Preparation and application of carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane

Abstract

The application discloses a preparation method and application of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film, and relates to the field of antibiotic desalination separation membranes. The ZnBDC MOF nanosheet is prepared by mixing terephthalic acid and zinc acetate dihydrate, and then mixed and dispersed with carboxymethyl cellulose to prepare a composite colloidal suspension; finally, the composite colloidal suspension solution is uniformly deposited on the surface of a support through vacuum-assisted self-assembly. The carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film prepared by the application has regular nanosheet arrangement, high water flux and excellent mechanical strength, and can realize rapid and efficient separation of antibiotic molecules and salt.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical separation, and relates to an antibiotic desalination separation membrane, in particular to a preparation method of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane. BACKGROUND

[0002] In recent years, antibiotics (such as tetracycline hydrochloride, doxorubicin hydrochloride and mycoprotein) play an important role in social security and production due to their efficient, timely, simple, economical and antimicrobial mode of action. Antibiotics are generally prepared by fermentation broth reaction of fungi or bacteria. In order to maintain the stability of the fermentation broth, inorganic salts such as NaCl and Na2SO4 are usually added during the preparation of antibiotics. Therefore, after the fermentation of antibiotics is completed, the antibiotics must be separated from the inorganic salts. The traditional desalination method of antibiotics is exchange resin adsorption. Although this method is mature and stable, it has limitations such as complicated processing, complex equipment, and the need for a large amount of organic solvent during operation, which limits its application. Therefore, there is an urgent need for an efficient and green antibiotic desalination technology. Membrane separation technology has the advantages of simple equipment, continuous operation, etc., and the process does not involve the use of organic reagents, which is more environmentally friendly, and has good application prospects in the field of antibiotic desalination.

[0003] Metal-organic frameworks (MOFs) are constructed by self-assembly of metal clusters and organic linkers, and have become good materials for preparing two-dimensional layered thin films due to their designability in porosity, specific surface area and customized affinity for target molecules, similar to graphene materials, and have attracted more and more attention in the preparation of molecular sieve membranes. The traditional MOF nanosheet has a large pore size and irregular stacking, and the membrane faces the trade-off effect between selectivity and permeability in the application of antibiotic desalination. Therefore, it is necessary to effectively assemble the traditional MOF nanosheet to improve other film-forming properties and stacking regularity, and to improve the efficiency in the process of antibiotic desalination. Carboxymethyl cellulose, as a natural polymer material, has good hydrophilicity and biocompatibility, and can be used to improve the performance of membrane materials, and is expected to be used as an adhesive for MOF nanosheets. SUMMARY

[0004] In view of the prior art, in order to simultaneously improve the water flux and retention rate of the membrane, the present research designs and prepares a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane for antibiotic desalination by using ZnBDC MOF nanosheets and carboxymethyl cellulose as assembly units, aiming to make up for the defects formed in the stacking process of the nanosheets by using the cross-linking effect of ZnBDC MOF nanosheets and carboxymethyl cellulose, so as to realize efficient application in the field of antibiotic desalination.

[0005] To solve the above technical problems, the application discloses a preparation method of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film, first, ZnBDC MOF nanosheets with a high length-width ratio are prepared, a suspension is prepared by cross-linking through hydrogen bonding between unreacted carboxyl groups on the ZnBDC MOF nanosheets and hydroxyl groups of carboxymethyl cellulose, and finally, the composite film is prepared through a vacuum-assisted self-assembly method, dried at room temperature, and further studied for antibiotic desalination and separation performance.

[0006] Step one: preparation of ZnBDC MOF nanosheets

[0007] A certain amount of zinc nitrate dihydrate is dissolved in a mixed solution of DMF and CH3CN, stirred at room temperature for 30 minutes until the ligand is completely dissolved, and recorded as solution A; a certain volume of a mixed solution of DMF and CH3CN is used as a spacer solution, recorded as solution B; terephthalic acid is dissolved in a mixed solution of DMF and CH3CN, stirred at room temperature for 30 minutes until the ligand is completely dissolved, and recorded as solution C. Solution A, solution B and solution C are sequentially added to a cuvette tube, reacted at room temperature for 24 hours, centrifuged at 2000 rpm for 10 minutes using a high-speed centrifuge, washed with DMF for 3 times in succession, and freeze-dried to obtain a white powder, which is ZnBDC MOF nanosheets;

[0008] Step two: preparation of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film

[0009] A certain amount of ZnBDC MOF nanosheets and carboxymethyl cellulose are weighed and mixed in a certain proportion to form a uniform assembly suspension in a suitable solvent, the obtained suspension is deposited on a polymer film through a vacuum-assisted self-assembly method, and a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film is formed after drying at room temperature.

[0010] In step one of the method, the concentration of zinc acetate dihydrate is 3 mg mL -1 -5 mg mL -1 ; the concentration of terephthalic acid is 3 mg mL -1 -5 mg mL -1 .

[0011] The MOF nanosheets include one or more of ZnBDC, CoBDC and CuBDC, and preferably ZnBDC MOF nanosheets.

[0012] A certain amount of ZnBDC MOF and carboxymethyl cellulose are weighed and mixed in a certain proportion, and the concentration of the suspension after mixing is 10 wt.% to 50 wt.%.

[0013] Carboxymethyl cellulose and ZnBDC MOF nanoplatelet composite suspension is deposited on the surface of porous polymer membrane by vacuum assisted self-assembly method. The porous polymer membrane includes polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, diacetate fiber, triacetate fiber, polysulfone, polyethersulfone and cellulose.

[0014] The carboxymethyl cellulose cross-linked ZnBDC MOF nanoplatelet composite membrane of the application is used for antibiotic desalination.

[0015] The operating temperature is room temperature, and the operating pressure is 1-6 bar, realizing antibiotic / salt separation; the antibiotic is one of doxorubicin, tetracycline, chloramphenicol, norfloxacin, etc., and the antibiotic concentration is 10 mg / L -1 -100 mg / L -1 ; the salt is one or more of sodium sulfate, magnesium sulfate, sodium chloride and potassium chloride, and the salt concentration is 0.5 g / L -1 -2 g / L -1 .

[0016] Compared with the prior art, the carboxymethyl cellulose cross-linked ZnBDC MOF nanoplatelet composite membrane of the application has a smooth surface, neat stacking, certain mechanical strength and flexibility. The nanoplatelet composite membrane obtained by the application is used for antibiotic desalination, and exhibits excellent separation performance. Large-sized antibiotics can be intercepted, small-sized salt ions can quickly permeate the membrane, and the membrane has excellent water flux and antibiotic / salt separation factor. Among them, the antibiotic interception rate is 37.18%-94.45%, the separation factor is 1-16.6, and the water permeation flux is 158.38-261.96 Lm -2 h -1 bar -1 . BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a surface scanning electron microscope image of film 1 of example 1;

[0018] Figure 2 is a cross-sectional scanning electron microscope image of film 1 of example 1;

[0019] Figure 3 is a surface scanning electron microscope image of film 2 of example 2;

[0020] Figure 4 is a cross-sectional scanning electron microscope image of film 2 of example 2;

[0021] Figure 5 is a surface scanning electron microscope image of film 3 of example 3;

[0022] Figure 6 is a cross-sectional scanning electron microscope image of film 3 of example 3;

[0023] Figure 7 is a surface scanning electron microscope image of the comparative film 4;

[0024] Figure 8 is a cross-section scanning electron microscope image of the comparative film 4;

[0025] Figure 9 is a performance comparison chart of antibiotic desalination of films 1-4;

[0026] Figure 10 is a schematic diagram of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane screening. DETAILED DESCRIPTION

[0027] The application will be further described below in conjunction with the accompanying drawings and specific embodiments thereof, but the following examples in no way limit the application.

[0028] Example 1

[0029] A carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane is prepared, and the steps are as follows:

[0030] Step one, preparation of ZnBDC MOF nanosheet: a certain amount of zinc nitrate dihydrate is dissolved in a mixed solution of DMF and CH3CN, and stirred at room temperature with a magnetic stirrer for 30 minutes until the ligand is completely dissolved, denoted as solution A; a certain volume of mixed solution of DMF and CH3CN is used as a spacer solution, denoted as solution B; terephthalic acid is dissolved in a mixed solution of DMF and CH3CN, and stirred at room temperature with a magnetic stirrer for 30 minutes until the ligand is completely dissolved, denoted as solution C. Solution A, solution B and solution C are sequentially added to a cuvette tube, and reacted at room temperature for 24 hours, centrifuged at 2000 rpm for 10 minutes using a high-speed centrifuge, and washed with DMF for 3 times in succession, and freeze-dried to obtain a white powder, which is ZnBDC MOF nanosheet.

[0031] Step two, preparation of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane:

[0032] 5 mg of ZnBDC MOF nanosheet and carboxymethyl cellulose are weighed and mixed in a certain proportion to form a uniform assembly in a suitable solvent to form a suspension with a concentration of 10 wt.%, and the obtained suspension is deposited on a polymer film by a vacuum-assisted self-assembly method, and after drying at room temperature, a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane is formed, denoted as film 1. Figure 1 is a surface scanning electron microscope image of the film 1, Figure 2 is a cross-section scanning electron microscope image of the film 1.

[0033] The membrane 1 was subjected to antibiotic desalination experiment: using nanofiltration cross-flow device, the operation temperature was room temperature, the operation pressure was 2 bar, chloramphenicol and sodium chloride aqueous solution were selected, the chloramphenicol rejection rate of the membrane 1 was 37.18%, the sodium chloride rejection rate was 0.3%, the separation factor was 1.5, and the water flux was 224.68 Lm -2 h -1 bar -1 .

[0034] Example 2, preparation of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane, the steps of Example 2 and Example 1 are basically the same, only the mass of ZnBDC MOF nanosheets in step 2) is changed to 10 mg, and finally a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane is obtained, which is denoted as membrane 2. Figure 3 is a surface scanning electron microscope image of the membrane 2, Figure 4 is a cross-sectional scanning electron microscope image of the membrane 2.

[0035] The membrane 2 was subjected to antibiotic desalination experiment: using nanofiltration cross-flow device, the operation temperature was room temperature, the operation pressure was 2 bar, chloramphenicol and sodium chloride aqueous solution were selected, the chloramphenicol rejection rate of the membrane 2 was 85.42%, the sodium chloride rejection rate was 0.2%, the separation factor was 7.7, and the water flux was 178.38 Lm -2 h -1 bar -1 .

[0036] Example 3, preparation of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane, the steps of Example 2 and Example 1 are basically the same, only the mass of ZnBDC MOF nanosheets in step 2) is changed to 15 mg, and finally a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane is obtained, which is denoted as membrane 3. Figure 5 is a surface scanning electron microscope image of the membrane 3, Figure 6 is a cross-sectional scanning electron microscope image of the membrane 3.

[0037] The membrane 3 was subjected to antibiotic desalination experiment: using nanofiltration cross-flow device, the operation temperature was room temperature, the operation pressure was 2 bar, chloramphenicol and sodium chloride aqueous solution were selected, the chloramphenicol rejection rate of the membrane 3 was 94.45%, the sodium chloride rejection rate was 0.3%, the separation factor was 16.6, and the water flux was 158.38 Lm -2 h -1 bar -1 .

[0038] Comparative Example 1, preparation of a ZnBDC MOF nanosheet composite membrane, the steps are as follows:

[0039] Step one: Preparation of ZnBDC MOF nanosheets: A certain amount of zinc nitrate dihydrate was dissolved in a mixed solution of DMF and CH3CN, and stirred at room temperature with a magnetic stirrer for 30 minutes until the ligand was completely dissolved, denoted as solution A; a certain volume of mixed solution of DMF and CH3CN was used as a spacer solution, denoted as solution B; terephthalic acid was dissolved in a mixed solution of DMF and CH3CN, and stirred at room temperature with a magnetic stirrer for 30 minutes until the ligand was completely dissolved, denoted as solution C. Solution A, solution B and solution C were added to a cuvette tube in turn, and reacted at room temperature for 24 hours, and then centrifuged at 2000 rpm for 10 minutes using a high-speed centrifuge, and washed with DMF for 3 times in succession, and freeze-dried to obtain a white powder, which was ZnBDC MOF nanosheets.

[0040] Step two: Preparation of ZnBDC MOF composite film: 15 mg of ZnBDC MOF nanosheets were weighed to form a uniform assembly in a suitable solvent to form a suspension with a concentration of 0.1 g / L, and the obtained suspension was deposited on a polymer film by a vacuum-assisted self-assembly method, and after drying at room temperature, a ZnBDC MOF nanosheet composite film was formed. Denoted as film 4. Figure 7 is a surface scanning electron microscope image of film 4, Figure 8 is a cross-sectional scanning electron microscope image of film 4.

[0041] The antibiotic desalination experiment of film 4 was carried out: a nanofiltration cross-flow device was used, the operating temperature was room temperature, the operating pressure was 2 bar, chloramphenicol and sodium chloride aqueous solution were selected, the chloramphenicol rejection rate of membrane 2 was 26.19%, the sodium chloride rejection rate was 0.1%, the separation factor was 1.4, and the water flux was 261.96 Lm -2 h -1 bar -1 .

[0042] By comparing the examples and the comparative examples, it can be seen that the ZnBDC MOF nanosheet composite film crosslinked by carboxymethyl cellulose is dense and defect-free on the surface, carboxymethyl cellulose is green, widely available and low in cost, which not only can act as an interlayer spacer to avoid the disorderly stacking of nanosheets, but also can form hydrogen bonds with the carboxyl groups of ZnBDC MOF nanosheets through the rich hydroxyl groups, so as to control the ordered stacking of nanosheets and make the nanosheet layered film more stable. Compared with the pure ZnBDC MOF nanosheet stacking film, the separation performance is significantly improved. Figure 9 is a comparison diagram of antibiotic desalination performance of films 1-4.

[0043] Although the present application has been described above with reference to specific embodiments, the above embodiments are merely illustrative and not restrictive, and many modifications and other embodiments of the present application can occur to those skilled in the art upon reading the foregoing description, which modifications and other embodiments fall within the scope of the present application.

Claims

1. A method for preparing a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film, characterized in that: The method includes preparing ZnBDC MOF nanosheets with a high aspect ratio, cross-linking them with carboxymethyl cellulose to prepare a suspension, and preparing a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane through vacuum-assisted self-assembly. The membrane has a smooth and dense surface and is neatly stacked. The composite membrane is prepared according to the following steps: Step 1: Preparation of ZnBDC MOF nanosheets: A certain mass of zinc nitrate dihydrate was dissolved in a mixed solution of N,N-dimethylformamide (DMF) and acetonitrile (CH3CN), and stirred with a magnetic stirrer at room temperature for 30 minutes until the zinc nitrate dihydrate ligand was completely dissolved, which was recorded as solution A; a certain volume of a mixed solution of DMF and CH3CN was used as a spacer solution, which was recorded as solution B; terephthalic acid was dissolved in a mixed solution of DMF and CH3CN, and stirred with a magnetic stirrer at room temperature for 30 minutes until the terephthalic acid ligand was completely dissolved, which was recorded as solution C. Solution A, solution B, and solution C were sequentially added to a cuvette tube, reacted at room temperature for 24 hours, centrifuged at 2000 rpm for 10 minutes using a high-speed centrifuge, washed three times with DMF, and freeze-dried to obtain a white powder, which is the ZnBDC MOF nanosheet; Step 2: Preparation of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane: A certain mass of ZnBDC MOF nanosheets and carboxymethyl cellulose are weighed and mixed in a certain proportion to form a uniform assembly suspension in an appropriate solvent. The resulting suspension is deposited on a polymer film by a vacuum-assisted self-assembly method and dried at room temperature to form a carboxymethyl cellulose-crosslinked ZnBDC MOF nanosheet composite film.

2. The method for preparing a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film according to claim 1, characterized in that: The concentration of zinc nitrate dihydrate is 3 mg·mL -1 -5mg·mL -1 ; The concentration of terephthalic acid is 3mg·mL -1 -5mg·mL -1 .

3. The method for preparing a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite film according to claim 1, characterized in that: The ZnBDC MOF nanosheets and carboxymethyl cellulose are mixed in a certain proportion, and the concentration of the suspension after mixing is 10 wt % to 50 wt %.

4. The method for preparing a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane according to claim 1, characterized in that: The composite suspension of carboxymethyl cellulose and ZnBDC MOF nanosheets was deposited on the surface of a porous polymer membrane by vacuum-assisted self-assembly. The porous polymer membrane materials included polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, diacetate, triacetate, polysulfone, polyethersulfone and cellulose.

5. Use of a carboxymethyl cellulose cross-linked ZnBDC MOF nanosheet composite membrane prepared according to the method of any one of claims 1 to 4 in antibiotic desalination.

6. The use according to claim 5, wherein the operating temperature is room temperature and the operating pressure is 1-6 bar, and the antibiotic / salt separation is achieved; the antibiotic is one of adriamycin, tetracycline, chloramphenicol, and norfloxacin, and the antibiotic concentration is 10 mg·L -1 -100mg·L -1 The salt is one or more of sodium sulfate, magnesium sulfate, sodium chloride, and potassium chloride, and the salt concentration is 0.5 g·L -1 -2g·L -1 .

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