A kind of membrane pore dynamic expansion nanofiltration membrane and its preparation method, use method and application

Abstract

The application provides a membrane hole dynamic expansion nanofiltration membrane and a preparation method, use method and application thereof, the membrane hole dynamic expansion nanofiltration membrane comprises a porous polymer matrix membrane and an oxidized graphene-pyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane; the membrane hole dynamic expansion nanofiltration membrane is prepared by sequentially performing suction filtration and reduction reaction on the porous polymer matrix membrane with a mixed solution containing pyrrole nanoparticles and oxidized graphene; by selecting and adjusting the electrode potential applied to the membrane hole dynamic expansion nanofiltration membrane, the membrane hole dynamic expansion can be realized in an electrochemical control mode, and the desalination performance of the nanofiltration membrane can be adjusted in situ, so that the application in water treatment can be realized; the application has the advantages of simple preparation process, wide application potential and the like.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a nanofiltration membrane with dynamically expandable pores, its preparation method, usage method, and application. Background Technology

[0002] Currently, membrane technology is an important technology in the field of water treatment, with wide applications in wastewater treatment, resource recovery, and seawater desalination. Among these applications, the desalination efficiency of water treatment membranes is a crucial indicator.

[0003] CN108745003A discloses a direct drinking water treatment membrane containing graphene microsheets and its preparation method. This method involves interfacial polymerization of m-phenylenediamine and trimesoyl chloride on the surface of a porous ceramic substrate to generate a polyamide desalination layer. Then, a series of processes are performed: coating with polyacrylamide adhesive, depositing graphene microsheets, coating with polyacrylamide adhesive again, depositing graphene microsheets, and finally laser drying and curing to obtain the direct drinking water treatment membrane. Compared with traditional methods, the direct drinking water treatment membrane prepared by this method uses polyacrylamide adhesive to fix the graphene microsheets to the initial state of the membrane, ensuring the high specific surface area and excellent adsorption and purification capacity of the graphene microsheets. When used for direct drinking water treatment, the multi-layered composite membrane allows for synergistic purification and adsorption, effectively adsorbing a large amount of nanoscale impurities in the water and ensuring drinking water safety. However, with prolonged operation, the desalination effect of the above-mentioned direct drinking water treatment membrane will significantly decrease.

[0004] CN105833743A discloses an aromatic polyamide reverse osmosis membrane modified with graphene oxide coating and its preparation method. The reverse osmosis membrane comprises four parts: a substrate support layer, a porous intermediate support layer, an ultrathin dense separation layer, and a graphene oxide coating; the thickness of the graphene oxide coating is 50-150 nm. This aromatic polyamide reverse osmosis membrane with graphene oxide coating, by coating graphene oxide onto the surface of the dense separation layer, can effectively improve the desalination rate, antifouling performance, and chlorine resistance of the composite reverse osmosis membrane, while reducing the required operating pressure. However, the retention effect of the above-mentioned aromatic polyamide reverse osmosis membrane with graphene oxide coating decreases with prolonged operation, resulting in a reduction in desalination efficiency.

[0005] With the development of high-tech industries and the increasing demand for a better life, the development of nanofiltration membranes with dynamically expandable pores can meet specific needs. For example, in zero-discharge industrial wastewater treatment and seawater desalination, the retention efficiency of commercial nanofiltration membrane modules decreases over time, leading to reduced desalination. Nanofiltration membranes with dynamically expandable pores can improve salt rejection by reducing pore size, thus restoring the membrane's desalination effect. Similarly, in drinking water purification products, there are scenarios where mineral water and purified water need to be switched at any time to meet residents' drinking water needs; this can also be achieved through membrane pore expansion. More importantly, the development of similar materials can achieve specific purposes such as mitigating membrane fouling, timed drug release, and dynamic selective separation. However, the pore size of traditional membrane materials such as polyamide is fixed once prepared and cannot be dynamically adjusted according to external stimuli, thus failing to meet the application requirements of the aforementioned scenarios. Furthermore, nanofiltration membranes with expandable pores require molecular-level design of nanoscale pores to ensure their stability and safety.

[0006] Therefore, there is an urgent need in this field to develop a novel nanofiltration membrane with dynamic pore expansion and contraction characteristics, thereby enabling dynamic adjustment of desalination performance. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a dynamically stretchable nanofiltration membrane, its preparation method, usage method and application. The dynamically stretchable nanofiltration membrane comprises a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The dynamically stretchable nanofiltration membrane is prepared by sequentially subjecting a mixed solution containing polypyrrole nanoparticles and graphene oxide to a porous polymer matrix membrane through filtration and reduction reactions. By selecting and adjusting the electrode potential applied to the dynamically stretchable nanofiltration membrane, the dynamic stretching and contraction of the membrane pores can be achieved through electrochemical control, thereby adjusting the desalination performance of the nanofiltration membrane in situ, and it can be applied to water treatment. The present invention has the advantages of simple preparation process and broad application potential.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] One of the objectives of this invention is to provide a dynamically stretchable nanofiltration membrane, which includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane.

[0010] The working principle of the dynamically stretchable nanofiltration membrane of the present invention is as follows: the porous polymer matrix membrane provides mechanical support for the graphene oxide-polypyrrole nanoparticle composite membrane, thereby improving its stability; while the graphene oxide-polypyrrole nanoparticle composite membrane, as the main key structure, has the structural feature of polypyrrole nanoparticles embedded between layered graphene. Graphene has stable and reliable layered nanochannels, and the area between the graphene sheets is the water channel. Therefore, the interlayer spacing of graphene is its membrane pore size. The volume of polypyrrole is affected by electrical stimulation. Under reduction potential, cations in the electrolyte solution intercalate into polypyrrole, increasing its volume and thus the interlayer spacing of graphene. This leads to an increase in the pore size of the graphene oxide-polypyrrole nanoparticle composite membrane, thereby reducing the desalination effect of the nanofiltration membrane. Under oxidation potential, cations in the electrolyte solution desorb from polypyrrole, decreasing its volume and thus the interlayer spacing of graphene. This results in a decrease in the pore size of the graphene oxide-polypyrrole nanoparticle composite membrane, thereby improving the desalination effect of the nanofiltration membrane. Therefore, this invention, by selecting and adjusting the electrode potential applied to the dynamically expanding and contracting nanofiltration membrane, can achieve dynamic expansion and contraction of the membrane pores through electrochemical regulation, thereby adjusting the desalination performance of the nanofiltration membrane in situ and applying it to water treatment.

[0011] As a preferred technical solution of the present invention, the thickness of the porous polymer matrix membrane is 100~200μm, for example 100μm, 110μm, 130μm, 140μm, 150μm, 160μm, 170μm, 190μm or 200μm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0012] Preferably, the pore size of the porous polymer matrix membrane is 80~120nm, such as 80nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 115nm or 120nm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0013] Preferably, the polymer of the porous polymer matrix membrane includes any one of polyvinylidene fluoride, polyethersulfone, cellulose acetate and polyamide, with polyvinylidene fluoride being the most preferred.

[0014] Preferably, the pore size of the graphene oxide-polypyrrole nanoparticle composite film is 7~15Å, such as 7Å, 8Å, 9Å, 10Å, 11Å, 12Å, 13Å, 14Å or 15Å, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0015] Preferably, the thickness of the graphene oxide-polypyrrole nanoparticle composite film is 50~200nm, such as 50nm, 70nm, 90nm, 100nm, 110nm, 130nm, 150nm, 180nm or 200nm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0016] Preferably, the graphene oxide-polypyrrole nanoparticle composite film is doped with large-volume anions.

[0017] It is worth noting that the graphene oxide-polypyrrole nanoparticle composite film of the present invention is specifically doped with large-volume anions, which are then doped with large-volume anions in the polypyrrole nanoparticles, and then the polypyrrole nanoparticles doped with large-volume anions form a graphene oxide-polypyrrole nanoparticle composite film with graphene.

[0018] Preferably, the bulky anion includes any one of alkylbenzene sulfonate ions, alkyl sulfonate ions, and alkyl sulfate ions; the alkyl group is a C9-C12 alkyl group.

[0019] It is worth noting that this invention further incorporates bulk anions into the graphene oxide-polypyrrole nanoparticle composite film. The poor migration properties of these bulk anions within polypyrrole enhance the overall dynamic expansion and contraction properties of the membrane pores under electrical stimulation. Specifically, because the bulk anions are bound to the polypyrrole, they do not migrate when an oxidation potential is applied, while cations are exchanged into the electrolyte solution. This shortens the distance between the chains in the polypyrrole, resulting in a reduction in the volume of the polypyrrole. As the graphene layer size decreases, the interlayer spacing of the graphene oxide decreases, resulting in a smaller pore size in the graphene oxide-polypyrrole nanoparticle composite membrane, thereby improving the desalination effect of the nanofiltration membrane. When a reduction potential is applied, the anions are fixed in the polymer due to their larger volume. To maintain charge balance, the cations in the electrolyte solution enter the graphene oxide-polypyrrole nanoparticle composite membrane, causing the polypyrrole to expand. This increase in polypyrrole volume leads to an increase in the interlayer spacing of the graphene oxide, resulting in an increase in the pore size of the graphene oxide-polypyrrole nanoparticle composite membrane, thereby reducing the desalination effect of the nanofiltration membrane.

[0020] Preferably, the alkylbenzene sulfonate ion is a dodecylbenzene sulfonate ion.

[0021] Preferably, the alkyl sulfate ion is a dodecyl sulfate ion.

[0022] Preferably, the alkyl sulfonate ion is a dodecyl sulfonate ion.

[0023] A second objective of this invention is to provide a method for preparing the dynamically stretchable nanofiltration membrane described in the first objective, the method comprising the following steps:

[0024] (1) Prepare a mixed solution containing polypyrrole nanoparticles and graphene oxide;

[0025] (2) The mixed solution described in step (1) is filtered to form a graphene oxide-polypyrrole nanoparticle composite membrane on a porous polymer matrix membrane;

[0026] (3) The graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) is subjected to a reduction reaction to obtain a membrane pore dynamic stretching nanofiltration membrane.

[0027] The preparation method of this invention requires first preparing polypyrrole nanoparticles, and then mixing them with graphene oxide to obtain a clear solution after complete dissolution. This effectively ensures that the polypyrrole nanoparticles and graphene oxide are uniformly distributed in the solution, thereby ensuring that the polypyrrole nanoparticles can be embedded between the layered graphene during subsequent preparation. Furthermore, the preparation method of this invention uses vacuum filtration to form a graphene oxide-polypyrrole nanoparticle composite film on a porous polymer matrix membrane. This effectively ensures that water molecules in the clear mixed solution after complete dissolution of polypyrrole nanoparticles can permeate through the porous polymer matrix membrane, while graphene oxide and polypyrrole nanoparticles are retained and uniformly distributed on the porous polymer matrix membrane to form the graphene oxide-polypyrrole nanoparticle composite film.

[0028] As a preferred technical solution of the present invention, in step (1), the polypyrrole nanoparticles are obtained by the following preparation method: adding pyrrole solution to ferric chloride solution and mixing evenly, adding hydrogen peroxide solution dropwise to carry out polymerization reaction, and obtaining the polypyrrole nanoparticles by evaporating the solvent.

[0029] It is worth noting that, compared to existing technologies that directly use ferric ions for polymerization, the preparation method described in this invention uses ferrous ions and an excess of hydrogen peroxide solution. On the one hand, the hydrogen peroxide solution can oxidize ferrous ions to form ferric ions, ensuring the polymerization reaction of pyrrole. On the other hand, the unreacted hydrogen peroxide solution will peroxidize the already generated polypyrrole molecules, introducing hydrophilic functional groups such as hydroxyl and carboxyl groups into the polypyrrole molecules. This can improve the solubility of polypyrrole nanoparticles in aqueous solution, facilitating the subsequent preparation of polypyrrole solutions of any concentration, thereby forming a uniform mixed solution of graphene oxide and polypyrrole. This provides a guarantee for the subsequent preparation of a dynamically stretchable nanofiltration membrane with a uniform and defect-free surface.

[0030] Preferably, the concentration of the ferric chloride solution is 2~4 mg / mL, such as 2 mg / mL, 2.2 mg / mL, 2.5 mg / mL, 2.8 mg / mL, 3 mg / mL, 3.2 mg / mL, 3.5 mg / mL, 3.8 mg / mL or 4 mg / mL, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0031] Preferably, the concentration of the pyrrole solution is 97~99 wt%, such as 97 wt%, 97.2 wt%, 97.5 wt%, 97.8 wt%, 98 wt%, 98.2 wt%, 98.5 wt%, 98.8 wt%, or 99 wt%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0032] Preferably, the concentration of the hydrogen peroxide solution is 35-45 wt%, such as 35 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, or 45 wt%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0033] Preferably, the mass ratio of the solutes in the pyrrole solution, the ferric chloride solution, and the hydrogen peroxide solution is 1:(0.1~0.5):(3~4), such as 1:0.1:3, 1:0.3:3, 1:0.5:3, 1:0.1:3.5, 1:0.3:3.5, 1:0.5:3.5, 1:0.1:4, 1:0.3:4, or 1:0.5:4, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0034] Preferably, the polymerization reaction temperature is -5 to -10°C, such as -5°C, -5.5°C, -6°C, -6.5°C, -7°C, -7.5°C, -8°C, -8.5°C, -9°C, or -10°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0035] Preferably, the polymerization reaction time is 8 to 12 hours, such as 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours or 12 hours, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0036] As a preferred technical solution of the present invention, in step (1), the polypyrrole nanoparticles are polypyrrole nanoparticles doped with large-volume anions.

[0037] Preferably, the polypyrrole nanoparticles doped with bulk anions are obtained by the following preparation method: pyrrole solution and bulk anion solution are added to ferric chloride solution and mixed evenly, hydrogen peroxide solution is added dropwise to carry out a polymerization reaction, and the polypyrrole nanoparticles doped with bulk anions are obtained by evaporating the solvent.

[0038] Preferably, the mass ratio of solute to the pyrrole solution and the bulk anionic solution is 1:(0.02~0.04), for example, 1:0.02, 1:0.025, 1:0.027, 1:0.029, 1:0.03, 1:0.031, 1:0.033, 1:0.035 or 1:0.04, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0039] Preferably, the concentration of the large-volume anionic solution is 0.3~0.6 mg / mL, such as 0.3 mg / mL, 0.35 mg / mL, 0.38 mg / mL, 0.4 mg / mL, 0.42 mg / mL, 0.45 mg / mL, 0.5 mg / mL, 0.55 mg / mL or 0.6 mg / mL, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] It is worth noting that, compared to the preparation method of simple polypyrrole nanoparticles, the preparation method of polypyrrole nanoparticles doped with large-volume anions described in this invention adds large-volume anions in the form of surfactants, while the addition of ferric chloride solution and hydrogen peroxide solution, the polymerization reaction temperature, and other parameters are the same; moreover, the preparation method requires controlling the mass ratio of solutes corresponding to pyrrole solution and large-volume anion solution to 1:(0.02~0.04). Only within this ratio range can the subsequently prepared graphene oxide-polypyrrole nanoparticle composite film have better conductivity.

[0041] As a preferred technical solution of the present invention, in step (1), the mixed solution is obtained by uniformly mixing polypyrrole nanoparticle solution and graphene oxide solution.

[0042] Preferably, the concentration of the polypyrrole nanoparticle solution is 0.1~0.5 mg / mL, such as 0.1 mg / mL, 0.15 mg / mL, 0.2 mg / mL, 0.25 mg / mL, 0.3 mg / mL, 0.35 mg / mL, 0.4 mg / mL, 0.45 mg / mL or 0.5 mg / mL, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0043] Preferably, the concentration of the graphene oxide solution is 1~2 mg / mL, such as 1 mg / mL, 1.2 mg / mL, 1.3 mg / mL, 1.4 mg / mL, 1.5 mg / mL, 1.6 mg / mL, 1.7 mg / mL, 1.8 mg / mL or 2 mg / mL, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0044] Preferably, the mass ratio of the solute to the graphene oxide solution and the polypyrrole nanoparticle solution is 1:(5~10), such as 1:5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9 or 1:10, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0045] It is worth noting that in the preparation method described in this invention, the mass ratio of the solutes corresponding to the graphene oxide solution and the polypyrrole nanoparticle solution is 1:(5~10). In the prepared dynamically stretchable nanofiltration membrane, the mass ratio of graphene to polypyrrole in the graphene oxide-polypyrrole nanoparticle composite membrane is also 1:(5~10). The two ratios are basically the same because the reduction process has little effect on the two ratios.

[0046] It is worth noting that the graphene oxide-polypyrrole nanoparticle composite film of the present invention needs to control the mass ratio of graphene to polypyrrole to be 1:(5~10) to effectively ensure the in-situ adjustability of the dynamic expansion and contraction of the membrane pores. If the mass ratio of graphene to polypyrrole is less than 1:5, that is, the mass of polypyrrole is less, the number of polypyrrole nanoparticles that can respond to electrical stimulation between graphene sheets will be less, resulting in a weaker control over the interlayer spacing of graphene. If the mass ratio of graphene to polypyrrole is greater than 1:10, that is, the mass of polypyrrole is more, it means that a large number of polypyrrole nanoparticles have been added during the preparation process, making it difficult for the graphene sheet structure to form well, resulting in a weaker control over the interlayer spacing of graphene.

[0047] Preferably, in step (2), the operating pressure of the filtration is 0.07~0.09MPa, such as 0.07MPa, 0.075MPa, 0.08MPa, 0.085MPa or 0.09MPa, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0048] Preferably, in step (3), the reduction reaction is a gas-phase reduction reaction carried out in an HI atmosphere.

[0049] Preferably, the gas-phase reduction reaction includes placing the graphene oxide-polypyrrole nanoparticle composite film above hydroiodic acid with a concentration of 45~55wt%, and heating the graphene oxide-polypyrrole nanoparticle composite film to conduct a gas-phase reduction reaction in an HI atmosphere.

[0050] It is worth noting that the reduction reaction described in this application uses a gas-phase reduction reaction to ensure that the graphene oxide-polypyrrole nanoparticle composite film can be effectively and uniformly reduced to form a graphene oxide-polypyrrole nanoparticle composite film. However, if the graphene oxide-polypyrrole nanoparticle composite film is immersed in a hydroiodic acid solution for a liquid-phase reduction reaction, a violent reduction reaction will occur at the first point of contact with the hydroiodic acid solution. The interlayer spacing of the graphene oxide sheets undergoing violent reduction is extremely small, which will prevent hydroiodic acid from entering the graphene sheets to reduce the lower graphene oxide sheets. This can easily lead to the graphene oxide-polypyrrole nanoparticle composite film not being uniformly reduced.

[0051] Preferably, in step (3), the temperature of the reduction reaction is 85~95℃, such as 85℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃ or 95℃, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0052] Preferably, in step (3), the reduction reaction time is 0.8 to 1.2 h, for example, 0.8 h, 0.9 h, 1 h, 1.1 h or 1.2 h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0053] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0054] (1) Mix a polypyrrole nanoparticle solution with a concentration of 0.1~0.5 mg / mL and a graphene oxide solution with a concentration of 1~2 mg / mL evenly, and control the mass ratio of the solutes in the graphene oxide solution to the polypyrrole nanoparticle solution to be 1:(5~10) to obtain a mixed solution containing polypyrrole nanoparticles and graphene oxide.

[0055] The polypyrrole nanoparticles are prepared by the following method: Ferric chloride is completely dissolved in deionized water, and the concentration of the ferric chloride solution is controlled at 2-4 mg / mL; while stirring, a pyrrole solution with a concentration of 97-99 wt% is added to the ferric chloride solution and mixed evenly; after the system is in equilibrium, a hydrogen peroxide solution with a concentration of 35-45 wt% is added dropwise, and the polymerization reaction begins immediately, and the entire system quickly turns black. Stirring is maintained, and the polymerization reaction temperature is kept at -5 to -10℃. The polymerization reaction ends after 8-12 hours, wherein the mass ratio of the solutes in the pyrrole solution, ferric chloride solution, and hydrogen peroxide solution is controlled at 1:(0.1-0.5):(3-4); and the polypyrrole nanoparticles in a brown powder state are obtained by evaporating the solvent.

[0056] (2) The mixed solution described in step (1) is used to form a graphene oxide-polypyrrole nanoparticle composite membrane on a porous polymer matrix membrane by vacuum filtration, and the operating pressure of vacuum filtration is controlled to be 0.07~0.09MPa;

[0057] (3) Place the graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) above hydroiodic acid with a concentration of 45~55wt%, and heat it to make the graphene oxide-polypyrrole nanoparticle composite membrane in HI atmosphere for gas-phase reduction reaction. Keep the temperature of the reduction reaction at 85~95℃, and after a reduction reaction of 0.8~1.2h, obtain a membrane pore dynamic stretching nanofiltration membrane.

[0058] A third objective of this invention is to provide a method for using the dynamically stretchable nanofiltration membrane described in one objective, the method comprising method (i) and / or method (ii):

[0059] The method (i) includes: applying a reduction potential to the dynamically stretchable nanofiltration membrane in a solution containing electrolytes to expand the pore size and reduce the desalination effect;

[0060] The method (ii) includes: applying an oxidation potential to the dynamically stretchable nanofiltration membrane in a solution containing electrolytes to reduce the pore size and improve the desalination effect.

[0061] It is worth noting that, in addition to conventionally applying oxidation potential to shrink the pore size to improve the desalination effect, water purification products for residential drinking water can achieve the switching between mineral water and purified water at any time through the dynamic expansion and contraction of membrane pores to meet the drinking water needs of different residents.

[0062] The fourth objective of this invention is to provide an application of the dynamically stretchable nanofiltration membrane described in the first objective, using the dynamically stretchable nanofiltration membrane for water treatment.

[0063] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0064] (1) The membrane dynamic expansion and contraction nanofiltration membrane of the present invention includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. By selecting and adjusting the electrode potential applied to the membrane dynamic expansion and contraction nanofiltration membrane, the membrane pore dynamic expansion and contraction can be achieved by electrochemical regulation, thereby adjusting the desalination performance of the nanofiltration membrane in situ and applying it to water treatment.

[0065] (2) The membrane dynamic stretching nanofiltration membrane of the present invention is prepared by sequentially filtering and reducing a mixed solution containing polypyrrole nanoparticles and graphene oxide on a porous polymer matrix membrane. It has the advantages of simple preparation process and broad application potential. Attached Figure Description

[0066] Figure 1 This is a scanning electron microscope image of the polypyrrole nanoparticles prepared in Example 1;

[0067] Figure 2 This is a cross-sectional view of the dynamically stretching nanofiltration membrane with pores prepared in Example 1 under a scanning electron microscope;

[0068] Figure 3 This is a scanning electron microscope image of the polypyrrole nanoparticles prepared in Example 7;

[0069] Figure 4 This is a graph showing the retention rate versus time for the dynamically stretching nanofiltration membrane prepared in Example 1.

[0070] Figure 5 This is a flux-time relationship diagram corresponding to the dynamically stretching nanofiltration membrane prepared in Example 1. Detailed Implementation

[0071] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0072] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0073] Example 1

[0074] This embodiment provides a dynamically stretchable nanofiltration membrane and its preparation method, the preparation method comprising the following steps:

[0075] (1) Mix a polypyrrole nanoparticle solution with a concentration of 0.2 mg / mL and a graphene oxide solution with a concentration of 1.5 mg / mL, and sonicate for 5 min to form a homogeneous solution. Control the mass ratio of the solutes in the graphene oxide solution to the polypyrrole nanoparticle solution to be 1:8 to obtain a mixed solution containing polypyrrole nanoparticles and graphene oxide.

[0076] The polypyrrole nanoparticles were prepared using the following method: Ferric chloride was completely dissolved in deionized water, and the concentration of the ferric chloride solution was controlled at 3 mg / mL. While stirring, a 97 wt% pyrrole solution was added to the ferric chloride solution and mixed thoroughly. After the system reached equilibrium, a 40 wt% hydrogen peroxide solution was added dropwise. The polymerization reaction immediately began, and the entire system rapidly turned black. Stirring was maintained, and the polymerization temperature was kept at -10°C. The polymerization reaction ended after 10 hours. The mass ratio of the solutes in the pyrrole solution, ferric chloride solution, and hydrogen peroxide solution was controlled at 1:0.2:3. Brown powdered polypyrrole nanoparticles were obtained by evaporating the solvent. A scanning electron microscope image of the obtained powder is shown below. Figure 1 As shown, the polypyrrole nanoparticles are irregular spherical with an average size between 50 and 90 nm. Furthermore, the polypyrrole nanoparticles are well dispersed and do not exhibit agglomeration or aggregation.

[0077] (2) The mixed solution in step (1) is used to form a graphene oxide-polypyrrole nanoparticle composite membrane on a porous polymer matrix membrane by vacuum filtration, and the operating pressure of vacuum filtration is controlled to be 0.08 MPa.

[0078] The porous polymer matrix membrane has a thickness of 150 μm, a pore size of 100 nm, and the polymer of the porous polymer matrix membrane is polyvinylidene fluoride.

[0079] (3) Place the graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) above 50wt% hydroiodic acid, and heat it to make the graphene oxide-polypyrrole nanoparticle composite membrane in HI atmosphere for gas phase reduction reaction. Keep the temperature of the reduction reaction at 90℃, and after 1 hour of reduction reaction, obtain the membrane pore dynamic stretching nanofiltration membrane.

[0080] The cross-sectional image of the dynamically stretching nanofiltration membrane prepared in this embodiment under a scanning electron microscope is shown below. Figure 2 As shown, the dynamically stretchable nanofiltration membrane has a double-layer structure, namely, the dynamically stretchable nanofiltration membrane includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene oxide-polypyrrole nanoparticle composite membrane can be measured to be approximately 120 nm.

[0081] Example 2

[0082] This embodiment provides a nanofiltration membrane with dynamic pore stretching and its preparation method. Compared with Embodiment 1, the difference is that the polypyrrole nanoparticles in step (1) are replaced with polypyrrole nanoparticles doped with large-volume anions. The specific details are as follows:

[0083] (1) Mix a solution of polypyrrole nanoparticles doped with large volume anions at a concentration of 0.2 mg / mL and a solution of graphene oxide at a concentration of 1.5 mg / mL, and sonicate for 5 min to form a homogeneous solution. Control the mass ratio of the solutes in the graphene oxide solution to the polypyrrole nanoparticles doped with large volume anions to be 1:8 to obtain a mixed solution containing polypyrrole nanoparticles doped with large volume anions and graphene oxide.

[0084] The polypyrrole nanoparticles doped with bulk anions were prepared using the following method: Ferric chloride was completely dissolved in deionized water, and the concentration of the ferric chloride solution was controlled at 3 mg / mL. While stirring, a 97 wt% pyrrole solution and a 0.5 mg / mL bulk anion solution were added to the ferric chloride solution and mixed thoroughly. After the system reached equilibrium, a 40 wt% hydrogen peroxide solution was added dropwise. The polymerization reaction immediately began, and the entire system rapidly turned black. Stirring was maintained, and the polymerization temperature was kept at -10°C. The polymerization reaction ended after 10 hours. The mass ratio of the solutes in the pyrrole solution, ferric chloride solution, and hydrogen peroxide solution was controlled at 1:0.2:3, and the mass ratio of the solutes in the pyrrole solution to the bulk anion solution was controlled at 1:0.03. The polypyrrole nanoparticles doped with bulk anions were obtained as a brown powder by evaporating the solvent.

[0085] Example 3

[0086] This embodiment provides a nanofiltration membrane with dynamic pore stretching and its preparation method. Compared with Embodiment 1, the difference is that in step (1), the mass ratio of the solutes corresponding to the graphene oxide solution and the polypyrrole nanoparticle solution is controlled to be 1:3.

[0087] The dynamically stretchable nanofiltration membrane prepared in this embodiment includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene oxide-polypyrrole nanoparticle composite membrane can be measured to be approximately 70 nm.

[0088] Example 4

[0089] This embodiment provides a nanofiltration membrane with dynamic pore stretching and its preparation method. Compared with Embodiment 1, the difference is that in step (1), the mass ratio of the solutes corresponding to the graphene oxide solution and the polypyrrole nanoparticle solution is controlled to be 1:5.

[0090] The dynamically stretchable nanofiltration membrane prepared in this embodiment includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene oxide-polypyrrole nanoparticle composite membrane can be measured to be approximately 100 nm.

[0091] Example 5

[0092] This embodiment provides a nanofiltration membrane with dynamic pore stretching and its preparation method. Compared with Embodiment 1, the difference is that in step (1), the mass ratio of the solutes corresponding to the graphene oxide solution and the polypyrrole nanoparticle solution is controlled to be 1:10.

[0093] The dynamically stretchable nanofiltration membrane prepared in this embodiment includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene oxide-polypyrrole nanoparticle composite membrane can be measured to be approximately 150 nm.

[0094] Example 6

[0095] This embodiment provides a nanofiltration membrane with dynamic pore stretching and its preparation method. Compared with Embodiment 1, the difference is that in step (1), the mass ratio of the solutes corresponding to the graphene oxide solution and the polypyrrole nanoparticle solution is controlled to be 1:20.

[0096] The dynamically stretchable nanofiltration membrane prepared in this embodiment includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene oxide-polypyrrole nanoparticle composite membrane can be measured to be approximately 300 nm.

[0097] Example 7

[0098] This embodiment provides a nanofiltration membrane with dynamic pore stretching and its preparation method. Compared with Embodiment 1, the difference is that in step (1), the polypyrrole nanoparticles are not prepared using hydrogen peroxide solution. The specific details are as follows:

[0099] Ferric chloride was completely dissolved in deionized water, and the concentration of the ferric chloride solution was controlled at 3 mg / mL. While stirring, a 97 wt% pyrrole solution was added dropwise to the ferric chloride solution. The polymerization reaction started immediately, and the entire system rapidly turned black. Stirring was maintained, and the polymerization temperature was kept at -10°C. The polymerization reaction ended after 10 hours. The mass ratio of pyrrole solution to ferric chloride solution was controlled at 1:0.2. Black, insoluble polypyrrole nanoparticles were obtained, and their scanning electron microscope images are shown below. Figure 3 As shown, the polypyrrole nanoparticles are irregularly shaped, some are approximately rod-shaped and some are irregular spheres. The polypyrrole nanoparticles are relatively large in size, with the length of the rod-shaped structure and the diameter of the sphere structure being approximately 1 μm. Furthermore, the polypyrrole nanoparticles aggregate into clusters and do not exhibit good dispersibility.

[0100] Example 8

[0101] This embodiment provides a nanofiltration membrane with dynamic pore stretching and its preparation method. Compared with Embodiment 1, the difference is that in step (3), the gas-phase reduction reaction is replaced by a liquid-phase reduction reaction. The specific details are as follows:

[0102] (3) Place the graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) in 50wt% hydroiodic acid to carry out a liquid-phase reduction reaction. At room temperature, the graphene oxide-polypyrrole nanoparticle composite membrane can undergo a rapid and intense reduction reaction. The reaction can be completed in a few seconds to obtain a membrane pore dynamic stretching nanofiltration membrane.

[0103] Example 9

[0104] This embodiment provides a dynamically stretchable nanofiltration membrane and its preparation method, the preparation method comprising the following steps:

[0105] (1) Mix a polypyrrole nanoparticle solution with a concentration of 0.1 mg / mL and a graphene oxide solution with a concentration of 1 mg / mL, and sonicate for 5 min to form a homogeneous solution. Control the mass ratio of the solutes in the graphene oxide solution to the polypyrrole nanoparticle solution to be 1:8 to obtain a mixed solution containing polypyrrole nanoparticles and graphene oxide.

[0106] The polypyrrole nanoparticles were prepared as follows: Ferric chloride was completely dissolved in deionized water, and the concentration of the ferric chloride solution was controlled at 2 mg / mL; while stirring, a 97 wt% pyrrole solution was added to the ferric chloride solution and mixed evenly; after the system reached equilibrium, a 35 wt% hydrogen peroxide solution was added dropwise, and the polymerization reaction immediately began, with the entire system rapidly turning black. Stirring was maintained, and the polymerization temperature was kept at -5°C. The polymerization reaction ended after 8 hours, with the mass ratio of solutes in the pyrrole solution, ferric chloride solution, and hydrogen peroxide solution controlled at 1:0.1:3; brown powder polypyrrole nanoparticles were obtained by evaporating the solvent.

[0107] (2) The mixed solution in step (1) is used to form a graphene oxide-polypyrrole nanoparticle composite membrane on a porous polymer matrix membrane by vacuum filtration, and the operating pressure of vacuum filtration is controlled to be 0.07 MPa.

[0108] The porous polymer matrix membrane has a thickness of 100 μm, a pore size of 80 nm, and the polymer of the porous polymer matrix membrane is polyvinylidene fluoride.

[0109] (3) Place the graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) above hydroiodic acid with a concentration of 45wt%, and heat it to make the graphene oxide-polypyrrole nanoparticle composite membrane in HI atmosphere for gas phase reduction reaction. Keep the temperature of the reduction reaction at 85℃, and after 0.8h of reduction reaction, obtain the membrane pore dynamic stretching nanofiltration membrane.

[0110] The dynamically stretchable nanofiltration membrane prepared in this embodiment includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene oxide-polypyrrole nanoparticle composite membrane can be measured to be approximately 120 nm.

[0111] Example 10

[0112] This embodiment provides a dynamically stretchable nanofiltration membrane and its preparation method, the preparation method comprising the following steps:

[0113] (1) Mix a polypyrrole nanoparticle solution with a concentration of 0.5 mg / mL and a graphene oxide solution with a concentration of 2 mg / mL, and sonicate for 5 min to form a homogeneous solution. Control the mass ratio of the solutes in the graphene oxide solution to the polypyrrole nanoparticle solution to be 1:8 to obtain a mixed solution containing polypyrrole nanoparticles and graphene oxide.

[0114] The polypyrrole nanoparticles were prepared as follows: Ferric chloride was completely dissolved in deionized water, and the concentration of the ferric chloride solution was controlled at 4 mg / mL; while stirring, a 99 wt% pyrrole solution was added to the ferric chloride solution and mixed thoroughly; after the system reached equilibrium, a 45 wt% hydrogen peroxide solution was added dropwise, and the polymerization reaction immediately began, rapidly turning the entire system black. Stirring was maintained, and the polymerization temperature was kept at -10°C. The polymerization reaction ended after 12 hours, with the mass ratio of solutes in the pyrrole solution, ferric chloride solution, and hydrogen peroxide solution controlled at 1:0.5:4; brown powder polypyrrole nanoparticles were obtained by evaporating the solvent.

[0115] (2) The mixed solution described in step (1) is used to form a graphene oxide-polypyrrole nanoparticle composite membrane on a porous polymer matrix membrane by vacuum filtration, and the operating pressure of vacuum filtration is controlled to be 0.09 MPa.

[0116] The porous polymer matrix membrane has a thickness of 200 μm, a pore size of 120 nm, and the polymer of the porous polymer matrix membrane is polyvinylidene fluoride.

[0117] (3) Place the graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) above hydroiodic acid with a concentration of 55wt%, and heat it to make the graphene oxide-polypyrrole nanoparticle composite membrane in HI atmosphere for gas phase reduction reaction. Keep the temperature of the reduction reaction at 95℃, and after 1.2h of reduction reaction, obtain the membrane pore dynamic stretching nanofiltration membrane.

[0118] The dynamically stretchable nanofiltration membrane prepared in this embodiment includes a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene oxide-polypyrrole nanoparticle composite membrane can be measured to be approximately 110 nm.

[0119] Comparative Example 1

[0120] This comparative example provides a nanofiltration membrane and its preparation method. Compared with Example 1, the difference is that in step (2), the vacuum filtration method is replaced by interfacial polymerization. The specific details are as follows:

[0121] An inorganic solution is coated onto a porous polymer matrix membrane using interfacial polymerization. The inorganic solution is the mixed solution described in step (1). After coating, the remaining solution is removed, and the membrane is allowed to stand and dry before coating with an organic phase solution of trimesoyl chloride. Through a two-phase interfacial polymerization reaction, a graphene-polypyrrole polyamide composite membrane is formed on the porous polymer matrix.

[0122] Comparative Example 2

[0123] This comparative example provides a nanofiltration membrane and its preparation method. Compared with Example 1, the difference is that polypyrrole nanoparticles are no longer added. The resulting nanofiltration membrane includes a porous polymer matrix membrane and a graphene membrane covering the surface of the porous polymer matrix membrane. The specific details are as follows:

[0124] (a) A graphene oxide membrane was formed on a porous polymer matrix membrane by vacuum filtration of a graphene oxide solution with a concentration of 1.5 mg / mL, and the operating pressure of vacuum filtration was controlled at 0.08 MPa.

[0125] The porous polymer matrix membrane has a thickness of 150 μm, a pore size of 100 nm, and the polymer of the porous polymer matrix membrane is polyvinylidene fluoride.

[0126] (b) The graphene oxide membrane described in step (a) is placed above 50 wt% hydroiodic acid, and the graphene oxide membrane is heated to carry out a gas-phase reduction reaction in an HI atmosphere. The temperature of the reduction reaction is maintained at 90°C, and after 1 hour of reduction reaction, a nanofiltration membrane with dynamic pore stretching is obtained.

[0127] The nanofiltration membrane prepared in this comparative example includes a porous polymer matrix membrane and a graphene membrane covering the surface of the porous polymer matrix membrane. The thickness of the graphene membrane can be measured to be approximately 50 nm.

[0128] Performance testing

[0129] The nanofiltration membrane to be characterized is placed in a membrane module that can be charged. One electrode is connected to the membrane surface, and the opposite electrode is placed parallel to the membrane surface in the membrane module. The type and magnitude of the applied potential are determined first, and then the membrane filtration experiment is carried out.

[0130] Desalination performance: The dynamically stretchable nanofiltration membrane prepared in Example 1 was used as the characterization object. A 2 g / L Na₂SO₄ solution was used as the feed liquid. A reduction potential was applied for 30 min, followed by a power-off and then 3.5 h of operation. During this time, the rejection rate and flux were tested to eliminate interference from electrostatic effects. Immediately afterwards, an oxidation potential was applied for 30 min, and the rejection rate and flux were tested using the same method. This cycle of applying reduction potential and applying oxidation potential was then repeated. The resulting rejection rate-time and flux-time graphs are shown below. Figure 4 and Figure 5 It can be seen that the membrane pore dynamic expansion nanofiltration membrane prepared in this embodiment can achieve dynamic expansion and contraction of the membrane pores by selecting and adjusting the electrode potential applied to the membrane pore dynamic expansion nanofiltration membrane, thereby adjusting the desalination performance of the nanofiltration membrane in situ.

[0131] Pore ​​Size: The graphene oxide-polypyrrole nanoparticle composite membrane serves as the main key structure, featuring polypyrrole nanoparticles embedded between layered graphene layers. Graphene possesses stable and reliable layered nanochannels, with the regions between graphene sheets serving as water channels. Therefore, the interlayer spacing of graphene is its pore size. A 2 g / L Na₂SO₄ solution was used as the salt solution to induce membrane pore expansion and contraction. A potential was applied to the membrane surface to induce changes in pore size. XRD characterization identified the characteristic peaks of the dynamically expanding and contracting membrane. The interlayer spacing was calculated and can be considered as the pore size of the dynamically expanding and contracting nanofiltration membrane. The test results related to the pore size of the nanofiltration membranes prepared in each embodiment and comparative example are shown in Table 1.

[0132] It is worth noting that the electrochemical regulation of nanofiltration membranes focuses on the change in pore size under different electrode potentials. As long as there is a significant change in pore size under different potentials, it can be proven that the nanofiltration membrane can achieve dynamic expansion and contraction of pores.

[0133] Table 1

[0134] Note: " / " indicates that it is not represented.

[0135] It is worth noting that, in the preparation method described in Comparative Example 1, since vacuum filtration was not used in step (2), the graphene and polypyrrole were difficult to continuously distribute on the membrane substrate through the two-phase interfacial polymerization reaction of the inorganic and organic phases. It was impossible to accurately control the composite membrane to be a graphene sheet structure, which resulted in the inability to form a graphene oxide-polypyrrole nanoparticle composite membrane on the porous polymer matrix membrane. Consequently, the graphene oxide-polypyrrole nanoparticle composite membrane could not be formed, and there was no need for characterization.

[0136] In summary, the dynamically expanding nanofiltration membrane of this invention comprises a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane. By selecting and adjusting the electrode potential applied to the dynamically expanding nanofiltration membrane, the dynamic expansion and contraction of the membrane pores can be achieved through electrochemical regulation, thereby enabling in-situ adjustment of the desalination performance of the nanofiltration membrane, which can be applied to water treatment. The dynamically expanding nanofiltration membrane of this invention is prepared by sequentially filtration and reduction reactions of a mixed solution containing polypyrrole nanoparticles and graphene oxide on a porous polymer matrix membrane, and has the advantages of simple preparation process and broad application potential.

[0137] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0138] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0139] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0140] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A nanofiltration membrane with dynamically stretchable pores, characterized in that, The dynamically stretchable nanofiltration membrane comprises a porous polymer matrix membrane and a graphene oxide-polypyrrole nanoparticle composite membrane covering the surface of the porous polymer matrix membrane; wherein hydrophilic functional groups are introduced into the polypyrrole molecules; The raw materials for preparing the graphene oxide-polypyrrole nanoparticle composite film include graphene oxide solution and polypyrrole nanoparticle solution. The mass ratio of the solute in the graphene oxide solution to the polypyrrole nanoparticle solution is 1:(5~10).

2. The nanofiltration membrane with dynamic pore stretching according to claim 1, characterized in that, The thickness of the porous polymer matrix membrane is 100~200μm.

3. The nanofiltration membrane with dynamic pore stretching according to claim 1, characterized in that, The porous polymer matrix membrane has a pore size of 80~120nm.

4. The nanofiltration membrane with dynamic pore stretching according to claim 1, characterized in that, The polymer of the porous polymer matrix membrane includes any one of polyvinylidene fluoride, polyethersulfone, cellulose acetate, and polyamide.

5. The nanofiltration membrane with dynamic pore stretching according to claim 4, characterized in that, The polymer of the porous polymer matrix membrane is polyvinylidene fluoride.

6. The nanofiltration membrane with dynamic pore stretching according to claim 1, characterized in that, The pore size of the graphene oxide-polypyrrole nanoparticle composite membrane is 7~15 Å.

7. The nanofiltration membrane with dynamic pore stretching according to claim 1, characterized in that, The thickness of the graphene oxide-polypyrrole nanoparticle composite film is 50~200nm.

8. The nanofiltration membrane with dynamic pore stretching according to claim 1, characterized in that... The graphene oxide-polypyrrole nanoparticle composite film is doped with large-volume anions.

9. The nanofiltration membrane with dynamic pore stretching according to claim 8, characterized in that, The bulky anion includes any one of alkylbenzenesulfonate ions, alkyl sulfonate ions, and alkyl sulfate ions; the alkyl group is a C9-C12 alkyl group.

10. The nanofiltration membrane with dynamic pore stretching according to claim 9, characterized in that, The alkylbenzene sulfonate ion is a dodecylbenzene sulfonate ion.

11. The nanofiltration membrane with dynamic pore stretching according to claim 9, characterized in that, The alkyl sulfate ion is a dodecyl sulfate ion.

12. The nanofiltration membrane with dynamic pore stretching according to claim 9, characterized in that, The alkyl sulfonate ion is a dodecyl sulfonate ion.

13. A method for preparing a nanofiltration membrane with dynamically stretchable pores as described in any one of claims 1 to 12, characterized in that, The preparation method includes the following steps: (1) Prepare a mixed solution containing polypyrrole nanoparticles and graphene oxide; (2) The mixed solution described in step (1) is filtered to form a graphene oxide-polypyrrole nanoparticle composite membrane on a porous polymer matrix membrane; (3) The graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) is subjected to a reduction reaction to obtain a membrane pore dynamic stretching nanofiltration membrane.

14. The preparation method according to claim 13, characterized in that, In step (1), the polypyrrole nanoparticles are obtained by the following preparation method: pyrrole solution is added to ferric chloride solution and mixed evenly, hydrogen peroxide solution is added dropwise to carry out polymerization reaction, and the polypyrrole nanoparticles are obtained by evaporating the solvent.

15. The preparation method according to claim 14, characterized in that, The concentration of the ferric chloride solution is 2~4 mg / mL.

16. The preparation method according to claim 14, characterized in that, The concentration of the pyrrole solution is 97-99 wt%.

17. The preparation method according to claim 14, characterized in that, The concentration of the hydrogen peroxide solution is 35-45 wt%.

18. The preparation method according to claim 14, characterized in that, The mass ratio of solutes in the pyrrole solution, the ferric chloride solution, and the hydrogen peroxide solution is 1:(0.1~0.5):(3~4).

19. The preparation method according to claim 14, characterized in that, The polymerization reaction is carried out at a temperature of -5 to -10°C.

20. The preparation method according to claim 14, characterized in that, The polymerization reaction takes 8 to 12 hours.

21. The preparation method according to claim 13, characterized in that, In step (1), the polypyrrole nanoparticles are polypyrrole nanoparticles doped with large-volume anions.

22. The preparation method according to claim 21, characterized in that, The polypyrrole nanoparticles doped with bulk anions were prepared by the following method: pyrrole solution and bulk anion solution were added to ferric chloride solution and mixed evenly, hydrogen peroxide solution was added dropwise to carry out a polymerization reaction, and the polypyrrole nanoparticles doped with bulk anions were obtained by evaporating the solvent.

23. The preparation method according to claim 22, characterized in that, The mass ratio of solute in the pyrrole solution to the bulk anionic solution is 1:(0.02~0.04).

24. The preparation method according to claim 22, characterized in that, The concentration of the large-volume anion solution is 0.3~0.6 mg / mL.

25. The preparation method according to claim 13, characterized in that, In step (1), the mixed solution is obtained by uniformly mixing polypyrrole nanoparticle solution and graphene oxide solution.

26. The preparation method according to claim 25, characterized in that, The concentration of the polypyrrole nanoparticle solution is 0.1~0.5 mg / mL.

27. The preparation method according to claim 25, characterized in that, The concentration of the graphene oxide solution is 1~2 mg / mL.

28. The preparation method according to claim 13, characterized in that, In step (2), the operating pressure of the filtration is 0.07~0.09MPa.

29. The preparation method according to claim 13, characterized in that, In step (3), the reduction reaction is a gas-phase reduction reaction carried out in an HI atmosphere.

30. The preparation method according to claim 29, characterized in that, The gas-phase reduction reaction involves placing the graphene oxide-polypyrrole nanoparticle composite film above hydroiodic acid with a concentration of 45-55 wt%, and heating the graphene oxide-polypyrrole nanoparticle composite film to conduct a gas-phase reduction reaction in an HI atmosphere.

31. The preparation method according to claim 13, characterized in that, In step (3), the temperature of the reduction reaction is 85~95℃.

32. The preparation method according to claim 13, characterized in that, In step (3), the reduction reaction takes 0.8 to 1.2 hours.

33. The preparation method according to claim 32, characterized in that, The preparation method includes the following steps: (1) Mix a polypyrrole nanoparticle solution with a concentration of 0.1~0.5 mg / mL and a graphene oxide solution with a concentration of 1~2 mg / mL evenly, and control the mass ratio of the solutes in the graphene oxide solution to the polypyrrole nanoparticle solution to be 1:(5~10) to obtain a mixed solution containing polypyrrole nanoparticles and graphene oxide. The polypyrrole nanoparticles are prepared by the following method: Ferric chloride is completely dissolved in deionized water, and the concentration of the ferric chloride solution is controlled at 2-4 mg / mL; while stirring, a pyrrole solution with a concentration of 97-99 wt% is added to the ferric chloride solution and mixed evenly; after the system is in equilibrium, a hydrogen peroxide solution with a concentration of 35-45 wt% is added dropwise, and the polymerization reaction begins immediately, and the entire system quickly turns black. Stirring is maintained, and the polymerization reaction temperature is kept at -5 to -10℃. The polymerization reaction ends after 8-12 hours, wherein the mass ratio of the solutes in the pyrrole solution, ferric chloride solution, and hydrogen peroxide solution is controlled at 1:(0.1-0.5):(3-4); and the polypyrrole nanoparticles in a brown powder state are obtained by evaporating the solvent. (2) The mixed solution described in step (1) is used to form a graphene oxide-polypyrrole nanoparticle composite membrane on a porous polymer matrix membrane by vacuum filtration, and the operating pressure of vacuum filtration is controlled to be 0.07~0.09MPa; (3) Place the graphene oxide-polypyrrole nanoparticle composite membrane described in step (2) above hydroiodic acid with a concentration of 45~55wt%, and heat it to make the graphene oxide-polypyrrole nanoparticle composite membrane in HI atmosphere for gas-phase reduction reaction. Keep the temperature of the reduction reaction at 85~95℃, and after a reduction reaction of 0.8~1.2h, obtain a membrane pore dynamic stretching nanofiltration membrane.

34. A method of using the dynamically stretchable nanofiltration membrane according to any one of claims 1 to 12, characterized in that, The method of use includes method (i) and / or method (ii): The method (i) includes: applying a reduction potential to the dynamically stretchable nanofiltration membrane in a solution containing electrolytes to expand the pore size and reduce the desalination effect; The method (ii) includes: applying an oxidation potential to the dynamically stretchable nanofiltration membrane in a solution containing electrolytes to reduce the pore size and improve the desalination effect.

35. An application of the nanofiltration membrane with dynamic pore stretching as described in any one of claims 1 to 12, characterized in that, The nanofiltration membrane with dynamically expanding pores is used for water treatment.

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