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

Abstract

© The Royal Society of Chemistry 2015. The incorporation of Lewis base sites and open metal cation sites into metal-organic frameworks (MOFs) is a potential route to improve selective CO<inf>2</inf> adsorption from gas mixtures. In this study, three novel amino-functionalized metal-organic frameworks (MOFs): Mg-ABDC [Mg<inf>3</inf>(ABDC)<inf>3</inf>(DMF)<inf>4</inf>], Co-ABDC [Co<inf>3</inf>(ABDC)<inf>3</inf>(DMF)<inf>4</inf>] and Sr-ABDC [Sr(ABDC)(DMF)] (ABDC = 2-aminoterephthalate) were synthesized by solvothermal reactions of 2-aminoterephthalic acid (H<inf>2</inf>ABDC) 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 N<inf>2</inf> sorption. The CO<inf>2</inf> and N<inf>2</inf> equilibrium adsorption capacities were measured at different temperatures (0 and 25 °C). The CO<inf>2</inf>/N<inf>2</inf> 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 CO<inf>2</inf> adsorption (>30 kJ mol<sup>-1</sup>). The Sr-ABDC displays good thermal stability but had a low adsorption capacity resulting from narrow pore apertures.