Preparation Of Highly Stable Metal-organic Framework Materials And Their Membrane Materials

Separation unit plays an important role in a chemical production process.Owing to the diversity in separation system and separation requirements,traditional separation technologies such as distillation,absorption,and extraction are difficult to meet the demands fully and efficiently,forcing people to develop new materials and technologies for separation.Membrane separation technology has been widely studied due to the andvantages in energy efficient and operation simplicity,and the improvement in membrane separation performance is largely depended on the development of novel membrane materials.Mixed matrix membranes(MMMs)developed by compositing polymer and porous materials may have advantages in exploring the merits of both polymers and porous materials,thus expanding the application range of membrane separation.Metal-organic framework(MOF)materials have attracted great attention for application in the separation field due to their adjustable pore structure and designable pore surface property.However,poor water stability of MOFs and difficulty in large-scale preparation and repeatability of MOF-based membranes are still the key problems that restrict their practical application in the fields of adsorption separation and membrane separation.The purpose of this paper is to develop new strategies for improving the water stability of MOFs and preparing water stable high performance MMMs based on MOFs with enhanced water stability,and to explore new methods for improving the repeatability in MOF-based MMMs fabrication.The main research contents are outlined as follows:(1)To improve the structural stability of Cu-BTC under wet conditions,we proposed a new in-situ modification strategy for one-step synthesis of water stability enhanced Cu-BTC by in-situ functionalization of Cu-BTC with isopropanol(IPA)during material synthesis.The methyl groups of IPA connected to the Cu²⁺sites can construct hydrophobic shielding microenvironments around the Cu²⁺sites,thus decreasing the local concentration of water molecules and preventing them from damaging the structure of Cu-BTC.The Cu-BTC-IPA sample can preserve high specific surface area and complete crystal structure after soaking in water for several days.Moreover,Cu-BTC-IPA sample can preserve 90%of its initial gas capacity and has high gas selectivity after soaking in water,which is beneficial to its application in CO₂ adsorption and separation;(2)On the basis of small molecule modifier,the application of macromolecules in improving water stability of MOFs was futher explored.A carboxyl group containing polymer,polyethylene-amine(PCH)was used to in-situ modify Cu-BTC.Owing to the steric hindrance effect and hydrophobicity of the polymer,water stability of Cu-BTC was obviously enhanced.The Cu-BTC-PCH can preserve its crystal structure and high specific surface area after soaking in water for several days.In addition,a variety of MOFs were also modified by PCH,and the water stability of these modified MOFs were also improved.This work indicates that macromolecules possess unique advantage in improving the water stability of MOFs,and has reference value for the development of stable MOFs;(3)The application of water stability enhanced MOFs in preparing stable MMMs for water containing mixture(such as flue gas)separation was further explored.In this work,sodium citrate(SC)was used to in-situ functionalize Cu-BTC to improve the stability in water environment.The obtained water stable Cu-BTC-SC was then used as fillers in the Pebax^?1657 polymer to pepare dense MMMs through spin coating on modified PSf ultrafiltraion membrane substrate.The results showed that Cu-BTC-SC can introduce additional transport channels as well as CO₂-philic open Cu²⁺sites,leading to great enhancement in CO₂ separation performance.Besides,separation performance tests under humid conditions suggest that the Cu-BTC-SC based MMMs can hold their stability for longer time;(4)Inhomogeneous distribution of filler particles in polymer matrix is a key problem that influences the scalable fabrication and repeatability of MMMs.Aiming on this,metal-organic polydedron(MOP)was selected for the preparation of MMMs.Comparing with MOF materials with three-dimensional structure,one of the advantages of MOP materials is its solubility in specific solvents,which endows them with better processing repeatability.In this work,UMOP-1-NH₂ was used as the filler in the preparation of a novel thin film nanocomposite(TFN)membrane through interfacial polymerization.The results suggest that the incorporation of UMOP-1-NH₂not only constructed additional tansport channels in the polyamide separation layer,but also facilitated the formation of uniform Turing structure the surface of the membrane,thus increased the contact area of the membrane surface with the solution as well as the water permeance of the membrane.At the same time,high retention rate towards dyes were well preserved.Furthermore,the membrane displayed excellent antifouling properties and anti-bacterial performance,which are beneficial for its application in actual separations.This work poves a new way for improving the repeatability of MMMs preparation,which may facilitate the research progress in scalable fabrication and application of MMMs;(5)On the basis of the previous work,UMOP-1-NH₂ was first exploited to totally replace the traditional small diamine monomers in aqueous phase to construct a novel porous polyamide TFC membrane through interfacial polymerization.The results suggest that the pore structure of UMOP-1-NH₂ can be fully exploited by using it as the only monomer in the water phase,thus endowing the membrane with higher water permeance and good dye/salt separation performance.At the same time,UMOP-1-NH₂/TMC membrane displayed excellent antifouling properties and anti-bacterial performance.This kind of new polyamide nanofiltration membrane with porous separation layer not only has developed pore structure,but also has the simplicity in preparation of polyamide membrane,therefore has good application potential in nanofiltration separation.