Preparation And Dye/Salt Separation Performance Study Of Composite Membrane Based On Porous Organic Polymer

Dye wastewater from textile industry has seriously polluted the environment and harmed human health.Membrane-based water purification technology is becoming a promising energy-saving and environmentally friendly technology.It has shown great potential in the field of water purification and wastewater treatment due to its high separation efficiency,low energy consumption and environmental friendliness.Porous organic polymers（POPs）,as a kind of porous amorphous nanomaterials connected by covalent bonds,have attracted extensive attention due to their high specific surface area,adjustable pore structure and excellent structural stability.The in-situ growth method has become one of the most effective methods for preparing thin-film composite membrane due to its simple operation and easy control.A continuous film with excellent performance membrane can be grown on the surface of the porous substrate via in-situ growth method.Therefore,this paper aims to uniformly grow a layer of porous organic polymer active layer with excellent performance on the surface of the support layer by in-situ growth method,and apply it to the field of dye wastewater treatment,in order to obtain membrane materials with high permeability and high rejection rate.The main research contents of the thesis are as follws:（1）Study on the preparation of HAzo-POP-based composite membrane and separation performance of dye/salt mixtureo-hydroxy azo-hierarchical porous organic polymer（HAzo-POP）have evinced huge potential in the field of membrane-based separations due to their impressive surface areas,high mesopore ratio,superior chemical stability,and catalytic abilities.For the first time,an HAzo-POP thin film was in-situ generated atop the polyacrylonitrile membrane support via diazo-coupling reaction under mild conditions.The analyses of SEM,FT-IR,XPS and AFM demonstrated the successful formation of a coherent,thin HAzo-POP film.Zeta potential and water contact angle measurements verified that the resultant POP composite membrane was negatively charged and hydrophilic（water contact angle=48^o）due to the abundance of hydroxyl groups.The roles of synthesis parameters（e.g.,the reaction time and the solution p H）in membrane structure and separation performance were studied in detail.The best-performing composite membrane presented a high pure water permeability(97.5 L m^-2 h^-1 bar^-1),high dye retentions(R_CR=99.6%,R_DR=98%,R_MB=98.8%and R_RB=95.4%),and low divalent salt retention（<15.0%）,demonstrating a high potential in separation of dye/salt mixtures.In addition,the thus-obtained HAzo-POP composite membrane was utilized as the catalyst to yield propylene carbonate in aqueous solution with a high conversion rate of 85%at room temperature.This study is expected to provide a useful guideline of in-situ formation of HAzo-POP-based thin film composite membrane for water purification and catalysis.（2）Research on the preparation of BILP-101x-based composite membrane and separation performance of dye/salt mixtureSince the thickness of the membrane is inversely proportional to the permeability of the membrane,in order to further improve the water permeability of the solution,another new type of porous organic polymer was introduced to reduce the thickness of the active layer of the composite membrane while maintaining a high retention.This article introduces a new porous organic polymer.Benzimidazole-linked polymers（BILP-101x）are amorphous powders with remarkable thermal and chemical stabilities.BILP-101x have narrower pores because of their highly cross-linked interpenetrated networks,rendering them more suitable for the separation of small molecules.Herein,a facile interfacial polymerization method to prepare BILP-101x composite membrane with a thickness of～95 nm has been reported.BILP-101x are formed by the chemical reaction of two different monomers and further characterized by several techniques（FI-IR,SEM,AFM,XRD,and XPS）.The results of SEM,XRD and FR-IR showed that BILP-101x composite membrane was successfully fabricated.It was found that the hydrophilicity of BILP-101x/HPAN composite membrane by water contact angles.Zeta potentials in a wide range of p H values are negative values.Due to the ultrathin nature and electronegative,the membrane exhibited a high pure water permeability(～255 L m^-2 h^-1 bar^-1),excellent rejection of dye molecules（>99%,Congo red）and low divalent salt retention（<10%）,demonstrating a high potential in separation of dye/salt mixtures.Meanwhile,the BILP-101x/HPAN composite membrane exhibited a preferable antibacterial property owing to the imidazole bonds in the BILP framework.