Structural characterization of micellar aggregates in sodium dodecyl sulfate/aluminum nitrate/urea/water system in the synthesis of mesoporous alumina

The mechanism of templated synthesis of ordered mesoporous alumina according to the recipe proposed by Yada et al. (Yada, M.; Machida, M.; Kijima, T. Chem. Commun. 1996, 769) using sodium dodecyl sulfate (SDS) as template, has been investigated by NMR self-diffusion and spin and fluorescence probe techniques. In the precursor solutions urea was found to produce a substantial shortening of the long entangled cylindrical aggregates characteristic of the SDS micellar solutions with aluminum salt in large excess. The formation of mesostructured hexagonal alumina was followed using spin probes incorporated in the SDS aggregates. No structural changes were observed during urea hydrolysis, before the onset of the precipitation. In the precipitate, the presence of the surfactant template is demonstrated as well as its interaction with the aluminum species. Time evolution of this interaction is also observed. Finally, the influence of the composition of the precursor system on the structure and thermal stability o...