Fabrication Of Graphene Oxide Modified Composite Membrane And Its Removal Of Metal Ions In Water

The recycling of sewage is one of the main goals of sewage treatment in my country in the new era.Nanofiltration technology is the most widely used in the removal of metal ions in water,especially in water softening.The disadvantages of traditional polyamide nanofiltration membranes and pure graphene oxide（GO）membranes in water treatment make it necessary to prepare new membrane materials.In this study,PVDF membrane was used as the supporting layer,and polydopamine（PDA）and polyethyleneimine（PEI）were used for dual modification.The GO/MXene＿PEI composite membrane was fabricated by vacuum filtration.The fabrication conditions such as the ratio of GO to MXene in the GO/MXene＿PEI composite membrane,the membrane load and the PEI soaking time were optimized.SEM,FTIR,XRD,XPS and other characterization methods were used to analyze the membrane materials.Selecting Na⁺,K⁺,Ca²⁺,Mg²⁺as the representatives of metal cations,the removal of different metal cations by the composite membrane and the influence of coexisting ions,coexisting organic matter,p H and other water quality conditions on the removal of metal ions by the composite membrane were investigated.Through characterization analysis,it was proved that GO nanosheets and MXene nanosheets were alternately arranged in GO/MXene＿PEI composite membrane.The composite membrane had a hydrophobic two-dimensional layered structure,and the surface of the membrane was positive.Studies had shown that the composite membrane with a GO/MXene mass ratio of 1:4 had the best water treatment performance when it was immersed in PEI for 10 min at a load of 100 mg·m^-2.The rejection rate of the composite membrane for the monovalent metal ions（Na⁺and K⁺）was about 50%;the rejection rate for the divalent metal ions(Ca²⁺and Mg²⁺)was about 80%.In the operation of repeated filtration for 5 times,the retention effect of the composite membrane did not change significantly.The trapping mechanism of the composite membrane for metal ions was mainly the synergistic effect of steric hindrance and electrostatic effects.Regarding the influence of water quality conditions,the coexistence of heavy metal ions Pb²⁺in water can increase the stability of the composite membrane to a certain extent,and improve the retention effect of the composite membrane on the four metal ions.Coexisting organic matter（sodium alginate,humic acid,bovine serum albumin）would reduce the water permeability of the composite membrane to a certain extent,and the retention effect of the composite membrane on metal ions increased temporarily and then decreased.In the range of p H 6-9,the change of p H had no obvious effect on the water treatment performance of the composite membrane.Under actual sewage conditions,the effect of the composite membrane on the metal ions in the secondary effluent of the sewage plant is better than that of the ultrafiltration effluent.The GO/MXene composite membrane modified by PEI has the advantages of high water flux,strong anti-pollution,and good softening effect,and has good application prospects.