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Volatile Organic Compound Adsorption on a Nonporous Silica Surface: How Do Different Probe Molecules Sense the Same Surface?

Herdes, C.; Ribeiro Carrott, M.M.L.; Russo, P.A.; Carrott, P.J.M.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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In this work, we compare experimental results to molecular simulation results of volatile organic compound (VOC) adsorption on nonporous silica.We adopted an effective model for the rough solid surface, obtained by a temperature annealing scheme, plus an experimental/simulation nitrogen adsorption tuning process over the silica energetic oxygen parameter. The measurement/prediction of selected VOCs, specifically, n-pentane and methylcyclohexane, is presented in terms of adsorption isotherms, with an emphasis on the angle distribution analysis of the three studied probe molecules with respect to the same modeled surface.

Adsorption of n-Pentane on Mesoporous Silica and Adsorbent Deformation

Gor, G.Y.; Paris, O.; Prass, J.; Russo, P.A.; Ribeiro Carrott, M.M.L.; Neimark, A.V.
Fonte: ACS Publications Publicador: ACS Publications
Tipo: Artigo de Revista Científica
ENG
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627.63086%
Development of quantitative theory of adsorption-induced deformation is important, e.g., for enhanced coalbed methane recovery by CO2 injection. It is also promising for the interpretation of experimental measurements of elastic properties of porous solids. We study deformation of mesoporous silica by n-pentane adsorption. The shape of experimental strain isotherms for this system differs from the shape predicted by thermodynamic theory of adsorption-induced deformation. We show that this difference can be attributed to the difference of disjoining pressure isotherm, responsible for the solid−fluid interactions. We suggest the disjoining pressure isotherm suitable for n-pentane adsorption on silica and derive the parameters for this isotherm from experimental data of n-pentane adsorption on nonporous silica. We use this isotherm in the formalism of macroscopic theory of adsorption-induced deformation of mesoporous materials, thus extending this theory for the case of weak solid−fluid interactions. We employ the extended theory to calculate solvation pressure and strain isotherms for SBA-15 and MCM-41 silica and compare it with experimental data obtained from small-angle X-ray scattering. Theoretical predictions for MCM-41 are in good agreement with the experiment...

Identification of metastasis-associated proteins in a human tumor metastasis model using the mass-mapping technique

Kreunin, Paweena; Urquidi, Virginia; Lubman, David M; Goodison, Steve
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/2004 EN
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281.58047%
For most cancer cell types, the acquisition of metastatic ability leads to clinically incurable disease. The identification of molecules whose expression is specifically correlated with the metastatic spread of cancer would facilitate the design of therapeutic interventions to inhibit this lethal process. In order to facilitate metastasis gene discovery we have previously characterized a pair of monoclonal cell lines from the human breast carcinoma cell line MDA-MB-435 that have different metastatic phenotypes in immune-compromised mice. In this study, serum-free conditioned media was collected from the cultured monoclonal cell lines and a mass mapping technique was applied in order to profile a component of each cell line proteome. We utilized chromatofocusing in the first dimension to obtain a high resolution separation based on protein pI, and nonporous silica reverse-phase high performance liquid chromatography was used for the second dimension. Selected proteins were identified on the basis of electrospray ionization time of flight mass spectrometry (ESI-TOF MS) intact protein mapping and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) peptide mass fingerprinting. Using this approach we were able to map over 400 proteins and plot them as a 2-D map of pI versus accurate Mr. This was performed over a pI range of 4.0–6.2...

Thiol Functionalized Silica-Mixed Matrix Membranes for Silver Capture from Aqueous Solutions: Experimental Results and Modeling

Ladhe, A. R.; Frailie, P.; Hua, D.; Darsillo, M.; Bhattacharyya, D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 20/01/2009 EN
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The study deals with an aqueous phase application of Mixed Matrix Membranes (MMMs) for silver ion (Ag+) capture. Silica particles were functionalized with 3-mercaptopropyltrimethoxy silane (MPTMS) to introduce free thiol (-SH) groups on the surface. The particles were used as the dispersed phase in the polysulfone or cellulose acetate polymer matrix. The membranes were prepared by the phase inversion method to create more open and interconnected porous structures suitable for liquid phase applications. The effects of the silica properties such as particle size, specific surface area, and porous/nonporous morphology on the silver ion capture capacity were studied. It was demonstrated that the membranes are capable of selectively capturing silver from a solution containing significant concentrations of other metal ions like Ca2+. The membranes were studied to quantify the dynamic capacity for silver ion capture and its dependence on residence time through the adjustment of transmembrane pressure. The thiol-Ag+ interaction was quantified with Quartz Crystal Microbalance in a continuous flow mode experiment and the observations were compared with the membrane results. One dimensional unsteady state model with overall volumetric mass transfer coefficient was developed and solved to predict the silver concentration in the liquid phase and the solid silica phase along the membrane thickness at varying time. The breakthrough data predicted using the model is comparable with the experimental observations. The study demonstrates successful application of the functionalized silica-mixed matrix membranes for selective aqueous phase Ag+ capture with high capacity at low transmembrane pressures. The technique can be easily extended to other applications by altering the functionalized groups on the silica particles.

Plasma Glycoprotein Profiling for Colorectal Cancer Biomarker Identification by Lectin Glycoarray and Lectin Blot

Qiu, Yinghua; Patwa, Tasneem H.; Xu, Li; Shedden, Kerby; Misek, David E.; Tuck, Missy; Jin, Gracie; Ruffin, Mack T.; Turgeon, Danielle K.; Synal, Sapna; Bresalier, Robert; Marcon, Norman; Brenner, Dean E.; Lubman, David M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
281.58047%
Colorectal cancer (CRC) remains a major worldwide cause of cancer-related morbidity and mortality largely due to the insidious onset of the disease. The current clinical procedures utilized for disease diagnosis are invasive, unpleasant, and inconvenient; hence, the need for simple blood tests that could be used for the early detection of CRC. In this work, we have developed methods for glycoproteomics analysis to identify plasma markers with utility to assist in the detection of colorectal cancer (CRC). Following immunodepletion of the most abundant plasma proteins, the plasma N-linked glycoproteins were enriched using lectin affinity chromatography and subsequently further separated by nonporous silica reverse-phase (NPS-RP)-HPLC. Individual RP-HPLC fractions were printed on nitrocellulose coated slides which were then probed with lectins to determine glycan patterns in plasma samples from 9 normal, 5 adenoma, and 6 colorectal cancer patients. Statistical tools, including principal components analysis, hierarchical clustering, and Z-statistic analysis, were employed to identify distinctive glycosylation patterns. Patients diagnosed with colorectal cancer or adenomas were shown to have dramatically higher levels of sialylation and fucosylation as compared to normal controls. Plasma glycoproteins with aberrant glycosylation were identified by nano-LC–MS/MS...

Analysis of Protein Glycosylation and Phosphorylation Using Liquid Phase Separation, Protein Microarray Technology, and Mass Spectrometry

Zhao, Jia; Patwa, Tasneem H.; Pal, Manoj; Qiu, Weilian; Lubman, David M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
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281.58047%
Protein glycosylation and phosphorylation are very common posttranslational modifications. The alteration of these modifications in cancer cells is closely related to the onset and progression of cancer and other disease states. In this protocol, strategies for monitoring the changes in protein glycosylation and phosphorylation in serum or tissue cells on a global scale and specifically characterizing these alterations are included. The technique is based on lectin affinity enrichment for glycoproteins, all liquid-phase two-dimensional fractionation, protein microarray, and mass spectrometry technology. Proteins are separated based on pI in the first dimension using chromatofocusing (CF) or liquid isoelectric focusing (IEF) followed by the second-dimension separation using nonporous silica RP-HPLC. Five lectins with different binding specificities to glycan structures are used for screening glycosylation patterns in human serum through a biotin–streptavidin system. Fluorescent phosphodyes and phosphospecific antibodies are employed to detect specific phosphorylated proteins in cell lines or human tissues. The purified proteins of interest are identified by peptide sequencing. Their modifications including glycosylation and phosphorylation could be further characterized by mass-spectrometry-based approaches. These strategies can be used in biological samples for large-scale glycoproteome/phosphoproteome screening as well as for individual protein modification analysis.

Plate heights below 50 nm for protein electrochromatography using silica colloidal crystals

Wei, Bingchuan; Malkin, Douglas S.; Wirth, Mary J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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405.36996%
Silica colloidal crystals formed from 330 nm nonporous silica spheres inside of 75-μm i.d. fused silica capillaries were evaluated for the efficiency of capillary electrochromatography of proteins. Three proteins, ribonuclease A, cytochrome C and lysozyme, each covalently labeled with fluorophor, were well separated over a distance of 1 cm by isocratic electromigration, using 40:60 acetonitrile:water with 0.1% formic acid. A van Deemter plot showed that the plate height for lysozyme, which was the purest of the three proteins, was diffusion-limited for electric fields ranging from 400 to 1400 V/cm. The plate height for lysozyme was below 50 nm at almost all of the migration velocities, and it approached 10 nm at the highest velocity. Eddy diffusion was negligible. Lysozyme migrated over a 12 mm separation length with more than 106 plates in 1.5 minutes. These results indicate that silica colloidal crystals are well suited for electrically driven separations of large, highly charged analytes such as proteins. The 106 plates observed for a separation length of barely more than a cm means they are potentially valuable for miniaturized separations in microchip and μTAS devices.

Field-free remobilization of proteins after isoelectric focusing in packed capillaries

Hua, Yimin; Koshel, Brooke; Wirth, Mary J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
281.58047%
Pressure-driven remobilization without an applied electric field is shown to be possible with capillary isoelectric focusing by using packed capillaries. The capillary dimensions are 100 μm i.d. and 2 cm in length, and the packing is made of 0.9 μm nonporous silica particles that are chemically modified with a brush layer of polyacrylamide. Both reversible and irreversible adsorption are shown to be negligible. The packed capillaries eliminate the problem of unwanted hydrodynamic flow between reservoirs. Three proteins are focused: trypsin inhibitor, carbonic anhydrase II and myoglobin. The time required for focusing in the packed capillaries is increased by only a factor of two compared to the open capillary, giving complete focusing in less than 15 min at 200 V/cm. The packed capillaries allow the use of higher electric fields, with resolution continually increasing up to at least 1500 V/cm. The packing obstructs diffusional broadening after the field is turned off: for trypsin inhibitor, D=6.1(±0.3)×10-8 cm2/s for the packed capillary vs. D=28.8(±0.3)×10-8 cm2/s for the open capillary. The broadening contributed by the packing during remobilization is from eddy diffusion, and it is described by its plate height, H, which is the variance per unit length: H=σ2/L=0.64 μm. This limits the resolution to 0.1 pH unit for the 2-cm capillary having a pH range of 3-10...

Fabrication and Characterization of Dense Zirconia and Zirconia-Silica Ceramic Nanofibers

Xu, Xiaoming; Guo, Guangqing; Fan, Yuwei
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/2010 EN
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308.56125%
The objective of this study was to prepare dense zirconia-yttria (ZY), zirconia-silica (ZS) and zirconia-yttria-silica (ZYS) nanofibers as reinforcing elements for dental composites. Zirconium (IV) propoxide, yttrium nitrate hexahydrate, and tetraethyl orthosilicate (TEOS) were used as precursors for the preparation of zirconia, yttria, and silica sols. A small amount (1–1.5 wt%) of polyethylene oxide (PEO) was used as a carry polymer. The sols were preheated at 70 °C before electrospinning and their viscosity was measured with a viscometer at different heating time. The gel point was determined by viscosity–time (η–t) curve. The ZY, ZS and ZYS gel nanofibers were prepared using a special reactive electrospinning device under the conditions near the gel point. The as-prepared gel nanofibers had diameters between 200 and 400 nm. Dense (nonporous) ceramic nanofibers of zirconia-yttria (96/4), zirconia-silica (80/20) and zirconia-yttria-silica (76.8/3.2/20) with diameter of 100–300 nm were obtained by subsequent calcinations at different temperatures. The gel and ceramic nanofibers obtained were characterized by scanning electron microscope (SEM), high-resolution field-emission scanning electron microscope (FE-SEM), thermogravimetric analyzer (TGA)...

Protein UTLC-MALDI-MS using thin films of submicrometer silica particles

Zhang, Zhaorui; Ratnayaka, Saliya N.; Wirth, Mary J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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399.13938%
Slides for ultra thin-layer chromatography (UTLC) slides were made by coating nonporous silica particles, chemically modified with polyacrylamide, as 15 μm films on glass or silicon. Three proteins, myoglobin, cytochrome c and lysozyme, are nearly baseline resolved by the mechanism of hydrophilic interaction chromatography. A plate height as low as 3 μm, with 3,900 plates, are observed in 14 mm. Varying silica particle diameter among 900, 700 and 350 nm showed that decreasing particle diameter slightly improves resolution but slows the separation. Matrix-assisted laser desorption/ionization (MALDI)-MS of the proteins after separation is demonstrated by wicking sufficient sinapinic acid into the separation medium.

The Impact of Silica Nanoparticle Design on Cellular Toxicity and Hemolytic Activity

Yu, Tian; Malugin, Alexander; Ghandehari, Hamidreza
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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334.42848%
Understanding the toxicity of silica nanoparticles (SiO2) on the cellular level is crucial for rational design of these nanomaterials for biomedical applications. Herein, we explore the impacts of geometry, porosity and surface charge of SiO2 on cellular toxicity and hemolytic activity. Nonporous Stöber silica nanospheres (115 nm diameter), mesoporous silica nanospheres (120 nm diameter, aspect ratio 1), mesoporous silica nanorods with aspect ratio of 2, 4 and 8 (width by length 80 × 200 nm, 150 × 600 nm, 130 × 1000 nm) as well as their cationic counterparts were evaluated on macrophages, lung carcinoma cells, and human erythrocytes. It was shown that the toxicity of SiO2 is cell-type dependent and that surface charge and pore size govern cellular toxicity. Using inductively coupled plasma mass spectrometry, the cellular association of SiO2 was quantitated with the association amount increasing in the following order: mesoporous SiO2 (aspect ratio 1, 2, 4, 8) < amine-modified mesoporous SiO2 (aspect ratio 1, 2, 4, 8) < amine-modified nonporous Stöber SiO2 < nonporous Stöber SiO2. Geometry did not seem to influence the extent of SiO2 association at early or extended time points. The level of cellular association of the nanoparticles was directly linked to the extent of plasma membrane damage...

Influence of Geometry, Porosity and Surface Characteristics of Silica Nanoparticles on Acute Toxicity: Their Vasculature Effect and Tolerance Threshold

Yu, Tian; Greish, Khaled; McGill, Lawrence D.; Ray, Abhijit; Ghandehari, Hamidreza
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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293.10352%
Silica nanoparticles (SiO2) are widely used in biomedical applications such as drug delivery, cell tracking and gene transfection. The capability to control the geometry, porosity, and surface characteristics of SiO2 further provides new opportunities for their applications in nanomedicine. Concerns however remain about the potential toxic effects of SiO2 upon exposure to biological systems. In the present study, the acute toxicity of SiO2 of systematically varied geometry, porosity and surface characteristics was evaluated in immune-competent mice when administered intravenously. Results suggest that in vivo toxicity of SiO2 was mainly influenced by nanoparticle porosity and surface characteristics. The maximum tolerated dose (MTD) increased in the following order: Mesoporous SiO2 (aspect ratio 1, 2, 8) at 30 – 65 mg/kg < amine-modified mesoporous SiO2 (aspect ratio 1, 2, 8) at 100 – 150 mg/kg < unmodified or amine-modified nonporous SiO2 at 450 mg/kg. The adverse reactions above MTDs were primarily caused by the mechanical obstruction of SiO2 in the vasculature that led to congestion in multiple vital organs and subsequent organ failure. It was revealed that hydrodynamic sizes of SiO2 post protein exposure had an important implication in relating SiO2 physicochemical properties with their vasculature impact and resultant tolerance threshold...

In Vivo Biodistribution and Pharmacokinetics of Silica Nanoparticles as a Function of Geometry, Porosity and Surface Characteristics

Yu, Tian; Hubbard, Dallin; Ray, Abhijit; Ghandehari, Hamidreza
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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312.17312%
The in vivo biodistribution and pharmacokinetics of silica nanoparticles (SiO2) with systematically varied geometries, porosities, and surface characteristics were investigated in immune-competent CD-1 mice via the intravenous injection. The nanoparticles were taken up extensively by the liver and spleen. Mesoporous SiO2 exhibited higher accumulation in the lung than nonporous SiO2 of similar size. This accumulation was reduced by primary amine modification of the nanoparticles. High aspect ratio, amine-modified mesoporous nanorods showed enhanced lung accumulation compared to amine-modified mesoporous nanospheres. Accumulation of the nanoparticles was mainly caused by passive entrapment in the discontinuous openings in the endothelium of the liver and spleen or in the pulmonary capillaries, and was highly dependent on nanoparticle hydrodynamic size in circulation. The SiO2 were likely internalized by the reticulo-endothelial system (RES) following physical sequestration in the liver and spleen. The nanoparticles that were transiently associated with the lung were re-distributed out of this organ without significant internalization. Pharmacokinetic analysis showed that all SiO2 were rapidly cleared from systemic circulation. Amine-modified or nonporous nanoparticles possessed a higher volume of distribution at steady state than their pristine counterparts or mesoporous SiO2. In all...

Polyacrylamide brush layer for Hydrophilic Interaction Liquid Chromatography of intact glycoproteins

Zhang, Zhaorui; Wu, Zhen; Wirth, Mary J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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281.58047%
A chromatographic column of nonporous silica particles with a bonded phase of linear polyacrylamide chains is evaluated for hydrophilic interaction liquid chromatography (HILIC) of intact glycoproteins. The column is shown to retain glycoproteins significantly more strongly than non-glycoproteins. A particle diameter of 700 nm gives two-fold higher resolution than does a 1.4 μm particle diameter, and the column efficiency is found to be mostly limited by packing heterogeneity. LCMS is able to resolve the five glycoforms of ribonuclease B and give high quality mass spectra, but there is loss of resolution of the isomers of glycoforms due to the lower amount of TFA. Compared to two leading commercial HILIC columns operated at 60 °C, the polyacrylamide column operated at 30 °C provided at least two-fold higher resolution for intact ribonuclease B, and showed peaks for glycoforms of prostate specific antigen, although not resolved.

Nonporous Silica Nanoparticles for Nanomedicine Application

Tang, Li; Cheng, Jianjun
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/2013 EN
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521.9234%
Nanomedicine, the use of nanotechnology for biomedical applications, has potential to change the landscape of the diagnosis and therapy of many diseases. In the past several decades, the advancement in nanotechnology and material science has resulted in a large number of organic and inorganic nanomedicine platforms. Silica nanoparticles (NPs), which exhibit many unique properties, offer a promising drug delivery platform to realize the potential of nanomedicine. Mesoporous silica NPs have been extensively reviewed previously. Here we review the current state of the development and application of nonporous silica NPs for drug delivery and molecular imaging.

Carboxymethyl chitosan-folic acid-conjugated Fe3O4@SiO2 as a safe and targeting antitumor nanovehicle in vitro

Li, Hongmei; Li, Zhen; Zhao, Jin; Tang, Baoqiang; Chen, Yanhong; Hu, Yikun; He, Zhengda; Wang, Yue
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 25/03/2014 EN
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299.13938%
A synthetic method to prepare a core-shell-structured Fe3O4@SiO2 as a safe nanovehicle for tumor cell targeting has been developed. Superparamagnetic iron oxide is encapsulated inside nonporous silica as the core to provide magnetic targeting. Carboxymethyl chitosan-folic acid (OCMCS-FA) synthesized through coupling folic acid (FA) with OCMCS is then covalently linked to the silica shell and renders new and improved functions because of the original biocompatible properties of OCMCS and the targeting efficacy of FA. Cellular uptake of the nanovehicle was assayed by confocal laser scanning microscope using rhodamine B (RB) as a fluorescent marker in HeLa cells. The results show that the surface modification of the core-shell silica nanovehicle with OCMCS-FA enhances the internalization of nanovehicle to HeLa cells which over-express the folate receptor. The cell viability assay demonstrated that Fe3O4@SiO2-OCMCS-FA nanovehicle has low toxicity and can be used as an eligible candidate for drug delivery system. These unique advantages make the prepared core-shell nanovehicle promising for cancer-specific targeting and therapy.

Metallkomplex-modifizierte-Kieselgelpartikel - Synthese und Charakterisierung von Stöber-SiO2-Materialien und Co-Schiff-Basen-Komplexen für deren Modifizierung; Metal complexe modified silica particles - Synthesis and characterization of Stöber-SiO2-Materials and Co-Schiff-base complexes for their modification

Ruff, Adrian
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Masterarbeit
DE_DE
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399.13938%
Monodisperse, sphärische, unporöse Kieselgelpartikel mit Durchmessern von 140 - 600 nm wurden nach dem Stöber-Prozess dargestellt und mittels DLS, REM, DRIFT und BET Messungen charakterisiert. Dabei wurde der Partikeldurchmesser durch die Temperatur kontrolliert. Für die Modifizierung der Partikel wurden verschiedene Co(II)-Komplexe mit vierzähnigen N2O2-Schiff-Basen-Liganden dargestellt und mit spektroskopischen (NMR, IR, MS) und elektroanalytischen Methoden (CV) untersucht. Mittels DRIFT-Spektroskopie und Elementaranalyse konnte die erfolgreiche Immobilisierung eines Co(II)-Komplexes mit Alkoxysilylsubstituenten auf einem mit Hydroxygruppen modifiziertem Kieselgelmaterial nachgewiesen werden.; Monodisperse, spherical, nonporous silica particles with diameters from 140 - 600 nm have been prepared by the Stöber process and were characterized by DLS, SEM, DRIFT and BET messurements. The particle diameter was controlled by temperature. Several Co(II) complexes with tetradentate N2O2-Schiff-base ligands have been synthesized as possible modifiers. These were studied by spectroscopic (NMR, IR, MS) and electrochemical (CV) methods. The successful immobilization of an alkoxysilyl substituted Co(II) complexe on hydroxy modified silica particles was studied by DRIFT spectroscopy and elemental analysis.

Redoxaktive Nanopartikel - Viologenmodifizierte Kieselgelmaterialien: Synthese und elektrochemische Charakterisierung; Redox-active nanoparticles – viologen modified silica materials: synthesis and electrochemical characterization

Ruff, Adrian
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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299.13938%
Die vorliegende Arbeit beschreibt die Synthese und elektrochemische Charakterisierung von viologenmodifizierten core/shell-Systemen auf Basis von monodispersen, sphärischen und nicht-porösen Stöber-Kieselgelpartikeln mit Durchmessern im Submikrometerbereich. Das Trägermaterial wurde hinsichtlich seiner physikalischen und chemischen Eigenschaften mit materialwissenschaftlichen Methoden (Rasterelektronenmikroskopie, dynamische Lichtstreuung, BET, He-Pyknometrie, Gay-Lussac-Pyknometrie und DRIFT-Spektroskopie) untersucht. Die mit redoxaktiven Verbindungen (Viologene) modifizierten Materialien wurden sowohl mit spektroskopischen Methoden (CP/MAS-NMR-, Reflexion UV/Vis-, DRIFT-Spektroskopie) als auch mittels der Rasterelektronenmikroskopie, dynamischer Lichtstreuung und EDX-Analyse charakterisiert. Durch eine kovalente Verankerung der aktiven Spezies auf der Partikeloberfläche wird ein hohes Maß an Stabilität gewährleistet. Die spezifische Oberflächenkonzentration wurde argentometrisch und über die Bestimmung des C-Gehalts bestimmt (10 – 100 µmol/g). Elektrochemische Untersuchungen in wässrigen und nicht wässrigen Elektrolyten mittels voltammetrischer Methoden (CV und DPV) zeigten, dass durch den Ladungstransfer von der Elektrode zu immobilisierten Viologeneinheiten Elektronen-Hopping Prozesse in der redoxaktiven Hülle der Partikel (core) induziert werden. Diese ermöglichen eine Ladungsdiffusion über das gesamte Partikel und/oder über Partikelcluster. Weiterhin konnte mittels der ESR- sowie der UV/Vis-Spektroelektroskopie gezeigt werden...

Silica membranes for hydrogen separation in coal gas processing. Final report, January 1993

Gavalas, G. R.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em /01/1993
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293.10352%
The general objective of this project was to synthesize permselective membranes suitable for hydrogen separation from coal gas. The specific objectives were: (i) to synthesize membranes by chemical vapor deposition (CVD) of SiO(sub 2) or other oxides on porous support tubes, (ii) characterize the membranes by permeation measurements of various gases and by electron microscopy, and (iii) obtain information about the mechanism and kinetics Of SiO(sub 2) deposition, and model the process of membrane formation. Silica glass and certain other glasses, in dense (nonporous) form, are highly selective to hydrogen permeation. Since this high selectivity is accompanied by low permeability, however, a practical membrane must have a composite structure consisting of a thin layer of the active oxide supported on a porous tube or plate providing mechanical support. In this project the membranes were synthesized by chemical vapor deposition (CVD) of SiO(sub 2), TiO(sub 2), Al(sub 2)O(sub 3) and B(sub 2)O(sub 3) layers inside the walls of porous Vycor tubes (5 mm ID, 7 mm OD, 40 (Angstrom) mean pore diameter). Deposition of the oxide layer was carried out using the reaction of SiCl(sub 4) (or TiCl(sub 4), AlCl(sub 3), BCl(sub 3)) and water vapor at elevated temperatures. The porous support tube was inserted concentrically into a larger quartz tube and fitted with flow lines and pressure gauges. The flow of the two reactant streams was regulated by mass flow controllers...

CHARACTERIZATION OF ULTRA FINE SILICA SUPPORTED IRON CATALYSTS PREPARED BY THE AMMONIA METHOD

Loaiza-Gil,A; Rodríguez,P; Velasquez,W; Gómez,D; Fontal,B; Reyes,M; Suárez,T
Fonte: Universidad Simón Bolívar; ; Publicador: Universidad Simón Bolívar; ;
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2002 EN
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New ultra fine particle size and nonporous Fe/SiO2 catalysts ranging 20-160 nm were prepared with a modified high loading ammonia method. Scanning electron microscopy (SEM) associate to x-ray energy dispersion spectroscopy and nitrogen fisisorption studies of the fresh catalysts dried at 353 K shows a non porous structure constituted by superimposed sheet of rectangular crystals of Phyllosilicate type. The chemical and structural composition of such solids changes with the thermal pretreatment under hydrogen flow. FT-IR studies performed at programmed reduction temperature suggests that the fresh catalyst is constituted by an iron complex like Fe(H2O)6+3 sandwiched between bi-dimensional sheets of Si2O5 phyllosilicate. The amount of -OH groups bonded to the iron complex and those associates to the Si2O5 polymeric groups decrease progressively to disappears by slowly heating at 1 K/min from 353 to 973 K under hydrogen flow. At the final reduction temperature, a new catalyst structure constituted by silica support finely dispersed iron crystallites arise suggesting a catalyst morphology and properties governed by the temperature.