[4 +3 +2] type covalent organic framework material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalytic materials, in particular to a [4 + 3 + 2] type covalent organic framework material and a preparation method and application thereof. According to the invention, 4, 4 ', 4' ', 4 '''-(pyrene-1, 3, 6, 8-tetrayl) tetraphenylamine, 4, 4 ', 4''-(1, 3, 5-triazinyl-2, 4, 6-triyl) tribenzaldehyde and 4, 4'-diamino tribenzene are used as raw materials, and a solvothermal reaction is carried out in an oxygen-free environment to obtain the [4 + 3 + 2] type covalent organic framework material. According to the invention, by introducing 4, 4 '-diamino triphenyl, the polarity, the electron delocalization degree and the crystallinity of the covalent organic framework material are regulated and controlled at the molecular level, so that the charge separation efficiency is effectively improved, the photocatalytic hydrogen production performance of the [4 + 3 + 2] type covalent organic framework material is improved, and the photocatalytic hydrogen production efficiency is improved. The technical defects existing when triazine and pyrene structures are cooperatively introduced into a covalent organic framework material in the prior art are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic materials, in particular to a [4+3+2] type covalent organic framework material and a preparation method and application thereof. Background Art

[0002] Currently, developing green, efficient, and sustainable energy conversion technologies has become a research hotspot. Photocatalytic hydrogen production technology is considered a key direction for the future development of the hydrogen energy industry because it can use solar energy to decompose water into hydrogen, has zero carbon emissions, and is based on abundant raw materials. However, traditional inorganic photocatalytic materials, such as TiO2, CdS, and ZnO, generally suffer from narrow light absorption wavelength ranges, low quantum efficiency, corrosion susceptibility, and a lack of design flexibility for the catalytic center, which greatly limits their practical application.

[0003] Covalent organic frameworks (COFs) are a class of highly crystalline porous materials self-assembled from organic units through covalent bonds. They possess highly ordered, designable skeletal structures, large specific surface areas, and excellent photoelectric properties, making them a leading research frontier for the next generation of photocatalytic materials. Covalent organic frameworks based on donor-acceptor structures, in particular, show promising application prospects due to their ability to effectively promote the separation and transport of photogenerated electrons and holes. However, the main challenges of existing COFs are: 1. Limited choice of structural functional units: Current photocatalytic COFs mostly use conventional aromatic units as connecting structures, lacking effective synergy between functional units, making it difficult to precisely control the light absorption range and electron transport pathways; 2. Severe photogenerated carrier recombination: Existing COFs exhibit high rates of photogenerated electron-hole recombination, resulting in low photocatalytic efficiency; and 3. Insufficient stability of COFs: Many COFs are susceptible to degradation under light, heat, or acid-base conditions, resulting in short photocatalytic lifetimes, which restricts their widespread application in practical systems.

[0004] Triazines, rich in nitrogen atoms, have strong electron-attracting abilities and are used as typical electron acceptor units in covalent organic framework materials. They can regulate the energy band structure of covalent organic framework materials and enhance electron transport behavior. However, their excessive use can easily lead to reduced efficiency of electron separation in the framework, requiring coordinated optimization with other structures. Pyrene is a typical large-conjugated rigid planar aromatic structure with good light absorption and stability. As an electron donor unit, it is widely used in the framework construction of covalent organic framework materials. However, pyrene has a large steric hindrance, and its excessive introduction can easily cause framework stacking disorders, affecting the crystallinity and pore connectivity of the covalent organic framework material.

[0005] Therefore, the key to research breakthroughs is to synergistically introduce triazine and pyrene structures into covalent organic framework materials to achieve efficient matching of structural functions and photocatalytic performance. However, the following problems still exist in the synergistic introduction of triazine and pyrene structures into covalent organic framework materials: 1. The problem of precise regulation of triazine and pyrene structures in covalent organic framework materials: It is difficult to effectively control the distribution and configuration of triazine and pyrene conjugated units in the skeleton of covalent organic framework materials, which limits the adjustment space of covalent organic framework materials' light absorption capacity and carrier migration efficiency.

[0006] 2. Insufficient separation efficiency of photogenerated electron-hole pairs: The carrier recombination rate is high and the electron-hole separation is insufficient, which limits the photocatalytic efficiency and activity of covalent organic framework materials.

[0007] 3. Long-term stability issues: Existing covalent organic framework materials have problems with structural instability and catalytic activity decay in continuous photocatalytic reactions, making it difficult to meet long-term use requirements.

[0008] 4. Lack of effective regulatory mechanism between molecular structure and electronic behavior: There is a lack of methods to specifically regulate the behavior of photogenerated carriers at the electronic structure level through molecular design, which limits the improvement of the photocatalytic performance of covalent organic framework materials. Summary of the Invention

[0009] In response to the deficiencies in the above-mentioned prior art, the present invention provides a [4+3+2] type covalent organic framework material, a preparation method thereof, and an application thereof. The present invention introduces an adjustable linear two-position linking unit, 4,4'-diaminoterphenyl, to replace some of the four-position linking units, and systematically regulates the number of benzene rings in the two-position linking units, thereby achieving molecular-level regulation of the polarity, electron delocalization, and crystallinity of the covalent organic framework material, thereby effectively improving the charge separation efficiency and enhancing the photocatalytic hydrogen production performance of the [4+3+2] type covalent organic framework material. This provides a new design strategy and addresses the technical defects of the existing method of synergistically introducing triazine and pyrene structures into covalent organic framework materials.

[0010] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: The present invention provides a method for preparing a [4+3+2] type covalent organic framework material, comprising the following steps: 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde and 4,4'-diaminoterphenyl are used as raw materials, dispersed together in a solvent, and subjected to solvothermal reaction in an oxygen-free environment to obtain a [4+3+2] type covalent organic framework material.

[0011] Preferably, the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde and 4,4'-diaminoterphenyl is 76:76:62~66. Too much 4,4'-diaminoterphenyl leads to excessive cross-linking, increased side reactions and decreased product purity; the crystallinity is impaired, defects increase, and orderly assembly is destroyed; unreacted monomers remain in the pores, blocking the pores or adsorbed on the surface, reducing the specific surface area; and separation and purification are difficult. Too little 4,4'-diaminoterphenyl leads to weak electron delocalization and poor crystallinity. As for weak electron delocalization, the degree of conjugation is insufficient, resulting in a decrease in the efficiency of photogenerated electron migration and a reduction in the photocatalytic rate; as for poor crystallinity, the skeleton is not rigid, resulting in the formation of a disordered structure or a low crystallinity structure in the [4+3+2] type covalent organic framework material, affecting the catalytic activity.

[0012] Preferably, the solvent thermal reaction conditions are: heating at 115° C. to 125° C. for 72 h.

[0013] Preferably, the solvent consists of 1,4-dioxane, mesitylene and an aqueous acetic acid solution, and the solvent composition is obtained through screening of hydrogen production experiments.

[0014] The present invention also protects a [4+3+2] type covalent organic framework material, which is prepared by the above preparation method.

[0015] Preferably, in the [4+3+2] type covalent organic framework material, 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine is the four-position connecting unit, 4,4',4''-(1,3,5-triazine ring-2,4,6-triyl)tribenzaldehyde is the three-position connecting unit, and by introducing a linear two-position connecting unit 4,4'-diaminoterphenyl to replace part of the four-position connecting unit, a [4+3+2] type covalent organic framework material is obtained.

[0016] The present invention also protects the use of a [4+3+2] type covalent organic framework material in the preparation of a visible light photolysis water hydrogen production catalyst, which is prepared according to the following steps: After dispersing the [4+3+2] type covalent organic framework material in an ascorbic acid solution, adding a chloroplatinic acid solution and performing light treatment, a visible light photolysis water hydrogen production catalyst is obtained. The visible light photolysis water hydrogen production catalyst is a [4+3+2] type covalent organic framework material with Pt loaded on the surface.

[0017] Preferably, in the [4+3+2] type covalent organic framework material with Pt loaded on the surface, the mass percentage of Pt is 3 wt % to 5 wt %.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde and a two-position connecting unit 4,4'-diaminoterphenyl as raw materials, and performs a solvent thermal reaction in an oxygen-free environment. During the solvent thermal reaction, the amino group of 4,4'-diaminoterphenyl and the aldehyde group of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde undergo a reversible Schiff base reaction, while releasing water molecules to form an imine bond. The imine bond can be reversibly broken / recombined under acidic or heating conditions, promoting defect repair and orderly crystal growth. 4,4'-diaminoterphenyl serves as a linear connecting unit. The triazine nodes are extended into a two-dimensional network structure by reacting the amino groups at both ends with two 4,4',4''-(1,3,5-triazine-2,4,6-triyl) tribenzaldehyde molecules. At the same time, the 120° bond angle between the benzene rings of 4,4'-diaminoterphenyl and its rigid linear structure help lock the square lattice topology and avoid the formation of disordered cross-links. 4,4'-diaminoterphenyl connects 4,4',4''-(1,3,5-triazine-2,4,6-triyl) tribenzaldehyde to form a basic grid. 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine as a four-node unit is further expanded into a three-dimensional interpenetrating or multilayer structure to obtain a [4+3+2] type covalent organic framework material.

[0019] 2. The preparation of the [4+3+2] type covalent organic framework material of the present invention adopts the following innovative strategies: (1) adopting the substoichiometric strategy + structure regulation method, by introducing a linear two-position connecting unit 4,4'-diaminoterphenyl with three benzene rings to adjust the structural polarity; (2) regulating the electronic structure behavior at the molecular level: by controlling the number of aromatic rings of the linear two-position connecting unit 4,4'-diaminoterphenyl, the molecular dipole moment is regulated, the built-in electric field is enhanced, the electron delocalization is expanded, and the exciton binding energy is reduced, thereby significantly improving the photocatalytic hydrogen production efficiency.

[0020] 3. This invention introduces a linear two-position linker, 4,4'-diaminoterphenyl, further enhancing photocatalytic performance. By introducing linear aniline linkers with varying numbers of benzene rings, the present invention optimizes the molecular polarity, electron delocalization, and crystallinity of the [4+3+2] covalent organic framework. This structural manipulation effectively enhances the separation efficiency of photogenerated carriers, reduces electron-hole recombination, and improves the stability of the [4+3+2] covalent organic framework.

[0021] This invention utilizes a substoichiometric strategy and structural control: By regulating the number of benzene rings in the linear aniline linker, the present invention further optimizes the photoelectric performance and catalytic efficiency of the [4+3+2] covalent organic framework material. The present invention specifically protects the application of the linear aniline linker in the synthesis of the [4+3+2] covalent organic framework material. By adjusting the number of benzene rings, the electronic structure, molecular polarity, and crystallinity of the [4+3+2] covalent organic framework material can be manipulated, thereby improving the photocatalytic hydrogen production performance.

[0022] 4. The present invention also protects the specific application of [4+3+2] type covalent organic framework materials in photocatalytic hydrogen production, especially the high hydrogen production efficiency and long-term stability under visible light irradiation. By optimizing the separation and transmission of photogenerated carriers, it exhibits excellent performance in photocatalytic reactions.

[0023] 5. The linear aniline linking unit introduced in the present invention precisely regulates the substoichiometric ratio of triazine monomers to pyrene monomers. Through this series of innovative means, the photocatalytic hydrogen production performance of the [4+3+2] type covalent organic framework material is enhanced, and its light absorption capacity, electron separation efficiency and stability are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the drawings of the present invention, P represents a pyrene monomer, specifically 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine; T represents a triazine monomer, specifically 4,4',4''-(1,3,5-triazine ring-2,4,6-triyl) tribenzaldehyde; COF represents a covalent organic framework material, PA represents p-phenylenediamine, BPA represents 4,4'-diaminobiphenyl, and TPA represents 4,4'-diaminoterphenyl.

[0025] Figure 1 This is the chemical reaction equation diagram of PT COF in Comparative Example 1.

[0026] Figure 2 This is a chemical reaction equation diagram of the PT-TPA COF of Example 1.

[0027] Figure 3 The figures are infrared spectra, wherein: a) is the infrared spectra of raw materials P, T, PA, BPA and TPA; b) is the infrared spectra of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3 and PT-TPA COF of Example 1; c) is the infrared spectra of PT COF of Comparative Example 1.

[0028] Figure 4X-ray diffraction patterns, wherein a) is the X-ray diffraction pattern of PT COF of Comparative Example 1; b) is the X-ray diffraction pattern of PT-PA COF of Comparative Example 2; c) is the X-ray diffraction pattern of PT-BPA COF of Comparative Example 3; d) is the X-ray diffraction experimental data graph and X-ray diffraction refinement graph of PT-TPA COF of Example 1, wherein the inset is a schematic diagram of the stacking model of PT-TPA COF.

[0029] Figure 5 Figures are exciton binding energy and dipole moment diagrams, wherein a) is the exciton binding energy diagram of PT-PA COF of Comparative Example 2, d) is the dipole moment diagram of PT-PA COF of Comparative Example 2, b) is the exciton binding energy diagram of PT-BPA COF of Comparative Example 3, e) is the dipole moment diagram of PT-BPA COF of Comparative Example 3, c) is the exciton binding energy diagram of PT-TPA COF of Example 1, and f) is the dipole moment diagram of PT-TPA COF of Example 1; the illustrations in a), b), and c are all diagrams showing the relationship between wavelength and fluorescence emission intensity.

[0030] Figure 6 Electrochemical performance diagram and transient fluorescence spectrum diagram, among which, a) is the PT-PA of comparative example 2 a) The figure shows the photocurrent response spectra of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, and PT-TPA COF of Example 1; b) The figure shows the electrochemical impedance spectroscopy of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, and PT-TPA COF of Example 1; c) The figure shows the transient fluorescence spectra of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, and PT-TPA COF of Example 1.

[0031] Figure 7 The figures are hydrogen production performance graphs and cycle test graphs, wherein: a) the figure is a hydrogen production reaction time process graph of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, PT-TPA COF of Example 1, and PT COF of Comparative Example 1; b) the figure is a hydrogen production performance bar graph of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, PT-TPA COF of Example 1, and PT COF of Comparative Example 1; c) the figure is a cycle test graph of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, and PT-TPA COF of Example 1.

[0032] Figure 8 Schematic diagram of the energy band structures of PT-PA COF of Comparative Example 2, PT-BPA COF of Comparative Example 3, and PT-TPA COF of Example 1.

[0033] Figure 9 1 and 2 are differential pulse voltammograms of the PT-PA COF of Comparative Example 2, the PT-BPA COF of Comparative Example 3, and the PT-TPA COF of Example 1. DETAILED DESCRIPTION

[0034] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention is further described below with reference to specific examples and accompanying drawings. However, the examples are not intended to limit the present invention. The following experimental and detection methods are conventional methods unless otherwise specified; the reagents and raw materials are commercially available unless otherwise specified.

[0035] Considering the defects of the above-mentioned prior art in which triazine and pyrene structures are synergistically introduced into covalent organic framework materials, the present invention overcomes the technical defects, specifically: In view of the problem that the existing technology is difficult to control the structure and distribution of triazine and pyrene units, resulting in the carrier migration rate failing to reach the optimal state, the present invention uses 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine as the four-position connecting unit and the triazine monomer as the three-position connecting unit. By introducing a linear two-position connecting unit TPA, part of the four-position connecting unit is replaced to achieve effective control of the structure and unit distribution, thereby achieving the purpose of precise structural control.

[0036] In view of the problems in the existing technology such as serious carrier recombination, insufficient separation efficiency of photogenerated electrons and holes, and frequent carrier recombination phenomena, which limit the improvement of photocatalytic activity, the present invention introduces a linear two-position connecting unit 4,4'-diaminoterphenyl to replace part of the four-position connecting unit, regulates the number of benzene rings, enhances the molecular polarity and built-in electric field, promotes the separation of photogenerated carriers, reduces the electron-hole recombination rate, and improves the photocatalytic efficiency.

[0037] In view of the problem that the existing covalent organic framework materials are insufficiently stable, have limited durability and structural stability during the photocatalytic process, and are difficult to ensure stable performance during long-term use, the present invention enhances the delocalization and crystallinity of the -conjugated electrons of the [4+3+2] type covalent organic framework materials by expanding the benzene ring, thereby improving the long-term photocatalytic activity of the framework.

[0038] In view of the fact that there is still insufficient room for improvement in the photocatalytic hydrogen production efficiency of existing covalent organic framework materials, especially the lack of optimization in molecular polarity, charge transfer and crystallinity, the present invention achieves a regular improvement in the photocatalytic hydrogen production performance through molecular structure design and connection mode optimization, providing new strategies and ideas for molecular-level regulation of the photogenerated carrier behavior of covalent organic framework materials.

[0039] The PT-TPA COF synthesized in this study exhibits broad tunability and excellent photocatalytic hydrogen production performance. This molecular design strategy allows for the regulation of the electronic structure of covalent organic frameworks, providing a scalable structural design framework and synthesis strategy for the future development of novel, highly efficient photocatalytic materials.

[0040] In summary, this invention demonstrates significant innovation in structural design, coordinated regulation of functional units, and enhanced photocatalytic performance. By proposing a novel molecular construction strategy, it addresses the key challenges of low electron-hole separation efficiency and poor structural stability in photocatalysis associated with conventional covalent organic frameworks that incorporate triazine and pyrene structures, demonstrating broad practical application prospects.

[0041] The following examples and comparative examples are used to further study the technical solution of the present invention. The specific research methods and results are as follows: Example 1 A method for preparing a [4+3+2] type covalent organic framework material comprises the following steps: Weigh 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde, 17 mg, 0.064 mmol of 4,4'-diaminoterphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, and 1 mL of 6 mol / L acetic acid aqueous solution, and add them together into a 15 mL ampoule. Perform three freeze-evacuation-thaw cycles to degas, then seal the solution, and heat under vacuum at 120 ° C for 72 h. After the reaction is completed, cool to room temperature to obtain a crude product.

[0042] The crude product was first filtered, then washed three times with ethanol and N,N-dimethylformamide, then extracted with acetone and tetrahydrofuran Soxhlet for 12 hours, and finally filtered and washed three times with ethanol and deionized water, placed in a freeze dryer, and freeze-dried at -70°C for 12 hours to obtain a [4+3+2] type covalent organic framework material, recorded as PT-TPA COF. The chemical reaction equation is as follows: Figure 2 shown.

[0043] Example 2 A method for preparing a [4+3+2] type covalent organic framework material comprises the following steps: Weigh 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde, 17.5 mg, 0.066 mmol of 4,4'-diaminoterphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, and 1 mL of 6 mol / L acetic acid aqueous solution, and add them together into a 15 mL ampoule. Perform three freeze-evacuation-thaw cycles to degas, then seal the solution, and heat under vacuum at 125 ° C for 72 h. After the reaction is completed, cool to room temperature to obtain a crude product.

[0044] The crude product was first filtered, then washed three times with ethanol and N,N-dimethylformamide, then extracted with acetone and tetrahydrofuran Soxhlet for 12 hours, and finally filtered and washed three times with ethanol and deionized water, placed in a freeze dryer, and freeze-dried at -70°C for 12 hours to obtain a [4+3+2] type covalent organic framework material.

[0045] Example 3 A method for preparing a [4+3+2] type covalent organic framework material comprises the following steps: Weigh 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde, 16.5 mg, 0.062 mmol of 4,4'-diaminoterphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, and 1 mL of 6 mol / L acetic acid aqueous solution, and add them together into a 15 mL ampoule. Perform three freeze-evacuation-thaw cycles to degas, then seal the solution, and heat under vacuum at 115 ° C for 72 h. After the reaction is completed, cool to room temperature to obtain a crude product.

[0046] The crude product was first filtered, then washed three times with ethanol and N,N-dimethylformamide, then extracted with acetone and tetrahydrofuran Soxhlet for 12 hours, and finally filtered and washed three times with ethanol and deionized water, placed in a freeze dryer, and freeze-dried at -70°C for 12 hours to obtain a [4+3+2] type covalent organic framework material.

[0047] Comparative Example 1 A method for preparing a covalent organic framework material, which has the same preparation steps as Example 1, except that 4,4'-diaminoterphenyl is not used as a raw material, comprises the following steps: Weigh 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde, 3 mL of 1,4-dioxane, 3 mL of mesitylene, and 0.6 mL of 6 mol / L acetic acid aqueous solution, and add them together into a 15 mL ampoule. Perform three freeze-evacuation-thaw cycles to degas, then seal and heat under vacuum conditions at 120 ° C for 72 h. After the reaction is completed, cool to room temperature to obtain a crude product.

[0048] The crude product was first filtered, then washed three times with ethanol and N,N-dimethylformamide, then extracted with acetone and tetrahydrofuran for 12 hours, and finally filtered and washed three times with ethanol and deionized water. It was placed in a freeze dryer and freeze-dried at -70°C for 12 hours to obtain a covalent organic framework material, denoted as PT COF. The chemical reaction equation is as follows: Figure 1 shown.

[0049] Comparative Example 2 A method for preparing a covalent organic framework material, which has the same preparation steps as Example 1, except that 4,4'-diaminoterphenyl is replaced with an equimolar amount of p-phenylenediamine, comprises the following steps: Weigh 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde, 7 mg, 0.064 mmol of p-phenylenediamine, 5 mL of 1,4-dioxane, 5 mL of mesitylene, and 1 mL of 6 mol / L acetic acid aqueous solution, and add them together into a 15 mL ampoule. Perform three freeze-evacuation-thaw cycles to degas, then seal the solution, and heat under vacuum at 120 ° C for 72 h. After the reaction is completed, cool to room temperature to obtain a crude product.

[0050] The crude product was first filtered, then washed three times with ethanol and N,N-dimethylformamide, then extracted with acetone and tetrahydrofuran Soxhlet for 12 hours, and finally filtered and washed three times with ethanol and deionized water, placed in a freeze dryer, and freeze-dried at -70°C for 12 hours to obtain a [4+3+2] type covalent organic framework material, recorded as PT-PA COF.

[0051] Comparative Example 3 A method for preparing a covalent organic framework material, which has the same preparation steps as Example 1, except that 4,4'-diaminoterphenyl is replaced with an equimolar amount of 4,4'-diaminobiphenyl, comprises the following steps: Weigh 43.2 mg, 0.076 mmol of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 30 mg, 0.076 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde, 12 mg, 0.064 mmol of 4,4'-diaminobiphenyl, 5 mL of 1,4-dioxane, 5 mL of mesitylene, and 1 mL of 6 mol / L acetic acid aqueous solution, and add them together into a 15 mL ampoule. Perform three freeze-evacuation-thaw cycles to degas, then seal the solution, and heat under vacuum at 120 ° C for 72 h. After the reaction is completed, cool to room temperature to obtain a crude product.

[0052] The crude product was first filtered, then washed three times with ethanol and N,N-dimethylformamide, then extracted with acetone and tetrahydrofuran Soxhlet for 12 hours, and finally filtered and washed three times with ethanol and deionized water, placed in a freeze dryer, and freeze-dried at -70°C for 12 hours to obtain a [4+3+2] type covalent organic framework material, recorded as PT-BPA COF.

[0053] Examples 1 to 3 of the present invention all produced [4+3+2]-type covalent organic framework materials with excellent catalytic performance for hydrogen production from water electrolysis. The following studies were conducted using the PT-PA COF of Comparative Example 2, the PT-BPA COF of Comparative Example 3, the PT-TPA COF of Example 1, and the PT COF of Comparative Example 1 as examples. The specific research methods and results are shown below: like Figure 3 The following is a Fourier transform infrared spectrum. The results show that the triazine monomer is located at 1699 cm -1 The characteristic peak of aldehyde group HC=O stretching vibration disappears, while in COF, it is located at 1613cm -1 The C=N stretching vibration peak appears at , indicating that the aldehyde group and the amino group undergo condensation reaction to form an imine bond. Figure 3 As shown in Figures b) and c), at 3430 cm -1 ~3190cm -1 The NH stretching vibration peak was detected in the region, while in PT-TPA COF, PT-BPA COF and PT-PA COF, this characteristic peak was not observed, which indicates that the free amine groups in the [4+3+2] type COF structure are basically non-existent, further verifying the formation of the framework. In addition, the synthesized COF structures all have a peak at 810 cm -1 The triazine in-plane stretching vibration peak is shown at , indicating that the triazine structural unit is retained, further confirming the stability and integrity of the framework.

[0054] Figure 4Powder X-ray diffraction results show that PT-TPA COF closely matches the orthorhombic stacking model; given the consistent synthesis methods for all COFs, it is speculated that PT-BPA COF and PT-PA COF also adopt an orthorhombic stacking model. PT COF exhibits four diffraction peaks at 2θ = 4.6°, 10.6°, 14.8°, and 22.2°. The broad diffraction peak at 2θ = 22.2° indicates a two-dimensional COF rather than a three-dimensional structure. Compared with PT COF, PT-TPA COF, PT-BPA COF and PT-PA COF all exhibit 8 to 9 significant diffraction peaks at different 2θ angles; for PT-PA COF, the diffraction peaks include 1.9°, 3.8°, 4.4°, 5.6°, 7.6°, 9.8°, 11.3°, and 24.2°; for PT-BPA COF, the diffraction peaks include 1.7°, 3.8°, 4.3°, 5.4°, 7.4°, 9.4°, 11.0°, and 25.2°; for PT-TPA COF, the diffraction peaks include 1.8°, 3.7°, 4.2°, 5.2°, 6.2°, 7.4°, 10.1°, 11.5°, and 23.7°; this shows that compared with PT COF, PT-TPA COF, PT-BPA COF and PT-PA COF have higher crystallinity, which is consistent with the design expectations. In COF systems, because pyrene has two possible connection modes, a periodically ordered COF structure can only be formed when the amine groups along the diagonal direction of pyrene undergo condensation reactions. However, when pyrene is present as a linking unit, free amine groups remain in the system, resulting in disordered reactions during the synthesis process, leading to structural defects and reduced crystallinity.

[0055] The present invention realizes effective regulation of intramolecular polarity by constructing PT-TPA COF, PT-BPA COF and PT-PACOF with different linear benzene ring connecting units, thereby significantly improving the electron-hole separation efficiency and carrier migration performance. Figure 5 The research results show that with the increase of the number of benzene rings in the connecting unit, the exciton binding energy decreases significantly and the dipole moment increases significantly, which helps to suppress the recombination of carriers and improve the effective utilization of photogenerated electrons.

[0056] The photocatalytic hydrogen production performance of the COFs was investigated. The specific method involved loading 3 wt% Pt onto the surfaces of PT COF, PT-TPA COF, PT-BPA COF, and PT-PA COF, respectively, and producing hydrogen via photocatalytic reduction. Specifically, 5 mg of PT COF, PT-TPA COF, PT-BPA COF, or PT-PA COF was dispersed in 100 mL of a 0.2 mol / L ascorbic acid solution. The ascorbic acid solution served as a sacrificial agent, consuming the photogenerated holes in the COFs and retaining the photogenerated electrons. Subsequently, 203 L of a 2 g / L chloroplatinic acid solution was added to obtain a reaction system. The reaction system was evacuated and exposed to light for 0.5 h, then evacuated again. Samples were taken every 0.5 h, and hydrogen production was measured using a gas chromatograph to evaluate the photocatalytic hydrogen production performance of the different COFs. Illumination was performed using a 300 W xenon lamp with a wavelength of λ > 420 nm.

[0057] Compared with PT-BPA COF and PT-PA COF, PT-TPA COF exhibits a more negative conduction band position and stronger visible light absorption ability. Its photocatalytic hydrogen production performance is significantly better than the other two materials, and it shows the highest hydrogen production rate under visible light irradiation, which is 10.44 mmol g -1 h -1 , and has the longest carrier lifetime, the strongest photocurrent response and the lowest charge transfer impedance, such as Figure 6 As shown, it fully demonstrates the excellent photoelectric conversion performance.

[0058] The present invention further improves the photocatalytic efficiency by selecting sacrificial agents, optimizing Pt loading and controlling reaction conditions. Figure 7 As shown, the PT-TPA COF exhibits good structural stability and reaction durability during multiple cycles, showing promising industrial application prospects. Compared with the prior art, the PT-TPA COF of the present invention combines high efficiency, stability, and safety, and can be widely used in the field of solar-driven photocatalytic hydrogen production.

[0059] Combine Figures 5 to 7 , and draw the following conclusions: PT-PA COF exhibits a certain degree of visible light absorption, with an absorption band edge of approximately 550 nm, a conduction band position of -0.79 V vs. NHE, and an exciton binding energy of 82.9 meV. The photocatalytic hydrogen production rate is 5.20 mmol g -1 h -1 Although electron-hole recombination is more significant, the PT-PA COF has good stability and its performance has basically not decayed after eight cycles, proving that its structure is stable and has practical potential.

[0060] PT-BPA COF has two benzene rings connecting the two units, and its intramolecular polarity is enhanced compared to PT-PA COF. Its dipole moment is 2.10D, the exciton binding energy is reduced to 63.3 meV, and the conduction band position is further negatively shifted to -0.88 V vs. NHE, which is conducive to promoting the proton reduction reaction. The photocatalytic hydrogen production rate is increased to 5.64 mmol g -1 h -1 , demonstrating superior charge separation and migration capabilities. Transient fluorescence spectra indicate an extended lifetime of photogenerated carriers, while electrochemical impedance spectroscopy demonstrates reduced charge transfer resistance, resulting in superior overall performance compared to PT-PA COF.

[0061] PT-TPA COF has the highest intramolecular polarity, with a dipole moment of 2.25D. Its electron-hole separation is the most significant, and the exciton binding energy is further reduced to 53.2 meV. The conduction band potential is -0.97 V vs. NHE, which is far higher than the thermodynamic 0V requirement for hydrogen generation. The photocatalytic hydrogen production rate is as high as 10.44 mmol g -1 h -1 , the highest among the three structures. It also exhibits the longest photogenerated carrier lifetime, the strongest photocurrent response, the lowest charge transfer resistance, and the lowest fluorescence emission intensity, indicating the lowest photogenerated carrier recombination rate. Surface photovoltage measurements and transient photovoltage lifetime results further confirm its excellent optoelectronic performance. The PT-TPA COF maintained structural and performance stability throughout eight cycles of testing, demonstrating its promising application prospects.

[0062] By manipulating the structural composition of linear aromatic amine units, from PA to BPA to TPA, this method systematically enhances the intramolecular polarity and photoelectric activity of the COF, significantly improving its photocatalytic hydrogen production capacity. The PT-TPA COF structure is the optimal solution, offering superior photoelectric performance and strong stability, making it suitable for widespread application.

[0063] Figure 8 The results show that the conduction band potential of PT-TPA COF is the most negative, which is -0.97V vs. NHE, the conduction band potential of PT-BPA COF is -0.88V vs. NHE, and the conduction band potential of PT-PA COF is -0.79V vs. NHE. The conduction band potential of PT-TPA COF is significantly higher than that of PT-BPA COF and PT-PA COF. Since the conduction band energy levels of all COFs are higher than 2H + The reduction potential of 1 / H2 is 0 V vs. NHE, indicating that they are all thermodynamically capable of proton reduction to produce hydrogen. Among them, PT-TPA COF exhibits the highest potential for photocatalytic hydrogen production due to its most negative conduction band potential and optimal light absorption performance.

[0064] Figure 9The differential pulse voltammetry test results further confirmed that PT-TPA COF has the most negative reduction potential, i.e. -0.958 V vs. NHE, which is significantly higher than PT-BPA COF (-0.880 V vs. NHE) and PT-PA COF (-0.810 V vs. NHE). Figure 8 The conduction band positions in the band structure shown are completely consistent, further confirming that PT-TPA COF has a stronger thermodynamic reduction driving force, which is directly related to its optimal photocatalytic hydrogen production performance.

[0065] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A method for preparing a [4+3+2] type covalent organic framework material, characterized in that: The steps include: 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde and 4,4'-diaminoterphenyl are used as raw materials, dispersed together in a solvent, and subjected to solvothermal reaction in an oxygen-free environment to obtain a [4+3+2] type covalent organic framework material.

2. The method for preparing a [4+3+2] type covalent organic framework material according to claim 1, characterized in that: The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde and 4,4'-diaminoterphenyl is 76:76:62~66.

3. The method for preparing a [4+3+2] type covalent organic framework material according to claim 1, characterized in that: The conditions of the solvent thermal reaction are: heating at 115°C~125°C for 72h.

4. The method for preparing a [4+3+2] type covalent organic framework material according to claim 1, characterized in that: The solvent consists of 1,4-dioxane, mesitylene and aqueous acetic acid solution.

5. A [4+3+2] type covalent organic framework material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 4.

6. The [4+3+2] type covalent organic framework material according to claim 5, characterized in that In the [4+3+2] type covalent organic framework material, 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraphenylamine is the four-position connecting unit, and 4,4',4''-(1,3,5-triazine ring-2,4,6-triyl)tribenzaldehyde is the three-position connecting unit. By introducing the linear two-position connecting unit 4,4'-diaminoterphenyl to replace part of the four-position connecting unit, the [4+3+2] type covalent organic framework material is obtained.

7. Use of the [4+3+2] type covalent organic framework material according to claim 5 in preparing a visible light photolysis water hydrogen production catalyst, characterized in that: The visible light photolysis water hydrogen production catalyst was prepared according to the following steps: After dispersing the [4+3+2] type covalent organic framework material in an ascorbic acid solution, adding a chloroplatinic acid solution and performing light treatment, a visible light photolysis water hydrogen production catalyst is obtained. The visible light photolysis water hydrogen production catalyst is a [4+3+2] type covalent organic framework material with Pt loaded on the surface.

8. The use according to claim 7, characterized in that In the [4+3+2] type covalent organic framework material with Pt loaded on the surface, the mass percentage of Pt is 3wt%~5wt%.

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