ZIF-8 self-supporting membrane based on ultra-small nano particle stacking and preparation method and application thereof
By simplifying the preparation method of ZIF-8 self-supporting membranes and using ultra-small nanoparticles to directly stack the membranes, the problems of complex preparation and high cost in existing technologies are solved, resulting in dense and defect-free ZIF-8 self-supporting membranes, which improves separation performance and repeatability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-25
- Publication Date
- 2026-03-27
AI Technical Summary
Existing ZIF-8 membrane preparation techniques are complex and costly, and it is difficult to prepare dense, defect-free self-supporting membranes, which affects separation performance.
Using ultra-small ZIF-8 nanoparticles of 10-30 nm, a self-supporting ZIF-8 membrane was prepared through a simple process of particle preparation, dispersion and concentration, and room temperature coating and drying. This process avoids the use of a support and exogenous components, thus maintaining the membrane's density and microporous structure.
The preparation process was simplified, the cost was reduced, the preparation efficiency and repeatability were improved, the membrane layer was made dense and free of permeation defects, the microporous structure and high specific surface area of ZIF-8 were preserved, and the separation performance was enhanced.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of MOF membrane material technology, specifically a ZIF-8 self-supporting membrane based on ultra-small nanoparticle stacking, its preparation method and application. Background Technology
[0002] Metal-organic frameworks (MOFs) exhibit broad application prospects in gas separation, liquid purification, and catalysis due to their controllable microporous structures, high specific surface areas, and excellent chemical stability. Among them, ZIF-8, as a typical MOF material, forms a dodecahedral crystal structure by the coordination of zinc ions and dimethylimidazole. Its unique pore size and good thermal / chemical stability make it an ideal building block for preparing high-performance separation membranes.
[0003] The separation performance of ZIF-8 membranes hinges on the density, continuity, and integrity of the microporous structure—only ZIF-8 membranes with minimal intercrystalline defects and well-preserved pores can achieve efficient molecular sieving and mass transfer regulation. However, existing ZIF-8 membrane preparation technologies still face numerous bottlenecks, making it difficult to balance process simplicity with membrane performance stability.
[0004] Currently, the mainstream preparation method for ZIF-8 membranes is the secondary growth method. This method requires first pre-forming a seed layer on the surface of a support such as ceramics or polymers, and then performing secondary crystallization under harsh reaction conditions such as solvothermal and microwave-assisted processes to form a continuous membrane. However, this process is cumbersome, has a long reaction cycle (usually several hours to tens of hours), and is sensitive to parameters such as reaction temperature, pressure, and ligand concentration, resulting in poor membrane reproducibility and high costs for large-scale production. At the same time, interfacial cracks are easily formed between the support and the ZIF-8 membrane, and uneven growth of the seed layer can also easily lead to membrane defects, affecting separation efficiency.
[0005] To simplify the process, some studies have attempted to prepare hybrid matrix membranes, which disperse ZIF-8 particles in a polymer matrix to form a composite membrane. However, these membranes have inherent defects: the polymer phase easily blocks the microporous channels of ZIF-8, resulting in a significant decrease in the specific surface area of the membrane and the loss of the structural advantages of MOF materials; moreover, the interfacial compatibility between ZIF-8 particles and the polymer matrix is poor, easily generating voids and making it difficult to form a truly dense separation layer, thus failing to meet the requirements of high-precision separation.
[0006] Furthermore, existing attempts to prepare self-supporting ZIF-8 membranes mostly employ ZIF-8 particles ranging from hundreds of nanometers to micrometers as building blocks. Due to the large particle size and limited specific surface area of these particles, their loose packing makes it difficult to achieve tight fusion through simple processes. As a result, the final membrane layer is prone to defects such as through-holes and cracks. Even if the packing effect is improved by introducing binders or crosslinking agents, the original pore structure of ZIF-8 will be destroyed, leading to a significant decrease in the membrane's adsorption and separation performance.
[0007] Therefore, developing a technology that is simple, low-cost, highly reproducible, and capable of stably preparing dense, defect-free, and well-preserved ZIF-8 self-supporting membranes has become an urgent problem to be solved in the field of MOF membrane materials. Summary of the Invention
[0008] The purpose of this invention is to provide a ZIF-8 self-supporting membrane based on ultra-small nanoparticle stacking, its preparation method, and its application, in order to solve the problems of complex ZIF-8 membrane preparation processes, dependence on supports or secondary growth processes, easy generation of interfacial cracks and penetration defects in the membrane layer, and insufficient purity leading to limited separation performance. This invention achieves the preparation of ZIF-8 self-supporting membranes without external supports and auxiliary binders, with a mild and simple process and high preparation efficiency, while obtaining pure ZIF-8 self-supporting membranes with smooth surfaces, uniform thickness, dense particle stacking, and intact microporous structures.
[0009] The objective of this invention is achieved through the following technical solution: Technical Solution 1: A method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking includes the following steps: S1. Preparation of ultra-small ZIF-8 nanoparticles with a particle size of 10-30 nm; S2. The ultra-small ZIF-8 nanoparticles are dispersed in methanol and concentrated by centrifugation to obtain a ZIF-8 nanoparticle slurry with a concentration of 50-90 mg / mL; S3. The ZIF-8 nanoparticle slurry is coated onto the substrate surface, allowed to air dry at room temperature, and then peeled off to obtain a ZIF-8 self-supporting film.
[0010] As some possible implementations of this application, in step S1, the preparation method of the ultra-small ZIF-8 nanoparticles is as follows: zinc salt and dimethylimidazole are dissolved in polar solvents respectively, and then the two solutions are stirred and reacted at room temperature for 0.5-4 hours. After the reaction is completed, ultra-small ZIF-8 nanoparticles are obtained by centrifugation, washing and drying.
[0011] As some possible embodiments of this application, the zinc salt is selected from any one or two of zinc nitrate and zinc chloride, and the polar solvent is selected from methanol, ethanol, water or a mixture thereof.
[0012] As one possible implementation of this application, the molar ratio of the zinc salt to dimethylimidazole is 1:(4-10).
[0013] As some possible implementations of this application, the drying is performed at room temperature for 6-24 hours.
[0014] As some possible implementations of this application, in step S2, the centrifugal concentration speed is 8000-18000 r / min, and the centrifugation time is 5-15 min.
[0015] As one possible implementation of this application, in step S2, the ultra-small ZIF-8 nanoparticles are dispersed by ultrasonic dispersion, with an ultrasonic power of 100-300W and an ultrasonic time of 10-30min.
[0016] As one possible implementation of this application, in step S3, the coating thickness is 50-60 μm.
[0017] As some possible implementations of this application, in step S3, the substrate is a glass plate, a quartz plate, or a silicon wafer.
[0018] Technical Solution Two: A ZIF-8 self-supporting membrane based on ultra-small nanoparticle stacking is prepared by the preparation method of technical solution one.
[0019] Technical Solution 3: Application of ZIF-8 self-supporting membrane based on ultra-small nanoparticle stacking in the field of gas separation.
[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses ultra-small ZIF-8 nanoparticles (10-30 nm) as building blocks to prepare a self-supporting ZIF-8 film through a simple process of "particle preparation - dispersion and concentration - coating and drying." This eliminates the need for a support, secondary growth process, and auxiliary binder phase, thus avoiding the complex seed preparation and solvothermal reactions required in traditional processes. The entire process requires no special precision equipment, and the simple operation steps help reduce the operational difficulty of the preparation process, while also reducing equipment investment and process control costs, and improving preparation efficiency.
[0021] 2. Because this invention eliminates the need for external components such as polymer matrices and binders, and does not rely on a support to carry the membrane layer, the prepared ZIF-8 self-supporting membrane is a pure ZIF-8 polycrystalline structure. This effectively avoids the problems of polymer phase clogging ZIF-8 microporous channels or interfacial cracks forming between the support and the membrane layer in traditional mixed matrix membranes. Combining the high specific surface area and good packing properties of ultra-small nanoparticles, the membrane layer can form a dense structure without penetrating defects, while retaining the excellent microporous structure and high specific surface area characteristics of ZIF-8 material, which helps to ensure the adsorption and separation performance of the membrane.
[0022] 3. In the preparation process of this invention, neither the synthesis of nanoparticles nor the formation of the film layer requires harsh conditions such as high temperature and high pressure. In particular, the film layer is formed by natural air drying at room temperature, which makes the process parameters easy to control. This reduces the product performance differences caused by fluctuations in reaction conditions, helps to improve batch-to-batch repeatability, and provides convenience for subsequent large-scale preparation.
[0023] 4. The ZIF-8 self-supporting membrane prepared by this invention, due to the absence of a support structure, can better adapt to different application environments, especially in gas separation applications requiring independent membrane layers or high-temperature, flexible scenarios, where it has good application potential. Simultaneously, the pure ZIF-8 membrane structure reduces interference from exogenous components in the separation and mass transfer process, contributing to improved separation efficiency and long-term stability. Attached Figure Description
[0024] Figure 1 XRD patterns of ZIF-8 nanoparticles and ZIF-8 films prepared in Example 1; Figure 2 The FT-IR image of the ZIF-8 film prepared in Example 1; Figure 3 The images show TEM and SEM images of the ZIF-8 ultrasmall nanoparticles prepared in Example 1; where a is a SEM image of the ZIF-8 nanoparticles and b is a SEM image of the ZIF-8 film. Figure 4 The images shown are SEM images of the ZIF-8 self-supporting film prepared in Example 1, where a is a top view SEM image of the ZIF-8 self-supporting film; b is a magnified top view SEM image of the ZIF-8 self-supporting film (500 nm scale bar); c is a cross-sectional SEM image of the ZIF-8 self-supporting film; and d is a magnified cross-sectional SEM image of the ZIF-8 self-supporting film. Figure 5 The N2 adsorption-desorption curve of the ZIF-8 membrane prepared in Example 1 was tested at 77K; Figure 6The graph shows the gas permeability test results of the ZIF-8 membrane prepared in Example 1; where a is the single gas permeability of the ZIF-8 membrane in Example 1 measured at 25°C and 0.15 MPa; b is the separation performance of the ZIF-8 membrane for C3H6 / C3H8 gases. Figure 7 XRD patterns of ZIF-8 nanoparticles and ZIF-8 films prepared in Example 2; Figure 8 SEM images of the ZIF-8 nanoparticles and ZIF-8 film prepared in Example 2 are shown. In the image, a is a SEM image of the ZIF-8 nanoparticles; b is a SEM image of the ZIF-8 film. Figure 9 XRD patterns of ZIF-8 nanoparticles and ZIF-8 films prepared in Example 3; Figure 10 The images show SEM images of the ZIF-8 nanoparticles and ZIF-8 film prepared in Example 3. In the images, a is the SEM image of the ZIF-8 nanoparticles, and b is the SEM image of the ZIF-8 film. Detailed Implementation
[0025] Example 1: Preparation of a ZIF-8 self-supporting membrane based on stacking of ultra-small nanoparticles.
[0026] S1: Preparation of ultrasmall ZIF-8 nanoparticles: 600 mL of methanol and 2.03 g (6.8 mmol) of zinc nitrate hexahydrate were added to a 1000 mL glass beaker and dissolved by sonication to obtain a colorless and clear solution A. 200 mL of methanol and 2.63 g (32 mmol) of dimethylimidazole were added to a 1000 mL glass beaker and dissolved by sonication to obtain a colorless and clear solution B. Solution B was then transferred to a stirring table and stirred at 400 rpm. Solution A was then slowly added to solution B, and the entire 600 mL of solution A was poured out over approximately 5 minutes. The mixture was stirred at 25°C for 4 hours, during which time the solution gradually changed from colorless to a white suspension. After the reaction was complete, the mixture was centrifuged at 18000 rpm for 10 minutes. Unreacted zinc ions and the dimethylimidazole ligand were then washed with methanol to obtain ZIF-8 ultrasmall nanoparticles. Ultrasonic dissolution ensures that the reactants are fully dispersed and avoids localized concentration unevenness from affecting the particle size uniformity of nanoparticles, which is the basis for preparing uniformly sized ultra-small nanoparticles. S2: Preparation of ZIF-8 nanoparticle slurry: Add 1 mL of methanol to ZIF-8 ultrafine nanoparticles and disperse to form a uniform ZIF-8 methanol slurry with a concentration of 70 mg / mL. Controlling the slurry concentration to 70 mg / mL ensures the compactness of particle stacking during subsequent coating and avoids poor slurry flow and uneven coating due to excessive concentration, or loose film layer and defects due to excessively low concentration. S3: Preparation of ZIF-8 self-supporting membrane: The above ZIF-8 methanol slurry was drop-coated onto a glass plate and air-dried at room temperature to obtain the ZIF-8 self-supporting membrane.
[0027] The ZIF-8 nanoparticles and ZIF-8 self-supporting films obtained in Example 1 were characterized and analyzed. The results are as follows: (1) XRD characterization: Figure 1 As shown, the XRD patterns of the prepared ZIF-8 particles and ZIF-8 films are completely consistent with the simulated ZIF-8 XRD patterns, indicating that the prepared ZIF-8 particles and self-supporting films have pure ZIF-8 crystal forms and no impurity crystal phases, proving that ZIF-8 particles and ZIF-8 self-supporting films have been successfully prepared. (2) FT-IR characterization: such as Figure 2 As shown, in the FT-IR spectrum of the ZIF-8 film, 424 cm⁻¹ -1 and 692 cm -1 A distinct characteristic absorption peak of Zn-N coordination bond appears at 3123 cm⁻¹. -1 925 cm -1 1581 cm -1 1460 cm -1 1419 cm -1 The presence of characteristic vibrational peaks of the imidazole ring further confirms the successful coordination of the imidazole ring with zinc ions in the ZIF-8 structure, and the chemical structure of the membrane conforms to the characteristics of ZIF-8. (3) TEM and SEM characterization (e.g.) Figure 3 ):like Figure 3 As shown in a, the prepared ZIF-8 ultrasmall nanoparticles exhibit the traditional ZIF-8 dodecahedral morphology and are uniform in size, with a particle size of approximately 20 nm. This ultrasmall particle size characteristic ensures the close packing of particles during subsequent film formation, laying the foundation for the preparation of defect-free self-supporting films. Figure 3 As shown in b, 20 nm ZIF-8 particles readily aggregate or cross-link, which is beneficial for subsequent film stacking and ensures film compactness. The SEM characterization image of the ZIF-8 self-supporting film is shown below. Figure 4 As shown, Figure 4 In the image 'a', the top-view SEM image of the ZIF-8 self-supporting membrane shows that the membrane surface is generally flat and uniform, without obvious large pores or cracks, and has good substrate coverage, forming a continuous membrane layer. Figure 4 In the image, b is a magnified top-view SEM image of the ZIF-8 self-supporting membrane (500nm scale), showing that the membrane surface is composed of tightly packed nano-sized ZIF-8 particles with tight inter-particle bonding and no obvious large pores, demonstrating excellent compactness. Figure 4In c, it is the cross-sectional SEM image of the ZIF-8 self-supporting membrane. It can be clearly observed that the membrane layer of this membrane has a uniform thickness, approximately 50 μm, without obvious delamination or defects; Figure 4 In d, it is the enlarged cross-sectional SEM image of the ZIF-8 self-supporting membrane, further verifying that the membrane layer of this membrane is a dense structure formed by stacking of nanoparticles, without through-holes. The above SEM characterization results jointly indicate that the prepared ZIF-8 self-supporting membrane has excellent characteristics such as a flat surface, uniform thickness, dense particle packing, and no obvious defects, which can meet the core requirements for the membrane layer structure in the separation field. (4)N2 adsorption and desorption characterization: As Figure 5 shown, the N2 adsorption and desorption curve of the ZIF-8 membrane at 77K shows that in the low-pressure section where the relative pressure P / P0 is close to 0, the adsorption volume increases rapidly, and then the adsorption amount basically remains stable with the increase of pressure, conforming to the adsorption and desorption characteristics of microporous materials (pore diameter < 2 nm), indicating that the prepared ZIF-8 self-supporting membrane completely retains the microporous structure of ZIF-8 itself; After calculation, the specific surface area of this ZIF-8 membrane is 864.9 m² / g, indicating that the crystal form and pore structure of ZIF-8 in the membrane are not damaged, and the pore retention is good, providing a structural guarantee for the adsorption and separation performance of the membrane.
[0028] (5)Perform gas permeability tests on the ZIF-8 membrane obtained in Example 1 (as Figure 6 ).
[0029] The test method is as follows: Gas separation performance: Place the prepared MOF membrane into a customized membrane cell and seal both sides of the membrane with silicone gaskets. The volume flow rate of the feed gas is 30 ml min-1, the outlet gas is introduced into the air, and the permeation side of the membrane is purged with 30 ml min-1 of Ar gas to quickly remove the gas permeating through the membrane, so as to ensure that the transmembrane partial pressure difference of the gas to be separated is one atmosphere. The outlet of the purge gas is connected to a gas chromatograph to test the concentration of the separated component in the permeation side.
[0030] From Figure 6 a, it can be seen that the gas permeability decreases significantly with the increase of the molecular kinetic diameter (He < CO2 < N2 < C3H6 < C3H8), conforming to the microporous sieving effect (the micropore diameter of ZIF-8 is about 0.34 nm, and small molecules are more likely to pass through). Due to the flexible rotation of the imidazole ligand in ZIF-8, the pore window will undergo dynamic expansion during practical application, and the effective pore diameter can reach 0.40 - 0.42 nm (4.0 - 4.2 Å) - this size is exactly between the kinetic diameters of propylene (4.0 Å) and propane (4.3 Å), so the sieving separation of the two can be achieved. From the test results, the ZIF-8 membrane prepared in Example 1 is dense and defect-free, showing certain gas separation performance. From Figure 6 Looking at b, the propylene permeation rate of the two-component system (16.5 barrer) is slightly lower than the value in the single-component gas test (22.5 barrer), while the propylene / propane selectivity of the two-component system (68.0) is slightly higher than that of the single-component system (34.0), possibly due to competitive adsorption; in other words, during mixed gas permeation, because propylene molecules are small and have strong adsorption in ZIF-8, propylene molecules preferentially permeate into the membrane, while the permeation of propylene will hinder the permeation of propane.
[0031] Example 2: Preparation of a ZIF-8 self-supporting membrane based on ultra-small nanoparticle stacking.
[0032] S1: Preparation of ultrasmall ZIF-8 nanoparticles: 100 mL of methanol and 1.46 g (4.8 mmol) of zinc nitrate hexahydrate were added to a 500 mL glass beaker and dissolved by sonication to obtain a colorless and clear solution A. 100 mL of methanol and 1.62 g (19.7 mmol) of dimethylimidazole were added to a 500 mL glass beaker and dissolved by sonication to obtain a colorless and clear solution B. Solution B was then transferred to a stirring table and stirred at 400 rpm. Solution A was then slowly added to solution B, and 100 mL of solution A was poured out over approximately 3 minutes. The mixture was stirred at 25°C for 30 minutes, and the solution gradually changed from colorless to a white suspension. The solution was then allowed to stand for 24 hours. After the reaction was complete, the mixture was centrifuged at 18000 rpm for 10 minutes, and then washed with methanol to obtain unreacted zinc ions and the dimethylimidazole ligand, yielding ZIF-8 ultrasmall nanoparticles. Ultrasonic dissolution ensures that the reactants are fully dispersed and avoids localized concentration unevenness from affecting the particle size uniformity of nanoparticles, which is the basis for preparing uniformly sized ultra-small nanoparticles. S2: Preparation of ZIF-8 nanoparticle slurry: Add 1 mL of methanol to ZIF-8 ultra-small nanoparticles and disperse to form a uniform ZIF-8 methanol slurry with a slurry concentration of 70 mg / mL.
[0033] S3: Preparation of ZIF-8 self-supporting membrane: The above ZIF-8 methanol slurry was drop-coated onto a glass plate and air-dried at room temperature to obtain the ZIF-8 self-supporting membrane.
[0034] The ZIF-8 nanoparticles and ZIF-8 self-supporting films obtained in Example 2 were characterized and analyzed, and the results are as follows: (1) XRD characterization: such as Figure 7 As shown, the prepared ZIF-8 particles are completely consistent with the simulated ZIF-8 XRD spectrum, indicating that the prepared ZIF-8 particles have a pure ZIF-8 crystal form and no impurity crystal phases exist, proving that the ZIF-8 particles have been successfully prepared.
[0035] (2) SEM characterization (e.g.) Figure 8 ):like Figure 8 As shown in a, the prepared ZIF-8 ultrasmall nanoparticles exhibit the traditional ZIF-8 dodecahedral morphology and are uniform in size, with a particle size of approximately 80 nm; from Figure 8 As can be observed in b, although there is adhesion between the particles, the film composed of ZIF-8 nanoparticles with a diameter of 80 nm is not completely dense.
[0036] Example 3: Preparation of a ZIF-8 self-supporting membrane based on ultra-small nanoparticle stacking.
[0037] S1: Preparation of ultrasmall ZIF-8 nanoparticles: 600 mL of methanol and 2.03 g (6.8 mmol) of zinc nitrate hexahydrate were added to a 1000 mL glass beaker and dissolved by sonication to obtain a colorless and clear solution A. 200 mL of methanol and 2.63 g (32 mmol) of dimethylimidazole were added to a 1000 mL glass beaker and dissolved by sonication to obtain a colorless and clear solution B. Solution B was then transferred to a stirring table and stirred at 400 rpm. Solution B was then slowly added to solution A, and 600 mL of solution A was poured off after approximately 5 minutes. The mixture was stirred at 25°C for 4 hours, during which time the solution gradually changed from colorless to a white suspension. After the reaction was complete, the mixture was centrifuged at 18000 rpm for 10 minutes. Unreacted zinc ions and the dimethylimidazole ligand were then washed with methanol to obtain ZIF-8 ultrasmall nanoparticles.
[0038] S2: Preparation of ZIF-8 nanoparticle slurry: Add 1 mL of methanol to ZIF-8 ultra-small nanoparticles and disperse to form a uniform ZIF-8 methanol slurry with a slurry concentration of 70 mg / mL.
[0039] S3: Preparation of ZIF-8 self-supporting membrane: The above ZIF-8 methanol slurry was drop-coated onto a glass plate and air-dried at room temperature to obtain the ZIF-8 self-supporting membrane.
[0040] The ZIF-8 nanoparticles and ZIF-8 self-supporting films obtained in Example 3 were characterized and analyzed, and the results are as follows: (1) XRD characterization: such as Figure 9 As shown, the prepared ZIF-8 particles are completely consistent with the simulated ZIF-8 XRD spectrum, indicating that the prepared ZIF-8 particles have a pure ZIF-8 crystal form and no impurity crystal phases exist, proving that the ZIF-8 particles have been successfully prepared.
[0041] (2) SEM characterization ( Figure 10 ):like Figure 10As shown in a, the prepared ZIF-8 ultrasmall nanoparticles exhibit the traditional dodecahedral morphology of ZIF-8 and are uniform in size, with a particle size of approximately 200 nm; from Figure 10 As can be observed in b, there is absolutely no cross-linking between the particles. The film composed of ZIF-8 nanoparticles with a particle size of 200 nm is just a simple accumulation of particles, not a dense film.
[0042] The above experiments show that the particle size of ZIF-8 significantly affects the density of the subsequent film formation. Among them, the 20 nm ZIF-8 particles are the smallest, with stronger adhesion between particles, making it easier to stack them into a dense and defect-free MOF film.
Claims
1. A method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking, characterized in that, Includes the following steps: S1. Preparation of ultra-small ZIF-8 nanoparticles with a particle size of 10-30 nm; S2. The ultra-small ZIF-8 nanoparticles are dispersed in methanol and concentrated by centrifugation to obtain a ZIF-8 nanoparticle slurry with a concentration of 50-90 mg / mL; S3. The ZIF-8 nanoparticle slurry is coated onto the substrate surface, allowed to air dry at room temperature, and then peeled off to obtain a ZIF-8 self-supporting film.
2. The method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking according to claim 1, characterized in that, In step S1, the preparation method of the ultra-small ZIF-8 nanoparticles is as follows: zinc salt and dimethylimidazole are dissolved in polar solvents respectively, and then the two solutions are stirred and reacted at room temperature for 0.5-4 hours. After the reaction is completed, the ultra-small ZIF-8 nanoparticles are obtained by centrifugation, washing and drying.
3. The method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking according to claim 2, characterized in that, The zinc salt is selected from any one or two of zinc nitrate and zinc chloride, and the polar solvent is selected from methanol, ethanol, water or a mixture thereof.
4. The method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking according to claim 2, characterized in that, The molar ratio of the zinc salt to dimethylimidazole is 1:(4-10).
5. The method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking according to claim 2, characterized in that, The drying process is carried out at room temperature for 6-24 hours.
6. The method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking according to claim 1, characterized in that, In step S2, the centrifugation speed is 8000-18000 r / min and the centrifugation time is 5-15 min.
7. The method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking according to claim 1, characterized in that, In step S2, the ultra-small ZIF-8 nanoparticles are dispersed by ultrasonic dispersion, with an ultrasonic power of 100-300W and an ultrasonic time of 10-30min.
8. The method for preparing a ZIF-8 self-supporting film based on ultra-small nanoparticle stacking according to claim 1, characterized in that, In step S3, the coating thickness is 50-60 μm.
9. A ZIF-8 self-supporting membrane based on ultra-small nanoparticle stacking, characterized in that, It is prepared by any one of the preparation methods of claims 1-8.
10. The application of the ZIF-8 self-supporting membrane according to claim 9 in the field of gas separation.