Preparation method of a metal-organic framework-based composite material encapsulating phthalocyanine molecules and application thereof

Abstract

The application provides a preparation method of a phthalocyanine molecule encapsulated metal-organic framework-based composite material, and comprises the following steps: A) dissolving a metal salt and a metal-organic framework material in an organic solvent, and obtaining a metal ion modified metal-organic framework material after heating reaction; B) dispersing the metal ion modified metal-organic framework material in an organic solvent containing o-phthalodinitrile, and obtaining a phthalocyanine molecule encapsulated metal-organic framework-based composite material after heating reaction. The preparation method of the phthalocyanine molecule encapsulated metal-organic framework-based composite material provided by the application can realize simple preparation of the metal-organic framework composite material, and encapsulate the metal phthalocyanine molecule in the metal-organic framework composite material. The metal-organic framework-based composite material prepared by the application has high selectivity when applied to an electrocatalytic carbon dioxide to carbonic acid dimethyl ester reaction.

Description

Technical Field

[0001] This invention belongs to the field of preparation and synthesis of metal-organic framework (MOF) materials, and particularly relates to a method for synthesizing a metal-organic framework-based composite material that encapsulates guest metal phthalocyanine molecules. Background Technology

[0002] Thanks to the unique structure and chemical properties of phthalocyanine molecules, metal phthalocyanine molecules have wide applications in catalysis. However, metal phthalocyanine molecules are prone to aggregation, leading to a decrease in catalytic activity. Therefore, suitable supports are needed to load and disperse phthalocyanine molecules to prevent aggregation.

[0003] Metal-organic frameworks (MOFs) are crystalline porous framework materials formed by the coordination self-assembly of metals (clusters) as nodes and organic ligands. Due to their high specific surface area, customizable pore structure, and modifiability and tailorability, they are ideal carriers. Dispersing and loading phthalocyanine molecules using porous MOFs provides an ideal solution to address the aggregation and deactivation of phthalocyanine molecules.

[0004] Currently, various synthetic strategies for metal-organic framework (MOF) composites loaded with metal phthalocyanines have been developed, including physical mixing, in-situ encapsulation, and ligand design. The physical mixing method typically involves dispersing pre-synthesized MOF crystals and phthalocyanine molecules in the same solvent, then collecting the phthalocyanine-loaded MOF solid powder by centrifugation or solvent evaporation. The in-situ encapsulation method disperses phthalocyanine molecules in the MOF synthesis solution to directly encapsulate them during MOF formation. The ligand design method introduces phthalocyanine functional units onto ligands, which requires a complex organic synthesis process. All of these methods have relatively high requirements for the reaction system and reaction conditions, resulting in relatively poor versatility.

[0005] In summary, developing a simple and universal synthetic method for encapsulating metal phthalocyanines within the pores of metal-organic framework materials is of great significance. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a method for preparing a metal-organic framework-based composite material encapsulating phthalocyanine molecules. The preparation method provided by this application can achieve in-situ confinement of metal phthalocyanine molecules within the pores of the metal-organic framework material through a simple method; and the metal-organic framework-based composite material encapsulating phthalocyanine molecules prepared by this application has high selectivity in the electrocatalytic reaction of carbon dioxide to dimethyl carbonate.

[0007] In view of this, this application provides a method for preparing a metal-organic framework-based composite material encapsulating phthalocyanine molecules, comprising the following steps:

[0008] A) Dissolve metal salts and metal-organic framework materials in an organic solvent, and then heat the reaction to obtain metal ion-modified metal-organic framework materials;

[0009] B) The metal ion-modified metal-organic framework material and phthalonitrile are dissolved in an organic solvent and heated to react, thereby obtaining a metal-organic framework-based composite material encapsulating phthalocyanine molecules.

[0010] Preferably, the preparation method of the metal-organic framework material is as follows:

[0011] Zirconium source, 2,5-thiophene dicarboxylic acid and formic acid are mixed in a solvent, heated, cooled and dried to obtain metal-organic framework material.

[0012] Preferably, in the step of obtaining the metal-organic framework material, the mass ratio of the zirconium source to the 2,5-thiophene dicarboxylic acid is 1:(0.4-0.8), the amount of formic acid used is 5.0-10.0 mL / 460 mg zirconium source, and the solvent is selected from a mixed solvent of dimethylformamide and N-methylpyrrolidone with a volume ratio of 1:(0.5-1.2).

[0013] Preferably, in the step of obtaining the metal-organic framework material, the heating temperature is 100-150°C.

[0014] Preferably, the metal salt is selected from CoCl2·6H2O and FeCl2·4H2O.

[0015] Preferably, when the metal salt is CoCl2·6H2O, the mass ratio of the metal-organic framework material to the CoCl2·6H2O is 1:(1-10); when the metal salt is FeCl2·4H2O, the mass ratio of the metal-organic framework material to the FeCl2·4H2O is 1:(1-10).

[0016] Preferably, in step A), the heating temperature is 50-100°C and the duration is 10-15 hours; the heating process also includes sequential cooling, washing, and drying.

[0017] Preferably, in step B), the organic solvent is selected from formamide, the heating temperature is 150-200°C, and the time is 10-30 min; the heating process also includes washing and drying.

[0018] This application also provides the application of metal-organic framework materials in the electrocatalytic preparation of dimethyl carbonate from carbon dioxide, wherein the metal-organic framework material is a metal-organic framework composite material prepared by the aforementioned preparation method.

[0019] Preferably, the preparation of dimethyl carbonate further includes:

[0020] The metal-organic framework composite material is vacuum activated at the heating temperature for 12–24 hours.

[0021] This application provides a method for preparing a metal-organic framework-based composite material encapsulating phthalocyanine molecules. First, a metal salt and a metal-organic framework material are dissolved in an organic solvent and heated to react, causing metal ions to anchor on the unsaturated coordinated zirconium oxide clusters of the metal-organic framework material, achieving uniform dispersion of the metal ions within the framework. The resulting metal-organic framework material is then dispersed in an organic solvent containing phthalonitrile. By introducing phthalonitrile to react with the metal ions modified on the zirconium oxide clusters, metal phthalocyanine molecules are obtained and confined in situ within the pores of the metal-organic framework, thus obtaining the metal-organic framework-based composite material encapsulating metal phthalocyanine molecules. The preparation method provided in this application is simple and does not require special conditions such as high pressure.

[0022] Furthermore, the metal-organic framework composite material for encapsulating phthalocyanine molecules prepared in this application is applied to the electrocatalytic preparation of dimethyl carbonate from carbon dioxide. By dispersing and loading phthalocyanine molecules through porous metal-organic framework materials, the aggregation and deactivation of phthalocyanine molecules are avoided, thereby enabling the reaction to have high selectivity. Attached Figure Description

[0023] Figure 1 These are powder X-ray diffraction patterns of the metal-organic framework materials prepared in Examples 1 and 2 of this invention;

[0024] Figure 2 The UV-Vis spectra of the MOF composite materials prepared in Examples 1 and 2 of this invention are shown below.

[0025] Figure 3 The nitrogen adsorption curves of the metal-organic framework materials prepared in Examples 1 and 2 of this invention at 77 K are shown.

[0026] Figure 4 The graph shows the electrocatalytic performance of the metal-organic framework materials prepared in Examples 1 and 2 of this invention for reducing carbon dioxide to dimethyl carbonate. Detailed Implementation

[0027] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0028] In view of the problems in the preparation of metal-organic framework-based composite materials encapsulating phthalocyanine molecules in the prior art, this application provides a method for preparing metal-organic framework-based composite materials encapsulating phthalocyanine molecules. First, metal ions such as Fe and Co are anchored in the metal-organic framework and coordinated onto unsaturated zirconium oxide clusters to achieve uniform dispersion of Fe and Co ions within the framework. Then, phthalonitrile is introduced to react with the Fe and Co ions modified on the zirconium oxide clusters to form phthalocyanine metal molecules, which are then confined in situ within the pores of the metal-organic framework. This method is easy to implement in terms of reaction system and conditions, and can completely encapsulate phthalocyanine molecules within the metal-organic framework material. Specifically, embodiments of this invention disclose a method for preparing metal-organic framework-based composite materials encapsulating phthalocyanine molecules, including the following steps:

[0029] A) Dissolve metal salts and metal-organic framework materials in an organic solvent, and then heat the reaction to obtain metal ion-modified metal-organic framework materials;

[0030] B) The metal ion-modified metal-organic framework material is dispersed in an organic solvent containing phthalonitrile and heated to obtain a metal-organic framework-based composite material encapsulating phthalocyanine molecules.

[0031] The method for preparing the metal-organic framework-based composite material for encapsulating phthalocyanine molecules provided in this application first involves dissolving a metal salt and a metal-organic framework material in an organic solvent, followed by heating and reaction to obtain a metal ion-modified metal-organic framework material. In this process, it is first necessary to synthesize a metal-organic framework material with a pore size matching the size of the encapsulated phthalocyanine molecule. In this application, the metal-organic framework material is selected from DUT-67 material, and its preparation method is as follows:

[0032] Zirconium source, 2,5-thiophene dicarboxylic acid and formic acid are mixed in a solvent, heated, cooled and dried, and finally activated under vacuum to obtain metal-organic framework material.

[0033] In the above-mentioned preparation process of DUT-67, the zirconium source is selected from zirconium chloride, and the solvent is selected from a mixed solvent of dimethylformamide and N-methylpyrrolidone. Specifically, the volume ratio of dimethylformamide to N-methylpyrrolidone is 1:(0.5-1.5). The mass ratio of the zirconium source to the 2,5-thiophene dicarboxylic acid is 1:(0.4-0.8), and the amount of formic acid used is 5.0-10.0 mL / 460 mg zirconium source. Specifically, the mass ratio of the zirconium source to the 2,5-thiophene dicarboxylic acid is 1:0.4, 1:0.5, 1:0.6, 1:0.7, or 1:0.8, and the amount of formic acid used is 5.0 mL / 460 mg zirconium chloride, 6.0 mL / 460 mg zirconium chloride, 7.0 mL / 460 mg zirconium chloride, 8.0 mL / 460 mg zirconium chloride, 9.0 mL / 460 mg zirconium chloride, or 10.0 mL / 460 mg zirconium chloride. The heating rate is 2–10 °C / min, the heating temperature is 100–150 °C, and the heating time is 48–96 h. After heating, the temperature is lowered to 30 °C at a rate of 2–10 °C / min. The solid obtained after cooling is washed sequentially with dimethylformamide and ethanol, and then dried to obtain DUT-67.

[0034] In the step of preparing the metal-organic framework material modified with metal ions, the metal salt is specifically selected from one of Fe salt and Co salt, more specifically, from one of CoCl2·6H2O and FeCl2·4H2O; when the metal salt is CoCl2·6H2O, the mass ratio of the metal-organic framework material to CoCl2·6H2O is 1:2.5; when the metal salt is FeCl2·4H2O, the mass ratio of the metal-organic framework material to FeCl2·4H2O is 1:1.25. The organic solvent is specifically selected from dimethylformamide and N-methylpyrrolidone. In this process, the heating rate is 2–10 °C / min, the heating temperature is 50–100 °C, and the time is 10–15 h. After heating, the temperature is lowered to 30 °C at a rate of 2–10 °C / min. The solid obtained after cooling is then washed with dimethylformamide and ethanol and dried.

[0035] In the above process, metal ions such as Fe and Co are anchored on the unsaturated zirconium oxide clusters in the metal-organic framework material, thereby achieving uniform dispersion of metal ions such as Fe and Co within the framework.

[0036] According to the present invention, the metal-organic framework material modified with metal ions is dispersed in an organic solvent containing phthalonitrile and heated to react, thereby obtaining a metal-organic framework-based composite material encapsulating phthalocyanine molecules. In this process, phthalonitrile is introduced to react with Fe, Co, and other metal ions on the zirconium oxide clusters of the metal-organic framework material to form phthalocyanine molecules, which are then confined in situ within the pores of the metal-organic framework, thus obtaining the metal-organic framework-based composite material encapsulating phthalocyanine molecules. Specifically, the mass ratio of the metal-organic framework material modified with metal ions to phthalonitrile is 5:2, and the organic solvent is selected from formamide. In this process, the heating temperature is 150–200°C, and the time is 10–30 min; the solid obtained after heating is then washed with dimethylformamide, dried, and then immersed in acetone to remove residual organic solvent, and finally vacuum dried.

[0037] This application also provides the application of the metal-organic framework-based composite material prepared above in the electrocatalytic preparation of dimethyl carbonate from carbon dioxide.

[0038] According to the present invention, before specific application, the metal-organic framework-based composite material is first dried under heating conditions, wherein the heating temperature is 100-200°C and the drying time is 12-24 hours.

[0039] In the application of the metal-organic framework-based composite material in the electrocatalytic preparation of dimethyl carbonate from carbon dioxide, the specific process is carried out in a manner well known to those skilled in the art, and no particular limitations are imposed here. In specific applications, the metal-organic framework-based composite material can be used as a cathode catalyst material, as an anode catalyst material, or as both a cathode catalyst material and an anode catalyst material. In a specific embodiment, the metal-organic framework-based composite material is used as both a cathode catalyst material and an anode catalyst material.

[0040] To further understand the present invention, the preparation method and application of the metal-organic framework composite material for encapsulating phthalocyanine molecules provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited to the following embodiments.

[0041] Example 1: MOF-based composite material internally encapsulated with cobalt phthalocyanine

[0042] (1) Preparation of metal-organic framework material DUT-67

[0043] 460 mg of zirconium chloride, 220 mg of 2,5-thiophene dicarboxylic acid, 8.9 mL of formic acid, and a mixed solvent of 20 mL of dimethylformamide and N-methylpyrrolidone (volume ratio 1:1) were added to a 100 mL hydrothermal reactor and stirred at room temperature for 3 h. The hydrothermal reactor was then sealed and placed in an oven, and the temperature of the oven was increased from room temperature to 120 °C at a heating rate of 5 °C / min and maintained at this temperature for 72 h. The mixture was then slowly cooled to room temperature at a cooling rate of 5 °C / min and allowed to stand for 14 h to obtain a white powdery precipitate. The collected solid was washed successively with dimethylformamide and ethanol, and then dried under vacuum to obtain DUT-67.

[0044] (2) Preparation of Co-DUT-67, a metal-organic framework material modified with cobalt ions

[0045] Take 40 mg of DUT-67 and place it in a 20 mL glass vial. Add 2 mL of dimethylformamide and sonicate at room temperature for 120 min. Take 100 mg of CoCl2·6H2O and place it in a 10 mL beaker. Add 1 mL of dimethylformamide and sonicate at room temperature for 120 min. Then add it to the dispersed DUT-67 and continue to sonicate for 10 min. Increase the temperature of the oven from room temperature to 85℃ at a heating rate of 5℃ / min and maintain it at 85℃ for 12 h. Then slowly cool it to room temperature at a cooling rate of 5℃ / min. Wash the collected solids with dimethylformamide and ethanol in sequence, and then vacuum dry to obtain Co-DUT-67.

[0046] (3) Preparation of CoPc@DUT-67, a metal-organic framework composite material encapsulating cobalt phthalocyanine molecules

[0047] Take 40 mg of activated Co-DUT-67 and place it in a 10 mL round-bottom flask. Add 1 mL of formamide and sonicate at room temperature for 120 min. Take 16 mg of o-phthalonitrile and place it in a 10 mL beaker. Add 1 mL of formamide and sonicate at room temperature for 120 min. Then add it to the dispersed Co-DUT-67 and continue to sonicate for 10 min. Keep the temperature constant at 190 °C in an oil bath for 15 min with stirring. Wash the collected solid with dimethylformamide until the supernatant is colorless. Dry it and then soak it in acetone. Change the acetone every 12 h and repeat six times to remove residual formamide and dimethylformamide. After vacuum drying, CoPc@DUT-67 is obtained.

[0048] The metal-organic framework material DUT-67, the cobalt-modified MOF material Co-DUT-67, and the MOF material CoPc@DUT-67 encapsulating phthalocyanine molecules were characterized by X-ray diffraction (XRD). Figure 1 As shown, by Figure 1As can be seen, the metal-organic framework material DUT-67, the cobalt ion modified MOF material Co-DUT-67, and the CoPc@DUT-67 material encapsulated with cobalt phthalocyanine are in high agreement with the simulation data, proving that the crystal structure of the MOF in the encapsulated cobalt phthalocyanine MOF material CoPc@DUT-67 prepared in this invention is maintained.

[0049] UV-Vis spectroscopy was performed on the cobalt-modified MOF material Co-DUT-67 and the MOF material CoPc@DUT-67 encapsulating phthalocyanine molecules, as shown in the figure. Figure 2 As shown, by Figure 2 This proves that the cobalt phthalocyanine molecule was successfully synthesized.

[0050] The pore size distribution of DUT-67, the cobalt-modified MOF material Co-DUT-67, and the CoPc@DUT-67 material encapsulated with cobalt phthalocyanine was characterized by nitrogen adsorption testing. Figure 3 As shown, by Figure 3 It can be seen that the CoPc@DUT-67 material encapsulated with cobalt phthalocyanine prepared in this invention has a lower specific surface area than DUT-67, which proves that the cobalt phthalocyanine molecules are encapsulated in the MOF pores.

[0051] Example 2: MOF-based composite material with internally encapsulated iron phthalocyanine

[0052] (1) Preparation of metal-organic framework material DUT-67

[0053] A mixture of 460 mg zirconium chloride, 220 mg 2,5-thiophene dicarboxylic acid, 8.9 mL formic acid, and 20 mL of dimethylformamide and N-methylpyrrolidone (volume ratio 1:1) was added to a 100 mL hydrothermal reactor and stirred at room temperature for 3 h. The reactor was then sealed and placed in an oven, and the temperature was increased from room temperature to 120 °C at a rate of 5 °C / min and maintained at this temperature for 72 h. The reactor was then slowly cooled to room temperature at a rate of 5 °C / min and allowed to stand for 14 h to obtain a white powdery precipitate. The collected solid was washed successively with dimethylformamide and ethanol, and then dried under vacuum to obtain DUT-67.

[0054] (2) Preparation of Fe-DUT-67, a metal-organic framework material modified with iron ions

[0055] Take 40 mg of activated DUT-67 and place it in a 20 mL glass vial. Add 2 mL of dimethylformamide and sonicate at room temperature for 120 min. Take 50 mg of FeCl2·4H2O and place it in a 10 mL beaker. Add 1 mL of N,N-dimethylformamide and sonicate at room temperature for 120 min. Then add it to the dispersed DUT-67 and continue to sonicate for 10 min. Increase the temperature of the oven from room temperature to 85℃ at a heating rate of 5℃ / min and maintain it at 85℃ for 12 h. Then slowly cool it to room temperature at a cooling rate of 5℃ / min. Wash the collected solids with dimethylformamide and ethanol in sequence, and then vacuum dry to obtain Fe-DUT-67.

[0056] (3) Preparation of FePc@DUT-67, a metal-organic framework composite material encapsulating iron phthalocyanine molecules

[0057] Take 40 mg of Fe-DUT-67 and place it in a 10 mL round-bottom flask. Add 1 mL of formamide and sonicate at room temperature for 120 min. Take 16 mg of o-phthalonitrile and place it in a 10 mL beaker. Add 1 mL of formamide and sonicate at room temperature for 120 min. Then add it to the dispersed Fe-DUT-67 and continue to sonicate for 10 min. Keep the temperature constant at 190 °C in an oil bath with stirring for 15 min. Wash the collected solid with dimethylformamide until the supernatant is colorless. Then soak it in acetone, changing it every 12 h. Repeat this process six times to remove residual formamide and dimethylformamide. After vacuum drying, FePc@DUT-67 can be obtained.

[0058] The metal-organic framework material DUT-67, the cobalt-modified MOF material Fe-DUT-67, and the MOF material FePc@DUT-67 encapsulating phthalocyanine molecules were characterized by X-ray diffraction (XRD). Figure 1 As shown, by Figure 1 As can be seen, the metal-organic framework material DUT-67, the cobalt ion modified MOF material Fe-DUT-67, and the FePc@DUT-67 material encapsulated with cobalt phthalocyanine are in high agreement with the simulation data, proving that the crystal structure of the MOF in the encapsulated cobalt phthalocyanine MOF material FePc@DUT-67 prepared in this invention is maintained.

[0059] UV-Vis spectroscopy was performed on cobalt-modified MOF material Fe-DUT-67 and MOF material FePc@DUT-67 encapsulating phthalocyanine molecules, as shown in the figure. Figure 2 As shown, by Figure 2 This proves that the cobalt phthalocyanine molecule was successfully synthesized.

[0060] The pore size distribution of DUT-67, cobalt-modified MOF material Fe-DUT-67, and FePc@DUT-67 material encapsulated with cobalt phthalocyanine was characterized by nitrogen adsorption testing. Figure 3 As shown, by Figure 3 It can be seen that the FePc@DUT-67 material encapsulated with cobalt phthalocyanine prepared in this invention has a lower specific surface area than DUT-67, which proves that the cobalt phthalocyanine molecules are encapsulated in the MOF pores.

[0061] Example 3: Application of MOF-based composite materials encapsulated with phthalocyanine in the electrocatalytic reaction of carbon dioxide to dimethyl carbonate.

[0062] A certain amount of the MOF-based composite materials CoPc@DUT-67 and FePc@DUT-67 encapsulated with phthalocyanine prepared in Examples 1 and 2 were taken and vacuum dried at 150°C for 12 hours.

[0063] Take 2 mg of activated CoPc-DUT-67 / FePc-DUT-67 and 2 mg of carbon black, add 400 μL of anhydrous ethanol, and sonicate at room temperature for 10 min. Then add 10 μL of Nafion solution and sonicate at room temperature for 30 min to obtain a uniformly dispersed catalyst dispersant. Then coat 60 μL of the catalyst dispersant onto a 1.0*1.0 cm² plate. 2 The reactor was constructed using carbon fiber paper electrodes; CoPc@DUT-67 was used as the cathode catalyst, and FePc@DUT-67 was used as the anode catalyst. CO2 gas (99.999%) was introduced at a flow rate of 10 mL / min into a 0.1 M KBr methanol solution containing 40 mg Pd / C. After 15 min of aeration, the reactor was sealed. Electrochemical tests were performed using a CHI 760E electrochemical workstation in constant current mode (tested at 8 mA, 12 mA, 16 mA, 20 mA, and 24 mA). Liquid products were obtained by... 1 ¹H NMR detection was performed by mixing 500 μL of electrolyte with 100 μL of deuterated dimethyl sulfoxide (d-DMSO) and suppressing the peak using solvent pre-saturated water. The test results are as follows: Figure 4 The reaction formula is as follows;

[0064]

[0065] Depend on Figure 4 It is evident that the MPc@DUT-67 catalyst can be used for electrocatalytic CO2 reduction reaction and directly synthesize C3 products. Under the reaction conditions, the MPc@DUT-67 catalyst can selectively produce dimethyl carbonate (DMC), demonstrating the advantages of the composite material synthesized in this invention.

[0066] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0067] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a metal-organic framework-based composite material encapsulating phthalocyanine molecules, comprising the following steps: A) Metal salts and metal-organic framework materials are dissolved in an organic solvent and heated to react, resulting in metal ion-modified metal-organic framework materials; B) The metal ion-modified metal-organic framework material is dispersed in an organic solvent containing phthalonitrile and heated to react, thereby obtaining a metal-organic framework-based composite material encapsulating phthalocyanine molecules. The specific method for preparing the metal-organic framework material is as follows: Zirconium source, 2,5-thiophene dicarboxylic acid and formic acid are mixed in a solvent, heated, cooled and dried to obtain metal-organic framework material; In the step of obtaining the metal-organic framework material, the mass ratio of the zirconium source to the 2,5-thiophene dicarboxylic acid is 1:(0.4~0.8), the amount of formic acid used is 5.0~10.0 mL / 460 mg zirconium source; the solvent is selected from a mixed solvent of dimethylformamide and N-methylpyrrolidone with a volume ratio of 1:(0.5~1.2). In the step of obtaining the metal-organic framework material, the heating temperature is 100~150 ℃; The metal salt is selected from CoCl2•6H2O and FeCl2•4H2O.

2. The preparation method according to claim 1, characterized in that, When the metal salt is CoCl2•6H2O, the mass ratio of the metal-organic framework material to CoCl2•6H2O is 1:(1~10); when the metal salt is FeCl2•4H2O, the mass ratio of the metal-organic framework material to FeCl2•4H2O is 1:(1~10).

3. The preparation method according to claim 1, characterized in that, In step A), the heating temperature is 50~100℃ and the duration is 10~15 h; the heating process also includes cooling, washing and drying in sequence.

4. The preparation method according to claim 1, characterized in that, In step B), the organic solvent is selected from formamide, the heating temperature is 150~200 ℃, and the time is 10~30 min; the heating process also includes cooling, washing and drying in sequence.

5. Application of metal-organic framework-based composite materials in the electrocatalytic preparation of dimethyl carbonate from carbon dioxide, wherein the metal-organic framework-based composite material is the metal-organic framework-based composite material prepared by the preparation method according to any one of claims 1 to 4.

6. The application according to claim 5, characterized in that, The preparation of dimethyl carbonate also includes: The metal-organic framework-based composite material was activated under vacuum by heating for 12-24 hours.

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