Formation mechanism of SBA-3, SBA-15 and SBA-16 type mesoporous silica in acidic solutions

Abstract

Abstract The evolution of the species in acidic solutions, prepared from tetraethoxysilane (TEOS), surfactant (Cetyltrimethylammonium bromide, Pluronic P123 or Pluronic F127) and HCl, was followed by visual observation and Dynamic Light Scattering (DLS) measurements between 25 and 90°C until their precipitation. The nature of the precipitated phases was studied by optical microscopy (in-situ in the reaction mixtures) and by SEM (after filtration and drying). In all cases, the first stage corresponds to the formation of micelles coated by siliceous species (composite colloids). In a second stage the modification of their colloidal characteristics leads to their aggregation with a phase separation into micron-sized liquid particles. In the third stage, the progress of the polycondensation transforms the latter into solid particles of mesoporous silica. The final morphology depends on the polycondensing degree of the silica before the phase separation and on the prevailing synthesis parameters (temperature and pH).