Fabrication Of Porous Graphene Oxide Nanofiltration Membranes And Performance Intensification

In recent year,the burgeoning 2D materials paves an avenue for ultrathin membrane manufacture.Thereinto,graphene oxide（GO）nanosheet,as graphene derivatives has emerged as a promising building block for ultrathin membrane benefited from its high aspect ratio ranging from 1500 to 45000.The thickness of GO membranes can be precisely manipulated from tens of nanometers down to atomic level and the laminated structure from the stacked GO nanosheets renders ordered transport channels for precise sieving.However,within the GO laminated membranes,water transport pathways along the interlayer space and the edge-to-edge slits of adjacent GO nanosheets are highly tortuous,restricting the further enhancement of the membrane flux.Most efforts have been paid on expanding the interlayer pathway by intercalating nanomaterials into the adjacent GO nanosheets.However,excessive expansion of the interlayer pathway will deteriorate the membrane stability and selectivity.Besides,the in-plane punching on GO nanosheets is recognized as an efficient way to shorten water transport pathways in GO-based membranes.In this study,porous GO（pGO）was chosen as the assembly block to introduce the in-plane channels;halloysite nanotubes（HNTs）and porous C₃N₄（pC₃N₄）nanosheets were selected as the intercalators to manipulate the interlayer channels and fabricate high-flux GO-based membranes.The primary research contents are as follows:（1）Preparation of pGO membrane and nanofiltration performance intensification.The top-down chemical etching approach is utilized to punch the GO nanosheets.Concentrated nitric acid is used as a chemical etchant.By increasing the ratio of concentrated nitric acid to the GO nanosheets,the water permeation of the pGO membrane is enhanced;at the same time,dislocation stacking of GO nanosheets and the interlayer spacing in the GO membrane ensure the rejection towards dye molecules.The optimized membrane exhibits the water permeance of 93.3 L m^-2 h^-1 bar^-1 with dye rejections over 96.9%towards Congo Red,Eriochrome Black T and Alcian Blue.（2）Preparation of HNTs/pGO membrane and nanofiltration performance intensification.One-dimensional HNTs are chosen to intercalate into the adjacent pGO nanosheets to manipulate the physical structure and chemical properties of the membrane surface,optimizing the interlayer spacing and the chemical microenvironment in GO membranes.Hence,water transfer across the membrane is accelerated and the water permeance achieves 206.7 L m^-2 h^-1 bar^-1 with the dye rejections over 98.5%.The hierarchical structures on the surface endow membrane surface with a robust hydration layer,intensifying the resistance towards the oil-in-water emulsions.（3）Preparation of pC₃N₄/pGO membrane and nanofiltration performance enhancement.Resultant pC₃N₄/GO membranes are prepared via the vacuum-assisted co-assembly process with the pC₃N₄ nanosheets and the pGO nanosheets.The porous structures of the pGO and pC₃N₄ nanosheets afford the in-plane transport channels for water molecules.The expanded interlayer distance renders more space for water transport.The constructed in-plane channels and the intensified interlayer channels in the resultant pC₃N₄/pGO membranes promote the rapid transfer of water molecules across the membrane,enhancing the membrane permeance to 119.3 L m^-2 h^-1 bar^-1with dye rejections over 98.7%towards Congo Red,Eriochrome Black T and Alcian Blue,providing a facile platform for rationally designing the high-performance GO-based membranes.