Creation of Interior Space, Architecture of Shell Structure, and Encapsulation of Functional Materials for Mesoporous SiO2 Spheres

Over the past two decades, systematic development of preparative methodology for silica (SiO2) based micro- and mesoporous materials has become a significant challenge for both fundamental science and advanced technology. In this work, we have developed a range of facile and versatile solvothermal methods for preparation of SiO2 hollow spheres and their related nanocomposites at the submicrometer scale. First, we employ the concept of Ostwald ripening to generate interior space for porous SiO2 spheres and prove this process is a simple, viable means to create large central cavities without using conventional hard or soft templates. Second, we devise a novel microemulsion system for synthesis of porous SiO2 spheres using 1-dodecanethiol as a soft-template (i.e., micelles) to create interior spaces. Third, we architect complex double-shelled porous SiO2 spheres by controlling the content of templating supramolecular assemblies. Along the synthesis of the phase-pure SiO2 spheres, we have further developed two solution-based methods to introduce functional materials into the central spaces of the SiO2 spheres; a total of 10 different core/shell nanocomposites have been made and investigated, which shows that these synthetic approaches indeed have a generality for design and architecture of the SiO2-based porous materials. In addition to the materials synthesis carried out inside the central cavities, communicability of the cylindrical channels of the shells and enclosed inorganic and organic nanomaterials have also been tested with photocatalytic reactions and oxidative combustions. The spherical SiO2 products can be broadly classified into five major architectural forms, and the mean diameter of the cylindrical channels in their shells are all uniformly in the range of 3.6-3.8 nm for the mesoporous products.