Methods for Preparing Silica Xerogel Monoliths

Silica xerogel monoliths are the major class of sol-gel process materials and their fabrication procedures were described extensively in many reviews and papers [54-58]. The principal concepts of fabrication of silica xerogel monoliths have already been described in Section 10.2, and the effects of parameters such as metal alkoxide precursor types, type of catalyst used, H2O Si molar ratio R), steric effect of precursor ligand groups, and functionality of organically modified silanes have also been discussed. Important pioneering research on the influence of these parameters on xerogel fabrication was presented in Refs [9,59-63]. 

Here are some examples of fabrication of silica xerogel monoliths by one- and two-step catalyst procedures. 

Fabrication procedures of silica monoliths by a one-step catalyst procedure are presented in Ref [20]. A basic procedure to prepare a silica xerogel monolith is by following the stoichiometry ratio (H2O Si) R = 4, while using a similar molar amount of alcohol as a common solvent for achieving homogeneous solution. In fabrication of sol-gel monoliths, the catalyst used has crucial influence. The common route for preparing silica monoliths is to use a recipe based on a one-step catalyst reaction. 

An example of a basic recipe is a starting solution consisting of CH3OH TMOS H2O catalyst = 4.8 1 4 0.25 in starting solution of 10.7 ml as follows 4.7ml methanol, 3.7ml TMOS, 1.8ml deionized water, and 0.5ml of IN acid/ 

In Ref. [65], an example of fabrication of silica xerogels by a two-step sol-gel reaction is presented. The procedure for the preparation consists of starting with a precursor solution with stoichiometry, 1 4 4 molar ratios (TEOS H2O  

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