A single-atom photocatalyst Cu-OmBpy-COF, its preparation method and application

Abstract

This invention relates to the field of photocatalysis, and particularly to a single-atom photocatalyst Cu-OmBpy-COF, its preparation method, and its applications. A novel OmBpy-COF linked by both imine and oxazole rings was synthesized via a one-pot method. The single-atom catalyst Cu-OmBpy-COF was then obtained by impregnating copper metal into a covalent organic framework. Compared to pure OmBpy-COF, Cu-OmBpy-COF improves carrier separation efficiency and significantly enhances the photocatalytic reduction of carbon dioxide to CO yield. Under xenon lamp irradiation for 5 hours, the CO yield reached 3815.94 μmol·g⁻¹. ‑1 It is 5.4 times that of pure OmBpy-COF. The anchoring of copper ions increases the number of carbon dioxide adsorption sites, enhances the carbon dioxide reduction activity and CO production selectivity, greatly improves the carbon monoxide yield, and exhibits excellent photocatalytic stability.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, and in particular to a single-atom photocatalyst Cu-OmBpy-COF, its preparation method, and its applications. Background Technology

[0002] Currently, the continuous rise in global carbon emissions is pushing the climate crisis to a more severe stage. Efficiently capturing and converting excess CO2 in the atmosphere has become a core challenge in solving the environmental dilemma. Against this backdrop, solar-driven photocatalytic CO2 reduction (CO2RR) has emerged as a key technology connecting carbon emission reduction and renewable energy utilization due to its unique advantages. Powered by solar energy, it can directionally convert the greenhouse gas CO2 into high-value CO, providing an important pathway to alleviate carbon emission pressure and break the cycle of "energy consumption-environmental degradation." Therefore, precisely designing and preparing high-performance, suitable photocatalysts for photocatalytic CO2 reduction is crucial to meet the needs of photocatalytic CO2 reduction.

[0003] Covalent organic frameworks (COFs), as a new class of crystalline porous materials, possess excellent crystallinity, tunable chemical composition, and efficient light absorption properties, making them a promising candidate for photocatalysis in the field of CO2 reduction. However, pure COFs exhibit low photogenerated electron-hole pair separation efficiency, and the excited charge carriers readily recombine, resulting in weak activation ability for CO2 molecules and a reduced number of effective charges participating in the CO2 reduction reaction. This still limits their application in the photocatalytic reduction of carbon dioxide. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a single-atom photocatalyst Cu-OmBpy-COF, its preparation method, and its application. The single-atom photocatalyst Cu-OmBpy-COF provided by this invention can photocatalytically reduce CO2 to CO, exhibiting high catalytic activity.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a single-atom photocatalyst Cu-OmBpy-COF, comprising the following steps: 1) Disperse 2,4,5-triamino-6-hydroxypyrimidine sulfate, [2,2'-bipyridine]-5,5-dicarboxaldehyde and acetic acid in an organic solvent to obtain a mixed solution; 2) The mixed solution described in step 1) is sequentially subjected to liquid nitrogen freezing, vacuuming, and thawing, followed by reaction to obtain the crude product; 3) The crude product obtained in step 2) is washed, Soxhlet extracted and vacuum dried sequentially to obtain the covalent organic framework OmBpy-COF material; 4) The covalent organic framework OmBpy-COF and anhydrous copper acetate obtained in step 3) are ultrasonically dispersed in acetonitrile, stirred, filtered and dried to obtain the single-atom photocatalyst Cu-OmBpy-COF.

[0006] Preferably, the mass ratio of 2,4,5-triamino-6-hydroxypyrimidine sulfate, [2,2'-bipyridine]-5,5-dicarboxaldehyde, the volume of acetic acid solution, and the volume of organic solvent in step 1) is 47.8 mg: 63.6 mg: 0.4 mL: 2 mL.

[0007] Preferably, the concentration of the acetic acid solution in step 1) is 6 mol / L; The organic solvent is N,N-dimethylacetamide and o-dichlorobenzene, and the volume ratio of N,N-dimethylacetamide and o-dichlorobenzene is 1:2.

[0008] Preferably, the liquid nitrogen freezing, vacuuming, and thawing cycle in step 2) is repeated 3 times; The reaction conditions include a temperature of 120°C and a time of 72 h.

[0009] Preferably, the crude product in step 3) is washed sequentially with acetone, tetrahydrofuran, and deionized water; The solvent used in the Soxhlet extraction was tetrahydrofuran, and the Soxhlet extraction time was 12 h. The vacuum drying temperature is 80℃ and the time is 12 h.

[0010] Preferably, in step 4), the mass ratio of the covalent organic framework OmBpy-COF, the mass of anhydrous copper acetate, and the volume ratio of acetonitrile is 30 mg:30 mg:30 mL.

[0011] Preferably, the ultrasonic dispersion time in step 4) is 30 min; The stirring time is 10 h; The drying conditions include a temperature of 80°C and a time of 12 hours.

[0012] The present invention also provides a single-atom photocatalyst Cu-OmBpy-COF prepared by the preparation method described in the above technical solution.

[0013] This invention also provides the application of the single-atom photocatalyst Cu-OmBpy-COF described in the above technical solution in the photocatalytic reduction of carbon dioxide to carbon monoxide.

[0014] Preferably, the application includes the following steps: dispersing the single-atom photocatalyst Cu-OmBpy-COF in a solvent, introducing carbon dioxide, and then reacting under 300W xenon lamp irradiation.

[0015] The beneficial effects of this invention are: (1) This invention uses 2,4,5-triamino-6-hydroxypyrimidine sulfate and [2,2'-bipyridine]-5,5-dicarboxaldehyde as monomers to synthesize a novel covalent organic framework OmBpy-COF for the first time using a one-pot method, which combines imine groups and oxazole rings. Based on the irreversibility of some imine bonds, a stable oxazole ring is formed. Compared with traditional COFs linked by imine bonds, this material has higher stability in the aqueous environment.

[0016] (2) This invention prepares a single-atom photocatalyst Cu-OmBpy-COF by anchoring a covalent organic framework (OmBpy-COF) with metallic copper ions, which increases the number of reactive sites and effectively promotes charge separation and transfer in the framework, thereby significantly improving the photocatalytic reduction yield. After irradiation with a xenon lamp (λ>420nm) for 5 hours, the carbon monoxide yield reaches 3815.94 μmol·g. -1 Furthermore, the single-atom photocatalyst Cu-OmBpy-COF prepared in this invention exhibits excellent photocatalytic stability.

[0017] (3) The raw materials used in this invention are inexpensive, the preparation method is simple, the synthesis conditions are mild, and the reaction process has low energy consumption. It has good economic benefits and application prospects for large-scale production and application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0019] Figure 1 XRD patterns of OmBpy-COF and Cu-OmBpy-COF; Figure 2 Infrared spectra of OmBpy-COF and Cu-OmBpy-COF; Figure 3 The UV-Vis diffuse reflectance spectra of OmBpy-COF and Cu-OmBpy-COF are shown; where a is the absorption spectrum, b is the band gap energy, and c is the energy level structure. Figure 4 shows scanning electron microscope images of OmBpy-COF and Cu-OmBpy-COF; Figure 5Synchrotron radiation diagrams of Cu atoms in the Cu-OmBpy-COF single-atom photocatalyst are shown; (a) is the normalized Cu k-edge X-ray near-edge structure (XANES) spectrum, and (b) is the experimental k-edge X-ray near-edge structure spectrum. 2 -Weighted Cu K-edge X-ray absorption fine structure spectrum (EXAFS); Figure 6 shows the electrochemical impedance spectroscopy (EIS) spectra of OmBpy-COF and Cu-OmBpy-COF. Figure 7 shows the photocatalytic performance of OmBpy-COF and Cu-OmBpy-COF photocatalysts in reducing CO2 to CO. Figure 8 shows the experimental results of the cycling stability of the Cu-OmBpy-COF photocatalyst; Figure 9 shows the in-situ infrared spectra of Cu-OmBpy-COF photocatalyzed CO2RR under different illumination times. Detailed Implementation

[0020] This invention provides a method for preparing a single-atom photocatalyst Cu-OmBpy-COF, comprising the following steps: 1) Disperse 2,4,5-triamino-6-hydroxypyrimidine sulfate, [2,2'-bipyridine]-5,5-dicarboxaldehyde and acetic acid in an organic solvent to obtain a mixed solution; 2) The mixed solution described in step 1) is sequentially subjected to liquid nitrogen freezing, vacuuming, and thawing, followed by reaction to obtain the crude product; 3) The crude product obtained in step 2) is washed, Soxhlet extracted and vacuum dried sequentially to obtain the covalent organic framework OmBpy-COF material; 4) The covalent organic framework OmBpy-COF and anhydrous copper acetate obtained in step 3) are ultrasonically dispersed in acetonitrile, stirred, filtered and dried to obtain the single-atom photocatalyst Cu-OmBpy-COF.

[0021] This invention disperses 2,4,5-triamino-6-hydroxypyrimidine sulfate, [2,2'-bipyridine]-5,5-dicarboxaldehyde, and acetic acid in an organic solvent to obtain a mixed solution. In this invention, the preferred volume ratio of the 2,4,5-triamino-6-hydroxypyrimidine sulfate, the [2,2'-bipyridine]-5,5-dicarboxaldehyde, the acetic acid solution, and the organic solvent is 47.8 mg:63.6 mg:0.4 mL:2 mL. The preferred concentration of the acetic acid solution is 6 mol / L. The preferred organic solvent is N,N-dimethylacetamide and o-dichlorobenzene, and the preferred volume ratio of N,N-dimethylacetamide and o-dichlorobenzene is 1:2.

[0022] In this invention, the mixed solution is sequentially subjected to liquid nitrogen freezing, vacuuming, and thawing, followed by a reaction to obtain a crude product. Preferably, the cycle of liquid nitrogen freezing for 1 minute, vacuuming, and thawing at room temperature is repeated three times. Preferably, the reaction conditions include a temperature of 120°C and a reaction time of 72 hours.

[0023] This invention involves sequentially washing, Soxhlet extraction, and vacuum drying of the crude product to obtain the covalent organic framework OmBpy-COF material. In this invention, the crude product is preferably washed sequentially with acetone, tetrahydrofuran, and deionized water. In this invention, the solvent used for the Soxhlet extraction is preferably tetrahydrofuran, and the Soxhlet extraction temperature is 100°C for 12 hours. In this invention, the vacuum drying temperature is preferably 80°C for 12 hours.

[0024] This invention involves ultrasonically dispersing the covalent organic framework OmBpy-COF and anhydrous copper acetate in acetonitrile, followed by stirring, filtration, and drying to obtain the single-atom photocatalyst Cu-OmBpy-COF. In this invention, the preferred mass ratio of the covalent organic framework OmBpy-COF, the anhydrous copper acetate, and the acetonitrile is 30 mg:30 mg:30 mL. The preferred ultrasonic dispersion time is 30 min. The preferred stirring time is 10 h. The preferred drying conditions include a temperature of 80°C and a time of 12 h.

[0025] The present invention also provides a single-atom photocatalyst Cu-OmBpy-COF prepared by the preparation method described in the above technical solution.

[0026] This invention also provides the application of the single-atom photocatalyst Cu-OmBpy-COF described in the above-mentioned technical solution in the photocatalytic reduction of carbon dioxide to carbon monoxide. In this invention, the application preferably includes the following steps: dispersing the single-atom photocatalyst Cu-OmBpy-COF in a solvent, introducing carbon dioxide, and then reacting under 300W xenon lamp irradiation.

[0027] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0028] Example 1 1. Preparation of OmBpy-COF photocatalyst (1) Accurately weigh 47.8 mg of 2,4,5-triamino-6-hydroxypyrimidine sulfate and 63.6 mg of [2,2'-bipyridine]-5,5-dicarboxaldehyde, put them into a glass synthesis tube, add 0.65 mL of N,N-dimethylacetamide and 1.35 mL of o-dichlorobenzyltrimethylbenzene, disperse the solvent by sonication, add 0.4 mL of 6M acetic acid aqueous solution, mix well again to obtain a mixed solution.

[0029] (2) After the above mixed solution was subjected to liquid nitrogen freezing-vacuuming-thawing cycle three times, it was vacuum sealed and placed in a constant temperature oven, kept at a constant temperature of 120℃, and reacted for 72 hours to obtain crude product.

[0030] (3) The above crude product was separated into solid and liquid. The solid was washed three times with acetone, tetrahydrofuran and deionized water in sequence. After the solid was separated by vacuum filtration, the obtained solid was dried under vacuum. After being wrapped with filter paper, it was extracted with tetrahydrofuran at a Soxhlet temperature of 100℃ for 12h. Then the solid after Soxhlet extraction was placed in a vacuum drying oven and dried under vacuum at 80℃ for 12h to obtain COF reddish-brown solid powder, which was named OmBpy-COF.

[0031] Example 2 2. Preparation of Cu-OmBpy-COF photocatalyst (1) Weigh 30 mg of OmBpy-COF and 30 mg of anhydrous copper acetate and place them in a 100 mL beaker. Add 30 mL of acetonitrile solvent, sonicate for 30 min, and magnetically stir for 10 h. (2) After stirring, the mixed solution after stirring is subjected to solid-liquid separation. The solid product after solid-liquid separation is washed with acetonitrile and then placed in a constant temperature oven at 80°C for 12 hours to obtain the single-atom photocatalyst Cu-OmBpy-COF.

[0032] 3. Photocatalytic performance test: To evaluate the catalytic performance of the single-atom photocatalyst Cu-OmBpy-COF, its photocatalytic CO2 reduction (CO2RR) effect was tested under visible light illumination (300W xenon lamp, λ>420 nm). All CO2RR experiments were conducted without the use of additional co-catalysts, sacrificial agents, or photosensitizers. The photocatalytic CO2 reduction was carried out in a 100 mL quartz reactor with temperature controlled by a water bath. 10 mg of the single-atom photocatalyst Cu-OmBpy-COF was dispersed in 30 mL of a mixed solvent (DMF / H2O, v=1:1) and stirred magnetically at 500 r / min in the reactor. -1The mixture was stirred at a high speed. Subsequently, the quartz reactor was sealed with a quartz glass top, and CO2 (99.999%) was introduced for purification for 30 min, while the reaction solution temperature was maintained at 25°C. After xenon lamp irradiation, CO was detected using a headspace sampler via gas chromatography-flame ionization detector (GC-FID), with samples taken every 1 hour.

[0033] 4. Results Analysis: (1) The PXRD patterns of the obtained OmBpy-COF and Cu-OmBpy-COF materials are shown in the figure. Figure 1 As can be seen from the figure, the COF is 4.98. 0 There is a strong diffraction peak at the (100) section, which indicates that the COF material has good crystallinity. The spectrum of OmBpy-COF did not change much after anchoring copper ions, which shows that anchoring copper ions does not affect its crystal structure.

[0034] (2) The Fourier transform infrared spectra of the monomers with OmBpy-COF and Cu-OmBpy-COF are shown in [reference needed]. Figure 2 Observations showed that after the synthesis of OmBpy-COF, the amino monomers were in the range of 3080-3350 cm⁻¹. -1 The stretching peak and aldehyde monomer at 1680 cm⁻¹ -1 All stretching peaks disappeared, but at 1590 cm⁻¹ -1 The C=N bond stretching signal appears at the point, and the characteristic peak of the COC conjugate stretching vibration corresponding to the fingerprint peak of the oxazole ring is in the range of 1100-1020 cm⁻¹. -1 The peak of the C=C conjugated stretching vibration of the ring skeleton appears at 1520 cm⁻¹, with the oxazole ring and pyrimidine ring conjugated. -1 The appearance of this further confirms the successful preparation of OmBpy-COF.

[0035] (3) The UV-Vis absorption spectrum of the novel covalent organic material OmBpy-COF supported monodisperse copper catalyst in this embodiment is shown in [reference needed]. Figure 3 In Figure (a), it can be seen that both COFs exhibit strong absorption in the visible light region, especially in the 400-500 nm range. The optical band gap results calculated from the Tauc plot are shown below. Figure 3 In (b), the band gap energy of Cu-OmBpy-COF is 2.18 eV, which is narrower than that of OmBpy-COF (2.43 eV). A schematic diagram of the energy level structure of the material is shown below. Figure 3In (c), both OmBpy-COF and Cu-OmBpy-COF satisfy the CO2 / CO reduction potential (-0.53 V vs NHE), which meets the thermodynamic requirements for reducing CO2 to CO. The synthesized single-atom photocatalyst Cu-OmBpy-COF absorbs visible light more effectively than pure OmBpy-COF.

[0036] (4) Scanning electron microscopy images of OmBpy-COF and Cu-OmBpy-COF are shown in [reference needed]. Figure 4 It can be observed that COF has a plate-like structure, and its morphology does not change after the introduction of Cu ions, indicating that the anchoring of metal Cu ions does not change the morphology and structure of COF.

[0037] (5) Normalized Cu k-edge XANES spectrum and experimental k-edge XANES of Cu-OmBpy-COF single-atom photocatalyst 2 - Weighted CuK-edge EXAFS curve as shown Figure 5 As shown, Cu-OmBpy-COF is a Cu-O / N with only one shell, and the Cu valence state is slightly lower than +2, making it a single-atom photocatalyst.

[0038] (6) Electrochemical impedance spectroscopy (EIS) of OmBpy-COF and Cu-OmBpy-COF, as shown in... Figure 6 As shown, compared with OmBpy-COF, Cu-OmBpy-COF has a smaller radius of curvature, indicating that Cu-OmBpy-COF has a lower charge transfer resistance and a faster charge transfer rate, thereby improving photocatalytic performance.

[0039] (7) The CO evolution rates of OmBpy-COF and Cu-OmBpy-COF are as follows: Figure 7 As shown, after 5 hours of continuous irradiation, the original OmBpy-COF can photocatalytically reduce CO2 to CO with a yield of 711.07 µmol g. -1 The CO yield of Cu-OmBpy-COF after anchoring copper ions was significantly increased to 3815.94 µmol g. -1 It is 5.4 times that of pure COF, indicating that copper ions, as the catalytic active center, significantly enhance the adsorption and activation capacity of CO2 and improve photocatalytic activity.

[0040] (8) Cu-OmBpy-COF cycle test results are as follows Figure 8 Cu-OmBpy-COF maintained good reducing performance even after being cycled 4 times in the mixed solution.

[0041] (9) In-situ diffuse reflectance infrared Fourier transform (DRIFTS) spectroscopy analysis of Cu-OmBpy-COF photocatalyzed CO2RR under different illumination times, as follows: Figure 9 As shown, after illumination, at 1300 ~ 2100 cm -1 Multiple peaks gradually appear within the range, corresponding to bidentate carbonate (b-CO3). 2- Monodentate carbonates (m-CO3) 2- The formation of the *COOH intermediates indicates that the photocatalytic CO2RR to CO pathway on Cu-OmBpy-COF follows the pattern CO2→*COOH→*CO→CO. Compared with OmBpy-COF, these new peaks appear significantly and their intensity gradually increases with increasing illumination time, indicating that the anchoring of single Cu ions can significantly promote the formation of C1 intermediates, thereby improving photocatalytic activity.

[0042] In summary, this invention presents the first synthesis of a novel covalent organic framework, OmBpy-COF, with an imine group and an oxazole ring doubly linked. Based on this, a copper-ion-anchored covalent organic framework single-atom photocatalyst, Cu-OmBpy-COF, was further prepared. Under conditions without the addition of sacrificial agents or photosensitizers, after continuous irradiation under visible light for 5 hours, Cu-OmBpy-COF exhibited optimal catalytic activity, achieving a CO yield as high as 3815.94 µmol g. -1 Furthermore, the CO selectivity is 100%. This photocatalyst not only possesses excellent photocatalytic stability but also provides new research ideas and directions for the structural design and performance optimization of highly efficient COF-based photocatalysts for carbon dioxide reduction.

[0043] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a single-atom photocatalyst Cu-OmBpy-COF, characterized in that, Includes the following steps: 1) Disperse 2,4,5-triamino-6-hydroxypyrimidine sulfate, [2,2'-bipyridine]-5,5-dicarboxaldehyde and acetic acid in an organic solvent to obtain a mixed solution; 2) The mixed solution described in step 1) is sequentially subjected to liquid nitrogen freezing, vacuuming, and thawing, followed by reaction to obtain the crude product; 3) The crude product described in step 2) is washed, Soxhlet extracted and vacuum dried sequentially to obtain the covalent organic framework OmBpy-COF material; 4) The covalent organic framework OmBpy-COF and anhydrous copper acetate obtained in step 3) are ultrasonically dispersed in acetonitrile, stirred, filtered and dried to obtain the single-atom photocatalyst Cu-OmBpy-COF.

2. The preparation method according to claim 1, characterized in that, In step 1), the mass ratio of 2,4,5-triamino-6-hydroxypyrimidine sulfate, the mass of [2,2'-bipyridine]-5,5-dicarboxaldehyde, the volume of acetic acid solution, and the volume of organic solvent is 47.8 mg: 63.6 mg: 0.4 mL: 2 mL.

3. The preparation method according to claim 1, characterized in that, Step 1) The concentration of the acetic acid solution is 6 mol / L; The organic solvent is N,N-dimethylacetamide and o-dichlorobenzene, and the volume ratio of N,N-dimethylacetamide and o-dichlorobenzene is 1:

2.

4. The preparation method according to claim 1, characterized in that, Step 2) involves three cycles of liquid nitrogen freezing, vacuuming, and thawing. The reaction conditions include a temperature of 120°C and a time of 72 h.

5. The preparation method according to claim 1, characterized in that, Step 3) The crude product is washed sequentially with acetone, tetrahydrofuran, and deionized water; The solvent used in the Soxhlet extraction was tetrahydrofuran, and the Soxhlet extraction time was 12 h. The vacuum drying temperature is 80℃ and the time is 12 h.

6. The preparation method according to claim 1, characterized in that, Step 4) The mass ratio of the covalent organic framework OmBpy-COF, the mass of anhydrous copper acetate, and the volume of acetonitrile is 30 mg:30 mg:30 mL.

7. The preparation method according to claim 1, characterized in that, Step 4) The ultrasonic dispersion time is 30 minutes; The stirring time is 10 h; The drying conditions include a temperature of 80°C and a time of 12 hours.

8. A single-atom photocatalyst Cu-OmBpy-COF prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the single-atom photocatalyst Cu-OmBpy-COF according to claim 8 in the photocatalytic reduction of carbon dioxide to carbon monoxide.

10. The application according to claim 9, characterized in that, The application includes the following steps: dispersing the single-atom photocatalyst Cu-OmBpy-COF in a solvent, introducing carbon dioxide, and then reacting under 300W xenon lamp irradiation.

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