Ultrathin defect-free MOF (Metal Organic Framework) mixed matrix membrane as well as preparation method and application thereof

Abstract

The invention belongs to the field of MOF (Metal Organic Framework) membranes, and relates to an ultrathin defect-free MOF mixed matrix membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: soaking the base membrane in a BPEI-metal salt ion aqueous solution, so that BPEI is uniformly attached to the surface layer of the polysulfone layer, and meanwhile, metal ions are uniformly riveted on the surface layer of the polysulfone layer; the preparation method comprises the following steps: pouring a mixed solution of a ligand and an organic phase monomer into one side of a polysulfone layer of a base membrane for soaking under the auxiliary condition of vacuum suction filtration, realizing interfacial polymerization reaction of a water phase monomer BPEI and the organic phase monomer while coordinating the ligand with metal ions, and cleaning and drying after the reaction is finished, thereby obtaining the ultrathin defect-free MOF mixed matrix membrane with highly interpenetrating MOF and PA. The membrane has a highly interpenetrating structure of MOF and PA, effectively improves intercrystalline defects on the surface of the membrane, realizes high permeation rate and good separation selectivity of the membrane material, and can be used for gas separation.

Description

Technical Field

[0001] The present invention belongs to the field of MOF membranes and relates to an ultra-thin defect-free MOF mixed matrix membrane and a preparation method and application thereof. Background Art

[0002] Membrane separation technology, with its advantages of small footprint, simple operation, high separation efficiency, energy conservation and environmental protection, strong scalability, and mild separation conditions, is widely used in the pharmaceutical, food, chemical, and environmental protection industries, generating significant economic and social benefits. It is considered a separation technology with great potential. In membrane applications, membrane materials with excellent separation selectivity are the core of membrane separation technology, determining the membrane's permselectivity, process design, membrane stability, and ultimately, the membrane's applicable system.

[0003] Metal-Organic Frameworks (MOFs) are crystalline porous materials formed by the self-assembly of metal ions or metal clusters with multidentate organic ligands containing oxygen, nitrogen, and other molecules through coordination bonds. Due to their advantages such as high porosity, large specific surface area, tunable pore size, and topological diversity, MOFs are widely used in adsorption separation, catalysis, and medicine. They hold particular promise for industrial application in membrane gas separation technology.

[0004] MOF mixed matrix membranes (MOF MMMs) typically refer to membranes prepared by uniformly distributing filler particles within a polymer matrix. Currently, due to limitations such as poor interfacial compatibility between MOFs and the support, uneven distribution of MOF materials, and intercrystalline defects within MOF, the permeation rate of MOF MMMs for gas separation is low, far from meeting the economic and technical requirements of practical applications. Therefore, the design and preparation of ultrathin separation membrane materials for gas separation that combine high permeation rate with good selectivity is of great significance for the large-scale preparation and industrial application of gas separation membranes. Summary of the Invention

[0005] In order to overcome the problems in the related art of poor interface compatibility, obvious intercrystalline defects on the membrane surface and poor separation selectivity of MOF MMMs used for gas separation, the present invention aims to provide an ultra-thin defect-free MOF mixed matrix membrane and its preparation method and application. The preparation of the ultra-thin defect-free MOF mixed matrix membrane is to simultaneously carry out the in-situ growth of MOF and the interfacial polymerization strategy to construct a highly interpenetrating structure of MOF and PA, effectively improve the intercrystalline defects on the membrane surface, achieve a higher permeation rate and good separation selectivity of the membrane material, and can be used for gas separation.

[0006] A first aspect of the present invention provides a method for preparing an ultrathin defect-free MOF mixed matrix membrane, the preparation method comprising the following steps:

[0007] S1. Immersing a base membrane having a polysulfone layer on one side in a BPEI-metal salt ion aqueous solution, causing the BPEI in the BPEI-metal salt ion aqueous solution to be uniformly attached to the surface of the polysulfone layer, while also causing the metal ions in the BPEI-metal salt ion aqueous solution to be uniformly riveted to the surface of the polysulfone layer, thereby obtaining a metal ion-loaded membrane;

[0008] S2. Under vacuum filtration, a mixed solution of the ligand and the organic phase monomer is poured into the side of the membrane with the metal ions for immersion treatment, so that the ligand is coordinated with the metal ions riveted on the polysulfone layer while realizing the interfacial polymerization reaction between the aqueous phase monomer BPEI and the organic phase monomer. After the reaction is completed, the membrane is cleaned and dried to obtain an ultra-thin defect-free MOF mixed matrix membrane with highly interpenetrating MOF and PA.

[0009] In some embodiments of the present invention, in step S1 of the above-mentioned preparation method, the immersion treatment of the base membrane in the BPEI-metal salt ion aqueous solution is specifically: pouring the BPEI-metal salt ion aqueous solution on the polysulfone layer of the base membrane, and allowing the polysulfone layer to soak in the BPEI-metal salt ion aqueous solution for 1-3 hours.

[0010] In some embodiments of the present invention, in the above preparation method, the BPEI-metal salt ion aqueous solution is BPEI-Zn 2+ Aqueous solution or BPEI-Zn 2+ / Co 2+ aqueous solution.

[0011] In some embodiments of the present invention, in the above preparation method, the BPEI-Zn 2+ / Co 2+ In the aqueous solution, the zinc ion concentration is 3% and the cobalt ion concentration is 0.75%-3%.

[0012] In some embodiments of the present invention, in the above preparation method, the ligand is 2-methylimidazole.

[0013] In some embodiments of the present invention, in the above preparation method, the organic phase monomer is 1,3,5-benzenetricarboxylic acid chloride.

[0014] In some embodiments of the present invention, in step S2 of the above preparation method, the soaking treatment is specifically: soaking the polysulfone layer with the metal ions fixed thereto in a mixed solution of the ligand and the organic phase monomer for 30-120 minutes.

[0015] The second aspect of the present invention provides an ultra-thin defect-free MOF mixed matrix membrane prepared by the above-mentioned preparation method.

[0016] In some embodiments of the present invention, the ultra-thin defect-free MOF mixed matrix membrane is composed of a MOF@PA selection layer, a polysulfone layer and a non-woven fabric layer arranged in sequence from top to bottom, and the MOF@PA selection layer is a separation selection layer in which MOF and PA are highly interpenetrating.

[0017] The third aspect of the present invention provides the use of the above-mentioned ultrathin defect-free MOF mixed matrix membrane in gas separation.

[0018] The embodiments of the present invention provide a method for constructing an ultrathin defect-free MOF mixed matrix membrane based on a coordinated growth strategy of in situ growth and interfacial polymerization, and a preparation method and application thereof, which have at least one of the following advantages:

[0019] (1) This invention, based on an in-situ growth and interfacial polymerization method, first anchors metal ions onto the base membrane and uniformly attaches aqueous monomers. Then, under vacuum filtration, the mixture reacts with a ligand and organic monomer solution to successfully prepare ultrathin, defect-free MOF MMMs. These MOF MMMs exhibit high permeation rates and excellent separation selectivity.

[0020] (2) The present invention prepares a MOF MMMs in which MOF heterogeneous nucleation growth and interfacial polymerization reaction proceed simultaneously, and uses BPEI-metal ion solution to modify the interface of the base membrane, so that the surface of the base membrane is uniformly attached with aqueous monomers and rich metal ions are riveted, thereby promoting the continuous densification growth of MOFs on the surface of the base membrane. At the same time, in the interfacial polymerization reaction of aqueous monomers and organic monomers, the poor interface compatibility between the MOF selection layer and the base membrane and the existence of intercrystalline defects in MOFs are improved, thereby realizing the density and defect-free MOFMMMs.

[0021] (3) The present invention introduces non-homologous metal ions into the BPEI-metal ion aqueous solution, thereby promoting the continuous densification growth of the MOF selective layer while constructing abundant metal active sites with strong affinity for gas molecules in MOF MMMs, further optimizing the gas separation selectivity of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0023] Figure 1Figures showing the morphology of ZIF@PA-1MMMs (a), ZIF@PA-2MMMs (b), and ZIF@PA-3MMMs (c): (1) low-magnification SEM image of the membrane surface; (2) medium-magnification SEM image of the membrane surface; (3) low-magnification SEM image of the membrane surface; (4) cross-sectional SEM image of the membrane; (5) AFM image of the membrane;

[0024] Figure 2 Figures representing the morphology of ZIF@PA-4MMMs (a), ZIF@PA-5MMMs (b), and ZIF@PA-6MMMs (c): (1) low-magnification SEM image of the membrane surface; (2) low-magnification SEM image of the membrane surface; (3) cross-sectional SEM image of the membrane;

[0025] Figure 3 is the structural representation diagram of the membrane: Figure 3 -(a) XRD spectra of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs obtained under experimental conditions; Figure 3 -(b) XRD spectra of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs obtained under experimental conditions;

[0026] Figure 4 This is the structural representation of the membrane: Figure 4 -(a) is the FTIR spectra obtained under the experimental conditions of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs, Figure 4 -(b) is the FTIR spectra obtained under the experimental conditions of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs;

[0027] Figure 5 is the gas separation performance of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs prepared in Examples 1-3: Figure 5 -(a) is the CO2 permeation rate of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under pure gas conditions; Figure 5 -(b) is the permeation rate of CH4 into ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under pure gas conditions; Figure 5 -(c) N2 permeation rates of ZIF@PA-1MMMs, ZIF@PA-2MMMs, and ZIF@PA-3MMMs under pure gas conditions; Figure 5-(d) CO2 / N2 separation selectivity of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under pure gas conditions; Figure 5 -(e) CO2 / CH4 separation selectivity of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under pure gas conditions; Figure 5 -(f) CH4 / N2 separation selectivity of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under pure gas conditions;

[0028] Figure 6 is the gas separation performance of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs prepared in Examples 1-3: Figure 6 -(a) is the CO2 permeation rate of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under mixed gas conditions; Figure 6 -(b) is the permeation rate of CH4 into ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under mixed gas conditions; Figure 6 -(c) N2 permeation rates of ZIF@PA-1MMMs, ZIF@PA-2MMMs, and ZIF@PA-3MMMs under mixed gas conditions; Figure 6 -(d) CO2 / N2 separation selectivity of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under mixed gas conditions; Figure 6 -(e) CH4 / N2 separation selectivity of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under mixed gas conditions; Figure 6 -(f) CO2 / CH4 separation selectivity of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs under mixed gas conditions;

[0029] Figure 7 The gas separation performance of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs prepared in Examples 4-6: Figure 7 -(a) is the CO2 permeation rate of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under pure gas conditions; Figure 7 -(b) is the permeation rate of CH4 into ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under pure gas conditions; Figure 7-(c) N2 permeation rates of ZIF@PA-4MMMs, ZIF@PA-5MMMs, and ZIF@PA-6MMMs under pure gas conditions; Figure 7 -(d) CH4 / N2 separation selectivity of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under pure gas conditions; Figure 7 -(e) CO2 / N2 separation selectivity of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under pure gas conditions; Figure 7 -(f) CO2 / CH4 separation selectivity of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under pure gas conditions;

[0030] Figure 8 The gas separation performance of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs prepared in Examples 4-6: Figure 8 -(a) is the CO2 permeation rate of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under mixed gas conditions; Figure 8 -(b) is the permeation rate of CH4 into ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under mixed gas conditions; Figure 8 -(c) N2 permeation rates of ZIF@PA-4MMMs, ZIF@PA-5MMMs, and ZIF@PA-6MMMs under mixed gas conditions; Figure 8 -(d) CO2 / N2 separation selectivity of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under mixed gas conditions; Figure 8 -(e) CH4 / N2 separation selectivity of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under mixed gas conditions; Figure 8 -(f) CO2 / CH4 separation selectivity of ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs under mixed gas conditions. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be further described in detail below through examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as limiting the present invention.

[0032] The models and manufacturers of the instruments used in the various embodiments of this application are as follows:

[0033] Field emission scanning electron microscope (SEM), model: Drop ShapeAnalyzer 100, manufactured by Bruker, Germany;

[0034] Atomic force microscope (AFM), model: Tensor II, produced by Hitachi, Japan;

[0035] X-ray diffraction (XRD), model: D2 Discover diffractometer, produced by Bruker, Germany;

[0036] Fourier transform infrared spectrometer (FTIR), model: ALPHAII, produced by Bruker, Germany;

[0037] The specifications and manufacturers of the various raw materials used in the examples of this application are all commercially available unless otherwise specified below:

[0038] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0039] Branched polyethyleneimine (BPEI) was purchased from San Chemical Technology Co., Ltd.;

[0040] 1,3,5-Benzenetricarboxylic acid chloride (TMC) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0041] m-phenylenediamine (MPD) was purchased from MacLean Biochemical Technology Co., Ltd.;

[0042] n-Hexane was purchased from MacLean Biochemical Technology Co., Ltd.;

[0043] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was purchased from MacLean Biochemical Technology Co., Ltd.;

[0044] 2-Methylimidazole, 99%, purchased from Aladdin Reagent Co., Ltd.

[0045] Anhydrous methanol, with a specification of 98%, was purchased from San Chemical Technology Co., Ltd.

[0046] Polysulfone (PSf) ultrafiltration membrane: average pore size 20-30nm, one side is non-woven fabric layer, provided by Zhongyi Filter Equipment Store in Zhouwangmiao Town, Haining City;

[0047] An embodiment of the first aspect of the present invention provides a method for preparing an ultrathin defect-free MOF mixed matrix membrane, the preparation method comprising the following steps:

[0048] S1. Immerse a base membrane having a polysulfone layer on one side in a BPEI-metal salt ion aqueous solution, so that the BPEI in the BPEI-metal salt ion aqueous solution is uniformly attached to the surface of the polysulfone layer, and at the same time, the metal ions in the BPEI-metal salt ion aqueous solution are uniformly riveted to the surface of the polysulfone layer, thereby obtaining a membrane with metal ion loading.

[0049] S2. Under vacuum filtration, a mixed solution of the ligand and the organic phase monomer is poured into the side of the membrane with the metal ions for immersion treatment, so that the ligand is coordinated with the metal ions riveted on the polysulfone layer while realizing the interfacial polymerization reaction between the aqueous phase monomer BPEI and the organic phase monomer. After the reaction is completed, the membrane is cleaned and dried to obtain an ultra-thin defect-free MOF mixed matrix membrane with highly interpenetrating MOF and PA.

[0050] The present invention first soaks the base membrane in a BPEI-metal salt ion aqueous solution to uniformly adhere the BPEI to the surface of the base membrane polysulfone layer, while uniformly riveting the metal ions to the base membrane polysulfone layer. Then, under vacuum filtration assistance, a mixed solution of the ligand and the organic phase monomer is poured into the polysulfone layer (the side of the membrane with the metal ions) for soaking, so that the ligand coordinates with the metal ions riveted to the polysulfone layer while achieving interfacial polymerization reaction between the aqueous phase monomer BPEI and the organic phase monomer. While ensuring the continuous growth of MOF, the PA layer formed by the interfacial polymerization is used to efficiently improve the MOF intercrystalline defects, construct a highly interpenetrating structure of MOF and PA, improve the spatial continuity problem of MOF, regulate the compatibility of the two-phase interface, achieve ultra-thin separation selection layer, and endow the membrane with excellent permeability rate and good separation selectivity.

[0051] In some embodiments of the present invention, in step S1 of the above preparation method, the immersion treatment of the base membrane in the BPEI-metal salt ion aqueous solution is specifically: pouring the BPEI-metal salt ion aqueous solution on the polysulfone layer of the base membrane and soaking it for 1-3 hours.

[0052] In some embodiments of the present invention, in step S1 of the above-mentioned preparation method, the base membrane is immersed in the BPEI-metal salt ion aqueous solution as follows: the base membrane coated with the polysulfone layer (PSf) is fixed on a vacuum filtration device with the side facing up, the BPEI-metal salt ion aqueous solution is measured and poured onto the surface of the base membrane, and after soaking for 1-3 hours, the excess solution is removed to obtain a membrane with a uniform metal ion load.

[0053] In some embodiments of the present invention, the BPEI-metal salt ion aqueous solution is BPEI-Zn 2+ aqueous solution.

[0054] In some embodiments of the present invention, the BPEI-metal salt ion aqueous solution is BPEI-Zn 2+ / Co 2+ Aqueous solution. Introduction of non-homologous metal ions Co 2+ , controllably construct reactive active sites with affinity for gas molecules in MOF MMMs, and enhance the ability of ultra-thin defect-free MOF mixed matrix membranes (MOF MMMs) to adsorb gas molecules.

[0055] In some embodiments of the present invention, in the above preparation method, the BPEI-Zn 2+ / Co 2+ In the aqueous solution, the zinc ion concentration is 3% and the cobalt ion concentration is 0.75%-3%.

[0056] In some embodiments of the present invention, in the above preparation method, the ligand is 2-methylimidazole.

[0057] In some embodiments of the present invention, in the above preparation method, the organic phase monomer is 1,3,5-benzenetricarboxylic acid chloride.

[0058] In some embodiments of the present invention, in step S2 of the above preparation method, the soaking treatment time is 30-120 minutes.

[0059] The second embodiment of the present invention provides an ultrathin defect-free MOF mixed matrix membrane prepared by the above-mentioned preparation method. The ultrathin defect-free MOF mixed matrix membrane comprises a MOF@PA selective layer, a polysulfone layer, and a non-woven fabric layer arranged in sequence from top to bottom.

[0060] The third aspect of the present invention provides the use of the above-mentioned ultrathin defect-free MOF mixed matrix membrane in gas separation.

[0061] The above technical implementation scheme will be illustrated by the following examples.

[0062] Example 1

[0063] Zn 2+ Preparation of BPEI aqueous solution: 2 g of BPEI and 3 g of Zn(NO3)2·6H2O were fully dissolved in 100 mL of deionized water solution and stirred for 1 h until completely homogeneous to obtain BPEI-Zn 2+ aqueous solution.

[0064] Preparation of ligand-TMC solution: 3.4 g of 2-methylimidazole and 0.2 g of 1,3,5-benzenetricarboxylic acid chloride were dissolved in 100 mL of n-hexane to obtain a ligand-organic phase monomer solution.

[0065] Preparation of membrane: First, fix the base membrane with the PSf-coated side facing up on a vacuum filtration device, and measure 50 mL of Zn 2+ -BPEI aqueous solution was poured onto the surface of the base membrane and soaked for 2 h. After removing the excess solution, a membrane with uniform metal ion loading was obtained.

[0066] Secondly, under the assistance of vacuum filtration, the ligand-TMC solution was poured into the membrane surface with uniform metal ion loading to carry out heterogeneous nucleation growth and interfacial polymerization reaction of MOF. After the reaction for 1 hour, it was taken out and placed in a 60°C oven to dry for 10 minutes. After drying, the impurities remaining on the membrane surface were cleaned with anhydrous methanol and placed in a 60°C oven to dry for 1 hour to obtain ZIF@PA-1MMMs.

[0067] The ZIF@PA-1MMMs membrane obtained above was scanned by SEM and AFM. The obtained SEM images are shown in the figure below. Figure 1 As shown, Figure 1 Figures a-(1), a-(2), and a-(3) are SEM images of the membrane surface at 200 nm, 400 nm, and 1 μm, respectively; Figure a-(4) is an SEM image of the membrane cross section at 300 nm; and Figure a-(5) is an AFM image of the membrane at 10 μm. It can be seen from Figures a-(1), a-(2), and a-(3) that when the heterogeneous nucleation growth and interfacial polymerization reaction of MOF are carried out for 1 hour, the surface of the ZIF@PA-1MMMs membrane is less granular and the particles are smaller. It can be seen from Figure a-(4) that the thickness of the obtained ZIF@PA-1MMMs is 99.25 nm, and it can be seen from Figure a-(5) that the roughness of the obtained ZIF@PA-1MMMs is 1.71 nm. This shows that the ZIF@PA-1MMMs prepared in Example 1 of the present invention are continuous, dense, and thin.

[0068] Example 2

[0069] Zn 2+ Preparation of BPEI aqueous solution: 2 g of BPEI and 3 g of Zn(NO3)2·6H2O were fully dissolved in 100 mL of deionized water solution and stirred for 1 h until completely homogeneous to obtain BPEI-Zn 2+ aqueous solution.

[0070] Preparation of ligand-TMC solution: 3.4 g of 2-methylimidazole and 0.2 g of 1,3,5-benzenetricarboxylic acid chloride were dissolved in 100 mL of n-hexane to obtain a ligand-TMC solution.

[0071] Preparation of membrane: First, fix the base membrane with the PSf-coated side facing up on a vacuum filtration device, and measure 50 mL of Zn 2+-BPEI aqueous solution was poured onto the surface of the base membrane and soaked for 2 h. After removing the excess solution, a membrane with uniform metal ion loading was obtained.

[0072] Secondly, under the assistance of vacuum filtration, the ligand-TMC solution was poured into the membrane surface with uniform metal ion loading to carry out heterogeneous nucleation growth and interfacial polymerization reaction of MOF. After the reaction for 2 hours, it was taken out and placed in a 60°C oven to dry for 10 minutes. After drying, the impurities remaining on the membrane surface were cleaned with anhydrous methanol and placed in a 60°C oven to dry for 1 hour to obtain ZIF@PA-2MMMs.

[0073] The ZIF@PA-2MMMs membrane obtained above was scanned by SEM and AFM. The obtained SEM images are shown in the figure below. Figure 1 As shown, Figure 1 Figures b-(1), b-(2), and b-(3) are SEM images of the membrane surface at 200 nm, 400 nm, and 1 μm, respectively; Figure b-(4) is an SEM image of the membrane cross section at 300 nm; and Figure b-(5) is an AFM image of the membrane at 10 μm. It can be seen from Figures b-(1), b-(2), and b-(3) that when the heterogeneous nucleation growth and interfacial polymerization reaction of MOF are carried out for 2 h, the surface granularity of the ZIF@PA-2MMMs membrane is more obvious and the particles are smaller. It can be seen from Figure b-(4) that the thickness of the obtained ZIF@PA-2MMMs is 103.62 nm, and it can be seen from Figure b-(5) that the roughness of the obtained ZIF@PA-2MMMs is 2.22 nm. This shows that the ZIF@PA-2MMMs prepared in Example 2 of the present invention are continuous and dense, and the membrane thickness has increased.

[0074] Example 3

[0075] Zn 2+ Preparation of BPEI aqueous solution: 2 g of BPEI and 3 g of Zn(NO3)2·6H2O were fully dissolved in 100 mL of deionized water solution and stirred for 1 h until completely homogeneous to obtain BPEI-Zn 2+ aqueous solution.

[0076] Preparation of ligand-TMC solution: 3.4 g of 2-methylimidazole and 0.2 g of 1,3,5-benzenetricarboxylic acid chloride were dissolved in 100 mL of n-hexane to obtain a ligand-TMC solution.

[0077] Preparation of membrane: First, fix the base membrane with the PSf-coated side facing up on a vacuum filtration device, and measure 50 mL of Zn 2+ -BPEI aqueous solution was poured onto the surface of the base membrane and soaked for 2 h. After removing the excess solution, a membrane with uniform metal ion loading was obtained.

[0078] Secondly, under the assistance of vacuum filtration, the ligand-TMC solution was poured into the membrane surface with uniform metal ion loading to carry out heterogeneous nucleation growth and interfacial polymerization reaction of MOF. After the reaction for 3 hours, it was taken out and placed in a 60°C oven to dry for 10 minutes. After drying, the impurities remaining on the membrane surface were cleaned with anhydrous methanol and placed in a 60°C oven to dry for 1 hour to obtain ZIF@PA-3MMMs.

[0079] The ZIF@PA-3MMMs membrane obtained above was scanned by SEM and AFM. The obtained SEM images are shown in the figure below. Figure 1 As shown, Figure 1 Figures c-(1), c-(2) and c-(3) are SEM images of the membrane surface at 200nm, 400nm and 1um respectively, and Figure c-(4) is a SEM image of the membrane cross section at 300nm; Figure c-(5) is an AFM image of the membrane at 10μm. Figure 1 As can be seen from Figures c-(1), c-(2), and c-(3) in Figure 3, when the heterogeneous nucleation growth and interfacial polymerization reaction of MOF are carried out for 3 hours, the surface of the ZIF@PA-3MMMs film is obviously granular and the particles are large. From Figure c-(4), it can be seen that the thickness of the obtained ZIF@PA-3MMMs is 144.2nm, and from Figure c-(5), it can be seen that the roughness of the obtained ZIF@PA-3MMMs is 6.7nm. This shows that the ZIF@PA-3MMMs prepared in Example 3 of the present invention are continuous and dense, and the film thickness is significantly increased.

[0080] Example 4

[0081] Zn 2+ -Co 2+ Preparation of BPEI aqueous solution: 2 g of BPEI, 3 g of Zn(NO3)2·6H2O and 0.75 g of Co(NO3)2·6H2O were fully dissolved in 100 mL of deionized water solution and stirred for 1 h until completely homogeneous to obtain BPEI-Zn 2+ -Co 2+ aqueous solution.

[0082] Preparation of ligand-organic phase monomer solution: 3.4 g of 2-methylimidazole and 0.2 g of 1,3,5-benzenetricarboxylic acid chloride were dissolved in 100 mL of n-hexane to obtain a ligand-organic phase monomer solution.

[0083] Preparation of membrane: First, fix the base membrane with the PSf-coated side facing up on a vacuum filtration device, and measure 50 mL of BPEI-Zn 2+ -Co 2+ The aqueous solution was poured onto the surface of the base membrane and soaked for 2 h. After removing the excess solution, a membrane with uniform metal ion loading was obtained.

[0084] Secondly, under the assistance of vacuum filtration, the ligand-TMC solution was poured into the membrane surface with uniform metal ion loading to carry out heterogeneous nucleation growth and interfacial polymerization reaction of MOF. After the reaction for 2 hours, it was taken out and placed in a 60°C oven to dry for 10 minutes. After drying, the impurities remaining on the membrane surface were cleaned with anhydrous methanol and placed in a 60°C oven to dry for 1 hour to obtain ZIF@PA-4MMMs.

[0085] The ZIF@PA-4MMMs membrane obtained above was scanned by SEM and AFM. The obtained SEM images are shown in the figure below. Figure 2 As shown, Figure 2 In the figure, a-(1) and a-(2) are SEM images of the membrane surface at 200nm and 1um respectively, and a-(3) is a SEM image of the membrane cross section at 400nm. It can be seen from a-(1) and a-(2) that when the heterogeneous nucleation growth and interfacial polymerization reaction of MOF are carried out for 2h and 0.75g of non-homologous Co is added 2+ When the ZIF@PA-4MMMs film surface is clearly granular and the particle size is uneven. As can be seen from Figure a-(3), the thickness of the obtained ZIF@PA-4MMMs is 103.62 nm. This shows that the ZIF@PA-4MMMs prepared in Example 4 of the present invention are continuous, dense, and thick.

[0086] Example 5

[0087] Zn 2+ -Co 2+ Preparation of BPEI aqueous solution: 2 g of BPEI, 3 g of Zn(NO3)2·6H2O and 1.5 g of Co(NO3)2·6H2O were fully dissolved in 100 mL of deionized water solution and stirred for 1 h until completely homogeneous to obtain BPEI-Zn 2+ -Co 2+ aqueous solution.

[0088] Preparation of ligand-TMC solution: 3.4 g of 2-methylimidazole and 0.2 g of 1,3,5-benzenetricarboxylic acid chloride were dissolved in 100 mL of n-hexane to obtain a ligand-TMC solution.

[0089] Preparation of membrane: First, fix the base membrane with the PSf-coated side facing up on a vacuum filtration device, and measure 50 mL of BPEI-Zn 2+ -Co 2+ The aqueous solution was poured onto the surface of the base membrane and soaked for 2 h. After removing the excess solution, a membrane with uniform metal ion loading was obtained.

[0090] Secondly, under the assistance of vacuum filtration, the ligand-TMC solution was poured into the membrane surface with uniform metal ion loading to carry out heterogeneous nucleation growth and interfacial polymerization reaction of MOF. After the reaction for 2 hours, it was taken out and placed in a 60°C oven to dry for 10 minutes. After drying, the impurities remaining on the membrane surface were cleaned with anhydrous methanol and placed in a 60°C oven to dry for 1 hour to obtain ZIF@PA-5MMMs.

[0091] The ZIF@PA-5MMMs membrane obtained above was scanned by SEM and AFM. The obtained SEM images are shown in the figure below. Figure 2 As shown, Figure 2 In the figure, b-(1) and b-(2) are SEM images of the membrane surface at 200nm and 1um respectively, and b-(3) is a SEM image of the membrane cross section at 400nm. It can be seen from b-(1) and b-(2) that when the heterogeneous nucleation growth and interfacial polymerization reaction of MOF are carried out for 2h and 1.5g of non-homologous Co is added 2+ When the ZIF@PA-5MMMs film surface is granular and evenly distributed, as can be seen from Figure b-(3), the thickness of the ZIF@PA-5MMMs obtained is 297.87 nm. This shows that the ZIF@PA-5MMMs prepared in Example 5 of the present invention are continuous and dense, and the film thickness is significantly increased.

[0092] Example 6

[0093] Zn 2+ -Co 2+ Preparation of BPEI aqueous solution: 2 g of BPEI, 3 g of Zn(NO3)2·6H2O and 3 g of Co(NO3)2·6H2O were fully dissolved in 100 mL of deionized water solution and stirred for 1 h until completely homogeneous to obtain BPEI-Zn 2+ -Co 2+ aqueous solution.

[0094] Preparation of ligand-TMC solution: 3.4 g of 2-methylimidazole and 0.2 g of 1,3,5-benzenetricarboxylic acid chloride were dissolved in 100 mL of n-hexane to obtain a ligand-TMC solution.

[0095] Preparation of membrane: First, fix the base membrane with the PSf-coated side facing up on a vacuum filtration device, and measure 50 mL of BPEI-Zn 2+ -Co 2+ The aqueous solution was poured onto the surface of the base membrane and soaked for 2 h. After removing the excess solution, a membrane with uniform metal ion loading was obtained.

[0096] Secondly, under the assistance of vacuum filtration, the ligand-TMC solution was poured into the membrane surface with uniform metal ion loading to carry out heterogeneous nucleation growth and interfacial polymerization reaction of MOF. After the reaction for 2 hours, it was taken out and placed in a 60°C oven to dry for 10 minutes. After drying, the impurities remaining on the membrane surface were cleaned with anhydrous methanol and placed in a 60°C oven to dry for 1 hour to obtain ZIF@PA-6MMMs.

[0097] The ZIF@PA-6MMMs membrane obtained above was scanned by SEM and AFM. The obtained SEM images are shown in the figure below. Figure 2 As shown, Figure 2 In the figure, c-(1) and c-(2) are SEM images of the membrane surface at 200nm and 1um respectively, and c-(3) is a SEM image of the membrane cross section at 400nm. It can be seen from c-(1) and c-(2) that when the heterogeneous nucleation growth and interfacial polymerization reaction of MOF are carried out for 2h and 3g of non-homologous Co is added 2+ When the ZIF@PA-5MMMs membrane surface is significantly accumulated and the particles are relatively large. As can be seen from Figure c-(3), the thickness of the ZIF@PA-6MMMs obtained is 544.2 nm. This shows that the ZIF@PA-6MMMs prepared in Example 6 of the present invention are continuous and dense, and the membrane thickness increases.

[0098] The ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs in Examples 1, 2 and 3 were tested by XRD and FTIR. The results are shown in the figure. Figure 3 Figure a and Figure 4 As shown in Figure a. Figure 3 As can be seen in Figure a, with the increase of in-situ growth and interfacial polymerization reaction time, the crystal structure of MOF is improved and the crystallinity increases. Figure 4 As can be seen from Figure a, with the increase of in-situ growth and interfacial polymerization reaction time, the Zn-N characteristic peak of MOF increases significantly, indicating that with the increase of reaction time, the in-situ growth of MOF on the base film is significantly improved.

[0099] The ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs in Examples 3, 4 and 5 were tested by XRD and FTIR. The results are shown in the figure. Figure 3 Figure b and Figure 4 As shown in Figure b. Figure 3 As can be seen in Figure b, when the optimal in situ growth and interfacial polymerization reaction time is selected, as the mass fraction of non-homologous metal ions increases, the crystal structure of MOF is significantly improved and the crystallinity is significantly increased. Figure 4It can be seen from Figure b that with the increase of the mass fraction of non-homologous metal ions, the Zn-N characteristic peak of MOF is higher, indicating that with the increase of the mass fraction of non-homologous metal ions, the in situ growth of MOF on the base membrane is significantly improved.

[0100] Test Case

[0101] For single gas permeation measurements, the membranes were mounted in stainless steel cells (effective membrane area = 0.25 cm 2 ), and the raw gas pressure is maintained at 0.5-2.0 bar (gauge pressure, transmembrane pressure), which is controlled by a precise pressure gauge.

[0102] The permeation gas flux was measured by a soap bubble flowmeter, and the gas permeability R (GPU, 1GPU = 1 × 10 -6 cm 3 (STP) cm -2 ·s -1 cmHg -1 =3.35×10 -10 mol·s -1 ·m -2 ·Pa -1 ) by the formula definition.

[0103] Where N i (mo ls -1 ) is the molar flow rate of the permeating component i, A(m 2 ) is the effective membrane area, Δp i (Pa) is the pressure difference between membranes. Ideal selectivity α i / j The permeability ratio of gas component i to component j is calculated according to the formula calculate.

[0104] The mixed gas permeability was measured using a laboratory-made stainless steel instrument at 30°C and 0.5-2.0 bar using a mixture of dry C3H6 / C3H8 (50 / 50 by volume), CH4 / N2 (50 / 50 by volume), and CO2 / N2 (50 / 50 by volume). The membrane gas permeability was measured using a constant pressure test device. The total feed gas flow rate was 40 mL / min. -1 The transmembrane pressure is controlled by the back pressure valve on the feed side. Dry helium is used as the downstream sweep gas (50mLmin -1 ) carries the permeate gas into a gas chromatograph. Downstream sweep gas composition is analyzed using a gas chromatograph equipped with a thermal conductivity detector (HP7890, PorapakN). Three different samples were measured for each membrane, with 18 points selected for each sample. Average permeate data and their standard deviations were obtained.

[0105] The permeation rates and gas separation selectivities of ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs obtained in Examples 1-3 were measured under pure gas and mixed gas conditions. The measured data are shown in the figure. Figure 5 and Figure 6 shown.

[0106] As can be seen from the figure, the ZIF@PA-1MMMs, ZIF@PA-2MMMs and ZIF@PA-3MMMs of the present application separate CH4, CO2 and N2 at different pressures. Under the pure gas condition of 2 bar, the CO2 permeation rates are 8990.41GPU, 7730.26GPU and 7341.76GPU, respectively; the CH4 permeation rates are 1000.565GPU, 860.88GPU and 726.49GPU, respectively; the N2 permeation rates are 371.24GPU, 166.67GPU and 132.93GPU, respectively; the CH4 / N2 selectivities are 4.02, 5.16 and 5.47, respectively; the CO2 / CH4 selectivities are 8.98, 8.97 and 10.69, respectively; and the CO2 / N2 selectivities are 38.6, 42.04 and 43.25, respectively. Through performance characterization, it can be seen that with the increase of in situ growth and interfacial polymerization reaction time, the permeation rate of the prepared membrane decreases significantly, but the gas separation selectivity of the membrane increases significantly, which shows that the gas separation performance of MOF MMMs obtained by the preparation method of MOF MMMs of the present application is significantly improved with the increase of reaction time. This may be because with the increase of reaction time, the crystallinity of MOF increases significantly, and the PA layer formed by the interfacial polymerization reaction reduces the intercrystalline defects of MOF, resulting in a significant decrease in the permeation rate of the membrane and a significant increase in the selectivity.

[0107] Based on the regulation of in-situ growth and interfacial polymerization reaction time, and through the changes in membrane separation selectivity, it can be determined that when the in-situ growth and interfacial polymerization reaction time is 2h, the membrane performance and membrane morphology are best.

[0108] In order to further optimize the gas separation performance of the membrane, the introduction of non-homologous metals was carried out, such as Figure 7 and Figure 8The ZIF@PA-4MMMs, ZIF@PA-5MMMs and ZIF@PA-6MMMs of the present application were used to separate CH4, CO2 and N2 at different pressures. Under the pure gas condition of 2 bar, the CO2 permeation rates were 7151.86GPU, 6124.03GPU and 5822.66GPU, respectively; the CH4 permeation rates were 887.75GPU, 694.88GPU and 599.71GPU, respectively; the N2 permeation rates were 265.32GPU, 128.67GPU and 118.89GPU, respectively; the CH4 / N2 selectivities were 5.02, 6.01 and 6.12, respectively; the CO2 / CH4 selectivities were 9.07, 11.02 and 11.20, respectively; and the CO2 / N2 selectivities were 46.81, 48.93 and 51.04, respectively. Through performance characterization, it can be seen that with the increase of the mass fraction of non-homologous metals, the permeation rate of the prepared membrane further decreases, but the gas separation selectivity of the membrane increases significantly, which shows that the gas separation performance of MOF MMMs obtained by the preparation method of MOF MMMs of the present application is significantly improved due to the increase of the mass fraction of non-homologous metals. This may be because with the increase of the mass fraction of non-homologous metals, the crystallinity of MOF increases significantly, enriching the metal active sites in the membrane, which is conducive to the preferential adsorption of gas molecules, resulting in a significant increase in the gas separation selectivity of the membrane.

[0109] In summary, the present application discloses a method for constructing an ultra-thin defect-free MOF mixed matrix membrane and its preparation method based on a coordinated growth strategy of in situ growth and interfacial polymerization. The entire process is carried out at room temperature. First, based on the simultaneous in situ growth and interfacial polymerization strategies, rich metal ions are riveted in the interface layer of the polymer support and a uniform aqueous monomer (BPEI) layer is loaded. Secondly, the ligand and organic monomer (TMC) solution are immersed under vacuum-assisted filtration conditions, and the in situ growth and interfacial polymerization reactions of MOF are carried out simultaneously. While ensuring the uniform and dense in situ growth of MOF, the PA layer formed by interfacial polymerization is used to repair the intercrystalline defects of MOF, thereby realizing ultra-thin and dense growth of the membrane and solving the interface compatibility problem between MOFs and the polymer support. In addition, in order to further optimize the gas separation performance of the membrane, non-homologous metal ions are introduced to enrich the metal active sites in the membrane, increase the preferential adsorption of gas molecules, and achieve a significant improvement in the gas separation selectivity of the membrane.

[0110] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing an ultrathin defect-free MOF mixed matrix membrane, characterized in that: The preparation method comprises the following steps: S1. Immersing a base membrane having a polysulfone layer on one side in a BPEI-metal salt ion aqueous solution, causing the BPEI in the BPEI-metal salt ion aqueous solution to be uniformly attached to the surface of the polysulfone layer, while also causing the metal ions in the BPEI-metal salt ion aqueous solution to be uniformly riveted to the surface of the polysulfone layer, thereby obtaining a metal ion-loaded membrane; S2. Under vacuum filtration, a mixed solution of the ligand and the organic phase monomer is poured into the side of the membrane with the metal ions for immersion treatment, so that the ligand and the metal ions are coordinated while the interfacial polymerization reaction of the aqueous phase monomer BPEI and the organic phase monomer is realized. After the reaction is completed, the membrane is cleaned and dried to obtain an ultra-thin defect-free MOF mixed matrix membrane with highly interpenetrating MOF and PA.

2. The preparation method according to claim 1, characterized in that In step S1, the soaking treatment is specifically as follows: pouring the BPEI-metal salt ion aqueous solution on the polysulfone layer of the base membrane, and soaking the polysulfone layer in the BPEI-metal salt ion aqueous solution for 1-3 hours.

3. The preparation method according to claim 1, characterized in that The BPEI-metal salt ion aqueous solution is BPEI-Zn 2+ Aqueous solution or BPEI-Zn 2+ / Co 2+ aqueous solution.

4. The preparation method according to claim 3, characterized in that The BPEI-Zn 2+ / Co 2+ In the aqueous solution, the zinc ion concentration is 3% and the cobalt ion concentration is 0.75%-3%.

5. The preparation method according to claim 3, characterized in that The ligand is 2-methylimidazole.

6. The preparation method according to claim 1, characterized in that The organic phase monomer is 1,3,5-benzenetricarboxylic acid chloride.

7. The preparation method according to claim 1, characterized in that In step S2, the soaking treatment is specifically: soaking the polysulfone layer with the metal ions fixed thereto in a mixed solution of the ligand and the organic phase monomer for 30-120 minutes.

8. An ultra-thin defect-free MOF mixed matrix membrane prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the ultrathin defect-free MOF mixed matrix membrane according to claim 8 in gas separation.

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