A Study of the Assembly Mechanism of the Mesoporous MSU-X Silica Two-Step Synthesis

Abstract

Several synthetic pathways of mesostructured porous silica using nonionic surfactants or copolymers have been reported since the discovery of this new family of materials. We developed a process, which we call a two-step synthesis, that allows us to synthesize MSU-X mesoporous silica, with very good reproducibility and high reaction yields. This reaction implies a first assembly step between silica oligomers and nonionic micelles, followed by a condensation step induced by the addition of sodium fluoride as catalyst. We characterized nanoscopic hybrid objects made of silica and nonionic poly(ethylene oxide) (PEO) surfactants obtained once the assembly between silica and surfactants had occurred, as intermediates in the two-step synthesis of mesoporous silica of the MSU-X family. NMR, small-angle X-ray scattering, and dynamic light scattering experiments allowed us to propose a structural model involving nucleophilic participation of external OH groups, where a low-density framework of silica grows out of ...