A three-dimensional beta-ketoenamine covalent organic framework material, a preparation method thereof and application thereof in photocatalytic preparation of hydrogen peroxide

Abstract

This invention discloses a three-dimensional β-ketoenamine covalent organic framework material, its preparation method, and its application in the photocatalytic preparation of hydrogen peroxide, belonging to the technical fields of photocatalytic materials and porous organic framework materials. The material uses tetrakis(4-aminophenyl)methane and 2,4,6-tricarboxymethyl phloroglucinol as monomers, and constructs a three-dimensional interconnected β-ketoenamine structural framework through a solvothermal condensation reaction, forming a three-dimensional COF material TAPM-Tp-COF with open pores and multidirectional electron transport channels. The TAPM-Tp-COF material can efficiently catalyze the two-electron reduction of oxygen to hydrogen peroxide under visible light conditions, with an apparent generation rate of 3672 μmol·h⁻¹. ‑1 ·g ‑1 Furthermore, it exhibits excellent cycle stability and requires no noble metal co-catalyst. This invention significantly improves hydrogen peroxide generation efficiency through three-dimensional structural design, providing an effective pathway for visible light-driven hydrogen peroxide generation.

Description

Technical Field

[0001] This invention belongs to the technical field of photocatalytic materials and porous organic framework materials, specifically relating to a three-dimensional β-keto-enamine covalent organic framework material, its preparation method, and its application in the photocatalytic preparation of hydrogen peroxide. Background Technology

[0002] Hydrogen peroxide (H2O2) is an important green oxidant, widely used in environmental pollution control, medical disinfection, fine chemical synthesis, and energy conversion. Traditional industrial production of hydrogen peroxide mainly relies on the anthraquinone process. While this method is mature, it suffers from problems such as complex processes, high energy consumption, large equipment investment, and safety hazards during transportation and storage. Therefore, developing a green synthesis technology that uses water and oxygen as raw materials to generate hydrogen peroxide in situ under mild conditions has significant scientific and practical value. In recent years, visible light-driven two-electron reduction of oxygen (2e2O2) has been studied... - The preparation of hydrogen peroxide using ORR (Organic Reactive Protein) has attracted widespread attention due to its mild reaction conditions, environmentally friendly system, and ability to achieve distributed preparation.

[0003] Among numerous photocatalytic material systems, covalent organic frameworks (COFs) are widely used in photocatalysis due to their highly designable structural units, regular pore structures, large specific surface areas, and tunable electronic structures. However, most reported COFs are predominantly two-dimensional layered structures with strong π-π stacking interactions between layers, which can easily lead to partial pore blockage, restricted charge transport direction, and insufficient exposure of active sites, thus affecting the separation efficiency of photogenerated carriers and the diffusion efficiency of reactants within the pores. Furthermore, some two-dimensional COFs may still suffer from limited interlayer electron migration efficiency or insufficient structural stability in photocatalytic systems, limiting their performance improvement in the photocatalytic generation of hydrogen peroxide. Therefore, constructing COFs with three-dimensional topological structures, stable bonding forms, and more open pore systems to improve electron transport paths and active site utilization is of great significance for enhancing the photocatalytic generation efficiency of hydrogen peroxide. Summary of the Invention

[0004] The purpose of this invention is to provide a three-dimensional β-keto-enamine covalent organic framework material, its preparation method, and its application in the photocatalytic preparation of hydrogen peroxide, so as to solve the problems of severe interlayer stacking, limited charge transport path, and insufficient utilization of active sites in the photocatalytic process of existing two-dimensional layered COF materials, thereby improving the efficiency of oxygen two-electron reduction reaction and the hydrogen peroxide generation rate.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a three-dimensional β-ketoenamine covalent organic framework material, comprising the following steps: S1. Tetra(4-aminophenyl)methane and 2,4,6-tricarboxymethyl phloroglucinol are added to a reaction vessel, and an organic solvent is added to form a homogeneous reaction system; S2. After replacing the reaction system obtained in step S1 with an inert gas, seal it and carry out a solvothermal reaction under a set temperature condition to cause the monomer to undergo a condensation reaction to form a three-dimensional β-ketoenamine structural framework. S3. After the reaction is complete, cool to room temperature, separate the solid product by filtration or centrifugation, and obtain the three-dimensional β-ketoenamine covalent organic framework material after solvent washing and drying.

[0006] Preferably, in step S1, the molar ratio between tetra(4-aminophenyl)methane and 2,4,6-tricarboxymethyl phloroglucinol is 1:(1-2).

[0007] Preferably, in step S1, the molar ratio between tetra(4-aminophenyl)methane and 2,4,6-tricarboxymethyl phloroglucinol is 3:4.

[0008] Preferably, in step S1, the organic solvent is selected from one or more of m-xylene, 1,4-dioxane, N,N-dimethylformamide, and ethanol.

[0009] Preferably, in step S1, an acidic catalyst is added to the reaction system to promote the condensation reaction, and the acidic catalyst is one or more of acetic acid, trifluoroacetic acid, and p-toluenesulfonic acid.

[0010] Preferably, in step S1, the raw materials are magnetically stirred or ultrasonically dispersed for 10–60 min to form a homogeneous reaction system.

[0011] Preferably, in step S2, the inert gas is nitrogen or argon; the solvothermal reaction temperature is 80–150°C, and the solvothermal reaction time is 1–7 days.

[0012] Preferably, in step S2, the solvothermal reaction temperature is 100-120°C and the solvothermal reaction time is 3 days.

[0013] Preferably, in step S3, the solvent washing involves multiple washes using one or more of water, dichloromethane, diethyl ether, ethanol, acetone, and tetrahydrofuran.

[0014] Furthermore, in step S3, the material is further purified by Soxhlet extraction for 12–48 hours.

[0015] Preferably, in step S3, the drying method is vacuum drying, the drying temperature is 50-120℃, and the drying time is 8-24 h.

[0016] To achieve the above-mentioned objectives, this invention also provides a three-dimensional β-ketoenamine covalent organic framework material prepared by the above-mentioned method, the three-dimensional β-ketoenamine covalent organic framework material being abbreviated as TAPM-Tp-COF, and its chemical structural formula is shown in Formula I: .

[0017] To achieve the above-mentioned objectives, this invention also provides the application of the above-mentioned three-dimensional β-ketoenamine covalent organic framework material in the photocatalytic preparation of hydrogen peroxide.

[0018] Furthermore, the specific application process involves dispersing a three-dimensional β-keto-enamine covalent organic framework material in a reaction system to carry out a photocatalytic reaction, thereby generating hydrogen peroxide.

[0019] Preferably, the dosage of the three-dimensional β-ketoenamine covalent organic framework material is 0.1–10 mg / mL.

[0020] Preferably, the reaction system is an aqueous system or a mixture of water and an alcohol solvent, wherein the alcohol solvent is ethanol, methanol, benzyl alcohol or isopropanol.

[0021] Furthermore, oxygen was continuously introduced into the reaction system for 20–60 min under light-protected conditions before illumination, so that the catalyst surface reached adsorption-desorption equilibrium.

[0022] Preferably, the light source is a visible light source, which is a xenon lamp equipped with a 420 nm cutoff filter and has a power of 200-500 W, more preferably 300 W.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention constructs a three-dimensional interconnected β-ketoenamine covalent organic framework structure by selecting tetrahedral monomer TAPM, thereby realizing the essential transformation of the framework dimension from two-dimensional layered to three-dimensional interconnected from the topological level, rather than simple monomer replacement or functional group modification. This three-dimensional structure effectively avoids the carrier quenching problem caused by interlayer π-π stacking in traditional two-dimensional COF materials, constructs continuous multi-directional electron transport channels and a more open pore system, which is conducive to the diffusion, adsorption and activation of oxygen molecules, thereby improving the separation efficiency of photogenerated carriers and the mass transfer efficiency of the reaction interface, and achieving the purpose of increasing the hydrogen peroxide generation rate.

[0024] (2) Under the same reaction conditions, the apparent hydrogen peroxide generation rate of the material of the present invention reaches 3672 μmol·h⁻¹. -1 ·g -1Compared to TAPT-Tp-COF, MA-Tp-COF, and TAPA-Tp-COF, the catalytic activity was improved by approximately 9.4% to 28.9%, demonstrating the significant impact of structural dimension regulation on catalytic performance. Simultaneously, the β-keto-enamine bond structure endows the material with excellent chemical and photostability, allowing it to retain over 90% of its catalytic activity after multiple cycles, exhibiting good durability and reusability.

[0025] (3) The material described in this invention can achieve efficient generation of hydrogen peroxide without the introduction of precious metal co-catalysts, which reduces costs and improves the green and environmentally friendly nature of the system, and has good application prospects.

[0026] Therefore, this invention improves the efficiency of photocatalytic hydrogen peroxide preparation by controlling structural dimensions and optimizing bonding forms, providing a new technical path for the application of three-dimensional COF materials in the fields of green energy and environment. Attached Figure Description

[0027] Figure 1 The infrared spectra of TAPM, Tp, and TAPM-Tp-COF in Example 1 are shown below. Figure 2 The graph shows the performance test results of TAPM-Tp-COF prepared in Example 1 for photocatalytic synthesis of H2O2. Figure 3 This is a graph showing the cyclic reaction test results of TAPM-Tp-COF prepared in Example 1 for photocatalytic synthesis of H2O2; Figure 4 The graph shows the performance test results of TAPA-Tp-COF prepared in Comparative Example 1 for photocatalytic synthesis of H2O2. Figure 5 The graph shows the performance test results of MA-Tp-COF prepared in Comparative Example 2 for photocatalytic synthesis of H2O2. Figure 6 The figure shows the performance test results of TAPT-Tp-COF prepared in Comparative Example 3 for photocatalytic synthesis of H2O2. Detailed Implementation

[0028] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described below in conjunction with specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention. All equivalent substitutions or modifications made based on the technical solutions of this invention should fall within the scope of protection of this invention.

[0029] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available products with a purity of analytical grade or higher. Example 1

[0030] A method for preparing a three-dimensional β-ketoenamine covalent organic framework material includes the following steps: S1. Add 57.1 mg (0.15 mmol) of tetra(4-aminophenyl)methane (TAPM) and 42.0 mg (0.20 mmol) of 2,4,6-tricarboxymethyl phloroglucinol (Tp) to a reaction tube, followed by 4 mL of a mixed solvent of m-xylene / 1,4-dioxane (volume ratio 1:1), and 0.3 mL of a 6 mol / L aqueous acetic acid solution as a catalyst. Disperse the mixture by sonication for 20 min to ensure thorough mixing of the raw materials and form a homogeneous reaction system. S2. The reaction system obtained in step S1 is purged with nitrogen multiple times to remove oxygen and establish an anaerobic environment. After sealing, it is placed in an oven and reacted at 120 °C for 72 h to allow the monomer to undergo a condensation reaction to form a three-dimensional β-ketoenamine structural framework. S3. After the reaction was completed and cooled to room temperature, the solid product was separated by centrifugation, washed three times successively with ethanol and tetrahydrofuran, and then subjected to Soxhlet extraction with tetrahydrofuran for 24 h to remove unreacted monomers and low-molecular-weight impurities. Finally, the obtained solid was vacuum dried at 80 °C for 12 h to obtain a brownish-yellow powdery three-dimensional β-ketoenamine covalent organic framework material TAPM-Tp-COF. The reaction equation is as follows: Figure 1 Infrared spectra of TAPM, Tp, and TAPM-Tp-COF. Compared to the monomer, TAPM exhibits higher infrared spectra at 3400 cm⁻¹. -1 The characteristic absorption peak of -NH2 and Tp at 2900 cm⁻¹ are nearby. -1 The characteristic absorption peaks of -CHO in the vicinity have all disappeared in TAPM-Tp-COF; meanwhile, at 1600 cm⁻¹... -1 A C=O related absorption peak appears nearby, at 1300 cm⁻¹. -1 The presence of characteristic absorption peaks of CN bonds nearby indicates that the target product TAPM-Tp-COF has been successfully formed. Example 2

[0031] Weigh 5 mg of TAPM-Tp-COF prepared in Example 1 and add it to 20 mL of a deionized water / ethanol mixed solution (volume ratio 9:1). The solution is then magnetically stirred to form a homogeneous suspension. Stirring is continued for 20 min under light-protected conditions, and high-purity oxygen is introduced into the system for 30 min to allow the catalyst surface to reach adsorption-desorption equilibrium. The resulting suspension is then transferred to a quartz photocatalytic reactor, and a photocatalytic reaction is carried out under irradiation with a 300 W xenon lamp equipped with a 420 nm cutoff filter. Samples are taken every 15 min during the reaction. After sampling, catalyst particles are removed by centrifugation, and the concentration of hydrogen peroxide in the solution is determined using iodometric titration to evaluate the photocatalytic synthesis performance of the material.

[0032] The results are as follows Figure 2 As shown, TAPM-Tp-COF exhibits excellent hydrogen peroxide generation capacity under visible light irradiation. The amount of hydrogen peroxide generated continuously increases with the extension of reaction time, reaching 18.36 μmol at 60 min. Based on the linear fitting results from 0 to 60 min, its apparent generation rate was calculated to be 3672 μmol·h⁻¹. -1 ·g -1 The efficiency is significantly higher than that of existing two-dimensional or planar COF materials. This result indicates that the three-dimensional β-ketoenamine structure facilitates the efficient separation and migration of photogenerated carriers and promotes the two-electron reduction reaction of oxygen, thereby achieving efficient hydrogen peroxide generation. Example 3

[0033] Cyclic experiments were conducted according to the conditions for photocatalytic hydrogen peroxide preparation described in Example 2. After each reaction, the catalyst was recovered by centrifugation, washed with deionized water and ethanol in sequence to remove surface residues, and then vacuum dried at 80 °C for 6 h before being reintroduced into the next round of reaction. Multiple cyclic tests were conducted to evaluate the cyclic stability and reusability of the TAPM-Tp-COF material in the photocatalytic system.

[0034] The results are as follows Figure 3 As shown, TAPM-Tp-COF maintained good photocatalytic stability during continuous cycling tests. After four cycles, the hydrogen peroxide generation remained above 90% of the initial value, with only slight fluctuations and no obvious deactivation was observed. These results indicate that the proposed three-dimensional β-ketoenamine covalent organic framework material possesses excellent structural stability and recyclability.

[0035] Comparative Example 1 29.0 mg (0.10 mmol) of tris(4-aminophenyl)amine (TAPA) and 21.0 mg (0.10 mmol) of 2,4,6-tricarboxymethyl phloroglucinol (Tp) were added to a reaction tube, along with 4 mL of a m-xylene / 1,4-dioxane (1:1 volume ratio) mixed solvent and 0.3 mL of a 6 mol / L acetic acid aqueous solution as a catalyst. The mixture was ultrasonically dispersed for 20 min to ensure thorough mixing and a homogeneous reaction system. The resulting reaction system was subjected to three nitrogen purging-vacuum treatments and sealed at 120 °C for 72 h. After cooling, the product was centrifuged, washed with ethanol and tetrahydrofuran, purified by Soxhlet extraction, and then vacuum dried at 80 °C for 12 h to obtain the material TAPA-Tp-COF, whose structure is as follows: .

[0036] The photocatalytic synthesis performance of the material TAPA-Tp-COF was evaluated according to the steps in Example 2, and the results are as follows: Figure 4 As shown, under the same reaction conditions, TAPA-Tp-COF produces 14.25 μmol of hydrogen peroxide after 60 min, corresponding to an apparent production rate of 2849 μmol·h⁻¹. -1 ·g -1 Compared to the TAPM-Tp-COF prepared in Example 1, its generation rate was significantly reduced, indicating that the COF constructed with a planar triphenylamine structure has certain limitations in terms of photogenerated carrier separation efficiency and oxygen diffusion capability.

[0037] Comparative Example 2 Melamine (MA) 12.6 mg (0.10 mmol) and 21.0 mg (0.10 mmol) of 2,4,6-tricarboxymethyl phloroglucinol (Tp) were added to a reaction tube, along with 4 mL of a m-xylene / 1,4-dioxane (1:1 volume ratio) mixed solvent and 0.3 mL of 6 mol / L acetic acid aqueous solution as a catalyst. The mixture was ultrasonically dispersed for 20 min to form a homogeneous reaction system. The resulting reaction system was subjected to three nitrogen purging-vacuum treatments to remove oxygen, and then sealed and reacted at 120 °C for 72 h. After the reaction was completed, the mixture was cooled to room temperature, and the solid product was separated by centrifugation. After washing with ethanol and tetrahydrofuran and purification by Soxhlet extraction, the product was vacuum dried at 80 °C for 12 h to obtain the material MA-Tp-COF, whose structure is as follows: .

[0038] The photocatalytic synthesis performance of the MA-Tp-COF material was evaluated according to the steps in Example 2, and the results are as follows: Figure 5 As shown, the amount of hydrogen peroxide generated by MA-Tp-COF at 60 min was 15.81 μmol, corresponding to an apparent generation rate of 3162 μmol·h⁻¹. -1 ·g-1 Although it represents an improvement over the TAPA-Tp-COF prepared in Comparative Example 1, it is still lower than the TAPM-Tp-COF prepared in Example 1. This indicates that the two-dimensional structure based on melamine units still has limitations in terms of charge migration and pore openness.

[0039] Comparative Example 3 34.9 mg (0.10 mmol) of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and 21.0 mg (0.10 mmol) of 2,4,6-tricarboxymethyl phloroglucinol (Tp) were added to a reaction tube, along with 4 mL of a m-xylene / 1,4-dioxane (1:1 v / v) mixed solvent and 0.3 mL of a 6 mol / L acetic acid aqueous solution as a catalyst. The mixture was ultrasonically dispersed for 20 min to form a homogeneous reaction system. The resulting reaction system was subjected to three nitrogen purging-vacuum treatments to remove oxygen, and then sealed and reacted at 120 °C for 72 h. After the reaction was completed and cooled to room temperature, the solid product was separated by centrifugation, washed with ethanol and tetrahydrofuran, and purified by Soxhlet extraction of tetrahydrofuran for 24 h. The purified product was then vacuum dried at 80 °C for 12 h to obtain the material TAPT-Tp-COF, whose structure is as follows: .

[0040] The photocatalytic synthesis performance of the material TAPT-Tp-COF was evaluated according to the steps in Example 2, and the results are as follows: Figure 6 As shown, the hydrogen peroxide production of TAPT-Tp-COF at 60 min was 16.78 μmol, corresponding to an apparent production rate of 3356 μmol·h⁻¹. -1 ·g -1 The performance of the sample was superior to that of TAPA-Tp-COF prepared in Comparative Example 1 and MA-Tp-COF prepared in Comparative Example 2, but still inferior to that of TAPM-Tp-COF prepared in Example 1. This indicates that although the triazine structure has certain advantages in rigidity and conjugation, it is still difficult to achieve a three-dimensional interconnected charge transport network in a two-dimensional stacked structure.

Claims

1. A method for preparing a three-dimensional β-ketoenamine covalent organic framework material, characterized in that, Includes the following steps: S1. Tetra(4-aminophenyl)methane and 2,4,6-tricarboxymethyl phloroglucinol are added to a reaction vessel, and an organic solvent is added to form a homogeneous reaction system; S2. After replacing the reaction system obtained in step S1 with an inert gas, seal it and carry out a solvothermal reaction under a set temperature condition to cause the monomer to undergo a condensation reaction to form a three-dimensional β-ketoenamine structural framework. S3. After the reaction is complete, cool to room temperature, separate the solid product by filtration or centrifugation, and obtain the three-dimensional β-ketoenamine covalent organic framework material after solvent washing and drying.

2. The method for preparing a three-dimensional β-ketoenamine covalent organic framework material according to claim 1, characterized in that, In step S1, the molar ratio between tetra(4-aminophenyl)methane and 2,4,6-tricarboxymethyl phloroglucinol is 1:(1-2); preferably 3:4; the organic solvent is selected from one or more of m-xylene, 1,4-dioxane, N,N-dimethylformamide, and ethanol.

3. The method for preparing a three-dimensional β-ketoenamine covalent organic framework material according to claim 1 or 2, characterized in that, In step S1, an acidic catalyst is added to the reaction system. The acidic catalyst is one or more of acetic acid, trifluoroacetic acid, and p-toluenesulfonic acid. The raw materials are magnetically stirred or ultrasonically dispersed for 10 to 60 minutes to form a homogeneous reaction system.

4. The method for preparing a three-dimensional β-ketoenamine covalent organic framework material according to claim 1 or 2, characterized in that, In step S2, the inert gas is nitrogen or argon; the solvothermal reaction temperature is 80–150°C, and the solvothermal reaction time is 1–7 days; preferably 100–120°C, and the reaction time is 3 days.

5. The method for preparing a three-dimensional β-ketoenamine covalent organic framework material according to claim 1 or 2, characterized in that, In step S3, the solvent washing is performed multiple times using one or more of water, dichloromethane, diethyl ether, ethanol, acetone, and tetrahydrofuran; the material is further purified by Soxhlet extraction for 12–48 h; the drying method is vacuum drying at 50–120 °C for 8–24 h.

6. A three-dimensional β-ketoenamine covalent organic framework material prepared by the preparation method according to any one of claims 1-5, wherein the three-dimensional β-ketoenamine covalent organic framework material is abbreviated as TAPM-Tp-COF, and its chemical structural formula is shown in Formula I: 。 7. The application of the three-dimensional β-ketoenamine covalent organic framework material prepared by the preparation method according to any one of claims 1-5 or the three-dimensional β-ketoenamine covalent organic framework material according to claim 6 in the photocatalytic preparation of hydrogen peroxide.

8. The application according to claim 7, characterized in that, The specific application process is as follows: three-dimensional β-keto-enamine covalent organic framework materials are dispersed in the reaction system to carry out photocatalytic reaction and realize the generation of hydrogen peroxide.

9. The application according to claim 8, characterized in that, The dosage of the three-dimensional β-ketoenamine covalent organic framework material is 0.1–10 mg / mL; the reaction system is an aqueous system or a mixture of water and an alcohol solvent, wherein the alcohol solvent is ethanol, methanol, benzyl alcohol or isopropanol; oxygen is continuously introduced into the reaction system for 20–60 min under light-protected conditions before light irradiation.

10. The application according to claim 8, characterized in that, The light source is a visible light source, which is a xenon lamp equipped with a 420nm cutoff filter and has a power of 200-500 W.

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