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 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The preparation of a novel carbon monolithic column for high performance liquid chromatography is described. A phenolic resin rod with embedded 10-microm silica beads was prepared by acid-catalyzed polymerization of a resorcinol/iron(III) complex and formaldehyde. This rod was carbonized and graphitized under inert atmosphere with a programmed temperature cycle from room temperature to 1250 degrees C. Subsequently, the silica beads along with iron catalysts were removed, leaving a porous carbon rod. Imaging of this monolithic rod by scanning and transmission electron microscopies revealed a highly interconnected bimodal porous structure. The porosity and pore size distribution of the mesopores were characterized by N2 absorption/desorption. Graphene sheets were found in the TEM images of the carbon rod, and the graphite index was characterized by Raman spectrum and X-ray diffraction. A monolithic column prepared with the aforementioned carbon rod was evaluated using a mixture of alkylbenzenes. It exhibited an excellent separation power and a low hydraulic resistance. The bundle-of-capillaries model was used to characterize the hydrodynamics of this monolith. Its permeability was found to agree well with the theoretical one.
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PMID:A graphitized-carbon monolithic column. 1467 70

Bone substitutes have been used for the treatment of bone defects. The objective of this study was to ultrastructurally evaluate the healing pattern of bone defects filled with a copolymer of polylactic/polyglycolic acid (FisiograftR) at a time point in which it is expected to be only partially degraded, with the purpose to ultrastructurally analyze how the bone is forming around the grafting material. Three 5-mm-diameter bone defects were created in each tibia from 5 rabbits (average weight 2.5 kg) in which the material was randomly implanted. Animals were sacrificed 30 days after surgery and the 30 bone defects were fixed in 2% glutaraldehyde-2.5% formaldehyde, under microwave irradiation, decalcified in EDTA, embedded in Spurr resin, and examined in a Jeol 1010 TEM. All the bone defects were filled with connective tissue, interspersed with different amounts of the filling material and newly formed bone trabeculae. In areas where the degrading copolymer was present in small amounts, newly formed bone matrix was detected; it was deposited by osteoblast-like cells in close relation to the copolymer. In areas where the degrading copolymer formed accumulates, an amorphous multilayered material was identified between the connective tissue and the copolymer. In summary, the copolymer of PLA/PGA studied appears to be an osteoconductive material when it is used to fill bone defects.
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PMID:Ultrastructure of bone healing in defects grafted with a copolymer of polylactic/polyglycolic acids. 1594 3

A novel organic-inorganic nanocomposite of methylene blue (MB) and silicon oxide was synthesized and characterized by TEM, FTIR, and UV-vis. The as-prepared material was able to transfer the electron of the MB to electrode and was different from other SiO2 spheres structurally. It can be used as mediator to construct a biosensor with horseradish peroxidase (HRP) coimmobilized in the gelatine matrix and cross-linked with formaldehyde. The resulting biosensor exhibited fast amperometric response and good stability to hydrogen peroxide (H2O2). The linear range for H2O2 determination was from 1 x 10(-5) to 1.2 x 10(-3) M, with a detection limit of 4 x 10(-6) M based on S/N = 3. Moreover, the lifetime is more than 3 months under dry conditions at 4 degrees C.
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PMID:Electrochemical study of a new methylene blue/silicon oxide nanocomposition mediator and its application for stable biosensor of hydrogen peroxide. 1602 65

An adsorptive silica-supported titania photocatalyst TiO(2)/SiO(2) was prepared by using nanosized titania (anatase) immobilized on silica gel by the sol-gel technique with the titanium tetra isopropoxide as the main raw material and acetic acid as the acid catalyst. Meanwhile the structure and properties of the TiO(2)/SiO(2) photocatalyst were studied by means of many modern analysis techniques such as TEM, XRD, and BET. Gas-solid heterogeneous photocatalytic decomposition of four carbonyl compounds mixture at low concentration levels over ultraviolet irradiated TiO(2)/SiO(2) photocatalyst were carried out with high degradation efficiencies in a coaxial triple-cylinder-type fluidized bed photocatalytic reactor, which provided efficient continuous contact of ultraviolet photons, silica-supported titania photocatalyst, and gaseous reactants. Experimental results showed that the photocatalyst had a high adsorption performance and a good photocatalytic activity for four carbonyl compounds mixture. Some factors influencing the photocatalytic decomposition of the mixed carbonyl compounds, i.e. the gas flowrate, relative humidity, concentration of oxygen, and illumination time, were discussed in detail. It is found that the photocatalytic reaction rate of four carbonyl compounds decreased in this order: propionaldehyde, acetone, acetaldehyde and formaldehyde.
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PMID:Photocatalytic degradation of mixed gaseous carbonyl compounds at low level on adsorptive TiO2/SiO2 photocatalyst using a fluidized bed reactor. 1641 94

A novel method for preparing poly(propylene-graft-2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester)-silver fibers (PPG-IAg fibers) by plasma-induced grafting polymerization is presented in this study. The chelating groups, -N(CH2COO-)2 (GMA-IDA), on the surface of the PPG-I fibers are the coordination sites for chelating silver ions. At these sites, Ag nanoparticles were grown first by reduction with UV light with a wavelength of 366 nm, and second, through immersion in a 24% formaldehyde solution with pH values set variously at 2, 5, 8, and 11. The characteristics of the PPG-I fibers with differing durations of plasma treatment were monitored by using a Fourier transform infrared (FT-IR) spectroscope. Scanning electronic microscopy (SEM) and elemental analysis show that the percentage of GMA-IDA grafted onto PP fiber reaches a maximum when the plasma treatment time is 3 min. Plasma treatment time beyond a certain length of time results in an abundance of free radicals and causes considerable cross-linking on the fiber surface which thus decreases the extent of grafting. Moreover, the crystalline phase of Ag nanoparticles is identified by using X-ray diffraction (XRD). When the PPG-I fibers are reduced by the UV light method, SEM and TEM microscopes reveal that the size of the Ag nanoparticles on the fiber surface decreases significantly with the increase of pH values in aqueous solutions. Notably, in the reduction of formaldehyde solution, the particle size of Ag nanoparticles reaches a minimum at the lowest pH value. The TEM observations show that Ag nanoparticles are distributed both in the exterior and interior of the grafting layer. In addition, under high pH values the distribution of the Ag nanoparticles permeate more deeply in the GMA-IDA grafting layer due to the swelling effect of the GMA-IDA polymer.
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PMID:Polypropylene fibers modified by plasma treatment for preparation of Ag nanoparticles. 1650 92

Long TiO2 hollow fibers with mesoporous walls have been fabricated with the sol-gel combined two-capillary spinneret electrospinning technique using a triblock copolymer (Pluronic, P123, (H(C2H5O)20(C3H7O)70 (C2H5O)20OH) as a pore-directing agent. The as-prepared hollow fibers were as long as 30 cm with an outer diameter of 0.1-4 microm and wall thickness of 60-500 nm. The diameters and wall thicknesses of the hollow fibers could be tuned by adjusting the electrospinning parameters. The fiber walls were composed of mesopores 6.7 nm in diameter as calculated from the N2 adsorption/desorption isotherm. The high-resolution TEM (HR-TEM) images exhibited that the mesopores were hexagonally aligned with a low order because of the curving of the pores. When comparing with other nanostructured TiO2 materials such as commercial TiO2 nanoparticles (P25, Degussa) and mesoporous TiO2 powders, the hollow fibers exhibited higher photocatalytic activities toward degradation of methylene blue and gaseous formaldehyde.
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PMID:Long TiO2 hollow fibers with mesoporous walls: sol-gel combined electrospun fabrication and photocatalytic properties. 1677 84

Gold micropatterns are deposited from aqueous solutions of NaAuCl(4) on boron-doped Si(100) surfaces (rho = 1.5 x 10(-4) Omega m) using a focused Ar(+) laser beam (TEM(00), lambda = 488 nm, w(0) = 1.5 mum, P = 20-80 mW). The finite-element method employed for computing the surface temperature profiles reveals that the maximum temperature at the precursor/silicon interface increases only to the range 316-372 K, which is not high enough for chemical reactions with formaldehyde in the precursor. This suggests a different mechanism to be responsible for the reduction of gold ions, namely, changes in the surface potential of Si caused by the Dember and Seebeck effects.
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PMID:Laser-induced gold deposition on p+-Si from liquid precursors: a study on the reduction of gold ions through competing Dember and Seebeck effects. 1685 81

The aim of this study was to investigate the relationship between proteoglycans (PGs) and collagen fibrils at the early mineralization process of mantle dentin. Ten first molar dental germs of rats were removed and fixed in glutaraldehyde/formaldehyde in cacodylate buffer and post-fixed in osmium tetroxide. The samples were dehydrated and embedded in epoxy resin. Ultrathin sections were contrasted and analyzed in TEM before and after treatment with EDTA, chondroitinases AC and ABC. After EDTA treatment, a electrondense substance associated with collagen fibril was removed, and did not stain again. A high magnification of these areas showed globular structures with 15 nm diameter surrounding collagen fibrils. In advanced mineralization areas, collagen fibrils showed a banded pattern and at high magnification the fibrils presented a light 10 nm ring inside and a dark 10 nm ring outside. After chondroitinase treatment, the electrondense substance associated with collagen fibrils was removed, showing a banded pattern of clear and dark areas along them. From morphological data, the authors proposed a model of interaction between PGs and collagen fibrils, where glicosaminoglycans chains are inside the fibrils, while the protein core remains outside. That stereochemical arrangement would start the crystal nucleation.
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PMID:A model of the early mineralization process of mantle dentin. 1699 43

A novel in situ autoreduction route has been developed, by which monodispersed silver nanoparticles with tunable sizes could be easily fabricated on silica-based materials, especially inside the channels of mesoporous silica (MPS). 13C CP/MAS NMR spectroscopy was employed to monitor the whole assembly process. It was demonstrated that the amino groups of APTS (aminopropyltriethoxyl silane)-modified MPS can be used to anchor formaldehyde to form novel reducing species (NHCH2OH), on which Ag(NH3)2NO3 could be in situ reduced. Monodispersed silver nanoparticles were thus obtained. In situ XRD and in situ TEM experiments were used to investigate and compare the thermal stabilities of silver nanoparticles on the external surface of silica gels (unconfined) and those located inside the channels of SBA-15 (confined). It was observed that unconfined silver nanoparticles tended to agglomerate at low temperatures (i.e., lower than 773 K). The aggregation of silver nanoparticles became more serious at 773 K. However, for those confined silver nanoparticles, no coarsening process was observed at 773 K, much higher than its Tammann temperature (i.e., 617 K). Only when the treating temperature was higher than 873 K could the agglomeration of those confined silver nanoparticles happen with time-varying via the Ostwald ripening process. The confinement of mesopores played a key role in improving the thermal stabilities of silver nanoparticles (stable up to 773 K without any observable coarsening), which is essential to the further investigations on their chemical (e.g., catalytic) properties.
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PMID:Toward monodispersed silver nanoparticles with unusual thermal stability. 1714 85

We present the synthesis and characterization of Fe-doped carbon aerogels (CAs) and demonstrate the ability to grow carbon nanotubes directly on monoliths of these materials to afford novel carbon aerogel-carbon nanotube composites. Preparation of the Fe-doped CAs begins with the sol-gel polymerization of the potassium salt of 2,4-dihydroxybenzoic acid with formaldehyde, affording K+-doped gels that can then be converted to Fe2+- or Fe3+-doped gels through an ion exchange process, dried with supercritical CO2, and subsequently carbonized under an inert atmosphere. Analysis of the Fe-doped CAs by TEM, XRD, and XPS revealed that the doped iron species are reduced during carbonization to form metallic iron and iron carbide nanoparticles. The sizes and chemical composition of the reduced Fe species were related to pyrolysis temperature as well as the type of iron salt used in the ion exchange process. Raman spectroscopy and XRD analysis further reveal that, despite the presence of the Fe species, the CA framework is not significantly graphitized during pyrolysis. The Fe-doped CAs were subsequently placed in a thermal CVD reactor and exposed to a mixture of CH4 (1000 sccm), H2 (500 sccm), and C2H4 (20 sccm) at temperatures ranging from 600 to 800 degrees C for 10 min, resulting in direct growth of carbon nanotubes on the aerogel monoliths. Carbon nanotubes grown by this method appear to be multiwalled (approximately 25 nm in diameter and up to 4 microm long) and grow through a tip-growth mechanism that pushes catalytic iron particles out of the aerogel framework. The highest yield of CNTs was grown on Fe-doped CAs pyrolyzed at 800 degrees C treated at CVD temperatures of 700 degrees C.
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PMID:Iron-doped carbon aerogels: novel porous substrates for direct growth of carbon nanotubes. 1738 Nov 46


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