Interface-assisted synthesis of mesoporous silica nanoparticles using neat tetraalkoxysilanes

Abstract

Here we propose an efficient and interface-assisted synthetic method of mesoporous silica nanoparticles (MSNs). MSNs have great potential for various functional applications, such as carriers for drug delivery, solid support of catalysts, and low-refractive-index components of antireflection coatings. However, there have still been difficulties in realizing easy synthesis of MSNs with accurate particle size and high porosity. In the present study, MSNs are synthesized by spreading neat tetraalkoxysilanes on aqueous solutions containing a template surfactant and a catalyst. Our strategy is to hydrolyze the silica sources at the tetraalkoxysilane–water interface and supply the hydrolyzed precursors into the aqueous phase gradually and constantly. In this case, nucleation of MSNs occurs in the initial stage of the reaction, and then steady growth of MSNs is promoted by the constant supply of the silica sources through the tetraalkoxysilane–water interface. MSNs with a spherical shape and high porosities are obtained when neat tetrapropoxysilane is used at 50 °C. The relationship between particle size of the resulting MSNs and reaction time is described by a simple numerical formula, which enables us to control or predict the particle sizes of MSNs with a narrow size distribution.