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.

No abstract

We report here a simple one-pot synthesis of MCM-41 functionalized with a reactive vinyl group (ν-MCM-41). The reaction involves co-condensation of tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) in a surfactant solution under basic conditions. A difficult question in many surface modifications of porous materials is whether functional groups are located on the internal pore surface, the external particle surface, or in the walls. Here a bromination reaction of ν-MCM-41 provides evidence for attachment of most vinyl groups to the accessible surface within the mesopore channels. This model reaction also demonstrates that ν-MCM-41 may be a versatile starting material for many other in situ reactions resulting in ordered, high surface area materials with specific functional groups.The interest in inorganic-organic hybrid materials arises from the advantages that the inorganic and organic moieties bring to the systems. 1,2 The inorganic components can provide mechanical, thermal, or structural stability, while the organic features are often more readily modified for specific applications in catalysis, separation, or sensing. 3 One way of preparing these materials is based on sol-gel processing, 4 which involves hydrolysis and condensation of metal alkoxides, often permitting mild reaction temperatures and pressures. In preparations of inorganic-organic hybrid materials, typical precursors are organically functionalized metal alkoxides whose Si-C bonds should be hydrolytically stable under acid or base conditions. However, the materials obtained in a simple sol-gel process are usually amorphous or randomly ordered unless structuredirecting materials are employed.

No abstract

No abstract