COF-0. 2A composite photocatalyst for enhancing generation of hydrogen peroxide and preparation method of COF-0. 2A composite photocatalyst

Abstract

The invention belongs to the field of preparation of photocatalysts, and particularly relates to a COF-0.2 A composite photocatalyst as well as a preparation method and application thereof. The composite catalyst is a covalent organic framework material with an imine bond and an imidazole bond, the composite catalyst is synthesized by regulating and controlling the proportion of the imine bond and the imidazole bond, a donor-acceptor structure is formed, the photocatalytic performance of the COF-0. 2A composite photocatalyst is improved, and the photocatalytic activity of the COF-0. 2A composite photocatalyst is improved. The yield of hydrogen peroxide is improved compared with the original imine bond catalyst and imidazole bond catalyst.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of photocatalysts, and particularly relates to a COF-0.2A composite photocatalyst, a preparation method thereof, and hydrogen peroxide generation in a photocatalytic aqueous solution system. Background Art

[0002] Due to the rapid growth of industrialization and population, energy resources have been rapidly consumed, thus bringing serious energy crises and environmental pollution problems. In recent years, the exploration of renewable energy alternatives has attracted extensive attention. Directly converting solar energy into chemical energy through artificial photosynthesis provides a green and environmentally friendly way to solve the energy crisis. Among them, hydrogen peroxide (H 2 O 2 ) as an important green oxidant and energy carrier has broad application prospects in the fields of environmental governance, energy storage, chemical synthesis, etc. However, traditional H 2 O 2 preparation methods (such as the anthraquinone method) have problems such as high energy consumption and large pollution, while photocatalytic H 2 O 2 production technology has become a research hotspot due to its green and sustainable characteristics. In recent years, covalent organic framework (COF) materials have shown broad application prospects in the field of photocatalysis due to their adjustable pore structures, high specific surface areas, and excellent optoelectronic properties. However, existing COF catalysts based on single chemical bonds (such as imine bonds or imidazole bonds) still have defects in synthesis methods and catalytic performance. The preparation of traditional COF materials mostly relies on Schlenk operations, which need to be carried out in a strict anaerobic environment and involve cumbersome steps such as vacuum pumps, liquid nitrogen cooling, and inert gas protection. These methods not only have high equipment requirements and complex operations, but also limit their large-scale preparation and practical applications. COF materials with single chemical bond structures have shortcomings in the photocatalytic process. Although imine bond materials have good charge transport capabilities, their light absorption range is relatively narrow, and the recombination rate of photo-generated carriers is high; although imidazole bond materials can broaden the light response range, their electron delocalization is poor, resulting in insufficient catalytic active sites. In addition, it is difficult to optimize the two-electron path of the oxygen reduction reaction (ORR) with a single bond type structure, resulting in low hydrogen peroxide generation rate and selectivity. Therefore, there is an urgent need to develop a composite COF photocatalyst with a simple synthesis method and both high light absorption and charge separation capabilities to break through the limitations of the existing technology and promote the practical application of photocatalytic H 2 O 2 technology. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a COF-0.2A composite photocatalyst and its preparation method and application in view of the deficiencies of the above-mentioned prior art. The composite catalyst is based on the synthesis of imine-bonded COF1 and imidazole-bonded COF2, and a new photocatalyst COF-0.2A is synthesized by regulating the ligand ratio of covalent organic framework materials. Compared with the imine-bonded COF1 material and the imidazole-bonded COF2 material, the COF-0.2A composite photocatalyst with specific ratio regulation has improved photocatalytic performance and increased the rate of hydrogen peroxide generation in water.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0005] A preparation method of a COF-0.2A composite photocatalyst, the specific steps are as follows:

[0006] (1) Using terephthalaldehyde and p-phenylenediamine as raw materials, N,N-dimethylformamide as a solvent, mixing evenly and then carrying out a solvothermal reaction. The solid product obtained from the reaction is then washed and dried to obtain the COF-0.2A composite photocatalyst.

[0007] According to the above scheme, in step (1), the molar ratio of terephthalaldehyde to p-phenylenediamine is 1:1, and the concentration ranges of terephthalaldehyde and p-phenylenediamine in the N,N-dimethylformamide solution are 0.085 - 0.092 mol / L and 0.03 - 0.05 mol / L respectively. The temperature range of the solvothermal reaction of N,N-dimethylformamide is 140 - 160 °C, and the time range is 3.5 - 4.5 h.

[0008] The COF-0.2A composite photocatalyst prepared by the above method can generate hydrogen peroxide in photocatalytic pure water. The specific application method is as follows: introducing an air atmosphere and carrying out visible light irradiation at room temperature to achieve the generation of hydrogen peroxide; the wavelength of visible light is greater than or equal to 420 nm, and the irradiation time is within 6 h; the preferred concentration of the composite photocatalyst in the aqueous solution is 0.4 - 0.5 mg / mL.

[0009] Compared with the prior art, the beneficial effects of the present invention are:

[0010] 1. When preparing the COF-0.2A composite photocatalyst of the present invention, the synthesis process of general covalent organic framework photocatalytic materials is simplified. Most other covalent organic framework materials require Schlenk operation, using a vacuum pump, liquid nitrogen and inert gas, and need to switch between vacuum and inert gas, and the process is relatively complex and cumbersome. However, the technology of this invention only requires oil bath reflux, simplifies the synthesis process, and can successfully synthesize the required composite photocatalytic material.

[0011] 2. The COF-0.2A composite photocatalyst of the present invention has both imine bonds of COF1 and imidazole bonds of COF2, forming a donor-acceptor structure in the composite photocatalyst, which can optimize the light absorption, charge separation and catalytic performance of the material. The π-π conjugation between the donor and acceptor units can enhance the electron delocalization, promote the separation and migration of photogenerated carriers. In addition, it can also optimize the two-electron path of ORR and improve the generation rate and selectivity of hydrogen peroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the activity diagram of the imine bond COF1 prepared in Comparative Example 1, the imidazole bond COF2 prepared in Comparative Example 2, and the COF-0.2A composite photocatalyst prepared in the Example for catalytic generation of hydrogen peroxide.

[0013] Figure 2 It is the scanning electron microscope image (SEM) of the COF-0.2A composite photocatalyst prepared in the Example.

[0014] Figure 3 It is the cyclic activity diagram (reaction time 25 h) of the COF-0.2A composite photocatalyst prepared in the Example. DETAILED DESCRIPTION OF THE INVENTION

[0015] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with the examples. However, the present invention is not limited to the following examples only.

[0016] Comparative Example 1

[0017] A preparation method of an imine bond COF1 is as follows:

[0018] Dissolve 0.001 mol of terephthalaldehyde in 5 ml of ethanol, and then add it to a 100 ml round-bottom flask equipped with a magnetic stirrer and a reflux condenser. Then, heat the mixture to 85 °C. Subsequently, dissolve 0.001 mol of p-phenylenediamine in 5 ml of ethanol as well, and then drop it into the flask, and stir and react at 85 °C for 6 hours. Finally, filter the reaction mixture, wash it with ethanol, and dry it in a vacuum drying oven at 70 °C for 24 hours to obtain the imine bond COF1 catalyst.

[0019] Use the above imine bond COF1 catalyst for photocatalytic production of hydrogen peroxide. The specific application process is as follows:

[0020] Take 20 ml of water and 5 mg of imine-bonded COF1 catalyst in a round-bottom flask, ultrasonicate for 15 min and then mix evenly, and introduce air for 15 min. Then let it stand for 30 min to reach adsorption-desorption equilibrium. Place the round-bottom flask on an iron stand and irradiate it with visible light (λ≥420 nm) for 5 h. Take out 1 ml of the sample every hour, use the iodometric method and an ultraviolet spectrophotometer. The solution has a maximum absorption wavelength at 350 nm, and calculate the concentration of hydrogen peroxide according to the standard curve.

[0021] Comparative Example 2

[0022] A preparation method of imidazole-bonded COF2 is as follows:

[0023] Dissolve 0.352 mmol of terephthalaldehyde in 4 ml of N,N-dimethylformamide (DMF), and then add it to a 100 ml round-bottom flask equipped with a magnetic stirrer and a reflux condenser. Subsequently, dissolve 0.352 mmol of phenyltetramine tetrahydrochloride in 4 ml of DMF, and then drop it into the flask. Heat the oil bath to 150 °C and stir and reflux for 4 hours. Finally, after cooling to room temperature, add 80 ml of water, filter the reaction mixture to collect the precipitate, wash it with water and ethanol successively, and dry it in a vacuum drying oven at 60 °C for 24 hours to obtain the imidazole-bonded COF2 catalyst.

[0024] Use the above imidazole-bonded COF2 catalyst for photocatalytic production of hydrogen peroxide. The specific application process is as follows:

[0025] Take 20 ml of water and 5 mg of imidazole-bonded COF2 catalyst in a round-bottom flask, ultrasonicate for 15 min and then mix evenly, and introduce air for 15 min. Then let it stand for 30 min to reach adsorption-desorption equilibrium. Place the round-bottom flask on an iron stand and irradiate it with visible light (λ≥420 nm) for 5 h. Take out 1 ml of the sample every hour, use the iodometric method and an ultraviolet spectrophotometer. The solution has a maximum absorption wavelength at 350 nm, and calculate the concentration of hydrogen peroxide according to the standard curve.

[0026] Example

[0027] A preparation method of COF-0.2A composite photocatalyst is as follows:

[0028] Dissolve 0.352 mmol of terephthalaldehyde in 4 ml of N,N-dimethylformamide (DMF), and then add it to a 100 ml round-bottom flask equipped with a magnetic stirrer and a reflux condenser. Subsequently, weigh 0.0352 mmol of p-phenylenediamine with a 10% content and 0.3168 mmol of phenyltetramine tetrahydrochloride with a 90% content, dissolve them in 4 ml of DMF, and then dropwise add them to the flask. Heat the oil bath to 150 °C and stir and reflux for 4 hours. Finally, after cooling to room temperature, add 80 ml of water, filter the reaction mixture to collect the precipitate, wash it successively with water and ethanol, and dry it in a vacuum drying oven at 60 °C for 24 hours to obtain the COF-0.2A composite photocatalyst.

[0029] The above COF-0.2A composite photocatalyst was used for photocatalytic production of hydrogen peroxide, and the specific application process is as follows:

[0030] Take 20 ml of water and 5 mg of the COF-0.2A composite photocatalyst in a round-bottom flask, ultrasonically mix for 15 min, then introduce air for 15 min, and then let it stand for 30 min to reach the adsorption-desorption equilibrium. Place the round-bottom flask on an iron stand and irradiate it with visible light (λ≥420 nm) for 5 h; take out 1 ml of the sample every hour, use the iodometric method and an ultraviolet spectrophotometer. The solution has a maximum absorption wavelength at 350 nm, and the concentration of hydrogen peroxide is calculated according to the standard curve.

[0031] As Figure 1 shown, it can be seen that the prepared COF-0.2A composite photocatalyst has higher hydrogen peroxide production activity. In comparison, the hydrogen peroxide concentration generated by the COF-0.2A composite photocatalyst in the fifth hour is 3 times that of the imine bond COF1 catalyst and 2 times that of the imidazole bond COF2 catalyst. In the first hour, the hydrogen peroxide production rate of the COF-0.2A composite catalyst reaches the highest of 536 μmol·g -1 h -1 .

[0032] As Figure 2 shown, on the surface of the COF-0.2A composite photocatalyst, irregular accumulations are formed and there are abundant pores, which are beneficial to gas adsorption and can greatly increase the catalytic reaction area.

[0033] As Figure 3 shown, the activity of the COF-0.2A composite photocatalyst decreases slightly after one cycle, but remains basically unchanged in the subsequent several cycle experiments. It can be seen that the prepared composite catalyst has good recyclability and stable structure.

[0034] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several improvements and modifications can be made, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a COF-0.2A composite photocatalyst, the specific steps are as follows: (1) terephthalaldehyde was dissolved in N,N-dimethylformamide (DMF) and then added into a round-bottom flask equipped with a magnetic stirrer and a reflux condenser; (2) Subsequently, p-phenylenediamine and tetraphenyltetramine tetrahydrochloride were weighed, dissolved in DMF, and then added dropwise to the flask. The oil bath was heated and stirred to reflux for reaction; (3) Finally, after cooling to room temperature, water was added, the reaction mixture was filtered to collect the precipitate, and the precipitate was washed with deionized water and ethanol, respectively, and dried in a vacuum drying oven to obtain the COF-0.2A composite photocatalyst.

2. The method for preparing a COF-0.2A composite photocatalyst according to claim 1, characterized in that: In step (1), the concentration range of terephthalaldehyde in the DMF solution is 0.085-0.092 mol / L.

3. The method for preparing a COF-0.2A composite photocatalyst according to claim 1, characterized in that: In step (2), the total concentration of p-phenylenediamine and benzenetetramine tetrahydrochloride added by weighing is in the range of 0.085-0.092 mol / L in the DMF solution.

4. The method for preparing a COF-0.2A composite photocatalyst according to claim 1, characterized in that: In step (2), the p-phenylenediamine and tetramine tetrahydrochloride added are weighed, and the amount of p-phenylenediamine is in the range of 18-22%, and the amount of tetramine tetrahydrochloride is in the range of 78-82%.

5. The method for preparing a Ni-CNZIS composite photocatalyst according to claim 1, characterized in that: In step (3), washing is performed using deionized water and anhydrous ethanol, and drying is performed using a vacuum oven.

6. The COF-0.2A composite photocatalyst prepared by the method according to any one of claims 1 to 5.

7. Use of the COF-0.2A composite photocatalyst according to claim 6 in enhancing the activity of hydrogen peroxide generation.

8. The use according to claim 7, characterized in that The specific application method is: adding the COF-0.2A composite photocatalyst into an aqueous solution, evenly dispersing it by ultrasonication, introducing an air atmosphere, and irradiating it with visible light to achieve the generation of hydrogen peroxide; wherein the wavelength of the visible light is not less than 420nm, and the irradiation time does not exceed 30h.

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