A hetero-linkage type COFs material based on melt polymerization, one-pot synthesis method and application thereof

Abstract

The application discloses a kind of based on melting polymerization hetero-linkage type COFs material, one-pot synthesis method and application thereof, the hetero-linkage type covalent organic framework material based on melting polymerization is formed frame structure by covalently connecting ethene bond and polyimide bond, the one-pot synthesis method includes that active methyl and amino-containing heterocyclic monomer, aromatic aldehyde monomer, aromatic dianhydride monomer are mixed with fluxing agent, under solvent-free condition, melting polymerization reaction is carried out, and the target product is obtained.The application creatively provides a kind of hetero-linkage type COFs material with the covalent connection bond of ethene bond and polyimide bond in frame structure, it contains the redox active site formed by carbonyl and heterocyclic simultaneously in its skeleton and the intrinsic electronic transmission channel constructed by ethene bond, with high active site density and intrinsic conductivity, show excellent structural stability and electrochemical performance, has wide application prospect in battery electrode material and electrocatalysis and other energy fields.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework materials technology, specifically relating to a heterobonded COFs material based on melt polymerization, its one-pot synthesis method, and its application. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers formed by light elements linked by strong covalent bonds. They have advantages such as high specific surface area, tunable pore structure, good chemical stability and structural designability, and show broad application prospects in fields such as gas adsorption and separation, heterogeneous catalysis, sensing, energy storage and conversion, and electrochemical energy storage.

[0003] Among various COF materials, those constructed based on irreversible covalent bonds have attracted considerable attention due to their excellent chemical and thermal stability. Ethylene-linked COFs, with their fully conjugated framework, exhibit high intrinsic electronic conductivity and good structural stability; while polyimide-linked COFs, due to their abundant carbonyl active sites, possess the potential for high theoretical capacity. However, current research shows that single-bond COFs often have inherent performance defects: although ethylene-linked COFs possess excellent electronic conductivity, their pure carbon-carbon double bond framework lacks efficient redox active sites, resulting in low theoretical capacity; while polyimide-linked COFs are rich in carbonyl active sites, their poor skeletal conjugation and extremely low intrinsic electronic conductivity lead to insufficient utilization of active sites at high rates.

[0004] In the construction of COFs with single-bond reversible covalent bonds, solvent-free melt polymerization has opened up new avenues for the green synthesis of COFs due to its advantages such as environmental friendliness, simple process, and ease of scale-up. Previous research (202111650887.5) "A Green Solid-Phase Synthesis Method for Covalent Organic Framework Materials" provides a green synthesis method for COFs with a single bonding site. This method involves condensing methyl-containing monomers and aldehyde monomers with the participation of anhydrides or carboxylic acid compounds to prepare vinyl COFs; condensing multi-headed anhydrides or carboxylic acid monomers and amino monomers with the participation of anhydrides or carboxylic acid compounds to prepare amide COFs; and condensing aldehyde monomers and amino monomers with the participation of anhydrides, imidazoles, or carboxylic acid compounds to prepare imine COFs. However, these methods are limited to single-bond COF materials and cannot overcome the competitive effects existing in the formation of different types of covalent bonds within the same framework structure, thus failing to achieve the preparation of COFs with multiple covalent bonds.

[0005] Traditional methods for constructing heterobonded COFs often employ multi-step post-modification or stepwise synthesis strategies, which are cumbersome, have low yields, and are difficult to control, contradicting the requirements for large-scale production. Exploring ways to balance or overcome the competing effects of heterobonded reactions to achieve the synthesis of heterobonded COFs, and obtaining heterobonded COFs with both conductivity and high active site density, has become a key issue in overcoming the performance bottlenecks of single materials. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a heterobonded COFs material based on melt polymerization, its one-pot synthesis method, and its applications. The heterobonded COFs material consists of a framework structure formed by the covalent linkage of ethylene bonds and polyimide bonds. Its framework simultaneously contains redox active sites composed of carbonyl groups and nitrogen heterocycles, as well as intrinsic electronic conduction channels constructed by ethylene bonds. This heterobonded COFs material exhibits both high active site density and intrinsic conductivity, demonstrating excellent structural stability and electrochemical performance, and has broad application prospects in energy fields such as battery electrode materials and electrocatalysis.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] On the one hand, a heterogeneous covalent organic framework (COF) material based on melt polymerization is provided, wherein the heterogeneous covalent organic framework material is formed by the covalent connection of ethylene bonds and polyimide bonds to form a framework structure.

[0009] On the other hand, a one-pot synthesis method for the above-mentioned heterogeneous covalent organic framework material based on melt polymerization is provided, comprising the following steps:

[0010] A nitrogen heterocyclic monomer containing active methyl and amino groups, an aromatic aldehyde monomer, an aromatic dianhydride monomer, and a flux are mixed and melt-polymerized under solvent-free conditions to obtain the target product.

[0011] On the other hand, an application of the above-mentioned heterogeneous covalent organic framework material based on melt polymerization is provided, including applications in battery electrode materials or electrocatalytic materials.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1. This invention proposes a heterobonded COFs material based on melt polymerization, which integrates the fast electron conduction network of ethylene bonds with the high-density carbonyl active centers of polyimide bonds into the same framework, possessing both high active site density and intrinsic conductivity, exhibiting excellent structural stability and electrochemical performance.

[0014] 2. This invention creatively provides a one-pot synthesis method for the above-mentioned heterocyclic COFs material based on melt polymerization. The method involves mixing nitrogen heterocyclic monomers containing active methyl and amino groups, aromatic aldehyde monomers, aromatic dianhydride monomers, and benzoic anhydride flux, and then preparing the material through melt polymerization under solvent-free conditions. This method achieves the simultaneous construction of two covalent bonds with different properties, namely ethylene bonds and polyimide bonds, in the same reaction system, avoiding the cumbersome process of traditional multi-step synthesis. The method is simple and efficient.

[0015] 3. This invention utilizes inexpensive industrial monomers and recyclable fluxes, significantly reducing material costs. Furthermore, the synthesis process is solvent-free, environmentally friendly, and easy to scale up for production.

[0016] 4. The heterobonded COFs material prepared by this invention exhibits high selectivity in electrocatalytic oxygen reduction reaction, and shows excellent two-electron oxygen reduction selectivity in 0.1M KOH electrolyte, with hydrogen peroxide selectivity reaching over 90%, showing broad application prospects in the field of energy materials.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 The images show the X-ray powder diffraction patterns of heterobonded COFs materials in Examples 1-4.

[0019] Figure 2 The Fourier transform infrared spectra of heterobonded COFs materials in Examples 1-4 are shown.

[0020] Figure 3 The nitrogen adsorption-desorption isotherms and pore size distribution diagrams of heterobonded COFs materials in Examples 1 and 2 are shown.

[0021] Figure 4 This is a graph showing the selectivity performance evaluation of the heterobonded COFs material in the electrocatalytic oxygen reduction reaction of Example 1.

[0022] Figure 5 The image shows the X-ray powder diffraction pattern of the COFs material in Comparative Example 1. Detailed Implementation

[0023] The technical solution will now be clearly and completely described with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0024] In the following description, the term "and / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural.

[0025] In the following description, the terms “including,” “containing,” “having,” and “containing” are open-ended terms, meaning that they include but are not limited to.

[0026] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0027] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] The technical principle upon which this invention is based: This invention provides a heterobonded covalent organic framework material whose framework structure is formed by the covalent connection of ethylene bonds and polyimide bonds. The raw materials include nitrogen heterocyclic monomers containing active methyl and amino groups, aromatic aldehyde monomers, and aromatic dianhydride monomers, as well as flux. Ethylene bonds and polyimide bonds are both irreversible covalent bonds, resulting in a high activation energy for the formation reaction. Under the action of benzoic anhydride flux, nitrogen heterocyclic monomers containing active methyl and amino groups, aromatic aldehyde monomers, and aromatic dianhydride monomers form amide intermediates and enamine intermediate active species. Simultaneously, the above-mentioned heterobonded covalent organic framework material is constructed in a one-pot method through Knoevenagel condensation (ethylene bonds) and imidization reaction (polyimide bonds). This effectively overcomes the conflict and competition effects of reaction conditions between different irreversible bond types, and achieves the synchronous and orderly construction and heterobonding balance of ethylene bonds and polyimide bonds in a single molten system.

[0030] In one aspect, this invention provides a heterobonded covalent organic framework material based on melt polymerization, wherein the heterobonded covalent organic framework material is formed by the covalent connection of ethylene bonds and polyimide bonds to form a framework structure. Its framework simultaneously contains redox active sites composed of carbonyl groups and nitrogen heterocycles, as well as intrinsic electron conduction channels constructed by ethylene bonds.

[0031] In some embodiments, the X-ray powder diffraction pattern of the heterobonded covalent organic framework material based on melt polymerization has a characteristic diffraction peak at a 2θ diffraction angle of 3 to 10°. Preferably, the X-ray powder diffraction pattern of the heterobonded covalent organic framework material based on melt polymerization has characteristic diffraction peaks at a 2θ diffraction angle of 3 to 10° and at 26.2 ± 0.2°.

[0032] In some embodiments, the ratio of ethylene bonds to polyimide bonds in the melt-polymerized heterogeneous covalent organic framework material is 2:1.

[0033] The above X-ray powder diffraction pattern shows that the heterogeneous covalent organic framework material based on melt polymerization of the present invention has a highly ordered layered stacked structure with a hexagonal uniform porous network morphology, and the ratio of ethylene bonds to polyimide bonds is 2:1.

[0034] In some embodiments, the Fourier transform infrared spectrum of the melt-polymerized heterogeneous covalent organic framework material is at 961±5 cm⁻¹. -1 A characteristic absorption peak belonging to the C=C bond appears at 1720±5 cm⁻¹. -1 and 1780±5 cm -1 Symmetric stretching vibration peaks and asymmetric stretching vibration peaks, respectively, belonging to the carbonyl group in the polyimide bond, appear at the locations.

[0035] This indicates that the heterogeneous covalent organic framework material based on melt polymerization of the present invention contains both ethylene bonds and polyimide bonds.

[0036] In some embodiments, the specific surface area of ​​the melt-polymerized heterogeneous covalent organic framework material is 300~1500 m² / g, and the pore size distribution is concentrated in the range of 1.0~2.5 nm; preferably, the specific surface area of ​​the melt-polymerized heterogeneous covalent organic framework material is 300~1000 m² / g, and the pore size distribution is concentrated in the range of 1.2~1.3 nm.

[0037] In some embodiments, the heterocyclic covalent organic framework material based on melt polymerization is prepared by melt polymerization of nitrogen heterocyclic monomers containing active methyl and amino groups, aromatic aldehyde monomers, aromatic dianhydride monomers, and fluxes under solvent-free conditions.

[0038] This invention selects a nitrogen-containing heterocyclic molecule with both active methyl and amino groups as the core building block. The two different reactive sites integrated on a single backbone significantly enhance the acidity of the ortho-methyl hydrogen by utilizing the electron-deficient nature of the nitrogen heterocycle, allowing for smooth Knoevenagel condensation with aromatic aldehydes to construct fully conjugated ethylene bonds. Simultaneously, it preserves the imidization reaction between the amino group and the aromatic dianhydride to construct polyimide bonds, balancing the competing effects of the two irreversible bonds in a one-pot melting system. Furthermore, it plays a crucial role in obtaining bifunctional heterobonded COFs, utilizing the intrinsic electron conduction channels constructed by the ethylene bonds to compensate for the poor conductivity of traditional polyimide COFs, while simultaneously synergistically increasing the redox active site density of the material through the synergistic interaction between the nitrogen heterocycle and the carbonyl sites of the polyimide. Furthermore, nitrogen heterocyclic monomers containing active methyl and amino groups synergistically interact with aromatic aldehyde monomers and aromatic dianhydride monomers in the melt. The high geometric symmetry of nitrogen heterocyclic monomers containing active methyl and amino groups exhibits excellent self-healing ability and directional arrangement characteristics in the solvent-free molten state, ensuring that the final product has both high chemical stability and a long-range ordered crystalline channel structure.

[0039] In some preferred embodiments, the structural formula of the melt-polymerized heterogeneous covalent organic framework material is shown in any one of the following four structural formulas:

[0040]

[0041] .

[0042] In another aspect, the present invention provides a one-pot synthesis method for the above-mentioned heterogeneous covalent organic framework material based on melt polymerization, comprising the following steps:

[0043] A nitrogen heterocyclic monomer containing active methyl and amino groups, an aromatic aldehyde monomer, an aromatic dianhydride monomer, and a flux are mixed and melt-polymerized under solvent-free conditions to obtain the target product.

[0044] Preferably, the flux is benzoic anhydride.

[0045] Benzoic anhydride, a fluxing agent, has both fluxing and catalytic functions. In reaction systems containing nitrogen heterocyclic monomers with active methyl and amino groups, aromatic aldehyde monomers, and aromatic dianhydride monomers, it achieves the unification of catalyst and reaction environment. It can effectively utilize the dual functions of fluxing and catalysis to reduce the viscosity of raw material melts, promote monomer diffusion and mass transfer, obtain amide intermediates and enamine intermediates, and achieve the simultaneous formation of ethylene bonds and polyimide bonds.

[0046] Preferably, the nitrogen-containing heterocyclic monomer with active methyl and amino groups is 2,6-dimethyl-4-aminopyridine, 2-amino-4,6-dimethylpyridine, 2-amino-4,6-dimethylpyrimidine, or 2-amino-4,6-dimethyl-1,3,5-triazine; the aromatic aldehyde monomer is terephthalaldehyde, biphenyl dicarboxaldehyde, or [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde; and the aromatic dianhydride monomer is pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride. Preferably, the nitrogen-containing heterocyclic monomer with active methyl and amino groups is 2,6-dimethyl-4-aminopyridine, the aromatic aldehyde monomer is terephthalaldehyde, and the aromatic dianhydride monomer is pyromellitic dianhydride. The COFs crystals obtained from these preferred monomers exhibit the highest degree of order.

[0047] In the reaction system of this invention, the nitrogen-containing heterocyclic monomers containing active methyl and amino groups are 2,6-dimethyl-4-aminopyridine, 2-amino-4,6-dimethylpyridine, 2-amino-4,6-dimethylpyrimidine, or 2-amino-4,6-dimethyl-1,3,5-triazine; the aromatic aldehyde monomers are terephthalaldehyde, biphenyl dicarboxaldehyde, or [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde; and the aromatic dianhydride monomers are pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride. This effectively achieves symmetrical matching of molecular structures and synergistic regulation of electronic effects: utilizing the high geometric symmetry of the above three monomers and... The rigid planar configuration serves as the topological basis for thermodynamic self-healing and long-range ordered stacking in the molten state. At the same time, the strong electron-withdrawing inductive effect of pyridine, pyrimidine, and triazine can enhance the acidity of the active methyl hydrogen at the ortho or para position, enabling it to undergo Knoevenagel condensation with aromatic aldehydes to construct highly conductive ethylene bonds. Meanwhile, its electrochemical environment promotes the imidization reaction of nucleophilic amino groups and aromatic dianhydrides to achieve kinetic equilibrium with the construction of ethylene bonds, reducing the competitive effect between different irreversible bonds in a single reaction system and realizing the synchronous and orderly integration of the electron conduction network and high-density redox active centers within the same framework.

[0048] Preferably, the molar ratio of the nitrogen heterocyclic monomer containing active methyl and amino groups, the aromatic aldehyde monomer, and the aromatic dianhydride monomer is (1~2):(1~2):(0.5~1); the total molar ratio of the flux to the nitrogen heterocyclic monomer containing active methyl and amino groups, the aromatic aldehyde monomer, and the aromatic dianhydride monomer is (2~8):1. Preferably, the molar ratio of the nitrogen heterocyclic monomer containing active methyl and amino groups, the aromatic aldehyde monomer, and the aromatic dianhydride monomer is 1:1:0.5; the total molar ratio of the flux to the nitrogen heterocyclic monomer containing active methyl and amino groups, the aromatic aldehyde monomer, and the aromatic dianhydride monomer is (3~4):1.

[0049] In this invention, the molar ratio of nitrogen heterocyclic monomers containing active methyl and amino groups, aromatic aldehyde monomers and aromatic dianhydride monomers is (1~2):(1~2):(0.5~1), and the total molar ratio of the flux to the nitrogen heterocyclic monomers containing active methyl and amino groups, aromatic aldehyde monomers and aromatic dianhydride monomers is (2~8):1. Raw material ratios that do not fall within the above range will not be able to obtain COFs with crystallinity.

[0050] Preferably, the melt polymerization reaction temperature is 180~250℃ and the reaction time is 3~7 days.

[0051] The melt polymerization reaction has a wide temperature window of 180~250℃, which can simultaneously meet the thermodynamic requirements of two irreversible bonds in a high temperature range of ≥473 K.

[0052] Preferably, the reaction is carried out in a closed reactor under an air atmosphere at a pressure of 0.1 Pa to 0.001 Pa.

[0053] Preferably, the preparation method further includes washing and drying the solid phase after the melt polymerization reaction in sequence; the washing includes washing with N,N-dimethylformamide 3 to 5 times, and then washing with methanol 3 to 5 times; the drying is vacuum drying, the drying temperature is 60 to 120°C, and the drying time is 6 to 12 hours.

[0054] A third objective of this invention is the application of heterogeneous covalent organic framework materials based on melt polymerization, as described in one objective, in the fields of battery electrode materials or electrocatalytic materials.

[0055] Prior to the application for this invention, a series of experiments were conducted. Some of the experimental results are listed below to provide a more detailed description of the invention. The following is a detailed description in conjunction with the embodiments.

[0056] Example 1

[0057] This embodiment provides a one-pot synthesis method for heterogeneous covalent organic framework materials based on melt polymerization. The reaction equation is as follows:

[0058]

[0059] The steps include:

[0060] 2,6-Dimethyl-4-aminopyridine (1.0 mmol), terephthalaldehyde (1.0 mmol), pyromellitic dianhydride (0.5 mmol), and benzoic anhydride (8.0 mmol) were mixed thoroughly and transferred to a closed reactor. The reactor was evacuated to near-vacuum conditions. The mixture was heated to 200°C under solvent-free conditions to allow for melt polymerization for 5 days. After the reaction was completed, the mixture was cooled to room temperature. The resulting solid product was washed three times with N,N-dimethylformamide and then three times with methanol. It was then vacuum dried at 80°C for 8 hours to obtain the target heterobonded COFs material, which was named COF-1.

[0061] Example 2

[0062] This embodiment provides a one-pot synthesis method for heterogeneous covalent organic framework materials based on melt polymerization. The reaction equation is as follows:

[0063]

[0064] The steps include:

[0065] 2,6-Dimethyl-4-aminopyridine (1.0 mmol), terephthalaldehyde (1.0 mmol), 3,3',4,4'-biphenyltetracarboxylic dianhydride (0.5 mmol), and benzoic anhydride (8.0 mmol) were mixed thoroughly and transferred to a closed reactor. The reactor was evacuated to near-vacuum conditions. The mixture was heated to 200°C under solvent-free conditions to allow for melt polymerization for 5 days. After the reaction was completed, the mixture was cooled to room temperature. The resulting solid product was washed three times with N,N-dimethylformamide and then three times with methanol. It was then vacuum dried at 80°C for 8 hours to obtain the target heterobonded COFs material, which was named COF-2.

[0066] Example 3

[0067] This embodiment provides a one-pot synthesis method for heterogeneous covalent organic framework materials based on melt polymerization. The reaction equation is as follows:

[0068]

[0069] The steps include:

[0070] 2,6-Dimethyl-4-aminopyridine (1.0 mmol), biphenyl dicarboxaldehyde (1.0 mmol), pyromellitic dianhydride (0.5 mmol), and benzoic anhydride (8.0 mmol) were mixed thoroughly and transferred to a closed reactor. The reactor was evacuated to near-vacuum conditions. The mixture was heated to 200°C under solvent-free conditions to allow for melt polymerization for 5 days. After the reaction was completed, the mixture was cooled to room temperature. The resulting solid product was washed three times with N,N-dimethylformamide and then three times with methanol. It was then vacuum dried at 80°C for 8 hours to obtain the target heterobonded COFs material, which was named COF-3.

[0071] Example 4

[0072] This embodiment provides a one-pot synthesis method for heterogeneous covalent organic framework materials based on melt polymerization. The reaction equation is as follows:

[0073]

[0074] The steps include:

[0075] 2,6-Dimethyl-4-aminopyridine (1.0 mmol), [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde (1.0 mmol), pyromellitic dianhydride (0.5 mmol), and benzoic anhydride (8.0 mmol) were mixed thoroughly and transferred to a closed reactor. The reactor was evacuated to near-vacuum conditions. The mixture was heated to 200°C under solvent-free conditions to allow for melt polymerization for 5 days. After the reaction was completed, the mixture was cooled to room temperature. The resulting solid product was washed three times with N,N-dimethylformamide, then three times with methanol, and finally dried under vacuum at 80°C for 8 hours to obtain the target heterobonded COFs material, which was named COF-4.

[0076] Comparative Example 1

[0077] This comparative example examines the influence of monomers on the structure and properties of the product, and provides a one-pot synthesis method for a valence organic framework material, comprising: mixing 2,6-dimethyl-4-aminopyridine (1.0 mmol), terephthalaldehyde (1.0 mmol), and benzoic anhydride (8.0 mmol) uniformly, transferring the mixture to a closed reactor, and evacuating it to near-vacuum conditions; heating the mixture to 200°C under solvent-free conditions to carry out a melt polymerization reaction for 5 days; cooling the mixture to room temperature after the reaction, washing the resulting solid product three times with N,N-dimethylformamide, then three times with methanol, and finally drying it under vacuum at 80°C for 8 hours to obtain the comparative material.

[0078] Performance Evaluation

[0079] The structural characterization and performance testing of each embodiment and the four heterobonded COFs materials prepared were performed:

[0080] from Figure 1 The X-ray powder diffraction patterns show that the material prepared in Example 1 exhibits characteristic diffraction peaks near 2θ angles of 4.7°, 8.1°, 9.6°, and 26.0°. Compared with the MS simulation curves, the positions and intensities of the main peaks in the material of Example 1 are consistent with the MS simulation data, and the heterobonded COFs obtained in Example 1 are consistent with the theoretical predictions. The material prepared in Example 2 exhibits characteristic diffraction peaks near 2θ angles of 4.4°, 7.6°, and 26.0°, the material prepared in Example 3 exhibits a characteristic diffraction peak near 2θ angle of 4.1°, and the material prepared in Example 4 exhibits a characteristic diffraction peak near 2θ angle of 3.4°, indicating that the materials have a highly ordered crystal structure.

[0081] from Figure 2 The Fourier transform infrared spectra of the four materials in Examples 1-4 all show a value at 961 cm⁻¹. -1 A characteristic absorption peak for the C=C bond appears nearby, at 1720 cm⁻¹. -1 and 1780 cm -1 The presence of symmetric and asymmetric stretching vibration peaks of the carbonyl group in the polyimide bond nearby confirms that the ethylene bond and the polyimide bond successfully coexist in the same framework.

[0082] from Figure 3 As can be seen from the nitrogen adsorption-desorption isotherms and pore size distribution diagrams, the materials prepared in Examples 1 and 2 all exhibit typical Type IV isotherms, with specific surface areas ranging from 300 to 1000 m². 2 Within the range of / g, the pore size distribution is concentrated in 1.2~1.3 nm, confirming that the material has a rich mesoporous structure.

[0083] The heterobonded COFs material prepared in Example 1 was used for performance evaluation in the oxygen reduction reaction to produce hydrogen peroxide. The evaluation method included: using the above material as the electrode active material, mixing it with conductive carbon black and polyvinylidene fluoride binder at a mass ratio of 8:1:1, coating it onto a carbon paper current collector to form a working electrode, using platinum wire as the counter electrode and Ag / AgCl as the reference electrode, and performing electrochemical tests in a 0.1 M KOH electrolyte. The results are as follows: Figure 4 As shown, the COF-1 material prepared in Example 1 exhibits excellent two-electron oxygen reduction selectivity and hydrogen peroxide selectivity of over 90% in 0.1 M KOH electrolyte, demonstrating good electrochemical activity and stability, indicating its potential application value in the field of electrocatalysis.

[0084] Figure 5 The X-ray powder diffraction pattern of the material shows that no obvious characteristic peaks were observed in the XRD pattern, indicating a disordered structure. This suggests that the method used in the comparative study did not yield a material with an ordered crystal structure.

Claims

1. A heterobonded covalent organic framework material based on melt polymerization, characterized in that, The heterogeneous covalent organic framework material is formed by the covalent connection of ethylene bonds and polyimide bonds to form a framework structure.

2. The heterogeneous covalent organic framework material based on melt polymerization according to claim 1, characterized in that, In the X-ray powder diffraction pattern of the heterobonded covalent organic framework material based on melt polymerization, the 2θ diffraction angle has a characteristic diffraction peak in the range of 3 to 10°.

3. The heterobonded covalent organic framework material based on melt polymerization according to claim 1, characterized in that, In the Fourier transform infrared spectrum of the heterobonded covalent organic framework material based on melt polymerization, at 961±5 cm⁻¹ -1 The characteristic absorption peak belonging to the C=C bond is observed at 1720±5 cm⁻¹. -1 and 1780±5 cm -1 Symmetric stretching vibration peaks and asymmetric stretching vibration peaks, respectively, belonging to the carbonyl group in the polyimide bond, appear at the locations.

4. The heterogeneous covalent organic framework material based on melt polymerization according to claim 1, characterized in that, The specific surface area of ​​the heterobonded covalent organic framework material based on melt polymerization is 300~1500 m². 2 / g, with pore size distribution concentrated in 1.0~2.5 nm.

5. The heterogeneous covalent organic framework material based on melt polymerization according to claim 1, characterized in that, The heterobonded covalent organic framework material based on melt polymerization is prepared by melt polymerization of nitrogen heterocyclic monomers containing active methyl and amino groups, aromatic aldehyde monomers, aromatic dianhydride monomers, and fluxes under solvent-free conditions.

6. A one-pot synthesis method for heterogeneous covalent organic framework materials based on melt polymerization as described in claim 1, characterized in that, include: A nitrogen heterocyclic monomer containing active methyl and amino groups, an aromatic aldehyde monomer, an aromatic dianhydride monomer, and a flux are mixed and melt-polymerized under solvent-free conditions to obtain the target product.

7. The method according to claim 6, characterized in that, The flux is benzoic anhydride; and / or, the nitrogen heterocyclic monomer containing active methyl and amino groups is 2,6-dimethyl-4-aminopyridine, 2-amino-4,6-dimethylpyridine, 2-amino-4,6-dimethylpyrimidine, or 2-amino-4,6-dimethyl-1,3,5-triazine; and / or, the aromatic aldehyde monomer is terephthalaldehyde, biphenyl dicarboxaldehyde, or [1,1':4',1''-terphenyl]-4,4''-dicarboxaldehyde; and / or, the aromatic dianhydride monomer is pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

8. The method according to claim 6, characterized in that, The melt polymerization reaction temperature is 180~250℃, and the reaction time is 3~7 days; and / or, the one-pot synthesis method further includes washing and drying the solid phase after the melt polymerization reaction in sequence. The washing includes washing with N,N-dimethylformamide 3~5 times and then washing with methanol 3~5 times. The drying is vacuum drying at a temperature of 60~120℃ for 6~12 hours.

9. The method according to claim 6, characterized in that, The molar ratio of the nitrogen heterocyclic monomer containing active methyl and amino groups, the aromatic aldehyde monomer, and the aromatic dianhydride monomer is (1~2):(1~2):(0.5~1); and / or, the total molar ratio of the flux to the nitrogen heterocyclic monomer containing active methyl and amino groups, the aromatic aldehyde monomer, and the aromatic dianhydride monomer is (2~8):

1.

10. An application of the heterogeneous covalent organic framework material based on melt polymerization as described in claim 1, including applications in battery electrode materials or electrocatalytic materials.

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