Anti-fouling Separation Membrane Based On Poly(aryl Ether Sulfone)containing Piperidine Propanesulfonate Zwitterion

Membrane separation technology is an efficient and energy-saving separation method,which has a wide range of applications in water treatment,food,medicine,environmental protection,chemical industry,metallurgy and other fields.However,as the core component of the membrane separation technology,separation membranes still have problems such as membrane fouling,membrane corrosion,and"trade-off"effects.Among them,the membrane fouling is widespread,complicated,and of a serious impact on the separation performance,which has become the most important factor in the degradation of membrane performance.Designing a novel anti-fouling membrane materials or modification processes is considered to be the most effective way to solve the problem of membrane fouling.However,most of the innovative anti-fouling membrane modification studies reported will increase the preparation steps of the separation membrane and increase the production cost.It is difficult to conclude a universally applicable modification strategy which satisfies different separation scales at the same time,so it does not have practical application potential.In this regard,this article proposes a zwitterionic modification method to improve the anti-pollution performance,by synthesizing a tertiary amine bisphenol precursor,and applying it to both non-solvent induced phase separation（NIPS）and interfacial polymerization（IP）to fabricate new ultrafiltration（UF）and nanofiltration（NF）.In addition,this method does not require additional post-processing steps when the membrane is prepared,which endows it with practical application potential.The first part of this work focuses on introducing zwitterionic groups into UF through the NIPS.First,a method for synthesizing a bisphenol monomer containing a tertiary amine structure（N-methyl-4,4-diphenol piperidine,NMPP）was introduced,and zwitterionic polymers were prepared by copolymerization and grafting（PAES-Z-x）.Subsequently,the copolymerization ratio was optimized:PAES-Z-x whose copolymerization ratio is less than 20%were suitable for the preparation of UF.Finally,by NIPS,PAES-Zs were directly prepared into ultrafiltration containing zwitterionic functional groups（UF-Z-x）.As zwitterionic groups increased from 5%to 20%,the hydrophilicity of the UF-Z-x increased,and the water contact angle decreased from78.3°to 71.6°,which was conducive to the improvement of anti-pollution performance.At the same time,the morphology of the membrane changed:the size of the finger holes was significantly increased.The separation performance test showed that when less than 15%zwitterionic groups were introduced into the polymer,the flux of pure water increased with the increase of the ratio of zwitterionic groups,and the flux began to decrease when it exceeded 15%.The rejection of bovine serum albumin（BSA）remained over 97%.The anti-fouling performance was improved with the introduction of zwitterionic groups,the normalized flux after fouling increased from 32%to 38%,and the normalized flux after cleaning increased from 60%to 83%.In the second part of the work,the introduction of zwitterionic groups into NF by IP was developed.Using the same precursor NMPP,a bisphenol monomer containing zwitterionic group（NMPP-Z）was synthesized.After optimizing the experimental conditions of IP,different proportions of NMPP-Z were introduced into IP,and a series of polyester nanofiltration containing zwitterionic groups（PENF-Z-x）were prepared.It’s shown that with the increase of the zwitterionic groups,the hydrophilicity of the membrane was improved,and the static water contact angle reduced from 77.8°to 59.1°,which was conducive to the improvement of anti-fouling performance.The functional layer had more folds,and the increased surface area was conducive to the improvement of permeability.The separation performance test showed that the flux of pure water increased with the increase of the zwitterionic groups,but the rejection of Na₂SO₄decreased.Considering both water flux and rejection,PENF-Z-4 had the best separation performance.Compared with PENF-0,membrane without zwitterionic group,the anti-fouling performance of PENF-Z-4 is significantly improved.The normalized flux after fouling was increased from 7.5%to 33.8%,and the normalized flux after cleaning was increased from 59.5%to 68.8%.In summary,in the two parts of the work above,through one precursor NMPP,the zwitterionic functional groups were successfully introduced,and the separation scale conversion from ultrafiltration to nanofiltration was achieved through the regulation of the interface structure.It shows that the zwitterionic groups can significantly improve the anti-fouling performance of the separation membrane.This modification strategy does not require additional processing steps after membrane has fabricated,which has practical application potential.