Formation of monodisperse mesoporous silica microparticles via spray-drying

In this work, a protocol to synthesize monodisperse mesoporous silica microparticles via a unique micro-fluidic jet spray-drying route is reported for the first time. The microparticles demonstrated highly ordered hexagonal mesostructures with surface areas ranging from similar to 900 up to 1500 m(2)/g and pore volumes from similar to 0.6 to 0.8 cm(3)/g. The particle size could be easily controlled from similar to 50 to 100 mu m from the same diameter nozzle via changing the initial solute content, or changing the drying temperature. The ratio of the surfactant (CTAB) and silica (TEOS), and the amount of water in the precursor were found to affect the degree of ordering of mesopores by promoting either the self-assembly of the surfactant-silica micelles or the condensation of the silica as two competing processes in evaporation induced self-assembly. The drying rate and the curvature of particles also affected the self-assembly of the mesostructure. The particle mesostructure is not influenced by the inlet drying temperature in the range of 92-160 degrees C, with even a relatively low temperature of 92 degrees C producing highly ordered mesoporous micropartides. The spray-drying derived mesoporous silica microparticles, while of larger sizes and more rapidly synthesized, showed a comparable performance with the conventional mesoporous silica MCM-41 in controlled release of a dye, Rhodamine B, indicating that these spray dried microparticles could be used for the immobilisation and controlled release of small molecules. (C) 2013 Elsevier Inc. All rights reserved.