Preparation of MOF / MXene composite membrane and application thereof in antibiotic desalination

Abstract

The application relates to a preparation method of a MOF / MXene composite film and application of the MOF / MXene composite film in the field of antibiotic desalination separation films. 2 The MOF nanosheet is prepared by mixing 2-amino terephthalic acid and zinc acetate dihydrate; the MXene is mixed with the ZnBDC-NH2 MOF nanosheet and dispersed to prepare a colloidal suspension; and then the colloidal suspension is uniformly deposited on the surface of a substrate by using a vacuum-assisted self-assembly technology to form a uniform stacking structure. The ZnBDC-NH2 MOF nanosheet composite film prepared by using the MXene as an intercalation layer has neat nanosheet arrangement, excellent mechanical strength and high water flux, so that efficient and rapid separation of antibiotic molecules and salt can be realized.

Description

[0001] This invention belongs to the field of chemical separation technology, and relates to antibiotic desalting separation membranes, and more particularly to a method for preparing a MOF / MXene composite membrane. Background Technology

[0002] In recent years, antibiotics (such as chloramphenicol, erythromycin, and streptomycin) have played a vital role in chemical and pharmaceutical production due to their simple, low-cost, and highly effective antimicrobial mechanisms of action. Antibiotics are generally extracted and purified from fermentation broth by specific microorganisms (fungi and bacteria) growing and multiplying under suitable culture media and environmental conditions. During antibiotic production, a certain amount of inorganic salts must be added to meet the needs of microbial growth and biological activity. Therefore, antibiotic desalting technology has become a crucial step in subsequent processes. Traditional antibiotic desalting methods include solvent extraction, ion exchange, resin adsorption, plate and frame filtration, and electrodialysis. While solvent extraction is a mature method, it is complex, requires sophisticated equipment, and involves the use of large amounts of organic solvents, which can have serious environmental impacts. In contrast, membrane separation technology offers advantages such as high efficiency, energy saving, and ease of operation. It is a green and efficient method for antibiotic desalting, operating under mild conditions without the use of organic reagents, making it more environmentally friendly and showing promising application prospects in the field of antibiotic desalting.

[0003] Metal-organic frameworks (MOFs) are porous materials formed by the self-assembly of metal clusters and organic ligands. Due to their highly tunable pore structure, specific surface area, and specific adsorption capacity for particular molecules, they have become ideal candidates for preparing two-dimensional layered films. However, traditional MOF nanosheets suffer from large pore sizes and irregular stacking, limiting their selectivity and permeability in antibiotic desalination applications. Therefore, effective assembly of these traditional MOF nanosheets is crucial to enhance their film-forming properties, improve stacking regularity, and increase antibiotic desalination efficiency. MXenes, as a novel class of two-dimensional materials, possess excellent conductivity, hydrophilicity, and abundant surface functional groups. These properties can enhance the stability of MOFs in composite materials and improve the separation performance of composite membranes. Summary of the Invention

[0004] To address the limitations of existing technologies and simultaneously improve the water flux and retention rate of membranes, this study designed and fabricated a MOF / MXene composite membrane using ZnBDC-NH2 MOF nanosheets and MXene as assembly units for antibiotic desalination. The aim is to utilize MXene as an intercalation layer to compensate for the defects in the stacking process of ZnBDC-NH2 MOF nanosheets, thereby achieving efficient application in the field of antibiotic desalination.

[0005] To address the aforementioned technical problems, this invention discloses a method for preparing a MOF / MXene composite membrane. First, ZnBDC-NH2 MOF nanosheets with a high aspect ratio are prepared. A suspension is then prepared by utilizing the strong hydrogen bonding between the unreacted carboxyl groups on the ZnBDC-NH2 MOF nanosheets and the hydroxyl groups of MXene. Finally, the composite membrane is prepared via vacuum-assisted self-assembly and naturally dried at room temperature. Its antibiotic desalting and separation performance is then further investigated. The method is implemented according to the following steps:

[0006] Step 1: Preparation of ZnBDC-NH2 MOF nanosheets:

[0007] A specific mass of 2-aminoterephthalic acid was dissolved in a specific volume of a mixed solution of DMF and CH3CN. The solution was then dispersed using ultrasound at room temperature for 20 minutes until the ligand was completely dissolved and uniformly dispersed. This solution was designated as solution A. A specific volume of the DMF and CH3CN mixed solution was used as an intervening solution, designated as solution B. A specific mass of zinc acetate dihydrate was dissolved in a specific volume of a mixed solution of N,N-dimethylformamide (DMF) and acetonitrile (CH3CN). The solution was then dispersed using ultrasound at room temperature for 20 minutes until completely dissolved and uniformly dispersed. This solution was designated as solution C. Solutions A, B, and C were sequentially added to cuvettes and allowed to react statically at room temperature for 24 hours. After the reaction, the solution was centrifuged at 2000 rpm for 10 minutes, washed three times with DMF, and then freeze-dried to obtain a brown powder, which was identified as ZnBDC-NH2 MOF nanosheets.

[0008] Step 2: Preparation of a MOF / MXene composite membrane:

[0009] A certain mass of ZnBDC-NH2 MOF nanosheets and MXene were weighed and mixed in a certain proportion, dissolved in an appropriate solvent to form a uniform and stable suspension. The resulting suspension was deposited on a polymer substrate film by vacuum-assisted self-assembly. After natural drying at room temperature, a ZnBDC-NH2 MOF nanosheet composite film with MXene as intercalation was formed.

[0010] In the method described in this invention, step one involves the zinc acetate dihydrate having a concentration of 2 mg / mL. -1 -8 mg mL -1 The concentration of the 2-aminoterephthalic acid is 2 mg / mL. -1 -8 mg mL -1 .

[0011] The MOF nanosheets include one or more of ZnBDC-NH2, CoBDC-NH2, and CuBDC-NH2, with ZnBDC-NH2 MOF nanosheets being preferred.

[0012] A certain mass of ZnBDC-NH2 MOF nanosheets and MXene were weighed and mixed in a certain proportion. The concentration of the resulting suspension was 8 wt.%-80 wt.%.

[0013] A suspension of MXene and ZnBDC-NH2 MOF nanosheets was stacked on the surface of a porous polymer substrate membrane using a vacuum-assisted self-assembly method. The porous polymer substrate membrane included polytetrafluoroethylene, cellulose diacetate, cellulose triacetate, polyacrylonitrile, polyvinylidene fluoride, polysulfone, polyethersulfone, and cellulose.

[0014] This patent invention relates to the preparation of a MOF / MXene composite membrane and its application in the field of antibiotic desalination separation membranes.

[0015] The operating temperature is room temperature, and the operating pressure is 1-8 bar to achieve antibiotic / salt separation; the antibiotic is one of tetracycline hydrochloride, chloramphenicol, norfloxacin, etc., and the concentration of the antibiotic is 0.01 mg / L. -1 -0.3 mg L -1 The salt is one or more of sodium sulfate, magnesium sulfate, sodium chloride, and potassium chloride, and the salt concentration is 100 mg / L. -1 -5000 mg L -1 .

[0016] Compared with existing technologies, the MOF / MXene composite membrane described in this invention has a uniform and orderly stacked surface, exhibiting certain flexibility and mechanical strength. When the nanosheet composite membrane obtained by this invention is used for antibiotic desalination, it demonstrates better separation performance, capable of retaining larger antibiotics while allowing smaller salt ions to permeate rapidly. It also exhibits high water flux and antibiotic / salt separation factor. Specifically, the antibiotic retention rate is 35.18%-97.59%, the separation factor is 1-37.33, and the water permeation flux is 120.38-294.18 Lm. -2 h -1 bar -1 .

[0017] Figure 1 is a scanning electron microscope image of the surface of film 1 in Example 1. picture;

[0018] Figure 2 is a cross-sectional scanning electron microscope image of membrane 1 from Example 1. picture;

[0019] Figure 3 is a scanning electron microscope image of the surface of film 2 in Example 2. picture;

[0020] Figure 4 is a cross-sectional scanning electron microscope image of membrane 2 from Example 2. picture;

[0021] Figure 5 is a scanning electron microscope image of the surface of film 3 in Example 3. picture;

[0022] Figure 6 is a cross-sectional scanning electron microscope image of membrane 3 in Example 3. picture;

[0023] Figure 7 is a scanning electron microscope image of the surface of film 4 in Example 4. picture;

[0024] Figure 8 is a cross-sectional scanning electron microscope image of membrane 4 from Example 4. picture;

[0025] Figure 9 is a scanning electron microscope image of the surface of film 5 in Example 5. picture;

[0026] Figure 10 is a cross-sectional scanning electron microscope image of film 5 from Example 5. picture;

[0027] Figure 11 shows a scanning electron microscope image of the surface of contrast film 6. picture;

[0028] Figure 12 is a cross-sectional scanning electron microscope image of contrast membrane 6. picture;

[0029] Figure 13 compares the antibiotic desalination performance of membranes 1-6. picture;

[0030] Figure 14 is a schematic diagram of the sieving process for a MOF / MXene composite membrane. picture.

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention.

[0032] Example 1: Preparation of a MOF / MXene composite membrane, the steps are as follows:

[0033] Step 1: Preparation of ZnBDC-NH2 MOF nanosheets: A certain mass of 2-aminoterephthalic acid was dissolved in a certain volume of a mixed solution of DMF and CH3CN. The solution was dispersed ultrasonically at room temperature for 20 minutes until the ligand was completely dissolved and uniformly dispersed. This solution was designated as solution A. A certain volume of the mixed solution of DMF and CH3CN was used as an interval solution, designated as solution B. A certain mass of zinc acetate dihydrate was dissolved in a certain volume of a mixed solution of N,N-dimethylformamide (DMF) and acetonitrile (CH3CN). The solution was dispersed ultrasonically at room temperature for 20 minutes until completely dissolved and uniformly dispersed. This solution was designated as metal solution C. Solutions A, B, and C were sequentially added to cuvettes and allowed to react statically at room temperature for 24 hours. After the reaction, the nanosheets were centrifuged at 2000 rpm for 10 minutes and washed three times with DMF. After freeze-drying, a brown powder was obtained, which is the ZnBDC-NH2 MOF nanosheet.

[0034] Step 2: Preparation of a MOF / MXene composite membrane:

[0035] Five mg of ZnBDC-NH2 MOF nanosheets were weighed and mixed with MXene in a certain proportion to form a homogeneous and stable suspension with a concentration of 10 wt.% in an appropriate solvent. The suspension was deposited onto a polymer substrate membrane using a vacuum-assisted self-assembly method, and after natural drying at room temperature, a MOF / MXene composite membrane was formed, denoted as membrane 1. Figure 1 is a surface scanning electron microscope (SEM) image of membrane 1, and Figure 2 is a cross-sectional SEM image of membrane 1.

[0036] Antibiotic desalination experiments were conducted on membrane 1: a nanofiltration cross-flow apparatus was used, operating at room temperature and 2 bar. A mixed aqueous solution of chloramphenicol and sodium chloride was selected. The chloramphenicol rejection rate of membrane 1 was 80.72%, the sodium chloride rejection rate was 0.27%, the separation factor was 5.17, and the water flux was 121.64 Lm. -2 h -1 bar -1 .

[0037] Example 2: Preparation of a MOF / MXene composite membrane. The steps in Example 2 are basically the same as in Example 1, except that the mass of the ZnBDC-NH2 MOF nanosheets is changed to 10 mg in step 2. The resulting ZnBDC-NH2 MOF nanosheet composite membrane with MXene as the intercalation layer is denoted as membrane 2. Figure 3 is a surface scanning electron microscope (SEM) image of membrane 2, and Figure 4 is a cross-sectional SEM image of membrane 2.

[0038] Antibiotic desalination experiments were conducted on membrane 2: a nanofiltration cross-flow apparatus was used, operating at room temperature and 2 bar. A mixed aqueous solution of chloramphenicol and sodium chloride was selected. The chloramphenicol rejection rate of membrane 2 was 97.33%, the sodium chloride rejection rate was 0.34%, the separation factor was 37.33, and the water flux was 284.16 Lm. -2 h -1 bar -1 .

[0039] Example 3: Preparation of a MOF / MXene composite membrane. The steps in Example 3 are basically the same as in Example 1, except that in step 2, the mass of the ZnBDC-NH2 MOF nanosheets was changed to 15 mg. The resulting ZnBDC-NH2 MOF nanosheet composite membrane with MXene as the intercalation layer is designated as membrane 3. Figure 5 is a surface scanning electron microscope (SEM) image of membrane 3, and Figure 6 is a cross-sectional SEM image of membrane 3.

[0040] Antibiotic desalination experiments were conducted on membrane 3: a nanofiltration cross-flow apparatus was used, operating at room temperature and 2 bar. A mixed aqueous solution of chloramphenicol and sodium chloride was selected. The chloramphenicol rejection rate of membrane 3 was 80.48%, the sodium chloride rejection rate was 2.38%, the separation factor was 5.0, and the water flux was 196.8 L / m³. -2 h-1 bar -1 .

[0041] Example 4: Preparation of a MOF / MXene composite membrane. The steps in Example 4 are basically the same as in Example 1, except that in step 2, the mass of the ZnBDC-NH2 MOF nanosheets was changed to 20 mg. The resulting ZnBDC-NH2 MOF nanosheet composite membrane with MXene as the intercalation layer is designated as membrane 4. Figure 7 is a surface scanning electron microscope (SEM) image of membrane 4, and Figure 8 is a cross-sectional SEM image of membrane 4.

[0042] Antibiotic desalination experiments were conducted on membrane 4: a nanofiltration cross-flow apparatus was used, operating at room temperature and 2 bar. A mixed aqueous solution of chloramphenicol and sodium chloride was selected. The chloramphenicol rejection rate of membrane 4 was 80.28%, the sodium chloride rejection rate was 4.27%, the separation factor was 4.85, and the water flux was 141.32 Lm. -2 h -1 bar -1 .

[0043] Example 5: Preparation of a MOF / MXene composite membrane. The steps in Example 5 are basically the same as in Example 1, except that in step 2, the mass of the ZnBDC-NH2 MOF nanosheets was changed to 25 mg. The resulting ZnBDC-NH2 MOF nanosheet composite membrane with MXene as the intercalation layer is denoted as membrane 5. Figure 9 is a surface scanning electron microscope (SEM) image of membrane 5, and Figure 10 is a cross-sectional SEM image of membrane 5.

[0044] Antibiotic desalination experiments were conducted on membrane 5: a nanofiltration cross-flow apparatus was used, operating at room temperature and 2 bar, and a mixed aqueous solution of chloramphenicol and sodium chloride was selected. Membrane 4 showed a chloramphenicol rejection rate of 78.67% and a sodium chloride rejection rate of 4.97%, a separation factor of 4.46, and a water flux of 140.54 Lm. -2 h -1 bar -1 .

[0045] Comparative Example 1: Preparation of ZnBDC-NH2 MOF nanosheet composite film, the steps are as follows:

[0046] Step 1: Preparation of ZnBDC-NH2 MOF nanosheets: A certain mass of 2-aminoterephthalic acid was dissolved in a certain volume of a mixed solution of DMF and CH3CN. The solution was dispersed ultrasonically at room temperature for 20 minutes until the ligand was completely dissolved and uniformly dispersed. This solution was designated as solution A. A certain volume of the mixed solution of DMF and CH3CN was used as an interval solution, designated as solution B. A certain mass of zinc acetate dihydrate was dissolved in a certain volume of a mixed solution of N,N-dimethylformamide (DMF) and acetonitrile (CH3CN). The solution was dispersed ultrasonically at room temperature for 20 minutes until completely dissolved and uniformly dispersed. This solution was designated as metal solution C. Solutions A, B, and C were sequentially added to cuvettes and allowed to react statically at room temperature for 24 hours. After the reaction, the nanosheets were centrifuged at 2000 rpm for 10 minutes and washed three times with DMF. After freeze-drying, a brown powder was obtained, which is the ZnBDC-NH2 MOF nanosheet.

[0047] Step 2: Preparation of ZnBDC-NH2 MOF composite membrane: 10 mg of ZnBDC-NH2 MOF nanosheets were weighed and formed into a uniform suspension in a suitable solvent. The resulting suspension mixture was stacked on a polymer substrate membrane using a vacuum-assisted self-assembly method. After natural drying at room temperature, a ZnBDC-NH2 MOF nanosheet composite membrane was formed, denoted as membrane 6. Figure 11 is a surface scanning electron microscope (SEM) image of membrane 6, and Figure 12 is a cross-sectional SEM image of membrane 6.

[0048] Antibiotic desalination experiments were conducted on membrane 6: a nanofiltration cross-flow apparatus was used, operating at room temperature and 2 bar, with a mixed aqueous solution of chloramphenicol and sodium chloride. Membrane 6 exhibited a chloramphenicol rejection rate of 62.75%, a sodium chloride rejection rate of 0.3%, a separation factor of 2.68, and a water flux of 137.63 Lm. -2 h -1 bar -1 .

[0049] Comparative examples and comparative figures show that the present invention utilizes a MOF / MXene composite membrane with a dense, defect-free surface. MXene is environmentally friendly, widely available, and inexpensive. It not only acts as a spacer between layers but also possesses abundant hydroxyl groups that form strong hydrogen bonds with the carboxyl groups of ZnBDC-NH2 MOF nanosheets, resulting in orderly stacking of the nanosheets and a more stable layered nanosheet membrane. Compared to pure ZnBDC-NH2 MOF nanosheet stacked membranes, the separation performance is significantly improved. Figure 13 is a comparison of the antibiotic desalination performance of membranes 1-6, and Figure 14 is a sieving mechanism diagram of an MOF / MXene composite membrane used for antibiotic desalination.

[0050] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention, and these modifications are all within the protection scope of the present invention.

Claims

1. A method for preparing a MOF / MXene composite membrane, characterized in that, ZnBDC-NH2 MOF nanosheets with high aspect ratio were prepared and then suspended with MXene. A ZnBDC-NH2 MOF nanosheet composite film with MXene as intercalation was prepared using a vacuum-assisted self-assembly method. This composite film exhibits a tightly packed, orderly stacked surface. The composite film was prepared according to the following steps: Step 1: Preparation of ZnBDC-NH2 MOF nanosheets: A certain mass of 2-aminoterephthalic acid was dissolved in a certain volume of a mixed solution of DMF and CH3CN, and dispersed by ultrasound at room temperature for 20 minutes until the ligand was completely dissolved and uniformly dispersed. This solution was designated as the ligand solution and labeled as solution A. A certain volume of the mixed solution of DMF and CH3CN was used as the spacer solution and labeled as solution B. A certain mass of zinc acetate dihydrate was dissolved in a certain volume of a mixed solution of N,N-dimethylformamide (DMF) and acetonitrile (CH3CN), and dispersed by ultrasound at room temperature for 20 minutes until it was completely dissolved and uniformly dispersed. This solution was designated as the metal solution and labeled as solution C. Solution A, solution B and solution C were added to a cuvette tube in sequence and allowed to react statically at room temperature for 24 hours. After the reaction was completed, the mixture was centrifuged at 2000 rpm for 10 minutes using a high-speed centrifuge, and then washed three times with DMF. After freeze-drying, a brown powder was obtained, which is ZnBDC-NH2 MOF nanosheets. Step 2: Preparation of a MOF / MXene composite membrane: After preparing ZnBDC-NH2 MOF nanosheets with high aspect ratio, MXene and ZnBDC-NH2 MOF nanosheets were mixed in a suitable solvent at a certain ratio to obtain a uniform assembly suspension. The suspension mixture was deposited on a substrate film using a vacuum-assisted self-assembly method and naturally dried at room temperature to form an MXene-intercalated ZnBDC-NH2 MOF nanosheet composite film. The resulting composite film has a tight, regular, two-dimensional ordered layer-by-layer stacked structure.

2. The method for preparing a MOF / MXene composite membrane according to claim 1, characterized in that, The concentration of zinc acetate dihydrate is 2 mg·mL. -1 -10 mg·mL -1 The concentration of the 2-aminoterephthalic acid is 3 mg·mL. -1 -8mg·mL -1 .

3. The method for preparing a MOF / MXene composite membrane according to claim 1, characterized in that, The ZnBDC-NH2 MOF and MXene are mixed in a certain proportion, and the concentration of the suspension after mixing is 8 wt.%-80 wt.%.

4. The method for preparing a MOF / MXene composite membrane according to claim 1, characterized in that, A composite suspension of MXene and ZnBDC-NH2 MOF nanosheets was stacked on the surface of a porous polymer substrate membrane using a vacuum-assisted self-assembly method. The porous polymer substrate membrane includes polytetrafluoroethylene, cellulose diacetate, cellulose triacetate, polyacrylonitrile, polyvinylidene fluoride, polysulfone, polyethersulfone, and cellulose.

5. The application of a MOF / MXene composite membrane prepared by the method according to any one of claims 1-4 in antibiotic desalting and separation.

6. The application according to claim 5, characterized in that, The procedure is performed at room temperature and an operating pressure of 1-8 bar to separate the antibiotic from the salt; the antibiotic is one of tetracycline hydrochloride, chloramphenicol, or norfloxacin, and the concentration of the antibiotic is 0.01 mg·L⁻¹. -1 -0.3 mg·L -1 The salt is one or more of sodium sulfate, magnesium sulfate, sodium chloride, and potassium chloride, and the salt concentration is 100 mg·L⁻¹. -1 -5000 mg·L -1 .

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