Synthesis of mesostructured or mesoporous aluminas in the presence of surfactants. Comprehension of the mechanisms of formation

Abstract

Synthesis of Mesostructured or Mesoporous Aluminas in the Presence of Surfactants. Comprehension of the Mechanisms of Formation-The aim of the present study was double: the synthesis of mesoporous aluminas in aqueous medium and the comprehension of their mechanisms of formation. Mesoporous aluminas were obtained from an acidic solution of the aluminum Keggin polycation and a mixed micelle of sodium palmitate and cetyltrimethylammonium bromide. The pore diameters could be increased by increasing the final pH. Aluminas were also obtained from a basic solution of sodium aluminate. Very important pore volumes and specific surface areas were obtained when washing with ethanol or acetone instead of water. A fundamental study to understand the mechanism of formation of a mesostructured alumina, whose symmetry was hexagonal, was also carried out in order to improve the procedures. The study of the interactions between the surfactant and the alumina framework allowed us to explain why the structure collapses upon calcination. A mechanism of formation, based on fluorescence observations, is also presented. It was established that the aluminum species interact with the micelles and polymerize within the palisade layer. However, the micelles are quasi spherical throughout the experiment and do not organize into a hexagonal array before a precipitate is observed.