A modified two-dimensional metal-organic framework nanosheet membrane and a preparation method and separation application thereof

Abstract

The application discloses a modified two-dimensional metal organic framework nanosheet membrane, a preparation method thereof and gas separation application. The original two-dimensional metal organic framework nanosheet membrane is controllably modified through solvent vapor treatment, the interaction force between adjacent nanosheet layers in the nanosheet membrane is enhanced, and the passage of macromolecular gas along the channel between the nanosheet layers is inhibited, so that the separation selectivity is improved. The preparation and modification method of the original nanosheet membrane comprises the following steps: (1) synthesizing a metal organic framework layered precursor by a solvothermal method; (2) combining a wet ball milling method and an ultrasonic dispersion method to delaminate the metal organic framework layered precursor to obtain two-dimensional metal organic framework nanosheets; (3) assembling the two-dimensional metal organic framework nanosheets into an original two-dimensional layered metal organic framework nanosheet membrane on the surface of a porous carrier; and (4) modifying the nanosheet membrane through solvent vapor treatment. The modified two-dimensional metal organic framework nanosheet membrane prepared by the application has excellent gas separation performance.

Description

Technical Field

[0001] The invention belongs to the field of membrane separation and relates to a modified two-dimensional metal organic framework nanosheet membrane and a preparation method and separation application thereof. Background Art

[0002] Compared to traditional gas separation technologies such as cryogenic distillation and absorption, gas membrane separation technology does not undergo phase change during the separation process, offering advantages such as low energy consumption and environmental friendliness. It is currently a research hotspot in the field of gas separation. Metal-organic frameworks (MOFs) are a new class of molecular sieve materials. Two-dimensional MOFs, with their ultra-high pore density, diverse pore structures and pore sizes, diverse surface chemical properties, and molecular-level thickness, hold great promise for application in gas membrane separation.

[0003] Two-dimensional molecular sieve nanosheet membranes have two types of pores: one is a straight-through pore (Type I pore) formed by the intrinsic oriented pore window structure on the nanosheet, and the other is a tortuous interlayer slit channel (Type II pore) formed by the layer-by-layer stacking of nanosheets. During the gas separation process, small molecular gases can directly penetrate the membrane through the Type I pores on the nanosheets, while large molecular gases can only penetrate the membrane through the tortuous Type II slit channels. Since two-dimensional metal organic framework nanosheets are generally flexible, this leads to uneven spacing between the slit channels between the nanosheet layers. Under high temperature conditions, the nanosheet membrane expands, causing more large molecular gases to diffuse through the membrane through the Type II channels, and the gas separation selectivity decreases significantly. Therefore, it is a difficult problem that needs to be solved in the field of two-dimensional nanosheet membrane gas separation to effectively enhance the interaction force between adjacent nanosheet layers and inhibit large molecular gases from passing through the membrane through the channels between the nanosheet layers to improve the separation selectivity. Summary of the Invention

[0004] The present invention aims to provide a modified metal-organic framework (MOF) nanosheet membrane, its preparation method, and separation applications. The method involves controllably modifying pristine MOF nanosheet membranes, resulting in membrane materials with excellent gas separation performance. This method utilizes solvent vapor treatment to controllably modify the pristine two-dimensional MOF nanosheet membranes, enhancing the interactions between adjacent nanosheets and inhibiting the passage of macromolecular gases along the interlayer channels within the nanosheets, thereby improving separation selectivity.

[0005] A method for preparing a modified two-dimensional metal-organic framework nanosheet membrane comprises first preparing a two-dimensional layered metal-organic framework precursor material, then peeling the layers from top to bottom using a wet ball milling and ultrasonic dispersion method to obtain two-dimensional metal-organic framework nanosheets, assembling the membrane into a membrane and drying the membrane, and finally treating the two-dimensional metal-organic framework nanosheet membrane with solvent vapor. The specific preparation process includes the following steps:

[0006] (1) Solvothermal synthesis of metal-organic framework layered precursors: divalent zinc salt, benzimidazole and organic solvent are mixed and reacted at 0-200°C for 24-168h to obtain a two-dimensional layered metal-organic framework precursor;

[0007] Among them, the molar ratio of each raw material is Zn 2+ : benzimidazole: organic solvent = 1: 0-1.0: 50-200, and the organic ligand cannot be 0;

[0008] (2) exfoliating the metal organic framework layered precursor by combining wet ball milling and ultrasonic dispersion to obtain two-dimensional metal organic framework nanosheets: mixing the two-dimensional layered metal organic framework precursor obtained in step (1) with an organic solvent, ball milling to obtain two-dimensional layered nanosheets, and then ultrasonically dispersing the two-dimensional layered nanosheets in the organic solvent to obtain a nanosheet dispersion, and allowing it to settle for 1-730 days;

[0009] Wherein, the mass concentration of the two-dimensional layered nanosheets in the nanosheet dispersion is 0.001-1%.

[0010] (3) assembling the two-dimensional metal organic framework nanosheets on the surface of the porous support into an original two-dimensional layered metal organic framework nanosheet membrane: coating the nanosheet dispersion obtained in step (2) on the surface of the porous support at room temperature -200°C to form a film, and drying to obtain an original two-dimensional metal organic framework nanosheet membrane;

[0011] (4) Modification of the nanosheet membrane by solvent vapor treatment: vacuum drying the original two-dimensional metal organic framework nanosheet membrane at 60-200 ° C for 0-12 h, and then treating it with solvent vapor driven by N2 at a flow rate of 5-50 ml / min for 1 min-24 h to obtain a modified two-dimensional metal organic framework nanosheet membrane.

[0012] Based on the above technical solution, preferably, in step (1), the divalent zinc salt is Zn(NO3)2, ZnCl2, etc.

[0013] Based on the above technical solution, preferably, in step (1), the reaction temperature is 80-120° C. and the reaction time is 24-72 h.

[0014] Based on the above technical solution, preferably, in step (1) and step (2), the organic solvent is anhydrous methanol, anhydrous ethanol, N,N-dimethylformamide, etc.

[0015] Based on the above technical solution, preferably, in step (2), the ball milling conditions are: rotation speed of 30-100 rpm, and ball milling time of 1-24 h.

[0016] Based on the above technical solution, preferably, in step (2), the method used to disperse the two-dimensional layered nanosheets in the organic solvent is ultrasonic dispersion, with ultrasonication for 0-60 min and a power of 300-600 W.

[0017] Based on the above technical solution, preferably, in step (2), the static sedimentation is more than 14 days and less than 365 days.

[0018] Based on the above technical solution, preferably, in step (3), the coating temperature is 60-120°C.

[0019] Based on the above technical solution, preferably, in step (3), the porous carrier is one of a silica carrier, an α-Al2O3 carrier, a γ-Al2O3 carrier, a TiO2 carrier, an anodic aluminum oxide carrier, and a stainless steel carrier; the pore size of the porous carrier is 5 nm to 1 μm; the shape of the porous carrier is a sheet structure, a fiber structure or a tubular structure.

[0020] Based on the above technical solution, preferably, in step (3), the coating method includes dipping-pulling, blade coating, spin coating, spray coating, drop coating, vacuum filtration, interface self-assembly method, Langmuir-Shaefer (LS) method, etc.

[0021] Based on the above technical solution, preferably, in step (3), when preparing the original two-dimensional metal organic framework nanosheet film, the amount of the two-dimensional layered nanosheet dispersion added is 1-50 mL / cm 2 carrier.

[0022] Based on the above technical solution, preferably, in step (3), the drying temperature is 60-200° C. and the drying time is 6-24 h.

[0023] Based on the above technical solution, preferably, in step (4), the vacuum drying temperature is 120-160° C., and the vacuum drying time is 3-6 h.

[0024] Based on the above technical solution, preferably, in step (4), the solvent includes at least one of ammonia water, ethylenediamine, diethylamine, 1,8-octanediamine, 1,12-dodecanediamine, p-phenylenediamine, 1,4-bis(imidazol-1-yl)butane, molten pyrazine, molten pyrimidine, molten 1,3,5-triazine, molten melamine, molten imidazole, oxazole, molten 2-aminopyrazine, molten 3-aminopyridine, molten 4-aminopyridine, and molten 3-aminopyrimidine.

[0025] Based on the above technical solution, preferably, in step (4), the treatment time is 10 min-6 h.

[0026] The metal organic framework nanosheet material described in the present invention is Zn2(Bim)3. When the solvent vapor is 1,8-octanediamine, the modified metal organic framework nanosheet film is M1-Zn2(Bim)3. When the solvent vapor is 1,12-dodecanediamine, the modified metal organic framework nanosheet film is M2-Zn2(Bim)3.

[0027] The present invention also relates to two-dimensional metal organic framework nanosheets prepared by the method described above and the modification of the nanosheets.

[0028] The present invention also relates to the application of the modified two-dimensional metal organic framework nanosheet membrane described above in gas separation, especially hydrogen / carbon dioxide separation.

[0029] Because metal-organic frameworks (MOFs) are rich in easily modifiable metal nodes and organic functional groups, post-synthesis modification methods can be used to graft various chemical groups onto preformed crystals, allowing for targeted manipulation of the framework structure and surface chemical properties. Using bichelate ligand vapor to modify adjacent nanosheets in MOF nanosheet membranes enhances the interlayer interactions and minimizes the narrow channels between nanosheets that allow macromolecular gases to pass through, resulting in high-performance separation membranes.

[0030] Beneficial Effects: The present invention first uses solvent thermal synthesis of a layered metal-organic framework (MOF) precursor, then peels the layers from top to bottom to obtain a two-dimensional layered nanosheet material, which is finally assembled into a two-dimensional layered nanosheet membrane on the surface of a porous support. By subjecting the nanosheet membrane to solvent vapor treatment, the interaction between adjacent nanosheet layers is enhanced, minimizing the narrow channels between the nanosheet layers that allow macromolecular gases to pass through, thereby obtaining a high-performance separation membrane. Using the preparation method described in the present invention, the two-dimensional MOF nanosheet membrane can be controllably modified to obtain a high-performance two-dimensional MOF nanosheet membrane material, which has great application prospects in the separation field. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention is attached Figure 6 The widths are:

[0032] Figure 1 This is a scanning electron microscope photograph of the Zn2(Bim)3 material synthesized in Example 1;

[0033] Figure 2 This is a scanning electron microscope photograph of the 1,8-octanediamine-modified M1-Zn2(Bim)3 material synthesized in Example 2.

[0034] Figure 3 This is a scanning electron microscope photograph of the 1,12-dodecanediamine-modified M2-Zn2(Bim)3 material synthesized in Example 3;

[0035] Depend on Figure 1-3 It can be seen that the material has an obvious two-dimensional lamellar structure and the lamellar morphology is not destroyed before and after modification.

[0036] Figure 4 This is the X-ray diffraction pattern of the Zn2(Bim)3 material synthesized in Example 1;

[0037] Figure 5 This is the X-ray diffraction pattern of the 1,8-octanediamine-modified M1-Zn2(Bim)3 material synthesized in Example 2;

[0038] Figure 6 This is the X-ray diffraction pattern of the 1,12-dodecanediamine-modified M2-Zn2(Bim)3 material synthesized in Example 3;

[0039] Depend on Figure 4-6 It can be seen that the crystal form remains intact before and after modification. DETAILED DESCRIPTION

[0040] The present invention will be further described in the following examples, but are not intended to limit the present invention.

[0041] Example 1 Preparation of Zn2(bim)3 Precursor

[0042] Dissolve 2 grams of zinc nitrate and 0.4 grams of benzimidazole in 80 milliliters of N,N-dimethylformamide and stir for 20 minutes. Transfer the mixture to a 100-milliliter reactor and incubate in an oven at 100 degrees Celsius for 72 hours. Remove the reactor and cool to room temperature. Centrifuge the resulting Zn2Bim3 nanoparticles, wash them repeatedly with methanol, and dry them in an oven at 60 degrees Celsius overnight. Collect the resulting Zn2(Bim)3 precursor powder.

[0043] Scanning electron microscope images show that the product has a distinct step-like layered morphology (such as Figure 1 ).

[0044] X-ray diffraction confirmed that the product had a Zn2(Bim)3 structure (such as Figure 4 ), proving that the precursor material was successfully synthesized.

[0045] Example 2 Modification of Zn2(bim)3 Precursor

[0046] The Zn2(bim)3 particles prepared in Example 1 were placed in a reactor, evacuated to 0.1 MPa, and vacuum dried at 120°C for 6 h. At 120°C, nitrogen was introduced through 500 mL of 1,8-octanediamine solvent at a flow rate of 20 mL / min. After continuous ventilation for 3 h, the residual solvent vapor in the reactor was purged with pure nitrogen. The heating was turned off, and the reactor was naturally cooled to room temperature. This yielded the 1,8-octanediamine-modified M1-Zn2(Bim)3 material.

[0047] Scanning electron microscope images show that the product still has a clear step-like layered morphology (such as Figure 2 ).

[0048] X-ray diffraction confirmed that the product had the same characteristic peaks as Zn2(Bim)3 (such as Figure 5 ), proving that the crystal structure of the material did not change after modification.

[0049] Example 3 Modification of Zn2(bim)3 Precursor

[0050] The Zn2(bim)3 particles prepared in Example 1 were placed in a reactor, evacuated to 0.1 MPa, and vacuum dried at 120°C for 6 h. At 120°C, nitrogen was introduced into the reactor at a flow rate of 20 mL / min through 500 mL of 1,12-dodecanediamine solvent. After continuous ventilation for 3 h, the residual solvent vapor in the reactor was purged with pure nitrogen. The heating was turned off, and the reactor was naturally cooled to room temperature. This yielded the 1,12-dodecanediamine-modified M2-Zn2(Bim)3 material.

[0051] Scanning electron microscope images show that the product still has a clear step-like layered morphology (such as Figure 3 ).

[0052] X-ray diffraction confirmed that the product had the same characteristic peaks as Zn2(Bim)3 (such as Figure 6 ), proving that the crystal structure of the material did not change after modification.

[0053] Example 4 Preparation of Ultrathin Two-Dimensional Layered Zn2(bim)3 Nanosheets

[0054] The Zn2(bim)3 particles prepared in Example 1 were dispersed in 100 ml of methanol, sealed in a 150 ml ball mill, and ball-milled at 60 rpm for 1 hour. The solution was then diluted 1.5-fold with the same solvent and subjected to water bath sonication at 600 watts for 30 minutes. The Zn2(bim)3 nanosheet dispersion was allowed to stand for two weeks to remove large, undelaminated particles.

[0055] Example 5 Preparation of Ultrathin Zn2(bim)3 Nanosheet Supported Film

[0056] The porous α-Al2O3 support was preheated to 100°C on a horizontal heating platform. 10 mL of the nanosheet dispersion obtained in Example 2 was then syringe-dropped onto the surface of an α-alumina support (circular, 0.9 cm radius) with a pore size of 70 nm until the solvent evaporated. This was a hot drop coating method. The prepared support membrane was dried at 100°C for 1 hour and stored in a Petri dish at room temperature to obtain an ultrathin nanosheet-supported Zn2(bim)3 membrane.

[0057] Example 6 Modification of Ultrathin Zn2(bim)3 Nanosheet Support Membrane

[0058] The ultrathin Zn2(bim)3 nanosheet-supported membrane obtained in Example 5 was placed in a reactor, evacuated to 0.1 MPa, and vacuum dried at 120°C for 6 hours. N2 was introduced into the reactor at a flow rate of 20 mL / min through 500 mL of 1,8-octanediamine solvent at 120°C. After continuous ventilation for 1 hour, the remaining solvent vapor in the reactor was purged with pure N2. The heating was turned off and the membrane was allowed to cool naturally to room temperature. This yielded the modified ultrathin nanosheet-supported membrane M1-Zn2(bim)3-a.

[0059] Example 7 Modification of Ultrathin Zn2(bim)3 Nanosheet Support Membrane

[0060] The ultrathin Zn2(bim)3 nanosheet-supported membrane obtained in Example 5 was placed in a reactor, evacuated to 0.1 MPa, and vacuum-dried at 120°C for 6 hours. N2 was introduced into the reactor at a flow rate of 20 mL / min through 500 mL of 1,8-octanediamine solvent at 120°C. After continuous ventilation for 3 hours, the remaining solvent vapor in the reactor was purged with pure N2. The heating was turned off and the membrane was allowed to cool naturally to room temperature. This yielded the modified ultrathin nanosheet-supported membrane M1-Zn2(bim)3-b.

[0061] Example 8 Modification of Ultrathin Zn2(bim)3 Nanosheet Support Membrane

[0062] The ultrathin Zn2(bim)3 nanosheet-supported membrane obtained in Example 5 was placed in a reactor, evacuated to 0.1 MPa, and vacuum dried at 120°C for 6 hours. N2 was introduced into the reactor at a flow rate of 20 mL / min through 500 mL of 1,8-octanediamine solvent at 120°C. After 6 hours of continuous ventilation, the remaining solvent vapor in the reactor was purged with pure N2. The heating was turned off and the membrane was allowed to cool naturally to room temperature. This yielded the modified ultrathin nanosheet-supported membrane M1-Zn2(bim)3-c.

[0063] Example 9 Modification of Ultrathin Zn2(bim)3 Nanosheet Support Membrane

[0064] The ultrathin Zn2(bim)3 nanosheet-supported membrane obtained in Example 5 was placed in a reactor, evacuated to 0.1 MPa, and vacuum dried at 120°C for 6 hours. At 120°C, nitrogen was introduced through 500 mL of 1,12-dodecanediamine solvent at a flow rate of 20 mL / min. After continuous ventilation for 1 hour, the remaining solvent vapor in the reactor was purged with pure nitrogen. The heating was turned off and the membrane was allowed to cool naturally to room temperature. This yielded the modified ultrathin nanosheet-supported membrane M2-Zn2(bim)3-a.

[0065] Example 10 Modification of Ultrathin Zn2(bim)3 Nanosheet Support Membrane

[0066] The ultrathin Zn2(bim)3 nanosheet-supported membrane obtained in Example 5 was placed in a reactor, evacuated to 0.1 MPa, and vacuum dried at 120°C for 6 hours. At 120°C, nitrogen was introduced through 500 mL of 1,12-dodecanediamine solvent at a flow rate of 20 mL / min. After continuous ventilation for 3 hours, the remaining solvent vapor in the reactor was purged with pure nitrogen. The heating was turned off and the membrane was allowed to cool naturally to room temperature. This yielded the modified ultrathin nanosheet-supported membrane M2-Zn2(bim)3-b.

[0067] Example 11 Modification of Ultrathin Zn2(bim)3 Nanosheet Support Membrane

[0068] The ultrathin Zn2(bim)3 nanosheet-supported membrane obtained in Example 5 was placed in a reactor, evacuated to 0.1 MPa, and vacuum-dried at 120°C for 6 hours. N2 was introduced into the reactor at a flow rate of 20 mL / min through 500 mL of 1,12-dodecanediamine solvent at 120°C. After 6 hours of continuous ventilation, the remaining solvent vapor in the reactor was purged with pure N2. The heating was turned off and the membrane was allowed to cool naturally to room temperature. This yielded the modified ultrathin nanosheet-supported membrane M2-Zn2(bim)3-c.

[0069] Example 12

[0070] The three mixed matrix membranes prepared in Examples 5-11 were encapsulated in a Wicke-Kallenbach membrane module and tested for hydrogen / carbon dioxide (50:50 ml / min) gas separation at room temperature and ΔP = 0 bar. (Under standard conditions, 1 GPU = 1×10 -6 cm 3 / cm 2 ·s·cmHg). The data in the table show that the mixed matrix membrane material exhibits excellent hydrogen / methane separation performance.

[0071] serial number Steaming time <![CDATA[H2 / CO2 separation factor]]> <![CDATA[H2 Permeability (GPU)]]> <![CDATA[CO2 Permeability (GPU)]]> <![CDATA[Zn2(bim)3]]> 0 190 938 4.94 <![CDATA[M1-Zn2(bim)3-a]]> 1h 366 961 2.63 <![CDATA[M1-Zn2(bim)3-b]]> 3h 384 863 2.25 <![CDATA[M1-Zn2(bim)3-c]]> 6h 231 906 3.92 <![CDATA[M2-Zn2(bim)3-a]]> 1h 289 1023 3.54 <![CDATA[M2-Zn2(bim)3-b]]> 3h 312 1099 3.52 <![CDATA[M2-Zn2(bim)3-c]]> 6h 347 1042 3.00

Claims

1. A method for preparing a modified two-dimensional metal organic framework nanosheet film, characterized in that: The steps include: (1) mixing a divalent zinc salt, benzimidazole, and an organic solvent, and reacting the mixture at 0-200° C. for 24-168 hours to obtain a precursor of a two-dimensional layered metal-organic framework; Among them, the molar ratio of each raw material is Zn 2+ : Benzimidazole: organic solvent = 1:0-1.0:50-200, and the organic ligand cannot be 0; (2) mixing the precursor of the two-dimensional layered metal-organic framework obtained in step (1) with an organic solvent, ball milling to obtain two-dimensional layered nanosheets, and then ultrasonically dispersing the two-dimensional layered nanosheets in the organic solvent to obtain a nanosheet dispersion, and allowing it to settle for 1-730 days; Wherein, the mass concentration of the two-dimensional layered nanosheets in the nanosheet dispersion is 0.001-1%; (3) coating the nanosheet dispersion obtained in step (2) on the surface of a porous support at room temperature to 200° C., and drying the nanosheet dispersion to obtain a two-dimensional metal organic framework nanosheet film; (4) vacuum drying the two-dimensional metal organic framework nanosheet membrane at 60-200° C. for 0-12 h, and then treating the two-dimensional metal organic framework nanosheet membrane with solvent vapor driven by nitrogen at a flow rate of 5-50 ml / min for 1 min-24 h to obtain a modified two-dimensional metal organic framework nanosheet membrane; In step (1) and step (2), the organic solvent is anhydrous methanol, anhydrous ethanol or N,N-dimethylformamide; In step (4), the solvent is at least one of ethylenediamine, diethylamine, 1,8-octanediamine, 1,12-dodecanediamine, p-phenylenediamine, 1,4-bis(imidazol-1-yl)butane, molten 2-aminopyrazine, molten 3-aminopyridine, molten pyrrole, molten 2-aminopyrrole, and molten 3-aminopyrimidine.

2. The preparation method according to claim 1, characterized in that In step (1), the divalent zinc salt is Zn(NO3)2 or ZnCl2.

3. The preparation method according to claim 1, characterized in that In step (2), the ball milling time is 1-24 hours and the rotation speed is 30-100 rpm.

4. The preparation method according to claim 1, characterized in that In step (2), the ultrasonic time is 0-60 min and the power is 300-600 W.

5. The preparation method according to claim 1, characterized in that In step (3), the porous carrier is one of a silica carrier, an α-Al2O3 carrier, a γ-Al2O3 carrier, a TiO2 carrier, an anodic aluminum oxide carrier, and a stainless steel carrier; the pore size of the porous carrier is 5 nm to 1 μm; the shape of the porous carrier is a sheet structure, a fiber structure, or a tubular structure; The coating method includes at least one of dipping-pulling, blade coating, spin coating, spray coating, drop coating, wiping coating, vacuum filtration, interface self-assembly method and Langmuir-Shaefer (LS) method.

6. The preparation method according to claim 1, characterized in that In step (3), the drying temperature is 60-200° C. and the drying time is 6-24 hours.

7. A two-dimensional metal organic framework nanosheet film prepared by the method according to any one of claims 1 to 6.

8. Use of the two-dimensional metal organic framework nanosheet membrane according to claim 7 in gas separation.

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