COF / MXene composite film and preparation method thereof

Abstract

The invention relates to the technical field of membrane separation, in particular to a COF / MXene composite membrane and a preparation method thereof. The preparation method comprises the following steps: carrying out condensation reaction on a first monomer and a second monomer in a first solvent to obtain a COF-TpBD material; the temperature of the condensation reaction is 15-60 DEG C, and the COF-TpBD material is spherical particles; a dispersion liquid containing the COF-TpBD material and a dispersion liquid containing MXene nanosheets are mixed under the assistance of ultrasonic waves, and then the mixed solution is directionally deposited on the surface of one side of a base membrane through vacuum filtration, so that a COF / MXene composite membrane is obtained; the mass ratio of the MXene nanosheet to the COF-TpBD material is (0.5 to 10) to 1. According to the COF / MXene composite membrane and the preparation method thereof, the anti-pollution performance of the composite membrane can be improved.

Description

Technical Field

[0001] This application relates to the field of membrane separation technology, and specifically relates to a COF / MXene composite membrane and a preparation method thereof. Background Art

[0002] At present, oil-containing wastewater generated from food production, metallurgy, petroleum and petrochemical industries, natural gas exploitation, and maritime transportation has caused serious harm to organisms and the environment. Therefore, there is an urgent need for an effective water purification technology to treat oil-containing wastewater.

[0003] Membrane separation technology has the advantages of low energy consumption, environmental protection, high separation efficiency, and reliable equipment performance. However, the problem of membrane fouling limits the application of membrane separation technology in the treatment of oil-containing wastewater. Summary of the Invention

[0004] This application provides a COF / MXene composite membrane and a preparation method thereof, which can improve the anti-fouling performance of the composite membrane.

[0005] In a first aspect, this application provides a preparation method of a COF / MXene composite membrane. The preparation method includes: performing a condensation reaction on a first monomer and a second monomer in a first solvent to obtain a COF-TpBD material; the temperature of the condensation reaction is 15 - 60 °C, and the COF-TpBD material is spherical particles; after mixing a dispersion liquid containing the COF-TpBD material and a dispersion liquid containing MXene nanosheets under ultrasonic assistance, subjecting the mixed solution to vacuum filtration to deposit it directionally on one surface of a substrate membrane to obtain a COF / MXene composite membrane; the mass ratio of MXene nanosheets to the COF-TpBD material is (0.5 - 10):1.

[0006] In some embodiments, the first solvent includes one or more of ethanol, methanol, acetonitrile, and acetic acid.

[0007] In some embodiments, the time of the condensation reaction is 30 - 60 min.

[0008] In some embodiments, the mass ratio of the first monomer to the second monomer is 1:(2 - 4).

[0009] In some embodiments, the first monomer includes 1,3,5-triformylphloroglucinol or 1,3,5-tris(4-aminophenyl)benzene.

[0010] In some embodiments, the second monomer includes benzidine or 2,5-divinylterephthalaldehyde.

[0011] In some embodiments, the step of condensing the first monomer and the second monomer in the first solvent includes: centrifuging the reaction solution containing the COF-TpBD material obtained, and washing the precipitate after centrifugation with the first solvent to obtain a first mixture; the rotation speed of the centrifugation is 8000 - 10000 rpm, and the time of the centrifugation is 5 - 10 min.

[0012] In some embodiments, the step of condensing the first monomer and the second monomer in the first solvent further includes: mixing the first mixture with a second solvent and then performing a first reflux treatment to remove the unreacted first monomer and second monomer in the first mixture to obtain a second mixture; mixing the second mixture with the first solvent and performing a second reflux treatment to remove the residual second solvent in the second mixture to obtain a third mixture.

[0013] In some embodiments, the time of the first reflux treatment is 3 - 5 h, and the temperature of the first reflux treatment is 150 - 200 °C.

[0014] In some embodiments, the time of the second reflux treatment is 1.5 - 2.5 h, and the temperature of the second reflux treatment is 80 - 100 °C.

[0015] In some embodiments, the second solvent includes N,N-dimethylformamide or tetrahydrofuran.

[0016] In some embodiments, the MXene nanosheets are prepared by a wet chemical etching method with an HCl-LiF system.

[0017] In some embodiments, the preparation method further includes: cleaning the COF / MXene composite membrane obtained by vacuum filtration.

[0018] In a second aspect, the present application provides a COF / MXene composite membrane, which is prepared by the preparation method of the first aspect of the present application; the COF / MXene composite membrane includes a base membrane, and a COF-TpBD material and MXene nanosheets located on one surface of the base membrane, the COF-TpBD material is spherical particles, and the mass ratio of the MXene nanosheets to the COF-TpBD material is (0.5 - 10):1.

[0019] In some embodiments, the MXene nanosheets are monolayer MXene nanosheets.

[0020] In some embodiments, the base membrane includes any one of a polyvinylidene fluoride membrane, a polyethersulfone membrane, a polysulfone membrane, and a polyethylene membrane.

[0021] In some embodiments, the average particle size of the COF-TpBD material is 100 - 200 nm.

[0022] In some embodiments, the MXene nanosheets include Ti3C2T x .

[0023] In some embodiments, the lateral size of the MXene nanosheets is 0.8 - 1.5 μm, and the thickness of the MXene nanosheets is 1 - 2 nm.

[0024] In the embodiments of the present application, the first monomer and the second monomer are prepared into a spherical COF-TpBD material through a condensation reaction at a temperature of 15 - 60 °C, and the MXene nanosheets and the COF-TpBD material are in a mass ratio of (0.5 - 10):1. The mixed solution is directionally deposited on one surface of the base film by vacuum filtration to obtain a COF / MXene composite film. The COF-TpBD material can increase the interlayer channels of the MXene nanosheets, endow the composite film with excellent permeability, reduce the problem of irreversible membrane fouling, and the surface of the COF / MXene composite film has superhydrophobic and superoleophobic properties, thereby improving the anti-fouling performance of the COF / MXene composite film. Description of the Drawings

[0025] By reading the following detailed description of the preferred embodiments, 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 be a limitation of the present application.

[0026] Figure 1 It is a scanning electron microscope (SEM) image of the COF-TpBD material provided by some embodiments of the present application; Figure 2 It is a Fourier transform infrared spectroscopy (FTIR) image of the COF-TpBD material provided by some embodiments of the present application; Figure 3 It is an X-ray diffraction (XRD) image of the COF-TpBD material provided by some embodiments of the present application; Figure 4 It is an X-ray diffraction (XRD) image of the MXene nanosheets provided by some embodiments of the present application; Figure 5 It is a scanning electron microscope (SEM) image of the surface of the COF / MXene composite film of Example 3; Figure 6 It is a scanning electron microscope (SEM) image of the cross-section of the COF / MXene composite film of Example 3; Figure 7 It is a scanning electron microscope (SEM) image of the surface of the MXene composite film of Comparative Example 1. Detailed Embodiments

[0027] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present application.

[0028] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application pertains; the terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "comprising" and "having" and any variations thereof in the specification and claims of the present application and the above description of the drawings are intended to cover non-exclusive inclusion.

[0029] Reference to "embodiments" in the present application means that a particular feature, structure, or characteristic described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears at various places in the specification and 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 in the present application can be combined with other embodiments.

[0030] In the description of the embodiments of the present 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 three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0031] In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two).

[0032] Unless otherwise specified, the test temperature of each parameter mentioned in the present application is 25 °C.

[0033] MXene has a large specific surface area, conductivity similar to that of metals, high mechanical properties, and uniform interlayer nanochannels, which can significantly improve the separation performance of the membrane. The hydrophilic groups (such as -OH, =O, -F) on its surface can also enhance the anti-fouling ability of the membrane. Therefore, MXene is widely used in the preparation of two-dimensional layered separation membranes. However, the complex transport path and compact interlayer structure of MXene increase the resistance of water molecules to pass through the nanochannels. The strong adsorption of the interface to MXene will cause irreversible membrane fouling, and long-term filtration will lead to swelling of the interlayer spacing and accumulation of pollutants, resulting in membrane fouling and affecting the stable operation of the MXene composite membrane.

[0034] Covalent organic frameworks (COF materials), as a class of crystalline porous polymer materials, are composed of monomers connected by strong and stable covalent bonds. They are characterized by a highly ordered structure, forming a porous topological structure with a large specific surface area, uniform channels, adjustable frameworks, excellent thermal stability and chemical stability. Therefore, they can be widely used in fields such as water treatment, gas separation, catalysts, energy storage, proton transport in batteries and biomedicine.

[0035] COF materials can be introduced into MXene membranes as intercalating agents to expand the interlayer nanochannels of MXene. However, the two-dimensional COF nanosheets added to MXene composite membranes are usually randomly distributed, which limits the expansion of interlayer nanochannels. And the preparation method of COF nanosheets generally uses the solvothermal method, which requires relatively harsh reaction conditions. The reaction is a reversible reaction, and the dynamic reaction process is affected by various factors, such as reaction time, temperature, pressure, pH value, solvent, catalyst, monomer concentration, etc.

[0036] In view of this, the present application provides a COF / MXene composite membrane and its preparation method, which can improve the anti-pollution performance of the composite membrane.

[0037] In the first aspect, the present application provides a preparation method of a COF / MXene composite membrane. The preparation method includes: carrying out a condensation reaction on a first monomer and a second monomer in a first solvent to obtain a COF-TpBD material; the temperature of the condensation reaction is 15-60 °C, and the COF-TpBD material is spherical particles; after mixing the dispersion liquid containing the COF-TpBD material and the dispersion liquid containing MXene nanosheets under ultrasonic assistance, the mixed solution is directionally deposited on one surface of a base membrane by vacuum filtration to obtain a COF / MXene composite membrane; the mass ratio of MXene nanosheets to the COF-TpBD material is (0.5-10):1.

[0038] Figure 1 is the scanning electron microscope (SEM) image of the COF-TpBD material provided by some embodiments of the present application. From Figure 1 it can be seen that the COF-TpBD material in the embodiments of the present application has a three-dimensional spherical structure.

[0039] In the embodiments of the present application, the first monomer and the second monomer are prepared into spherical COF-TpBD materials through a condensation reaction at a temperature of 15-60 °C, and MXene nanosheets and COF-TpBD materials are in a mass ratio of (0.5-10):1. The mixed solution is directionally deposited on one surface of the base film by vacuum filtration to obtain a COF / MXene composite film. The COF-TpBD material can increase the interlayer channels of the MXene nanosheets, endow the composite film with excellent permeability, reduce the problem of irreversible membrane fouling, and the surface of the COF / MXene composite film has superhydrophobic and superoleophobic properties, thereby improving the anti-fouling performance of the COF / MXene composite film.

[0040] In addition, the preparation method of the COF / MXene composite film in the present application has a simple process, and the obtained COF / MXene composite film can be applied to the wastewater treatment process for a long time.

[0041] In some embodiments, the mass ratio of the MXene nanosheets to the COF-TpBD material can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0042] When the mass ratio of the MXene nanosheets to the COF-TpBD material is within the above range, the MXene nanosheets and the COF-TpBD material can cooperate with each other, increasing the surface roughness of the COF / MXene composite film. While further reducing the problem of irreversible membrane fouling, the COF / MXene composite film can also have good separation performance.

[0043] In some embodiments, the first solvent may include one or more of ethanol, methanol, acetonitrile, and acetic acid.

[0044] In some embodiments, the first solvent is ethanol. As a typical organic solvent, ethanol has a relatively low price. It can remove the unreacted first monomer and second monomer in the condensation reaction, improve the purity of the COF-TpBD material, displace the aqueous solution in the first mixed solution, facilitate drying and collection of the material. Ethanol has a low boiling point, which is convenient for reflux treatment and can also be used to displace the second solvent in the second mixed solution later.

[0045] In some embodiments, the time of the condensation reaction can be 30-60 min, for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or the range composed of any two of the above values. When the time of the condensation reaction is within the above range, both the first monomer and the second monomer can react sufficiently and the reaction yield can be improved.

[0046] In some embodiments, the mass ratio of the first monomer to the second monomer can be 1:(2 - 4), for example, it can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, or the range composed of any two of the above values. This can enable the reaction to proceed more fully.

[0047] In some embodiments, the first monomer can include 1,3,5-triformylphloroglucinol or 1,3,5-tris(4-aminophenyl)benzene.

[0048] In some embodiments, the second monomer can include benzidine or 2,5-divinylterephthalaldehyde.

[0049] In some embodiments, the first monomer is 1,3,5-triformylphloroglucinol and the second monomer is benzidine.

[0050] In some embodiments, the step of carrying out the condensation reaction of the first monomer and the second monomer in the first solvent may include: centrifuging the reaction solution containing the COF-TpBD material obtained, and washing the precipitate after centrifugation with the first solvent to obtain a first mixed solution.

[0051] In some embodiments, the rotation speed of the centrifugation can be 8000 - 10000 rpm, and the time of the centrifugation can be 5 - 10 min.

[0052] By adjusting the rotation speed and time of the centrifugation within the above ranges, unreacted first monomer and second monomer can be separated, further improving the separation efficiency of the COF-TpBD material in the reaction solution of the COF-TpBD material.

[0053] In some embodiments, the step of carrying out the condensation reaction of the first monomer and the second monomer in the first solvent may further include: mixing the first mixed solution with a second solvent and then carrying out a first reflux treatment to remove the unreacted first monomer and second monomer in the first mixed solution to obtain a second mixed solution; Mixing the second mixed solution with the first solvent and carrying out a second reflux treatment to remove the residual second solvent in the second mixed solution to obtain a third mixed solution.

[0054] In some embodiments, the time of the first reflux treatment can be 3 - 5 h, and the temperature of the first reflux treatment can be 150 - 200 °C.

[0055] In some embodiments, the time of the second reflux treatment can be 1.5 - 2.5 h, and the temperature of the second reflux treatment can be 80 - 100 °C.

[0056] It should be noted that the temperature of the first reflux treatment only needs to be greater than the boiling point of the second solvent, and similarly, the temperature of the second reflux treatment only needs to be greater than the boiling point of the first solvent.

[0057] In some embodiments, the second solvent includes N,N-dimethylformamide or tetrahydrofuran.

[0058] In some embodiments, the MXene nanosheets can be prepared by a wet chemical etching method using an HCl-LiF system.

[0059] By wet chemical etching of the MAX phase using an HCl-LiF system, monolayer MXene nanosheets can be obtained.

[0060] In some embodiments, in the HCl-LiF system, the molar concentration of hydrochloric acid is 9-11 mol / L, the mass content of LiF is 0.02-0.05 g / mL, and the mass content of MAX powder is 0.02-0.04 g / mL.

[0061] MAX powder refers to a natural layered carbonitride inorganic non-metallic material composed of three elements. MAX powder is a type of nano-layered transition metal compound with a hexagonal lattice structure, and its molecular formula is M n+1 AX n , (where M is generally a pre-transition group metal, A is mainly a group 13-15 main group element, X is carbon or / and nitrogen, and n generally takes values from 1 to 3). MAX powder has a unique crystal structure with alternating stacking of MX sheets and A sheets.

[0062] In some embodiments, the steps of wet chemical etching of MAX powder using an HCl-LiF system include: adding MAX powder to a LiF / HCl mixed solution, continuously stirring at 30°C - 40°C for 30 - 40 h to completely etch the "Al" layer. Adding pure water for centrifugal washing until the pH value of the supernatant is about 6. After centrifugation, taking the precipitate, dispersing it in deionized water, and ultrasonically treating it for 3 - 5 h under a nitrogen atmosphere, and then centrifuging to collect the supernatant, which is the MXene nanosheets.

[0063] In some embodiments, the MXene nanosheets can include Ti3C2T x .

[0064] In some embodiments, the lateral size of the MXene nanosheets can be 0.8 - 1.5 μm, and the thickness of the MXene nanosheets can be 1 - 2 nm.

[0065] The size of the MXene nanosheets can be measured by atomic force microscopy.

[0066] In some embodiments, the preparation method may further include: pre-treating the substrate film before vacuum filtration, and the pre-treatment includes ultrasonic treatment. The pre-treatment can remove impurities on the surface of the substrate film, thereby increasing the binding force between the MXene nanosheets and the substrate film, and increasing the binding force between the COF-TpBD material and the substrate film.

[0067] Exemplarily, the ultrasonication can include putting the base film into deionized water for ultrasonication.

[0068] In some embodiments, the preparation method may further include: cleaning the COF / MXene composite film obtained by vacuum filtration. Exemplarily, deionized water can be used to perform filtration treatment on the COF / MXene composite film.

[0069] Performing filtration on the COF / MXene composite film with deionized water can strengthen the intercalation structure of the composite film and obtain a COF / MXene composite film with a stable structure.

[0070] In some embodiments, the pressure of the filtration treatment can be 0.5 - 1 bar, and the time of the filtration treatment can be 5 - 10 min.

[0071] In a second aspect, the present application provides a COF / MXene composite film, which is prepared by the preparation method of the first aspect of the present application; the COF / MXene composite film includes a base film, and a COF-TpBD material and MXene nanosheets located on one surface of the base film. The COF-TpBD material is spherical particles, and the mass ratio of the MXene nanosheets to the COF-TpBD material is (0.5 - 10):1.

[0072] The COF-TpBD material is located between the layers of the MXene nanosheets, which can expand the interlayer nanochannels of the MXene nanosheets and improve the permeability, anti-pollution performance and stability of the composite film.

[0073] In some embodiments, the water contact angle of the COF / MXene composite film is greater than 150°, the underwater oil contact angle of the COF / MXene composite film is greater than 150°, and the oil-water contact angle of the COF / MXene composite film is greater than 150°. Thus, the COF / MXene composite film can have excellent anti-pollution performance.

[0074] The water contact angle can be measured in the following way: Cut the composite film into a 1 cm × 1 cm square, paste it face-up on a glass slide and then place it on a contact angle meter. Use a 5 μL probe to drop deionized water onto the film surface, measure its water contact angle, and then analyze it with OneAttension software. Measure 5 times and take the average value.

[0075] The underwater oil contact angle can be measured in the following way: Cut the composite film into a 1 cm × 1 cm square, paste it face-up on a glass slide and place it in a glass container filled with deionized water, then place it on a contact angle meter. Use a 5 μL probe to drop the oil phase onto the film surface, measure its underwater oil contact angle, and then analyze it with OneAttension software. Measure 5 times and take the average value.

[0076] The underwater contact angle of the oil can be measured as follows: The COF / MXene composite membrane is completely immersed in a n - heptane solution with a density of 0.71 g / mL. The contact angle meter is set to the manual photography mode. 1 mL of pure water is aspirated with a micro - syringe and vertically titrated above the surface of the composite membrane. The non - deformed contact angle value is selected, and multiple groups of experiments are carried out and the average value is calculated.

[0077] The COF / MXene composite membrane of the embodiments of the present application exhibits both hydrophobic and oleophobic characteristics. The reason may be that the surface of the COF / MXene composite membrane has a concave - convex structure, which enables the membrane surface to always preferentially capture the first - contacted liquid and form a liquid column in the depression in the wet state. The metastable liquid column can resist subsequent liquid droplets. For example, after the COF / MXene composite membrane is immersed underwater, it first captures water at the concave - convex structure and forms a metastable water column to resist oil - phase droplets. Similarly, after the COF / MXene composite membrane is immersed under oil, it first captures oil at the concave - convex structure and forms a metastable oil column to resist water - phase droplets.

[0078] In some embodiments, the surface roughness (Ra) of the COF / MXene composite membrane is 70 - 90 nm.

[0079] The COF - MXene intercalation and blending constructs a micro - nano - level rough structure, making the surface of the composite membrane exhibit hydrophobic properties.

[0080] In some embodiments, the deposition amount of the COF - TpBD material and the MXene nanosheets on the surface of the base membrane can be 0.05 - 0.15 mg / cm 2 . In the embodiments of the present application, the deposition amount of the COF - TpBD material and the MXene nanosheets on the surface of the base membrane refers to the total mass of the COF - TpBD material and the MXene nanosheets per unit area.

[0081] In some embodiments, the MXene nanosheets are monolayer MXene nanosheets.

[0082] By combining spherical COF - TpBD materials with monolayer MXene nanosheets, the COF - TpBD materials can be located between the layers of the monolayer MXene nanosheets, which can expand the interlayer nano - channels of the monolayer MXene nanosheets and further improve the permeability, anti - fouling performance and stability of the composite membrane.

[0083] In some embodiments, the average particle size of the COF - TpBD material can be 100 - 200 nm.

[0084] This can enable the COF - TpBD material to have a large specific surface area, thereby increasing the contact area with the liquid and further improving the permeability of the composite membrane.

[0085] In some embodiments, the MXene nanosheets include Ti3C2T x .

[0086] In some embodiments, the lateral size of the MXene nanosheets is 0.8 - 1.5 μm, and the thickness of the MXene nanosheets is 1 - 2 nm. This can endow the MXene nanosheets with a large specific surface area. The lateral size of the MXene nanosheets refers to the size in the length direction or width direction of the MXene nanosheets when they are laid flat on a plane.

[0087] In some embodiments, the base film can include any one of a polyvinylidene fluoride film, a polyethersulfone film, a polysulfone film, and a polyethylene film.

[0088] In some embodiments, the base film is a polyethersulfone film. The polyethersulfone film has advantages such as high chemical and thermal stability and high mechanical strength. In the embodiments of the present application, a hydrophilic polyethersulfone film is selected, and its own characteristics facilitate the formation of a stable structure with MXene.

[0089] The COF / MXene composite film of the embodiments of the present application can be used for wastewater treatment.

[0090] In some embodiments, the wastewater includes wastewater containing an oil-water mixed emulsion.

[0091] Exemplarily, the oil phase in the oil-water mixed emulsion includes one or more of n-hexane, isooctane, gasoline, and soybean oil in n-heptane.

[0092] Example The following examples describe the content of the present application more specifically. These examples are only for illustrative purposes, because various modifications and changes within the scope of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0093] Example 1 Preparation of MXene Nanosheets In a 100 mL Teflon beaker, 1.0 g of LiF was dissolved in 30 mL of an aqueous HCl solution (HCl concentration: 10 mol / L). After stirring at room temperature for 40 min, 1.0 g of MAX powder (Ti3AlC2) was slowly added in portions and the temperature was raised to 35 °C. After stirring for 36 h, centrifugation and washing were performed multiple times until the pH of the supernatant reached approximately 6. The resulting precipitate (accordion-like layered Ti3C2) was dispersed in 100 mL of deionized water and sonicated for 4 h under a N2 atmosphere. The supernatant collected by centrifugation was the solution of monolayer MXene (Ti3C2T x ) nanosheets.

[0094] Preparation of COF-TpBD material 1,3,5-Trimethoxybenzene (Tp, 0.30 mmol) and benzidine (BD, 0.45 mmol) were separately dissolved in 20 mL of ethanol and then mixed in a 100 mL flask. After stirring at 25 °C for 30 min, the light brown suspension was collected, centrifuged at 10000 rpm for 5 min, and then washed with ethanol. The obtained COF-TpBD material was refluxed with DMF for 4 h to remove unreacted residual Tp and BD, and then refluxed with ethanol for 2 h to exchange DMF. The ethanol mixture containing the COF-TpBD material was evacuated overnight at 25 °C to remove ethanol, obtaining the COF-TpBD material.

[0095] Preparation of composite membrane 0.1 mg of MXene nanosheets and 0.0125 mg of COF-TpBD material were added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the interlayer structure of the composite membrane was further strengthened by filtering deionized water, obtaining the COF / MXene composite membrane.

[0096] Example 2 Except for the following differences, the preparation method of the COF / MXene composite membrane was the same as that in Example 1.

[0097] 0.1 mg of MXene nanosheets and 0.025 mg of COF-TpBD material were added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the interlayer structure of the composite membrane was further strengthened by filtering deionized water, obtaining the COF / MXene composite membrane.

[0098] Example 3 Except for the following differences, the preparation method of the COF / MXene composite membrane was the same as that in Example 1.

[0099] 0.1 mg of MXene nanosheets and 0.05 mg of COF-TpBD material were added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the intercalation structure of the composite membrane was further strengthened by filtering deionized water to obtain a COF / MXene composite membrane.

[0100] Example 4 The preparation method of the COF / MXene composite membrane was the same as that of Example 1 except for the following differences.

[0101] 0.1 mg of MXene nanosheets and 0.1 mg of COF-TpBD material were added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the intercalation structure of the composite membrane was further strengthened by filtering deionized water to obtain a COF / MXene composite membrane.

[0102] Example 5 The preparation method of the COF / MXene composite membrane was the same as that of Example 1 except for the following differences.

[0103] 0.1 mg of MXene nanosheets and 0.2 mg of COF-TpBD material were added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the intercalation structure of the composite membrane was further strengthened by filtering deionized water to obtain a COF / MXene composite membrane.

[0104] Example 6 The preparation method of the COF / MXene composite membrane was the same as that of Example 3 except for the following differences.

[0105] Preparation of COF-TpBD Material 1,3,5-triformylphloroglucinol (Tp, 0.30 mmol) and benzidine (BD, 0.45 mmol) were respectively dissolved in 20 mL of ethanol, and then mixed in a 100 mL flask. Under the condition of 15 °C, after stirring for 30 min, a light brown suspension was collected. Under the condition of a rotation speed of 10,000 rpm, it was centrifuged for 5 min, and then washed with ethanol. The obtained COF-TpBD material was refluxed with DMF for 4 h to remove the untreated residual Tp and BD, and then refluxed with ethanol for 2 h to exchange DMF. The ethanol mixed solution containing the COF-TpBD material was evacuated overnight at 25 °C to remove ethanol to obtain the COF-TpBD material.

[0106] Example 7 The preparation method of the COF / MXene composite membrane is the same as that of Example 3, except for the following differences.

[0107] Preparation of COF-TpBD material Dissolve 1,3,5-triformylphloroglucinol (Tp, 0.30 mmol) and benzidine (BD, 0.45 mmol) separately in 20 mL of ethanol, and then mix them in a 100 mL flask. Under the condition of 60 °C, after stirring for 30 min, collect the light brown suspension, centrifuge for 5 min at a speed of 10,000 rpm, and then wash with ethanol. The obtained COF-TpBD material is refluxed with DMF for 4 h to remove the untreated residual Tp and BD, and then refluxed with ethanol for 2 h to exchange DMF. The ethanol mixture containing the COF-TpBD material is evacuated overnight at 25 °C to remove ethanol, and the COF-TpBD material is obtained.

[0108] Example 8 The preparation method of the COF / MXene composite membrane is the same as that of Example 3, except for the following differences.

[0109] Preparation of COF-TpBD material Dissolve 1,3,5-triformylphloroglucinol (Tp, 0.30 mmol) and benzidine (BD, 0.45 mmol) separately in 20 mL of methanol, and then mix them in a 100 mL flask. Under the condition of 25 °C, after stirring for 30 min, collect the light brown suspension, centrifuge for 5 min at a speed of 10,000 rpm, and then wash with methanol. The obtained COF-TpBD material is refluxed with DMF for 4 h to remove the untreated residual Tp and BD, and then refluxed with methanol for 2 h to exchange DMF. The methanol mixture containing the COF-TpBD material is evacuated overnight at 25 °C to remove methanol, and the COF-TpBD material is obtained.

[0110] Example 9 The preparation method of the COF / MXene composite membrane is the same as that of Example 3, except for the following differences.

[0111] Preparation of COF-TpBD material 1,3,5-triformylphloroglucinol (Tp, 0.30 mmol) and benzidine (BD, 0.45 mmol) were separately dissolved in 20 mL of acetic acid, and then mixed in a 100 mL flask. Under the condition of 25 °C, after stirring for 30 min, the light brown suspension was collected, centrifuged at 10,000 rpm for 5 min, and then washed with acetic acid. The obtained COF-TpBD material was refluxed with DMF for 4 h to remove the untreated residual Tp and BD, and then refluxed with acetic acid for 2 h to exchange DMF. The acetic acid mixed solution containing the COF-TpBD material was evacuated overnight at 25 °C to remove acetic acid, and the COF-TpBD material was obtained.

[0112] Comparative Example 1 Except for the following differences, the preparation method of the remaining MXene composite membranes was the same as that in Example 3.

[0113] 0.1 mg of MXene nanosheets was added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the intercalation structure of the composite membrane was further strengthened by filtering deionized water to obtain a COF / MXene composite membrane.

[0114] Comparative Example 2 Except for the following differences, the preparation method of the remaining COF / MXene composite membranes was the same as that in Example 1.

[0115] 0.1 mg of MXene nanosheets and 0.008 mg of the COF-TpBD material were added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the intercalation structure of the composite membrane was further strengthened by filtering deionized water to obtain a COF / MXene composite membrane.

[0116] Comparative Example 3 Except for the following differences, the preparation method of the remaining COF / MXene composite membranes was the same as that in Example 1.

[0117] 0.1 mg of MXene nanosheets and 0.3 mg of the COF-TpBD material were added to deionized water to obtain a mixed solution. The mixed solution was deposited on the surface of a polyethersulfone membrane with an area of 2.01 cm 2 through a vacuum filtration device, and the intercalation structure of the composite membrane was further strengthened by filtering deionized water to obtain a COF / MXene composite membrane.

[0118] Testing Section (1) Morphology testing of COF-TpBD material and COF / MXene composite membrane The morphology of the COF-TpBD material and the COF / MXene composite film was characterized by scanning electron microscopy (SEM).

[0119] (2) Characterization of MXene nanosheets and COF-TpBD materials Fourier transform infrared spectroscopy experiments were used to detect the synthesis of the COF-TpBD material. As Figure 2 can be seen, the infrared spectrum image shows characteristic peaks at 1595 cm -1 (C=C), 1465 cm -1 (Ar(C=C)), and 1259 cm -1 (C-N), indicating the successful preparation of the COF-TpBD material. At the same time, Figure 3 the XRD image shows that the prepared COF-TpBD material has moderate crystallinity, and the first diffraction peak is at a low angle of 3.31°, corresponding to the (100) lattice plane.

[0120] The preparation process of MXene nanosheets was analyzed by XRD patterns. As Figure 4 can be seen, in the spectrum of MAX powder, the peaks of the aluminum layer appear at 2θ = 38.8° for the 104 plane and 2θ = 9.4° for the 002 plane. In the spectrum of Ti3C2T x nanosheets, the 104 peak disappears, and the 002 peak shifts to the low-angle region, indicating that the aluminum layer has been selectively removed, thus demonstrating the successful synthesis of MXene nanosheets by the LiF / HCl etching process.

[0121] (3) Testing of water flux and flux recovery rate Water flux The flux of the membrane was measured by recording the volume of water passing through the membrane within a certain time. A certain volume of pure water passed through a composite membrane with an effective area of 2.01 cm 2 under a pressure of 1 bar.

[0122] Before the formal test, it was compacted with 1 bar of pressure and pure water for 10 min to reduce errors during the test. The water flux (J, in units of L·m -2 ·h -1 ·bar -1 ) is calculated as follows: J = V / (A×t×P) where V (in units of L) is the volume of water collected within t (in units of h), A (in units of m 2 ) is the effective area of the composite membrane, and P (in units of bar) is the pressure.

[0123] Flux recovery rate Using a n - heptane / water emulsion (volume ratio of water to n - heptane is 99:1) as the simulated wastewater, after filtration, it is washed with water respectively. The flux recovery rate (FRR) is calculated by the following formula: FRR = F1 / F0×100% Wherein, F0 and F1 represent the initial water flux and the water flux after cleaning respectively.

[0124] (4)Testing of rejection rate The calculation formula for the rejection rate of the oil - water emulsion is as follows: R =(1 - C1 / C0)×100% Wherein, C0 and C1 represent the concentrations of oil in the feed emulsion and the filtrate sample respectively, and can be quantified by measuring the absorbance of the oil - water emulsion at 507 nm using an ultraviolet spectrophotometer (UV5100, China).

[0125] In the preparation of the oil - water emulsion, the volume ratio of water to the oil phase is 99:1. Oil red is added to make the concentration of the oil - water emulsion in the oil - water emulsion 20 mg / L, and it is stirred at a speed of 3500 rpm for 24 h to mix evenly.

[0126] (5)Testing of cyclic performance The composite membrane is placed in a dead - end filtration device, and pure water / n - heptane oil - water emulsion (volume ratio of water to n - heptane is 99:1) is continuously injected while maintaining a pressure of 1 bar. The weight of the filtrate is measured every 5 min, and it is converted according to the density of pure water (1.0 g / mL) to obtain the flux of pure water or n - heptane oil - water emulsion.

[0127] The test results of Examples 1 - 9 and Comparative Examples 1 - 3 are shown in Table 1.

[0128] Table 1

[0129] From the test results in Table 1, it can be seen that the composite membranes of the examples of this application have excellent permeability and relatively high rejection rates. With the increase of the content of COF - TpBD, the phenomenon of agglomeration of COF - TpBD materials may occur, but it will not have an obvious impact on the stability and screening performance of the COF / MXene composite membrane.

[0130] The test results of the cyclic performance of Example 3 are shown in Table 2.

[0131] Table 2

[0132] As can be seen from Table 2, after 3 hours of cycling, the COF / MXene composite membrane can still maintain excellent oil-water emulsion separation ability. After continuous separation for 3 hours, the flux recovery rate reaches more than 86.12%, and the COF / MXene composite membrane has excellent anti-fouling ability.

[0133] Figure 5 It is a scanning electron microscope (SEM) image of the surface of the COF / MXene composite membrane of Example 3. Figure 6 It is a scanning electron microscope (SEM) image of the cross-section of the COF / MXene composite membrane of Example 3. As Figure 5 and Figure 6 shown, the surface of the COF / MXene composite membrane has protrusions, and the particles of the COF-TpBD material are completely or partially wrapped by MXene nanosheets in the cross-sectional image. Figure 7 It is a scanning electron microscope (SEM) image of the surface of the MXene composite membrane of Comparative Example 1. From Figure 5 and Figure 7 it can be seen that compared with the MXene composite membrane, the surface roughness of the COF / MXene composite membrane is significantly increased.

[0134] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered by the scope of the claims and the description of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a COF / MXene composite film, characterized in that: The preparation method comprises: Carrying out a condensation reaction between a first monomer and a second monomer in a first solvent to obtain a COF-TpBD material; the condensation reaction temperature is 15-60° C., and the COF-TpBD material is spherical particles; After mixing the dispersion containing the COF-TpBD material and the dispersion containing MXene nanosheets under the assistance of ultrasound, the mixed solution is directionally deposited on the surface of one side of the base film by vacuum filtration to obtain a COF / MXene composite film; the mass ratio of the MXene nanosheets to the COF-TpBD material is (0.5-10):

1.

2. The preparation method according to claim 1, characterized in that: The condensation reaction satisfies one or more of the following conditions (1)-(5): (1) The first solvent includes one or more of ethanol, methanol, acetonitrile, and acetic acid; (2) The condensation reaction time is 30-60 minutes; (3) The mass ratio of the first monomer to the second monomer is 1:(2-4); (4) the first monomer includes 1,3,5-triformylphloroglucinol or 1,3,5-tris(4-aminophenyl)benzene; (5) The second monomer includes benzidine or 2,5-divinylterephthalaldehyde.

3. The preparation method according to claim 1, characterized in that: The step of condensing the first monomer and the second monomer in the first solvent comprises: centrifuging the obtained reaction solution containing the COF-TpBD material, and washing the precipitate after centrifugation with the first solvent to obtain a first mixed solution; The rotation speed of the centrifugal treatment is 8000-10000 rpm, and the time of the centrifugal treatment is 5-10 min.

4. The preparation method according to claim 3, characterized in that: The step of subjecting the first monomer and the second monomer to a condensation reaction in the first solvent further includes: subjecting the first mixed solution to a first reflux treatment after mixing the first mixed solution with the second solvent to remove the first monomer and the second monomer that have not reacted completely in the first mixed solution to obtain a second mixed solution; The second mixed liquid is mixed with the first solvent and subjected to a second reflux treatment to remove the second solvent remaining in the second mixed liquid, thereby obtaining a third mixed liquid.

5. The preparation method according to claim 4, characterized in that: The time of the first reflux treatment is 3-5 hours, and the temperature of the first reflux treatment is 150-200° C.; and / or, The second reflux treatment time is 1.5-2.5 hours, and the second reflux treatment temperature is 80-100° C.; and / or, The second solvent includes N,N-dimethylformamide or tetrahydrofuran.

6. The preparation method according to claim 1, characterized in that: The MXene nanosheets are prepared by a HCl-LiF system wet chemical etching method.

7. The preparation method according to claim 1, characterized in that: The preparation method further comprises: cleaning the COF / MXene composite membrane obtained by vacuum filtration.

8. A COF / MXene composite film, characterized in that Prepared by the preparation method according to any one of claims 1 to 7; The COF / MXene composite film includes a base film, and a COF-TpBD material and a MXene nanosheet located on one side surface of the base film, the COF-TpBD material is a spherical particle, and the mass ratio of the MXene nanosheet to the COF-TpBD material is (0.5-10):

1.

9. The COF / MXene composite film according to claim 8, characterized in that The MXene nanosheet is a single-layer MXene nanosheet; and / or, The base film includes any one of a polyvinylidene fluoride film, a polyethersulfone film, a polysulfone film, and a polyethylene film.

10. The COF / MXene composite film according to claim 8, characterized in that The average particle size of the COF-TpBD material is 100-200 nm; and / or, The MXene nanosheets include Ti3C2T x and / or, The lateral size of the MXene nanosheet is 0.8-1.5 μm, and the thickness of the MXene nanosheet is 1-2 nm.

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