Silica Gels Preparation and General Properties

The commercial silica gel sorbents are mesoporous, that is, with pores mostly larger than 20 A. Silica gel can be formed by two routes (1) polymerization 

Adsorbents Fundamentals and Applications, Edited By Ralph T. Yang ISBN 0-471-29741-0 Copyright 2003 John Wiley Sons, Inc. 

NazSiOs + 2HC1 + nHzO 2NaCl + SiOz-nHzO + H2O (6.1) 

The silica gel is amorphous. By use of high-resolution electron microscopy, it is known that its amorphous framework is composed of small globular (primary) particles having sizes of 10 to 20 A (Rouquerol et al., 1999). Still another route for preparing silica gel involves reactions of silicon alkoxides with water, and a wide variety of materials can be produced in this manner (Jones, 1989 Drinker and Sherer, 1990). The processes based on this ronte are referred to as sol-gel processing, and they offer many promising possibilities. For silica gel, the reaction is 

The silicic acids thus formed can then polymerize via  

---