Inorganic Monoliths

The morphology of a typical inorganic monolith is fundamentally different from that of organic polymers (Figure 1.4a). The sttucture is rather sponge- than brush-like and is consttucted by interconnected silica rods in the low micrometer size. This composition leads to a discrete distribution of flow channels, which can be deduced by comparison of macropore disttibution of a typical organic... 

Although inorganic, monolithic columns attracted considerable attention in the last 10 years, the preparation of silica-based monoliths does not yet offer the broad chemical variety of precursors and porogens for specific adjustment of separation compared with their organic counterpart. The preparation of silica monoliths uses the classical sol-gel process of hydrolysis and polycondensation of organosilicium compounds. 

Even if the diminishment of interparticnlate voids as well as the convective mass transfer are generally assnmed to be the main reasons for the enhanced chromatographic properties of monolithic colnmns, the characteristics of organic and inorganic monolithic snpports have to be separately discnssed and evalnated, since they have been shown to complement one another regarding their applicability [29,100]. 

The main advantage of the grid approach is that the catalyst position is well defined. This is easy to do with solid catalysts, but not with homogeneous ones in solution. One way of solving this problem is to attach the homogeneous catalysts to a solid support, such as polymer beads [45] peptide scaffolds [46], or inorganic monoliths [47]. 

Inorganic monolithics like calcium aluminate, calcium silicate, sodium silicate and potassium silicate gunites are able to withstand the dry flue gases at high temperatures. Because they are porous and tend to crack, however, they allow acid vapors to reach the substrate and condense. 

Polymer spheres have also been used for the formation of non-ordered porous systems in inorganic structures and such structures are being tested in applications such as bone tissue implants [32]. Below are examples of casting of discrete entities to form inorganic monoliths or film structures using either sol-gel or nanoparticle infiltration. 

Cam F, Colin A, Richard MF, Deleuze H, Seiler E, Birot M, et al. Inorganic monoliths hierarchically textured via concentrated direct emulsion and micellar templates. J Mater Chem 2004 14 1370-6. 

Until now, a considerable variety of functionalized and non-fimctionalized monolithic materials based on either organic or inorganic polymers are available. While inorganic monoliths are usually prepared from silica precursors, for example, Si(OR)4, via sol-gel techniques, organic continuous beds have... 

Figure 323 SEM visualization of the inorganic monolith-type material macrostructure, (a and b) ISi-HIPE, (c and d) 2Si-HIPE, and (e and f) 3Si-HIPE. (Adapted with permission of Royal Society of Chemistry, Copyright 2004.)...

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