Photocatalytic material with core-shell structure as well as preparation method and application of photocatalytic material

Abstract

The invention belongs to the technical field of photocatalytic synthesis of ammonia, and particularly relates to a photocatalytic material with a core-shell structure as well as a preparation method and application of the photocatalytic material. The invention provides a photocatalytic material with a core-shell structure, which is characterized in that an organic ligand and Fe3O4 (at) C are bonded together through a binder, then a metal source is introduced, and a coating shell is formed outside the Fe3O4 (at) C through a coating reaction. The photocatalytic material prepared by the invention has a stable and porous core-shell structure, and the yield of photocatalytic synthesis ammonia is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic ammonia synthesis, and more specifically relates to a core-shell structured photocatalytic material, its preparation method and application. Background Art

[0002] Ammonia (NH3) is an important component of commercial synthetic fertilizers and refrigerants. In addition, NH3 is also an ideal hydrogen storage material because it can be easily condensed into a liquid for storage. Therefore, NH3 can play a key role in the hydrogen economy and can be used as a fuel for fuel cells, providing a powerful strategy for solving the energy crisis. Currently, industrial ammonia is produced by the Haber-Bosch process, which uses high-purity nitrogen (N2) and hydrogen (H2) flows as raw materials under high pressure (15 - 25 MPa) and high temperature (400 - 500 °C), consuming a large amount of energy and funds.

[0003] Porous materials of metal-organic frameworks (MOFs) can be used for photocatalytic ammonia synthesis. The porous materials are assembled from metal ions or inorganic clusters and organic linkers using strong bonds with permanent porosity, especially biocompatible MOFs. However, there are still many deficiencies in the current metal-organic frameworks for photocatalytic ammonia synthesis. For example, some MOFs (such as the IRMOF series) have a fast electron-hole recombination rate and low utilization rate of photo-generated charges, and cannot effectively drive the nitrogen reduction reaction (NRR). At the same time, the metal nodes of some MOFs (such as HKUST-1) are overly wrapped by ligands, hindering the contact of N2 molecules with active sites. Therefore, how to improve the performance of metal-organic frameworks in photocatalytic ammonia synthesis has become a difficult problem that needs to be overcome by those skilled in the art. Summary of the Invention

[0004] The purpose of the present invention is to provide a core-shell structured photocatalytic material, its preparation method and application, and more specifically to provide a core-shell structured photocatalytic material prepared by coating Fe3O4@C with MOFs and its application in photocatalytic ammonia synthesis to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: Provide a core-shell structured photocatalytic material, the photocatalytic material has an octahedral Fe3O4@C as the core and MOFs as the shell;

[0007] The Fe3O4@C is obtained by calcining Fe-BDC.

[0008] Further, the MOFs include ZIF67 or ZIF-8.

[0009] Further, the calcination temperature is 350 - 550 °C and the time is 2 h.

[0010] The photocatalytic material with a core - shell structure provided by the present invention has a dodecahedron structure. The core inside is an octahedral Fe3O4@C structure. A heterojunction is formed between Fe3O4 (semiconductor) and the conductive carbon layer, which promotes the migration of photo - generated electrons to the carbon layer and inhibits recombination. In addition, the high specific surface area and micro - mesoporous structure of the dodecahedron promote N2 adsorption and expose the Fe 2+ / Fe 3+ redox sites.

[0011] The second technical solution of the present invention: provides a preparation method of the above - mentioned photocatalytic material with a core - shell structure, and the steps include:

[0012] Bond the organic ligand and Fe3O4@C together through a binder, and then introduce a metal source. A coating shell is formed outside Fe3O4@C through a coating reaction to obtain the photocatalytic material with a core - shell structure.

[0013] In the present invention, Fe3O4@C and the organic ligand are bonded together through a binder. Subsequently, the organic ligand outside Fe3O4@C will react with the ions of the introduced metal source to form a MOFs shell coated outside Fe3O4@C.

[0014] Further, the binder includes polyvinylpyrrolidone (PVP) and / or cetyltrimethylammonium bromide.

[0015] Optionally, the binder is polyvinylpyrrolidone (PVP).

[0016] Further, the organic ligand includes 2 - methylimidazole (2 - MIN) or terephthalic acid (H2BDC).

[0017] Optionally, the organic ligand is 2 - methylimidazole (2 - MIN).

[0018] Further, the metal source includes Co(NO3)3·6H2O or Zn(NO3)2·6H2O.

[0019] Optionally, the metal source is Co(NO3)3·6H2O.

[0020] Further, the molar ratio of the metal source to the organic ligand is 1:16.

[0021] In the present invention, by increasing the proportion of the organic ligand, the MOFs after the reaction can be more fully coated outside Fe3O4@C.

[0022] Further, the dosage ratio of the Fe3O4@C to the organic ligand is 30 mg: 16 mmol.

[0023] Further, the mass ratio of the Fe3O4@C to the binder is 0.03: 0 - 2, and the mass of the binder is not zero.

[0024] Further, the time of the coating reaction is 10 - 60 min.

[0025] If the time of the coating reaction is too short, the reaction will be insufficient and the coating will be incomplete. If the time is too long, the MOFs will grow rapidly, affecting the morphology of the final product, and then affecting the N2 adsorption activity and reducing the photocatalytic nitrogen fixation performance. With the increase of the number of coating reactions, the organic ligand and the metal source are continuously introduced, and the shell outside the Fe3O4@C will continuously increase, making the photocatalytic nitrogen fixation performance gradually increase, thus preparing a catalyst with higher photocatalytic performance.

[0026] Further, it also includes the step of repeating the bonding ligand at least once and introducing the metal source to carry out the coating reaction to form a coating shell.

[0027] By controlling the ratio of the organic ligand to the metal source and the number of coating reactions, the present invention regulates the microstructure, specific surface area and catalytic performance of the product, and prepares a photocatalytic material with a core-shell structure in which nanoparticles are uniformly distributed. It uses octahedral Fe3O4@C as the core and MOFs as the shell, and has higher photocatalytic ammonia synthesis activity compared with pure Fe3O4@C or MOFs.

[0028] Further, the preparation steps of the Fe3O4@C include:

[0029] Dissolve the iron source in DMF, add terephthalic acid, after heating and reacting, calcine the obtained solid product to obtain the Fe3O4@C.

[0030] The Fe3O4@C material prepared by the present invention has an octahedral structure.

[0031] Optionally, the iron source includes FeCl3·6H2O and / or Fe(NO3)3·9H2O.

[0032] Preferably, the iron source is FeCl3·6H2O.

[0033] Optionally, the molar ratio of the iron source to terephthalic acid is 1:1.

[0034] Optionally, the dosage ratio of the iron source to DMF is 1 mmol: 25 mL.

[0035] Optionally, the temperature of the heating reaction is 120 - 180 °C, and the time is 12 - 24 h.

[0036] More preferably, the temperature of the heating reaction is 120 °C and the time is 16 h.

[0037] The temperature of the above-mentioned heating reaction is preferably 120 °C and the time is preferably 16 h. If the reaction temperature is too high (higher than 180 °C), it will destroy the framework of the obtained solid product (FeMOF). If the reaction time is too short (lower than 12 h), it will affect the morphological characteristics of the product.

[0038] Optionally, the temperature of the calcination is 350 - 550 °C and the time is 2 h.

[0039] Preferably, the temperature of the calcination is 450 °C and the time is 2 h.

[0040] Regarding the above-mentioned calcination temperature, when the calcination temperature is too low (lower than 350 °C), the carbon content of the Fe3O4@C material will decrease. When the calcination temperature is too high (higher than 550 °C), the magnetism of the obtained Fe3O4@C material will be too strong, causing it to adsorb on the outside of the MOFs during subsequent coating, affecting the coating effect.

[0041] The third technical solution of the present invention: Provide an application of the above core-shell structured photocatalytic material in the field of photocatalytic ammonia synthesis.

[0042] The present invention discloses the following technical effects:

[0043] The preparation method of the core-shell structured photocatalytic material provided by the present invention is simple, and it has the characteristics of high catalytic performance, high stability, low cost and environmental friendliness.

[0044] By incorporating Fe3O4@C into MOFs and utilizing their synergistic effect, the present invention enhances the performance of MOFs. Specifically, the present invention uses octahedral FeMOF calcined into Fe3O4@C as the core and MOFs as the outer shell to prepare a photocatalytic material with a core-shell structure that works in concert. Using MOFs as the shell prevents the adhesion of supermagnetic particles, and the C layer in Fe3O4@C and the carbon layer of the uncoated Fe3O4@C on the outside form a channel for electron and hole conversion, thereby enhancing the electron and hole transfer rate and enhancing the photocatalytic performance of this core-shell structure.

[0045] The core-shell structured photocatalytic material of the present invention can effectively improve the pore size and hole-electron recombination rate of pure Fe3O4@C and MOFs, and can also regulate the morphology of the MOFs material to prepare a core-shell structured photocatalyst with a dodecahedral morphology. The photocatalytic material prepared by the present invention has a stable and porous core-shell structure, and the yield of photocatalytic ammonia synthesis has been significantly improved.

[0046] In the present invention, octahedral Fe3O4@C is used as the core and MOFs are introduced as the shell. With the assistance of a binder, a photocatalytic material with a unique morphology and structure (dodecahedron) and a large specific surface area is obtained. The obtained photocatalytic material retains the superparamagnetism of the core and the porosity of the shell, effectively improving the catalytic activity of the MOF photocatalyst. Introducing Fe3O4@C as the core and MOFs as the shell can increase the proportion of coordinatively unsaturated metal active sites exposed on the surface of MOFs, thereby enhancing the redox activity of the metal center. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0048] Figure 1 SEM images of the photocatalytic materials prepared in Example 1 and Examples 4-5. Among them, a is Fe3O4@C-ZIF67-1, b is Fe3O4@C-ZIF67-2, c is Fe3O4@C-ZIF67-3, and d is Fe3O4@C-ZIF67-4.

[0049] Figure 2 SEM images of FeBDC obtained in step S1 of Example 1, Fe3O4@C obtained in step S2 of Example 1, and ZIF67. Among them, (a) is FeBDC, (b) is ZIF67, and (c) is Fe3O4@C.

[0050] Figure 3 XRD patterns of Fe3O4@C obtained in step S2 of Example 1, the core-shell structured Fe3O4@C-ZIF67 photocatalytic materials prepared in Example 1 and Examples 4-5, and ZIF67.

[0051] Figure 4 SEM image of the Fe3O4-ZIF67 photocatalytic material prepared in Comparative Example 3.

[0052] Figure 5 Comparison of the photocatalytic ammonia synthesis performance of the photocatalytic materials prepared in Examples 1-3 and Example 6.

[0053] Figure 6 Comparison of the photocatalytic ammonia synthesis performance of the photocatalytic materials prepared in Example 1 and Comparative Example 1.

[0054] Figure 7 Comparison of the photocatalytic ammonia synthesis performance of the photocatalytic materials prepared in Example 1 and Comparative Example 3.

[0055] Figure 8Performance comparison of the photocatalytic materials prepared in Example 1 and Examples 4 - 5 and Fe3O4@C and ZIF67 in Example 1 for photocatalytic ammonia synthesis.

[0056] Figure 9 N2 adsorption - desorption isotherms and pore size distribution diagrams of ZIF - 67, Fe3O4@C in Example 1, and Fe3O4@C - ZIF67 - 3, where (a) is the N2 adsorption - desorption isotherm and (b) is the pore size distribution diagram. Detailed implementation manners

[0057] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be regarded as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0058] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0059] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0060] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are also obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0061] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open - ended terms, meaning including but not limited to.

[0062] The raw materials and reagents used in the specific implementation schemes of the present invention are all commercially available products.

[0063] It should be noted that the parts not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0064] Example 1

[0065] The preparation steps of the core-shell structure Fe3O4@C-ZIF67 photocatalytic material include:

[0066] S1. Dissolve 1 mmol of FeCl3·6H2O in 25 mL of DMF, add 1 mmol of terephthalic acid, heat to 120 °C in an oven, and react for 16 h to obtain Fe-BDC;

[0067] S2. Place the Fe-BDC obtained in step S1 in a muffle furnace and calcine at 450 °C for 2 h under argon atmosphere to obtain Fe3O4@C;

[0068] S3. Dissolve 0.289 g of Co(NO3)3·6H2O in 20 mL of methanol, and ultrasonically disperse it evenly to obtain a metal source solution;

[0069] S4. Dissolve 0.03 g of the Fe3O4@C obtained in step S2, 2 g of PVP, and 1.312 g of 2-methylimidazole in 20 mL of methanol, perform ultrasonic treatment at 300 W for 15 min, let it stand for 15 min. After 2-methylimidazole is bonded to the surface of Fe3O4@C through PVP, mix it with the metal source solution prepared in step S3, ultrasonically disperse it evenly and then let it stand for 30 min, centrifuge and dry. Repeat steps S3 and S4 for a total of 3 coatings to obtain the core-shell structure Fe3O4@C-ZIF67-3 photocatalytic material.

[0070] Example 2

[0071] The preparation steps of the core-shell structure Fe3O4@ZIF67 photocatalytic material include:

[0072] S1. Dissolve 1 mmol of FeCl3·6H2O in 25 mL of DMF, add 1 mmol of terephthalic acid, heat to 120 °C in an oven, and react for 16 h to obtain Fe-BDC;

[0073] S2. Place the Fe-BDC obtained in step S1 in a muffle furnace and calcine at 350 °C for 2 h under argon atmosphere to obtain Fe3O4@C;

[0074] S3. Dissolve 0.289 g of Co(NO3)3·6H2O in 20 mL of methanol, and ultrasonically disperse it evenly to obtain a metal source solution;

[0075] S4. Dissolve 0.03 g of Fe3O4@C obtained in step S2, 2 g of PVP, and 1.312 g of 2-methylimidazole in 20 mL of methanol, ultrasonically treat for 15 min at 300 W, let stand for 15 min. After 2-methylimidazole is adhered to the surface of Fe3O4@C through PVP, mix it with the metal source solution prepared in step S3, ultrasonically disperse evenly and then let stand for 30 min, centrifuge and dry. Repeat steps S3 and S4 for a total of 3 coatings to obtain the core-shell structured Fe3O4@C-ZIF67 photocatalytic material.

[0076] Example 3

[0077] The preparation steps of the core-shell structured Fe3O4@ZIF67 photocatalytic material include:

[0078] S1. Dissolve 1 mmol of FeCl3·6H2O in 25 mL of DMF, add 1 mmol of terephthalic acid, heat in an oven to 120 °C, and react for 16 h to obtain Fe-BDC.

[0079] S2. Place the Fe-BDC obtained in step S1 in a muffle furnace, calcine at 550 °C for 2 h under argon atmosphere to obtain Fe3O4@C.

[0080] S3. Dissolve 0.289 g of Co(NO3)3·6H2O in 20 mL of methanol, ultrasonically disperse evenly to obtain the metal source solution.

[0081] S4. Dissolve 0.03 g of Fe3O4@C obtained in step S2, 2 g of PVP, and 1.312 g of 2-methylimidazole in 20 mL of methanol, ultrasonically treat for 15 min at 300 W, let stand for 15 min. After 2-methylimidazole is adhered to the surface of Fe3O4@C through PVP, mix it with the metal source solution prepared in step S3, ultrasonically disperse evenly and then let stand for 30 min, centrifuge and dry. Repeat steps S3 and S4 for a total of 3 coatings to obtain the core-shell structured Fe3O4@C-ZIF67 photocatalytic material.

[0082] Example 4

[0083] Compared with Example 1, the difference is only that the coating steps of steps S3 and S4 are not repeated, that is, only coated once, denoted as Fe3O4@C-ZIF67-1.

[0084] Example 5

[0085] Compared with Example 1, the difference is only that the coating steps of steps S3 and S4 are repeated 1 time or 3 times, for a total of 2 coatings or 4 coatings, denoted as Fe3O4@C-ZIF67-2 and Fe3O4@C-ZIF67-4 respectively.

[0086] Example 6

[0087] Compared with Example 1, the only difference is that the calcination temperature in step S2 is 500 °C.

[0088] Comparative Example 1

[0089] Compared with Example 1, the difference is that in step S4, no PVP material is added. The preparation steps of the Fe3O4@C-ZIF67 photocatalytic material include:

[0090] S1. Dissolve 1 mmol of FeCl3·6H2O in 25 mL of DMF, add 1 mmol of terephthalic acid, heat to 120 °C in an oven, and react for 16 h to obtain Fe-BDC;

[0091] S2. Place the Fe-BDC obtained in step S1 in a muffle furnace, calcine at 450 °C for 2 h under argon conditions to obtain Fe3O4@C;

[0092] S3. Dissolve 0.289 g of Co(NO3)3·6H2O in 20 mL of methanol, and ultrasonically disperse it evenly to obtain a metal source solution;

[0093] S4. Dissolve 0.03 g of the Fe3O4@C obtained in step S2 and 1.312 g of 2-methylimidazole in 20 mL of methanol, ultrasonically treat it at 300 W for 15 min, let it stand for 15 min, then mix it with the metal source solution prepared in step S3, ultrasonically disperse it evenly and let it stand for 30 min, centrifuge and dry it, and repeat steps S3 and S4 for a total of 3 coatings to obtain the Fe3O4@C-ZIF67 photocatalytic material.

[0094] Comparative Example 2

[0095] Compared with Example 3, the difference is that in step S4, no PVP material is added. The preparation steps of the Fe3O4@C-ZIF67 photocatalytic material include:

[0096] S1. Dissolve 1 mmol of FeCl3·6H2O in 25 mL of DMF, add 1 mmol of terephthalic acid, heat to 120 °C in an oven, and react for 16 h to obtain Fe-BDC;

[0097] S2. Place the Fe-BDC obtained in step S1 in a muffle furnace, calcine at 550 °C for 2 h under argon conditions to obtain Fe3O4@C;

[0098] S3. Dissolve 0.289 g of Co(NO3)3·6H2O in 20 mL of methanol, and ultrasonically disperse it evenly to obtain a metal source solution;

[0099] S4. Dissolve 0.03 g of Fe3O4@C obtained in step S2, 2 g of PVP, and 1.312 g of 2-methylimidazole in 20 mL of methanol, sonicate for 15 min with 300 W, let stand for 15 min, then mix with the metal source solution prepared in step S3. After ultrasonic dispersion and uniform mixing, let stand for 30 min, centrifuge and dry. Repeat steps S3 and S4 for a total of 3 coatings to obtain the core-shell structured Fe3O4@C-ZIF67 photocatalytic material.

[0100] Comparative Example 3

[0101] The preparation steps of the core-shell structured Fe3O4@ZIF67 photocatalytic material include:

[0102] S1. Dissolve 0.289 g of Co(NO3)3·6H2O in 20 mL of methanol, and ultrasonically disperse it evenly to obtain a metal source solution;

[0103] S2. Dissolve 0.03 g of Fe3O4 powder, 2 g of PVP, and 1.312 g of 2-methylimidazole in 20 mL of methanol, sonicate for 15 min with 300 W, let stand for 15 min. After bonding 2-methylimidazole to the surface of Fe3O4@C through PVP, mix it with the metal source solution prepared in step S1. After ultrasonic dispersion and uniform mixing, let stand for 30 min, centrifuge and dry. Repeat steps S1 and S2 for a total of 3 coatings to obtain the core-shell structured Fe3O4@ZIF67 photocatalytic material, denoted as Fe3O4@ZIF67-3.

[0104] Test Example

[0105] The preparation steps of ZIF67 include:

[0106] S1. Dissolve 0.289 g of Co(NO3)3·6H2O in 20 mL of methanol, and ultrasonically disperse it evenly to obtain a metal source solution;

[0107] S2. Dissolve 1.312 g of 2-methylimidazole in 20 mL of methanol, and ultrasonically disperse it evenly to obtain a ligand solution;

[0108] S3. Mix the metal source solution in step S1 and the ligand solution in step S2, ultrasonically disperse it evenly, let stand for 30 min, centrifuge and dry to obtain ZIF67.

[0109] Figure 1SEM images of the photocatalytic materials prepared in Example 1 and Examples 4 - 5. Among them, a is Fe3O4@C-ZIF67-1, b is Fe3O4@C-ZIF67-2, c is Fe3O4@C-ZIF67-3, and d is Fe3O4@C-ZIF67-4. It can be seen from the figure that as the coating times increase, the outer ZIF67 gradually becomes smooth, Fe3O4@C gradually disappears on the outside, and the outside of the material gradually becomes smooth.

[0110] Figure 2 SEM images of FeBDC obtained in step S1 of Example 1, Fe3O4@C obtained in step S2 of Example 1, and ZIF67. Among them, (a) is FeBDC, (b) is ZIF67, and (c) is Fe3O4@C. It can be seen from the figure that FeBDC presents a novel octahedral structure, and the morphology of Fe3O4@C obtained from FeBDC after calcination remains unchanged. ZIF67 presents a dodecahedral structure with an average size of about 1 μm.

[0111] Figure 3 XRD patterns of Fe3O4@C obtained in step S2 of Example 1, the core-shell structured Fe3O4@C-ZIF67 photocatalytic materials prepared in Example 1 and Examples 4 - 5, and ZIF67. It can be seen from the figure that the crystal planes in the Fe3O4@C-ZIF67 series of materials include the crystal planes of pure Fe3O4@C and ZIF67, and no impurity peaks are found, indicating the successful synthesis of the Fe3O4@C-ZIF67 series of materials. The unique dodecahedral core-shell structured Fe3O4@C-ZIF67 series of materials can not only provide a larger specific surface area to contact with N2 molecules to improve the catalytic performance of the catalyst, but also effectively separate photo-generated electron-hole pairs.

[0112] Figure 4 SEM image of the Fe3O4-ZIF67 photocatalytic material prepared in Comparative Example 3. It can be seen from the figure that when the core material is replaced with ordinary iron oxide powder, Fe3O4 is coated on the outside of ZIF67, thereby reducing its photocatalytic ammonia synthesis performance.

[0113] Photocatalytic ammonia synthesis experiments were carried out on the photocatalytic materials obtained in Examples 1 - 5 and Comparative Examples 1 - 3, using Fe3O4@C obtained in step S2 of Example 1 and pure ZIF67 as reference control groups. The specific steps include:

[0114] 15 mg of photocatalyst was added to 50 mL of ultrapure water. First, N2 was introduced until saturation under dark reaction conditions. After adsorption saturation, a 300 W xenon lamp with a 420 nm filter was used to start the photocatalysis experiment. During the photocatalysis process, 5 mL of the solution was extracted every 10 min using a 5 mL syringe, and the absorbance of the solution at different time intervals was measured using an ultraviolet-visible spectrophotometer.

[0115] Figure 5 For the comparison of the photocatalytic ammonia synthesis performance of the photocatalytic materials prepared in Examples 1-3 and Example 6. As can be seen from the figure, the calcination temperature of 350-550 °C defined in the present invention makes the photocatalytic ammonia synthesis performance of the prepared catalyst show a volcano-shaped curve, and the photocatalytic ammonia synthesis performance is optimal under the calcination temperature of 450 °C.

[0116] Figure 6 For the comparison of the photocatalytic ammonia synthesis performance of the photocatalytic materials prepared in Example 1 and Comparative Example 1 (the difference lies in whether PVP is used as a binder). As can be seen from the figure, PVP was used as a binder in Example 1, while PVP material was not used in Comparative Example 1. The photocatalytic ammonia synthesis performance of the prepared photocatalytic materials is significantly different, indicating that the coated core-shell structure optimizes the photocatalytic performance of Fe3O4@C and ZIF67, making them have a synergistic effect. The addition of PVP makes Fe3O4@C and ZIF67 fit better.

[0117] Figure 7 For the comparison of the photocatalytic ammonia synthesis performance of the photocatalytic materials prepared in Example 1 and Comparative Example 3. As can be seen from the figure, when Fe3O4@C is replaced with ordinary Fe3O4, it will significantly affect the photocatalytic ammonia synthesis performance of the material.

[0118] Figure 8 For the comparison of the photocatalytic ammonia synthesis performance of the photocatalytic materials prepared in Example 1 and Examples 4-5, as well as Fe3O4@C and ZIF67 in Example 1.

[0119] Figure 9 For the nitrogen adsorption-desorption isotherm and pore size distribution diagram of ZIF-67, Fe3O4@C in Example 1, and Fe3O4@C-ZIF67-3, where (a) is the nitrogen adsorption-desorption isotherm and (b) is the pore size distribution diagram.

[0120] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0121] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A core-shell structured photocatalytic material, characterized in that, The photocatalytic material has an octahedral-structured Fe3O4@C as the core and MOFs as the shell; The Fe3O4@C is obtained by calcining Fe-BDC.

2. The photocatalytic material with a core-shell structure according to claim 1, wherein The MOFs include ZIF67 or ZIF-8; and / or, the calcination temperature is 350 - 550 °C and the time is 2 h.

3. A method for preparing the core-shell structured photocatalytic material according to claim 1 or 2, characterized in that the steps It includes: An organic ligand is bonded to Fe3O4@C through a binder, and then a metal source is introduced. Through a coating reaction, a coating shell is formed outside the Fe3O4@C to obtain the photocatalytic material with the core-shell structure.

4. The preparation method according to claim 3, characterized in that, The binder includes polyvinylpyrrolidone and / or cetyltrimethylammonium bromide; and / or, the organic ligand includes 2-methylimidazole or terephthalic acid; and / or, the metal source includes Co(NO3)3·6H2O or Zn(NO3)2·6H2O.

5. The preparation method according to claim 3, characterized in that, The molar ratio of the metal source to the organic ligand is 1:16; and / or, the dosage ratio of Fe3O4@C to the organic ligand is 30 mg:16 mmol; and / or, the mass ratio of Fe3O4@C to the binder is 0.03:0 - 2, and the mass of the binder is not 0.

6. The preparation method according to claim 3, characterized in that, The time of the coating reaction is 10 - 60 min; and / or, it further includes the step of repeating the bonding of the ligand and introducing the metal source for the coating reaction to form the coating shell at least once.

7. The preparation method according to claim 3, characterized in that, The preparation steps of the Fe3O4@C include: Dissolve an iron source in DMF, add terephthalic acid, after heating and reacting, perform calcination treatment on the obtained solid product to obtain the Fe3O4@C.

8. The preparation method according to claim 7, characterized in that, The iron source includes FeCl3·6H2O and / or Fe(NO3)3·9H2O; and / or, the molar ratio of the iron source to terephthalic acid is 1:1; and / or, the dosage ratio of the iron source to DMF is 1 mmol:25 mL.

9. The preparation method according to claim 7, characterized in that, The temperature of the heating reaction is 120 - 180 °C and the time is 12 - 24 h; and / or, the calcination temperature is 350 - 550 °C and the time is 2 h.

10. Application of the photocatalytic material with the core-shell structure according to claim 1 or 2 in the field of photocatalytic ammonia synthesis.

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