Sandwich type film as well as preparation method and application thereof

Abstract

The invention relates to the field of water treatment, in particular to a sandwich type membrane as well as a preparation method and application thereof. The interlayer type membrane comprises a microporous membrane middle layer, an upper surface layer and a lower surface layer, the microporous membrane middle layer comprises a base membrane, a metal oxide and fluorosilane; the upper surface layer and the lower surface layer respectively and independently comprise a structural unit from dopamine and a structural unit from polyethyleneimine; the middle layer of the microporous membrane is a fully-hydrophobic layer, and the upper surface layer and the lower surface layer are respectively and independently hydrophilic layers. On one hand, the interlayer type membrane provided by the invention obtains good anti-wetting performance through the microporous membrane middle layer with the full-hydrophobic performance; on the other hand, high flux is obtained through the hydrophilic upper surface layer and the hydrophilic lower surface layer; and under the matching action of the middle layer, the upper surface layer and the lower surface layer of the microporous membrane, good anti-pollution performance is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of water treatment, in particular to a sandwich type membrane and its preparation method and application. BACKGROUND

[0002] Water pollution and water resource shortage are serious challenges facing our era, posing a major threat to the global economy, ecological environment health and global sustainable development strategy. Membrane distillation (MD) technology is a non-isothermal membrane separation process driven by the vapor pressure gradient between the hot feed side and the cold permeate side. Water vaporizes on the membrane surface of the hot feed side to form steam, which enters the cold side through the membrane pores and condenses to enrich, while non-volatile pollutants are retained on the membrane feed side, to obtain purified water while concentrating wastewater. Compared with other membrane separation processes, membrane distillation process has unique advantages, such as theoretically 100% retention of non-volatile molecules, lower operating temperature and pressure, not limited by osmotic pressure, and can utilize low-quality heat (such as production waste heat, solar energy, geothermal energy, etc.) to reduce its energy consumption, making it a very potential water treatment technology.

[0003] Despite the above advantages, with the development of the water industry and the demand for ecological protection, membrane distillation technology is facing more complex treatment objects, such as industrial wastewater, contaminated seawater or brackish water, oil-containing wastewater, dye wastewater, etc. These complex wastewaters inevitably contain pollutants such as hydrophobic substances and amphiphilic substances that can interact with the membrane. The composition of these pollutants is complex and their content varies, making the long-term operation stability and reliability of the membrane subject to the dual challenges of membrane wetting and membrane fouling. Currently, the commonly used method to improve the anti-fouling and anti-wetting properties of the membrane is to modify the hydrophilic and omniphobic properties on the surface of the hydrophobic membrane, respectively, to construct hydrophilic-hydrophobic membranes and omniphobic membranes. CN114471166A discloses a method for preparing a membrane for membrane distillation. The membrane uses alginate, a positively charged polyelectrolyte and a divalent metal salt solution as the hydrophilic modification raw material, and a series of composite membranes are obtained by controlling the number of cycles and reaction conditions. The membrane can maintain stable membrane distillation performance when treating saltwater feed containing 1 g / L hexadecane and during long-term testing. However, the membrane for membrane distillation does not disclose the performance of resisting high concentrations of surfactants.

[0004] In addition, Janus membranes and omniphobic membranes usually have low flux due to the increased additional mass transfer resistance and deterioration of temperature difference polarization. Therefore, it is more valuable to develop membrane materials with anti-wetting, anti-fouling and high flux. SUMMARY

[0005] The purpose of the present application is to overcome the problems of poor membrane anti-wetting and anti-fouling properties and low flux in the prior art, and to provide a sandwich type membrane and its preparation method and application. The sandwich type membrane includes a microporous membrane middle layer, an upper surface layer and a lower surface layer, so that the sandwich type membrane has excellent anti-wetting and anti-fouling properties while having a high flux.

[0006] To achieve the above objectives, the present invention provides a sandwich membrane, wherein the sandwich membrane includes a microporous membrane intermediate layer, an upper surface layer, and a lower surface layer;

[0007] The intermediate layer of the microporous membrane includes a base membrane, a metal oxide, and a fluorosilane;

[0008] The upper and lower layers each independently include structural units derived from dopamine and structural units derived from polyethyleneimine;

[0009] The middle layer of the microporous membrane is a completely hydrophobic layer, and the upper and lower surface layers are each independently hydrophilic layers.

[0010] A second aspect of the present invention provides a method for preparing a sandwich membrane, the method comprising the following steps:

[0011] (1) The base film is subjected to a hydrothermal reaction with a solution containing metal to obtain a base film with roughened surface;

[0012] (2) The roughened base film was modified with low surface energy using a fluorosilane solution to obtain a microporous membrane intermediate layer.

[0013] (3) A solution containing dopamine and polyethyleneimine is subjected to self-polymerization under an oxygen atmosphere to obtain a self-polymerized solution;

[0014] (4) Using a self-polymerizing solution, self-deposition is performed on the upper and lower surfaces of the intermediate layer of the microporous membrane to obtain a sandwich membrane.

[0015] The third aspect of the present invention provides a sandwich membrane prepared by the preparation method described in the second aspect.

[0016] The fourth aspect of the present invention provides an application of the sandwich membrane described in the first or third aspect in the field of water treatment.

[0017] Through the above technical solutions, the sandwich membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0018] (1) The sandwich membrane provided by the present invention comprises a microporous membrane intermediate layer, an upper surface layer, and a lower surface layer, wherein the microporous membrane intermediate layer comprises a base membrane, a metal oxide, and a fluorosilane, giving the microporous membrane intermediate layer a fully hydrophobic property, which can effectively improve the anti-wetting performance of the sandwich membrane. Specifically, the sandwich membrane provided by the present invention can operate stably in complex pollutant wastewater (such as a water-oil mixture).

[0019] (2) The upper and lower layers of the sandwich membrane provided by the present invention are hydrophilic layers, which makes the sandwich membrane have a high flux during membrane distillation.

[0020] (3) The hydrophilic upper and lower surface layers can work well with the microporous membrane intermediate layer, so that the provided sandwich membrane has good antifouling properties.

[0021] (4) In the preparation method of the sandwich membrane provided by the present invention, preferably, a specific ratio of dopamine and polyethyleneimine mixed solution is used to deposit the dopamine polyethyleneimine copolymer on the surface of the intermediate layer of the microporous membrane, which can further improve the water permeability while ensuring the high salt rejection rate of the membrane. Attached Figure Description

[0022] Figure 1 This is a flowchart of the preparation process for sandwich membranes.

[0023] Figure 2 This is a scanning electron microscope image of the surface of the membrane prepared in Comparative Example 1.

[0024] Figure 3 This is a scanning electron microscope image of the surface of the membrane prepared in Comparative Example 2.

[0025] Figure 4 This is a scanning electron microscope image of the surface of the membrane prepared in Example 1.

[0026] Figure 5 These are cross-sectional scanning electron microscope (SEM) images and EDS energy dispersive spectroscopy (O and N elements) of the membrane prepared in Example 1.

[0027] Figure 6 The water contact angles in air for the membranes prepared in Comparative Example 1, Comparative Example 2, and Example 1 are shown.

[0028] Figure 7 The water contact angle in air and the water and ethanol mixture contact angle of the membranes prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 5 are shown. Detailed Implementation

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] The present invention provides a sandwich membrane, wherein the sandwich membrane includes a microporous membrane intermediate layer, an upper surface layer and a lower surface layer;

[0031] The intermediate layer of the microporous membrane includes a base membrane, a metal oxide, and a fluorosilane;

[0032] The upper and lower layers each independently include structural units derived from dopamine and structural units derived from polyethyleneimine;

[0033] The middle layer of the microporous membrane is a completely hydrophobic layer, and the upper and lower surface layers are each independently hydrophilic layers.

[0034] In this invention, the middle layer of the microporous membrane is a fully hydrophobic layer, possessing both oleophobic and hydrophobic properties. This effectively prevents the erosion of substances with good wetting properties, such as alcohols and surfactants, thereby giving the sandwich membrane excellent anti-wetting properties.

[0035] In this invention, the upper and lower surface layers each independently comprise structural units derived from dopamine and structural units derived from polyethyleneimine. These structural units endow the upper and lower surface layers with good hydrophilic properties, which helps resist hydrophobic contaminants and rapidly absorb water molecules, thereby enabling the sandwich membrane to exhibit good antifouling performance and high flux during membrane distillation.

[0036] In this invention, the fully hydrophobic microporous membrane interlayer works in conjunction with the hydrophilic upper and lower surface layers to effectively prevent the adhesion and deposition of organic and / or inorganic contaminants on the membrane surface and within the pores. This results in excellent antifouling properties, effectively preventing membrane failure and enabling long-term stable mass transfer. Furthermore, the combination of the hydrophilic upper and lower surface layers with the fully hydrophobic microporous membrane interlayer effectively increases the transmembrane transport capacity of water molecules at the hydrophilic-fully hydrophobic interface, giving the sandwich membrane a higher flux.

[0037] In this invention, the selection range of the base membrane is relatively wide; it can be a polymer membrane with hydrophobic properties or an inorganic membrane, and those skilled in the art can select according to actual needs. Preferably, the base membrane is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, and polyvinylidene fluoride-hexafluoropropylene, more preferably polyvinylidene fluoride and / or polyvinylidene fluoride-hexafluoropropylene.

[0038] In this invention, unless otherwise specified, the side in contact with the contaminated liquid is the upper surface, and the side in contact with the purified water is the lower surface. The upper surface primarily functions to resist contamination, while the lower surface primarily functions to better receive water vapor for condensation.

[0039] According to a particularly preferred embodiment of the present invention, the pore size of the base film is 0.1-2 μm, for example, it can be a specific value or a range between the two, such as 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2 μm.

[0040] In this invention, the source of the base film is broadly selectable; it can be purchased or prepared, and those skilled in the art can choose according to actual needs. For example, it can be prepared by methods such as electrospinning, phase inversion, or stretching.

[0041] The present invention allows for a wide range of selections of the metal oxides, which can be chosen by those skilled in the art according to actual needs. Preferably, the metal oxide is selected from at least one of TiO2, ZnO, CuO, MnO2, ZrO2, Co3O4, SnO2, F3O4, WO3, MoO3, and MgO, and more preferably ZnO.

[0042] According to a particularly preferred embodiment of the present invention, the metal oxide is grown in situ on the base film.

[0043] According to a particularly preferred embodiment of the present invention, the fluorosilane is selected from 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, triethyl(trifluoromethyl)silane, 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, 1H,1H,2H,2H-perfluorododecyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, triethyl(trifluoromethyl)silane, triethyl The membrane is modified using at least one of the following: oxy(1H,1H,2H,2H-nonafluorohexyl)silane, trichloro(1H,1H,2H,2H-tetrafluoron-octyl)silane, 1H,1H,2H,2H-perfluorooctyltrichlorosilane, and 3,3,3-trifluoropropyltriethoxysilane; more preferably, at least one of 1H,1H,2H,2H-perfluorodecyltriethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, and 1H,1H,2H,2H-perfluorododecyltriethoxysilane. By using fluorosilanes within the preferred range described above, the base membrane is modified to give the sandwich membrane antifouling and antiwetting properties.

[0044] Furthermore, when the base membrane is polyvinylidene fluoride and / or polyvinylidene fluoride-hexafluoropropylene, modifying it with fluorosilanes within the above preferred range can give the sandwich membrane superior antifouling and antiwetting properties.

[0045] According to a particularly preferred embodiment of the present invention, the mass ratio of the base film, the metal oxide, and the fluorosilane is 1:0.01-0.05:0.001-0.02, more preferably 1:0.01-0.02:0.001-0.01. Adopting a mass ratio within the above range allows for a better synergistic effect between the base film, the metal oxide, and the fluorosilane, enabling the interlayer of the microporous membrane to better avoid erosion by substances with good wettability, thereby giving the sandwich membrane excellent anti-wetting properties.

[0046] According to a particularly preferred embodiment of the present invention, the thickness of the intermediate layer of the microporous membrane is 30-200 μm, for example, it can be a specific value or a range between the two such as 30, 60, 90, 120, 140, 170, 200 μm, preferably 50-100 μm.

[0047] In this invention, the thickness is measured using a scanning electron microscope.

[0048] According to a particularly preferred embodiment of the present invention, the air contact angle between the microporous membrane intermediate layer and water is 130-170°, for example, it can be a specific value or a range between 130°, 140°, 150°, 160°, 170°, etc., and more preferably 160-170°.

[0049] According to a particularly preferred embodiment of the present invention, the underwater contact angle between the microporous membrane intermediate layer and the oily substance is 2-50°, for example, it can be a specific value or a range between 2°, 10°, 20°, 30°, 40°, 50°, etc., and more preferably 2-15°. The oily substance refers to hexadecane.

[0050] In this invention, the contact angle is tested using a Dropmeter A-200 contact angle measuring instrument from MAIST Corporation, China.

[0051] When the air contact angle between the interlayer of the microporous membrane and water is 130-170° and the underwater contact angle with oily substances is 2-50°, the sandwich membrane has better anti-wetting properties.

[0052] According to a particularly preferred embodiment of the present invention, the number-average molecular weight of the polyethyleneimine is 200-20000 Da, for example, it can be a specific value or a range between 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 5000, 10000, 15000, 20000, etc. Using polyethyleneimine with a number-average molecular weight within the above range allows for better interaction with dopamine, enabling the upper and / or lower surface layers to independently acquire better hydrophilicity, and better interaction with the microporous membrane interlayer, resulting in a higher flux of the sandwich membrane.

[0053] According to a particularly preferred embodiment of the present invention, in the upper surface layer, based on the total weight of the upper surface layer, the content of the structural units derived from dopamine is 20-80 wt%, for example, it can be a specific value such as 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, or a range between the two; the content of the structural units derived from polyethyleneimine is 20-80 wt%, for example, it can be a specific value such as 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, or a range between the two. By adopting the dopamine and polyethyleneimine structural unit contents within the above-mentioned ranges, the adhesion and deposition of organic and / or inorganic contaminants in the upper surface layer and its pores can be better avoided, giving the sandwich membrane good antifouling performance.

[0054] According to a particularly preferred embodiment of the present invention, in the upper surface layer, the mass ratio of structural units derived from dopamine to structural units derived from polyethyleneimine is 1:0.2-2, preferably 1:0.5-1.5. Adopting a mass ratio within the above range can further prevent the adhesion and deposition of organic and / or inorganic contaminants in the upper surface layer and its pores, thereby further improving the antifouling performance of the sandwich membrane.

[0055] According to a particularly preferred embodiment of the present invention, in the lower surface layer, based on the total weight of the lower surface layer, the content of the structural units derived from dopamine is 20-80 wt%, for example, it can be a specific value such as 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, or a range between the two; the content of the structural units derived from polyethyleneimine is 20-80 wt%, for example, it can be a specific value such as 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, or a range between the two. Adopting the dopamine and polyethyleneimine structural unit contents within the above-mentioned range can better promote the condensation of water vapor on the permeate side, resulting in a lower water vapor mass transfer resistance in the sandwich membrane.

[0056] According to a particularly preferred embodiment of the present invention, in the lower surface layer, the mass ratio of structural units from dopamine to structural units from polyethyleneimine is 1:0.2-2, preferably 1:0.5-1.5. Adopting a mass ratio within the above range can further reduce the water vapor mass transfer resistance of the sandwich membrane.

[0057] According to a particularly preferred embodiment of the present invention, the total mass ratio of the upper and lower surface layers to the mass ratio of the microporous membrane intermediate layer is 0.01-0.2:1, for example, it can be a specific ratio or a range between the two such as 0.01:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, etc.

[0058] According to a particularly preferred embodiment of the present invention, the thickness of the upper surface layer is 1-10 μm, preferably 1-5 μm. Adopting a thickness within this range better maintains the temperature difference across the sandwich membrane, facilitating the migration of water vapor within the sandwich membrane.

[0059] According to a particularly preferred embodiment of the present invention, the thickness of the lower surface layer is 1-10 μm, preferably 1-5 μm. Adopting a thickness within this range better maintains the temperature difference across the sandwich membrane, facilitating the migration of water vapor within the sandwich membrane.

[0060] By simultaneously satisfying the requirements of a microporous membrane interlayer thickness of 50-100 μm, an upper surface layer thickness of 1-5 μm, and a lower surface layer thickness of 1-5 μm, the upper and lower surface layers can better integrate with the microporous membrane interlayer. This allows for a further increase in flux without compromising the antifouling and antiwetting properties of the sandwich membrane.

[0061] According to a particularly preferred embodiment of the present invention, the contact angle between the upper surface layer and water is 30-60°, for example, it can be a specific value or a range between 30°, 35°, 40°, 45°, 50°, 55°, 60°, etc., preferably 35-45°. Taking a contact angle within the above range can make the upper surface layer have more suitable hydrophilic properties, thereby better cooperating with the microporous membrane intermediate layer, and obtaining higher flux without reducing the antifouling performance and antiwetting performance of the sandwich membrane.

[0062] According to a particularly preferred embodiment of the present invention, the contact angle between the lower surface layer and water is 30-60°, for example, it can be a specific value such as 30°, 35°, 40°, 45°, 50°, 55°, 60°, or a range between the two, preferably 35-45°. Adopting a contact angle within the above range allows the lower surface layer to have more suitable hydrophilic properties, thereby better cooperating with the microporous membrane intermediate layer and promoting water vapor condensation to obtain a higher flux.

[0063] According to a particularly preferred embodiment of the present invention, the underwater contact angle between the upper surface layer and the oily substance is 100-160°, for example, it can be a specific value or a range between 100°, 110°, 120°, 130°, 140°, 150°, 160°, etc., preferably 115-135°.

[0064] According to a particularly preferred embodiment of the present invention, the underwater contact angle between the lower surface layer and the oily substance is 100-160°, for example, it can be a specific value or a range between 100°, 110°, 120°, 130°, 140°, 150°, 160°, etc., preferably 115-135°.

[0065] A second aspect of the present invention provides a method for preparing a sandwich membrane, the method comprising the following steps:

[0066] (1) The base film is subjected to a hydrothermal reaction with a solution containing metal to obtain a base film with roughened surface;

[0067] (2) The roughened base film was modified with low surface energy using a fluorosilane solution to obtain a microporous membrane intermediate layer.

[0068] (3) A solution containing dopamine and polyethyleneimine is subjected to self-polymerization under an oxygen atmosphere to obtain a self-polymerized solution;

[0069] (4) Using a self-polymerizing solution, self-deposition is performed on the upper and lower surfaces of the intermediate layer of the microporous membrane to obtain a sandwich membrane.

[0070] In this invention, the range of types of hydrothermal reactions is relatively wide, as long as they can roughen the surface of the base film. Those skilled in the art can select according to actual needs. Preferably, it is at least one of the following: hydrothermal crystallization, hydrothermal oxidation, hydrothermal reduction, hydrothermal precipitation, hydrothermal decomposition, and hydrothermal synthesis.

[0071] In this invention, the selection range of the base film is as described in the first aspect above, and will not be repeated here.

[0072] In this invention, the hydrothermal reaction causes the metal in the solution to combine with the base film in the form of oxides, resulting in a base film with a roughened surface, thereby providing modification sites for fluorosilane modification.

[0073] According to a particularly preferred embodiment of the present invention, the metal oxide is grown in situ on the base film.

[0074] In this invention, the shape of the metal oxide can be selected from a wide range, as long as it can achieve surface roughening of the base film. Those skilled in the art can select the shape according to actual needs. For example, the shape of the metal oxide can be linear, rod-shaped, plate-shaped, granular, flower-shaped, etc.

[0075] The present invention allows for a wide range of metal selection, as long as it can achieve surface roughening of the base film. Those skilled in the art can select according to actual needs. Preferably, the metal is selected from at least one of Ti, Zn, Cu, Mn, Zr, Co, Sn, F, W, Mo, and Mg, and more preferably Zn.

[0076] In this invention, the range of solutes that can be selected for the metal-containing solution is relatively wide; any solution containing metal can be obtained, and those skilled in the art can select according to actual needs. For example, the solute can be an elemental metal or a metal compound. Preferably, the solute is at least one of the following: an amorphous hydroxide of a metal, a metal oxide, an elemental metal, a metal soluble salt-compound-precipitant complex, a metal hydroxide, or an oxygen-containing salt of a metal.

[0077] In this invention, the range of solvents that can be selected for the metal-containing solution is relatively wide, as long as they can dissolve the elemental metal and / or metal compounds. Those skilled in the art can select the appropriate solvent based on actual needs. Preferably, the solvent for the metal-containing solution is ethanol.

[0078] In this invention, the concentration range of the metal in the metal-containing solution is relatively wide, as long as it can achieve the goal of roughening the surface of the base film. Those skilled in the art can select the appropriate concentration based on actual needs. Preferably, the concentration of the metal in the metal-containing solution is 10-500 mmol / L, more preferably 50-500 mmol / L.

[0079] According to a particularly preferred embodiment of the present invention, the amounts of the base film and the metal solution are such that the mass ratio of the base film to the metal oxide in the surface-roughened base film is 1:0.01-0.05. For example, it can be a specific ratio or a range between 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, etc., preferably 1:0.01-0.02. Adopting a ratio within the above range allows for better roughening of the base film surface, thereby providing more suitable modification sites for fluorosilane modification.

[0080] In this invention, the selection range for the hydrothermal reaction conditions is relatively wide; any condition that enables the hydrothermal reaction can be used. Those skilled in the art can select the appropriate conditions according to actual needs. Preferably, the hydrothermal reaction conditions include: a reaction temperature of 50-200℃, more preferably 50-150℃; and a reaction time of 1-48h, more preferably 12-48h.

[0081] According to a particularly preferred embodiment of the present invention, the hydrothermal reaction includes a further heating treatment after the first heating treatment to better promote the growth of the metal oxide.

[0082] In this invention, the selection range for the conditions of continued heating is relatively wide, as long as drying can be achieved. Those skilled in the art can select the appropriate conditions according to actual needs. Preferably, the temperature for continued heating is 80-120℃, and the heating time is 1-24 hours.

[0083] In this invention, the range of fluorosilanes that can be selected is relatively wide, as long as they can modify the surface roughened base film. Those skilled in the art can select according to actual needs. Preferably, the fluorosilane is selected from 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, triethyl(trifluoromethyl)silane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1H,1H,2H,2H-perfluorododecyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, triethyl(trifluoromethyl)silane, triethoxy(1H, At least one of 1H,2H,2H-nonafluorohexyl)silane, trichloro(1H,1H,2H,2H-tetrafluoron-octyl)silane, 1H,1H,2H,2H-perfluorooctyltrichlorosilane, and 3,3,3-trifluoropropyltriethoxysilane, more preferably at least one of 1H,1H,2H,2H-perfluorodecyltriethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, and 1H,1H,2H,2H-perfluorododecyltriethoxysilane. By using fluorosilanes within the above preferred range to modify the base membrane, the sandwich membrane acquires antifouling and antiwetting properties.

[0084] Furthermore, when the base membrane is polyvinylidene fluoride and / or polyvinylidene fluoride-hexafluoropropylene, modifying it with fluorosilanes within the above preferred range can give the sandwich membrane superior antifouling and antiwetting properties.

[0085] In this invention, the range of solvents that can be selected for the fluorosilane solution is relatively wide, as long as they can dissolve the fluorosilane. Those skilled in the art can select the appropriate solvent according to actual needs. Preferably, the solvent in the fluorosilane solution is at least one selected from ethyl acetate, ethanol, n-hexane, acetone, trichloroethylene, isopropanol, triethanolamine, and cyclohexane.

[0086] According to a particularly preferred embodiment of the present invention, the concentration of fluorosilane in the fluorosilane solution is 0.1-10 v / v%, for example, it can be a specific value or a range between the two, such as 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 v / v%.

[0087] According to a particularly preferred embodiment of the present invention, the mass ratio of the base film to fluorosilane in the microporous membrane interlayer is 1:0.001-0.05. For example, it can be a specific ratio or a range between 1:0.001, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, etc., preferably 1:0.001-0.01. Adopting a mass ratio within the above range allows the fluorosilane to better modify the base film, resulting in the microporous membrane interlayer exhibiting superior anti-wetting properties.

[0088] Furthermore, when the mass ratio of the base film to the metal oxide is 1:0.01-0.02, adopting the mass ratio of the base film to the fluorosilane within the above range can achieve a better combination effect between the base film, the metal oxide, and the fluorosilane, enabling the intermediate layer of the microporous membrane to further avoid erosion by substances with good wetting properties, thereby further improving the anti-wetting performance of the sandwich membrane.

[0089] In this invention, the selection range for the low surface energy modification conditions is relatively wide; any condition that achieves low surface energy modification is acceptable, and those skilled in the art can select the appropriate condition based on actual needs. Preferably, the low surface energy modification conditions include: a modification temperature of 40-80℃ and a modification time of 5-120 min. Adopting modification conditions within the above range allows the prepared microporous membrane interlayer to possess a more suitable low surface energy, thereby enabling the subsequently prepared sandwich membrane to exhibit excellent anti-wetting properties.

[0090] According to a particularly preferred embodiment of the present invention, the number-average molecular weight of the polyethyleneimine is 200-20000 Da, for example, it can be a specific value or a range between 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 5000, 10000, 15000, 20000, etc. Using polyethyleneimine with a number-average molecular weight within the above range allows for better interaction with dopamine, enabling the upper and / or lower surface layers to independently acquire better hydrophilicity, and better interaction with the microporous membrane interlayer, resulting in higher antifouling performance and flux of the sandwich membrane.

[0091] In this invention, the oxygen atmosphere refers to an atmosphere with an oxygen concentration higher than 8 mg / L.

[0092] According to a particularly preferred embodiment of the present invention, the self-polymerization temperature is 20-30°C and the self-polymerization time is 4-8 hours.

[0093] According to a particularly preferred embodiment of the present invention, the concentration of dopamine in the solution containing dopamine and polyethyleneimine is 0.5-4 g / L.

[0094] According to a particularly preferred embodiment of the present invention, the concentration of polyethyleneimine in the solution containing dopamine and polyethyleneimine is 0.5-4 g / L.

[0095] According to a particularly preferred embodiment of the present invention, in the solution containing dopamine and polyethyleneimine, the mass ratio of dopamine to polyethyleneimine is 1:0.2-2, for example, it can be a specific ratio or a range between 1:0.2, 1:0.5, 1:1, 1:1.5, 1:2, etc., preferably 1:0.5-1.5. Adopting a mass ratio within the above range can better prevent the adhesion and deposition of organic and / or inorganic contaminants on the upper surface and within its pores, giving the sandwich membrane good antifouling performance and low mass transfer resistance.

[0096] According to a particularly preferred embodiment of the present invention, the solvent in the solution containing dopamine and polyethyleneimine is an aqueous solution of tris(hydroxymethyl)aminomethane.

[0097] According to a particularly preferred embodiment of the present invention, the concentration of tris(hydroxymethyl)aminomethane in the aqueous solution is 10-100 mmol / L, for example, it can be a specific value or a range between the two, such as 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 mmol / L.

[0098] According to a particularly preferred embodiment of the present invention, the pH value of the tris(hydroxymethyl)aminomethane aqueous solution is 8-12, for example, it can be a specific value such as 8, 9, 10, 11, 12, or a range between the two, preferably 8-9. In the present invention, the pH value of the tris(hydroxymethyl)aminomethane aqueous solution can be adjusted by an acid-base regulator.

[0099] In this invention, a wide range of acid-base regulators can be selected, as long as they can adjust the pH value. Those skilled in the art can choose according to actual needs. For example, HCl or NaOH can be used as acid-base regulators.

[0100] In this invention, the selection range for the self-deposition conditions is relatively wide; as long as self-deposition can be achieved, it is acceptable. Those skilled in the art can select the appropriate conditions according to actual needs. Preferably, the self-deposition conditions include: a self-deposition temperature of 12-30℃ and a self-deposition time of 2-12 hours. For example, the self-deposition time can be a specific value or a range between 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 hours. Adopting self-deposition conditions within the above range allows the prepared upper and lower surface layers to have more suitable thicknesses, better maintain the temperature difference, and facilitate water vapor migration. It also allows for better integration with the microporous membrane interlayer, further increasing the flux without reducing the antifouling performance of the sandwich membrane.

[0101] According to a particularly preferred embodiment of the present invention, the amount of the self-polymerizing solution and the microporous membrane intermediate layer is such that the mass ratio of the total mass of the upper and lower surface layers to the mass of the microporous membrane intermediate layer is 0.01-0.2:1, for example, it can be a specific ratio or a range between the two such as 0.01:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, etc.

[0102] According to a particularly preferred embodiment of the present invention, step (4) includes: heat-treating the microporous membrane after the intermediate layer is in contact with the self-polymerization solution.

[0103] In this invention, a wide range of heat treatment methods can be selected, as long as heat treatment can be achieved. Those skilled in the art can choose according to actual needs. For example, heat treatment methods include heating with a heating plate, purging with hot air inside a forced-air oven, etc.

[0104] According to a particularly preferred embodiment of the present invention, the heat treatment conditions include: a heat treatment temperature of 40-80°C and a heat treatment time of 2-12 hours. A third aspect of the present invention provides a sandwich membrane prepared by the preparation method described in the second aspect.

[0105] The fourth aspect of the present invention provides an application of the sandwich membrane described in the first or third aspect in the field of water treatment.

[0106] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available. Specifically, polyvinylidene fluoride (PVDF) was purchased from Solvay, with a number-average molecular weight of 700,000 Da; polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was purchased from Solvay, with a number-average molecular weight of 600,000 Da; and polyethyleneimine was purchased from Aladdin, with a number-average molecular weight of 600 Da.

[0107] The Tris buffer solution refers to an aqueous solution of tris(hydroxymethyl)aminomethane, the pH of which is adjusted by HCl.

[0108] Example 1

[0109] (1) Dissolve 10g of polyvinylidene fluoride in 100mL of a mixture of dimethylacetamide and acetone (the weight ratio of dimethylacetamide to acetone is 4:1) and stir at 50℃ for 12h to obtain a spinning solution.

[0110] (2) The spinning solution was poured into a syringe with an inner diameter of 0.51 mm, and aluminum foil was used as the receiving material. The spinning speed was adjusted to 140 rpm. The PVDF base film was obtained by spinning for 6 h under the conditions of an applied voltage of 16 kV, a needle tip to collector distance of 15 cm, and a push speed of 0.5 mL / h.

[0111] (3) The PVDF base film was transferred to a 70 mmol / L Zn(CH3COO)2 ethanol solution and heat-treated at 80 °C for 1 h. Then, it was heated at 120 °C for another 2 h to obtain a ZnO-modified PVDF film.

[0112] (4) The ZnO-modified PVDF membrane was washed with deionized water and then dried in an oven at 60°C for 2 hours to obtain a roughened base membrane (ZnO-PVDF membrane).

[0113] (5) The surface roughened base film was immersed in an ethanol solution of 1 v / v% of 1H,1H,2H,2H perfluorodecyltriethoxysilane for 24 h, and then heat-treated at 80 °C for 2 h to obtain the microporous membrane intermediate layer (FZnO-PVDF membrane).

[0114] (6) Dopamine and polyethyleneimine are dissolved in Tris buffer solution (50 mmol / L, pH=8.5) to obtain a mixed solution with a dopamine concentration of 2 g / L and a polyethyleneimine concentration of 2 g / L. The mixed solution is then subjected to self-polymerization at 25°C under oxygen aeration to obtain a solution.

[0115] (7) Immerse the intermediate layer of the microporous membrane in the solution for 6 hours, then wash it with deionized water and dry it at 60°C for 2 hours to obtain the sandwich membrane S1.

[0116] The thicknesses of the upper surface layer, the microporous membrane intermediate layer (hereinafter referred to as the intermediate layer), and the lower surface layer in S1, the total mass of the upper and lower surface layers to the mass ratio of the intermediate layer, the mass percentage of dopamine residues and polyethyleneimine residues, and the types and contents of the base membrane, metal oxides, and fluorosilanes are shown in Table 1.

[0117] Example 2

[0118] The preparation steps are the same as in Example 1, except that the metal oxide precursor solution used in step (3) is changed from Zn(CH3COO)2 to Cu(CH3COO)2, and finally the sandwich membrane S2 is obtained.

[0119] The thicknesses of the upper, middle, and lower layers of S2, the ratio of the total mass of the upper and lower layers to the mass of the middle layer, the mass percentage of dopamine residues and polyethyleneimine residues, and the types and contents of the base film, metal oxides, and fluorosilanes are shown in Table 1.

[0120] Example 3

[0121] The preparation steps are the same as in Example 1, except that the concentration of dopamine used in step (6) is 2 g / L and the concentration of polyethyleneimine is 3 g / L, and the sandwich membrane S3 is finally obtained.

[0122] The thicknesses of the upper, middle, and lower layers of S3, the ratio of the total mass of the upper and lower layers to the mass of the middle layer, the mass percentages of dopamine residues and polyethyleneimine residues, and the types and contents of the base film, metal oxides, and fluorosilanes are shown in Table 1.

[0123] Example 4

[0124] The preparation steps are the same as in Example 1, except that the concentration of dopamine used in step (6) is 2 g / L and the concentration of polyethyleneimine is 1 g / L, and the sandwich membrane S4 is finally obtained.

[0125] The thicknesses of the upper, middle, and lower layers of S4, the ratio of the total mass of the upper and lower layers to the mass of the middle layer, the mass percentage of dopamine residues and polyethyleneimine residues, and the types and contents of the base film, metal oxides, and fluorosilanes are shown in Table 1.

[0126] Example 5

[0127] The preparation steps are the same as in Example 1, except that the fluorosilane used in step (5) is changed to 3,3,3-trifluoropropyltriethoxysilane, and finally the sandwich membrane S5 is obtained.

[0128] The thicknesses of the upper, middle, and lower layers of S5, the ratio of the total mass of the upper and lower layers to the mass of the middle layer, the mass percentage of dopamine residues and polyethyleneimine residues, and the types and contents of the base film, metal oxides, and fluorosilanes are shown in Table 1.

[0129] Example 6

[0130] The preparation steps are the same as in Example 1, except that the polymer used in step (1) is changed to polyvinylidene fluoride-hexafluoropropylene, and finally a sandwich membrane S6 is obtained.

[0131] The thicknesses of the upper, middle, and lower layers of S6, the ratio of the total mass of the upper and lower layers to the mass of the middle layer, the mass percentage of dopamine residues and polyethyleneimine residues, and the types and contents of the base film, metal oxides, and fluorosilanes are shown in Table 1.

[0132] Example 7

[0133] The preparation steps are the same as in Example 6, except that the fluorosilane used in step (5) is changed to 1H,1H,2H,2H-perfluorododecyltriethoxysilane, and finally the sandwich membrane S7 is obtained.

[0134] The thicknesses of the upper, middle, and lower layers of S7, the ratio of the total mass of the upper and lower layers to the mass of the middle layer, the mass percentage of dopamine residues and polyethyleneimine residues, and the types and contents of the base film, metal oxides, and fluorosilanes are shown in Table 1.

[0135] Comparative Example 1

[0136] The preparation steps are the same as in Example 1, except that steps (3)-(7) are not performed, and PVDF base film D1 is obtained.

[0137] The thickness of the membrane in D1, as well as the type and content of the base membrane, are shown in Table 1.

[0138] Comparative Example 2

[0139] The preparation steps are the same as in Example 1, except that steps (6) and (7) are not performed, and the microporous membrane intermediate layer D2 (FZnO-PVDF membrane) is obtained.

[0140] The thickness of the membrane in D2, as well as the types and contents of the base membrane, metal oxides, and fluorosilanes, are shown in Table 1.

[0141] Comparative Example 3

[0142] The preparation steps are the same as in Example 7, except that steps (6) and (7) are not performed, and the microporous membrane intermediate layer D3 is obtained.

[0143] The thickness of the D3 film, as well as the types and contents of the base film, metal oxides, and fluorosilanes, are shown in Table 1.

[0144] Comparative Example 4

[0145] The preparation steps are the same as in Example 1, except that steps (3) and (4) are not performed, and the sandwich membrane D4 is obtained.

[0146] The thicknesses of the top, middle, and bottom layers of D4, the ratio of the total mass of the top and bottom layers to the mass of the middle layer, the mass percentages of dopamine residues and polyethyleneimine residues, and the types and contents of the base film and fluorosilanes are shown in Table 1.

[0147] Comparative Example 5

[0148] The preparation steps are the same as in Example 1, except that steps (5)-(7) are not performed, and a roughened base film D5 (ZnO-PVDF film) is obtained.

[0149] Test Example 1

[0150] The surface morphology of D1, D2, and S1 was characterized using scanning electron microscopy, and their surface morphologies are shown below. Figures 2-5 As shown.

[0151] Figure 2 This is a scanning electron microscope (SEM) image of the surface of the PVDF base film D1. From... Figure 2 It can be seen that the PVDF base film has a porous structure.

[0152] Figure 3 This is a scanning electron microscope (SEM) image of the FZnO-PVDF film D2. From... Figure 3 It can be seen that the surface of the FZnO-PVDF membrane has micron-sized rod-shaped, uniformly distributed zinc oxide, forming a fibrous network structure.

[0153] Figure 4 This is a scanning electron microscope (SEM) image of the surface of the sandwich-type membrane S1. From... Figure 4 It can be seen that the sandwich membrane S1, through further hydrophilic modification, changed the original fibrous network structure and had polymer deposition on its surface.

[0154] Figure 5 These are cross-sectional scanning electron microscope (SEM) images and EDS spectra (O and N elements) of the sandwich-type membrane S1. Figure 4 It can be seen that in the sandwich membrane S1, the thickness of the upper and lower surface layers is 4.1 μm, and the thickness of the middle layer is 56.5 μm.

[0155] Test Example 2

[0156] The contact angles of S1-S7 and D1-D5 in air were measured using a Dropmeter A-200 contact angle meter from MAIST Corporation, China. The test method was as follows: water droplet volume was 9 μL, test temperature was 25℃, test time was instantaneous, and test pressure was 1 atmosphere.

[0157] The contact angles of membrane samples S1-S7 and D1-D5 underwater were measured using a Dropmeter A-200 contact angle meter from MAIST (China). The test method involved placing the membrane sample face down in a quartz test cell filled with deionized water. Then, a 9 μL drop of oil was quantitatively dropped onto the membrane surface in an aqueous environment using a U-shaped syringe. The Youngs-Laplace method was used to fit the droplet shape and obtain the contact angle values. The test temperature was 25℃, the test time was instantaneous, and the test pressure was 1 atmosphere.

[0158] Test results are as follows Figure 6 , Figure 7 As shown in Table 2.

[0159] Figure 6 It represents the water contact angle in air for the PVDF-based membrane D1, the FZnO-PVDF membrane D2, and the sandwich membrane S1. Figure 6It can be seen that the surface contact angle of the FZnO-PVDF membrane is significantly larger than that of the PVDF base membrane, indicating that the hydrophobicity of the base membrane is significantly improved under the action of metal oxide and fluorosilane; at the same time, it can also be seen that the surface of the sandwich membrane S1 is hydrophilic.

[0160] Figure 7 These are the water contact angles in air and the contact angles in a mixture of water and ethanol for PVDF-based membrane D1, FZnO-PVDF membrane D2, and ZnO-PVDF membrane D5. Figure 7 It can be seen that the surface contact angle of the FZnO-PVDF film is significantly larger than that of the PVDF base film, indicating that the hydrophobic properties of the base film are significantly improved under the action of metal oxide and fluorosilane.

[0161] Test Example 3

[0162] Membrane distillation (MD) tests were conducted on S1-S7 and D1-D4 to treat a water-oil mixture containing 2.4 g / L hexadecane, 35 g / L NaCl, and 0.24 g / L sodium dodecyl sulfate, and performance was compared. Membrane distillation parameters were set as follows: feed-side temperature 60℃, permeate-side temperature 20℃, and flow rate 0.5 LPM. The mass of the permeate-side solution was recorded using an electronic balance, and the conductivity of the distillate-side water was monitored using a conductivity meter. Membrane flux (J) and salt rejection (SR) were calculated using the following formulas: J = Δm / At, SR = (C f -C p ) / C f ×100%. Where Δm is the permeate-side mass change, A is the effective membrane area, t is the test time, and C is the permeate-side mass change. f C represents the concentration of NaCl in the original solution. p The concentration of NaCl in the permeate is given.

[0163] The test results are shown in Tables 2 and 3.

[0164] Table 1

[0165]

[0166]

[0167] Table 2

[0168]

[0169]

[0170]

[0171] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A sandwich type film, characterized by, The sandwich type film comprises a microporous membrane intermediate layer, an upper surface layer and a lower surface layer; The microporous membrane intermediate layer comprises a base film, a metal oxide and a fluorosilane; The upper surface layer and the lower surface layer each independently comprise structural units from dopamine and structural units from polyethyleneimine; The microporous membrane intermediate layer is a full-slip layer, and the upper surface layer and the lower surface layer are each independently a hydrophilic layer.

2. The sandwich type membrane according to claim 1, wherein, The base film is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyvinylidene fluoride-hexafluoropropylene, more preferably polyvinylidene fluoride and / or polyvinylidene fluoride-hexafluoropropylene; Preferably, the pore size of the base film is 0.1-2 μm; Preferably, the metal oxide is selected from at least one of TiO2, ZnO, CuO, MnO2, ZrO2, Co3O4, SnO2, F3O4, WO3, MoO3, MgO, more preferably ZnO; Preferably, the metal oxide is grown in situ on the base film; Preferably, the fluorosilane is selected from at least one of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1H,1H,2H,2H-perfluorododecyltriethoxysilane, triethyl(trifluoromethyl)silane, 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, triethyl(trifluoromethyl)silane, triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane, trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl)silane, 1H,1H,2H,2H-perfluorooctyltrichlorosilane, 3,3,3-trifluoropropyltriethoxysilane, more preferably at least one of 1H,1H,2H,2H-perfluorodecyltriethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, 1H,1H,2H,2H-perfluorododecyltriethoxysilane; Preferably, the mass ratio of the base film, metal oxide and fluorosilane is 1:0.01-0.05:0.001-0.05; More preferably, the mass ratio of the base film, metal oxide and fluorosilane is 1:0.01-0.02:0.001-0.01; Preferably, the thickness of the microporous membrane intermediate layer is 30-200 μm, more preferably 50-100 μm; Preferably, the air contact angle of the microporous membrane intermediate layer with water is 130-170°, more preferably 160-170°; Preferably, the underwater contact angle of the microporous membrane intermediate layer with oily substances is 2-50°, more preferably 2-15°.

3. The sandwich type membrane according to claim 1 or 2, wherein The number average molecular weight of the polyethyleneimine is 200-20000 Da; Preferably, in the upper surface layer, the content of the structural units from dopamine is 20-80 wt% and the content of the structural units from polyethyleneimine is 20-80 wt% based on the total weight of the upper surface layer; Preferably, the content of the structural unit from dopamine in the lower surface layer is 20-80 wt%, and the content of the structural unit from polyethyleneimine is 20-80 wt%, based on the total weight of the lower surface layer; Preferably, the mass ratio of the total mass of the upper surface layer and the lower surface layer to the mass of the microporous membrane intermediate layer is 0.01-0.2:1; Preferably, the thickness of the upper surface layer is 1-10 μm; Preferably, the thickness of the lower surface layer is 1-10 μm; Preferably, the contact angle of the upper surface layer with water is 30-60°; Preferably, the contact angle of the lower surface layer with water is 30-60°; Preferably, the underwater contact angle of the upper surface layer with oily substances is 100-160°; Preferably, the underwater contact angle of the lower surface layer with oily substances is 100-160°.

4. A preparation method of a sandwich type film, comprising the following steps: (1) hydrothermally reacting a base film with a solution containing a metal to obtain a surface-roughened base film; (2) using a fluorosilane solution to modify the surface-roughened base film to obtain a microporous membrane intermediate layer; (3) using a solution containing dopamine and polyethyleneimine to perform self-polymerization under an oxygen atmosphere to obtain a self-polymerization solution; (4) using the self-polymerization solution to perform self-deposition on the upper and lower surfaces of the microporous membrane intermediate layer to obtain a sandwich type film.

5. The method for producing a sandwich type film according to claim 4, wherein The base film is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyvinylidene fluoride-hexafluoropropylene, preferably polyvinylidene fluoride and / or polyvinylidene fluoride-hexafluoropropylene; Preferably, the pore size of the base film is 0.1-2 μm; Preferably, the metal is selected from at least one of Ti, Zn, Cu, Mn, Zr, Co, Sn, F, W, Mo, Mg, more preferably Zn; Preferably, the concentration of the metal in the solution containing the metal is 10-500 mmol / L; Preferably, the use amount of the base film and the metal solution is such that, in the surface-roughened base film, the mass ratio of the base film to the metal oxide is 1:0.01-0.05, preferably 1:0.01-0.02; Preferably, the hydrothermal reaction conditions include: a reaction temperature of 50-200°C, preferably 50-150°C; and a reaction time of 1-48 h, preferably 12-48 h.

6. The method for producing a sandwich type film according to claim 4 or 5, wherein the fluorosilane is at least one of 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane, 1H, 1H, 2H, 2H-perfluorododecyltriethoxysilane, triethyl(trifluoromethyl)silane, 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, triethyl(trifluoromethyl)silane, triethoxy(1H, 1H, 2H, 2H-nonafluorohexyl)silane, trichloro(1H, 1H, 2H, 2H-tridecafluoro-n-octyl)silane, 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane, 3,3,3-trifluoropropyltriethoxysilane, more preferably at least one of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, 1H, 1H, 2H, 2H-perfluorododecyltriethoxysilane; Preferably, the solvent in the fluorosilane solution is at least one of ethyl acetate, ethanol, n-hexane, acetone, trichloroethylene, isopropyl alcohol, triethanolamine, cyclohexane; Preferably, the concentration of the fluorosilane in the fluorosilane solution is 0.1-10 v / v%; Preferably, the surface-roughened base film and the fluorosilane solution are used in an amount such that the mass ratio of the base film to the fluorosilane in the microporous membrane intermediate layer is 1:0.001-0.05, preferably 1:0.001-0.01; Preferably, the low-surface-energy modification condition comprises a modification temperature of 40-80℃ and a modification time of 5-120 min.

7. The method for producing a sandwich type film according to any one of claims 4 to 6, wherein The number average molecular weight of the polyethyleneimine is 200-20000 Da; Preferably, the concentration of the dopamine in the solution containing dopamine and polyethyleneimine is 0.5-4 g / L; Preferably, the concentration of the polyethyleneimine in the solution containing dopamine and polyethyleneimine is 0.5-4 g / L; Preferably, the mass ratio of the dopamine to the polyethyleneimine in the solution containing dopamine and polyethyleneimine is 1:0.2-2; Preferably, the solvent in the solution containing dopamine and polyethyleneimine is a tris(hydroxymethyl)aminomethane aqueous solution; Preferably, the concentration of the tris(hydroxymethyl)aminomethane in the tris(hydroxymethyl)aminomethane aqueous solution is 10-100 mmol / L; Preferably, the pH value of the tris(hydroxymethyl)aminomethane aqueous solution is 8-12.

8. The method for producing a sandwich type film according to any one of claims 4 to 7, wherein The self-deposition condition comprises a self-deposition temperature of 12-30℃ and a self-deposition time of 2-12 h; Preferably, the self-polymerization solution and the microporous membrane intermediate layer are used in an amount such that the mass ratio of the upper and lower surface layers to the microporous membrane intermediate layer is 0.01-0.2:1; Preferably, step (4) comprises heat treating the microporous membrane intermediate layer after it is contacted with the self-polymerization solution; Preferably, the heat treatment condition comprises a heat treatment temperature of 40-80℃ and a heat treatment time of 2-12 h.

9. The sandwich-type membrane prepared by the preparation method of any one of claims 4-8.

10. Use of the interlayer film according to any one of claims 1 to 3 and 9 in the field of water treatment.

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