Iron-based metal organic framework material based on supergravity-assisted hydrothermal method as well as preparation method and application of iron-based metal organic framework material

Abstract

The invention discloses an iron-based metal organic framework material based on a supergravity-assisted hydrothermal method as well as a preparation method and application of the iron-based metal organic framework material. The method comprises the following steps: respectively preparing a ferric chloride solution and a fumaric acid-DMF mixed solution, and then mixing the ferric chloride solution and the fumaric acid-DMF mixed solution to obtain a raw material mixed solution; transferring the raw material mixed solution into a high-pressure reaction kettle for hydrothermal reaction; then, the raw material mixed solution obtained after the hydrothermal reaction is put into a centrifugal machine to be subjected to multiple times of supergravity centrifugation, and then a centrifugal mixed solution obtained after multiple times of supergravity centrifugation is obtained; and finally, collecting the precipitate in the centrifugal mixed solution obtained by the last supergravity centrifugation, and carrying out vacuum drying on the collected precipitate to obtain the final iron-based metal organic framework material. The preparation method disclosed by the invention is simple and efficient, can improve the production efficiency while ensuring the high performance of the material, and is suitable for wide application in the fields of electro-catalysis and energy.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of metal-organic framework materials, and particularly relates to an iron-based metal-organic framework material based on a rotating packed bed-assisted hydrothermal method, a preparation method thereof, and an application thereof. Background Art

[0002] Iron-based metal-organic frameworks (Metal-Organic Frameworks, abbreviated as MOFs) are a class of porous materials formed by connecting metal ions or metal clusters with organic ligands through coordination bonds. Due to their highly ordered pore structure, large specific surface area, adjustable pore size, and rich active sites, iron-based metal MOFs have shown broad application prospects in the fields of gas storage, separation, catalysis, electrochemical energy storage and conversion, etc. Especially in key energy conversion technologies such as electrocatalytic oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and carbon dioxide reduction (CO2RR), iron-based metal MOFs have attracted much attention due to their good electrical conductivity, adjustable electronic structure, and high catalytic activity.

[0003] At present, common methods for synthesizing iron-based metal MOFs include solvothermal method, hydrothermal method, precipitation method, template method, and electrochemical deposition method, etc. Among them, the hydrothermal method is widely used because of its controllable reaction conditions and relatively simple operation. However, when preparing iron-based metal MOFs by the traditional hydrothermal method, there are the following main problems: 1. Impurity residue problem: Since it is difficult to completely remove reactants and by-products during the hydrothermal reaction process, the final product may contain unreacted precursors or by-products, reducing the material purity and affecting its catalytic performance. 2. Difficulty in controlling crystal growth: The structure and properties of MOFs are closely related to their crystal morphology, and factors such as the solvent environment, reaction temperature, and pressure in the hydrothermal synthesis process have a great influence on crystal growth, making it difficult to accurately control the structure of the material. 3. Complex post-treatment steps: The traditional hydrothermal method usually requires multiple washing, filtration, or long-term static sedimentation to remove impurities in the reaction, which not only increases the synthesis time, but may also affect the structural stability of the material and even cause partial material loss. 4. Low production efficiency: In the batch synthesis process, it is difficult for the traditional method to balance high purity and high yield. Especially when the target material is applied in the fields of electrocatalysis or energy storage, it is necessary to prepare MOFs with a high specific surface area and good stability, further increasing the preparation difficulty. There is an urgent need in the prior art for a preparation method of an iron-based metal-organic framework material that can effectively remove impurities. Summary of the Invention

[0004] To solve the problems in the background art, the present invention provides an iron-based metal-organic framework material based on a high gravity-assisted hydrothermal method, its preparation method and application. By subjecting the hydrothermal reaction product to multiple centrifugal separations and purifications in a high gravity field, impurities are effectively removed, the product purity is significantly improved, the subsequent processing steps are simplified, and at the same time, the structural stability of the product is ensured.

[0005] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions:

[0006] I. A preparation method of an iron-based metal-organic framework material based on a high gravity-assisted hydrothermal method, comprising the following steps:

[0007] Step S1: Prepare a ferric chloride solution and a fumaric acid-DMF mixed solution respectively, and then mix the ferric chloride solution and the fumaric acid-DMF mixed solution to obtain a raw material mixed solution;

[0008] Step S2: Hydrothermal reaction: Transfer the raw material mixed solution obtained in Step S1 to a high-pressure reaction kettle, and carry out the hydrothermal reaction for a preset time at a set reaction temperature;

[0009] Step S3: High gravity centrifugation: Place the raw material mixed solution after the hydrothermal reaction in Step S2 in a centrifuge for multiple high gravity centrifugations, and then obtain a centrifuged mixed solution after multiple high gravity centrifugations;

[0010] Step S4: Pour out the supernatant in the centrifuged mixed solution in Step S3, collect the precipitate in the centrifuged mixed solution obtained from the last high gravity centrifugation in Step S3, and vacuum-dry the collected precipitate at a temperature of 80°C to 90°C to obtain the final iron-based metal-organic framework material.

[0011] The specific content of the said Step S1 is as follows:

[0012] Step S1.1: Prepare a ferric chloride solution: Mix ferric chloride and deionized water in a certain proportion, and stir thoroughly under magnetic stirring until the solution is uniform to obtain a ferric chloride solution;

[0013] Step S1.2: Prepare a fumaric acid-DMF mixed solution: Mix fumaric acid and N,N-dimethylformamide (DMF) in a certain proportion, and stir until completely uniform under magnetic stirring to obtain a fumaric acid-DMF mixed solution;

[0014] Step S1.3: Preparation of the raw material mixed solution: Under magnetic stirring conditions, slowly drop the ferric chloride solution in Step S1.1 into the fumaric acid-DMF mixed solution in Step S1.2, and continuously stir until uniformly mixed to obtain the raw material mixed solution.

[0015] The specific content of the said Step S3 is as follows:

[0016] Step S3.1, primary high-gravity centrifugation: Transfer the raw material mixed solution after the hydrothermal reaction in Step S2 to a centrifuge tube, and then place the centrifuge tube in a centrifuge for high-gravity centrifugation. After running at a set rotation speed for a certain time, a centrifuged mixed solution is obtained;

[0017] Step S3.2, secondary high-gravity centrifugation: Pour out the supernatant in the centrifuged mixed solution from the previous step, redisperse the remaining precipitate in the centrifuged mixed solution in a sufficient amount of deionized water or absolute ethanol, and place the centrifuge tube containing deionized water / absolute ethanol and the precipitate in the centrifuge again for high-gravity centrifugation for further purification. After running at a set rotation speed for a certain time, a centrifuged mixed solution is obtained again;

[0018] Step S3.3, repeat Step S3.2 multiple times to further remove impurities in the raw material mixed solution, and collect the centrifuged mixed solution obtained from the last high-gravity centrifugation.

[0019] In the said Step S1.1, the dosage of ferric chloride is 0.1 - 20 mmol, and the dosage of deionized water is 5 - 100 mL.

[0020] In the said Step S1.2, the dosage of fumaric acid is 0.1 - 20 mmol, and the dosage of N,N-dimethylformamide is 5 - 100 mL.

[0021] In the said Step S2, the reaction temperature of the hydrothermal reaction is 20 - 100 °C, and the reaction time is 1 - 24 h.

[0022] In the said Step S3, the rotation speed of the high-gravity centrifugation is 1000 - 14000 rpm, and the time of the high-gravity centrifugation is 3 - 10 min.

[0023] In the said Step S3, the number of times of high-gravity centrifugation is 6 - 10 times.

[0024] II. An iron-based metal-organic framework material based on a high-gravity assisted hydrothermal method: The iron-based metal-organic framework material is prepared by the above preparation method.

[0025] III. Application of the iron-based metal-organic framework material prepared by the above method in the oxygen evolution reaction of alkaline water electrolysis.

[0026] The principle of the present invention is as follows:

[0027] The present invention prepares iron-based metal-organic framework materials by a hypergravity-assisted hydrothermal method, combining the controllability of the hydrothermal reaction with the efficient mass transfer characteristics of the hypergravity field to optimize the structure and electrocatalytic performance of the materials. In the hydrothermal reaction stage, a ferric chloride solution and a fumaric acid-DMF mixed solution undergo self-assembly under high-pressure conditions to form a primary metal-organic framework structure through coordination. However, the products prepared by the traditional hydrothermal method often have problems such as particle aggregation, pore blockage, and uneven crystal quality, thus affecting their electrochemical performance. Therefore, the present invention introduces a hypergravity field after the hydrothermal reaction, and realizes efficient separation and purification through multiple high-speed centrifugations. Under the action of the hypergravity field, the microscopic particles in the liquid phase system are controlled to settle, promoting the uniform growth of crystal grains and effectively removing unreacted precursors and by-products. In addition, the dynamic shear force of the hypergravity field can, to a certain extent, regulate the microstructure of the framework material, endowing it with a better pore distribution and specific surface area, thereby improving the accessibility and stability of its active sites. Finally, the solvent residue is further removed by vacuum drying to obtain an iron-based metal-organic framework material with high purity and stable structure. The method of the present invention not only improves the crystallinity and uniformity of the material, but also significantly enhances its electrocatalytic performance, making it have a broader application prospect in energy conversion fields such as alkaline water electrolysis oxygen evolution reaction (OER). By regulating the centrifugal speed to generate different hypergravity field conditions, the efficient preparation of MIL-88A is realized, and the morphology and electrochemical performance of the material are significantly improved. The results show that as the hypergravity field strength increases, the surface impurities of MIL-88A gradually decrease, and the structural integrity is significantly improved. The MIL-88A prepared under the optimal hypergravity condition (2862g, g = 9.8m / s 2 ) has the least surface impurities and the most complete structure, and its oxygen evolution reaction (OER) performance in 1M KOH solution reaches the best, with an overpotential of 2.05V required at a current density of 100mA / cm 2 . However, further increasing the hypergravity field strength will lead to damage to the material structure and performance degradation. The preparation method of the present invention is simple and efficient, can improve the production efficiency while ensuring the high performance of the material, and is suitable for wide applications in the fields of electrocatalysis and energy.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. In the present invention, the iron-based metal-organic framework prepared by hypergravity field centrifugation-assisted purification hydrothermal method successfully improves the product purity, reduces the impurity residue, significantly simplifies the subsequent treatment steps, and at the same time optimizes the electrochemical performance.

[0030] 2. By introducing the hypergravity field technology, the present invention significantly improves the product purity during the hydrothermal reaction process, simplifies the purification steps, and at the same time maintains the structural integrity of the material, thereby improving its application performance. Brief Description of the Drawings

[0031] Figure 1 Flow chart for the preparation of iron-based metal-organic framework based on the hypergravity-assisted hydrothermal method;

[0032] Figure 2 Scanning electron micrograph of Example 1 of the present invention;

[0033] Figure 3 Scanning electron micrograph of Example 2 of the present invention;

[0034] Figure 4 Scanning electron micrograph of Example 3 of the present invention;

[0035] Figure 5 Transmission electron micrograph of Example 4 of the present invention;

[0036] Figure 6 Transmission electron micrograph of Example 5 of the present invention;

[0037] Figure 7 Electrochemical oxygen evolution performance curve of Examples 1-5 in 1M KOH. Detailed implementation manners

[0038] The following combines the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. It should be particularly noted that the following-described embodiments are only a part of the implementation manners of the present invention, not all implementation manners. Based on the content of the present invention, other implementation manners obtained by those of ordinary skill in the art without creative efforts all fall within the protection scope of the present invention.

[0039] Example 1: Preparation of iron-based metal-organic framework (MIL-88A), as Figure 1 shown:

[0040] Step S1: Prepare a ferric chloride solution and a fumaric acid-DMF mixed solution respectively, and then mix the ferric chloride solution and the fumaric acid-DMF mixed solution to obtain a raw material mixed solution;

[0041] Among them, step S1 is specifically as follows:

[0042] Step S1.1: Prepare a ferric chloride solution: Take 5 mmol of ferric chloride and dissolve it in 15 mL of deionized water, and stir magnetically until completely dissolved to obtain a ferric chloride solution;

[0043] Step S1.2: Prepare a fumaric acid-DMF mixed solution: Take 5 mmol of fumaric acid and dissolve it in 15 mL of N,N-dimethylformamide (DMF), and stir magnetically until uniform to obtain a fumaric acid-DMF mixed solution;

[0044] Step S1.3, Preparation of raw material mixed solution: Under magnetic stirring conditions, slowly drop the ferric chloride solution in Step S1.1 into the fumaric acid - DMF mixed solution in Step S1.2, and continue to stir for 30 minutes under stirring at 1800 rpm to obtain a uniformly mixed raw material mixed solution.

[0045] Step S2, Hydrothermal reaction: Transfer the raw material mixed solution obtained in Step S1 to a high - pressure reactor, and carry out a hydrothermal reaction at a reaction temperature of 65 °C for 4 hours to complete the hydrothermal reaction;

[0046] Step S3, High - gravity centrifugation: Place the raw material mixed solution after the hydrothermal reaction in Step S2 in a centrifuge for multiple high - gravity centrifugations, and then obtain a centrifuged mixed solution after multiple high - gravity centrifugations;

[0047] Step S3 is specifically as follows:

[0048] Step S3.1, Primary high - gravity centrifugation: Transfer the raw material mixed solution after the hydrothermal reaction in Step S2 to a centrifuge tube, and then place the centrifuge tube in a centrifuge for high - gravity centrifugation. Centrifuge at 4000 rpm for 5 minutes in the centrifuge to obtain a centrifuged primary centrifuged mixed solution;

[0049] Step S3.2, Secondary high - gravity centrifugation: Pour out the supernatant in the primary centrifuged mixed solution in Step S3.1, redisperse the remaining precipitate in the primary centrifuged mixed solution in sufficient deionized water, and place the centrifuge tube containing deionized water and the precipitate in the centrifuge again for high - gravity centrifugation for further purification. Centrifuge at 4000 rpm for 5 minutes in the centrifuge to obtain a centrifuged secondary centrifuged mixed solution;

[0050] Step S3.3, Tertiary high - gravity centrifugation: Pour out the supernatant in the secondary centrifuged mixed solution in Step S3.2, redisperse the remaining precipitate in the secondary centrifuged mixed solution in sufficient anhydrous ethanol, and place the centrifuge tube containing anhydrous ethanol and the precipitate in the centrifuge again for high - gravity centrifugation for further purification. Centrifuge at 4000 rpm for 5 minutes in the centrifuge to obtain a centrifuged tertiary centrifuged mixed solution;

[0051] Step S3.4, Quaternary high - gravity centrifugation: Pour out the supernatant in the tertiary centrifuged mixed solution in Step S3.3, redisperse the remaining precipitate in the tertiary centrifuged mixed solution in sufficient deionized water, and place the centrifuge tube containing deionized water and the precipitate in the centrifuge again for high - gravity centrifugation for further purification. Centrifuge at 4000 rpm for 5 minutes in the centrifuge to obtain a centrifuged quaternary centrifuged mixed solution;

[0052] Step S3.5, Five - time high - gravity centrifugation: Pour out the supernatant in the four - time centrifugation mixed solution of Step S3.4, redisperse the remaining precipitate in the four - time centrifugation mixed solution in a sufficient amount of absolute ethanol, and place the centrifuge tube containing absolute ethanol and the precipitate in the centrifuge again for high - gravity centrifugation for further purification. After centrifuging at 4000 rpm for 5 minutes in the centrifuge, a centrifuged five - time centrifugation mixed solution is obtained;

[0053] Step S3.6, Six - time high - gravity centrifugation: Pour out the supernatant in the five - time centrifugation mixed solution of Step S3.5, redisperse the remaining precipitate in the five - time centrifugation mixed solution in a sufficient amount of deionized water, and place the centrifuge tube containing deionized water and the precipitate in the centrifuge again for high - gravity centrifugation for further purification. After centrifuging at 4000 rpm for 5 minutes in the centrifuge, a centrifuged six - time centrifugation mixed solution is obtained;

[0054] Step S4: Pour out the supernatant in the centrifugation mixed solution of Step S3.6, collect the precipitate in the centrifugation mixed solution obtained from the last high - gravity centrifugation in Step S3.6, and vacuum - dry the collected precipitate at 80 °C for 6 h to obtain the final iron - based metal - organic framework material, named MIL - 88A(715 g).

[0055] Example 2: Preparation of iron - based metal - organic framework (1609 g):

[0056] Except that the centrifuge speed is changed to 6000 rpm, the other steps are the same as in Example 1, and finally MIL - 88A(1609 g) is obtained;

[0057] Example 3: Preparation of iron - based metal - organic framework (2862 g):

[0058] Except that the centrifuge speed is changed to 8000 rpm, the other steps are the same as in Example 1, and finally MIL - 88A(2862 g) is obtained;

[0059] Example 4: Preparation of iron - based metal - organic framework (4471 g):

[0060] Except that the centrifuge speed is changed to 10000 rpm, the other steps are the same as in Example 1, and finally MIL - 88A(4471 g) is obtained;

[0061] Example 4: Preparation of iron - based metal - organic framework (6438 g):

[0062] Except that the centrifuge speed is changed to 12000 rpm, the other steps are the same as in Example 1, and finally MIL - 88A(6438 g) is obtained;

[0063] Figure 2SEM image of MIL-88A (715 g) in Example 1. As can be seen from Figure 2 , a large amount of impurities adhered to the surface of MIL-88A (715 g). Figure 3 SEM image of MIL-88A (1609 g) in Example 2. Compared with Example 1, the impurities adhered to the surface of MIL-88A (1609 g) were significantly reduced. Figure 4 SEM image of MIL-88A (2862 g) in Example 3. The surface of MIL-88A (2862 g) was clean, and the impurities were successfully removed by the high gravity field. Figure 5 SEM image of MIL-88A (4471 g) in Example 4. It can be observed that under a higher high gravity field, the structure of MIL-88A (4471 g) was slightly damaged. Figure 6 SEM image of MIL-88A (6438 g) in Example 5. Under the condition of further enhanced high gravity field, the structure of MIL-88A (4471 g) was significantly damaged.

[0064] Figure 7 Shows the OER polarization curves of the electrolytic water oxygen evolution reaction in 1 M KOH solution for Examples 1-5. As can be observed from Figure 7 , with the increase of the centrifugal rotation speed (corresponding to the high gravity G value), the overpotential required for MIL-88A at 100 mA / cm 2 showed a trend of first decreasing and then increasing. Specifically, 715 g required 2.15 V, 1609 g required 2.10 V, 2862 g required 2.05 V, 4471 g required 2.08 V, and 6438 g required 2.19 V. This indicates that with the increase of the centrifugal rotation speed (high gravity G value), the electrochemically oxygen evolution performance of MIL-88A first increased and then decreased. In addition, the change in performance was significantly correlated with the morphology of the material: the MIL-88A prepared under the condition of 2862 g had the least impurities and the most complete structure, and its electrochemical performance also reached the best state.

[0065] In summary, the present invention provides a new method for preparing iron-based metal-organic framework (MIL-88A) based on high gravity-assisted hydrothermal method. By adjusting the high gravity field strength, the morphology and performance of the product can be significantly optimized. Without departing from the principle of the present invention, those of ordinary skill in the art can make reasonable improvements to the implementation manners, and these improvements all fall within the protection scope of the present invention.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of an iron-based metal-organic framework material based on a hypergravity-assisted hydrothermal method, characterized in that, The following steps are involved: Step S1, preparing a ferric chloride solution and a fumaric acid-DMF mixed solution respectively, and then mixing the ferric chloride solution and the fumaric acid-DMF mixed solution to obtain a raw material mixed solution; Step S2, hydrothermal reaction: transferring the raw material mixed solution obtained in step S1 to a high-pressure reactor, and completing the hydrothermal reaction after reacting at a set reaction temperature for a preset time; Step S3, ultragravity centrifugation: placing the raw material mixed solution after the hydrothermal reaction in step S2 in a centrifuge for multiple ultragravity centrifugation, and then obtaining a centrifuged mixed solution after multiple ultragravity centrifugation; Step S4, collecting the precipitate in the centrifuged mixed solution obtained in step S3, and vacuum drying the collected precipitate at a temperature of 80° C. to 90° C. to obtain the final iron-based metal organic framework material.

2. The preparation method of an iron-based metal-organic framework material based on a supergravity-assisted hydrothermal method according to claim 1, wherein: The step S1 is specifically as follows: Step S1.1, preparing a ferric chloride solution: mixing ferric chloride and deionized water in a certain proportion, and stirring the mixture under magnetic stirring until the solution is uniform, thereby obtaining a ferric chloride solution; Step S1.2, preparing a fumaric acid-DMF mixed solution: mixing fumaric acid and N,N-dimethylformamide in a certain proportion, stirring under magnetic stirring until completely uniform, to obtain a fumaric acid-DMF mixed solution; Step S1.3, preparation of raw material mixed solution: under magnetic stirring conditions, slowly drop the ferric chloride solution in step S1.1 into the fumaric acid-DMF mixed solution in step S1.2, and continue stirring until the mixture is uniform to obtain a raw material mixed solution.

3. The preparation method of an iron-based metal-organic framework material based on a supergravity-assisted hydrothermal method according to claim 1, characterized in that: The step S3 is specifically as follows: Step S3.1, initial ultragravity centrifugation: transferring the raw material mixed solution after the hydrothermal reaction in step S2 into a centrifuge tube, placing the centrifuge tube in a centrifuge for ultragravity centrifugation, and running at a set speed for a certain period of time to obtain a centrifuged mixed solution; Step S3.2, re-ultragravity centrifugation: pour out the supernatant in the centrifuged mixed solution in the previous step, redisperse the remaining precipitate in the centrifuged mixed solution in deionized water or anhydrous ethanol, and place it in a centrifuge again for ultragravity centrifugation, and after running at a set speed for a certain period of time, obtain a centrifuged mixed solution again; Step S3.3, repeating step S3.2 multiple times to further remove impurities in the raw material mixed solution, and collecting the centrifuged mixed solution obtained by the last ultragravity centrifugation.

4. The preparation method of an iron-based metal-organic framework material based on a supergravity-assisted hydrothermal method according to claim 2, wherein: In the step S1.1, the amount of ferric chloride used is 0.1-20 mmol, and the amount of deionized water used is 5-100 mL.

5. The preparation method of an iron-based metal-organic framework material based on a supergravity-assisted hydrothermal method according to claim 2, characterized in that: In the step S1.2, the amount of fumaric acid used is 0.1-20 mmol, and the amount of N,N-dimethylformamide used is 5-100 mL.

6. The preparation method of an iron-based metal-organic framework material based on a supergravity-assisted hydrothermal method according to claim 1, characterized in that: The reaction temperature of the hydrothermal reaction in step S2 is 20-100° C., and the reaction time is 1-24 h.

7. The preparation method of an iron-based metal-organic framework material based on a supergravity-assisted hydrothermal method according to claim 1, characterized in that: In step S3, the rotation speed of ultragravity centrifugation is 1000-14000 rpm, and the ultragravity centrifugation time is 3-10 min.

8. The preparation method of an iron-based metal-organic framework material based on a hypergravity-assisted hydrothermal method according to claim 1, characterized in that: In step S3, the number of ultragravity centrifugation is 6-10 times.

9. An iron-based metal-organic framework material based on a hypergravity-assisted hydrothermal method, characterized in that: The iron-based metal organic framework material is prepared by the preparation method as described in any one of claims 1-8.

10. Use of the iron-based metal-organic framework material prepared by the method according to any one of claims 1-8 in the oxygen evolution reaction of alkaline electrolytic water.

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