Preparation And Characterization Of BPPO-Based Ultrafiltration Membranes And Anion Exchange Membranes

Membrane technology,with substantial merits such as high efficiency and low energy consumption,has attracted a great deal of interest for the purpose of relieving water shortage and developing new energy sources.In the field of pressure-driven membrane,ultrafiltration（UF）membrane can separate substances including macromolecular protein and colloid solution with size-sieving effect,and it has been widely applied in various areas.In the field of ion exchange membrane,anion exchange membrane（AEM）as an important part of alkaline fuel cell,can block fuel and transfer hydroxide ions.With the development of society and production,higher requirements are proposed for the performance of the membranes.In this work,we employed brominated poly（2,6-dimethyl-1,4-phenylene oxide）（BPPO）as membrane matrix,and performed structure design and preparation regulation taking advantage of the activity of brominated-methyl group,to obtain high-performance ultrafiltration membranes and anion exchange membranes.The dissertation could be divided into four chapters:The first chapter is the introduction,we made a brief overview mainly for ultrafiltration membrane and anion exchange membrane,and then introduced the preparation of BPPO-based ultrafiltration membrane and anion exchange membrane.Finally,the research idea of this dissertation was put forward.In the second chapter,inspired by natural Murray network from vascular plants,we develop hierarchical membranes via a straightforward yet robust strategy,using isocyanate as a muti-functional additive.The effects of toluene 2,4-diisocyanate（TDI）content and different kinds of isocyanate on the membrane structure and properties were systematically discussed.Furthermore,with the ability of isocyanate active functional groups to react with functional molecules（polyethylene imine PEI,polyvinyl alcohol PVA）in the coagulation bath,the membrane surface functionalization was synchronously triggered during the phase inversion process.The results showed that the CO₂ produced by isocyanate hydrolysis could perform as a pore-forming agent,and improved the porosity of the membrane.And hydrolysis-induced amine groups could react with bromine-methyl group of BPPO simultaneously,contributing to the cross-linking and correspondingly the mechanical strength of the membrane.The addition of TDI had a significant effect on the coagulation point and viscosity of the casting solution together with the phase inversion process,generating different morphologies and structures of the membranes.As the TDI content increased,the size of finger pore membrane grew up and the water flux gradually increased.When TDI content was 1.8 wt%,the maximum water flux reached to 218 L/m~2·h·bar,while maintaining high protein rejections.With further increase of TDI addition,the phase separation process was slowed down and spongy pores were formed,giving rise to a decreased water flux.Besides aromatic isocyanate of TDI,alicyclic and aliphatic isocyanates were also suitable for the system.Moreover,the flux of the membrane could be furtherly promoted to 334 L/m~2·h·bar via PEI synchronous surface functionalization,and the membrane also demonstrated an excellent anti-fouling ability（flux recovery rate of the membrane was as high as 97.9%,after BSA pollution followed by a simple cleaning）.The hydrophilicity and fouling-resistance capability of the membrane with PVA surface functionalization,were also improved significantly.In the third chapter,a series of anion exchange membranes containing rotaxanes were designed and constructed based on the host-guest interaction between N,N,N,N,N-pentamethyldiethyl triamine（PMDETA）and a macrocyclic molecule（Noria）.The influence of PMDETA and Noria content on membrane properties as well as the temperature on the ionic conductivity were investigated.The results showed that Noria’s hydrophilicity and water retention ability promoted the formation of microphase separation structure of QAPPO-Noria_x membrane,and provided a good water environment for hydroxide ion transport.Noria with a large rigid structure could reduce the stacking density of polymer main chains,expand the free volume for ion transport,reduce the transmission resistance of hydroxide ions,and finally improve the ionic conductivity of the membrane.The conductivity of QAPPO-Noria₁₅ membrane could achieve 0.15 S/cm at 80 ^oC.Meanwhile,Noria’s electron-rich nature and water-retaining ability helped to protect the ion-exchange group and improve the alkaline resistance of the membrane.After soaking 1 mol/L Na OH at 60 ^oC for 32 days,the ionic conductivity of QAPPO-Noria_1.5membrane could still remain at a high level.The fourth chapter is a summary of the whole work.A series of high performance ultrafiltration membranes were prepared by combining chemical reaction modification and phase inversion in one step.The structures and properties of ultrafiltration membranes were effectively controlled,and the separation performance was significantly improved.Furthermore,synchronous surface modification could also endow the membranes with excellent anti-fouling properties.To solve the problems such as low ionic conductivity and poor alkaline resistance of anion exchange membrane,rotaxane-incorporated anion exchange membranes with high performance were prepared.Our work paved a promising path for the development of BPPO-based ultrafiltration membranes and anion exchange membranes.