Manganese dioxide / bismuth oxybromide heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a manganese dioxide / bismuth oxybromide heterojunction photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalytic reduction of carbon dioxide by a nano material. The preparation method of the manganese dioxide / bismuth oxybromide heterojunction photocatalyst comprises the following steps: dispersing a bismuth source and manganese dioxide into water to obtain a suspension, adding a bromine source into the suspension, and reacting bismuth ions in the bismuth source with bromine ions in the bromine source by a chemical precipitation method to obtain the manganese dioxide / bismuth oxybromide heterojunction photocatalyst. A bismuth oxybromide nanosheet is loaded on the surface of manganese dioxide, and the manganese dioxide / bismuth oxybromide heterojunction photocatalyst is obtained. In the preparation process, a bromine source and a bismuth source are subjected to in-situ synthesis on the surface of manganese dioxide to obtain bismuth oxybromide, and the prepared manganese dioxide / bismuth oxybromide heterojunction photocatalyst has excellent photocatalytic performance.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic reduction of carbon dioxide by nanomaterials, and more particularly to a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the extensive use of fossil fuels and the excessive emission of harmful gases, ecological pollution and energy shortage have become two major global challenges, seriously threatening the living environment of human beings. Green and efficient environmental governance and energy management strategies, especially the conversion of carbon dioxide into valuable organic substances driven by solar energy using advanced materials, have received extensive attention because of some outstanding advantages, such as inexhaustible solar energy, no secondary pollution, mild reaction conditions, low cost, etc.

[0003] However, many photocatalysts reported currently, including titanium dioxide, sulfides, nitrides, etc., have problems such as insufficient light absorption, low charge separation efficiency, and unclear reaction mechanism, which greatly limit their practical applications. Therefore, exploring new visible-light-responsive photocatalysts and investigating the relationship between their structures and properties are crucial for the development of photocatalytic technology.

[0004] In recent years, researchers usually improve the performance of bismuth oxybromide photocatalysts by methods such as metal / non-metal doping, construction of heterojunctions, exposure of crystal planes, deposition of noble metals, and structural defects. Compared with single materials, the construction of heterostructures is a commonly used strategy. However, in the process of constructing heterostructures in the prior art, the method of first synthesizing two required substances separately and then compounding them together results in easy recombination of photo-generated carriers in the formed heterojunction, low separation efficiency, and a narrow light absorption range, thus making the reduction effect of the photocatalyst poor. Summary of the Invention

[0005] Aiming at the above problems, the present invention provides a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, a preparation method thereof, and an application thereof. During the preparation process, bismuth oxybromide is in-situ synthesized on the surface of manganese dioxide from a bromine source and a bismuth source, and the prepared manganese dioxide / bismuth oxybromide heterojunction photocatalyst has excellent photocatalytic performance.

[0006] The first object of the present invention is to provide a preparation method of a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, comprising the following steps: Disperse a bismuth source and manganese dioxide in water to obtain a suspension, add a bromine source to the suspension, and make the bismuth ions in the bismuth source react with the bromine ions in the bromine source through a chemical precipitation method to form bismuth oxybromide nanosheets on the surface of manganese dioxide, thereby obtaining a manganese dioxide / bismuth oxybromide heterojunction photocatalyst.

[0007] In a preferred embodiment of the present invention, the reaction temperature of the chemical precipitation method is room temperature.

[0008] In a preferred embodiment of the present invention, the reaction time of the chemical precipitation method is 4 h to 6 h. For example, the reaction time of the chemical precipitation method is 4 h, 4.5 h, 5 h, 5.5 h, 6 h, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0009] In a preferred embodiment of the present invention, the molar ratio of the bismuth source to manganese dioxide is 1:0.3 to 0.6. For example, the molar ratio of the bismuth source to manganese dioxide is 1:0.3, 1:0.4, 1:0.5, 1:0.6, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0010] In a preferred embodiment of the present invention, the molar ratio of the bismuth source to manganese dioxide is 1:0.5.

[0011] In a preferred embodiment of the present invention, the molar ratio of the bismuth source to the bromine source is 1:0.9 to 1.1. For example, the molar ratio of the bismuth source to the bromine source is 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0012] In a preferred embodiment of the present invention, the molar ratio of the bismuth source to the bromine source is 1:1.

[0013] In a preferred embodiment of the present invention, the bismuth source is bismuth nitrate pentahydrate or bismuth nitrate; the bromine source is sodium bromide or potassium bromide.

[0014] The second object of the present invention is to provide a manganese dioxide / bismuth oxybromide heterojunction photocatalyst prepared by the above preparation method.

[0015] The third object of the present invention is to provide the above-mentioned manganese dioxide / bismuth oxybromide heterojunction photocatalyst for photocatalytic reduction of CO 2 applications.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, by means of the chemical precipitation method, bismuth oxybromide nanosheets are loaded on the surface of manganese dioxide to construct a manganese dioxide / bismuth oxybromide heterojunction photocatalyst formed by the composite of bismuth oxybromide nanosheets and manganese dioxide. When the method of the present invention is used for preparation, an in-situ synthesis method is adopted, so that the manganese dioxide and bismuth oxybromide heterojunction are tightly combined, thereby having good photocatalytic activity.

[0017] In the present invention, by compounding bismuth oxybromide with manganese dioxide, on the one hand, the heterojunction structure formed by bismuth oxybromide and manganese dioxide enables photo-generated electrons to transfer from bismuth oxybromide to manganese dioxide, while photo-generated holes remain in bismuth oxybromide, separating electrons and holes in different materials and reducing the recombination probability of electron-hole pairs; and the effective separation and transfer of electrons enable more photo-generated charges to participate in the photocatalytic reaction, improving the reaction efficiency. On the other hand, after compounding, the manganese dioxide / bismuth oxybromide photocatalyst effectively expands the light absorption range, and the expanded light absorption range enables the photocatalyst to utilize more solar energy and improve the photocatalytic efficiency.

[0018] The present invention uses manganese dioxide as a transition metal oxide. Its narrow bandgap can effectively absorb visible light, enhancing its light absorption ability in the photocatalytic process. At the same time, the stability of its structure enables it to maintain its performance during the photocatalytic process, not easily deactivate, and the preparation method is simple. In addition, the introduction of manganese dioxide in the present invention not only improves the photocatalytic efficiency but also enhances the stability of the material, with a small decline in photocatalytic activity during recycling; the stable heterojunction structure formed during the stirring process makes its structure stable during long-term use and not easily degraded.

[0019] The CO 2 conversion rate of the manganese dioxide / bismuth oxybromide heterojunction photocatalyst prepared in the present invention is 10.97 times that of pure bismuth oxybromide; and after 5 cycles, the CO yield still does not show an obvious decline, and the manganese dioxide / bismuth oxybromide heterojunction photocatalyst has good stability.

[0020] In the present invention, a bismuth source and manganese dioxide are added to water, and then a bromine source is added, and the manganese dioxide / bismuth oxybromide heterojunction photocatalyst is synthesized under stirring at room temperature. Its preparation process is simple, easy to operate, the raw materials are cheap and easily available, and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD patterns of the materials prepared in Comparative Examples 1 to 2 and Examples 1 to 3.

[0022] Figure 2 SEM image of the material prepared in Example 2.

[0023] Figure 3 Photocatalytic CO 2 reduction performance of the materials prepared in Comparative Examples 1 to 2 and Examples 1 to 3.

[0024] Figure 4 CO reduction performance diagram of the material prepared in Example 2 under different conditions. 2

[0025] Figure 5 ​Photocatalytic stability test chart of the material prepared in Example 2.

[0026] Figure 6 Performance of the photocatalysts prepared by different mixing methods for Comparative Example 3 and Example 2. Detailed implementation manners

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] To solve the problems in the background art, the present invention starts from in-situ synthesis of heterojunctions and designs a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to the S-type heterojunction carrier transport mechanism.

[0029] The present invention provides a preparation method of a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, comprising the following steps: Adding a bismuth source and manganese dioxide into water, and then adding a bromine source; under stirring at room temperature, reacting bismuth ions provided by the bismuth source and bromine ions provided by the bromine source, and forming bismuth oxybromide nanosheets on the surface of manganese dioxide to obtain a manganese dioxide / bismuth oxybromide heterojunction photocatalyst formed by the composite of manganese dioxide and bismuth oxybromide nanosheets, denoted as MnO 2 / BiOBr.

[0030] It should be noted that bismuth oxybromide is a semiconductor material with a layered structure, having a wide light absorption range, especially strong absorption ability in the visible light region. Moreover, bismuth oxybromide has a strong ability to generate photo-generated electrons and holes, but its photo-generated electron-hole pairs are easily recombined, which limits its photocatalytic performance. As a transition metal oxide, manganese dioxide can effectively absorb visible light with its narrow bandgap, enhancing its light absorption ability in the photocatalytic process. At the same time, the stability of its structure enables it to maintain its performance during the photocatalytic process and is not easily deactivated, and the preparation method is simple.

[0031] In the present invention, bismuth oxybromide and manganese dioxide are combined to form a heterojunction structure. The interface between manganese dioxide and bismuth oxybromide can effectively promote the transfer of electrons and reduce the recombination probability of photo-generated electrons and holes. The formation of the heterojunction can optimize the energy band structure between the two components, promote the transfer of electrons from bismuth oxybromide to manganese dioxide, and enhance the separation efficiency of electron-hole pairs. Moreover, the heterojunction design helps to reduce the recombination of photo-generated electrons and holes, improve the utilization efficiency of photo-generated charges, and enhance the photocatalytic activity. In addition, manganese dioxide has a wide light absorption range and can absorb more ultraviolet and visible light. The introduction of manganese dioxide significantly enhances the visible light absorption ability of the composite material, and the wide absorption range enables more photo-generated electrons and holes to be excited, increasing the initial carrier concentration of the photocatalytic reaction. At the same time, the addition of manganese dioxide prevents the recombination of electrons and holes inside bismuth oxybromide, provides a large number of active sites, helps photo-generated electrons to participate in the catalytic reaction, and further improves the photocatalytic efficiency.

[0032] In the description of the present invention, unless otherwise specified, the reagents used are commercially available, and the methods used are conventional techniques in the art.

[0033] Example 1 This example provides a preparation method of a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, including the following steps: 1.1) Disperse 1.9402 g of Bi(NO 3 ) 3 ·5H 2 O and 0.1044 g of manganese dioxide into 50 mL of deionized water, ultrasonicate for 15 min, and stir for 30 min to obtain a suspension.

[0034] 1.2) Dissolve 0.4116 g of NaBr in 10 mL of deionized water to obtain a NaBr solution.

[0035] 1.3) Mix the obtained NaBr solution with the above suspension at room temperature, stir for 5 h, wash several times with deionized water, filter, and dry in an oven at 80 °C for 8 h to obtain a manganese dioxide / bismuth oxybromide heterojunction photocatalyst (MnO 2 / BiOBr), denoted as 3MB.

[0036] Example 2 This example provides a preparation method of a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, including the following steps: 1.1) Disperse 1.9402 g of Bi(NO 3 ) 3 ·5H 2 O and 0.1392 g of manganese dioxide into 50 mL of deionized water, ultrasonicate for 15 min, and stir for 30 min to obtain a suspension.

[0037] 1.2) Dissolve 0.4116 g of NaBr in 10 mL of deionized water to obtain a NaBr solution.

[0038] 1.3) Mix and stir the obtained NaBr solution with the above suspension at room temperature for 5 h, wash it several times with deionized water, filter, and dry it in an oven at 80 °C for 8 h to obtain a manganese dioxide / bismuth oxybromide heterojunction photocatalyst (MnO 2 / BiOBr), denoted as 4MB.

[0039] Example 3 This example provides a method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, including the following steps: 1.1) Disperse 1.9402 g of Bi(NO 3 ) 3 ·5H 2 O and 0.1738 g of manganese dioxide in 50 mL of deionized water, ultrasonicate for 15 min, and stir for 30 min to obtain a suspension.

[0040] 1.2) Dissolve 0.4116 g of NaBr in 10 mL of deionized water to obtain a NaBr solution.

[0041] 1.3) Mix and stir the obtained NaBr solution with the above suspension at room temperature for 5 h, wash it several times with deionized water, filter, and dry it in an oven at 80 °C for 8 h to obtain a manganese dioxide / bismuth oxybromide heterojunction photocatalyst (MnO 2 / BiOBr), denoted as 5MB.

[0042] Example 4 This example provides a method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, including the following steps: 1.1) Disperse 1.9402 g of Bi(NO 3 ) 3 ·5H 2 O and 0.2087 g of manganese dioxide in 50 mL of deionized water, ultrasonicate for 15 min, and stir for 30 min to obtain a suspension.

[0043] 1.2) Dissolve 0.37 g of NaBr in 10 mL of deionized water to obtain a NaBr solution.

[0044] 1.3) Mix and stir the obtained NaBr solution with the above suspension at room temperature for 4 h, wash it several times with deionized water, filter, and dry it in an oven at 80 °C for 8 h to obtain a manganese dioxide / bismuth oxybromide heterojunction photocatalyst (MnO 2 / BiOBr).

[0045] Example 5 This example provides a preparation method of a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, including the following steps: 1.1) Disperse 1.58 g of Bi(NO 3 ) 3 and 0.1391 g of manganese dioxide into 50 mL of deionized water, ultrasonicate for 15 min, and stir for 30 min to obtain a suspension.

[0046] 1.2) Dissolve 0.524 g of KBr in 10 mL of deionized water to obtain a KBr solution.

[0047] 1.3) Mix and stir the obtained KBr solution with the above suspension at room temperature for 4 h, wash several times with deionized water, filter, and dry in an oven at 80 °C for 8 h to obtain a manganese dioxide / bismuth oxybromide heterojunction photocatalyst (MnO 2 / BiOBr).

[0048] Comparative Example 1 This comparative example provides a preparation method of bismuth oxybromide (BiOBr), including the following steps: 1.1) Place 2.425 g of Bi(NO 3 ) 3 ·5H 2 O in 50 mL of deionized water and ultrasonicate for 15 min, 1.2) Dissolve 0.5145 g of NaBr in 10 mL of water.

[0049] 1.3) Mix and stir the NaBr solution and the Bi(NO 3 ) 3 solution at room temperature for 3 h. Cool and filter the obtained suspension, wash 5 times with deionized water, place in an oven at 80 °C for 8 h, and collect to obtain bismuth oxybromide, i.e., pure BiOBr.

[0050] Comparative Example 2 This comparative example provides a preparation method of manganese dioxide, including the following steps: 1.1) Dissolve 0.948 g of KMnO 4 and 0.339 g of MnSO 4 ·H 2 O in 80 mL of deionized water and stir at room temperature for 30 min to dissolve it.

[0051] 1.2) Transfer it to a 100 mL reaction vessel and react at 120 °C for 12 h. Cool to room temperature, wash several times, filter by suction, and obtain a black solid. Vacuum-dry the obtained sample at 80 °C for 10 h, and collect manganese dioxide (MnO 2 ).

[0052] Comparative Example 3 In this comparative example, bismuth oxybromide and manganese dioxide were mechanically mixed, including the following steps: 1.1) Weigh bismuth oxybromide and manganese dioxide according to a mass ratio of 1:1. Put the weighed MnO 2 and BiOBr powders into a mortar.

[0053] 1.2) Grind and mix with a pestle for 30 minutes until uniform. Place it in an oven and dry at 60 °C for 2 h to obtain a mechanical mixture of bismuth oxybromide and manganese dioxide.

[0054] In Examples 1 to 3 of the present invention, manganese dioxide / bismuth oxybromide heterojunction photocatalysts were all prepared. Below, taking the materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 as examples for research, the specific research methods are as follows: (1) Material characteristics: Using Cu Kα as the radiation source, the crystal structure of the catalyst was detected with a D8 X-ray diffractometer (XRD). The morphology and energy spectrum of the catalyst were characterized using an S-4800 scanning electron microscope (SEM).

[0055] Figure 1 The XRD patterns of BiOBr prepared in Comparative Example 1, MnO 2 prepared in Comparative Example 2, and 3MB, 4MB, and 5MB prepared in Examples 1 to 3. From Figure 1 it can be seen that the diffraction peaks of BiOBr all correspond to the standard card (JCPDS: 09-0393); this proves that tetragonal BiOBr was synthesized. The peak shape of the characteristic peaks of BiOBr is very sharp and the intensity is relatively high, indicating that the crystallinity of BiOBr is very good. MnO 2 Four characteristic peaks were observed and can correspond to the MnO 2 standard card (JCPDS: 80-1098), proving the successful synthesis of MnO 2 , but the crystallinity of MnO 2 is poor. For different ratios of BiOBr / MnO 2 heterojunctions, the characteristic diffraction peaks of BiOBr can be clearly observed, but due to the low content of MnO 2 and the poor crystallinity of MnO 2 , the characteristic peaks of MnO 2 cannot be observed. In addition, it can be found that as MnO 2With the increase in the content, the intensity of the (001) peak of BiOBr in the heterojunction gradually decreases, which can provide evidence for the successful synthesis of BiOBr / MnO 2 heterojunction

[0056] Figure 2 SEM image of 4MB prepared in Example 2; 4MB retains the morphologies of BiOBr and MnO 2 and presents a nanoflower structure. In addition, it can be clearly observed that after the formation of the heterojunction, the looseness of the nanoflowers increases and the nanoflowers become thinner.

[0057] (2) Photocatalytic test: Under the irradiation of a 300 W xenon lamp (PLS-SXE 300D), the photocatalytic CO 2 reduction performance of 3MB, 4MB, and 5MB prepared in Examples 1 to 3, BiOBr prepared in Comparative Example 1, and MnO 2 prepared in Comparative Example 2 was tested; the specific implementation method is as follows: Put 10 mg of the sample and 10 mL of distilled water into a weighing bottle, ultrasonicate for 20 min, dry in an oven at 60 °C for 10 h; then place it in a reactor and evacuate for 15 min; and introduce high-purity carbon dioxide gas and 10 μL of deionized water into the reactor; irradiate the reactor under a 200 mW∙cm −2 xenon lamp for 3 h; the reduction product was determined on a Huifen GC-7800 gas chromatograph equipped with an FID detector and a TCD detector.

[0058] As can be seen from Figure 3 , the CO 2 reduction performance of 4MB prepared in Example 2 was 217.72 μmol·g -1 ·h -1 respectively; compared with the CO 2 reduction performance of single MnO 2 and BiOBr, the 4MB prepared in the present invention significantly improved the photocatalytic CO 2 reduction efficiency; among them, when 1.6 mol of manganese dioxide was added per 1 mol of bismuth source, the CO 2 conversion rate of 4MB was 10.97 times that of pure bismuth oxybromide, showing the best CO 2 reduction performance. This may be because in 4MB prepared in Example 2, BiOBr has more oxygen vacancies, making the CO 2 reduction performance excellent.

[0059] Figure 4 CO 2 reduction performance graph of 4MB prepared in Example 2 under different conditions. As Figure 4 shown, without adding a catalyst, without adding water, without light, or replacing CO 2When the atmosphere is changed to an Ar atmosphere, almost no CO is detected, indicating that the CO source is CO 2 , indicating that the CO in the reaction system 2 , water, photocatalyst, and light irradiation are all necessary conditions for the photocatalytic reaction.

[0060] Figure 5 Photocatalytic stability test chart of MnO 2 / BiOBr prepared in Example 2. The cyclic experiment shows that after 5 cycles, the CO yield remains basically unchanged without obvious attenuation, proving that the MnO 2 / BiOBr prepared in Example 2 has good stability; it shows that the manganese dioxide / bismuth oxybromide heterojunction photocatalyst prepared by the present invention has a stable structure during long-term use and is not easily degraded.

[0061] Figure 6 For the performance of the photocatalysts prepared by Comparative Example 3 and Example 2 according to different mixing methods, the photocatalytic ability of the MnO 2 / BiOBr heterojunction in Example 2 is significantly stronger than that of the mechanical mixture of MnO 2 and BiOBr prepared in Comparative Example 3. The CO 2 reduction performance of the mechanical mixture prepared in Comparative Example 3 is 30 μmol·g -1 ·h -1 , indicating that the heterojunction structure plays a crucial role in the reaction.

[0062] The present invention synthesizes a manganese dioxide / bismuth oxybromide composite material with oxygen vacancies on the surface by a simple chemical precipitation method. Due to the enhanced light absorption ability and the construction of the S-type heterojunction, the performance of carbon dioxide reduction is significantly enhanced. Among them, the MnO 2 / BiOBr heterojunction prepared in Example 2 exhibits the best light absorption ability and carrier separation ability, and the photocatalytic reduction performance of the catalyst is the best, with the CO generation rate being 217.72 μmol·g -1 ·h -1 , and the CO yield is 10.97 times that of pure BiOBr.

[0063] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0064] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst, characterized in that: The following steps are involved: A bismuth source and manganese dioxide are dispersed in water to obtain a suspension, a bromine source is added to the suspension, and bismuth ions in the bismuth source react with bromide ions in the bromine source through a chemical precipitation method to load bismuth oxybromide nanosheets on the surface of manganese dioxide to obtain a manganese dioxide / bismuth oxybromide heterojunction photocatalyst.

2. The method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 1, characterized in that: The reaction temperature of the chemical precipitation method is room temperature.

3. The method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 1, characterized in that: The reaction time of the chemical precipitation method is 4h~6h.

4. The method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 1, characterized in that: The molar ratio of the bismuth source to manganese dioxide is 1:0.3~0.

6.

5. The method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 4, characterized in that: The molar ratio of the bismuth source to manganese dioxide is 1:0.

5.

6. The method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 1, characterized in that: The molar ratio of the bismuth source to the bromine source is 1:0.9~1.

1.

7. The method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 6, characterized in that: The molar ratio of the bismuth source to the bromine source is 1:

1.

8. The method for preparing a manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 1, characterized in that: The bismuth source is bismuth nitrate pentahydrate or bismuth nitrate; the bromine source is sodium bromide or potassium bromide.

9. A manganese dioxide / bismuth oxybromide heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the manganese dioxide / bismuth oxybromide heterojunction photocatalyst according to claim 9 in photocatalytic reduction of CO2.

Images