Preparation Of Polymer-supported Ultrathin Metal-organic Framework Membranes And Their Gas Separation Properties

Gas separation membrane technology has great application prospects in the field of gas separation and purification due to its advantages of green,high efficiency,energy saving,emission reduction and simple operation.Membrane material,as a core component,directly determines the purity and efficiency of gas membrane separation process.Among various kinds of gas separation membranes,polymer-supported separation membrane has the advantages of low cost and easy amplification,which has become a research hotspot.However,the permeability and selectivity of traditional polymer-supported gas separation membranes is difficult to meet the economic and technical requirements of large-scale industrial applications.The development of polymer-supported metal-organic frameworks(MOFs)membranes with high permeability and high selectivity is expected to solve these problems and promote the application of membrane separation technology.In this paper,a series of ultra-thin and compact MOF membranes,including ZIF-8 membrane,DZIF-8membrane,Cu BTC membrane,ZIF-L membrane and CuTCPP membrane,were prepared by using active organic interface layer as the core,which provided reference and basis for the development of high-performance polymer-supported MOFs based gas separation membrane.The main research contents are as follows:(1)A new method for in-situ preparation of ultra-thin MOF membranes by interfacial induced polarization was proposed.The growth of MOFs crystal nuclei were induced by a high active polyvinyl alcohol(PVA)-metal ion organic interface layer.By means of protonation of adsorbed ligands on the interface layer,the metal ions,ligands and metal ion-ligand complexes in the solution system were uniformly adsorbed onto the interface for self-assembly to form the ultra-thin and compact ZIF-8and Cu BTC membranes.Due to the interfacial polarization,the prepared MOF membranes had unsaturated metal vacancies.The results showed that the prepared MOF membranes had good separation performance for CO₂/CH₄ with the permeability of 4000-5000 GPU and selectivity of 15-30.(2)DZIF-8 membrane was prepared by interfacial induced polarization with in-situ modification of diethanolamine(DEA).DEA would accelerate the protonation of ligands and increase the competitive adsorption with polarized ligands at the interface layer,further strengthen the formation of unsaturated metal vacancies in MOFs,forming ultra-thin and low-crystalline DZIF-8 membrane.The results showed that the prepared DZIF-8 membrane had optimal permeability of 2000-3000 GPU for C₃H₆and excellent selectivity of 90-120 for C₃H₆/C₃H₈.(3)In the subnanometer confined space near the PVA-Zn²⁺interfacial layer,using the interaction force between free crystal nuclei and riveted crystal nuclei,the ultra-thin ZIF-L membranes were prepared by interfacial induced in-situ exfoliation.ZIF-L membranes with thickness ranging from micron to less than 100 nm were in situ prepared by adjusting the PVA-Zn²⁺interfacial layer and ligand content.The results showed that the prepared ZIF-L membrane had good permeability and selectivity for CO₂/CH₄ system.(4)Ultra-thin CuTCPP membrane with thickness less than 10 nm was in situ prepared for the first time by regulating the nucleation growth of MOFs at the interface layer under the synergistic mechanism of polymer.The design of PVA-Cu²⁺interface layer increased heterogeneous nucleation sites of CuTCPP on the interface layer.The PVP polymer as surface modifier was introduced to regulate the anisotropic growth of CuTCPP nucleus and induce the growth and assembly of ultra-thin CuTCPP nanosheets at the interface layer.The CuTCPP membrane showed excellent permeability and selectivity for CO₂/CH₄.