A cobalt / manganese vanadate composite photocatalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic material preparation, and particularly relates to a cobalt oxide / manganese vanadate composite photocatalyst, a preparation method and application thereof. CoO nanowires are prepared by a gas phase cation exchange method, CoO / ZnO nanowires are obtained by a pulling film reaction, and finally, in-situ synthesized CoO / Mn3V2O8 heterojunction composite catalysts, referred to as heterojunction composite catalysts, are obtained by the gas phase cation exchange method. Compared with the prior art, the application has the beneficial effects that: the material synthesis reaction is fast and short in time, greatly reducing the time cost of reaction synthesis; the preparation method is relatively systematic, impurities are not generated in the preparation process by using the gas phase ion exchange method, the purity is high, and it is easier to synthesize uniformly distributed nanostructures; the application has good catalytic performance, and the photocatalytic reaction can be well carried out by using the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic material preparation technology, specifically relating to a cobalt oxide / manganese vanadate composite photocatalyst, its preparation method, and its application. Background Technology

[0002] In the context of addressing global climate change and the energy crisis, the development of sustainable and clean energy conversion and storage technologies is of paramount importance. Photocatalysis, as an emerging green chemistry approach, can utilize solar energy to drive chemical reactions, thereby achieving environmental governance goals such as hydrogen splitting from water, photocatalytic reduction of carbon dioxide, and degradation of organic pollutants. The photocatalytic performance of photocatalytic materials largely depends on their light absorption, charge separation and transfer capabilities, as well as the absorption and activation abilities of reactants. However, most existing photocatalysts suffer from narrow light absorption ranges, high carrier recombination rates, and slow redox reactions. Therefore, constructing heterojunctions and introducing charge trapping centers (such as surface defects and functional groups) to accelerate photoinduced charge separation and transfer is crucial for improving photocatalytic performance.

[0003] In the field of photocatalytic material preparation technology, cobalt oxide (CoO) and manganese vanadate (Mn3V2O8) have gradually become research hotspots due to their unique physicochemical properties and excellent photocatalytic performance. Cobalt oxide (CoO) possesses good visible light absorption and a reasonable band structure, which can effectively support the generation of photogenerated electron-hole pairs. Furthermore, the synthesis process of cobalt oxide is relatively simple, and its components are abundant and inexpensive, meeting the dual requirements of effectiveness and economy. Manganese vanadate (Mn3V2O8) also exhibits good reactivity and stability in the photocatalytic process. It can absorb light energy over a wide wavelength range, especially in the visible light region. This provides a good foundation for its application in clean energy conversion and environmental remediation. In summary, cobalt oxide and manganese vanadate photocatalytic materials not only possess excellent catalytic performance but can also effectively utilize solar energy, promoting environmental pollution control and the development of renewable energy. Therefore, researching the construction of heterojunctions combining and applying these two materials to achieve better photocatalytic performance has significant scientific and practical value, contributing to the achievement of sustainable development goals.

[0004] Currently, commonly used methods for constructing heterostructures mainly include hydrothermal methods, coprecipitation methods, and electrochemical deposition methods. Among these, the hydrothermal method, by inducing a chemical reaction in a high-temperature, high-pressure environment, can achieve uniform mixing of materials and controllable growth of nanostructures. Generally, the hydrothermal method has a slow reaction rate, requiring a long reaction time and resulting in low production efficiency; the synthesis of a single material often takes more than 10 hours. Furthermore, the mixture after the hydrothermal reaction usually contains a large amount of solvent, unreacted raw materials, and byproducts, making product separation and purification difficult. Multiple separation and purification techniques, such as filtration, centrifugation, washing, and drying, are required, which not only increases preparation costs and time but may also affect the performance of the product. The coprecipitation method separates or combines different substances simultaneously through a precipitation reaction. Although simple to operate and widely applicable, it may introduce impurity ions during precipitation, significantly affecting the purity of the product. Photodeposition involves depositing metal or semiconductor nanoparticles onto the surface of a substrate material under light conditions. This method is relatively simple and fast, and the type and quantity of deposited particles can be controlled. However, it is greatly affected by external factors such as light, making it difficult to form uniformly distributed heterostructure materials, thus affecting material performance. These methods each have their own advantages and disadvantages, so there is an urgent need to adopt a simple and efficient method for constructing heterojunctions to realize the catalyst construction of CoO / Mn3V2O8 heterojunctions. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings and deficiencies of existing photocatalysts and provide a method for preparing a highly efficient CoO / Mn3V2O8 composite catalyst with excellent photocatalytic performance. This addresses the problems of complex preparation processes, stringent preparation conditions, and significant influence from external factors in existing synthesis methods. CoO and Mn3V2O8 form a heterojunction structure, enhancing the catalytic activity for photocatalysis and providing a new composite material for efficient photocatalytic water splitting. The preparation method first utilizes stretched FTO conductive glass to obtain a single-crystal zinc oxide (ZnO) nanowire seed layer; then, CoO nanowires are prepared using a gas-phase cation exchange method; subsequently, the ZnO seed solution is repeatedly used for film stretching to obtain CoO / ZnO nanowires; finally, the CoO / Mn3V2O8 heterojunction composite catalyst is prepared using manganese chloride powder, vanadium chloride powder, and CoO / ZnO nanowires via a gas-phase cation exchange method. Another objective of this invention is to provide the aforementioned cobalt oxide / manganese vanadate composite photocatalyst for applications in photocatalytic water splitting and photocatalytic degradation of pollutants.

[0006] The specific technical solution is as follows: A method for preparing a cobalt oxide / manganese vanadate composite photocatalyst, firstly, CoO nanowires are prepared by gas-phase cation exchange, then CoO / ZnO nanowires are obtained by film stretching reaction, and finally, CoO / Mn3V2O8 heterojunction composite catalyst is obtained by gas-phase cation exchange, which is referred to as heterojunction composite catalyst.

[0007] Preferably, the CoO nanowire preparation carrier is a stretched FTO conductive glass with a single-crystal zinc oxide nanowire seed layer, or simply FTO glass with a seed layer.

[0008] Preferably, the preparation of FTO glass with a seed layer is as follows: First, FTO conductive glass is stretched and immersed in ZnO seed solution. After being removed from the solution, the FTO conductive glass is heated to 90-105°C and held for 8-15 minutes to obtain the prepared ZnO seed layer. Then, the FTO glass with the seed layer is heated at 450-520°C for 50-80 minutes. After the heating is completed, it is cooled to obtain stretched FTO conductive glass with a single-crystal zinc oxide nanowire seed layer.

[0009] Preparation of CoO / ZnO nanowires: First, cobalt chloride powder and FTO glass with a seed layer are heated to 500-600°C and held for 20-60 minutes to obtain an FTO sheet loaded with CoO nanowires; then, the FTO sheet loaded with CoO nanowires is repeatedly stretched using ZnO seed solution to grow ZnO on the CoO nanowires to obtain CoO / ZnO nanowires.

[0010] Preparation of heterojunction composite catalyst: FTO sheets containing manganese chloride, vanadium trichloride and CoO / ZnO nanowires were heated to 500-600°C and held for 20-60 minutes to obtain FTO glass sheets carrying CoO / Mn3V2O8 heterojunction materials.

[0011] Preferably, the preparation steps of CoO / ZnO nanowires are as follows:

[0012] S31. Weigh cobalt chloride powder and place it in a porcelain boat, then place it on the right side of the vacuum tube furnace chamber.

[0013] S32. Place the FTO glass with the seed layer in another ceramic boat, which is placed in the center of a vacuum tube furnace, and seal the furnace opening.

[0014] S33. After purging the furnace tube with argon gas, maintain the vacuum state inside the furnace tube;

[0015] S34. Heat the tube furnace to 500-600°C and hold for 20-60 minutes. After holding, cool to room temperature, open the gas inlet and purge with argon gas to atmospheric pressure. Open the gas inlet and remove the FTO sheet loaded with CoO nanowires.

[0016] S35. Using an FTO sheet loaded with CoO nanowires, ZnO is grown on the CoO nanowires by repeatedly stretching the film with ZnO seed solution to obtain CoO / ZnO nanowires.

[0017] Preferably, the preparation steps of the heterojunction composite catalyst are as follows:

[0018] S41, manganese chloride and vanadium trichloride are placed in a porcelain boat in a mass ratio of 2:1, and the porcelain boat is placed on the far right side of the vacuum tube furnace.

[0019] S42. Place the FTO sheet of CoO / ZnO nanowires in another ceramic boat, place it in the center of the far right side of the vacuum tube furnace, and seal the furnace opening.

[0020] S43. Use argon gas to flush the furnace tubes and maintain a vacuum inside the furnace tubes;

[0021] S44. Heat the tube furnace to 500-600°C and hold for 20-60 minutes. After holding, cool to room temperature, open the inlet and purge with argon to atmospheric pressure. Open both sealed ends and remove the FTO glass slide containing the CoO / Mn3V2O8 heterojunction material. Gently scrape it off with a knife to obtain a brown powder product.

[0022] Preferably, the method for preparing FTO glass with a seed layer is as follows:

[0023] S21. Preparation of ZnO seed solution: Add ethylene glycol methyl ether to a beaker, then add monoethanolamine (MEA) dropwise. Weigh zinc acetate and add it to the beaker. Stir magnetically at room temperature until the solution is completely clear to obtain ZnO seed solution.

[0024] S22. Place the prepared ZnO seed solution in a vacuum drying oven at 75-85℃, heat for 1-3 hours, then remove and place in a beaker.

[0025] S23. Take FTO conductive glass, dry it with nitrogen gas, clamp the upper end of FTO conductive glass with the chuck of the film stretching machine, stretch the film, adjust the film stretching speed, and slowly and vertically immerse the FTO conductive glass into the ZnO seed solution. After it is completely submerged, let it stand.

[0026] S24. After standing for 20-80 seconds, it slowly rises until it is completely separated from the solution. Remove the FTO conductive glass, wipe the solution clean on the non-conductive surface with lens paper, place it in a muffle furnace, heat it to 90-105°C, keep it at that temperature for 8-15 minutes, remove it and cool it down to obtain the prepared ZnO seed layer.

[0027] S25. Place the FTO glass with the seed layer in a muffle furnace and heat it at 450-520°C for 50-80 minutes. After heating, cool it with the furnace and rinse it with anhydrous ethanol and deionized water until there are no agglomerates on the surface. Dry it with nitrogen to obtain a stretched FTO conductive glass with a single-crystal zinc oxide nanowire seed layer.

[0028] Preferably, the ZnO seed solution is prepared as follows: ethylene glycol methyl ether is added to a beaker, followed by the dropwise addition of monoethanolamine (MEA). Zinc acetate is weighed and added to the beaker. The solution is then magnetically stirred at room temperature until it becomes completely clear, thus obtaining the ZnO seed solution.

[0029] Preferably, the concentration of ethylene glycol methyl ether is 99.8%, the concentration of monoethanolamine is 99.5%, and the volume ratio of ethylene glycol methyl ether to monoethanolamine is 2:1.

[0030] A cobalt oxide / manganese vanadate composite photocatalyst was prepared using the method described above.

[0031] Application of a cobalt oxide / manganese vanadate composite photocatalyst: The cobalt oxide / manganese vanadate composite photocatalyst prepared by the above method is used in hydrogen production through total water splitting and photocatalytic degradation of pollutants.

[0032] This application describes the in-situ synthesis of cobalt oxide on ZnO single-crystal nanowires via gas-phase cation exchange. Cobalt oxide / zinc oxide nanowires are then prepared via secondary film stretching, and a cobalt oxide / manganese vanadate heterojunction photocatalyst based on the cobalt oxide / zinc oxide substrate is developed. Comparative experiments demonstrate that the CoO / Mn3V2O8 heterojunction composite photocatalyst prepared in this application significantly improves the hydrogen production efficiency of the material.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The material synthesis reaction of the present invention is fast and short, which greatly reduces the time cost of reaction synthesis.

[0035] (2) The preparation method of the present invention is relatively systematic. It uses gas phase ion exchange method, and no impurities are generated in the preparation process. The purity is high and it is easier to synthesize uniformly distributed nanostructures.

[0036] (3) The present invention has good catalytic performance, and photocatalytic reactions can be carried out well using this catalyst. Attached Figure Description

[0037] Figure 1 This is a scanning electron microscope image of the ZnO single-crystal nanowires obtained in step S2 of Example 1.

[0038] Figure 2 This is a scanning electron microscope image of CoO / ZnO obtained in step S3 of Example 1.

[0039] Figure 3 This is a scanning electron microscope (SEM) image of the CoO / Mn3V2O8 heterojunction material obtained in step S4 of Example 1 at a scale of 500 nm.

[0040] Figure 4This is a scanning electron microscope (SEM) image of the CoO / Mn3V2O8 heterojunction material obtained in step S4 of Example 1 at a scale of 5 μm.

[0041] Figure 5 The XRD analysis is the X-ray diffraction analysis of the CoO / Mn3V2O8 heterojunction material in step S4 of Example 1.

[0042] Figure 6 This is a bar chart showing the results of photocatalytic water splitting for hydrogen production using CoO / Mn3V2O8 heterojunction materials.

[0043] Figure 7 This is a bar chart showing the photocatalytic water splitting results for hydrogen production using only CoO and Mn3V2O8. Detailed Implementation

[0044] To facilitate understanding of the present invention, it will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0045] A method for preparing a cobalt oxide / manganese vanadate composite photocatalyst, comprising the following steps:

[0046] S1. Pre-treatment of FTO: Cut the FTO glass into slices, clean and dry them, and set aside.

[0047] S2. Preparation of FTO glass with seed layer:

[0048] S21. Preparation of ZnO seed solution: Add ethylene glycol methyl ether to a beaker, then add monoethanolamine (MEA) dropwise. The volume ratio of ethylene glycol methyl ether to monoethanolamine is 2:1. Weigh zinc acetate and add it to the beaker. Stir magnetically at room temperature until the solution is completely clear to obtain ZnO seed solution. The molar ratio of zinc acetate, monoethanolamine, and ethylene glycol methyl ether is approximately 1:30:60.

[0049] S22. Place the prepared ZnO seed solution in a vacuum drying oven at 75-85℃, heat for 1-3 hours, then remove and place in a beaker.

[0050] S23. Take FTO conductive glass, dry it with nitrogen gas, clamp the upper end of FTO conductive glass with the chuck of the film stretching machine, stretch the film, adjust the film stretching speed, and slowly and vertically immerse the FTO conductive glass into the ZnO seed solution. After it is completely submerged, let it stand.

[0051] S24. After standing for 20-80 seconds, it slowly rises until it is completely separated from the solution. Remove the FTO conductive glass, wipe the solution clean on the non-conductive surface with lens paper, place it in a muffle furnace, heat it to 90-105°C, keep it at that temperature for 8-15 minutes, remove it and cool it down to obtain the prepared ZnO seed layer.

[0052] S25. Place the FTO glass with the seed layer in a muffle furnace and heat it at 450-520°C for 50-80 minutes. After heating, cool it with the furnace and rinse it with anhydrous ethanol and deionized water until there are no agglomerates on the surface. Dry it with nitrogen to obtain a stretched FTO conductive glass with a single-crystal zinc oxide nanowire seed layer.

[0053] S3. Preparation of CoO / ZnO nanowires using gas-phase cation exchange and repeated film stretching:

[0054] S31. Weigh cobalt chloride powder and place it in a porcelain boat, then place it on the right side of the vacuum tube furnace chamber.

[0055] S32. Place the FTO glass with the seed layer in another ceramic boat, which is placed in the center of a vacuum tube furnace, and seal the furnace opening.

[0056] S33. After purging the furnace tube with argon gas, maintain the vacuum state inside the furnace tube;

[0057] S34. Heat the tube furnace to 500-600°C and hold for 20-60 minutes. After holding, cool to room temperature, open the inlet and purge with argon gas to atmospheric pressure. Open the two closed ends and remove the FTO sheet loaded with CoO nanowires.

[0058] S35. The FTO sheet carrying CoO nanowires is placed into the heated ZnO seed solution again by film stretching. The film stretching parameters and operations are repeated to obtain the prepared CoO / ZnO nanowire FTO conductive glass.

[0059] S4. The CoO / Mn3V2O8 heterojunction composite catalyst, referred to as the heterojunction composite catalyst, was synthesized in situ via a gas-phase cation exchange method. The preparation steps are as follows:

[0060] S41. Manganese chloride and vanadium trichloride are placed in a ceramic boat at a mass ratio of 2:1. The ceramic boat is placed on the far right side of the vacuum tube furnace. The amount of manganese chloride used is equal to the amount of cobalt chloride used in step S3.

[0061] S42. Place the FTO sheet loaded with CoO / ZnO nanowires in another ceramic boat, place it in the center of the far right side of the vacuum tube furnace, and seal the furnace opening.

[0062] S43. Use argon gas to flush the furnace tubes and maintain a vacuum inside the furnace tubes;

[0063] S44. Heat the tube furnace to 500-600°C and hold for 20-60 minutes. After holding, cool to room temperature, open the inlet and purge with argon to atmospheric pressure. Open both sealed ends and remove the FTO glass slide containing the CoO / Mn3V2O8 heterojunction material. Gently scrape it off with a knife to obtain a brown powder product.

[0064] This invention utilizes stretched FTO conductive glass to obtain a seed layer of single-crystal zinc oxide (ZnO) nanowires; then, CoO nanowires are prepared using a gas-phase cation exchange method, followed by secondary stretching to further obtain CoO / ZnO nanowires; finally, an in-situ synthesized CoO / Mn3V2O8 heterojunction composite catalyst is obtained through a gas-phase cation exchange method, forming a highly efficient and widely applicable photocatalyst based on cobalt oxide.

[0065] Example 1: A method for preparing a cobalt oxide / manganese vanadate composite photocatalyst, comprising the following steps:

[0066] S1. FTO Pretreatment: Cut the FTO glass into 2.5cm×2.5cm squares and perform three alcohol and water washes using an ultrasonic cleaner. The alcohol wash is ethanol washing, where the FTO is placed in a beaker containing ethanol and ultrasonically cleaned for 15 minutes. The water wash is deionized water washing, where the FTO is placed in a beaker containing deionized water and ultrasonically cleaned for 15 minutes. Dry the washed FTO glass with a hair dryer to ensure that there are no ethanol residue marks on the FTO glass, and use it as a carrier for the ZnO single crystal nanowire seed layer.

[0067] S2. Preparation of ZnO seed layer: First, add ethylene glycol methyl ether (EDM) to a beaker. The concentration of EDM is 99.8%, and the volume is 80 ml. Then, add monoethanolamine (MEA) dropwise at a rate of 4 s / drop. The concentration of MEA is 99.5%, and the volume is 40 ml. Weigh 2.75 g of zinc acetate and add it to the beaker. Stir magnetically at room temperature until the solution is completely clear to obtain ZnO seed solution. Place the prepared ZnO seed solution in a vacuum drying oven at 80℃ and heat for 2 hours. Then remove it and place it in a beaker. After cleaning the FTO glass in step S1, dry it with nitrogen gas. Then, clamp the upper end of the FTO conductive glass with the chuck of a film stretching machine and stretch it. Adjust the stretching speed to 0.5 cm / s, allowing the FTO conductive glass to be slowly and vertically immersed in the ZnO seed solution. After it is completely submerged, let it stand for 30 seconds, then slowly rise until it is completely removed from the solution. Remove the FTO conductive glass, wipe the solution off the non-conductive surface with lens paper, and place it in a muffle furnace. Heat it at 100°C for 10 minutes. After heating, remove it and let it cool. Repeat the above process three times to obtain the prepared ZnO seed layer. Place the prepared FTO glass with the seed layer in a muffle furnace and heat it at 500°C for 1 hour. After heating, cool it with the furnace and rinse it with anhydrous ethanol and deionized water until there are no agglomerates on the surface. Dry it with nitrogen gas to obtain the FTO glass with the seed layer.

[0068] Ethylene glycol methyl ether, as a solvent, provides a suitable dissolution environment for the reaction. Monoethanolamine, being basic, reacts with zinc acetate, causing zinc acetate to dissociate into zinc ions in solution. Monoethanolamine can also coordinate with zinc ions, forming a zinc-monoethanolamine complex. This complex is uniformly dispersed in the solution, gradually clarifying it. This reaction provides seeds for the growth of ZnO crystals, facilitating the uniform growth of ZnO single-crystal nanowires and other subsequent operations. When FTO conductive glass is immersed in the ZnO seed solution and heated at 500°C for 1 hour, the zinc-monoethanolamine complex on the conductive glass decomposes, and simultaneously, zinc ions combine with oxygen to form FTO glass with a seed layer.

[0069] Preparation of S3, CoO / ZnO nanowires: Weigh 0.2g of cobalt chloride (CoCl2) powder and place it in a ceramic boat, which is then placed on the right side of the vacuum tube furnace chamber. Place the FTO sheet containing ZnO single-crystal nanowires prepared in step S2 in another ceramic boat, which is then placed in the center of the vacuum tube furnace, and seal the furnace opening. Turn on the vacuum pump to evacuate the tube furnace to a vacuum state, then open the gas inlet and fill the tube furnace with argon gas at a flow rate of 50 sccm for 10 minutes. When the vacuum pressure gauge shows a pressure close to atmospheric pressure, close the gas inlet switch and simultaneously turn on the vacuum pump. This completes one gas flushing process. Repeat the flushing process three times, closing both gas inlets to maintain a vacuum state (approximately 1.37 kPa) inside the furnace tube. After cleaning, the tube furnace is heated to 500-600°C and held for 30 minutes. After holding, it is cooled to room temperature, the inlet is opened and argon gas is introduced to atmospheric pressure, the two closed ends are opened, and the FTO sheet carrying CoO nanowires is taken out. The FTO sheet carrying CoO nanowires is then placed into the heated ZnO seed solution again using film stretching. The film stretching parameters and operations are repeated to obtain the prepared CoO / ZnO nanowire FTO conductive glass.

[0070] In this step, a vacuum tube furnace is used for heating, employing gas-phase cation exchange to first prepare CoO nanowires. Under high-temperature conditions, cobalt vapor generated by the sublimation of CoCl2 diffuses onto the FTO glass surface carrying ZnO single-crystal nanowires. Catalyzed by the ZnO single-crystal nanowires, the cobalt chloride vapor reacts with oxygen ions from the ZnO surface to generate cobalt oxide (CoO). The ZnO single-crystal nanowires act as a catalyst, providing nucleation sites and promoting the growth of CoO nanowires. Simultaneously, under the catalysis of the ZnO seed layer, the CoO nanowires grow along a specific crystal direction, forming a uniformly distributed nanowire structure. Finally, the ZnO seed solution is repeatedly used for film stretching, ensuring a tight bond between ZnO and CoO, thus preparing CoO / ZnO nanowires.

[0071] S4, CoO / Mn3V2O8 heterojunction: Place 0.2g of MnCl2 powder and 0.1g of VCl3 powder in a ceramic boat, which is then placed on the far right side of the vacuum tube furnace chamber. Place the CoO / ZnO FTO sheet obtained in step S3 in another ceramic boat, which is then placed in the center of the far right side of the vacuum tube furnace chamber, and seal the furnace opening. Repeat the gas purging process in step S3 three times, maintaining a vacuum state inside the furnace tube. After purging, heat the tube furnace to 500-600°C, hold for 30 minutes, and then cool to room temperature. Open the gas inlet and purge with argon gas to atmospheric pressure. Open both sealed ends and remove the FTO glass sheet containing the CoO / Mn3V2O8 heterojunction material. Finally, gently scrape the brown powder product off the FTO glass sheet with a knife.

[0072] This step utilizes a vacuum tube furnace for heating, employing a gas-phase cation exchange method to synthesize the CoO / Mn3V2O8 heterojunction material. At high temperatures, MnCl2 and VCl3 sublimate to form metal vapors, which diffuse to the FTO glass surface within the tube furnace. On the CoO / ZnO surface, the MnCl2 and VCl3 vapors undergo a cation exchange reaction with ZnO, generating Mn3V2O8 in situ. CoO serves as a substrate, providing nucleation sites and promoting the growth of Mn3V2O8. During cooling, Mn3V2O8 forms a heterojunction structure in situ on the CoO surface, yielding an FTO glass sheet carrying the CoO / Mn3V2O8 heterojunction material.

[0073] The products obtained in steps S2-S4 were scanned by electron microscopy, such as... Figure 1-4 As shown. Figure 1 This indicates that the ZnO on the FTO glass with the seed layer prepared in step S2 exhibits a nanowire structure and grows uniformly, providing a good template for the next step of ion exchange. Figure 2 This indicates that the CoO / ZnO on the FTO sheet loaded with CoO / ZnO nanowires in step S3 is linear and grows uniformly, maintaining the original template shape of the ZnO nanowires. This demonstrates that the CoO / ZnO prepared by combining ion exchange and film stretching methods is effective. Figure 3-4 This indicates that the Mn3V2O8 material is a linear structure that is tightly bonded in situ on CoO / ZnO nanowires. The tight bond between the two ensures the transport of electrons at the interface and facilitates the separation of photogenerated carriers.

[0074] X-ray diffraction analysis of CoO / Mn3V2O8 heterojunction materials, such as Figure 5 As shown, by Figure 5 It can be seen that the synthesized composite structure contains the phases of CoO and Mn3V2O8, confirming the successful synthesis of the heterojunction. The XRD pattern shows fewer phase and impurity peaks compared to the monomer material, indicating that the reaction purity is high.

[0075] Figure 3-5 The advantages of the gas-phase ion exchange method for synthesizing CoO / Mn3V2O8 heterojunction materials are demonstrated: 1. Atomic-level tight bonding: The in-situ growth method directly grows heterogeneous components on the surface of CoO / ZnO materials, forming atomically tight interfacial contacts, avoiding the weak interfacial bonding problems caused by physical mixing in traditional non-in-situ synthesis. This strong interfacial effect reduces the introduction of defects and impurities, improving the stability and lifespan of the heterojunction. 2. Suppression of interfacial charge recombination: The tight interfacial structure can effectively promote the separation of photogenerated electron-hole pairs and reduce the probability of charge recombination.

[0076] The cobalt oxide / manganese vanadate composite photocatalyst prepared in this application is used for hydrogen production through total water splitting. Specifically, 40 mg of the prepared CoO / Mn3V2O8 heterojunction material was added to 40 ml of water, along with 10 mL of methanol as a sacrificial agent. The mixture was stirred for 10 h, and the amount of hydrogen produced was determined using an online gas chromatography system. The results are as follows: Figure 6 As shown, the calculated hydrogen production amount is 315 mmol / g, and the hydrogen production rate is 31.5 mmol / g / h.

[0077] A comparative experiment was designed, changing the catalyst type to use either CoO or Mn3V2O8 as a single material. The specific procedure was as follows: 40 mg of CoO or Mn3V2O8 was ultrasonically dispersed in 40 mL of deionized water, and 10 mL of methanol was added as a sacrificial agent. Argon gas was bubbled into the solution before light exposure to remove dissolved oxygen. Hydrogen production was automatically measured by injection at regular intervals. The results are as follows: Figure 7 As shown. Combined with Figure 6 The hydrogen production using CoO was significantly lower than that using Mn3V2O8, and the hydrogen production using Mn3V2O8 in the first three hours was about half that using the CoO / Mn3V2O8 heterojunction material. The comparative results indicate that the formation of the CoO / Mn3V2O8 heterojunction significantly improved the hydrogen production efficiency of the material.

[0078] The relevant test specifications involved in this application:

[0079] The instrument used for characterizing the surface morphology of the samples using scanning electron microscopy was a Hitachi S-4800 cold field emission scanning electron microscope. This instrument was also equipped with a Genesis XM2 energy dispersive spectroscopy (EDS) instrument, manufactured by EDAX, for analyzing the composition and elemental distribution of the samples. This scanning electron microscope has a magnification range of 30-2Kx in low-magnification mode and 100-800Kx in high-magnification mode; the accelerating voltage range is 0.5-30kV, with an acceleration of ≥0.1kV, and adjustable resolutions of 1.0nm and 1.4nm. The parameters set for characterizing the surface morphology of CoO samples were: accelerating voltage of 5.0kV, normal current, and an electron gun distance of approximately 8mm from the sample.

[0080] Phase analysis of the samples was performed using an X-ray diffractometer, model D8advance, manufactured by Bruker Corporation. The parameters set for X-ray diffraction analysis in this patent were: scanning range of 20°~80°, and scanning speed of 2°min. -1 The positioning rate is 1500°min. -1 The step size is 0.0001°.

[0081] The photocatalytic activity was evaluated using an online gas chromatograph to test the photocatalytic hydrogen production performance of CoO / Mn3V2O8. During the experiment, the device was illuminated by a 300W xenon lamp (manufactured by Beijing Pofilai Technology Co., Ltd., with a light intensity of 200mW / cm²). 2 A photocatalytic water splitting experiment was conducted to produce hydrogen. The specific procedure was as follows: 40 mg of catalyst was ultrasonically dispersed in 40 mL of deionized water, and 10 mL of methanol was added as a sacrificial agent. Argon gas was introduced into the solution before light exposure to remove dissolved oxygen. Hydrogen yield was automatically measured by injection at regular intervals. The gas chromatograph used was a GC-2014C, manufactured by Shimadzu Corporation. The column oven temperature range was room temperature +10℃ to 420℃, with an internal volume of 15.8 L and a room temperature variation correlation of 0.01. The injection port temperature was <420℃, the pressure setting range was 0~970 kPa, and the program ratio setting range was -400~400 kPa / min. The detector unit temperature range was also <420℃.

[0082] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for preparing a cobalt / manganese vanadate composite photocatalyst, characterized by, The CoO / ZnO nanowire is prepared by film drawing reaction after CoO nanowire is prepared by gas phase cation exchange method on FTO glass with seed layer. The method comprises the following steps: S1, the FTO conductive glass film is immersed in the ZnO seed solution to obtain the film-drawing FTO conductive glass loaded with the single-crystal ZnO nanowire seed layer, i.e. the FTO glass with the seed layer; S2, the CoO nanowire is prepared: the cobalt chloride powder and the FTO glass with the seed layer are heated to 500-600°C, and the temperature is kept for 20-60 min to obtain the FTO sheet loaded with the CoO nanowire; S3, the CoO / ZnO nanowire is prepared: the FTO sheet loaded with the CoO nanowire is repeatedly used for film drawing with the ZnO seed solution to grow ZnO on the CoO nanowire, and the CoO / ZnO nanowire is obtained; S4, the heterojunction composite catalyst is prepared: the manganese chloride, the vanadium trichloride and the CoO / ZnO nanowire FTO sheet are heated to 500-600°C, and the temperature is kept for 20-60 min to obtain the FTO glass sheet loaded with the CoO / Mn3V2O8 heterojunction material.

2. The method for preparing a cobalt oxide / manganese vanadate composite photocatalyst according to claim 1, characterized by, The FTO glass with the seed layer is prepared as follows: the FTO conductive glass film is immersed in the ZnO seed solution, and after being separated from the solution, the FTO conductive glass is heated to 90-105°C, and the temperature is kept for 8-15 min to obtain the prepared ZnO seed layer; then the FTO glass with the ZnO seed layer is heated at 450-520°C for 50-80 min, and after the heating is completed, the FTO glass is cooled to obtain the film-drawing FTO conductive glass loaded with the single-crystal ZnO nanowire seed layer.

3. The method for preparing a cobalt oxide / manganese vanadate composite photocatalyst according to claim 2, characterized by, The preparation steps of the CoO / ZnO nanowire are as follows: S31, the cobalt chloride powder is weighed and placed in a porcelain boat, which is placed on the right side of the furnace chamber of a vacuum tube furnace; S32, the FTO glass with the seed layer is placed in another porcelain boat, which is placed in the center of the vacuum tube furnace, and the furnace opening is closed; S33, after the furnace tube is flushed with argon, the vacuum state in the furnace tube is maintained; S34, the tube furnace is heated to 500-600°C, and the temperature is kept for 20-60 min; after the temperature keeping is completed, the temperature is cooled to room temperature, argon is filled to normal pressure through the gas inlet, the gas inlet is opened, and the FTO sheet loaded with the CoO nanowire is taken out; S35, the FTO sheet loaded with the CoO nanowire is repeatedly used for film drawing with the ZnO seed solution to grow ZnO on the CoO nanowire, and the CoO / ZnO nanowire is obtained.

4. The method for preparing a cobalt oxide / manganese vanadate composite photocatalyst according to claim 2, characterized by, The preparation steps of the heterojunction composite catalyst are as follows: S41, the manganese chloride and the vanadium trichloride are placed in a porcelain boat according to the mass ratio of 2:1, and the porcelain boat is placed on the rightmost side of the furnace chamber of a vacuum tube furnace; S42, the CoO / ZnO nanowire FTO sheet is placed in another porcelain boat, which is placed in the center of the furnace chamber of the vacuum tube furnace, and the furnace opening is closed; S43, the furnace tube is flushed with argon, and the vacuum state in the furnace tube is maintained; S44, the tube furnace is heated to 500-600°C, and the temperature is kept for 20-60 min; after the temperature keeping is completed, the temperature is cooled to room temperature, argon is filled to normal pressure through the gas inlet, the gas inlet is opened, and the FTO glass sheet loaded with the CoO / Mn3V2O8 heterojunction material is taken out. S44, heating the tubular furnace to 500-600°C, and maintaining for 20-60 min, and then cooling to room temperature, opening the gas inlet to fill argon to normal pressure, opening the two closed ends, taking out the FTO glass sheet loaded with the CoO / Mn3V2O8 heterojunction material, and gently scraping off with a knife to obtain a brown powder product.

5. The method of claim 2, wherein the method is characterized by: Preparation method of FTO glass with seed layer S21, preparing ZnO seed solution: adding ethylene glycol methyl ether in a beaker, then adding monoethanolamine MEA dropwise, weighing zinc acetate and adding into the beaker, and magnetically stirring at room temperature until the solution is completely clear to obtain ZnO seed solution; S22, placing the prepared ZnO seed solution in a vacuum drying box at 75-85°C, taking it out after heating for 1-3 h, and placing it in a beaker; S23, taking FTO conductive glass, blowing dry with nitrogen, clamping the upper end of the FTO conductive glass with the chuck of a film drawing machine, drawing the film, adjusting the film drawing speed to slowly immerse the FTO conductive glass vertically into the ZnO seed solution, and standing after complete immersion; S24, after standing for 20-80 s, slowly rising to completely separate from the solution, taking out the FTO conductive glass, wiping the solution on the non-conductive surface clean with a lens paper, and placing it in a muffle furnace, heating to 90-105°C, and maintaining for 8-15 min, and then taking out and cooling to obtain the prepared ZnO seed layer; S25, placing the FTO glass with the ZnO seed layer in a muffle furnace, heating at 450-520°C for 50-80 min, cooling in the furnace after heating is completed, washing with anhydrous ethanol and deionized water until there is no agglomeration on the surface, blowing dry with nitrogen, and obtaining the film-drawn FTO conductive glass with a single-crystal zinc oxide nanowire seed layer.

6. The method of claim 2, wherein the method is characterized by: Preparation of ZnO seed solution: adding ethylene glycol methyl ether in a beaker, then adding monoethanolamine MEA dropwise, weighing zinc acetate and adding into the beaker, and magnetically stirring at room temperature until the solution is completely clear to obtain ZnO seed solution.

7. The method of claim 6, wherein the method is characterized by: The concentration of ethylene glycol methyl ether is 99.8%, the concentration of monoethanolamine is 99.5%, and the volume ratio of ethylene glycol methyl ether and monoethanolamine is 2:

1.

8. A cobalt / manganese vanadate composite photocatalyst, characterized by, Prepared by any of the methods of claims 1-7.

9. Use of a cobalt / manganese vanadate composite photocatalyst, characterized in that, The application of the cobalt oxide / manganese vanadate composite photocatalyst in claim 8 in the full water splitting for hydrogen production and photocatalytic degradation of pollutants.

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