Tetraalkoxysilanes hydrolysis reaction

In the sol-gel processing of silica, a silica precursor undergoes hydrolysis. Most often, a tetraalkoxysilane is used as the silica precursor. The hydrolysis reaction can be illustrated as follows ... 

In the starting mixture that includes tetraalkoxysilane and water, the following hydrolysis reactions occur ... 

This is the first stage of the sol-gel process. A complete hydrolysis reaction of a tetraalkoxysilane molecule has the following form ... 

The example is the reaction between tetraalkoxysilanes and water. This reaction in solution takes place in consecutive steps of hydrolysis,... 

According the method of Stober et al. [1] colloids with a narrow size distribution are prepared via ammonium hydroxide-catalyzed hydrolysis and condensation of tetraalkoxysilanes and titanium tetraethoxide. The particle size can also be adjusted by variation of several reaction parameters (monomer, NH3 and H2O concentration solvent temperature) and by controlled cocondensation. The last method enables the incorporation of chromophores in two different ways ... 

Silica is an attractive material for inorganic gel applications because it is non-toxic, non-flammable and easy to dispose of. Dry silica gels have a translucent, bluish appearance. For gel synthesis at lab-scale, a tetraalkoxysilane Si(OR)4, commonly tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS), dissolved in the respective alcohol ROH, acts as the silica source. When water is added, two chemical reactions occur the first, hydrolysis. 

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