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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Bioactive fibers were produced using a sol-gel method. The rheological properties of two different sol compositions prepared from a mixture of TEOS, phosphorous alkoxide and calcium nitrate, or calcium chloride in a water-ethanol solution, are reported. The sols were extruded through a spinneret to produce continuous 10 microm-diameter fibers. Discontinuous fibers and fibrous mats were prepared by air-spraying the multicomponent sols. The sol-gel fibers were converted to the bioactive fibers by three different thermal treatments at either 600 degrees, 700 degrees, or 900 degrees C for 3 h. SEM, BET, EDX, and FTIR were used to characterize the morphology and structure of the fibers. The BET measured surface area of the fibers sintered at 900 degrees C was 0 m(2)/gm compared to a value of 200 m(2)/gm for a typical sol-gel-derived particle of similar composition. Both the continuous and discontinuous fibers exhibited in vitro bioactivity in a simulated body fluid.
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PMID:Novel sol-gel bioactive fibers. 1128 73

Silica xerogels were prepared by thermal drying wet gels in an electric oven (70 degrees C) after certain duration of ambient drying, and the relevant effect is investigated on the mesopore structures and surface fractal dimensions of the resultant xerogels. The silica gels were derived from a hydrochloric acid-catalyzed TEOS (tetraethylorthaosilicate) system, and both magnetic stirring and ultrasonic vibration were adopted during sol preparation. The percentage mesoporosity and surface fractal dimensions are evaluated using image analysis methods, based on FE-SEM (field emission gun-scanning electron microscopy) images. The results show that the mesoporosity of the resultant xerogels decreases with the duration of ambient drying for samples prepared using magnetic stirring and low-intensity ultrasonic vibration, while samples subjected to high-intensity ultrasound show a somewhat reverse trend. Samples prepared with magnetic stirring have almost constant surface fractal dimensions (nearly 3), irrespective of the ambient drying before thermal drying. The surface fractal dimensions of samples prepared using ultrasound increase with the duration of ambient drying.
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PMID:Influence of drying procedure on the mesoporosity and surface fractal dimensions of silica xerogels prepared with different agitation methods. 1629 Mar 93

In this article, a systematic study of the design and development of surface-modification schemes for silica nanoparticles is presented. The nanoparticle surface design involves an optimum balance of the use of inert and active surface functional groups to achieve minimal nanoparticle aggregation and reduce nanoparticle nonspecific binding. Silica nanoparticles were prepared in a water-in-oil microemulsion and subsequently surface modified via cohydrolysis with tetraethyl orthosilicate (TEOS) and various organosilane reagents. Nanoparticles with different functional groups, including carboxylate, amine, amine/phosphonate, poly(ethylene glycol), octadecyl, and carboxylate/octadecyl groups, were produced. Aggregation studies using SEM, dynamic light scattering, and zeta potential analysis indicate that severe aggregation among amine-modified silica nanoparticles can be reduced by adding inert functional groups, such as methyl phosphonate, to the surface. To determine the effect of various surface-modification schemes on nanoparticle nonspecific binding, the interaction between functionalized silica nanoparticles and a DNA chip was also studied using confocal imaging/fluorescence microscopy. Dye-doped silica nanoparticles functionalized with octadecyl and carboxylate groups showed minimal nonspecific binding. Using these surface-modification schemes, fluorescent dye-doped silica nanoparticles can be more readily conjugated with biomolecules and used as highly fluorescent, sensitive, and reproducible labels in bioanalytical applications.
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PMID:Surface modification of silica nanoparticles to reduce aggregation and nonspecific binding. 1661 87

Mesoporous SBA-16 and SBA-15 were studied in order to control their possible morphologies. SBA-16 is synthesized using a silicon source (tetraethoxysilane, TEOS) and a ternary system consisting of surfactant F127 (EO106PO70EO106), water, and butanol. The same ternary system, with higher butanol concentration, is used to form SBA-15 material as well. An increase of the TEOS concentration results in a morphology shift of SBA-16 from micron-sized spheres, over randomly shaped aggregated particles, to macrospheres with a size of 15 mm. An identical increase in TEOS concentration also results in the formation of SBA-15 macrospheres, which can be controlled in size. Micron-sized spheres of SBA-15 were formed using a quaternary system of surfactant P123 (EO20PO70EO20), cetyltrimethylammonium bromide (CTAB), ethanol, and water. All mesoporous silica materials were characterized using SEM, XRD, and N2 sorption techniques.
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PMID:Investigation of the morphology of the mesoporous SBA-16 and SBA-15 materials. 1667 32

Al-MCM-41 mesoporous sieves were synthesized at the ambient temperature by using TEOS as silica source, Al(NO)3 x 9H2O as Al source, and cetyl trimethylammonium bromide as templating agent. The framework and surface structures of the synthesized samples were characterized by XRD, N2-adsorption/desorption isotherms, FTIR and SEM etc. The results showed that the samples were the typical Al-MCM-41 mesoporous sieves with the higher ordered-degree and specific surface area (up to 816 m2 x g(-1)) and the narrower pore diameter distribution. Controlling the highest value of Al/Si with the range of 0.06-0.13, and taking temperature programmed calcination would be beneficial to the formation of the highly ordered Al-MCM-41 mesoporous sieves. The evaluating results showed that the synthesized Al-MCM-41 molecular sieves have a higher catalytic activity for isomerization of endo-tetrahydrodicyclo-pentadiene (endo-TCD) into exo-tetrahydrodicyclo-pentadiene (exo-TCD) and adamantane.
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PMID:[Synthesis and catalytic-isomerization performance of Al-MCM-41 mesoporous sieves]. 1794 16

A number of nanosize mordenite (MOR) analogues with particle size ranging from 5 to 50 nm were synthesized by the hydrothermal method. The effect of various growth parameters like: alkalinity of the medium, type of silica source, etc. on crystal morphology and the crystal size of MOR type of zeolites was investigated. Specific surface and micropore volume were investigated by the Brunauer-Emmett-Teller (BET) method. XRD, SEM, TEM studies indicate nanosize growth of the MOR type crystals. Electron diffraction patterns confirm the crystalline nature of the nanoparticles and the results of their indexing prove that the material is MOR. These synthesized materials show microporous as well mesoporous character. In the case of MOR material synthesized using sodium silicate, it was found that an increase in the alkalinity of the medium led to changes in the morphology and crystal size of the material. For low concentrations of NaOH, the crystallites were spherical in shape whereas at high concentrations, they were in the shape of nanorods of diameter 25 to 50 nm. The morphology of the MOR material synthesized using tetraethyl orthosilicate (TEOS), on the other hand, did not change when the NaOH concentration was increased beyond 2.0 molar.
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PMID:Synthesis and morphological studies of nanocrystalline MOR type zeolite material. 1858 31

CdTe@SiO(2) fluorescent particles were synthesized via hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in water-in-oil (W/O) emulsion. Uniform luminophore-doped silica nanoparticles with 100nm in diameter were obtained using microemulsion method and characterized by SEM. Antibody proteins were successfully conjugated to the fluorescent particles by the reaction of avidin and biotin, which were confirmed by fluorescence spectra. CdTe@SiO(2) fluorescent particles were potentially useful for the applications in biolabeling and imaging.
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PMID:The application of CdTe@SiO2 particles in immunoassay. 1876 Nov 54

Direct sol-gel reactions in supercritical CO2 (scCO2) have attracted significant interest for synthesizing nanomaterials by reacting alkoxides with a carboxylic acid. In this study, the hydrolysis of silicon alkoxides (TEOS or TMOS) was carried out using scCO2 as the solvent to generate silica nanoparticles within the matrix of polyethylene for the synthesis of polymeric nanocomposites. This methodology provides advantages of combining the sol-gel reactions and drying into a one-step process for producing polymer nanocomposites. The synthesized polymer silica composites were characterized by SEM, FTIR, and XPS. When the TEOS loading was below 10 wt % Si content, nanometer-sized silica particles were formed that were well dispersed within the polyethylene matrix. The mechanism of the silicon alkoxides reacting with acetic acid in scCO2 was further studied using online GC-MS and offline 13C NMR. Oligomer structures with a bridging methoxyl group between the two silicon atoms and the acetate monodentate were observed. This study suggests a new sol-gel pathway in scCO2 that is different from the hydrolysis-condensation reactions using the conventional sol-gel process.
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PMID:Study of the sol-gel reaction mechanism in supercritical CO2 for the formation of SiO2 nanocomposites. 1923 32

Owing to their unique structure and properties, carbon nanotubes (CNTs) have become the highlight of research since they were discovered. Part of the research interest lies in introducing them into solid state matrix to make them materialized. However, CNTs tend to aggregate in the matrix, which makes it difficult to make homogeneous composites. In order to solve this problem, we first modified the surface of CNTs by chemically bonding them to 3-aminopropyltrie-thoxysilane (NH2 (CH2)3Si(OC2H5)3, APTES) using three-step reactions, and then connected them to silica network by sol-gel technique. In the present paper, CNTs were first treated with HNO3 to get CNTs-COOH, which were then treated with SOCl2 to be transferred to CNTs-COCl, and finally CNTs-COCl reacted with APTES to get CNTs-APTES. After that, CNTs were introduced into silica net work through the individual hydrolysis of CNTs-APTES, tetrathyloxysilane (Si(OC2H5)4, TEOS) and 3-glycidoxy-propltrimethoxysilane (CH2OCHCH2O(CH2)3Si(OCH3)3, GPTMS) as sol-gel precursors, and the copolymerization of their hydrolysis products. FTIR and SEM were used to characterize the composition and microstructure of the obtained samples. (Owing to the connection of CNTs with silica network, little aggregation of CNTs was observed and high-quality CNTs/SiO2 composite gel glass was obtained. A model of CNTs/SiO2 network was also given.
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PMID:[Preparation of surface-modified carbon nanotubes/silica composite gel glass]. 1938 4

Submicron particles of mesoporous MSU-2 silica have been obtained by using Tergitol NP-9 as nonionic surfactant and TEOS as silica precursor. The material has been chemically modified with 5-mercapto-1-methyltetrazole and characterized by powder X-ray diffraction, TEM, SEM, N2 adsorption, FT-IR spectroscopy, 29Si-NMR spectroscopy, thermogravimetric analysis and elemental analysis. The enviromental application of such material (denoted MTTZ-MSU-2b) in the treatment of heavy metal-contaminated waters has been demonstrated. The maximum adsorption capacity of this material was found to be 0.73 +/- 0.01 mmol/g for Pb(II) and 0.94 +/- 0.01 mmol/g for Zn(II), and is higher than the capacity of most of the other functionalized mesoporous materials previously reported. The very high access of these metal ions to the binding sites in the adsorbent has also been demonstrated (adsorption efficiency equal to 0.88 and 1.13 for Pb(II) and Zn(II), respectively).
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PMID:Synthesis and characterization of novel mesoporous silicas of the MSU-X family for environmental applications. 1992 67


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