Triazinyl covalent organic framework material and application thereof in photocatalytic production of hydrogen peroxide

Abstract

The invention discloses a preparation method of a triazinyl covalent organic framework (COF) material and application of the triazinyl covalent organic framework material in photocatalytic production of hydrogen peroxide. The amino starting monomer is regulated and controlled through a side chain regulation and control strategy to obtain the COF with a functional group, and the COF can be connected into a ring by thienopyridine through post-modification to replace an original imine bond, so that the planarity and the conjugation degree of the COF are obviously improved, and the COF has good light absorption capacity and a proper band gap; therefore, the COFs photocatalyst has excellent photocatalytic hydrogen peroxide production capacity in a water-benzyl alcohol system under a light source, and a beneficial thought can be provided for designing a high-performance COFs photocatalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and particularly relates to a triazine-based covalent organic framework (COF) material and its application in photocatalytic production of hydrogen peroxide. Background Art

[0002] Artificial photosynthesis is a promising approach to convert and store solar energy in the form of chemical bonds. Among all the chemical products produced by artificial photosynthesis, hydrogen peroxide has attracted considerable attention due to its rapidly growing demand in modern energy and environmental applications. However, most of the materials reported for photocatalytic hydrogen peroxide synthesis suffer from low charge separation efficiency. Therefore, it is of great significance to develop efficient photocatalysts with high stability, a suitable visible light absorption range, and improved charge separation efficiency for photocatalytic hydrogen peroxide production. Summary of the Invention

[0003] The present invention aims to provide a method for preparing triazine-based covalent organic frameworks for photocatalytic hydrogen peroxide production. This method primarily introduces benzene ring units and thiophene units with excellent photoelectric properties to p-phenylenediamine, resulting in the synthesized COFs with a wider light absorption range, faster photocurrent response, and a higher specific surface area. Using these COFs for photocatalytic hydrogen peroxide production can achieve higher hydrogen peroxide yields. Furthermore, post-modification of the COF containing the thiophene units into a ring increases the COF's planarity and conjugation, thereby promoting the separation and migration of photogenerated excitons and further enhancing the photocatalytic effect.

[0004] To achieve the above object, the present invention adopts the following technical solutions: A triazine-based covalent organic framework material, the preparation of which comprises the following steps: (1) 2,5-dibromo-p-phenylenediamine, 5-methylthiophene-2-boronic acid pinacol ester, tetrakis(triphenylphosphine)palladium and potassium carbonate were mixed and added to a mixed solvent of 1,4-dioxane and water. After three cycles of degassing, the reaction system was heated to reflux. After the reaction was completed, the product was washed with water until neutral, and then other impurities were washed with n-hexane and methanol respectively to obtain a light yellow powder of 2,5-bis(5-methylthiophene-2-yl)benzene-1,4-diamine. (2) 2,5-bis(5-methylthiophen-2-yl)benzene-1,4-diamine and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde were mixed and added to a mixed solvent of n-butanol and o-dichlorobenzene, followed by an acetic acid solution. The mixture was frozen in a liquid nitrogen bath and vacuum-thawed for three cycles, then flame-sealed and subjected to a solvent thermal reaction. After filtration, the reaction product was Soxhlet extracted with tetrahydrofuran (THF) overnight, and the product was collected after vacuum drying.

[0005] Furthermore, the molar ratio of 2,5-dibromo-p-phenylenediamine, 5-methylthiophene-2-boronic acid pinacol ester, tetrakis(triphenylphosphine)palladium and potassium carbonate used in step (1) is 1:(2-3):0.23:4.34.

[0006] Furthermore, the volume ratio of 1,4-dioxane to water in the mixed solvent of step (1) is 4:1.

[0007] Furthermore, the heating reflux temperature in step (1) is 110-120°C and the time is 48-72 h.

[0008] Furthermore, the molar ratio of 2,5-bis(5-methylthiophen-2-yl)benzene-1,4-diamine and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde used in step (2) is 3:2.

[0009] Furthermore, the volume ratio of n-butanol to o-dichlorobenzene in the mixed solvent of step (2) is 1:9-3:7.

[0010] Furthermore, the concentration of the acetic acid solution in step (2) is 3-6 mol / L, and the volume ratio of the added amount to the mixed solvent used is 1:10.

[0011] Furthermore, the temperature of the solvent thermal reaction in step (2) is 120°C to 150°C, and the time is 3-7 days.

[0012] The triazine-based covalent organic framework material can be used for photocatalytic production of hydrogen peroxide. The application method is to use the triazine-based covalent organic framework material directly or after post-modification as a photocatalyst, add it into a water-benzyl alcohol system to carry out a photocatalytic reaction, thereby generating hydrogen peroxide.

[0013] Furthermore, the post-modification is to mix the triazine-based covalent organic framework material with toluene in a saturated oxygen atmosphere, add trifluoroacetic acid, and then heat and stir after sealing.

[0014] Furthermore, the ratio of the triazine-based covalent organic framework material to toluene is 40-60 mg / 3 mL, preferably, 50 mg / 3 mL.

[0015] Furthermore, the volume ratio of toluene to trifluoroacetic acid is 2:1-1:1, preferably, the volume ratio is 3:2.

[0016] Furthermore, the heating and stirring is carried out at 100° C. for 1-3 days, preferably, the heating is carried out for 2 days.

[0017] Furthermore, the volume concentration of benzyl alcohol in the water-benzyl alcohol system is 10%.

[0018] Furthermore, the amount of photocatalyst added to the water-benzyl alcohol system was 5 mg / 20 mL.

[0019] Furthermore, the temperature of the photocatalytic reaction is 25° C., the wavelength of the light source is ≥420 nm, and the light intensity is ≥50 W.

[0020] The present invention has at least the following beneficial effects: (1) Based on the side chain regulation strategy, the present invention regulates the amino starting monomer at the molecular level to obtain a COF with functional groups. The COF can be post-modified to form a ring with thienopyridine to replace the original imine bond, so that the planarity and conjugation of the COF are significantly improved, and the COF has good light absorption ability and a suitable band gap, thereby showing excellent photocatalytic hydrogen peroxide production ability under light source and in the water-benzyl alcohol system. Therefore, the present invention can provide useful ideas for the design of high-performance COFs.

[0021] (2) The equipment and chemical reagents used in the present invention are cheap and readily available, and the process operation is simple, which can improve the utilization rate of solar energy and has research significance and application potential in the field of photocatalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the synthesis process of Example and Comparative Examples 1 and 2.

[0023] Figure 2 The X-ray diffraction (XRD) comparison diagram of the COFs photocatalysts synthesized in Example and Comparative Examples 1 and 2.

[0024] Figure 3 FT-IR comparison of the COFs photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2.

[0025] Figure 4 The scanning electron microscope (SEM) comparison diagram of the COFs photocatalysts synthesized in Example and Comparative Examples 1 and 2 is shown.

[0026] Figure 5 Comparison of N2 adsorption-desorption isotherm curves of COFs photocatalysts synthesized in Example 1 and Comparative Examples 1 and 2.

[0027] Figure 6 This is a comparison chart of the yields of photocatalytic hydrogen peroxide production in a water-benzyl alcohol system of the COFs photocatalysts synthesized in Example and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0028] A triazine-based covalent organic framework material, the preparation of which comprises the following steps: (1) 2,5-dibromo-p-phenylenediamine, 5-methylthiophene-2-boronic acid pinacol ester, tetrakis(triphenylphosphine)palladium and potassium carbonate were added to a round-bottom flask in a molar ratio of 1:(2-3):0.23:4.34, and then a mixed solvent of 1,4-dioxane and water in a volume ratio of 4:1 was added. After three cycles of degassing, the reaction system was heated to 110-120 °C and refluxed for 48-72 h. After the reaction was completed, the product was washed with water until neutral, and then other impurities were washed with n-hexane and methanol respectively to obtain a light yellow powder of 2,5-bis(5-methylthiophene-2-yl)benzene-1,4-diamine; (2) 2,5-bis(5-methylthiophen-2-yl)benzene-1,4-diamine and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde were placed in a Pyrex tube in a molar ratio of 3:2, and a mixed solvent of n-butanol and o-dichlorobenzene in a volume ratio of 1:9-3:7 was added. Then, 10% of the volume of the mixed solvent and a 3-6 mol / L acetic acid solution was added. After three cycles of freeze-vacuum thawing in a liquid nitrogen bath, the tube was flame-sealed and placed in an oven at 120 ℃~150 ℃ for reaction for 3-7 days. After filtration, the reaction product was Soxhlet extracted with tetrahydrofuran (THF) overnight and vacuum dried to obtain the product.

[0029] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0031] Example Preparation of COF photocatalyst S-COF and its modified product XS-COF: (1) 2.00 mmol of 2,5-dibromo-p-phenylenediamine, 5.50 mmol of 5-methylthiophene-2-boronic acid pinacol ester, 0.46 mmol of tetrakis(triphenylphosphine)palladium, and 8.68 mmol of potassium carbonate were added to a round-bottom flask. 16 mL of 1,4-dioxane and 4 mL of water were then added. After the mixture was degassed through three cycles, the reaction system was heated to 115 °C and refluxed for 60 h. After the reaction was completed, the crude product was filtered and washed with water until neutral. Other impurities were then washed with n-hexane and methanol, respectively, to obtain a light yellow powder.

[0032] (2) 0.06 mmol of 2,5-bis(5-methylthiophene-2-yl)benzene-1,4-diamine and 0.04 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde were placed in a 10 mL Pyrex tube, followed by the addition of 0.4 mL of n-butanol, 1.6 mL of o-dichlorobenzene, and 0.2 mL of 6 mol / L acetic acid solution. The Pyrex tube was then flame-sealed under liquid nitrogen freezing and negative pressure conditions. The tube was then placed in an oven, heated to 120 °C, and kept warm for 3 days. The crude product obtained from the reaction was washed three times with methanol and THF, filtered, and then extracted with THF overnight. The product was vacuum dried and collected to obtain a red COF photocatalyst S-COF.

[0033] (3) 50 mg of S-COF was mixed with 3 mL of toluene, and oxygen was passed through the mixture for 10 min to saturate the mixture. 2 mL of trifluoroacetic acid was then added, and the mixture was sealed. The temperature was raised from room temperature to 100 °C under stirring and kept warm for 2 days to obtain the post-modified orange COF photocatalyst XS-COF.

[0034] Comparative Example 1 Preparation of COF Photocatalyst O-COF: 0.06 mmol of p-phenylenediamine and 0.04 mmol of 4,4',4''-(1,3,5-triazinecyclo-2,4,6-triyl)tribenzaldehyde were placed in a 10 mL Pyrex tube. 0.4 mL of n-butanol, 1.6 mL of o-dichlorobenzene, and 0.2 mL of 6 mol / L acetic acid solution were then added. The Pyrex tube was then flame-sealed under liquid nitrogen freezing and negative pressure. The tube was then placed in an oven, heated to 120°C, and incubated for 3 days. The crude product was washed three times with methanol and THF, collected by filtration, and then Soxhlet extracted with THF overnight. The product was then vacuum-dried and collected to yield the yellow COF photocatalyst, O-COF.

[0035] Comparative Example 2 Preparation of COF Photocatalyst B-COF: 0.06 mmol of 1,1':4',1''-terphenyl-2',5'-diamine and 0.04 mmol of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde were placed in a 10 mL Pyrex tube. 0.4 mL of n-butanol, 1.6 mL of o-dichlorobenzene, and 0.2 mL of 6 mol / L acetic acid solution were then added. The Pyrex tube was then flame-sealed under liquid nitrogen freezing and negative pressure. The tube was then placed in an oven, heated to 120°C, and incubated for 3 days. The crude product was washed three times with methanol and THF, collected by filtration, and then Soxhlet extracted with THF overnight. The product was then vacuum-dried and collected to yield the light green COF photocatalyst B-COF.

[0036] Figure 2 The XRD comparison diagrams of the prepared COFs photocatalysts are shown below. The peak near 3.20° is a characteristic diffraction peak of COF, confirming the successful synthesis of COFs. The peak position of the post-modified XS-COF remains essentially unchanged, demonstrating that the post-modification process did not destroy the crystallinity of the XS-COF.

[0037] Figure 3 The Fourier infrared spectrum of the prepared COFs photocatalyst is shown in Figure 1. -1 The stretching vibration of the carbon-oxygen double bond is about 1620 cm -1 The stretching vibration of the carbon-nitrogen double bond at 1620 cm-1 corresponds to the stretching vibration of the carbon-oxygen double bond in the synthesized COFs. It can be clearly seen that the carbon-oxygen double bond in the synthesized COFs has basically reacted to form a carbon-nitrogen double bond, which further proves the successful preparation of COFs photocatalysts. -1 The peak of the carbon-nitrogen double bond at the 37°C becomes weaker, indicating the formation of a pyridine ring.

[0038] Figure 4 The SEM comparison images of the prepared COFs photocatalysts show that the material has a flaky amorphous morphology.

[0039] Figure 5 Comparison of nitrogen adsorption-desorption isotherms of the prepared COFs photocatalysts. In the figure, all four COFs show typical type IV adsorption isotherms, indicating the presence of a mesoporous structure. The Brunauer-Emmett-Teller (BET) specific surface areas of O-COF, B-COF, S-COF, and XS-COF are 365, 662, 1293, and 685 m2, respectively. 2 / g -1 .

[0040] Example 2 COFs photocatalytic production of hydrogen peroxide: 5 mg of catalyst, 18 mL of water, and 2 mL of benzyl alcohol were added to a sealed Schlenk flask. The suspension was evenly distributed by ultrasonic treatment for 5 minutes, and O2 was blown into the suspension to allow the reaction system to reach adsorption-desorption equilibrium. The reaction temperature was maintained at 25 °C, and the mixture was irradiated with a 420 nm LED light while stirring. Samples were taken at different irradiation times, and the samples were centrifuged to separate the catalyst and the supernatant was collected. Hydrogen peroxide can react with Ti(SO4)2 to produce Ti (IV) -H2O2 complex and showed the characteristics of yellow solution. The absorption intensity at a wavelength of 410nm was detected by UV / Vis spectrophotometer (Lambda 2UV / Vis), and the concentration of hydrogen peroxide in the reaction solution was calculated. The results are shown in Table 1 and Figure 6 .

[0041] Table 1

[0042] From Table 1 and Figure 6 As shown in the results, S-COF and the post-modified XS-COF have good activity, and after post-modification, the photocatalytic hydrogen peroxide production performance of XS-COF is significantly improved, which is better than the existing reported level.

[0043] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a triazine-based covalent organic framework material, characterized in that: The following steps are involved: (1) 2,5-dibromo-p-phenylenediamine, 5-methylthiophene-2-boronic acid pinacol ester, tetrakis(triphenylphosphine)palladium and potassium carbonate were mixed and added to a mixed solvent of 1,4-dioxane and water. After three cycles of degassing, the reaction system was heated to reflux. After the reaction was completed, the product was washed with water until neutral, and then washed with n-hexane and methanol to remove impurities, respectively, to obtain a light yellow powder of 2,5-bis(5-methylthiophene-2-yl)benzene-1,4-diamine. (2) 2,5-bis(5-methylthiophene-2-yl)benzene-1,4-diamine and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde were mixed and added to a mixed solvent of n-butanol and o-dichlorobenzene, followed by an acetic acid solution. The mixture was frozen in a liquid nitrogen bath and vacuum-thawed for three cycles, then flame-sealed and subjected to a solvent thermal reaction. After filtration, the reaction product was extracted with tetrahydrofuran overnight and vacuum-dried to obtain the product.

2. The preparation method according to claim 1, wherein: The molar ratio of 2,5-dibromo-p-phenylenediamine, 5-methylthiophene-2-boronic acid pinacol ester, tetrakis(triphenylphosphine)palladium and potassium carbonate used in step (1) is 1:(2-3):0.23:4.34; the volume ratio of 1,4-dioxane and water in the mixed solvent is 4:

1.

3. The preparation method according to claim 1, wherein: The heating reflux temperature in step (1) is 110-120°C and the time is 48-72 h.

4. The preparation method according to claim 1, wherein: The molar ratio of 2,5-bis(5-methylthiophene-2-yl)benzene-1,4-diamine and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tritylaldehyde used in step (2) is 3:2; the volume ratio of n-butanol and o-dichlorobenzene in the mixed solvent is 1:9-3:7; the concentration of the acetic acid solution is 3-6 mol / L, and the volume ratio of the amount of acetic acid added to the mixed solvent is 1:

10.

5. The preparation method according to claim 1, wherein: The temperature of the solvent thermal reaction in step (2) is 120°C to 150°C, and the time is 3-7 days.

6. A triazine-based covalent organic framework material prepared by the method according to any one of claims 1 to 5.

7. Use of the triazine-based covalent organic framework material according to claim 6 in photocatalytic production of hydrogen peroxide, characterized in that: The application method is to use the triazine-based covalent organic framework material directly or after post-modification as a photocatalyst, add it into a water-benzyl alcohol system to carry out a photocatalytic reaction, thereby generating hydrogen peroxide.

8. The use according to claim 7, characterized in that: The post-modification is performed by mixing the triazine-based covalent organic framework material with toluene in a saturated oxygen atmosphere, adding trifluoroacetic acid, sealing, and heating and stirring.

9. The use according to claim 8, characterized in that: The ratio of the triazine-based covalent organic framework material to toluene is 40-60 mg / 3 mL; the volume ratio of toluene to trifluoroacetic acid is 2:1-1:1; and the heating and stirring is carried out at 100° C. for 1-3 days.

10. The use according to claim 7, characterized in that: The volume concentration of benzyl alcohol in the water-benzyl alcohol system is 10%; the amount of photocatalyst added to the water-benzyl alcohol system is 5 mg / 20 mL; the temperature of the photocatalytic reaction is 25° C., the wavelength of the light source is ≥420 nm, and the light intensity is ≥50 W.

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