When it comes to aerogels, many people may have heard of an old method, which involves using precursor substances such as organic alcohol salts. Through a hydrolysis polymerization reaction, a wet gel is first formed, and then the liquid phase inside is removed to obtain the final dry gel. This method, also known as the sol-gel route or molecular route, is a common route for preparing aerogels such as silica and alumina.
However, this method has a drawback. The precursors themselves are difficult to obtain, and there are safety concerns. Therefore, it has only been successfully applied in a few oxide systems.
Now what? The situation is different.
The concept of "aerogel" itself is also constantly evolving. The early definition indeed emphasized that it was a porous material with nanometer-sized pores obtained by removing the solvent from the wet gel.
But later, the emergence of new aerogels made this definition lag behind the times. Some new aerogels no longer meet the characteristics of nanometer-sized pores, and some are even prepared by the gas-phase method.