Double-bond-connected two-dimensional metal cluster-based MCOFs and their preparation methods and applications

Abstract

The present invention discloses a double-bond-connected two-dimensional metal cluster-based MCOF, as well as a preparation method and application thereof. The MCOFs are composed of an aldehyde group of a three-linked molecule A and a methyl group of a three-linked molecule B, which are interconnected in a two-dimensional plane through a condensation reaction to form a double bond. In at least a portion of the MCOFs, each three-linked molecule A is connected to three adjacent three-linked molecules B, and each three-linked molecule B is connected to three adjacent three-linked molecules A, forming a two-dimensional HCB topological network structure. The MCOFs of the present invention have high crystallinity and a unique pore structure. Due to the high stability of the ethylene bond, this novel MCOF exhibits excellent application potential in electrocatalytic nitrate reduction.

Description

Technical Field

[0001] The present invention belongs to the field of metal covalent organic frameworks (MCOFs) materials, and specifically relates to a highly stable double-bond-connected two-dimensional metal cluster-based MCOFs and a preparation method thereof, as well as an application in an electrocatalytic nitrate reduction reaction. Background Art

[0002] Human activities have severely disrupted the natural nitrogen cycle. Excessive use of nitrogen-containing fertilizers has led to increased nitrate levels in surface water and groundwater, while emissions of nitrogen oxides have caused serious air pollution. Nitrogen has long been a major component of the air and is widely used to produce ammonia on a large scale to meet agricultural needs and support global population growth. In the past decade, researchers have been committed to developing environmentally friendly ammonia synthesis processes to solve the energy consumption and carbon emission problems of the Haber-Bosch process. Among them, the electrochemical nitrate reduction reaction (NO3RR) is a technology that has attracted much attention. It uses renewable energy as power to remove nitrates and produce ammonia. This research field has developed rapidly in recent years, attracting increasing attention and investment.

[0003] Currently, copper-based catalysts are widely studied due to their high catalytic efficiency and good stability in the electro-ammonia synthesis reaction, but how to improve the exposure of copper-based catalysts in the reaction system and increase their active sites has also attracted much attention. Covalent organic frameworks (COFs), as an emerging crystalline porous polymer, can significantly improve the utilization efficiency of active sites due to their high stability and porous structure, making them have broad prospects in the application field of electrocatalytic NO3RR. However, the stability of traditional imine bond-linked COFs materials is still insufficient, and the structure is easily damaged during the electrocatalytic process, resulting in catalytic inactivation. Using tridentate metal clusters to construct highly stable double-bond (or vinyl)-linked metal cluster-based covalent organic frameworks (MCOFs) materials as catalysts for electrocatalytic nitrate reduction can not only introduce metal active sites, but its unique double bond connection can also ensure the stability of the catalytic material during the electrocatalytic process.

[0004] Based on this, the present invention uses tridentate metal clusters as electrocatalytic active sites and framework building blocks. Based on the principles of framework chemistry, these clusters are reversibly assembled with building blocks of specific molecular symmetry to construct a series of highly stable two-dimensional double-bonded metal cluster-based MCOFs. Electrocatalytic nitrate reduction performance tests demonstrate that these MCOFs exhibit excellent electrocatalytic activity and stability. Summary of the Invention

[0005] The present invention provides a double-bonded two-dimensional metal cluster-based covalent organic framework (MCOF) compound, its preparation method, and application. The MCOF material of the present invention has high crystallinity and a porous structure, and has good application prospects in the electrocatalytic reduction of nitrates.

[0006] The technical solutions of the present invention are as follows:

[0007] A double-bond-linked two-dimensional metal cluster-based covalent organic framework compound, comprising an aldehyde group of a three-linked molecule A and a methyl group of a three-linked molecule B, which are interconnected in a two-dimensional plane through a condensation reaction to form a double bond; in at least a portion of the double-bond-linked two-dimensional metal cluster-based covalent organic framework compound, each three-linked molecule A is respectively connected to three adjacent three-linked molecules B, and each three-linked molecule B is respectively connected to three adjacent three-linked molecules A, forming a two-dimensional HCB topological network structure;

[0008] The three-linked molecule A is a tridentate metal cluster (abbreviated as: TMC), and the structural formula is shown in formula (1);

[0009] The three-linked molecule B is selected from one of trimethylpyridine or pyrimidine benzene (abbreviated as: TMPB) and trimethylpyridine or pyrimidine (abbreviated as: TMT); the structural formulas of TMPB and TMT are shown in formula (2) and formula (3), respectively;

[0010]

[0011] In formula (1): R is H or CH3; X1 is a mixture of one or more of Cu, Ag, and Au;

[0012] In formula (2) or formula (3), X2 is C or N.

[0013] The BET specific surface area of ​​the double-bond-connected two-dimensional metal cluster-based covalent organic framework compound of the present invention is 100 to 2000 m 2 / g, pore size is 0.6~3.0nm.

[0014] In at least a portion of the double-bond-linked two-dimensional metal cluster-based covalent organic framework compound of the present invention, the molar ratio of the three-linked molecules A to the three-linked molecules B is 0.8-1.2:0.8-1.2, preferably 1:1.

[0015] The double-bond-connected two-dimensional metal cluster-based covalent organic framework compound of the present invention has a connecting group of -C=C- and a topological network structure of hcb, preferably including a skeleton unit shown in formula (4) or formula (5);

[0016]

[0017] In formula (4) or formula (5), the definitions of R, X1, and X2 are the same as in formulas (1) to (3).

[0018] The method for preparing the double-bond-connected two-dimensional metal cluster-based covalent organic framework compound of the present invention comprises:

[0019] The three-linked molecule A, the three-linked molecule B, benzoic anhydride and benzoic acid (benzoic acid may not be added) are mixed, degassed by freeze-thaw cycles, and then sealed. The mixture is heated to 150-250° C. (preferably 200° C.) and reacted for 72-168 hours (preferably 120 hours). The reaction mixture is then post-treated to obtain the double-bond-linked two-dimensional metal cluster-based covalent organic framework compound.

[0020] The molar ratio of the three-linked molecule A to the three-linked molecule B is 0.8-1.2:0.8-1.2, preferably 1:1;

[0021] The molar ratio of the three-linked molecule A to benzoic anhydride is 0.8-1.2:2-6, preferably 1:3;

[0022] The molar ratio of the three-linked molecule A and benzoic acid is 0.8-1.2:0.4-0.6, preferably 1:0.5;

[0023] The post-treatment method is as follows: after the reaction is completed, the system is cooled to room temperature, and a solid substance is generated in the system. The solid substance is first soaked and washed with N,N-dimethylformamide at 60°C for 12 to 24 hours, then soaked and washed in an ethanol solution of sodium hydroxide at 60°C for 12 to 24 hours, and then Soxhlet extraction is performed with tetrahydrofuran and acetone respectively for 24 to 48 hours. Finally, the solid substance is placed in a vacuum drying oven, vacuumed to 20mTorr at 80°C and dried for 24 hours to obtain the double-bond-connected two-dimensional metal cluster-based covalent organic framework compound.

[0024] The double-bond-connected two-dimensional metal cluster-based covalent organic framework compound of the present invention can be used in electrocatalytic nitrate reduction reaction.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention provides an assembly strategy for highly stable, double-bonded, two-dimensional metal cluster-based covalent organic frameworks. This strategy uses tridentate metal cluster aldehyde building blocks and specific symmetry building blocks to construct highly crystalline, double-bonded, two-dimensional metal cluster-based covalent organic frameworks through a reversible condensation reaction. The metal covalent organic framework compounds of this invention possess high crystallinity and a unique pore structure. Due to the high stability of the vinyl bond, these novel metal covalent organic frameworks demonstrate promising application potential in electrocatalytic nitrate reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : Flow chart for the preparation of double-bond-linked two-dimensional metal cluster-based covalent organic framework compounds according to Examples 1-3 of the present invention.

[0028] Figure 2: Schematic diagram of the topological structure of the covalent organic framework compounds based on double-bond-connected two-dimensional metal clusters in Example 1, Example 2, and Example 3 of the present invention; (a): TT-1-COF, (b): TT-2-COF, (c): TT-3-COF.

[0029] Figure 3 : Powder X-ray (PXRD) (a) test spectrum and simulated spectrum and infrared (FT-IR) spectrum (b) of the covalent organic framework compound TT-1-COF with double-bond connection of two-dimensional metal clusters in Example 1 of the present invention.

[0030] Figure 4 : Powder X-ray (PXRD) (a) test spectrum and simulated spectrum and infrared (FT-IR) spectrum (b) of the covalent organic framework compound TT-2-COF with double-bond connection of two-dimensional metal clusters in Example 2 of the present invention.

[0031] Figure 5 : Powder X-ray (PXRD) (a) test spectrum and simulated spectrum and infrared (FT-IR) spectrum (b) of the covalent organic framework compound TT-3-COF with double-bond connection of two-dimensional metal clusters in Example 3 of the present invention.

[0032] Figure 6 : Performance diagram of the electrocatalytic nitrate reduction of double-bond-connected two-dimensional metal cluster-based covalent organic framework compounds synthesized in Example 1, Example 2, and Example 3 of the present invention; among them, the Ferrari efficiency of TT-1-COF reaches the best 90%. DETAILED DESCRIPTION

[0033] The following further describes the objectives, technical solutions and advantages of the present invention in detail with reference to the embodiments and drawings. The specific embodiments described are only used to explain the present invention and are not intended to limit the present invention.

[0034] In the following examples,

[0035] The TCC-H and TCC-Me three-linked molecules were prepared with reference to Angew.Chem.Int.Ed.2023, e202302808, and the structural formula is as follows:

[0036]

[0037] The purity of TMPB and TMT triple linker molecules was >95% and both were purchased from Shanghai Tengqian Biotechnology Co., Ltd.

[0038] Example 1

[0039] The preparation method of a covalent organic framework compound having a double-bond-connected two-dimensional metal cluster (abbreviated as TT-1-COF) comprises the following steps:

[0040] See the synthesis diagram at Figure 1 1,3,5-Tris(4-methylpyrimidinyl)benzene (TMPB) (35.4 mg, 0.1 mmol), TCC-H (57.4 mg, 0.1 mmol), benzoic anhydride (67.8 mg, 0.3 mmol) and benzoic acid (6.1 mg, 0.05 mmol) were added to a high-temperature resistant quartz glass tube. It was quickly frozen at 77K in a liquid nitrogen bath and vacuumed using a tube sealer, degassed three times, and then sealed. The glass tube was placed in a 200°C oven at a constant temperature for 5 days. After the reaction was completed, it was cooled to room temperature and a brown solid was collected. The collected solid was soaked in N,N-dimethylacetamide and 3M sodium hydroxide ethanol solution for 24 hours. The solid was Soxhlet extracted with tetrahydrofuran and acetone for 48 hours, respectively, and then vacuum dried at 80°C for 24 hours to obtain 74.2 mg of dark green powder with a yield of 80%.

[0041] Example 2

[0042] The preparation method of a covalent organic framework compound having a double-bond-connected two-dimensional metal cluster (abbreviated as TT-2-COF) comprises the following steps:

[0043] See the synthesis diagram at Figure 1 , 2,4,6-trimethyl-1,3,5-triazine (TMT) (12.3 mg, 0.1 mmol), TCC-H (47.5 mg, 0.1 mmol) and benzoic anhydride (67.8 mg, 0.3 mmol) were added to a high-temperature resistant quartz glass tube. Quickly freeze at 77K in a liquid nitrogen bath, evacuate with a tube sealer, degas three times, and then seal. The glass tube was placed in a 200°C oven at a constant temperature for 5 days. After the reaction was completed, it was cooled to room temperature and a brown solid was collected. The collected solid was soaked in N,N-dimethylacetamide and 3M sodium hydroxide ethanol solution for 24 hours. After the solid was Soxhlet extracted with tetrahydrofuran and acetone for 48 hours, it was vacuum dried at 80°C for 24 hours to obtain 46.6 mg of brown powder with a yield of 76%.

[0044] Example 3

[0045] The preparation method of a covalent organic framework compound having a double-bond-connected two-dimensional metal cluster (abbreviated as TT-3-COF) comprises the following steps:

[0046] See the synthesis diagram at Figure 1, 2,4,6-trimethyl-1,3,5-triazine (TMT) (12.3 mg, 0.1 mmol), TCC-Me (57.4 mg, 0.1 mmol) and benzoic anhydride (67.8 mg, 0.3 mmol) were added to a high-temperature resistant quartz glass tube. Quickly freeze at 77K in a liquid nitrogen bath, evacuate with a tube sealer, cycle three times for degassing, and then seal. The glass tube was placed in a 200°C oven at a constant temperature for 5 days. After the reaction was completed, it was cooled to room temperature and a brown solid was collected. The collected solid was soaked in N,N-dimethylacetamide and 3M sodium hydroxide ethanol solution for 24 hours. After the solid was Soxhlet extracted with tetrahydrofuran and acetone for 48 hours, it was vacuum dried at 80°C for 24 hours to obtain 54.3 mg of brown powder with a yield of 78%.

[0047] Product characterization:

[0048] See Figure 3 In (a), PXRD analysis shows that TT-1-COF exhibits diffraction peaks at 4.32°, 7.63°, 8.95°, 11.59°, and 26.74°, confirming the successful synthesis of highly crystalline TT-1-COF. Materials Studio software was used to simulate and analyze the crystal structure of TT-1-COF. The simulated PXRD pattern agrees well with the experimentally observed PXRD pattern, further confirming the accuracy of the structure.

[0049] See Figure 3 In (b), the infrared spectra of the monomers required for synthesis and the corresponding product TT-1-COF were compared by Fourier transform infrared (FT-IR) spectroscopy. -1 The characteristic stretching vibration of C=C bond was generated, proving the successful synthesis of TT-1-COF.

[0050] See Figure 4 In (a), PXRD analysis shows that TT-2-COF exhibits diffraction peaks at 6.22°, 10.74°, and 26.94°, confirming the successful synthesis of highly crystalline TT-2-COF. Materials Studio software was used to simulate and analyze the TT-2-COF crystal structure. The simulated PXRD pattern agrees well with the experimentally observed PXRD pattern, further confirming the accuracy of the structure.

[0051] See Figure 4 In (b), the infrared spectra of the relevant monomers required for synthesis and the corresponding product TT-2-COF were compared by Fourier transform infrared (FT-IR) spectroscopy. -1 The characteristic stretching vibration of C=C bond was generated, proving the successful synthesis of TT-2-COF.

[0052] See Figure 5 In (a), PXRD analysis shows that TT-3-COF exhibits diffraction peaks at 6.26°, 10.76°, and 26.74°, confirming the successful synthesis of highly crystalline TT-3-COF. Materials Studio software was used to simulate and analyze the crystal structure of TT-3-COF. The simulated PXRD pattern agrees well with the experimentally observed PXRD pattern, further confirming the accuracy of the structure.

[0053] See Figure 5 In (b), the infrared spectra of the monomers required for synthesis and the corresponding product TT-3-COF were compared by Fourier transform infrared (FT-IR) spectroscopy. -1 The characteristic stretching vibration of C=C bond was generated, proving the successful synthesis of TT-3-COF.

[0054] Performance testing:

[0055] TT-1-COF, TT-2-COF or TT-3-COF (2 mg) was dispersed in a mixture of H2O (0.7 mL), isopropanol (0.25 mL) and Nafion (50 μL, 5 wt.%) and ultrasonicated for 30 minutes to form a catalyst ink. Then, 50 μL of the catalyst ink was evenly spread on an area of ​​1×1 cm 2 on carbon paper and at 0.1 mg cm -2 The catalyst loading was used as the working electrode. Ag / AgCl and Pt plates were used as the reference electrode and counter electrode, respectively.

[0056] The electroreduction of nitrate was carried out in an H-type cell with a three-electrode system, where the cathode and anode compartments were separated by a Nafion 117 membrane at room temperature. The electrolytes at both the cathode and anode were a mixture of 1 M KOH and 200 ppm KNO3 (40 mL).

[0057] See Figure 6 , at -0.6V, initial 1M KOH and 200ppm KNO3 (equivalent to 2mmol NO3 - ) Electrochemical test conditions of electrolyte, H2, NO3 in TT-1-COF, TT-2-COF, TT-3-COF electrocatalytic nitrate reduction experiment - and the Faradaic efficiency of NH3.

[0058] The embodiments described above only express the preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be understood as limiting the scope of protection of the present invention. The various technical features of the embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the various technical features in the above embodiments are described, but as long as there are no contradictions in these combinations involved, they should be considered to be within the scope of this specification. For those of ordinary skill in the art, several modifications and changes can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A double-bond-connected two-dimensional metal cluster-based covalent organic framework compound, characterized in that: The aldehyde group of the three-linked molecule A and the methyl group of the three-linked molecule B form a double bond through a condensation reaction, and are interconnected in a two-dimensional plane; in at least a portion of the double-bond-connected two-dimensional metal cluster-based covalent organic framework compound, each three-linked molecule A is respectively connected to three adjacent three-linked molecules B, and each three-linked molecule B is respectively connected to three adjacent three-linked molecules A, forming a two-dimensional hcb topological network structure; The structural formula of the three-linked molecule A is shown in formula (1); The structural formula of the three-linked molecule B is shown in formula (2); In formula (1): R is H or CH3; X1 is a mixture of one or more of Cu, Ag, and Au; In formula (2), X2 is C or N.

2. The double-bond-connected two-dimensional metal cluster-based covalent organic framework compound according to claim 1, characterized in that: In at least a portion of the double-bond-linked two-dimensional metal cluster-based covalent organic framework compound, the molar ratio of the three-linked molecules A to the three-linked molecules B is 0.8-1.2:0.8-1.

2.

3. The double-bond-connected two-dimensional metal cluster-based covalent organic framework compound according to claim 1, characterized in that: The double-bond-connected two-dimensional metal cluster-based covalent organic framework compound includes a skeleton unit shown in formula (4); In formula (4), the definitions of R, X1, and X2 are the same as in formulas (1) to (2).

4. The method for preparing a double-bond-connected two-dimensional metal cluster-based covalent organic framework compound according to claim 1, wherein: The method comprises: The three-linked molecule A, the three-linked molecule B, benzoic anhydride and benzoic acid are mixed, degassed after freeze-thaw cycle, sealed, heated to 150-250° C. and reacted for 72-168 hours. The reaction mixture is then post-treated to obtain the double-bond-linked two-dimensional metal cluster-based covalent organic framework compound.

5. The preparation method according to claim 4, characterized in that: The molar ratio of the three-linked molecule A to the three-linked molecule B is 0.8-1.2:0.8-1.

2.

6. The preparation method according to claim 4, characterized in that: The molar ratio of the three-linked molecule A to benzoic anhydride is 0.8-1.2:2-6.

7. The preparation method according to claim 4, characterized in that: The molar ratio of the three-linked molecule A to benzoic acid is 0.8-1.2:0.4-0.

6.

8. The preparation method according to claim 4, characterized in that: The post-treatment method is as follows: after the reaction is completed, the system is cooled to room temperature, and a solid substance is generated in the system. The solid substance is first soaked and washed with N,N-dimethylformamide at 60°C for 12 to 24 hours, then soaked and washed in an ethanol solution of sodium hydroxide at 60°C for 12 to 24 hours, and then Soxhlet extraction is performed with tetrahydrofuran and acetone respectively for 24 to 48 hours. Finally, the solid substance is placed in a vacuum drying oven, vacuumed to 20mTorr at 80°C and dried for 24 hours to obtain the double-bond-connected two-dimensional metal cluster-based covalent organic framework compound.

9. Use of the double-bond-linked two-dimensional metal cluster-based covalent organic framework compound as claimed in claim 1 in the electrocatalytic nitrate reduction reaction.

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