Computer-aided development of bio-inspired routes to highly ordered green mesoporous silica

Abstract

Bio-inspired routes to producing porous silica materials offer great potential to make the currently adopted synthesis routes more sustainable through the use of milder synthesis conditions, short reaction times and non-toxic reagents. Ordered mesoporous silica (OMS) synthesis would benefit greatly from these green synthesis routes, but a lack of mechanistic understanding of bio-inspired silica synthesis makes applying these approaches directly to OMS synthesis challenging. In this work, we apply a unique combination of design of experiments and multi-scale modelling to better understand how the structure of OMS can be controlled by manipulating synthesis conditions, with a focus on using bio-inspired additives to facilitate mild synthesis conditions and improve yield, whilst maintaining highly ordered pore structures. Our simulation results show that the silica/surfactant ratio plays a crucial role in the promotion of ordered mesophases by controlling the delicate balance between charge-matching interactions at the surface of silica/surfactant micelles. However, a trade-off is observed between the degree of order and the product yield, which decreases as the silica concentration increases. This problem can be addressed by the inclusion of the bio-inspired additive pentaethylenehexamine, which we hypothesize to have a catalytic effect on the silica condensation reaction occurring at the silica/surfactant interface. Our results indicate that the properties of the material are determined by an interplay between self-assembly and reaction kinetics, such that ordered materials can be obtained by first allowing the mesophase to self-assemble at high pH, then rapidly lowering the pH in the presence of the bio-inspired additive to “lock-in” the mesostructure through silica polymerization. Based on these insights, we propose a novel synthesis route to produce highly ordered OMS materials more rapidly, under milder synthesis conditions and with higher yield than has been previously reported.