| The lack of clean water and the pollution of limited freshwater resource have become a great challenge all over the world resulting from the fast economics growing demands and rapid population growth.The research of carbon nanomaterials and nanotechnologies has provided possibilities for the preparation of nanofiltration membranes with high flux,high rejections and high structural stability.Recently,graphene oxide(GO)has been widely used as membrane candidate upon nanofiltration process due to its ultrathin 2D structure,abundant functional groups and excellent tolerance to organic solvents or under harsh chemical environment.In this thesis,electrospraying technique was used to prepare large-area GO membranes.Furthermore,sandwich and multilayer structured GO membranes were designed and prepared using electrospraying combined with electrospinning technique,which greatly enhanced the structural stability.In order to improve the nanofiltration performance of GO membranes,GO membranes with broadening interlayer spacing were prepared using nanoparticles and COF-LZU1 as intercalation materials.Their nanofiltration performance,structural stability and anti-fouling properties were investigated.Firstly,in view of the problems existing in the preparation of GO membranes by the traditional liquid-phase formation techniques,this work innovatively used electrospraying technique to prepare high performance and large-area GO membranes,and systematically investigated their nanofiltration performance and anti-fouling properties.The GO(120)nanofiltration membrane demonstrates a high water flux of 11.13 L m-2 h-1 bar-1,and high organic dyes rejection rate(>98%)due to physical size sieving and electrostatic interaction.Furthermore,the GO membranes demonstrate excellent anti-fouling property and high flux recovery ratio by DI water washing.Secondly,in view of the swelling problem of GO membranes,a high structural stability GO/nylon 6 nanofiber multilayer membrane was designed and prepared using electrospraying combined with electrospinning technique.The stability of this membrane is enhanced due to the tightly locked structure by nylon 6 nanofibers network.This novel nanofiltration membrane demonstrates a pure water flux up to 9.55 L m-2 h-1 bar-1,while keeping high organic dye rejection rate(>95%for Methylene blue,and>99%for Methyl orange).Thirdly,in view of the low water/solvent permeate flux owing to the tortuous and long route within the GO layers,sandwich structured nanoparticles intercalated GO membranes with broadening interlayer spacing were prepared using electrospraying combined with electrospinning technique.As expected,the interlayer spacing is increased with the introduce of TiO2 nanoparticles,and the water flux is up to 13.77 L m-2 h-1 bar-1,which increased by 80.7%than that of the pure GO membrane(with the same GO wight)without sacrificing the high rejection rate for organic dyes(>99%).Furthermore,the sandwich structure enhances the structural stability of GO membranes.Finally,in view of the limited enhancement of permeate flux owing to the intrinsic impermeability of intercalation materials,a hierarchically nanostructured GO membrane was designed and prepared using COF-LZU1 as intercalation material.The superhydrophilic COF-LZU1 not only increases the interlay spacing of GO membranes,but also provides additional fast transport nanochannels for water and organic solvents molecules in GO matrix.The hierarchically nanostructured GO/COF-LZU1 hybrid membranes demonstrate excellent water(59 L m-2 h-1 bar-1),ethanol(51 L m-2 h-1 bar-1)permeate flux and superior organic dyes rejection rates(above 99%)both in aqueous and organic solvents.Additionally,intercalation of COF-LZU1 reduces the GO matrix swelling while enhances membrane structural stability.This work provides a new fabrication method for the design of high structural stability GO based nanofiltration membrane,and also gives a comprehensive understanding of permeate and rejection mechanism of GO based membrane. |
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