Water treatment membrane as well as preparation method and application thereof

Abstract

The invention provides a water treatment membrane and a preparation method and application thereof, and the preparation method comprises the following steps: (1) treating a carbon nanotube with an acidic solution to obtain an acidified carbon nanotube; (2) polymerizing N-vinylpyrrolidone, an acrylic acid compound, an RAFT reagent and the acidified carbon nano tube to obtain a modified carbon nano tube; (3) carrying out grafting reaction on maleic anhydride and polyvinylidene fluoride to obtain modified polyvinylidene fluoride; and (4) polymerizing the modified polyvinylidene fluoride, the modified carbon nanotubes and polyvinylpyrrolidone to obtain the water treatment membrane. Carbon nanotubes and polyvinylidene fluoride are modified and then polymerized with polyvinylpyrrolidone, so that the carbon nanotubes are orderly and firmly fixed on the modified polyvinylidene fluoride, the surfaces of the carbon nanotubes are coated with polyvinylpyrrolidone molecules with strong hydrophilicity, and the high-flux water treatment membrane is obtained.

Description

Technical Field

[0001] This invention relates to the field of water treatment membrane technology, and in particular to a water treatment membrane, its preparation method, and its application. Background Technology

[0002] Polyvinylidene fluoride (PVDF) is widely used as a separation membrane material in water treatment, biomedicine, and energy storage due to its excellent mechanical strength, chemical stability, and weather resistance. However, its strong hydrophobicity leads to membrane fouling, which limits its application in water treatment. Therefore, modifying separation membrane materials to enhance their antifouling ability and permeability, and increase water flux, has become a hot research topic in membrane modification.

[0003] Carbon nanotubes have a hollow tubular structure and nanoscale size, forming interconnected channels and reducing mass transfer resistance. Water molecules can pass through this hollow structure smoothly, while other ions need to overcome related resistance to pass through. Therefore, modifying PVDF membranes with carbon nanotubes is an effective way to improve membrane performance. However, the hydrophilicity of carbon nanotubes and their dispersion and filling effect on the membrane substrate can seriously affect water flux.

[0004] CN109589800B discloses a method for preparing a click-on carbon nanotube separation membrane on a PVDF membrane surface. This method prepares a PVDF-based membrane containing thiol groups by blending carbon nanotubes and PVDF. Click chemistry is then used to react the thiol groups on the PVDF-based membrane with the alkynyl groups on a hydrophilic polymer, effectively improving the hydrophobicity of the PVDF membrane and increasing the grafting rate, grafting density, and water flux on the PVDF membrane surface. However, this method requires multiple reaction steps, uses toxic reagents, is costly, and has a complex process.

[0005] CN109621756A discloses a PVDF ultrafiltration membrane, which is modified by grafting a copolymer with carbon nanotubes. PEGMA, containing hydrophilic functional groups, is grafted onto PVDF to improve its hydrophilicity, significantly increasing the membrane's flux, recovery flux, and antifouling performance. While PEGMA enhances hydrophilicity, it may gradually hydrolyze or dissolve under long-term use or extreme conditions, leading to a decrease in antifouling performance. Furthermore, carbon nanotubes are highly hydrophobic and have poor compatibility with PVDF, making them prone to interfacial delamination.

[0006] CN103865092B discloses a method for preparing anion exchange membranes by hybridizing modified carbon nanotubes with PVDF. By modifying carbon nanotubes and introducing them into the preparation of PVDF anion exchange membranes, the hydrophilicity, ion exchange capacity, and conductivity of the membrane are improved. However, the preparation method involves many steps and requires precise control of parameters in multiple stages such as modification, dispersion, polymerization, film formation, and quaternization. The control is difficult and the process is complex, making it unsuitable for large-scale production.

[0007] Therefore, developing a water treatment membrane with high flux is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a water treatment membrane, its preparation method, and its application. This invention modifies carbon nanotubes and polyvinylidene fluoride (PVDF) to coat the surface of carbon nanotubes with strong hydrophilic groups and fix them uniformly and orderly on the modified PVDF, thereby obtaining a water treatment membrane with high flux.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a water treatment membrane, the method comprising the following steps:

[0011] (1) Carbon nanotubes are treated with an acidic solution to obtain acidified carbon nanotubes;

[0012] (2) N-vinylpyrrolidone (NVP), acrylic compounds, RAFT reagent and acidified carbon nanotubes are polymerized to obtain modified carbon nanotubes;

[0013] (3) Maleic anhydride was grafted onto polyvinylidene fluoride to obtain modified polyvinylidene fluoride.

[0014] (4) Modified polyvinylidene fluoride, modified carbon nanotubes and polyvinylpyrrolidone (PVP) are polymerized to obtain a water treatment membrane.

[0015] This invention utilizes NVP and acrylic compounds to graft copolymerize with acidified carbon nanotubes under the action of a RAFT reagent. The carboxyl groups in the acrylic compounds combine with the hydroxyl groups on the surface of the acidified carbon nanotubes. Simultaneously, the RAFT method allows the end groups of the graft copolymer to retain their reactivity (the end groups are alkenyl groups). Then, modified carbon nanotubes, modified PVDF, and polyvinylpyrrolidone are polymerized. By reacting the double bonds in maleic anhydride with the active end groups of the polymer on the modified carbon nanotubes, the modified carbon nanotubes can be ordered and firmly fixed on the modified PVDF, and the two are chemically bonded together. At the same time, the surface of the modified carbon nanotubes is coated with highly hydrophilic PVP molecules, thus obtaining a high-flux water treatment membrane.

[0016] In this invention, the introduction of RAFT reagent enables the polymer to retain active groups at both ends. Without the addition of RAFT reagent, the modified carbon nanotubes do not have active groups at both ends and cannot be chemically bonded to the modified PVDF. The modified carbon nanotubes and modified PVDF are only bonded through physical adsorption, resulting in weak interfacial bonding of the water treatment membrane and consequently a decrease in water flux.

[0017] Preferably, the acidic solution includes nitric acid and sulfuric acid.

[0018] Preferably, the volume ratio of nitric acid to sulfuric acid is 1:(2-4), for example, it can be 1:2.5, 1:3 or 1:3.5, etc.

[0019] Preferably, the processing temperature is 50-80℃, for example, it can be 55℃, 60℃, 65℃, 70℃ or 75℃, etc.

[0020] Preferably, the processing time is 15-20 hours, for example, 16 hours, 17 hours, 18 hours or 19 hours.

[0021] Preferably, the process further includes filtration, washing, and drying.

[0022] Preferably, the washing is performed by washing with water until the solution is neutral.

[0023] Preferably, the drying temperature is 60-80°C, for example, 65°C, 70°C or 75°C.

[0024] Preferably, the drying time is 12-24 hours, for example, 14 hours, 16 hours, 18 hours, 20 hours or 22 hours.

[0025] Preferably, the mass ratio of N-vinylpyrrolidone, acrylic acid compound, RAFT reagent to acidified carbon nanotubes is 100:(5-10):(1-3):(0.1-0.5), for example, it can be 100:6:2.5:0.2, 100:7:2:0.3, 100:8:3:0.4, 100:9:2.2:0.5 or 100:10:2.9:0.1, etc.

[0026] If too much N-vinylpyrrolidone is used, the adsorption of PVP on the surface of modified carbon nanotubes will reach saturation after polymerization. Excessive PVP will not improve the dispersibility of modified carbon nanotubes and will instead cause unnecessary waste. If too little is used, the PVP after polymerization will not be able to fully coat the modified carbon nanotubes, causing the modified carbon nanotubes to agglomerate and resulting in a decrease in the water flux of the membrane.

[0027] Preferably, in step (2), the polymerization temperature is 60-90℃, for example, it can be 65℃, 70℃, 75℃, 80℃ or 85℃.

[0028] Preferably, in step (2), the polymerization time is 6-10 hours, for example, 7 hours, 8 hours or 9 hours.

[0029] Preferably, in step (2), the polymerization is carried out in the presence of an initiator.

[0030] Preferably, the mass ratio of the initiator to N-vinylpyrrolidone is (0.2-0.5):100, for example, it can be 0.25:100, 0.3:100, 0.35:100, 0.4:100 or 0.45:100, etc.

[0031] Preferably, the acrylic compound includes acrylic acid and / or methacrylic acid.

[0032] Preferably, the RAFT reagent includes dithioesters and / or trithiocarbonates.

[0033] Preferably, the dithioesters include at least one of benzyl dithiobenzoate, 2-cyano-2-propyl dithiobenzoate, 2-(dodecyl trithiocarbonate)-2-methylpropionic acid, benzyl dithiobenzoate, or 4-cyano-4-(thiobenzoyl)valerate.

[0034] Preferably, the trithiocarbonate class includes at least one of 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, 2-cyano-2-propyldodecyltrithiocarbonate, or 4-cyano-4-(dodecylthiocarbonyl)thiopentanoic acid.

[0035] Preferably, in step (2), the polymerization process further includes filtration and / or drying.

[0036] Preferably, the mass ratio of maleic anhydride to polyvinylidene fluoride is (8-12):100, for example, it can be 9:100, 10:100 or 11:100.

[0037] Preferably, in step (3), the grafting reaction method includes placing the material in a twin-screw extruder for blending and extrusion.

[0038] Preferably, the blending temperature is 170-190°C, for example, 175°C, 180°C or 185°C.

[0039] Preferably, the blending time is 8-15 minutes, for example, 10 minutes, 12 minutes or 14 minutes.

[0040] Preferably, in step (3), the grafting reaction is carried out in the presence of an initiator.

[0041] Preferably, in step (3), the mass ratio of polyvinylidene fluoride to initiator is 100:(0.2-0.5), for example, it can be 100:0.25, 100:0.3, 100:0.35, 100:0.4 or 100:0.45, etc.

[0042] Preferably, the mass ratio of the modified polyvinylidene fluoride, modified carbon nanotubes and polyvinylpyrrolidone is (20-30):(0.5-2):(1-5), for example, it can be 22:0.6:2, 24:1:3, 26:1.4:4, 28:1.6:3 or 30:1.8:2, etc.

[0043] If too much modified carbon nanotube is used, the high concentration of modified carbon nanotubes will agglomerate due to van der Waals forces, blocking the membrane pores, reducing the effective mass transfer channels, and causing a decrease in water flux. If too little is used, it will reduce the number of pore structures in the modified PVFD membrane, which will also lead to a decrease in water flux.

[0044] Preferably, in step (4), the polymerization is carried out in a solvent.

[0045] Preferably, the mass ratio of the solvent to the modified carbon nanotubes is (7-8):(2-3), for example, it can be 7.2:2.1, 7.4:2.3, 7.6:2.5, 7.8:2.7 or 7.9:2.9, etc.

[0046] Preferably, the solvent comprises any one or a combination of at least two of tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, or toluene.

[0047] Preferably, the polymerization is carried out in the presence of an initiator.

[0048] Preferably, the amount of the initiator added is 0.2-0.5% based on the mass of the modified carbon nanotubes, modified polyvinylidene fluoride and polyvinylpyrrolidone as 100%, for example, it can be 0.3%, 0.35%, 0.4% or 0.45%, etc.

[0049] Preferably, steps (2)-(4) are each carried out independently in the presence of an initiator.

[0050] Preferably, the initiator includes inorganic peroxide initiators, organic peroxide initiators, or azo initiators.

[0051] Preferably, the inorganic peroxide initiator includes any one or a combination of at least two of sodium persulfate, potassium persulfate, ammonium persulfate, or hydrogen peroxide.

[0052] Preferably, the organic peroxide initiator includes any one or a combination of at least two of dicumyl peroxide, tert-butyl peroxide, or di-tert-butyl peroxide.

[0053] Preferably, the azo initiator includes azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0054] Preferably, the strength of the electric field is 400-600V / m, for example, it can be 450V / m, 500V / m or 550V / m.

[0055] Preferably, the polymerization process further includes a phase transformation.

[0056] Preferably, the phase transition includes dissolving the product obtained in step (4) in a polar solvent and then placing it in water or an alcohol solvent, whereby PVDF, being insoluble in water or alcohol, slowly precipitates to form a film.

[0057] Preferably, the polar solvent includes DMF and / or NMP.

[0058] In a second aspect, the present invention provides a water treatment membrane, which is prepared by the preparation method described in the first aspect.

[0059] Thirdly, the present invention provides an application of the water treatment membrane as described in the second aspect in water treatment.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] This invention modifies carbon nanotubes by graft copolymerization of NVP and acrylic compounds with acidified carbon nanotubes under the action of a RAFT reagent. The RAFT method allows the end groups of the graft copolymer to retain their reactivity (alkenyl groups). Then, the modified carbon nanotubes, modified PVDF, and polyvinylpyrrolidone are polymerized. By reacting the double bonds in maleic anhydride with the active end groups of the polymer on the modified carbon nanotubes, the modified carbon nanotubes are ordered and firmly fixed onto the modified PVDF, achieving chemical bonding between the two. Simultaneously, the surface of the modified carbon nanotubes is coated with highly hydrophilic PVP molecules, thus obtaining a high-flux water treatment membrane. Detailed Implementation

[0062] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0063] The raw material information involved in the specific embodiments of this invention is as follows:

[0064] Carbon nanotubes: Zhongke Times carbon nanotubes, with a diameter of 15-20nm and a length of 20-30μm.

[0065] Polyvinylidene fluoride: Arkema, France, GM-15.

[0066] Polyvinylpyrrolidone: Yuang Technology, PVP K30.

[0067] Example 1

[0068] This embodiment provides a water treatment membrane and its preparation method, the preparation method comprising the following steps:

[0069] (1) Place 10g of carbon nanotubes in 40mL of an acidic solution with a volume ratio of nitric acid and sulfuric acid of 1:3, treat at 65℃ for 18h, then filter the carbon nanotubes and wash them with water until neutral, and dry them in an oven at 80℃ for 24h to obtain acidified carbon nanotubes.

[0070] (2) 100g N-vinylpyrrolidone, 8g acrylic acid, 2g 2-(dodecyltrithiocarbonate)-2-methylpropionic acid and 0.3g acidified carbon nanotubes were ultrasonically dispersed, 0.3g sodium persulfate was added, and polymerization was carried out at 75℃ for 8h. The insoluble matter was removed by filtration with a 0.3μm filter screen, and the filtrate was dried to obtain modified carbon nanotubes.

[0071] (3) Place 10g maleic anhydride, 100g polyvinylidene fluoride and 0.4g dicumyl peroxide in a twin-screw extruder to carry out grafting reaction, blend at 180℃ for 10min, and extrude to obtain modified polyvinylidene fluoride.

[0072] (4) 1.5g of modified carbon nanotubes, 25g of modified polyvinylidene fluoride and 3g of polyvinylpyrrolidone were placed in 80mL of DMF to prepare a homogeneous solution. 0.3g of azobisisobutyronitrile was added and polymerization was initiated under an external electric field of 500V / m. 10g of the product, 1g of polyvinylpyrrolidone and 100mL of DMF were placed in a three-necked flask and stirred at 60℃ for 5h until a transparent and homogeneous casting solution was formed. The solution was allowed to stand for 12h to remove bubbles. The degassed casting solution was cast onto a glass plate and scraped to 200μm with a doctor blade. The membrane was then immersed in a coagulation bath (water) for 20min. After the membrane was completely detached, it was placed in distilled water for 24h to obtain a water treatment membrane.

[0073] Example 2

[0074] This embodiment provides a water treatment membrane and its preparation method, the preparation method comprising the following steps:

[0075] (1) Place 10g of carbon nanotubes in 40mL of an acidic solution with a volume ratio of nitric acid and sulfuric acid of 1:2, treat at 50℃ for 20h, then filter the carbon nanotubes and wash them with water until neutral, and dry them in an oven at 70℃ for 12h to obtain acidified carbon nanotubes.

[0076] (2) 100g N-vinylpyrrolidone, 10g methacrylic acid, 3g 2-(dodecyltrithiocarbonate)-2-methylpropionic acid and 0.5g acidified carbon nanotubes were ultrasonically dispersed, 0.5g potassium persulfate was added, and polymerization was carried out at 60℃ for 6h. The insoluble matter was removed by filtration with a 0.3μm filter screen, and the filtrate was dried to obtain modified carbon nanotubes.

[0077] (3) Place 12g maleic anhydride, 100g polyvinylidene fluoride and 0.5g dicumyl peroxide in a twin-screw extruder to carry out grafting reaction, mix at 170℃ for 15min, and extrude to obtain modified polyvinylidene fluoride.

[0078] (4) 2g of modified carbon nanotubes, 30g of modified polyvinylidene fluoride and 5g of polyvinylpyrrolidone were placed in 90mL of DMF to prepare a homogeneous solution. 0.5g of azobisisobutyronitrile was added and polymerization was initiated under an external electric field of 400V / m. 10g of the product, 1g of polyvinylpyrrolidone and 120mL of NMP were placed in a three-necked flask and stirred at 70℃ for 8h until a transparent and homogeneous casting solution was formed. The solution was allowed to stand for 18h to remove bubbles. The degassed casting solution was cast onto a glass plate and scraped to 200μm with a doctor blade. The membrane was then immersed in a coagulation bath (water) for 30min. After the membrane was completely detached, it was placed in distilled water for 36h to obtain a water treatment membrane.

[0079] Example 3

[0080] This embodiment provides a water treatment membrane and its preparation method, the preparation method comprising the following steps:

[0081] (1) Place 10g of carbon nanotubes in 40mL of an acidic solution with a volume ratio of nitric acid and sulfuric acid of 1:4, treat at 80℃ for 15h, then filter the carbon nanotubes and wash them with water until neutral, and dry them in an oven at 90℃ for 24h to obtain acidified carbon nanotubes.

[0082] (2) 100g N-vinylpyrrolidone, 5g acrylic acid, 1g 2-(dodecyltrithiocarbonate)-2-methylpropionic acid and 0.1g acidified carbon nanotubes were ultrasonically dispersed, 0.2g hydrogen peroxide was added, and polymerization was carried out at 90℃ for 10h. The insoluble matter was removed by filtration with a 0.3μm filter screen, and the filtrate was dried to obtain modified carbon nanotubes.

[0083] (3) Place 8g maleic anhydride, 100g polyvinylidene fluoride and 0.2g dicumyl peroxide in a twin-screw extruder for grafting reaction, mix at 190℃ for 8min, and extrude to obtain modified polyvinylidene fluoride.

[0084] (4) 1g of modified carbon nanotubes, 20g of modified polyvinylidene fluoride and 1g of polyvinylpyrrolidone were placed in 75mL of DMF to prepare a homogeneous solution. 0.2g of azobisisobutyronitrile was added and polymerization was initiated under an external electric field of 600V / m. 10g of the product, 1g of polyvinylpyrrolidone and 100mL of DMF were placed in a three-necked flask and stirred at 60℃ for 5h until a transparent and homogeneous casting solution was formed. The solution was allowed to stand for 12h to remove bubbles. The degassed casting solution was cast onto a glass plate and scraped to 200μm with a doctor blade. The membrane was then immersed in a coagulation bath (water) for 20min. After the membrane was completely detached, it was placed in distilled water for 24h to obtain a water treatment membrane.

[0085] Example 4

[0086] This embodiment provides a water treatment membrane and its preparation method. The only difference from Example 1 is that in step (2), the amount of N-vinylpyrrolidone is 100g and the amount of acidified carbon nanotubes is 0.6g. The rest are the same as in Example 1.

[0087] Example 5

[0088] This embodiment provides a water treatment membrane and its preparation method. The only difference from Example 1 is that in step (2), the amount of N-vinylpyrrolidone is 100g and the amount of acidified carbon nanotubes is 0.07g. The rest are the same as in Example 1.

[0089] Example 6

[0090] This embodiment provides a water treatment membrane and its preparation method. The only difference from Embodiment 1 is that in step (4), the amount of modified carbon nanotubes is 0.4g and the amount of modified polyvinylidene fluoride is 30g. The rest are the same as in Embodiment 1.

[0091] Example 7

[0092] This embodiment provides a water treatment membrane and its preparation method. The only difference from Embodiment 1 is that in step (4), the amount of modified carbon nanotubes is 2.5g and the amount of modified polyvinylidene fluoride is 20g. All other steps are the same as in Embodiment 1.

[0093] Comparative Example 1

[0094] This comparative example provides a water treatment membrane and its preparation method. The only difference from Example 1 is that in step (2), RAFT reagent is not added, and the rest is the same as in Example 1.

[0095] Comparative Example 2

[0096] This comparative example provides a water treatment membrane and its preparation method. The only difference from Example 1 is that acrylic acid is not added in step (2), and the rest is the same as in Example 1.

[0097] Performance testing

[0098] (1) Water flux: Tested in accordance with GB / T 32360-2015.

[0099] (2) Methylene blue solution interception rate: A 10 mg / L methylene blue solution was prepared and passed through a water treatment membrane under 0.1 MPa conditions. The absorbance at the maximum wavelength of the methylene blue solution was measured using a UV spectrophotometer. The interception rate was calculated using the following formula: R = (1 - C P / C0)×100%; R is the membrane's interception rate (%), C P C0 represents the concentration of the solute in the permeate (mg / L) and C0 represents the concentration of the solute in the feed solution (mg / L).

[0100] The performance of the water treatment membranes in the above embodiments and comparative examples was tested, and the results are shown in Table 1:

[0101] Table 1

[0102] <![CDATA[Water flux (L / m 2 ·h)]]> Methylene blue solution interception rate (%) Example 1 1560 99.5 Example 2 1480 99 Example 3 1450 98.7 Example 4 1010 61 Example 5 890 47 Example 6 920 87.4 Example 7 1050 86.2 Comparative Example 1 650 33 Comparative Example 2 730 45

[0103] As shown in Table 1, the water treatment membrane provided by this invention has a high water flux, reaching 1560 L / m³. 2 The methylene blue solution achieved an interception rate of up to 99.5%.

[0104] As can be seen from the comparison between Examples 1 and Examples 4-5, when the amounts of N-vinylpyrrolidone and acidified carbon nanotubes are within the limits of this invention, the treated membrane has a high water flux and a high methylene blue solution interception rate.

[0105] As can be seen from the comparison between Example 1 and Examples 6-7, in step (4), the modified carbon nanotubes and modified polyvinylidene fluoride are within the scope of the present invention, and the treated membrane has a high water flux and methylene blue solution interception rate.

[0106] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, the addition of RAFT reagent and acrylic compounds results in the copolymer grafted onto the modified carbon nanotubes having active groups at both ends, which can be chemically bonded to the modified PVDF, making the modified carbon nanotubes and modified PVDF more firmly bonded, thereby improving the water flux and methylene blue solution interception rate of the water treatment membrane.

[0107] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a water treatment membrane, characterized in that, The preparation method includes the following steps: (1) Carbon nanotubes are treated with an acidic solution to obtain acidified carbon nanotubes; (2) N-vinylpyrrolidone, acrylic compounds, RAFT reagent and acidified carbon nanotubes are polymerized to obtain modified carbon nanotubes; (3) Maleic anhydride was grafted onto polyvinylidene fluoride to obtain modified polyvinylidene fluoride. (4) Modified polyvinylidene fluoride, modified carbon nanotubes and polyvinylpyrrolidone are polymerized to obtain a water treatment membrane.

2. The preparation method according to claim 1, characterized in that, The acidic solution includes nitric acid and sulfuric acid; Preferably, the volume ratio of nitric acid to sulfuric acid is 1:(2-4); Preferably, the processing temperature is 50-80℃; Preferably, the processing time is 15-20 hours; Preferably, the process further includes filtration, washing, and drying.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of N-vinylpyrrolidone, acrylic acid compounds, RAFT reagent, and acidified carbon nanotubes is 100:(5-10):(1-3):(0.1-0.5). Preferably, in step (2), the polymerization temperature is 60-90℃; Preferably, in step (2), the polymerization time is 6-10 hours; Preferably, in step (2), the polymerization is carried out in the presence of an initiator.

4. The preparation method according to any one of claims 1-3, characterized in that, The acrylic compounds include acrylic acid and / or methacrylic acid; Preferably, the RAFT reagent includes dithioesters and / or trithiocarbonates; Preferably, the dithioesters include at least one of benzyl dithiobenzoate, 2-cyano-2-propyl dithiobenzoate, 2-(dodecyl trithiocarbonate)-2-methylpropionic acid, benzyl dithiobenzoate, or 4-cyano-4-(thiobenzoyl)valerate. Preferably, the trithiocarbonates include at least one of 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, 2-cyano-2-propyldodecyltrithiocarbonate, or 4-cyano-4-(dodecylthiothiocarbonyl)thiopentanoic acid. Preferably, in step (2), the polymerization process further includes filtration and / or drying.

5. The preparation method according to any one of claims 1-4, characterized in that, The mass ratio of maleic anhydride to polyvinylidene fluoride is (8-12):100; Preferably, in step (3), the grafting reaction method includes placing the material in a twin-screw extruder for blending and extrusion; Preferably, the blending temperature is 170-190℃; Preferably, the blending time is 8-15 minutes.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (3), the grafting reaction is carried out in the presence of an initiator.

7. The preparation method according to any one of claims 1-6, characterized in that, The mass ratio of the modified polyvinylidene fluoride, modified carbon nanotubes, and polyvinylpyrrolidone is (20-30):(0.5-2):(1-5); Preferably, in step (4), the polymerization is carried out in a solvent; Preferably, the mass ratio of the solvent to the modified carbon nanotubes is (7-8):(2-3); Preferably, the solvent comprises any one or a combination of at least two of tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, or toluene; Preferably, the polymerization is carried out in the presence of an initiator.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (4), the polymerization is carried out under an applied electric field; Preferably, the strength of the electric field is 400-600 V / m; Preferably, the polymerization process further includes a phase transformation to form a film.

9. A water treatment membrane, characterized in that, The water treatment membrane is prepared by the preparation method according to any one of claims 1-8.

10. An application of the water treatment membrane as described in claim 9 in water treatment.