Preparation And Separation Performance Of Metal-organic Framework Membranes Made By Metal Oxide Convention Method

Separation is a key operational unit in the chemical industry,accounting for about50%of the industry’s total energy consumption.Therefore,energy conservation and emission reduction in the separation process are crucial.Compared with traditional separation processes such as distillation,drying,and pressure swing adsorption,membrane separation technology has significant advantages such as lower energy consumption,less carbon emissions,simple operation,and small space occupation.In recent years,significant progress has been made in the preparation,modification,and separation applications of Metal-Organic Framework（MOF）membranes.However,due to the poor compatibility between MOFs and most substrates and the limited heterogeneous nucleation sites on their surfaces,it is still difficult to achieve efficient and large-scale preparation of MOF membranes,and research on MOF membranes with both high stability and separation performance is not in-depth,which greatly hinders the practical application process of MOF membranes.Thus,we utilized optimization and modification strategies of the substrate,using highly active metal oxides as precursors,to successfully transform and prepare MOF membranes for gas separation and seawater desalination,improving the separation stability of these MOF membranes.These details are as follows:1.A novel,environmentally friendly and efficient solvent-free zinc oxide conversion method was developed,using zinc oxide（Zn O）as a metal precursor and three imidazole ligands.Through a simple grinding-pressing-heat treatment process,three free-standing MOF membranes were prepared under solvent-free conditions.This method avoids the use of large amounts of solvents and the cumbersome pre-treatment process of substrates in traditional methods.The prepared free-standing MOF membranes has good mechanical strength,overcoming the shortcomings of insufficient mechanical properties of previous free-standing MOF membranes.Meanwhile,SEM images and Mercury intrusion porosimetry experiments have shown that the free-standing MOF membranes have a unique asymmetric membrane structure,which a dense and continuous surface layer is conducive to selective gas permeation,while the intermediate layer containing large amounts of micrometer sized pores is conducive to gas transport.This allows these free-standing MOF membranes to exhibit excellent H₂permeance and H₂/CO₂ separation performance.ZIF-8 membrane had a H₂ permeance of 2653.7 GPU(8.89×10^-7 mol m^-2 s^-1 Pa^-1,with a good H₂/CO₂ selectivity of 17.1.The H₂ permeance of Zn（Et Im）₂ membrane can reach 6268.7 GPU(2.10×10^-6 mol m^-2 s^-1Pa^-1)and the H₂/CO₂ selectivity is 22.1.This study provides a new approach for preparing free-standing MOF membranes with good gas separation performance,which provides a broad application prospect for the efficient and large-scale preparation of MOF membranes.2.A simple and effective activeγ-alumina（γ-Al₂O₃）conversion strategy was employed for the facile and reliable fabrication of a high-quality MIL-96 membrane.In this case,the highly activeγ-Al₂O₃ alumina layer was used as the active aluminum source and transformed into MIL-96 membrane through in-situ hydrothermal growth.Control experiments have shown that the highly activeγ-Al₂O₃ can not only effectively control the heterogeneous nucleation,avoid bulk crystallization and promote the formation of defect-free MOF membranes,but also enhance the binding force between the membranes and substrate,further enhancing the separation stability of the MOF membranes.Due to the appropriate aperture size and robust structure,the MIL-96membrane afforded an excellent H₂/CO₂ separation performance at high temperatures.Moreover,it also has remarkable durability and recycling performance under harsh hydrothermal conditions.This work lays the research foundation for the simple and effective preparation of high-performance and highly durable gas separation MOF membranes.3.In this chapter,a highly water-stable MIL-160 membrane was prepared by activeγ-alumina conversion strategy and its desalination performance was studied.Due to the suitable aperture size and excellent water adsorption performance,the prepared MIL-160 membrane delivered excellent desalination performance for various metal salt ions at room temperature,with salt rejection rates of over 99.5%and a water flux of12.6 L m^-2 h^-1.In addition,the high water stability also enabled MIL-160 membrane to exhibit favorable desalination performance at high temperatures and different salinities,and its performance could be well maintained under continuous operation for up to 100hours,demonstrating good water stability.This work expands the application of water-stable MOF membranes in the field of seawater desalination.