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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The synthesis and characterization of colloidal mesoporous silica (CMS) functionalized with vinyl-, benzyl-, phenyl-, cyano-, mercapto-, aminopropyl- or dihydroimidazole moieties is reported. Uniform mesoporous particles ranging in size from 40 to 150 nm are generated in a co-condensation process of tetraethylorthosilicate (TEOS) and organotriethoxysilanes (RTES) in alkaline aqueous media containing triethanolamine (TEA) in combination with cetyltrimethylammonium chloride (CTACl) serving as a structure-directing agent. The materials are obtained as colloidal suspensions featuring long-term stability after template removal by ion exchange with an ethanolic solution of ammonium nitrate or HCl. The spherical particles exhibit a wormlike pore system with defined pore sizes and high surface areas. Samples are analyzed by a number of techniques including TEM, SEM, DLS, TGA, Raman, and cross-polarized (29)Si-MAS NMR spectroscopy, as well as nitrogen sorption measurements. We demonstrate that co-condensation and grafting methods result in similar changes in the nitrogen adsorption behavior, indicating a successful internal lining of the pores with functional groups through both procedures.
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PMID:Colloidal suspensions of functionalized mesoporous silica nanoparticles. 1920 12

Extremely high surface area, mesostructured LaCoO3 perovskite has been synthesized by nanocasting from mesoporous cubic (Ia3d) vinyl silica. Thus-prepared material was characterized by XRD, TEM, and N2-sorption, and its catalytic property was also tested in methane combustion. The catalytic results demonstrated that thus-prepared mesostructured LaCoO3 perovskite had higher activity than the conventional bulk LaCoO3 perovskite prepared by citrate method. Further analysis showed that both the high surface area and the existence of high valent cobalt ions (Co4+, XPS analysis) were contributed to the high activity.
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PMID:Nanocasted synthesis of the mesostructured LaCoO3 perovskite and its catalytic activity in methane combustion. 1944 25

A series of finely dispersed poly(vinyl-2-pyrrolidone)-stabilized platinum colloidal nanocatalysts (PVP-Pt) were prepared and characterized by TEM. Hydrogenation of monochlorobenzene (MCB) was carried out in a batch mode using hydrogen over PVP-Pt at 298 K and atmospheric pressure. The product consisted of benzene and cyclohexane during the reaction, and nearly 100% selectivity to cyclohexane could be obtained at approximately 100% conversion of MCB. The catalytic performance of the PVP-Pt colloids is dependent on the preparation conditions. The small amount of the stabilizing polymer (PVP) in the preparation of colloidal platinum could not protect the platinum colloid commendably, but the large amount of PVP hindered the contact of reactant with catalyst surface and the desorption of product. Extra PVP added in the reaction system has some inhibiting effect on the reaction activity, and also resulting in some decrease in selectivity to cyclohexane. The reaction was verified to be first order to the concentration of MCB. The polymer-stabilized noble metal nanoparticles could be suitable to be hydrodehalogenation and reduction catalysts forthe remediation of various chloroaromatic compounds in the environment.
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PMID:Hydrogenation of chlorobenzene to cyclohexane over colloidal Pt nanocatalysts under ambient conditions. 1945 10

Hollow silica nanospheres with mesoporous shells were successfully fabricated with a new one-pot strategy by using a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAm), as a reversible template without the need of further calcination or chemical etching. By simply regulating the solution temperature with respect to the lower critical solution temperature (LCST) of PNIPAm, PNIPAm chains can reversibly form aggregates or dissolve in aqueous solution. The thermosensitive character makes PNIPAm chains behave as soft templates for the formation of core-shell silica nanospheres at elevated temperature (>LCST), and they will then diffuse out of the cores at lower temperature (<LCST), leading to the formation of hollow silica nanospheres. The TEM, SEM, XRD, and N(2) adsorption-desorption results indicate that the shells of such hollow silica nanospheres also contain large quantities of irregular mesopores. This new strategy was also tested with another thermosensitive polymer, poly(vinyl methyl ether) (PVME). However, only solid silica nanospheres with a broad size distribution were obtained when PVME was used. We speculated on the possible formation mechanism of hollow silica nanospheres with PNIPAm templates. The effects of the initial concentration of PNIPAm, the molecular weight of PNIPAm, and the pretreatment of silica precursor on the morphology and size of the resultant hollow silica nanospheres were also investigated. The PNIPAm soft templates were confirmed to be recyclable.
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PMID:One-pot preparation of hollow silica spheres by using thermosensitive poly(N-isopropylacrylamide) as a reversible template. 1976 Dec 58

Herein, we report the in situ generation of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized palladium(0) nanoclusters and their catalytic activity in hydrogen generation from the methanolysis of ammonia-borane (AB). The PVP-stabilized palladium(0) nanoclusters with an average particle size of 3.2 +/- 0.5 nm were formed from the reduction of palladium(II) acetylacetonate during the methanolysis of AB in the presence of PVP at room temperature. The palladium(0) nanoclusters are highly stable in solution for extended periods of time, can be isolated as solid materials, are redispersible in methanol and show catalytic activity after redispersion. The nanoclusters were characterized by TEM, XPS, FTIR, UV-Vis, XRD, and SAED techniques. Mercury poisoning experiments indicate that PVP-stabilized palladium(0) nanoclusters are heterogeneous catalysts in the methanolysis of ammonia-borane. The PVP-stabilized palladium(0) nanoclusters are highly active and stable catalysts as they provide 23,000 turnovers in hydrogen generation from the methanolysis of AB over 27 h before deactivation at room temperature. A kinetic study shows that the catalytic methanolysis of AB is first order with respect to catalyst concentration and zero order with respect to substrate concentration. The activation energy of the methanolysis of AB catalyzed by PVP-stabilized palladium(0) nanoclusters was determined to be E(a) = 35 +/- 2 kJ mol(-1).
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PMID:In situ-generated PVP-stabilized palladium(0) nanocluster catalyst in hydrogen generation from the methanolysis of ammonia-borane. 1989 May 40

A core-shell multilayered composite microsphere with electric and magnetic features was designed and prepared on the basis of mutilayered fabrication. This kind of microspheres was obtained by introducing a rod-like conductive polyanilline (PANI) or its derivatives onto the surface of magnetic Fe3O4 nanoparticles with 4,4'-diphenylmethane diisocyanate as a anchor molecule. Subsequently, the Fe3O4/PANI or Fe3O4/aniline oligomers microspheres, as a secondary core, were covered with a cross-linked shell layer which was constructed by a dispersion polymerization process of methacrylic acid and vinyl pyrrolidone. The structure and morphologies were characterized by using a FTIR, XRD, UV-vis, SEM, TEM and TGA. The average diameter of Fe3O4 nanoparticles prepared is about 10.7 nm, and the PANI nanobars hold the size in the range of about 20.4-25.6 nm. The PANI nanobars are covalently assembled on the surface of Fe3O4 nanoparticles mainly in a mode of extended or horizontal arrangements through XRD and TEM results. The electromagnetic properties were examined based on different polymerization degrees and component ratios of PANI or its derivatives, showing characteristics of soft magnetic materials and controllable conductivity. The multilayer microspheres can be readily used to perform separation and magnetism guide, even electric and pH-modulated drug release in the light of swelling determination and a laser diffraction particle size analyzer, and are potentially of interest for drug targeting purpose.
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PMID:Fe3O4/PANI/P(MAA-co-NVP) multilayer composite microspheres with electric and magnetic features: assembly and characterization. 1990 47

Amyloid fibrils are a misfolded state, formed by many proteins when subjected to denaturing conditions. Their constituent amino acids make them ideally suited as a readily functionalized nanoscaffold for enzyme immobilization and their strength, stability, and nanometer size are attractive features for exploitation in the creation of new bionanomaterials. We report successful functionalization of amyloid fibrils by conjugation to glucose oxidase (GOD) using glutaraldehyde. GOD retained activity upon attachment and successful cross-linking was determined using electrophoresis, centrifugation, sucrose gradient centrifugation, and TEM. The resulting functionalized enzyme scaffold was then incorporated into a model poly(vinyl alcohol) (PVOH) film, to create a new bionanomaterial. The antibacterial effect of the functionalized film was then tested on E. coli, the growth of which was inhibited, demonstrating the incorporation of GOD antibacterial activity into the PVOH film. The incorporation of the GOD-functionalized amyloid fibrils into PVOH provides an excellent 'proof of concept' model for the creation of a new bionanomaterial using a functionalized amyloid fibril scaffold.
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PMID:Amyloid fibrils as a nanoscaffold for enzyme immobilization. 1991 61

A new amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) (PVOH-b-PAN) copolymer obtained by selective hydrolysis of well-defined poly(vinyl acetate)-b-poly(acrylonitrile) copolymer synthesized by cobalt mediated radical polymerization was used for the preparation of PVOH-b-PAN based micelles with embedded silver nanoparticles. The successful formation of silver loaded micelles has been confirmed by UV-vis, DLS and TEM analysis and their antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa) and spore solution of Bacillus subtilis (B. subtilis) has been studied. PVOH-b-PAN based micelles with embedded silver nanoparticles showed a strong bactericidal effect against E. coli, S. aureus and P. aeruginosa and the minimum bactericidal concentration for each system (MBC) has been determined.
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PMID:Antibacterial activity of poly(vinyl alcohol)-b-poly(acrylonitrile) based micelles loaded with silver nanoparticles. 2007 42

In this study, we synthesized organic/inorganic hybrid materials containing cadmium sulfide (CdS) nanoparticles using a novel amphiphilic conducting block copolymer as a synergistic structure-directing template and an efficient exciton quencher of the hybrid. The amphiphilic rod-coil block copolymer of polyphenylene-b-poly(2-vinyl pyridine) (PPH-PVP) was first prepared from its coil-coil precursor block copolymer of poly(1,3-cyclohexadiene)-b-poly(2-vinyl pyridine) (PCHD-PVP) by using sequential anionic polymerization followed by the aromatization reaction of converting the PCHD block to form conducting PPH. The synthesized PCHD-PVP block copolymers self-assembled into different bulk nanostructures of lamellae, cylinders, and spheres at a volume fraction similar to that of many coil-coil block copolymer systems. However, an enhanced chain-stiffness-induced morphological transformation was observed after the aromatization reaction. This is evidenced by the TEM observation in which both spherical and cylindrical structured PCHD-PVPs transform into lamellar structured PPH-PVPs after aromatization. In addition to the bulk-phase transformation, the rigid-rod characteristic of the conducting PPH block also affects the self-assembling property of the block copolymers in their solution state. CdS nanoparticles were synthesized in situ in a selective solvent of THF using PCHD-PVP and PPH-PVP micelles as nanoreactors. The PPH-PVP/Cd ion in THF exhibits a new ringlike structure of uniform size (approximately 50 nm) with PPH in the inner rim and complexed PVP/Cd ions in the outer rim as a result of the effects of strong intermolecular forces between PPH segments and the solvophobic interaction. CdS nanoclusters were subsequently synthesized in situ from the PPH-PVP/Cd(2+) ring structure, forming a nanohybrid with intimate contact between the PPH domain and CdS nanoparticles. In particular, we found that there is an efficient energy/electron transfer between the conducting PPH domain and CdS nanoparticles in the hybrid, resulting in an enhanced PL quenching effect. The novel nanohybrid shows the potential to be used for optoelectronic applications.
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PMID:In-situ template synthesis of a polymer/semiconductor nanohybrid using amphiphilic conducting block copolymers. 2009 18

A great variety of polymer/layered silicate (PLS) nanocomposites have been reported, however, there are few exfoliated PLS nanocomposites and their inorganic-organic interfaces are still a great problem, especially for the elastomers. In this research, a kind of exfoliated elastomer/silicate layer nanocompound was prepared and proved by XRD and TEM, in which 10 phr Na(+)-montmorillonite was dispersed in butadiene-styrene-vinyl pyridine rubber by latex compounding method with acidic flocculants. Moreover, a dynamic mechanical thermal analyzer (DMTA) suggested a strong interfacial interaction (interaction parameter B(H) = 4.91) between the silicate layers and macromolecules in addition to the weak inorganic-organic interfacial interaction, and solid state (15)N NMR indicated the formation of a strong ionic interface through the acidifying pyridine. Subsequently, a remarkable improvement of the dispersing morphology, mechanical performance and gas barrier property appeared, compared to that using calcium ion flocculants. This supports the formation of an exfoliated structure and an improved interfacial interaction.
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PMID:The preparation of an elastomer/silicate layer nanocompound with an exfoliated structure and a strong ionic interfacial interaction by utilizing an elastomer latex containing pyridine groups. 2017 42


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