Compatible Precursor for Sol–Gel Mineralization of Colloidal Systems. Mini-Review

Colloidal systems used as templates in the sol–gel synthesis are of great interest owing to their structural diversity; however, they are very sensitive to experimental conditions. The introduction of a precursor; the release of an organic solvent during hydrolysis; the addition of a catalyst, e.g., an acid or an alkali; and heating lead to rearrangements and phase transformations. As a result, the final state turns out to be significantly changed compared to the initial one, and such changes cannot be predicted a priori. This review is devoted to precursors containing ethylene glycol residues. In contrast to tetraethoxysilane, which is used in the traditional sol–gel synthesis, such precursors are hydrophilic, soluble in water, undergo hydrolysis in neutral aqueous solutions, and do not require the addition of a catalyst and heating. Moreover, unlike ethanol, ethylene glycol present in the amounts in which it is released during hydrolysis causes no transformations in colloidal systems. The review covers the preparation of the precursors, the issues of sol–gel chemistry, and examples of the formation of various functional materials that are synthesized using a simpler protocol in a single step under conditions that are determined by a template being mineralized rather than the sol–gel process. Many of the mentioned silica materials can be synthesized only using ethylene glycol-containing silanes.