ZIF-67-like framework nanosheet as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of two-dimensional nanosheet materials, and particularly relates to a ZIF-67 framework-like nanosheet as well as a preparation method and application thereof.The two-dimensional nanosheet material is prepared by adopting a hydrothermal method and introducing a long molecular chain ligand, the size and thickness of the two-dimensional nanosheet are optimized, the two-dimensional nanosheet has thinner thickness and larger specific surface area, and the ZIF-67 framework-like nanosheet is prepared through a hydrothermal method. Therefore, the film-forming property and the separation property of the film are remarkably improved. According to the method, the film-forming property of the MOF film material is improved, the adaptability of the MOF film material is enhanced, and a solution with potential is provided for the fields of dye separation, water treatment and the like. According to the invention, a hydrothermal method is adopted, the ligand only needs to be dissolved in a solvent, the solution is placed in a glass bottle, and a reaction is carried out in a drying oven for a required time. The reaction method is simple and convenient, does not need complex operation steps, and has relatively high repeatability; and the yield is high, and more ZIF-67-like framework nanosheets can be prepared by increasing the use amount of the ligand. In addition, required equipment is simple and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional nanosheet materials, and particularly relates to ZIF-67 framework-like nanosheets, a preparation method thereof, and applications thereof. Background Art

[0002] Metal-Organic Frameworks (MOFs) have become a research hotspot in the field of gas-liquid separation due to their excellent thermal stability, chemical stability, operational stability, and separation performance. MOF materials have a large specific surface area, rich chemical functions, adjustable pore structures, and good thermal stability, making them occupy an important position in membrane material research. In particular, polycrystalline MOF-based membranes have demonstrated excellent gas and liquid separation performance in experiments. However, in recent years, the rise of two-dimensional (2D) MOF membranes has provided a new strategy for the construction of high-performance membrane materials and shown significant advantages over traditional three-dimensional (3D) MOF materials.

[0003] Two-dimensional MOF membranes are assembled from MOF nanosheets, and their unique structure endows them with many characteristics superior to three-dimensional MOF materials. First, the thickness of two-dimensional MOF membranes is extremely thin, usually at the nanometer level, which results in shorter mass transfer paths and higher permeation fluxes during the separation process, significantly improving the separation efficiency. Second, the layered structure of two-dimensional MOF membranes gives them higher mechanical flexibility and processability, enabling them to better adapt to complex application environments. In addition, two-dimensional MOF membranes have a larger surface area and more surface active sites, providing more possibilities for their applications in adsorption, catalysis, and separation. In contrast, although traditional three-dimensional MOF materials have high porosity and adjustable pore sizes, their poor processability in fluid processing makes it difficult to achieve large-scale production, which severely limits their applications in industry. Two-dimensional MOF membranes, due to their ultrathin structure and excellent mechanical properties, can be more easily processed and integrated into existing membrane separation systems, thus providing the possibility for large-scale applications.

[0004] Two-dimensional MOF membranes not only inherit the advantages of three-dimensional MOF materials such as high specific surface area and adjustable pore sizes but also overcome the deficiencies of three-dimensional MOF materials in terms of processability and mechanical strength through their ultrathin structure and layered characteristics. However, in the prior art, the preparation of two-dimensional MOF membranes usually adopts an in-situ growth method, which has the disadvantage that the uneven growth of nanosheets affects the subsequent film-forming properties. Summary of the Invention

[0005] The purpose of the present invention is to provide ZIF-67 framework-like nanosheets, a preparation method thereof, and applications thereof, so as to solve the technical problems of uneven nanosheet sizes and non-dense filtration membranes in the prior art.

[0006] To achieve the above object, the present invention is implemented by the following technical solutions: In the first aspect, the present application discloses a method for preparing ZIF-67 framework-like nanosheets, including: Adding Co(NO3)2·6H2O and a long molecular chain ligand into a mixed solution of DMF, deionized water, and ethanol to obtain a mixed solution; Heating and reacting the mixed solution to obtain a suspension, centrifuging and washing the suspension, and then drying to obtain ZIF-67 framework-like nanosheets.

[0007] Preferably, the long molecular chain ligand includes: 2-(4-methylphenyl)benzimidazole and 1-(6-hydroxyethyl)imidazole; the molar ratio of Co(NO3)2·6H2O to 2-(4-methylphenyl)benzimidazole is (2-3):(1-2); the molar ratio of Co(NO3)2·6H2O to 1-(6-hydroxyethyl)imidazole is (2-3):(1-2).

[0008] Preferably, the 1-(6-hydroxyethyl)imidazole is obtained through the following steps: Mixing imidazole, potassium hydroxide, and dimethyl sulfoxide evenly to obtain a mixture; Heating and refluxing the mixture, and continuously stirring during the reflux until the mixture is completely dissolved to obtain a transparent solution; Adding deionized water and dichloromethane to the transparent solution, stirring evenly, separating the liquid, and washing to obtain the CH2Cl2 phase; Performing rotary evaporation on the CH2Cl2 phase to obtain 1-(6-hydroxyethyl)imidazole.

[0009] Preferably, the volume ratio of DMF, deionized water, and ethanol is 1:1:1; the volume ratio of Co(NO3)2·6H2O to DMF is 15:(4-6).

[0010] Preferably, the heating temperature for the heating reaction is 120°C to 140°C, and the reaction duration is 10 h to 14 h.

[0011] In the second aspect, the present application discloses ZIF-67 framework-like nanosheets prepared by using the preparation method described in any one of the above.

[0012] In the third aspect, the present application discloses the application of ZIF-67 framework-like nanosheets in the preparation of a separation membrane, including the following steps: Preparing an ethanol dispersion of ZIF-67 framework-like nanosheets; Transferring the ethanol dispersion of ZIF-67 framework-like nanosheets to PAN-400 through a negative pressure sand core suction filtration device to obtain a ZIF-67 framework-like nanosheet separation membrane.

[0013] Preferably, the concentration of the ethanol dispersion is 0.1~0.2 mg·ml -1 .

[0014] Preferably, the negative pressure for transferring the ZIF-67 framework nanosheets to PAN-400 is 0.8~1.0 bar.

[0015] Preferably, the thickness of the ZIF-67 framework nanosheet separation membrane is 100~200 nm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention adopts the hydrothermal method, only needs to dissolve the ligand in the solvent, and place the solution in a glass bottle, and react in an oven until the required time. This reaction method is simple and convenient, without complex operation steps, and has strong repeatability; the yield is high, and more new ZIF-67 can be prepared by increasing the dosage of the ligand. In addition, the equipment required by the present invention is simple and the cost is low.

[0017] 2) Innovatively, the present invention respectively introduces the new ligands 2-(4-methylphenyl)benzimidazole and 1-(6-hydroxyethyl)imidazole to prepare two-dimensional nanosheet materials by the one-pot hydrothermal method, optimizes the size and thickness of the two-dimensional nanosheets, and significantly improves the performance of the MOF membrane material in separating dyes. This method not only improves the film-forming property of the MOF membrane material, but also enhances its adaptability, providing a potential solution for fields such as dye separation and water treatment.

[0018] 3) By introducing the new ligands 2-(4-methylphenyl)benzimidazole and 1-(6-hydroxyethyl)imidazole, the size and thickness of the nanosheets are effectively optimized, making it have a larger surface area and a thinner structure. This structural feature significantly prevents the passage of larger molecules (such as congo red and acid fuchsin), improving both the rejection performance and the flux of the membrane material.

[0019] 4) The membrane material in the present invention exhibits excellent flux and rejection rate in performance. Thanks to the synthesis of the new ligand, the ligand effectively promotes the controllable regulation of the membrane structure. Through the precise regulation of the membrane material, its structure can be repeatedly adjusted according to needs during use. This unique property not only effectively avoids the performance degradation problem of traditional membrane materials during long-term use, but also significantly improves the durability and adaptability of the membrane, ensuring its stability and high efficiency during multiple cycles of use, thus expanding its wide applicability in practical applications. Description of the Drawings

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0021] Figure 1 is the flowchart of the method of the embodiment of the present invention; Figure 2 is the scanning electron microscope image of the ZIF-67 framework-like nanosheets prepared in the embodiment of the present invention; among them, (a) is the scanning electron microscope image of Co-Mpbdi prepared in Example 1; (b) is the scanning electron microscope image of Co-Heid prepared in Example 2; Figure 3 is the transmission electron microscope image of the ZIF-67 framework-like nanosheets prepared in the embodiment of the present invention; among them, (a) is the transmission electron microscope image of Co-Mpbdi prepared in Example 1; (b) is the transmission electron microscope image of Co-Heid prepared in Example 2; Figure 4 is the atomic force microscope image of the ZIF-67 framework-like nanosheets prepared in the embodiment of the present invention; among them, (a) is the atomic force microscope image of Co-Mpbdi prepared in Example 1; (b) is the height profile diagram of Co-Mpbdi prepared in Example 1; (c) is the atomic force microscope image of Co-Heid prepared in Example 2; (d) is the height profile diagram of Co-Heid prepared in Example 2; Figure 5 is the XRD diagram of the ZIF-67 framework-like and traditional ZIF-67 nanosheets prepared in the embodiment of the present invention; among them, (a) is the XRD diagram of Co-Mpbdi prepared in Example 1; (b) is the XRD diagram of Co-Heid prepared in Example 2; Figure 6 is the Fourier infrared spectrum of the ZIF-67 framework-like nanosheets prepared in the embodiment of the present invention; among them, (a) is the Fourier infrared spectrum of traditional ZIF-67; (b) is the Fourier infrared spectrum of ZIF-67-like (Co-Mpbdi); Figure 7 is the separation performance diagram of the separation membrane of the embodiment of the present invention for five organic dyes with different molecular weights before and after ultraviolet light irradiation; among them, (a) is the separation performance diagram of traditional ZIF-67; (b) is the separation performance diagram of ZIF-67-like (Co-Mpbdi). Detailed implementation manners

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meanings understood by those skilled in the art with respect to the present invention. In case of conflicts, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not in any way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0024] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the ranges (including integers and fractions).

[0025] In this article, unless otherwise specified, the terms "comprise", "include", "contain", "have", or similar terms cover the meanings of "consist of" and "consist essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0026] In this article, for the sake of brevity of description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there are no contradictions in the combinations of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0027] The following further describes the present invention in detail with reference to the accompanying drawings: See Figure 1 , this application discloses a method for preparing ZIF-67 framework-like nanosheets, including: S1: Adding Co(NO3)2·6H2O and long molecular chain ligands into a mixed solution of DMF, deionized water, and ethanol to obtain a mixed solution; S2: Heating the mixed solution for reaction to obtain a suspension, centrifuging and washing the suspension, and then drying to obtain ZIF-67 framework-like nanosheets.

[0028] This application can promote the rapid formation of materials by adopting a simple hydrothermal synthesis strategy and reasonably designing the ratio of reactants and reaction time. This preparation method effectively solves the problems of the original materials in terms of insufficient film-forming property, poor structural stability, and poor dye separation performance.

[0029] In some embodiments, the long molecular chain ligands include: 2-(4-methylphenyl)benzimidazole and 1-(6-hydroxyethyl)imidazole; the molar ratio of Co(NO3)2·6H2O to 2-(4-methylphenyl)benzimidazole is (2-3):(1-2); the molar ratio of Co(NO3)2·6H2O to 1-(6-hydroxyethyl)imidazole is (2-3):(1-2).

[0030] In some embodiments, a method for preparing ZIF-67 framework-like nanosheets includes: adding Co(NO3)2·6H2O (500 mg) and 2-(4-methylphenyl)benzimidazole (250 mg) into a mixed solution of DMF, deionized water, and ethanol, ultrasonically treating the above mixed solution (for 15-20 minutes), heating the mixed solution in a reaction kettle (at 120 °C) after the ultrasonic treatment ends, reacting for 12 h to obtain a purple-black suspension, centrifuging and washing it multiple times, and finally obtaining a uniformly dispersed suspension of ZIF-67 framework-like nanosheets (Co-Mpbdi). After drying the suspension of ZIF-67 framework-like nanosheets (Co-Mpbdi), ZIF-67 framework-like nanosheets (Co-Mpbdi) are obtained.

[0031] In some embodiments, a method for preparing ZIF-67 framework-like nanosheets includes: adding Co(NO3)2·6H2O (1 g) and 1-(6-hydroxyethyl)imidazole (500 mg) into a mixed solution of DMF, deionized water, and ethanol, ultrasonically treating the above mixed solution (for 15-20 minutes), heating the mixed solution in a reaction kettle (at 120 °C) after the ultrasonic treatment ends, reacting for 12 h to obtain a black suspension, centrifuging and washing it multiple times, and finally obtaining a uniformly dispersed suspension of ZIF-67 framework-like nanosheets (Co-Heid).

[0032] As a further optimization of the method for preparing two types of ZIF-67 framework-like nanosheets of the present invention: the molar ratio of the addition amounts of Co(NO3)2·6H2O and 2-(4-methylphenyl)benzimidazole in step S1 is 2:1.

[0033] In some embodiments, the 1-(6-hydroxyethyl)imidazole is obtained through the following steps: Mix imidazole, potassium hydroxide, and dimethyl sulfoxide evenly to obtain a mixture; Heat the mixture under reflux and continuously stir during the reflux process until the mixture is completely dissolved to obtain a transparent solution; Add deionized water and dichloromethane to the transparent solution, stir evenly, separate the liquid, and wash to obtain the CH2Cl2 phase; Perform rotary evaporation on the CH2Cl2 phase to obtain 1-(6-hydroxyethyl)imidazole.

[0034] In some embodiments, the 1-(6-hydroxyethyl)imidazole is obtained by the following steps: 60 g imidazole, 49.2 g potassium hydroxide (KOH) and 400 g dimethyl sulfoxide (DMSO) are weighed and added to a flask in sequence. Ensure accurate weighing and use a magnetic stirrer to preliminarily stir the mixture evenly. Place the flask on a heating device, set the temperature to 70 ° C, and start heating and reflux. During the reflux process, continue to stir the mixture until the solid is completely dissolved and the solution is uniform and transparent. This step usually takes 1-2 hours, depending on the dissolution rate. After the solid is completely dissolved, stop heating and cool the reaction system naturally to room temperature. Subsequently, add 100 g of transparent solution to the flask (the specific substance needs to be determined according to the experimental design), and continue to stir the reaction at room temperature for 24 hours to ensure that the reaction is fully carried out. After the reaction is completed, add 50 mL of deionized water and 50 mL of dichloromethane (CH2Cl2) to the reaction mixture, stir well and perform liquid separation. Repeat this washing step 5 times to remove unreacted raw materials and by-products. The organic phase (CH2Cl2 phase) after separation is washed three times with 50 mL of deionized water to completely remove the residual inorganic salts and water-soluble impurities. The washed CH2Cl2 phases are combined and transferred to a rotary evaporator. The solvent CH2Cl2 is removed by rotary evaporation at an appropriate temperature (usually 40-50 °C) and reduced pressure to finally obtain the target product. The product can be further dried (such as vacuum drying) to improve its purity.

[0035] In some embodiments, the volume ratio of DMF, deionized water and ethanol is 1:1:1; the volume ratio of Co(NO3)2·6H2O to DMF is 15:(4-6).

[0036] In some embodiments, the heating temperature of the heating reaction is 120° C. to 140° C., and the reaction time is 10 h to 14 h.

[0037] In some embodiments, before the mixed solution is heated for reaction, the mixed solution is subjected to water bath ultrasonic treatment, the power of the water bath ultrasonic treatment is 200-300 W, and the cumulative ultrasonic treatment time is 15-20 min.

[0038] In some embodiments, the centrifugal washing suspension is centrifuged at a speed of 8000-10000 r / min, the centrifugal time is 5-7 min, and the centrifugal washing operation is performed for no less than 5 times.

[0039] In some embodiments, methanol is used during centrifugation of the wash suspension.

[0040] The present application also discloses a ZIF-67-like framework nanosheet, which is prepared by any of the preparation methods described above.

[0041] The present application also discloses the application of a ZIF-67 framework-like nanosheet in the preparation of a separation membrane, including the following steps: Prepare an ethanol dispersion of the ZIF-67 framework-like nanosheet; Transfer the ZIF-67 framework-like nanosheet to PAN-400 through a negative pressure sand core suction filtration device using the ethanol dispersion to obtain a ZIF-67 framework-like nanosheet separation membrane.

[0042] In some embodiments, the application of a ZIF-67 framework-like nanosheet in the preparation of a separation membrane includes: Prepare an ethanol dispersion with a concentration of 0.1 mg·ml -1 of the above-prepared ZIF-67 framework-like nanosheet (Co-Mpbdi). Take 10 ml of this dispersion and transfer the ZIF-67 framework-like nanosheet to PAN-400 through a negative pressure sand core suction filtration device at a negative pressure of 0.9 bar to obtain a ZIF-67 framework-like nanosheet (Co-Mpbdi) separation membrane.

[0043] Further preferably, the thickness of the novel ZIF-67 membrane is 100-200 nm.

[0044] Further preferably, the membrane separation performance of the ZIF-67 framework-like nanosheet (Co-Mpbdi) separation membrane is verified by a dead-end separation device. All measurements are carried out at room temperature and under the condition of a transmembrane pressure of 5.0 bar. The solvent permeability of each membrane is obtained by collecting the filtrate over a certain period of time and averaging it, and each data point is obtained from three consecutive tests.

[0045] The above preferred technical features can be combined with each other as long as they do not conflict with each other.

[0046]

Example 1

[0047] Prepare the novel ZIF-67 (Co-Mpbdi) The mixed solution was ultrasonically treated (for 15 - 20 minutes). After the ultrasonic treatment, the mixed solution was heated in a reaction kettle (at 120 °C). Among them, the oven heating temperature was 120 °C and the heating time was 12 h. After the reaction, the obtained purple - black suspension was centrifugally washed with methanol. Among them, the centrifugation speed was 8000 - 10000 r / min, the centrifugation time was about 5 - 7 min, and the centrifugal washing operation was not less than 5 times. Subsequently, the washed purple - black suspension was dried under vacuum at 100 °C to obtain ZIF - 67 - like framework nanosheets, or the washed purple - black suspension was dropped with ethanol to prepare a ZIF - 67 - like dispersion with a certain concentration.

[0048] 3) Preparation of the separation membrane The ZIF - 67 - like framework nanosheets were configured into an ethanol dispersion with a concentration of 0.1 mg·ml -1 . 10 ml of this dispersion was taken, and the ZIF - 67 - like framework nanosheets were transferred to PAN - 400 through a negative - pressure sand - core suction filtration device with a negative pressure of 0.9 bar to obtain a ZIF - 67 - like framework nanosheet separation membrane.

[0049] Organic dye separation test The membrane separation performance of the ZIF - 67 - like framework nanosheet separation membrane was verified by a dead - end separation device. All measurements were carried out at room temperature and under the condition of a transmembrane pressure of 5.0 bar. The solvent permeation rate of each membrane was obtained by collecting the filtrate within a certain time and averaging, and each data point was obtained from three consecutive tests.

[0050]

Example 2

[0051] 2) Preparation of novel ZIF - 67 (Co - Heid) The mixed solution prepared in step (1) was ultrasonically treated (for 15 - 20 minutes). After the ultrasonic treatment, the mixed solution was heated in a reaction kettle (at 120 °C). Among them, the oven heating temperature was 120 °C and the heating time was 12 h. After the reaction, the obtained black suspension was centrifugally washed with methanol. Among them, the centrifugation speed was 8000 - 10000 r / min, the centrifugation time was about 5 - 7 min, and the centrifugal washing operation was not less than 5 times. Subsequently, the washed black suspension was dried under vacuum at 100 °C to obtain ZIF - 67 - like.

[0052]

Example 3

[0053] Prepare novel ZIF-67 (Co-Mpbdi) Ultrasonically treat the mixed solution (for 20 minutes). After the ultrasonic treatment, place the mixed solution in a reaction kettle and heat it (at 140 °C). Among them, the oven heating temperature is 140 °C, and the heating time is 10 h. After the reaction, wash the obtained purple-black suspension by centrifugation with methanol. Among them, the centrifugation speed is 8000-10000 r / min, and the centrifugation time is about 5-7 min. At the same time, the centrifugal washing operation is not less than 5 times. Subsequently, dry the washed purple-black suspension under vacuum at 100 °C to obtain ZIF-67 framework nanosheets, or drop the washed purple-black suspension into ethanol to prepare a ZIF-67 dispersion with a certain concentration.

[0054] 3) Prepare a separation membrane Prepare an ethanol dispersion of ZIF-67 framework nanosheets with a concentration of 0.1 mg·ml -1 Take 10 ml of this dispersion and transfer the ZIF-67 framework nanosheets to PAN-400 through a negative pressure sand core suction filtration device with a negative pressure of 0.8 bar to obtain a ZIF-67 framework nanosheet separation membrane.

[0055]

Example 4

[0056] 2) Prepare novel ZIF-67 (Co-Heid) The mixed solution prepared in step (1) was ultrasonically treated (for 20 minutes). After the ultrasonic treatment, the mixed solution was heated in a reaction kettle (at 130 °C). Among them, the heating temperature in the oven was 130 °C, and the heating time was 11 h. After the reaction, the obtained black suspension was centrifugally washed with methanol. Among them, the centrifugal rotation speed was 10,000 r / min, and the centrifugal time was about 5 minutes. At the same time, the centrifugal washing operation was not less than 5 times. Subsequently, the washed black suspension was dried under vacuum at 100 °C to obtain ZIF-67-like material.

[0057]

Example 5

[0058] Preparation of novel ZIF-67-like (Co-Mpbdi) The mixed solution was ultrasonically treated (for 18 minutes). After the ultrasonic treatment, the mixed solution was heated in a reaction kettle (at 130 °C). Among them, the heating temperature in the oven was 130 °C, and the heating time was 11 h. After the reaction, the obtained purple-black suspension was centrifugally washed with methanol. Among them, the centrifugal rotation speed was 8,000 r / min, and the centrifugal time was about 7 minutes. At the same time, the centrifugal washing operation was not less than 5 times. Subsequently, the washed purple-black suspension was dried under vacuum at 100 °C to obtain ZIF-67-like framework nanosheets, or the washed purple-black suspension was dropped into ethanol to prepare a dispersion of ZIF-67-like framework nanosheets with a certain concentration.

[0059] 3) Preparation of the separation membrane The ZIF-67-like framework nanosheets were configured into an ethanol dispersion with a concentration of 0.1 mg·ml -1 −1. 10 ml of this dispersion was taken, and the ZIF-67-like framework nanosheets were transferred to PAN-400 through a negative pressure sand core suction filtration device with a negative pressure of 0.9 bar to obtain a ZIF-67-like framework nanosheet separation membrane.

[0060]

Example 6

[0061] 2) Preparation of novel ZIF-67-like (Co-Heid) The mixed solution obtained in step (1) was ultrasonically treated (for 18 minutes). After the ultrasonic treatment, the mixed solution was heated in a reaction kettle (at 130 °C). Among them, the heating temperature in the oven was 130 °C and the heating time was 11 h. After the reaction, the obtained black suspension was centrifugally washed with methanol. Among them, the centrifugal speed was 9000 r / min and the centrifugal time was about 5 - 7 min. Meanwhile, the centrifugal washing operation was carried out no less than 5 times. Subsequently, the washed black suspension was dried under vacuum at 100 °C, and the ZIF-67-like framework nanosheets were thus prepared.

[0062] <Morphology and Structure Characterization of ZIF-67-like Framework Nanosheets> Morphology Characterization 1 mL of the ZIF-67-like framework nanosheet dispersions prepared in Example 1 and Example 2 were respectively added into centrifuge tubes, diluted with 10 mL of ethanol. 5 μL of each was taken and dropped onto silicon wafers and observed under a scanning electron microscope. Then, 1 mL of the novel ZIF-67 nanomaterial dispersions prepared in Example 1 and Example 2 were respectively added into centrifuge tubes, diluted with 50 mL of ethanol. Then, 10 μL of each was taken and dropped onto silicon wafers and copper grids and observed under an atomic force microscope and a transmission electron microscope.

[0063] As Figure 2 (a) and (b) respectively show the surface morphology characteristics of (Co-Mpbdi) and (Co-Heid). It can be seen from the scanning electron microscope (SEM) photos that the synthesized nanosheets not only become thinner, but also increase in size, the surface is denser, and the structure is more uniform. These novel nanosheets have a higher aspect ratio and a more consistent size distribution, further optimizing the performance of the membrane separation material. This kind of ZIF-67-like nanosheets optimized through ligand design has higher efficiency in membrane separation applications, can improve the mass transfer rate, reduce energy consumption during the separation process, and is more stable.

[0064] As Figure 3 (a) and (b) respectively show the low-magnification TEM images of (Co-Mpbdi) and (Co-Heid). It can be seen from the transmission electron microscope (TEM) photos that the nanosheet structures of the two novel ZIF-67s. The samples exhibit a highly regular two-dimensional nanosheet structure. These nanosheets are close to planar in shape or approximately rectangular, with smooth edges and no obvious defects. This morphological feature highly coincides with the synthesis design goal of two-dimensional nanosheets, indicating that the synthesis method adopted successfully prepares an ideal two-dimensional nanosheet material with regular structure and uniform morphology.

[0065] As Figure 4(a) and (b) respectively represent the AFM images of (Co-Mpbdi) and (Co-Heid) and the height profiles of the nanosheets. It can be seen from the atomic force microscope (AFM) photos that the thickness of the (Co-Mpbdi) nanosheets is about 25 nm, and the thickness of the (Co-Heid) nanosheets is about 7 nm. The thickness of the single-layer nanosheets can be clearly observed, showing its excellent two-dimensional structural characteristics. The thickness and length of the nanosheets can be accurately measured, and its uniform size distribution is confirmed.

[0066] Structure characterization Take 30 mg each of the ZIF-67 framework nanosheet dispersions prepared in Example 1 and Example 2 respectively for XRD testing. Another 5 mg each of the ZIF-67 framework nanosheet dispersions prepared in Example 1 and Example 2 are taken respectively for Fourier transform infrared spectroscopy testing.

[0067] As Figure 5 (a) and (b) respectively represent the XRD images of (Co-Mpbdi) and (Co-Heid). Conventional ZIF-67 and two new types of ZIF-67 nanosheets both show similar characteristic peaks in the XRD pattern, indicating the successful synthesis of the ZIF-67 structure. For ZIF-67 NS, only two main peaks at 13° and 26° are observed, which can be attributed to the

[211] and

[422] crystal planes of ZIF-67. The appearance of these two diffraction peaks indicates that whether it is the conventional ZIF-67 nanosheets or the Co-Mpbdi and Co-Heid nanosheets synthesized by ligand optimization, their crystal structures have consistent characteristics and preferential growth along specific crystal planes. In particular, the results show that the crystals of ZIF-67 nanosheets, Co-Mpbdi nanosheets, and Co-Heid nanosheets have a preferential growth trend along the

[211] crystal plane. This indicates that the pore size of these nanosheets is relatively more uniform in the direction of this crystal plane, showing a more uniform distribution characteristic compared with isotropic ZIF-67 particles.

[0068] As Figure 6 (a) and (b) respectively represent the infrared spectra of (Co-Mpbdi) and (Co-Heid). In the infrared spectrum, the absorption peaks at 1600 cm -1 and 1288 cm -1 correspond to the -C-N bond vibration in the 2-methylimidazole ring and the Co-N bond vibration in the ZIF-67 nanosheets respectively. The infrared spectra of the two new types of ZIF-67 are consistent with the infrared spectral characteristics in the literature of conventional ZIF-67, indicating that the synthesis process is smooth and the materials are successfully prepared. Specifically, the -C-N bond vibration peak at 1600 cm -1 reflects the stretching vibration of the carbon-nitrogen bond in the 2-methylimidazole ring, while 1288 cm-1 The vibration peak of the Co-N bond at [location] indicates the formation of a coordination bond between metallic cobalt and nitrogen atoms. The intensity and position of these characteristic peaks are almost exactly the same in Co-Mpbdi, Co-Heid, and traditional ZIF-67, indicating that Co-Mpbdi and Co-Heid maintain the typical structural characteristics of ZIF-67 during the synthesis process.

[0069]

Dye Separation Performance of ZIF-67-like

[0070] As Figure 7 shown, (a) and (b) are the separation performances of traditional ZIF-67 and ZIF-67-like (Co-Mpbdi), respectively. The new ZIF-67-like can significantly improve the flux while maintaining a small decrease in the rejection rate of five dyes (Congo Red, Rose Bengal, Acid Fuchsin, Methylene Blue, Rhodamine B). Among them, the flux of Acid Fuchsin increased significantly from 30 L·m -2 ·h -1 ·bar -1 to 80 L·m -2 ·h -1 ·bar -1 , while maintaining a high rejection rate (>95%). This is evidence of the improvement of the nanosheets after changing to a new ligand. Since the nanosheets are thinner, the membrane is thinner and denser, and the flux of dye molecules increases significantly while maintaining a high rejection rate.

[0071] The following further elaborates on the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0072] Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturers. Various raw materials are used in the following examples. Unless otherwise specified, commercially available products with conventional specifications in the art are used. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratios represent weight ratios.

[0073] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of ZIF-67 framework nanosheets, characterized in that, Comprising: Adding Co(NO3)2·6H2O and a long molecular chain ligand into a mixed solution of DMF, deionized water, and ethanol to obtain a mixed solution; Heating and reacting the mixed solution to obtain a suspension, centrifuging and washing the suspension, and then drying to obtain ZIF-67 framework-like nanosheets.

2. The preparation method of a ZIF-67 framework-like nanosheet according to claim 1, characterized in that, The long molecular chain ligand includes: 2-(4-methylphenyl)benzimidazole and 1-(6-hydroxyethyl)imidazole; the molar ratio of Co(NO3)2·6H2O to 2-(4-methylphenyl)benzimidazole is (2 - 3)∶(1 - 2); the molar ratio of Co(NO3)2·6H2O to 1-(6-hydroxyethyl)imidazole is (2 - 3)∶(1 - 2).

3. A method for preparing ZIF-67 framework nanosheets according to claim 2, characterized in that, The 1-(6-hydroxyethyl)imidazole is obtained through the following steps: Mixing imidazole, potassium hydroxide, and dimethyl sulfoxide evenly to obtain a mixture; Heating the mixture under reflux and continuously stirring during the reflux process until the mixture is completely dissolved to obtain a transparent solution; Adding deionized water and dichloromethane to the transparent solution, stirring evenly, separating the liquid, and washing to obtain the CH2Cl2 phase; Performing rotary evaporation on the CH2Cl2 phase to obtain 1-(6-hydroxyethyl)imidazole.

4. A method for preparing a ZIF-67 framework nanosheet-like material according to claim 1, characterized in that, The volume ratio of DMF, deionized water, and ethanol is 1∶1∶1; the volume ratio of Co(NO3)2·6H2O to DMF is 15∶(4 - 6).

5. A method for preparing ZIF-67 framework nanosheets according to claim 1, characterized in that, The heating temperature for the heating reaction is 120°C - 140°C, and the reaction duration is 10 h - 14 h.

6. A ZIF-67 framework-like nanosheet, characterized in that, Prepared by using the preparation method according to any one of claims 1 to 5.

7. Application of a ZIF-67 framework nanosheet in the preparation of a separation membrane, characterized in that, Including the following steps: Preparing the ZIF-67 framework-like nanosheets into an ethanol dispersion; Transferring the ZIF-67 framework-like nanosheets in the ethanol dispersion to PAN-400 through a negative pressure sand core suction filtration device to obtain a ZIF-67 framework-like nanosheet separation membrane.

8. Use of a ZIF-67 framework nanosheet according to claim 7 in the preparation of a separation membrane, characterized in that, The concentration of the ethanol dispersion is 0.1~0.2 mg·ml -1 .

9. Use of a ZIF-67 framework-like nanosheet according to claim 7 in the preparation of a separation membrane, characterized in that, The negative pressure for transferring the ZIF-67 framework-like nanosheets to PAN-400 is 0.8 - 1.0 bar.

10. Use of a ZIF-67 framework-like nanosheet according to claim 7 in the preparation of a separation membrane, characterized in that, The thickness of the ZIF-67 framework-like nanosheet separation membrane is 100 - 200 nm.

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