Construction And Properties Of Cationic Cross-linked Graphene Oxide/sodium Alginate Hybrid Nanofiltration Membrane

The rapid development of industrialization has led to the excessive discharge of toxic and harmful pollutants,and the destruction of fresh water resources has seriously threatened human production,life,and health,the problem of water pollution needs to be solved urgently.Graphene and its derivatives have become new membrane materials in the field of water treatment because of their unique two-dimensional structure and excellent physical and chemical properties.Compared with other membrane materials,graphene oxide（GO）membranes have good water flux and pollutant removal rates,and antibacterial properties.In this paper,we report a graphene oxide nanofiltration membrane with high separation performance.Through the modification of graphene oxide membrane to enhance the various properties of graphene oxide membrane,this paper selected a natural polysaccharide sodium alginate modified graphene oxide membrane,sodium alginate has good biocompatibility and biodegradability sex,sodium alginate modification will not cause secondary pollution to the environment.The graphene oxide/sodium alginate composite membrane（Na⁺/GO-SAx）was prepared by vacuum filtration.Compared with the layer spacing of GO membrane（GOM）（0.82 nm）,the layer spacing of the composite membrane increased to 0.85-1.07 nm,the increase of nano-channels in the membrane makes the composite membrane have faster water molecule transport ability,the retention performance of cationic dyes（MB and RB）can be improved to 99.97%and 99.99%,and that of anionic dyes（MO and EB）can be improved to 53.13%and 99.58%.Sodium alginate can chelate with metal cations.Subsequently,this paper added metal cations to the membrane construction and prepared a new type of graphene oxide/sodium alginate composite membrane(Ba²⁺/GO-SAx,Fe³⁺/GO-SAx).The effect of different cations on the performance of composite membranes was studied.The water permeability of the cationic crosslinked composite membrane is 3.1 times higher than that of GOM,and had a great breakthrough in the interception of dyes.The interception performance of methyl orange dye can reach up to more than 90%.In addition,the composite membrane has good acid and alkali resistance,combined with BET,Zeta potential,and other tests to analyze the separation mechanism of the composite membrane.（1）Graphene oxide was prepared by the improved Hummers method,and the graphene oxide/sodium alginate composite（GO-SA）was prepared by simple mechanical mixing.A series of analysis tests were conducted on composite materials and membranes,including FTIR,TGA,TEM,AFM.The tests showed that GO and GO-SA were successfully prepared.The roughness of the prepared composite membrane（69.52 nm）was greater than that of GOM（51.24 nm）.The composite membrane after adding GO-SA still maintained a good Layered structure.（2）The cations can also chelate with graphene oxide while reacting with sodium alginate.Subsequently,a cationic double cross-linked graphene oxide/sodium alginate composite film was prepared by vacuum filtration.The composite membrane was characterized and analyzed.The laminated structure of the composite membrane after double crosslinking remained intact.The roughness of the composite membrane（91.56 nm,97.94 nm）after crosslinking was greater than that of Na⁺/GO-SAx（69.52 nm）,which was the result of double crosslinking.The addition of cations made the internal structure of the membrane compact and increased the wrinkling of the membrane.（3）Furthermore,we tested all the composite membranes（M/GO-SAx）,and The water permeability of M/GO-SAx is 3.1 times higher than that of GOM,which is due to the increased interlayer spacing（0.85-1.07 nm）of the modified composite membranes,and is more conducive to the transportation of water molecules.Combining the water permeability of the composite membrane and the interception of Evans blue,select the membrane with the optimal ratio(Na⁺/GO-SA3,Ba²⁺/GO-SA4,Fe³⁺/GO-SA4).Three kinds of dyes（RB,MB,MO）were selected to test the wide application of the composite membrane,and the interception performance of cationic dyes MB and RB reached more than 95%.Combined with XRD,Zeta potential,BET,and other tests,the separation mechanism of the composite membrane was analyzed.Graphene oxide nanofiltration membranes with high cut-off performance have high research value.These studies provide new ideas and methods for designing nanofiltration membranes,which can be used to design and develop new nanofiltration membranes for water treatment.