Family of Single-Micelle-Templated Organosilica Hollow Nanospheres and Nanotubes Synthesized through Adjustment of Organosilica/Surfactant Ratio

Abstract

A family of hollow organosilica nanospheres and nanotubes was synthesized at appropriately low organosilica-precursor/block-copolymer-surfactant ratios. In Pluronic F127 (EO₁₀₆PO₇₀EO₁₀₆) block copolymer templated synthesis of ethylene-bridged organosilicas in the presence of a swelling agent, the lowering of the organosilica-precursor/surfactant ratio led to a change from highly ordered face-centered cubic structure of spherical mesopores to individual hollow spherical nanoparticles. It was hypothesized that at low ratios of organosilica precursor to PEO-PPO-PEO, the framework precursor is solubilized in the micelles and its concentration on their surface is not sufficient to induce appreciable cross-linking between the resulting nanoobjects and the consolidation into larger particles. The inner pore size of the nanospheres was adjusted by varying the micelle expander, allowing us to obtain pore diameters up to ∼20 nm. By employing low precursor/surfactant ratios, hollow spheres of methylene-, ethenylene-, and phenylene-bridged organosilicas were synthesized. Hollow silica spheres were also obtained through judicious choice of block copolymer. The synthesis strategy involving the adjustment of the framework-precursor/surfactant ratio was further extended on organosilica nanotubes synthesized using Pluronic P123 surfactant and cyclohexane as a swelling agent. One can envision a large number of framework compositions for which hollow nanospheres and nanotubes can be obtained using our synthesis approach