Xerogels

Xerogel is a solid obtained by drying a gel so that the liquid phase is removed by evaporation, leaving behind a rigid, porous network. In gel formation, a sol-gel process creates a three-dimensional network of inorganic or organic material within a liquid. When the liquid is removed by evaporation at ambient or moderate pressure, capillary forces cause shrinkage and result in a xerogel, in contrast to an aerogel produced by supercritical drying that minimizes capillary damage.

Xerogels commonly use silica, but metal oxides such as alumina and titania and organic polymers can also form xerogels. Wet gels are produced by sol-gel reactions of precursors, followed by gelation, aging, and drying. The resulting materials exhibit high porosity and a large internal surface area, though typically less porosity and more shrinkage than aerogels. The pore structure is often a combination of interparticle pores and some microporosity.

Applications include catalyst supports, adsorbents, chromatography supports, insulating materials, sensors, optical hosts, and energy storage components. Silica xerogels are widely used as desiccants and insulation due to their porosity and low density.

Compared with aerogels, xerogels generally have higher bulk density and lower porosity, and their drying-induced shrinkage reduces pore volume but can increase mechanical strength. Preparation parameters such as solvent choice, drying rate, and post-treatment influence pore size distribution and surface area, shaping performance for specific applications.