Oil-water separation membrane, and preparation method therefor and use thereof

Abstract

The present application relates to the field of gas field brine pretreatment, and relates to an oil-water separation membrane, and a preparation method therefor and a use thereof. The oil-water separation membrane comprises a nanofiber membrane substrate and an MOFs layer loaded on at least part of the surface of the nanofiber membrane substrate; the MOFs layer comprises a two-dimensional MOFs nanosheet; the nanofiber membrane substrate is prepared by electrospinning three-dimensional MOFs and an organic polymer; and the two-dimensional MOFs nanosheet is obtained by means of secondary growth on the surface of the nanofiber membrane substrate via hydrothermal recrystallization. The oil-water separation membrane can efficiently separate petroleum pollutants and solid suspended matters in oil and gas field produced water, and can be coupled with a sulfate radical-based advanced oxidation process to synchronously and efficiently remove oil, suspended particles and organic matters in the oil and gas field produced water.

Description

Oil-water separation membrane, preparation method and application thereof

[0001] The present application claims priority to the Chinese patent application No. 202410867274.4, filed on June 28, 2024, and entitled "Oil-water separation membrane, preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application belongs to the field of gas field brine pretreatment, and particularly relates to an oil-water separation membrane, a preparation method and application thereof. BACKGROUND

[0003] With the secondary development of oil and gas fields, the amount of produced water in oil and gas fields will increase significantly. The composition of produced water in oil and gas fields is complex, usually including salts, oils, solid suspended particles and organic chemical agents and other impurities. At present, the treatment technology of oil and gas field sewage mainly adopts a step-by-step treatment method combining physical, chemical and biological methods. The physical method mainly includes air flotation, coagulation sedimentation and filtration, but this treatment method has low treatment efficiency, poor water quality and high treatment cost, and cannot effectively meet the current environmental protection requirements.

[0004] In order to meet the water quality requirements of reinjection and standard discharge, efficient and low-cost pretreatment of produced water in oil and gas fields is required.

[0005] Membrane separation technology is widely used in the treatment of complex wastewater, and has the characteristics of high treatment efficiency, scalable productivity and low energy consumption. In recent years, biomimetic super-wetting membranes have shown high efficiency in the treatment of oily wastewater due to their excellent oil-water selective permeability, and have broad industrial application prospects. However, commercially available super-wetting membranes usually have single function, and can only separate oil and solid suspended particles in gas field brine by controlling membrane pore size and wettability, but cannot efficiently remove organic matter in brine.

[0006] However, the existing oil-water separation membrane has limited treatment efficiency when applied to treat produced wastewater in oil and gas fields. SUMMARY

[0007] Therefore, the present application provides an oil-water separation membrane, which can efficiently remove organic pollutants in produced wastewater in oil and gas fields while efficiently separating oil pollutants and solid suspended particles in produced wastewater in oil and gas fields.

[0008] In order to achieve the above purpose, the present application adopts the following technical solutions.

[0009] In a first aspect of the present application, an oil-water separation membrane is provided, which comprises a nanofiber membrane substrate and a MOFs layer loaded on at least part of the surface of the nanofiber membrane substrate.

[0010] The MOFs layer comprises two-dimensional MOFs nanosheets.

[0011] The oil-water separation membrane, the MOFs comprise at least one of Co-MOFs and Zn-MOFs.

[0012] In the present application, Co-based MOFs or Zn-based MOFs can make peroxymonosulfate (such as PMS potassium monopersulfate) or persulfate generate sulfate radicals, thereby, coupled with sulfate radical-based advanced oxidation processes AOPs, the oil-water separation membrane according to the present application can realize efficient degradation of organic matter in oil and gas field wastewater.

[0013] The oil-water separation membrane, the nanofiber membrane substrate comprises organic polymer fibers and three-dimensional MOFs materials.

[0014] In the present application, the nanofiber membrane substrate refers to a nanoscale fiber-shaped membrane substrate formed by an organic polymer, and the nanofiber membrane substrate can further comprise a nanomaterial, for example, three-dimensional MOFs, and the presence of three-dimensional MOFs is beneficial to the nanofiber membrane substrate to have a roughness of micro-nano structure.

[0015] The present application does not particularly limit the nanofiber membrane substrate, which can be a commonly used nanofiber membrane substrate in the art.

[0016] The oil-water separation membrane, the nanofiber membrane substrate can be a hydrophilic polymer nanofiber membrane substrate.

[0017] That is, the oil-water separation membrane, the organic polymer fibers are hydrophilic polymer fibers.

[0018] In the present application, when the organic polymer fibers in the nanofiber membrane substrate are hydrophilic polymer fibers, the two-dimensional MOFs nanosheets generated in the hydrothermal recrystallization process are loaded on the hydrophilic polymer fibers, which can further increase the contact area of water and the surface of the nanofiber membrane, thereby improving the hydrophilicity of the nanofiber membrane and realizing superhydrophilic performance, i.e., a static water contact angle of 0° in air and superwettability, thereby improving the removal efficiency of the nanofiber membrane substrate for suspended impurities and oil in produced water of oil and gas fields.

[0019] The oil-water separation membrane, the hydrophilic polymer nanofiber membrane substrate can be a polyacrylic acid nanofiber membrane substrate or a polyacrylonitrile nanofiber membrane substrate. That is, the organic polymer for preparing the nanofiber membrane substrate is polyacrylic acid nanofiber or polyacrylonitrile nanofiber.

[0020] The oil-water separation membrane, the nanofiber membrane substrate is prepared by electrospinning of three-dimensional MOFs and organic polymers. Preferably, the three-dimensional MOFs are in a powder state.

[0021] In the present application, the MOFs with three-dimensional structure are co-spun with organic polymers to form a nanofiber membrane, and then two-dimensional MOFs nanosheets are grown on the nanofiber membrane. The two-dimensional MOFs nanosheets are loaded on the nanofiber membrane to form an oil-water separation membrane with hierarchical micro-nano rough structure and sub-micron pore structure, which has superhydrophilicity and superoleophobicity underwater, and can realize efficient removal of suspended impurities and oil in gas field water. The two-dimensional MOFs nanosheets loaded have porous structure and larger specific surface area, and can be coupled with advanced oxidation processes (AOPs) based on sulfate radical to realize degradation of organic matter in gas field water.

[0022] The oil-water separation membrane described above, wherein the MOFs comprise at least one of Co-MOFs and Zn-MOFs.

[0023] The oil-water separation membrane described above, wherein the organic polymer is a hydrophilic polymer.

[0024] The oil-water separation membrane described above, wherein the organic polymer comprises at least one of polyacrylonitrile and polyacrylic acid.

[0025] In the present application, the two-dimensional MOFs nanosheet refers to a nanoscale sheet-shaped metal organic framework (MOFs), and the two-dimensional MOFs nanosheet has a microporous structure.

[0026] In the present application, after the two-dimensional nanosheet is grown on the nanofiber membrane substrate, the obtained oil-water separation membrane has a sub-micron pore structure, and the two-dimensional nanosheet itself has a microporous structure.

[0027] The oil-water separation membrane described above, wherein the size of the two-dimensional MOFs nanosheet is 500-1000 nm.

[0028] The oil-water separation membrane described above, wherein the thickness of the MOFs layer is less than 50 nm.

[0029] The oil-water separation membrane described above, wherein the MOFs layer can be loaded on part of the surface of the nanofiber membrane substrate, or can be loaded on the entire surface of the nanofiber membrane substrate.

[0030] In the second aspect of the present application, a preparation method of any one of the oil-water separation membranes described above is provided, and the preparation method comprises the following steps:

[0031] 1) synthesizing three-dimensional MOFs;

[0032] 2) dispersing the three-dimensional MOFs obtained in step 1) in a first organic solvent, adding an organic polymer to form an electrospinning precursor solution, and electrospinning the electrospinning precursor solution to obtain a nanofiber membrane substrate;

[0033] 3) placing the nanofiber membrane substrate in a hydrothermal precursor solution to perform a hydrothermal recrystallization reaction, so as to load two-dimensional MOFs nanosheets on at least part of the surface of the nanofiber membrane substrate, to obtain an oil-water separation membrane.

[0034] In the method for preparing the oil-water separation membrane, in the step 1), the three-dimensional MOFs are obtained by reacting a transition metal nitrate with an organic ligand. Preferably, the three-dimensional MOFs are in a powder state.

[0035] In the method for preparing the oil-water separation membrane, in the step 1), the transition metal nitrate includes at least one of cobalt nitrate and zinc nitrate.

[0036] In the method for preparing the oil-water separation membrane, in the step 1), the organic ligand includes 2-methylimidazole.

[0037] In the method for preparing the oil-water separation membrane, in the step 2), the content of the three-dimensional MOFs is 0.5wt%-2.0wt% and the content of the organic polymer is 8wt%-10wt% based on the total mass of the electrospinning precursor solution.

[0038] In the present application, the precursor solution including the three-dimensional MOFs and the organic polymer is used to prepare the nanofiber membrane substrate by electrospinning, which is beneficial to uniformly distribute the three-dimensional MOFs in the nanofiber membrane substrate. The MOFs can be used as the crystal seeds in the subsequent hydrothermal recrystallization reaction, which is beneficial to the secondary growth of the MOFs layer with the two-dimensional MOFs nanosheet structure on the surface of the nanofiber membrane substrate.

[0039] In the present application, the content of the three-dimensional MOFs is controlled to be 0.5wt%-2.0wt% and the content of the organic polymer is controlled to be 8wt%-10wt%. Within this range, the nanofiber substrate obtained by electrospinning has a relatively complete structure and a relatively uniform nanofiber size.

[0040] In the method for preparing the oil-water separation membrane, in the step 2), the first organic solvent includes at least one of N-N dimethylformamide and N-methylpyrrolidone.

[0041] In the method for preparing the oil-water separation membrane, in the step 2), the organic polymer is a hydrophilic organic polymer.

[0042] In the method for preparing the oil-water separation membrane, in the step 2), the organic polymer includes at least one of polyacrylonitrile (PAN) and polyacrylic acid.

[0043] In the method for preparing the oil-water separation membrane, in the step 2), the electrospinning is performed by using an electrostatic spinning method.

[0044] In the present application, the electrospinning can adopt the electrospinning method in the art.

[0045] In the preparation method of the oil-water separation membrane, in the step 2), in the electrospinning process, the negative voltage for spinning is -1.8 to -2.2 kV, and the positive voltage for spinning is 8 to 12 kV.

[0046] In the present application, the electrospinning process parameters are adjusted according to the electrospinning process to obtain suitable electrospinning process parameters.

[0047] In the preparation method of the oil-water separation membrane, in the step 2), in the electrospinning process, the injection speed is 0.5 to 0.7 mL / h, and the receiving distance is 14 to 16 cm.

[0048] In the preparation method of the oil-water separation membrane, in the step 2), in the electrospinning process, the receiver is an aluminum foil covered metal cylinder, the receiver rotation speed is 20 to 100 rpm; the injector translation speed is 80 to 120 mm / min, the translation range is 15 to 25 cm, the environmental temperature is controlled at 25±1℃, the environmental relative humidity is 40±5%, and the whole spinning process lasts for 4 to 8 hours.

[0049] In the preparation method of the oil-water separation membrane, in the step 3), the hydrothermal precursor solution is obtained by mixing the transition metal nitrate and the organic ligand in the second organic solvent.

[0050] In the preparation method of the oil-water separation membrane, in the step 3), the transition metal nitrate includes at least one of cobalt nitrate and zinc nitrate.

[0051] In the preparation method of the oil-water separation membrane, in the step 3), the organic ligand includes 2-methyl imidazole.

[0052] In the preparation method of the oil-water separation membrane, in the step 3), the second organic solvent includes an organic alcohol with 1 to 4 carbon atoms.

[0053] In the preparation method of the oil-water separation membrane, in the step 3), the second organic solvent includes at least one of methanol, ethanol, propanol and butanol.

[0054] In the preparation method of the oil-water separation membrane, in the step 3), in the hydrothermal recrystallization reaction, the temperature is 80 to 90℃, and the time is 6 to 10 hours.

[0055] In the preparation method of the oil-water separation membrane, in the step 3), the nanofiber membrane substrate is vertically fixed and placed in the hydrothermal precursor solution for hydrothermal recrystallization reaction.

[0056] In the preparation method of the oil-water separation membrane, in the step 3), the nanofiber membrane substrate prepared in the step 2) is dried and then placed in a hydrothermal precursor solution to perform a hydrothermal recrystallization reaction.

[0057] In the preparation method of the oil-water separation membrane, in the step 3), the hydrothermal recrystallization reaction is performed in a hydrothermal reactor.

[0058] The application adopts a nanofiber membrane substrate containing three-dimensional MOFs as a substrate material, and prepares an oil-water separation membrane containing two-dimensional MOF layers by a hydrothermal recrystallization method, wherein the ligand and the transition metal salt first undergo coordination, and the reaction forms MOF precipitates in the hydrothermal reaction. The three-dimensional MOFs in the nanofiber membrane substrate provide crystal seeds for the formation of MOF precipitates in the hydrothermal recrystallization process, so as to facilitate the hydrothermal deposition of MOFs on the surface of the nanofiber membrane substrate in the recrystallization process, thereby forming two-dimensional MOFs.

[0059] The application first forms a nanofiber membrane by co-spinning with organic matter, and then obtains two-dimensional MOF nanosheets by a hydrothermal recrystallization method, so as to convert the three-dimensional MOFs into two-dimensional nanosheet-loaded nanofiber membranes, thereby solving the problem that the MOF material mainly exists in the form of powder in the prior art, which causes secondary pollution in the treatment of wastewater, and also solving the technical problem that the MOF material is easy to agglomerate in the form of powder, which is unexpected by the person skilled in the art. The application utilizes the two-dimensional nanosheet loading to improve the surface roughness of the fiber membrane, realizes a larger water contact area, and improves the surface superhydrophilicity. At the same time, the MOFs can be coupled with PMS or persulfate to generate sulfate radicals by advanced oxidation, thereby realizing the degradation of organic matter in the gas field water.

[0060] The preparation method of the oil-water separation membrane provided by the application is simple in operation and suitable for wide application.

[0061] According to a third aspect of the application, an application of an oil-water separation membrane in the field of oil and gas field produced wastewater treatment is provided, wherein the oil-water separation membrane is any of the oil-water separation membranes described above, or is prepared by the preparation method of any of the oil-water separation membranes described above.

[0062] In the application of the oil-water separation membrane, the oil-water separation membrane is coupled with sulfate radical-based advanced oxidation method AOPs to treat the oil and gas field produced wastewater.

[0063] Advanced oxidation processes (AOPs) are one of the most effective ways to remove organic pollutants. In advanced oxidation processes, sulfate radicals stand out compared to hydroxyl radicals due to their higher redox potential, superior selectivity and longer half-life. By taking advantage of these properties, sulfate radical-based AOPs exhibit stronger degradation ability of organic pollutants. Sulfate radicals are usually generated by the decomposition of peroxymonosulfate (PMS) or persulfate.

[0064] In the application of the above oil-water separation membrane, sulfate radicals are generated by the decomposition of peroxymonosulfate (also known as peroxysulfate) and / or persulfate (also known as peroxodisulfate).

[0065] In the application of the above oil-water separation membrane, the peroxymonosulfate (or peroxysulfate) includes at least one of ammonium peroxymonosulfate, sodium peroxymonosulfate and potassium peroxymonosulfate.

[0066] In the application of the above oil-water separation membrane, the persulfate includes at least one of ammonium persulfate, sodium persulfate and potassium persulfate.

[0067] The oil-water separation membrane according to the present application comprises a nanofiber membrane substrate and a MOFs layer loaded on at least part of the surface of the nanofiber membrane substrate; the MOFs layer comprises two-dimensional MOFs nanosheets. The nanofiber membrane substrate and the MOFs layer can form a hierarchical micro-nano rough structure and a sub-micron pore structure, have superhydrophilic or superoleophobicity under water, and can achieve efficient removal of suspended impurities and oils in oil and gas field wastewater.

[0068] Secondly, the MOFs material can activate peroxymonosulfate or persulfate to generate sulfate radicals, so that the oil-water separation membrane according to the present application can be combined with sulfate radical-based advanced oxidation method AOPs to treat oil and gas field produced wastewater, and achieve simultaneous removal of oils, suspended particles and organic pollutants in the oil and gas field produced wastewater.

[0069] Thirdly, the conventional MOFs powder material has a difficult-to-solve secondary pollution problem when used for wastewater treatment. The MOFs with a two-dimensional nanosheet structure in the oil-water separation membrane according to the present application does not have the secondary pollution problem caused by the MOF powder material to the environment when used for wastewater treatment.

[0070] In addition, the two-dimensional MOFs nanosheet in the oil-water separation membrane according to the present application has a porous structure and a larger specific surface area, which can be coupled with sulfate radical-based advanced oxidation process (AOPs) to achieve more efficient degradation of organic matter in oil and gas field wastewater.

[0071] Therefore, the oil-water separation membrane according to the present application can achieve efficient removal of various pollutants in oil and gas field wastewater, and has high industrial application value.

[0072] In the present application, the above technical features can be freely combined to form new technical solutions without conflict.

[0073] The above technical solutions provided by the present application have the following beneficial technical effects:

[0074] (1) The oil-water separation membrane according to the present application comprises a nanofiber membrane substrate and a MOFs layer loaded on at least part of the surface of the nanofiber membrane substrate, and the nanofiber membrane substrate and the MOFs layer form a hierarchical micro-nano rough structure and a sub-micron pore structure, which can efficiently remove suspended impurities in oil and gas field wastewater.

[0075] (2) The present application co-spins MOFs with a three-dimensional structure and organic polymers to form a nanofiber membrane, and then grows two-dimensional MOFs nanosheets on the nanofiber membrane. The prepared oil-water separation membrane has a hierarchical micro-nano rough structure and a sub-micron pore structure, has superhydrophilicity / ultra-oleophobicity underwater, and can realize efficient removal of suspended impurities and oils in gas field water. The two-dimensional MOFs nanosheets loaded have a porous structure and a larger specific surface area, and can be coupled with advanced oxidation processes (AOPs) based on sulfate radicals to realize degradation of organic matter in gas field water.

[0076] (3) The oil-water separation membrane according to the present application has hydrophilic organic polymer nanofibers in the nanofiber membrane substrate, which makes it have superhydrophilicity or ultra-oleophobicity underwater, and can realize efficient separation of oil and water in oil and gas field wastewater, so as to recover oil and water respectively.

[0077] (4) In the oil-water separation membrane according to the present application, the two-dimensional MOFs nanosheets in the MOFs layer have a porous structure and a larger specific surface area, and can be coupled with advanced oxidation processes (AOPs) based on sulfate radicals to realize synchronous removal of suspended particles, oils and organic pollutants in oil and gas field produced water, simplify the gas field water pretreatment process, and reduce the processing cost and enhance the wastewater treatment effect.

[0078] (5) The preparation method of the oil-water separation membrane provided by the present application is simple in operation and suitable for wide application. BRIEF DESCRIPTION OF DRAWINGS

[0079] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed in the description of the embodiments of the present application or the related art are briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other related drawings without creative labor on the basis of these drawings.

[0080] Figure 1 is a SEM image of the three-dimensional MOFs powder in Example 1 of the present application;

[0081] Figure 2 is a SEM image of the oil-water separation membrane obtained in Example 1 of the present application;

[0082] Figure 3 is a magnified view of Figure 2;

[0083] Figure 4 is a SEM image of the oil-water separation membrane obtained in Example 2 of the present application;

[0084] Figure 5 is a SEM image of the oil-water separation membrane obtained in Comparative Example 1 of the present application;

[0085] Figure 6 is a magnified view of Figure 5;

[0086] Figure 7 is a water spreading wetting process diagram of the oil-water separation membrane obtained in Example 1 of the present application in the super-hydrophilic test in air;

[0087] Figure 8 is a water spreading wetting process diagram of the oil-water separation membrane obtained in Comparative Example 1 of the present application in the super-hydrophilic test in air. DETAILED DESCRIPTION

[0088] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without any creative effort fall within the scope of protection of the present application.

[0089] Throughout the specification, the mention of “one embodiment”, “some embodiments”, “an embodiment” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present application. Therefore, the phrases “one embodiment”, “an embodiment”, “one example” or “an example” appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, specific features, structures or characteristics can be combined in any appropriate combination and / or sub-combination in one or more embodiments or examples.

[0090] Unless otherwise specifically mentioned, the various raw materials, reagents, instruments and equipment, etc. used in the present application can be purchased from the market or can be prepared by existing methods.

[0091] Some embodiments of the first aspect of the present application provide an oil-water separation membrane, which comprises a nanofiber membrane substrate and a MOFs layer loaded on at least part of the surface of the nanofiber membrane substrate; the MOFs layer comprises two-dimensional MOFs nanosheets.

[0092] According to some embodiments of the first aspect of the present application, the MOFs comprise at least one of Co-MOFs and Zn-MOFs. Co-based MOFs or Zn-based MOFs can enable peroxymonosulfate (such as PMS, potassium hydrogen peroxymonosulfate) or persulfate to generate sulfate radicals, thereby, coupled with sulfate radical-based advanced oxidation processes (AOPs), the oil-water separation membrane according to the present application can achieve efficient degradation of organic matter in oil and gas field wastewater.

[0093] According to some embodiments of the first aspect of the present application, the nanofiber membrane substrate comprises organic polymer fibers and three-dimensional MOFs materials.

[0094] In the present application, the nanofiber membrane substrate refers to a nanoscale fiber-like membrane substrate formed by organic polymers. The nanofiber membrane substrate can also comprise nanomaterials, for example, three-dimensional MOFs. The presence of three-dimensional MOFs is conducive to the nanofiber membrane substrate having a roughness of micro-nano structure.

[0095] According to some embodiments of the first aspect of the present application, the nanofiber membrane substrate is a hydrophilic polymer nanofiber membrane substrate. That is, the organic polymer fibers are hydrophilic polymer fibers.

[0096] In the present application, when the organic polymer fibers in the nanofiber membrane substrate are hydrophilic polymer fibers, the two-dimensional MOFs nanosheets generated in the hydrothermal recrystallization process are loaded on the hydrophilic polymer fibers, which can further increase the contact area of water and the surface of the nanofiber membrane, thereby improving the hydrophilicity of the nanofiber membrane and achieving superhydrophilic performance, i.e., static water contact angle of 0° in air and superwetting, thereby improving the removal efficiency of the nanofiber membrane substrate for suspended impurities and oil in oil and gas field produced water.

[0097] According to some embodiments of the first aspect of the present application, the hydrophilic polymer nanofiber membrane substrate can be a polyacrylic acid nanofiber membrane substrate or a polyacrylonitrile nanofiber membrane substrate. That is, the organic polymer for preparing the nanofiber membrane substrate is polyacrylic acid nanofiber or polyacrylonitrile nanofiber.

[0098] According to some embodiments of the first aspect of the present application, the nanofiber membrane substrate is prepared by electrospinning of three-dimensional MOFs and organic polymers.

[0099] According to some embodiments of the first aspect of the present application, the three-dimensional MOFs are in a powder state.

[0100] In the present application, the MOFs with three-dimensional structure are co-spun with hydrophilic organic polymers to form a nanofiber membrane, and then two-dimensional MOFs nanosheets are grown on the nanofiber membrane. The two-dimensional MOFs nanosheets are loaded on the nanofiber membrane to form an oil-water separation membrane with hierarchical micro-nano rough structure and sub-micron pore structure, which has superhydrophilicity / ultra-oleophobicity underwater and can realize efficient removal of suspended impurities and oil in gas field water. The two-dimensional MOFs nanosheets loaded have porous structure and larger specific surface area, which can be coupled with advanced oxidation processes (AOPs) based on sulfate radical to realize degradation of organic matter in gas field water.

[0101] According to some embodiments of the first aspect of the present application, the MOFs include at least one of Co-MOFs and Zn-MOFs; and the organic polymer is a hydrophilic polymer.

[0102] According to some embodiments of the first aspect of the present application, the organic polymer includes at least one of polyacrylonitrile and polyacrylic acid.

[0103] In the present application, after the two-dimensional nanosheets are grown on the nanofiber membrane substrate, the obtained oil-water separation membrane has a sub-micron pore structure, and the two-dimensional nanosheets themselves have a microporous structure.

[0104] According to some embodiments of the first aspect of the present application, the size of the two-dimensional MOFs nanosheets is 500-1000 nm.

[0105] According to some embodiments of the first aspect of the present application, the thickness of the MOFs layer is less than 50 nm.

[0106] According to some embodiments of the second aspect of the present application, a preparation method of any of the above oil-water separation membranes is provided, and the preparation method includes the following steps:

[0107] 1) Synthesizing three-dimensional MOFs;

[0108] 2) Dispersing the three-dimensional MOFs in a first organic solvent, adding an organic polymer to form an electrospinning precursor solution, and electrospinning the electrospinning precursor solution to obtain a nanofiber membrane substrate;

[0109] 3) Placing the nanofiber membrane substrate in a hydrothermal precursor solution to perform a hydrothermal recrystallization reaction, so that two-dimensional MOFs nanosheets are loaded on at least part of the surface of the nanofiber membrane substrate to obtain an oil-water separation membrane.

[0110] According to some embodiments of the second aspect of the present application, in step 1), the three-dimensional MOFs are obtained by reacting a transition metal nitrate with an organic ligand; the transition metal nitrate includes at least one of cobalt nitrate and zinc nitrate, and the organic ligand includes 2-methylimidazole.

[0111] According to some embodiments of the second aspect of the present application, in the step 1), the three-dimensional MOFs are in a powder state.

[0112] According to some embodiments of the second aspect of the present application, in the step 2), the content of the three-dimensional MOFs is 0.5wt% to 2.0wt% (for example, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.7wt% or 1.9wt%) and the content of the organic polymer is 8wt% to 10wt% (for example, 8.2wt%, 8.4wt%, 8.5wt%, 8.8wt%, 9.0wt%, 9.2wt%, 9.4wt%, 9.5wt% or 9.8wt%) based on the total mass of the electrospinning precursor solution.

[0113] In the present application, the precursor solution including three-dimensional MOFs and organic polymer is used to prepare the nanofiber membrane substrate by electrospinning, which is beneficial to uniformly distribute the three-dimensional MOFs in the nanofiber membrane substrate. The MOFs can be used as crystal seeds in the subsequent hydrothermal recrystallization reaction, which is beneficial to secondary growth on the surface of the nanofiber membrane substrate to obtain a MOFs layer with a two-dimensional MOFs nanosheet structure.

[0114] In the present application, the content of the three-dimensional MOFs is controlled to be 0.5wt% to 2.0wt% and the content of the organic polymer is controlled to be 8wt% to 10wt%, within which range, the nanofiber substrate obtained by electrospinning has a relatively complete structure and a relatively uniform nanofiber size.

[0115] According to some embodiments of the second aspect of the present application, in the step 2), the first organic solvent includes at least one of N-N dimethylformamide and N-methyl pyrrolidone.

[0116] According to some embodiments of the second aspect of the present application, in the step 2), the organic polymer is a hydrophilic organic polymer, and the hydrophilic organic polymer includes at least one of polyacrylonitrile (PAN) and polyacrylic acid.

[0117] In the present application, the electrospinning precursor solution formed by mixing Co-MOFs or Zn-MOFs with organic polymers is electrospun to form MOFs@organic polymer nanofiber membranes, such as Co-MOFs@PAN nanofiber membranes (or Zn-MOFs@PAN nanofiber membranes). The Co-MOFs@PAN nanofiber membranes (or Zn-MOFs@PAN nanofiber membranes) are placed in a solution containing Co(NO3)2 (or Zn(NO3)2) seed crystals and 2-methylimidazole ligands to perform a hydrothermal recrystallization reaction, so that Co-MOFs (or Zn-MOFs) are secondarily grown to form two-dimensional nanosheet structures with larger specific surface areas loaded on the surface of nanofibers. The nanofiber membranes have hierarchical micro-nano rough structures and sub-micron pore structures, have superhydrophilicity / ultra-oleophobicity underwater, and can achieve efficient removal of suspended impurities and oils in gas field water. At the same time, the two-dimensional nanosheets of Co-MOFs (or Zn-MOFs) have a porous structure and a larger specific surface area, and can realize the degradation of organic matter in gas field water by coupling with PMS (potassium monopersulfate) through advanced oxidation.

[0118] According to some embodiments of the second aspect of the present application, in the step 2), the electrospinning is performed by using an electrospinning method.

[0119] In the present application, the electrospinning can be performed by using a conventional electrospinning method in the art.

[0120] According to some embodiments of the second aspect of the present application, in the step 2), during the electrospinning, the negative voltage is -1.8 to -2.2 kV (for example, -1.9 kV, -2 kV or -2.1 kV), and the positive voltage is 8 to 12 kV (for example, 8.5 kV, 9 kV, 9.5 kV, 10 kV, 10.5 kV, 11 kV or 11.5 kV).

[0121] In the present application, the skilled person in the art can obtain suitable electrospinning process parameters by making conventional adjustments to the process parameters of the electrospinning process according to the electrospinning process.

[0122] According to some embodiments of the second aspect of the present application, in the step 2), during the electrospinning, the injection speed is 0.5 to 0.7 mL / h (for example, 0.55 mL / h, 0.6 mL / h, 0.625 mL / h, 0.65 mL / h or 0.68 mL / h), and the receiving distance is 14 to 16 cm (for example, 14.5 cm, 15 cm or 15.5 cm).

[0123] According to some embodiments of the second aspect of the present application, in the step 2), in the electrospinning process, the receiver is an aluminum foil covered metal drum, the receiver rotation speed is 30-80 rpm (for example, 40 rpm, 50 rpm, 60 rpm or 70 rpm); the injector translation speed is 80-120 mm / min (for example, 90 mm / min, 100 mm / min or 110 mm / min), the translation range is 15-25 cm (for example, 16 cm, 18 cm, 20 cm, 21 cm or 23 cm), the environmental temperature is controlled to be 25±1℃, the environmental relative humidity is controlled to be 40±5%, and the whole spinning process lasts for 4-8 hours (for example, 5 hours, 6 hours or 7 hours).

[0124] According to some embodiments of the second aspect of the present application, in the step 3), the hydrothermal precursor solution is obtained by mixing a transition metal nitrate and an organic ligand in a second organic solvent; the transition metal nitrate includes at least one of cobalt nitrate and zinc nitrate; the organic ligand includes 2-methylimidazole; and the second organic solvent includes an organic alcohol with 1-4 carbon atoms.

[0125] According to some embodiments of the second aspect of the present application, in the step 3), the second organic solvent includes at least one of methanol, ethanol, propanol and butanol.

[0126] According to some embodiments of the second aspect of the present application, in the step 3), in the hydrothermal recrystallization reaction, the temperature is 80-90℃ (for example, 81℃, 83℃, 85℃, 86℃, 88℃ or 89℃), and the time is 6-10 hours (for example, 7 hours, 8 hours, 9 hours or 9.5 hours).

[0127] According to some embodiments of the second aspect of the present application, in the step 3), the nanofiber membrane substrate prepared in the step 2) is dried and then placed in the hydrothermal precursor solution to perform the hydrothermal recrystallization reaction.

[0128] The embodiments of the present application first form a nanofiber membrane by co-spinning the three-dimensional MOFs with organic matters, and then obtain two-dimensional MOFs nanosheets through hydrothermal recrystallization, so as to convert the three-dimensional MOFs into two-dimensional nanosheet loaded nanofiber membranes, solve the problem that the MOFs material mainly exists in powder form in the prior art, causing secondary pollution in the sewage treatment, and also solve the technical problem that the two-dimensional nanosheet structure is easy to agglomerate in powder state, which is unexpected by the person skilled in the art. The present application utilizes the two-dimensional nanosheet loading to improve the surface roughness of the fiber membrane, realizes a larger water contact area, and improves the surface superhydrophilicity. At the same time, the MOFs can be coupled with PMS or persulfate to generate sulfate radicals through advanced oxidation, realizing the degradation of organic matters in the gas field water.

[0129] According to some embodiments of the third aspect of the present application, the oil-water separation membrane is coupled with sulfate radical-based advanced oxidation processes (AOPs) to treat oil and gas field produced wastewater.

[0130] According to some embodiments of the third aspect of the present application, the oil-water separation membrane is coupled with sulfate radical-based advanced oxidation processes (AOPs) to treat oil and gas field produced wastewater.

[0131] Advanced oxidation processes (AOPs) are one of the most effective ways to remove organic pollutants. In advanced oxidation processes, sulfate radicals stand out compared to hydroxyl radicals due to their higher oxidation-reduction potential, superior selectivity, and extended half-life. By taking advantage of these characteristics, sulfate radical-based AOPs exhibit stronger organic pollutant degradation capacity. Sulfate radicals are often generated through the decomposition of peroxymonosulfate (PMS) or persulfate.

[0132] In the following, the technical solutions of the present application will be further explained and described in combination with specific embodiments. Among them, since Zn-MOFs and Co-MOFs belong to similar organic metal framework materials, the preparation methods of the two kinds of three-dimensional MOFs are the same, except that the transition metal sources used in the preparation of the two kinds of three-dimensional MOFs are different (i.e., Co-based MOFs use cobalt nitrate, and Zn-based MOFs use zinc nitrate). The preparation methods of the oil-water separation membranes containing Zn-MOFs and Co-MOFs are also the same, and the performances of the oil-water separation membranes finally obtained are also similar. That is, Co-based MOFs or Zn-based MOFs can make peroxymonosulfate (such as PMS potassium peroxymonosulfate) or persulfate generate sulfate radicals, so as to be coupled with sulfate radical-based advanced oxidation processes (AOPs), and thus the oil-water separation membrane can realize efficient degradation of organic matter in oil and gas field wastewater. Therefore, in the following, the oil-water separation membrane containing Co-MOFs and the preparation method thereof will be taken as an example to further explain and describe the technical solutions of the present application.

[0133] In addition, field emission scanning electron microscopy is used to observe the morphology of the three-dimensional MOFs prepared in each embodiment of the present application; scanning electron microscopy is used to observe the surface micro-morphology of the oil-water separation membranes in each embodiment of the present application.

[0134] Example 1

[0135] The oil-water separation membrane comprises a nanofiber membrane substrate and two-dimensional MOFs nanosheets loaded on the nanofiber membrane substrate, wherein the nanofiber membrane substrate comprises polyacrylonitrile nanofibers and three-dimensional MOFs with a mass ratio of 1:0.2, and the average particle size of the three-dimensional MOFs is 200 nm; the MOFs layer in the oil-water separation membrane has a hierarchical micro-nano rough structure and a sub-micron pore structure, the MOFs layer comprises two-dimensional MOFs nanosheets with a size of 50-1000 nm, and the thickness of the MOFs layer is less than 50 nm.

[0136] The preparation method of the oil-water separation membrane of the embodiment comprises the following steps:

[0137] S1: 10.8g 2-methylimidazole is dissolved in 100mL deionized water to obtain a first solution; then 0.7g of Co(NO3)2·6H2O is dissolved in 100mL deionized water to obtain a second solution; the second solution is quickly added to the first solution, and the reaction is carried out at room temperature for 3 hours; after the reaction is completed, three-dimensional MOFs (Co-MOFs) are obtained by centrifugal separation, and are washed and dried to obtain three-dimensional MOFs powder;

[0138] S2: 0.2g of the three-dimensional MOFs powder synthesized in step 1) is added to 10mL of N,N dimethylformamide solution and ultrasonically dispersed for 30 minutes, then 1g of polyacrylonitrile (PAN) powder is added and stirred for 30 minutes to mix uniformly, to obtain an electrospinning precursor solution; wherein in the electrospinning precursor solution, the mass of the three-dimensional MOFs powder accounts for 2%, and the mass of the polyacrylonitrile accounts for 10%;

[0139] Then, the precursor solution is added to a 5mL syringe with a needle, and is spun by using an electrostatic spinning machine to obtain a nanofiber membrane substrate crude product, which is placed in a 60℃ vacuum drying oven for drying to remove surface un-volatile organic solvents (N,N dimethylformamide) and moisture, to obtain a nanofiber membrane substrate product; wherein during the spinning process of the electrostatic spinning machine, the negative voltage for spinning is -2kV, and the positive voltage for spinning is +10kV; the injection speed is 0.625mL / h, and the receiving distance is 15cm; the receiver is an aluminum foil covered metal drum, and the rotation speed of the receiver is 50rpm; the translation speed of the syringe is 100mm / min, the translation range is 20cm, the environmental temperature is controlled to be 25±1℃, and the environmental relative humidity is controlled to be 40±5%, and the entire spinning process lasts for 6h;

[0140] S3: 2 g of Co(NO3)2·6H2O was added to 60 mL of methanol, and stirred to dissolve to obtain solution A; 0.8 g of 2-methylimidazole was dissolved in 60 mL of methanol to obtain solution B, solution B was quickly poured into solution A and stirred to mix uniformly, and then transferred into an autoclave; at the same time, the dried nanofiber membrane substrate product in step S2 was vertically fixed in the autoclave, and hydrothermal reaction was carried out at 80°C for 6h, the membrane obtained after the reaction was rinsed with methanol three times, and dried in a vacuum drying oven at 60°C, to obtain a nanofiber membrane substrate with a MOFs layer loaded on the surface, i.e. an oil-water separation membrane.

[0141] Example 2

[0142] An oil-water separation membrane, comprising a nanofiber membrane substrate and two-dimensional MOFs nanosheets loaded on the nanofiber membrane substrate, wherein the nanofiber membrane substrate comprises polyacrylonitrile nanofibers and three-dimensional MOFs at a mass ratio of 1:0.1, and the average particle size of the three-dimensional MOFs is 200 nm; the oil-water separation membrane has a sub-micron gap (or pore) structure; the MOFs layer comprises two-dimensional MOFs nanosheets with a size of 50-1000 nm, and the thickness of the MOFs layer is less than 50 nm.

[0143] The preparation method of the oil-water separation membrane of the present embodiment comprises the following steps:

[0144] S1: 10.8 g of 2-methylimidazole was dissolved in 100 mL of deionized water to obtain a first solution; then 0.7 g of Co(NO3)2·6H2O was dissolved in 100 mL of deionized water to obtain a second solution; the second solution was quickly added to the first solution, and reacted at room temperature for 3 hours, after the reaction, three-dimensional MOFs (Co-MOFs) were obtained by centrifugation, and washed and dried;

[0145] S2: 0.1 g of three-dimensional MOFs prepared in step 1) was added to 10 mL of N,N dimethylformamide solution and ultrasonically dispersed for 30 minutes, then 0.8 g of polyacrylonitrile powder was added and stirred for 30 minutes to mix uniformly, to obtain a precursor solution; wherein the mass percentage content of three-dimensional MOFs in the precursor solution is 1%, and the mass percentage content of polyacrylonitrile is 8%;

[0146] The precursor solution is added to a 5 mL syringe with a needle, and a nanofiber membrane substrate is obtained by spinning with an electrostatic spinning machine. The obtained nanofiber membrane substrate is placed in a 60℃ vacuum drying oven for drying to remove the surface un-volatile organic solvent (N,N dimethylformamide) and moisture; a nanofiber membrane substrate is obtained; wherein, during the spinning process of the electrostatic spinning machine, the negative voltage for spinning is -2 kV, and the positive voltage for spinning is +10 kV; the injection speed is 0.625 mL / h, and the receiving distance is 15 cm; the receiver is an aluminum foil covered metal drum, the rotating speed of the receiver is 50 rpm; the translation speed of the syringe is 100 mm / min, the translation range is 20 cm, the environmental temperature is controlled to be 25±1℃, the relative humidity of the environment is 40±5%, and the entire spinning process lasts for 6 h;

[0147] S3: 2g of Co(NO3)2·6H2O is added to 60mL of methanol, and stirred to dissolve to obtain solution A; 0.8g of 2-methylimidazole is dissolved in 60mL of methanol to obtain solution B, solution B is quickly poured into solution A and stirred to mix uniformly, and then transferred into an autoclave; at the same time, the dried nanofiber membrane substrate in step S2 is vertically fixed in the autoclave, and hydrothermal reaction is carried out at 80℃ for 6h; the membrane obtained after the reaction is rinsed with methanol for three times, and dried in a 60℃ vacuum drying oven, and finally an oil-water separation membrane is obtained.

[0148] Comparative Example 1

[0149] An oil-water separation membrane includes a nanofiber membrane substrate and two-dimensional MOFs nanosheets loaded on the nanofiber membrane substrate. The oil-water separation membrane is different from the oil-water separation membrane in Example 1 in that the nanofiber membrane substrate does not include three-dimensional MOFs.

[0150] The preparation method of the oil-water separation membrane includes the following steps:

[0151] S1: 1g of polyacrylonitrile powder is added to a 10mL solution of N,N dimethylformamide, and ultrasonic dispersion is carried out for 30 minutes to mix uniformly, and a precursor solution is obtained;

[0152] The precursor solution is added to a 5 mL syringe with a needle, and is spun using an electrostatic spinning machine to obtain a nanofiber membrane substrate. The obtained nanofiber membrane substrate is placed in a 60℃ vacuum drying oven for drying to remove the surface un-volatile organic solvent (N,N dimethylformamide) and moisture; and a nanofiber membrane substrate is obtained. In the electrostatic spinning machine spinning process, the negative voltage is -2 kV, the positive voltage is +10 kV; the injection speed is 0.625 mL / h, and the receiving distance is 15 cm; the receiver is an aluminum foil covered metal drum, the receiver rotation speed is 50 rpm; the syringe translation speed is 100 mm / min, the translation range is 20 cm, the environmental temperature is controlled to be 25±1℃, the environmental relative humidity is 40±5%, and the entire spinning process lasts for 6 h.

[0153] S3: 2 g of Co(NO3)2·6H2O is added to 60 mL of methanol, and is stirred and dissolved to obtain solution A; 0.8 g of 2-methylimidazole is dissolved in 60 mL of methanol to obtain solution B, solution B is quickly poured into solution A and is stirred and mixed uniformly, and is then transferred into an autoclave; at the same time, the dried nanofiber membrane substrate in step S2 is fixed vertically in the autoclave, and is subjected to hydrothermal reaction at 80℃ for 6 h; the obtained membrane after the reaction is rinsed with methanol three times, and is dried in a 60℃ vacuum drying oven, and finally an oil-water separation membrane is obtained.

[0154] Micro-morphology of the oil-water separation membrane

[0155] The field emission scanning electron microscope (SEM) is used to observe the micro-morphology of the three-dimensional MOFs powder in each example and the comparative example; and the field emission scanning electron microscope is used to observe the surface micro-morphology of the oil-water separation membrane in each example. FIG. 1 is a micro-morphology diagram of the three-dimensional MOFs powder in Example 1 of the present application. FIG. 2 is a micro-morphology diagram of the oil-water separation membrane in Example 1 of the present application. FIG. 3 is an enlarged view of FIG. 2. FIG. 4 is an SEM diagram of the oil-water separation membrane in Example 2 of the present application. FIG. 5 is a morphology diagram of the oil-water separation membrane in Comparative Example 1 of the present application, and FIG. 6 is an enlarged view of the oil-water separation membrane in FIG. 5.

[0156] As shown in FIG. 1, the MOFs powder prepared in Example 1 is in a three-dimensional granular shape, and the average particle size is 200 nm.

[0157] As shown in FIGS. 2 and 3, the oil-water separation membrane prepared in Embodiment 1 of the present application, i.e., the super-hydrophilic two-dimensional MOFs nanosheet loaded nanofiber membrane, has a surface covered by uniform nanofibers, and the petal-shaped sheet structure exists on the surface of the nanofibers, and the vertically staggered nanosheet structure completely wraps the nanofibers. It can be seen that the two-dimensional MOFs nanosheet loaded nanofiber membrane has a sub-micron level void structure, the average pore size is about 1 μm, the thickness of the two-dimensional MOFs nanosheet is less than 50 nm; and the two-dimensional MOFs nanosheet is uniform in size and uniformly distributed on the nanofiber membrane; the nanofiber membrane has a complete structure and uniform size.

[0158] As shown in FIG. 4, the surface micro-morphology of the nanofiber membrane prepared in Embodiment 2 can also be observed to have a similar two-dimensional nanosheet structure wrapping the nanofibers as in Embodiment 1.

[0159] As shown in FIGS. 5 and 6, compared with the microstructure diagram of the oil-water separation membrane in Embodiment 1 (as shown in FIGS. 2 and 3), the surface of the oil-water separation membrane prepared in Comparative Example 1 does not have a two-dimensional nanosheet structure, but only has sporadic three-dimensional particles. It can be known that the preparation method in Comparative Example 1 cannot obtain an oil-water separation membrane having a two-dimensional MOFs nanosheet structure. This shows that the pre-adding of MOFs powder in the manufacture of the nanofiber substrate has a key influence on the formation of the microstructure of the oil-water separation membrane according to the present application.

[0160] Wettability of the oil-water separation membrane

[0161] The water wettability of the oil-water separation membranes prepared in each embodiment and comparative example in the present application was tested by using a water contact angle measuring instrument. The specific testing process was as follows: first, the oil-water separation membranes of each embodiment and comparative example were fixed on a sample holder, and it was ensured that the surface of the oil-water separation membrane was flat; the wetting process of the water droplet in the air was recorded by the snapshot mode of the contact angle measuring instrument, and the test liquid volume used in the test of the static contact angle was 3 μL.

[0162] FIG. 7 shows the wettability schematic diagram of the oil-water separation membrane in Embodiment 1 of the present application, and FIG. 8 shows the wettability schematic diagram of the oil-water separation membrane in Comparative Example 1 of the present application.

[0163] As shown in FIG. 7, the water droplet (3 μL) in the air can completely spread on the surface of the oil-water separation membrane in Embodiment 1, the static water contact angle after stabilization is 0°, and the whole wetting process only takes 1.2 s.

[0164] As can be seen from Fig. 8, although the water droplets (3 μL) in the air can completely spread on the surface of the oil-water separation membrane of Comparative Example 1, and the static water contact angle after stabilization is also 0°, the time for complete spreading wetting is more than twice that of the surface of the oil-water separation membrane of Example 1, which is 2.6 s. This indicates that the oil-water separation membrane prepared in Example 1 has better superhydrophilicity than the oil-water separation membrane prepared in Comparative Example 1, which also means better water permeability and water permeation flux.

[0165] Oil-water separation membrane in gas field water pretreatment performance

[0166] The pretreatment of the gas field water was carried out by a vertical tubular separation device at room temperature. The oil-water separation membranes prepared in Example 1 and Comparative Example 1 were fixed at the flange opening of the tubular separation device, and the raw gas field water sample was added from the upper port of the tubular separation device (a certain amount of PMS was also added at the same time), and the filtrate after separation flowed out from the lower port. The driving force required for separation was only provided by the gravity of the water sample to be separated. The filtrate after separation was collected and the suspended solids, COD and oil indicators in the filtrate were detected.

[0167] Table 1 shows the suspended solids, COD and oil indicators in the filtrate obtained by separating the gas field water using the oil-water separation membranes prepared in Example 1 and Comparative Example 1.

[0168] As can be seen from the test results in Table 1, the concentrations of suspended solids, COD and oil in the raw water sample (i.e. the gas field water) are 50, 263 and 1.5 mg / L respectively, and the concentrations of suspended solids, COD and oil in the filtrate after separation are 6, 39 and 0.36 mg / L respectively. While the same gas field water is separated by the membrane prepared in Comparative Example 1, the concentrations of suspended solids, COD and oil in the filtrate are 27, 96 and 0.74 mg / L respectively. This indicates that the membrane prepared in Comparative Example 1 has a certain separation effect on the suspended solids, COD and oil in the gas field water, but the efficiency is much lower than that of the membrane prepared in Example 1. In summary, it is confirmed that the oil-water separation membrane provided in the present application has excellent removal effect on the suspended solids, COD and oil in the gas field water.

[0169] Table 1:

[0170] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part 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 application.

Claims

1. An oil-water separation membrane, wherein, The oil-water separation membrane comprises a nanofiber membrane substrate and a MOFs layer loaded on at least part of the surface of the nanofiber membrane substrate. The MOFs layer comprises two-dimensional MOFs nanosheets. The two-dimensional MOFs nanosheets comprise at least one of Co-MOFs and Zn-MOFs.

2. The oil-water separation membrane according to claim 1, wherein, The nanofiber membrane substrate comprises organic polymer fibers and three-dimensional MOFs materials.

3. The oil-water separation membrane according to any one of claims 1-2, wherein, The nanofiber membrane substrate is prepared by electrospinning of three-dimensional MOFs and organic polymers.

4. The oil-water separation membrane according to claim 3, wherein, The MOFs comprise at least one of Co-MOFs and Zn-MOFs; and the organic polymers are hydrophilic polymers.

5. The oil-water separation membrane according to claim 4, wherein, The organic polymers comprise at least one of polyacrylonitrile and polyacrylic acid.

6. The oil-water separation membrane according to any one of claims 1-5, wherein, The oil-water separation membrane has a sub-micron pore structure.

7. The oil-water separation membrane according to any one of claims 1-6, wherein, The two-dimensional MOFs nanosheets have a size of 500-1000 nm.

8. The oil-water separation membrane according to any one of claims 1-7, wherein, The MOFs layer has a thickness of less than 50 nm.

9. A method for producing the oil-water separation membrane according to any one of claims 1 to 8, wherein, comprising the following steps: 1) synthesizing three-dimensional MOFs; 2) dispersing the three-dimensional MOFs in a first organic solvent, adding organic polymers to form an electrospinning precursor solution, and electrospinning the electrospinning precursor solution to obtain a nanofiber membrane substrate; 3) placing the nanofiber membrane substrate in a hydrothermal precursor solution for a hydrothermal recrystallization reaction to load two-dimensional MOFs nanosheets on at least part of the surface of the nanofiber membrane substrate to obtain an oil-water separation membrane.

10. The method for producing an oil-water separation membrane according to claim 9, wherein, In step 2), based on the total mass of the electrospinning precursor solution, the weight of the three-dimensional MOFs is 0.5wt%-2.0wt%, and the weight of the organic polymers is 8wt%-10wt%.

11. The method for preparing an oil-water separation membrane according to claim 10, wherein, In step 2), the first organic solvent comprises at least one of N-N dimethylformamide and N-methyl pyrrolidone; and the organic polymers comprise at least one of polyacrylonitrile and polyacrylic acid.

12. The preparation method of the oil-water separation membrane according to any one of claims 9-11, wherein, In step 2), during the electrospinning process, the negative voltage for spinning is -1.8kV to -2.2kV, and the positive voltage for spinning is 8kV to 12kV; and / or, In step 2), during the electrospinning process, the injection speed is 0.5-0.7mL / h, and the receiving distance is 14-16cm.

13. The preparation method of the oil-water separation membrane according to any one of claims 9-12, wherein, In step 1), the three-dimensional MOFs are obtained by reacting transition metal nitrate with organic ligand; and / or In step 3), the hydrothermal precursor solution is obtained by mixing transition metal nitrate with organic ligand in a second organic solvent.

14. The method for producing an oil-water separation membrane according to any one of claims 9 to 13, wherein, In step 1) or 3), the transition metal nitrate comprises at least one of cobalt nitrate and zinc nitrate; and the organic ligand comprises 2-methylimidazole.

15. The preparation method of the oil-water separation membrane according to any one of claims 9-14, wherein, In the hydrothermal recrystallization reaction, the temperature is 80-90℃, and the time is 6-10h.

16. The method of claim 13, wherein, In step 3), the second organic solvent comprises an organic alcohol having a carbon atom number of 1-4.

17. The method for producing an oil-water separation membrane according to any one of claims 9 to 16, wherein, In step 3), the nanofiber membrane substrate is vertically fixed and placed in the hydrothermal precursor solution to perform a hydrothermal recrystallization reaction.

18. Use of an oil-water separation membrane in the field of produced wastewater treatment in oil and gas fields, wherein, The oil-water separation membrane is the oil-water separation membrane according to any one of claims 1-8, or is prepared by the method of preparing the oil-water separation membrane according to any one of claims 9-17.

19. Use of the oil-water separation membrane according to claim 18 in the field of oil and gas field produced wastewater treatment, wherein, The oil-water separation membrane is coupled with sulfate radical-based advanced oxidation processes (AOPs) to treat oil and gas field produced wastewater.

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