Porous materials, silica

Micropore volumes of samples under study were determined by the application of the i-method (Table 2). This method is based on the comparison of nitrogen isotherm on solid under investigation with normalized nitrogen isotherm on proper reference non-porous material (silica Davisil, Supelco, USA). The details of this method are given elsewhere [15]. The micropore volume of ZSM-5/3, ZSM-5/7 and ZSM-5/10 samples is smaller than that of the pure ZSM-5 it decreases from 0.163 cm /g for ZSM-5/3 to 0.126 cmVg for ZSM-5/10. This decrease can be attributed to the increasing surface area of mesopores. The Si04 tetrahedra on the mesopore surface do not contribute to the formation of zeolitic channel walls [16]. Thus, as the mesopore surface area increases the micropore volume decreases. 

Gel-filled mineral porous material Silica filled with dextran gels. Composite porous particles filled with viscoelastic synthetic gels High sorption capacity at high flow rates, high resolution, noncompressibility HyperD, BioSepra... 

Schaefer D.W., Keefer K.D. Structure of random porous materials Silica aerogel. Phys. Rev. Lett. 1986 56 2199-2202... 

Usually they are employed as porous pellets in a packed bed. Some exceptions are platinum for the oxidation of ammonia, which is in the form of several layers of fine-mesh wire gauze, and catalysts deposited on membranes. Pore surfaces can be several hundred mVg and pore diameters of the order of 100 A. The entire structure may be or catalytic material (silica or alumina, for instance, sometimes exert catalytic properties) or an active ingredient may be deposited on a porous refractory carrier as a thin film. In such cases the mass of expensive catalytic material, such as Pt or Pd, may be only a fraction of 1 percent. 

Information on the morphology of the nanohybrid sorbents also was revealed with SEM analysis. Dispersed spherical polymer-silica particles with a diameter of 0.3-5 pm were observed. Every particle, in one s turn, is a porous material with size of pores to 200 nm and spherical particles from 100 nm to 500 nm. Therefore, the obtained samples were demonstrated to form a nanometer - scale porous structure. 

Presently, the most successful adsorbents arc microporous carbons, but there is considerable interest in other possible adsorbents, mainly porous polymers, silica based xerogels or zeolite type materials. Regardless of the type of material, the above principles still apply to achieving a satisfactory storage capacity. The limiting storage uptake will be directly proportional to the accessible micropore volume per volume of storage capacity. 

Adsorption A physical process in which a molecule of a vapor or gas (adsorbate) is condensed on and taken up by the surface of a porous material (adsorbent) such as silica gel or activated carbon. 

Packing material Spherical porous gels (silica or polymeric) None Spherical solid gels (silica or polymeric) None... 

HOPC uses solid porous materials such as porous silica. Most of the porous gels made of cross-linked polymers, widely used in SEC, will not be appropriate. It is necessary to use porous materials that withstand a high... 

Adsorption is the property of certain extremely porous materials to hold vapors in the pores until the desiccant is either heated or exposed to a drier gas. The material is a solid at all times and operates alternately through drying and reactivation cycles with no change in composition. Adsorbing materials in principal use are activated Alumina and silica gel. Molecular sieves are also used. Atmospheric dew points of minus 1000°F are readily obtained using adsorption. 

Some manufacturers use the principle of the adsorption of a gas by a porous material such as silica gel or charcoal. Since the adsorbent is a solid and cannot migrate from the phial, these valves cannot suffer reversal of charge. 

Porous materials, such as silica and alumina, have thermal diffusion lengths of approximately 10 m, which is much less than the typical thickness of pressed discs. The small thermal diffusion length gives photoacoustic spectroscopy a larger dynamic range than transmission methods when applied to powdered samples. An additional advantage is the ease of sample preparation, since photoacoustic spectroscopy uses powdered samples with no special preparation required. 

Zeolites. In heterogeneous catalysis porosity is nearly always of essential importance. In most cases porous materials are synthesized using the above de.scribed sol-gel techniques resulting in so-called amorphous catalysts. Porosity is introduced in the agglomeration process in which the sol is transformed into a gel. From X-ray Diffraction patterns it is clear that the material shows only weak broad lines, characteristic of non-crystalline materials. Silica and alumina are typical examples. Zeolites are an exception they are crystalline materials but nevertheless exhibit high (micro) porosity. Zeolites belong to the class of molecular sieves, which are porous solids with pores of molecular dimensions, i.e., typically the pore diameter ranges from 0.3 to 10 nm. Examples of molecular sieves are carbons, oxides and zeolites. 

Fig. 3.23 shows pore volume distributions of some commercially important porous materials. Note that zeolites and activated carbon consist predominantly of micropores, whereas alumina and silica have pores mainly in the me.sopore range. Zeolites and active carbons have a sharp peak in pore size distribution, but in the case of the activated carbon also larger pores are present. The wide-pore silica is prepared specially to facilitate internal mass-transfer. 

The use of SPE with porous materials such as alumina, diatomaceous earth, Horisil and silica for the cleanup of fat-soluble organochlorine pesticides in fatty foods such as meat, flsh, shellfish, milk and vegetable oils has been well documented. The choice of elution solvents is critical because relatively small amounts of lipid in the final extract can cause rapid deterioration of GC capillary columns and also contaminate the gas chromatograph. A number of workers have used a porous material in tandem with Cig to effect an improved cleanup.Di Mucchio employed a multicartridge system comprising Extrelut, silica and Cig to extract organophosphorus pesticides from oils and fatty extracts. Relatively few literature applications include the pyrethroids, but Ramesh and Balasubramanian reported a simple carbon-based SPE method for the analysis of pyrethroids in vegetable oil. 

Many inorganic oxides can be manufactured to provide granular, porous materials with high surface areas, which can readily adsorb organic liquids. Preliminary screening of a range of oxides, namely aluminium oxides, titanium dioxides, zinc oxide, hydrotalcites, zeolites and silicas, indicated that the latter two materials were able to retain the largest quantities of biocide. 

IUPAC classification, mesoporous materials are defined as porous materials with diameters in the range 2-50 nm, which is rather dose to the dimensions of functional biomolecules such as proteins. Therefore, unexplored phenomena and functions could be observed for biomolecules confined in mesopore channels due to their restricted motion and orientation. In this chapter, we briefly introduce recent developments on the immobilization of biomolecules in mesoporous media, where the use of mesoporous silica and mesoporous carbon are mainly discussed. 

Silica sol-gel glasses are porous materials, which means some kind of solid material that has holes in it. These holes are also called pores. To call a material a porous material, there is usually some kind of implicit assumption of homogenization and length scale. The holes must be smaller enough, compared to the typical size of the piece of material that is considered, so that it is reasonable to consider the material as a mixture of solid framework and pores28. 

In this chapter, we demonstrate the potential of such agents as catalysts/promoters in key steps for the derivatization of sugars. The most significant catalytic approaches in carbohydrate chemistry that use aluminosilicate porous materials, namely zeolites and montmorillonite clays, are reviewed and discussed. Silica gel is a porous solid silicate that has also been used for heterogeneous catalysis of organic reactions in general. We include here its usefulness as promoter and reagent support for the reactions under consideration. 

The first thing you need is an adsorbant, a porous material that can suck up liquids and solutions. Paper, silica gel, alumina (ultrafine aluminum oxide), corn starch and kitty litter (unused) are all fine adsorbants. Only the first three are used for chromatography. You may or may not need a solid support with these. Paper hangs together, is fairly stiff, and can stand up by itself. Silica gel, alumina, corn starch, and kitty litter are more or less powders and will need a solid support to hold them. 

Optical lithography, in compound semiconductor processing, 22 193 Optically active citronellol, 24 506 Optically transparent porous gel-silica, 23 75, 76 Optical materials nonlinear, 17 442-460 second-order nonlinear, 17 444—453 third-order nonlinear, 17 453-457 Optical memory, photochromic material application, 6 602 Optical microscopy, 16 467-487 history of, 16 467-469 in kinetic studies, 14 622 liquid immersion, 15 186 Optical mode density, 14 849, 850-852 Optical multichannel analyzers (OMAs), 23 143... 

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