The Fabrication Of MOFs Self-assembly Composite Membrane And Performance Research

The progress of human industrial activities has greatly increased the emission of atmospheric CO₂,and energy-efficient CO₂ separation technology is an effective way to achieve carbon capture.Among the many separation technologies,membrane separation technology has attracted widespread attention because of its advantages of relatively low energy consumption,green environmental protection and small footprint.Polymer membrane materials have been widely used,and the inherent trade-off effect makes it difficult to effectively improve the performance,MOFs porous materials have the advantages of rich pore structure,small gas transfer resistance and other advantages are ideal materials for constructing high-performance separation membranes,mixed matrix membranes（MMMs）can be combined with the respective advantages of polymers and porous materials at the same time,with good industrial application prospects.However,the disorderly arrangement of porous materials in the mixed matrix membrane greatly weakens the pore advantage of the porous material,and at the same time,the phenomenon of particle agglomeration is easy to occur due to poor interface compatibility,which will reduce the separation performance of the prepared membrane.In view of the above problems,the research idea of this work uses the self-assembly effect of polymers and metal-organic frameworks（MOFs）to construct composite films,and the superparticle structure formed by the self-assembly of MOFs makes MOFs arranged in the membrane in an orderly and tightly packed form,which greatly increases the amount of MOFs added.The polymer only fills the gap between the particles of the MOFs to prevent defects.At the same time,the orderly assembly makes the surrounding chemical ring of MOFs particles basically the same,which can make full use of the pore structure of MOFs to achieve effective separation,and predict membrane performance.In view of the research ideas,the main research content of this paper is as follows:The currently reported ZIF-8 has rich morphology,and after analysis,ZIF-8 with dodecahedral structure can prevent the accumulation of MOF surfaces and block the pores,and can also use the pores between MOFs particles to enhance gas diffusion.Therefore,the synthesis method of ZIF-8 was first explored,the influence of the proportion of zinc metal ions,ligands and surfactant CTAB on morphology was investigated,the dodecahedral structure was constructed,and the change law and morphology formation mechanism of pore structure were investigated.Subsequently,the polymer and ZIF-8 were used to realize the self-assembly of the binary system,and the self-assembly composite film with assembly structure was prepared by high temperature solvent evaporation induction method and room temperature solvent evaporation induction method,respectively.Polyvinyl alcohol（PVA）,polyethyleneimine（PEI）and polyether block polyimide（Pebax）aqueous solution were used as polymer solution,and ZIF-8 dispersion was added to prepare PVA/PEI and Pebax self-assembled composite film.The effects of ZIF-8 addition and PVA to PEI ratio on the self-assembly effect and CO₂/N₂ separation performance of ZIF-8 were investigated.The results show that the self-assembly membrane prepared by the high-temperature solvent evaporation induction method can obtain a separation membrane with a ZIF-8 concentration of 250 mg/m L and a solvent evaporation temperature of 65°C.Under the conditions of 35°C and 35%relative humidity,ZIF-8 dispersion with a concentration of 100 mg/m L was prepared by room temperature solvent evaporation induction method to obtain a separation membrane with good self-assembly effect.Under the same test pressure,the self-assembled separation membrane with a regular arrangement structure showed high CO₂ permeation performance.