Study On Preparation And Performance Of Zwitterionic Nanfiltration Membrane

Nanofiltration membrane is a kind of pressure-driven membrane,whose pore size is between ultrafiltration membrane and reverse osmosis membrane.The separation mechanism of nanofiltration membrane is the combination of Donnan effect and steric hindrance effect.Nanofiltration membrane can be applied in the preparation of domestic water,the treatment of wastewater and the separation in the field of food and medicine.The separation efficiency can be enhanced in the process of application when nanofiltration membrane possesses high flux and anti-fouling property.Therefore,it has been widely researched to construct nanofiltration membrane with high flux and anti-fouling property.In this work,based on the design of the molecular structure of nanofiltration membranes,a series of zwitterionic membranes were constructed and prepared through interfacial polymerization and surface modification in order to realize the properties of high-flux and anti-fouling.Firstly,interfacial polymerization was conducted via the incorporation of zwitterionic multi-walled carbon nanotubes（AEPPS-PD@MWCNTs）with amino groups to prepare high-flux hybrid nanofiltration membranes.Subsequently,in order to enhance the anti-fouling property of nanofiltration membranes,neutrally charged zwitterionic nanofiltration membranes were obtained via incorporating N,N-diethylethylenediamine（DEEDA）in the process of interfacial polymerization and then using p-xylylene dichloride（XDC）as cross-linker.Then,1,3-propanesultone（1,3-PS）was used as zwitterionic material to fabricate high-flux and anti-fouling nanofiltration membranes containing sulfobetaine.Finally,in order to exert the properties and enhance the content of zwitterions,controllable surface initiated-atom transfer radical polymerization was used to prepare zwitterionic nanofiltration membranes with tunable thickness of separation layer.（1）Fabrication of AEPPS-PD@MWCNTs/polyamide hybrid nanofiltration membranes via interfacial polymerization.AEPPS-PD@MWCNTs was obtained via co-deposition method and it was incorporated into interfacial polymerization system to fabricate negatively charged hybrid membranes.When the concentration of AEPPS-PD@MWCNTs was 3 wt%of the concentration of piperazine,the membrane（Hybrid M3）possessed optimal performance,with water permeance of 12.7 L.m^-2.h^-1.bar^-1 and Na₂SO₄ rejection of98.0%.Hybrid M3 showed high concentration efficiency of the mixed solution（Na₂SO₄/Na Cl or PEG400/Na Cl）.（2）Fabrication of neutrally charged zwitterionic nanofiltration membranes via the combination of interfacial polymerization and surface modification.PA-DEEDA with tertiary amine groups were obtained via interfacial polymerization.Subsequently,XDC was used to modify PA-DEEDA-0.5 and the neutrally charged zwitterionic membranes were obtained.When the concentration of XDC was 1.0 wt%,the permeance of the membrane was 9.1 L.m^-2.h^-1.bar^-1,with high Na₂SO₄（91.3%）and Ca Cl₂（90.8%）rejection.In addition,hydrophilic zwitterionic membrane showed good anti-fouling property.The flux recovery ratios to bovine serum albumin,lysozyme and sodium alginate were 95.0%,94.0%and 94.0%,respectively.（3）Fabrication of zwitterionic nanofiltration membranes containing sulfobetaine via the combination of interfacial polymerization and surface modification.Interfacial polymerization was conducted to fabricate PA-DEEDA with tertiary amine groups.Subsequently,zwitterionic nanofiltration membranes（PA-ZWI）containing sulfobetaine were prepared via the ring-opening reaction with 1,3-PS.The zwitterionic nanofiltration membrane showed optimal performance when the reaction time was 6 h.PA-ZWI-6h showed water permeance of 14.6 L.m^-2.h^-1.bar^-1 and Na₂SO₄rejection of 96.6%.Meanwhile,PA-ZWI-6h exhibited high erythromycin（ERY）rejection and low Na Cl rejection,which could separate mixed solution of ERY/Na Cl efficiently.Furthermore,hydrophilic PA-ZWI-6h showed good anti-fouling property.The flux recovery ratios to bovine serum albumin,lysozyme and sodium alginate were 96.2%,95.9%and 95.1%,respectively.（4）Fabrication of nanofiltration membranes grafted with zwitterions via the combination of interfacial polymerization and surface modification.Interfacial polymerization was conducted to fabricate polyamide membranes incorporated with 2-bromopropionyl bromide uniformly.Subsequently,poly（sulfobetaine methacrylate）were grafted on the surface of membranes via surface initiated-atom transfer radical polymerization method to prepare zwitterionic membranes.The thickness of the zwitterionic layer could be adjusted by the polymerization time.When the polymerization time was 0.2 h,the zwitterionic membrane showed water permeance of 16.8 L.m^-2.h^-1.bar^-1 and Na₂SO₄ rejection higher than 97.0%.When the polymerization time was 1 h,the membrane exhibited low Na Cl rejection（17.2%）,which showed high separation efficiency to mixed solution of Na Cl/raffinose.The anti-fouling properties of zwitterionic membranes to single pollutant,single pollutant/salt and mixed pollutants systems in water were also investigated.From the results,zwitterionic membranes exhibited good anti-fouling properties to all the systems due to the incorporation of polyzwitterions.The hydrophilic polyzwitterions could combine water molecules and form hydration layer on the surface of the membranes,which were beneficial to the enhancement of anti-fouling property.In conclusion,this work focused on the fabrication of high-flux and anti-fouling membranes.The relationships between the molecular structures,preparing methods and performances of the membranes were investigated.High-flux and anti-fouling zwitterionic membranes without sacrificing the selectivity were obtained via constructing the hydrophilic surfaces.This work provided a guidance to fabricate zwitterionic membranes with high nanofiltration performance.