Mesoporous organic moieties

The second method of catalyst incorporation in mesoporous materials involves, generally, multi-step syntheses where organic moieties (i.e. amines, phosphines, thiols) are immobilized followed by post modification toward the final product. Alternatively, the catalyst may be synthesized as the corresponding alkoxysilane complex followed by immobilization into the mesostructured materials. For instance, Kiihn and co-workers demonstrated covalent... 

Surface areas and mesoporous volumes of the functionalized MTS are lower than the corresponding values for the parent silica as already reported in the case of lining the mineral walls by organic moieties [17]. 

Incorporation of Organic Moieties within Mesoporous Silica 483... 

INCORPORATION OF ORGANIC MOIETIES WITHIN MESOPOROUS SILICA... 

For many applications, the mesoporous materials are expected to show enhanced properties when their inner channel walls are functionalized with organic moieties to fine-tune host-guest interactions. This is particularly important for drug delivery systems which require the drug to be released at a slow rate in order to generate the desired depot-effect [19]. 

Many of the non-silica compositions showed problems with the stability and quality of the structure. Efforts to address these issues have been on going and quite successful in some cases such as all-alumina compositions (see below). Silica-based materials remain dominant as the most versatile and best quality molecular sieves (structure and stability) available by a facile synthesis. These attributes, especially the convenient synthesis made mesoporous silicate attractive for post-synthesis functionalization with other elements as well as organic moieties with active groups/ccnters. Recently the compositional diversity has been extended further to include both silica and organic moieties within the framework. The new class is referred to as periodic mesoporous organosilicas (PMOs). The synthesis involves surfactant-assisted assembly by hydrolysis of organo-silicon compounds. Additional discussion of the PMOs is presented below. 

As an alternative to the two-step approach, mesoporous silica with organic moieties covalently linked to their internal surface could be obtained in a single-step cocondensation of siloxane and organosiloxane precursors using similar supramolecular templating techniques as those for the synthesis of pure silica. Successful one-step syntheses of MCM-41 silicas modified with alkyl, phenyl, vinyl. cyanoethyL amine, thiol, and propylsulfonic acid moieties were reported in the literature.Similar preparations were extended to MCM-48 silica and to meso-... 

A short description of each pathway with typical examples follows. In all cases, organic modification of the mesoporous material is feasible either by adsorption of organic moieties onto the mesoporous material or by grafting of the organic material onto the preprepared mesoporous oxide. Erom a surface manipulation point of view, mesoporous materials are no different from amorphous silicates. 

Second, amine moiety-functionalized mesoporous materials have been also synthesized by co-condensation under various reaction conditions for uniform distribution of organic groups and to prevent Si-C cleavage upon template removal. Many researches have shown that co-condensation is one of the most successful pathways to hybrid materials with uniform distribution of the organic moiety. The reaction pathway with a template such as a polyethylene oxide-based amphiphile under acidic conditions is used. This pathway provides not only hexagonal but also cubic structures. 

Recently, organic moiety-functionalized mesoporous materials could be introduced onto the internal pore surfaces through the direct design of organic functional groups targeted for a variety of applications such as catalysis, sensing, and separation. 

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