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

Abstract

The present invention discloses a preparation method and application of a nitrogen-containing heterocyclic porous covalent organic framework material. First, trialdehyde phloroglucinol and a nitrogen-containing heterocyclic monomer are mixed in a certain mass ratio, an organic catalyst and a mixed solvent are added, the mixture is sealed after degassing, synthesized by solvent thermal reaction, and then washed with a polar solvent, purified by Soxhlet extraction and dried to obtain a nitrogen-containing heterocyclic porous covalent organic framework material. The method uses pyridazine units and trialdehyde phloroglucinol as monomers to construct a nitrogen-containing heterocyclic COF skeleton, forming an asymmetric π-conjugated structure, achieving efficient electron-hole spatial separation, and the electron-rich characteristics of the pyridazine unit optimize the charge distribution of the active site, thereby enhancing the adsorption and activation ability of oxygen molecules. The present invention adopts green solvents, has mild reaction conditions, avoids the use of toxic reagents, conforms to green environmental protection, and provides a new approach for the photocatalytic synthesis of hydrogen peroxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor photocatalytic materials, and in particular 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 chemical synthesis, wastewater treatment, metallurgy, electronics, and energy storage, with a rapidly growing global market. However, current industrial synthesis relies primarily on the energy-intensive anthraquinone process, which not only consumes significant amounts of energy but also produces large amounts of hazardous waste, resulting in severe environmental pollution. Furthermore, due to slow recombination rates and reaction kinetics, current H2O2 photosynthetic yields are insufficient to meet industrial demand. Therefore, the development of green and efficient production methods is urgently needed.

[0003] Photocatalytic production of H2O2 is an environmentally friendly alternative technology. It uses water and oxygen as raw materials, driven by sunlight, to mimic the natural photosynthesis process. Compared with traditional methods, photocatalytic H2O2 synthesis offers significant green advantages due to its low energy consumption and lack of byproducts. However, conventional photocatalysts (such as TiO2 and carbon nitride) have limited practical applications due to their wide band gaps, limited absorption of ultraviolet light (3%-5% of the solar spectrum), high recombination rates of photogenerated carriers, and slow reaction kinetics.

[0004] In recent years, covalent organic frameworks (COFs) have become promising candidates for photocatalysis due to their long-range ordered structure, broad light absorption range (visible light region), customizable pores, and functional sites. By integrating functional units such as (diarylamino)benzenes, bipyridines, and heptazine, COFs can promote electron transfer and accelerate the activation and decomposition of oxygen, thereby increasing H2O2 yield. However, existing COF-based photocatalysts still face the following challenges:

[0005] (1) Insufficient microenvironmental regulation: The symmetrical structure leads to spatial overlap of oxidation and reduction sites, disordered electron transfer pathways, and unbalanced reaction kinetics;

[0006] (2) Complex synthesis process: often requires toxic solvents, high temperature conditions or precious metal catalysts, low yield and difficult to scale up;

[0007] (3) Stability defects: Some COFs are prone to structural collapse during the photocatalytic cycle, affecting long-term use.

[0008] Therefore, further research and optimization of COF-based photocatalysts is of paramount importance. To address these challenges, this paper proposes a nitrogen-containing heterocyclic COF-structured photocatalytic material and its preparation method. This optimizes the charge separation pathway; at the same time, the electron-rich nature of the nitrogen heterocycle precisely regulates the charge distribution at the active site, enhancing oxygen adsorption and activation. Summary of the Invention

[0009] To address the above technical issues, the present invention provides a method for preparing and applying a nitrogen-containing heterocyclic porous covalent organic framework material. By introducing pyridazine (EQ) units and trialdehyde phloroglucinol to construct an asymmetric π-conjugated framework, the present invention produces a nitrogen-containing heterocyclic COF material (TP-EQ). This optimizes the charge separation pathway and, by leveraging the electron-rich properties of the nitrogen heterocycle, precisely regulates the charge distribution at the active sites, enhancing oxygen molecule adsorption and activation, thereby significantly improving the efficiency and stability of photocatalytic H2O2 synthesis.

[0010] The technical solution adopted in the present invention is:

[0011] A method for preparing a nitrogen-containing heterocyclic porous covalent organic framework material comprises the following steps:

[0012] S1. Preparation of amine monomer (EQ): 3,6-dibromopyridazine and 4-aminophenylboronic acid pinacol ester are reacted under an inert atmosphere with tetrakis(triphenylphosphine)palladium as a catalyst, and a basic compound is added. The reaction is refluxed 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 and washed with water and methanol to obtain 4,4'-(pyridazine-3,6-diyl)diphenylamine, denoted as EQ.

[0013] S2. Synthesis of TP-EQ: The EQ obtained in step S1 is mixed with 1,3,5-triformylphloroglucinol (TP) at a molar ratio of 1-3:1. An organic amine catalyst and a mixed solvent are added. After ultrasonic dispersion and freeze-thaw degassing, the mixture is reacted in a closed environment at 110-130°C for 50-80 hours. The resulting precipitate is washed, Soxhlet extracted, and dried to obtain TP-EQ as a brown powder.

[0014] Furthermore, 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 amount of tetrakis(triphenylphosphine)palladium used is 0.5%-1% of the total molar amount of the reactants.

[0015] Furthermore, in step S1, the mixed solvent is a mixture of 1,4-dioxane and water in a volume ratio of 3-6:1, preferably 4-5:1.

[0016] Furthermore, in step S1, the reflux reaction time is 40-50 hours, preferably 42-48 hours.

[0017] Furthermore, in step S1, the temperature of the reflux reaction is 80-120°C, preferably 100-110°C.

[0018] Furthermore, in step S1, washing is performed sequentially with water and methanol for 2-5 times, preferably 3-4 times.

[0019] Furthermore, in step S2, the mass ratio of 1,3,5-trialdehyde phloroglucinol to 4,4'-(pyridazine-3,6-diyl)diphenylamine is 1:1-3, preferably 1:1.5-2; and the organic amine catalyst is one of pyrrolidine, piperidine or tetramethylguanidine.

[0020] Furthermore, in step S2, the mixed solvent is a mixture of n-butanol and 1,4-dioxane in a volume ratio of 1:15-25, preferably 1:20-22.

[0021] Furthermore, in step S2, the reaction temperature is preferably 110-120° C., and the reaction time is preferably 70-80 hours.

[0022] Furthermore, in step S2, washing is performed using a polar aprotic solvent and / or an ether solvent, the polar aprotic solvent is N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc), the ether solvent is tetrahydrofuran (THF) or dioxane, and the Soxhlet extraction time is 24-72 hours.

[0023] The above-mentioned nitrogen-containing heterocyclic porous covalent organic framework material is used for photocatalytic synthesis of H2O2 and exhibits excellent photocatalytic activity.

[0024] The beneficial effects of the present invention are:

[0025] (1) The present invention uses pyridazine (EQ) and 1,3,5-trialdehyde phloroglucinol as monomers to construct a nitrogen-containing heterocyclic COF skeleton, forming an asymmetric π-conjugated structure, inducing a strong built-in electric field and achieving efficient spatial separation of electrons and holes. At the same time, the electron-rich properties of the pyridazine unit optimize the charge distribution of the active site, enhancing the adsorption and activation of oxygen molecules.

[0026] (2) The present invention uses a solvothermal method to precisely control the COF interlayer spacing and pore size, providing a confinement effect to enrich reactants and shorten the mass transfer path.

[0027] (3) The present invention uses green solvents and mild reaction conditions, avoiding the use of toxic reagents, and is a green and environmentally friendly process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the powder X-ray diffraction pattern (PXRD) of the material obtained in Example 1. Both nitrogen-containing heterocyclic COFs show visible diffraction peaks at 2.8°, indicating that the material has an ordered periodic porous structure.

[0029] Figure 2This is a scanning electron microscope (SEM) image of the TP-EQ obtained in Example 1. It can be seen that the prepared TP-EQ has a porous granular structure.

[0030] Figure 3 This is a scanning electron microscope (SEM) image of the TP-SQ obtained in Comparative Example 1. It can be seen that the prepared TP-SQ has a porous sheet structure.

[0031] Figure 4 This is the Fourier transform infrared spectrum (FT-IR) of the material obtained in Example 1. -1 Obvious stretching vibration peaks of imine bonds were found at , indicating that COFs were successfully synthesized.

[0032] Figure 5 The photocatalytic hydrogen peroxide production activity of the materials obtained in Example 1 and Comparative Example 1 was tested. The average photocatalytic rates of the prepared TP-EQ under visible light irradiation in pure water and seawater were 3336 μmol g -1 h -1 and 3360 μmol g -1 h -1 , which exhibits excellent photocatalytic activity. DETAILED DESCRIPTION

[0033] 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.

[0034] Example 1

[0035] Step 1, Synthesis of 4,4'-(pyridazine-3,6-diyl)diphenylamine (EQ):

[0036] 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) were added to a round-bottom flask. The reaction system was degassed and refilled with argon. A degassed mixture of 1,4-dioxane (48 mL) and water (12 mL) was then 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, and then dried in a desiccator under vacuum for 12 h to obtain EQ in a 68% yield.

[0037] Step 2, synthesis of TP-EQ:

[0038] A glass tube was charged with 15 mg of 1,3,5-trialdehyde phloroglucinol (TP) and 30 mg of EQ, followed by 0.21 mL of pyrrolidine as a catalyst. Subsequently, 0.1 mL of n-butanol and 2 mL of 1,4-dioxane were injected into the test tube as solvents. After degassing via a freeze-pump-thaw cycle, the glass tube was flame-sealed and heated at 120°C for 72 hours. The mixture was filtered and washed several times with DMF, DMAC, and THF. To completely remove unreacted monomer, catalyst, and other impurities, the raw material was Soxhlet extracted with 1,4-dioxane and THF for 48 hours and finally dried under vacuum for 12 hours to obtain light brown TP-EQ.

[0039] Example 2

[0040] Step 1, Synthesis of 4,4'-(pyridazine-3,6-diyl)diphenylamine (EQ):

[0041] 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) were added to a round-bottom flask. The reaction system was degassed and refilled with argon. A degassed mixture of 1,4-dioxane (48 mL) and water (12 mL) was then 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, and then dried in a desiccator under vacuum for 12 h to obtain EQ in a 68% yield.

[0042] Step 2, synthesis of TP-EQ:

[0043] A glass tube was charged with 15 mg of 1,3,5-trialdehyde phloroglucinol (TP) and 30 mg of EQ, followed by 0.21 mL of pyrrolidine as a catalyst. Subsequently, 0.1 mL of n-butanol and 2 mL of 1,4-dioxane were injected into the test tube as solvents. After degassing via a freeze-pump-thaw cycle, the glass tube was flame-sealed and heated at 130°C for 80 hours. The mixture was filtered and washed several times with DMF, DMAC, and THF. To completely remove unreacted monomer, catalyst, and other impurities, the raw material was Soxhlet extracted with 1,4-dioxane and THF for 48 hours and finally dried under vacuum for 12 hours to obtain light brown TP-EQ.

[0044] Example 3

[0045] Step 1, Synthesis of 4,4'-(pyridazine-3,6-diyl)diphenylamine (EQ):

[0046] 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) were added to a round-bottom flask. The reaction system was degassed and refilled with argon. A degassed mixture of 1,4-dioxane (40 mL) and water (20 mL) was then 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, and then dried in a desiccator under vacuum for 12 h to obtain EQ in a 68% yield.

[0047] Step 2, synthesis of TP-EQ:

[0048] A glass tube was charged with 15 mg of 1,3,5-trialdehyde phloroglucinol (TP) and 30 mg of EQ, followed by 0.16 mL of pyrrolidine as a catalyst. Subsequently, 0.1 mL of n-butanol and 1.5 mL of 1,4-dioxane were added to the test tube as solvents. After degassing via a freeze-pump-thaw cycle, the tube was flame-sealed and heated at 120°C for 72 hours. The mixture was filtered and washed several times with DMF, DMAC, and THF. To completely remove unreacted monomer, catalyst, and other impurities, the raw material was Soxhlet extracted with 1,4-dioxane and THF for 48 hours and finally dried under vacuum for 12 hours to obtain light brown TP-EQ.

[0049] The materials obtained in the above examples were characterized and tested, with Example 1 being a typical example. The characterization results are described as follows:

[0050] The powder X-ray diffraction pattern (PXRD) of the material obtained in Example 1 is as follows: Figure 1 As shown by Figure 1 It can be seen that both nitrogen-containing heterocyclic COFs have visible diffraction peaks at 2.8°, indicating that the materials have an ordered periodic porous structure.

[0051] The scanning electron microscope (SEM) images of TP-EQ obtained in Example 1 and TP-SQ obtained in Comparative Example 1 are shown as follows: Figure 2 and Figure 3 As shown by Figure 2 It can be seen that TP-EQ is a porous granular structure. Figure 3 It can be seen that TP-SQ has a porous sheet structure.

[0052] The Fourier transform infrared spectrum (FT-IR) of the material obtained in Example 1 is as follows: Figure 4 As shown by Figure 4 It can be seen that at 1628cm -1 Obvious stretching vibration peaks of imine bonds were found at , indicating that COFs were successfully synthesized.

[0053] Comparative Example 1

[0054] Step 1, Synthesis of 4,4'-(1,2,4,5-tetrazine-3,6-diyl)diphenylamine (SQ):

[0055] First, 8 g of p-aminobenzonitrile was dissolved in 25 mL of ethanol. Then, 17 mL of hydrazine hydrate (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, the solution was washed several times with ethanol and acetone. It was then dried in a vacuum oven at 60°C for 12 hours to obtain a bright yellow powder. This bright yellow powder was then dispersed in dry dimethyl sulfoxide (DMSO), stirred, and bubbled with oxygen for 12 hours. 150 mL of distilled water was added to this oxidized compound, precipitating a bright red product. The filtered and dried red powder was then dispersed in a 5 wt% H2O2 solution for full oxidation. The red product was isolated by centrifugation and dried in vacuo to yield SQ.

[0056] Step 2, synthesis of TP-SQ:

[0057] To a glass tube, 11 mg of trialdehyde phloroglucinol and 20 mg of SQ were added, followed by the catalyst (0.16 mL of 6MHAc aqueous solution). Subsequently, 1 mL of 1,4-dioxane and 0.5 mL of mesitylene were added to the test tube as solvent. After degassing via a freeze-pump-thaw cycle, the tube was flame-sealed and incubated at 135°C for 96 hours. The mixture was filtered and washed several times with THF and acetone. To completely remove unreacted monomer, catalyst, and other impurities, the raw material was subjected to Soxhlet extraction with THF and acetone for 48 hours. Finally, it was dried under vacuum for 12 hours to obtain orange TP-SQ.

[0058] The photocatalytic hydrogen peroxide production activity of the materials obtained in Example 1 and Comparative Example 1 was tested as follows: Figure 5 As shown by Figure 5 It can be seen that the average hydrogen peroxide production rates of the prepared TP-EQ in pure water and seawater under visible light are 3336 μmol g -1 h -1 and 3360 μmol g -1 h -1 , compared with the corresponding value of 1811 μmol g for TP-SQ -1 h-1 and 1854 μmol g -1 h -1 The improvement is nearly doubled, thus the asymmetric π-conjugated structure in TP-EQ plays a key role in charge separation.

[0059] Comparative Example 2

[0060] The rest is the same as Example 1, except that the volume ratio of n-butanol to 1,4-dioxane is adjusted to 1:10.

[0061] The experimental results show that the COF crystallinity decreased significantly and the hydrogen peroxide H2O2 production rate was 2245 μmol·g -1 ·h -1 , it can be seen that the appropriate volume ratio of mixed solvents is very important for the crystallinity and performance of COF.

[0062] Comparative Example 3

[0063] The rest is the same as Example 1, except that the reaction temperature is increased to 160°C.

[0064] The experimental results show that the material structure has obviously collapsed, which shows that the appropriate reaction temperature is very important.

Claims

1. A method for preparing a nitrogen-containing heterocyclic porous covalent organic framework material, characterized in that: The steps include: S1. Preparation of an amine monomer: 3,6-dibromopyridazine and 4-aminophenylboronic acid pinacol ester are reacted under an inert atmosphere with tetrakis(triphenylphosphine)palladium as a catalyst, and a basic compound is added. The reaction is refluxed 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 and washed with water and methanol to obtain 4,4'-(pyridazine-3,6-diyl)diphenylamine, denoted as EQ. S2. Synthesis of TP-EQ: EQ obtained in step S1 is mixed with 1,3,5-triformylphloroglucinol at a molar ratio of 1-3:1, an organic amine catalyst and a mixed solvent are added, and after ultrasonic dispersion and freeze-thaw degassing, the mixture is reacted in a sealed environment at 110-130°C for 50-80 hours. The resulting precipitate is washed, Soxhlet extracted, and dried to obtain TP-EQ as a brown powder. In step S1, the molar ratio of 3,6-dibromopyridazine to 4-aminophenylboronic acid pinacol ester is 1:2-6, and the amount of tetrakis(triphenylphosphine)palladium used is 0.5%-1% of the total molar amount of the reactants; In step S1, the mixed solvent is a mixture of 1,4-dioxane and water in a volume ratio of 3-6:1; In step S2, the mass ratio of 1,3,5-trialdehyde phloroglucinol to 4,4'-(pyridazine-3,6-diyl)diphenylamine is 1:1-3; the organic amine catalyst is pyrrolidine; and the mixed solvent is a mixture of n-butanol and 1,4-dioxane in a volume ratio of 1:15-25.

2. The method for preparing a 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.

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

4. The method for preparing a nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, characterized in that: In step S1, washing is performed sequentially with water and methanol for 2-5 times.

5. The method for preparing a 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.

6. The method for preparing a nitrogen-containing heterocyclic porous covalent organic framework material according to claim 1, characterized in that: In step S2, washing is performed using a polar aprotic solvent and / or an ether solvent. The polar aprotic solvent is N,N-dimethylformamide or N,N-dimethylacetamide. The ether solvent is tetrahydrofuran or dioxane. The Soxhlet extraction time is 24-72 hours.

7. Use of the nitrogen-containing heterocyclic porous covalent organic framework material obtained by the preparation method according to any one of claims 1 to 6 in the photocatalytic synthesis of H2O2.

Images