Preparation method of polyamide composite nanofiltration membrane containing polystyrene-polyacrylamide nanosphere intermediate layer

Abstract

The present invention belongs to the technical field of composite membrane material preparation, and particularly relates to a preparation method of a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer. The method comprises the following steps: First, prepare polystyrene-polyacrylamide nanospheres with a core-shell structure by emulsion polymerization; then, dilute the prepared polymer nanospheres in deionized water, perform ultrasonic dispersion, and deposit the polymer nanospheres on the surface of the microfiltration membrane by pressure filtration or suction filtration to construct a nanosphere intermediate layer; finally, prepare a polyamide separation layer on the polymer nanosphere intermediate layer by interfacial polymerization, and then obtain a polyamide composite nanofiltration membrane with a multi-layer structure through heat treatment curing. This method strengthens the ability to store aqueous monomers through the polymer nanosphere intermediate layer with a core-shell structure, effectively regulates the interfacial polymerization process, and thus improves the performance of the polyamide nanofiltration membrane.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite membrane material preparation, and particularly relates to a preparation method of a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nano-microsphere intermediate layer. Background Art

[0002] Membrane separation is a recognized energy-saving and environment-friendly separation technology. Among them, nanofiltration membranes have a nano-scale pore structure and are charged on the surface, with excellent water softening, small molecule pollutant removal, and monovalent / divalent salt separation performance, and have broad application prospects in the fields of seawater desalination, industrial sewage, domestic sewage, drinking water treatment, etc. Constructing a nano-material intermediate layer between the base membrane and the polyamide layer has a good effect on improving the performance of polyamide composite nanofiltration membranes, and is an effective means to solve the "Trade-off" between permeation flux and rejection rate. The team of Livingston constructed an intermediate layer on an ultrafiltration membrane with Cd(OH)2 nanowires, and then prepared a polyamide layer with a thickness of only 10 nm, and the permeability of the membrane was greatly improved (Science, 2015, 348(6241): 1347). Carbon nanotubes, two-dimensional MXene nanosheets, graphene, metal-organic frameworks (MOFs), etc. can also be used as intermediate layer materials to construct polyamide membranes. The nano-material intermediate layer increases the effective permeation area and water channels of the membrane. An appropriate nano-material intermediate layer can play a role in storing monomers, thereby regulating the interfacial polymerization process, preparing a polyamide layer with more controllable structure, and making the membrane have better permeation performance. However, the nano-materials commonly used to construct the intermediate layer at present have complex preparation processes and high production costs, and there is an urgent need to develop simple and economically feasible intermediate layer materials.

[0003] Organic materials have rich functional groups and are easy to modify, and are suitable for constructing intermediate layers. A variety of organic substances such as polydopamine, tannic acid, polyvinyl alcohol, and polyphenols are often used as intermediate layers of polyamide composite nanofiltration membranes. Core-shell structured polymer nano-microspheres are a type of polymer particles with a double-layer or multi-layer structure. Microspheres with a core-shell structure having a nano-scale particle size can be prepared by emulsion polymerization. By selecting polymerization monomers and polymerization methods, the synthesis process can be designed at the molecular level, which is convenient for controlling the particle size and monodispersity, and endowing them with specific functions. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a preparation method of a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nano-microsphere intermediate layer. A macroporous microfiltration base membrane is modified with core-shell structured polystyrene-polyacrylamide nano-microspheres, and then interfacial polymerization is carried out to prepare a polyamide nanofiltration membrane. The polymer nano-microsphere intermediate layer enhances the ability to store aqueous monomers, effectively regulates the interfacial polymerization process, and thus improves the performance of the polyamide nanofiltration membrane.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A preparation method of a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer, comprising the following steps:

[0007] (1) Preparation of polystyrene-polyacrylamide nanospheres: Add an aqueous monomer, an auxiliary agent, an initiator, and a surfactant to deionized water, stir well to form a uniform aqueous solution, then add an oil-phase monomer to the above aqueous solution, continue to stir, after sufficient pre-emulsification, heat to 70 °C for emulsion polymerization reaction, and then add a reaction terminator to the reaction system to stop the polymerization reaction, obtaining a colloidal solution of polystyrene-polyacrylamide nanospheres, and placing it at room temperature for cooling and standby.

[0008] Further, the aqueous monomer is acrylamide (AM), and the mass concentration is 0.1% - 0.5%.

[0009] Further, the auxiliary agent is N,N'-methylenebisacrylamide (MBA), and the mass ratio of MBA to the aqueous monomer is 1:2.

[0010] Further, the initiator is ammonium persulfate (APS), and the mass concentration is 0.05% - 0.2%.

[0011] Further, the surfactant is any one of Span80 or sodium dodecyl ether sulfate sulfonic acid (AES), and the mass concentration is 0.05% - 0.3%.

[0012] Further, the oil-phase monomer is one or a mixture of two of styrene (St) or divinylbenzene; the mass ratio of the oil-phase monomer to the aqueous solution is 1:8 - 1:4.

[0013] Further, the time of the emulsion polymerization reaction is 2 - 4 h; the reaction terminator is vitamin C (VC), and the mass concentration is 0.5% - 1%.

[0014] (2) Microfiltration membrane pretreatment: Put the microfiltration membrane into deionized water and soak it sufficiently to remove impurities on the surface and in the pores of the microfiltration membrane.

[0015] Further, the material of the microfiltration membrane is any one of mixed cellulose esters, polyethersulfone, or polysulfone, and the average pore diameter of the microfiltration membrane is 0.1 - 0.5 μm.

[0016] (3) Take an appropriate amount of the colloidal solution obtained in step (1), dissolve it in deionized water, disperse it evenly by ultrasonic wave, then use a filtration device to deposit the polystyrene-polyacrylamide nanospheres in the solution onto the surface of the pretreated microfiltration membrane by suction filtration or pressure filtration, and then rinse it with deionized water, and place it at room temperature to dry until there are no obvious water drops on the surface.

[0017] Further, the volume ratio of the colloidal particle solution to deionized water is 1:1000; the deposition amount of the polystyrene-polyacrylamide nanospheres on the surface of the microfiltration membrane is 0.1 - 1.0 mg / cm 2 .

[0018] (4) The surface of the microfiltration membrane with deposited polystyrene-polyacrylamide nanospheres obtained in step (3) is first fully soaked with an aqueous solution of amine monomer, and the excess solution on the surface of the microfiltration membrane is removed by purging with compressed air. Then, it is fully soaked with a hexane solution of the organic phase monomer, and the excess solution is removed by purging. Finally, heat treatment is carried out to obtain a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer.

[0019] Further, the amine monomer is any one of piperazine (PIP), ethylenediamine (EDA), or polyethyleneimine (PEI), and the mass concentration is 0.1% - 2%.

[0020] Further, the organic phase monomer is trimesoyl chloride (TMC), and the mass concentration is 0.05% - 0.5%.

[0021] Further, the heat treatment is as follows: put it into an oven and heat at 50 - 90 °C for 3 - 10 min.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The core-shell structured polystyrene-polyacrylamide nanospheres are prepared by the soap-free emulsion polymerization method. The large-pore microfiltration substrate membrane is modified with polymer microspheres, and then interfacial polymerization is carried out to prepare a polyamide nanofiltration membrane. The polystyrene core makes the nanospheres have a stable structure, while the longer polyacrylamide chain segments in the outer layer can make the polymer microspheres with smaller particle sizes spread on the surface of the large-pore substrate membrane, facilitating the subsequent interfacial polymerization reaction, thereby realizing the preparation of the composite nanofiltration membrane.

[0024] 2. The polyacrylamide shell improves the hydrophilicity of the nanospheres, can store the aqueous phase monomer, and effectively regulates the interfacial polymerization process. The preparation process of the core-shell structured polymer nanospheres used in the present invention is simple and low-cost, providing a new technical route for constructing the intermediate layer of the polyamide composite nanofiltration membrane. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the preparation process of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer;

[0026] Figure 2 It is a schematic diagram of the preparation process of the polystyrene-polyacrylamide nanospheres;

[0027] Figure 3 It is a TEM image of the polystyrene-polyacrylamide nanospheres;

[0028] Figure 4 It is the particle size distribution diagram of polystyrene - polyacrylamide nanospheres;

[0029] Figure 5 It is the SEM image of the mixed cellulose ester microfiltration membrane;

[0030] Figure 6 It is the SEM image of polystyrene - polyacrylamide nanospheres deposited on the surface of the microfiltration membrane;

[0031] Figure 7 It is the SEM image of the polyamide composite nanofiltration membrane containing a polystyrene - polyacrylamide nanosphere interlayer;

[0032] Figure 8 It is the pure water contact angle of the MCE membrane, MCE - PNs membrane and MCE - PNs - PA membrane in Example 1;

[0033] Figure 9 It is the rejection rate of the polyamide composite nanofiltration membrane prepared in Example 1 for polyethylene glycol (PEG) with different molecular weights. Detailed implementation mode

[0034] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but it is not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

[0035] Example 1

[0036] A preparation method of a polyamide composite nanofiltration membrane containing a polystyrene - polyacrylamide nanosphere interlayer, the schematic diagram of the preparation process is as Figure 1 shown, and it includes the following steps:

[0037] (1) Dissolve 0.5 g of AM, 0.25 g of MBA, 0.15 g of APS and 0.23 g of AES in 100 ml of deionized water under stirring, stir for 30 min to make a uniform aqueous phase; similarly under stirring, add 15 g of St to the aqueous phase solution, pre - emulsify for 60 min, then heat to 70 °C, carry out emulsion polymerization reaction for 120 min, and then add 0.5 g of VC to the reaction system to terminate the polymerization reaction. After the prepared solution is cooled at room temperature, centrifuge it at 13000 revolutions per minute for 30 min, the large - particle - size colloidal particles are separated at the bottom, and take the upper - layer colloidal particle solution of polystyrene - polyacrylamide nanospheres for standby.

[0038] (2) Immerse a mixed cellulose ester microfiltration membrane with an average pore size of 0.22 μm (denoted as MCE) in deionized water at 70 °C for 24 h, changing the water 3 times during the process to thoroughly remove impurities on the membrane surface and in the pores. Take 1 mL of the colloidal particle solution prepared in step (1) (the content of polymer nanospheres is 30 mg / mL) and dissolve it in 1000 mL of deionized water, ultrasonically treat it for 30 min, and use a filtration device to pressure-filter the above-diluted solution onto the surface of the microfiltration membrane (the effective area of the membrane is 177 cm 2 , the operating pressure is 0.1 MPa, and the deposition amount of polymer nanospheres is 0.17 mg / cm 2 ), and then rinse it with 2000 mL of deionized water to obtain a microfiltration membrane modified with polystyrene-polyacrylamide nanospheres, denoted as MCE-PNs.

[0039] (3) Air-dry the microfiltration membrane deposited with polystyrene-polyacrylamide nanospheres obtained in step (2) at room temperature until there are no obvious water droplets on the surface, then fix the microfiltration membrane using a polytetrafluoroethylene mold, immerse the membrane surface in a 1% PIP aqueous solution for 3 min, then use compressed air at 0.2 MPa to blow and remove the excess solution on the membrane surface, immediately immerse the membrane surface in a n-hexane solution of 0.1% TMC, after reacting for 15 s, remove the excess solution, and finally place it in an oven and heat-treat it at 60 °C for 5 min to obtain a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer, denoted as MCE-PNs-PA.

[0040] Figure 2 is a schematic diagram of the preparation process of polystyrene-polyacrylamide nanospheres. In the emulsion polymerization system, under the sufficient emulsification of the surfactant, the mixed solution presents an oil-in-water emulsion state. The AM aqueous solution is the continuous phase, and St is stably dispersed in the continuous phase through the AES surfactant. This polymerization characteristic makes the prepared colloidal particles have a core-shell heterogeneous structure, where the core is mainly composed of styrene segments, and the shell is mainly composed of acrylamide segments. Therefore, the prepared polymer colloidal particles have good hydrophilic functions. Figure 3 is the TEM image of polystyrene-polyacrylamide nanospheres. It can be seen that the nanospheres have an obvious core-shell structure, and the inner core of the sphere is darker in color in the TEM image, while the outer layer is lighter in color. Figure 4 is the particle size distribution diagram of polymer nanospheres measured by a laser particle size analyzer. It can be obtained that the particle size distribution is relatively concentrated, and the average particle size is 125.5 nm. The particle size distribution measured by the laser particle size analyzer is larger than the particle size observed by TEM. This is because the polymer nanospheres are dispersed in water for particle size measurement, and the acrylamide segments on the surface layer affect the particle size measurement results, while in the TEM measurement, the free acrylamide segments on the surface layer cannot be detected.

[0041] Figure 5SEM image of the mixed cellulose ester microfiltration membrane. It can be seen that the microfiltration membrane has an obvious macroporous honeycomb structure, and the pore size is not uniform. Figure 6 SEM image of the microfiltration membrane modified with polymer nanospheres. The clear spherical morphology of the polymer nanospheres can be observed, and the microspheres are evenly spread on the surface of the microfiltration membrane. Constructing a polystyrene-polyacrylamide nanosphere intermediate layer can well improve the macroporous structure of the membrane surface, facilitating subsequent interfacial polymerization reactions. Figure 7 SEM image of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer. The polyamide layer completely covers the polymer nanosphere layer, and the membrane surface is uneven, greatly increasing the effective membrane area of the polyamide membrane, which has a positive effect on improving the permeation performance.

[0042] Figure 8 Pure water contact angles of the MCE membrane, MCE-PNs membrane, and MCE-PNs-PA membrane in this example. As can be seen from the figure, after the polymer nanospheres are deposited on the surface of the microfiltration membrane, the hydrophilicity becomes worse. However, after the interfacial polymerization reaction, the hydrophilicity of the prepared polyamide composite nanofiltration membrane is greatly improved, showing good hydrophilicity.

[0043] A self-made cross-flow flat membrane test device was used to evaluate the performance of the prepared polyamide composite nanofiltration membrane. The operating pressure was 0.1 - 0.6 MPa. After a stable pre-pressurization for 30 min, tests were carried out to measure the pure water flux, salt solution flux, and inorganic salt rejection rate (Na2SO4, MgSO4, MgCl2, NaCl) of the nanofiltration membrane. The salt concentration of the inorganic salt solution was determined by measuring the conductivity with a conductivity meter and then fitting it with a standard curve. At an operating pressure of 0.5 MPa, the pure water flux of the polyamide composite nanofiltration membrane was 18.9 L·m -2 ·h -1 ·bar -1 , and the flux and rejection rate of the 2000 ppm inorganic salt solution are shown in Table 1.

[0044] Table 1: Inorganic salt solution flux and rejection rate of the polyamide composite nanofiltration membrane

[0045] Types of inorganic salts <![CDATA[Flux / L·m -2 ·h -1 ·bar -1 > Rejection rate / % Sodium sulfate 13.1 96.4 Magnesium sulfate 16.4 91.0 Sodium chloride 18.3 25.1 Magnesium chloride 13.7 87.1

[0046] As can be seen from the results, the prepared polyamide composite nanofiltration membrane has good separation performance for monovalent / divalent salts.

[0047] The rejection effect of small molecule organic substances is also one of the important indicators for evaluating the performance of nanofiltration membranes. The rejection rates of the nanofiltration membrane for polyethylene glycol with different molecular weights (200, 300, 400, 600, and 1000 Da) were measured through experiments, and the results are shown in Table 2.

[0048] Table 2: Rejection Rates of Polyamide Composite Nanofiltration Membrane for Polyethylene Glycols with Different Molecular Weights

[0049] Molecular weight of polyethylene glycol / Da Rejection rate / % 200 71.1 300 80.2 400 87.5 600 92.7 1000 95.5

[0050] As can be seen from Table 2, the polyamide composite nanofiltration membrane prepared in the present invention has good rejection effect on small molecule organic substances. Usually, the molecular weight of polyethylene glycol with a rejection rate of 90% is used as the effective rejection molecular weight of the nanofiltration membrane. The rejection molecular weight of the polyamide composite nanofiltration membrane can be obtained by fitting as 476 Da, as Figure 9 shown.

[0051] Example 2

[0052] Compared with Example 1, in step (2), 2 mL of the polymer nanosphere solution was diluted in 2000 mL of deionized water, and after ultrasonic treatment, it was filtered onto the surface of the base membrane. The deposition amount of the polymer nanospheres on the microfiltration membrane was 0.34 mg / cm 2 , and other experimental steps were the same as those in Example 1.

[0053] The prepared polyamide composite nanofiltration membrane was subjected to performance testing. The pure water flux was 16.3 L·m -2 ·h -1 ·bar -1 , and the fluxes and rejection rates of the 2000 ppm inorganic salt solution are shown in Table 3.

[0054] Table 3: Fluxes and Rejection Rates of Polyamide Composite Nanofiltration Membrane for Inorganic Salt Solution

[0055] Types of inorganic salts <![CDATA[Flux / L·m -2 ·h -1 ·bar -1 > Rejection rate / % Sodium sulfate 12.7 97.4 Magnesium sulfate 15.9 92.3 Sodium chloride 17.7 30.1 Magnesium chloride 12.6 88.9

[0056] Example 3

[0057] Compared with Example 1, in step (3), the mass concentration of the PIP aqueous solution used for interfacial polymerization was 0.5%, and other experimental steps were the same as those in Example 1.

[0058] The prepared polyamide composite nanofiltration membrane was subjected to performance testing. The pure water flux was 20.6 L·m -2 ·h -1 ·bar -1 , and the fluxes and rejection rates of the 2000 ppm inorganic salt solution are shown in Table 4.

[0059] Table 4: Fluxes and Rejection Rates of Polyamide Composite Nanofiltration Membrane for Inorganic Salt Solution

[0060] Types of inorganic salts <![CDATA[Flux / L·m -2 ·h -1 ·bar -1 > Rejection rate / % Sodium sulfate 16.5 94.7 Magnesium sulfate 18.3 89.6 Sodium chloride 20.3 22.9 Magnesium chloride 15.7 85.9

[0061] Example 4

[0062] Compared with Example 1, in step (3), the mass concentration of the hexane solution of TMC used for interfacial polymerization is 0.3%, and other experimental steps are the same as those in Example 1.

[0063] The performance of the prepared polyamide composite nanofiltration membrane was tested. The pure water flux was 18.0 L·m -2 ·h -1 ·bar -1 , and the fluxes and rejection rates of the 2000 ppm inorganic salt solution are shown in Table 5.

[0064] Table 5: Fluxes and rejection rates of inorganic salt solutions of polyamide composite nanofiltration membranes

[0065] Types of inorganic salts <![CDATA[Flux / L·m -2 ·h -1 ·bar -1 > Rejection rate / % Sodium sulfate 12.6 95.6 Magnesium sulfate 17.3 91.6 Sodium chloride 17.9 26.3 Magnesium chloride 12.9 85.6

[0066] Example 5

[0067] Compared with Example 1, in step (2), the base membrane used was a polyethersulfone microfiltration membrane with an average pore size of 0.22 μm, and other experimental steps were the same as those in Example 1.

[0068] The performance of the prepared polyamide composite nanofiltration membrane was tested. The pure water flux was 14.7 L·m -2 ·h -1 ·bar -1 , and the fluxes and rejection rates of the 2000 ppm inorganic salt solution are shown in Table 6. Compared with Example 1, both the permeability and the inorganic salt rejection rate of the nanofiltration membrane decreased slightly, and the rejection rate trend was the same, showing the rejection characteristics of the poly(piperazine amide) nanofiltration membrane. It shows that the method of constructing a polyamide composite nanofiltration membrane with core-shell structured polymer nanospheres as the intermediate layer is feasible for different microfiltration base membranes.

[0069] Table 6: Fluxes and rejection rates of inorganic salt solutions of polyamide composite nanofiltration membranes

[0070] Types of inorganic salts <![CDATA[Flux / L·m -2 ·h -1 ·bar -1 > Rejection rate / % Sodium sulfate 12.6 93.3 Magnesium sulfate 13.5 90.2 Sodium chloride 14.2 22.2 Magnesium chloride 13.6 58.3

[0071] Comparative Example 1

[0072] Compared with Example 1, the 0.22 μm mixed cellulose ester microfiltration membrane was directly soaked and cleaned, and then the interfacial polymerization reaction in step (3) was carried out without depositing polymer nanospheres on the microfiltration membrane. Other experimental steps were the same as those in Example 1.

[0073] The performance of the prepared polyamide composite nanofiltration membrane was tested. The pure water flux was 15.8 L·m -2 ·h -1 ·bar -1, the inorganic salt solution fluxes and rejection rates at 2000 ppm are shown in Table 7. Both the permeability of the nanofiltration membrane and the inorganic salt rejection rate are significantly lower than those in Example 1, indicating that constructing a polymer nanosphere interlayer between the microfiltration substrate membrane and the polyamide layer in Example 1 can effectively improve the performance of the nanofiltration membrane.

[0074] Table 7: Inorganic salt solution fluxes and rejection rates of polyamide composite nanofiltration membranes

[0075]

[0076]

Claims

1. A method for preparing a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer, characterized in that, It includes the following steps: (1) Preparation of polystyrene-polyacrylamide nanospheres: Add aqueous phase monomers, additives, initiators, and surfactants into deionized water, stir well to make a uniform aqueous solution, then add oil phase monomers into the above aqueous solution, continue to stir, after sufficient pre-emulsification, heat to 70 °C for emulsion polymerization reaction, then add a reaction terminator into the reaction system to stop the polymerization reaction, obtain a colloidal solution of polystyrene-polyacrylamide nanospheres, and place it at room temperature for cooling and standby; (2) Pretreatment of the microfiltration membrane: Immerse the microfiltration membrane in deionized water for sufficient soaking to remove impurities on the surface and in the pores of the microfiltration membrane; (3) Take an appropriate amount of the colloidal solution obtained in step (1), dissolve it in deionized water, disperse it evenly by ultrasonic wave, then use a filtration device to deposit polystyrene-polyacrylamide nanospheres in the solution onto the surface of the pretreated microfiltration membrane, and then rinse it with deionized water, and place it at room temperature to air dry until there are no obvious water droplets on the surface; (4) First, soak the surface of the microfiltration membrane deposited with polystyrene-polyacrylamide nanospheres obtained in step (3) with an aqueous solution of amine monomer, blow to remove the excess solution on the surface, then soak it with a n-hexane solution of organic phase monomer, blow to remove the excess solution on the surface, and finally perform heat treatment to obtain a polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer.

2. The preparation method of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer according to claim 1, characterized in that In step (1), the aqueous phase monomer is acrylamide, and the mass concentration is 0.1%-0.5%; and / or, the additive is N,N'-methylenebisacrylamide, and the mass ratio of N,N'-methylenebisacrylamide to the aqueous phase monomer is 1:2; and / or, the initiator is ammonium persulfate, and the mass concentration is 0.05%-0.2%; and / or, the surfactant is any one of Span80 or sodium dodecyl ether sulfate sulfonate, and the mass concentration is 0.05%-0.3%.

3. The preparation method of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer according to claim 1, characterized in that, In step (1), the oil phase monomer is one or a mixture of two of styrene or divinylbenzene; the mass ratio of the oil phase monomer to the aqueous solution is 1:8-1:

4.

4. The preparation method of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer according to claim 1, characterized in that, In step (1), the time of the emulsion polymerization reaction is 2-4 h; the reaction terminator is vitamin C, and the mass concentration is 0.5%-1%.

5. The preparation method of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer according to claim 1, characterized in that, In step (2), the material of the microfiltration membrane is any one of mixed cellulose esters, polyethersulfone or polysulfone, and the average pore size of the microfiltration membrane is 0.1-0.5 μm.

6. The preparation method of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer according to claim 1, characterized in that, In step (3), the volume ratio of the colloidal particle solution to deionized water is 1:1000; the deposition amount of the polystyrene-polyacrylamide nanospheres on the surface of the microfiltration membrane is 0.1-1.0 mg / cm 2 .

7. The preparation method of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere intermediate layer according to claim 1, characterized in that, In step (3), the method of using the filtration device to deposit polystyrene-polyacrylamide nanospheres onto the surface of the pretreated microfiltration membrane is any one of suction filtration or pressure filtration.

8. The preparation method of the polyamide composite nanofiltration membrane containing a polystyrene-polyacrylamide nanosphere interlayer according to claim 1, characterized in that, In step (4), the amine monomer is any one of piperazine, ethylenediamine or polyethyleneimine, and the mass concentration is 0.1%-2%; and / or, the organic phase monomer is trimesoyl chloride, and the mass concentration is 0.05%-0.5%; and / or, the heat treatment is: put it into an oven and heat at 50-90 °C for 3-10 min.

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