Synthesis and characterization of three amino-functionalized metal–organic frameworks based on the 2-aminoterephthalic ligand

Abstract

The incorporation of Lewis base sites and open metal cation sites into metal–organic frameworks (MOFs) is a potential route to improve selective CO₂ adsorption from gas mixtures. In this study, three novel amino-functionalized metal–organic frameworks (MOFs): Mg-ABDC [Mg₃(ABDC)₃(DMF)₄], Co-ABDC [Co₃(ABDC)₃(DMF)₄] and Sr-ABDC [Sr(ABDC)(DMF)] (ABDC = 2-aminoterephthalate) were synthesized by solvothermal reactions of 2-aminoterephthalic acid (H₂ABDC) with magnesium, cobalt and strontium metal centers, respectively. Single-crystal structure analysis showed that Mg-ABDC and Co-ABDC were isostructural compounds comprising two-dimensional layered structures. The Sr-ABDC contained a three-dimensional motif isostructural to its known Ca analogue. The amino-functionalized MOFs were characterized by powder X-ray diffraction, thermal gravimetric analysis and N₂ sorption. The CO₂ and N₂ equilibrium adsorption capacities were measured at different temperatures (0 and 25 °C). The CO₂/N₂ selectivities of the MOFs were 396 on Mg-ABDC, 326 on Co-ABDC and 18 on Sr-ABDC. Both Mg-ABDC and Co-ABDC exhibit high heat of CO₂ adsorption (>30 kJ mol⁻¹). The Sr-ABDC displays good thermal stability but had a low adsorption capacity resulting from narrow pore apertures.