Preparation method of solid-liquid interface polymerization for constructing strong interlayer bonding nanofiltration membrane, product and application thereof

Abstract

The application belongs to the technical field of nanofiltration membranes, and particularly relates to a preparation method of a solid-liquid interface polymerization constructed strong interlayer combined nanofiltration membrane and products and applications thereof. The application improves the mechanical properties of the crystalline porous material composite nanofiltration membrane, and has better operation stability and service life. Compared with the crystalline porous material composite membrane reported in the current research, the crystalline porous material-base membrane combination is better. Meanwhile, the COF layer can be uniformly grown without agglomeration. The application simplifies the preparation process of the interface polymerization method, uses less organic solvent, has simpler reaction conditions, consumes less energy, makes the COF membrane have the possibility of industrialization, the COF layer and the base film are better combined without obvious interface, and the defects are reduced through the staggered and ordered arrangement of the one-dimensional COF material. The pore size tends to the ideal pore size of periodic directional arrangement. The rejection performance that cannot be achieved by conventional synthesis of COF membranes is achieved.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane technology, specifically relating to a method for preparing a strong interlayer bonded nanofiltration membrane by solid-liquid interface polymerization, as well as its products and applications. Background Technology

[0002] Membrane separation technology, as an emerging technology, has broad application prospects in fields such as air and water pollution control, carbon capture, resource extraction, and seawater desalination due to its characteristics of low energy consumption, low pollution, small carbon footprint, and ease of production. Crystalline porous materials, with their porous structure and uniform pore size resulting from ordered arrangement, are gradually gaining attention in the field of separation membranes. Crystalline porous materials refer to materials with ordered crystal structures and internal pore networks formed by connecting organic molecular units through coordination bonds, covalent bonds, or van der Waals forces. Among them, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are widely used in membrane separation. MOFs are mainly composed of inorganic metal centers and bridging organic ligands that self-assemble and link together. They possess abundant functional sites, good porosity, and chemical stability, making them an emerging building block for separation membranes. With the development of MOFs, more and more different MOFs are being used to prepare MOF membranes, such as ZIF-8, UiO-66, and MIL-101. However, MOF membranes currently suffer from problems such as insufficient mechanical strength in powder form and poor adhesion to commonly used polymer-based membranes through coating or in-situ growth methods. Covalent organic framework materials, on the other hand, form a periodic framework structure through reversible covalent bonds, resulting in ordered arrangement, uniform pore size, and high specific surface area. Furthermore, the size, symmetry, and connectivity of the joints determine the geometry of the resulting framework. This allows for a wide range of adjustments to the membrane pore size to separate guest molecules with different van der Waals volumes. Stable covalent bonds enable COF membranes to be used in various extreme environments. In increasingly in-depth research on COF membranes, different monomers have been used in their synthesis, from the self-condensation of easily hydrolyzable borate esters to the formation of more stable imine links between aldehydes and amines. However, the difficult processing of COFs, long preparation times, and complex reaction conditions limit their industrialization and large-scale production. The weak mechanical strength of self-standing COF membranes, the adhesion between COFs and substrates, and defects during COF growth hinder the application of COF membranes.

[0003] Currently, the main methods for preparing crystalline porous material membranes are as follows: 1. Powder forming; 2. Nanosheet stacking; 3. In-situ growth; 4. Interfacial polymerization.

[0004] 1. Powder molding:

[0005] Powder molding was the first proposed preparation method. MOFs / COFs powders are directly added to an organic solvent along with a polymer to obtain a homogeneous stock solution. The solution is then poured onto a glass plate or nonwoven fabric to form a thin film of a certain thickness, followed by immersion in water to form the final film. This method can easily form flexible MOF / COF films, is simple to prepare, and has promising industrial application prospects. However, MOFs powders have poor adhesion to commonly used polymer-based films, often leading to defects. While COFs powders exhibit better adhesion to polymer substrates, the imperfect adhesion between COF crystals and the polymer substrate affects the precise control of pore size. Furthermore, powder-doped films lose their ideal continuous periodic framework structure, failing to form uniform pore sizes and resulting in separation defects.

[0006] 2. Nanosheet stacking:

[0007] Due to the limited crystallinity of powder molding, nanosheet stacking is used to create highly crystalline MOF / COF nanosheets to address membrane defects. Methods such as vacuum filtration, spin coating, or drop casting of MOF / COF nanosheets onto a substrate are used to coat or filter the synthesized MOF / COF nanosheets onto the substrate surface. There are also methods that press COF powder or nanosheets into membranes. However, MOF / COF composite membranes prepared by these methods suffer from bonding problems between the nanosheets and the substrate, making them prone to detachment. While increased crystallinity of COF nanosheets facilitates the utilization of one-dimensional nanochannels within the COF structure, and MOF nanosheet stacking significantly improves separation performance, membranes developed using MOF / COF nanosheets are inevitably discontinuous. The sheets adhere through van der Waals forces, resulting in low bonding strength with the supporting substrate, leading to crack defects and wafer detachment. Furthermore, nanosheet stacking disrupts the stable pore size exhibited by the continuous arrangement of MOF / COF materials, and uncontrolled inter-sheet defects often result in selective defects.

[0008] 3. In-situ growth:

[0009] In-situ growth involves directly immersing the substrate in a growth solution containing MOF metal ions and a binder (or COF reaction solution); or, using a casting-coating method, coating the substrate surface with the growth solution to prepare a separation membrane. This method effectively controls the thickness and structure of the MOF / COF membrane, resulting in small defects and good adhesion. Furthermore, continuous in-situ growth minimizes intercrystalline defects in the MOF / COF. However, the direct polymerization in in-situ growth is uncontrollable, leading to polycrystalline and disordered membranes. This method is still unsuitable for synthesizing ideal continuous periodic framework structures. It also has a long reaction time, requires large amounts of solvent, and easily generates byproducts. Additionally, it imposes limitations on the reactants (e.g., some in-situ grown COF membranes require salt monomers).

[0010] 4. Interface aggregation:

[0011] Interfacial polymerization involves dissolving the metal ions of MOFs and the linker (two monomers of COFs) separately in two incompatible solvents for synthesis. Although some pioneering studies have explored IP synthesis methods for MOF membranes, these studies have mostly focused on MOF membranes based on single metal ions or low-nucleus clusters with simple structures, low activation energies, and ease of fabrication. In contrast, the preparation of high-valence cluster-based MOF membranes using kinetically driven IP technology, which requires high activation energies, is challenging in terms of both crystallinity and continuity. Currently, the main approach is to encapsulate MOFs within polymers using interfacial polymerization to improve the flux and stability of composite membranes. Interfacial polymerization is particularly suitable for preparing thin, continuous COF-based membranes. This method is also the mainstream preparation method for COF membranes. Interfacial polymerization is inherently more controllable than the methods mentioned above. By changing the diffusion rate of monomers, it can alter the membrane thickness, domain orientation, and reaction rate, thereby controlling the membrane morphology and forming continuous membrane layers with fewer defects. While interfacial polymerization holds promise for large-scale fabrication of COF membranes, the resulting COF membranes are typically polycrystalline, hundreds of nanometers thick, and have limited crystallinity. Without specifically controlling the crystal growth orientation, films synthesized via interfacial polymerization do not exhibit oriented one-dimensional nanochannels. Interfacial polymerization can prepare self-standing COF films, or COF can be formed on the substrate surface through gas-liquid interfacial polymerization and infiltration. However, the COF layer in gas-liquid interfacial polymerization only grows on the substrate surface, resulting in poor adhesion between the COF layer and the substrate. Solid-gas interfacial polymerization suffers from stringent reaction conditions and a narrow range of applicable substrates, leading to the inability to continuously grow the COF periodic framework, resulting in high industrialization difficulty and COF layer defects. Current research on solid-liquid interfacial polymerization often involves grafting relevant monomers onto dense inorganic substrates to grow crystalline porous materials, but this also has problems such as stringent reaction conditions (high temperature, high pressure) and substrate limitations (dense inorganic substrates), and the resulting films have poor toughness. Interfacial polymerization and infiltration methods also suffer from problems such as uneven COF layer growth, detachment, and poor adhesion to the substrate due to the difficulty in controlling the diffusion rate of the two monomers in two different solvents. Summary of the Invention

[0012] The English abbreviations and their corresponding full Chinese names involved in this invention are as follows:

[0013] PES: Polyethersulfone

[0014] PVP: Polyvinylpyrrolidone

[0015] DMF: N,N-dimethylformamide

[0016] TP: 2,4,6-Tricarboxyloylphloroglucinol

[0017] TAPA: Tris(4-aminophenyl)amine

[0018] PEI: Polyethyleneimine

[0019] TOC: Total Organic Carbon

[0020] PEG: Polyethylene Glycol

[0021] SEM: Scanning Electron Microscopy

[0022] EDS: Energy Dispersive X-ray Spectroscopy

[0023] XRD: X-ray diffraction

[0024] XPS: X-ray photoelectron spectroscopy.

[0025] As one aspect of the present invention, the present invention provides a method for preparing a nanofiltration membrane with strong interlayer bonding by solid-liquid interfacial polymerization, which includes the following steps:

[0026] (1) Preparation of polymer base film containing first monomer: The first monomer, pore-forming agent and film-forming polymer are added to a solvent to obtain a casting solution. After forming a base film layer by scraping or spinning, the film is placed in a coagulation bath to stand and form a film; wherein, the first monomer includes 2,4,6-tricarboxymethyl phloroglucinol;

[0027] (2) Preparation of reaction solution containing the second monomer: Dissolve the second monomer in its solvent to obtain the reaction solution; wherein the second monomer is tris(4-aminophenyl)amine;

[0028] (3) Interfacial polymerization reaction: The polymer base membrane containing the first monomer obtained in step (1) is immersed in the reaction solution prepared in step (2), so that the first monomer diffuses from the inside of the base membrane to the outside of the membrane and undergoes a polymerization reaction with the second monomer in the reaction solution inside and on the surface of the base membrane to generate a crystalline porous material separation layer, thereby obtaining the nanofiltration membrane.

[0029] As a preferred embodiment of the method for preparing a strong interlayer bonded nanofiltration membrane by solid-liquid interface polymerization according to the present invention: in step (1), the film-forming polymer includes one of polyethersulfone, polysulfone, polyvinylidene fluoride or polyacrylonitrile, and cellulose diacetate; the pore-forming agent is polyvinylpyrrolidone; and the solvent is N,N-dimethylformamide.

[0030] As a preferred embodiment of the method for preparing a strong interlayer bond nanofiltration membrane by solid-liquid interface polymerization according to the present invention: in step (1), the mass fraction of the first monomer in the casting solution is 0.5~2%; the mass fraction of the film-forming polymer in the casting solution is 15-25%; and the mass fraction of the pore-forming agent in the casting solution is 3~10%.

[0031] As a preferred embodiment of the method for preparing a strong interlayer bond nanofiltration membrane by solid-liquid interface polymerization according to the present invention: in step (2), the solvent is water, ethanol or a mixture of water and ethanol.

[0032] As a preferred embodiment of the method for preparing a strong interlayer bond nanofiltration membrane by solid-liquid interface polymerization according to the present invention: in step (2), a polymer additive is added to the reaction solution, and the polymer additive is polyethyleneimine.

[0033] As a preferred embodiment of the method for preparing a strong interlayer bond nanofiltration membrane by solid-liquid interface polymerization according to the present invention: in step (2), the concentration of the second monomer in the reaction solution is 0.5~1 mmol / L; the mass concentration of the polymer additive in the reaction solution is 5~20 g / L.

[0034] As a preferred embodiment of the method for preparing a strong interlayer bonded nanofiltration membrane by solid-liquid interface polymerization according to the present invention: in step (2), the reaction solution further contains a catalyst, the catalyst being acetic acid, and the concentration of the acetic acid being 2~5 vol.

[0035] As a preferred embodiment of the method for preparing a strong interlayer bond nanofiltration membrane by solid-liquid interfacial polymerization according to the present invention: in step (3), the interfacial polymerization reaction is carried out at 20~30℃ for 24~72 hours. After the reaction is completed, the obtained membrane is cured under the following conditions: 50~70℃ and -0.6~-1.0 MPa for 10~20 minutes.

[0036] The present invention also provides a nanofiltration membrane prepared by the method of constructing a strong interlayer bond nanofiltration membrane by solid-liquid interface polymerization, which includes a polymer porous support layer and a crystalline porous material separation layer grown in situ inside and on the surface of the support layer; the separation layer and the support layer are tightly bonded, and the separation layer is mainly composed of a covalent organic framework material and polyethyleneimine, wherein the covalent organic framework material is formed by polymerization of 2,4,6-tricarboxymethyl phloroglucinol and tris(4-aminophenyl)amine.

[0037] This invention also provides the application of the nanofiltration membrane in the treatment of wastewater containing monovalent or polyvalent ions, seawater desalination pretreatment, or dye wastewater decolorization, wherein the monovalent or polyvalent ions include La. 3+ 、Sr 2+ Mg 2+ Ca 2+ Cs + Li + One or more of them.

[0038] The beneficial effects of this invention are as follows: This invention improves the mechanical properties of crystalline porous material composite nanofiltration membranes, resulting in better operational stability and service life. Compared to currently reported crystalline porous material composite membranes, it exhibits better bonding between the crystalline porous material and the base membrane. Simultaneously, it can grow a uniform, non-agglomerated COF layer. This invention simplifies the preparation process of interfacial polymerization, uses less organic solvent, has simpler reaction conditions, and consumes less energy, making COF membranes industrially feasible. The COF layer of this invention has better bonding with the base membrane and no obvious interface; the staggered and ordered arrangement of one-dimensional COF materials reduces defect formation. The pore size tends towards an ideal periodic directional arrangement. It achieves retention performance that conventionally synthesized COF membranes cannot reach. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein:

[0040] Figure 1 The surface SEM image of the nanofiltration membrane prepared for Comparative Example 1.

[0041] Figure 2 The image shows a cross-sectional SEM image of the nanofiltration membrane prepared for Comparative Example 1.

[0042] Figure 3 The image shows a surface SEM image of the nanofiltration membrane prepared in Example 1.

[0043] Figure 4 The image shows a cross-sectional SEM image of the nanofiltration membrane prepared in Example 1.

[0044] Figure 5 The image shows the cross-sectional EDS diagram of the nanofiltration membrane prepared in Example 1, where a is the EDS diagram of sulfur and b is the EDS diagram of nitrogen.

[0045] Figure 6 The infrared spectrum of the nanofiltration membrane prepared for Comparative Example 1.

[0046] Figure 7 The image shows the XRD pattern of the nanofiltration membrane prepared in Comparative Example 1.

[0047] Figure 8 The infrared spectrum of the nanofiltration membrane prepared in Example 1 is shown.

[0048] Figure 9 XPS image of the nanofiltration membrane prepared in Example 1.

[0049] Figure 10The images show a comparison of the acid resistance of a commercial nanofiltration membrane and the nanofiltration membrane prepared in Example 1. In the images, a is a SEM image of the surface of the commercial nanofiltration membrane before acid leaching, b is a SEM image of the surface of the commercial nanofiltration membrane after acid leaching, c is a SEM image of the surface of the nanofiltration membrane prepared in Example 1 before acid leaching, and d is a SEM image of the surface of the nanofiltration membrane prepared in Example 1 after acid leaching.

[0050] Figure 11 This is to demonstrate the long-term operational stability of Example 1. Detailed Implementation

[0051] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0052] Experimental materials: 2,4,6-tricarboxymethyl phloroglucinol (TP, 98%) was purchased from Shanghai Dipo Chemical Technology Co., Ltd., polyvinylpyrrolidone (PVP, MW: 45000-58000, K30), N,N-dimethylformamide, polyethersulfone (PES, MW: 60000), anhydrous ethanol (99.5%) and acetic acid (99%) were purchased from Shanghai Titan Technology Co., Ltd., and polyethyleneimine (PEI, Mw=10000, 99%) was purchased from Shanghai McLean Technology Co., Ltd.

[0053] Comparative Example 1:

[0054] (1) Preparation of TAPA@PES base film: First, 0.5 g of TAPA monomer was dissolved in 37.8 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TAPA was 1%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Subsequently, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath. A 1% TAPA@PES base film was obtained and stored in deionized water.

[0055] (2) Preparation of TP reaction solution: Dissolve 20.7 mg (0.1 mmol) of TP in 300 mL of ethanol, add 150 μL of acetic acid, sonicate for 30 minutes to prepare TP ethanol solution.

[0056] (3) Preparation of TAPA-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TAPA@PES base membrane was cut and immersed in TP ethanol solution. The reaction was carried out at 50 °C for 72 h. Then it was cured at 70 °C for 10 min at -0.8 MPa and washed with ethanol. The thickness of the obtained TAPA-TP@PES composite nanofiltration membrane was 121 μm.

[0057] Example 1:

[0058] (1) Preparation of TP@PES base film: First, 0.5 g of TP monomer was dissolved in 37.8 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TP was 1%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 1% TP@PES base film, which was stored in deionized water.

[0059] (2) Preparation of TAPA / PEI reaction solution: Dissolve 0.1 mmol of TAPA and 1 g of PEI in a mixed solution of 100 mL of deionized water and 50 mL of ethanol, add 5 mL of acetic acid, and sonicate for 30 minutes to prepare TAPA / PEI ethanol-water solution.

[0060] (3) Preparation of TAPA-PEI-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TP@PES base membrane was cut and immersed in TAPA / PEI ethanol-water solution. The reaction was continued at room temperature (20 ℃) ​​for 72 h. Then it was cured at -0.8 MPa and 70 ℃ for 10 min. After washing with ethanol, the thickness of the obtained TAPA-PEI-TP@PES composite nanofiltration membrane was 148 μm.

[0061] Example 2:

[0062] (1) Preparation of TP@PES base film: First, 0.25 g of TP monomer was dissolved in 40.25 g of DMF to prepare a premix solution. Then, 1.5 g of PVP and 8 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TP was 0.5%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 0.5% TP@PES base film, which was stored in deionized water.

[0063] (2) Preparation of TAPA / PEI reaction solution: Dissolve 0.1 mmol of TAPA and 0.75 g of PEI in a mixed solution of 100 mL of deionized water and 50 mL of ethanol, add 3 mL of acetic acid, and sonicate for 30 minutes to prepare TAPA / PEI ethanol-water solution.

[0064] (3) Preparation of TAPA-PEI-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TP@PES base membrane was cut and immersed in TAPA / PEI ethanol-water solution. The reaction was continued at room temperature (20 ℃) ​​for 48 h, and then cured at -0.8 MPa and 60 ℃ for 10 min. After washing with ethanol, the thickness of the obtained TAPA-PEI-TP@PES composite nanofiltration membrane was 111 μm.

[0065] Example 3:

[0066] (1) Preparation of TP@PES base film: First, 1 g of TP monomer was dissolved in 32.5 g of DMF to prepare a premixing solution. Then, 5 g of PVP and 11.5 g of PES were dissolved in the premixing solution to prepare a 50 g mixture, in which the mass fraction of TP was 2%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 2% TP@PES base film, which was stored in deionized water.

[0067] (2) Preparation of TAPA / PEI reaction solution: Dissolve 0.1 mmol of TAPA and 3 g of PEI in a mixed solution of 100 mL of deionized water and 50 mL of ethanol, add 7 mL of acetic acid, and sonicate for 30 minutes to prepare TAPA / PEI ethanol-water solution.

[0068] (3) Preparation of TAPA-PEI-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TP@PES base membrane was cut and immersed in TAPA / PEI ethanol-water solution. The reaction was continued at room temperature (20 ℃) ​​for 72 h. Then it was cured at -0.8 MPa and 70 ℃ for 20 min. After washing with ethanol, the thickness of the obtained TAPA-PEI-TP@PES composite nanofiltration membrane was 153 μm.

[0069] Comparative Example 2:

[0070] (1) Preparation of TAP@PES base film: First, 0.2 g of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAP) monomer was dissolved in 38.1 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TAP was 0.4%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 0.4% TAP@PES base film, which was stored in deionized water.

[0071] (2) Preparation of HBAB reaction solution: Dissolve 0.1 mmol of HBAB monomer synthesized using 2-hydroxy-1,3,5-benzenetriformaldehyde (HB) and 2-bromoethyltrimethylammonium bromide (AB) in 150 mL of deionized water, add 5 mL of acetic acid, and sonicate for 30 minutes to prepare HBAB reaction solution.

[0072] (3) Preparation of TAP-HBAB@PES composite nanofiltration membrane: A 6 cm × 12 cm TAP@PES base membrane was cut and immersed in HBAB reaction solution. The reaction was carried out at room temperature (20 ℃) ​​for 72 h. Then it was cured at 70 ℃ for 10 min at -0.8 MPa and washed with ethanol to obtain the TAP-HBAB@PES composite nanofiltration membrane.

[0073] Because 2,4,6-tris(4-aminophenyl)−1,3,5-triazine cannot diffuse in the reaction solution, the grown COF layer has excessive defects and cannot achieve the ideal retention performance.

[0074] Comparative Example 3:

[0075] (1) Preparation of TP@PES base film: First, 0.5 g of TP monomer was dissolved in 37.8 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TP was 1%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 1% TP@PES base film, which was stored in deionized water.

[0076] (2) Preparation of PA reaction solution: Dissolve 0.1 mmol of p-phenylenediamine in 150 mL of deionized water, add 5 mL of acetic acid, and sonicate for 30 minutes to prepare PA reaction solution.

[0077] (3) Preparation of TP-PA@PES composite nanofiltration membrane: A 6 cm × 12 cm TP@PES base membrane was cut and immersed in PA reaction solution. The reaction was carried out at room temperature (20 ℃) ​​for 72 h. Then it was cured at 70 ℃ for 10 min at -0.8 MPa and washed with ethanol to obtain the TP-PA@PES composite nanofiltration membrane.

[0078] The periodic framework structure formed by monomers is too small to adapt to growth within the pores and thus cannot achieve the ideal retention performance.

[0079] Comparative Example 4:

[0080] (1) Preparation of TAPA@PES base film: First, 0.5 g of TAPA monomer was dissolved in 37.8 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TAPA was 1%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Subsequently, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath. A 1% TAPA@PES base film was obtained and stored in deionized water.

[0081] (2) Preparation of TP organic phase solution: Dissolve 20.7 mg (0.1 mmol) of TP in 100 mL of mesitylene and sonicate for 30 minutes to prepare TP organic phase solution.

[0082] (3) Preparation of aqueous solution of acid catalyst: Dissolve 150 μL of acetic acid in 50 mL of deionized water and sonicate for 30 minutes to prepare aqueous solution of acid catalyst.

[0083] (4) Preparation of TAPA-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TAPA@PES base membrane was cut and immersed in an acid catalyst aqueous solution for 5 min, and then immersed in a TP organic solution for 3 min. After repeating 3 times, it was cured at -0.8 MPa and 70 °C for 10 min, and washed with ethanol to obtain the TAPA-TP@PES composite nanofiltration membrane.

[0084] The COF layer grown by this method blocks the internal pores of the base film.

[0085] Comparative Example 5:

[0086] (1) Preparation of TAP@PES base film: First, 0.2 g of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAP) monomer was dissolved in 38.1 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TAP was 0.4%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 0.4% TAP@PES base film, which was stored in deionized water.

[0087] (2) Preparation of HBAB reaction solution: Dissolve 0.1 mmol of HBAB monomer synthesized using 2-hydroxy-1,3,5-benzenetriformaldehyde (HB) and 2-bromoethyltrimethylammonium bromide (AB) in 150 mL of deionized water and sonicate for 30 minutes to prepare HBAB reaction solution.

[0088] (3) Preparation of TAP reaction solution: Dissolve 0.1 mmol of TAP monomer and 150 μL of acetic acid in 150 mL of n-butanol and sonicate for 30 minutes to prepare TAP reaction solution.

[0089] (4) Preparation of TAP-HBAB@PES composite nanofiltration membrane: A 6 cm × 12 cm TAP@PES base membrane was cut and fixed on a self-made synthesis unit with the top surface facing upwards. Subsequently, HBAB reaction solution was added to the synthesis pool on the lower surface of the membrane, and TAP reaction solution was added to the synthesis pool on the upper surface of the membrane. The reaction was continued at room temperature (20 ℃) ​​for 72 h, and then cured at 70 ℃ for 10 min at -0.8 MPa. After washing with ethanol, the TAP-HBAB@PES composite nanofiltration membrane was obtained.

[0090] The preparation process of this method is cumbersome, and the monomer diffusion is unstable, making it difficult to control the growth of COF.

[0091] Comparative Example 6:

[0092] (1) Preparation of TP@PES base film: First, 0.5 g of TP monomer was dissolved in 37.8 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TP was 1%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 1% TP@PES base film, which was stored in deionized water.

[0093] (2) Preparation of TAPA / PEI reaction solution: Dissolve 0.1 mmol of TAPA and 1 g of PEI in 150 mL of ethanol solution, add 5 mL of acetic acid, and sonicate for 30 minutes to prepare TAPA / PEI ethanol solution.

[0094] (3) Preparation of TAPA-PEI-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TP@PES base membrane was cut and immersed in TAPA / PEI reaction solution. The reaction was carried out at room temperature (20 ℃) ​​for 72 h. Then it was cured at 70 ℃ for 10 min at -0.8 MPa and washed with ethanol to obtain the TAPA-PEI-TP@PES composite nanofiltration membrane.

[0095] An excessively rapid diffusion rate caused the COF layer to detach from the base film, resulting in experimental failure.

[0096] Comparative Example 7:

[0097] (1) Preparation of TP@PES base film: First, 0.5 g of TP monomer was dissolved in 37.8 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TP was 1%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 1% TP@PES base film, which was stored in deionized water.

[0098] (2) Preparation of TAPA / PEI reaction solution: Dissolve 0.1 mmol of TAPA and 1 g of PEI in 150 mL of deionized water, add 5 mL of acetic acid, and sonicate for 30 minutes to prepare TAPA / PEI aqueous solution.

[0099] (3) Preparation of TAPA-PEI-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TP@PES base membrane was cut and immersed in TAPA / PEI reaction solution. The reaction was carried out at room temperature (20 ℃) ​​for 72 h. Then it was cured at 70 ℃ for 10 min at -0.8 MPa and washed with ethanol to obtain the TAPA-PEI-TP@PES composite nanofiltration membrane.

[0100] As a water-insoluble solid monomer, TP caused COF to grow too densely within the base membrane, resulting in a nanofiltration membrane that ultimately failed to exhibit effective water flux.

[0101] Comparative Example 8:

[0102] (1) Preparation of TP@PES base film: First, 0.5 g of TP monomer was dissolved in 37.8 g of DMF to prepare a premix solution. Then, 2.7 g of PVP and 9 g of PES were dissolved in the premix solution to prepare a 50 g mixture, in which the mass fraction of TP was 1%. The mixture was stirred at 60 °C for 10 h to form a uniform casting solution. Then, it was degassed under vacuum at 60 °C and -0.8 MPa for 30 min. Then, the casting solution was spread onto the substrate using an automatic film casting machine and quickly (within 20 s) immersed in a 20 °C water coagulation bath to obtain a 1% TP@PES base film, which was stored in deionized water.

[0103] (2) Preparation of TAPA / PEI reaction solution: Dissolve 0.1 mmol of TAPA and 1 g of PEI in a mixed solution of 100 mL of deionized water and 50 mL of ethanol, add 5 mL of acetic acid, and sonicate for 30 minutes to prepare TAPA / PEI ethanol-water solution.

[0104] (3) Preparation of TAPA-PEI-TP@PES composite nanofiltration membrane: A 6 cm × 12 cm TP@PES base membrane was cut and immersed in TAPA / PEI ethanol-water solution and reacted at 90℃ for 72 h. Then it was cured at -0.8 MPa and 70℃ for 10 min. After washing with ethanol, the TAPA-PEI-TP@PES composite nanofiltration membrane was obtained.

[0105] Defects in the bonding between the COF layer and the base film caused experimental failure.

[0106] Experimental results of the above embodiments and comparative examples:

[0107] The permeation flux of the composite nanofiltration membrane was determined at room temperature and an operating pressure of 0.6 MPa. The sample was pre-pressurized for 30 min before testing. The membrane flux was calculated using the following formula: J = V / (A × t), where J is the water flux (L / m³). -2 h -1 V is the permeate volume of the aqueous solution (L), and A is the membrane area (m²). 2 ), where t is the filtering time (h).

[0108] The retention performance of nanofiltration membranes was characterized using six single-component salt solutions (LaCl3, SrCl2, MgCl2, CaCl2, CsCl, and LiCl) in a cross-flow filtration apparatus. The test method was as follows: First, six single-component salt solutions (LaCl3, SrCl2, MgCl2, CaCl2, CsCl, and LiCl) with a concentration of 1 g / L were prepared as feed solutions. The nanofiltration membrane to be tested was cut to a suitable size and installed in the cross-flow apparatus. After pre-compression at 0.6 MPa using the feed solution for 0.5 h, a certain volume of permeate was retained. The ion concentration in the solution was calculated using conductivity (DDS-307A, China), and the retention rate of the single-component salt solution of the nanofiltration membrane was calculated. The experimental results are shown in Table 1.

[0109] Table 1

[0110]

[0111] The pore size and retention performance of membranes were characterized using polyethylene glycol (PEG) solution in a cross-flow filtration device. The test method was as follows: First, a PEG solution with a concentration of 0.1 g / L was prepared as the feed solution. The membrane to be tested was cut to a suitable size and installed in the cross-flow device. After pre-pressurizing with the feed solution at 0.6 MPa for 0.5 h, a certain volume of permeate was retained. The PEG concentration in the solution was calculated using a TOC (Total Organic Carbon) analyzer (TOC-L CPH, China), and the membrane's PEG solution rejection rate was calculated using the following formula. The experimental results are shown in Table 2.

[0112] Table 2

[0113]

[0114] Figure 1 SEM image of the surface of the nanofiltration membrane prepared for Comparative Example 1. From... Figure 1 It can be seen that, under the method of Comparative Example 1, the crystalline material was successfully grown onto the surface of the base film.

[0115] Figure 2 This is a cross-sectional SEM image of the nanofiltration membrane prepared for Comparative Example 1. From... Figure 2 It can be seen that, under the method of Comparative Example 1, there is a good, tooth-like bonding performance between the crystalline material and the base film.

[0116] Figure 3 The image shows a surface SEM image of the nanofiltration membrane prepared in Example 1. It can be seen that, under the method of Example 1, the crystalline material was successfully grown onto the surface of the base membrane, and the growth was more uniform and obvious.

[0117] Figure 4 The image shows a cross-sectional SEM image of the nanofiltration membrane prepared in Example 1. It can be seen that under the method of Example 1, the crystalline material is grown more densely and there is no obvious boundary between it and the base membrane.

[0118] Figure 5 The image shows the cross-sectional EDS diagram of the nanofiltration membrane prepared in Example 1, where a is the EDS diagram of S element and b is the EDS diagram of N element. It can be seen that the crystalline material is uniformly distributed under the method of Example 1.

[0119] Figure 6 The infrared spectrum of the nanofiltration membrane prepared in Comparative Example 1 shows the successful synthesis of the crystalline material.

[0120] Figure 7 The XRD pattern of the nanofiltration membrane prepared in Comparative Example 1 further confirms the successful synthesis of the crystalline material.

[0121] Figure 8 The infrared spectrum of the nanofiltration membrane prepared in Example 1 shows the successful synthesis of the crystalline material.

[0122] Figure 9 The XPS image of the nanofiltration membrane prepared in Example 1 shows the successful synthesis of the crystalline material, the emergence of a more stable β-ketoenamine structure, and the successful grafting of PEI.

[0123] The membrane prepared in Example 1 was immersed in an acid solution with a pH of 1 prepared using sulfuric acid for 14 days. After immersion in the acid solution, the membrane was removed, washed with deionized water, and then stored. Figure 10 The images show a comparison of the acid resistance of a commercial NF 90 nanofiltration membrane and a nanofiltration membrane prepared in Example 1. In the images, a is a SEM image of the surface of the commercial nanofiltration membrane before acid leaching, b is a SEM image of the surface of the commercial nanofiltration membrane after acid leaching, c is a SEM image of the surface of the nanofiltration membrane prepared in Example 1 before acid leaching, and d is a SEM image of the surface of the nanofiltration membrane prepared in Example 1 after acid leaching.

[0124] The long-term operational stability of nanofiltration membranes was characterized by comparing flux and retention changes when a LaCl3 single-component salt solution was continuously operated in a cross-flow filtration device. The test method was as follows: First, a 1 g / L LaCl3 single-component salt solution was prepared as the feed solution. The nanofiltration membrane to be tested was cut to a suitable size and installed in the cross-flow device. After pre-pressurization with the feed solution at 0.6 MPa for 0.5 h, a certain volume of permeate was retained, and the device was operated continuously for 70 h. The ion concentration in the solution was calculated using conductivity (DDS-307A, China), and the single-component salt solution retention rate of the nanofiltration membrane was calculated. Figure 11 This is to demonstrate the long-term operational stability of Example 1.

[0125] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a nanofiltration membrane with strong interlayer bonding through solid-liquid interfacial polymerization, characterized in that: Includes the following steps: (1) Preparation of polymer base film containing first monomer: The first monomer, pore-forming agent and film-forming polymer are added to a solvent to obtain a casting solution. After forming a base film layer by scraping or spinning, the film is placed in a coagulation bath to stand and form a film; wherein, the first monomer includes 2,4,6-tricarboxymethyl phloroglucinol; (2) Preparation of reaction solution containing the second monomer: Dissolve the second monomer in its solvent to obtain the reaction solution; the second monomer is tris(4-aminophenyl)amine; the solvent is a mixture of water and ethanol; The reaction solution also contains a polymer additive, which is polyethyleneimine. (3) Interfacial polymerization reaction: The polymer base membrane containing the first monomer obtained in step (1) is immersed in the reaction solution prepared in step (2), so that the first monomer diffuses from the inside of the base membrane to the outside of the membrane and undergoes a polymerization reaction with the second monomer in the reaction solution inside and on the surface of the base membrane to generate a crystalline porous material separation layer, thereby obtaining the nanofiltration membrane.

2. The method for preparing a strong interlayer-bonded nanofiltration membrane by solid-liquid interfacial polymerization according to claim 1, characterized in that: In step (1), the film-forming polymer includes one of polyethersulfone, polysulfone, polyvinylidene fluoride or polyacrylonitrile, and cellulose diacetate; the pore-forming agent is polyvinylpyrrolidone; and the solvent is N,N-dimethylformamide.

3. The method for preparing a strong interlayer-bonded nanofiltration membrane by solid-liquid interfacial polymerization according to claim 1 or 2, characterized in that: In step (1), the mass fraction of the first monomer in the casting solution is 0.5-2%; the mass fraction of the film-forming polymer in the casting solution is 15-25%; and the mass fraction of the pore-forming agent in the casting solution is 3-10%.

4. The method for preparing a strong interlayer-bonded nanofiltration membrane by solid-liquid interfacial polymerization according to claim 1, characterized in that: In step (2), the concentration of the second monomer in the reaction solution is 0.5~1 mmol / L; the mass concentration of the polymer additive in the reaction solution is 5~20 g / L.

5. The method for preparing a strong interlayer-bonded nanofiltration membrane by solid-liquid interfacial polymerization according to claim 1 or 2, characterized in that: In step (2), the reaction solution also contains a catalyst, which is acetic acid, and the concentration of acetic acid is 2-5 vol.

6. The method for preparing a strong interlayer-bonded nanofiltration membrane by solid-liquid interfacial polymerization according to claim 1 or 2, characterized in that: In step (3), the interfacial polymerization reaction is carried out at 20~30℃ for 24~72 hours. After the reaction is completed, the resulting film is cured under the following conditions: 50~70℃ and -0.6~-1.0 MPa for 10~20 minutes.

7. The nanofiltration membrane prepared by the method for constructing a strong interlayer bond nanofiltration membrane through solid-liquid interfacial polymerization according to claim 1 is characterized in that: It includes a polymer porous support layer and a crystalline porous material separation layer grown in situ inside and on the surface of the support layer; the separation layer and the support layer are tightly bonded together, and the separation layer is composed of a covalent organic framework material and polyethyleneimine, wherein the covalent organic framework material is formed by polymerization of 2,4,6-tricarboxymethyl phloroglucinol and tris(4-aminophenyl)amine.

8. The application of the nanofiltration membrane according to claim 7 in the treatment of wastewater containing monovalent or polyvalent ions, pretreatment of seawater desalination, or decolorization of dye wastewater, characterized in that: The monovalent or multivalent ions include La 3+ 、Sr 2+ Mg 2+ Ca 2+ Cs + Li + One or more of them.

Images