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

TLDR

Vinyl-functionalized MCM‑41 was synthesized either by postsynthesis grafting or by direct co‑condensation, and the resulting materials were compared in terms of structure, stability, and reactivity, with the direct synthesis products’ mesoscopic order depending on precursor type and vinylsiloxane‑to‑alkoxysilane ratio. The vinyl‑grafted MCM‑41 retained the hexagonal pore order of the host, but the vinyl groups were nonuniformly distributed in the grafted material and more uniformly distributed in the directly synthesized version, which also exhibited greater hydrothermal stability and the ability to absorb nonpolar solvents from aqueous mixtures or emulsions.

Abstract

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. On the basis of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and bromination kinetics data, the vinyl groups appeared to be nonuniformly distributed in v-gr-MCM-41 prepared by the present PSG process, 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 nonpolar solvents from aqueous mixtures or emulsions.