Engineering MIL‐88B crystallites for enhanced H 2 uptake capacity: The role of ultramicropores

In this study, a strategy that optimizes the pore size to enhance the adsorbed H2 amount (at 298 K) is investigated. Pore size and ultramicropore fraction (ultramicropore volume/total pore volume) were controlled by Fe:TPA ratio. The highest H2 adsorption capacity of 0.47 wt% (298 K and 7.6 bar) belongs to MIL-88B-3, which is higher than those of reported metal-organic frameworks (MOFs) (MIL-100, MIL-101 [Cr], HKUST-1, MOF-5, and ZIF-8). The enhanced H2 sorption capacity (1.96 times) is a consequence of the high fraction (89%) and volume (0.22 cm3/g) of ultramicropores with pore diameters of 0.6 nm. Our results demonstrate that pore size, fraction, and volume of ultramicropores control the amount of H2 adsorbed also at 298 K. With the use of perturbation assisted nanofusion synthesis strategy that introduces textural pores to the pore structure, a Brunauer-Emmett-Teller (BET) surface area higher than those of reported MIL-88Bs has been achieved, and a strategy to synthesize MOFs with enhanced H2 sorption capacities is suggested.