Control of the pore wall thickness and thermal stability in low-cost bimodal porous silicas

Abstract

A new hierarchical bimodal mesoporous silica, labelled as UVM-12 (acronym of University of Valencia Materials), has been prepared by using a solution of sodium silicate as low-cost silicon source. The final self-assembling between cationic micelles of CTAB and anionic inorganic Si-based oligomers occurs in a homogeneous aqueous medium. The reaction is carried out from low-sized building blocks through a bottom-up approach. The UVM-12 solids combine two mesopore systems according to N2 adsorption–desorption isotherms, what is corroborated by TEM micrographs and XRD patterns. This material has been inorganically modified by incorporation of Al or Ti (M-UVM-12, M = Al, Ti) without alteration of the parent architecture. Moreover, we have carried out a study of the UVM-12 thermal stability by means of N2 adsorption–desorption and XRD. For comparison, in this analysis we have included other two nanoparticulated bimodal silicas that share structure and morphology with UVM-12 (UVM-7 and UVM-10). Both the mesopore wall thickness and the condensation degree (measured through NMR) in the silica framework of each type of material successfully correlates with the thermal stability of their samples.