One-step preparation of thiol-modified mesoporous silica spheres with various functionalization levels and different pore structures

Abstract

A wide range of mercaptopropyl-functionalized silica spherical particles of MCM-41 and MCM-48 (M41S family) have been prepared by co-condensation of mercaptopropyl trimethoxysilane (MPTMS) or mercaptopropyl triethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. It was possible to control the mesostructure type (hexagonal or cubic) by monitoring the water-to-ethanol ratio and the type of organoalkoxysilane precursor employed. Materials displaying various functionalization levels were obtained by varying the MPTMS or MPTES contents from 3 to 50% in the co-condensation synthesis medium. This gave rise to a wide range of porous solids with approximately the same particle size and morphology but featuring different functionalization levels and various degrees of structural order. They were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms and BET analysis, scanning and transmission electron microscopy, 29Si and 13C solid state nuclear magnetic resonance (NMR), particle size distribution measurements, and elemental chemical analysis. Mercaptopropyl groups were readily incorporated with high yields (>90%) by the co-condensation route. All samples exhibited spherical morphology with similar particle size but both the level of ordering and porosity of solids obtained by co-condensation were found to decrease when increasing the amount of organo-functional groups.