Effect of Co-exist Elements in Porous Silica-gel on Solubility into Hot Water.

The solubility of porous silica-gel into water is one of serious problems for application of porous silica-gel for catalyst and other sophisticated usage. In particular, the surface area is so large that active surface of silica-gel quickly reacts with water and the basic structure destroys by dissolving silica and oxygen which compose the porous materials. However, the quantitative studies of solubility in hot water as well as cold water have been seldom found in this field because the dissolution phenomena is very complicated. In the first place, the method to measure the solubility in hot water was designed in this study and the condition, at 180 °C, 1hr. was fixed to evaluate the solubility. The effect of co-exist elements on the solubility into hot water has been widely surveyed. There are three groups where the solubility changes were observed and the several elements which were considered to react with silica showed the excellent results to reduce the solubility. Aluminum is one of the best co-exist element. Al-modified silica-gel had small solubility although the surface area of porous silica-gel did not decrease. NMR measurements showed that the surface chemical structure of aluminum replaced silica-gel changed and especially OH moiety decreased remarkably.