Surface area of MOFs

TABLE 6.1 Effects of Extended Linkers on Hydrogen Storage Capacities and Surface Areas of MOFs and COFs... 

Therefore, in contrast to zeolites it has been extremely straightforward to prepare MOFs with the required pore dimension. Very frequently the pore dimensions, porosity, and surface area of MOFs are much larger than those that can be achieved with zeolites [30]. Moreover, MOFs are currently at the top of the list of materials with the lowest framework density, meaning the lowest mass per unit volume leaving a considerable percentage, sometimes about 80%, of empty space. All of the above considerations make MOFs particularly suitable as catalysts for liquid-phase reactions provided that the reaction conditions are compatible with the structural... 

The measured storage capacities at 77 K ranged from less than 1.6 wt% for a low surface area MOF-5 sample (BET SSA = 572 m g ) [88,89] prepared by the so-called Huang s synthesis [90] to 7 wt% when the sample was prepared in an inert atmosphere with complete absence of water and moisture, leading to a material with a B ET specific surface area of 3800m g [91]. These discrepancies were attributed to different factors related to the synthesis procedure, such as (i) the decomposition of MOE-5 and formation of a non-porous second phase in the presence of moisture [91],... 

Figure 2.11 Correlation between the hydrogen storage capacity and the apparent Langmuir specific surface area of different MOFs obtained from reference [86] and references [13, 88]. The...

Table 5 contains also the corresponding values of the relative pressure p/pa.x(A), which were used to find the monolayer capacities for the samples studied. Thus, the minimum or inflection point on APDs for nitrogm/active carbon systems at 77 K around 4 kJ mof gives A X(a) and consequently, p/p ojc(A), which marks on the corresponding adsorption isotherm the value of the monolayer capacity. The latter can be easily converted to the total specific surface area S rfA) if the area occupied by single adsorbate molecule is known. A comparison of the total specific surface area (see St,x(A) in Table 4) and those evaluated by the BET method (see Smst in Table 1) and by the a>-plot method (see St in Table 4) shows that the APD method gives much smaller values. The values of seem to be more realistic than those obtained by the BET method and Us-plot analysis, which are based on the BET model, because in contrast to the BET model the APD method allows for a more accurate estimation of the amount adsorbed in the monolayer. Tire methods based on the BET model do not take into account the correction for molecules adsorbed inside micropores and therefore, they overestimate the total specific surface area of microporous solids. It should be mentioned that the evaluation of the total specific surface area on the basis of the Kj-plot is usually done by... 

Much higher surface areas were obtained by employing three-dimensional tetrahedral monomers (Fig. 12) [20]. For example, COF-103 [20] exhibited an apparent BET surface area of 4,210 m g, which is comparable with the highest surface areas observed in MOFs. These remarkable polymeric networks exhibit some of the lowest densities known for any crystalline material. COF materials also have excellent... 

---