Study On Preparation And Properties Of Nanofiltration Membranes With Adjustable Pore Size

In recent years,the non-standard discharge of wastewater leads to the deterioration of water ecological environment,which aggravates the shortage of water resources.At present,the use of porous functional membrane for wastewater treatment and resource recovery is the general trend in the field of water treatment.The molecular weight cut-off range of nanofiltration membrane is 200～1000 Da.The surface of membrane is usually rich in charge,which has excellent separation effect for multivalent ions and small molecular active substances.All above advantages can make wastewater treatment move towards the direction of green and sustainable development.At present,the pore size of commercial nanofiltration membrane widely used in the field of water treatment is relatively single,the hydration radius of separated substances and the pore size of membrane can not be matched properly.The rejection and permeace are mutually restricted,which can cause many problems,such as low separation efficiency.The lack of adjustable pore size of membrane greatly limits the application of nanofiltration membrane in various fields.It is very important to adjust the pore structure of the composite nanofiltration membrane to obtain a certain separation accuracy to meet the separation requirements of different kinds of substances.The PEI/TMC membrane was prepared by interfacial polymerization.After optimizing the reaction conditions,the permeance of the composite nanofiltration membrane was 12.01 L m^-2h^-1bar^-1,and the rejection of Mg Cl₂ was 92.83%.On this basis,three kinds of polyamide composite nanofiltration membranes with excellent separation performance were obtained by controlling the pore size and pore size distribution through molecular design.The composite nanofiltration membranes were characterized by FTIR-ATR,XPS,SEM,hydrophilicity,zeta potential,pore size distribution,separation performance,anti pollution performance and long-term stability.By coating the middle layer of tannic acid between PAN and polyamide separation layer,the rejection of TA-PEI/TMC membrane was still maintained at the original level and the permeance increased by 46.63%.The membrane pore diameter is expanded from0.56 nm to 0.67 nm.Another way was to introduce third monomer into the separation layer to adjust the pore structure of the membrane.The PEI-PIP/TMC membrane was obtained by introducing small molecule piperazine into the separation layer.The pure water permeance of the membrane was as high as 23.70 L m^-2h^-1bar^-1,and it showed high rejections for dyes.The dense PEI/TMC-TPC membrane can be prepared by introducing terephthaloyl chloride.The order of heavy metal ion rejection was as follows:Cu²⁺（99.37%）>Ni²⁺（98.04%）>Pb²⁺（97.23%）>Cd²⁺（96.54%）.The modified three kinds of composite nanofiltration membranes had good anti-fouling property to natural organic pollutant humic acid.The long-term stability test was carried out to explore the stable separation performance.In addition,TA-PEI/TMC nanofiltration membrane was used to separate different antibiotics,which exhibited excellent separation performance.Through the research,it was found that the introduction of the middle layer or the third monomer as the structural regulator in the process of interfacial polymerization can effectively adjust the pore structure of polyamide nanofiltration membrane to improve its separation performance,which provided direction for large-scale production of high-performance polyamide nanofiltration membrane.