A New Role of the Surfactant in the Synthesis of Mesostructured Phases:  Dodecyl Phosphate as Template and Reactant for Aluminophosphates

Lamellar mesostructured aluminophosphates were synthesized from aluminum triisopropoxide and phosphoric acid; monododecyl phosphate surfactant was used as structure-directing template. Depending on the relative Al/P ratio in the samples, variable relative amounts of tetrahedrally and octahedrally coordinated Al are found, indicating that both aluminophosphate and aluminum oxide species (as thermodynamically favored) are being formed in the syntheses. This is investigated quantitatively by Al K-edge XANES spectroscopy. The same syntheses were carried out without phosphoric acid, resulting in similar lamellar structures. The inorganic lamellae of these products consist to a significant extent of aluminophosphate rather than exclusively of aluminum oxide, which means that the phosphate headgroups of the surfactant molecules become incorporated into the inorganic network. Thus, for the first time, the surfactant serves as both template and reactant.