Triazinyl COFs, preparation method thereof and application of triazinyl COFs in production of hydrogen peroxide

Abstract

The invention discloses triazinyl COFs (Covalent Organic Frameworks), the triazinyl COFs take 4, 4 ', 4' '-(1, 3, 5-triazine-2, 4, 6-triyl) triphenylamine and 2, 5-dihydroxy-1, 4-benzene dicarboxyaldehyde as construction units, and the triazinyl COFs are in a coralline shape. The invention also discloses a preparation method of the triazinyl COFs, and the preparation method comprises the following steps: uniformly mixing 4, 4 ', 4' '-(1, 3, 5-triazine-2, 4, 6-triyl) triphenylamine, 2, 5-dihydroxy-1, 4-benzene dicarboxyaldehyde, N-methyl pyrrolidone and a catalyst, and carrying out a reaction to obtain the triazinyl COFs. The invention also discloses the triazinyl COFs and application of the triazinyl COFs prepared by the method in photocatalytic production of hydrogen peroxide. The invention also discloses a method for producing hydrogen peroxide by using water. The triazinyl COFs provided by the invention can greatly improve the efficiency of producing H2O2 by photocatalysis.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and in particular to triazine-based COFs and a preparation method thereof, and an application thereof in producing hydrogen peroxide. Background Art

[0002] Photocatalytic technology is an efficient, safe and environmentally friendly environmental purification technology. It is generally based on the redox ability of photocatalysts under light conditions to achieve the purpose of purifying pollutants, synthesizing and converting substances. For example, hydrogen peroxide (H2O2) is one of the 100 most important chemicals in the world and is widely used in chemical production, environmental protection, energy storage and microbial disinfectants. H2O2 is a clean energy source with an energy density comparable to that of compressed hydrogen and is easier to store and transport. The anthraquinone method is the most commonly used method for preparing H2O2 in industry. This method usually uses metal catalysts such as palladium, which consumes a lot of energy and produces a lot of waste. Therefore, using photocatalytic materials to generate H2O2 through the photocatalytic reaction of water and O2 under sunlight is a clean and safe preparation method, which has great potential compared with other H2O2 preparation methods.

[0003] At present, most of the reported photocatalytic materials are based on metal oxides and metal organic frameworks, which are prone to cause greater environmental pollution, which limits their widespread application in water treatment systems in real life. In addition, most of the photocatalysts reported so far require the use of sacrificial agents to quench electrons or holes, improve the efficiency of charge separation, introduce other substances into the reaction system, and generate byproducts while producing H2O2. Due to the presence of water-soluble sacrificial agents and their oxidation products, the separation and purification required to obtain pure H2O2 solutions is costly and cumbersome. Therefore, photocatalytic production of H2O2 is crucial without the use of sacrificial agents. In order to solve the above problems, a rationally designed photocatalytic material is urgently needed to solve the challenge of producing H2O2 in pure water. Covalent organic frameworks (COFs) are organic porous materials connected by covalent bonds, which have highly tunable structures, broadened light absorption, and a wide range of active sites, making them widely used in the field of photocatalysis.

[0004] However, so far, most of the existing COFs photocatalytic materials rely on the use of sacrificial agents to improve photocatalytic performance, which will cause the generation of by-products and increase the cost of extracting H2O2. The poor separation of electrons and holes in pure water by COFs materials seriously limits their photocatalytic performance. Some COFs materials also have low photocatalytic H2O2 production when no sacrificial agents are used. Summary of the invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a triazine-based COFs and a preparation method thereof, and an application in producing hydrogen peroxide. The present invention introduces triazine-based structure and coral-shaped COFs, which can greatly improve the efficiency of photocatalytic H2O2 production.

[0006] The present invention provides a triazine-based COFs, wherein the triazine-based COFs uses 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde as building units, and the triazine-based COFs is coral-shaped.

[0007] Preferably, the specific surface area of ​​the triazine-based COFs is 2800-3000 m 2 / g.

[0008] The present invention also provides a method for preparing the triazine-based COFs, comprising the following steps: mixing 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine, 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde, N-methylpyrrolidone and a catalyst, and reacting to obtain triazine-based COFs.

[0009] Preferably, the catalyst is acetic acid.

[0010] Preferably, the molar ratio of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine to 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde is 1:0.8-1.2.

[0011] Preferably, the usage ratio of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and N-methylpyrrolidone is 1 mol:4.5-5.5 L.

[0012] Preferably, the volume ratio of N-methylpyrrolidone to the catalyst is 9-11:1.

[0013] Preferably, the reaction temperature is 150-170° C., and the reaction time is 60-84 h.

[0014] Preferably, the reaction is carried out in an inert gas atmosphere.

[0015] The inert gas mentioned above may be argon or the like.

[0016] Preferably, after the reaction is completed, purification is performed to obtain triazine-based COFs.

[0017] Preferably, the purification step comprises: after the reaction is completed, collecting the solid, washing the solid with ethanol, and drying to obtain triazine-based COFs.

[0018] Preferably, the solid is washed with ethanol at 70-90°C.

[0019] The present invention also proposes the use of the above triazine-based COFs and the triazine-based COFs prepared by the above method in the photocatalytic production of hydrogen peroxide.

[0020] The present invention also proposes a method for producing hydrogen peroxide using water, comprising the following steps: mixing a photocatalyst with water, introducing oxygen, and irradiating with light to obtain hydrogen peroxide, wherein the photocatalyst is the above-mentioned triazine-based COFs or the triazine-based COFs prepared by the above-mentioned method.

[0021] Preferably, the illumination is performed using a xenon lamp.

[0022] The water mentioned above can be deionized water, purified water, etc.

[0023] The present invention uses 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde as building units, and uses a suitable organic solvent and a preparation method to finally prepare coral-shaped triazine-based COFs, which have high crystallinity and high specific surface area. Its specific structure can provide a large number of active sites to participate in the photocatalytic water-to-H2O2 reaction, and there is no need to use a sacrificial agent to consume photogenerated carriers to improve its photogenerated electron-hole pair separation ability, thereby solving the problem that most existing COFs photocatalytic materials rely on sacrificial agents to cause by-product generation, and the photogenerated carriers are seriously recombinated and the utilization rate is low.

[0024] Compared with COFs materials using 1,3,5-tri(4-aminophenyl)benzene as a building block, the present invention introduces triazine groups into COFs materials, further enhancing the separation capability of photogenerated electrons and holes during the reaction process and improving its photocatalytic efficiency; compared with phenyl, the photocatalytic H2O2 production activity of the coral-shaped triazine-based COFs of the present invention is increased by about 3 times.

[0025] The present invention adopts a one-pot polymerization to obtain coral-shaped triazine-based COFs, the preparation method is simple, and the COFs material has the characteristics of being generally applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1-3 The scanning electron microscope spectra (a) and transmission electron microscope spectra (b) of the COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown respectively.

[0027] Figure 4 The X-ray diffraction patterns of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown, wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1, and Tapb-COF is Comparative Example 2.

[0028] Figure 5The infrared spectrum of the triazine-based COFs prepared in Example 1, wherein NMP-COF is Example 1, Tapt is 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine, and DHTA is 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde.

[0029] Figure 6 This is the carbon nuclear magnetic resonance spectrum of the triazine-based COFs prepared in Example 1.

[0030] Figure 7 This is the X-ray photoelectron spectrum (XPS) of the triazine-based COFs prepared in Example 1, wherein a is the full spectrum, b is the C1s spectrum, c is the N1s spectrum, and d is the O1s spectrum.

[0031] Figure 8 The H2O2 production of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 within 2 hours under visible light irradiation, wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1, and Tapb-COF is Comparative Example 2.

[0032] Fig. 9 The long-term H2O2 production performance diagram (a) and cyclic H2O2 production performance diagram (b) of the triazine-based COFs prepared in Example 1 under visible light irradiation.

[0033] Fig.10 The water contact angle test results of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown, wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1, and Tapb-COF is Comparative Example 2.

[0034] Fig.11 The photoluminescence spectra of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. 1 , wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1 and Tapb-COF is Comparative Example 2. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is described in detail below through specific embodiments.

[0036] Example 1

[0037] A method for preparing triazine-based COFs comprises the following steps:

[0038] 0.354 g (1 mmol) of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 0.166 g (1 mmol) of 2,5-dihydroxy-1,4-benzenedicarboxylic acid were weighed and placed in a three-necked flask. 5 mL of N-methylpyrrolidone and 0.5 mL of acetic acid were added in sequence. The mixture was stirred for 5 min and then ultrasonicated for 10 min. Then, the mixture was heated at 160 °C in an oil bath under an argon atmosphere and condensed and refluxed for 72 h. A red solid was obtained by filtration. The red solid was repeatedly washed with ethanol for several times until the washing liquid was colorless and transparent (the steps of each washing were: heating at 80 °C in a water bath and stirring for 10 min), and then dried to obtain triazine-based COFs, which was recorded as NMP-COF.

[0039] Example 2

[0040] A method for preparing triazine-based COFs comprises the following steps:

[0041] 0.354 g (1 mmol) of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 0.133 g (0.8 mmol) of 2,5-dihydroxy-1,4-benzenedicarboxylic acid were weighed and placed in a three-necked flask. 4.5 mL of N-methylpyrrolidone and 0.5 mL of acetic acid were added in sequence. The mixture was stirred for 5 min and then ultrasonicated for 10 min. Then, the mixture was heated at 150 °C in an oil bath under an argon atmosphere and condensed and refluxed for 84 h. A red solid was obtained by filtration. The red solid was repeatedly washed with ethanol for several times until the washing liquid was colorless and transparent (the steps of each washing were: heating at 70 °C in a water bath and stirring for 10 min), and then dried to obtain triazine-based COFs.

[0042] Example 3

[0043] A method for preparing triazine-based COFs comprises the following steps:

[0044] 0.354 g (1 mmol) of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 0.199 g (1.2 mmol) of 2,5-dihydroxy-1,4-benzenedicarboxylic acid were weighed and placed in a three-necked flask. 5.5 mL of N-methylpyrrolidone and 0.5 mL of acetic acid were added in sequence. The mixture was stirred for 5 min and then ultrasonicated for 10 min. Then, the mixture was heated at 170 °C in an oil bath under an argon atmosphere and condensed and refluxed for 60 h. A red solid was obtained by filtration. The red solid was repeatedly washed with ethanol for several times until the washing liquid was colorless and transparent (the steps of each washing were: heating at 90 °C in a water bath and stirring for 10 min), and then dried to obtain triazine-based COFs.

[0045] Comparative Example 1

[0046] A method for preparing triazine-based COFs comprises the following steps:

[0047] "N-methylpyrrolidone" was replaced by "o-dichlorobenzene", and the rest was the same as in Example 1, recorded as o-DCB-COF.

[0048] Comparative Example 2

[0049] A method for preparing phenyl COFs comprises the following steps:

[0050] The mixture was the same as in Example 1 except that “1 mmol of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine” was replaced by “1 mmol of 1,3,5-tris(4-aminophenyl)benzene” and “N-methylpyrrolidone” was replaced by “o-dichlorobenzene”. The mixture was recorded as Tapb-COF.

[0051] The COFs obtained in Example 1, Comparative Example 1 and Comparative Example 2 were tested. The results are as follows: Figure 1-11 shown.

[0052] Figure 1-3 The scanning electron microscope spectra (a) and transmission electron microscope spectra (b) of the COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown respectively.

[0053] Depend on Figure 1-3 It can be seen that the triazine-based COFs prepared in Example 1 are accumulated in a coral-like manner, while the triazine-based COFs prepared in Comparative Example 1 are accumulated in a granular manner, and the phenyl COFs prepared in Comparative Example 2 are accumulated in spheres of different sizes; the specific surface area of ​​the triazine-based COFs prepared in Example 1 is 2960.6 m 2 / g, the mother core of triazine-based COFs (the mother core structure is as follows Figure 6 The macrocyclic pore size formed by the photocatalytic reaction (as shown in the structural formula in ) is 2.37 nm; the differences in building units and organic solvents will lead to different microstructures of the final product and thus affect its photocatalytic performance.

[0054] Figure 4 The X-ray diffraction patterns of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown, wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1, and Tapb-COF is Comparative Example 2.

[0055] Depend on Figure 4 It can be seen that the triazine-based COFs prepared in Example 1 have a higher crystallinity than the COFs prepared in Comparative Examples 1 and 2.

[0056] Figure 5The infrared spectrum of the triazine-based COFs prepared in Example 1, wherein NMP-COF is Example 1, Tapt is 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine, and DHTA is 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde.

[0057] Figure 6 This is the carbon nuclear magnetic resonance spectrum of the triazine-based COFs prepared in Example 1.

[0058] Figure 7 This is the X-ray photoelectron spectrum (XPS) of the triazine-based COFs prepared in Example 1, wherein a is the full spectrum, b is the C1s spectrum, c is the N1s spectrum, and d is the O1s spectrum.

[0059] Depend on Figure 5-7 It can be seen that the formation of an imine bond (C=N) proves that Example 1 successfully prepared triazine-based COFs.

[0060] The COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 were used as photocatalysts to produce H2O2, respectively. The specific steps included: taking 0.002 g of the photocatalyst and placing it in a reaction bottle, adding 30 mL of deionized water and stirring to mix, passing oxygen for 20 minutes, and then irradiating with a 300 W xenon lamp, and taking 1 mL of the reaction solution every 30 minutes to detect the concentration of H2O2.

[0061] The detection method of H2O2 is as follows: filter 1 mL of the reaction solution, add it to 2 mL of the detection solution (the detection solution is composed of equal volumes of 0.4 mol / L potassium iodide aqueous solution and 0.1 mol / L potassium hydrogen phthalate aqueous solution), shake well to develop color, use a UV-visible spectrophotometer to measure the liquid absorbance, and calculate the H2O2 concentration based on the absorbance. The results are as follows Figure 8 shown.

[0062] Figure 8 The H2O2 production of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 within 2 hours under visible light irradiation, wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1, and Tapb-COF is Comparative Example 2.

[0063] Depend on Figure 8 It can be seen that the photocatalytic H2O2 production performance of the triazine-based COFs prepared in Example 1 is much higher than that of Comparative Examples 1-2.

[0064] Fig. 9 The long-term H2O2 production performance diagram (a) and cyclic H2O2 production performance diagram (b) of the triazine-based COFs prepared in Example 1 under visible light irradiation.

[0065] Depend on Fig. 9It can be seen that the triazine-based COFs prepared in Example 1 have a stable catalytic effect within 6 hours and have good cycle stability.

[0066] Fig.10 The water contact angle test results of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown, wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1, and Tapb-COF is Comparative Example 2.

[0067] Depend on Fig.10 It can be seen that the COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are all super hydrophilic and can be well dispersed in water.

[0068] Fig.11 The photoluminescence spectra of COFs prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. 1 , wherein NMP-COF is Example 1, o-DCB-COF is Comparative Example 1 and Tapb-COF is Comparative Example 2.

[0069] Depend on Fig.11 It can be seen that the triazine-based COFs prepared in Example 1 have stronger photogenerated carrier migration and separation capabilities, and more photogenerated charges participate in the reaction, thereby improving the photocatalytic H2O2 production performance.

[0070] In summary, the present invention introduces a triazine-based structure to promote the separation of photogenerated carriers and improve the efficiency of photocatalytic H2O2 production. The present invention selects a suitable organic solvent and a preparation method to obtain coral-like triazine-based COFs, which have a high degree of crystallinity and a large specific surface area. Its specific microstructure enables it to provide a large number of active sites to participate in the photocatalytic H2O2 production reaction, thereby greatly improving the efficiency of photocatalytic H2O2 production. The coral-like triazine-based COFs described in the present invention have broad market application prospects.

[0071] The method described in the present invention can provide a stable synthesis method for regulating the structure of COFs. By introducing or replacing electron-withdrawing or electron-donating groups, the movement of electrons in the COFs structure can be adjusted to achieve efficient carrier migration and separation, thereby solving the problem that most existing COFs photocatalytic materials require the additional use of sacrificial agents and have low efficiency in photogenerated carrier migration and separation.

[0072] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A triazine-based COFs, characterized in that: The triazine-based COFs are constructed with 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde as building blocks, and the triazine-based COFs are coral-shaped.

2. The triazine-based COFs according to claim 1, characterized in that: The specific surface area of ​​the triazine-based COFs is 2800-3000 m 2 / g.

3. A method for preparing triazine-based COFs as claimed in claim 1 or 2, characterized in that: The method comprises the following steps: mixing 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine, 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde, N-methylpyrrolidone and a catalyst, and reacting the mixture to obtain triazine-based COFs.

4. The method for preparing triazine-based COFs according to claim 3, characterized in that: The catalyst is acetic acid.

5. The method for preparing triazine-based COFs according to claim 3 or 4, characterized in that: The molar ratio of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine to 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde is 1:0.8-1.

2.

6. The method for preparing triazine-based COFs according to any one of claims 3 to 5, characterized in that: The dosage ratio of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine and N-methylpyrrolidone is 1 mol:4.5-5.5 L; preferably, the volume ratio of N-methylpyrrolidone to the catalyst is 9-11:

1.

7. The method for preparing triazine-based COFs according to any one of claims 3 to 6, characterized in that: The reaction temperature is 150-170° C., and the reaction time is 60-84 h. Preferably, the reaction is carried out in an inert gas atmosphere.

8. The method for preparing triazine-based COFs according to any one of claims 3 to 7, characterized in that: After the reaction is completed, purification is performed to obtain triazine-based COFs; preferably, the purification step comprises: after the reaction is completed, collecting the solid, washing the solid with ethanol, and drying to obtain triazine-based COFs; preferably, washing the solid with ethanol at 70-90°C.

9. Use of the triazine-based COFs according to claim 1 or 2, or the triazine-based COFs prepared by the method according to any one of claims 3 to 8 in photocatalytic production of hydrogen peroxide.

10. A method for producing hydrogen peroxide using water, characterized in that The method comprises the following steps: mixing a photocatalyst with water, introducing oxygen, and irradiating with light to obtain hydrogen peroxide, wherein the photocatalyst is the triazine-based COFs described in claim 1 or 2 or the triazine-based COFs obtained by the method described in any one of claims 3 to 8; preferably, irradiating with a xenon lamp.

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