Highly spongy hierarchical structured meso-macroporous aluminosilicates with high tetrahedral aluminium content and 3D interconnectivity from a single-source molecular precursor (sec-BuO) 2–Al–O–Si(OEt) 3: Effect of silicon co-reactant

Abstract

The effect of tetraethoxysilane (TEOS), tetrapropoxysilane (TPOS), tetrabutoxysilane (TBOS) and a mixture of tetramethoxysilane (TMOS) and TEOS as silicon co-reactant on the formation of hierarchically structured meso-macroporous aluminosilicates and the tetrahedral aluminium content in the framework using a single molecular alkoxide precursor, (sec-BuO) 2–Al–O–Si(OEt) 3, has been intensively investigated. The use of alkoxysilane as a co-reactant and highly alkaline media improves the heterocondensation rates between the highly reactive aluminium-alkoxide part of the single molecular precursor and the added alkoxysilanes, and minimizes the cleavage of the intrinsic Al–O–Si linkage. The very unique hierarchical meso-macroporosity was auto-generated by the hydrodynamic flow of solvents released during the rapid hydrolysis and condensation processes of this double alkoxide and the inorganic silica co-reactant. No external structural agent was required to template these porous structures. The particles obtained featured outstanding macrostructure with regular micrometer-sized macrovoids and displaying 3D interconnections. Importantly, the diameter of the micrometer-sized macrovoids found in the final materials and the thickness of the mesoporous walls separating these voids can be tuned by adjusting the reactivity of alkoxysilanes used as co-reactant. Higher reactivity of alkoxysilanes can improve the tetrahedral aluminium content in the meso-macroporous framework and reduce the cleavage of Al–O–Si linkage of the single molecular precursor. These correlations are of primary importance for targeting advanced materials with well defined meso- and macroporosities and tetrahedral aluminium content.