CoNi-MOF powder, CoNi-MOF based hybrid membrane as well as preparation method and application of CoNi-MOF based hybrid membrane

Abstract

The invention belongs to the technical field of hybrid membrane preparation and gas separation, and particularly relates to CoNi-MOF powder, a CoNi-MOF-based hybrid membrane and a preparation method and application of the CoNi-MOF-based hybrid membrane. The alkyl chain is successfully introduced into the MOFs to construct the confinement nano channel. By utilizing the steric hindrance effect of an alkyl chain, the gradient regulation and control of the aperture is realized. The optimized hybrid membrane prepared by doping the CoNi-epoz into the PIM-1 / 6FDA-DAM blended polymer matrix shows excellent O2 / N2 separation performance, the O2 permeability is 275.5 Barrer, and the O2 / N2 selectivity is 7.2. Meanwhile, the membrane module prepared based on the CoNi-epoz hybrid membrane provides the O2 permeation rate of 47.5 GPU and the O2 / N2 selectivity of 5.1 under the feeding pressure of 1-3 bar, and the practical industrial application potential is shown.

Description

Technical Field

[0001] This invention belongs to the field of hybrid membrane preparation and gas separation technology, and specifically relates to a CoNi-MOF powder, a CoNi-MOF-based hybrid membrane, its preparation method and application. Background Technology

[0002] Air separation is a core process in modern chemical and energy industries. Oxygen and nitrogen, as basic industrial gases, play irreplaceable roles in metallurgy, chemical engineering, medical applications, electronics manufacturing, and clean energy. Although mainstream cryogenic distillation technology is mature, the close boiling points of oxygen (-183°C) and nitrogen (-196°C) result in drawbacks such as high energy consumption and large equipment investment. Therefore, developing new separation technologies with low carbon emissions and low energy consumption has become an urgent need for modern industry.

[0003] Membrane separation technology is widely recognized as an effective strategy for next-generation air separation due to its low energy consumption, simple operation, and high modularity. However, existing commercial polymer membranes are limited by the trade-off between permeability and selectivity, making it difficult to reach the minimum threshold for industrial applications. Overcoming this bottleneck requires the development of membrane materials with high separation performance. Hybrid membranes based on metal-organic frameworks (MOFs) show great potential in the field of O2 / N2 separation by synergistically combining the processability of the polymer matrix with the excellent separation performance of MOF packings.

[0004] MOF materials, due to their customizable crystal structures, ultra-high specific surface areas, and precisely tunable pore sizes, have been extensively studied as fillers for hybrid matrix membranes (MMMs). Given the similar physicochemical properties of O2 and N2 (polarizability: O2 is 15.812 × 10⁻⁶),... -25 cm -3 N2 is 17.403 × 10 -25 cm -3(Kinetic diameters: 3.46 Å for O2, 3.64 Å for N2); Membrane-based O2 / N2 separation is primarily regulated by a molecular sieving mechanism. This mechanism achieves preferential oxygen permeation and efficient separation by precisely adjusting the MOF pore size to fall between the kinetic diameters of O2 and N2. Among numerous MOF materials, ZIF-8 is widely used in O2 / N2 separation research due to its pore size (approximately 3.4 Å) being close to the O2 kinetic diameter. For example, Liu et al. prepared ZIF-8 / PIM-1 composite membranes by growing ZIF-8 particles on one side of PIM-1, improving the ideal O2 / N2 selectivity to 3.7; Jin et al. prepared ZIF-8-based MMMs using carboxylated PI as the polymer matrix, utilizing the nano-etching effect of carboxyl groups on ZIF-8 to ensure a tight bond between the filler and the polymer, resulting in an O2 permeability of 459.0 Barrer and an ideal O2 / N2 selectivity of 4.6; Hadi et al. prepared hollow fiber MMMs embedded with ZIF-8 nanoparticles using a dry-wet spinning method, significantly improving the O2 / N2 selectivity of the membrane samples by leveraging the molecular sieving ability of ZIF-8, with the optimal sample achieving an ideal selectivity of 5.25. Furthermore, Wang et al. combined ZIF-8 with Fe3O4, achieving highly efficient O2 / N2 separation through the synergistic effect of magnetic sieving and molecular sieving, with an O2 / N2 selectivity as high as 12.0 and an O2 permeability of 194 Barrer. These studies demonstrate the potential of ZIF-8 materials in the field of O2 / N2 separation.

[0005] However, the imidazole ligand of ZIF-8 exhibits rotational flexibility under external stimuli (such as temperature or pressure), leading to pore size expansion to 4.0-4.2 Å, significantly reducing its molecular sieving ability and thus limiting its application in O2 / N2 separation. To overcome this limitation, researchers have increasingly focused on rigid MOF materials with stable pore structures to construct high-performance MOF-based molecular molecular sieving (MMMs). For example, Xiang et al. achieved O2 / N2 molecular sieving by locking flexible ZIF-7 in a macroporous morphology (ZIF-7-I), obtaining MMMs with an O2 permeability of 3 Barrer and an O2 / N2 selectivity as high as 15; Cao et al. constructed a SIFSIX-3-Zn shell on the Fe3O4 surface, combining magnetic separation and synergistic sieving effects to achieve efficient O2 / N2 separation, with an O2 permeability of 365 Barrer and an ideal O2 / N2 selectivity of 6.88. Although these studies highlight the potential of hybrid membranes with molecular sieving effects, MOF materials with precisely tunable pore sizes remain very limited, and there is an urgent need to design novel MOFs with well-defined tunable pore structures. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a CoNi-MOF powder, a CoNi-MOF-based hybrid film, its preparation method, and its application.

[0007] This invention uses typical Hofmann-type MOF materials as a platform and employs a microwave-assisted synthesis method to graft alkyl chains (such as ethyl) onto the MOF framework, achieving controllable regulation of pore size and pore environment to form confined nanochannel structures suitable for O2 / N2 separation. Specifically, three functionalized Hofmann-type MOF materials were designed and synthesized by introducing carbon chains of different lengths through a mixed ligand strategy: CoNi-mpyz (methyl ligand), CoNi-epyz (ethyl ligand), and CoNi-ppyz (propyl ligand). The steric hindrance effect of the alkyl carbon chains was utilized to achieve gradient regulation of pore size, significantly enhancing the molecular sieving selectivity of the materials. Subsequently, the materials were blended with a polymer matrix, and a planar MOF-based hybrid membrane was prepared by a blade coating method. O2 / N2 separation tests were then performed directly using air as the feed gas.

[0008] The first objective of this invention is to provide a method for preparing CoNi-MOF, comprising the following steps: firstly, Co(NO3)2·6H2O and a pyrazine pyz-type mixed ligand are dissolved in a methanol / water mixed solution, then K2[Ni(CN)4]·nH2O aqueous solution is added, and the reaction is carried out in a microwave reactor. The reaction product is collected by centrifugation, washed three times with methanol, and activated in a vacuum oven at 60°C for 12 hours to finally obtain CoNi-MOF powder.

[0009] Furthermore, the molar ratio of the Co(NO3)2·6H2O and pyrazine pyz mixed ligands was 1:1, and the molar ratio of the K2[Ni(CN)4]·nH2O and pyrazine pyz mixed ligands was 1:1. The concentration of the K2[Ni(CN)4]·nH2O aqueous solution was 0.25 mmol / L; the concentration of Co(NO3)2·6H2O in the methanol / water mixed solution was 0.05 mmol / L; and the concentration of pyrazine pyz in the methanol / water mixed solution was 0.05 mmol / L.

[0010] Furthermore, the methanol / water mixture has a methanol:water volume ratio of 1:1. Furthermore, the microwave reaction conditions are 25°C for 2 minutes.

[0011] Furthermore, the pyrazine pyz mixed ligand is one of the following: a mixed ligand of pyrazine and 2-methylpyrazine, a mixed ligand of pyrazine and 2-ethylpyrazine, or a mixed ligand of pyrazine and 2-propylpyrazine, wherein the molar ratio of the two ligands in the mixed ligand is 1:1.

[0012] A second objective of this invention is to provide a method for preparing a CoNi-MOF-based hybrid film, comprising the following steps: S1. Disperse CoNi-MOF powder in chloroform and sonicate for 30 minutes to obtain a uniform suspension; S2. Dissolve PIM-1 and 6FDA-DAM polymer in MOF suspension and physically blend, stirring continuously for 24 hours; S3. The casting solution obtained in S2 is uniformly coated onto a glass plate by a scraping method, then transferred to a PDMS-coated PSf substrate, and finally the film sample is dried in a vacuum oven at 60°C for 12 hours.

[0013] Furthermore, the CoNi-MOF loading is 5-20 wt%.

[0014] Furthermore, the PIM-1 content is 5-15 wt%. The PIM-1 content is the percentage (wt%) of PIM-1 by mass relative to the total mass of PIM-1 and 6FDA-DAM polymer.

[0015] A third objective of this invention is to provide a CoNi-MOF-based hybrid film prepared by the above-described preparation method, wherein the thickness of the hybrid film is 4-6 μm.

[0016] A fourth objective of this invention is to provide the application of the CoNi-MOF-based hybrid membrane in O2 / N2 separation.

[0017] Beneficial technical effects of the present invention: This invention successfully introduces alkyl chains (methyl, ethyl, propyl) into MOFs to construct confined nanochannels. Based on the CoNi-pyz framework (pore size ~3.9 Å), a series of alkyl-functionalized MOFs were synthesized using a mixed ligand strategy. Gradient control of pore size was achieved by utilizing the steric hindrance effect of the alkyl chains. An optimized hybrid membrane prepared by incorporating CoNi-epyz into a PIM-1 / 6FDA-DAM blend polymer matrix exhibited excellent O2 / N2 separation performance (O2 permeability 275.5 Barrer, O2 / N2 selectivity 7.2), surpassing the 2015 Robeson limit. Simultaneously, membrane modules based on the CoNi-epyz hybrid membrane provided an O2 permeation rate of 47.5 GPU and an O2 / N2 selectivity of 5.1 at feed pressures of 1-3 bar, demonstrating potential for practical industrial applications. Attached Figure Description

[0018] Figure 1 (a) Magnified FT-IR spectra of the epyz, CoNi-epyz, and CoNi-pyz samples. (b) PXRD spectra of the original CoNi-pyz and CoNi-epyz samples.

[0019] Figure 2 (a) FT-IR spectra of the mpyz, CoNi-mpyz and CoNi-pyz samples and (b) magnified view of the local area.

[0020] Figure 3 FT-IR spectra of epyz, CoNi-epyz and CoNi-pyz samples.

[0021] Figure 4 (a) FT-IR spectra of the ppyz, CoNi-ppyz and CoNi-pyz samples and (b) magnified view of the local area.

[0022] Figure 5 PXRD patterns of (a) CoNi-mpyz and (b) CoNi-ppyz samples.

[0023] Figure 6 SEM images of the CoNi-pyz, (b) CoNi-mpyz, (c) CoNi-epyz and (d) CoNi-ppyz samples.

[0024] Figure 7 (a) Ar adsorption isotherm measured at 87 K and (b) corresponding pore size distribution of CoNi-pyz and CoNi-epyz samples.

[0025] Figure 8 (a) Ar adsorption isotherms of CoNi-pyz and CoNi-mpyz samples and (b) corresponding pore size distribution.

[0026] Figure 9 (a) Ar adsorption isotherms of CoNi-pyz and CoNi-ppyz samples and (b) corresponding pore size distribution.

[0027] Figure 10 Schematic diagram of the Connolly surface of the CoNi-pyz, (b) CoNi-mpyz, (c) CoNi-epyz and (d) CoNi-ppyz samples.

[0028] Figure 11 Stress-strain curves of hybrid films with different PIM-1 contents.

[0029] Figure 12 (a) PXRD patterns and (b) FT-IR spectra of CoNi-epyz-based hybrid films with different loadings. Cross-sectional SEM images of different MOF-based hybrid film samples (Examples 7, Examples 10-12): (c) CoNi-pyz (Comparative Example 3), (d) CoNi-mpyz (Example 8), (e) CoNi-epyz (Example 7) and (f) CoNi-ppyz (Example 9), all with a MOF loading of 15 wt%.

[0030] Figure 13(a) XRD patterns and (b) FT-IR spectra of CoNi-MOF-based hybrid films with the same filler loading (15 wt%) (Examples 7-9, Comparative Example 3).

[0031] Figure 14 (a) Cross-sectional SEM images of the original blended polymer membrane and (b) 5 wt%, (c) 10 wt% and (d) 20 wt% CoNi-epyz-based hybrid membranes with different filler loadings (Examples 7, Examples 10-12).

[0032] Figure 15 (a) Gas separation performance of different CoNi-MOF-based hybrid membranes, (b) Air separation performance of CoNi-epyz-based hybrid membranes with different filler loadings, (c) Gas separation performance of a 15 wt% CoNi-epyz-based hybrid membrane under different feed pressures, (d) Long-term stability of a 15 wt% CoNi-epyz-based hybrid membrane. All tests were conducted at 25 °C using air as the feed gas.

[0033] Figure 16 Comparison of O2 / N2 gas separation performance of CoNi-epyz-based hybrid membranes with different filler loadings with the upper limit in 2015.

[0034] Figure 17 (a) Permeability tests of various membrane samples using gases with different kinetic diameters (test conditions: 1 bar feed pressure, 25°C); (b) Positron annihilation lifetime spectrum (PALS) data of each membrane sample.

[0035] Figure 18 (a) Diffusion coefficient and (b) solubility coefficient of different membrane samples and their corresponding O2 / N2 selectivity (test conditions: 25℃, 1 bar feed pressure).

[0036] Figure 19 (a) Photographs of the prepared large-area membrane and the corresponding spiral wound membrane module; (b) SEM micrograph of the prepared 15 wt% CoNi-epyz-based hybrid membrane; (c) PXRD pattern of the obtained hybrid membrane; (d) Actual air separation performance of the obtained membrane module at 25℃ and different feed pressures. Detailed Implementation

[0037] Example 1: Synthesis of CoNi-mpyz filler First, Co(NO3)2·6H2O (1 mmol) and a mixed ligand (1 mmol) were dissolved in 20 mL of a methanol / water mixture, wherein the mixed ligand was a 1:1 molar ratio of pyrazine (pyz) and 2-methylpyrazine (mpyz). Then, 4 mL of a K2[Ni(CN)4]·nH2O (1 mmol) aqueous solution was added, and the reaction was carried out in a microwave reactor (Makewave, MKM-H1B) at 25°C for 2 minutes. The reaction product was collected by centrifugation, washed three times with methanol, and activated in a vacuum oven at 60°C for 12 hours to finally obtain CoNi-mpyz powder.

[0038] Example 2 Synthesis of CoNi-epyz filler The difference between Example 2 and Example 1 is that the mixed ligands are pyrazine (pyz) and 2-ethylpyrazine (epyz) in a molar ratio of 1:1, while the other conditions are exactly the same.

[0039] Example 3 Synthesis of CoNi-ppyz filler The difference between Example 3 and Example 1 is that the mixed ligands are pyrazine (pyz) and 2-propylpyrazine (ppyz) in a molar ratio of 1:1, while the other conditions are exactly the same.

[0040] Comparative Example 1: Synthesis of CoNi-pyz Filler First, Co(NO3)2·6H2O (1 mmol) and pyrazine pyz ligand (1 mmol) were dissolved in 20 mL of methanol / water mixture, followed by the addition of 4 mL of K2[Ni(CN)4]·nH2O (1 mmol) aqueous solution. The reaction was carried out in a microwave reactor (Makewave, MKM-H1B) at 25°C for 2 minutes. The reaction product was collected by centrifugation, washed three times with methanol, and activated in a vacuum oven at 60°C for 12 hours to finally obtain light orange CoNi-pyz powder.

[0041] Characterization of CoNi-MOF filler: (1) Fourier transform infrared spectroscopy (FT-IR) analysis and powder X-ray diffraction (PXRD) analysis like Figure 1 As shown in a, 2, 3, and 4, the characteristic absorption peak observed at 1460 cm⁻¹ corresponds to the shear deformation vibration of CH in ethyl and propyl groups, and 1408 cm⁻¹... -1 The absorption peak at 843 cm⁻¹ is due to the CH deformation vibration, while the absorption peak at 843 cm -1 The characteristic peaks at [location] were identified as out-of-plane bending vibrations of CH. These characteristic peaks collectively provide conclusive evidence for the successful synthesis of the mixed-ligand MOF sample. Furthermore, the crystal structure of the CoNi-MOF material was characterized using powder X-ray diffraction (PXRD). Figure 1As shown in b and 5, the PXRD patterns of the CoNi-MOF samples are completely consistent with those of the CoNi-pyz samples at the positions of the main characteristic peaks (2θ = 12.3° and 17.4°), and are in high agreement with the theoretical simulation results. Notably, the diffraction peak intensities of all CoNi-MOF samples did not show significant attenuation, providing strong evidence for the preservation of their Hofmann-type framework structure.

[0042] (2) Scanning electron microscopy (SEM) analysis Scanning electron microscope (SEM) images such as Figure 6 The CoNi-MOF samples exhibit a similar microstructure to the original CoNi-pyz. Notably, the introduction of carbon chains led to a significant increase in particle size, which effectively suppressed the aggregation of nanoparticles during subsequent film formation.

[0043] (3) Analysis of Ar (Ar) adsorption isotherm at 87K combined with NLDFT pore size distribution The effect of carbon chain introduction on the pore structure of CoNi-MOF materials was systematically studied by combining 87K argon (Ar) adsorption isotherm with NLDFT pore size distribution analysis. Figure 7 , 8 As shown in Figure 9, all samples exhibit typical Type I adsorption isotherm characteristics. The pore size gradually decreases with increasing carbon chain length in the ligands. Notably, the pore size distribution of CoNi-epyz shifts significantly to the left, with a peak at ~3.5 Å. This size falls precisely between the molecular dynamic diameters of oxygen (3.46 Å) and nitrogen (3.64 Å), thus significantly enhancing the molecular sieving ability for O2 / N2 separation. The corresponding Brunauer-Emmett-Teller (BET) specific surface area and pore volume data for the CoNi-MOF materials are listed in Table 1.

[0044] Table 1. Pore structure characteristics of different CoNi-MOF materials.

[0045]

[0046] (4) Objectless Connolly surface simulation To elucidate the pore characteristics of a series of optimized CoNi-MOF materials, a guestless Connolly surface simulation was used to visualize the accessible pores and the connectivity of internal channels. For example... Figure 10As shown, the pore size of the original CoNi-pyz sample is 3.9 Å, which is highly consistent with the pore size distribution results. However, this pore size still allows some nitrogen molecules to pass through the channels, resulting in limited molecular sieving ability. Notably, functionalized CoNi-MOF materials with carbon chains of different lengths exhibit significantly different pore configurations: CoNi-mpyz failed to achieve effective pore size control due to limited steric hindrance from methyl groups; the pore size of CoNi-epyz was precisely controlled to 3.2 Å, effectively enhancing the molecular sieving effect and ensuring preferential diffusion of O2 within the MOF channels; while the pore size of CoNi-ppyz further shrank to 2.8 Å, simultaneously blocking oxygen and nitrogen molecules from entering the MOF channels, leading to a significant decrease in gas separation performance. These findings highlight the importance of optimizing separation efficiency through fine-tuning of pore chemistry and the pore microenvironment.

[0047] Example 4 First, 7.5 mg of PIM-1 and 142.5 mg of 6FDA-DAM polymer were dissolved in 3 mL of chloroform, with the mass of PIM-1 being 5 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a doctor blade coating method, and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain the hybrid membrane.

[0048] Example 5 First, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in 3 mL of chloroform, with the mass of PIM-1 being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was then uniformly coated onto a glass plate using a blade coating method and transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain the hybrid membrane.

[0049] Example 6 First, 22.5 mg of PIM-1 and 127.5 mg of 6FDA-DAM polymer were dissolved in 3 mL of chloroform, with the mass of PIM-1 being 5 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a doctor blade coating method, and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain the hybrid membrane.

[0050] Comparative Example 2 First, 150 mg of 6FDA-DAM polymer was dissolved in 3 mL of chloroform, with PIM-1 at 0 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a blade coating method, and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain the hybrid membrane.

[0051] This invention uses a blend of PIM-1 and 6FDA-DAM as the polymer matrix, leveraging the inherent microporous structure of PIM-1 to enhance the free volume of the polyimide (PI) film. Based on the suitable mechanical properties of the blended polymer... Figure 11 Ultimately, a PIM-1 / 6FDA-DAM blend system with a PIM-1 content of 10 wt% was selected as the polymer matrix for subsequent preparation of CoNi-MOF-based hybrid membranes.

[0052] Example 7 Preparation of 15wt% CoNi-epyz hybrid film First, CoNi-epyz powder was dispersed in 3 mL of chloroform and sonicated for 30 minutes to obtain a homogeneous suspension. Then, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in the MOF dispersion and physically blended, with the mass fraction of PIM-1 being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a doctor blade coating method and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain a hybrid membrane with a CoNi-epyz powder loading of 15 wt%.

[0053] Example 8 Preparation of 15wt% CoNi-mpyz hybrid film First, CoNi-mpyz powder was dispersed in 3 mL of chloroform and sonicated for 30 minutes to obtain a homogeneous suspension. Then, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in the MOF dispersion and physically blended, with the PIM-1 mass fraction being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a blade coating method and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a 60°C vacuum oven for 12 hours to obtain a hybrid membrane with a CoNi-mpyz powder loading of 15 wt%.

[0054] Example 9 Preparation of 15wt% CoNi-ppyz hybrid film First, CoNi-mpyz powder was dispersed in 3 mL of chloroform and sonicated for 30 minutes to obtain a homogeneous suspension. Then, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in the MOF dispersion and physically blended, with the mass fraction of PIM-1 being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a blade coating method and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain a hybrid membrane with a CoNi-mpyz powder loading of 15 wt%.

[0055] Comparative Example 3: Preparation of 15wt% CoNi-pyz hybrid film First, CoNi-mpyz powder was dispersed in 3 mL of chloroform and sonicated for 30 minutes to obtain a homogeneous suspension. Then, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in the MOF dispersion and physically blended, with the mass fraction of PIM-1 being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a doctor blade coating method and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain a hybrid membrane with a CoNi-pyz powder loading of 15 wt%.

[0056] Example 10 First, CoNi-epyz powder was dispersed in 3 mL of chloroform and sonicated for 30 minutes to obtain a homogeneous suspension. Then, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in the MOF dispersion and physically blended, with the mass fraction of PIM-1 being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a blade coating method and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain a hybrid membrane with a CoNi-epyz powder loading of 5 wt%.

[0057] CoNi-MOF loading (wt%) = m CoNi-MOF / m CoNi-MOF + m 聚合物 (1) Example 11 First, CoNi-epyz powder was dispersed in 3 mL of chloroform and sonicated for 30 minutes to obtain a homogeneous suspension. Then, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in the MOF dispersion and physically blended, with the mass fraction of PIM-1 being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a blade coating method and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a vacuum oven at 60°C for 12 hours to obtain a hybrid membrane with a CoNi-epyz powder loading of 10 wt%.

[0058] Example 12 First, CoNi-epyz powder was dispersed in 3 mL of chloroform and sonicated for 30 minutes to obtain a homogeneous suspension. Then, 15 mg of PIM-1 and 135 mg of 6FDA-DAM polymer were dissolved in the MOF dispersion and physically blended, with the PIM-1 mass fraction being 10 wt% of the total mass of PIM-1 and 6FDA-DAM polymer. The mixture was stirred continuously for 24 hours. The resulting casting solution was uniformly coated onto a glass plate using a blade coating method and then transferred to a PDMS-coated PSf substrate. Finally, the membrane sample was dried in a 60°C vacuum oven for 12 hours to obtain a hybrid membrane with a CoNi-epyz powder loading of 20 wt%.

[0059] The hybrid films prepared in Examples 7-12 and Comparative Example 3 were characterized as follows: X-ray diffraction (XRD) pattern Figure 12 (a and 13a) showed distinct characteristic diffraction peaks at 2θ = 12.3° and 17.4°, which clearly belonged to the crystal structure of CoNi-MOF, and the peak intensity showed a positive correlation with the increase of filler loading (Examples 7, Examples 10-12). FT-IR spectroscopy analysis ( Figure 12 (b and 13b) further confirmed the structural integrity of the MOF filler in the polymer matrix. The microstructure of the membrane samples was then observed using SEM (b and 13b). Figure 12 cf and Figure 14 The results showed that all MOF packings exhibited a uniform dispersion in the polymer matrix (Examples 7, 10-12). No obvious non-selective voids appeared at the interface, indicating the formation of an optimized microstructure, thus providing a structural basis for efficient oxygen and nitrogen separation performance.

[0060] O membrane material 2 / N2 separation performance To evaluate the separation capability of the CoNi-MOF membrane, an air permeation test was conducted at 25°C and a feed pressure of 1 bar. Figure 15As shown in Figure a, the CoNi-epyz-based hybrid membrane exhibits the best O2 / N2 separation performance, with an O2 / N2 selectivity of 7.2 and an O2 permeability of 275.5 Barrer, significantly superior to the original polymer membrane (O2 / N2 selectivity 3.4, O2 permeability 151.0 Barrer) and other CoNi-MOF-based membranes. Combined with structural characterization results, it is shown that the introduction of carbon chains can precisely control the reduction of MOF pore size to between the molecular dynamic diameters of O2 and N2, thereby significantly enhancing the molecular sieving effect of the membrane. As the carbon chain length increases from CoNi-pyz to CoNi-epyz, the O2 / N2 selectivity of the corresponding membrane significantly increases from 3.6 to 7.2, while the permeability slightly decreases from 354.8 Barrer to 275.5 Barrer. However, when the carbon chain extends further to CoNi-ppyz, the MOF pores shrink to below the molecular dynamic diameter of O2, which hinders the diffusion of O2 and N2, resulting in an overall deterioration in separation performance (O2 permeability 202.1 Barrer, O2 / N2 selectivity 5.4).

[0061] To verify the molecular sieving ability of CoNi-epyz within the membrane, the gas separation performance of hybrid membranes with different CoNi-epyz loadings was systematically evaluated. Test results ( Figure 15 (b) indicates that the incorporation of CoNi-epyz simultaneously improved both the O2 permeability and O2 / N2 selectivity of the membrane sample. When the CoNi-epyz loading increased from 5 wt% to 15 wt%, the O2 permeability of the membrane sample significantly increased from 175.3 Barrer to 275.5 Barrer, and the O2 / N2 selectivity increased from 4.5 to 7.2. However, when the filler loading was further increased to 20 wt%, the O2 permeability significantly increased to 380.6 Barrer, while the O2 / N2 selectivity decreased to 5.0. This phenomenon is attributed to the formation of non-selective voids at the filler-polymer interface within the membrane.

[0062] Subsequently, to simulate the actual operating conditions that the membrane material might face, air separation tests were conducted on a typical 15 wt% CoNi-epyz-based hybrid membrane under different feed pressures. For example... Figure 15 As shown in Figure c, when the feed pressure increased from 0.5 bar to 3 bar, the O2 permeability increased from 273.5 Barrer to 284.9 Barrer, while the O2 / N2 selectivity remained stable in the range of 6.9–7.4. This membrane exhibits excellent pressure stability; the slight decrease in selectivity can be attributed to the increased pressure forcing some nitrogen molecules through the molecular sieve channels constructed from alkyl chains. Furthermore, this CoNi-epyz-based hybrid membrane demonstrated excellent long-term stability during a seven-day stability test. Figure 15d), its O2 permeability (273.8-288.8 Barrer) and O2 / N2 selectivity (7.1-7.3) remained stable throughout the testing period. Compared with other O2 / N2 separation studies reported in recent years (Table 2), the 15 wt% CoNi-epyz-based hybrid membrane still exhibited excellent mixed gas separation performance under air as the feed gas condition, and broke through the separation upper limit of 2015 ( Figure 16 ).

[0063] Table 2. Comparison of O2 / N2 separation performance of hybrid membranes reported in recent years and those obtained in this invention.

[0064]

[0065] Hybrid membrane separation mechanism To investigate the separation mechanism of the CoNi-MOF membrane, a single gas permeation test was first conducted at 25°C and a feed pressure of 1 bar. Figure 17 As shown in Figure a, the molecular sieving effect of the CoNi-MOF membrane on O2 and N2 molecules significantly increases with the alkyl chain length from CoNi-pyz to CoNi-epyz. The O2 permeability of the CoNi-pyz, CoNi-mpyz, and CoNi-epyz samples remained stable, while the N2 permeability gradually decreased, exhibiting an increasingly significant "retention" effect. This led to a sharp increase in the ideal O2 / N2 selectivity from 3.8 for the CoNi-pyz membrane to 7.1 for the CoNi-epyz membrane. Furthermore, due to further pore size reduction, the gas permeability of both O2 and N2 molecules decreased in the CoNi-ppyz membrane, resulting in a significant decrease in the ideal O2 / N2 selectivity to 4.4. Therefore, the size sieving effect of CoNi-MOF leads to the differential separation of O2 and N2 molecules.

[0066] The O2 / N2 separation mechanism of the CoNi-MOF substrate was further investigated using positron annihilation lifetime spectroscopy (PALS). Figure 17 As shown in b and Table 3, compared with the polymer blend samples, the introduction of CoNi-MOF effectively increased the free volume fraction (FFV), which is beneficial for efficient oxygen diffusion. Simultaneously, as the carbon chain length increased from CoNi-pyz to CoNi-ppyz based hybrid films, the free volume radius of the CoNi-MOF based hybrid films gradually decreased from 3.60 to 3.54, demonstrating the stepwise control of pore size by the carbon chain. These findings further confirm the size shrinkage effect of the pores in the CoNi-MOF based films.

[0067] Table 3. PALS test results of the blended polymer membrane and the CoNi-MOF-based hybrid membrane with a filler loading of 15 wt%.

[0068]

[0069] To further investigate intramembrane transport behavior, the solubility-diffusion characteristics of O2 and N2 molecules were measured using the constant-volume pressure swing method. The corresponding diffusion coefficients (D) and solubility coefficients (S) are shown in the figure. Figure 18 And Table 4. The results show that the incorporation of CoNi-pyz reduced the O2 diffusion coefficient from 4.92 × 10⁻⁶ in the polymer film. -8 cm 2 / s significantly increased to 13.21 × 10⁻⁶ for the hybrid film. -8 cm 2 / s, indicating that the MOF packing provides an efficient transport channel for gas molecules; at the same time, the N2 diffusion coefficient is only 3.14×10 -8 cm² / s increased to 5.89 × 10 -8 cm 2 The O2 / N2 diffusion selectivity was increased from 1.56 to 2.24 by increasing the alkyl chain length from CoNi-mpyz to CoNi-ppyz, preliminarily confirming the molecular sieving effect of the CoNi-pyz filler. Notably, as the alkyl chain length increased from CoNi-mpyz to CoNi-ppyz, the O2 diffusion coefficient of the corresponding hybrid membrane increased from 10.78 × 10⁻⁶ / s. - 8 cm 2 / s gradually decreased to 6.59×10 -8 cm 2 / s, while the N2 diffusion coefficient is 3.64×10 -8 cm 2 / s decreased significantly to 2.25×10 - 8 cm 2 / s. Since the O2 diffusion coefficient decreased less than that of N2, the O2 / N2 diffusion selectivity increased from 2.96 to 4.02, reflecting a continuous enhancement in molecular sieving ability. The differential separation of O2 and N2 diffusion was achieved through alkyl chain-confined nanochannels. However, when the CoNi-ppyz pore size shrank to below the molecular dynamic diameter of O2, it simultaneously hindered the diffusion of both O2 and N2, causing the O2 / N2 diffusion selectivity to decrease to 2.93, a result consistent with experimental data.

[0070] Meanwhile, the introduction of MOF filler increased the O2 solubility coefficient of the membrane sample from 14.04 × 10⁻¹ cm⁻¹ to that of the blend membrane. 3 / cm 3 / cmHg decreased slightly to 11.25×10 of the CoNi-mpyz membrane. -1 cm 3 / cm 3 / cmHg, correspondingly the O2 / N2 solubility selectivity decreased from 2.15 to 1.67. When using the mixed ligand CoNi-MOF, the solubility coefficient and solubility selectivity remained stable. It can be inferred that the excellent O2 / N2 separation performance is mainly due to the diffusion differences caused by the size sieving effect of CoNi-MOFs.

[0071] Table 4. Dissolution-diffusion test results.

[0072]

[0073] Example 13 Gas separation performance of CoNi-epyz based membrane module To evaluate the practical application value of CoNi-epyz-based hybrid films, a film with an area of ​​2400 cm² was prepared. 2 Large area membrane ( Figure 19 a). Even after scale-up preparation, the CoNi-epyz filler remains uniformly dispersed in the polymer matrix. Figure 19 b). The resulting membrane was then rolled into a laboratory membrane module ( Figure 19 c) Using air as the feed gas, gas separation performance was tested at 25°C and a feed pressure of 1-3 bar. For example... Figure 19 As shown in Figure d, despite the influence of concentration polarization, the component maintains excellent O2 / N2 separation performance: the O2 permeation rate remains stable at 47.5 GPU, and the O2 / N2 selectivity consistently reaches 5.1 under different feed pressures. These results indicate that CoNi-epyz-based hybrid membranes have significant application potential in industrial air separation.

[0074] Conclusion: To achieve efficient O2 / N2 separation, alkyl chains (methyl, ethyl, propyl) were successfully introduced into MOFs to construct confined nanochannels. Based on the CoNi-pyz framework (pore size ~3.9 Å), a series of alkyl-functionalized MOFs were synthesized using a mixed ligand strategy. Pore size gradient control was achieved by utilizing the steric hindrance effect of the alkyl chains. The optimized hybrid membrane prepared by incorporating CoNi-epyz into a PIM-1 / 6FDA-DAM blend polymer matrix exhibited excellent O2 / N2 separation performance (O2 permeability 275.5 Barrer, O2 / N2 selectivity 7.2), exceeding the 2015 Robeson limit. Furthermore, the membrane module based on the CoNi-epyz hybrid membrane provided an O2 permeation rate of 47.5 GPU and an O2 / N2 selectivity of 5.1 at feed pressures of 1–3 bar, demonstrating potential for practical industrial applications.

Claims

1. A method for preparing CoNi-MOF, characterized in that: The method comprises the following steps: firstly, Co(NO3)2·6H2O and a mixed ligand of pyrazine pyz are dissolved in a methanol / water mixed solution; then, an aqueous solution of K2[Ni(CN)4]·nH2O is added; the reaction is carried out in a microwave reactor; the reaction product is collected by centrifugation, washed with methanol three times, activated in a vacuum oven at 60°C for 12 hours, and finally CoNi-MOF powder is obtained.

2. The method of claim 1, wherein: The molar ratio of Co(NO3)2·6H2O to the mixed ligand of pyrazine pyz is 1:1, and the molar ratio of K2[Ni(CN)4]·nH2O to the mixed ligand of pyrazine pyz is 1:1; the concentration of the aqueous solution of K2[Ni(CN)4]·nH2O is 0.25 mmol / L; the concentration of Co(NO3)2·6H2O in the methanol / water mixed solution is 0.05 mmol / L; and the concentration of pyrazine pyz in the methanol / water mixed solution is 0.05 mmol / L.

3. The method of claim 1, wherein: The reaction condition of the microwave reaction is 2 minutes of reaction at 25°C.

4. The method of claim 1, wherein: The mixed ligand of pyrazine pyz is one of the following: a mixed ligand of pyrazine pyz and 2-methylpyrazine mpyz, a mixed ligand of pyrazine pyz and 2-ethylpyrazine epyz, and a mixed ligand of pyrazine pyz and 2-propylpyrazine ppyz, wherein the molar ratio of the two ligands in the mixed ligand is 1:

1.

5. A CoNi-MOF prepared by the method of any one of claims 1-4, characterized by: The pore size of the CoNi-MOF gradually decreases with the increase of the length of the introduced carbon chain.

6. A method for preparing a CoNi-MOF-based hybrid membrane, characterized in that: The method comprises the following steps: S1. dispersing the CoNi-MOF powder prepared by the preparation method in any one of claims 1-4 in chloroform, and obtaining a uniform suspension by ultrasonic treatment for 30 minutes; S2. physically blending PIM-1 and a 6FDA-DAM polymer in the MOF suspension, and continuously stirring for 24 hours; S3. uniformly coating the casting solution obtained in S2 on a glass plate by a doctor blade method, transferring to a PSf substrate, and finally drying the membrane sample in a vacuum oven at 60°C for 12 hours.

7. The method for preparing the CoNi-MOF-based hybrid film according to claim 5, characterized in that: The CoNi-MOF loading is 5-20 wt%.

8. The method for preparing the CoNi-MOF-based hybrid film according to claim 5, characterized in that: The content of PIM-1 is 5-15 wt%.

9. A CoNi-MOF based hybrid membrane prepared by the method of any one of claims 5-8, characterized by: The thickness of the hybrid membrane is 4-6 μm.

10. Use of the CoNi-MOF-based hybrid membrane prepared by the preparation method in any one of claims 5-8 in O2 / N2 separation.

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