Design And Synthesis Of Functionalized Metal-organic Frameworks And Their Gas Adsorption Properties

Metal-Organic Frameworks （MOFs） are attracting a great deal of attention for theirpotential application in gas storage, drug delivery, selective adsorption of organic molecules, andcatalysis. Though a lot of differently structural MOFs have been reported recently, few functional-MOFs have been synthetized, because the functional groups of the organic linkers can be easilydestroyed during the solvothermal reaction, which make the synthesis of the functional-MOFs abig challenge. However, functional-MOFs have some desirable properties. Otherwise, they can bechanged to other functional-MOFs by some simple chemical reactions. So the synthesis of thefunctional-MOFs has profound significance.In this work, Amine-functionalized metal-organic framework （MOF） was synthesized usingzinc nitrate hexahydrate （Zn（NO3）2·6H₂O） and5-aminotetrazole （CH3N5） in N’N-dimethyl-formamide （DMF） solution at certain conditions. The resulting compound is well crystallized andthe single-crystal X-ray diffraction （XRD） study shows it has a2D structure, which is likegrapheme （we call the resulting compound as2D-MOF all over the following text）. Besides, the2D-MOF shows high thermal stability, with a decomposing temperature above300oC in air andthe structure don’t change even when it is immersed in water for a few days. In addition, it exhibitshigh CO₂adsorption capacity up to1.76mmol·g-1at1bar and25oC.Moreover, we successfully make the amino groups of the2D-MOF changed to some otherfunctional groups by two simple chemical reactions with acetic acid （Ac）, trimesoylchloride （TMC）separately. We sign the two new resulting compounds as2D-MOF-Ac and2D-MOF-TMC, andthey also have high thermal and chemical stabilities as2D-MOF. Nevertheless, both functionalitiesare able to interact with CO₂molecules, as evidenced by the unequally distributed ESP nearby thecarbonyl groups. In other words,2D-MOF-Ac and2D-MOF-TMC provide extra adsorption sites to bind CO₂in addition to the amino groups. Therefore, the CO₂capture ability of2D-MOF-Acand2D-MOF-TMC, which exhibits high CO₂adsorption capacity up to1.86and1.92mmol·g-1at1bar and25oC, separately, is still excellent.Finally, we have synthetized a composite material containing PEI and NH₂-MIL-101, and thecomposite material exhibits high CO₂adsorption ability, comparing with NH₂-MIL-101, especiallyfor the selectivity of the mixed gas of CH₄and CO₂, at the same test condition. For example, thecomposite material PEI@NH₂-MIL-101can adsorb the amount of3.6mmolg-1of CO₂at roomtemperature, even when the temperature rise up to75oC, the selectivity of the composite materialabout CO₂and CH₄can reach up to175.6.We anticipate that functional groups in the as-prepared MOFs offer a method for other amino-MOFs, so is the composite material, as an exploration of further functionality, which may lead topotential applications in catalysis and separation fields.