A MOF-802 separation membrane, its preparation method, and its application in H2 purification.

Abstract

This invention discloses a MOF-802 separation membrane, its preparation method, and its application in H2 purification. The preparation method of the MOF-802 separation membrane includes the following steps: preparing a MOF-802 seed solution; depositing a MOF-802 seed layer on the surface of a support; and generating a MOF-802 membrane layer on the surface of the support with the deposited MOF-802 seed layer using an induced interfacial coordination growth method. This invention demonstrates the construction of a continuous and alternating growth MOF-802 membrane through a novel seed-induced interfacial coordination growth strategy. This method avoids the explosive nucleation and rapid growth of MOF-802 in the reaction solution, thereby forming a MOF-802 membrane layer on the support surface. The prepared MOF-802 membrane exhibits excellent separation performance for H2 / CO2. Even in the presence of water vapor in the feed gas, the H2 permeability reaches 3270 GPU, and the selectivity reaches 19, demonstrating its great potential for purifying H2 in practical applications.

Description

Technical Field

[0001] This invention relates to a MOF-802 separation membrane, its preparation method, and its application in H2 purification, belonging to the field of separation membrane preparation technology. Background Technology

[0002] Membrane separation technology offers advantages such as ease of operation, small footprint, and environmental friendliness, thus demonstrating immense application potential in gas separation. Traditional polymer membranes often suffer from a trade-off effect, where permeability and selectivity are mutually exclusive. In contrast, porous inorganic membranes with ordered pore structures and good stability have the potential to overcome this constraint. Metal-organic frameworks (MOFs) are a novel type of membrane material, formed by the coordination of metal ions or metal clusters with organic ligands. They possess rich chemical composition, large specific surface area, and tunable pore size, and are currently widely used in the preparation of high-performance separation membranes.

[0003] Over the past two decades, significant breakthroughs have been achieved in MOF-based separation membrane research; however, these breakthroughs have primarily focused on zeolite imidazoline frame (ZIF) membranes for gas separation. Jürgen Caro et al. first reported the preparation of a defect-free ZIF-8 membrane for high-performance H2 separation, opening the door to the application of ZIF membranes in gas separation (Non-Patent Literature 1). Sankar Nair et al. prepared a well-developed symbiotic ZIF-8 membrane exhibiting excellent H2 / C3H8 separation performance with a separation factor as high as 37022 (Non-Patent Literature 2). Jiang et al. discovered a metal-organic framework material with superior glass-forming ability for gas separation, namely the ZIF-62 membrane, with an H2 / CH4 separation factor as high as 50.7, far exceeding the Robeso upper limit (Non-Patent Literature 3). Despite these breakthroughs in gas separation research, the application of MOF materials remains relatively limited, especially in the purification and separation of H2 in the presence of water vapor, due to their poor water stability.

[0004] Zr-MOFs are a novel type of MOF material with diverse topologies and unique properties, showing great promise for practical applications. MOF-802 is a well-known Zr-MOF material formed by the coordination of a carboxylic acid ligand H₂PZDC (1H-pyrazole-3,5-dicarboxylic acid) with a high-valent Zr(IV) ion cluster. The carboxylic acid ligand can be considered a hard base, while the Zr(IV) ion can be considered a hard acid. Based on the soft / hard basogen theory, MOF-802 has a high number of connections, resulting in a more stable structure. Therefore, MOF-802 has great application potential for developing highly stable gas separation membranes to separate gas mixtures containing water vapor. However, fabricating continuous MOF-802 membranes still faces significant challenges, and there are currently no reports on the use of MOF-802 membranes for gas separation. This can be attributed to several factors. Firstly, due to the high connectivity of MOF-802, the coordination of ligands with metal clusters generates greater steric hindrance, causing MOF-802 and the crystalline film to interweave, easily leading to non-selective defects (such as cracks or gaps). Secondly, the reaction rate of MOF-802 is quite fast when water is used as a solvent, making it difficult to obtain continuous films using traditional in-situ solvothermal synthesis methods, as MOF crystals preferentially form in the reaction solution. Therefore, exploring novel film preparation methods is crucial for constructing defect-free MOF-802 films.

[0005] Non-patent literature 1: Bux H, Liang F, Li Y, Cravillon J, Wiebcke M, Caro J. ZeoliticImidazolate Framework Membrane with Molecular Sieving Properties by Microwave-Assisted Solvothermal Synthesis. Journal of the American Chemical Society. 2009; 131(44): 16000-16001;

[0006] Non-patent literature 2: Brown AJ, Brunelli NA, Eum K, et al.Interfacial microfluidicprocessing of metal-organic framework hollow fiber membranes.Science.2014;345(6192):72-75;

[0007] Non-patent literature 3: Wang Y, Jin H, Ma Q, et al. A MOF Glass Membrane for Gas Separation. Angewandte Chemie International Edition. 2020; 59(11):4365-4369. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a MOF-802 separation membrane, its preparation method, and its application in H2 purification. A continuous and alternating growth of MOF-802 membrane is constructed using a seed-induced interfacial coordination growth strategy. This method avoids the explosive nucleation and rapid growth of MOF-802 in the reaction solution, thereby forming a MOF-802 membrane layer on the support surface. The prepared MOF-802 membrane exhibits excellent separation performance for H2 / CO2.

[0009] The technical solution adopted in this invention is as follows:

[0010] A method for preparing a MOF-802 separation membrane includes the following steps:

[0011] Preparation of MOF-802 seed solution;

[0012] A MOF-802 seed layer was deposited on the surface of the support.

[0013] The induced interface coordination growth method generates a MOF-802 film on the surface of a support with a MOF-802 seed layer deposited on its surface.

[0014] Preferably, the support is any one of porous Al2O3, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), nylon, and polytetrafluoroethylene (PTFE).

[0015] The loading of the MOF-802 seed layer on the surface of the support is 20-50 cm. 2 The surface loading is 0.05-2 mg.

[0016] Preferably, the MOF-802 seed solution is prepared by interfacial coordination growth, specifically as follows:

[0017] The metal source solution and the organic ligand solution were placed on both sides of a porous medium, heated to 50-70℃ and kept at that temperature for 3-6 hours. The precipitate on the metal source solution side was collected by centrifugation and dried to obtain MOF-802 seed crystals. The MOF-802 seed crystals were then dispersed in deionized water and sonicated for 1-3 hours to obtain the MOF-802 seed crystal solution.

[0018] Preferably, a MOF-802 seed layer is deposited on the surface of the support substrate by a filtration method. The specific operating conditions are: 0.5-2 bar pressure driving the MOF-802 seed layer to be deposited on the surface of the support substrate; and then the support with the seed layer deposited on the surface is dried at 40-80°C.

[0019] Preferably, the specific method for generating the MOF-802 film layer on the surface of the support is as follows:

[0020] The metal source solution and the organic ligand solution are placed on both sides of a support on which a MOF-802 seed layer is deposited, respectively. The temperature is raised and maintained. Then the support on which the MOF-802 film is formed is washed and dried.

[0021] Preferably, the heating and holding conditions are: 50-70℃, 2-6h; the drying conditions after washing the support for forming the MOF-802 film on the surface are: 75-90℃, 10-15h.

[0022] Preferably, the metal source solution is obtained by dissolving ZrOCl2-8H2O in an aqueous acetic acid solution, wherein the ratio of ZrOCl2-8H2O, acetic acid, and water is (210-280) mg: (8-15) mL: (30-60) mL;

[0023] The organic ligand solution was obtained by dispersing 3,5-pyrazole dicarboxylic acid H2PZDC in an aqueous solution of acetic acid, wherein the ratio of H2PZDC, acetic acid and water was (1-4) mg: (8-15) mL: (30-60) mL.

[0024] Furthermore, the weight ratio of ZrOCl2-8H2O to 3,5-pyrazole dicarboxylic acid is 150-300:1.5-2.5.

[0025] A MOF-802 separation membrane is prepared by any of the methods described above.

[0026] The above-mentioned MOF-802 separation membrane is used in H2 purification.

[0027] Preferably, the MOF-802 separation membrane is used to separate H2 from a mixture of H2 with CO2, N2, CH4, C3H6 or C3H8.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention demonstrates the construction of continuous and interleaved MOF-802 films through a novel seed-induced interface coordination growth (SICG) strategy. This method avoids the explosive nucleation and rapid growth of MOF-802 in the reaction solution, thereby forming continuous and interleaved MOF-802 film layers on the support surface. Furthermore, depositing a MOF seed layer on the support surface is crucial for the growth of continuous MOF films, providing abundant nucleation sites and inducing the interleaved growth of MOF-802 crystals into a continuous film.

[0030] 2. The MOF-802 membrane prepared by the method provided in this invention exhibits excellent separation performance for H2 / CO2. Even in the presence of water vapor in the feed gas, due to its excellent water stability, the H2 permeability can reach 3270 GPU, and the selectivity reaches 19, demonstrating its great potential for purifying H2 in practical applications. The MOF-802 membrane constructed by this method can promote the development of high-valent MOF membranes. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating the seed-induced interfacial coordination growth (SICG) method for MOF-802 membranes. (a) Side view of a porous substrate with a pre-deposited MOF-802 seed layer in the membrane synthesis apparatus; the left side is the metal cluster solution, and the right side is the excess organic ligand solution. (b) Driven by osmotic pressure difference, the ligand diffuses from right to left, reacts with the metal cluster, and gradually grows MOF-802 using the seed layer as a nucleation site, thereby forming a well-grown MOF membrane on the substrate surface.

[0032] Figure 2 Schematic diagrams of MOF-802 seed layer preparation (a) and MOF-802 film preparation by interfacial coordination growth method;

[0033] Figure 3 Scanning electron microscope (SEM) images of the surface and cross-section of MOF-802 films prepared by conventional hydrothermal methods at temperatures of 70℃ (b and e) and 80℃ (c and f) on blank Al2O3 supports (a and d); (g) images of different reaction times (temperature 60℃, metal source and organic ligand concentrations of 0.065 mmol·mL⁻¹). -1 and 0.075 mmol·mL -1 A photograph of the precursor solution for synthesizing MOF-802;

[0034] Figure 4 SEM surface images of (a) porous supports without and (d) containing seed layers; (b)-(c) and (e)-(f) corresponding MOF-802 films; (f)-(i) cross-sectional SEM images of continuous MOF-802 films with adjustable thickness;

[0035] Figure 5 SEM image (a) and XRD pattern (b) of MOF-802 seed crystals;

[0036] Figure 6 SEM surface images of porous supports with MOF-802 seed layers attached under different MOF-802 crystal loadings;

[0037] Figure 7 (a) XRD patterns of porous supports with MOF-802 seed layers under different MOF-802 crystal loadings; (b) XPS detection of MOF-802 films; (c) FTIR patterns of MOF-802; (d) TGA curves of MOF-802 films.

[0038] Figure 8 SEM images of MOF-802 films prepared by interfacial coordination growth method at different time points; the mass of MOF-802 seed crystals deposited on the surface of the porous support is 0.1 mg.

[0039] Figure 9 SEM images of MOF-802 films with different MOF-802 seed loadings generated by the induced interface coordination growth method;

[0040] Figure 10 The XRD patterns of MOF-802 films with different MOF-802 seed loadings generated by the induced interface coordination growth method are shown.

[0041] Figure 11 SEM images of the surface and cross sections of MOF-802 films grown on PAN, Nylon and PTFE supports;

[0042] Figure 12 (a) The time-dependent permeation of the metal source and organic ligand in the support was determined by calculating the concentrations of the metal source and organic ligand on the permeation side; (b) XRD patterns of the MOF-802 membrane tested at different temperatures (25-80℃); N2 adsorption and desorption isotherms of the MOF-802 membrane; (c) H2 and CO2 adsorption isotherms at 298K;

[0043] Figure 13 This is a schematic diagram of a gas separation performance system;

[0044] Figure 14 The effect of membrane thickness on the separation performance of MOF-802 membrane;

[0045] Figure 15The permeation of H2, CO2, N2, CH4, C3H6, and C3H8 through the MOF-802 membrane is shown, with the insertion of H2's selectivity for other gases.

[0046] Figure 16 (a) Effects of operating temperature (a), feed pressure (c), and steam (d) on the separation performance of the MOF-802 membrane; (b) Activation energies of H2 and CO2 passing through the MOF-802 membrane;

[0047] Figure 17 For (a) the long-term stability test of the MOF-802 membrane at 1 bar and 25°C, the feed was a H2 / CO2 (50 / 50, volume percentage) gas mixture; and (b) the performance comparison of the MOF-802 membrane with state-of-the-art gas separation membranes (including two-dimensional membranes, composite membranes, carbon molecular sieve membranes, MOF membranes and polymer membranes). Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0049] This embodiment proposes a seed-induced interfacial coordination growth (SICG) strategy to prepare MOF-802 membranes for H2 / CO2 separation. Figure 1 First, a MOF seed layer, providing numerous nucleation sites, is uniformly distributed on a porous polymer substrate using vacuum filtration. This seed layer is then fixed in the center of a U-shaped device that separates the metal source solution from the high-concentration organic ligand solution. During synthesis, the MOF-802 membrane is generated via reverse diffusion. Based on the diffusion rate difference caused by the different osmotic pressures on both sides, the organic ligands diffuse through the porous substrate to its interface and coordinate with the metal clusters, thus growing a continuous MOF-802 membrane on the abundant nucleation sites provided by the seed layer. This embodiment also investigates in detail the influence of the seed layer on MOF membrane preparation, the physicochemical properties of the MOF membrane, and the effects of operating conditions (such as temperature, feed pressure, and operating time) on gas separation performance.

[0050] Example 1: Preparation of MOF-802 seed crystals

[0051] MOF-802 seed crystals were synthesized via interfacial coordination growth. In short, the metal source solution and the organic ligand solution were synthesized separately. The specific procedure is as follows: 242 mg of ZrOCl₂⁻₈H₂O (242 mmol) was dissolved in a water / acetic acid (40 mL / 10 mL) solvent, labeled as solution A; simultaneously, 1.96 mg of H₂PZDC (3,5-pyrazole dicarboxylic acid, 11.25 mmol) was dispersed in the same solution (water / acetic acid (40 mL / 10 mL)), labeled as solution B. The pre-synthesized solutions A and B were then poured onto opposite sides of a porous PVDF (polyvinyl chloride) U-shaped glass apparatus, which was then placed in a 60°C oven for 4 hours. Finally, the white precipitate on the left side of solution A was collected by centrifugation and vacuum dried to obtain the MOF seed crystals. 10 mg of MOF-802 seed crystals were dispersed in 100 mL of deionized water and sonicated for 2 hours to prepare the MOF-802 seed crystal solution.

[0052] Example 2: Preparation of MOF-802 seed layer

[0053] The MOF-802 seed layer was prepared by a simple vacuum filtration method. Figure 2 (Region a). Specifically, under a pressure of 1 bar, 0.1 mg of MOF-802 crystals were deposited on the surface of a 4.7 cm diameter PVDF substrate to form a seed layer, which was then dried at 50 °C and used for the preparation of MOF-802 membranes.

[0054] Example 3: Preparation of MOF-802 membrane by interfacial coordination growth method

[0055] The interfacial coordination growth process for preparing the MOF-802 film is similar to that for preparing MOF seeds. The difference lies in that a blank porous substrate or the substrate coated with the MOF-802 seed layer obtained in Example 2 is placed in the center of a U-shaped glass apparatus, and then the U-shaped glass apparatus is placed in an oven at 60°C for 4h, 5h, and 6h respectively. Figure 2 (Region b). Finally, the prepared MOF-802 membrane was washed with deionized water and dried at 80°C for 12 hours. The effect of seed coating on the properties of the synthesized MOF-802 membrane was investigated by comparing a blank porous substrate with a substrate coated with a seed layer.

[0056] Comparative Example 1: Preparation of MOF-802 membranes using a conventional hydrothermal method

[0057] First, one side of the homemade alumina substrate was sanded with 1200-grit sandpaper for several minutes, then rinsed with water to remove any residual powder. Next, a certain amount of H₂PZDC (3,5-pyrazole dicarboxylic acid (0.65 g, 3.75 mmol)) and ZrOCl₂-8H₂O (1.05 g, 3.25 mmol) were added to a 50 mL water / acetic acid (40 mL / 10 mL) mixture, and the mixture was stirred at room temperature for 10 minutes to prepare the precursor solution for synthesizing the MOF-802 membrane. Finally, the dried alumina substrate was vertically placed into the above solution and heated at different temperatures (70 °C, 80 °C) for 12 hours.

[0058] Basic characterization of samples

[0059] The morphology of the samples was characterized by field emission scanning electron microscopy (FESEM, JSM-7600F, Japan). The structural features of the powder and film were characterized by X-ray diffraction (XRD) (Rigaku, Miniflex 600, Japan) at 40 kV and 15 mA using Cu Kα irradiation. The thermal and chemical properties of the samples were determined by thermogravimetric analysis (TGA, STA449F3, NETZSCH, Germany), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR, Thermo Nicolet 8700), and X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250, USA). Gas adsorption experiments were performed using a BELSORP-HP (MicrotracBEL, Japan). The concentrations of metal sources and organic ligands in aqueous solutions were detected using a conductivity meter (DDS-307, Shanghai Leici Instruments Co., Ltd., China).

[0060] Gas separation test

[0061] The gas transport behavior through the MOF-802 membrane was evaluated using the constant pressure-variable volume method to assess separation performance. Gas permeation tests were conducted at room temperature and 1 bar. Once the system reached steady state, the gas permeation rate P was the average of three or more tests. The calculation formula is as follows:

[0062]

[0063] Where P represents gas permeability (1 GPU = 10⁻⁶). -6 ·cm 3 (STP)·cm -2 ·s -1 ·cmHg -1 Δp is the transmembrane pressure (atm), Patm refers to atmospheric pressure (atm), T represents temperature (°C), and A is the effective membrane area (m²). 2 ), dV / dt corresponds to the volumetric displacement rate in the soap bubble flow meter.

[0064] For the mixed gas experiment, a total flux of 30 mL / min was used. -1 The feed gas was a 50 / 50 H2 / CO2 ratio (volume percentage). Additionally, a total flux of 30 mL / min was selected. -1 Ar gas is used as the scavenging gas. The selectivity of the H2 / CO2 binary mixture can be calculated by the following formula:

[0065]

[0066] Where X and Y are the volume fractions of a component on the feed side and the permeate side, respectively.

[0067] Membrane preparation

[0068] Compared with Example 1, MOF-802 membranes were prepared using a traditional hydrothermal method. Porous alumina ceramic substrates possess advantages such as high mechanical strength, low transport resistance, good thermal stability, and good chemical stability; therefore, we initially used them as the support. Figure 3 (Regions a and d in the middle). However, a continuous MOF-802 film was not obtained; instead, it was distributed on the support surface in the form of independent crystals, such as... Figure 3 The SEM images of regions b and e are shown. This is because the coordination reaction between the metal cluster and the H2PZDC ligand is too rapid, causing MOF crystals to preferentially form in the reaction solution. Figure 3 As shown in region g, MOF-802 crystals are generated rapidly, but the reaction and growth cease after 20 minutes, further confirming that the reaction rate of MOF-802 is too fast and difficult to control. Therefore, a reliable method is needed to prepare continuous MOF-802 films with controllable crystallization rates.

[0069] Subsequently, to avoid explosive nucleation and rapid growth in the reaction solution, we prepared continuous MOF-802 films using an interfacial coordination growth method. First, we placed a blank support (PVDF) between pre-synthesized metal clusters and an organic ligand solution and reacted at 60°C for 4 h. Figure 2 Region b). Nevertheless, this method still yielded a cracked layer generated by MOF crystal stacking (region b). Figure 4 The low nucleation density of MOF crystals on the support surface makes it extremely difficult to prepare defect-free MOF-802 films. This is because pre-depositing MOF seeds on the support surface provides abundant nucleation sites, thereby promoting continuous growth of the MOF film. In Example 2, MOF-802 seeds were synthesized and then deposited on the support (PVDF) surface using a vacuum filtration method. Figure 2 Middle a region and Figure 5The loading of MOF seeds can be finely adjusted by controlling the amount of crystals added to the filtrate. Figure 4 Middle d region Figure 6 and Figure 7 (Region a). It can be clearly observed that the uniformly distributed MOF seeds are firmly attached to the surface of the support. After reacting at 60℃ for 4 hours using the seed-induced interfacial coordination growth method, the MOF-802 film gradually formed a continuous and well-interfacially grown film. Figure 4 Region e, region f and Figure 8 XRD, XPS, FTIR, and TGA characterization also confirmed this. Figure 12 Middle B region and Figure 7 (Regions b, c, and d in the middle). This is because during the induced interfacial coordination growth process, a sufficient amount of reactants migrates to the support surface, allowing MOF-802 to gradually grow on the seed crystal surface, thus forming a continuous MOF-802 film. Furthermore, we found that the deposition amount of MOF seed crystals between 0.1 and 1 mg had no significant effect on the formation of the MOF-802 film. Figure 9-10 It is worth noting that by optimizing the synthesis conditions (such as time and temperature), controllable continuous MOF-802 films with thicknesses between 0.8 and 3.8 μm can be prepared on different polymer supports (including PAN, Nylon, and PTFE), demonstrating good versatility. Figure 4 Central fi region and Figure 11 ).

[0070] Physicochemical property characterization of membranes

[0071] Before studying the physicochemical properties of the MOF-802 membrane (prepared by reacting 0.1 mg seed-loaded PVDF at 60 °C for 4 h via interfacial coordination growth), we further investigated the diffusion rate during membrane preparation to understand the method of induced interfacial coordination growth. For example... Figure 12 As shown in Figure a, we found that the diffusion rate of the ligands is much higher than that of the metal clusters, which is due to the higher osmotic pressure generated by the linear configuration and higher concentration. This indicates that during the induced interfacial coordination growth process, the metal source can be considered static, and a sufficient number of ligands continuously diffuse to the support surface to coordinate with the metal clusters, thereby inducing the growth of the MOF-802 film at the seed layer. The XRD pattern of the obtained MOF-802 film is compared with the simulated pattern. Figure 1 This indicates that MOF-802 films were successfully prepared using the induced interfacial coordination growth method. Figure 12 (Region b). Meanwhile, as the temperature rises to 80℃, the MOF-802 membrane still maintains structural stability. Figure 12The presence of the b-region indicates that MOF-802 is expected to exhibit stable separation performance at different operating temperatures, meeting the needs of practical applications. Furthermore, MOF-802 has a BET specific surface area of ​​992.02 m². 2 ·g -1 The micropore size is mainly distributed in the range of ~0.44 nm. Figure 12 (Middle c region). Furthermore, MOF-802 exhibits a higher gas adsorption rate for CO2 compared to H2. Figure 12 (in the middle d region), which enables the MOF-802 membrane with strong adsorption enthalpy to overcome the energy barrier for CO2 molecules to enter the MOF-802 channels and diffuse through them.

[0072] Gas separation performance

[0073] The gas permeation performance of MOF-802 membranes prepared by interfacial coordination growth at 60℃ for 4 hours with PVDF seed loading of 0.1 mg was investigated. Figure 13 First, the transport characteristics of H2 and CO2 by MOF-802 membranes of different thicknesses were studied. The results showed that gas permeability gradually decreased, while H2 / CO2 selectivity increased. Figure 14 The MOF-802 membrane with a thickness of approximately 1.5 μm exhibits the best H2 / CO2 separation performance, with an H2 permeability of approximately 3785 GPU and a selectivity of approximately 24. Figure 15 This is because of the H2 molecule (kinetic diameter: Compared to ), the dynamic diameter is larger. Larger CO2 molecules encounter greater transport resistance when passing through the MOF-802 membrane. Furthermore, we tested the permeation of the optimized MOF-802 membrane for gases with different kinetic diameters: nitrogen (N2), methane (CH4), propylene (C3H6), and propane (C3H8). Surprisingly, compared to N2 and CH4, the smaller CO2 molecules exhibited lower permeability. Figure 15 This is because there are favorable intermolecular interactions between CO2 and MOF-802, and MOF-802 has a high adsorption capacity for CO2, such as... Figure 12 The gas adsorption results in the middle d region are shown. The selectivity for H2 / C3H6 and H2 / C3H8 gas pairs exceeds 45%, indicating extremely strong molecular sieving ability, with molecular resolution down to the sub-nanometer scale. This excellent H2 sieving performance can be attributed to the abundant sub-nanometer channels in the MOF-802 membrane and its preferential adsorption capacity for CO2 molecules.

[0074] This invention also investigated the effects of operating conditions (such as temperature and pressure) on H2 / CO2 separation performance. Figure 16As shown in region a, the gas permeability increases with increasing test temperature due to the enhanced driving force. Although the H2 / CO2 selectivity shows a slight decreasing trend, the MOF-802 membrane (prepared by reacting 0.1 mg seed-loaded PVDF at 60 °C for 4 h via interfacial coordination growth) still exhibits excellent separation performance. Even when the temperature is assessed at 65 °C, its H2 permeability remains as high as ~4672 GPU, and its selectivity is as high as ~15.1. This can be attributed to its good mechanical stability at different temperatures, which is also confirmed by XRD results. Figure 4 (Region b). To better understand the relationship between separation performance and temperature, we also calculated the activation energies Ea of H2 and CO2 molecules based on the Arrhenius equation. Figure 16 (Region b). The results showed that the activation energy of CO2, Ea (12.18 kJ·mol⁻¹), was... -1 (5.43 kJ·mol) is greater than H2. -1 This indicates that as temperature increases, the permeability of CO2 increases more significantly than that of H2, leading to a slight decrease in selectivity. Furthermore, as feed pressure increases, a slight increase in selectivity is observed, while the permeability of H2 and CO2 decreases slightly. This is because increased pressure enhances the adsorption of H2 and CO2, thus hindering their transport. Figure 12 Middle d region and Figure 16 (Middle c region). We found that adding water vapor to the feed gas slightly decreased the H2 permeability and H2 / CO2 selectivity. Figure 16 The separation efficiency is still quite good, with an H2 permeability of approximately 3270 GPU and a selectivity of approximately 19%. This is because the high connectivity provides a steric barrier for the metal clusters and gives MOF-802 high stability to water, thus demonstrating the potential application of MOF-802 membranes in H2 purification.

[0075] Furthermore, this invention also evaluated the effect of operating time on the separation performance of the MOF-802 membrane (prepared by reacting 0.1 mg seed-loaded PVDF at 60 °C for 4 h via interfacial coordination growth). Figure 17 As shown in region a, with an H2 / CO2 mixed gas (volume ratio of 50:50) as feed, no decrease in gas permeability and selectivity of the MOF-802 membrane was observed during long-term continuous measurements exceeding 100 hours. This indicates that the MOF-802 membrane possesses excellent structural stability and can withstand long-term continuous gas permeation. Its separation performance exceeds the upper limit of conventional polymer membranes as proposed by Robeson in 2008, and is also superior to most membranes currently reported, including two-dimensional membranes, composite membranes, carbon molecular sieve membranes, and MOF membranes. Figure 17The b region (as shown in Table 1) demonstrates great potential in the H2 purification process.

[0076] Table 1 Comparison of H2 / CO2 separation performance between MOF-802 membrane and existing membranes

[0077]

[0078] In summary, this invention demonstrates the construction of continuous and alternating growth of MOF-802 membranes through a novel seed-induced interface coordination growth (SICG) strategy. The study found that this method avoids the explosive nucleation and rapid growth of MOF-802 in the reaction solution, thereby forming a MOF-802 membrane layer on the support surface. Furthermore, the MOF seed layer is crucial for the growth of continuous MOF membranes. It provides abundant nucleation sites, inducing the alternating growth of MOF-802 crystals into a continuous membrane. The prepared MOF-802 membrane exhibits excellent H2 / CO2 separation performance. Even in the presence of water vapor in the feed gas, due to its excellent water stability, the H2 permeability reaches 3270 GPU, with a selectivity of 19, demonstrating its great potential for purifying H2 in practical applications. The MOF-802 membrane constructed using this method can promote the development of high-valent MOF membranes.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a MOF-802 separation membrane, characterized in that, Includes the following steps: Preparation of MOF-802 seed solution; A MOF-802 seed layer was deposited on the surface of the support. The induced interface coordination growth method generates a MOF-802 film on the surface of a support with a MOF-802 seed layer deposited on the surface. The interface coordination growth method includes the following steps: The metal source solution and the organic ligand solution were placed on opposite sides of a porous medium and kept at 50-70℃ for 3-6 hours. The precipitate from the metal source solution side was collected by centrifugation and dried to obtain MOF-802 seed crystals. The MOF-802 seed crystals were then dispersed in deionized water and sonicated for 1-3 hours to obtain the MOF-802 seed crystal solution. The metal source solution was obtained by dissolving ZrOCl2-8H2O in an aqueous acetic acid solution, and the organic ligand solution was obtained by dispersing 3,5-pyrazole dicarboxylic acid in an aqueous acetic acid solution. The specific method for generating a MOF-802 film on the surface of the support is as follows: The metal source solution and the organic ligand solution are placed on both sides of a support on which a MOF-802 seed layer is deposited, respectively. The temperature is raised and maintained. Then the support on which the MOF-802 film is formed is washed and dried.

2. The method for preparing the MOF-802 separation membrane according to claim 1, characterized in that, The support is any one of porous Al2O3, polyvinylidene fluoride, polyacrylonitrile, nylon and polytetrafluoroethylene; The loading of the MOF-802 seed layer on the surface of the support is 20-50 cm. 2 The surface loading is 0.05-2 mg.

3. The method for preparing the MOF-802 separation membrane according to claim 1, characterized in that, MOF-802 seed layer is deposited on the surface of the support substrate by filtration. The specific operating conditions are: 0.5-2 bar pressure to drive the MOF-802 seed layer to be deposited on the surface of the support substrate; and then the support with the seed layer deposited on the surface is dried at 40-80℃.

4. The method for preparing the MOF-802 separation membrane according to claim 1, characterized in that, The conditions for heating and holding at that temperature are: 50-70℃ for 2-6 hours; the conditions for drying the support for forming the MOF-802 film on the surface after washing are: 75-90℃ for 10-15 hours.

5. The method for preparing the MOF-802 separation membrane according to claim 1, characterized in that, In the metal source solution, the ratio of ZrOCl2-8H2O, acetic acid, and water is (210-280) mg: (8-15) mL: (30-60) mL; In the organic ligand solution, the ratio of 3,5-pyrazole dicarboxylic acid, acetic acid, and water is (1-4) mg: (8-15) mL: (30-60) mL; Furthermore, the weight ratio of ZrOCl2-8H2O to 3,5-pyrazole dicarboxylic acid is 150-300:1.5-2.

5.

6. A MOF-802 separation membrane, characterized in that, Prepared by the method described in any one of claims 1-5.

7. The application of the MOF-802 separation membrane according to claim 6 in H2 purification.

8. The application of the MOF-802 separation membrane according to claim 7 in H2 purification, characterized in that, The MOF-802 separation membrane is used to separate H2 from a mixture of H2 with CO2, N2, CH4, C3H6 or C3H8.

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