Covalent organic frameworks materials

A second area that will be important in the future is the continued development of MOFs and ZlFs [152]. Much as the discovery of AlP04-based materials revolutionized the catalyhc use of zeolites when only aluminosilicates were known, MOFs and ZlFs have the potential to revolutionize low temperature processes such as oxidations and organic reachons [153]. Newly discovered materials along these same lines are covalent organic frameworks, the so-called COFs [154]. These materials have similar channels to those known for MOFs and ZlFs but tend to have higher thermal stability. 

Figure 4.6 Illustration of a covalent organic framework (COF) material composed of hexahydroxytriphenylene and either tetra(4-dihydroxyborylphenyl)methane or silane crosslinking moieties. (From Reference [56] with permission.)...

Very recently covalent organic frameworks (COFs) 33 have been designed and synthesized by simply condensation of phenyl diboronic acid with hexahy-droxytriphenylene (67) (Fig. 14). Material 33 is composed of expanded porous graphitic layers, with pore sizes up to 27 A. Covalent organic framework (33) is thermally stable till 500-600°C and have a surface area of 1590 m g. This exceeds the highest reported surface area of 1300 m g for macroporous ordered silica. 

In addition to polystyrene, several other polymers have been provided with the hypercrosslinked structure, and, in addition to the postcrosslinking of preformed polymeric chains, other synthetic approaches to hypercrosslinked open networks have been developed, including the direct polymerization and polycondensation of appropriate monomers or co-monomers. The recently developed metal-organic frameworks and covalent organic frameworks constitute three-dimensional coordination and element-organic polymers with an unusually h%h free volume they fit into the new and rapidly growing class of hypercrosslinked network materials as well. 

Microporous materials have important potential applications for many fields of science, including gas storage, heterogeneous catalysis and chemical separations. Examples of microporous networked materials include metal organic frameworks (MOFs), " covalent organic frameworks (COFs), zeolites and microporous organic polymers (MOPs). ... 

The presence of water vapour will define which materials can be used based on their hydrolytic stability. As an example metal-organic frameworks (MOFs) and covalent organic framework (COFs) are crystalline microporous materials which can exhibit exceptionally high surface areas and gas sorption capacities and, as such, have been proposed as potential materials for CCS. However, some of these materials can be unstable in the presence of moisture. The IRMOF series and the more recently produced COF materials are particularly unstable (e.g., loss of porosity at room temperature in air). Clearly, materials of this type would be unsuitable for CCS application. If such materials are to be used, more stable types are required for example, one class of MOF known as zeolitic imidazole frameworks (ZIFs) are reported to have greatly improved hydrolytic stability. 

The separation factor of these organic polymer membranes is typically located in a moderate range, of around 5 and 10, but rarely higher than 20. As a rule of thumb and proven by recent publications, the membrane selectivity can be approximated as the product of the adsorption selectivity and diffusion selectivity [2]. This chapter provides a wealth of information on diffusion inside micro- and mesoporous structures using concepts and ideas that originate from Maxwell and Stefan. A molecular-level understanding of diffusion in a variety of materials such as zeolites, MOFs, covalent organic frameworks (COFs), carbon nanotubes, and cylindrical silica pores is provided with the aid of extensive data sets of molecular... 

FIGURE 32. Highly interpenetrated hydrogen bonded networks form porous materials that serve as precursors to covalent organic frameworks. 

In Chapter 6, B. M. Rombo et al. delve into the formation of boronate-linked supramolecular architectures based on boronate ester formation—for example, small molecule diesters form supramolecular self-assemblies in the solid state based on a phenyl-boron-phenyl sandwich motif in which these small oligomers link together to generate macrocycles and other polymers. The polymeric macrocyclics and linear structures demonstrate self-repair capabilities and constitute a new class of wide band-gap semiconducting materials. Through the incorporation of polyvalent boronates, covalent organic frameworks are described, which create highly crystalline, porous network materials. 

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