Ce-doped Bi4O5Br2-CdS composite photocatalyst, and preparation method and application thereof

Abstract

The application relates to the technical field of catalysts, in particular to a Ce-doped Bi4O5Br2-CdS composite photocatalyst as well as a preparation method and application thereof. The catalyst comprises Ce-doped Bi4O5Br2 nanosheets and CdS nanoparticles distributed on the surfaces of the nanosheets, the CdS and the Ce-doped Bi4O5Br2 form an S-type heterojunction structure, Ce is doped in the Bi4O5Br2 crystal lattice in the form of mixed valence and induces the formation of lattice oxygen vacancies. 4+ and Ce 3+ are mixed in the form of mixed valence and are doped in the Bi4O5Br2 crystal lattice and induce the formation of lattice oxygen vacancies. The catalyst constructs an electron transport channel through the Ce 4+ ↔Ce 3+ redox cycle, enhances CO2 adsorption and activation by taking the lattice oxygen vacancies as surface active sites, and improves the efficiency and selectivity of photocatalytic CO2 reduction to CO by the multiple synergistic mechanisms of the built-in electric field of the S-type heterojunction driving the directional migration and spatial separation of photo-generated carriers, so that CO2 resource utilization is realized.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a Ce-doped Bi4O5Br2-CdS composite photocatalyst, its preparation method, and its application. Background Technology

[0002] Reducing carbon dioxide (CO2) into high-value-added chemicals such as carbon monoxide, methane, and methanol using photocatalysis is an important strategy for addressing the greenhouse effect and energy crisis. As the core of photocatalysis, the low efficiency of photogenerated carrier separation and insufficient CO2 adsorption and activation capacity of the catalyst are key bottlenecks restricting the development of this technology. Therefore, developing highly efficient CO2 reduction photocatalysts is a significant challenge currently facing research.

[0003] Existing research shows that metal doping can improve the band structure of photocatalysts and introduce oxygen vacancies, thereby enhancing light utilization and CO2 adsorption and activation capabilities; constructing heterojunction composite photocatalysts can promote the separation of photogenerated carriers.

[0004] Bismuth-rich bismuth oxybromine (Bi4O5Br2) is an n-type semiconductor photocatalyst with wide applications in photocatalysis, but single-component Bi4O5Br2 exhibits limitations in catalytic performance. To address this, metal doping with manganese, cobalt, nickel, and molybdenum is used to replace the Bi in the crystal lattice. 3+ Defects such as oxygen vacancies and lattice distortion can be induced, and band structure and surface active sites can be modulated to enhance catalytic performance; however, the photogenerated electron-hole recombination rate remains high. Studies have shown that constructing heterojunctions can reduce the photogenerated electron-hole recombination rate, such as the Z-type heterojunction formed by Bi4O5Br2 and BiOIO3, and the S-type heterojunction obtained by Bi4O5Br2 and g-C3N4. The built-in electric field and band bending at the heterojunction interface accelerate the separation and transport of photogenerated carriers, retaining electrons in the conduction band of the reducing agent and holes in the valence band of the oxidizing agent, thus promoting CO2 reduction and water oxidation. However, these heterostructures have few surface active sites and weak adsorption and activation capabilities for CO2 molecules, limiting their catalytic activity; furthermore, constructing heterostructures requires a high degree of band matching between the two materials. Summary of the Invention

[0005] To address the problems of insufficient active sites on the surface of heterojunction composite photocatalysts during photocatalytic CO2 reduction, resulting in inadequate CO2 adsorption and activation capacity, low catalytic activity, and poor product selectivity, this invention provides a Ce-doped Bi4O5Br2-CdS composite photocatalyst, its preparation method, and its applications. This invention introduces cerium (Ce) doping into the Bi4O5Br2 lattice. Because Ce... 4+ / Ce 3+ Replace Bi 3+By adjusting the band structure of Bi4O5Br2 and introducing oxygen vacancy defects, Bi4O5Br2 was combined with cadmium sulfide (CdS) to construct a Ce-doped Bi4O5Br2-CdS S-type heterojunction catalyst through in-situ chemical reaction. This catalyst combines the synergistic advantages of metal doping and heterojunction modification, and can significantly improve the efficiency and selectivity of CO2 reduction to CO.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] This invention provides a Ce-doped Bi4O5Br2-CdS composite photocatalyst, wherein CdS nanoparticles are in-situ loaded onto the surface of Ce-doped Bi4O5Br2 nanosheets to form an S-type heterojunction structure; the Ce in the Ce-doped Bi4O5Br2 nanosheets is Ce... 4+ and Ce 3+ The mixed valence state of Ce is doped into Bi4O5Br2 nanosheets, and the doping amount of Ce is 1% to 4% of the molar amount of Bi4O5Br2 nanosheets; the loading amount of CdS nanoparticles is 10% to 75% of the mass of Ce-doped Bi4O5Br2 nanosheets.

[0008] Preferably, the Ce-doped Bi4O5Br2-CdS composite photocatalyst is formed by the self-assembly of two-dimensional nanosheet-like Ce-doped Bi4O5Br2 nanosheets into a petal-like morphology, and CdS nanoparticles are dispersed on the surface of the petal-like morphology, forming an S-type heterojunction structure.

[0009] The second objective of this invention is to provide a method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst, comprising the following steps: A potassium bromide ethanol solution and a bismuth nitrate pentahydrate ethylene glycol solution were mixed, and cerium nitrate was added at pH=10 to obtain a Ce-doped Bi4O5Br2 precursor solution. The Ce-doped Bi4O5Br2 precursor solution was mixed with a cadmium nitrate-thiourea ethylene glycol solution and subjected to a hydrothermal reaction at 150℃~170℃, which caused the Ce-doped Bi4O5Br2 nanosheets to self-assemble into a petal-like morphology, and CdS nanoparticles were dispersed on the surface of the petal-like morphology to form an S-type heterojunction structure. After centrifugation, a Ce-doped Bi4O5Br2-CdS composite photocatalyst was prepared.

[0010] Mix potassium bromide ethanol solution with bismuth nitrate pentahydrate ethylene glycol solution, Bi 3+ With Br − A hydrolysis reaction occurs to form BiOBr precipitate (Bi 3+ +Br − +H₂O→BiOBr↓+2H +After adjusting the solution pH to 10, BiOBr undergoes dehalogenation and hydroxylation under alkaline conditions to precipitate Bi4O5Br2 (4BiOBr + 2OH-). − →Bi4O5Br2↓+2Br − +H2O), while adding cerium nitrate to make Ce 4+ / Ce 3 The cadmium nitrate was uniformly dispersed in the precursor to obtain a Ce-doped Bi4O5Br2 precursor; this precursor was then mixed with a cadmium nitrate-thiourea ethylene glycol coordination solution, wherein Cd... 2+ It forms a stable complex with thiourea to prevent premature precipitation, followed by a hydrothermal reaction at 150℃~170℃. During this process: (a) it promotes the recrystallization of the precursor, Ce 4+ / Ce 3 Substitute Bi through thermal diffusion into the Bi4O5Br2 lattice. 3+ (a) Achieving uniform doping; (b) High-temperature decomposition of thiourea releasing S 2- , and Cd 2+ In-situ generation of CdS (Cd 2+ +(NH2)2CS + 2H2O → CdS↓ + 2NH4 + +CO2↑), and uniformly loaded onto the surface of Ce-doped Bi4O5Br2 to form a heterostructure. Finally, Ce-doped Bi4O5Br2-CdS composite photocatalyst was obtained by centrifugation, washing and drying.

[0011] Preferably, the molar ratio of potassium bromide to bismuth nitrate pentahydrate is 1:2 to 6.

[0012] Preferably, the molar ratio of cerium nitrate to bismuth nitrate pentahydrate is 0.01 to 0.04:1.

[0013] Preferably, the molar ratio of cadmium nitrate to thiourea in the cadmium nitrate-thiourea glycol solution is 1:1; and the molar ratio of cadmium nitrate-thiourea to bismuth nitrate pentahydrate is 0.025 to 0.187:1.

[0014] Preferably, the pH value is 10.

[0015] Preferably, the hydrothermal reaction temperature is 160℃±5℃, and the reaction time is 15h~17h.

[0016] The third objective of this invention is to provide an application of Ce-doped Bi4O5Br2-CdS composite photocatalyst in photocatalytic reduction of CO2. The application method is as follows: the Ce-doped Bi4O5Br2-CdS composite photocatalyst is dispersed in ethanol to obtain a dispersion, the dispersion is made into a thin film, and placed in CO2 and water, and the photocatalytic reduction of CO2 is carried out under light irradiation.

[0017] The beneficial effects of this invention are: 1. The Ce-doped Bi4O5Br2-CdS composite photocatalyst of the present invention introduces cerium (Ce) doping into the Bi4O5Br2 lattice. Because Ce... 4+ / Ce 3+ Replace Bi 3+ By adjusting the band structure of Bi4O5Br2 and introducing oxygen vacancy defects, Bi4O5Br2 is then combined with cadmium sulfide (CdS) to construct a Ce-doped Bi4O5Br2-CdS S-type heterojunction catalyst through in-situ chemical reaction. This composite photocatalyst combines the synergistic advantages of metal doping and heterojunction modification, significantly improving the efficiency and selectivity of CO2 reduction to CO. It addresses the problems of insufficient active sites on the surface of heterojunction composite photocatalysts, resulting in inadequate CO2 adsorption and activation capacity, low catalytic activity, and poor product selectivity during photocatalytic CO2 reduction.

[0018] 2. The Ce-doped Bi4O5Br2-CdS composite photocatalyst prepared in this invention combines the advantages of metal doping and heterojunction modification, with Ce as the... 4+ Mainly, with a small amount of Ce 3+ Mixed valence states are doped into the Bi4O5Br2 lattice and partially replace Bi. 3+ Sites induce the formation and distribution of lattice oxygen vacancies on the surface and near-surface region of Bi4O5Br2, serving as surface active sites. Under illumination, Ce... 4+ Capture electrons and Ce 3+ Ce is formed by losing electrons. 4+ +e - ↔Ce 3+ -e - A redox cycle constructs a fast transport channel for photogenerated electrons. CdS nanoparticles are uniformly distributed on the surface of Ce-doped Bi4O5Br2 nanosheets and form an S-shaped heterojunction structure through close heterojunction contact. A built-in electric field at the heterojunction drives the directional migration and spatial separation of photogenerated carriers. Based on Ce… 4+ / Ce 3 + Through a multi-synergistic mechanism involving redox cycles, lattice oxygen vacancy active sites, and the built-in electric field of the S-type heterojunction, this composite photocatalyst can improve the efficiency and selectivity of photocatalytic CO2 reduction to CO, thereby realizing the resource utilization of CO2. Attached Figure Description

[0019] Figure 1 The XRD patterns of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3 are shown.

[0020] Figure 2 The image shows a scanning electron microscope image of the composite photocatalyst prepared in Example 3.

[0021] Figure 3The UV-Vis absorption spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3 are shown.

[0022] Figure 4 The X-ray photoelectron spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 3 are shown.

[0023] Figure 5 High-resolution X-ray photoelectron spectra of the photocatalysts prepared in Example 3, Comparative Example 1 and Comparative Example 3: (a) Ce element; (b) O element.

[0024] Figure 6 The graph shows the yields of CO and CH4, the CO2 reduction products, of the photocatalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 3.

[0025] Figure 7 The graph shows the CO stability test results of the composite photocatalyst prepared in Example 3 after multiple cycles. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The technical solution of the present invention will be further described below through specific embodiments.

[0029] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0030] Example 1 A method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst includes the following steps: S1. Dissolve 0.36g of KBr in 30mL of anhydrous ethanol to obtain potassium bromide ethanol solution; dissolve 2.91g of Bi(NO3)3·5H2O in 20mL of ethylene glycol to obtain bismuth nitrate pentahydrate ethylene glycol solution; then mix the potassium bromide ethanol solution and the bismuth nitrate pentahydrate ethylene glycol solution and stir evenly to obtain solution A.

[0031] S2. Mix 5 mL of ammonia water with solution A and stir until homogeneous. Adjust the pH of the solution to 10 to obtain solution B.

[0032] S3. Add 0.078g of Ce(NO3)3·6H2O to solution B to obtain solution C, which is the Ce-doped Bi4O5Br2 precursor solution.

[0033] S4. Dissolve 0.115g of Cd(NO3)2·4H2O and 0.029g of CH4N2S in 20mL of ethylene glycol to obtain solution D, which is cadmium nitrate-thiourea ethylene glycol solution.

[0034] S5. Mix solution D with solution C to obtain solution E. Transfer solution E to an autoclave and keep it at 160°C for 16 hours. After the hydrothermal reaction, cool to room temperature to obtain the reaction solution.

[0035] S6. Centrifuge the reaction solution at 1200 r / min for 5 min to precipitate, wash it 5 times with anhydrous ethanol, and dry it at 60℃ for 10 h to obtain Ce-doped Bi4O5Br2-CdS composite photocatalyst, denoted as 3Ce-Bi4O5Br2 / 25CdS.

[0036] In the 3Ce-Bi4O5Br2 / 25CdS composite photocatalyst, the amount of Ce doping is 3% (approximately 25.2 mg) of the molar amount of Bi4O5Br nanosheets; CdS nanoparticles are uniformly loaded on the surface of CeBi4O5Br2 nanosheets, and the CdS loading is approximately 25 wt% (approximately 0.054 g).

[0037] Example 2 A method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst. The difference between this embodiment and Example 1 is that in step S4, the amounts of Cd(NO3)2·4H2O and CH4N2S are adjusted to 0.046g and 0.012g, respectively. The remaining steps are the same as in Example 1, and a Ce-doped Bi4O5Br2-CdS composite photocatalyst is obtained, denoted as 3Ce-Bi4O5Br2 / 10CdS.

[0038] In the 3Ce-Bi4O5Br2 / 10CdS composite photocatalyst, the amount of Ce doping is 3% (approximately 25.2 mg) of the molar amount of Bi4O5Br nanosheets; CdS nanoparticles are uniformly loaded on the surface of CeBi4O5Br2 nanosheets, and the CdS loading is approximately 10 wt% (approximately 0.022 g).

[0039] Example 3 A method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst. The difference between this embodiment and Example 1 is that in step S4, the amounts of Cd(NO3)2·4H2O and CH4N2S are adjusted to 0.231g and 0.057g, respectively. The remaining steps are the same as in Example 1, and a Ce-doped Bi4O5Br2-CdS composite photocatalyst is obtained, denoted as 3Ce-Bi4O5Br2 / 50CdS.

[0040] In the 3Ce-Bi4O5Br2 / 50CdS composite photocatalyst, the amount of Ce doping is 3% (approximately 25.2 mg) of the molar amount of Bi4O5Br nanosheets; CdS nanoparticles are uniformly loaded on the surface of CeBi4O5Br2 nanosheets, and the CdS loading is approximately 50 wt% (approximately 0.108 g).

[0041] Example 4 A method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst. The difference between this embodiment and Example 1 is that in step S4, the amounts of Cd(NO3)2·4H2O and CH4N2S are adjusted to 0.346g and 0.086g, respectively. The remaining steps are the same as in Example 1, and the Ce-doped Bi4O5Br2-CdS composite photocatalyst is obtained, denoted as 3Ce-Bi4O5Br2 / 75CdS.

[0042] In the 3Ce-Bi4O5Br2 / 75CdS composite photocatalyst, the amount of Ce doping is 3% (approximately 25.2 mg) of the molar amount of Bi4O5Br nanosheets; CdS nanoparticles are uniformly loaded on the surface of CeBi4O5Br2 nanosheets, and the CdS loading is approximately 75 wt% (approximately 0.162 g).

[0043] Example 5 A method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst includes the following steps: S1. Dissolve 0.36g of KBr in 30mL of anhydrous ethanol, and dissolve 2.91g of Bi(NO3)3·5H2O in 20mL of ethylene glycol. Then mix the two solutions and stir to obtain solution A.

[0044] S2. Mix 5 mL of ammonia water with solution A, stir until homogeneous, and adjust the pH to 10 to obtain solution B.

[0045] S3. Add 0.052g of Ce(NO3)3·6H2O to solution B to obtain solution C.

[0046] S4. Dissolve 0.231g of Cd(NO3)2·4H2O and 0.057g of CH4N2S in 20mL of ethylene glycol to obtain solution D.

[0047] S5. Mix solution D with solution C to obtain solution E. Transfer solution E to an autoclave and keep it at 160°C for 16 hours. After the reaction, cool to room temperature to obtain the reaction product.

[0048] S6. The reaction product F was centrifuged at 1200 r / min for 5 min, washed 5 times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain Ce-doped Bi4O5Br2-CdS composite photocatalyst, denoted as 2Ce-Bi4O5Br2 / 50CdS.

[0049] In the 2Ce-Bi4O5Br2 / 50CdS composite photocatalyst, the amount of Ce doping is 1% (approximately 16.8 mg) of the molar amount of Bi4O5Br nanosheets; CdS nanoparticles are uniformly loaded on the surface of CeBi4O5Br2 nanosheets, and the CdS loading is approximately 50 wt% (approximately 0.108 g).

[0050] Example 6 A method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst. The difference between this embodiment and Example 5 is that in step S3, the amount of Ce(NO3)3·6H2O is adjusted to 0.026g. The remaining steps are the same as in Example 5, and the Ce-doped Bi4O5Br2-CdS composite photocatalyst is obtained, denoted as 1Ce-Bi4O5Br2 / 50CdS.

[0051] In the 1Ce-Bi4O5Br2 / 50CdS composite photocatalyst, the amount of Ce doping is 1% (approximately 8.4 mg) of the molar amount of Bi4O5Br nanosheets; CdS nanoparticles are uniformly loaded on the surface of CeBi4O5Br2 nanosheets, and the CdS loading is approximately 50 wt% (approximately 0.108 g).

[0052] Example 7 A method for preparing a Ce-doped Bi4O5Br2-CdS composite photocatalyst. The difference between this embodiment and Example 5 is that in step S3, the amount of Ce(NO3)3·6H2O is adjusted to 0.104g. The remaining steps are the same as in Example 5, and the Ce-doped Bi4O5Br2-CdS composite photocatalyst is obtained, denoted as 4Ce-Bi4O5Br2 / 50CdS.

[0053] In the 4Ce-Bi4O5Br2 / 50CdS composite photocatalyst, the amount of Ce doping is 4% (approximately 33.6 mg) of the molar amount of Bi4O5Br nanosheets; CdS nanoparticles are uniformly loaded on the surface of CeBi4O5Br2 nanosheets, and the CdS loading is approximately 50 wt% (approximately 0.108 g).

[0054] Comparative Example 1 The preparation of a pure Bi4O5Br2 photocatalyst includes the following steps: 0.36 g of KBr was dissolved in 30 mL of anhydrous ethanol, and 2.91 g of Bi(NO3)3·5H2O was dissolved in 20 mL of ethylene glycol. The two were mixed and stirred, and 5 mL of ammonia water was added to adjust the pH to 10. The mixture was then transferred to a high-pressure reactor and reacted at 160 °C for 16 h. After natural cooling, the mixture was centrifuged, washed, and dried to obtain pure Bi4O5Br2 photocatalyst, denoted as Bi4O5Br2.

[0055] Comparative Example 2 The preparation of a pure CdS photocatalyst includes the following steps: 0.231 g of Cd(NO3)2·4H2O and 0.057 g of thiourea were dissolved in 20 mL of ethylene glycol, transferred to a high-pressure reactor, reacted at 160 °C for 16 h, cooled naturally, centrifuged, washed and dried to obtain pure CdS photocatalyst, denoted as CdS.

[0056] Comparative Example 3 A method for preparing a Ce-doped Bi4O5Br2 photocatalyst includes the following steps: S1. Dissolve 0.36g of KBr in 30mL of anhydrous ethanol, and dissolve 2.91g of Bi(NO3)3·5H2O in 20mL of ethylene glycol. Then mix the two solutions and stir to obtain solution A.

[0057] S2. Mix 5 mL of ammonia water with solution A and stir until homogeneous. Adjust the pH to 10 to obtain solution B.

[0058] S3. Add 0.078g of Ce(NO3)3·6H2O to solution B to obtain solution C.

[0059] S4. Transfer solution C to a high-pressure reactor and keep it at 160°C for 16 hours. After the reaction, cool to room temperature to obtain the reaction product.

[0060] S5. The reaction product was centrifuged at 1200 r / min for 5 min to precipitate, washed 5 times with anhydrous ethanol, and dried at 60℃ for 10 h to obtain Ce-doped Bi4O5Br2 photocatalyst, denoted as 3Ce-doped Bi4O5Br2.

[0061] The photocatalysts prepared in Example 3 and Comparative Examples 1 to 3 were subjected to XRD tests, and the results are as follows: Figure 1 As shown, the horizontal axis represents the diffraction angle (2θ), and the vertical axis represents the intensity of the diffraction peak. Figure 1This indicates that Bi4O5Br2 has a monoclinic structure, CdS has a hexagonal structure, and the diffraction peaks of the composite heterojunction catalyst all contain characteristic peaks of both Bi4O5Br2 and CdS, indicating the successful preparation of the 3Ce-Bi4O5Br2 / 50CdS composite photocatalyst. It can be seen that compared to Bi4O5Br2, the diffraction peaks of 3Ce-Bi4O5Br2 do not show significant changes, indicating that Ce doping did not affect the crystal structure of Bi4O5Br2. Compared to CdS, the peak intensity of some CdS crystal planes in 3Ce-Bi4O5Br2 / 50CdS is weakened, which is attributed to the formation of the heterojunction interface hindering the crystallization or growth of some CdS crystal planes.

[0062] The composite photocatalyst prepared in Example 3 was tested using scanning electron microscopy, such as... Figure 2 As shown. From Figure 2 It can be seen that CdS nanoparticles are uniformly dispersed on the surface of petals formed by the self-assembly of two-dimensional nanosheets 3Ce-Bi4O5Br2, forming a heterojunction composite photocatalyst. This indicates that a rich heterojunction interface is formed in the composite photocatalyst 3Ce-Bi4O5Br2 / 50CdS, and these heterojunction interfaces can promote the migration and separation of photogenerated carriers.

[0063] The photocatalysts prepared in Example 3 and Comparative Examples 1 to 3 were subjected to UV-Vis absorption tests, and the results are as follows: Figure 3 As shown, the horizontal axis represents wavelength (Wavelength), and the vertical axis represents normalized absorbance (normalized1). Figure 3 It can be seen that the absorption edge of pure CdS (536.7 nm) is in the ultraviolet spectrum range (200 nm to 400 nm), the absorption edge of pure Bi4O5Br2 (459.7 nm) is in the visible spectrum range (400 nm to 800 nm), the absorption edge of 3Ce-Bi4O5Br2 (542.6 nm) is in the visible spectrum range (400 nm to 800 nm), and the maximum light absorption edge of the composite photocatalyst 3Ce-Bi4O5Br2 / 50CdS is 729.9 nm.

[0064] X-ray photoelectron analysis was performed on the photocatalysts prepared in Example 3 and Comparative Examples 1 to 3. Figure 4 As shown, the composite photocatalyst 3Ce-Bi4O5Br2 / 50CdS contains six elements: Ce, Bi, Cd, O, S, and Br.

[0065] High-resolution X-ray photoelectron spectroscopy (XPS) spectra of the photocatalysts prepared in Example 3, Comparative Example 1, and Comparative Example 3: (a) Ce element; (b) O element. Figure 5 As shown, it can be seen that Ce 3d is based on Ce 4+ and Ce 3+Both valence states exist simultaneously, and Ce 4+ The dominant form is O 1s; O exists in three forms: H2O, oxygen vacancies, and Bi-O, with Bi-O being the dominant form. This indicates that Ce doping exists. 4+ and Ce 3+ Two valence states are introduced, and an oxygen vacancy is introduced.

[0066] The photocatalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to UV-Vis diffuse reflectance absorption spectroscopy tests, and the results are shown in Table 1.

[0067] Table 1. Results of UV-Vis diffuse reflectance absorption spectra of different photocatalysts Note: "-" indicates no data.

[0068] As shown in Table 1, the maximum light absorption edge of the 3-Ce-Bi4O5Br2 / 50CdS photocatalyst prepared in Example 3 is 729.9 nm, which includes the visible light range of CdS, Bi4O5Br2 and 3Ce-Bi4O5Br2, and exhibits a red shift, achieving almost full-spectrum absorption of ultraviolet and visible light, thus improving the utilization rate of visible light.

[0069] The photocatalysts prepared in Examples 1-4 and Comparative Examples 1-3 were used for photocatalytic reduction of CO2. The specific steps were as follows: 10 mg of photocatalyst was added to 1 g of anhydrous ethanol and ultrasonically vibrated for 4 h to obtain a catalyst suspension; the catalyst suspension was poured into a petri dish and dried at 60 °C to obtain a catalyst film; the catalyst film was placed in a light-transmitting sealed reactor, filled with CO2 and sufficient water, the reactor was sealed, and the reaction was carried out under sunlight for 1 h; after the reaction was completed, the composition of the gas in the reactor was analyzed, and the main components were CO2, CO, O2 and CH4.

[0070] Figure 6 This is a graph showing the yields of CO and CH4, the CO reduction products, of the composite photocatalysts prepared in Comparative Example 1 (Bi4O5Br2), Comparative Example 2 (CdS), Comparative Example 3 (3Ce-Bi4O5Br2), and Examples 1-4. The horizontal axis represents the type of composite catalyst, and the vertical axis represents the yield. Figure 6 As shown in Table 2, with the increase of the amount of cadmium nitrate tetrahydrate and thiourea in the composite photocatalyst (i.e., the molar ratio of CdS to 3Ce-Bi4O5Br2 increases), the yields of CO and CH4 show a trend of first increasing and then decreasing.

[0071] Table 2. Effects of different photocatalysts on the yield and selectivity of CO and CH4, the photocatalytic CO2 reduction products. Note: "-" indicates no data.

[0072] As shown in Table 2, the CO yields of pure Bi4O5Br2 and CdS are 12.56 μmol·g, respectively. -1 ·h -1 and 5.56 μmol·g -1 ·h -1 The CH4 yield was 1.06 μmol·g. -1 ·h -1 and 0.56 μmol·g -1 ·h -1 The CO and CH4 yields of 3Ce-Bi4O5Br2 were 16.95 μmol·g. -1 ·h -1 and 1.26 μmol·g -1 ·h -1 The composite photocatalyst exhibited higher CO and CH4 yields than pure Bi4O5Br2, CdS, and 3Ce-Bi4O5Br2. When the molar ratio of CdS to 3Ce-Bi4O5Br2 was 0.5:1, i.e., the 3Ce-Bi4O5Br2 / 50CdS prepared in Example 3 produced the highest CO yield of 25.37 μmol·g. -1 ·h -1 The highest corresponding CH4 yield was 2.81 μmol·g. -1 ·h -1 The catalyst has a selectivity of 90% for CO.

[0073] Figure 7 This is a graph showing the CO stability of the product after five cycles of the 3Ce-Bi4O5Br2 / 50CdS composite photocatalyst prepared in Example 3. The horizontal axis represents the number of cycles, and the vertical axis represents the yield. Figure 7 As shown in Table 3, the above photocatalytic decomposition of CO2 was repeated under simulated sunlight conditions, and the experimental data are shown in Table 3.

[0074] Table 3. Effect of the number of photocatalyst cycles prepared in Example 3 on the yields of CO and CH4 products. As shown in Table 3, the number of cycles has little effect on the yield of CO and CH4 products from the photocatalytic reduction of CO2 by 3Ce-Bi4O5Br2 / 50CdS. The yield of CO and CH4 shows a slight decrease with the increase of the number of cycles.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Ce-doped Bi4O5Br2-CdS composite photocatalyst, characterized in that, The Ce-doped Bi4O5Br2-CdS composite photocatalyst is formed by in-situ loading CdS nanoparticles on the surface of Ce-doped Bi4O5Br2 nanosheets and forming an S-type heterojunction structure. The Ce in the Ce-doped Bi4O5Br2 nanosheets is Ce 4+ and Ce 3+ Ce is doped in Bi4O5Br2 nanosheets in mixed valence states, and the doping amount of Ce is 1% to 4% of the molar amount of Bi4O5Br2 nanosheets; The loading of the CdS nanoparticles is 10% to 75% of the mass of the Ce-doped Bi4O5Br2 nanosheets.

2. The composite photocatalyst according to claim 1, characterized in that, The Ce-doped Bi4O5Br2-CdS composite photocatalyst is formed by the self-assembly of two-dimensional nanosheets of Ce-doped Bi4O5Br2 into a petal-shaped morphology, with CdS nanoparticles dispersed on the surface of the petal-shaped morphology, thus forming an S-type heterojunction structure.

3. A method for preparing the Ce-doped Bi4O5Br2-CdS composite photocatalyst according to claim 2, characterized in that, Includes the following steps: A potassium bromide ethanol solution and a bismuth nitrate pentahydrate ethylene glycol solution were mixed, and cerium nitrate was added at pH=10 to obtain a Ce-doped Bi4O5Br2 precursor solution. The Ce-doped Bi4O5Br2 precursor solution was mixed with a cadmium nitrate-thiourea ethylene glycol solution and subjected to a hydrothermal reaction at 150℃~170℃, which caused the Ce-doped Bi4O5Br2 nanosheets to self-assemble into a petal-like morphology, and CdS nanoparticles were dispersed on the surface of the petal-like morphology to form an S-type heterojunction structure. After centrifugation, a Ce-doped Bi4O5Br2-CdS composite photocatalyst was prepared.

4. The preparation method of the Ce-doped Bi4O5Br2-CdS composite photocatalyst according to claim 3, characterized in that, The molar ratio of potassium bromide to bismuth nitrate pentahydrate is 1:2 to 6.

5. The preparation method of the Ce-doped Bi4O5Br2-CdS composite photocatalyst according to claim 3, characterized in that, The molar ratio of cerium nitrate to bismuth nitrate pentahydrate is 0.01 to 0.04:

1.

6. The preparation method of the Ce-doped Bi4O5Br2-CdS composite photocatalyst according to claim 3, characterized in that, The molar ratio of cadmium nitrate to thiourea in the cadmium nitrate-thiourea glycol solution is 1:

1. The molar ratio of cadmium nitrate-thiourea to bismuth nitrate pentahydrate is 0.025 to 0.187:

1.

7. The preparation method of the Ce-doped Bi4O5Br2-CdS composite photocatalyst according to claim 3, characterized in that, The hydrothermal reaction temperature is 160℃±5℃, and the reaction time is 15h~17h.

8. The application of the Ce-doped Bi4O5Br2-CdS composite photocatalyst according to claims 1-2 in the photocatalytic reduction of CO2, characterized in that, The application method is as follows: Ce-doped Bi4O5Br2-CdS composite photocatalyst is dispersed in ethanol to obtain a dispersion, the dispersion is made into a thin film, and placed in CO2 and water to carry out photocatalytic reduction of CO2 under light irradiation.

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