Silica preparation

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

The antibody of human epidermal growth factor (EGF) was coupled to diol silica (prepared from silica and 3-glycidoxypropyltrimethoxysilane via an epoxy silica) by means of CDI. This supported antibody was utilized for immunoaffinity HPLC analysis of human epidermal growth factor. 213 ... 

Okitsu K, Murakami M, Tanabe S, Matsumoto H (2000) Catalytic behavior of Au core/Pd shell bimetallic nanoparticles on silica prepared by sonochemical and sol-gel processes. Chem Lett 29 1336-1337... 

FIGURE 7.3 Scanning electron micrographs of monolithic silica prepared from sol-gel methods, (a) monolithic silica prepared from TMOS in a test tube, and monolithic silica columns prepared from a mixture of TMOS and MTMS, (b) in a 50-pm fused silica capillary, (c) in a lOO-pm fused silica capillary, and (d) in a 200-pm fused silica capillary tube (reproduced from the reference, Motokawa et al. (2002), with permission from Elsevier). 

Mesoporous Silica Prepared by the Lizard Template Method 65... 

Fig. 2.27 HR-TEM images of mesoporous silica prepared by the lizard template method (A) before hydrolysis (as-synthesized) (B) after hydrolysis. Reprinted with permission from [106],...

FIGURE 12.1 SEM photographs of monolithic silica columns (A) monolithic silica prepared from TMSO in a test tube (B) 50 /mi inner diameter silica skeleton, size 2 /(m, through-pore size 4.5 (ini. (Source From Ikegami, T. and Tanaka, N., Curr. Opin. Chem. Biol., 2004, 8, 527. With permission from Elsevier Scientific Publishing.)... 

The variety of finely divided silica known as hexagonal mesoporous silica (HMS) [6,34] is generally prepared by the copolymerization of a silica precursor such as tetraethylorthosilicate (TEOS), in presence of a suitable template. This acid or base catalyzed reaction follows the sol-gel route and it has been found [28] that during silica preparation by this technique, it is also possible to add an organotriethoxysilane [RSi(OEt)3] that would... 

Na,PdCI4 Phosphinated silica [prepared by reaction (6)j Ally chloride or butadiene with HSiCI, 115... 

New Organically Modified Hexagonal Mesoporous Silicas Preparation and Applications in Catalysis... 

Surfactant extractions have been attempted previously, but mainly for HMS materials (mesoporous silicas, prepared using neutral amines as the surfactant). Due to the much weaker S°I° interaction, compared to the S+I interaction, these surfactants can be extracted relatively easily [6], Some reports have been published on the extraction of the cationic surfactant, but the resulting material is mostly inferior to the calcined one and in most cases, still a posttreatment at high temperatures is required [7], We describe an extraction procedure for MCM-48, that does not require a post-treatment and that produces materials with a better quality than the calcined ones. 

Figures 4a and 4b depict selected Nitrogen adsorption-desoprtion isotherms and pore size distributions (PSDs) for the same series of samples. As seen here and also in Table 1, all hexagonal phases exhibited pore sizes mostly above 5 nm, while typical pore sizes of MCM-41 silica prepared in the presence of CTAB under more common temperatures, i.e., 80 - 120 °C, have 3.5 to 4 nm pores [5, 19]. Earlier work showed that direct synthesis or postsynthesis hydrothermal restructuring in the mother liquor at high temperature, e.g. 150 °C gave rise to...

Fig. 2. Practical absorptivity1 spectra for transition elements in fused silica prepared by flame hydrolysis absorptivity is given in terms of ppbw metal4 . (Reproduced by permission of The American Ceramic Society)...

By changing the method and specific parameters of the silica preparation, surface area, pore volume, pore size and particle size are, to some extent, independently controllable. These are the four variables, governing the chemical and physical behaviour of silica. Each of them will be discussed in detail in the subsequent paragraphs. Initial interest is directed to the methods of preparation and the various types obtained. A survey of these methods and their main characteristics is presented in table 1.1. 

The physical properties of the different silicas, prepared by the above mentioned methods, are compared in table 1.2. 

From the above mentioned silica preparation paths, the sol-gel route is the most studied and consequently most documented. Sol-gel processing is used not only for the preparation of silica gels, but also for the synthesis of ceramic products, ranging from thin films and coatings over porous membranes to composite bodies.4... 

Treat a fused-silica capillary tube (50-100 pm I.D., 370 pm O.D.) with 1M NaOH solution at 40°C for 3 h, prior to the silica preparation. 

Fig. 5.2. (a), Scanning electron micrograph of a continuous monolithic silica prepared in a fused silica capillary (100 pm) [16] (b), SEM photograph of monolithic silica prepared in a capillary (75 pm). Reproduced from ref. 19, with permission. 

Fig. 5.3. Plots of the skeleton size against the through-pore size of the continuous monolithic silica prepared in a capillary (O), and the larger-sized silica rod columns (7 mm x 83 mm) having constant through-pore size/skeleton size ratio ( ) [15]. Also plotted are the particle size (vertical axis) against the size of interstitial voids (25-40% of dp as indicated by the bars) found with a conventional particle-packed column.

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