Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
 ...
PMID:Electrochemical study of a new methylene blue/silicon oxide nanocomposition mediator and its application for stable biosensor of hydrogen peroxide. 1602 65

The growth of ordered filamentous carbon, catalytically generated from the decomposition of ethylene, has been studied over the temperature range 673-898 K using an 11% w/w Ni/SiO2 catalyst doped to varying degrees (0.1-9.3% w/w) with a range of alkali metal bromides. The effect of these alkali metal/halogen adatoms in promoting/inhibiting carbon growth has been assessed and variations in the associated carbon structural characteristics have been examined. The introduction of Li consistently promoted filamentous carbon growth (where 723 K<T<823 K) while the presence of Na, K, Rb, or Cs resulted in an equivalent or lower carbon yield. The degree of carbon deposition was strongly dependent on the nature and loading of the alkali metal, the Ni/Br ratio in the activated catalyst, and reaction temperature; conditions for optimum carbon growth are identified. The response of carbon yield and structural order to alkali bromide doping is discussed in terms of Ni particle electronic structure and metal/support interaction(s). High-resolution transmission electron microscopy (HRTEM) has been used to probe the filamentous carbon structure and the dispersion/morphology/size of the supported Ni crystallites. Highly curved and helical filaments predominated over the doped (particularly CsBr) samples and this is attributed to a disruption in carbon diffusion through the Ni particle caused by a spreading/coating of the particle by the alkali adatom. Temperature-programmed oxidation studies have highlighted the changes in the graphitic nature of the carbon due to catalyst doping; the results are consistent with the TEM analysis.
 ...
PMID:Growth of filamentous carbon from the surface of Ni/SiO2 doped with alkali metal bromides. 1629 Jun 32

A significant challenge in materials characterization is the determination of the structure of nanoparticle assemblies that have been deposited on solid substrates, such as SiO2. The best method for obtaining quantitative information about structure, size, and spacing on the nanometer-length scale is TEM; however, commercially available TEM grids offer a limited range of substrate materials. In addition, the compositions of these grids do not permit much chemical processing. Here we describe silicon-based grids with electron-transparent SiO2 windows suitable for use as substrates for high-resolution TEM that can be easily fabricated using standard silicon microfabrication techniques. These grids are physically and chemically robust and exhibit the same surface chemistry and chemical stability as an oxide grown on a silicon wafer. Thus, the grids make possible the concurrent investigation of chemical and structural information on the same sample. Convenient modification of the surfaces of the grids provides access to a wide range of new substrates for the direct imaging of chemically modified surfaces by TEM. We demonstrate the utility of these grids by aligning DNA on the chemically modified SiO2 surface in order to direct the assembly of linear arrays of nanoparticles. Using these grids, we are able to quantify the effects of assembly conditions on nanoparticle size, spacing, and dispersity in the arrays.
 ...
PMID:Substrates for direct imaging of chemically functionalized SiO2 surfaces by transmission electron microscopy. 1638 40

The surface properties of bimetallic Ni-Pt/SiO2 catalysts with variable Ni/Ni + Pt atomic ratio (0.75, 0.50, and 0.25) were studied using N2O decomposition and N2O reduction by hydrogen reactions as probes. Catalysts were prepared by incipient wetness impregnation of the silica support with aqueous solutions of the metal precursors to a total metal loading of 2 wt %. For both model reactions, Pt/SiO2 catalyst was substantially more active than Ni/SiO2 catalyst. Mean particle size by TEM was about the same (in the range 6-8 nm) for all catalysts and truly bimetallic particles (more than 95%) were evidenced by EDS in the Ni-Pt/SiO2 catalysts. CO adsorption on the bimetallic catalysts showed differences in the linear CO absorption band as a function of the Ni/Pt atomic ratio. Bimetallic Ni-Pt/SiO2 catalysts showed, for the N2O decomposition, a catalytic behavior that points out an ensemble-size sensitive behavior for Ni-rich compositions. For the N2O + H2 reaction, the bimetallic catalysts were very active at low temperature. The following activity order at 300 K was observed: Ni75Pt25 > Ni25Pt75 approximately Ni50Pt50 > Pt. TOF values for these catalysts increased 2-5 times compared to the most active reference catalyst (Pt/SiO2). The enhancement of the activity in the Ni75Pt25 bimetallic catalysts is explained in terms of the presence of mixed Ni-Pt ensembles.
 ...
PMID:Surface properties of Ni-Pt/SiO2 catalysts for N2O decomposition and reduction by H2. 1685 Dec 31

The effects of oxygen-hydrogen pretreatments of nanosilver catalysts in cycle mode on the structure and particle size of silver particles, and subsequently the activity of the catalyst toward CO oxidation (or CO selective oxidation in the presence of H2), are reported in this paper. Ag/SiO2 catalyst with silver particle sizes of ca. 6 approximately 8 nm shows relatively high activity in the present reaction system. The adopting of a cycle of oxidation/reduction pretreatment has a marked influence on the activity of the catalyst. Oxygen pretreatment at 500 degrees C results in the formation of subsurface oxygen and activates the catalyst. As evidenced by in-situ XRD and TEM, the following H2 treatment at low temperatures (100 approximately 300 degrees C) causes surface faceting and redispersing of the silver particles without destroying the subsurface oxygen species. The subsequent in-situ FTIR and catalytic reaction results show that CO oxidation occurs at -75 degrees C and complete CO conversion can be obtained at 40 degrees C over such a nanosilver catalyst pretreated with oxygen at 500 degrees C followed by H2 at 100 degrees C. However, prolonged hydrogen treatment at high temperatures (>300 degrees C) after oxygen pretreatment at 500 degrees C induces the aggregation of silver particles and also depletes so much subsurface oxygen species that the pathway of CO oxidation by the subsurface oxygen species is inhibited. Meanwhile, the ability of the catalyst to adsorb reactants is greatly depressed, resulting in a 20 approximately 30% decrease in the activity toward CO oxidation. However, the activity of the catalyst pretreated with oxygen at 500 degrees C followed by hydrogen treatment at high temperatures (>300 degrees C) is still higher than that directly pretreated with H2. This kind of catalytic behavior of silver catalyst is associated with physical changes in the silver crystallites because of surface restructuring and crystallite redispersion during the course of oxygen-hydrogen pretreatment steps.
 ...
PMID:Restructuring and redispersion of silver on SiO2 under oxidizing/reducing atmospheres and its activity toward CO oxidation. 1685 13

The temporal changes to supported Ni sites during the growth of graphitic carbon nanofibers (GCNs) via the decomposition of chlorobenzene over Ni/SiO2 at 873 K have been investigated. The reaction of chlorobenzene with hydrogen also generated benzene, via catalytic hydrodechlorination, as the principal competing reaction. Reaction selectivity was found to be time dependent with a switch from a preferential hydrodechlorination to a predominant decomposition that generated an increasingly more structured carbon product over prolonged time-on-stream. These findings are discussed in terms of Cl/catalyst interaction(s) leading to metal site restructuring, the latter manifest in a sintering and faceting of the Ni metal particles. The pressure exerted on the metal/support interface due to fiber formation was of sufficient magnitude to extract the Ni particle from the support; the occurrence of an entrapped Ni particle at the fiber tip is a feature common to the majority of GCNs with the incorporation of Ni fragments along the length of the GCN. Metal site restructuring has been probed by temperature-programmed reduction of the passivated samples, H2 chemisorption/temperature-programmed desorption (TPD) and XANES/EXAFS analyses. This restructuring serves to enhance destructive chemisorption and/or facilitate carbon diffusion to generate the resultant GCN. The nature of the carbonaceous product has been characterized by a combination of TEM-EDX, SEM, XRD and temperature-programmed oxidation (TPO).
 ...
PMID:Ni/SiO2 promoted growth of carbon nanofibers from chlorobenzene: characterization of the active metal sites. 1686 Aug 17

Eu3+ Complexes with benzoic acid and 1,10-phenanthroline incorporated in SiO2, SiO2-B2O3 and SiO2-B2O3-Na2O matrices were prepared via the sol-gel method. Eu-doped SiO2, SiO2-B2O3 and SiO2-B2O3-Na2O luminescence materials were synthesized. The luminescence of Eu3+ was studied with excitation spectra and emission spectra. Different forms of dopants could influence the luminescence properties. The structure of Eu-doped glass was studied by comparing IR, TEM and XRD. The results showed that after the materials were annealed at 1 000 degrees C the structure was very stable because ingredient was already removed totally. The emission spectrum showed that the typical optical spectrum of Eu3+ is 5D0 --> 7Fj (j = 1, 2) at 588 nm and 614 nm. Comparing EuCl3 with Eu3+ complexes with benzoic acid and 1,10-phenanthroline as dopant, the latter has strong luminescence property though it has small mass fraction. The luminescence intensity of Eu(3+)-doped SiO2-B2O3 glass material was weaker than that of Eu(3+)-doped SiO2 glass material, and the former's spectrum showed that there were Si-O-B bonds. The luminescence intensity of Eu3+ was quenched by this kind of structure. The luminescence intensity of Eu(3+)-doped SiO2-B2O3-Na2O glass material was greatly increased, and the infrared spectrum illustrated that there was not vibration absorption of Si-O-B bonds. Probably Na replaced B, and Si-O-Na bonds formed. This kind of structure could enhance luminescence intensity of Eu3+ to some extend.
 ...
PMID:[Structure and luminescence properties of Eu3+ complexes with benzoic acid and 1,10-phenanthroline incorporated in SiO2, SiO2-B2O3 and SiO2-B2O3-Na2O matrices]. 1688 41

Mesoporous SnO2/SiO2 composite particles (Si/Sn < or = 0.25) sustainable to calcination up to 600 degrees C have been fabricated using a stepwise sol-gel technique on nonionic surfactant template (tetradecylamine, TDA). The newly designed preparation method involved the pre-formation of SnO2 sol solution from SnCl4. Subsequently, SnO2 nanocrystals were covered by the silicate species (from the hydrolysis of tetraethylorthosilicate, TEOS) in a pH controlled colloidal solution. Upon mixing with the surfactant solution, mesophase composite was obtained. After the removal of templates at various temperatures (400 to 600 degrees C), worm-like mesoporous SnO2/SiO2 with large specific surface area and pore volume as high as 362 m2/g and 0.33 cc/g were obtained, respectively. High thermal stability is mainly due to the effective inhibition of SnO2 crystal growth (mean crystallite size <30 A) by the amorphous SiO2 species at the grain boundaries. Formation of mesoporous silicate skeleton such as M41S family material was prevented. The obtained materials maintain the relatively narrow pore size distribution typically in the range of 30 to 70 A. Relations between material properties and key synthesis parameters (i.e. TDA/Si/Sn molar ratio and calcination temperature) were investigated by TGA, wide/small-angle X-ray scattering, (HR)TEM, BET, and FTIR techniques. Mechanisms on the mesostructure formation and crystal growth inhibition were also proposed with detailed discussion.
 ...
PMID:Synthesis and mechanism study of mesoporous SnO2/SiO2 composites. 1702 23

Organic-inorganic hybrid particles have many potential applications, but almost all of this research was focused on the hybrid particles containing one kind of inorganic nanoparticles. This paper presented a facile preparation method for SiO2/PS/TiO2 multilayer core-shell hybrid microspheres. In this approach, positively charged SiO2/PS core-shell hybrid particles were first synthesized by miniemulsion polymerization using cationic initiator and emulsifier. These positively charged SiO2/PS hybrid particles were mixed with tetra-n-butyl titanate for sol-gel reaction to directly form SiO2/PS/TiO2 multilayer core-shell hybrid microspheres. Some influencing parameters such as surfactant concentration, tetra-n-butyl titanate amount, and glacial acetic acid amount were investigated. TEM, TGA, and EDX analyses indicated that titania layers were successfully coated onto the surfaces of hybrid microspheres.
 ...
PMID:Facile preparation method of SiO2/PS/TiO2 multilayer core-shell hybrid microspheres. 1710 18

In order to improve its dispersion condition in dental composite resin and enhance its interaction with the matrix, single-walled carbon nanotubes(SWNTs) were refluxed and oxidized, then treated by APTE. Their outer surface were coated by nano-SiO2 particles using sol-gel process, then further treated by organosilanes ATES. IR and TEM were used to analyze modification results. TEM pictures showed nano-particles were on the surface of SWNTs; IR showed characteristic adsorbing bands of SiO2. Composite resin specimen with modified SWNTs was prepared and examined by TEM. SWNTs were detected in composite resin matrix among other inorganic fillers.
 ...
PMID:[Surface modification and microstructure of single-walled carbon nanotubes for dental composite resin]. 1722 26


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>