Method for synthesizing liquid-liquid interface and regulating MOF pervaporation membrane

Abstract

The invention discloses a method for synthesizing a liquid-liquid interface and regulating and controlling an MOF pervaporation membrane, and relates to the field of pervaporation membranes. The method comprises the following steps: providing a metal salt dispersion liquid prepared from a proper solvent; providing an organic ligand aqueous solution, and adding a surfactant into the organic ligand solution to change interfacial tension so as to regulate and control nucleation and growth behaviors of MOF particles on a liquid-liquid interface; a deprotonation agent is added into an organic ligand solution to regulate and control the deprotonation process of an organic ligand, so that the reaction rate is accelerated, and the morphology and the size of the MOF membrane are precisely regulated and controlled; according to the method, through the synergistic effect of multiple regulation and control mechanisms, the film forming rate and the film quality are remarkably improved, and the MOF film with a continuous structure and performance can be obtained.

Description

Technical Field

[0001] This invention relates to the field of pervaporation membranes, and particularly to formulations for the synthesis and regulation of liquid-liquid interfaces and continuous, intact MOF membranes. Background Technology

[0002] Metal-organic frameworks (MOFs) and their derivatives have shown great application potential in gas storage, adsorption separation, electro / photochemical sensing, wearable devices, and catalysis. For these applications, controlling the integrity of MOF films and the size and morphology of the crystals is particularly important. As a new class of crystalline porous materials, various types of MOFs have been reported, such as MOF-5, ZIFs (zeolite imidazole frameworks), the MIL series, UiO-66, HKUST-1, and PCN-222. However, some limitations exist, including synthetic complexity, stability issues, high cost, difficulty in control, selectivity and throughput limitations, and processing difficulty. Related techniques generally involve the preparation of MOF films on substrates, including solvothermal methods; liquid-phase epitaxy; back-diffusion; rapid thermal deposition; dip-coating-thermal conversion; electrochemical deposition; interfacial microfluidic film processing; gel-vapor deposition; and ligand induction.

[0003] However, in related technologies, it is difficult to directly and uniformly nucleate MOF membranes on porous substrates, resulting in large defects and cracks in the MOF membrane formation. This makes it difficult to guarantee the continuity and uniformity of the membrane, and also hinders the effective control of its size and morphology. Some researchers have synthesized particles at the liquid-liquid interface and then retrieved them using a base membrane, but most of these methods result in simple particle stacking, requiring the coating of the MOF membrane surface with organic matter to compensate for defects and ensure the membrane's continuity and density. This invention can directly synthesize continuous MOF membranes at the liquid-liquid interface by controlling parameters such as interfacial tension, diffusion rate, and reaction rate, and apply this technology to the field of pervaporation preferential alcohol percolation, thereby improving the separation factor. Summary of the Invention

[0004] This invention provides a formulation for rapidly generating continuous MOF membranes at the liquid-liquid interface, which can solve technical problems such as membrane defects existing in related technologies.

[0005] Specifically, the following technical solutions are included:

[0006] (1) Provide a suitable solvent to prepare the metal salt dispersion corresponding to the MOF;

[0007] (2) Provide an aqueous solution of the organic ligand corresponding to MOF, and change the interfacial tension by adding a surfactant to the aqueous solution of the organic ligand to regulate the nucleation and growth behavior of MOF particles at the liquid-liquid interface; or regulate the deprotonation process of the organic ligand by adding a deprotonating agent to the aqueous solution of the organic ligand to accelerate the reaction rate and achieve precise control of the morphology and size of the MOF film.

[0008] (3) The metal salt dispersion from step (1) is steadily added dropwise to the surface of the organic ligand aqueous solution (preferably along the edge of the container), and left to stand for a period of time. During this process, the MOF generates an integral membrane structure at the liquid-liquid interface.

[0009] The metal salt dispersion described in step (1) includes: a metal salt and a dispersant;

[0010] The dispersant is selected from at least one of n-octanol, isopropanol, n-butanol, N,N-2-methylacetamide, n-propanol, and n-heptane, and isopropanol and N,N-2-methylacetamide are not used alone; preferably, n-butanol and the volume ratio of n-butanol to isopropanol is 3:1.

[0011] The metal salt is selected from cobalt nitrate hexahydrate, zinc nitrate, copper nitrate, nickel nitrate, zirconium chloride, and ferric chloride.

[0012] The metal salt dispersion has a mass concentration of 0.1%-15%.

[0013] In the aqueous solution of the organic ligand, the solvent is deionized water, and the mass concentration of the organic ligand is 0.1%-2%.

[0014] The organic ligand mentioned in step (2) is selected from 2-methylimidazole.

[0015] The surfactant is selected from octadecyldiethylsilane, hexadecyltrimethylammonium chloride, and hexadecyltrimethylammonium bromide; the mass concentration of the surfactant is 0.027%-1.35%.

[0016] The deprotonating agent is sodium bicarbonate or ammonia water, with a mass concentration of 0.04%-1%, and is added to the aqueous phase containing organic ligands.

[0017] The base film includes at least one of organic base film, inorganic base film, and silicon wafer.

[0018] The MOF membrane obtained by this invention is formed by diffusion-reaction-growth extension of MOF precursor at the liquid-liquid interface; the film formation process and thickness of the MOF membrane are controlled by adjusting the amount of metal salt dispersion and organic ligand aqueous solution.

[0019] The MOF membrane obtained by this invention is applied in the field of pervaporation with preferential alcohol permeation for alcohol-water separation.

[0020] To regulate the interfacial MOF film, a dispersion of metal salt is slowly added dropwise to the surface of the organic ligand solution using a pipette. The organic ligand and metal salt diffuse and react at the stable interface constructed by the solvent, and connect to form a film under the action of interfacial tension. Surfactants and deprotonators regulate the film morphology by controlling the interfacial tension, diffusion rate, and reaction rate. Adding a surfactant alters the MOF morphology at the interface due to changes in interfacial tension. Adding a deprotonator accelerates the deprotonation process of the organic ligand, thus increasing the reaction rate and nucleation rate, facilitating the formation of a continuous, dense, and smooth film; the addition of a deprotonator is preferred.

[0021] The base membrane is first immersed in the aqueous solution of the organic ligand obtained in step (2) to form a MOF membrane. Then, the base membrane is slowly lifted to transfer the MOF membrane onto the base membrane; or the lower layer solution is released from below the liquid-liquid interface to transfer the MOF membrane onto the base membrane. The composite membrane is then dried.

[0022] The base film includes at least one of organic base film, inorganic base film, and silicon wafer.

[0023] Composite membranes are used as pervaporation membranes, specifically as preferred pervaporation membranes for alcohol-water separation.

[0024] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0025] The method for generating MOF films at a liquid-liquid interface provided in this invention constructs a stable liquid-liquid interface that enables two-dimensional film growth by controlling the solvent. Surfactants and deprotonators are added to the aqueous phase to further accelerate the reaction rate and control the film morphology, ultimately obtaining an ideal MOF film at the interface. The key to film formation lies in constructing a stable interface. This method controls parameters such as interfacial tension, diffusion rate, and reaction rate by selecting appropriate solvent types, solvent ratios, surfactant content, and deprotonator content, thereby precisely controlling the morphology and size of the MOF film.

[0026] Figure 1 A scanning electron microscope image of the ZIF-67 film provided in Example 1;

[0027] Figure 2 A scanning electron microscope image of the ZIF-67 film provided in Example 2;

[0028] Figure 3 A scanning electron microscope image of the ZIF-67 film provided in Example 2;

[0029] Figure 4 A scanning electron microscope image of the ZIF-67 film provided in Example 3;

[0030] Figure 5 A scanning electron microscope image of the ZIF-67 film provided in Example 4;

[0031] Figure 6 A scanning electron microscope image of the ZIF-67 film provided in Example 5;

[0032] Figure 7 Scanning electron microscope image of cross-section of ZIF-67 membrane provided in Example 6

[0033] Figure 8 A scanning electron microscope image of the ZIF-67 film provided in Example 7;

[0034] Figure 9 A scanning electron microscope image of the ZIF-67 film provided in Example 8;

[0035] Figure 10 A scanning electron microscope image of the ZIF-67 film provided in Example 11;

[0036] Figure 11 XRD patterns of the ZIF-67 membranes provided in Examples 3 and 4;

[0037] Figure 12 The pervaporation performance diagrams are for the ZIF-67 / PTFE membranes provided in Examples 1, 2, 3 and 4. Detailed Implementation

[0038] To make the technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0039] On one hand, embodiments of the present invention provide a method for synthesizing and controlling MOF membranes at a liquid-liquid interface, the method comprising:

[0040] Step S1: Provide a metal salt dispersion prepared with a suitable solvent.

[0041] Step S2: Provide an organic ligand solution. By adding a surfactant to the organic ligand solution, the interfacial tension is changed, thereby regulating the nucleation and growth behavior of MOF particles at the liquid-liquid interface.

[0042] Step S3: By adding a deprotonating agent to the organic ligand solution to regulate the deprotonation process of the organic ligand, the reaction rate is accelerated, thereby achieving precise control of the morphology and size of the MOF membrane.

[0043] The method for synthesizing and controlling MOF membranes at a liquid-liquid interface provided in this invention involves dropwise addition of a dispersion containing a metal salt to the surface of an organic ligand solution. Due to the properties of the solvent itself, a stable liquid-liquid interface is formed at the contact between the two phases, promoting the two-dimensional growth of the membrane. Adding surfactants and deprotonators to the aqueous phase further accelerates the reaction rate and controls the membrane morphology, ultimately yielding an ideal MOF membrane at the interface. The key to membrane formation lies in constructing a stable interface. This method controls parameters such as interfacial tension, diffusion rate, and reaction rate by selecting appropriate solvent types, solvent ratios, surfactant content, and deprotonator content, thereby precisely controlling the morphology and size of the MOF membrane.

[0044] The following provides an exemplary description of the implementation methods and functions of each step involved in the MOF membrane preparation method provided in the embodiments of the present invention.

[0045] In this embodiment of the invention, the metal salt dispersion comprises: a metal salt and a dispersant; the dispersant includes n-octanol, isopropanol, n-butanol, N,N-2-methylacetamide, n-propanol, and n-heptane; the metal salt is cobalt nitrate hexahydrate; the organic ligand is 2-methylimidazole; the surfactant is selected from octadecyl diethylsilane, hexadecyl trimethylammonium chloride, and hexadecyl trimethylammonium bromide; the deprotonating agent is sodium bicarbonate and ammonia; and the solvent for the organic ligand is deionized water.

[0046] The metal salt dispersion prepared with a suitable solvent can be obtained by the following method:

[0047] The preferred mass concentration of the metal salt is 1.5%. In some examples, ultrasonic disruption is used to uniformly disperse the metal salt in the dispersant. For example, an ultrasonic disruptor is used to perform the disruption and stirring, and the stirring time can be 1 min to 20 min. This is because the metal salt is poorly soluble in solvents such as n-heptane, making it difficult to disperse uniformly. Ultrasonic disruption can ensure uniform dispersion of the metal salt in the solvent, thus solving this technical problem. In other examples, since the metal salt is readily soluble in solvents such as n-butanol and n-octanol, direct stirring can achieve good dispersion.

[0048] For the organic ligand solution, the organic ligand includes 2-methylimidazole, and the solvent is deionized water.

[0049] For example, the mass concentration of the organic ligand solution is 0.65% of the organic ligand, the mass concentration of the surfactant is 0.027%-0.135% of the surfactant, and the mass concentration of the deprotonating agent is 0.04%-0.2% of the deprotonating agent.

[0050] In some examples, a dispersion containing a metal salt is slowly added dropwise to the surface of the organic ligand solution using a pipette.

[0051] For example, the settling time is 40 min. Then, lift the base film so that the MOF film generated at the liquid-liquid interface slowly falls onto the base film surface, and dry it in an oven at 60-80 ℃ for at least 1 hour.

[0052] In some examples, appropriate amounts of surfactants or deprotonators are added to the aqueous phase to control the size and morphology of the MOF membrane.

[0053] In summary, the liquid-liquid interface synthesis and regulation of MOF membranes provided in this embodiment of the invention is simple, easier to operate, has mild conditions and low energy consumption, and the direct film formation at the interface facilitates its transfer to various substrates, thus having great application potential.

[0054] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0055] Example 1 (Comparative Example)

[0056] This embodiment 1 provides a ZIF-67 film generated at the liquid-solid interface at room temperature, which is prepared by the following method:

[0057] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-butanol and stirred for 5 min to obtain a homogeneous dispersion. A PTFE-based membrane was immersed in the dispersion for 8 h, then removed. 150 ml of a 1.5% (w / w) 2-methylimidazole aqueous solution was poured into a 100 mm × 50 mm crystallizing dish, and the PTFE-based membrane was then immersed in the solution and allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-solid interface. The membrane was then dried in an oven at 60 ℃ for 1-2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 1 .

[0058] The composite membrane obtained in this embodiment was tested for separation performance of the ethanol / water system. The effective area of ​​the composite membrane was 4.9 cm². 2 The feed concentration was 5 wt.%, the feed temperature was 50 °C, and pressure was provided by a vacuum pump, with the downstream permeation pressure reaching -0.1 MPa. After membrane separation, the permeation flux was 22 kg·m³. -2 ·h -1 The separation factor is 4.1.

[0059] Example 2

[0060] This embodiment 2 provides a ZIF-67 membrane prepared by constructing a liquid-liquid interface using a mixed solvent and generating the membrane at the interface, which is obtained by the following method:

[0061] 0.291 g of cobalt nitrate hexahydrate was dispersed in a mixture of 19.709 g of n-butanol and isopropanol (mass ratio of n-butanol:isopropanol = 3:1), and stirred for 5-10 min to obtain a uniform dispersion.

[0062] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. Then, the base membrane (pre-placed below the surface of the 2-methylimidazole solution) was slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the base membrane. The membrane was then dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 2 , Figure 3 .

[0063] The composite membrane obtained in this embodiment was tested for separation performance of the ethanol / water system. The effective area of ​​the composite membrane was 4.9 cm². 2 The feed concentration was 5 wt.%, the feed temperature was 50 °C, and pressure was provided by a vacuum pump, with the downstream permeation pressure reaching -0.1 MPa. After membrane separation, the permeation flux was 15 kg·m³. -2 ·h -1 The separation factor is 5.3.

[0064] Example 3

[0065] Example 3 provides a ZIF-67 film generated at the interface using a surfactant, which is prepared by the following method:

[0066] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-butanol and stirred for 5 min to obtain a uniform dispersion.

[0067] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 0.081% (w / w) octadecyldiethylsilane was added to the dish, and the mixture was stirred for 5 min to ensure uniform dispersion. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The base membrane was then slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the base membrane. The membrane was dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 4 .

[0068] The composite membrane obtained in this embodiment was tested for separation performance of the ethanol / water system. The effective area of ​​the composite membrane was 4.9 cm². 2 The feed concentration was 5 wt.%, the feed temperature was 50 °C, and pressure was provided by a vacuum pump, with the downstream permeation pressure reaching -0.1 MPa. After membrane separation, the permeation flux was 10.5 kg·m³. -2 ·h -1 The separation factor is 6.2.

[0069] ZIF-67 films synthesized using a surfactant-controlled liquid-liquid interface growth method were subjected to SEM scanning. The obtained SEM images are shown in [reference 1]. Figure 4 Appropriate amounts of surfactants can significantly reduce the surface tension or interfacial tension between two liquids, between liquid and gas, or between liquid and solid. These surfactants can lower the interfacial tension between oil and water phases, thereby regulating the growth rate of ZIF-67 and making the ZIF-67 film more continuous. However, excessive addition can lead to excessively low interfacial tension between the two phases, resulting in uneven particle size distribution and poor crystal structure.

[0070] Example 4

[0071] Example 4 provides a ZIF-67 film generated at the interface using a deprotonating agent, which is prepared by the following method:

[0072] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-butanol and stirred for 5 min to obtain a uniform dispersion.

[0073] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 0.045% (w / w) ammonia solution was added to the dish, and the mixture was stirred for 5 min to ensure uniform dispersion. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The substrate membrane was then slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the substrate membrane. The membrane was dried in an oven at 60 °C for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 5 The separation performance of the composite membrane obtained in this embodiment for the ethanol / water system was tested, and the effective area of ​​the composite membrane was 4.9 cm². 2 The feed concentration was 5 wt.%, the feed temperature was 50 °C, and the permeate pressure was provided by a vacuum pump, with the downstream permeate pressure reaching -0.1 MPa. After membrane separation, the permeate flux was 10.2 kg·m³. -2 ·h -1 The separation factor is 7.3.

[0074] Deprotonating agents can increase the pH of the reaction system, promoting the deprotonation of ligands and generating more organic anions. These anions can coordinate with metal cations, thereby accelerating the crystal nucleation process. Due to the rapid decrease in supersaturation in the reaction system, smaller structures may be formed, potentially causing morphological changes. The generated ZIF-67 particles have a diameter of approximately 80-100 nm.

[0075] Compared to ZIF-67 membranes synthesized at the liquid-solid interface, membranes synthesized at the liquid-liquid interface exhibit better separation factors and excellent permeation flux. Furthermore, the addition of surfactants and deprotonators significantly enhances their separation performance. XRD analyses were performed on the ZIF-67 membranes synthesized at the liquid-liquid interface with added surfactants and deprotonators. The obtained XRD results are shown in the attached XRD diagrams. Figure 11 The XRD results show the successful synthesis of ZIF-67 and the improvement of its crystallinity by surfactants and deprotonators.

[0076] Example 5

[0077] Example 5 provides a ZIF-67 membrane prepared by constructing a liquid-liquid interface using n-octanol and generating the membrane at the interface, which is obtained by the following method:

[0078] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-octanol and stirred for 5 min to obtain a uniform dispersion.

[0079] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge to the surface of the 2-methylimidazole solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The substrate membrane was then slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the substrate membrane. The membrane was then dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 6 .

[0080] Example 6

[0081] Example 6 provides a ZIF-67 membrane prepared by constructing a liquid-liquid interface using n-heptane and generating the membrane at the interface, which is obtained by the following method:

[0082] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-heptane and ultrasonically broken up for 10-15 min to obtain a uniform dispersion.

[0083] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge to the surface of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The substrate membrane was then slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the substrate membrane. The membrane was then dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 7 .

[0084] Example 7

[0085] Example 7 provides a ZIF-67 membrane prepared by constructing a liquid-liquid interface using a mixed solvent and generating the membrane at the interface, which is obtained by the following method:

[0086] Disperse 0.291 g of cobalt nitrate hexahydrate in a mixture of 19.709 g of n-butanol and isopropanol (mass ratio of n-butanol:isopropanol = 1:1) and stir for 5-10 min to obtain a uniform dispersion.

[0087] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge to the surface of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The substrate membrane was then slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the substrate membrane. The membrane was then dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 8 .

[0088] Example 8

[0089] Example 8 provides a ZIF-67 membrane prepared by constructing a liquid-liquid interface using a mixed solvent and generating the membrane at the interface, which is obtained by the following method:

[0090] Disperse 0.291 g of cobalt nitrate hexahydrate in a mixture of 19.709 g of n-butanol and isopropanol (mass ratio of n-butanol:isopropanol = 1:3) and stir for 5-10 min to obtain a uniform dispersion.

[0091] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge to the surface of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The substrate membrane was then slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the substrate membrane. The membrane was then dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 9 .

[0092] Example 9

[0093] Example 9 provides a ZIF-67 membrane prepared by constructing a liquid-liquid interface using a mixed solvent and generating the membrane at the interface, which is obtained by the following method:

[0094] Disperse 0.291 g of cobalt nitrate hexahydrate in a mixture of 19.709 g of n-butanol and isopropanol (mass ratio of n-butanol:isopropanol = 1:2) and stir for 5-10 min to obtain a uniform dispersion.

[0095] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge to the surface of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The base membrane was then slowly lifted to allow the ZIF-67 membrane at the interface to fall smoothly onto the base membrane. The membrane was then dried in an oven at 60 °C for 1–2 h to obtain the ZIF-67 composite membrane.

[0096] The scanning electron microscope (SEM) images provided in Examples 1, 2, and 5-9 show that the ZIF-67 film was successfully prepared at the interface. The change in the morphology of the ZIF-67 formed at the interface is related to the solubility parameter of the solvent. As the type of solvent changes, the solubility parameter of the solvent also changes continuously, as shown in Tables 1 and 2, thus affecting the interfacial tension between the water and oil phases. Due to the different interfacial tensions, the diffusion rate of the solute also differs, resulting in changes in the morphology of the ZIF-67 formed at the interface.

[0097] Based on the SEM images of the ZIF-67 membrane in the example above, it is evident that a suitable solvent needs to be selected to construct a stable interface with water, allowing the ZIF-67 membrane to tend towards two-dimensional growth. This solvent must have a solubility parameter difference with water within a certain range and ensure good dispersion of cobalt nitrate within it. This allows the metal precursor in the solvent to fully contact and react with the organic ligand, forming a film at the interface.

[0098] Compared with the ZIF-67 membrane prepared by the traditional liquid-solid interface method (comparative example), Examples 1, 2, 5-9 precisely controlled the two-dimensional growth process of the ZIF-67 membrane at the interface.

[0099] The morphology of the ZIF-67 films provided in Examples 1, 2, and 5-9 changed with variations in solvent solubility parameters. The ZIF-67 film synthesized using n-octanol as a solvent exhibited significantly higher interfacial tension than that synthesized using n-butanol due to the increased difference in solubility parameters between it and water (|δSolvent - δWater|). This resulted in a slower reaction rate, leading to an increase in particle size of approximately 500 nm - 1 µm, decreased crystallinity, and poorer crystal structure. Conversely, the ZIF-67 film synthesized using n-heptane as a solvent had a smaller particle size (approximately 400 nm - 1 µm) and uneven particle size distribution due to poor dispersion of the metal precursor in the solvent. Compared to single solvents, mixed solvents allow for more precise control of solubility parameters. By changing the volume ratio of the mixed solvents, the desired solubility parameters were obtained, thereby constructing a stable interface with interfacial tension within a certain range, promoting the two-dimensional growth of ZIF-67. The thickness of the synthesized ZIF-67 film was approximately 2.4 µm.

[0100] Table 1. Solubility parameters of the solvents used in the examples.

[0101]

[0102] Table 2 Solubility parameters of the mixed solvent of n-butanol and isopropanol

[0103]

[0104] (N in the table represents n-butanol, I represents isopropanol, and δ represents...) d For the dispersive component, δ p For polar components, δ h Hydrogen bond component, .

[0105] Example 10

[0106] Example 10 provides a ZIF-67 film generated at the interface using a surfactant, which is prepared by the following method:

[0107] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-butanol and stirred for 5 min to obtain a uniform dispersion.

[0108] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 0.135% (w / w) octadecyldiethylsilane was added to the dish, and the mixture was stirred for 5 min to disperse it evenly. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge to the surface of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The base membrane was then slowly lifted to allow the ZIF-67 membrane at the interface to fall smoothly onto the base membrane. The membrane was dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane.

[0109] Example 11

[0110] Example 11 provides a ZIF-67 film generated at the interface using a surfactant, which is prepared by the following method:

[0111] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-butanol and stirred for 5 min to obtain a uniform dispersion.

[0112] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 0.081% (w / w) hexadecyltrimethylammonium bromide was added to the dish, and the mixture was stirred for 5 min to ensure uniform dispersion. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The base membrane was then slowly lifted, allowing the ZIF-67 membrane at the interface to fall smoothly onto the base membrane. The membrane was dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane. The obtained SEM images are shown below. Figure 10 .

[0113] Example 12

[0114] This embodiment 12 provides a ZIF-67 film generated at the interface by using a deprotonating agent, which is prepared by the following method:

[0115] 0.291 g of cobalt nitrate hexahydrate was dispersed in 19.709 g of n-butanol and stirred for 5 min to obtain a uniform dispersion.

[0116] 150 ml of a 1.5% (w / w) 2-methylimidazole solution was poured into a 100 mm × 50 mm crystallizing dish. 0.12% (w / w) sodium bicarbonate was added to the dish, and the mixture was stirred for 5 min to disperse it evenly. 2000 μL of a dispersion containing cobalt nitrate hexahydrate was slowly added dropwise along the edge to the surface of the 2-methylimidazole aqueous solution using a pipette. The mixture was allowed to stand for 40 min to allow the ZIF-67 membrane to form at the liquid-liquid interface. The base membrane was then slowly lifted to allow the ZIF-67 membrane at the interface to fall smoothly onto the base membrane. The membrane was dried in an oven at 60 ℃ for 1–2 h to obtain the ZIF-67 composite membrane.

[0117] The above description is merely for the purpose of enabling those skilled in the art to understand the technical solutions of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for rapidly generating continuous MOF films at a liquid-liquid interface, characterized in that, Including the following technical solutions: (1) Provide a metal salt dispersion prepared with a suitable solvent; (2) Provide an aqueous solution of organic ligands, and change the interfacial tension by adding surfactants to the aqueous solution of organic ligands to regulate the nucleation and growth behavior of MOF particles at the liquid-liquid interface; or regulate the deprotonation process of organic ligands by adding deprotonating agents to the aqueous solution of organic ligands to accelerate the reaction rate and achieve precise control of MOF film morphology and size. (3) The metal salt dispersion from step (1) is steadily added to the surface of the organic ligand aqueous solution and left to stand for a period of time. During this process, the MOF generates an overall membrane structure at the liquid-liquid interface.

2. The method according to claim 1, characterized in that, The metal salt dispersion comprises: a metal salt and a dispersant; The dispersant is selected from at least one of n-octanol, isopropanol, n-butanol, N,N-2-methylacetamide, and n-propanol; and isopropanol and N,N-2-methylacetamide are not used alone; The metal salt is selected from at least one of cobalt nitrate hexahydrate, zinc nitrate, copper nitrate, nickel nitrate, zirconium chloride, and ferric chloride; The metal salt dispersion has a mass concentration of 0.1%-15%.

3. The method according to claim 1, characterized in that, The organic ligand is selected from 2-methylimidazole; the mass concentration of the organic ligand is 0.1%-2%.

4. The method according to claim 1, characterized in that, The surfactant is selected from octadecyldiethylsilane, hexadecyltrimethylammonium chloride, and hexadecyltrimethylammonium bromide; the mass concentration of the surfactant is 0.027%-1.35%.

5. The method according to claim 1, characterized in that, In the organic ligand solution, the deprotonating agent is sodium bicarbonate or ammonia; the mass concentration of the deprotonating agent is 0.04%-1%.

6. The method according to claim 1, characterized in that, Pour 150 ml of 1.5% 2-methylimidazole solution into a 100 mm × 50 mm crystallizing dish. Slowly add 2000 μL of a dispersion containing cobalt nitrate hexahydrate along the edge of the 2-methylimidazole solution using a pipette. Let stand for 40 min.

7. The method according to claim 1, characterized in that, The base membrane is first immersed in the aqueous solution of the organic ligand obtained in step (2) to form a MOF membrane. Then, the base membrane is slowly lifted to transfer the MOF membrane onto the base membrane; or the lower layer solution is released from below the liquid-liquid interface to transfer the MOF membrane onto the base membrane. The composite membrane is then dried.

8. The method according to claim 7, characterized in that, The base film includes at least one of organic base film, inorganic base film, and silicon wafer.

9. The MOF membrane prepared according to any one of claims 1-8.

10. The application of the MOF membrane prepared according to any one of claims 1-8 as a pervaporation-preferred alcohol permeation membrane.

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