A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function

Abstract

This invention discloses a method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function, comprising the following steps: (1) preparing a spinning solution; (2) preparing a braided tube reinforced hollow nanofiber membrane; (3) preparing a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires; and (4) preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function. The preparation method of this invention is simple and effective, the membrane material is not easily contaminated and is easy to regenerate, and can be scaled up industrially. The prepared ZIF-8@zinc oxide heterojunction modified braided tube reinforced hollow nanofiber membrane has switchable interface wettability, exhibiting excellent separation and filtration capabilities for oil-water emulsions. It can complete self-cleaning and regeneration under near-infrared or solar irradiation, thereby achieving continuous oil-water emulsion separation.

Description

Technical Field

[0001] This invention belongs to the field of oil-water separation technology, specifically relating to a method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function. Background Technology

[0002] With rapid industrial development, the discharge of industrial and domestic wastewater has placed enormous pressure on the ecological environment, causing pollution of some surface water and groundwater. Currently, the separation and purification of complex oily wastewater exceeding natural remediation capacity has become a crucial problem urgently needing to be solved. Industrial wastewater is typically a complex mixture, likely containing various oils, organic solvents, textile dyes, surfactants, harmful substances, and other pollutants. The key to reducing treatment costs lies in how to simply treat this complex oily wastewater to significantly reduce the concentration of pollutants.

[0003] Nanofiber membranes have attracted widespread attention in wastewater treatment due to their high porosity, flexibility, excellent permeability, ease of operation, and adjustable functionality. Currently, there are numerous research reports on the treatment of various complex oily wastewaters using nanofiber membranes. Chinese patent application number 202111572814.9 discloses a polyelectrolyte-grafted polyvinyl alcohol spun membrane for oil-water emulsion separation, which exhibits good hydrophilicity and can combine emulsion demulsification and oil-water separation operations to achieve highly efficient separation of oil-water emulsions. Chinese patent application number 202010709575.6 discloses a fiber membrane composed of a superhydrophilic and superoleophilic electrospun membrane demulsification layer and a superhydrophobic and superoleophilic electrospun membrane barrier layer, exhibiting asymmetric superhydrophilic and superhydrophobic properties, achieving a separation efficiency of over 97% for oil-water emulsions. Although the aforementioned nanofiber membranes demonstrate high separation efficiency in oil-in-water or water-in-oil emulsions, their stability and antifouling performance require further optimization. Based on the classic Young's equation, the water contact angle (WCA) and oil contact angle (OCA) on a given membrane surface are always complementary, meaning that the same surface typically exhibits hydrophilic / underwater oleophobic or hydrophobic / oil-underwater hydrophobic properties. Since oil / water filtration membranes with relatively singular wettability cannot meet the requirements of current complex oily wastewater treatment, some membranes with switchable wettability have been developed. The switchable wettability of these membranes is mainly responsive to several methods, such as temperature, ultraviolet irradiation, pH, and voltage. However, the special dual hydrophobic state may be metastable or require stringent conditions to achieve. Chinese patent application number 202110322691.7 discloses a method for preparing a superamphilic nitrocellulose membrane, which combines dopamine (PDA) and polyethyleneimine (PEI) with a nitrocellulose membrane, achieving a transformation from hydrophobic to superamphilic properties. This membrane exhibits superamphilic properties in air, superoleophobic properties underwater, and superhydrophobic properties under oil, and can be reused for oil-water separation and emulsion separation. However, during long-term filtration with the accumulation of contaminants, the selective wettability of the membrane surface gradually disappears, leading to separation failure. Furthermore, oil-water separation nanofiber membranes are easily fouled by various oils and organic pollutants, significantly shortening their lifespan.

[0004] ZnO, due to its high photocatalytic activity, low cost, non-toxicity, and environmental friendliness, is often used as the main photocatalyst for modifying nanofiber membranes and is one of the most promising photocatalytic materials. However, its responsiveness only to ultraviolet light not only affects the lifetime of nanofiber membranes but also limits their application efficiency under outdoor sunlight. Metal-organic frameworks are typical crystalline-inorganic-organic hybrid porous materials. Due to their large surface area, high chemical stability, thermal stability, and tunable structure, they are widely used in gas separation, gas storage, sensing, and photocatalysis. For example, Xie et al. developed a polydopamine-coated cellulose membrane modified with a zeolite imidazole ester framework structure material (ZIF-8) using coordination-driven in-situ self-assembly technology. This membrane exhibits switchable wettability and high separation efficiency under negative pressure for both oil-in-water and water-in-oil emulsions. After ultraviolet irradiation, it can effectively alleviate problems such as oil contamination and organic solvent contamination. This technology was published in the journal *Separation and Purification Technology*, 2020, Vol. 236, No. 116273, titled: "Dual superlyophobic zeolitic imidazolate framework-8 modified membrane for controllable oil / water emulsion separation [J]. Separation and Purification Technology, 2020, 236: 116273." However, given its wide band gap (approximately 4.9–5.4 eV), it can only be photoactivated by ultraviolet irradiation. Under ultraviolet light irradiation, its base cellulose membrane will suffer irreversible damage, making it unsuitable for long-term use. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function. This oil-water separation membrane is simple to prepare, low in cost, has good hydrophilic / hydrophobic effects, is easy to eliminate membrane fouling, and has switchable interface wettability, thus possessing significant value.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function includes the following steps:

[0008] (1) Add the fiber-forming polymer and zinc acetate dihydrate particles to an organic solvent and stir until homogeneous to obtain a spinning solution;

[0009] (2) Place the spinning solution in step (1) into an electrospinning machine, then put the braided tube on the negative electrode surface of the electrospinning machine as a receiver, and perform electrospinning. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained.

[0010] (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2), heat treatment is performed. After the heat treatment is completed, the membrane is placed in a zinc oxide growth solution and subjected to a constant temperature reaction. After the reaction is completed, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained.

[0011] (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires in step (3) is washed and vacuum dried, and then placed in dimethylimidazole-ethanol / water solution for in-situ etching reaction. After the reaction is completed, it is washed and dried to obtain the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function.

[0012] Preferably, the fiber-forming polymer in step (1) is one of polyacrylonitrile, polyvinylidene fluoride, polyethersulfone, poly(m-phenylene isophthalamide), and cellulose acetate; and the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and acetone.

[0013] Preferably, the mass fraction of the fiber-forming polymer in the spinning solution in step (1) is 5-20%; the mass fraction of zinc acetate dihydrate in the spinning solution is 0.5-5%; and the stirring temperature is 25-80℃.

[0014] Specifically, this invention uses zinc acetate dihydrate as a zinc oxide precursor and adds it to the spinning solution to allow it to take root and sprout, resulting in better adhesion to the fiber membrane.

[0015] Preferably, the braided tube in step (2) has an outer diameter of 1-5 mm and an inner diameter of 0.3-4 mm; the braided tube can be woven from one or more of the following: polyacrylonitrile fiber, polyvinylidene fluoride fiber, polyethylene terephthalate fiber, polyamide fiber, and polypropylene fiber.

[0016] Specifically, the braided tube added in this invention can serve as a carrier for nanofibers and a support for later use. The braided tube is hollow and has high strength. Furthermore, the fiber membrane separation layer constructed on the surface of the braided tube greatly reduces the time required for spinning.

[0017] Preferably, the electrospinning process in step (2) is as follows: positive pressure range 10-15kV, negative pressure range 0--5kV, receiving distance 10-25cm, receiving roller speed 300-1000rpm, and the entire spinning process time is maintained at 40-100min.

[0018] Preferably, the heat treatment in step (3) is performed at a temperature of 110-120°C for 8-24 hours.

[0019] Specifically, through heat treatment, the zinc acetate dihydrate inside the fiber membrane is converted into ZnO, allowing zinc oxide seed crystals to grow from the inside.

[0020] Preferably, the zinc oxide growth solution in step (3) is composed of zinc nitrate hexahydrate and hexamethylenetetramine, with the same concentration of zinc nitrate hexahydrate and hexamethylenetetramine, both being 0.01-0.2 mol / L; the isothermal reaction temperature is 80-90℃, and the reaction time is 3-6 h.

[0021] Specifically, zinc oxide nanowires are formed by in-situ growth of zinc oxide in a zinc oxide growth solution.

[0022] Preferably, the vacuum drying temperature in step (4) is 60°C and the time is 6-12 hours.

[0023] Preferably, in step (4), the mass fraction of dimethylimidazole in the dimethylimidazole-ethanol / water solution is 10-15%, and the volume ratio of ethanol to water in the ethanol / water solution is 1:1; the in-situ etching temperature is 20-30℃, and the time is 6-12h.

[0024] Specifically, the present invention uses dimethylimidazole-ethanol / water solution with specific components and concentrations to obtain a more suitable ratio of ZIF-8 and ZnO, resulting in higher visible light response and catalytic activity.

[0025] This invention also protects an oil-water separation membrane prepared by the aforementioned method, which has switchable interface wettability and light-driven self-cleaning function.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention provides a method for preparing an oil-water separation membrane with switchable interface wettability and photo-driven self-cleaning function. The membrane preparation process is simple and effective, the membrane material is not easily contaminated and is easy to regenerate, and can be scaled up industrially. Electrospinning is used to spin a polymer containing zinc oxide precursor into a nanofiber membrane on a braided tube substrate. After heat treatment and in-situ growth of zinc oxide nanowires, ZIF-8 is grown by ion exchange-etching method to further construct ZIF-8@zinc oxide heterojunction. Its unique micro-nano structure gives it switchable interface wettability, and the separation of oil and water emulsion can be completed under gravity drive alone. By constructing this heterojunction, the response and photocatalytic self-cleaning effect in the entire solar spectrum region can be achieved, which greatly expands the application range and service life.

[0028] (2) The present invention provides a method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function. The prepared ZIF-8@zinc oxide heterojunction modified braided tube reinforced hollow nanofiber membrane has switchable interface wettability and exhibits excellent separation and filtration capabilities for oil-water emulsions.

[0029] (3) The present invention provides a method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function. The prepared ZIF-8@zinc oxide heterojunction modified braided tube reinforced hollow nanofiber membrane can complete self-cleaning and regeneration under near-infrared or solar irradiation, thereby achieving continuous oil-water emulsion separation effect. Attached Figure Description

[0030] Figure 1 The images shown are electron microscope (EM) images of the surface and cross-section of the ZIF-8@zinc oxide heterojunction modified braided tube reinforced hollow nanofiber membrane in Example 3 of the present invention. Figures (a) and (b) are overall surface and cross-section images, and Figures (c) and (d) are electron microscope (EM) images of the growth of ZIF-8@zinc oxide heterojunctions formed on the nanofiber surface.

[0031] Figure 2 The diagrams (a & b) and physical image (c) show the oil-water separation performance test in Example 3 of this invention. The prepared braided tube reinforced hollow nanofiber membrane is assembled into a membrane module and used to separate and filter oil-water emulsions (Figure a, separation under non-light conditions, regeneration by light) and complex oil-water emulsions (Figure b, under online light conditions) under gravity-driven conditions.

[0032] Figure 3 The interface wettability of the ZIF-8@zinc oxide heterojunction modified braided tube enhanced hollow nanofiber membrane in Example 3 of the present invention is shown in the water pre-wetting oleophobic condition (a) and the oil pre-wetting hydrophobic effect (b).

[0033] Figure 4 These are optical photographs of the oil-in-water emulsion (O / W), the oil-in-water stabilized emulsion containing surfactant (O / WSSEs), the water-in-oil emulsion (W / O), and the water-in-oil stabilized emulsion containing surfactant (W / OSSEs) in Example 3 of the present invention. The oils (from left to right) are hexane, dichloromethane, kerosene, diesel oil, and peanut oil, respectively.

[0034] Figure 5 These are optical and microscopic photographs of the ZIF-8@zinc oxide heterojunction modified braided tube reinforced hollow nanofiber membrane in Example 3 of the present invention before and after separation of oil-water emulsion under gravity.

[0035] Figure 6This is a comparison of images before and after regeneration by light irradiation for 60 minutes following the separation and filtration of complex oily wastewater using a ZIF-8@zinc oxide heterojunction modified braided tube reinforced hollow nanofiber membrane in Example 3 of the present invention.

[0036] Figure 7 In Example 3 of this invention, the ZIF-8@zinc oxide heterojunction modified braided tube reinforced hollow nanofiber membrane was assembled into a membrane module. Under gravity drive (non-light and light conditions), a single separation and filtration was performed on oil-in-water emulsions (O / W, containing MB or BPA) and stable oil-in-water emulsions containing surfactants (O / WSSEs, containing MB or BPA). The separation effect of the membrane on oil-water emulsions and the removal of pollutants were measured. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function includes the following steps:

[0039] (1) Dry the fiber-forming polymer thoroughly, weigh a certain mass of the fiber-forming polymer and zinc oxide precursor zinc acetate dihydrate particles, add them to an organic solvent, and prepare a uniform spinning solution with a fiber-forming polymer concentration of 5-20 wt% at 25-80℃. The mass fraction of zinc acetate dihydrate in the spinning solution is 0.5-5 wt%.

[0040] Preferably, the fiber-forming polymer is one of polyacrylonitrile, polyvinylidene fluoride, polyethersulfone, poly(m-phenylene isophthalamide), and cellulose acetate; and the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and acetone.

[0041] More preferably, the concentration of the fiber-forming polymer in the spinning solution can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, and the mass fraction of zinc acetate dihydrate can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%.

[0042] (2) Place the spinning solution in step (1) into an electrospinning machine, and then put a braided tube with an outer diameter of 1-5 mm and an inner diameter of 0.3-4 mm onto the negative electrode surface of the electrospinning machine as a receiver to perform electrospinning. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained.

[0043] Preferably, the braided tube can be woven from one or more of the following: polyacrylonitrile fiber, polyvinylidene fluoride fiber, polyethylene terephthalate fiber, polyamide fiber, and polypropylene fiber; the electrospinning process is as follows: positive pressure range 10-15kV, negative pressure range 0--5kV, receiving distance 10-25cm, receiving roller speed 300-1000rpm, and the entire spinning process time is maintained at 40-100min.

[0044] More preferably, the positive voltage range can be 10kV, 11kV, 12kV, 13kV, 14kV, or 15kV; the negative voltage range can be 0kV, -1kV, -2kV, -3kV, -4kV, or -5kV; the receiving distance can be 10cm, 11cm, 12cm, 13cm, 14cm, 15cm, 16cm, 17cm, 18cm, 19cm, 20cm, 21cm, 22cm, 23cm, 24cm, or 25cm; the receiving roller speed can be 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, or 1000rpm; and the spinning time can be 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min, 80min, 85min, 90min, 95min, or 100min.

[0045] (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2) to constant weight, heat-treat it at 110-120℃ for 8-24h. After heat treatment, a braided tube reinforced hollow nanofiber membrane with zinc oxide is obtained. Then, the braided tube reinforced hollow nanofiber membrane with zinc oxide is placed in a zinc oxide growth solution and subjected to a constant temperature reaction. After the reaction is completed, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained.

[0046] Preferably, the heat treatment temperature can be 110℃, 111℃, 112℃, 113℃, 114℃, 115℃, 116℃, 117℃, 118℃, 119℃, or 120℃, and the treatment time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, or 24h. The zinc oxide growth solution is composed of zinc nitrate hexahydrate and hexamethylenetetramine, with the same concentration of zinc nitrate hexahydrate and hexamethylenetetramine, both 0.01-0.2mol / L, which can be 0.01mol / L or 0. The concentrations are 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.10 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, and 0.20 mol / L; the isothermal reaction temperature is 80-90℃, and the reaction time is 3-6 hours.

[0047] (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide in step (3) is washed and vacuum dried, and then placed in dimethylimidazole-ethanol / water solution for in-situ etching reaction. After the reaction is completed, it is washed and dried to obtain the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function.

[0048] Preferably, the vacuum drying temperature is 60°C and the time is 6-12 hours; in the dimethylimidazole-ethanol / water solution, the mass fraction of dimethylimidazole is 10-15 wt%, and the volume ratio of ethanol to water in the ethanol / water solution is 1:1; the in-situ etching temperature is 20-30°C and the time is 6-12 hours.

[0049] More preferably, in the dimethylimidazole-ethanol / aqueous solution, the mass fraction of dimethylimidazole can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%; the in-situ etching temperature can be 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃, and the time can be 6h, 7h, 8h, 9h, 10h, 11h, or 12h.

[0050] (5) Oil-water separation performance test: The oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function obtained in step (4) is assembled into a membrane module and filtered for various oil-water emulsions under gravity drive (under light or non-light conditions) to test the separation effect of the oil-water separation membrane on oil-water emulsions.

[0051] Preferably, the oil-water emulsion includes oil-in-water emulsion (O / W), oil-in-water stabilized emulsion with surfactant (O / WSSEs), water-in-oil emulsion (W / O), and water-in-oil stabilized emulsion with surfactant (W / OSSEs).

[0052] More preferably, the oil-in-water emulsion (O / W) is prepared by adding 1 mL of oil (i.e., n-hexane, dichloromethane, kerosene, diesel oil, and peanut oil) to 99 mL of deionized water, followed by ultrasonic treatment at 40 kHz for 30 minutes and mechanical stirring (1000 rpm) for 12 hours to obtain various milky white oil-in-water emulsions; the oil-in-water stabilized emulsion containing surfactant (O / WSSEs) is prepared by adding 1 mL of oil (i.e., n-hexane, dichloromethane, kerosene, diesel oil, and peanut oil) to 99 mL of deionized water containing 20 mg of sodium dodecyl sulfate surfactant, followed by ultrasonic treatment at 40 kHz. Various milky white water-in-oil stabilized emulsions containing surfactants (O / WSSEs) were obtained by adding 1 mL of deionized water to 99 mL of the aforementioned oils and subjecting them to the same ultrasonic and mechanical stirring process. The water-in-oil stabilized emulsions containing surfactants (W / OSSEs) were obtained by adding 1 mL of deionized water to 99 mL of each oil containing 0.1 g Span 80, followed by ultrasonic treatment at 40 kHz for 30 minutes and mechanical stirring (1000 rpm) for 12 hours. Figure 4 Both the aforementioned stable emulsions (O / WSSEs) and (W / OSSEs) remained stable for at least 7 days.

[0053] Furthermore, the oil-water emulsion was measured and regenerated 10 times.

[0054] Furthermore, the membrane regeneration process after oil-water separation is subjected to 60 minutes of simulated sunlight irradiation with a 300W xenon lamp or 3 hours of sunlight irradiation on a sunny afternoon in spring / autumn (light intensity between 45 and 95 mW·cm²). -2 (The range) is obtained.

[0055] Furthermore, the switching of wettability can be achieved through the aforementioned light irradiation process to regenerate the membrane, or by cleaning and drying the membrane surface with ethanol to complete the membrane regeneration. The regenerated membrane is then used after being wetted with the appropriate liquid (water / oil); that is, water wettation achieves hydrophilicity and oleophobicity, while oil wettation achieves hydrophobicity and oleophilicity (e.g.,...). Figure 3 ).

[0056] Furthermore, for complex oily wastewater, a small amount of methylene blue (MB), methyl orange (MO) dye or bisphenol A (BPA) is added to the aforementioned oil-in-water emulsion (O / W) or oil-in-water stabilized emulsion containing surfactants (O / WSSEs) and the concentration is maintained at 5 ppm to obtain a complex oily wastewater emulsion.

[0057] The oil used in the following specific embodiments is kerosene.

[0058] Example 1

[0059] A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function includes the following steps:

[0060] (1) After the polyacrylonitrile powder is fully dried, it is added to N,N-dimethylacetamide along with zinc acetate dihydrate particles and mixed at 60°C to form a uniform spinning solution with a polyacrylonitrile mass fraction of 10 wt% and a zinc acetate dihydrate mass fraction of 3 wt%.

[0061] (2) Place the spinning solution from step (1) into an electrospinning machine, and then place a polyethylene terephthalate fiber braided tube with an outer diameter of 3 mm and an inner diameter of 2.6 mm onto the negative electrode surface of the electrospinning machine as a receiver for electrospinning. The electrospinning process parameters are: positive voltage = 12 kV, negative voltage = -5 kV, receiving distance = 10 cm, receiving roller speed = 1000 rpm, and spinning time = 60 min. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained.

[0062] (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2) to constant weight, heat-treat it at 120℃ for 12h. After heat treatment, a braided tube reinforced hollow nanofiber membrane with zinc oxide is obtained. Then, the braided tube reinforced hollow nanofiber membrane with zinc oxide is placed in a zinc oxide growth solution. The zinc oxide growth solution is composed of zinc nitrate hexahydrate and hexamethylenetetramine, both of which have a molar concentration of 0.1mol / L. It is grown at 80℃ for 4h. After growth, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained.

[0063] (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires in step (3) was washed with ultrapure water and ethanol, dried in a vacuum oven at 60°C for 6 hours, and then placed in a dimethylimidazole-ethanol / water solution (ethanol to water volume ratio 1:1, and dimethylimidazole mass fraction in the solution is 13wt%). It was etched in situ at 25°C for 12 hours. After the reaction was completed, it was washed and dried to obtain a braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure, which is the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function.

[0064] (5) Oil-water separation performance test: The prepared braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure was assembled into a membrane module and various oil-water emulsions were separated and filtered under gravity drive (non-light conditions). The separation effect of the membrane on oil-water emulsions was tested. After being pre-wetted with water, its separation efficiency for oil-in-water emulsion (O / W) and oil-in-water stable emulsions containing surfactants (O / WSSEs) reached 98.6% and 97.5%, respectively, and did not decrease after 72 hours of continuous use. After being pre-wetted with oil, its separation efficiency for water-in-oil emulsion (W / O) and water-in-oil stable emulsions containing surfactants (W / OSSEs) reached 99.2% and 97.5%, respectively, and did not decrease after 72 hours of continuous use.

[0065] Example 2

[0066] A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function includes the following steps:

[0067] (1) After the polyvinylidene fluoride powder is fully dried, it is added to N,N-dimethylacetamide along with zinc acetate dihydrate particles and mixed at 70°C to form a uniform spinning solution with a polyacrylonitrile mass fraction of 12 wt% and a zinc acetate dihydrate mass fraction of 5 wt%.

[0068] (2) Place the spinning solution from step (1) into an electrospinning machine, and then place a polyethylene terephthalate fiber braided tube with an outer diameter of 2.5 mm and an inner diameter of 1.5 mm onto the negative electrode surface of the electrospinning machine as a receiver for electrospinning. The electrospinning process parameters are: positive voltage = 10 kV, negative voltage = 0 kV, receiving distance = 12 cm, receiving roller speed = 800 rpm, and spinning time = 50 min. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained.

[0069] (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2) to constant weight, heat-treat it at 110℃ for 16h. After heat treatment, a braided tube reinforced hollow nanofiber membrane with zinc oxide is obtained. Then, the braided tube reinforced hollow nanofiber membrane with zinc oxide is placed in a zinc oxide growth solution. The zinc oxide growth solution is composed of zinc nitrate hexahydrate and hexamethylenetetramine, both of which have a molar concentration of 0.2mol / L. It is grown at 80℃ for 5h. After growth, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained.

[0070] (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires in step (3) was washed with ultrapure water and ethanol, dried in a vacuum oven at 60°C for 6 hours, and then placed in a dimethylimidazole-ethanol / water solution (ethanol to water volume ratio 1:1, and dimethylimidazole mass fraction in the solution is 11wt%). It was etched in situ at 30°C for 6 hours. After the reaction was completed, it was washed and dried to obtain a braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure, which is the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function.

[0071] (5) Oil-water separation performance test: The prepared braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure was assembled into a membrane module and various oil-water emulsions were separated and filtered under gravity drive (non-light conditions). The separation effect of the membrane on oil-water emulsions was tested. After being pre-wetted with water, its separation efficiency for oil-in-water emulsion (O / W) and oil-in-water stable emulsions containing surfactants (O / WSSEs) reached 98.9% and 97.9%, respectively, and did not decrease after 72 hours of continuous use. After being pre-wetted with oil, its separation efficiency for water-in-oil emulsion (W / O) and water-in-oil stable emulsions containing surfactants (W / OSSEs) reached 99.6% and 97.8%, respectively, and did not decrease after 72 hours of continuous use.

[0072] Example 3

[0073] A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function includes the following steps:

[0074] (1) After the polyvinylidene fluoride powder is fully dried, it is added to N,N-dimethylacetamide along with zinc acetate dihydrate particles and mixed at 70°C to form a uniform spinning solution with a polyacrylonitrile mass fraction of 13 wt% and a zinc acetate dihydrate mass fraction of 2 wt%.

[0075] (2) Place the spinning solution from step (1) into an electrospinning machine, and then place a polyethylene terephthalate fiber braided tube with an outer diameter of 1.8 mm and an inner diameter of 1.2 mm onto the negative electrode surface of the electrospinning machine as a receiver for electrospinning. The electrospinning process parameters are: positive voltage = 10 kV, negative voltage = -5 kV, receiving distance = 10 cm, receiving roller speed = 1000 rpm, and spinning time = 40 min. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained.

[0076] (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2) to constant weight, heat-treat it at 120℃ for 12h. After heat treatment, a braided tube reinforced hollow nanofiber membrane with zinc oxide is obtained. Then, the braided tube reinforced hollow nanofiber membrane with zinc oxide is placed in a zinc oxide growth solution. The zinc oxide growth solution is composed of zinc nitrate hexahydrate and hexamethylenetetramine, both of which have a molar concentration of 0.1mol / L. It is grown at 80℃ for 6h. After growth, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained.

[0077] (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires from step (3) was washed with ultrapure water and ethanol, dried in a vacuum oven at 60°C for 6 hours, and then placed in a dimethylimidazole-ethanol / water solution (ethanol to water volume ratio 1:1, and dimethylimidazole mass fraction in the solution is 13wt%). It was then etched in situ at 25°C for 8 hours. After the reaction was complete, it was washed and dried to obtain a braided tube reinforced hollow nanofiber membrane with a ZIF-8@zinc oxide heterostructure, which is the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function. Figure 1 ).

[0078] (5) Oil-water separation performance test: The prepared braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure was assembled into a membrane module, and various oil-water emulsions were separated and filtered under gravity (non-light conditions). Figure 2 The membrane was tested for its separation efficiency of oil-water emulsions. After pre-wetting with water, the separation efficiency for oil-in-water emulsions (O / W) and stable oil-in-water emulsions containing surfactants (O / WSSEs) reached 99.4% and 98.7%, respectively, and did not decrease after 72 hours of continuous use. After pre-wetting with oil, the separation efficiency for water-in-oil emulsions (W / O) and stable water-in-oil emulsions containing surfactants (W / OSSEs) reached 99.6% and 98.5%, respectively, and did not decrease after 72 hours of continuous use. Optical and microscopic images before and after emulsion separation are shown below. Figure 5 As shown, the original emulsion contained a large number of small particles with diameters ranging from a few micrometers to tens of micrometers. After separation, almost no small particles were observed under an optical microscope. The used membrane was regenerated by irradiation with a 300W xenon lamp simulating sunlight for 60 minutes. After appropriate pre-wetting treatment, the regenerated membrane achieved separation efficiencies of 99.1% and 99.4% for oil-in-water emulsions (O / W) and water-in-oil emulsions (W / O), respectively; and separation efficiencies exceeding 98.5% for stabilized oil-in-water emulsions containing surfactants (O / WSSEs) and stabilized water-in-oil emulsions containing surfactants (W / OSSEs).

[0079] The prepared braided tube reinforced hollow nanofiber membrane was assembled into a membrane module. After appropriate pre-wetting treatment, it was used to separate and filter oil-in-water emulsions (O / W, containing MB or BPA) and oil-in-water stabilized emulsions containing surfactants (O / WSSEs, containing MB or BPA) under gravity drive (light irradiation). The membrane's separation efficiency for both oil-in-water emulsions (O / W, containing MB or BPA) and oil-in-water stabilized emulsions containing surfactants (O / WSSEs, containing MB or BPA) exceeded 97%. Simultaneously, the removal efficiencies for MB and BPA contaminants reached 87.65% and 72.4%, respectively (see...). Figure 7 After 48 hours of continuous use, the separation efficiency remained unchanged, demonstrating excellent treatment performance for complex oily wastewater emulsions. Images before and after regeneration under 60 minutes of light irradiation following separation and filtration of complex oily wastewater (MB = 5 ppm methylene blue oil-water emulsion) are shown below. Figure 6 .

[0080] Example 4

[0081] A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function includes the following steps:

[0082] (1) After the polyethersulfone powder is fully dried, it is added to N,N dimethylformamide along with zinc acetate dihydrate particles and mixed at 75°C to form a uniform spinning solution with a polyacrylonitrile mass fraction of 9 wt% and a zinc acetate dihydrate mass fraction of 3 wt%.

[0083] (2) Place the spinning solution from step (1) into an electrospinning machine, and then place a polyethylene terephthalate fiber braided tube with an outer diameter of 1.8 mm and an inner diameter of 1.2 mm onto the negative electrode surface of the electrospinning machine as a receiver for electrospinning. The electrospinning process parameters are: positive voltage = 10 kV, negative voltage = -3 kV, receiving distance = 15 cm, receiving roller speed = 1000 rpm, and spinning time = 80 min. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained.

[0084] (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2) to constant weight, heat-treat it at 110℃ for 10h. After heat treatment, a braided tube reinforced hollow nanofiber membrane with zinc oxide is obtained. Then, the braided tube reinforced hollow nanofiber membrane with zinc oxide is placed in a zinc oxide growth solution. The zinc oxide growth solution is composed of zinc nitrate hexahydrate and hexamethylenetetramine, both of which have a molar concentration of 0.15mol / L. It is grown at 70℃ for 8h. After growth, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained.

[0085] (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires in step (3) was washed with ultrapure water and ethanol, dried in a vacuum oven at 60°C for 6 hours, and then placed in a dimethylimidazole-ethanol / water solution (ethanol to water volume ratio 1:1, and dimethylimidazole mass fraction in the solution is 13wt%). It was etched in situ at 25°C for 12 hours. After the reaction was completed, it was washed and dried to obtain a braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure, which is the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function.

[0086] (5) Oil-water separation performance test: The prepared braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure was assembled into a membrane module. Various oil-water emulsions were separated and filtered under gravity drive (non-light conditions). The separation effect of the membrane on oil-water emulsions was measured. After being pre-wetted with water, its separation efficiency for oil-in-water emulsion (O / W) and oil-in-water stable emulsion containing surfactant (O / WSSEs) reached 98.6% and 97.5%, respectively, and did not decrease after 72 hours of continuous use. After being pre-wetted with oil, its separation efficiency for water-in-oil emulsion (W / O) and water-in-oil stable emulsion containing surfactant (W / OSSEs) reached 99.2% and 97.5%, respectively, and did not decrease after 72 hours of continuous use.

[0087] Comparative Example 1

[0088] A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function includes the following steps:

[0089] (1) After the polyvinylidene fluoride powder is fully dried, it is added to N,N-dimethylacetamide and prepared into a uniform spinning solution with a polyacrylonitrile mass fraction of 13wt% at 70℃.

[0090] (2) Place the spinning solution from step (1) into an electrospinning machine, and then place a polyethylene terephthalate fiber braided tube with an outer diameter of 1.8 mm and an inner diameter of 1.2 mm onto the negative electrode surface of the electrospinning machine as a receiver for electrospinning. The electrospinning process parameters are: positive voltage = 10 kV, negative voltage = -5 kV, receiving distance = 10 cm, receiving roller speed = 1000 rpm, and spinning time = 40 min. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained.

[0091] (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2) to constant weight, it is immersed in a zinc acetate dihydrate solution with a mass fraction of 2wt% for 10 min. After taking it out, it is dried at 110℃ for 10 h to obtain a braided tube reinforced hollow nanofiber membrane with zinc oxide on the surface. Then, the braided tube reinforced hollow nanofiber membrane with zinc oxide is placed in a zinc oxide growth solution, which is composed of 0.1 mol / L zinc nitrate and 0.1 mol / L hexamethylenetetramine. It is grown at 80℃ for 6 h. After the growth is completed, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained.

[0092] (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires in step (3) was washed with ultrapure water and ethanol, dried in a vacuum oven at 60°C for 6 hours, and then placed in a dimethylimidazole-ethanol / water solution (ethanol to water volume ratio 1:1, and dimethylimidazole mass fraction in the solution is 13wt%). It was etched in situ at 25°C for 8 hours. After the reaction was completed, it was washed and dried to obtain a braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure, which is the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function.

[0093] (5) Oil-water separation performance test: The prepared braided tube reinforced hollow nanofiber membrane with ZIF-8@zinc oxide heterostructure was assembled into a membrane module. Various oil-water emulsions were separated and filtered under gravity (non-light conditions). The separation effect of the membrane on oil-water emulsions was tested. After pre-wetting with water, its separation efficiency for oil-in-water emulsions (O / W) and oil-in-water emulsions containing surfactants (O / WSSEs) reached 79.3% and 72.5%, respectively. After continuous use for more than 24 hours, its separation efficiency for oil-in-water emulsions (O / W) was further improved. The separation efficiencies of water-in-oil emulsions (W / O) and water-in-oil surfactant-containing stabilized emulsions (W / OSSEs) decreased to 62.3% and 54.1%, respectively. After pre-wetting with oil, the separation efficiencies of water-in-oil emulsions (W / O) and water-in-oil surfactant-containing stabilized emulsions (W / OSSEs) reached 80.7% and 71.9%, respectively. After continuous use for more than 24 hours, the separation efficiencies of water-in-oil emulsions (W / O) and water-in-oil surfactant-containing stabilized emulsions (W / OSSEs) decreased to 72.1% and 57.6%, respectively.

[0094] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function, characterized in that, Includes the following steps: (1) Add the fiber-forming polymer and zinc acetate dihydrate particles to an organic solvent and stir until homogeneous to obtain a spinning solution; (2) Place the spinning solution in step (1) into an electrospinning machine, then put the braided tube on the negative electrode surface of the electrospinning machine as a receiver, and perform electrospinning. After spinning, a braided tube reinforced hollow nanofiber membrane is obtained. (3) After drying the braided tube reinforced hollow nanofiber membrane in step (2), heat treatment is performed. After the heat treatment is completed, the membrane is placed in a zinc oxide growth solution and subjected to a constant temperature reaction. After the reaction is completed, a braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires is obtained. (4) The braided tube reinforced hollow nanofiber membrane with zinc oxide nanowires in step (3) is washed and vacuum dried, and then placed in dimethylimidazole-ethanol / water solution for in-situ etching reaction. After the reaction is completed, it is washed and dried to obtain the oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function. In step (4), the mass fraction of dimethylimidazole in the dimethylimidazole-ethanol / water solution is 10-15%, and the volume ratio of ethanol to water in the ethanol / water solution is 1:1; the in-situ etching temperature is 20-30℃, and the time is 6-12h.

2. The method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function according to claim 1, characterized in that, The fiber-forming polymer mentioned in step (1) is one of polyacrylonitrile, polyvinylidene fluoride, polyethersulfone, poly(m-phenylene isophthalamide), and cellulose acetate; the organic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and acetone.

3. The method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function according to claim 1, characterized in that, In step (1), the mass fraction of the fiber-forming polymer in the spinning solution is 5-20%; the mass fraction of zinc acetate dihydrate in the spinning solution is 0.5-5%; and the stirring temperature is 25-80℃.

4. The method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function according to claim 1, characterized in that, The braided tube in step (2) has an outer diameter of 1-5 mm and an inner diameter of 0.3-4 mm. The braided tube is made of one or more of the following: polyacrylonitrile fiber, polyvinylidene fluoride fiber, polyethylene terephthalate fiber, polyamide fiber, and polypropylene fiber.

5. The method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function according to claim 1, characterized in that, The electrospinning process described in step (2) is as follows: positive pressure range 10~15kV, negative pressure range 0~-5kV, receiving distance 10~25cm, receiving roller speed 300~1000rpm, and the entire spinning process time is maintained at 40~100min.

6. The method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function according to claim 1, characterized in that, The heat treatment in step (3) is performed at a temperature of 110-120℃ for 8-24 hours.

7. The method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function according to claim 1, characterized in that, The zinc oxide growth solution in step (3) is composed of zinc nitrate hexahydrate and hexamethylenetetramine, with the same concentration of zinc nitrate hexahydrate and hexamethylenetetramine, both being 0.01-0.2 mol / L; the temperature of the isothermal reaction is 80-90℃, and the reaction time is 3-6h.

8. The method for preparing an oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function according to claim 1, characterized in that, The vacuum drying temperature in step (4) is 60°C and the time is 6-12 hours.

9. An oil-water separation membrane with switchable interface wettability and light-driven self-cleaning function prepared by the preparation method according to any one of claims 1-8.

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