Study On Preparation Of Nanofiltration Membrane And Separation Performance Of Dye/Salt Based On Modified Mica Nanosheets

Due to their unique atomic thickness and structure,Two-Dimensional(2D)materials possess remarkable properties that differ from those of traditional bulk materials,making them a subject of extensive study and application in diverse fields such as gas separation,seawater desalination,catalysis,energy conversion,and storage.Among the 2D materials,mica nanosheets exhibit graphene-like layered structure,excellent stability,and hydrophilicity,thus presenting immense potential in membrane separation.In this research,2D mica nanosheets were exfoliated successfully from natural mica powder using liquid-assisted ultrasonic exfoliation and further modified to suitably construct membranes.Subsequently,a loose nanofiltration(LNF)membrane was constructed based on the PEI-modified mica nanosheets(PEI-mica)for the separation of dye/inorganic salts,and the performance of the membrane in this aspect was explored.To further improve the retention rate of inorganic salts by the nanofiltration membrane,a polyamide(TFN)nanofiltration membrane with a PEI-mica intermediate layer was constructed,and its performance in the separation of inorganic salts was investigated.A novel loose NF membrane was prepared by the assembly of PEI-mica and cellulose nanofibers(CNFs)on hydrolyzed polyacrylonitrile(HPAN)substrate via facile vacuum filtration.The combination of PEI-mica nanosheets and CNFs constructed a thin and loose "brick-mud" structure via electrostatic attraction and hydrogen bonding.The assembly of 2D and 1D nanomaterials significantly expands the nanochannels inside the composite membrane,which is beneficial to improve the permeability and selectivity of the membrane.Due to the well-designed lamellar structure along with the excellent hydrophilicity,the PEI-mica/CNFs membrane possessed high water permeability(62.18 LMH/bar)and superior dye/salt separation efficiency,with outstanding dye retentions(i.e.,Coomassie Brilliant Blue R250:99.66%,Congo Red:98.89%,and Evans Blue:98.64%)and low salt rejections(e.g.,NaCl:3.42%and Na2SO4:15.63%).Besides,the nanofiltration membrane also showed good antifouling properties and operation stability,indicating its promising potential for practical textile wastewater treatment.A new type of polyamide nanofiltration membrane with a PEI-mica intermediate layer was constructed using interfacial polymerization reaction.The combined effect of the intermediate layer and the PA layer charge improved the membrane’s selectivity for inorganic salts,achieving a synergistic enhancement of membrane permeability and selectivity.The nanofiltration membrane with the intermediate layer has a higher water permeability(16.51 LMH/bar)and selectivity of inorganic salts(KCl:14.90%,NaCl:16.11%,CaCl2:67.71%,MgSO4:91.05%,Na2SO4:97.10%).In addition,the optimized TFN nanofiltration membrane showed excellent stability during a 20-hour cross-flow filtration experiment in a 1000 ppm Na2SO4 solution,indicating its broad potential in water treatment applications.This research fully leverages the advantages of PEI-mica nanosheets to prepare two types of composite nanofiltration membranes,which are used for the separation of dye/salt mixed solution and the removal of inorganic salts in water.It has certain guiding significance for the application of two-dimensional materials in the field of membrane separation.