Mastering Syntheses of Siliceous Hierarchical Porous Self-Standing Monoliths through the Integration of the Sol-Gel Process, Complex Fluids, and a Planetary Mixer.

Abstract

Self-standing siliceous monoliths bearing hierarchical porosity have been synthesized while combining the sol-gel process, complex fluids, and a planetary mixer. The mechanically well-defined and a priori reproducible stirring procedure leads to a precise control over the final hierarchical porous characteristics of the materials: Both the macroscopic cell and interconnecting throat dimensions in the monoliths, i.e., macroporosity, can be tuned by choosing the rotation speed. The fabrication process also leads to well-defined macrocellular wall thicknesses that can be tuned in the range of 30-90 nm by stirring control. Final high internal phase emulsion-based siliceous materials, Si(HIPE), are offering around 80-90% porosity, decreasing with stirring speed, and a broadly mixing invariant BET specific surface area of about 860 ± 60 m2 g-1, where the microporous surface area is rather constant at 480 ± 20 m2 g-1, with the BJH (mesoporous) area being more spread in the range of 380 ± 80 m2 g-1.