ABSTRACT
Aluminosilicates can be regarded as a large group of nanostructured materials having in common a skeleton based on tetrahedral SiO4 units in which a certain number of silicon atoms have been isomorphically substituted by aluminum ones. As a result, a defect of positive charge is produced in the lattice. Compensation of this excess of negative charge requires the attachment of cationic species to the aluminosilicate framework. SiO4 and AlO4 tetrahedral units act as building units for constructing a wide variety of structures, including porous (zeolites, sepiolite) to laminar aluminosilicates (montmorillonite, kaolinite). Since the preparation (Beck et al., 1992) of periodic mesoporous silica (MCM-41), a variety of silica-based mesoporous materials have been synthesized with variable degree of ordering, stability, and Al/Si ratios. An important group of materials is constituted by porous silica spheres (Hah et al., 2003).
