Preparation method and application of tannic acid metal polyphenol network modified PVDF ultrafiltration membrane

Abstract

The invention discloses a preparation method and application of a tannic acid metal polyphenol network modified PVDF ultrafiltration membrane. The modified PVDF ultrafiltration membrane comprises transition metal chloride, tannic acid, polyvinylidene fluoride and N, N-dimethylacetamide, and is prepared by adopting a phase inversion membrane preparation method. Tannic acid contains a large amount of catechol and pyrogallol groups and can be complexed with metal ions to form a stable octahedral complex, so that the toxicity of metal elements is reduced, and the biocompatibility of metal is improved; tannic acid has good hydrophilicity and can be introduced into the PVDF ultrafiltration membrane to greatly improve the flux of the membrane, so that the separation efficiency of the membrane is improved; a metal polyphenol network is formed through coordination of tannic acid and metal ions, the surface property of the membrane is improved, adsorption of pollutants is reduced, the problem of membrane pollution is effectively solved, the service life of the membrane is prolonged, and the modified ultrafiltration membrane has a wider application prospect in the fields of biological separation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafiltration membranes, and particularly to a preparation method and application of a tannic acid metal polyphenol network modified PVDF ultrafiltration membrane. Background Art

[0002] Ultrafiltration membrane technology has been widely applied in many fields such as water treatment, bioseparation, and food processing. However, the problem of membrane fouling has always been a key factor restricting the performance and service life of ultrafiltration membranes. Membrane fouling can lead to a decrease in membrane flux, unstable rejection rate, increased operating costs, and maintenance difficulties. Therefore, developing effective anti-fouling ultrafiltration membrane materials and preparation methods has important practical significance.

[0003] Polyvinylidene fluoride (PVDF) has excellent chemical stability, mechanical properties, and thermal stability, and is a commonly used ultrafiltration membrane material. However, PVDF itself has poor hydrophilicity and is prone to adsorbing pollutants, resulting in serious membrane fouling. To improve the anti-fouling performance of PVDF ultrafiltration membranes, researchers have tried various modification methods, such as surface coating, blending modification, grafting modification, etc.

[0004] Tannic acid (TA) is a natural polyphenolic compound containing a large number of catechol and pyrogallol groups, and has good hydrophilicity and metal complexing ability. The metal polyphenol network is a new type of material formed by the coordination of tannic acid and metal ions, and has unique structures and properties. Introducing the tannic acid-based metal polyphenol network into PVDF ultrafiltration membranes is expected to improve the hydrophilicity and anti-fouling performance of the membranes. Summary of the Invention

[0005] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract, and the title. However, such simplifications or omissions shall not be used to limit the scope of the present invention.

[0006] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0007] The purpose of the present invention is to provide a preparation method and application of a tannic acid metal polyphenol network modified PVDF ultrafiltration membrane to solve the problem of membrane fouling existing in the existing PVDF ultrafiltration membranes and improve the flux and anti-fouling performance of the membranes.

[0008] To solve the above technical problems, the present invention provides the following technical solutions:

[0009] The present invention first provides a tannic acid metal polyphenol network modified PVDF ultrafiltration membrane. The composition of the PVDF ultrafiltration membrane by weight percentage includes: 0.5% - 1.5% of transition metal chloride, 0.5% - 1.5% of tannic acid, 15% - 17% of polyvinylidene fluoride, and 81% - 83% of N,N-dimethylacetamide.

[0010] As a preferred embodiment of the modified PVDF ultrafiltration membrane of the present invention, wherein: the composition of the PVDF ultrafiltration membrane by weight percentage includes: 1% - 1.5% of transition metal chloride, 1% - 1.5% of tannic acid, 15% - 17% of polyvinylidene fluoride, and 81% - 83% of N,N-dimethylacetamide.

[0011] As a preferred embodiment of the modified PVDF ultrafiltration membrane of the present invention, wherein: the transition metal is any one or more of iron, cobalt, copper, and zinc, and the transition metal ions (such as Fe 3+ 、Co 2+ 、Cu 2+ 、Zn 2+ ) have the ability to coordinate with the TA material and hydrophilicity.

[0012] Furthermore, the transition metal is iron.

[0013] The present invention secondly provides a preparation method of the above-mentioned tannic acid metal polyphenol network modified PVDF ultrafiltration membrane, including the following steps:

[0014] (1) Preparation of the casting solution:

[0015] Disperse the transition metal chloride evenly in DMAC (N,N-dimethylacetamide) to obtain solution A; dissolve TA (tannic acid) in DMAC (N,N-dimethylacetamide) to obtain solution B; add solution B to solution A and perform ultrasonic treatment to promote the coordination reaction between tannic acid and transition metal ions to form a metal polyphenol network and obtain solution C; add PVDF (polyvinylidene fluoride) to solution C and dissolve it fully to form a uniform and stable casting solution.

[0016] (2) Membrane preparation: Perform defoaming treatment on the uniformly stirred casting solution. Eliminate the bubbles in the casting solution to avoid defects during the film-forming process. Use the prepared casting solution and adopt conventional film-forming methods such as the phase inversion method to prepare the membrane.

[0017] As a preferred embodiment of the preparation method of the modified PVDF ultrafiltration membrane of the present invention, in the preparation process of solution A, operations such as ultrasonic treatment and stirring can be used to promote the uniform dispersion of transition metal chlorides. In an embodiment of the present invention, ultrasonic mixing is carried out at 80% power for 1 h. Ultrasonic treatment helps the uniform dispersion of FeCl3, CoCl2, CuCl2, and ZnCl2 in DMAC, providing good conditions for the subsequent coordination reaction with tannic acid.

[0018] As a preferred embodiment of the preparation method of the modified PVDF ultrafiltration membrane of the present invention, in the preparation process of solution B, operations such as ultrasonic treatment and stirring can be used to fully dissolve TA. In an embodiment of the present invention, ultrasonic mixing is carried out at 80% power for 1 h to fully dissolve tannic acid in DMAC to form a uniform solution.

[0019] As a preferred embodiment of the preparation method of the modified PVDF ultrafiltration membrane of the present invention, the ultrasonic treatment is carried out by mixing ultrasonic waves at 100% power for 1 h to promote the coordination reaction between tannic acid and transition metal ions.

[0020] As a preferred embodiment of the preparation method of the modified PVDF ultrafiltration membrane of the present invention, the full dissolution is carried out by stirring at 75 °C for 12 h. Stirring for a long time at this temperature allows PVDF to fully dissolve in the mixed solution to form a uniform and stable casting solution.

[0021] As a preferred embodiment of the preparation method of the modified PVDF ultrafiltration membrane of the present invention, the defoaming treatment is to carry out ultrasonic defoaming of the uniformly stirred casting solution at 100% power for 1 h and then let it stand for 2 h.

[0022] In an embodiment of the present invention, the membrane is prepared by the phase inversion method: the standing casting solution is evenly spread on a clean glass plate, and then the glass plate is quickly immersed in a coagulation bath (such as deionized water) to cause phase separation of the casting solution to form a solid membrane. The membrane is carefully removed from the glass plate and repeatedly rinsed with deionized water to remove the residual solvent and impurities on the membrane surface, and then the membrane is soaked in deionized water for standby. TA / Fe, TA / Co, TA / Cu, and TA / Zn mixed matrix flat membranes (abbreviated as TA / Fe, TA / Co, TA / Cu, and TA / Zn membranes) are prepared.

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

[0024] Improve the hydrophilicity and flux of the membrane: Tannic acid has good hydrophilicity. Introducing it into the PVDF ultrafiltration membrane can greatly improve the flux of the membrane, thereby improving the separation efficiency of the membrane.

[0025] Reducing the toxicity of metal elements and improving biocompatibility: Tannic acid contains a large number of catechol and pyrogallol groups, which can complex with metal ions to form stable octahedral complexes, reducing the toxicity of metal elements and improving the biocompatibility of metals. This enables the modified ultrafiltration membrane to have a broader application prospect in the field of biological separation and other fields.

[0026] Optimizing the anti-fouling performance of the membrane: The metal polyphenol network formed by the coordination of tannic acid and Fe 3+ improves the surface properties of the membrane, reduces the adsorption of pollutants, effectively alleviates the membrane fouling problem, and extends the service life of the membrane.

[0027] Exploring the optimal ratio: Exploring the optimal ratio of Fe 3+ and TA with the metal concentration as a single variable helps to further optimize the performance of the membrane and improve the comprehensive performance index of the membrane. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. Among them:

[0029] Figure 1 It is a flux test data graph of the TA / Fe membrane separating the HA solution.

[0030] Figure 2 It is a rejection rate and rejection flux graph of the TA / Fe membrane separating the HA solution.

[0031] Figure 3 It is an anti-fouling recovery effect graph of the TA / Fe membrane.

[0032] Figure 4 It is a flux test data graph of the TA / Co membrane separating the HA solution.

[0033] Figure 5 It is a rejection rate and rejection flux graph of the TA / Co membrane separating the HA solution.

[0034] Figure 6 It is an anti-fouling recovery effect graph of the TA / Co membrane.

[0035] Figure 7 It is a flux test data graph of the TA / Cu membrane separating the HA solution.

[0036] Figure 8 It is a rejection rate and rejection flux graph of the TA / Cu membrane separating the HA solution.

[0037] Figure 9 This is the anti-pollution recovery effect diagram of TA / Cu membrane.

[0038] Figure 10 This is the flux test data diagram of TA / Zn membrane separating HA solution.

[0039] Figure 11 This is the rejection rate and rejection flux diagram of TA / Zn membrane separating HA solution.

[0040] Figure 12 This is the anti-pollution recovery effect diagram of TA / Zn membrane. DETAILED DESCRIPTION

[0041] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0042] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0044] Raw materials and reagents used in the examples of the invention: PVDF (Solvay); humic acid (HA) Aladdin; tannic acid (TA) purchased from Sigma Aldrich; anhydrous ferric chloride, anhydrous cupric chloride, anhydrous zinc chloride, and anhydrous cobalt chloride purchased from Sigma Aldrich.

[0045] The instruments used in the embodiments of the present invention include: a vacuum drying oven (QSH-VHX, ALARGE) for drying and dehumidifying the polymer; an electronic balance (XPE-105, Sartorius) for weighing the medicine; an ultrapure water machine (E2-30TH, EPED) for obtaining experimental water; a magnetic stirrer (MR Hei-Tec, HE1DOLPH) for stirring the casting solution; an ultraviolet visible spectrophotometer (UV-1900, AOE) for testing the membrane retention effect; and a freeze dryer (Refrigerantdryer) for preserving the sample.

[0046] Performance testing method:

[0047] Pure water flux test: The pure water permeability of the membrane was tested using a dead-end filtration device under a transmembrane pressure of 1 bar. After the filtered liquid passed through the membrane, it was weighed by an electronic balance to calculate the filtration flux. The calculation formula is as follows:

[0048]

[0049] where J is the filtration flux (L m -2 h -1 , LMH), ΔG is the mass of the filtrate within Δt time (g), A is the filtration area (taking the effective membrane area as 9.616 cm 2 ), and ρ is the density of the filtrate (approximately 1 g / mL).

[0050] Retention performance test: The retention of HA (100 ppm) by the membrane was tested using a cross-flow system under a transmembrane pressure of 1 bar. The concentration of HA was measured at 201 nm using an ultraviolet spectrophotometer. The retention rate calculation formula is as follows:

[0051]

[0052] where R is the retention rate (%), Cp is the concentration of the permeate (g / L), and Cf is the concentration of the stock solution (g / L).

[0053] Anti-fouling performance test: The tested membrane was rinsed with deionized water for 1 min, and then subjected to pure water testing after soaking for 12 hours. The flux recovery rate FRR was calculated by the equation

[0054]

[0055] where Jw is the pure water flux of the original membrane (L / m 2 h), and Jr is the pure water flux after soaking or light exposure (L / m 2 h).

[0056] The reversible fouling rate Rr was calculated by the equation

[0057]

[0058] where JL is the water flux during filtration of HA (L / m 2 h).

[0059] The irreversible fouling rate Rir was calculated by the equation

[0060]

[0061] The total fouling rate Rt was calculated by the equation

[0062]

[0063] The photocatalytic degradation reversible fouling rate Rpr was calculated by the equation

[0064] R pr = R rs - R rl (7)

[0065] where Rrs is the reversible fouling rate after immersion treatment (%), and Rrl is the reversible fouling after light treatment (%).

[0066] The present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1, Preparation of TA / Fe film

[0068] Solution preparation: Accurately weigh 12.3 g of DMAC into a clean beaker, and then weigh 0.15 g of anhydrous ferric chloride and add it to DMAC. Place the beaker in an ultrasonic cleaner, set the ultrasonic power to 80%, and ultrasonically treat for 1 h. Stir appropriately during this period to ensure that FeCl3 is evenly dispersed in DMAC.

[0069] Take another clean beaker, weigh 12.3 g of DMAC and 0.3 g of tannic acid. Similarly, place the beaker in an ultrasonic cleaner and ultrasonically treat at a power of 80% for 1 h until the tannic acid is completely dissolved.

[0070] Slowly pour the DMAC solution containing tannic acid into the DMAC solution containing FeCl3, place it in an ultrasonic cleaner, adjust the ultrasonic power to 100%, and ultrasonically treat for 1 h to allow the two to react fully.

[0071] Add 4.8 g of PVDF to the above mixed solution, place the beaker on a magnetic stirrer, set the temperature to 75 °C, and stir for 12 h to completely dissolve PVDF and form a uniform casting solution.

[0072] Put the stirred casting solution back into the ultrasonic cleaner and ultrasonically treat at a power of 100% for 1 h for defoaming, and then let the casting solution stand for 2 h to allow the tiny bubbles in the solution to escape fully.

[0073] Evenly scrape the standing casting solution onto a clean glass plate, and then quickly immerse the glass plate in a coagulation bath (such as deionized water) to cause phase separation of the casting solution and form a solid film. Carefully remove the film from the glass plate, repeatedly rinse it with deionized water to remove the residual solvent and impurities on the film surface, and then soak the film in deionized water for standby.

[0074] The performance test results are as Figures 1 - 3 , and the ratios in the figure are all TA / Fe (wt%).

[0075] Figure 1Flux test data graph of TA / Fe membrane separating HA solution. From Figure 1 It can be seen that compared with the base membrane, the fluxes of the modified membranes have increased significantly, and the recovery rates are all above 95%, while the base membrane is about 80%.

[0076] Figure 2 Rejection rate and rejection flux graph of TA / Fe membrane separating HA solution. From Figure 2 It can be seen that when the iron content is more than the metal, the rejection flux is slightly higher. By comprehensively comparing the TA / Fe membranes of 1 / 1, 1.5 / 1.5, and 0.5 / 0.5, the 1 / 1 has the best effect.

[0077] Figure 3 Anti-pollution recovery effect diagram of TA / Fe membrane. From Figure 3 It can be seen that the FRR of the modified membrane is above 95%, and some exceed 100%, with excellent recovery performance. The reversible pollution rate is below 40%, and the irreversible pollution rate is within -20% - 10%, with excellent anti-pollution performance.

[0078] Example 2, Preparation of TA / Co membrane

[0079] Solution preparation: Accurately weigh 12.3 g of DMAC into a clean beaker, and then weigh 0.15 g of anhydrous cobalt chloride and add it to DMAC. Place the beaker in an ultrasonic cleaner, set the ultrasonic power to 80%, and ultrasonically treat for 1 h. Stir appropriately during this period to ensure that CoCl2 is evenly dispersed in DMAC.

[0080] Take another clean beaker, weigh 12.3 g of DMAC and 0.3 g of tannic acid. Similarly, place the beaker in an ultrasonic cleaner and ultrasonically treat at a power of 80% for 1 h until the tannic acid is completely dissolved.

[0081] Slowly pour the DMAC solution dissolved with tannic acid into the DMAC solution containing CoCl2, place it in an ultrasonic cleaner, adjust the ultrasonic power to 100%, and ultrasonically treat for 1 h to make the two react fully.

[0082] Add 4.8 g of PVDF to the above mixed solution, place the beaker on a magnetic stirrer, set the temperature to 75 °C, and stir for 12 h to completely dissolve PVDF and form a uniform casting solution.

[0083] Put the stirred casting solution into the ultrasonic cleaner again, ultrasonically treat at a power of 100% for 1 h for defoaming, and then let the casting solution stand for 2 h to allow the tiny bubbles in the solution to fully escape.

[0084] The well - standing casting solution was evenly spread on a clean glass plate, and then the glass plate was quickly immersed in a coagulation bath (such as deionized water) to cause phase separation of the casting solution and form a solid membrane. The membrane was carefully removed from the glass plate, repeatedly rinsed with deionized water to remove the residual solvent and impurities on the membrane surface, and then the membrane was soaked in deionized water for standby.

[0085] The performance test results are as Figures 4 - 6 , and the ratios in the figures are all TA / Co (wt%).

[0086] Figure 4 It is a flux test data graph of the TA / Co membrane for separating HA solution. From Figure 4 it can be seen that the pure water flux of the TA / Co membrane is higher than that of the TA / Fe membrane, up to 220 Lm -2 h -1 , which is three times higher than that of the base membrane.

[0087] Figure 5 It is a rejection rate and rejection flux graph of the TA / Co membrane for separating HA solution. From Figure 5 it can be seen that the rejection flux is three times that of the base membrane. When the content of cobalt metal is more than that of tannic acid, the rejection flux is higher. After comprehensive comparison of 0.5 / 0.5, 1 / 1, and 1.5 / 1.5, the TA / Co membrane with 1.5 / 1.5 has the best rejection rate and rejection flux.

[0088] Figure 6 It is an anti - fouling recovery effect diagram of the TA / Co membrane. From Figure 6 it can be seen that the FRR effect of the TA / Co membrane is worse than that of the TA / Fe membrane, but the FRR of the 1 / 1 and 1.5 / 1.5 membranes is 90%, and the recovery effect is good. Both the reversible fouling and irreversible fouling are better than those of the base membrane, proving the success of the modification of the 1 / 1 and 1.5 / 1.5 TA / Co membranes.

[0089] Example 3, Preparation of TA / Cu membrane

[0090] Solution preparation: Accurately weigh 12.3 g of DMAC into a clean beaker, and then weigh 0.15 g of anhydrous copper chloride and add it to the DMAC. Place the beaker in an ultrasonic cleaner, set the ultrasonic power to 80%, and ultrasonically treat for 1 h. Stir appropriately during this period to ensure that CuCl2 is evenly dispersed in the DMAC.

[0091] Take another clean beaker, weigh 12.3 g of DMAC and 0.3 g of tannic acid. Similarly, place the beaker in the ultrasonic cleaner and ultrasonically treat at a power of 80% for 1 h until the tannic acid is completely dissolved.

[0092] Slowly pour the DMAC solution dissolved with tannic acid into the DMAC solution containing CuCl₂, place it in an ultrasonic cleaner, adjust the ultrasonic power to 100%, and ultrasonically treat for 1 h to allow the two to react fully.

[0093] Add 4.8 g of PVDF to the above mixed solution, place the beaker on a magnetic stirrer, set the temperature to 75 °C, and stir for 12 h to completely dissolve PVDF and form a uniform casting solution.

[0094] Put the stirred casting solution into the ultrasonic cleaner again, perform defoaming treatment by ultrasonically treating at 100% power for 1 h, and then let the casting solution stand for 2 h to allow the tiny bubbles in the solution to escape fully.

[0095] Evenly scrape the standing casting solution onto a clean glass plate, and then quickly immerse the glass plate in a coagulation bath (such as deionized water) to cause phase separation of the casting solution and form a solid membrane. Carefully remove the membrane from the glass plate, repeatedly rinse it with deionized water to remove the residual solvent and impurities on the membrane surface, and then soak the membrane in deionized water for standby.

[0096] The performance test results are as Figures 7 - 9 , and the ratios in the figure are all TA / Cu (wt%).

[0097] Figure 7 It is a flux test data graph of the TA / Cu membrane for separating HA solution. From Figure 7 It can be seen that the pure water flux, rejection flux, and recovery flux of the 1 / 1 TA / Cu membrane are all in the first place. When the content of the modifier is more, the flux is higher, and it is more suitable at 1 / 1, 1 / 1.5, and 1.5 / 1.

[0098] Figure 8 It is a rejection rate and rejection flux graph of the TA / Cu membrane for separating HA solution. From Figure 8 It can be seen that when the metal copper is more than tannic acid, the rejection flux of the TA / Cu membrane is slightly higher. After comprehensive comparison, the 1 / 1 TA / Cu membrane has the highest rejection rate and rejection flux.

[0099] Figure 9 It is an anti-pollution recovery effect diagram of the TA / Cu membrane. From Figure 9 It can be seen that the FRR of the TA / Cu membrane is all above 100%, and the recovery performance is excellent. The irreversible pollution rate is within -25%, the anti-pollution performance is excellent, and the flux decay rate is within 25%, proving that the membrane has good stability.

[0100] Example 4, Preparation of TA / Zn Membrane

[0101] Solution preparation: Accurately weigh 12.3 g of DMAC into a clean beaker, and then weigh 0.15 g of anhydrous zinc chloride and add it to the DMAC. Place the beaker in an ultrasonic cleaner, set the ultrasonic power to 80%, and ultrasonically treat for 1 h. During this period, stir appropriately to ensure that ZnCl2 is evenly dispersed in the DMAC.

[0102] Take another clean beaker, weigh 12.3 g of DMAC and 0.3 g of tannic acid. Similarly, place the beaker in an ultrasonic cleaner and ultrasonically treat at a power of 80% for 1 h until the tannic acid is completely dissolved.

[0103] Slowly pour the DMAC solution containing tannic acid into the DMAC solution containing ZnCl2, place it in an ultrasonic cleaner, adjust the ultrasonic power to 100%, and ultrasonically treat for 1 h to allow the two to react fully.

[0104] Add 4.8 g of PVDF to the above mixed solution, place the beaker on a magnetic stirrer, set the temperature to 75 °C, and stir for 12 h to completely dissolve the PVDF and form a uniform casting solution.

[0105] Put the stirred casting solution into the ultrasonic cleaner again, ultrasonically treat at a power of 100% for 1 h for defoaming, and then let the casting solution stand for 2 h to allow the tiny bubbles in the solution to fully escape.

[0106] Evenly scrape the standing casting solution onto a clean glass plate, and then quickly immerse the glass plate in a coagulation bath (such as deionized water) to cause phase separation of the casting solution and form a solid membrane. Carefully remove the membrane from the glass plate, repeatedly rinse it with deionized water to remove the residual solvents and impurities on the membrane surface, and then soak the membrane in deionized water for standby.

[0107] The performance test results are as Figures 10 - 12 , and the ratios in the figure are all TA / Zn (wt%).

[0108] Figure 10 It is a graph of the flux test data of the TA / Zn membrane for separating HA solution. From Figure 10 It can be seen that the flux of the 0.5 / 1 TA / Zn membrane is the best, the flux of the 0.5 / 0.5 TA / Co membrane is the lowest, and the flux of the 1 / 1 TA / Zn membrane ranks second.

[0109] Figure 11 It is a graph of the rejection rate and rejection flux of the TA / Zn membrane for separating HA solution. From Figure 11 It can be seen that, contrary to iron, cobalt, and copper, the fluxes of the 0.5 / 0.5 and 0.5 / 1 membranes are higher than those of the 1.5 / 1 and 1 / 1.5 membranes. The flux of the 0.5 / 1 membrane is the highest, but the rejection rate of the 1 / 1 TA / Zn membrane is the highest. Considering comprehensively, the 1 / 1 TA / Zn membrane is selected as the membrane with the best effect of metallic zinc.

[0110] Figure 12 The anti-pollution recovery effect diagram of the TA / Zn film. From Figure 12 It can be seen that the FRR of the TA / Zn film is between 100% and 120%, and the recovery ability is the best among the four metals of iron, cobalt, copper and zinc. The reversible pollution rate is within 40%, and the irreversible pollution rate is also within -20% to 40%. The anti-pollution ability is inferior to that of iron, cobalt and copper, but superior to that of the base film.

[0111] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A tannic acid metal polyphenol network modified PVDF ultrafiltration membrane, characterized in that, The composition of the PVDF ultrafiltration membrane by weight ratio includes: transition metal chloride 0.5% - 1.5%, tannic acid 0.5% - 1.5%, polyvinylidene fluoride 15% - 17% and N,N-dimethylacetamide 81% - 83%.

2. The tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to claim 1, characterized in that, The composition of the PVDF ultrafiltration membrane by weight ratio includes: transition metal chloride 1% - 1.5%, tannic acid 1% - 1.5%, polyvinylidene fluoride 15% - 17% and N,N-dimethylacetamide 81% - 83%.

3. The tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to claim 1, wherein The transition metal is any one or more of iron, cobalt, copper, and zinc.

4. The tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to claim 1, characterized in that, The transition metal is iron.

5. The preparation method of the tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to any one of claims 1-4, characterized in that, It includes the following steps: (1) Preparation of the casting solution: Disperse the transition metal chloride evenly in N,N-dimethylacetamide to obtain solution A; dissolve tannic acid in N,N-dimethylacetamide to obtain solution B; add solution B to solution A and perform ultrasonic treatment to obtain solution C; add polyvinylidene fluoride to solution C and dissolve it fully to obtain the casting solution. (2) Membrane preparation: After defoaming the casting solution, use the phase inversion method to prepare the membrane.

6. The preparation method of the tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to claim 5, characterized in that, The ultrasonic treatment in step (1) is carried out at 100% power for 1 - 2 h.

7. The preparation method of the tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to claim 5, characterized in that, Add polyvinylidene fluoride to solution C and stir at 75 - 80 °C for 10 - 12 h.

8. The preparation method of the tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to claim 5, characterized in that, The defoaming treatment is: ultrasonically defoam the casting solution at 100% power for 1 h and let it stand for more than 2 h.

9. The preparation method of the tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to claim 5, characterized in that, The method of preparing the membrane by the phase inversion method: evenly scrape the casting solution on a clean glass plate, immerse it in a coagulation bath to cause phase separation of the casting solution to form a solid membrane; remove the membrane from the glass plate and rinse it with deionized water to obtain it.

10. The tannic acid metal polyphenol network modified PVDF ultrafiltration membrane according to any one of claims 1 - 5 is used in the field of water treatment.

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