Preparation And Properties Of Grafted Heavy Metal Ion Imprinted Membrane

With the rapid development of industrialization and a large increase in population,environmental pollution is becoming more and more serious,especially the pollution of heavy metal ions.It has the characteristics of high toxicity,hard to degrade and easy to enrich,so the removal of heavy metal ions is imminent.Membrane separation is a new type of separation technique with simple operation,high efficiency and low cost.However,the general separation membrane can not achieve selective separation.The ion imprinted technology combined with membrane technology was applied to prepare the grafted heavy metal ion imprinted membrane,which effectively realized the selective separation of heavy metal ions.A new type of surface imprinting technique was made by grafting/crosslinking with ion imprinting,and the graft type ion imprinting membrane was prepared.In this paper,chloromethylation polysulfone asymmetric porous microfiltration membrane?CMPSF?was prepared by phase transformation method,using chloromethylated polysulfone as raw material,N,N-two methyl acetamide as reagents,and polyethylene glycol-400 as porogen.Then it was chemically modified with ethylenediamine to prepare an aminated polysulfone asymmetric porous microfiltration membrane?AMPSF?.The-NH₂/S₂O₈^2-surface initiating system consisting of the amino group on the surface of the amine-based polysulfone membrane and the initiator ammonium persulfate enables the polymerization of the monomeric sodium styrene sulfonate?SSS?on the surface of the membrane to obtain a asymmetric porous grafted membrane PSF-g-PSSS.The grafted membrane was characterized by Fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?and gravimetric method.The main factors influencing the graft polymerization werethoroughlyinvestigatedandthegraftingconditionswere optimized.Adsorption properties of four heavy metal ions,such as Cd²⁺,Cu²⁺,Zn²⁺and Pb²⁺,were investigated by static adsorption experiments.The effects of pH and temperature on the adsorption performance were also studied.The optimal adsorption conditions were determined.The experimental results show that in the-NH₂/S₂O₈^2-surface initiating system,the monomer SSS can be successfully grafted and polymerized on the surface of the membrane.With the increase of the amine group content on the surface of the AMPSF membrane,the degree of grafting also increases.The optimum conditions are as follows:the temperature is 70?,the concentration of ammonium persulfate is 0.4 wt%,and the reaction time is 18 h.Under this condition,the graft degree of polymer PSSS is the largest,which is 0.7mg/cm².With strong electrostatic interaction,the grafted membrane PSF-g-PSSS showed strong adsorption capacity for heavy metal ions Cd²⁺,Cu²⁺,Zn²⁺and Pb²⁺,and the best pH value for Cd²⁺and Cu²⁺adsorption was 5,the best pH value for Pb²⁺adsorption was 6,the best pH value for Zn²⁺adsorption is 4,the optimal temperature for Zn²⁺,Cd²⁺,Cu²⁺adsorption is 25?,and the optimal temperature for Pb²⁺ion adsorption is 30?.Based on the results of the above experiments,the-NH₂/S₂O₈^2-surface initiating system was constructed at the interface between the AMPSF membrane and the aqueous solution,and Cd²⁺and Zn²⁺were used as template ions,and N,N-methylenebisacrylamide?MBA?was used as crosslinking.Using the methods of grafting/crosslinking and ion-imprinting simultaneously,performing ion-implantation of Zn²⁺and Cd²⁺on the membrane surface,and then washing away the template ions to obtain Cd²⁺ion-imprinted membranes with grafting type?GIIM?and Zn²⁺ion-imprinted membranes with grafting type?GIIM?.The chemical structure of the imprinted membrane was characterized by Fourier transform infrared spectroscopy?FTIR?.The morphology of the imprinted membrane was characterized by scanning electron microscopy?SEM?and optical microscope?OM?.The main factors affecting the selection coefficient of imprinted membrane were further studied,and the imprinting conditions were optimized.Using static binding,competitive adsorption,separation and penetration,and other experimental methods,the identification selectivity and permeation separation performance of imprinted membranes for template ions were thoroughly investigated.The results showed that theion-imprintedmembraneswithgraftingtype?GIIM?hasgoodbinding affinity,recognition selectivity and osmotic separation for template ions.Compared with Pb²⁺and Zn²⁺,the selective coefficients of Cd²⁺for the imprinted membrane were 9.97 and 11.9,respectively.And compared with the reference ion Pb²⁺and Cd²⁺,select the coefficient of Zn²⁺ion imprinted membrane for Zn²⁺respectively.9.44 and 12.8.