Isostructural functionalization by –OH and –NH2: different contributions to CO2 adsorption†
Two isostructural mfj-type metal–organic frameworks, [Cu2(ABDPB)(H2O)]n (HHU-3, HHU for Hohai University; H4ABDPB for 5-amino-1,3-bis(3,5-dicarboxylphenyl)-benzene) and [Cu2(OBDPB)(H2O)]n (HHU-4; H4OBDPB for 5-hydroxyl-1,3-bis(3,5-dicarboxylphenyl)-benzene) were successfully synthesized by V-shaped tetracarboxylic ligand with amino and hydroxyl groups, respectively. Compared with the prototypical MOF, PCN-306, both MOFs exhibit obviouse decreases in BET surface area and pore volume, with the values of 2354 m2 g−1 and 0.920 cm3 g−1 for HHU-3, and 2353 m2 g−1 and 0.954 cm3 g−1 for HHU-4. Although both functional groups are believed to be effective in strengthen CO2 interactions with the framework, in this type of MOF, amino group works better due to its basic nature. Meanwhile, the decoration of amino groups grafted HHU-3 high CO2 adsorption capacity (25.6 wt% at 1 bar and 273 K) and high CO2 selectivity (SCO2/N2 = 129).