Polyamide composite membranes and their preparation methods and water purification methods

Abstract

This invention belongs to the field of membrane separation technology, specifically relating to a polyamide composite membrane and its preparation method and water purification method. Piperazine is dissolved in deionized water to prepare a PIP solution, wherein the concentration of piperazine in the PIP solution is 0.05~2wt%; fumarate chloride is dissolved in a first organic solvent to prepare an FC / organic solution, wherein the concentration of fumarate chloride in the FC / organic solution is 0.2wt%; a substrate membrane is immersed in the PIP solution to allow the substrate membrane to fully adsorb PIP, removing excess aqueous phase from the surface of the substrate membrane and forming a uniform aqueous environment, thus obtaining a treated substrate membrane; the FC / organic solution is transferred to the surface of the treated substrate membrane, causing the FC and PIP to undergo a polymerization reaction; the polymerization reaction is terminated by washing with a second organic solvent; and the membrane is dried to obtain the polyamide composite membrane. The preparation method can rapidly construct the polyamide layer at room temperature and pressure, allowing for controllable adjustment of the polyamide layer morphology, and the resulting membrane structure is stable and has good repeatability.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a polyamide composite membrane, its preparation method, and a water purification method. Background Technology

[0002] Membrane separation technology has advantages such as simple operation, low energy consumption, and high separation efficiency, and is widely used in seawater desalination and wastewater treatment. Among them, polyamide (PA) composite membranes, with their excellent chemical stability and high selectivity, have become the core material for nanofiltration and reverse osmosis membranes, and are widely used in scenarios such as dye / salt separation and organic pollutant removal.

[0003] While traditional polyamide membranes achieve excellent salt retention through their highly cross-linked polyamide networks, their dense structure also limits the transport efficiency of water molecules and neutral organic matter, resulting in a typical contradiction of "high selectivity and low permeability." Furthermore, they are prone to pollutant adsorption and membrane fouling during operation, thus limiting their long-term stable operation and potential for large-scale industrial application.

[0004] Therefore, while maintaining the high selectivity of polyamide membranes, how to improve their permeation performance and balance process feasibility and economy is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a polyamide composite membrane, its preparation method, and a water purification method. The preparation method of the polyamide composite membrane provided by this invention is simple to operate, with mild reaction conditions, and can rapidly construct the polyamide layer under normal temperature and pressure. It offers more flexible control over monomer diffusion and reaction rates, allowing for controllable adjustment of the polyamide layer morphology. The resulting membrane structure is stable and has good repeatability, making it suitable for the efficient separation and resource recovery of dyes and salts in dyeing and printing wastewater.

[0006] The first aspect of the present invention is to provide a method for preparing a polyamide composite membrane, comprising the following steps: dissolving piperazine in deionized water to prepare a piperazine solution, wherein the concentration of piperazine in the piperazine solution is 0.05~2wt%; dissolving fumarate chloride in a first organic solvent to prepare a fumarate chloride solution, wherein the concentration of fumarate chloride in the fumarate chloride solution is 0.2wt%; immersing a base membrane in the piperazine solution to allow the base membrane to fully adsorb piperazine, removing excess aqueous phase from the surface of the base membrane to obtain a treated base membrane; transferring the fumarate chloride solution to the surface of the treated base membrane to allow the fumarate chloride and piperazine to undergo a polymerization reaction, drying, and obtaining the polyamide composite membrane.

[0007] In some embodiments of the present invention, the basement membrane is immersed in the piperazine solution for 0.5 to 10 minutes.

[0008] In some embodiments of the present invention, the polymerization reaction time of fumarate chloride and piperazine is controlled to be 0.5 to 10 min.

[0009] In some embodiments of the present invention, the method for controlling the time of the polymerization reaction is to terminate the polymerization reaction by washing with a second organic solvent.

[0010] In some embodiments of the present invention, the first organic solvent and the second organic solvent are each independently selected from organic solvents that are immiscible with water and have a density less than that of water; selected from n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, and toluene.

[0011] In some embodiments of the present invention, the drying conditions are a drying temperature of 40~80℃ and a drying time of 2~10min.

[0012] In some embodiments of the present invention, the base membrane is selected from one of polyethersulfone membrane, cellulose acetate membrane, nylon membrane, and polytetrafluoroethylene membrane.

[0013] In some embodiments of the present invention, the pore size of the base membrane is 0.22~0.50 μm.

[0014] A second aspect of the present invention is to provide a polyamide composite film, wherein the polyamide composite film is prepared by the method for preparing polyamide composite film described in the first aspect.

[0015] A third aspect of the present invention is to provide a water purification method, which uses the polyamide composite membrane described in the second aspect or a polyamide composite membrane prepared by the method described in the first aspect for water purification.

[0016] The beneficial effects of the present invention include at least one of the following:

[0017] To address the issues of low permeability and limited selectivity in existing polyamide composite membranes (PA membranes) during dye / salt separation, this invention provides a novel control strategy for optimizing the PA layer of the polyamide composite membrane. By optimizing the interfacial polymerization monomer structure and reaction kinetics, the excessive cross-linking and densification of the PA layer (hereinafter also described as the selective layer or polyamide layer) are effectively alleviated, resulting in a thinner selective layer with a more uniform pore structure. This structure not only reduces water molecule transport resistance and significantly improves the permeability of the PA membrane, but also maintains excellent dye rejection, achieving a balance between permeability and selectivity.

[0018] The preparation method provided by this invention is simple to operate, with mild reaction conditions, and can rapidly construct polyamide layers at room temperature and pressure. Compared with existing systems using trifunctional acyl chloride monomers, this method offers more flexible control over monomer diffusion and reaction rates, enabling controllable adjustment of the polyamide layer morphology. The resulting membrane structure is stable and reproducible, offering advantages such as low cost and scalability. It is suitable for the efficient separation and resource recovery of dyes and salts in dyeing and printing wastewater. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0020] Figure 1 The water permeability, Na2SO4 rejection rate, and Coomassie Brilliant Blue rejection rate of the polyamide composite membranes obtained in Examples 1, 2, and 3 of this invention, and the polyamide composite membrane obtained in Comparative Example 2;

[0021] Figure 2 The water flux and the rejection rates of NaCl and Na2SO4 of the polyamide composite membrane obtained in Example 1 and Comparative Example 1 are respectively.

[0022] Figure 3 The rejection rates of Direct Red 80, Reactive Red 120, Reactive Brilliant Blue and Coomassie Brilliant Blue for the polyamide composite film obtained in Example 1 and the polyamide composite film obtained in Comparative Example 1 are shown.

[0023] Figure 4 The dye / Na2SO4 selectivity of the polyamide composite film obtained in Example 1 and the polyamide composite film obtained in Comparative Example 1 for DR80, RR120, KN-R and BBG;

[0024] Figure 5 The image shown is a scanning electron microscope image of the polyamide composite film obtained in Example 1.

[0025] Figure 6 The image shows a scanning electron microscope (SEM) image of the polyamide composite film obtained in Comparative Example 1.

[0026] The attached diagram shows Direct Red 80 (DR80), Reactive Red 120 (RR120), Reactive Brilliant Blue (KN-R), and Coomassie Brilliant Blue (BBG). Detailed Implementation

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0028] 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 invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0029] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] Polyamide (PA) composite membranes, with their excellent chemical stability and high selectivity, have become the core material for nanofiltration and reverse osmosis membranes, and are widely used in dye / salt separation and organic pollutant removal. While the highly cross-linked polyamide network achieves excellent salt retention, it also significantly limits the transport of water molecules and neutral organic matter, thus exhibiting a "high selectivity, low permeability" characteristic. This "permeability-selectivity trade-off" has become the core bottleneck for polyamide membranes in dye / salt separation and high-salt organic wastewater treatment. An overly dense structure not only reduces water flux but also easily leads to pollutant adsorption and membrane fouling during operation, limiting its long-term stable operation and industrial application potential.

[0032] To address this issue, existing technologies employ methods such as regulating the interfacial polymerization rate, altering monomer structures, or introducing functional nanofillers (e.g., graphene oxide, metal-organic frameworks) to adjust the membrane's microstructure, aiming to improve permeation performance while maintaining good selectivity. However, existing methods still suffer from problems such as difficulty in controlling the reaction, poor material compatibility, and high synthesis costs, making it difficult to simultaneously achieve both high permeability and high selectivity in the membrane.

[0033] Highly cross-linked structures can improve separation performance, but they also limit the rate at which molecules pass through, resulting in lower membrane flux. This inherent contradiction restricts the further improvement of separation efficiency in traditional polyamide membranes. Furthermore, because the formation process of the polyamide layer is greatly influenced by reaction kinetics, it is difficult to achieve precise control of the membrane structure under mild conditions.

[0034] To overcome the contradiction between "permeability" and "selectivity," this invention provides a method for preparing a polyamide composite membrane using FC polymerization that is simple to operate, has mild reaction conditions, and a high flux.

[0035] The method for preparing the polyamide composite film provided by the present invention includes the following steps:

[0036] (a) Solution preparation

[0037] Piperazine (PIP) was dissolved in deionized water to prepare a PIP solution with a concentration of 0.05-2 wt%.

[0038] In some embodiments, the concentration of PIP in the PIP solution may be 0.2 wt%, 0.5 wt%, 0.8 wt%, 1.2 wt%, or 2 wt%. It should be noted that the concentration of PIP in the PIP solution is any of the foregoing values ​​or any one of the ranges described above.

[0039] Fumaryl chloride (FC) was dissolved in a first organic solvent to prepare a fumaryl chloride solution (also described as FC / organic solution), with a fumaryl chloride concentration of 0.2 wt%. Increasing the fumaryl chloride concentration further increases the degree of polymerization of the formed polyamide layer, thereby reducing water permeability; conversely, too low a fumaryl chloride concentration results in an overly porous membrane structure and insufficient selectivity. Therefore, a concentration of 0.2 wt% yields the composite membrane with optimal overall performance.

[0040] The first organic solvent is selected from organic solvents that are immiscible with water and have a density less than water, such as n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, and toluene.

[0041] It should be noted that the organic solvent used in this invention should have the property of being immiscible with water but capable of dissolving FC.

[0042] In some embodiments of the present invention, ultrasonic dispersion of the PIP solution and the FC / organic solution is also included. For example, the ultrasonic time is 10 min, and the ultrasonic treatment volume is 10~50 mL. For example, the ultrasonic treatment volume is 10 mL, 20 mL, 30 mL, 40 mL, 50 mL, etc. Those skilled in the art can also choose other dispersion techniques. The purpose of dispersion is to break up the nanoscale aggregates that are easy to form in the solution, ensure uniform molecular-level distribution, and uniformly dispersed aqueous or organic phase solutions can form a more regular active layer, enhance separation accuracy and flux, and help improve the consistency of membrane structure.

[0043] In some embodiments of the present invention, the density of the crosslinked network formed by the subsequent reaction of FC and PIP can be adjusted by controlling the concentration of the PIP solution and the concentration of the FC / organic solution. When the concentration of the PIP solution is low, the reaction forms a looser network with a larger average pore size. When the PIP concentration is high, the number of reaction sites increases, forming a denser crosslinked structure with a smaller average pore size.

[0044] It should be noted that those skilled in the art can adjust the concentration of the PIP solution and the FC / organic solution, or adjust the type of organic solvent used, as long as the technical principle of the present invention can be achieved.

[0045] (II) Basement membrane pretreatment

[0046] In some embodiments, the base membrane used is selected from one of polyethersulfone membrane, cellulose acetate membrane, nylon membrane, and polytetrafluoroethylene membrane. The pore size of the base membrane is 0.22~0.50 μm.

[0047] The basement membrane was immersed in a PIP solution to allow it to fully adsorb the PIP. Then, excess aqueous phase was removed from the surface of the basement membrane to create a homogeneous aqueous environment, resulting in the treated basement membrane.

[0048] It should be noted that the immersion time of the basement membrane in the PIP solution is 0.5–10 min. The immersion time can be 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min, or 10 min, or any of the aforementioned values ​​or any combination thereof. The purpose of controlling the immersion time of the basement membrane in the PIP solution is to allow PIP molecules to permeate into the membrane pores. Those skilled in the art can select the appropriate time as needed. Ensuring sufficient adsorption of PIP by the basement membrane and minimizing the immersion time is more beneficial for improving preparation efficiency.

[0049] In addition, it should be noted that the method of removing excess aqueous phase (PIP solution) from the surface of the basement membrane is a well-known technique to those skilled in the art, and they may choose scraping, centrifugation or other methods to remove excess aqueous phase from the surface of the basement membrane as needed.

[0050] (III) Polymerization reaction of FC and PIP

[0051] FC / organic solution is transferred to the surface of the treated substrate membrane to allow FC to polymerize with PIP.

[0052] In some embodiments, the polymerization reaction time of FC and PIP is 0.5 to 10 minutes. The time can be 0.5 minutes, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 10 minutes, or any of the aforementioned values ​​or any combination thereof. By controlling the polymerization reaction time, the degree of crosslinking can also be controlled, alleviating the traditional contradiction between "permeability and selectivity".

[0053] In some embodiments, the mass ratio of PIP solution to FC / organic solution used is 1:5, 1:3, 2:3, 1:1, 3:2, 3:1, or 5:1.

[0054] By controlling the concentrations of PIP solution and FC / organic solution, as well as the mass ratio of PIP solution to FC / organic solution, the interfacial polymerization kinetics are regulated, so that the prepared polyamide composite membrane can maintain sieving capacity while ensuring permeability, thus alleviating the contradiction of "permeability-selectivity" in traditional composite membranes.

[0055] It should be noted that the mass ratio of the PIP solution to the FC / organic solution can be 1:5, 1:3, 2:3, 1:1, 3:2, 3:1, or 5:1, and those skilled in the art can choose according to their needs. High mass ratio solutions will accelerate the rapid diffusion of amine monomers from the aqueous phase to the organic phase, easily forming a thicker and rougher polyamide layer, leading to a decrease in water flux. Under low mass ratio conditions, the interface position is more stable, and the diffusion of amine monomers into the organic phase is somewhat restricted, resulting in a thinner and more uniform polyamide layer, which is beneficial for improving the water permeation flux of the membrane.

[0056] (iv) Post-processing

[0057] The substrate membrane subjected to the polymerization reaction of FC and PIP was washed with a second organic solvent to terminate the polymerization reaction, and then dried to obtain a polyamide composite membrane.

[0058] The second organic solvent is selected from organic solvents that are immiscible with water and have a density less than water, such as n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, and toluene.

[0059] In some embodiments, the drying conditions are a drying temperature of 40~80℃ and a drying time of 2~10min. The drying temperature can be 40℃, 45℃, 55℃, 60℃, 70℃, or 80℃, or any one or any combination of the aforementioned values. The drying time can be 2min, 4min, 6min, 8min, or 10min, or any one or any combination of the aforementioned values.

[0060] It should be noted that the prepared polyamide composite membrane should be stored in deionized water or pure water.

[0061] The preparation method provided by this invention is simple to operate, with mild reaction conditions, and can rapidly construct polyamide layers at room temperature and pressure. Compared with existing systems using trifunctional acyl chloride monomers, this method offers more flexible control over monomer diffusion and reaction rates, enabling controllable adjustment of the polyamide layer morphology. The resulting membrane structure is stable and reproducible, offering advantages such as low cost and scalability. It is suitable for the efficient separation and resource recovery of dyes and salts in dyeing and printing wastewater.

[0062] This invention provides a water purification method using a polyamide composite membrane prepared according to the method of this invention. This method solves the problems of low permeability and limited selectivity in traditional polyamide composite membranes (PA membranes) during dye / salt separation. By optimizing the interfacial polymerization monomer structure and reaction kinetics, this invention effectively alleviates the problems of excessive cross-linking and densification of the PA layer, thereby forming a thinner selective layer with a more uniform pore structure. This structure not only reduces the resistance to water molecule transport and significantly improves the permeability of the PA membrane, but also maintains excellent dye rejection, achieving a balance between permeability and selectivity.

[0063] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0064] Example 1

[0065] (1) Preparation of PIP solution: Dissolve 0.02 g PIP in 10 mL of deionized water and then sonicate for 10 min to obtain a uniform PIP solution.

[0066] Preparation of FC / organic solution: Dissolve 5 μL of FC in 10 mL of n-hexane, and then sonicate for 10 min to obtain a homogeneous FC / n-hexane solution.

[0067] (2) Immerse the basement membrane completely in the PIP solution for 3 min to allow the basement membrane to fully adsorb PIP and form an aqueous environment. Then, remove the excess aqueous phase from the surface of the basement membrane.

[0068] (3) Transfer the FC / organic solvent obtained in (1) to the surface of the basement membrane and react for 2 min.

[0069] (4) Washing and post-treatment: The composite membrane prepared in (3) was washed in hexane, dried at 60°C for 5 min, and stored in deionized water to obtain FC-PIP-1 membrane.

[0070] After preparation, the FC-PIP-1 membrane was characterized for surface morphology and other parameters. It was then applied to the separation of NaCl, Na₂SO₄, DR80, RR120, KN-R, and BBG. The test and analysis results are as follows: Figures 1-5 As shown.

[0071] like Figure 1 As shown, the water permeability of the FC-PIP-1 membrane is 103.95 L / m. -2 h -1 bar -1 Meanwhile, the rejection rate for Na2SO4 was 23.08%, and the rejection rate for BBG was 99.35%.

[0072] like Figure 2 As shown, the water permeability of the FC-PIP-1 membrane is 103.35 L / m. -2 h -1 bar -1 Meanwhile, the rejection rate for Na2SO4 was 35.32%, and the rejection rate for NaCl was 4.08%.

[0073] like Figure 3 As shown, the FC-PIP-1 membrane has a rejection rate of 99.35% for DR80, 99.11% for RR120, 99.00% for KN-R, and 99.13% for BBG.

[0074] like Figure 4 As shown, the FC-PIP-1 membrane has a selectivity of 118.33 for DR80, a selectivity of 72.45 for RR120, a selectivity of 64.48 for KN-R, and a selectivity of 74.11 for BBG.

[0075] like Figure 5 and Figure 6As shown, the surface of the FC-PIP-1 membrane is relatively flat.

[0076] Example 2

[0077] (1) Preparation of PIP solution: Dissolve 0.05 g PIP in 10 mL of deionized water and then sonicate for 10 min to obtain a uniform PIP solution.

[0078] Preparation of FC / organic solution: Dissolve 5 μL of FC in 10 mL of n-hexane, and then sonicate for 10 min to obtain a homogeneous FC / n-hexane solution.

[0079] (2) Immerse the basement membrane completely in the PIP solution for 3 min to allow the basement membrane to fully adsorb PIP and form an aqueous environment. Then, remove the excess aqueous phase from the surface of the basement membrane.

[0080] (3) Transfer the FC / organic solvent obtained in (1) to the surface of the basement membrane and react for 2 min.

[0081] (4) Washing and post-treatment: The composite membrane prepared in (3) was washed in hexane, dried at 60°C for 5 min, and stored in deionized water to obtain FC-PIP-2 membrane.

[0082] After preparation, the FC-PIP-2 membrane was characterized for surface morphology and other aspects. It was then applied to the separation of Na2SO4 and BBG, and the resulting test and analysis results are as follows: Figure 1 As shown.

[0083] like Figure 1 As shown, the water permeability of the FC-PIP-2 membrane is 26.04 L / m. -2 h -1 bar -1 Meanwhile, the rejection rate for Na2SO4 was 67.45%, and the rejection rate for BBG was 99.35%.

[0084] Example 3

[0085] (1) Preparation of PIP solution: Dissolve 0.08 g PIP in 10 mL of deionized water and then sonicate for 10 min to obtain a homogeneous PIP solution.

[0086] Preparation of FC / organic solution: Dissolve 5 μL of FC in 10 mL of n-hexane, and then sonicate for 10 min to obtain a homogeneous FC / n-hexane solution.

[0087] (2) Immerse the basement membrane completely in the PIP solution for 3 min to allow the basement membrane to fully adsorb PIP and form an aqueous environment. Then, remove the excess aqueous phase from the surface of the basement membrane.

[0088] (3) Transfer the FC / organic solvent obtained in (1) to the surface of the basement membrane and react for 2 min.

[0089] (4) Washing and post-treatment: The composite membrane prepared in (3) was washed in hexane, then dried at 60°C for 5 min and stored in deionized water to obtain the FC-PIP-3 membrane.

[0090] After preparation, the FC-PIP-3 membrane was characterized for surface morphology and other aspects. It was then applied to the separation of Na2SO4 and BBG, and the test and analysis results are as follows: Figure 1 As shown.

[0091] like Figure 1 As shown, the water permeability of the FC-PIP-3 membrane is 7.35 L / m. -2 h -1 bar -1 Meanwhile, the rejection rate for Na2SO4 was 71.80%, and the rejection rate for BBG was 99.56%.

[0092] Comparative Example 1

[0093] (1) Dissolve 0.02 g PIP in 10 mL of deionized water and then sonicate for 10 min to obtain a homogeneous PIP solution. Then, dissolve 0.013 g TMC in 10 mL of n-hexane and then sonicate for 10 min to obtain a homogeneous TMC / n-hexane solution.

[0094] (2) Immerse the basement membrane completely in the PIP solution for 3 min to allow the basement membrane to fully adsorb PIP and form an aqueous environment. Then, remove the excess aqueous phase from the surface of the basement membrane.

[0095] (3) Transfer the FC / organic solvent obtained in (1) to the surface of the basement membrane and react for 2 min.

[0096] (4) Washing and post-treatment: The composite membrane prepared in (3) was rinsed in hexane, dried at 60°C for 5 min, and stored in deionized water to obtain the TFC membrane.

[0097] After preparation, the TFC membrane was characterized for surface morphology and other parameters. It was then applied to the separation of NaCl, Na₂SO₄, DR80, RR120, KN-R, and BBG. The test and analysis results are as follows: Figures 2-5 As shown.

[0098] like Figure 2 As shown, the water permeability of the TFC membrane is 6.80 L / m. -2 h -1 bar -1It also has a Na2SO4 rejection rate of 98.17% and a NaCl rejection rate of 19.11%.

[0099] like Figure 3 As shown, the TFC membrane exhibits a retention rate of 99.61% for DR80, 99.33% for RR120, 99.00% for KN-R, and 99.35% for BBG.

[0100] like Figure 4 As shown, the TFC membrane has a selectivity of 5.29 for DR80, a selectivity of 3.07 for RR120, a selectivity of 1.84 for KN-R, and a selectivity of 3.14 for BBG.

[0101] like Figure 5 and Figure 6 As shown, the surface of the TFC membrane is relatively rough.

[0102] Compared to the FC-PIP-1 membrane, the TFC membrane has a slightly higher rejection rate but much lower permeability. This is mainly due to the formation of a relatively dense separation layer with smaller pore sizes in the TFC membrane. Therefore, the TFC membrane has much lower permeability to water, and consequently, lower dye / Na2SO4 selectivity.

[0103] Comparative Example 2

[0104] (1) Dissolve 0.10 g PIP in 10 mL of deionized water and then sonicate for 10 min to obtain a homogeneous PIP solution. Then, dissolve 5 μL FC in 10 mL of n-hexane and then sonicate for 10 min to obtain a homogeneous FC / n-hexane solution.

[0105] (2) Immerse the basement membrane completely in the PIP solution for 3 min to allow the basement membrane to fully adsorb PIP and form an aqueous environment. Then, remove the excess aqueous phase from the surface of the basement membrane.

[0106] (3) Transfer the FC / organic solvent obtained in (1) to the surface of the basement membrane and react for 2 min.

[0107] (4) Washing and post-treatment: The composite membrane prepared in (3) was washed in hexane, dried at 60°C for 5 min, and stored in deionized water to obtain FC-PIP-4 membrane.

[0108] After preparation, the FC-PIP-4 membrane was characterized for surface morphology and other aspects. It was then applied to the separation of Na2SO4 and BBG, and the resulting test and analysis results are as follows: Figure 1 As shown.

[0109] like Figure 1As shown, the water permeability of the FC-PIP-1 membrane is 3.6 L / m³. -2 h -1 bar -1 Meanwhile, the rejection rate for Na2SO4 was 89.81%, and the rejection rate for BBG was 100%.

[0110] Compared to the FC-PIP-1 membrane, the FC-PIP-4 membrane exhibits relatively poor performance, primarily due to the formation of a more dense membrane under higher PIP concentrations. The FC-PIP-4 membrane has a smaller average pore size and a denser structure than the FC-PIP-1 membrane, resulting in decreased water permeability and increased rejection rates for dyes and salts.

[0111] In summary, this invention effectively alleviates the problems of excessive cross-linking and densification of the PA layer by optimizing the structure and reaction kinetics of the interfacial polymerization monomers, thereby forming a thinner selective layer with a more uniform pore structure. This structure not only reduces the resistance to water molecule transport and significantly improves the permeability of the PA membrane, but also maintains excellent dye rejection, achieving a balance between permeability and selectivity.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a polyamide composite film, characterized in that, Includes the following steps: Piperazine was dissolved in deionized water to prepare a piperazine solution, wherein the concentration of piperazine in the piperazine solution was 0.2 wt%. Fumaryl chloride was dissolved in a first organic solvent to prepare a fumaryl chloride solution, wherein the concentration of fumaryl chloride in the fumaryl chloride solution was 0.2 wt%. The basement membrane is immersed in the piperazine solution to allow the basement membrane to fully adsorb the piperazine, thereby removing excess aqueous phase from the surface of the basement membrane and obtaining the treated basement membrane. The fumarate chloride solution is transferred to the surface of the treated substrate membrane, where fumarate chloride and piperazine undergo a polymerization reaction. After drying, the polyamide composite membrane is obtained.

2. The preparation method according to claim 1, characterized in that, The basement membrane is immersed in the piperazine solution for 0.5 to 10 minutes.

3. The preparation method according to claim 1, characterized in that, The polymerization reaction time of fumarate chloride and piperazine is controlled to be 0.5~10 min.

4. The preparation method according to claim 3, characterized in that, The polymerization reaction time is controlled by washing with a second organic solvent to terminate the polymerization reaction.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The first organic solvent and the second organic solvent are each independently selected from organic solvents that are immiscible with water and have a density less than that of water; Selected from n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, and toluene.

6. The preparation method according to claim 1, characterized in that, The drying conditions are a drying temperature of 40~80℃ and a drying time of 2~10min.

7. The preparation method according to claim 1, characterized in that, The base membrane is selected from one of polyethersulfone membrane, cellulose acetate membrane, nylon membrane, and polytetrafluoroethylene membrane.

8. The preparation method according to claim 1, characterized in that, The pore size of the base membrane is 0.22~0.50μm.

9. A polyamide composite film, characterized in that, The polyamide composite film is prepared by the method for preparing polyamide composite film according to any one of claims 1 to 8.

10. A water purification method, characterized in that, Water purification is performed using the polyamide composite membrane according to claim 9 or the polyamide composite membrane prepared by the method of any one of claims 1 to 8.

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