Preparation Of High-performance MXene-based Separation Membrane And Its Application In The Treatment Of Dyeing Wastewater

With the rapid development of the global economy and the rapid increase of industrialization levels,water pollution and water shortages have become issues of common concern for all humanity.The search for efficient water treatment technologies to carry out seawater desalination and wastewater reuse is an important way to increase freshwater resources.Membrane separation technology has advantages such as high efficiency,energy-saving,environmental protection,and has been widely used in water purification,industrial wastewater treatment,and seawater desalination.The development of new high-performance membrane materials is the primary issue to promote the development of membrane separation technology.2D material membranes have unique physical and chemical properties and controllable size channels,which are expected to break the balance limit between traditional polymer membranes’permeability and selectivity（"trade-off"effect）,achieving efficient ion separation.Transition metal carbide/nitride（MXene）is a new type of binary nanomaterial developed in recent years.Due to its characteristics such as high aspect ratio,good conductivity,excellent optical-thermal conversion efficiency,and surface hydrophilicity,it has been widely used in environmental and energy catalysis fields,and is also regarded as a promising candidate material in the field of membrane separation.However,the size of the transport channels formed by MXene 2D nanosheets is limited,which affects the transport rate of water molecules in the membrane channels,thereby limiting the increase of membrane permeability.In order to further improve the separation performance of MXene membranes and expand their application in liquid-liquid separation,the specific research content of this paper is as follows:1.Selective etching of MAX（Ti₃Al C₂）phase using LiF+concentration HCl was carried out,and MXene（Ti₃C₂T_x）nanosheets dispersed liquid was prepared by ultrasonic stripping.In-situ water heat reaction and vacuum suction filtration were further used to successfully insert photocatalytic nanocrystals Bi₂S₃ into the interlayer of Ti₃C₂T_x nanosheets,obtaining a bi-functional 2D material composite membrane including separation and photocatalytic functions.The results showed that the membrane demonstrated good separation performance,with a high pure water flux of up to～760 L·m^-2·h^-1·MPa^-1,and retention rates of over 90%for water-soluble dye molecules larger than 1.2 nm.The performance was much better than other reported2D material separation membranes.Further,Ti₃C₂T_x/Bi₂S₃ membrane showed smaller band gap and broader optical absorption range than pure Bi₂S₃ photocatalysts.Electrochemical impedance spectroscopy（EIS）and photoluminescent spectroscopy（PL）results also showed that Ti₃C₂T_x/Bi₂S₃ had a fast electron transfer rate and low light-electron-hole pair recombination rate,which were beneficial for the transfer of photogenerated carriers,extended the service life of photogenerated electrons and holes,and conferred excellent photocatalytic degradation self-cleaning abilities.After filtering a dye molecule rhodamine B on the membrane,it was re-suspended in simulated solar light for 20 minutes,and the water flux recovery rate was up to 98%.In addition,Ti₃C₂T_x/Bi₂S₃ composite membrane showed good stability,with little change in permeability after five separation-degradation cycles,and the removal efficiency of dye molecules remained above 90%.Active oxygen species capture experiment and low-temperature electron spin resonance（ESR）technology showed that Ti₃C₂T_x/Bi₂S₃ produced·OH and O^2-active substances in the process of degradation of rhodamine B under light.The results of the infrared thermal imager indicate that Ti₃C₂T_x/Bi₂S₃has good photothermal conversion ability,and the absorbed heat is converted into high temperature,which is conducive to the photocatalytic degradation reaction and improves the photothermal sterilization performance of Ti₃C₂T_x/Bi₂S₃ membrane.Under light,Ti₃C₂T_x/Bi₂S₃composite membrane also showed good photothermal bactericidal performance against E.coli and S.aureus（the bactericidal rates were 95%and 85%respectively）.The preparation method of this membrane is relatively simple,cost-effective,and is expected to achieve industrial expansion of production.2.To address the problem of membrane biofouling,Ti₃C₂T_x-PDDA composite membranes with anti-pollution and anti-bacterial properties were prepared by introducing polydimethyldiallylammonium chloride（PDDA）polycationic chains between Ti₃C₂T_xnanosheet layers.The results showed that the Ti₃C₂T_x-PDDA composite membranes exhibited excellent separation properties due to the intercalation of PDDA,which imparted good hydrophilicity and positive charge to the Ti₃C₂T_x membrane surface.The pure water flux of the Ti₃C₂T_x-PDDA membrane increased from 96 L·m^-2·h^-1·MPa^-1 to 145 L·m^-2·h^-1·MPa^-1at 25°C and 0.6 MPa,and the retention rate of Mg Cl₂ was up to 90%.In addition,the Ti₃C₂T_x-PDDA membranes were easier to clean and significantly prevented the adhesion of organic contaminants sodium dodecyl sulfate and bovine serum proteins,with a water flux recovery rate of 89%.Further,the Ti₃C₂T_x-PDDA membranes also showed excellent anti-adhesion and anti-bacterial activity against Gram-negative bacteria（E.coli）and Gram-positive bacteria（S.aureus）,with 90%and 95%inhibition against E.coli and S.aureus respectively.The bactericidal ability in natural river water was also tested and an antibacterial rate of 95%was achieved.Therefore,Ti₃C₂T_x-PDDA nanofiltration membranes have good permeability and excellent antibacterial properties,and have broad application prospects in the future practical water treatment field.