A polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane, its preparation method and application

Abstract

This invention discloses a polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane, its preparation method, and its application. The preparation method includes: (1) neutralization of AMPS and DEA; (2) preparation of P(AMPS-DEA) amphoteric polyelectrolyte-modified PVDF casting solution; (3) ion-induced coordination crosslinking of P(AMPS-DEA) amphoteric polyelectrolyte in a metal ion solution; and (4) osmotic equilibrium in water. The modification method of this invention can significantly improve the wettability, water permeability, and antifouling performance of the PVDF flat sheet membrane. The "organic-polar, ion-covalent hybrid crosslinking network" of the metal ion-induced coordination crosslinked P(AMPS-DEA) amphoteric polyelectrolyte-modified PVDF enables the modified flat sheet membrane to withstand long-term cyclic oil-water separation tests and harsh chemical environment immersion tests, proving that the hydrophilic polymer is not easily detached and has excellent hydrophilic modification stability.

Description

Technical Field

[0001] This invention relates to the field of PVDF flat sheet microfiltration membrane modification, specifically to a polyvinylidene fluoride (PVDF) microfiltration membrane modified with a solvent-induced phase separation amphoteric polyelectrolyte microgel, its preparation method, and its application. Background Technology

[0002] With the development of production and daily life, water pollution is becoming increasingly serious. Membrane separation technology is considered one of the important cutting-edge research directions in the field of separation due to its advantages such as continuous automatic operation, small equipment footprint, low energy consumption, no need for chemical additives, and no secondary environmental pollution. PVDF (polyvinylidene fluoride) microfiltration membranes, due to their stable chemical structure, have a wider range of applications and a long service life. However, their strong hydrophobicity also leads to many problems in the separation process. The main challenges are as follows: PVDF microfiltration membranes have very low surface energy, resulting in poor wettability and typically low pure water flux. In addition, the strong hydrophobicity of PVDF microfiltration membranes makes them more prone to scaling when treating aqueous solutions rich in organic pollutants such as oil and protein, increasing the frequency of membrane cleaning and replacement, and consequently increasing maintenance and operating costs. Therefore, designing a PVDF microfiltration membrane with high water flux and high antifouling performance has broad application prospects.

[0003] Currently, the hydrophilic modification methods for PVDF microfiltration membranes mainly include two types: surface modification and bulk modification. Surface modification mainly involves coating the surface of the PVDF membrane with a hydrophilic coating to improve its hydrophilicity. Shao Lu et al. [Shao Lu, Wang Zhenxing, Ding Shangang. A modification method for preparing highly hydrophilic coatings using dopamine-induced sol-gel method [P]. CN201410384326.9 2014-08-06] immersed the PVDF base membrane in an alkaline dopamine solution to construct a gel coating on its surface. The modified PVDF microfiltration membrane exhibited good wettability and water contact angle. However, the gel layer formed by this modification method has poor stability under varying environments and is prone to aging and peeling. Furthermore, alkaline solutions can degrade the mechanical properties of the PVDF membrane. Regarding bulk modification, Zhang Xiaowei et al. [Zhang Xiaowei, Zhang Longhui, Ni Xiaolu, Shen Zhilin, Ye Dalin. A method for preparing hydrophilic polyvinylidene fluoride microfiltration membrane [P]. CN202210335289.72022-03-31] designed a hydrophilic copolymer of polyethyleneimine, polyacrylamide, and polyethylene oxide to modify PVDF. They utilized the compatibilizing effect of the copolymer to improve the retention of the hydrophilic modifier in the PVDF membrane. The modified PVDF microfiltration membrane showed a significant reduction in water contact angle and improved hydrophilicity. However, discussions on antifouling performance only focused on hydrophilicity and hydrophobicity. Therefore, the currently reported surface modification and bulk modification methods for simultaneously improving the water flux and antifouling performance of PVDF flat sheet membranes are difficult to achieve in practical applications. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing a modified PVDF filter membrane that is simple in process, convenient in operation, uses readily available raw materials, has low cost, and has high water flux and long-lasting antifouling ability.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing a polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane includes the following steps:

[0007] (1) Add the neutralized amount of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and diethanolamine (DEA) to an organic solvent to allow them to undergo a neutralization reaction, thereby obtaining a monomeric solution of 2-acrylamido-2-methylpropanesulfonic acid (AMPS-DEA).

[0008] (2) Add polyvinylidene fluoride (PVDF), pore-forming agent and initiator to the AMPS-DEA monomer solution obtained in step (1) and mix evenly to obtain a prepolymer solution. The prepolymer solution is polymerized to obtain a casting solution.

[0009] (3) The obtained casting solution is degassed under vacuum and immersed in a solution containing metal ions for more than 1 hour to obtain a film material;

[0010] (4) The membrane material obtained in step (3) is immersed in water until osmotic equilibrium is reached to obtain the polyelectrolyte microgel modified polyvinylidene fluoride PVDF microfiltration membrane.

[0011] Furthermore, the organic solvent is selected from one or more of dimethylacetamide (DMAC), dimethyl sulfoxide, and dimethylformamide.

[0012] Furthermore, the mass fraction of PVDF in the obtained prepolymer solution is 16wt% to 18wt%, more preferably 16.5wt% to 17.5wt%.

[0013] Furthermore, the total mass fraction of AMPS-DEA monomers in the obtained prepolymer solution is 0.6 wt% to 0.9 wt%.

[0014] Furthermore, the pore-forming agent in the obtained prepolymer solution has a mass fraction of 2 wt% to 4 wt%, more preferably 2.5 wt% to 3.5 wt%.

[0015] Furthermore, in the obtained prepolymer solution, the molar amount of initiator is 0.1% to 0.5% of the molar amount of AMPS-DEA monomer, for example, 0.15%, 0.2%, 0.3%, 0.35%, or 0.4%.

[0016] Furthermore, the pore-forming agent is selected from one or more of polyvinylpyrrolidone (PVP), hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), sodium carboxymethyl cellulose (CMC-Na), and polyethylene glycol (PEG).

[0017] Furthermore, the initiator is a free radical initiator or a thermal initiator.

[0018] When the initiator is a thermal initiator, the prepolymerization and crosslinking conditions are: 60-90°C, preferably 70°C, in a water bath, with stirring for 8-12 hours. The thermal initiator is selected from one or more of ammonium persulfate (APS), potassium persulfate, hydrogen peroxide, and barium peroxide.

[0019] Furthermore, the vacuum degassing temperature of the casting solution is 60-80°C, the negative pressure is -0.08 to -0.1 MPa, and the vacuum degassing time is 60-90 min.

[0020] Furthermore, before the casting solution is immersed in the metal ion solution, it undergoes a film-forming pretreatment, including the following steps:

[0021] (1) Leveling of casting liquid; the leveling method includes scraping, spraying, spin coating, casting, etc.; the leveling substrate can be glass; for example, a scraper is used to scrape the casting liquid on the glass plate into a film at a uniform speed.

[0022] (2) Spray droplets or mist of undesirable solvent onto the surface of the casting solution and leave it for 5-10 minutes. The presence of undesirable solvent droplets on the surface of the casting solution can cause pre-phase separation and the formation of sponge-like pores on the membrane surface, which restricts the precipitation of amphoteric polyelectrolytes into the coagulation bath during the phase separation process.

[0023] Furthermore, the unsuitable solvent is water. For example, water mist produced by a humidifier can be used to treat the leveled casting solution surface, with a mist intensity of 1–5 mL / min. -1 cm -2 .

[0024] Furthermore, the thickness of the film after leveling with the casting solution is 200–400 μm, for example, 200 μm, 250 μm, 300 μm, or 350 μm. The film thickness is generally slightly less than the leveling thickness. Therefore, if the leveling thickness is less than 100 μm, the film thickness is too small, resulting in poor mechanical properties. On the other hand, if the thickness is too large, it can easily lead to membrane pore collapse and a low equilibrium water flux.

[0025] Further, the concentration of metal ions in the metal ion solution is 0.01–0.03 mol / L, for example, 0.015 mol / L, 0.02 mol / L, or 0.025 mol / L; the metal ions are selected from one or more of CaCl2, ZnCl2, FeCl3, and AlCl3; the soaking time is 1–24 hours. The metal ion solution is used as a coagulation bath to induce phase separation and form amphoteric polyelectrolyte microgels. Too low a concentration of the metal ion coagulation bath will result in poor coordination and failure to form microgels; while too high a concentration will lead to an excessively strong induction effect, causing the amphoteric polyelectrolyte to precipitate out of the base film.

[0026] Further, step (4) involves immersing the membrane material obtained in step (3) in water until phase separation reaches equilibrium. The equilibrium time is 12 to 36 hours, and the water is changed every 4 to 6 hours.

[0027] The second objective of this invention is to provide a polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane, which is prepared using the method described above.

[0028] A third objective of this invention is to provide applications for the polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane, used for gas filtration, liquid filtration, adsorption materials, anti-adhesion coatings, oil transportation, or oil spill containment materials.

[0029] This invention introduces a DEA (dimethylamino acid) with weak basicity, high coordination ability, and abundant hydrogen bonds into the membrane system. The DEA can undergo acid-base neutralization with the sulfonic acid groups of AMPS, activating the sulfonic acid ions to participate in metal ion coordination reactions, while also participating in metal ion coordination reactions itself. The resulting P(AMPS-DEA) amphoteric polyelectrolyte's DEA unit contains two hydroxyl groups (-OH) and one ethylamine group (-NH2), exhibiting abundant intermolecular and intramolecular hydrogen bonds. The acid-base neutralization reaction of the amine groups further promotes the intermolecular hydrogen bonding between the P(AMPS-DEA) amphoteric polyelectrolyte DEA unit and the PVDF molecule, enhancing the molecular chain entanglement between the DEA unit and the PVDF matrix. In the non-solvent-induced phase separation (metal ion coagulation bath) process of PVDF microfiltration membranes, the coordination of metal ions with P(AMPS-DEA) induces the separation of hydrophilic P(AMPS-DEA) from the hydrophobic PVDF phase. This results in both molecular chain entanglement and phase separation occurring simultaneously between the PVDF matrix and the dispersed amphoteric polyelectrolyte. Therefore, an "organic-polar, ionic-covalent hybrid cross-linked" gel microphase structure can be formed at the phase separation boundary (membrane surface and pores). This structure effectively enhances the hydrogen bonding interaction between the amphoteric polyelectrolyte and the PVDF molecular chains and effectively fixes the entanglement between the molecular chains. Furthermore, the introduction of inorganic ions reduces the adhesion on the PVDF microfiltration membrane surface, thereby significantly improving the antifouling performance of the PVDF membrane during multiple separation cycles.

[0030] The present invention provides a method for modifying PVDF high-flux antifouling filtration membranes with hydrophilic polymer chain interpenetrating microgels. The modification process is simple and easy to control. The modified flat sheet membrane possesses both high water flux and high antifouling performance. Compared with general non-electrolyte hydrophilic polymers, the interaction force between the polyelectrolyte molecular chains and water is more than an order of magnitude higher. Therefore, during the solvent-induced phase separation preparation process, this amphoteric polyelectrolyte rapidly undergoes a metal ion coordination reaction within the strongly hydrophobic continuous phase PVDF membrane to obtain a metal ion coordination-enhanced microgel. This metal ion coordination-enhanced microgel possesses a novel two-phase composite structure, where the continuous phase is a strongly hydrophobic PVDF matrix, and the dispersed phase consists of ion-crosslinked gel microparticles. This endows the flat sheet membrane with excellent antifouling properties. This will become a common method for preparing solvent-induced phase separation amphoteric polyelectrolyte microgel high-flux long-lasting antifouling PVDF microfiltration membranes.

[0031] Compared with the prior art, the present invention has the following advantages and significant progress:

[0032] 1) The preparation process of this invention is simple, the production cycle is short, the process conditions are simple, the raw materials are readily available, and the production cost is low.

[0033] 2) This invention introduces hydrophilic P(AMPS-DEA) amphoteric polyelectrolytes into PVDF membranes through in-situ polymerization, forming an entangled structure with the PVDF chains. The amphoteric polyelectrolytes are enriched on the membrane surface and at the membrane pores by metal ion induction, giving the microfiltration membrane high water flux. Furthermore, metal ion cross-linked microgels are formed at the membrane pores. The resulting modified flat sheet membrane can withstand long-term circulating oil-water separation tests and harsh chemical environment immersion tests, proving that the hydrophilic polymer is not easily detached and has excellent hydrophilic modification stability. It has broad application prospects in the field of hydrophilic modified PVDF microfiltration membranes for water treatment. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the preparation process of the solvent-induced phase separation amphoteric polyelectrolyte microgel modified PVDF microfiltration membrane of this application;

[0035] Figure 2 This is a schematic diagram illustrating the hydrophilic modification principle of the solvent-induced phase separation amphoteric polyelectrolyte microgel-modified PVDF microfiltration membrane in this application. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] In the following embodiments:

[0038] The PVDF powder used for hydrophilic modification was purchased from Sanai New Materials Technology Co., Ltd., and its grade is FR904.

[0039] The preparation method of PVDF casting solution modified by amphoteric polyelectrolyte P (AMPS-DEA) microgel is as follows: polyvinylpyrrolidone (PVP), AMPS-DEA monomer, ammonium sulfate (APS), and 17g of PVDF are added to 80g of DMAC and reacted at 70℃ for 8h with stirring.

[0040] The preparation method of solvent-induced phase separation amphoteric polyelectrolyte microgel modified PVDF membrane is as follows: the PVDF / P (AMPS-DEA) membrane after water mist-assisted pre-phase separation is immersed in 0.025 mol / L AlCl3 solution for solution-induced ion coordination, and then transferred to deionized water for phase separation and permeation equilibrium.

[0041] The experimental procedure and the corresponding principles are as follows: Figure 1 As shown.

[0042] Example 1

[0043] Step 1: Dissolve 0.50g AMPS (0.0024mol) and 0.25g DEA (0.0024mol) in 80g DMAC and stir at 25℃ for 20min to carry out monomer neutralization reaction, so as to obtain a DMAC solution containing AMPS-DEA monomer.

[0044] Step 2: Add 0.003g of thermal initiator APS (0.000012mol), 3g of pore-forming agent PVP, and 17g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in Step 1, and react with mechanical stirring at 250rpm in a 70℃ water bath for 8h to obtain P(AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (AMPS-DEA monomer mass fraction in casting solution is 0.75wt%).

[0045] Step 3: Dissolve the casting solution obtained in Step 2 at a rate of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper with a thickness of 200 μm), allowed to stand in the air for 20 seconds to level, and then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 cm -2 ).

[0046] Step 4: Immerse the microfiltration membrane obtained in Step 3 after prephase separation in a 0.025 mol / L AlCl3 solution for 6 h to perform metal ion coordination crosslinking.

[0047] Step 5: Soak the microfiltration membrane obtained in Step 4 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0048] Example 2

[0049] Step 1: Dissolve 0.45g AMPS (0.0021mol) and 0.23g DEA (0.0021mol) in 80g DMAC and stir at 25℃ for 20min to carry out monomer neutralization reaction, so as to obtain a DMAC solution containing AMPS-DEA monomer.

[0050] Step 2: Add 0.003g of thermal initiator APS (0.000012mol), 3.5g of pore-forming agent PVP, and 16.5g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in Step 1, and react with mechanical stirring at 250rpm in a 70℃ water bath for 8h to obtain P(AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (AMPS-DEA monomer mass fraction in casting solution is 0.68wt%).

[0051] Step 3: Dissolve the casting solution obtained in Step 2 at a rate of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper with a thickness of 200 μm), allowed to stand in the air for 20 seconds to level, and then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 cm -2 ).

[0052] Step 4: Immerse the microfiltration membrane obtained in Step 3 after prephase separation in a 0.025 mol / L AlCl3 solution for 6 h to perform metal ion coordination crosslinking.

[0053] Step 5: Soak the microfiltration membrane obtained in Step 4 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0054] Example 3

[0055] Step 1: Dissolve 0.40g AMPS (0.0019mol) and 0.20g DEA (0.0019mol) in 80g DMAC and stir at 25℃ for 20min to carry out monomer neutralization reaction, so as to obtain a DMAC solution containing AMPS-DEA monomer.

[0056] Step 2: Add 0.003g of thermal initiator APS (0.000012mol), 3.5g of pore-forming agent PVP, and 16.5g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in Step 1, and react with mechanical stirring at 250rpm in a 70℃ water bath for 8h to obtain P(AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (AMPS-DEA monomer mass fraction in casting solution is 0.60wt%).

[0057] Step 3: Dissolve the casting solution obtained in Step 2 at a rate of 7-8 cm·s -1The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper with a thickness of 200 μm), allowed to stand in the air for 20 seconds to level, and then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 cm -2 ).

[0058] Step 4: Immerse the microfiltration membrane obtained in Step 3 after prephase separation in a 0.025 mol / L AlCl3 solution for 6 h to perform metal ion coordination crosslinking.

[0059] Step 5: Soak the microfiltration membrane obtained in Step 4 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0060] Example 4

[0061] Step 1: Dissolve 0.55g AMPS (0.0026mol) and 0.28g DEA (0.0026mol) in 80g DMAC and stir at 25℃ for 20min to carry out monomer neutralization reaction, so as to obtain a DMAC solution containing AMPS-DEA monomer.

[0062] Step 2: Add 0.003g of thermal initiator APS (0.000012mol), 2.5g of pore-forming agent PVP, and 17.5g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in Step 1, and react with mechanical stirring at 250rpm in a 70℃ water bath for 8h to obtain P(AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (AMPS-DEA monomer mass fraction in casting solution is 0.83wt%).

[0063] Step 3: Dissolve the casting solution obtained in Step 2 at a rate of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper with a thickness of 200 μm), allowed to stand in the air for 20 seconds to level, and then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 cm -2 ).

[0064] Step 4: Immerse the microfiltration membrane obtained in Step 3 after prephase separation in a 0.025 mol / L AlCl3 solution for 6 h to perform metal ion coordination crosslinking.

[0065] Step 5: Soak the microfiltration membrane obtained in Step 4 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0066] Example 5

[0067] Step 1: Dissolve 0.60g AMPS (0.0029mol) and 0.30g DEA (0.0029mol) in 80g DMAC and stir at 25℃ for 20min to carry out monomer neutralization reaction, so as to obtain a DMAC solution containing AMPS-DEA monomer.

[0068] Step 2: Add 0.003g of thermal initiator APS (0.000012mol), 2.5g of pore-forming agent PVP, and 17.5g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in Step 1, and react with mechanical stirring at 250rpm in a 70℃ water bath for 8h to obtain P(AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (AMPS-DEA monomer mass fraction in casting solution is 0.90wt%).

[0069] Step 3: Dissolve the casting solution obtained in Step 2 at a rate of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper with a thickness of 200 μm), allowed to stand in the air for 20 seconds to level, and then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 cm -2 ).

[0070] Step 4: Immerse the microfiltration membrane obtained in Step 3 after prephase separation in a 0.025 mol / L AlCl3 solution for 6 h to perform metal ion coordination crosslinking.

[0071] Step 5: Soak the microfiltration membrane obtained in Step 4 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0072] Comparative Example 1

[0073] Step 1: Dissolve 0.50g AMPS and 0.25g DEA in 80g DMAC and stir at 25℃ for 20min to carry out monomer neutralization reaction, so as to obtain a DMAC solution containing AMPS-DEA monomers.

[0074] Step 2: Add 0.5 mol% of thermal initiator APS, 3 g of pore-forming agent PVP, and 17 g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in Step 1. React the mixture in a water bath at 70°C and 250 rpm for 8 hours to obtain P(AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution.

[0075] Step 3: Pour the casting solution obtained in Step 2 at a speed of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper with a thickness of 200 μm), allowed to stand in the air for 20 seconds to level, and then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 cm -2 ).

[0076] Step 4: Soak the microfiltration membrane obtained in Step 3 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain the amphoteric polyelectrolyte modified PVDF / P (AMPS-DEA) microfiltration membrane after phase separation.

[0077] Comparative Example 2

[0078] Step 1: Add 0.50g AMPS monomer, 0.5mol% thermal initiator APS, 3g pore-forming agent PVP, and 17g PVDF to 80g DMAC solution, and react with mechanical stirring at 250rpm in a water bath at 70℃ for 8h to obtain P(AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution.

[0079] Step 2: Pour the casting solution obtained in Step 1 at a rate of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper with a thickness of 200 μm), allowed to stand in the air for 20 seconds to level, and then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 cm -2 ).

[0080] Step 3: Immerse the microfiltration membrane obtained in Step 2 after prephase separation in a 0.025 mol / L AlCl3 solution for 6 h to perform metal ion coordination crosslinking.

[0081] Step 4: Soak the microfiltration membrane obtained in Step 3 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain solvent-induced phase separation polyelectrolyte microgel modified Al after phase separation. 3+ @PVDF / PAMPS microfiltration membrane.

[0082] Antifouling performance test:

[0083] Step 1: A Tween-80-stabilized oil-in-water emulsion was prepared to simulate real wastewater and to evaluate the oil-water separation performance of the membrane: 0.5 g of mineral oil was added to 500 mL of deionized water, and 0.1 g of Tween-80 was used as an emulsifier. The mixture was then stirred at 6000 rpm for 3 h with a high-speed reflux stirrer to obtain the oil-in-water emulsion.

[0084] Step 2: At room temperature, compact the membrane under a negative pressure of 0.1 MPa for 30 minutes to achieve a stable water flux before starting the circulating oil-water separation test. Each cycle is defined as first testing the deionized water flux for 15 minutes, then filtering the oil-in-water emulsion obtained in Step 1 for 60 minutes.

[0085] Step 3: Immerse the membrane after separation in Step 2 in a 1% citric acid (CA) solution and ultrasonically wash for 10 minutes, then rinse briefly with deionized water. Perform three consecutive tests and record the oil-water flux in each of the three cycles as J. p1 J p2 J p3 The water flux is denoted as J. w1 J w2 J w3 .

[0086] Step 4: The flux recovery rate (FRR) and flux decay rate (FDR) after the second cycle are used to determine the antifouling performance of the filter membrane. The calculation formula is as follows:

[0087]

[0088] In the formula, J w1 This is the stable water flux measured during the first test of the filter membrane, in L·m. -2 ·h -1 ·bar -1 J w2 This is the steady-state water flux of the filter membrane during the second test, measured in L·m. -2 ·h -1 ·bar -1 J p1 The oil-water flux of the filtration membrane during its first test is expressed in L·m. -2 ·h -1 ·bar -1 .

[0089] Water flux test:

[0090] Step 1: Solvent-induced phase separation of amphoteric polyelectrolyte microgels to modify Al 3+ @PVDF / P(AMPS-DEA) microfiltration membrane was cut into 5cm×5cm samples.

[0091] Step 2: Fix the sample obtained in Step 1 on an area S of 1.32 × 10 -3 m 2 On the water flux tester, ensure good airtightness between the sample and the tester.

[0092] Step 3: Add an appropriate amount of deionized water to the measuring cup above the sample fixed in Step 2, adjust the test negative pressure P of the water flux tester to stabilize at -0.1MPa, start timing after the deionized water is stably extracted through the flat membrane, pre-pressurize for 30 minutes, perform the first oil-water separation cycle, and take the stable water flux of the first water cycle.

[0093] Step 4: Calculate the water flux J of the filtration membrane by the ratio of the volume of deionized water extracted to the product of the test time, the test membrane area, and the test pressure. w， The calculation formula is as follows:

[0094]

[0095] In the formula, J w This is the pure water flux during the initial oil-water separation process, measured in L·m⁻¹. -2 ·h -1 ·bar -1 V represents the volume of deionized water extracted, in liters (L); ΔT represents the test time, in hours (h); and S represents the membrane area, in square meters (m²). 2 P represents the applied pressure, measured in bar.

[0096] The water flux and antifouling properties of the hydrophilic modified PVDF filter membranes obtained in the above embodiments and comparative examples are shown in Table 1 below:

[0097] Table 1: Water flux and antifouling properties of hydrophilic modified PVDF filter membranes

[0098]

[0099] Examples 1-5, under identical conditions, controlled the total mass of the casting solution base system to 100g, and varied the content of AMPS-DEA amphoteric polyelectrolyte monomers (keeping the ratio of the two components the same) to prepare solvent-induced phase separation amphoteric polyelectrolyte microgels modified with Al. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane; Comparative Example 1, based on Example 1, omits the use of a metal ion coagulation bath to prepare an amphoteric polyelectrolyte microgel-modified PVDF / P(AMPS-DEA) microfiltration membrane; Comparative Example 2, based on Example 1, omits the addition of DEA and only allows in-situ polymerization of PAMPS to prepare a polyelectrolyte microgel-modified Al 3+ @PVDF / PAMPS microfiltration membrane.

[0100] Based on the data in Table 1:

[0101] As can be seen from Examples 1-5 and Comparative Example 1, the sample Al of the present invention 3+ Steady-state water flux of @PVDF / P(AMPS-DEA) (2571.48~2770.32 L·m) -2 ·h -1 ·bar -1 The flux recovery rates of the second and third oil-water separation cycles (84.3–89.8%) were significantly better than those of the stable water flux of the PVDF / P (AMPS-DEA) microfiltration membrane (1984.24 L·m⁻¹). -2 ·h -1 ·bar -1 The flux recovery rate of the second and third oil-water separation cycles was 56.0%. This is because the original hydrophilic porogen PVP is rapidly lost during multiple cycles and washing. Without the use of metal ion coordination to induce microgel formation, the hydrophilic amphoteric polyelectrolyte P (AMPS-DEA) easily precipitates from the base membrane into the water during phase separation, causing the hydrophilic modifier to be lost like the porogen, failing to achieve a long-term modification effect; while Al... 3+ In PVDF / P(AMPS-DEA) membranes, the formation of microgel phases in the membrane pores and on the membrane surface is induced by the coordination and cross-linking of metal ions, which can effectively prevent oil from entering the membrane pores and causing irreversible pollution.

[0102] As can be seen from Examples 1-5 and Comparative Example 2, the sample Al of the present invention 3+ Steady-state water flux of @PVDF / P(AMPS-DEA) (2571.48~2770.32 L·m) -2 ·h -1 ·bar -1 The flux recovery rates of the second and third oil-water separation cycles (84.3%–89.8%) were significantly better than those of Al. 3+ The steady-state water flux of the PVDF / PAMPS microfiltration membrane was 1925.67 L·m⁻¹. -2 ·h -1 ·bar -1 The flux recovery rate of the second and third oil-water separation cycles was 50.9%. This is due to Al 3+ In PVDF / PAMPS microfiltration membranes, the hydrophilically modified PAMPS exhibits weak acidity and a low degree of ionization, lacking the strong coordination ability of DEA. Therefore, its coordination with metal ions is poor, and it cannot form a microgel phase. This results in poor interaction between the modified material and the base membrane, preventing long-term retention. During long-term separation, it gradually detaches, causing oil contamination and pore clogging.

[0103] The above embodiments are merely illustrative examples of the technical solutions of the present invention. The method for modifying high-flux, long-lasting, antifouling PVDF microfiltration membranes using solvent-induced phase separation and amphoteric polyelectrolyte microgels, as described in the present invention, is not limited to the methods described in the above embodiments, but is defined by the scope of the claims. Any modifications, additions, or equivalent substitutions made by those skilled in the art based on these embodiments are within the scope of protection claimed in the claims of this invention.

Claims

1. A method for preparing a polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane, characterized in that, Includes the following steps: (1) Add the neutralized amount of 2-acrylamide-2-methylpropanesulfonic acid and diethanolamine to an organic solvent to allow them to undergo a neutralization reaction, thereby obtaining an AMPS-DEA monomer solution; (2) Add polyvinylidene fluoride, pore-forming agent and initiator to the AMPS-DEA monomer solution obtained in step (1) and mix evenly to obtain a prepolymer solution. The prepolymer solution is polymerized to obtain a casting solution. The initiator is a free radical initiator or a thermal initiator. (3) The obtained casting solution is degassed under vacuum, and after film-forming pretreatment, it is immersed in a solution containing metal ions for more than 1 hour to obtain a film material; The film-forming pretreatment includes leveling the casting solution and spraying a droplet-shaped or mist-shaped undesirable solvent onto the surface of the casting solution, and leaving it for 5-10 minutes; the metal ions are selected from one or more of CaCl2, ZnCl2, FeCl3, and AlCl3. (4) The membrane material obtained in step (3) is immersed in water until osmotic equilibrium is reached to obtain the polyelectrolyte microgel modified polyvinylidene fluoride PVDF microfiltration membrane.

2. The preparation method according to claim 1, characterized in that, The organic solvent is selected from one or more of dimethylacetamide, dimethyl sulfoxide, and dimethylformamide.

3. The preparation method according to claim 1, characterized in that, In the obtained prepolymer solution, The mass fraction of PVDF is 16 wt%~18 wt%; The total mass fraction of AMPS-DEA monomers is 0.6 wt%~0.9 wt%; The pore-forming agent has a mass fraction of 2 wt% to 4 wt%. The amount of initiator used is 0.1% to 1% of the molar amount of AMPS-DEA monomer.

4. The preparation method according to claim 1, characterized in that, The pore-forming agent is selected from one or more of polyvinylpyrrolidone (PVP), hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), sodium carboxymethyl cellulose (CMC-Na), and polyethylene glycol (PEG).

5. The preparation method according to claim 1, characterized in that, The unsuitable solvent is water.

6. The preparation method according to claim 1, characterized in that, The thickness of the casting solution after leveling is 200~400μm.

7. The preparation method according to claim 1, characterized in that, The concentration of metal ions in the metal ion solution is 0.01~0.03 mol / L.

8. A polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

9. An application of the polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane according to claim 8, characterized in that, Used for gas filtration, liquid filtration, adsorption materials, anti-adhesion coatings, oil transportation, or oil spill containment materials.

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