Mesoporous Silica Microspheres by Super-Fast Alkaline Etching of Micrometer-Sized Stöber Particles

A one-pot Stöber synthesis of silica particles in the micrometer range is established, using a continuous addition of tetraethoxy silane monomer (CAM of TEOS) to an aqueous ammonia solution with KCl in ethanol. The initial seed particle formation and growth rate are harmonized to yield monodisperse silica particles up to 2 μm (and potentially beyond) in a single step. Therefore, a diluted TEOS solution is slowly added to the ethanolic aqueous ammonia solution at 0 °C in a first phase to build seed particles. After a waiting time, a systematic particle growth is achieved by dosing ethanolic TEOS at 40 °C. The particle diameter scales with the cubic root of the amount of added TEOS. A fast etching procedure (3.5 min at 95 °C) of the received Stöber particles using 0.025 M NaOH in water is developed. The progress of the etching is monitored by the time dependance of the pH value. Quenching of the hydrolytic etching in ethanol is allowed to isolate mesoporous, monodisperse micrometer-sized silica particles with a pore volume of 160 μL g⁻¹ and a pore-size range between 100 and 4 nm (>200% enhancement over the parent particle).