Alkaline lignin-silver interlayer polyamide nanofiltration membrane, preparation method and application thereof

Abstract

The application discloses a kind of basic lignin-silver intermediate layer polyamide nanofiltration membrane and its preparation method and application.The preparation method includes the following steps: preparation obtains basic lignin-silver composite material;The ratio of silver salt and lye is 1.0-1.4g / L;The ratio of basic lignin and lye is 5-10g / L;Subsequently, the surface of base film is sequentially contacted with aqueous solution containing basic lignin-silver composite material and amine monomer, organic phase solution containing acyl chloride monomer, interfacial polymerization is carried out, and polyamide nanofiltration membrane is obtained.The basic lignin-silver intermediate layer is constructed by using basic lignin-silver composite material as additive, which not only reduces the flux decay rate of polyamide nanofiltration membrane, improves the flux recovery rate, but also has higher water flux, divalent salt / monovalent salt selectivity and good antibacterial effect.Polyamide nanofiltration membrane can be applied in sewage treatment equipment, seawater desalination equipment, industrial wastewater treatment and reuse equipment and other devices.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater and sewage treatment, and more specifically, relates to an alkaline lignin-silver interlayer polyamide nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Nanofiltration (NF) membranes have shown great potential in drinking water purification and wastewater treatment due to their excellent solute-water and solute-solute separation capabilities. Currently, the most widely used NF membrane is a thin-film composite polyamide (TFC PA) membrane prepared by interfacial polymerization (IP). This membrane consists of a dense PA selective layer for solute separation and a porous polymer support layer to ensure mechanical stability. However, the traditional IP process for preparing polyamide nanofiltration membranes faces two main challenges: the irregular pore structure on the porous base membrane leads to uneven monomer distribution in the aqueous solution, and the uncontrollable rapid reaction kinetics of monomers during IP. These problems result in a suboptimal PA layer structure, which causes a persistent "trade-off" effect between permeate flux and solute selectivity in polyamide nanofiltration membranes prepared by traditional processes: it is difficult to simultaneously improve both permeate flux and solute selectivity. Furthermore, biofouling caused by microbial metabolites in practical applications will significantly reduce membrane performance. Therefore, there is an urgent need to construct nanofiltration membranes with excellent permeability and selectivity, as well as excellent resistance to biofouling. This is the key to using nanofiltration membranes for low-carbon and efficient treatment of sewage and wastewater.

[0003] To achieve these dual objectives, current strategies for optimizing polyamide nanofiltration membranes primarily focus on altering the nanostructure of the PA layer or incorporating antibacterial materials during the IP process. However, most methods encounter difficulties in simultaneously improving both separation and antibacterial properties. For example, when incorporating contact antibacterial materials into the PA layer, it is necessary to embed non-antibacterial components within the PA layer while exposing the antibacterial components on the surface. However, monomers diffuse randomly during the one-step IP reaction, making precise control of molecular spatial arrangement a significant challenge. Furthermore, surface grafting after IP often leads to swelling or increased thickness of the PA layer, thereby reducing separation efficiency. Moreover, release-type bactericidal nanomaterials (such as zinc oxide, titanium dioxide, and silver nanoparticles) often aggregate during the IP process, causing structural defects in the PA layer and resulting in decreased selectivity of the final polyamide nanofiltration membrane.

[0004] Patent publication number CN116371221A discloses a polyamide nanofiltration membrane that uses alkaline lignin as an additive to promote the reaction between amine monomers in the aqueous phase and acyl chloride monomers in the oil phase. The polyamide nanofiltration membrane prepared has good water flux, divalent salt rejection rate and divalent salt / monovalent salt selectivity. However, in the actual application of the above-mentioned polyamide nanofiltration membrane, the flux decay is relatively serious and the flux recovery is poor, making it difficult to perform multiple cycles. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the primary objective of this invention is to provide a method for preparing an alkaline lignin-silver interlayer polyamide nanofiltration membrane. This method uses an alkaline lignin-silver composite material as an additive to construct a uniformly dispersed alkaline lignin-silver interlayer on the surface of the base membrane. By controlling the polymerization reactions of amine monomers and acyl chloride monomers during the interfacial polymerization process, this method not only reduces the flux decay rate of the polyamide nanofiltration membrane and improves the flux recovery rate, but also provides the polyamide nanofiltration membrane with higher water flux, divalent / monovalent salt selectivity, and good antibacterial effects.

[0006] A second objective of this invention is to provide an alkaline lignin-silver interlayer polyamide nanofiltration membrane prepared by the aforementioned preparation method.

[0007] A third objective of this invention is to provide the application of the alkaline lignin-silver interlayer polyamide nanofiltration membrane in wastewater and sewage treatment, seawater desalination, or water resource recycling.

[0008] A fourth objective of this invention is to provide an alkaline lignin-silver composite material as an aqueous phase additive for improving the water flux of polyamide nanofiltration membranes, or for improving the divalent / monovalent salt selectivity of polyamide nanofiltration membranes, or for reducing the flux decay rate and improving the flux recovery rate of polyamide nanofiltration membranes.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0010] This invention claims protection for a method for preparing an alkaline lignin-silver interlayer polyamide nanofiltration membrane, comprising the following steps:

[0011] S1. Alkaline solution, silver salt, and alkaline lignin are mixed evenly to prepare an alkaline lignin-silver composite material; the ratio of silver salt to alkaline solution is 1.0-1.4 g / L; the ratio of alkaline lignin to alkaline solution is 5-10 g / L.

[0012] S2. The base film surface is brought into contact with an aqueous solution containing alkaline lignin-silver composite material and amine monomers, left to stand, and the aqueous solution is removed;

[0013] S3. The surface of the base membrane after removing the aqueous solution in step S2 is brought into contact with an organic phase solution containing acyl chloride monomer to perform interfacial polymerization, and then dried to prepare a polyamide nanofiltration membrane.

[0014] This invention first mixes an alkaline solution, silver salt, and basic lignin. The phenolic hydroxyl and methoxy functional groups on the basic lignin molecule possess reducing properties, capable of reducing silver ions in the solution to silver nanoparticles, thus preparing an basic lignin-silver composite material. Through long-term research, the inventors discovered that during the preparation of polyamide nanofiltration membranes, the uniform adsorption of basic lignin on the base membrane surface induces a uniform distribution of silver nanoparticles on the membrane surface. Compared to polyamide nanofiltration membranes prepared using only basic lignin as an additive, the polyamide nanofiltration membrane prepared using the basic lignin-silver interlayer in this invention exhibits higher permeate flux, reducing the pressure required during operation and thus alleviating pollutant accumulation. Furthermore, the basic lignin-silver interlayer possesses antibacterial properties, mitigating bacterial adhesion to the membrane surface. The polyamide nanofiltration membrane regulated by the basic lignin-silver interlayer significantly reduces the flux decay rate and improves the flux recovery rate, resulting in better dynamic resistance to biofouling and greater advantages in treating practical wastewater containing bacteria.

[0015] Furthermore, the inventors discovered through research that pre-constructing a uniformly dispersed alkaline lignin-silver interlayer on the base membrane surface is beneficial for enriching more amine monomers on the base membrane surface. Since alkaline lignin can be uniformly adsorbed on the base membrane surface, it induces a uniform distribution of silver nanoparticles on the membrane surface. Benefiting from this, the dispersion and enrichment of amine monomers on the base membrane surface are more uniform, thus promoting the formation of thinner and denser polyamides, which helps to improve the water permeation flux and divalent / monovalent salt selectivity of the polyamide nanofiltration membrane.

[0016] Preferably, the silver salt is selected from silver nitrate; the alkaline solution is selected from ammonia. Ammonia provides OH-. - It dissolves Ag ions; on the other hand, its NH3 molecules act as ligands to form soluble [Ag(NH3)2] with Ag ions. + Complex ions.

[0017] Preferably, the concentration of ammonia is 1-30 wt%. More preferably, the concentration of ammonia is 2-10 wt%. More preferably, the concentration of ammonia is 3-5 wt%.

[0018] Preferably, the ratio of silver salt to alkali solution is 1.1-1.3 g / L; and / or the ratio of basic lignin to alkali solution is 6.5-8.5 g / L. Most preferably, the ratio of silver salt to alkali solution is 1.2 g / L; and / or the ratio of basic lignin to alkali solution is 7.5 g / L. Under these preferred conditions, the prepared polyamide nanofiltration membrane exhibits a lower flux decay rate, a higher flux recovery rate, higher water flux, divalent / monovalent salt selectivity, and good antibacterial effect.

[0019] Preferably, the amine monomer is selected from one or more of piperazine, m-phenylenediamine, ethylenediamine, polyethyleneamine, diethylenetriamine, and polyethyleneimine; and / or the concentration of the amine monomer in the aqueous solution is 3-10 g / L.

[0020] More preferably, the amine monomer is piperazine.

[0021] More preferably, the concentration of the amine monomer is 4-6 g / L. Most preferably, the concentration of the amine monomer is 5 g / L.

[0022] Preferably, the acyl chloride monomer is selected from one or more of 1,3,5-pyromellitic acid chloride, terephthaloyl chloride, and isophthaloyl chloride; and / or the concentration of the acyl chloride monomer in the organic phase solution is 0.1-5 g / L.

[0023] More preferably, the acyl chloride monomer is 1,3,5-pyromellitic acid chloride.

[0024] More preferably, the concentration of the acyl chloride monomer in the organic phase solution is 0.5-3 g / L. More preferably, the concentration of the acyl chloride monomer in the organic phase solution is 0.8-1.5 g / L. Most preferably, the concentration of the acyl chloride monomer in the organic phase solution is 1.0 g / L.

[0025] Preferably, the base film is polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, polyethylene, polyvinyl chloride, or polytetrafluoroethylene.

[0026] Preferably, in step S2, the settling time is 1-10 minutes; in step S3, the interface aggregation time is 0.5-3 minutes. Preferably, in step S2, the settling time is 2-5 minutes; in step S3, the interface aggregation time is 0.5-2 minutes.

[0027] Preferably, in step S3, the drying temperature is 40-80°C. More preferably, in step S3, the drying temperature is 60-80°C.

[0028] Preferably, the organic solvent used in the organic phase solution is selected from one or more of hexaane, heptane, octane, decanane, and cyclohexane.

[0029] Furthermore, the present invention seeks protection for the alkaline lignin-silver interlayer polyamide nanofiltration membrane prepared by the above preparation method.

[0030] Furthermore, the present invention seeks protection for the application of the above-mentioned alkaline lignin-silver interlayer polyamide nanofiltration membrane in wastewater and sewage treatment, or in seawater desalination, or in water resource recycling.

[0031] More specifically, this invention claims protection for the application of the above-described alkaline lignin-silver interlayer polyamide nanofiltration membrane in the separation of divalent salts / monovalent salts. More specifically, this invention claims protection for the application of the above-described alkaline lignin-silver interlayer polyamide nanofiltration membrane in the treatment of wastewater and sewage containing bacteria.

[0032] More specifically, the bacteria can be Gram-negative and / or Gram-positive. More specifically, the bacteria include, but are not limited to, Escherichia coli and Staphylococcus aureus.

[0033] Furthermore, this invention claims protection for the application of alkaline lignin-silver composite material as an aqueous phase additive in improving the water flux of polyamide nanofiltration membranes, or in improving the divalent / monovalent salt selectivity of polyamide nanofiltration membranes, or in reducing the flux decay rate and improving the flux recovery rate of polyamide nanofiltration membranes. The preparation method of alkaline lignin-silver composite material is as follows: alkaline solution, silver salt and alkaline lignin are mixed evenly to obtain alkaline lignin-silver composite material; the ratio of silver salt to alkaline solution is 1.0-1.4 g / L; the ratio of alkaline lignin to alkaline solution is 5-10 g / L.

[0034] More specifically, the divalent salt is Na₂SO₄, and the monovalent salt is NaCl.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention provides a method for preparing an alkaline lignin-silver interlayer polyamide nanofiltration membrane. The method uses an alkaline lignin-silver composite material as an additive to construct a uniformly dispersed alkaline lignin-silver interlayer on the surface of the base membrane. By controlling the polymerization reaction of amine monomers and acyl chloride monomers during the interfacial polymerization process, the method not only reduces the flux decay rate of the polyamide nanofiltration membrane and improves the flux recovery rate, but also provides the polyamide nanofiltration membrane with higher water flux, divalent / monovalent salt selectivity, and good antibacterial effect. Attached Figure Description

[0037] Figure 1 Scanning electron microscope images of the surface of the polyamide nanofiltration membranes prepared in Examples 1, 1-3, and 6. Detailed Implementation

[0038] The present invention will be further described below with reference to the specification and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0039] Example 1: Preparation of alkaline lignin-silver interlayer polyamide nanofiltration membrane

[0040] (1) 7.5g of alkaline lignin (alkaline lignin was purchased from Sigma-Aldrich, CAS: 8068-05-1, structural formula as shown in formula (I)) and 1.2g of AgNO3 were added to 1L of ammonia solution with a concentration of 4.5 wt% and stirred at 300 rpm for 60 min to obtain alkaline lignin-silver composite material;

[0041]

[0042] (I).

[0043] (2) Add 5.0 g piperazine to the above alkaline lignin-silver composite material and stir at 100 rpm for 10 min to obtain a piperazine-alkaline lignin-silver mixed aqueous solution.

[0044] (3) Pour piperazine-alkaline lignin-silver mixed solution into the surface of polysulfone-based film (US020, Zhongke Ruiyang) and let it stand for 3 minutes. After pouring out the solution, remove excess droplets from the surface of the base film with an air knife to obtain polysulfone-based film of piperazine-alkaline lignin-silver composite material intermediate layer.

[0045] (4) Add 1.0 g of 1,3,5-benzenetricarboxyl chloride to 1 L of n-hexane solution. After complete dissolution, an organic phase solution is obtained. Pour the solution onto the surface of the treated polysulfone-based membrane and let it stand for 0.5 min to carry out interfacial polymerization. After pouring off the solution on the membrane surface, wash the membrane surface with n-hexane solution to remove unreacted 1,3,5-benzenetricarboxyl chloride. Heat treat the membrane in a 60℃ oven for 10 min to obtain an alkaline lignin-silver interlayer polyamide nanofiltration membrane.

[0046] Example 2: Preparation of alkaline lignin-silver interlayer polyamide nanofiltration membrane

[0047] The difference between this embodiment and embodiment 1 is that in step (2), 6.0g of piperazine is added.

[0048] Example 3: Preparation of alkaline lignin-silver interlayer polyamide nanofiltration membrane

[0049] The difference between this embodiment and embodiment 1 is that in step (4), 1.25g of 1,3,5-benzenetricarboxylic acid chloride is added.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that in step (1), 0.4g AgNO3 is added.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that in step (1), 0.8g AgNO3 is added.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that in step (1), 1.6g of AgNO3 was added.

[0056] Comparative Example 4

[0057] The difference between this comparative example and Example 1 is that AgNO3 was not added in step (1).

[0058] Comparative Example 5

[0059] The difference between this comparative example and Example 1 is that no alkaline lignin was added in step (1).

[0060] Comparative Example 6

[0061] The difference between this comparative example and Example 1 is that step (1) is not performed; and in step (2), the alkaline lignin-silver composite material is not added.

[0062] Test Example 1

[0063] The surface morphology of the polyamide nanofiltration membranes prepared in Example 1, Comparative Examples 1-3, and Comparative Example 6 was observed using a field emission scanning electron microscope (FESEM, Quanta 400). The polyamide nanofiltration membranes were dried in a vacuum drying oven beforehand. Before observation, conductive adhesive was applied to the copper stage of the sample, and small square-cut membrane pieces were fixed onto the conductive adhesive. The sample surface was then sputter-coated with gold and observed under an accelerating voltage of 5 kV.

[0064] Figure 1 Scanning electron microscope (SEM) images of the surface of the polyamide nanofiltration membranes prepared in Examples 1, Comparative Examples 1-3, and Comparative Example 6. Figure 1 It can be seen that the polyamide selective layer of Comparative Example 6 exhibits a typical nodular morphology, which is formed by the reaction of piperazine and 1,3,5-benzenetricarboxylic acid chloride on the surface of the porous substrate membrane. Examples 1 and Comparative Examples 1-3 are polyamide nanofiltration membranes prepared by adding basic lignin-silver composite materials. It can be observed that when the added AgNO3 content varies, the polyamide selective layer on the surface of the polyamide nanofiltration membrane displays different degrees of wrinkled morphology. The appearance of these wrinkles is because basic lignin reduces the interfacial tension at the water-oil interface, causing more piperazine molecules to diffuse from the water to the oil phase to participate in the reaction, thereby increasing interfacial instability. Furthermore, as the AgNO3 content increases, the wrinkled morphology on the membrane surface gradually decreases, which may be because the increased content of silver nanoparticles promotes heat and mass transfer on the membrane surface, reducing interfacial instability.

[0065] Test Example 2

[0066] (1) Experiments on water permeation flux and salt rejection rate of polyamide nanofiltration membrane

[0067] The pure water permeate flux and salt rejection rate of the polyamide nanofiltration membranes prepared in the examples and comparative examples were tested, and the specific methods are as follows:

[0068] 1) Pure water flux measurement:

[0069] Filtration experiments were conducted using a cross-flow filtration device (CF016D; Stellitech, USA). The experimental parameters were: effective membrane area of ​​16 × 10⁻⁶. -4 m 2 The filtration experiment was conducted at a temperature of 25±2℃ and a test pressure of 5 bar.

[0070] At the start of the test, pure water was pre-pressurized at 5 bar for 60 minutes to reach a stable flux. The volume of pure water passing through the polyamide nanofiltration membrane was continuously measured over a certain period, and the permeation flux J of the polyamide nanofiltration membrane was calculated. W (Lm -2 h - 1 bar -1 The formula for its calculation is:

[0071] (1)

[0072] In the formula, V is the permeation volume, m 3 A is the effective area of ​​the membrane, in meters. 2 t is the sample filtration time, in seconds; ΔP is the operating pressure of the device, in bars.

[0073] 2) Determination of salt rejection rate and selectivity:

[0074] A cross-flow filtration device was used to conduct filtration experiments. The rejection rate R of the polyamide nanofiltration membrane prepared in the examples and comparative examples for Na2SO4 or NaCl was obtained according to formula (2), and the selective permeability of the polyamide nanofiltration membrane to salt was characterized by this.

[0075] Prepare 1000 mg L of each -1 Using Na2SO4 or NaCl solution as the feed solution, when testing with different feed solutions, the feed solution is pre-pressurized at 5 bar for 30 min to achieve a stable flux. The concentrate and permeate are collected, and their conductivity is tested. The salt rejection rate R (%) is calculated using equation (2). 2- / Cl - The selectivity coefficient α is calculated by formula (3):

[0076] (2)

[0077] (3)

[0078] Among them, CP and C F The values ​​represent the conductivity of the permeate and concentrate, respectively, in μS / cm.

[0079] (2) Antibacterial test of polyamide nanofiltration membrane

[0080] All materials were sterilized under ultraviolet light for 30 minutes before use. Representative Gram-negative bacteria *Escherichia coli* and Gram-positive bacteria *Staphylococcus aureus* (approximately 10...) were selected. 8 CFU L -1 The polyamide nanofiltration membranes prepared in the examples and comparative examples were each cut to 1.5 × 1.5 cm. 2 The cultures were placed in centrifuge tubes containing 2 mL of bacterial suspension. These cultures were then incubated at 30°C for 12 hours. Subsequently, the bacterial suspension was diluted with phosphate-buffered saline solution at a ratio of 1:10. 5 Dilute 100 μL of the diluted sample evenly onto an LB agar plate. Incubate at 30°C for 24 h and count the colonies. Determine the antibacterial effect of the modified membrane using formula (4). R A :

[0081] (4)

[0082] Wherein, N0 and N represent the colony counts on the polyamide nanofiltration membranes of the examples and comparative examples, respectively.

[0083] (3) Dynamic resistance to biofouling performance test

[0084] The dynamic resistance to biofouling in Examples 1, 4, and 5 was evaluated using a cross-flow filtration system. The initial water flux was 40 L / m³. 2 Under the condition of ·h, using a concentration of 2×10 8 A synthetic wastewater solution containing CFU / L Escherichia coli, inorganic salts (8 mmol / L sodium chloride, 0.15 mmol / L magnesium sulfate, 0.5 mmol / L sodium bicarbonate, 0.4 mmol / L ammonium chloride, 0.2 mmol / L calcium chloride, and 0.2 mmol / L dipotassium hydrogen phosphate) and 0.6 mmol / L glucose was used to test the permeate flux changes over three consecutive filtration cycles. Each cycle included the following consecutive steps: (1) Pre-pressing the membrane with deionized water for 30 minutes to achieve hydraulic stabilization, followed by recording the initial water flux (J0, L / m). 2 (2) Filter synthetic wastewater for 300 minutes to examine the degree of flux decay; (3) Rinse the membrane with deionized water for 30 minutes, and then perform a second pressurized water flux measurement to determine the recovered water flux, denoted as J. w (L / m) 2·h·bar). Calculate the flux recovery rate (FRR) according to formula (5).

[0085] (5)

[0086] Wherein, FRR (%) represents the antifouling performance of the polyamide nanofiltration membrane. J W This indicates the amount of water flux restored in each cycle. J O1 This indicates the initial water flux of the membrane during the first cycle (L / m). 2 ·h·bar).

[0087] To assess the membrane's dynamic resistance to biofouling during operation, the flux decay rate D (%) of the membrane in each cycle was calculated according to formula (6):

[0088] (6)

[0089] in, J f1 and J f2 These represent the initial flux and the final flux in each cycle, respectively.

[0090] (4) Test results

[0091] The pure water permeation flux, Na2SO4 / NaCl rejection rate, and SO4 content of the polyamide nanofiltration membranes prepared in the examples and comparative examples are as follows: 2- / Cl - The selective test results are shown in Table 1 (where the antibacterial effect of polyamide nanofiltration membranes without antibacterial properties is indicated by / ).

[0092] Table 1

[0093]

[0094] As shown in Table 1, the polyamide nanofiltration membrane prepared by this invention has excellent water flux and SO42--- 2- / NaCl - Selectivity and good antibacterial properties.

[0095] The dynamic antifouling capabilities of the polyamide nanofiltration membranes prepared in Examples 1, 4, and 5 are shown in Table 2.

[0096] Table 2

[0097]

[0098] As shown in Table 2, the dynamic anti-biofouling test results indicate that the polyamide nanofiltration membranes with only silver or only alkaline lignin exhibit higher flux decay rates and lower flux recovery rates during operation compared to the polyamide nanofiltration membrane prepared in this invention. More specifically, after three filtration cycles, the flux decay rate of the polyamide nanofiltration membrane prepared in this invention is reduced by 59.3% and 70.63% compared to Comparative Examples 4 and 5, respectively; the flux recovery rate is increased by 7.82% and 8.07% compared to Comparative Examples 4 and 5, respectively. Therefore, the polyamide nanofiltration membrane prepared in this invention has greater potential for anti-biofouling in the fields of providing high-quality drinking water and wastewater treatment.

[0099] The foregoing examples are merely illustrative, used to explain some features of the method described in this invention. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are demonstrated by the applicant's actual experimental results. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of the invention. Some numerical ranges used in the claims also include sub-ranges within them, and variations within these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. The application of an alkaline lignin-silver interlayer polyamide nanofiltration membrane in wastewater treatment, seawater desalination, or water resource recovery, characterized in that, The alkaline lignin-silver interlayer polyamide nanofiltration membrane is prepared by a method comprising the following steps: S1. Alkaline solution, silver salt, and basic lignin are mixed evenly to prepare an basic lignin-silver composite material; the ratio of silver salt to alkaline solution is 1.1-1.3 g / L; the ratio of basic lignin to alkaline solution is 6.5-8.5 g / L. S2. Add amine monomer to the above-mentioned basic lignin-silver composite material to obtain an aqueous solution containing basic lignin-silver composite material and amine monomer; the surface of the base film is in contact with the aqueous solution containing basic lignin-silver composite material and amine monomer, allowed to stand, and the aqueous solution is removed. S3. The surface of the base membrane after removing the aqueous solution in step S2 is contacted with an organic phase solution containing acyl chloride monomer to perform interfacial polymerization, and then dried to prepare a polyamide nanofiltration membrane; The base film is polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, polyethylene, polyvinyl chloride, or polytetrafluoroethylene; The silver salt is selected from silver nitrate; the alkaline solution is selected from ammonia water; the concentration of ammonia water is 1-30 wt%; The amine monomer is selected from piperazine; in the aqueous solution, the concentration of the amine monomer is 4-6 g / L; The acyl chloride monomer is selected from 1,3,5-pyromellitic tricarboxylate chloride; the concentration of the acyl chloride monomer in the organic phase solution is 0.8-1.5 g / L; The structural formula of alkaline lignin is shown in formula (I) below: （I）。 2. The application according to claim 1, characterized in that, In step S2, the settling time is 1-10 minutes; in step S3, the interface aggregation time is 0.5-3 minutes.

3. The application according to claim 1, characterized in that, The alkaline lignin-silver interlayer polyamide nanofiltration membrane is used for the separation of divalent and monovalent salts; the divalent salt is Na2SO4, and the monovalent salt is NaCl.

4. The application according to claim 1, characterized in that, In step S3, the drying temperature is 40-80℃.

5. The application according to claim 1, characterized in that, The organic solvent used in the organic phase solution is selected from one or more of hexane, heptane, octane, decane, and cyclohexane.

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