Preparation of a Schiff base covalent organic framework material and artificial photosynthesis of urea

Abstract

The present invention relates to the preparation of a Schiff base covalent organic framework material and artificial photosynthesis of urea. The present invention provides a novel covalent organic framework material (TFBD‑PDA‑COF‑R) with confined dynamic active centers, the purpose of which is to solve the problems of low efficiency of photocatalytic synthesis of urea and low visible light utilization rate of existing covalent organic framework materials. Method: 1. Preparation of TFBD‑PDA‑COF raw materials; 2. Preparation of TFBD‑PDA‑COF‑R. The preparation process of the present invention is simple and effective, with low reagent consumption and high yield; and the photocatalyst provided by the present invention can effectively improve the efficiency of photosynthesis of urea. The present invention is applied to the field of photocatalytic synthesis of urea, and experiments have shown that the material has excellent photocatalytic synthesis of urea performance, and the urea yield can reach 107.1μg·g under visible light irradiation. ‑1 .

Description

Technical Field

[0001] The invention relates to the preparation of a Schiff base covalent organic framework material and the photocatalytic synthesis of urea from nitrogen and carbon dioxide. Background Art

[0002] With the growing population, the demand for food is increasing. The use of nitrogen fertilizers has significantly fueled the rapid development of modern agriculture, with approximately 27% of global agricultural production relying on nitrogen fertilizers. Urea, a widely used high-nitrogen fertilizer, accounts for approximately 66% of global nitrogen fertilizer use. my country, a major grain producer, consumes approximately 55 million tons of urea annually. Therefore, developing the urea industry is crucial for meeting this growing food demand. Traditional urea synthesis typically requires two reactions: ① N₂ + H₂ → NH₃; and ② NH₃ + CO₂ → CO(NH₂)₂. These two reactions must be carried out under high temperature (150–200°C) and high pressure (15–25 MPa), consuming significant amounts of energy and causing a range of environmental problems. Photocatalytic technology, which can directly utilize free and clean solar energy, is considered an ideal strategy for addressing energy crises and environmental challenges.

[0003] Covalent organic frameworks (COFs) are porous crystalline materials composed of light elements such as carbon, boron, oxygen, nitrogen, and silicon linked by covalent bonds. They possess advantages such as light weight, low density, high specific surface area, regular structure, uniform pores, relatively stable structure, and ease of functionalization. These advantages make COFs highly promising for applications in a variety of fields, including gas storage and separation, catalysis, sensing, energy storage, and photoelectric conversion. Schiff base COFs possess superior visible light absorption, maximizing their utilization. Therefore, the use of Schiff base COFs for photocatalytic reactions is feasible. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of photocatalytic synthesis of urea with existing materials and to provide a preparation method of Schiff base covalent organic framework material and the application of photocatalytic synthesis of urea.

[0005] The preparation method of a Schiff base covalent organic framework material of the present invention is completed by the following steps:

[0006] 1. Preparation of TFBD-PDA-COF material: 3,3',5,5'-tetraformyl-4,4'-dihydroxybiphenyl and p-phenylenediamine were added to a heat-resistant glass tube, followed by a mixed solution of 1,4-dioxane and mesitylene. The mixture was ultrasonically treated at an ultrasonic frequency of 40 kHz for 30 to 35 minutes. Acetic acid solution was added and degassed by three freeze-thaw cycles in a liquid nitrogen bath. The mixture was sealed and heated at 80 to 120°C for 72 to 120 hours. The mixture was filtered, washed several times with tetrahydrofuran, and then vacuum-dried for 12 hours to obtain the TFBD-PDA-COF material.

[0007] 2. Add the dried TFBD-PDA-COF material, trans-4-fluoro-L-proline and anhydrous potassium carbonate into a round-bottom flask, and then add N,N-dimethylformamide solution. Circulate nitrogen three times, adjust the temperature to 80-100°C, and reflux the reactants with stirring for 36 hours. After the mixture is cooled, wash it with N,N-dimethylformamide and ethanol, collect the solid product, and dry it in a vacuum oven at 120°C for later use.

[0008] The masses of 3,3',5,5'-tetraformyl-4,4'-dihydroxybiphenyl and p-phenylenediamine described in step 1 are 14-29.8 mg and 12-21.6 mg, respectively;

[0009] The molar ratio of 3,3',5,5'-tetraformyl-4,4'-dihydroxybiphenyl and p-phenylenediamine in step 1 is 1:2;

[0010] The mass ratio of TFBD-PDA-COF material and trans-4-fluoro-L-proline in step 2 is 1.66:1;

[0011] The volume ratio of 1,4-dioxane and mesitylene in step 1 is 1:1;

[0012] The concentration of acetic acid used in step 1 is 1 mol·L -1 ;

[0013] After sealing as described in step 1, heat at 120°C for 72h;

[0014] The masses of the TFBD-PDA-COF material, trans-4-fluoro-L-proline, and anhydrous potassium carbonate described in step 2 are 22.1 mg, 13.3 mg, and 30 mg, respectively;

[0015] The volume concentration of N,N-dimethylformamide in step 2 is 10 ml;

[0016] The temperature in step 2 is regulated to 80°C;

[0017] The mixture was dried under vacuum at 120°C for 72 h as described in step 2;

[0018] Beneficial effects of the present invention:

[0019] The present invention uses a solvothermal method to successfully synthesize the TFBD-PDA-COF material using 3,3',5,5'-tetraformyl-4,4'-dihydroxybiphenyl and p-phenylenediamine as raw materials. However, the material has poor visible light absorption capacity and does not have the ability to photosynthesize urea. Therefore, the present invention combines TFBD-PDA-COF with trans-4-fluoro-L-proline Williamson synthesis reaction to synthesize a new COF material TFBD-PDA-COF-R (covalent organic framework material functionalized after synthesis). This material realizes CN coupling of nitrogen and carbon dioxide, which can effectively solve the difficulties of poor charge separation performance of semiconductors and the difficulty of N2 and CO2 molecules to chemically adsorb on the catalyst surface, thereby greatly improving the activity of artificial photosynthesis reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Figure 2 X-ray powder diffraction patterns of TFBD-PDA-COF and TFBD-PDA-COF-R materials, respectively;

[0021] Figure 3 Figure 4 The infrared spectra of TFBD-PDA-COF and TFBD-PDA-COF-R materials;

[0022] Figure 5 Performance diagram of photocatalytic synthesis of urea by TFBD-PDA-COF and TFBD-PDA-COF-R materials. DETAILED DESCRIPTION

[0023] The present invention is further described below with reference to examples. These examples are merely for illustrating the method of the present invention and have no limitation on the scope of application of the present invention.

[0024] Example 1: The preparation of a TFBD-PDA-COF-R material of this embodiment is completed by the following steps:

[0025] I. Preparation of TFBD-PDA-COF: p-phenylenediamine (PDA: 32.4 mg, 0.15 mmol), TFBD (44.7 mg, 0.075 mmol), mesitylene (1.5 ml), and 1,4-dioxane (1.5 ml) were added sequentially to a 10 mL Schlenk tube. The mixture was sonicated for 20 minutes before the addition of 0.5 ml of 1 M aqueous acetic acid. The mixture was then freeze-degassing-thawed in a liquid nitrogen bath three times. After natural thawing, the mixture was reacted at 120°C for three days. After cooling, the precipitate was collected by filtration, extracted with tetrahydrofuran for 12 hours, dried, and then soaked in acetone for 48 hours, with the acetone replaced several times. Finally, the mixture was dried under vacuum at 120°C for 12 hours.

[0026] Preparation of TFBD-PDA-COF-R: The dried TFBD-PDA-COF material (22.1 mg), trans-4-fluoro-L-proline (13.3 mg), and anhydrous potassium carbonate (30 mg) were added to a round-bottom flask, followed by N,N-dimethylformamide solution (10 mL). Nitrogen was circulated three times, and the temperature was adjusted to 80-100°C. The reactants were stirred under reflux for 36 h. After the mixture cooled, it was washed with N,N-dimethylformamide and ethanol. The solid product was collected and dried in a vacuum oven at 120°C for 24 h. The sample was then set aside.

[0027] The following tests were performed to verify the beneficial effects of the present invention:

[0028] In order to investigate the photocatalytic synthesis of urea by TFBD-PDA-COF and TFBD-PDA-COF-R materials, their visible light photocatalytic synthesis of urea performance was tested according to the following method. The test process is as follows: TFBD-PDA-COF and TFBD-PDA-COF-R (10 mg) were used as photocatalysts, deionized water was used as the reaction liquid, and ultrasonicated for 30 minutes to form a uniform suspension. The suspension was poured into the reactor and a mixed gas (CO2:N2=15%:85%) was introduced for 30 minutes to exhaust the air in the reactor. A xenon lamp was then used as the light source. After 30 minutes of illumination, the reaction suspension was taken and the catalyst was filtered out with a 1 mL needle with a filter and the liquid was collected. The collected 1 ml of the test liquid was added with 1 ml of diacetyl monoxime solution and 2 ml of ferric acid solution, mixed thoroughly, and ultrasonicated for 1 minute. The mixture was heated in an oven at 100°C and maintained for 15 minutes. Figure 5 As shown in Figure 2, the photocatalytic efficiency of TFBD-PDA-COF in synthesizing urea under visible light is low, only 0.0032 mg·g -1 TFBD-PDA-COF-R material showed good performance in photocatalytic synthesis of urea, with a photocatalytic efficiency of 0.1071 mg·g -1 .

Claims

1. A method for preparing a Schiff base covalent organic framework material, characterized in that The preparation method is carried out according to the following steps: Step 1, preparation of TFBD-PDA-COF material: 3,3',5,5'-tetraformyl-4,4'-dihydroxybiphenyl and p-phenylenediamine were added to a heat-resistant glass tube, followed by a mixed solution of 1,4-dioxane and mesitylene, and ultrasonically treated at an ultrasonic frequency of 40 kHz for 30 to 35 minutes. Acetic acid solution was added and degassed by freeze-thaw cycles three times in a liquid nitrogen bath. After sealing, the mixture was heated at 80 to 120°C for 72 to 120 hours, filtered, washed several times with tetrahydrofuran, and vacuum dried for 12 hours to obtain TFBD-PDA-COF material; Step 2: Add the dried TFBD-PDA-COF material, trans-4-fluoro-L-proline and anhydrous potassium carbonate to a round-bottom flask, then add N,N-dimethylformamide solution, circulate nitrogen three times, adjust the temperature to 80~100℃, reflux and stir the reactants for 36 hours, and after the mixture is cooled, wash with N,N-dimethylformamide and ethanol, collect the solid product, dry it in a vacuum oven at 120℃, and set aside for later use.

2. The method for preparing a Schiff base covalent organic framework material according to claim 1, characterized in that The masses of the TFBD-PDA-COF material, trans-4-fluoro-L-proline, and anhydrous potassium carbonate described in step 2 are 22.1 mg, 13.3 mg, and 30 mg, respectively.

3. The method for preparing a Schiff base covalent organic framework material according to claim 1, characterized in that The mass ratio of the TFBD-PDA-COF material to trans-4-fluoro-L-proline in step 2 is 1.66:

1.

4. The method for preparing a Schiff base covalent organic framework material according to claim 1, characterized in that The volume of N,N-dimethylformamide in step 2 is 10 ml.

5. The method for preparing a Schiff base covalent organic framework material according to claim 1, characterized in that In step 2, the temperature is regulated to 80°C.

6. The method for preparing a Schiff base covalent organic framework material according to claim 1, characterized in that In step 2, the product was dried in vacuum at 120°C for 72 h.

7. Use of a Schiff base covalent organic framework material according to any one of claims 1 to 6 in photocatalytic synthesis of urea.

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