MOF (Metal Organic Framework) membrane as well as preparation method and application thereof

Abstract

The invention provides an MOF (Metal Organic Framework) film as well as a preparation method and application thereof. The MOF film is prepared by the preparation method; the preparation method comprises the following steps: adding a nickel source, 1H-pyrazole-4-carboxylic acid and pyrazine into a reaction kettle, adding N, N-dimethylformamide and water to obtain a mixed solution, remaining 1 / 2 of the mixed solution as a mixed solution A, and taking out 1 / 2 of the mixed solution as a mixed solution B; a substrate sheet is perpendicular to the mixed solution A, a first reaction is carried out, after cooling, the substrate sheet is taken out, washed and dried, and a seed crystal layer substrate sheet is obtained; putting the mixed solution B into a reaction kettle, enabling a crystal seed layer substrate sheet to be perpendicular to the mixed solution B, carrying out second reaction, taking out and washing after cooling, and then activating to obtain the crystal seed layer. According to the preparation method provided by the invention, the raw materials are cheap and easy to obtain, the operation is simple, the repeatability is high, the common defects of the MOF membrane in the preparation process are avoided, and the separation performance of the membrane is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation membranes, and in particular relates to a MOF membrane and a preparation method and application thereof. Background Art

[0002] With the intensification of the contradiction between industrial development and resources and the environment, efficient and energy-saving separation technology has become the key to solving energy shortages, environmental pollution and chemical industry upgrades. Under this trend, membrane separation technology has become a key technical direction in modern separation science with its low energy consumption, easy operation and scalability. As a crystalline porous material, MOF has also become an ideal candidate material for membrane separation due to its high designability and controllability. However, due to the large number of reaction conditions that affect the synthesis of MOF membranes and the complex growth process of MOF crystals, the synthesized MOF membranes often have some inevitable defects, including mesopores, grain boundary defects, pinholes and cracks. The non-selective channels formed by these defects will seriously affect the separation performance of MOF membranes, so it is extremely important to develop a simple and easy method for repairing MOF membrane defects.

[0003] To date, a variety of methods have been developed to repair defects in MOF membranes. For example, Zhang et al. proposed an in situ solvothermal crystallization method based on competitive coordination to synthesize continuous defect-free MOF membranes on polymer substrates coated with metal-phenolic networks. Zhao et al. proposed a re-coordination strategy, further immersing the synthesized membrane in a ligand solution for solvothermal treatment, and also synthesized defect-free MOF membranes. Caro et al. prepared defect-free MOF composite membranes by coating polymers. However, although many methods for repairing defects in MOF membranes have been proposed, most of them are complex and require precise and strict control of reaction conditions. In addition, other preparation raw materials besides MOF may further increase the cost. These all limit their large-scale industrial application. Therefore, when developing methods for preparing defect-repairing membranes, the current urgent issue is to further simplify the process, reduce costs, and increase the simplicity of the method in all aspects.

[0004] At the same time, MOF membrane separation technology is widely used in C 2 H 4 / C 2 H 6 The separation field also faces several challenges. 2 H 4 / C 2 H 6 (C 2 H 4 : C 2 H 6 : ) have a small difference in kinetic diameter (0.028nm), and the precise separation of these two compounds is still very difficult. Therefore, the separation selectivity of most MOF membranes currently used for ethylene / ethane separation is usually less than 10. 2 -MIL-125 membrane achieved a separation selectivity of 13.6, but its ethylene permeability was low at only 50 GPU.

[0005] Therefore, MOF membranes are applied to C 2 H 4 / C 2 H 6 A pressing issue in separation is how to develop MOF membrane materials that achieve high permeability and high stability while maintaining high selectivity.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The object of the present invention is to provide a MOF membrane and a preparation method and application thereof to solve the above problems.

[0008] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:

[0009] A method for preparing a MOF film, the preparation method comprising the following steps:

[0010] S1: A certain proportion of nickel source, 1H-pyrazole-4-carboxylic acid (pca) and pyrazine (pyz) are placed in a polytetrafluoroethylene liner of a reaction kettle, and then appropriate amounts of N,N-dimethylformamide and water are added, and ultrasonic stirring is performed to fully dissolve the raw materials to obtain a mixed solution, and 1 / 2 of the mixed solution is retained in the liner, which is recorded as mixed solution A, and 1 / 2 of the mixed solution is taken out for standby use, which is recorded as mixed solution B;

[0011] Preferably, the nickel source comprises Ni(NO 3 )·6H 2 O、NiCl 2 6H 2 O.Ni(CH 3 COO 2 One or more of .

[0012] Preferably, the certain ratio is: the molar ratio of the nickel source, the 1H-pyrazole-4-carboxylic acid (pca) and the pyrazine (pyz) is (0.75-1.5):(0.75-1.5):(0.75-1.5);

[0013] More preferably, the molar ratio of the nickel source, the 1H-pyrazole-4-carboxylic acid (pca) and the pyrazine (pyz) is 1:1:1; Ni 2+ as the central metal ion, usually tends to form a six-coordinated configuration; 1H-pyrazole-4-carboxylic acid and pyrazine provide carboxylic acid groups and dinitrogen coordination sites, respectively. The following goals can be achieved by using a molar ratio of 1:1:1: the carboxylic acid group of 1H-pyrazole-4-carboxylic acid and Ni 2 + Form stable monodentate or bidentate coordination to build a rigid framework. Pyrazine, as a bridging ligand, connects adjacent Ni nodes through dinitrogen sites to form a three-dimensional columnar structure, enhancing the stability of the framework. If 1H-pyrazole-4-carboxylic acid or pyrazine is excessive, it may cause uncoordinated ligands to remain or form competitive coordination modes (such as monocoordination or chelation), destroying the target topological structure.

[0014] Optionally, in the mixed solution, the concentration of the nickel source is 0.045-0.05 mol / L;

[0015] Preferably, the concentration of 1H-pyrazole-4-carboxylic acid (pca) is 0.045-0.05 mol / L;

[0016] Preferably, the concentration of pyrazine (pyz) is 0.045-0.05 mol / L; too low a concentration may result in a decrease in the nucleation rate in the reaction system, which may lead to incomplete crystal growth or the formation of amorphous products, reducing the specific surface area and porosity of MOF. When the concentration is too high, rapid nucleation can easily lead to small grain size or agglomeration. At the same time, at high concentrations, ligands may self-aggregate to form a competitive coordination mode, destroying the framework regularity.

[0017] S2: vertically place the alumina substrate in the mixed solution A obtained in S1, heat to 373-393K for 3h after packaging to perform the first reaction to generate a seed layer, take out the substrate after the reaction after cooling, wash it with methanol, first rinse the surface with methanol, then wash it with methanol for 24h, and then dry it at 353-373K for 12h to obtain a seed layer substrate;

[0018] S3: The mixed solution B obtained in S1 is placed separately in the polytetrafluoroethylene liner of the reaction kettle, and the seed layer substrate obtained in S2 is placed vertically in the mixed solution B. After packaging, it is heated to 373-393K for a second reaction for 24 hours. After cooling, the seed layer substrate after the reaction is taken out and washed with methanol. The surface is first rinsed with methanol, and then washed with methanol for 24 hours, and then activated at 353-373K for 24 hours to obtain an initial MOF membrane.

[0019] Preferably, the preparation method further comprises: heat treating the MOF film obtained from S3 for 0.5-8h under vacuum conditions at a temperature of 393-403K, and then cooling. The MOF structure of the initial MOF film will collapse only under 523K conditions in the TGA test, so the temperature range of 393-403K is selected for vacuum heating, which is far lower than the structural collapse temperature, and can ensure the stability of the overall structure of MOF during the repair process, and will not cause the MOF structure to be destroyed due to excessive temperature, thereby ensuring its framework integrity and functional characteristics. If the temperature is too high, thermal stress may be generated in the film, resulting in new defects in the film or further expansion of the original defects. This temperature range is relatively mild, which can reduce the generation of thermal stress and avoid additional damage to the film material. After vacuuming, heat is mainly transferred by radiation, which can avoid local overheating and protect the topological structure of MOF. During the heating treatment, the molecular motion in the film is intensified, which helps to release the internal stress, and the internal stress may cause defects such as microcracks on the surface of the film, thereby healing the defects such as microcracks to a certain extent. Heating can also enhance the flexibility of the MOF membrane, enabling it to better adapt to changes in the external environment, reduce new defects caused by stress concentration, and also facilitate the self-repair of existing defects.

[0020] The present invention also provides a MOF film, and the MOF film is prepared by the preparation method.

[0021] The present invention provides an application of a MOF membrane, wherein the MOF membrane is used for C 2 H 4 / C 2 H 6 The present invention utilizes the method of vacuum heating to heal the cracks on the surface of the initial MOF membrane, thereby solving some non-selective defects generated during the preparation process of conventional MOF membranes and improving the C 2 H 4 / C 2 H 6 Selective.

[0022] Beneficial effects of the present invention:

[0023] The invention provides a method for C 2 H 4 / C 2 H 6 The preparation method of the separated MOF membrane uses cheap and readily available raw materials, simple and highly repeatable operating methods, and utilizes the method of heating to repair the surface defects of the initial MOF membrane, thus avoiding the non-selective defects that are easily generated during the preparation process of conventional MOF membranes.

[0024] The MOF (Ni-pca-pyz) membrane prepared by the present invention maintains C 2 H4 / C 2 H 6 It has a high selectivity of 5.91 and a C of 299 GPU. 2 H 4 High flux; solves the problem of conventional MOF membranes in C 2 H 4 / C 2 H 6 The trade-off effect between selectivity and permeation flux that usually exists in the separation process also improves the C of MOF membranes. 2 H 4 / C 2 H 6 Selectivity and C 2 H 4 Permeate flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 XRD spectra of the MOF films prepared in Examples 1-5 and Comparative Examples 1-5;

[0027] Figure 2 Surface scanning electron microscope images of the MOF membranes prepared in Examples 4-5 and Comparative Example 1;

[0028] Figure 3 The surface scanning electron microscope image of the MOF film prepared in Comparative Example 4-5;

[0029] Figure 4 The cross-sectional scanning electron microscope images of the MOF membranes prepared in Examples 4-5 and Comparative Example 1;

[0030] Figure 5 The XPS spectra of the MOF films prepared in Examples 4-5 and Comparative Example 1;

[0031] Figure 6 is the XPS spectrum of Ni 2p;

[0032] Figure 7 The surface scanning electron microscope image of the MOF film prepared in Comparative Example 4-5;

[0033] Figure 8The figure is a test result diagram of the separation performance of the MOF membranes prepared in Comparative Example 1 and Examples 1-5;

[0034] Fig. 9 The figure is a test result diagram of the separation performance of the MOF membranes prepared in Comparative Examples 2-5;

[0035] Fig.10 This is a graph showing the separation performance test results of the MOF membrane prepared in Comparative Example 6. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] This embodiment provides a MOF film and a preparation method thereof, which specifically comprises the following steps:

[0039] S1: First weigh 0.356 g (1.2 mmol) Ni(NO 3 )·6H 2 O, 0.135 g (1.2 mmol) 1H-pyrazole-4-carboxylic acid (pca) and 0.097 g (1.2 mmol) pyrazine (pyz) were placed in a polytetrafluoroethylene-lined reactor, 20 ml N,N-dimethylformamide (DMF) and 5 ml deionized water were added, and ultrasonic stirring was performed for 5 min to fully dissolve the raw materials to obtain a mixed solution, which was divided into two equal parts, one of which was taken out for later use;

[0040] S2: Then, a smooth alumina substrate is placed vertically downward in a polytetrafluoroethylene liner, the liner is encapsulated in a reactor, and then the reactor is transferred to an oven for heating, and the reaction is carried out at 378K for 3 hours to generate a seed layer. After the system is cooled to room temperature, the substrate is taken out and the surface is rinsed with methanol, and then the substrate is washed with methanol for 24 hours; after washing, the substrate is transferred to a vacuum oven and dried at 353K for 12 hours to obtain a seed layer substrate;

[0041] S3: Take out the reserved mixed liquid from S1 and place it separately in the polytetrafluoroethylene liner of the reactor, and place the seed layer substrate sheet prepared by S2 vertically downward in the polytetrafluoroethylene liner, seal the liner in the reactor, and then transfer the reactor to an oven for heating, react at 378K for 24h, and after the system cools to room temperature, take out the seed layer substrate sheet and rinse the surface with methanol, and then wash with methanol for 24h; after washing, transfer the reacted seed layer substrate sheet to a vacuum oven and activate it at 353K for 24h to obtain the initial MOF membrane;

[0042] S4: The initial MOF film obtained in step S3 is further heated under vacuum conditions at 393 K for 0.5 h. After the system is cooled, the MOF film provided in the present application, i.e., the Ni-pca-pyz film, is obtained.

[0043] Example 2

[0044] The difference from Example 1 is that the heating time in step S4 is 2 hours.

[0045] Example 3

[0046] The difference from Example 1 is that the heating time in step S4 is 4 hours.

[0047] Example 4

[0048] The difference from Example 1 is that the heating time in step S4 is 6 hours.

[0049] Example 5

[0050] The difference from Example 1 is that the heating time in step S4 is 8 hours.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that Comparative Example 1 does not have the S4 vacuum heating step.

[0053] Comparative Example 2

[0054] The difference from Example 2 is that the heating condition in step S4 is a non-vacuum condition.

[0055] Comparative Example 3

[0056] The difference from Example 3 is that the heating condition in step S4 is a non-vacuum condition.

[0057] Comparative Example 4

[0058] The difference from Example 4 is that the heating condition in step S4 is a non-vacuum condition.

[0059] Comparative Example 5

[0060] The difference from Example 5 is that the heating condition in step S4 is a non-vacuum condition.

[0061] Comparative Example 6

[0062] This comparative example provides a method for preparing a MOF film, which specifically comprises the following steps:

[0063] S1: First weigh 0.356 g (1.2 mmol) Ni(NO 3 )·6H 2 O, 0.135 g (1.2 mmol) 1H-pyrazole-4-carboxylic acid and 0.097 g (1.2 mmol) pyrazine were placed in a polytetrafluoroethylene-lined reactor, 20 ml N,N-dimethylformamide (DMF) and 5 ml deionized water were added, and ultrasonic stirring was performed for 5 min to fully dissolve the raw materials to obtain a mixed solution;

[0064] S2: Then, a smooth alumina substrate is placed vertically downward in a polytetrafluoroethylene liner, the liner is encapsulated in a reactor, and then the reactor is transferred to an oven for heating, and the reaction is carried out at 378K for 3 hours to generate a seed layer. After the system is cooled to room temperature, the substrate is taken out and the surface is rinsed with methanol, and then the substrate is washed with methanol for 24 hours; after washing, the substrate is transferred to a vacuum oven and dried at 353K for 12 hours to obtain a seed layer substrate;

[0065] S3: Place the seed layer substrate obtained in S2 vertically downward in the polytetrafluoroethylene liner in S2, continue heating, and react at 378K for 24 hours. After the system cools to room temperature, take out the seed layer substrate and rinse the surface with methanol, and then wash with methanol for 24 hours. After washing, transfer the reacted seed layer substrate to a vacuum oven and activate at 353K for 24 hours to obtain an initial MOF membrane.

[0066] S4: The initial MOF film obtained in step S3 is further heated under vacuum conditions at 393 K for 0 h, 2 h, 4 h, 6 h and 8 h, respectively, and after the system is cooled, a MOF film is obtained.

[0067] The XRD spectra of the MOF films prepared in Examples 1-5 and Comparative Examples 1-5 are as follows: Figure 1 As shown, Figure 1 (a) is the XRD spectra of the MOF films provided in Examples 1-5 and Comparative Example 1, Figure 1 (b) is the XRD spectrum of the MOF film provided in Comparative Examples 2-5. Figure 1(a) It can be seen that the XRD of the MOF film (0h, 0.5h, 2h, 4h, 6h, 8h) obtained after vacuum heating for different lengths of time at 393-403K is consistent with the simulated XRD diffraction peak data, indicating that the high-crystallinity pure phase material of Ni-pca-pyz was successfully synthesized, and vacuum heating for different lengths of time will not destroy the crystal structure of the MOF. Figure 1 (b) It can be seen that when the heating conditions in step S4 are changed from vacuum conditions to non-vacuum conditions, the XRD spectra of comparative examples 1-5 do not undergo significant changes, and compared with the XRD spectra of the embodiments, the intensity ratio of the two diffraction peaks at 2θ=9.3° and 12.5° does not gradually decrease as in the embodiments, which indicates that non-vacuum heating cannot cause changes in the crystal orientation of the MOF film, thereby optimizing the crystal phase interface and repairing the surface defects of the MOF film.

[0068] The surface scanning electron microscopy images of the MOF membranes prepared in Comparative Example 1 and Examples 4-5 are as follows: Figure 2 As shown, Figure 2 (a-1) and (a-2) are SEM images of the MOF membrane surface provided in Comparative Example 1 at magnifications of 1k and 3k, respectively. Figure 2 (b-1) and (b-2) are SEM images of the MOF membrane surface at magnifications of 1k and 3k respectively in Example 4, i.e., the vacuum heating time is 6h. Figure 2 (c-1) and (c-2) are SEM images of the membrane surface at magnifications of 1k and 3k respectively in Example 5, i.e., the membrane was heated in vacuum for 8 h.

[0069] Figure 3 The surface scanning electron microscope image of the MOF membrane prepared in Comparative Example 4-5 is shown in FIG. Figure 3 (a-1) and (a-2) are SEM images of the MOF membrane surface obtained in Comparative Example 4, i.e., the non-vacuum heating time is 6 h, at magnifications of 2k and 3k, respectively. Figure 3 (b-1) and (b-2) are SEM images of the MOF membrane surface at magnifications of 2k and 3k respectively in comparative example 5, i.e., the non-vacuum heating time of 8h.

[0070] pass Figure 2 and Figure 3 It can be seen that there are many cracks on the surface of the MOF membrane provided in the comparative example, resulting in a large number of surface defects, which in turn leads to a low gas separation selectivity. As the vacuum heating proceeds, the crack defects on the surface of the MOF membrane heal. The MOF membrane obtained by the present invention is applied to C 2 H 4 / C 2 H 6 When the separation of 2 H 4The permeability decreased and the gas separation selectivity increased, reaching the highest selectivity when the vacuum heating lasted for 6 hours. When the vacuum heating time reached 8 hours, the crystals of the Ni-pca-pyz material transformed and formed another morphology, and the crack phenomenon observed in the initial MOF crystal disappeared. However, more surface voids were exposed on the membrane surface, resulting in the C 2 H 4 As permeability increases, selectivity decreases.

[0071] The cross-sectional scanning electron microscopy images of the MOF membranes prepared in Examples 4-5 and Comparative Example 1 are as follows: Figure 4 As shown, Figure 4 (a) is a cross-sectional SEM image of the MOF film provided in Comparative Example 1, Figure 4 (b) is a cross-sectional SEM image of the MOF membrane in Example 4, i.e., the vacuum heating time is 6 h. Figure 4 (c) is a cross-sectional SEM image of the film in Example 5, i.e., the vacuum heating time is 8 h. Figure 4 From the scanning electron microscope (SEM) cross-sectional image, it can be seen that after the initial MOF membrane was vacuum heated, the membrane healed. At the same time, the thickness of the membrane also decreased slightly, from about 12.5μm to 10μm.

[0072] from Figure 1-3 It can be seen that after the prepared initial MOF film was vacuum heated for different lengths, the relative intensity of the diffraction peaks at 2θ=9.3° and 12.5° in its XRD spectrum changed significantly. As the heating time increased, the diffraction peak at 9.3° weakened, while the diffraction peak at 12.5° strengthened. This indicates that during the further vacuum heat treatment of the membrane material, the crystal morphology of MOF has changed due to the healing of the membrane surface defects.

[0073] The XPS spectra of the MOF membranes prepared in Examples 4-5 and Comparative Example 1 are as follows: Figure 5 As shown in Figure 2, the XPS spectrum of Ni 2p is as follows: Figure 6 To further explore the internal structural changes of the MOF membrane during vacuum heating, XPS characterization was performed on the membranes of Comparative Example 1 without vacuum heating and Comparative Examples 4-5 with vacuum heating for 6h and 8h. Figure 6 From the comparison, it can be seen that the intensity of the element peak signal changed only slightly before and after heating, while the binding energy of each element remained unchanged. Similarly, in the high-resolution spectrum of Ni 2p, the binding energies of Ni 2p1 / 2 and Ni 2p3 / 2 were always 874.18eV and 856.28eV, respectively, and no displacement was detected before and after heating. This shows that the valence state of the Ni element did not change during the heating process, and the bonding configuration of Ni remained unchanged before and after heating. Therefore, the MOF film maintained structural stability after vacuum heating.

[0074] The surface electron microscopy image of the MOF film prepared in Comparative Example 6 is as follows: Figure 7 As shown, Figure 7 (a-1), Figure 7 (a-2) are surface electron micrographs of the MOF membrane obtained in comparative example 6 with a vacuum heating time of 0 h at 3k and 1k magnifications, respectively. Figure 7 (b-1), Figure 7 (b-2) are surface electron micrographs of the MOF membrane obtained in comparative example 6 by vacuum heating for 6 h at 3k and 1k magnifications, respectively. Figure 7 (c-1), Figure 7 (c-2) are surface electron micrographs of the MOF membrane prepared in comparative example 6 with vacuum heating for 8 h at 3k and 1k magnifications, respectively.

[0075] Membrane separation performance test:

[0076] The MOF membranes prepared in the examples and comparative examples were transferred to the gas chromatograph membrane cell for gas separation performance testing. 2 H 4 and C 2 H 6 Single component permeation experiments and C 2 H 4 / C 2 H 6 The permeation test of mixed components was carried out under the mixed feed of (50:50, v / v) and the operating temperature was 25°C; the measured results are as follows Figure 8-10 As shown, Figure 8 , Fig. 9 , Fig.10 Separation performance test diagrams of the MOF membranes prepared in Comparative Example 1 and Examples 1-5, separation performance test diagrams of the MOF membranes prepared in Comparative Examples 2-5, and separation performance test diagrams of the MOF membranes prepared in Comparative Example 6 are shown in sequence; Figure 8 It can be seen that with the increase of vacuum heating time of MOF membrane, C 2 H 4 The permeability of the membrane first decreases and then increases, while the selectivity first increases and then decreases. When the vacuum heating time reaches 6h, the separation performance of the membrane reaches the best, C 2 H 4 / C 2 H 6 The actual separation selectivity of the membrane reached 5.91, which was 155% higher than that of the unheated MOF membrane in Comparative Example 1. This further confirmed that under vacuum heating conditions, the surface defects of the membrane were gradually repaired. As the defects were continuously repaired, the MOF membrane had a higher selectivity for C 2 H 4 / C2 H 6 The gas separation performance of the separation was continuously enhanced. However, when the vacuum heating time was extended to 8h, the permeate flux rebounded, while the separation selectivity decreased. At this time, this was because the morphology of the MOF material on the membrane surface changed, and part of the substrate surface was exposed, resulting in a decrease in the separation performance of the membrane.

[0077] Fig. 9 , Fig.10 It shows that when the MOF membranes are prepared by the methods described in Comparative Examples 1-5, the same effects as in Examples 1-5 cannot be achieved. The separation performance of the membranes prepared in Comparative Examples 2-5 is as follows: Fig. 9 As shown in the figure, it can be seen that the MOF film heated under non-vacuum conditions has only C 2 H 4 A slight increase in flux, while C 2 H 4 / C 2 H 6 The separation selectivity did not change significantly, indicating that the heat treatment under vacuum conditions in Examples 1-5 is a key factor in improving the separation performance of MOF membranes. Under vacuum conditions, the volatilization of pyrazine in MOF ligands can be promoted, which can promote the change of crystal structure and thus improve the gas separation efficiency. Fig.10 The performance of the membrane prepared by the method of Comparative Example 6 is shown in the figure. It can be seen from the figure that with the increase of vacuum heating time, the MOF separation performance does not change much in terms of flux and selectivity, and the selectivity is close to C 2 H 4 / C 2 H 6 The Knudsen diffusion selectivity indicates that the secondary growth in Examples 1-5 is also an important step in preparing high-performance MOF membranes.

[0078] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing a MOF membrane, characterized in that: The preparation method comprises the following steps: S1: a certain proportion of nickel source, 1H-pyrazole-4-carboxylic acid (pca) and pyrazine (pyz) are placed in a polytetrafluoroethylene liner of a reaction kettle, and then appropriate amounts of N,N-dimethylformamide and water are added to fully dissolve to obtain a mixed solution, 1 / 2 of the mixed solution is retained in the liner, recorded as mixed solution A, and 1 / 2 of the mixed solution is taken out for standby use, recorded as mixed solution B; S2: vertically placing the substrate sheet in the mixed solution A obtained in S1, heating after encapsulation to perform a first reaction to generate a seed layer, taking out the substrate sheet after the reaction after cooling, washing it with methanol, and then drying it to obtain a seed layer substrate sheet; S3: The mixed solution B obtained in S1 is placed separately in the polytetrafluoroethylene lining of the reaction kettle, and the seed layer substrate obtained in S2 is placed vertically in the mixed solution B. After packaging, it is heated to perform the second reaction. After cooling, the seed layer substrate after the reaction is taken out, washed with methanol, and then activated at a certain temperature to obtain a MOF membrane.

2. The preparation method according to claim 1, characterized in that: The nickel source includes one or more of Ni(NO3)·6H2O, NiCl2·6H2O, and Ni(CH3COO)2.

3. The preparation method according to claim 1 or 2, characterized in that: The certain ratio described in S1 is: the molar ratio of the nickel source, the 1H-pyrazole-4-carboxylic acid (pca) and the pyrazine (pyz) is (0.75-1.5):(0.75-1.5):(0.75-1.5).

4. The preparation method according to claim 1, characterized in that: In the mixed solution, the concentration of the nickel source is 0.045-0.05 mol / L; Preferably, the concentration of 1H-pyrazole-4-carboxylic acid (pca) is 0.045-0.05 mol / L; Preferably, the concentration of pyrazine (pyz) is 0.045-0.05 mol / L.

5. The preparation method according to claim 1, characterized in that: The substrate includes an aluminum oxide substrate.

6. The preparation method according to claim 1, characterized in that: The preparation method further comprises: heat treating the MOF film obtained in S3 under vacuum conditions at a temperature of 393-403K for 0.5-8h, and then cooling.

7. The preparation method according to claim 1, characterized in that: The temperature of the first reaction is 373-393K and the time is 3h; Preferably, the temperature of the second reaction is 373-393K and the time is 24h.

8. The preparation method according to claim 1, 6 or 7, characterized in that: The activation temperature in S3 is 353-373K and the activation time is 24h.

9. A MOF membrane, characterized in that: The MOF membrane is prepared by the preparation method according to any one of claims 1 to 8.

10. An application of a MOF membrane obtained by the method for preparing a MOF membrane according to any one of claims 1 to 8, characterized in that: The MOF membrane was used for the separation of C2H4 / C2H6.

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