A copper single-atom anchored covalent organic framework material, its preparation method and application

Abstract

The present invention discloses a copper single atom anchored covalent organic framework material and its preparation method and application, which relates to the field of functional material technology. The preparation method of the copper single atom anchored covalent organic framework material of the present invention comprises: dispersing the covalent organic framework and a copper-containing metal salt in an organic solvent, and heating and refluxing the mixture under a protective gas atmosphere to obtain the covalent organic framework material. The copper single atom anchored covalent organic framework material of the present invention has excellent visible light response, high carrier mobility, and more reactive sites exposed on the surface, so that it has a strong absorption capacity for visible light, exhibits efficient photocatalytic carbon dioxide reduction performance and extremely high product selectivity, and has the advantage of simple synthesis steps, and has a wider application prospect in carbon dioxide conversion. The application of the copper single atom anchored covalent organic framework material of the present invention as a photocatalyst in carbon dioxide conversion has a carbon monoxide yield of up to 15.2 μmol / g / h and a selectivity of up to 97.3%.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and in particular to a single-atom copper-anchored covalent organic framework material, a preparation method thereof, and applications thereof. Background Art

[0002] Excessive carbon dioxide emissions have caused irreversible harm to the global environment, such as the greenhouse effect, climate anomalies, sea level rise, and marine ecological damage. Efficient carbon dioxide conversion will simultaneously alleviate the two major global challenges of environment and energy. Artificial photosynthesis for photocatalytic carbon dioxide reduction is a promising approach due to its inherent advantages. The design and construction of photocatalysts is a key factor in achieving efficient carbon dioxide conversion, involving a series of complex processes such as light capture, separation and transfer of photogenerated carriers, adsorption and activation of carbon dioxide, and redox reactions on the catalyst surface. Therefore, the ideal photocatalyst must meet both the thermodynamic and kinetic conditions for carbon dioxide conversion.

[0003] Covalent organic frameworks (COFs) have attracted the interest of researchers due to their tunable molecular or electronic structures, band gap adjustment through control of different monomers, and excellent visible light response. The π-conjugated stacking structure provides unique properties for the separation and transport of photocarriers, enhancing their photocatalytic performance. In the field of photocatalytic CO2 conversion, COFs with excellent photocatalytic activity have emerged as promising candidates. However, COFs themselves still have shortcomings. For example, most COF catalysts have a small number of unclear active sites, which significantly affects the separation and transport of charge carriers, limiting their photocatalytic activity and significantly restricting their CO2 conversion performance under visible light. Summary of the Invention

[0004] The present invention provides a copper single-atom anchored covalent organic framework material, a preparation method, and an application thereof. The covalent organic framework material of the present invention has a sea urchin-like micromorphology, excellent visible light response, fast carrier mobility, and abundant catalytic active sites, enabling it to have a high carbon dioxide conversion efficiency.

[0005] The present invention can specifically adopt the following technical solutions:

[0006] One of the purposes of the present invention is to provide a copper single atom anchored covalent organic framework material, wherein the covalent organic framework material is a COFs topological structure having a minimum structural unit as shown in the following formula (I);

[0007]

[0008] Wherein, R1 is at least one of -NH2, -NH-, and -N=C-; R2 is at least one of -Cl, -NO3, -I, and acetylacetonate; the wavy line structure indicates that it continues to be specifically connected with the wavy line structure shown in formula (I) in a topological structure to extend infinitely.

[0009] In a preferred embodiment of the present invention:

[0010] The covalent organic framework material is a sea urchin-like or multi-level layered structure, wherein the sea urchin-like structure is a spherical central surface with needle-like or nanowire-like structures. Preferably, the particle size of the covalent organic framework material is 200-1000 nm. The sea urchin-like or multi-level layered covalent organic framework material of the present invention can have a larger specific surface area and more reactive sites; and / or,

[0011] The loading amount of copper atoms in the covalent organic framework material is 0.1 to 5 wt%.

[0012] A second object of the present invention is to provide a method for preparing a copper single atom-anchored covalent organic framework material as described in one of the objects of the present invention, the method comprising:

[0013] The covalent organic framework and the copper-containing metal salt are dispersed in an organic solvent, and heated under a protective gas atmosphere for reflux reaction to prepare the covalent organic framework material.

[0014] The following solutions can be adopted:

[0015] The covalent organic framework and copper-containing metal salt are uniformly dispersed in an organic solvent, and a protective gas (such as argon or nitrogen) is introduced. The solution is refluxed overnight under heating conditions. After the reaction is completed, the solution is centrifuged and washed, for example, with water and ethanol 2 to 5 times, respectively. The solution is then dried under vacuum at 50 to 70°C to obtain a covalent organic framework material in which copper atoms are anchored by nitrogen and nitrogen-coordination. The present invention employs a simple gas-protected reflux method to anchor copper atoms to the covalent organic framework by nitrogen and nitrogen-coordination. The copper atoms are evenly distributed, stable, and not prone to overflow, which plays a crucial role in improving the efficiency of photocatalytic carbon dioxide conversion.

[0016] In a preferred embodiment of the present invention:

[0017] The mass ratio of the copper atoms in the copper-containing metal salt to the covalent organic framework is (0.001-0.05):1, preferably (0.005-0.02):1;

[0018] The amount of the organic solvent used is not particularly limited, as long as it can evenly disperse the covalent organic framework and the copper-containing metal salt. Those skilled in the art can adjust the amount according to actual needs.

[0019] In a preferred embodiment of the present invention, the covalent organic framework is prepared by the following method:

[0020] The covalent organic framework is prepared by a solution method by adding 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,6-pyridinedicarboxaldehyde in a reaction reagent. The covalent organic framework is prepared by a simple room temperature solution method through a Schiff base condensation reaction.

[0021] In a preferred embodiment of the present invention:

[0022] The molar ratio of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to 2,6-pyridinedicarboxaldehyde is (0.4-2):1, preferably (0.5-0.8):1;

[0023] The amount of the reaction reagent is not particularly limited, as long as it can disperse and dissolve 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,6-pyridinedicarboxaldehyde to ensure that the solution method can proceed smoothly. Those skilled in the art can make adaptive adjustments according to actual needs.

[0024] In a preferred embodiment of the present invention:

[0025] The reaction reagent is a mixture of mesitylene and 1,4-dioxane, preferably, the volume ratio of mesitylene to 1,4-dioxane is (1-10):1, more preferably (2-5):1; and / or,

[0026] The reaction temperature of the solution method is 5 to 40° C. (room temperature), and / or the reaction time is 48 to 72 hours.

[0027] In a preferred embodiment of the present invention:

[0028] After the solution method reaction is completed, the covalent organic framework powder is obtained by washing, for example, using acetone, methanol, ether, and tetrahydrofuran for multiple times, drying, for example, vacuum drying at 50-70° C., and grinding.

[0029] In a preferred embodiment of the present invention:

[0030] The copper-containing metal salt is at least one of copper chloride, copper nitrate, copper acetylacetonate, copper sulfate, and copper iodide; and / or,

[0031] The organic solvent is at least one of ethanol, methanol, isopropanol, and N,N-dimethylformamide.

[0032] In a preferred embodiment of the present invention:

[0033] The reaction temperature of the heating reflux reaction is 30 to 80° C., preferably 40 to 60° C., and / or the reaction time is 5 to 20 hours, preferably 10 to 16 hours.

[0034] The third object of the present invention is to provide a copper single atom anchored covalent organic framework material as described in one of the objects of the present invention or a copper single atom anchored covalent organic framework material prepared by the method described in the second object of the present invention as a photocatalyst in the field of carbon cycle and clean energy production, preferably in carbon dioxide conversion.

[0035] Since copper atoms have good electrical conductivity and strong carbon dioxide adsorption and conversion capabilities, the introduction of copper atoms enables the covalent organic framework material of the present invention to have a strong adsorption capacity for carbon dioxide. In addition, the covalent organic framework material of the present invention has a suitable band gap and good electrical conductivity, which can greatly improve the photocatalytic carbon dioxide conversion performance and product selectivity.

[0036] Furthermore, the carbon dioxide adsorption and reaction active sites on the surface of semiconductor photocatalytic materials contribute to improved carbon dioxide conversion performance. Therefore, the present invention introduces more copper single-atom sites as active sites on the surface of the covalent organic framework and anchors the copper single atoms to improve its carbon dioxide conversion efficiency.

[0037] The copper single-atom-anchored covalent organic framework material of the present invention has excellent visible light response, high carrier mobility, and more exposed reactive sites on the surface, resulting in strong visible light absorption. It exhibits efficient photocatalytic carbon dioxide reduction performance and extremely high product selectivity. Furthermore, it has the advantage of a simple synthesis step, which has broad application prospects in carbon dioxide conversion. The use of the copper single-atom-anchored covalent organic framework material of the present invention as a photocatalyst in carbon dioxide conversion has achieved a carbon monoxide yield of up to 15.2 μmol / g / h and a selectivity of up to 97.3%.

[0038] Compared with the prior art, the present invention has at least the following beneficial effects:

[0039] 1. The preparation method of the copper single atom anchored covalent organic framework material of the present invention is simple, the raw materials are readily available, and the operation is simple, which is very critical for industrial application.

[0040] 2. In the present invention, by controlling the structure of the covalent organic framework, a sea urchin-shaped covalent organic framework is prepared, which can increase its specific surface area and active sites, thereby facilitating improved photocatalytic carbon dioxide conversion efficiency; copper single atoms are anchored to the covalent organic framework through pyridinic nitrogen sites, making them firmly and stably attached and less likely to overflow; the introduction of copper single atoms can significantly improve the electron transfer efficiency and carbon dioxide adsorption capacity, and can improve the covalent organic framework's utilization of visible light, thereby improving the photocatalytic carbon dioxide conversion efficiency and product selectivity.

[0041] 3. The copper single-atom anchored covalent organic framework material of the present invention is a high-performance photocatalyst with high efficiency and good stability in photocatalytic carbon dioxide conversion, which facilitates the recovery and reuse of the photocatalyst. It can be applied in carbon recycling and clean energy production, such as in photocatalytic carbon dioxide conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a SEM image of the covalent organic framework of Example 1 of the present invention;

[0043] Figure 2 TEM image of the covalent organic framework of Example 1 of the present invention;

[0044] Depend on Figure 1 and 2 It can be seen that the covalent organic framework exhibits a sea urchin-like structure;

[0045] Figure 3 This is an SEM image of the copper single atom anchored covalent organic framework material of Example 1 of the present invention;

[0046] Figure 4 This is a TEM image of the copper single atom anchored covalent organic framework material of Example 1 of the present invention;

[0047] Depend on Figure 3 and 4 It can be seen that the material still maintains the sea urchin-like structure after anchoring the copper single atoms;

[0048] Figure 5 This is a spherical aberration corrected transmission electron microscopy image of the copper single atom anchored covalent organic framework material of Example 1 of the present invention.

[0049] Depend on Figure 5 It can be clearly seen that the copper single atom (red circle in the figure) has been successfully modified onto the surface of the covalent organic framework, forming a copper single atom-anchored covalent organic framework structure;

[0050] Figure 6This is a graph showing the yield of the copper single-atom-anchored covalent organic framework material and the covalent organic framework photocatalytically converting carbon dioxide into carbon monoxide and methane according to Example 1 of the present invention. The yields of the products are calculated by gas chromatography testing;

[0051] Figure 7 This is a graph showing the selectivity results of the copper single-atom-anchored covalent organic framework material and the covalent organic framework photocatalytic conversion of carbon dioxide to carbon monoxide in Example 1 of the present invention. The calculation formula is: carbon monoxide selectivity = carbon monoxide production / (carbon monoxide production + methane production) × %. DETAILED DESCRIPTION

[0052] The following is a further description of specific embodiments of the present invention in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0053] The raw materials used in the embodiments of the present invention are all commercially available products, and their specific information is shown in Table 1 below:

[0054] Table 1

[0055]

[0056]

[0057] Example 1

[0058] 1. Preparation of Covalent Organic Framework Materials

[0059] 0.75 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1.125 mmol of 2,6-pyridinedicarboxaldehyde were added to 4.5 mL of mesitylene and 4.5 mL of 1,4-dioxane solvent, and the mixture was reacted at room temperature (25°C) for 48 hours. The mixture was washed with tetrahydrofuran and centrifuged several times to obtain a covalent organic framework.

[0060] 2. Preparation of Covalent Organic Framework Materials Anchored by Copper Single Atoms

[0061] The above 30 mg of covalent organic framework powder was ground into fine powder and 0.6 mg of copper-containing metal salt copper chloride (containing 0.3 mg of copper atoms) was dispersed into 30 ml of ethanol solution, ultrasonicated for 10 minutes to make it evenly dispersed, and stirred at 60°C for 12 hours under argon protection. After the reaction, the product was centrifuged and then washed three times with water and ethanol respectively, and finally dried in a vacuum oven at 60°C to obtain a covalent organic framework material with a pyridine nitrogen structure connected by an imine bond anchored by a copper single atom. The specific structure is shown in the above formula (I), wherein R1 is -N=C-, R2 is -Cl, the copper single atom is fixed at the pyridine nitrogen structure, and the copper single atom loading is 1 wt%.

[0062] Example 2

[0063] 1. Preparation of Covalent Organic Framework Materials

[0064] 0.5 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1.125 mmol of 2,6-pyridinedicarboxaldehyde were added to 9 mL of mesitylene and 4.5 mL of 1,4-dioxane solvent, and the mixture was reacted at room temperature (10°C) for 60 hours. The mixture was washed several times with ethanol to obtain a covalent organic framework.

[0065] 2. Preparation of Covalent Organic Framework Materials Anchored by Copper Single Atoms

[0066] The above 30 mg of covalent organic framework powder was ground into fine powder and 2.4 mg of copper-containing metal salt copper acetylacetonate (containing 0.6 mg of copper atoms) was dispersed into 50 ml of isopropanol solution, ultrasonicated for 10 minutes to make it evenly dispersed, and stirred at 30°C under nitrogen protection for 6 hours. After the reaction, the product was centrifuged and then washed three times with water and methanol respectively, and finally dried in a vacuum oven at 60°C to obtain a covalent organic framework material with a pyridine nitrogen structure connected by an imine bond anchored by a copper single atom. The specific structure is shown in the above formula (I), wherein R1 is -N=C-, R2 is an acetylacetonate group, the copper single atom is fixed at the pyridine nitrogen structure, and the copper single atom loading is 2 wt%.

[0067] Example 3

[0068] 1. Preparation of Covalent Organic Framework Materials

[0069] 2 mmol of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1.125 mmol of 2,6-pyridinedicarboxaldehyde were added to 20 mL of mesitylene and 4.5 mL of 1,4-dioxane solvent, and the mixture was reacted at room temperature (35°C) for 72 hours. The mixture was washed several times with tetrahydrofuran to obtain a covalent organic framework.

[0070] 2. Preparation of Covalent Organic Framework Materials Anchored by Copper Single Atoms

[0071] The above 30 mg of covalent organic framework powder was ground into fine powder and 3.5 mg of copper-containing metal salt copper nitrate (containing 1.2 mg of copper atoms) was dispersed into a mixed solution of 70 ml of methanol and ethanol, wherein the methanol and ethanol were 35 mL respectively. Ultrasonic treatment was carried out for 10 minutes to make the dispersion uniform. The mixture was stirred at 80 ° C for 20 hours under argon protection. After the reaction was completed, the product was centrifuged and then washed three times with water and ethanol respectively. Finally, it was dried in a vacuum oven at 60 ° C to obtain a covalent organic framework material with a pyridine nitrogen structure connected by an imine bond anchored by a copper single atom. The specific structure is shown in the above formula (I), wherein R1 is -N=C-, R2 is -NO3, the copper single atom is fixed at the pyridine nitrogen structure, and the copper single atom loading is 4 wt%.

[0072] The copper single atom anchored covalent organic framework material and the covalent organic framework prepared in Example 1 were used as samples to perform photocatalytic carbon dioxide conversion tests, respectively. The specific test methods are as follows:

[0073] Take 10 mg of sample and add it to a mixed solution of 4 ml of deionized water, 2 ml of triethanolamine, and 6 ml of acetonitrile. Mix well and put it into a photocatalytic reactor. Wrap it with tin foil to avoid light for half an hour, then pass condensed water through it, turn on the xenon lamp light source, and start the photocatalytic reaction.

[0074] The test results are as follows Figure 6 and 7 As shown in the figure, it can be seen that the efficiency of catalytic carbon dioxide conversion of the copper single atom anchored covalent organic framework material is significantly better than that of the original covalent organic framework, up to 15.2 μmol / g / h; and it has a higher product selectivity, with a selectivity of up to 97.3%.

[0075] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations to these embodiments may be made without departing from the principles and spirit of the present invention, and these changes and modifications still fall within the scope of protection of the present invention.

Claims

1. A copper single atom anchored covalent organic framework material, wherein the covalent organic framework material is a COFs topological structure having a minimum structural unit as shown in the following formula (I); in, R1 is at least one of -NH2 and -N=C-; R2 is at least one of -Cl, -NO3, -I, and acetylacetonato; the wavy structure indicates that it continues to be specifically connected with the wavy structure shown in formula (I) in a topological structure to extend infinitely; The covalent organic framework material is in the shape of a sea urchin; The loading amount of copper atoms in the covalent organic framework material is 1 to 5 wt%; The preparation method of the covalent organic framework material comprises: Dispersing a covalent organic framework and a copper-containing metal salt in an organic solvent, and heating under reflux reaction in a protective gas atmosphere to obtain the covalent organic framework material; The covalent organic framework is prepared by the following method: The covalent organic framework is prepared by a solution method using 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,6-pyridinedicarboxaldehyde in a reaction reagent; The reaction reagent is a mixture of mesitylene and 1,4-dioxane, and the volume ratio of mesitylene to 1,4-dioxane is (1-10):1; The reaction temperature of the solution method is 5 to 40° C., and the reaction time is 48 to 72 hours.

2. The covalent organic framework material according to claim 1, characterized in that: The particle size of the covalent organic framework material is 200-1000 nm.

3. A method for preparing a copper single atom anchored covalent organic framework material according to claim 1 or 2, the method comprising: The mass ratio of the copper atoms in the copper-containing metal salt to the covalent organic framework is (0.001-0.05):

1.

4. The method according to claim 3, wherein: The molar ratio of the 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to 2,6-pyridinedicarboxaldehyde is (0.4-2):

1.

5. The method according to claim 3, wherein: The copper-containing metal salt is at least one of copper chloride, copper nitrate, copper acetylacetonate, copper sulfate, and copper iodide; and / or, The organic solvent is at least one of ethanol, methanol, isopropanol, and N,N-dimethylformamide.

6. The method according to claim 3, wherein: The reaction temperature of the heating reflux reaction is 30 to 80° C., and / or the reaction time is 5 to 20 hours.

7. Use of a copper single atom anchored covalent organic framework material as claimed in claim 1 or 2, or a copper single atom anchored covalent organic framework material prepared by the method according to any one of claims 3 to 6 as a photocatalyst in the fields of carbon cycle and clean energy production.

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