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

Abstract

The invention discloses a preparation method of a yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst, which specifically comprises the following steps: putting indium salt and urea into deionized water, uniformly stirring and mixing, reacting the mixture at 120-130 DEG C, carrying out solid-liquid separation on the reaction product to obtain precipitate, washing, drying and roasting the precipitate to obtain In2O3; the preparation method comprises the following steps: putting In2O3, bismuth salt, yttrium salt and potassium bromide into deionized water, uniformly stirring and mixing, transferring into a hydrothermal kettle, and reacting at 170-190 DEG C, so as to obtain the bismuth-yttrium bromide-In2O3 composite material, the catalyst has a lower band gap and a wider light absorption range, the recombination of electrons and holes is reduced due to the formation of heterojunction, the electron transmission is increased due to the introduction of Y (yttrium), and the catalyst shows better photocatalytic activity and has a relatively large application prospect in the field of photocatalytic CO2 reduction.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth element-doped heterojunction photocatalytic materials, and particularly relates to a preparation method and application of a yttrium-doped BiOBr / In 2 O 3 heterojunction composite photocatalyst. Background Art

[0002] With the rapid development of human civilization, green energy technology has become an urgent need to reduce the use of fossil fuels and the generation of pollutants. Photocatalysis technology is considered to have great potential because it can directly utilize solar energy and can be applied to fields such as water splitting for hydrogen production, CO 2 reduction, degradation of organic pollutants, promotion of organic synthesis, etc. Photocatalysts are the core of photocatalysis technology, and many semiconductor materials such as TiO 2 , CdS, ZnO, In 2 O 3 and BiOBr can be used as photocatalysts. However, single semiconductor materials have some disadvantages. For example, photo-generated electron-hole pairs are prone to rapid recombination rather than participating in the photocatalytic reaction, which limits their photocatalytic activity.

[0003] To inhibit the recombination of electron-hole pairs and improve photocatalytic activity, constructing heterojunction photocatalytic materials has become a promising method. Heterojunction photocatalytic materials can be classified into types such as type II heterojunctions, Schottky type heterojunctions, Z type heterojunctions, and S type heterojunctions according to the energy band structures of adjacent materials. These heterojunction materials can effectively inhibit the recombination of electron-hole pairs and improve the overall photocatalytic activity of the materials, becoming an important branch of the photocatalyst family.

[0004] To further improve the electron transfer rate and enhance the absorption of visible light, introducing rare earth elements into semiconductor materials is considered a promising method. Rare earth elements are mainly divided into light rare earths and heavy rare earths. Among them, light rare earths include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), etc.; heavy rare earths include gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), etc. And Y (yttrium), as a special rare earth element, has excellent optical properties. Combining it with semiconductor materials can effectively reduce the band gap and improve the light absorption ability.

[0005] In 2 O 3 (Indium oxide) is an n-type semiconductor material and shows great application potential in the field of photocatalysis due to its unique electronic structure and optical properties. In 2 O 3As a semiconductor with a relatively wide bandgap, it has very stable chemical properties and a relatively low electron recombination rate. Its wide bandgap limits its further applications.

[0006] As one of the Bi 3+ materials, its relatively narrow bandgap has a good response to visible light and is considered suitable for preparing catalysts for ethanol. However, due to its high electron recombination rate, its further production of ethanol is limited.

[0007] Combining In 2 O 3 with other semiconductor materials to form heterojunction photocatalytic materials, and doping rare earth elements on the surface of the heterojunction are effective ways to overcome the above defects. The research group of Professor Can Xue at Nanyang Technological University (10.1016 / j.apcatb.2013.10.029) in-situ grew In 2 O 3 nanowafers on the g-C 3 N 4 lamellae, and the obtained In 2 O 3 / g-C 3 N 4 hybrid structure showed significantly improved photocatalytic activity for H 2 generation and CO 2 reduction. The enhanced activity is attributed to the interfacial transfer of photogenerated electrons and holes between g-C 3 N 4 and In 2 O 3 , thus effectively promoting charge separation. The research group of Professor Honggang Fu 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 O 5 / g-C 3 N 4 to promote charge transfer and CO 2 adsorption, resulting in a great increase in the methane production rate.

[0008] So far, no reports have been found on doping the rare earth element Y (yttrium) into the heterojunction BiOBr / In 2 O 3 for the construction of composite materials, preparation methods, and applications. Summary of the Invention

[0009] The present invention provides a yttrium-doped BiOBr / In 2 O3 Preparation method of heterojunction composite photocatalyst, which adopts hydrothermal method and high-temperature calcination method, with simple preparation process and low cost; through the staggered energy band structure between BiOBr and In 2 O 3 to form a heterojunction, construct a transport space for photo-generated carriers, promote the efficient separation of photo-generated electron-hole pairs, and at the same time, by doping Y (yttrium) element, enhance the light utilization rate of BiOBr / In 2 O 3 heterojunction, and finally achieve a significant improvement in photocatalytic activity.

[0010] The yttrium-doped BiOBr / In 2 O 3 heterojunction composite photocatalyst of the present invention is prepared by placing indium salt and urea in deionized water, stirring and mixing evenly, reacting the mixture at 120-130 °C for 4 h, separating the solid and liquid of the reaction product to obtain a precipitate, and calcining the precipitate after washing and drying. 2 O 3 ; In 2 O 3 , bismuth salt, yttrium salt, and potassium bromide are placed in deionized water, stirred and mixed evenly, and then transferred to a hydrothermal reactor to react at 170-190 °C for 12 h to obtain.

[0011] The molar ratio of the indium salt to urea is 1: 1-2; the molar ratio of In 2 O 3 to the bismuth salt is 1: 1-2, the molar ratio of In 2 O 3 to potassium bromide is 1: 1-2, and the molar ratio of the yttrium salt to In 2 O 3 is 1:10-20.

[0012] Another object of the present invention is to apply the yttrium-doped BiOBr / In 2 O 3 heterojunction composite photocatalyst prepared by the above method to photocatalytic CO 2 reduction for ethanol preparation.

[0013] Advantages and technical effects of the present invention: The present invention forms a heterojunction through the staggered energy band structure between BiOBr and In 2 O 3 to construct a transport space for photo-generated carriers, promote the efficient separation of photo-generated electron-hole pairs, and at the same time, by doping Y (yttrium) element, enhance the light utilization rate of BiOBr / In 2 O 3 heterojunction, and finally achieve a significant improvement in photocatalytic activity; the catalyst of the present invention has excellent photocatalytic performance in photocatalytic CO 2In the reduction preparation of ethanol, the yield of ethanol can be greatly improved. Description of the Drawings

[0014] Figure 1 XRD images of the catalysts of Example 1 and Comparative Examples 1, 2, and 3 of the present invention; Figure 2 Scanning electron microscope (SEM) morphology diagrams of the catalysts of Example 1 and Comparative Example 3, where Figure a is the catalyst of Comparative Example 3; Figure b is the catalyst of Example 1; Figure 3 High-resolution transmission electron microscope (HRTEM) morphology diagram (Figure a) and element distribution diagram (Figure b) of the catalyst of Example 1; Figure 4 Photocatalytic CO 2 Reduction experimental results of Example 1 and Comparative Examples 1-3 catalysts, where Figure a is the photocatalytic CO 2 Reduction product yield diagram, and Figure b is the product selectivity diagram. Detailed Embodiments

[0015] The technical solution of the present invention will be elaborated in detail through specific examples and drawings. However, it should be clear that the present invention is not limited to the following technical solutions. In the present invention, unless otherwise specifically stated, the reagents, methods, and equipment used are common reagents, methods, and equipment in the technical field. Those of ordinary skill in the art can implement and apply the present invention based on relevant reference books, scientific and technological literature, or instructions, manuals, etc. before the filing date of the present invention application, combined with their own experience and professional knowledge.

[0016] Example 1: Preparation and Application of Yttrium-Doped BiOBr / In 2 O 3 Heterojunction Composite Photocatalyst 1. Dissolve 25 mmol of indium nitrate and 50 mmol of urea in 40 mL of deionized water. After stirring and mixing evenly, transfer the mixed solution to a reaction kettle, react at 125 °C for 4 h, naturally cool, and then centrifuge. Take the solid, wash it 5 times with deionized water, and dry it in a vacuum oven at 60 °C for 12 h to obtain a white powder; put the white powder into a ceramic boat and place it in a muffle furnace. Heat it to 350 °C at a rate of 5 °C / min and keep it warm for 4 h, and then naturally cool to obtain In 2 O 3 ; Add 1 mmol of bismuth nitrate, 1 mmol of potassium bromide, and 0.05 mmol of yttrium nitrate to 60 mL of deionized water. After ultrasonic dispersion, add 1 mmol of indium oxide, and perform ultrasonic stirring to obtain a solid-liquid mixture. Transfer the solid-liquid mixture to a reaction kettle, react at 180 °C for 12 h, naturally cool, and then centrifuge. Wash the solid 5 times with deionized water and dry it in a vacuum oven at 60 °C for 12 h to obtain yttrium-doped BiOBr / In2 O 3 Heterojunction composite photocatalyst Y / BiOBr / In 2 O 3 ; Using the In 2 O 3 material prepared in Step 1 of Example 1 as Comparative Example 1; Comparative Example 2: Add 1 mmol of bismuth nitrate and 1 mmol of potassium bromide to 60 mL of deionized water, stir ultrasonically to obtain a solid-liquid mixture, transfer the solid-liquid mixture to a reaction kettle, react at 180 °C for 12 h, cool naturally and then centrifuge, wash the solid 5 times with deionized water, and dry in a vacuum oven at 60 °C for 12 h to obtain a two-dimensional layered BiOBr photocatalyst; Comparative Example 3: According to the In prepared in Step 1 of Example 1 2 O 3 , add 1 mmol of bismuth nitrate and 1 mmol of potassium bromide to 60 mL of deionized water, ultrasonically disperse and then add 1 mmol of In 2 O 3 , stir ultrasonically to obtain a solid-liquid mixture, transfer the solid-liquid mixture to a reaction kettle, react at 180 °C for 12 h, cool naturally and then centrifuge, wash the solid 5 times with deionized water, and dry in a vacuum oven at 60 °C for 12 h to obtain a BiOBr / In 2 O 3 heterojunction catalyst; The XRD of the above catalysts is shown in Figure 1 , and the figure shows that the catalyst of Comparative Example 3 is mainly composed of BiOBr. The peaks at 10.907°, 31.718°, and 39.326° show the phase of BiOBr, and the peaks at 30.585°, 35.462°, and 51.024° show the phase of In 2 O 3 . After doping with Y element in the catalyst Y / BiOBr / In 2 O 3 of Example 1, the overall peak position did not shift much, but the relative peak intensity of BiOBr changed. The intensities of the peaks at 31.718° and 32.241° changed relative to BiOBr / In 2 O 3 , indicating that Y was doped into the lattice of BiOBr; subsequent SEM and TEM phase changes further demonstrated that Y element was successfully doped into the lattice of BiOBr ( Figure 2 , 3 ), Figure 2 a of BiOBr / In 2 O 3 in the SEM phase diagram of BiOBr exists in the form of a layered structure, while In2 O 3 is unevenly dispersed on the surface of layered BiOBr, and the interplanar spacing between layers is relatively large. And Figure 2 Y / BiOBr / In of b 2 O 3 After doping with Y, the interplanar spacing of the catalyst becomes smaller, which indicates that the introduction of Y reduces the interplanar spacing between the BiOBr / In 2 O 3 heterojunctions. It also indirectly shows that Y has been successfully doped into the lattice of BiOBr. The morphology of the Y / BiOBr / In 2 O 3 catalyst is shown in Figure 3 a, where the interplanar spacing of BiOBr is 0.198 nm, while that of In 2 O 3 is 0.295 nm. From the TEM phase of Y / BiOBr / In 2 O 3 , it is also found that there is an obvious lattice boundary between the lattices of BiOBr and In 2 O 3 , which indicates that there is indeed a heterostructure between BiOBr and In 2 O 3 . We performed elemental mapping analysis on Y / BiOBr / In 2 O 3 and found that Y elements are evenly doped on the surface of the BiOBr / In 2 O heterojunction ( Figure 3 b).

[0017] 2. Photocatalytic CO 2 reduction experiment of the catalyst prepared by the above method Add 10 mg of the catalyst to a centrifuge tube containing 8 mL of deionized water, sonicate for 10 min to disperse it evenly; then pour it into a high-pressure reactor, continuously introduce N 2 for 30 min and keep the pressure at 0.1 MPa to exhaust the air in the reactor. Then continuously introduce CO 2 for 30 min and keep the pressure at 0.1 MPa to displace N 2 so that the reactor is filled with CO 2 . Then, under the irradiation of a 300 W xenon lamp (CEL-HUVUV300 from Zhongjiao Jinyuan) with a 420 nm filter and without a sacrificial agent, continuously introduce CO 2 , react continuously for 5 h, and introduce the collected gas-liquid products into a gas chromatograph (GC9790Ⅱ) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) for analysis.

[0018] Results Figure 4 It can be seen from the figure that Comparative Example 1 In 2 O 3 Catalyst photocatalysis CO 2 No ethanol was produced in the reduced product, while a small amount of ethanol was produced by the BiOBr catalyst in Comparative Example 2. 4 and CO, after forming a heterojunction, it can be found that BiOBr / In 2 O 3 The CH 3 CH 2 The yield and selectivity of OH have been greatly improved. This may be because the formation of the heterojunction promotes the separation of charges, allowing other electrons that were originally annihilated by the recombination of holes to re-enter the reaction, thereby promoting the production of ethanol. However, the selectivity and yield of ethanol are still not very high ( Figure 4 b) and CH 3 CH 2 The yield of OH is only about 30 μmol / g / h. After the introduction of Y (yttrium), Y-doped BiOBr / In 2 O 3 Heterojunction catalyst Y / BiOBr / In 2 O 3 Photocatalytic CO 2 The performance of reducing to ethanol is the best ( Figure 4 a), the ethanol yield is about 105μmol / g / h, and the ethanol selectivity is 61.02%. This is attributed to the unique structure of rare earth elements, which can enhance the absorption of visible light, allowing more electrons to participate in the entire reaction system, thereby promoting CH 3 CH 2 The generation of OH ( Figure 4 b).

[0019] Example 2: Yttrium-doped BiOBr / In 2 O 3 Preparation and application of heterojunction composite photocatalysts The preparation method of this embodiment is the same as that of embodiment 1, except that the amount of yttrium nitrate added is 0.1 mmol, and the prepared catalyst is subjected to photocatalytic CO 2 Reduction experiment, the results of this example catalyst to CO 2 The ethanol yield of the reduced product was 79.4 μmol / g / h, and the ethanol selectivity was 56.2%.

[0020] The above specific embodiments have further elaborated in detail the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst, characterized in that: Indium salt and urea are placed in deionized water, stirred and mixed, and the mixture is reacted at 120-130°C. The reaction product is separated into solid and liquid to obtain a precipitate, and the precipitate is 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 autoclave for reaction at 170-190°C to obtain a yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst.

2. The method for preparing the yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst 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 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.

3. The yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst prepared by the preparation method of the yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst according to claim 1 or 2.

4. Use of the yttrium-doped BiOBr / In2O3 heterojunction composite photocatalyst according to claim 3 in photocatalytic CO2 reduction.

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