Preparation method of a two-dimensional metal organic framework-based double-sided choroid membrane and application thereof

Abstract

The application discloses a two-dimensional metal organic framework-based double-sided Janus membrane preparation method and application thereof. Different two-dimensional metal organic framework nanosheets with different charge properties are doped in a high polymer to form a mixed matrix double-sided Janus membrane through scraping, a trade-off relationship between permeability and repellency is broken, the anti-pollution ability and hydrophilic performance of the membrane are greatly enhanced, and the double-sided Janus membrane has a water flux of 598.37 L·m ‑2 ·h ‑1 ·bar ‑1 ; the constructed double-sided Janus membrane has excellent separation performance on different charged antibiotics and other new pollutants, the removal rate of the negatively charged pollutant tetracycline in water is as high as 99.83%, the removal rate of the positively charged pollutant methicillin is 90.54%, and in the antibiotic / heavy metal complex system, the double-sided Janus membrane can effectively realize complex breaking and separation, and the separation factor is as high as 149, which has great utilization value on the separation of antibiotics and other new pollutants and heavy metals.

Description

Technical Field

[0001] This application relates to the field of nanofiltration membrane separation technology, and in particular to a method for preparing a two-dimensional metal-organic framework-based bifacial membrane and its application. Background Technology

[0002] Traditional nanofiltration membranes are mostly polyamide membranes. The separation membrane layer is synthesized by constructing a polyamide functional layer on a supporting matrix through interfacial polymerization of an organic phase and an aqueous phase. This method makes it difficult to control and customize separation performance, and they also exhibit poor chlorine resistance. More importantly, polymer nanofiltration membranes have a dense selective layer, presenting a difficult trade-off between permeability and repulsion. Due to their uniform surface charge, small specific surface area, and high hydrophobicity, they still face challenges in advanced wastewater treatment, such as poor removal of micropollutants.

[0003] Polyvinylidene fluoride (PVDF), polyethersulfone, and other polymer membranes possess excellent chemical resistance, thermal stability, and antioxidant properties, making them ideal materials for membrane formation. However, the traditional preparation of PVDF membranes often involves adding pore-forming agents such as polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) to create a loose and porous membrane layer. This typically only allows ultrafiltration membranes to retain large molecules, and the membrane surface has high hydrophobicity, which easily leads to membrane fouling during advanced wastewater treatment, greatly limiting its application.

[0004] Metal-organic frameworks (MOFs) possess advantages such as large specific surface area, abundant pores, tunable pore size, and ease of post-modification, making them a common choice for membrane modification. However, most commonly used MOF membranes are single-charge membranes, which cannot simultaneously achieve good interception effects for pollutants with different charges, and cationic MOF membranes often face the problem of easy fouling. Therefore, there is an urgent need to develop a dual-charge, fouling-resistant nanofiltration membrane for applications such as pharmaceutical wastewater and municipal sewage separation.

[0005] The present invention aims to develop a double-sided membrane utilizing two-dimensional MOFs to overcome the shortcomings of single-sided membranes in terms of selectivity, improve the membrane's antifouling properties, and achieve a win-win situation in terms of selectivity and permeability. Summary of the Invention

[0006] Technical problems to be solved:

[0007] The technical problem this application aims to solve is that traditional polyamide membranes face an insurmountable trade-off between permeability and repulsion, making it difficult to control customized separation performance. They also exhibit poor chlorine resistance, have a single charge, and cannot simultaneously retain anionic and cationic small molecules. Furthermore, their small specific surface area and high hydrophobicity result in poor removal of micro-pollutants in advanced wastewater treatment. Traditional polymer membranes can only intercept large molecules, and their high surface hydrophobicity easily leads to membrane fouling during advanced wastewater treatment, hindering the effective removal of small molecules. Based on the shortcomings of existing technologies, this application provides a method for preparing a bifacial membrane based on a two-dimensional metal-organic framework and its application. This membrane exhibits high interception rates for novel small-molecule pollutants with different charges, while also possessing high throughput, thus breaking the trade-off between permeability and selectivity.

[0008] Technical solution:

[0009] A method for preparing a two-dimensional metal-organic framework-based bifacial membrane includes the following steps:

[0010] S1. Preparation of layered bimetallic hydroxide LDH: Dissolve 8-12 parts of divalent metal salt and 4-6 parts of trivalent metal salt in 100 parts of deionized water to prepare a solution. Then weigh 40-60 parts of urea and dissolve it in the above solution. Transfer the solution to a high-pressure reactor with a stainless steel Teflon liner and perform a hydrothermal reaction at 80-150℃ for 12-36 hours. Wash the obtained LDH powder three times each with deionized water and ethanol, and then vacuum dry overnight.

[0011] S2. Preparation of two-dimensional anionic / cationic metal-organic frameworks (MOFs): 10-20 parts of LDH powder (vacuum-dried overnight) from S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 20-40 parts of anionic / cationic functional group organic ligands were added. After sonication for another 30 min, the mixture was transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 120-250 °C for 24-48 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum-dried overnight to obtain anionic / cationic MOFs.

[0012] S3: Preparation of anionic MOF membranes; Weigh 5-15 parts of organic polymer into a three-necked flask according to the mass ratio, add 50-100 parts of DMF solution, stir at 50-70℃ for 12-24h, add anionic MOFs and continue stirring thoroughly for 6-12h, let stand for 6-12h, and then degas under vacuum for 2-6h to obtain casting solution. Then coat the casting solution onto nonwoven fabric, and use a doctor blade to coat a membrane with a thickness of 200-400μm. Let stand in air for 30-60s, and then transfer to a deionized water bath to fully complete the phase inversion. Replace the deionized water every 12h.

[0013] S4: Preparation of the double-sided MOF membrane; Weigh 5-15 parts of organic polymer into a three-necked flask according to the mass ratio, add 50-100 parts of DMF solution, stir at 50-70℃ for 12-24h, add cationic MOFs and continue stirring thoroughly for 6-12h, let stand for 6-12h, and then degas under vacuum for 2-6h to obtain the casting solution. Coat the back of the anionic MOF membrane in S3 above with the casting solution, and use a doctor blade to coat the membrane to a thickness of 200-400μm. Let stand in air for 30-60s, and then transfer to a deionized water bath to fully complete the phase inversion. Replace the deionized water every 12h.

[0014] As a preferred technical solution of this application: in S3 and S4, when the phase transformation is fully completed in the deionized water bath, the water bath temperature is controlled at 20°C and the phase transformation time is 2 days.

[0015] As a preferred technical solution of this application: the mass ratio of anionic / cationic MOFs to organic polymer in S3 or S4 is 10 to 100%.

[0016] As a preferred technical solution of this application: the thickness of the double-sided membrane of the two-dimensional MOFs is 400-800 μm.

[0017] As a preferred technical solution of this application: the anionic functional group organic ligand is one or more of terephthalic acid, trimesic acid, and 2,5-dihydroxyterephthalic acid; the cationic functional group organic ligand is one or more of 2-aminoterephthalic acid, 2-methylimidazole, and benzimidazole.

[0018] As a preferred technical solution of this application: the divalent metal salt is one or more of cobalt nitrate Co(NO3)2·6H2O, zinc nitrate Zn(NO3)2·6H2O, nickel nitrate Ni(NO3)2·6H2O, and magnesium nitrate Mg(NO3)2·6H2O; the trivalent metal salt is one or more of ferric nitrate Fe(NO3)3·9H2O and / or aluminum nitrate Al(NO3)3·9H2O, and the molar ratio of trivalent metal salt to divalent metal salt is 1:2.

[0019] As a preferred technical solution of this application: the organic polymer in S3 and S4 is polyvinylidene fluoride (PVDF) or polyether sulfone (PES).

[0020] As a preferred technical solution of this application, the thickness of the single-sided film is controlled at 300μm.

[0021] The application of a bifacial membrane prepared by a two-dimensional metal-organic framework in the complex-breaking and separation of heavy metal / antibiotic complexes, wherein the anion side of the bifacial membrane faces the heavy metal / antibiotic complexes.

[0022] As a preferred technical solution of this application: the concentration of the heavy metal / antibiotic complexing system is 200-500 μg / L, and the ion concentration in the saline is 0.5-1 mM.

[0023] The technical principle of this application is as follows: This invention provides a two-dimensional metal-organic framework (MOF) converted from LDH, which is then used to construct a double-sided membrane. During the LDH conversion process, different organic ligands are controlled to synthesize MOFs with different charge properties. The double-sided membrane, coated using a phase inversion method, has different charge properties. These different charge properties mean that it can achieve a high interception rate when treating new pollutants with different charge properties, simultaneously retaining both anions and cations. Furthermore, the anion-side feed solution method used in this invention, due to its negative charge, exhibits charge repulsion when facing negatively charged macromolecular pollutants in wastewater, effectively mitigating membrane fouling problems of cation-side membranes in polluted solutions, improving the membrane's antifouling performance, and achieving a win-win situation of selectivity and permeability.

[0024] Beneficial effects:

[0025] The method for preparing a two-dimensional metal-organic framework-based bifacial membrane and its application described in this application have the following technical advantages compared with the prior art:

[0026] 1. The two-dimensional MOFs double-sided membrane utilized in this invention breaks the trade-off between permeability and repulsion of traditional polyamide membranes, and has high water flux and selectivity for new pollutants.

[0027] 2. The two-dimensional MOFs double-sided membrane utilized in this invention can effectively alleviate the serious membrane fouling problem faced by cation-type membranes in wastewater treatment and has a high anti-fouling ability.

[0028] 3. The two-dimensional MOFs double-sided membrane utilized in this invention can effectively and rapidly remove pollutants with different charges in water simultaneously. The removal rate of tetracycline, a negatively charged pollutant, is as high as 99.83%, and the removal rate of trimethoprim, a positively charged pollutant, is 90.54%.

[0029] 4. The two-dimensional MOFs double-sided membrane utilized in this invention has a good separation effect in heavy metal / antibiotic systems with a separation factor as high as 149.1, which can effectively remove new pollutants such as antibiotics and effectively recover resources from wastewater.

[0030] 5. It overcomes the shortcomings of single-sided membranes in terms of selectivity, effectively alleviates membrane fouling problems of cation-coated membranes in polluted solutions, improves membrane antifouling, and has high membrane flux, achieving a win-win situation of selectivity and permeability. It can effectively break the complex and separate the two in antibiotic / heavy metal mixed systems.

[0031] 6. Breaking the trade-off between permeability and repulsion, greatly enhancing the membrane's antifouling ability and hydrophilicity, achieving a viscosity of 598.37 L·m. -2 ·h -1 ·bar -1 Water flux. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the preparation process of the two-dimensional MOFs double-sided membrane of this application;

[0033] Figure 2 The XRD spectra of the precursor LDH and the two-dimensional MOFs material of this application are shown.

[0034] Figure 3 The images show the FTIR spectra of the precursor LDH and the two-dimensional MOFs material of this application.

[0035] Figure 4 The Zeta potential diagrams of the precursor LDH and two-dimensional MOFs materials of this application at different pH values ​​are shown.

[0036] Figure 5 SEM image of the two-dimensional MOFs double-sided membrane synthesized at 160℃ in this application;

[0037] Figure 6 The antibiotic retention performance (left) and molecular weight cutoff (right) of the two-dimensional MOFs double-sided membrane synthesized at 160℃ in this application are shown.

[0038] Figure 7 The antibiotic retention performance (left) and molecular weight cutoff (right) of the two-dimensional MOFs double-sided membrane synthesized at 220℃ in this application are shown.

[0039] Figure 8 The figure shows the flux of the two-dimensional MOFs bifacial membrane synthesized at 220℃ according to this application.

[0040] Figure 9 This is a pollution cycle diagram of the two-dimensional MOFs double-sided membrane synthesized at 220℃ in this application.

[0041] Figure 10 This is a performance comparison diagram of the two-dimensional MOFs double-sided membrane synthesized at 220℃ in this application with other two-dimensional membranes. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example 1:

[0044] A method for preparing bifacial MOFs based on two-dimensional metal-organic frameworks (MOFs) involves using LDH as a precursor to coordinate with organic ligands under hydrothermal conditions to form two-dimensional MOFs superstructured nanosheets with different charges. These nanosheets are then coated with organic polymers via a phase inversion method to form a film. The specific synthetic route is as follows:

[0045] S1. Preparation of layered bimetallic hydroxide LDH: Dissolve 5 parts Al(NO3)3·9H2O and 10 parts Mg(NO3)2·6H2O in 100 parts deionized water by molar ratio, then weigh 50 parts urea and dissolve them in the above solution. Transfer the solution to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally react at 110°C for 24 hours. Wash the obtained LDH powder three times each with deionized water and ethanol, and then vacuum dry overnight.

[0046] S2. Preparation of two-dimensional anionic metal-organic frameworks (MOFs): 10 parts of LDH powder synthesized in S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 20 parts of terephthalic acid were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 160 °C for 36 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum dried overnight to obtain the anionic MOFs, namely MgAl-BDC.

[0047] S3. Preparation of two-dimensional cationic metal-organic frameworks (MOFs): 10 parts of LDH powder synthesized in S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 25 parts of 2-aminoterephthalic acid were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 160 °C for 36 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum dried overnight to obtain the cationic MOFs, namely MgAl-BDC-NH2.

[0048] S4: Preparation of anionic MOF membranes; 7.54 parts of PVDF were weighed into a three-necked flask according to the mass ratio, and 50 parts of DMF solution were added. The mixture was stirred at 65℃ for 12 h, and 3.77 parts of anionic MOFs, namely MgAl-BDC, were added and stirred thoroughly for 6 h. After standing for 6 h, the mixture was degassed under vacuum for 4 h to obtain the casting solution. The casting solution was then coated onto a nonwoven fabric, and a film layer with a thickness of 300 μm was coated using a doctor blade. The film was left to stand in air for 60 s, and then transferred to a deionized water bath to fully complete the phase inversion. The deionized water was replaced every 12 h.

[0049] S5: Preparation of the double-sided membrane; 7.54 parts of PVDF were weighed into a three-necked flask according to the mass ratio, and 50 parts of DMF solution were added. The mixture was stirred at 65°C for 12 hours. Then, 3.77 parts of cationic MOFs, namely MgAl-BDC-NH2, were added and stirred thoroughly for 6 hours. After standing for 6 hours, the mixture was degassed under vacuum for 4 hours to obtain the casting solution. The casting solution was coated onto the back side of the anionic MOF membrane in S4 above. The membrane layer thickness was 300 μm using a doctor blade. The membrane was left to stand in air for 60 seconds and then transferred to a deionized water bath to fully complete the phase inversion. The deionized water was replaced every 12 hours.

[0050] Example 2

[0051] A method for preparing bifacial MOFs based on two-dimensional metal-organic frameworks (MOFs) involves using LDH as a precursor to coordinate with organic ligands under hydrothermal conditions to form two-dimensional MOFs superstructured nanosheets with different charges. These nanosheets are then coated with organic polymers via a phase inversion method to form a film. The specific synthetic route is as follows:

[0052] S1. Preparation of layered bimetallic hydroxide LDH: Dissolve 5 parts Al(NO3)3·9H2O and 10 parts Mg(NO3)2·6H2O in 100 parts deionized water by molar ratio, then weigh 50 parts urea and dissolve them in the above solution. Transfer the solution to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally react at 110°C for 24 hours. Wash the obtained LDH powder three times each with deionized water and ethanol, and then vacuum dry overnight.

[0053] S2. Preparation of two-dimensional anionic metal-organic frameworks (MOFs): 10 parts of LDH powder synthesized in S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 20 parts of terephthalic acid were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 220 °C for 36 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum dried overnight to obtain the anionic MOFs, namely MgAl-BDC.

[0054] S3. Preparation of two-dimensional cationic metal-organic frameworks (MOFs): 10 parts of LDH powder synthesized in S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 25 parts of 2-aminoterephthalic acid were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 220 °C for 36 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum dried overnight to obtain the cationic MOFs, namely MgAl-BDC-NH2.

[0055] S4: Preparation of anionic MOF membranes; 7.54 parts of PVDF were weighed into a three-necked flask according to the mass ratio, and 50 parts of DMF solution were added. The mixture was stirred at 65℃ for 12 h, and 3.77 parts of anionic MOFs, namely MgAl-BDC, were added and stirred thoroughly for 6 h. After standing for 6 h, the mixture was degassed under vacuum for 4 h to obtain the casting solution. The casting solution was then coated onto a nonwoven fabric, and a film layer with a thickness of 300 μm was coated using a doctor blade. The film was left to stand in air for 60 s, and then transferred to a deionized water bath to fully complete the phase inversion. The deionized water was replaced every 12 h.

[0056] S5: Preparation of the double-sided membrane; 7.54 parts of PVDF were weighed into a three-necked flask according to the mass ratio, and 50 parts of DMF solution were added. The mixture was stirred at 65°C for 12 hours. 3.77 parts of cation MOFs, namely MgAl-BDC-NH2, were added and stirred thoroughly for 6 hours. After standing for 6 hours, the mixture was degassed under vacuum for 4 hours to obtain the casting solution. The casting solution was coated onto the back side of the anionic MOF membrane in S4 above. The membrane layer thickness was 300 μm using a doctor blade. The membrane was left to stand in air for 60 seconds and then transferred to a deionized water bath to fully complete the phase inversion. The deionized water was replaced every 12 hours.

[0057] Example 3

[0058] A method for preparing bifacial MOFs based on two-dimensional metal-organic frameworks (MOFs) involves using LDH as a precursor to coordinate with organic ligands under hydrothermal conditions to form two-dimensional MOFs superstructured nanosheets with different charges. These nanosheets are then coated with organic polymers via a phase inversion method to form a film. The specific synthetic route is as follows:

[0059] S1. Preparation of layered bimetallic hydroxide LDH: Dissolve 5 parts Al(NO3)3·9H2O and 10 parts Mg(NO3)2·6H2O in 100 parts deionized water by molar ratio, then weigh 50 parts urea and dissolve them in the above solution. Transfer the solution to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally react at 110°C for 24 hours. Wash the obtained LDH powder three times each with deionized water and ethanol, and then vacuum dry overnight.

[0060] S2. Preparation of two-dimensional anionic metal-organic frameworks (MOFs): 10 parts of LDH powder synthesized in S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 20 parts of terephthalic acid were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 250 °C for 36 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum dried overnight to obtain the anionic MOFs, namely MgAl-BDC.

[0061] S3. Preparation of two-dimensional cationic metal-organic frameworks (MOFs): 10 parts of LDH powder synthesized in S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 25 parts of 2-aminoterephthalic acid were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 250 °C for 36 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum dried overnight to obtain the cationic MOFs, namely MgAl-BDC-NH2.

[0062] S4: Preparation of anionic MOF membranes; 7.54 parts of PVDF were weighed into a three-necked flask according to the mass ratio, and 50 parts of DMF solution were added. The mixture was stirred at 65℃ for 12 h, and 3.77 parts of anionic MOFs, namely MgAl-BDC, were added and stirred thoroughly for 6 h. After standing for 6 h, the mixture was degassed under vacuum for 4 h to obtain the casting solution. The casting solution was then coated onto a nonwoven fabric, and a film layer with a thickness of 300 μm was coated using a doctor blade. The film was left to stand in air for 60 s, and then transferred to a deionized water bath to fully complete the phase inversion. The deionized water was replaced every 12 h.

[0063] S5: Preparation of the double-sided membrane; 7.54 parts of PVDF were weighed into a three-necked flask according to the mass ratio, and 50 parts of DMF solution were added. The mixture was stirred at 65°C for 12 hours. Then, 3.77 parts of cationic MOFs, namely MgAl-BDC-NH2, were added and stirred thoroughly for 6 hours. After standing for 6 hours, the mixture was degassed under vacuum for 4 hours to obtain the casting solution. The casting solution was coated onto the back side of the anionic MOF membrane in S4 above. The membrane layer thickness was 300 μm using a doctor blade. The membrane was left to stand in air for 60 seconds and then transferred to a deionized water bath to fully complete the phase inversion. The deionized water was replaced every 12 hours.

[0064] Example 4

[0065] Membrane antifouling properties

[0066] (1) Bovine serum albumin (100 mg / L) was used as a simulated pollutant and dissolved in water. Membrane antifouling experiments were conducted using a cross-flow apparatus.

[0067] (2) The bifacial membranes of Examples 1-3 were subjected to membrane fouling experiments. The anionic MOFs membranes were used with the membrane surface facing the pollutant solution. The changes in water flux of the membrane were measured to explore their antifouling ability.

[0068] Example 5

[0069] Membrane antifouling properties

[0070] (1) Bovine serum albumin (100 mg / L) was used as a simulated pollutant and dissolved in water. Membrane antifouling experiments were conducted using a cross-flow apparatus.

[0071] (2) The bifacial membranes of Examples 1-3 were subjected to membrane fouling experiments. The membranes were made with the cationic MOFs facing the pollutant solution, and the changes in water flux were measured to explore their antifouling ability.

[0072] Example 6

[0073] Membrane retention and separation performance

[0074] Antibiotics (200 μg / L) were dissolved in water as small molecule pollutants. Membrane retention and separation performance were tested using a cross-flow apparatus.

[0075] The membrane retention and separation performance of the double-sided membranes in Examples 1-3 were tested.

[0076] Example 7

[0077] Antibiotic / salt separation performance test

[0078] Antibiotics (200 μg / L) were used as small molecule pollutants, and inorganic salts (NaCl, NaSO4, CaCl2) (0.5 mM) were dissolved in water. Membrane retention and separation performance experiments were conducted using a cross-flow apparatus.

[0079] The membrane retention and separation performance of the double-sided membranes in Examples 1-3 were tested.

[0080] Example 8

[0081] Antibiotic / Heavy Metal Separation Performance Test

[0082] Antibiotics (200 μg / L) were used as small molecule pollutants, and heavy metal salts (1 mM) were dissolved in water. Membrane retention and separation performance experiments were conducted using a cross-flow apparatus.

[0083] The membrane retention and separation performance of the double-sided membranes in Examples 1-3 were tested.

[0084] II. Test Results

[0085] 2.1 Experimental Setup

[0086] Experimental setup: The experimental setup used in this invention includes a cross-flow device and a flux testing unit (PGC-1502, Adam, UK). At a transmembrane pressure of 0.2 MPa, the concentrations of antibiotics, heavy metals, and ionic conductivity at the effluent were measured.

[0087] 2.2 Experimental Methods and Results

[0088] 2.2.1 Test Methods

[0089] The concentration of the antibiotic solution used in the test was 200–500 μg / L. Samples were taken at 10, 20, 30, 60, and 120 min to detect the removal efficiency of antibiotics, ions, and heavy metals. The retention rate (R) was calculated using the following equation: R = (C f -C p ) / C f ×100%, where C f and C p The concentrations of the feed solution and permeate solution were measured, respectively. The concentration of antibiotics in the solution was measured by liquid chromatography, the ion separation effect was detected by a conductivity meter, and the separation effect of heavy metals was detected by ICP-AES. Membrane flux was measured using a cross-flow apparatus.

[0090] 2.2.2 Results

[0091] The test results of the membrane in Example 6 are compared as shown in Table 1 below:

[0092] Table 1. Retention effect of different membranes on antibiotics in water.

[0093] Example 1 - Vaginal membrane 93.75 70.11 80.73 30.47 Example 1 - Positive membrane 88.72 57.18 60.32 68.9 Example 1 - Double-sided nerve membrane 97.8 82.11 85.9 72.3 Example 2 - Vaginal membrane 94.21 82.11 84.5 35.25 Example 2 - Positive membrane 80.43 58.43 54.32 69.2 Example 2 - Double-sided nerve membrane 99.83 90.19 93.9 90.54 Example 3 - Vaginal membrane 92.31 73.43 74.38 37.32 Example 3 - Positive membrane 82.72 51.18 55.32 74.29 Example 3: Double-sided membrane 96.76 78.21 80.19 80.32

[0094] By comparing the test data, we can find that:

[0095] (1) The invention proposes a two-dimensional MOFs-based double-sided membrane that can combine the anion membrane and the cation membrane, which has high selectivity for pollutants with different charges and has better performance than single membranes.

[0096] (2) The two-dimensional MOF-based bifacial membrane proposed in this invention possesses both high selectivity and high water flux, such as... Figure 8 As shown, this achieves a simultaneous improvement in both penetration and selectivity.

[0097] The test results of the double-sided nerve mask in Example 8 are listed in Table 2 below.

[0098] Table 2

[0099] Example 1 - Double-sided nerve membrane 97.53％ 4.38％ 5.63％ 4.58％ Example 2 - Double-sided nerve membrane 99.37％ 5.56％ 6.09％ 4.77％ Example 3: Double-sided membrane 96.82％ 4.67％ 5.18％ 3.79％

[0100] By comparing the test data, we can find that:

[0101] The present invention proposes a method for separating heavy metal / antibiotic complexation systems using a two-dimensional MOF-based bifacial membrane, which exhibits superior complex-breaking and separation performance. Figure 10 As shown, the tetracycline-heavy metal separation capacity is as high as 149, which is far higher than that of the two-dimensional membranes reported in the past, and the flux is increased by 1 to 2 orders of magnitude.

[0102] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional metal-organic framework-based bifacial membrane, characterized in that, Specifically, the following steps are included: S1. Preparation of layered bimetallic hydroxide LDH: Dissolve 8-12 parts of divalent metal salt and 4-6 parts of trivalent metal salt in 100 parts of deionized water to prepare a solution. Then weigh 40-60 parts of urea and dissolve it in the above solution. Transfer the solution to a high-pressure reactor with a stainless steel Teflon liner and perform a hydrothermal reaction at 80-150 °C for 12-36 h. Wash the obtained LDH powder three times each with deionized water and ethanol, and then vacuum dry overnight. S2. Preparation of two-dimensional anionic metal-organic frameworks (MOFs): 10-20 parts of LDH powder (vacuum-dried overnight) from S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 20-40 parts of anionic functional group organic ligand were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and subjected to hydrothermal reaction at 120-250℃ for 24-48 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum-dried overnight to obtain anionic MOFs. The anionic functional group organic ligand is one or more of terephthalic acid, trimesic acid, and 2,5-dihydroxyterephthalic acid. S3. Preparation of two-dimensional cationic metal-organic frameworks (MOFs): 10-20 parts of LDH powder (vacuum-dried overnight) from S1 were dissolved in 60 parts of N,N-dimethylformamide (DMF) solution by molar ratio. After sonication for 30 min, 20-40 parts of cationic functional group organic ligands were added, and sonication was continued for another 30 min. The mixture was then transferred to a high-pressure reactor with a stainless steel Teflon liner and hydrothermally reacted at 120-250℃ for 24-48 h. After cooling, the mixture was washed three times each with DMF and ethanol, and then vacuum-dried overnight to obtain cationic MOFs. The cationic functional group organic ligands were one or more of 2-aminoterephthalic acid, 2-methylimidazole, and benzimidazole. S4. Preparation of anionic MOF membranes: Weigh 5-15 parts of organic polymer into a three-necked flask, add 50-100 parts of DMF solution, stir at 50-70℃ for 12-24 h, add anionic MOFs and continue stirring thoroughly for 6-12 h, let stand for 6-12 h, and then degas under vacuum for 2-6 h to obtain casting solution. Then coat the casting solution onto nonwoven fabric, and use a doctor blade to coat a membrane with a thickness of 200-400 μm. Let stand in air for 30-60 s, and then transfer to a deionized water bath to fully complete the phase inversion. Replace the deionized water every 12 h. S5. Preparation of the double-sided MOF membrane: Weigh 5-15 parts of organic polymer into a three-necked flask according to the mass ratio, add 50-100 parts of DMF solution, stir at 50-70℃ for 12-24h, add cationic MOFs and continue stirring thoroughly for 6-12h, let stand for 6-12h, and then degas under vacuum for 2-6h to obtain the casting solution. Coat the back of the anionic MOF membrane in S4 above with the casting solution, and use a doctor blade to coat the membrane to a thickness of 200-400μm. Let it stand in air for 30-60s, and then transfer it to a deionized water bath to fully complete the phase inversion. Replace the deionized water every 12h.

2. The method for preparing a two-dimensional metal-organic framework-based bifacial membrane according to claim 1, characterized in that: In S3 and S4, when the phase transformation is fully completed in the deionized water bath, the water bath temperature is controlled at 20°C and the phase transformation time is 2 days.

3. The method for preparing a two-dimensional metal-organic framework-based bifacial membrane according to claim 1, characterized in that: The mass ratio of anionic / cationic MOFs to organic polymers in S3 or S4 is 10 to 100%.

4. The method for preparing a two-dimensional metal-organic framework-based bifacial membrane according to claim 1, characterized in that: The thickness of the bifacial membrane of the two-dimensional metal-organic framework is 400 ~ 800 μm.

5. The method for preparing a two-dimensional metal-organic framework-based bifacial membrane according to claim 1, characterized in that: The divalent metal salt is one or more of cobalt nitrate Co(NO3)2·6H2O, zinc nitrate Zn(NO3)2·6H2O, nickel nitrate Ni(NO3)2·6H2O, and magnesium nitrate Mg(NO3)2·6H2O; the trivalent metal salt is one or more of ferric nitrate Fe(NO3)3·9H2O and / or aluminum nitrate Al(NO3)3·9H2O, and the molar ratio of the trivalent metal salt to the divalent metal salt is 1:

2.

6. The method for preparing a two-dimensional metal-organic framework-based bifacial membrane according to claim 1, characterized in that, The organic polymers in S3 and S4 are polyvinylidene fluoride (PVDF) or polyether sulfone (PES).

7. The method for preparing a two-dimensional metal-organic framework-based bifacial membrane according to claim 1, characterized in that, The thickness of the membrane on one side is controlled at 300 μm.

8. The application of a bifacial membrane prepared by the method of any one of claims 1-7 based on a two-dimensional metal-organic framework in the complex-breaking and separation of heavy metal / antibiotic complexing systems, characterized in that: The double-sided membrane is designed with the anterior side facing the heavy metal / antibiotic complexation system.

9. The application according to claim 8, characterized in that: The concentration of the heavy metal / antibiotic complex system is 200~500 μg / L, and the ion concentration in the saline is 0.5~1 mM.

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