Silica gels structural chemistry

Research of Soviet scientists is surveyed. Contributions to various aspects of the colloid chemistry of silica are examined preparation and stabilization of silica hydrosols preparation of silica gels structural characterization of silicas surface chemistry elucidation adsorption and ion-exchange property examination and geometric and chemical modification of silicas, silica coatings, and so forth. 

The surface chemistry of SAMs of silanes on planar substrates such as oxidized silicon wafers is comparable to the chemistry of silica gel, with the absence of a porous structure [47]. 

Abstract. Structural and adsorption characteristics of various adsorbents such as fumed silicas, silica gels, activated carbons and carbon/silicas were analyzed. The adsorption of a variety of compounds reveals the effects of adsorbent grain size, specific surface area, pore volume, pore size distribution, surface chemistry, conditions of adsorbent synthesis and pre-treatment. Both dynamic (nonequilibrium) and static (equilibrium) adsorption conditions are addressed. 

Highly structured mesoporous silicas using a surfactant template provide a well characterized, ultra-high surface area material.5 In this volume Jaroniec provides an excellent summary of various novel materials based on this chemistry for Hg2+ adsorption. In this report we discuss results from a recent study utilizing two types of silica gels and a nanoparticulate fumed silica, all surface modified with complexing functional groups, for the adsorption of Cu2+ and Pb2+. 

Figure 5.9 Schematic diagram of the structure of (a) silica sol, (b) silica gel, and (c) amorphous SiC>2. Reprinted from Ralph K. Her The Colloid Chemistry of Silica and Silicates. Copyright 1995 by Cornell University (Copyright renewed 1983). Used by permission of the publisher, Cornell University Press...

Neimark (Institute of Physical Chemistry, the Ukrainian S.S.R. Academy of Sciences, Kiev) and colleagues (Slinyakova, Sheinfain, Piontkovska-ya, Vysotsky, Chertov, Khatset, Rastenko, Il in, Chuiko, Tertykh, and others) studied the synthesis and control of porous structures and the modification of the silica surface and other mineral sorbents. The theoretical principles for the formation of a porous structure were worked out (28, 29). Numerous silica gels were prepared that had pores ranging from very wide to very fine the latter had molecular-sieve properties (28-32). 

It has been pointed out (2) that we do not yet understand the complexities of sol-gel chemistry sufficiently well to accurately predict the microscopic structure, and hence the macroscopic properties of the material that will result from a particular polymerization recipe. Nevertheless, some generalities have been estabhshed that are useful in narrowing down the choices that need to be made in formulating a sol-gel recipe, and it is becoming increasingly possible to tailor material properties of silicon-based materials to suit specihc applications. A brief description of the mechanism of some of the elementary steps in formation of sol-gel materials can be found below, which emphasizes the relation between some of the synthetic variables and the resultant structures. First, some of the relevant properties of silica gels are described. 

Her, R.K. (1979) The Chemistry of Silica, Wiley, New York. Every aspect of the chemistry of silica in aqneous systems, including polymerization, gelation, gel structure, and applications, is discussed in this classic text. 

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