Showing papers on "Sol-gel published in 2006"

Sol–gel preparation of mesoporous photocatalytic TiO2 films and TiO2/Al2O3 composite membranes for environmental applications

Abstract: This study describes the application of novel chemistry methods for the fabrication of robust nanostructured titanium oxide (TiO2) photocatalysts. Such materials can be applied in the development of efficient photocatalytic systems for the treatment of water. Mesoporous photocatalytic TiO2 films and membranes were synthesized via a simple synthesis method that involves dip-coating of appropriate substrates into an organic/inorganic sol composed of isopropanol, acetic acid, titanium tetraisopropoxide, and polyoxyethylenesorbitan monooleate surfactant (Tween 80) followed by calcination of the coating at 500 8C. Controlled hydrolysis and condensation reactions were achieved through in-taking of water molecules released from the esterification reaction of acetic acid with isopropanol. The subsequent stable incorporation of Ti–O–Ti network onto self-assembled surfactants resulted in TiO2 photocatalysts with enhanced structural and catalytic properties. The properties included high surface area (147 m 2 /g) and porosity (46%), narrow pore size distribution ranging from 2 to 8 nm, homogeneity without cracks and pinholes, active anatase crystal phase, and small crystallite size (9 nm). These TiO2 photocatalysts were highly efficient for the destruction of methylene blue and creatinine in water. High water permeability and sharp polyethylene glycol retention of the prepared photocatalytic TiO2/Al2O3 composite membranes evidenced the good structural properties of TiO2 films. In addition, the multi-coating procedure made it possible to effectively control the physical properties of TiO2 layer such as the coating thickness, amount of TiO2, photocatalytic activity, water permeability and organic retention. # 2005 Elsevier B.V. All rights reserved.

Metal oxide nanoparticles: synthesis, characterization and application

Abstract: The synthesis of metal oxide nanoparticles is described in terms of precursor formation, nucleation, growth, and aging processes. The main parameters governing these processes are the solution properties, including the solvent viscosity, dielectric constant and the presence of adsorbing anions, the solubility of the metal oxide, and the metal oxide surface energy.

Sol-gel synthesis of Au/TiO2 thin films for photocatalytic degradation of phenol in sunlight

Abstract: Thin films of Au/TiO2 on glass substrates have been prepared by simple sol–gel dip coating method using a sol of colloidal gold doped titanium peroxide (Au/TiO2 sol). The sol of colloidal gold and titanium peroxide forms a viscous gel after 1–3 h depending on the concentration of both colloidal gold and titania. The sol of particular viscosity range (140–2800 cps) was used to deposit the Au/TiO2 thin films of uniform thickness on various substrates such as glass slides, glass helix and silica rashig rings. Films deposited on glass plates after drying were transparent, uniform in color as well as thickness. Optical characterization by UV–vis spectrophotometer showed a shift in optical absorption wavelength to visible region may be due to the incorporation of gold nanoparticles into titania structure. The optimum concentration of gold loading was found to be 1–2% (by weight) beyond this the gold particles disturb the gel network resulting the formation of gelatinous precipitate. Thin film photo-catalyst prepared was characterized by various techniques such as UV–vis, TG-DTA, XRD, ICP-OES and TEM. The photo-activity of the thin films was tested in sunlight using phenol as model pollutant. The kinetic study showed that the rate of decomposition of phenol using Au/TiO2 photo-catalyst was improved by 2–2.3 times than undoped TiO2.

Nanoparticle Assembly of Ordered Multicomponent Mesostructured Metal Oxides via a Versatile Sol−Gel Process

Abstract: Multicomponent metal oxides have attracted attention for their potential use in electronic, (photo)catalytic, photovoltaic, and energy storage applications. The ability to simultaneously control the nanoscale structure and composition of such materials using simple and inexpensive routes is important for that potential to be realized. Here we introduce a simple and widely applicable methodology for the synthesis of multicomponent mesostructured metal oxides (MMMOs) from the combination of inexpensive and commercially available polymers with metal alkoxides solubilized in a sol−gel solution consisting of acetic acid, hydrochloric acid, and ethanol (AcHE). MMMOs obtained utilizing the AcHE system have tunable pore structures, a high degree homogeneity, and in certain cases thermal stability above 1000 °C. The ability to easily process these diverse MMMOs in the form of thin films, free-standing membranes, and monoliths provides distinct advantages over previously reported MMO synthesis proceduresespecially ...

New insight in the role of modifying ligands in the sol-gel processing of metal alkoxide precursors: A possibility to approach new classes of materials

Abstract: This paper summarizes recent literature data and presents new experimental data on the mechanisms of chemical modification, hydrolysis and polycondensation of the alkoxides and demonstrates possibilities to approach new classes of materials, exploiting these mechanisms. Low reactivity of silicon alkoxides is improved by either basic catalysis exploiting an SN2 mechanism or acidic catalysis facilitating a proton-assisted SN1 mechanism as well as by modification with chelating ligands. Metal alkoxides are much stronger Lewis bases compared to silicon alkoxides and the acidity of water is strong enough to achieve their rapid hydrolysis via proton-assisted SN1 pathway even in the absence of additional catalysts. Introduction of the modifying chelating ligands is leading generally to increased charge distribution in the precursor molecules. Modifying chelating ligands are also appreciably smaller than the alkoxide ligands they replace. The modification with chelating ligands is thus facilitating the kinetics of hydrolysis and polycondensation. The size and shape of the primary particles formed in sol-gel treatment of metal alkoxides are defined not by kinetic factors in their hydrolysis and polycondensation but by the interactions on the phase boundary, which is in its turn directed by the ligand properties. The products of the fast hydrolysis and condensation sequence consist of micelles templated by self-assembly of ligands (mainly oxo-species). This concept provides explanations for commonly observed material properties and allows for the development of new strategies for the preparation of materials. We discuss the formation of inverted micelles, obtained by the appropriate choice of solvents, which allows for the formation of hollow spheres. The modifying β-diketonate ligands act as the surfactant and form an interface between the hollow sphere and the solvent. Retention of ligands inside the gel particles is possible only if ligands possessing both chelating and bridging properties are applied. Application of such ligands, for example, diethanolamine, permits to prepare new transition metal oxide based microporous membranes.

Synthesis and Characterization of Carbon-Coated Lithium Transition Metal Phosphates LiMPO4 (M = Fe , Mn, Co, Ni) Prepared via a Nonaqueous Sol-Gel Route

Abstract: An organic solvent-based sol-gel method has been utilized for the synthesis of lithium transition metal phosphates. With this simple and versatile method, particles with sub-μm size and uniform size distribution are obtained for all the LiMPO 4 (M = Fe, Mn, Co. Ni) materials investigated. Homogeneous in situ carbon coating of a few weight percent is achieved with all of them, except LiCoPO 4 , where the in situ carbon coating is only 0.6 wt %. The best-performing as-prepared LiFePO 4 , with in situ surface carbon coating of 1.8 wt %, achieves an electronic conductivity on the order of 10 -2 S/cm and exhibits highly promising electrochemical performance, with only slight dependence on the carbon content of the composite electrode in certain range. Carbon-coated LiFePO 4 samples prepared at lower temperatures exhibit lower electronic conductivity, evidently due to lower specific conductivity of the surface carbon. The dependence of the morphology and electrochemical performance of the synthesized LiFePO 4 on the precursor concentration and the aging time of the gel is investigated. The results also yield information for understanding of the mechanisms of the sol-gel synthesis process, which are discussed. Electrochemical performance of the carbon-coated LiMnPO 4 and LiCoPO 4 was tested and discussed.

TiO2 photocatalytic films on stainless steel: The role of Degussa P-25 in modified sol–gel methods

Abstract: The role of Degussa P-25 loading (0–100 g/L) in the alkoxide sol was investigated for the synthesis of immobilized TiO 2 photocatalytic films on 304 stainless steel using the P-25 powder-modified sol–gel method (PPMSGM). The structural properties of the films (PPMSGFs) obtained after gel drying and calcination at 600 °C were examined using different materials characterization techniques including X-day diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of films with good adherence to the stainless steel support were evaluated using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant and UV-A radiation. The P-25 loading did not have a significant effect on the size of the crystallites in the films. However, increasing the P-25 loading in the sol resulted in an increase in (i) the amount of crystalline material retained on the support (i.e., for both anatase (1 0 1) and rutile (1 1 0) crystal phases); (ii) the number of grains (aggregates of P-25 particles and crystallites formed from the alkoxide sol); (iii) the number of pores in the film (in the range of 0–50 g/L); and (iv) the number of microcracks on the surface of PPMSGFs. On the other hand, increasing the P-25 loading in the sol resulted in a decrease in the size of grains on the surface of PPMSGFs. XPS analysis revealed the presence of Cr 3+ , Mn 3+ and Fe 3+ on the surface of PPMSGFs as a result of diffusion of these species from the stainless steel support during film calcination at 600 °C. The concentration of these foreign species on the film surface decreased with an increase in the P-25 loading in the sol. Increasing P-25 loading in the sol yielded films with higher photocatalytic activity but a concentration of 50 g/L P-25 in the sol was found as the maximum for obtaining films with good adherence on the stainless steel support. Increase in the photocatalytic activity of the films with increasing P-25 loading in the sol was mainly attributed to the enhancement of the number of P-25 active sites exposed to the solution due to film morphology and surface characteristics and to the reduction in Cr 3+ and Fe 3+ concentrations on the surface of the films.

Monolithic TiO2 with controlled multiscale porosity via a template-free sol-gel process accompanied by phase separation

Abstract: This article describes the fabrication of multiscale porous nanocrystalline TiO2 monoliths through a one-step method that combines a sol−gel process and phase separation in template-free conditions A large-dimension monolith with well-defined macropores and a mesostructured anatase-type TiO2 gel skeleton is spontaneously obtained by controlling the solution pH during the hydrolysis and polycondensation reactions of titanium alkoxides The size of the macropores is adjusted by the starting composition, and a crystallized anatase TiO2 skeleton is formed without heat treatment The use of titanium alkoxide strengthens the gel network by the formation of chemical bonding in the condensation reaction, which yields porous monoliths with higher mechanical strength than for the case of porous monoliths derived from colloidal TiO2 using freeze drying to maintain the porous morphology The average crystallite size of anatase TiO2 nanocrystals was found to be about 36 nm for the dried gel and about 50 nm for the

Sol−Gel Assembly of CdSe Nanoparticles to Form Porous Aerogel Networks

Abstract: A detailed study of CdSe aerogels prepared by oxidative aggregation of primary nanoparticles (prepared at room temperature and high temperature conditions, >250 °C), followed by CO2 supercritical drying, is described. The resultant materials are mesoporous, with an interconnected network of colloidal nanoparticles, and exhibit BET surface areas up to 224 m2/g and BJH average pore diameters in the range of 16−32 nm. Powder X-ray diffraction studies indicate that these materials retain the crystal structure of the primary nanoparticles, with a slight increase in primary particle size upon gelation and aerogel formation. Optical band gap measurements and photoluminescence studies show that the as-prepared aerogels retain the quantum-confined optical properties of the nanoparticle building blocks despite being connected into a 3-D network. The specific optical characteristics of the aerogel can be further modified by surface ligand exchange at the wet-gel stage, without destroying the gel network.

Characterization of Zr-doped TiO2 nanocrystals prepared by a nonhydrolytic sol-gel method at high temperatures.

Abstract: Highly crystalline and surface-modified Zr-doped TiO2 nanorods were successfully prepared using a nonhydrolytic sol−gel method that involves the condensation of metal halides with alkoxides in anhydrous trioctylphosphine oxide (TOPO) at either 320 or 400 °C. In addition, the interaction of the cross-condensation between the Ti and Zr species was studied by characterizing the morphologies, crystalline structures, chemical compositions, surface properties, and band gaps of the nanocrystals obtained at different reaction temperatures and Zr-to-Ti stoichiometric ratios. Increases in the concentration of Zr4+ and in the reaction temperature led to large nanorods and regular shapes, respectively. In addition, only the anatase form was observed in the Zr-doped TiO2 nanorods. The Zr-to-Ti ratios obtained ranged from 0.01 to 2.05, all of which were far below the stoichiometric ratios used during the preparation of the samples (0.25−4). Moreover, the Zr4+ units accumulated mainly at the surface of the TiO2 nanocrys...

Characterization and application of Fe3O4/SiO2 nanocomposites

Abstract: A sol-gel procedure was used to cover Fe3O4 nanoparticles with SiO2 shell, forming a core/shell structure. The core/shell nanocomposites were synthesized by a two-step process. First, Fe3O4 nanoparticles were obtained through co-precipitation and dispersed in aqueous solution through electrostatic interactions in the presence of tetramethylammonium hydroxide (TMAOH). In the second step, Fe3O4 was capped with SiO2 generated from the hydrolyzation of tetraethyl orthosilicate (TEOS). The structure and properties of the formed Fe3O4/SiO2 nanocomposites were characterized and the results indicate that the Fe3O4/SiO2 nanocomposites are superparamagnetic and are about 30 nm in size. Bioconjugation to IgG was also studied. Finally, the mechanism of depositing SiO2 on magnetic nanoparticles was discussed.

Nanostructured In2O3-SnO2 sol-gel thin film as material for NO2 detection

Abstract: Nanocrystalline SnO2, In2O3 and In2O3–SnO2 thin films have been prepared by modified sol–gel methods making use of no-standard precursors and a suitable surfactant. The oxide thin films have been used as gas-sensing layers in chemoresistive gas sensors and their performances in the detection of nitrogen dioxide (2–20 ppm in dry air) have been analysed by electrical characterization in controlled atmosphere. The samples have been structurally and morphologically characterized by X-ray diffraction and SEM, respectively. Good gas-sensing responses towards NO2 have been found for all the prepared samples with improved performances for the In2O3–SnO2 based sensor. The performances of the sensors have been discussed according to the surface chemical reactions between the gas phase and the semiconductor.

Surface engineering of poly(dimethylsiloxane) microfluidic devices using transition metal sol-gel chemistry.

Abstract: We report the coating of poly(dimethylsiloxane) (PDMS) microchannels using transition metal sol−gel chemistry and the subsequent characterization of the coatings. The channels were created using soft polymer lithography, and three metal alkoxide sol−gel precursors were investigated, titanium isopropoxide, zirconium isopropoxide, and vanadium triisobutoxide oxide. The metal alkoxides were diffused into the sidewalls of a PDMS channel and subsequently hydrolyzed using water vapor. This procedure resulted in the formation of durable metal oxide surfaces of titania, zirconia, or vanadia. The resulting surfaces were characterized using contact angle, X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and electroosmotic mobility (EOM) measurements. All of the metal oxide-modified PDMS surfaces were significantly more hydrophilic than native PDMS. Contact angles for the coatings were 90° for PDMS−ZrO2, 61° for ...

AMORPHOUS POROUS MIXED OXIDES: Sol-Gel Ways to a Highly Versatile Class of Materials and Catalysts

Abstract: ▪ Abstract This review discusses the preparation, characterization, and application of amorphous porous mixed oxides, a rapidly growing class of materials with wide applications and a huge potential for the tailoring of chemical composition, microstructure, porosity, and surface properties. In contrast to crystalline materials, these amorphous mixed oxides are prepared under mild reaction conditions in ambient atmosphere. An ever-increasing variety of precursors, additives, modifiers, solvents, catalysts, and posttreatment conditions provide ample fine-tuning options. These materials often display properties commonly associated with well-defined crystalline phases. The functional properties of such solids are largely unexplored and provide a tremendous opportunity for the development of new or alternative materials (solids with a function). Here, emphasis is paid to micro- and mesoporous mixed oxides and their catalytic properties. Easy access to these materials is offset by their much more problematic ch...

Agarose template for the fabrication of macroporous metal oxide structures.

Abstract: Agarose gels have been applied as templates for the formation of macroporous metal oxide structures. The preparation of the agarose template is extremely simple, and with variation of the agarose content, control over morphology is demonstrated: The average pore size decreases from 180 to 55 nm and the surface area increases from 238 to 271 m2 g(-1) with increasing agarose content in the gel. The gelling temperature was also found to influence the final template morphology. Conducting sol-gel chemistry within the template structure followed by removal of the template by heating to 450 degrees C gives porous inorganic oxides. The technique has been demonstrated for the oxides of titanium, zirconium, niobium, and tin. The final morphology of the metal oxide is homogeneous and results from a coating of the agarose structure. The pore diameter decreased and the specific surface area of the titanium dioxide materials increased from 28 to 66 m2 g(-1) as the agarose content in the template is increased from 0.5 to 5.0 wt%. The overall pore size and surface area are lower than the original gel due to shrinkage occurring with the sol-gel process, as well as crystallization and a loss of microporosity in the final material.

Synthesis and Characterization of CoFe2O4 Nanoparticles Dispersed in a Silica Matrix by a Sol−Gel Autocombustion Method

Abstract: A very fast self-combustion reaction was applied for the first time to the synthesis of a series of magnetic CoFe2O4−SiO2 nanocomposites in a wide range of compositions (from 5 to 50 wt % CoFe2O4). Combining a gelation method that adopts metal nitrates, citric acid and tetraethoxysilane as precursors with controlled thermal treatments, a wide variety of samples with properties finely modulated were obtained. Particle formation and evolution of the structural and magnetic properties with the temperature were investigated by thermal analysis, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, nitrogen physisorption, IR, and magnetic susceptibility measurements. It was shown that the formation of metal ammonium carboxylate complexes takes place in all the gel precursors, contributing to the control of nucleation and growth of the nanoparticles. Spherical particles with narrow particle size distribution, uniformly dispersed in the matrix, are obtained in the...

Synthesis and characterization of sol-gel derived Mn 2+ doped In 2 S 3 nanocrystallites embedded in a silica matrix

Abstract: Mn2+ doped In2S3–SiO2 nanocomposite thin films were synthesized by sol-gel technique. The films were annealed in air at different temperatures (473–623 K) and characterized by optical, microstructural and electron spin resonance (ESR) study. Optical transmittance study revealed the manifestation of quantum size effect while ESR indicated the presence of manganese in indium sulphide as dispersed dopant rather than manganese cluster.

Anticorrosively enhanced PMMA–SiO2 hybrid coatings prepared from the sol–gel approach with MSMA as the coupling agent

Abstract: A series of sol–gel derived organic–inorganic hybrid coatings consisting of organic poly(methyl methacrylate) (PMMA) and inorganic silica (SiO2) were successfully synthesized by using 3-(Trimethoxysilyl)propyl methacrylate as a coupling agent. In this work, MSMA is first copolymerized with methyl methacrylate monomer at specific feeding ratio by using benzoyl peroxide (BPO) as initiator. Subsequently, the as-prepared copolymer (i.e., sol–gel precursor) is then cohydrolyzed with various contents of tetraethyl orthosilicate (TEOS) to afford chemical bondings to the forming silica networks, giving a series of hybrid sol–gel coatings. Transparent organic–inorganic hybrid sol–gel coatings with different contents of silica are always achieved. The as-synthesized hybrid sol–gel materials were subsequently characterized by Fourier-Transformation infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The hybrid sol–gel coatings with low silica loading (e.g., 5 wt.%) on cold-rolled steel (CRS) coupons were found much superior in anticorrosion efficiency over those of neat PMMA based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current, and corrosion rate in 5 wt.% aqueous NaCl electrolyte. The enhancement of corrosion protection effect of hybrid sol–gel coatings may be due to the increase of adhesion strength of hybrid sol–gel coatings on CRS coupons relative to neat PMMA, which was further evidenced by the Scotch tape test evaluation. The increase of adhesion strength of hybrid sol–gel coatings on CRS coupons may be attributed to the formation of Fe–O–Si covalent bonds at the interface of coating/CRS system based on the FTIR–RAS (reflection absorption spectroscopy) studies. Effects of the material composition on the thermal stability, mechanical strength, wettability, and surface morphology of neat copolymer and a series of hybrid sol–gel materials, in the form of coating/film, were also studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), hardness tests, contact angle measurement, and atomic force microscopy (AFM), respectively.