Preparation method and application of surface grafted biomimetic zwitterionic anti-fouling polyamide membrane

Abstract

The application discloses a preparation method and application of a surface grafted biomimetic zwitterionic anti-fouling polyamide membrane and belongs to the membrane technical field. The preparation steps of the anti-fouling polyamide membrane comprise the following steps: modifying the polyamide membrane by using a silane coupling agent containing an unsaturated double bond, dropping a solution containing a hydrophobic initiator on the surface of the modified polyamide membrane, dropping an oxidized trimethylamine monomer solution after the solvent on the surface of the polyamide membrane is volatilized, and preparing the anti-fouling polyamide membrane through ultraviolet irradiation. The super-wetting assisted grafting technology is adopted, that is, a super-wetting stable initiator layer is formed on the membrane surface, the interface reaction between the zwitterionic monomer and the membrane surface is promoted, and then a controllable grafting is formed between the zwitterionic monomer and the membrane surface. The anti-protein performance of the novel zwitterionic anti-fouling polyamide membrane in the application is far better than that of a traditional zwitterionic anti-fouling polyamide membrane, and the grafting density is adjustable, so that the water production flux of the nanofiltration membrane can be ensured while the anti-fouling is guaranteed, and the shortcomings of the flux reduction and the insufficient anti-fouling performance caused by the traditional grafting method and the traditional zwitterionic anti-fouling polyamide membrane are overcome.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, specifically relating to a method for preparing and applying an antifouling polyamide membrane with a surface grafted with biomimetic zwitterions. Background Technology

[0002] Nanofiltration is a promising membrane technology for seawater desalination and wastewater treatment. Typically, nanofiltration membranes have a molecular weight cutoff of 100-2000 Da and a pore size of approximately 1 nm, enabling them to separate monovalent salts and water from polyvalent salts and low-molecular-weight organic matter. Furthermore, nanofiltration technology offers a good balance between energy consumption and treatment capacity. However, the biggest drawback of membrane technology is membrane fouling. Membrane fouling affects water permeate flux, reduces the quality of the produced water, shortens membrane lifespan, and leads to additional energy consumption.

[0003] To alleviate pollution problems, the research and development of antifouling membranes has become an important field. Grafted polymer brushes are the most advanced method for imparting antifouling properties to material surfaces. Among them, surface-initiated atom transfer radical polymerization (SI-ATRP) is currently the most commonly used method for preparing polymer brushes. However, SI-ATRP has many problems, such as the initiator being a halide with high toxicity, large monomer consumption, use of metal salt catalysts, and low polymerization efficiency.

[0004] Generally, among a wide range of extensively studied antifouling polymers, zwitterionic polymers have attracted considerable attention in recent years as antifouling modifiers due to their unique properties of containing both cationic and anionic groups while maintaining electroneutrality and high hydrophilicity. Unlike hydrophilic materials such as polyethylene glycol, which bind to water molecules through hydrogen bonds, the zwitterionic portion can tightly bind to water molecules through electrostatic / dipole polarization interactions. Typically, one zwitterionic group can bind approximately eight water molecules, generating a strong hydration layer. This strong hydration layer acts as both a physical barrier (the spatial repulsion of the polymer chains) and an energy barrier (reducing the entropy of protein adsorption, thus hindering protein adsorption), minimizing the interaction between the material surface and contaminants and increasing the Gibbs free energy of the system, thereby making zwitterionic polymers more effective in combating contamination. However, seawater is a complex mixture with an average salinity of 3.5%, which significantly reduces the surface hydration of these traditional zwitterionic polymers, affecting their antifouling performance. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing and applying an antifouling polyamide membrane with surface grafted biomimetic zwitterions. The provided antifouling polyamide membrane with surface grafted biomimetic zwitterions exhibits enhanced hydrophilicity and antifouling properties without compromising performance, effectively resisting fouling by salts and proteins.

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

[0007] One of the technical solutions of this invention is to provide a method for preparing an antifouling polyamide film with a surface grafted with biomimetic zwitterions, comprising the following steps:

[0008] A polyamide membrane was modified using a silane coupling agent containing unsaturated double bonds. A solution containing a hydrophobic initiator was then dropped onto the surface of the modified polyamide membrane. After the solvent on the surface of the polyamide membrane evaporated, a solution of trimethylamine oxide (TMAO) monomer was dropped onto it. After irradiation with ultraviolet light, an anti-fouling polyamide membrane with biomimetic zwitterions grafted onto its surface was obtained.

[0009] Preferably, the ultraviolet irradiation process further includes a cleaning step to remove unreacted trimethylamine oxide monomer.

[0010] Preferably, the ultraviolet irradiation time is 1 to 5 minutes, more preferably 1 minute.

[0011] Preferably, the silane coupling agent containing unsaturated double bonds is 3-(methacryloyloxy)propyltrimethoxysilane (TMSPMA); the hydrophobic initiator is 2,2-diethoxyacetophenone (DEAP), 2-hydroxy-2-methylphenylpropanone (HMP), benzophenone (BP), or 4-methylbenzophenone (MBP).

[0012] More preferably, when modifying the polyamide film using TMSPMA, the method is to immerse the polyamide film in a TMSPMA solution, wherein the TMSPMA solution is prepared by 2 wt% TMSPMA, 95 wt% ethanol, and 3 wt% water, and the immersion time is 5 to 24 hours, preferably 5 hours.

[0013] More preferably, the concentration of the solution containing DEAP is 0.2 to 0.5 wt%, most preferably 0.28 wt%, and the solvent is methanol.

[0014] Preferably, the polyamide membrane includes either a nanofiltration membrane or a reverse osmosis membrane.

[0015] Preferably, the concentration of the trimethylamine oxide monomer solution is 0.08 mol / 15 mL, and the solvent is an equal volume mixture of methanol and water.

[0016] Preferably, the preparation steps of trimethylamine oxide monomer include: adding an aqueous hydrogen peroxide solution dropwise into a preheated aqueous dimethylaminopropylacrylamide solution, maintaining the preheated temperature during the reaction, cooling the solution, and purifying it with ethyl acetate to obtain the trimethylamine oxide monomer.

[0017] More preferably, the mass fraction of the hydrogen peroxide aqueous solution is 30%; the concentration of the dimethylaminopropylacrylamide aqueous solution is 0.2–2 mol / L, most preferably 0.5–1 mol / L; the mass ratio of dimethylaminopropylacrylamide in the dimethylaminopropylacrylamide aqueous solution to hydrogen peroxide in the hydrogen peroxide aqueous solution is 3–5:1, most preferably 3:1; the preheating temperature is 60–70°C, most preferably 65°C; and the reaction time is 6–8 h, most preferably 8 h.

[0018] More preferably, after purification with ethyl acetate, the process further includes a freeze-drying step, with the freeze-drying time being 24 to 48 hours, preferably 48 hours.

[0019] The above-mentioned optimal parameters were all obtained from experimental results.

[0020] The second technical solution of the present invention provides a surface-grafted biomimetic zwitterionic antifouling polyamide film prepared according to the above-mentioned preparation method of surface-grafted biomimetic zwitterionic antifouling polyamide film.

[0021] The third technical solution of the present invention provides an application of the above-mentioned surface-grafted biomimetic zwitterionic antifouling polyamide membrane in wastewater treatment.

[0022] Preferably, the wastewater is wastewater with high organic matter and / or high salt content.

[0023] The beneficial technical effects of the present invention are as follows:

[0024] This invention utilizes the zwitterionic TMAO from biomimetic fish mucus. This type of compound has no gap between its positive and negative charges, and its strong electrostatic induction and hydration capabilities allow it to form a dense hydration layer on the membrane surface. Compared to other zwitterions, it exhibits superior hydrophilicity, salt tolerance, and antifouling properties, maintaining strong hydration even in high-salinity seawater environments.

[0025] Secondly, this invention utilizes a superwetting interface-assisted grafting method. This method leverages the hydrophobic interaction between the initiator and the silane coupling agent-modified membrane surface to form a stable initiator layer, promoting efficient interfacial reactions between the monomer and the membrane surface. Controllable grafting is then achieved through simple UV-initiated polymerization. This method ensures that antifouling is achieved without affecting the permeate flux of the reverse osmosis membrane, and the grafting density is controllable. It is simple to operate, beneficial for large-area membrane surface modification, and environmentally friendly, without the use of toxic substances. Attached Figure Description

[0026] Figure 1 The 1H NMR spectrum of the TMAO prepared in Example 2.

[0027] Figure 2The X-ray photoelectron spectrum of NF270-TMAO prepared in Example 2.

[0028] Figure 3 The water permeability of the nanofiltration membranes prepared in Examples 1-4.

[0029] Figure 4 The permeability of the nanofiltration membrane and NF270 nanofiltration membrane prepared in Example 2 to various salt solutions.

[0030] Figure 5 The salt rejection rates of the nanofiltration membrane prepared in Example 2 and the NF270 nanofiltration membrane are shown.

[0031] Figure 6 The antifouling performance test results of the NF270 nanofiltration membrane, the NF270-SBMA membrane prepared in Example 5, and the NF270-TMAO nanofiltration membrane prepared in Example 2. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0033] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0035] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0036] The reagents and instruments used in the embodiments of this invention are all commercially available products, and the detection methods are conventional methods well known in the art.

[0037] The dimethylaminopropylacrylamide used in this embodiment of the invention has the CAS number 3845-76-9 and the structural formula as follows:

[0038] Example 1

[0039] An antifouling nanofiltration membrane with surface-grafted biomimetic zwitterions is prepared by the following method:

[0040] (1) Preparation of TMAO zwitterionic monomers

[0041] 15.61 g of DMAPA (dimethylaminopropylacrylamide) was dissolved in 100 mL of ultrapure water (1 mol / L) and stirred until homogeneous to obtain an aqueous solution of dimethylaminopropylacrylamide.

[0042] Place 17g of a 30% hydrogen peroxide aqueous solution (1.5mol / L) into a constant pressure dropping funnel;

[0043] The aqueous solution of dimethylaminopropylacrylamide was placed in an oil bath at a temperature of 65°C.

[0044] A reflux condenser and a constant-pressure dropping funnel containing an aqueous solution of hydrogen peroxide were installed on a three-necked flask. The aqueous solution of hydrogen peroxide was slowly added dropwise and stirred at 65°C for 8 hours.

[0045] After the reaction solution cooled to room temperature, it was purified by extraction with ethyl acetate and freeze-dried for 24 hours to obtain purified TMAO.

[0046] (2) Preparation of antifouling nanofiltration membrane (NF270-TMAO) with surface grafted biomimetic zwitterions

[0047] The NF270 nanofiltration membrane was modified with TMSPMA (2wt% TMSPMA, 95wt% ethanol, 3wt% water), a silane coupling agent containing unsaturated double bonds, and soaked for 5h.

[0048] Rinse the membrane surface to remove unreacted silane coupling agent;

[0049] After drying, 1 mL of 0.28 wt% DEAP methanol solution was added to the membrane surface. After the methanol evaporated, a superwetting layer with controllable thickness was obtained.

[0050] Subsequently, TMAO monomer solution was added dropwise to the surface, with a ratio of 0.6 mmol monomer dissolved in 15 mL of methanol-water mixture (volume ratio 1:1).

[0051] After irradiating with ultraviolet light for 5 minutes, zwitterions were grafted onto the membrane via vinyl bonding. Finally, the membrane surface was rinsed with deionized water to remove unreacted TMAO, resulting in a zwitterion-modified nanofiltration membrane.

[0052] Example 2

[0053] An antifouling nanofiltration membrane with surface-grafted biomimetic zwitterions is prepared by the following method:

[0054] Same as Example 1, except that in step (2), the TMAO monomer solution is prepared by dissolving 0.8 mmol of the monomer in 15 mL of a mixed solution of methanol and water (volume ratio of 1:1).

[0055] The 1H NMR spectrum of the TMAO prepared in Example 2 is shown below. Figure 1 .

[0056] The X-ray photoelectron spectrum of NF270-TMAO prepared in Example 2 is shown below. Figure 2 .

[0057] Example 3

[0058] An antifouling nanofiltration membrane with surface-grafted biomimetic zwitterions is prepared by the following method:

[0059] Same as Example 1, except that in step (2), the TMAO monomer solution is prepared by dissolving 1.0 mmol of monomer in 15 mL of a mixed solution of methanol and water (volume ratio of 1:1).

[0060] Example 4

[0061] An antifouling nanofiltration membrane with surface-grafted biomimetic zwitterions is prepared by the following method:

[0062] Same as Example 1, except that in step (2), the TMAO monomer solution is prepared by dissolving 1.2 mmol of monomer in 15 mL of a mixed solution of methanol and water (volume ratio of 1:1).

[0063] Example 5

[0064] An antifouling nanofiltration membrane with surface-grafted biomimetic zwitterions is prepared by the following method:

[0065] Same as Example 2, except that in step (2), the TMAO monomer solution is replaced with a methacryloyl ethyl sulfobetaine (SBMA) monomer solution, with the same concentration.

[0066] Performance testing:

[0067] The original membrane (NF270 nanofiltration membrane) and the membranes prepared in Examples 1-4 were placed in a nanofiltration apparatus to test their separation performance. The specific process is as follows:

[0068] The tests were conducted using a nanofiltration testing device, which is an independent pressure osmosis device. The effective test area of ​​the membrane module was 15.9 cm². 2The test solution was pure water or a 2000 ppm salt solution (sodium sulfate, magnesium sulfate, magnesium chloride, or sodium chloride). A cross-flow method was used, with a flow rate controlled at 44.4 cm / s and a pressure of 4 bar. The NF270 nanofiltration membrane and the nanofiltration membranes prepared in Examples 1-3 were fixed onto the membrane module. The instrument was run for 30 minutes, and after stabilization, the time was recorded and samples were taken to determine the mass and conductivity of the permeate, thereby obtaining the water permeability and salt rejection rate of the nanofiltration membrane.

[0069] The water permeability of the nanofiltration membranes prepared in Examples 1-4 is shown in the figure. Figure 3 ,from Figure 3 As can be seen, the nanofiltration membrane prepared with the highest water permeability is when the concentration of the TMAO monomer solution is 0.8 mol / 15 mL.

[0070] The permeability of the nanofiltration membrane prepared in Example 2 and the NF270 nanofiltration membrane to various salt solutions is shown in the figure. Figure 4 .

[0071] The salt rejection rates of the nanofiltration membrane prepared in Example 2 and the NF270 nanofiltration membrane are shown in the figure. Figure 5 .

[0072] Using 500 ppm bovine serum albumin as a model contaminant, fouling experiments were conducted on the NF270 nanofiltration membrane, the NF270-SBMA membrane prepared in Example 5, and the NF270-TMAO nanofiltration membrane prepared in Example 2. The fouling experiments included three stages: a 2-hour baseline stage, a 12-hour fouling stage, and a 2-hour recovery stage after cleaning.

[0073] The results of the anti-pollution test are shown below. Figure 6 , Figure 6 The nanofiltration membrane prepared in Example 2 shows significantly better antifouling performance.

[0074] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a surface grafted biomimetic zwitterionic anti-fouling polyamide membrane, characterized in that, The method comprises the following steps: The polyamide membrane is modified by a silane coupling agent containing unsaturated double bonds, and then a solution containing a hydrophobic initiator is added dropwise on the surface of the modified polyamide membrane. After the solvent on the surface of the polyamide membrane is volatilized, a trimethylamine oxide monomer solution is added dropwise, and a surface grafted biomimetic zwitterionic anti-pollution polyamide membrane is prepared after ultraviolet irradiation. The silane coupling agent containing unsaturated double bonds is 3-(methacryloyloxy) propyl trimethoxysilane; and the hydrophobic initiator is 2,2-diethoxyacetophenone, 2-hydroxy-2-methylphenylpropanone, benzophenone or 4-methylbenzophenone.

2. The method for preparing a surface grafted biomimetic zwitterionic antifouling polyamide membrane according to claim 1, characterized in that, After ultraviolet irradiation, a cleaning step is further included to remove unreacted trimethylamine oxide monomers.

3. The method for preparing a surface grafted biomimetic zwitterionic antifouling polyamide membrane according to claim 1, characterized in that, The polyamide membrane includes any one of nanofiltration membranes and reverse osmosis membranes.

4. The method for preparing a surface grafted biomimetic zwitterionic antifouling polyamide membrane according to claim 1, characterized in that, The concentration of the trimethylamine oxide monomer solution is 0.08 mol / 15 mL, and the solvent is an equal volume mixture of methanol and water.

5. The method for preparing the antifouling polyamide film with surface grafted biomimetic zwitterionic ions according to claim 1, characterized in that, The preparation steps of the trimethylamine oxide monomer include: dropping a hydrogen peroxide aqueous solution into a preheated dimethylamine propyl acrylamide aqueous solution, maintaining the preheated temperature for reaction, cooling, purifying with ethyl acetate, and obtaining the trimethylamine oxide monomer.

6. The method for preparing a surface grafted biomimetic zwitterionic antifouling polyamide membrane according to claim 5, characterized in that, The mass fraction of the hydrogen peroxide aqueous solution is 30%; the concentration of the dimethylamine propyl acrylamide aqueous solution is 0.2-2 mol / L; the mass ratio of dimethylamine propyl acrylamide in the dimethylamine propyl acrylamide aqueous solution to hydrogen peroxide in the hydrogen peroxide aqueous solution is 3-5:1; the preheated temperature is 60-70℃; and the reaction time is 6-8 h.

7. The surface grafted biomimetic zwitterionic anti-pollution polyamide membrane prepared by the method of claim 1.

8. The application of the surface grafted biomimetic zwitterionic anti-pollution polyamide membrane of claim 7 in wastewater treatment.

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