Fabrication of SiO₂, Al₂O₃, and TiO₂ Microcapsules with Hollow Core and Mesoporous Shell Structure

Abstract

A simple and useful route to synthesize mesoporous SiO2, Al2O3, and TiO2 microcapsules with a hollow macrocore structure was studied. The deposition of hydrophilic precursor sol containing surfactants in the hydrophobic solvents onto the monodispersed polymer surfaces has been applied to produce the mesoporous shells after calcination. The surface of PMMA polymer spheres was modified by ionic liquid salts to control the interfacial properties through the formation of adsorbed double layers for promoting the subsequent deposition of inorganic sols. On the basis of that method, inorganic hollow spheres having mesopores in the wall of the shell with various shell compositions or with different macrocavity sizes could be fabricated successfully. The chiral catalysts were loaded and entrapped inside of silica microcapsules, and their activity was examined in the synthesis of chiral β-blockers. These heterogeneous catalysts offered practical advantages in the application, showing the good activity and enantioselectivity up to 98% ee, as well as simple recovery and reuse.