IRMOF series

Isoreticular Zn(ll) carboxylates the iso-recticular metal-organic framework (IRMOF) series... 

The IRMOF series of complexes are based upon [Zn40] nodes linked by linear ditopic carboxylate ligands (Fig. 11.4) (Rosi et al, 2003 Rowsell... 

A large majority of studies have been conducted on MOFs such as the IRMOFs series consisting of discrete SBUs. Nevertheless, other periodic arrays of large channels can be formed as well when linear links are used to connect infinite inorganic rods. Quite often, an auxiliary bridging moiety, such as hydroxide, is present in the backbone of these infinite SBUs (119, 123, 128). 

CH4 and CO2 adsorption capacities for the IRMOF series compotmds are high due to their high surface areas and pore volumes. IRMOF-1 (MOF-5) and IRMOF-3... 

The large pore volume of MOF-177 makes it an ideal material for CO2 adsorption and it has much higher CO2 adsorption capacity than the IRMOF series compounds discussed above. At 298 K and 42 bar, MOF-177 can adsorb 33.5 mmol g CO2, which is also higher than the best CO2 capacity reported for a zeolite (7.4 mmol g for zeohte 13X) and activated carbon (25 mmol g for MAXSORB) [31]. 

A large number of MOFs have been synthesized and reported by researchers to date. Isoreticular metal-orgarric frameworks (IRMOFs) denoted as IRMOF-w ( = 1 through 7, 8, 10, 12, 14, and 16) are one of the most widely studied MOFs in the literature. These compounds possess cubic framework structures in whieh each member shares the same eubic topology [3, 21]. Figme 4 shows tire structure of IRMOF-l(MOF-5) as simplest member of IRMOF series. 

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. 

A unique feature of MOFs, which distinguishes these systems from other materials (such as metal oxides), is the absence of an inaccessible volume (so-called dead volume) [52], Moreover, owing to their open architecture, the intrinsic diffusion coefficients of reactant molecules are only slightly less than in the bulk of the solvent, that is, mass transfer in the porous framework system of MOFs is not hindered. The pore sizes in MOFs vary in a tunable manner in a range from 0.4 to 3 nm (eg, for the IRMOF series), with the proper choice of the organic linker determining the pore diameter [4]. 

MIL-53 materials provide a convenient model for comparison with traditional sorbents with similar geometric characteristics, such as activated charcoals and zeoUtes. The specific surface area estimated for MIL-53,1100 mVg (BET method), is similar to the average value for nanocarbon materials and exceeds that for zeolites. The framework of MIL-53 comprises unidimensional channels of 8.5 A in diameter, which is similar to the pore diameter in zeolites (6-12 A) and smaller than that in the IRMOF series, including MOF-5 (12-15 A). At the same time, the hydrogen adsorption capacity of MIL-53 is somewhat higher than that of the zeolite CaX (2.19wt.%, Table 2) and activated charcoals (2.15 wt.%) [179]. It is possible that this parameter is affected by the channel geometry, because zeolites more often have a 3D channel system, as opposed to the unbranched unidimensional channels in MIL-53. However, additional experiments on the adsorption mechanism are required to draw more definitive conclusions. 

The effect of chemical modification of the organic component while preserving the topology of an MOF can be illustrated by the synthesis of the IRMOF series. It turned out that hydrogen adsorption per formula unit, both at 77 K and room temperature, increased with... 

Figure 4.2 Structure of some of the IRMOF series of MOFs and the corresponding hgands A = IRMOF-1 B = IRMOF-6 C = IRMOF-8. Reprinted with permission from Rosi et al., 2003 f Copyright (2003) AAAS...

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