resolver

Chapter 2 23
appealing perspectives of this method on CUSs modification/introduction, this method is
expected to receive much attention in next years. This kind of modification of MOFs are
also involved in this dissertation. Further details will come in Chapter 4 and 5.
2.3.4 Application of MOFs
What have been addressed above show rather a broad picture demonstrating that MOFs
are attractive porous materials with a huge diversity of structures, functionalities, and
facile modification. All these make MOFs very promising for a range of applications
(Figure 2.15), [147] especially in gas storage, selective adsorption and separation.
Hydrogen and methane are good candidates for on-board fuel. A tank loaded with porous
absorbent allows gas to be stored at much lower pressure in comparison with the
identical tank without an adsorbent. Due to the high porosity and well-defined structures,
MOFs has gained significant attention being a new class of adsorbents. A lot of MOFs have
been evaluated for gas storage such as hydrogen and methane, [24, 26] which provides a
safer and more economical gas storage method. For example, MOF-5 has shown a rapid
and fully-reversible H2 storage density (66 g L -1 at 77 K, 100 bar), [148] which is very close
to the value observed for liquid hydrogen (71 g L -1 at 20.4 K, 1 bar). Later, it was found
that most of the MOFs like MOF-5 demonstrate poor performance at 298 K due to rather
weak interactions between H2 and the framework. However, remarkable enhancement of
H2 adsorption enthalpy can be achieved by designing MOFs with CUSs, [65, 70, 89]
catenation/interpenetration [149] or MOFs with heavy transition metals (e.g. Pd) which can
afford spillover effect for hydrogen storage. [150] For instance, respectively designed
Mn3[(Mn4Cl)3(BTT)8]2 bearing CUSs exhibits H2 uptake of 1.49 total wt% and 12.1 g L -1 at
298 K and 90 bar, [89] what is 77% greater than that of compressed H2 under the same
conditions. Furthermore, HKUST-1 and Ni2(dobdc) have also demonstrated high total
volumetric methane uptakes at 35 bar (225 and 235 v/v, respectively). [26] Significantly,
PCN-14 (Cu2(adip) (adip 4- = 5,5’-(9,10-anthracenediyl)di-isophthalate) containing Cu-
CUSs is also one of the best reported so far MOFs for methane storage (230 v/v, 290K, 35
bar). Note, that 35 bar is the maximum pressure achievable by most inexpensive singlestage
compressors, [151] which is also a widely used standard pressure for evaluating
adsorbents for adsorbed natural gas storage. Both rigid and flexible MOFs as well as MOF
membranes can be utilized as adsorbents for selective gas adsorption on the basis of