Search results for "silica"

Infrared spectroscopy on lead silicate glass

1993

The reflectance spectra of some lead silicate glasses of general formula (PbO)x(SiO2)y have been measured in the infrared frequency range from 50 to 4000 cm−1. The dispersion and absorption spectra in the range 50–2000 cm−1 have been calculated from the reflectance data using the Kramers-Kronig relations. The band at ∼ 135 cm−1 is assigned to the stretching vibration of lead-oxygen bonds. The shoulder band of the silicon-oxygen stretching mode at ∼900 cm−1 shows a weak coupling of those bonds to the Pb2+ modifier. The vibration strength of those bands shows that the number of the Pb2+ modifier increases first up approximately to 50 Mol% with the increase of PbO content and then decreases ra…

Photolysis of Adsorbed Phases: Ethanoic Acid-Insulators and Semiconductors Systems. Influence of Acid-Base Properties.

1986

The paper reports the results of experiments in which the photodecomposition of adsorbed ethanoic acid (and in few cases of adsorbed acetone and ethanol) was carried out by using several silica gel samples, whose properties were modified by adding oxidic dopants as γ-Al2O3, which is acidic in character, and MgO, which is mainly basic. Also the related system MgO-Al2O3 was investigated. Few IR spectra on selected pure specimens and on specimens containing adsorbed ethanoic acid were recorded with the aim of following the variation of the surfaces-adsorbate interaction with the variation of the acid-base properties. It was also of interest to compare the photoreactivity of insulators and semi…

Synthesis of high-surface area CeO2 through silica xerogel template: influence of cerium salt precursor”;

2010

Abstract Ceria nanosized oxides with high surface area were synthesized by means of a templating approach, using a porous silica xerogel with surface area as high as 718 m2/g. After impregnation of the silica template with the cerium salt solution and further calcination at 600 °C, the final ceria oxide was recovered by dissolving the silica framework in NaOH solution. The effect of cerium counteranion, nitrate or chloride, on the textural and reduction properties of the ceria oxide was examined. Characterizations by BET and pore size distribution, XRD, TPR and SEM/EDX techniques were performed. The silica xerogel templated approach resulted in the preparation of ceria with surface area of …

Different kinds of solid solutions in the V2O5-ZrSiO4-NaF system by sol-gel processes and their characterization

1993

Abstract In the V2O5-ZrSiO4-NaF system, three kinds of substances have been identified by sol-gel methods depending on the V2O5 amounts in the composition. Their characterization by X-ray diffraction, measurements of unit cell parameters, UV-visible (UV-V) spectroscopy, differential thermal analysis and lab colour parameter determination allow the consideration of three kinds of solid solution in the zircon lattice: (a) V+5,V+4-ZrSiO4, thermally stable and with a deep green colour; (b) V+4-ZrSiO4, thermally stable and blue coloured, made by the sol-gel method and with V2O5 amounts lower than 0·03 mol per formula weight; and (c) Na+,F−,V+4-ZrSiO4, a solid solution with a deep blue-turquoise …

EVA copolymer based nanocomposites: rheological behavior under shear and isothermal and non-isothermal elongational flow

2006

Abstract Nanocomposites are a very promising new class of polymer composites that exhibit an interesting combination of chemical, physical and mechanical properties. Only small amounts of nanofiller are sufficient to generate great variation of many properties. This work focuses on the rheological properties of poly[ethylene- co -(vinyl acetate)] (EVA copolymer) based nanocomposites in shear and in isothermal and non-isothermal elongational flow. The nanocomposites, at two different filler contents, were prepared in two different extruders and intercalates were obtained for all the samples. The twin-screw compounder is more efficient. The change of rheological properties, both in shear and …

2019

Abstract The preparation method of a polymer composite and the filler loading are amongst the factors that influence the properties of the final composites. This article studies the effect of these factors on the thermal stability and thermal degradation kinetics of poly(methyl methacrylate) (PMMA)/mesoporous silica (MCM-41) composites filled with small amounts of MCM-41. The PMMA/MCM-41 composites were prepared through in situ polymerisation and melt mixing methods, with MCM-41 loadings of 0.1, 0.3, and 0.5 wt.%. The presence of MCM-41 increased the thermal stability of PMMA/MCM-41 composites prepared by melt mixing, but in the case of the in situ polymerised samples, the MCM-41 accelerate…

Distribution of molecularly imprinted polymer layers on macroporous silica gel particles by STEM and EDX

2005

Abstract Using transmission electron microscopy (TEM) in parallel and scanning mode (STEM) combined with energy dispersive X-ray spectroscopy (EDX) the distribution of molecularly imprinted polymer layers covalently grafted on the inner and outer surface of macroporous silica gel particles was observed. The grafting was achieved using a special initiator system ( iniferter ) and applied on a well known model system producing molecularly imprinted layers with l -phenyl alanine analide ( l -PA) as template. By staining the sample with RuO 4 before its embedment in epoxy resin and cutting ultra thin slices it was possible to identify the stained grafted polymer on the silica matrix by EDX. Bas…

Mesoporous silica-based materials for use in biosensors

2012

Abstract There have been great advancements in the development of biosensors capable of characterizing and quantifying biomolecules. This article gives an overview of the formation, the properties and the electrochemical applications of ordered mesoporous silica-based materials in electrocatalysis, electrosorption, matrix immobilization, construction of systems for controlled release of active compounds, sensors, biosensors and immunosensors. We also present a comprehensive overview of current developments and key issues in the determination of some biological molecules with particular emphasis on the evaluation of models.

Mesoporous silica materials for use in electrochemical immunosensing

2013

Abstract Silica-based electrochemical immunosensors recently gained much importance for detecting antigens and biomarkers responsible for cancer diagnosis. This review describes fabrication and chemical modification of the surfaces of mesoporous silica materials for biomedical and immunosensing applications. We also present a comprehensive overview of current developments and key issues in the determination of some biological molecules with particular emphasis on evaluating the models.

Synthesis and Characterization of the Hybrid Clay-Based Material Montmorillonite-Melanoidin: A Potential Soil Model

2010

The study of the interactions among metals, minerals, and humic substances is essential in understanding the migration of inorganic pollutants in the geosphere. A considerable amount of organic matter in the environment is associated with clay minerals. To understand the role of organic matter in the environment and its association with clay minerals, a hybrid clay-based material (HCM), montmorillonite (STx-1)-melanoidin, was prepared from L-tyrosine and L-glutamic acid by the Maillard reaction. The HCM was characterized by elemental analysis, nuclear magnetic resonance, x-ray photoelectron spectroscopy (XPS), scanning transmission x-ray microscopy (STXM), and thermal analysis. The presence…