Polyimide composite separation membrane, and preparation method and application thereof

Abstract

The present application relates to the technical fields of separation membrane material and oil-water separation, and relates to a polyimide composite separation membrane and a preparation method and application thereof, comprising the following steps: S1, obtaining a polyimide fiber membrane by electrospinning process and thermal imidization treatment with polyamide acid solution as a precursor; S2, loading UiO-66-NH2 nanoparticles on the surface of the polyimide fiber membrane by in-situ synthesis to obtain a polyimide / UiO-66-NH2 fiber membrane; and S3, immersing the polyimide / UiO-66-NH2 fiber membrane in dopamine / Tris-HCl solution and PEI / Tris-HCl solution in sequence to obtain a polyimide / UiO-66-NH2@PDA / PEI composite separation membrane. The composite separation membrane prepared by the present application has the characteristics of superhydrophilicity in air and superoleophobicity under water, is beneficial to the separation of various oil-water mixtures, and has stable performance and low cost.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials and oil-water separation technology, and in particular to a polyimide composite separation membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation technology has become a core technology route for key research and large-scale application in the field of water treatment due to its advantages such as simple preparation process, high oil-water separation efficiency, low equipment modification difficulty, and low operating energy consumption.

[0003] Existing oil-water separation membrane materials are mainly divided into two categories: superhydrophobic and oleophilic, and superhydrophilic / underwater superoleophobic. Among them, superhydrophobic and oleophilic membranes have a strong affinity for the oil phase, require low driving pressure to treat oily wastewater, and can retain the aqueous phase to collect pure oil products. However, these membranes are easily clogged by oil and have poor antifouling performance. After long-term circulation, their flux and separation efficiency decline rapidly. In contrast, superhydrophilic / underwater superoleophobic membranes rely on a large number of hydrophilic groups and a three-dimensional interconnected porous structure on their surface to preferentially adsorb water molecules and form a hydrated barrier layer on the membrane surface, effectively repelling oil phase adhesion. They have excellent anti-oil self-cleaning ability and high oil retention rate, making them more suitable for long-term continuous water treatment conditions.

[0004] However, existing research and development of superhydrophilic / underwater superoleophobic membranes still face technical bottlenecks. For example, in order to improve the wettability of the membrane surface and enhance the oil-water selectivity, current solutions generally introduce functional inorganic nanofillers into the fiber system. However, there is a problem of poor interfacial compatibility between functional inorganic nanofillers (such as MOF materials) and organic fiber substrates, which results in a limited loading capacity of the introduced inorganic fillers and easy detachment, thereby affecting the hydrophilicity and stability of the membrane. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a method for preparing a polyimide composite separation membrane and its application. By adjusting the thermal imidization temperature and controlling the loading of UiO-66-NH2, a micro-nano hierarchical rough structure and a high density of hydrophilic amino sites are constructed on the fiber surface. The PDA / PEI layer enhances the bonding strength between UiO-66-NH2 and the fiber, preventing filler detachment, thereby endowing the composite membrane with superhydrophilic, underwater superoleophobic, high flux, and oil-resistant self-cleaning properties.

[0006] The technical solution of this invention is as follows: a method for preparing a polyimide composite separation membrane, comprising the following steps: S1, preparation of a polyimide fiber membrane: using a polyamic acid solution as a precursor, a polyamic acid fiber membrane is prepared by electrospinning, and the polyamic acid fiber membrane is subjected to thermal imidization treatment to obtain a polyimide fiber membrane; S2, loading of UiO-66-NH2: using an in-situ synthesis method, UiO-66-NH2 nanoparticles are loaded onto the surface of the polyimide fiber membrane to obtain a polyimide / UiO-66-NH2 fiber membrane; S3, coating with a PDA / PEI layer: the polyimide / UiO-66-NH2 fiber membrane is immersed in a dopamine / Tris-HCl solution to allow dopamine to self-polymerize and form a PDA layer; subsequently, it is immersed in a PEI / Tris-HCl solution for PEI modification to obtain a polyimide / UiO-66-NH2@PDA / PEI composite separation membrane.

[0007] The polyamic acid solution was prepared by the following method: 4,4′-diaminodiphenyl ether was dissolved in N,N-dimethylacetamide. After it was completely dissolved, 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added in portions and mechanically stirred in an ice bath to obtain a polyamic acid solution with a mass fraction of 10wt% to 14wt%.

[0008] The thermal imidization treatment includes placing the polyamic acid fiber membrane into a heating device for programmed temperature rise, wherein the final temperature of the programmed temperature rise is 280℃~320℃.

[0009] The heating program of the heating device includes: heating from room temperature to 180°C at 10°C / min, holding at that temperature for 1 hour, then heating to the final temperature at 5°C / min, holding at that temperature for 1 hour, and then naturally cooling to room temperature.

[0010] The in-situ synthesis method specifically includes the following steps: Zirconium tetrachloride and 2-aminoterephthalic acid are dissolved in N,N-dimethylformamide at a molar ratio of 1:1 and ultrasonically dispersed to obtain a mixed solution; then the mixed solution is transferred to a stainless steel reactor lined with polytetrafluoroethylene, and the polyimide fiber membrane obtained in S1 is added to the reactor together to carry out in-situ growth and loading of UiO-66-NH2 nanoparticles on the surface of the polyimide fiber membrane. The in-situ growth and loading of UiO-66-NH2 nanoparticles on the surface of a polyimide fiber membrane further includes the following steps: reacting at 120°C for 24 hours in a reactor; after the reaction, removing the fiber membrane, washing it with N,N-dimethylformamide to remove unreacted ligands, then soaking it in anhydrous methanol for 24 hours to exchange the N,N-dimethylformamide in the pores and activate the pores; and finally vacuum drying at 120°C to obtain a polyimide / UiO-66-NH2 fiber membrane.

[0011] The dopamine concentration in the dopamine / Tris-HCl solution is 2 g / L, and the PEI concentration in the PEI / Tris-HCl solution is 2 g / L.

[0012] The technical solution of the present invention also includes a polyimide composite separation membrane prepared by the above preparation method, comprising polyimide nanofibers, UiO-66-NH2 nanoparticles loaded on the surface of the polyimide nanofibers, and a PDA / PEI surface modification layer wrapped around the UiO-66-NH2 nanoparticles and the polyimide nanofibers, wherein the diameter of the polyimide nanofibers is 200nm to 800nm, and the particle size of the UiO-66-NH2 nanoparticles is 30nm to 100nm.

[0013] The loading amount of the UiO-66-NH2 nanoparticles on the polyimide nanofibers is 25wt% to 40wt%.

[0014] The technical solution of the present invention also includes the application of the above-mentioned polyimide composite separation membrane in the field of oil-water separation.

[0015] The present invention has the following beneficial effects: (I) This invention uses thermal imidization treatment to retain certain polar sites such as carboxyl groups, amide groups, and carbonyl groups on the fiber surface. These polar sites are related to Zr. 4+ The precursor undergoes adsorption and coordination, thereby promoting the uniform nucleation and stable growth of UiO-66-NH2 on the fiber surface, avoiding the problems of MOF agglomeration, uneven dispersion and easy detachment caused by simple physical doping.

[0016] (II) The present invention uses PDA chemical deposition to construct a continuous coating layer on the surface of PI fiber membrane loaded with UiO-66-NH2. PDA forms multiple bonds with PI fiber and UiO-66-NH2 particles through coordination, hydrogen bonding, π-π interaction and interfacial crosslinking, thereby forming an adhesion transition layer between PI fiber and UiO-66-NH2 and on the outside of PI fiber and UiO-66-NH2, fixing UiO-66-NH2 more firmly to the fiber surface. At the same time, the surface of this continuous coating layer also provides a stable reaction platform for subsequent secondary grafting of PEI, which is more suitable for high loading, strong binding and anti-detachment modification of nanoparticles in porous fiber membrane systems.

[0017] (III) This invention constructs a hydrophilic amino enrichment layer through a secondary reaction between PDA and PEI. The surface of the composite separation membrane coated with PDA contains active sites such as quinone groups, phenolic hydroxyl groups, and amino groups, which can undergo Schiff base reactions and Michael addition reactions with primary and secondary amines in branched polyethyleneimine. Simultaneously, hydrogen bonds can be formed between the two, allowing PEI to be stably bound to the surface of the PDA-modified layer. PDA acts as an interfacial bridge in this process, avoiding the loss of PEI due to physical adsorption alone, and further enhancing the multi-level interfacial bonding between PI fibers, UiO-66-NH2, PDA, and PEI. Meanwhile, the PEI molecular chain contains a large number of amino groups, which significantly increase the density of hydrophilic groups on the membrane surface and, together with the hydroxyl and amino groups in PDA, constitute a hydrophilic modified layer. This hydrophilic modified layer rapidly adsorbs water molecules in an aqueous environment and forms a stable hydration layer, giving the composite membrane superhydrophilic properties in air and superoleophobic properties underwater. The oil-water separation flux of this composite membrane is up to approximately 8900 L·m⁻¹. -2 ·h -1 It still maintains approximately 7900 L·m after 30 cycles. -2 ·h -1 The separation efficiency is consistently above 98%, demonstrating excellent oil-water separation performance and circulation stability. Attached Figure Description

[0018] Figure 1 SEM image of polyamic acid fiber membrane; Figure 2 SEM images of polyimide fiber membranes prepared at different thermal imidization temperatures, wherein... Figure 2 (a) A polyimide fiber membrane prepared at 250°C. Figure 2 (b) is a polyimide fiber membrane prepared at 300°C. Figure 2 (c) is a polyimide fiber membrane prepared at 350°C; Figure 3 SEM images of PI / UiO-66-NH2 fiber membranes prepared at different thermal imidization temperatures, wherein... Figure 3 (a) is a PI / UiO-66-NH2 fiber membrane prepared at 250℃. Figure 3 (b) is a PI / UiO-66-NH2 fiber membrane prepared at 300℃. Figure 3 (c) PI / UiO-66-NH2 fiber membrane prepared at 350℃; Figure 4 This is a SEM image of the PI / UiO-66-NH2@PDA / PEI composite separation membrane prepared in Example 1; Figure 5A comparison of the water contact angles in air for the PI, PI / UiO-66-NH2, and PI / UiO-66-NH2@PDA / PEI composite separation membranes prepared in Example 1; Figure 6 This is a comparison diagram of the underwater oil contact angle of the PI / UiO-66-NH2@PDA / PEI composite separation membrane prepared in Example 1 in different oil-water mixtures; Figure 7 This is a comparison chart of the separation flux and separation efficiency of the PI / UiO-66-NH2@PDA / PEI composite separation membrane prepared in Example 1 in different oil-water mixtures; Figure 8 The graph shows a comparison of the oil-water separation flux of the composite separation membranes prepared in Examples 1, 2, 3, 4, 5, Comparative Example 1, and Comparative Example 2 for n-hexane / water mixtures. Figure 9 This is a graph showing the changes in water flux and oil-water separation efficiency during the cyclic test of the PI / UiO-66-NH2@PDA / PEI composite separation membrane prepared in Example 1; Figure 10 The image shows the oil resistance performance of the PI / UiO-66-NH2@PDA / PEI composite separation membrane prepared in Example 1. Detailed Implementation

[0019] The technical solutions of the present invention will now be described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] This invention provides a method for preparing a polyimide composite separation membrane, the specific steps of which include: S1. Preparation of polyimide fiber membrane: First, a polyamic acid solution is prepared: 4,4′-diaminodiphenyl ether (ODA) is added to a three-necked flask containing N,N-dimethylacetamide (DMAc), and mechanically stirred for 20 min under ice bath conditions to completely dissolve the monomer. Then, 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) is added to the aforementioned flask in portions, with the amount added decreasing as the number of additions increases. Each addition is allowed to proceed only after the BPDA has completely dissolved, with an interval of 30 min. After the addition is completed, the mixture is rapidly mechanically stirred for 1 h to ensure the monomer reacts fully, finally yielding a polyamic acid solution. Then, the polyamic acid solution is used as a precursor for electrospinning to obtain a polyamic acid fiber membrane. The polyamic acid fiber membrane is then placed in a muffle furnace for controlled-temperature thermal imidization treatment to obtain a polyimide fiber membrane.

[0021] S2, Loading UiO-66-NH2: Zirconium tetrachloride (ZrCl4) and 2-aminoterephthalic acid (NH2-BDC) were dissolved in N,N-dimethylformamide (DMF) at a molar ratio of 1:1 and ultrasonically dispersed until a homogeneous solution was formed. The resulting mixture was then transferred to a stainless steel reactor lined with polytetrafluoroethylene, and the polyimide fiber membrane obtained in S1 was placed in the reactor together. The reaction was carried out at 120°C for 24 h, allowing UiO-66-NH2 nanoparticles to grow in situ on the surface of the polyimide fiber membrane. After the reaction was completed, the fiber membrane was removed, washed three times with DMF to remove unreacted ligands, and then soaked in anhydrous methanol for 24 h to exchange the residual DMF in the pores. During this period, the methanol was replaced 2 to 3 times. Subsequently, the membrane was vacuum dried to obtain the PI / UiO-66-NH2 fiber membrane.

[0022] S3: Coating with PDA / PEI layer: The PI / UiO-66-NH2 fiber membrane is immersed in a dopamine (DA) / Tris-HCl solution and stirred for 12 h to deposit PDA on the surface of the fiber membrane, thus obtaining a PI / UiO-66-NH2@PDA fiber membrane; then the PI / UiO-66-NH2@PDA fiber membrane is immersed in a PEI / Tris-HCl solution and stirred for 12 h to obtain a PI / UiO-66-NH2@PDA / PEI composite separation membrane.

[0023] Furthermore, the concentration of the polyamic acid solution in S1 is 10wt%~14wt%; the 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) monomer should be added in 3~4 portions after the 4,4′-diaminodiphenyl ether (ODA) monomer is completely dissolved in DMAc.

[0024] Furthermore, the electrospinning process described in S1 is as follows: a cylindrical roller receiver with a diameter of 12cm and a length of 30cm is used to collect nanofibers; the parameters are adjusted as follows: the rotation speed is 150r / min, the distance from the spinneret to the roller receiver surface is 15cm, the high voltage power supply voltage is 20kV, the feeding speed is 0.5mL / h, and the spinneret swings laterally from the center position with an amplitude of 50cm and a swing speed of 5mm / s.

[0025] Furthermore, the muffle furnace heating program in S1 is set as follows: the temperature is increased from room temperature to 180℃ at 10℃ / min, held for 1 hour, then increased to the final temperature at 5℃ / min, held for 1 hour, and then naturally cooled to room temperature to obtain a polyimide fiber membrane; wherein, the final temperature is set to 280℃~320℃.

[0026] Furthermore, the dopamine concentration in the dopamine / Tris-HCl solution in S3 is 2 g / L, and the PEI concentration in the PEI / Tris-HCl solution is 2 g / L, in order to form a PDA / PEI modified layer of moderate thickness and uniform and stable properties.

[0027] The polyimide / UiO-66-NH2@PDA / PEI composite separation membrane prepared by the above preparation method includes polyimide nanofibers, UiO-66-NH2 nanoparticles loaded on the surface of polyimide nanofibers, and a PDA / PEI surface modification layer wrapped around the UiO-66-NH2 nanoparticles and the surface of polyimide nanofibers. The diameter of the polyimide nanofibers is 200 nm to 800 nm, and the particle size of the UiO-66-NH2 nanoparticles is 30 nm to 100 nm.

[0028] Furthermore, the UiO-66-NH2 nanoparticles are uniformly nucleated and stably grown on the polyimide nanofibers treated at a thermal imidization temperature of 280℃~320℃, and the loading amount is 25wt%~40wt% under the condition of ensuring uniform growth of UiO-66-NH2 and stability of film structure.

[0029] The preparation method is as follows: Example 1 Weigh 22 mL of N,N-dimethylacetamide (DMAc) into a three-necked flask, and weigh 1.2077 g of 4,4'-diaminodiphenyl ether (ODA) and 1.7923 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). First, add ODA to the three-necked flask and fix it in place. Turn on the mechanical stirrer and stir for 20 min to ensure complete dissolution of the monomer. Then, add BPDA to the flask in 3-4 portions, decreasing the amount added with each addition. Add the next portion only after each addition has completely dissolved, with an interval of approximately 30 min. After all additions are complete, continue rapid mechanical stirring for 1 h to ensure complete reaction of the monomer, generating a 12 wt% polyamic acid precursor solution.

[0030] The electrospinning parameters were set as follows: rotation speed 150 r / min, distance from the spinneret to the roller receiving surface 15 cm, high voltage power supply voltage 20 kV, feed rate 0.5 mL / h, oscillation at the center position with an amplitude of 50 cm and an oscillation speed of 5 mm / s, electrospinning time 360 ​​min, and a cylindrical roller receiver with a diameter of 12 cm and a length of 30 cm was used to collect the nanofibers, resulting in the following... Figure 1 The polyamic acid fiber membrane shown.

[0031] The obtained polyamic acid fiber membrane was dried in an oven at 60℃ for 12 hours. After drying, it was transferred to a muffle furnace, and the heating program of the muffle furnace was set as follows: the temperature was increased from room temperature to 180℃ at a rate of 10℃ / min, held at that temperature for 1 hour, then increased from 180℃ to 300℃ at a rate of 5℃ / min, held at that temperature for 1 hour, and then naturally cooled to room temperature to obtain the desired result. Figure 2 (b) shows the polyimide fiber membrane.

[0032] 0.466 g of zirconium tetrachloride (ZrCl4) and 0.362 g of 2-aminoterephthalic acid (NH2-BDC) were dissolved in 160 mL of N,N-dimethylformamide (DMF). After ultrasonic dispersion, the mixture was transferred to a stainless steel reactor lined with polytetrafluoroethylene (PTFE). The prepared polyimide fiber membrane was placed in the reactor and reacted at 120 °C for 24 h to achieve in-situ growth of UiO-66-NH2. After the reaction, the fiber membrane was removed, washed three times with DMF, and then soaked in 50 mL of anhydrous methanol for 24 h, changing the methanol 2-3 times during this period. It was then vacuum dried to obtain the desired product. Figure 3 (b) shows the PI / UiO-66-NH2 fiber membrane.

[0033] The PI / UiO-66-NH2 fiber membrane obtained by thermal imidization treatment at 300℃ was thoroughly dried to constant weight and recorded as M1. Unloaded UiO-66-NH2 polyimide fiber membranes from the same batch were dried to constant weight and recorded as M0. The UiO-66-NH2 loading was calculated using the formula: Loading = (M1−M0) / M0×100%. In this experiment, the loading was approximately 30wt%.

[0034] 100 mL of Tris-HCl buffer solution was measured and the pH was adjusted to 8.5. The prepared PI / UiO-66-NH2 fiber membrane was added, along with 0.2 g of dopamine hydrochloride. The mixture was magnetically stirred at room temperature for 12 h to allow dopamine hydrochloride to self-polymerize and deposit on the fiber membrane surface to form a PDA layer. After the reaction was complete, the fiber membrane was removed and washed with deionized water to obtain the PI / UiO-66-NH2@PDA fiber membrane. Subsequently, the PI / UiO-66-NH2@PDA fiber membrane was placed in 100 mL of PEI / Tris-HCl solution, with 0.2 g of PEI added. The mixture was magnetically stirred at room temperature for 12 h to introduce PEI onto the membrane surface. After the reaction was complete, the fiber membrane was removed, thoroughly washed with deionized water, and freeze-dried for 12 h to obtain the desired product. Figure 4 The PI / UiO-66-NH2@PDA / PEI composite separation membrane shown includes polyimide nanofibers with a diameter of 200nm to 800nm ​​supporting UiO-66-NH2 nanoparticles with a particle size of 30nm to 100nm and a PDA / PEI surface modification layer.

[0035] Example 2 Weigh 29 mL of N,N-dimethylacetamide (DMAc) into a three-necked flask, and weigh 1.2077 g of 4,4'-diaminodiphenyl ether (ODA) and 1.7923 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). First, add ODA to the three-necked flask and fix it in place. Turn on the mechanical stirrer and stir for 20 min to ensure complete dissolution of the monomer. Then, add BPDA to the flask in 3-4 portions, decreasing the amount added with each addition. Add the next portion only after each addition has completely dissolved, with an interval of approximately 30 min. After the addition is complete, continue rapid mechanical stirring for 1 h to ensure complete reaction of the monomer, generating a 10 wt% polyamic acid precursor solution.

[0036] The electrospinning parameters were set as follows: rotation speed of 150 r / min, distance from the spinneret to the roller receiving surface of 15 cm, high voltage power supply voltage of 20 kV, feeding speed of 0.5 mL / h, oscillation at the center position with an amplitude of 50 cm and an oscillation speed of 5 mm / s, and electrospinning time of 360 min. A cylindrical roller receiver with a diameter of 12 cm and a length of 30 cm was used to collect the nanofibers to obtain a polyamic acid fiber membrane.

[0037] The obtained polyamic acid fiber membrane was placed in an oven at 60°C and dried for 12 hours. After drying, it was transferred to a muffle furnace and the heating program of the muffle furnace was set as follows: the temperature was increased from room temperature to 180°C at 10°C / min, held for 1 hour, then increased from 180°C to 300°C at 5°C / min, held for 1 hour, and then naturally cooled to room temperature to obtain the polyimide fiber membrane.

[0038] 0.466 g of zirconium tetrachloride (ZrCl4) and 0.362 g of 2-aminoterephthalic acid (NH2-BDC) were dissolved in 160 mL of N,N-dimethylformamide (DMF). After ultrasonic dispersion, the mixture was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The prepared polyimide fiber membrane was placed in the reactor and reacted at 120 °C for 24 h to achieve in-situ growth of UiO-66-NH2. After the reaction, the fiber membrane was removed, washed three times with DMF, and then soaked in 50 mL of anhydrous methanol for 24 h, during which the methanol was replaced 2-3 times. Subsequently, it was vacuum dried to obtain the PI / UiO-66-NH2 fiber membrane.

[0039] The PI / UiO-66-NH2 fiber membrane obtained by thermal imidization treatment at 300℃ was thoroughly dried to constant weight and recorded as M1. Unloaded UiO-66-NH2 polyimide fiber membranes from the same batch were dried to constant weight and recorded as M0. The UiO-66-NH2 loading was calculated using the formula: Loading = (M1−M0) / M0×100%. In this experiment, the loading was approximately 30wt%.

[0040] 100 mL of Tris-HCl buffer solution was measured, and the pH was adjusted to 8.5. The prepared PI / UiO-66-NH2 fiber membrane was added, along with 0.2 g of dopamine hydrochloride. The mixture was magnetically stirred at room temperature for 12 h to allow dopamine hydrochloride to self-polymerize and deposit on the fiber membrane surface to form a PDA layer. After the reaction was complete, the fiber membrane was removed and washed with deionized water to obtain the PI / UiO-66-NH2@PDA fiber membrane. Subsequently, the PI / UiO-66-NH2@PDA fiber membrane was placed in 100 mL of PEI / Tri... In an s-HCl solution, 0.2 g of PEI was added and magnetically stirred at room temperature for 12 h to introduce PEI onto the membrane surface. After the reaction was completed, the fiber membrane was removed, thoroughly washed with deionized water, and freeze-dried for 12 h to obtain a PI / UiO-66-NH2@PDA / PEI composite separation membrane. This composite separation membrane consists of polyimide nanofibers with a diameter of 200 nm to 800 nm supporting UiO-66-NH2 nanoparticles with a particle size of 30 nm to 100 nm and a PDA / PEI surface modification layer.

[0041] Example 3 Weigh 20 mL of N,N-dimethylacetamide (DMAc) into a three-necked flask, and weigh 1.2077 g of 4,4'-diaminodiphenyl ether (ODA) and 1.7923 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). First, add ODA to the three-necked flask and fix it in place. Turn on the mechanical stirrer and stir for 20 min to ensure complete dissolution of the monomer. Then, add BPDA to the flask in 3-4 portions, decreasing the amount added with each addition. Add the next portion only after each addition has completely dissolved, with an interval of approximately 30 min. After all additions are complete, continue rapid mechanical stirring for 1 h to ensure complete reaction of the monomer, generating a 14 wt% polyamic acid precursor solution.

[0042] The electrospinning parameters were set as follows: rotation speed of 150 r / min, distance from the spinneret to the roller receiving surface of 15 cm, high voltage power supply voltage of 20 kV, feeding speed of 0.5 mL / h, oscillation at the center position with an amplitude of 50 cm and an oscillation speed of 5 mm / s, and electrospinning time of 360 min. A cylindrical roller receiver with a diameter of 12 cm and a length of 30 cm was used to collect the nanofibers to obtain a polyamic acid fiber membrane.

[0043] The obtained polyamic acid fiber membrane was placed in an oven at 60°C and dried for 12 hours. After drying, it was transferred to a muffle furnace and the heating program of the muffle furnace was set as follows: the temperature was increased from room temperature to 180°C at 10°C / min, held for 1 hour, then increased from 180°C to 300°C at 5°C / min, held for 1 hour, and then naturally cooled to room temperature to obtain the polyimide fiber membrane.

[0044] 0.466 g of zirconium tetrachloride (ZrCl4) and 0.362 g of 2-aminoterephthalic acid (NH2-BDC) were dissolved in 160 mL of N,N-dimethylformamide (DMF). After ultrasonic dispersion, the mixture was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The prepared polyimide fiber membrane was placed in the reactor and reacted at 120 °C for 24 h to achieve in-situ growth of UiO-66-NH2. After the reaction, the fiber membrane was removed, washed three times with DMF, and then soaked in 50 mL of anhydrous methanol for 24 h, during which the methanol was replaced 2-3 times. Subsequently, it was vacuum dried to obtain the PI / UiO-66-NH2 fiber membrane.

[0045] The PI / UiO-66-NH2 fiber membrane obtained by thermal imidization treatment at 300℃ was thoroughly dried to constant weight and recorded as M1. Unloaded UiO-66-NH2 polyimide fiber membranes from the same batch were dried to constant weight and recorded as M0. The UiO-66-NH2 loading was calculated using the formula: Loading = (M1−M0) / M0×100%. In this experiment, the loading was approximately 30wt%.

[0046] 100 mL of Tris-HCl buffer solution was measured, and the pH was adjusted to 8.5. The prepared PI / UiO-66-NH2 fiber membrane was added, along with 0.2 g of dopamine hydrochloride. The mixture was magnetically stirred at room temperature for 12 h to allow dopamine hydrochloride to self-polymerize and deposit on the fiber membrane surface to form a PDA layer. After the reaction was complete, the fiber membrane was removed and washed with deionized water to obtain the PI / UiO-66-NH2@PDA fiber membrane. Subsequently, the PI / UiO-66-NH2@PDA fiber membrane was placed in 100 mL of PEI / Tri... In an s-HCl solution, 0.2 g of PEI was added and magnetically stirred at room temperature for 12 h to introduce PEI onto the membrane surface. After the reaction was completed, the fiber membrane was removed, thoroughly washed with deionized water, and freeze-dried for 12 h to obtain a PI / UiO-66-NH2@PDA / PEI composite separation membrane. This composite separation membrane consists of polyimide nanofibers with a diameter of 200 nm to 800 nm supporting UiO-66-NH2 nanoparticles with a particle size of 30 nm to 100 nm and a PDA / PEI surface modification layer.

[0047] Example 4 Weigh 22 mL of N,N-dimethylacetamide (DMAc) into a three-necked flask, and weigh 1.2077 g of 4,4'-diaminodiphenyl ether (ODA) and 1.7923 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). First, add ODA to the three-necked flask and fix it in place. Turn on the mechanical stirrer and stir for 20 min to ensure complete dissolution of the monomer. Then, add BPDA to the flask in 3-4 portions, decreasing the amount added with each addition. Add the next portion only after each addition has completely dissolved, with an interval of approximately 30 min. After all additions are complete, continue rapid mechanical stirring for 1 h to ensure complete reaction of the monomer, generating a 12 wt% polyamic acid precursor solution.

[0048] The electrospinning parameters were set as follows: rotation speed of 150 r / min, distance from the spinneret to the roller receiving surface of 15 cm, high voltage power supply voltage of 20 kV, feeding speed of 0.5 mL / h, oscillation at the center position with an amplitude of 50 cm and an oscillation speed of 5 mm / s, and electrospinning time of 360 min. A cylindrical roller receiver with a diameter of 12 cm and a length of 30 cm was used to collect the nanofibers to obtain a polyamic acid fiber membrane.

[0049] The obtained polyamic acid fiber membrane was placed in an oven at 60°C and dried for 12 hours. After drying, it was transferred to a muffle furnace and the heating program of the muffle furnace was set as follows: the temperature was increased from room temperature to 180°C at 10°C / min, held for 1 hour, then increased from 180°C to 280°C at 5°C / min and held for 1 hour, and then naturally cooled to room temperature to obtain the polyimide fiber membrane.

[0050] 0.466 g of zirconium tetrachloride (ZrCl4) and 0.362 g of 2-aminoterephthalic acid (NH2-BDC) were dissolved in 160 mL of N,N-dimethylformamide (DMF). After ultrasonic dispersion, the mixture was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The prepared polyimide fiber membrane was placed in the reactor and reacted at 120 °C for 24 h to achieve in-situ growth of UiO-66-NH2. After the reaction, the fiber membrane was removed, washed three times with DMF, and then soaked in 50 mL of anhydrous methanol for 24 h, during which the methanol was replaced 2-3 times. Subsequently, it was vacuum dried to obtain the PI / UiO-66-NH2 fiber membrane.

[0051] The PI / UiO-66-NH2 fiber membrane obtained by thermal imidization treatment at 280℃ was thoroughly dried to constant weight and recorded as M1; the weight of the polyimide fiber membrane dried to constant weight before loading UiO-66-NH2 was recorded as M0. The UiO-66-NH2 loading was calculated according to the formula: loading = (M1−M0) / M0×100%, and the loading in this experiment was approximately 40wt%.

[0052] 100 mL of Tris-HCl buffer solution was measured, and the pH was adjusted to 8.5. The prepared PI / UiO-66-NH2 fiber membrane was added, along with 0.2 g of dopamine hydrochloride. The mixture was magnetically stirred at room temperature for 12 h to allow dopamine hydrochloride to self-polymerize and deposit on the fiber membrane surface to form a PDA layer. After the reaction was complete, the fiber membrane was removed and washed with deionized water to obtain the PI / UiO-66-NH2@PDA fiber membrane. Subsequently, the PI / UiO-66-NH2@PDA fiber membrane was placed in 100 mL of PEI / Tri... In an s-HCl solution, 0.2 g of PEI was added and magnetically stirred at room temperature for 12 h to introduce PEI onto the membrane surface. After the reaction was completed, the fiber membrane was removed, thoroughly washed with deionized water, and freeze-dried for 12 h to obtain a PI / UiO-66-NH2@PDA / PEI composite separation membrane. This composite separation membrane consists of polyimide nanofibers with a diameter of 200 nm to 800 nm supporting UiO-66-NH2 nanoparticles with a particle size of 30 nm to 100 nm and a PDA / PEI surface modification layer.

[0053] Example 5 Weigh 22 mL of N,N-dimethylacetamide (DMAc) into a three-necked flask, and weigh 1.2077 g of 4,4'-diaminodiphenyl ether (ODA) and 1.7923 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). First, add ODA to the three-necked flask and fix it in place. Turn on the mechanical stirrer and stir for 20 min to ensure complete dissolution of the monomer. Then, add BPDA to the flask in 3-4 portions, decreasing the amount added with each addition. Add the next portion only after each addition has completely dissolved, with an interval of approximately 30 min. After all additions are complete, continue rapid mechanical stirring for 1 h to ensure complete reaction of the monomer, generating a 12 wt% polyamic acid precursor solution.

[0054] The electrospinning parameters were set as follows: rotation speed of 150 r / min, distance from the spinneret to the roller receiving surface of 15 cm, high voltage power supply voltage of 20 kV, feeding speed of 0.5 mL / h, oscillation at the center position with an amplitude of 50 cm and an oscillation speed of 5 mm / s, and electrospinning time of 360 min. A cylindrical roller receiver with a diameter of 12 cm and a length of 30 cm was used to collect the nanofibers to obtain a polyamic acid fiber membrane.

[0055] The obtained polyamic acid fiber membrane was placed in an oven at 60°C and dried for 12 hours. After drying, it was transferred to a muffle furnace and the heating program of the muffle furnace was set as follows: the temperature was increased from room temperature to 180°C at 10°C / min, held for 1 hour, then increased from 180°C to 320°C at 5°C / min and held for 1 hour, and then naturally cooled to room temperature to obtain the polyimide fiber membrane.

[0056] 0.466 g of zirconium tetrachloride (ZrCl4) and 0.362 g of 2-aminoterephthalic acid (NH2-BDC) were dissolved in 160 mL of N,N-dimethylformamide (DMF). After ultrasonic dispersion, the mixture was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The prepared polyimide fiber membrane was placed in the reactor and reacted at 120 °C for 24 h to achieve in-situ growth of UiO-66-NH2. After the reaction, the fiber membrane was removed, washed three times with DMF, and then soaked in 50 mL of anhydrous methanol for 24 h, during which the methanol was replaced 2-3 times. Subsequently, it was vacuum dried to obtain the PI / UiO-66-NH2 fiber membrane.

[0057] The PI / UiO-66-NH2 fiber membrane obtained by thermal imidization treatment at 320℃ was thoroughly dried to constant weight and recorded as M1; the weight of the polyimide fiber membrane dried to constant weight before loading UiO-66-NH2 was recorded as M0. The UiO-66-NH2 loading was calculated according to the formula: loading = (M1−M0) / M0×100%, and the loading in this experiment was approximately 25wt%.

[0058] 100 mL of Tris-HCl buffer solution was measured, and the pH was adjusted to 8.5. The prepared PI / UiO-66-NH2 fiber membrane was added, along with 0.2 g of dopamine hydrochloride. The mixture was magnetically stirred at room temperature for 12 h to allow dopamine hydrochloride to self-polymerize and deposit on the fiber membrane surface to form a PDA layer. After the reaction was complete, the fiber membrane was removed and washed with deionized water to obtain the PI / UiO-66-NH2@PDA fiber membrane. Subsequently, the PI / UiO-66-NH2@PDA fiber membrane was placed in 100 mL of PEI / Tri... In an s-HCl solution, 0.2 g of PEI was added and magnetically stirred at room temperature for 12 h to introduce PEI onto the membrane surface. After the reaction was completed, the fiber membrane was removed, thoroughly washed with deionized water, and freeze-dried for 12 h to obtain a PI / UiO-66-NH2@PDA / PEI composite separation membrane. This composite separation membrane consists of polyimide nanofibers with a diameter of 200 nm to 800 nm supporting UiO-66-NH2 nanoparticles with a particle size of 30 nm to 100 nm and a PDA / PEI surface modification layer.

[0059] Comparative Example 1 Unlike Example 1, the heating program for the muffle furnace was set as follows: the temperature was increased from room temperature to 180°C at a rate of 10°C / min, held for 1 hour, then increased from 180°C to 250°C at a rate of 5°C / min, held for 1 hour, and then naturally cooled to room temperature, resulting in the following... Figure 2 (a) shows a polyimide fiber membrane made of Figure 3(a) It can be seen that the surface of the sample treated at 250℃ has a relatively high loading of UiO-66-NH2 particles, but the uniformity of particle distribution is relatively poor, and there is a certain degree of local accumulation. The PI / UiO-66-NH2 fiber membrane obtained by thermal imidization treatment at 250℃ was thoroughly dried to constant weight and recorded as M1; the weight of the polyimide fiber membrane dried to constant weight before loading UiO-66-NH2 was recorded as M0. The loading of UiO-66-NH2 was calculated according to the formula: loading = (M1−M0) / M0×100%, and the loading in this experiment was approximately 47wt%.

[0060] This phenomenon indicates that a lower heat treatment temperature is beneficial for the nucleation and growth of UiO-66-NH2 on the fiber surface. However, excessive or uneven particle accumulation can easily lead to excessively high surface roughness of the membrane and partial pore blockage, thereby affecting the permeation performance and subsequent stability of the composite membrane.

[0061] Comparative Example 2 Unlike Example 1, the heating program for the muffle furnace was set as follows: the temperature was increased from room temperature to 180°C at a rate of 10°C / min, held for 1 hour, then increased from 180°C to 350°C at a rate of 5°C / min, held for 1 hour, and then naturally cooled to room temperature, resulting in the following... Figure 2 (c) shows a polyimide fiber membrane made of Figure 3 (c) It can be seen that the surface of the sample treated at 350℃ is relatively smooth, and the loading of UiO-66-NH2 particles is significantly reduced, indicating that excessively high heat treatment temperature is not conducive to the in-situ nucleation and loading of UiO-66-NH2 on the fiber surface. The PI / UiO-66-NH2 fiber membrane obtained by thermal imidization treatment at 350℃ was thoroughly dried to constant weight and recorded as M1; the weight of the polyimide fiber membrane dried to constant weight before loading UiO-66-NH2 was recorded as M0. The loading of UiO-66-NH2 was calculated according to the formula: loading = (M-M0) / M0×100%, and the loading in this experiment was approximately 15wt%.

[0062] The reason is that the higher temperature allows the fiber surface to interact with Zr. 4+ The number of active polar sites is reduced, thereby decreasing the growth density of UiO-66-NH2.

[0063] The testing method is as follows: Hydrophilicity test: The PI, PI / UiO-66-NH2, and PI / UiO-66-NH2@PDA / PEI composite separation membranes prepared in Example 1 were cut into rectangular samples of 3cm × 2cm, fixed on glass slides or test platforms, and their contact angles with water in air were measured using a contact angle meter. The test results are as follows: Figure 5As shown, the unmodified PI membrane has a relatively high initial water contact angle of about 145°, and it remains basically stable within 60 s. This indicates that the original PI membrane surface is highly hydrophobic, making it difficult for water droplets to spread and penetrate quickly on its surface.

[0064] In contrast, the water contact angle of the PI / UiO-66-NH2 membrane modified with UiO-66-NH2 decreased significantly with contact time, reaching 0° within approximately 10 s, indicating that the introduction of UiO-66-NH2 improved the hydrophilicity of the PI membrane surface. This is mainly due to the presence of amino and metal-organic framework structures on the UiO-66-NH2 surface, which enhances the membrane surface's ability to bind water molecules.

[0065] After further modification with PDA and PEI, the initial water contact angle of the resulting PI / UiO-66-NH2@PDA / PEI membrane was significantly reduced, rapidly decreasing to 0° within 3 seconds, exhibiting stronger hydrophilicity and rapid wetting ability. This is because PDA and PEI contain abundant hydrophilic groups such as hydroxyl and amino groups, which can form hydrogen bonds with water molecules, thereby promoting the rapid spreading and penetration of water droplets on the membrane surface.

[0066] These results demonstrate that the present invention, by introducing UiO-66-NH2 onto the PI membrane surface and further functionalizing it with PDA / PEI, can significantly improve the hydrophilicity of the membrane material. Enhanced hydrophilicity of the membrane surface facilitates the formation of a stable hydration layer in an aqueous environment, thereby improving the membrane material's resistance to oil fouling and separation stability during oil-water separation.

[0067] Underwater superoleophobic performance test: The composite separation membrane prepared in Example 1 was cut into rectangular samples of 3cm × 2cm, fixed in the testing device, and immersed in a water tank. Different oil drops were then added to the membrane surface in the following order: n-hexane, n-heptane, petroleum ether, and dichloroethane. The underwater oil contact angle was then measured, and the test results are as follows: Figure 6 As shown, the composite separation membrane exhibits high underwater oil contact angles for various oil phases. For n-hexane, n-heptane, petroleum ether, and dichloroethane, the underwater oil contact angles are all above 150°. This indicates that the PI / UiO-66-NH2@PDA / PEI membrane possesses excellent oleophobic properties for multiple oil phases underwater and can be classified as an underwater superoleophobic membrane.

[0068] Oil-water separation test: Oil-water mixtures of n-hexane / water, n-heptane / water, petroleum ether / water, and vegetable oil / water were prepared, with an oil-to-water volume ratio of 1:1 and a total volume of 100 mL for each mixture. The composite separation membrane prepared in Example 1 was fixed in a filtration device, and the oil-water mixture was poured into the device. Separation was performed under gravity-driven conditions. The separation time was recorded, and the mass of the permeate water phase was weighed. The water flux was calculated based on the permeate volume, effective membrane area, and separation time. The separation efficiency was calculated based on the change in the mass of the water phase before and after separation. The test results are shown below. Figure 7 As shown, the composite separation membrane has a high flux for oil-water separation of hexane / water, heptane / water, and petroleum ether / water mixtures, all exceeding 8200 L·m⁻¹. -2 ·h -1 The above parameters were achieved, with separation efficiencies exceeding 99%; the oil-water separation flux for plant-based oil / water mixtures was approximately 5200 L·m⁻¹. -2 ·h -1 The separation efficiency is approximately 97%.

[0069] Prepare 100 mL of a 1:1 hexane / water oil-water mixture. Fix the composite separation membranes prepared in Examples 1, 2, 3, 4, 5, Comparative Example 1, and Comparative Example 2 into separate filtration devices. Pour the oil-water mixture into the device and perform separation under gravity. Record the separation time and weigh the permeate phase. Calculate the water flux based on the permeate volume, effective membrane area, and separation time. Calculate the separation efficiency based on the change in water phase mass before and after separation. The test results are as follows: Figure 8 As shown, the composite separation membrane prepared in Example 1 has an oil-water separation flux of 8900 L·m⁻¹ for the hexane / water mixture. -2 ·h -1 The separation efficiency was 99%. In contrast, Comparative Examples 1 and 2 experienced reduced membrane structure modulation effects due to excessively high and low UiO-66-NH2 loadings, respectively, resulting in separation fluxes of approximately 3200 L·m⁻¹. -2 ·h -1 and 3600 L·m -2 ·h -1 .

[0070] Oil-water separation circulation test: Prepare 100 mL of a 1:1 hexane / water oil-water mixture. Fix the composite separation membrane prepared in Example 1 in a filtration device. Pour the oil-water mixture into the device and separate the oil and water under gravity-driven conditions. Calculate the oil-water separation time and the change in oil and water mass before and after separation, and calculate the separation efficiency. After completing the oil-water separation experiment, immerse the composite separation membrane in the filtration device in 30 mL of ethanol solution, wash repeatedly, rinse with deionized water, freeze-dry, and repeat the above oil-water separation experiment. Measure the water flux and separation efficiency after each cycle. The test results are as follows: Figure 9 As shown, after 30 oil-water separation cycles, the composite separation membrane still maintains a water separation flux of approximately 7900 L·m⁻¹. -2 ·h -1 The separation efficiency remained stable at over 98%, demonstrating good cycle stability and regeneration performance.

[0071] Antifouling performance test: Dichloroethane was stained with Oil Red for observation. Then, oil droplets were slowly pressed onto the surface of the composite separation membrane in an underwater environment. The adhesion, rolling, and detachment behavior of the oil droplets on the membrane surface were observed. The test results are as follows: Figure 10 As shown, when the dyed oil phase is introduced into the aqueous phase and gradually approaches the membrane surface, the oil phase does not spread or permeate significantly on the membrane surface. Even when the oil phase comes into contact with the membrane surface, no obvious dyed oil residue appears on the surface of the composite separation membrane, indicating that the membrane has a good repulsion effect on the oil phase in the underwater environment. Furthermore, after pre-compression, the oil droplets can still maintain a relatively intact shape and are not captured or spread significantly by the membrane surface. When the needle is slowly withdrawn, the oil droplets can easily detach from the membrane surface, and there is almost no oil phase residue on the membrane surface. These results indicate that the composite separation membrane not only has a high underwater oil contact angle but also exhibits low oil adhesion.

[0072] The above phenomenon is mainly attributed to the abundant hydrophilic groups on the surface of the composite separation membrane, which can rapidly bind water molecules in an aqueous environment and form a stable hydration layer on the membrane surface. This hydration layer effectively blocks direct contact between the oil phase and the membrane substrate, thereby reducing the adhesion of oil droplets on the membrane surface and mitigating the clogging of membrane pores by oil contamination. Therefore, the composite separation membrane exhibits excellent underwater oleophobicity, oil contamination resistance, and recycling potential in oil-water separation processes.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide composite oil-water separation membrane, characterized in that, The process includes the following steps: S1, Preparation of polyimide fiber membrane: Using a polyamic acid solution as a precursor, a polyamic acid fiber membrane is prepared by electrospinning. The polyamic acid fiber membrane is then subjected to thermal imidization treatment to obtain a polyimide fiber membrane. The thermal imidization treatment includes placing the polyamic acid fiber membrane in a heating device for programmed temperature control, wherein the final temperature of the programmed temperature control is 280℃~320℃. S2, Loading of UiO-66-NH2: Using an in-situ synthesis method, UiO-66-NH2 is loaded... 2 nanoparticles were loaded onto the surface of a polyimide fiber membrane to obtain a polyimide / UiO-66-NH2 fiber membrane; S3, coating a PDA / PEI layer: the polyimide / UiO-66-NH2 fiber membrane was immersed in a dopamine / Tris-HCl buffer solution to allow dopamine to self-polymerize and form a PDA layer; then it was immersed in a polyethyleneimine / Tris-HCl solution for PEI modification to obtain a polyimide / UiO-66-NH2@PDA / PEI composite separation membrane.

2. The preparation method according to claim 1, characterized in that, The polyamic acid solution was prepared by the following method: 4,4′-diaminodiphenyl ether was dissolved in N,N-dimethylacetamide. After it was completely dissolved, 3,3′,4,4′-biphenyltetracarboxylic dianhydride was added in portions and mechanically stirred in an ice bath to obtain a polyamic acid solution with a mass fraction of 10wt% to 14wt%.

3. The preparation method according to claim 1, characterized in that, The heating program of the heating device includes: heating from room temperature to 180°C at 10°C / min, holding at that temperature for 1 hour, then heating to the final temperature at 5°C / min, holding at that temperature for 1 hour, and then naturally cooling to room temperature.

4. The preparation method according to claim 1, characterized in that, The in-situ synthesis method specifically includes the following steps: Zirconium tetrachloride and 2-aminoterephthalic acid are dissolved in N,N-dimethylformamide at a molar ratio of 1:1 and ultrasonically dispersed to obtain a mixed solution; then the mixed solution is transferred to a stainless steel reactor lined with polytetrafluoroethylene, and the polyimide fiber membrane obtained in S1 is added to the reactor together to carry out in-situ growth and loading of UiO-66-NH2 nanoparticles on the surface of the polyimide fiber membrane.

5. The preparation method according to claim 4, characterized in that, The in-situ growth and loading of UiO-66-NH2 nanoparticles on the surface of a polyimide fiber membrane further includes the following steps: reacting at 120°C for 24 hours in a reactor; after the reaction, removing the fiber membrane, washing it with N,N-dimethylformamide to remove unreacted ligands, then soaking it in anhydrous methanol for 24 hours to exchange the N,N-dimethylformamide in the pores and activate the pores; and finally vacuum drying at 120°C to obtain a polyimide / UiO-66-NH2 fiber membrane.

6. The preparation method according to claim 1, characterized in that: The dopamine concentration in the dopamine / Tris-HCl solution is 2 g / L, and the polyethyleneimine concentration in the polyethyleneimine / Tris-HCl solution is 2 g / L.

7. A polyimide composite separation membrane prepared by the preparation method according to any one of claims 1-6, characterized in that, It includes polyimide nanofibers, UiO-66-NH2 nanoparticles loaded on the surface of polyimide nanofibers, and a PDA / PEI surface modification layer wrapped around the surface of UiO-66-NH2 nanoparticles and polyimide nanofibers, wherein the diameter of the polyimide nanofibers is 200 nm to 800 nm, and the particle size of the UiO-66-NH2 nanoparticles is 30 nm to 100 nm.

8. The composite separation membrane according to claim 7, characterized in that, The loading amount of the UiO-66-NH2 nanoparticles on the polyimide nanofibers is 25wt% to 40wt%.

9. An application of the composite separation membrane as described in claim 7 or 8, including the application of the polyimide composite separation membrane in the field of oil-water separation.

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