A method for inducing low-crystalline aggregate structure to prepare a supported MOF membrane, the MOF membrane and applications

Abstract

The application relates to a method for preparing a supported MOF membrane by inducing a low-crystal aggregate structure, an MOF membrane and application. 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 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 to obtain the Al-MOF membrane material; the supersaturated solution comprises an aluminum salt, a ligand and a coordination regulator. The method 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.

Description

TECHNICAL FIELD

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

[0002] Sub-nanometer scale separation processes, including selective transport 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 effects.

[0003] Membrane materials are the core of membrane separation technology. Polymer membrane materials have driven the development of membrane technology application systems from the microscale to the nanoscale. However, for sub-nanometer scale molecular separation needs, existing commercialized 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 their research and application in the field of molecular scale separation membranes.

[0004] Metal-organic frameworks (MOFs) are a new type of porous crystalline material assembled by metal ions or ion clusters and organic ligands. Compared to traditional zeolite molecular sieve materials, MOFs not only have regular and penetrating nanochannels, but also, in particular, the pore size of MOFs can be designed and precisely adjusted at the sub-nanometer scale.

[0005] High-stability MOFs formed by coordination of high-valence metal cations and carboxylic acid organic ligands have excellent thermal, chemical, and mechanical stability. MOF membranes precisely constructed therefrom are expected to meet the precise and stable separation needs of molecular scale separation systems. However, existing technologies are mostly for 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 Al-based MOF materials tend to grow into rods, with inconsistent growth rates in each direction axis, 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 materials is high, making it difficult to precisely control and balance the nucleation rate and growth direction of MOFs, and the topological morphology is mainly anisotropic rod-shaped crystals, making it difficult to grow and coexist, inevitably producing grain 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 grain boundary symbiosis of the membranes is poor, and the grain 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 membrane, and the separation performance of the membrane 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 the amount of solute in the solution exceeding 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, etc. The divalent MOF material is easy to control its nucleation rate and crystal growth direction when forming a crystal, and it is easy to make the growth rate of each direction about the same, and then it is easy to obtain a spherical crystal nucleus, and the spherical crystal nucleus is continuously grown, and it is easy to grow into a continuous MOF membrane. However, for high-valence MOF materials such as Al-MOF materials, etc., 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 crystal, 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 then 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 crystallization, 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 the group consisting of one or more of a combination 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 the group consisting of one or more of a combination 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 the group consisting of one or more of a combination of formic acid, acetic acid, benzoic acid, and o-fluorobenzoic acid.

[0019] In some embodiments, the basic coordination regulator is selected from the group consisting of one or more of a combination 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 and 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 to 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 to 10 minutes.

[0027] In some embodiments, the thickness of the low-crystal Al-MOF aggregate layer is 1 to 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 to 150°C.

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

[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 to 150°C.

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

[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 preheating step of the porous support and a drop coating step.

[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 refer 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 performed 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 support or a porous polymer support.

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

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

[0051] In some embodiments, the porous alumina support 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 a combination of one or more of 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 the separation of 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 use of the above technical solutions, the application has the following advantages compared with the prior art:

[0059] (1) The present application utilizes the continuous low-crystalline aggregate layer to transform and grow into a dense Al-MOF film layer, which is significantly different from the most common seed-second growth method, which relies on the independent growth of single seeds to prepare a continuous MOF film. The continuous layer to continuous layer transformation of the present application ingeniously avoids the problem of grain boundary incompatibility when single seeds grow independently into a film, reduces the difficulty of preparing a dense film MOF film, and realizes the universal preparation of high-valence MOF films 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, etc., and the film material has excellent separation performance and running stability in the molecular separation system. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

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

[0065] Figure 5 Separation performance diagram of the Al-bttotb film prepared in Example 1;

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

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

[0068] Figure 8 Separation performance diagram of the oriented Al-bttotb film prepared in Example 2;

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

[0070] Figure 10SEM image of PVDF supported Al-bttotb membrane prepared for Example 4;

[0071] Figure 11 SEM image of MIL-53 membrane prepared for Example 5;

[0072] Figure 12 XRD pattern of MIL-53 membrane prepared for Example 5;

[0073] Figure 13 Separation performance plot of MIL-53 membrane prepared for Example 5;

[0074] Figure 14 SEM image of MIL-160 membrane prepared for Example 6;

[0075] Figure 15 XRD pattern of MIL-160 membrane prepared for Example 6;

[0076] Figure 16 Separation performance plot of MIL-160 membrane prepared for Example 6;

[0077] Figure 17 SEM image of CAU-10-H membrane prepared for Example 7;

[0078] Figure 18 XRD pattern of CAU-10-H membrane prepared for Example 7;

[0079] Figure 19 Separation performance plot of CAU-10-H membrane prepared for Example 7;

[0080] Figure 20 SEM image of KMF-1 membrane prepared for Example 8;

[0081] Figure 21 Separation performance plot of KMF-1 membrane prepared for Example 8;

[0082] Figure 22 SEM image of Al-fum membrane prepared for Example 9;

[0083] Figure 23 XRD pattern of Al-fum membrane prepared for Example 9;

[0084] Figure 24 Separation performance plot of Al-fum membrane prepared for Example 9;

[0085] Figure 25 SEM image of low crystalline MOF aggregate layer prepared for Comparative Example 1;

[0086] Figure 26-27 SEM image of membrane prepared for Comparative Example 1;

[0087] Figure 28-30 SEM image of low crystal growth and film growth of Comparative Example 2;

[0088] Figure 31-32 SEM image of the film 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.

[0090] Example 1

[0091] The present embodiment provides an Al-bttotb film prepared by a low crystal aggregate state induction method, and the preparation steps are as follows:

[0092] (1) The porous sheet type alumina support body (pore size of 200 nm) was polished with 600 mesh and 1200 mesh sandpaper for 5 min, then ultrasonic cleaned in methanol solution for 15 min, the ultrasonic frequency was 50 KHz, then placed in a 150°C vacuum drying oven for heat treatment for 2 h, then taken out and sealed for standby.

[0093] (2) Al-bttotb nanoparticles (particle size of 150 nm) were prepared by combining solvothermal method and mechanical ball milling method, specifically: metal and ligand were added to DMF / water / formic acid (15 / 5 / 1 mL) mixed solvent, stirred at room temperature for 30 minutes, then transferred to a 100 mL polytetrafluoroethylene reaction kettle, then the reaction kettle was transferred to an oven with a preset temperature of 150°C for 1 day. White crystals were obtained after the reaction cooled to room temperature. The white crystals are rod-shaped crystals of 10-20 μm. Then 1.5 g of rod-shaped crystals and 47 g of ball milling agate balls were added to the ball milling tank, and a vertical planetary ball mill XQM-12 was used to run at a rotation speed of 400 rpm for 240 minutes. The ball milling product was collected by differential centrifugation at 7000 rpm to obtain spherical crystals with a particle size of about 150 nm. Then the Al-bttotb nanoparticles prepared as described above were dispersed in a methanol solution to obtain a seed dispersion liquid, wherein the mass fraction of Al-bttotb nanoparticles was 0.015 wt.%.

[0094] (3) The seed dispersion liquid was coated on the porous alumina support body by hot drop coating, specifically: the support body was preheated to 80°C, then 1 mL of seed dispersion liquid was transferred to the polished side of the support body using a 1 mL pipette gun, dried for 30 s, and the above operation was repeated 3 times to obtain a uniform seed layer on the surface of the support body.

[0095] (4) Take 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, dissolve in 20 mL of DMF solvent, prepare a supersaturated solution, transfer the supersaturated solution to a polytetrafluoroethylene (volume ~ 50 mL) reactor, then vertically place the support deposited with Al-bttotb nanocrystal seeds in it, and react at 100°C for 1 h to convert the nanocrystal layer into a continuous low-crystalline MOF aggregate layer.

[0096] (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 a high temperature of 150°C for 3 h to convert the low-crystalline structure into an Al-bttotb film with a highly ordered lattice.

[0097] The low-crystalline MOF aggregate layer prepared in step (4) is subjected to scanning electron microscope (SEM) and powder X-ray diffraction (XRD) tests, and the results are shown in Figure 1 and 2 respectively, Figure 2 wherein the precursor layer corresponds to the support carrier containing the low-crystalline MOF aggregate layer, and it can be seen that a continuous low-crystalline MOF aggregate layer is formed on the surface of the porous alumina support, with a thickness of about 2 μm.

[0098] The Al-bttotb film prepared in step (5) is subjected to scanning electron microscope (SEM) and powder X-ray diffraction (XRD) tests (2D-XRD), and the results are shown in Figure 3 and 4 respectively, and it can be seen that a high-quality Al-bttotb film is successfully prepared on the porous support, with a continuous surface and cross section and no grain boundary defects, and a thickness of about 10 μm.

[0099] The aforementioned Al-bttotb film is subjected to pervaporation separation tests, and the results are shown in Figure 5 respectively (wherein nHex represents n-hexane, 3MP represents 3-methylpentane, and 22DMB represents 2,2-dimethylbutane), and 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, and the film exhibits excellent n-hexane, 3-methylpentane and cyclohexanone permeation selectivity, respectively.

[0100] Example 2

[0101] The embodiment provides an oriented Al-bttotb film, the preparation steps of which are basically same as those of the embodiment 1, and the only difference is that: the porous alumina support after the polishing treatment in the step (1) is subjected to surface chemical modification, and the surface properties thereof are adjusted from hydrophilicity to oleophilicity; the alumina support is immersed into a 2 wt.% dimethyldichlorosilane n-heptane solution, and after 2 h of reaction at room temperature, the alumina support is taken out and washed with deionized water for 3 times, and is prepared for use; in addition, water is introduced into the supersaturated solution in the step (4) as a cosolvent, and the volume ratio of DMF to water is 3:1, and the total volume of the two is still 20 mL. Finally, a highly c-axis oriented Al-bttotb film is obtained.

[0102] The highly c-axis oriented Al-bttotb film is subjected to scanning electron microscope (SEM) and powder X-ray diffraction (XRD) tests, and the results are shown in Figs. Figure 6 and 7 It can be seen that the continuous dense and highly 1D channel oriented Al-bttotb film with a thickness of about 10 μm is successfully prepared on the porous support.

[0103] The aforementioned oriented Al-bttotb film is subjected to a pervaporation separation test, and the result is shown in Fig. Figure 8 It can be seen that the separation performance of the film on the hexane isomer three-component system and the cyclohexanone / cyclohexanol system is doubled compared with the random oriented film of the embodiment 1, and especially the permeation fluxes of n-hexane and cyclohexanone.

[0104] Embodiment 3

[0105] The embodiment provides an Al-bttotb film, the preparation steps of which are basically same as those of the embodiment 1, and the only difference is that: the porous sheet type alumina support is replaced by a porous pipe type alumina support. The SEM image of the finally obtained film is shown in Fig. Figure 9 It can be seen that the high-quality continuous Al-bttotb film is successfully prepared, which shows that the method of the application can be applied to various support carriers and has universality.

[0106] Embodiment 4

[0107] The embodiment provides an Al-bttotb film, the preparation steps of which are basically same as those of the embodiment 1, and the only difference is that: the porous sheet type alumina support is replaced by a porous PVDF support. The SEM image of the finally obtained film is shown in Fig. Figure 10 It can be seen that the high-quality continuous Al-bttotb film is successfully prepared, which shows that the method of the application can be applied to various support carriers and has universality.

[0108] Embodiment 5

[0109] The present example provides a MIL-53 film prepared by a low-crystal aggregate induction method, and the preparation steps are as follows:

[0110] (1) The same as example 1;

[0111] (2) The MIL-53 particles of nanoscale are prepared by a solvothermal method and a mechanical ball milling method, and the particle size is 150 nm; and the seed dispersion solution is prepared in the same manner as example 1.

[0112] (3) The same as example 1.

[0113] (4) 0.4 g of aluminum nitrate nonahydrate, 0.6 g of 1,4-benzenedicarboxylic acid and 0.8 g of benzoic acid are taken, dissolved in 20 mL of DMF solvent 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 MIL-53 nanocrystals are deposited is vertically placed therein, and the nanocrystal layer is converted into a continuous low-crystal MOF aggregate layer at 150°C for 1 h.

[0114] (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 high-temperature reaction is carried out at 200°C for 3 h, so that the low-crystal structure is converted into a MIL-53 film with a highly ordered lattice.

[0115] SEM of MIL-53 film Figure 11 and X RD Figure 12 The successful preparation of the high-quality MIL-53 film with a thickness of about 13.8 μm is confirmed. The pervaporation separation test of the film Figure 13 (wherein Flux is the flux, SF is the separation factor, and the feed concentration is the mass ratio of acetic acid and water) shows that the film can separate the acetic acid / water system, and exhibits excellent acetic acid permeation selectivity and permeability.

[0116] Example 6

[0117] The present example provides a MIL-160 film prepared by a low-crystal aggregate induction method, and the preparation steps are as follows:

[0118] (1) The same as example 1;

[0119] (2) The MIL-160 particles of nanoscale are prepared by a solvothermal method and a mechanical ball milling method, and the particle size is 150 nm; and the seed dispersion solution is prepared in the same manner as example 1.

[0120] (3) The same as example 1.

[0121] (4) Take 0.4 g of aluminum chloride, 0.6 g of 2,5-furan dicarboxylic acid and 0.8 g of sodium formate, dissolve in 20 mL of DMF / water mixed solvent (volume ratio of 3:1), prepare a supersaturated solution, transfer the supersaturated solution to a polytetrafluoroethylene (volume ~ 50 mL) reactor, then vertically place the support deposited with MIL-160 nanocrystal seeds therein, react at 100°C for 1 h, and the nanocrystal layer can be converted into a continuous low-crystalline MOF aggregate layer.

[0122] (5) The support with the low-crystalline MOF aggregate layer grown thereon is vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and high-temperature reaction is carried out at 100°C for 3 h, so that the low-crystalline structure is converted into a MIL-160 film with a highly ordered lattice.

[0123] SEM of the film Figure 14 and X RD Figure 15 The successful preparation of the high-quality MIL-160 film with a thickness of about 30 μm is verified. The pervaporation separation test of the film Figure 16 ) shows that the film can separate the xylene isomer system and exhibits excellent permeation selectivity and permeability for p-xylene.

[0124] Example 7

[0125] This example provides a CAU-10-H film prepared by using a low-crystalline aggregate induction method, and the preparation steps are as follows:

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

[0127] (2) Nanoscale CAU-10-H particles with a particle size of 50 nm are prepared by a solvothermal method, and the seed dispersion liquid is prepared in the same manner as in Example 1.

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

[0129] (4) Take 0.4 g of aluminum sulfate, 0.6 g of isophthalic acid and 0.8 g of sodium hydroxide, dissolve in 20 mL of water, prepare a supersaturated solution, transfer the supersaturated solution to a polytetrafluoroethylene (volume ~ 50 mL) reactor, then vertically place the support deposited with CAU-10-H nanocrystal seeds therein, react at 100°C for 1 h, and the nanocrystal layer can be converted into a continuous low-crystalline MOF aggregate layer.

[0130] (5) The support with the low-crystalline MOF aggregate layer grown thereon is vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reactor, and high-temperature reaction is carried out at 100°C for 3 h, so that the low-crystalline structure is converted into a MIL-160 film with a highly ordered lattice.

[0131] SEM of the membrane Figure 17 and X RD Figure 18 The successful preparation of high-quality CAU-10-H membranes was confirmed. The pervaporation separation test Figure 19 ) of the membranes showed that the membranes were able to separate carbon dioxide / methane, carbon dioxide / nitrogen and ethylene / ethane systems, exhibiting excellent separation selectivity, where Fulii, Horipu and Shimadzu refer to the corresponding instruments for testing by the corresponding manufacturers.

[0132] Example 8

[0133] This example provides a KMF-1 membrane prepared by using a low-crystal aggregate induction method, and the preparation steps are as follows:

[0134] (1) The same as in Example 1;

[0135] (2) Nanoscale KMF-1 particles with a particle size of 100 nm were prepared by a solvothermal method, and a seed dispersion solution was prepared in the same manner as in Example 1.

[0136] (3) The same as in Example 1.

[0137] (4) 0.4 g of aluminum chloride, 0.6 g of 2,5-pyrrole dicarboxylic acid and 0.8 g of sodium hydroxide were taken, dissolved in 20 mL of water to prepare a supersaturated solution, and the supersaturated solution was transferred to a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, then the support on which the KMF-1 nanocrystal seeds were deposited was vertically placed therein, and reacted at 80°C for 1 h, so that the nanocrystal seed layer was converted into a continuous low-crystal MOF aggregate layer.

[0138] (5) The support on which the low-crystal MOF aggregate layer was grown was vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, and reacted at 80°C for 3 h, so that the low-crystal structure was converted into a KMF-1 membrane with a highly ordered crystal lattice.

[0139] SEM of the membrane Figure 20 The successful preparation of high-quality KMF-1 membranes was confirmed. The pervaporation separation test Figure 21 ) of the membranes showed that the membranes were able to separate hexane isomer systems, exhibiting excellent separation selectivity.

[0140] Example 9

[0141] This example provides an Al-fum membrane prepared by using a low-crystal aggregate induction method, and the preparation steps are as follows:

[0142] (1) The same as in Example 1;

[0143] (2) Nanoscale Al-fum particles with a particle size of 100 nm were prepared by a solvothermal method, and a seed dispersion liquid was prepared in the same manner as in Example 1.

[0144] (3) The same as in Example 1.

[0145] (4) 0.4 g of sodium aluminate, 0.6 g of fumaric acid and 0.8 g of sodium acetate were taken, dissolved in 20 mL of a DMF / water mixed solvent (volume ratio of 3:1), and prepared into a supersaturated solution. The supersaturated solution was transferred into a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, and then the support on which the Al-fum nanocrystals were deposited was vertically placed therein, and reacted at 120°C for 1 h, so as to convert the nanocrystal layer into a continuous low-crystalline MOF aggregate layer.

[0146] (5) The support on which the low-crystalline MOF aggregate layer was grown was vertically placed into a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, and reacted at 100°C for 3 h, so as to convert the low-crystalline structure into an Al-fum film with a highly ordered lattice.

[0147] SEM of the film Figure 22 and X RD Figure 23 The successful preparation of the high-quality Al-fum film with a thickness of about 10 μm was confirmed. The pervaporation separation test of the film Figure 24 indicated that the film could separate the hexane isomer system, and exhibited excellent separation selectivity of n-hexane.

[0148] Comparative Example 1

[0149] 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 respectively 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, and the prepared solution was unsaturated. The low-crystalline MOF aggregate and the Al-bttotb film prepared were subjected to a scanning electron microscope (SEM) test, and the results are shown in Figure 25-27 . The low-crystalline Al-MOF aggregate exhibited a discontinuous state on the surface of the porous support Figure 25 , and the film converted therefrom also had obvious grain boundary defects Figure 26-27 .

[0150] Comparative Example 2

[0151] The same as example 1, the only difference is that no formic acid is added in step (4), i.e. no coordination regulator is added in the supersaturated solution. Scanning electron microscope (SEM) test is performed on the low crystal growth and film growth, and the results are shown in Figure 28-30 ), it can be seen that no low crystal Al-MOF aggregate is obtained on the surface of the porous support Figure 28 ), and thus it cannot be used for conversion into Al-bttotb film with high lattice order Figure 29-30 ).

[0152] Comparative example 3

[0153] Preparation of Al-bttotb film by common secondary crystal seed growth method:

[0154] Steps (1)-(3): the same as example 1;

[0155] 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 are prepared into a reaction solution, and the reaction solution is transferred into a polytetrafluoroethylene (volume ~ 50 mL) reaction kettle, and the support on which Al-bttotb nanocrystals are deposited is directly placed vertically therein, and high-temperature reaction is performed at 150°C for 12 h. Scanning electron microscope (SEM) test is performed on the prepared Al-bttotb film, and the results are shown in Figure 31-32 , it can be seen that a continuous Al-bttotb film layer is obtained, but there are too many intercrystalline gaps, and the morphology is irregular.

[0156] 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 it 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; the supersaturated solution comprises an aluminum salt, a ligand and a coordination regulator, and the dissolved amounts of the aluminum salt, the ligand and the ligand regulator exceed the respective corresponding saturated solubilities; the aluminum salt is selected from a combination of one or more of aluminum nitrate, aluminum isopropoxide, sodium metaaluminate, aluminum chloride, aluminum acetate, polyaluminum chloride and aluminum sulfate octadecahydrate; the ligand is a carboxylic acid ligand and 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-pyrroledicarboxylic acid and fumaric acid; and the coordination regulator is selected from an acidic coordination regulator or an alkaline coordination regulator, 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.

2. 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.

3. The method of claim 1, wherein: 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 into 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 carrier or a porous polymer support.

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

12. 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.

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

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

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