An oxadiazole-based covalent organic framework material, a preparation method and application thereof

Abstract

This invention discloses an oxadiazole-based covalent organic framework material, its preparation method, and its applications, belonging to the field of photocatalytic materials technology. The material is prepared by a solvothermal reaction of 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde and 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine as monomers, under the catalysis of a mixed solvent of n-butanol and o-dichlorobenzene and acetic acid, yielding AZD-COF. This invention significantly improves the separation efficiency of photogenerated carriers and the stability in aqueous phase by constructing a highly crystalline two-dimensional conjugated framework through the synergistic construction of rigid nitrogen heterocyclic units. The obtained material achieves sacrificial agent-free photocatalytic production of H2O2 in pure water under visible light, with a maximum rate of 4013.6 μmolg. ‑1 h ‑1 ,2e ‑ The oxygen reduction process exhibits high selectivity and few side reactions. This invention provides a mild, environmentally friendly, and low-cost preparation process suitable for large-scale production, showing promising application prospects in the efficient and green synthesis of hydrogen peroxide.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photocatalytic materials technology, specifically relating to an oxadiazole-based covalent organic framework material, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide (H2O2) is a green and efficient oxidant, bleaching agent and disinfectant, with irreplaceable application value in fine chemical synthesis, environmental water treatment, papermaking and textiles, medical and health care and energy conversion.

[0003] Photocatalytic oxygen reduction to produce H2O2 uses solar energy as the sole energy input and water and oxygen as raw materials. The reaction conditions are mild, the process is pollution-free, and the products are easily separated, making it widely recognized as the most promising green synthesis route for H2O2 industrialization. The core of the photocatalytic system is a highly efficient, stable, and highly selective semiconductor photocatalyst.

[0004] Covalent organic frameworks (COFs) are a class of crystalline porous polymers formed by organic monomers linked by covalent bonds. They possess unique advantages such as high crystallinity, large specific surface area, ordered channels, and precisely designable conjugated frameworks and electronic structures, showing great application potential in photocatalytic water splitting, CO2 reduction, organic synthesis, and pollutant degradation. Among them, imine-linked COFs have become one of the most widely studied systems in the field of photocatalysis due to their mild synthesis conditions, strong structural tunability, and wide availability of monomers.

[0005] Although imine-based COFs have made some progress in photocatalytic H2O2 production, the existing technology still faces four major bottlenecks that severely restrict its practical application:

[0006] Poor stability of aqueous phase structure: Most imine COFs are prone to framework hydrolysis, crystal collapse or pore blockage under aqueous solution and visible light irradiation conditions, resulting in short catalytic cycle life and difficulty in meeting the requirements of continuous industrial use.

[0007] Photogenerated carrier recombination is severe: Traditional COFs have limited conjugation and disordered electron transport paths, resulting in rapid recombination of photogenerated electron-hole pairs in the bulk phase, narrow visible light absorption range, and low quantum efficiency.

[0008] Insufficient oxygen reduction selectivity: uneven distribution of catalytic active sites, poor energy level matching, 2e - The oxygen reduction pathway is uncontrollable and prone to 4e oxidation. - The reduction to produce H2O or the hydrogen evolution side reaction make it difficult to achieve both selectivity and yield of H2O2.

[0009] Low accessibility of active sites: unreasonable design of pore size, pore diameter distribution and hydrophilicity / hydrophobicity of framework, limited substrate diffusion, insufficient exposure of catalytic sites, and apparent catalytic activity far below theoretical expectations.

[0010] In recent years, nitrogen-containing heterocyclic units (such as triazine, pyridine, and oxadiazole) have been used to modify the COF (carbon dioxide fraction) framework to improve charge separation and catalytic selectivity. Among them, the 1,3,4-oxadiazole unit possesses strong electron-withdrawing properties, high rigidity, high chemical stability, and excellent electron transport capabilities, which can effectively modulate the band structure of COFs, enhance conjugation effects, and suppress carrier recombination. However, the orderly assembly of bisoxadiazole units and pyridyl trialdehyde units to construct highly crystalline, stable, and selective imine-based COFs, and their application in the efficient photocatalytic production of H₂O₂ in a pure water system without sacrificial agents, has not yet been publicly reported.

[0011] Therefore, it is necessary to develop a method with high crystallinity, high stability, high carrier separation efficiency, and high 2e content. - The development of oxygen reduction-selective oxadiazole-based covalent organic framework photocatalysts, along with a mild, green, and scalable preparation process to achieve efficient photocatalytic production of H2O2 in pure water systems, has become a key technical problem urgently needing to be solved in this field. Summary of the Invention

[0012] To address the technical problems of existing imine-based COFs, such as poor aqueous-phase stability, high photogenerated carrier recombination rate, low oxygen reduction selectivity, and insufficient H2O2 yield, this invention provides an oxadiazole-based covalent organic framework material, its preparation method, and its applications. This material possesses advantages such as high crystallinity, high stability, and high activity, enabling efficient and highly selective photocatalytic H2O2 production. This invention uses pyridine trialdehyde and bis(oxadiazole) diamine as building blocks, forming a fully conjugated two-dimensional crystalline framework through imine bonds. Crystallization is controlled using a mixed solvent of n-butanol and o-dichlorobenzene, with acetic acid catalysis and mild solvothermal conditions. The strong electron-withdrawing ability of the oxadiazole unit and the rigid structure synergistically enhance charge separation, stability, and 2e yield. - Selectivity.

[0013] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0014] An oxadiazole-based covalent organic framework material is obtained by covalently linking 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde and 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine via a solvothermal reaction in the presence of an organic solvent and a catalyst to form a crystalline porous framework. The resulting oxadiazole-based covalent organic framework material is named AZD-COF, and its structural formula is as follows:

[0015] .

[0016] The preparation method of the above-mentioned oxadiazole-based covalent organic framework material includes the following steps:

[0017] S1. Add 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde, 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine, organic solvent and catalyst to the reactor, seal and then perform ultrasonic treatment;

[0018] S2. The reaction solution obtained in step S1 is rapidly frozen and degassed using a liquid nitrogen bath, followed by a nitrogen pumping and thawing cycle. After vacuum sealing, it is reacted in an oil bath to form a yellow precipitate.

[0019] S3. The yellow precipitate obtained in step S2 is washed, centrifuged and dried to obtain a yellow powder, namely AZD-COF.

[0020] Further, in step S1, the molar ratio of 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde to 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine is 1:2.5~4.5.

[0021] Furthermore, in step S1, the organic solvent is a mixed solvent composed of n-butanol and o-dichlorobenzene, with a volume ratio of 1:0.3~3, preferably 1:1~2. This mixed solvent system has moderate polarity and good solubility, which can take into account both monomer solubility and framework crystallization kinetics, and is suitable for the controllable synthesis of highly crystalline two-dimensional COFs.

[0022] Further, in step S1, the catalyst is acetic acid, using an acetic acid solution with a concentration of 4-8 mol / L, the volume of which is 2%-15% of the total volume of the reaction system, preferably 4%-8%. Acetic acid, as a mild protic acid catalyst, can efficiently catalyze the condensation of aldehydes and amines to form imine bonds, while avoiding monomer decomposition or framework hydrolysis caused by strong acids, ensuring the selectivity and mildness of the reaction. A suitable concentration and dosage range can provide appropriate catalytic activity, ensuring the condensation reaction rate without damaging the framework structure due to excessive acidity or dosage.

[0023] Furthermore, in step S2, the freezing-nitrogen pumping-thawing cycle is repeated 2 to 4 times. This number of cycles can achieve sufficient degassing while avoiding increased energy consumption and complicated operation caused by excessive cycles, thus balancing degassing effect and process efficiency.

[0024] Furthermore, in step S2, the oil bath reaction temperature is 110~130 ℃ and the reaction time is 60~84 h. Through solvothermal reaction, the orderly connection of covalent bonds and slow crystal growth are promoted to obtain a highly crystalline and stable two-dimensional framework structure.

[0025] Furthermore, in step S3, the drying temperature is 50~70℃ and the drying time is 10~14 h.

[0026] The aforementioned oxadiazole-based covalent organic framework material was used for the photocatalytic preparation of hydrogen peroxide. AZD-COF was dispersed in pure water, and a sacrificial agent-free photocatalytic reaction was carried out under visible light irradiation, selectively passing through 2e⁻. - The oxygen reduction pathway generates H2O2. AZD-COF itself, as a metal-free photocatalyst, possesses a rigid conjugated framework that rapidly separates photogenerated electron-hole pairs. The oxadiazole active sites efficiently adsorb and activate oxygen molecules, significantly inhibiting 4e-2+. - The reduction and hydrogen evolution side reaction achieves highly selective hydrogen peroxide production.

[0027] Furthermore, the photocatalytic reaction system is a pure water system, with AZD-COF used at a concentration of 0.05~0.2 mg / mL pure water (i.e., 0.05~0.2 mg of AZD-COF per mL of pure water). The visible light wavelength is 420~780 nm, and the H2O2 generation rate reaches as high as 4013.6 μmol g. -1 h -1 .

[0028] Terminology Explanation:

[0029] 2e - The oxygen reduction pathway (two-electron oxygen reduction reaction pathway) refers to the reaction pathway in which oxygen is reduced to hydrogen peroxide (H2O2) via a two-electron transfer, as opposed to the four-electron pathway that produces water. - path.

[0030] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0031] (1) The AZD-COF prepared in this invention exhibits a photocatalytic H2O2 production rate of up to 4013.6 μmol g in a pure water sacrificial agent-free system. -1 h -1 It is far superior to conventional imine-based COFs, and has excellent visible light response and carrier separation efficiency.

[0032] (2) The material of this invention is constructed from rigid pyridine and oxadiazole units to form a two-dimensional conjugated framework, exhibiting strong aqueous phase stability and allowing for precise passage of 2e. - The oxygen reduction pathway generates H2O2, effectively suppressing side reactions and exhibiting high product selectivity.

[0033] (3) The present invention adopts a solvothermal method, which is mild and does not require precious metals. It uses a low-toxicity mixed solvent and a weak acid catalyst, and has a wide range of monomer ratios and reaction parameters, making it easy to scale up and industrialize.

[0034] (4) The material of the present invention can operate efficiently in a pure water system, avoiding separation and pollution problems caused by sacrificial agents, and has practical potential in the fields of green oxidation, water treatment, energy and chemical industry. Attached Figure Description

[0035] Figure 1 XRD patterns of AZD-COF, AZO-COF, AZT-COF, TPA-COF and TPT-COF.

[0036] Figure 2 The images are scanning electron microscope (SEM) images of AZD-COF, where (a) is a schematic diagram of AZD-COF magnified 10,000 times under a scanning electron microscope, and (b) is a schematic diagram of AZD-COF magnified 20,000 times under a scanning electron microscope.

[0037] Figure 3 Fourier transform infrared spectra of AZD-COF, AZO-COF, AZT-COF, TPA-COF, and TPT-COF.

[0038] Figure 4 The graph shows the rate of photocatalytic H2O2 production by AZD-COF, AZO-COF, AZT-COF, TPA-COF, and TPT-COF under visible light irradiation. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0040] Example 1

[0041] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (6.64 mg, 0.017 mmol), 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine (15.13 mg, 0.06 mmol), n-butanol (0.5 mL), o-dichlorobenzene (1.5 mL), and 6 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 120 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0042] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 1 is 4013.6 μmolg. -1 h -1 .

[0043] Example 2

[0044] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (7.82 mg, 0.020 mmol), 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine (12.61 mg, 0.050 mmol), n-butanol (0.5 mL), o-dichlorobenzene (1.5 mL), and 6 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 120 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0045] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 2 is 3865.4 μmolg. -1 h -1 .

[0046] Example 3

[0047] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (5.86 mg, 0.015 mmol), 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine (16.99 mg, 0.0675 mmol), n-butanol (0.5 mL), o-dichlorobenzene (1.5 mL), and 6 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 120 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0048] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 3 is 3922.8 μmol / g. -1 h -1 .

[0049] Example 4

[0050] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (6.64 mg, 0.017 mmol), 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine (15.13 mg, 0.06 mmol), n-butanol (1.0 mL), o-dichlorobenzene (1.0 mL), and 6 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 120 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0051] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 4 is 3956.3 μmolg. -1 h -1 .

[0052] Example 5

[0053] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (6.64 mg, 0.017 mmol), 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine (15.13 mg, 0.06 mmol), n-butanol (1.5 mL), o-dichlorobenzene (0.5 mL), and 6 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 120 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0054] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 5 is 3890.1 μmol / g. -1 h -1 .

[0055] Example 6

[0056] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (6.64 mg, 0.017 mmol), 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine (15.13 mg, 0.06 mmol), n-butanol (0.5 mL), o-dichlorobenzene (1.5 mL), and 4 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 120 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0057] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 6 is 3758.7 μmolg. -1 h -1 .

[0058] Example 7

[0059] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (6.64 mg, 0.017 mmol), 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine (15.13 mg, 0.06 mmol), n-butanol (0.5 mL), o-dichlorobenzene (1.5 mL), and 8 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 120 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0060] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 7 is 3988.7 μmol / g. -1 h -1 .

[0061] Example 8

[0062] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (6.64 mg, 0.017 mmol), 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine (15.13 mg, 0.06 mmol), n-butanol (0.5 mL), o-dichlorobenzene (1.5 mL), and 6 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 110 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0063] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 8 is 3802.45 μmol / g. -1 h -1 .

[0064] Example 9

[0065] 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde (6.64 mg, 0.017 mmol), 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine (15.13 mg, 0.06 mmol), n-butanol (0.5 mL), o-dichlorobenzene (1.5 mL), and 6 mol / L acetic acid aqueous solution (0.2 mL) were added to an ampoule. The ampoule was sealed with wire and a rubber stopper and then sonicated for 2 minutes. It was then rapidly frozen and degassed using a liquid nitrogen bath at 77 K through three cycles of freezing-nitrogen pumping-thawing. After vacuum sealing, the ampoule was heated in an oil bath at 130 °C for 3 days to form a yellow precipitate. The precipitate was washed three times sequentially with tetrahydrofuran, acetone, dichloromethane, and methanol, and then centrifuged. The resulting solid was dried in a drying oven at 60 °C for 12 h to obtain a yellow powder, namely AZD-COF.

[0066] Experimental results show that the photocatalytic H2O2 production rate of the AZD-COF obtained in Example 9 is 3877.6 μmolg. -1 h -1 .

[0067] Comparative Example 1

[0068] The rest is the same as in Example 1, except that 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde is used instead of 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde to synthesize AZO-COF, whose structural formula is as follows:

[0069] .

[0070] Experimental results show that the photocatalytic H2O2 production rate of AZO-COF obtained in Comparative Example 1 is 1865.3 μmolg. -1 h -1 Using pyridine-free triazine units resulted in decreased crystallinity and reduced stability of the obtained material.

[0071] Comparative Example 2

[0072] The rest is the same as in Example 1, except that 1,3,5-tris(2-formylpyridin-5-yl)benzene is used instead of 4,4',4''-(pyridin-2,4,6-triyl)tribenzaldehyde to synthesize AZT-COF, whose structural formula is as follows:

[0073] .

[0074] Experimental results show that the photocatalytic H2O2 production rate of AZT-COF obtained in Comparative Example 2 is 1692.5 μmolg. -1 h -1 Using pyridine-free benzene units, the resulting material exhibits poor charge separation.

[0075] Comparative Example 3

[0076] The rest is the same as in Example 1, except that 4,4'-diaminoterphenyl is used instead of 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine to synthesize TPA-COF, whose structural formula is as follows:

[0077] .

[0078] Experimental results show that the photocatalytic H2O2 production rate of TPA-COF obtained in Comparative Example 3 is 1207.9 μmolg. -1 h -1 Since the raw material does not contain oxadiazole units, the conjugation of the resulting material is significantly reduced.

[0079] Comparative Example 4

[0080] The rest is the same as in Example 1, except that 4,4',4''-(1,3,5-triazinecyclo-2,4,6-triyl)tribenzaldehyde is used instead of 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde, and 4,4'-diaminoterphenyl is used instead of 4,4'-(1,3,4-oxadiazol-2,5-diyl)diphenylamine to synthesize TPT-COF, whose structural formula is as follows:

[0081] .

[0082] Experimental results show that the photocatalytic H2O2 production rate of TPA-COF obtained in Comparative Example 4 is 956.2 μmol / g. -1 h -1 The raw materials contained neither oxadiazole units nor pyridine, resulting in the material with the lowest activity.

[0083] AZD-COF is illustrated using the product obtained in Example 1 as a typical example.

[0084] The XRD patterns of AZD-COF, AZO-COF, AZT-COF, TPA-COF, and TPT-COF are as follows: Figure 1 As shown, from Figure 1 It can be seen that there is a very sharp absorption peak between 2 and 10°, proving the successful synthesis of COF.

[0085] Scanning electron microscope (SEM) image of AZD-COF as shown below Figure 2 As shown, from Figure 2 It can be seen that the prepared AZD-COF is in the form of strips and columns.

[0086] Fourier transform infrared spectra of AZD-COF, AZO-COF, AZT-COF, TPA-COF, and TPT-COF are shown below. Figure 3 As shown, from Figure 3 It can be seen that the aldehyde group (1700cm) -1 The absorption peak of the imine bond (1627 cm⁻¹) disappears. -1 The formation of ) proves that the imine condensation reaction was successful.

[0087] The rate graphs of photocatalytic H2O2 production by AZD-COF, AZO-COF, AZT-COF, TPA-COF, and TPT-COF under visible light irradiation are shown below. Figure 4 As shown, by Figure 4 It can be seen that AZD-COF is as high as 4013.6 μmolg. -1 h -1 It is far superior to AZO-COF, AZT-COF, TPA-COF and TPT-COF, and also surpasses most currently reported COF photocatalysts, exhibiting excellent photocatalytic activity.

Claims

1. An oxadiazole-based covalent organic framework material, characterized in that, A crystalline porous framework, named AZD-COF, is formed by covalently linking 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde and 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine via a solvothermal reaction in the presence of an organic solvent and catalyst. The resulting oxadiazole-based covalent organic framework is shown below: 。 2. The method for preparing the oxadiazole-based covalent organic framework material as described in claim 1, characterized in that, Includes the following steps: S1. Add 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde, 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine, organic solvent and catalyst to the reactor, seal and then perform ultrasonic treatment; S2. The reaction solution obtained in step S1 is rapidly frozen and degassed using a liquid nitrogen bath, followed by a nitrogen pumping and thawing cycle. After vacuum sealing, it is reacted in an oil bath to form a yellow precipitate. S3. The yellow precipitate obtained in step S2 is washed, centrifuged and dried to obtain a yellow powder, namely AZD-COF.

3. The preparation method according to claim 2, characterized in that, In step S1, the molar ratio of 4,4',4''-(pyridine-2,4,6-triyl)tribenzaldehyde to 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylamine is 1:2.5~4.

5.

4. The preparation method according to claim 2, characterized in that, In step S1, the organic solvent is a mixed solvent composed of n-butanol and o-dichlorobenzene, with a volume ratio of n-butanol to o-dichlorobenzene of 1:0.3~3.

5. The preparation method according to claim 2, characterized in that, In step S1, the catalyst is acetic acid, and an acetic acid solution with a concentration of 4~8 mol / L is used, the volume of which is 2%~15% of the total volume of the reaction system.

6. The preparation method according to claim 2, characterized in that, In step S2, the freezing-nitrogen pumping-thawing cycle is repeated 2 to 4 times.

7. The preparation method according to claim 2, characterized in that, In step S2, the oil bath reaction temperature is 110~130℃, and the reaction time is 60~84h.

8. The preparation method according to claim 2, characterized in that, In step S3, the drying temperature is 50~70℃ and the drying time is 10~14h.

9. The application of the oxadiazole-based covalent organic framework material according to claim 1 in the photocatalytic preparation of hydrogen peroxide, characterized in that, AZD-COF was dispersed in pure water and subjected to a sacrificial-free photocatalytic reaction under visible light irradiation, selectively passing through 2e⁻. - The oxygen reduction pathway generates H2O2.

10. The application as described in claim 9, characterized in that, The photocatalytic reaction system was a pure water system, with AZD-COF used at a concentration of 0.05–0.2 mg / mL pure water. The visible light wavelength was 420–780 nm, and the H₂O₂ generation rate reached a high of 4013.6 μmol g⁻¹. -1 h -1 .

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