Mixed matrix membrane for efficient ion separation and preparation method thereof

Abstract

The invention provides a mixed matrix membrane for efficient ion separation and a preparation method thereof, and belongs to the technical field of separation membranes. The preparation method comprises the following steps: mixing aluminum salt and sodium hydroxide in an organic solvent, and then adding a nitrogen-containing heterocyclic organic ligand to obtain an MOF precursor solution; adding polyimide into the MOF precursor solution to obtain a membrane casting solution; pouring the membrane casting solution into a mold, performing vacuum heating, performing stripping, performing soaking with ethanol, and then performing drying to obtain the mixed matrix membrane for efficient ion separation. The MOF-303 is uniformly dispersed in the whole substrate by controlling the loading capacity of the MOF, and a continuous ion channel is constructed by a uniformly dispersed MOF-303 crystal structure, so that the selectivity of the membrane on monovalent ions is further improved. Operation is simple, and cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membranes, and in particular to a mixed matrix membrane for efficient ion separation and a preparation method thereof. Background Art

[0002] The application of separation membranes in ion screening is a key research and development area strongly supported by my country. The screening of monovalent ions by separation membranes plays an irreplaceable role in the fields of seawater desalination and potassium therapy. Metal organic frameworks (MOFs) have great application potential in ion screening due to their uniform and adjustable pore structure that can form ordered sub-nano channels. Mixed matrix membranes are a composite membrane material that combines inorganic nanofillers (such as metal organic framework materials MOFs, porous organic frameworks COFs, graphene oxide GO, etc.) with polymer matrices. This membrane structure combines the flexibility of polymers with the high selectivity of inorganic fillers, showing excellent separation performance and broad application prospects. In the field of ion separation, mixed matrix membranes can significantly improve the selective transmission and separation efficiency of ions by optimizing the type, structure and distribution of fillers. MOF-based mixed matrix membranes have the combined advantages of the solution processability of polymer matrices and the targeting ability of nanoporous crystals. As a feasible nano-flow platform, however, it is still a huge challenge to make mixed matrix membranes have both high selectivity and high permeability for ions. This is mainly because the dispersion and continuity of MOF fillers will greatly affect the performance of mixed matrix membranes, limiting the separation performance of the membranes. In addition, the differences in the physical and chemical properties of the organic polymer matrix and the inorganic fillers (such as MOFs and nanoparticles) may lead to interface defects (such as voids and cracks), reducing the integrity and selectivity of the membrane. The preparation process is complex and costly, requiring precise control of filler dispersion, interface modification and membrane formation conditions (such as solvent evaporation rate). The process is complex and difficult to scale up.

[0003] Therefore, how to obtain a separation membrane with excellent separation performance and simple process and a preparation method thereof is a technical problem that needs to be solved at present. Summary of the invention

[0004] The object of the present invention is to provide a mixed matrix membrane for efficient ion separation and a preparation method thereof, so as to solve the above technical problems.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a mixed matrix membrane for efficient ion separation, comprising the following steps:

[0007] 1) mixing aluminum salt and sodium hydroxide in an organic solvent, stirring for the first time, then adding a nitrogen-containing heterocyclic organic ligand, stirring for the second time, to obtain a MOF precursor solution;

[0008] 2) adding polyimide to the MOF precursor solution, stirring and ultrasonically treating for the third time to obtain a casting solution;

[0009] 3) pouring the casting solution into a mold and heating it in vacuum, peeling it off and soaking it in ethanol, and then drying it to obtain a mixed matrix membrane for efficient ion separation.

[0010] Furthermore, the aluminum salt comprises aluminum chloride; and the nitrogen-containing heterocyclic organic ligand comprises pyrazoledicarboxylic acid.

[0011] Furthermore, the organic solvent comprises dimethylformamide.

[0012] Furthermore, the mass ratio of the aluminum salt, the nitrogen-containing heterocyclic organic ligand and the sodium hydroxide is 2 to 4:2 to 3:1;

[0013] The mass ratio of the polyimide to sodium hydroxide is 0.1-0.8:1.

[0014] Furthermore, the rotation speed of the first stirring is 40 to 60 r / min, and the time of the first stirring is 1 to 1.5 h.

[0015] Furthermore, the second stirring speed is 30 to 50 r / min, and the second stirring time is 15 to 25 min;

[0016] The rotation speed of the third stirring is 40-50 r / min, and the time of the third stirring is 1-3 h.

[0017] Furthermore, the frequency of the ultrasonic treatment is 60 to 100 kHz, and the time of the ultrasonic treatment is 20 to 40 minutes.

[0018] Furthermore, the vacuum heating temperature is 90-110° C., and the vacuum heating time is 0.5-2 h; the drying temperature is 50-70° C., and the drying time is 30-50 min.

[0019] The present invention also provides a mixed matrix membrane for efficient ion separation, wherein the loading amount of MOF in the mixed matrix membrane for efficient ion separation is 9-40%.

[0020] Beneficial effects of the present invention:

[0021] The invention provides a mixed matrix membrane for efficient ion separation, which has the advantages that MOF-303 is uniformly dispersed in a polyimide matrix by a tape casting method, and in-situ growth forms ion channels that run through the upper and lower surfaces of the mixed matrix membrane, which has high selectivity for monovalent ions. The invention realizes uniform dispersion of MOF-303 in the entire substrate by controlling the MOF loading amount, and constructs continuous ion channels by the uniformly dispersed MOF-303 crystal structure, further improving the selectivity of the membrane for monovalent ions. The method of the invention is simple to operate and has low cost.

[0022] The technical scheme of the present invention includes three stirrings and one ultrasonic operation performed in sequence, wherein each additional reagent added to the reaction system is stirred once, which makes the reaction system more uniform. On the one hand, pyrazole dicarboxylic acid promotes the growth of MOF-303 by coordinating with aluminum ions, and on the other hand, the carboxyl group forms a strong hydrogen bond with the imide atomic group in the substrate, so that the combination of MOF-303 and the polyimide substrate is more continuous and dense. Further, the finally prepared MOF-303 / PI-X membrane has good ion selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 SEM images of the surface, cross section, and bottom surface of MOF-303 / PI-X mixed matrix membranes with different MOF-303 loadings;

[0024] Figure 2 is the XRD patterns of pure PI membrane and MOF-303 / PI-X mixed matrix membranes with different MOF-303 loadings;

[0025] Figure 3 is the FT-IR spectra of pure PI membrane and MOF-303 / PI-X mixed matrix membranes with different MOF-303 loadings;

[0026] Figure 4 is the IV curve of MOF-303 / PI-X mixed matrix membranes with different MOF-303 loading amounts;

[0027] Figure 5 (a) Ionic conductivity and (b) ion selectivity curves of mixed matrix membranes with different MOF-303 loadings;

[0028] Figure 6 The IV curves of the MOF-303 / PI-2 membrane prepared in Example 2 of the present invention at different voltages are (a) 0.1V, (b) 0.4V, (c) 1.5V, (d) 1V, and (e) 2V;

[0029] Figure 7Graphs of (a) ionic conductivity and (b) ionic selectivity of the MOF-303 / PI-2 membrane prepared in Example 2 of the present invention at different voltages;

[0030] Figure 8 The IV curves of the MOF-303 / PI-2 membrane prepared in Example 2 of the present invention at different effective test diameters: (a) Φ2cm, (b) Φ4cm, (c) Φ6cm;

[0031] Fig. 9 Graphs of (a) ionic conductivity and (b) ionic selectivity of the MOF-303 / PI-2 membrane prepared in Example 2 of the present invention at different effective test diameters;

[0032] Fig.10 Schematic diagram of the H-type electrolytic cell used in the test of the present invention. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing a mixed matrix membrane for efficient ion separation, comprising the following steps:

[0034] 1) mixing aluminum salt and sodium hydroxide in an organic solvent, stirring for the first time, then adding a nitrogen-containing heterocyclic organic ligand, stirring for the second time, to obtain a MOF precursor solution;

[0035] 2) adding polyimide to the MOF precursor solution, stirring and ultrasonically treating for the third time to obtain a casting solution;

[0036] 3) pouring the casting solution into a mold and heating it in vacuum, peeling it off and soaking it in ethanol, and then drying it to obtain a mixed matrix membrane for efficient ion separation.

[0037] In the present invention, the mixed matrix membrane for efficient ion separation is denoted as MOF-303 / PI-X membrane.

[0038] In the present invention, the aluminum salt is preferably aluminum chloride; the nitrogen-containing heterocyclic organic ligand is preferably pyrazoledicarboxylic acid.

[0039] In the present invention, the organic solvent is preferably dimethylformamide.

[0040] In the present invention, the mass ratio of the aluminum salt, the nitrogen-containing heterocyclic organic ligand and the sodium hydroxide is 2 to 4:2 to 3:1, preferably 3:2.2:1;

[0041] The mass ratio of the polyimide to sodium hydroxide is 0.1 to 0.8:1, preferably 0.175 to 0.7:1, and more preferably 0.35 to 0.6:1.

[0042] In the present invention, the polyimide is preferably a powdered polyimide.

[0043] In the present invention, the rotation speed of the first stirring is 40 to 60 r / min, preferably 50 r / min; the time of the first stirring is 1 to 1.5 h, preferably 1 h.

[0044] In the present invention, the second stirring speed is 30 to 50 r / min, preferably 40 r / min; the second stirring time is 15 to 25 min, preferably 20 min;

[0045] The rotation speed of the third stirring is 40-50 r / min, preferably 50 r / min; the time of the third stirring is 1-3 h, preferably 2 h.

[0046] In the present invention, the stirring method in the preparation method adopts a cantilever electric stirrer to stir at room temperature.

[0047] In the present invention, the mold is preferably a polytetrafluoroethylene mold; the method of peeling the film from the mold is preferably to immerse the mold in deionized water; the ethanol immersion method is preferably to immerse three times, each time for 5 minutes.

[0048] In the present invention, the frequency of the ultrasonic treatment is 60 to 100 kHz, preferably 80 kHz; the time of the ultrasonic treatment is 20 to 40 min, preferably 30 min.

[0049] Furthermore, the vacuum heating temperature is 90-110°C, preferably 100°C; the vacuum heating time is 0.5-2h, preferably 1h; the drying temperature is 50-70°C, preferably 60°C; the drying time is 30-50min, preferably 40min.

[0050] In the present invention, the above preparation method includes three stirring steps and one ultrasonic step, the purpose of which is to make the reaction system evenly dispersed; the purpose of using the film casting method in step 3) is to make MOF-303 more evenly dispersed. After film formation, the ion channels formed by MOF-303 can be continuously distributed on the substrate; the role of soaking the mold in deionized water in step 3) is to facilitate the peeling of the membrane, and soaking in ethanol three times is used to remove unreacted ligands and non-volatile impurities.

[0051] The purpose of the present invention is to provide a polyimide-based mixed matrix membrane with a through-type MOF-303 ion channel and a preparation method thereof, which solves the problems in the prior art: due to the poor dispersibility of MOF filler in the substrate, MOF cannot construct a continuous ion channel in the substrate, resulting in poor separation performance of the separation membrane for monovalent ions; and the poor interface compatibility between the filler and the matrix leads to defects at the interface; and the unique polytetrafluoroethylene mold in-situ heat-assisted casting method is simple to operate, low cost, and greatly reduces the difficulty of film formation.

[0052] The present invention also provides a mixed matrix membrane for efficient ion separation, wherein the loading amount of MOF in the mixed matrix membrane for efficient ion separation is 9 to 40%, preferably 10 to 30%, and more preferably 17.54%.

[0053] In the present invention, the mixed matrix membrane for efficient ion separation can be used for screening of monovalent ions.

[0054] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0055] Example 1

[0056] Step 1): 0.03625 g aluminum chloride hexahydrate (AlCl3·6H2O) and 0.012 g sodium hydroxide (NaOH) were dissolved in 7 ml dimethylformamide (DMF), stirred at 50 r / min for 1 h at room temperature, and then 0.0262 g pyrazole dicarboxylic acid (PZDC) was added, and stirred at 40 r / min for 20 min at room temperature to make it evenly dispersed to obtain a MOF precursor solution.

[0057] Step 2): 0.7 g of polyimide (PI) powder was added to the above MOF precursor solution, stirred at 50 r / min for 2 h at room temperature, and then ultrasonically treated at a frequency of 80 kHz for 30 min to eliminate bubbles to obtain a uniformly dispersed casting solution.

[0058] Step 3): Pour the casting liquid into a polytetrafluoroethylene mold, place the mold in a vacuum oven, heat at 100°C for 1 hour, cool naturally to room temperature, and then soak the mold in deionized water. Peel the membrane from the mold and soak it in ethanol three times, each time for 5 minutes, and then vacuum dry it at 60°C for 40 minutes to obtain a MOF-303 / PI-1 membrane with a MOF loading of 9.61%.

[0059] Example 2

[0060] Step 1): 0.0725 g aluminum chloride hexahydrate (AlCl3·6H2O) and 0.024 g sodium hydroxide (NaOH) were dissolved in 7 ml dimethylformamide (DMF), stirred at 50 r / min for 1 h at room temperature, and then 0.0524 g pyrazole dicarboxylic acid (PZDC) was added, and stirred at 40 r / min for 20 min at room temperature to make it evenly dispersed to obtain a MOF precursor solution.

[0061] Step 2): 0.7 g of polyimide (PI) powder was added to the above MOF precursor solution, stirred at 50 r / min for 2 h at room temperature, and then ultrasonically treated at a frequency of 80 kHz for 30 min to eliminate bubbles to obtain a uniformly dispersed casting solution.

[0062] Step 3): Pour the casting liquid into a polytetrafluoroethylene mold, place the mold in a vacuum oven, heat at 100°C for 1 hour, cool naturally to room temperature, and then soak the mold in deionized water. Peel the membrane from the mold and soak it in ethanol three times, each time for 5 minutes, and then vacuum dry it at 60°C for 40 minutes to obtain a MOF-303 / PI-2 membrane with a MOF loading of 17.54%.

[0063] Example 3

[0064] Step 1): 0.1450 g aluminum chloride hexahydrate (AlCl3·6H2O) and 0.048 g sodium hydroxide (NaOH) were dissolved in 7 ml dimethylformamide (DMF), stirred at 50 r / min for 1 h at room temperature, and then 0.1048 g pyrazole dicarboxylic acid (PZDC) was added, and stirred at 40 r / min for 20 min at room temperature to make it evenly dispersed to obtain a MOF precursor solution.

[0065] Step 2): 0.7 g of polyimide (PI) powder was added to the above MOF precursor solution, stirred at 50 r / min for 2 h at room temperature, and then ultrasonically treated at a frequency of 80 kHz for 30 min to eliminate bubbles to obtain a uniformly dispersed casting solution.

[0066] Step 3): Pour the casting liquid into a polytetrafluoroethylene mold, place the mold in a vacuum oven, heat at 100°C for 1 hour, cool naturally to room temperature, and then soak the mold in deionized water. Peel the membrane from the mold and soak it in ethanol three times, each time for 5 minutes, and then vacuum dry it at 60°C for 40 minutes to obtain a MOF-303 / PI-3 membrane with a MOF loading of 29.84%.

[0067] Example 4

[0068] Step 1): 0.02175 g aluminum chloride hexahydrate (AlCl3·6H2O) and 0.072 g sodium hydroxide (NaOH) were dissolved in 7 ml dimethylformamide (DMF), stirred at 50 r / min for 1 h at room temperature, and then 0.1572 g pyrazole dicarboxylic acid (PZDC) was added, and stirred at 40 r / min for 20 min at room temperature to make it evenly dispersed to obtain a MOF precursor solution.

[0069] Step 2): 0.7 g of polyimide (PI) powder was added to the above MOF precursor solution, stirred at 50 r / min for 2 h at room temperature, and then ultrasonically treated at a frequency of 80 kHz for 30 min to eliminate bubbles to obtain a uniformly dispersed casting solution.

[0070] Step 3): Pour the casting liquid into a polytetrafluoroethylene mold, place the mold in a vacuum oven, heat at 100°C for 1 hour, cool naturally to room temperature, and then soak the mold in deionized water. Peel the membrane from the mold and soak it in ethanol three times, each time for 5 minutes, and then vacuum dry it at 60°C for 40 minutes to obtain a MOF-303 / PI-4 membrane with a MOF loading of 38.95%.

[0071] The MOF loading in the above examples refers to the percentage of the mass of MOF-303 to the total mass of the MOF-303 / PI-X membrane.

[0072] Test example:

[0073] The ion transport test of the single solution of the present invention is tested under an electrochemical workstation. The prepared membrane is sealed in the middle of a silica gel gasket with a diameter of 4 mm, and then clamped in the center of an H-type electrolytic cell, and a transmembrane voltage is applied through an Ag / AgCl electrode. In order to study the ion transmembrane transport behavior of the membrane under different salt solutions, 5 ml of the same 0.1M salt solution, including KCl, NaCl, LiCl and MgCl2, is added to the chambers on both sides of the H-type electrolytic cell. The working electrode and the counter electrode are placed on both sides, and the two electrodes are as close to the membrane surface as possible to reduce the solution resistance. The selectivity of cations is studied by recording the ion current during the potential scanning process generated by ion transmembrane transport. Once the measurement series of different cations is completed, the cell is thoroughly washed with deionized water to remove residual salt. Repeat this process until the membrane shows the conductivity characteristics of pure deionized water. After washing, the membrane is stored in pure deionized water and then measured with other cations.

[0074] Table 1 Ion separation performance of MOF-303 / PI-X mixed matrix membranes with different loading amounts

[0075]

[0076]

[0077] Table 1 shows the K values ​​of MOF-303 / PI-X membranes prepared in Examples 1 to 4. + Comparison of permeation flux and different ion selectivity. The data in Table 1 show that the MOF-303 / PI-X membrane prepared by controlling the MOF loading at 15%-30% has both high selectivity and high permeability. The MOF-303 / PI-2 membrane with a MOF loading of 17.54% prepared in Example 2 has extremely high selectivity for monovalent ions. The conductivity and selectivity data and error range of MOF-303 / PI-X membranes with different MOF loadings can be found in Figure 5 .

[0078] From the data of Example 1, it can be seen that when the MOF loading is low, the membrane separation performance is poor because MOF cannot construct a continuous ion channel in the substrate; from the data of Examples 3 and 4, it can be seen that the separation performance decreases when the MOF loading is large. The reason for this is that the filler agglomerates and causes the membrane performance to decrease. The present invention further tests the MOF-303 / PI-2 membrane with a MOF loading of 17.54% prepared in Example 2. The separation performance of the membrane under different voltages and different effective test diameters is shown in FIG. Figure 7 and Fig. 9 shown.

[0079] (1) SEM morphology analysis. Figure 1 As shown in the figure, with the increase of MOF content, more and more MOF-303 particles are exposed on the surface of the membrane, while the bottom shows a loose and porous structure. This asymmetric structure is caused by solidification and solvent evaporation during the phase inversion process. The dense MOF layer on the surface of the membrane serves as the main separation layer, mainly used for selective filtration of target ions, while the porous bottom serves as a support layer, providing mechanical strength and providing a looser channel for ions after passing through the selection layer, accelerating the rapid transmission of target ions. It is worth noting that in the cross-sectional view, we found a special structure different from other mixed matrix membranes. In the part between the surface selection layer and the bottom support layer, we observed more MOF-303. Compared with the surface of the membrane, the MOF particles in this part have smaller grain size, reaching the nanometer level, and are more numerous and more evenly distributed. This part can be used as a second selection layer to perform secondary screening of interfering ions when the surface selection layer fails to screen successfully.

[0080] (2) XRD analysis. Figure 2As shown in the figure, compared with the standard XRD pattern of the simulated MOF-303, the characteristic diffraction peaks of MOF-303 appeared in the mixed matrix membranes with different contents, which proved that the MOF-303 crystals were successfully synthesized during the in situ growth process and could stably exist in the mixed matrix membrane, further confirming the chemical stability of MOF-303. With the increase of the loading amount, the intensity of the MOF characteristic diffraction peaks of the mixed matrix membrane gradually increased.

[0081] (3) FT-IR analysis. Figure 3 As shown in Figure 2, characteristic peaks of PI were found in the mixed matrix membranes with different contents, such as at 1778 cm -1 The characteristic absorption peak of asymmetric stretching vibration of C=O appears at 1720cm -1 The characteristic absorption peak of the symmetrical stretching vibration of C=O appears at 1376cm -1 The absorption peak at 725 cm is the characteristic absorption peak of the stretching vibration of C=N of the imide group. -1 The absorption peak at is attributed to the out-of-plane bending vibration absorption of CNC in the imide group. Due to the low MOF loading, the characteristic absorption peak intensity of MOF-303 in the mixed matrix membrane is also weak. The overall results show that due to the good compatibility between the filler (MOF-303) and the matrix (PI), the in-situ growth of MOF in the matrix does not affect or destroy the structure of PI.

[0082] (4) Analysis of ion separation performance of MOF-303 / PI-X mixed matrix membranes with different MOF-303 loadings. Figure 4 and Figure 5 As shown in Figure 2, the slope of the IV curve increases with the increase of the loading amount of MOF-303, and its slope corresponds to the ionic conductivity value. For the tested membrane, the larger the slope, the faster the ion transmembrane rate. MOF-303 / PI-2 has the largest ion selectivity, K + / Mg 2+ It can reach 15.65, but when the MOF-303 loading continues to increase, the ion selectivity drops sharply. These results show that adding a moderate amount of MOF-303 can improve ion permeability and selectivity at the same time. However, for higher loadings, the aggregation of MOF-303 particles will produce non-selective ion transport pathways in the membrane, thereby reducing ion selectivity.

[0083] (5) Analysis of ion separation performance of MOF-303 / PI-2 membrane prepared in Example 2 of the present invention at different voltages. Figure 6 and Figure 7As shown in the figure, with the increase of voltage bias, the ion current increases significantly. This is because when the transmembrane resistance remains unchanged, the increase of applied voltage will directly lead to the increase of ion current and may enhance the electric field strength, thereby accelerating the migration rate of ions. Too high bias voltage may cause a certain degree of damage to the mixed matrix membrane and form a large leakage current. Therefore, with the increase of bias voltage, the ion selectivity drops sharply after ±0.4V, and K + / Mg 2+ The value of the applied voltage decreased from 15.65 to 5.07. These results indicate that appropriate applied voltage is beneficial to ion separation, while too high voltage has a certain negative impact on the ion selectivity of mixed matrix membranes.

[0084] (6) Analysis of ion separation performance of MOF-303 / PI-2 membrane prepared in Example 2 of the present invention at different effective test diameters. Figure 8 and Fig. 9 As shown in the figure, with the increase of the effective test diameter, the current of all ions gradually increases. This is because the increase of the effective area of ​​the membrane increases the path for ions to enter the membrane channel, and the ion flux increases accordingly. By calculating the ion conductance under different effective diameters, we can see that all ions show an increasing trend accordingly. The K+ conductance of the mixed matrix membrane with a test diameter of 6mm reaches 8.22μs, which is about 4.7 times larger than that of the mixed matrix membrane with a test diameter of 2mm, and for Na + , Li + and Mg 2+ , also increased by a similar proportion. It is worth noting that the ion selectivity of the three effective test diameters is almost unchanged, which indicates that the surface of the prepared MOF-303 / PI-2 mixed matrix membrane is uniform and defect-free, and the size of the effective test diameter does not have a negative impact on the ion selectivity.

[0085] As can be seen from the above embodiments, the present invention provides a mixed matrix membrane for efficient ion separation and a preparation method thereof. The mixed matrix membrane for efficient ion separation provided by the present invention has the advantages that MOF-303 is uniformly dispersed in a polyimide matrix by a tape casting method, and in-situ growth forms ion channels that run through the upper and lower surfaces of the mixed matrix membrane, which has high selectivity for monovalent ions. The present invention achieves uniform dispersion of MOF-303 in the entire substrate by controlling the MOF loading amount, and constructs a continuous ion channel by the uniformly dispersed MOF-303 crystal structure, further improving the selectivity of the membrane for monovalent ions. The method of the present invention is simple to operate and has low cost.

[0086] 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a mixed matrix membrane for efficient ion separation, characterized in that: The following steps are involved: 1) mixing aluminum salt and sodium hydroxide in an organic solvent, stirring for the first time, then adding a nitrogen-containing heterocyclic organic ligand, stirring for the second time, to obtain a MOF precursor solution; 2) adding polyimide to the MOF precursor solution, stirring and ultrasonically treating for the third time to obtain a casting solution; 3) pouring the casting solution into a mold and heating it in vacuum, peeling it off and soaking it in ethanol, and then drying it to obtain a mixed matrix membrane for efficient ion separation.

2. The preparation method according to claim 1, characterized in that: The aluminum salt comprises aluminum chloride; and the nitrogen-containing heterocyclic organic ligand comprises pyrazoledicarboxylic acid.

3. The preparation method according to claim 1 or 2, characterized in that: The organic solvent includes dimethylformamide.

4. The preparation method according to claim 3, characterized in that: The mass ratio of the aluminum salt, the nitrogen-containing heterocyclic organic ligand and the sodium hydroxide is 2-4:2-3:1; The mass ratio of the polyimide to sodium hydroxide is 0.1-0.8:

1.

5. The preparation method according to claim 1 or 4, characterized in that: The rotation speed of the first stirring is 40-60 r / min, and the time of the first stirring is 1-1.5 h.

6. The preparation method according to claim 5, characterized in that: The second stirring speed is 30-50 r / min, and the second stirring time is 15-25 min; The rotation speed of the third stirring is 40-50 r / min, and the time of the third stirring is 1-3 h.

7. The preparation method according to claim 1 or 6, characterized in that: The frequency of the ultrasonic treatment is 60 to 100 kHz, and the time of the ultrasonic treatment is 20 to 40 minutes.

8. The preparation method according to claim 7, characterized in that: The temperature of the vacuum heating is 90-110° C., and the time of the vacuum heating is 0.5-2 hours; the temperature of the drying is 50-70° C., and the time of the drying is 30-50 minutes.

9. A mixed matrix membrane for high-efficiency ion separation prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The loading amount of MOF in the mixed matrix membrane for efficient ion separation is 9-40%.

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