Silica-based microspheres with interconnected macroporosity by phase separation

Abstract

This work reports on a novel method which combines emulsion templating with an adapted sol–gel technique, to create silica-based microspheres with tailored interconnected porosity at the nano, but mostly at the macroscale, due to phase separation by spinodal decomposition. These new materials have potential application in many domains, as support materials, or microscaffolds for (photo)catalysis, biomedical materials, energy storage, or separation, etc. In order to achieve microspheres with the desired coexisting porosity, a water-in-oil (W/O) emulsion is prepared, and phase separation between siloxane-rich domains and water-rich phase is promoted to occur within the aqueous droplets of the emulsion. No specific gelation promoting additives are employed in this work, contrary to other works present in the state of the art. Instead, the silane combination was selected to provide an inherent gelation capability, through the oxirane group of the epoxy silane employed. The obtained microspheres display a diameter and a characteristic size ranging from 26 to 130 µm and 149 ± 11 to 485 ± 38 nm, respectively, as well as a large amount of interconnected macropores, peaked at 164–405 nm, depending on the sample, i.e., on the hydrolysis and emulsification parameters. Longer hydrolysis time and lower hydrolysis pH were found to lead to smaller but more porous microspheres, and higher amount of surfactant was found to lead to smaller microspheres. The achieved microspheres are silica based, of hybrid nature with some organic epoxy functionality, if dried at 150 °C, or of inorganic nature, if heat treated at 700 °C.