Uniform-aperture negatively-charged enhanced nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention provides a negatively charged enhanced nanofiltration membrane with uniform pore size as well as a preparation method and application thereof. The nanofiltration membrane comprises a supporting bottom membrane and an active separation layer loaded on the supporting bottom membrane, the active separation layer comprises an interfacial polymerization product of post-treated and modified polyamine and polyacyl chloride; the polyamine comprises polyamine containing double bonds and negatively charged functional groups and polyamine without double bonds and negatively charged functional groups; the post-treatment modification comprises grafting by using a functional monomer containing sulfydryl and a negatively charged functional group. The nanofiltration membrane has a larger pore diameter, narrower pore diameter distribution and enhanced electronegativity, and can improve the permeation flux of water and chloride ions, improve the salt separation efficiency and enhance the anti-scaling and anti-pollution capacities on the premise of not reducing the retention rate of Na2SO4. The nanofiltration membrane disclosed by the invention has high water flux, high sodium sulfate rejection rate and relatively high monovalent and bivalent anion selectivity, and has a wide application prospect in the zero discharge and recycling process of high-salinity wastewater.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a negatively charged nanofiltration membrane, its preparation method and application, and particularly to a negatively charged nanofiltration membrane with uniform pore size, its preparation method and application. Background Technology

[0002] In various industrial production processes such as chemical engineering, seawater desalination, and coal chemical engineering, the discharge of high-salinity wastewater is increasing year by year. Direct discharge of this wastewater leads to serious environmental problems, such as water pollution, soil salinization, and long-term irreversible damage to ecosystems. Furthermore, high-salinity wastewater contains a large amount of inorganic salts. If these inorganic salts can be recovered and utilized during wastewater treatment, it will greatly improve the economic and social benefits of enterprises and contribute to the capacity expansion of related factories. The selective separation of inorganic salts is a crucial step in the treatment and resource recovery process of high-salinity wastewater, directly affecting the resource recovery rate of sodium chloride and sodium sulfate, as well as the overall treatment effect of high-salinity wastewater. Therefore, the selective separation of chloride ions (Cl⁻) and sulfate ions (SO₄²⁻) in high-salinity wastewater treatment is essential. 2- The efficient separation of ions has become an important research area for resource utilization and pollution control.

[0003] Currently, salt separation processes are mainly divided into two categories: thermal salt separation and nanofiltration salt separation. Thermal salt separation is a relatively mature process that separates and recovers inorganic salts through evaporation and crystallization. It has a wide range of applications and mature technology. However, its high energy consumption, large equipment footprint, and unstable quality of crystallized salt are also significant problems, which limits its application in the resource utilization of high-salinity wastewater. In contrast, nanofiltration salt separation, by employing nanofiltration membrane technology, helps reduce energy consumption and equipment investment in the evaporation and crystallization stages, while obtaining higher quality crystallized salt, thus demonstrating greater technological potential in the resource treatment of high-salinity wastewater. However, the salt separation performance of commercial nanofiltration membranes still faces multiple challenges. For example, there is a significant "trade-off" effect between membrane permeability and ion selectivity, meaning that increasing membrane flux often leads to a decrease in selective separation performance. In addition, in actual operation, nanofiltration membranes may still experience problems such as fouling, scaling, and clogging, which further accelerate the degradation of membrane performance and affect its long-term stability and economic viability.

[0004] While optimizing operating parameters (including temperature, pH, flow rate, and filtration mode) can improve salt separation performance and slow down the decline in membrane performance to some extent, the ability to improve performance through parameter control is limited. Therefore, starting with membrane material and structural design, and developing innovative nanofiltration membranes that combine high permeability, selectivity, and antifouling capabilities is the most effective way to fundamentally overcome performance bottlenecks.

[0005] Patent CN109758929A optimized the interfacial polymerization process by introducing a surfactant, resulting in a nanofiltration membrane with higher ion separation efficiency. However, the improvement in water flux was limited, failing to completely overcome the performance bottleneck of traditional membranes. Patent CN110354683A, on the other hand, introduced adamantane into the oil phase solution. Its unique cage-like structure increased the free volume inside the membrane, improving the separation of NaCl and SO4. 2- The selectivity of separation is limited. However, when the water flux reaches a certain level, the rejection rate for divalent sulfate ions still decreases significantly, demonstrating the limitation of "selectivity and flux imbalance". Similar flux-selectivity trade-off issues also appear in other disclosed salt separation nanofiltration membranes, such as those disclosed in CN115228300A and CN101934201A.

[0006] Therefore, developing a high-flux, highly selective, and fouling-resistant salt separation nanofiltration membrane is an urgent problem to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a negatively charged nanofiltration membrane, its preparation method, and its applications, particularly a uniformly pore-sized, negatively charged enhanced nanofiltration membrane, its preparation method, and its applications. The uniformly pore-sized, negatively charged enhanced nanofiltration membrane of the present invention is constructed by using polyamines containing double bonds and negatively charged functional groups to build a separation layer containing double bonds. Further, functional monomers containing thiol groups and negatively charged functional groups are used to target and modify the macropores of the separation layer through a thiol-double bond click reaction, ultimately obtaining a uniformly pore-sized, negatively charged enhanced nanofiltration membrane. This nanofiltration membrane, due to its larger pore size, narrower pore size distribution, and enhanced negative charge, can increase the permeation flux of water and chloride ions, improve the separation coefficient of monovalent and divalent anions, and enhance anti-scaling and anti-fouling capabilities without reducing the Na₂SO₄ rejection rate.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] On one hand, the present invention provides a negatively charged enhanced nanofiltration membrane, the negatively charged enhanced nanofiltration membrane comprising a supporting substrate membrane and an active separation layer loaded on the supporting substrate membrane; the active separation layer comprising an interfacial polymerization product of a post-treated modified polyamine and a polyacrylamide chloride; the polyamine comprising polyamines containing double bonds and negatively charged functional groups and polyamines not containing double bonds and negatively charged functional groups; the post-treatment modification comprising grafting with functional monomers containing thiol groups and negatively charged functional groups.

[0010] In this invention, while the polyamine and polyacryl chloride form a polyamide at the interface, double bonds are introduced into the primary layer of the separation membrane. The double bonds in the primary layer of the separation membrane can react with thiol groups via a click reaction to introduce sulfonic acid or carboxyl functional groups into the separation layer, such as... Figure 1 As shown. Furthermore, since the grafted functional monomers containing thiol groups and negatively charged functional groups are small-molecule organic compounds, it ensures that while increasing the negative charge and reducing the pore size and pore size distribution, it does not affect the passage of pure water. This results in the active separation layer of the negatively charged enhanced nanofiltration membrane having a narrower pore size distribution, uniform pore size, high hydrophilicity, and strong negative charge, which is beneficial for improving Cl... - SO4 2- Separation selectivity, pollution resistance and water flux.

[0011] In this invention, the polyamine containing double bonds and negatively charged functional groups includes any one or a combination of at least two of diaminostilbene disulfonic acid, diaminostilbene dicarboxylic acid, sodium diaminostilbene disulfonate, or sodium diaminostilbene dicarboxylic acid.

[0012] Preferably, the polyamine that does not contain double bonds and negatively charged functional groups includes any one or a combination of at least two of piperazine, m-phenylenediamine, o-phenylenediamine, or p-phenylenediamine.

[0013] Preferably, the polyacrylamide chloride includes any one or a combination of at least two of the following: pyromellitic trimethylolpropionate chloride, phthaloyl chloride, terephthaloyl chloride, 1,5-naphthalenedisulfonyl chloride, 1,3,6-naphthalenedisulfonyl chloride, 1,3,5-cyclohexanetrimethylolpropionate chloride, or pyromellitic tetramethylolpropionate chloride.

[0014] Preferably, the functional monomer containing thiol and negatively charged functional groups includes any one or a combination of at least two of the functional monomers containing thiol and sulfonic acid groups and functional monomers containing thiol and carboxyl groups.

[0015] Preferably, the functional monomer containing thiol and sulfonic acid groups includes any one or a combination of at least two of 2-mercaptoethanesulfonic acid, sodium 2-mercaptoethanesulfonate, sodium 3-mercapto-1-propanesulfonate, or sodium 2,3-dimercaptopropanesulfonate.

[0016] Preferably, the functional monomer containing thiol and carboxyl groups includes any one or a combination of at least two of thioglycolic acid, 4-mercaptobenzoic acid, thiosuccinic acid, sodium thioglycolate, 4-mercaptobutyric acid, 3-mercaptopropionic acid, or 3-mercaptobenzoic acid.

[0017] Preferably, the material of the supporting substrate includes any one or a combination of at least two of polysulfone, polyethersulfone, polyimide, polyamide, polyethylene, or polyacrylonitrile.

[0018] Preferably, the supporting substrate comprises a polymer porous layer and a nonwoven fabric layer stacked sequentially.

[0019] Preferably, the polymer porous layer is any one or a combination of at least two of the following: a polysulfone porous layer, a polyethersulfone porous layer, a polyetherimide porous layer, or a polytetrafluoroethylene porous layer.

[0020] Preferably, the thickness of the supporting substrate is 100~300 μm, for example, it can be 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, etc.

[0021] Preferably, the thickness of the polymer porous layer is 80~100 μm, for example, it can be 85 μm, 90 μm, 95 μm, 100 μm, etc.

[0022] Preferably, the thickness of the nonwoven fabric layer is 100~150 μm, for example, it can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, etc.

[0023] Preferably, the thickness of the active separation layer is 50 nm to 5 μm, for example, it can be 100 nm, 200 nm, 500 nm, 1 μm, 2 μm, 3 μm, 4 μm, etc., and more preferably 100 nm to 3 μm.

[0024] In a second aspect, the present invention provides a method for preparing a negatively charged enhanced nanofiltration membrane according to the first aspect, the method comprising the following steps:

[0025] (1) A supporting substrate, polyamine, and polyacryl chloride are mixed and reacted;

[0026] (2) The product of step (1) is soaked in a solution of functional monomers containing thiol and negatively charged functional groups and grafted under ultraviolet light to obtain the negatively charged enhanced nanofiltration membrane.

[0027] In this invention, the purpose of grafting is to further increase the negative charge and hydrophilicity of the active separation layer surface and to regulate the pore structure of the separation layer.

[0028] The preparation method of this invention first involves interfacial polymerization of a mixed solution of a polyamine containing double bonds and negatively charged functional groups and a polyamine without double bonds and negatively charged functional groups with a polyacryl chloride. This introduces double bonds and negatively charged functional groups into the interfacial polymerization product. Then, a solution of functional monomers containing thiol and negatively charged functional groups is used to soak the interfacial polymerization product of the polyamine and polyacryl chloride. Simultaneously with the interfacial polymerization reforming, a double bond-thiol click reaction is used to graft sulfonic acid or carboxyl functional groups into the separation membrane. Figure 1As shown. This process enhances the electronegativity and hydrophilicity of the nanofiltration membrane, resulting in a composite nanofiltration membrane with uniform pore size, high hydrophilicity, and strong negative charge. This significantly improves the selective separation and antifouling performance of the composite nanofiltration membrane for monovalent and divalent anions. Compared to traditional polyamide nanofiltration membranes, the composite nanofiltration membrane has a higher flux and a Cl- / SO4 ratio. 2- Separation selectivity is improved.

[0029] Preferably, the preparation method in step (1) includes:

[0030] The supporting substrate was impregnated with a polyamine aqueous solution, removed, dried, and then impregnated with a polyacrylamide chloride / oil phase solution to carry out an interfacial polymerization reaction.

[0031] In this invention, the preparation method of the polyamine aqueous solution includes: dissolving a polyamine containing double bonds and negatively charged functional groups and a polyamine without double bonds and negatively charged functional groups in water respectively, and then mixing them in proportion to obtain a polyamine aqueous solution.

[0032] Preferably, the solvent of the oil phase solution includes any one or a combination of at least two of petroleum ether, n-hexane, cyclohexane, n-pentane, or cyclopentane.

[0033] Preferably, the immersion time in the polyamine aqueous solution is 3 to 20 minutes, for example, 4 minutes, 6 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes or 25 minutes.

[0034] Preferably, the mass percentage of the polyamine in the aqueous solution is 0.1% to 1%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, etc.

[0035] Preferably, the ratio of polyamines containing double bonds and negatively charged functional groups to polyamines without double bonds and negatively charged functional groups in the polyamine aqueous solution is 1:10 to 10:1, for example, it can be 1:10, 1:5, 1:2, 1:1, 3:1, 5:1, 8:1 or 10:1, etc.

[0036] Preferably, the mass percentage of the polyacryl chloride in the oil phase solution of the polyacryl chloride is 0.05~0.3%, for example, it can be 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.22%, 0.25% or 0.28%, etc.

[0037] Preferably, the reaction time in step (1) is 10~120 s, for example, it can be 12 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 90 s, 100 s or 120 s.

[0038] Preferably, the reaction in step (1) is followed by drying.

[0039] Preferably, the mass percentage of the functional monomer in the functional monomer solution containing thiol and negatively charged functional groups in step (2) is 0.01~1%, for example, it can be 0.01%, 0.12%, 0.35%, 0.54%, 0.67%, 0.88%, 0.95% or 1%, etc.

[0040] Preferably, the soaking time in step (2) is 3 to 180 min, for example, it can be 3 min, 30 min, 60 min, 80 min, 120 min, 150 min or 180 min.

[0041] Preferably, the ultraviolet light irradiation time in step (2) is 3 to 180 min, for example, it can be 3 min, 30 min, 60 min, 80 min, 120 min, 150 min or 180 min.

[0042] Preferably, the wavelength of the ultraviolet light in step (2) is 365 nm.

[0043] Preferably, the intensity of the ultraviolet light in step (2) is 200-700 mw / cm², for example.

[0044] Preferably, after the grafting reaction in step (2), the process further includes rinsing with deionized water for 10 to 30 seconds, such as 10 seconds, 12 seconds, 14 seconds, 16 seconds, 18 seconds, 20 seconds, 22 seconds, 24 seconds, 26 seconds, 28 seconds, or 30 seconds.

[0045] In this invention, the grafting process further includes a rinsing step with deionized water, the purpose of which is to remove unreacted functional monomers.

[0046] Thirdly, the present invention provides the application of the negatively charged enhanced nanofiltration membrane as described above in wastewater treatment.

[0047] Preferably, it is used, especially in the zero discharge or resource utilization treatment of high-salinity wastewater.

[0048] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] The negatively charged enhanced nanofiltration membrane of this invention has a large pore size, a narrow pore size distribution, and a relatively uniform pore size, exhibiting enhanced negative charge. It can increase the permeation flux of water and chloride ions without reducing the Na₂SO₄ rejection rate, thereby improving salt separation efficiency and enhancing anti-scaling and anti-fouling capabilities. The nanofiltration membrane of this invention possesses high water flux, high sodium sulfate rejection rate, and high selectivity for monovalent and divalent anions, showing broad application prospects in the zero-discharge and resource recovery processes of high-salinity wastewater. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the preparation process of the uniformly sized, negatively charged enhanced nanofiltration membrane.

[0052] Figure 2 This is a schematic diagram of the permeation performance testing device for the salt separation nanofiltration membrane provided by the present invention. Detailed Implementation

[0053] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0054] Example 1

[0055] This embodiment provides a uniformly pore-sized, negatively charged nanofiltration membrane, comprising a supporting substrate and an active separation layer loaded on the supporting substrate; the active separation layer comprises an interfacial polymerization product of a post-treated modified polyamine and a polyacrylamide chloride; the polyamine includes polyamines containing double bonds and negatively charged functional groups and polyamines without double bonds and negatively charged functional groups; the post-treatment modification comprises grafting with functional monomers containing thiol groups and negatively charged functional groups. The interfacial polymerization product is 0.01 g of trimesoyl chloride (M... W =265.48 (purchased from Aladdin, CAS: 4422-95-1) and 0.01 g of an aqueous polyamine to form an interfacial polymer; the aqueous polyamine includes piperazine (M) in a mass ratio of 1:1. W =86.14, purchased from Aladdin, CAS: 110-85-0) and 4,4'-diaminostilbene-2,2'-disulfonic acid (M W =370.40, purchased from Aladdin, CAS: 81-11-8); the mass ratio of the pyromellitic acid chloride to the aqueous solute was 1:1, and the post-treatment modification included the use of 0.005 g of 2-mercaptoethanesulfonic acid (M W =142.20, purchased from Aladdin, CAS: 3375-50-6) grafted onto the surface of the interfacial polymer product.

[0056] This embodiment provides a method for preparing the separation membrane, the specific steps of which include:

[0057] (1) First, cut the polyethersulfone ultrafiltration membrane to a suitable size, place it in the membrane container, and immerse the support layer with 0.1 w / v% aqueous reaction solution for 5 min; remove it and remove the surface moisture, then immerse the support layer with 0.1 w / v% oil reaction solution for 20 s, and then dry it.

[0058] (2) Then, the interfacial polymerization product obtained in step (1) is soaked in 0.05 w / v% 2-mercaptoethanesulfonic acid aqueous solution for 10 min, and grafting reaction is carried out under ultraviolet light irradiation to obtain the uniform pore size negatively charged enhanced nanofiltration membrane. Wherein, the ultraviolet light wavelength is 365 nm and the intensity is 435 mw / cm²;

[0059] The method for preparing the aqueous reactant solution includes:

[0060] Diaminostilbene disulfonic acid and piperazine were dissolved separately in deionized water, and then mixed in proportion after complete dissolution to obtain the aqueous polyamine solution.

[0061] The method for preparing the oil phase reactant solution includes:

[0062] The pyromellitic chloride was fully dissolved in n-hexane to obtain an oil phase solution.

[0063] The method for preparing the grafted monomer solution includes:

[0064] 2-Mercaptoethanesulfonic acid was fully dissolved in deionized water to obtain a grafted monomer solution.

[0065] Example 2

[0066] This embodiment provides a separation membrane, which differs from Embodiment 1 only in that the grafted monomer is sodium 3-mercaptopropionate; the other raw materials and proportions are the same as in Embodiment 1.

[0067] Example 3

[0068] This embodiment provides a separation membrane, which differs from Embodiment 1 only in that the grafted monomer is sodium 2,3-dimercaptopropanesulfonate; the other raw materials and proportions are the same as in Embodiment 1.

[0069] Example 4

[0070] This embodiment provides a separation membrane, which differs from Example 1 only in that the grafted monomer is sodium mercaptoacetate; the other raw materials and proportions are the same as in Example 1.

[0071] Example 5

[0072] This embodiment provides a separation membrane, which differs from Embodiment 1 only in that the grafted monomer is mercaptosuccinic acid; the other raw materials and proportions are the same as in Embodiment 1.

[0073] Example 6

[0074] This embodiment provides a separation membrane, which differs from Embodiment 1 in that the 4,4'-diaminostilbene-2,2'-disulfonic acid in step (1) is replaced with sodium diaminostilbene dicarboxylate, and the mass ratio of piperazine to sodium diaminostilbene dicarboxylate is 4:1; other raw materials and proportions are the same as in Embodiment 1.

[0075] Comparative Example 1

[0076] This comparative example provides a separation membrane, which differs from Example 1 only in that step (2) is not performed.

[0077] Comparative Example 2

[0078] The comparative example used is the NF30 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.

[0079] Comparative Example 3

[0080] This comparative example uses the NF60 commercial nanofiltration membrane, purchased from Hunan Aowei Membrane Technology Co., Ltd.

[0081] Comparative Example 4

[0082] The comparative example used was the NF270 commercial nanofiltration membrane, purchased from DuPont.

[0083] Comparative Example 5

[0084] This comparative example uses a DK commercial nanofiltration membrane, purchased from Suez.

[0085] Comparative Example 6

[0086] This comparative example uses an XC-N commercial nanofiltration membrane, purchased from DuPont.

[0087] Comparative Example 7

[0088] The only difference from Example 1 is that piperazine is replaced with an equal mass of 4,4'-diaminostilbene-2,2'-disulfonic acid. It was found that interfacial polymerization to form a film could not be performed in step (1).

[0089] Comparative Example 8

[0090] The only difference from Example 1 is that the 4,4'-diaminostilbene-2,2'-disulfonic acid is replaced with an equal mass of piperazine.

[0091] Performance testing

[0092] The composite nanofiltration membranes provided in Examples 1-5 and Comparative Examples 1-6 were tested for selectivity in water and inorganic salts.

[0093] Water flux and inorganic salt retention performance of the composite nanofiltration membrane were tested in a low-pressure cross-flow apparatus (purchased from Hangzhou Saifei Membrane Separation Technology Co., Ltd.). The effective membrane area was 7 cm². 2 The filtration process employs a full-circulation mode, operating at a cross-flow velocity of 40 L / H. The water flux is calculated using the following formula:

[0094] .

[0095] Where P is the permeation flux (Lm) -2 h -1 bar -1 Vp is the volume of permeate collected within time t (L); Am is the effective membrane area (m²). 2 ); t is the running time (h); TMP is the transmembrane pressure (bar).

[0096] The retention rate of inorganic salts is calculated using the following formula:

[0097] .

[0098] Where Cp and Cr represent the concentrations of the solute in the permeate and retentate, respectively; for inorganic salt solutions, the concentration ratio can be replaced by the conductivity ratio. The above tests were conducted at 25°C with an inorganic salt solution concentration of 1000 ppm.

[0099] The separation factors for sodium chloride and sodium sulfate are calculated using the following formula:

[0100] .

[0101] like Figure 2 A schematic diagram of the permeation performance testing device for nanofiltration membranes provided by the present invention.

[0102] The specific test results are shown in Table 1:

[0103] Table 1

[0104]

[0105] As shown in the table above, the separation membrane provided by the present invention first introduces negatively charged functional groups such as sulfonic acid or carboxyl groups into the aqueous phase. These functional groups with ultra-high space charge density can generate electrostatic interactions with piperazine in the aqueous phase, thereby slowing down the diffusion rate of monomers, reducing membrane thickness and making the membrane more porous, which promotes the transport of water molecules and chloride ions in the membrane. In step (2), the interfacial polymerization product generated in step (1) is targeted modified by double bond-thiol click reaction, which further increases the negative charge density of the membrane while controlling the pore size and uniformity, which is beneficial to the high retention of sulfate ions. Ultimately, the separation membrane provided by the present invention has high water flux, high sodium sulfate rejection rate, low sodium chloride rejection rate and higher selectivity for monovalent and divalent ions.

[0106] A comparison of Examples 1-5 with Comparative Example 1 shows that the surface grafting in step (2) can improve the water flux and sodium chloride / sodium sulfate separation factor of the nanofiltration membrane. A comparison of Examples 1-5 with Comparative Examples 2-6 shows that the pure water flux and the selectivity for monovalent and divalent salt ions of the composite nanofiltration membrane prepared in this invention are superior to those of commercial nanofiltration membranes. A comparison of Examples 1-5 with Comparative Example 8 shows that if 4,4'-diaminostilbene-2,2'-disulfonic acid is not present in step (1), the sodium sulfate rejection rate of the membrane is low, ultimately resulting in a low sodium chloride / sodium sulfate separation factor.

[0107] In summary, the uniformly pore-sized negatively charged nanofiltration membrane provided by this invention, due to its larger pore size, narrower pore size distribution, and enhanced negative charge, can increase the permeation flux of water and chloride ions, improve salt separation efficiency, and enhance anti-scaling and anti-fouling capabilities without reducing the Na2SO4 rejection rate.

[0108] The applicant declares that the present invention is illustrated by the above embodiments to demonstrate the nanofiltration membrane, its preparation method, and its application. However, the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A negatively charged enhanced nanofiltration membrane, characterized in that, The negatively charged enhanced nanofiltration membrane includes a supporting substrate membrane and an active separation layer loaded on the supporting substrate membrane; The active separation layer comprises an interfacial polymerization product of post-treated modified polyamines and polyacryl chlorides; The polyamines include polyamines containing double bonds and negatively charged functional groups and polyamines not containing double bonds and negatively charged functional groups. The post-processing modification includes grafting with functional monomers containing thiol groups and negatively charged functional groups.

2. The negative charge-enhanced nanofiltration membrane according to claim 1, characterized in that, The polyamine containing double bonds and negatively charged functional groups includes any one or a combination of at least two of diaminostilbene disulfonic acid, diaminostilbene dicarboxylic acid, sodium diaminostilbene disulfonate, and sodium diaminostilbene dicarboxylate. Preferably, the polyamine that does not contain double bonds and negatively charged functional groups includes any one or a combination of at least two of piperazine, m-phenylenediamine, o-phenylenediamine, or p-phenylenediamine.

3. The charge-enhanced nanofiltration membrane according to claim 1 or 2, characterized in that, The polyacrylic chloride includes any one or a combination of at least two of the following: pyromellitic trimethylol chloride, phthaloyl chloride, terephthaloyl chloride, 1,5-naphthalenedisulfonyl chloride, 1,3,6-naphthalenedisulfonyl chloride, 1,3,5-cyclohexanetrimethylol chloride, or pyromellitic tetramethylol chloride.

4. The charge-enhanced nanofiltration membrane according to any one of claims 1-3, characterized in that, The functional monomers containing thiol and negatively charged functional groups include any one or a combination of at least two of the functional monomers containing thiol and sulfonic acid groups and functional monomers containing thiol and carboxyl groups. Preferably, the functional monomer containing thiol and sulfonic acid groups includes any one or a combination of at least two of 2-mercaptoethanesulfonic acid, sodium 2-mercaptoethanesulfonate, sodium 3-mercapto-1-propanesulfonate, or sodium 2,3-dimercaptopropanesulfonate. Preferably, the functional monomer containing thiol and carboxyl groups includes any one or a combination of at least two of thioglycolic acid, 4-mercaptobenzoic acid, thiosuccinic acid, sodium thioglycolate, 4-mercaptobutyric acid, 3-mercaptopropionic acid, or 3-mercaptobenzoic acid.

5. The charge-enhanced nanofiltration membrane according to any one of claims 1-4, characterized in that, The supporting substrate membrane comprises a polymer porous layer and a non-woven fabric layer stacked sequentially; Preferably, the polymer porous layer is any one or a combination of at least two of the following: a polysulfone porous layer, a polyethersulfone porous layer, a polyetherimide porous layer, or a polytetrafluoroethylene porous layer. Preferably, the thickness of the supporting substrate is 100~300 μm; Preferably, the thickness of the polymer porous layer is 80~100 μm; Preferably, the thickness of the nonwoven fabric layer is 100~150 μm; Preferably, the thickness of the active separation layer is 50 nm to 5 μm, and more preferably 100 nm to 3 μm.

6. The method for preparing a negatively charged enhanced nanofiltration membrane according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) A supporting substrate, polyamine, and polyacryl chloride are mixed and reacted; (2) The product of step (1) is soaked in a solution of functional monomers containing thiol and negatively charged functional groups and grafted under ultraviolet light to obtain the negatively charged enhanced nanofiltration membrane.

7. The preparation method according to claim 6, characterized in that, The specific operation of step (1) is as follows: impregnate the supporting substrate with a polyamine aqueous solution, take it out, dry it, impregnate the supporting substrate with an oil phase solution of polyacrylamide chloride, and carry out the interfacial polymerization reaction; Preferably, the solvent of the oil phase solution includes any one or a combination of at least two of petroleum ether, n-hexane, cyclohexane, n-pentane, or cyclopentane; Preferably, the immersion time in the polyamine aqueous solution is 3-20 min; Preferably, the mass percentage of the polyamine in the aqueous solution is 0.1% to 1%. Preferably, the ratio of polyamines containing double bonds and negatively charged functional groups to polyamines without double bonds and negatively charged functional groups in the aqueous solution of the polyamine is 1:10 to 10:

1. Preferably, the mass percentage of the polyacrylamide chloride in the oil phase solution of the polyacrylamide chloride is 0.05~0.3%.

8. The preparation method according to claim 6, characterized in that, The reaction described in step (1) is carried out at room temperature for a time of 10-120 s; Preferably, the reaction in step (1) is followed by drying.

9. The preparation method according to claim 6, characterized in that, The functional monomer in the solution containing thiol and negatively charged functional groups described in step (2) has a mass percentage of 0.01-1%. Preferably, the soaking time in step (2) is 3 to 180 min; Preferably, the ultraviolet light irradiation time in step (2) is 3~180 min; Preferably, the wavelength of the ultraviolet light in step (2) is 365 nm; Preferably, the intensity of the ultraviolet light in step (2) is 200-700 mw / cm²; Preferably, after the grafting reaction in step (2), the process further includes rinsing with deionized water for 10-30 seconds.

10. The application of the charge-enhanced nanofiltration membrane according to any one of claims 1-5 in wastewater treatment; Preferably, the application is in the zero discharge of high-salinity wastewater or the resource utilization treatment of high-salinity wastewater.

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