Method for preparing supported MOF membrane by low-crystallinity aggregated-state structure induction, MOF membrane, and use thereof

Abstract

Provided are a method for preparing a supported MOF membrane by low-crystallinity aggregated-state structure induction, an MOF membrane and the use thereof. The preparation method comprises the following steps: 1) depositing an Al-MOF seed crystal on the surface of a porous support body, so as to obtain an Al-MOF seed crystal layer; 2) placing in a supersaturated solution the porous support body having the Al-MOF seed crystal layer deposited on the surface and carrying out a reaction to grow a continuous low-crystallinity Al-MOF aggregate layer on the surface of the porous support body; and 3) performing a crystallization reaction on the porous support body having the continuous low-crystallinity Al-MOF aggregate layer grown on the surface, so as to obtain an Al-MOF membrane material, wherein the supersaturated solution comprises an aluminum salt, a ligand, and a coordination regulator. The method can prepare a dense high-valent metal MOF crystal membrane material; and the membrane material can be used for efficient separation for separation systems of various molecular scales.

Description

A method for preparing a supported MOF membrane by inducing a low-crystal aggregate structure, a MOF membrane and applications TECHNICAL FIELD

[0001] The present application relates to a method for preparing a supported MOF membrane by inducing a low-crystal aggregate structure, a MOF membrane and applications. BACKGROUND

[0002] Sub-nanometer scale separation processes, including selective transfer and separation of gases, liquids, etc., play a key role in catalysis, energy, material conversion, and other systems. Traditional separation technologies such as rectification and absorption are complex to operate, have high energy consumption and carbon emission intensity, while membrane separation technology is green, safe and efficient, and is not limited by thermodynamic equilibrium, with the advantages of reduced investment and operating costs, energy saving and consumption reduction, and process intensification due to integration.

[0003] Membrane materials are the core of membrane separation technology. High polymer membrane materials have driven the application system of membrane technology from the microscale to the nanoscale. However, for sub-nanometer scale molecular separation requirements, existing commercialized high polymer membrane materials have limitations in structure, resulting in separation precision that does not meet the requirements of industrial applications, which to a large extent restricts the research and application of molecular scale separation membranes.

[0004] Metal-organic framework (MOF) is a new type of porous crystalline material assembled by metal ions or ion clusters and organic ligands. Compared with traditional zeolite molecular sieve materials, MOF not only has regular and penetrating nanochannels, but also can be designed and precisely adjusted in sub-nanometer scale.

[0005] High-stability MOF formed by coordination of high-valence metal cations and carboxylic acid organic ligands has excellent thermal, chemical and mechanical stability. MOF membranes precisely constructed therefrom are expected to meet the precise and stable separation requirements of molecular scale separation systems. However, existing technologies mainly use low-valence MOF materials such as Al-MOF, and high-valence MOF materials such as Al-MOF are less common. The reason may be that the crystal seeds of Al-based MOF materials grow into rods, and their growth speed in each direction axis is inconsistent, making it difficult to form a dense MOF material film. That is, the nucleation energy barrier of high-valence MOF crystals such as Al-MOF material is high, making it difficult to precisely control and balance the nucleation rate and growth direction of MOF, and the topological morphology is mainly anisotropic rod-shaped crystals, making it difficult to grow and coexist, resulting in unavoidable crystal boundary defects, which seriously weaken the intrinsic separation performance of the membrane material.

[0006] Therefore, it is still challenging to prepare high-valence MOF membranes by relying on current technologies, and the crystal boundary symbiosis of the membranes is poor, and the crystal boundary defect problem limits the intrinsic separation performance of the MOF channels, and it is more difficult to cooperatively control the channel orientation of the MOF membranes, and the separation performance of the membranes needs to be further improved. SUMMARY

[0007] The purpose of the present application is to provide a method for preparing a supported MOF membrane by inducing a low-crystal aggregate structure, which can prepare a dense high-valence metal MOF crystal membrane material, and the membrane material can be used for efficient separation of various molecular scale separation systems.

[0008] To achieve the above purpose, the technical scheme adopted by the present application is:

[0009] A preparation method of an Al-MOF membrane material, the preparation method comprising the following steps: 1) depositing Al-MOF seeds on the surface of a porous support to obtain an Al-MOF seed layer; 2) placing the porous support with the Al-MOF seed layer deposited on the surface in a supersaturated solution for reaction, growing a continuous low-crystal Al-MOF aggregate layer on the surface of the porous support; 3) performing a crystallization reaction on the porous support with the continuous low-crystal Al-MOF aggregate layer grown on the surface to obtain the Al-MOF membrane material; the supersaturated solution comprises an aluminum salt, a ligand, and a coordination regulator.

[0010] In the present application, the supersaturated solution refers to a solution in which the amount of solute exceeds its saturation solubility. For example, in the aforementioned supersaturated solution, the dissolution amount of the aluminum salt, the ligand, and the ligand regulator exceeds the respective saturation solubility.

[0011] In the prior art, the MOF membrane material is mostly divalent MOF material, such as Zn-MOF material. When the divalent MOF material forms a crystal, it is easy to control its nucleation rate and crystal growth direction, and it is easy to make the growth rates of each direction similar, thereby easily obtaining spherical crystal nuclei, and the spherical crystal nuclei grow continuously to easily grow into a continuous MOF membrane. However, for high-valence MOF materials such as Al-MOF materials, the nucleation energy barrier is high, and it is difficult to accurately control and balance the nucleation rate and growth direction of the MOF, and the topological morphology is mainly anisotropic rod-shaped crystals, which leads to difficulty in crystal growth symbiosis, and it is difficult to form a continuous dense membrane, which leads to defects in the membrane material, and thus significantly affects its separation performance.

[0012] The inventors of the present application found through research that, by first depositing a seed layer on a porous carrier, then using the method provided by the present application to induce the seed to first grow into a continuous low-crystalline aggregate layer by means of the principle of supersaturation, and then further crystallizing the low-crystalline aggregate to realize the transformation of "continuous low-crystalline film-continuous MOF crystalline film", a dense and defect-free MOF film can be prepared. The two-step reaction corresponds to the nucleation and growth of crystals, making the crystallization and growth behavior of MOF highly controllable, and thus realizing the preparation of high-performance MOF films.

[0013] However, in the prior art, for divalent MOF materials, although the method of seed growth is usually used to synthesize MOF films, the pre-coated or deposited seeds are in a dispersed state and are not in a continuous state, i.e., the seed method of the prior art is a one-time growth into a continuous final MOF film and does not involve the transition form of the low-crystalline aggregate layer of the present application. Using the traditional seed growth method, it is impossible to prepare a continuous and dense film layer of high-valence MOF.

[0014] In some embodiments, the aluminum salt is selected from a combination of one or more of aluminum nitrate, aluminum isopropoxide, sodium aluminate, aluminum chloride, aluminum acetate, polyaluminum chloride, and aluminum sulfate octadecahydrate.

[0015] In some embodiments, the ligand is a carboxylic acid ligand.

[0016] In some embodiments, the ligand is selected from a combination of one or more of 4,4',4''-(phenyl-1,3,5-trioxo)-benzoic acid, 1,4-benzenedicarboxylic acid, isophthalic acid, 2,5-furandicarboxylic acid, 2,5-pyrrole dicarboxylic acid, and fumaric acid.

[0017] In some embodiments, the coordination regulator is selected from an acidic coordination regulator or a basic coordination regulator.

[0018] In some embodiments, the acidic coordination regulator is selected from a combination of one or more of formic acid, acetic acid, benzoic acid, and o-fluorobenzoic acid.

[0019] In some embodiments, the basic coordination regulator is selected from a combination of one or more of sodium hydroxide, sodium formate, and sodium acetate.

[0020] In some embodiments, the total mass of the aluminum salt and the ligand accounts for 4%-20% of the mass of the supersaturated solution.

[0021] In some embodiments, in the supersaturated solution, the mass ratio of the aluminum salt to the ligand is 1:1-1.5.

[0022] In some embodiments, the mass of the coordination regulator accounts for 1%-5% of the mass of the supersaturated solution.

[0023] In some embodiments, the solvent of the supersaturated solution is selected from the group consisting of one or both of DMF and water. Preferably, the solvent of the supersaturated solution is a mixture of DMF and water. Further preferably, in the mixture, the volume ratio of DMF to water is 3:1~1.5.

[0024] In some embodiments, the preparation method further comprises a step of preparing the supersaturated solution: dissolving the aluminum salt in a solvent, adding the ligand and the coordination regulator to the solvent, stirring at room temperature to obtain the supersaturated solution.

[0025] In some embodiments, the stirring is mechanical stirring.

[0026] In some embodiments, the stirring is for 5~10 min.

[0027] In some embodiments, the thickness of the low-crystal Al-MOF aggregate layer is 1~3 μm.

[0028] In some embodiments, the morphology of the low-crystal Al-MOF aggregate layer is continuous small hill shape.

[0029] In some embodiments, the reaction in step 2) is carried out at 80~150℃.

[0030] In some embodiments, the reaction in step 2) is carried out for 0.5~2 h.

[0031] In some embodiments, the reaction in step 2) is carried out in a closed reactor. Preferably, the closed reactor is a polytetrafluoroethylene reactor.

[0032] In some embodiments, the crystallization reaction in step 3) is carried out at 80~150℃.

[0033] In some embodiments, the crystallization reaction in step 3) is carried out for 3~10 h.

[0034] In some embodiments, the crystallization reaction in step 3) is carried out in a closed reactor. Preferably, the closed reactor is a polytetrafluoroethylene reactor.

[0035] In some embodiments, the Al-MOF seed crystals are the same as the Al-MOF crystals in the Al-MOF film material, or the Al-MOF seed crystals have the same topological structure as the Al-MOF crystals in the Al-MOF film material. That is, the seed crystals can be homologous structure seed crystals, which are the same material as the subsequently prepared MOF film; or can be heterogeneous structure MOF crystals, which have the same topology and metal salt as the subsequently prepared MOF film, but different ligands. Taking the MIL-160 film as an example, the homologous seed crystals are MIL-160 nanocrystals, and the heterogeneous phase crystals are CAU-10-R and KMF-1, etc.

[0036] In some embodiments, the particle size of the Al-MOF seed crystals is 50-300 nm.

[0037] In some embodiments, the deposition in step 1) is achieved by a hot drop coating method, a spin coating method, a vacuum filtration method or a slide coating method, wherein the hot drop coating method comprises a step of preheating the porous support and a step of drop coating.

[0038] Further, when preheating, the porous support is heated to 80-100°C.

[0039] Further, when using the hot drop coating method or the spin coating method, the seed crystal dispersion liquid is drop coated or spin coated onto the surface of the support.

[0040] Further, the mass concentration of the seed crystals in the seed crystal dispersion liquid is 0.01-0.015 wt.%.

[0041] In some embodiments, the thickness of the Al-MOF seed crystal layer is 0.5-5 μm.

[0042] In some embodiments, the Al-MOF seed crystals are prepared by a preparation method selected from one or both of a solvothermal method and a mechanical ball milling method. The mechanical ball milling method can further reduce the particle size of the seed crystals, making it easy to reach the nm level. The specific preparation method can be carried out according to the literature (J. Am. Chem. Soc., 2020, 142, 6925-6929).

[0043] In some embodiments, the preparation method further comprises a step of polishing or ultrasonic cleaning the porous support before depositing the Al-MOF seed crystals, and drying.

[0044] Further, the drying is vacuum drying, preferably, the temperature of the vacuum drying is 150-200°C.

[0045] Further, the polishing is carried out using sandpaper. The particle size of the sandpaper can be 600-1200 mesh.

[0046] Further, the polishing time is 5-10 min.

[0047] Further, the ultrasonic cleaning time is 10-30 min, and the frequency is 50-120 KHz.

[0048] In some embodiments, the porous support is selected from a porous alumina carrier or a porous polymer support.

[0049] In some embodiments, the porous alumina carrier has a pore size of 100-300 nm.

[0050] In some embodiments, the porous alumina carrier is in a plate, tube or hollow fiber form.

[0051] In some embodiments, the porous alumina carrier is unmodified or modified to be surface lipophilic.

[0052] In some embodiments, the porous polymer support is made of nylon, polyacrylonitrile, polydimethylsiloxane, polyethersulfone or polyvinylidene fluoride.

[0053] In some embodiments, the Al-MOF is selected from one or more of the following: Al-bttotb, MIL-53, CAU-10-R, CAU-23, MIL-160, KMF-1 and Al-fum.

[0054] The application also provides an Al-MOF membrane material prepared by the above method.

[0055] The application also provides the use of the above Al-MOF membrane material for separating carbon dioxide / methane, carbon dioxide / nitrogen, ethylene / ethane, hexane isomers, cyclohexanol / cyclohexanone, dimethylbenzene isomers and acetic acid / water. Among them, carbon dioxide / methane, carbon dioxide / nitrogen and propylene / propane are gas separation, while hexane isomers, cyclohexanol / cyclohexanone, dimethylbenzene isomers and acetic acid / water are liquid separation.

[0056] The application also provides a membrane assembly for separation, which comprises the above Al-MOF membrane material and a stainless steel support.

[0057] The assembly and preparation method of the membrane assembly for separation both use existing conventional methods.

[0058] Thanks to the above technical solutions, the application has the following advantages compared with the prior art:

[0059] (1) The present application utilizes continuous low-crystalline aggregate layer to transform and grow into dense Al-MOF film layer, which is significantly different from the most common seed-second growth method, which is to prepare continuous MOF film by independent growth of single crystal seeds. The transformation of continuous layer to continuous layer of the present application ingeniously avoids the problem of grain boundary incompatibility when single crystal seeds grow into film independently, reduces the difficulty of preparing dense film MOF film, and realizes the universal preparation of high-valence MOF film such as Al-MOF; in addition, the transformation of the film preparation method also to a certain extent weakens the influence of the support structure on the film preparation, so that the separation performance of the MOF film is not limited by the support structure and material, and the application potential of the MOF material and film is significantly improved.

[0060] (2) The Al-MOF material prepared by the present application is a high-valence MOF material, which has excellent structural stability, including water, heat, chemical and mechanical stability, and the film material has excellent separation performance and running stability in the molecular separation system. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is a SEM graph of the low-crystalline MOF aggregate layer prepared in Example 1;

[0062] Figure 2 is an XRD graph of the low-crystalline MOF aggregate layer prepared in Example 1;

[0063] Figure 3 is a SEM graph of the Al-bttotb film prepared in Example 1;

[0064] Figure 4 is an XRD graph of the Al-bttotb film prepared in Example 1;

[0065] Figure 5 is a separation performance graph of the Al-bttotb film prepared in Example 1;

[0066] Figure 6 is a SEM graph of the oriented Al-bttotb film prepared in Example 2;

[0067] Figure 7 is an XRD graph of the oriented Al-bttotb film prepared in Example 2;

[0068] Figure 8 is a separation performance graph of the oriented Al-bttotb film prepared in Example 2;

[0069] Figure 9 is a SEM graph of the tubular alumina-supported Al-bttotb film prepared in Example 3;

[0070] Figure 10 is a SEM graph of the PVDF-supported Al-bttotb film prepared in Example 4;

[0071] Figure 11 is a SEM graph of the MIL-53 film prepared in Example 5;

[0072] Figure 12 is an XRD graph of the MIL-53 film prepared in Example 5;

[0073] Figure 13 is a plot of the separation performance of the MIL-53 membrane prepared in Example 5;

[0074] Figure 14 is a SEM image of the MIL-160 membrane prepared in Example 6;

[0075] Figure 15 is an XRD plot of the MIL-160 membrane prepared in Example 6;

[0076] Figure 16 is a plot of the separation performance of the MIL-160 membrane prepared in Example 6;

[0077] Figure 17 is a SEM image of the CAU-10-H membrane prepared in Example 7;

[0078] Figure 18 is an XRD plot of the CAU-10-H membrane prepared in Example 7;

[0079] Figure 19 is a plot of the separation performance of the CAU-10-H membrane prepared in Example 7;

[0080] Figure 20 is a SEM image of the KMF-1 membrane prepared in Example 8;

[0081] Figure 21 is a plot of the separation performance of the KMF-1 membrane prepared in Example 8;

[0082] Figure 22 is a SEM image of the Al-fum membrane prepared in Example 9;

[0083] Figure 23 is an XRD plot of the Al-fum membrane prepared in Example 9;

[0084] Figure 24 is a plot of the separation performance of the Al-fum membrane prepared in Example 9;

[0085] Figure 25 is a SEM image of the low crystalline MOF aggregate layer prepared in Comparative Example 1;

[0086] Figures 26-27 are SEM images of the membrane prepared in Comparative Example 1;

[0087] Figures 28-30 are SEM images of the low crystalline growth and membrane growth in Comparative Example 2;

[0088] Figures 31-32 are SEM images of the membrane prepared in Comparative Example 3. DETAILED DESCRIPTION

[0089] The technical solutions of the present application will be described in detail below with specific examples, so that those skilled in the art can better understand and implement the technical solutions of the present application, but the present application is not limited in the scope of the described examples. Example 1

[0090] The embodiment provides a Al-bttotb film prepared by using a low-crystal aggregate induction method, and the preparation steps are as follows:

[0091] (1) The porous sheet type alumina support body (pore size is 200 nm) is polished by 600 mesh and 1200 mesh sandpaper respectively for 5 min, then is cleaned by ultrasonic in a methanol solution for 15 min, the ultrasonic frequency is 50 KHz, and then is placed in a 150 o C vacuum drying box for heat treatment for 2 h, and then is taken out and sealed for standby use.

[0092] (2) The Al-bttotb nanoparticles (particle size is 150 nm) are prepared by combining a solvent thermal method and a mechanical ball milling method, specifically: the metal and the ligand are added into a DMF / water / formic acid (15 / 5 / 1 mL) mixed solvent, stirred at room temperature for 30 min, and then transferred into a 100 mL polytetrafluoroethylene reaction kettle, and then the reaction kettle is transferred into an oven with a preset temperature of 150 o C for 1 day. After the reaction is cooled to room temperature, white crystals are obtained. The white crystals are rod-shaped crystals with a size of 10-20 μm. Then, 1.5 g of the rod-shaped crystals and 47 g of ball milling agate balls are added into a ball milling tank, and a vertical planetary ball mill XQM-12 is used to run at a rotating speed of 400 rpm for 240 min. The ball milling product is collected by adopting a 7000 rpm differential centrifugation program to obtain spherical crystals with a particle size of about 150 nm. Then, the Al-bttotb nanoparticles prepared in the foregoing are dispersed into a methanol solution to obtain a crystal seed dispersion liquid, and the mass fraction of the Al-bttotb nanoparticles is 0.015 wt.%.

[0093] (3) The crystal seed dispersion liquid is coated on the porous alumina support body in a hot drop coating mode, specifically: the support body is heated to 80℃ in advance, then 1 mL of the crystal seed dispersion liquid is transferred to one side of the support body which is polished by using a 1 mL pipette, and after drying for 30 s, the above operation is repeated for 3 times, so that a uniform crystal seed layer is obtained on the surface of the support body.

[0094] (4) 0.4 g of aluminum chloride, 0.6 g of 4,4',4''-(phenyl-1,3,5-trioxo)-benzoic acid and 0.8 g of formic acid are dissolved in 20 mL of a DMF solvent to prepare a supersaturated solution, the supersaturated solution is transferred into a polytetrafluoroethylene (volume is about 50 mL) reaction kettle, and then the support body on which the Al-bttotb nanocrystal seeds are deposited is vertically placed in the reaction kettle, and the nanocrystal seed layer is converted into a continuous low-crystal MOF aggregate layer after reaction at 100℃ for 1 h.

[0095] (5) The support with the low-crystalline MOF aggregate layer grown thereon was vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and reacted at 150 °C for 3 h to convert the low-crystalline structure into an Al-bttotb film with a highly ordered lattice.

[0096] The low-crystalline MOF aggregate layer prepared in step (4) was subjected to scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) tests, and the results are shown in FIGS. 1 and 2, respectively. In FIG. 2, the precursor layer corresponds to the support carrier with the low-crystalline MOF aggregate layer. It can be seen that a continuous low-crystalline MOF aggregate layer with a thickness of about 2 μm was formed on the surface of the porous alumina support.

[0097] The Al-bttotb film prepared in step (5) was subjected to scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) tests (2D-XRD), and the results are shown in FIGS. 3 and 4, respectively. It can be seen that a high-quality Al-bttotb film was successfully prepared on the porous support, and the film is continuous in surface and cross-section, and has no grain boundary defects, with a thickness of about 10 μm.

[0098] The aforementioned Al-bttotb film was subjected to a pervaporation separation test, and the results are shown in FIG. 5 (where nHex represents n-hexane, 3MP represents 3-methylpentane, and 22DMB represents 2,2-dimethylbutane). It can be seen that the film can efficiently separate the n-hexane isomer three-component system and the cyclohexanone / cyclohexanol system, respectively. n-Hexane and 3-methylpentane can permeate through the film, while 2,2-dimethylbutane cannot permeate through the film. The film exhibits excellent n-hexane, 3-methylpentane, and cyclohexanone permeation selectivity, respectively. Example 2

[0099] This example provides an oriented Al-bttotb film. The preparation steps are basically the same as those in Example 1, except that the porous alumina support after polishing in step (1) was subjected to surface chemical modification to adjust the surface properties from hydrophilicity to lipophilicity: the alumina support was immersed in a 2 wt.% dimethyldichlorosilane solution in n-heptane, and after reaction at room temperature for 2 h, the alumina support was washed with deionized water for 3 times, and was ready for use. In addition, water was introduced as a cosolvent in the supersaturated solution in step (4), and the volume ratio of DMF to water was 3:1. The total volume of the two solvents was still 20 mL. Finally, a highly c-axis oriented Al-bttotb film was obtained.

[0100] The highly c-axis oriented Al-bttotb film was subjected to scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) tests, and the results are shown in FIGS. 6 and 7, respectively. It can be seen that a continuous and dense Al-bttotb film with a highly 1D channel orientation was successfully prepared on the porous support, with a thickness of about 10 μm.

[0101] The pervaporation separation test was performed on the aforementioned oriented Al-bttotb membrane, and the results are shown in FIG. 8. It can be seen that the separation performance of the membrane for the hexane isomer three-component system and the cyclohexanone / cyclohexanol system is multiplied compared with the random oriented membrane of Example 1, especially the permeation fluxes of n-hexane and cyclohexanone. Example 3

[0102] This example provides an Al-bttotb membrane, the preparation steps of which are basically the same as those of Example 1, except that the porous sheet-shaped alumina support is replaced by a porous tubular alumina support. The SEM image of the finally obtained membrane is shown in FIG. 9. It can be seen that a high-quality continuous Al-bttotb membrane is successfully prepared, indicating that the method of the present application can be applied to various support carriers and has universality. Example 4

[0103] This example provides an Al-bttotb membrane, the preparation steps of which are basically the same as those of Example 1, except that the porous sheet-shaped alumina support is replaced by a porous PVDF support. The SEM image of the finally obtained membrane is shown in FIG. 10. It can be seen that a high-quality continuous Al-bttotb membrane is successfully prepared, indicating that the method of the present application can be applied to various support carriers and has universality. Example 5

[0104] This example provides a MIL-53 membrane prepared by using a low-crystal aggregate induction method, and the preparation steps are as follows:

[0105] (1) The same as Example 1;

[0106] (2) Nanoscale MIL-53 particles with a particle size of 150 nm were prepared by a solvothermal method and a mechanical ball milling method, and a seed dispersion solution was prepared in the same way as Example 1.

[0107] (3) The same as Example 1.

[0108] (4) 0.4 g of aluminum nitrate nonahydrate, 0.6 g of 1,4-benzenedicarboxylic acid and 0.8 g of benzoic acid were dissolved in 20 mL of DMF solvent to prepare a supersaturated solution, and the supersaturated solution was transferred to a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, and then the support on which the MIL-53 nanocrystals were deposited was vertically placed therein, and reacted at 150°C for 1 h, so that the nanocrystal layer was converted into a continuous low-crystal MOF aggregate layer.

[0109] (5) The support with the low-crystalline MOF aggregate layer grown thereon is vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and reacted at 200°C for 3 h, so as to convert the low-crystalline structure into a MIL-53 film with a highly ordered lattice.

[0110] The SEM image 11 and the XRD image 12 of the MIL-53 film prove the successful preparation of the high-quality MIL-53 film with a thickness of about 13.8 μm. The pervaporation separation test (Fig. 13, where Flux is flux, SF is separation factor, and the feed concentration is the mass ratio of acetic acid and water) of the film shows that the film can separate the acetic acid / water system and exhibits excellent acetic acid permeation selectivity and permeability. Example 6

[0111] This example provides a MIL-160 film prepared by using a low-crystalline aggregate induction method, and the preparation steps are specifically as follows:

[0112] (1) The same as in Example 1;

[0113] (2) The MIL-160 nanoparticles with a particle size of 150 nm are prepared by a solvothermal method and a mechanical ball milling method, and the seed dispersion liquid is prepared in the same manner as in Example 1.

[0114] (3) The same as in Example 1.

[0115] (4) 0.4 g of aluminum chloride, 0.6 g of 2,5-furan dicarboxylic acid, and 0.8 g of sodium formate are taken and dissolved in 20 mL of a DMF / water mixed solvent (volume ratio of 3:1) to prepare a supersaturated solution, the supersaturated solution is transferred into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and then the support with the MIL-160 nanoseeds deposited thereon is vertically placed therein, and reacted at 100°C for 1 h, so as to convert the nanoseed layer into a continuous low-crystalline MOF aggregate layer.

[0116] (5) The support with the low-crystalline MOF aggregate layer grown thereon is vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and reacted at 100°C for 3 h, so as to convert the low-crystalline structure into a MIL-160 film with a highly ordered lattice.

[0117] The SEM image 14 and the XRD image 15 of the film prove the successful preparation of the high-quality MIL-160 film with a thickness of about 30 μm. The pervaporation separation test (Fig. 16) of the film shows that the film can separate the xylene isomer system and exhibits excellent p-xylene permeation selectivity and permeability. Example 7

[0118] The present embodiment provides a CAU-10-H film prepared by using a low-crystal aggregate induction method, and the preparation steps are as follows:

[0119] (1) The same as in Embodiment 1;

[0120] (2) Nanoscale CAU-10-H particles with a particle size of 50 nm are prepared by a solvothermal method, and a seed dispersion solution is prepared in the same manner as in Embodiment 1.

[0121] (3) The same as in Embodiment 1.

[0122] (4) 0.4 g of aluminum sulfate, 0.6 g of isophthalic acid and 0.8 g of sodium hydroxide are taken, dissolved in 20 mL of water to prepare a supersaturated solution, and the supersaturated solution is transferred to a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, then the support on which the CAU-10-H nanocrystal seeds are deposited is vertically placed therein, and reacted at 100°C for 1 h, so that the nanocrystal seed layer is converted into a continuous low-crystal MOF aggregate layer.

[0123] (5) The support on which the low-crystal MOF aggregate layer is grown is vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, and reacted at 100°C for 3 h, so that the low-crystal structure is converted into a CAU-10-H film with a highly ordered lattice.

[0124] The SEM image 17 and the XRD image 18 of the film confirm the successful preparation of the high-quality CAU-10-H film. The pervaporation separation test (Figure 19) of the film shows that the film can separate carbon dioxide / methane, carbon dioxide / nitrogen and ethylene / ethane systems, and exhibits excellent separation selectivity, where Perma, Hollerpu and Shimadzu respectively refer to the corresponding components tested by the detection instruments of the corresponding manufacturers. Embodiment 8

[0125] The present embodiment provides a KMF-1 film prepared by using a low-crystal aggregate induction method, and the preparation steps are as follows:

[0126] (1) The same as in Embodiment 1;

[0127] (2) Nanoscale KMF-1 particles with a particle size of 100 nm are prepared by a solvothermal method, and a seed dispersion solution is prepared in the same manner as in Embodiment 1.

[0128] (3) The same as in Embodiment 1.

[0129] (4) Take 0.4 g of aluminum chloride, 0.6 g of 2,5-pyrrole dicarboxylic acid and 0.8 g of sodium hydroxide, dissolve in 20 mL of water, and prepare a supersaturated solution. Transfer the supersaturated solution to a polytetrafluoroethylene (volume ~ 50 mL) reactor, then vertically place the support deposited with KMF-1 nanocrystal seeds therein, and react at 80°C for 1 h, so as to convert the nanocrystal seed layer into a continuous low-crystalline MOF aggregate layer.

[0130] (5) Vertically place the support with the low-crystalline MOF aggregate layer grown thereon into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and react at 80°C for 3 h, so as to convert the low-crystalline structure into a KMF-1 film with highly ordered lattice.

[0131] The SEM image 20 of the film proves the successful preparation of the high-quality KMF-1 film. The pervaporation separation test (Fig. 21) of the film shows that the film can separate the hexane isomer system and exhibits excellent separation selectivity. Example 9

[0132] This embodiment provides an Al-fum film prepared by using a low-crystalline aggregate induction method, and the preparation steps are as follows:

[0133] (1) The same as in Example 1;

[0134] (2) Prepare nanoscale Al-fum particles with a particle size of 100 nm by a solvothermal method, and prepare a seed dispersion liquid in the same manner as in Example 1.

[0135] (3) The same as in Example 1.

[0136] (4) Take 0.4 g of sodium aluminate, 0.6 g of fumaric acid and 0.8 g of sodium acetate, dissolve in 20 mL of a DMF / water mixed solvent (volume ratio of 3:1), and prepare a supersaturated solution. Transfer the supersaturated solution to a polytetrafluoroethylene (volume ~ 50 mL) reactor, then vertically place the support deposited with Al-fum nanocrystal seeds therein, and react at 120°C for 1 h, so as to convert the nanocrystal seed layer into a continuous low-crystalline MOF aggregate layer.

[0137] (5) Vertically place the support with the low-crystalline MOF aggregate layer grown thereon into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and react at 80°C for 3 h, so as to convert the low-crystalline structure into a KMF-1 film with highly ordered lattice.

[0138] SEM 22 and XRD 23 of the film confirmed the successful preparation of high quality Al-fum film with a thickness of about 10 μm. The pervaporation separation test (Fig. 24) of the film showed that the film was able to separate the hexane isomer system, exhibiting excellent separation selectivity of n-hexane. Comparative Example 1

[0139] The procedure was substantially the same as in Example 1, except that in step (4), 0.4 g of aluminum chloride, 0.6 g of 4,4',4''-(phenyl-1,3,5-trioxo)-benzoic acid and 0.8 g of formic acid were replaced by 0.08 g of aluminum chloride, 0.06 g of 4,4',4''-(phenyl-1,3,5-trioxo)-benzoic acid and 0.8 g of formic acid, respectively, and the prepared solution was unsaturated. The low-crystalline MOF aggregates and Al-bttotb film prepared were subjected to scanning electron microscope SEM test, and the results are shown in Figs. 25-27. The low-crystalline Al-MOF aggregates on the surface of the porous support showed a discontinuous state (Fig. 25), and the film converted therefrom also had obvious grain boundary defects (Figs. 26-27). Comparative Example 2

[0140] The procedure was substantially the same as in Example 1, except that in step (4), no formic acid was added, i.e., no coordination regulator was added to the supersaturated solution. The low-crystalline growth and film growth were subjected to scanning electron microscope SEM test, and the results are shown in Figs. 28-30. It can be seen that no low-crystalline Al-MOF aggregates were obtained on the surface of the porous support (Fig. 28), and thus the Al-bttotb film with a high degree of lattice order could not be converted (Figs. 29-30). Comparative Example 3

[0141] Preparation of Al-bttotb film by common secondary crystal seed growth method:

[0142] Steps (1)-(3): same as in Example 1;

[0143] Step (4): 0.08 g of aluminum chloride, 0.12 g of 4,4',4''-(phenyl-1,3,5-trioxo)-benzoic acid and 0.8 g of formic acid were prepared into a reaction solution, and the reaction solution was transferred to a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle. The support on which the Al-bttotb nanocrystal seeds were deposited was directly placed vertically in the reaction kettle, and the reaction was carried out at 150 o C for 12 h. The Al-bttotb film prepared was subjected to scanning electron microscope SEM test, and the results are shown in Figs. 31-32. It can be seen that a continuous Al-bttotb film layer was obtained, but there were too many intergranular gaps, and the morphology was irregular.

[0144] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method of preparing an Al-MOF membrane material, characterized by: The preparation method comprises the following steps: 1) depositing Al-MOF crystal seeds on the surface of a porous support to obtain an Al-MOF crystal seed layer; 2) placing the porous support with the Al-MOF crystal seed layer deposited on the surface thereof in a supersaturated solution to perform a reaction, and growing a continuous low-crystal Al-MOF aggregate layer on the surface of the porous support; and 3) performing a crystallization reaction on the porous support with the continuous low-crystal Al-MOF aggregate layer grown on the surface thereof to obtain the Al-MOF film material; and the supersaturated solution comprises an aluminum salt, a ligand and a coordination regulator.

2. The method of claim 1, wherein: The aluminum salt is selected from a combination of one or more of aluminum nitrate, aluminum isopropylate, sodium metaaluminate, aluminum chloride, aluminum acetate, polyaluminum chloride and aluminum sulfate octadecahydrate; and / or the ligand is a carboxylic acid ligand, preferably the ligand is selected from a combination of one or more of 4,4',4''-(phenyl-1,3,5-trioxo)-benzoic acid, 1,4-benzenedicarboxylic acid, isophthalic acid, 2,5-furandicarboxylic acid, 2,5-pyrrole dicarboxylic acid and fumaric acid; and / or the coordination regulator is selected from an acidic coordination regulator or an alkaline coordination regulator, preferably the acidic coordination regulator is selected from a combination of one or more of formic acid, acetic acid, benzoic acid and o-fluorobenzoic acid; and the alkaline coordination regulator is selected from a combination of one or more of sodium hydroxide, sodium formate and sodium acetate.

3. The method of claim 1, wherein: The total mass of the aluminum salt and the ligand accounts for 4%-20% of the mass of the supersaturated solution; and / or in the supersaturated solution, the mass ratio of the aluminum salt to the ligand is 1:1-1.5; and / or the mass of the coordination regulator accounts for 1%-5% of the mass of the supersaturated solution; and / or the solvent of the supersaturated solution is selected from a combination of one or both of DMF and water.

4. The method of claim 1, wherein: The preparation method further comprises a step of preparing the supersaturated solution: dissolving the aluminum salt in a solvent, adding the ligand and the coordination regulator to the solvent, and stirring at room temperature to obtain the supersaturated solution.

5. The method of claim 1, wherein: The thickness of the low-crystal Al-MOF aggregate layer is 1-3 μm.

6. The method of claim 1, wherein: The reaction in step 2) is performed at 80-150 ℃; and / or the reaction in step 2) is performed for 0.5-2 h; and / or the reaction in step 2) is performed in a closed reactor.

7. The method of claim 1, wherein: The crystallization reaction in step 3) is performed at 80-150 ℃; and / or the crystallization reaction in step 3) is performed for 3-10 h; and / or the crystallization reaction in step 3) is performed in a closed reactor.

8. The method of claim 1, wherein: The Al-MOF crystal seeds are the same as the Al-MOF crystals in the Al-MOF film material, or the Al-MOF crystal seeds have the same topological structure as the Al-MOF crystals in the Al-MOF film material; and / or the particle size of the Al-MOF crystal seeds is 50-300 nm; and / or the deposition in step 1) is achieved by a hot drop coating method, a spin coating method, a vacuum suction filtration method or a slide coating method, wherein the hot drop coating method comprises a step of preheating the porous support and a step of drop coating; and / or the thickness of the Al-MOF crystal seed layer is 0.5-5 μm.

9. The method of claim 1, wherein: The Al-MOF seed crystals are prepared by a preparation method selected from one or both of a solvothermal method and a mechanical ball milling method; and / or, the preparation method further comprises a step of polishing or ultrasonic cleaning the porous support and drying the porous support before depositing the Al-MOF seed crystals.

10. The method of claim 1, wherein: The porous support is selected from a porous alumina support or a porous polymer support; preferably, the porous alumina support has a pore size of 100-300 nm, and the porous alumina support is in a plate type, a tube type or a hollow fiber type; and the porous polymer support is made of a material selected from nylon, polyacrylonitrile, polydimethylsiloxane, polyethersulfone or polyvinylidene fluoride.

11. The method of claim 1, wherein: The Al-MOF is selected from a combination of one or more of Al-bttotb, MIL-53, CAU-10-H, CAU-23, MIL-160, KMF-1 and Al-fum.

12. An Al-MOF membrane material prepared by the preparation method of any one of claims 1-11.

13. Use of the Al-MOF membrane material of claim 12 for separation of carbon dioxide / methane, carbon dioxide / nitrogen, ethylene / ethane, hexane isomers, cyclohexanol / cyclohexanone, xylene isomers, acetic acid / water.

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