Application of high-selectivity nanofiltration membrane regulated and controlled by chitosan hydrogel to separation of mineral ions and perfluorinated compounds in mineral salt solution

Abstract

The invention relates to application of a high-selectivity nanofiltration membrane regulated and controlled by chitosan hydrogel to separation of salt ions and perfluorinated compounds in a mineral salt solution. The invention provides application of a high-selectivity nanofiltration membrane regulated and controlled by chitosan hydrogel to separation of salt ions and perfluorinated compounds in a mineral salt solution. The high-selectivity nanofiltration membrane comprises a base membrane, and a hydrogel layer and a polyamide layer which are respectively arranged on the surface of the base membrane. Experiments prove that when natural water is treated, the total salt rejection rate is reduced along with the increase of the concentration of the middle layer, the conductivity is reduced under the combined action of the size screening effect of the cut-off molecular weight and electronegative electrostatic repulsion, and the modified membrane can permeate more mineral elements.

Description

Technical Field

[0001] The present invention relates to the technical fields of nanofiltration membrane technology and municipal water treatment technology, and in particular to the application of a highly selective nanofiltration membrane regulated by chitosan hydrogel for separating mineral ions and perfluorinated compounds in a mineral salt solution. Background Art

[0002] 1. PFAS Pollution and Current Situation of Nanofiltration Membrane Application

[0003] With the advancement of the industrialization process, the content of PFAS in the water system shows an increasing trend. Even at low concentrations, PFAS can pose a serious threat to human health, covering aspects such as decreased immunity, thyroid diseases, and liver damage.

[0004] Nanofiltration (NF), as an important membrane separation technology, is widely used in the field of drinking water treatment. Its retention molecular weight is usually in the range of 200 - 1000 Da, and it can be used to remove natural organic matter and trace organic compounds such as pharmaceuticals, personal care products, steroid hormones, and pesticides. However, there are many problems in the actual application of existing nanofiltration membranes.

[0005] 2. Limitations of Existing Nanofiltration Membranes

[0006] Existing nanofiltration membranes have a relatively high retention rate for divalent cations (mainly Ca 2+ and Mg 2+ ). Low concentrations of Ca 2+ will weaken the chemical stability and enhance the corrosiveness of the NF permeate water. At the same time, Ca 2+ and Mg 2+ , as essential minerals for the human body, too high a retention rate will not only lead to their insufficient content in water, but also cause membrane fouling due to poorly soluble salts such as CaCO3, especially when the water recovery rate is relatively high, the energy consumption will increase significantly.

[0007] In order to improve the membrane performance, existing technologies mainly customize the membrane performance by adjusting the interfacial polymerization conditions. For example, changing conditions such as monomer type and concentration, reaction time, etc., these operations will affect the membrane pore size, surface charge, and hydrophilicity. In terms of enhancing the rejection ability of the membrane to new contaminants, the key lies in promoting the water transport of the membrane and inhibiting the penetration of new contaminants. Usually, the membrane nanostructure is adjusted to improve water permeability (such as creating additional water transport pathways using nanomaterials), or the solute permeability coefficient is adjusted by controlling the membrane-solute interaction (such as surface modification).

[0008] 3. Membrane Interface Stability Problem

[0009] Most nanofiltration membranes form a polyamide active layer through interfacial polymerization technology. The commonly used monomers are piperazine in the aqueous phase and trimesoyl chloride in the organic phase. Due to the poor interfacial stability of traditional membranes, the present invention uses a reactive / functional intermediate layer to solve this problem. This intermediate layer can not only effectively enhance the interfacial stability of the membrane, but also improve water permeability and selectivity for inorganic salts, organic pollutants, etc. Compared with discrete nanoparticles, one-dimensional or two-dimensional nanomaterials, interfacial coatings have more significant advantages in enhancing membrane separation because their super permeability and continuity can produce a more effective groove effect.

[0010] 4. Precise control problem of hydrogel-assisted interfacial polymerization

[0011] As a continuous three-dimensional polymer, hydrogel has been applied to the preparation process of polyamide thin films. It can increase the storage of amines and provide a more effective aqueous interface for interfacial polymerization. However, precisely controlling the hydrogel-assisted interfacial polymerization process is challenging. Nevertheless, hydrogel is very effective in increasing the surface negative charge density and hydrophilicity of the membrane. The polyamide thin film synthesized by the hydrogel-assisted interfacial polymerization method exhibits high water permeability. This high water permeability benefits from the reduction of the selective layer thickness and the defect-free thin polyamide layer generated by uniform interfacial polymerization at the perfect interface between hexane and hydrogel. Therefore, the comprehensive properties of hydrogel, such as high hydrophilicity, improved negative charge, and significant interaction ability, are extremely beneficial for the rejection of PFAS and the passage of divalent cations.

[0012] The interfacial stability of traditional membranes is poor because there is a lack of chemical bonding between the polyamide layer and the substrate, and they have different swelling tendencies. In addition, the impact of introducing nanomaterials into the membrane on the long-term operation stability of the membrane has always been controversial. In some cases, nanoscale fillers will seriously aggregate in the nanofiltration membrane, resulting in a decrease in the selectivity and integrity of the membrane. Moreover, surface-modified nanofiltration membranes often cause a significant reduction in water permeability (up to 50%), which will undoubtedly lead to a significant increase in unit energy consumption. Summary of the Invention

[0013] To solve the above technical problems, the present invention provides an application of a highly selective nanofiltration membrane regulated by chitosan hydrogel in separating mineral ions and perfluorinated compounds in a mineral salt solution. The present invention aims to utilize the unique advantages of hydrogel to develop an innovative modification strategy to improve the separation performance of mineral salts (especially Ca 2+ and Mg 2+) Selective separation ability from PFAS. Specifically, by leveraging the characteristics of the hydrogel such as high hydrophilicity, enhanced negative charge, and significant interaction ability, this goal is achieved by adjusting the pore size distribution and charge density. The present invention focuses on enhancing the performance of the nanofiltration membrane in the process of treating municipal water, especially an innovative technology for the selective separation of per- and polyfluoroalkyl substances (PFAS) and divalent cations.

[0014] The object of the present invention is to provide an application of a highly selective nanofiltration membrane regulated by chitosan hydrogel for separating salt ions and perfluorinated compounds in a mineral salt solution; the highly selective nanofiltration membrane includes a base membrane, and a hydrogel layer and a polyamide layer respectively disposed on the surface of the base membrane.

[0015] In some embodiments of the present invention, the mineral salt in the mineral salt solution includes calcium ions and / or magnesium ions.

[0016] In some embodiments of the present invention, the perfluorinated compounds include one or more of perfluorobutyric acid, perfluorobutane sulfonic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluorohexane sulfonic acid, and perfluorooctane sulfonic acid.

[0017] In some embodiments of the present invention, the thickness of the highly selective nanofiltration membrane is 60 - 80 nm;

[0018] The thickness of the hydrogel layer is 30 - 50 nm;

[0019] The thickness of the polyamide layer is 25 - 50 nm.

[0020] In some embodiments of the present invention, the highly selective nanofiltration membrane regulated by chitosan hydrogel is prepared by the following method:

[0021] (1) Immerse the membrane substrate in an aqueous chitosan solution, add an aqueous glutaraldehyde solution, and carry out a cross-linking reaction to obtain a hydrogel layer on the surface of the membrane substrate;

[0022] (2) Immerse the membrane substrate with the hydrogel layer obtained in step (1) in an aqueous piperazine solution to obtain a PES substrate with piperazine monomers on its surface. Then, add a solution containing trimesoyl chloride to the surface of the PES substrate with piperazine monomers on its surface, and carry out an interfacial polymerization reaction to form a polyamide layer on the surface of the hydrogel layer, obtaining a polyamide nanofiltration precursor membrane;

[0023] (3) Thermally cure the polyamide nanofiltration precursor membrane obtained in step (2) to obtain the highly selective nanofiltration membrane.

[0024] In some embodiments of the present invention, in step (1), the membrane substrate is selected from a PES substrate and / or a PS substrate;

[0025] The concentration of the chitosan aqueous solution is 0.25 wt% - 1 wt%;

[0026] The soaking time is 5 - 10 min.

[0027] In some embodiments of the present invention, in step (1), the concentration of the glutaraldehyde aqueous solution is 0.25 wt% - 1 wt%;

[0028] The cross-linking reaction time is 30 s - 3 min.

[0029] In some embodiments of the present invention, in step (2), the concentration of the piperazine aqueous solution is 0.25 wt% - 1 wt%;

[0030] The soaking time is 1 - 2 min.

[0031] In some embodiments of the present invention, in step (2), the concentration of trimellitic acid chloride in the trimellitic acid chloride solution is 0.15 wt% - 0.2 wt%;

[0032] The interfacial polymerization time is 30 s - 1 min.

[0033] In some embodiments of the present invention, in step (2), the solvent of the trimellitic acid chloride solution is hexane and / or Isopar - G.

[0034] In some embodiments of the present invention, in step (3), the temperature of thermal curing is 60 - 80 °C, and the time is 3 - 5 min.

[0035] The above technical solution of the present invention has the following advantages compared with the prior art:

[0036] The present invention utilizes the key technical point of chitosan hydrogel-assisted interfacial polymerization. Chitosan itself has hydrophilicity. During the interfacial polymerization process, it can regulate the negative charge and thickness of the membrane surface, limit the diffusion of piperazine, and at the same time react with trimellitic acid chloride, thereby enhancing the stability of the three-dimensional structure of the nanofiltration membrane, which is conducive to the formation of a thinner and more electronegative nanofiltration membrane.

[0037] The present invention realizes the efficient selective separation of perfluorinated compounds and calcium and magnesium ions. The modified membrane has a slightly expanded membrane pore size distribution. At the same time, due to the increased surface carboxyl density, it has stronger electronegativity. Since the negative charge on the surface of perfluorinated compounds and the negative charge on the membrane surface can generate a greater electrostatic repulsion, offsetting the negative impact brought by the enlarged pore size distribution, and the improvement of the surface carboxyl density is conducive to the permeability of calcium and magnesium mineral ions.

[0038] The present invention has better separation performance for natural organic matter, perfluorinated compounds, calcium and magnesium ions in natural surface water. Specifically, it has a lower retention rate of mineral elements and a higher retention rate of organic matter. Through experimental verification, when treating natural water, the total salt retention rate decreases with the increase of the concentration of the intermediate layer. The size sieving effect and the electronegative electrostatic repulsion of the retention molecular weight work together to reduce the conductivity, and the modified membrane can permeate more mineral elements. For the retention rate of natural organic matter, the retention rate of total organic carbon of all membranes exceeds 60%, and the retention rate of UV 254 exceeds 80%, and the increase in the modified concentration does not lead to a significant decrease in the rejection rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the drawings, wherein,

[0040] Figure 1 is a schematic diagram for the preparation of the nanofiltration membrane of the present invention.

[0041] Figure 2 are the scanning electron microscope, transmission electron microscope and atomic force microscope characterization diagrams of the prepared nanofiltration membrane of the present invention.

[0042] Figure 3 is the surface potential characterization diagram of the prepared nanofiltration membrane of the present invention.

[0043] Figure 4 is the removal effect diagram of the separation of perfluorinated compounds and ions in tap water by the modified nanofiltration membrane of the present invention.

[0044] Figure 5 is the removal effect diagram of the retention of anions and cations in surface water by the nanofiltration membrane of the present invention.

[0045] Figure 6 is the removal effect diagram of the retention of natural organic matter in surface water by the nanofiltration membrane of the present invention.

[0046] Figure 7 is the long-term stability test effect diagram of the nanofiltration membrane of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The following further illustrates the present invention in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the examples given are not intended to limit the present invention.

[0048] Example 1

[0049] This embodiment provides an innovative method for fabricating polyamide nanofiltration membranes using chitosan hydrogels. This method involves multiple key steps, including PES substrate treatment, hydrogel construction, immersion in piperazine aqueous solution, interfacial polymerization reaction, and thermal curing, as follows:

[0050] (1) Immerse the top surface of the PES substrate in a 0.25 wt% chitosan aqueous solution for 5 minutes. Then, pour out the remaining solution and further remove the excess solution with a rubber roller. Next, add a 0.25 wt% glutaraldehyde aqueous solution to crosslink with chitosan for 1 minute to construct the hydrogel. After that, pour out the remaining solution again and use the rubber roller to further remove the excess solution.

[0051] (2) Immerse the top surface of the PES substrate with the hydrogel loaded on its surface in an appropriate amount of 0.25 wt% piperazine aqueous solution for 2 minutes. Then, pour out the remaining solution and use a rubber roller to further remove the excess solution to obtain a PES substrate with the surface filled with piperazine monomers. Subsequently, add a hexane solution containing 0.15 wt% trimesoyl chloride to the surface of the PES substrate with the surface filled with piperazine monomers and conduct an interfacial polymerization reaction at room temperature for 1 minute to form a polyamide layer on top of the hydrogel. Remove the excess organic phase solution to obtain a polyamide nanofiltration precursor membrane.

[0052] (3) Place the polyamide nanofiltration precursor membrane obtained in step (2) in an oven and conduct thermal curing at a temperature of 60 °C for 5 minutes to finally obtain a hydrogel-assisted polyamide nanofiltration membrane.

[0053] Example 2

[0054] This embodiment provides an innovative method for fabricating polyamide nanofiltration membranes using chitosan hydrogels. This method involves multiple key steps, including PES substrate treatment, hydrogel construction, immersion in piperazine aqueous solution, interfacial polymerization reaction, and thermal curing, as follows:

[0055] (1) Immerse the top surface of the PES substrate in a 0.5 wt% chitosan aqueous solution for 5 minutes. Then, pour out the remaining solution and further remove the excess solution with a rubber roller. Next, add a 0.5 wt% glutaraldehyde aqueous solution to crosslink with chitosan for 1 minute to construct the hydrogel. After that, pour out the remaining solution again and use the rubber roller to further remove the excess solution.

[0056] (2) Immerse the top surface of the PES substrate loaded with hydrogel into an appropriate amount of 0.25 wt% piperazine aqueous solution. After soaking for 2 minutes, pour out the residual solution, and further remove the excess solution with a rubber roller to obtain a PES substrate with the surface filled with piperazine monomers. Subsequently, add a hexane solution containing 0.15 wt% trimesoyl chloride to the surface of the PES substrate with the surface filled with piperazine monomers, and carry out an interfacial polymerization reaction at room temperature for 1 minute, thereby forming a polyamide layer on the top of the hydrogel. Remove the excess organic phase solution to obtain a polyamide nanofiltration precursor membrane.

[0057] (3) Finally, remove the excess organic phase solution. Immediately place the polyamide nanofiltration precursor membrane obtained in step (2) into an oven and carry out thermal curing at a temperature of 60 °C for a curing time of 5 minutes to finally obtain a hydrogel-assisted polyamide nanofiltration membrane.

[0058] Example 3

[0059] This example provides an innovative membrane preparation method for regulating polyamide nanofiltration membranes using chitosan hydrogel. This method covers multiple key steps, including PES substrate treatment, hydrogel construction, soaking in piperazine aqueous solution, interfacial polymerization reaction, and thermal curing, as follows:

[0060] (1) Immerse the top surface of the PES substrate into a 1 wt% chitosan aqueous solution for a soaking time of 5 minutes. Then pour out the residual solution, and further remove the excess solution with a rubber roller. Next, add a 1 wt% glutaraldehyde aqueous solution to crosslink with chitosan for a reaction time of 1 minute to construct the hydrogel. Then pour out the residual solution again and use a rubber roller to further remove the excess solution.

[0061] (2) Immerse the top surface of the PES substrate loaded with hydrogel into an appropriate amount of 0.25 wt% piperazine aqueous solution. After soaking for 2 minutes, pour out the residual solution, and further remove the excess solution with a rubber roller to obtain a PES substrate with the surface filled with piperazine monomers. Subsequently, add a hexane solution containing 0.15 wt% trimesoyl chloride to the surface of the PES substrate with the surface filled with piperazine monomers, and carry out an interfacial polymerization reaction at room temperature for 1 minute, thereby forming a polyamide layer on the top of the hydrogel. Remove the excess organic phase solution to obtain a polyamide nanofiltration precursor membrane.

[0062] (3) Finally, remove the excess organic phase solution. Immediately place the polyamide nanofiltration precursor membrane obtained in step (2) into an oven and carry out thermal curing at a temperature of 60 °C for a curing time of 5 minutes to finally obtain a hydrogel-assisted polyamide nanofiltration membrane.

[0063] Comparative Example 1

[0064] Similar to Example 1, the difference is that step (1) is missing, that is, the hydrogel-assisted interface is missing.

[0065] The specific preparation process is as follows:

[0066] (1) Immerse the top surface of the PES substrate in an appropriate amount of 0.25 wt% piperazine aqueous solution. After soaking for 2 minutes, pour out the residual solution, and further remove the excess solution with a rubber roller to obtain a PES substrate with the surface filled with piperazine monomers. Subsequently, add a hexane solution containing 0.15 wt% trimesoyl chloride to the surface of the PES substrate with the surface filled with piperazine monomers, carry out an interfacial polymerization reaction at room temperature for 1 minute, and remove the excess organic phase solution to obtain a polyamide nanofiltration precursor membrane.

[0067] (2) Immediately put the polyamide nanofiltration precursor membrane obtained in step (1) into an oven and carry out thermal curing at a temperature of 60 °C for a curing time of 5 minutes to finally obtain a hydrogel-assisted polyamide nanofiltration membrane.

[0068] Characterization

[0069] The surface and cross-sectional morphologies of the hydrogel-assisted polyamide nanofiltration membrane obtained in Example 1 were analyzed by field emission scanning electron microscopy (Zeiss Sigma 300, UK) and transmission electron microscopy (FEI Tecnai 12, USA), respectively. Atomic force microscopy (Dimension ICON, Bruker, Germany) was used to determine the surface roughness of the hydrogel-assisted polyamide nanofiltration membrane obtained in Example 1. The surface charge of the nanofiltration membrane was measured using a zeta potential analyzer (SurPASS, Anton Par, Austria). The experimental results are shown in Figure 2 and Figure 3 .

[0070] Experimental results: It was observed by Figure 2 scanning electron microscopy that the control membrane exhibited a typical nodular structure of the polyamide layer. When chitosan hydrogel was introduced, a wrinkled structure appeared on the membrane surface, providing a larger filtration area and contributing to the improvement of the water permeability observed in the modified membrane. Cross-sectional transmission electron microscopy analysis showed that, compared with the control membrane, the hydrogel-assisted strategy resulted in a thinner polyamide layer, which could reduce the water transport resistance and thus increase the water permeability. Although the hydrogel had a certain thickness, the reason for the higher flux could be attributed to the groove effect, which promoted the transport of water through the membrane. Due to the presence of the wrinkled structure, the roughness of the hydrogel-assisted membrane increased compared with the polyamide nanofiltration membrane obtained in Comparative Example 1. The average surface roughness of the polyamide nanofiltration membrane obtained in Comparative Example 1 and Example 2 was 10.6 nm and 12.4 nm, respectively. The improved surface roughness not only increased the effective surface area but also enhanced the water permeability.

[0071] Experimental results: Figure 3The interaction between the hydrogel and piperazine diffusion results in a more negatively charged membrane surface. The abundance of carboxyl groups at low crosslinking degrees further enhances this effect, which is consistent with a more negative zeta potential. Therefore, the higher negatively charged surface corresponds well with the low rejection rate of mineral ions, highlighting the potential for effective separation of mineral ions and perfluorinated compounds.

[0072] Performance Testing

[0073] 1. Feasibility and Stability Advantages in Drinking Water Treatment

[0074] Taking the nanofiltration membrane modified with 0.5 wt% chitosan as an example, the rejection rates of magnesium ions and calcium ions and perfluorinated compounds in tap water medium were tested. The experimental procedure was as follows: Six perfluorinated compounds (perfluorobutyric acid, perfluorobutane sulfonic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluorohexane sulfonic acid, and perfluorooctane sulfonic acid) with a concentration of 50 μg / L added to tap water were used to evaluate the removal efficiency of the nanofiltration membrane. A 4-hour stable filtration period was required before determining the rejection rate. The concentration was quantified using an ultra-high performance liquid chromatography-tandem mass spectrometer (SCIEX 6500+, Shimadzu). Experimental results: The rejection rates of MgCl2 and CaCl2 were 21.7% and 16.4% respectively, and the rejection rates of short-chain perfluorinated compounds and long-chain perfluorinated compounds were 83%-89% and over 90% respectively.

[0075] It can be seen from Figure 4 that among the modified nanofiltration membranes, the perfluorinated compound rejection performance of the hydrogel-assisted polyamide nanofiltration membrane obtained in Example 2 was similar to that of the control membrane. The rejection rate of short-chain PFAS was 83%-89%, and the rejection rate of long-chain PFAS exceeded 90%. The higher negatively charged surface corresponded well with the low rejection rate of mineral ions, highlighting the potential for effective separation of mineral ions and PFAS. The average rejection rate of six typical perfluorinated compounds exceeded 90%.

[0076] It can be seen from Figure 5 that a natural surface water collected from a campus river was used to evaluate the performance of the membrane in retaining mineral salts. The total salt rejection rate decreased with the increase in the hydrogel concentration. Nevertheless, when treating natural water, the modified membrane permeated more mineral elements. Due to the ion competition effect, the reduction of Ca 2+ and Mg 2+ was much smaller. The reason for this phenomenon may be the interference of other components in natural water, such as the complexation of natural organic compounds. For the monovalent ion Na + , the rejection rate gradually decreased with the increase in the hydrogel concentration, which was consistent with the change in the membrane pore size.

[0077] It can be seen from Figure 6It can be seen that a kind of natural surface water collected from the campus river was used to evaluate the performance of the membrane in intercepting natural organic matter. For the interception of natural organic matter in surface water, the rejection rates of all membranes for total organic carbon exceeded 60%, while the rejection rate of UV 254 exceeded 80%. It is worth noting that the increase in the hydrogel concentration had no significant effect on the rejection rate of natural organic matter, indicating the robustness of the modified membrane.

[0078] It can be seen from Figure 7 that during the continuous filtration process of 120 hours, the hydrogel-assisted polyamide nanofiltration membrane obtained in Example 2 showed continuous water permeability and Na2SO4 rejection rate in 1000 ppm Na2SO4 solution, fully demonstrating the remarkable stability of chitosan hydrogel in the polyamide matrix.

[0079] Obviously, the above examples are only for illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An application of a high-selectivity nanofiltration membrane regulated by chitosan hydrogel to separate salt ions and perfluorinated compounds in a mineral salt solution; the high-selectivity nanofiltration membrane comprises a basement membrane, and a hydrogel layer and a polyamide layer respectively arranged on the surface of the basement membrane.

2. The use according to claim 1, characterized in that: The perfluoro compound includes one or more of perfluorobutyric acid, perfluorobutane sulfonic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluorohexane sulfonic acid and perfluorooctane sulfonic acid.

3. The use according to claim 1, characterized in that: The thickness of the hydrogel layer is 30-50 nm; The thickness of the polyamide layer is 25-50 nm.

4. The use according to any one of claims 1 to 3, characterized in that: The high-selectivity nanofiltration membrane regulated by chitosan hydrogel is prepared by the following method: (1) immersing the membrane substrate in a chitosan aqueous solution, adding a glutaraldehyde aqueous solution, and performing a cross-linking reaction to obtain a hydrogel layer on the surface of the membrane substrate; (2) immersing the membrane substrate of the hydrogel layer obtained in step (1) in a piperazine aqueous solution to obtain a PES substrate whose surface is filled with piperazine monomers, and then adding a solution containing trimesoyl chloride to the surface of the PES substrate whose surface is filled with piperazine monomers to perform an interfacial polymerization reaction, thereby forming a polyamide layer on the surface of the hydrogel layer to obtain a polyamide nanofiltration precursor membrane; (3) thermally curing the polyamide nanofiltration precursor membrane obtained in step (2) to obtain the high-selectivity nanofiltration membrane.

5. The use according to claim 4, characterized in that: In step (1), the membrane substrate is selected from a PES substrate and / or a PS substrate; The concentration of the chitosan aqueous solution is 0.25wt%-1wt%; The soaking time is 5-10 minutes.

6. The use according to claim 4, characterized in that: In step (1), the concentration of the glutaraldehyde aqueous solution is 0.25wt%-1wt% ； The cross-linking reaction time is 30s-3min.

7. The use according to claim 4, characterized in that: In step (2), the concentration of the piperazine aqueous solution is 0.25wt%-1wt% ； The soaking time is 1-2 minutes.

8. The use according to claim 4, characterized in that: In step (2), the concentration of trimesoyl chloride in the solution containing trimesoyl chloride is 0.15wt%-0.2wt%; The time of the interfacial polymerization is 30s-1min.

9. The use according to claim 4, characterized in that: In step (2), the solvent containing the trimesoyl chloride solution is n-hexane and / or Isopar-G solvent.

10. The use according to claim 4, characterized in that: In step (3), the thermal curing temperature is 60-80°C and the time is 3-5 minutes.

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