Preparation Of Diphenyl Polyether Ether Ketone Separation Membrane And In Situ Construction And Properties Of MOF Separation Interface

Environmental energy is the material basis for human survival and development.With the continuous improvement of social progress and living standards,people’s awareness of environmental protection is also being strengthened,and they are increasingly aware that"Lucian waters and lush mountains are invaluable assets".In the current"peak carbon dioxide emission and carbon neutrality"background,low energy consumption of green industrial form has become the only way to industrial development,while traditional energy-intensive industries will continue to fade out of the historical stage.Today,the separation and purification of organic chemicals consumes huge amounts of energy every year,and chemical pollutants also pose a hazard to the environment and human health.Therefore,the recovery of organic chemical pollutants and the separation and purification of green and low energy consumption organic chemicals have become a great challenge we face.Membrane separation technology is a pressure-driven separation technology with low energy consumption.If it can be applied in the separation of chemical pollutants and recovery of chemicals,it will be one of the effective ways to solve the above problems.In recent decades,membrane separation technology has made continuous progress and been successfully promoted in the field of water treatment.Currently,most desalination equipment adopts membrane separation for desalting treatment.Therefore,membrane separation is expected to be popularized in the chemical industry.At present,the challenges that the application of membrane separation technology faces in the separation of organic solvents are the lack of polymer materials for special separation membranes with solvent resistance and corrosion resistance and the construction of an efficient and specific separation interface.Polymers suitable for the separation of organic solvents require to possess superb chemical resistance properties.Among many available polymers,polyether ether ketone（PEEK）is one of the most ideal materials for the preparation of solvent-resistant separation membranes due to its high temperature resistance,corrosion resistance and organic solvent resistance.However,the crystalline nature of polyether ether ketone polymers makes them difficult to process in solution,limiting their application in the field of special separation membrane materials.At the same time,polyether ether ketone resins（glass transition temperature～143°C）suffer from membrane deformation and pore size shrinkage due to the movement of molecular chain segments when used in high temperature separations.In order to overcome the technical difficulty of preparing porous separation membranes of crystalline polyether ether ketone,and prepare solvent resistant separation membranes of crystalline polyether ether ketone with higher heat resistance grade.In the first part of this paper,from the perspective of molecular structure design,a biphenyl poly aryl ether ketone copolymer（PEDEKt）containing an aryl Schiff base side group with high glass transition temperature（T_g）was synthesized.The solubility of the copolymer is improved due to the existence of an aryl Schiff base.At the same time,the aryl Schiff base can be hydrolyzed and removed under acidic conditions,and the copolymer can be transformed into crystalline biphenyl poly aryl ether ketone.Based on this,a porous membrane containing an aryl Schiff base was used to obtain a crystalline poly diphenyl ether ether ketone（PEDEK）separation membrane by heterogeneous hydrolysis.Compared with traditional PEEK,the thermal properties of the prepared PEDEK were significantly improved,with T_g increased by 31℃and melting point（T_m）increased by 82℃.PEDEK membranes have excellent separation properties for macromolecular proteins(Mw:66446 g mol^-1)and dyes(Mw:1017.63 g mol^-1).The structure of the membrane was still intact after a long time treatment with high temperature organic solvent.It is proved that the PEDEK separation membrane prepared in this work has good solvent resistance and high temperature resistance,and has abundant and unimpeded nanometer（～3.2 nm）pore channels on the surface of the membrane,which is a good polymer matrix membrane.It is difficult for the separation membranes prepared by non-solvent induced phase separation（NIPS）method to separate small and medium-sized solutes(Mw<1000 g mol^-1)in organic solvents.In order to realize the accurate and efficient separation of small and medium-sized pollutants in organic solvents,the second part of this paper constructs an efficient MOF（Ui O-66）nano separation interface on the solvent-resistant membrane to study the organic solvent nanofiltration performance of the nanocomposite membrane based on the PEDEK.In order to solve the interface problem between the organic polymer PEDEK membrane and MOF,the photopolymerization experiment of in situ acrylic acid interface induced by the carbonyl group on the surface of the PEDEK membrane was carried out,and the functional interface of the chemical bond bridging polyacrylic acid was obtained.Then,Ui O-66 membranes were grown in situ on PEDEK membranes by solvothermal method,taking advantage of the feature that carboxyl groups of acrylic acid can participate in the nucleation and growth of MOF.The chemical bond bridging effect of polyacrylic acid stabilizes the interface between PEDEK and MOF,and realizes the preparation of highly stable organic-inorganic composite membranes.The influence of surface photopolymerization conditions on the interface and properties of PEDEK membranes was studied in depth.The conditions for the in situ growth of MOF membranes and the rules of crystal growth were investigated.The prepared PEDEK@Ui O-66 composite nanofiltration membrane showed excellent resistance to high temperature and solvent.At the same time,the composite membrane achieved efficient separation of dyes in organic solvents,and showed excellent rejection for small molecules(Mw≥696.68 g mol^-1)dyes,and the ethanol flux could reach 72.36 L m^-2 h^-1 bar^-1.In conclusion,in the above two parts of the work,through the monomer structure design and reaction condition control,the problem of difficult solution processing of the solvent-resistant PEDEK base membrane was solved,and the heat resistance of the solvent-resistant PEDEK base membrane was greatly improved.Combined with the ingenious design,the PEDEK@Ui O-66 composite nanofiltration membrane with a stable interface was prepared by the bridge action of polyacrylic acid.The composite membrane has excellent resistance to organic solvents and efficient separation of small molecular pollutants.In summary,PEDEK@Ui O-66 composite membrane prepared in this work perfectly shows the organic-inorganic binary synergistic effect,and fully takes advantage of the solvent resistance and easy processing characteristics of polymer membrane and the excellent separation characteristics of MOF membrane.This preparation strategy is instructive for solvent resistant separation membranes.