Physicochemical Basis and Principles of Sol-Gel Processing

I - stable sol II - gel III - sources of additional catalytic chemical functionality  

Sol-gel processing is a sequence of operations including chemical reactions and physical processes (phase separation, dissolution, evaporation, phase transition, etc.) leading to the formation of porous solids (metal oxides or oxide-free materials) from liquid solutions of molecular precursors. Its general principles and the physicochemical basis of separate steps are well described and analyzed in many comprehensive books and reviews [2, 3, 

Activation of sol-gel precursors is needed when they are chemically inert and cannot participate in condensation reactions directly. It most often involves hydrolysis of solvated metal ions in aqueous solutions or metal aUcoxides in 

Besides addition of bases, hydrolysis of hydrated metal cations may be initiated by addition of another proton scavenger, like propylene oxide [18, 19]. Protonation of the epoxide oxygen by an acidic proton of a water ligand is followed by the epoxide ring opening through nucleophilic attack of the conjugated base. 

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