Preparation method of modified ultrafiltration membrane for efficient separation of nanoplastics in water body

Abstract

The application relates to a preparation method of a modified ultrafiltration membrane for high-efficiency separation of nanoplastics in water bodies, and belongs to the field of environmental engineering water treatment. The application provides a preparation method of a modified ultrafiltration membrane for high-efficiency separation of nanoplastics in water bodies, which is prepared by impregnation modification of the ultrafiltration membrane by tea polyphenol and 3-aminopropyl triethoxysilane, realizes high hydrophilicity of the membrane surface and high separation efficiency of nanoplastics in water bodies. The application provides a polyvinylidene fluoride ultrafiltration membrane modification method based on synergistic modification, the hydrophilicity and anti-pollution performance of the membrane surface are obviously improved by optimizing the modification process, the nanoplastics exhibit excellent removal efficiency, and the removal rate is more than 99%; meanwhile, the stability of the modified layer is improved through a chemical crosslinking mechanism, the service life of the membrane is effectively prolonged, the limitations of insufficient separation precision and hydrophobicity of the membrane surface in the prior art are overcome, and an innovative solution is provided for high-efficiency separation of nanoplastics in water bodies.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental engineering water treatment, and particularly relates to a preparation method of a modified ultrafiltration membrane for efficient separation of nanoplastics in water bodies. BACKGROUND

[0002] Microplastic pollution has become a hot issue in water environmental governance worldwide. In particular, nanoscale microplastics (nanoplastics) with a diameter less than 1 μm can more easily penetrate conventional separation systems and enter drinking water due to their smaller particle size and larger specific surface area, posing a potential threat to drinking water safety. In addition, nanoplastics can further exacerbate their harm to the ecological environment and human health due to their high active surface that can adsorb heavy metals, organic pollutants and microorganisms. Therefore, it is of great significance to develop water treatment technologies that can efficiently remove nanoplastics.

[0003] Ultrafiltration membrane separation technology is a commonly used water treatment method that can efficiently remove suspended particles, colloids and larger size microplastics in water bodies. However, existing ultrafiltration technologies have significant limitations in dealing with nanoplastics removal:

[0004] 1. Insufficient separation precision:

[0005] The separation pore size of commercial polyvinylidene fluoride (PVDF) ultrafiltration membranes is usually between 0.01-0.1 μm, and for nanoplastics with a diameter below 200 nm, the separation effect is difficult to achieve ideal levels, especially during long-term operation, membrane pore expansion or pollution intensification will further reduce the separation precision.

[0006] 2. Membrane fouling problem is prominent:

[0007] The hydrophobicity of PVDF membranes makes them prone to contamination by organic matter, microorganisms and plastic particles when treating high-concentration microplastic contaminated water bodies, resulting in membrane surface blockage, pollution layer accumulation and membrane flux decline. This contamination not only affects the separation efficiency, but also significantly shortens the service life of the membrane and increases the maintenance cost.

[0008] 3. Limited surface modification effect:

[0009] Existing research uses physical coating or chemical grafting surface modification methods to improve the hydrophilicity of polyvinylidene fluoride membranes to alleviate membrane fouling problems, but these methods often have problems such as poor stability of the modified layer, high modification cost and inability to significantly improve the separation efficiency of nanoplastics.

[0010] However, in recent years, surface modification of ultrafiltration membranes has provided new ideas for solving the above problems. For example, natural organic matter (such as tea polyphenols) has been used for hydrophilic modification of membranes due to its good hydrophilicity, antioxidant properties and environmental friendliness, while silane coupling agents (such as 3-aminopropyl triethoxysilane) can enhance the stability of the modified layer through chemical bonding. However, current researches mostly focus on the separation performance of larger particle size microplastics (>1 μm), and there is still a lack of targeted research and modification strategies for efficient removal of nano-plastics. In addition, the existing modification techniques still have limited effect on alleviating membrane fouling during long-term operation. SUMMARY

[0011] In order to solve the above problems existing in the prior art, the present application provides a preparation method of a modified ultrafiltration membrane for efficient separation of nano-plastics in water.

[0012] The present application provides a polyvinylidene fluoride ultrafiltration membrane modification method based on synergistic modification. By optimizing the modification process, the hydrophilicity and anti-fouling performance of the membrane surface are significantly improved, and the membrane exhibits excellent removal efficiency (removal rate of more than 99%) for nano-plastics. At the same time, the method improves the stability of the modified layer through chemical cross-linking mechanism, effectively prolongs the service life of the membrane, and overcomes the limitations of insufficient separation precision and hydrophobic membrane surface in the prior art, providing an innovative solution for efficient separation of nano-plastics in water.

[0013] A preparation method of a modified ultrafiltration membrane for efficient separation of nano-plastics in water, which is completed according to the following steps:

[0014] I. Pretreatment of ultrafiltration membrane:

[0015] After soaking and wetting the ultrafiltration membrane with a solvent, the membrane is rinsed with the solvent and naturally dried to obtain a pretreated ultrafiltration membrane;

[0016] II. Dissolve tea polyphenols in anhydrous ethanol to obtain a tea polyphenol-ethanol mixed solution; immerse the pretreated ultrafiltration membrane in the tea polyphenol-ethanol mixed solution for a period of time, take it out and air dry to obtain a tea polyphenol-modified ultrafiltration membrane;

[0017] III. Dissolve 3-aminopropyl triethoxysilane in anhydrous ethanol to obtain a 3-aminopropyl triethoxysilane-ethanol mixed solution; uniformly drop the 3-aminopropyl triethoxysilane-ethanol mixed solution onto the tea polyphenol-modified ultrafiltration membrane to obtain a 3-aminopropyl triethoxysilane-modified ultrafiltration membrane;

[0018] IV. Add anhydrous ethanol into the Tris-HCl buffer solution of tea polyphenols to obtain a mixed solution; immerse the ultrafiltration membrane modified by 3-aminopropyl triethoxysilane into the mixed solution for a period of time, take it out, clean it, and then put it into an oven for drying to obtain the modified ultrafiltration membrane for efficient separation of nano-plastics in water bodies.

[0019] The application provides a preparation method of a modified ultrafiltration membrane for efficient separation of nano-plastics in water bodies.

[0020] The application has the following beneficial effects:

[0021] 1. The application performs surface modification on the ultrafiltration membrane through synergistic modification, introduces hydrophilic groups on the surface of the original membrane, and greatly improves the hydrophilicity of the membrane surface and the removal efficiency of nano-sized micro-plastics without damaging the original membrane structure.

[0022] 2. The modifier used in the application is widely available and low in cost, and the process is simple and easy to operate, so the application has good practical application prospects and promotional value.

[0023] 3. The application can greatly improve the hydrophilicity of the membrane surface: the water contact angle of the modified membrane surface is as low as 18.8-43.4° (the water contact angle of the original membrane surface is 112.3°).

[0024] 4. The application improves the pure water flux of the membrane: the pure water flux of the modified ultrafiltration membrane is increased to 12868.2-14381.5 L·m -2 ·h -1 ·bar -1 (the pure water flux of the original membrane is 7945.0 L·m -2 ·h -1 ·bar -1 );

[0025] 5. The application can greatly improve the removal rate of the membrane to nano-sized polystyrene plastic microspheres: the removal rate of the modified ultrafiltration membrane can be as high as 90% or more (the removal rate of the original membrane is 11.5%). DETAILED DESCRIPTION

[0026] Figure 1 A scanning electron microscope image of the modified ultrafiltration membrane for efficient separation of nano-plastics in water bodies prepared in Example 3;

[0027] Figure 2Static water contact angle of the modified ultrafiltration membrane for efficient separation of nano-plastic in water body prepared by commercial polyvinylidene fluoride ultrafiltration membrane and example 3, (a) is the commercial polyvinylidene fluoride ultrafiltration membrane, (b) is the modified ultrafiltration membrane for efficient separation of nano-plastic in water body prepared by example 3;

[0028] Figure 3 Infrared spectrum of the membrane surface, (a) is the commercial polyvinylidene fluoride ultrafiltration membrane, (b) is the modified ultrafiltration membrane for efficient separation of nano-plastic in water body prepared by example 3. DETAILED DESCRIPTION

[0029] Specific embodiment one: a preparation method of the modified ultrafiltration membrane for efficient separation of nano-plastic in water body, which is completed according to the following steps:

[0030] I. Pretreatment of the ultrafiltration membrane:

[0031] After the ultrafiltration membrane is soaked and wetted by the solvent, the solvent is used for flushing and natural airing to obtain the pretreated ultrafiltration membrane;

[0032] II. Dissolve the tea polyphenol in anhydrous ethanol to obtain a tea polyphenol-ethanol mixed solution; immerse the pretreated ultrafiltration membrane in the tea polyphenol-ethanol mixed solution for a period of time, take it out and air dry to obtain the tea polyphenol modified ultrafiltration membrane;

[0033] III. Dissolve 3-aminopropyl triethoxysilane in anhydrous ethanol to obtain a 3-aminopropyl triethoxysilane-ethanol mixed solution; uniformly drop the 3-aminopropyl triethoxysilane-ethanol mixed solution on the tea polyphenol modified ultrafiltration membrane to obtain the 3-aminopropyl triethoxysilane modified ultrafiltration membrane;

[0034] IV. Add anhydrous ethanol to the tea polyphenol Tris-HCl buffer solution to obtain a mixed solution; immerse the 3-aminopropyl triethoxysilane modified ultrafiltration membrane in the mixed solution for a period of time, take it out, wash and then put it in the oven for drying to obtain the modified ultrafiltration membrane for efficient separation of nano-plastic in water body.

[0035] Specific embodiment two: the difference between the embodiment and specific embodiment one is that the material of the ultrafiltration membrane in step one is PVDF, PTFE, PES or PSU. The other steps are the same as those in specific embodiment one.

[0036] Specific embodiment three: the difference between the embodiment and specific embodiment one or two is that the solvent in step one is anhydrous ethanol or deionized water. The other steps are the same as those in specific embodiment one or two.

[0037] Specific embodiment four: the difference between this embodiment and one of the specific embodiments one to three is that the reaction time in step two is 20 min to 40 min. The other steps are the same as specific embodiments one to three.

[0038] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the concentration of tea polyphenols in the tea polyphenol-ethanol mixed solution in step two is 30 mg / mL to 60 mg / mL. The other steps are the same as specific embodiments one to four.

[0039] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the volume fraction of 3-aminopropyl triethoxysilane in the 3-aminopropyl triethoxysilane-ethanol mixed solution in step three is 30% to 60%. The other steps are the same as specific embodiments one to five.

[0040] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the dropwise addition amount of the 3-aminopropyl triethoxysilane-ethanol mixed solution in step three is 0.15 mL / cm 2 ~ 0.50 mL / cm 2 . The other steps are the same as specific embodiments one to six.

[0041] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that the volume fraction of anhydrous ethanol in the mixed solution in step four is 10% to 20%. The other steps are the same as specific embodiments one to seven.

[0042] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the concentration of tea polyphenols in the tea polyphenol-Tris-HCl buffer solution in step four is 1 mg / mL to 5 mg / mL; the concentration of Tris-HCl buffer solution is 0.01 mol / L to 1 mol / L, and the pH value is 8.5. The other steps are the same as specific embodiments one to eight.

[0043] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the reaction time in step four is 12 h to 36 h. The other steps are the same as specific embodiments one to nine.

[0044] The following examples are used to verify the beneficial effects of the present application:

[0045] Example 1: a preparation method of a modified ultrafiltration membrane for efficient separation of nanoplastics in water bodies, which is completed according to the following steps:

[0046] I. Pretreatment of ultrafiltration membrane:

[0047] The ultrafiltration membrane is soaked and wetted with anhydrous ethanol for 30 minutes, then rinsed with deionized water and naturally dried to obtain a pretreated ultrafiltration membrane;

[0048] The material of the ultrafiltration membrane in step one is a commercial PVDF ultrafiltration membrane;

[0049] II. Dissolve tea polyphenols in anhydrous ethanol to obtain a tea polyphenol-ethanol mixed solution; immerse the pretreated ultrafiltration membrane in the tea polyphenol-ethanol mixed solution for 30 minutes, then take it out and air dry to obtain a tea polyphenol-modified ultrafiltration membrane;

[0050] The concentration of tea polyphenols in the tea polyphenol-ethanol mixed solution in step two is 50 mg / mL;

[0051] III. Dissolve 3-aminopropyl triethoxysilane in anhydrous ethanol to obtain a 3-aminopropyl triethoxysilane-ethanol mixed solution; uniformly drop the 3-aminopropyl triethoxysilane-ethanol mixed solution onto the tea polyphenol-modified ultrafiltration membrane to obtain a 3-aminopropyl triethoxysilane-modified ultrafiltration membrane;

[0052] The volume fraction of 3-aminopropyl triethoxysilane in the 3-aminopropyl triethoxysilane-ethanol mixed solution in step three is 50%;

[0053] The dropwise addition amount of the 3-aminopropyl triethoxysilane-ethanol mixed solution in step three is 0.25 mL / cm 2 ;

[0054] IV. Add 5 mL of anhydrous ethanol to 25 mL of tea polyphenol Tris-HCl buffer solution to obtain a mixed solution; immerse the 3-aminopropyl triethoxysilane-modified ultrafiltration membrane in the mixed solution for 12 hours, then rinse it with deionized water and anhydrous ethanol in sequence to remove the excess solution on the membrane surface, and then place it in an oven with a temperature of 60°C for drying for 30 minutes to obtain a modified ultrafiltration membrane for efficient separation of nano-plastics in water bodies;

[0055] The concentration of tea polyphenols in the tea polyphenol Tris-HCl buffer solution in step four is 2 mg / mL, the concentration of the Tris-HCl buffer solution is 1.0 mol / L, and the pH value is 8.5.

[0056] The permeation flux of the modified ultrafiltration membrane for efficient separation of nano-plastics in water bodies prepared in Example 1 to pure water is 13018.6 L·m -2 ·h -1 ·bar -1 at room temperature under constant pressure, and the water contact angle on the surface of the membrane is 43.4°. Replace the pure water with a polystyrene microsphere aqueous solution with a concentration of 50 mg / L, and filter for 1 hour at room temperature under constant pressure. The removal rate of the filter membrane to the polystyrene microspheres is 16.05%.

[0057] Example 2: The difference between this example and Example 1 is that the modified ultrafiltration membrane after modification of 3-aminopropyl triethoxysilane is immersed in the mixed solution for 24h in step four. The other steps and parameters are the same as those in Example 1.

[0058] The modified ultrafiltration membrane prepared in Example 2 for efficient separation of nano-plastics in water has a water permeation flux of 14381.5 L·m -2 ·h -1 ·bar -1 at room temperature under constant pressure test. The water contact angle on the surface of the membrane is 19.6°. The pure water is replaced with a polystyrene microsphere aqueous solution with a concentration of 50mg / L, and the constant pressure filtration is carried out at room temperature for 1h. The removal rate of the polystyrene microspheres by the filter membrane is 24.53%.

[0059] Example 3: The difference between this example and Example 1 is that the modified ultrafiltration membrane after modification of 3-aminopropyl triethoxysilane is immersed in the mixed solution for 36h in step four. The other steps and parameters are the same as those in Example 1.

[0060] The modified ultrafiltration membrane prepared in Example 3 for efficient separation of nano-plastics in water has a water permeation flux of 12868.2 L·m -2 ·h -1 ·bar -1 at room temperature under constant pressure test. The water contact angle on the surface of the membrane is 18.8°. The pure water is replaced with a polystyrene microsphere aqueous solution with a concentration of 50mg / L, and the constant pressure filtration is carried out at room temperature for 1h. The removal rate of the polystyrene microspheres by the filter membrane is 91.03%.

[0061] Example 4: The difference between this example and Example 1 is that the constant pressure filtration time of the filter membrane to the polystyrene microsphere solution with a concentration of 50mg / L is changed. After constant pressure filtration at room temperature for 1h, the deionized water is backwashed at the same pressure for 10min, and then the constant pressure filtration is continued for 1h. The other steps and parameters are the same as those in Example 1.

[0062] Example 5: The difference between this example and Example 2 is that the constant pressure filtration time of the filter membrane to the polystyrene microsphere solution with a concentration of 50mg / L is changed. After constant pressure filtration at room temperature for 1h, the deionized water is backwashed at the same pressure for 10min, and then the constant pressure filtration is continued for 1h. The other steps and parameters are the same as those in Example 2.

[0063] Example 6: The difference between this example and Example 3 is that the constant pressure filtration time of the filter membrane to the polystyrene microsphere solution with a concentration of 50mg / L is changed. After constant pressure filtration at room temperature for 1h, the deionized water is backwashed at the same pressure for 10min, and then the constant pressure filtration is continued for 1h. The other steps and parameters are the same as those in Example 3.

[0064] The removal rate of polystyrene microspheres by the filter membrane in the second constant pressure filtration stage is shown in Table 1.

[0065] Table 1

[0066] Examples Removal rate / % Example 4 94.99 Example 5 98.13 Example 6 99.91

[0067] Comparative Example 1:

[0068] A commercially available PVDF ultrafiltration membrane was immersed in anhydrous ethanol for 30 min, rinsed with deionized water, and air-dried. Under constant pressure at room temperature, the membrane's permeation flux to pure water was measured to be 7945.0 L·m⁻¹. -2 ·h -1 ·bar -1 The water contact angle on the membrane surface was 112.3°. When pure water was replaced with a 50 mg / L aqueous solution of polystyrene microspheres and filtered at room temperature under constant pressure for 1 hour, the removal rate of polystyrene microspheres by the filter membrane was 11.50%.

[0069] Comparative Example 2:

[0070] The constant pressure filtration time of the filter membrane for the polystyrene microsphere solution was changed. After constant pressure filtration at room temperature for 1 hour, the membrane was backwashed with deionized water for 10 minutes under the same pressure, and then constant pressure filtration was continued for another 1 hour. Other steps were the same as those in Comparative Example 1. The modified membrane was prepared and tested. In the second constant pressure filtration stage, the removal rate of polystyrene microspheres by the filter membrane was 28.96%.

[0071] Figure 1 Scanning electron microscope image of the modified ultrafiltration membrane for efficient separation of nanoplastics in water prepared in Example 3;

[0072] from Figure 1 It can be seen that the hydrophilic modification process generates hydrophilic polymer nanoparticles on the membrane surface.

[0073] Figure 2 The static water contact angles of the commercial polyvinylidene fluoride ultrafiltration membrane and the modified ultrafiltration membrane prepared in Example 3 for efficient separation of nanoplastics in water are shown in the figure. (a) is the commercial polyvinylidene fluoride ultrafiltration membrane, and (b) is the modified ultrafiltration membrane prepared in Example 3 for efficient separation of nanoplastics in water.

[0074] from Figure 2 It can be seen that the contact angle of the modified membrane surface in Example 3 decreased from 112.3° to 18.8°, and the hydrophilicity was significantly improved.

[0075] Figure 3 The image shows the infrared spectrum of the membrane surface. In the image, (a) is a commercial polyvinylidene fluoride ultrafiltration membrane, and (b) is the modified ultrafiltration membrane prepared in Example 3 for efficient separation of nanoplastics in water.

[0076] From Figure 3 It can be seen that the modified membrane in Example 3 shows peaks at 3349.6, 3290.8, 3189.8 cm -1 which indicate the introduction of hydroxyl and amine groups on the membrane surface. In addition, after the hydrolysis of 3-aminopropyl triethoxysilane, -Si-OH is generated, which further crosslinks with the membrane surface to form -Si-O-Si or Si-O-C bonds (which is manifested as a new peak at 2948.4 cm -1 ).

Claims

1. A method for preparing a modified ultrafiltration membrane for efficient separation of nanoplastics in water bodies, characterized by The preparation method is specifically completed according to the following steps: I. Pretreatment of the ultrafiltration membrane: After the ultrafiltration membrane is soaked and wetted with a solvent, the solvent is used for flushing and natural airing to obtain the pretreated ultrafiltration membrane; II. Dissolving tea polyphenols in anhydrous ethanol to obtain a tea polyphenol-ethanol mixed solution; immersing the pretreated ultrafiltration membrane in the tea polyphenol-ethanol mixed solution for 20 min to 40 min, and then taking out and air-drying to obtain the tea polyphenol-modified ultrafiltration membrane; The concentration of tea polyphenols in the tea polyphenol-ethanol mixed solution in step II is 30 mg / mL to 60 mg / mL; III. Dissolving 3-aminopropyl triethoxysilane in anhydrous ethanol to obtain a 3-aminopropyl triethoxysilane-ethanol mixed solution; uniformly dropping the 3-aminopropyl triethoxysilane-ethanol mixed solution onto the tea polyphenol-modified ultrafiltration membrane to obtain the 3-aminopropyl triethoxysilane-modified ultrafiltration membrane; The dropwise addition amount of the 3-aminopropyltriethoxysilane-ethanol mixed solution described in Step three is 0.15 mL / cm 2 ~ 0.50 mL / cm 2 ; IV. Adding anhydrous ethanol to a tea polyphenol Tris-HCl buffer solution to obtain a mixed solution; immersing the 3-aminopropyl triethoxysilane-modified ultrafiltration membrane in the mixed solution for 12 h to 36 h, taking out, washing, and then placing in an oven for drying to obtain the modified ultrafiltration membrane for efficient separation of water body nano-plastics; The concentration of tea polyphenols in the tea polyphenol Tris-HCl buffer solution in step IV is 1 mg / mL to 5 mg / mL; the concentration of the Tris-HCl buffer solution is 0.01 mol / L to 1 mol / L, and the pH value is 8.

5.

2. The preparation method of the modified ultrafiltration membrane for efficient separation of nano-plastics in water bodies according to claim 1, characterized in that The material of the ultrafiltration membrane in step I is PVDF, PTFE, PES, or PSU.

3. The method for preparing a modified ultrafiltration membrane for efficient separation of nanoplastics in water according to claim 1, characterized in that... The solvent in step I is anhydrous ethanol or deionized water.

4. The method for preparing a modified ultrafiltration membrane for efficient separation of nanoplastics in water according to claim 1, characterized in that... The volume fraction of 3-aminopropyl triethoxysilane in the 3-aminopropyl triethoxysilane-ethanol mixed solution in step III is 30% to 60%.

5. The method according to claim 1, wherein The volume fraction of anhydrous ethanol in the mixed solution in step IV is 10% to 20%.

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