A simple method for nanostructure engineering of mesoporous zinc silicate particles

We report a novel method to engineer a nanostructure of zinc silicate particles. In this method, a mixture of tetraethoxysilane, zinc acetate, and cetyltrimethylammonium chloride (CTAC) was reacted in water at 80 °C for ∼3 h, followed by calcination. This method produced mesoporous zinc silicate particles with a core-shell structure in which the core contained a mixed oxide of ZnO and SiO₂, whereas the shell was pure SiO₂. We found a faster formation of mixed oxide than pure SiO₂, which is believed to be responsible for the core-shell structure. On the basis of this understanding, we engineered the nanostructure of the synthesized particles: (1) zinc oxide in the core was dissolved by citrate buffer to produce hollow mesoporous silica particles, and (2) a layer-by-layer deposition technique was used to grow mesoporous shells on the existing particles, producing multishell mesoporous particles with various morphologies. Using a nitrogen sorption method, the average pore diameter of mesoporous zinc silicate particles was found to be 3.4 nm, which is similar to the diameter of spherical CTAC micelles. We also tested the adsorption capacity of hollow mesoporous silica particles using water-soluble anionic (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt) and cationic (rhodamine B) dyes, and we found a high adsorption capacity for the cationic dye but negligible adsorption for the anionic dye. Finally, we compared release profiles of rhodamine B from hollow mesoporous silica particles with different morphologies.