Polyamide nanofiltration membrane for water purification and method for its preparation

Abstract

The application discloses a kind of polyamide nanofiltration membrane for water purification and preparation method thereof, and it relates to the field of membrane separation technology.The foregoing preparation method includes: mixing monomer solution and initiator solution to obtain base reaction solution;Place the base in the base reaction solution, stir, wash, dry to obtain the modified base;A certain amount of piperazine and trimesoyl chloride are added to water and n-hexane respectively, dissolved at room temperature to obtain piperazine solution and trimesoyl chloride solution;The modified base is infiltrated with piperazine solution, then trimesoyl chloride solution is added to the surface of the base, and after a period of reaction at room temperature, it is washed and dried to obtain a polyamide nanofiltration membrane.The thickness of the polyamide selective layer on the surface of the nanofiltration membrane prepared by the application is less than 50 nm, and it uniformly covers the vertical polyaniline nanofiber layer, and the nanofiltration membrane can realize rapid and accurate separation of divalent / monovalent salt ions, and has the advantages of fast flow rate, high separation efficiency, and good reusability.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a polyamide nanofiltration membrane for water purification and its preparation method. Background Technology

[0002] With the rapid development of modern industry, the development of high-efficiency precision separation materials and technologies to achieve precise separation at the ion and molecular scale will have a transformative impact on fields such as energy, water, chemical engineering, and pharmaceuticals, and is an urgent need and a goal we are constantly pursuing. Membrane separation, with its advantages of low energy consumption, mild separation conditions, and ease of operation, has been widely used in various fields of industrial mass production and daily life. However, the preparation of nanoporous membrane materials with highly uniform pore sizes to achieve precise separation of ions or small molecule compounds still faces significant challenges. Summary of the Invention

[0003] The purpose of this invention is to provide a simple and convenient method for the industrial production of polyamide nanofiltration membranes, solving the problems of low separation efficiency and slow flow rate of traditional polyamide nanofiltration membranes. This method first grows vertical polyaniline nanofiber structures on a substrate surface, and then uses interfacial polycondensation to prepare a polyamide nanofiltration membrane on the surface of the vertical polyaniline nanofiber structures.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a polyamide nanofiltration membrane for water purification includes the following steps: S1. Preparation of the base reaction solution: The monomer solution and the initiator solution are mixed to obtain the base reaction solution; S2. Substrate modification: The substrate is placed in the substrate reaction solution prepared in step S1, stirred, washed, and dried to obtain the modified substrate; S3. Preparation of interfacial polycondensation reaction solution: Add appropriate amounts of piperazine and trimesoyl chloride to water and n-hexane respectively, and dissolve at room temperature to obtain piperazine solution and trimesoyl chloride solution; S4. Preparation of polyamide nanofiltration membrane: The substrate modified in step S2 is impregnated with the piperazine solution prepared in step S3, and then the trimesoyl chloride solution prepared in step S3 is added to the surface of the substrate. After reacting at room temperature for a period of time, the substrate is washed and dried to obtain the polyamide nanofiltration membrane.

[0005] Specifically, the above preparation method includes the following steps: S1. Preparation of the base reaction solution: Mix equal volumes of monomer solution and initiator solution to obtain the base reaction solution; S2. Substrate modification: The substrate is placed in the substrate reaction solution prepared in step S1 and magnetically stirred at 0°C for 6–24 h. Then the substrate is washed with pure water and dried in an oven at 60°C for 2–3 h to obtain the modified substrate. S3. Preparation of interfacial polycondensation reaction solution: A certain amount of piperazine and pyromellitic chloride were added to water and n-hexane respectively and dissolved at room temperature to obtain piperazine solution and pyromellitic chloride solution; S4. Preparation of polyamide nanofiltration membrane: The substrate modified in step S2 is impregnated with the piperazine solution prepared in step S3, and then the trimesoyl chloride solution prepared in step S3 is added to the surface of the substrate. After reacting at room temperature for a period of time, the substrate is washed with n-hexane and dried in an oven at 60°C for 0.5 to 1 hour to obtain the polyamide nanofiltration membrane.

[0006] In step S1, the molar ratio of the monomer solution to the initiator solution is 2:1.

[0007] In step S1, the monomer solution and the initiator solution are prepared by the following steps: dissolving the monomer and the initiator in an acidic aqueous solution to prepare the monomer solution and the initiator solution.

[0008] The monomer is aniline, and the initiator is ammonium persulfate.

[0009] The acidic aqueous solution is a perchloric acid aqueous solution with a concentration of 1 mol / L.

[0010] The monomer solution is an aniline solution, and the initiator solution is an ammonium persulfate solution.

[0011] In step S2, the substrate includes, but is not limited to, a commercial polyethersulfone microfiltration membrane with a pore size and diameter of 0.45 μm and 47 mm, respectively.

[0012] In step S3, the mass concentration ratio of the piperazine solution and the trimesoyl chloride solution is 1:1 to 10:1; preferably 5:1, 1:1 or 10:1.

[0013] In step S3, the mass ratio of piperazine to pyromellitic trimethylol chloride is 1:1 to 10:1; preferably 5:1, 1:1, or 10:1.

[0014] In step S3, the volume ratio of water to n-hexane is 1:1.

[0015] In step S4, the reaction time at room temperature is 0.5 to 1 minute; preferably 0.5 minutes or 1 minute.

[0016] Another object of the present invention is to provide a polyamide nanofiltration membrane for water purification, which is prepared by the above-described method for preparing a polyamide nanofiltration membrane for water purification.

[0017] The surface of the polyamide nanofiltration membrane is a polyamide selective layer that is uniformly covered on a vertical polyaniline nanofiber layer, and the thickness of the polyamide selective layer is less than 50 nm.

[0018] The preparation method of this invention utilizes a vertical polyaniline nanofiber structure to regulate the interfacial polycondensation process of piperazine and trimesoyl chloride to prepare a polyamide nanofiltration membrane with high separation efficiency and fast flow rate. The key point is to first grow vertical polyaniline nanofibers on a substrate through substrate modification, followed by interfacial polymerization. The vertical polyaniline nanofiber structure is used to regulate the interfacial polymerization, resulting in a high-performance polyamide nanofiltration membrane. The nanofiltration membrane prepared by this invention has a polyamide selective layer thickness of less than 50 nm, uniformly covering the vertical polyaniline nanofiber layer. Furthermore, the nanofiltration membrane can achieve rapid and precise separation of divalent / monovalent salt ions, while also possessing advantages such as high flow rate, high separation efficiency, and good reusability. Moreover, the preparation process of this invention is simple, the raw materials are readily available, and the cost is low, making it suitable for large-area preparation and applicable to waterworks, chemical plants, sewage treatment plants, and other similar applications. Attached Figure Description

[0019] Figure 1 The images show optical images of the original polyethersulfone microfiltration membrane and the modified polyethersulfone microfiltration membrane in Example 1. The left image a is the original polyethersulfone microfiltration membrane, and the right image b is the modified polyethersulfone microfiltration membrane. Figure 2 The images are scanning electron microscope (SEM) images of the original polyethersulfone (PES) microfiltration membrane and the modified PES microfiltration membrane in Example 1. Left image a shows the front view of the original PES microfiltration membrane, middle image b shows the front view of the modified PES microfiltration membrane, and right image c shows the cross-section of the modified PES microfiltration membrane. Figure 3 The images are scanning electron microscope (SEM) images of the polyamide nanofiltration membrane obtained in Example 1. Left image a is a cross-section of the polyamide nanofiltration membrane, and right image b is the front view of the polyamide nanofiltration membrane. Figure 4 This is a transmission electron microscope image of the polyamide nanofiltration membrane obtained in Example 1; Figure 5 The diagram shows the salt rejection performance of the polyamide nanofiltration membrane obtained in Example 1. Detailed Implementation

[0020] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention. It should be noted in advance that the following embodiments were completed in a laboratory setting. Those skilled in the art should understand that the amounts of each component given in the embodiments only represent the ratio between the components, and are not specific limitations. Example 1

[0021] (1) Preparation of the base reaction solution: A certain mass of aniline and ammonium persulfate were dissolved in 1 mol / L perchloric acid solution to prepare 0.02 mol / L aniline solution and 0.01 mol / L ammonium persulfate solution, and then the equal volumes were mixed.

[0022] (2) Substrate modification: Place the reaction solution from step (1) in an ice-water bath for 30 minutes, then immerse the polyethersulfone microfiltration membrane in the reaction solution, stir the reaction in an ice-water bath for 12 hours, remove it, wash it with pure water, and dry it in a 60°C oven for 2 hours.

[0023] (3) Preparation of interfacial polycondensation reaction solution: Add 1g piperazine and 0.2g pyromellitic chloride to 100mL water and 100mL n-hexane respectively, and sonicate for 30min to prepare a 0.01g / L piperazine solution and a 0.002g / L pyromellitic chloride solution.

[0024] (4) Preparation of polyamide nanofiltration membrane: The substrate in step (2) was wetted with the piperazine solution in step (3), and then the pyromellitic chloride solution in step (3) was added to the substrate surface. The reaction was carried out at room temperature for 0.5 min. The substrate was washed with n-hexane and dried in an oven at 60°C for 0.5 h.

[0025] Optical photographs of the original polyethersulfone microfiltration membrane and the modified polyethersulfone microfiltration membrane are shown below. Figure 1 As shown, after modification, the original polyethersulfone microfiltration membrane changed from white to dark green, indicating that polyaniline was successfully grown on the surface of the polyethersulfone microfiltration membrane; Figure 2 As shown, the modified polyethersulfone microfiltration membrane has vertically arranged polyaniline nanofibers uniformly distributed on its surface; as Figure 3 As shown, the resulting polyamide selective layer covers the surface of the vertical polyaniline nanofiber structure, and local wrinkles are present; as Figure 4 As shown, the thickness of the resulting polyamide selective layer is relatively small, less than 50 nm; Figure 5 As shown, the obtained polyamide nanofiltration membrane exhibited retention rates of 99.47%, 99.52%, 95.02%, 91.54%, and 24.28% for 1000 ppm Na₂SO₄, MgSO₄, MgCl₂, CaCl₂, and NaCl, respectively, with the flow rate maintained at 15 L / m². -2 h -1 bar -1 This indicates that it can achieve high-speed and precise separation of divalent / monovalent salt ions. Example 2

[0026] (1) Preparation of the base reaction solution: A certain mass of aniline and ammonium persulfate were dissolved in 1 mol / L perchloric acid solution to prepare 0.4 mol / L aniline solution and 0.2 mol / L ammonium persulfate solution, and then the equal volumes were mixed.

[0027] (2) Substrate modification: Place the reaction solution from step (1) in an ice-water bath for 30 minutes, then immerse the polyethersulfone microfiltration membrane in the reaction solution, stir the reaction in an ice-water bath for 6 hours, remove it, wash it with pure water, and dry it in a 60°C oven for 3 hours.

[0028] (3) Preparation of interfacial polycondensation reaction solution: Add 2g piperazine and 2g trimesoyl chloride to 100mL water and 100mL n-hexane respectively, and sonicate for 30min to prepare 0.02g / L piperazine solution and 0.02g / L trimesoyl chloride solution.

[0029] (4) Preparation of polyamide nanofiltration membrane: The substrate in step (2) was wetted with the piperazine solution in step (3), and then the pyromellitic chloride solution in step (3) was added to the substrate surface. The reaction was carried out at room temperature for 0.5 min. The substrate was washed with n-hexane and dried in an oven at 60°C for 1 h. Example 3

[0030] (1) Preparation of the base reaction solution: A certain mass of aniline and ammonium persulfate were dissolved in 1 mol / L perchloric acid solution to prepare 0.1 mol / L aniline solution and 0.05 mol / L ammonium persulfate solution, and then the equal volumes were mixed.

[0031] (2) Substrate modification: Place the reaction solution from step (1) in an ice-water bath for 30 minutes, then immerse the polyethersulfone microfiltration membrane in the reaction solution, stir the reaction in an ice-water bath for 18 hours, remove it, wash it with pure water, and dry it in a 60°C oven for 2 hours.

[0032] (3) Preparation of interfacial polycondensation reaction solution: Add 4g piperazine and 0.4g pyromellitic chloride to 100mL water and 100mL n-hexane respectively, and sonicate for 30min to prepare a 0.04g / L piperazine solution and a 0.004g / L pyromellitic chloride solution.

[0033] (4) Preparation of polyamide nanofiltration membrane: The substrate in step (2) was wetted with the piperazine solution in step (3), and then the pyromellitic chloride solution in step (3) was added to the substrate surface. The reaction was carried out at room temperature for 1 min. The substrate was washed with n-hexane and dried in an oven at 60°C for 0.5 h.

[0034] Examples 2 and 3 are similar to Example 1, all of which produce polyamide nanofiltration membranes with a surface polyamide selective layer thickness of less than 50 nm that are uniformly covered on a vertical polyaniline nanofiber layer.

[0035] The selection of monomers, initiators, and acidic solutions used for modifying the substrate, as well as the molar ratio of monomers to initiators, are key to forming vertical polyaniline nanofiber structures. The three embodiments described above all formed vertical polyaniline nanofiber structures by selecting aniline as the monomer used for modifying the substrate, ammonium persulfate as the initiator used for modifying the substrate, and perchloric acid solution as the acidic solution used for modifying the substrate, and by controlling the molar ratio of monomers to initiators at 2:1.

[0036] In summary, the preparation method of this invention mainly includes steps such as the preparation of a substrate reaction solution, substrate modification, preparation of an interfacial polycondensation reaction solution, and membrane preparation. It primarily utilizes a vertical polyaniline nanofiber structure to regulate the interfacial polycondensation process of piperazine and trimesoyl chloride to prepare a polyamide nanofiltration membrane with high separation efficiency and fast flow rate. The key point is to first grow vertical polyaniline nanofibers on the substrate through substrate modification, and then perform interfacial polymerization, using the vertical polyaniline nanofiber structure to regulate the interfacial polymerization, thus obtaining a high-performance polyamide nanofiltration membrane. The nanofiltration membrane prepared by this invention has a polyamide selective layer thickness of less than 50 nm on its surface, uniformly covering the vertical polyaniline nanofiber layer. Furthermore, the nanofiltration membrane can achieve rapid and precise separation of divalent / monovalent salt ions, while possessing advantages such as high flow rate, high separation efficiency, and good reusability. Moreover, the preparation process of this invention is simple, the raw materials are readily available, and the cost is low, making it suitable for large-area preparation and applicable to waterworks, chemical plants, sewage treatment plants, and other similar settings.

[0037] It is also worth mentioning that the polyamide nanofiltration membrane based on the vertical polyaniline nanofiber structure prepared by this invention has a thinner selective layer, a narrower pore size distribution, and excellent separation efficiency and separation rate. When used for seawater desalination, it allows monovalent salt ions in the water to pass through while blocking divalent salt ions, thereby achieving precise separation at the ion and molecular scales.

[0038] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0039] Finally, it should be emphasized that, in order to make it easier for those skilled in the art to understand the improvements of the present invention compared with the prior art, some descriptions of the present invention have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements can also constitute the content of the present invention.

Claims

1. A method for preparing a polyamide nanofiltration membrane for water purification, characterized in that, Includes the following steps: S1. Preparation of the base reaction solution: The monomer solution and the initiator solution are mixed to obtain the base reaction solution; S2. Substrate modification: The substrate is placed in a substrate reaction solution, stirred, washed, and dried to obtain the modified substrate; S3. Preparation of interfacial polycondensation reaction solution: Add appropriate amounts of piperazine and trimesoyl chloride to water and n-hexane respectively, and dissolve at room temperature to obtain piperazine solution and trimesoyl chloride solution; S4. Preparation of polyamide nanofiltration membrane: The modified substrate was impregnated with piperazine solution, and then pyromellitic methyl chloride solution was added to the surface of the substrate. After reacting at room temperature for 0.5 min, the substrate was washed and dried to obtain polyamide nanofiltration membrane. When the polyamide nanofiltration membrane is used for water purification, it allows monovalent salt ions to pass through while blocking divalent salt ions. In step S1, the molar ratio of the monomer solution to the initiator solution is 2:1; the monomer solution and the initiator solution are prepared by the following steps: dissolving the monomer and the initiator in acidic aqueous solution respectively to prepare the monomer solution and the initiator solution; the monomer is aniline, the initiator is ammonium persulfate; the acidic aqueous solution is perchloric acid aqueous solution.

2. The method for preparing a polyamide nanofiltration membrane for water purification according to claim 1, characterized in that: In step S2, the substrate is a polyethersulfone microfiltration membrane.

3. The method for preparing a polyamide nanofiltration membrane for water purification according to claim 1, characterized in that: In step S3, the mass concentration ratio of the piperazine solution and the pyromellitic methyl chloride solution is (1-10):

1.

4. A polyamide nanofiltration membrane for water purification, characterized in that: It is prepared by the method for preparing polyamide nanofiltration membrane for water purification according to any one of claims 1-3.

5. The polyamide nanofiltration membrane for water purification according to claim 4, characterized in that: The surface of the polyamide nanofiltration membrane is a polyamide selective layer that is uniformly covered on a vertical polyaniline nanofiber layer, and the thickness of the polyamide selective layer is less than 50 nm.

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