Preparation method and application of nitrogen-containing heterocyclic porous covalent organic framework material

Abstract

The invention discloses a preparation method and application of a nitrogen-containing heterocyclic porous covalent organic framework material. The preparation method comprises the following steps: mixing trialdehyde phloroglucinol and a nitrogen heterocyclic ring-containing monomer according to a certain mass ratio, adding an organic catalyst and a mixed solvent, degassing, sealing, carrying out solvothermal reaction synthesis, washing with a polar solvent, carrying out Soxhlet extraction and purification, and drying to obtain the nitrogen heterocyclic ring-containing porous covalent organic framework material. According to the method, a pyridazine unit and trialdehyde phloroglucinol are used as monomers to construct a COF skeleton of a nitrogen heterocyclic ring, an asymmetric pi-conjugated structure is formed, efficient electron-hole space separation is achieved, active site charge distribution is optimized through the electron-rich characteristic of the pyridazine unit, and the oxygen molecule adsorption and activation capacity is enhanced. The method adopts a green solvent, is mild in reaction condition, avoids the use of toxic reagents, is green and environment-friendly, and provides a new way for photocatalytic synthesis of hydrogen peroxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor photocatalytic materials, and particularly relates to a preparation method and application of a nitrogen-containing heterocyclic porous covalent organic framework material. Background Art

[0002] Hydrogen peroxide (H2O2) is an important industrial raw material and clean energy source, widely used in fields such as chemical synthesis, wastewater treatment, metallurgy, electronics, and energy storage, with a rapidly growing global market. However, current industrial synthesis mainly relies on the energy-intensive anthraquinone process, which not only consumes a large amount of energy but also generates a large amount of harmful waste, causing serious environmental pollution. In addition, due to the slow recombination rate and reaction kinetics, the existing photosynthetic yield of H2O2 is difficult to meet industrial demands. Therefore, it is urgent to develop green and efficient production methods.

[0003] Photocatalytic production of H2O2 is an environmentally friendly alternative technology that uses water and oxygen as raw materials and drives the reaction through sunlight, mimicking the natural photosynthesis process. Compared with traditional methods, photocatalytic synthesis of H2O2 has low energy consumption and no by-products, showing significant green advantages. However, traditional photocatalysts (such as TiO2, carbon nitride) have a wide bandgap and can only absorb ultraviolet light (accounting for 3%-5% of the solar spectrum), and have a high recombination rate of photo-generated carriers and slow reaction kinetics, resulting in limited practical applications.

[0004] In recent years, covalent organic frameworks (COFs) have become ideal candidate materials in the field of photocatalysis due to their long-range ordered structure, wide light absorption range (visible light region), customizable pores, and functional sites. By integrating functional units such as (diarylamino)benzene, bipyridine, and heptazine, COFs can promote electron transfer and accelerate the activation and decomposition of oxygen, thereby increasing the H2O2 yield. However, existing COF-based photocatalysts still have the following problems: (1) Insufficient microenvironment regulation: The symmetric structure leads to spatial overlap of oxidation and reduction sites, chaotic electron transport paths, and unbalanced reaction kinetics; (2) Complex synthesis process: Often requires toxic solvents, high-temperature conditions, or noble metal catalysts, with low yields and difficulty in scaling up; (3) Stability defects: Some COFs are prone to structural collapse during the photocatalytic cycle, affecting long-term use.

[0005] Therefore, it is of great significance to conduct further research and optimization based on COF-based photocatalysts. In response to the above challenges, the present invention proposes a nitrogen-containing heterocyclic COF-structured photocatalytic material and its preparation method. Optimize the charge separation path; at the same time, the electron-rich characteristics of the nitrogen heterocycle precisely regulate the charge distribution of active sites, enhancing the oxygen molecule adsorption and activation ability. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a preparation method and application of a nitrogen-containing heterocyclic porous covalent organic framework material. By introducing a pyridazine (EQ) unit and phloroglucinol trialdehyde to construct an asymmetric π-conjugated framework, a nitrogen-containing heterocyclic COF material (TP-EQ) is obtained, optimizing the charge separation path, and precisely regulating the charge distribution of active sites by combining the electron-rich characteristics of the nitrogen heterocycle, enhancing the oxygen molecule adsorption and activation ability, thereby significantly improving the efficiency and stability of photocatalytic synthesis of H2O2.

[0007] The technical solution adopted by the present invention is as follows: A preparation method of a nitrogen-containing heterocyclic porous covalent organic framework material, comprising the following steps: S1. Preparation of amine monomer (EQ): 3,6-dibromopyridazine and 4-aminophenylboronic acid pinacol ester are refluxed in a mixed solvent of 1,4-dioxane and water under an inert atmosphere with tetrakis(triphenylphosphine)palladium as a catalyst, adding a basic compound; after the mixture is cooled to room temperature, water is added to the mixture, and the yellow solid is collected by filtration, washed with water and methanol to obtain 4,4'-(pyridazine-3,6-diyl)dianiline, denoted as EQ; S2. Synthesis of TP-EQ: EQ obtained in step S1 and 1,3,5-triformylphloroglucinol (abbreviated as TP) are mixed at a molar ratio of 1-3:1, adding an organic amine catalyst and a mixed solvent, after ultrasonic dispersion and freeze-thaw degassing, reacting at 110-130 °C for 50-80 hours in a sealed environment; the obtained precipitate is washed, Soxhlet extracted and dried to obtain brown powdery TP-EQ.

[0008] Further, in step S1, the molar ratio of 3,6-dibromopyridazine to 4-aminophenylboronic acid pinacol ester is 1:2-6, preferably 1:3-5, and the dosage of tetrakis(triphenylphosphine)palladium is 0.5%-1% of the total molar amount of the reactants.

[0009] Further, in step S1, the mixed solvent is a mixed solution of 1,4-dioxane and water with a volume ratio of 3-6:1, preferably 4-5:1.

[0010] Further, in step S1, the reflux reaction time is 40-50 hours, preferably 42-48 hours.

[0011] Further, in step S1, the reflux reaction temperature is 80-120 °C, preferably 100-110 °C.

[0012] Further, in step S1, the washing is sequentially carried out with water and methanol for 2-5 times, preferably 3-4 times.

[0013] Further, in step S2, the mass ratio of 1,3,5-triformylphloroglucinol to 4,4'-(pyridazine-3,6-diyl)dianiline is 1:1 - 3, preferably 1:1.5 - 2; the organic amine catalyst is one of pyrrolidine, piperidine or tetramethylguanidine.

[0014] Further, in step S2, the mixed solvent is a mixture of n-butanol and 1,4-dioxane with a volume ratio of 1:15 - 25, preferably 1:20 - 22.

[0015] Further, in step S2, the reaction temperature is preferably 110 - 120 °C, and the reaction time is preferably 70 - 80 hours.

[0016] Further, in step S2, the washing is carried out using a polar aprotic solvent or / and an ether solvent. The polar aprotic solvent is N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc), and the ether solvent is tetrahydrofuran (THF) or dioxane. The Soxhlet extraction time is 24 - 72 hours.

[0017] The above nitrogen-containing heterocyclic porous covalent organic framework material is used for photocatalytic synthesis of H2O2 and exhibits excellent photocatalytic activity.

[0018] The beneficial effects of the present invention are as follows: (1) The present invention uses pyridazine (EQ) and 1,3,5-triformylphloroglucinol as monomers to construct a nitrogen-containing heterocyclic COF skeleton, forming an asymmetric π-conjugated structure, inducing a strong built-in electric field, and realizing efficient spatial separation of electrons and holes. At the same time, the electron-rich property of the pyridazine unit optimizes the charge distribution of the active sites and enhances the oxygen molecule adsorption and activation ability.

[0019] (2) The present invention precisely controls the COF layer spacing and pore size through the solvothermal method, provides a confinement effect to enrich reactants, and shortens the mass transfer path.

[0020] (3) The present invention uses green solvents, the reaction conditions are mild, the use of toxic reagents is avoided, and it belongs to a green and environmentally friendly process. Description of the Drawings

[0021] Figure 1 It is the powder X-ray diffraction pattern (PXRD) of the material obtained in Example 1. Visible diffraction peaks appear at 2.8° for both nitrogen-containing heterocyclic COFs, indicating that the material has an ordered periodic porous structure.

[0022] Figure 2 It is the scanning electron microscope (SEM) image of TP-EQ obtained in Example 1. It can be seen that the prepared TP-EQ is a porous granular structure.

[0023] Figure 3The scanning electron microscope (SEM) image of TP-SQ obtained in Comparative Example 1 shows that the prepared TP-SQ is a porous flake structure.

[0024] Figure 4 The Fourier transform infrared spectroscopy (FT–IR) of the material obtained in Example 1 shows an obvious stretching vibration peak of the imine bond at 1628 cm -1 , indicating the successful synthesis of COFs.

[0025] Figure 5 The photocatalytic hydrogen peroxide production activity tests of the materials obtained in Example 1 and Comparative Example 1 show that the average rates of the photocatalytic performance of the prepared TP-EQ under visible light illumination in pure water and seawater are 3336 μmol g -1 h -1 and 3360 μmol g -1 h -1 respectively, indicating its excellent photocatalytic activity. Detailed implementation manners

[0026] 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.

[0027] Example 1 Step 1, Synthesis of 4,4'-(pyridazine-3,6-diyl)dianiline (EQ): 3,6-dibromopyridazine (0.808 g, 3.4 mmol), 4-aminophenylboronic acid pinacol ester (2.235 g, 10.2 mmol), K2CO3 (1.877 g, 13.6 mmol) and Pd(PPh3)4 (196.5 mg, 0.17 mmol). In a round-bottom flask, the reaction system was degassed and then refilled with argon. Then, a mixture of degassed 1,4-dioxane (48 mL) and water (12 mL) was added, and the reaction system was heated at 110 °C for 48 h. After the mixture was cooled to room temperature, water (30 mL) was added to the mixture, and the yellow solid was collected by filtration, washed with water and methanol, and then dried in a desiccator and dried in vacuo for 12 hours to obtain EQ with a yield of 68%.

[0028] Step 2, Synthesis of TP-EQ: Add 15 mg of 1,3,5-triformylphloroglucinol (TP) and 30 mg of EQ into a glass tube, and then add 0.21 mL of pyrrolidine as a catalyst. Then, inject 0.1 mL of n-butanol and 2 mL of 1,4-dioxane into the test tube as solvents. After degassing through a freeze-pump-thaw procedure, the glass tube is flame-sealed and heated at 120 °C for 72 hours. The mixture is filtered and washed several times with DMF, DMAC, and THF in sequence. To completely remove unreacted monomers, catalysts, and other impurities, the raw materials are Soxhlet-extracted with 1,4-dioxane and THF for 48 hours, and finally dried in vacuo for 12 hours to obtain light brown TP-EQ.

[0029] Example 2 Step 1, Synthesis of 4,4'-(pyridazine-3,6-diyl)dianiline (EQ): 3,6-dibromopyridazine (0.808 g, 3.4 mmol), 4-aminophenylboronic acid pinacol ester (2.235 g, 10.2 mmol), K2CO3 (1.877 g, 13.6 mmol), and Pd(PPh3)4 (196.5 mg, 0.17 mmol). In a round-bottom flask, the reaction system is degassed and argon is reinjected. Then, a mixture of degassed 1,4-dioxane (48 mL) and water (12 mL) is added, and the reaction system is heated at 110 °C for 48 h. After the mixture is cooled to room temperature, water (30 mL) is added to the mixture, the yellow solid is collected by filtration, washed with water and methanol, and then dried in a desiccator and dried in vacuo for 12 hours to obtain EQ with a yield of 68%.

[0030] Step 2, Synthesis of TP-EQ: Add 15 mg of 1,3,5-triformylphloroglucinol (TP) and 30 mg of EQ into a glass tube, and then add 0.21 mL of pyrrolidine as a catalyst. Then, inject 0.1 mL of n-butanol and 2 mL of 1,4-dioxane into the test tube as solvents. After degassing through a freeze-pump-thaw procedure, the glass tube is flame-sealed and heated at 130 °C for 80 hours. The mixture is filtered and washed several times with DMF, DMAC, and THF in sequence. To completely remove unreacted monomers, catalysts, and other impurities, the raw materials are Soxhlet-extracted with 1,4-dioxane and THF for 48 hours, and finally dried in vacuo for 12 hours to obtain light brown TP-EQ.

[0031] Example 3 Step 1, Synthesis of 4,4'-(pyridazine-3,6-diyl)dianiline (EQ): 3,6-Dibromopyridazine (0.808 g, 3.4 mmol), 4-aminophenylboronic acid pinacol ester (2.235 g, 10.2 mmol), K2CO3 (1.877 g, 13.6 mmol) and Pd(PPh3)4 (196.5 mg, 0.17 mmol). In a round-bottom flask, the reaction system was degassed and refilled with argon. Then a mixture of degassed 1,4-dioxane (40 mL) and water (20 mL) was added, and the reaction system was heated at 110 °C for 48 h. After the mixture was cooled to room temperature, water (30 mL) was added to the mixture. The yellow solid was collected by filtration, washed with water and methanol, then dried in a desiccator and dried in vacuo for 12 h to obtain EQ with a yield of 68%.

[0032] Step 2, Synthesis of TP-EQ: 15 mg of 1,3,5-triformylphloroglucinol (TP) and 30 mg of EQ were added to a glass tube, and then 0.16 mL of pyrrolidine was added as a catalyst. Then, 0.1 mL of n-butanol and 1.5 mL of 1,4-dioxane were injected into the test tube as solvents. After degassing by a freeze-pump-thaw procedure, the glass tube was flame-sealed and heated at 120 °C for 72 h. The mixture was filtered and washed several times with DMF, DMAC, and THF in sequence. To completely remove unreacted monomers, catalysts, and other impurities, the raw material was Soxhlet-extracted with 1,4-dioxane and THF for 48 h and finally dried in vacuo for 12 h to obtain light brown TP-EQ.

[0033] The materials obtained in the above examples were characterized and tested. Taking Example 1 as a typical representative, the characterization results are described as follows: The powder X-ray diffraction pattern (PXRD) of the material obtained in Example 1 is as Figure 1 shown. It can be seen from Figure 1 that visible diffraction peaks appear at 2.8° for both nitrogen-containing heterocyclic COFs, indicating that the material has an ordered periodic porous structure.

[0034] The scanning electron microscopy (SEM) images of TP-EQ obtained in Example 1 and TP-SQ obtained in Comparative Example 1 are respectively as Figure 2 and Figure 3 shown. It can be seen from Figure 2 that TP-EQ has a porous particulate structure. It can be seen from Figure 3 that TP-SQ has a porous flaky structure.

[0035] The Fourier transform infrared spectrum (FT–IR) of the material obtained in Example 1 is as Figure 4 shown. It can be seen from Figure 4 that at 1628 cm-1 An obvious stretching vibration peak of the imine bond was found, indicating the successful synthesis of COFs.

[0036] Comparative Example 1 Step 1, Synthesis of 4,4'-(1,2,4,5-tetrazine-3,6-diyl)dianiline (SQ): First, 8 g of 4-aminobenzonitrile was dissolved in 25 mL of ethanol. Then, 17 mL of hydrazine hydrate (concentration: 80 wt%) and 4 g of sulfur powder were added. The resulting solution was heated at 90 °C with vigorous stirring for 10 hours. After filtration, it was washed several times with ethanol and acetone. It was dried in a vacuum oven at 60 °C for 12 hours to obtain a bright yellow powder. Then, the bright yellow powder was dispersed in dry dimethyl sulfoxide, stirred, and oxygen was introduced for 12 hours. 150 mL of distilled water was added to this oxidized compound, and a bright red product was precipitated. The filtered and dried red powder was fully oxidized in a 5 wt% H2O2 solution. The red product was separated by centrifugation and dried in vacuo to obtain SQ.

[0037] Step 2, Synthesis of TP-SQ: 11 mg of phloroglucinol trialdehyde and 20 mg of SQ were added to a glass tube, and then 0.16 mL of 6 M HAc aqueous solution as a catalyst was added. Then, 1 mL of 1,4-dioxane and 0.5 mL of mesitylene were injected into the test tube as solvents. After degassing through a freeze-pump-thaw procedure, the glass tube was flame-sealed and heated at 135 °C for 96 h. The mixture was filtered and washed several times with THF and acetone. To completely remove unreacted monomers, catalysts, and other impurities, the raw materials were Soxhlet-extracted with THF and acetone for 48 hours. Finally, it was dried in vacuo for 12 hours to obtain orange TP-SQ.

[0038] The photocatalytic hydrogen peroxide production activities of the materials obtained in Example 1 and Comparative Example 1 were tested as Figure 5 shown by Figure 5 It can be seen that the average rates of hydrogen peroxide production of the prepared TP-EQ under visible light irradiation in pure water and seawater are 3336 μmol g -1 h -1 and 3360 μmol g -1 h -1 respectively, compared with the corresponding values of 1811 μmol g -1 h -1 and 1854 μmol g -1 h -1 of TP-SQ, with the improvement amplitude approaching twice, thus demonstrating the crucial role of the asymmetric π-conjugated structure in TP-EQ for charge separation.

[0039] Comparative Example 2 The rest is the same as in Example 1, except that the volume ratio of n-butanol to 1,4-dioxane is adjusted to 1:10.

[0040] The experimental results show that the crystallinity of COF decreases significantly, and the production rate of hydrogen peroxide H2O2 is 2245 μmol·g -1 ·h -1 , from which it can be seen that the appropriate volume ratio of the mixed solvent is very important for the crystallinity and performance of COF.

[0041] Comparative Example 3 The rest is the same as in Example 1, except that the reaction temperature is raised to 160 °C.

[0042] The experimental results show that the material structure collapses significantly, from which it can be seen that the appropriate reaction temperature is very important.

Claims

1. A preparation method of a nitrogen-containing heterocyclic porous covalent organic framework material, characterized in that, It includes the following steps: S1. Preparation of amine monomer: 3,6-dibromopyridazine and 4-aminophenylboronic acid pinacol ester are refluxed in an inert atmosphere with tetrakis(triphenylphosphine)palladium as a catalyst, adding a basic compound, and in a mixed solvent of 1,4-dioxane and water; after the mixture is cooled to room temperature, water is added to the mixture, and the yellow solid is collected by filtration, washed with water and methanol to obtain 4,4'-(pyridazine-3,6-diyl)dianiline, denoted as EQ. S2. Synthesis of TP-EQ: EQ obtained in step S1 and phloroglucinol trialdehyde are mixed at a molar ratio of 1-3:1, adding an organic amine catalyst and a mixed solvent, after ultrasonic dispersion and freeze-thaw degassing, reacting at 110-130 °C for 50-80 hours in a closed environment; the obtained precipitate is washed, Soxhlet extracted and dried to obtain brown powdered TP-EQ.

2. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, characterized in that, In step S1, the molar ratio of 3,6-dibromopyridazine to 4-aminophenylboronic acid pinacol ester is 1:2-6, and the dosage of tetrakis(triphenylphosphine)palladium is 0.5%-1% of the total molar amount of the reactants.

3. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, wherein, In step S1, the mixed solvent is a mixture of 1,4-dioxane and water with a volume ratio of 3-6:

1.

4. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, characterized in that In step S1, the reflux reaction time is 40-50 hours.

5. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, characterized in that, In step S1, the reflux reaction temperature is 80-120 °C.

6. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, characterized in that, In step S1, the washing is carried out successively with water and methanol for 2-5 times.

7. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, wherein, In step S2, the mass ratio of phloroglucinol trialdehyde to 4,4'-(pyridazine-3,6-diyl)dianiline is 1:1-3; the organic amine catalyst is one of pyrrolidine, piperidine or tetramethylguanidine; the mixed solvent is a mixture of n-butanol and 1,4-dioxane with a volume ratio of 1:15-25.

8. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, characterized in that, In step S2, the reaction temperature is 110-120 °C, and the reaction time is 70-80 hours.

9. The preparation method of the nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, wherein In step S2, the washing is carried out with a polar aprotic solvent or / and an ether solvent, the polar aprotic solvent is N,N-dimethylformamide or N,N-dimethylacetamide, the ether solvent is tetrahydrofuran or 1,4-dioxane, and the Soxhlet extraction time is 24-72 hours.

10. Application of the nitrogen-containing heterocyclic porous covalent organic framework material obtained by the preparation method according to any one of claims 1 to 9 in photocatalytic synthesis of H2O2.

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