Nanofiltration membranes, their preparation methods, and filtration devices

Abstract

This application provides a nanofiltration membrane, its preparation method, and a filtration device. The nanofiltration membrane preparation method includes: immersing a polymer-based membrane in an aqueous solution containing an aqueous monomer to wet the surface of the polymer-based membrane with the aqueous monomer; applying an oil-phase solution containing a first oil-phase monomer and a second oil-phase monomer to the surface of the polymer-based membrane wetted with the aqueous monomer to undergo an interfacial polymerization reaction, forming a separation layer on the surface of the polymer-based membrane; and post-treating the separation layer to prepare the nanofiltration membrane; wherein the interfacial polymerization reaction time is >30s; the first oil-phase monomer and the second oil-phase monomer are respectively capable of undergoing an amidation reaction with the aqueous monomer; the molecular weight of the second oil-phase monomer is less than that of the first oil-phase monomer, the binding capacity of the second oil-phase monomer with the aqueous monomer is greater than that of the first oil-phase monomer with the aqueous monomer, and the reactivity of the second oil-phase monomer with the aqueous monomer is not less than that of the first oil-phase monomer with the aqueous monomer.

Description

Technical Field

[0001] This application relates to the field of nanofiltration membrane preparation technology, and in particular to a nanofiltration membrane, its preparation method, and a filtration device. Background Technology

[0002] Nanofiltration is a pressure-driven membrane separation technology that falls between ultrafiltration and reverse osmosis. It has been widely applied in advanced drinking water treatment and point-of-use drinking water treatment, and shows great promise. An ideal nanofiltration membrane for drinking water treatment should have a suitable molecular weight cutoff and the highest possible negative charge density on its surface. Nanofiltration membranes meeting these characteristics exhibit high selectivity for both mineral ions and organic pollutants, meaning they can efficiently remove natural organic matter and micro-organic pollutants from water while retaining beneficial mineral ions such as calcium, magnesium, and bicarbonate, which are advantageous for pipeline distribution, drinking water taste, and human health.

[0003] Furthermore, nanofiltration membranes experience membrane fouling during application. Membrane fouling refers to the deposition of particulate or dissolved substances in water on the membrane surface and inside the membrane material, or the growth of microorganisms on the membrane surface, leading to a decline in membrane separation or water permeability. Chemical cleaning is the primary method for removing membrane fouling. Generally speaking, a thicker membrane separation layer is more conducive to withstanding the negative impacts of membrane cleaning on the membrane material, meaning a longer membrane lifespan.

[0004] When preparing nanofiltration membranes using traditional interfacial polymerization methods, it is difficult to achieve a balance in three important indicators: membrane pore size, membrane surface charge density, and separation layer thickness, so that they can be suitable for advanced drinking water treatment and point-of-use drinking water treatment.

[0005] Therefore, we continue to provide a method for preparing nanofiltration membranes that can take into account membrane pore size, membrane surface negative charge density, and separation layer thickness. Summary of the Invention

[0006] Based on this, this application provides a nanofiltration membrane that can achieve good balance between membrane pore size, membrane surface negative charge density, and separation layer thickness, as well as its preparation method and filtration device.

[0007] The first aspect of this application provides a method for preparing a nanofiltration membrane, comprising the following steps:

[0008] The polymer base film is immersed in an aqueous solution containing an aqueous monomer to wet the surface of the polymer base film with the aqueous monomer.

[0009] An oil phase solution containing a first oil phase monomer and a second oil phase monomer is applied to the surface of the polymer base film impregnated with the aqueous phase monomer to conduct an interfacial polymerization reaction and form a separation layer on the surface of the polymer base film; the time of the interfacial polymerization reaction is >30s.

[0010] The separation layer is post-processed to prepare the nanofiltration membrane;

[0011] The first oil phase monomer and the second oil phase monomer are respectively capable of undergoing amidation reaction with the aqueous phase monomer; the molecular weight of the second oil phase monomer is smaller than that of the first oil phase monomer, the binding capacity of the second oil phase monomer with the aqueous phase monomer is greater than that of the first oil phase monomer with the aqueous phase monomer, and the reactivity of the second oil phase monomer with the aqueous phase monomer is not less than that of the first oil phase monomer with the aqueous phase monomer.

[0012] In some embodiments, the second oil phase monomer comprises an aliphatic acyl halide containing two acyl halide functional groups;

[0013] Optionally, the second oil phase monomer includes one or more of carbonyl halides;

[0014] Further optionally, the second oil phase monomer includes one or more of oxaloyl chloride, malonyl chloride, succinyl chloride, and adipyl chloride.

[0015] In some embodiments, the first oil phase monomer comprises an aromatic acyl halide containing a plurality of acyl halide functional groups;

[0016] Optionally, the first oil phase monomer includes one or more of pyromellitic chloroformyl chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride.

[0017] In some embodiments, the mass ratio of the first oil phase monomer to the second oil phase monomer is (0.01-0.2):(0.01-0.2); and / or

[0018] The first oil phase monomer has a mass percentage of 0.01wt%-0.2wt% in the oil phase solution; and / or

[0019] The second oil phase monomer has a mass percentage of 0.01wt%-0.2wt% in the oil phase solution; and / or

[0020] The organic solvent contained in the oil phase solution includes one or more of the following: n-hexane, cyclohexane, n-heptane, petroleum ether, and isoparaffins.

[0021] In some embodiments, the aqueous monomer accounts for 0.05 wt%-5 wt% of the mass of the aqueous solution; and / or

[0022] The aqueous monomer includes polyamines;

[0023] Optionally, the aqueous monomer includes one or more of aliphatic polyamines and aromatic polyamines;

[0024] Further optionally, the aliphatic polyamine includes one or more of piperazine, methylpiperazine, ethylpiperazine, methylpiperazine carboxylate, ethylpiperazine carboxylate, ethylenediamine, propylenediamine, butanediamine, and pentanediamine;

[0025] Further optionally, the aromatic polyamine includes one or more of m-phenylenediamine, p-phenylenediamine, pyromellitic triamine, diaminobenzoic acid, and diaminobenzenesulfonic acid.

[0026] In some embodiments, the polymer-based film is made of one or more of the following materials: polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyethylene, polypropylene, and ceramic materials; and / or

[0027] The polymer-based film also contains a nonwoven support layer.

[0028] In some embodiments, the post-processing includes a thermosetting process;

[0029] Optionally, prior to the thermosetting step, the separation layer may be further subjected to solvent activation treatment.

[0030] The second aspect of this application provides a nanofiltration membrane, which is prepared using the nanofiltration membrane preparation method of the first aspect of this application.

[0031] In some embodiments, the nanofiltration membrane includes a polymer base membrane and a separation layer located on the surface of the polymer base membrane, wherein the thickness of the separation layer is ≥100nm, and optionally 100nm-200nm;

[0032] Optionally, the nanofiltration membrane has at least one of the following features (1)-(3):

[0033] (1) The surface of the nanofiltration membrane carries a negative charge;

[0034] (2) The surface of the nanofiltration membrane is negatively charged, and the absolute value of the Zeta potential on the surface of the nanofiltration membrane is ≥40mV under the condition of pH 6.5-7.5.

[0035] (3) The molecular weight cut of the nanofiltration membrane is 200 Da-300 Da.

[0036] A third aspect of this application provides a filtration device including a nanofiltration membrane as described in the second aspect of this application.

[0037] The nanofiltration membrane preparation method described above includes a first oil phase monomer and a second oil phase monomer with different physicochemical properties in the oil phase solution. This allows the first oil phase monomer to participate mainly in the amidation reaction and the crosslinking reaction in the early stage of the interfacial polymerization reaction, while the second oil phase monomer participates mainly in the amidation reaction and the grafting reaction in the later stage of the interfacial polymerization reaction. At the same time, the interfacial polymerization reaction time is extended to more than 30 seconds, thereby simultaneously increasing the negative charge density on the surface of the nanofiltration membrane, reducing the pore size of the nanofiltration membrane, and increasing the thickness of the separation layer. The prepared nanofiltration membrane has the advantages of high retention selectivity and resistance to chemical cleaning. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 The water permeability coefficient and the retention rates of xylose, MgCl2, and NaCl were used for Comparative Example 1, Example 1, Example 2, Example 3, and Example 4.

[0040] Figure 2 The water permeability coefficient and the retention rates of xylose, MgCl2, and NaCl were used for Comparative Examples 1, 5, 6, 7, and 8.

[0041] Figure 3 The molecular weight cutoff values ​​for Comparative Example 1, Example 1, Example 5, Example 6, Example 7, and Example 8;

[0042] Figure 4 The thickness of the separation layer in the nanofiltration membranes of Comparative Example 1, Example 1, Example 5, Example 6, Example 7, and Example 8;

[0043] Figure 5 The water permeability coefficients and the retention rates of xylose, MgCl2, and NaCl for Comparative Examples 1, 2, 3, 4, and 5 are given.

[0044] Figure 6 The water permeability coefficients and the retention rates of xylose, MgCl2, and NaCl in Examples 1, 9, 10, 11, and 12 are used for the following examples.

[0045] Figure 7 The water permeability coefficients and the retention rates of xylose, MgCl2, and NaCl for Comparative Examples 6, 7, 8, 9, and 10 are used.

[0046] Figure 8 The water permeability coefficients of Comparative Examples 11, 12, 13, 14, and 15, as well as the concentrations of xylose, MgCl2, and Na... 2S O4 retention rate;

[0047] Figure 9 Comparison graph of zeta potential measured under neutral pH conditions (pH=7) for Comparative Examples 2, 5, 11, 14, 9, and 12.

[0048] Figure 10 A comparison chart of nitrogen and oxygen content on the surface of the active layer of Comparative Example 2, Comparative Example 1, Example 9 and Example 1, as measured by XPS.

[0049] Figure 11 The thickness of the separation layer in the nanofiltration membranes of Comparative Examples 2, 5, 6, 9, 9, 10, 12 and 1 is shown.

[0050] Figure 12 The water permeability coefficients and the retention rates of xylose, MgCl2, and NaCl in Comparative Example 1, Example 1, and Comparative Example 16 are used to determine the water permeability coefficients and the retention rates of xylose, MgCl2, and NaCl.

[0051] Figure 13 The thickness of the separation layer in the nanofiltration membranes of Comparative Example 1, Example 1, and Comparative Example 16 is shown. Detailed Implementation

[0052] To facilitate understanding of the present invention, a more complete description of this application will be provided below with reference to relevant embodiments. Preferred embodiments of the present application are given below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the disclosure of this application will be achieved.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0054] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0055] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0056] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0057] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0058] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0059] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0060] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0061] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0062] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0063] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0064] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, but sequentially is preferred.

[0065] Interfacial polymerization is currently the "gold standard" for nanofiltration membrane preparation. The most commonly used aqueous monomer is piperazine (PIP), and the most commonly used oil-phase monomer is trimesoyl chloride (TMC). When preparing nanofiltration membranes using traditional interfacial polymerization, it is difficult to achieve a balance between three crucial parameters: membrane pore size, membrane surface charge density, and separation layer thickness, making them suitable for advanced drinking water treatment and point-of-use water treatment. For example, adjusting the conditions of the interfacial polymerization reaction can reduce the membrane pore size and increase the separation layer thickness, but this simultaneously reduces the negative charge density on the membrane surface. Using a "two-stage reaction method" can increase the negative charge density on the nanofiltration membrane surface, but it significantly reduces the separation layer thickness and sometimes even increases the membrane pore size. Furthermore, the two-stage reaction method increases the membrane preparation process, significantly increasing the cost.

[0066] Therefore, a method for preparing nanofiltration membranes that can take into account membrane pore size, membrane surface charge density, and separation layer thickness is further provided.

[0067] Based on the above problems, this application uses two oil-phase monomers with different physicochemical properties in the preparation of nanofiltration membranes, so that differentiated oil-phase monomer competitive reactions can be achieved during the interfacial polymerization reaction. This enables synergistic control of the negative charge density, membrane pore size and separation layer thickness on the nanofiltration membrane surface, which in turn helps to improve the "mineral ion / organic pollutant" retention selectivity of the nanofiltration membrane, and at the same time enhances the chemical cleaning resistance of the nanofiltration membrane.

[0068] One or more embodiments of this application provide a method for preparing a nanofiltration membrane, comprising the following steps:

[0069] The polymer-based membrane is immersed in an aqueous solution containing an aqueous monomer to wet the surface of the polymer-based membrane with the aqueous monomer; an oil solution containing a first oil monomer and a second oil monomer is applied to the surface of the polymer-based membrane wetted with the aqueous monomer to cause an interfacial polymerization reaction and form a separation layer on the surface of the polymer-based membrane; the separation layer is post-treated to prepare a nanofiltration membrane.

[0070] Among them, the interfacial polymerization reaction time is >30s; the first oil phase monomer and the second oil phase monomer can respectively undergo amidation reaction with the aqueous phase monomer; the molecular weight of the second oil phase monomer is less than that of the first oil phase monomer, the binding ability of the second oil phase monomer with the aqueous phase monomer is greater than that of the first oil phase monomer with the aqueous phase monomer, and the reactivity of the second oil phase monomer with the aqueous phase monomer is not less than that of the first oil phase monomer with the aqueous phase monomer.

[0071] It should be noted that the molecular weight of the second oil phase monomer is smaller than that of the first oil phase monomer, which is beneficial to the mass transfer of the second oil phase monomer in the reaction zone.

[0072] The binding capacity between the second oil phase monomer and the aqueous phase monomer is greater than that between the first oil phase monomer and the aqueous phase monomer. In other words, the second oil phase monomer and the aqueous phase monomer have sufficient non-chemical reaction binding capacity. This is manifested in the fact that the non-chemical reaction binding enthalpy change between the second oil phase monomer and the aqueous phase monomer is lower than that between the first oil phase monomer and the aqueous phase monomer. This allows the aqueous phase monomer to diffuse further, which is beneficial to increasing the thickness of the reaction zone and ultimately increasing the thickness of the membrane separation layer.

[0073] The amidation reaction capability of the second oil-phase monomer with the aqueous-phase monomer is no less than that of the first oil-phase monomer with the aqueous-phase monomer. This means that the amidation reaction energy barrier between the second oil-phase monomer and the aqueous-phase monomer is no higher than that between the first oil-phase monomer and the aqueous-phase monomer. This facilitates the grafting reaction between the second oil-phase monomer and the aqueous-phase monomer or the residual amino groups on the primary separation layer during the later stages of the interfacial polymerization reaction. The primary separation layer is mainly formed after the reaction between the first oil-phase monomer and the aqueous-phase monomer.

[0074] The interfacial polymerization time mentioned in the context refers to the time between applying the oil phase solution to the surface of the polymer base film and before post-treatment. Prolonging the interfacial polymerization time facilitates the grafting reaction between the second oil phase monomer and the aqueous phase monomer or residual amino groups on the primary separation layer in the later stages of the reaction, thereby increasing the thickness of the separation layer.

[0075] Understandably, the nanofiltration membrane preparation method provided in this application includes a first oil phase monomer and a second oil phase monomer with different physicochemical properties in the oil phase solution. This allows the first oil phase monomer to participate mainly in the amidation reaction and the crosslinking reaction in the early stage of the interfacial polymerization reaction, while the second oil phase monomer participates mainly in the amidation reaction and the grafting reaction in the later stage of the interfacial polymerization reaction. At the same time, the interfacial polymerization reaction time is extended to more than 30 seconds, thereby simultaneously increasing the negative charge density on the surface of the nanofiltration membrane, reducing the pore size of the nanofiltration membrane, and increasing the thickness of the separation layer. The prepared nanofiltration membrane has the advantages of high retention selectivity and resistance to cleaning.

[0076] In this application, terms such as "first oil phase monomer" and "second oil phase monomer" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first" and "second" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0077] In some embodiments, the second oil phase monomer comprises an aliphatic acyl halide containing multiple acyl halide functional groups. Optionally, the aliphatic acyl halide contains two acyl halide functional groups.

[0078] As one possible implementation, the second oil phase monomer includes one or more carbonyl halides. It should be noted that a carbonyl halide is a compound containing a carbonyl group (C=O) and a halogen atom, wherein the carbon atom in the carbonyl group is bonded to the halogen atom.

[0079] In some exemplary embodiments, the second oil phase monomer includes one or more of oxaloyl chloride, malonyl chloride, succinyl chloride, and adipyl chloride.

[0080] As one possible implementation, the mass ratio of the first oil phase monomer to the second oil phase monomer is (0.01-0.2):(0.01-0.2); for example, it can be, but is not limited to, 0.01:0.2, 0.02:0.2, 0.04:0.2, 0.06:0.2, 0.08:0.2, 0.1:0.2, 0.12:0.2, 0.14:0.2, 0.16:0.2, 0.18:0.2, 0.2:0.2, 0.2:0.18, 0.2:0.16, 0.2:0.14, 0.2:0.12, 0.2:0.1, 0.2:0.08, 0.2:0.06, 0.2:0.04, 0.2:0.02, 0.2:0.01, or any range between any two of the above ratios. When the mass ratio of the first oil phase monomer to the second oil phase monomer is within the above range, it will not affect the formation of the initial separation layer in the early stage of the interfacial polymerization reaction, and the molecular weight cut of the initial separation layer is moderate.

[0081] In some optional embodiments, the mass percentage of the first oil phase monomer in the oil phase solution is 0.01wt%-0.2wt%; for example, it can be, but is not limited to, 0.01wt%, 0.02wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.17wt%, 0.2wt%, or any range between two of the above mass percentages. When the mass percentage of the first oil phase monomer in the oil phase solution is within the above range, it will not affect the formation of the initial separation layer in the early stage of the interfacial polymerization reaction, and the molecular weight cutoff of the formed initial separation layer is moderate.

[0082] In some embodiments, the first oil phase monomer comprises an aromatic acyl halide containing multiple acyl halide functional groups. The aromatic acyl halide containing two or more acyl halide functional groups is advantageous for forming a network cross-linked structure in the resulting separation layer polymer.

[0083] In some alternative embodiments, the first oil phase monomer includes one or more of pyromellitic chloroformyl chloride, terephthaloyl chloride, isophthaloyl chloride, and phthaloyl chloride.

[0084] As one possible implementation, the mass percentage of the second oil phase monomer in the oil phase solution is 0.01wt%-0.2wt%; for example, it can be, but is not limited to, 0.01wt%, 0.02wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.17wt%, 0.2wt%, or any range between two of the above mass percentages. When the mass percentage of the second oil phase monomer in the oil phase solution is within the above range, it is beneficial for the second oil phase monomer to fully exert its corresponding role in the initial and later stages of the interfacial polymerization reaction, respectively.

[0085] In some embodiments, the mass percentage of the aqueous monomer in the aqueous solution is 0.05wt%-5wt%; for example, it can be, but is not limited to, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, or any range between two of the above mass percentages. When the mass percentage of the aqueous monomer in the aqueous solution is within the above range, it will not affect the formation of the primary separation layer in the early stage of the interfacial polymerization reaction, and the molecular weight cutoff of the formed primary separation layer is moderate.

[0086] As one possible implementation, the aqueous monomer includes polyamines.

[0087] In some alternative embodiments, the aqueous monomer includes one or more of aliphatic polyamines and aromatic polyamines.

[0088] In some alternative embodiments, the aliphatic polyamine includes one or more of piperazine, methylpiperazine, ethylpiperazine, methylpiperazine carboxylate, ethylpiperazine carboxylate, ethylenediamine, propylenediamine, butanediamine, and pentanediamine.

[0089] In some exemplary embodiments, the aromatic polyamine includes one or more of m-phenylenediamine, p-phenylenediamine, pyromellitic triamine, diaminobenzoic acid, and diaminobenzenesulfonic acid.

[0090] In some embodiments, the polymer-based film is made of one or more of the following materials: polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyethylene, polypropylene, and ceramic materials.

[0091] In some exemplary embodiments, the polymer-based film also includes a nonwoven support layer.

[0092] As one possible implementation, the organic solvent contained in the oil phase solution includes one or more of n-hexane, cyclohexane, n-heptane, petroleum ether, and isoalkanes.

[0093] In some embodiments, the post-treatment includes a thermosetting process to further promote the interfacial polymerization of the remaining mixed acyl halide monomers and residual amino groups. As a non-limiting example, the thermosetting process is carried out at a temperature of 40°C–80°C for 1–10 minutes.

[0094] In some alternative embodiments, prior to the thermosetting step, the separation layer is further subjected to solvent activation treatment.

[0095] As a non-limiting example, the separation layer is solvent-activated by applying an organic solvent such as n-alkanes, cycloalkanes, isoalkanes, petroleum ethers, or alcohols over the formed separation layer.

[0096] One or more embodiments of this application provide a nanofiltration membrane prepared using the nanofiltration membrane preparation method described above. This nanofiltration membrane exhibits high retention selectivity and is resistant to washing.

[0097] In some embodiments, the nanofiltration membrane includes a polymer base membrane and a separation layer located on the surface of the polymer base membrane, the separation layer having a thickness ≥100 nm. This helps to improve the chemical cleaning resistance of the nanofiltration membrane.

[0098] In some optional embodiments, the thickness of the separation layer is 100nm-200nm; for example, it can be, but is not limited to, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 150nm, 170nm, 180nm, 190nm, 200nm or any range between two of the above thicknesses.

[0099] In some implementations, the surface of the nanofiltration membrane carries a negative charge; this is beneficial for improving the nanofiltration membrane's selectivity for "mineral ions / organic pollutants".

[0100] As one possible implementation, the surface of the nanofiltration membrane carries a negative charge, and the absolute value of the Zeta potential on the surface of the nanofiltration membrane is ≥40mV under the condition of pH 6.5-7.5; thereby, it is beneficial to further improve the "mineral ion / organic pollutant" retention selectivity of the nanofiltration membrane.

[0101] In some optional embodiments, the nanofiltration membrane has a molecular weight cutoff of 200 Da to 300 Da; for example, it can be, but is not limited to, 200 Da, 210 Da, 220 Da, 230 Da, 240 Da, 250 Da, 260 Da, 270 Da, 280 Da, 290 Da, 300 Da, or any range between two of the above molecular weight cutoffs. This is beneficial for further improving the nanofiltration membrane's selectivity for "mineral ions / organic pollutants".

[0102] One or more embodiments of this application provide a filtration device including the nanofiltration membrane described above.

[0103] The technical solution of the present invention will be described in detail below with reference to specific embodiments. It should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this invention, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0104] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0105] I. Preparation of Nanofiltration Membranes

[0106] Example 1

[0107] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.02 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0108] Example 2

[0109] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.04 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0110] Example 3

[0111] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0112] Example 4

[0113] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.06 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0114] Example 5

[0115] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.04 wt% succinyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0116] Example 6

[0117] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% succinyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0118] Example 7

[0119] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.04 wt% adipyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0120] Example 8

[0121] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% adipyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0122] Example 9

[0123] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.02 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 10 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0124] Example 10

[0125] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.02 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 20 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0126] Example 11

[0127] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.02 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 30 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0128] Example 12

[0129] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.02 wt% oxaloyl chloride (second oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 45 s; then, it was removed and heat-cured at 65 °C for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0130] Comparative Example 1

[0131] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a 0.1 wt% hexane solution of trimesoyl chloride (first oil phase monomer) for 1 min; then, it was taken out and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0132] Comparative Example 2

[0133] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a 0.1 wt% hexane solution of trimesoyl chloride (first oil phase monomer) for 10 s; then, it was taken out and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0134] Comparative Example 3

[0135] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a 0.1 wt% hexane solution of trimesoyl chloride (first oil phase monomer) for 20 s; then, it was taken out and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0136] Comparative Example 4

[0137] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a 0.1 wt% hexane solution of trimesoyl chloride (first oil phase monomer) for 30 s; then, it was taken out and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0138] Comparative Example 5

[0139] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a 0.1 wt% hexane solution of trimesoyl chloride (first oil phase monomer) for 45 s; then, it was taken out and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0140] Comparative Example 6

[0141] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% isophthaloyl chloride (first oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 10 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0142] Comparative Example 7

[0143] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% isophthaloyl chloride (first oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 20 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0144] Comparative Example 8

[0145] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% isophthaloyl chloride (first oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 30 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0146] Comparative Example 9

[0147] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% isophthaloyl chloride (first oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 45 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0148] Comparative Example 10

[0149] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% isophthaloyl chloride (first oil phase monomer) and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0150] Comparative Example 11

[0151] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 10 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0152] Comparative Example 12

[0153] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 20 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0154] Comparative Example 13

[0155] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 30 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0156] Comparative Example 14

[0157] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 45 s; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0158] Comparative Example 15

[0159] The polysulfone-based membrane was immersed in a 2.0 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, an interfacial polymerization reaction was carried out in a hexane solution containing 0.05 wt% sulfonyl chloride and 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; then, it was removed and heat-cured at 65℃ for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0160] Comparative Example 16

[0161] The polysulfone-based membrane was immersed in a 0.6 wt% piperazine aqueous solution (aqueous phase solution) for 2 min to remove excess aqueous solution from the surface; then, interfacial polymerization was carried out in a hexane solution containing 0.1 wt% trimesoyl chloride (first oil phase monomer) for 1 min; followed by interfacial polymerization in a hexane solution containing 0.02 wt% oxaloyl chloride (second oil phase monomer) for 1 min; then, it was removed and heat-cured at 65°C for 4 min; finally, the prepared nanofiltration membrane was rinsed with deionized water and its filtration performance was tested.

[0162] The raw materials and preparation parameters for Examples 1-12 and Comparative Examples 1-16 are shown in Table 1.

[0163] Table 1

[0164]

[0165] II. Performance Testing

[0166] The nanofiltration membranes prepared in the above embodiments and comparative examples were tested using a laboratory-scale cross-flow filtration system. This system had three parallel filtration units. The effective area of ​​each cell was 20.6 cm². 2 Three independent membrane sheets cut from the same membrane were used in parallel experiments. Before sampling, the membranes were pre-compressed at 8 bar for at least 30 min to ensure stability. Subsequent tests were conducted under cross-flow conditions at an operating pressure of 0.5 MPa and a water temperature of 20℃–25℃. The ionic strength of the inorganic salt solutions used in the tests was 10 mmol / L, and the concentration of the single solute solutions of glycerol, xylose, glucose, and sucrose was 100 mg / L (their rejection rates were used to calculate the molecular weight cutoff and pore size of the composite nanofiltration membrane). The xylose rejection rate was determined using a TOC analyzer. The thickness of the separation layer in the selected nanofiltration membranes was measured by TEM (transmission electron microscopy). The elemental distribution on the surface of the selected nanofiltration membranes was measured by XPS (x-ray photoelectron spectroscopy).

[0167] Depend on Figure 1It can be seen that, under an operating pressure of 0.5 MPa, the water permeability coefficient of Examples 1-4 decreased from 3.0 L / m² in Comparative Example 1. -2 h -1 bar -1 It increased sequentially to 3.9 L m -2 h -1 bar -1 4.0 L m -2 h -1 bar -1 4.4 L m -2 h -1 bar -1 5.2L m -2 h -1 bar -1 This indicates that as the concentration of oxaloyl chloride increases, the separation layer of the nanofiltration membrane gradually becomes looser, and the corresponding xylose rejection rate also decreases from 75% in Comparative Example 1 to 63%, 47%, 38%, and 32%, respectively. Furthermore, the salt rejection rate of the nanofiltration membrane also decreased significantly. However, it is noteworthy that compared to the sodium chloride rejection rate, which only decreased from 50.5% in Comparative Example 1 to 33.7% in Example 4, the magnesium chloride rejection rate showed a more significant decreasing trend, decreasing from 75.0% in Comparative Example 1 to 17.2% in Example 4. Moreover, the magnesium chloride rejection rate in Examples 1-4 was lower than that of sodium chloride, which is a clear characteristic of a strongly negatively charged membrane.

[0168] Depend on Figure 2 Similarly, by adding succinyl chloride and adipic acid chloride to traditional acyl chloride monomers, the prepared nanofiltration membranes exhibit similar retention properties to those in Examples 1-4, all showing a trend where the magnesium chloride rejection rate is lower than that of sodium chloride. This indicates that a series of small-molecule organic acyl chlorides can effectively improve the negative charge on the nanofiltration membrane surface within a certain concentration range. The reason for this is that the small-molecule organic acyl chlorides mainly undergo amidation grafting reactions in the later stages of interfacial polymerization, and the remaining acyl chloride groups undergo hydrolysis reactions to generate carboxyl groups, thereby making the nanofiltration membrane surface negatively charged.

[0169] Depend on Figure 3 It can be seen that, compared to the comparative example's cleavage molecular weight of 200.3 Da, the cleavage molecular weights of Examples 1, 5, 6, 7, and 8 decreased to 236.5 Da, 257.6 Da, 277.5 Da, 263.0 Da, and 276.3 Da, respectively. However, the cleavage molecular weight is still less than 300 Da, maintaining a high rejection level for organic pollutants. Therefore, the nanofiltration membrane prepared based on the blending of small-molecule organic polyacrylamide halide monomers exhibits high selectivity for both calcium and magnesium ions and organic pollutants.

[0170] At the same time, by Figure 4 It can be seen that, compared with the thickness of 83.6 nm in the nanofiltration membrane of Comparative Example 1, the thickness of the separation layer in the nanofiltration membranes of Examples 1, 5, 6, 7 and 8 increased to 138.0 nm, 127.2 nm, 119.3 nm, 121.3 nm and 117.4 nm, respectively. This indicates that the mixing of small molecule organic polyacrylamide halogen monomers effectively improved the thickness of the separation layer in the nanofiltration membrane, which is beneficial to the stable operation of the nanofiltration membrane under long-term cleaning.

[0171] Depend on Figure 5 and Figure 6 It can be seen that with the increase of reaction time, the water flux of Comparative Examples 1-5 decreased, while the xylose rejection rate and salt rejection rate increased slightly. However, overall, the impact on the performance of traditional nanofiltration membranes prepared from a single oil phase monomer was not significant. In contrast, the reaction time had a significant impact on nanofiltration membranes prepared with the addition of small molecule organic diacyl chlorides: in the short time (10 s-30 s), small molecule organic diacyl chlorides could not effectively increase the negative charge density on the membrane surface, and the magnesium chloride rejection rate in Examples 9-10 was much greater than that in Sodium chloride. With further extension of the reaction time, only when the reaction time was greater than 30 s could the small molecule organic diacyl chlorides increase the negative charge density on the membrane surface, and the magnesium chloride rejection rate in Examples 1 and Examples 11-12 was less than that in Sodium chloride.

[0172] Depend on Figure 7 and 8 It is known that when aromatic diacyl chloride (isophthaloyl chloride) and thioyl halide (sulfonyl chloride) are used as the second oil phase monomers and added to the oil phase solution of traditional acyl chloride monomers for interfacial polymerization at different reaction times, the magnesium chloride rejection rate of the prepared aromatic diacyl chloride blended membrane increases with the extension of reaction time, while the thioyl halide blended membrane maintains a high magnesium chloride rejection rate. Obviously, neither of the two blended membranes can reduce the rejection rate of calcium and magnesium ions, and cannot meet the high selective separation performance of "calcium and magnesium ions / organic pollutants".

[0173] Depend on Figure 9 It can be seen that extending the interfacial polymerization reaction time has little effect on the surface charge of the nanofiltration membranes in the comparative example, all of which exhibit weak negative charge. However, the zeta potential of the nanofiltration membrane prepared by blending small molecule organic diacyl chlorides decreased from -32 mV at 10 s to -50 mV at 45 s under pH conditions of 6.5-7.5, indicating that the negative charge density on the surface of the nanofiltration membrane in Example 12 was significantly enhanced.

[0174] Depend on Figure 10It is known that due to the interference effect of small-molecule organic diacyl chlorides in the short term, a greater amount of nitrogen diffuses to the membrane surface. However, as the interfacial polymerization reaction time increases, more small-molecule organic diacyl chlorides tend to participate in the interfacial polymerization reaction primarily through grafting. Therefore, in Example 1, the oxygen content on the nanofiltration membrane surface increases significantly. Further... Figure 11 It is known that, due to the mechanism of small-molecule organic diacyl chloride's initial interference followed by reaction, the relatively dense separation layer surface formed in a short time will develop into a loose layer composed of grafted and cross-linked small-molecule organic diacyl chloride and residual piperazine. This significantly increases the thickness of the separation layer in the nanofiltration membrane. Figure 12 and 13 It can be seen that, in the final comparison of the performance of the nanofiltration membrane prepared by one-step blending of small molecule organic diacyl chloride and the nanofiltration membrane prepared by two-step grafting of oil phase monomers, the small molecule organic diacyl chloride has a small molecular structure, which makes it easy to enter the primary separation layer formed by the interfacial polymerization of traditional aqueous phase monomers and oil phase monomers, and undergo amidation reaction with residual amino groups. Although the two-step preparation of nanofiltration membrane by grafting oil phase monomers can also increase the negative charge density on the membrane surface and reduce the molecular weight cut of the membrane, the thickness of the separation layer in the prepared nanofiltration membrane is small, which is far from the thickness of the separation layer in the nanofiltration membrane prepared by one-step blending of small molecule organic diacyl chloride.

[0175] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0176] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a nanofiltration membrane, characterized in that, Includes the following steps: The polymer base film is immersed in an aqueous solution containing an aqueous monomer to wet the surface of the polymer base film with the aqueous monomer. An oil phase solution containing a first oil phase monomer and a second oil phase monomer is applied to the surface of the polymer base film impregnated with the aqueous phase monomer to conduct an interfacial polymerization reaction and form a separation layer on the surface of the polymer base film; the time of the interfacial polymerization reaction is >30s. The separation layer is post-processed to prepare the nanofiltration membrane; The first and second oil phase monomers are respectively capable of undergoing amidation reactions with the aqueous phase monomer; the molecular weight of the second oil phase monomer is smaller than that of the first oil phase monomer, the binding affinity of the second oil phase monomer to the aqueous phase monomer is greater than that of the first oil phase monomer to the aqueous phase monomer, and the reactivity of the second oil phase monomer to the aqueous phase monomer is not less than that of the first oil phase monomer to the aqueous phase monomer; the second oil phase monomer includes succinyl chloride; the mass percentage of the second oil phase monomer in the oil phase solution is 0.04wt%-0.05wt%; the first oil phase monomer includes trimesoyl chloride, and the mass percentage of the first oil phase monomer in the oil phase solution is 0.1wt%. The thickness of the separation layer of the prepared nanofiltration membrane is ≥100nm; the surface of the nanofiltration membrane is negatively charged, and the absolute value of the Zeta potential on the surface of the nanofiltration membrane is ≥40mV under the condition of pH 6.5-7.5; the molecular weight cutoff of the nanofiltration membrane is 200Da-300Da.

2. The preparation method according to claim 1, characterized in that, The organic solvent contained in the oil phase solution includes one or more of the following: n-hexane, cyclohexane, n-heptane, petroleum ether, and isoparaffins.

3. The preparation method according to claim 1, characterized in that, The aqueous monomer has a mass percentage of 0.05wt%-5wt% in the aqueous solution; and / or The aqueous monomers include polyamines.

4. The preparation method according to claim 3, characterized in that, The aqueous monomer includes one or more of aliphatic polyamines and aromatic polyamines.

5. The preparation method according to claim 4, characterized in that, The aliphatic polyamines include one or more of piperazine, methylpiperazine, ethylpiperazine, methylpiperazine carboxylate, ethylpiperazine carboxylate, ethylenediamine, propylenediamine, butanediamine, and pentanediamine.

6. The preparation method according to claim 4, characterized in that, The aromatic polyamines include one or more of m-phenylenediamine, p-phenylenediamine, pyromellitic triamine, diaminobenzoic acid, and diaminobenzenesulfonic acid.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The polymer-based film is made of one or more of the following materials: polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyethylene, polypropylene, and ceramic materials. The polymer-based film also contains a nonwoven support layer.

8. The preparation method according to any one of claims 1 to 6, characterized in that, The post-processing includes thermosetting.

9. The preparation method according to claim 8, characterized in that, Prior to the thermosetting process, the process further includes solvent activation of the separation layer.

10. A nanofiltration membrane, characterized in that, It was prepared by the preparation method according to any one of claims 1 to 9; The nanofiltration membrane comprises a polymer base membrane and a separation layer located on the surface of the polymer base membrane, the thickness of the separation layer being ≥100nm; the surface of the nanofiltration membrane carries a negative charge, and the absolute value of the Zeta potential on the surface of the nanofiltration membrane is ≥40mV under pH conditions of 6.5-7.5; the molecular weight cutoff of the nanofiltration membrane is 200Da-300Da.

11. A filtration device, characterized in that, The filtration device includes the nanofiltration membrane as described in claim 10.

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