Preparation And Characterization Of The Self-crosslinked MXene Membrane And Its Application In The Field Of Ion Separation

The separation process is an essential unit operation in chemical production.It accounts for a huge proportion of the total energy consumption in the total energy consumption.Membrane separation technology has many advantages,such as low energy consumption,small equipment footprint and simple operation,which is expected to become a substitute for traditional separation technology.However,the traditional separation membrane materials also have many problems,for example,the membrane is easily contaminated and it is difficult to achieve the requirements of high permeability and high selectivity at the same time.Research on new membrane separation materials with high performance is the key to the development of membrane separation technology.In recent years,a new type of separation membrane,two-dimensional membrane,has attracted much attention in the field of membrane separation.Two-dimensional membranes are usually formed by stacking two-dimensional nanosheets through a certain arrangement structure.They have excellent physical and chemical properties and ordered mass transfer channels of two-dimensional materials.Transition metal carbon?nitrogen?compound?MXene?is a new type of inorganic two-dimensional material,which was successfully prepared by Yury Gogotsi's research group in 2011.The material can be prepared by selective etching and intercalation stripping of a type of MAX compound with three-dimensional structure.The inorganic two-dimensional membrane formed by stacking and assembly of MXene nanosheets has designable mass transfer channels,and the surface of MXene nanosheets is rich in oxygen-containing functional groups,thereby giving the mass transfer channels excellent hydrophilic properties and achieving high efficiency of the liquid phase separation,such as ion trapping,organic solvent dehydration,dye wastewater treatment,etc.However,the use of two-dimensional MXene membranes for separation in liquid-phase systems requires a challenging problem:the swelling of two-dimensional membranes,that is,when immersed in liquid,water molecules easily enter the interlayer channels of the two-dimensional membrane,which increases the interlayer spacing,The membrane structure collapses and loses its ability to retain small-sized molecules.In order to solve this problem,this paper proposes a simple and convenient"self-crosslinking"strategy to enhance the anti-swelling performance of MXene membranes in water,and to achieve high-efficiency monovalent ion retention and selective separation of lithium ions.In this thesis,a two-dimensional MXene membrane for monovalent ion interception was first prepared.Using Li F and HCl as selective etchants,the MXene?Ti₃C₂T_x?nanosheet solution was prepared by aqueous solution ultrasonic stripping.Then,by means of vacuum-assisted suction filtration,the MXene nanosheets were assembled into a MXene film with a thickness of 500 nm,and self-crosslinking treatment was performed under a vacuum atmosphere.It is used in the process of low-cost small-size metal ion interception.In order to study the effects of different self-crosslinking temperatures on the MXene self-crosslinking process and the monovalent ion retention performance,we studied the self-crosslinking MXene membranes at three temperatures.We tested the retention performance of self-crosslinked MXene membranes prepared under different conditions to 0.2 M Li Cl,Na Cl and KCl solutions under normal pressure.The results show that as the cross-linking temperature increases,the self-crosslinking degree of MXene becomes greater and greater,and the ability to retain monovalent ions becomes stronger and stronger.In addition,in order to explore the stability of the self-crosslinking MXene membrane in different test environments,we conducted self-crosslinking MXene membranes under acidic?p H=3?and alkaline?p H=11?environments for ion rejection tests.The results show that the p H of the test solution has no significant effect on the structure and performance of the self-crosslinking MXene membrane,the self-crosslinking MXene membrane can run stably under acidic and alkaline conditions.Secondly,in order to further adjust the effective layer spacing of self-crosslinked MXene membrane and optimize the interlayer channel,it is applied to the selective separation of high value-added metal lithium ions,we will contain chain sulfonic acid group PSS?polystyrene sulfonate sodium?Introduced into the interlayer,by adjusting the amount of addition,so that the interlayer spacing is stable within the ideal range,because the modification of the interlayer channel by the sulfonate group will selectively permeate lithium ions,and other monovalent and divalent metal ions Effective retention.In this paper,the inductively coupled plasma-mass spectrometry?ICP-MS?technique is used to study the lithium extraction performance of MXene@PSS composite membrane under multi-ion solution and the lithium extraction performance of composite membranes with different film thicknesses,the mechanism of lithium extraction was thoroughly explored.The thesis first proposed the"self-crosslinking"strategy and applied it to the study of monovalent metal ion interception and selective lithium extraction.In-depth exploration has laid a certain theoretical and experimental basis for the application of MXene membrane in the field of selective ion screening and nanoflow.