MXene-based composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention provides an MXene-based composite nanofiltration membrane as well as a preparation method and application thereof, and belongs to the technical field of nanofiltration membranes. An MXene two-dimensional nanosheet is adopted as a polyanion electrolyte and is combined with a polycation electrolyte, an MXene dispersion liquid and a polycation electrolyte solution are alternately sucked and filtered to the surface of a base membrane by pressure driving in an alternate suction filtration coating mode, and the composite nanofiltration membrane with a heterogeneous interface is formed on the base membrane through layer-by-layer self-assembly. The surface of the composite nanofiltration membrane is a compact separation layer formed by alternately stacking MXene sheet layers and polycation electrolyte. The prepared nanofiltration membrane has high ion rejection rate and high flux, the flux is larger than or equal to 24 L.m <-2 >. H <-1 > (3 bar), and the rejection rate of 500 mg / L Na2SO4 solution is larger than or equal to 82%.

Description

Technical Field

[0001] The present invention relates to the field of nanofiltration membrane technology, and in particular to a MXene-based composite nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] Nanofiltration membranes play a pivotal role in water treatment and separation technologies, playing a particularly crucial role in drinking water purification and wastewater treatment. Their significant advantage lies in their ability to efficiently remove micro-pollutants, heavy metal ions, pathogenic microorganisms, and organic matter from water, while effectively retaining minerals and other beneficial components that are beneficial to human health, thereby ensuring safe and healthy water quality. This characteristic has led to their widespread application in various water treatment systems, such as industrial wastewater treatment, seawater desalination, and household drinking water purification.

[0003] The separation mechanism of nanofiltration membranes relies primarily on two key mechanisms: pore size selection and charge effects. First, nanofiltration membranes have pore sizes intermediate between those of reverse osmosis membranes and ultrafiltration membranes, typically ranging from 1 to 10 nanometers. This allows them to effectively intercept pollutants such as particulate matter, viruses, bacteria, and most dissolved organic matter in water through physical separation. Through this physical separation, nanofiltration membranes filter out fine, harmful substances while allowing water molecules and beneficial minerals such as certain dissolved inorganic salts to pass through. Furthermore, the surface of nanofiltration membranes typically carries a negative or positive charge, creating a charge interaction between the membrane and the water flow. This charge effect, particularly the Donnan repulsion effect, plays a crucial role in the membrane's separation process. Specifically, when ions in water approach the membrane surface, ions with the same charge are repelled, while ions with the opposite charge are attracted, further enhancing the membrane's separation capability for charged ions. This mechanism significantly enhances the efficiency of nanofiltration membranes in separating charged pollutants (such as monovalent and divalent cations), and is particularly effective in removing heavy metal ions and other harmful ions from water. Therefore, through the synergistic effect of pore size screening and charge repulsion, nanofiltration membranes can not only significantly improve water quality and reduce the concentration of harmful substances, but also ensure that beneficial minerals and trace elements in the water are retained, avoiding negative impacts on human health. Their efficient separation performance and multiple advantages have led to their widespread application in the water treatment industry, and in the future sustainable use of water resources and environmental protection, the technical development and application prospects of nanofiltration membranes will be even broader.

[0004] Patent CN117942778A discloses a modified polyamide composite nanofiltration membrane and its preparation method. This composite nanofiltration membrane uses a modified meta-aramid hollow fiber membrane as the base membrane. A modifier is used to positively modify the MXene membrane on the base membrane surface, resulting in a MXene / modifier composite layer. This layer is then formed through interfacial polymerization to form an ultra-thin polyamide layer. This layer has a magnesium chloride rejection rate of only 40% to 92%, and the preparation process uses organic solvents, resulting in a low safety factor. Consequently, existing composite nanofiltration membrane preparation processes are environmentally unfriendly or suffer from low flux and salt rejection. Patent CN107029562A discloses a MXene-based composite nanofiltration membrane and its preparation method. However, the preparation process requires heat treatment at a temperature of 20-100°C for 2-30 minutes, resulting in a long heat treatment time and a relatively complex preparation method. Summary of the Invention

[0005] The object of the present invention is to provide a MXene-based composite nanofiltration membrane and its preparation method and application. The MXene-based composite nanofiltration membrane has a high divalent salt retention rate and high flux, and the preparation method is simple, safe and easy to implement.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a MXene-based composite nanofiltration membrane, comprising the following steps:

[0008] The MXene aqueous dispersion is used as the polyanion electrolyte dispersion;

[0009] mixing a polycation electrolyte with a salt solution to obtain a polycation electrolyte solution;

[0010] The base membrane is fixed, and the polyanion electrolyte dispersion and the polycation electrolyte solution are alternately filtered onto the surface of the base membrane by vacuum filtration. The alternate filtration is repeated until a multilayer structure is formed to obtain a MXene-based composite nanofiltration membrane.

[0011] Preferably, the concentration of the polyanion electrolyte dispersion is 1 to 10 g / L.

[0012] Preferably, the polycationic electrolyte includes polyacrylamine hydrochloride, polyvinylamine or polydimethyldiallylammonium chloride, and the concentration of the polycationic electrolyte solution is 1 to 10 g / L.

[0013] Preferably, the volume of the polyanion electrolyte dispersion or polycation electrolyte solution filtered each time is independently 10 to 20 mL.

[0014] Preferably, the temperature of each filtration is independently 15-25° C., and the pressure is independently 0.5-1.0 bar.

[0015] Preferably, the number of layers of the multi-layer structure formed by the alternating filtration is 2 to 10.

[0016] Preferably, after each filtration, the membrane is washed with water until the conductivity is constant before the next filtration.

[0017] Preferably, the preparation method of the MXene material includes: mixing Ti3AlC2 with a hydrogen fluoride solution, performing an etching reaction, and obtaining MXene; the amount ratio of the Ti3AlC2 to the hydrogen fluoride solution is 2-10 g:50 mL; the temperature of the etching reaction is 20-50°C, and the time is 24-48 hours.

[0018] The present invention provides a MXene-based composite nanofiltration membrane prepared by the preparation method described in the above technical solution.

[0019] The present invention provides the application of the MXene-based composite nanofiltration membrane described in the above technical solution in water treatment.

[0020] The present invention provides a method for preparing a MXene-based composite nanofiltration membrane. The present invention adopts MXene two-dimensional nanosheets as polyanion electrolytes and combines them with polycation electrolytes. The MXene dispersion and the polycation electrolyte solution are alternately filtered to the surface of the base membrane by pressure driving in an alternating filtration coating manner. A composite nanofiltration membrane with a heterogeneous interface is formed on the base membrane through layer-by-layer self-assembly. The surface of the composite nanofiltration membrane is formed by alternating stacking of MXene sheets and polycation electrolytes to form a dense separation layer.

[0021] The present invention can flexibly regulate the ion separation performance of the nanofiltration membrane by adjusting the addition amount of MXene, thereby optimizing the selectivity and flux of the membrane. The alternating assembly of MXene two-dimensional nanosheets and polycationic electrolytes, driven by the entropy increase effect, allows MXene and polycationic electrolytes with opposite charges to be precisely combined through self-assembly, thereby forming a composite membrane with excellent separation performance composed of alternating coatings of MXene and polycations. The layer-by-layer self-assembly method not only ensures the efficient separation ability of the membrane, but also significantly improves the flux of the membrane. Therefore, the nanofiltration membrane of the present invention not only exhibits a higher pure water flux, but also has a stronger ion separation ability, and is particularly suitable for efficient separation and filtration of ions and pollutants in water, and has broad prospects in solving water pollution problems and breaking the dilemma of low water purification efficiency.

[0022] The composite nanofiltration membrane of the present invention has mild preparation conditions, simple and easy operation, and does not require the use of organic solvents (safety) or high-temperature treatment. The prepared nanofiltration membrane has both high ion retention rate (retention rate for Na2SO4 is 98%) and high flux (46L·m -2·h-1, 3bar), which has significant application value in the fields of water purification and salt separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM image of the MXene nanosheet in Example 1;

[0024] Figure 2 TEM image of MXene nanosheets in Example 1;

[0025] Figure 3 This is the AFM image of the MXene nanosheet in Example 1;

[0026] Figure 4 This is a cross-sectional SEM image of the MXene-based composite nanofiltration membrane in Example 1;

[0027] Figure 5 This is the surface SEM image of the MXene-based composite nanofiltration membrane in Example 1;

[0028] Figure 6 The nanofiltration membrane water flux diagram at different MXene concentrations in Examples 1 to 4;

[0029] Figure 7 This is a graph of the salt rejection rate of the nanofiltration membrane at different MXene concentrations in Examples 1 to 4. DETAILED DESCRIPTION

[0030] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0031] The present invention provides a method for preparing a MXene-based composite nanofiltration membrane, comprising the following steps:

[0032] The MXene aqueous dispersion is used as the polyanion electrolyte dispersion;

[0033] mixing a polycation electrolyte with a salt solution to obtain a polycation electrolyte solution;

[0034] The base membrane is fixed, and the polyanion electrolyte dispersion and the polycation electrolyte solution are alternately filtered onto the surface of the base membrane by vacuum filtration. The alternate filtration is repeated until a multilayer structure is formed to obtain a MXene-based composite nanofiltration membrane.

[0035] In the present invention, the preparation method of the MXene material preferably includes: mixing Ti3AlC2 with a hydrogen fluoride solution, performing an etching reaction, and after the etching reaction is completed, centrifuging the resulting product (to separate the supernatant from the MXene sediment), and washing with water until the pH of the supernatant is 5.5-6.5 and the color of the supernatant is dark green, thereby obtaining a MXene aqueous dispersion.

[0036] In the present invention, the usage ratio of the Ti3AlC2 and hydrogen fluoride solution is preferably 2-10 g:50 mL, more preferably 2 g:50 mL; the concentration of the hydrogen fluoride solution is preferably 10 wt%; the temperature of the etching reaction is preferably 20-50°C, more preferably 35-40°C, and the time is preferably 24-48 h, more preferably 24-36 h; the centrifugal speed is preferably 1000-5000 rpm, more preferably 2000-3500 rpm, the centrifugal time is preferably 10-60 min, more preferably 40 min, and the number of water washings is preferably 3-10 times to obtain a MXene aqueous dispersion and configure it to the required concentration.

[0037] In the present invention, the concentration of the polyanion electrolyte dispersion is preferably 1 to 10 g / L, more preferably 3 to 5 g / L.

[0038] In the present invention, the polycationic electrolyte preferably includes polyacrylamine hydrochloride, polyvinylamine or polydimethyldiallylammonium chloride, and the concentration of the polycationic electrolyte solution is preferably 1-10 g / L, more preferably 2-5 g / L; the salt solution is preferably a 0.5 mol / L NaCl aqueous solution.

[0039] In the present invention, the base membrane is preferably a polysulfone flat membrane. The present invention has no particular limitation on the base membrane, and the base membrane can be a commercial product well known in the art or can be prepared in-house using methods well known in the art.

[0040] The present invention has no particular limitation on the order of alternately filtering the polyanion electrolyte dispersion and the polycation electrolyte solution. Either the polyanion electrolyte dispersion or the polycation electrolyte solution may be preferentially filtered on the surface of the basement membrane.

[0041] The present invention preferably fixes the base membrane in a vacuum filtration device, and drives the MXene aqueous dispersion and the polycation electrolyte solution to be alternately filtered onto the surface of the base membrane by pressure. After each layer is filtered, it is rinsed with deionized water until the conductivity of the eluate is ≤10us / cm, and the excess liquid on the membrane surface is blown dry with compressed air. The alternating filtration is repeated until a multi-layer composite membrane structure is formed.

[0042] In the present invention, the volume of the polyanionic electrolyte dispersion or polycationic electrolyte solution filtered each time is preferably 10 to 20 mL, more preferably 15 to 20 mL.

[0043] In the present invention, the temperature of each filtration is preferably 15-25°C, more preferably 20°C, and the pressure is preferably 0.5-1.0 bar, more preferably 1.0 bar; the filtration temperature is the temperature of the polyanion electrolyte dispersion or polycation electrolyte solution.

[0044] The present invention promotes the coating liquid to be deposited on the membrane surface through the pressure effect of the filtration process to form a uniform coating.

[0045] In the present invention, the number of layers of the multilayer structure formed by the alternating filtration is preferably 2 to 10, more preferably 6 to 8. The present invention obtains a coating of a specific thickness by limiting the filtration concentration and filtration volume.

[0046] In the present invention, after each filtration, the membrane is preferably washed with water until the conductivity is constant before the next filtration.

[0047] The present invention provides a MXene-based composite nanofiltration membrane prepared by the preparation method described in the above technical solution.

[0048] The present invention provides the use of the MXene-based composite nanofiltration membrane described in the above technical solution in water treatment. The present invention does not specifically limit the method of the application, and the application can be carried out according to methods well known in the art.

[0049] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0050] The following experimental methods and detection methods, unless otherwise specified, are conventional methods; the following reagents and raw materials, unless otherwise specified, are commercially available.

[0051] Example 1

[0052] 2 g of Ti3AlC2 was reacted with 50 mL of HF solution (concentration of 10 wt%) at 35 ° C for 24 h. After the reaction was stopped, the product was centrifuged with deionized water at 3500 rpm for 40 min and washed repeatedly with deionized water 5 times until the supernatant turned dark green (pH = 6) to obtain a MXene aqueous dispersion containing MXene nanosheets;

[0053] The MXene aqueous dispersion and polyacrylamine hydrochloride solution were alternately coated on the polysulfone flat membrane using the suction coating method:

[0054] (1) Prepare 20 mL of 1 g / L MXene aqueous dispersion, fix the polysulfone flat membrane on the filter element of the filtration bottle, pour the MXene aqueous dispersion, start the filtration device, maintain the MXene aqueous dispersion temperature at 20 ° C, and filter under the pressure of 1.0 bar to form the first layer of coating, rinse with deionized water until the conductivity of the eluate is ≤10 us / cm, and blow dry the excess liquid on the membrane surface with compressed air;

[0055] (2) Prepare 20 mL of a 2 g / L polyacrylamine hydrochloride solution, using a 0.5 M NaCl solution obtained by dissolving 0.5 mol of sodium chloride in 1 L of deionized water as the solvent; maintain the polyacrylamine hydrochloride solution at 20°C, pour the polyacrylamine hydrochloride solution into the membrane, start the filtration device, and filter under a pressure of 1.0 bar to form a second coating layer. Rinse with deionized water until the conductivity of the eluate is ≤10 μS / cm, and blow off the excess liquid on the membrane surface with compressed air;

[0056] (3) Steps (1) and (2) were performed alternately until six layers of polyelectrolyte coating were formed on the polysulfone flat membrane to obtain a MXene-based composite nanofiltration membrane, which was named NF-1.

[0057] Characterization and testing

[0058] Figure 1 is the SEM image of MXene nanosheets in Example 1, Figure 1 It can be seen that the size of the prepared MXene nanosheets is between 50-500nm.

[0059] Figure 2 This is the TEM image of the MXene nanosheet in Example 1, as shown Figure 2 As shown in Figure 2, MXene nanosheets appear nearly transparent under an electron beam scanning electron microscope, indicating that they have thin structural features.

[0060] Figure 3 This AFM image of the MXene nanosheets in Example 1 further verifies that the uniform thickness of the MXene nanosheets is approximately 1.7 nm, which is consistent with the reported thickness of a single-layer MXene nanosheet of approximately 1 nm. This result demonstrates that the present invention successfully synthesized single-layer MXene flakes, and the synthesized MXene has good single-layer structural characteristics.

[0061] Figure 4 This is a cross-sectional SEM image of the MXene-based composite nanofiltration membrane in Example 1. Figure 4 As shown in the figure, the cross-section exhibits a distinct sponge-like pore structure. MXene sheets self-assemble layer by layer to form a separation layer, which has good structural stability and efficient separation performance. This structure shows that the arrangement of MXene sheets plays a key role in the pore structure and performance of the membrane.

[0062] Figure 5This is a surface SEM image of the MXene-based composite nanofiltration membrane in Example 1, clearly showing the accumulation of MXene flakes. The MXene flakes evenly cover the surface of the base membrane, successfully obscuring the membrane's pores. This uniform flake coverage not only improves the membrane's surface properties but also enhances its filtration performance, further increasing its selectivity and flux.

[0063] Nanofiltration membrane flux and salt rejection test:

[0064] The separation performance of the LBL nanofiltration membrane was evaluated using a flat membrane cross-flow filtration system. All measurements were performed at a crossflow velocity of 0.25 m / s at 3 bar. Deionized water (DI water) was used as the feed solution for calculating the water permeability coefficient, which was calculated using Equation (I):

[0065]

[0066] In formula (I), P(L / m 2 ·h·bar) is the permeability, ΔV(L) is the permeation volume, A(m 2 ) is the effective membrane area, Δt(h) is the permeate collection time, and Δp(bar) is the average transmembrane pressure at the inlet and outlet of the membrane module in formula (I).

[0067] The salt rejection of the membrane was tested using MgCl2, Na2SO4, and MgSO4 salt solutions with a concentration of 500 ppm, and the ion concentrations in the feed and permeate were measured using a conductivity meter.

[0068]

[0069] In formula (II), R is the retention rate (%), C p is the permeate concentration (mg / L), C f is the feed solution concentration (mg / L).

[0070] Figure 6 The water flux diagram of the nanofiltration membrane with different MXene concentrations in Examples 1 to 4 is shown in FIG. Figure 6 It can be seen that under the test conditions of 3 bar, the flux of the nanofiltration membrane with a concentration of 1g / L of MXene aqueous dispersion to MgCl2, MgSO4, and Na2SO4 with a concentration of 500mg / L is 24Lm -2 h -1 about.

[0071] Figure 7 The salt rejection rate of the nanofiltration membrane with different MXene concentrations in Examples 1 to 4 is shown in FIG. Figure 7Under 3 bar test conditions, the nanofiltration membrane, containing a 1 g / L MXene aqueous dispersion, exhibited a retention rate for 500 mg / L metal salts of MgCl₂, MgSO₄, and Na₂SO₄ in the order of Na₂SO₄ > MgSO₄ > MgCl₂. The membrane retained 82% and 79% of Na₂SO₄ and MgSO₄, respectively, while its MgCl₂ retention rate was relatively low at 20%.

[0072] Example 2

[0073] The only difference from Example 1 is:

[0074] Prepare 20 mL of 3 g / L MXene aqueous dispersion; prepare 20 mL of 2 g / L polyacrylamine hydrochloride solution (solvent is 0.5 M NaCl solution) to obtain a MXene-based composite nanofiltration membrane, named NF-2.

[0075] like Figure 6 As shown in the figure, after increasing the concentration of MXene aqueous dispersion, oxygen-containing functional groups are introduced into the separation layer of the nanofiltration membrane, which can form hydrogen bonds with water molecules, enhance the hydrophilicity of the material, and thus enhance the hydrophilicity of the nanofiltration membrane; under the test conditions of 3 bar, the flux of the nanofiltration membrane to MgCl2, MgSO4, and Na2SO4 with a concentration of 500 mg / L is 30Lm -2 h -1 about.

[0076] like Figure 7 As shown in the figure, after increasing the concentration of MXene aqueous dispersion, amino groups were introduced into the separation layer of the nanofiltration membrane, thereby enhancing the negative charge of the nanofiltration membrane and thus improving the SO4 2- Under the test condition of 3 bar, the rejection rate of the nanofiltration membrane for Na2SO4 and MgSO4 was 85% and 83% respectively; while the rejection rate for MgCl2 was relatively low, at 17%.

[0077] Example 3

[0078] The only difference from Example 1 is:

[0079] 20 mL of 5 g / L MXene aqueous dispersion and 20 mL of 2 g / L polyacrylamine hydrochloride solution (solvent is 0.5 M NaCl solution) were prepared to obtain a MXene-based composite nanofiltration membrane, named NF-3.

[0080] like Figure 6As shown in the figure, after increasing the concentration of MXene aqueous dispersion, oxygen-containing functional groups are introduced into the separation layer of the nanofiltration membrane, which can form hydrogen bonds with water molecules, enhance the hydrophilicity of the material, and thus enhance the hydrophilicity of the nanofiltration membrane. Under the test conditions of 3 bar, the flux of the nanofiltration membrane to MgCl2, MgSO4, and Na2SO4 with a concentration of 500 mg / L is 41Lm -2 h -1 about.

[0081] like Figure 7 As shown in the figure, after increasing the concentration of MXene aqueous dispersion, amino groups were introduced into the separation layer of the nanofiltration membrane, thereby enhancing the negative charge of the nanofiltration membrane and thus improving the SO4 2- Under the test condition of 3 bar, the rejection rate of the nanofiltration membrane for Na2SO4 and MgSO4 was 93% and 90% respectively; while the rejection rate for MgCl2 was relatively low, at 13%.

[0082] Example 4

[0083] The only difference from Example 1 is:

[0084] 20 mL of 10 g / L MXene aqueous dispersion and 20 mL of 2 g / L polyacrylamine hydrochloride solution (solvent is 0.5 M NaCl solution) were prepared to obtain a MXene-based composite nanofiltration membrane, named NF-4.

[0085] like Figure 6 As shown in the figure, after increasing the concentration of MXene aqueous dispersion, oxygen-containing functional groups are introduced into the separation layer of the nanofiltration membrane, which can form hydrogen bonds with water molecules, enhance the hydrophilicity of the material, and thus enhance the hydrophilicity of the nanofiltration membrane. Under the test conditions of 3 bar, the flux of the nanofiltration membrane to MgCl2, MgSO4, and Na2SO4 with a concentration of 500 mg / L is 46Lm -2 h -1 about.

[0086] like Figure 7 As shown in the figure, after increasing the concentration of MXene aqueous dispersion, amino groups were introduced into the separation layer of the nanofiltration membrane, thereby enhancing the negative charge of the nanofiltration membrane and thus improving the SO4 2- Under the test condition of 3 bar, the rejection rate of the nanofiltration membrane for Na2SO4 and MgSO4 was 98% and 95% respectively; while the rejection rate for MgCl2 was relatively low, at 9%.

[0087] Example 5

[0088] The only difference from Example 1 is:

[0089] 20 mL of 5 g / L MXene aqueous dispersion and 20 mL of 2 g / L polyvinylamine solution (solvent is 0.5 M NaCl solution) were prepared to obtain a composite self-assembled nanofiltration membrane.

[0090] Under the test conditions of 3 bar, the flux of the nanofiltration membrane for MgCl2, MgSO4, and Na2SO4 with a concentration of 500 mg / L is 43 Lm -2 h -1 The rejection rates of nanofiltration membranes for Na2SO4 and MgSO4 are 90% and 86% respectively; while the rejection rate for MgCl2 is relatively low, at 12%.

[0091] Example 6

[0092] The only difference from Example 1 is:

[0093] Prepare 20 mL of 5 g / L MXene aqueous dispersion and 20 mL of 5 g / L polyvinylamine solution (solvent is 0.5 M NaCl solution) to obtain a composite self-assembled nanofiltration membrane.

[0094] Under the test conditions of 3 bar, the flux of the nanofiltration membrane for MgCl2, MgSO4, and Na2SO4 with a concentration of 500 mg / L is 45 Lm -2 h -1 The rejection rates of the nanofiltration membrane for Na2SO4 and MgSO4 are 92% and 88% respectively; while the rejection rate for MgCl2 is relatively higher, at 43%.

[0095] Example 7

[0096] The only difference from Example 1 is:

[0097] Prepare 20 mL of 5 g / L MXene aqueous dispersion and 20 mL of 5 g / L polyvinylamine solution (solvent is 0.5 M NaCl solution), and filter alternately until 8 layers of polyelectrolyte coating are formed on the membrane to obtain a composite self-assembled nanofiltration membrane.

[0098] Under the test conditions of 3 bar, the flux of the nanofiltration membrane for MgCl2, MgSO4, and Na2SO4 with a concentration of 500 mg / L is 45 Lm -2 h -1 The rejection rates of the nanofiltration membrane for Na2SO4 and MgSO4 are 99% and 93% respectively; while the rejection rate for MgCl2 is relatively high, at 56%.

[0099] Example 8

[0100] The only difference from Example 7 is that:

[0101] Prepare 20 mL of 5 g / L polyvinylamine solution (solvent is 0.5 M NaCl solution) and 20 mL of 5 g / L MXene aqueous dispersion. Preferentially filter the polyvinylamine solution on the polysulfone flat membrane, and alternately filter until 8 layers of polyelectrolyte coating are formed on the membrane to obtain a composite self-assembled nanofiltration membrane.

[0102] Under the test conditions of 3 bar, the flux of the nanofiltration membrane for MgCl2, MgSO4, and Na2SO4 with a concentration of 500 mg / L is 43 Lm -2 h -1 The rejection rates of the nanofiltration membrane for Na2SO4 and MgSO4 are 90% and 88% respectively; while the rejection rate for MgCl2 is improved to 86%.

[0103] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a MXene-based composite nanofiltration membrane, characterized in that: The following steps are involved: The MXene aqueous dispersion is used as the polyanion electrolyte dispersion; mixing a polycation electrolyte with a salt solution to obtain a polycation electrolyte solution; The base membrane is fixed, and the polyanion electrolyte dispersion and the polycation electrolyte solution are alternately filtered onto the surface of the base membrane by vacuum filtration. The alternate filtration is repeated until a multilayer structure is formed to obtain a MXene-based composite nanofiltration membrane.

2. The preparation method according to claim 1, characterized in that The concentration of the polyanion electrolyte dispersion is 1-10 g / L.

3. The preparation method according to claim 1, characterized in that The polycation electrolyte includes polyacrylamine hydrochloride, polyvinylamine or polydimethyldiallylammonium chloride, and the concentration of the polycation electrolyte solution is 1-10 g / L.

4. The preparation method according to claim 2 or 3, characterized in that The volume of the polyanion electrolyte dispersion or polycation electrolyte solution filtered each time is independently 10 to 20 mL.

5. The preparation method according to claim 4, characterized in that The temperature of each filtration is independently 15-25°C, and the pressure is independently 0.5-1.0 bar.

6. The preparation method according to claim 5, characterized in that The number of layers of the multi-layer structure formed by the alternating filtration is 2 to 10.

7. The preparation method according to claim 6, characterized in that After each filtration, the membrane was washed with water until the conductivity was constant before the next filtration.

8. The preparation method according to claim 1, characterized in that The preparation method of the MXene material includes: mixing Ti3AlC2 with a hydrogen fluoride solution and performing an etching reaction to obtain MXene; the usage ratio of the Ti3AlC2 to the hydrogen fluoride solution is 2-10 g:50 mL; the temperature of the etching reaction is 20-50° C., and the time is 24-48 hours.

9. A MXene-based composite nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the MXene-based composite nanofiltration membrane according to claim 9 in water treatment.

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