Rational design of Pickering emulsion-templated silica capsules loaded with ionic liquids: tailoring intrinsic textural properties via interfacial sol–gel kinetics

Abstract

The encapsulation of ionic liquids (ILs) within porous silica capsules templated from a Pickering emulsion offers a powerful platform for designing efficient microreactors in biphasic systems. However, a fundamental understanding of how synthesis parameters govern the textural properties and structural integrity of the porous silica capsules remains limited. This study presents a comprehensive investigation into the sol–gel synthesis of IL-containing silica capsules, establishing crucial structure–property relationships. We demonstrate that for the study of textural properties, supercritical CO₂ drying is a prerequisite for preserving the capsule's native morphology and porosity, whereas conventional ambient drying causes severe shrinkage and structural collapse due to capillary forces. Leveraging this preservation method, we show that acidic catalysis (more precisely, at pH below the isoelectric point of silica, which is pH < 2) favors the formation of highly mesoporous capsules with better structural cohesion, while basic conditions result in capsules more prone to severe fragmentation. Furthermore, optimization of the reaction temperature, time and water-to-alkoxysilane ratio is found to be essential for balancing shell growth kinetics with mechanical stability. These findings provide a rational framework for engineering robust, tailored silica capsules for advanced applications in catalysis and controlled release.