Abstract—Adsorption properties of silica gel have been attributed to the surface hydroxyl groups of silica gel. Some hydroxyl groups are free standing and called free silanol groups. Some are hydrogen bonded to neighbouring silanol groups. Christy has shown that a high silanol number and a balanced concentration proportionality between these two different types of hydroxyl groups is necessary for effective adsorption of water molecules. Thermal treatment of silica gel samples alters the proportions of these groups and the above fact was investigated by using thermally treated silica gel samples. Two silica gel samples of varying surface areas and silanol numbers were dried under vacuum at 200 o C and their adsorption characteristics were followed by using NIR spectroscopy. Then the samples were subjected to heating at 350, 450, 600 degrees to cause changes in the concentrations of the surface silanol groups and their surface and adsorption characteristics were followed. The results clearly indicate that the heating process both remove free and hydrogen bonded silanol groups and alter the ratio between the two. Furthermore, the heating causes reduction in silanol umber and upsets the balance in the proportionality of the silanol groups for effective adsorption of water molecules.
Index Terms—Silanol groups, adsorption NIR spectroscopy, second derivative profiles
Alfred A. Christy is with the Department of Science, Faculty of Engineering and Science, University of Agder, 4604 Kristiansand, Norway(email: alfred.christy@uia.no).
Cite: Alfred A. Christy, "Effect of Heat on the Adsorption Properties of Silica Gel," International Journal of Engineering and Technology vol. 4, no. 4, pp. 484-488, 2012.
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