Preparation method and application of super-hydrophobic separation membrane

Abstract

The application provides a super-hydrophobic separation membrane and a preparation method and application thereof, and relates to the field of two-dimensional membrane material preparation. The preparation method comprises the following steps: mixing MXene, trimesic aldehyde, p-phenylenediamine, acetic acid and 1,4-dioxane to obtain a mixed solution; stirring the mixed solution to generate a precipitate, and performing centrifugation, cleaning and drying on the precipitate to obtain a COF@MXene composite material; dispersing the COF@MXene composite material in an organic solvent to obtain a dispersion liquid; and performing vacuum filtration on the dispersion liquid on a microfiltration membrane to form a membrane, thereby obtaining the super-hydrophobic separation membrane. The COF molecules with low surface energy are covalently assembled with the multi-layer structure of MXene, the layered structure with precise interlayer spacing of MXene is fixed, rich channels are provided for molecular separation, the problems of easy oxidation and easy expansion and peeling of MXene in the separation process are overcome, and the flux of emulsion separation and the long-term stability of the separation membrane are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional membrane material preparation, specifically to a superhydrophobic separation membrane, its preparation method, and its application. Background Technology

[0002] With the increasing demand for petrochemical products, the resulting large quantities of oily wastewater have become increasingly complex and diverse in composition. Compared to clearly stratified oil-water mixtures, the separation of surfactant-stabilized emulsions is more challenging, making demulsification a major hurdle. Membrane separation technology, due to its high efficiency and ease of operation, has been widely explored for emulsion separation. These membranes, with their abundant micro- and nano-pores, enable selective passage of substances. Therefore, controlling the spatial structure and pore size of the membrane is a key breakthrough for achieving ultra-high-throughput emulsion separation. However, poor separation performance, unstable mechanical properties, and complex preparation processes remain challenges currently facing membrane separation technology.

[0003] MXene, as an emerging two-dimensional transition metal carbide or nitride material, has great potential in membrane construction and molecular separation due to its high electrical conductivity, good mechanical flexibility, excellent physicochemical properties, hydrophilic surface, and advanced thermal stability. For example, patent document CN113461011A discloses a superhydrophobic MXene / carbon quantum dot hybrid hollow microsphere, which is ultrasonically dispersed and then vacuum filtered and deposited on a microporous filter membrane to prepare a porous MXene film, which exhibits good separation efficiency for stable water-in-oil emulsions. In addition, some literature reports the use of MXene in emulsion separation (Long X, Zhao G, Hu J, Jiao F, et al. Cracked-earth-like titanium carbide MXene membranes with abundant hydroxyl groups for oil-in-water emulsion separation. J Colloid Interface Sci 2022, 607(Pt 1), 378-388. Zhang, H.; Wang Z, Shen Y, Li J, et al. Ultrathin 2D Ti3C2Tx MXene membrane for effective separation of oil-in-water emulsions in acidic, alkaline, and salty environment. J Colloid Interface Sci 2020, 561, 861-869.), but all of these works prepared hydrophilic separation membranes, and the emulsion separation performance was not outstanding. In addition, this two-dimensional material has some unresolved bottlenecks in the field of membrane separation, which seriously affect the long-term stability of separation performance. For example, it is easy to oxidize and swell and peel off in aqueous solution, so the flux of emulsion separation and the long-term stability of the separation membrane still need to be improved. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the shortcomings of existing MXene films in terms of throughput for emulsion separation and long-term stability characteristics, so as to provide a superhydrophobic separation membrane with simple preparation method and ultra-high throughput for separating water-in-oil emulsions, as well as its preparation method and application.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a superhydrophobic separation membrane, comprising the following steps:

[0007] (1) Mix MXene, pyromellitic aldehyde, p-phenylenediamine, acetic acid and 1,4-dioxane to obtain a mixed solution;

[0008] (2) Stir the mixed solution to produce a precipitate, and centrifuge, wash and dry the precipitate to obtain the COF@MXene composite material;

[0009] (3) The COF@MXene composite material is dispersed in an organic solvent to obtain a dispersion;

[0010] (4) The dispersion is filtered onto a microfiltration membrane by vacuum filtration to form a membrane, thereby obtaining the superhydrophobic separation membrane.

[0011] Further, in step (1), the weight parts of each raw material are as follows: MXene 80-150 parts, pyromellitic 20-80 parts, p-phenylenediamine 20-80 parts, acetic acid 5-27 parts and 1,4-dioxane 50-250 parts.

[0012] Further, in step (1), the weight parts of each raw material are as follows: MXene 90-150 parts, pyromellitic aldehyde 32-75 parts, p-phenylenediamine 36-80 parts, acetic acid 6-25 parts and 1,4-dioxane 115-250 parts.

[0013] Further, in step (1), the weight parts of each raw material are as follows:

[0014] MXene 90 parts, pyromellitic 32 parts, p-phenylenediamine 36 parts, acetic acid 6 parts, and 1,4-dioxane 115 parts; or

[0015] MXene 125 parts, pyromellitic 48 parts, p-phenylenediamine 50 parts, acetic acid 9 parts, and 1,4-dioxane 185 parts; or

[0016] MXene 145 parts, pyromellitic 58 parts, p-phenylenediamine 63 parts, acetic acid 20 parts, and 1,4-dioxane 180 parts; or

[0017] MXene 150 parts, pyromellitic 75 parts, p-phenylenediamine 80 parts, acetic acid 25 parts and 1,4-dioxane 250 parts.

[0018] Further, in step (1), the MXene selects Ti3C2T. x -MXene.

[0019] Furthermore, in step (2),

[0020] The stirring was carried out at room temperature and pressure for 48–72 hours.

[0021] The cleaning process involves multiple centrifugal washes using 1,4-dioxane and anhydrous ethanol until the supernatant is colorless.

[0022] Furthermore, in step (3),

[0023] The organic solvent includes at least one of dichloromethane, toluene, pentane, hexane, octane, chloroform, methanol, ethanol, isopropanol, ethyl acetate, and acetone.

[0024] The mass-to-volume ratio of the COF@MXene composite material to the organic solvent is 0.05–0.5:10–100 g / mL, preferably 0.2–0.5:30–50 g / mL.

[0025] Further, in step (4), the microfiltration membrane is selected from any one of polyvinylidene fluoride membrane, nylon membrane, polyethersulfone membrane, polytetrafluoroethylene membrane, mixed cellulose ester membrane, and polypropylene membrane.

[0026] Furthermore, in step (4), the thickness of the superhydrophobic separation membrane obtained by filtration is 120–520 μm.

[0027] Secondly, the present invention provides a superhydrophobic separation membrane obtained by the preparation method described above.

[0028] Thirdly, the present invention provides the application of the superhydrophobic separation membrane obtained by the preparation method described above in emulsion separation.

[0029] The technical solution of this invention has the following advantages:

[0030] 1. In the preparation method of the superhydrophobic separation membrane provided by the present invention, the low surface energy COF (Covalent Organic Framework) molecules are covalently assembled with the MXene multilayer structure to fix the MXene with a layered structure with precise interlayer spacing, providing abundant channels for molecular separation. It exhibits excellent separation performance when separating surfactant-stable water-in-oil emulsions, and also overcomes the problems of easy oxidation and easy expansion and peeling of MXene during the separation process, greatly improving the throughput of emulsion separation and the long-term stability of the separation membrane.

[0031] 2. The superhydrophobic separation membrane provided by this invention has a simple preparation method, mild reaction conditions, and does not involve environmentally harmful post-treatment processes such as fluoride.

[0032] 3. The superhydrophobic separation membrane prepared by this invention exhibits outstanding separation performance, achieving ultra-high flux and high efficiency separation of complex water-in-oil emulsions. Numerous fine pores and excellent superhydrophobic properties allow the oil phase after demulsification to rapidly permeate through. The separation membrane designed in this invention achieves an emulsion separation flux of 54280 L / m³ under gravity. 2h, retention rate greater than 99.7%; emulsion separation flux under vacuum filtration is 640508 L / m 2 hbar, retention rate greater than 99.4%. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is an image showing the contact angle (156.2°) between the superhydrophobic separation membrane prepared in Example 1 of this invention and water.

[0035] Figure 2 These are scanning electron microscope images of the Ti3AlC2, MXene, and COF@MXene composite materials in Example 1 of the present invention, wherein (a) is Ti3AlC2, (b) is MXene, and (c) is the COF@MXene composite material;

[0036] Figure 3 This is a schematic diagram of the separation process of the superhydrophobic separation membrane in Embodiment 1 of the present invention, wherein (a) is a schematic diagram of the molecular size distribution of the emulsion before separation, and (b) is a schematic diagram of the molecular size distribution of the filtrate after separation. Detailed Implementation

[0037] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0038] The raw materials used in the examples are from the following sources:

[0039] p-Phenylenediamine, acetic acid, trimethylolpropionate, 1,4-dioxane, anhydrous ethanol, hydrofluoric acid, and Ti3AlC2 were purchased from Shanghai Maclean Biochemical Co., Ltd.; polyvinylidene fluoride membrane was purchased from Haiyan New Oriental Plastics Technology Co., Ltd.

[0040] In the examples, MXene was prepared according to the following method:

[0041] 80g of aluminum carbide (Ti3AlC2) material was added to 200g of hydrofluoric acid solution (mass fraction 40%), and the mixture was stirred in a sealed container at 30℃ for 24 hours. The precipitate was centrifuged and washed with deionized water until the pH of the solution was greater than 6. The precipitate was then vacuum dried to obtain MXene.

[0042] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. All raw materials or instruments used are commercially available conventional products, including but not limited to those used in the embodiments of this application.

[0043] Example 1

[0044] This embodiment provides a method for preparing a superhydrophobic separation membrane, the specific steps of which are as follows:

[0045] (1) Mix 90g of MXene, 32g of pyromellitic aldehyde, 36g of p-phenylenediamine, 6g of acetic acid and 115g of 1,4-dioxane to obtain a mixed solution;

[0046] (2) Stir the mixed solution at room temperature and pressure for 48 hours to produce a precipitate. Centrifuge the precipitate, wash it twice with 1,4-dioxane, and then centrifuge and wash it multiple times with anhydrous ethanol until the supernatant is colorless. Take the precipitate and dry it to obtain the COF@MXene composite material.

[0047] (3) 0.3 g of COF@MXene composite material was ultrasonically dispersed in 30 mL of anhydrous ethanol to obtain a dispersion;

[0048] (4) The dispersion was filtered onto a polyvinylidene fluoride membrane by vacuum filtration to obtain a superhydrophobic separation membrane with a thickness of 290 μm.

[0049] The superhydrophobic separation membrane obtained by the preparation method provided in this embodiment is dark green, and the emulsion separation flux under gravity drive is 54280 L / m³. 2 h, retention rate greater than 99.7%; emulsion separation flux under vacuum filtration is 640508 L / m 2 hbar, rejection rate greater than 99.4%; after every 10 separation cycles, the membrane was washed and dried with anhydrous ethanol, and then the separation cycle was repeated. After repeating this 35 times, there was no significant decrease in flux and rejection rate in the experiment.

[0050] like Figure 1 The image shows a photograph of the COF@MXene superhydrophobic separation membrane prepared in Example 1. Water droplets on the membrane form a perfect sphere, with a water contact angle of 156.2°. Scanned images of the COF@MXene composite material are shown below. Figure 2As shown, COF is uniformly grown on the multilayer structure of MXene. Further investigation was conducted on the demulsification performance of the COF@MXene superhydrophobic separation membrane prepared in Example 1, as shown... Figure 3 As shown, the particle size distribution of the emulsion before separation is 0.1–0.35 μm and 1.3–1.8 μm, while the particle size distribution of the filtrate after separation is basically less than 0.1 μm.

[0051] Example 2

[0052] This embodiment provides a method for preparing a superhydrophobic separation membrane, the specific steps of which are as follows:

[0053] (1) Mix 125g of MXene, 48g of pyromellitic aldehyde, 50g of p-phenylenediamine, 9g of acetic acid and 185g of 1,4-dioxane to obtain a mixed solution;

[0054] (2) Stir the mixed solution at room temperature and pressure for 48 hours to produce a precipitate. Centrifuge the precipitate, wash it twice with 1,4-dioxane, and then centrifuge and wash it multiple times with anhydrous ethanol until the supernatant is colorless. Take the precipitate and dry it to obtain the COF@MXene composite material.

[0055] (3) 0.2 g of COF@MXene composite material was ultrasonically dispersed in 30 mL of anhydrous ethanol to obtain a dispersion;

[0056] (4) The dispersion was filtered onto a polyvinylidene fluoride membrane by vacuum filtration to obtain a superhydrophobic separation membrane with a thickness of 250 μm.

[0057] The superhydrophobic separation membrane obtained by the preparation method provided in this embodiment is dark green, and the emulsion separation flux under gravity is 53302 L / m. 2 h, retention rate greater than 99.6%; emulsion separation flux under vacuum filtration is 600308 L / m 2 hbar, rejection rate greater than 99.7%. After every 10 separation cycles, the membrane was washed and dried with anhydrous ethanol, and then the separation cycle was repeated. After repeating this 35 times, there was no significant decrease in flux and rejection rate in the experiment.

[0058] Example 3

[0059] This embodiment provides a method for preparing a superhydrophobic separation membrane, the specific steps of which are as follows:

[0060] (1) Mix 145g of MXene, 58g of pyromellitic aldehyde, 63g of p-phenylenediamine, 20g of acetic acid and 180g of 1,4-dioxane to obtain a mixed solution;

[0061] (2) Stir the mixed solution at room temperature and pressure for 48 hours to produce a precipitate. Centrifuge the precipitate, wash it twice with 1,4-dioxane, and then centrifuge and wash it multiple times with anhydrous ethanol until the supernatant is colorless. Take the precipitate and dry it to obtain the COF@MXene composite material.

[0062] (3) 0.3 g of COF@MXene composite material was ultrasonically dispersed in 50 mL of anhydrous ethanol to obtain a dispersion;

[0063] (4) The dispersion was filtered onto a polyvinylidene fluoride membrane by vacuum filtration to obtain a superhydrophobic separation membrane with a thickness of 290 μm.

[0064] The superhydrophobic separation membrane obtained by the preparation method provided in this embodiment is dark green, and the emulsion separation flux under gravity drive is 56648 L / m³. 2 h, retention rate greater than 99.8%; emulsion separation flux under vacuum filtration is 626540 L / m 2 hbar, rejection rate greater than 99.4%. After every 10 separation cycles, the membrane was washed and dried with anhydrous ethanol, and then the separation cycle was repeated. After repeating this 35 times, there was no significant decrease in flux and rejection rate in the experiment.

[0065] Example 4

[0066] This embodiment provides a method for preparing a superhydrophobic separation membrane, the specific steps of which are as follows:

[0067] (1) Mix 150g of MXene, 75g of pyromellitic aldehyde, 80g of p-phenylenediamine, 25g of acetic acid and 250g of 1,4-dioxane to obtain a mixed solution;

[0068] (2) Stir the mixed solution at room temperature and pressure for 48 hours to produce a precipitate. Centrifuge the precipitate, wash it twice with 1,4-dioxane, and then centrifuge and wash it multiple times with anhydrous ethanol until the supernatant is colorless. Take the precipitate and dry it to obtain the COF@MXene composite material.

[0069] (3) 0.5 g of COF@MXene composite material was ultrasonically dispersed in 50 mL of anhydrous ethanol to obtain a dispersion;

[0070] (4) The dispersion was filtered onto a polyvinylidene fluoride membrane by vacuum filtration to obtain a superhydrophobic separation membrane with a thickness of 510 μm.

[0071] The superhydrophobic separation membrane obtained by the preparation method provided in this embodiment is dark green, and the emulsion separation flux under gravity drive is 50280 L / m³. 2 h, retention rate greater than 99.7%; emulsion separation flux under vacuum filtration is 580620 L / m 2hbar, rejection rate greater than 99.8%. After every 10 separation cycles, the membrane was washed and dried with anhydrous ethanol, and then the separation cycle was repeated. After repeating this 35 times, there was no significant decrease in flux and rejection rate in the experiment.

[0072] Experimental Example

[0073] This experiment investigates the stability properties of MXene films and COF@MXene films. The specific steps are as follows:

[0074] (1) Preparation of experimental samples:

[0075] ①MXene membrane: Take 0.2g of MXene powder and ultrasonically disperse it evenly in 50mL of deionized water. Use a PVDF membrane as the supporting membrane and obtain an MXene membrane with a thickness of 200μm by vacuum filtration.

[0076] ②COF@MXene membrane: Take 0.2g of the COF@MXene composite material prepared in Example 1 and ultrasonically disperse it uniformly in 50mL of dichloromethane. Using a PVDF membrane as the supporting membrane, a COF@MXene membrane with a thickness of 250μm is obtained by vacuum filtration.

[0077] (2) Soak and observe

[0078] The prepared MXene membrane was gently placed into a container filled with deionized water and allowed to stand for 0 h, 200 h, and 500 h, respectively.

[0079] The prepared MXene membrane was gently placed into a container containing dichloromethane and allowed to stand for 0 h, 200 h, and 500 h, respectively.

[0080] The prepared COF@MXene membrane was gently placed into a container containing dichloromethane and allowed to stand for 0 h, 200 h, and 500 h, respectively.

[0081] The results showed that the MXene membrane expanded and deformed, while the COF@MXene membrane did not show significant changes.

[0082] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a superhydrophobic separation membrane, characterized in that, Includes the following steps: (1) Mix MXene, pyromellitic aldehyde, p-phenylenediamine, acetic acid and 1,4-dioxane to obtain a mixed solution; (2) Stir the mixed solution to produce a precipitate, and centrifuge, wash and dry the precipitate to obtain the COF@MXene composite material; (3) The COF@MXene composite material was dispersed in an organic solvent to obtain a dispersion: (4) The dispersion is vacuum filtered onto a microfiltration membrane to form a membrane, thereby obtaining the superhydrophobic separation membrane. In step (1), the weight parts of each raw material are as follows: MXene 80-150 parts, trimesin 20-80 parts, p-phenylenediamine 20-80 parts, acetic acid 5-27 parts, and 1,4-dioxane 50-250 parts; wherein the MXene is Ti3C2T x -MXene; In step (2), the stirring is carried out at room temperature and pressure for 48 to 72 hours; In step (3), the mass-volume ratio of the COF@MXene composite material to the organic solvent is 0.05~0.5:10~100g / ml.

2. The method for preparing the superhydrophobic separation membrane according to claim 1, characterized in that, In step (1), the raw materials are in the following weight proportions: MXene 90~150 parts, pyromellitic aldehyde 32~75 parts, p-phenylenediamine 36~80 parts, acetic acid 6~25 parts and 1,4-dioxane 115~250 parts.

3. The method for preparing the superhydrophobic separation membrane according to claim 1, characterized in that, In step (3), the mass-to-volume ratio of the COF@MXene composite material to the organic solvent is 0.2~0.5:30~50g / ml.

4. The method for preparing the superhydrophobic separation membrane according to claim 1, characterized in that, In step (1), the weight parts of each raw material are as follows: MXene 90 parts, pyromellitic 32 parts, p-phenylenediamine 36 parts, acetic acid 6 parts, and 1,4-dioxane 115 parts; or MXene 125 parts, pyromellitic 48 parts, p-phenylenediamine 50 parts, acetic acid 9 parts, and 1,4-dioxane 185 parts; or MXene 145 parts, pyromellitic 58 parts, p-phenylenediamine 63 parts, acetic acid 20 parts, and 1,4-dioxane 180 parts; or MXene 150 parts, pyromellitic 75 parts, p-phenylenediamine 80 parts, acetic acid 25 parts and 1,4-dioxane 250 parts.

5. The method for preparing the superhydrophobic separation membrane according to claim 1, characterized in that, In step (2), the washing is performed by multiple centrifugation washing with 1,4-dioxane and anhydrous ethanol until the supernatant is colorless.

6. The method for preparing the superhydrophobic separation membrane according to claim 1, characterized in that, In step (3), the organic solvent includes at least one of dichloromethane, toluene, pentane, hexane, octane, chloroform, methanol, ethanol, isopropanol, ethyl acetate, and acetone.

7. The method for preparing the superhydrophobic separation membrane according to claim 1, characterized in that, In step (4), the microfiltration membrane is selected from any one of polyvinylidene fluoride membrane, nylon membrane, polyethersulfone membrane, polytetrafluoroethylene membrane, mixed cellulose ester membrane, and polypropylene membrane; the thickness of the superhydrophobic separation membrane obtained by vacuum filtration is 120~520 μm.

8. The superhydrophobic separation membrane obtained by the preparation method according to any one of claims 1 to 7.

9. The application of the superhydrophobic separation membrane obtained by the preparation method according to any one of claims 1 to 7 in emulsion separation.

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