Preparation method and application of nitrogen-containing ring D-A type COFs photocatalyst

Abstract

This invention discloses a method for preparing a nitrogen-containing heterocyclic D-A type COF photocatalyst and its application. The specific steps are as follows: Step S1, an aldehyde ligand and an amino ligand are added to a Pyrex reaction tube at a molar ratio of 2:3. The aldehyde ligand is a trialdehyde pyrogallol, and the amino ligand is an aromatic amine compound containing a nitrogen-containing heterocyclic ring. Step S2, a mixed organic solvent composed of mesitylene and 1,4-dioxane is added to the Pyrex reaction tube from Step S1, and an aqueous acetic acid solution is added as a catalyst to obtain mixture a. Step S3, the Pyrex reaction tube containing mixture a from Step S2 is ultrasonically treated to form a uniform suspension. This invention relates to the field of functional materials and photocatalysis technology. The structure is precisely designed, and the nitrogen-containing heterocyclic ring significantly modulates the D-A effect. In this invention, the 1,3,5-trihydroxypyrogallol and the nitrogen-containing heterocyclic amine ligand are covalently linked to form a donor-acceptor (D-A) structure with a significant electron push-pull effect within a covalent organic framework.

Description

Technical Field

[0001] This invention relates to the field of functional materials and photocatalysis technology, and in particular to a method for preparing a nitrogen heterocyclic DA-type COF photocatalyst and its application. Background Technology

[0002] Hydrogen peroxide (H2O2), as an important green oxidant and potential energy carrier, is experiencing continuous growth in global demand, projected to reach 5.7 million tons by 2027. Currently, over 90% of H2O2 production relies on the energy-intensive and high-risk anthraquinone process, making the development of green and low-carbon synthetic routes crucial. Photocatalysis, utilizing solar energy to drive the synthesis of H2O2 from H2O and O2, offers advantages such as mild reaction conditions and a clean process, making it one of the important pathways to achieving this goal.

[0003] Early photocatalysts were mainly inorganic semiconductors such as TiO2 and ZnO, but their wide bandgap limited the utilization of visible light, and their electronic structure was difficult to control, making it difficult to improve catalytic efficiency. In recent years, covalent organic frameworks (COFs) have become ideal materials for photocatalytic H2O2 synthesis due to their designable crystal structure, high specific surface area, and tunable band structure and electronic properties. However, most current research still focuses on optimizing the oxygen reduction reaction (ORR), which often requires the addition of organic sacrificial agents to provide holes, failing to achieve synergistic effects between the water oxidation reaction (WOR) and ORR, thus limiting overall energy efficiency and practicality.

[0004] Constructing sacrificial agent-free bifunctional photocatalysts requires meeting the following key requirements: band structure matching the thermodynamic potentials of ORR (~0.68 V vs. NHE) and WOR (~1.23 V vs. NHE); achieving efficient separation and directional migration of photogenerated electrons and holes; and precisely controlling the reaction pathway to promote the two-electron transfer process and suppress side reactions. Therefore, to overcome these limitations and meet the conditions for bifunctional catalysts, constructing donor-acceptor (DA) type COFs is a promising solution. DA type COFs can promote the separation and directional transport of photogenerated charge carriers and suppress charge carrier recombination through a built-in electric field, achieving separation of oxidation and reduction sites. Notably, nitrogen heterocyclic compounds exhibit unique advantages in controlling the energy level structure and active sites of COF materials due to their excellent electronic properties and structural tunability. The introduction of heteroatoms can not only change the energy level distribution of molecular orbitals, but their lone pairs of electrons can also form a special electronic conjugation effect with neighboring carbon atoms. These characteristics provide the possibility of simultaneously optimizing the ORR and WOR reaction pathways. Furthermore, the isomerization design of nitrogen heterocycles can further regulate the electronic structure and catalytic performance of materials, providing new research ideas for the development of highly efficient bifunctional photocatalysts. Summary of the Invention

[0005] To address the key problems commonly found in existing photocatalytic H2O2 synthesis technologies, such as insufficient visible light utilization, rapid charge recombination, dependence on sacrificial agents, and difficulty in achieving synergistic WOR and ORR dual-pathway synthesis, this invention aims to synthesize a class of DA-type nitrogen heterocyclic covalent organic framework bifunctional photocatalysts. These catalysts, through precise molecular-level design, simultaneously achieve efficient photogenerated charge separation, broad-spectrum absorption, and synergistic dual-pathway catalysis, thereby enabling efficient and green synthesis of H2O2 using H2O and O2 as raw materials without sacrificial agents. To achieve the above objective, this invention applies for: a method for preparing a nitrogen heterocyclic DA-type COF photocatalyst and its application.

[0006] The technical solution of the present invention to achieve the above objectives is a method for preparing a nitrogen heterocyclic DA-type COF photocatalyst, the specific steps of which are as follows:

[0007] Step S1: Add the aldehyde ligand and the amino ligand to the Pyrex reaction tube at a molar ratio of 2:3. The aldehyde ligand is trialdehyde phloroglucinol (hereinafter referred to as Tp), and the amino ligand is an aromatic amine compound containing a nitrogen heterocycle.

[0008] Step S2: Continue to add a mixed organic solvent consisting of mesitylene and 1,4-dioxane to the Pyrex reaction tube from step S1, and add an aqueous acetic acid solution as a catalyst to obtain mixture a;

[0009] Step S3: The Pyrex reaction tube containing mixture a from step S2 is subjected to ultrasonic treatment to form a uniform suspension.

[0010] Step S4: Fill the reaction tube from step S3 with nitrogen gas, seal the reaction tube, place it in an oven and let it stand for heating reaction; after the reaction is completed, cool the Pyrex reaction tube to room temperature and collect the solid product by filtration.

[0011] Step S5: Wash the solid product collected in step S4 sequentially with anhydrous N,N-dimethylacetamide, tetrahydrofuran and acetone until the washing solution is colorless;

[0012] In step S6, the solid product washed in step S5 is solvent-exchanged with acetone and then freeze-dried to obtain a donor-acceptor type nitrogen heterocyclic covalent organic framework photocatalyst.

[0013] The nitrogen-containing heterocyclic aromatic amine compound in step S1 is 5,5'-(1,4-phenyl)bis(pyrimidin-2-amine) (hereinafter referred to as: PMA) or 5-(4-(bis(4-(6-aminopyridin-3-yl)phenyl)amino)phenyl)pyridin-2-amine (hereinafter referred to as: PDA) nitrogen-containing heterocyclic aromatic amine compounds.

[0014] In step S2, the concentration of the acetic acid aqueous solution is 4-6 M, and the ratio of its added volume to the total volume of the organic solvent is in the range of 1:15 - 1:10.

[0015] In step S4, the heating reaction temperature is 150 °C and the reaction time is 72 h.

[0016] In step S6, acetone is used to replace the high-boiling-point solvents, namely mesitylene and 1,4-dioxane, remaining in the pores.

[0017] In step S6, the freeze-drying temperature is -60 ℃.

[0018] This invention also provides an application of the nitrogen heterocyclic DA-type COFs photocatalyst prepared by the above preparation method in the photocatalytic synthesis of H2O2.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] 1. Precise structural design and significant modulation of the DA effect by nitrogen heterocyclic compounds. In this invention, the 1,3,5-trihydroxypyrogallol and the nitrogen heterocyclic amine ligand are covalently linked to form a donor-acceptor (DA) structure with a significant electronic push-pull effect within a covalent organic framework. This structure not only effectively broadens the light absorption range of the material but also enables the construction of a built-in electric field within the framework, generating efficient intramolecular charge transfer under photoexcitation and achieving directional separation of photogenerated carriers. This provides a kinetic possibility for simultaneously and efficiently driving the two half-reactions of water oxidation (WOR) and oxygen reduction (ORR), thereby eliminating dependence on sacrificial agents.

[0021] 2. Excellent catalytic performance, achieving efficient H2O2 synthesis under sacrificial agent-free conditions. This invention introduces a nitrogen heterocycle to construct a DA structure, enabling the catalyst to exhibit superior H2O2 synthesis rates in a pure water system without relying on any sacrificial agent. Specifically, the TpPMA photocatalyst achieves an H2O2 yield of up to 5571 μmol g⁻¹ h⁻¹ under sacrificial agent-free conditions, representing a performance improvement of approximately 12.5 times compared to the isomorphic but nitrogen-free comparative (TpBZA, yield 449.4 μmol g⁻¹ h⁻¹). This demonstrates a significant breakthrough in catalytic efficiency achieved through a green and simple reaction pathway. Furthermore, with the addition of a sacrificial agent, the yield further increases to 7351.1 μmol g⁻¹ h⁻¹, proving the material's inherent ability to efficiently separate and utilize photogenerated charges.

[0022] 3. Applications align with the trend of green chemical engineering. The catalyst of this invention uses only water and oxygen / air as raw materials, utilizing solar energy to drive the production of H2O2, with zero carbon emissions and no pollution throughout the entire process. The achieved sacrificial agent-free and highly efficient synthesis solves the problem of adding and separating organic sacrificial agents in traditional photocatalytic processes. This provides an ideal platform for green H2O2 synthesis and holds promise for applications in environmental remediation, portable disinfection, and green chemical synthesis. Attached Figure Description

[0023] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0024] Figure 1 Schematic diagrams of the catalyst synthesis routes described in Examples 1 (TpPMA), 2 (TpPDA), and Comparative Example 1 (TpBZA).

[0025] Figure 2 X-ray powder diffraction (PXRD) patterns of the catalysts described in Example 1 (TpPMA), Example 2 (TpPDA), and Comparative Example 1 (TpBZA).

[0026] Figure 3 Fourier transform infrared (FT-IR) spectra of the catalyst described in Comparative Example 1 (TpBZA) and the monomers prepared from it, namely trialdehyde phloroglucinol (Tp) and 4,4'-diaminotriphenyl (BZA).

[0027] Figure 4 FT-IR spectra of the catalyst described in Example 1 (TpPMA) and its preparation monomers trialdehyde phloroglucinol (Tp) and 5,5'-(1,4-phenyl)bis(pyrimidin-2-amine) (PMA).

[0028] Figure 5 FT-IR spectra of the catalyst described in Example 2 (TpPDA) and its preparation monomers trialdehyde phloroglucinol (Tp) and 5-(4-(bis(4-(6-aminopyridin-3-yl)phenyl)amino)phenyl)pyridin-2-amine (PDA).

[0029] Figure 6 UV-Vis diffuse reflectance spectra of the catalysts described in Example 1 (TpPMA), Example 2 (TpPDA), and Comparative Example 1 (TpBZA).

[0030] Figure 7A comparison of the photosynthesis performance of the catalysts described in Example 1 (TpPMA), Example 2 (TpPDA), and Comparative Example 1 (TpBZA) under a nitrogen atmosphere.

[0031] Figure 8 A comparison of the photosynthesis performance of the catalysts described in Example 1 (TpPMA), Example 2 (TpPDA), and Comparative Example 1 (TpBZA) in an air atmosphere.

[0032] Figure 9 A comparison of the photosynthesis performance of the catalysts described in Example 1 (TpPMA), Example 2 (TpPDA), and Comparative Example 1 (TpBZA) under an oxygen atmosphere.

[0033] Figure 10 A comparison of the photosynthesis performance of the catalysts described in Example 1 (TpPMA), Example 2 (TpPDA), and Comparative Example 1 (TpBZA) for H2O2 under an oxygen atmosphere with the addition of 10 vol% isopropanol.

[0034] Figure 11 Time-yield curve of photocatalytic synthesis of H2O2 using the catalyst described in Example 1 (TpPMA). Detailed Implementation

[0035] To clearly and completely describe the technical solution and its specific working process of the present invention, the specific embodiments of the present invention are as follows, in conjunction with the accompanying drawings:

[0036] Example 1

[0037] This embodiment provides a method for preparing a nitrogen-heterocyclic DA-type covalent organic framework photocatalyst. The specific steps of the method are as follows:

[0038] Step S1: Add the aldehyde ligand and the amino ligand to the Pyrex reaction tube at a molar ratio of 2:3. The aldehyde ligand is trialdehyde phloroglucinol (abbreviated as Tp), and the amino ligand is an aromatic amine compound containing a nitrogen-containing heterocyclic ring.

[0039] In step S2, a mixed organic solvent consisting of mesitylene and 1,4-dioxane is added to the Pyrex reaction tube from step S1, and an aqueous acetic acid solution is added as a catalyst to obtain mixture a.

[0040] Step S3: The Pyrex reaction tube containing mixture a from step S2 is subjected to ultrasonic treatment to form a uniform suspension.

[0041] Step S4: Fill the Pyrex reaction tube from step S3 with nitrogen gas, seal the Pyrex reaction tube, place it in an oven and let it stand for heating reaction; after the reaction is completed, cool the Pyrex reaction tube to room temperature and collect the solid product by filtration.

[0042] Step S5: Wash the solid product collected in step S4 sequentially with anhydrous N,N-dimethylacetamide, tetrahydrofuran and acetone until the washing solution is colorless;

[0043] Step S6: Solvent exchange is performed on the solid product washed in step S5 using acetone, followed by freeze drying to obtain the DA-type nitrogen heterocyclic covalent organic framework photocatalyst (TpPMA).

[0044] Furthermore, the nitrogen-containing heterocyclic aromatic amine compound in step S1 is 5,5'-(1,4-phenyl)bis(pyrimidin-2-amine) (abbreviated as: PMA).

[0045] Furthermore, in step S2, the volume ratio of the added acetic acid aqueous solution (6 M) to the total volume of the organic solvent is 1:10.

[0046] Furthermore, in step S4, the heating reaction temperature is 150 °C and the reaction time is 72 h.

[0047] Furthermore, in step S6, the freeze-drying temperature is -60 ℃.

[0048] The structure and light absorption properties of the TpPMA photocatalyst prepared in this embodiment were characterized, and the results were verified with reference to the accompanying drawings in the specification as follows:

[0049] like Figure 2 As shown, the PXRD pattern of TpPMA exhibits sharp diffraction peaks, demonstrating that the prepared TpPMA possesses high crystallinity and a long-range ordered structure. Figure 4 The FT-IR spectrum corresponding to TpPMA is shown below. Compared with monomeric Tp and PMA, at 1573 cm⁻¹ -1 The appearance of a new C=C peak and 3300 cm -1 The disappearance of NH4+ confirms the successful synthesis of TpPMA. Figure 6 As shown, the UV-Vis spectrum curve of TpPMA shows a wide absorption range between 300-800 nm, indicating that TpPMA has strong light absorption capabilities in both the ultraviolet and visible regions, demonstrating a broad spectral response capability.

[0050] In summary, this embodiment successfully prepared a nitrogen heterocyclic DA-type COF photocatalyst (TpPMA) with a well-defined structure, high crystallinity, and a wide absorption range.

[0051] Example 2

[0052] This embodiment provides a method for preparing a nitrogen-heterocyclic DA-type covalent organic framework photocatalyst. The specific steps of the method are as follows:

[0053] Step S1: Add the aldehyde ligand and the amino ligand to the Pyrex reaction tube at a molar ratio of 2:3. The aldehyde ligand is trialdehyde phloroglucinol (abbreviated as Tp), and the amino ligand is an aromatic amine compound containing a nitrogen-containing heterocyclic ring.

[0054] In step S2, a mixed organic solvent consisting of mesitylene and 1,4-dioxane is added to the Pyrex reaction tube from step S1, and an aqueous acetic acid solution is added as a catalyst to obtain mixture a.

[0055] Step S3: The Pyrex reaction tube containing mixture a from step S2 is subjected to ultrasonic treatment to form a uniform suspension.

[0056] Step S4: Fill the Pyrex reaction tube from step S3 with nitrogen gas, seal the Pyrex reaction tube, place it in an oven and let it stand for heating reaction; after the reaction is completed, cool the Pyrex reaction tube to room temperature and collect the solid product by filtration.

[0057] Step S5: Wash the solid product collected in step S4 sequentially with anhydrous N,N-dimethylacetamide, tetrahydrofuran and acetone until the washing solution is colorless;

[0058] Step S6: Solvent exchange is performed on the solid product washed in step S5 using acetone, followed by freeze drying to obtain the DA-type nitrogen heterocyclic covalent organic framework photocatalyst (TpPDA).

[0059] Furthermore, the nitrogen-containing heterocyclic aromatic amine compound in step S1 is 5-(4-(bis(4-(6-aminopyridin-3-yl)phenyl)amino)phenyl)pyridin-2-amine (abbreviated as: PDA).

[0060] Furthermore, in step S2, the volume ratio of the added acetic acid aqueous solution (6 M) to the total volume of the organic solvent is 1:10.

[0061] Furthermore, in step S4, the heating reaction temperature is 150 °C and the reaction time is 72 h.

[0062] Furthermore, in step S6, the freeze-drying temperature is -60 ℃.

[0063] The TpPDA prepared in this embodiment was characterized in terms of structure and light absorption properties. For example... Figure 2The PXRD spectrum of TpPDA shows that the sharp diffraction peaks of TpPDA confirm its high crystallinity and long-range ordered structure; as shown in the figure. Figure 5 The FT-IR spectrum of TpPDA is shown below. Compared with monomeric Tp and PDA, the 1563 cm⁻¹ spectrum... -1 The appearance of a new C=C peak and 3300 cm -1 The disappearance of NH at the site confirms the successful synthesis of TpPDA; as Figure 6 As shown, its UV-Vis spectrum indicates that TpPDA exhibits a wide absorption range between 300-800 nm, demonstrating that TpPDA also possesses a wide spectral response capability.

[0064] In summary, this embodiment successfully prepared another nitrogen heterocyclic DA-type COF photocatalyst (TpPDA) with a well-defined structure, high crystallinity, and a wide absorption range.

[0065] Comparative Example 1

[0066] This comparative example provides a method for preparing a covalent organic framework photocatalyst without nitrogen heterocycles. The specific steps of the method are as follows:

[0067] Step S1: Add the aldehyde ligand and the amino ligand to the Pyrex reaction tube at a molar ratio of 2:3. The aldehyde ligand is trialdehyde phloroglucinol (abbreviated as Tp), and the amino ligand is an aromatic amine compound containing a nitrogen-containing heterocyclic ring.

[0068] In step S2, a mixed organic solvent consisting of mesitylene and 1,4-dioxane is added to the Pyrex reaction tube from step S1, and an aqueous acetic acid solution is added as a catalyst to obtain mixture a.

[0069] Step S3: The Pyrex reaction tube containing mixture a from step S2 is subjected to ultrasonic treatment to form a uniform suspension.

[0070] Step S4: Fill the Pyrex reaction tube from step S3 with nitrogen gas, seal the Pyrex reaction tube, place it in an oven and let it stand for heating reaction; after the reaction is completed, cool the Pyrex reaction tube to room temperature and collect the solid product by filtration.

[0071] Step S5: Wash the solid product collected in step S4 sequentially with anhydrous N,N-dimethylacetamide, tetrahydrofuran and acetone until the washing solution is colorless;

[0072] Step S6: Solvent exchange is performed on the solid product washed in step S5 using acetone, followed by freeze drying to obtain the DA-type nitrogen heterocyclic covalent organic framework photocatalyst (TpBZA).

[0073] Furthermore, the nitrogen-containing heterocyclic aromatic amine compound in step S1 is 4,4'-diaminotriphenyl (abbreviated as: BZA).

[0074] Furthermore, in step S2, the volume ratio of the added acetic acid aqueous solution (6 M) to the total volume of the organic solvent is 1:15.

[0075] Furthermore, in step S4, the heating reaction temperature is 150 °C and the reaction time is 72 h.

[0076] Furthermore, in step S6, the freeze-drying temperature is -60 ℃.

[0077] The structure and light absorption properties of the TpBZA photocatalyst prepared in this comparative example were characterized, and the results were verified with reference to the accompanying drawings in the specification as follows:

[0078] The structure and light absorption properties of the sample prepared in this comparative example were characterized. Figure 2 The PXRD pattern of TpBZA shows that the sharp diffraction peaks of TpBZA confirm its high crystallinity and long-range ordered structure; as shown in the figure. Figure 3 The FT-IR spectrum of TpBZA is shown below. Compared with monomeric Tp and BZA, at 1567 cm⁻¹ -1 The appearance of a new C=C peak and 3300 cm -1 The disappearance of NH at the site confirms the successful synthesis of TpBZA; as Figure 6 As shown, its UV-Vis spectrum indicates that TpBZA exhibits a wide absorption range between 300-800 nm, demonstrating that TpBZA also possesses a wide spectral response capability.

[0079] In summary, this comparative example successfully prepared a nitrogen-free DA-type COF photocatalyst (TpBZA) with good crystallinity and broad-spectral absorption.

[0080] Example 3

[0081] The photocatalytic synthesis performance of the catalysts prepared in Examples 1-2 and Comparative Example 1 was determined. The specific methods are as follows: 5 mg of the prepared catalyst was weighed and dispersed in 20 ml of ultrapure water. Oxygen was introduced into the reactor to ~80 kPa, and after sealing, the reactor was irradiated with a xenon lamp at 25 °C. After 1 h of reaction, the concentration of H2O2 in the solution was determined by iodometric titration, and the formation rate was calculated. The results are as follows. Figure 9 As shown.

[0082] The results show:

[0083] Comparative Example 1 (TpBZA): The rate of H2O2 formation was 449.4 μmol g⁻¹ h⁻¹.

[0084] Example 2 (TpPDA): The H2O2 generation rate was 1572.4 μmol g⁻¹ h⁻¹, which is about 3.5 times higher than that of the comparative example TpBZA.

[0085] Example 1 (TpPMA): The H2O2 generation rate was 5571 μmol g⁻¹ h⁻¹, which is about 12.5 times higher than that of the comparative example TpBZA.

[0086] like Figure 9 As shown, under an oxygen atmosphere, the nitrogen-containing heterocyclic DA-type COFs (TpPMA and TpPDA) prepared in this invention exhibit superior H2O2 synthesis performance compared to the nitrogen-free comparative example TpBZA. Among them, TpPMA showed the best performance, with an improvement of approximately 12.5 times compared to TpBZA and approximately 3.5 times compared to TpPDA. Under these conditions, the time and yield curves of the TpPMA catalyst were monitored, as shown in the figure. Figure 11 As shown, the H2O2 yield of TpPMA continuously increases with increasing reaction time, indicating that its catalytic ability has good stability. Under an oxygen atmosphere, the introduction of nitrogen heterocycles significantly enhances the photocatalytic H2O2 production activity of COFs materials, with TpPMA exhibiting the best performance and good reaction stability.

[0087] Example 4

[0088] Referring to the test method of Example 3, only the reaction atmosphere was changed from oxygen to air, while the other conditions remained unchanged, in order to examine the catalytic performance under different oxygen sources.

[0089] The results show:

[0090] Comparative Example 1 (TpBZA): The rate of H2O2 formation was 336 μmol g⁻¹ h⁻¹.

[0091] Example 2 (TpPDA): The H2O2 generation rate was 927 μmol g⁻¹ h⁻¹.

[0092] Example 1 (TpPMA): The H2O2 generation rate was 4273 μmol g⁻¹ h⁻¹.

[0093] like Figure 8 The results show that the catalyst of the present invention can still maintain excellent catalytic activity in air, and the performance of TpPMA is far superior to that of the control sample, demonstrating good potential for practical application.

[0094] Example 5

[0095] Referring to the test method of Example 3, only the reaction atmosphere was changed from oxygen to nitrogen, while the other conditions remained unchanged, to verify the ability of the catalyst H2O to oxidize to H2O2.

[0096] The results show:

[0097] Comparative Example 1 (TpBZA): The rate of H2O2 formation was 205 μmol g⁻¹ h⁻¹.

[0098] Example 2 (TpPDA): The H2O2 generation rate was 242 μmol g⁻¹ h⁻¹.

[0099] Example 1 (TpPMA): The H2O2 generation rate was 256 μmol g⁻¹ h⁻¹.

[0100] like Figure 7 The results show that the catalyst of this invention still has catalytic activity under a nitrogen atmosphere, confirming that the catalyst generates H2O2 synergistically through the WOR and ORR dual pathways, and that the performance of TpPMA is far superior to that of the control sample.

[0101] Example 6

[0102] Referring to the test method in Example 3, 10 vol% isopropanol was added to the reaction system as a hole sacrificial agent, and the other conditions remained unchanged, and the photocatalytic performance was tested.

[0103] The results show:

[0104] Comparative Example 1 (TpBZA): The rate of H2O2 formation was 720 μmol g⁻¹ h⁻¹.

[0105] Example 2 (TpPDA): The H2O2 generation rate was 1730 μmol g⁻¹ h⁻¹.

[0106] Example 1 (TpPMA): The H2O2 generation rate was 7351 μmol g⁻¹ h⁻¹.

[0107] like Figure 10 The results showed that the yield of all catalysts was improved after the addition of the hole sacrificial agent. Among them, TpPMA showed the largest increase, with a yield of 7351 μmol g⁻¹ h⁻¹, further demonstrating its efficient photogenerated charge separation capability.

[0108] Based on the test results of Examples 3-6, the nitrogen-heterocyclic DA-type COF photocatalyst prepared in this invention exhibits excellent photocatalytic performance for H2O2 synthesis under different reaction conditions (nitrogen, oxygen, air, and sacrificial agent addition). Compared with the comparative example TpBZA without nitrogen heterocycles, the performance is significantly improved, which is attributed to the fact that the introduction of nitrogen heterocycles optimizes the electronic structure of the material and promotes the separation and transport of photogenerated charges. Furthermore, the difference in performance between the TpPDA and TpPMA examples stems from the number of nitrogen atoms in the structural units, further illustrating the performance regulation role of nitrogen heterocycles in photocatalysis.

[0109] It should be noted that:

[0110] Figure 1 The molecular structures and synthetic routes of the catalysts of this invention (TpPMA, TpPDA) and the comparative catalyst (TpBZA) are shown.

[0111] Figures 2 to 5 The successful synthesis of the catalyst and its crystallization properties were demonstrated.

[0112] Figure 6 The light absorption characteristics of each catalyst are shown, indicating that they all possess excellent ultraviolet-visible light absorption capabilities.

[0113] Figures 7 to 10 This demonstrates the photocatalytic performance of each catalyst in producing H2O2 under different reaction conditions.

[0114] Figure 11 Example 1 shows the relationship between the H2O2 yield and time during the reaction process of the catalyst, reflecting the stability of its catalytic performance.

[0115] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-heterocyclic DA-type COF photocatalyst, characterized in that, The specific steps are as follows: Step S1: Add the aldehyde ligand and the amino ligand to the Pyrex reaction tube at a molar ratio of 2:

3. The aldehyde ligand is trialdehyde phloroglucinol, and the amino ligand is an aromatic amine compound containing a nitrogen heterocycle. Step S2: Continue to add a mixed organic solvent consisting of mesitylene and 1,4-dioxane to the Pyrex reaction tube from step S1, and add an aqueous acetic acid solution as a catalyst to obtain mixture a; Step S3: The Pyrex reaction tube containing mixture a from step S2 is subjected to ultrasonic treatment to form a uniform suspension. Step S4: Fill the Pyrex reaction tube from step S3 with nitrogen gas, seal the Pyrex reaction tube, place it in an oven and let it stand for heating reaction; after the reaction is completed, cool the Pyrex reaction tube to room temperature and collect the solid product by filtration. Step S5: Wash the solid product collected in step S4 sequentially with anhydrous N,N-dimethylacetamide, tetrahydrofuran and acetone until the washing solution is colorless; Step S6: Solvent exchange is performed on the solid product washed in step S5 using acetone, followed by freeze drying to obtain a donor-acceptor type nitrogen heterocyclic covalent organic framework photocatalyst. The nitrogen-containing heterocyclic aromatic amine compound in step S1 is 5,5'-(1,4-phenyl)bis(pyrimidin-2-amine) or 5-(4-(bis(4-(6-aminopyridin-3-yl)phenyl)amino)phenyl)pyridin-2-amine; In step S2, the concentration of the acetic acid aqueous solution is 4-6 M, and the ratio of its added volume to the total volume of the organic solvent is in the range of 1:15 - 1:

10. In step S4, the heating reaction temperature is 150 °C and the reaction time is 72 h.

2. The method for preparing a nitrogen heterocyclic DA-type COF photocatalyst as described in claim 1, characterized in that, In step S6, the freeze-drying temperature is -60 ℃.

3. The application of the nitrogen heterocyclic DA-type COF photocatalyst prepared by the method of any one of claims 1 to 2 in the photocatalytic synthesis of hydrogen peroxide.

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