Preparation method and application of modified zirconium-based MOF (Metal Organic Framework)-based super-hydrophilic / underwater super-oleophobic PVDF (Polyvinylidene Fluoride) membrane
The PVDF film was surface coated by oxalic acid and ethylenediamine modified zirconium-based MOF materials and dopamine hydrochloride to prepare a superhydrophilic/underwater superoleophobic PVDF film, which solved the problem of insufficient hydrophilicity of the PVDF film and was susceptible to contamination of oily substances, and achieved efficient oil-water separation effect.
Patent Information
- Application Number
- CN202510403495.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-01
- Publication Date
- 2025-07-08
AI Technical Summary
The existing PVDF membranes have insufficient hydrophilicity during oil-water separation and are susceptible to contamination by oil-based substances, resulting in limited separation efficiency and service life. The traditional modification method has not been effective.
The PVDF film was surface coated and modified with oxalic acid and ethylenediamine to prepare superhydrophilic/underwater superoleophobic PVDF film.
The prepared modified membrane exhibits an oil-water separation efficiency of up to 99.9%, with excellent hydrophilicity and pollution resistance, which solves the problem that PVDF membrane is susceptible to contamination by oil substances and broadens its application in the field of underwater superoleophobic water treatment.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of polymer materials, and particularly to a preparation method and application of a modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane. Background Art
[0002] As a high-performance membrane material, PVDF (polyvinylidene fluoride) membrane has been widely used in the field of oil-water separation due to its good chemical stability, thermal stability and mechanical strength. However, the PVDF membrane itself has the problem of insufficient hydrophilicity, which leads to easy contamination by oily substances during the water treatment process, and its separation efficiency and service life are greatly limited, and further improvement is still needed. The hydrophilicity and hydrophobicity of the membrane will have a great impact on its water flux and anti-pollution performance, which is one of the important parameters of membrane performance. In order to improve the hydrophilicity and anti-pollution performance of the PVDF membrane, researchers have tried various surface modification methods. However, although the current traditional modification materials and methods have improved the performance of the PVDF membrane to a certain extent, the effects are not ideal, and there are still problems such as insufficient hydrophilicity and easy shedding of the modified layer, and excellent underwater superoleophobic performance cannot be achieved.
[0003] In recent years, metal-organic framework (MOF) materials have shown great potential in the field of membrane modification due to their high specific surface area, adjustable pore size and chemical properties. Especially the zirconium-based MOF material UIO-66 has become a hot material for membrane modification due to its excellent stability and modifiability. However, the improvement effect of unmodified UIO-66 on the PVDF membrane still needs to be improved. Therefore, there is an urgent need to develop a new PVDF membrane modification method to simultaneously achieve superhydrophilic / underwater superoleophobic and excellent anti-pollution performance. Summary of the Invention
[0004] The purpose of the present invention is to provide a preparation method and application of a modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane to solve the above problems in the background art. The present invention uses a zirconium-based MOF material (UIO-66-NH-EDA) modified with oxalic acid and ethylenediamine and dopamine hydrochloride to perform surface coating modification on the PVDF membrane, and successfully prepares a PVDF modified membrane with superhydrophilic / underwater superoleophobic and strong anti-pollution properties, and uses it in the field of oil-water separation, with obvious performance advantages.
[0005] To achieve the above purpose, the present invention provides the following technical solutions:
[0006] One of the technical solutions of the present invention: Provide a preparation method of a modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane, including the following steps:
[0007] Prepare the zirconium-based MOF material (UIO-66-NH-EDA) after modification with oxalic acid and ethylenediamine, and then mix it with dopamine hydrochloride (DA) in a solvent to obtain a coating material;
[0008] Put the PVDF membrane into the coating material for surface modification treatment to obtain the modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane.
[0009] Preferably, the zirconium-based MOF material after modification with oxalic acid and ethylenediamine is prepared by first reacting UIO-66-NH2 with oxalic acid and then continuing to react with ethylenediamine.
[0010] Preferably, after the surface modification treatment, a drying step is further included; the drying equipment is a vacuum drying oven or a vacuum freeze dryer.
[0011] Preferably, the mass ratio of the zirconium-based MOF material after modification with oxalic acid and ethylenediamine to dopamine hydrochloride is 0.05-0.7:2.
[0012] Preferably, the mixing is carried out under ultrasonic conditions, the frequency of the ultrasonic wave is 35KHz, and the time is 10min.
[0013] Preferably, after the mixing operation, a step of adjusting the pH to 8.5 is further included.
[0014] Preferably, the solvent is water.
[0015] Preferably, the temperature of the surface modification treatment is 25°C and the time is 7h.
[0016] The second technical solution of the present invention: Provide a modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane obtained according to the above preparation method.
[0017] The third technical solution of the present invention: Provide an application of the above modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane in the field of oil-water separation.
[0018] The beneficial technical effects of the present invention are as follows:
[0019] In the present invention, the zirconium-based MOF material (UIO-66-NH-EDA) modified with oxalic acid and ethylenediamine and dopamine hydrochloride are used to perform surface coating modification on the PVDF membrane, and a PVDF modified membrane with superhydrophilic / underwater superoleophobic and strong anti-pollution properties is successfully prepared and used in the field of oil-water separation, with a separation efficiency as high as 99.9%, and obvious performance advantages. UIO-66-NH-EDA and dopamine hydrochloride have excellent hydrophilic modification effects on the PVDF membrane, and their modification effects are significantly better than those of the unmodified MOF material (UIO-66-NH2).
[0020] The PVDF modified membrane prepared by the present invention has a good filtration effect on the vast majority of oily organic reagents, fully demonstrating its universality of underwater superoleophobicity and having good application prospects in the field of oil-water emulsion separation. The product of the present invention has good anti-pollution performance against oil substances, solves the problem that the PVDF membrane is easily polluted by oil substances, and can broaden its application in the field of underwater superoleophobic water treatment. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. 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.
[0022] Figure 1 It is a schematic synthesis route diagram of oxalic acid and ethylenediamine modified zirconium-based MOF material UIO-66-NH-EDA.
[0023] Figure 2 It is a comparison diagram of the product in Example 1 before and after modification. Among them, (a) is the macroscopic physical diagram of the PVDF raw material membrane in Example 1, and (b) is the macroscopic physical diagram of the product in Example 1.
[0024] Figure 3 It is the Fourier infrared spectrum diagram of M0, M2, M3, M4, M5, and M6.
[0025] Figure 4 It is a comparison of the water contact angles of M1 and M5. Among them, (a) is M1, and (b) is M5.
[0026] Figure 5 It is a comparison of the water contact angles of the PVDF membrane before and after hydrophilic modification.
[0027] Figure 6 It is a test diagram of the underwater oil contact angle of M0 and M2. Among them, (a), (b), and (c) are the test diagrams of M0 before, during, and after contact, and (d), (e), and (f) are the test diagrams of M2 before, during, and after contact.
[0028] Figure 7 It is a test diagram of the underwater oil adhesion experiment of M0. Among them, (a), (b), and (c) are the test diagrams of soybean oil before, during, and after contact, and (d), (e), and (f) are the test diagrams of chloroform before, during, and after contact.
[0029] Figure 8It is a test diagram of underwater oil adhesion for M2. Among them, (a), (b), and (c) are the test diagrams before, during, and after the contact of soybean oil, and (d), (e), and (f) are the test diagrams before, during, and after the contact of chloroform.
[0030] Figure 9 It is the characterization of the average pore size, maximum pore size, and minimum pore size of the PVDF original membrane and the modified membrane.
[0031] Figure 10 It is a comparison diagram of the feed liquid and its permeate of test group A.
[0032] Figure 11 It is a test diagram of the rejection rate of the PVDF original membrane and the modified membrane for filtering oil-water emulsion.
[0033] Figure 12 It is a test diagram of the water flux recovery rate of the PVDF original membrane and the modified membrane after filtering oil-water emulsion. Detailed implementation manners
[0034] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention.
[0035] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.
[0036] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.
[0037] Regarding the "comprising", "including", "having", "containing", etc. used in the present invention, they are all open-ended terms, that is, they are meant to include but not limited to.
[0038] The preparation method of the Tris-HCl buffer solution (pH = 8.5) in the present invention is as follows: Weigh 6.0567 g of tris(hydroxymethyl)aminomethane (Tris) drug into a beaker, add deionized water until it is completely dissolved, then pour it into a 500 mL volumetric flask, add 14.7 mL of 1 mol / L hydrochloric acid solution and make up the volume with deionized water to obtain the precursor solution of the Tris-HCl buffer solution, and then dilute it with deionized water at a volume ratio of 1:1 to obtain the Tris-HCl buffer solution (pH = 8.5).
[0039] In the present invention, "room temperature" is calculated as 10 - 30 °C unless otherwise specified.
[0040] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.
[0041] Example 1
[0042] A preparation method of a modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane is as follows:
[0043] (1) Preparation of UIO-66-NH-EDA: ① Dissolve zirconium tetrachloride (1.6872 g) and glacial acetic acid (12.5 mL) in dry DMF (150 mL), add 2-aminoterephthalic acid (1.3050 g), and ultrasonically dissolve until completely dissolved. Then add 0.54 mL of ultrapure water. After ultrasonic mixing of the solution (20 min), place it in a reaction kettle and react at 120 °C for 24 h. Centrifuge, wash three times with DMF, wash once with methanol, and dry in vacuum at 60 °C for 72 h to obtain the zirconium-based MOF material UIO-66-NH2. ② Ultrasonically dissolve oxalic acid (9 g), 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDCI, 15.9750 g), N-hydroxysuccinimide (NHS, 7.6727 g), and triethylamine (TEA, 20 mL) in DMF (150 mL) to obtain solution A. Ultrasonically disperse UIO-66-NH2 (3.5 g) in DMF (50 mL) to obtain solution B. Under stirring conditions, slowly add solution B into solution A and react at room temperature for 24 h. Centrifuge, wash three times with DMF, wash once with methanol, and dry in vacuum at 60 °C for 72 h to obtain the oxalic acid-modified zirconium-based MOF material UIO-66-NH-OA. ③ Ultrasonically disperse UIO-66-NH-OA (3.5 g), 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDCI, 2.4843 g), N-hydroxysuccinimide (NHS, 1.343 g), and triethylamine (TEA, 3 mL) in DMF (150 mL) to obtain solution C. Dissolve ethylenediamine (EDA, 1.2 mL) in DMF (50 mL) to obtain solution D. Under stirring conditions, slowly add solution D into solution A and react at room temperature for 24 h. Centrifuge, wash three times with DMF, wash once with methanol, and dry in vacuum at 60 °C for 72 h to obtain the oxalic acid- and ethylenediamine-modified zirconium-based MOF material UIO-66-NH-EDA( Figure 1 (Schematic diagram of the synthesis route of the oxalic acid- and ethylenediamine-modified zirconium-based MOF material UIO-66-NH-EDA);
[0044] (2) Preparation of UIO-66-NH-EDA / DA: Weigh 0.3200 g of dopamine hydrochloride solid (DA) into beaker ① and add 40 mL of deionized water. Weigh 0.0080 g of UIO-66-NH-EDA solid into beaker ② and add 40 mL of deionized water;
[0045] Place beaker ① and beaker ② together in an ultrasonic cleaner. Set the instrument parameters to a working frequency of 35 KHz and a working efficiency of 100%. Ultrasonic for 10 min to completely dissolve the solid components in the beakers. Then pour the solution in beaker ② into beaker ①, mix evenly, and add 80 mL of the Tris-HCl buffer solution precursor to obtain 160 mL of the coating material with a pH of 8.5 (where the DA concentration is 2 mg / mL and the UIO-66-NH-EDA concentration is 0.05 mg / mL).
[0046] (3) Preparation of the modified PVDF membrane: Pour the prepared coating material into a reaction box. Then soak the commercial PVDF membrane successively in ethanol and deionized water (the soaked membrane is denoted as M0), and then place it in the reaction box (with the membrane side facing up). Place the reaction box on a digital display constant temperature water bath oscillator at 25 °C. After the reaction box is placed, start oscillating (ensure that the membrane side of the PVDF membrane is always facing up during the oscillation) until the 7-hour oscillation ends. After the oscillation ends, use tweezers to take out the modified PVDF membrane from the reaction box, simply rinse it with deionized water, and soak it in a container filled with deionized water for 4 days (change the water once a day) to obtain the modified PVDF membrane precursor.
[0047] (4) Dry the modified PVDF membrane precursor with a vacuum freeze dryer for subsequent performance testing. The drying method of the vacuum freeze dryer is as follows: Cut the modified PVDF membrane precursor into an appropriate size, place it on filter paper, mark the concentration, time and other identifications, then fold the filter paper and fix it with a paper clip. Open the vacuum freeze dryer, adjust the rubber ring to close the crack of the upper rubber ring. After closing the machine door, turn on the circulation pump, pre-freezing valve, and compressor. Wait until the shelf temperature drops to -30 °C, and then place the sample on the shelf (note: the sensor needs to be covered with the membrane). After the sample temperature is lower than the shelf temperature, observe whether the rubber ring is tightly closed, and adjust appropriately to ensure no air leakage. Close the pre-freezing valve and open the cold trap valve. After the condenser temperature drops to -60 °C, turn on the vacuum pump. After the vacuum degree drops to 60 Pa, open the supplementary cooling valve and heating. After the sample temperature is higher than the shelf temperature, turn off all the operating parts on the panel, connect the tube to the air outlet at the lower end of the chassis, and exhaust. Then open the door and take out the sample to obtain the modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane (denoted as M2).
[0048] Figure 2 It is a comparison diagram of the products in Example 1 before and after modification. Among them, (a) is the macroscopic physical picture of the PVDF raw material membrane in Example 1, and (b) is the macroscopic physical picture of the product in Example 1.
[0049] From Figure 2 it can be clearly seen that the PVDF membrane in Example 1 has undergone obvious color changes after modification.
[0050] Example 2
[0051] The difference from Example 1 is only that the concentrations of the raw materials in the coating material are adjusted by only modifying the addition amounts of UIO-66-NH-EDA and UIO-66-NH2, and the prepared modified PVDF membranes are numbered. The composition of the specific coating material is shown in Table 1.
[0052] Table 1 Composition of the coating material
[0053]
[0054]
[0055] It can be verified from Example 2 that different mass concentrations of UIO-66-NH-EDA have different modification effects on the modified PVDF membranes.
[0056] Figure 3 Fourier transform infrared spectra of M0, M2, M3, M4, M5, and M6.
[0057] From Figure 3 it can be clearly seen that two strong peaks caused by the stretching vibrations of C-F bonds and C-C bonds appear at 1178 cm -1 and 869 cm -1 respectively; for the modified membranes with the addition of UIO-66-NH-EDA, due to the presence of O-H and N-H bonds, a broad stretching vibration can be seen between 3100 and 3600 cm -1 , and as the mass concentration of UIO-66-NH-EDA increases, the intensity of this characteristic peak becomes stronger and stronger; in addition, in the band of 1650 - 1750 cm -1 , the characteristic peak of the amide bond can be clearly seen, indicating that UIO-66-NH-EDA can be successfully coated on the surface of the PVDF membrane during the experiment.
[0058] Effect verification
[0059] 1. Membrane surface wettability performance
[0060] The hydrophilicity and hydrophobicity of the membrane will have a great impact on its water flux and anti-pollution performance, which is one of the important parameters of the membrane performance. By measuring the contact angle and the droplet disappearance time, the hydrophilic and oleophobic properties of the membrane can be judged. Generally speaking, the smaller the water contact angle on the membrane surface and the shorter the droplet disappearance time, the better the hydrophilic property of the membrane. When the underwater oil contact angle reaches 150°, the membrane can be said to have superoleophobic properties.
[0061] 1.1 Water contact angle
[0062] The present invention conducted water contact angle tests on the original PVDF membrane (M0) before modification and the modified membranes (M1 - M6). The details are shown in Table 2.
[0063] Table 2 Water Contact Angles of PVDF Membranes before and after Modification
[0064]
[0065] In Table 2, —— indicates that the droplet did not disappear within the set picture storage time (60 s).
[0066] The data results in Table 2 show that the water contact angle of M0 is 129.86°. After modification with UIO - 66 - NH - EDA, the water contact angles all decreased to the range of 20° - 27°. That is, the modified PVDF membranes with UIO - 66 - NH - EDA all exhibited good hydrophilic properties, indicating that UIO - 66 - NH - EDA and dopamine hydrochloride have excellent hydrophilic modification effects on PVDF membranes.
[0067] Figure 4 For the comparison of the water contact angles of M2 and M6. Among them, (a) is M2 and (b) is M6.
[0068] According to Figure 4 the water contact angle data of M2 and M6 in Figure 3 it can be seen that compared with the 129.86° of the original membrane, both MOF materials can achieve hydrophilic modification effects. However, by comparing the two figures in Figure 3 it can be clearly seen from a macroscopic perspective that the water contact angle of M6 is smaller. From the perspective of data analysis, it can also be clearly concluded that the water contact angle of M6 is smaller than that of M2. This shows that the hydrophilic modification effect of the MOF material (UIO - 66 - NH - EDA) modified with ethylenediamine and oxalic acid is significantly better than that of the unmodified MOF material (UIO - 66 - NH2).
[0069] Figure 5 For the comparison of the water contact angles (WCA) of PVDF membranes before and after hydrophilic modification.
[0070] Figure 5 In Figure 5 from the change of the water contact angles of M2 - M6, after changing the addition amount of UIO - 66 - NH - EDA in the coating material, the change trend is first to increase and then to decrease. It can be seen that when the concentration of UIO - 66 - NH - EDA is 0.05 mg / mL, the hydrophilic modification effect is the best. With the increase of the concentration of UIO - 66 - NH - EDA, the modification effect slightly decreases. When the concentration reaches 0.3 mg / mL, the modification effect is relatively at the lowest value, and the infiltration speed is slower, but it is still much higher than that of the membrane M1 modified with UIO - 66 - NH2.
[0071] 1.2 Underwater Oil Contact Angle
[0072] The underwater oil contact angle of the membrane was tested by a water contact angle tester (SCI4000), and the entire process of the oil droplet in contact with the membrane (before, during, and after contact) was recorded. The test reagents were six different oil reagents, namely toluene, petroleum ether, soybean oil, vacuum pump oil, n - hexane, and cyclohexane, and the calculation and measurement were carried out through the contact angle analysis software. When the oil reagent was toluene, the test results of M0 and M2 are shown in Figure 6 .
[0073] Figure 6 are the underwater oil contact angle test diagrams of M0 and M2. Among them, (a), (b), and (c) are the test diagrams of M0 before, during, and after contact, and (d), (e), and (f) are the test diagrams of M2 before, during, and after contact.
[0074] Figure 6 It shows that before modification (M0), the PVDF original membrane has a certain adsorption effect on toluene. After the oil droplet contacts the membrane surface, it will be adsorbed on the membrane, causing certain pollution to the membrane, which will lead to membrane pore blockage and affect the oil - water separation effect of the PVDF membrane; while after modification (M2), the toluene oil droplets will not adhere to the modified membrane, showing a certain super - oleophobic effect.
[0075] Table 3 Underwater oil contact angles of PVDF membranes before and after modification for different organic reagents
[0076]
[0077] Table 3 summarizes the underwater oil contact angle data of M0 and the PVDF modified membrane; for the PVDF membrane modified by UIO - 66 - NH - EDA, its underwater oil contact angles are all between 151.37° and 158.59°, and the error is less than 2°. It shows that the modified membrane has a good filtration effect on the vast majority of oily organic reagents, fully proving the universality of the underwater super - oleophobic property of the PVDF modified membrane and having good application prospects in the field of oil - water emulsion separation.
[0078] By placing the membrane samples of M0 and M2 in deionized water, tilting them, then using Sudan Ⅲ as a staining agent to dye the soybean oil and chloroform reagents red, and spraying the stained oil droplets onto the surfaces of M0 and M2 with a syringe, the entire process (before, during, and after contact) was photographed to observe the influence of the oil droplets on the membrane samples. The test results are shown in Figures 7-8 .
[0079] Figure 7 are the underwater oil adhesion experiment test diagrams of M0. Among them, (a), (b), and (c) are the test diagrams of soybean oil before, during, and after contact, and (d), (e), and (f) are the test diagrams of chloroform before, during, and after contact.
[0080] Figure 8 It is the test diagram of underwater oil adhesion experiment for M3. Among them, (a), (b) and (c) are the test diagrams before, during and after the contact of soybean oil, and (d), (e) and (f) are the test diagrams before, during and after the contact of chloroform.
[0081] From Figure 7 it can be seen that M0 has a great adsorption effect on oil substances. The oil droplets will adhere to and infiltrate into the membrane, causing membrane pollution and resulting in poor oil-water separation effect.
[0082] From Figure 8 the opposite phenomenon can be seen. The modified PVDF membrane (M3) shows excellent underwater superoleophobic performance. After the oil droplets of soybean oil and chloroform come into contact with the surface of the membrane sample, they will be affected by their own density and move away from the membrane surface. They neither adhere to the modified membrane sample nor infiltrate into the modified membrane sample, and it is difficult to cause pollution to the PVDF modified membrane.
[0083] Combined with Figures 7-8 it can be shown that the modified PVDF membrane has excellent underwater superoleophobic performance and anti-pollution performance against oil substances, solves the problem that the PVDF membrane is easily polluted by oil substances, and can broaden its application in the field of underwater superoleophobic water treatment.
[0084] The present invention also studies the acid and alkali resistance of the PVDF modified membrane. The modified membrane (M5) is fixed on a glass slide and then immersed in four prepared solutions with pH values of 3, 5, 9, and 11 for different times, and then the underwater oil contact angle test is carried out on it. The test results are shown in Table 4.
[0085] Table 4 Variation of underwater petroleum ether contact angle of modified membrane with time under different pH environments
[0086]
[0087]
[0088] It can be clearly seen from Table 4 that the PVDF modified membrane is not easily affected by the pH environment. Even after soaking for 4 days, its underwater petroleum ether contact angle changes little, and is greater than 150°, still having excellent underwater superoleophobic effect.
[0089] Table 5 Variation of underwater n-hexane contact angle of modified membrane with time under different pH environments
[0090]
[0091] It can also be further seen from the data in Table 5 that for the PVDF modified membrane (M5), even after being immersed for 4 days in different pH environments, the underwater n-hexane contact angle changes little and is greater than 150°, showing excellent underwater superoleophobicity. Therefore, the PVDF modified membrane has good acid and alkali resistance.
[0092] 2. Pore size of the membrane
[0093] The pore sizes of the PVDF membrane before and after modification were tested by a bubble pressure method pore size analyzer. The change in the pore size of the membrane will affect its flux, and the pore size test can also quantitatively test the pore size distribution of the membrane pores.
[0094] Figure 9 Characterized by the average pore size, maximum pore size, and minimum pore size of M0, M1, M2, M3, M4, M5, and M6.
[0095] Figure 9 It is recorded that the average pore size of M0 is 0.7220 μm; the average pore size, maximum pore size, and minimum pore size of the modified membrane are all smaller than those of the original membrane (M0) and change with the increase in the mass concentration of UIO-66-NH-EDA. This is mainly because the coating of UIO-66-NH-EDA blocks the membrane pores and changes the porous structure, resulting in a decrease in the average pore size, maximum pore size, and minimum pore size. When the mass concentration of UIO-66-NH-EDA is 0.05 mg / mL, the average pore size of the membrane is 0.7093 μm, the maximum pore size is 0.8870 μm, and the minimum pore size is 0.5020 μm.
[0096] 3. Determination of water flux and anti-pollution performance
[0097] The water flux test and anti-pollution filtration experiment were carried out on the PVDF modified membrane. The test sequence was deionized water, water-in-oil emulsion, and deionized water. The test group with the water-in-soybean oil emulsion as the feed liquid and M2 as the filtration membrane was used as test group A, and its test results are as Figure 10 shown.
[0098] Figure 10 It is a comparison diagram of the feed liquid and its permeate of test group A.
[0099] Figure 10 What is shown is a comparison diagram of the feed liquid (water-in-soybean oil emulsion) and its permeate in the membrane flux test. From a macroscopic perspective, it can be clearly seen that the milky white feed liquid becomes a clear and transparent permeate sample after being separated by the PVDF modified membrane, which can preliminarily indicate that the PVDF modified membrane has excellent oil-water separation performance.
[0100] The fluxes of the membrane samples of the PVDF membrane before and after modification were tested by a low-pressure flat membrane experimental device.
[0101] Figure 11It shows the rejection rate test diagrams of the PVDF original membrane and the modified membranes (M0-M6) for filtering water-in-soybean oil emulsion. As can be seen from Figure 11 it, the rejection rates of the UIO-66-NH-EDA modified membranes (M3-M6) are all higher than 99.9%, higher than that of the PVDF original membrane (M0, 98%), indicating that the PVDF modified membranes have excellent oil-water separation performance.
[0102] Figure 12 The following shows the flux recovery rate (FRR) test diagrams of the PVDF original membrane and the modified membranes (M0-M6). It can be seen from the figure that compared with the original membrane M0 (FRR = 70.09%), the flux recovery rates of the UIO-66-NH-EDA modified membranes (M2-M6) (FRR>90%) are greatly improved, indicating that the PVDF modified membranes have good anti-fouling performance.
[0103] The embodiments described above are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.
Claims
1. A preparation method of a modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane, characterized in that, It includes the following steps: Prepare a zirconium-based MOF material treated with oxalic acid and ethylenediamine, and then mix it with dopamine hydrochloride in a solvent to obtain a coating material; Put the PVDF membrane into the coating material for surface modification treatment to obtain the modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane.
2. The preparation method according to claim 1, wherein The zirconium-based MOF material treated with oxalic acid and ethylenediamine is prepared by first reacting UIO-66-NH2 with oxalic acid and then continuing to react with ethylenediamine.
3. The preparation method according to claim 1, characterized in that, The mass ratio of the zirconium-based MOF material treated with oxalic acid and ethylenediamine to dopamine hydrochloride is 0.05-0.7:
2.
4. The preparation method according to claim 1, characterized in that, The mixing is carried out under ultrasonic conditions, and the frequency of the ultrasonic wave is 35KHz and the time is 10min.
5. The preparation method according to claim 1, wherein After the mixing, it also includes the step of adjusting the pH to 8.
5.
6. The preparation method according to claim 1, wherein, The solvent is water.
7. The preparation method according to claim 1, wherein The temperature of the surface modification treatment is 25°C and the time is 7h.
8. A modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane obtained by the preparation method according to any one of claims 1-7.
9. An application of the modified zirconium-based MOF-based superhydrophilic / underwater superoleophobic PVDF membrane according to claim 8 in the field of oil-water separation.