Design Of Membrane Materials And Their Separation And Mass Transfer Properties Based On Metal-organic Framework

Energy conservation and emission reduction is an important way to achieve the global sustainable development strategy and the double carbon target of"carbon emission peak and carbon neutrality".In the textile industry,the separation of harmful gases from fossil energy combustion,the purification of low-carbon energy and the efficient capture of harmful substances are important links to realize energy conservation and emission reduction.As a new membrane separation technology,membrane separation is widely used in gas separation and printing and dyeing wastewater treatment because of its advantages of green low energy consumption,high efficiency and sustainability.Metal-Organic Frameowks（MOFs）have become one of the thermal separation materials for the preparation of high-performance membrane materials due to their characteristics of high porosity,high specific surface area,adjustable pore size and diverse structure.However,the limitations of interfacial compatibility and membrane-making technology make it difficult for membrane materials to give full play to their highest performance and limit their large-scale application.In this work,a series of dense and defect-free high performance membrane materials were prepared by means of in-situ interfacial self-repair,dual induction mechanism,MOFs interfacial polymer modification and filtration assisted interfacial polymerization from the perspectives of large area defect-free growth regulation of membrane materials,precise regulation of membrane structure active sites and interfacial channel construction of MOF mixed matrix membranes（MOF MMMs）.The main research contents of this paper are as follows:（1）In this work,an organo-metal ion hybrid interfacial layer containing Co²⁺ion layer and polyvinyl alcohol（PVA）-Co²⁺complex layer was used to induce high density heterogeneous nucleation and intergrowth of MOFs to achieve in in-situ interfacial self-repair and to prepare a supportive ultra-thin,defection-free ZIF-67 membrane.By enhancing the deprotonation process of ligand（2-methylimidazole）through the PVA interface,the induced segregation effect of organic-metal ion hybrid interface layer is enhanced,and the dynamic release process of Co²⁺ions in the interface layer is controlled,providing a stable interfacial metal source for continuous nucleation and defect repair of MOFs,and achieving the preparation of continuous dense MOF layer.The effective separation layer thickness and gas separation performance of ZIF-67membrane were optimized by adjusting the content of imidazole ligand.The membrane shows excellent performance for CO₂/N₂ separation:CO₂ performance is 4257 GPU and the CO₂/N₂ selectivity is 56.（2）In this work,a kind of MOF MMMs with abundant metal open sites was prepared through the dual induction mechanism of in-situ doping Co²⁺ions and post-modification of polydimethylsiloxane（PDMS）solution.The introduction of Co²⁺ions effectively limits the Zn-N bonds coordination during ZIF nucleation and increases the number of open metal sites in the ZIF layer.In addition,weakly acidic PDMS solution could etch unstable structures in ZIF,further increasing the number and density of open metal sites in the ZIF layer.The post-modification of PDMS could also repair the grain boundary defects and reduce the non-selective area of MOF membrane.The membrane shows excellent performance for N₂/CH₄ separation,N₂ performance is 1367 GPU and N₂/CH₄ selectivity is 6.（3）In this work,a polymer-grafted ZIF-8（BZIF-8）induced secondary interfacial polymerization was proposed to prepare thin film composite membranes with ultra-high MOF loading capacity（TFC@MOFs）.The graft of branchized polyethylenimide（BPEI）was used to impart abundant amino groups on the ZIF-8 interface,which induced secondary interfacial polymerization of residual organic monomers in the primary PA membrane,thus improving the interfacial compatibility and structural crosslinking degree.The N₂/CH₄and CO₂/CH₄ separation performance of TFC@MOFs was optimized by regulating the loading capacity of BZIF-8 nanoparticles.The performance of N₂ and CO₂ can reach 5160 GPU and 14588.23 GPU,respectively,and the selectivities of N₂/CH₄ and CO₂/CH₄ can reach 7.38 and 23.1,respectively.（4）In this work,a thin-film composite membrane with homogeneous distribution of bulk phase was prepared by filtration assisted interfacial polymerization strategy.The chelation between the partially exposed Zn²⁺sites on the interface of ZIF-L and the amine monomer was used to realize the organic combination of ZIF-L and the aqueous monomer,which effectively improved the compatibility of ZIF-L interface.The prepared membranes showed good separation performance of dye/salt.The permeability is 1001.4 L/m²·h·bar,the Congo red（CR）rejection is 99.98%,the Na₂SO₄rejection is 10.01%,and the CR/Na₂SO₄ selectivity is 10.1.