Preparation method and application of organic / cof composite nanofiber membrane based on polyacrylonitrile material

Abstract

The application relates to a preparation method and application of an organic / COF composite nanofiber membrane based on a polyacrylonitrile material, and belongs to the oil-water separation technical field, in particular to a preparation method and application of an organic / COF composite nanofiber membrane based on a polyacrylonitrile material. In the application, polyacrylonitrile is used as a supporting framework of COF, rigid COF nanoparticles are introduced into nanofibers and outside the fibers, and thus a polyacrylonitrile organic composite membrane is formed. In the oil-water separation process, the hydrophilic COF nanoparticles can endow the membrane with excellent hydrophilicity, play a demulsification role in the oil-water separation, and meanwhile, the rigid structure of the COF can accelerate the demulsification process, and the oil removal rate is high. The polyacrylonitrile base material is adopted, and the obtained membrane material has high strength; the organic / COF composite nanofiber membrane based on the polyacrylonitrile material prepared by the application has a hydrophilic structure, exhibits excellent stability, high permeability, low long-term operation permeability attenuation and a long cleaning cycle.

Description

Technical Field

[0001] This invention belongs to the field of oil-water separation technology, specifically relating to a method for preparing and applying an organic / COF composite nanofiber membrane based on polyacrylonitrile material. Background Technology

[0002] Membrane separation technology, as an emerging separation technology, has advantages over traditional oil-water separation methods such as gravity, centrifugation, and adsorption, including simple operation, high selectivity, and low energy consumption. Therefore, developing a novel, high-efficiency oil-water separation membrane material has become an urgent problem to be solved in the treatment of oil-water mixtures.

[0003] Covalent organic frameworks (COFs) are a class of novel porous crystalline materials with two-dimensional (2D) or three-dimensional (3D) structures and periodic units linked by covalent bonds. Compared with traditional polymers, COFs have advantages such as large specific surface area, ordered pore arrangement, uniform pore size, high pore density, and tunable pore size and structure, making them highly promising for constructing high-performance separation membranes. However, COFs also have several drawbacks, including difficulty in forming membranes independently, which limits their potential for further development in practical applications. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for preparing and applying an organic / COF composite nanofiber membrane based on polyacrylonitrile material; using polyacrylonitrile as a supporting framework, COF is loaded on the framework, and the COF nanofiber membrane prepared by this invention is used in an oil-water separation process, with a high oil removal rate.

[0005] The organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared by this invention has COF nanoparticles loaded inside and on the surface of the nanofibers.

[0006] A method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material is carried out according to the following steps:

[0007] I. Preparation of polyacrylonitrile / multi-amino monomer nanofiber membranes:

[0008] Polyacrylonitrile and polyamino COF monomers were dissolved in a nitrogen-containing organic solvent to obtain a casting solution containing polyacrylonitrile and polyamino COF monomers; the casting solution containing polyacrylonitrile and polyamino COF monomers was electrospun to obtain a polyacrylonitrile / polyamino monomer nanofiber membrane.

[0009] II. Preparation of acidic mixed solutions of multi-functional aldehyde COF monomers:

[0010] The multi-aldehyde COF monomer was dissolved in an acidic mixed solution to obtain an acidic mixed solution of the multi-aldehyde COF monomer.

[0011] III. Hydrothermal reaction:

[0012] The polyacrylonitrile / multi-amino monomer nanofiber membrane was immersed in an acidic mixed solution of multi-aldehyde COF monomers, and then transferred to a tetrafluoroethylene hydrothermal reactor for hydrothermal reaction. After washing and drying, an organic / COF composite nanofiber membrane based on polyacrylonitrile material was obtained.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] I. After preparing a polyacrylonitrile nanofiber membrane, COF nanoparticles are grown in situ on the surface and inside of the polyacrylonitrile nanofiber membrane. During the oil-water separation process, the hydrophilic properties and rigid structure of COF can play a role in demulsification, thereby increasing the water removal rate.

[0015] Furthermore, this invention prepares a polyacrylonitrile nanofiber membrane containing multiple amino monomers through electrospinning, and prepares a polyacrylonitrile / COF composite nanofiber membrane through a hydrothermal synthesis reaction. This membrane has a rich pore structure with pore sizes ranging from 0.1 to 2.0 μm. Using polyacrylonitrile as a substrate, the resulting organic / COF composite nanofiber membrane based on polyacrylonitrile material exhibits excellent strength properties. The organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared by this invention is hydrophilic, exhibits excellent stability, high permeability, low permeability decay over long-term operation, and a long cleaning cycle.

[0016] Data from the examples show that the organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared in this invention has a permeability of greater than 35,000 L·m⁻¹ to various oil-in-water emulsions. -2 ·h -1 ·bar -1 The flux reduction rate of the n-octane-in-water emulsion was less than 8% after 5 hours, the flux recovery rate was more than 95%, the irreversible fouling rate was less than 3%, the flux reduction rate after 30 days was less than 10%, the cleaning cycle was more than 7 days, and the strength was more than 25 MPa. It has application potential in the treatment of oily wastewater. Attached Figure Description

[0017] Figure 1 The figures show the microstructure of the fiber membranes. In the figures, (a) and (b) are polyacrylonitrile nanofiber membranes, and (c) and (d) are organic / COF composite nanofiber membranes based on polyacrylonitrile materials prepared in Example 1.

[0018] Figure 2Infrared spectra of polyacrylonitrile and the organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared in Example 1. Detailed Implementation

[0019] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0020] Specific Implementation Method 1: This implementation method describes a method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material, which is completed according to the following steps:

[0021] I. Preparation of polyacrylonitrile / multi-amino monomer nanofiber membranes:

[0022] Polyacrylonitrile and polyamino COF monomers were dissolved in a nitrogen-containing organic solvent to obtain a casting solution containing polyacrylonitrile and polyamino COF monomers; the casting solution containing polyacrylonitrile and polyamino COF monomers was electrospun to obtain a polyacrylonitrile / polyamino monomer nanofiber membrane.

[0023] II. Preparation of acidic mixed solutions of multi-functional aldehyde COF monomers:

[0024] The multi-aldehyde COF monomer was dissolved in an acidic mixed solution to obtain an acidic mixed solution of the multi-aldehyde COF monomer.

[0025] III. Hydrothermal reaction:

[0026] The polyacrylonitrile / multi-amino monomer nanofiber membrane was immersed in an acidic mixed solution of multi-aldehyde COF monomers, and then transferred to a tetrafluoroethylene hydrothermal reactor for hydrothermal reaction. After washing and drying, an organic / COF composite nanofiber membrane based on polyacrylonitrile material was obtained.

[0027] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the mass fraction of polyacrylonitrile in the casting solution containing polyacrylonitrile and polyamino COF monomers in step one is 5% to 25%; more preferably 10% to 20%; and the mass fraction of polyamino COF monomers in the casting solution containing polyacrylonitrile and polyamino COF monomers in step one is 5% to 25%. Other steps are the same as in Specific Implementation Method One.

[0028] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the mass ratio of polyacrylonitrile to polyaminoCOF monomer in the casting solution containing polyacrylonitrile and polyaminoCOF monomer in step 1 is (0.1-10):1, more preferably (0.4-6):1. Other steps are the same as in Specific Implementation Method 1 or 2.

[0029] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the sum of the mass fractions of polyacrylonitrile and polyamino COF monomers in the casting solution containing polyacrylonitrile and polyamino COF monomers in step one is 10% to 40%, more preferably 15% to 25%. The other steps are the same as in Specific Implementation Methods One to Three.

[0030] Specific Embodiment Five: This embodiment differs from Specific Embodiments One to Four in that: the polyamino COF monomer mentioned in step one is one or a mixture of several of p-phenylenediamine, hexaaminobenzene, and diaminoanthracene; the nitrogen-containing organic solvent mentioned in step one is one or a mixture of several of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and N-methylpyrrolidone (NMP). The other steps are the same as in Specific Embodiments One to Four.

[0031] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the electrospinning conditions described in step one include: a voltage of 10kV to 30kV, more preferably 12 to 25kV; an injection rate of 0.0001mm / s to 0.01mm / s, more preferably 0.0002mm / s; and a roller speed of 100r / min to 500r / min, more preferably 150r / min to 400r / min. The other steps are the same as in Specific Implementation Methods One to Five.

[0032] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the polyaldehyde COF monomer mentioned in step two is one or more of trialdehyde-based phloroglucinol, pyromellitic phloroglucinol, pyromellitic tricarboxaldehyde, and 2,5-dichloroterephthalaldehyde. The other steps are the same as in Specific Implementation Methods One to Six.

[0033] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the acidic mixture in step two is composed of dichloromethane and acetic acid, with the mass fraction of acetic acid being 1% to 5%; the mass ratio of the polyaldehyde COF monomer and acetic acid in step two is 1:(10 to 15), preferably 1:10. Other steps are the same as in Specific Implementation Methods One to Seven.

[0034] Specific Embodiment Nine: This embodiment differs from Specific Embodiments One to Eight in that: the hydrothermal reaction temperature in step three is 80℃~150℃, and the hydrothermal reaction time is 18h~30h; the thickness of the organic / COF composite nanofiber membrane based on polyacrylonitrile material in step three is 20μm~200μm, more preferably 150μm. Other steps are the same as in Specific Embodiments One to Eight.

[0035] Specific Implementation Method 10: This implementation method is based on the application of organic / COF composite nanofiber membranes made of polyacrylonitrile material in oil-water separation.

[0036] In this embodiment, the oil-water mixture preferably includes toluene / water, n-octane / water, or soybean oil / water, and the oil-water mixture is preferably an oil-in-water emulsion.

[0037] The beneficial effects of the present invention are verified using the following embodiments:

[0038] Example 1: A method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material, which is carried out according to the following steps:

[0039] I. Preparation of polyacrylonitrile / multi-amino monomer nanofiber membranes:

[0040] Polyacrylonitrile and p-phenylenediamine were dissolved in DMF to obtain PAN / Pa casting solution; the PAN / Pa casting solution was electrospun to obtain PAN / Pa nanofiber base film.

[0041] The mass fraction of polyacrylonitrile in the PAN / Pa casting solution mentioned in step one is 12%, and the mass ratio of polyacrylonitrile to p-phenylenediamine is 2:1.

[0042] The conditions for electrospinning described in step one include: a voltage of 20 kV, an injection rate of 0.0002 mm / s, a roller speed of 210 r / min, and a coaxial electrospinning time of 10 h.

[0043] II. Preparation of acidic mixed solutions of multi-functional aldehyde COF monomers:

[0044] Trialdehyde phloroglucinol and acetic acid were dissolved in dichloromethane to obtain an acidic mixed solution of polyaldehyde COF monomers;

[0045] The mass ratio of trialdehyde phloroglucinol to acetic acid in step two is 1:10;

[0046] The sum of the mass fractions of trialdehyde phloroglucinol and acetic acid in the acidic mixed solution of the polyaldehyde COF monomers described in step two is 3%.

[0047] III. Hydrothermal reaction:

[0048] The PAN / Pa nanofiber substrate membrane was immersed in an acidic mixed solution of multi-functional aldehyde COF monomers, and then transferred to a tetrafluoroethylene hydrothermal reactor for hydrothermal reaction. After washing and drying, an organic / COF composite nanofiber membrane (PAN / COF) based on polyacrylonitrile material was obtained.

[0049] The hydrothermal reaction in step three is carried out at a temperature of 120°C for 20 hours.

[0050] The organic / COF composite nanofiber membrane based on polyacrylonitrile material described in step three has a thickness of 150 μm and a pore size of 0.5 μm.

[0051] Figure 1 The image shows the microstructure of the organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared in Example 1.

[0052] from Figure 1 It can be seen that the COF nanofiber membrane is composed of nanoparticles and nanofibers, with obvious micro-nano structure, which endows the separation membrane with excellent separation performance.

[0053] Example 2: This example differs from Example 1 in that the mass fraction of polyacrylonitrile in the PAN / Pa casting solution in step one is 20%, and the mass ratio of polyacrylonitrile to p-phenylenediamine is 3:1. All other steps and parameters are the same as in Example 1.

[0054] Example 3: This example differs from Example 1 in that the trialdehyde phloroglucinol in step two is replaced with trimesodium pyromellitic acid, and the mass ratio of trimesodium pyromellitic acid to acetic acid is 1:15; the sum of the mass fractions of trimesodium pyromellitic acid and acetic acid in the acidic mixed solution of the polyaldehyde COF monomers in step two is 5%. All other steps and parameters are the same as in Example 1.

[0055] Comparative Example 1:

[0056] Commercially available polyethersulfone hydrophilic filter membranes with an average pore size of 0.22 μm were used.

[0057] Comparative Example 2:

[0058] The difference between Comparative Example 2 and Example 1 is that p-phenylenediamine is not added in step one. All other steps and parameters are the same as in Example 1.

[0059] Comparative Example 3:

[0060] The difference between Comparative Example 3 and Example 1 is that a hydrothermal reaction is not performed in step three. All other steps and parameters are the same as in Example 1.

[0061] Comparative Example 4:

[0062] The difference between Comparative Example 4 and Example 1 is that polyacrylonitrile in step one is replaced with polyethersulfone. All other steps and parameters are the same as in Example 1.

[0063] The membranes of Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, with the volume ratios of soybean oil / water and n-hexane / water both being 99:1. The results are shown in Table 1.

[0064] Table 1. Performance data of the membranes in Examples 1-3 and Comparative Examples 1-4.

[0065]

[0066]

[0067] As can be seen from Table 1, the organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared in the embodiments of the present invention has excellent oil-water separation performance. The soybean oil / water flux is more than 200 times that of commercial polyethersulfone superhydrophilic filter membrane, and the dehydration rate is high. However, when polyacrylonitrile is replaced with polyethersulfone material, due to the characteristics of polyethersulfone itself, it dissolves in the solvent in the hydrothermal synthesis and cannot produce a complete membrane.

[0068] The organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared in this embodiment of the invention exhibits a permeability greater than 35000 L·m⁻¹ to various oil-in-water emulsions. -2 ·h -1 ·bar -1 The flux reduction rate of the n-octane-in-water emulsion was less than 8% after 5 hours, the flux recovery rate was more than 95%, the irreversible fouling rate was less than 3%, the flux reduction rate after 30 days was less than 10%, the cleaning cycle was more than 7 days, and the strength was more than 25 MPa. It has application potential in oil refining.

Claims

1. A method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material, characterized in that... The preparation method is completed according to the following steps: I. Preparation of polyacrylonitrile / multi-amino monomer nanofiber membranes: Polyacrylonitrile and polyamino COF monomers were dissolved in a nitrogen-containing organic solvent to obtain a casting solution containing polyacrylonitrile and polyamino COF monomers; the casting solution containing polyacrylonitrile and polyamino COF monomers was electrospun to obtain a polyacrylonitrile / polyamino monomer nanofiber membrane. The mass fraction of polyacrylonitrile in the casting solution containing polyacrylonitrile and polyamino COF monomers mentioned in step one is 5%~25%; The mass fraction of the polyacrylonitrile and polyamino COF monomer in the casting solution mentioned in step one is 5%~25%; The polyamino COF monomer mentioned in step one is one or a mixture of several of p-phenylenediamine, hexaaminobenzene and diaminoanthracene; the nitrogen-containing organic solvent mentioned in step one is one or a mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone. II. Preparation of acidic mixed solutions of multi-functional aldehyde COF monomers: The multi-aldehyde COF monomer was dissolved in an acidic mixed solution to obtain an acidic mixed solution of the multi-aldehyde COF monomer. The polyaldehyde COF monomer mentioned in step two is one or more of the following: trialdehyde phloroglucinol, pyromellitic phloroglucinol, pyromellitic tricarboxaldehyde, and 2,5-dichloroterephthalaldehyde; III. Hydrothermal reaction: The polyacrylonitrile / multi-amino monomer nanofiber membrane was immersed in an acidic mixed solution of multi-aldehyde COF monomers, and then transferred to a tetrafluoroethylene hydrothermal reactor for hydrothermal reaction. After washing and drying, an organic / COF composite nanofiber membrane based on polyacrylonitrile material was obtained.

2. The method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material according to claim 1, characterized in that... In step one, the mass ratio of polyacrylonitrile to polyaminoCOF monomer in the casting solution containing polyacrylonitrile and polyaminoCOF monomer is (0.1~10):

1.

3. The method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material according to claim 1, characterized in that... The sum of the mass fractions of polyacrylonitrile and polyamino COF monomers in the casting solution containing polyacrylonitrile and polyamino COF monomers mentioned in step one is 10%~40%.

4. The method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material according to claim 1, characterized in that... The electrospinning conditions described in step one include: voltage of 10kV~30kV, injection rate of 0.0001mm / s~0.01mm / s, and roller speed of 100r / min~500r / min.

5. The method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material according to claim 1, characterized in that... The acidic mixture mentioned in step two is composed of dichloromethane and acetic acid, with the mass fraction of acetic acid being 1% to 5%; the mass ratio of the polyaldehyde COF monomer and acetic acid mentioned in step two is 1:(10 to 15).

6. The method for preparing an organic / COF composite nanofiber membrane based on polyacrylonitrile material according to claim 1, characterized in that... The hydrothermal reaction temperature in step three is 80℃~150℃, and the hydrothermal reaction time is 18h~30h; the thickness of the organic / COF composite nanofiber membrane based on polyacrylonitrile material in step three is 20μm~200μm.

7. The application of the organic / COF composite nanofiber membrane based on polyacrylonitrile material prepared by the preparation method according to any one of claims 1 to 6, characterized in that... Application of organic / COF composite nanofiber membranes based on polyacrylonitrile materials in oil-water separation.

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