Use of an asymmetric MXene membrane in ion-selective separations

Abstract

This invention discloses the application of an asymmetric MXene membrane in ion-selective separation. When the asymmetric MXene membrane described in this invention is used for ion-selective separation, it effectively separates the target ion Li. + Na + ,K + ,Rb + Cs + With excellent separation selectivity, ultra-high permeability, and high water permeability, it has good application prospects in the resource utilization of salt lakes and the recovery of high-value-added ions from seawater. Since the asymmetric MXene membrane of this invention is formed first and then modified, the membrane performance is uniform when performing selective ion separation in specific applications. It is not affected by batch preparation or operating process. Under a fixed modification process, the ion separation selectivity will not change abruptly. At the same time, the separation selectivity will not change abruptly under complex operating conditions. Moreover, the preparation cost is low, the operation is simple, and it is suitable for subsequent large-scale production and application.

Description

Technical Field

[0001] This invention belongs to the field of ion separation, specifically relating to the application of an asymmetric MXene membrane in ion selective separation. Background Technology

[0002] Currently in the field of two-dimensional membranes, in order to obtain membrane materials with different functions, researchers have introduced functional groups or third-party substances into the two-dimensional membrane structure through a "one-pot" pre-modification or post-modification method, thereby endowing the two-dimensional membrane with different separation properties.

[0003] In existing technologies for preparing two-dimensional membranes with different separation properties, most methods involve directly mixing and stirring modifiers with two-dimensional nanosheets, followed by membrane formation through methods such as vacuum filtration, spraying, and pressure filtration. While these methods can impart certain specific separation properties to the two-dimensional membrane structure, such as for Li... + Or K + While exhibiting selective permeability, the randomness of its mixing and the uncertainty of the binding mechanism between the modifier and the two-dimensional nanosheets result in highly inhomogeneous post-modified two-dimensional membrane structures. This ultimately leads to no significant improvement in separation performance, with inconsistent and even difficult-to-reproduce results. Furthermore, large-scale fabrication is challenging. The root cause of these problems and deficiencies lies in the fact that many methods have not explored the microstructure and structure-property relationships of two-dimensional membranes. They have neglected the charge properties and confined mass transfer characteristics of two-dimensional structures, focusing only on the functionalization of two-dimensional nanosheets while ignoring the design of the overall two-dimensional membrane structure. This phenomenon arises because the research on two-dimensional sub-nanometer confined structures is currently in a "black box" stage; the theoretical relationship between mass transfer and structure remains unclear. Consequently, researchers have abandoned modifying membrane structures and instead sought simpler methods for modifying two-dimensional nanosheets. Summary of the Invention

[0004] In order to overcome the shortcomings and disadvantages of the prior art, the purpose of this invention is to provide an application of an asymmetric MXene membrane in ion selective separation.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An application of an asymmetric MXene membrane in ion selective separation includes the following steps: placing an asymmetric MXene membrane modified for specific recognition of the metal cation to be separated in an ion separation device, adding a test ion salt solution to the feed side and adding deionized water to the other side, and achieving selective separation of the metal cation to be separated under the drive of the concentration difference;

[0007] The metal cation to be separated is Li + Na + K+ Rb + Cs + Mg 2+ Ca 2+ Sr 2+ Ba 2+ Al 3+ At least one of the following, wherein the concentration of the metal cation to be separated is 0.001-1 mol / L;

[0008] The asymmetric MXene film is obtained by impregnating and modifying a two-dimensional layered MXene film after it has been formed in a specific modifying solvent.

[0009] Preferably, the method for preparing the asymmetric MXene film specifically includes the following steps:

[0010] (1) Mix lithium salt with acid solution to obtain a mixture, then add three-dimensional bulk MAX powder to the mixture, stir, wash and dry to obtain two-dimensional layered MXene powder;

[0011] (2) Mix the two-dimensional layered MXene powder with a solvent, sonicate, centrifuge, and take the supernatant to obtain a solution containing two-dimensional MXene nanosheets;

[0012] (3) The solution containing two-dimensional MXene nanosheets obtained in step (2) is deposited onto a porous filter membrane substrate by positive pressure filtration and dried to obtain a two-dimensional layered MXene membrane.

[0013] (4) After the pressure filtration operation is completed, the two-dimensional layered MXene membrane is impregnated with a specific modified solvent that has a recognition function and dried to obtain an asymmetric MXene membrane.

[0014] Preferably, the specific modifying solvent is at least one of crown ether and crown ether derivatives, the impregnation time is 1 min to 12 h, and the concentration of the specific modifying solvent is 1 mg / ml to 10 g / ml.

[0015] Preferably, the specific modifying solvent is 18-crown-6-ether or 15-crown-5-ether.

[0016] Preferably, the thickness of the asymmetric MXene film shown is 10nm-100μm.

[0017] Preferably, the asymmetric MXene film material is at least one selected from Ti3C2, Ti2C, V2C, V4C3, Ti4C3, Nb4C3, Nb2C, Ti3CN, MoC2, and Ta4C3.

[0018] Preferably, the test ionic salt solution used is one or more selected from LiCl, NaCl, KCl, RbCl, CsCl, MgCl2, CaCl2, SrCl3, BaCl2, AlCl3, LiNO3, NaNO3, KNO3, RbNO3, CsNO3, Mg(NO3)2, Ca(NO3)2, Sr(NO3)3, Ba(NO3)2, Al(NO3)3, LiSO4, NaSO4, KSO4, RbSO4, CsSO4, MgSO4, CaSO4, SrSO4, BaSO4, and Al2(SO4)3, and the concentration of the test ionic salt solution is 0.001-2 mol / L.

[0019] Preferably, the concentration of the test ionic salt solution is 0.25 mol / L.

[0020] Preferably, the asymmetric MXene membrane is used in seawater desalination and desalination applications.

[0021] The asymmetric MXene membrane of this invention is obtained by impregnating and modifying a two-dimensional layered MXene membrane after it has been formed. The impregnation time is 1 min to 12 h, and the concentration of the impregnation modification solution is 1 mg / ml to 10 g / ml. The preparation method of the two-dimensional layered MXene membrane is the same as that in the patent "Application of a Two-Dimensional Self-Crosslinked MXene Membrane in Ion Separation".

[0022] This invention involves post-modification of a two-dimensional layered MXene membrane through impregnation. The prepared MXene membrane is clamped onto a filtration cup, and then a modification solution is poured onto the clamped MXene membrane. By controlling the concentration and height of the modification solution, MXene membranes with different degrees of asymmetry can be obtained. Furthermore, the resulting membrane can freely detach from the substrate after drying, forming an unsupported, flexible sheet-like membrane, which can be flexibly combined with different substrates according to the application field.

[0023] This invention achieves enhanced separation selectivity by performing asymmetric modification on the structure of layered MXene films and stabilizing the interlayer structure through the interaction of the modifier with the functional groups of the nanosheets in the modified layer. This fundamentally solves the problem of random and disordered layered structures formed after nanosheets are modified with the modifier. While ensuring the specific selectivity of the layered MXene film for ions, its asymmetric structure promotes the rapid transport of selected ions.

[0024] The application of the asymmetric MXene membrane described in this invention in ion separation, wherein the ions refer to ions with a hydrated diameter in the nanometer range (generally less than 1 nm), and the ions are generally cations, including Li. + Na + K+ Rb + Cs + Mg 2+ Ca 2+ Sr 2+ Ba 2+ Al 3+ At least one of them.

[0025] The ion separation refers to the selective separation of ions in solution through permeation using an asymmetric MXene membrane.

[0026] The application of the asymmetric MXene membrane in ion-selective separation includes the following steps:

[0027] An asymmetric MXene membrane is placed in a permeation separation test device. A test ion salt solution is added to the feed side, and deionized water is added to the other side. Under concentration-driven conditions, ion-selective separation is achieved.

[0028] The thickness of the asymmetric MXene film shown is 10nm-100μm.

[0029] The salt solution used in the test is one or more of the following: LiCl, NaCl, KCl, RbCl, CsCl, MgCl2, CaCl2, SrCl3, BaCl2, AlCl3, LiNO3, NaNO3, KNO3, RbNO3, CsNO3, Mg(NO3)2, Ca(NO3)2, Sr(NO3)3, Ba(NO3)2, Al(NO3)3, LiSO4, NaSO4, KSO4, RbSO4, CsSO4, MgSO4, CaSO4, Sr3(SO4)2, BaSO4, and Al2(SO4)3, with a concentration of 0.001-1 mol / L.

[0030] This invention applies an asymmetric MXene film to Li + Na + K + Rb + Cs + Mg 2+ Ca 2+ Sr 2+ Ba 2+ Al 3+ In plasma-selective separation, it exhibits excellent ion selectivity (Li). + Na + ,K + ,Rb + Cs +With high-value-added monovalent ions and ultra-fast target ion stability, it has significant industrial application value in the fields of resource utilization of salt lakes, lithium extraction from seawater, rubidium extraction, cesium extraction, and high-value-added ion recovery.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) When the asymmetric MXene membrane of the present invention is used for ion-selective separation, it can effectively separate the target ion Li. + Na + ,K + ,Rb + Cs + With excellent separation selectivity, ultra-high permeability, and high water permeability, it has good application prospects in the fields of resource utilization of salt lakes and high value-added ion recovery from seawater.

[0033] (2) Due to its asymmetric nanolayer structure, the present invention allows the selection layer and the transport layer to be independent and synergistic. While selecting target ions, the transport layer can quickly extract them. It can be used at atmospheric pressure to ten atmospheres, and the membrane area can be customized as needed, without being limited by the substrate. It has low energy consumption and is suitable for complex working conditions with high acidity / alkalinity.

[0034] (3) Since the asymmetric MXene membrane of the present invention is formed first and then modified, the membrane performance is uniform during selective ion separation and is not affected by batch preparation and operation process. Under a fixed modification process, the ion separation selectivity will not change abruptly. At the same time, the separation selectivity will not change abruptly under complex working conditions. Furthermore, the preparation cost is low, the operation is simple, and it is suitable for subsequent large-scale production. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the fabrication of asymmetric MXene films;

[0036] Figure 2 Example 1 has Rb + Permeation rate diagram of specific recognition membranes for selective separation of asymmetric MXene membranes;

[0037] Figure 3 Example 2 has K + Permeation rate diagram of specific recognition membranes for selective separation of asymmetric MXene membranes;

[0038] Figure 4 Example 3 contains Na + Permeation rate diagram of specific recognition membranes for selective separation of asymmetric MXene membranes;

[0039] Figure 5 Example 4 has Li +A graph showing the specific recognition membrane permeation rate of asymmetric MXene membranes with selective separation. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0041] like Figure 1 As shown, the preparation method of the asymmetric MXene film described in Examples 1-4 includes the following steps:

[0042] (1) Mix 2g of lithium fluoride with 120ml of concentrated hydrochloric acid solution, add 2g of three-dimensional bulk MAX powder, stir for 12h, then wash the reactants with deionized water until the pH is close to 7, dry the lower layer product to obtain MXene powder product.

[0043] (2) Mix 20 mg of MXene powder with 100 ml of deionized water and disperse by ultrasonication; centrifuge at 300 rpm for 30 min, take the supernatant to obtain a solution of MXene nanosheets with uniform thickness and size, and control its concentration at 2 mg / ml;

[0044] (3) The above MXene solution was deposited onto a polyethersulfone organic substrate with a pore size of 0.35 μm and a diameter of 35 mm by positive pressure filtration;

[0045] (4) After the pressure filtration operation is completed, the modifier solution with recognition function, with a concentration of 1 mg / ml and a volume of 20 ml, is poured into the pressure filtration cup. Under the action of gravity and concentration gradient, the modifier permeates into the membrane. After 30 min, the modifier solution is removed and placed in an argon drying oven to dry, thus obtaining an asymmetric MXene membrane.

[0046] Example 1

[0047] Will pass through Rb + An asymmetric MXene membrane modified with ion-specific recognition (12-crown-4 ether solution) was placed in a self-made ion separation device. LiCl, NaCl, KCl, RbCl, CaCl2, MgCl2, and AlCl3 salt solutions (concentration 0.25 mol / L) and deionized water (resistance: 18.2 megohms) were added to the feed and permeation sides, respectively. The ionic conductivity on the permeation side was measured using an ion conductivity meter, and the molar concentration was then calculated based on the molar ionic conductivity. The ion permeation rate is as follows: Figure 2 As shown, this is the product prepared in Example 1 with Rb + Permeation rate diagrams of asymmetric MXene membranes with selective transport capabilities applied to the separation of different types of ions.

[0048] The ion permeation rate of various ions at room temperature (25℃) was experimentally measured to be VRb. + =0.16mol h -1 m -2 VK + =0.01mol h -1 m -2 VNa + =0.03mol h -1 m -2 ,VLi + =0.036mol h -1 m -2 ,VCa 2+ =0.003mol h -1 m -2 VMg 2+ =0.002mol h -1 m -2 ,VAl 3+ =0.0003mol h -1 m -2 In this embodiment, the water flux is between 0.1 and 0.15 L / h. -1 m -2 ba r-1 As can be seen from the above, after Rb + Ion-specific recognition of modified asymmetric MXene films for Rb + have

[0049] The ion permeation rate of the MXene membrane without asymmetric modification did not change significantly during the ion permeation test, indicating that it has no significant ion separation performance.

[0050] Example 2

[0051] Will pass through K + An asymmetric MXene membrane modified with ion-specific recognition (18-crown-6 ether solution) was placed in a self-made ion separation device. LiCl, NaCl, KCl, RbCl, CaCl2, MgCl2, and AlCl3 salt solutions (concentration 0.25 mol / L) and deionized water (resistance: 18.2 megohms) were added to the feed and permeation sides, respectively. The ionic conductivity on the permeation side was measured using an ion conductivity meter, and the molar concentration was then calculated based on the molar ionic conductivity. The ion permeation rate is as follows: Figure 3 As shown, this is the product prepared in Example 1 with Rb + Permeation rate diagrams of asymmetric MXene membranes with selective transport capabilities applied to the separation of different types of ions.

[0052] The ion permeation rate of various ions at room temperature (25℃) was experimentally measured to be VRb. +=0.001mol h -1 m -2 VK + =0.15mol h -1 m -2 VNa+=0.002mol h -1 m -2 ,VLi + =0.0026mol h -1 m -2 ,VCa 2+ =0.001mol h -1 m -2 VMg 2+ =0.0002mol h -1 m -2 ,VAl 3+ =0.0001mol h -1 m -2 In this embodiment, the water flux is between 0.08 and 0.16 L / h. -1 m -2 bar -1 .

[0053] Example 3

[0054] Will pass through Na + An asymmetric MXene membrane modified with ion-specific recognition (15-crown-5-ether solution) was placed in a self-made ion separation device. LiCl, NaCl, KCl, RbCl, CaCl2, MgCl2, and AlCl3 salt solutions (concentration 0.25 mol / L) and deionized water (resistance: 18.2 megohms) were added to the feed and permeation sides, respectively. The ionic conductivity on the permeation side was measured using an ion conductivity meter, and the molar concentration was then calculated based on the molar ionic conductivity. The ion permeation rate is as follows: Figure 4 As shown, this is the product prepared in Example 1 with Rb + Permeation rate diagrams of asymmetric MXene membranes with selective transport capabilities applied to the separation of different types of ions.

[0055] The ion permeation rate of various ions at room temperature (25℃) was experimentally measured to be VRb. + =0.0029mol h -1 m -2 VK + =0.001mol h -1 m -2 VNa + =0.2mol h -1 m -2 ,VLi + =0.015mol h -1 m-2 ,VCa 2+ =0.002mol h -1 m -2 VMg 2+ =0.0009mol h -1 m -2 ,VAl 3+ =0.0001mol h -1 m -2 In this embodiment, the water flux is between 0.12 and 0.18 L / h. - 1 m -2 bar -1 .

[0056] Example 4

[0057] Will pass through Li + An asymmetric MXene membrane modified with ion-specific recognition (1-amino-12-crown-4-ether solution) was placed in a self-made ion separation device. LiCl, NaCl, KCl, RbCl, CaCl2, MgCl2, and AlCl3 salt solutions (concentration 0.25 mol / L) and deionized water (resistance: 18.2 megohms) were added to the feed and permeation sides, respectively. The ionic conductivity on the permeation side was measured using an ion conductivity meter, and the molar concentration was then calculated based on the molar ionic conductivity. The ion permeation rate is as follows: Figure 5 As shown, this is the product prepared in Example 1 with Rb + Permeation rate diagrams of asymmetric MXene membranes with selective transport capabilities applied to the separation of different types of ions.

[0058] The ion permeation rate of various ions at room temperature (25℃) was experimentally measured to be VRb. + =0.01mol h -1 m -2 VK + =0.005mol h -1 m -2 VNa + =0.006mol h -1 m -2 ,VLi + =0.1mol h -1 m -2 ,VCa 2+ =0.002mol h -1 m -2 VMg 2+ =0.0016mol h -1 m -2 ,VAl 3+ =0.0001mol h -1 m-2 In this embodiment, the water flux is between 0.12 and 0.18 L / h. - 1 m -2 bar -1 .

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An application of an asymmetric MXene membrane in ion-selective separation, characterized in that, Includes the following steps: An asymmetric MXene membrane modified for specific recognition of the metal cations to be separated is placed in an ion separation device. A test ion salt solution is added to the feed side, and deionized water is added to the other side. Driven by the concentration difference, selective separation of the metal cations to be separated is achieved. The concentration of the metal cations to be separated is 0.001-1 mol / L. The asymmetric MXene membrane is obtained by impregnating and modifying a two-dimensional layered MXene membrane after film formation in a specific modifying solvent. The impregnation time is 1 min-12 h. The concentration of the specific modifying solvent is 1 mg / ml-10 g / ml. When the metal cation to be separated is Li + the specific modified solvent is 1-amino-12-crown-4 ether; When the metal cation to be separated is Na + the specific modified solvent is 15-crown-5 ether; When the metal cation to be separated is K + the specific modified solvent is 18-crown-6 ether; The metal cation to be separated is Rb + The specific modifying solvent is 12-crown-4 ether. The method for preparing the asymmetric MXene film specifically includes the following steps: (1) Mix lithium salt with acid solution to obtain a mixture, then add three-dimensional bulk MAX powder to the mixture, stir, wash and dry to obtain two-dimensional layered MXene powder; (2) Mix the two-dimensional layered MXene powder with a solvent, sonicate, centrifuge, and take the supernatant to obtain a solution containing two-dimensional MXene nanosheets; (3) The solution containing two-dimensional MXene nanosheets obtained in step (2) is deposited onto a porous filter membrane substrate by positive pressure filtration and dried to obtain a two-dimensional layered MXene membrane. (4) After the pressure filtration operation is completed, the two-dimensional layered MXene membrane is impregnated and modified with a specific modified solvent with identification function. The specific modified solvent is poured onto the MXene membrane. By controlling the concentration and height of the specific modified solvent, the specific modified solvent permeates into the two-dimensional layered MXene membrane under the action of gravity and concentration gradient. After the modification is completed, all solvents are removed and the asymmetric MXene membrane is obtained after drying.

2. The application of the asymmetric MXene membrane according to claim 1 in ion selective separation, characterized in that, The thickness of the asymmetric MXene film shown is 10 nm-100 μm.

3. The application of the asymmetric MXene membrane according to claim 1 in ion selective separation, characterized in that, The asymmetric MXene film material is at least one of Ti3C2, Ti2C, V2C, V4C3, Ti4C3, Nb4C3, Nb2C, Ti3CN, MoC2, and Ta4C3.

4. The application of the asymmetric MXene membrane according to claim 1 in ion selective separation, characterized in that, The test ionic salt solution used is at least one selected from LiCl, NaCl, KCl, RbCl, CsCl, MgCl2, CaCl2, SrCl3, BaCl2, AlCl3, LiNO3, NaNO3, KNO3, RbNO3, CsNO3, Mg(NO3)2, Ca(NO3)2, Sr(NO3)2, Ba(NO3)2, Al(NO3)3, Li2SO4, Na2SO4, K2SO4, Rb2SO4, Cs2SO4, MgSO4, CaSO4, SrSO4, BaSO4, and Al2(SO4)3, and the concentration of the test ionic salt solution is 0.001-2 mol / L.

5. The application of the asymmetric MXene membrane according to claim 4 in ion selective separation, characterized in that, The concentration of the test ionic salt solution was 0.25 mol / L.

6. The application of the asymmetric MXene membrane according to any one of claims 1 to 5 in ion selective separation, characterized in that, The asymmetric MXene membrane is used in seawater desalination and desalination applications.

Images