Preparation method and application of renewable cellulose-based ultrafiltration membrane with closed-loop recoverability

Abstract

The invention discloses a preparation method and application of a renewable cellulose-based ultrafiltration membrane with closed-loop recoverability, and the preparation method of the ultrafiltration membrane comprises the following steps: reacting ethyl cellulose EC with alpha-bromo-isobutyryl bromide to obtain a macroinitiator EC-Br; carrying out ATRP (Atom Transfer Radical Polymerization) reaction on the macromolecular initiator EC-Br, a hydrophilic monomer MEO2MA and an FMA monomer containing a furan structure to obtain a functional polymer EC-g-P; a furan group of a functional polymer EC-g-P and bismaleimide BMI are subjected to a DA reaction to form a cross-linked network polymer, then in the presence of PEG, a membrane is prepared through a non-solvent induced phase separation method, and finally the ultrafiltration membrane with a microporous structure is obtained through water bath phase inversion. The membrane disclosed by the invention has high-efficiency separation performance, anti-pollution performance and closed-loop recoverability, and can be widely applied to treatment and recycling of printing and dyeing wastewater, domestic sewage and other high-pollution organic wastewater.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a method for preparing a regenerable cellulose-based ultrafiltration membrane with closed-loop recyclability and its application in the treatment of textile dye wastewater. Background Technology

[0002] Membrane separation technology is widely used in drinking water treatment and seawater desalination, offering advantages such as no phase change required, low operating pressure, and small footprint. However, existing membrane materials are mostly fossil-based polymers (such as PVDF, PES, and PSF), which are non-degradable. In particular, increasing concerns about the environmental risks of PVDF, including the recent regulations on per- and polyfluoroalkyl substances (PFAS) by the European Chemicals Agency (ECHA), highlight the urgent need for sustainable membrane materials. Currently, membranes typically follow a linear lifecycle model: use—performance degradation—landfill or incineration. This not only causes environmental pollution but also contradicts the sustainable development goals of the membrane industry. Furthermore, long-term operation of membrane materials leads to severe clogging due to pollutant accumulation, making recycling and regeneration difficult, resulting in large quantities of waste membranes being landfilled or incinerated, releasing harmful substances. Although attempts have been made to convert waste RO membranes into UF / NF membranes for reuse through chemical cleaning, severe performance degradation and the need for additional chemical agents prevent the restoration of their original function.

[0003] Therefore, how to achieve closed-loop recycling of membrane materials, partially or completely replace fossil-based polymers with renewable polymers, reduce environmental burden, and improve membrane sustainability are key issues that current membrane separation technologies urgently need to address. Summary of the Invention

[0004] To overcome the technical problems of non-recyclable membrane materials, severe pollution, and heavy environmental burden in existing technologies, the present invention aims to provide a method for preparing a regenerable cellulose-based ultrafiltration membrane with closed-loop recyclability and its application in the treatment of textile dye wastewater. The membrane of the present invention possesses high-efficiency separation performance, anti-fouling properties, and closed-loop recyclability, and can be widely used in the treatment and reuse of dyeing and printing wastewater, domestic sewage, and other highly polluting organic wastewater.

[0005] The technical solution adopted in this invention is as follows: A method for preparing a regenerable cellulose-based ultrafiltration membrane with closed-loop recyclability includes the following steps: Step 1: React ethyl cellulose EC with α-bromoisobutyryl bromide to obtain the macromolecular initiator EC-Br; Step 2: The macromolecular initiator EC-Br reacts with the hydrophilic monomer MEO2MA and the furan-containing FMA monomer via ATRP to obtain the functional polymer EC-gP; Step 3: The furan groups of the functional polymer EC-gP and bismaleimide BMI form a cross-linked network polymer in a solvent via a DA reaction. Subsequently, a film is prepared by a non-solvent-induced phase separation method in the presence of pore-forming agent PEG. Step 4: After the membrane is formed in step 3, it undergoes phase transformation in a water bath to obtain an ultrafiltration membrane with a microporous structure.

[0006] Furthermore, in step 1, the molar ratio of ethyl cellulose EC to α-bromoisobutyryl bromide is 2-5:1, and the reaction is carried out in the presence of TEA, with a molar ratio of TEA to EC of 0.8-1.5:1.

[0007] Furthermore, in step 1, the reaction is carried out at room temperature for 30-60 hours using THF as the solvent.

[0008] Furthermore, in step 2, the molar ratio of monomer MEO2MA to FMA monomer is 0.8-1.2:1, and the molar amount of monomer MEO2MA is 80-120 times the molar amount of Br in initiator EC-Br.

[0009] Furthermore, in step 2, the reaction is carried out in the presence of monovalent Cu salt and PMDETA, with the feed ratio of monovalent Cu salt to initiator EC-Br being 0.05-0.2 mmol:1 g, and the feed ratio of PMDETA to initiator EC-Br being 0.1-0.3 mmol:1 g.

[0010] Furthermore, in step 2, the reaction is carried out using THF as a solvent, at a temperature of 35-45℃, and for a time of 15-20 hours.

[0011] Further, in step 3, the molar amount of BMI is 40-60% of the molar amount of furan groups in EC-gP, preferably 50%; the DA reaction in step 3 uses DMAc as a solvent, and the temperature of the DA reaction is 60-70℃; in step 3, the pore-forming agent PEG is mixed in the DA reaction system to form a casting solution, the mass of EC-gP is 10-20% of the mass of the casting solution, the molecular weight of PEG is 200-600, and the final concentration of PEG in the casting solution is 1-3wt%.

[0012] Furthermore, in step 3, the film formation process using the non-solvent-induced phase separation method involves cooling the reaction solution after the DA reaction and using it as the casting solution. This casting solution is then coated onto a substrate, and the film is formed after the solvent evaporates in the air. In this invention, the pore-forming agent PEG plays a role in creating pores during the film formation process.

[0013] Furthermore, step 4, the water bath phase transformation step, involves immersing the substrate with the film formed on its surface in a deionized water coagulation bath to induce phase separation, thereby obtaining an ultrafiltration membrane with a microporous structure.

[0014] The present invention also discloses the application of the ultrafiltration membrane in wastewater treatment.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: 1) The membrane contaminated by textile wastewater can be decrosslinked by heating in DMAc at a temperature above 110°C, triggering a reverse DA reaction. The membrane dissolves into a homogeneous solution. Dyes and salts are separated into the aqueous phase by water / dichloromethane liquid-liquid extraction. The polymer enters the organic phase and is recovered by nitrogen blowing. The recovered polymer can be reused to make membranes again. The recovered membrane is comparable to the original membrane in terms of morphology, chemical structure, thermal stability, mechanical properties, hydrophilicity, and separation performance, realizing closed-loop recycling of membrane materials and achieving at least two closed-loop recyclings.

[0016] 2) This invention uses ethyl cellulose (EC) to replace fossil-based polymers to construct membrane materials. The membrane materials are renewable and biodegradable, which is in line with the concept of green manufacturing.

[0017] 3) The membrane of the present invention has high flux, high pollutant removal rate and excellent antifouling ability; 4) By introducing a covalent adaptive network through thermally triggered DA reaction, chemical-free closed-loop recycling and reuse can be achieved, reducing membrane waste emissions; reducing the risk of environmental pollution and resource waste, and significantly improving the sustainability of the membrane separation process.

[0018] 5) The covalent adaptive network itself serves as a cross-linking strategy, enabling the membrane of this invention to have ideal stability and effectively improving the problem of poor stability of traditional bio-based membranes.

[0019] 6) The membrane of the present invention has a smooth surface and uniform micropores as shown by SEM, and the cross-section has a continuous sponge-like structure with a narrow pore size distribution (coefficient of variation CV 0.12), which is beneficial for precise separation and has significantly improved hydrophilicity. Attached Figure Description

[0020] Figure 1 These are the chemical and surface morphology characterization results of the CAN film; (a) Fourier transform infrared spectra of EC-gP (MEO2MA-FMA), BMI, and CAN films. (b) In-situ infrared spectra of C=O tensile vibrations in the DA adduct; Figure 2 This is a comparison of the water contact angle of the CAN membrane (M1) with that of the original EC membrane (M0).

[0021] Figure 3 This is the DSC curve of the CAN membrane.

[0022] Figure 4The results show a comparison of the gel content of the CAN crosslinked membrane of Example 1 and the uncrosslinked membrane of Example 3 after soaking in ethanol, methanol, and N,N dimethylformamide (DMF) for 72 hours.

[0023] Figure 5 These are the cutoff curves of CAN membranes for PEG / PEO of different molecular weights.

[0024] Figure 6 This is a comparison of the pollutant removal performance of the original membrane and the recycled membrane. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0026] The ethyl cellulose (EC, ethoxy: 48 wt.%; degree of substitution: 2.46) used in the embodiments of the present invention was purchased from Sigma, catalog number 200697-250G.

[0027] Example 1: Preparation of a regenerable cellulose-based ultrafiltration membrane with closed-loop recyclability Step 1: Synthesis of the macromolecular initiator EC-Br: .

[0028] In a 250 mL flask, 4.618 g (20 mmol) of ethyl cellulose (EC) was dissolved in 60 mL of THF until completely dissolved. Then, 2.96 mL (20 mmol) of triethylamine (TEA) was added, and the mixture was magnetically stirred at room temperature. Next, 0.742 mL (6 mmol) of α-bromoisobutyryl bromide was mixed with 15 mL of tetrahydrofuran and slowly added dropwise to the flask under an ice-water bath (0 °C). The mixture was then reacted at room temperature for 48 hours. After the reaction was complete, the reaction mixture was purified by adding it dropwise to deionized water to precipitate a flocculent precipitate. This precipitate was filtered, dissolved in tetrahydrofuran, and precipitated again. This purification process was repeated three times to remove impurities, yielding the macromolecular initiator EC-Br.

[0029] Step 2: Synthesis of the functional polymer EC-gP (MEO2MA-FMA): 1 g of EC-Br (containing 0.1 mmol Br, determined by 1H NMR) was dissolved in 40 mL of tetrahydrofuran in a Schlenk flask. 0.1 mmol CuBr was added, and the solution was degassed by three cycles of freeze-degassing and purging, then sealed with a silicone stopper. 10 mmol of MEO2MA, 10 mmol of furfuryl methacrylate (FMA), and 0.2 mmol of N,N,N',N'',N''-pentamethyldivinyltriamine (PMDETA) were mixed in 10 mL of THF. Dissolved oxygen was removed by bubbling with N2 for 30 minutes. The mixture was then transferred to a reaction flask using a nitrogen-purified syringe. The reaction flask was immersed in an oil bath at 40°C to initiate the reaction, and polymerization was terminated by exposure to air after 18 hours. The reaction solution was purified by passing it through a neutral alumina column to remove divalent copper salts from the system. The alumina column was then washed with cyclopentanone to obtain the product solution, which was then precipitated with a large amount of deionized water. The purification process was repeated three times, and the solution was then freeze-dried to obtain the functional polymer EC-gP (MEO2MA-FMA).

[0030] .

[0031] Step 3: Preparation of the CAN membrane: The CAN membrane was prepared by non-solvent-induced phase separation (NIPS): 0.6 g EC-gP (MEO2MA-FMA) and 0.086 g PEG400 were completely dissolved in 3.6 g DMAc and continuously stirred at 60 °C and 300 rpm for 24 h. Then, maleimide BMI was added, with the molar amount of maleimide being 50% of the molar amount of furan groups in EC-gP (the furan group content was detected by 1H NMR spectroscopy). The mixture was heated to 120 °C and stirred until homogeneous, then rapidly cooled in an ice-water bath. The mixture was then transferred to a heated stirrer and heated to 60 °C to initiate a forward Diels-Alder (DA) crosslinking reaction. After approximately 45 min, a suitable viscosity was reached. The mixture was then removed from the heated stirrer and rapidly cooled in a cold water bath to stop the DA reaction, yielding the casting solution. After removing air bubbles, the casting solution was applied to a clean glass plate using an automated coating applicator and a 300 μm thick doctor's blade. After evaporation in the air for 40 seconds, the plate is immersed in a deionized water (DI) coagulation bath to induce phase separation, and the CAN membrane is obtained and stored in deionized water (the CAN membrane is insoluble in water) for further use.

[0032] Example 2: Preparation method of the original EC membrane. The preparation steps of the CAN membrane in Example 1 were repeated, except that "in step 3, during the preparation of the CAN membrane, the polymer EC-gP was replaced with an equal mass of ethyl cellulose EC, and BMI was not added". All other conditions were the same, and the original EC membrane was obtained.

[0033] Example 3: Preparation method of non-crosslinked membrane. The preparation steps of CAN membrane in Example 1 are repeated, except that BMI is not added in step 3, and all other conditions remain the same.

[0034] CAN membrane manufacturing and characterization:

[0035] Unless otherwise specified, the following membrane tests refer to the test results of the CAN membrane obtained under the DA reaction at 60°C (i.e., the CAN membrane prepared in Example 1).

[0036] The FTIR spectrum comparison results of the functional polymer EC-gP (MEO2MA-FMA), BMI, and CAN films in Example 1 are shown below. Figure 1 Figure a shows the CAN membrane at 1775 cm⁻¹. -1 The vicinity exhibits characteristic C=O tensile vibration peaks of DA adducts, while at 688 cm⁻¹... -1 The absorption band of the maleimide group disappeared. This clearly demonstrates that EC-gP (MEO2MA-FMA) and BMI were successfully crosslinked via the DA reaction.

[0037] The temperature-driven reversible DA cycloaddition reaction based on the furan-maleimide structure was studied using in-situ infrared spectroscopy. The effect of different temperatures on the DA adduct during the DA reaction was investigated (the preparation process of the DA adduct is as described in Example 1). The results are shown in [link to example]. Figure 1 Figure b shows the degree of dissociation of the DA adduct, characterized by monitoring the stretching vibration of C=O at approximately 1750–1770 cm⁻¹ at different temperatures (60–145 °C). At low temperatures of 60–70 °C, the C=O peak intensity remained essentially constant, indicating that the DA reaction occurred in the forward direction. When the temperature rose above 120 °C, the C=O peak disappeared, indicating that above this temperature threshold, the dissociation reaction became the dominant reaction, and the DA reaction occurred in the reverse direction.

[0038] The DSC curve test results of the CAN membrane are shown below. Figure 3 ,from Figure 3 The DSC results show an endothermic peak starting at 110℃, which is attributed to the reverse DA reaction. These results demonstrate that a covalent adaptive network was successfully introduced into the CAN film via the DA reaction.

[0039] The comparison results of the water contact angles of the CAN membrane (M1) prepared in Example 1 and the original EC membrane (M0) prepared in Example 2 are shown in the figure. Figure 2 The CAN membrane exhibits enhanced hydrophilicity, with a water contact angle of 34.27 ± 4.31° (M1), compared to 58.87 ± 3.39° (M0) for the original EC membrane. This enhanced hydrophilicity can be attributed to the synergistic effect of the inherent hydroxyl groups on the EC backbone and the grafted hydrophilic monomer (MEO2MA).

[0040] The CAN (crosslinked) membrane of Example 1 and the non-crosslinked membrane of Example 3 were compared. The CAN (crosslinked) membrane and the non-crosslinked membrane were immersed in three organic solvents (ethanol, methanol, and N,N-dimethylformamide) at room temperature for 72 hours each. The mass difference of the membrane before and after solvent immersion was then measured. The initial mass before immersion was recorded as m0, and the mass of the membrane after 72 hours of immersion, washing with deionized water, and drying was recorded as m1. The gel content was calculated as m1 / m0 * 100%. Figure 4 The gel content of cross-linked and non-cross-linked CAN membranes after immersion in ethanol, methanol, and DMF for 72 hours was shown. Significant differences in solvent resistance were observed between the cross-linked and non-cross-linked membranes. The gel content of the CAN membrane exceeded 75% in all solvents, while the gel content of the non-cross-linked membrane was less than 10%. Figure 4 The lower the gel content, the worse the chemical stability of the membrane. The CAN membrane maintained good structural integrity after prolonged immersion, while the uncrosslinked membrane underwent severe structural degradation. These results confirm that DA crosslinking significantly enhances the chemical stability of the CAN membrane.

[0041] Separation performance of CAN membrane:

[0042] The stable permeability of the CAN membrane to deionized water is 193 ± 24.56 L·m. -2 ·h -1 ·bar -1 (LMH) falls within the ultrafiltration range. Pore size distribution is a key parameter controlling membrane permeability and selectivity, and is characterized by the coefficient of variation (CV), which is the ratio of the standard deviation σ to the average membrane pore radius r.

[0043] Under operating pressure of 0.1 bar and room temperature, the membrane filtered aqueous solutions (solute concentration of 200 mg / L) of a series of solutes with different molecular weights, namely polyethylene glycol (PEG, 20 kDa) and polyethylene oxide (PEOs, 80 kDa, 100 kDa, 300 kDa, and 1000 kDa). A graph was plotted with the molecular weight of the solute on the x-axis and the membrane's rejection rate on the y-axis. The rejection curves of the CAN membrane for different molecular weights of PEG / PEO are shown below. Figure 5 ,according to Figure 5 The results can be used to calculate the molecular weight of the solute corresponding to different membrane rejection rates.

[0044] The molecular weight cutoff (MWCO) of a membrane is defined as the molecular weight of the solute molecules that achieve a membrane retention rate of 90%. According to... Figure 5 As a result, the MWCO of the CAN membrane is 170 kDa.

[0045] The average membrane pore radius r is estimated based on the molecular weight cutoff (MWCO) of the membrane. The Stokes radius (r, nm) of PEG and PEO is calculated based on the molecular weight (Mw, Da) using the following two formulas. The Stokes radius of MWCO is estimated as the average membrane pore radius.

[0046] Mw represents the molecular weight of the PEG solute; Mw represents the molecular weight of the PEO solute.

[0047] The standard deviation (σ) was obtained by dividing the solute size at a rejection rate of 84.13% by the solute size at a rejection rate of 50%, resulting in a σ of 1.42. Finally, the CV of the CAN membrane was calculated to be 0.12. The CV of the CAN membrane is smaller than that of a typical phase inversion ultrafiltration membrane (CV = 0.2), indicating a narrower pore size distribution.

[0048] Application Example 1: Experiment 1: The separation performance of the CAN membrane was evaluated by treating textile wastewater posing significant environmental and health risks. This experiment simulated textile wastewater containing 10 ppm Coomassie Brilliant Blue (CBB), 25 ppm polystyrene microspheres (PS), and 1000 ppm NaCl. These were filtered using a CAN membrane to evaluate its filtration performance against these pollutants. Under an operating pressure of 1 bar, the CAN membrane separated the simulated textile wastewater. After stabilization for 10-15 minutes, its separation performance was tested. The membrane achieved removal rates of over 97% for both CBB and PS, but only 3.72% for NaCl.

[0049] Experiment 2: To verify the membrane's ability to separate dyes and salts, 10 ppm aqueous solutions of Alcian Blue (AB) and Fast Green (FG) were tested under the same conditions as in Experiment 1. The CAN membrane also showed good removal performance for these dyes, with removal rates exceeding 95%. It also maintained low removal rates for aqueous solutions of sodium sulfate (Na₂SO₄), magnesium chloride (MgCl₂), and magnesium sulfate (MgSO₄), three common inorganic salts in the textile industry (all at 1000 ppm), at 12.41%, 3.49%, and 6.1%, respectively. The CAN membrane's ability to selectively retain dyes and microplastics while allowing high salt permeability is particularly advantageous for textile wastewater treatment.

[0050] Experiment 3: The antifouling performance of the CAN membrane was evaluated using a 100 ppm bovine serum albumin (BSA) aqueous solution and a 100 ppm dye-CBB aqueous solution. First, the membrane was pre-pressed with deionized water at 1 bar for 30 minutes to achieve stable permeation (recorded as J0). Then, the BSA aqueous solution or the dye-CBB aqueous solution was filtered for 60 minutes at an operating pressure of 1 bar to obtain fouled permeation. After backwashing with deionized water for 15 minutes, the pure water permeability was re-measured (recorded as J). w The flux recovery rate (FRR) is calculated using the formula: FRR = The above cycle was repeated three times. The membrane exhibited an excellent flux recovery rate. The CAN membrane had an FRR of 85.29% for BSA and 97.6% for CBB. The superior antifouling performance of the CAN membrane highlights its potential for continuous operation in wastewater treatment applications.

[0051] Application Example 2 1) Membrane closed-loop recovery experiment: A recovery experiment was conducted on the CAN membrane contaminated by wastewater in Experiment 1 of Application Example 1. The experimental procedure was as follows: The CAN membrane contaminated by wastewater was dissolved in DMAc and heated at 120°C for about 15 minutes (ensuring complete dissolution of the membrane by DMAc). The contaminants (dyes and salts) and polymer EC-gP were separated according to their different solubilities. An equal volume of dichloromethane (DCM) and water was added and mixed, i.e., the volume ratio of DMAc, DCM, and water was 1:1:1. The polymer dissolved in the DCM phase, while DMAc and contaminants (dyes and salts) were extracted into the aqueous phase. After standing for 10 minutes, the DCM phase was collected, and the DCM was purged with nitrogen to recover the polymer EC-gP. The recovered polymer EC-gP was then reused in membrane manufacturing according to the steps of Example 1 above to obtain a recycled membrane. Its performance was evaluated to verify the closed-loop recyclability of the CAN membrane.

[0052] The above solution is a strategy for applying membranes to textile wastewater treatment. If the membrane is applied to other fields, different strategies can be used to remove pollutants as needed, such as oil-water separation. After the oil-contaminated membrane is dissolved in DMAc, there is no need for liquid-liquid extraction. It will automatically separate into layers after standing. Since oil is not soluble in the system, a clean polymer can be obtained by simply removing the oil layer for membrane remanufacturing.

[0053] 2) Performance evaluation of CAN membrane after recycling The CAN membrane, after being contaminated by simulated textile wastewater, was recycled in a closed loop according to the method described in step 1) of the "Membrane Closed-Loop Recycling Experiment" above, to obtain a regenerated membrane (i.e., a recycled membrane). The recycled membrane retained the key structural features of the original membrane, including a relatively smooth membrane surface, uniformly distributed micropores, and a consistent sponge-like cross-sectional structure. These features remained almost unchanged during the recycling process, indicating that the CAN membrane can be recycled and remanufactured while retaining its original morphology and structure.

[0054] The FTIR spectra of the original and recycled membranes showed almost identical spectra, confirming that the crosslinked structure and chemical composition remained unchanged after recycling. Both the original and recycled membranes exhibited the reverse DA reaction at the same temperature, indicating that the dynamic covalent network maintained thermal reversibility.

[0055] The separation performance of the recovered membrane was evaluated through a pollutant retention test, using the same method as described in Application Example 1 above. The test results are shown in [Figure Number]. Figure 6 The membranes recovered in both trials maintained high PS removal rates of 97.49% and 94.24%, respectively; and consistently demonstrated high dye removal performance, with CBB and AB removal rates both exceeding 95%. The consistency and separation performance demonstrate the feasibility of the closed-loop recovery strategy.

[0056] Furthermore, the pure water flux of the two recovered membranes was 164.01±23.91 LMH and 176±11.2 LMH, respectively, which were comparable to the original membrane. The pure water flux of the original CAN membrane was 193±24.56 L·m. -2 ·h -1 ·bar -1 (LMH).

[0057] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a regenerable cellulose-based ultrafiltration membrane with closed-loop recyclability, characterized in that, Includes the following steps: Step 1: React ethyl cellulose EC with α-bromoisobutyryl bromide to obtain the macromolecular initiator EC-Br; Step 2: The macromolecular initiator EC-Br reacts with the hydrophilic monomer MEO2MA and the furan-containing FMA monomer via ATRP to obtain the functional polymer EC-gP; Step 3: The furan groups of the functional polymer EC-gP and bismaleimide BMI form a cross-linked network polymer through a DA reaction. Then, in the presence of the pore-forming agent PEG, a film is prepared by a non-solvent-induced phase separation method. Step 4: After the membrane is formed in step 3, it undergoes phase transformation in a water bath to obtain an ultrafiltration membrane with a microporous structure.

2. The preparation method according to claim 1, characterized in that, In step 1, the molar ratio of ethyl cellulose EC to α-bromoisobutyryl bromide is 2-5:1, and the reaction is carried out in the presence of TEA, with a molar ratio of TEA to EC of 0.8-1.5:

1.

3. The preparation method according to claim 1, characterized in that, In step 1, the reaction is carried out using THF as a solvent at room temperature for 30-60 hours.

4. The preparation method according to claim 1, characterized in that, In step 2, the molar ratio of monomer MEO2MA to FMA monomer is 0.8-1.2:1, and the molar amount of monomer MEO2MA is 80-120 times the molar amount of Br in initiator EC-Br.

5. The preparation method according to claim 1, characterized in that, In step 2, the reaction is carried out in the presence of monovalent Cu salt and PMDETA. The feed ratio of monovalent Cu salt to initiator EC-Br is 0.05-0.2 mmol:1 g, and the feed ratio of PMDETA to initiator EC-Br is 0.1-0.3 mmol:1 g.

6. The preparation method according to claim 1, characterized in that, In step 2, the reaction is carried out using THF as a solvent, at a temperature of 35-45℃, and for a time of 15-20 hours.

7. The preparation method according to claim 1, characterized in that, In step 3, the molar amount of BMI is 40-60% of the molar amount of furan groups in EC-gP, preferably 50%; the DA reaction in step 3 uses DMAc as a solvent, and the temperature of the DA reaction is 60-70℃; in step 3, the pore-forming agent PEG is mixed in the DA reaction system to form a casting solution, the mass of EC-gP is 10-20% of the mass of the casting solution, the molecular weight of PEG is 200-600, and the final concentration of PEG in the casting solution is 1-3wt%.

8. The preparation method according to claim 1, characterized in that, Step 3, the process of preparing the membrane by non-solvent-induced phase separation, is to use the cooled reaction solution after the DA reaction as the casting solution, coat the casting solution onto the substrate, and form a membrane after the solvent evaporates in the air; Step 4, the water bath phase transformation step, is to immerse the substrate with the membrane formed on the surface in a deionized water coagulation bath to induce phase separation and obtain an ultrafiltration membrane with a microporous structure.

9. An ultrafiltration membrane prepared by any one of the methods described in claims 1-8.

10. The application of the ultrafiltration membrane as described in claim 9 in wastewater treatment.

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