The Regulation Of Interfacial Polymerization And Performance Improvement Of Thin Film Composite Nanofiltration Membranes

In recent years,nanofiltration membranes have been widely used in drinking water purification,brackish water desalination,and wastewater recovery/reuse.Commercial nanofiltration membranes are mostly thin film composite（TFC）structures,consisting of a selective layer and a porous support layer.The selective layer is formed on the interface of oil-water,wherein water phase monomers（such as piperazine）polymerized with organic phase monomers（such as trimesoyl chloride）,and it primarily determines the separation performance of the membrane;the substrate is usually ultrafiltration/microfiltration membrane,which mainly plays the role of mechanical support.Therefore,the interfacial polymerization process is the key to determining the structure,morphology and performance of the composite membrane.In this thesis,the introduction of an interlayer and the employment of macrocyclic Noria-assisted support-free interfacial polymerization were designed to control the interfacial polymerization process for the purpose of achieving high-performance nanofiltration membranes.This thesis is divided into four chapters:The first chapter is the introduction.First,it briefly introduces nanofiltration membrane,then mainly summarizes the research progress of nanofiltration membrane,and finally puts forward the research ideas and main work of this thesis.In the second chapter,water-soluble PVA（wsPVA）fibers were firstly loaded on a polysulfone ultrafiltration substrate as the sacrificial template interlayer,and a TFC nanofiltration membrane was prepared.The effect of wsPVA loadings on the membrane properties and morphologies were studied.Furthermore,the wsPVA was dissolved in 90℃water,and the properties and morphologies of membrane were also investigated after removing the interlayer.The hydrogen bonding between wsPVA and PIP could effectively regulate the interfacial polymerization;the results show that increasing of wsPVA loading,membrane surface changes from spotty to stripe and finally to crumples and membrane thickness decreases,the membrane flux increases to 63.1 L/m²·h,and salt rejection remains at a high level.After removing the interlayer,the membrane surface morphology does not change significantly,but additional nanovoids appear in membrane structure,the water flux further increases to 83.5 L/m²·h.The membrane shows negative charged and has excellent rejection of different dyes（CR,MB,RB19,VB）（>98%）,and also maintains excellent stability during long-term operation.In the third chapter,Noria,a macrocyclic molecule,was used to assist support-free interfacial polymerization via Noria-PIP host-guest chemistry and polyphenol chemistry to prepare freestanding nanofilms,then those nanofilms were transferred to various substrates construct TFC nanofiltration membranes.The host-guest chemistry of Noria and PIP was firstly determined,the effects of C_Noria/C_PIP,the total concentration of Noria+PIP and the reaction time on the performance of nanofiltration membranes was subsequently studied.Focused on the impact of Noria on the adhesion between PA layer and substrate.Support-free interfacial polymerization could occur at a low monomer concentration,and the host-guest chemistry and hydrogen bond interaction between Noria and PIP can effectively regulate this process.At the same time,Noria intrinsic polyphenol adhesion contributes to the formation of a stable TFC nanofiltration membrane.By optimizing the PA layer and the substrate respectively,varieties of TFC membranes with excellent comprehensive performance can be obtained.For example,the water flux of Noria-PA/PAN membrane is as high as 43.0 L/m²·h·bar and the rejection of Na₂SO₄is 95.3%.Noria-PA/PP membrane can be used for the permeation of polar and non-polar solvent.In addition,the prepared TFC membrane has excellent pollution resistance and stability.The fourth chapter is the summary and outlook of the thesis.We focus on the principal problems of state-of-art nanofiltration membranes such as low permeability,“trade-off”effect between permeability and selectivity.Through rational design,the interfacial polymerization process is effectively controlled and advanced nanofiltration membrane is finally obtained.This work sheds light on the development of high-performance composite nanofiltration membranes.