A method for preparing metal-organic framework nanosheets and its application

Abstract

A method for preparing metal-organic framework nanosheets and its application belongs to the field of photocatalytic materials technology. This invention utilizes the transition metal Cu. 2+ Using 2,7-dicarboxyanthraquinone as a ligand, a three-dimensional layered metal-organic framework (MOF) material was constructed via a solvothermal synthesis strategy. Subsequently, a physical exfoliation technique was employed to efficiently prepare ultrathin monolayer MOF nanosheets with high catalytic activity. The two-dimensional copper-based MOF nanosheets prepared in this invention exhibit a large number of uniformly distributed copper nodes, providing abundant coordination sites for the formation of Cu−Cl chromophores from the highly electrophilic free radical precursor chloride ions. Simultaneously, the AQ ligands on the surface of the ultrathin 2D copper-based MOF nanosheets are effective photoactivators for oxygen activation in photocatalytic organic conversion. Benefiting from the synergistic effect of the two active sites on the ultrathin 2D MOF nanosheets with high surface utilization, inert C−H bonds and molecular oxygen are effectively activated in a mild environment, thereby achieving efficient aerobic oxidation of alkanes.

Description

Technical Field

[0001] This invention relates to a method for preparing metal-organic framework nanosheets and their applications, belonging to the field of metal-organic framework catalytic materials technology. Background Technology

[0002] As the most basic structural unit, C(sp) 3 C(sp)−H bonds are present in almost all organic compounds. Therefore, C(sp) 3 The selective oxidation of C(sp)−H bonds can directly convert low-cost industrial raw materials into high-value fine chemicals, which has attracted widespread attention in organic synthesis and industrial chemistry. However, the inert and nonpolar C(sp)−H bonds... 3 Converting C(sp)-H bonds into value-added products through inexpensive, safe, and mild conditions remains a challenging task in modern chemistry. Among reported activation methods, three-dimensional (3D) metal-organic frameworks (MOFs) with ordered organic linkers and inorganic metal cluster nodes are considered promising catalytic materials. Integrating various functional units into a single network structure provides a finely tuned catalytic platform for cascading multiple synergistic catalytic processes, which is difficult to achieve in other manifolds. Photoredox-mediated hydrogen atom transfer catalysis (HAT) has emerged as a promising strategy for the direct activation and functionalization of various C(sp)-H bonds. 3 )−H bond. Ligand-metal charge transfer (LMCT) is a common photoexcitation mechanism found in high-valence transition metal complexes with vacant valence shells, such as Cu. II Ni II Ce IV Fe III and Bi III They can directly generate highly reactive free radicals from inert C(sp) through a typical HAT process. 3 Hydrogen atoms are abstracted from the H-H bond. Meanwhile, reactive oxygen species (ROS) stand out due to their economic efficiency and powerful oxidizing properties, such as singlet oxygen formed through energy transfer (EnT). 1 O2) and superoxide radicals (O2) formed through photoinduced electron transfer (PET). •− Recent advances suggest that simultaneously integrating LMCT, HAT, and oxygen activation (EnT or PET) events into a single MOF reveals the potential for achieving inert C(sp). 3 Activation and oxidation of H-bonds.

[0003] However, 3D MOFs suffer from problems such as pore size confinement, slow electron transport, and substrate diffusion, which limit their application to inert C(sp) substrates. 3Photocatalytic activity of H-bond oxidation. Meanwhile, over the past few decades, various ultrathin two-dimensional (2D) layered nanocatalytic materials (such as metal oxides and hydroxides, boron / carbonitrides, graphene and graphene oxide, and transition metal disulfides) have been developed as powerful strategies to improve catalytic conversion efficiency, exhibiting surprising activity in photocatalytic activation and conversion. Their high surface area and abundant, easily accessible active sites enhance communication between catalytic active sites and substrate molecules, minimizing pathways related to mass / charge transfer. Ultrathin 2D MOF nanosheets formed by in-situ exfoliation of 3D MOFs provide more accessible active sites, ultra-high flexibility, faster diffusion, and improved host-guest affinity between active sites and substrate / product molecules within the 2D MOF nanosheets. This method enables ultrathin 2D MOF nanosheets with HAT reagents to promote the oxidation of inert C(sp) bonds. 3 Ideal candidate material for the activation and transformation of )−H bonds, which facilitates the development of MOF-based photo-mediated HAT catalysts, thereby opening inert C(sp) bonds. 3 The generalized and diverse manifolds of C(sp)-H bonds provide a promising strategy. Although some ultrathin 2D MOF nanosheets have been constructed for specific catalytic transformations, to our knowledge, few 2D MOF nanosheets synthesized from inexpensive starting materials have been used for inert C(sp)-H bonds. 3 Reports on the activation and oxidation of H-bonds. Summary of the Invention

[0004] To achieve the above objectives and solve the problems existing in the prior art, the technical solution adopted by the present invention is: a metal-organic framework nanosheet, using Cu transition metal ions... 2+ Using L as a ligand, a three-dimensional layered metal-organic framework (MOF) material was constructed via a solvothermal synthesis strategy. Subsequently, highly catalytically active MOF nanosheets were efficiently prepared using a physical exfoliation technique. The synthetic route is as follows:

[0005] Cu 2+ +L→Cu-L

[0006] The ligand L is selected from H2AQ;

[0007] The transition metal salt is selected from copper nitrate;

[0008] The ligand H2AQ has the following molecular structural formula (A).

[0009] .

[0010] Specifically, a metal-organic framework nanosheet is prepared by the following steps: a three-dimensional layered metal-organic framework material Cu−AQ, which is newly prepared by inorganic copper salt and 2,7-dicarboxyanthraquinone via a solvothermal method, is dispersed in an organic solvent and ultrasonically sonicated to obtain a colloidal suspension. After centrifugation or filtration and drying, the metal-organic framework nanosheet Cu−AQ-NS is obtained.

[0011] The organic solvent is selected from at least one of ethylene glycol, acetonitrile and ethanol, and the ratio of Cu−AQ to organic solvent is 1 mg to 4 mg: 2 ml.

[0012] Some specific steps in the preparation of the metal-organic framework nanosheets involve sonication for 6–48 h.

[0013] Some specific steps in the preparation of the metal-organic framework nanosheets involve sonication for 6–36 h.

[0014] Some specific steps in the preparation of the metal-organic framework nanosheets include an ultrasonic time of 20-30 h and an ultrasonic frequency of 50-60 kHz.

[0015] The metal-organic framework nanosheet preparation steps of the present invention can obtain the metal-organic framework nanosheets by centrifugation and filtration.

[0016] Some specific steps in the preparation of the metal-organic framework nanosheets include centrifugation at a speed of 6000~10000 rpm for 3~30 min.

[0017] Some specific steps in the preparation of the metal-organic framework nanosheets include centrifugation at a speed of 6000~10000 rpm for 4~10 min.

[0018] In some specific technical solutions, the preparation steps of the three-dimensional layered metal-organic framework material Cu−AQ are as follows: copper salt and 2,7-dicarboxyanthraquinone are dissolved in an organic solvent, tetrafluoroboric acid is added, and the mixture is heated to 70-90 ºC for 3-5 h and reacted for 15-30 h in a high-pressure reactor. Then, the mixture is cooled to room temperature for 15-30 h, washed, and dried to obtain Cu-AQ.

[0019] The copper salt is selected from at least one of copper nitrate and copper perchlorate.

[0020] The organic solvent is selected from at least one of N,N-dimethylacetamide, N,N-dimethylacetamide, methanol, and acetonitrile.

[0021] In some specific technical solutions, the mass ratio of copper salt to 2,7-dicarboxyanthraquinone is 1:1.5~2.0.

[0022] In some specific technical solutions, the ratio of tetrafluoroboric acid to organic solvent is 2 μl to 3 μl: 1 ml.

[0023] In some specific technical solutions, the preparation steps of the three-dimensional layered metal-organic framework material Cu−AQ are as follows: copper nitrate and 2,7-dicarboxyanthraquinone are dissolved in a mixed solution of N,N-dimethylformamide and acetonitrile in a mass ratio of 1:1.6 at a volume ratio of 3:1. Tetrafluoroboric acid is added, and the mixture is heated to 80 ºC for 20 h in a high-pressure reactor after 4 h and then cooled to room temperature for 20 h. After washing and drying, Cu−AQ is obtained.

[0024] The three-dimensional layered metal-organic framework material Cu−AQ of this invention can be prepared using methods disclosed in the prior art, for example, according to the literature Zhang Z, Yoshikawa H, Awaga K. Monitoring the solid-state electrochemistry of Cu (2, 7-AQDC)(AQDC = anthraquinone dicarboxylate) in alithium battery: coexistence of metal and ligand redox activities in a metal–organic framework[J]. Journal of the American Chemical Society, 2014, 136(46): 16112-16115.

[0025] A specific method for preparing metal-organic framework nanosheets includes the following steps:

[0026] Step 1: Under ice bath conditions, 10.8 g (0.1 mol) benzyl alcohol was added dropwise to 150 mL of dry toluene while stirring. 40.0 g (0.3 mol) anhydrous aluminum chloride was added to the mixture, and the mixture was heated to 110ºC and refluxed for 4 h. After cooling, 25.0 g crushed ice, 45 mL of water, and 40 mL of concentrated hydrochloric acid were added sequentially to the reaction solution. After filtration, the filter cake was collected and washed three times successively with 50 mL of water, 40 mL of ethyl acetate, and 40 mL of saturated sodium carbonate solution. The crude product was dried in an oven at 80ºC to obtain a crude pale yellow solid. The crude product was recrystallized from glacial acetic acid to finally obtain 4.5 g of a bright gray product, with a yield of 21.6%.

[0027] Step 2: Dissolve 1.0 g of the bright gray product obtained in Step 1 in 150 mL of boiling glacial acetic acid. Dissolve 1.0 g (10 mmol) of chromium trioxide in a small amount of water and slowly add it to the above solution. Reflux for 30 to 40 min, until the solution turns green. After cooling, pour the reaction solution into a large amount of ice water and filter to obtain the product. Dry the crude product in a vacuum drying oven to obtain a milky white solid, approximately 1.1 g, with a yield of 93%.

[0028] Step 3: Under ice bath conditions, add 6.6 g (66 mmol) of chromium trioxide to a mixed solution of 0.3 mL concentrated sulfuric acid, 1.8 mL acetic anhydride, and 40 mL glacial acetic acid. Heat the mixture to 35 ºC, and slowly add 1.3 g of the milky white solid obtained in Step 2 in several portions. After the addition is complete, raise the reaction temperature to 120 ºC and reflux for 4 h. After cooling to room temperature, pour the reaction solution into 400 mL of water and filter. Wash the upper filter cake with water to obtain a pale yellow product, approximately 1.4 g, with a yield of 87%.

[0029] Step 4: Dissolve 15.0 mg of the white powder obtained in Step 3 and 24.0 mg of Cu(NO3)2·3H2O in a mixed solution of 3 mL N,N-dimethylacetamide and 1 mL acetonitrile. Then, sonicate the solution until it is completely dissolved. Add 10 μL of tetrafluoroboric acid to the clear solution and place it in a high-pressure reactor. After 4 h, heat the solution to 80 °C and keep it at that temperature for 20 h. Then, cool the solution to room temperature for 20 h. Filter and collect the solution. Wash the crystals with 5 mL of ethanol and dry them to obtain blue-green blocky crystals.

[0030] Step 5: Disperse 10.0 mg of the blue-green blocky crystals obtained in Step 4 in 10 mL of ethylene glycol and sonicate at room temperature for about 24 h. Then, centrifuge the blue-green colloidal suspension at 8000 rpm for 5 min, and vacuum dry the resulting powder overnight to obtain Cu−AQ-NS (where Cu represents the metal node, AQ represents the anthraquinone ligand H2AQ, and NS represents the layered nanomaterial).

[0031] The metal-organic framework nanosheets prepared by the method are used in the catalytic coupling reaction of cyclohexane with benzenemethylene malononitrile and in the catalytic aerobic oxidation reaction of cyclohexane.

[0032] The beneficial effects of this invention are: a method for preparing metal-organic framework nanosheets and their applications, wherein the metal-organic framework nanosheets utilize Cu in transition metal salts. 2+Using 2,7-dicarboxyanthraquinone as a ligand, metal-organic framework (MOF) materials are prepared via a solvothermal reaction, followed by physical exfoliation to obtain MOF nanosheets. The two-dimensional copper-based MOF nanosheets prepared in this invention combine the characteristics of hexagons and triangles, forming a stable network structure. This network structure not only effectively disperses external forces but also provides strong support, significantly improving the structural stability of the MOF nanosheets and ensuring porosity. Simultaneously, the numerous coordinating unsaturated copper sites provide a favorable environment for the Cu-Cl coordinated LMCT process. The exfoliated MOF nanosheets expose more porous structures and sufficient anthraquinone active centers, which is beneficial for oxygen adsorption and conversion, thereby generating sufficient reactive oxygen species and achieving higher catalytic activity. Compared with existing technologies, the MOF nanosheets prepared by this method have low raw material costs, high yields, and chemically stable compounds, making them easy to apply in practice. Furthermore, they can efficiently catalyze the coupling reaction of cyclohexane with benzenemethylene malononitrile and the aerobic oxidation reaction of cyclohexane under mild light conditions. Attached Figure Description

[0033] Figure 1 This is a structural diagram of the target compound Cu−AQ-NS from Example 3 of the present invention.

[0034] Figure 2 This is the XRD pattern of Cu−AQ-NS, the target compound in Example 3 of this invention.

[0035] Figure 3 This is a TEM image of Cu−AQ-NS, the target compound in Example 3 of this invention.

[0036] Figure 4 This is a graph showing the yield of the target compound Cu−AQ-NS in Example 3 of this invention as a function of time in the catalytic reaction of benzenemethylene malononitrile and cyclohexane under light irradiation.

[0037] Figure 5 This is a cyclic test diagram of the aerobic oxidation reaction of cyclohexane catalyzed by the target compound Cu−AQ-NS under light irradiation in Example 3 of the present invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments. Example 1

[0039] Under ice bath conditions, benzyl alcohol (10.0 g, 0.1 mol) was added dropwise to 150 mL of toluene. After the addition was complete, anhydrous aluminum chloride (40.0 g, 0.3 mol) was added to the mixture in small amounts several times. After the addition was complete, the temperature of the mixture was gradually raised to room temperature and stirred for 30 minutes at room temperature, then the temperature was raised to 110 °C and reacted for 3 h. After the reaction was completed and cooled to room temperature, the reaction solution was slowly poured into an ice-water mixture, and then 40 mL of concentrated hydrochloric acid was added to produce a yellow precipitate. The precipitate was filtered and washed three times successively with deionized water, ethyl acetate, saturated sodium carbonate solution, and deionized water. After drying, a light yellow solid was obtained, which was then recrystallized from glacial acetic acid to obtain 4.5 g of light yellow powder, with a yield of 21.6% (based on the molar mass of benzyl alcohol), namely 2,7-dimethylanthracene. 1 H NMR (600 MHz, CDCl3, ppm): δ 8.36−8.16 (m, 2H), 7.88 (d,2H), 7.72 (s, 2H), 7.31−7.26 (m, 4H), 2.54 (s, 6H).

[0040] Chromium trioxide (1.0 g, 10.0 mmol) was dissolved in deionized water (1.0 g) by ultrasonication to prepare 1 mL of the first solution. 2,7-Dimethylanthraquinone (1.0 g, 5 mmol) from the previous step was added to 150 mL of glacial acetic acid. The mixture was heated to 130 ºC until the solid completely dissolved, preparing the second solution. The first solution was slowly added dropwise to the second solution, and the reaction was carried out at 130 ºC for 45 minutes, after which the solution turned dark green. The reaction was stopped, and after cooling to room temperature, the solution was poured into 1000 mL of deionized water. A white precipitate was formed by standing, vacuum filtration, and washing the filter cake with 300 mL of deionized water. The precipitate was then vacuum dried to obtain 1.1 g of a white solid, with a yield of 93%, namely 2,7-dimethylanthraquinone. 1 H NMR (600 MHz, CDCl3, ppm): δ 8.19 (d, 2H), 8.08 (d, 2H), 7.58 (dd, 2H), 2.53 (s, 6H).

[0041] Chromium trioxide (6.6 g, 65.5 mmol) was added to a mixed solution of 0.3 mL concentrated sulfuric acid, 1.8 mL acetic anhydride, and 40 mL glacial acetic acid and placed at 0 ºC. Then, the white solid of 2,7-dimethylanthraquinone (1.3 g, 5.4 mmol) obtained above was slowly added to the mixed solution. After the addition was complete, the reaction temperature was raised to 120 ºC and stirred continuously for 5 h. The reaction was stopped, and after the reaction temperature was cooled to room temperature, the solution was poured into 500 mL of deionized water, and allowed to stand to precipitate a yellow precipitate. The precipitate was filtered under vacuum, and the filter cake was washed with 300 mL of deionized water and dried under vacuum to obtain 1.4 g of a bright yellow solid, with a yield of 87%, namely ligand H2AQ. 1 H NMR (600 MHz, DMSO- d 6, ppm): δ 13.75 (s, 1H), 8.69 (d, 2H), 8.43 (d, 2H), 8.34 (dd, 2H). Example 2

[0042] Organic ligand H₂AQ (15.0 mg) and Cu(NO₃)₂·3H₂O (24.0 mg) were added to a mixed solution of 3 mL N,N-dimethylacetamide and 1 mL acetonitrile, and sonicated for 30 minutes until completely dissolved. After sonication, 10 μL of HBF₄ (40%) solution was added dropwise to the clear solution, and the mixture was placed in a 25 mL high-pressure reactor and reacted in an oven at 80 °C for 20 h. After cooling to room temperature, green blocky crystals were obtained. The crystals were filtered off, washed three times with DMF and ethanol, and dried at room temperature. The yield was 25% (calculated based on the molar mass of ligand H₂AQ). The crystal structure diagram is shown below. Figure 1 As shown. Example 3

[0043] Freshly prepared Cu−AQ (10.0 mg) was dispersed in ethylene glycol (10 mL) and sonicated at 53 kHz for approximately 24 h at room temperature. The blue-green colloidal suspension was then centrifuged at 8000 rpm for 5 min, and the resulting powder was vacuum-dried overnight to obtain Cu−AQ-NS nanosheets. The XRD pattern of the compound Cu−AQ-NS is shown below. Figure 2 As shown. TEM image of compound Cu−AQ-NS, as shown. Figure 3 As shown. (Through) Figure 2 and 3 It can be seen that the expected single-layer nanosheets were successfully obtained through the exfoliation technique. Example 4

[0044] Freshly prepared Cu−AQ (10.0 mg) was dispersed in ethylene glycol (10 mL) and sonicated at a working frequency of 53 kHz for about 12 h at room temperature. The blue-green colloidal suspension was then centrifuged at 8000 rpm for 5 min, and the resulting powder was vacuum dried overnight to obtain Cu−AQ-NS nanosheet materials. Example 5

[0045] Freshly prepared Cu−AQ (10.0 mg) was dispersed in ethylene glycol (10 mL) and sonicated at a working frequency of 53 kHz for about 6 h at room temperature. The blue-green colloidal suspension was then centrifuged at 8000 rpm for 5 min, and the resulting powder was vacuum dried overnight to obtain Cu−AQ-NS nanosheet materials. Example 6

[0046] Freshly prepared Cu−AQ (10.0 mg) was dispersed in ethylene glycol (10 mL) and sonicated at a working frequency of 53 kHz for approximately 36 h at room temperature. The blue-green colloidal suspension was then centrifuged at 8000 rpm for 5 min, and the resulting powder was vacuum dried overnight to obtain Cu−AQ-NS nanosheet materials. Example 7

[0047] Freshly prepared Cu−AQ (10.0 mg) was dispersed in ethanol (10 mL) and sonicated at a working frequency of 53 kHz for approximately 24 h at room temperature. The blue-green colloidal suspension was then centrifuged at 8000 rpm for 5 min, and the resulting powder was vacuum dried overnight to obtain Cu−AQ-NS nanosheet materials. Example 8

[0048] Freshly prepared Cu−AQ (10.0 mg) was dispersed in acetonitrile (10 mL) and sonicated at a working frequency of 53 kHz for approximately 24 h at room temperature. The blue-green colloidal suspension was then centrifuged at 8000 rpm for 5 min, and the resulting powder was vacuum dried overnight to obtain Cu−AQ-NS nanosheet materials. Example 9

[0049] Freshly prepared Cu−AQ (10.0 mg) was dispersed in ethylene glycol (10 mL) and sonicated at a working frequency of 53 kHz for approximately 24 h at room temperature. The blue-green colloidal suspension was then filtered, and the resulting powder was vacuum-dried overnight to obtain Cu−AQ-NS nanosheet materials.

[0050] Example 10: Coupling reaction of cyclohexane and benzenemethylene malononitrile catalyzed by Cu−AQ-NS

[0051]

[0052] In a 10 mL photocatalytic reaction tube, 3 mL of acetonitrile solution was added first, followed by 5.0 mg of Cu−AQ-NS, 2.0 mg of NH4Cl, 15.4 mg of benzenemethylmalononitrile, and 10 μL of cyclohexane. The tube was sealed with a stopper, and argon gas was introduced for ten minutes to eliminate interference from other gases. After the gas introduction, the tube was sealed with a sealing film and irradiated under a 420 nm lamp for 6 h. After the reaction, the yield was calculated using 1,3,5-trimethoxybenzene as an internal standard. The results showed that benzenemethylmalononitrile was converted to 2-(cyclohexylphenylmethyl)malononitrile with a yield greater than 90%. Figure 4 As shown.

[0053] Example 11: Aerobic oxidation of cyclohexane catalyzed by Cu−AQ-NS

[0054]

[0055] In a 10 mL photoreaction tube, 3 mL of acetonitrile solution was added first, followed by 5.0 mg of Cu−AQ-NS, 2.0 mg of NH4Cl, 15.4 mg of benzenemethylene malononitrile, and 10 μL of cyclohexane. The tube was sealed with a stopper, and oxygen was introduced for ten minutes to eliminate interference from other gases. After the aeration was complete, an oxygen bulb was connected to the photoreaction tube to ensure oxygen supply. The tube was irradiated under a 420 nm light source for 18 h. After the reaction, the yield was calculated using 1,3,5-trimethoxybenzene as an internal standard. The results showed that 60% of cyclohexane was converted to cyclohexanone, with a selectivity greater than 97%. Figure 5 As shown.

[0056] Example 12: Cu−AQ-NS catalyzed coupling reaction of cyclohexane with benzenemethylene malononitrile and aerobic oxidation reaction of cyclohexane prepared in Examples 4-9

[0057] The catalytic effects of Cu−AQ-NS prepared in Examples 4-9 on the coupling reaction of cyclohexane with benzenemethylene malononitrile and the aerobic oxidation reaction of cyclohexane were studied according to the methods of Examples 10 and 11. The specific data are shown in Tables 1 and 2.

[0058] Table 1. Data on the coupling reaction of cyclohexane and benzenemethylene malononitrile catalyzed by Cu−AQ-NS prepared in Examples 3-8.

[0059]

[0060] Table 2. Data on the Cu-AQ-NS catalytic aerobic oxidation of cyclohexane prepared in Examples 3-8

[0061]

[0062] As can be seen from the data in Tables 1 and 2, the Cu−AQ-NS prepared in Examples 3-9 has a good catalytic effect on the coupling reaction of cyclohexane with benzenemethylene malononitrile and the aerobic oxidation reaction of cyclohexane.

[0063] The advantages of this invention are: the metal-organic framework materials prepared by this method have low raw material costs, high yields, and the resulting compounds have stable chemical properties and are easy to apply in practice. As a catalyst, it exhibits high catalytic conversion efficiency for in-situ catalytic oxidation of the alkane cyclohexane under light irradiation.

Claims

1. An application of a metal-organic framework nanosheet, characterized in that: Application of the metal-organic framework nanosheets in the catalytic coupling reaction of cyclohexane and benzenemethylene malononitrile; The nanosheets are prepared by the following steps: the three-dimensional layered metal-organic framework material Cu-AQ, which is newly prepared by inorganic copper salt and 2,7-dicarboxyanthraquinone via a solvothermal method, is dispersed in an organic solvent and ultrasonicated to obtain a colloidal suspension. After centrifugation or filtration and drying, the metal-organic framework nanosheets Cu-AQ-NS are obtained. The organic solvent is selected from at least one of ethylene glycol, acetonitrile and ethanol, and the ratio of Cu-AQ to organic solvent is 1 mg to 4 mg: 2 ml.

2. An application of a metal-organic framework nanosheet, characterized in that: Application of the metal-organic framework nanosheets in the catalytic aerobic oxidation reaction of cyclohexane; The nanosheets are prepared by the following steps: the three-dimensional layered metal-organic framework material Cu-AQ, which is newly prepared by inorganic copper salt and 2,7-dicarboxyanthraquinone via a solvothermal method, is dispersed in an organic solvent and ultrasonicated to obtain a colloidal suspension. After centrifugation or filtration and drying, the metal-organic framework nanosheets Cu-AQ-NS are obtained. The organic solvent is selected from at least one of ethylene glycol, acetonitrile and ethanol, and the ratio of Cu-AQ to organic solvent is 1 mg to 4 mg: 2 ml.

3. The application according to claim 1 or 2, characterized in that: The ultrasound duration is 6-48 hours.

4. The application according to claim 1 or 2, characterized in that: The ultrasound duration is 6-36 hours.

5. The application according to claim 1 or 2, characterized in that: The ultrasound duration is 20-30 hours, and the ultrasound frequency is 50-60 kHz.

6. The application according to claim 1 or 2, characterized in that: Centrifuge at 6000-10000 rpm for 3-30 min.

7. The application according to claim 1 or 2, characterized in that, The preparation steps of the three-dimensional layered metal-organic framework material Cu-AQ are as follows: copper salt and 2,7-dicarboxyanthraquinone are dissolved in an organic solvent, tetrafluoroboric acid is added, and the mixture is heated to 70-90 ºC for 2-5 h and reacted for 15-30 h in a high-pressure reactor. Then, the mixture is cooled to room temperature within 15-30 h, washed, and dried to obtain Cu-AQ. The copper salt is selected from at least one of copper nitrate and copper perchlorate; In the preparation step of Cu-AQ, the organic solvent is selected from at least one of N,N-dimethylacetamide, N,N-dimethylacetamide, methanol, and acetonitrile.

8. The application according to claim 7, characterized in that, The mass ratio of copper salt to 2,7-dicarboxyanthraquinone is 1:1.5-2.0, and the volume ratio of tetrafluoroboric acid to organic solvent is 2 μl-3 μl:1 ml.

9. The application according to claim 7, characterized in that, The preparation steps of the three-dimensional layered metal-organic framework material Cu-AQ are as follows: copper nitrate and 2,7-dicarboxyanthraquinone are dissolved in a mixed solution of N,N-dimethylformamide and acetonitrile in a mass ratio of 1:1.6 at a volume ratio of 3:

1. Tetrafluoroboric acid is added, and the mixture is heated to 80 °C and reacted for 20 h in a high-pressure reactor after 4 h. Then, it is cooled to room temperature within 20 h, washed, and dried to obtain Cu-AQ.

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