Preparation And Interface Regulation Of High Performance Polyether Ether Ketone Separation Membrane

Clean water is an essential resource for maintaining human life activity and ecosystem stability.However,with the continuous growth of the population,the water shortage problem has attracted more attention.In the food,textile,metal,paper,and chemical industries that require a lot of water,the recycling and reuse of wastewater will greatly help reduce the consumption of water resources and relieve the pressure caused by the shortage of fresh water resources to a large extent.As an emerging approach,membrane separation technology can not only desalinate seawater and brackish water but also be used for wastewater recovery.This technology has the advantages of high efficiency,easy operation,low cost,and low energy consumption,and is one of the main technologies of sustainable environmental pollution control projects.Fundamentally,the separation performance of membranes is limited by their structure and properties.In terms of membranes materials,polymer membranes are receiving increasing attention in the laboratory and industrial-scale water treatment.However,these traditional membrane materials have the limitations of selectivity and permeability,low antifouling performance,and poor corrosion resistance in harsh environments.Therefore,in order to overcome these critical limitations,novel membranes need to be designed and manufactured to increase stability,stain resistance,and separation performance.Polyether ether ketone（PEEK）series polymer is famous for its solvent resistance and corrosion resistance,which is the top product of special engineering plastics.Its excellent solvent resistance is due to the stability of its molecular structure and semi-crystalline aggregates.PEEK is a good base resin for organic solvent separation membranes.However,due to its crystallization characteristics,the solution processing of materials is limited,which hinders its application and research in the field of separation membrane materials.In spite of this,some research work on preparing PEEK separation membranes by eliminating the crystallinity of materials through functional groups has been reported successively.This method destroys the original crystal structure and improves the solvent processing properties of materials,but the loss of crystallinity limits the use of membranes in some specific solvents.If the crystalline PEEK membranes material can be prepared,the solvent resistance and stability of the membranes will be greatly improved and the application field will be broadened.Some researchers use strong acid（concentrated sulfuric acid and methanesulfonic acid,etc.）as solvents to prepare crystalline PEEK separation membranes.The chemical stability and resistance of such membranes materials to organic solvents have been significantly improved,but a large amount of acid is generated in the process of membrane preparation,which brings great challenges to the environment and membranes making equipment.In this paper,the problem that PEEK is difficult to process into membranes by solution is solved through the clever design of molecular structure and has a good application prospect.In this process,the amorphous poly（aryl ether amine）polymer was firstly prepared,then the precursor membranes were prepared by the traditional nonsolvent phase separation（NIPS）method,and finally,the PEEK membranes with adjustable pore size were prepared by the heterogeneous phase hydrolysis technology.Then the interface functionalization of PEEK membranes was regulated,including the introduction of charge selective layer,construct multilevel nano separation interface and the layer assembly of organic-inorganic materials,PEEK/SPEEK-x composite membranes impregnated with negative charge polyether ether ketone（SPEEK）,crystalline SPEEK based composite membranes with nano-ridged functional layer and crystalline SPEEK composite membranes with graphene oxide（GO）multifunctional layer were prepared.The details are as follows:（1）Polyether ether ketone precursor（PEEKt）was synthesized by hydroquinone and N-phenyl（4,4-difluorobenzene）ketone amine,N-Methylpyrrolidone（NMP）was used as a solvent to prepare PEEKt membranes by nonsolvent induced phase separation（NIPS）method,and PEEK membranes were obtained by heat treatment under acidic condition.The mechanism of structure change of PEEK membranes during heat treatment was systematically studied,and the effects of different treatment temperatures on membranes structure,pore size,and separation performance were explored.At the same time,the separation performance of organic dyes with different molecular weights by PEEK membranes at different temperatures was investigated.The results showed that PEEK membranes could effectively separate organic dyes at a specific temperature.After soaking in organic solvents and strong acid,the separation performance of PEEK membranes has good reproducibility.Compared with the traditional commercial polymer membranes（polyacrylonitrile and cellulose acetate membranes）,PEEK membranes have excellent chemical stability.（2）Negatively charged polyether ether ketone precursor（SPEEKt）was prepared from the point of view of charged membrane on the basis of previous work.Due to the rich-SO₃H,the surface of the membranes has excellent hydrophilicity and more negative charge,which has a good repulsive effect on the solute with negative charge.Therefore,a series of crystalline PEEK/SPEEK-x composite membranes were obtained by using SPEEKt as the impregnation solution and the aforementioned PEEK membranes as the substrate,and then heat treatment under acidic conditions to promote the hydrolysis and crystallization of the impregnating layer into the SPEEK.The water flux of PEEK/SPEEK-2 wt%increased about 9 times than that of commercially used NF270(14.5 L m^-2 h^-1 bar^-1)with the same solutes rejection rate.Due to the high rejection rate of organic dyes and low rejection rate of salt,the PEEK/SPEEK-x membranes can effectively separate salt and dye from textile wastewater.In addition,after 10 cycles of testing,the CR rejection rate and water flux remained unchanged.After ethanol cleaning,the separation performance of the membranes recovered completely,and the structure remained intact,indicating that the membranes had long-term stability and good regeneration performance.（3）The interface morphology of multistage nano separation interface separation membrane has an important effect on its separation performance.Because regular nanostructures in the separation interface can improve the membranes rejection rate without reducing the membranes flux,it is an effective means to solve the“trade-off”effect of separation membranes.Therefore,in this work,a series of Tob/Cyclam-TMC-x composite membranes were prepared by interfacial polymerization using crystallized SPEEK separation membranes as the support layer.In this paper,tobramycin（Tob）and Cyclam（Cyclam）aqueous solution were used as solution phase,and N-hexane（TMC）aqueous solution was used as organic phase.Finally,by optimizing the conditions of interface polymerization,a layer with nano-ridge was successfully prepared at the interface of SPEEK membranes cortex.We then studied the effects of Cyclam content on the structure and properties of the composite membranes.It was found that in interfacial polymerization,with the increase of Cyclam content,the viscosity of the solution phase increased,resulting in diffusion-driven instability,thus realizing the change of the structure of the functional layer from nano nodules to nano ridges.The change of functional layer structure increases membranes contact area and solute retention without affecting membranes flux.Meanwhile,the surface of the composite membranes has a strong negative charge,and according to the Donan effect,the rejection rate of the negative charge organic small molecule dyes is high.In addition,the antibacterial test showed that Tob/Cyclam-TMC-x composite membranes could inhibit the bacterial growth on its surface and had good resistance to biological contamination.（4）Study on the solvent resistant PEEK based two-dimensional nano organic solvent separation composite membranes with graphene oxide（GO）as separation layer.Two-dimensional nanomaterials have good corrosion resistance and solvent resistance.Their uniform size can provide excellent screening performance for solute molecules,but their self-support and stability are poor.Therefore,combined with the advantages of crystalline PEEK with organic resistance and large-scale preparation,the binary coordination effect of PEEK based GO organic solvent separation composite membranes was studied.The organic-inorganic interface is stabilized by the interaction between GO and-SO₃H of the crystalline SPEEK.Subsequently,a series of SPEEK@GO/PEI/GA-x composite membranes were prepared by filling polyvinyl imine（PEI）and crosslinking with glutaraldehyde（GA）.By using PEI to fill the defects,the composite membranes can effectively separate organic small molecular dyes in organic solvents.In addition,the morphology and separation performance of the composite membranes remained unchanged under the condition of long-term filtration and ultrasonic treatment,indicating that the membranes had excellent stability.