Study On The Structure And Properties Of Nanofiltration Membrane Regulated By Functionalized Ionic Liquid

Compared with traditional separation technology,membrane separation technology has many advantages,such as low energy consumption,high efficiency and no pollution.Nanofiltration membrane separation technology has been widely used in water treatment,pharmaceutical and food industries,but low permeance is the main problem,hindering the further development of nanofiltration membrane.Interfacial polymerization（IP）,as the most commonly used method to prepare nanofiltration membrane selection layer,is the diffusion of amine monomer from aqueous solution to water-organic interface,and the instantaneous reaction with organic monomer to form a membrane.Therefore,the membrane structure and properties are largely determined by the diffusion behavior of amine monomer.In this study,a series of high-performance nanofiltration membranes were prepared based on the membrane formation process and membrane structure,which can be designed by using ionic liquid（IL）structure and its special diffusion behavior in aqueous solution.Functional ILs was used to regulate the IP process and the membrane structure,the influence of ILs on the membrane structure and membrane separation performance was further explored.The enhanced mechanism of ILs during water transport is revealed.This thesis mainly carries out the following research:（1）We revisited polyethylene imine（PEI）and cyanuric chloride（CC）as the pristine acid-resistant membrane.Then,1-aminopropyl-3-methylimidazolium chloride（[AEMIm][Cl]）and1-aminopropyl-3-methylimidazolium bis（（trifluoromethyl）sulfonyl）imide（[AEMIm][Tf₂N]）ILs were used to regulate the interfacial polymerization process,and AEMIC-PEI-CC and AEMIT-PEI-CC were prepared.SEM,XPS and Zeta potential were used to analyze the surface morphology and properties of the membrane.The results showed that ILs was successfully added to the membrane,the membrane surface was smooth,membrane thickness was reduced,and the positive charge of the surface was enhanced.Secondly,the effects of the type and amount of IL on the membrane separation performance were studied.[AEMIm][Cl]shows better regulation effect than[AEMIm][Tf₂N],which is related to the size and hydrophilicity of ILs anions.Compared with[Tf₂N]^-,[Cl]^-has smaller ionic volume and excellent hydrophilicity.In order to further explore the regulation of ILs on IP process,molecular dynamics（MD）was used to simulate the diffusion behavior of ILs and PEI in aqueous solution,the pore size distribution and porosity of the membrane.It was proposed that ILs could provide an orderly channel for the transport of PEI in the interfacial polymerization process to prepare membranes with smaller pore size and higher porosity.Finally,the membrane permeance regulated by[AEMIm][Cl]is up to 79.1 L m^-2 h^-1 bar^-1,1.36 times that of the pristine PEI-CC membrane,and the Y³⁺rejection is 97.5%.Meanwhile,after soaking in HCl solution with p H=1 for 30 days,the membrane separation performance remained stable and showed excellent long-term acid resistance.（2）Based on the above mentioned result,that is the membrane permeance was improved by[AEMIm][Cl],we further use[AEMIm][Cl]to regulate the nanofiltration membrane structure.Herein,a novel metal-ionic liquid（Zn-IL）coordination compound was synthesized by in situ growth to improve the permeance of PA nanofiltration membranes,in which using[AEMIm][Cl]as a ligand and react with Zn（NO₃）₂.The Zn-IL/PIP-TMC membrane was prepared by using PA layer to cover the Zn-IL complex,in which PA layer was synthesiszed by piperazine（PIP）and trimesoyl chloride（TMC）.Firstly,XPS,FTIR and XRD were used to analyze The Zn-IL nanoparticles.The results show that[AEMIm][Cl]successfully coordinated with Zn（NO₃）₂.Zn-IL is a spherical nanometer particle with excellent water absorption.Furthermore,the morphology and properties of Zn-IL/PIP-TMC membrane was analyzed.The results showed that Zn-IL/PIP-TMC membrane showed a smooth surface morphology,increasing membrane thickness and decreasing surface potential after Zn-IL was added.Secondly,the influence of Zn（NO₃）₂ concentration on membrane separation performance was investigated.With the increase of Zn（NO₃）₂concentration,the permeance first increase and then decreased,which attributed to the increased resistance of water transport by excessive nanoparticles.Meanwhile,five different Zn-IL composite structure regulatory membranes were prepared by changing the preparation sequence,among which Zn-IL/PIP-TMC membrane showed excellent performance.Low-field NMR was used to measure the state of water in the membrane,it is revealed that Zn-IL reduces the content of bound water and increases the content of free water in the membrane,thus achieving ultra-fast water transport.Finally,the permeance of Zn-IL/PIP-TMC membrane was up to 26.5 L m^-2 h^-1 bar^-1,which was 3 times that of the pristine membrane.At the same time,the Zn-IL/PIP-TMC membrane also showed good long-term stability.