Preparation method and application of yttrium-doped BiOBr / In2O3 heterojunction photocatalyst

Abstract

The application discloses a preparation method of a yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst, and specifically comprises the following steps: placing indium salt and urea in deionized water, stirring and uniformly mixing, reacting the mixture at 120-130 DEG C, performing solid-liquid separation on a reaction product to obtain a precipitate, and preparing In2O3 by washing, drying and calcining the precipitate; and placing In2O3, bismuth salt, yttrium salt and potassium bromide in deionized water, stirring and uniformly mixing, and then transferring into an autoclave to react at 170-190 DEG C to obtain the product; the catalyst has a lower band gap and a wider light absorption range, and the formation of the heterojunction reduces the recombination of electrons and holes; the introduction of Y (yttrium) increases the electron transmission, and the catalyst shows better photocatalytic activity, and has a great application prospect in the field of photocatalytic CO2 reduction.

Description

Technical Field

[0001] This invention belongs to the field of rare earth element-doped heterojunction photocatalytic materials technology, specifically relating to a method for preparing and applying a yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst. Background Technology

[0002] With the rapid development of human civilization, green energy technologies have become an urgent need to reduce the use of fossil fuels and the generation of pollutants. Photocatalysis technology, due to its ability to directly utilize solar energy, is considered to have enormous potential and can be applied to fields such as water splitting for hydrogen production, CO2 reduction, degradation of organic pollutants, and promotion of organic synthesis. Photocatalysts are the core of photocatalysis technology, and many semiconductor materials such as TiO2, CdS, ZnO, In2O3, and BiOBr can serve as photocatalysts. However, single semiconductor materials have some drawbacks, such as the tendency for photogenerated electron-hole pairs to recombine rapidly rather than participate in the photocatalytic reaction, which limits their photocatalytic activity.

[0003] To suppress electron-hole recombination and improve photocatalytic activity, constructing heterojunction photocatalytic materials has become a promising approach. Heterojunction photocatalytic materials can be classified into type II heterojunctions, Schottky heterojunctions, Z-type heterojunctions, and S-type heterojunctions based on the band structure of adjacent materials. These heterojunction materials can effectively suppress electron-hole recombination and improve the overall photocatalytic activity of the material, thus becoming an important branch of the photocatalyst family.

[0004] Introducing rare earth elements into semiconductor materials is considered a promising approach to further improve electron transport rates and enhance visible light absorption. Rare earth elements are mainly divided into light and heavy rare earth elements. Light rare earth elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu); heavy rare earth elements include gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Yttrium (Y), as a special rare earth element, possesses excellent optical properties. Combining it with semiconductor materials can effectively reduce the band gap and improve light absorption.

[0005] Indium oxide (In₂O₃) is an n-type semiconductor material that shows great potential in photocatalysis due to its unique electronic structure and optical properties. However, as a semiconductor with a relatively wide band gap, In₂O₃ is chemically very stable and has a relatively low electron recombination rate. Its wide band gap limits its further applications.

[0006] BiOBr is one type of Bi 3+The material, with its narrow band gap, has a good response to visible light and is considered a suitable catalyst for the preparation of ethanol. However, its high electron recombination rate limits its further production of ethanol.

[0007] Combining In₂O₃ with other semiconductor materials to form heterojunction photocatalytic materials, and doping rare earth elements onto the surface of heterojunctions, are effective ways to overcome the aforementioned defects. Professor Xue Can's research group at Nanyang Technological University (10.1016 / j.apcatb.2013.10.029) grew In₂O₃ nanocrystals in situ on g-C₃N₄ sheets, and the resulting In₂O₃ / g-C₃N₄ hybrid structure significantly improved the photocatalytic activity for H₂ generation and CO₂ reduction. The enhanced activity is attributed to the interfacial transfer of photogenerated electrons and holes between g-C₃N₄ and In₂O₃, thus effectively promoting charge separation. Professor Fu Honggang's research group at Heilongjiang University (Energy & Environmental Science 17.14 (2024): 5039-5047.) doped the rare earth element Ho (holmium) into Mg. 1.2 Ti 1.8 O5 / g-C3N4 promotes charge transfer and CO2 adsorption, which greatly improves the yield of methane.

[0008] To date, there have been no reports on the construction, preparation methods, and applications of composite materials by doping rare earth element Y (yttrium) into heterojunction BiOBr / In2O3. Summary of the Invention

[0009] This invention provides a method for preparing a yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst. The method employs a hydrothermal method and a high-temperature calcination method, which is simple and low-cost. By forming a heterojunction through the misaligned band structure between BiOBr and In2O3, a transport space for photogenerated carriers is constructed, promoting the efficient separation of photogenerated electrons and holes. At the same time, by doping with Y (yttrium), the light utilization efficiency of the BiOBr / In2O3 heterojunction is enhanced, ultimately achieving a significant improvement in photocatalytic activity.

[0010] The yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst of this invention is prepared by placing indium salt and urea in deionized water, stirring and mixing, and then reacting the mixture at 120-130℃ for 4 hours. The reaction product is separated into solid and liquid phases to obtain a precipitate, which is then washed, dried, and calcined to obtain In2O3. In2O3, bismuth salt, yttrium salt, and potassium bromide are placed in deionized water, stirred and mixed, and then transferred to a hydrothermal reactor for reaction at 170-190℃ for 12 hours to obtain the final product.

[0011] The molar ratio of indium salt to urea is 1:1-2; the molar ratio of In2O3 to bismuth salt is 1:1-2; the molar ratio of In2O3 to potassium bromide is 1:1-2; and the molar ratio of yttrium salt to In2O3 is 1:10-20.

[0012] Another objective of this invention is to apply the yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst prepared by the above method to the photocatalytic reduction of CO2 to produce ethanol.

[0013] Advantages and technical effects of the present invention:

[0014] This invention forms a heterojunction through the misaligned band structure between BiOBr and In2O3, constructing a transport space for photogenerated carriers and promoting efficient separation of photogenerated electrons and holes. At the same time, by doping with Y (yttrium), the utilization rate of light by the BiOBr / In2O3 heterojunction is enhanced, ultimately achieving a significant improvement in photocatalytic activity. In the photocatalytic reduction of CO2 to ethanol, the catalyst of this invention can greatly improve the yield of ethanol. Attached Figure Description

[0015] Figure 1 The images show the XRD patterns of the catalysts in Example 1 and Comparative Examples 1, 2, and 3 of this invention.

[0016] Figure 2 The images show scanning electron microscope (SEM) morphology images of the catalysts of Example 1 and Comparative Example 3, where image a is the catalyst of Comparative Example 3 and image b is the catalyst of Example 1.

[0017] Figure 3 This is the elemental distribution diagram of the catalyst in Example 1;

[0018] Figure 4 The results of the photocatalytic CO2 reduction experiments of the catalysts in Example 1 and Comparative Examples 1-3 are shown, where Figure a is the yield of photocatalytic CO2 reduction products and Figure b is the product selectivity. Detailed Implementation

[0019] The technical solutions of this invention will be described in detail through specific embodiments and accompanying drawings. However, it should be noted that this invention is not limited to the following technical solutions. In this invention, unless otherwise specified, the reagents, methods, and equipment used are all commonly used reagents, methods, and equipment in this technical field. Those skilled in the art can implement and apply this invention based on relevant reference books, scientific and technological documents, specifications, manuals, etc., prior to the filing date of this invention, combined with their own experience and professional knowledge.

[0020] Example 1: Preparation and application of yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst

[0021] 1. Dissolve 25 mmol indium nitrate and 50 mmol urea in 40 mL of deionized water. After stirring and mixing, transfer the mixture to a reaction vessel and react at 125 °C for 4 h. After natural cooling, centrifuge and take the solid. Wash the solid 5 times with deionized water and dry it in a vacuum oven at 60 °C for 12 h to obtain a white powder. Place the white powder in a ceramic boat and place it in a muffle furnace. Heat the furnace to 350 °C at 5 °C / min and hold for 4 h. After natural cooling, obtain In2O3. Add 1 mmol bismuth nitrate, 1 mmol potassium bromide, and 0.05 mmol yttrium nitrate to 60 mL of deionized water. After ultrasonic dispersion, add 1 mmol indium oxide and stir ultrasonically to obtain a solid-liquid mixture. Transfer the solid-liquid mixture to a reaction vessel and react at 180 °C for 12 h. After natural cooling, centrifuge and wash the solid 5 times with deionized water. Dry it in a vacuum oven at 60 °C for 12 h to obtain the yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst Y / BiOBr / In2O3.

[0022] The In2O3 material obtained in step 1 of Example 1 was used as Comparative Example 1;

[0023] Comparative Example 2: 1 mmol of bismuth nitrate and 1 mmol of potassium bromide were added to 60 mL of deionized water and stirred ultrasonically to obtain a solid-liquid mixture. The solid-liquid mixture was transferred to a reaction vessel and reacted at 180 °C for 12 h. After natural cooling, the mixture was centrifuged. The solid was washed 5 times with deionized water and dried in a vacuum oven at 60 °C for 12 h to obtain a two-dimensional layered BiOBr photocatalyst.

[0024] Comparative Example 3: In2O3 was prepared according to step 1 of Example 1. 1 mmol of bismuth nitrate and 1 mmol of potassium bromide were added to 60 mL of deionized water. After ultrasonic dispersion, 1 mmol of In2O3 was added and ultrasonically stirred to obtain a solid-liquid mixture. The solid-liquid mixture was transferred to a reaction vessel and reacted at 180 °C for 12 h. After natural cooling, it was centrifuged. The solid was washed 5 times with deionized water and dried in a vacuum oven at 60 °C for 12 h to obtain the BiOBr / In2O3 heterojunction catalyst.

[0025] XRD of the above catalysts are shown in Figure 1The figure shows that the catalyst of Comparative Example 3 is mainly composed of BiOBr. The peaks at 10.907°, 31.718°, and 39.326° represent the BiOBr phase, while the peaks at 30.585°, 35.462°, and 51.024° represent the In2O3 phase. In Example 1, after doping the catalyst Y / BiOBr / In2O3, the overall peak positions did not shift significantly, but the relative peak intensities of BiOBr changed. The intensities of the peaks at 31.718° and 32.241° changed relative to BiOBr / In2O3, indicating that Y was incorporated into the BiOBr lattice. Subsequent SEM and TEM measurements of phase changes further confirmed that Y was successfully incorporated into the BiOBr lattice. Figure 2 , 3 ), Figure 2 In the SEM phase diagram of BiOBr / In2O3, BiOBr exists in a layered structure, while In2O3 is unevenly dispersed on top of the layered BiOBr, and the interplanar spacing between the layers is relatively large. Figure 2 After Y doping, the interplanar spacing of the Y / BiOBr / In2O3 catalyst decreased, indicating that the introduction of Y reduced the interplanar spacing between the BiOBr / In2O3 heterojunctions, which also indirectly proves that Y was successfully doped into the BiOBr lattice. Elemental analysis of Y / BiOBr / In2O3 revealed that Y was uniformly doped on the surface of the BiOBr / In2O heterojunction. Figure 3 ).

[0026] 2. Photocatalytic CO2 reduction experiment of the catalyst prepared by the above method

[0027] 10 mg of catalyst was added to a centrifuge tube containing 8 mL of deionized water and sonicated for 10 min to disperse it evenly. The mixture was then poured into a high-pressure reactor, and N2 was continuously introduced for 30 min while maintaining a pressure of 0.1 MPa to purge the air from the reactor. Next, CO2 was continuously introduced for 30 min while maintaining a pressure of 0.1 MPa to replace the N2 and fill the reactor with CO2. The reactor was then continuously reacted for 5 h under irradiation with a 300W xenon lamp (Zhongjiao Jinyuan CEL-HUVUV300) and a 420 nm filter, without sacrificial agents. The collected gas-liquid phase products were analyzed using a gas chromatograph (GC9790Ⅱ) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID).

[0028] See results Figure 4As shown in the figure, no ethanol was generated in the photocatalytic CO2 reduction products of Comparative Example 1 (In2O3 catalyst), while a trace amount of ethanol was generated in Comparative Example 2 (BiOBr catalyst). Both catalysts produced CH4 and CO. After the formation of the heterojunction, the yield and selectivity of CH3CH2OH in the catalytic products of the BiOBr / In2O3 catalyst were significantly improved. This is likely because the formation of the heterojunction promoted charge separation, allowing electrons that were originally annihilated with holes to re-enter the reaction, thus promoting ethanol production. However, the selectivity and yield of ethanol were still not very high. Figure 4 b) The yield of CH3CH2OH is only about 30 μmol / g / h; after the introduction of Y (yttrium), the Y-doped BiOBr / In2O3 heterojunction catalyst Y / BiOBr / In2O3 exhibits the best performance in photocatalytic reduction of CO2 to ethanol. Figure 4 a) The ethanol yield was approximately 105 μmol / g / h, and the ethanol selectivity was 61.02%. This was attributed to the unique structure of rare earth elements, which enhances the absorption of visible light, allowing more electrons to participate in the entire reaction system, thereby promoting the formation of CH3CH2OH. Figure 4 b).

[0029] Example 2: Preparation and application of yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst

[0030] The preparation method of this embodiment is the same as that of Example 1, except that the amount of yttrium nitrate added is 0.1 mmol. The catalyst prepared is subjected to photocatalytic CO2 reduction experiment using the method in step 2 of Example 1. The results show that the catalyst in this embodiment has an ethanol yield of 79.4 μmol / g / h in the CO2 reduction product and an ethanol selectivity of 56.2%.

[0031] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst in the photocatalytic reduction of CO2 to ethanol, characterized in that: The yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst is prepared by placing indium salt and urea in deionized water, stirring and mixing, reacting the mixture at 120-130℃, separating the solid and liquid products to obtain a precipitate, and then washing, drying, and calcining the precipitate to obtain In2O3; or by placing In2O3, bismuth salt, yttrium salt, and potassium bromide in deionized water, stirring and mixing, transferring the mixture to a hydrothermal reactor and reacting at 170-190℃ to obtain the final product. The molar ratio of In2O3 to bismuth salt is 1:1-2; the molar ratio of yttrium salt to In2O3 is 1:10-20.

2. The application according to claim 1, characterized in that: The molar ratio of indium salt to urea is 1:1-2; the molar ratio of In2O3 to potassium bromide is 1:1-2.

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