Ultramicroporous Building Units as a Path to Bi-microporous Metal-Organic Frameworks with High Acetylene Storage and Separation Performance

摘要

A strategy called ultramicroporous building unit (UBU) is introduced. It allows the creation of hierarchical bi-porous features that work in tandem to enhance gas uptake capacity and separation. Smaller pores from UBUs promote selectivity, while larger inter-UBU packing pores increase uptake capacity. The effectiveness of this UBU strategy is shown with a cobalt MOF (denoted SNNU-45) in which octahedral cages with 4.5 angstrom pore size serve as UBUs. The C2H2 uptake capacity at 1 atm reaches 193.0 cm(3) g(-1) (8.6 mmol g(-1)) at 273 K and 134.0 cm(3) g(-1) (6.0 mmol g(-1)) at 298 K. Such high uptake capacity is accompanied by a high C2H2/CO2 selectivity of up to 8.5 at 298 K. Dynamic breakthrough studies at room temperature and 1 atm show a C2H2/CO2 breakthrough time up to 79 min g(-1), among top-performing MOFs. Grand canonical Monte Carlo simulations agree that ultrahigh C2H2/CO2 selectivity is mainly from UBU ultramicropores, while packing pores promote C2H2 uptake capacity.