Preparation methods and applications of organic films modified with composite nanomaterials

Abstract

This invention provides a novel method for preparing and applying a composite nanomaterial-modified organic membrane, belonging to the technical field of filtration membranes for wastewater treatment. The method involves adding a modified carbon nitride nanocomposite material (made from graphitic carbon nitride nanomaterials) and a pore-forming agent to an organic solvent, followed by ultrasonic treatment to obtain a mixed solution. Then, a polymeric membrane material is added to the mixed solution, and the mixture is stirred at a constant temperature and allowed to stand to remove bubbles, forming a casting solution. The prepared casting solution is then used to prepare the composite nanomaterial-modified organic membrane. This invention improves the hydrophilicity and dispersibility of C3N4 nanomaterials in the casting solution, accelerates the phase transformation rate of the composite membrane, increases the membrane porosity, increases the membrane's negative charge, and improves the membrane's antifouling performance. It also solves the problems of low flux and severe membrane fouling that exist in the operation of composite organic membranes.

Description

Technical Field

[0001] This invention relates to the field of filtration membrane technology for wastewater treatment, specifically to a method for preparing and applying a composite nanomaterial-modified organic membrane. Background Technology

[0002] Membrane technology, with its advantages of high separation efficiency and low energy consumption, is widely used in various fields. Organic membranes such as polyvinylidene fluoride (PVDF), polysulfone (PSF), polyethersulfone (PES), polyacrylonitrile (PAN), and polytetrafluoroethylene (PTFE) membranes have been widely used in industrial microfiltration and ultrafiltration processes due to their excellent mechanical properties, thermal stability, chemical resistance, and simple preparation processes. However, because organic membranes are highly hydrophobic, they are easily fouled by adsorbing organic impurities, thereby increasing membrane resistance, reducing membrane flux, and requiring frequent chemical cleaning and replacement. Adding hydrophilic nanomaterials to ultrafiltration membranes to construct hybrid matrix ultrafiltration membranes is a convenient and effective method to improve membrane antifouling performance.

[0003] Graphitic carbon nitride (g-C3N4) possesses numerous nanopores, providing transport channels and molecular sieving effects during solution transport. Based on g-C3N4, a series of C3N4 derivatives with larger specific surface areas and superior photocatalytic performance can be obtained through modification, such as mesoporous g-C3N4 (MCN), nitrogen-rich g-C3N4 (NCN), and defective g-C3N4 (DCN). Nitrogen-defective g-C3N4 (DCN) exhibits higher surface area, more reaction sites, and stronger interactions with the membrane matrix. However, DCN's insufficient hydrophilicity hinders the improvement of composite membrane flux and antifouling performance, thus requiring further modification. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying a composite nanomaterial-modified organic membrane, so as to solve at least one of the technical problems existing in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing a composite nanomaterial-modified organic film, comprising:

[0007] Modified carbon nitride nanocomposite material prepared from graphite phase carbon nitride nanomaterials and pore-forming agent are added to an organic solvent and ultrasonically treated to obtain a mixed solution. Then, polymeric membrane material is added to the mixed solution, stirred at a constant temperature, and allowed to stand to remove bubbles to form a casting solution.

[0008] The composite nanomaterial-modified organic membrane was prepared using the prepared casting solution.

[0009] Preferably, the modified carbon nitride nanocomposite material is obtained by grinding graphitic carbon nitride nanomaterials and graphene oxide at a mass ratio of 1:1.

[0010] Preferably, the mass ratio of modified carbon nitride nanocomposite material to pore-forming agent is 1:1-2.5:1, the mass ratio of pore-forming agent to organic solvent is 1:81-1:84, and the mass ratio of modified carbon nitride nanocomposite material to polymeric membrane material is 1:6-1:15.

[0011] Preferably, the modified carbon nitride nanocomposite material is prepared by ultrasonically dispersing graphite-phase carbon nitride nanomaterials and dopamine hydrochloride in Tris buffer, centrifuging the mixed solution, washing and drying it to obtain a polydopamine-encapsulated C3N4 composite material.

[0012] Preferably, the mass ratio of modified carbon nitride nanocomposite material to pore-forming agent is in the range of 1:1-1:3, the mass ratio of pore-forming agent to organic solvent is in the range of 1:27-1:83, and the mass ratio of modified carbon nitride nanocomposite material to PFM is 1:10-1:15.

[0013] Preferably, the pH of the Tris buffer solution is 7.8-8.5, the dopamine concentration is 1-10 g / L, and the mass ratio of graphitic carbon nitride nanomaterials to dopamine is 1:0.2-1:2.

[0014] Preferably, the graphitic carbon nitride nanomaterial is one of mesoporous g-C3N4, nitrogen-rich g-C3N4, or defective g-C3N4.

[0015] Preferably, the polymeric membrane material is one of polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile, or polytetrafluoroethylene.

[0016] Preferably, the pore-forming agent is polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG).

[0017] Preferably, the organic solvent is one of 1-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), or dimethylacetamide (DMAc).

[0018] The beneficial effects of this invention are: it improves the hydrophilicity and dispersibility of C3N4 nanomaterials in casting solution, accelerates the phase transformation rate of composite membranes, increases membrane porosity, increases membrane negative charge, improves membrane antifouling performance, and solves problems such as low flux and severe membrane fouling in the operation of composite organic membranes.

[0019] The advantages of additional aspects of the invention will be set forth more clearly in the following description or will be learned by practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The PVDF membrane and PVDF / GO@DCN described in the embodiments of the present invention 2.0 SEM images of the composite membrane surface; where (a) is the PVDF membrane; and (b) is the PVDF / GO@DCN membrane. 2.0 Composite membrane.

[0022] Figure 2 The image shows the contact angle measurement of the GO and DCN modified composite membrane and the PVDF membrane described in the embodiments of the present invention.

[0023] Figure 3 The diagram shows the three-phase diagrams of the GO and DCN modified composite membrane and the PVDF membrane described in the embodiments of the present invention.

[0024] Figure 4 This is a diagram showing the interaction between the GO and DCN modified composite membrane and the PVDF membrane described in the embodiments of the present invention and bovine serum albumin.

[0025] Figure 5 This is a schematic diagram illustrating the interaction between GO@DCN and the composite film according to an embodiment of the present invention. Wherein, Figure 5 (a,b) Electrostatic potential distribution of GO@DCN, (c) Graph of the sign of RDG of PVDF / GO@DCN multiplied by the electron density (ρ) by the second Hessian eigenvalue (λ2), (d) RDG isosurface of PVDF / GO@DCN (s=0.5au).

[0026] Figure 6 The figure shows the experimental results of the permeability (pure water flux) and retention of bovine serum albumin of the GO and DCN modified composite membrane described in the embodiments of the present invention.

[0027] Figure 7 The figure shows the cyclic experiment results of bovine serum albumin filtration using the GO and DCN modified composite membrane described in this embodiment of the invention.

[0028] Figure 8 The PVDF2 membrane and PVDF2 / PDA described in the embodiments of the present invention 2.5 Cross-sectional and surface SEM images of the DCN composite membrane; (a) PVDF2 membrane; (b) PVDF2 / PDA 2.5 @DCN composite membrane.

[0029] Figure 9 The PVDF2 / PDA described in the embodiments of the present invention 2.5 @Contact angle measurement diagrams of DCN composite membrane, PVDF2 / DCN composite membrane and PVDF2 membrane.

[0030] Figure 10 The PVDF2 / PDA described in the embodiments of the present invention 2.5 Three-phase diagrams of DCN composite membrane, PVDF2 / DCN composite membrane, and PVDF2 membrane.

[0031] Figure 11 The PVDF2 / PDA described in the embodiments of the present invention 2.5 Viscosity diagrams of @DCN, PVDF2 / DCN, and PVDF2 casting solutions.

[0032] Figure 12 The PVDF2 membrane, PVDF2 / DCN composite membrane, and PVDF2 / PDA described in the embodiments of the present invention. 2.5 The interaction energy between the DCN composite membrane and BSA.

[0033] Figure 13 The figure shows the experimental results of the permeability (pure water flux) and the retention of bovine serum albumin of the DCN and PDA@DCN modified composite membrane described in the embodiments of the present invention.

[0034] Figure 14 The figure shows the cyclic experiment results of the DCN and PDA@DCN modified composite membrane used for filtering bovine serum albumin according to the embodiments of the present invention. Detailed Implementation

[0035] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0036] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as here.

[0038] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or groups thereof.

[0039] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0040] To facilitate understanding of the present invention, the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0041] Those skilled in the art should understand that the accompanying drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily essential for implementing the present invention.

[0042] Example 1

[0043] In this embodiment 1, a method for preparing a GO@DCN modified organic membrane is provided, comprising:

[0044] Step 1) Grind modified carbon nitride (C3N4) and graphene oxide (GO) in a glass mortar at a mass ratio of 1:1 for 50 minutes until completely homogeneous. This mixture is denoted as GO@C3N4 nanocomposite material.

[0045] Step 2) Add GO@C3N4 and pore-forming agent to organic solvent, wherein the mass ratio of GO@C3N4 to pore-forming agent is 1:1-2.5:1, and the mass ratio of pore-forming agent to organic solvent is 1:81-1:84. Sonicate to obtain a mixed solution, and then add polymeric membrane material PFM to the mixed solution, wherein the mass ratio of GO@C3N4 to PFM is 1:6-1:15. Stir at constant temperature, let stand to remove bubbles, and form a casting solution.

[0046] Step 3) Pour the prepared casting solution onto one side of a clean, dry glass plate. Use a square coater to scrape the liquid film. Immerse the glass plate with the scraped liquid film in deionized water for phase exchange. After the casting solution solidifies into a film, remove the film and soak it in deionized water to remove residual organic solvents, thus obtaining the GO@C3N4 modified organic film.

[0047] The graphitic carbon nitride (C3N4) is one of mesoporous g-C3N4 (MCN), nitrogen-rich g-C3N4 (NCN), or defective g-C3N4 (DCN). Graphene oxide (GO) is one of sulfonated graphene oxide or carboxylated graphene oxide. PFM is one of polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile, or polytetrafluoroethylene. The pore-forming agent is one of polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG), and the organic solvent is one of 1-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), or dimethylacetamide (DMAc).

[0048] In step 1), the ultrasonic power is 500W, the ultrasonic time is 1 hour; the constant temperature stirring temperature is 50℃, the speed is 200 rpm, the stirring time is 12 hours; and the settling and degassing time is 12 hours. In step 2), before immersing the glass plate with the prepared liquid film into deionized water for phase exchange, the glass plate with the prepared liquid film needs to be left to stand in air for 15 seconds. In step 2), the liquid film thickness is 250 μm, and the immersion time in deionized water is 24 hours.

[0049] PFM stands for polyvinylidene fluoride (PVDF), and the mass ratio of GO@DCN to PVDF is 1:15.

[0050] In this embodiment, the GO@C3N4 modified organic membrane prepared by the above method and its application in the catalytic degradation of pollutants in water are described.

[0051] In Example 1, the oxygen-containing functional groups of GO inhibited the aggregation of C3N4, while the covalent interaction between C3N4 and GO expanded the interlayer spacing of GO. The ordered interlayer spacing improved the membrane's permeability and stability. This resulted in a 2.3-fold increase in flux and a 91.6% increase in rejection rate of the prepared composite membrane. The accelerated thermodynamic phase transformation of the GO@C3N4 modified organic membrane led to increased porosity, thereby opening channels for water molecules. The GO@C3N4 modified organic membrane is easy to recycle and reuse, solving the problems of difficult material separation and recycling and the potential for secondary pollution. Simultaneously, the increased negative charge of the GO@C3N4 modified organic membrane repelled negatively charged pollutants in the water, enhancing the membrane's antifouling performance. The removal efficiency of the modified membrane for pollutants in water was directly examined at room temperature.

[0052] In Example 1, the prepared C3N4 and GO modified organic membrane was applied to retain target pollutants. The mechanical grinding of C3N4 and GO improved film-forming properties, while the modified organic membrane solved problems such as low flux and severe membrane fouling in ultrafiltration membrane operation. The C3N4 and GO modified organic membrane showed a 2.3-fold increase in flux and a 91.6% increase in BSA rejection rate. It exhibited good membrane structure and performance stability, and the preparation method was simple, mild, and low-cost, making it easy to mass-produce and showing broad application prospects.

[0053] Example 2

[0054] In this embodiment 2, a method for preparing a PDA@C3N4 modified organic membrane is provided, comprising:

[0055] Step 1) Weigh a certain amount of C3N4 nanomaterials and dopamine hydrochloride and sonicate them in Tris buffer (10 mmol·L⁻¹). -1 In a solution of (pH≈8.5), after stirring at 25°C for 24 hours, the mixture was centrifuged, washed, and dried to obtain a polydopamine-encapsulated C3N4 composite material, named PDA@C3N4.

[0056] Step 2) Add PDA@C3N4 and pore-forming agent to organic solvent. The mass ratio of PDA@C3N4 to pore-forming agent is in the range of 1:1-1:3, and the mass ratio of pore-forming agent to organic solvent is in the range of 1:27-1:83. Sonicate to obtain a mixed solution. Add polymeric membrane material PFM to the mixed solution. The mass ratio of PDA@C3N4 to PFM is 1:10-1:15. Stir at constant temperature, let stand to remove bubbles, and form a casting solution.

[0057] Step 3) Pour the casting solution onto a glass plate and scrape it into a liquid film. After exposing it to air for a period of time, immerse the glass plate in deionized water to solidify it and obtain the PDA@C3N4 composite film.

[0058] Graphitic carbon nitride (C3N4) is one of mesoporous g-C3N4 (MCN), nitrogen-rich g-C3N4 (NCN), or defective g-C3N4 (DCN).

[0059] In step 1), the pH of the Tris buffer solution is 7.8-8.5, the dopamine concentration is 1-10 g / L, and the mass ratio of carbon nitride (C3N4) to dopamine is 1:0.2-1:2; the reaction time is 24 h; the temperature is controlled at 25 °C; centrifugation is performed at 10,000 rpm for 5-10 min; the product is washed 3 times with deionized water; and the product is dried in an oven at 60 °C for 8-12 h.

[0060] In step 2), the ultrasonic power is 500W and the ultrasonic time is 1h; the constant temperature stirring temperature is 50℃, the speed is 200rpm, and the stirring time is 12h; the standing degassing time is 12h.

[0061] PFM is one of polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile, or polytetrafluoroethylene.

[0062] The pore-forming agent is one of polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG), and the organic solvent is one of 1-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc).

[0063] Before immersing the glass plate with the prepared liquid film into deionized water for phase exchange in step 3), the glass plate with the prepared liquid film needs to be left to stand in the air for 15 seconds.

[0064] In step 3), the liquid film thickness is 250 μm, and the soaking time in deionized water is 24 h.

[0065] PFM stands for polyvinylidene fluoride (PVDF), and the mass ratio of PDA@C3N4 to PVDF is 1:10-1:15.

[0066] In Example 2, PDA can adhere to the C3N4 surface through covalent, non-covalent interactions, and π-π bonds. PDA attachment to the C3N4 surface provides more hydrophilic groups, increasing the dispersibility of C3N4 in solution and enhancing interfacial compatibility, resulting in more uniform dispersion of PDA@C3N4 in the membrane matrix. The resulting composite membrane exhibits superior hydrophilicity, retention capacity, and antifouling properties, with pure water flux increased by up to 77% compared to the pure membrane, and BSA rejection exceeding 90%. It achieves self-cleaning under visible light irradiation, with a flux recovery rate of 84%, and demonstrates good stability in membrane structure and performance. This method is simple to operate, operates under mild conditions, has low production costs, is easy to mass-produce, and has broad application prospects.

[0067] In Example 2, the prepared C3N4 and PDA-modified organic membrane was applied to the catalytic degradation of organic pollutants in water. The pure water flux of the prepared C3N4 and PDA-modified organic membrane was increased by 77% compared with the pure membrane, and the BSA rejection rate reached over 90%. Furthermore, it could achieve self-cleaning under light irradiation, with a flux recovery rate of 84%. In addition, PDA modification improved the composite membrane's UV resistance, reduced light damage to the membrane structure, and extended the membrane's lifespan. It exhibited good stability in membrane structure and performance, and the preparation method was simple, mild, and low-cost, making it easy to mass-produce and showing broad application prospects.

[0068] Example 3

[0069] This embodiment 3 provides a method for preparing a GO-modified defective carbon nitride (DCN)-modified PVDF ultrafiltration membrane, particularly relating to a method for preparing a PVDF / GO@DCN composite membrane, comprising:

[0070] Step 1) Grind 500mg of defective carbon nitride (DCN) and 500mg of graphene oxide (GO) in a mortar for 50 minutes until homogeneous, and record it as GO@DCN composite material.

[0071] Step 2) Add 33 mg GO@DCN and 33 mg polyvinylpyrrolidone (PVP) to 3000 mg 1-methyl-2-pyrrolidone (NMP), and sonicate in a 500 W ultrasonic cleaner for 1 h to obtain a mixed solution. Then add 500 mg PVDF (i.e., polymeric membrane material PFM) to the mixed solution, stir at 50 °C for 12 h, and let stand for 12 h to remove bubbles to form a casting solution.

[0072] Step 3) Pour the prepared casting solution onto one side of a clean, dry glass plate. Use a square coater to scrape a 250 μm thick liquid film. After the glass plate with the liquid film is scraped is left to stand in the air for 15 seconds, quickly immerse the glass plate in deionized water to complete the phase inversion process. After the casting solution solidifies into a film, take out the film and soak it in deionized water for 24 hours to remove residual NMP solvent, and obtain the PVDF / GO@DCN composite membrane.

[0073] In addition, PVDF / GO, PVDF / DCN, and PVDF / GO@DCN composite films with the following mass ratios were prepared: PVDF / GO was prepared by adding 33 mg of GO nanomaterials, accounting for 1% of the total casting solution mass. 1.0 Add 33 mg of DCN nanomaterial, accounting for 1% of the total casting solution mass, denoted as PVDF / DCN. 1.0 Add 33 mg of GO@DCN nanomaterial, accounting for 1% of the total casting solution mass, denoted as PVDF / GO@DCN. 1.0 Add 49.5 mg of GO@DCN nanomaterial, accounting for 1.5% of the total casting solution mass, denoted as PVDF / GO@DCN. 1.5 Add 66 mg of GO@DCN nanomaterial, accounting for 2% of the total casting solution mass, denoted as PVDF / GO@DCN. 2.0 Add 82.5 mg of GO@DCN nanomaterial, accounting for 2.5% of the total casting solution mass, denoted as PVDF / GO@DCN. 2.5 The amount of PVDF and other materials should be added in proportion.

[0074] Application experiments were conducted using PVDF / GO@DCN composite films obtained at different ratios as described above. Details are as follows:

[0075] Figure 1 Here are the SEM images for this embodiment: (a) is an SEM image of the PVDF membrane surface, showing a smooth surface and low porosity; (b) PVDF / GO@DCN 2.0 The SEM image of the composite membrane surface shows a significant increase in porosity. This is because adding GO@DCN nanocomposite material to the polymer solution can increase the phase transformation rate by increasing thermodynamic instability, thereby increasing the membrane porosity.

[0076] Figure 2 This is a comparison measurement chart of the contact angles of the GO and DCN modified PVDF composite film and the PVDF film in this embodiment, with reference to... Figure 1 It can be seen that the contact angle of the obtained nanocomposite film decreases and follows the rule PVDF > PVDF / DCN. 1.0 PVDF / GO 1.0 >PVDF / GO@DCN 1.0 >PVDF / GO@DCN 2.0 The order. This indicates PVDF / GO@DCN 2.0 The nanocomposite membrane becomes more hydrophilic. Compared to the unmodified pure PVDF membrane with a water contact angle of 72.37°, the PVDF / GO@DCN membrane exhibits a higher water contact angle. 2.0 The water contact angle of the composite membrane decreased to 64.12°, indicating that the hydrophilicity of the membrane was significantly improved after the addition of the nanomaterial GO@DCN. The covalent interaction between DCN and GO altered the interlayer spacing, increased surface roughness, and enhanced the hydrophilicity of the membrane. Furthermore, the addition of GO@DCN significantly improved the hydrophilicity of the membrane by exposing oxygen-containing functional groups and enhancing the polar structure of PVDF, thus transitioning from the α-phase to the β-phase.

[0077] Figure 3 The diagram shows the three-phase diagrams of the GO and DCN-modified PVDF composite membrane and the PVDF membrane in this embodiment. The miscibility gap (the distance between the polymer-solvent axis and the cloud point curve) gradually decreases with the addition of GO, DCN, and GO@DCN, indicating that the liquid-liquid phase separation thermodynamic conversion rate is accelerated, resulting in an increase in the porosity of the composite membrane. Specifically, the PVDF / GO@DCN... 2.0 It exhibits the fastest phase transformation rate and the highest porosity.

[0078] Figure 4 This diagram shows the interaction between the GO and DCN-modified PVDF composite membrane and the PVDF membrane with bovine serum albumin (BSA) in water, as described in this implementation example. It can be seen that the addition of GO, DCN, and GO@DCN-modified PVDF composite membranes has a relatively low attraction for BSA, with the PVDF / DCN membrane showing the strongest effect. 2.0 The reduction by half indicates that the composite membrane's repulsion against bovine serum albumin was greatly enhanced after the addition of the nanomaterial GO@DCN.

[0079] Figure 5 Electrostatic potential distributions of DCN and GO and the interaction of PVDF / GO@DCN obtained from DFT calculations. Figure 5 Images (a) and (b) show that the oxygen-containing functional groups in GO and the nitrogen-deficient regions in the DCN structure possess strong positive and negative charges. Therefore, a strong electrostatic potential penetration is formed between graphene oxide and DCN, enhancing the dispersibility of GO@DCN. Furthermore, RDG analysis was used to investigate the non-covalent interactions between GO@DCN and PVDF molecules, such as... Figure 5 As shown in (c), the presence of low-density green spikes indicates strong van der Waals interactions in the PVDF / GO@DCN system. Meanwhile, the low-density red regions represent weak repulsive forces within the system. Finally, Figure 5 (d) The locations of the aforementioned interactions were determined using VMD software. Van der Waals interactions exist in the interaction layer between GO and DCN, and in the interaction region between PVDF and GO@DCN. Therefore, the strong interactions within the PVDF / GO@DCN system promote membrane permeability and antifouling properties, consistent with the conclusions of thermodynamics and XDLVO.

[0080] Figure 6 The flux of the sample and its retention performance for bovine serum albumin (BSA, molecular weight 66.430 kDa) in water were measured. The addition of hydrophilic materials GO, DCN, and GO@DCN significantly improved the water flux; especially PVDF / GO@DCN. 2.0 The water flux reached 387.80 L / m³. -2 h -1 The addition of GO@DCN effectively improves the hydrophilicity and surface roughness of the membrane; therefore, the membrane can absorb more water molecules. The addition of GO@DCN leads to transient phase separation; this increases the membrane porosity, resulting in better water flux. Simultaneously, all nanocomposite membranes exhibit higher BSA rejection rates than pure PVDF membranes. PVDF / GO@DCN 2.0 The retention rate was the highest, reaching 91.6%.

[0081] After one cycle (90 min), the membrane was hydraulically backwashed and then filtered a second time to evaluate the membrane's reusability. The membrane was evaluated using 5 complete filtration cycles. (Refer to...) Figure 7 In this embodiment, PVDF / GO@DCN 2.0 Even after five uses, the composite membrane still exhibits superior reusability compared to pure PVDF membranes. Therefore, the PVDF / GO@DCN composite membrane demonstrates excellent stability and practical applicability.

[0082] Example 4

[0083] This embodiment provides a method for preparing a polydopamine PDA-modified carbon nitride PDA@C3N4 modified organic membrane, and particularly relates to a method for preparing a PVDF / PDA@DCN composite membrane, comprising:

[0084] Step 1) Weigh a certain amount of DCN nanomaterials and dopamine hydrochloride and sonicate them in Tris buffer (10 mmol·L⁻¹). -1 In a solution with pH ≈ 8.5, the concentration of DCN in the solution was 5 g / L and the concentration of dopamine was 2.5 g / L. The mixture was stirred at 25 °C for 24 h at a stirring speed of 750 rpm. The mixture was then centrifuged at 10,000 rpm for 6 min. The solution was washed three times with deionized water and dried in an oven at 60 °C for 12 h to obtain a polydopamine-attached DCN composite material, named PDA@DCN.

[0085] Step 2) Add 33 mg PDA@DCN and 33 mg polyvinylpyrrolidone (PVP) to 3000 mg 1-methyl-2-pyrrolidone (NMP), sonicate for 1 h to obtain a mixed solution, then add 500 mg PVDF (i.e. polymeric membrane material PFM) to the mixed solution, wherein the mass ratio of PDA@DCN to PFM is 1:15, stir at 50 °C for 12 h, and let stand for 12 h to remove bubbles to form a casting solution;

[0086] Step 3) After degassing, the casting solution is poured onto a glass plate. A 250 μm thick liquid film is scraped using a square coater. The glass plate with the scraped liquid film is left to stand in the air for 15 seconds, and then quickly immersed in deionized water to complete the phase exchange process. After the liquid film solidifies, it is taken out and soaked in deionized water for 24 hours to remove residual solvent, thus obtaining the PVDF / PDA@DCN composite membrane.

[0087] PVDF / PDA@DCN composite membranes with different dopamine to carbon nitride and PVP mass ratios were prepared and named PVDF. X / PDA Y @DCN, where X represents the amount of PVP added in step 2, and Y represents the concentration of dopamine in step 1. PDA concentrations were 1, 2.5, 5, and 10 g / L, and the PVP addition amount was 1-3% of the total casting solution. The PDA@DCN addition amount was 33 mg. Application experiments were conducted using PVDF / PDA@DCN composite membranes obtained with different ratios. Details are as follows:

[0088] Figure 8 This is the SEM image of this embodiment. a1 and b1 are PVDF2 and PVDF2 / PDA, respectively. 2.5 @DCN cross-sectional SEM image. Add PDA 2.5After @DCN, the finger pores of the composite membrane become longer and wider, reducing the resistance to water transport within the membrane. Tables a2 and b2 show PVDF2 and PVDF2 / PDA, respectively. 2.5 @DCN surface SEM image. PVDF2 / PDA 2.5 The number of pores on the @DCN surface is significantly increased, and their distribution is more uniform.

[0089] The hydrophilicity of a composite membrane surface is usually expressed by the static contact angle of pure water on the membrane surface. The smaller the contact angle, the better the hydrophilicity of the membrane surface. Figure 9 This embodiment uses PVDF2 / PDA. 2.5 @Measurement diagram of water contact angle of DCN composite membrane, PVDF2 / DCN composite membrane and PVDF2 membrane. Figure 9 In the middle, PVDF2 / PDA 2.5 The water contact angles of the @DCN composite membrane, PVDF2 / DCN composite membrane, and PVDF2 membrane were 64.2°, 73.2°, and 73.6°, respectively, indicating that the hydrophilicity of the membrane was greatly improved after the addition of the nanomaterial PDA@DCN.

[0090] Figure 10 Compared to PVDF2 and PVDF2 / DCN, PVDF2 / PDA 2.5 The double-nodal line of @DCN is closer to the polymer-solvent axis, indicating that PVDF2 / PDA 2.5 @DCN's casting solution requires minimal non-solvent (water) during phase transition and is thermodynamically the least stable. The poorer the thermodynamic stability of the casting solution, the faster the phase transition, resulting in a composite membrane with higher porosity.

[0091] exist Figure 11 The diagram shows PVDF2, PVDF2 / DCN, and PVDF2 / PDA. 2.5 @DCN casting solution viscosity. PDA 2.5 The viscosity of the DCN / PVDF2 casting solution is less than that of the PVDF2 / DCN solution, but slightly greater than that of the PVDF2 casting solution, indicating that the PDA... 2.5 @DCN reduces the increase in viscosity compared to DCN, and also due to the nanomaterial PDA 2.5 @DCN enhances the hydrophilicity of the casting solution, thereby accelerating the exchange rate between solvent and non-solvent and increasing porosity.

[0092] Figure 12 For PVDF2, PVDF2 / DCN and PVDF2 / PDA 2.5 Interaction diagram of @DCN and BSA. BSA compared to PVDF2 and PVDF2 / DCN with PVDF2 / PDA. 2.5 The total interaction energy between @DCNs decreased by 33% and 25%, respectively. This indicates that PVDF2 / PDA2.5 The DCN composite membrane exhibits reduced BSA attraction, resulting in stronger antifouling capabilities.

[0093] The performance of the composite membrane samples was evaluated by assessing their permeability and contaminant retention. Before testing, the membrane was pre-pressurized at 0.15 MPa for 1 hour, and the average pure water flux was measured. Contaminant retention experiments were performed by filtering bovine serum albumin (BSA, 500 ppm) solution at 0.10 MPa. The filtration performance of the membrane was evaluated by comparing the ratio of ABS values ​​before and after BSA filtration using a UV spectrophotometer. The permeability and BSA retention of the composite membrane were determined by referring to… Figure 13 Optimal performance PVDF1 / PDA 2.5 @DCN composite membrane increases pure water flux by 77% compared to PVDF1 membrane, PVDF2 / PDA 2.5 Compared to the PVDF2 / DCN composite membrane, the @DCN composite membrane increases pure water flux by 34%. While maintaining a higher pure water flux, the PVDF / PDA@DCN composite membrane also exhibits higher BSA rejection, with the optimal performance achieved by the PVDF2 / PDA membrane. 2.5 @DCN composite membrane achieves a BSA rejection rate of 94%, while PVDF2 / DCN composite membrane and PVDF2 membrane have BSA rejection rates of 87% and 85%, respectively.

[0094] After one cycle (90 min), the membrane was hydraulically backwashed and then filtered a second time to evaluate the membrane's reusability. Five complete filtration cycles were used for evaluation. (Refer to...) Figure 14 The PVDF2 / PDA of the present invention 2.5 After five applications, the DCN composite membrane still achieved a BSA removal rate of 91.7%. Optimal performance of PVDF2 / PDA. 2.5 The flux recovery rate of the DCN composite membrane was 62.7%, which is approximately 12.7% higher than that of the PVDF1 membrane. PVDF2 / PDA 2.5 The DCN composite membrane still exhibits the highest pure water flux and BSA flux after multiple cycles, indicating that the PVDF2 / PDA 2.5 @DCN composite membrane has good stability and practical applicability.

[0095] The photocatalytic self-cleaning performance of the samples was assessed by filtering BSA through the prepared membrane for 1 hour, then irradiating it with visible light for 2 hours under a 300W xenon lamp that filters out wavelengths below 420nm. The membrane flux was measured again, and the FRR value was used to evaluate the membrane's self-cleaning ability. Each experiment was repeated three times to ensure accuracy. Figure 14 The image shows the photocatalytic self-cleaning results of the composite membrane for BSA. After 2 hours of visible light irradiation, compared to the 47.7% flux recovery rate of the pure PVDF1 membrane, the PVDF2 / PDA membrane...2.5 The flux recovery rate of the @DCN composite membrane can reach 84.6%, an increase of 36.9%. Meanwhile, Figure 14 Display PVDF2 / PDA 2.5 The @DCN composite membrane maintained good separation performance even after 5 light irradiations, indicating that the PDA@DCN nanoparticles not only have photocatalytic activity and endow the membrane with self-cleaning ability, but also exhibit high performance stability and service life during visible light irradiation.

[0096] In summary, this invention provides a method for preparing and applying organic ultrafiltration membranes modified with graphene oxide (GO) or dopamine (PDA)-modified C3N4 composite materials, addressing the shortcomings of existing technologies. Graphene oxide (GO) is a product of chemical oxidation and exfoliation of graphite powder, possessing advantages such as resistance to organic solvents, rich in oxygen-containing functional groups, ability to reduce interfacial energy, and ease of modification. Furthermore, GO is relatively inexpensive. Combining hydrophilic GO materials with modified C3N4 through mechanical grinding is a simple preparation method that improves the electronegativity and film-forming properties of the material. Polydopamine (PDA) is formed by the auto-oxidative polymerization of dopamine (DA) under weakly alkaline conditions. Through the formation of strong covalent and non-covalent bonds with the matrix at the interface, it can be stably deposited on various inorganic materials. The hydrophilic functional groups in PDA disrupt the van der Waals forces between g-C3N4 particles and enhance solvent compatibility, improving the dispersibility of the composite material in solvents. The hydroxyl (-OH) and amino (-NH) groups in polydopamine can act as electron donors, providing hydrogen atoms to replace free radicals generated during photodegradation and thus limit photodegradation, improving the composite membrane's resistance to photoaging. Modified DCN nanomaterials with GO and PDA promote the exchange rate between solvent and non-solvent during the non-solvent phase transition, increasing the thermodynamic instability of the casting solution, which is beneficial to enhancing the composite membrane's performance in terms of membrane kinetics and thermodynamics. The main strategies for addressing membrane fouling are reducing the interaction forces between contaminants and the membrane surface and improving the self-cleaning properties of contaminants on the membrane surface. Introducing hydrophilically modified carbon nitride nanomaterials can enhance the hydrophilicity and surface electronegativity of the composite membrane, thereby reducing the interaction between contaminants and the membrane surface and decreasing contaminant adhesion.

[0097] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solutions disclosed in the present invention, various modifications or variations that can be made by those skilled in the art without creative effort should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite nanomaterial-modified organic film, characterized in that, include: Modified carbon nitride nanocomposite materials prepared from graphitic carbon nitride nanomaterials and pore-forming agents are added to an organic solvent and ultrasonically treated to obtain a mixed solution. Then, a polymeric membrane material is added to the mixed solution, stirred at a constant temperature, and allowed to stand to remove bubbles to form a casting solution. The modified carbon nitride nanocomposite material is obtained by grinding graphitic carbon nitride nanomaterials and graphene oxide at a mass ratio of 1:

1. Alternatively, the modified carbon nitride nanocomposite material is obtained by ultrasonically dispersing graphitic carbon nitride nanomaterials and dopamine hydrochloride in Tris buffer, centrifuging the mixed solution, washing, and drying to obtain polydopamine-encapsulated C3N4 composite material. The composite nanomaterial-modified organic membrane was prepared using the prepared casting solution.

2. The method for preparing the composite nanomaterial-modified organic film according to claim 1, characterized in that, When the modified carbon nitride nanocomposite material is obtained by grinding graphitic carbon nitride nanomaterials and graphene oxide at a mass ratio of 1:1, the mass ratio of the modified carbon nitride nanocomposite material to the pore-forming agent is 1:1-2.5:1, the mass ratio of the pore-forming agent to the organic solvent is 1:81-1:84, and the mass ratio of the modified carbon nitride nanocomposite material to the polymer membrane material is 1:6-1:

15.

3. The method for preparing the composite nanomaterial-modified organic film according to claim 1, characterized in that, When the modified carbon nitride nanocomposite is a polydopamine-encapsulated C3N4 composite material, the mass ratio of the modified carbon nitride nanocomposite to the pore-forming agent ranges from 1:1 to 1:3, the mass ratio of the pore-forming agent to the organic solvent ranges from 1:27 to 1:83, and the mass ratio of the modified carbon nitride nanocomposite to the polymeric membrane material is 1:10 to 1:

15.

4. The method for preparing the composite nanomaterial-modified organic film according to claim 1, characterized in that, The Tris buffer solution has a pH of 7.8-8.5, a dopamine concentration of 1-10 g / L, and a mass ratio of graphitic carbon nitride nanomaterials to dopamine of 1:0.2-1:

2.

5. The method for preparing the composite nanomaterial-modified organic film according to claim 1, characterized in that, The graphitic carbon nitride nanomaterials are one of mesoporous g-C3N4, nitrogen-rich g-C3N4, or defective g-C3N4.

6. The method for preparing the composite nanomaterial-modified organic film according to claim 1, characterized in that, The polymeric membrane material is one of polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile, or polytetrafluoroethylene.

7. The method for preparing the composite nanomaterial-modified organic film according to claim 1, characterized in that, The pore-forming agent is polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG).

8. The method for preparing the composite nanomaterial-modified organic film according to claim 1, characterized in that, The organic solvent is one of 1-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), or dimethylacetamide (DMAc).

Images