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Silica Matrix (silica + matrix)

Distribution by Scientific Domains

Chemistry	59%
Polymers and Materials Science	18%
Life Sciences	9%

Distribution within Chemistry

General & Introductory Chemistry	22%

Selected Abstracts

ChemInform Abstract: Superparamagnetic Behavior of ,-Fe2O3 Nanoparticles Dispersed in a Silica Matrix.

CHEMINFORM, Issue 23 2001
C. Cannas
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Properties of Ionic Liquid Confined in Porous Silica Matrix

CHEMPHYSCHEM, Issue 9 2010
Manish Pratap Singh
Abstract Porous silica matrices of different pore sizes with confined ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) [BMIM] [PF6] were prepared by sol-gel technique using a tetraethyl orthosilicate (TEOS) precursor with an aim to study the changes in physico-chemical properties of ionic liquid on confinement. It is found that on confinement 1) melting point decreases, 2) fluorescence spectra shows a red shift and 3) the vibrational bands are affected particularly those of imadazolium ring, which interacts more with the walls of the silica matrix. Preliminary theoretical calculations suggest that SiO2 matrix interact more with the heterocyclic group of [BMIM] cation than the tail alkyl chain end group resulting in significant changes in the aromatic vibrations. [source]

Chilean high-altitude hot-spring sinters: a model system for UV screening mechanisms by early Precambrian cyanobacteria

GEOBIOLOGY, Issue 1 2006
V. R. PHOENIX
ABSTRACT Before the build-up of stratospheric ozone, Archean and early Proterozoic phototrophs existed in an environment subjected to highly elevated levels of ultraviolet (UV) radiation. Therefore, phototrophic life would have required a protective habitat that balanced UV attenuation and photosynthetically active radiation (PAR) transmission. Here we report on aspects of the phototroph geomicrobiology of El Tatio geothermal field, located at 4300 m in the Andes Mountains of northern Chile (22 °S), as an analogue system to early Precambrian environments. El Tatio microbes survive in a geochemical environment of rapidly precipitating amorphous silica (sinter) and unusually high solar radiation (including elevated UV-B flux) due to the high-altitude, low-latitude location. Cyanobacteria produce 10-mm-thick surface mats containing filaments encased in amorphous silica matrices up to 5 µm thick. Relative radiation absorbance of these silica matrices was UV-C > UV-B > UV-A > PAR, suggesting the silica provides a significant UV shield to the cyanobacteria. Cyanobacteria also occur in cryptoendolithic communities 1,10 mm below siliceous sinter surfaces, and in siliceous stromatolites, where viable cyanobacteria are found at least ,10 mm below the sinter surface. UV-B was dramatically attenuated within ,1 mm of the sinter surface, whereas UV-C (a frequency range absent today but present in the early Precambrian) was attenuated even more efficiently. PAR was attenuated the least, and minimum PAR levels required for photosynthesis penetrated 5,10 mm into the sinter. Thus, a favourable niche occurs between approximately 1,10 mm in siliceous sinters where there is a balance between PAR transmission and UV attenuation. These deposits also would have strongly attenuated Archean and early Precambrian levels of UV and thus, by analogy, cyanobacteria of early Precambrian shallow aquatic environments, inhabiting silicified biofilms and silica stromatolites, would have similarly been afforded protection against high-intensity UV radiation. [source]

Synthesis of high fluorescent silica hybrid materials by immobilization of orange peel extract in silica-silsesquioxane matrix

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2009
I. Lacatusu
Abstract Sol,gel chemistry can be easily modified to the changing needs of society to produce fine-tuned sol,gel nanostructured materials for relevant applications. In this context, there is an increasing need for natural and versatile raw materials as well as biocompatible compounds that could be extensively used as biomarkers for bioimaging in diagnosis or therapy. Silica-based materials are widely used in the field of biomedicine due to their chemical inertness and biocompatibility. In the present paper, orange peel extract was immobilized inside inorganic silica and hybrid silica-silsesquioxane polymeric networks. Silica and organo-modified silica matrices were synthesized through a templated sol,gel route of TEOS and an organosilsesquioxane (octaisobutyltetracyclo[7.3.3.15,11] octasiloxane- endo -3,7-diol), with D -glucose as template, and for comparison a non-ionic surfactant (tetraethylene glycol mono-hexadecyl ether) was also used. The bioactive properties of the molecules from orange peel extract were preserved after immobilization in both silica and silica-silsesquioxane networks. Moreover, the fluorescence properties were amplified by 10,20 times more than the native orange peel extract. The structural properties of the final materials have been studied by FT-IR, UV,Vis-NIR, and fluorescence spectroscopy. Dynamic light scattering measurements and transmission electron microscopy were used to estimate the size and morphology of the hybrid materials with orange peel extract immobilized in silica networks. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Properties of Ionic Liquid Confined in Porous Silica Matrix

[Ru(0)]@SiO2 and [RuO2]@SiO2 Hybrid Nanomaterials: From Their Synthesis to Their Application as Catalytic Filters for Gas Sensors

ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009
Victor Matsura
Abstract [Ru(0)]@SiO2 and [RuO2]@SiO2 hybrid nanomaterials are produced following a facile method consisting of the synthesis of size-controlled ruthenium nanoparticles as elemental bricks. This route takes advantage of the organometallic approach and the use of a bifunctional ligand for the synthesis of ruthenium nanoparticles from [Ru(COD)(COT)](COD,=,1,3-cyclooctadiene, COT,=,1,3,5-cyclooctatriene) as metal precursor and (PhCH2)2N(CH2)11O(CH2)3Si(OEt)3 (benzenemethanamine) as stabilizer. Hydrolysis and polycondensation steps via a sol,gel approach lead to the formation of the silica materials containing the metal nanoparticles. A final calcination step in air at 400,°C yields the [RuO2]@SiO2 nanocomposites. Such hybrid nanomaterials display a good dispersion of the nanoparticles inside the silica matrix and interesting porosity properties making them attractive materials for catalytic applications. This is shown by using [RuO2]@SiO2 hybrid nanomaterials as catalytic filters for gas sensors. [source]

Garnet-filled trails associated with carbonaceous matter mimicking microbial filaments in Archean basalt

GEOBIOLOGY, Issue 4 2009
K. LEPOT
The study of the earliest traces of life on Earth can be complicated by abiotically formed biomorphs. We report here the finding of clustered micrometer-sized filaments of iron- and calcium-rich garnets associated with carbonaceous matter in an agate amygdale from a 2.7-billion-year-old basalt of the Maddina Formation, Western Australia. The distribution of carbonaceous matter and the mineral phases composing the filaments were analyzed using a combination of confocal laser scanning microscopy, laser-Raman micro-spectroscopy, focused ion beam sectioning and transmission electron microscopy. The results allow consideration of possible biogenic and abiotic processes that produced the filamentous structures. The filaments have a range of sizes, morphologies and distributions similar to those of certain modern iron-mineralized filamentous bacteria and some ancient filamentous structures interpreted as microfossils. They also share a high morphological similarity with tubular structures produced by microbial boring activity. However, the microstructures and the distribution of carbonaceous matter are more suggestive of an abiotic origin for the filaments. They are characteristic features of trails produced by the displacement of inclusions associated with local dissolution of their silica matrix. Organic compounds found in kerogen or bitumen inclusions may have contributed significantly to the dissolution of the quartz (or silica gel) matrix driving filamentous growth. Discriminating the products of such abiotic organic-mediated processes from filamentous microfossils or microbial borings is important to the interpretation of the scarce Precambrian fossil record and requires investigation down to the nanoscale. [source]

Cover Picture: Composite Silica Spheres with Magnetic and Luminescent Functionalities (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2006
Mater.
Abstract Photographs of a colloidal dispersion of composite nanoparticles with magnetic and luminescent functionalities are shown (left, in column), which are schematically illustrated in the main image. As reported by Salgueiriño-Maceira and co-workers on p.,509, such functionalities are imparted by magnetic and semiconductor nanoparticles within a silica matrix. In the absence of a magnetic field the particles are uniformly dispersed, although they accumulate and can be dragged under the influence of a magnetic field. Their movement can be monitored by their photoluminescence. A new class of highly fluorescent, photostable, and magnetic core/shell nanoparticles in the submicrometer size range has been synthesized from a modified Stöber method combined with the layer-by-layer (LbL) assembly technique. Luminescent magnetic nanoparticles are prepared via two main steps. The first step involves controlled addition of tetraethoxysilane to a dispersion of Fe3O4/,-Fe2O3 nanoparticles, which are thereby homogeneously incorporated as cores into monodisperse silica spheres. The second step involves the LbL assembly of polyelectrolytes and luminescent CdTe quantum dots onto the surfaces of the silica-coated magnetite/maghemite particles, which are finally covered with an outer shell of silica. These spherical particles have a typical diameter of 220,±,10,nm and a saturation magnetization of 1.34,emu,g,1 at room temperature, and exhibit strong excitonic photoluminescence. Nanoparticles with such a core/shell architecture have the added benefit of providing a robust platform (the outer silica shell) for incorporating diverse functionalities into a single nanoparticle. [source]

Hybrid Organic-Inorganic Materials Derived from a Monosilylated Hoveyda-type Ligand as Recyclable Diene and Enyne Metathesis Catalysts

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2007
Xavier Elias
Abstract The synthesis of a monosilylated Hoveyda-type monomer is described as well as the preparation of several organic-inorganic hybrid materials derived from it by sol-gel processes and by anchoring to commercial silica gel and MCM-41. The resulting materials were treated with first and/or second generation Grubbs' catalyst to generate Hoveyda,Grubbs' type alkylidene ruthenium complexes covalently bonded to the silica matrix. These materials are efficient recyclable catalysts for the ring-closing metathesis reaction of dienes and enynes, even for the formation of tri- and tetrasubstituted olefins. [source]

Hybrid-Bridged Silsesquioxane as Recyclable Metathesis Catalyst Derived from a Bis-Silylated Hoveyda-Type Ligand

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2006
Xavier Elias
Abstract The synthesis of a bis-silylated Hoveyda-type monomer is described as well as the preparation of several organic-inorganic hybrid materials derived from it by a sol-gel process (with and without tetraethyl orthosilicate) and by anchoring to MCM-41. The resulting materials were treated with second generation Grubbs' catalyst to generate second generation Hoveyda,Grubbs-type alkylideneruthenium complexes covalently bonded to the silica matrix. These materials are recyclable catalysts for the ring-closing metathesis reaction of dienes and enynes. [source]

DIATOM SILICA BIOMINERALIZATION: AT NANOSCALE LEVEL A CHEMICALLY UNIFORM PROCESS

JOURNAL OF PHYCOLOGY, Issue 2000
E. G. Vrieling
Using a high-brilliance synchrotron X-ray source, combined small- and wide-angle X-ray scattering (SAXS and WAXS) was applied to study nanoscale characteristics, in particular pore size in the range of 3 to 65 nm, of a variety of unialgal cultures of centric and pennate diatoms, and of mixed diatom populations sampled in the field. Results of scattering analysis were compared with details of pore size, structure and orientation visible at the electron microscopic level. WAXS patterns did not reveal any crystalline phase or features of microcrystallinity (resolution 0.07 to 0.51 nm), which implies a totally amorphous character of the SiO2 matrix of the frustule material. SAXS data (resolution 3 to 65 nm) provided information on geometry, size, and distribution of pores in the silica. Overall, two pore regions were recognized that were common to the silica of all samples: the smallest (d less than 10 nm) regularly spaced and shaped spherically, the larger (up to 65 nm) being cylinders or slits. Apparently, at a nanoscale level diatomaceous silica is quite homologous among species, in agreement with the chemical principles of silica polymerization under the conditions of pH and precursor concentrations inside the silicon deposition vesicle. The final frustule "macro"-morphology is of course species-specific, being determined genetically. Synthetically-derived MCM-type silicas have a similarly organized pore distribution in an amorphous silica matrix as we found in all diatom species studied. We therefore suggest that organic molecules of a kind used as structure-directing agents to produce these artificial silicas play a role in the nucleation of the silica polymerization reaction and the shaping of pore morphology inside the silicon deposition vesicle of diatoms. Structure-directing molecules now await isolation from the SDV, followed by identification and characterisation by molecular techniques. [source]

The influence of porosity on the Phillips Cr/silica catalyst 2.

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2009
Polyethylene elasticity
Abstract The Phillips Cr/silica catalyst produces low levels of long chain branching (LCB) in polyethylene, which have a powerful influence on industrial molding behavior. Although many catalyst and reactor variables determine the degree of LCB, perhaps the most significant of these is the morphology of the silica support. In this study many different types of silicas were converted into Cr/silica catalysts, which were tested in ethylene polymerization, and the resultant polymer elasticity was then determined. In some experiments, the surface area of the catalyst seemed to correlate quite well with polymer elasticity. In other tests, however, no connection with surface area was evident but the pore volume was quite influential. Together, all these studies suggest that it is the degree of structural reinforcement of the silica matrix, rather than any one physical measurement of porosity, that influences elasticity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 845,865, 2009 [source]

Synthesis and characterization of stereoregular poly(methyl methacrylate),silica hybrid utilizing stereocomplex formation

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2004
Achimuthu Ashok Kumar
Abstract Stereoregular poly(methyl methacrylate) (PMMA),silica nanocomposites were prepared using stereocomplex formation between i -PMMA and s -PMMA by an in situ method. The methodology adopted here is the simultaneous formation of organic gel and inorganic gel, the so-called interpenetrating polymer network (IPN) formation. The gelation of i - and s -PMMA were performed by stereocomplex formation with the associated segments forming the crosslinking points in the presence of tetramethoxysilane (TMOS). The effects of the i/s -ratio, PMMA concentration, molecular weight, and solvent nature on the hybrid materials formation were addressed. The presence of the stereocomplex in the silica matrix was confirmed by DSC and solvent extraction methods. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 785,794, 2004 [source]

Raman scattering of acoustical modes of silicon nanoparticles embedded in silica matrix,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 1-3 2006
M. Ivanda
Abstract The Raman scattering from acoustical phonons of silicon quantum dots in glass matrix was investigated. Two peaks that correspond to symmetric and quadrupolar spheroidal vibrations were found. A model calculation for in- and off-resonance scattering conditions was used, which considered the homogeneous broadening due to interaction with matrix and the inhomogeneous broadening due to particle size distribution. A strong dependence of the light-to-vibration coupling coefficient on the particles size was needed for fitting the Raman data. This result suggests that resonance with electronic transitions of the silicon nanoparticles is important for excitation at 514.5 nm. The size distribution obtained from the Raman data is in agreement with the results of high-resolution transmission electron microscopy. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Evaluation of HPLC columns: A study on surface homogeneity of chemically bonded stationary phases

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 3-4 2003
Bogus, aw Buszewski
Abstract The aim of the current work is to study the heterogeneity of the adsorbent surface on the basis of physicochemical investigations and chromatographic tests. A series of packing materials with octadecyl chains chemically bonded to a silica matrix were prepared for this purpose. The surface and structural properties of bare silica and silica-based octadecyl phases were characterized by porosimetry, elemental analysis, 29Si CP/MAS NMR, etc. The most advanced characterization methods based on adsorption microcalorimetry (heat of wetting) measurements were employed to obtain information about the heterogeneity and topography of unmodified and modified silica gel. For the chromatographic study, these phases were evaluated on the basis of the retention data under non-aqueous conditions. A test series of solutes with various chemical properties, such as pK a values, was used. It was found that heterogeneity of the packing surface results in low HPLC resolution. Use of a non-aqueous mobile phase (n -hexane) reduces analytical interference by eliminating hydrophobic interactions between alkyl ligands and the analyte. [source]

Synthesis, characterization and single crystal structure determination of aluminum alkoxydisilanolates: precursors for silica,alumina composite

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2010
Mostafa M. Amini
Abstract Several novel aluminum alkoxydisilanolate complexes were prepared by reaction of triphenylsilanol with aluminum 2-methoxyethoxide, aluminum 2-ethoxyethoxide, aluminum sec -butoxide and aluminum iso -propoxide. All new complexes, [(Ph3SiO)2Al(OR)]2 [where R = CH2CH2OCH3 (1), CH2CH2OC2H5 (2), CH(CH3)CH2CH3 (3) and CH(CH3)2 (4)] were characterized by elemental analysis, mass spectrometry and infrared spectroscopy (IR), as well as 1H, 13C, 29Si and 27Al NMR spectroscopies. The solid-state structures of the representative compound 2 and 4 were also verified by single-crystal X-ray analyses. Complexes 2 and 4 are dimers having distorted trigonal bipyramidal and tetrahedral coordination at the aluminum center, respectively. The 27Al NMR spectrum of compound 2 showed that the solid-state structure of the complex was not retained in solution, and tetracoordinated aluminum was found in solution in contrast to the pentacoordinated geometry in the solid state. The hydrothermal treatment of 1 and 4 at 200 °C and the subsequent calcination at 1000 °C resulted in the formation of alumina,silica composite (4SiO2·Al2O3) with ,-alumina in the silica matrix. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Synthesis of Novel Porous Magnetic Silica Microspheres as Adsorbents for Isolation of Genomic DNA

BIOTECHNOLOGY PROGRESS, Issue 2 2006
Zhichao Zhang
An improved procedure is described for preparation of novel mesoporous microspheres consisting of magnetic nanoparticles homogeneously dispersed in a silica matrix. The method is based on a three-step process, involving (i) formation of hematite/silica composite microspheres by urea-formaldehyde polymerization, (ii) calcination of the composite particles to remove the organic constituents, and (iii) in situ transformation of the iron oxide in the composites by hydrogen reductive reaction. The as-synthesized magnetite/silica composite microspheres were nearly monodisperse, mesoporous, and magnetizable, with as typical values an average diameter of 3.5 ,m, a surface area of 250 m2/g, a pore size of 6.03 nm, and a saturation magnetization of 9.82 emu/g. These magnetic particles were tested as adsorbents for isolation of genomic DNA from Saccharomyces cerevisiae cells and maize kernels. The results are quite encouraging as the magnetic particle based protocols lead to the extraction of genomic DNA with satisfactory integrity, yield, and purity. Being hydrophilic in nature, the porous magnetic silica microspheres are considered a good alternative to polystyrene-based magnetic particles for use in biomedical applications where nonspecific adsorption of biomolecules is to be minimized. [source]

Encapsulation and Sustained Release of Curcumin using Superparamagnetic Silica Reservoirs

CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2009
Fun Chin
Abstract For controlled release and targeted delivery of curcumin in an aqueous medium a method of encapsulating curcumin and magnetic nanoparticles inside porous silica matrix has been developed. Curcumin and superparamagnetic nanoparticles are loaded inside porous silica in a single process. The graphic shows the TEM image of microtomed sample of Fe3O4 particles surrounded by a silica matrix. [source]

Periodic Mesoporous Organosilicas: A Type of Hybrid Support for Water-Mediated Reactions

CHEMISTRY - AN ASIAN JOURNAL, Issue 7 2007
Ying Wan Prof.
Abstract Hybrid mesoporous periodic organosilicas (Ph-PMOs) with phenylene moieties embedded inside the silica matrix were used as a heterogeneous catalyst for the Ullmann coupling reaction in water. XRD, N2 sorption, TEM, and solid-state NMR spectroscopy reveal that mesoporous Ph-PMO supports and Pd/Ph-PMO catalysts have highly ordered 2D hexagonal mesostructures and covalently bonded organic,inorganic (all Si atoms bonded with carbon) hybrid frameworks. In the Ullmann coupling reaction of iodobenzene in water, the yield of biphenyl was 94,%, 34,%, 74,% and for palladium-supported Ph-PMO, pure silica (MCM-41), and phenyl-group-modified Ph-MCM-41 catalysts, respectively. The selectivity toward biphenyl reached 91,% for the coupling of boromobenzene on the Pd/Ph-PMO catalyst. This value is much higher than that for Pd/Ph-MCM-41 (19,%) and Pd/MCM-41 (0,%), although the conversion of bromobenzene for these two catalysts is similar to that for Pd/Ph-PMO. The large difference in selectivity can be attributed to surface hydrophobicity, which was evaluated by the adsorption isotherms of water and toluene. Ph-PMO has the most hydrophobic surface, and in turn selectively adsorbs the reactant haloaryls from aqueous solution. Water transfer inside the mesochannels is thus restricted, and the coupling reaction of bromobenzene is improved. [source]