suggested that the catalysis was caused by a formation of hydrogen bonds between hydroxyl groups in macromolecules and products of precursor hydrolysis (silanols), and it was demonstrated that the polysaccharides radically changed the structure of biomaterials.
Abstract: New monolithic nanocomposite silica biomaterials were synthesized on the basis of various natural polysaccharides and recently introduced completely water-soluble precursor tetrakis(2-hydroxyethyl) orthosilicate. The sol-gel processes were performed in aqueous solutions without the addition of organic solvents and catalysts. The silica polymerization was promoted by the polysaccharides through acceleration and catalytic effect on the processes. By introducing poly(vinyl alcohol) or poly(ethylene oxide) in the precursor solution, it was shown that the jellification took place in the case of the hydroxyl-containing polymer. Therefore, it was suggested that the catalysis was caused by a formation of hydrogen bonds between hydroxyl groups in macromolecules and products of precursor hydrolysis (silanols). It was also demonstrated that the polysaccharides radically changed the structure of biomaterials. In place of the cross-linked nanoparticles, there was a three-dimensional network from crossed or branched fibers and uncrossed spherical particles that filled the mesh space. The density of network, thickness of fibers, and properties of synthesized biomaterials depended on the polysaccharide type, charged degree of their macromolecule, and concentration. By varying these parameters, it was possible to manipulate the structural organization of hybrid polysaccharide-silica nanocomposites.
TL;DR: In this paper, it was found that the transformation temperature increases as the SiO 2 content in the ZrO 2 -SiO 2 binary oxide increases, and the most significant results were from samples containing only 2 mol% SiO2, where the metastable tetragonal phase formed at low temperatures and remained stable over a broad temperature range.
Abstract: Gel-glasses of various compositions in the xZrO 2 .(10-x)SiO 2 system were fabricated by the sol-gel process. Precipitation due to the different reactivities between tetraethyl orthosilicate (TEOS) and zirconium(IV) n-propoxide has been eliminated through the use of 2-methoxyethanol as a chelating agent. Thermal treatment of these gels produced crystalline ZrO 2 particles. While monoclinic is the stable crystalline phase of zirconia at low temperatures, the metastable tetragonal phase is usually the first crystalline phase formed on heat treatment. However, stability of the tetragonal phase is low, and it transforms to the monoclinic phase on further heat treatment. In this study, it has been found that the transformation temperature increases as the SiO 2 content in the ZrO 2 -SiO 2 binary oxide increases. The most significant results were from samples containing only 2 mol% SiO 2 , where the metastable tetragonal phase formed at low temperatures and remained stable over a broad temperature range. X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to elucidate the structure of these binary oxides as a function of temperature.
TL;DR: In this paper, hard and transparent organic-inorganic hybrid coatings with covalent links between the inorganic and the organic networks were prepared by the sol-gel method using a commercially available, acrylate end-capped polyurethane oligomeric resin, hexanedioldiacrylate (HDDA) as a reactive solvent, 3-(trimethoxysilyl)propoxymethacrylate, MPTMS as a coupling agent between the organic and inorganic phase, and a metal alkoxide, tetraethylorth
TL;DR: In this paper, the effects of ions diffused from the glass substrate on TiO2 photocatalysis were investigated using X-ray photoemission spectroscopy (XPS), XRD, ellipsometry, and absorption spectrograms.
Abstract: To study the effects of ions diffused from the glass substrate on TiO2 photocatalysis, TiO2 thin films were prepared on different kinds of glass substrates at different heating temperatures. The TiO2 films were characterized using X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), ellipsometry, and absorption spectroscopy. The photocatalytic activities of the TiO2 thin films were evaluated using the degradation reaction of trichloroethylene (TCE). Diffused ions such as Na+ and Si4+ raised the anatase formation temperature and increased the particle size of TiO2 thin films (rc). The photocatalytic activity of the thin films largely depended on the particle size of TiO2; the reciprocal number of the half-life of the TCE degradation, t1/2-1, was roughly proportional to rc-1.8. The conventional recombination center hypothesis for the Na+ ions might not hold for the sol−gel TiO2 films.
TL;DR: In this paper, a spin-coated SnO2 thin film was grown on soda-lime glass substrate using a simple spincoating method using microstructural and luminescent measurements.
TL;DR: In this article, a nonhydrolytic cross-condensation method was also extended to the binary metal oxides nanocrystals, i.e., HfO2−ZrO2, ZrO 2−TiO2 and Hf O2−NiO2.
Abstract: A nonhydrolytic sol−gel process closely following that of Hyeon et al. for the synthesis of ZrO2 nanocrystals (J. Am. Chem. Soc. 2003, 125, 6553−6557) was used to synthesize highly crystalline and monodisperse HfO2 nanoparticles. Reactions of hafnium isopropoxide with hafnium halides at high temperature in a strongly coordinating solvent yield nanometer-sized particles of HfO2. The size, shape, and crystalline phase of the hafnia particles depend on both the reaction temperature and the halide. The nonhydrolytic cross-condensation method was also extended to the binary metal oxides nanocrystals, i.e., HfO2−ZrO2, ZrO2−TiO2, and HfO2−TiO2. Efforts to prepare nanocrystals of HfxZr1-xO2 over a wide range of x were successful; however, this method could not be used to prepare either ZrxTi1-xO2 or HfxTi1-xO2. In conjunction with X-ray powder diffraction and high-resolution transmission electron microscopy, Raman spectroscopy identifies the structural phase of the nanocrystals and also proves the formation of th...
TL;DR: In this article, nanosized TiO2 powders for photocatalytic degradation of organic pollutants are prepared by sol-gel method by synthesizing by hydrolysis and controlled condensation of titanium isopropoxide Ti(O-iC3H7)4.
TL;DR: In this article, the structure of cerium-doped anatase lattice was visualized through crystal simulation to investigate the possible substitution of Ti 4+ by Ce +4 ions.
TL;DR: In this article, a modified sol-gel method was used to obtain pure titania, zirconia, and binary TiO 2 -ZrO 2 oxides with molar ratios of 1:3, 1:1 and 3:1.
Abstract: Pure titania, zirconia, and binary TiO 2 –ZrO 2 oxides with Ti/Zr molar ratios of 1:3, 1:1 and 3:1 were prepared by a modified sol–gel method. The samples were calcined at different temperatures and characterized by nitrogen adsorption porosimetry, XRD, DSC–TGA and FT-IR. After calcination at 450 °C the pure titania and zirconia are in the crystalline phase (anatase and tetragonal, respectively) while the binary oxides remain in the amorphous phase. The binary oxides are crystallized after calcination at temperatures above 800 °C, but only the TiO 2 –ZrO 2 (1:1) sample is in the single phase of crystalline TiZrO 4 while the other two binary oxides contain TiZrO 4 and tetragonal (or monoclinc) zirconia and rutile phases, respectively. The crystallization temperature for the formation of ZrTiO 4 phase in the three binary oxides increases with titania content (respectively at 606, 716 and 754 °C). Different from the pure oxides, which exhibit two types of surface OH group, the binary oxides after calcination at 450 °C only have surface terminal OH group. The OH surface density decreases and, after passing through a minimum at about equimolar composition of Ti/Zr, increases with increasing titania content. The mixed oxides exhibit a large amount of surface acid sites.
TL;DR: Aluminum doped zinc oxide polycrystalline thin films (AZO) were prepared by sol-gel dip-coating process as discussed by the authors, and they are transparent from the near ultraviolet to the near infrared, presenting an absorption cutoff at almost 290 nm, irrespective of the nature of the catalyst and doping level.
Abstract: Aluminum doped zinc oxide polycrystalline thin films (AZO) were prepared by sol-gel dip-coating process. The sol was prepared from an ethanolic solution of zinc acetate using lithium hydroxide or succinic acid as hydrolytic catalyst. The quantity of aluminum in the sol was varied from 1 to 10 mol%. The structural characteristics studied by X-ray diffractometry were complemented by resistivity measurements and UV–Vis-NIR spectroscopy. The films are transparent from the near ultraviolet to the near infrared, presenting an absorption cut-off at almost 290 nm, irrespective of the nature of the catalyst and doping level. The best conductors were obtained for the AZO films containing 3 mol% of aluminum, prepared under acidic and basic catalysis and sintered at 450 °C. Their optical band-gap of 4.4 eV calculated from the absorption cut-off is larger than the values for band-gap widening predicted by the standard model for polar semiconductors. These polycrystalline films are textured with preferential orientation of grains along the wurtzite c -axis or the (100) direction.
TL;DR: In this article, the sublimation of cyclohexane circumvents the capillary pressures which cause pore collapse during the normal solvent removal process, and the resulting materials are very porous with specific surface areas as high as 250 m 2 /g.
Abstract: Vanadium oxide aerogels have received considerable interest as a reversible electrode material for lithium secondary batteries. The aerogel morphology is a critical factor in obtaining the electrochemical properties of these materials. The present paper reports on the synthesis of V 2 O 5 by freeze-drying, an alternative approach for producing a material with an aerogel-like morphology. In this synthesis, the sublimation of cyclohexane circumvents the capillary pressures which cause pore collapse during the normal solvent removal process. The resulting materials are very porous with specific surface areas as high as 250 m 2 /g. The electrochemical properties of the freeze-dried material are strongly influenced by both the specific surface area of the solid phase and crystallite size. The controlled heat-treatment of the aerogel produces a ω-Li x V 2 O 5 -type phase with improved capacity and reversibility.
TL;DR: In this article, the CdS−TiO 2 mixed sols were further treated with the hydrothermal processing at the temperatures of 120-240°C by casting the resulting sol onto F:SnO 2 conducting glass and a subsequent heat treatment at 400°C under air.
TL;DR: In this paper, pure and rare earth doped gadolinium oxide (Gd 2 O 3 ) waveguide films were prepared by a simple sol-gel process and dip-coating method.
TL;DR: In this paper, different heat-treatments were applied on powders and pellets of Na2Ti3O7 and N2Ti6O13 and the effects were studied by XRD, dilatometry, TGA-DTA, SEM and electrochemical impedance spectroscopy.
TL;DR: In this article, the size and shape of ITO(20-30nm) particles were controlled by pH of co-precipitation solution, thermal oxidation temperature and tin contents.
TL;DR: In this paper, the authors reported the preparation of mixed oxides of different composition, incorporating the biopolymer chitosan to the precursor mixed sol, producing a hybrid xerogel.
TL;DR: In this article, the anatase to rutile phase transition in sol-gel TiO 2 has been investigated and it was found that incorporation of about 0.17-at% of Sn completely transforms anatase TiO2 to the Rutile form at a calcination temperature as low as 500°C.
TL;DR: The biocompatibility of the oxide layers which was investigated by in vitro tests is improved as compared to uncoated and TiO2 sol–gel coated cp-titanium concerning the spreading of cells, collagen I synthesis and wettability.
Abstract: Thin biocompatible oxide films with an optimised composition and structure on the surface of titanium and its alloys can improve the implant integration. The preparation of these thin oxide layers with the intended improvement of the surface properties can be realised by means of the sol-gel process. Nb2O5 is a promising coating material for this application because of its extremely high corrosion resistance and thermodynamic stability. In this study, thin Nb2O5 layers ( < 200 nm) were prepared by spin coating of polished discs of cp-titanium with a sol consisting of a mixture of niobium ethoxide, butanol and acetylacetone. The thickness, phase composition, corrosion resistance and the wettability of the oxide layers were determined after an optimisation of the processing parameters for deposition of oxide without any organic impurities. The purity of the oxide layer is an important aspect in order to avoid a negative response to the cell adhesion. The biocompatibility of the oxide layers which was investigated by in vitro tests (morphology, proliferation rate, WST-1, cell spreading) is improved as compared to uncoated and TiO2 sol-gel coated cp-titanium concerning the spreading of cells, collagen I synthesis and wettability.
TL;DR: Both approaches resulted in the formation of nanocrystalline carbonated hydroxyapatite films but with different Ca/P ratios and structures, the Inorganic Route-formed film having a lower Ca/p ratio and having a more irregular topography.
TL;DR: In this paper, a sol-gel route to c-axis oriented undoped and Co, Fe and Mn doped ZnO films was reported, which was spin-coated on to hydrophilic sapphire substrates then dried, annealed and post-annealed.
Abstract: A novel sol-gel route to c-axis oriented undoped and Co, Fe and Mn doped ZnO films is reported. Sols were prepared from a hydrated zinc acetate precursor and dimethylformamide (DMF) solvent. Films were spin-coated on to hydrophilic sapphire substrates then dried, annealed and post-annealed, producing almost purely uniaxial ZnO nanocrystallites and a high degree of long-range structural order. Specific orientation of hexagonal crystallites is demonstrated both perpendicular and parallel to the substrate surface. Cobalt doping resulted in the formation of disconnected oriented ZnO nanocrystals. Vanadium doped films formed the spinel oxide ZnAl2O4. Structural, optical and morphological characterisation demonstrated the high quality of the films and shows the suitability of the method for cost-effective fabrication studies in areas of oxide research that traditionally employ epitaxial growth techniques.