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

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.

Enhanced ultrafiltration PES membranes doped with mesostructured functionalized silica particles

“…However, certain drawbacks are associated with post-synthesis grafting. Thus, this method usually results in inhomogeneous surface coverage due to preferential organic moiety congregation near the entries of the mesopores and the exterior surface [33]. In addition, a restricted loading level of functional groups can be grafted because of the limited density of silanol groups at the reactive surface [34].…”

Adsorption of hydrogen peroxide on functionalized mesoporous silica surfaces

“…There are three general paths to achieve surface functionalization of mesoporous silica surface [28]: postsynthetic functionalization (the so-called ''grafting'') and two methods involved in the silica preparation process-co-condensation and condensation of bridged organosilica precursors forming periodic mesoporous organosilicas. The use of grafting method usually preserves the mesostructure of the starting silica phase, but the distribution of organic moieties anchored to the silica surface is solvent dependent [29] and sometimes leads to pores blockage [30]. Another advantage of this method is that it can be applied to a diversity of organic molecules, from small ones like aminopropyltrimethoxysilane [29] or compounds used in our experiment, to large moieties as dendrimers [31] and fullerenes [32].…”

Effects of decomposition-treatment temperature on infiltration pressure of a surface modified nanoporous silica gel

“…The mixture was stirred at room temperature (20 • C) for 10 min, and then refluxed at 90 • C for 5 days. During this process, the chlorotrimethylsilane molecules diffused into the nanopores and deactivated the negatively charged hydroxyl groups, forming OSi(CH 3 ) 3 groups [11]. Due to the relatively long treatment time, the surface group density was saturated; that is, further increase in treatment time would not lead to detectable variation in the degree of hydrophobicity [12].…”