Isostructural functionalization by –OH and –NH2: different contributions to CO2 adsorption

Abstract

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 (S_CO2/N2 = 129).