A method for preparing a binary copolymer functionalized polyacrylonitrile ultrafiltration membrane and its application

Abstract

This invention discloses a method for preparing a binary copolymer functionalized polyacrylonitrile ultrafiltration membrane and its application, belonging to the field of membrane separation. This invention utilizes chemical grafting technology to introduce a sulfonic acid-containing binary copolymer onto the membrane surface, constructing a functionalized ultrafiltration membrane with both strong negative charge and controllable pore size. This functionalized membrane utilizes the strong negative charge imparted by the sulfonic acid groups to efficiently repel negatively charged dye molecules through the Donnan effect; simultaneously, the grafted polymer brush can precisely control the membrane pore structure, forming a narrow pore size distribution, enhancing size sieving, and allowing other substances to pass through while precisely removing target pollutants, thus achieving separation. The functionalized ultrafiltration membrane of this invention can effectively remove dye pollutants and separate salts from high-salt dye wastewater, and improves the antifouling performance of the ultrafiltration membrane, significantly enhancing long-term operational stability, laying a solid foundation for the resource reuse of wastewater.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of membrane separation, and particularly relates to a preparation method of a binary copolymer functionalized polyacrylonitrile ultrafiltration membrane and application thereof. BACKGROUND

[0002] With the rapid development of textile, printing and dyeing industries, efficient treatment of high-salt dye wastewater has become an urgent demand for water resource recycling. Such wastewater is complex in composition, usually containing high concentrations of organic dye molecules and a large amount of inorganic salt ions, which poses great challenges to separation and recovery technologies. At present, the mainstream membrane separation technology for treating high-salt dye wastewater is a multi-stage combined process of nanofiltration and reverse osmosis. However, this technical route has the disadvantages of high energy consumption and complex process. Although ultrafiltration membrane technology has the advantages of low operating pressure and high flux, its large pore size makes it difficult to effectively intercept small molecular weight dyes by size sieving mechanism. Therefore, ultrafiltration membranes are often used as a pretreatment unit in the current process to remove macromolecular pollutants in water bodies, and cannot directly achieve the core goal of dye / salt separation.

[0003] To improve the interception rate of ultrafiltration membranes for small molecules, the existing technology usually selects to regulate the pore size to the nanofiltration level, but this method will inevitably cause the "trade-off effect" of the membrane, that is, while improving the interception rate, the membrane flux will be significantly reduced, which cannot meet the demand for high flux in large-scale water treatment. In addition, a single pore size regulation strategy cannot achieve selective separation of dye molecules and inorganic salt ions. On the other hand, organic pollutants in dye wastewater are prone to adsorption and deposition on the membrane surface and in the membrane pores, forming a pollution layer, which causes a sharp decline in membrane flux. Although the existing anti-pollution strategies (such as hydrophilic modification of the membrane surface) can alleviate pollution to some extent, their durability and pertinence are insufficient for complex systems with high salt and high dye concentrations, and the membrane performance will still quickly decline in long-term operation.

[0004] Polyacrylonitrile (PAN) ultrafiltration membranes have good mechanical strength, water permeability and sunlight resistance, and are widely used in industrial wastewater treatment. However, they have inherent defects such as electrically neutral surface, wide pore size distribution and poor anti-pollution ability, which face two core bottlenecks of low dye interception rate and rapid membrane flux decline in the treatment of high-salt dye wastewater. Membrane surface functionalization can be a core strategy to break through the above limitations. By using polymer-based separation layer construction technology, functional polymers can be introduced by chemical grafting to simultaneously regulate the charge characteristics, hydrophilicity and hydrophobicity, and pore size distribution of the membrane surface, thereby endowing the membrane material with customized separation performance and anti-pollution ability. SUMMARY

[0005] In view of this, the application provides a preparation method of a binary copolymer functionalized polyacrylonitrile ultrafiltration membrane and application thereof. The application adopts a functionalization strategy of synergistic reinforcement of charge repulsion and pore size screening, introduces a binary copolymer (PAMPS-M) containing amino and negative sulfonic acid groups to the surface of a carboxylated polyacrylonitrile (PAN) ultrafiltration membrane through chemical grafting. The condensation reaction of EDC / NHS activated carboxyl and amino is used to realize covalent grafting of the polymer, and the long-term stability of the modified layer is ensured. The introduction of sulfonic acid groups significantly enhances the negative charge on the membrane surface, so that the negatively charged dye molecules in water are repelled by the Donnan effect. This rejection mode can effectively alleviate the trade-off effect, so as to ensure that the functionalized membrane has a high dye rejection rate while maintaining the ultrafiltration level flux. At the same time, the high hydrophilicity of the sulfonic acid group also helps to form a hydration layer, combined with charge repulsion, which can inhibit the adhesion of negatively charged organic pollutants in dye wastewater on the membrane surface, thereby improving the anti-pollution performance, significantly reducing the membrane pollution rate, prolonging the service life, and ensuring the stability of the membrane module flux in long-term operation. In addition, the grafting of the polymer can accurately control the pore structure of the membrane, so that the functionalized membrane forms a narrow pore size distribution to strengthen its size screening effect, so as to accurately remove target pollutants while allowing other substances (such as inorganic salts) to pass through to achieve the separation purpose, which can greatly simplify the subsequent deep treatment or salt crystallization process, and lay a solid foundation for the resource utilization of wastewater. The application expands the application field of ultrafiltration membranes from the traditional pretreatment or macromolecule screening to the precise separation of small molecule pollutants in complex scenes, and provides a new type of high-efficiency and low-energy consumption technology for solving the problem of high-salinity and high-organic wastewater treatment.

[0006] The preparation method of the binary copolymer functionalized polyacrylonitrile ultrafiltration membrane of the application comprises the following steps:

[0007] Step 1: Dissolve the polymer monomer in deionized water, add the initiator under the protection of nitrogen, heat and react to obtain a binary polymer product (PAMPS).

[0008] Step 2: Dry polyacrylonitrile (PAN) powder, pore-forming agent polyvinylpyrrolidone (PVP) and solvent N,N-dimethylformamide (DMF) solution are configured into a casting solution, heated and stirred to mix uniformly; the casting solution is poured on a wet non-woven fabric, uniformly coated with a doctor blade, and phase-separated in a coagulation bath to form a PAN-M ultrafiltration membrane.

[0009] Step 3: The PAN-M ultrafiltration membrane prepared in step 2 is placed in a sodium hydroxide (NaOH) solution and stirred vigorously under heating conditions to obtain a carboxylated PAN ultrafiltration membrane (denoted as HPAN-M, the same below).

[0010] Step 4: Put the HPAN-M membrane prepared in step 3 into the activation solution, and carry out the activation reaction in a constant temperature oscillator to improve the activity of the carboxyl group on the membrane.

[0011] Step 5: Put the activated HPAN-M membrane in step 4 into the functional polymer solution obtained in step 1, and carry out the condensation reaction in a constant temperature oscillator to obtain a functional membrane (denoted as PAMPS-M, same below).

[0012] Further technical solutions are as follows:

[0013] In step 1, the polymer monomers are 2-aminoethyl methacrylate hydrochloride (AEMA) and 2-acrylamido-2-ethylpropanesulfonic acid (AMPS).

[0014] Preferably, in step 1, the molar ratio of the two polymer monomers is 10:90.

[0015] Preferably, in step 1, the initiator is AIBA.

[0016] Preferably, in step 1, the molar ratio of the reactants (total molar amount of polymer monomers) to the initiator in the reaction system is 100:1.

[0017] Preferably, in step 1, the reaction temperature is 70°C, and the reaction time is 24 h.

[0018] In step 2, the mixing ratio of PAN, PVP and DMF solution is 18:1:81 in molar ratio.

[0019] Preferably, in step 2, the heating temperature of the casting solution is 65°C, and the stirring speed is 250 rpm.

[0020] Preferably, in step 2, the non-woven fabric needs to be moistened with ethanol before the membrane is scraped, and the non-woven fabric is in a semi-dry state before the membrane is scraped at a uniform and slow speed with a membrane scraping knife.

[0021] Preferably, in step 2, the thickness of the membrane scraping knife is 220 μm.

[0022] Preferably, in step 2, the coagulation bath is a 10vt% DMF solution, and the phase inversion process is carried out for 5 min.

[0023] In step 3, the concentration of the sodium hydroxide solution is 1 mol / L.

[0024] Preferably, in step 3, the heating temperature is 60°C, the reaction time is 0.5-2 h, and preferably 1.5 h.

[0025] In step 4, the activation solution is formed by dissolving 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) in a phosphate (PBS) buffer solution with pH = 5.0, and the molar ratio of the two reagents is 2:1.

[0026] Preferably, in step 4, the activation reaction temperature is 50℃, the oscillation speed is 150 rpm, and the activation reaction time is 0.5-2 h, preferably 1 h.

[0027] In step 5, the concentration of the functional polymer solution is 90-450 mg / L, preferably 360 mg / L.

[0028] Preferably, in step 5, the condensation reaction temperature is 50℃, the oscillation speed is 150 rpm, and the condensation reaction time is 2-10 h, preferably 4 h.

[0029] Application of the binary copolymer functionalized polyacrylonitrile ultrafiltration membrane in high-salt dye wastewater treatment.

[0030] Specifically, the binary copolymer functionalized polyacrylonitrile ultrafiltration membrane is used for high-salt dye wastewater treatment, which realizes efficient interception of small molecule dyes while maintaining membrane flux, and has excellent anti-pollution performance.

[0031] The salt includes one or more of Na2SO4, MgSO4, MgCl2, and NaCl. The total salt concentration is controlled at 1000 mg / L during experiment verification.

[0032] The small molecule dye includes one or more of malachite green, congo red, acid fuchsin, acid orange G, phenol red, and methylene blue.

[0033] The binary polymer containing amino and sulfonic acid groups is first prepared, the polyacrylonitrile ultrafiltration membrane with carboxyl groups after alkali treatment is chemically condensed and grafted with the binary polymer with amino groups, and finally a negatively charged functionalized ultrafiltration membrane is prepared through phase inversion. The characterization results of the polymer and the membrane show that the polymer is successfully synthesized and the surface chemical grafting of the functionalized membrane is successful, and the basic performance of the ultrafiltration membrane is retained.

[0034] Compared with the prior art, the beneficial effects of the present application are as follows:

[0035] 1. The surface modification is performed on the polyacrylonitrile ultrafiltration membrane after alkali treatment by using the method of chemical grafting, the functional polymer is anchored on the membrane surface, and the stability of the functionalized membrane is improved.

[0036] 2. The PAN membrane is modified by grafting binary polymer for charge-assisted functionalization, which has excellent small molecule dye rejection ability and synergistically enhanced anti-fouling performance on the basis of retaining ultrafiltration level flux.

[0037] 3. The method of chemical grafting is used to realize the precise control of membrane pore size, realize the synergistic enhancement of charge repulsion and pore size screening, and break through the "trade-off effect" of traditional membrane separation process.

[0038] 4. The functionalized membrane can effectively permeate inorganic salts and reject most negative dye molecules, and has excellent salt-dye separation and selective removal ability. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creating any creative labor.

[0040] Figure 1 The synthetic route map of the preparation method of the present application.

[0041] Figure 2 The surface morphology structure diagram of the membrane samples obtained in Example 1 and Comparative Examples 1-2. Wherein (a) is PAN-M, (b) is HPAN-M, and (c) is PAMPS-M.

[0042] Figure 3 The characterization diagram of the membrane samples obtained in Example 1 and Comparative Examples 1-2. Wherein (a) is the infrared absorption spectrum of the membrane product, and (b) is the X-ray photoelectron spectrogram of the membrane product.

[0043] Figure 4 The pore size distribution and molecular weight rejection diagram of the membrane samples obtained in Example 1 and Comparative Example 1. Wherein (a) is the pore size distribution diagram of the membrane product, and (b) is the molecular weight rejection diagram of the membrane product.

[0044] Figure 5 The charge characteristic and hydrophilic-hydrophobic property test diagram of the membrane samples obtained in Example 1 and Comparative Examples 1-2. Wherein (a) is the zeta potential diagram of the membrane product, and (b) is the water contact angle diagram of the membrane product.

[0045] Figure 6 The salt-dye separation and long-term rejection test diagram of the membrane samples obtained in Example 1 and Comparative Examples 1-2. Wherein (a) is the rejection effect diagram of the membrane product on different dyes, and (b) is the long-term rejection test diagram of the membrane product on Congo red.

[0046] Figure 7 The salt dyeing selectivity test diagram of the membrane samples obtained in Example 1 and Comparative Examples 1-2 is shown in the figure. In the figure, (a) is a diagram showing the retention effect of the membrane product on sodium chloride and acid orange, and (b) is a diagram showing the retention effect of the membrane product on acid orange and four mixed salt solutions.

[0047] Figure 8 The anti-organic contamination and flux recovery test diagram of the membrane samples obtained in Example 1 and Comparative Example 1 is shown in the figure. In the figure, (a) is a diagram showing the flux change of the membrane product in humic acid organic contaminated wastewater, and (b) is a diagram showing the flux recovery rate of the membrane product under three contamination-recovery cycles. DETAILED DESCRIPTION

[0048] The technical solutions of the present application are further analyzed and described below through specific examples.

[0049] The preparation method of the binary copolymer functionalized polyacrylonitrile ultrafiltration membrane of the present application comprises the following steps:

[0050] Step 1: Dissolve the polymer monomer in deionized water, add the initiator under nitrogen protection, and heat to react to obtain a binary polymerization product (PAMPS).

[0051] Step 2: Dry polyacrylonitrile (PAN) powder, pore-forming agent polyvinylpyrrolidone (PVP), and solvent N,N-dimethylformamide (DMF) solution are configured into a casting solution, heated and stirred to make the mixture uniform. Pour the casting solution onto a wet non-woven fabric, evenly spread with a spatula, and separate in a coagulation bath to form a PAN-M ultrafiltration membrane.

[0052] Step 3: Put the membrane prepared in step 2 into a sodium hydroxide (NaOH) solution, and stir vigorously under heating conditions to obtain a carboxylated PAN ultrafiltration membrane (denoted as HPAN-M, the same below).

[0053] Step 4: Put the HPAN-M membrane prepared in step 3 into an activation solution and perform an activation reaction in a constant temperature oscillator to improve the activity of the carboxyl groups on the membrane.

[0054] Step 5: Put the activated HPAN-M membrane in step 4 into the functionalized polymer solution obtained in step 1, and perform a condensation reaction in a constant temperature oscillator to obtain a functionalized membrane (denoted as PAMPS-M, the same below).

[0055] Regarding Step 1: Dissolve different polymer monomers in deionized water, add the initiator under nitrogen protection, and heat to react to obtain a binary polymerization product (PAMPS).

[0056] In the present application, the two polymer monomers are 2-aminoethyl methacrylate hydrochloride (abbreviated as AEMA, same below) and 2-acrylamido-2-methylpropanesulfonic acid (abbreviated as AMPS, same below) respectively. The sources of AEMA and AMPS are not limited, and commercially available products can be used.

[0057] In the present application, the molar ratio of AEMA:AMPS added for preparing the binary polymer is 10:90.

[0058] In the present application, the initiator added is AIBA, and the amount added is 0.2 mmol.

[0059] In the present application, the reaction temperature is 70℃.

[0060] In the present application, the reaction time is 24 h.

[0061] In the present application, the preparation process of step 1 is preferably as follows: two reaction monomers of AEMA and AMPS are added into a three-necked flask in a molar ratio of 10:90, dissolved with deionized water, 0.2 mmol of AIBA is added as a free radical initiator under nitrogen protection, and the reaction is carried out at 70℃ oil bath for 24 h. After the reaction is completed, the water solvent and residual monomers in the polymer solution are evaporated using a rotary evaporator, and the binary polymerization product powder (PAMPS) is obtained by freeze-drying and stored at 4℃.

[0062] Regarding step 2: dry polyacrylonitrile (PAN) powder, pore-forming agent polyvinylpyrrolidone (PVP), and solvent N,N-dimethylformamide (DMF) solution are configured into a casting solution, heated and stirred to make the mixture uniform. The casting solution is poured onto a wet non-woven fabric, uniformly coated with a doctor blade, and phase-separated in a coagulation bath to form a PAN-M ultrafiltration membrane.

[0063] In the present application, the sources of the PAN powder, PVP, and solvent DMF are not limited, and commercially available products can be used.

[0064] In the present application, the specification of the PAN powder is 150 kDa.

[0065] In the present application, the mixing ratio of the PAN, PVP, and DMF solution is a molar ratio of 18:1:81.

[0066] In the present application, the heating temperature of the casting solution is 65℃, and the stirring speed is 250 rpm.

[0067] In the present application, the sources of the doctor blade and non-woven fabric are not limited, and commercially available products can be used. The thickness of the doctor blade is preferably 200 μm.

[0068] In the present application, the coagulation bath is a 10% DMF solution, and the phase inversion process is performed for 5 min.

[0069] In the present application, the reaction environment temperature is 25℃, and the humidity is 55%.

[0070] In the present application, the preparation process of step 2 is preferably as follows: dry PAN powder and pore-forming agent PVP are dissolved in a DMF solvent, and the molar ratio of PAN:PVP:DMF is 18:1:81. The above mixed solution is stirred and dissolved at 65℃ and 250 rpm to obtain a uniform casting solution, which is placed in a vacuum drying box for vacuum degassing. In a closed blade coating chamber with a temperature of 25℃ and an air humidity of 55%, the casting solution is uniformly poured onto a wet non-woven fabric, and a blade coating knife with a thickness of 200 μm is used to uniformly coat the solution onto the surface of the non-woven fabric. Then, the membrane plate is placed in a 10 vt% DMF coagulation bath for a phase inversion process of 5 min to prepare a PAN-M ultrafiltration membrane, which is stored at 4℃.

[0071] Regarding step 3: the membrane prepared in step 2 is placed in a sodium hydroxide (NaOH) solution and stirred vigorously under heating conditions to obtain a carboxylated PAN ultrafiltration membrane (denoted as HPAN-M, same below).

[0072] In the present application, the source of NaOH is not limited and can be a commercially available product.

[0073] In the present application, the concentration of the NaOH solution is 1 mol / L.

[0074] In the present application, the heating temperature is 60℃.

[0075] In the present application, the reaction time is 0.5-2 h, and can be specifically 0.5 h, 1 h, 1.5 h, and 2 h, preferably 1.5 h.

[0076] In the present application, the preparation process of step 3 is preferably as follows: the PAN-M membrane prepared in step 2 is placed in a 1 mol / L NaOH solution and heated in a water bath at 60℃, and stirred vigorously for 1.5 h to obtain a carboxylated PAN ultrafiltration membrane (denoted as HPAN-M, same below).

[0077] Regarding step 4: the HPAN-M membrane prepared in step 3 is placed in an activation solution and subjected to an activation reaction in a constant temperature shaker to improve the activity of the carboxyl groups on the membrane.

[0078] In the present application, the activation solution is formed by dissolving 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and methacryloyloxyethyl trimethylammonium chloride (NHS) in a phosphate (PBS) buffer solution with pH=5.0. The present application does not limit the source of EDC, NHS and PBS, and commercially available products can be used.

[0079] In the present application, the molar ratio of the two reagents EDC and NHS is 2:1.

[0080] In the present application, the activation reaction temperature is 50℃, and the oscillation speed is 150 rpm.

[0081] In the present application, the activation reaction time is 0.5-2 h, and can be specifically 0.5 h, 1 h, 1.5 h and 2 h, and is preferably 1 h.

[0082] In the present application, the preparation process of step 4 is preferably as follows: 0.5 mol EDC and 0.25 mol NHS are completely dissolved in a PBS buffer solution (pH=5.0) to prepare an activation solution. The HPAN-M film prepared in step 3 is placed in the activation solution, and reacted in a constant temperature oscillator at 50℃ and 150 rpm for 1 h to improve the activity of the carboxyl groups on the film.

[0083] Regarding step 5: the activated HPAN-M film in step 4 is placed in the functional polymer solution obtained in step 1, and a condensation reaction is carried out in a constant temperature oscillator to obtain a functional film (denoted as PAMPS-M, the same below).

[0084] In the present application, the concentration of the functional polymer solution is 90-450 mg / L, and can be specifically 90 mg / L, 180 mg / L, 270 mg / L, 360 mg / L and 450 mg / L, and is preferably 360 mg / L.

[0085] In the present application, the condensation reaction temperature is 50℃, and the oscillation speed is 150 rpm.

[0086] In the present application, the condensation reaction time is 2-10 h, and can be specifically 2 h, 4 h, 6 h, 8 h and 10 h, and is preferably 4 h.

[0087] In the present application, the preparation process of step 5 is preferably as follows: the activated HPAN-M film in step 4 is placed in a 360 mg / L functional polymer solution, and reacted in a constant temperature oscillator at 50℃ and 150 rpm for 4 h to obtain a functional film (denoted as PAMPS-M, the same below).

[0088] The synthetic route of the preparation method of the present application is shown in Figure 1 .

[0089] In order to further explain the present application, the preferred embodiments of the present application are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations on the claims of the present application.

[0090] Example 1:

[0091] (1) Two kinds of reaction monomers, 2-aminoethyl methacrylate hydrochloride (AEMA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS), were added into a three-necked flask in a molar ratio of 10:90, dissolved in deionized water, and 0.2 mmol of AIBA was added as a free radical initiator under nitrogen protection, and reacted for 24 h under an oil bath at 70°C. After the reaction was completed, the water solvent and residual monomers in the polymer solution were evaporated using a rotary evaporator, and the binary polymer product powder (PAMPS) was obtained by freeze-drying and stored at 4°C.

[0092] (2) Dry polyacrylonitrile (PAN) powder and pore-forming agent polyvinylpyrrolidone (PVP) were dissolved in N,N-dimethylformamide (DMF) solvent, and the molar ratio of PAN:PVP:DMF was 18:1:81. The above mixed solution was dissolved under stirring at 65°C and 250 rpm to obtain a uniform casting solution, which was vacuum degassed in a vacuum drying box. In a closed blade coating chamber with a temperature of 25°C and an air humidity of 55%, the casting solution was uniformly poured onto a wet non-woven fabric, and a 200 μm-thick blade coating knife was used to uniformly coat the solution onto the surface of the non-woven fabric. Then, the membrane plate was placed in a 10% DMF coagulation bath for a 5 min phase inversion process, and a PAN-M ultrafiltration membrane was prepared, which was stored at 4°C.

[0093] (3) The PAN-M membrane prepared in step 2 was placed in a 1 mol / L sodium hydroxide (NaOH) solution and heated in a water bath at 60°C with vigorous stirring for 1.5 h to obtain a carboxylated PAN ultrafiltration membrane (denoted as HPAN-M, same below).

[0094] (4) 0.5 mol of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and 0.25 mol of methacryloyloxyethyl trimethylammonium chloride (NHS) were completely dissolved in a phosphate (PBS) buffer solution (pH=5.0) to prepare an activation solution. The HPAN-M membrane prepared in step 3 was placed in the activation solution and reacted in a constant temperature oscillator at 50°C and 150 rpm for 1 h to improve the activity of the carboxyl groups on the membrane.

[0095] (5) Put the activated HPAN-M membrane in step 4 into the 360 mg / L functional polymer solution, and react in a constant temperature oscillator at 50°C and 150 rpm for 4 h to obtain a functional membrane (denoted as PAMPS-M, same below).

[0096] Comparative Example 1: PAN-M ultrafiltration membrane

[0097] According to the implementation of Example 1, only step (2) is performed to obtain an original PAN-M ultrafiltration membrane as a blank control.

[0098] Comparative Example 2: HPAN-M ultrafiltration membrane with surface hydroxylation

[0099] According to the implementation of Example 1, only steps (2) and (3) are performed, and the preparation of the polymer, the activation grafting step are not performed, to obtain a HPAN-M ultrafiltration membrane with surface carboxyl grafting sites.

[0100] Example 3: Product morphology characterization

[0101] The membrane samples obtained in Example 1 and Comparative Examples 1-2 are characterized by scanning electron microscopy (SEM), and the results are shown in Figure 2 , wherein Figure 2 a-c are the surface morphology structure diagrams of the membrane samples obtained in Comparative Example 1, Comparative Example 2 and Example 1, respectively. It can be seen that the HPAN-M membrane after alkali treatment has fewer membrane pore distributions and smaller membrane pore sizes than the PAN-M membrane. This is because the nitrile groups on the polyacrylonitrile membrane after alkali treatment are hydrolyzed to carboxyl groups, resulting in shorter original long polymer chains and enhanced hydration capacity. Therefore, in the macroscopic change, the surface layer is swollen and the pore channel is contracted. After the grafting functionalization of the binary polymer, the carboxyl groups on the membrane surface are consumed, and the surface layer is restored to the strong polar polymer chain structure due to the grafting of the polymer, resulting in alleviation of the swelling phenomenon, an increase in the membrane pore distribution, and a recovery of the pore size. The swelling and extrusion of the surface layer of the HPAN-M membrane after alkali treatment result in basically invisible clear large pore structures. After functionalization, the PAMPS-M membrane surface appears a clean small pore structure, and the pore size is smaller and the distribution is more uniform.

[0102] Example 4: Infrared absorption spectrum and XPS element analysis characterization

[0103] The membrane samples obtained in Example 1 and Comparative Examples 1-2 are characterized by infrared absorption spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS), and the results are shown in Figure 3 . Figure 3 a is the FTIR diagram of the membrane samples obtained in Comparative Examples 1-2 and Example 1. It can be seen that in the process of grafting the functional polymer, the characteristic peak of the main functional groups of the ultrafiltration membrane changes in the range of 1600 cm -1 to 1000 cm-1 between 1200 cm"1and 1300 cm"1. After the base treatment, the -CN groups on the PAN-M membrane were hydrolyzed to -COOH, so the HPAN-M membrane showed a characteristic peak at 1700 cm"1, which was from the vibration of the hydroxyl group on the carboxyl group. After the functional polymer was grafted by EDC / NHS activation, the functional membrane showed a characteristic peak at 1566 cm"1, which was from the vibration of the amide group. In addition, the binary polymer functional membrane PAMPS-M membrane showed a stretching peak of sulfonic acid group at 1352 cm"1, which represented the success of the grafting of the functional polymer. -1 -1 -1

[0104] Figure 3 b The XPS graphs of the membrane samples obtained from Comparative Example 1-2 and Example 1. After the base treatment, the nitrile groups on the PAN-M membrane were hydrolyzed to carboxyl groups, so the proportion of nitrogen elements in the HPAN-M membrane decreased, and the proportion of oxygen elements increased. After the binary copolymer was grafted, the sulfonic acid group in the introduced polymer caused the proportion of oxygen elements in the finally obtained PAMPS-M membrane to increase, and a new sulfur element peak appeared.

[0105] Example 5: Test of pore size and molecular weight cut-off

[0106] The pore size and distribution of the membrane samples obtained from Example 1 and Comparative Example 1 were tested by PEG cut-off experiment, and the results are shown in Table 2. Figure 4 The surface pore size of the functional membrane PAMPS-M membrane became smaller due to the swelling effect and polymer brush grafting caused by the base treatment of polyacrylonitrile, and the molecular weight cut-off decreased from 72.59 kDa of the original PAN-M membrane to 13.92 kDa, and the corresponding pore size decreased from 7.74 nm to 2.88 nm. The reduction of the pore size represented that the range of the substances that could be cut off by the functional ultrafiltration membrane was further widened, which was particularly beneficial to the cut-off and separation of some small-molecule organic pollutants. At the same time, the pore size distribution experiment showed that the pore size distribution of the functional PAMPS-M membrane was narrower than that of the original membrane, which meant that the functional membrane had better selectivity in the separation process, and the filtration precision was further improved.

[0107] Example 6: Test of charge characteristics and hydrophilicity and hydrophobicity

[0108] The charge characteristics of the membrane samples obtained from Example 1 and Comparative Example 1-2 were tested by zeta potential, and the results are shown in Table 3. Figure 5 ​​​As shown in Figure a, the original PAN-M membrane exhibits negative charge within a pH range of 3–9. This is due to the presence of numerous polar groups (such as nitrile groups) on its surface. These polar groups cause electron cloud shift and inductive effects, resulting in an overall negative charge on the molecular chain. The alkali-treated HPAN-M membrane, however, has more carboxyl groups, further shifting the membrane surface potential negatively. Since the sulfonic acid groups on the PAMPS-M membrane are more negatively charged than the carboxyl groups, with functionalization, the alkali-treated membrane not only retains this negative charge but also enhances it, further strengthening the negative charge of the PAMPS-M membrane and providing a stronger electrostatic repulsion force for separating negatively charged pollutants.

[0109] The hydrophilicity and hydrophobicity of the membrane samples obtained in Example 1 and Comparative Examples 1-2 were tested using the water contact angle, and the results are as follows: Figure 5 As shown in b, the original PAN-M membrane is quite hydrophilic due to the strong hydrogen bonding forces of the nitrile groups, with a contact angle of 58.2°. However, the carboxyl groups formed after alkali treatment are strongly hydrophilic, causing the contact angle of the HPAN-M membrane to decrease to 23.8°, significantly enhancing its hydrophilicity. After polymer grafting, the sulfonic acid groups are also hydrophilic, but the long carbon chain of the polymer backbone weakens this property. Nevertheless, the PAMPS-M membrane still retains good hydrophilic properties, with a contact angle of 33.6°. In summary, the functionalized membranes show a significant improvement in hydrophilicity compared to the original membranes, which is beneficial for effectively resisting the adhesion of organic pollutants in practical wastewater treatment.

[0110] Example 7: Salt Retention and Long-Term Retention Test

[0111] Six dyes with different properties—malachite green (MG), Congo red (CR), acid fuchsin (AF), acid orange G (AOG), phenol red (PR), and methylene blue (MB)—were tested to investigate the dye rejection characteristics of the membrane samples obtained in Example 1 and Comparative Example 1. The dye concentration in the feed solution was prepared to be 100 mg / L. The membrane was first pressurized in a cross-flow system at 0.2 MPa for 1 h, and then stabilized at 0.1 MPa for 0.5 h. After the pure water flux stabilized, the dye rejection effect of different properties was measured at 0.1 MPa pressure and 50 LPH flow rate, and the effluent flux and dye concentration were recorded in real time. The test results showed that ( Figure 6a) When dye sizes (e.g., CR and AF) are similar, the functionalized membrane PAMPS-M exhibits a higher repulsion rate for CR dye molecules with stronger negative charges. When retaining organic dyes with similar zeta potentials (e.g., CR, AOG, and PR), the functionalized membrane shows a higher repulsion rate for CR dye molecules with larger molecular weights. However, for cationic dyes such as MG and MB, which have strong positive charges, the retention effect of the functionalized membrane is poor. These characteristic retention experimental results indicate that the functionalized membrane simultaneously relies on the electrostatic repulsion of the surface negative charge and the retention effect of small pores to retain and separate dyes. Therefore, the functionalized membrane achieves the removal of organic dye contamination through a combination of pore size sieving and the Donnan effect. Notably, for the small-pore and negatively charged AOG dye, the functionalized membrane exhibits an excellent retention rate (97%); this shows that the Donnan effect of the functionalized membrane plays a greater role than the pore size sieving mechanism in dye retention performance. Furthermore, the introduction of a surface polymer layer into the functionalized membrane increases its hydrophilicity, enabling the functionalized membrane to maintain high flux while stably enhancing selectivity for small molecule dyes. This means that the charge-repulsion-dominated retention functionalized membrane reduces dependence on pore size sieving, avoids improving selectivity through extreme pore size reduction, effectively mitigates flux loss caused by the trade-off effect in membrane separation, and thus retains a larger pore size to maintain flux.

[0112] Using Congo red (CR) as a representative dye pollutant, the long-term retention effect of the membrane samples obtained in Example 1 and Comparative Example 1 was studied. Figure 6 As shown in b, after filtering a 100 ppm CR solution for 360 min at 1 bar pressure using both PAN-M and PAMPS-M membranes, the functionalized PAMPS-M membrane exhibited excellent continuous operation stability. Initially, in the first 120 min of filtration, the CR rejection rates of the PAN-M and PAMPS-M membranes remained above 95.6% and 100.0%, respectively. During this stage, the blank membrane achieved a high removal rate of Congo red through dye adsorption. However, as the filtration time increased, the dye adsorbed on the blank membrane affected the membrane surface properties, leading to a significant decrease in the flux and dye rejection rate of the PAN-M membrane. In contrast, the PAMPS-M membrane, with its strong repulsion of negatively charged dyes, maintained a relatively stable permeate flux and a 100% complete removal rate throughout the filtration process. The functionalized PAMPS-M membrane demonstrated more stable flux and rejection performance than the original PAN-M membrane, indicating that it can maintain better continuous operation stability in dye wastewater, thus improving operational efficiency.

[0113] Example 8: Selective Separation Test of Salt Dyeing

[0114] The dye / salt selective separation effect of the membrane samples obtained in Example 1 and Comparative Examples 1-2 was studied with acid orange G (AOG) as a representative negatively charged dye pollutant. The membrane was first pressed in a cross-flow system at 0.2 MPa for 1 h, and then stably operated at 0.1 MPa for 0.5 h. After the pure water flux was stabilized, the dye rejection effect was measured at a pressure of 0.1 MPa and a flow rate of 50 LPH, and the effluent flux and dye concentration were recorded in real time. During the test, a sample was taken every 30 min, and the membrane flux and effluent dye concentration were tested, a total of 12 times, and the total test time was 6 h. In the preparation of the dye / salt mixed feed solution, the concentration of the characteristic dye (AOG) in the simulated high-salt dye wastewater was kept at 100 mg / L, and four kinds of inorganic salts (Na2SO4, MgSO4, MgCl2 and NaCl) were added, respectively, and the concentration was controlled at 1000 mg / L. Figure 7 The results show that the PAMPS-M membrane maintains a dye rejection rate of 94% in the mixed salt dye solution, and the separation factor is 20.3. The removal rate of AOG by the PAN-M membrane is less than 20%. At the same time, the rejection rate of sodium chloride by the PAMPS-M membrane is less than 5%, which is basically close to the PAN-M ultrafiltration membrane before functionalization, and similar results are also shown in other mixed salt dye solutions. This shows that the functionalized PAMPS-M membrane can effectively permeate inorganic salts and reject most negatively charged dye molecules, and exhibits excellent salt-dye separation and removal selectivity. It is worth mentioning that the functionalized membrane maintains an ultrafiltration level flux of 121.8 L·m -2 ·h -1 ·bar -1 ·bar during removal. The mixed salt dye rejection test proves that the coverage of the negatively charged functional polymer layer significantly improves the screening performance of the ultrafiltration membrane for negatively charged dyes. Therefore, the PAMPS-M membrane after negatively charged functionalization has excellent dye / salt selective separation performance while maintaining excellent permeability, and has broad application prospects in the field of high-salt dye wastewater treatment.

[0115] Example 9: Anti-organic pollution and flux recovery test

[0116] The anti-fouling performance of the membrane samples obtained in Example 1 and Comparative Example 1 was tested in simulated organic contaminated wastewater with humic acid (HA) as a representative organic contaminant. The membrane was compacted at 0.2 MPa pressure, and then the mass of water output per minute was recorded by an electronic balance at 0.1 MPa and a flow rate of 50 LPH, and the stable membrane pure water flux was calculated. Then, 5 L of the feed solution was pumped into the membrane filtration system, and after 60 min of contamination, the membrane flux after contamination was recorded, and then the organic contaminant solution in the membrane device was replaced with deionized water for physical cleaning for 30 min. After cleaning, the pure water flux of the original PAN-M and functionalized PAMPS-M ultrafiltration membrane was measured to calculate the flux recovery rate. The above steps were repeated, the deionized water was replaced with the HA solution, and the "contamination-cleaning" experiment was repeated under the simulated organic wastewater feeding cycle at 0.1 MPa, and the results are shown in Figure 8 The results show that after three cycles of contamination with humic acid, the PAMPS-M membrane can still maintain 95% of the original flux. In contrast, the original membrane has only a recovery rate of 70%. The functionalized membrane has excellent anti-interference ability under organic contamination, which is due to the strong negative charge on the surface of the functionalized membrane and the hydrophilic property of the polymer layer. The functionalized membrane effectively inhibits the adhesion of negatively charged pollutants on the surface, and removes part of the filter cake layer to restore the flux by strong water action.

[0117] The principles and implementations of the present application are described in the specific examples in this paper, and the above examples are only used to help understand the method of the present application and its core idea, including the best mode, and also enable any person skilled in the art to practice the present application, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, without departing from the principles of the present application, some improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application. The scope of protection of the present application is defined by the claims, and can include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the wording of the claims, or if they include equivalent structural elements to the wording of the claims without substantial differences, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing a binary copolymer functionalized polyacrylonitrile ultrafiltration membrane, characterized in that The method comprises the following steps: Step 1: Dissolve the polymer monomer in deionized water, add initiator azobisdimethylvaleronitrile AIBA under nitrogen protection, heat the reaction to obtain a binary polymer product PAMPS; Step 2: Dry polyacrylonitrile powder, pore-forming agent polyvinylpyrrolidone and solvent N,N-dimethylformamide are configured into a casting solution, heated and stirred to mix uniformly; the casting solution is poured onto a wet non-woven fabric, uniformly coated with a doctor blade, and phase-separated in a coagulation bath to form a PAN-M ultrafiltration membrane; Step 3: The PAN-M ultrafiltration membrane prepared in step 2 is placed in a sodium hydroxide solution and stirred vigorously under heating conditions to obtain a carboxylated PAN ultrafiltration membrane, denoted as HPAN-M; Step 4: The HPAN-M membrane prepared in step 3 is placed in an activation solution and subjected to an activation reaction in a constant-temperature oscillator to improve the activity of the carboxyl groups on the membrane; Step 5: The activated HPAN-M membrane in step 4 is placed in the functional polymer solution obtained in step 1 and subjected to a condensation reaction in a constant-temperature oscillator to obtain a functional polyacrylonitrile ultrafiltration membrane PAMPS-M; In step 1, the polymer monomers are 2-aminoethyl methacrylate hydrochloride AEMA and 2-acrylamido-2-methylpropanesulfonic acid AMPS; the molar ratio of AEMA and AMPS in the two polymer monomers is 10:90; In step 1, the reaction temperature is 70℃ and the reaction time is 24 h; In step 3, the concentration of the sodium hydroxide solution is 1 mol / L, the heating temperature is 60℃, and the reaction time is 0.5-2 h; In step 4, the activation solution is 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride EDC and N-hydroxysuccinimide NHS dissolved in a phosphate buffer solution with pH=5.0 to form, wherein the molar ratio of EDC and NHS is 2:1; the activation reaction temperature is 50℃, the oscillation speed is 150 rpm, and the activation reaction time is 0.5-2 h; In step 5, the concentration of the functional polymer solution is 90-450 mg / L; the condensation reaction temperature is 50℃, the oscillation speed is 150 rpm, and the condensation reaction time is 2-10 h.

2. Application of the binary copolymer functional polyacrylonitrile ultrafiltration membrane prepared according to claim 1 in high-salt dye wastewater treatment.

3. The application according to claim 2, characterized in that: The binary copolymer functional polyacrylonitrile ultrafiltration membrane is used for high-salt dye wastewater treatment, which can maintain the membrane flux while efficiently retaining small-molecule dyes and has excellent anti-pollution performance; The salt includes one or more of Na2SO4, MgSO4, MgCl2 and NaCl; The small-molecule dye includes one or more of malachite green, congo red, acid fuchsin, acid orange G, phenol red and methylene blue.

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