Modification And Antifouling Of Polyethersulfone (PES) Membrane

As the fast developing of economic society, environment was being polluted anddamaged terribly. This phenomena slacks the continuable development of the wholesociety. Membrane separation technology as an advanced water treatment technology,is playing a more and more important role in environmental protection. However, inpractical application, the polymer membranes are easy to be polluted, which seriouslyaffects the membrane performance. As to this problem, in this paper, the PESmembrane was modified by blending and surface coating methods.In the experiment process, ZnO/PES composite membrane was prepared byphase inversion method. By comparing with the PES membrane, the properties ofZnO/PES composite membrane were investigated. The Langmuir-Blodgett (LB)technique was learnt. The phospholipid membranes were prepared by LB technique.The effects of Cu2+on phospholipid membranes were investigated. Layer-by-layerself-assembly (LBL) developed from LB technique was used to modify PESmembrane. The properties of prepared polyelectrolyte/PES composite membraneswere investigated.With ZnO as an additive, a series of ZnO/PES composite membranes wereprepared by a phase-inversion method. Experimental results show that, with theincreasing of addition weight of ZnO the contact angle decreases and the thermodecomposition temperature increases. When the addition of ZnO is0.0500g/g, thewater contact angle is54.86°and the thermal decomposition tempureture is improvedby94.4℃.The porosity of ZnO/PES hybrid membrane is improved by adding ZnO.The flux of ZnO/PES composite membrane reached to125.40kg/m2h, which exhibitsan improvement of254%relative to that of the PES membrane, whereas the rejectionchanges little. After90min of continuous filtrating of BSA solution (1g/L, pH=7.4), the decreased flux ratio of the ZnO/PES membrane (0.0375g/g ZnO added) is only7.8%, which implies the antifouling property is significantly improved relative to theantifouling property of the PES membrane.The effects of Cu2+on phospholipid (DPPC, DPPG, DMPC and DMPG) at theair/water interface were studied by a Langmuir film balance. The results show thatCu2+ions interact strongly with the negatively charged DMPG. This interactionchanges the phase transition pressure from the LE (liquid-expanded) to the LC(liquid-condensed) state. The introduction of low concentration Cu2+leads to largelyincreased ionic strength, which causes to an expansion of the DMPG membrane.However, high concentration of Cu2+tends to lower pH. The decreased pH and thedirect binding between Cu2+and DMPG together induced a condensed effect onDMPG membrane. The phase transition pressure decreases with the increasingconcentration of Cu2+. The electrostatic repulsion drives DMPG to plant-branch shapedomains. While on the Cu2+solution, the electrostatic repulsion is largely weakened,and circular shape domains appear. Because of strong electrostatic repulsion, the finalmembrane on water subphase is less uniform than that on Cu2+solution subphase.The PES microfiltration membrane was modified by the layer by layerself-assembly (LBL) method. To obtain polyelectrolyte/PES composite membrane,29.2g/L NaCl as a support electrolyte solution, one layer ofdiallyldimethylammonium chloride (PDADMAC)/polystyrene sulfonate (PSS) wascoated onto the PES surface. The result shows that the surface of compositemembrane charges more negatively. The charge value is-35.02mV. The water contactangle decreased from59.86°for PES membrane to37.99°for the compositemembrane. The surface morphology shows that the surface of composite membrane issmoother, and the pore size distribution is more uniform. Filtrating of0.02g/L humicacid in120min, the decreased flux rate of PES membrane is39.4%, while thedecreased flux rate for the composite membrane is15.5%. The composite membraneshow higher antifouling ability.