Pore modulation of metal–organic frameworks towards enhanced hydrothermal stability and acetylene uptake via incorporation of different functional brackets

Abstract

Metal–organic frameworks (MOFs), as a class of adjustable porous crystalline materials, have received considerable attention in recent years. In this study, starting from an unstable MIL-88 type Co(II)-MOF as the prototype structure, two isoreticular stabilized MOFs with similar structural features but different water/thermal stabilities and acetylene sorption behaviors were prepared, which can be modulated by incorporating different functional brackets in the pores. MOF 1 equipped with open metal sites (OMSs) decomposed quickly in water solution, while the free N-donor functionalized MOF 2 could be stable in water with improved thermostability. The gas sorption study reveals that activated material 2 has a significantly enhanced acetylene uptake capacity with a lower Q_st value than those of activated 1, showing a 79% increase (242 vs. 135 cm³ g⁻¹) at 273 K and 91% increase (165 vs. 86 cm³ g⁻¹) at 298 K. The acetylene uptake capacity of activated material 2 is extraordinarily high among MOFs without OMSs, and is even comparable to some famous MOFs with much stronger C₂H₂ binding ability which however require considerably higher energy for regeneration. The experimental results were further confirmed by the molecular mechanics (MM) calculations, grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) studies.