A zif-8 modified polyimide membrane and a preparation method and application thereof

Abstract

This invention provides a ZIF-8 modified polyimide membrane, its preparation method, and its application. The ZIF-8 modified polyimide membrane comprises a polyimide membrane and ZIF-8 particles in contact with the surface of the polyimide membrane. The ZIF-8 modified polyimide membrane provided by this invention has the characteristics of high oil-water separation flux and high oil-water separation efficiency.

Description

Technical Field

[0001] This invention relates to a ZIF-8 modified polyimide membrane, its preparation method and application, belonging to the field of separation membrane technology. Background Technology

[0002] With the acceleration of industrialization and the increase in energy demand, leaks and emissions of petroleum and petrochemical products, as well as problems with produced water from oil fields, have become increasingly serious, leading to large amounts of oil-water mixtures entering the environment and severely polluting ecosystems and water resources. Oil-water separation technology has become crucial for solving these problems. However, traditional physical and chemical separation methods, such as gravity sedimentation, flotation, and chemical flocculation, while effective, suffer from drawbacks such as complex equipment, high cost, and difficult operation. In contrast, membrane separation technology has become a research hotspot in the field of oil-water separation due to its advantages of high efficiency, energy saving, ease of operation, and ability to achieve continuous separation. There are various methods for manufacturing fiber membranes, such as stretching, template synthesis, self-assembly, microphase separation, and electrospinning. Among these, electrospinning is widely used due to its simple operation, wide applicability, and high production efficiency.

[0003] In recent years, nanofiber membranes with large specific surface area and high porosity have been applied to oil-water separation. Compared with polymer membranes prepared by traditional phase inversion, nanofiber membranes have several key advantages, including high porosity, relatively low flow resistance, and higher filtration efficiency. The electrospun fibers used for oil-water separation typically possess superhydrophobic / superoleophilic surface properties, which makes the separation membrane less prone to fouling and enables it to efficiently and selectively filter or absorb oil from oil-water mixtures.

[0004] In practical applications, oil-water separation operations often encounter extreme environments such as high temperatures, strong acids, and strong alkalis. However, current fiber separation membranes struggle to maintain structural and performance stability under these harsh conditions. Polyimide (PI) fiber, as a high-performance aromatic heterocyclic polymer with outstanding comprehensive properties, possesses characteristics such as high temperature resistance, flame retardancy, insulation, low dielectric constant, and radiation resistance, while also exhibiting the strength and modulus of high-performance fibers.

[0005] Existing technologies utilize polyimide electrospun membranes for oil-water separation. For example, patent CN109012237B discloses a polyimide oil-water separation membrane modified with polydimethylsiloxane-silica nanoparticles (PDMS-SNPs) for use under harsh conditions such as high temperature, strong acid, and strong alkali, enhancing the membrane's resilience. Patent CN109012238B discloses a polydopamine / polytetrafluoroethylene-polyimide membrane, combining the high mechanical strength of polyimide with the oleophilic and hydrophobic properties of a polydopamine-polytetrafluoroethylene composite dispersion. Patent CN111437730A discloses a polyimide nanofiber membrane modified with polydimethylsiloxane-zinc oxide (PDMS-ZnO), further strengthening the membrane's resilience. However, the preparation methods disclosed in these patents are overly complex, and the resulting products suffer from low oil-water separation throughput and efficiency.

[0006] Therefore, developing a separation material with high oil-water separation flux and efficiency has become a current research direction. Summary of the Invention

[0007] This invention provides a ZIF-8 modified polyimide membrane, which has the characteristics of high oil-water separation flux and high oil-water separation efficiency.

[0008] The present invention also provides a method for preparing a ZIF-8 modified polyimide film, which has the advantage of simple preparation process.

[0009] The present invention also provides an oil-water separation method, which has the characteristic of high separation efficiency.

[0010] The first aspect of the present invention provides a ZIF-8 modified polyimide film, comprising a polyimide film and ZIF-8 particles in contact with the surface of the polyimide film.

[0011] The ZIF-8 modified polyimide membrane described above has an oil-water separation flux greater than or equal to 12500 L·m. 2 ·h -1 Oil-water separation efficiency is greater than or equal to 99.85%; and / or,

[0012] The glass transition temperature of the ZIF-8 modified polyimide film is 400℃~450℃.

[0013] The ZIF-8 modified polyimide film as described above is prepared by a method comprising the following steps:

[0014] 1) The raw polyimide film is subjected to at least one contact-drying treatment using a zinc salt solution to obtain a pretreated polyimide film;

[0015] 2) The pretreated polyimide membrane is mixed with an aqueous solution containing zinc ions and hexamethylenetetramine, and the resulting mixture is subjected to a first heat treatment to obtain a ZnO / PI fiber membrane.

[0016] 3) The ZnO / PI fiber membrane is mixed with solvent and 2-methylimidazole, and the resulting mixture is subjected to a second heat treatment to obtain the ZIF-8 modified polyimide membrane.

[0017] A second aspect of the present invention provides a method for preparing a ZIF-8 modified polyimide film, comprising the following steps:

[0018] 1) The raw polyimide film is subjected to at least one contact-drying treatment using a zinc salt solution to obtain a pretreated polyimide film;

[0019] 2) The pretreated polyimide membrane is mixed with an aqueous solution containing zinc ions and hexamethylenetetramine, and the resulting mixture is subjected to a first heat treatment to obtain a ZnO / PI fiber membrane.

[0020] 3) The ZnO / PI fiber membrane is mixed with solvent and 2-methylimidazole, and the resulting mixture is subjected to a second heat treatment to obtain the ZIF-8 modified polyimide membrane.

[0021] In the preparation method described above, the first heat treatment is performed at a temperature of 100℃-120℃ for a time of 10min-30min.

[0022] In the preparation method described above, the second heat treatment is performed at a temperature of 60-120°C for 1-2 hours.

[0023] The solvent is selected from at least one of deionized water, methanol, and DMF.

[0024] In the preparation method described above, in step 2), the mass of 2-methylimidazole is 1-5 wt% of the mass of the solvent; and / or,

[0025] In step 1), before the raw polyimide film is subjected to at least one contact-drying treatment with zinc salt solution, the raw polyimide film is further subjected to plasma treatment in a vacuum after being contacted with an aqueous solution including potassium permanganate and alkali metal hydroxide.

[0026] In the preparation method described above, in step 1), the raw material polyimide film is prepared by a method comprising the following steps:

[0027] 1) In a polar aprotic solvent, aromatic diamine and aromatic dianhydride are mixed to obtain polyamic acid slurry;

[0028] 2) The polyamic acid slurry is prepared into a precursor film using an electrospinning device;

[0029] 3) The precursor membrane is treated at temperatures of 80-120℃, 180-220℃ and 280-320℃ for 30 minutes each to obtain the raw material polyimide membrane.

[0030] In the preparation method described above, the applied voltage of the electrospinning equipment is 10-50kV, the spinning distance is 15-25cm, the inner diameter of the spinneret is 0.41mm, the flow rate is 1-2mL / h, the rotation speed of the collecting drum is 50-150rpm, the collecting substrate is a brass screen, the relative humidity is 40-60%, and the temperature is 20-28℃.

[0031] A third aspect of the present invention provides a water-oil separation method, comprising using any of the ZIF-8 modified polyimide membranes described above to separate a mixture comprising water and oil.

[0032] The ZIF-8 modified polyimide membrane provided by this invention has the characteristics of high oil-water separation flux and high oil-water separation efficiency. Attached Figure Description

[0033] Figure 1 This is a statistical chart of the contact angles of different liquids in Example 3;

[0034] Figure 2 The SEM image is from Example 3;

[0035] Figure 3 The image shown is the SEM image for Comparative Example 1.

[0036] Figure 4 A comparison of the Fourier Transform Infrared (FTIR) spectra of the PI film, PI / ZnO film, and PI / ZIF-8 film in Example 1;

[0037] Figure 5 The image is a thermogravimetric analysis (TGA) image of the PI / ZIF-8 membrane in Example 1;

[0038] Figure 6 This is a static thermomechanical analysis (DMA) image of the PI / ZIF-8 membrane in Example 1. Detailed Implementation

[0039] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The first aspect of the present invention provides a ZIF-8 modified polyimide film, the ZIF-8 modified polyimide film comprising a polyimide film and ZIF-8 particles in contact with the surface of the polyimide film; the surface of the polyimide film is uniformly covered by ZIF-8 particles.

[0041] The ZIF-8 modified polyimide film provided by this invention is a composite material comprising a polyimide film and ZIF-8 particles in contact with the surface of the polyimide film. ZIF-8 refers to polyimide particles composed of zinc ions (Zn...). 2+ A substance formed by coordination of 2-methylimidazole (2-MiM).

[0042] The inventors have discovered that the ZIF-8 modified polyimide membrane provided by this invention exhibits high oil-water separation flux and efficiency. The inventors believe this performance improvement is likely due to two key factors: First, the ZIF-8 particles possess extremely high hydrophobicity and can be uniformly distributed on the surface of the polyimide fibers. This uniform distribution helps improve the membrane's hydrophobic properties, allowing oil droplets to pass through more easily while effectively blocking water. Second, the membrane surface possesses a high content and high density of ZIF-8 nanoparticles. This characteristic is achieved by increasing the surface roughness of the polyimide fibers, allowing ZnO crystals to firmly adhere to the uneven areas of the fiber surface. Subsequently, these ZnO crystals are converted in situ into ZIF-8, further promoting the enrichment of ZIF-8 functional particles on the membrane surface. In summary, due to the high hydrophobicity of ZIF-8 and its uniform distribution on the surface of polyimide fibers, as well as the high content and high density of ZIF-8 nanoparticles achieved by increasing fiber surface roughness and ZnO in-situ conversion technology, the ZIF-8 modified polyimide membrane provided by this invention has the characteristics of high oil-water separation flux and oil-water separation efficiency.

[0043] This invention does not limit the method of increasing fiber surface roughness; conventional methods in the art can be used. In one embodiment, the fiber surface roughness can be increased by contacting the polyimide film with a solution comprising alkali metal hydroxide and alkali metal permanganate, or by subjecting the polyimide film to plasma treatment.

[0044] The ZIF-8 modified polyimide membrane provided by this invention also has an oil-water separation flux greater than or equal to 12500 L·m 2 ·h -1It features an oil-water separation efficiency of ≥99.85%. The oil-water separation flux refers to the liquid flow rate per square meter of contact area per hour when this ZIF-8 modified polyimide membrane is used for oil-water separation. The oil-water separation efficiency is negatively correlated with the ratio of the water content of the liquid after separation to that before separation when using this ZIF-8 modified polyimide membrane for oil-water separation; the lower the ratio, the higher the oil-water separation efficiency.

[0045] Furthermore, the ZIF-8 modified polyimide membrane provided by this invention has a water contact angle greater than or equal to 147°, and its glass transition temperature is 400°C to 450°C. By incorporating ZIF-8 into the polyimide, the high hydrophobicity helps improve the membrane's antifouling ability and durability, while the high thermal stability of the polyimide ensures the membrane material's durability under high-temperature operating conditions. In summary, the ZIF-8 modified polyimide membrane exhibits excellent performance in high-temperature oil-water separation and is suitable for treating oily wastewater and other oil-water mixtures. Therefore, the ZIF-8 modified polyimide membrane provided by this invention also possesses good hydrophobicity and high-temperature resistance.

[0046] In one embodiment, the ZIF-8 modified polyimide film provided by the present invention is prepared by a method comprising the following steps:

[0047] 1) The raw polyimide film is subjected to at least one contact-drying treatment using a zinc salt solution to obtain a pretreated polyimide film;

[0048] 2) The pretreated polyimide membrane is mixed with an aqueous solution containing zinc ions and hexamethylenetetramine, and the resulting mixture is subjected to a first heat treatment to obtain a ZnO / PI fiber membrane.

[0049] 3) The ZnO / PI fiber membrane was mixed with solvent and 2-methylimidazole, and the resulting mixture was subjected to a second heat treatment to obtain a ZIF-8 modified polyimide membrane.

[0050] The raw material polyimide film is a commonly used polyimide film in the art. The preparation method provided by this invention is not limited to the preparation method of the raw material polyimide film; it can be prepared using commonly used methods in the art. For example, in one embodiment, 4,4'-diphenyl ether diamine (ODA) can be dissolved in a polar aprotic solvent, and pyromellitic dianhydride (PMDA) can be added to the solution in batches while continuously stirring to obtain a polyamic acid slurry. The raw material polyimide film can then be prepared using at least one of the methods commonly used in the art: stretching, template synthesis, self-assembly, microphase separation, and electrospinning.

[0051] A zinc salt solution is an aqueous solution obtained by dissolving a soluble zinc salt in water. This invention does not limit the specific selection of the zinc salt, as long as it meets the requirement of being soluble in water. In one embodiment, the zinc salt is selected from at least one of zinc nitrate hydrate, zinc chloride, zinc sulfate, and zinc acetate. This invention does not limit the concentration of zinc ions in the zinc salt solution; in one embodiment, the concentration range is 0.1-1 mol / L.

[0052] The contact-drying process involves contacting the raw polyimide film with a zinc salt solution, causing the zinc ions in the zinc salt solution to adhere to the surface of the raw polyimide film. The film is then removed from the zinc salt solution and dried (including but not limited to indoor air drying, heat drying, etc., simply to evaporate the moisture from the surface of the film), converting the zinc ions adhering to the surface of the film into a zinc oxide crystal layer. Furthermore, the contact-drying process is performed at least once.

[0053] In step 2), the pretreated polyimide film is mixed with an aqueous solution containing zinc ions and hexamethylenetetramine, and the resulting mixture is subjected to a first heat treatment. During the first heat treatment, zinc oxide is loaded onto the surface of the pretreated polyimide film to obtain a ZnO / PI fiber film. Hexamethylenetetramine is a chelating agent with exposed electron pairs, which can form coordinate bonds, enabling it to form a stable complex with zinc ions. This protects the zinc ions from the influence of other ions in the environment, facilitating the formation of zinc oxide loaded onto the surface of the treated polyimide film. This invention does not limit the specific processing conditions of the first heat treatment; commonly used processing conditions in the art can be used. In one embodiment, the processing temperature of the first heat treatment is 80-150°C, and the processing time is 10-30 minutes.

[0054] In step 3), the ZnO / PI fiber membrane is mixed with a solvent and 2-methylimidazole, and the resulting mixture is subjected to a second heat treatment to obtain a ZIF-8 modified polyimide membrane. During the second heat treatment, 2-methylimidazole reacts with zinc oxide, converting the zinc oxide loaded on the surface of the polyimide membrane into ZIF-8 particles, thereby obtaining the ZIF-8 modified polyimide membrane. This invention does not limit the specific processing conditions of the second heat treatment; commonly used processing conditions in the art can be used. In one embodiment, the processing temperature of the second heat treatment is 50-150°C, and the processing time is 0.5-3 hours.

[0055] In the above-described mixture, the solvent is selected from at least one of deionized water, methanol, and DMF. This invention does not limit the amount of 2-methylimidazole added; amounts commonly used in the art can be used. In one embodiment, the mass of 2-methylimidazole is 0.5-10 wt% of the solvent mass.

[0056] A second aspect of this invention provides a method for preparing a ZIF-8 modified polyimide film, which can be used to obtain the ZIF-8 modified polyimide film provided in the first aspect of this invention. The method includes the following steps:

[0057] 1) The raw polyimide film is subjected to at least one contact-drying treatment using a zinc salt solution to obtain a pretreated polyimide film;

[0058] 2) The pretreated polyimide membrane is mixed with an aqueous solution containing zinc ions and hexamethylenetetramine, and the resulting mixture is subjected to a first heat treatment to obtain a ZnO / PI fiber membrane.

[0059] 3) The ZnO / PI fiber membrane was mixed with solvent and 2-methylimidazole, and the resulting mixture was subjected to a second heat treatment to obtain a ZIF-8 modified polyimide membrane.

[0060] The meanings of raw material polyimide film, zinc salt solution, contact-drying treatment, first heat treatment, and second heat treatment are the same as those mentioned above, and will not be repeated here.

[0061] The preparation method provided by this invention uses common raw materials to prepare ZIF-8 modified polyimide films, and has the advantage of simple preparation process.

[0062] In one specific embodiment, to further improve the oil-water separation flux and efficiency of the ZIF-8 modified polyimide membrane provided by the present invention, the processing temperature of the first heat treatment can be controlled at 100-120℃ and the processing time at 10-30 min, and the processing temperature of the second heat treatment can be controlled at 60-120℃ and the processing time at 1-2 h. These processing conditions, by increasing the surface roughness of the polyimide fibers, allow zinc oxide crystals to adhere to the uneven surfaces of the fibers, thus enabling the ZIF-8 modified polyimide membrane provided by the present invention to have higher oil-water separation flux and efficiency.

[0063] In one embodiment, in step 2), the mass of 2-methylimidazole is 1-5 wt% of the solvent mass. Due to the appropriate addition amount, 2-methylimidazole can react more efficiently with zinc oxide to generate ZIF-8, thereby the ZIF-8 modified polyimide membrane provided by the present invention has higher oil-water separation flux and oil-water separation efficiency.

[0064] Further, in one embodiment, before step 1) performing at least one contact-drying treatment on the raw polyimide film using a zinc salt solution, the process further includes contacting the raw polyimide film with an aqueous solution comprising potassium permanganate and an alkali metal hydroxide (at least one selected from sodium hydroxide and potassium hydroxide) followed by plasma treatment in a vacuum. By placing the polyimide film in a dilute solution of potassium permanganate and potassium hydroxide, the polyimide reacts under the action of the alkali: PI + 2KOH → K₂O + KOPI + H₂O. Here, PI represents polyimide, KOH represents potassium hydroxide, and KOPI represents potassium polyimide salt. This treatment can cause cracking on the surface of the raw polyimide film, increasing its roughness and generating carboxylic acid groups and sodium ions (Na₂O) on the PI surface structure. + ) or potassium ions (K + The zinc ions (Zn) react with carboxylic acid groups to form sodium carboxylate or potassium carboxylate, which are then exchanged via ion exchange. 2+ The zinc oxide is incorporated into the chain. Finally, a PI-ZnO composite fiber membrane is generated by high temperature or reducing agent treatment. Zinc oxide can be loaded onto the surface of the polyimide membrane more efficiently and uniformly, thus the ZIF-8 modified polyimide membrane provided by this invention has higher oil-water separation flux and oil-water separation efficiency.

[0065] In one embodiment, the concentration of potassium permanganate in the aqueous solution of potassium permanganate and alkali metal hydroxide is controlled to be 10-20 g / L, and the concentration of sodium hydroxide is controlled to be 4-8 g / L. The plasma treatment conditions are 300 seconds at 500 W under a vacuum of 10 Pa. The ZIF-8 modified polyimide membrane prepared using the above conditions has higher oil-water separation flux and oil-water separation efficiency.

[0066] High-energy electrons in the plasma collide with the material surface, transferring energy to molecules and atoms, causing surface molecules to be excited or ionized. The material sputtered out by etching is excited in the plasma and diffuses back towards the surface, re-aggregating while being etched, forming conical or spherical protrusions, further increasing the roughness of the thin film surface.

[0067] In one embodiment, in step 1), the raw material polyimide film is prepared by a method comprising the following steps:

[0068] 1) In a polar aprotic solvent, aromatic diamine and aromatic dianhydride are mixed to obtain polyamic acid slurry;

[0069] 2) The polyamic acid slurry was prepared into a precursor membrane using electrospinning equipment;

[0070] 3) The precursor membrane was treated sequentially at temperatures of 80-120℃, 180-220℃ and 280-320℃ for 30 minutes each to obtain the raw material polyimide membrane.

[0071] Both the aromatic diamine and the aromatic dianhydride can be selected from commonly used raw materials in the art. For example, the aromatic diamine can be selected from 4,4'-diphenyl ether diamine (4,4'-ODA), 3,3'-diphenyl ether diamine (3,3'-ODA), 3,4'-diphenyl ether diamine (3,4'-ODA), p-phenylenediamine (pPDA), 2,2'-dimethylbenzidine diamine (DMB), 2,2'-di(trifluoromethyl)benzidine diamine (PFMB), and 4,4'-diaminodiphenylmethane (MDA). The aromatic dianhydride can be selected from pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenone dianhydride (BTDA), diphenyl ether dianhydride (OPDA), and hexafluorodianhydride (6FDA). In one embodiment, the aromatic diamine is 4,4'-diphenyl ether diamine, and the aromatic dianhydride is pyromellitic dianhydride. The polar aprotic solvent is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP).

[0072] Specifically, in a polar aprotic solvent, an aromatic diamine and an aromatic dianhydride undergo a polycondensation reaction to obtain a polyamic acid slurry. This slurry can then be used to prepare a precursor film using electrospinning equipment. This invention does not limit the specific reaction conditions for the polycondensation reaction between the aromatic diamine and the aromatic dianhydride; commonly used reaction conditions in the art can be used. Subsequently, the obtained precursor film is sequentially treated at temperatures of 80-120°C, 180-220°C, and 280-320°C for 30 minutes each to induce an imidization reaction, thereby obtaining the raw material polyimide film.

[0073] Electrospinning equipment is characterized by high production efficiency. Using electrospinning equipment to prepare raw material polyimide films can make the preparation method provided by this invention even more efficient.

[0074] In one embodiment, the electrospinning equipment uses an applied voltage of 10-50 kV, a spinning distance of 15-25 cm, a spinneret inner diameter of 0.41 mm, a flow rate of 1-2 mL / h, a collecting drum rotation speed of 50-150 rpm, a brass screen as the collecting substrate, a relative humidity of 40-60%, and a temperature of 20-28 °C. Due to these suitable operating parameters, the efficiency of the preparation method provided by this invention can be further improved.

[0075] A third aspect of this invention provides a method for separating water and oil, which uses a ZIF-8 modified polyimide membrane provided in the first aspect of this invention to separate a mixture comprising water and oil. Since the ZIF-8 modified polyimide membrane provided in the first aspect of this invention has high oil-water separation flux and high oil-water separation efficiency, the water-oil separation method provided by this invention has high separation efficiency.

[0076] The following will provide a detailed description of the ZIF-8 modified polyimide film, its preparation method, and its applications, with reference to specific embodiments.

[0077] Raw material source:

[0078] 4,4'-Diphenyl ether diamine, 98%, Adamas;

[0079] Pyromellitic dianhydride, ≥98%, Adamas;

[0080] N,N-Dimethylformamide, ≥99.5%, Shanghai test;

[0081] N,N-Dimethylacetamide, ≥99.0%, Shanghai test;

[0082] N-methylpyrrolidone, ≥99.0%, Shanghai test;

[0083] Potassium permanganate, ≥99.5%, Shanghai test.

[0084] Sodium hydroxide, ≥96.0%, Shanghai test;

[0085] Potassium hydroxide, ≥85.0%, Shanghai test;

[0086] Zinc nitrate, ≥99.0%, Shanghai test;

[0087] Hexamethylenetetramine, ≥98.0%, Shanghai test;

[0088] 2-Methylimidazole, 98%, Wokai;

[0089] All chemical reagents and solvents were obtained from commercial suppliers and were ready for use without further purification.

[0090] Example 1

[0091] 1) Preparation of raw material polyimide film:

[0092] Nitrogen gas was introduced into a 500 mL dry four-necked flask. 0.01 mol of 4,4'-diphenyl ether diamine was dissolved in dimethylacetamide at room temperature. Then, pyromellitic dianhydride (PMDA to ODA molar ratio of 1:1) was added to the solution in portions, and the mixture was stirred continuously for 6 hours to obtain a 20 wt% polyamic acid slurry. That is, the sum of the masses of 4,4'-diphenyl ether diamine and pyromellitic dianhydride in this polyamic acid slurry was 20% of the total mass of the slurry. The slurry was then fed into an injection pump and spun to obtain a precursor membrane (electrospinning parameters: room temperature, air humidity approximately 40%, electrospinning voltage 30 kV / m, injection pump feed rate 1.2 mL / h, water injection pump needle with 21G tip, needle inner diameter 0.514 mm, rotor speed 100 rpm). The precursor film was heated in an oven at 60°C and 180°C for 1 hour each, and finally heated at 350°C for 0.5 hours to imidize the precursor film, thus obtaining the raw material polyimide film (PI film).

[0093] 2) Preparation of pretreated polyimide membranes:

[0094] The raw polyimide film was immersed in a 0.025M zinc nitrate hexahydrate (Zn(NO3)2·6H2O) solution and kept at room temperature for 2 hours. The raw polyimide film was then removed and dried in air for 1 hour. This process was repeated 5 times to form ZnO seed crystals on the PI fiber surface, resulting in a pretreated polyimide film.

[0095] 3) Preparation of PI / ZnO membrane:

[0096] The pretreated polyimide film was placed in 0.025M Zn(NO3)2·6H2O and 0.025M hexamethylenetetramine (C6H2O). 12 The PI / ZnO membrane was prepared by transferring the PI / ZnO membrane into a homogeneous mixed solution of N4 (N2). The solution was then transferred to a PTFE-lined stainless steel reactor and heated at 90°C for 6 hours. After the reaction was complete, the membrane was repeatedly washed with deionized water several times and finally dried in an oven at 80°C for 2 hours to obtain the PI / ZnO membrane.

[0097] 4) Preparation of ZIF-8 modified polyimide film:

[0098] The ZnO / PI fiber membrane was immersed in a 1:1 methanol:H2O mixture, and then 2 wt% (based on the mass of the mixed solvent) of 2-methylimidazole (C4H6N2) was added to the mixture. The resulting reaction system was placed in a 100 mL Teflon-lined reactor and heated in an oven at 80 °C for 24 h. The fiber membrane was then removed, cleaned with deionized water, and dried in an oven at 80 °C for 2 h to obtain a ZIF-8 modified polyimide membrane (PI / ZIF-8 membrane).

[0099] Example 2

[0100] This embodiment is basically the same as Embodiment 1, except that step 2) uses the following method to prepare the pretreated polyimide film:

[0101] The raw polyimide film was treated in a mixed solution containing KMnO4 and NaOH for 5 minutes, and then the film was subjected to plasma treatment at 500W for 300 seconds under vacuum conditions of 10Pa to obtain a pretreated polyimide film.

[0102] In the mixed solution, the concentration of KMnO4 is 12 g / L and the concentration of NaOH is 4 g / L.

[0103] A ZIF-8 modified polyimide film (PI / ZIF-8 film) was prepared.

[0104] Example 3

[0105] This embodiment is basically the same as Example 1, except that step 4) uses the following method to prepare the ZIF-8 modified polyimide film:

[0106] The ZnO / PI fiber membrane was immersed in a 1:1 DMF:H2O mixed solvent. 1 wt% of 2-methylimidazole (C4H6N2) was added to the mixed solvent. The resulting mixture was placed in a 100 mL Teflon-lined reactor and heated in an oven at 100 °C for 1 h. The fiber membrane was then removed, cleaned with deionized water, and dried in an oven at 80 °C for 2 h to obtain the ZIF-8 / PI nanofiber membrane.

[0107] Comparative Example 1

[0108] Comparative Example 1 uses the same raw material, polyimide film, as Example 1, and the remaining steps are as follows:

[0109] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in a mixed solvent of DMF and H2O and stirred at room temperature for 5-10 minutes until a clear first solution was formed. 2-Methylimidazole (C4H6N2) was dissolved in a mixed solvent of DMF and H2O and stirred at room temperature for 5-10 minutes until a clear second solution was formed. The raw polyimide membrane was cut into 8 cm × 8 cm squares. The raw polyimide membrane was immersed in the first solution for 1 hour, then removed and immersed in the second solution. The reaction was continued for 1 hour. The PI nanofiber membrane was then removed, washed with a mixed solvent including DMF and H2O, and dried at room temperature to obtain the ZIF-8 modified polyimide membrane.

[0110] Comparative Example 2

[0111] This comparative example is basically the same as Example 1, except that step 4) uses the following method to prepare the ZIF-8 modified polyimide film:

[0112] The ZnO / PI fiber membrane was immersed in a mixed solvent of DMF:H2O in a 1:1 ratio. 1 wt% of 2-methylimidazole (C4H6N2) was added to the mixed solvent, and the reaction was continued for 2 hours. The PI nanofiber membrane was then removed, washed with a mixed solvent of DMF and H2O, and dried at room temperature to obtain the ZIF-8 modified polyimide membrane.

[0113] Comparative Example 3

[0114] This comparative example uses the polyimide film obtained in step 1) of Example 1 as the sample.

[0115] Test case

[0116] 1. SEM analysis was performed on the ZIF-8 modified polyimide films prepared in Example 3 and Comparative Example 1 to obtain... Figure 2 and Figure 3 .observe Figure 2 and Figure 3 It can be seen that in Example 3 (see...) Figure 2 The fiber surface was observed to exhibit a smooth characteristic, indicating that the ZIF-8 particles achieved uniform dispersion and loading on the fiber surface. This uniform loading may contribute to improving specific fiber properties, such as enhancing its adsorption capacity for certain substances or improving its mechanical properties. In contrast, in Comparative Example 1 (see Comparative Example 1...) Figure 3 Large-sized ZIF-8 particles were found in the fiber membrane. The uneven distribution of these particles indicates that although ZIF-8 is indeed present inside the fiber membrane, it does not form a uniform coating on the fiber surface. This uneven loading may lead to inconsistent performance of the fiber membrane, affecting its effectiveness in practical applications.

[0117] In Example 1, the PI film, PI / ZnO film, and PI / ZIF-8 film were subjected to infrared spectroscopy tests. The obtained infrared spectra (FTIR) are shown below. Figure 4 .Depend on Figure 4 It can be seen that as ZnO is loaded into the PI film, the peaks at 490 and 1090 cm⁻¹ are related to the metal oxide stretching vibrations of the Zn-O bond, and the peak at 3440 cm⁻¹ is related to the metal oxide stretching vibrations of the Zn-O bond. -1 The broadband at 2972 ​​cm⁻¹ corresponds to the stretching vibration of the OH bond, indicating the presence of moisture. On the ZIF-8 / PI membrane, the characteristic peak at 2972 ​​cm⁻¹ corresponds to the vibration of CH in the imidazole ring, while the characteristic peaks at 1147 cm⁻¹ and 995 cm⁻¹ are related to CN in the imidazole ring.

[0118] 2. The water contact angle of the samples prepared in each embodiment and comparative example was tested. The test method is as follows:

[0119] To evaluate the hydrophobicity and oleophilicity of the thin film, we employed a contact angle measuring instrument, which can accurately measure the angle at which a droplet contacts a solid surface. In the experiment, the thin film sample was first placed on the instrument's platform, ensuring its correct positioning. Then, distilled water and oil droplets (e.g., silicone oil) were sequentially added to the film surface. By observing the behavior of the droplets on the film, we concluded that if the water droplet remained spherical and did not diffuse, the film exhibited hydrophobicity; if the oil droplet rapidly diffused and was absorbed on the film, it indicated oleophilicity. By accurately measuring the contact angles of these droplets, we were able to quantitatively analyze the hydrophobic and oleophilic properties of the film, thus providing a scientific basis for further applications of the material.

[0120] The test results are shown in Table 1.

[0121] Table 1

[0122] serial number Water contact angle (°) Example 1 149.8 Example 2 153.2 Example 3 151.4 Comparative Example 1 131.9 Comparative Example 2 137.8 Comparative Example 3 81.5

[0123] As shown in Table 1, the samples prepared in each embodiment have a larger water contact angle compared to the samples prepared in each comparative example, exhibiting high hydrophobicity and indicating their potential application in self-cleaning membranes. Meanwhile, the contact angle of the sample prepared in Comparative Example 1 is smaller than that of the sample prepared in Example 3. This may be because the seed crystals required for ZIF-8 growth in Comparative Example 1 cannot be sufficiently fixed on the PI film surface, preventing ZIF-8 from fully encapsulating the PI fiber membrane, thus resulting in a smaller water contact angle.

[0124] 3. The ZIF-8 modified polyimide film prepared in Example 3 was subjected to contact angle tests with water, milk, cola, red wine, and coffee. The test methods were the same as in Example 2. The test results are shown in [Figure 2]. Figure 1 .

[0125] Depend on Figure 1 It can be seen that the ZIF-8 modified polyimide film prepared in Example 3 has a large contact angle to water, milk, cola, red wine and coffee, showing good resistance and meeting the anti-fouling requirements of complex working conditions.

[0126] 4. The oil-water separation efficiency and throughput of the samples prepared in each embodiment and comparative example were tested using the following methods:

[0127] A graduated cylinder filter was used to separate an oil-water mixture. The filter consists of three parts: a graduated cylinder filter cup at the top and bottom, and a frosted interface in the middle. After being secured with clamps, the device was fixed to an iron stand. An oil-water mixture of carbon tetrachloride and deionized water (v / v = 1:1) was prepared. The oil-water mixture was poured into the separator from above. Under the influence of gravity, the liquid mixture came into contact with the membrane. The oil quickly penetrated the membrane and flowed to the bottom of the lower filter cup, while the water remained on the membrane surface and did not permeate the ZIF-8 / PI membrane. This demonstrated the hydrophobicity of the ZIF-8 / PI membrane to water, proving that this membrane has both superhydrophobicity and oleophilicity, and exhibits excellent oil-water separation performance.

[0128] Oil-water mixtures are separated using a cartridge filter, and the oil-water separation efficiency and throughput are calculated.

[0129]

[0130] The unit of flux is L·m 2 ·h -1 The separation efficiency is expressed as a percentage.

[0131] The test results are shown in Table 2;

[0132] Table 2

[0133]

[0134] As shown in Table 2, compared with the samples prepared in Comparative Examples 1-3, the samples prepared in Examples 1-3 have higher oil-water separation throughput and oil-water separation efficiency. The inventors believe that the reason may be that the sample in Comparative Example 1 did not form a uniform coating layer on the fiber surface, the sample in Comparative Example 2 did not undergo a solution thermal reaction during preparation, and the sample in Comparative Example 3 did not have ZIF-8 particles loaded on its surface.

[0135] 5. Thermogravimetric analysis was performed on the PI / ZIF-8 membrane prepared in Example 1. The results are shown in [Figure 1]. Figure 5 .Depend on Figure 5 It can be seen that the temperature at which the mass loss of the sample is 5% is 550℃, which indicates that the PI / ZIF-8 membrane prepared in Example 1 has a small mass loss under high temperature conditions and has good high temperature resistance.

[0136] 6. The glass transition temperature (T0) of the PI / ZIF-8 film prepared in Example 1 was tested. g The specific testing method is as follows: use a dynamic thermal analyzer for detection, nitrogen atmosphere, heating rate 5℃ / min.

[0137] Test results are available Figure 6 .

[0138] Depend on Figure 6It can be seen that when 400 °C < T < 450 °C, the sample undergoes a glass transition, and the glass transition point of this sample is around 420 °C.

[0139] From Test Examples 5 and 6, it can be seen that due to the rigidity of the macromolecular chains of the PMDA-4,4-ODA system polyimide fiber, its glass transition temperature is higher than that of most fiber systems, that is, it has better high-temperature resistance.

[0140] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments and comparative examples, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ZIF-8 modified polyimide film, characterized in that, It includes a polyimide film and ZIF-8 particles in contact with the surface of the polyimide film.

2. The ZIF-8 modified polyimide film according to claim 1, characterized in that, Oil-water separation flux greater than or equal to 12500 L·m 2 ·h -1 Oil-water separation efficiency is greater than or equal to 99.85%; and / or, The glass transition temperature of the ZIF-8 modified polyimide film is 400℃~450℃.

3. The ZIF-8 modified polyimide film according to claim 1 or 2, characterized in that, It is prepared by a method including the following process: 1) The raw polyimide film is subjected to at least one contact-drying treatment using a zinc salt solution to obtain a pretreated polyimide film; 2) The pretreated polyimide membrane is mixed with an aqueous solution containing zinc ions and hexamethylenetetramine, and the resulting mixture is subjected to a first heat treatment to obtain a ZnO / PI fiber membrane. 3) The ZnO / PI fiber membrane is mixed with solvent and 2-methylimidazole, and the resulting mixture is subjected to a second heat treatment to obtain the ZIF-8 modified polyimide membrane.

4. A method for preparing a ZIF-8 modified polyimide film according to any one of claims 1-3, characterized in that, Includes the following steps: 1) The raw polyimide film is subjected to at least one contact-drying treatment using a zinc salt solution to obtain a pretreated polyimide film; 2) The pretreated polyimide membrane is mixed with an aqueous solution containing zinc ions and hexamethylenetetramine, and the resulting mixture is subjected to a first heat treatment to obtain a ZnO / PI fiber membrane. 3) The ZnO / PI fiber membrane is mixed with solvent and 2-methylimidazole, and the resulting mixture is subjected to a second heat treatment to obtain the ZIF-8 modified polyimide membrane.

5. The method according to claim 4, characterized in that, The first heat treatment is performed at a temperature of 100℃-120℃ for a time of 10min-30min.

6. The method according to claim 4 or 5, characterized in that, The second heat treatment is performed at a temperature of 60-120℃ for 1-2 hours. The solvent is selected from at least one of deionized water, methanol, and DMF.

7. The method according to any one of claims 4-6, characterized in that, In step 2), the mass of 2-methylimidazole is 1-5 wt% of the mass of the solvent; and / or, In step 1), before the raw polyimide film is subjected to at least one contact-drying treatment with zinc salt solution, the raw polyimide film is further subjected to plasma treatment in a vacuum after being contacted with an aqueous solution including potassium permanganate and alkali metal hydroxide.

8. The method according to any one of claims 4-7, characterized in that, In step 1), the raw material polyimide film is prepared by a method comprising the following steps: 1) In a polar aprotic solvent, aromatic diamine and aromatic dianhydride are mixed to obtain polyamic acid slurry; 2) The polyamic acid slurry is prepared into a precursor film using an electrospinning device; 3) The precursor membrane is treated at temperatures of 80-120℃, 180-220℃ and 280-320℃ for 30 minutes each to obtain the raw material polyimide membrane.

9. The method according to any one of claims 4-8, characterized in that, The electrospinning equipment has an applied voltage of 10-50kV, a spinning distance of 15-25cm, a spinneret inner diameter of 0.41mm, a flow rate of 1-2mL / h, a collecting drum rotation speed of 50-150rpm, a collecting substrate of brass screen, a relative humidity of 40-60%, and a temperature of 20-28℃.

10. A method for separating water and oil, characterized in that, The ZIF-8 modified polyimide membrane according to any one of claims 1-3 is used to separate mixtures including water and oil.

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