A nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate, and a preparation method and application thereof

Abstract

The present invention proposes a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate, and a preparation method and application thereof, belonging to the technical field of membrane preparation. The nanofiltration membrane is sequentially provided with a hydrophobic PVDF substrate, a lysozyme protective layer and a polyamide layer from bottom to top; the preparation method thereof comprises the following steps: depositing a lysozyme layer growth liquid on a hydrophobic PVDF substrate to form a lysozyme protective layer; and forming a polyamide layer on the lysozyme protective layer with an aqueous phase monomer solution and an oil phase monomer solution by interfacial polymerization reaction. The nanofiltration membrane prepared by the present invention has good selective permeability and can be simultaneously applied to the separation of monovalent and divalent salts and the separation of organic solvents.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane preparation, and in particular relates to a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate, and a preparation method and application thereof. Background Art

[0002] Nanofiltration is a typical pressure-driven membrane separation technology that can remove divalent ions and organic compounds with a molecular weight of 200-1000Da from water. Currently, thin film composite nanofiltration membranes (TFC) based on polyamide (PA) chemistry are most widely used in the production of softened water and drinking water. Interfacial polymerization is the most widely studied and applied method for preparing TFC nanofiltration membranes in academia and industry. During the interfacial polymerization process, the porous substrate is first impregnated with an aqueous monomer solution containing amine monomers, and then further contacted with an incompatible organic phase containing acyl chloride groups for a certain period of time to form an ultrathin cross-linked PA selective layer. Factors such as monomer concentration and substrate properties have a great influence on the interfacial polymerization reaction process, so people have conducted extensive research on the prepared TFC PA nanofiltration membranes to optimize the nanofiltration membrane structure and separation performance.

[0003] Polyvinylidene fluoride (PVDF) membrane is a polymer material widely used in the preparation of microfiltration and ultrafiltration membranes due to its excellent mechanical strength, chemical resistance and thermal stability in harsh environments. However, it is rarely used as a porous substrate for TFC PA nanofiltration membranes. This is because its hydrophobic surface cannot be well wetted in the aqueous phase due to the capillary effect, and it is difficult to form a continuous ultra-thin PA layer, which affects the permeability and retention performance of the nanofiltration membrane. Therefore, the modification and regulation of the hydrophobic PVDF substrate, and then the control and optimization of the interfacial polymerization process, are helpful to improve the interfacial polymerization process and nanofiltration membrane preparation technology.

[0004] In summary, how to prepare a highly selectively permeable hydrophobic PVDF-based nanofiltration membrane is a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate, and a preparation method and application thereof.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate. The nanofiltration membrane is provided with a hydrophobic PVDF substrate, a lysozyme protective layer and a polyamide layer in sequence from bottom to top.

[0009] Preferably, the thickness of the polyamide layer is 55±5 nm, the roughness is 407±25 nm, and the cross-linking degree is 76.9%.

[0010] The second technical solution of the present invention:

[0011] The method for preparing the above-mentioned nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate comprises the following steps:

[0012] depositing the lysozyme layer growth liquid on a hydrophobic PVDF substrate to form a lysozyme protective layer;

[0013] The aqueous monomer solution and the oily monomer solution are used to form a polyamide layer on the lysozyme protective layer by interfacial polymerization.

[0014] Preferably, the lysozyme layer growth solution is prepared by dissolving lysozyme and tris(2-carboxyethyl)phosphine hydrochloride (TCEP) in Tris-HCl buffer;

[0015] The mass volume ratio of the lysozyme, tris(2-carboxyethyl)phosphine hydrochloride and Tris-HCl buffer is: 0.04 g: 0.143 g: 20 mL.

[0016] Furthermore, the preparation process of the lysozyme layer growth liquid is as follows: firstly dissolve the lysozyme in Tris-HCl buffer, the mass volume ratio of the lysozyme to the Tris-HCl buffer is 4 mg: 10 mL, to obtain a 4 mg / mL lysozyme solution, and then mix the lysozyme solution and the Tris-HCl buffer containing TCEP in equal volumes, to a final concentration of 2 mg / mL.

[0017] Preferably, the pH of the lysozyme layer growth liquid is 6.5-8.5; preferably 6.5, 7.5 and 8.5; more preferably 7.5.

[0018] Preferably, the deposition time in the deposition process is 5-20 min; preferably 5, 10 and 20 min; more preferably 5 min.

[0019] Preferably, the mass concentration of the aqueous monomer solution is 0.1-2%; preferably 0.5%, 1.0%, 1.5% and 2.0%; more preferably 1.0%;

[0020] The mass concentration of the oil phase monomer solution is 0.02-0.2%; preferably 0.05%, 0.10% and 0.15%; more preferably 0.10%.

[0021] Preferably, the monomer in the aqueous monomer solution is a polyamine, including any one of piperazine, m-phenylenediamine or polyethyleneimine;

[0022] The monomer in the oil phase monomer solution is a polyacid chloride, including any one of trimesoyl chloride, isophthaloyl chloride, cyclohexanetrichloride, cyclopentanetrichloride, propanoyl chloride or glutaryl chloride.

[0023] Preferably, the method comprises the following steps:

[0024] Dissolve lysozyme and tris(2-carboxyethyl)phosphine hydrochloride (TCEP) in Tris-HCl buffer respectively, stir and ultrasonicate to obtain lysozyme solution and TCEP solution, and then mix equal volumes to obtain lysozyme layer growth solution;

[0025] The hydrophobic PVDF substrate is floated on the lysozyme layer growth liquid for deposition (the lysozyme layer is deposited only on one side of the hydrophobic PVDF substrate), taken out and immersed in anhydrous ethanol, and then washed with water to obtain a PVDF substrate containing lysozyme;

[0026] The aqueous monomer solution is evenly spread on the PVDF substrate containing lysozyme, allowed to stand, excess aqueous monomer solution is removed, and then the oily monomer solution is evenly spread on the PVDF substrate containing lysozyme to react and dry, thereby obtaining a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate.

[0027] The reaction principle and beneficial effects involved in the above technical solution are:

[0028] The present invention first dissolves lysozyme and TCEP in Tris-HCl buffer respectively and mixes them to obtain a lysozyme layer growth liquid, floats a hydrophobic PVDF substrate on the lysozyme layer growth liquid, and obtains a lysozyme-containing PVDF substrate after wetting with ethanol and rinsing with deionized water. Lysozyme forms a continuous and uniform intermediate layer on the hydrophobic PVDF substrate through hydrophobic-hydrophobic interaction, improves the hydrophilicity of the PVDF substrate, and compared with the original PVDF substrate (water contact angle of 130°), the water contact angle of the loaded lysozyme layer is reduced to 45°, thereby increasing the storage of polyamine molecules, and the lysozyme protective layer can play a role in reducing surface tension. The nanofiltration membrane of the present invention uses lysozyme as an intermediate layer, increases the storage capacity of amine monomers and accelerates interfacial polymerization reaction (IP reaction), thereby obtaining a polyamide layer with a lotus leaf-like structure; reduces the thickness of the polyamide layer to 55±5nm, and increases the cross-linking degree of the polyamide layer to 76.9%, thereby improving the selective permeability of the nanofiltration membrane; and simultaneously, due to the solvent resistance of the PVDF substrate, the nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate prepared by the present invention can be applied to organic solvent separation.

[0029] In the present invention, the deposition time of the lysozyme layer, the pH value of the lysozyme layer growth liquid and the monomer concentration are the key to the high permselective nanofiltration membrane. The longer the deposition time, the thicker the lysozyme layer formed. Although there are enough polyamine molecules, such as piperazine molecules, to participate in the interfacial polymerization, the salt rejection rate of the nanofiltration membrane tends to be stable and the water permeability is greatly reduced; the pH value of the lysozyme layer growth liquid will affect the pore size of the lysozyme protective layer surface, and the moderate pore size will promote the completion of the interfacial polymerization, and obtain a polyamide layer with fewer defects and higher water permeability; the concentration of the aqueous phase monomer and the oil phase monomer will affect the interfacial polymerization reaction. For example, in the embodiment of the present invention, the greater the concentration of PIP (piperazine) and TMC (trimethylenediamine chloride), the more monomer molecules will participate in the interfacial polymerization, and a denser and uniformly thick polyamide layer will be obtained, and the water permeability will be greatly reduced. The present invention regulates the deposition time of lysozyme, the pH value of the lysozyme layer growth liquid and the concentration of the monomer, while ensuring that there are enough monomers to participate in and complete the IP reaction, a more complete and thinner polyamide layer is obtained, so that the nanofiltration membrane has excellent permselective properties.

[0030] Therefore, the present invention obtains a nanofiltration membrane with excellent permselectivity, and has high water permeability and salt rejection rate under relatively low pressure, and can be applied to organic solvent separation.

[0031] The third technical solution of the present invention:

[0032] The use of the above-mentioned nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate in the separation of monovalent and / or divalent salts.

[0033] The fourth technical solution of the present invention:

[0034] As mentioned above, the nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate is used in the separation of organic solvents.

[0035] Compared with the prior art, the present invention has the following advantages and technical effects:

[0036] In the present invention, lysozyme is used to form a continuous and uniform intermediate layer on a hydrophobic PVDF substrate through hydrophobic-hydrophobic interaction, and then interfacial polymerization is performed to obtain a novel nanofiltration membrane. Compared with interfacial polymerization directly performed on a PVDF substrate, the lysozyme intermediate layer increases the storage of amine monomers and promotes a complete IP reaction, and the obtained nanofiltration membrane has a more complete and rougher polyamide layer, which improves the water permeability of the nanofiltration membrane while maintaining a high salt rejection rate.

[0037] The PVDF substrate in the present invention has resistance to organic solvents, so that the nanofiltration membrane can be used for organic solvent separation.

[0038] Moreover, compared with the existing patent CN115400604A in which the lysozyme layer is coated on the outermost layer and the functional group is used to improve the surface charge of the membrane, the present invention arranges the lysozyme in the middle layer and uses the middle layer lysozyme to improve the hydrophilicity of the substrate and increase the storage of amine monomers, which has a different effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0040] Figure 1 The water permeability and salt rejection rate of the nanofiltration membrane prepared by lysozyme under different deposition time conditions in Example 1, wherein the bar graph is the water permeability graph, and the line graph is the salt rejection rate graph;

[0041] Figure 2 The water permeability and salt rejection of the nanofiltration membrane prepared by lysozyme at different pH in Example 2, wherein the bar graph is the water permeability graph, and the line graph is the salt rejection graph;

[0042] Figure 3 The water permeability and salt rejection of the nanofiltration membrane prepared at different PIP concentrations in Example 3, wherein the bar graph is the water permeability graph, and the line graph is the salt rejection graph;

[0043] Figure 4 The water permeability and salt rejection of the nanofiltration membrane prepared at different TMC concentrations in Example 4, wherein the bar graph is the water permeability graph, and the line graph is the salt rejection graph;

[0044] Figure 5 The water permeability and salt rejection of the nanofiltration membrane prepared without depositing the lysozyme layer for four different inorganic salts in Comparative Example 1;

[0045] Figure 6 The water permeability and salt rejection rate of the nanofiltration membrane prepared under the optimal conditions of Example 1 for four different inorganic salts;

[0046] Figure 7 The permeability of the nanofiltration membrane prepared under the optimal conditions of Example 1 to different organic solvents;

[0047] Figure 8 This is the surface morphology of the nanofiltration membrane prepared under the optimal conditions of Example 1;

[0048] Fig. 9 This is the surface roughness diagram of the nanofiltration membrane prepared under the optimal conditions of Example 1;

[0049] Fig.10 This is a cross-sectional thickness diagram of the nanofiltration membrane prepared under the optimal conditions of Example 1. DETAILED DESCRIPTION

[0050] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0051] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0052] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0053] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0054] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0055] The present invention provides a method for preparing a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate, comprising the following steps:

[0056] Dissolve lysozyme and TCEP in Tris-HCl buffer respectively, mix the lysozyme solution and TCEP solution in a volume ratio of 1:1 to obtain a lysozyme layer growth solution, adjust the pH of the solution and let it stand at room temperature; wherein the pH of the solution is adjusted using 1M hydrochloric acid solution and 1M sodium hydroxide solution;

[0057] The hydrophobic PVDF substrate is floated on the lysozyme layer growth liquid, taken out and immersed in anhydrous ethanol, and then rinsed with deionized water for multiple times to obtain the lysozyme-containing PVDF substrate;

[0058] The aqueous monomer solution is evenly spread on the lysozyme-containing PVDF substrate, allowed to stand, excess aqueous monomer solution is removed, and then the oily monomer solution is evenly spread on the lysozyme-containing PVDF substrate for reaction and drying to obtain the lysozyme intermediate layer nanofiltration membrane.

[0059] Further, the method for modifying the hydrophobic PVDF substrate nanofiltration membrane containing the lysozyme intermediate layer comprises the following steps:

[0060] (1) Dissolving lysozyme and TCEP in Tris-HCl buffer respectively, stirring and ultrasonicating to obtain lysozyme solution and TCEP solution, mixing the lysozyme solution and TCEP solution in a volume ratio of 1:1 to obtain a lysozyme layer growth solution, adjusting the pH of the solution and standing at room temperature for 1 hour;

[0061] (2) floating a hydrophobic PVDF substrate on a lysozyme layer growth solution for deposition, taking it out and soaking it in anhydrous ethanol for 1 min, and then rinsing it with deionized water for multiple times to obtain a lysozyme-containing PVDF substrate;

[0062] (3) pouring the aqueous monomer solution onto the lysozyme-containing PVDF substrate, allowing it to stand, removing excess aqueous monomer solution, then pouring the oily monomer solution into it for reaction, and drying to obtain the lysozyme intermediate layer nanofiltration membrane.

[0063] In some preferred embodiments, the pH value of the Tris-HCl buffer in step (1) is 7.5.

[0064] In some preferred embodiments, the ratio of lysozyme to Tris-HCl buffer in step (1) is 0.04 g:10 mL.

[0065] In some preferred embodiments, the ratio of TCEP to Tris-HCl buffer in step (1) is 0.143 g:10 mL.

[0066] In some preferred embodiments, in step (1), the ultrasonic power is 400 W and the ultrasonic time is 5 min;

[0067] In some preferred embodiments, the magnetic stirring speed in step (1) is 400 rpm and the stirring time is 5 min.

[0068] In some preferred embodiments, the pH of the lysozyme layer growth solution in step (1) is 6.5-8.5.

[0069] In some preferred embodiments, the deposition time in step (2) is 5-20 min;

[0070] In some preferred embodiments, the purity of anhydrous ethanol in step (2) is 99.5%.

[0071] In some preferred embodiments, the aqueous monomer solution in step (3) is prepared by dissolving a polyamine in deionized water;

[0072] The polyamine is one of piperazine, m-phenylenediamine or polyethyleneimine; and the mass concentration of the polyamine in the aqueous monomer solution is 0.1-2%.

[0073] In some preferred embodiments, the oil phase monomer solution in step (3) is prepared by dissolving polyacid chloride in an organic solvent;

[0074] Wherein, the polyacyl chloride is one of trimesoyl chloride, isophthaloyl chloride, cyclohexanetrichloride, cyclopentanetrichloride, propanetrichloride or glutarylchloride; the mass concentration of the polyacyl chloride is 0.02-0.2%;

[0075] The organic solvent is one of n-hexane, n-heptane, dodecane or tetradecane.

[0076] In some preferred embodiments, the standing time in step (3) is 1-5 min;

[0077] The reaction time was 60 s, and the excess oil phase monomer solution was removed after the reaction was completed;

[0078] The drying temperature is 60°C and the drying time is 5-10 minutes.

[0079] In some preferred embodiments, before evenly spreading the aqueous monomer solution on the lysozyme-containing PVDF substrate membrane in step (3), the lysozyme-containing PVDF circular membrane needs to be fixed on a fixture.

[0080] The present invention also provides a nanofiltration membrane prepared by a method for preparing a nanofiltration membrane by modifying a hydrophobic PVDF substrate with a lysozyme intermediate layer.

[0081] All raw materials used in the examples of the present invention are purchased from the market. Lysozyme and TCEP described in the examples of the present invention were purchased from Aladdin Biochemical Technology Co., Ltd. with a purity of 95-99%; the hydrophobic PVDF substrate was purchased from Zhejiang Haining Delv New Material Technology Co., Ltd.

[0082] The technical solution of the present invention is further illustrated by the following embodiments.

[0083] Example 1

[0084] This example studies the effect of different deposition times of lysozyme on the salt rejection rate and water permeability of a nanofiltration membrane. The method for preparing a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate comprises the following steps:

[0085] (1) 0.429 g TCEP and 0.12 g lysozyme were dissolved in 30 mL Tris-HCl solution at pH = 7.5, respectively, and each was treated with ultrasound (ultrasound power of 400 W) and stirring (magnetic stirring speed of 400 rpm) at room temperature for 5 min, mixed in a volume ratio of 1:1 and the pH value was adjusted to 7.5 to obtain a lysozyme layer growth solution, which was allowed to stand at room temperature for 1 h;

[0086] (2) floating a hydrophobic PVDF substrate on a lysozyme layer growth solution, depositing lysozyme for 5 / 10 / 20 minutes respectively, taking it out and soaking it in anhydrous ethanol for 1 minute, and then rinsing it with deionized water for multiple times to obtain a lysozyme-containing PVDF substrate;

[0087] (3) dissolving piperazine in deionized water and mixing by ultrasonication to obtain an aqueous monomer solution, wherein the mass concentration of piperazine in the aqueous phase is 1%;

[0088] (4) dissolving trimesoyl chloride (TMC) in n-hexane and mixing by ultrasonication to obtain an oil phase monomer solution, wherein the mass concentration of trimesoyl chloride in the oil phase monomer solution is 0.1%;

[0089] (5) Fixing the lysozyme-containing PVDF substrate prepared in step (2) on a fixture, and then evenly spreading the aqueous monomer solution prepared in step (3) on the surface thereof, removing the excess aqueous monomer solution after standing for 2 minutes, and drying it, and then evenly spreading the oily monomer solution prepared in step (4) on the surface thereof, reacting for 60 seconds, removing the excess oily monomer solution, and drying it at 60° C. for 10 minutes to obtain a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate.

[0090] Example 2

[0091] This example studies the effect of the pH value of the lysozyme layer growth liquid on the salt rejection rate and water permeability of the nanofiltration membrane. The method for preparing the nanofiltration membrane differs from that in Example 1 in that the lysozyme deposition time is fixed at 5 min, and the pH values ​​of the lysozyme layer growth liquid are 6.5, 7.5, and 8.5, respectively.

[0092] The remaining steps are the same as in Example 1.

[0093] Example 3

[0094] This example studies the effect of PIP concentration on the salt rejection rate and water permeability of the nanofiltration membrane. The method for preparing the nanofiltration membrane is different from that in Example 1 in that the lysozyme deposition time is fixed at 5 min, the pH value of the lysozyme layer growth solution is 7.5, and the mass concentrations of PIP are 0.5%, 1.0%, 1.5% and 2.0%, respectively.

[0095] The remaining steps are the same as in Example 1.

[0096] Example 4

[0097] This example studies the effect of TMC concentration on the salt rejection rate and water permeability of the nanofiltration membrane. The method for preparing the nanofiltration membrane is different from that in Example 1 in that the lysozyme deposition time is fixed at 5 min, the pH value of the lysozyme layer growth solution is 7.5, the mass concentration of PIP is 1.0%, and the concentrations of TMC are 0.05%, 0.10% and 0.15%, respectively.

[0098] The remaining steps are the same as in Example 1.

[0099] The three nanofiltration membranes prepared above were placed in a nanofiltration device to test their separation performance, and the specific process was the same as in Example 1.

[0100] Comparative Example 1

[0101] Compared with the method for preparing a hydrophobic PVDF-based nanofiltration membrane containing a lysozyme intermediate layer modified under the optimal conditions in Example 1, the present comparative example does not carry out the lysozyme deposition process, and the other processes are the same as the preparation process under the optimal conditions in Example 1.

[0102] in, Figure 1 The nanofiltration membrane with a deposition time of 0 is the nanofiltration membrane prepared in this comparison.

[0103] Effect verification

[0104] Effect 1: Verify the separation effect of the nanofiltration membrane prepared in Examples 1-3 on sodium sulfate solution

[0105] The specific testing process is as follows:

[0106] The test was conducted using a nanofiltration test device, which is an independent pressure permeation device. The effective test area of ​​the membrane module is 15.9 cm 2 Four different inorganic salt solutions (sodium sulfate, magnesium sulfate, magnesium chloride, sodium chloride) with a test stock solution of 2000ppm were used for separate tests, and the flow rate was controlled at 44.4cm / s and the pressure was 4bar by cross-flow. The nanofiltration membranes prepared in Examples 1-3 were fixed on the membrane assembly respectively, and the instrument was operated for 30min. After the operation was stable, the time was recorded and samples were taken, and the quality and conductivity of the permeate obtained were measured, and then the water permeability and salt rejection rate of the nanofiltration membrane were obtained.

[0107] Figure 1The water permeability and salt cutoff of the nanofiltration membrane prepared by lysozyme under different deposition time conditions in Example 1 can be found that as the deposition time increases, the water permeability of the prepared nanofiltration membrane gradually decreases, and the salt cutoff gradually increases and tends to be stable. This is mainly because the lysozyme intermediate layer not only affects the formation of polyamide, but also affects the mass transfer resistance of water molecules, thereby causing changes in water permeability and salt cutoff. Therefore, selecting a suitable lysozyme deposition time can effectively improve the separation performance of the nanofiltration membrane without destroying the integrity of the polyamide layer. Therefore, the nanofiltration membrane obtained when the deposition time of lysozyme is 5min has the best effect, which improves the water permeability of the nanofiltration membrane while maintaining a high salt cutoff.

[0108] Figure 2 The water permeability and salt rejection of the nanofiltration membrane prepared by lysozyme at different pH in Example 2 show that the water permeability of the nanofiltration membrane is U-shaped, while the salt rejection is the opposite. This is mainly because the pore size of the lysozyme layer is too small at low pH values, resulting in insufficient PIP storage and the inability to produce a dense and complete PA layer; while at high pH values, the pore size of the lysozyme layer is too large, the PIP storage is sufficient, and the oil phase monomers involved in the reaction are fixed, resulting in insufficient interfacial polymerization reaction and the formation of a defective PA layer, thereby reducing the salt rejection of the nanofiltration membrane. Therefore, selecting a lysozyme layer growth solution with a suitable pH value is the key to a membrane with both high salt rejection and high-flux nanofiltration.

[0109] Figure 3 The water permeability and salt rejection rate of the nanofiltration membrane prepared at different PIP concentrations in Example 3 show that, as the mass concentration of PIP increases, the water permeability of the prepared nanofiltration membrane gradually decreases, while the salt rejection rate gradually increases and tends to be stable. This is mainly because the mass concentration of PIP affects the formation of the polyamide layer, which leads to changes in water permeability and salt rejection. Therefore, selecting a suitable PIP mass concentration can effectively improve the separation performance of the nanofiltration membrane without destroying the integrity of the polyamide layer. Therefore, when the mass concentration of PIP is 1.0%, the nanofiltration membrane obtained has the best effect, which improves the water permeability of the nanofiltration membrane while maintaining a high salt rejection rate.

[0110] Figure 4 The water permeability and salt rejection rate of the nanofiltration membrane prepared at different TMC concentrations in Example 4 show that, as the mass concentration of TMC increases, the water permeability of the prepared nanofiltration membrane gradually decreases, while the salt rejection rate gradually increases and tends to be stable. This is mainly because the mass concentration of TMC affects the formation of the polyamide layer, which leads to changes in water permeability and salt rejection. Therefore, selecting a suitable TMC mass concentration can effectively improve the separation performance of the nanofiltration membrane without destroying the integrity of the polyamide layer. Therefore, the nanofiltration membrane obtained when the mass concentration of TMC is 0.1% has the best effect, which improves the water permeability of the nanofiltration membrane while maintaining a high salt rejection rate.

[0111] Figure 5 The water permeability and salt rejection of the nanofiltration membrane without lysozyme layer in Comparative Example 1 for four different inorganic salts show that the rejection rate of the nanofiltration membrane for four different inorganic salts is low. This is mainly because the hydrophobic PVDF stores less PIP, resulting in incomplete interfacial polymerization and the formation of a defective polyamide layer.

[0112] Figure 6 The water permeability and salt rejection rate of the lysozyme intermediate layer nanofiltration membrane prepared under the optimal experimental conditions in Example 1 for four different inorganic salts can be found that the nanofiltration membrane has a higher salt rejection rate for divalent ions and a lower rejection rate for monovalent ions, while maintaining a higher water permeability. This is because the lysozyme layer promotes the storage of amine monomers, obtains a more cross-linked and denser polyamide layer, and increases the rejection rate for divalent ions.

[0113] In summary, it can be seen that the nanofiltration membrane prepared when the lysozyme deposition time is 5 minutes, the pH value of the lysozyme layer growth solution is 7.5, the PIP concentration is 1%, and the TMC concentration is 0.1% has the best effect. While maintaining a high salt rejection rate, it also improves the water permeability of the nanofiltration membrane. The water permeability of the nanofiltration membrane prepared under the optimal conditions is 12.1Lm -2 H -1 bar -1 , the salt rejection rate is 99.5%.

[0114] Effect 2: Verification of the permeability of the nanofiltration membranes prepared in Examples 1-3 to organic solvents

[0115] The nanofiltration membrane prepared under the optimal conditions in Example 1 (lysozyme deposition time was fixed at 5 min, pH value of lysozyme layer growth solution was 7.5, mass concentration of PIP was 1.0%, mass concentration of TMC was 0.1%) was selected to test the organic solvent permeability.

[0116] The test was conducted using a solvent resistance nanofiltration test device, which is an independent pressure permeation device. The effective test area of ​​the membrane module is 9.6 cm 2 The test stock solution is eight kinds of organic solvents (including Figure 7 DMF is N, N-dimethylformamide; THF is tetrahydrofuran; acetone is acetone; toluene is 2,5-dimethoxytoluene; hexane is hexane; ethanol is ethanol; methanol is methanol; acetonitrile is acetonitrile) were tested separately, using a cross-flow method, controlling the flow rate to 44.4 cm / s and the pressure to 4 bar.

[0117] The remaining steps are the same as the test steps in effect 1.

[0118] Figure 7 The permeability of the nanofiltration membrane prepared in Example 1 to different organic solvents, the permeability and the physical parameters of the solvent (δη -1 d -2 ) is linearly fitted, R 2 =0.955, δ represents the solvent dipole force, η represents the viscosity, and d represents the molecular diameter. The solvent has low viscosity, small diameter, strong affinity to the membrane, and will have a higher permeability value. Figure 5 It can be seen that acetonitrile has the highest polar solubility parameter, relatively low viscosity, small molecular diameter, and nanofiltration permeability can reach 28LMH / bar. Toluene has the lowest solvent physical parameter value, and the nanofiltration membrane permeability is 3.16LMH / bar. Due to the organic solvent resistance of PVDF, it can be used in the field of organic solvent separation.

[0119] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate, characterized in that: The nanofiltration membrane is provided with a hydrophobic PVDF substrate, a lysozyme protection layer and a polyamide layer in sequence from bottom to top; The preparation method comprises the following steps: depositing the lysozyme layer growth liquid on a hydrophobic PVDF substrate to form a lysozyme protective layer; Using an interfacial polymerization reaction, the aqueous monomer solution and the oily monomer solution form a polyamide layer on the lysozyme protective layer; The lysozyme layer growth solution is prepared by dissolving lysozyme and tris(2-carboxyethyl)phosphine hydrochloride in a Tris-HCl buffer; The mass volume ratio of the lysozyme, tris(2-carboxyethyl)phosphine hydrochloride and Tris-HCl buffer is: 0.04 g: 0.143 g: 20 mL.

2. The method for preparing a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate according to claim 1, characterized in that: The pH of the lysozyme layer growth liquid is 6.5-8.

5.

3. The method for preparing a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate according to claim 1, characterized in that: The deposition time in the deposition process is 5-20 minutes.

4. The method for preparing a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate according to claim 1, characterized in that: The mass concentration of the aqueous monomer solution is 0.1-2%; The mass concentration of the oil phase monomer solution is 0.02-0.2%.

5. The method for preparing a nanofiltration membrane containing a lysozyme intermediate layer modified with a hydrophobic PVDF substrate according to claim 4, characterized in that: The monomer in the aqueous monomer solution is a polyamine, including any one of piperazine, m-phenylenediamine or polyethyleneimine; The monomer in the oil phase monomer solution is a polyacid chloride, including any one of trimesoyl chloride, isophthaloyl chloride, cyclohexanetrichloride, cyclopentanetrichloride, propanoyl chloride or glutaryl chloride.

6. Use of the nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 5 in separating monovalent and / or divalent salts.

7. Use of the nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 5 in separating organic solvents.

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