Preparation and use of a bimetallic covalent organic framework material

Abstract

The application belongs to the field of covalent organic framework materials, and particularly relates to synthesis of a compound, a covalent organic framework material containing bimetal units, a preparation method and use thereof. The structural unit belongs to a hexagonal crystal system P3 space group, and cell parameters are alpha=90°, beta=90°, gamma=120°. Due to the uniqueness of the material structure, the material can be used as a photocatalyst, and can directly perform a gas-liquid catalytic reaction under visible light driving to reduce carbon dioxide into carbon monoxide, with a yield of 320 micromoles per gram ‑1 , and an average of 64 micromoles per gram ‑1 h ‑1 per hour.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework materials, specifically relating to the synthesis of a novel chemical compound and the preparation of a covalent organic framework material containing a bimetallic structure, as well as its application in photocatalytic gas-liquid carbon dioxide reduction.

[0002] In recent years, the excessive combustion of traditional fossil fuels has led to a continuous increase in atmospheric CO2 concentration. The resulting environmental pollution and climate change have threatened human survival and development. In 2022, global energy-related carbon dioxide emissions reached a new high of over 36.8 billion tons, an increase of 321 million tons (0.9%) over the previous year, seriously threatening human survival. Converting CO2 into carbon resources for energy recycling is the best way to solve energy shortages and environmental problems. Developing environmentally friendly new technologies to reduce CO2 levels is imperative. Among the technologies currently being explored, photocatalytic CO2 reduction technology, based on the mimicry of photosynthesis in green plants, uses solar energy to convert CO2 and H2O into fuels such as CO and CH4, and is considered one of the potential strategies for solving the energy crisis and environmental pollution. However, the low conversion efficiency severely limits the practical application of photocatalytic CO2 reduction; therefore, designing high-performance photocatalysts is currently a research hotspot.

[0003] In photocatalytic reactions, the active sites of the catalyst are crucial for the CO2 adsorption process. However, under normal temperature and pressure conditions, the active sites of the photocatalyst cannot achieve high-density contact with CO2, leading to a slow adsorption process and delaying the entire catalytic process. Therefore, improving the catalytic ability of photocatalysts can be achieved by enhancing their CO2 adsorption capacity. Currently, the method to improve adsorption capacity is to construct porous materials. Covalent organic frameworks (COFs), as crystalline porous materials, are classic examples due to their large specific surface area and tunable crystalline structure. COFs are a class of structurally stable crystalline porous framework materials developed after MOFs. They are two-dimensional or three-dimensional porous structures constructed by the orderly connection of organic molecules through strong covalent bonds (C=N, CN, C=C, etc.). As crystalline porous materials, COFs have outstanding specific surface area and gas adsorption capacity. COFs also have the significant advantage of high stability under water, organic solvents, and acidic / alkaline conditions. Furthermore, metal sites with strong adsorption capacity and high catalytic activity can be constructed simultaneously by introducing metal ions. In addition, two-dimensional (2D) COFs are mostly composed of rigidly conjugated monomers, possessing a large planar conjugated system and strong interlayer π-π interactions. These intralayer and interlayer conjugation interactions are beneficial for charge transport and the absorption of visible light. Currently, COFs have become a new class of visible light-responsive catalysts. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synthesizing a novel compound and preparing a material containing a bimetallic covalent organic framework, and its application in photocatalytic gas-solid carbon dioxide reduction.

[0005] The technical solution adopted in this invention is as follows:

[0006] A covalent organic framework material containing a bimetallic structure, characterized in that the structural unit belongs to the hexagonal crystal system, space group P3, and the unit cell parameters are... α=90°, β=90°, γ=120.

[0007] The method for synthesizing the novel compound described above is characterized by the following steps: (1) 2,4,6-3 (p-hydroxyphenyl)triazine, hexamethylenetetramine and trifluoroacetic acid are added to a round-bottom flask at one time, heated to reflux at 100-120°C, and after reacting for 10-12 hours, hydrolyzed with glacial acetic acid.

[0008] The crude product obtained in step (1) was filtered and washed repeatedly with water, tetrahydrofuran, ethanol and acetone until the filtrate was colorless. After evaporating the solvent in a vacuum drying oven at 100-120°C for 48-120 hours, a novel compound in yellow solid form was obtained.

[0009] In step (1), 2,4,6-tris(p-hydroxyphenyl)triazine and hexamethylenetetramine are weighed out, and the ratio of the two monomers is 1:6 to 1:8.

[0010] The volume of trifluoroacetic acid weighed in step (1) is 20-40 mL.

[0011] The concentration of glacial acetic acid weighed in step (1) is 7–9 mol / L. -1 Add 20-40 mL of glacial acetic acid.

[0012] The preparation method of the bimetallic covalent organic framework material described above is characterized by including the following steps:

[0013] (2) 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-formylphenyl)benzene, cyclohexanediamine, zinc acetate, trimethylbenzene and dioxane were added sequentially to a Pyrex tube. After sonication for 3 hours, an aqueous acetic acid solution was added, and liquid nitrogen freezing degassing was performed three times to achieve a vacuum oxygen-free condition for the reaction system. After the Pyrex tube was naturally thawed after the degassing operation, it was placed in an oven and heated at 100-170°C for the reaction. After 72-120 hours, the oven was turned off and the tube was allowed to cool naturally to room temperature.

[0014] The crude product obtained in step (2) was filtered and washed repeatedly with N,N-dimethylformamide and ethanol until the filtrate was colorless. Solvent exchange was performed using methanol and acetone, and the solvent was evaporated in a vacuum drying oven at 100–150°C for 24–72 hours to obtain a yellow powdery covalent organic framework material based on a double-Salen structure.

[0015] In step (2), the molar ratio of 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-formylphenyl)benzene, cyclohexanediamine, and zinc acetate is 1:3:3 to 1:5:5.

[0016] In step (2), trimethylbenzene and dioxane with a molar ratio of 1:2 to 2:1 are placed in a tube.

[0017] The concentration of acetic acid in step (2) is 3–6 mol / L. -1 The volume of acetic acid added is 0.2 to 0.5 mL.

[0018] The beneficial effects of this invention are:

[0019] Based on the design of the double Salen structure, bimetallic structures are introduced in situ to prepare covalent organic frameworks with bimetallic structures. Due to the synergistic effect of the bimetallic structures and the uniqueness of the material structure, they can be used as photocatalysts to carry out gas-liquid photocatalytic reactions to reduce carbon dioxide to carbon monoxide. Attached Figure Description

[0020] Figure 1 Synthesis route diagram of specific embodiment 1 of the present invention;

[0021] Figure 2 The nuclear magnetic resonance spectrum of specific embodiment 1 of the present invention;

[0022] Figure 3 Synthesis route diagram of specific embodiment 2 of the present invention;

[0023] Figure 4 XRD diffraction pattern of specific embodiment 2 of the present invention;

[0024] Figure 5 Infrared spectrum of specific embodiment 2 of the present invention;

[0025] Figure 6 Photocatalytic gas-liquid carbon dioxide reduction performance diagram of specific embodiment 2 of the present invention. Detailed implementation method:

[0026] The present invention will be further described in detail below with reference to embodiments:

[0027] A covalent organic framework material containing a bimetallic structure, characterized in that the structural unit belongs to the hexagonal crystal system, space group P3, and the unit cell parameters are... α=90°, β=90°, γ=120°.

[0028] The method for synthesizing the novel compound described above is characterized by the following steps: (1) 2,4,6-3 (p-hydroxyphenyl)triazine, hexamethylenetetramine and trifluoroacetic acid are added to a round-bottom flask at one time, heated to reflux at 100-120°C, and after reacting for 10-12 hours, hydrolyzed with glacial acetic acid.

[0029] The crude product obtained in step (1) was filtered and washed repeatedly with water, tetrahydrofuran, ethanol and acetone until the filtrate was colorless. After evaporating the solvent in a vacuum drying oven at 100-120°C for 48-120 hours, a novel compound in yellow solid form was obtained.

[0030] In step (1), 2,4,6-tris(p-hydroxyphenyl)triazine and hexamethylenetetramine are weighed out, and the ratio of the two monomers is 1:6 to 1:8.

[0031] The volume of trifluoroacetic acid weighed in step (1) is 20-40 mL.

[0032] The concentration of glacial acetic acid weighed in step (1) is 7–9 mol / L. -1 Add 20-40 mL of glacial acetic acid.

[0033] The preparation method of the bimetallic covalent organic framework material described above is characterized by including the following steps:

[0034] (2) 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-formylphenyl)benzene, cyclohexanediamine, zinc acetate, trimethylbenzene and dioxane were added sequentially to a Pyrex tube. After sonication for 3 hours, an aqueous acetic acid solution was added, and liquid nitrogen freezing degassing was performed three times to achieve a vacuum oxygen-free condition for the reaction system. After the Pyrex tube was naturally thawed after the degassing operation, it was placed in an oven and heated at 100-170°C for the reaction. After 72-120 hours, the oven was turned off and the tube was allowed to cool naturally to room temperature.

[0035] The crude product obtained in step (2) was filtered and washed repeatedly with N,N-dimethylformamide and ethanol until the filtrate was colorless. Solvent exchange was performed using methanol and acetone, and the solvent was evaporated in a vacuum drying oven at 100–150°C for 24–72 hours to obtain a yellow powdery covalent organic framework material based on a bimetallic structure.

[0036] In step (2), the molar ratio of 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-formylphenyl)benzene, cyclohexanediamine, and zinc acetate is 1:3:3 to 1:5:5.

[0037] In step (2), trimethylbenzene and dioxane with a molar ratio of 1:2 to 2:1 are placed in a tube.

[0038] The concentration of acetic acid in step (2) is 3–6 mol / L. -1 The volume of acetic acid added is 0.2 to 0.5 mL.

[0039] The present invention is described in more detail in the following embodiments, but these embodiments do not constitute a limitation of the invention. Specific embodiments:

[0040] 1 g of 2,4,6-tris(p-hydroxyphenyl)triazine, 2 g of hexamethylenetetramine, and 30 mL of trifluoroacetic acid were added all at once to a round-bottom flask. The mixture was subjected to five liquid nitrogen cryogenic degassing cycles to establish a vacuum-free, oxygen-free reaction system. The degassed round-bottom flask was then placed in an oil bath and heated to reflux at 110 °C. After reacting for 10 hours, the mixture was drained using 30 mL of 8 mol / L... -1 Hydrolysis was performed using glacial acetic acid. After natural cooling, the solid was filtered. The filtered solid product was washed repeatedly with water, tetrahydrofuran, ethanol, and acetone until the filtrate was colorless. The solvent was evaporated by placing the filtrate in a vacuum drying oven at 100°C for 72 hours, yielding 0.2 g of the novel compound.

[0041] Its nuclear magnetic resonance (NMR) is as follows Figure 2 As shown in the figure, the peaks representing hydroxyl, aldehyde, and benzene rings can be clearly seen. The peak areas show that the ratio of hydroxyl H, aldehyde H, and benzene ring H is 1:2:2, which proves that the structure of the synthesized 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-dialdehyde)benzene is correct.

[0042] 0.02618 g of 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-dialdehyde)benzene, 0.01715 g of cyclohexanediamine, 0.0400 g of zinc acetate, 1.5 ml of trimethylbenzene, and 1.5 ml of dioxane were sequentially added to a Pyrex tube. After sonicating at room temperature for three hours, 0.2–0.5 mL of a solution with a concentration of 3–6 mol / L was added using a pipette. -1 An aqueous solution of acetic acid was prepared, and the reaction system underwent three liquid nitrogen cryogenic degassing operations to achieve a vacuum oxygen-free condition. After natural thawing, the degassed Pyrex tubes were placed in an oven and heated to 120–150°C for 72–120 hours. The oven was then closed, allowing the tubes to cool naturally to room temperature. The solid product was filtered and washed repeatedly with tetrahydrofuran and methanol until the filtrate was colorless. After solvent exchange with acetone, the solid powder was placed in a vacuum drying oven at 100°C for 48 hours to evaporate the solvent, yielding 0.0215 g of a covalent organic framework material containing a bimetallic structure.

[0043] The XRD patterns of the product and the XRD patterns of the product powder simulated by AA packing are as follows: Figure 4 As shown, the peaks at 3.62°, 7.44°, and 26.47° correspond to the 100, 200, and 001 crystal planes, respectively. From... Figure 4 As can be seen, the peak shapes of the experimental and simulated spectra match perfectly, indicating that the obtained product is a covalent organic framework material containing a bimetallic structure. Its infrared spectrum is as follows: Figure 5 As shown in the figure, the obtained product is at 1658 cm⁻¹. -1 The C=O peak (of the monomer) disappears at 1638 cm⁻¹. -1 There is a strong absorption nearby, corresponding to C=N, indicating that the two monomers underwent a condensation reaction.

[0044] The photocatalytic performance test results of the product for reducing carbon dioxide in gas and liquid phases are shown in the figure below. Figure 6 10 ml of water, 40 g of acetonitrile, and 0.010 g of a covalent organic framework material with a bimetallic structure were ultrasonically homogenized and placed in a gas-liquid reactor. After continuously bubbling pure carbon dioxide for a period of time, the light source was turned on to carry out a photocatalytic reaction. The yield of the reduction product, carbon monoxide, reached as high as 320 μmol g after 5 hours. -1 64 μmol g per hour on average -1 .

Claims

1. A covalent organic framework material containing a bimetallic structure, the repeating unit of its chemical structure shown in Figure 2, characterized in that... The structural unit belongs to the hexagonal crystal system, space group P3, and its unit cell parameters are... , α=90°, β=90°, γ=120°, 。 Figure 2 2. A method for preparing a covalent organic framework material containing a bimetallic structure as described in claim 1, characterized in that, The preparation method includes the following steps: (1) 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-formylphenyl)benzene, cyclohexanediamine, zinc acetate, trimethylbenzene and dioxane are added sequentially to a Pyrex tube, ultrasonicated for 3 hours, and then an aqueous acetic acid solution is added. The tube is then subjected to three liquid nitrogen freezing degassing operations to achieve a vacuum oxygen-free condition for the reaction system. After the Pyrex tube has been naturally thawed, it is placed in an oven and heated at 100-170°C for reaction. After 72-120 hours, the oven is turned off and allowed to cool naturally to room temperature. The crude product obtained in step (1) is filtered and washed multiple times with N,N-dimethylformamide and ethanol until the filtrate is colorless. Methanol and acetone are used for solvent exchange, and the solvent is evaporated in a vacuum drying oven at 100-150°C for 24-72 hours to obtain a yellow powdery covalent organic framework material based on a bimetallic structure.

3. The method for preparing a covalent organic framework material containing a bimetallic structure according to claim 2, characterized in that, In step (1), the molar ratio of 1,3,5-triazine-2,4,6-tris(4'-hydroxy-3',5'-formylphenyl)benzene, cyclohexanediamine, and zinc acetate is 1:3:3 to 1:5:

5.

4. The method for preparing a covalent organic framework material containing a bimetallic structure according to claim 2, characterized in that, In step (1), trimethylbenzene and dioxane with a molar ratio of 1:2 to 2:1 are placed in a tube.

5. The method for preparing a covalent organic framework material containing a bimetallic structure according to claim 2, characterized in that, The concentration of acetic acid in step (1) is 3-6 mol / L, and the volume of acetic acid added is 0.2-0.5 mL.

6. The bimetallic covalent organic framework material according to claim 1, due to the uniqueness of its structure, can be used as a photocatalyst to perform gas-liquid photocatalytic reactions, reducing carbon dioxide to carbon monoxide.

Images