Bases for the synthesis of nanoparticulated silicas with bimodal hierarchical porosity

Porous silicas with pore sizes at two length scales (meso and large meso/macroporous) have been prepared through a one-pot surfactant assisted procedure by using a simple template agent and starting from silicon atrane complexes as hydrolytic inorganic precursors. The special organization of these bimodal porous silicas can be related to the nanometric character of their constituent mesoporous particles. Whereas the small intra-particle mesopore system is generated by the templating effect of the surfactant, the large pore system is defined by inter-particle voids. We have studied the effect of different procedural parameters on the small pore system and also on the nucleation and growth of the nanoparticles. The formation of these hierarchical materials is explained on the basis of kinetic (hydrolysis and condensation reaction rates) and thermodynamic (silica solubility) concepts.