Search results for "Silica Gel"
showing 10 items of 91 documents
Pore structural characterization of monolithic silica columns by inverse size-exclusion chromatography
2007
In this work, a parallel pore model (PPM) and a pore network model (PNM) are developed to provide a state-of-art method for the calculation of several characteristic pore structural parameters from inverse size-exclusion chromatography (ISEC) experiments. The proposed PPM and PNM could be applicable to both monoliths and columns packed with porous particles. The PPM and PNM proposed in this work are able to predict the existence of the second inflection point in the experimental exclusion curve that has been observed for monolithic materials by accounting for volume partitioning of the polymer standards in the macropores of the column. The appearance and prominence of the second inflection …
Spherical ordered mesoporous silicas and silica monoliths as stationary phases for liquid chromatography
2006
Ordered mesoporous silicas such as micelle-templated silicas (MTS) feature unique textural properties in addition to their high surface area (approximately 1000 m2/g): narrow mesopore size distributions and controlled pore connectivity. These characteristics are highly relevant to chromatographic applications for resistance to mass transfer, which has never been studied in chromatography because of the absence of model materials such as MTS. Their synthesis is based on unique self-assembly processes between surfactants and silica. In order to take advantage of the perfectly adjustable texture of MTS in chromatographic applications, their particle morphology has to be tailored at the microme…
A molecular approach to remove lead from drinking water
2005
Abstract Corrosion of lead-containing plumbings is responsible for significant contamination of tap water, which can reach several hundreds of micrograms per liter. According to a decision of the European Council applicable in 2013, the maximal lead level in tap water should not exceed 10 μg l −1 . A new concept has been explored that relies on solid-phase extraction by covalent attachment of a lead-selective macrocyclic sequestering agent onto the surface of silica gel. An N -carbamoylmethyl substituted 1,4,8,11-tetraazacyclotetradecane (cyclam) derivative was shown to exhibit favorable protonation properties together with an almost 10 6 -fold selectivity for lead over calcium. Structural …
Dynamic properties of solvent confined in silica gels studied by broadband dielectric spectroscopy
2007
Abstract We report the results of a broadband (10−2–107 Hz) dielectric spectroscopy study on a solvent system (glycerol–water solution) confined in a porous silica matrix. The dielectric relaxation of the system is studied as a function of both temperature (120–280 K) and solvent composition (0–36 glycerol molar percentage), at constant matrix composition. Our data show that glycerol–water systems confined inside silica gel are characterized by a very complex dynamics quite different from that observed in solution, thus indicating that confinement may deeply modify solvent dynamics. Indeed in addition to the relaxation processes similar to those occurring in bulk samples, new dielectric rel…
Stereoselective synthesis of substituted tetrahydropyran rings via 6-exo and 6-endo selenoetherification
2002
Eight unsaturated alcohols were cyclized by selenoetherification in 6-exo or 6-endo manner to give substituted tetrahydropyran rings. Yields, regio- and stereoselectivities were discussed in terms of steric and electroniceffects such as Se-O interaction. For the first time examples of the use of silica gel in selenoetherification and the effect of the X - counter ion of PhSe + on the reaction course are discussed. These effects are related to the occurrence of Se-O interaction.
Surface molecularly imprinted silica for selective solid-phase extraction of biochanin A, daidzein and genistein from urine samples
2015
Selective molecularly imprinted silica polymer (SiO2MIP) for extraction of biochanin A, daidzein and genistein was synthesized using the surface molecular imprinting technique with the silica gel as a support. Biochanin A (BCA) was used as a template, 3-aminopropyltriethoxysilane (APTES) as a functional monomer, and tetraethoxysilicane (TEOS) as a cross-linker. Non-imprinted polymer with the sol–gel process (SiO2NIP) was also prepared for comparison. The synthesized polymers were characterized by Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM) and a standard Brunauer-Emett-Teller (BET) and Barret–Joyner–Halenda (BJH) analysis. The obtained results indicate…
Photodecomposition of adsorbed ethanoic acid over silica gel catalyst in a flow system
1986
Abstract The photodecomposition of ethanoic acid adsorbed on silica gels from various sources was studied at wavelengths greater than 300 nm. The experiments were carried out in a flow apparatus. A few photoreactivity tests using acetone or ethanol were also performed. The photodecomposition of ethanoic acid and acetone produced mainly carbon dioxide and methane, in the ratio 2:1, and traces of ethane and methanol. Adsorbed ethanol was not affected at all by the radiation. Infrared and UV-vis reflectance spectra of ethanoic acid adsorbed on silica gels as well as UV-vis reflectance spectra of acetone and ethanol adsorbed on silica gels were recorded. The spectra show the presence of a varie…
The Nature of Silanol Groups on the Surfaces of Silica, Modified Silica and Some Silica Based Materials
2014
Silica gel, a material that is produced from the condensation polymerisation of silicic acid, contains surface silanol groups formed during the condensation. The silanol groups on the surface are mostly of free and vicinal silanol groups. These silanol groups can be modified in several different ways. Thermal treatment and hydrothermal treatment can be carried out to alter the concentration proportions between free and hydrogen bonded silanol groups on the surface. They can also be chemically treated with suitable chlorosilanes to modify the silanol groups into polar or non polar materials that can be used in separation science.This article explores the chemical nature of silanol groups on …
Supported ionic liquids. New recyclable materials for the L-proline-catalyzed aldol reaction
2006
New materials for L-proline recycling have been developed. These materials have been applied to the L-proline-catalyzed aldol reaction between acetone and several aldehydes. The L-proline has been supported on the surface of modified silica gels with a monolayer of covalently attached ionic liquid with or without additional adsorbed ionic liquid. Good yields and ee values, comparable with those obtained under homogeneous conditions, have been obtained especially with imidazolinium-modified and 4-methylpyridinium-modified silica gels. Moreover, these materials have been easily recovered by simple filtration and studies about their reuse have been carried out. These studies showed that these …
Multiarm cyclam-grafted mesoporous silica: a strategy to improve the chemical stability of silica materials functionalized with amine ligands
2009
We have explored in this work the stability and the reactivity of multiarm cyclam-grafted mesoporous silica samples in aqueous solution. A series of hybrid materials have been prepared by grafting silylated cyclam molecules bearing one, two, or four silyl groups onto both amorphous silica gel (K60) and ordered mesoporous silica (SBA15). Under these conditions, cyclam moieties are attached to the silica walls via one, two, or four arms. Various physicochemical techniques have been applied to characterize the functionalized solids (elemental analysis, 1H-29Si and 1H-13C CPMAS NMR, and N2 adsorption-desorption isotherms). The interest in two and four arms for improving the chemical stability i…