Thin film composite film based on hollow metal-organic framework as well as preparation method and application of thin film composite film

Abstract

The invention discloses a thin film composite membrane based on a hollow metal-organic framework and a preparation method and application thereof, and belongs to the technical field of membrane separation. Comprising the following steps: firstly synthesizing a hollow metal-organic framework material, then soaking a support base membrane in an amine monomer aqueous dispersion containing the hollow metal-organic framework, and then soaking the support base membrane in a multi-acyl chloride organic solution for interfacial polymerization reaction to prepare the thin-film composite membrane based on the hollow metal-organic framework. Due to the unique nano-porous and hollow structure of the hollow metal-organic framework, a rapid selective transmission channel can be provided for target molecules; rich amino groups on a shell layer on the surface of the hollow metal-organic framework are covalently cross-linked with multi-element acyl chloride, so that the hollow metal-organic framework is anchored in the membrane, the loss of a nano material in an operation process is prevented, and the long-term operation stability is facilitated. The preparation process is simple, convenient and controllable, the prepared membrane is applied to pervaporation ethanol-water separation, high permeation flux and high separation factors are shown, and good long-term operation stability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane material preparation and membrane separation, and in particular to a thin film composite membrane based on a hollow metal-organic framework, and a preparation method and application thereof. Background Art

[0002] In the chemical production and biopharmaceutical industries, separation costs account for over half of total costs, making the development of efficient separation technologies of strategic importance. Membrane separation technology offers advantages such as ease of operation, simple processes, high energy efficiency, and environmental friendliness. Pervaporation membranes, in particular, can overcome the phase equilibrium limitations of traditional distillation processes and further optimize product purity. Bioethanol is a renewable energy source that can effectively alleviate environmental pollution and energy shortages. However, the water formed during the production process forms an azeotrope with ethanol, making it difficult to obtain high-purity ethanol. Membrane materials are crucial for membrane separation. Polyamide-based thin-film composite membranes have become commercially available due to their advantages such as ease of processing, thinness, and excellent solvent resistance. However, conventional polyamide thin-film composite membranes suffer from insufficient surface hydrophilicity, low chain packing density, and irregular dynamic free volume cavities, resulting in poor separation performance in pervaporation applications and difficulty overcoming the trade-off between permeability and selectivity. Previous work has focused on in-situ anchoring of quantum dots in polyamide thin-film composite membranes to enhance water-selective separation, but the molecular mass transfer channels remain disordered free volume cavities. Constructing regular and orderly mass transfer channels in polyamide thin film composite membranes may be more conducive to the transport of molecules.

[0003] Metal-organic frameworks (MOFs) are a class of crystalline porous materials constructed from inorganic metal centers (such as metal ions or metal clusters) and organic ligands through coordination bonds. They possess a well-ordered pore structure and are easily modifiable. Although pure MOF membranes have been developed for pervaporation separation, the nucleation and growth characteristics of MOFs complicate their preparation, often resulting in thick films to compensate for defects such as pinholes, making MOF thin film preparation difficult. Thin film composite membranes prepared by doping MOFs into polyamides combine the properties of both polymers and MOFs. By manipulating the behavior of polymer chains through MOFs and simultaneously constructing additional regular porous channels within the membrane, this is an effective strategy for synergistically improving permeability and selectivity. Lee et al. synthesized zwitterionic MOFs and filled them into polyamides to produce zwitterionic MOF-based thin film composite membranes, improving isopropyl alcohol-water separation. Xu et al. fabricated thin film composite membranes with ZIF interlayers on ceramic-based membranes, significantly improving the separation factor while slightly reducing the permeate flux (CN202110402976.1). This is due to the mismatch between the pore orientation caused by the random dispersion of MOFs and the molecular diffusion pathways, which hinders the permeability of thin-film composite membranes. Furthermore, the weak interaction between MOFs and polymers is detrimental to the stability of the membranes during long-term operation. Therefore, the rational design of porous MOF structures is crucial for improving membrane performance. Summary of the Invention

[0004] In view of the above problems, the present invention designs and synthesizes hollow metal-organic framework materials, and provides a preparation method of a thin film composite membrane based on the hollow metal-organic framework and its application in pervaporation ethanol-water separation.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The preparation method of the hollow metal-organic framework thin film composite membrane comprises the following steps:

[0007] Step 1. Preparation of hollow NHZIF: 2-Methylimidazole and zinc nitrate hexahydrate (molar ratio 8:1) were dissolved in methanol, mixed and reacted for a period of time, and centrifuged to obtain a white powder. The white powder was dispersed in a tannic acid aqueous solution and reacted in the dark for a period of time. The white powder was centrifuged to obtain a light yellow powder. The white powder was then dispersed in a Tris-HCl buffer solution containing an amine monomer and reacted. After the reaction, the dark yellow powder was obtained by centrifugation.

[0008] Step 2: Membrane preparation: Hollow NHZIF is blended with amine monomer to form an aqueous dispersion, the supporting base membrane is immersed in the aqueous dispersion for a period of time, and then immersed in a polyacyl chloride organic solution to undergo interfacial polymerization reaction. After heat treatment, a thin film composite membrane based on hollow NHZIF is obtained.

[0009] As a preferred embodiment of the method for preparing a thin film composite membrane based on a hollow metal-organic framework according to the present invention, the blending reaction time in step 1 is 2-6 hours; the tannic acid concentration is 2-10 mg / mL; and the light-avoiding reaction time is 10-60 minutes.

[0010] As a preferred embodiment of the method for preparing a thin film composite membrane based on a hollow metal-organic framework according to the present invention, the buffer solution containing an amine monomer in step one, wherein the amine monomer is one of ethylenediamine, m-phenylenediamine, diethylenetriamine and polyethyleneimine, and the concentration of the amine monomer is 2-10 mg / mL; and the reaction time is 3-6 hours.

[0011] As a preferred embodiment of the method for preparing a thin film composite membrane based on a hollow metal-organic framework according to the present invention, the amine monomer in step 2 is one of ethylenediamine, m-phenylenediamine, diethylenetriamine and polyethyleneimine; and the concentration of the amine monomer in the aqueous dispersion is 0-0.3 wt%.

[0012] As a preferred embodiment of the method for preparing a thin film composite membrane based on a hollow metal-organic framework according to the present invention, the porous supporting base membrane described in step 2 is one of a polyacrylonitrile ultrafiltration membrane, a polyvinyl chloride membrane, a polytetrafluoroethylene ultrafiltration membrane and a polyethersulfone membrane.

[0013] As a preferred embodiment of the method for preparing the thin film composite membrane based on the hollow metal-organic framework according to the present invention, the concentration of the hollow NHZIF in the aqueous dispersion in step 2 is 0.05-0.15 wt %.

[0014] As a preferred embodiment of the method for preparing the thin film composite membrane based on the hollow metal-organic framework according to the present invention, the polyacyl chloride in step 2 is one of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride; and the concentration of the polyacyl chloride is 0.1-0.2 wt%.

[0015] As a preferred embodiment of the method for preparing a thin film composite membrane based on a hollow metal-organic framework according to the present invention, the immersion time of the aqueous dispersion in step 2 is 5-30 minutes, the interfacial polymerization reaction time is 1-5 minutes, the heat treatment temperature is 60-80°C, and the heat treatment time is 5-20 minutes.

[0016] Another object of the present invention is to provide a thin film composite membrane based on a hollow metal-organic framework.

[0017] Another object of the present invention is to provide a thin film composite membrane based on a hollow metal-organic framework for application in pervaporation ethanol-water separation.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The hollow NHZIF designed and synthesized in this invention possesses a multi-level pore structure. The micropores in the surface shell can be used for molecular screening and enhance molecular selectivity. The internal hollow structure can create additional regular and ordered pore channels in the membrane, reducing mass transfer resistance and enhancing molecular diffusion. Furthermore, the abundant amino groups in the surface shell can form covalent crosslinks with acyl chlorides, anchoring and strengthening their interfacial compatibility with polymers, improving membrane structural stability while also enhancing the membrane's hydrophilicity. The present invention has a simple and controllable preparation process, enabling efficient pervaporation ethanol-water separation, and provides a new approach for enhancing the separation performance of thin-film composite membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Transmission electron microscopy images of ZIF and NHZIF;

[0021] Figure 2 is the XRD pattern of NHZIF;

[0022] Figure 3 This is a surface scanning electron microscope image of Example 1;

[0023] Figure 4 This is a surface scanning electron microscope image of Comparative Example 1;

[0024] Figure 5 This is a long-term operational stability diagram of Example 1. DETAILED DESCRIPTION

[0025] In order to further understand the purpose, content and advantages of the present invention, now specific embodiments of the present invention are described in detail below, but can not be limited to the following examples, and will be freely matched according to actual conditions. The endpoints and any values ​​of the scope disclosed in this article are not limited to this accurate scope and value. For numerical ranges, between the endpoint values ​​of each scope, between the endpoint values ​​of each scope and a separate point value, and between the separate point value, can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article.

[0026] The following is further described in conjunction with some specific embodiments and comparative examples:

[0027] The porous support base polyacrylonitrile ultrafiltration membrane was placed in a 1.5M sodium hydroxide aqueous solution at a temperature of 55° C. for heat treatment for 1 hour, repeatedly washed with deionized water until the pH was neutral, and dried to obtain a hydrolyzed polyacrylonitrile ultrafiltration membrane.

[0028] Example 1

[0029] This embodiment provides a method for preparing a thin film composite membrane based on a hollow metal-organic framework, specifically:

[0030] Step 1. Preparation of hollow NHZIF: 5.26 g of 2-methylimidazole and 2.38 g of zinc nitrate hexahydrate were dissolved in 80 mL of methanol, mixed and reacted for 3 h, and centrifuged to obtain a white powder. The white powder was dispersed in a 0.5 mg / mL aqueous solution of tannic acid, reacted in the dark for 30 min, and centrifuged to obtain a light yellow powder. The powder was then dispersed in a 0.5 mg / mL Tris-HCl buffer solution containing diethylenetriamine and reacted for 3-5 h. The dark yellow powder was obtained by centrifugation. Figure 1 Transmission electron microscope images of ZIF and NHZIF. Figure 2 This is the XRD pattern of NHZIF.

[0031] Step 2, membrane preparation: hollow NHZIF and diethylenetriamine are blended to form an aqueous dispersion, wherein the concentration of hollow NHZIF is 0.05wt% and the concentration of diethylenetriamine is 0.15wt%. The hydrolyzed polyacrylonitrile ultrafiltration membrane is immersed in the aqueous dispersion for 10 minutes, and then immersed in 0.15wt% trimesoyl chloride in n-hexane to undergo interfacial polymerization reaction for 3 minutes, and heat-treated at 60°C for 10 minutes to obtain a thin film composite membrane based on hollow NHZIF, which is recorded as membrane 1.

[0032] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 3591 g m -2 h -1 , the separation factor is 1772; Figure 3 This is a surface scanning electron microscope image of membrane 1.

[0033] Example 2

[0034] The difference between this embodiment and embodiment 1 is that the concentration of NHZIF in step 2 is adjusted to 0.01 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 2.

[0035] Membrane 2 was used for pervaporation ethanol-water separation. When the operating temperature was 76 °C and the water content of the feed liquid was 10 wt%, the permeation flux was 3192 g m -2 h -1 , the separation factor is 617.

[0036] Example 3

[0037] The difference between this embodiment and embodiment 1 is that the concentration of NHZIF in step 2 is adjusted to 0.03 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 3.

[0038] Membrane 3 was used for pervaporation ethanol-water separation. When the operating temperature was 76 °C and the water content of the feed liquid was 10 wt%, the permeation flux was 3435 g m -2 h -1 , the separation factor is 891.

[0039] Example 4

[0040] The difference between this embodiment and embodiment 1 is that the concentration of NHZIF in step 2 is adjusted to 0.10 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 4.

[0041] Membrane 4 was used for pervaporation ethanol-water separation. When the operating temperature was 76 °C and the water content of the feed liquid was 10 wt%, the permeation flux was 2959 g m -2 h -1 , the separation factor is 642.

[0042] Example 5

[0043] The difference between this embodiment and embodiment 1 is that the concentration of NHZIF in step 2 is adjusted to 0.15 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 5.

[0044] Membrane 5 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 3237 g m -2 h -1 , the separation factor is 288.

[0045] Example 6

[0046] The difference between this embodiment and embodiment 1 is that the concentration of diethylenetriamine in step 2 is adjusted to 0.01 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 6.

[0047] Membrane 6 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 7691 g m -2 h -1 , the separation factor is 24.

[0048] Example 7

[0049] The difference between this embodiment and embodiment 1 is that the concentration of diethylenetriamine in step 2 is adjusted to 0.05 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 7.

[0050] Membrane 7 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 3704 g m -2 h -1 , the separation factor is 568.

[0051] Example 8

[0052] The difference between this embodiment and embodiment 1 is that the concentration of diethylenetriamine in step 2 is adjusted to 0.10 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 8.

[0053] Membrane 8 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 3305 g m -2 h -1 , the separation factor is 1111.

[0054] Example 9

[0055] The difference between this embodiment and embodiment 1 is that the concentration of diethylenetriamine in step 2 is adjusted to 0.20 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 9.

[0056] Membrane 9 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 4222 g m -2 h -1 , the separation factor is 163.

[0057] Example 10

[0058] The difference between this embodiment and embodiment 1 is that the concentration of diethylenetriamine in step 2 is adjusted to 0.30 wt %. The remaining steps and processes are the same as those in embodiment 1, and a hollow NHZIF thin film composite membrane is obtained, which is recorded as membrane 10.

[0059] Membrane 10 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 3714 g m -2 h -1 , the separation factor is 196.

[0060] Example 11

[0061] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 30°C and the water content of the feed liquid was 10 wt%, the permeation flux was 398 g m -2 h -1 , the separation factor is 1316.

[0062] Example 12

[0063] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 40°C and the water content of the feed liquid was 10 wt%, the permeation flux was 637 g m -2 h -1 , the separation factor is 1435.

[0064] Example 13

[0065] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 50°C and the water content of the feed liquid was 10 wt%, the permeation flux was 1061 g m -2 h -1 , the separation factor is 1530.

[0066] Example 14

[0067] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 60°C and the water content of the feed liquid was 10 wt%, the permeation flux was 1732 g m -2 h -1 , the separation factor is 1616.

[0068] Example 15

[0069] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 70°C and the water content of the feed liquid was 10 wt%, the permeation flux was 2456 g m -2 h -1 , the separation factor is 1760.

[0070] Example 16

[0071] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 76 °C and the water content of the feed liquid was 5 wt%, the permeation flux was 389 g m -2 h -1 , the separation factor is 1750.

[0072] Example 17

[0073] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 15 wt%, the permeation flux was 4465 g m -2 h -1 , the separation factor is 1325.

[0074] Example 18

[0075] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 20 wt%, the permeation flux was 7940 g m -2 h -1 , the separation factor is 1163.

[0076] Example 19

[0077] Membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 76 °C and the water content of the feed liquid was 30 wt%, the permeation flux was 8284 g m -2 h -1 , the separation factor is 890.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that NHZIF is no longer added in the adjustment step 2, and the remaining steps and processes are the same as those in Example 1, to obtain a blank thin film composite membrane of this comparative example, which is recorded as comparative membrane 1.

[0080] Comparative membrane 1 was used for pervaporation ethanol-water separation. When the operating temperature was 76°C and the water content of the feed liquid was 10 wt%, the permeation flux was 2720 g m -2 h -1 , the separation factor is 221. Figure 4 This is the surface scanning electron microscope image of comparative film 1;

[0081] Table 1

[0082]

[0083]

[0084] Table 2

[0085] membrane <![CDATA[Permeation flux (g m -2 h -1 )]]> Separation factor Film 1 (76°C) 3591 1772 Example 11 (30°C) 398 1316 Example 12 (40°C) 637 1435 Example 13 (50°C) 1061 1530 Example 14 (60°C) 1732 1616 Example 15 (70°C) 2456 1760

[0086] Table 3

[0087] membrane <![CDATA[Permeation flux (g m -2 h -1 )]]> Separation factor Film 1 (10 wt%) 3591 1772 Example 16 (5 wt%) 389 1750 Example 17 (15 wt%) 4465 1325 Example 18 (20 wt%) 7940 1163 Example 19 (30 wt%) 8284 890

[0088] From the results in Table 1, it can be seen that the permeation flux and separation factor of the thin film composite membrane based on hollow NHZIF are improved to varying degrees, and as the separation factor of the hollow NHZIF content first increases and then decreases, the permeation flux is higher than that of the blank thin film composite membrane. This is mainly due to the unique multi-level pore structure characteristics of the hollow NHZIF. The micropores of the surface shell can play a molecular sieving role, selectively and preferentially passing small-sized water molecules; the internal hollow structure can enhance the diffusion process of molecules and reduce the mass transfer resistance of water molecules. Changing the diethylenetriamine content can change the membrane separation performance. As the diethylenetriamine content increases, the separation factor first increases and then decreases, and the permeation flux decreases until it changes slightly. When the content of hollow NHZIF and diethylenetriamine is 0.05wt% and 0.15wt%, the separation performance of the membrane is optimal, and the membrane exhibits good separation stability during long-term operation ( Figure 5 ), indicating that covalently anchoring the hollow NHZIF stabilizes the membrane structure and prevents degradation of membrane performance due to loss of the hollow NHZIF during operation. Furthermore, the separation performance of the optimal membrane under different operating conditions was investigated (Tables 2 and 3). The proposed method for preparing hollow metal-organic framework-based thin-film composite membranes is simple and controllable, and has broad application prospects in the field of organic solvent dehydration, laying a good foundation for the application of thin-film composite membranes in pervaporation.

[0089] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many variations without departing from the purpose of the present invention, and these are all protected by the present invention.

[0090] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent replacement or modification made by a person skilled in the art according to the technical solution and concept of the present invention within the technical scope disclosed by the present invention shall be covered by the scope of protection of the present invention. It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other unless there is a conflict.

Claims

1. A method for preparing a thin film composite membrane based on a hollow metal-organic framework, characterized in that: The steps include: Step 1: Preparation of hollow NHZIF: 2-methylimidazole and zinc nitrate hexahydrate are dissolved in methanol, mixed and reacted for a period of time, and centrifuged to obtain a white powder. The white powder is dispersed in a tannic acid aqueous solution, reacted in the dark, and centrifuged to obtain a light yellow powder. The white powder is then dispersed in a buffer solution containing an amine monomer for reaction, and centrifuged to obtain a dark yellow powder after the reaction. Step 2: Membrane preparation: Hollow NHZIF is blended with amine monomer to form an aqueous dispersion, the supporting base membrane is immersed in the aqueous dispersion for a period of time, and then immersed in a polyacyl chloride organic solution to undergo interfacial polymerization reaction. After heat treatment, a thin film composite membrane based on hollow NHZIF is obtained.

2. The method for preparing a hollow metal-organic framework thin film composite membrane according to claim 1, characterized in that: The blending reaction time in step 1 is 2-6 hours; the tannic acid concentration is 2-10 mg / mL; and the light-proof reaction time is 10-60 minutes.

3. The method for preparing a hollow metal-organic framework thin film composite membrane according to claim 1, wherein: The buffer solution containing an amine monomer in step 1, wherein the amine monomer is one of ethylenediamine, m-phenylenediamine, diethylenetriamine and polyethyleneimine, and the concentration of the amine monomer is 2-10 mg / mL; the reaction time is 3-6 hours.

4. The method for preparing a hollow metal-organic framework thin film composite membrane according to claim 1, wherein: The amine monomer in step 2 is one of ethylenediamine, m-phenylenediamine, diethylenetriamine and polyethyleneimine; and the concentration of the amine monomer in the aqueous dispersion is 0-0.3 wt %.

5. The method for preparing a hollow metal-organic framework thin film composite membrane according to claim 1, characterized in that: The porous supporting base membrane described in step 2 is one of polyacrylonitrile ultrafiltration membrane, polyvinyl chloride membrane, polytetrafluoroethylene ultrafiltration membrane and polyethersulfone membrane.

6. The method for preparing a hollow metal-organic framework thin film composite membrane according to claim 1, wherein: The concentration of the hollow NHZIF in the aqueous dispersion in step 2 is 0.05-0.15 wt %.

7. The method for preparing a hollow metal-organic framework thin film composite membrane according to claim 1, characterized in that: The polyacyl chloride in step 2 is one of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride; the concentration of the polyacyl chloride is 0.1-0.2 wt%.

8. The method for preparing a hollow metal-organic framework thin film composite membrane according to claim 1, characterized in that: The immersion time of the aqueous dispersion in step 2 is 5-30 minutes, and the interfacial polymerization reaction time is 1-5 minutes; the heat treatment temperature is 60-80° C., and the heat treatment time is 5-20 minutes.

9. A hollow metal-organic framework thin film composite membrane prepared according to the preparation method according to any one of claims 1 to 8.

10. Application of the hollow metal-organic framework thin film composite membrane according to claim 9 in the field of pervaporation ethanol-water separation.

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