Structural similarity, synthesis, and adsorption properties of aluminum-based metal-organic frameworks

A general procedure has been developed for synthesizing four MOFs sharing similar chains of AlO6 octahedra (CAU-10, NOTT-300, MIL-53-TDC, and MIL-160). CAU-10 has been synthesized with eight differently substituted ligands to impart different characteristics into the pore space. Isotherms of CO2, CH4, and N2 were measured on all MOFs synthesized in this work to assess the effects of functional group and surface area on adsorption behavior. At low pressure (100 mbar), structures incorporating polar functional groups have the highest adsorption of CO2, while the structures with the highest surface areas have the highest adsorption of CO2 at higher pressure (1000 mbar). The heterocyclic and amine-substituted structures show the greatest CO2 adsorption and Henry’s law selectivity among all CAU-10 structures in this work. Comparison of CAU-10 MOFs substituted with a nitro group at different positions on the ligand (carbon 4 vs 5) showed that positioning the nitro group at the side of the pore rather than the center resulted in increased loading of all adsorbates over the studied pressure range up to 1 bar.