Preparation And Separation Performance Of Graphene Oxide/Chitosan Nanofiltration Membranes

Layered nanofiltration membranes prepared from graphene oxide(GO)nanosheets with the advantages of simple preparation process,excellent performance,and easy-to-scale production,and have attracted widespread attention in the field of membrane separation.GO nanofiltration membranes use nano-layered channels between adjacent GO sheet layers to block macromolecular substances and permeate water molecules,thereby achieving the effect of retaining and concentrating substances in waste liquid.However,GO membranes have the problems of low separation efficiency and poor stability in practical application.For this,the high-performance GO nanofiltration membranes with stable structure and strong hydrophilicity were prepared by using chitosan(CS)single molecular chain as a macromolecular cross-linking agent,and the relationship between the structure regulation mechanism and separation efficiency of the membrane was investigated.The specific research content is as follows:First,the CS intercalation-crosslinked GO nanofiltration membrane were prepared by filtration.Mix the GO dispersion with a lateral dimension of about 250 nm and the CS solution to obtain the CS@GO mixed solution.The mixed solution was filtered on the surface of the microfiltration membranes to prepare the nanofiltration membranes.The thickness of the membrane is 70.2 nm,and it has interlayer nanochannels of 1.51 nm.Its ultra-thin cross-section structure and large interlayer channels are beneficial to rapid transmission of water molecules.In addition,the segmented polymer CS and GO nanosheets are crosslinked with each other through covalent bonds to improve the stability of the membrane.The test results show that the membrane has a pure water flux of 91 L m-2 h-1 bar-1 and a retention rate of 92%for the dye DY.At the same time,the membrane is still to maintain stable separation performance after long-term acid treatment or under strong cross-flow conditionsSecondly,on the basis of the filtration method,the layer-by-layer self-assembly method was used to "fix" GO membrane surface defects to prepare GO nanofiltration membranes with better separation performance.Firstly,a sacrificial layer of Ni(OH)2 was built on the surface of the microfiltration membrane.Then,the GO dispersion with a lateral dimension of 70 nm was mixed with the CS solution to obtain the CS@GO mixed solution.And CSx@GOy nanofiltration membranes were prepared by filtering the CS@GO mixed solution on the surface of the sacrificial layer of Ni(OH)2.Finally,the(CSx@GOy)-n nanofiltration membranes were fabricated by alternately assembling CS and GO nanosheets on the surface of the CSx@GOy nanofiltration membrane using the layer-by-layer self-assembly method.The smaller-sized GO nanosheets and the layer-by-layer self-assembly method make the membrane have shorter water transport channel paths and a more "regular" membrane surface.The test results show that the nanofiltration membrane with a thickness of 75 nm is obtained by the filtration method,the membrane flux is 317 L m-2 h-1 bar-1,and the dye DY rejection rate is only 40%.After assembling four layers of GO nanosheets on this membrane,its pure water flux decreased to 118 L m-2 h-1 bar-1,and the rejection rate of dye DY rose to 97%.Aiming at the problems of low separation efficiency and poor stability of the GO membrane during the separation process,two high performance GO membranes were prepared.The membranes have simple preparation process,excellent separation performance and strong stability,and thus have potential application prospects in water treatment.