Preparation of Al Chelate Compounds with Different Carbon Chain Length and Its Application for Surface Modifier of Silica

Al chelate compounds with different carbon chain length were synthesized by reactions of aluminum sec-butoxide with β-ketoesters having different carbon chain length, such as acetoacetic acid ethyl ester (n=2), acetoacetic acid pentyl ester (n=5), acetoacetic acid octyl ester (n=8) and acetoacetic acid oleyl ester (n=18). Silica was modified by aluminum sec-butoxide and these Al chelate compounds (ALK, C2, C5, C8 and C18 respectively). Then the modified silica was dried at 100°C and heated up to 400°C. We studied the influence of carbon chain length on the hydrophilic-hydrophobic property of dried silica by measurement of adsorption amount of water vapor. In addition the surface property of heated silica was studied by measurement of specific surface area and pore size distribution. It was found that the adsorption amount of water vapor on dried silica decreased with increasing the length of carbon chain such as ALK, C2 and C5. Adsorption amount of water vapor was the same on C5, C8 and C18. Porous Al2O3 was prepared from ALK and C2 by drying at 100°C by hydrolysis of aluminum sec-butoxide and Al chelate compounds. Porous Al2O3 was also prepared by thermal decomposition of Al chelate compounds from C5, C8 and C18 by heating at 200°C. The mechanism of pore formation changed according to the carbon chain length of Al chelate compounds. The porous Al2O3 prepared from Al chelate compounds had smaller and more uniform pore size than that prepared from aluminum sec-butoxie.