A preparation method of a TFP-TAPA / SPEEK composite membrane

Abstract

The application relates to the technical field of film materials, and discloses a preparation method of a TFP-TAPA / SPEEK composite film, which comprises the following steps: S1: dissolving TFP in dichloromethane and dissolving TAPA in DMF, and then performing ultrasonic treatment to obtain an aldehyde solution A and an amine solution B; S2: reacting the aldehyde solution A with the amine solution B in an aqueous acetic acid solution, and then standing at room temperature to obtain a preliminary film; S3: washing the preliminary film with a solvent, and then drying to obtain a dried film; S4: placing the dried film into deionized water and performing ultrasonic treatment to obtain a TFP-TAPA nanosheet water suspension; and S5: mixing the nanosheet suspension with a SPEEK solution, coating the mixture on a substrate, drying, and then performing functional modification and crosslinking treatment. Through composite film structure design, an ion sieving membrane with high stability and adjustable pore size is formed, and through optimization of nanosheet dispersion and crosslinking treatment, the chemical stability and mechanical strength of the membrane are enhanced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of film materials, in particular to a preparation method of a TFP-TAPA / SPEEK composite film. BACKGROUND

[0002] In recent years, with the rapid development of energy conversion and storage technology, functional membrane materials play an important role in the fields of fuel cells, flow batteries, ion sieving, seawater desalination and the like. Among them, polymer-based composite membranes have become a research focus due to their excellent flexibility, processability and high chemical stability. SPEEK is a widely used ion exchange membrane material, which has high application value in the fields of fuel cells and water electrolysis due to its excellent proton conductivity and good chemical stability. At the same time, covalent organic framework materials have attracted more and more attention in the field of separation membranes due to their regular pore structure, high specific surface area and good structural stability. In recent years, by doping COF nanosheets into the polymer matrix, the pore structure of the membrane can be further optimized, and the ion transmission channel can be improved, so as to improve the selective permeation performance of the membrane. However, the existing preparation method of COF / polymer composite membrane still has certain limitations, and it is difficult to ensure the mechanical strength of the membrane while considering high ion selectivity and chemical stability.

[0003] Although existing researches have tried to improve the performance of the composite membrane by doping COF materials, due to the difficulty in controlling the uniform dispersion of COF nanosheets, the pore structure of the composite membrane is not uniform, which affects the ion transmission rate. In addition, the compatibility of part of the COF filler in the membrane matrix is poor, which easily causes phase separation, and weakens the mechanical properties and long-term use stability of the membrane. On the other hand, although SPEEK has high proton conductivity, it has a risk of degradation in a high-acid or strong-oxidation environment, which limits its application in harsh working conditions. The existing preparation method of the composite membrane is usually difficult to improve the ion sieving ability of the membrane while considering the structural stability, chemical corrosion resistance and long service life of the membrane. Therefore, how to ensure the uniform dispersion of COF materials and optimize the microstructure of the composite membrane through reasonable composite strategy to improve the comprehensive performance has become a technical problem to be solved in the field. SUMMARY

[0004] In view of the deficiencies of the prior art, the application provides a preparation method of a TFP-TAPA / SPEEK composite film, which solves the problems of improving ion selectivity, uniformity and long-term stability of the membrane.

[0005] To achieve the above object, the application is implemented by the following technical scheme: a preparation method of a TFP-TAPA / SPEEK composite film, comprising the following steps:

[0006] Dissolve 21mg-50mg of TFP in 80mL-200mL of dichloromethane, and ultrasonic treatment for 30min-60min to obtain aldehyde solution A, and then dissolve 29mg-60mg of TAPA in 50mL-100mL of DMF, and ultrasonic treatment for 30min-60min to obtain amine solution B;

[0007] Slowly pour the aldehyde solution A into the bottom of a beaker containing 50mL-100mL of 3mol / L aqueous acetic acid solution, and then dropwise add the amine solution B to the upper layer of the aqueous acetic acid solution, and stand for 1-3 days to obtain a TFP-TAPA film;

[0008] Wash the obtained TFP-TAPA film with dichloromethane, ethanol, acetone, DMF and deionized water, respectively, and each solvent is washed for 3-5 times to ensure that the unreacted chemicals are removed, and then dry the washed TFP-TAPA film in a vacuum oven to obtain a dried TFP-TAPA film;

[0009] Put 50mg-100mg of the dried TFP-TAPA film into 200mL-400mL of deionized water, and use 280W ultrasonic treatment for 6h-12h to ensure uniform dispersion of the nanosheets, and obtain a TFP-TAPA nanosheet water suspension;

[0010] Mix the TFP-TAPA nanosheet water suspension with the SPEEK solution at a mass ratio of 1:1-2, and shake on a constant temperature shaker for more than 12 hours to ensure uniformity of the composite solution, and then coat the composite solution on a substrate, and after the solution is completely dried to form a composite film, perform functional modification on the obtained composite film, and finally perform crosslinking treatment on the modified composite film.

[0011] Preferably, in the forming step of the TFP-TAPA film, the ratio of the aldehyde solution A to the amine solution B is 1:1-1:2, and the reaction temperature is room temperature to 25-40℃.

[0012] Preferably, in the drying of the TFP-TAPA film, the temperature of the vacuum oven is set to 60-80℃, the drying time is 2-3h, and the humidity is controlled to be 30%-50%.

[0013] Preferably, the concentration of the SPEEK solution is 5%-10%, and the solution is stirred for more than 6 hours at a temperature of 50-70℃ to ensure complete dissolution of the SPEEK.

[0014] Preferably, the composite film is coated on the substrate by a doctor blade method, the film thickness is 20-100μm, and the film is dried in a vacuum condition for 4-6h at a drying temperature of 60-80℃.

[0015] Preferably, the functional modification of the composite membrane includes introducing sulfonic acid groups or amino groups on the surface or channel of the membrane, the introduction of sulfonic acid groups is treated by an acidic solution for 6-12 hours, and the introduction of amino groups is treated by ammonia gas for 4-8 hours.

[0016] Preferably, the cross-linking step of the composite membrane includes adding a cross-linking agent glutaraldehyde and reacting at 60-80 DEG C for 12-24 hours, and the concentration of the cross-linking agent is 0.1-1%.

[0017] Preferably, the TFP-TAPA nanosheet water suspension is centrifuged to remove undispersed particles, the centrifugation conditions are 3000-5000 rpm for 30-60 minutes, and uniformly dispersed nanosheets are obtained.

[0018] Preferably, the composite membrane has a higher hydrogen ion permeability than vanadium ion permeability, and a selectivity ratio S is greater than 5, and the selectivity S is calculated by the following formula: + And vanadium ion Vn +

[0019]

[0020] Wherein, P H+ And P Vn+ Respectively represent the permeability of hydrogen ion and vanadium ion.

[0021] Preferably, the composite membrane has a porosity of at least 50%, and a pore size distribution of 0.2-1.0 nm, and the porosity and pore size are determined by scanning electron microscopy and nitrogen adsorption method.

[0022] The application provides a preparation method of a TFP-TAPA / SPEEK composite membrane.

[0023] 1、The application forms an ion sieve membrane with high stability and adjustable pore size through the structure design of the TFP-TAPA / SPEEK composite membrane, and the chemical stability and mechanical strength of the membrane are enhanced by optimizing the dispersion of nanosheets and cross-linking treatment.

[0024] ​2、The aldehyde amine condensation forms a covalent organic framework structure, and a high-ordered ion transmission channel is constructed in the membrane, ensuring the high efficient ion screening ability of the membrane. Generally, the ion screening precision is difficult to guarantee due to the random distribution of pores in the polymer membrane, resulting in unstable permeability in actual application. The fine control of the pore size is realized through the controllable covalent organic framework self-assembly process, the hydrogen ion permeation rate is improved, and the permeation of other large size ions is inhibited, so that the membrane material has more excellent ion selectivity and longer service life.

[0025] 3、The TFP-TAPA nanosheet is prepared by ultrasonic peeling, the high dispersibility and stability of the material are ensured, and the basis for uniform molding of the composite membrane is provided. Compared with the uneven dispersion of the nanofiller in the polymer matrix in the prior art, the problems of unstable membrane structure and increased local defects are solved, the ultrasonic peeling power and time are optimized, the uniformity and size controllability of the nanosheet are ensured, so that the mechanical strength of the composite membrane is improved, the internal stress is reduced, and the overall stability is improved.

[0026] 4、The durability and chemical stability of the membrane are further improved through cross-linking enhancement technology after the membrane is formed. The ordinary SPEEK membrane is easy to degrade in strong acid and strong oxidizing environment, and has a short service life. The solvent resistance and chemical corrosion resistance of the membrane are improved through the cross-linking strategy, the problem of structure collapse of the membrane during use is avoided, the membrane can stably operate for a long time under more harsh working conditions, and the application requirements of fuel cells, flow batteries and the like are met. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The preparation method flow chart of the present application is shown in the figure. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the specification of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0029] Please refer to the drawings of the present application Figure 1 The embodiment of the present application provides a preparation method of TFP-TAPA / SPEEK composite membrane, comprising the following steps:

[0030] S1, dissolve 21 mg-50 mg of TFP in 80 mL-200 mL of dichloromethane, ultrasonic treatment for 30 min-60 min to obtain aldehyde solution A, and then dissolve 29 mg-60 mg of TAPA in 50 mL-100 mL of DMF, ultrasonic treatment for 30 min-60 min to obtain amine solution B;

[0031] S2, slowly pour the aldehyde solution A into the bottom of a beaker containing 50 mL-100 mL of 3 mol / L aqueous acetic acid, then dropwise add the amine solution B to the upper layer of the aqueous acetic acid, and stand for 1 day-3 days to obtain a TFP-TAPA film;

[0032] S3, wash the obtained TFP-TAPA film with dichloromethane, ethanol, acetone, DMF and deionized water in turn, each solvent is washed for 3-5 times to ensure that the unreacted chemicals are removed, and the washed TFP-TAPA film is dried in a vacuum oven to obtain a dried TFP-TAPA film;

[0033] S4, place 50 mg-100 mg of the dried TFP-TAPA film into 200 mL-400 mL of deionized water, and use 280 W ultrasonic treatment for 6 h-12 h to ensure uniform dispersion of the nanosheets, to obtain a TFP-TAPA nanosheet water suspension;

[0034] S5, mix the TFP-TAPA nanosheet water suspension with the SPEEK solution at a mass ratio of 1:1-2, shake on a constant temperature shaker for more than 12 hours to ensure uniformity of the composite solution, coat the composite solution on a substrate, dry the solution completely to form a composite film, then functionalize the obtained composite film, and finally crosslink the modified composite film;

[0035] In the formation step of the TFP-TAPA film, the ratio of the aldehyde solution A to the amine solution B is 1:1-1:2, and the reaction temperature is room temperature to 25℃-40℃;

[0036] When drying the TFP-TAPA film, the temperature of the vacuum oven is set to 60℃-80℃, the drying time is 2 h-3 h, and the humidity is controlled between 30%-50%;

[0037] The concentration of the SPEEK solution is 5%-10%, and the solution temperature is 50℃-70℃ when stirring for more than 6 hours to ensure complete dissolution of the SPEEK;

[0038] The composite film is coated on the substrate by the blade coating method, the film thickness is 20 μm-100 μm, and the film is dried in a vacuum condition for 4 h-6 h, and the drying temperature is 60℃-80℃;

[0039] The functional modification of the composite membrane includes introducing sulfonic acid groups or amino groups on the surface or in the pores of the membrane. The introduction of sulfonic acid groups is carried out by treating with an acidic solution for 6-12 hours, and the introduction of amino groups is carried out by treating with ammonia gas for 4-8 hours.

[0040] The cross-linking step of the composite membrane includes adding a cross-linking agent glutaraldehyde and reacting at 60-80°C for 12-24 hours, and the concentration of the cross-linking agent is 0.1%-1%.

[0041] The TFP-TAPA nanosheet water suspension is centrifuged to remove undispersed particles under the condition of 3000-5000 rpm for 30-60 minutes to obtain uniformly dispersed nanosheets.

[0042] The composite membrane has a higher permeability to hydrogen ions H + than to vanadium ions Vn + , and a selectivity ratio S greater than 5, and the selectivity calculation formula is:

[0043]

[0044] wherein P H+ and P Vn+ represent the permeability of hydrogen ions and vanadium ions, respectively.

[0045] The composite membrane has a porosity of at least 50%, and a pore size distribution of 0.2-1.0 nm, and the porosity and pore size are determined by scanning electron microscopy and nitrogen adsorption method.

[0046] Specifically, in the S1 step, the aldehyde solution A and the amine solution B are obtained by dissolving TFP and TAPA respectively and then ultrasonic treatment. This step is the first key step for forming the TFP-TAPA composite membrane. In this step, the dissolution of TFP and TAPA, and the ultrasonic treatment process are crucial for the subsequent reaction and the structural stability of the membrane.

[0047] In this embodiment, 21-50 mg of TFP is first dissolved in 80-200 mL of dichloromethane. TFP, as an aldehyde compound, has strong reactivity and can react with amine compound TAPA to form a covalent organic framework (COF) structure. In this process, dichloromethane as a solvent can effectively dissolve TFP and maintain its activity. In order to ensure the complete dissolution of TFP, ultrasonic treatment is used in this embodiment, and the ultrasonic time is set to 30-60 minutes. In this case, ultrasonic waves not only can promote the dissolution process, but also can effectively break up large particles in the solution, enhancing the uniformity of dissolution. It is worth noting that after the dissolution of the TFP solution A, it can provide uniform precursor dispersion for the subsequent chemical reaction.

[0048] Meanwhile, 29 mg to 60 mg of TAPA is dissolved in 50 mL to 100 mL of DMF. As a polar solvent, DMF can effectively dissolve TAPA, ensuring its full reaction. Similar to aldehyde solution A, amine solution B also needs to be ultrasonically treated for 30 minutes to 60 minutes. This ultrasonic treatment not only helps to homogenize the solution, but also improves the dispersibility of TAPA molecules, ensuring their uniform distribution in the solvent, thereby facilitating the smooth progress of subsequent reactions. Specifically, in this step, by controlling the solubility of TFP and TAPA, the ultrasonic treatment time and the concentration of the solution, the reactivity of the film and the final performance of the film can be optimized.

[0049] The dissolution and ultrasonic treatment steps of aldehyde solution A and amine solution B ensure the uniformity and stability of the raw materials required for the reaction, providing the necessary conditions for the formation of TFP-TAPA film. An effective dissolution process avoids incomplete reactions or uneven solutions, thereby improving the quality of the film material. Specifically, the uniform dissolution of TFP and TAPA ensures the smooth progress of the reaction between them, ultimately forming a covalent organic framework film with a stable structure.

[0050] In some embodiments, the ultrasonic treatment power is set to 280 W to 500 W, and the duration can be adjusted according to actual needs, with a specific range of 30 minutes to 60 minutes. Generally, longer ultrasonic treatment helps to speed up the dissolution process, but if the ultrasonic power is too high, it may cause the local temperature of the solution to be too high, thereby affecting the controllability of the reaction. Therefore, it is recommended to flexibly adjust the ultrasonic time and power according to the solubility of TFP and TAPA and the properties of the solvent to achieve the best dissolution effect.

[0051] In this embodiment, the mass ratio of TFP to TAPA ranges from 1:1 to 1:2, and the specific ratio can be adjusted according to the reaction requirements. By reasonably selecting the mass ratio of TFP to TAPA, the final performance of the composite film can be controlled, such as the thickness, porosity and ion sieving performance of the film. To ensure the best reaction effect, the ratio of aldehyde solution A to amine solution B can be further optimized according to specific experimental needs.

[0052] During the reaction of aldehyde solution A and amine solution B, the reaction kinetics can be described by the following formula:

[0053]

[0054] where C final is the final concentration of TFP in the solution after the reaction (unit: mg / mL); M TFP is the mass of dissolved TFP (unit: mg); V solvent is the volume of solvent used (unit: mL).

[0055] By adjusting the ratio of TFP to TAPA and the amount of solvent, the molecular density and pore structure of the final membrane material can be precisely controlled. The above formula helps to calculate the concentration after dissolution, which is helpful for the optimization of reaction conditions.

[0056] In some embodiments, the dissolved concentration of TFP during the reaction should be controlled within a certain range to ensure the controllability of the reaction. If the concentration is too high, the reaction rate may be too fast, and the structure of the membrane material may not be stable; while if the concentration is too low, the reaction may not be complete, resulting in poor quality of the final product.

[0057] In the S2 step, after the dissolution and uniform dispersion of TFP and TAPA are completed, a specific reaction step is needed to form the membrane material. This step is a key link to ensure the stability of the covalent organic framework (COF) network structure. Generally, the condensation reaction of aldehyde groups and amine groups is affected by the solvent system, acid catalysis, and the control of the solution interface, and the formed membrane may have differences in structure and thickness. Therefore, in the specific implementation process, it is necessary to strictly control the addition method of aldehyde solution A and amine solution B and the interface reaction conditions to obtain a stable TFP-TAPA membrane. This step involves a layered reaction of the solution to ensure uniform reaction and finally form a stable membrane layer with a porous structure.

[0058] In this embodiment, aldehyde solution A is slowly poured into the bottom of a beaker containing 50 mL to 100 mL of 3 mol / L acetic acid aqueous solution, and the pouring speed is controlled to prevent the solution from mixing violently. Generally, liquid-liquid interface reaction depends on intermolecular diffusion, and if aldehyde solution A is poured too fast, it may cause unstable interface and affect the uniformity of the final membrane. To avoid interface disturbance, the relative flow rate between aldehyde solution A and acetic acid aqueous solution should be kept low, so that the aldehyde solution forms a stable layer at the bottom, which facilitates the subsequent diffusion of amine solution into the reaction area.

[0059] As an alternative, amine solution B is added dropwise to the upper layer of acetic acid aqueous solution to control the reaction rate and maintain the uniformity of the interface. The dropwise addition rate of amine solution B can be adjusted to 0.5 mL / min to 2 mL / min to ensure uniform diffusion of amine groups to the interface and condensation reaction with aldehyde groups. Specifically, the condensation reaction of amine groups and aldehyde groups follows the mechanism of Schiff base formation, i.e.:

[0060]

[0061] wherein R-CHO+R' represents the aldehyde group structure in TFP; R'-NH2represents the amine group structure in TAPA, and the generation of water during the reaction process will affect the structural stability of the membrane; R-CH=N-R' represents the Schiff base; and H2O represents water as a byproduct. Therefore, in some embodiments, the condensation efficiency can be improved by appropriately controlling the water content of the reaction system, optimizing the reaction conditions, and preventing the formation of non-uniform structures.

[0062] Generally, the rate of condensation reaction is regulated by pH value, and appropriate adjustment of the concentration of acetic acid solution can improve the reaction kinetics. In one possible implementation, a 3 mol / L aqueous acetic acid solution can provide a suitable acidic environment to promote the formation of Schiff base bonds, while inhibiting the occurrence of side reactions, avoiding the problems of excessive cross-linking or uneven molecular aggregation. In order to further optimize the formation of the membrane, the reaction system generally needs to be left for 1-3 days, so that the membrane is gradually deposited and stabilized at the liquid-liquid interface.

[0063] In some embodiments, the reaction temperature can be adjusted in the range of room temperature to 40°C, and appropriate increase in temperature can accelerate molecular diffusion and improve the condensation rate. However, too high a temperature can affect the reaction selectivity of aldehyde groups and amine groups, leading to the formation of irregular structures. Therefore, it is recommended to optimize the temperature within the temperature control range according to experimental requirements to obtain a membrane with better mechanical strength and uniform pore size.

[0064] In the specific implementation process, the formed TFP-TAPA membrane generally has a multi-layer structure, and the pore size and membrane thickness are affected by the reaction time and deposition rate. Generally, longer standing time can promote the ordered arrangement of molecules at the interface, improve the compactness of the membrane, and form a stable COF network. For different application requirements, the thickness and pore distribution of the membrane can be controlled by adjusting the reaction time, so that it is suitable for different membrane separation or selective permeation scenarios.

[0065] In one possible operation mode, if a more regular membrane layer structure is desired, a slow stirring mode (such as 50 rpm-150 rpm) can be used to improve the uniformity of solution mixing and prevent particle aggregation to form defects. At the same time, the solvent environment can be optimized by adjusting the solvent ratio (such as the volume ratio of DMF and acetic acid being 1:2 to 1:4), so that the reaction system is more stable and the uniformity of the membrane is improved.

[0066] In the experimental condition optimization process, the formation rate of the membrane is closely related to the solution concentration, temperature and interface control factors. The key of this process is to reasonably control the layered structure of the solution, so that the reaction of aldehyde groups and amine groups proceeds at an appropriate rate, and finally a uniform and stable TFP-TAPA membrane is formed.

[0067] After the TFP and TAPA have reacted to form the membrane material in step S3, the next step is to wash and dry the resulting TFP-TAPA membrane. This process is critical to remove unreacted starting materials, solvents, and byproducts, and also to effectively control the final structure and properties of the membrane. The thoroughness of the washing and the drying conditions directly affect the porosity, mechanical strength, and stability and reliability of the membrane in subsequent applications.

[0068] In this embodiment, the formed TFP-TAPA membrane is first removed from the reaction system and washed sequentially with dichloromethane, ethanol, acetone, DMF, and deionized water. The number of washes for each solvent is set to 3 to 5 times. The purpose of these solvents is to effectively remove unreacted starting materials, solvents, and other impurities that may remain from the reaction process, ensuring the purity of the membrane.

[0069] In some embodiments, to ensure thorough washing, an ultrasonic cleaning device can be used to assist in the penetration and removal of solvents. The use of ultrasonic cleaning not only improves washing efficiency but also avoids waste of solvents. Special attention should be paid to the amount of solvent used and the temperature during washing. Too little solvent or too high a temperature can cause damage to the membrane structure. Therefore, in general, the amount of solvent used should be able to cover the surface of the membrane, and the temperature should be controlled between 15°C and 40°C to avoid deformation or excessive dissolution of the membrane due to high temperature.

[0070] As an alternative, the washing operation can be carried out in batches, first using a polar solvent such as dichloromethane to remove organic impurities, then sequentially using more polar solvents such as ethanol, acetone, and DMF to further remove organic impurities. Finally, deionized water is used to thoroughly wash the membrane surface of any remaining solvent and other inorganic impurities. The membrane after each washing can be gently rinsed with deionized water to ensure that no harmful substances are left behind. Through such a systematic washing step, the high purity and uniformity of the TFP-TAPA membrane can be effectively ensured.

[0071] In one possible implementation, to further improve the washing effect, a small amount of surfactant can be added during the washing process to reduce the surface tension of the solution and help remove impurities from the membrane surface. The concentration of the surfactant is usually 0.01% to 0.1%, which can ensure that the structure of the membrane is not damaged while enhancing the washing effect.

[0072] After the washing operation is completed, the next step is to dry the membrane. To ensure the mechanical properties and porosity of the membrane, in this embodiment, the membrane is dried using a vacuum oven. The drying temperature is controlled between 60°C and 80°C, the drying time is 2h to 3h, and the humidity should be maintained between 30% and 50% to ensure the stability of the membrane morphology and avoid excessive drying. Through this control, the membrane can uniformly remove water and solvents, ensuring that its structure remains intact and does not shrink or deform.

[0073] Through meticulous washing and drying steps, the present application can ensure the high purity and stability of TFP-TAPA membranes. Proper washing can effectively remove impurities generated during the reaction, avoiding their negative impact on membrane performance, especially in ion sieving applications. By controlling the drying temperature and humidity, excessive drying of the membrane can be effectively prevented, ensuring that the porosity and mechanical strength of the membrane are within the desired range. The high quality of this membrane material lays a solid foundation for subsequent functional modification and membrane applications.

[0074] In some embodiments, the drying step of the membrane can be experimentally optimized under different temperature and time conditions. Specifically, by adjusting the temperature and humidity, the pore structure and surface properties of the membrane can be controlled. For example, higher drying temperatures (such as 80°C) can cause the membrane surface to harden, which is suitable for applications requiring higher mechanical strength; while lower drying temperatures (such as 60°C) are suitable for maintaining the flexibility of the membrane.

[0075] During the drying process of the membrane, the water removal rate R dry can be described by the following formula:

[0076]

[0077] where R dry represents the drying rate (unit: g / h); m wet and m dry represent the mass of the membrane before and after drying (unit: g), respectively; t represents the drying time (unit: hours).

[0078] By adjusting the drying time and temperature, the water removal rate of the membrane can be controlled, thereby optimizing the final quality of the membrane.

[0079] In step S4, the dried TFP-TAPA membrane is converted into a nanosheet water suspension. This process is crucial for the subsequent preparation of composite membranes. By ultrasonic treatment, the effective substances in the membrane are broken into nanosheets and uniformly dispersed in the water phase, providing the necessary raw materials for the uniform coating of the next step composite membrane.

[0080] In this embodiment, 50mg-100mg of dried TFP-TAPA membrane is placed in 200mL-400mL of deionized water, and treated with 280W ultrasonic waves for 6-12 hours to ensure uniform dispersion of the nanosheets. The ultrasonic power and treatment time in this process are crucial for the size and dispersion of the nanosheets.

[0081] Generally, the power of the ultrasonic waves is set to 280-500 W, and the processing time is 6-12 hours, which can ensure that the TFP-TAPA substance in the film is effectively broken into uniform nanosheets, and these nanosheets can be completely dispersed in water without aggregation. Using higher power and longer processing time can help improve the processing effect, but at the same time it can also cause changes in the structure of the film material. Therefore, the specific operating conditions should be adjusted according to the characteristics of the film and the desired size of the nanosheets.

[0082] As an option, different frequency ranges can be selected during ultrasonic treatment. For example, using low-frequency ultrasonic waves (20-40 kHz) helps to more evenly disperse large-size particles in the film, while high-frequency ultrasonic waves (above 100 kHz) are suitable for processing smaller particles or improving the uniformity of the solution. In order to avoid excessive breaking of the effective components in the film, the intensity of the treatment can be adjusted by controlling the intermittent action of the ultrasonic waves.

[0083] In this embodiment, the processing time of 6-12 hours can ensure that all TFP-TAPA molecules in the film are completely broken and form a stable nanosheet water suspension. It is worth noting that ultrasonic treatment not only needs to ensure the uniform dispersion of nanosheets, but also needs to avoid excessively high temperature, which can cause thermal degradation of the film material and affect the structure of the final film. Therefore, in some embodiments, a temperature control device can be used in conjunction with the ultrasonic treatment instrument to ensure that the ultrasonic treatment temperature is controlled within the range of 20-40°C.

[0084] Through the above ultrasonic treatment step, the TFP-TAPA nanosheet water suspension generated has good dispersibility, which provides high-quality raw materials for the subsequent preparation of composite films. The uniform dispersion of nanosheets directly affects the uniformity of the composite film and the pore structure of the film. If the nanosheets are not uniformly dispersed, it can cause irregular channels in the film, thereby affecting the performance of the film.

[0085] In some embodiments, during the ultrasonic treatment process, the suspension can be stirred regularly to enhance the overall uniformity of the solution and avoid local precipitation. Specifically, the stirring rate can be set to 50-200 rpm to maintain the continuous dispersion of nanosheets during ultrasonic treatment. During the treatment process, the energy transfer efficiency η of the ultrasonic waves is closely related to the processing time t and the power P, which can be described by the following formula:

[0086]

[0087] wherein η is the energy transfer efficiency (unit: J / mL); P is the power of the ultrasonic waves (unit: W); t is the ultrasonic treatment time (unit: hours); and V is the volume of the solution (unit: mL).

[0088] By adjusting the ultrasonic power, time, and solution volume, the treatment effect of the membrane material can be optimized to ensure that the dispersion degree of the nanosheets reaches the best. The formula helps to calculate the energy transfer efficiency of ultrasonic treatment, thereby providing a basis for experimental operation.

[0089] In actual operation, the heat generated during ultrasonic treatment needs to be dissipated in time, otherwise it may affect the stability of the membrane material. Generally, a water cooling system or regular water change can be used to ensure the stability of the temperature during the treatment process. Through appropriate temperature control and adjustment of ultrasonic power, overheating or damage of the membrane material can be avoided, and the quality of the final product can be improved.

[0090] In addition, the concentration and dispersity of the TFP-TAPA nanosheet aqueous suspension are crucial for the formation of the composite membrane in the subsequent membrane preparation process. By changing the ultrasonic treatment time, power, or treatment interval frequency, the pore structure and membrane performance of the membrane can be further optimized. For example, a higher concentration of nanosheet aqueous suspension helps to improve the mechanical strength of the membrane, but too high a concentration may result in a too large thickness of the membrane, affecting the permeability. By flexibly adjusting these operating parameters, a membrane material that meets the requirements can be prepared according to the application requirements.

[0091] In step S5, the nanosheets are compounded with the SPEEK solution to form a uniform and stable composite membrane. In order to optimize the physical and chemical properties of the composite membrane, functional modification and cross-linking treatment of the membrane are also key steps. By controlling the coating method, drying conditions, and modification and cross-linking process, the mechanical properties, ion sieving characteristics, and stability of the composite membrane can be improved, laying a foundation for its final application.

[0092] In this embodiment, the TFP-TAPA nanosheet aqueous suspension and the SPEEK solution are mixed in a mass ratio of 1:1 to 2, and shaken on a constant temperature shaker for at least 12 hours to ensure that they are fully integrated to form a uniform composite solution. Generally, the temperature of the shaker should be maintained between 25°C and 50°C, and too high a temperature may cause the nanosheets to agglomerate, while too low a temperature may reduce the solubility of SPEEK, thereby affecting the uniformity of the final membrane.

[0093] As an option, the composite solution can be vacuum degassed before coating to remove any small bubbles that may be present, avoiding holes or defects in the membrane. Specifically, the vacuum degassing time can be set to 10 to 30 minutes to ensure that the membrane has good density and uniformity after coating.

[0094] In one possible implementation, the coating of the composite membrane is performed by using a blade coating method, which uniformly coats the composite solution on the substrate with a film thickness controlled between 20 μm and 100 μm. The blade coating operation needs to be performed in a clean environment to prevent impurities from polluting the membrane and affecting the quality of the membrane. During the coating process, the applied pressure should be moderate, and excessive pressure can cause damage to the structure of the membrane, and insufficient pressure can affect the uniformity.

[0095] Generally, the composite membrane after coating needs to be dried to remove excess solvent and stabilize the structure of the membrane. In this embodiment, the drying conditions are set to 60°C to 80°C, and the drying time is 4 hours to 6 hours, and a vacuum environment is used to improve the evaporation rate of the solvent and reduce the probability of defects on the surface of the membrane. In order to further optimize the pore structure of the membrane, a stepwise drying method can be used in some embodiments, that is, pre-drying at a lower temperature (such as 50°C) and then gradually increasing the temperature to the final set temperature.

[0096] The dried composite membrane needs to be functionally modified to improve its ion sieving ability and chemical stability. In this embodiment, the functional modification includes the introduction of sulfonic acid groups or amino groups. Specifically, the introduction of sulfonic acid groups uses an acidic solution, and the treatment time is 6 hours to 12 hours, and the concentration of the acidic solution is controlled in the range of 0.5 mol / L to 2 mol / L to ensure the modification effect without causing damage to the membrane structure. As an alternative, the introduction of amino groups can be completed by ammonia treatment, and the treatment time is 4 hours to 8 hours, and the ammonia flow is controlled at 10 mL / min to 50 mL / min to ensure the uniformity of the modification.

[0097] In some embodiments, the modified membrane needs to be thoroughly washed to remove excess unreacted substances. Generally, deionized water or appropriate organic solvents can be used for multiple washes, and each washing time can be controlled between 10 minutes and 30 minutes to ensure the cleanliness of the membrane surface.

[0098] In order to further improve the stability and solvent resistance of the composite membrane, the membrane is cross-linked in this embodiment. The cross-linking agent is selected as glutaraldehyde, and the cross-linking reaction is performed at 60°C to 80°C, and the time is controlled between 12 hours and 24 hours, and the concentration of the cross-linking agent is set to 0.1% to 1%. In one possible implementation, the cross-linking can be performed by using a solution immersion method, which immerses the composite membrane in a cross-linking agent solution and appropriately stirs to improve the cross-linking efficiency.

[0099] Generally, after cross-linking treatment, the structure of the membrane will be more stable, and the mechanical properties and durability will be improved. For some special applications, the type and concentration of the cross-linking agent can be further optimized to adapt to different chemical environments.

[0100] The uniformity of the coating of the composite membrane can be calculated by the following formula to calculate the thickness deviation Δd of the coating:

[0101]

[0102] where d max and d min represent the maximum and minimum thickness of the coated film (unit: pm), respectively; d arg is the average thickness of the film (unit: pm); and Ad is the thickness deviation (unit: %).

[0103] This formula can be used to evaluate the thickness uniformity of the film. By optimizing the knife coating parameters, controlling the solution viscosity, and adjusting the drying conditions, the deviation of the film thickness can be reduced, and the uniformity of the composite film can be improved.

[0104] In addition, the calculation of the crosslinking degree (X c ) can be carried out by the following formula:

[0105]

[0106] where X c is the crosslinking degree (unit: %); W0 is the initial mass of the film before crosslinking (unit: mg); and W t is the mass of the film after crosslinking (unit: mg).

[0107] This formula can be used to characterize the effect of crosslinking treatment. The improvement of the crosslinking degree usually enhances the mechanical strength and chemical resistance of the film.

[0108] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a TFP-TAPA / SPEEK composite membrane, characterized in that, The method comprises the following steps: 21mg-50mg of TFP is dissolved in 80mL-200mL of dichloromethane, and ultrasonic treatment is performed for 30min-60min to obtain an aldehyde solution A, and 29mg-60mg of TAPA is dissolved in 50mL-100mL of DMF, and ultrasonic treatment is performed for 30min-60min to obtain an amine solution B; The aldehyde solution A is slowly poured into the bottom of a beaker containing 50mL-100mL of 3mol / L aqueous acetic acid solution, and the amine solution B is added dropwise to the upper layer of the aqueous acetic acid solution, and is left to stand for 1 day-3 days to obtain a TFP-TAPA membrane; The obtained TFP-TAPA membrane is washed with dichloromethane, ethanol, acetone, DMF and deionized water in sequence, and each solvent is used for washing 3-5 times to ensure that the unreacted chemicals are removed, and the washed TFP-TAPA membrane is dried in a vacuum oven to obtain a dried TFP-TAPA membrane; 50mg-100mg of the dried TFP-TAPA membrane is placed in 200mL-400mL of deionized water, and is treated with 280W ultrasonic waves for 6h-12h to ensure uniform dispersion of the nanosheets, and a TFP-TAPA nanosheet water suspension is obtained; The TFP-TAPA nanosheet water suspension and a SPEEK solution are mixed in a mass ratio of 1:1-2, and a constant-temperature shaking bed is shaken for more than 12 hours to ensure uniformity of the composite solution, the composite solution is coated on a substrate, the solution is completely dried to form a composite membrane, the obtained composite membrane is subjected to functionalization modification, and finally the modified composite membrane is subjected to crosslinking treatment; The functionalization modification of the composite membrane comprises introducing an amino group on the surface or in the pores of the membrane, and the introduction of the amino group is performed by ammonia treatment, and the treatment time is 4h-8h; The crosslinking step of the composite membrane comprises adding a crosslinking agent glutaraldehyde, and reacting at 60℃-80℃ for 12h-24h, and the concentration of the crosslinking agent is 0.1%-1%; The composite membrane has a porosity of at least 50%, and a pore size distribution of 0.2nm-1.0nm.

2. The method for preparing a TFP-TAPA / SPEEK composite membrane according to claim 1, characterized in that, In the forming step of the TFP-TAPA membrane, the ratio of the aldehyde solution A to the amine solution B is 1:1-1:2, and the reaction temperature is room temperature to 25℃-40℃.

3. The method for preparing a TFP-TAPA / SPEEK composite membrane according to claim 1, characterized in that, In the drying of the TFP-TAPA membrane, the temperature of the vacuum oven is set to 60℃-80℃, the drying time is 2h-3h, and the humidity is controlled to be 30%-50%.

4. The method for preparing a TFP-TAPA / SPEEK composite membrane according to claim 1, characterized in that, The concentration of the SPEEK solution is 5%-10%, and the solution is stirred for more than 6 hours at a temperature of 50℃-70℃ to ensure complete dissolution of the SPEEK.

5. The method for preparing a TFP-TAPA / SPEEK composite membrane according to claim 1, characterized in that, The composite membrane is coated on a substrate by a blade coating method, the thickness of the membrane is 20μm-100μm, and the membrane is dried in a vacuum condition for 4h-6h, and the drying temperature is 60℃-80℃.

6. The method for preparing a TFP-TAPA / SPEEK composite membrane according to claim 1, characterized in that, The TFP-TAPA nanosheet water suspension is centrifuged to remove undispersed particles, the centrifugation condition is 3000rpm-5000rpm for 30min-60min, and uniformly dispersed nanosheets are obtained.

7. The method of claim 1, wherein the TFP-TAPA / SPEEK composite membrane is prepared by the steps of: The composite membrane supports hydrogen ions and vanadium ions The sieving effect is that hydrogen ion permeability is higher than vanadium ion permeability, and the selectivity ratio is higher. For values ​​greater than 5, the selective calculation formula is: ； wherein, and represent the permeability of hydrogen ions and vanadium ions, respectively.

8. The method for preparing a TFP-TAPA / SPEEK composite membrane according to claim 1, characterized in that, The porosity and the pore size are determined by scanning electron microscopy and nitrogen adsorption method.

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