Pore size and surface charge tunable nanofiltration membranes and methods of making the same

Abstract

The application belongs to the technical field of nanofiltration membrane separation, and particularly relates to a kind of nanofiltration membrane with adjustable pore size and surface charge and a preparation method thereof. The application uses amino carbon quantum dots as an aqueous monomer to prepare nanofiltration membrane through interfacial polymerization. By adjusting the concentration of amino carbon quantum dots, a nanofiltration membrane without defects can be prepared, and the pore size and surface charge of the nanofiltration membrane can be effectively controlled. The prepared loose nanofiltration membrane with negative charge and large pore size has a low rejection rate for inorganic salts and a high dye / inorganic salt separation effect. The preparation method of the amino carbon quantum dot regulated nanofiltration membrane provided by the application is simple and suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane separation technology, and specifically relates to a nanofiltration membrane with adjustable pore size and surface charge and its preparation method. Background Technology

[0002] Nanofiltration, a membrane separation technology intermediate between ultrafiltration and reverse osmosis, boasts advantages such as low operating pressure and high separation efficiency, and is widely used in water purification and softening, wastewater treatment, industrial purification and recovery. With continuous societal development and increasingly complex separation systems, higher demands are placed on the separation performance of nanofiltration membranes. For example, nanofiltration membranes used for dyeing and printing wastewater treatment require a loose separation layer structure, high dye rejection, and low inorganic salt rejection; nanofiltration membranes used for hard water softening and desalination require high inorganic salt rejection rates. However, traditional commercial nanofiltration membranes, such as polyamide nanofiltration membranes prepared by interfacial polymerization of piperazine and trimesoyl chloride, exhibit high rejection for divalent salts and moderate rejection for monovalent salts due to their small pore size and negative surface charge, failing to achieve effective separation of dyes and inorganic salts; their rejection rates for divalent cations (magnesium ions, copper ions) are relatively low (lower than sodium sulfate), hindering efficient hard water softening. Therefore, how to regulate the separation performance of nanofiltration membranes has become one of the current hot topics in nanofiltration membrane research.

[0003] The separation performance of nanofiltration membranes is mainly determined by pore size sieving and electrostatic repulsion. Several patents, such as CN112516822B and CN 114471197 A, have disclosed methods for preparing nanofiltration membranes with tunable surface charge, but these methods require post-treatment after membrane formation. The literature [J. Mater. Chem. A, 2018, 6, 20242] prepared nanofiltration membranes with tunable pore size and surface charge by controlling the concentration of interfacial polymerized amine monomers. This method first prepares an unsupported selective separation layer through polymerization at the water-n-hexane interface, and then transfers this separation layer onto a support material, a complex process. Therefore, there is an urgent need for simple and economical methods to effectively control the pore size and surface charge of nanofiltration membranes, thereby regulating their separation performance to meet the separation requirements of different applications. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a nanofiltration membrane with adjustable pore size and surface charge. This method can prepare a defect-free nanofiltration membrane by adjusting the concentration of amino carbon quantum dots and achieve effective control over the pore size and surface charge of the nanofiltration membrane. The prepared porous nanofiltration membrane with negative charge and large pore size has a low rejection rate of inorganic salts and a high dye / inorganic salt separation effect.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A method for preparing a nanofiltration membrane with tunable pore size and surface charge, the method comprising the following steps:

[0007] (1) Using amino acids as the carbon source, pyrolyze at 240℃±5℃ for 0.5h-2h, cool to room temperature, add an appropriate amount of water and sonicate for 30min to obtain a dispersion of carbon quantum dots.

[0008] Larger particles were removed by filtration, the dispersion was placed in a dialysis bag and dialyzed for more than 72 hours, and finally freeze-dried to obtain amino carbon quantum dot solids;

[0009] (2) Prepare an aqueous solution of amino carbon quantum dots with a concentration of 0.5-12 mg / mL;

[0010] The polyacryl chloride monomer is dissolved in an organic solvent to obtain an organic phase solution with a polyacryl chloride concentration of 0.05-0.3 wt%; the polyacryl chloride is selected from pyromellitic methyl methacrylate chloride, isophthaloyl chloride, phthaloyl chloride or terephthaloyl chloride, and the organic solvent is n-hexane, cyclohexane or heptane;

[0011] (3) Immerse the surface of the ultrafiltration membrane in the aqueous solution of step (2) for 0.5-10 min. After taking it out, remove the excess aqueous solution from the surface of the supporting membrane. When there are no obvious water droplets on the surface, immerse it in the organic solution. The interfacial polymerization time is 0.5-5 min. After removing the excess organic solution, heat-treat the obtained membrane at 40-60℃ for 5-20 min. After washing with deionized water, the nanofiltration membrane is obtained.

[0012] Preferably, the amino acid mentioned in step (1) is selected from at least one of lysine, aspartic acid, glycine or arginine, with lysine being preferred; the ultrafiltration membrane mentioned in S2 is selected from one of polyacrylonitrile, polysulfone or polyethersulfone ultrafiltration membrane.

[0013] As a preferred option, in step (1), 1g of amino acid is used as the carbon source, pyrolyzed at 240℃ for 0.5h, cooled to room temperature, and then 20mL of deionized water is added and sonicated for 30min to obtain a dispersion of amino carbon quantum dots.

[0014] Preferably, in step (2), the concentration of amino carbon quantum dots in the aqueous solution is 1.0-10 mg / mL.

[0015] Preferably, in step (2), the polyacryl chloride in the organic phase solution is pyromellitic tricarboxylate chloride, the organic solvent is n-hexane, and the concentration of the polyacryl chloride is 0.1-0.25 wt%.

[0016] Preferably, the soaking time in the aqueous phase in step (3) is 0.5-2 min.

[0017] Preferably, the interface aggregation time in step (3) is 0.5-2 min.

[0018] Preferably, the heat treatment temperature in step (3) is 40-50℃ and the heat treatment time is 10-20min.

[0019] At the same concentration of amino carbon quantum dots, changes in these conditions in steps (2) and (3) will affect the rejection rate and water flux. Under the above preferred conditions, nanofiltration membrane products with better rejection rate and water flux performance will be obtained.

[0020] This invention discloses a nanofiltration membrane with adjustable pore size and surface charge prepared by the method described herein. According to experimental results, when the concentration of amino carbon quantum dots is 0.1 wt%, the prepared nanofiltration membrane exhibits low rejection rates for inorganic salts such as sodium sulfate, magnesium chloride, and sodium chloride, but high rejection rates for dyes such as methylene blue and Congo red, making it a highly efficient nanofiltration membrane for separating dyes / inorganic salts. When the concentration of amino carbon quantum dots is ≤0.5 wt%, the prepared nanofiltration membrane is negatively charged, exhibiting low rejection rates for divalent magnesium salts and high rejection rates for sodium sulfate, making it unsuitable for softening hard water. When the concentration of amino quantum dots is 0.8-1.0 wt%, the prepared nanofiltration membrane is positively charged, exhibiting high rejection rates for divalent magnesium salts, and can achieve the softening of hard water.

[0021] The beneficial effects of this invention are as follows: This invention uses aminocarbon quantum dots as the aqueous phase monomer to prepare nanofiltration membranes via interfacial polymerization. By adjusting the concentration of aminocarbon quantum dots, defect-free nanofiltration membranes can be prepared, and effective control over the pore size and surface charge of the nanofiltration membrane can be achieved. The prepared negatively charged, large-pore-size, porous nanofiltration membrane has a low rejection rate for inorganic salts and exhibits high dye / inorganic salt separation efficiency. The prepared positively charged, small-pore-size nanofiltration membrane has a magnesium chloride rejection rate >97% and can be used for hard water softening. The preparation method of the aminocarbon quantum dot-controlled nanofiltration membrane provided by this invention is simple and suitable for large-scale industrial production. Attached Figure Description

[0022] Figure 1 The pore size and pore size distribution of nanofiltration membranes prepared in Examples 1, 4 and 5 are shown.

[0023] Figure 2 The surface charge of the nanofiltration membranes prepared in Examples 2, 3, 4 and 5. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0025] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0026] The performance evaluation method of the nanofiltration membrane of the present invention is as follows: The nanofiltration membrane is placed in a nanofiltration membrane performance evaluation instrument (Hangzhou Saifei Membrane Separation Technology Co., Ltd., SF-SA type). Before testing, it is pre-pressurized at 0.6 MPa for 1 hour, and then the water flux (J) and salt rejection rate (R) of the nanofiltration membrane are measured at 0.6 MPa and 25°C. The calculation formula is as follows: Where A is the effective membrane area (22.5 cm²). 2 ); t is the time required to collect volume V of permeate; C p and C f The concentrations of the feed solution and the permeate are respectively. The concentration of inorganic salts was determined by a conductivity meter, and the dye concentration was determined by ultraviolet-visible absorption spectroscopy.

[0027] Example 1:

[0028] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0029] Prepare a 0.1 wt% aqueous solution of amino carbon quantum dots; immerse the surface of the polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain the nanofiltration membrane.

[0030] The prepared nanofiltration membrane exhibits a pure water flux of 82 L / m² at 25 °C and 0.6 MPa. -2 h -1 For 1g L -1 The retention rates for sodium sulfate, magnesium chloride, and sodium chloride were 14.19%, 11.21%, and 12.03%, respectively, for 0.1 g L. -1 The rejection rates for methylene blue and Congo red were 98.96% and 99.44%, respectively, enabling effective separation of dyes and inorganic salts.

[0031] Example 2:

[0032] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0033] Prepare a 0.2 wt% aqueous solution of amino carbon quantum dots; immerse the surface of the polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain the nanofiltration membrane.

[0034] Example 3:

[0035] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0036] Prepare a 0.5 wt% aqueous solution of amino carbon quantum dots; immerse the surface of the polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain the nanofiltration membrane.

[0037] Example 4:

[0038] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0039] Prepare a 0.8 wt% aqueous solution of amino carbon quantum dots; immerse the surface of the polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain the nanofiltration membrane.

[0040] Example 5:

[0041] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0042] Prepare a 1.0 wt% aqueous solution of amino carbon quantum dots; immerse the surface of a polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain a nanofiltration membrane.

[0043] Example 6:

[0044] Using 1g of arginine as the carbon source, the mixture was pyrolyzed at 240℃ for 0.5h. After cooling to room temperature, 20mL of deionized water was added and the mixture was sonicated for 30min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0045] Prepare a 0.5 wt% aqueous solution of amino carbon quantum dots; immerse the surface of the polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain the nanofiltration membrane.

[0046] Example 7:

[0047] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0048] Prepare a 0.2 wt% aqueous solution of amino carbon quantum dots; immerse the surface of a polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 20 min. After washing with deionized water, obtain a nanofiltration membrane.

[0049] Example 8:

[0050] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0051] Prepare a 0.2 wt% aqueous solution of amino carbon quantum dots; immerse the surface of a polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.25 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 1 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain a nanofiltration membrane.

[0052] Example 9:

[0053] Using 1 g of lysine as the carbon source, the mixture was pyrolyzed at 240 °C for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and the mixture was sonicated for 30 min to obtain a dispersion of carbon quantum dots. Larger particles were removed by centrifugation, and the dispersion was dialyzed in a dialysis bag for 72 h. Finally, the carbon quantum dots were freeze-dried to obtain solid carbon quantum dots.

[0054] Prepare a 0.2 wt% aqueous solution of amino carbon quantum dots; immerse the surface of a polysulfone ultrafiltration membrane in the above aqueous solution for 2 min, remove it and remove excess aqueous solution from the surface, then immerse it in a 0.2 wt% solution of trimesoyl chloride and hexane for interfacial polymerization for 2 min. After removing excess organic phase solution, place the membrane in an oven and heat-treat at 50°C for 15 min. After washing with deionized water, obtain a nanofiltration membrane.

[0055] Application examples

[0056] The nanofiltration membranes prepared in the above embodiments were subjected to a test at 25°C and 0.6 MPa for 1 g L. -1 The retention rates of sodium sulfate, magnesium chloride, and sodium chloride were tested, and the results are shown in Table 1.

[0057] The surface charge of the membrane at 25°C and pH 6.0 was determined using a SurPASS Anton Paar surface potentiometer with 0.001M KCl aqueous solution as background solution.

[0058] Table 1

[0059]

[0060]

[0061] The pore size and pore size distribution of the nanofiltration membranes prepared in Examples 1, 4, and 5 were measured. The retention rates of the nanofiltration membranes for polyethylene glycol of different molecular weights (200, 400, 600, 800, 1000, and 2000 Da) were determined using the formula... The nanofiltration membrane pore size and pore diameter were calculated, and the results are as follows: Figure 1 As shown, according to Figure 1 It can be seen that as the concentration of amino quantum dots increases, the pore size of the nanofiltration membrane decreases, and the pore size distribution narrows, indicating that the size of the nanofiltration membrane pores can be effectively controlled by adjusting the concentration of amino quantum dots.

[0062] Comparing the data obtained from Example 1 and Table 1, the nanofiltration membrane prepared in Example 1 has a larger pore size and is a loose nanofiltration membrane. Therefore, when the concentration of amino carbon quantum dots is 0.1 wt%, the nanofiltration membrane prepared has a low rejection rate for inorganic salts sodium sulfate, magnesium chloride and sodium chloride, but a high rejection rate for dyes methylene blue and Congo red. It is a nanofiltration membrane with high efficiency for separating dyes / inorganic salts.

[0063] The surface charge of the nanofiltration membranes prepared in Examples 2, 3, 4, and 5 was detected, and the results are as follows: Figure 2 As shown, according to Figure 2 It is known that when the concentration of amino carbon quantum dots is ≤0.5wt%, the prepared nanofiltration membrane is negatively charged, exhibiting low rejection of divalent magnesium salts and high rejection of sodium sulfate, making it unsuitable for softening hard water. When the concentration of amino carbon quantum dots is 0.8-1.0wt%, the prepared nanofiltration membrane is positively charged, exhibiting high rejection of divalent magnesium salts and enabling the softening of hard water. Therefore, by adjusting the concentration of amino carbon quantum dots, the surface charge of the nanofiltration membrane can be altered, achieving a reversal of surface charge (from negative to positive), thereby changing the selective separation properties of the nanofiltration membrane and broadening its application areas.

[0064] Comparing Examples 2-5, as the concentration of amino carbon quantum dots increases, the water flux of the nanofiltration membrane gradually decreases, while the rejection rate of inorganic salts significantly increases, indicating that the degree of cross-linking of the nanofiltration membrane increases and the pore size decreases. Simultaneously, it can be observed that the surface charge of the nanofiltration membrane changes from negative to positive. Specifically, the nanofiltration membrane prepared in Example 5 exhibits a magnesium chloride rejection rate >98%, effectively removing magnesium ions from water and achieving water softening.

[0065] Compared with Examples 3 and 6, arginine has more amino groups than lysine. Therefore, the nanofiltration membrane prepared has a higher positive charge on its surface at the same concentration of amino carbon quantum dots. The improved surface positive charge is beneficial to the removal of magnesium ions, thus exhibiting higher retention performance for magnesium chloride.

[0066] Comparing Examples 2 and 7-9, the increase in the concentration of pyromellitic methyl chloride, the extension of the interfacial polymerization reaction time, or the increase in the heat treatment time all led to a decrease in the flux of the nanofiltration membrane and an increase in the rejection rate, indicating the formation of a denser nanofiltration membrane with smaller pore size.

[0067] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0068] The above provides a detailed description of the nanofiltration membrane with tunable pore size and surface charge, and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the invention. These examples are merely illustrative to aid in understanding the method and core concepts of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A method for preparing a nanofiltration membrane with adjustable pore size and surface charge, characterized in that... Includes the following steps: (1) Using amino acids as the carbon source, the carbon quantum dots were pyrolyzed at 240℃±5℃ for 0.5 h-2 h, cooled to room temperature, and then sonicated for 30 min with an appropriate amount of water to obtain a dispersion of carbon quantum dots. Larger particles were removed by filtration, the dispersion was placed in a dialysis bag and dialyzed for more than 72 hours, and finally freeze-dried to obtain amino carbon quantum dot solids; (2) The amino carbon quantum dots are prepared into an aqueous solution with an amino carbon quantum dot concentration of 0.5-12 mg / mL, wherein the aqueous solution is composed of the amino carbon quantum dots and water; The polyacryl chloride monomer is dissolved in an organic solvent to obtain an organic phase solution with a polyacryl chloride concentration of 0.05-0.3 wt%; the polyacryl chloride is selected from pyromellitic methyl methacrylate chloride, isophthaloyl chloride, phthaloyl chloride or terephthaloyl chloride, and the organic solvent is n-hexane, cyclohexane or heptane; (3) Immerse the surface of the ultrafiltration membrane in the aqueous solution of step (2) for 0.5-10 min. After taking it out, remove the excess aqueous solution from the surface of the supporting membrane. When there are no obvious water droplets on the surface, immerse it in the organic solution. The interfacial polymerization time is 0.5-5 min. After removing the excess organic solution, heat-treat the obtained membrane at 40-60℃ for 5-20 min. After washing with deionized water, the nanofiltration membrane is obtained. The amino acid mentioned in step (1) is selected from at least one of lysine, aspartic acid, glycine or arginine; the ultrafiltration membrane mentioned in step (3) is selected from one of polyacrylonitrile, polysulfone or polyethersulfone ultrafiltration membrane.

2. The preparation method according to claim 1, characterized in that: In step (1), 1 g of amino acid was used as the carbon source and pyrolyzed at 240℃ for 0.5 h. After cooling to room temperature, 20 mL of deionized water was added and sonicated for 30 min to obtain a dispersion of amino carbon quantum dots.

3. The preparation method according to claim 1, characterized in that: In step (2), the concentration of amino carbon quantum dots in the aqueous solution is 1.0-10 mg / mL.

4. The preparation method according to claim 1, characterized in that: In step (2), the polyacryl chloride in the organic phase solution is pyromellitic tricarboxylate chloride, the organic solvent is n-hexane, and the concentration of the polyacryl chloride is 0.1-0.25 wt%.

5. The preparation method according to claim 1, characterized in that: The soaking time in the aqueous phase in step (3) is 0.5-2 min.

6. The preparation method according to claim 1, characterized in that: The interface aggregation time in step (3) is 0.5-2 min.

7. The preparation method according to claim 1, characterized in that: The heat treatment temperature in step (3) is 40-50℃ and the heat treatment time is 10-20 min.

8. A nanofiltration membrane with adjustable pore size and surface charge obtained by the preparation method of claim 1.

Images