The role of solvent preparation in soft template assisted synthesis of mesoporous alumina

Synthesis of mesoporous aluminas (MAs) in aqueous and alcoholic solutions in soft template assisted sol-gel process was systematically studied with a particular attention to the role of the initial solvent preparation. Two synthesis pathways were employed, namely, the aqueous phase synthesis in water and water/ethanol mixtures and the solvent evaporation-induced self-assembly (EISA) synthesis in alcohols (ethanol, isopropanol and n-butanol). The results showed that in all the reaction mediums, the hydrolysis of aluminium isopropoxide played a crucial role. Decreasing water proportion reduced the hydrolysis rate of aluminium isopropoxide and consequently led to a more uniform stacking of the boehmite colloids formed and narrower the pore size distribution (PSD), higher surface area and greater pore volume of the MA synthesized. For the EISA pathway conducted in alcohols, the tardiness and incompleteness of hydrolysis in isopropanol provoked a random stacking of the aluminium precursor species, resulted in a disordered mesoporosity and a broad PSD. Under the experimental conditions studied for the EISA pathway, the addition of 3.0 mL HNO₃ per 20 mmol of aluminium isopropoxide in ethanol favoured the formation of a uniform MA with very narrow PSD.