A high-flux MOF membrane material, preparation method and application

Abstract

This invention provides a high-throughput MOF membrane material, its preparation method, and its application, belonging to the field of gas separation. The method involves introducing water and triethylamine to achieve simple preparation of Co-MOF two-dimensional nanosheets at room temperature. These nanosheets are then deposited onto a substrate surface using vacuum filtration, followed by a coupled "seed etching-secondary growth" process to prepare the MOF crystalline membrane. The preparation method provided by this invention is simple, reliable, and environmentally friendly, and the prepared MOF membrane exhibits excellent gas separation performance.

Description

Technical Field

[0001] This invention belongs to the field of gas separation and relates to a high-throughput MOF membrane material, its preparation method, and its application. Background Technology

[0002] Because the combustion of traditional fossil fuels emits large amounts of greenhouse gases (CO2, CH4, N2O, etc.), contributing to global warming and climate change (GWCC), carbon capture and storage (CCS) is of paramount importance. Traditional separation methods (such as adsorption and absorption) suffer from high energy consumption. Membrane separation, with its advantages of low energy consumption, small footprint, easy coupling, and environmental friendliness, has broad application prospects in the field of gas separation. The membrane material, as the core component, determines the membrane separation performance.

[0003] Metal-organic frameworks (MOFs) are a class of porous structures with periodic networks, self-assembled from metal ions and organic ligands. They exhibit diverse structures and functions, and their unsaturated metal sites can coordinate with gas molecules, facilitating selective gas transport. MOFs possess abundant porous structures, and their pore size is easily controlled, making it easy to achieve high selective gas permeability. Traditional MOF membranes are typically prepared using in-situ growth methods. Caro et al. used an in-situ growth method to prepare ZIF-8 crystalline membranes on a silane coupling agent-modified AAO substrate, achieving an H2 / CO2 selectivity of 6.5 and an H2 permeation flux of 9.5 × 10⁻⁶. -8 mol·m -2 s -1 pa -1 However, the membrane thickness is approximately 12 μm. This is due to the low density and uneven distribution of crystal nuclei generated by the in-situ growth method, resulting in poor film formation. Therefore, the only way to ensure gas selectivity is to increase the membrane thickness, which significantly increases the transport path and gas transport resistance, thus reducing the membrane's permeation flux. High permeation flux is precisely the key to industrial applications.

[0004] Researchers have proposed introducing dense and uniform seed crystals beforehand to increase the nucleus density and thus improve the membrane's compactness. Two-dimensional materials (such as GO and Mxene) possess characteristics such as single-atom-layer thickness, high specific surface area, and high chemical and mechanical stability. Their abundant metal ions or oxygen-containing functional groups on their surfaces can provide nucleation sites for MOF growth, and therefore they are often used in secondary growth methods to prepare MOF membranes. For example, using GO nanosheets as a seed layer can produce ultrathin, defect-free ZIF-8 membranes. Under test conditions of 25℃ and 1 bar, the ZIF-8 / GO membrane exhibits a selectivity of up to 405 for H2 / C3H8. The introduction of an ultrathin seed layer effectively improves the density of the seed crystals, significantly reducing non-selective defects during secondary growth, thus greatly reducing the membrane thickness and improving gas flux. However, due to the impermeability of most two-dimensional materials, they become obstacles to gas transport in MOF membrane structures, hindering the improvement of gas flux. Therefore, how to balance the defect-free structure and high permeability of MOF membranes has become a current research focus in the field of separation membranes.

[0005] Two-dimensional MOF nanosheets also possess atomic-level thickness, and their abundant porous structure allows for the permeation of various gas molecules. However, the surface of two-dimensional MOF nanosheets is rich in saturated metal sites, thus failing to provide growth sites for seed crystals. Therefore, this invention proposes using organic ligands to etch two-dimensional MOF nanosheets, transforming their surface metal sites into an unsaturated state; the etched two-dimensional MOF nanosheets are then used as a secondary growth seed layer, enabling the fabrication of ultrathin, dense MOF films. The introduced two-dimensional MOF nanosheets do not impede gas transport, thus achieving high gas selectivity and high permeability, meeting industrial requirements and possessing broad prospects for industrial applications. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing high-throughput MOF membrane materials, which can produce high-throughput MOF membranes.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a high-flux MOF membrane material includes the following steps:

[0009] Step 1: Prepare reaction solution A

[0010] Cobalt source was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 1.2–3.6 mmol of cobalt source was added to every 25 mL of DMF solution.

[0011] Step 2: Preparation of reaction solution B

[0012] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 1-25 mL of water, and 1-25 mL of triethylamine were added to every 30 mL of the mixed solution.

[0013] Step 3: Crystallization

[0014] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 3-12 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:0.25-1:4.

[0015] The reaction mechanism of this step is as follows: water has a specific coordination effect with the Co active sites on the surface of Co-MOF nanosheets, thus competing with phthalic acid for coordination and occupying the active sites on the nanosheet surface, inhibiting the growth of Co-MOF crystals along the normal direction, thereby realizing the preparation of ultrathin nanosheets; at the same time, triethylamine can promote the deprotonation of terephthalic acid, thereby lowering the reaction temperature, thus enabling the formation of Co-MOF nanosheets at room temperature.

[0016] Step 4: Seed Etching

[0017] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 0.5-2 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 2-6 h, the nanosheets were deposited onto the substrate surface by vacuum filtration. After standing for 2-12 h, the Co-MOF seed layer was obtained after the film dried.

[0018] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in a forced-air drying oven at 30-80℃ for 1-4 hours to react and etch, finally obtaining the seed layer.

[0019] The reaction mechanism of this step is as follows: 2-methylimidazole is used to replace the OH on the surface of the 2D Co-MOF seed layer. The organic ligand 2-methylimidazole is exposed on the surface of the 2D Co-MOF seed layer, thereby changing the saturated metal site into an unsaturated active site. It can further coordinate with metal ions in the synthesis solution, improve the induction ability of the seed layer, and provide high-density and high-activity growth sites for the subsequent growth of MOF film.

[0020] Step 5: Secondary Growth

[0021] 5.1) Add methanol solution A containing a metal source to methanol solution B containing an organic ligand and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0022] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a forced-air drying oven at 30-160℃ for 1-12 hours to obtain the MOF film.

[0023] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 1-24 hours. Afterward, remove the MOF membrane, allow it to dry, and it can then be used for characterization and gas separation testing.

[0024] The reaction process in this step is as follows: the Co-MOF seed layer is etched to provide heterogeneous nucleation active sites, the metal source preferentially coordinates with the 2-methylimidazolium ligand on the surface of the seed layer, and then the MOF crystal can grow heterogeneously on the surface of the seed layer, eventually forming a continuous and defect-free MOF film.

[0025] Furthermore, the cobalt source in the first step includes cobalt nitrate, cobalt chloride, and cobalt acetate.

[0026] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0027] Furthermore, the substrate in the fourth step includes α-Al2O3, PES, PTFE, PVDF, and PP.

[0028] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 1-4M.

[0029] Furthermore, in the fifth step, the concentration of the metal source in methanol solution A is 0.5-2 mol / L; the concentration of the organic ligand in methanol solution B is 0.5-2 mol / L, and the concentration of sodium formate is 1 mol / L.

[0030] Furthermore, in the fifth step, the metal source can be zinc nitrate, cobalt nitrate, nickel nitrate, nickel chloride, zinc chloride, or cobalt chloride. The organic ligand can be benzimidazole, 2-methylimidazole, terephthalic acid, trimesic acid, or 4,4-bipyridine.

[0031] A high-flux MOF membrane material is provided, wherein the MOF membrane material has a 2D Co-MOF@MOF composite structure. The ultrathin and porous 2D Co-MOF layer has ultra-low mass transfer resistance to gas molecules, ensuring high gas permeability of the composite membrane, and effectively promotes heterogeneous nucleation and growth of MOF crystal membrane, ensuring high gas selectivity.

[0032] Applications of a high-throughput MOF membrane material for H2 purification, including: H2 / N2, H2 / CO2, H2 / O2, and H2 / CH4.

[0033] The beneficial effects of this invention are:

[0034] (1) The method of the present invention can achieve the simple preparation of 2D MOF nanosheets at room temperature by adding water and triethylamine. The reaction medium used has low toxicity and is an environmentally friendly reaction.

[0035] (2) The method of the present invention uses organic ligands to etch the surface of 2D MOF nanosheets, so that the saturated metal on the surface is converted into an unsaturated active state, providing active sites for subsequent MOF growth, promoting the formation of defect-free MOF films, and facilitating a significant reduction in film thickness.

[0036] (3) The method of this invention uses 2D MOF nanosheets as seed crystals. Their ultrathin and porous structure can significantly shorten the gas transport path, reduce gas permeation resistance, and increase the gas flux of the membrane. This method has low raw material costs and simple experimental operation. Attached Figure Description

[0037] Figure 1 This is a SEM image of the Co-MOF nanosheets prepared in Example 1.

[0038] Figure 2 The images show the FT-IR spectra of the Co-MOF nanosheets prepared in Example 3, the etched Co-MOF seed layer, and the ZIF-8 film.

[0039] Figure 3 In Example 3, a is the XRD pattern of the Co-MOF nanosheet seed layer on the substrate, and b is the XRD pattern of the etched seed layer and ZIF-8 film.

[0040] Figure 4 In Figure a, the surface SEM image of the MOF film prepared by the seed-secondary growth method in Example 4 is shown; in Figure b, the cross-sectional MOF image of the ZIF-8 film prepared in Example 3 is shown.

[0041] Figure 5 This is a graph showing the permeation flux of the MOF membrane for H2 and CO2 and its separation performance for H2 / CO2 under different feed pressures in Example 4. Detailed Implementation

[0042] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0043] Example 1

[0044] Step 1: Prepare reaction solution A

[0045] Cobalt nitrate was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 3.6 mmol of cobalt nitrate was added to every 25 mL of DMF solution.

[0046] Step 2: Preparation of reaction solution B

[0047] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 1 mL of water, and 5 mL of triethylamine were added to every 30 mL of the mixed solution.

[0048] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0049] Step 3: Crystallization

[0050] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 3 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:4.

[0051] Step 4: Seed Etching

[0052] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 2 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 6 h, the nanosheets were deposited onto the surface of a PVDF substrate by vacuum filtration. After standing for 6 h, the Co-MOF seed layer was obtained after the film dried.

[0053] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in an 80°C drying oven for 4 hours to etch and finally obtain the seed layer.

[0054] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 4M.

[0055] Step 5: Secondary Growth

[0056] 5.1) Add methanol solution A containing zinc nitrate to methanol solution B containing benzimidazole and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0057] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a forced-air drying oven at 120°C for 1 hour to obtain the MOF film.

[0058] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 1 hour. Afterward, remove the MOF membrane and allow it to dry before using it for characterization and gas separation testing.

[0059] Furthermore, in the fifth step, the concentration of zinc nitrate in methanol solution A is 2 mol / L; the concentration of benzimidazole in methanol solution B is 0.5 mol / L, and the concentration of sodium formate is 1 mol / L.

[0060] like Figure 1 As shown, the prepared Co-MOF nanosheets have a two-dimensional ultrathin structure with a size of about 500 nm, which is suitable for the preparation of seed layers.

[0061] At 1 bar and 298 K, the H2 flux of the obtained MOF membrane was 2 × 10⁻⁶. -6 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 4.2, for H2 / N2 it was 3.5, for H2 / O2 it was 4.7, and for H2 / CH4 it was 6.2.

[0062] Example 2

[0063] Step 1: Prepare reaction solution A

[0064] Cobalt nitrate was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 1.2 mmol of cobalt nitrate was added to every 25 mL of DMF solution.

[0065] Step 2: Preparation of reaction solution B

[0066] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 5 mL of water, and 25 mL of triethylamine were added to every 30 mL of the mixed solution.

[0067] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0068] Step 3: Crystallization

[0069] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:0.25.

[0070] Step 4: Seed Etching

[0071] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 1 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 4 h, the nanosheets were deposited onto the surface of an α-Al2O3 substrate by vacuum filtration. After standing for 8 h, the Co-MOF seed layer was obtained after the film dried.

[0072] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in an 80°C drying oven for 2 hours to etch and finally obtain the seed layer.

[0073] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 1M.

[0074] Step 5: Secondary Growth

[0075] 5.1) Add methanol solution A containing nickel chloride to methanol solution B containing pyromellitic acid and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0076] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a forced-air drying oven at 160°C for 12 hours to obtain the MOF membrane.

[0077] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 24 hours. Afterward, remove the MOF membrane, allow it to dry, and it can be used for characterization and gas separation testing.

[0078] Furthermore, in the fifth step, the concentration of nickel chloride in methanol solution A is 1 mol / L; the concentration of trimesic acid in methanol solution B is 2 mol / L, and the concentration of sodium formate is 1 mol / L.

[0079] At 1 bar and 298 K, the H2 flux of the obtained MOF membrane was 2 × 10⁻⁶. -7 mol·m -2 ·s -1 ·Pa -1The selectivity for H2 / CO2 was 8.7, for H2 / N2 it was 7.5, for H2 / O2 it was 8.7, and for H2 / CH4 it was 9.2.

[0080] Example 3

[0081] Step 1: Prepare reaction solution A

[0082] Cobalt acetate was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 2.4 mmol of cobalt acetate was added to every 25 mL of DMF solution.

[0083] Step 2: Preparation of reaction solution B

[0084] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 5 mL of water, and 1 mL of triethylamine were added to every 30 mL of the mixed solution.

[0085] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0086] Step 3: Crystallization

[0087] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 12 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:0.25.

[0088] Step 4: Seed Etching

[0089] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 1 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 4 h, the nanosheets were deposited onto the surface of a PTFE substrate by vacuum filtration. After standing for 12 h, the Co-MOF seed layer was obtained after the film dried.

[0090] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in a 30°C oven for etching for 4 hours to finally obtain the seed layer.

[0091] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 1M.

[0092] Step 5: Secondary Growth

[0093] 5.1) Add methanol solution A containing zinc chloride to methanol solution B containing 2-methylimidazole and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0094] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a 30°C forced-air drying oven for 4 hours to obtain the MOF film.

[0095] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 8 hours. Afterward, remove the MOF membrane, allow it to dry, and it can then be used for characterization and gas separation testing.

[0096] Furthermore, in the fifth step, the concentration of zinc chloride in methanol solution A is 0.5 mol / L; the concentration of 2-methylimidazole in methanol solution B is 0.5 mol / L, and the concentration of sodium formate is 1 mol / L.

[0097] like Figure 2 As shown, at 1550cm -1 and 1350cm -1 The characteristic peak appearing at 1660 cm⁻¹ is generated by the stretching vibration of the C=O double bond in terephthalic acid. After etching, the peak at 1660 cm⁻¹... -1 The strong peak at the point is attributed to the stretching vibration of C=N, thus proving the successful binding of 2-methylimidazole to Co-MOF.

[0098] like Figure 3 As shown, the XRD peak positions of the obtained Co-MOF are consistent with the standard peaks. The XRD peak positions of the seed layer after etching match those of the standard ZIF-67, indicating that ZIF-67 seeds were formed on the surface of the seed layer after etching. The peak position of the prepared MOF film is: 7.3. ° 10.3 ° 12.7 ° 14.7 ° 16.4 ° 18.0 ° 22.2 ° 24.6 ° and 26.6 ° The results are consistent with the standard ZIF-8, indicating that the preparation of the ZIF-8 film was successfully induced using the Co-MOF seed layer.

[0099] At 1 bar and 298 K, the H2 flux of the obtained MOF membrane was 1.5 × 10⁻⁶. -7 mol·m-2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 10.2, for H2 / N2 it was 9.5, for H2 / O2 it was 11.7, and for H2 / CH4 it was 13.2.

[0100] Example 4

[0101] Step 1: Prepare reaction solution A

[0102] Cobalt nitrate was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 2.4 mmol of cobalt nitrate was added to every 25 mL of DMF solution.

[0103] Step 2: Preparation of reaction solution B

[0104] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. For every 30 mL of the mixed solution, 0.6 mmol of terephthalic acid, 5 mL of water, and 5 mL of triethylamine were added.

[0105] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0106] Step 3: Crystallization

[0107] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:1.2.

[0108] Step 4: Seed Etching

[0109] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 1 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 4 h, the nanosheets were deposited onto the surface of an α-Al2O3 substrate by vacuum filtration. After standing for 8 h, the Co-MOF seed layer was obtained after the film dried.

[0110] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in a 60°C oven for etching for 2 hours to finally obtain the seed layer.

[0111] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 2M.

[0112] Step 5: Secondary Growth

[0113] 5.1) Add methanol solution A containing zinc chloride to methanol solution B containing 2-methylimidazole and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0114] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a forced-air drying oven at 80°C for 4 hours to obtain the MOF film.

[0115] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 12 hours. Afterward, remove the MOF membrane, allow it to dry, and it can then be used for characterization and gas separation testing.

[0116] Furthermore, in the fifth step, the concentration of zinc chloride in methanol solution A is 1 mol / L; the concentration of 2-methylimidazole in methanol solution B is 1 mol / L, and the concentration of sodium formate is 1 mol / L.

[0117] At 1 bar and 298 K, the H2 flux of the obtained MOF membrane was 7.6 × 10⁻⁶. -6 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 13.4, for H2 / N2 it was 12.5, for H2 / O2 it was 13.7, and for H2 / CH4 it was 16.2.

[0118] like Figure 5 As shown, the MOF membrane maintains stable flux and separation selectivity under different pressures, demonstrating excellent gas separation performance.

[0119] Example 5

[0120] Step 1: Prepare reaction solution A

[0121] Cobalt chloride was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 1.2 mmol of cobalt chloride was added to every 25 mL of DMF solution.

[0122] Step 2: Preparation of reaction solution B

[0123] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 25 mL of water, and 5 mL of triethylamine were added to every 30 mL of the mixed solution.

[0124] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0125] Step 3: Crystallization

[0126] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 3 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:1.2.

[0127] Step 4: Seed Etching

[0128] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 0.5 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 2 h, the nanosheets were deposited onto the surface of a PES substrate by vacuum filtration. After standing for 12 h, the Co-MOF seed layer was obtained after the film dried.

[0129] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in a 30°C oven for etching for 1 hour to finally obtain the seed layer.

[0130] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 4M.

[0131] Step 5: Secondary Growth

[0132] 5.1) Add methanol solution A containing cobalt nitrate to methanol solution B containing 2-methylimidazole and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0133] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a 30°C forced-air drying oven for 8 hours to obtain the MOF film.

[0134] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 1 hour. Afterward, remove the MOF membrane and allow it to dry before using it for characterization and gas separation testing.

[0135] Furthermore, in the fifth step, the concentration of cobalt nitrate in methanol solution A is 0.5 mol / L; the concentration of 2-methylimidazole in methanol solution B is 2 mol / L, and the concentration of sodium formate is 1 mol / L.

[0136] At 1 bar and 298 K, the H2 flux of the obtained MOF membrane was 5 × 10⁻⁶. -6 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 3.5, for H2 / N2 it was 2.5, for H2 / O2 it was 3.7, and for H2 / CH4 it was 6.2.

[0137] Example 6

[0138] Step 1: Prepare reaction solution A

[0139] Cobalt acetate was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 3.6 mmol of cobalt acetate was added to every 25 mL of DMF solution.

[0140] Step 2: Preparation of reaction solution B

[0141] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 5 mL of water, and 1 mL of triethylamine were added to every 30 mL of the mixed solution.

[0142] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0143] Step 3: Crystallization

[0144] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:4.

[0145] Step 4: Seed Etching

[0146] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 1 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 4 h, the nanosheets were deposited onto the surface of a PP substrate by vacuum filtration. After standing for 6 h, the Co-MOF seed layer was obtained after the film dried.

[0147] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in a 60°C oven for etching for 1 hour to finally obtain the seed layer.

[0148] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 2M.

[0149] Step 5: Secondary Growth

[0150] 5.1) Add methanol solution A containing cobalt chloride to methanol solution B containing 2-methylimidazole and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0151] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to an 80°C forced-air drying oven for 1 hour to obtain the MOF film.

[0152] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 8 hours. Afterward, remove the MOF membrane, allow it to dry, and it can then be used for characterization and gas separation testing.

[0153] Furthermore, in the fifth step, the concentration of cobalt chloride in methanol solution A is 2 mol / L; the concentration of 2-methylimidazole in methanol solution B is 1 mol / L, and the concentration of sodium formate is 1 mol / L.

[0154] At 1 bar and 298 K, the H2 flux of the obtained ZIF-8 membrane was 6 × 10⁻⁶. -5 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 4.6, for H2 / N2 it was 3.5, for H2 / O2 it was 4.7, and for H2 / CH4 it was 6.2.

[0155] Example 7

[0156] Step 1: Prepare reaction solution A

[0157] Cobalt nitrate was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 2.4 mmol of cobalt nitrate was added to every 25 mL of DMF solution.

[0158] Step 2: Preparation of reaction solution B

[0159] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 25 mL of water, and 5 mL of triethylamine were added to every 30 mL of the mixed solution.

[0160] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0161] Step 3: Crystallization

[0162] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 12 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:2.5.

[0163] Step 4: Seed Etching

[0164] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 0.5 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 2 h, the nanosheets were deposited onto the surface of an α-Al2O3 substrate by vacuum filtration. After standing for 2 h, the Co-MOF seed layer was obtained after the film dried.

[0165] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in a 60°C oven for etching for 2 hours to finally obtain the seed layer.

[0166] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 4M.

[0167] Step 5: Secondary Growth

[0168] 5.1) Add methanol solution A containing zinc nitrate to methanol solution B containing terephthalic acid and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0169] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a forced-air drying oven at 120°C for 12 hours to obtain the MOF membrane.

[0170] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 12 hours. Afterward, remove the MOF membrane, allow it to dry, and it can then be used for characterization and gas separation testing.

[0171] Furthermore, in the fifth step, the concentration of zinc nitrate in methanol solution A is 1 mol / L; the concentration of terephthalic acid in methanol solution B is 0.5 mol / L, and the concentration of sodium formate is 1 mol / L.

[0172] At 1 bar and 298 K, the H2 flux of the obtained MOF membrane was 5 × 10⁻⁶. -5 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 3.4, for H2 / N2 it was 2.7, for H2 / O2 it was 3.7, and for H2 / CH4 it was 7.1.

[0173] Example 8

[0174] Step 1: Prepare reaction solution A

[0175] Cobalt chloride was added to an N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution A. 2.4 mmol of cobalt chloride was added to every 25 mL of DMF solution.

[0176] Step 2: Preparation of reaction solution B

[0177] Terephthalic acid was added to a mixed solution of N,N-dimethylformamide and anhydrous ethanol, and stirred at room temperature. Water and triethylamine were added during stirring, and stirring continued until completely dissolved to obtain reaction solution B. Specifically, 0.6 mmol of terephthalic acid, 1 mL of water, and 25 mL of triethylamine were added to every 30 mL of the mixed solution.

[0178] Furthermore, in the second step of the mixed solution, the volume ratio of N,N-dimethylformamide to anhydrous ethanol is 5:1.

[0179] Step 3: Crystallization

[0180] The reaction solution A prepared in the first step was added to the reaction solution B prepared in the second step, and the mixture was stirred at room temperature for 9 hours. After the reaction was completed, the mixture was centrifuged three times each with N,N-dimethylformamide and anhydrous ethanol, and then dried (centrifuge speed: 8000 r / min, centrifugation time: 10 min, drying temperature: 60℃, drying time: 12 h) to obtain 2D Co-MOF. The volume ratio of reaction solution A to reaction solution B was 1:2.5.

[0181] Step 4: Seed Etching

[0182] The 2D Co-MOF nanosheets prepared in the third step were placed in a n-propanol solution, with 2 mg of 2D Co-MOF added to every 50 mL of n-propanol solution. After ultrasonic dispersion for 6 h, the nanosheets were deposited onto the surface of an α-Al2O3 substrate by vacuum filtration. After standing for 2 h, the Co-MOF seed layer was obtained after the film dried.

[0183] The Co-MOF seed layer was transferred to a methanol solution containing 2-methylimidazole, and then placed in a 60°C oven for etching for 2 hours to finally obtain the seed layer.

[0184] Furthermore, the concentration of 2-methylimidazole in the methanol solution in the fourth step is 1M.

[0185] Step 5: Secondary Growth

[0186] 5.1) Add methanol solution A containing nickel nitrate to methanol solution B containing 4,4-bipyridine and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0187] 5.2) After transferring the mixed solution to the reaction vessel, the seed layer etched in step four is vertically placed into the mixed solution and then transferred to a forced-air drying oven at 160°C for 8 hours to obtain the MOF membrane.

[0188] 5.3) After the MOF membrane cools, wash it several times with methanol solution, then immerse the MOF membrane in methanol solution for 24 hours. Afterward, remove the MOF membrane, allow it to dry, and it can be used for characterization and gas separation testing.

[0189] Furthermore, in the fifth step, the concentration of nickel nitrate in methanol solution A is 1 mol / L; the concentration of 4,4-bipyridine in methanol solution B is 2 mol / L, and the concentration of sodium formate is 1 mol / L.

[0190] At 1 bar and 298 K, the H2 flux of the obtained MOF membrane was 9 × 10⁻⁶. -6 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 7.4, for H2 / N2 it was 6.8, for H2 / O2 it was 7.7, and for H2 / CH4 it was 10.0.

[0191] Comparative Example 1

[0192] In situ growth

[0193] (1) Add methanol solution A containing zinc chloride to methanol solution B containing 2-methylimidazole and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0194] (2) After transferring the mixed solution to the reaction vessel, the α-Al2O3 substrate was vertically placed into the mixed solution and then transferred to an 80°C drying oven for 4 hours to obtain the MOF membrane.

[0195] (3) After the MOF membrane cools down, wash it several times with methanol solution, and then soak the MOF membrane in methanol solution for 12 hours. After that, take out the MOF membrane and let it dry before using it for characterization and gas separation testing.

[0196] Furthermore, in step (1), the concentration of zinc chloride in methanol solution A is 1 mol / L; the concentration of 2-methylimidazole in methanol solution B is 1 mol / L, and the concentration of sodium formate is 1 mol / L. At 1 bar and 298 K, the H2 flux of the obtained MOF membrane is 7 × 10⁻⁶. -8 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 2.9, for H2 / N2 it was 2.6, for H2 / O2 it was 3.7, and for H2 / CH4 it was 5.1.

[0197] Without using a Co-MOF seed layer, MOF membranes prepared by direct in-situ growth have low gas permeation flux due to their thicker membrane layers; at the same time, the lack of highly active sites on the substrate leads to defects in the MOF membranes, resulting in low selectivity.

[0198] Comparative Example 2

[0199] In situ growth

[0200] (1) Add methanol solution A containing zinc chloride to methanol solution B containing 2-methylimidazole and sodium formate, wherein the volume ratio of methanol solution A to methanol solution B is 1:1.

[0201] (2) After transferring the mixed solution to the reaction vessel, the α-Al2O3 substrate was vertically placed into the mixed solution and then transferred to an 80°C drying oven for 12 hours to obtain the MOF membrane.

[0202] (3) After the MOF membrane cools down, wash it several times with methanol solution, and then soak the MOF membrane in methanol solution for 12 hours. After that, take out the MOF membrane and let it dry before using it for characterization and gas separation testing.

[0203] Furthermore, in step (1), the concentration of zinc chloride in methanol solution A is 1 mol / L; the concentration of 2-methylimidazole in methanol solution B is 1 mol / L, and the concentration of sodium formate is 1 mol / L. At 1 bar and 298 K, the H2 flux of the obtained MOF membrane is 2 × 10⁻⁶. -8 mol·m -2 ·s -1 ·Pa -1 The selectivity for H2 / CO2 was 7.5, for H2 / N2 it was 6.6, for H2 / O2 it was 7.9, and for H2 / CH4 it was 10.2.

[0204] Further increasing the in-situ growth time of the MOF membrane and compensating for non-selectivity defects by increasing the membrane thickness resulted in an increase in gas selectivity, but the permeation flux was further reduced.

[0205] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method of preparing a high-flux MOF membrane material, characterized in that, The method comprises the following steps: Step 1: preparing reaction liquid A The cobalt source is added to a DMF solution, and stirred at room temperature until completely dissolved to prepare reaction liquid A; Step 2: preparing reaction liquid B The terephthalic acid is added to a mixed solution of DMF and anhydrous ethanol, and stirred at room temperature, and water and triethylamine are added during the stirring process, and the stirring is continued until completely dissolved to obtain reaction liquid B; Step 3: crystallization The reaction liquid A prepared in step 1 is added to the reaction liquid B prepared in step 2, and stirred at room temperature for 3-12 hours, and after the reaction is completed, centrifugation and drying are performed to obtain 2D Co-MOF nanosheets; the volume ratio of the reaction liquid A to the reaction liquid B is 1:0.25-1:4; Step 4: seed etching The 2D Co-MOF nanosheets prepared in step 3 are placed in a n-propyl alcohol solution, 0.5-2 mg of 2D Co-MOF is added to 50 mL of the n-propyl alcohol solution, and after ultrasonic dispersion for 2-6 hours, the solution is deposited on the surface of a substrate, and after standing for 2-12 hours, the film is dried to obtain a Co-MOF seed layer; The Co-MOF seed layer is transferred to a methanol solution containing 2-methyl imidazole, and then placed in a blast drying oven at 30-80 DEG C for reaction etching for 1-4 hours to obtain a seed layer; Step 5: secondary growth Methanol solution A containing a metal source is added to methanol solution B containing an organic ligand and sodium formate, and the volume ratio of the methanol solution A to the methanol solution B is 1:1; the obtained mixed solution is transferred to a reaction kettle, and the seed layer etched in step 4 is vertically placed in the mixed solution, and then transferred to a blast drying oven at 30-160 DEG C for reaction for 1-12 hours to obtain a MOF film, and after cooling and washing, the MOF film is immersed in a methanol solution for 1-24 hours; then the MOF film is taken out, and after drying, a continuous defect-free MOF film is obtained.

2. The method of claim 1, wherein the MOF material is a high flux MOF membrane material. The cobalt source in step 1 includes cobalt nitrate, cobalt chloride and cobalt acetate, and 1.2-3.6 mmol of the cobalt source is added to 25 mL of the DMF solution.

3. The method of claim 1, wherein the MOF material is a high flux MOF membrane material. In step 2, 0.6 mmol of terephthalic acid, 1-25 mL of water and 1-25 mL of triethylamine are added to 30 mL of the mixed solution, and the volume ratio of DMF to anhydrous ethanol in the mixed solution is 5:

1.

4. The method of claim 1, wherein the MOF material is a high flux MOF membrane material. The substrate in step 4 includes alpha-Al2O3, PES, PTFE, PVDF and PP.

5. The method of claim 1, wherein the MOF material is a high flux MOF membrane material. The concentration of 2-methyl imidazole in the methanol solution in step 4 is 1-4 M.

6. The method of claim 1, wherein the MOF material is a high flux MOF membrane material. In step 5, the concentration of the metal source in the methanol solution A is 0.5-2 mol / L, the concentration of the organic ligand in the methanol solution B is 0.5-2 mol / L, and the concentration of sodium formate is 1 mol / L.

7. The method of claim 1, wherein the MOF material is a high flux MOF membrane material. In step 5, the metal source can be zinc nitrate, cobalt nitrate, nickel nitrate, nickel chloride, zinc chloride or cobalt chloride; and the organic ligand can be benzimidazole, 2-methyl imidazole, terephthalic acid, trimesic acid or 4,4-bipyridine.

8. A high flux MOF membrane material characterized in that, The MOF film material prepared by the preparation method in any one of claims 1-7 has a 2D Co-MOF@MOF composite structure, the ultrathin porous 2D Co-MOF layer has ultralow mass transfer resistance to gas molecules, ensures high gas permeation capacity of the composite film, and effectively promotes heterogeneous nucleation and growth of the MOF crystal film, and ensures high gas selectivity.

9. Use of the high-flux MOF membrane material of claim 8, characterized in that, It is used for purification of H2, including: H2 / N2, H2 / CO2, H2 / O2, H2 / CH4.

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