Comparative Studies of Grafting and Direct Syntheses of Inorganic-Organic Hybrid Mesoporous Materials

Vinyl-functionalized MCM-41 samples were prepared by either a postsynthesis grafting (PSG) process or a direct co-condensation synthesis. The structures, stabilities, and reactivities of products from both methods were compared. The mesoscopic order of the hexagonal pore structure of vinyl-grafted MCM-41 (v-gr-MCM-41) resembled that of the MCM-41 host. Based on powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS) and bromination kinetics data, the vinyl groups appeared to be non-uniformly distributed in v-gr-MCM-41, with a large proportion of vinyl groups on the external surface of the crystallites or inside channels but near the channel openings. The mesoscopic order of products from the direct synthesis (v-MCM-41) depended on the type of alkoxysilane precursor used and on the ratio of vinylsiloxane to alkoxysilane in the reaction mixture. The vinyl groups appeared to be more uniformly distributed in v-MCM-41. Vinyl-grafted MCM-41 exhibited greater hydrothermal stability than unmodified MCM-41 and was capable of absorbing non-polar solvents from aqueous mixtures or emulsions.