MOF / COF film integrated forming method, film and application

Abstract

The invention provides an integrated forming method of an MOF / COF membrane, the membrane and mixed gas separation application, and belongs to the technical field of membrane materials, in particular to the integrated forming method of the MOF / COF membrane, which comprises the following steps: S1, mixing 1, 3, 5-triformyl phloroglucinol and octanoic acid to form a solution A; s2, 2, 5-diaminobenzene sulfonic acid and deionized water are mixed, and a solution B is formed; s3, mixing the solution A and the solution B, and reacting to obtain a COF concentrated solution; s4, mixing the COF concentrated solution and the first precursor solution, and reacting to obtain a second precursor solution; and S5, dip-coating a carrier by using the second precursor solution, and reacting the carrier to obtain the MOF / COF membrane. The MOF / COF film is prepared by adopting a one-step method, and the MOF / COF film is uniform in component distribution, free of intercrystalline defects and good in stability and gas separation performance.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and more specifically, to a method for integrally forming MOF / COF membranes, the membranes themselves, and their applications. Background Technology

[0002] Metal-organic frameworks (MOFs) are porous crystalline materials assembled from metal ions or metal clusters and organic ligands through coordination bonds. They possess characteristics such as ultra-high specific surface area, tunable pore structure, and abundant active sites. However, single MOF materials have certain limitations in gas separation applications. Covalent organic frameworks (COFs) are crystalline porous materials formed by organic monomers linked by covalent bonds. They have uniform pore size and tunable surface properties, but most COFs have low mechanical strength and are prone to cracks or defects during film formation. Furthermore, the adhesion between COFs and the substrate is weak, making it difficult for the membrane stability to meet practical application requirements.

[0003] To combine the advantages of MOF and COF while overcoming their respective shortcomings, researchers have begun exploring the construction of MOF-COF composite systems. However, due to the significant differences in the growth kinetics of MOF and COF, uneven component distribution occurs during the co-assembly process, leading to the failure of MOF-COF membrane preparation. Therefore, existing technologies mostly employ a "stepwise preparation" method to prepare MOF-COF membranes. For example, Chinese invention patent application CN117654316A discloses a MOF-COF hybrid membrane and its preparation method, which uses a COF membrane and MOF precursor solution as raw materials to prepare the MOF-COF hybrid membrane. However, the "stepwise preparation" method is relatively complex and not conducive to industrial applications. Summary of the Invention

[0004] The purpose of this invention is to simplify the preparation process of MOF / COF membranes, making them easier to use in industrial applications.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for integrally forming MOF / COF membranes, specifically including the following steps: S1: Mix 1,3,5-tricarboxymethyl phloroglucinol and octanoic acid to form solution A; S2: Mix 2,5-diaminobenzenesulfonic acid and deionized water to form solution B; S3: Mix solution A and solution B, and after reaction, obtain COF concentrate; S4: Mix the COF concentrate and the first precursor solution, and react to obtain the second precursor solution; S5: The carrier is dipped and coated with a second precursor solution, and the MOF / COF membrane is obtained after the carrier reacts.

[0006] Preferably, in step S4, the first precursor solution includes a metal node, an organic ligand, and a solvent, and the first precursor solution simultaneously satisfies a~c, wherein: a. The metal node is selected from any one or more of divalent zinc ions, divalent cobalt ions, trivalent chromium ions, and trivalent iron ions; b. The organic ligand is a nitrogen-containing heterocyclic compound; c. The solvent forms a homogeneous system with octanoic acid during the reaction, the solvent forms a homogeneous system with water during the reaction, and the solvent is inert during the reaction.

[0007] Preferably, in step S1, the concentration of 1,3,5-triformylphloroglucinol in solution A is 2.5~60mM.

[0008] Preferably, in step S2, the concentration of 2,5-diaminobenzenesulfonic acid in solution B is 2.5~60mM.

[0009] Preferably, in step S3, the mixing volume ratio of solution A and solution B is 1:(0.25~4).

[0010] Preferably, in step S4, the volume ratio of the COF concentrate to the first precursor solution is 1:(1.5~15).

[0011] Preferably, step S4 specifically includes the following steps: Stir the first precursor solution until the MOF grain diameter is 20~200nm, then add COF concentrate, and continue stirring for 1~10min to obtain the second precursor solution.

[0012] Preferably, in step S5, the heating temperature is 120~300℃ and the heating time is 5~30min.

[0013] The integrated molding method for MOF / COF membranes provided by this invention enables one-step bonding of MOF / COF membranes. In this method, COF and MOF can be simultaneously dispersed in water, laying the foundation for the subsequent synchronous crystallization of MOF and COF without phase separation. Furthermore, in preparing the second precursor solution, this invention first pre-grows MOF crystals to a particle size of 20-200 nm, providing growth sites for the subsequent COF monomers and enabling covalent bonding between the sulfonic acid groups in COF and the metal nodes in MOF. Finally, this invention dip-coats the support with the second precursor solution at 120-300°C. This step triggers the coordination reaction of MOF and the condensation reaction of COF, ultimately forming the MOF / COF membrane.

[0014] A second aspect of the present invention provides a MOF / COF membrane, wherein the MOF / COF membrane is prepared by the integral molding method of the MOF / COF membrane described in the first aspect.

[0015] A third aspect of the present invention provides an application of the MOF / COF membrane described in the second aspect, the application comprising using the MOF / COF membrane for the separation of a mixed gas, wherein the mixed gas is any one of a hydrogen-helium mixture, a helium-nitrogen mixture, a helium-methane mixture, a carbon dioxide-methane mixture, a carbon dioxide-nitrogen mixture, and a propylene-propane mixture.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a precursor solution to directly form MOF / COF membranes, omitting the stepwise synthesis and layer-by-layer assembly steps of MOF or COF membranes, which can effectively shorten the production time of MOF / COF membranes; 2. This invention uses a homogeneous solvent system to ensure that MOF and COF crystallize simultaneously, overcoming the defect of uneven component distribution in traditional MOF / COF films. The MOF / COF film prepared by the method provided in this invention has the advantages of dense structure and no intergranular defects. 3. Because the MOF / COF membrane obtained by this invention has a dense structure and no intergranular defects, it has high mechanical strength and can exhibit extremely strong stability under gas separation pressure. 4. The MOF / COF membrane prepared by this invention has a uniform pore structure, which can realize the separation of various mixed gases and has broad application prospects in petrochemical, industrial flue gas and other fields. Attached Figure Description

[0017] Figure 1 The XRD characterization results are for product M1 in Comparative Example 1 of this invention. Figure 2 The above are the SEM characterization results of product M1 in Comparative Example 1 of this invention; Figure 3 The XRD characterization results are for product M7 in Embodiment 1 of this invention; Figure 4 The above are the SEM characterization results of product M7 in Embodiment 1 of the present invention; Figure 5 The results of cross-sectional SEM characterization of product M7 in Embodiment 1 of the present invention; Figure 6 The infrared spectral detection results of product C1 in Embodiment 2 of the present invention; Figure 7 The above are the SEM characterization results of product C1 in Embodiment 2 of the present invention; Figure 8 The above are the SEM characterization results of product C1 in Embodiment 2 of the present invention. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the present invention.

[0019] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] As described in the background section, MOF / COF membranes suffer from defects such as uneven component distribution and complex preparation processes. Therefore, this invention provides a method for integrally molding MOF / COF membranes, comprising the following steps: S1: Mix 1,3,5-tricarboxymethyl phloroglucinol and octanoic acid to form solution A; S2: Mix 2,5-diaminobenzenesulfonic acid and deionized water to form solution B; S3: Mix solution A and solution B, and after reaction, obtain COF concentrate; S4: Mix the COF concentrate and the first precursor solution, and react to obtain the second precursor solution; S5: The carrier is dipped and coated with a second precursor solution, and the MOF / COF membrane is obtained after the carrier reacts.

[0021] More specifically, in the above embodiments, the support can be selected from any one of α-Al2O3 support, γ-Al2O3 support, anodic aluminum oxide support, TiO2 support, and polymer support.

[0022] In the above embodiments, the COF concentrate contains a sulfonic acid covalent organic framework material (TpPa-SO3H), and the sulfonic acid groups in TpPa-SO3H can be covalently linked to the MOF after being incorporated into the MOF.

[0023] In the above embodiments, the COF concentrate is synthesized by a "two-phase method", which includes using 1,3,5-tricarboxymethyl phloroglucinol and octanoic acid to synthesize the top layer solution A, 2,5-diaminobenzenesulfonic acid and deionized water to synthesize the bottom layer solution B, and then dialysis after mixing solutions A and B to obtain the COF concentrate.

[0024] In step S4 of the above embodiment, the first precursor liquid includes a metal node, an organic ligand, and a solvent, and the first precursor liquid simultaneously satisfies a~c, wherein: a. The metal node is selected from any one or more of divalent zinc ions, divalent cobalt ions, trivalent chromium ions, and trivalent iron ions; b. The organic ligand is a nitrogen-containing heterocyclic compound; c. The solvent forms a homogeneous system with octanoic acid during the reaction, the solvent forms a homogeneous system with water during the reaction, and the solvent is inert during the reaction.

[0025] More specifically, in the above embodiments, the organic ligand in the first precursor solution is preferably one or more of imidazole-2-carboxaldehyde, 2-methylimidazolium, benzimidazole, 2-aminobenzimidazole, and imidazole.

[0026] More specifically, in the above embodiments, the solvent is preferably an aqueous solution of N,N-dimethylacetamide (DMAc).

[0027] More specifically, in the above embodiments, the preferred molar ratio of metal nodes, organic ligands, water, and DMAc in the first precursor solution is 1:(0.2~4):(20~200):(10~100).

[0028] More specifically, in the above embodiments, the first precursor liquid is preferably any one of ZIF-8, ZIF-7, ZIF-93, ZIF-67, and ZIF-90, with ZIF-8 and ZIF-90 being the most preferred.

[0029] In step S1 of the above embodiment, the concentration of 1,3,5-tricarboxymethyl phloroglucinol in solution A is 2.5~60mM.

[0030] In step S2 of the above embodiment, the concentration of 2,5-diaminobenzenesulfonic acid in solution B is 2.5~60mM.

[0031] In step S3 of the above embodiment, the mixing volume ratio of solution A and solution B is 1:(0.25~4).

[0032] In step S4 of the above embodiment, the volume ratio of the COF concentrate to the first precursor solution is 1:(1.5~15).

[0033] In the above implementation, step S4 specifically includes the following steps: Stir the first precursor solution until the MOF grain diameter is 20~200nm, then add COF concentrate, and continue stirring for 1~10min to obtain the second precursor solution.

[0034] In step S5 of the above embodiment, the heating temperature is 120~300℃ and the heating time is 5~30min.

[0035] The MOF / COF membrane prepared using the above-described method features COF nanoparticles uniformly embedded within the MOF crystal network, forming a hybrid structure where the MOF framework supports the COF nanoparticles. The coordination bonds of the MOF and the covalent bonds of the COF framework combine, enhancing the membrane's thermal and chemical stability while simultaneously reducing the pore size, resulting in a continuous and dense hybrid membrane. The process is completed through a series of steps: mixing a concentrated COF solution with a first precursor solution, dip-coating, and heat curing. This requires no complex equipment, and the COF / MOF ratio can be controlled by the precursor solution concentration, ensuring high repeatability. Furthermore, the dip-coating method ensures a strong bond between the membrane and the support, improving the adhesion between the COF and the substrate. The prepared membrane exhibits a uniform structure, strong stability, and high gas separation performance.

[0036] The technical solutions of the present invention are further described below through specific embodiments. Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art. In some cases, terms with a conventional understanding are limited herein for clarification or ease of reference, and such limitations should not be construed as indicating a significant difference from the conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and have been adopted by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0037] Comparative Example 1 Comparison with CN111841333A The ZIF-8 precursor solution was synthesized using the preparation method disclosed in Chinese invention patent application CN111841333A, with a molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, H2O and DMAc of 1:2:45:18. After dipping an Al2O3 support in the solution, the reaction was carried out in a forced-air oven at 200 °C for 15 min to obtain the ZIF-8 membrane. The experiment was repeated three times, and the products were designated as M1~M3.

[0038] The results of the carbon dioxide / nitrogen separation selectivity and permeability test of products M1~M3 are shown in Table 1. As can be seen from Table 1, the ZIF-8 membrane disclosed in CN111841333A does not have the ability to separate carbon dioxide / nitrogen mixed gas.

[0039] Table 1 Product M1 was subjected to XRD characterization, and the results are as follows: Figure 1 As shown, by Figure 1As can be seen, product M1 exhibits the characteristic peak of a metal-organic framework at 2θ=7.3°.

[0040] Product M1 was subjected to SEM characterization, and the results are as follows: Figure 2 As shown, by Figure 2 It is evident that product M1 has a complete crystal morphology and a continuous and smooth film layer.

[0041] Example 1 Effect of different COF concentrate incorporation volumes on ZIF-8 / COF membranes S1: Mix 0.6 mmol of 1,3,5-tricarboxymethyl phloroglucinol and 120 mL of octanoic acid to form solution A; S2: Mix 0.9 mmol of 2,5-diaminobenzenesulfonic acid and 180 mL of deionized water to form solution B; S3: Add solution B to solution A, react for 5 days, and then dialyze in deionized water for 3 days to obtain 140 mL of COF concentrate. The test showed that TpPa-SO3H nanosheets in the COF concentrate were uniformly distributed in water with a mass concentration of 0.003 g / mL. S4: The first precursor solution was synthesized according to the molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, H2O and DMAc of 1:2:45:18. 7.5 mL of the first precursor solution was stirred until the crystals grew to a diameter of 20~200 nm. 1~4 mL of COF concentrate was added, and the reaction was stirred for 5 min to obtain the second precursor solution. S5: The Al2O3 support is dip-coated with the second precursor solution. After the Al2O3 support is dip-coated, it is reacted in a blower at 200°C for 15 min to obtain the MOF / COF membrane.

[0042] To ensure the accuracy of the experimental results, each parameter of the above experiment was repeated 3 times. The final products were marked as M4~M15, as shown in Table 1.

[0043] The selectivity and permeability of carbon dioxide / nitrogen separation for products M4~M15 are shown in Table 2. As can be seen from Table 2, when the amount of COF concentrate added is 2 mL, the MOF / COF membrane prepared in this example exhibits excellent carbon dioxide / nitrogen separation performance. When the doping amount is lower or higher than this ratio, the carbon dioxide / nitrogen separation performance of the MOF / COF membrane will decrease.

[0044] Table 2 Product M7 was subjected to XRD characterization. The XRD characterization results of product M7 are as follows: Figure 3 As shown, Figure 3 It can be seen that the characteristic peak of the metal-organic framework is displayed at 2θ=7.3°.

[0045] Product M7 was subjected to SEM characterization. The SEM characterization results of product M7 are as follows: Figure 4 As shown, Figure 4 It can be seen that COF nanoparticles are uniformly embedded in MOF crystals, and MOF grains are much larger than COF nanoparticles.

[0046] SEM images of the cross-section of product M7 are shown below. Figure 5 As shown, by Figure 5 It can be seen that the film thickness of product M7 is 1.87 μm.

[0047] Example 2 Preparation of ZIF-8 / COF powder S1: Mix 0.6 mmol of 1,3,5-tricarboxymethyl phloroglucinol and 120 mL of octanoic acid to form solution A; S2: Mix 0.9 mmol of 2,5-diaminobenzenesulfonic acid and 180 mL of deionized water to form solution B; S3: Add solution B to solution A, react for 5 days, and then dialyze in deionized water for 3 days to obtain 140 mL of COF concentrate. S4: The first precursor solution was synthesized according to the molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, H2O and DMAc of 1:2:45:18. 7.5 mL of the first precursor solution was stirred until the crystals grew to a diameter of 20~200 nm. 5 mL of COF concentrate was added, and the reaction was stirred for 15 min to obtain the second precursor solution. S5: The second precursor solution was placed in a 200°C blower and reacted for 15 minutes to obtain the MOF / COF membrane.

[0048] The above experiment was conducted three times to obtain products C1 to C3.

[0049] The infrared spectrum (IR) of product C1 was detected, and the characterization results are as follows: Figure 6 As shown, by Figure 6 As can be seen, the infrared spectrum shows the CN characteristic peak, which indicates that the sulfonic acid-based covalent organic framework material in the COF concentrate is incorporated into ZIF-8.

[0050] SEM characterization results of product C1 at different resolutions are as follows: Figure 7 and Figure 8 As shown, by Figure 7 and Figure 8 It is evident that COF nanoparticles have been incorporated into MOF, which is consistent with the characterization results of Example 1.

[0051] Example 3 Preparation of ZIF-90 / COF membrane S1: Mix 0.6 mmol of 1,3,5-tricarboxymethyl phloroglucinol and 120 mL of octanoic acid to form solution A; S2: Mix 0.9 mmol of 2,5-diaminobenzenesulfonic acid and 180 mL of deionized water to form solution B; S3: Add solution B to solution A, react for 5 days, and then dialyze in deionized water for 3 days to obtain 140 mL of COF concentrate; S4: Dissolve 0.577 g imidazole-2-carboxaldehyde in 15 ml methanol at 80 °C, cool to room temperature, add 0.66 g zinc acetate dihydrate, stir in an ice bath for 8 min to obtain the first precursor solution, stir 7.5 mL of the first precursor solution until the crystals grow to a diameter of 20~200 nm, add 2 mL of COF concentrate, stir the reaction for 5 min to obtain the second precursor solution; S5: The Al2O3 support is dip-coated with the second precursor solution. After the Al2O3 support is dip-coated, it is reacted in a blower at 200°C for 15 min to obtain the MOF / COF membrane.

[0052] The above experiment was repeated three times, and the resulting products were labeled M16~M18. The results of the carbon dioxide / methane separation selectivity and carbon dioxide permeability of products M16~M18 are shown in Table 3.

[0053] Table 3 As shown in Table 3, when ZIF-90 is used, the prepared MOF / COF membrane also has good gas separation performance.

[0054] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for integrally forming a MOF / COF film, characterized by, The method comprises the following steps: S1: mixing 1,3,5-triformylphloroglucinol and octanoic acid to form solution A; S2: mixing 2,5-diaminobenzenesulfonic acid and deionized water to form solution B; S3: mixing solution A and solution B to obtain COF concentrated solution after reaction; S4: mixing the COF concentrated solution and a first precursor solution to obtain a second precursor solution, wherein the first precursor solution is a MOF precursor solution; S5: using the second precursor solution to dip coat a carrier to obtain a MOF / COF membrane after reaction.

2. The integral molding method of MOF / COF membrane as described in claim 1, characterized in that, In the step S4, the first precursor solution comprises metal nodes, organic ligands and a solvent, and the first precursor solution simultaneously satisfies conditions a-c, wherein: a. the metal nodes are selected from any one or more of divalent zinc ions, divalent cobalt ions, trivalent chromium ions and trivalent iron ions; b. the organic ligands are nitrogen-containing heterocyclic compounds; c. the solvent forms a homogeneous system with octanoic acid in the reaction process, the solvent forms a homogeneous system with water in the reaction process, and the solvent is inert in the reaction process.

3. The integral molding method of the MOF / COF membrane as described in claim 1, characterized in that, In the step S1, the concentration of 1,3,5-triformylphloroglucinol in the solution A is 2.5-60 mM.

4. The integral molding method of MOF / COF membrane as described in claim 1, characterized in that, In the step S2, the concentration of 2,5-diaminobenzenesulfonic acid in the solution B is 2.5-60 mM.

5. The integral molding method of the MOF / COF membrane as described in claim 1, characterized in that, In the step S3, the volume ratio of the mixture of solution A and solution B is 1: (0.25-4).

6. The integral molding method of the MOF / COF membrane as described in claim 1, characterized in that, In the step S4, the volume ratio of the COF concentrated solution and the first precursor solution is 1: (1.5-15).

7. The integral molding method of the MOF / COF membrane as described in claim 1, characterized in that, The step S4 specifically comprises the following steps: stirring the first precursor solution to a MOF crystal grain diameter of 20-200 nm, then adding the COF concentrated solution, and continuing to stir for 1-10 min to obtain the second precursor solution.

8. The integral molding method of the MOF / COF membrane as described in claim 1, characterized in that, In the step S5, the heating temperature is 120-300°C, and the heating time is 5-30 min.

9. A MOF / COF film, characterized in that, The MOF / COF membrane is prepared by the one-piece forming method of the MOF / COF membrane according to any one of claims 1-8.

10. Use of the MOF / COF film according to claim 9, characterized in that The MOF / COF membrane is used for separating mixed gas, and the mixed gas is any one of hydrogen-helium mixed gas, helium-nitrogen mixed gas, helium-methane mixed gas, carbon dioxide-methane mixed gas, carbon dioxide-nitrogen mixed gas and propylene-propane mixed gas.

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