Method for preparing COP film by constructing solid-liquid-like interface

Abstract

The invention belongs to the field of separation membrane preparation, and discloses a method for preparing a COP membrane by constructing a solid-liquid-like interface, and the method comprises the following steps: (1) preparing a wet base membrane with a functional group; (2) preparing a non-aqueous solution of a first monomer by using a pre-selected non-aqueous solvent; enabling the base membrane to be in contact with a non-aqueous solution of a first monomer, and obtaining the base membrane with a solid-phase-like anchoring layer after the non-aqueous solvent is volatilized; and (3) contacting the base membrane with an aqueous solution of a second monomer, triggering solid-liquid interfacial polymerization reaction, and generating the COP membrane with the covalent organic framework structure on the base membrane. On the basis of a reverse deposition strategy, a first monomer is anchored on the surface of a base membrane with a functional group preferentially, the base membrane is in contact with a non-aqueous solution of the first monomer to form a solid-phase-like structure, and then the solid-phase-like structure and an aqueous solution of a second monomer are subjected to a polymerization reaction at a solid-liquid-like interface to generate a COP selection layer, so that excellent water flux is achieved; the method is suitable for dye wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the field of separation membrane preparation, and more specifically, relates to a method for preparing a COP (covalent organic polymers) membrane by constructing a solid-liquid interface. In particular, the method can construct a solid-liquid interface and prepare a COP membrane at room temperature and pressure. The obtained COP membrane can be applied to dye wastewater treatment. Background Art

[0002] Efficient and economical membrane separation technology has become a key strategy to meet the challenges of water purification and resource recovery. The research and development of high-performance membrane materials, especially the exploration of ideal separation membranes with both high flux and excellent selectivity, plays a decisive role in the effectiveness of membrane separation technology. However, traditional polymer membranes often face an irreconcilable trade-off between permeability and retention capacity, and new material solutions are urgently needed to break this dilemma.

[0003] Covalent organic framework materials (COFs), as a class of crystalline porous materials connected by covalent bonds, can theoretically prepare ultra-thin defect-free selective films, but in actual operation they face challenges such as long growth and crystallization cycles (usually greater than 48 hours). In contrast, covalent organic polymers (COPs) materials that exist in a semi-crystalline or amorphous state not only have highly cross-linked porous structures, functionality, and size screening properties similar to COFs, but also have significantly shorter preparation cycles (less than 1 hour), providing a more flexible approach for the preparation of selective layers.

[0004] In the preparation of COP selective membranes, interfacial polymerization (IP) is the most commonly used synthesis method. However, traditional liquid-liquid IP is prone to runaway reaction rates due to uneven monomer diffusion, and it is difficult to effectively confine the reaction to the liquid-liquid interface, which in turn causes loose stacking of COPs and even clogging of membrane pores, severely limiting the membrane separation efficiency. In order to optimize the IP process, researchers have tried various methods such as electric field assistance, introduction of surfactants, pre-grown seed crystals, and base membrane modification to regulate monomer diffusion and interfacial reactions. Although the separation performance has been improved to a certain extent, the inherent instability and easy disturbance of traditional interfacial polymerization and other dynamic complexity problems still need to be solved.

[0005] Existing interfacial polymerization techniques use a solid phase that is not easily disturbed to replace the conventional liquid phase, enabling interfacial polymerization to occur at a relatively stable solid-liquid or solid-gas interface to improve the dynamic complexity of interfacial polymerization and thus obtain a more complete and ordered selective layer. For example, Niaz Ali Khan constructed a more stable solid-gas interface and carried out a polymerization reaction at 150 °C to achieve the coordination of the COF polymerization and crystallization processes. However, current solid-phase interfacial reactions generally involve high-temperature treatments (often requiring high temperatures above 120 °C, such as 150 °C, 180 °C, etc.), with cumbersome steps and high energy consumption. There is an urgent need to develop a simpler and more efficient solid-phase interface construction strategy. Summary of the Invention

[0006] In view of the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a method for preparing a covalent organic polymer (COP) membrane by constructing a quasi-solid-liquid interface. Based on the reverse deposition strategy, a first monomer (such as an aldehyde-containing monomer, such as 1,3,5-triformylphloroglucinol Tp) is preferentially anchored on the surface of a substrate film with functional groups. By contacting the substrate film with a non-aqueous solution of the first monomer, after the non-aqueous solvent volatilizes, a quasi-solid-phase structure is formed. Subsequently, a polymerization reaction occurs at the quasi-solid-liquid interface with an aqueous solution of a second monomer (such as an amine-containing monomer, such as p-phenylenediamine Pa) to generate a COP selective layer, thereby solving the technical problems of unstable liquid-liquid interfaces and high energy consumption in solid-phase interfacial reactions. The process of the present invention is simple, environmentally friendly, has excellent water flux, and is applicable to the field of dye wastewater treatment.

[0007] To achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a covalent organic polymer (COP) membrane by constructing a quasi-solid-liquid interface, characterized in that the method uses a first monomer and a second monomer that can undergo a polymerization reaction with each other to form a covalent organic framework structure as raw materials, wherein the first monomer is soluble in a pre-selected non-aqueous solvent, and the second monomer is soluble in water. The preparation method includes the following steps:

[0008] (1) Prepare a moist substrate film with functional groups, wherein the functional groups can form hydrogen bond interactions with the first monomer;

[0009] (2) Prepare a non-aqueous solution of the first monomer using a pre-selected non-aqueous solvent, wherein the density of the non-aqueous solvent is less than that of water; contact the substrate film with the non-aqueous solution of the first monomer, then remove the non-aqueous solution of the first monomer, and wash the substrate film with the same non-aqueous solvent to remove the unanchored first monomer. After the non-aqueous solvent volatilizes completely, a substrate film with a quasi-solid-phase anchoring layer can be obtained;

[0010] (3) Contact the substrate film obtained in step (2) with an aqueous solution of the second monomer to trigger a quasi-solid-liquid interfacial polymerization reaction, and generate a COP membrane with a covalent organic framework structure on the substrate film.

[0011] As a further preference of the present invention, both step (2) and step (3) are carried out under normal temperature and pressure.

[0012] As a further preference of the present invention, the first monomer is an aldehyde-containing monomer, preferably at least one of 1,3,5-triformylphloroglucinol (Tp) and terephthalaldehyde (Tb);

[0013] The second monomer is an amine-containing monomer, preferably at least one of p-phenylenediamine (Pa), p-aminobenzenesulfonic acid (Pa-SO3H), 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (Tta), 4,4'-azodianiline (Azo), and melamine (Me);

[0014] The aqueous solution of the second monomer further contains a catalyst that can promote the polymerization reaction between the first monomer and the second monomer; the catalyst is preferably acetic acid, and 100 μL to 500 μL of acetic acid is contained in every 20 mL of the aqueous solution of the second monomer; the concentration of the second monomer in the aqueous solution of the second monomer is 0.005 wt% to 0.5 wt%.

[0015] As a further preference of the present invention, it further includes the step of:

[0016] (4) Thermally curing the COP film obtained in step (3) to obtain a heat-treated COP film.

[0017] As a further preference of the present invention, in step (4), the thermal curing is carried out by heat treatment and curing at 60-90 °C for 3-10 min.

[0018] As a further preference of the present invention, in step (1), the functional group is at least one of a carboxyl group, a sulfoxide group, a hydroxyl group, and an amino group.

[0019] As a further preference of the present invention, in step (1), the base film having a functional group is selected from a polysulfone film, a polyethersulfone film, an alkali-treated functionalized polyacrylonitrile (PAN) film, an alkali-treated functionalized polyimide (PI) film, and an alkali-treated functionalized polyvinylidene fluoride (PVDF) film;

[0020] Preferably, the alkali treatment is to immerse the original base film in a NaOH solution, carry out alkali treatment under heating conditions, and then rinse with deionized water to remove the residual alkali solution;

[0021] More preferably, the concentration of the NaOH solution is 1.5 mol / L, the alkali treatment is carried out at a constant temperature of 45 °C, and the alkali treatment time is 2 h.

[0022] As a further preference of the present invention, in step (2), the non-aqueous solvent is any one of n-hexane, n-butanol, and heptane, and the concentration of the first monomer in the non-aqueous solution of the first monomer is 0.005-0.05 wt%.

[0023] According to another aspect of the present invention, the present invention provides a COP membrane prepared by the above method.

[0024] According to still another aspect of the present invention, the present invention provides the application of the above COP membrane in treating dye wastewater.

[0025] Through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0026] (1) In the method for constructing the quasi-solid-liquid interface in the present invention, a reverse deposition strategy is adopted, and a quasi-solid phase structure is formed through physical confinement and anchoring, solving the inherent instability problem of the traditional liquid-liquid interface. The COP membrane (covalent organic polymer membrane) obtained in the present invention is a covalent organic framework existing in an amorphous or semi-crystalline state, which is obtained by the reaction of a first monomer and a second monomer. Among them, the first monomer can be dissolved in the selected non-aqueous solvent and can react with the second monomer to form a covalent organic framework structure; the second monomer can be dissolved in an aqueous solution and can react with the first monomer to form a covalent organic framework structure.

[0027] Taking the first monomer as Tp, the second monomer as Pa, and the alkali-treated functionalized PAN-based membrane as an example, the carboxylate groups on the surface of the alkali-treated functionalized PAN-based membrane anchor Tp through hydrogen bond forces, forming a monomer anchoring layer on the surface of the wet alkali-treated functionalized PAN-based membrane. When using a non-aqueous solution of 1,3,5-triformylphloroglucinol, a non-aqueous solvent with a density less than that of water is used to prepare it, which can limit the diffusion space of the aldehyde monomer Tp, ensuring that Tp is only distributed on the surface of the base membrane (such as the alkali-treated functionalized PAN-based membrane) and does not penetrate into the interior of the base membrane. Then, the base membrane with a quasi-solid phase anchoring layer is contacted with an aqueous solution containing an amine monomer, triggering a quasi-solid-liquid interface polymerization reaction (the quasi-solid-liquid interface is the interface between the anchoring layer with solid-phase physical properties formed through physical confinement and the liquid-phase reactants), and a ketoenamine structure is generated on the base membrane (taking the amine monomer as Pa as an example, Tp and Pa react through an aldehyde-amine Schiff base reaction to form a ketoenamine structure), and a selective layer can be formed on the base membrane to obtain a COP membrane.

[0028] (2) In the present invention, the formation of the covalent organic framework structure by the first monomer and the second monomer can preferably be carried out at normal temperature and pressure. The process is simple and environmentally friendly, avoiding the high energy consumption problem of existing solid-phase construction technologies. The COP membrane prepared by the solid-liquid interface polymerization of the present invention has high water permeability compared with the traditional liquid-liquid interface polymerization. Taking Example 1 hereinafter as an example, the thickness of the selective layer of the COP membrane prepared in the present invention is 33 nm, the water flux reaches 161 L m-2h-1bar-1 (3.7 times higher than that of the traditional liquid-liquid interface polymerization), and the rejection rate of Congo red (CR) is 98.8%.

[0029] (3) The COP membrane prepared by the solid-liquid interface polymerization of the present invention has structural integrity and excellent rejection ability, and can be particularly applied to the treatment of dye wastewater, showing broad application prospects in the field of dye wastewater treatment. Taking the following examples as an example, the rejection rate of Congo red is 98.8%, and that of various dyes is greater than 97.5%. Description of the Drawings

[0030] Figure 1 is a schematic flow chart of the preparation of the COP membrane based on the solid-liquid interface of the present invention.

[0031] Figure 2 is a schematic conceptual diagram of the solid-liquid interface polymerization.

[0032] Figure 3 is the reaction mechanism diagram of the COP synthesis in Example 1.

[0033] Figure 4 is the SEM cross-sectional view of the COP membrane prepared in Example 1.

[0034] Figure 5 is the SEM cross-sectional view of the COP membrane prepared in Comparative Example 4 at different magnifications. Detailed Embodiments

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Taking the first monomer as Tp and the second monomer as Pa as an example, Figure 1 The following shows a schematic flow chart of the preparation of the COP membrane based on the solid-liquid interface of the present invention. As shown in the figure, the Tp monomer is anchored on the surface of the HPAN base membrane and undergoes interfacial polymerization after contacting with the aqueous solution of the Pa monomer. The mechanism of the reaction between Tp and Pa to synthesize COP is as Figure 3 shown. Tp and Pa react through the aldehyde-amine Schiff base reaction to form a ketoenamine structure.

[0037] As Figure 2 shown in the conceptual schematic diagram of the quasi-solid-liquid interfacial polymerization, Tp is anchored on the surface of the base film through hydrogen bonding to form a quasi-solid phase, and quasi-solid-liquid interfacial polymerization occurs after contacting with the aqueous phase.

[0038] The following are specific examples:

[0039] Example 1:

[0040] Taking the use of alkali-treated PAN base film (HPAN) as an example, the method for constructing a quasi-solid-liquid interface and preparing a COP film in the present invention may include the following steps:

[0041] S1. Preparation of the base film: Polyacrylonitrile (PAN) powder is dried under vacuum at 60 °C for 24 hours before use. PAN, LiCl, EtOH, and NMP are mixed according to a mass ratio of 14:4:5:77, stirred at 60 °C for 24 hours to obtain a homogeneous casting solution, and left standing at room temperature for 6 h to defoam before use. The casting solution is scraped onto a clean glass plate with a 150-μm stainless steel scraper, and then transferred to a water bath for nonsolvent-induced phase separation (NIPS). In order to further remove NMP, LiCl, and EtOH in the film, the deionized water is replaced in a timely manner and soaked for more than 12 hours to obtain the original PAN base film.

[0042] S2. Functionalization of the base film by alkali treatment: The PAN base film is immersed in a 1.5 mol / L NaOH solution and treated at a constant temperature of 45 °C for 2 hours. To remove the excess NaOH solution, after taking it out, it is soaked in deionized water for 1 h and then rinsed 3 times to obtain the alkali-treated PAN base film (HPAN). The internal pores of the alkali-treated functionalized PAN base film (HPAN base film) are completely wetted by water and maintained in a wet state.

[0043] S3. Preparation of the COP film: A 6*8 cm-sized wet HPAN base film is fixed in a reaction device, the residual moisture on the surface is removed by lens paper, contacted with a Tp hexane solution (0.02 wt%), the solution is removed after standing for 1 min, and the surface is immediately rinsed thoroughly with hexane 3 times to remove the unanchored Tp monomers, and left standing in the air for 2 min to ensure that the hexane solvent completely volatilizes (the boiling point of the hexane solvent is 69 °C and completely volatilizes in a 2-min air bath, thereby forming a stable Tp quasi-solid phase). 20 ml of an aqueous Pa solution (0.5 wt%, containing 100 μl of acetic acid) is added, and the solution is poured off after an interfacial reaction for 2 min. In this interfacial reaction, Tp and Pa react to form a ketenimine structure through an aldehyde-amine Schiff base reaction under normal temperature and pressure conditions, as Figure 3 shown, thereby obtaining a COP film with a ketenimine structure. In order to further improve the stability of the COP film, the obtained COP film is heat-treated at 70 °C for 5 min to cure the structure, and a heat-treated COP composite film is obtained.

[0044] The above method can be divided into three processes: ① pre-treatment of alkali treatment functionalization of the base film + ② construction of a quasi-solid-liquid interface + ③ post-treatment of thermal curing. Among them, the process of constructing a quasi-solid-liquid interface is carried out at normal temperature and pressure.

[0045] The heat-treated COP composite membrane obtained in this example is composed of a base film and a selective layer formed by reaction. The cross-sectional film thickness of the selective layer is 33 nm, which has the characteristic of being ultra-thin. As Figure 4 shown, the cross-sectional film thickness of the COP membrane selective layer is 33 nm, and the COP selective layer presents a uniform and ultra-thin layer on the surface of the base film without the phenomenon of embedding into the base film.

[0046] The water flux of this heat-treated COP composite membrane is 161 ± 2.6 L m-2h-1bar-1, and the rejection rate for Congo Red (CR) is 98.8 ± 0.02%. Among them, the water flux and CR rejection rate are tested using a dead-end filtration device, and the effective membrane area for testing is 11.96 cm 2 , prepare a 100 ppm CR aqueous solution as the feed solution, and perform a 15-minute pre-pressurization before testing to stabilize the membrane performance. The test conditions are 25 ± 1 °C and a transmembrane pressure of 2 bar.

[0047] Comparative Example 1: Preparation of COP membrane by liquid-liquid interfacial polymerization under the same conditions

[0048] The method for preparing the COP membrane by liquid-liquid interfacial polymerization is as follows: Prepare the HPAN base film using the same steps as in Steps S1 and S2 of Example 1. Fix a 6*8 cm-sized wet HPAN base film in the reaction device, contact it with 20 ml of Pa aqueous solution (0.5 wt%, containing 100 μl of acetic acid), remove the solution after standing for 1 minute, absorb the residual moisture on the surface with lens paper, add a Tp n-hexane solution (0.02 wt%), remove it after 2 minutes of interfacial reaction, and cure the structure by heat treatment at 70 °C for 5 minutes to obtain a COP composite membrane. Table 1 shows the performance comparison of the COP membranes prepared in Example 1 and Comparative Example 1.

[0049] Table 1: Performance comparison of the COP membranes prepared in Example 1 and Comparative Example 1

[0050]

[0051] It can be seen that compared with the COP prepared by liquid-liquid interfacial polymerization under the same conditions, the quasi-solid-liquid interfacial polymerization proposed by the present invention exhibits excellent permeability while maintaining a high level of dye molecule rejection rate, and has obvious performance advantages, better addressing the often difficult-to-reconcile trade-off problem between permeability and rejection ability in traditional methods.

[0052] Comparative Example 2:

[0053] The base film used in the present invention needs to be able to interact with the first monomer. Taking the first monomer as Tp, for a base film that does not inherently have functional groups capable of interacting with Tp, the base film needs to be modified through a pretreatment step to obtain functional groups capable of interacting with Tp to achieve the anchoring of Tp (taking the PAN base film as an example, it is necessary to introduce carboxylate groups through alkali treatment). This comparative example discusses the necessity of the base film having functional groups capable of forming hydrogen bond interactions with the first monomer.

[0054] This comparative example omits the S2 step of Example 1 and only performs steps S1 and S3 of Example 1. Since the PAN base film itself does not have the ability to anchor Tp, the prepared COP film has poor selectivity. Table 2 shows the performance comparison of the COP films prepared in Example 1 and Comparative Example 2.

[0055] Table 2: Performance comparison of the COP films prepared in Example 1 and Comparative Example 2

[0056]

[0057] It can be seen that when the base film does not have functional groups capable of forming hydrogen bond interactions with the first monomer, the obtained COP film hardly has the sieving ability.

[0058] Example 2:

[0059] This example discusses the use of different base film systems.

[0060] The preparation method of the COP film of the present invention is based on the interfacial reaction between Tp and Pa. Therefore, the base film needs to be able to interact with the Tp monomer to achieve the anchoring of Tp. In addition to the alkali-treated functionalized PAN film, the base film can also be:

[0061] a) Alkali-treated functionalized polyimide (PI) and alkali-treated functionalized polyvinylidene fluoride (PVDF). Since these two membrane materials have carboxylate groups, similar to the alkali-treated functionalized PAN, they have hydrogen bond interactions with Tp and can achieve the anchoring of Tp on the base film.

[0062] b) Polysulfone (Psf) and polyethersulfone (PES). These two membrane materials contain sulfoxide groups, have hydrogen bond interactions with Tp, and can achieve the anchoring of Tp on the base film.

[0063] Taking the case of using Psf as the base membrane, a casting solution with a mass ratio of Psf:PEG-400:NMP of 18:16:66 can be prepared. Using steps similar to those in step S1 of Example 1 (except for the different composition and ratio of the casting solution, the drying pretreatment of the Psf powder, as well as subsequent operations such as defoaming, scraping, non-solvent induced phase separation of the casting solution, and the soaking operation to remove PEG and NMP from the membrane are all exactly the same as those in step S1 of Example 1), a Psf base membrane is obtained; then, using steps similar to those in step S3 of Example 1 (except for the different base membrane, the composition of the Tp solution, the composition of the Pa solution, and other operation processes are all exactly the same as those in step S3 of Example 1).

[0064] The corresponding heat-treated COP composite membrane with Psf as the base membrane has the performance shown in Table 3.

[0065] Table 3: Performance comparison of COP membranes prepared with different base membranes

[0066]

[0067] In addition, if using alkali-treated functionalized polyimide (PI) and alkali-treated functionalized polyvinylidene fluoride (PVDF) as the base membrane to prepare the COP membrane, it can be carried out by imitating steps S1, S2, and S3 of Example 1.

[0068] If using polyethersulfone (PES) as the base membrane to prepare the COP membrane, it can be carried out by imitating steps S1 and S3 of Example 1 (similar to using Psf as the base membrane to prepare the COP membrane, step S2 of Example 1 can be omitted).

[0069] Comparative Example 3:

[0070] The solvent of the Tp solution selected in the present invention needs to satisfy that the density is less than that of water, ensuring that it will not deposit into the interior of the base membrane because it is heavier than water, but will be confined to the surface of the base membrane due to the light density effect. When using a heavy solvent (solvent density greater than water), such as dichloromethane (density: 1.325 g / cm 3 ), preparing the heat-treated COP composite membrane according to steps S1, S2, and S3 of Example 1 (except for the different solvents used in the Tp solution and the solvents used for rinsing, the parameter conditions and operation processes used in each step are the same as those in the corresponding steps of Example 1), the permeability drops significantly. Table 4 shows the performance comparison of the COP membranes prepared in Example 1 and Comparative Example 3.

[0071] Table 4: Performance comparison of COP membranes prepared using light solvents and heavy solvents respectively

[0072]

[0073] It can be seen that when using heavy solvents, the flux of the COP membrane obtained decreases significantly, demonstrating the importance of using light solvents (solvent density less than water) in the present invention.

[0074] Example 3:

[0075] This example discusses the use of different solvents when preparing the Tp solution (of course, if the solvent changes, the solvent used for rinsing to remove unanchored Tp monomers will also change synchronously; that is, the solvent used for rinsing is the same as the type of solvent used in the Tp solution).

[0076] The solvent used when preparing the Tp solution needs to be an organic phase solvent with a density less than water.

[0077] In this example, n-butanol and heptane are used as solvents, and the heat-treated COP composite membrane is prepared according to the steps S1, S2, and S3 of Example 1 (except that the solvents used for the Tp solution and the rinsing are different, the parameter conditions and operation processes used in each step are the same as those in the corresponding steps of Example 1).

[0078] The corresponding heat-treated COP composite membrane has the performance shown in Table 5.

[0079] Table 5: Comparison of physical properties of different solvents and performance of the prepared COP membrane

[0080]

[0081] Comparative Example 4:

[0082] In the preparation process of the COP membrane in the present invention, to construct a stable quasi-solid phase, the internal pores of the base membrane are wetted by water and maintained in a wet state. The water in the internal pores hinders the deposition of the Tp solution into the interior of the base membrane. If the internal pores of the base membrane are dry, it will cause the growth of COP in the membrane pores.

[0083] In this comparative example, after performing steps S1 and S2 of Example 1, the water in the internal pores of the HPAN base membrane obtained in step S2 is removed to obtain a completely dry HPAN base membrane. Then, the completely dry HPAN base membrane is fixed in the reaction device, contacted with the Tp hexane solution, and the subsequent steps of S3 are carried out. The completely dry HPAN base membrane is obtained by the solvent replacement method (the specific steps are: soaking the HPAN base membrane in methanol for 5 minutes, then transferring it to another portion of methanol and soaking for 5 minutes, standing in the air for 5 minutes, and after the methanol completely volatilizes, a completely dry HPAN base membrane is obtained).

[0084] The SEM cross-sectional view of the sample obtained in this comparative example is as Figure 5 shown, and the COP of the prepared COP membrane cannot be limited to grow on the surface, and COP particles also grow in the pores of the base membrane.

[0085] Moreover, the COP film prepared on the dry base film could not be tested because it was extremely prone to cracking, resulting in the failure of the experiment. It can be seen that the wetting of the internal pores of the base film with water and the maintenance of the wet state are important for the solid-liquid interface polymerization.

[0086] Comparative Example 5:

[0087] In the preparation process of the COP film of the present invention, in order to construct a stable solid-like phase, after contacting the Tp solution preferentially, it is left standing in the air for 2 min to ensure that the n-hexane is completely volatilized, and then the aqueous phase is contacted. If the solvent is not completely volatilized, the instability of the solid-like phase will affect the performance of the obtained COP film. In this comparative example, the heat-treated COP composite film was prepared according to the steps S1, S2, and S3 of Example 1 (except that the operation of standing in the air for 2 min was deleted in S3 and the subsequent operations were directly carried out, and the parameter conditions and operation processes adopted in each step were the same as those in the corresponding steps of Example 1). Table 6 shows the performance comparison of the COP films prepared in Example 1 and Comparative Example 5.

[0088] Table 6: Performance comparison of COP films prepared with complete and incomplete solvent volatilization

[0089]

[0090] It can be seen that if the n-hexane is not completely volatilized, the water flux of the obtained COP film will decrease and the film performance will be lost, demonstrating the importance of standing in the air to stabilize the solid-like phase.

[0091] Example 4:

[0092] In addition to the Tp monomer used in Example 1, other monomers that make up the covalent organic framework and are dissolved in the selected non-aqueous solvent and can react with the second monomer to form a covalent organic framework structure can also be used as the first monomer to form the COP structural unit.

[0093] In this example, trimesic aldehyde (Tb) was used as the aldehyde monomer, and the heat-treated COP composite film was prepared according to the steps S1, S2, and S3 of Example 1. The parameter conditions and operation processes adopted in each step were the same as those in the corresponding steps of Example 1 (correspondingly, a 0.02 wt% Tb n-hexane solution was used in step 3). The performance and morphology of the prepared COP film were comparable to those of the COP film obtained in Example 1.

[0094] Example 5:

[0095] In addition to the Pa monomer used in Example 1, other monomers that make up the covalent organic framework and are dissolved in the aqueous solution and can react with the first monomer to form a covalent organic framework structure can also be used as the second monomer to form the COP structural unit.

[0096] In this example, 4 different amine monomers are used, and the corresponding aqueous solution concentrations are as follows:

[0097] a) The concentration of sulfanilic acid (Pa-SHO3) is 0.25 wt%, and each 20 mL of the Pa-SHO3 aqueous solution contains 100 μL of acetic acid;

[0098] b) The concentration of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (Tta) is 0.01 wt%, and each 20 mL of the Tta aqueous solution contains 500 μL of acetic acid;

[0099] c) The concentration of 4,4'-azodianiline (Azo) is 0.005 wt%, and each 20 mL of the Azo aqueous solution contains 500 μL of acetic acid;

[0100] d) The concentration of melamine (Me) is 0.005 wt%, and each 20 mL of the Me aqueous solution contains 100 μL of acetic acid;

[0101] The heat-treated COP composite membrane is prepared according to the steps S1, S2, and S3 of Example 1. Except that the interfacial reaction time of the above 4 amine monomers is adjusted to 5 min, the parameter conditions and operation processes adopted in each step are the same as those in the corresponding steps of Example 1.

[0102] The corresponding heat-treated COP composite membrane has the performance shown in Table 7.

[0103] Table 7: Parameters and performance of COP membranes prepared with different amine monomers

[0104]

[0105] Example 6:

[0106] In this example, the rejection performance of a variety of dyes is tested on the heat-treated COP composite membrane prepared in Example 1.

[0107] The dead-end filtration device is used to test the sieving performance of the COP membrane. The effective membrane area for the test is 11.96 cm 2 , and the membrane performance is stabilized by pre-pressing for 15 min before the test. The test conditions are 25 ± 1 °C and a transmembrane pressure of 2 bar. Using Victoria Blue (VB), Coomassie Brilliant Blue G (CBB-G), Coomassie Brilliant Blue R (CBB-R), Congo Red (CR), Direct Red 80 (DR 80), and Evans Blue (EB) as dyes, a 100 ppm feed solution is prepared to test the rejection performance of the COP membrane. Table 8 shows the dye information and the rejection performance of the COP membrane. It can be seen that the COP membrane prepared based on the present invention has a rejection of more than 97.5% for a variety of dyes.

[0108] Table 8: Dye Information and Retention Performance of the Heat-Treated COP Composite Membrane Prepared in Example 1

[0109]

[0110] The above embodiments are only examples. For example, the specific types and solution concentrations of the first monomer and the second monomer can be adjusted according to actual needs and actual situations (for example, the concentration of the aqueous solution of the amine monomer can be flexibly adjusted according to the water solubility of the amine monomer). In addition, heat curing is an optional step, and static curing can also be used (of course, using heat curing can further improve the stability of the COP membrane); the catalyst is an optional addition (of course, when using a catalyst, the reaction time can be shortened, and when not using a catalyst, the reaction time can be extended), and the type of the catalyst can be adjusted according to the specific types of the first monomer and the second monomer. Normal temperature in the present invention is 25 ± 1 °C.

[0111] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a covalent organic polymer COP membrane by constructing a solid-liquid interface, characterized in that: The method uses a first monomer and a second monomer that can undergo polymerization reaction to form a covalent organic framework structure as raw materials, wherein the first monomer can be dissolved in a pre-selected non-aqueous solvent, and the second monomer can be dissolved in water. The preparation method includes the following steps: (1) preparing a wet base film having a functional group, wherein the functional group is capable of forming a hydrogen bond interaction with a first monomer; (2) using a pre-selected non-aqueous solvent to prepare a non-aqueous solution of the first monomer, wherein the density of the non-aqueous solvent is less than that of water; contacting the base film with the non-aqueous solution of the first monomer, then removing the non-aqueous solution of the first monomer, and washing the base film with the same non-aqueous solvent to remove the unanchored first monomer, and after the non-aqueous solvent is completely evaporated, a base film having a solid-phase anchoring layer can be obtained; (3) contacting the base film obtained by the treatment in step (2) with an aqueous solution of a second monomer to trigger a solid-liquid interfacial polymerization reaction, thereby generating a COP film having a covalent organic framework structure on the base film.

2. The method according to claim 1, characterized in that: Both step (2) and step (3) are carried out at normal temperature and pressure.

3. The method according to claim 1, characterized in that: The first monomer is an aldehyde-containing monomer, preferably at least one of 1,3,5-triformylpyrogallol (Tp) and trimesaldehyde (Tb); The second monomer is an amine-containing monomer, preferably at least one of p-phenylenediamine (Pa), p-aminobenzenesulfonic acid (Pa-SO3H), 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (Tta), 4,4'-azodiphenylamine (Azo), and melamine (Me); The aqueous solution of the second monomer also contains a catalyst capable of promoting the polymerization reaction of the first monomer and the second monomer; the catalyst is preferably acetic acid, and each 20 mL of the aqueous solution of the second monomer contains 100 μL to 500 μL of acetic acid; the concentration of the second monomer in the aqueous solution of the second monomer is 0.005 wt% to 0.5 wt%.

4. The method according to claim 1, characterized in that: Also includes the steps: (4) thermally curing the COP film obtained in step (3) to obtain a heat-treated COP film.

5. The method according to claim 4, characterized in that: In step (4), the thermal curing is performed by heat treatment at 60-90° C. for 3-10 minutes.

6. The method according to claim 1, characterized in that: In step (1), the functional group is at least one of a carboxyl group, a sulfoxide group, a hydroxyl group, and an amino group.

7. The method according to claim 1, characterized in that: In step (1), the base membrane having a functional group is selected from a polysulfone membrane, a polyethersulfone membrane, an alkali-treated functionalized polyacrylonitrile (PAN) membrane, an alkali-treated functionalized polyimide (PI) membrane, and an alkali-treated functionalized polyvinylidene fluoride (PVDF) membrane; Preferably, the alkali treatment is to immerse the original base film in a NaOH solution, perform alkali treatment under heating conditions, and then rinse with deionized water to remove residual alkali solution; More preferably, the concentration of the NaOH solution is 1.5 mol / L, the alkali treatment is carried out at a constant temperature of 45° C., and the alkali treatment time is 2 h.

8. The method according to claim 1, characterized in that: In step (2), the non-aqueous solvent is any one of n-hexane, n-butanol and heptane, and the concentration of the first monomer in the non-aqueous solution of the first monomer is 0.005-0.05 wt %.

9. A COP membrane prepared by the method according to any one of claims 1 to 8.

10. Use of the COP membrane as claimed in claim 9 in treating dye wastewater.

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