Prparation Of High Performance Mixed Matrix Membranes Based On Porous Organic Frameworks And Its Application CO₂ Separation

The increasing emission of CO₂ in the atmosphere has caused serious greenhouse effect and a series of environmental issues.Among many carbon capture technologies,membrane separation has attracted much attention due to its advantages of low energy consumption,small land occupation and simple operation.Mixed-matrix membrane（MMM）is prepared by adding inorganic filler into polymer matrix,which integrates the merits of polymer membrane and inorganic membrane.Porous organic frameworks such as metal-organic frameworks（MOFs）and covalent-organic frameworks（COFs）have been widely used as fillers in the preparation of MMMs for gas separation thanks to their adjustable pore structure and pore size,as well as extremely high specific surface area.The key challenges in the fabrication of MMMs are the poor interfacial compatibility between the filler and the polymer matrix,as well as the undesired particle sedimentation and agglomeration,that give rise to irregular morphology and non-selective interfacial defects.To solve these problems,in this thesis,we have developed new strategies for the preparation of MOF-and COF-based mixed-matrix membranes,which include a new in-situ“bottom-up”growth strategy for the manufacture of COF based MMMs and the introduction of COF layer on MOF core to enhance the interfacial compatibility between MOF phase and polymer matrix.The main research results of this thesis include:（1）Two dimensional COF-based mixed matrix membrane is prepared by in-situ"bottom-up"synthesis approach which involve the admixing of COF precursors with PEO monomers at the molecular level in a solvent-free system.The two dimensional COF with uniform distributions are further generated via the covalent linkages of precursors within the cross-linked polymer network under microwave assisted Zincke reaction.The new strategy can narrow the pore sizes of COF due to the sheltering effects and the interlock of PEG networks,which favor the improvement of gas separation performances.The resulting mixed-matrix membrane exhibits a remarkable permeability of 803.9barrer for CO₂ and selectivities of 61.4,19.8,15.0 for CO₂/N₂,CO₂/CH₄,CO₂/H₂,respectively,exceeding the known upper-bound limits reported for polymer membranes.Meanwhile,the membranes displayed a one-month stability confirming its exceptional long-term operational stability and great potential for industrial gas separations.（2）The MOF@COF hybrid porous crystalline material was synthesized by growing COFs layers on the surface of NH₂-Ui O-66.By integrating the molecular sieve effect of MOFs and the pure organic nature of COFs,the interface defects between MOF fillers and polymers were eliminated,thereby greatly improving the gas separation performance of CO₂.By optimizing the doping amounts of MOF and COF precursors,four types of Ui O@VCOF hybrid porous crystalline materials and their corresponding mixed matrix membranes were prepared.Among them,Ui O@VCOF-50 shows good morphology,with uniform coating with COF layer.The resulting mixed matrix membrane containing 2 wt%Ui O@VCOF-50 exhibits a permeability of 549.3 barrer for CO₂ and selectivities of 56.6,21.2,14.5 for CO₂/N₂,CO₂/CH₄,CO₂/H₂,respectively,achieving or even exceeding the known upper-bound limits reported for polymer membranes.（3）The Ui O@LZU1 hybrid porous crystalline material was also prepared.The thickness of COFs layer was modulated by altering the doping amounts of MOF and COF precursors.The Ui O@LZU1 hybrid materials were characterized by SEM,TEM and XPS.Mixed matrix membranes with different Ui O@LZU1 loading amounts were prepared,and the mixed matrix membrane with 2 wt%Ui O@LZU1-4 loading reveals the better separation performance,with 138.6%increase in CO₂ permeability,164.0%increase in CO₂/N₂selectivity and 153.5%increase in CO₂/CH₄ selectivity.Aiming at the separation of carbon dioxide,this paper designed,synthesized and studied the high performance mixed matrix membranes based on porous organic frameworks,which has certain theoretical research and practical application significance for the design,synthesis and application of high performance membranes.