Dopa / pei-mxene / pvdf hydrophilic anti-pollution composite membrane, and preparation method and application thereof

Abstract

The application provides a DOPA / PEI-MXene / PVDF hydrophilic anti-pollution composite membrane and a preparation method and application thereof, and relates to the technical field of separation membrane manufacturing for water treatment. In the phase inversion process, the MXene / PVDF composite membrane is prepared in situ, the MXene nanosheet is fixed on the membrane surface at the same time when the membrane is formed, in order to prevent the MXene nanosheet from falling off on the membrane surface, the DOPA / PEI deposition solution is prepared to cross-link and fix the MXene nanosheet on the membrane surface, the hydrophilicity and the anti-pollution performance of the composite membrane are improved, and the filtering and separating efficiency of the composite membrane is improved.

Description

Technical Field

[0001] This invention relates to the field of separation membrane manufacturing technology for water treatment, specifically to a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation wastewater treatment technology is one of the most effective strategies for improving water quality and alleviating water scarcity. However, the accumulation of organic, inorganic, and biological pollutants on the membrane leads to membrane fouling, which reduces membrane permeability and shortens membrane lifespan, limiting the further development of membrane technology. Therefore, fouling mitigation strategies have become a major technical challenge for the widespread application of membrane separation wastewater treatment technology.

[0003] Previous research has shown that hybrid matrix membranes, made by incorporating nanomaterials into polymer membrane matrices, benefit from the strong hydrophilicity, high surface area, abundant pores, and effective antibacterial properties of the nanomaterials themselves. This leads to improved hydrophilicity, increased negative potential, increased porosity and permeability, and tunable pore structure, thus enhancing the antifouling ability of the hybrid matrix membrane. Currently, the main methods for preparing hybrid matrix membranes include blending and deposition. Blending involves mixing nanoparticles into a polymer solution before membrane casting, while deposition involves depositing nanoparticles onto the membrane surface. While blending is simpler, it doesn't fully utilize the functionality of the nanoparticles because most are trapped within the membrane matrix rather than on the surface, leading to agglomeration during the blending process. Compared to blending, deposition better utilizes the functionality of the nanoparticles; however, it may require additional processing steps to ensure stable bonding of the nanoparticles to the membrane surface. Therefore, a simple and effective membrane modification method is still needed to prepare cost-effective hybrid matrix membranes.

[0004] Polyvinylidene fluoride (PVDF) membranes are highly favored due to their high thermal stability, excellent mechanical properties, and good chemical resistance. However, the inherent strong hydrophobicity of PVDF membranes limits their development in the field of water treatment. Transition metal carbonitrides (MXenes), as an emerging hydrophilic two-dimensional nanomaterial, possess high hydrophilicity, mechanical stability, and thermal conductivity, making them ideal materials for membrane modification development. Currently, the main preparation methods for MXene / PVDF composite membranes include blending and vacuum filtration. Vacuum filtration cannot accurately control the membrane thickness by adjusting the amount and mass difference of the solution. When the MXene layer is too thick, the interfacial structure between MXene and PVDF may be unstable, and the surface active layer may easily peel off, negatively impacting the quality of the composite membrane. This drawback limits this method to the experimental stage, resulting in low production efficiency and making it difficult to use for large-scale industrial production. Summary of the Invention

[0005] The purpose of this invention is to provide a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane, its preparation method, and its applications. Compared to unmodified pure PVDF membranes, the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared by this invention exhibits significantly improved hydrophilicity and membrane flux. Furthermore, it prevents MXene nanosheets from detaching from the membrane surface and demonstrates high rejection rates for large molecular proteins (e.g., bovine serum albumin BSA) and anionic dyes (Congo red (CR)). It also improves membrane flux recovery and can be widely applied in water treatment. The preparation process of this invention is simple, with high modification efficiency and low cost, resulting in significant economic benefits and enabling large-scale industrial production.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane, comprising the following steps:

[0008] The MAX phase raw material was placed in an acidic solution and stirred and etched to obtain MXene nanosheets;

[0009] The MXene nanosheets were mixed with water to obtain an MXene water coagulation bath;

[0010] Polyvinylidene fluoride powder, pore-forming agent and organic solvent are mixed to obtain PVDF casting solution;

[0011] The PVDF casting solution is coated onto a nonwoven fabric, then immersed in the MXene aqueous coagulation bath, and dried to obtain an MXene / PVDF composite membrane.

[0012] Dopamine hydrochloride and polyethyleneimine were dissolved in Tris-HCl buffer solution to obtain a precipitation solution;

[0013] The MXene / PVDF composite membrane was immersed in the deposition solution, and the resulting composite membrane was removed and dried to obtain a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane.

[0014] Preferably, the acidic solution comprises fluoride and hydrochloric acid; the concentration of the hydrochloric acid is 5-10 mol / L; and the ratio of the amount of fluoride to hydrochloric acid is 1 g: 20-50 mL.

[0015] Preferably, the temperature of the stirring etching is 30–50°C; the stirring speed of the stirring etching is 20–50 rpm; and the stirring etching time is 24–72 h.

[0016] Preferably, the mass ratio of MXene nanosheets to water in the MXene aqueous coagulation bath is 1:1000 to 25000.

[0017] Preferably, the mass ratio of the polyvinylidene fluoride powder, the pore-forming agent, and the organic solvent is 1:1 to 5:6 to 10;

[0018] The pore-forming agent includes at least one of polyvinylpyrrolidone and polyethylene glycol;

[0019] The organic solvent includes at least one of dimethyl sulfoxide and N,N-dimethylacetamide.

[0020] Preferably, the soaking temperature is 20–30°C; and the soaking time is 12–24 hours.

[0021] Preferably, the MXene / PVDF composite membrane comprises a nonwoven fabric, a PVDF substrate membrane loaded on the nonwoven fabric, and MXene nanosheets loaded on the PVDF substrate membrane.

[0022] Preferably, the mass ratio of polyethyleneimine to dopamine hydrochloride is 1:1 to 3;

[0023] The concentration of the Tris-HCl buffer solution is 0.01–1 mol / L, and the pH value is 8–9.

[0024] The present invention provides a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared by the preparation method described above.

[0025] This invention provides the application of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane described above in the field of water treatment.

[0026] This invention provides a method for preparing a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane. The method involves in-situ preparation of the MXene / PVDF composite membrane during phase transformation. MXene nanosheets are immobilized on the membrane surface simultaneously with the formation of the PVDF substrate membrane. To prevent MXene nanosheets from detaching from the membrane surface, a DOPA / PEI deposition solution is used to crosslink and immobilize the MXene nanosheets on the membrane surface, thereby improving the hydrophilicity and antifouling properties of the composite membrane and enhancing its filtration and separation efficiency. After modification, the flux of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane is increased by 71.43%, the BSA rejection rate reaches 94.57%, the flux recovery rate reaches 82.68%, and the CR rejection rate reaches 82.68%.

[0027] Furthermore, the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane provided by this invention enhances hydrophilicity, improves the retention rates of BSA and CR, exhibits high antifouling properties, excellent reusability and chemical stability, has a relatively simple process, can greatly improve production efficiency, reduce production costs, and is suitable for large-scale industrial production. Attached Figure Description

[0028] Figure 1 EDS spectra of MXene nanosheets prepared for the example;

[0029] Figure 2 Contact angle and zeta potential diagram of MXene nanosheets prepared for the example;

[0030] Figure 3 FTIR spectra of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the example and the MXene / PVDF composite membrane prepared for the comparative example;

[0031] Figure 4 The contact angles of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the example and the MXene / PVDF composite membrane prepared for the comparative example;

[0032] Figure 5 The BSA and CR rejection rates of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the example and the MXene / PVDF composite membrane prepared for the comparative example;

[0033] Figure 6 Pure water flux of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the example and the MXene / PVDF composite membrane prepared for the comparative example;

[0034] Figure 7 Antifouling properties analysis of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the examples and the MXene / PVDF composite membrane prepared for the comparative examples. Detailed Implementation

[0035] This invention provides a method for preparing a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane, comprising the following steps:

[0036] The MAX phase raw material was placed in an acidic solution and stirred and etched to obtain MXene nanosheets;

[0037] The MXene nanosheets were mixed with water to obtain an MXene water coagulation bath;

[0038] Polyvinylidene fluoride (PVDF) powder, a pore-forming agent, and an organic solvent are mixed to obtain a PVDF casting solution.

[0039] The PVDF casting solution is coated onto a nonwoven fabric, then immersed in the MXene aqueous coagulation bath, and dried to obtain an MXene / PVDF composite membrane.

[0040] Dopamine hydrochloride (DOPA) and polyethyleneimine (PEI) were dissolved in Tris-HCl buffer solution to obtain a precipitation solution;

[0041] The MXene / PVDF composite membrane was immersed in the deposition solution, and the resulting composite membrane was removed and dried to obtain a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane.

[0042] This invention involves placing a MAX phase raw material in an acidic solution and then stirring and etching it to obtain MXene nanosheets. In this invention, the MAX phase raw material is preferably Ti3AlC2 powder; the particle size of the MAX phase raw material is preferably 20–50 μm, more preferably 30–38 μm. In this invention, the mass ratio of the MAX phase raw material to the acidic solution is preferably 1 g: 20–50 mL, more preferably 1 g: 30–40 mL.

[0043] In this invention, the acidic solution preferably comprises a fluoride and hydrochloric acid. The fluoride preferably comprises a fluoride salt, more preferably lithium fluoride, sodium fluoride, potassium fluoride, or ammonium fluoride. The concentration of the hydrochloric acid is preferably 5–10 mol / L, more preferably 6–9 mol / L. The ratio of fluoride to hydrochloric acid is preferably 1 g: 20–50 mL, more preferably 1 g: 30–40 mL.

[0044] In this invention, the temperature of the stirring etching is preferably 30-50°C, more preferably 40-45°C; the stirring speed of the stirring etching is preferably 20-50 rpm, more preferably 30-45 rpm; and the stirring etching time is preferably 24-72 h, more preferably 36-48 h.

[0045] Preferably, after the stirring etching, the resulting etched system is acid-washed, centrifuged, and the supernatant is removed. The system is then repeatedly washed with water until the pH of the reaction solution is neutral, followed by vacuum drying to obtain MXene nanosheets. In this invention, the acid washing reagent is preferably an aqueous hydrochloric acid solution; the volume ratio of hydrochloric acid to water in the aqueous hydrochloric acid solution is preferably 1:1 to 5, more preferably 1:1; the concentration of the hydrochloric acid is preferably 12 mol / L. In this invention, the centrifugation speed is preferably 3000 to 15000 rpm, more preferably 5000 to 10000 rpm; the centrifugation time is preferably 5 to 10 min, more preferably 6 to 8 min. In this invention, the vacuum drying temperature is preferably 60 to 100℃, more preferably 70 to 80℃; the vacuum drying time is preferably 12 to 24 h, more preferably 24 h.

[0046] In this invention, the thickness of the MXene nanosheets is preferably 2 to 15 μm; the sheet diameter is preferably 700 to 900 nm.

[0047] After obtaining MXene nanosheets, the present invention mixes the MXene nanosheets with water to obtain an MXene aqueous coagulation bath. In the present invention, the water is preferably deionized water. In the present invention, the mixing is preferably carried out under ultrasonic conditions. In the present invention, the ultrasonic time is preferably 20–40 min, more preferably 30 min.

[0048] In this invention, the mass ratio of MXene nanosheets to water in the MXene aqueous coagulation bath is preferably 1:1000 to 25000, more preferably 1:1250 to 20000.

[0049] This invention involves mixing PVDF powder, a pore-forming agent, and an organic solvent to obtain a PVDF casting solution. In this invention, the preferred mass ratio of the PVDF powder, pore-forming agent, and organic solvent is 1:1 to 5:6 to 10, more preferably 1:1 to 3:6 to 8. In this invention, the preferred particle size of the PVDF powder is 100 to 200 μm, more preferably 120 to 180 μm. In this invention, the pore-forming agent preferably includes at least one of polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG); when the pore-forming agent contains both PVP and PEG, the preferred mass ratio of PVP to PEG is 1:1. In this invention, the preferred molecular weight of the PVP is 44,000 to 54,000, more preferably 40,000; the preferred molecular weight of the PEG is 200 to 800, more preferably 400. In this invention, the organic solvent preferably includes at least one of dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMAc); when the organic solvent contains both DMSO and DMAc, the mass ratio of DMSO to DMAc is preferably 1:1.

[0050] In this invention, the mixing of PVDF powder, pore-forming agent, and organic solvent preferably includes adding PVDF powder to a mixed solution containing the pore-forming agent and organic solvent. In this invention, the mixing is preferably carried out under heating and stirring conditions; the heating and stirring temperature is preferably 60–80°C, more preferably 70–80°C; the heating and stirring time is preferably 12–24 hours, more preferably 12–20 hours. In this invention, the heating and stirring is preferably performed using a glass rod. Compared with mechanical stirring, manual glass rod stirring allows for a more complete reaction of the organic solvent and avoids the problem of PVDF powder agglomeration.

[0051] After obtaining the PVDF casting solution, the present invention coats the PVDF casting solution onto a nonwoven fabric, then immerses it in the MXene aqueous coagulation bath, and dries it to obtain an MXene / PVDF composite membrane. In the present invention, the PVDF casting solution preferably includes a degassing treatment before coating. In the present invention, the degassing treatment is preferably static degassing. In the present invention, the vacuum degassing temperature is preferably 60–80°C, more preferably 70–80°C. In the present invention, the degassing treatment is preferably carried out in a vacuum drying oven. In the present invention, the degassing treatment time is preferably 1–3 hours, more preferably 2 hours.

[0052] In this invention, the coating method is preferably coating; the equipment used for coating is preferably a film scraper. In this invention, the coating thickness is preferably set to 200-300 μm, more preferably 250 μm; the settling time after coating is preferably 10-30 s, more preferably 20-30 s.

[0053] In this invention, the nonwoven fabric preferably comprises polyester nonwoven fabric.

[0054] In this invention, the soaking temperature is 20–30°C, more preferably 25°C; the soaking time is preferably 12–24 hours, more preferably 20–24 hours. During the soaking process, the material undergoes a phase transformation.

[0055] In this invention, the drying temperature is preferably 40-80°C, more preferably 45-60°C; the drying time is preferably 5-12 hours, more preferably 8-10 hours.

[0056] In this invention, the MXene / PVDF composite membrane comprises a nonwoven fabric, a PVDF substrate membrane loaded on the nonwoven fabric, and MXene nanosheets loaded on the PVDF substrate membrane. In this invention, the particle size of the MXene nanosheets is preferably 700–900 nm. In this invention, the thickness of the PVDF substrate membrane is preferably 205–215 μm.

[0057] This invention involves dissolving DOPA and PEI in a Tris-HCl buffer solution to obtain a deposition solution. In this invention, the mass ratio of PEI to DOPA is preferably 1:1 to 3, more preferably 1:2.1 to 2.5. In this invention, the concentration of the Tris-HCl buffer solution is preferably 0.01 to 1 mol / L, more preferably 0.05 mol / L; the pH value is preferably 8 to 9, more preferably 8.5. In this invention, the concentration of DOPA in the deposition solution is preferably 1 to 2 g / L, more preferably 1.2 to 1.5 g / L; the concentration of PEI in the deposition solution is preferably 0.5 to 1 g / L, more preferably 0.6 to 0.8 g / L.

[0058] After obtaining the deposition solution, the present invention immerses the MXene / PVDF composite membrane in the deposition solution, removes the resulting composite membrane, and dries it to obtain a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane. In the present invention, before immersing the MXene / PVDF composite membrane in the deposition solution, it preferably further includes: first immersing the MXene / PVDF composite membrane in anhydrous ethanol, washing with deionized water and drying it, and then immersing it in anhydrous ethanol a second time. In the present invention, the first immersion time of the MXene / PVDF composite membrane in anhydrous ethanol is preferably 10–60 min, more preferably 30–50 min; the drying temperature is preferably 40–60°C, more preferably 45–55°C; the drying time is preferably 2–5 h, more preferably 3–4 h; and the second immersion time in anhydrous ethanol is preferably 1–10 min, more preferably 2–8 min.

[0059] The purpose of the above-mentioned operation in this invention is to prevent MXene from falling off the surface of the composite film and to prepare a DOPA / PEI coating to form a mesh structure that can fix MXene.

[0060] In this invention, the immersion is performed in a constant-temperature incubator with an oscillator. The immersion temperature of the MXene / PVDF composite membrane in the deposition solution is preferably 30–60°C, more preferably 40–50°C; the immersion is preferably performed under oscillation conditions; the oscillation time is preferably 2–10 h, more preferably 5–8 h; and the oscillation speed is preferably 120–200 r / min, more preferably 160–180 r / min.

[0061] In this invention, the MXene / PVDF composite membrane is immersed in the deposition solution to form a coating on the surface of the composite membrane to fix MXene nanosheets.

[0062] In this invention, after the obtained composite membrane is removed, it is preferably cleaned with deionized water to remove any loosely coated material, and then dried. In this invention, the drying is preferably vacuum drying. In this invention, the drying temperature is preferably 40–60°C, more preferably 45°C; the drying time is preferably 12–24 hours, more preferably 12 hours.

[0063] This invention provides a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared by the preparation method described above. In this invention, the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane comprises a nonwoven fabric, a PVDF substrate membrane loaded on the nonwoven fabric, and MXene nanosheets in situ modified on the surface of the PVDF substrate membrane, and a DOPA / PEI deposition layer with cross-linked and fixed MXene nanosheets. In this invention, the thickness of the DOPA / PEI deposition layer is preferably 10–30 nm, more preferably 15–20 nm.

[0064] This invention utilizes the reaction of PEI with DOPA. PEI forms a network structure that immobilizes MXene through electrostatic attraction and hydrogen bonding, resulting in a uniform and stable coating and improving the integrity of the DOPA thin film. Finally, negatively charged MXene nanosheets are immobilized on the membrane surface through electrostatic interactions between PEI and MXene. Furthermore, the amino groups in PEI can form strong hydrogen bonds with the oxygen groups in MXene, facilitating the formation of a hydrophilic layer on the membrane surface.

[0065] The present invention provides the application of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane described above in the field of water treatment, preferably as a separation membrane for separating macromolecular proteins or anionic dyes.

[0066] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0067] Example

[0068] (1) Weigh 6g of LiF raw material and 180mL of hydrochloric acid (mass concentration of 9mol / L) and add them to a polytetrafluoroethylene etching cup for magnetic stirring to obtain a mixture; then weigh 6g of aluminum carbide (Ti3AlC2) and slowly add it to the mixture in multiple batches, heat it to 40℃ under a magnetic stirrer, stir at 45rpm, and etch for 48h;

[0069] (2) After the reaction is complete, prepare a hydrochloric acid aqueous solution with a volume ratio of 1:1 of water and hydrochloric acid (concentration of 12 mol / L) as the acid washing reagent. Wash the reactants obtained in step (1) with acid and centrifuge several times until the hydrochloric acid aqueous solution is used up. The centrifuge speed is 10000 rpm and centrifuge for 8 minutes each time. Discard the supernatant liquid after acid washing, add distilled water, shake well and centrifuge, discard the supernatant liquid, and repeat the water washing until the water washing liquid is neutral.

[0070] (3) The obtained powder was vacuum dried at 80°C for 24 hours to obtain MXene nanosheets.

[0071] (4) Weigh 0.3g, 1.2g, 2.4g and 4.8g of the MXene nanosheets respectively and add them to 50mL of deionized water and sonicate to mix evenly. Then add them to a coagulation bath containing 5.95L of deionized water to obtain MXene water coagulation baths, which are numbered M1 (corresponding to 0.3g of MXene nanosheets), M2 (corresponding to 1.2g of MXene nanosheets), M3 (corresponding to 2.4g of MXene nanosheets) and M4 (corresponding to 4.8g of MXene nanosheets).

[0072] (5) Weigh 80 mL of DMSO and 80 mL of DMAc organic solvent and place them in a wide-mouth bottle. Mix them evenly with a glass rod. Add 20 mL of PEG porogen (molecular weight of 400 Da) and mix. Then slowly add 20 g of PVDF powder (particle size of 120 μm) several times. Place the mixture in an electric heating drying oven at 80 °C and stir with a glass rod for 12 h to obtain PVDF casting solution.

[0073] (6) The PVDF casting liquid was placed in a vacuum oven at 80°C for 2 hours to remove bubbles. The thickness of the scraper blade of the scraper was adjusted to 250μm. The liquid was then coated onto the nonwoven fabric and evaporated for 30 seconds to obtain the PVDF / nonwoven fabric composite material.

[0074] Four PVDF / nonwoven composite materials were prepared according to the methods in steps (5) to (6). They were placed in the MXene hydrosolidization bath (M1, M2, M3, M4) described in step (4) and soaked for 24 hours. Finally, they were dried in a drying oven at 45°C for 8 hours to obtain MXene / PVDF composite films, which were numbered MD1 (corresponding to M1), MD2 (corresponding to M2), MD3 (corresponding to M3), and MD4 (corresponding to M4) in sequence.

[0075] (7) MD1, MD2, MD3 and MD4, which are circular films with a radius of 4.5 cm, were first immersed in anhydrous ethanol for 30 min, washed with deionized water and then placed in a drying oven at 45°C for 3 h for pretreatment to clean impurities from the film surface.

[0076] (8) Weigh 0.3g DOPA and 150μL PEI and dissolve them in 250mL of 0.05mol / L Tris-HCl buffer solution with a pH of 8.5. Mix well to obtain a sedimentation solution.

[0077] (9) After cleaning in step (7), MD1, MD2, MD3 and MD4 were immersed in anhydrous ethanol for 2 min for the second time, and then placed in the deposition solution described in step (8). They were shaken at 40°C for 5 h in a constant temperature incubator with a rotation speed of 160 r / min. DOPA and PEI were crosslinked to fix MXene nanosheets on the membrane surface.

[0078] (10) Take out MD1, MD2, MD3 and MD4 after soaking in step (9), wash them with deionized water, and then vacuum dry them at 45℃ for 12h to obtain DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membranes, which are numbered as MP1 (corresponding to MD1), MP2 (corresponding to MD2), MP3 (corresponding to MD3) and MP4 (corresponding to MD4) in sequence.

[0079] Comparative Example

[0080] Using M3 in the examples as the MXene water coagulation bath, an MXene / PVDF composite membrane, designated M0, was prepared according to the method described in the examples.

[0081] Structural characterization

[0082] According to the preparation method of the above embodiments, the nonwoven fabric in the embodiments was changed to a glass plate to prepare a hydrophilic antifouling MXene / PVDF composite membrane for structural characterization.

[0083] EDS spectra of the MXene nanosheets prepared in the examples are shown below. Figure 1 As shown, the prepared MXene nanosheets contain C, O, Ti, and F elements, but not Al elements, indicating that the etching was successful.

[0084] The contact angle and zeta potential diagrams of the MXene nanosheets prepared in the examples are shown below. Figure 2 As shown, the prepared MXene nanosheets are hydrophilic and have a negative potential.

[0085] The FTIR spectra of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared in the examples and the MXene / PVDF composite membrane prepared in the comparative examples are shown below. Figure 3 As shown, it can be seen that at 878cm -1 and 1402cm -1 The vibration at 1273cm is caused by the deformation of CF2. -1It exhibits -CF3 tensile vibration. 3100-3500cm -1 The broad peak at 2917 cm⁻¹ represents the OH stretching vibration and the NH stretching vibration. -1 The adsorption peak at 1748 cm⁻¹ is due to CH stretching. -1 The absorption peaks around 1654 cm⁻¹ are due to the C=O vibration. -1 The absorption peaks on the left and right sides are due to the C=N vibration, at 1531 cm⁻¹. -1 The absorption peaks around 761 cm⁻¹ indicate NH vibration, suggesting successful coating. -1 The peak at 840 cm⁻¹ belongs to the α-phase crystallization of PVDF material. -1 The peak belongs to the β-phase crystallization, and the membrane preparation process can transform the α-phase of PVDF into the β-phase.

[0086] Test Example 1

[0087] MP1, MP2, MP3, MP4, and M0 were placed in MSC-300 ultrafiltration cups to test pure water flux and antifouling performance. The membranes to be tested (MP1, MP2, MP3, MP4, or M0) were loaded into the ultrafiltration cups, and pure water was introduced through the upper solution inlet. After ensuring the ultrafiltration cups were airtight, the gas cylinder and valve were opened, allowing water molecules to pass through the membrane pores under gas pressure. The filtered water flowed out from the lower outlet, and the membrane was pre-pressurized at 0.1 MPa for half an hour. First, the pure water flux (Jw1) was measured, then the flux of a 1 g / L BSA solution (Jp) was measured to simulate protein contamination. After cleaning the contaminated membrane, the pure water flux of the cleaned membrane was measured again (Jw2).

[0088] BSA standard solutions of 0.1 g / L, 0.3 g / L, 0.5 g / L, 0.7 g / L, 0.9 g / L, and 1.0 g / L were prepared for use. The BSA solutions of different concentrations were tested at 280 nm using a TU-1950 UV-Vis spectrophotometer. Based on the absorbance, a BSA standard curve was obtained, y = 0.5801x, where x is the concentration of the BSA solution in g / L and y is the absorbance.

[0089] The formula for calculating the pure water flux (Jw1) is shown in Equation 1:

[0090] In Equation 1, Jw1 represents the pure water flux, with units of L·m -2 ·h -1 V1 represents the volume of pure water, in liters (L); A1 represents the effective area of ​​the membrane under test, in square meters (m²). 2 T1 represents the filtration time, in hours (h).

[0091] The formula for calculating the BSA solution flux (Jp) is shown in Equation 2:

[0092] In Equation 2, Jp represents the BSA solution flux, with units of L·m -2 ·h -1 V P The volume of the BSA solution is expressed in liters (L); A P This represents the effective area of ​​the membrane under test, in meters (m²). 2 ;T P This indicates the filtration time, in hours (h).

[0093] The formula for calculating the pure water flux (Jw2) of the cleaning membrane is shown in Equation 3:

[0094] In Equation 3, Jw2 represents the pure water flux of the cleaning membrane, in L·m -2 ·h -1 V2 represents the volume of pure water, in liters (L); A2 represents the effective area of ​​the cleaning membrane, in square meters (m²). 2 T2 represents the filtration time, in hours (h).

[0095] The formula for calculating the BSA rejection rate (R) is shown in Equation 4:

[0096] In Equation 4, R represents the BSA rejection rate, in percentage (%); C f This indicates the initial concentration of the BSA solution, in g / L; C p This indicates the concentration of the filtered solution calculated using the BSA standard curve, expressed in g / L.

[0097] The formula for calculating flux recovery rate (FRR) is shown in Equation 5:

[0098]

[0099] The formula for calculating the total pollution rate (Rt) is shown in Equation 6:

[0100]

[0101] The formula for calculating the reversible contamination rate (Rr) is shown in Equation 7:

[0102]

[0103] The formula for calculating the irreversible contamination rate (Rir) is shown in Equation 8:

[0104]

[0105] Test Example 2

[0106] MP1, MP2, MP3, MP4, and M0 were soaked in deionized water for 12 hours to remove surface impurities, and then dried in a vacuum drying oven at 45°C for 3 hours. An 800 mg / L Congo red solution was prepared. The membrane to be tested was placed in an ultrafiltration cup, and the Congo red solution was introduced through the upper solution inlet. After ensuring the ultrafiltration cup was airtight, the gas cylinder and valve were opened, and the membrane was subjected to a pressure of 0.03 MPa to obtain Congo red filtrate. Congo red standard solutions of 10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, 80 mg / L, and 100 mg / L were prepared for later use. The different concentrations of Congo red were tested at 488 nm using a TU-1950 UV-Vis spectrophotometer. Based on the absorbance, a Congo red standard curve was obtained: y = 0.0079x, where x is the concentration of the Congo red solution in g / L, and y is the absorbance. The formula for calculating the rejection rate (R) of Congo red is shown in Equation 9:

[0107]

[0108] In Equation 9, R represents the rejection rate of Congo red, C0 is the initial concentration of the Congo red solution in mg / L, and C1 is the concentration of the filtered solution calculated using the Congo red standard curve in mg / L.

[0109] Test Example 3

[0110] Five sheets of MP1, MP2, MP3, MP4, and M0 were cut to a size of 2.5cm × 7cm. After soaking in distilled water for 24 hours, they were dried in a 45℃ oven for 12 hours. The sheets were then attached to glass slides with double-sided tape, and the contact angles of the membrane surfaces were measured using a contact angle meter. Pure water was used as the liquid medium for measuring the membrane contact angles under constant room temperature and humidity conditions. The droplet volume was set to 4μL, and measurements were taken at five different points for each sample, with the average value calculated.

[0111] Figure 4 The contact angles of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the example and the MXene / PVDF composite membrane prepared for the comparative example; Figure 5 The BSA and CR rejection rates of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the example and the MXene / PVDF composite membrane prepared for the comparative example; Figure 6 Pure water flux of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the example and the MXene / PVDF composite membrane prepared for the comparative example; Figure 7 Antifouling properties of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared for the examples and the MXene / PVDF composite membrane prepared for the comparative examples were analyzed. Figures 4-7The results show that the composite membrane M0, modified solely by in-situ with MXene nanosheets, has a contact angle of 45.18° and a pure water flux of 246 L / (m²). 2 The rejection rates for BSA and CR were 96.28% and 92.65%, respectively. The flux recovery rate after physical cleaning following BSA filtration was 72.59%, and the reversible fouling rate was 17.48%. This is because the hydrophilic MXene sheets deposited on the membrane surface altered the hydrophilicity of the composite membrane.

[0112] The pure water flux of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane is significantly improved compared with that of the MXene / PVDF composite membrane. Furthermore, the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane exhibits good flux recovery. The contact angles of the modified membranes MP1, MP2, MP3, and MP4 are 27.10°, 22.41°, 18.27°, and 23.55°, respectively, with pure water fluxes of 198 L / (m²). 2 ·h), 414L / (m 2 ·h), 693L / (m 2 ·h), 379L / (m 2 The rejection rates for BSA were 91.02%, 93.21%, 94.57%, and 92.53%, respectively, while the rejection rates for CR were 91.9%, 88.72%, 86.84%, and 86.15%, respectively. The flux recovery rates were 66.70%, 77.95%, 82.68%, and 67.02%, respectively, and the reversible fouling rates were 26.35%, 20.94%, 19.56%, and 16.46%, respectively. The decrease in flux and rejection rate of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane may be due to the fact that the higher the concentration of MXene nanosheets in the coagulation bath, the more nanosheets will be deposited on the membrane surface, thus clogging some of the surface pores.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane, characterized in that, Includes the following steps: The MAX phase raw material was placed in an acidic solution and stirred and etched to obtain MXene nanosheets; The MXene nanosheets were mixed with water to obtain an MXene water coagulation bath; Polyvinylidene fluoride powder, pore-forming agent and organic solvent are mixed to obtain PVDF casting solution; The PVDF casting solution is coated onto a nonwoven fabric, then immersed in the MXene aqueous coagulation bath, and dried to obtain an MXene / PVDF composite membrane; the immersion temperature is 20~30℃; the immersion time is 12~24h; Dopamine hydrochloride and polyethyleneimine were dissolved in Tris-HCl buffer solution to obtain a precipitation solution; The MXene / PVDF composite membrane was immersed in the deposition solution, and the resulting composite membrane was removed and dried to obtain a DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane. The temperature of the stirring etching is 30~50℃; the stirring speed of the stirring etching is 20~50rpm; and the stirring etching time is 24~72h. The mass ratio of MXene nanosheets to water in the MXene aqueous coagulation bath is 1:1000~25000; The mass ratio of the polyvinylidene fluoride powder, the pore-forming agent, and the organic solvent is 1:1~5:6~10; The pore-forming agent includes at least one of polyvinylpyrrolidone and polyethylene glycol; The organic solvent includes at least one of dimethyl sulfoxide and N,N-dimethylacetamide.

2. The preparation method according to claim 1, characterized in that, The acidic solution comprises fluoride and hydrochloric acid; the concentration of the hydrochloric acid is 5-10 mol / L; the ratio of the amount of fluoride to hydrochloric acid is 1 g: 20-50 mL.

3. The preparation method according to claim 1, characterized in that, The MXene / PVDF composite membrane includes a nonwoven fabric, a PVDF substrate membrane loaded on the nonwoven fabric, and MXene nanosheets loaded on the PVDF substrate membrane.

4. The preparation method according to claim 1, characterized in that, The mass ratio of polyethyleneimine to dopamine hydrochloride is 1:1~3; The concentration of the Tris-HCl buffer solution is 0.01~1 mol / L, and the pH value is 8~9.

5. The DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the DOPA / PEI-MXene / PVDF hydrophilic antifouling composite membrane as described in claim 5 in the field of water treatment.

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