Controlled Synthesis Of Ultramicroporous Coordination Polymers With High Density Of Polar Sites And Study On Their CO₂ Capture Performance

Excessive emission of CO₂ is an important factor causing global climate problems.Among all solutions to this problem,physical adsorption technology is a promising research direction due to that it has a lot of advantages such as low energy consumption and non-corrosive equipment.Among the reported adsorbents,the metal-organic framework(MOF)material is a promising CO₂capture material because of that its unique advantages such as rich topological types,highly ordered structure,high porosity,adjustable pore size and easy functionalization.It is well known that polarity sites strongly interact with CO₂molecules.By means of crystal engineering,designing and synthesizing ultra-microporous metal-organic framework materials containing high-density polar sites make them have suitable pore sizes and high-density polar sites.It is a very cutting-edge research direction in this field.In this paper,we designed and synthesized two cases of ultramicroporous MOFs by using two kinds of small size ligands with high density polarity atoms.They have high density polarity sites and named SXU-5 and Mela-Cu,respectively.And we systematically and comprehensively characterized the properties of these two cases of ultramicroporous MOF respectively.The details are as follows:(1)SXU-5 also has a medium level of CO₂ adsorption capacity,CO₂adsorption selectivity,water vapor stability and it is suitable for using as a CO₂capture material.According to the crystal structure characterization,this material is an ultramicroporous MOFs with high density(3.77 mol·L^-1)CO₂philic polarity sites and without open metal sites(OMS).The MOFs have good CO₂adsorption capacity(99 cm³g^-1and 56.6 cm³g^-1at 273 K and 298K,respectively),selectivity(118 at 298 K and 15:85 CO₂/N₂),and water vapor stability.The theoretical calculation shows that the appropriate distance of adjacent ketone atoms plays an important role in promoting the selective capture of CO₂.(2)A three-coordination(Cu(?))MOFs was synthesized with the ligand of melamine and copper ions(The polar atomic density is 22.05 mol·L^-1).The structure has high density CO₂philic polarity site and high stability(maintaining structure stability in p H=12,0.1 mol HCl,organic solvents and boiling water).According to the CO₂mono-component adsorption curve,the CO₂adsorption capacity of this material can reach 113 cm³g^-1and 73 cm³g^-1at 273 K and 298 K,respectively.Interestingly,the selectivity of this material is as high as 36,687 at 298 K when the ratio of CO₂/N₂ is 15:85.