Modified MXene piezoelectric ion screening membrane as well as preparation and application thereof

Abstract

The invention belongs to the technical field of functional materials and membrane separation, and discloses a modified MXene piezoelectric ion screening membrane and preparation and application thereof, and a preparation method comprises the following steps: S1, preparing a two-dimensional MXene nanosheet dispersion liquid; and S2, adding a polydentate ligand into the mixture for modification, carrying out vacuum filtration, carrying out spin coating or blade coating on a porous substrate, and carrying out vacuum drying to obtain the modified MXene membrane. According to the preparation method, a bionic strategy is combined with piezoelectric characteristics of a material, an MXene nanosheet is modified by polydentate ligand (such as DOTA, EDTA, PA or Cyclone) molecules, an anti-swelling sub-nano channel is constructed, a piezoelectric effect is activated by combining mechanical stimulation such as ultrasonic and stirring, a piezoelectric channel is formed, and the preparation method is applied to the field of membrane separation by utilizing electromigration and a staggered electric field mechanism. The technical problems of swelling, insufficient mechanical stability, lack of dynamic regulation and control capability and the like of a traditional membrane material can be effectively solved, and particularly, efficient selective screening of monovalent / divalent ions can be realized.

Description

Technical Field

[0001] The present invention belongs to the field of functional materials and membrane separation technology. More specifically, it relates to a modified MXene piezoelectric ion screening membrane and its preparation and application. It can form a piezoelectric channel and is particularly applicable to seawater desalination, resource recovery and high-precision ion screening. Background Art

[0002] Biological ion channels achieve ultra-selective transport of ions through the synergistic effect of sub-nanometer pore size, specific binding sites and charge density, providing important inspiration for the research and development of artificial ion channel membranes.

[0003] Existing technologies, such as sub-nanochannels constructed from materials like graphene oxide (GO) and metal-organic frameworks (MOFs), can achieve preliminary ion separation through size exclusion, but their selectivity is limited by the lack of a dynamic response mechanism. Furthermore, conventional membrane materials commonly suffer from swelling and poor mechanical stability, making them difficult to adapt to separation requirements in complex environments.

[0004] As a new type of two-dimensional material, MXene has excellent mechanical flexibility and a diversity of surface functional groups. Although it has piezoelectricity, its interlayer interaction is weak, and the application of piezoelectricity in membrane separation has not yet been fully developed. Studies have achieved preliminary ion screening effects by regulating the MXene interlayer spacing through intercalation chemistry, but this type of static design cannot reproduce the dynamic response characteristics of biological systems. More importantly, traditional external field regulation (such as applying voltage or adjusting pH) will introduce additional energy consumption and chemical interference, which seriously restricts its practical application potential. Therefore, the development of a biomimetic ion separation membrane with high stability, dynamic responsiveness and universality has important scientific significance and application value. Summary of the Invention

[0005] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a modified MXene piezoelectric ion screening membrane and its preparation and application. By combining the piezoelectric properties of the material with a biomimetic strategy, MXene nanosheets are modified with multidentate ligands (such as DOTA, EDTA, PA or Cyclen) to construct anti-swelling sub-nano channels. The piezoelectric effect is activated by mechanical stimulation such as ultrasound and stirring to form piezoelectric channels. The electromigration and staggered electric field mechanism are used in the field of membrane separation, which can effectively solve the technical problems of traditional membrane materials such as swelling, insufficient mechanical stability and lack of dynamic regulation ability, and especially can achieve efficient selective screening of monovalent and divalent ions (K + / Mg 2+ Selectivity up to 156).

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a piezoelectric channel ion sieving modified MXene membrane is provided, characterized in that it comprises the following steps:

[0007] S1: Mixing lithium salt and acid solution to obtain a mixed solution, then adding three-dimensional layered MAX raw materials to the mixed solution, stirring, centrifugal washing, ultrasonication, and centrifugation to obtain a two-dimensional MXene nanosheet dispersion;

[0008] S2: Add a multidentate ligand to the two-dimensional MXene nanosheet dispersion obtained in step S1, react at 20-35°C under stirring for 2-8 hours to modify the MXene nanosheets, and then vacuum filter, spin-coat or scrape the modified MXene nanosheet solution onto a porous substrate, and then vacuum dry at 50-80°C for 4-12 hours to obtain a modified MXene membrane.

[0009] As a further preferred embodiment of the present invention, in step S2, the multidentate ligand is any one of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracarboxylic acid (DOTA), ethylenediaminetetraacetic acid (EDTA), phytic acid (PA), and 1,4,7,10-tetraazacyclododecane (Cyclen); the mass ratio of MXene to the multidentate ligand in the two-dimensional MXene nanosheet dispersion is (1-6 mg): (50-200 mg); preferably 3 mg:150 mg;

[0010] The porous substrate is any one of PES, PVDF, PTFE, Nylon and Al2O3 ceramic membrane, and the pore size of the porous substrate is in the range of 0.1-0.5 μm;

[0011] Preferably, the porous substrate is circular with a diameter of 5-7 cm;

[0012] The stirring rate of the stirring is 200-500 rpm; the reaction time is preferably 6 hours;

[0013] The drying is preferably carried out at 60° C. for 6 hours.

[0014] As a further preferred embodiment of the present invention, in step S1, the lithium salt is any one of lithium fluoride, lithium chloride, lithium bromide, lithium sulfate and lithium nitrate;

[0015] The acid solution is any one of hydrochloric acid, hydrofluoric acid, phosphoric acid, sulfuric acid and nitric acid;

[0016] Preferably, the ratio of the mass of the lithium salt to the volume of the acid solution is (2-4) g: (30-50) ml, and the concentration of the acid solution is 6-12 mol / L.

[0017] As a further preferred embodiment of the present invention, in step S1, the stirring time is 24-48 hours, the stirring speed is 100-400 rpm; the stirring temperature is 30-40° C., preferably 36° C.;

[0018] The centrifugal washing is performed 10-15 times with deionized water at a centrifugal speed of 8000-10000 rpm; each centrifugal washing time is 30-60 minutes;

[0019] The power of the ultrasound is 100-400W, and the time of the ultrasound is 30-60min;

[0020] The centrifugal treatment after ultrasound is performed at a speed of 2000-4000 rpm, divided into 3-6 times, and the time of each centrifugation is 30-60 minutes.

[0021] According to another aspect of the present invention, the present invention provides a piezoelectric channel ion sieving modified MXene membrane prepared by the above preparation method.

[0022] According to another aspect of the present invention, the present invention provides the use of the above-mentioned piezoelectric channel ion sieving modified MXene membrane in membrane separation and sieving ions.

[0023] According to another aspect of the present invention, the present invention provides the use of the above-mentioned piezoelectric channel ion sieving modified MXene membrane to form dynamic piezoelectric channels under mechanical stimulation in membrane separation and sieving ions.

[0024] As a further preferred embodiment of the present invention, the mechanical stimulation is at least one of ultrasonic stimulation, stirring stimulation, and liquid flow stimulation;

[0025] Preferably, the ultrasonic power of the ultrasonic stimulation is less than or equal to 400W, preferably 100-400W, more preferably 300W;

[0026] The stirring speed of the stirring stimulation is 100-400 rpm;

[0027] The flow rate of the slurry flow stimulation is 5-40 mL / min.

[0028] As a further preferred embodiment of the present invention, the membrane separation is specifically to separate +1-valent metal cations from multivalent metal cations, or to separate +1-valent metal cations from another +1-valent metal cation;

[0029] The multivalent metal cation is at least one of a +2-valent metal cation and a +3-valent metal cation; preferably, the +1-valent metal cation Li + 、Na + , K + At least one of the polyvalent metal cations Mg2+ , Ca 2+ 、Al 3+ At least one of;

[0030] More preferably, the application is to place an ion separation device equipped with a piezoelectric channel ion screening modified MXene membrane in an ultrasonic cleaning machine, add the solution to be separated on the feed side and deionized water on the other side, and drive the concentration difference and the mechanical stimulation of ultrasound to achieve the selective separation of +1-valent metal cations and multivalent metal cations, or to achieve the selective separation of +1-valent metal cations and another +1-valent metal cation; in the solution to be separated, the ion concentration of the metal cation is preferably 0.001-2 mol / L.

[0031] As a further preference of the present invention, the solution to be separated is seawater, and the application is specifically application in seawater desalination.

[0032] Compared with the existing technology, the above technical solution conceived by the present invention modifies MXene nanosheets with multidentate ligands (such as DOTA, EDTA, PA or Cyclen) molecules to construct anti-swelling sub-nanochannels. The piezoelectric effect can be activated by mechanical stimulation such as ultrasound and stirring to form piezoelectric channels, and membrane separation applications such as efficient screening of monovalent / divalent ions can be achieved by utilizing electromigration and staggered electric field mechanisms.

[0033] The present invention adds a multidentate ligand to a dispersion of two-dimensional MXene nanosheets and reacts them at 20-35°C with stirring for 2-8 hours, thereby strengthening the interaction between adjacent MXene sheets through the synergistic effect of covalent and hydrogen bonds. The multidentate ligand introduced in the present invention can strengthen the interaction between adjacent MXene sheets and also enhance the spontaneous polarization of MXene, thereby improving the piezoelectricity of MXene. Based on the present invention, any one of DOTA, EDTA, PA or Cyclen can be preferably used as a multidentate ligand to strengthen the interaction between adjacent MXene (for example, DOTA and EDTA anchor adjacent MXene sheets through Ti-COO-covalent bonds and hydrogen bonds, PA anchors adjacent MXene sheets through Ti-POO-covalent bonds, and Cyclen anchors adjacent MXene sheets through hydrogen bonds). The temperature condition is 20-35°C (especially room temperature 25°C), which is mild. In addition, the multidentate ligand can enhance the self-polarization of MXene, improve its piezoelectricity, and lay the foundation for the construction of piezoelectric channels.

[0034] It is known in the prior art that MXene can achieve a preliminary ion screening effect by regulating the interlayer spacing through intercalation chemistry, but this type of static design cannot reproduce the dynamic response characteristics of biological systems. More importantly, traditional external field regulation (such as applying voltage or adjusting pH) will introduce additional energy consumption and chemical interference, which seriously restricts the potential for practical applications. In addition, the weak interaction between MXene sheets causes it to swell easily in aqueous solution, which not only affects its film-forming stability, but also destroys the long-term stability of sub-nanometer channels, thereby restricting ion separation performance. The present invention proposes an innovative piezoelectric channel strategy, which realizes the dynamic regulation of biomimetic ion channels by utilizing the piezoelectric effect of MXene. We modified MXene by organic cross-linking to strengthen the interaction between adjacent MXenes, and discovered for the first time that ultrasonically induced mechanical vibrations can generate periodic polarized electric fields between MXene layers. This in-situ generated piezoelectric field simulates the force-electric conversion mechanism of biological example channels, making the membrane responsive to K + / Mg 2+ The selectivity of the membrane was increased to 156, setting a new record for biomimetic membranes. Most importantly, this mechanism does not rely on external chemical regulation and can achieve autonomous response only through environmental mechanical energy (such as fluid pressure and membrane vibration).

[0035] Specifically, the present invention can achieve the following beneficial effects:

[0036] (1) The present invention utilizes multidentate ligands (e.g., DOTA, EDTA, PA, or Cyclen) to crosslink MXene nanosheets, and the resulting modified MXene membrane has excellent anti-swelling properties.

[0037] (2) The modified MXene membrane of the present invention combines the piezoelectric properties of MXene, activating the piezoelectric effect within the membrane through mechanical stimulation, thereby improving monovalent / divalent ion selectivity. Under mechanical stimulation, it can be applied to membrane separation applications such as efficient screening of monovalent / divalent ions.

[0038] (3) The mechanically responsive modified MXene membrane of the present invention has broad application prospects in seawater desalination, resource recovery and high-precision ion screening.

[0039] In summary, the modified MXene biomimetic ion separation membrane obtained by the present invention exhibits dynamic responsiveness, high stability, and universal applicability. It has excellent anti-swelling properties, can be stably maintained in saline solutions, and exhibits excellent mechanical responsiveness, making it suitable for applications such as seawater desalination and resource recovery. Based on the modified MXene membrane obtained by the present invention, a mechanically responsive ion separation system can be further constructed. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the surface morphology of the MXene@DOTA film prepared in Example 1.

[0041] Figure 2 This is a graph showing the morphological changes of the MXene prepared in Comparative Example 1 and the MXene@DOTA membrane prepared in Example 2 after being immersed in water for 3 hours.

[0042] Figure 3 This is a performance diagram of the permeability of the MXene prepared in Comparative Example 2 and the MXene@DOTA membrane prepared in Example 3 to different metal ions.

[0043] Figure 4 These are the XRD patterns of the MXene prepared in Comparative Example 2 and the MXene@DOTA membrane prepared in Example 3 in pure water and different salt solution environments.

[0044] Figure 5 This is a comparison of the nanoscratch performance of the MXene prepared in Example 2 and the MXene@DOTA film prepared in Example 3.

[0045] Figure 6 This is the XRD pattern of the GO membrane prepared in comparative example 3 in dry / wet states.

[0046] Figure 7 This is a comparison chart of the ion screening performance of the MXene prepared in Example 4, the MXene@EDTA prepared in Example 4, and the piezoelectric channel MXene@EDTA membrane (referred to as "piezoelectric channel membrane") formed by mechanical stimulation of the MXene@EDTA prepared in Example 4.

[0047] Figure 8 This is a graph showing the morphological changes of the MXene prepared in Comparative Example 1 and the MXene@DOTA film prepared in Example 2 after being subjected to an ultrasonic field for 1 hour.

[0048] Figure 9 This is a graph of the piezoelectric voltage signals generated by the MXene prepared in Comparative Example 1 and the MXene@DOTA film prepared in Example 2 under the action of an ultrasonic field.

[0049] Figure 10 This is a schematic diagram of the preparation process of the MXene@DOTA membrane of the present invention and the piezoelectric channel separation mechanism (taking DOTA modification as an example, the same applies to EDTA, PA, and Cyclen modifications). DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0051] The three-dimensional layered MAX raw materials, DOTA (i.e., 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracarboxylic acid), EDTA (i.e., ethylenediaminetetraacetic acid), PA (i.e., phytic acid), Cyclen (i.e., 1,4,7,10-tetraazacyclododecane), and GO (i.e., graphene oxide) used in the examples below were all purchased from commercial sources.

[0052] Example 1

[0053] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0054] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 300 rpm for 36 h. The reaction temperature was 36°C.

[0055] (2) The reaction product in step (1) was centrifuged and washed 12 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 30 minutes;

[0056] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 400 W and a treatment time of 30 min;

[0057] (4) centrifuging the product in step (3) 6 times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0058] (5) The dispersion containing 3 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 150 mg of DOTA was added to the MXene dispersion and reacted at 20 ° C for 6 h. The DOTA-modified MXene nanosheet dispersion was then vacuum filtered onto a PES substrate with a diameter of 5 cm and a pore size of 0.22 μm. Finally, the prepared MXene membrane was heated in a vacuum oven at 60 ° C for 6 h to obtain a MXene@DOTA membrane;

[0059] Ion screening performance test of the membrane: The ion separation device equipped with MXene@DOTA membrane was placed in an ultrasonic cleaning machine, 50 mL of test ion salt solution was added to the feed side, the composition of which was a mixed salt solution of KCl and MgCl2 (including 0.2 M KCl and 0.2 M MgCl2), and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the K + The permeation flux is 0.021 mol m -2 h -1 , K+ / Mg 2+ The selectivity is 64.2; when the ultrasonic mechanical stimulation with a power of 300W is applied, efficient metal cation selective separation can be achieved. The experimentally measured K + The permeation flux is 0.12 mol m -2 h -1 , K + / Mg 2+ The selectivity is 156.

[0060] Example 2

[0061] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0062] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 300 rpm for 36 h. The reaction temperature was 36°C.

[0063] (2) The reaction product in step (1) was centrifuged and washed 12 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 30 minutes;

[0064] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 400 W and a treatment time of 30 min;

[0065] (4) centrifuging the product in step (3) 6 times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0066] (5) The dispersion containing 3 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 150 mg of DOTA was added to the MXene dispersion and reacted at 20 ° C for 6 h. The DOTA-modified MXene nanosheet dispersion was then vacuum filtered onto a PES substrate with a diameter of 5 cm and a pore size of 0.22 μm. Finally, the prepared MXene membrane was heated in a vacuum oven at 60 ° C for 6 h to obtain a MXene@DOTA membrane;

[0067] Ion screening performance test of the membrane: The ion separation device equipped with MXene@DOTA membrane was placed in an ultrasonic cleaning machine. 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the K + The permeation flux is 0.021 mol m -2 h -1 , K+ / Mg 2+ The selectivity is 64.2; when the ultrasonic mechanical stimulation with a power of 400W is applied, efficient metal cation selective separation can be achieved. The experimentally measured K + The permeation flux is 0.15 mol m -2 h -1 , K + / Mg 2+ The selectivity is 188.

[0068] Example 3

[0069] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0070] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 400 rpm for 48 h. The reaction temperature was 40°C.

[0071] (2) The reaction product in step (1) was centrifuged and washed 15 times at a centrifugal speed of 8000 rpm, with each centrifugal washing time of 60 min;

[0072] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 100 W and a treatment time of 60 min;

[0073] (4) centrifuging the product in step (3) three times at a speed of 4000 rpm for 30 min to obtain a MXene nanosheet dispersion;

[0074] (5) The dispersion containing 2 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 200 mg of DOTA was added to the MXene dispersion and reacted at 35 ° C for 2 h. The DOTA-modified MXene nanosheet dispersion was then vacuum filtered onto a Nylon substrate with a diameter of 7 cm and a pore size of 0.50 μm. Finally, the prepared MXene film was heated in a vacuum oven at 80 ° C for 4 h to obtain a MXene@DOTA film;

[0075] Ion screening performance test of the membrane: The ion separation device equipped with MXene@DOTA membrane was placed in an ultrasonic cleaning machine. 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the K + The permeation flux is 0.0024 mol m -2 h -1 , K+ / Mg 2+ The selectivity is 44.2; when the ultrasonic mechanical stimulation with a power of 200W is applied, efficient metal cation selective separation can be achieved. The experimentally measured K + The permeation flux is 0.076 mol m -2 h -1 , K + / Mg 2+ The selectivity is 98.6.

[0076] Example 4

[0077] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0078] (1) 2.0 g of lithium chloride was mixed with 30 mL of 12 mol / L hydrofluoric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 100 rpm for 24 h. The reaction temperature was 30°C.

[0079] (2) The reaction product in step (1) was centrifuged and washed 10 times at a centrifugal speed of 9000 rpm, with each centrifugal washing time of 40 min;

[0080] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 200 W and a treatment time of 60 min;

[0081] (4) centrifuging the product in step (3) three times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0082] (5) The dispersion containing 1 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 50 mg of EDTA was added to the MXene dispersion and reacted at room temperature for 8 h. The EDTA-modified MXene nanosheet dispersion was then vacuum filtered onto a Nylon substrate with a diameter of 7 cm and a pore size of 0.50 μm. Finally, the prepared MXene film was heated in a vacuum oven at 50 ° C for 12 h to obtain a MXene@EDTA film;

[0083] Ion screening performance test of the membrane: The ion separation device equipped with MXene@EDTA membrane was placed in an ultrasonic cleaning machine. 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. The K + The permeation flux is 0.011 mol m -2 h -1 , K+ / Mg 2+ The selectivity is 42.6. When the ultrasonic mechanical stimulation with a power of 100W is applied, the metal cation selective separation is achieved efficiently. + The permeation flux is 0.028 mol m -2 h -1 , K + / Mg 2+ The selectivity is 72.8.

[0084] Example 5

[0085] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0086] (1) 4.0 g of lithium bromide was mixed with 50 mL of 6 mol / L sulfuric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 400 rpm for 48 h. The reaction temperature was 40°C.

[0087] (2) The reaction product in step (1) was centrifuged and washed 15 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 45 minutes;

[0088] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 200 W and a treatment time of 60 min;

[0089] (4) centrifuging the product in step (3) three times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0090] (5) The dispersion containing 6 mg MXene in step (4) was ultrasonically dispersed uniformly, and then 200 mg PA was added to the MXene dispersion and reacted at room temperature for 4 h. The PA-modified MXene nanosheet dispersion was then vacuum filtered onto a PVDF substrate with a diameter of 7 cm and a pore size of 0.22 μm. Finally, the prepared MXene membrane was heated in a vacuum oven at 80 ° C for 8 h to obtain a MXene@PA membrane;

[0091] Ion screening performance test of the membrane: The ion separation device equipped with MXene@PA membrane was placed in a magnetic stirring chamber with a stirring rate of 100 rpm. 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the experimental K + The permeation flux is 0.039 mol m -2 h -1 , K+ / Mg 2+ The selectivity is 8.5; when mechanical stimulation is applied at a stirring rate of 100 rpm, K + The permeation flux is 0.036 mol m -2 h -1 , K + / Mg 2+ The selectivity is 10.8, which is significantly improved compared to when no mechanical stimulation is applied.

[0092] Example 6

[0093] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0094] (1) 2.4 g of lithium sulfate was mixed with 30 mL of 9 mol / L phosphoric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 400 rpm for 48 h. The reaction temperature was 40°C.

[0095] (2) The reaction product in step (1) was centrifuged and washed 15 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 45 minutes;

[0096] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 200 W and a treatment time of 60 min;

[0097] (4) centrifuging the product in step (3) three times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0098] (5) The dispersion containing 2 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 100 mg of PA was added to the MXene dispersion and allowed to react at room temperature for 4 h. The PA-modified MXene nanosheet dispersion was then vacuum filtered onto a Nylon substrate with a diameter of 7 cm and a pore size of 0.5 μm. Finally, the prepared MXene film was heated in a vacuum oven at 80 ° C for 8 h to obtain a MXene@PA film;

[0099] Ion screening performance test of the membrane: The MXene@PA membrane was placed in an ion separation device, 50 mL of test ion salt solution consisting of 2 M KCl and 2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the experimental measured K + The permeation flux is 0.42 mol m -2 h -1 , K + / Mg2+ The selectivity is 9.7; when the solution flow rate is 5mL / min, the K + The permeation flux is 0.37 mol m -2 h -1 , K + / Mg 2+ The selectivity is 12.2, which is significantly improved compared to when no mechanical stimulation is applied.

[0100] Example 7

[0101] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0102] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 400 rpm for 48 h. The reaction temperature was 40°C.

[0103] (2) The reaction product in step (1) was centrifuged and washed 15 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 45 minutes;

[0104] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 200 W and a treatment time of 60 min;

[0105] (4) centrifuging the product in step (3) three times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0106] (5) The dispersion containing 2 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 100 mg of PA was added to the MXene dispersion and reacted at room temperature for 4 h. The PA-modified MXene nanosheet dispersion was then vacuum filtered onto an Al2O3 substrate with a diameter of 7 cm and a pore size of 0.1 μm. Finally, the prepared MXene film was heated in a vacuum oven at 80 ° C for 8 h to obtain a MXene@PA film;

[0107] Ion screening performance test of the membrane: The MXene@PA membrane was placed in an ion separation device, 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the experimental measured K + The permeation flux is 0.034 mol m -2 h -1 , K + / Mg 2+The selectivity is 9.6; when the solution flow rate is 40mL / min, the selective separation of metal cations is achieved efficiently. + The permeation flux is 0.029 mol m -2 h -1 , K + / Mg 2+ The selectivity is 13.5, which is significantly improved compared to when no mechanical stimulation is applied.

[0108] Example 8

[0109] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0110] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 300 rpm for 36 h. The reaction temperature was 36°C.

[0111] (2) The reaction product in step (1) was centrifuged and washed 12 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 30 minutes;

[0112] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 400 W and a treatment time of 30 min;

[0113] (4) centrifuging the product in step (3) 6 times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0114] (5) The dispersion containing 3 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 150 mg of DOTA was added to the MXene dispersion and reacted at 20 ° C for 6 h. The DOTA-modified MXene nanosheet dispersion was then vacuum filtered onto a PES substrate with a diameter of 5 cm and a pore size of 0.22 μm. Finally, the prepared MXene membrane was heated in a vacuum oven at 60 ° C for 6 h to obtain a MXene@DOTA membrane;

[0115] Ion screening performance test of the membrane: The ion separation device equipped with MXene@DOTA membrane was placed in an ultrasonic cleaning machine. 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M NaCl was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the K + The permeation flux is 0.018 mol m -2 h -1 , K+ / Na + The selectivity is 4.2; when the ultrasonic mechanical stimulation with a power of 300W is applied, efficient metal cation selective separation can be achieved. The experimentally measured K + The permeation flux is 0.13 mol m -2 h -1 , K + / Na + The selectivity is 5.7.

[0116] Example 9

[0117] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0118] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 300 rpm for 36 h. The reaction temperature was 36°C.

[0119] (2) The reaction product in step (1) was centrifuged and washed 12 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 30 minutes;

[0120] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 400 W and a treatment time of 30 min;

[0121] (4) centrifuging the product in step (3) 6 times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0122] (5) The dispersion containing 3 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 150 mg of DOTA was added to the MXene dispersion and reacted at 20 ° C for 6 h. The DOTA-modified MXene nanosheet dispersion was then vacuum filtered onto a PES substrate with a diameter of 5 cm and a pore size of 0.22 μm. Finally, the prepared MXene membrane was heated in a vacuum oven at 60 ° C for 6 h to obtain a MXene@DOTA membrane;

[0123] Ion screening performance test of the membrane: The ion separation device equipped with MXene@DOTA membrane was placed in an ultrasonic cleaning machine. 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M AlCl3 was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the K + The permeation flux is 0.015 mol m -2 h -1 , K+ / Al 3+ The selectivity is 73.2. When the ultrasonic mechanical stimulation with a power of 300W is applied, efficient metal cation selective separation can be achieved. The experimentally measured K + The permeation flux is 0.16 mol m -2 h -1 , K + / Al 3+ The selectivity is 175.8.

[0124] Example 10

[0125] A preparation method and application of a piezoelectric channel ion screening modified MXene membrane, comprising the following steps:

[0126] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 300 rpm for 36 h. The reaction temperature was 36°C.

[0127] (2) The reaction product in step (1) was centrifuged and washed 12 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 30 minutes;

[0128] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 400 W and a treatment time of 30 min;

[0129] (4) centrifuging the product in step (3) 6 times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0130] (5) The dispersion containing 3 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then 150 mg of Cyclen was added to the MXene dispersion and reacted at 20 ° C for 6 h. The MXene nanosheet dispersion modified by Cyclen was then vacuum filtered onto a PES substrate with a diameter of 5 cm and a pore size of 0.22 μm. Finally, the prepared MXene membrane was heated in a vacuum oven at 60 ° C for 6 h to obtain a MXene@Cyclen membrane;

[0131] Membrane ion screening performance test: The ion separation device equipped with MXene@Cyclen membrane was placed in a magnetic stirring chamber at a stirring rate of 400 rpm. 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. Driven by the concentration difference, the experimental K + The permeation flux is 0.028 mol m -2h -1 , K + / Mg 2+ The selectivity was 33.5; when mechanical stimulation was applied at a stirring rate of 400 rpm, K + The permeation flux is 0.022 mol m -2 h -1 , K + / Mg 2+ The selectivity was 58.3, which was significantly improved compared with the case when no mechanical stimulation was applied.

[0132] Comparative Example 1

[0133] This comparative example prepares a conventional unmodified MXene membrane without a multidentate ligand. No multidentate ligand is used in the preparation process. The specific steps are as follows:

[0134] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 300 rpm for 36 h. The reaction temperature was 36°C.

[0135] (2) The reaction product in step (1) was centrifuged and washed 12 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 30 minutes;

[0136] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 300 W and a treatment time of 30 min;

[0137] (4) centrifuging the product in step (3) 6 times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0138] (5) The dispersion containing 3 mg of MXene in step (4) was ultrasonically dispersed uniformly and vacuum filtered onto a PES substrate with a diameter of 5 cm and a pore size of 0.22 μm to obtain a MXene membrane.

[0139] Comparative Example 2

[0140] This comparative example prepares a conventional unmodified MXene membrane without a multidentate ligand. No multidentate ligand is used in the preparation process. The specific steps are as follows:

[0141] (1) 2.4 g of lithium fluoride was mixed with 30 mL of 9 mol / L hydrochloric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 400 rpm for 48 h. The reaction temperature was 40°C.

[0142] (2) The reaction product in step (1) was centrifuged and washed 15 times at a centrifugal speed of 8000 rpm, with each centrifugal washing time of 60 min;

[0143] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 100 W and a treatment time of 60 min;

[0144] (4) centrifuging the product in step (3) three times at a speed of 4000 rpm for 30 min to obtain a MXene nanosheet dispersion;

[0145] (5) The dispersion containing 2 mg of MXene in step (4) was uniformly dispersed by ultrasonication, and then vacuum filtered onto a Nylon substrate with a diameter of 7 cm and a pore size of 0.50 μm to obtain a MXene membrane.

[0146] Comparative Example 3

[0147] The conventional unmodified GO membrane prepared in this comparative example does not contain a multidentate ligand. No multidentate ligand is used in the preparation process. The specific steps are as follows:

[0148] (1) The commercially available GO dispersion was uniformly dispersed by ultrasonication and then vacuum filtered onto a Nylon substrate with a diameter of 7 cm and a pore size of 0.22 μm to obtain a GO membrane.

[0149] Comparative Example 4

[0150] This comparative example prepares a conventional unmodified MXene membrane without a multidentate ligand. No multidentate ligand is used in the preparation process. The specific steps are as follows:

[0151] (1) 2.0 g of lithium chloride was mixed with 30 mL of 12 mol / L hydrofluoric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 100 rpm for 24 h. The reaction temperature was 30°C.

[0152] (2) The reaction product in step (1) was centrifuged and washed 10 times at a centrifugal speed of 9000 rpm, with each centrifugal washing time of 40 min;

[0153] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 200 W and a treatment time of 60 min;

[0154] (4) centrifuging the product in step (3) three times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0155] (5) The dispersion containing 1 mg of MXene in step (4) was ultrasonically dispersed uniformly, and then vacuum filtered onto a Nylon substrate with a diameter of 7 cm and a pore size of 0.50 μm to obtain a MXene membrane.

[0156] Ion screening performance test of the membrane: The MXene membrane was placed in an ion separation device, 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M MgCl2 was added to the feed side, and 50 mL of deionized water was added to the other side. + The permeation flux is 0.038 mol m -2 h -1 , K + / Mg 2+ The selectivity is 6.8.

[0157] Comparative Example 5

[0158] This comparative example prepares a conventional unmodified MXene membrane without a multidentate ligand. No multidentate ligand is used in the preparation process. The specific steps are as follows:

[0159] (1) 2.4 g of lithium chloride was mixed with 30 mL of 9 mol / L hydrofluoric acid solution to obtain a mixed solution, and then 1.5 g of three-dimensional layered MAX raw material was added to the mixed solution, and stirred at 300 rpm for 36 h. The reaction temperature was 30°C.

[0160] (2) The reaction product in step (1) was centrifuged and washed 12 times at a centrifugal speed of 10,000 rpm, with each centrifugal washing time of 30 minutes;

[0161] (3) The reaction product in step (2) was subjected to ultrasonic treatment under nitrogen protection, with an ultrasonic power of 400 W and a treatment time of 30 min;

[0162] (4) centrifuging the product in step (3) 6 times at a speed of 2000 rpm for 60 min to obtain a MXene nanosheet dispersion;

[0163] (5) The dispersion containing 3 mg of MXene in step (4) was uniformly dispersed by ultrasonication, and then vacuum filtered onto a PES substrate with a diameter of 5 cm and a pore size of 0.22 μm to obtain a MXene membrane.

[0164] Ion screening performance test of the membrane: The MXene membrane was placed in an ion separation device, 50 mL of test ion salt solution consisting of 0.2 M KCl and 0.2 M NaCl was added to the feed side, and 50 mL of deionized water was added to the other side. +The permeation flux is 0.032 mol m -2 h -1 , K + / Na + The selectivity is 1.6.

[0165] Figure 1 This is an environmental scanning electron microscope morphology image of the piezoelectric channel ion screening MXene@DOTA membrane prepared in Example 1. It is not difficult to see that the MXene@DOTA membrane still maintains the wrinkled structure of the MXene membrane and its surface is defect-free, laying the foundation for subsequent efficient ion screening.

[0166] The MXene prepared in Comparative Example 1 and the MXene@DOTA membrane prepared in step (5) of Example 2 were soaked in deionized water for 3 h respectively. The morphology changes before and after soaking are shown in Figure 2. Figure 2 As shown in the figure, it is not difficult to see that MXene exhibits obvious swelling phenomenon, while the MXene@DOTA film has better anti-swelling properties due to the interaction between adjacent MXene sheets strengthened by DOTA, and its morphology is almost unchanged.

[0167] The MXene prepared in Comparative Example 2 and the MXene@DOTA membrane prepared in step (5) of Example 3 were placed in an ion separation device, respectively. 50 mL of a 0.2 M test ion salt solution (one of KCl, NaCl, LiCl, CaCl2, and MgCl2) was added to the feed side, and 50 mL of deionized water was added to the other side. The ion permeation flux was tested under the drive of the concentration difference. The results are shown in FIG. Figure 3 As shown in the figure, it is not difficult to see that the MXene@DOTA membrane and the original MXene membrane show the same ion permeation order: K + >Na + >Li + >>Ca 2+ >Mg 2+ This phenomenon is closely related to the differences in hydration diameter and dehydration energy of each ion. According to the hydrated ion transport theory, ions need to partially remove their hydration shells when passing through sub-nanometer channels, and the energy barrier of this process is positively correlated with the hydration energy. It is worth noting that the ion permeability of MXene@DOTA is significantly lower than that of the original MXene membrane, which is attributed to the steric hindrance effect caused by the cross-linking of DOTA to form smaller and more stable channel sizes.

[0168] The MXene prepared in Comparative Example 2 and the MXene@DOTA membrane prepared in step (5) of Example 3 were placed in deionized water, 0.2M KCl solution, 0.2M NaCl solution, 0.2M LiCl solution, 0.2M CaCl2 solution and 0.2M MgCl2 solution, respectively, and XRD tests were performed. The results are as follows: Figure 4 As shown in the figure, it is easy to see that when the MXene@DOTA film is immersed in a salt solution, its diffraction peak at position 002 does not shift significantly, remaining at around 5.5°. In contrast, when the MXene film is placed in a salt solution, its diffraction peak at position 002 shifts significantly, from an initial 6.0° to a maximum of 5.0°, indicating swelling. This comparison clearly demonstrates that the MXene@DOTA film's anti-swelling properties have been effectively improved.

[0169] The MXene prepared in Comparative Example 2 and the MXene@DOTA film prepared in step (5) of Example 3 were subjected to nanoscratch tests, and the results are as follows: Figure 5 As shown, it is not difficult to see that the critical load of the MXene@DOTA film reaches 31.28 mN, which is 4 times higher than that of the original MXene film (7.67 mN), fully demonstrating the enhancing effect of DOTA on interlayer interaction.

[0170] The GO membrane prepared in Comparative Example 3 was placed in deionized water and subjected to XRD testing. The results were as follows: Figure 6 As shown, it is not difficult to see that compared with the dry state, the diffraction peak of the wet GO film shifts significantly, from the initial 10.05° to 11.47°, indicating that its anti-swelling property is poor.

[0171] The ion screening performance of the MXene membrane prepared in step (5) of comparative example 4 and the MXene@EDTA membrane prepared in step (5) of example 4 were compared under concentration drive and non-ultrasonic stimulation. The results are as follows: Figure 7 As shown, it is not difficult to see that EDTA modification significantly enhances the ion screening performance of the MXene membrane, and its selectivity is further improved after applying ultrasound.

[0172] The MXene prepared in Comparative Example 1 and the MXene@DOTA film prepared in step (5) of Example 2 were placed in an ultrasonic field with a power of 300W for 1 hour. The morphological changes before and after ultrasonication are shown in the following table. Figure 8 As shown in the figure, it is not difficult to see that the morphology of the MXene film is severely damaged, while the MXene@DOTA film still maintains the integrity of its morphology due to the interaction between adjacent MXene sheets strengthened by DOTA, indicating that the mechanical stability of the MXene@DOTA film is enhanced.

[0173] The MXene prepared in Comparative Example 1 and the MXene@DOTA membrane prepared in step (5) of Example 2 were placed in an ion separation device and an ultrasonic cleaner, respectively. 50 mL of a test ion salt solution consisting of a mixed salt solution of KCl and MgCl2 (including 0.2 M KCl and 0.2 M MgCl2) was added to the feed side, and 50 mL of deionized water was added to the other side. The piezoelectric voltage signal in an ultrasonic field with a power of 300 W was measured by an oscilloscope. The results are shown in FIG. Figure 9 As shown in the figure, it is not difficult to see that the piezoelectric voltage signal of MXene@DOTA film (+8 / -8V) is significantly stronger than that of MXene film (+3 / -3V), indicating that DOTA modification enhances the mechanical responsiveness of MXene. Figure 9 The piezoelectric response results shown also indicate that the modified MXene film obtained in the present invention can reproduce the dynamic response characteristics of biological systems.

[0174] Figure 10 The figure is a schematic diagram of the preparation process and piezoelectric channel separation mechanism of the MXene@DOTA membrane of the present invention. Through DOTA molecular modification, a stable covalent and hydrogen bond cross-linked network is formed between the MXene nanosheets, constructing size-controllable, anti-swelling sub-nanochannels, which give the membrane excellent monovalent / multivalent ion selectivity. After further introduction of ultrasonic stimulation, the piezoelectric channel induced by the piezoelectric effect in the membrane significantly extends the transmission path of multivalent ions and enhances their transmission resistance through electromigration and staggered electric field mechanisms, thereby improving selectivity. The same principle applies when other multidentate ligands (such as EDTA, PA, Cyclen) are used.

[0175] The above embodiment is only an example. The metal cation to be separated is Li + , Na + , K + , Mg 2+ , Ca 2+ , Al 3+ At least two of the above (for example, in addition to separating +1-valent and +2-valent metal cations, it can also be used to separate two types of +1-valent metal cations). For another example, in addition to using DOTA, EDTA, PA, and Cyclen multidentate ligands, other multidentate ligand materials with a tooth number of not less than 2 (or even not less than 4) can also be used to modify MXene. The mass ratio of MXene to multidentate ligand can also be preferably (1-6 mg): (50-200 mg).

[0176] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a piezoelectric channel ion screening modified MXene membrane, characterized in that: The following steps are involved: S1: Mixing lithium salt and acid solution to obtain a mixed solution, then adding three-dimensional layered MAX raw materials to the mixed solution, stirring, centrifugal washing, ultrasonication, and centrifugation to obtain a two-dimensional MXene nanosheet dispersion; S2: Add a multidentate ligand to the two-dimensional MXene nanosheet dispersion obtained in step S1, react at 20-35°C under stirring for 2-8 hours to modify the MXene nanosheets, and then vacuum filter, spin-coat or scrape the modified MXene nanosheet solution onto a porous substrate, and then vacuum dry at 50-80°C for 4-12 hours to obtain a modified MXene membrane.

2. The preparation method according to claim 1, wherein In step S2, the multidentate ligand is preferably any one of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracarboxylic acid (DOTA), ethylenediaminetetraacetic acid (EDTA), phytic acid (PA), and 1,4,7,10-tetraazacyclododecane (Cyclen); the mass ratio of MXene to the multidentate ligand in the two-dimensional MXene nanosheet dispersion is (1-6 mg): (50-200 mg); preferably 3 mg:150 mg; The porous substrate is any one of PES, PVDF, PTFE, Nylon and Al2O3 ceramic membrane, and the pore size of the porous substrate is in the range of 0.1-0.5 μm; Preferably, the porous substrate is circular with a diameter of 5-7 cm; The stirring rate of the stirring is 200-500 rpm; the reaction time is preferably 6 hours; The drying is preferably carried out at 60° C. for 6 hours.

3. The preparation method according to claim 1, wherein In step S1, the lithium salt is any one of lithium fluoride, lithium chloride, lithium bromide, lithium sulfate and lithium nitrate; The acid solution is any one of hydrochloric acid, hydrofluoric acid, phosphoric acid, sulfuric acid and nitric acid; Preferably, the ratio of the mass of the lithium salt to the volume of the acid solution is (2-4) g: (30-50) ml, and the concentration of the acid solution is 6-12 mol / L.

4. The preparation method according to claim 1, wherein In step S1, the stirring time is 24-48 hours, the stirring speed is 100-400 rpm; the temperature during the stirring is 30-40° C., preferably 36° C.; The centrifugal washing is performed 10-15 times with deionized water at a centrifugal speed of 8000-10000 rpm; each centrifugal washing time is 30-60 minutes; The power of the ultrasound is 100-400W, and the time of the ultrasound is 30-60min; The centrifugal treatment after ultrasound is performed at a speed of 2000-4000 rpm, divided into 3-6 times, and the time of each centrifugation is 30-60 minutes.

5. The piezoelectric channel ion sieving modified MXene membrane prepared by the preparation method according to any one of claims 1 to 4.

6. Application of the piezoelectric channel ion sieving modified MXene membrane as claimed in claim 5 in membrane separation and ion sieving.

7. Application of the piezoelectric channel ion sieving modified MXene membrane as claimed in claim 5 to form dynamic piezoelectric channels under mechanical stimulation in membrane separation and ion sieving.

8. The use according to claim 7, characterized in that The mechanical stimulation is at least one of ultrasonic stimulation, stirring stimulation, and liquid flow stimulation; Preferably, the ultrasonic power of the ultrasonic stimulation is less than or equal to 400W, preferably 100-400W, more preferably 300W; The stirring speed of the stirring stimulation is 100-400 rpm; The flow rate of the slurry flow stimulation is 5-40 mL / min.

9. The use according to claim 7 or 8, characterized in that The membrane separation is specifically to separate +1-valent metal cations from multivalent metal cations, or to separate +1-valent metal cations from another +1-valent metal cation; The multivalent metal cation is at least one of a +2-valent metal cation and a +3-valent metal cation; preferably, the +1-valent metal cation Li + 、Na + , K + At least one of the polyvalent metal cations Mg 2+ , Ca 2+ 、Al 3+ At least one of; More preferably, the application is to place an ion separation device equipped with a piezoelectric channel ion screening modified MXene membrane in an ultrasonic cleaning machine, add the solution to be separated on the feed side and deionized water on the other side, and drive the concentration difference and the mechanical stimulation of ultrasound to achieve the selective separation of +1-valent metal cations and multivalent metal cations, or to achieve the selective separation of +1-valent metal cations and another +1-valent metal cation; in the solution to be separated, the ion concentration of the metal cation is preferably 0.001-2 mol / L.

10. The use according to claim 6 or 7, characterized in that: The solution to be separated is seawater, and the application is specifically application in seawater desalination.

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