A nanofiltration membrane, a preparation method and application thereof
By introducing a composite intermediate layer of one-dimensional inorganic materials and two-dimensional MOF nanosheets into the nanofiltration membrane, the "trade-off" problem of permeability and salt rejection performance of existing nanofiltration membranes is solved, and a high-efficiency nanofiltration membrane suitable for the separation of various inorganic salts is prepared.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV
- Filing Date
- 2023-09-22
- Publication Date
- 2026-06-09
AI Technical Summary
Existing nanofiltration membranes, while ensuring selectivity, struggle to simultaneously improve permeability and salt rejection performance, and the increased thickness of the intermediate layer leads to reduced stability.
A complete and defect-free nanofiltration membrane was prepared by using a composite intermediate layer of one-dimensional inorganic materials and two-dimensional MOF nanosheets, which was grown uniformly on a porous substrate through hydrothermal reaction, and then formed into a polyamide surface layer through interfacial polymerization.
It significantly improves the water permeability and salt retention performance of nanofiltration membranes, reduces water transport resistance, enhances the mechanical support performance of membranes, and achieves efficient retention of a variety of inorganic salts.
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Figure CN117160248B_ABST
Abstract
Description
Technical Field
[0001] This invention pertains to separation membranes, their preparation methods and applications, specifically a nanofiltration membrane and its preparation method and applications. Background Technology
[0002] With the rapid growth of the world's population and the acceleration of industrialization and urbanization, water scarcity has become a global challenge, driving the development of energy-saving water treatment technologies. Producing freshwater by treating unconventional water sources such as seawater, brackish water, and municipal sewage (which are saline or damaged) is one of the main solutions to water scarcity. Membrane technology, due to its low energy consumption and environmental friendliness, has become a model for freshwater production. Nanofiltration, a pressure-driven membrane technology between reverse osmosis and ultrafiltration, holds promise as a replacement for traditional water treatment technologies due to its high separation efficiency, suitable operating conditions, and wide applicability.
[0003] Currently, commercial nanofiltration membranes are mainly prepared through interfacial polymerization, consisting of a macroporous substrate and a polyamide surface layer. In a typical interfacial polymerization process, two reactive monomers dissolved in two immiscible phases react at the interface to form the polyamide surface layer. However, due to the rapid, irreversible, and complex polymerization process, and its dependence on monomer diffusion rates, precisely controlling this process is extremely difficult, leading to a trade-off between permeability and selectivity in nanofiltration membranes. Therefore, improving the water permeability of nanofiltration membranes while maintaining selectivity remains a technical challenge.
[0004] By establishing a nanoporous interlayer between a porous substrate and a polyamide layer, it is expected to accelerate water transport, thereby overcoming the permeability-selectivity tradeoff. Simultaneously, the interlayer can improve the mechanical properties of the polyamide surface by enhancing the adhesion between the interlayer and the substrate, thus improving the structural stability of the nanofiltration membrane. In recent years, various multifunctional nanomaterials have been used as interlayers, such as zeolites, graphene oxide, carbon nanotubes, covalent organic frameworks, and metal-organic frameworks (MOFs). Among them, MOFs show great potential in constructing high-performance nanofiltration membranes due to their high porosity, tunable pore size, and good compatibility with polymers. Chinese invention patents CN115463557A and CN114768547B both disclose a method for preparing nanofiltration membranes using 3D MOFs as an interlayer, but both suffer from the problem of increased selective layer thickness and MOF aggregation in the prepared nanofiltration membrane, thereby reducing the salt rejection performance and stability of the nanofiltration membrane. 2D MOF nanosheets can effectively address these drawbacks because their ultrathin thickness and abundant functional groups can significantly reduce the mass transfer resistance of water molecules and effectively enhance the compatibility between the polyamide surface layer and the interlayer. Liu et al. (J.Membr.Sci.2022,653(5):120520) used nickel-based 2D MOFs as the interlayer material and improved the water permeability of the membrane through the abundant functional groups on the 2D MOF nanosheets. However, large-sized 2D MOF nanosheets are prone to wrinkling during vacuum deposition, which increases the thickness of the interlayer and the mass transfer resistance of water molecules, which is not conducive to enhancing water permeability.
[0005] In summary, the existing "trade-off" limit of nanofiltration membranes still needs to be overcome, and salt rejection performance and water permeability need to be further improved. Summary of the Invention
[0006] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a nanofiltration membrane with good mechanical support performance, small thickness and low water molecule transport resistance. Another purpose of this invention is to provide a complete, defect-free, simple and convenient method for preparing a nanofiltration membrane. A further purpose of this invention is to provide an application of a nanofiltration membrane in sodium sulfate, calcium sulfate, magnesium sulfate, sodium chloride, calcium chloride and magnesium chloride to simultaneously improve water permeability and salt retention performance.
[0007] Technical solution: The nanofiltration membrane of the present invention comprises a porous substrate, a composite intermediate layer and a polyamide surface layer in sequence. The composite intermediate layer is uniformly composed of one-dimensional inorganic (1D) material and two-dimensional MOFs (2D MOFs) nanosheets.
[0008] Furthermore, the one-dimensional inorganic material is one or more of the following: carbon nanotubes, boron nitride nanowires, zirconium oxide nanowires, molybdenum sulfide nanowires, gallium phosphide nanowires, and titanium oxide nanowires.
[0009] Furthermore, the porous substrate is one or more of the following: polyethersulfone membrane, polysulfone membrane, polyvinylidene fluoride membrane, and polyacrylonitrile membrane.
[0010] The present invention discloses a method for preparing a nanofiltration membrane, comprising the following steps:
[0011] Step 1: Mix ethanol and N,N-dimethylformamide, then add a one-dimensional inorganic material and disperse to obtain mixed solution A;
[0012] Step 2: Add the metal precursor, organic ligand and polyvinylpyrrolidone to the mixed solution A, and obtain two-dimensional MOF nanosheets, i.e. composite intermediate layer, by hydrothermal reaction on a one-dimensional inorganic material under confined growth.
[0013] Step 3: Deposit the composite intermediate layer onto the porous substrate to obtain the composite substrate;
[0014] Step four: Immerse the composite substrate in a piperazine aqueous solution, let it stand and dry, then immerse it in a solution of trimesoyl chloride dissolved in n-hexane to carry out interfacial polymerization reaction, and finally heat to cure it to obtain a nanofiltration membrane.
[0015] Furthermore, in step one, the volume ratio of ethanol to N,N-dimethylformamide is 1:1 to 1:5, and the mass-volume ratio of the one-dimensional inorganic material to the total volume of ethanol and N,N-dimethylformamide is 5 to 15:64.
[0016] Further, in step two, the metal precursor is copper nitrate trihydrate, zinc nitrate hexahydrate, nickel nitrate hexahydrate, or cobalt nitrate hexahydrate. The organic ligand is 5,10,15,20-tetra(4-carboxyphenyl)porphyrin, tetra(2-carboxyphenyl)porphyrin, 5,10,15,20-tetra(4-carboxymethoxyphenyl)porphyrin, or meso tetra(3,5-dicarboxyphenyl)porphyrin. The hydrothermal reaction temperature is 75–80 °C.
[0017] Further, in step four, the mass percentage of the piperazine aqueous solution is 0.025–0.5 wt%, and the mass percentage of the hexane-trimethylammonium chloride solution is 0.02–0.4 wt%. The wetting time is 0.5–15 min; the interfacial polymerization time is 0.5–15 min; and the heating curing time is 5–30 min.
[0018] The present invention relates to the application of a nanofiltration membrane in the separation of sodium sulfate, calcium sulfate, magnesium sulfate, sodium chloride, calcium chloride, and magnesium chloride, which simultaneously improves water permeability and salt retention performance.
[0019] Preparation Principle: This invention provides a nanofiltration membrane that, by introducing a uniform interlayer composed of 1D materials and 2D MOFs, prepares a complete and defect-free nanofiltration membrane. This significantly improves the water flux of the nanofiltration membrane, and the introduction of a uniformly distributed interlayer facilitates the formation of a uniform nanofiltration membrane, enhancing its retention capacity for inorganic salts. The composite of 1D inorganic materials and 2D MOFs improves the supporting strength of the nanofiltration membrane and reduces the water transport path. Furthermore, the inherent framework structure of MOFs provides additional water transport channels. Introducing a carboxyl-rich interlayer controls PIP diffusion, facilitating the preparation of a nanofiltration membrane with uniform pore size and significantly increasing the surface electronegativity of the nanofiltration membrane, thus enhancing the Donnan effect.
[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant features:
[0021] 1. The obtained nanofiltration membrane can overcome the upper limit of the traditional nanofiltration membrane "trade-off" and has excellent salt rejection performance and water permeability;
[0022] 2. For the first time, based on 1D materials, a well-morphologically shaped and uniformly dispersed 1D / 2D composite intermediate layer was obtained by controlling the threshold growth of 2D MOF nanosheets.
[0023] 3. The obtained 1D / 2D composite interlayer is beneficial for preparing complete and defect-free nanofiltration membranes, reducing the overall thickness of the interlayer and polyamide layer, while providing sufficient mechanical support. For the first time, based on 1D materials, a well-morphologically sound and uniformly dispersed 1D / 2D composite interlayer was obtained by controlling the threshold growth of nanosheets. Attached Figure Description
[0024] Figure 1 This is a scanning electron microscope image of the surface layer of the nanofiltration membrane polyamide in Embodiment 2 of the present invention.
[0025] Figure 2 This is a scanning electron microscope image of the surface layer of the nanofiltration membrane polyamide in Embodiment 3 of the present invention.
[0026] Figure 3 This is a scanning electron microscope image of the surface layer of the nanofiltration membrane polyamide in Embodiment 4 of the present invention.
[0027] Figure 4 This is a comparison chart of the retention performance of nanofiltration membranes for various salt solutions in Example 3 of the present invention.
[0028] Figure 5 This is a scanning electron microscope image of the intermediate layer material in Comparative Example 1.
[0029] Figure 6 This is a scanning electron microscope image of the intermediate layer material in Comparative Example 2.
[0030] Figure 7 This is a scanning electron microscope image of the intermediate layer material in Embodiment 1 of the present invention. Detailed Implementation
[0031] In the following embodiments, the carbon nanotubes are from the Pioneer Nanotechnology brand, with a diameter of 1-2 nm and a length of 5-30 μm.
[0032] Example 1
[0033] A method for preparing a nanofiltration membrane includes the following steps:
[0034] Step 1: Mix 48 mL of ethanol and 144 mL of N,N-dimethylformamide, add carbon nanotubes, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0035] Step 2: Add 30 mg of copper nitrate trihydrate, 72 mg of 5,10,15,20-tetra(4-carboxyphenyl)porphyrin and 120 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 80 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0036] Step 3: Deposit one part of the composite intermediate layer onto the porous substrate to obtain the composite substrate, wherein the porous substrate is a polyethersulfone membrane.
[0037] Step 4: Immerse the composite substrate in a 0.125wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 1 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.1wt%. Finally, heat and cure at 60℃ for 10 min to obtain the nanofiltration membrane.
[0038] The composite intermediate layer obtained in steps one and two of this embodiment is diluted in 150 mL of ethanol, and 5 mL is diluted in 25 mL of ethanol. 1 mL is defined as 1 part.
[0039] Example 2
[0040] A method for preparing a nanofiltration membrane includes the following steps:
[0041] Step 1: Mix 96 mL of ethanol and 288 mL of N,N-dimethylformamide, add carbon nanotubes, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0042] Step 2: Add 60 mg of copper nitrate trihydrate, 144 mg of 5,10,15,20-tetra(4-carboxyphenyl)porphyrin and 240 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 80 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0043] Step 3: Deposit two composite intermediate layers onto a porous substrate to obtain a composite substrate, wherein the porous substrate is a polyethersulfone membrane.
[0044] Step 4: Immerse the composite substrate in a 0.125wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 1 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.1wt%. Finally, heat and cure at 60℃ for 10 min to obtain the nanofiltration membrane.
[0045] Example 3
[0046] A method for preparing a nanofiltration membrane includes the following steps:
[0047] Step 1: Mix 240 mL of ethanol and 720 mL of N,N-dimethylformamide, add carbon nanotubes, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0048] Step 2: Add 150 mg of copper nitrate trihydrate, 360 mg of 5,10,15,20-tetra(4-carboxyphenyl)porphyrin and 600 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 80 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0049] Step 3: Deposit 5 portions of the composite intermediate layer onto a porous substrate to obtain the composite substrate, which is a polyethersulfone membrane.
[0050] Step 4: Immerse the composite substrate in a 0.125wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 1 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.1wt%. Finally, heat and cure at 60℃ for 10 min to obtain the nanofiltration membrane.
[0051] Test 1
[0052] The surface morphology of the nanofiltration membranes obtained in Examples 1-3 was analyzed using scanning electron microscopy, such as... Figures 1-3As can be seen, the three 1D / 2D composite intermediate layer reinforced nanofiltration membranes prepared in Examples 1 to 3 are characterized by being composed of a porous substrate, a 1D / 2D composite intermediate layer and a polyamide surface layer. The polyamide surface layer of the nanofiltration membrane exhibits a complete morphology, and the surface of the nanofiltration membranes in Examples 1 to 3 gradually becomes smooth.
[0053] Test 2
[0054] The nanofiltration membranes obtained in Examples 1-3 were subjected to various salt solution retention performance tests, and the specific methods are as follows:
[0055] (1) The separation performance of the nanofiltration membrane was tested using a cross-flow filtration device in the laboratory. The effective filtration membrane area was 7.065 cm². 2 To ensure pressure stability during testing, the nanofiltration membranes of Examples 2-4 were pre-pressed with pure water at 4 bar for 1 hour at room temperature before filtration with various salt solutions.
[0056] (2) Water permeability: Prepare aqueous solutions of 1 g / L Na₂SO₄, MgSO₄, CaSO₄, MgCl₂, CaCl₂, and NaCl. Run the cross-flow filtration device for 1 hour at room temperature and 4 bar. Collect the effluent volume from the nanofiltration membrane obtained in the above examples and calculate the water permeability. When replacing the salt solutions, rinse the nanofiltration membrane three times with pure water. The test results are as follows: Figure 4 As shown.
[0057] (3) Multiple salt rejection rates: The salt solution concentrations in the influent and effluent water were measured using a conductivity meter, and the salt solution rejection rates were calculated accordingly. The test results are as follows: Figure 4 As shown.
[0058] The preferred embodiment is Embodiment 2. (By...) Figure 4 As can be seen, the order of salt ion rejection of the nanofiltration membrane obtained in Example 2 is Na2SO4 > MgSO4 > CaSO4 > MgCl2 > CaCl2 > NaCl. This indicates that the high-performance nanofiltration membrane's rejection of salt ions is based on the Donnan effect and size sieving.
[0059] Example 4
[0060] A method for preparing a nanofiltration membrane includes the following steps:
[0061] Step 1: Mix 48 mL of ethanol and 48 mL of N,N-dimethylformamide, add boron nitride nanowires, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0062] Step 2: Add 30 mg of zinc nitrate hexahydrate, 72 mg of tetra(2-carboxyphenyl)porphyrin and 120 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 75 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0063] Step 3: Deposit one part of the composite intermediate layer onto the porous substrate to obtain the composite substrate, wherein the porous substrate is a polysulfone membrane.
[0064] Step four: Immerse the composite substrate in a 0.025 wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 0.5 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.02 wt%. Finally, heat and cure at 60°C for 5 min to obtain the nanofiltration membrane.
[0065] Example 5
[0066] A method for preparing a nanofiltration membrane includes the following steps:
[0067] Step 1: Mix 48 mL of ethanol and 240 mL of N,N-dimethylformamide, add zirconium oxide nanowires, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0068] Step 2: Add 30 mg of nickel nitrate hexahydrate, 72 mg of 5,10,15,20-tetra(4-carboxymethoxyphenyl)porphyrin and 120 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 77 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0069] Step 3: Deposit one part of the composite intermediate layer onto the porous substrate to obtain the composite substrate. The porous substrate is a polyvinylidene fluoride membrane.
[0070] Step 4: Immerse the composite substrate in a 0.5 wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 15 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.4 wt%. Finally, heat and cure at 60°C for 30 min to obtain the nanofiltration membrane.
[0071] Example 6
[0072] A method for preparing a nanofiltration membrane includes the following steps:
[0073] Step 1: Mix 48 mL of ethanol and 80 mL of N,N-dimethylformamide, add molybdenum sulfide nanowires, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0074] Step 2: Add 30 mg of cobalt nitrate hexahydrate, 72 mg of racemic tetra(3,5-dicarboxyphenyl)porphyrin and 120 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 78 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0075] Step 3: Deposit one part of the composite intermediate layer onto the porous substrate to obtain the composite substrate, which is a polyacrylonitrile membrane.
[0076] Step 4: Immerse the composite substrate in a 0.345wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 10 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.2wt%. Finally, heat and cure at 60℃ for 20 min to obtain the nanofiltration membrane.
[0077] Example 7
[0078] A method for preparing a nanofiltration membrane includes the following steps:
[0079] Step 1: Mix 48 mL of ethanol and 200 mL of N,N-dimethylformamide, add gallium phosphide nanowires, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0080] Step 2: Add 30 mg of zinc nitrate hexahydrate, 72 mg of 5,10,15,20-tetra(4-carboxymethoxyphenyl)porphyrin and 120 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 79 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0081] Step 3: Deposit one part of the composite intermediate layer onto the porous substrate to obtain the composite substrate, wherein the porous substrate is a polysulfone membrane.
[0082] Step 4: Immerse the composite substrate in a 0.42wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 5 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.1wt%. Finally, heat and cure at 60℃ for 15 min to obtain the nanofiltration membrane.
[0083] Example 8
[0084] A method for preparing a nanofiltration membrane includes the following steps:
[0085] Step 1: Mix 48 mL of ethanol and 170 mL of N,N-dimethylformamide, add titanium dioxide nanowires, and sonicate using a cell disruptor probe at an intensity of 1000 W for 9 hours to obtain mixed solution A.
[0086] Step 2: Add 30 mg of nickel nitrate hexahydrate, 72 mg of tetra(2-carboxyphenyl)porphyrin and 120 mg of polyvinylpyrrolidone to mixed solution A, sonicate for 10 min, transfer to a high-pressure reactor and heat at 76 °C for 3 h. Two-dimensional MOF nanosheets with confined growth on one-dimensional inorganic materials are obtained through hydrothermal reaction, thus obtaining a uniform composite intermediate layer.
[0087] Step 3: Deposit one part of the composite intermediate layer onto the porous substrate to obtain the composite substrate. The porous substrate is a polyvinylidene fluoride membrane.
[0088] Step 4: Immerse the composite substrate in a 0.25wt% piperazine aqueous solution, let it stand and dry for 4 min, then immerse it in a pyromellitic chloride solution dissolved in n-hexane for 8 min to complete the interfacial polymerization reaction. The mass percentage of the pyromellitic chloride solution in n-hexane is 0.3wt%. Finally, heat and cure at 60℃ for 25 min to obtain the nanofiltration membrane.
[0089] Comparative Example 1
[0090] A method for fabricating a 1D intermediate layer includes the following steps:
[0091] (1) Mix 48 mL of ethanol and 144 mL of N,N-dimethylformamide, add 30 mg of carbon nanotubes, and sonicate with a cell disruptor probe at an intensity of 1000 W for 9 h to obtain mixed solution A.
[0092] (2) The carbon nanotubes were centrifuged and washed with ethanol, and dispersed in 150 mL of ethanol to obtain a 1D intermediate layer.
[0093] Comparative Example 2
[0094] A method for preparing a 2D intermediate layer includes the following steps:
[0095] (1) Mix 48 mL of ethanol and 144 mL of N,N-dimethylformamide to obtain mixed solution A;
[0096] (2) Add 30 mg of copper nitrate trihydrate, 120 mg of polyvinylpyrrolidone and 72 mg of 5,10,15,20-tetra(4-carboxyphenylporphyrin) to the mixed solution in (1), sonicate for 10 min, transfer to a high-pressure reactor and heat at 80 °C for 3 h, centrifuge and wash with ethanol, disperse in 150 mL of ethanol to obtain a 2D intermediate layer.
[0097] The intermediate layers obtained in Comparative Example 1, Comparative Example 2, and Example 1 were observed using a scanning electron microscope. Figure 5 The 1D intermediate layer obtained in Comparative Example 1, when deposited densely on a porous substrate, increases water transport resistance, which is detrimental to the preparation of enhanced nanofiltration membranes. For example... Figure 6 The 2D intermediate layer obtained in Comparative Example 2 was excessively wrinkled, making it impossible to prepare a complete and defect-free nanofiltration membrane. For example... Figure 7 The 1D / 2D composite interlayer obtained in Example 1, while ensuring controllable 1D carbon nanotube quantity, can restrict the growth of 2D MOF nanosheets, thereby obtaining an enhanced nanofiltration membrane. Therefore, the interlayer material obtained by the method in Example 1 is the most ideal.
[0098] Comparative Example 3
[0099] The commercial membrane used is the NF270 model from Zhongke Ruiyang, used directly as a nanofiltration membrane. The specifications for this commercial nanofiltration membrane are: water flux of 8.70 and 9.34 Lm. -2 h -1 bar -1 The Na2SO4 retention rates were 98.45% and 97.83%.
Claims
1. A nanofiltration membrane, characterized in that: The material comprises a porous substrate, a composite intermediate layer, and a polyamide surface layer. The composite intermediate layer is uniformly composed of a one-dimensional inorganic material and two-dimensional MOF nanosheets. The preparation method of the composite intermediate layer is as follows: ethanol and N,N-dimethylformamide are mixed, and then a one-dimensional inorganic material is added and dispersed to obtain a mixed solution A. A metal precursor, an organic ligand, and polyvinylpyrrolidone are added to the mixed solution A, and two-dimensional MOF nanosheets with confined growth on the one-dimensional inorganic material are obtained through a hydrothermal reaction. The one-dimensional inorganic material is one or more of the following: carbon nanotubes, boron nitride nanowires, zirconium oxide nanowires, molybdenum sulfide nanowires, gallium phosphide nanowires, and titanium oxide nanowires.
2. The nanofiltration membrane according to claim 1, characterized in that: The porous substrate is one or more of the following: polyethersulfone membrane, polysulfone membrane, polyvinylidene fluoride membrane, and polyacrylonitrile membrane.
3. A method for preparing a nanofiltration membrane, characterized in that, Includes the following steps: Step 1: Mix ethanol and N,N-dimethylformamide, then add a one-dimensional inorganic material and disperse to obtain mixed solution A; Step 2: Add the metal precursor, organic ligand and polyvinylpyrrolidone to the mixed solution A, and obtain two-dimensional MOF nanosheets, i.e. composite intermediate layer, by hydrothermal reaction on a one-dimensional inorganic material under confined growth. Step 3: Deposit the composite intermediate layer onto the porous substrate to obtain the composite substrate; Step 4: Immerse the composite substrate in a piperazine aqueous solution, let it stand and dry, then immerse it in a solution of trimesoyl chloride dissolved in n-hexane to carry out interfacial polymerization reaction, and finally heat to cure it to obtain a nanofiltration membrane. The one-dimensional inorganic material is one or more of the following: carbon nanotubes, boron nitride nanowires, zirconium oxide nanowires, molybdenum sulfide nanowires, gallium phosphide nanowires, and titanium oxide nanowires.
4. The method for preparing a nanofiltration membrane according to claim 3, characterized in that: In step one, the volume ratio of ethanol to N,N-dimethylformamide is 1:1 to 1:5, and the mass-volume ratio of the one-dimensional inorganic material to the total volume of ethanol and N,N-dimethylformamide is 5 to 15:
64.
5. The method for preparing a nanofiltration membrane according to claim 3, characterized in that: In step two, the metal precursor is copper nitrate trihydrate, zinc nitrate hexahydrate, nickel nitrate hexahydrate, or cobalt nitrate hexahydrate.
6. The method for preparing a nanofiltration membrane according to claim 3, characterized in that: In step two, the organic ligand is 5,10,15,20-tetra(4-carboxyphenyl)porphyrin, tetra(2-carboxyphenyl)porphyrin, 5,10,15,20-tetra(4-carboxymethoxyphenyl)porphyrin, or meso-tetra(3,5-dicarboxyphenyl)porphyrin.
7. A method for preparing a nanofiltration membrane according to claim 3, characterized in that: In step two, the temperature of the hydrothermal reaction is 75~80 ℃.
8. A method for preparing a nanofiltration membrane according to claim 3, characterized in that: In step four, the mass percentage of the piperazine aqueous solution is 0.025~0.5 wt%, and the mass percentage of the hexane-pyromellitic chloride solution is 0.02~0.4 wt%.