An Ag-T-COF material, its preparation method, and its application in photocatalytic CO2 reduction.

Abstract

The application relates to an Ag-T-COF material, a preparation method thereof and application of the Ag-T-COF material in photocatalytic CO2 reduction, and focuses on preparation and photocatalytic conversion technology of metal organic framework and covalent organic framework materials. Ag3L3 ring trinuclear metal CMOFs are synthesized by taking 1H-pyrazole-4-formaldehyde (HL) as a ligand and silver as a metal source, Ag3L3 and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) are subjected to a solvothermal reaction at a certain temperature, and the material Ag-T-COF is successfully prepared. The ring trinuclear structure provides metal active sites for subsequent CMOFs construction and constructs a dynamic covalent bond skeleton, improves the CO2 adsorption capacity and electronic transmission efficiency of the material from the structural root, and solves the core problems of poor CO2 adsorption and easy recombination of photo-generated electrons and holes of traditional semiconductor photocatalytic materials. Under the solid-liquid reaction condition, after 5 hours of light treatment, the Ag-T-COF material exhibits excellent photocatalytic performance, and the CO yield is up to 62 umol g ‑1 h ‑1 above.

Description

Technical Field

[0001] The technical field of this invention is the preparation of covalent metal-organic framework derived materials and the field of photocatalytic carbon dioxide reduction technology, specifically a method for preparing Ag-T-COF materials and their photocatalytic applications. Background Technology

[0002] Currently, advanced combustion technologies are being used to optimize the efficiency of fossil fuel utilization, and a transition is underway to renewable energy systems utilizing solar, wind, and tidal power. Simultaneously, significant research investments are being made in carbon capture and storage (CFS) innovations aimed at sequestering carbon dioxide in geological reservoirs through supercritical phase transitions. Paradoxically, the thermodynamic limitations currently requiring substantial energy inputs undermine their environmental benefits and long-term sustainability. This complex situation underscores the urgency of developing carbon reduction technologies that not only reduce emissions but also provide practical pathways for the utilization of captured carbon dioxide, potentially transforming this environmental responsibility into an industrial resource. The scientific community has been working to biomimeticly replicate natural photosynthesis through an artificial photosynthesis systems engineering photochemical platform designed to drive the photoreduction of carbon dioxide using solar radiation.

[0003] Currently, many semiconductor photocatalysts have been used in the field of photocatalytic carbon dioxide reduction. However, the development of semiconductor materials in the field of photocatalysis is limited by the easy recombination of photogenerated electrons and holes and the poor adsorption capacity of carbon dioxide.

[0004] Covalent metal-organic frameworks (CMOFs) possess characteristics such as high crystallinity, ultra-high specific surface area, variable pore size, and high density of coordinated unsaturated metal sites, attracting widespread attention in the field of photocatalytic carbon dioxide reduction. The composition and performance of CMOFs can be tuned through modification with organic ligands, metal ions, and active components, thereby expanding their light absorption range, promoting electron transfer, and enhancing their photocatalytic carbon dioxide reduction performance. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to solve the issues of poor CO2 adsorption and easy recombination of photogenerated electrons and holes. First, a cyclic trinuclear MOF material is prepared, and then a covalent metal-organic framework material is synthesized via solvothermal synthesis. The electron-rich (ER)-electron-deficient (ED) structure in Ag-T-COF promotes the separation of photogenerated electrons and holes. The method for preparing Ag-T-COF includes the following steps: (1) Preparation of Ag3L3: Silver salt and 1H-pyrazole-4-carboxaldehyde HL were added to the reaction solvent and sonicated to dissolve them completely. Then, the solution was reacted in the dark at 0-45 °C for 1-10 h, filtered, washed and dried to obtain a white Ag3L3 solid sample.

[0006] In step (1), the molar ratio of silver salt to HL is 1-4:1-4; preferably 1:1. The silver salt in step (1) includes AgNO3 and CH3COOAg, preferably AgNO3; The reaction solvent in step (1) is one or a mixture of several of N,N-dimethylformamide, water, ethanol, acetonitrile and triethylamine, wherein acetonitrile and triethylamine are preferred; The reaction described in step (1) is carried out in the dark at 0–45 °C for 1–10 h, preferably at 25 °C for 2 h.

[0007] (2) Preparation of Ag-T-COF: A certain amount of Ag3L3 and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) were added to a Schlenk tube containing the reaction solvent. The mixture was sonicated to ensure homogeneity, and finally, an acidic catalyst was added. After heating to room temperature, a solvothermal reaction was carried out at a certain temperature, 50–100 °C, for 6–72 h. After the reaction was completed, the sample was washed with organic reagents, filtered, and vacuum dried to obtain a yellow Ag-T-COF powder sample.

[0008] The ratio of Ag3L3 to 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) is 1-4:1-4, preferably 1:1; The reaction solvent in step (2) is one or a mixture of several of benzyl alcohol, 1,2-dichlorobenzene, 1,4-dioxane, and mesitylene, preferably benzyl alcohol and 1,2-dichlorobenzene; The acidic catalyst in step (2) is trifluoroacetic acid and acetic acid, preferably trifluoroacetic acid; The concentration of the acidic catalyst in step (2) ranges from 3 to 12 M, with 6 M being preferred; The solvothermal reaction described in step (2) is carried out in an oil bath at 50–100 °C for 6–72 h, preferably at 65 °C for 8 h. Step (2) also includes degassing the reaction system before the solvothermal reaction.

[0009] (3) A procedure for testing Ag-T-COF photocatalytic carbon dioxide reduction: A certain amount of catalyst powder was poured into a centrifuge tube containing deionized water. The centrifuge tube containing the catalyst solution was then placed in an ultrasonic oscillator for sonication to form a homogeneous solution dispersed on quartz wool. The quartz bottle was then placed in darkness, and the reaction vessel underwent multiple vacuum treatments before being injected with carbon dioxide of a certain purity up to atmospheric pressure. The photocatalytic carbon dioxide reduction performance was tested using a 300 W xenon lamp as the light source. Throughout the reaction, the gaseous products were measured using an online gas chromatograph and detector, with argon as the carrier gas.

[0010] The catalyst addition amount is 1-3 mg; the wavelength range of the light source must be within the light absorption range of the material, λ>420 nm; the reaction temperature is at room temperature and the irradiation time is 3-24 h, preferably 5 h.

[0011] After the reaction is complete, Ag-T-COF is recovered, dried, and reactivated to achieve N cycles of preparation, where N is greater than or equal to 3.

[0012] The specific beneficial effects of this material are manifested as follows: (1) The covalent metal-organic framework Ag-T-COF material synthesized in this invention has an ER-ED type structure, which significantly improves the separation efficiency of photogenerated carriers.

[0013] (2) It maintains high catalytic activity and low catalyst loss in multiple cycles and has good stability.

[0014] (3) This invention uses a 300 W xenon lamp as the light source and the covalent metal-organic framework Ag-T-COF as the photocatalyst to conduct photocatalytic carbon dioxide reduction tests. The Ag-T-COF material exhibits excellent photocatalytic performance, with a CO yield as high as 62 μmol g. -1 h -1 The above demonstrates excellent photocatalytic activity. Attached Figure Description

[0015] Figure 1 This is a synthesis route diagram of the Ag3L3 material in this invention.

[0016] Figure 2 This is the XRD pattern of the Ag3L3 material in this invention.

[0017] Figure 3 This is a synthesis route diagram of the Ag-T-COF material in this invention.

[0018] Figure 4 This is the XRD pattern of the Ag-T-COF material in this invention.

[0019] Figure 5 The solid Ag-T-COF material in this invention 13C nuclear magnetic resonance spectrum.

[0020] Figure 6 This is the FT-IR image of the Ag-T-COF material in this invention.

[0021] Figure 7 This is the nitrogen adsorption-desorption isotherm diagram of the Ag-T-COF material in this invention.

[0022] Figure 8 This is a diagram showing the photocatalytic reduction performance of the Ag-T-COF material in this invention.

[0023] Figure 9 This is a cyclic activity diagram of the Ag-T-COF material in this invention.

[0024] Figure 10 This is an XRD comparison diagram of samples before and after Ag-T-COF catalytic conversion in this invention.

[0025] Figure 11 This is a blank control diagram of the Ag-T-COF material in this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the following implementation examples, but the present invention is not limited to the following implementation examples.

[0027] Example 1 Synthesis of Ag3L3: AgNO3 and HL were added to a reactor containing acetonitrile and triethylamine, and sonicated to dissolve them completely. Then, the solution was reacted in the dark at 25 °C for 2 h. After filtration, washing and drying, a white Ag3L3 solid sample was obtained.

[0028] Synthesis of Ag-T-COF: Ag3L3 and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) were added to a Schlenk tube containing benzyl alcohol and 1,2-dichlorobenzene. The mixture was sonicated to ensure homogeneity, and finally, a 6 M trifluoroacetic acid solution was added. The resulting mixture was degassed under three freeze-thaw cycles and sealed under vacuum. After heating to room temperature, a solvothermal reaction was carried out at 65 °C. The mixture was washed with methanol to obtain Ag-T-COF.

[0029] Figure 1 This is a synthesis route diagram of the Ag3L3 material in this invention.

[0030] Figure 2 The image shows the XRD pattern of the Ag3L3 material in this invention. The XRD characteristic peaks of the fitted Ag3L3 and the prepared Ag3L3 can be clearly observed to be well compared, which proves the successful preparation of the Ag3L3 material.

[0031] Figure 3 This is a synthesis route diagram of the Ag-T-COF material in this invention.

[0032] Figure 4 The XRD pattern of the Ag-T-COF material in this invention shows that characteristic diffraction peaks appear at 4.3° and 7.5°, corresponding to the (100) and (110) crystal planes, respectively. These results agree well with the simulated AA packing model, proving the successful preparation of the material. The difference curves show the weighted profile R factor (Rwp) and the unweighted profile R factor (Rp). The Rp of Ag-T-COF is 5.31% and the Rwp is 7.13%. Furthermore, the negligible difference profile of Ag-T-COF indicates that the simulated PXRD patterns of Ag-T-COF agree well with the experimental data. Figure 5 The solid Ag-T-COF material in this invention 13 In the C NMR spectrum, the aldehyde carbon (─C═O) signal of Ag-T-COF disappeared at about 160 ppm, while the imine carbon showed a new resonance peak at about 150 ppm, confirming the successful construction of imine bonds within the COF framework.

[0033] Figure 6 The image shows the FT-IR spectrum of the Ag-T-COF material in this invention, with TAPT values ​​between 3500 and 3200 cm⁻¹. -1 The stretching vibration of NH at the location and the ~1652 cm of Ag3L3 -1 The disappearance of the C=O stretching vibration at ~1563 cm, and at ~1563 cm -1 The appearance of a new peak representing the characteristic C=N stretching confirms the formation of imine bonds in the skeleton.

[0034] Figure 7 The image shows the nitrogen adsorption-desorption isotherm of the Ag-T-COF material in this invention. Ag-T-COF exhibits a type IV isotherm and has a specific surface area of ​​35.27 m². 2 g -1 Pore ​​size distribution analysis shows that the pore size is around 2.0 nm, consistent with the theoretical value predicted by the AA packing structure.

[0035] Example 1-1 0.2 mmol AgNO3 and 0.4 mmol HL were added to a reactor containing acetonitrile and triethylamine, and the solutions were sonicated to dissolve them completely. The solutions were then reacted in the dark at 25 °C for 2 h. The solutions were filtered, washed, and dried to obtain a white Ag3L3 solid sample.

[0036] Examples 1-2 0.4 mmol AgNO3 and 0.3 mmol HL were added to a reactor containing acetonitrile and triethylamine, and the solutions were sonicated to dissolve them completely. The solutions were then reacted in the dark at 25 °C for 2 h. The solutions were filtered, washed, and dried to obtain a white Ag3L3 solid sample.

[0037] Examples 1-3 0.2 mmol AgNO3 and 0.2 mmol HL were added to a reactor containing acetonitrile and triethylamine, and the solutions were sonicated to dissolve them completely. The solutions were then reacted in the dark at 65 °C for 2 h. After filtration, washing, and drying, a white Ag3L3 solid sample was obtained.

[0038] Examples 1-4 0.05 mmol Ag3L3 and 0.05 mmol 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) were added to a Schlenk tube containing benzyl alcohol and 1,2-dichlorobenzene. The mixture was sonicated to ensure homogeneity, and finally, 6M trifluoroacetic acid solution was added. The resulting mixture was degassed by three freeze-thaw cycles and sealed under vacuum. After heating to room temperature, a solvothermal reaction was carried out at 65 °C for 10 h. After the reaction was completed, the precipitate was collected by filtration and washed with methanol to obtain Ag-T-COF.

[0039] Examples 1-5 0.05 mmol Ag3L3 and 0.05 mmol 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) were added to a Schlenk tube containing benzyl alcohol and 1,2-dichlorobenzene. The mixture was sonicated to ensure homogeneity, and finally, 6M trifluoroacetic acid solution was added. The resulting mixture was subjected to a solvothermal reaction at 65 °C for 10 h. After the reaction was complete, the precipitate was collected by filtration and washed with methanol; Ag-T-COF was not obtained.

[0040] Example 2 Photocatalytic carbon dioxide reduction performance test: 1 mg of Ag-T-COF catalyst was poured into a centrifuge tube containing 2 mL of deionized water. The centrifuge tube containing the catalyst solution was then placed in an ultrasonic shaker and sonicated to form a homogeneous solution dispersed on quartz wool. The quartz bottle was then placed in darkness, and the reaction vessel underwent three vacuum treatments before carbon dioxide was injected to atmospheric pressure. The photocatalytic carbon dioxide reduction performance was tested using a 300 W xenon lamp as the light source. Throughout the reaction, gaseous products were measured using an online gas chromatograph and detector, with argon as the carrier gas.

[0041] Figure 8The graph shows the photocatalytic reduction performance of the Ag-T-COF material in this invention. When the reaction time is 5 h, Ag-T-COF exhibits the highest photocatalytic carbon dioxide reduction activity, with a CO yield of 62 μmol·g⁻¹. -1 ·h -1 .

[0042] Example 3 Cyclic stability test: Ag-T-COF was used as a photocatalyst for the photocatalytic reduction of carbon dioxide in Example 2, producing CO. After the reaction, the Ag-T-COF catalyst was recovered, dried, and then subjected to further photocatalytic reaction experiments. The cycle was repeated at least three times under the conditions of Example 3 to systematically evaluate its cycling stability.

[0043] Figure 9 The cycling activity diagram of the Ag-T-COF material in this invention and Figure 10 The images show a comparison of XRD patterns of the Ag-T-COF samples before and after catalytic conversion in this invention. Experimental results indicate that the carbon dioxide reduction activity remains high even after three cycles. Furthermore, the XRD patterns of Ag-T-COF before and after the three cycles remain essentially unchanged, demonstrating that Ag-T-COF exhibits good photocatalytic cycle stability.

[0044] Example 4 Blank control test: Using Ag-T-COF as a photocatalyst, photocatalytic tests were conducted under a nitrogen atmosphere without changing other reaction conditions to determine the source of carbon; photocatalytic tests were conducted under anhydrous conditions to determine the source of oxygen in oxygen; tests were conducted under light-free conditions to determine that the catalyst is light-driven; and photocatalytic tests were conducted under catalyst-free conditions to determine that only the catalyst in the system has the ability to reduce carbon dioxide.

[0045] Figure 11 This is a blank control diagram of the Ag-T-COF material in this invention. The control experimental system verified the necessary conditions for the catalytic reaction. No CO products were detected when the catalyst, light, or water vapor were removed. This confirms that all conditions for the photocatalytic reaction are indispensable.

[0046] The above results demonstrate the successful preparation of this CMOF material. This invention uses HL as a ligand and silver as a metal source to synthesize Ag3L3. Compared with conventional monometallic / dual-core MOF materials, the cyclic trinuclear structure provides metal active sites for subsequent CMOF construction and constructs a dynamic covalent bond framework. This structurally improves the material's CO2 adsorption capacity and electron transport efficiency, solving the core problems of poor CO2 adsorption and easy recombination of photogenerated electrons and holes in traditional semiconductor photocatalytic materials. This provides a new approach for future research in the field of photocatalysis.

[0047] The above description is merely a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in this embodiment. Therefore, any equivalent or modified versions made without departing from the spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. An Ag-T-COF material, characterized in that, The X-ray powder diffraction of the covalent metal-organic framework material includes a characteristic diffraction peak at approximately 4.37°, attributed to the 100 crystal plane. The covalent metal-organic framework material is an imine CMOF, formed by the condensation of -NH₂ and -CHO to create a C=N bond, with a peak at 1652 cm⁻¹. -1 The aldehyde stretching vibration peak is absent at 3500-3200 cm⁻¹. -1 There is no -NH stretching vibration peak at 1563 cm⁻¹. -1 The appearance of the C=N stretching vibration peak indicates the formation of imine bonds in the skeleton.

2. A method for preparing the Ag-T-COF material as described in claim 1, characterized in that, Includes the following steps: 1) Add silver salt and 1H-pyrazole-4-carboxaldehyde HL to the reaction solvent and react under dark conditions. After post-treatment, Ag3L3 is obtained. 2) Ag3L3 and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine TAPT were subjected to a solvothermal reaction in the presence of an organic solvent and an acidic catalyst, and crystalline Ag-T-COF material was obtained after post-treatment.

3. The method for preparing Ag-T-COF according to claim 2, characterized in that, In step 1), the molar ratio of silver salt to HL is 1-4:1-4; preferably 1:

1. The silver salt includes AgNO3, Ag2SO4, and CH3COOAg, with AgNO3 being preferred. The reaction solvent is N,N - A mixture of one or more of dimethylformamide, water, ethanol, acetonitrile and triethylamine, wherein acetonitrile and triethylamine are preferred; The reaction is carried out in the dark at 0–45°C for 1–10 h, preferably at 25°C for 2 h.

4. The preparation method according to claim 1, characterized in that, The reaction solvent in step 2) is one or a mixture of several of benzyl alcohol, 1,2-dichlorobenzene, 1,4-dioxane, and mesitylene, preferably benzyl alcohol and 1,2-dichlorobenzene; The acidic catalyst is trifluoroacetic acid and acetic acid, preferably trifluoroacetic acid; The concentration of the acidic catalyst ranges from 3 to 12 M, with 6 M being preferred. The solvothermal reaction is carried out in an oil bath at 50–100 °C for 6–72 h, preferably at 65 °C for 8 h.

5. The preparation method according to any one of claims 2-4, characterized in that, Steps 1) and 2) also include post-processing steps, which include filtration, washing, and drying; Step 2) also includes degassing the reaction system before the solvothermal reaction.

6. An application of the Ag-T-COF material as described in claim 1 in the field of photocatalytic CO2 reduction, characterized in that, The Ag-T-COF material was used as a photocatalyst to achieve the reaction of CO2 reduction to CO under visible light irradiation.

7. The application according to claim 6, characterized in that, The photocatalytic CO2 reduction reaction conditions are as follows: light source wavelength λ > 420 nm, a 300 W xenon lamp is used as the light source, the reaction temperature is room temperature, the light irradiation reaction time is 3 to 24 h, the reaction system is a solid-liquid system containing deionized water, and no sacrificial agent is required.

8. The application according to claim 7, characterized in that, The photoreaction time is 5 hours.

9. The application according to claim 6, characterized in that, The Ag-T-COF material can be recovered, dried, and activated after photocatalytic reaction, enabling multiple cycles of photocatalytic CO2 reduction with a cycle number N≥3, and the crystal form and catalytic activity of the material remain basically unchanged after cycling.

10. The application according to claim 9, characterized in that, The photocatalytic CO2 reduction reaction system needs to be vacuum-treated before injecting high-purity CO2 to atmospheric pressure. The reaction products are detected by an online gas chromatograph, with argon as the carrier gas. The high-purity CO2 refers to CO2 with a purity greater than 99.9%.

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