Preparation method and application of Bi2Sn2O7 / Bi2MoO6 S type heterojunction composite material
By constructing a Bi2Sn2O7/Bi2MoO6 S-type heterojunction composite material, the electron diffusion path and interfacial charge transport were improved, solving the problem of high electron-hole recombination rate in Bi2MoO6 photocatalyst and achieving a highly efficient photocatalytic nitrogen fixation effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- KUNMING UNIV OF SCI & TECH
- Filing Date
- 2025-12-23
- Publication Date
- 2026-04-21
AI Technical Summary
The high electron-hole recombination rate of Bi2MoO6 photocatalyst during photocatalytic nitrogen fixation leads to low photocatalytic activity and efficiency.
A Bi2Sn2O7/Bi2MoO6 S-type heterojunction composite material was constructed, which formed a strong coupling interface through defect-induced chemical bonding, thereby improving the electron diffusion path and interfacial charge transport.
It significantly improves the nitrogen reduction reaction rate, increasing the ammonia generation rate by 10.4-18.6 times, and does not require high temperature and high pressure conditions under visible light, which is in line with the concept of green chemistry.
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Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material and its application, belonging to the field of photocatalytic nitrogen fixation. Background Technology
[0002] Ammonia is a crucial industrial raw material for the synthesis of fertilizers, fibers, and pharmaceuticals. Currently, the standard industrial ammonia synthesis reaction is mainly achieved through the Haber-Bosch process under high temperature and pressure, which not only consumes a large amount of energy but also generates numerous harmful byproducts. Given the importance of reducing greenhouse gas emissions such as N2O (following carbon dioxide and CH4), there is an urgent need to develop green and sustainable new ammonia synthesis processes. The utilization of solar energy offers a powerful solution to the problems of consuming large amounts of fossil fuels and polluting the environment in traditional processes. In recent years, photocatalytic nitrogen fixation technology has received increasing attention due to its advantages such as mild reaction conditions, low cost, and environmental friendliness.
[0003] Bi₂MoO₆ is considered a promising visible-light-driven photocatalyst due to its unique layered structure, low cost, non-toxicity, and strong light absorption capacity. However, when Bi₂MoO₆ is used for photocatalytic nitrogen fixation, its photocatalytic activity is limited by its few N₂ adsorption activation sites and high electron-hole recombination rate, resulting in low photocatalytic nitrogen fixation efficiency. Bi₂Sn₂O₇ and Bi₂MoO₆ not only have similar atomic compositions but also staggered band structures, and both readily generate vacancy defects on their surfaces, making it easy for them to form tight heterojunction structures through defect-induced chemical bonding. Constructing heterojunctions can create strongly coupled interfaces linked by defect-induced chemical bonds, which can not only improve the structural stability of the heterojunction interface but also establish effective electron diffusion pathways and improve interfacial charge transport, thus enhancing the activity and efficiency of photocatalytic nitrogen fixation. Summary of the Invention
[0004] To address the technical problems of high photogenerated carrier recombination rate and low nitrogen fixation efficiency in Bi2MoO6 photocatalysts, this invention provides a method for preparing Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite materials and their applications. The Bi2Sn2O7 / Bi2MoO6 heterojunction constructed by this invention can form a strongly coupled interface connected by defect-induced chemical bonds, which can not only improve the structural stability of the heterojunction interface, but also establish an effective electron diffusion path and improve interfacial charge transport, thus improving the photocatalytic nitrogen fixation activity and efficiency of the composite material.
[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material includes the following steps: Step (a): First, Bi(NO3)3 is dissolved in an ethanol / ethylene glycol mixed solution. Then, Na2MoO4 is added under magnetic stirring. After stirring until clear, the mixture is transferred to a polytetrafluoroethylene reactor and heated at a certain temperature. After the reaction is completed and cooled, the precipitate is centrifuged and washed alternately with ultrapure water and ethanol. After drying, Bi2MoO6 nanosheets are obtained. In step (b), Bi(NO3)3 and Na2SnO3 are dissolved in ultrapure water, and the two solutions are mixed. The pH value is adjusted by dilute acid and dilute alkali under magnetic stirring, and a certain amount of Bi2MoO6 nanosheets prepared in step (a) is added. After magnetic stirring and mixing, the above mixed solution is transferred to a polytetrafluoroethylene reactor and heated for hydrothermal reaction. After the reaction is completed and cooled, the precipitate is separated by centrifugation and washed alternately with ultrapure water and ethanol. After drying, Bi2Sn2O7 / Bi2MoO6 heterojunction composite material is obtained.
[0006] When preparing the solution according to this invention, the molar ratio of each substance must be strictly controlled. If the molar ratio is not followed, a product with other phases may be obtained.
[0007] In step (a), the molar ratio of Bi(NO3)3 to Na2MoO4 is (1.9-2.1):1.
[0008] In step (a), the volume ratio of ethanol to ethylene glycol in the ethanol / ethylene glycol mixed solution is (2-4):1.
[0009] In step (a), the polytetrafluoroethylene reactor is heated to a temperature of 160-190℃ for 12-24 hours.
[0010] In step (b), the molar ratio of Bi(NO3)3 to Na2SnO3 is (0.9-1.1):1, and the molar ratio of Bi(NO3)3 to Bi2MoO6 is (1-12):100.
[0011] In step (b), adjust the pH value to 10-11.
[0012] In step (b), the hydrothermal reaction in the polytetrafluoroethylene reactor is carried out at a temperature of 190-200℃ for 2-6 hours.
[0013] In steps (a) and (b), the drying is vacuum drying, the drying temperature is 60-80℃, and the drying time is 12-24h.
[0014] The present invention also provides the application of the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material prepared by the above preparation method as a photocatalytic nitrogen fixation material.
[0015] The technical solution of the present invention has the following advantages: In the Bi2Sn2O7 / Bi2MoO6 heterojunction composite material prepared by this invention, Bi2Sn2O7 and Bi2MoO6 form an S-shaped heterostructure. Bi2Sn2O7 has a relatively negative conduction band and a narrow band gap. The S-shaped heterojunction has a strong charge separation capability and can also retain the strong reducing ability of Bi2Sn2O7. Both Bi2Sn2O7 and Bi2MoO6 prepared by this invention have abundant surface defects, making it easier for the heterojunction interface to be connected by defect-induced chemical bonds. This results in a more stable structure, which is beneficial for accelerating electron transport. It can effectively promote the separation and migration of photogenerated charges, enhance light absorption efficiency and improve carrier separation efficiency, thereby improving the photocatalytic nitrogen reduction reaction activity.
[0016] The Bi₂Sn₂O₇ / Bi₂MoO₆ heterojunction composite material prepared in this invention significantly improves the nitrogen reduction reaction rate during nitrogen fixation. Under visible light, the ammonia generation rate reaches 284.67 µmol g⁻¹h⁻¹, which is 10.4 and 18.6 times higher than that of pure Bi₂Sn₂O₇ and Bi₂MoO₆, respectively, demonstrating excellent photocatalytic performance. Moreover, this photocatalytic system uses solar energy as an energy source, does not require high temperature and high pressure conditions, and does not require the addition of hole scavenging reagents, which is in line with the concepts of sustainable development and green chemistry, with low energy consumption and no environmental pollution. Attached Figure Description
[0017] Figure 1 This is the TEM spectrum of Bi2MoO6 prepared in Example 1; Figure 2 This is a TEM spectrum of the Bi2Sn2O7 / Bi2MoO6 heterojunction composite material prepared in Example 1; Figure 3 The images show the XRD patterns of the Bi2Sn2O7 / Bi2MoO6 heterojunction composite materials prepared in Examples 1-5 and the Bi2MoO6 nanosheets and Bi2Sn2O7 nanoparticles prepared in Comparative Examples 1 and 2. Figure 4 These are the XRD patterns of the Bi2Sn2O7 / Bi2MoO6 heterojunction composite materials prepared in Examples 1, 6 and 7; Figure 5 This is a schematic diagram of the charge transfer mechanism of the S-shaped heterostructure between Bi2Sn2O7 and Bi2MoO6 in the Bi2Sn2O7 / Bi2MoO6 heterostructure composite material; Figure 6 The figures show the nitrogen fixation performance of the Bi2Sn2O7 / Bi2MoO6 heterojunction composite materials prepared in Examples 1-5, Comparative Examples 1 and 2, and Bi2MoO6 and Bi2Sn2O7 as photocatalysts. Detailed Implementation
[0018] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. However, those skilled in the art should know that the specific embodiments of the present invention do not limit the present invention in any way, and any equivalent substitutions made on the basis of the present invention fall within the protection scope of the present invention. For process parameters not specifically specified, conventional techniques can be referred to.
[0019] Example 1 (a) 2 mmol Bi(NO3)3·5H2O was dissolved in an ethanol / ethylene glycol mixed solution, which was obtained by mixing 20 mL of ethylene glycol and 40 mL of ethanol. The mixture was stirred at room temperature for 1 h, and then 1 mmol Na2MoO4·4H2O was added. The mixture was stirred at room temperature for 2 h until it became clear and transparent. The mixture was then transferred to a polytetrafluoroethylene reactor and heated at 160 °C for 24 h. After cooling, the precipitate was separated by centrifugation and washed with ultrapure water and ethanol alternately 4 times. The precipitate was then placed in a vacuum drying oven at 60 °C and vacuum dried for 12 h to obtain Bi2MoO6 nanosheets. (b) Dissolve 0.1 mmol Bi(NO3)3·5H2O and 0.1 mmol Na2SnO3·3H2O in 30 mL of ultrapure water, stir at room temperature for 1 h, mix the two solutions, and adjust the pH to 10-11 with 1 mol / L dilute nitric acid and 1 mol / L NaOH solution while stirring; weigh 0.95 g of Bi2MoO6 (1.57 mmol) prepared in step (a) and add it to the above solution (Bi2Sn2O7 loading is 6%), stir magnetically at room temperature for 2 h to mix, then transfer the above mixed solution to a polytetrafluoroethylene reactor, hydrothermally react at 190 °C for 6 h, after cooling, centrifuge to separate the precipitate, wash with ultrapure water and ethanol alternately 4 times, and then place it in a vacuum drying oven at 60 °C for 10 h to obtain Bi2Sn2O7 / Bi2MoO6 heterojunction composite material.
[0020] Example 2 The difference from Example 1 is that in step (b), 6.038 g (9.9 mmol) of Bi2MoO6 and 1% of Bi2Sn2O7 were added.
[0021] Example 3 The difference from Example 1 is that in step (b), 1.972 g (3.23 mmol) of Bi2MoO6 and 3% of Bi2Sn2O7 were added.
[0022] Example 4 The difference from Example 1 is that in step (b), 0.617 g (1.01 mmol) of Bi2MoO6 and 9% Bi2Sn2O7 were added.
[0023] Example 5 The difference from Example 1 is that in step (b), 0.477 g (0.73 mmol) of Bi2MoO6 was added and the Bi2Sn2O7 loading was 12%.
[0024] Example 6 (a) 2 mmol Bi(NO3)3·5H2O was dissolved in an ethanol / ethylene glycol mixed solution, which was obtained by mixing 20 mL ethylene glycol and 40 mL ethanol. The mixture was stirred at room temperature for 1 h, and then 1 mmol Na2MoO4·4H2O was added. The mixture was stirred at room temperature for 2 h until it became clear and transparent. The mixture was then transferred to a polytetrafluoroethylene reactor and heated at 180 °C for 18 h. After cooling, the precipitate was separated by centrifugation and washed 4 times alternately with ultrapure water and ethanol. The precipitate was then placed in a vacuum drying oven at 70 °C and vacuum dried for 24 h to obtain Bi2MoO6 nanosheets. (b) Dissolve 0.1 mmol Bi(NO3)3·5H2O and 0.1 mmol Na2SnO3·3H2O in 30 mL of ultrapure water, stir at room temperature for 1 h, mix the two solutions, and adjust the pH to 10-11 with 1 mol / L dilute nitric acid and 1 mol / L NaOH solution while stirring; weigh 0.95 g of Bi2MoO6 (1.57 mmol) prepared in step (a) and add it to the above solution (Bi2Sn2O7 loading is 6%), stir magnetically at room temperature for 2 h to mix, then transfer the above mixed solution to a polytetrafluoroethylene reactor, hydrothermally react at 190 °C for 5.5 h, after cooling, centrifuge to separate the precipitate, wash with ultrapure water and ethanol alternately 4 times, and then place it in a vacuum drying oven at 60 °C for 10 h to obtain Bi2Sn2O7 / Bi2MoO6 heterojunction composite material.
[0025] Example 7 (a) 2 mmol Bi(NO3)3·5H2O was dissolved in an ethanol / ethylene glycol mixed solution, which was obtained by mixing 10 mL of ethylene glycol and 40 mL of ethanol. The mixture was stirred at room temperature for 1 h, and then 1 mmol Na2MoO4·4H2O was added. The mixture was stirred at room temperature for 2 h until it became clear and transparent. The mixture was then transferred to a polytetrafluoroethylene reactor and heated at 190 °C for 12 h. After cooling, the precipitate was separated by centrifugation and washed with ultrapure water and ethanol alternately 4 times. The precipitate was then placed in a vacuum drying oven at 80 °C for 12 h to obtain Bi2MoO6 nanosheets. (b) Dissolve 0.1 mmol Bi(NO3)3·5H2O and 0.1 mmol Na2SnO3·3H2O in 30 mL of ultrapure water, stir at room temperature for 1 h, mix the two solutions, and adjust the pH to 10-11 with 1 mol / L dilute nitric acid and 1 mol / L NaOH solution while stirring; weigh 0.95 g of Bi2MoO6 (1.57 mmol) prepared in step (a) and add it to the above solution (Bi2Sn2O7 loading is 6%), stir magnetically at room temperature for 2 h to mix, then transfer the above mixed solution to a polytetrafluoroethylene reactor, hydrothermally react at 200℃ for 2 h, after cooling, centrifuge to separate the precipitate, wash with ultrapure water and ethanol alternately 4 times, and then place it in a vacuum drying oven at 60℃ for 10 h to obtain Bi2Sn2O7 / Bi2MoO6 heterojunction composite material.
[0026] Example 8 (a) 2.1 mmol Bi(NO3)3·5H2O was dissolved in an ethanol / ethylene glycol mixed solution, which was obtained by mixing 10 mL of ethylene glycol and 40 mL of ethanol. The mixture was stirred at room temperature for 1 h, and then 1 mmol Na2MoO4·4H2O was added. The mixture was stirred at room temperature for 2 h until it became clear and transparent. The mixture was then transferred to a polytetrafluoroethylene reactor and heated at 160 °C for 24 h. After cooling, the precipitate was separated by centrifugation and washed with ultrapure water and ethanol alternately 4 times. The precipitate was then placed in a vacuum drying oven at 70 °C and vacuum dried for 15 h to obtain Bi2MoO6 nanosheets. (b) Dissolve 0.11 mmol Bi(NO3)3·5H2O and 0.1 mmol Na2SnO3·3H2O in 30 mL of ultrapure water, stir at room temperature for 1 h, mix the two solutions, and adjust the pH to 10-11 with 1 mol / L dilute nitric acid and 1 mol / L NaOH solution while stirring; weigh 0.95 g of Bi2MoO6 (1.57 mmol) prepared in step (a) and add it to the above solution (Bi2Sn2O7 loading is 6%), stir magnetically at room temperature for 2 h to mix, then transfer the above mixed solution to a polytetrafluoroethylene reactor, hydrothermally react at 195 °C for 4 h, after cooling, centrifuge to separate the precipitate, wash with ultrapure water and ethanol alternately 4 times, and then place it in a vacuum drying oven at 70 °C for 15 h to obtain Bi2Sn2O7 / Bi2MoO6 heterojunction composite material.
[0027] Example 9 (a) 1.9 mmol Bi(NO3)3·5H2O was dissolved in an ethanol / ethylene glycol mixed solution, which was obtained by mixing 10 mL of ethylene glycol and 40 mL of ethanol. The mixture was stirred at room temperature for 1 h, and then 1 mmol Na2MoO4·4H2O was added. The mixture was stirred at room temperature for 2 h until it became clear and transparent. The mixture was then transferred to a polytetrafluoroethylene reactor and heated at 170 °C for 15 h. After cooling, the precipitate was separated by centrifugation and washed with ultrapure water and ethanol alternately 4 times. The precipitate was then placed in a vacuum drying oven at 70 °C and vacuum dried for 15 h to obtain Bi2MoO6 nanosheets. (b) Dissolve 0.09 mmol Bi(NO3)3·5H2O and 0.1 mmol Na2SnO3·3H2O in 30 mL of ultrapure water, stir at room temperature for 1 h, mix the two solutions, and adjust the pH to 10-11 with 1 mol / L dilute nitric acid and 1 mol / L NaOH solution while stirring; weigh 0.95 g of Bi2MoO6 (1.57 mmol) prepared in step (a) and add it to the above solution (Bi2Sn2O7 loading is 6%), stir magnetically at room temperature for 2 h to mix, then transfer the above mixed solution to a polytetrafluoroethylene reactor, hydrothermally react at 190 °C for 5 h, after cooling, centrifuge to separate the precipitate, wash with ultrapure water and ethanol alternately 4 times, and then place it in a vacuum drying oven at 70 °C for 15 h to obtain Bi2Sn2O7 / Bi2MoO6 heterojunction composite material.
[0028] Comparative Example 1 2 mmol Bi(NO3)3·5H2O was dissolved in an ethanol / ethylene glycol mixed solution, which was obtained by mixing 20 mL of ethylene glycol and 40 mL of ethanol. The mixture was stirred at room temperature for 1 h, and then 1 mmol Na2MoO4·4H2O was added. The mixture was stirred at room temperature for 2 h until it became clear and transparent. The mixture was then transferred to a polytetrafluoroethylene reactor and heated at 160 °C for 24 h. After cooling, the precipitate was separated by centrifugation and washed four times with ultrapure water and ethanol, respectively. The precipitate was then vacuum dried in a vacuum drying oven at 60 °C for 12 h to obtain Bi2MoO6 nanosheets.
[0029] Comparative Example 2 0.1 mmol Bi(NO3)3·5H2O and 0.1 mmol Na2SnO3·3H2O were dissolved in 30 mL of ultrapure water, respectively, and stirred at room temperature for 1 h. The two solutions were mixed, and the pH was adjusted to 10-11 with 1 mol / L dilute nitric acid and 1 mol / L NaOH solution while stirring. The mixed solution was transferred to a polytetrafluoroethylene reactor and reacted at 190 °C for 6 h. After cooling, the precipitate was separated by centrifugation and washed 4 times with ultrapure water and ethanol, respectively. Then it was placed in a vacuum drying oven at 60 °C for 10 h to obtain Bi2Sn2O7 nanoparticles.
[0030] Transmission electron microscopy (TEM) images of Bi₂MoO₆ prepared in Example 1 are shown below. Figure 1 As shown, from Figure 1 As can be seen, Bi2MoO6 exhibits ultrathin nanosheets with a smooth surface, which is conducive to the construction of surface defects and the loading of Bi2Sn2O7.
[0031] Transmission electron microscopy (TEM) images of the Bi2Sn2O7 / Bi2MoO6 heterojunction composite material prepared in Example 1 are shown below. Figure 2 As shown, from Figure 2 As can be seen, the Bi2Sn2O7 / Bi2MoO6 heterojunction composite material generally exhibits nanoflowers assembled from nanosheets, with fine nanoparticles loaded on its surface.
[0032] The XRD patterns of the Bi₂Sn₂O₇ / Bi₂MoO₆ heterojunction composite materials prepared in Examples 1-7 and the Bi₂MoO₆ nanosheets and Bi₂Sn₂O₇ nanoparticles prepared in Comparative Examples 1 and 2 are shown below. Figure 3 and Figure 4 As shown, from Figure 3 As can be seen from the XRD, the orthogonal structure of Bi2MoO6 is mainly observed. Compared with the standard card JCPDS#72-1524, the prepared Bi2Sn2O7 / Bi2MoO6 can be well matched. In addition, the diffraction peak of Bi2Sn2O7 was observed at 29°, which proves the successful preparation of Bi2Sn2O7 / Bi2MoO6 composite material.
[0033] A schematic diagram of the charge transfer mechanism of the S-shaped heterostructure between Bi2Sn2O7 and Bi2MoO6 in the Bi2Sn2O7 / Bi2MoO6 heterojunction photocatalytic nitrogen fixation material is shown below. Figure 5As shown, it can be inferred that after the heterojunction is formed, electrons transfer from Bi₂Sn₂O₇, which has a lower work function and a higher Fermi level, to Bi₂MoO₆, which has a higher work function and a lower Fermi level. This process continues until the Fermi level reaches equilibrium. Therefore, electron redistribution occurs at the interface, forming a built-in electric field (IEF) pointing from Bi₂Sn₂O₇ to Bi₂MoO₆. Subsequently, the IEF causes the energy band of Bi₂Sn₂O₇ to bend upward, while the energy band of Bi₂MoO₆ bends downward. Under illumination, both Bi₂Sn₂O₇ and Bi₂MoO₆ are activated. Under the influence of energy band bending and the built-in electric field, holes generated in the valence band of Bi₂Sn₂O₇ recombine with electrons generated in the conduction band of Bi₂MoO₆. As a result, electrons accumulate in the conduction band of Bi2Sn2O7 and holes accumulate in the valence band of Bi2MoO6. This charge transfer process is consistent with the S-type heterojunction mechanism, which not only significantly improves the electron-hole separation efficiency, but also maintains the strong reducing ability of Bi2Sn2O7.
[0034] The Bi₂Sn₂O₇ / Bi₂MoO₆ heterojunctions prepared in Examples 1 to 5, the Bi₂MoO₆ prepared in Comparative Example 1, and the Bi₂Sn₂O₇ prepared in Comparative Example 2 were used as photocatalysts for photocatalytic nitrogen reduction experiments. A 300W xenon lamp (equipped with an AM1.5 filter) was used as the light source, and the photocatalytic nitrogen reduction experiments were carried out in a 100mL quartz reactor. The specific process is as follows: 50 mg of catalyst was dispersed in 50 mL of ultrapure water and sonicated for 10 minutes without adding any sacrificial reagent. The solution was then transferred to a quartz reactor equipped with a water cooling system and maintained at 25 °C. High-purity N2 (99.999%) was continuously bubbled through the reactor in the dark for 0.5 h to create a pure N2 environment. After irradiation for 3 h, 5 mL of the reaction liquid was removed, and the catalyst was removed using a 0.22 µm filter. Subsequently, NH4 was determined by indophenol blue spectrophotometry. + Ion concentration.
[0035] The results of photocatalytic nitrogen fixation performance are as follows Figure 6 As shown, from Figure 6 As can be seen from this, the NH4+ of the Bi2Sn2O7 / Bi2MoO6 heterojunction photocatalytic nitrogen fixation material... + The yields of the Bi2Sn2O7 / Bi2MoO6 heterojunction photocatalytic nitrogen fixation material prepared in Example 1 were all higher than those of Bi2Sn2O7 and Bi2MoO6. +The yield reached 284.67 µmol g⁻¹ h⁻¹, which was 10.4 and 18.6 times higher than that of pure Bi₂Sn₂O₇ and Bi₂MoO₆, respectively, and also higher than that of Bi₂Sn₂O₇ / Bi₂MoO₆ heterojunction materials prepared in other examples with different ratios. This is because the Bi₂Sn₂O₇ / Bi₂MoO₆ heterojunction prepared in Example 1 has an appropriate ratio, thereby forming a tightly coupled interface between Bi₂Sn₂O₇ and Bi₂MoO₆, which significantly improves carrier mobility and separation efficiency. In addition, the establishment of the S-shaped heterostructure between Bi₂Sn₂O₇ and Bi₂MoO₆ promotes the accumulation of highly reducing electrons on Bi₂Sn₂O₇, thus endowing the Bi₂Sn₂O₇ / Bi₂MoO₆ heterojunction photocatalytic nitrogen fixation material with excellent photocatalytic nitrogen fixation ability.
[0036] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.
Claims
1. A method for preparing a Bi₂Sn₂O₇ / Bi₂MoO₆ S-type heterojunction composite material, characterized in that, Includes the following steps: (a) Dissolve Bi(NO3)3 in a mixed solution of ethanol / ethylene glycol, add Na2MoO4 under magnetic stirring, stir until clear, heat the mixture to react, cool and centrifuge the precipitate, wash with ultrapure water and ethanol alternately, and dry to obtain Bi2MoO6 nanosheets. (b) Dissolve Bi(NO3)3 and Na2SnO3 in ultrapure water respectively, then mix the two solutions, adjust the pH value under magnetic stirring and add Bi2MoO6 nanosheets from step (a), stir and mix well, then carry out hydrothermal reaction of the mixed solution, cool and centrifuge the precipitate, wash it alternately with ultrapure water and ethanol, and dry it to obtain Bi2Sn2O7 / Bi2MoO6 heterojunction composite material.
2. The method for preparing the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material according to claim 1, characterized in that, In step (a), the molar ratio of Bi(NO3)3 to Na2MoO4 is (1.9-2.1):
1.
3. The method for preparing the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material according to claim 1, characterized in that, In step (a), the volume ratio of ethanol to ethylene glycol in the ethanol / ethylene glycol mixed solution is (2-4):
1.
4. The method for preparing the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material according to claim 1, characterized in that, In step (a), the heating temperature is 160-190℃ and the heating time is 12-24h.
5. The method for preparing the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material according to claim 1, characterized in that, In step (b), the molar ratio of Bi(NO3)3 to Na2SnO3 is (0.9-1.1):1, and the molar ratio of Bi(NO3)3 to Bi2MoO6 is 1-12:
100.
6. The method for preparing the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material according to claim 1, characterized in that, In step (b), adjust the pH value to 10-11.
7. The method for preparing the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material according to claim 1, characterized in that, In step (b), the hydrothermal reaction temperature is 190-200℃ and the time is 2-6h.
8. The method for preparing the Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material according to claim 1, characterized in that, In steps (a) and (b), the drying is vacuum drying, the drying temperature is 60-80℃, and the drying time is 12-24h.
9. The Bi2Sn2O7 / Bi2MoO6 S-type heterojunction composite material prepared by the method described in claim 1 is used as a photocatalytic material in the field of nitrogen fixation.