The competitive and synergistic effect between adsorption enthalpy and capacity in D2/H2 separation of M2(m-dobdc) frameworks

Abstract Hydrogen isotope separation is a challenging task due to their similar properties. Herein, based on the chemical affinity quantum sieve (CAQS) effect, the D2/H2 separation performance of M2(m-dobdc) (M = Co, Ni, Mg, Mn; m-dobdc4- = 4,6-dioxido-1,3-benzenedicarboxylate), a series of honeycomb-shaped MOFs with high stability and abundant open metal sites, are studied by gases sorption and breakthrough experiments, in which two critical factors, gas uptake and adsorption enthalpy, are taken into consideration. Among these MOFs, Co2(m-dobdc) exhibits the longest D2 retention time of 180 min/g (H2/D2/Ne: 1/1/98) at 77 K because of its second-highest adsorption enthalpy (10.7 kJ/mol for H2 and 11.8 kJ/mol for D2) and the best sorption capacity (5.22 mmol/g for H2 and 5.49 mmol/g for D2) under low pressure of 1 kPa and 77 K), which make it a promising material for industrial hydrogen isotope separation. Moreover, the results indicate that H2 and D2 capacities under low pressure (about 1 kPa) dominate the final D2/H2 separation property of MOFs.