Covalent organic framework material, transition metal complex and covalent organic framework composite photocatalytic material and application

Abstract

The invention belongs to the field of photocatalytic organic synthesis of new energy materials, and discloses a covalent organic framework material, a transition metal complex and covalent organic framework composite photocatalytic material and application. The covalent organic framework material is a covalent organic framework material connected by imine bonds and synthesized by 4, 4 ', 4' ', 4 '''-(benzo [1, 2-d: 4, 5-d '] bis (oxazole)-2, 4, 6, 8-tetrayl) tetraphenylamine and an aldehyde group-containing monomer in the presence of a first solvent and a catalyst by adopting a solvothermal method. The covalent organic framework material disclosed by the invention exerts the characteristic of being beneficial to light energy absorption, forms a unique metal coordination environment while improving light responsiveness, and is beneficial to efficient photocatalysis of carbon dioxide reduction under the synergistic effect of doping the material into metal ions.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalytic organic synthesis new energy materials, and more specifically, relates to a covalent organic framework material and a transition metal complex@covalent organic framework composite photocatalytic material and application thereof. Background Art

[0002] As the world's overall industrial level continues to improve, the environmental pollution caused by the development and utilization of traditional fossil energy has become more and more serious. Reducing greenhouse gas emissions and controlling climate change have become the consensus of the international community. Covalent organic frameworks (COFs) have been widely synthesized and used as potential catalysts for artificial photosynthesis and photocatalysis. With the characteristics of adjustable synthesis and post-modification of structure, they have become a popular material for energy-saving and carbon reduction technologies by designing and optimizing catalytic centers and promoting efficient electron transfer in photocatalytic systems.

[0003] Therefore, it is urgent to propose a new type of covalent organic framework material. Summary of the invention

[0004] The purpose of the present invention is to provide a covalent organic framework material and a transition metal complex @ covalent organic framework composite photocatalytic material and application. The covalent organic framework material of the present invention has the characteristics of being conducive to light energy absorption, improving the light responsiveness, and forming a unique metal coordination environment, which is conducive to the synergistic effect of metal ions incorporating into the material for efficient photocatalytic carbon dioxide reduction.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a covalent organic framework material, which is a covalent organic framework material connected by imine bonds (i.e., benzoxazolyl covalent organic framework material BBO-COF) synthesized by a solvothermal method from 4,4',4",4"'-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine and an aldehyde-containing monomer under the conditions of a first solvent and a catalyst.

[0006] According to the present invention, preferably, the molar concentration ratio of the 4,4',4",4''-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine and the aldehyde group-containing monomer is (0.8-1.2):(1.5-2.5).

[0007] According to the present invention, preferably, the aldehyde-containing monomer is at least one of 5,5'-dialdehyde-2,2'-bipyridine, terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde, 2,5-diethyl-1,4-terephthalaldehyde, 3,3'-bipyridine-6,6'-dicarboxaldehyde, 4,4'-biphenyldicarboxaldehyde, 2,2'-bipyridine-4,4'-dicarboxaldehyde, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, 2,2'-bipyridine-6,6'-dicarboxaldehyde, 4,4'-([2,2'-bipyridine]-5,5'-diyl)dibenzaldehyde and 1,10-phenanthroline-3,8-dicarboxaldehyde.

[0008] According to the present invention, preferably, the first solvent is selected from at least one of chloroform, 1,3,5-trimethylbenzene, 1,4-dioxane, carbon tetrachloride and dichloromethane.

[0009] According to the present invention, preferably, the catalyst is an aqueous acetic acid solution, the concentration of the aqueous acetic acid solution is 0.1-8 mol / L, and the ratio of the added volume of the aqueous acetic acid solution to the total solution volume of the solvothermal synthesis system is (1-3):10.

[0010] In the present invention, the total solution of the solvothermal synthesis system includes 4,4',4",4"'-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine, an aldehyde-containing monomer, a first solvent and an acetic acid aqueous solution.

[0011] According to the present invention, preferably, the method for preparing the covalent organic framework material comprises:

[0012] S1: mixing the 4,4',4",4"'-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine, the aldehyde group-containing monomer, the first solvent and the catalyst and performing ultrasonic treatment to obtain a mixed uniform solution;

[0013] S2: Degassing and sealing the equipment containing the mixed uniform solution in step S1 with liquid nitrogen;

[0014] S3: subjecting the mixed uniform solution in the device after the treatment in step S2 to a solvothermal reaction to obtain a precipitate, washing and vacuum drying the precipitate to obtain the covalent organic framework material.

[0015] In the present invention, in step S2: the liquid nitrogen degassing and sealing treatment includes: sequentially performing liquid nitrogen freezing, vacuuming and thawing on the equipment containing the mixed uniform solution of step S1, and after 3-4 cycles, using an alcohol burner to seal the equipment containing the mixed uniform solution of step S1.

[0016] According to the present invention, preferably, in step S3:

[0017] The temperature of the solvent thermal reaction is 90-125° C. and the time is 48-96 hours. The present invention utilizes the solvent thermal method to prepare the benzoxazolyl covalent organic framework material BBO-COF under mild conditions.

[0018] The washing solvent used for washing is at least one of N,N-dimethylformamide, pure water, anhydrous ethanol and acetone;

[0019] The vacuum drying temperature is 55-125°C and the time is 10-16h.

[0020] The second aspect of the present invention provides a transition metal complex @ covalent organic framework composite photocatalytic material, wherein the composite photocatalytic material is prepared by a coordination reaction between a covalent organic framework material and a transition metal salt under a second solvent condition;

[0021] The covalent organic framework material is the above-mentioned covalent organic framework material.

[0022] According to the present invention, preferably, the transition metal salt is at least one of ferric chloride, cobalt acetate, nickel acetate, zinc sulfate and copper sulfate.

[0023] According to the present invention, preferably, the concentration of the transition metal salt in the total solution of the coordination reaction system before the coordination reaction is performed is 1-5 mg / mL.

[0024] In the present invention, the total solution of the coordination reaction system includes a covalent organic framework material, a transition metal salt and a second solvent.

[0025] According to the present invention, preferably, the second solvent is a mixture of ethanol and water, wherein the volume ratio of anhydrous ethanol to water is (1-3):1.

[0026] According to the present invention, preferably, the usage ratio of the covalent organic framework material to the second solvent is (1-5): (0.1-10) g / L.

[0027] According to the present invention, preferably, the coordination reaction is carried out at a temperature of 65-125° C. and for a time of 12-36 h.

[0028] According to the present invention, preferably, the preparation method of the transition metal complex @ covalent organic framework composite photocatalytic material (a post-functional modification method, in which a transition metal is modified on a covalent organic framework material to obtain a transition metal complex @ covalent organic framework composite photocatalytic material) comprises:

[0029] (1) mixing the covalent organic framework material, the transition metal salt and the second solvent and subjecting the mixture to ultrasonic treatment to obtain a uniform solution;

[0030] (2) The uniform solution of the system is subjected to coordination reaction under stirring conditions to obtain a product, and the product is washed and vacuum dried to obtain the transition metal complex@covalent organic framework composite photocatalytic material.

[0031] According to the present invention, preferably, in step (2):

[0032] The washing solvent used for washing is at least one of anhydrous ethanol, chloroform, tetrahydrofuran, acetone and deionized water;

[0033] The vacuum drying temperature is 55-80°C and the time is 10-16h.

[0034] The third aspect of the present invention provides the use of the transition metal complex@covalent organic framework composite photocatalytic material in photocatalytic carbon dioxide.

[0035] According to the present invention, preferably, the method for photocatalyzing carbon dioxide comprises:

[0036] The photocatalyst is mixed with a third solvent, a photosensitizer, a sacrificial agent and water and subjected to ultrasonic treatment to obtain a photocatalytic reaction system solution;

[0037] The photocatalytic reaction system solution is contacted with carbon dioxide under sealed conditions and light irradiation to perform a photocatalytic reaction to obtain a reaction gas containing carbon monoxide;

[0038] The photocatalyst is the above-mentioned transition metal complex@covalent organic framework composite photocatalytic material.

[0039] In the present invention, in the method for photocatalytic carbon dioxide generation, the photocatalytic reaction system solution selectively reduces CO2 to CO, and also reduces H2O in the photocatalytic reaction system solution to generate H2.

[0040] According to the present invention, preferably, the photosensitizer is tris(2,2'-bipyridyl)ruthenium(II) chloride.

[0041] According to the present invention, preferably, the sacrificial agent is at least one of triethanolamine, methanol, ethanol, lactic acid and sodium persulfate.

[0042] According to the present invention, preferably, the third solvent is acetonitrile (for dissolving carbon dioxide).

[0043] According to the present invention, preferably, the usage ratio of the transition metal complex@covalent organic framework composite photocatalytic material, the third solvent, the photosensitizer, the sacrificial agent and water is (0.8-1.2):(5-7):(3-5):(1-3):(1-3) g / L / g / L / L.

[0044] According to the present invention, preferably, the light source of the illumination is a 250-350W xenon lamp, and the illumination time is 4.5-5.5h.

[0045] The beneficial effects of the technical solution of the present invention are as follows:

[0046] The present invention studies a novel benzoxaazole-based covalent organic framework material. The material uses 4,4',4",4"'-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine as a fixed donor building unit and different aldehyde-containing monomers as acceptor building units to form an electron donor-acceptor structure. The conjugated system of the benzoxaazole structure is beneficial to light energy absorption, and while improving the light responsiveness, a unique metal coordination environment is formed, which is beneficial to the synergistic effect of metal ions incorporated into the material for efficient photocatalytic carbon dioxide reduction.

[0047] The benzoxazolyl covalent organic framework material prepared by the present invention is connected by imine bonds formed by condensation of aldehyde groups and amine groups, and has good solvent stability and thermal stability. The benzoxazolyl covalent organic framework material prepared by the present invention can be further treated with metal salt coordination to obtain a transition metal complex @ covalent organic framework composite photocatalytic material. The covalent organic framework material of the present invention is an asymmetric covalent organic framework material containing benzoxazolyl groups. The asymmetric structural units containing benzoxazolyl groups and the adjusted metal coordination environment enable the material to exhibit strong photocatalytic activity (specifically, the introduction of asymmetric structural units containing benzoxazolyl groups in the material structure design and the adjustment of the transition metal coordination environment play a crucial role in improving the photocatalytic performance of the material. The unique coordination environment can maintain good catalytic activity and stability. The incorporation of the transition metal enables the material to produce more active sites, providing additional possibilities for the adsorption and reaction of CO2 molecules, helping the original material to form a narrower band gap, enhancing the light absorption range, and improving the photocatalytic activity. From the perspective of electron transfer, the presence of the transition metal is also conducive to inhibiting the charge recombination process and promoting more efficient electron transfer. The synergistic effect of these mechanisms jointly contributes to the outstanding activity of the material in photocatalytic carbon dioxide reduction).

[0048] The synthesis method of the present invention has simple process conditions and operations, and a benzoxazolyl covalent organic framework material is obtained by a mature solvent thermal method, and a transition metal complex @ covalent organic framework composite photocatalytic material is obtained by further metal salt coordination treatment, which has good repeatability and high crystallinity of the obtained material.

[0049] The transition metal complex@covalent organic framework composite photocatalytic material obtained by the metal salt coordination treatment of the present invention has good stability and strong photocatalytic activity, which is conducive to the application of the material in photocatalytic carbon dioxide reduction.

[0050] The present invention regulates the coordination environment of transition metals by using different aldehyde-containing monomers, thereby enhancing the loading capacity of transition metals in COF, and accelerating the electron transfer process from photosensitizer to catalyst in the application of photocatalytic carbon dioxide reduction.

[0051] The unique metal coordination environment of the covalent organic framework material of the present invention can load different types of metal ions, providing a modification approach for studying the covalent organic framework material for efficient photocatalytic carbon dioxide reduction.

[0052] After screening the loaded metal ions, the research data show that the synergistic effect between the transition metal and the photosensitizer in the transition metal complex @ covalent organic framework composite photocatalytic material of the present invention enhances the interaction between the material and CO2, helps to maintain the stability of the metal active center, promotes the formation of key intermediates in the carbon dioxide reduction reaction, and especially significantly improves the selectivity of the reduction product CO, and its CO yield can reach 10552.15 μmol g -1 h -1 , with a selectivity of 91%.

[0053] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0055] Figure 1 The figure shows a synthesis diagram of a covalent organic framework material provided by the present invention (R represents an aldehyde-containing monomer).

[0056] Figure 2 The X-ray diffraction patterns of the covalent organic framework materials provided in Examples 1-3 of the present invention are shown (Intensity is intensity, 2θ (degree) is angle).

[0057] Figure 3 The structural unit diagram of a transition metal complex @ covalent organic framework composite photocatalytic material X@BBO-DHTA-COF provided in Example 6 of the present invention is shown.

[0058] Figure 4The photocatalytic carbon dioxide reduction performance diagram of Examples 7-9 of the present invention and Comparative Examples 1-3 is shown (Production amount is CO production, Time is time).

[0059] Figure 5 The selectivity diagram of photocatalytic carbon dioxide reduction of Examples 7-9 of the present invention and Comparative Examples 1-3 is shown (Production rate is CO production rate, selectivity is selectivity). DETAILED DESCRIPTION

[0060] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0061] In the following embodiments:

[0062] 5,5'-Dialdehyde-2,2'-bipyridine (BPY), terephthalaldehyde (PDA), and 2,5-dihydroxyterephthalaldehyde (DHTA) were purchased from Shanghai MacLean Biochemical Technology Co., Ltd., Shanghai Chemical Industry Park, Shanghai.

[0063] Example 1

[0064] This embodiment provides a covalent organic framework material BBO-BPY-COF, and the preparation method includes:

[0065] 4,4',4",4"'-(Benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine (10.49 mg, 0.02 mmol) and 5,5'-dialdehyde-2,2'-bipyridine (8.49 mg, 0.04 mmol) were placed in a Pyrex tube (volume about 5 mL, length 20 cm, diameter 1 cm), and then 1 mL of 1,3,5-trimethylbenzene, 1 mL of 1,4-dioxane, and 0.2 mL of 1M acetic acid aqueous solution were added to the Pyrex tube, mixed, and ultrasonicated for 2-3 minutes until the solution was completely dispersed to obtain a mixed uniform solution;

[0066] The Pyrex tube was then rapidly frozen in a 77K liquid nitrogen bath, evacuated (to an internal pressure of 0 mbar), and thawed in three cycles, and the Pyrex tube was sealed using an alcohol burner flame.

[0067] After the sealed Pyrex tube reaches room temperature, it is placed in an oven at 120°C for 3 days. The precipitate is collected and filtered, and washed three times with N,N-dimethylformamide, pure water, and acetone. It is then placed in a vacuum oven at 60°C and dried for 12 hours to obtain orange powder BBO-BPY-COF.

[0068] Example 2

[0069] This embodiment provides a covalent organic framework material BBO-PDA-COF, and the preparation method is the same as that of Example 1.

[0070] The aldehyde-containing monomer is terephthalaldehyde (PDA).

[0071] Example 3

[0072] This embodiment provides a covalent organic framework material BBO-DHTA-COF, and the preparation method is the same as that of Example 1.

[0073] The aldehyde-containing monomer is 2,5-dihydroxyterephthalaldehyde (DHTA).

[0074] Example 4

[0075] This embodiment provides a transition metal complex @ covalent organic framework composite photocatalytic material X@BBO-BPY-COF, and the preparation method includes:

[0076] The covalent organic framework material BBO-BPY-COF (30 mg) of Example 1, anhydrous ethanol (5 mL), deionized water (5 mL), and cobalt acetate transition metal salt (the concentration of the transition metal salt in the total solution of the coordination reaction system before the coordination reaction is 5 mg / mL) are placed in a beaker, and ultrasonicated until the material is evenly dispersed to obtain a uniform solution of the system;

[0077] Then, the uniform solution of the system was poured into the reactor, heated at a constant temperature of 70°C, and magnetically stirred for 24 hours for coordination reaction. After the reaction, it was washed with anhydrous ethanol and vacuum dried at 60°C for 12 hours to obtain orange-red powder X@BBO-BPY-COF.

[0078] Example 5

[0079] This embodiment provides a transition metal complex@covalent organic framework composite photocatalytic material X@BBO-PDA-COF, and the preparation method is the same as that of Example 4.

[0080] The aldehyde-containing monomer is terephthalaldehyde (PDA).

[0081] Example 6

[0082] This embodiment provides a transition metal complex@covalent organic framework composite photocatalytic material X@BBO-DHTA-COF, and the preparation method is the same as that of Example 4.

[0083] The aldehyde-containing monomer is 2,5-dihydroxyterephthalaldehyde (DHTA).

[0084] Example 7

[0085] This embodiment uses the transition metal complex @ covalent organic framework composite photocatalytic material X@BBO-BPY-COF of embodiment 4 as a photocatalyst to photocatalyze carbon dioxide, and the method includes:

[0086] Weigh 10 mg of X@BBO-BPY-COF and place it in a 250 ml beaker, and add 40 mg of photosensitizer tri(2,2'-bipyridyl)ruthenium(II) chloride, 20 ml of sacrificial agent triethanolamine, 20 ml of deionized water, and 60 ml of acetonitrile. Ultrasonicate for 15 min, and the material is evenly dispersed in the mixed solution to obtain a photocatalytic reaction system solution.

[0087] The photocatalytic reaction system solution was added into the sample chamber of the all-glass automatic online trace gas analysis system, which was sealed, evacuated and then CO2 gas was introduced to normal pressure. The operation was repeated three times until the all-glass automatic online trace gas analysis system was filled with pure CO2 gas. A 300W xenon lamp was used as a light source to irradiate the sample chamber for 5 hours. The gas composition after the photocatalytic reaction was detected by gas chromatography (GC7900), and the amounts of CO and H2 produced during the photocatalytic process were quantitatively determined.

[0088] The results show that the CO yield of X@BBO-BPY-COF photocatalytic reduction of CO2 to CO is 10552.15 μmol g -1 h -1 , the selectivity is 91%, as shown in Figure 4 , 5 shown.

[0089] Embodiment 8-9

[0090] Examples 8-9 used X@BBO-PDA-COF and X@BBO-DHTA-COF as photocatalysts to photocatalyze carbon dioxide in the same manner as in Example 7. The results are shown in FIG. Figure 4 , 5 shown.

[0091] Comparative Examples 1-3

[0092] Comparative Examples 1-3 use BBO-BPY-COF, BBO-PDA-COF and BBO-DHTA-COF as photocatalysts to photocatalyze carbon dioxide in the same manner as Example 7.

[0093] The CO yield of BBO-BPY-COF photocatalytic reduction of CO2 to CO was 5024.87 μmol g -1 h -1 , the selectivity is 89%, as shown in Figure 4 , 5 shown.

[0094] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A covalent organic framework material, characterized in that: The covalent organic framework material is a covalent organic framework material connected by imine bonds and synthesized by a solvothermal method using 4,4',4",4''-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine and an aldehyde-containing monomer in the presence of a first solvent and a catalyst.

2. The covalent organic framework material according to claim 1, wherein The molar concentration ratio of the 4,4',4",4"'-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine and the aldehyde group-containing monomer is (0.8-1.2):(1.5-2.5); The aldehyde-containing monomer is at least one of 5,5'-dialdehyde-2,2'-bipyridine, terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde, 2,5-diethyl-1,4-terephthalaldehyde, 3,3'-bipyridine-6,6'-dicarboxaldehyde, 4,4'-biphenyldicarboxaldehyde, 2,2'-bipyridine-4,4'-dicarboxaldehyde, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarboxaldehyde, 2,2'-bipyridine-6,6'-dicarboxaldehyde, 4,4'-([2,2'-bipyridine]-5,5'-diyl)benzaldehyde and 1,10-phenanthroline-3,8-dicarboxaldehyde; The first solvent is selected from at least one of chloroform, 1,3,5-trimethylbenzene, 1,4-dioxane, carbon tetrachloride and dichloromethane; The catalyst is an acetic acid aqueous solution, the concentration of the acetic acid aqueous solution is 0.1-8 mol / L, and the ratio of the added volume of the acetic acid aqueous solution to the total solution volume of the solvothermal synthesis system is (1-3):

10.

3. The covalent organic framework material according to claim 1, wherein The preparation method of the covalent organic framework material comprises: S1: mixing the 4,4',4",4"'-(benzo[1,2-d:4,5-d']bis(oxazole)-2,4,6,8-tetrayl)tetraphenylamine, the aldehyde group-containing monomer, the first solvent and the catalyst and performing ultrasonic treatment to obtain a mixed uniform solution; S2: Degassing and sealing the equipment containing the mixed uniform solution in step S1 with liquid nitrogen; S3: subjecting the mixed uniform solution in the device after the treatment in step S2 to a solvothermal reaction to obtain a precipitate, washing and vacuum drying the precipitate to obtain the covalent organic framework material.

4. The covalent organic framework material according to claim 3, wherein In step S3: The temperature of the solvent thermal reaction is 90-125°C and the time is 48-96h; The washing solvent used for washing is at least one of N,N-dimethylformamide, pure water, anhydrous ethanol and acetone; The vacuum drying temperature is 55-125°C and the time is 10-16h.

5. A transition metal complex@covalent organic framework composite photocatalytic material, characterized in that: The composite photocatalytic material is prepared by a coordination reaction between a covalent organic framework material and a transition metal salt under a second solvent condition; The covalent organic framework material is the covalent organic framework material according to any one of claims 1 to 4.

6. The transition metal complex@covalent organic framework composite photocatalytic material according to claim 5, wherein: The transition metal salt is at least one of ferric chloride, cobalt acetate, nickel acetate, zinc sulfate and copper sulfate; The concentration of the transition metal salt in the total solution of the coordination reaction system before the coordination reaction is performed is 1-5 mg / mL; The second solvent is a mixture of ethanol and water, wherein the volume ratio of anhydrous ethanol to water is (1-3):1; The usage ratio of the covalent organic framework material to the second solvent is (1-5): (0.1-10) g / L; The temperature of the coordination reaction is 65-125° C. and the time is 12-36 hours.

7. The transition metal complex@covalent organic framework composite photocatalytic material according to claim 5, wherein: The preparation method of the transition metal complex@covalent organic framework composite photocatalytic material comprises: (1) mixing the covalent organic framework material, the transition metal salt and the second solvent and subjecting the mixture to ultrasonic treatment to obtain a uniform solution; (2) allowing the uniform solution of the system to undergo coordination reaction under stirring conditions to obtain a product, and washing and vacuum drying to obtain the transition metal complex@covalent organic framework composite photocatalytic material; Preferably, in step (2): The washing solvent used for washing is at least one of anhydrous ethanol, chloroform, tetrahydrofuran, acetone and deionized water; The vacuum drying temperature is 55-80°C and the time is 10-16h.

8. Use of the transition metal complex@covalent organic framework composite photocatalytic material according to any one of claims 5 to 7 in photocatalytic carbon dioxide production.

9. The use according to claim 8, wherein: The method for photocatalyzing carbon dioxide comprises: The photocatalyst is mixed with a third solvent, a photosensitizer, a sacrificial agent and water and subjected to ultrasonic treatment to obtain a photocatalytic reaction system solution; The photocatalytic reaction system solution is contacted with carbon dioxide under sealed conditions and light irradiation to perform a photocatalytic reaction to obtain a reaction gas containing carbon monoxide; The photocatalyst is the transition metal complex@covalent organic framework composite photocatalytic material.

10. The use according to claim 9, wherein: The photosensitizer is tris(2,2'-bipyridyl)ruthenium(II) chloride; The sacrificial agent is at least one of triethanolamine, methanol, ethanol, lactic acid and sodium persulfate; The third solvent is acetonitrile; The amount ratio of the transition metal complex@covalent organic framework composite photocatalytic material, the third solvent, the photosensitizer, the sacrificial agent and water is (0.8-1.2): (5-7): (3-5): (1-3): (1-3) g / L / g / L / L; The light source of the illumination is a 250-350W xenon lamp, and the illumination time is 4.5-5.5h.

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