Preparation method and application of a three-component covalent organic framework (T / 4E-COF) photocatalyst

Abstract

This invention belongs to the field of photocatalytic material preparation, specifically relating to a method for preparing and applying a three-component covalent organic framework (T / 4E-COF) photocatalyst. The catalyst is synthesized using a D-A structure as the synthetic approach. By controlling the proportions of the monomers in the covalent organic framework material, a new three-component photocatalyst, T / 4E-COF, is synthesized, enabling efficient and stable photocatalytic synthesis of hydrogen peroxide in a pure water system without co-catalysts or sacrificial agents. The preparation process of this invention is simple, and the resulting material exhibits high photocatalytic activity and good stability, showing broad application prospects in solar energy conversion and green energy synthesis.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a multi-component donor-acceptor (DA) type covalent organic framework photocatalyst for photocatalytic production of hydrogen peroxide from pure water, its preparation method and application. Background Technology

[0002] Hydrogen peroxide (H2O2), as an environmentally friendly and highly efficient oxidant, is a high-consumption chemical raw material widely used in environmental protection, medicine, textiles, fine chemical synthesis, and other fields. It is also a potential energy carrier for H2O2 fuel cell power generation. Currently, the traditional anthraquinone process for producing H2O2 requires multiple high-pressure reactions and a large number of organic intermediates, resulting in high energy consumption, process complexity, and hazardous production processes. Therefore, developing novel, green, low-cost, and low-energy solar-driven photocatalytic H2O2 production technology has become an ideal alternative to the anthraquinone process. Covalent organic frameworks (COFs) have attracted widespread attention in the field of photocatalysis due to their tunable structure, high specific surface area, and ordered pores. In particular, constructing donor-acceptor (DA) type COFs can effectively promote photogenerated charge separation and improve photocatalytic efficiency. However, traditional binary DA type COFs often only achieve single-path charge transport, with limited utilization of photogenerated electrons and holes, making it difficult to simultaneously and efficiently drive the oxygen reduction reaction (ORR) and water oxidation reaction (WOR). Therefore, there is an urgent need to design a novel COF photocatalyst that can achieve dual-channel reaction and has higher charge separation efficiency. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a photocatalyst based on a three-component covalent organic framework (T / 4E-COF) to address the shortcomings of the existing technology. This catalyst is synthesized by constructing a DA structure and by adjusting the proportions of the monomers in the covalent organic framework material to synthesize a new three-component T / 4E-COF photocatalyst. Compared with E-COF materials, the T / 4E-COF photocatalyst with specifically adjusted proportions simultaneously drives ORR and WOR in photocatalytic performance, significantly improving the performance of photocatalytic H2O2 production.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: A method for preparing a three-component covalent organic framework (T / 4E-COF) includes the following steps: (1) Ethidium bromide (EB), 1,3,6,8-tetra-(p-aminophenyl)-pyrene (TPY) and 2,4,6-tricarboxymethyl phloroglucinol (Tp) were added to a Schlenk reaction flask as raw materials; (2) Subsequently, mesitylene and 1,4-dioxane were slowly added and ultrasonically dispersed evenly. Acetic acid was added and ultrasonically dispersed again. The mixture was then sealed after being frozen, degassed, and thawed three times using liquid nitrogen. (3) The reaction tube was placed in an oven for a solvothermal reaction to obtain a solid powder product. After washing and drying, a red three-component T / 4E-COF photocatalyst was obtained.

[0005] According to the above scheme, in step (1), the total concentration of ethidium bromide and 1,3,6,8-tetra-(p-aminophenyl)-pyrene in the solvent ranges from 0.025 to 0.1 mol / L.

[0006] According to the above scheme, in step (1), the concentration range of 2,4,6-tricarboxymethyl phloroglucinol in the solvent is 0.05-0.15 mol / L.

[0007] According to the above scheme, in step (2), the volume range of mesitylene and 1,4-dioxane added during preparation is 0.5-2 mL.

[0008] According to the above scheme, in step (2), the concentration range of the added acetic acid is 3-6 mol / L and the volume range is 100-500 μL.

[0009] According to the above scheme, in step (3), the temperature range of the solvothermal reaction is 100-130℃ and the time range is 71-73h.

[0010] According to the above scheme, in step (3), the washing is done with acetone and tetrahydrofuran, and the drying is done with vacuum drying.

[0011] The three-component T / 4E-COF photocatalyst prepared by the above method can be used to photocatalyze the production of hydrogen peroxide from pure water. The specific application method is as follows: the three-component T / 4E-COF photocatalyst is added to an aqueous solution, ultrasonically dispersed or stirred evenly, and then irradiated with visible light at room temperature and in an air atmosphere to achieve the generation of hydrogen peroxide in pure water; the visible light wavelength is greater than or equal to 420 nm, and the irradiation time is within 3 h; the preferred concentration of the three-component T / 4E-COF photocatalyst in the aqueous solution is 0.2-0.3 mg / mL.

[0012] Compared with the prior art, the beneficial effects of the present invention are: 1. In the preparation of this three-component T / 4E-COF photocatalyst, the present invention successfully achieved spatial separation of oxidation sites (EB) and reduction sites (TPY) by precisely controlling the ratio of the three components. This spatial separation effect greatly suppresses the bulk recombination of photogenerated electrons and holes, providing a structural basis for simultaneously driving two half-reactions. Photogenerated electrons are enriched at the β-sites to generate H2O2 via ORR, while photogenerated holes are retained at the hexadiazine bromide sites to generate oxygen via WOR, thus achieving full utilization of photogenerated charges.

[0013] 2. The three-component T / 4E-COF photocatalyst described in this invention uses only pure water and oxygen as raw materials. In a system without co-catalysts or sacrificial agents, the yield of photocatalytic synthesis of H2O2 is significantly higher than that of the traditional binary E-COF comparison sample, which meets the requirements of green chemistry and sustainable development. Attached Figure Description

[0014] Figure 1 This is a comparison chart of the photocatalytic hydrogen peroxide production rates in water in the first hour for the E-COF prepared in Comparative Example 1, the multi-component photocatalysts T-COF, T / E-COF, T / 2E-COF, T / 3E-COF, T / 4E-COF, T / 5E-COF, T / 6E-COF prepared in Comparative Example 2 with different ligand ratios, and the three-component T / 4E-COF photocatalyst prepared in the Example.

[0015] Figure 2 The images show scanning electron microscope (SEM) images (Figure a) and transmission electron microscope (TEM) images (Figure b) of the three-component T / 4E-COF photocatalyst prepared in the examples.

[0016] Figure 3 This is a cyclic activity diagram of the three-component T / 4E-COF photocatalyst prepared in the example (reaction time 12 h).

[0017] Figure 4 This is a comparison of the photocatalytic transient photocurrent of the E-COF prepared in Comparative Example 1 and the three-component T / 4 E-COF prepared in the Example. Detailed Implementation

[0018] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the present invention is not limited to the following embodiments.

[0019] Comparative Example 1 A method for preparing a two-component E-COF photocatalyst, the specific steps of which are as follows: Ethidium bromide (EB, 0.12 mmol) and 2,4,6-tricarboxymethyl phloroglucinol (Tp, 0.08 mmol) were added to a 10 mL Schlenk reaction tube. 1.4 mL of mesitylene and 0.6 mL of 1,4-dioxane were slowly added, and the mixture was sonicated for 15 min to ensure uniform dispersion. Then, 100 μL of acetic acid (0.6 M) was added, and the mixture was sonicated again for 10 min. The reaction tube was then sealed after a three-stage freezing-degassing-thawing process using liquid nitrogen. The reaction tube was placed in an oven at 120 °C for 72 h. After cooling to room temperature, the tube was washed three times with acetone and tetrahydrofuran, and then dried in a vacuum drying oven at 80 °C for 24 h to obtain a dark red two-component E-COF.

[0020] The above-mentioned E-COF photocatalyst is used for photocatalytic water production of hydrogen peroxide. The specific application process is as follows: Add 20 mL of water and 5 mg of E-COF catalyst to a round-bottom flask, sonicate for 15 min, mix thoroughly, and then purge with air for 15 min. Allow the mixture to adsorb in the dark for 30 min to reach adsorption-desorption equilibrium. Fix the round-bottom flask on an iron stand and irradiate with visible light (λ≥420 nm) for 3 h. Take out 1-1.5 mL of sample every 15 minutes, perform a colorimetric reaction using the iodometric method, and then measure the absorbance of the solution at the maximum absorption wavelength of 351 nm using a UV spectrophotometer. Calculate the concentration of hydrogen peroxide based on the standard curve.

[0021] Comparative Example 2 A method for preparing a multi-component photocatalyst with different ligand ratios, the specific steps of which are as follows: 1,3,6,8-Tetra-(p-aminophenyl)pyrene (TPY) and ethidium bromide (EB) were added to a 10 mL Schlenk reaction flask in ratios of 1:1, 1:2, 1:3, 1:4, 1:5, and 1:6 with 2,4,6-tricarboxymethyl phloroglucinol (Tp, 0.2 mmol). 1.4 mL of mesitylene and 0.6 mL of 1,4-dioxane were slowly added, and the mixture was sonicated for 15 min to ensure uniform dispersion. 100 μL of acetic acid (0.6 M) was added, and the mixture was sonicated again for 10 min. The reaction was then subjected to a three-stage freezing-degassing-thawing process using liquid nitrogen before sealing. The reaction tube was placed in an oven at 120 °C for 72 h, cooled to room temperature, washed three times with acetone and tetrahydrofuran, and dried in a vacuum drying oven at 80 °C for 24 h to obtain a three-component COF composite catalyst with different ligand ratios. T-COF is obtained by using 0.06 mmol of 1,3,6,8-tetra-(p-aminophenyl)-pyrene and 0.08 mmol of 2,4,6-tricarboxymethylphloroglucinol as raw materials, and the remaining steps are the same as above.

[0022] The above-mentioned multi-component photocatalysts with different ligand ratios were used for photocatalytic water production of hydrogen peroxide. The specific application process is as follows: Add 20 mL of water and 5 mg of catalyst to a round-bottom flask, sonicate for 15 min, mix thoroughly, and then purge with air for 15 min. Allow the mixture to adsorb in the dark for 30 min to reach adsorption-desorption equilibrium. Fix the round-bottom flask on an iron stand and irradiate with visible light (λ≥420 nm) for 3 h. Take out 1-1.5 mL of sample every 15 minutes, perform a colorimetric reaction using the iodometric method, and then test the absorbance of the solution at the maximum absorption wavelength of 351 nm on a UV spectrophotometer. Calculate the concentration of hydrogen peroxide based on the standard curve. Example

[0023] A method for preparing a three-component T / 4E-COF photocatalyst, the specific steps of which are as follows: Ethidium bromide (EB, 0.08 mmol), 1,3,6,8-tetra-(p-aminophenyl)pyrene (TPY, 0.02 mmol), and 2,4,6-tricarboxymethyl phloroglucinol (Tp, 0.2 mmol) were added to a 10 mL Schlenk reaction flask. 1.4 mL of mesitylene and 0.6 mL of 1,4-dioxane were slowly added, and the mixture was sonicated for 15 min to ensure uniform dispersion. 100 μL of acetic acid (0.6 M) was added, and the mixture was sonicated again for 10 min. The reaction mixture was then subjected to a three-stage freezing-degassing-thawing process using liquid nitrogen before sealing. The reaction tube was placed in an oven at 120 °C for 72 h. After cooling to room temperature, the mixture was washed three times with acetone and tetrahydrofuran, and then dried in a vacuum drying oven at 80 °C for 24 h to obtain a red three-component T / 4E-COF.

[0024] The above three-component T / 4E-COF photocatalyst was used for photocatalytic hydrogen peroxide production from water. The specific application process is as follows: Add 20 mL of water and 5 mg of catalyst to a round-bottom flask, sonicate for 15 min, mix thoroughly, and then purge with air for 15 min. Allow the mixture to adsorb in the dark for 30 min to reach adsorption-desorption equilibrium. Fix the round-bottom flask on an iron stand and irradiate with visible light (λ≥420 nm) for 3 h. Take out 1-1.5 mL of sample every 15 minutes, perform a colorimetric reaction using the iodometric method, and then test the absorbance of the solution at the maximum absorption wavelength of 350 nm on a UV spectrophotometer. Calculate the concentration of hydrogen peroxide based on the standard curve.

[0025] like Figure 1As shown, the piezometric group is typically a good electron acceptor and photosensitizer. Introducing piezometric groups into E-COF can construct a more efficient donor-acceptor (DA) structure. The piezometric unit can serve as an active site for the oxygen reduction reaction (ORR), providing more reaction centers for the reduction of O2 to H2O2. Therefore, the performance of the multi-component catalyst continuously improves with the increase of TPY ligand content. However, excessive piezometrics may lead to misalignment, stacking defects, or even an increase in amorphous regions during synthesis. These structural defects often become charge recombination centers, accelerating electron-hole recombination and offsetting the advantages brought by the DA structure, thus causing the performance of the multi-component catalyst to decline. Among them, after 1 h of illumination, the T / 4E-COF exhibited the highest photocatalytic hydrogen peroxide production rate from water, reaching 1434 μmol g. -1 h -1 It is an E-COF photocatalyst (444 μmol g) -1 h -1 3.2 times that of ).

[0026] like Figure 2 As shown, the three-component T / 4E-COF photocatalyst exhibits a relatively rough, blocky stacked structure on its surface under a scanning electron microscope (Fig. a), which can provide sufficient active sites for O2 adsorption and activation to promote the reaction. This can also be confirmed by the transmission electron microscope (TEM) image in Fig. b.

[0027] like Figure 3 As shown, a catalytic activity cycling experiment was conducted on the T / 4E-COF catalyst with a reaction time of 12 h. After the first cycle test, the activity of the T / 4E-COF photocatalyst decreased slightly, but its catalytic performance remained basically stable in subsequent cycles. This phenomenon indicates that the composite material possesses excellent recyclability and robust structural stability.

[0028] like Figure 4 As shown, comparing the photocurrent densities of E-COF and T / 4E-COF under intermittent light irradiation (light on / off period of 100 s), the results show that T / 4E-COF exhibits a superior photocurrent density, indicating that the photogenerated electron migration speed is accelerated, the recombination of electron-hole pairs is delayed, the charge transfer inside the T / 4E-COF material is promoted, and its photocatalytic performance is improved.

[0029] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing and applying a three-component covalent organic framework (T / 4E-COF) photocatalyst, characterized in that, The main steps are as follows: (1) Ethidium bromide (EB), 1,3,6,8-tetra-(p-aminophenyl)-pyrene (TPY) and 2,4,6-tricarboxymethyl phloroglucinol (Tp) were added to a Schlenk reaction flask as raw materials; (2) Subsequently, mesitylene and 1,4-dioxane were slowly added and ultrasonically dispersed evenly. Acetic acid was added and ultrasonically dispersed again. The mixture was then sealed after being frozen, degassed, and thawed three times using liquid nitrogen. (3) The reaction tube was placed in an oven for a solvothermal reaction to obtain a solid powder product. After washing and drying, a red three-component T / 4E-COF photocatalyst was obtained.

2. The method for preparing a three-component T / 4E-COF photocatalyst according to claim 1, characterized in that, In step (1), the total concentration of ethidium bromide and 1,3,6,8-tetra-(p-aminophenyl)-pyrene in the solvent ranges from 0.025 to 0.1 mol / L.

3. The method for preparing a three-component T / 4E-COF photocatalyst according to claim 1, characterized in that, In step (1), the concentration of 2,4,6-tricarboxymethyl phloroglucinol in the solvent ranges from 0.05 to 0.15 mol / L.

4. The method for preparing a three-component T / 4E-COF photocatalyst according to claim 1, characterized in that, In step (2), the volume range of mesitylene and 1,4-dioxane added during preparation is 0.5-2 mL.

5. The method for preparing a three-component T / 4E-COF photocatalyst according to claim 1, characterized in that, In step (2), the concentration of the added acetic acid is 3-6 mol / L and the volume is 100-500 μL.

6. The method for preparing a three-component T / 4E-COF photocatalyst according to claim 1, characterized in that, In step (3), the temperature range of the solvothermal reaction is 100-130℃ and the time range is 71-73 h.

7. The method for preparing a three-component T / 4E-COF photocatalyst according to claim 1, characterized in that, In step (3), the washing process uses acetone and tetrahydrofuran, and the drying process uses vacuum drying.

8. The three-component T / 4E-COF photocatalyst prepared by the method according to any one of claims 1-7.

9. The application of the three-component T / 4E-COF photocatalyst according to claim 8 in the photocatalytic production of hydrogen peroxide from pure water.

10. The application according to claim 9, characterized in that... The specific application method is as follows: the three-component T / 4E-COF photocatalyst is added to an aqueous solution, ultrasonically dispersed evenly, and then irradiated with visible light under room temperature air conditions to achieve the production of hydrogen peroxide; wherein the visible light wavelength is not less than 420 nm and the irradiation time does not exceed 12 h.

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