A filtration membrane and a method for producing the same

Abstract

The application provides a filter membrane and a preparation method thereof, and the preparation method comprises the following steps: placing a porous filter membrane substrate in an environment containing plasma and a precursor, and performing plasma treatment to obtain the filter membrane; wherein the precursor comprises at least one of hexamethyldisiloxane, perfluorooctyltriethoxysilane, pentane, ethylene, toluene, perfluorohexane, styrene, divinylbenzene, hexamethyldisiloxane, tetramethylsilane, tetraethoxysilane, tetrafluoroethylene, hexafluoropropylene. The filter membrane prepared by the preparation method can significantly reduce the swelling rate in an organic solvent, and simultaneously improve the permeation flux, so that the precise molecular weight cut-off is realized.

Description

Technical Field

[0001] This invention relates to the field of organic solvent nanofiltration technology, and in particular to a filter membrane and its preparation method. Background Technology

[0002] Organic solvent nanofiltration (OSN) is a pressure-driven, high-efficiency separation technology with advantages such as energy saving, simple operation, and high separation accuracy. It has outstanding application value in fields such as chemical purification, environmental remediation, and pharmaceutical refining, and is a key supporting technology for promoting the green and efficient development of related industries.

[0003] Traditional nanofiltration membranes have poor solvent stability and are prone to swelling and degradation in organic solvents such as N,N-dimethylacetamide, methanol, tetrahydrofuran (THF), and heptane. This not only leads to a significant decrease in flux and retention performance and a shortened service life, but also makes it difficult to achieve precise molecular weight retention, which seriously limits the industrial application of OSN technology.

[0004] To improve the solvent resistance of membranes, the main preparation technologies developed in the industry include coating, interfacial polymerization, and crosslinking modification. However, existing technologies cannot meet the core requirements of efficient separation and precise retention control in industrial production. Among them, coating is prone to reduced flux due to pore permeation or excessively thick porous solvent-resistant layers; interfacial polymerization struggles to balance solvent resistance and precise retention; and crosslinking modification is limited by material properties and cannot simultaneously achieve high permeation efficiency and precise molecular weight retention.

[0005] Therefore, it is necessary to develop a highly stable organic solvent nanofiltration membrane that can simultaneously improve permeation flux, achieve precise molecular weight cutoff, and possess excellent solvent resistance properties, thereby breaking through existing technological bottlenecks and promoting the large-scale industrial application of OSN technology. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a filter membrane. The filter membrane prepared using this method can accurately retain impurities of a specified molecular weight in organic solvents, while simultaneously achieving a synergistic improvement in resistance to organic solvent swelling, permeation flux, and retention rate, thus stably meeting the various core performance requirements of the filter membrane.

[0007] This invention provides a filter membrane that, in organic solvents, can significantly reduce swelling rate and simultaneously increase permeation flux, thereby achieving precise molecular weight cutoff.

[0008] In a first aspect, a method for preparing a filter membrane includes the following steps:

[0009] The porous filter membrane substrate is placed in an environment containing plasma and precursors and subjected to plasma treatment to obtain the filter membrane.

[0010] The precursor includes at least one of hexamethyldisiloxane, perfluorooctyltriethoxysilane, pentane, ethylene, toluene, perfluorohexane, styrene, divinylbenzene, hexamethyldisiloxane, tetramethylsilane, tetraethoxysilane, tetrafluoroethylene, and hexafluoropropylene.

[0011] Furthermore, the porosity of the porous filter membrane substrate is 20%~80%;

[0012] And / or, the average pore size of the porous filter membrane substrate is 1 nm to 500 nm;

[0013] And / or, the porous filter membrane substrate is made of polyetheretherketone and / or polyacrylonitrile.

[0014] Furthermore, the plasma preparation process includes the following steps: using ionized gas for radio frequency ionization treatment to generate the plasma.

[0015] Furthermore, the ionized gas includes at least one of methane, pentane, 4-vinylpyridine, trichlorosilane, tetrahydrofuran, oxygen, hydrogen, and inert gas.

[0016] Furthermore, the discharge power of the radio frequency ionization treatment is 1W~100W, the pressure is 1Pa~200Pa, and the temperature is 273K~333K.

[0017] Furthermore, the temperature of the plasma treatment is 273K~333K;

[0018] And / or, the discharge power of the plasma treatment is 1W~100W;

[0019] And / or, the pressure of the plasma treatment is 1 Pa to 200 Pa;

[0020] And / or, the plasma treatment time is 1 min to 60 min.

[0021] In a second aspect, the present invention provides a filter membrane obtained by the method for preparing the filter membrane as described in the first aspect, the filter membrane comprising the porous filter membrane substrate and a porous solvent-resistant layer disposed on at least a portion of the surface of the porous filter membrane substrate.

[0022] Furthermore, the degree of crosslinking of the porous solvent-resistant layer is greater than 80%.

[0023] Furthermore, the porous solvent-resistant layer comprises at least one of fluorocarbon chains, siloxane alkyl groups, phenyl groups, carbon-carbon unsaturated bonds, and alkyl groups;

[0024] And / or, the thickness of the porous solvent-resistant layer is 1 nm to 150 nm;

[0025] And / or, the porosity of the porous solvent-resistant layer is 60%~80%;

[0026] And / or, the surface roughness Rq of the porous solvent-resistant layer is 1 nm to 2.5 nm.

[0027] Furthermore, the filter membrane satisfies at least one of the following conditions:

[0028] a. After the filter membrane is immersed in an organic solvent at 20℃~25℃ for 72h~168h, the mass retention rate of the immersed filter membrane is ≥99%;

[0029] b. The molecular weight cutoff of the filter membrane is 300 Da to 600 Da;

[0030] c. The permeation flux of the filter membrane is 3.7 L•m -2 •h -1 •bar -1 ~11.5 L•m -2 •h -1 •bar -1 .

[0031] This invention provides a method for preparing a filter membrane. The method involves placing a porous filter membrane substrate in an environment containing plasma and a precursor for plasma treatment. During the preparation process, the plasma activates molecules on the surface of the porous filter membrane substrate, generating active groups (such as hydroxyl groups). Simultaneously, the plasma causes the precursor to dissociate, generating fragments of hydrophobic groups. This results in the construction of a highly cross-linked, hydrophobic, nanoporous solvent-resistant layer on the surface of the porous filter membrane substrate. The filter membrane prepared using this method can retain impurities of a fixed molecular weight, while simultaneously achieving a synergistic improvement in resistance to organic solvent swelling, permeate flux, and retention rate, thus stably meeting the core performance requirements of the filter membrane.

[0032] This invention provides a filter membrane comprising a porous filter membrane substrate and a porous solvent-resistant coating. The porous structure of the filter membrane substrate provides a basic molecular retention framework, enabling molecular separation within the target molecular weight range. The porous structure of the porous solvent-resistant layer synergistically matches the porous structure of the substrate, further refining the filtration channels and precisely intercepting target molecules within this range while allowing smaller molecules (such as solvent impurities) to pass freely. Simultaneously, the solvent resistance of the porous solvent-resistant layer maintains the overall structural integrity and dimensional stability of the filter membrane, ensuring the bonding strength between the porous solvent-resistant layer and the substrate. This prevents the coating from degrading or detaching under long-term contact with organic solvents, stably maintaining the pore size structure and pore distribution of the filter membrane, and ensuring consistently high core separation performance. Ultimately, the porous filter membrane substrate and the porous solvent-resistant layer work together to achieve precise separation and efficient filtration, enabling long-term stable operation in organic solvent environments and meeting practical application requirements. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the preparation apparatus 1 used in Example 1;

[0035] Figure 2 Here is the surface atomic force morphology of filter membrane S-1;

[0036] Figure 3 The surface atomic force morphology of filter membrane S-6 is shown.

[0037] Figure 4 This is a scanning electron microscope image of filter membrane S-1.

[0038] Figure 5 This is a scanning electron microscope image of filter membrane S-6;

[0039] Figure 6 Line graphs showing the permeation flux and rejection rate of filter membranes S-1, S-2, S-4, and P-2;

[0040] Figure 7 Line graphs showing the permeation flux and rejection rate of filter membranes S-9, S-10, S-11, and P-1.

[0041] Explanation of reference numerals in the attached figures

[0042] 1-Preparation apparatus; 11-RF generator, 12-Electrode, 13-Vacuum pump, 14-Inlet pipe; 15-Carrier plate. Detailed Implementation

[0043] To enable those skilled in the art to better understand the solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0044] In a first aspect, the present invention provides a method for preparing a filter membrane, comprising the following steps:

[0045] A porous filter membrane substrate is placed in an environment containing plasma and precursors for plasma treatment to obtain a filter membrane.

[0046] The precursor includes at least one of hexamethyldisiloxane, perfluorooctyltriethoxysilane, pentane, ethylene, toluene, perfluorohexane, styrene, divinylbenzene, hexamethyldisiloxane, tetramethylsilane, tetraethoxysilane, tetrafluoroethylene, and hexafluoropropylene.

[0047] The method for preparing a filter membrane provided by the present invention can obtain a filter membrane that is resistant to the raw material to be filtered; wherein the raw material to be filtered includes organic solvent and / or water.

[0048] In some embodiments, the organic solvent includes, but is not limited to, at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, dimethylmarine, tetrahydrofuran, methanol, ethanol, and heptane.

[0049] In some embodiments, pentane includes n-pentane and / or isopentane.

[0050] In preparing the above-mentioned filter membrane, the porous filter membrane substrate is placed in an environment containing both plasma and precursor for plasma treatment. The two work together to form a porous solvent-resistant layer on the surface of the porous filter membrane substrate, thereby obtaining the above-mentioned filter membrane.

[0051] Plasma, as a high-energy activation and reaction-driving medium, can excite molecules on the surface of porous filter membrane substrates to generate active groups, providing stable binding sites for coating grafting and providing sufficient energy for the dissociation and cross-linking reactions of the precursor. The precursor, as the core material source of the porous solvent-resistant layer, contains components such as hexamethyldisiloxane, perfluorohexane, and styrene. Under the high-energy drive of plasma, it dissociates to generate active hydrophobic groups such as siloxane alkyl groups, fluorocarbon chains, phenyl groups, and alkyl groups. These active hydrophobic groups further undergo grafting and cross-linking reactions with the active groups on the surface of the porous filter membrane substrate, ultimately forming a porous solvent-resistant layer with hydrophobicity, solvent resistance, and a specific pore structure, giving the porous solvent-resistant layer a three-dimensional network cross-linked structure.

[0052] Under the plasma treatment conditions of the present invention, the above-mentioned precursor can form a stable vapor and enter the reaction chamber in gaseous form to participate in subsequent reactions. Most of the active fragments / active particles generated by the precursor during the plasma treatment process will be combined with the surface of the porous filter membrane substrate or the porous solvent-resistant layer by chemical bonding, grafting or cross-linking.

[0053] The simultaneous presence of plasma and precursor enables the processes of substrate surface activation, precursor dissociation, grafting and crosslinking of active hydrophobic groups, and coating formation, ensuring the structural and performance stability of the porous solvent-resistant layer. This, in turn, enables the prepared filter membrane to meet core performance indicators such as organic solvent resistance stability, retention accuracy, and permeation flux.

[0054] This preparation method is simple to operate and highly controllable. It achieves rapid and uniform deposition of porous solvent-resistant layers through plasma treatment without the need for complex subsequent processing steps. It can efficiently prepare highly stable filter membranes with high permeability, precise retention, and excellent solvent resistance.

[0055] The aforementioned precursors all provide hydrophobic groups for the porous solvent-resistant layer, ensuring that the porous solvent-resistant layer has excellent hydrophobicity and organic solvent resistance. At the same time, they achieve a tight bond between the porous solvent-resistant layer and the porous filter membrane substrate, ensuring that the core performance of the filter membrane, such as molecular weight cutoff, permeate flux, and mass retention rate, meets the standards. This solves the technical problems of complex filter membrane preparation methods, poor coating performance, and low preparation efficiency, improves the preparation efficiency and product quality of filter membranes, and meets the performance and preparation requirements of filter membranes in practical applications.

[0056] The porous filter membrane substrate has a porous structure, which can reduce the fluid flow resistance during the filtration process of the raw material to be filtered, providing basic support for the smooth passage of fluid. The porous solvent-resistant layer avoids the decrease in flux caused by its own excessive density, and at the same time, it works synergistically with the retention performance of the substrate. While ensuring the retention accuracy, it ensures that organic solvents can pass through the filter membrane efficiently, and ultimately makes the permeation flux of the filter membrane stable within the preset range.

[0057] In some embodiments, the porosity of the porous filter membrane substrate is 20% to 80%;

[0058] And / or, the average pore size of the porous filter membrane substrate is 1 nm to 500 nm;

[0059] And / or, the porous filter membrane substrate is made of materials including polyetheretherketone (PEEK) and / or polyacrylonitrile (PAN).

[0060] For example, the porosity of the porous filter membrane substrate is any value or a range of any two of the following: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%.

[0061] For example, the average pore size of the porous filter membrane substrate is any value or a range of any two of the following: 1 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc.

[0062] The porosity of the porous filter membrane substrate is 20%~80%, which can provide a low-resistance flow channel for fluids, laying the foundation for the permeate flux performance of the filter membrane. At the same time, it ensures that the porous filter membrane substrate has sufficient mechanical strength to stably support the porous solvent-resistant layer on the surface, thus providing support for the overall structural stability of the filter membrane.

[0063] The average pore size of the porous filter membrane substrate is 1nm~500nm, which is compatible with the pore structure of the porous solvent-resistant layer to further refine the filtration channels and achieve the requirement that the filtration membrane has a molecular weight cutoff (MWCO) of 300Da~600Da, thereby improving the retention accuracy of the filtration membrane and ensuring the precise interception of target molecules.

[0064] The materials used in porous filter membrane substrates include polyetheretherketone (PEEK) and / or polyacrylonitrile (PAC). These materials have excellent resistance to organic solvents and mechanical stability, enabling them to work stably in organic solvent environments for extended periods. This provides a fundamental support for the overall solvent resistance stability of the filter membrane, ensuring that the membrane maintains a high quality retention rate even when immersed in organic solvents, thus further enhancing the practical value and service life of the filter membrane.

[0065] In some embodiments, the plasma preparation process includes the following steps: radio frequency ionization treatment using ionized gas to generate plasma.

[0066] Plasma preparation via radio frequency ionization (RF ionization) enables highly efficient ionization of gases, generating a large number of active and stable high-energy particles. The RF ionization process is highly controllable, allowing for precise adjustment of plasma concentration and activity according to preparation requirements. The plasma generated by RF ionization exhibits excellent stability, ensuring sufficient dissociation of precursor molecules without excessive decomposition. This guarantees the structural uniformity and performance stability of the porous solvent-resistant layer, avoiding coating defects caused by insufficient or unstable plasma activity. This plasma preparation method is simple to operate and highly efficient, providing a stable and controllable plasma environment for filter membrane preparation. It ensures uniform deposition and performance regulation of the porous solvent-resistant layer, thereby improving the product consistency and core performance stability of the filter membrane.

[0067] This invention does not limit the order of radio frequency ionization treatment and plasma treatment.

[0068] In some example implementations, the ionized gas is subjected to radio frequency ionization to generate plasma, while the precursor is simultaneously subjected to plasma treatment. The plasma obtained from the radio frequency ionization of the ionized gas coexists with the precursor.

[0069] In some example implementations, the ionized gas is subjected to radio frequency ionization to generate plasma; after the radio frequency ionization is completed, the plasma is collected, and the collected plasma and precursor are then subjected to plasma treatment.

[0070] In some embodiments, the ionized gas includes at least one of methane, pentane, 4-vinylpyridine, trichlorosilane, tetrahydrofuran, oxygen, hydrogen, and an inert gas.

[0071] In some embodiments, the inert gas includes, but is not limited to, nitrogen and / or argon.

[0072] Although the aforementioned ionized gas, as an auxiliary material, cannot directly provide hydrophobic groups, it can indirectly further optimize the preparation process and the performance of the porous solvent-resistant layer.

[0073] Specifically, inert gases can regulate the stability of the plasma environment, optimize the concentration distribution of high-energy particles in the plasma, ensure the smooth progress of the reaction, and guarantee the uniform and dense deposition of the porous solvent-resistant layer. Methane and pentane can be used as diluents to regulate the concentration of precursors, optimize the pore structure and thickness of the porous solvent-resistant layer, further improve the permeation flux and retention accuracy of the filter membrane, and make the core performance of the filter membrane more stable. Oxygen and hydrogen can form active oxygen and active hydrogen particles in the plasma, participate in the oxidation, dehydrogenation and bonding modification of the system, improve the cross-linking density and interfacial bonding strength of the coating, and enhance the solvent resistance of the porous solvent-resistant layer. 4-Vinylpyridine, trichlorosilane and tetrahydrofuran are auxiliary components. These auxiliary components can be used as solvent phases to disperse the molecules of the porous solvent-resistant layer, assist in the formation of separation pores on the porous solvent-resistant layer, regulate the reactivity of the reaction system, help the dissociation and cross-linking reaction of precursor molecules proceed smoothly, enhance the bonding force between the porous solvent-resistant layer and the porous filter membrane substrate, improve the structural stability of the porous solvent-resistant layer, and thus ensure the overall performance stability of the filter membrane.

[0074] In some implementations, the discharge power of the radio frequency ionization treatment is 1W to 100W, the pressure is 1Pa to 200Pa, and the temperature is 273K to 323K.

[0075] For example, the discharge power of the radio frequency ionization treatment is any value or a range of any two of the following: 1 W, 20 W, 40 W, 60 W, 80 W, 100 W.

[0076] For example, the pressure of the radio frequency ionization treatment is any value of 1 Pa, 50 Pa, 100 Pa, 150 Pa, 200 Pa, or a range of any two of these values.

[0077] For example, the temperature of the radio frequency ionization treatment is any value or a range of any two of the following: 273 K, 283 K, 293 K, 303 K, 313 K, 323 K, etc.

[0078] Radio frequency ionization is performed under conditions of 1 W to 100 W discharge power, 1 Pa to 200 Pa pressure, and 273 K to 323 K temperature. This range of conditions enables stable plasma generation and efficient ionization, which is suitable for the preparation of filter membranes.

[0079] Specifically, within this range, the discharge power can precisely control the concentration of high-energy particles in the plasma, ensuring the complete dissociation of precursor molecules and providing sufficient energy for the grafting and cross-linking reactions of precursor fragments and surface active groups of porous filter membrane substrate, thus ensuring the structural integrity of the porous solvent-resistant layer.

[0080] Specifically, within this pressure range, the contact efficiency between the plasma and the precursor can be optimized, promoting the uniform dispersion and reaction of precursor fragments, and ensuring that the porous solvent-resistant layer is uniformly deposited on the surface of the porous filter membrane substrate.

[0081] Specifically, within this temperature range, thermal damage to the porous filter membrane substrate and precursor can be avoided, while ensuring that the reaction rate is within a reasonable range, ensuring that the porous solvent-resistant layer forms a stable structure, thereby guaranteeing the core performance of the filter membrane, such as its resistance to organic solvents, retention accuracy, and permeation flux.

[0082] Under the above-mentioned radio frequency ionization treatment conditions, methane, oxygen, hydrogen, and inert gases are in a gaseous state at room temperature and pressure; pentane, 4-vinylpyridine, trichlorosilane, and tetrahydrofuran are in a liquid state at room temperature and pressure. However, under the low-pressure, carrier gas-carried, or temperature-controlled vaporization conditions of the radio frequency ionization treatment conditions of this invention, they can form stable vapors and enter the reaction chamber in gaseous form to participate in radio frequency ionization and subsequent reactions as ionized gases.

[0083] This invention prepares different plasmas by adjusting the type of precursor and the process parameters for plasma preparation.

[0084] In some example embodiments, when the precursor includes hexamethyldisiloxane, the discharge power, pressure and temperature conditions are 20W, 50Pa and 298K. The prepared plasma has a high concentration of active oxygen and silicon-containing precursor fragments, which can efficiently initiate grafting and cross-linking reactions on the substrate surface to form a dense coating rich in siloxanes. The surface roughness Rq of the porous solvent-resistant layer is 1.3nm~1.4nm.

[0085] In some example embodiments, when the precursor includes perfluorohexane, the discharge power, pressure and temperature conditions are 20W, 50Pa and 298K. The prepared plasma has the ability to stably dissociate the fluorine-containing precursor in an inert (nitrogen / argon) atmosphere, generating abundant fluorocarbon active fragments, thereby constructing a porous solvent-resistant layer with excellent hydrophobicity and solvent resistance on the substrate surface.

[0086] In some example embodiments, when the precursor includes ethylene, the discharge power, pressure, and temperature conditions are 15W, 100Pa, and 298K. The plasma prepared has the property of promoting the formation of carbon-carbon unsaturated bonds in a reducing atmosphere (such as hydrogen). This is beneficial for the carbon-containing fragments generated by the dissociation of the precursor to form stable alkyl or carbon-carbon unsaturated bond structures through cross-linking, thereby increasing the formation rate of the porous solvent-resistant layer.

[0087] In the process of plasma treatment of porous filter membrane substrate, the high-energy particles (electrons, ions, free radicals, etc.) in the plasma play a dual role. On the one hand, they stimulate the activation of molecules on the surface of the porous filter membrane substrate, generating active groups and providing binding sites for subsequent coating grafting. On the other hand, they stimulate the dissociation of precursor molecules, generating various active fragments.

[0088] Specifically, hexamethyldisiloxane, tetramethylsilane, and tetraethoxysilane dissociate to produce silicon-containing fragments, which then form siloxane alkyl groups during the reaction; n-pentane and ethylene dissociate to produce carbon-containing fragments, forming alkyl and carbon-carbon unsaturated bonds; toluene, styrene, and divinylbenzene dissociate to produce benzene ring-containing fragments, forming phenyl groups; and perfluorohexane, tetrafluoroethylene, and hexafluoropropylene dissociate to produce fluorine-containing fragments, forming fluorocarbon chains. These dissociated precursor active fragments undergo grafting and cross-linking reactions with the active groups on the surface of the porous filter membrane substrate, ultimately depositing a porous solvent-resistant layer uniformly on the surface of the porous filter membrane substrate.

[0089] In some implementations, the plasma treatment temperature is 273K~323K;

[0090] And / or, the discharge power of the plasma treatment is 1W~100W;

[0091] And / or, the plasma treatment pressure is 1 Pa to 200 Pa;

[0092] And / or, the plasma treatment time is 1 min to 60 min.

[0093] For example, the temperature of plasma treatment is any value or a range of any two of the following: 273 K, 283 K, 293 K, 303 K, 313 K, 323 K, etc.

[0094] For example, the plasma treatment pressure is any value or a range of any two of the following: 1 Pa, 50 Pa, 100 Pa, 150 Pa, 200 Pa, etc.

[0095] For example, the plasma treatment time is any value or a range of any two of the following: 1 min, 20 min, 40 min, 60 min, etc.

[0096] The present invention can adjust the surface morphology of the product filter membrane and change its hydrophobicity by adjusting the discharge power, pressure, temperature conditions and precursor type of the plasma treatment.

[0097] The plasma treatment temperature is 273 K~323 K, which can prevent the porous filter membrane substrate from undergoing structural deformation or performance degradation due to high temperature. At the same time, it ensures the reactivity of precursor molecules and the stability of plasma, ensuring that the porous solvent-resistant layer is tightly bonded to the porous filter membrane substrate and improving the adhesion of the porous solvent-resistant layer.

[0098] The plasma treatment pressure is 1 Pa to 200 Pa, which can optimize the stability of the plasma environment and the dispersion of precursors, promote the uniform reaction and deposition of precursor fragments, avoid defects such as uneven porosity and weak bonding in the porous solvent-resistant layer caused by improper pressure, and improve the structural stability of the porous solvent-resistant layer.

[0099] The plasma treatment time is 1 min to 60 min, which can ensure that the precursor reacts fully and regulate the thickness of the porous solvent-resistant layer. This ensures the functional integrity of the porous solvent-resistant layer and achieves a stable bond between the porous solvent-resistant layer and the porous filter membrane substrate. In this way, the core performance of the filter membrane is synergistically optimized, ensuring the stability and consistency of product quality and improving the yield of filter membrane preparation.

[0100] In some embodiments, when the precursor is pentane and the plasma treatment time is 5 min, the thickness of the porous solvent-resistant layer is 12 nm to 20 nm.

[0101] In some embodiments, when the precursor is pentane and the plasma treatment time is 20 min, the thickness of the porous solvent-resistant layer is 50 nm to 85 nm.

[0102] In some embodiments, when the precursor is hexamethyldisiloxane and the plasma treatment time is 5 min, the thickness of the porous solvent-resistant layer is 35 nm to 55 nm.

[0103] In some embodiments, when the precursor is hexamethyldisiloxane and the plasma treatment time is 20 min, the thickness of the porous solvent-resistant layer is 110 nm to 147 nm.

[0104] In some embodiments, when the precursor is toluene and the plasma treatment time is 5 min, the thickness of the porous solvent-resistant layer is 42 nm to 60 nm.

[0105] In some embodiments, when the precursor is toluene and the plasma treatment time is 20 min, the thickness of the porous solvent-resistant layer is 103 nm to 144 nm.

[0106] In some implementations, the discharge power, pressure, and temperature conditions of the radio frequency ionization treatment are independent of the corresponding parameter conditions of the plasma treatment.

[0107] For example, the discharge power, pressure, and temperature conditions of the aforementioned radio frequency ionization treatment and the corresponding parameters of the plasma treatment can be set and controlled independently, achieved through the phased independent parameter control unit of the preparation device. First, relying on the radio frequency generator, vacuum pump, gas inlet pipe, and matching temperature control unit, the discharge power, chamber pressure, and temperature are independently controlled to complete the radio frequency ionization treatment of the ionized gas to stably generate plasma. The parameters at this stage are only used for efficient plasma generation. After plasma generation is complete, the output power of the radio frequency generator, the chamber pressure matched with the vacuum pump and gas inlet pipe, and the chamber temperature set by the temperature control unit are readjusted through the independent control module of the preparation device to enter the plasma treatment stage. The parameters at this stage are independent of the radio frequency ionization treatment stage and are specifically adapted to the reaction requirements of precursor dissociation, active fragment grafting crosslinking, and porous solvent-resistant layer deposition. Through the above-mentioned phased and independent parameter control method, the process parameters of radio frequency ionization treatment and plasma treatment can be independently controlled, respectively meeting the different process requirements of plasma generation and coating formation, improving the controllability and adaptability of the reaction process.

[0108] In some preferred embodiments, the discharge power, pressure, and temperature conditions of the radio frequency ionization treatment are the same as the corresponding parameters of the plasma treatment.

[0109] The present invention does not limit the apparatus for preparing the filter membrane, as long as the apparatus is compatible with the above-mentioned filter membrane preparation process to obtain the filter membrane of the present invention.

[0110] For example, using such Figure 1 The preparation apparatus 1 shown prepares a filter membrane. The preparation apparatus 1 includes a radio frequency generator 11, an electrode 12, a vacuum pump 13, an air inlet pipe 14, and a carrier plate 15.

[0111] The plasma treatment includes the following steps: ultrasonic cleaning with isopropanol and deionized water for 15 minutes sequentially, followed by drying in a 60°C vacuum oven for 12 hours. The pretreated porous filter membrane substrate is then removed and fixed onto a carrier plate 15. The carrier plate 15 is then placed inside the cavity of the preparation device 1, positioning the porous filter membrane substrate in the reaction region between the electrodes 12. The vacuum pump 13 is activated to evacuate the cavity of the preparation device 1, creating a low-pressure environment for plasma treatment. Raw material gas, including precursor gas and ionized gas, is introduced into the cavity through the inlet pipe 14. The working pressure inside the cavity is maintained stable at 1 Pa to 200 Pa (i.e., the pressure for plasma treatment) through the coordinated regulation of the vacuum pump 13 and the inlet pipe 14.

[0112] The radio frequency generator 11 is turned on and maintained for 1 to 60 minutes. Under conditions of a discharge power of 1W to 100W (i.e., the discharge power for both radio frequency ionization and plasma treatment is 1W to 100W) and a cavity temperature of 273 K to 323 K (i.e., the temperature for both radio frequency ionization and plasma treatment is 273 K to 323 K), the ionized gas is subjected to radio frequency ionization to generate plasma. The high-energy particles in the plasma excite molecules on the surface of the porous filter membrane substrate to generate active groups, and simultaneously cause precursor molecules to dissociate, generating active hydrophobic groups containing siloxane alkyl groups, fluorocarbon chains, phenyl groups, alkyl groups, and carbon-carbon unsaturated bonds. These active hydrophobic groups undergo grafting and cross-linking reactions with the active groups on the surface of the porous filter membrane substrate, depositing a three-dimensional network of cross-linked porous solvent-resistant layers on the surface of the porous filter membrane substrate. The plasma treatment time is controlled within 1 to 60 minutes to ensure that the structure and performance of the porous solvent-resistant layer meet the standards.

[0113] After plasma treatment, turn off the radio frequency generator 11 and keep the raw material gas flowing for 0.5 min to 2 min. Then, turn off the gas inlet pipe 14 and wait for the pressure in the chamber to return to normal pressure before taking out the membrane. Anneal it in a vacuum oven at 120°C for 2 hours to obtain a filter membrane with a porous solvent-resistant layer.

[0114] Among them, the carrier plate 15 is a fluoropolymer carrier plate, and aluminum foil is laid between the two working electrodes 12.

[0115] This invention forms a nanoscale porous solvent-resistant layer on the surface of a porous filter membrane substrate through plasma treatment. The aforementioned radio frequency ionization treatment is the core component of the plasma treatment and a key step in plasma generation and maintenance. Therefore, the discharge power, pressure, and temperature conditions of the aforementioned radio frequency ionization treatment are the same parameters as the corresponding parameters of the plasma treatment, which are unified parameters in the same continuous process and run through the entire process of plasma generation, substrate activation, precursor dissociation, and coating deposition.

[0116] In a second aspect, the present invention provides a filter membrane obtained using the method for preparing a filter membrane according to the first aspect, the filter membrane comprising a porous filter membrane substrate and a porous solvent-resistant layer disposed on at least a portion of the surface of the porous filter membrane substrate.

[0117] This invention provides a filter membrane comprising a porous membrane substrate and a porous solvent-resistant layer. Through synergistic adaptation of their structures and performance, these two components jointly achieve the core function of the filter membrane. The porous membrane substrate serves as the basic support, providing the fundamental framework for molecular retention, while the porous solvent-resistant layer further optimizes filtration performance and imparts solvent resistance. Together, they optimize the filtration channels, balance filtration efficiency and retention precision, and maintain membrane structural stability, ensuring the porous solvent-resistant layer does not fail. Ultimately, they synergistically achieve precise separation and efficient filtration, enabling the filter membrane to operate stably for extended periods in organic solvent environments, thus meeting practical application requirements.

[0118] The porous solvent-resistant layer is obtained by plasma treatment of the aforementioned precursor and plasma. It possesses excellent solvent resistance properties, resisting the erosion of organic solvents and preventing degradation, dissolution, or detachment. At the same time, the porous solvent-resistant layer is disposed on at least part of the surface of the porous filter membrane substrate, forming a cross-linked structure with the porous filter membrane substrate, and is tightly bonded. This effectively maintains the overall structural integrity and dimensional stability of the filter membrane, reduces the loss of filter membrane components in organic solvents, and ensures that the filter membrane can maintain a high quality retention rate even after long-term contact with organic solvents.

[0119] In some preferred embodiments, the filter membrane satisfies at least one of the following conditions:

[0120] a. After immersing the filter membrane in an organic solvent at 25°C for 168 h, the mass retention rate of the filter membrane is ≥99%;

[0121] b. The molecular weight cutoff of the filter membrane is 300 Da~600 Da;

[0122] c. The permeation flux of the filter membrane is 3.7 L·m -2 ·h -1 ·bar -1 ~11.5 L·m -2 ·h -1 ·bar -1 .

[0123] For example, the quality retention rate mentioned above is any value or a range of any two of 99%, 99.2%, 99.4%, 99.6%, 99.8%, 100%.

[0124] For example, the molecular weight cutoff of the filter membrane is any value of 300 Da, 40 Da, 500 Da, 600 Da, or any combination of both.

[0125] For example, the permeation flux of the filter membrane is 3.7 L·m -2 ·h -1 ·bar -1 4.0 L·m-2 ·h -1 ·bar -1 4.5 L·m -2 ·h -1 ·bar -1 5 L·m -2 ·h -1 ·bar -1 5.5 L·m -2 ·h -1 ·bar -1 6 L·m -2 ·h -1 ·bar -1 6.5 L·m -2 ·h -1 ·bar -1 7 L·m -2 ·h -1 ·bar -1 7.5 L·m -2 ·h -1 ·bar -1 8 L·m -2 ·h -1 ·bar -1 8.5 L·m -2 ·h -1 ·bar -1 9 L·m -2 ·h -1 ·bar -1 9.5 L·m -2 ·h -1 ·bar -1 10 L·m -2 ·h -1 ·bar -1 10.5 L·m -2 ·h -1 ·bar -1 11 L·m -2 ·h -1 ·bar -1 11.5 L·m -2 ·h -1 ·bar -1 The range of any value in the range, or any combination of both.

[0126] Through the synergistic effect of the porous filter membrane substrate and the porous solvent-resistant layer, the filter membrane can achieve a mass retention rate of ≥99% after immersion in organic solvent at 25°C for 168 hours.

[0127] The porous structure of the porous filter membrane substrate provides a basic molecular retention framework, laying the foundation for molecular separation within the target molecular weight range. The porous solvent-resistant layer further refines the filtration channels, precisely matching the retention requirements of 300 Da to 600 Da. This allows for the accurate interception of target molecules within this range while allowing smaller molecules (such as solvent impurities) to pass freely, thus achieving precise sieving of specific molecules and meeting the preset molecular weight cutoff requirements. Through the synergistic adaptation of the porous structure of the porous filter membrane substrate and the porous solvent-resistant layer, the molecular weight cutoff (MWCO) of the filter membrane can be stabilized within the range of 300 Da to 600 Da.

[0128] The porous membrane substrate possesses a porous structure, which reduces fluid flow resistance during the filtration process, providing a fundamental support for smooth fluid passage. The porous solvent-resistant layer's porous structure prevents excessive density that could lead to flux reduction, and synergizes with the substrate's retention performance. This ensures efficient passage of organic solvents through the membrane while maintaining retention accuracy, ultimately stabilizing the membrane's permeation flux within a preset range. Through the synergistic effect of the porous structure of the membrane substrate and the porous solvent-resistant layer, the permeation flux of the membrane in the filtered material can be maintained at 3.7 L·m⁻¹. -2 ·h -1 ·bar -1 ~11.5 L·m -2 ·h -1 ·bar -1 .

[0129] In some embodiments, the organic solvent includes, but is not limited to, at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, dimethylmarine, tetrahydrofuran, methanol, ethanol, and heptane.

[0130] In some embodiments, after the filter membrane is immersed in N,N-dimethylacetamide for 168 h, the permeate flux of the immersed filter membrane is 2.3 L·m. -2 ·h -1 ·bar -1 ~7.5 L·m -2 ·h -1 ·bar -1 .

[0131] In some embodiments, after the filter membrane is immersed in tetrahydrofuran for 168 h, the permeate flux of the immersed filter membrane is 1.6 L·m. -2 ·h -1 ·bar -1 ~4.9 L·m -2 ·h -1 ·bar -1 .

[0132] In some embodiments, after the filter membrane is immersed in methanol for 168 h, the permeate flux of the immersed filter membrane is 3.7 L·m. -2 ·h -1 ·bar -1 ~11.5 L·m -2 ·h -1 ·bar -1 .

[0133] In some embodiments, after the filter membrane is immersed in heptane for 168 h, the permeate flux of the immersed filter membrane is 3.4 L·m. -2 ·h -1 ·bar -1 ~7.2 L·m -2 ·h -1 ·bar -1 .

[0134] In some embodiments, after the filter membrane is immersed in N,N-dimethylacetamide for 168 h, the molecular weight cutoff of the immersed filter membrane is 150 Da to 800 Da.

[0135] In some embodiments, after the filter membrane is soaked in tetrahydrofuran for 168 h, the molecular weight cutoff of the soaked filter membrane is 150 Da to 800 Da.

[0136] In some embodiments, after the filter membrane is soaked in methanol for 168 h, the molecular weight cutoff of the soaked filter membrane is 150 Da to 600 Da.

[0137] In some embodiments, after the filter membrane is soaked in heptane for 168 h, the molecular weight cutoff of the soaked filter membrane is 150 Da to 700 Da.

[0138] In some embodiments, after the filter membrane is soaked in the above-mentioned organic solvent for 72h to 168h, the mass retention rate of the soaked filter membrane is ≥99% and the swelling rate is 1% to 3%.

[0139] In some embodiments, the filter membrane has a rejection rate of ≥99% for crystal violet in a crystal violet-methanol solution.

[0140] In some embodiments, the porous solvent-resistant layer has a three-dimensional network cross-linked structure.

[0141] In some preferred embodiments, the degree of crosslinking of the porous solvent-resistant layer is greater than 80%.

[0142] For example, the degree of crosslinking is any value or a range of any two of 80%, 85%, 90%, 95%, 100%, etc.

[0143] The porous solvent-resistant layer has a three-dimensional network cross-linked structure, which can significantly improve the structural stability and density of the porous solvent-resistant layer itself, providing a solid structural support for the organic solvent resistance and retention accuracy of the filter membrane, enabling the porous solvent-resistant layer to stably perform its filtration and solvent resistance functions.

[0144] The cross-linking degree of the porous solvent-resistant layer is greater than 80%, which enables the molecular chains of the porous solvent-resistant layer to form a stable three-dimensional network structure, enhances the bonding strength between the porous solvent-resistant layer and the porous filter membrane substrate, improves the mechanical properties of the porous solvent-resistant layer, ensures that the porous solvent-resistant layer maintains structural integrity during long-term use and immersion in organic solvents, guarantees the long-term stability of the core performance of the filter membrane, and further adapts to the long-term service requirements in organic solvent environments.

[0145] In some embodiments, the porous solvent-resistant layer includes at least one of fluorocarbon chains, siloxane alkyl groups, phenyl groups, carbon-carbon unsaturated bonds, and alkyl groups;

[0146] And / or, the thickness of the porous solvent-resistant layer is 1 nm to 150 nm;

[0147] And / or, the porosity of the porous solvent-resistant layer is 60%~80%;

[0148] And / or, the surface roughness Rq of the porous solvent-resistant layer is 1 nm to 2.5 nm.

[0149] For example, the thickness of the porous solvent-resistant layer is any value or a range of any two of the following: 1 nm, 30 nm, 60 nm, 90 nm, 120 nm, 150 nm.

[0150] For example, the porosity of the porous solvent-resistant layer is any value of 60%, 65%, 70%, 75%, 80%, or any combination of both.

[0151] For example, the surface roughness Rq of the porous solvent-resistant layer is any value of 1 nm, 1.5 nm, 2 nm, 2.5 nm, or a range of any combination of both.

[0152] The porous solvent-resistant layer includes at least one of fluorocarbon chains, siloxane groups, phenyl groups, carbon-carbon unsaturated bonds, and alkyl groups. All of these groups are hydrophobic, effectively improving the hydrophobicity and organic solvent resistance of the porous solvent-resistant layer, and enhancing the stability of the filter membrane in organic solvent environments. The stability of these hydrophobic groups stems from the presence of highly energetic covalent bonds (such as Si-O bonds, CF bonds, etc.) within or between molecules, resulting in chemical stability and resistance to solvent corrosion or reactions.

[0153] The thickness of the porous solvent-resistant layer in this invention refers to the dimension of the coating perpendicular to the surface of the porous filter membrane substrate. It is used to characterize the thickness of the coating and is distinguished from the planar dimensions such as the length and width of the substrate and the coating. This range can ensure the functional integrity of the porous solvent-resistant layer while avoiding the decrease in permeation flux caused by excessive thickness, thus achieving a synergistic improvement in solvent resistance and permeation flux, and balancing filtration efficiency and structural stability.

[0154] The porous solvent-resistant layer has a porosity of 60% to 80%, which can form a reasonable fluid flow channel. This ensures the retention accuracy of the filter membrane and reduces fluid flow resistance, thus guaranteeing that the filter membrane can achieve the target permeation flux.

[0155] The surface roughness Rq of the porous solvent-resistant layer is 1nm~2.5nm, which can reduce the adsorption of pollutants on the surface of the porous solvent-resistant layer during the filtration process, improve the anti-fouling ability of the filter membrane, and at the same time ensure the surface smoothness of the porous solvent-resistant layer to ensure uniform fluid flow and further improve the stability of filtration performance.

[0156] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0157] The present invention will be further described below with reference to specific embodiments.

[0158] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be obtained through commercial channels.

[0159] The following examples all use the following: Figure 1 The preparation apparatus 1 shown is used to prepare a filter membrane, wherein the cavity volume of the preparation apparatus 1 is 31.8L.

[0160] like Figure 1 As shown, the preparation apparatus 1 includes a radio frequency generator 11, an electrode 12, a vacuum pump 13, an air inlet pipe 14, and a carrier plate 15.

[0161] Example 1

[0162] The filter membrane was prepared using the following method:

[0163] The porous filter membrane substrate was ultrasonically cleaned sequentially with isopropanol and deionized water for 15 minutes each, and then dried in a vacuum oven at 60°C for 12 hours. The pretreated porous filter membrane substrate was then removed and fixed onto a carrier plate 15. The carrier plate 15 was then placed inside the cavity of the preparation apparatus 1, positioning the porous filter membrane substrate within the reaction region between the electrodes 12. The vacuum pump 13 was activated to evacuate the cavity of the preparation apparatus 1, adjusting the pressure inside the cavity to <5.0 × 10⁻⁶. -3 Pa. Raw material gas, including precursor gas and ionized gas, is introduced into the cavity through the air inlet pipe 14. The working pressure in the cavity is maintained at 50 Pa (i.e., the pressure of plasma treatment is 50 Pa) through the coordinated regulation of vacuum pump 13 and air inlet pipe 14.

[0164] Turn on the radio frequency generator 11 and maintain it at a discharge power of 20W and a temperature of 298K for 10 minutes to perform plasma treatment on the raw material gas (the raw material gas includes the precursor gas and the ionized gas). (That is, the discharge power, pressure and temperature conditions of the radio frequency ionization treatment are the same as the corresponding parameters of the plasma treatment.)

[0165] After turning off the power to the RF generator 11 and maintaining the flow of raw gas for 1 minute, the inlet pipe 14 is closed. After the pressure inside the chamber returns to normal, the membrane is removed and annealed in a vacuum oven at 120°C for 2 hours to obtain the filter membrane S-1 with a porous solvent-resistant layer.

[0166] In this process, a precursor gas (hexamethyldisiloxane vapor) was prepared using a precursor (hexamethyldisiloxane, purity ≥99.0%), and the precursor gas was carried out using an argon (Ar) carrier gas in a 30°C bubble bottle at a flow rate of 5 ml / min; the ionized gases were oxygen and Ar.

[0167] The ultrafiltration membrane made of polyacrylonitrile (PAN) is used as the porous membrane substrate. The porous membrane substrate has a porosity of 45% and an average pore size of 80 nm.

[0168] Example 2

[0169] Example 2 is essentially the same as Example 1, except that the precursor is perfluorohexane (PFH) and the ionized gases are nitrogen and argon. The precursor gas (perfluorohexane vapor) was prepared using perfluorohexane, and a 0°C ice-water bath bubble flask was used to carry the precursor gas out via Ar carrier gas at a flow rate of 10 ml / min. The resulting filter membrane S-2 was obtained.

[0170] Example 3

[0171] Example 3 is essentially the same as Example 1, except that the precursor is ethylene (i.e., the precursor gas is ethylene, flow rate 5 ml / min), the ionization gas is hydrogen (flow rate 40 ml / min), the plasma treatment discharge power is 15 W (continuous wave, 13.56 MHz), the time is 5 min, and the pressure is 100 Pa. The resulting filter membrane S-3 was obtained.

[0172] Example 4

[0173] Example 4 is essentially the same as Example 1, except that the precursor is tetramethylsilane and the ionization gases are nitrogen and argon. The precursor gas (tetramethylsilane vapor) is prepared using tetramethylsilane, and a 0°C ice-water bath bubble flask is used to carry it out via argon carrier gas at a flow rate of 10 ml / min. The plasma treatment discharge power is 30 W, the time is 15 min, and the temperature is 333 K. The resulting filter membrane is S-4.

[0174] Example 5

[0175] Example 5 is essentially the same as Example 1, except that the precursor is perfluorooctyltriethoxysilane and the ionization gas is argon. The precursor gas (perfluorooctyltriethoxysilane vapor) was prepared using perfluorooctyltriethoxysilane, and a 60°C bubble bottle was used to carry the precursor gas out via Ar carrier gas at a flow rate of 2 ml / min. The plasma treatment time was 30 min at a temperature of 313 K. The resulting filter membrane S-5 was obtained.

[0176] Example 6

[0177] Example 6 is essentially the same as Example 1, except that the precursor is n-pentane. A filter membrane S-6 was obtained.

[0178] Example 7

[0179] Example 7 is essentially the same as Example 1, except that the precursor is isopentane. A filter membrane S-7 was obtained.

[0180] Example 8

[0181] Example 8 is basically the same as Example 1, except that the precursor is toluene. A filter membrane S-8 was obtained.

[0182] Example 9

[0183] Example 9 is essentially the same as Example 1, except that the porous filter membrane substrate is an ultrafiltration membrane made of polyetheretherketone (PEEK) material (porosity 45%, average pore size 80nm). Filter membrane S-9 is obtained.

[0184] Example 10

[0185] Example 10 is basically the same as Example 2, except that the porous filter membrane substrate is a PEEK ultrafiltration membrane (porosity of 45%, average pore size of 80nm). Filter membrane S-10 is obtained.

[0186] Example 11

[0187] Example 11 is basically the same as Example 6, except that the porous filter membrane substrate is a PEEK ultrafiltration membrane (porosity 45%, average pore size 80nm). Filter membrane S-11 is obtained.

[0188] Examples 12-17

[0189] Examples 12-17 are basically the same as Example 1, with the only difference being Table 1 below.

[0190] Table 1:

[0191]

[0192] Comparative Example 1

[0193] Preparation of a PEEK membrane:

[0194] A 12wt% PEEK solution was coated onto a polypropylene nonwoven fabric substrate, followed by film formation via phase inversion and sequential solvent replacement (water, acetone, tetrahydrofuran). Finally, the film was dried and cured at 120°C to obtain PEEK film P-1.

[0195] Comparative Example 2

[0196] Preparation of a PAN film:

[0197] A 12 wt% PAN solution was coated onto a polypropylene nonwoven fabric substrate, followed by film formation via phase inversion and sequential solvent replacement (water, acetone, tetrahydrofuran). Finally, the film was dried and cured at 120°C to obtain PAN film P-2.

[0198] Test Example 1

[0199] Under test conditions of 25℃ and 0.2MPa, a methanol solution containing 1% crystal violet (solute: crystal violet, solvent: methanol, mass ratio of crystal violet to methanol: 1:99) and an aqueous solution containing 1% Na2SO4 (solute: Na2SO4, solvent: deionized water, mass ratio of Na2SO4 to deionized water: 1:99) were used as test systems to perform performance tests on the filter membranes prepared in Examples 1-5 and 9-11, as well as the PEEK membrane prepared in Comparative Example 1. Membrane sheets of uniform size were cut from each test membrane, ensuring they were undamaged and wrinkle-free, and the effective filtration area of ​​the membrane sheet was recorded (denoted as A, unit: m²). The membrane sheets were then placed in an ultrafiltration / nanofiltration test device and sealed tightly. The results are shown in Table 2. The specific test and calculation methods are as follows:

[0200] 1) Retention rate of crystal violet in methanol solution: Using a methanol solution of crystal violet as the test medium, the concentration of crystal violet in the raw material solution before filtration (C) was measured. o ) and the concentration of crystal violet in the permeate after filtration (C p The retention rate is calculated using the following formula 1:

[0201] Formula 1;

[0202] Where R1 is the methanol solution rejection rate of crystal violet (unit: %); C o The concentration of crystal violet in the feed solution (unit: mg / L); C p The concentration of crystal violet in the permeate (unit: mg / L).

[0203] 2) Retention rate of Na2SO4 in aqueous solution: Using an aqueous solution of Na2SO4 as the test medium, the concentration of Na2SO4 in the raw material solution before filtration (C) was measured. o ') and the concentration of Na2SO4 in the filtered permeate (C p The retention rate is calculated using the following formula 2:

[0204] Formula 2;

[0205] Wherein, R2 is the aqueous solution rejection rate of Na2SO4 (unit: %); C o 'C' represents the concentration of Na2SO4 in the feed solution (unit: g / L); p 'This represents the concentration of Na2SO4 in the permeate (unit: g / L).

[0206] 3) Calculate the permeation flux of methanol in the methanol solution of crystal violet and the permeation flux of water in the aqueous solution of Na2SO4 according to Formula 3. The results are shown in Table 2.

[0207] Formula 3;

[0208] Where J: permeation flux (unit: L·m) -2 ·h -1 ·bar -1 V: Total volume of solvent (or solution) permeating the membrane during the test period (unit: L); A: Effective filtration area of ​​the membrane (unit: m²). 2 ); t: total test time (in hours); P: transmembrane pressure applied across the membrane (in bar).

[0209] Table 2:

[0210]

[0211] Test Example 2

[0212] The swelling properties and degradation properties of the filter membranes prepared in Examples 1-5 and Comparative Example 1 were tested, and the results are shown in Table 3. The specific testing and calculation methods are as follows:

[0213] Rectangles of 5 cm in length and width were cut from the membrane to be tested. All samples were then dried in a vacuum drying oven at 50°C to constant weight to completely remove moisture and residual solvent. The samples were accurately weighed using an analytical balance and recorded as dry weight m1. The dried membrane samples were then completely immersed in a sealed container containing N,N-dimethylacetamide solvent, ensuring complete solvent coverage, at 25°C. Samples were taken and weighed at 24 hours, 72 hours, and 168 hours of immersion to investigate time dependence.

[0214] After the predetermined time is reached, the membrane sample is removed with tweezers, and the solvent droplets adhering to the surface but not absorbed are quickly and gently absorbed with filter paper. The wet weight m1' is weighed immediately, and the swelling rate for the corresponding treatment time is calculated using Formula 4.

[0215] The membrane, after 168 hours of soaking, was dried in a vacuum drying oven at 50°C to constant weight to completely remove moisture and residual solvent. The membrane was accurately weighed using an analytical balance and recorded as dry weight m2. The mass retention rate was calculated using Formula 5.

[0216] Formula 4;

[0217] Formula 5;

[0218] Where m1 is the dry weight of the membrane sample before immersion, in grams; m1' is the wet weight of the membrane sample after the corresponding immersion time (24 h, 72 h, 168 h), in grams; and m2 is the dry weight of the membrane sample after immersion for 168 h and drying to constant weight.

[0219] Table 3:

[0220]

[0221] Test Example 3

[0222] The surface morphology and structural parameters of the test samples (filter membranes prepared in Examples 1 and 6) were detected using atomic force microscopy (AFM). The method is as follows: The test samples were cut to appropriate sizes and firmly fixed on the sample stage. Pre-test balancing was performed in a dust-free and vibration-proof environment at room temperature. A tapping mode was selected, matched with a flexible microcantilever probe, and the scanning range was set to 50 nm–100 μm and the scanning speed to 1–10 μm / s. A3D atomic force morphology images and raw height data of the composite membrane surface were acquired. The morphology images were preprocessed using the instrument's accompanying analysis software, including baseline correction, plane fitting, and noise filtering. Surface height distribution data were extracted, and the root mean square roughness Rq was calculated. The average pore size and porosity of the filter membrane were obtained through image analysis using the software's image analysis module. A cross-sectional sample of the composite membrane was prepared to expose the coating-base membrane interface. AFM morphology images of the cross-section were acquired, and the height difference between the coating and the base membrane was measured to determine the thickness of the porous coating. The results are shown in Table 4. Figure 2 The surface atomic force topography diagram is shown in Example 1. Figure 3 This is a surface atomic force topography image of Example 6. Figure 2 and Figure 3 The middle arrow indicates the pore structure of the porous coating.

[0223] Test Example 4

[0224] The retention performance of the composite membrane was tested using polyethylene glycol (PEG) standard solutions (polyethylene glycol as solute and water as solution) with molecular weights of 200 Da, 300 Da, 400 Da, 500 Da, 600 Da, and 800 Da. By measuring the retention rate of PEG at each molecular weight of the composite membrane, molecular weight retention curves were plotted and fitted to calculate the average pore size of the composite membrane. The results are shown in Table 4.

[0225] Table 4:

[0226]

[0227] Test Example 5

[0228] After immersing the filter membrane S-1 in an aqueous system (containing methanol / ethanol, water, and sodium sulfate, with a mass ratio of 80:19:1) at 25℃ for 5 minutes, samples were taken for testing, and scanning electron microscope (SEM) images were obtained. Figure 4 As shown.

[0229] The filter membrane S-6 was immersed in a tetrahydrofuran (THF) system (containing tetrahydrofuran, water, and magnesium sulfate, with a mass ratio of 80:19:1) at 25°C for 5 minutes, and then samples were taken for testing to obtain scanning electron microscope (SEM) images. Figure 5 As shown.

[0230] Test Example 6

[0231] The filter membranes prepared in Examples 1, 2, 4, 9-11, the PEEK membrane P-1 prepared in Comparative Example 1, and the PAN membrane P-2 prepared in Comparative Example 2 were used as test samples.

[0232] The relationship between the molecular weight cutoff and the retention rate was tested on the test samples.

[0233] The specific testing and calculation methods are as follows:

[0234] Pre-test preparation:

[0235] 1) Prepare test raw material solution

[0236] A tetrahydrofuran standard solution of styrene oligomers with molecular weights of 200 Da, 300 Da, 400 Da, 500 Da, 600 Da, and 800 Da was prepared as the test raw material solution.

[0237] Cut membrane pieces of the same size from each filter membrane to be tested, ensuring that the membrane pieces are undamaged and wrinkle-free, and record the effective filtration area of ​​the membrane piece (denoted as A, in m²); put the membrane pieces into the nanofiltration test device and seal it tightly.

[0238] 2) Test condition calibration: Start the test device and adjust the test temperature to 30℃, maintain the constant temperature for 30 minutes to ensure the temperature of the entire test system is stable; gradually adjust the test pressure to 30 bar, keep the pressure constant, remove air bubbles in the device, so that the test system reaches a stable operating state and avoid temperature and pressure fluctuations from interfering with the permeation flux and rejection rate.

[0239] 3) Test Operation Steps

[0240] The sample was soaked in the above-mentioned raw material solution (tetrahydrofuran solution of styrene oligomers) for 160 hours at 30 bar and 30°C.

[0241] The feed solution before filtration and the permeate after filtration were collected separately. The concentration of styrene oligomers in both solutions was accurately determined using gel permeation chromatography (GPC), and denoted as the concentration of styrene oligomers in the feed solution (B0) and the concentration of styrene oligomers in the permeate (B2). p ).

[0242] Calculate the retention rate (R, in %) using Formula 6:

[0243] Formula 6;

[0244] Wherein, B0 is the concentration of styrene oligomers in the feed solution before filtration (unit: g / L); B p R represents the concentration of styrene oligomers in the permeate after filtration (in g / L); R is the retention rate of the filtration membrane (in %).

[0245] The molecular weight cutoff (MWCO) at the corresponding cutoff rate is usually the molecular weight of the oligomer when the cutoff rate reaches 90%.

[0246] Record the molecular weight cutoffs corresponding to different retention rates, and plot the cutoff curves of the relationship between the molecular weight cutoff and the retention rate. The results are as follows: Figure 6 and Figure 7 As shown.

[0247] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a filter membrane, characterized in that, Includes the following steps: The porous filter membrane substrate is placed in an environment containing both plasma and precursor, and plasma treatment is performed to obtain the filter membrane. The precursor includes at least one of perfluorooctyltriethoxysilane, pentane, ethylene, toluene, perfluorohexane, styrene, divinylbenzene, hexamethyldisiloxane, tetramethylsilane, tetraethoxysilane, tetrafluoroethylene, and hexafluoropropylene. The porosity of the porous filter membrane substrate is 20%~80%; The average pore size of the porous filter membrane substrate is 1 nm to 500 nm. The porous filter membrane substrate is made of polyetheretherketone and / or polyacrylonitrile. The plasma treatment temperature is 273K~333K; The discharge power of the plasma treatment is 1W~100W; The plasma treatment pressure is 1 Pa to 200 Pa; The plasma treatment time is 1 min to 60 min; The plasma preparation process includes the following steps: radio frequency ionization treatment using ionized gas to generate the plasma; The ionized gas includes at least one of oxygen, hydrogen, and inert gas; The discharge power of the radio frequency ionization treatment is 1W~100W, the pressure is 1Pa~200Pa, and the temperature is 273K~333K.

2. A filter membrane obtained by the method for preparing the filter membrane as described in claim 1, characterized in that, The filter membrane includes the porous filter membrane substrate and a porous solvent-resistant layer disposed on at least a portion of the surface of the porous filter membrane substrate.

3. The filter membrane according to claim 2, characterized in that, The degree of crosslinking of the porous solvent-resistant layer is greater than 80%.

4. The filter membrane according to claim 2, characterized in that, The thickness of the porous solvent-resistant layer is 1 nm to 150 nm. And / or, the porosity of the porous solvent-resistant layer is 60%~80%; And / or, the surface roughness Rq of the porous solvent-resistant layer is 1 nm to 2.5 nm.

5. The filter membrane according to any one of claims 2-4, characterized in that, The filter membrane satisfies at least one of the following conditions: a. After the filter membrane is immersed in an organic solvent at 20℃~25℃ for 72h~168h, the mass retention rate of the immersed filter membrane is ≥99%; b. The molecular weight cutoff of the filter membrane is 300 Da to 600 Da; c. The permeation flux of the filter membrane is 3.7 L•m -2 •h -1 •bar -1 ~11.5 L•m -2 •h -1 •bar -1 .

Images