Preparation of Silica Membranes by Sol-Gel Method

Silicon dioxide, commonly known as silica, is one of the most studied materials for the preparation of inorganic membranes. Although silica has several crystalline polymorphs, amorphous silica has been widely studied for the preparation of both mesoporous and microporous membranes. Amorphous silica can be easily synthesized through sol-gel approaches which lend themselves to the use of different techniques for the formation of thin film membranes. First of all, this chapter will describe the sol-gel synthesis of silica. Depending on synthesis operating conditions it is possible to tailor the pore size of the amorphous silica in the range of both mesopores and micropores. In order to form a membrane, a continuous and uniform layer of silica needs to be realized. The most studied technique to form very thin silica layer is the dip-coating method. This chapter will introduce the dip-coating technique in order to extract the main parameter for the synthesis of effective silica membranes. Some approaches to increase the poor hydrothermal stability of silica have been attempted and emerging deposition techniques (e.g., ink-jet printing) can be effectively coupled with the sol-gel method in order to form selective silica membranes.