Monatomic photocatalyst Co-COF-C4N as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalysis, in particular to a monatomic photocatalyst Co-COF-C4N as well as a preparation method and application thereof. COF-C4N is synthesized through a solvothermal method, and cobalt metal is anchored into a covalent organic framework through an impregnation method, so that the monatomic catalyst Co-COF-C4N is obtained. Compared with pure COF-C4N, the Co-COF-C4N has the advantages that the carrier separation efficiency can be improved, the yield of H2O2 produced through photocatalysis can be remarkably enhanced, and the yield of H2O2 is 6979 mu mol.g <-1 >. H <-1 > under irradiation of a xenon lamp and is 1.6 times that of the pure COF-C4N. The anchoring of cobalt atoms increases oxygen adsorption sites, improves the hydrophilicity of the photocatalyst, and greatly improves the yield of hydrogen peroxide. The hydrogen peroxide is produced through indirect 2e-ORR and direct 2e-WOR double channels in deionized water under the oxygen condition, and excellent photocatalytic stability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysis, and particularly relates to a single-atom photocatalyst Co-COF-C4N, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is an important green oxidant. It can not only be used as a clean energy source, but also plays an important role in various industries such as chemical engineering, food and medicine, water treatment, and metallurgy. In addition, hydrogen peroxide is easier to store and transport than other clean energy sources (such as hydrogen), so there is a huge demand and consumption for hydrogen peroxide in the market. At present, the mature industrial production method of H2O2 is the anthraquinone method, but the anthraquinone method for producing H2O2 has disadvantages such as high energy consumption, heavy pollution, great potential safety hazards, and many adverse by-products, and its applicability is limited. In contrast, photocatalytic oxygen reduction (ORR) of pure water and air or oxygen provides an efficient and environmentally friendly technology for the production of H2O2. Therefore, it is crucial to develop a suitable photocatalyst for the production of hydrogen peroxide.

[0003] Covalent organic frameworks, also known as COFs, are a new type of crystalline porous polymer material composed of organic molecules connected by covalent bonds. They have a large specific surface area, regular porous channels, a π-π conjugate structure, and structural designability, making them a new type of photocatalyst. However, the relatively fast recombination of photo-generated carriers and the lack of sufficient WOR sites in COFs still limit their application in the overall photosynthesis for the production of H2O2. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a single-atom photocatalyst Co-COF-C4N, a preparation method thereof, and an application thereof. Using the single-atom photocatalyst Co-COF-C4N provided by the present invention, the H2O2 yield is increased, and the stability of the photocatalyst is improved.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a single-atom photocatalyst Co-COF-C4N, comprising the following steps:

[0007] 1) Dispersing 2,3,6,7,10,11-hexamminotriphenylene hexahydrochloride, hexaketocyclohexane octahydrate, and acetic acid solution in an organic solvent to obtain a mixed solution;

[0008] 2) Subjecting the mixed solution obtained in step 1) to vacuum pumping and degassing, and performing a thermal reaction to obtain a crude reactant;

[0009] 3) Wash, purify, and vacuum dry the crude reactants obtained in step 2) to obtain the covalent organic framework COF-C4N;

[0010] 4) Disperse the covalent organic framework COF-C4N obtained in step 3) and cobalt acetate tetrahydrate in methanol and sonicate, then stir and dry in sequence to obtain the single-atom photocatalyst Co-COF-C4N.

[0011] Preferably, the mass ratio of 2,3,6,7,10,11-hexamminetriphenylene hexahydrochloride, the mass of cyclohexanehexone octahydrate, the volume of acetic acid solution, and the volume of organic solvent in step 1) is 25.5 mg: 25 mg: 0.5 mL: 3 mL;

[0012] The concentration of the acetic acid solution is 4 mol / L;

[0013] The organic solvent is mesitylene and 1,4-dioxane, and the volume ratio of mesitylene to 1,4-dioxane is 1:1.

[0014] Preferably, after introducing nitrogen in step 2), evacuate the air and degas by the freeze-thaw method; repeat evacuation and degassing 3 times.

[0015] Preferably, the conditions for the thermal reaction in step 2) include: temperature is 150 °C and time is 72 h.

[0016] Preferably, use tetrahydrofuran for washing in step 3);

[0017] The purification method includes: Soxhlet extraction with tetrahydrofuran at a temperature of 100 °C for 12 h;

[0018] The conditions for vacuum drying include: temperature is 120 °C and time is 12 h.

[0019] Preferably, the mass ratio of the covalent organic framework COF-C4N, the mass of cobalt acetate tetrahydrate, and the volume of methanol in step 4) is: 30 mg: 30 mg: 30 mL.

[0020] Preferably, the sonication time in step 4) is 40 min;

[0021] The stirring time is 12 h;

[0022] The conditions for drying include: temperature is 80 °C and time is 12 h.

[0023] The present invention also provides a single-atom photocatalyst Co-COF-C4N prepared by the preparation method described in the above technical solution.

[0024] The present invention also provides an application of the single-atom photocatalyst Co-COF-C4N described in the above technical solution in the preparation of hydrogen peroxide.

[0025] Preferably, it includes the following steps: After mixing the single-atom photocatalyst Co-COF-C4N and deionized water, hydrogen peroxide is prepared under the irradiation of a 300W xenon lamp and gas.

[0026] The mass ratio of the single-atom photocatalyst Co-COF-C4N to the volume of water is 10mg:40mL.

[0027] The gas includes oxygen, air or argon.

[0028] Advantages of the present invention:

[0029] The preparation method provided by the present invention is simple, easy to operate, and has practical application significance. The present invention prepares a single-atom photocatalyst by embedding cobalt atoms into a covalent organic framework (COF-C4N), which can effectively improve the carrier separation rate, thereby significantly increasing the hydrogen peroxide yield. After 1 hour of irradiation with a xenon lamp (λ>420nm), the hydrogen peroxide yield reaches 6979 μmol·g -1 ·h -1 , and the single-atom photocatalyst Co-COF-C4N prepared by the present invention has excellent photocatalytic stability. Description of the drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments.

[0031] Figure 1 XRD spectra of COF-C4N and Co-COF-C4N;

[0032] Figure 2 Infrared spectra of COF-C4N and Co-COF-C4N;

[0033] Figure 3 UV-Vis diffuse reflectance spectra (UV-Vis) of COF-C4N and Co-COF-C4N; among them, a is the absorption spectrum, and b is the band gap energy diagram;

[0034] Figure 4 Transmission electron micrograph of the Co-COF-C4N single-atom photocatalyst;

[0035] Figure 5 Synchrotron radiation diagram of Co atoms in the Co-COF-C4N single-atom photocatalyst; among them, (a) is the normalized Co k-edge X-ray absorption near-edge structure (XANES) spectrum of Co atoms, and (b) is the experimental k 2- Weighted Co K-edge X-ray absorption fine structure spectrum (EXAFS) curve;

[0036] Figure 6 Are the electrochemical impedance spectroscopy (EIS) diagrams of COF-C4N and Co-COF-C4N;

[0037] Figure 7 Are the photocatalytic hydrogen peroxide production performance diagrams of COF-C4N and Co-COF-C4N photocatalysts in an oxygen environment under visible light;

[0038] Figure 8 Is the comparison diagram of the photocatalytic hydrogen peroxide production performance of Co-COF-C4N photocatalyst in oxygen, air, and argon environments under visible light;

[0039] Figure 9 Is the dynamic curve of the photocatalytic H2O2 production rate of Co-COF-C4N photocatalyst reused 6 times in deionized water;

[0040] Figure 10 Is the long-term continuous photosynthesis experimental curve of Co-COF-C4N. Detailed implementation mode

[0041] The present invention provides a preparation method of a single-atom photocatalyst Co-COF-C4N, which includes the following steps:

[0042] 1) Dispersing 2,3,6,7,10,11-hexamminotriphenylene hexahydrochloride, hexaketocyclohexane octahydrate, and acetic acid solution in an organic solvent to obtain a mixed solution;

[0043] 2) Subjecting the mixed solution obtained in step 1) to vacuum pumping and degassing, and performing a thermal reaction to obtain a crude reactant;

[0044] 3) Washing, purifying, and vacuum drying the crude reactant obtained in step 2) in sequence to obtain a covalent organic framework COF-C4N;

[0045] 4) Dispersing the covalent organic framework COF-C4N obtained in step 3) and cobalt acetate tetrahydrate in methanol for ultrasonic treatment, and then successively stirring and drying to obtain a single-atom photocatalyst Co-COF-C4N.

[0046] In the present invention, 2,3,6,7,10,11-hexamine triphenyl hexahydrochloride, cyclohexanehexone octahydrate and acetic acid solution are dispersed in an organic solvent to obtain a mixed solution. In the present invention, the mass ratio of 2,3,6,7,10,11-hexamine triphenyl hexahydrochloride, the mass of cyclohexanehexone octahydrate, the volume of acetic acid solution and the volume of organic solvent is preferably 25.5 mg: 25 mg: 0.5 mL: 3 mL. In the present invention, the concentration of the acetic acid solution is preferably 4 mol / L. In the present invention, the organic solvent is preferably mesitylene and 1,4-dioxane, and the volume ratio of mesitylene and 1,4-dioxane is preferably 1:1. The present invention has no special limitation on the sources of the above reagents, and conventional commercially available products can be used.

[0047] The present invention evacuates and degasses the obtained mixed solution, and obtains a crude reactant after thermal reaction. The present invention preferably evacuates after introducing nitrogen, and the present invention preferably uses a freeze-thaw method for degassing. The present invention preferably uses liquid nitrogen for freezing and thawing. The present invention preferably repeats evacuation and degassing 3 times. In the present invention, the conditions of the thermal reaction preferably include: the temperature is 150 °C and the time is 72 h.

[0048] The present invention washes, purifies and vacuum-dries the obtained crude reactant to obtain a covalent organic framework COF-C4N. The present invention preferably uses tetrahydrofuran for washing. In the present invention, the purification method preferably includes: Soxhlet extraction with tetrahydrofuran, the temperature is 100 °C and the time is 12 h. In the present invention, the conditions of the vacuum drying preferably include: the temperature is 120 °C and the time is 12 h.

[0049] The present invention disperses the obtained covalent organic framework COF-C4N and cobalt acetate tetrahydrate in methanol for ultrasonic treatment, and then obtains a single-atom photocatalyst Co-COF-C4N after stirring and drying in sequence. In the present invention, the mass ratio of the covalent organic framework COF-C4N, the mass of cobalt acetate tetrahydrate and the volume of methanol is preferably 30 mg: 30 mg: 30 mL. In the present invention, the mixing preferably uses an ultrasonic method, and the time is preferably 40 min. In the present invention, the stirring time is preferably 12 h. In the present invention, the conditions of the drying preferably include: the temperature is 80 °C and the time is 12 h.

[0050] The present invention also provides a single-atom photocatalyst Co-COF-C4N prepared by the preparation method described in the above technical solution.

[0051] The present invention also provides the application of the single-atom photocatalyst Co-COF-C4N described in the above technical solution in the preparation of hydrogen peroxide. In the present invention, the application preferably includes the following steps: after mixing the single-atom photocatalyst Co-COF-C4N and water, hydrogen peroxide is prepared under the irradiation of a 300W xenon lamp and a gas; the mass ratio of the single-atom photocatalyst Co-COF-C4N to the volume of deionized water is 10mg:40mL; the gas includes oxygen, air or argon.

[0052] To further illustrate the present invention, the present invention will be described in detail below with reference to embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0053] Example 1

[0054] 1. Preparation of Co-COF-C4N photocatalyst

[0055] 1.1 COF-C4N was prepared by a solvothermal method: 25.5 mg of 2,3,6,7,10,11-hexamminotriphenylene hexahydrochloride, 25 mg of hexaketocyclohexane octahydrate and 0.5 mL of 4M acetic acid solution were ultrasonically dispersed in a mixed solution of 1.5 mL of mesitylene and 1.5 mL of 1,4-dioxane at room temperature for 30 min. Then, nitrogen was passed through the mixed solution - evacuated, and then frozen - thawed with liquid nitrogen for degassing, and this operation was repeated 3 times; then the degassed dispersion was placed in a blast drying oven at 150 °C for reaction for 72 h. After the temperature of the drying oven dropped to room temperature, the test tube was taken out to obtain a crude reaction product; the crude reaction product was filtered and washed with tetrahydrofuran, and after drying, a brownish-black solid product was obtained; the solid product was subjected to Soxhlet extraction with tetrahydrofuran at a temperature of 100 °C for 12 h for thorough washing; the obtained solid product was vacuum dried at 120 °C for 12 h to obtain COF-C4N;

[0056] 1.2 At room temperature, 30 mg of the COF-C4N obtained in step 1 and 30 mg of cobalt acetate tetrahydrate were added to 30 mL of methanol, ultrasonically treated for 40 min, and then stirred for 12 h (1000R / min). The dispersion solution was washed with methanol and dried at 80 °C for 12 h to obtain the single-atom photocatalyst Co-COF-C4N.

[0057] 2. Photocatalytic performance test:

[0058] To investigate the photocatalytic H2O2 production yield of the single-atom photocatalyst Co-COF-C4N, under the irradiation of a 300 W xenon lamp (λ > 420 nm), in the absence of a sacrificial agent, and in an oxygen environment, the H2O2 production in deionized water of the sample was measured. 10 mg of the single-atom photocatalyst Co-COF-C4N and 40 mL of deionized water were added to the reactor. Then the mixture was sonicated for 10 min, stirred in the dark for 30 min, and oxygen, air, and argon were continuously introduced separately. A circulating cooling system was used to maintain the temperature at 25 °C. After reaching the adsorption-desorption equilibrium, the xenon lamp was turned on, and samples were taken every 20 min. The cerium sulfate method was used to measure the H2O2 production yield.

[0059] 2Ce 4+ +H2O2→2Ce 3+ +2H + +O2

[0060]

[0061] 3. Results analysis:

[0062] 3.1 The XRD patterns of COF-C4N and Co-COF-C4N are as Figure 1 shown. In the pattern of COF-C4N, two peaks at 2θ = 7.2° and 27° can be clearly observed, corresponding to the 100 crystal plane and 001 crystal plane respectively. By observing the pattern of Co-COF-C4N and comparing the peaks, it can be seen that the pattern of COF-C4N basically remains unchanged after doping with metal Co, indicating that embedding cobalt atoms into COF-C4N does not affect its crystal structure.

[0063] 3.2 The Fourier transform infrared spectra (FT-IR) of COF-C4N and Co-COF-C4N are as Figure 2 shown. By observing the spectra of COF-C4N and Co-COF-C4N, the diffraction absorption peaks at 1509, 1458, and 1389 cm -1 −1 can prove the formation of phenazine bonds, indicating that COF-C4N has been successfully prepared, and after embedding metal Co, the phenazine structure remains unchanged. And a new absorption peak appears at around 1500 cm -1 −1 after metal coordination. It is inferred that this is the absorption peak of the acetic acid group that appears after metal coordination and is embedded in the COF framework. The FT-IR spectra of COF-C4N and Co-COF-C4N basically remain unchanged, indicating that the introduction of metal ions does not change the original structure of COF-C4N.

[0064] 3.3 The ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) of COF-C4N and Co-COF-C4N are as Figure 3As shown in a), it can be seen that both COF-C4N and Co-COF-C4N exhibit absorption in the visible light range. According to the calculation, the band gap of Co-COF-C4N is smaller than that of the original COFs ( Figure 3 in b), indicating that the synthesized single-atom photocatalyst is more effective in absorbing visible light than pure COFs.

[0065] 3.4 The transmission electron microscopy images of the Co-COF-C4N photocatalyst are as Figure 4 shown. It can be seen from the figure that the prepared photocatalyst has a nanosheet structure and a hexagonal honeycomb structure, indicating the successful synthesis of the catalyst.

[0066] 3.5 The normalized Co k-edge XANES spectra and experimental k 2 -weighted Co K-edge EXAFS curves of the Co-COF-C4N single-atom photocatalyst are as Figure 5 shown in a and b, indicating that Co-COF-C4N is a single-atom photocatalyst, and divalent Co is coordinated with two N and two O.

[0067] 3.6 The electrochemical impedance spectra (EIS) of COF-C4N and Co-COF-C4N are as Figure 6 shown. Compared with pure COF-C4N, Co-COF-C4N has a smaller radius of curvature, indicating that Co-COF-C4N has a small resistance to charge transfer and a fast charge transfer rate, thereby improving the photocatalytic performance.

[0068] 3.7 Under the condition of no sacrificial agent, the H2O2 production of COF-C4N and Co-COF-C4N in deionized water in an oxygen environment was compared. From Figure 7 it can be seen that Co-COF-C4N exhibits the highest photocatalytic ORR activity. The H2O2 production rate of Co-COF-C4N is 6979 μmol·g -1 ·h -1 within 1 h under the irradiation of a xenon lamp (λ > 420 nm), which is approximately 1.6 times that of COF-C4N (4501 μmol·g -1 ·h -1 ), indicating that the embedding of cobalt atoms into COF-C4N improves the photocatalytic activity.

[0069] 3.8 Under the condition of no sacrificial agent, the H2O2 production of Co-COF-C4N in deionized water in oxygen, air, and argon environments was compared ( Figure 8 ). The production rates of Co-COF-C4N in oxygen, air, and argon environments are 6979 μmol·g -1 ·h -1 , 6398 μmol·g -1 ·h-1 、1398 μmol·g -1 ·h -1 。The yield is lower in air atmosphere than in oxygen atmosphere. The production of H2O2 in argon environment indicates the existence of the WOR pathway.

[0070] 3.9 The cyclic stability of Co-COF-C4N was examined by short-time photocatalytic cycles. In Figure 9 Six consecutive photocatalytic cycles (1 h for each cycle) were carried out, indicating that the prepared Co-COF-C4N photocatalyst has excellent photocatalytic reusability.

[0071] 3.10 The long-term continuous photocatalytic H2O2 production performance of Co-COF-C4N was tested. From Figure 10 it can be seen that for the Co-COF-C4N photocatalytic H2O2 production rate in the first 6 h, the amount of H2O2 increases with time, showing good long-term stability.

[0072] In summary, the present invention successfully synthesized a cobalt atom-anchored covalent organic framework single-atom photocatalyst, and the photocatalyst photocatalytically synthesizes hydrogen peroxide from deionized water through indirect 2e - ORR and direct 2e - WOR dual channels. For the synthesized Co-COF-C4N photocatalyst, under the irradiation of a xenon lamp (λ > 420 nm), the hydrogen peroxide production rate reaches 6979 μmol·g -1 ·h -1 within 1 h. The photocatalyst not only has excellent photocatalytic stability but also provides a new research direction for the design of catalysts for photosynthetic hydrogen peroxide synthesis in water.

[0073] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments without creative efforts based on these embodiments, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A method for preparing a single-atom photocatalyst Co-COF-C4N, characterized in that: The following steps are involved: 1) dispersing 2,3,6,7,10,11-hexamidotriphenyl hexahydrochloride, hexaketone cyclohexane octahydrate and acetic acid solution in an organic solvent to obtain a mixed solution; 2) vacuumizing and degassing the mixed solution obtained in step 1), and performing a thermal reaction to obtain a crude reactant; 3) washing, purifying and vacuum drying the crude reactant obtained in step 2) to obtain a covalent organic framework COF-C4N; 4) The covalent organic framework COF-C4N obtained in step 3) and cobalt acetate tetrahydrate are dispersed in methanol and subjected to ultrasound, and then stirred and dried in sequence to obtain the single-atom photocatalyst Co-COF-C4N.

2. The preparation method according to claim 1, characterized in that: In the step 1), the mass ratio of 2,3,6,7,10,11-hexaaminotriphenylhexahydrochloride, the mass of hexaketone cyclohexane octahydrate, the volume of acetic acid solution and the volume ratio of organic solvent is 25.5 mg:25 mg:0.5 mL:3 mL; The concentration of the acetic acid solution is 4 mol / L; The organic solvent is mesitylene and 1,4-dioxane, and the volume ratio of mesitylene to 1,4-dioxane is 1:

1.

3. The preparation method according to claim 1, characterized in that: In the step 2), nitrogen was introduced and then vacuumed, and degassing was performed by freeze-thaw method; vacuuming and degassing were repeated 3 times.

4. The preparation method according to claim 1, characterized in that: The conditions of the thermal reaction in step 2) include: temperature of 150° C. and time of 72 h.

5. The preparation method according to claim 1, characterized in that: The step 3) is washed with tetrahydrofuran; The purification method includes: using tetrahydrofuran for Soxhlet extraction at a temperature of 100° C. for 12 hours; The vacuum drying conditions include: temperature of 120° C. and time of 12 h.

6. The preparation method according to claim 1, characterized in that: In the step 4), the volume ratio of the mass of the covalent organic framework COF-C4N, the mass of cobalt acetate tetrahydrate and methanol is 30 mg:30 mg:30 mL.

7. The preparation method according to claim 1, characterized in that: The ultrasonic time in step 4) is 40 min; The stirring time is 12h; The drying conditions include: temperature of 80° C. and time of 12 h.

8. A single-atom photocatalyst Co-COF-C4N prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the single-atom photocatalyst Co-COF-C4N according to claim 8 in the preparation of hydrogen peroxide.

10. The use according to claim 9, characterized in that: The method comprises the following steps: mixing the single-atom photocatalyst Co-COF-C4N with deionized water, and preparing hydrogen peroxide under irradiation of a 300W xenon lamp and gas; The mass ratio of the single-atom photocatalyst Co-COF-C4N to the volume ratio of deionized water is 10 mg:40 mL; The gas includes oxygen, air or argon.

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