The Application Of Microporous Metal-organic Frameworks In Gas Storage And Separation

Metal-Organic Frameworks（MOFs）are widely used in catalysis,gas storage and separation,chemical sensing and drug delivery due to their high porosity,high surface areas,structural diversity and framework designability.In particular,microporous MOFs have become a hot research topic in the field of gas adsorption and separation in recent years due to small pore size,strong interactions between the microporous pores and gas molecules and high selectivity.In this thesis,firstly,two examples of microporous MOFs with high alkyne storage capacity and excellent separation performance were constructed using two rigid ligands.Secondly,a series of microporous MOFs with novel structures were synthesized using four flexible ligands,and their applications in low-carbon hydrocarbon gas storage and separation were explored.Firstly,two examples of microporous MOFs（1 and 2）were synthesized by diffusion method using rigid triangular ligand 1,3,5-Trimethyl-2,4,6-Tris（4-pyridyl）benzene)（TMTPB）and quadrangle ligand 1,2,4,5-tetra（4-pyridyl）benzene（TPB）respectively.1presents a novel hexagonal channel along the c axis,which has high water and thermal stability.Gas sorption isotherms display that 1 has ultrahigh C₂H₂ and C₃H₄ adsorption capacity of 150 cm³/g and 159 cm³/g at 298 K and 1 bar,respectively.The breakthrough column separation experiments show that the separation times of 1/99 C₂H₂/C₂H₄ and1/99 C₃H₄/C₃H₆ can reach 230 min/g and 600 min/g,respectively.The tests with different flow rate and three-cycle breakthrough tests further demonstrate that 1 has remarkable C₂-C₃ alkyne/alkene separation performance.2 exhibits a 4,6-connected fsc topology with two different pore sizes of diamond channels along the b axis.The adsorption capacity of C₂H₂ is 95 cm³/g at 298 K and 1 bar.More notably,2 has a high C₂H₂ uptake of 28 cm³/g at 0.01 bar,significantly higher than that of C₂H₄（0.1 cm³/g）.The isosteric enthalpies of adsorption for C₂H₂ and C₂H₄ further prove that the adsorption affinity of 2 with C₂H₂ is much stronger than that for C₂H₄.Ideal adsorbed solution theory shows that the separation selectivity of 2 for 1/99 C₂H₂/C₂H₄ and 50/50 C₂H₂/C₂H₄ can be up to 14.2and 12.5,respectively,indicating that 2 has the potential to separate C₂H₂/C₂H₄efficiently.Secondly,we synthesized a series of microporous MOFs（3-10）with novel structure by using four flexible ligands.Except for complex 4,which has a one-dimensional chain structure,other complexes show two-dimensional layered structures with a large amount of free Si F₆^2-anions between the layers.Single-component gas adsorption tests revealed that complex 3 exhibits different adsorption behaviors for CO₂,C₂H₂,C₂H₄,C₃H₄ and C₃H₆,and has the potential to separate C₂H₂/C₂H₄,C₃H₄/C₃H₆ and C₂H₂/CO₂.In summary,microporous MOFs have broad application prospects in the field of gas storage and separation.