A method for preparing a polymer-supported vertical metal-organic framework (MOF) composite membrane

Abstract

This invention relates to a method for preparing a polymer-supported vertical MOF composite membrane. The method includes: adding dopamine to a metal and ligand synthesis solution; vertically immersing a polymer substrate in the synthesis solution; and directly preparing a vertically oriented MOF composite membrane at room temperature using an in-situ growth method. The advantages of this invention are that the synthesis process does not use a template agent, is carried out in an aqueous phase at room temperature, and yields a MOF membrane with good vertical orientation, demonstrating potential for large-scale preparation.

Description

Technical Field

[0001] This invention belongs to the field of composite membrane technology, specifically relating to a method for vertically growing MOF layers on a polymer substrate. Background Technology

[0002] Compared to traditional separation technologies such as absorption and distillation, membrane separation technology does not involve phase change and has advantages such as small carbon footprint, small footprint, and continuous operation, making it an emerging separation technology. Currently, the separation membrane materials on the market are mainly polymers. Polymer membranes have low production costs, high flux, and good mechanical strength, but they also have problems such as easy aging, poor thermal and chemical stability, and low selectivity.

[0003] Metal-organic frameworks (MOFs) are constructed by combining metals or metal clusters as nodes with organic ligands. Compared to traditional polymers, their large specific surface area, suitable pore size, and tunable chemical properties facilitate the separation of small molecules after film formation. Two-dimensional MOFs are an important branch of MOF materials, exhibiting two asymmetric pore structures after assembly: "MOF self-pores" and "lamellar pores." Compared to horizontal layer-by-layer stacking utilizing tortuous interlayer channels for transport, vertically oriented MOF layers provide direct small molecule transport channels, significantly reducing mass transfer resistance during separation and increasing throughput. Existing methods for synthesizing vertically oriented MOF films mainly include seed-assisted (secondary) growth or template methods. Seed-assisted growth involves pre-embedding a seed layer on a substrate and using microwave-assisted, solvothermal methods to increase the nucleation and growth rate of the crystal, thereby controlling the crystal orientation. Template methods involve first depositing an oriented precursor or template to induce directional crystal growth. These methods often require multiple steps, have long growth times (over 20 hours), and have high requirements for the pore size and chemical group type of the base film, as well as demanding growth environments. Currently, there is a lack of universally applicable methods for growing vertical MOF films.

[0004] This invention addresses the problems of complex operations in the traditional preparation of vertically grown MOFs by employing a one-step method to rapidly synthesize a polymer composite film with vertically grown MOF layers. The MOF crystals can be grown by immersing the polymer substrate in the synthesis solution at room temperature, resulting in a composite film with vertical orientation. Summary of the Invention

[0005] The purpose of this invention is to provide a simple method for vertically growing MOF layers on a polymer substrate to prepare defect-free MOF composite membranes.

[0006] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0007] Step (1): Prepare a 0.02–0.2 mol / L metal ion solution using water as the solvent, according to Zn2+ Prepare an organic ligand solution by mixing imidazole at a ratio of 1:4 to 1:12 and stirring thoroughly.

[0008] Step (2): Pour the metal ion solution into the organic ligand solution, mix and stir, then vertically place the polymer substrate into the synthesis solution and react for 4 to 12 hours;

[0009] Step (3): Rinse and dry the membrane after the reaction to obtain a polymer composite membrane with vertically aligned MOF layers; the drying temperature is 20-70℃ and the drying time is 8 hours to 2 days.

[0010] In step (2) of the present invention, the polymer substrate is polyethersulfone, nylon, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, etc., and the pore size of the porous carrier is 1 to 50,000 nm; the porous carrier includes symmetrical materials or asymmetrical materials.

[0011] In step (2) of this invention, the solution preparation operation is achieved through the following steps:

[0012] Weigh a certain amount of zinc nitrate hexahydrate or cobalt nitrate hexahydrate and dissolve it in 80 mL of deionized water to prepare a metal ion aqueous solution A with a concentration of 0.02–0.2 mol / L. Weigh a certain amount of dimethylimidazole and dissolve it in a Tris-HCl buffer solution with pH = 8.5, add 1–5 mg / mL of dopamine, and stir until homogeneous.

[0013] The above step (2) is achieved by the following operation steps: stick the film processed in step (1) onto the glass plate and insert it vertically into the beaker.

[0014] In step (3) above, rinse with deionized water 3-5 times.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects:

[0016] In the in-situ grown vertically oriented MOF layer polymer composite film described in this application, the metal ions and organic ligands are not directly mixed. Instead, dopamine is added to the organic ligand solution. On the one hand, imidazole is deprotonated first, and on the other hand, during the crystal growth process, the viscosity of dopamine is used to increase the interaction force between MOF sheets and reduce grain boundary defects.

[0017] The preparation method of the present invention is simple and mild, and can prepare a well-oriented and defect-free MOF composite membrane in one step. Attached Figure Description

[0018] Figure 1 These are the XRD patterns of the films prepared in Examples 1, 2, and 3;

[0019] Figure 2This is a cross-sectional electron microscope image of the membrane prepared in Example 1;

[0020] Figure 3 This is an electron microscope image of the surface of the membrane prepared in Example 1;

[0021] Figure 4 This is a cross-sectional electron microscope image of the membrane prepared in Example 2;

[0022] Figure 5 This is a cross-sectional electron microscope image of the membrane prepared in Example 5;

[0023] Figure 6 This is an electron microscope image of the surface of the film prepared in Example 6;

[0024] Figure 7 This is a cross-sectional electron microscope image of the membrane prepared in Example 6;

[0025] Figure 8 This is a cross-sectional electron microscope image of the membrane prepared in Example 7;

[0026] Figure 9 This is an electron microscope image of the surface of the membrane prepared in Example 7. Detailed Implementation

[0027] The technical solution of the present invention will be further described below through several specific embodiments, but this does not limit the present application. Any variations and implementations that do not depart from the content and scope of the present invention should be included within the technical scope of the present invention.

[0028] Example 1

[0029] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymeric composite films is described below:

[0030] The substrate is polyethersulfone. Before use, it should be cleaned with deionized water, cut and pasted onto a glass plate for later use.

[0031] Preparation of metal ion solution: Dissolve 4.76g of zinc nitrate hexahydrate in 80mL of deionized water for later use.

[0032] Buffer solution preparation: Weigh 0.6057 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Make up to 500 mL of water to prepare a 10 mmol / L buffer solution. Adjust the pH of the buffer solution to 8.5 with concentrated hydrochloric acid before use.

[0033] Preparation of organic ligand solution: Weigh 10.51 g of dimethylimidazole and dissolve it in 80 mL of buffer solution, then add 0.48 g (3 mg / mL) of dopamine hydrochloride.

[0034] Synthesis of ZIF-L / PES membrane: A metal ion solution was poured into an organic ligand solution, and a polyethersulfone substrate was vertically placed into the synthesis solution. The reaction was carried out for 6 hours. After the reaction, the membrane was removed, rinsed three to five times with deionized water, and dried at room temperature to obtain a ZIF-L / PES (0.48) membrane. Figure 2 , 3 (SEM image).

[0035] XRD characterization of the ZIF-L / PES film showed that both CPO(020 / 004) and CPO(020 / 112) increased, further proving that the ZIF-L crystals are highly vertically oriented.

[0036] Example 2

[0037] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymer composite membranes, with steps 1, 2, and 3 being the same as in Example 1.

[0038] Preparation of organic ligand solution: Weigh 10.51 g of dimethylimidazole and dissolve it in 80 mL of buffer solution, then add 0.64 g (4 mg / mL) of dopamine hydrochloride.

[0039] Synthesis of ZIF-L / PES membrane: A metal ion solution was poured into an organic ligand solution, and a polyethersulfone substrate was vertically placed into the synthesis solution. The reaction was carried out for 6 hours. After the reaction, the membrane was removed, rinsed three to five times with deionized water, and dried at room temperature to obtain a ZIF-L / PES (0.64) membrane. Figure 4 (SEM image)

[0040] As dopamine concentration increases, the ZIF-L nanosheets become more tightly packed.

[0041] Example 3

[0042] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymer composite membranes, with steps 1, 2, and 3 being the same as in Example 1.

[0043] Preparation of organic ligand solution: Weigh 10.51 g of dimethylimidazole and dissolve it in 80 mL of buffer solution, then add 0.80 g (5 mg / mL) of dopamine hydrochloride.

[0044] Synthesis of ZIF-L / PES membrane: The metal ion solution was poured into the organic ligand solution, and the polyethersulfone substrate was vertically placed into the synthesis solution. The reaction was carried out for 6 hours. After the reaction was completed, the membrane was taken out and rinsed with deionized water three to five times and dried at room temperature to obtain ZIF-L / PES (0.80) membrane.

[0045] Example 4

[0046] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymer composite membranes, with step 1 being the same as in Example 1.

[0047] Preparation of metal ion solution: Dissolve 4.66g of cobalt nitrate hexahydrate in 80mL of deionized water for later use.

[0048] Buffer solution preparation: Weigh 0.6057 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Make up to 500 mL of water to prepare a 10 mmol / L buffer solution. Adjust the pH of the buffer solution to 8.5 with concentrated hydrochloric acid before use.

[0049] Preparation of organic ligand solution: Weigh 10.51 g of dimethylimidazole and dissolve it in 80 mL of buffer solution, then add 0.80 g (5 mg / mL) of dopamine hydrochloride.

[0050] Synthesis of ZIF-L-Co / PES membrane: The metal ion solution was poured into the organic ligand solution, and the polyethersulfone substrate was vertically placed into the synthesis solution. The reaction was carried out for 12 hours. After the reaction was completed, the membrane was taken out and rinsed with deionized water three to five times and dried at room temperature to obtain the ZIF-L-Co / PES membrane.

[0051] Example 5

[0052] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymeric composite films is described below:

[0053] The substrate is nylon with a pore size of 100nm. Before use, it should be cleaned with deionized water, cut and pasted onto a glass plate for later use.

[0054] Preparation of metal ion solution: Dissolve 4.76g of zinc nitrate hexahydrate in 80mL of deionized water for later use.

[0055] Buffer solution preparation: Weigh 0.6057 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Make up to 500 mL of water to prepare a 10 mmol / L buffer solution. Adjust the pH of the buffer solution to 8.5 with concentrated hydrochloric acid before use.

[0056] Preparation of organic ligand solution: Weigh 10.51 g of dimethylimidazole and dissolve it in 80 mL of buffer solution, then add 0.32 g (2 mg / mL) of dopamine hydrochloride.

[0057] Synthesis of ZIF-L / PA membrane: The metal ion solution was poured into the organic ligand solution, and the nylon substrate was vertically placed into the synthesis solution and reacted for 6 hours. After the reaction was completed, the membrane was taken out and rinsed with deionized water three to five times and dried at room temperature to obtain ZIF-L / PA(0.32) membrane.

[0058] The surface and cross-section of the prepared ZIF-L / PA(0.32) film were characterized using scanning electron microscopy.

[0059] Example 6

[0060] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymer composite membranes is described, using ZIF-L MOF. Steps 1, 2, and 3 are the same as in Example 4.

[0061] Preparation of organic ligand solution: Weigh 10.51 g of dimethylimidazole and dissolve it in 80 mL of buffer solution, then add 0.16 g (1 mg / mL) of dopamine hydrochloride.

[0062] Synthesis of ZIF-L / PA membrane: The metal ion solution was poured into the organic ligand solution, and the nylon substrate was vertically placed into the synthesis solution. The reaction was carried out for 6 hours. After the reaction was completed, the membrane was taken out and rinsed with deionized water three to five times and dried at room temperature to obtain ZIF-L / PA(0.16) membrane.

[0063] Example 7

[0064] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymer composite films is described below:

[0065] The substrate is polyacrylonitrile. Before use, it should be cleaned with deionized water, cut and pasted onto a glass plate, and then set aside.

[0066] Preparation of metal ion solution: Weigh 4.76g of zinc nitrate hexahydrate, dissolve it in 80mL of deionized water, and stir.

[0067] Preparation of organic ligand solution: Weigh 10.51 g of dimethylimidazole and dissolve it in 80 mL of Tris-HC buffer solution with pH = 8.5. Add 0.16 g (1 mg / mL) of dopamine and stir to dissolve.

[0068] Synthesis of ZIF-L / PAN membrane: The metal ion solution was poured into the organic ligand solution, and the PAN membrane was vertically inserted into the synthesis solution. The reaction was carried out for 6 hours. After the reaction was completed, the membrane was taken out and rinsed with deionized water three to five times and dried at room temperature to obtain ZIF-L / PAN(0.16) membrane.

[0069] Example 8

[0070] A rapid and simple method for synthesizing vertically oriented metal-organic framework (MOF) layer polymeric composite films is described below:

[0071] The substrate is polyethersulfone. Before use, it should be cleaned with deionized water, cut, and then pasted onto a glass plate for later use.

[0072] Preparation of metal ion solution: Dissolve 1.18g of zinc nitrate hexahydrate in 80mL of deionized water to prepare a 0.02mol / L metal ion solution for later use.

[0073] Buffer solution preparation: Weigh 0.6057 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Make up to 500 mL of water to prepare a 10 mmol / L buffer solution. Adjust the pH of the buffer solution to 8.5 with concentrated hydrochloric acid before use.

[0074] Preparation of organic ligand solution: according to Zn 2+ The ratio of dimethylimidazole to imidazole is 1:12. Weigh 3.91g of dimethylimidazole and dissolve it in 80mL of buffer solution. Add 0.32g (2mg / mL) of dopamine hydrochloride.

[0075] Synthesis of ZIF-L / PES membrane: The metal ion solution was poured into the organic ligand solution, and the polyethersulfone substrate was vertically placed into the synthesis solution. The reaction was carried out for 12 hours. After the reaction was completed, the membrane was taken out and rinsed with deionized water three to five times and dried at room temperature to obtain ZIF-L(0.02) / PES(0.32) membrane.

[0076] Although embodiments of the present invention have been shown and described above, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Although the one-step preparation of polymer-supported vertical MOF composite membranes is listed, it is not limited to the preparation of ZIF-L / PES (or PA, PAN) composite membranes. That is, those skilled in the art, under the guidance of the present invention, can achieve the vertical growth of MOFs on polymer substrates in one step without departing from the spirit of the present invention, and these are all within the protection scope of the present invention.

Claims

1. A method for preparing a polymer-supported vertical MOF composite membrane, characterized in that, include: ZIF-L was synthesized at room temperature using zinc nitrate hexahydrate solution or cobalt nitrate hexahydrate solution and 2-methylimidazole solution as raw materials. The 2-methylimidazole solution is prepared by adding dopamine hydrochloride to an aqueous solution of 2-methylimidazole / tris(hydroxymethyl)aminomethane (Tris). A porous polymer substrate is vertically placed in a synthesis solution to grow a dense MOF layer, thereby obtaining the polymer-supported vertical MOF composite membrane.

2. The method for preparing a polymer-supported vertical MOF composite membrane according to claim 1, characterized in that, The specific steps include: Step 1: Select a porous polymer substrate. Step 2: Dissolve zinc nitrate hexahydrate or cobalt nitrate hexahydrate in 80 mL of deionized water, stir, and prepare a 0.02~0.2 mol / L metal ion solution A. Prepare a Tris-HCl buffer solution with pH=8.

5. Dissolve dopamine hydrochloride (1~5 mg / mL) and dimethylimidazole together in 80 mL of the buffer solution, stir, and prepare an organic ligand solution B. Step 3: Adhere and fix the porous polymer substrate to the glass plate. Step 4: After complete dissolution, pour solution A into solution B, stir at 1200 r / min for 5 minutes, then vertically insert the glass plate into the beaker to begin the reaction. Step 5: After the reaction is complete, remove the glass plate, rinse it with deionized water three to five times, and dry it to obtain the MOF membrane; the drying temperature is 20~70 ℃, and the drying time is 8 hours to 2 days.

3. The method as described in claim 2, characterized in that: The concentration ratio of zinc nitrate hexahydrate or cobalt nitrate hexahydrate to dimethylimidazole used in step two is 1:4 to 1:

12.

4. The method as described in claim 2, characterized in that: The porous polymer substrate mentioned in step three has a pore size of 1~50000 nm; the porous polymer substrate has a uniform porous structure or a porous structure; the porous polymer substrate is an unmodified polymer substrate or a polymer substrate modified by acid, alkali or polymer.

5. The method as described in claim 2, characterized in that: The reaction time in step four is 4 to 12 hours.

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