Large-area continuous MOF membrane, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a large-area continuous MOF membrane, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: S1, dissolving zirconium tetrachloride and 1,3,5-tris(4-carboxyphenyl)benzene in a solvent, i.e., N,N-dimethylformamide, then adding formic acid and water thereto, sealing the resulting mixed solution, placing same in an oven, maintaining the temperature, then adding a sulfonation reagent thereto, performing refluxing for a period of time, then leaving same to stand, and then performing centrifugal washing with ultrapure water to obtain a homogeneous dispersion; S2, cleaning a substrate in ethanol and deionized water respectively for later use; S3, fixing the substrate on a blade coater, blade-coating and spreading the prepared dispersion onto the surface of the substrate, and drying same to obtain an MOF membrane; and S4, transferring the MOF membrane to a vacuum oven to further stabilize the structure thereof. In the present invention, two-dimensional MOF nanosheets can be conveniently and quickly prepared by means of a solvothermal method, and a large-area continuous MOF membrane can be prepared via rapid self-assembly by means of a blade coating method, which MOF membrane exhibits a good lithium ion selectivity and permeability under the dual regulation of a size effect and the affinity effect of sulfonic acid groups.

Description

A large-area continuous MOF membrane, its preparation method and application Technical Field

[0001] This invention belongs to the field of membrane material preparation and membrane separation technology, specifically relating to a large-area continuous MOF membrane and its preparation method and application. Background Technology

[0002] With the rapid development of human society, the problem of resource scarcity is becoming increasingly prominent. Separation membranes, due to their unique structure and mass transfer properties, have broad application prospects in fields such as ion / molecule separation, seawater desalination, catalysis, and energy storage and conversion. Among them, two-dimensional layered membranes formed by stacking atomically thin nanosheets are ideal materials for separation membranes.

[0003] Existing nanosheets include graphene and its derivatives, MoS2, and two-dimensional transition metal carbonitrides (MXene). However, these traditional non-porous two-dimensional layered nanosheets force ions / molecules to transport along highly tortuous in-plane nanochannels, which to some extent hinders the improvement of permeation flux and cannot avoid the trade-off between permeability and selectivity.

[0004] Two-dimensional metal-organic frameworks (MOFs), as a type of porous two-dimensional layered nanosheets, benefit from the inherent porosity of MOF nanosheets. This allows ions / molecules to pass directly through the nanosheets, rather than being restricted to in-plane transport, effectively reducing the length and tortuosity of the transport path. While the porous nature of MOF materials provides numerous transport paths, which is beneficial for improving the permeation flux of films, it is difficult to fabricate large-area continuous MOF films, and they also suffer from problems such as fragility and pulverization.

[0005] Common methods for preparing MOF membranes include interfacial synthesis, liquid phase epitaxy, impregnation, atomic layer deposition, chemical vapor deposition, and vacuum filtration. However, these methods can only produce MOFs of limited size, and the operation process is complex, requiring high-quality equipment and a suitable operating environment.

[0006] An article published in *Nano Letters*, Volume 24, Issue 9, entitled "Two-dimensional sulfonate-functionalized metal-organic framework membranes for efficient lithium-ion sieving," describes the addition of a PSS polymer to a MOF dispersion and the formation of a composite membrane on an anodic alumina (AAO) substrate using vacuum filtration to improve MOF membrane stability. However, the use of the PSS polymer additive affects the shelf life of the MOF dispersion, causing sedimentation. Furthermore, AAO substrates are expensive, difficult to mass-produce, and brittle, making them prone to breakage during transfer. During film drying, the rigid AAO substrate often warps at the edges or even detaches from the substrate because it cannot match the slight deformation during film shrinkage. Therefore, film formation on AAO substrates requires careful control of the drying rate and conditions, and the membranes obtained using this method are relatively small, with a diameter of 1.5 cm. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems in the prior art by proposing a large-area continuous MOF membrane, its preparation method, and its application.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A first aspect of the present invention is to provide a method for preparing a large-area continuous MOF film, comprising the following steps:

[0010] S1: Zirconium tetrachloride and 1,3,5-tris(4-carboxyphenyl)benzene were dissolved in the solvent N,N-dimethylformamide, then formic acid and water were added. The resulting mixed solution was sealed and placed in an oven for heat preservation. Then, sulfonating reagent was added, and the mixture was refluxed for a period of time and allowed to stand. Then, it was washed by centrifugation with ultrapure water to obtain a homogeneous dispersion.

[0011] S2: Wash the substrate in ethanol and deionized water respectively and set aside for use;

[0012] S3: Fix the substrate on the coating machine and coat the prepared dispersion evenly on the substrate surface. After drying, the MOF film is obtained.

[0013] S4: Transfer the MOF membrane to a vacuum oven to further stabilize the structure.

[0014] The present invention is further configured such that, in step S1, the mass ratio of zirconium tetrachloride and 1,3,5-tris(4-carboxyphenyl)benzene is 1:1 to 1:1.5.

[0015] The present invention is further configured such that, in step S1, the mass fraction of formic acid in the mixed solution is 10% to 16%, and the mass fraction of water is 8% to 15%.

[0016] The present invention is further configured such that, in step S1, the sulfonating agent is p-sulfobenzoic acid or sodium isophthalic acid-5-sulfonate, preferably p-sulfobenzoic acid.

[0017] The present invention is further configured such that, in step S1, the molar ratio of the sulfonating agent to zirconium tetrachloride is 1:1 to 13:1, preferably 6:1 to 13:1.

[0018] The present invention is further configured such that, in step S1, the reflux temperature is 70-90°C and the reflux time is 8-12 hours.

[0019] The present invention is further configured such that, in step S2, the substrate is selected from one of polystyrene substrate, glass fiber substrate and polyacrylonitrile substrate, preferably PAN substrate.

[0020] The present invention is further configured such that, in step S3, the drying temperature is 110-130°C and the drying time is 1-3 hours.

[0021] The present invention is further configured such that, in step S4, the drying temperature of the vacuum oven is 80-120°C and the drying time is 8-12 hours.

[0022] A second aspect of the present invention is to provide a large-area continuous MOF membrane prepared by the above-described preparation method.

[0023] A third aspect of the present invention is to provide the application of the large-area continuous MOF membrane prepared by the above preparation method in lithium ion sieving.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) This invention enables the convenient and rapid preparation of two-dimensional MOF nanosheets using a solvothermal method, and allows for the rapid self-assembly of large-area continuous MOF films via a blade coating method. The area of ​​the MOF film can reach the level of several hundred square centimeters, depending on the area of ​​the substrate and the capacity of the blade coating equipment. This method can form large-area continuous MOF films on various substrates in a short time at room temperature, with low requirements for equipment, simple operation, and mild conditions, which is conducive to large-scale application.

[0026] (2) The present invention uses a solvothermal method to construct 2D Zr-BTB nanosheets from bottom to top using zirconium tetrachloride (ZrCl4) and 1,3,5-tris(4-carboxyphenyl)benzene (BTB) as raw materials. Subsequently, during the synthesis process, sulfonating agents are used to directly modify the sulfonic acid functional groups on the metal cluster sites. The resulting MOF dispersion is uniform and stable, has a long shelf life, and is conducive to film formation. The MOF film prepared by the blade coating method exhibits excellent lithium ion selectivity and permeability under the dual regulation of size effect and affinity effect of sulfonic acid groups.

[0027] (3) The two-dimensional MOF membrane prepared by this invention combines the advantages of two-dimensional materials and MOF materials, overcomes the defect of traditional MOF materials being difficult to form films, and makes up for the shortcomings of traditional two-dimensional membranes having tortuous transport paths and difficult permeation rates. The intralayer pores of the nanosheets and the interlayer spacing of the layered membrane can both serve as ion transport entrances, providing a dual path for ion transport within the membrane. Attached Figure Description

[0028] Figure 1 is a schematic diagram of the bottom-up construction of 2D Zr-BTB-S nanosheets.

[0029] Figure 2 is a comparison chart of the stability tests of the dispersions of Example 1 and Comparative Example 1.

[0030] Figure 3 is a TEM image of 2D Zr-BTB-S nanosheets.

[0031] Figure 4 is an optical image of the large-area MOF film on the PAN substrate prepared in Example 2.

[0032] Figure 5 is a SEM image of the large-area MOF film on the PAN substrate prepared in Example 2.

[0033] Figure 6 is a schematic diagram of the H-type test mold. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and thoroughly described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art without creative effort should be covered within the protection scope of the present invention.

[0035] Unless otherwise specified in the following examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0036] As shown in Figure 1, this invention employs a solvothermal method to construct 2D Zr-BTB nanosheets from the bottom up using zirconium tetrachloride (ZrCl4) and 1,3,5-tris(4-carboxyphenyl)benzene (BTB) as raw materials. Subsequently, the 2D Zr-BTB nanosheets are functionalized using sulfonating agents to obtain 2D Zr-BTB-S nanosheets. In other words, during the synthesis process, sulfonic acid functional groups are directly modified on the metal cluster sites, and a large-area continuous two-dimensional MOF film is prepared by a blade coating method.

[0037] Example 1

[0038] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.125 g) were dissolved in 50 mL of N,N-dimethylformamide (DMF), and then formic acid (9.6 g) and water (6 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 2 hours. Then, 0.525 g of p-sulfobenzoic acid was added, and the mixture was refluxed at 90 °C for 12 hours and then allowed to stand for 12 hours. After washing five times by centrifugation with ultrapure water (5000 rpm, 5 min), a homogeneous 2DZr-BTB-S nanosheet (MOF) dispersion was obtained.

[0039] Comparative Example 1

[0040] Following the synthesis of 2D Zr-BTB nanosheets and 2D Zr-BTB-PSS nanosheets (S2) in the article "Two-dimensional sulfonate-functionalized metal–organic framework membranes for efficient lithium-ion sieving" published in Nano Letters, Volume 24, Issue 9, a 2D Zr-BTB-PSS nanosheet (MOF) dispersion was prepared.

[0041] The sulfonic acid-functionalized MOF dispersions prepared in Example 1 and Comparative Example 1 were stored at room temperature and pressure for one week. The storage effect is shown in Figure 2. The dispersion with added polymer in Comparative Example 1 showed obvious sedimentation and was difficult to store for a long time, which increased the cost of use. However, the dispersion prepared in Example 1 remained uniform and stable.

[0042] Example 2

[0043] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.125 g) were dissolved in 50 mL of DMF, and then formic acid (9.6 g) and water (6 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 2 hours. After washing with DMF and ultrapure water (5000 rpm, 5 min), 0.525 g of p-sulfobenzoic acid was added, and the mixture was refluxed at 90 °C for 12 h and then allowed to stand for 12 h. After washing five times by centrifugation with ultrapure water (5000 rpm, 5 min), a homogeneous 2D Zr-BTB-S nanosheet dispersion was obtained. Its TEM image is shown in Figure 3. The figure shows that the lateral size of the nanosheets is about 300 nm, and the obvious lattice striations indicate that it has good crystallinity.

[0044] The polyacrylonitrile (PAN) substrate was washed with ethanol and deionized water for 10 min each and then set aside. The PAN substrate was fixed on a doctor blade coater, and the prepared dispersion was spread evenly on the substrate surface. After drying for 30 min, a MOF film was obtained. Subsequently, the MOF film was transferred to a vacuum oven at 120℃ for 8 h for further drying. The optical images and SEM images of the obtained MOF film are shown in Figures 4 and 5. The MOF area shown in Figure 4 is 15 cm * 21 cm. As can be seen from Figure 5, the prepared MOF film has a smooth surface and no obvious defects.

[0045] Example 3

[0046] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.1 g) were dissolved in 50 mL of DMF, and then formic acid (6.5 g) and water (6 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 24 hours. After washing with DMF and ultrapure water (5000 rpm, 5 min), 0.105 g of p-sulfobenzoic acid was added, and the mixture was refluxed at 70 °C for 8 h and then allowed to stand for 12 h. After washing five times by centrifugation with ultrapure water (5000 rpm, 5 min), a homogeneous 2D Zr-BTB-S nanosheet dispersion was obtained.

[0047] The PAN substrate was washed with ethanol and deionized water for 10 min each and then set aside. The PAN substrate was fixed on a doctor blade coater, and the prepared dispersion was spread evenly on the substrate surface. After drying for 30 min, the MOF membrane was obtained. Subsequently, the MOF membrane was transferred to a vacuum oven at 120℃ for 8 h for further drying.

[0048] Example 4

[0049] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.15 g) were dissolved in 50 mL of DMF, and then formic acid (9.6 g) and water (6 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 2 hours. After washing with DMF and ultrapure water (5000 rpm, 5 min), 1.05 g of p-sulfobenzoic acid was added, and the mixture was refluxed at 90 °C for 12 h and then allowed to stand for 12 h. After washing five times by centrifugation with ultrapure water (5000 rpm, 5 min), a homogeneous 2D Zr-BTB-S nanosheet dispersion was obtained.

[0050] The PAN substrate was washed with ethanol and deionized water for 10 min each and then set aside. The PAN substrate was fixed on a doctor blade coater, and the prepared dispersion was spread evenly on the substrate surface. After drying for 30 min, the MOF membrane was obtained. Subsequently, the MOF membrane was transferred to a vacuum oven at 120℃ for 8 h for further drying.

[0051] Example 5

[0052] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.125 g) were dissolved in 50 mL of DMF, and then formic acid (6.5 g) and water (9 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 12 hours. After washing with DMF and ultrapure water, 0.525 g of sodium isophthalate-5-sulfonate was added, and the mixture was refluxed at 90 °C for 12 hours and then allowed to stand for 12 hours. After washing five times by centrifugation with ultrapure water (5000 rpm, 5 min), a homogeneous 2D Zr-BTB-S nanosheet dispersion was obtained.

[0053] The PAN substrate was washed with ethanol and deionized water for 10 min each and then set aside. The PAN substrate was fixed on a doctor blade coater, and the prepared dispersion was spread evenly on the substrate surface. After drying for 30 min, the MOF membrane was obtained. Subsequently, the MOF membrane was transferred to a vacuum oven at 120℃ for 8 h for further drying.

[0054] Example 6

[0055] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.125 g) were dissolved in 50 mL of DMF, and then formic acid (9.6 g) and water (6 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 2 hours. Then, 0.525 g of p-sulfobenzoic acid was added, and the mixture was refluxed at 90 °C for 12 hours and then allowed to stand for 12 hours. After washing five times by centrifugation with ultrapure water (5000 rpm, 5 min), a homogeneous 2D Zr-BTB-S nanosheet dispersion was obtained.

[0056] The polystyrene substrate was washed with ethanol and deionized water for 10 min each and then set aside. The polystyrene substrate was fixed on a doctor blade coater, and the prepared dispersion was spread evenly on the substrate surface. After drying for 30 min, the MOF membrane was obtained. Subsequently, the MOF membrane was transferred to a vacuum oven at 120 °C for 8 h to further stabilize the structure.

[0057] Example 7

[0058] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.125 g) were dissolved in 50 mL of DMF, and then formic acid (9.6 g) and water (6 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 2 hours. Then, 0.525 g of p-sulfobenzoic acid was added, and the mixture was refluxed at 90 °C for 12 hours and then allowed to stand for 12 hours. After washing five times by centrifugation with ultrapure water (5000 rpm, 5 min), a homogeneous 2D Zr-BTB-S nanosheet dispersion was obtained.

[0059] The glass fiber substrate was washed with ethanol and deionized water for 10 min each and then set aside. The glass fiber substrate was fixed on a doctor blade coater, and the prepared dispersion was spread evenly on the substrate surface. After drying for 30 min, the MOF membrane was obtained. Subsequently, the MOF membrane was transferred to a vacuum oven at 120℃ for 8 h to further stabilize the structure.

[0060] Comparative Example 2

[0061] Comparative Example 2 is basically the same as Example 2, except that p-sulfobenzoic acid was not added to the dispersion. Specifically:

[0062] Zirconium tetrachloride (0.1 g) and 1,3,5-tris(4-carboxyphenyl)benzene (0.125 g) were dissolved in 50 mL of DMF, and then formic acid (9.6 g) and water (6 mL) were added to prepare a mixed solution. The mixed solution was sealed and placed in an oven at 120 °C for 2 hours. After washing with DMF and ultrapure water five times by centrifugation (5000 rpm, 5 min), a 2D Zr-BTB nanosheet dispersion was obtained.

[0063] The PAN substrate was washed with ethanol and deionized water for 10 min each and then set aside. The PAN substrate was fixed on a doctor blade coater, and the prepared dispersion was spread evenly on the substrate surface. After drying for 30 min, the MOF membrane was obtained. Subsequently, the MOF membrane was transferred to a vacuum oven at 120℃ for 8 h for further drying.

[0064] The MOF membranes prepared by Examples 2-7 and Comparative Example 2 were clamped in the H-type test mold shown in Figure 6 and subjected to the following permeation performance test.

[0065] Test 1

[0066] The feed solution and permeate on both sides of the MOF membrane are equal volumes of 100mM LiCl solution and ultrapure water, respectively. The conductivity of the permeate side is monitored at regular intervals and converted into ion concentration. Finally, the lithium ion permeation rate is calculated by the following formula (1), and the results are shown in Table 1.

[0067] Ion permeation rate J s (mol·m -2 h -1 ):

[0068] Where C is the ion concentration on the permeate side (mol / L), V is the volume (L), and A is the effective test membrane area (m²). 2 ), where Δt is the infiltration time (h).

[0069] Test 2

[0070] The feed solution and permeate on both sides of the MOF membrane are equal volumes of a 100 mM mixed solution (equimolar concentrations of LiCl and KCl, or equimolar concentrations of LiCl and MgCl2) and ultrapure water, respectively. The ion concentration on the permeate side is monitored periodically. The MOF membrane's response to Li... + / K + Li + / Mg 2+ The selectivity factors are shown in Table 1.

[0071] Ion selectivity factor:

[0072] Among them, J x and J y The ion permeation rate is calculated from the above formula (1), where x is the Li + y is K + or Mg 2+ .

[0073] Table 1

[0074] As shown in Table 1, the MOF membrane modified with sulfonic acid functional groups prepared in this invention has a high lithium ion permeation rate and exhibits good retention effects for both magnesium and potassium ions.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a large-area continuous MOF membrane, characterized in that, Includes the following steps: S1: Zirconium tetrachloride and 1,3,5-tris(4-carboxyphenyl)benzene were dissolved in the solvent N,N-dimethylformamide, then formic acid and water were added. The resulting mixed solution was sealed and placed in an oven for heat preservation. Then, sulfonating reagent was added, and after reflux for a period of time, it was allowed to stand. Then, it was washed by centrifugation with ultrapure water to obtain a homogeneous dispersion. S2: Wash the substrate in ethanol and deionized water respectively and set aside for use; S3: Fix the substrate on the coating machine and coat the prepared dispersion evenly on the substrate surface. After drying, the MOF film is obtained. S4: Transfer the MOF membrane to a vacuum oven to further stabilize the structure.

2. The method for preparing a large-area continuous MOF membrane according to claim 1, characterized in that, In step S1, the mass ratio of zirconium tetrachloride to 1,3,5-tris(4-carboxyphenyl)benzene is 1:1 to 1:1.5; In the mixed solution, the mass fraction of formic acid is 10%–16%, and the mass fraction of water is 8%–15%.

3. The method for preparing a large-area continuous MOF membrane according to claim 1, characterized in that, In step S1, the sulfonating agent is p-sulfobenzoic acid or sodium isophthalic acid-5-sulfonate.

4. The method for preparing a large-area continuous MOF film according to claim 1, characterized in that, In step S1, the molar ratio of the sulfonating agent to zirconium tetrachloride is 1:1 to 13:

1.

5. The method for preparing a large-area continuous MOF membrane according to claim 1, characterized in that, In step S1, the reflux temperature is 70–90°C and the reflux time is 8–12 h.

6. The method for preparing a large-area continuous MOF membrane according to claim 1, characterized in that, In step S2, the substrate is selected from one of polystyrene substrate, glass fiber substrate, and polyacrylonitrile substrate.

7. The method for preparing a large-area continuous MOF membrane according to claim 1, characterized in that, In step S3, the drying temperature is 110–130°C and the drying time is 1–3 hours.

8. The method for preparing a large-area continuous MOF membrane according to claim 1, characterized in that, In step S4, the drying temperature of the vacuum oven is 80-120℃, and the drying time is 8-12h.

9. A large-area continuous MOF membrane, characterized in that, The large-area continuous MOF membrane is prepared by the method for preparing the large-area continuous MOF membrane according to any one of claims 1 to 8.

10. An application of a large-area continuous MOF membrane, characterized in that, The large-area continuous MOF membrane is prepared by the method of any one of claims 1 to 8 and is used for lithium ion sieving.

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