Antibacterial surface segregation covalent organic framework as well as preparation method and application thereof

Abstract

The invention provides an antibacterial surface segregation covalent organic framework as well as a preparation method and application thereof, and relates to the field of separation membrane materials. The organic framework material disclosed by the invention is prepared by taking a covalent organic framework nanosheet with an internal antibacterial function as a segregation agent, physically blending the covalent organic framework nanosheet with a polymer matrix and utilizing a non-solvent induced phase separation process. The method comprises the following steps: firstly, synthesizing a covalent organic framework nanosheet dispersion liquid through a single-phase method, then blending the covalent organic framework nanosheet dispersion liquid with a high polymer material to prepare a membrane casting liquid, and finally, constructing a compact functional skin layer on the surface of the membrane and in pore channels through a non-solvent phase inversion process by utilizing the spontaneous surface segregation effect of covalent organic framework nanosheets in a phase separation process. The prepared membrane is of a typical asymmetric structure, and the antibacterial rate of the membrane on escherichia coli is high; the developed finger-shaped pore structure endows the membrane with high flux characteristic. The method effectively solves the problem of membrane biological pollution in the field of water treatment, and has the synergistic advantages of high flux, high interception and efficient antibiosis.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials, and in particular to an antibacterial surface segregation covalent organic framework, its preparation method, and its application. Background Technology

[0002] Membrane separation technologies, such as microfiltration, ultrafiltration, and nanofiltration, have been widely used in water treatment due to their high efficiency and energy savings. However, membrane fouling, especially biofouling caused by the attachment and reproduction of microorganisms on the membrane surface and within the pores, is the primary challenge leading to decreased membrane flux, increased operating pressure, frequent cleaning, and shortened membrane lifespan. Biofilms formed by microorganisms and their metabolic products are extremely difficult to remove, severely limiting the operational efficiency and economic viability of membrane technologies.

[0003] To mitigate biofouling, existing technologies typically employ the following strategies: (1) surface modification of membrane materials to introduce hydrophilic groups to reduce initial microbial adhesion; (2) blending or grafting inorganic antibacterial agents (such as silver nanoparticles, graphene oxide) or organic antibacterial agents (such as quaternary ammonium salts) to impart bactericidal function to the membrane. However, these methods still have limitations: inorganic nanoparticles are easily leached from the membrane, leading to a decrease in antibacterial performance and potentially causing secondary pollution; small-molecule organic antibacterial agents may have problems such as poor chemical stability and short shelf life.

[0004] Covalent organic frameworks (COFs) are a class of crystalline porous materials formed by organic monomers linked by strong covalent bonds. They possess advantages such as regular pore structure, tunable structure, high specific surface area, and good chemical stability. In recent years, research has attempted to combine COFs with polymer membranes to improve membrane separation performance. However, how to closely integrate the excellent properties of COFs with the antifouling requirements of membranes, especially utilizing the structural characteristics of COFs themselves to achieve efficient, long-lasting, and stable antibacterial functions, while simultaneously using ingenious membrane fabrication processes to precisely distribute them on the membrane surface—the initial pollution region—remains a pressing technical challenge in the field. Summary of the Invention

[0005] In view of this, the present invention proposes an antibacterial surface segregation covalent organic framework, its preparation method and application.

[0006] The design concept of an antibacterial surface-segregating covalent organic framework membrane proposed in this invention is as follows: the membrane uses covalent organic framework nanosheets with intrinsic antibacterial function as segregating agents and a polymer material as the film-forming matrix; through the spontaneous migration effect in the non-solvent-induced phase separation process, the covalent organic framework nanosheets are selectively enriched on the membrane surface and surface pores, thereby constructing a stable and durable antibacterial functional layer. The membrane exhibits an asymmetric structure, including a dense skin layer composed of covalent organic framework nanosheets and a porous support layer with finger-like pores; the dense skin layer, with a thickness of 10~40μm, not only provides sieving function but is also the main battlefield for antibacterial action; the porous support layer, with a thickness of 60~390μm, provides an efficient channel for transmembrane mass transfer. The intrinsic antibacterial activity of the antibacterial covalent organic framework nanosheets and their spontaneous surface segregation characteristics during the film-forming process are key to achieving long-term biofouling resistance of the membrane. The enrichment of nanosheets on the membrane surface maximizes the exposure and efficient utilization of antibacterial functional groups at the fouling initiation site, endowing the membrane with active and long-lasting contact sterilization capabilities. Furthermore, by adjusting the types of covalent organic framework monomers, the concentration of nanosheets, and the membrane formation process parameters, the surface chemistry, skin structure, and separation performance of the membrane can be precisely controlled, thereby enabling targeted membrane design and performance optimization for different water treatment applications.

[0007] The technical solution of this invention is implemented as follows: A method for preparing an antibacterial surface segregation covalent organic framework membrane involves reacting aldehyde monomers and amino monomers under the action of a catalyst to prepare covalent organic framework nanosheets. The covalent organic framework nanosheets serve as segregating agents, and a polymer material is used as a matrix. The matrix, segregating agent, and organic solvent are mixed and uniformly dispersed by physical blending to obtain a casting solution. Subsequently, an antibacterial surface segregation covalent organic framework membrane is prepared by a non-solvent phase inversion method.

[0008] Furthermore, the preparation method of the antibacterial surface segregation covalent organic framework membrane includes the following steps: (1) Dissolve the aldehyde monomer in organic solvent a, sonicate for 10-20 minutes, and record the resulting solution as solution A; Dissolve the amino monomer in organic solvent b, sonicate for 10-20 minutes, and the resulting solution is denoted as solution B. Dissolve the catalyst in organic solvent C, sonicate for 10-20 minutes, and record the resulting solution as solution C. Solution A was added dropwise to solution B under stirring to obtain a mixture of A and B. Then, solution C was added dropwise to the mixture of A and B. The mixture was allowed to stand at a constant temperature of 20-30℃ for 24-48 hours to obtain a dispersion of covalent organic framework nanosheets. (2) Disperse the polymer material and the covalent organic framework nanosheet dispersion from step (1) in organic solvent d to obtain casting solution; scrape the casting solution onto a glass plate to obtain a nascent membrane; pre-evaporate in air for 10-30 seconds, then immerse in a coagulation bath of deionized water, ethanol aqueous solution or methanol aqueous solution for 20-30 hours to obtain an antibacterial surface segregation covalent organic framework membrane.

[0009] Further, in step (1), the aldehyde monomer is at least one of trimethylolpropionyl phloroglucinol, pyromellitic pyrrolizaldehyde, terephthalaldehyde, and trimethylolpropionylbenzene; the amino monomer is at least one of triamine guanidine hydrochloride, melamine, diaminoimidazole, and 4-aminopyridine; and the catalyst is at least one of acetic acid, p-toluenesulfonic acid, trifluoroacetic acid, triethylamine, and zinc chloride.

[0010] Further, in step (1), the organic solvent a is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone; the organic solvent b is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone; and the organic solvent c is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone.

[0011] Further, in step (1), the molar volume ratio of the aldehyde monomer to organic solvent a is 1:(1.5-2.0); the molar volume ratio of the amino monomer to organic solvent b is 1:(1.5-2.0); the concentration of the catalyst in solution C is 0.2~1.3 mol / L; the molar ratio of the aldehyde monomer to the amino monomer is (0.9-1.1):(0.9-1.1); and the molar ratio of the aldehyde monomer to the catalyst is (0.9-1.1):(0.15-0.25).

[0012] Further, in step (2), the organic solvent d is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone; the polymer material is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethersulfone, polysulfone, polyphenylsulfone, polyvinyl chloride, polyetherimide, and polyimide. Further, in step (2), the mass-to-volume ratio of the polymeric material to the organic solvent d is 15-20:70-80 (g / mL).

[0013] Further, in step (2), the mass ratio of covalent organic framework nanosheets to polymer materials in the covalent organic framework nanosheet dispersion is 10:(15-20).

[0014] Furthermore, the covalent organic framework nanosheet is at least one of the following: trimethylaldehyde-resorcinol-triamineguanidine hydrochloride, trimethylaldehyde-resorcinol-melamine, trimethylaldehyde-resorcinol-diaminoimidazole, trimethylaldehyde-resorcinol-4-aminopyridine, pyromellitic methylaldehyde-triamineguanidine hydrochloride, pyromellitic methylaldehyde-melamine, pyromellitic methylaldehyde-diaminoimidazole, pyromellitic methylaldehyde-4-aminopyridine, terephthalaldehyde-triamineguanidine hydrochloride, terephthalaldehyde-melamine, terephthalaldehyde-diaminoimidazole, terephthalaldehyde-4-aminopyridine, trimethylaldehyde-phenyl-triamineguanidine hydrochloride, trimethylaldehyde-phenyl-melamine, trimethylaldehyde-phenyl-diaminoimidazole, and trimethylaldehyde-phenyl-4-aminopyridine.

[0015] Further, in step (2), the thickness of the nascent membrane is 100~400μm.

[0016] An antibacterial surface segregation covalent organic framework membrane is prepared by any one of the preparation methods described in this invention.

[0017] Furthermore, the membrane has a thickness of 100~400μm and exhibits an asymmetric cross-section. The membrane includes a dense skin layer and a porous support layer. The thickness of the dense skin layer is 10~40μm. The porous support layer has an asymmetric finger-like pore structure and a thickness of 60~290μm.

[0018] The application of the antibacterial surface segregation covalent organic framework membrane according to any one of the present invention in water treatment.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) The antibacterial surface segregation covalent organic framework membrane of the present invention uses covalent organic framework nanosheets whose monomers or framework structures possess intrinsic, physical antibacterial mechanisms (such as contact sterilization and cell membrane disruption), rather than relying on easily leached bactericidal ions; this mechanism makes the antibacterial function more durable and stable, effectively inhibiting the formation of biofilms on the membrane surface, and has efficient and durable antibacterial and antifouling performance; driven by the thermodynamics of the NIPS process, the hydrophilic covalent organic framework nanosheets will spontaneously migrate to and accumulate at the membrane-coagulation bath interface during phase separation; this "in-situ construction" method ensures the antibacterial function. The layer is precisely located at the primary location of contamination—the membrane surface and surface pores—maximizing the utilization of functional materials and avoiding excessive impact on the membrane structure. The introduction of covalent organic framework nanosheets improves the dynamics of the casting solution through its nano-effects and hydrophilicity, helping to form a more developed porous support layer and reducing water mass transfer resistance. On the other hand, the surface-enriched covalent organic framework nanosheets enhance the hydrophilicity and negative surface charge of the skin layer, which can reduce the adsorption of hydrophobic pollutants and negatively charged bacteria through physical repulsion, achieving a dual anti-fouling synergistic mechanism of "anti-adhesion" and "bactericidal".

[0020] (2) The preparation method described in this invention combines the synthesis of covalent organic frameworks with the preparation of membranes. The process is simple, has good compatibility with the non-solvent phase separation membrane preparation process widely used in industry, does not require complicated post-processing steps, and has good prospects for large-scale production. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the preparation process of the antibacterial surface segregated covalent organic framework of the present invention. Figure 2 The images are scanning electron microscope (SEM), transmission electron microscope (TEM), and atomic force microscope (AFM) images of the nanosheets synthesized in Examples 1, 2, 3, and 4, where (a), (b), and (c) are SEM, TEM, and AFM images of the antibacterial surface segregated covalent organic framework of Example 1, respectively. (d), (e), and (f) are scanning electron microscope, transmission electron microscope, and atomic force microscope images of the antibacterial surface segregated covalent organic framework of Example 2, respectively. (g), (h), and (i) are scanning electron microscope (SEM), transmission electron microscope (TEM), and atomic force microscope (AFM) images of the antibacterial surface segregated covalent organic framework of Example 4, respectively.

[0022] Figure 3 The images shown are scanning electron microscope (SEM) images of the surface and cross-section of the membranes in Example 1, Comparative Examples 1 and 2, where: (a) and (b) are electron microscope images of the surface and cross-section of the antibacterial surface segregated covalent organic framework membrane of Example 1, respectively. (c) and (d) are electron microscope images of the surface and cross-section of the antibacterial surface segregated covalent organic framework membrane of Comparative Example 1, respectively. (e) and (f) are electron micrographs of the surface and cross-section of the antibacterial surface segregated covalent organic framework membrane of Comparative Example 2, respectively. Figure 4 The images show the anti-E. coli effect of the membranes in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Detailed Implementation

[0023] Unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods; Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0024] Membrane biofouling is one of the core challenges that has long faced in the water treatment field, severely restricting the operating efficiency, stability, and economy of membrane separation technology. As the "heart" of the membrane system, the separation membrane is extremely susceptible to microbial adhesion, forming a biofilm that is difficult to remove. This leads to a sharp decline in membrane flux, an increase in cleaning frequency, and a shortened service life, thus limiting the widespread application of this technology in high-standard scenarios such as wastewater treatment and reuse.

[0025] To address the aforementioned issues, the applicant provides an antibacterial surface-segregating covalent organic framework membrane and its preparation method. This method couples a non-solvent-induced phase separation process with the spontaneous surface segregation behavior of functional nanosheets, representing an important attempt to construct a long-lasting antifouling membrane using a porous skin layer with inherent antibacterial function. The prepared antibacterial surface-segregating covalent organic framework membrane exhibits stable anchoring of the covalent organic framework nanosheets to the membrane surface and pores during phase separation, resulting in durable and highly efficient antibacterial properties. The covalent organic framework nanosheet skin layer utilizes its regular pore structure and surface hydrophilic / hydrophobic design to preferentially adsorb and transport water molecules, while its inherent antibacterial activity (such as contact sterilization) precisely inhibits microorganisms, endowing the composite membrane with high resistance to biofouling. The well-developed finger-like pore structure of the membrane matrix possesses extremely high porosity and permeability, effectively enhancing the permeation flux of water molecules within the membrane.

[0026] An antibacterial surface segregation covalent organic framework membrane of the present invention comprises the following components: a covalent organic framework nanosheet functional layer and a membrane matrix composed of polymer materials.

[0027] Specifically, the covalent organic framework nanosheets of the present invention serve as segregating agents, uniformly distributed on the surface and within the pores of the membrane, forming a dense skin layer with a thickness of 10–40 μm that combines separation and antibacterial functions; the membrane matrix cross-section of the present invention exhibits a typical asymmetric finger-like pore structure, forming a porous support layer with a thickness of 60–390 μm that provides good mechanical strength to the membrane, ultimately forming an antibacterial surface segregating covalent organic framework membrane with a total thickness of 100–400 μm.

[0028] In one embodiment, the material of the covalent organic framework nanosheet of the present invention is any one of the following: trialdehyde-resorcinol-triamineguanidine hydrochloride, trialdehyde-resorcinol-melamine, trialdehyde-resorcinol-diaminoimidazole, trialdehyde-resorcinol-4-aminopyridine, pyromellitic methyl methacrylate-triamineguanidine hydrochloride, pyromellitic methyl methacrylate-melamine, pyromellitic methyl methacrylate-diaminoimidazole, pyromellitic methyl methacrylate-4-aminopyridine, terephthalaldehyde-triamineguanidine hydrochloride, terephthalaldehyde-melamine, terephthalaldehyde-diaminoimidazole, terephthalaldehyde-4-aminopyridine, trialdehyde-phenylene-triamineguanidine hydrochloride, trialdehyde-phenylene-melamine, trialdehyde-phenylene-diaminoimidazole, and trialdehyde-phenylene-4-aminopyridine.

[0029] In one embodiment, the polymeric material of the present invention includes one or more combinations of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethersulfone, polysulfone, polyphenylsulfone, polyvinyl chloride, polyetherimide, and polyimide.

[0030] The applicant also provided a method for preparing the aforementioned antibacterial surface segregation covalent organic framework membrane, such as... Figure 1 As shown, Figure 1 This is a schematic flowchart of one embodiment of the preparation method of an antibacterial surface segregation covalent organic framework membrane according to the present invention.

[0031] S100. Preparation of covalent organic framework nanosheet dispersion: Aldehyde monomers, amino monomers, and catalysts of the covalent organic framework are dispersed in any one of the following organic solvents: dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone, respectively, to obtain an organic solution with an aldehyde monomer concentration of 10–80 mmol / L, an amino monomer concentration of 10–80 mmol / L, and a catalyst concentration of 0.7–1.3 mol / L. The aldehyde monomer solution is added to the amino monomer solution, and then the organic solvent containing the catalyst is added to the mixture. The mixture is allowed to stand at a constant temperature for 24–48 hours to allow for complete reaction, thus obtaining a covalent organic framework nanosheet dispersion with antibacterial function.

[0032] S200. Preparation of casting solution: The polymer material and the covalent organic framework nanosheet dispersion obtained in step S100 are dispersed in an organic solvent. The polymer material is any one or more combinations of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethersulfone, polysulfone, polyphenylsulfone, polyvinyl chloride, polyetherimide, and polyimide. The organic solvent is any one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone. After mechanical stirring for 6-12 hours and standing for degassing for 4-8 hours, a uniform casting solution is obtained. The mass concentration of the polymer material in the casting solution is 12%-20%, and the mass concentration of the covalent organic framework nanosheets in the casting solution is 0.05%-5% based on the solid mass of the covalent organic framework nanosheets.

[0033] S300, Non-solvent-induced phase separation film formation: The casting solution obtained in step S200 is coated onto a support such as a glass plate, and the coating thickness is controlled to be 100-400 μm; after pre-evaporation in air for 10-30 seconds, it is immersed in a non-solvent coagulation bath at a temperature of 20-40℃, wherein the coagulation bath is deionized water, ethanol aqueous solution or methanol aqueous solution; soaking in the coagulation bath for 12-24 hours to ensure complete solvent replacement, and finally obtaining the antibacterial surface segregation covalent organic framework membrane.

[0034] Example 1 Preparation of trialdehyde-resenpyrogallol-triamineguanidine hydrochloride covalent organic framework nanosheets / polyvinylidene fluoride segregation membrane (1) Preparation of covalent organic framework nanosheets: Weigh 30 mmol of trialdehyde phloroglucinol and dissolve it in 50 mL of dimethyl sulfoxide. Sonicate for 15 minutes to obtain solution A.

[0035] Weigh 30 mmol of triamine guanidine hydrochloride and dissolve it in 50 mL of dimethyl sulfoxide. Sonicate for 15 minutes to obtain solution B.

[0036] Take 1 mL of 6M acetic acid solution and dissolve it in 20 mL of N-methylpyrrolidone. Dissolve by sonication to obtain solution C.

[0037] Under magnetic stirring, solution A was slowly added dropwise to solution B and mixed thoroughly. Then, solution C was slowly added dropwise to the mixture. Stirring was stopped, and the mixture was allowed to stand at 25°C for 36 hours to obtain a pale yellow, semi-transparent dispersion of covalent organic framework nanosheets.

[0038] like Figure 2 As shown, Figure 2 As can be observed in (a), (b), and (c), the prepared nanosheets are uniformly dispersed and have a thickness of 8.8 nm.

[0039] (2) Preparation of casting solution and membrane preparation: Weigh 16 g of polyvinylidene fluoride into a flask, add 74 mL of N-methylpyrrolidone, and add 10 g of the covalent organic framework nanosheet dispersion prepared in step (1) (the covalent organic framework has a mass fraction of 0.3% in the casting solution on a solid basis). Stir mechanically at 60 °C until completely dissolved, then allow to stand for 8 hours to remove bubbles. Use a spatula to scrape the casting solution onto a glass plate to form a nascent membrane with a thickness of 200 μm. After pre-evaporation in air for 15 seconds, immerse in a 25 °C deionized water coagulation bath to solidify. After soaking for 24 hours, remove the membrane to obtain segregated membrane E1.

[0040] like Figure 3 As shown, Figure 3 As can be observed in (a) and (b), the prepared segregation membrane has a continuous surface without obvious defects, a dense cross-section, and an overall asymmetric structure. The membrane's performance was evaluated under 1 bar operating conditions. The membrane exhibited a pure water flux of 550 LMH, a 1 g / LBSA rejection rate of 95%, and an anti-E. coli rate of 94%.

[0041] Example 2: Preparation of Trimethylbenzenealdehyde-melamine covalent organic framework nanosheets / polyethersulfone segregation membrane (1) Preparation of covalent organic framework nanosheets: Following the method in Example 1, 40 mmol of pyromellitic aldehyde and 40 mmol of melamine were used as reactants, and trifluoroacetic acid was used as a catalyst. The reaction was carried out in dimethylacetamide solvent for 24 hours to obtain a covalent organic framework nanosheet dispersion. Figure 2 As can be observed in (d), (e), and (f), the prepared nanosheets are uniformly dispersed and have a thickness of 9.2 nm.

[0042] The preparation of covalent organic framework nanosheets specifically includes the following steps: Weigh 40 mmol of trimesin and dissolve it in 60 mL of dimethylacetamide. Sonicate for 15 minutes to obtain solution A.

[0043] Weigh 40 mmol of melamine and dissolve it in 60 mL of dimethylacetamide. Sonicate for 15 minutes to obtain solution B.

[0044] Take 1 mL of 6M trifluoroacetic acid solution and dissolve it in 20 mL of dimethylacetamide. Dissolve by sonication to obtain solution C.

[0045] Under magnetic stirring, solution A was slowly added dropwise to solution B, and after mixing thoroughly, solution C was then slowly added dropwise to the mixture. Stirring was stopped, and the mixture was allowed to stand at 25°C for 24 hours to obtain a covalent organic framework nanosheet dispersion.

[0046] (2) Preparation of casting solution and membrane preparation: Weigh 18 g of polyvinylidene fluoride into a flask, add 76.5 mL of N-methylpyrrolidone and 5 g of the above covalent organic framework dispersion (based on solids, the mass fraction of the covalent organic framework in the casting solution is 0.1%), and stir to dissolve at 50 °C. The membrane thickness is 200 μm, the pre-evaporation time is 20 seconds, and the coagulation bath is an ethanol / water mixture (volume ratio 1:4) at 40 °C to obtain the segregated membrane E2.

[0047] The performance of the E2 membrane was evaluated. Under the operating condition of 1 bar, the membrane had a pure water flux of 472 LMH, a 1 g / LBSA rejection rate of 84%, and an anti-E. coli rate of 81%.

[0048] Example 3 Preparation of high-content covalent organic framework nanosheet segregation membrane The main difference between the preparation process and Example 1 is that 40g of covalent organic framework nanosheet dispersion (with a covalent organic framework mass fraction of 1.2% in the casting solution on a solid basis) was added to the polyvinylidene fluoride / N-methylpyrrolidone solution. The film thickness was 300 μm, resulting in segregated film E3.

[0049] The specific steps are as follows: (1) The preparation of the covalent organic framework nanosheet dispersion was the same as in Example 1.

[0050] (2) Weigh 16 g of polyvinylidene fluoride into a flask, add 74 mL of N-methylpyrrolidone, and add 40 g of the covalent organic framework nanosheet dispersion prepared in step (1) (the mass fraction of the covalent organic framework in the casting solution is 1.2% on a solid basis). Stir mechanically at 60 °C until completely dissolved, and then let stand for 8 hours to remove bubbles. Use a spatula to scrape the casting solution onto a glass plate to form a nascent membrane with a thickness of 300 μm. After pre-evaporating in air for 15 seconds, immerse in a 25 °C deionized water coagulation bath to solidify and shape. After soaking for 24 hours, remove the membrane to obtain segregated membrane E3.

[0051] The performance of the E3 membrane was evaluated. Under the operating condition of 1 bar, the membrane had a pure water flux of 568 LMH, a 1 g / LBSA rejection rate of 81%, and an anti-E. coli rate of 99%.

[0052] Example 4 Preparation of terephthalaldehyde-diaminoimidazolium covalent organic framework nanosheets / polysulfone segregation membranes (1) Preparation of covalent organic framework nanosheets: Following the method in Example 1, 50 mmol of terephthalaldehyde and 50 mmol of diaminoimidazole were used as reactants, and p-toluenesulfonic acid was used as a catalyst. The reaction was carried out in dimethyl sulfoxide solvent for 48 hours to obtain a covalent organic framework nanosheet dispersion. Figure 2As can be observed in (g), (h), and (i), the prepared nanosheets are uniformly dispersed and have a thickness of 9.7 nm.

[0053] The preparation of covalent organic framework nanosheets specifically includes the following steps: Weigh 50 mmol of terephthalaldehyde and dissolve it in 80 mL of dimethyl sulfoxide. Sonicate for 15 minutes to obtain solution A.

[0054] Weigh 50 mmol of diaminoimidazole and dissolve it in 80 mL of dimethyl sulfoxide. Sonicate for 15 minutes to obtain solution B.

[0055] Transfer 1 mL of 6M p-toluenesulfonic acid solution to 20 mL of N-methylpyrrolidone, and dissolve by sonication to obtain solution C.

[0056] Under magnetic stirring, solution A was slowly added dropwise to solution B and mixed thoroughly. Then, solution C was slowly added dropwise to the mixture. Stirring was stopped, and the mixture was allowed to stand at 25°C for 48 hours to obtain a covalent organic framework nanosheet dispersion.

[0057] (2) Preparation of casting solution and membrane preparation: Weigh 15 g of polysulfone into a flask, add 83 mL of N-methylpyrrolidone and 15 g of the above covalent organic framework dispersion (based on solids, the mass fraction of the covalent organic framework in the casting solution is 0.45%), and stir to dissolve at 60 °C. The membrane thickness is 200 μm, the pre-evaporation time is 10 seconds, and the coagulation bath is 20 °C deionized water, yielding segregated membrane E4.

[0058] The performance of the E4 membrane was evaluated. Under the operating condition of 1 bar, the membrane had a pure water flux of 527 LMH, a 1 g / LBSA rejection rate of 89%, and an anti-E. coli rate of 92%.

[0059] Comparative Example 1 Preparation of pure polymer membranes 16 g of polyvinylidene fluoride (PVDF) was weighed and dissolved directly in 84 mL of N-methylpyrrolidone (N-Methylpyrrolidone) without adding any covalent organic framework nanosheets. Subsequent film formation steps were identical to those in Example 1. A pure PVDF membrane, CE1, was obtained.

[0060] like Figure 3 As shown, Figure 3 As observed in (c) and (d), the prepared segregation membrane surface is continuous and without obvious defects, and the membrane as a whole exhibits an asymmetric structure, but it cannot form complete permeable finger pores. Compared with E1, the permeate flux is significantly reduced. The membrane performance was evaluated under 1 bar operating conditions. The membrane had a pure water flux of 98 LMH, a 1 g / LBSA rejection rate of 75%, and an anti-E. coli rate of 0%.

[0061] Comparative Example 2 Physically blended small molecule antibacterial film Weigh 16 g of polyvinylidene fluoride and 0.3 g (equivalent to the mass of the covalent organic framework solid in Example 1) of triamine guanidine hydrochloride (monomer, non-covalent organic framework), dissolve in 84 mL of N-methylpyrrolidone, and stir to dissolve. Subsequent film-forming steps are exactly the same as in Example 1. A physically blended small molecule membrane CE2 is obtained.

[0062] like Figure 3 As shown, Figure 3 As observed in (e) and (f), the prepared segregated membrane surface exhibits a complete structure. The overall membrane structure is asymmetric due to the influence of the non-solvent phase inversion method, but small molecules do not significantly affect the formation of the permeate finger pores. Compared to E1, the permeate flux is significantly reduced. Membrane performance was evaluated under 1 bar operating conditions. The membrane showed a pure water flux of 148 LMH, a 1 g / LBSA rejection rate of 74%, and an anti-E. coli rate of 46%.

[0063] Comparative Example 3: Covalent organic framework membranes without surface segregation Solution casting was used instead of a solvent-free phase separation method. After the casting solution of Example 1 was coated onto a glass plate, it was not immersed in a coagulation bath, but directly placed in an 80°C oven to dry for 12 hours to allow the solvent to evaporate completely.

[0064] This method lacks a phase separation process; the covalent organic framework nanosheets cannot migrate to the surface but are randomly distributed within the membrane bulk. Membrane performance was evaluated under 1 bar operating conditions. The membrane exhibited a pure water flux of 326 LMH, a 1 g / LBSA rejection rate of 68%, and an anti-E. coli rate of 33%.

[0065] The pure water flux, 1 g / LBSA rejection rate, and anti-E. coli effect of the membranes of the above embodiments and comparative examples, E1, E2, E3, E4 and CE1, CE2, CE3, tested at 1 bar pressure are summarized in Table 1.

[0066] Table 1. Comparison of membrane performance between the examples and comparative examples

[0067] As shown in the table above, the antibacterial surface segregation covalent organic framework membranes prepared in Examples 1 to 4 have a pure water flux of 472 ~ 568 L / m³. -2 h -1 bar -1The BSA retention rate (81% ~ 95%) and anti-E. coli rate (81% ~ 99%) were significantly better than those of Comparative Examples 1 to 3. Among them, the membrane prepared in Example 1 (E1) showed particularly outstanding overall performance, maintaining a 550 μm... -2 h -1 bar -1 While achieving high throughput, it also achieved a high BSA retention rate of 95% and an excellent antibacterial rate of 94%. Example 3 (E3) exhibited the best antibacterial performance, with an anti-E. coli rate as high as 99%. In contrast, the Comparative Example 1 (CE1) membrane, which does not contain covalent organic framework nanosheets, has a basic retention function, but its throughput is extremely low and it has no antibacterial ability at all. The Comparative Example 2 (CE2) membrane, which physically blends small molecule antibacterial agents, has an antibacterial rate (46%) and throughput that are much lower than those of the corresponding Example 1, proving that the performance is unstable due to the easy loss of small molecules. As for Comparative Example 3 (CE3), due to the lack of a non-solvent-induced phase separation process, the covalent organic framework nanosheets cannot segregate on the surface, resulting in the lowest antibacterial rate (33%) and retention rate (68%). This strongly proves that the surface segregation effect is crucial for achieving the high-efficiency antibacterial and separation functions of the membrane.

[0068] This is mainly due to the unique "function-structure" integrated structure-activity relationship of the antibacterial surface segregation covalent organic framework membrane designed in this invention: On the one hand, the spontaneous surface segregation of covalent organic framework nanosheets during the non-solvent phase separation process constructs a continuous, stable, and antibacterial functional group-rich active skin layer (such as guanidino and imidazole groups) on the membrane surface and within the pores, maximizing the exposure and efficient utilization of antibacterial function at the contamination initiation site, thus endowing the membrane with long-lasting and efficient contact bactericidal ability; on the other hand, the introduction of covalent organic framework nanosheets synergistically regulates the membrane's microstructure. Its hydrophilicity and nucleation effect promote the formation of macroporous structures such as finger pores, significantly reducing the mass transfer resistance of water, thereby achieving high permeation flux. At the same time, the dense covalent organic framework enriched skin layer also ensures effective sieving of BSA molecules. In contrast, Comparative Example 1, lacking a functional skin layer; Comparative Example 2, with unstable antibacterial components; and Comparative Example 3, with its antibacterial components encapsulated, all failed to simultaneously achieve a synergistic improvement in high flux, high retention, and high antibacterial activity.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an antibacterial surface-segregated covalent organic framework membrane, characterized in that, Covalent organic framework nanosheets are prepared by reacting aldehyde monomers and amino monomers under the action of a catalyst. The covalent organic framework nanosheets are used as segregating agents, and a polymer material is used as a matrix. The matrix, segregating agent and organic solvent are mixed and uniformly dispersed by physical blending to obtain a casting solution. Subsequently, an antibacterial surface segregating covalent organic framework membrane is prepared by a non-solvent phase inversion method.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: (1) Dissolve the aldehyde monomer in organic solvent a, sonicate for 10-20 minutes, and record the resulting solution as solution A; Dissolve the amino monomer in organic solvent b, sonicate for 10-20 minutes, and the resulting solution is denoted as solution B. Dissolve the catalyst in organic solvent C, sonicate for 10-20 minutes, and record the resulting solution as solution C. Solution A was added dropwise to solution B under stirring to obtain a mixture of A and B. Then, solution C was added dropwise to the mixture of A and B. The mixture was allowed to stand at a constant temperature of 20-30℃ for 24-48 hours to obtain a dispersion of covalent organic framework nanosheets. (2) Disperse the polymer material and the covalent organic framework nanosheet dispersion from step (1) in organic solvent d to obtain casting solution; scrape the casting solution onto a glass plate to obtain a nascent membrane; pre-evaporate in air for 10-30 seconds, then immerse in a coagulation bath of deionized water, ethanol aqueous solution or methanol aqueous solution for 20-30 hours to obtain an antibacterial surface segregation covalent organic framework membrane.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the aldehyde monomer is at least one of trimethylolpropionyl phloroglucinol, pyromellitic pyrrolizaldehyde, terephthalaldehyde, and trimethylolpropionylbenzene; the amino monomer is at least one of triamine guanidine hydrochloride, melamine, diaminoimidazole, and 4-aminopyridine; and the catalyst is at least one of acetic acid, p-toluenesulfonic acid, trifluoroacetic acid, triethylamine, and zinc chloride.

4. The preparation method according to claim 2, characterized in that, In step (1), the organic solvent a is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone; the organic solvent b is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone; and the organic solvent c is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone. In step (1), the molar volume ratio of the aldehyde monomer to organic solvent a is 1:(1.5-2.0); the molar volume ratio of the amino monomer to organic solvent b is 1:(1.5-2.0); the concentration of the catalyst in solution C is 0.2~1.3 mol / L; the molar ratio of the aldehyde monomer to the amino monomer is (0.9-1.1):(0.9-1.1); the molar ratio of the aldehyde monomer to the catalyst is (0.9-1.1):(0.15-0.25). In step (2), the organic solvent d is at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N-ethylpyrrolidone; the polymer material is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethersulfone, polysulfone, polyphenylsulfone, polyvinyl chloride, polyetherimide, and polyimide. In step (2), the mass-to-volume ratio of the polymer material to the organic solvent d is 15-20:70-80 (g / mL).

5. The preparation method according to claim 1 or 2, characterized in that, In step (2), the mass ratio of covalent organic framework nanosheets to polymer materials in the covalent organic framework nanosheet dispersion is 10:(15-20).

6. The preparation method according to claim 1 or 2, characterized in that, The covalent organic framework nanosheets are at least one of the following: trimethylaldehyde-resorcinol-triamineguanidine hydrochloride, trimethylaldehyde-resorcinol-melamine, trimethylaldehyde-resorcinol-diaminoimidazole, trimethylaldehyde-resorcinol-4-aminopyridine, pyromellitic methylaldehyde-triamineguanidine hydrochloride, pyromellitic methylaldehyde-melamine, pyromellitic methylaldehyde-diaminoimidazole, pyromellitic methylaldehyde-4-aminopyridine, terephthalaldehyde-triamineguanidine hydrochloride, terephthalaldehyde-melamine, terephthalaldehyde-diaminoimidazole, terephthalaldehyde-4-aminopyridine, trimethylaldehyde-phenyl-triamineguanidine hydrochloride, trimethylaldehyde-phenyl-melamine, trimethylaldehyde-phenyl-diaminoimidazole, and trimethylaldehyde-phenyl-4-aminopyridine.

7. The preparation method according to claim 2, characterized in that, In step (2), the thickness of the nascent membrane is 100~400μm.

8. An antibacterial surface-segregating covalent organic framework membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The antibacterial surface segregation covalent organic framework membrane according to claim 8, characterized in that, The membrane has a thickness of 100~400μm and exhibits an asymmetric cross-section. The membrane includes a dense skin layer and a porous support layer. The thickness of the dense skin layer is 10~40μm. The porous support layer has an asymmetric finger-like pore structure and a thickness of 60~290μm.

10. The application of the antibacterial surface segregation covalent organic framework membrane according to any one of claims 8-9 in water treatment.

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