A method for constructing amorphous mixed matrix membranes based on low temperature induction

Abstract

The application discloses a method for constructing amorphous mixed matrix membrane based on low-temperature induction, and belongs to the technical field of mixed matrix membrane preparation. The steps of the low-temperature induction construction method comprise the following steps: dissolving an organic ligand and a metal salt respectively, mixing the organic ligand and the metal salt to obtain a MOF precursor solution; performing heat treatment on the MOF precursor solution to obtain MOF nanosheets; blending the MOF nanosheets and a polymer in a solvent to prepare a casting solution; preparing a mixed matrix membrane by using the casting solution; and finally performing crystalline-to-amorphous transformation on the mixed matrix membrane, and obtaining an amorphous mixed matrix membrane after cooling. The amorphous MOF nanosheet mixed matrix membrane can be prepared in situ by the simple method under the premise that only a coordination guest molecule is removed; the problems of poor compatibility between fillers and matrix, low selectivity and the like existing in the current mixed matrix membrane are solved; and the prepared amorphous MOF nanosheet mixed matrix membrane is used for gas separation.

Description

Technical Field

[0001] This invention belongs to the field of mixed matrix membrane preparation technology, specifically relating to a method for constructing amorphous mixed matrix membranes based on low-temperature induction. Background Technology

[0002] Excessive greenhouse gas emissions have led to various environmental problems, such as global warming, ocean acidification, and ecological damage. The need to capture carbon dioxide from natural gas and flue gas is increasingly prominent. However, traditional capture technologies are energy-intensive and uneconomical. Membrane separation processes have attracted considerable attention due to their inherent advantages, such as high efficiency, reliability, and small footprint. While polymer membranes are attractive for industrial-scale molecular separation, commercial membranes still require improvement, primarily due to inherent permeability / selectivity trade-offs, limited thermal stability, and high sensitivity to plasticizers. Mixed matrix membranes (MMMs), composed of a polymer matrix and porous fillers, offer higher permeability due to the well-defined adsorption properties of the fillers, potentially addressing these issues. However, MOF particles, due to limitations in traditional synthesis methods, often exhibit nearly non-dispersed agglomerates, leading to unavoidable interfacial defects. Furthermore, realizing the advantages of MOFs typically requires high MOF loadings, which can affect the mechanical integrity of the composite material. High aspect ratio MOF nanostructures can improve the integration between the two components in the composite material, thereby overcoming these obstacles. Amorphous MOF nanosheets combine the common properties of crystalline MOFs, such as excellent thermal stability, chemical stability, high surface area, large porosity, tunable pore size, and chemical functionality, with the unique properties of amorphous structures, such as structural disorder, absence of grain boundaries, abundant defects and active sites, and flexibility. These characteristics provide opportunities for fabricating defect-free interfaces. Therefore, developing a simple and effective method to improve the compatibility between polymer matrices and fillers has become a key issue in improving the selectivity of hybrid matrix films. Summary of the Invention

[0003] The purpose of this invention is to provide a method for constructing amorphous mixed matrix membranes based on low-temperature induction. This method allows for the in-situ preparation of amorphous MOF nanosheet mixed matrix membranes by simply removing only the coordinating guest molecules; it solves the problems of poor compatibility between fillers and matrix, and low selectivity found in current mixed matrix membranes; and the resulting amorphous MOF nanosheet mixed matrix membranes can be used for gas separation.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] One of the technical solutions of this invention is to provide a method for constructing an amorphous mixed matrix film based on low-temperature induced construction, comprising the following steps:

[0006] Organic ligands and metal salts are dissolved and mixed to obtain MOF precursor solutions; the MOF precursor solutions are heat-treated to obtain MOF nanosheets; the MOF nanosheets are blended with polymers in a solvent to prepare a casting solution; a mixed matrix membrane is prepared using the casting solution; finally, the mixed matrix membrane is treated at 160–220 °C for 1–36 h to undergo an amorphous transformation, and after cooling, an amorphous mixed matrix membrane is obtained.

[0007] Preferably, the solvent for dissolving the organic ligand and the metal salt is a mixture of N,N-dimethylformamide (DMF) and acetonitrile in a volume ratio of 15:1.

[0008] Preferably, the molar ratio of the organic ligand to the metal salt is 1–55:1; and the concentration of the metal ions in the MOF precursor solution is 0.5–50.8 mmol·L⁻¹. -1 .

[0009] The conditions defined in this invention can be used to prepare ultrathin MOF nanosheets with preferred orientation and high aspect ratio, with an aspect ratio of up to 1800.

[0010] Preferably, the organic ligand is a carboxylic acid ligand, specifically 2,5-dibromoterephthalic acid, 2,5-dihydroxyterephthalic acid, or terephthalic acid; the metal salt is a divalent or trivalent metal salt.

[0011] Preferably, the heat treatment temperature is 30–100°C and the time is 1–100 min.

[0012] More preferably, the heat treatment method is microwave heating.

[0013] Microwave heating can accelerate the nucleation rate and save reaction time.

[0014] Preferably, the MOF nanosheets further include a cleaning step before the casting solution is prepared.

[0015] More preferably, the washing solution in the cleaning step is DMF and chloroform / dichloromethane; specifically, the prepared MOF nanosheets are dispersed in DMF, shaken thoroughly, centrifuged, and repeated 3-4 times; then the DMF cleaning method is repeated with chloroform or dichloromethane, also 3-4 times. The purpose of cleaning is to remove physically attached guest molecules.

[0016] Preferably, the polymer is selected from polysulfone (PSF), polyimide (PI), polyethylene oxide (PEO), microporous polymer (PIM), or polyvinylidene fluoride (PVDF); the solvent of the casting solution is N,N-dimethylformamide, chloroform, dichloromethane, or methanol; the mass fraction of MOF nanosheets in the casting solution is 0.1-30%, and the mass fraction of the polymer is 1-40%.

[0017] Preferably, the cooling rate does not exceed 5°C / min.

[0018] The second technical solution of the present invention provides an amorphous mixed matrix membrane prepared according to the above-mentioned method for constructing an amorphous mixed matrix membrane based on low temperature induction.

[0019] The third technical solution of the present invention provides an application of the above-mentioned amorphous mixed matrix membrane in gas separation.

[0020] The beneficial technical effects of the present invention are as follows:

[0021] (1) Compared with conventional methods for preparing mixed matrix films by doping, the method provided by the present invention can prepare amorphous MOF nanosheets in situ in a polymer matrix by removing solvent guest molecules blocked in the framework or removing solvent molecules coordinated with metal ions under mild conditions and simple operation.

[0022] (2) This invention solves the fundamental problems of poor interfacial compatibility and low selectivity of mixed matrix membranes by thermally inducing the in-situ preparation of amorphous MOF nanosheets in mixed matrix membranes.

[0023] (3) Compared with the mixed matrix film prepared by ordinary doping, the mixed matrix film prepared by the method provided by the present invention improves the specific surface area and porosity of the nanosheets to the greatest extent by removing the solvent molecules blocked in the framework or removing the solvent molecules coordinated with the metal ions, thereby exposing a large number of metal sites to interact with the target molecules and thus improving selectivity; and the in-situ conversion strategy improves the compatibility problem between the matrix and the nanosheets.

[0024] (4) This invention utilizes low temperature to induce the transformation of crystalline to amorphous mixed matrix membranes, which greatly improves the permeability of the mixed matrix membranes and also shows significantly improved CO2 / CH4 and CO2 / N2 selectivity, and has good application prospects. Attached Figure Description

[0025] Figure 1 The image shows the XRD patterns of the mixed matrix film before and after the amorphous transformation in Example 1.

[0026] Figure 2 This is a SEM image of the amorphous mixed matrix film prepared in Example 2. Detailed Implementation

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0028] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] Example 1

[0032] Preparation of amorphous hybrid matrix films:

[0033] (1) Dissolve 0.21 g of 2,5-dihydroxyterephthalic acid in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 The concentration obtained in the ratio of 3:1 was 37.9 mmol / L. -1 Solution A. Dissolve 0.07 g of copper nitrate trihydrate in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 A concentration of 10.3 mmol / L was obtained in a ratio of 1:3. -1 Solution B. Solutions A and B were dissolved separately by sonication for 2 minutes. Solution B was then added to solution A to obtain the MOF precursor solution.

[0034] (2) The obtained precursor solution was poured into a microwave reactor and placed in a microwave reactor for heat treatment at 50°C for 30 min; brown MOF (CuBDC-(OH)2) nanosheets were formed in the reactor. After natural cooling, the nanosheets were dispersed in 25 mL of DMF solution and centrifuged at 10000 rpm for 30 min. This process was repeated 3 times, and then washed 3 times with chloroform (in the same way as DMF washing). The obtained MOF nanosheets were dispersed in chloroform solution and stored.

[0035] (3) Disperse the MOF nanosheet dispersion prepared in step (2) in chloroform, wherein the mass fraction of MOF nanosheets is 1%, and stir for 20 min to ensure thorough dispersion; then add 10 wt% PI polymer powder while stirring to prevent polymer powder aggregation. Stir the mixed casting solution at room temperature for 24 h to ensure thorough mixing and dispersion; ultrasonically treat the stirred casting solution for 1 h to degas. Finally, cast the treated casting solution using a casting method. When casting the solution into the petri dish, the speed should be fast to prevent the solvent from evaporating too quickly and causing film defects. Finally, allow it to air dry at room temperature.

[0036] (4) Transfer the membrane from step (3) to a forced-air drying oven for heat treatment. Heat treatment at 180°C for 23 hours to achieve amorphous transformation. During the heat treatment, use a glass plate to press the mixed matrix membrane to prevent the membrane from curling. Then, perform slow annealing at a cooling rate of 4°C / min to prevent the formation of defects.

[0037] Figure 1 The images show the XRD patterns of the mixed matrix film before and after the amorphous transformation in Example 1. The curve at 30°C represents the crystalline mixed matrix film, which shows obvious diffraction peaks in its XRD pattern. After heat treatment at 180°C, the XRD pattern shows large peaks belonging only to the amorphous state, confirming that it is an amorphous mixed matrix film.

[0038] Example 2

[0039] Preparation of amorphous hybrid matrix films:

[0040] (1) Dissolve 0.21 g of 2,5-dihydroxyterephthalic acid in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 The concentration obtained in the ratio of 3:1 was 37.9 mmol / L. -1 Solution A. Dissolve 0.07 g of copper nitrate trihydrate in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 A concentration of 10.3 mmol / L was obtained in a ratio of 1:3. -1 Solution B. Solutions A and B were dissolved separately by sonication for 2 minutes. Solution B was then added to solution A to obtain the MOF precursor solution.

[0041] (2) The obtained precursor solution was poured into a microwave reactor and placed in a microwave reactor for heat treatment at 50°C for 30 min; brown MOF (CuBDC-(OH)2) nanosheets were formed in the reactor. After natural cooling, the nanosheets were dispersed in 25 mL of DMF solution and centrifuged at 10000 rpm for 30 min. This process was repeated 3 times, and then washed 3 times with chloroform (in the same way as DMF washing). The obtained MOF nanosheets were dispersed in chloroform solution and stored.

[0042] (3) Disperse the MOF nanosheet dispersion prepared in step (2) in chloroform, wherein the mass fraction of MOF nanosheets is 1%, and stir for 20 min to ensure thorough dispersion; then add 10 wt% PI polymer powder while stirring to prevent polymer powder aggregation. Stir the mixed casting solution at room temperature for 24 h to ensure thorough mixing and dispersion; ultrasonically treat the stirred casting solution for 1 h to degas. Finally, cast the treated casting solution using a casting method. When casting the solution into the petri dish, the speed should be fast to prevent the solvent from evaporating too quickly and causing film defects. Finally, allow it to air dry at room temperature.

[0043] (4) Transfer the membrane from step (3) to a forced-air drying oven for heat treatment. Heat treatment at 180°C for 23 hours to achieve amorphous transformation. During the heat treatment, use a glass plate to press the mixed matrix membrane to prevent the membrane from curling. Then, perform slow annealing at a cooling rate of 4°C / min to prevent the formation of defects.

[0044] The mixed matrix membrane of this embodiment, which undergoes low-temperature induced in-situ transformation from crystalline to amorphous state, is applied to gas separation:

[0045] The prepared amorphous mixed matrix membrane was sealed with epoxy resin in a permeation cell for gas separation testing. An equimolar mixture of CO2 / N2 or CO2 / CH4 binary gas was injected into the shell side of the mixed matrix membrane for gas permeation. A 1:1 mixed gas was added to the feed side of the membrane, and the permeated gas was removed from the permeate side using scavenging gas (Ar). The gas separation performance was calculated after detection using an Agilent gas chromatograph 7890A.

[0046] Figure 2 This is a SEM image of the amorphous mixed matrix film prepared in Example 2.

[0047] The amorphous mixed matrix membrane prepared in this embodiment has a CO2 flux of 96 Barrer and CO2 / N2 or CO2 / CH4 selectivity as high as 135.3 and 112, respectively. The permeability and selectivity are both increased by 2 times compared with the mixed matrix membrane that has not undergone amorphous transformation. This result shows that the mixed matrix membrane prepared by the present invention has excellent performance and good application prospects.

[0048] Example 3

[0049] Preparation of amorphous hybrid matrix films:

[0050] (1) Dissolve 0.21 g of 2,5-dibromoterephthalic acid in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 The concentration obtained in the ratio of 3:1 was 23.2 mmol / L. -1 Solution A. Dissolve 0.005 g of copper nitrate trihydrate in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 The concentration obtained in the ratio of 1:3 was 0.74 mmol / L. -1 Solution B. Solutions A and B were dissolved separately by sonication for 2 minutes. Solution B was then added to solution A to obtain the MOF precursor solution.

[0051] (2) The obtained precursor solution was poured into a microwave reactor and placed in a microwave reactor for heat treatment at 80°C for 30 min; light blue MOF (CuBDC-(Br)2) nanosheets were formed in the reactor. After natural cooling, the nanosheets were dispersed in 25 mL of DMF solution and centrifuged at 10000 rpm for 30 min. This process was repeated 3 times, and then washed 3 times with dichloromethane (in the same way as DMF washing). The obtained MOF nanosheets were dispersed in dichloromethane solution and stored.

[0052] (3) Disperse the MOF nanosheet dispersion prepared in step (2) in dichloromethane, wherein the mass fraction of MOF nanosheets is 1%, and stir for 20 min to ensure thorough dispersion; then add 10 wt% PI polymer powder while stirring to prevent polymer powder aggregation. Stir the mixed casting solution at room temperature for 24 h to ensure thorough mixing and dispersion; ultrasonically treat the stirred casting solution for 1 h to degas. Finally, cast the treated casting solution using a casting method. When casting the solution into the petri dish, the speed should be fast to prevent the solvent from evaporating too quickly and causing membrane defects. Finally, allow it to air dry at room temperature.

[0053] (4) Transfer the membrane from step (3) to a forced-air drying oven for heat treatment. Heat treatment at 200°C for 23 hours to achieve amorphous transformation. During the heat treatment, use a glass plate to press the mixed matrix membrane to prevent the membrane from curling. Then, perform slow annealing at a cooling rate of 4°C / min to prevent the formation of defects.

[0054] The mixed matrix membrane of this embodiment, which undergoes low-temperature induced in-situ transformation from crystalline to amorphous state, is applied to gas separation:

[0055] The prepared amorphous mixed matrix membrane was sealed with epoxy resin in a permeation cell for gas separation testing. An equimolar mixture of CO2 / N2 or CO2 / CH4 binary gas was injected into the shell side of the mixed matrix membrane for gas permeation. A 1:1 mixed gas was added to the feed side of the membrane, and the permeated gas was removed from the permeation side using scavenging gas (Ar). The gas separation performance was calculated after detection using an Agilent gas chromatograph 7890A.

[0056] The amorphous mixed matrix membrane prepared in this embodiment has a CO2 flux of 73.6 Barrer and CO2 / N2 or CO2 / CH4 selectivity as high as 63.8 and 76.5, respectively, indicating that the mixed matrix membrane prepared by this invention has excellent performance and good application prospects.

[0057] Example 4

[0058] Preparation of amorphous hybrid matrix films:

[0059] (1) Dissolve 0.21 g of 2,5-dichloroterephthalic acid in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 The concentration obtained in the ratio of 3:1 was 31.9 mmol / L. -1 Solution A. Dissolve 0.007 g of copper nitrate trihydrate in 28 mL of a mixed solution of DMF and acetonitrile (V DMF :V 乙腈 The concentration obtained in the ratio of 1:3 was 1.03 mmol / L. -1 Solution B. Solutions A and B were dissolved separately by sonication for 2 minutes. Solution B was then added to solution A to obtain the MOF precursor solution.

[0060] (2) The obtained precursor solution was poured into a microwave reactor and placed in a microwave reactor for heat treatment at 70°C for 30 min; light blue MOF (CuBDC-(Cl)2) nanosheets were formed in the reactor. After natural cooling, the nanosheets were dispersed in 25 mL of DMF solution and centrifuged at 10000 rpm for 30 min. This process was repeated 3 times, and then washed 3 times with chloroform (in the same way as DMF washing). The obtained MOF nanosheets were dispersed in chloroform solution and stored.

[0061] (3) Disperse the MOF nanosheet dispersion prepared in step (2) in chloroform, wherein the mass fraction of MOF nanosheets is 1%, and stir for 20 min to ensure full dispersion; then add 10 wt% PI polymer powder while stirring to prevent polymer powder aggregation, and stir the mixed casting solution at room temperature for 24 h to ensure full mixing and dispersion; ultrasonically treat the stirred casting solution for 1 h to degas. Finally, spin-coat the treated casting solution to form a film. The spin-coating substrate is α-Al2O3, the spin-coating speed is 8000 rpm, and the spin-coating time is 60 s to allow the solvent to completely evaporate.

[0062] (4) Transfer the membrane from step (3) to a forced-air drying oven for heat treatment. Heat treatment at 220°C for 23 hours to achieve amorphous transformation. During the heat treatment, use a glass plate to press the mixed matrix membrane to prevent the membrane from curling. Then, perform slow annealing at a cooling rate of 4°C / min to prevent defect formation.

[0063] The mixed matrix membrane of this embodiment, which undergoes low-temperature induced in-situ transformation from crystalline to amorphous state, is applied to gas separation:

[0064] The prepared amorphous mixed matrix membrane was sealed with epoxy resin in a permeation cell for gas separation testing. An equimolar mixture of CO2 / N2 or CO2 / CH4 binary gas was injected into the shell side of the mixed matrix membrane for gas permeation. A 1:1 mixed gas was added to the feed side of the membrane, and the permeated gas was removed from the permeate side using scavenging gas (Ar). The gas separation performance was calculated after detection using an Agilent gas chromatograph 7890A.

[0065] The amorphous mixed matrix membrane prepared in this embodiment has a CO2 flux of 78 Barrer and CO2 / N2 or CO2 / CH4 selectivity as high as 65.5 and 74.3, respectively, indicating that the mixed matrix membrane prepared by this invention has excellent performance and good application prospects.

[0066] Example 5

[0067] Compared with Example 2, the difference is that in step (3), the mass fraction of MOF nanosheets is 0.15%, and then 10 wt% of PI polymer is added.

[0068] The amorphous mixed matrix membrane prepared in this embodiment has a CO2 flux of 32.4 Barrer and CO2 / N2 or CO2 / CH4 selectivity as high as 64.2 and 52.5, respectively.

[0069] Example 6

[0070] Compared with Example 2, the difference is that in step (3), the mass fraction of MOF nanosheets is 0.5%, and then 10 wt% of PI polymer is added.

[0071] The amorphous mixed matrix membrane prepared in this embodiment has a CO2 flux of 72.6 Barrer and CO2 / N2 or CO2 / CH4 selectivity as high as 96.3 and 85.4, respectively.

[0072] Example 7

[0073] Compared with Example 2, the difference is that in step (3), the mass fraction of MOF nanosheets is 3%, and then 10 wt% of PI polymer is added.

[0074] The amorphous mixed matrix membrane prepared in this embodiment has a CO2 flux of 122.3 Barrer and CO2 / N2 or CO2 / CH4 selectivity as high as 106.5 and 95.6, respectively.

[0075] Example 8

[0076] Compared with Example 2, the difference is that in step (3), the mass fraction of MOF nanosheets is 5%, and then 10 wt% of PI polymer is added.

[0077] The amorphous mixed matrix membrane prepared in this embodiment has a CO2 flux of 150.2 Barrer and CO2 / N2 or CO2 / CH4 selectivity as high as 75.6 and 65.9, respectively.

[0078] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for constructing an amorphous hybrid matrix membrane based on low-temperature induced construction, characterized in that, Includes the following steps: Organic ligands and metal salts are dissolved and mixed separately to obtain a MOF precursor solution; the MOF precursor solution is heat-treated to obtain MOF nanosheets; the MOF nanosheets are blended with a polymer in a solvent to prepare a casting solution; a mixed matrix membrane is prepared using the casting solution; finally, the mixed matrix membrane is treated at 160–220 °C for 1–36 h to undergo an amorphous transformation, and after cooling, an amorphous mixed matrix membrane is obtained. The molar ratio of the organic ligand to the metal salt is 1–55:1; the concentration of the metal ion in the MOF precursor solution is 0.5–50.8 mmol·L⁻¹. -1 ; The organic ligand is a carboxylic acid ligand, specifically 2,5-dibromoterephthalic acid, 2,5-dihydroxyterephthalic acid, or terephthalic acid; the metal salt is a divalent or trivalent metal salt. The heat treatment temperature is 30–100°C, and the time is 1–100 min.

2. The method for constructing an amorphous hybrid matrix membrane based on low-temperature induced formation according to claim 1, characterized in that, The heat treatment method is microwave heating.

3. The method for constructing an amorphous hybrid matrix membrane based on low-temperature induced formation according to claim 1, characterized in that, The MOF nanosheets also include a cleaning step before the casting solution is prepared.

4. The method for constructing an amorphous hybrid matrix membrane based on low-temperature induced formation according to claim 1, characterized in that, The polymer is selected from polysulfone, polyimide, polyethylene oxide, microporous polymer or polyvinylidene fluoride; the solvent of the casting solution is N,N-dimethylformamide, chloroform, dichloromethane or methanol; the mass fraction of MOF nanosheets in the casting solution is 0.1-30%, and the mass fraction of polymer is 1-40%.

5. The method for constructing an amorphous hybrid matrix membrane based on low-temperature induced formation according to claim 1, characterized in that, The cooling rate shall not exceed 5°C / min.

6. An amorphous mixed matrix membrane prepared by the method of low-temperature induced construction of an amorphous mixed matrix membrane according to any one of claims 1 to 5.

7. The application of the amorphous mixed matrix membrane according to claim 6 in gas separation.

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