Composite film, its preparation method and application

Abstract

This application belongs to the field of membrane separation technology, and particularly relates to a composite membrane, a preparation method thereof, and an application. The preparation method comprises the following steps: soaking a polylactic acid membrane in an alkaline solution, and then placing it in a metal-organic framework reaction solution for in-situ growth to obtain the composite membrane. The preparation method of the composite membrane in this application is simple in operation, and the preparation process is low-carbon and environmentally friendly; the composite membrane obtained by the preparation method has high permeability and excellent oil-water mixture separation performance.

Description

Technical Field

[0001] This application belongs to the technical field of membrane separation, and specifically relates to a composite membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Oily wastewater is an important source of global water pollution, especially in the case of marine oil spills and industrial production processes. Its complex pollutant components pose a serious threat to water quality, biodiversity, and ecosystem functions. In the past decade, significant progress has been made in the basic research and industrial application fields of oily wastewater treatment technology, especially in water environment restoration and waste oil resource recovery. Currently, the treatment methods for oily wastewater mainly include mechanical skimming, flotation, centrifugation, chemical flocculation, electrocoagulation, and membrane separation technology, etc. Membrane separation technology has become a key solution to the problem of oily wastewater due to its efficient separation performance and low energy consumption. Despite significant progress in membrane research and development, there are still many challenges in achieving rapid and large-scale customized applications. In addition, the inherent trade-off between permeability and selectivity remains the main bottleneck restricting the further development of membrane separation technology. The complexity of the membrane structure and transport mechanism makes it a difficult task to simultaneously achieve high permeability and high selectivity.

[0003] Therefore, there is an urgent need for a comprehensive strategy to address these challenges and optimize the separation performance of the membrane.

[0004] Metal-organic frameworks (MOFs) are porous crystalline materials with high surface area, pre-designed pore sizes, and uniformly dispersed active sites, composed of metal cations or metal clusters and organic ligands. Their rich variety, high porosity, and precise pore structure regulation endow them with customization capabilities, which can be used to achieve precise and high-speed molecular screening for membrane separation. However, existing MOF membranes face many problems, such as low catalytic activity and intercrystalline defects that cannot effectively intercept pollutants. In addition, MOFs mainly exist in the form of fine powders or tiny particles, and due to the characteristics of the powders themselves, it is difficult to process them into dense and defect-free membranes through conventional solvent and melt processing techniques.

[0005] Therefore, it is crucial to develop a composite membrane to overcome the above defects. Summary of the Invention

[0006] In view of the above problems, this application provides a composite membrane, a preparation method thereof, and an application thereof. The preparation method of the composite membrane is simple to operate and low-carbon and environmentally friendly in the preparation process; the composite membrane obtained by the preparation method has high permeability and excellent oil-water mixture separation performance.

[0007] In the first aspect, this application provides a preparation method of a composite membrane, and the preparation method includes the following steps:

[0008] The polylactic acid film is soaked in an alkaline solution and then placed in a metal organic framework (MOF) reaction solution for in-situ growth to obtain the composite film.

[0009] In the technical solution of the embodiment of this application, the polylactic acid (PLA) membrane is immersed in an alkaline solution to etch the surface of the PLA membrane, forming a rough surface and active groups, thereby increasing the hydrophilicity of the PLA membrane surface and facilitating the in-situ growth of MOFs. Specifically, the alkaline hydrolysis reaction destroys the ester bonds in the polylactic acid (PLA), forming carboxylate groups and alcohols. This chemical change not only increases the hydrophilicity of the PLA surface but also introduces active carboxyl groups on the surface. These carboxyl groups serve as functional active sites, effectively promoting the anchoring of MOF metal centers and the nucleation of MOF crystals. At the same time, the alkaline treatment also increases the surface roughness and microporous structure, providing a larger surface area and more active sites for uniform MOF coverage and growth.

[0010] The membrane was then placed in a metal-organic framework reaction solution for in situ growth. The advantage of NaOH pretreatment is that it significantly increases the hydrophilicity and activity of the PLA membrane surface. This allows the MOF precursor solution to more easily diffuse and evenly cover the PLA surface, thereby improving the efficiency and uniformity of MOF growth on the PLA surface. Furthermore, the surface carboxylation enhances the interaction between the MOF and the PLA substrate, improving the stability and durability of the MOF structure by forming strong coordination bonds. The roughened surface structure also provides more active sites and a larger specific surface area for the nucleation and growth of MOF crystals, increasing the likelihood of successful MOF growth.

[0011] Therefore, the preparation method of the present application is simple to operate, the preparation process is low-carbon and environmentally friendly, and the obtained composite membrane has a large flux, high permeability, and excellent oil-water separation performance.

[0012] In this application, PLA film can be commercially available or homemade, for example, using 3D printing. PLA is derived from renewable resources and exhibits excellent biodegradability, making it an ideal environmentally friendly material. PLA's low melting point (170-230°C) not only makes the printing process more efficient and energy-efficient, but also ensures high printing precision. Furthermore, PLA's cost is lower than ABS and nylon, offering an excellent price-performance ratio, making it suitable for large-scale production and rapid prototyping.

[0013] In some embodiments, the concentration of the alkaline solution is 5 to 15 g / L, such as 6 g / L, 8 g / L, 10 g / L, 12 g / L, 14 g / L, etc.; and / or;

[0014] The alkali in the alkaline solution includes sodium hydroxide.

[0015] In the technical solution of the embodiment of the present application, the concentration of the alkaline solution is within the above range for the following reasons: A suitable concentration can effectively increase the surface roughness and active groups of the PLA film, thus facilitating the in-situ growth of MOF; if the concentration is too high, the mechanical strength of the PLA film will decrease and even break because the strong alkalinity will hydrolyze the ester bonds of PLA excessively, resulting in the breakage of polymer chains; if the concentration is too low, the change in surface roughness will not be obvious, making it difficult for MOF to grow in-situ successfully on the PLA surface because there are not enough active groups to promote the nucleation and anchoring of MOF.

[0016] In some embodiments, the temperature of the soaking is 50 - 70 °C, such as 52 °C, 54 °C, 56 °C, 58 °C, 60 °C, 62 °C, 64 °C, 66 °C, 68 °C, etc.; and / or;

[0017] The time of the soaking is 20 - 40 min, such as 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min, 38 min, etc.

[0018] In the technical solution of the embodiment of the present application, the temperature of the soaking is within the above range for the following reasons: If the temperature is too high, the PLA film will bend rapidly, making the surface uneven and difficult to form a film; if the temperature is too low, the change in surface roughness will not be obvious, making it difficult for MOF to grow in-situ successfully on the PLA surface because there are not enough active groups to promote the nucleation and anchoring of MOF.

[0019] The time of the soaking is within the above range for the following reasons: If the time is too long, the PLA material will react excessively and its mechanical properties will become weak or even break; if the time is too short, the change in surface roughness will not be obvious, making it difficult for MOF to grow in-situ successfully on the PLA surface because there are not enough active groups to promote the nucleation and anchoring of MOF.

[0020] In some embodiments, after the soaking, an operation of cleaning the polylactic acid film is further included.

[0021] In the present application, the specific method for cleaning the polylactic acid film is not limited and can adopt methods well-known in the art; as an example, the alkaline solution on the surface of the polylactic acid film can be cleaned with water.

[0022] In the present application, the MOF in the metal-organic framework reaction solution can be any one or a combination of at least two of cobalt-based MOF materials, copper-based MOF materials, iron-based MOF materials, or zirconium-based MOF materials; optionally, a cobalt-based MOF material can be selected.

[0023] In some embodiments, the raw materials for preparing the metal-organic framework reaction solution include 2-aminoterephthalic acid, cobalt-based metal salts, and methanol; and / or;

[0024] The mass ratio of the 2-aminoterephthalic acid to the cobalt-based metal salt is 1:(1.5 - 2.5), where 1.5 - 2.5 can be 1.6, 1.8, 2, 2.2, 2.4, etc.

[0025] In the technical solution of the embodiment of the present application, a combination of 2-aminoterephthalic acid, a cobalt-based metal salt, and methanol is used as a raw material for preparing a metal-organic framework reaction solution. The advantages are as follows: This MOF can be synthesized at room temperature with low energy consumption, and is synthesized by a one-pot method with simple operation and can be prepared on a large scale; the formed metal-organic framework has enhanced hydrophilicity due to the presence of amino groups, which is beneficial for oil-water separation.

[0026] Among them, the mass ratio of the 2-aminoterephthalic acid to the cobalt-based metal salt is within the above range because: if the mass ratio of the two is too high, it will cause excessive reaction on the surface of the MOF and excessive growth; if the mass ratio of the two is too low, it will be difficult to form crystals or no MOF will be produced, resulting in the failure of the reaction.

[0027] As an example, the cobalt-based metal salt can be cobalt sulfate heptahydrate.

[0028] As an example, the mass concentration of 2-aminoterephthalic acid in the metal-organic framework reaction solution is 0.1 - 10 g / L, such as 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, etc. It is calculated based on the mass and volume ratio of 2-aminoterephthalic acid to methanol.

[0029] In some embodiments, the method for preparing the metal-organic framework reaction solution includes: mixing 2-aminoterephthalic acid, a cobalt-based metal salt, and methanol, and performing ultrasonic treatment to obtain the metal-organic framework reaction solution; and / or;

[0030] The time for the ultrasonic treatment is 5 - 6 min, such as 5.2, 5.4, 5.6, 5.8, etc.

[0031] In the technical solution of the embodiment of the present application, the time for the ultrasonic treatment is within the above range because: if the time is too long, it will cause waste of energy as the solution is already homogeneous and continuous ultrasonic treatment is unnecessary; if the time is too short, the solution will not be homogeneous, resulting in slow growth of the MOF.

[0032] In some embodiments, the time for in-situ growth is 24 - 50 h, such as 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, etc.

[0033] As an example, the raw material for preparing the metal-organic framework reaction solution further includes a dispersant, and the dispersant includes polyvinylpyrrolidone.

[0034] In some embodiments, the preparation method includes the following steps:

[0035] (1) Mix 2-aminoterephthalic acid and a cobalt-based metal salt with methanol, and perform ultrasonic treatment for 5 - 6 min to obtain a metal-organic framework reaction solution;

[0036] The mass ratio of the 2-aminoterephthalic acid to the cobalt-based metal salt is 1:(1.5 - 2.5);

[0037] Immerse the polylactic acid film in an alkaline solution with a concentration of 5 - 15 g / at 50 - 70 °C for 20 - 30 min, and then wash it;

[0038] (2) Place the polylactic acid film in the metal-organic framework reaction solution and perform in-situ growth for 24 - 50 h to obtain the composite film.

[0039] Exemplarily, the preparation method of the composite film described in this application includes the following steps:

[0040] (1) Prepare a PLA film.

[0041] In the embodiments of this application, by using a melting-type 3D printer to deposit molten PLA filaments layer by layer, precise control of the film structure and size is achieved. The initial design of the PLA film model is completed using Siemens NX software, and the slicing operation is performed by Simplify3D software. Subsequently, the sliced model is imported into the 3D printer, and the molten thermoplastic filaments are extruded onto the printing platform through the FDM technology (Fused Deposition Modeling technology) to form a strong and uniform film composed of two layers of intertwined filaments layer by layer.

[0042] (2) Pretreat the PLA film with an alkali solution.

[0043] In some embodiments of this application, the PLA film is placed in an alkali solution for pretreatment to achieve the effect of chemical etching and increase the surface roughness.

[0044] Specifically, the concentration of the alkali solution is 5 - 15 g / L, and the treatment time with NaOH can be 20 min - 30 min.

[0045] (3) Prepare the composite film by in-situ growth method.

[0046] In some embodiments of this application, the metal-organic framework is grown on the surface of the PLA film by the in-situ growth method, and the composite film is prepared by utilizing the interaction between the metal-organic framework and the carboxyl and hydroxyl groups on the PLA film.

[0047] Second, this application provides a composite film, which is obtained by the preparation method described in the first aspect;

[0048] The composite film includes pores, and the diameter of the circumscribed circle of the pores is 100 - 250 μm, such as 120 μm, 140μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, etc.; and / or;

[0049] The porosity of the composite film is 10% - 30%, such as 15%, 20%, 25%, etc., and optionally 20%.

[0050] As an example, the shape of the pores includes quasi - circular, circular, regular or irregular polygons (triangle, quadrilateral, pentagon, etc.); as an example, the shape of the pores is rectangular, with a length of 100 - 200 μm (such as 120 μm, 140 μm, 160 μm, 180 μm, etc.) and a width of 50 - 150 μm (such as 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, etc.), and optionally a length of 150 μm and a width of 100 μm.

[0051] As an example, the pore size of the composite film is adjusted by adjusting the extrusion ratio of the extrusion head in fused deposition modeling. The extrusion ratio is in the range of 75% - 85%, and pores with a circumscribed circle diameter of 100 - 250 μm are obtained. For example, when the extrusion ratio is 80%, pores with a length of 150 μm and a width of 100 μm can be obtained;

[0052] The porosity of the composite film is adjusted by adjusting the extrusion rate. Specifically, the porosity of the composite film is equal to 1 - the extrusion rate. By controlling the extrusion rate in the range of 70% - 90%, the porosity of the composite film is adjusted in the range of 10% - 80%.

[0053] In a third aspect, the present application provides an application of the composite film described in the second aspect in water purification.

[0054] Compared with the prior art, the present application has at least the following advantages:

[0055] (1) The preparation method of the present application is simple to operate, and the preparation process is low - carbon and environmentally friendly.

[0056] (2) The composite film obtained by the preparation method of the present application has at least high permeability and excellent oil - water mixture separation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to limit the present application. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0058] Figure 1 Process flow chart of the preparation method of the composite film for some embodiments;

[0059] Figure 2 Scanning electron micrograph of the PLA film prepared in Comparative Example 1;

[0060] Figure 3 Scanning electron micrograph of the PLA@MOF composite film prepared in Example 1;

[0061] Figure 4 Water contact angle diagram and underwater oil contact angle diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1;

[0062] Figure 5 Flux test performance diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for n-hexane oil-water mixture;

[0063] Figure 6 Rejection performance diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for n-hexane oil-water mixture;

[0064] Figure 7 Rejection performance and flux test performance result diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for petroleum ether oil-water mixture;

[0065] Figure 8 Rejection performance and flux test performance result diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for n-heptane oil-water mixture;

[0066] Figure 9 Rejection performance and flux test performance result diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for n-hexane water mixture;

[0067] Figure 10 Rejection performance and flux test performance result diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for cyclohexane oil-water mixture;

[0068] Figure 11 Rejection performance and flux test performance result diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for gasoline oil-water mixture;

[0069] Figure 12 Rejection performance and flux test performance result diagram of the PLA@MOF composite film prepared in Example 1 and the PLA film prepared in Comparative Example 1 for soybean oil oil-water mixture. Detailed implementation manners

[0070] The embodiments of the technical solution of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present application more clearly, so they are only examples and cannot be used to limit the protection scope of the present application.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the description of the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0072] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means more than two unless otherwise specifically defined.

[0073] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0074] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "2-10" means that all real numbers between "2-10" have been fully listed herein, and "2-10" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0075] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: the existence of A, the simultaneous existence of A and B, and the existence of B. Additionally, in this document, the character " / " generally represents an "or" relationship between the associated objects before and after.

[0076] Hereinafter, the composite film and its preparation method in this application will be further described in conjunction with specific embodiments; the materials and reagents used in the following embodiments, unless otherwise specified, can all be commercially available products without limitation.

[0077] Example 1

[0078] This embodiment provides a method for preparing a composite film, as shown in the schematic diagram Figure 1 shown, and the preparation method includes the following steps:

[0079] (1) Using a melting-type 3D printer, precise control of the film structure and size is achieved by depositing molten PLA filaments layer by layer. The initial design of the PLA film model is completed using Siemens NX software, and the slicing operation is performed using Simplify3D software. Subsequently, the sliced model is imported into the 3D printer, and the molten thermoplastic filaments are extruded onto the printing platform through the fused deposition modeling technology (FDM technology) to form a strong and uniform film composed of two layers of intertwined filaments layer by layer;

[0080] Specifically, the parameters involved in the fused deposition process are as follows: extruder head temperature 180 °C; printer bed temperature 70 °C; layer height 0.2 mm; printing speed 96 mm / s; flow rate 2.8 mm 3 / s; extruder head diameter 0.4 mm; extruder head extrusion rate 80%, extrusion magnification 70%.

[0081] (2) Immerse the PLA film obtained in step (1) in a 10 g / L NaOH solution at 60 °C for soaking and etching for 30 min to roughen its surface.

[0082] (3) Rinse the NaOH-pretreated PLA film obtained in step (2) with deionized water and set aside for later use.

[0083] (4) Prepare the CoBDC-NH2 reaction solution. The specific method is as follows: Ultrasonically treat a mixed solution composed of 0.9 g of cobalt(II) sulfate heptahydrate, 0.4 g of polyvinylpyrrolidone, 0.43 g of 2-aminoterephthalic acid, and 100 mL of methanol for 5 min.

[0084] (5) Place the deionized water-rinsed NaOH-pretreated PLA film obtained in step (3) into the reaction solution obtained in step (4) to allow in-situ growth of the PLA film for 48 h to obtain the composite film with a porosity of 20%, rectangular holes, and a pore size of 150 μm × 100 μm.

[0085] Example 2

[0086] (1) Use a fused deposition 3D printer to precisely control the membrane structure and size by layer-by-layer deposition of molten PLA filaments. The initial design of the PLA film model is completed using Siemens NX software, and the slicing operation is carried out through Simplify3D software. Subsequently, import the sliced model into the 3D printer, and extrude the molten thermoplastic filaments onto the printing platform through FDM technology to form a strong and uniform film composed of two layers of intertwined filaments layer by layer;

[0087] Specifically, the parameters involved in the fused deposition process are as follows: extruder head temperature 180 °C; printer bed temperature 70 °C; layer height 0.2 mm; printing speed 96 mm / s; flow rate 2.8 mm 3 / s; extruder head diameter 0.4 mm; extruder head extrusion rate 90%, extrusion magnification 70%.

[0088] (2) Immerse the PLA film obtained in step (1) in a 15 g / L NaOH solution at 50 °C for soaking and etching for 20 min to roughen its surface.

[0089] (3) Rinse the NaOH-pretreated PLA film obtained in step (2) with deionized water and set aside for later use.

[0090] (4) Prepare the CoBDC-NH2 reaction solution, and the specific method is as follows: A mixed solution composed of 0.9 g of cobalt(II) sulfate heptahydrate, 0.4 g of polyvinylpyrrolidone, 0.43 g of 2-aminoterephthalic acid, and 100 mL of methanol is ultrasonically treated for 6 min.

[0091] (5) Put the NaOH-pretreated PLA membrane rinsed with deionized water obtained in step (3) into the reaction solution obtained in step (4), and let the PLA membrane grow in-situ for 24 h to obtain the composite membrane. The porosity is 10%, the holes are rectangular, and the pore size is 150 μm × 100 μm.

[0092] Example 3

[0093] (1) Use a melting-type 3D printer to precisely control the membrane structure and size by layer-by-layer depositing molten PLA filaments. The initial design of the PLA membrane model is completed using Siemens NX software, and the slicing operation is performed using Simplify3D software. Subsequently, the sliced model is imported into the 3D printer, and the molten thermoplastic filaments are extruded onto the printing platform through FDM technology, and stacked layer by layer to form a strong and uniform membrane composed of two layers of intertwined filaments;

[0094] Specifically, the parameters involved in the fused deposition process are as follows: extruder head temperature 180 °C; printer bed temperature 70 °C; layer height 0.2 mm; printing speed 96 mm / s; flow rate 2.8 mm3 / s; extruder head diameter 0.4 mm; extruder head extrusion rate 70%, extrusion magnification 70%.

[0095] (2) Immerse the PLA membrane obtained in step (1) in a 5 g / L NaOH solution at 70 °C for etching for 40 min to make its surface rough.

[0096] (3) Rinse the NaOH-pretreated PLA membrane obtained in step (2) with deionized water and set it aside.

[0097] (4) Prepare the CoBDC-NH2 reaction solution, and the specific method is as follows: A mixed solution composed of 0.9 g of cobalt(II) sulfate heptahydrate, 0.4 g of polyvinylpyrrolidone, 0.43 g of 2-aminoterephthalic acid, and 100 mL of methanol is ultrasonically treated for 5.5 min.

[0098] (5) Put the NaOH-pretreated PLA membrane rinsed with deionized water obtained in step (3) into the reaction solution obtained in step (4), and let the PLA membrane grow in-situ for 50 h to obtain the composite membrane. The porosity is 30%, the holes are rectangular, and the pore size is 150 μm × 100 μm.

[0099] Example 4-5

[0100] The difference between Example 4-5 and Example 1 lies in the different concentrations of the NaOH solution, which are 4 g / L (Example 4) and 16 g / L (Example 5) respectively, and the rest are the same as Example 1.

[0101] Example 6-7

[0102] The difference between Example 6-7 and Example 1 lies in the different soaking times in step (2), which are 18 min (Example 6) and 42 min (Example 7) respectively, and the rest are the same as Example 1.

[0103] Example 8-9

[0104] The difference between Example 8-9 and Example 1 lies in the different mass ratios of 2-aminoterephthalic acid and cobalt(II) sulfate heptahydrate in step (4), specifically as follows:

[0105] Example 8: The addition amount of 2-aminoterephthalic acid is 0.43 g, and the addition amount of 0.9 g cobalt(II) sulfate heptahydrate is 0.43 g. The mass ratio of the two is 1:1, and the rest are the same as Example 1.

[0106] Example 9: The addition amount of 2-aminoterephthalic acid is 0.43 g, and the addition amount of 0.9 g cobalt(II) sulfate heptahydrate is 1.29 g. The mass ratio of the two is 1:3, and the rest are the same as Example 1.

[0107] Example 10

[0108] The difference between this example and Example 1 is that methanol is replaced with an equal volume of dimethylformamide, and the rest are the same as Example 1.

[0109] Example 11

[0110] The difference between this example and Example 1 is that 2-aminoterephthalic acid is replaced with an equal mass of terephthalic acid, and the rest are the same as Example 1.

[0111] Example 12

[0112] The difference between this example and Example 1 is that cobalt(II) sulfate heptahydrate is replaced with an equal mass of cobalt nitrate, and the rest are the same as Example 1.

[0113] Comparative Example 1

[0114] The difference between this comparative example and Example 1 is that steps (2), (4) and (5) are not included, and the rest are the same as Example 1.

[0115] Comparative Example 2

[0116] The difference between this comparative example and Example 1 is that it does not include step (2), and the rest are the same as those in Example 1.

[0117] Performance Test

[0118] (1) Surface morphology: Taking Example 1 and Comparative Example 1 as examples, the obtained films were respectively analyzed for their morphology using a scanning electron microscope, and the results are as Figure 2 and Figure 3 shown. Compared with Comparative Example 1, the surface of Example 1 is rough and there are many flaky objects. These flaky objects are the metal-organic framework CoBDC-NH2.

[0119] (2) Wettability: Wettability is reflected by the water contact angle. The measurement of the water contact angle is carried out using a contact angle measuring instrument from Konw Instruments Co., Ltd., USA. The composite film is pasted on a glass slide using double-sided tape, and then the contact angle measuring instrument is used for measurement.

[0120] Taking Example 1 and Comparative Example 1 as examples, the results are as Figure 4 shown. For the PLA film after in-situ growth of MOF (PLA@MOF film) in Example 1, compared with the original PLA film in Comparative Example 1, its water contact angle has decreased significantly, from 106.83° of the original PLA film to 20.53°, which proves that the hydrophilicity of the PLA@MOF film after in-situ growth of MOF has been improved, that is, the composite film obtained by the preparation method described in this application has better hydrophilicity.

[0121] (3) Determination of test pore size:

[0122] The separation performance of the composite film of Example 1 and the PLA film of Comparative Example 1 was tested, and it was applied to the filtration separation of n-hexane oil-water mixture to select the optimal pore size.

[0123] Specifically, composite films with different pore sizes were prepared in a similar method by adjusting the extrusion ratio in step (1);

[0124] The extrusion ratio for a pore size of 150 μm × 100 μm is 80%;

[0125] The extrusion ratio for a pore size of 250 μm × 220 μm is 70%;

[0126] The extrusion ratio for a pore size of 200 μm × 180 μm is 60%.

[0127] The results are as Figure 5 and Figure 6As shown in the figure, the rejection rates of the three different pore-sized PLA membranes in Comparative Example 1 for the n-hexane oil-water mixture were all lower than 3%. In Example 1, the rejection rates of the three different pore-sized PLA@MOF composite membranes were not good for the pore sizes of 250 μm×220 μm and 200 μm×180 μm, and the PLA@MOF composite membrane with a pore size of 150 μm×100 μm showed a separation efficiency of 99.7%.

[0128] Therefore, all subsequent tests were carried out using a pore size of 150 μm×100 μm.

[0129] (4) Rejection performance of the oil-water mixture:

[0130] Integrate the composite membrane into a tubular device with an effective separation area of 1.78 cm². In the experiment, the oil phase and the water phase were mixed at a volume ratio of 1:1. The oil phase was dyed red with Oil Red O, and the water phase was dyed blue with Coomassie Brilliant Blue. Throughout the experiment, the separation was driven only by gravity without using any pressurizing equipment. The separation efficiency was evaluated by the following formula (1):

[0131] Separation efficiency (%) = (1)

[0132] In formula (1), m1 and m0 represent the weight of the permeated oil and the oil before separation, respectively.

[0133] The oil permeation flux J (L·m -2 ·h -1 ) can be calculated according to formula (2):

[0134] (2)

[0135] Wherein, V, A, and T represent the volume of the permeated oil (L), the effective membrane area (m 2 ), and the permeation time (h), respectively.

[0136] Taking the example of the examples, the results are as Figures 7 - 12 shown, and the separation performance tests of six different oil-water mixtures were carried out; the composite membrane showed a separation efficiency higher than 99.2% and a flux of 2.88 × 10 5 L·m -2 ·h -1 for all six different oil-water mixtures.

[0137] Therefore, the composite membrane obtained by the preparation method described in this application has at least high permeability and excellent separation performance for oil-water mixtures.

[0138] The separation efficiencies and fluxes of petroleum ether for each example and comparative example are summarized in Table 1.

[0139] Table 1

[0140]

[0141] Analysis of Comparative Examples 1-2 and Example 1 shows that the performance of Comparative Examples 1-2 is inferior to that of Example 1, proving that the composite membrane obtained by the preparation method described in this application has better performance.

[0142] Analysis of Examples 4-5 and Example 1 shows that the performance of Examples 4-5 is inferior to that of Example 1, proving that the composite membrane prepared with the alkali solution concentration in the range of 5-15 g / L has better performance. Among them, the composite membrane of Example 5 ruptured and the data was not tested.

[0143] Analysis of Examples 6-7 and Example 1 shows that the performance of Examples 6-7 is inferior to that of Example 1, proving that the composite membrane prepared with the alkali solution soaking time in the range of 20-40 min has better performance. Among them, the composite membrane of Example 7 ruptured and the data was not tested.

[0144] Analysis of Examples 8-9 and Example 1 shows that the performance of Examples 8-9 is inferior to that of Example 1, proving that the composite membrane prepared with the mass ratio of 2-aminoterephthalic acid to cobalt metal salt in the range of 1:(1.5-2.5) has better performance.

[0145] Analysis of Examples 10-12 and Example 1 shows that the performance of Examples 10-12 is inferior to that of Example 1, proving that the composite membrane prepared with 2-aminoterephthalic acid, cobalt metal salt and methanol as the raw materials of the metal-organic framework reaction solution has better performance.

[0146] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of this application, not to limit them; although this application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the various examples of this application, and they should all be covered by the scope of the claims and the description of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in each example can be combined in any way. This application is not limited to the specific examples disclosed in the text, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for preparing a composite membrane, characterized in that, The preparation method includes the following steps: After soaking the polylactic acid film in an alkaline solution, it is then placed in a metal-organic framework reaction solution for in-situ growth to obtain the composite film.

2. The preparation method according to claim 1, characterized in that, The concentration of the alkaline solution is 5 - 15 g / L; and / or; The alkali in the alkaline solution includes sodium hydroxide.

3. The preparation method according to claim 1, characterized in that, The temperature of the soaking is 50 - 70 °C; and / or; The time of the soaking is 20 - 40 min.

4. The preparation method according to claim 1, characterized in that, After the soaking, an operation of cleaning the polylactic acid film is further included.

5. The preparation method according to claim 1, characterized in that, The raw materials for preparing the metal-organic framework reaction solution include 2-aminoterephthalic acid, a cobalt-based metal salt, and methanol; and / or; The mass ratio of 2-aminoterephthalic acid to the cobalt-based metal salt is 1:(1.5 - 2.5).

6. The preparation method according to claim 1, characterized in that, The preparation method of the metal-organic framework reaction solution includes: mixing 2-aminoterephthalic acid, a cobalt-based metal salt, and methanol, and performing ultrasonic treatment to obtain the metal-organic framework reaction solution; and / or; The time of the ultrasonic treatment is 5 - 6 min.

7. The preparation method according to claim 1, characterized in that The time of the in-situ growth is 24 - 50 h.

8. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix 2-aminoterephthalic acid and a cobalt-based metal salt with methanol, and perform ultrasonic treatment for 5 - 6 min to obtain a metal-organic framework reaction solution; The mass ratio of 2-aminoterephthalic acid to the cobalt-based metal salt is 1:(1.5 - 2.5); Soak the polylactic acid film in an alkaline solution with a concentration of 5 - 15 g / at 50 - 70 °C for 20 - 40 min, and then clean it; (2) Place the polylactic acid film in the metal-organic framework reaction solution for in-situ growth for 24 - 50 h to obtain the composite film.

9. A composite film, characterized in that, The composite film is obtained by the preparation method according to any one of claims 1 - 8; The composite film includes pores, and the diameter of the circumscribed circle of the pores is 100 - 250 μm; and / or; The porosity of the composite film is 10% - 30%.

10. Use of the composite film according to claim 9 in water purification.

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