Sol-gel synthesis of α-Al2O3 with enhanced porosity via dicarboxylic acid templating

One of the major routes to synthesize macroporous alpha-Al2O3 is the sol-gel process in presence of templates. Templates include polymers as well as carboxylic acids, such as citric acid. By careful choice of the template, pore diameters can be adjusted between 110 nm and several mu m. We report the successful establishment of plain short-chain dicarboxylic acids (DCA) as porogenes in the sol-gel synthesis of macroporous alpha-Al2O3. By this extension of the recently developed synthesis route, a very precise control of pore diameters is achieved, in addition to enhanced macropore volumes in alpha-Al2O3. The formation mechanism thereof is closely related to the one postulated for citric acid, as thermal analyses show. However, since branching in the DCA-linked alumina nuclei is not possible, close monomodal pore width distributions are attained, which are accompanied by enhanced pore volumes. This is a significant improvement in terms of controlled enhanced porosity in the synthesis of macroporous alpha-Al2O3.