A Robust Approach to Inorganic Aerogels: The Use of Epoxides in Sol–Gel Synthesis

Abstract

Over the last decade, the diversity of metal oxide materials prepared using sol–gel techniques has increased significantly. This transformation can be attributed, in part, to the development of the technique known as epoxide-initiated gelation. The process utilizes organic epoxides as initiators for the sol–gel polymerization of simple inorganic metal salts in aqueous or alcoholic media. In this approach, the epoxide acts as an acid scavenger in the sol–gel reaction, driving the hydrolysis and condensation of hydrated metal species. This process is general and applicable to the synthesis of a wide range of metal oxide aerogels, xerogels, and nanocomposites. In addition, modification of synthetic parameters allows for control over the structure and properties of the sol–gel product. This method is particularly amenable to the synthesis of multi-component or composite sol–gel systems with intimately mixed nanostructures. This chapter describes both the reaction mechanisms associated with epoxide-initiated gelation as well as the variety of materials that have been prepared using this technique.