One-pot synthesis of silica core–shell particles with double shells and different pore orientations from their nonporous counterparts

Silica core–shell particles (CSPs) have been successfully synthesized from their nonporous counterparts under basic conditions in the presence of the cationic surfactant cetyltrimethylammonium chloride and NH4F using a new one-pot templated dissolution and templated redeposition hybrid method. This method leads to high yield (85%) CSPs with an extremely narrow particle size distribution (no particle aggregation or fine particles) and allows us to vary reaction time to rapidly and conveniently control shell thickness up to the radius of the core particles. The resultant porous shells possess a unique double ordered pore arrangement with the inner and outer shells consisting of wormhole-like and radially oriented pores, respectively. To the best of our knowledge, this is the first report describing the fabrication of double shells in one step with the ability to manipulate the shell thickness from preformed silica particles in the presence of a surfactant. A mechanism to account for the formation of porous shells with different pore morphologies is presented. The resultant CSP particles have the combined characteristics of narrow particle distribution, narrow pore size distribution, unique double shells, and controlled shell thickness, surface area, and pore volume. These properties make them ideal candidates for fast and highly efficient chromatographic separation applications. The ability to control shell thickness while not dissolving the entire nonporous silica protective layer is particularly important to prepare functional core–shell particles (e.g., quantum dot core–nonporous silica shell–porous silica shell) for biomedical applications while avoiding toxic nanoparticles being directly exposed to the body. It is expected that this new hybrid synthesis method could be extended to generate a superficially porous silica layer with a controlled shell thickness and dual mesopore structure from any materials with a sol–gel silica coating.