Preparation Of High Performance Nanofiltration Membrane Based On Porous Polymer

Nanofiltration technology is widely used in purification and separation field.Its separation performance mainly depends on the thickness of selective layer,hydrophilicity,roughness and pore structure.The key of nanofiltration technology lies in the development of nanofiltration membrane materials.Due to the trade-off effect of flux and rejection,the application of traditional nanofiltration membrane in water treatment is greatly limited.In this paper,the preparation of high-performance nano composite nanofiltration membrane is the research direction.Through the synthesis and design of new porous polymer,the high-performance nanofiltration membrane with high flux,controllable pore size adjustment and size gradient design is realized.On the one hand,Covalent organic framework（COFs）films were prepared on porous polysulfone（PSf）substrates by interfacial polymerization.Specifically,A thin and stable TpBd COFs selective layer of keto-enol tautomerism,or TpBdMe COFs cortex of azine-enol keto tautomerism,was prepared by in-situ interfacial polymerization on PSf porous substrate with trialdehyde phloroglucinol（Tp）and benzidine（Bd）or melamine（Me）as assembly units.The results showed that the permeability of TpBdMe/PSf membrane was 62.2 L·m^-2·h^-1·bar^-1,which was about 1.9 times of that of TpBd/PSf membrane,and the TpBd/PSf and TpBdMe/PSf membranes can be effectively used for dye separation,and the rejection of congo red was over 99.0%.The effects of monomer type,monomer concentration and reaction time on the properties of COFs were investigated.Through the analysis of the mechanism of COFs membrane rejection,it is found that the size screening effect and electrostatic repulsion effect are the main factors to control the dye molecule rejection.In addition,TpBd/PSf and TpBdMe/PSf membranes have good anti fouling performance,chemical stability and thermal stability.On the other hand,metal-induced microporous polymer（MMP）with water stability was synthesized by using polyethyleneimine（PEI）as amine rich linear polymer,copper acetate as divalent metal ion donor,and 4-chloro-isophthalic acid as halocarboxylic acid linker.MMP-3 particle was synthesized by polymer oriented chemical synthesis（PDCS）.The average pore size of MMP-3 particle was 0.63 nm,and nano size was 25-50 nm.The PA-MMP-3/PSf nanofiltration membrane was obtained by loading water-stable MMP-3 particle into the polyamide（PA）layer by blending.MMP-3 particle is rich in amino groups,which can react with trimesoyl chloride（TMC）in the process of interfacial polymerization to enhance the interfacial compatibility.At the same time,the high porosity of MMP-3 particle provided water transport channel.Therefore,the water permeability of PA-MMP-3/PSf membrane was 15 L·m^-2·h^-1·bar^-1,2 times that of PA/PSf membrane.However,the rejection of Na₂SO₄ and MgSO₄ remained at a high level（～94%）,while the rejection of NaCl was about 20%,which had a significant salt separation effect.