Silica cages with controllable frameworks: synthesis, structure-tailoring, and formation mechanism

Abstract

A simple method was developed for the synthesis of novel macroporous silica cages with tailored pore architecture and high thermal stability. The silica cages possess anamorphic spherical morphology and narrow particle size distribution (∼1.5 µm), consisting of numerous channels interconnected with one another to form a fully open three-dimensional network. The morphology and structure of macroporous silica cages are strongly affected by synthetic conditions, including the molar compositions of reactants, the evaporation time of solvent, and the aging conditions. The number of silica crystal nuclei in the synthesis system is the major factor that determines the formation of silica cages and the disorder-to-order transformation, which can be controlled by changing the reactant molar concentrations and the solvent evaporation time. Using the appropriate aging time in ethanol provides the possibility of effecting the transformation from disordered twisting silica nanofibers with random branches to silica cages. The transformation from the macroporous cages to the mesostructures and the formation mechanism of the cages are also discussed in detail.