Study On Preparation And Properties Of Positively Charged Nanofiltration Membrane By Polyethyleneimine Grafting

Nanofiltration membranes fill in the blanks of reverse osmosis and ultrafiltration membranes with are often used to separate different valence and charged molecules.With the development of industry and heavy industry,the pollution problem is becoming more and more serious,especially the pollution of dye and heavy metal ions.This paper aims to prepare a new type of charged positive electric nanofiltration membrane for the removal of heavy metal salt and dye pollution in water.In this work,we prepared the nanofiltration membrane in two steps.Firstly,the original nanofiltration membrane was prepared by conventional interfacial polymerization using polysulfone?PSF?ultrafiltration membrane as the base membrane,piperazine and diaminodipropyl amine as the aqueous monomers,and tribenzoyl chloride?TMC?as the oil-phase monomers.Finally,2-chloro-1-methyl iodide pyridine?CMPI?and sodium hydroxide were used as active agents,and polyethylenimine?PEI?was grafted onto the surface of the original nanofiltration membrane in the form of covalent bond by surface grafting method.Fourier transform infrared spectroscopy?ATR-FTIR?,X-ray photoelectron spectroscopy?XPS?and scanning electron microscopy?SEM?were used to characterize the prepared films.The charge analyzer,or Zeta potential evaluator,tests the surface chargeability.The performance of heavy metal salt and inorganic salt separation,dye removal and molecular weight retention were tested by cross flow filtration in a laboratory cell.X-ray photoelectron spectroscopy?XPS?and Fourier transform infrared spectroscopy?ATR-FTIR?verified the successful preparation of the positively charged nanofiltration membrane.Scanning electron microscopy?SEM?images showed the changes in the surface structure of the grafted membrane,and Zeta potentiometer test showed that the grafted membrane surface was positively charged.Through the evaluation of the membrane performance,it was found that the membrane had a high removal rate and separation performance for heavy metal salts and inorganic salts,such as CuCl₂:96%,NiCl₂:95.8%,CrCl₃:98.0%,MgCl₂:97.1%,CaCl₂:96.8%,Na₂SO₄:83.5%,MgSO₄:87.3%,NaCl:49%,LiCl:32%and so on.The films were also evaluated with different charge dyes,such as neutral red,semixylenol orange,golden lotus orange 0 and Victoria blue B.The results showed that the order of removal rates of the prepared films was Victoria blue B>?99.2%?>semixylene orange?99%?>golden lotus orange 0?98.3%?>neutral red?98.2%?.It can be seen that the membrane has a high interception rate to the pollutant dye in water.