Preparation of sols

All cited polysaccharides and PVA are water-soluble macromolecules that form viscous colloidal solutions when dissolved in water. The resulting solutions are of hydrophilic sol nature owing to 

Stock solutions of polysaccharide sols were prepared by stepwise addition of the reagent powder to doubly distilled water while rapidly and continually stirring the solution to avoid the formation of lumps, which swell with difficulty. 

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First demonstrated by David Avnir in 1984, the principle is as simple as it is potent. Due to the low temperature needed for the preparation of sol-gel matrices, almost all of the 18 million existing organic and bio organic molecules that could not be doped in glass, because glass is prepared at elevated temperatures (about 1000 °C), can now be entrapped in sol-gel glasses. 

When in 1994 the US and European patent offices recognized that the doped sol-gel technology had been invented by David Avnir and colleagues, granting the Hebrew University of Jerusalem a series of patents covering the generic methodology for the preparation of sol-gel materials, and their use in various applications, the time was ripe for the foundation of the first sol-gel chemical companies. 

Scheme 4.2 Preparation of sol-gel nanocoatings (Adapted from ref. 25, with permission.)...

T. Lopez, J. Navarrete, R. Gomez, O. Novaro, E. Eigueras, and H. Armendariz, Preparation of sol-gel sulfated Zr02-Si02 and characterization of its surface acidity, Appl. Catal. A 125, 217-232 (1995). 

The pore volume and surface area of sol-PILB-Cn samples are closer to those of the corresponding MCM41 solid prepared with silica fume and the same surfactant used in the preparation of sol-PILB-Cn, rather than to that of sol PILB. For example, the total pore volume and BET specific surface area of sol-PILB-C16 are 0.84 cm3/g and 756 m2/g, respectively, much larger than those for sol-PILB, 0.24 cm3/g and 404 m2/g, but comparable to those for MCM41-C16, 0.94 cm3/g and 790 m2/g. These results suggest that treatment with surfactants of quaternary ammonium salts alters the structure of the sol pillared clay radically. 

The structure of final product prepared by sol-gel method is in shape preliminarily in solution, and following process is relevant to the characteristic of sol directly. So the characteristic of sol is very important. The essential reason for transformation of homogeneous solution into sol is the hydrolysis of alcoholate and the condensation polymerization. Controlling conditions for hydrolysis of alcoholate is the key to the preparation of sol with promising quality. 

Solvent is important to preparation of sol. -OR group in alcoholate is easy to exchange with -OR group in solvent, which results in the variation of activity of hydrolysis of alcoholate. If the same alcoholate chooses different solvent, its hydrolysis rate and gel time will follow to be different. In the experiment, three kinds of solvent are selected alcohol, isopropanol and n-butyl alcohol. The research result reveals that sol will be formed in all occasions, but gel time was greatly different. Particle size and surface area also vary slightly. That is because that polarity, pole moment, and achievement ability to active proton result in different effects on the exchange reaction in sol. 

For the preparation of sol, 25% solution of NH3 was added in small portions (2 mL) to 1 L of 1 M solution of ZrOCU while heating under mechanical stirring. The temperature of solution did not exceed 90°C. Each following portion of NH3 solution was added only after complete dissolution of the zirconium hydroxide precipitate. The addition of the NH3 solution was terminated once the zirconium hydroxide precipitate did not dissolve within 20 min. The raw sol obtained was boiled using a reflux condenser for 25 h to allow the formation of the crystalline strucmre. Thereafter the sol was cooled to ambient temperature and filtered. Ceramic materials were immersed in 1 M sol of zirconium dioxide that was prepared as described... 

A quite different approach from that of colloidal sols in the preparation of sol-gel derived membranes utilizes polymeric sols. In this category of sols the dispersed phase results from the hydrolysis and condensation of metal organic precursors in organic media. In most cases this process deals with the polymerization of metal alkoxides in alcohol according to the following reactions ... 

The aim of this work is to develop new Fe-Mo containing mixed oxides highly dispersed in a titania matrix, prepared by the sol-gel method, and to compare these materials to those of iron molybdate prepared by conventional methods (i.e. impregnation). Here, we report the preparation of sol-gel derived iron molybdenum titanium mixed oxides. The bulk composition and the textural properties of these materials are investigated by elemental chemical analysis and N2 adsorption, respectively. 

Results in figure 7 evidence that calcination of sol-gel catalysts under air flow leads to a strong loss of activity, attributable to loss of volatile species of Mo during calcination step. The use of halogenated precursors in preparation of sol-gel catalysts occasions loss of activity, eventually due to the formation of halogenated species on catalysts surface that are inactive or less active. Unfortunately it was not possible to identify such hypothetical species. 

Preparation of sol-gel encapsulated Rh catalyst (i.e. 1.9 wt% Rh/ sol-gel catalyst). Preparation of sol-gel encapsulated Rh catalyst involves addition of... 

The preparation of sol-gels is a simple and straightforward process. Because the precursor sol has a low viscosity, it is easy to place it into any mold (including a microfiuidic channel) and... 

Scheme 7.5 Preparation of sol-gel silica-filled NR (adapted from ref 22).

Delattre, L. and Babonneau, R 1997. O Solution NMR characterization of the preparation of sol-gel derived Si02/Ti02 and Si02/Zr02 glasses. Chem. Mater. 9 2385-2394. 

Sol-gel films can be used to immobilize biomolecules. For example, Dong etal. developed thin sol-gel films on electrodes in which enzymes horseradish peroxidase (HRP) and glucose oxidase (GOD) were used to determine enzyme substrates [12]. A vapor-deposition sol-gel process [13] featuring a thin film of aqueous HRP solution into which titanium isopropoxide vapor was diffused to form a Ti02 sol-gel film incorporating HRP prevented denaturation of the enzyme. Surfactants were used in preparation of sol-gel films incorporating redox proteins on electrodes to improve porosity and electrochemical and catalytic performance [14]. 

In contrast to liquid droplets, solid particles usually have an irregular shape with planes having different interfacial tensions. In that case, Ostwald ripening manifests itself as a change toward more perfect crystals. This phenomenon, often referred to as aging, is applied in the preparation of sols and suspensions to obtain particles having better-defined interfacial characteristics. 

Sydney L E (1983) Preparation of sols and gels. British Patent No. 2,111,966... 

Other preparations of sols with particles under 5 nm in diameter and their stabilization have been discussed under the heading of polysilicates and silicates Sols of such small particles stabilized with relatively large amounts of base assume some of the characteristics of soluble silicates or polysilicates rather than of colloidal silicas. 

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