Preparation,Regulation And Its Separation Performance Of Graphene Oxide-Polyethylenimine Composite Ultrafiltration Membrane

Water is the most precious resource on earth,which is becoming scare and polluted.To address the challenge of lack of safe and adequate water,it is of great importance for developing sustainable technology to increase the supply of water resources.Pressure-driven membrane separation technology has been widely used in the field of seawater desalination,treatment of drinking water and micro-pollutants removal from water.In this dissertation,the characteristics,fabrication methods and application in water treatment of different kind of membrane materials were systemically summarized.In view of the trade-off between membrane permeability and selectivity,as well as the low response to external environment,a series of graphene oxide-polyethylenimine composite ultrafiltration membrane with different surface properties and internal structures were constructed.First,the effects of surface properties and internal structure on the separation performance of protein,bacteria,organic macromolecules and nanoparticles were systematiclly studied.Thereafetr the interaction mechanism bteween pollutants and membrane interface was discussed,and the structure-property relationship between membrane surface properties and separation performance was illustrated.The results provide new ideas for the design and construction of graphene oxide based membrane in water treatment.The main conclusions and innovations of the study are as follows:(1)A novel additive,GO-PEI,bearing a positive charge and hydrophilic nature was prepared by polyethylenimine covalent grafting with graphene oxide,foll wed by blending with polyethersulfone to fabricate the graphene containing nanocomposite membranes(NCMs).The strong ?-? interaction between benzene ring of PES and the aromatic ring of the GO-PEI contribute to the uniform dispersion of GO-PEI without leaching.The addition of GO-PEI can not only improve the hydrophilicity of the membrane surface,but also make the surface charge change to positive,which realizes the ordered regulation of urface properties of NCM.In addition,the addition of GO-PEI effectively regulates the internal structure of NCM which significantly increases the water flux of NCM.To filter charged proteins,the designed NCM exhibited a high flux while maintaining its high retention rate,breaking the restriction between permeability and selectivity.At the same time,the synergy between the hydrophilicity and the charged functional groups contribute to form a dense hydration layer on the NCM surface,which exhibits excellent antifouling performance.The above results indicate that the surface properties and internal structure of NCM can be regulated by using the GO-PEI as additive,which demonstrate potential for high performance pollutant removal in water treatments process.(2)A pH-responsive graphene oxide membranes(GPM)was developed by alternative deposition of negatively charged graphene oxide and positively charged polyethylenimine(PEI),in a layer-by-layer manner.The potential sturcture alteration of GPM in pH range from 3 to 11 was studied through AFM in liquids.The results of chemical composition and internal structure of GPM indicated that the PEI molecules not only cross-linked the GO sheets through amide bond to ensure the membrane stability in acid and base environment,but also reversibly altered the internal structure of GPM according to the surrounding pH that the gates of GPM were widened with the decrease in pH of the feed and vice-versa because the PEI chains,as the spacers,will extend at low pH driven by the amine group protonation.Since the conformation change of PEI molecule is reversible,the internal structure change of GPM is also reversible.In the filtration tests,the permeate flux of GPM was decreased with the increase of feed pH,and it was reversible and exhibits excellent cycle-ability.The filtration experiment further indicated that the flux change of GPM was caused by the pore size change,so adjusment of the feed pH can continuously regulate the pore of GPM,which can be used for separation of Polyvinylpyrrolidone(PVP)and Polyethylene oxide(PEO)mixtures by shifting pH of the mixture from 3 to 11 during filtration.The pH-responsive GPM may control the penetration of any molecules with cetain size by simply adjusting pH,which indicate great potential for advanced molecular separation in the field of water purification.