Bi4O5Br2-ZnO composite photocatalyst as well as preparation method and application thereof
By forming a heterojunction catalyst by combining Bi4O5Br2 and ZnO, the problems of narrow light absorption range and low carrier mobility in the photocatalytic carbon dioxide reduction process are solved, achieving efficient carbon dioxide reduction and selectivity of the product carbon monoxide, which has economic benefits.
Patent Information
- Application Number
- CN202511136193.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-14
- Publication Date
- 2025-11-28
AI Technical Summary
Existing Bi4O5Br2 and ZnO photocatalysts suffer from narrow light absorption range, low carrier mobility, and insufficient active sites during photocatalytic carbon dioxide reduction, which limits their efficiency.
By chemically reacting Bi4O5Br2 with ZnO to form a heterojunction catalyst, the absorption range of light waves is broadened, the migration and separation of photogenerated carriers are promoted, and crystal defects are formed in the hydrothermal reaction as active sites.
It improves the efficiency and selectivity of photocatalytic carbon dioxide reduction, enhances the utilization rate of visible light, and reduces catalyst costs, resulting in good economic benefits.
Smart Images
Figure CN121016801A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst preparation, specifically relating to a Bi4O5Br2-ZnO composite photocatalyst, its preparation method, and its application. Background Technology
[0002] The global climate and environmental crisis caused by excessive carbon dioxide (CO2) emissions has become a pressing issue for the scientific and industrial communities. Photocatalytic carbon dioxide reduction technology, with its advantages of renewable solar energy reaction, mild conditions, and environmental friendliness, can convert carbon dioxide into chemicals such as carbon monoxide, methane, and methanol, making it an effective strategy for reducing atmospheric carbon dioxide concentration and alleviating the energy crisis. Therefore, developing highly efficient photocatalysts for carbon dioxide reduction and conversion is a current challenge in scientific research. Research shows that constructing heterojunction composite photocatalysts can significantly improve the efficiency of photocatalytic carbon dioxide reduction.
[0003] Among many catalysts, Bi4O5Br2 is one composed of [Bi2O2]. 2+ and double [Br] - Alternating layered semiconductor materials exhibit narrow band gaps (2.3–2.8 eV) and excellent visible light absorption (400–600 nm), despite their bismuth-rich induced oxygen vacancies and double [Br] structures. - The layer-enhanced built-in electric field promotes the separation of photogenerated carriers, but the carrier mobility perpendicular to the layer direction is low, which limits its photocatalytic activity to some extent. ZnO is a hexagonal crystal system with a wurtzite structure, an n-type semiconductor material with a band gap of about 3.37 eV. It has strong oxidizing properties, low cost, and is environmentally friendly. However, its wide band gap makes it highly responsive to ultraviolet light (<387 nm), which limits its utilization of visible light. Summary of the Invention
[0004] To address the above problems, this invention provides a Bi4O5Br2-ZnO composite photocatalyst and its preparation method.
[0005] The heterojunction catalyst Bi4O5Br2-ZnO, formed by chemically combining bismuth-rich bismuth oxybromide (Bi4O5Br2) and zinc oxide (ZnO), combines the advantages of both: (1) it can broaden the light absorption range and improve the full spectrum utilization; (2) the interface and built-in electric field formed between the two can promote the migration and separation of photogenerated carriers, thereby enhancing the oxidation / reduction reaction of carbon dioxide; (3) the crystal defects (interstitial atoms, oxygen vacancies) formed during the hydrothermal reaction can serve as active sites, reducing the adsorption energy barrier for carbon dioxide. Therefore, the Bi4O5Br2-ZnO composite photocatalyst can improve the photocatalytic reduction performance of carbon dioxide.
[0006] To achieve the above objectives, this invention provides a method for preparing a Bi4O5Br2-ZnO composite photocatalyst, comprising the following steps:
[0007] S1: Mix an aqueous solution of sodium bromide with an ethanolic solution of bismuth nitrate pentahydrate and stir to obtain solution A;
[0008] S2: Mix ammonia water with solution A and stir until homogeneous to obtain solution B;
[0009] S3: Add nano zinc oxide to solution B to obtain solution C;
[0010] S4: Transfer solution C to a high-pressure reactor for hydrothermal reaction. After the reaction is complete, cool to obtain reaction product D;
[0011] S5: Centrifuge the reaction product D, wash it with anhydrous ethanol, and dry it to obtain the Bi4O5Br2-ZnO composite photocatalyst.
[0012] Furthermore, the molar ratio of sodium bromide to bismuth nitrate pentahydrate in S1 is 1:4.
[0013] Furthermore, the ammonia in S2 is used to adjust the pH of solution B to 11.
[0014] Furthermore, the molar ratio of nano zinc oxide to bismuth nitrate pentahydrate in S3 is 0.25 to 2:1.
[0015] Furthermore, the hydrothermal reaction conditions described in S4 are a temperature of 160–180°C and a reaction time of 11–13 h.
[0016] The present invention also provides a Bi4O5Br2-ZnO composite photocatalyst, characterized in that it is prepared by the above method, wherein the Bi4O5Br2 in the catalyst is in the form of flakes and the ZnO is in the form of particles.
[0017] This invention also provides an application of the Bi4O5Br2-ZnO composite photocatalyst, comprising the following steps:
[0018] S1: The above Bi4O5Br2-ZnO composite photocatalyst was dispersed in anhydrous ethanol to obtain a catalyst suspension;
[0019] S2: Pour the catalyst suspension into a petri dish and dry it to obtain a catalyst film;
[0020] S3: Place the catalyst film into a light-transmitting sealed reactor, fill it with CO2 and water vapor, and react it under sunlight or simulated sunlight.
[0021] The beneficial effects of this invention are:
[0022] This invention provides a Bi4O5Br2-ZnO composite photocatalyst, its preparation method, and its application. The method involves uniformly mixing an aqueous solution of sodium bromide with an ethanolic solution of bismuth nitrate pentahydrate in a specific ratio. Ammonia is then added to adjust the pH of the solution to alkaline (pH=11). Nano-zinc oxide is then added, and the mixture is stirred uniformly. The resulting solution is placed in an autoclave and reacted hydrothermally under constant temperature and sufficient reaction time. After the reaction, the reactants are cooled, precipitated, washed, and dried to obtain the Bi4O5Br2-ZnO composite photocatalyst. The preparation method of this invention is simple, the raw materials are readily available, and it is suitable for large-scale production.
[0023] The Bi4O5Br2-ZnO composite photocatalyst prepared in this invention, when dispersed in anhydrous ethanol and dried in a petri dish to obtain a catalyst film, exhibits better performance. The Bi4O5Br2-ZnO composite photocatalyst combines the advantages of both: compared to pure Bi4O5Br2 and ZnO, the composite photocatalyst exhibits a redshift in light absorption, expanding the light absorption range and improving visible light utilization; the interface formed through the reaction and the built-in electric field promote the migration and separation of photogenerated carriers, thus accelerating the carbon dioxide reduction reaction; the crystal defects (interstitial atoms, oxygen vacancies) formed during the hydrothermal reaction can serve as active sites, reducing the catalyst's adsorption energy for carbon dioxide and lowering the reaction energy barrier. Through photocatalytic reduction of carbon dioxide, the selectivity of the catalyst for the product carbon monoxide is improved, increasing the yield of carbon monoxide and achieving the goal of carbon dioxide disposal and resource utilization. Furthermore, the low cost of zinc oxide reduces the overall cost of the composite photocatalyst, demonstrating good economic benefits and development prospects. Attached Figure Description
[0024] Figure 1 XRD patterns of pure Bi4O5Br2, pure ZnO, and Bi4O5Br2-ZnO composite photocatalysts;
[0025] Figure 2 Scanning electron microscope image of pure Bi4O5Br2;
[0026] Figure 3 Scanning electron microscope image of Bi4O5Br2-ZnO composite photocatalyst;
[0027] Figure 4 The UV-Vis absorption spectra of pure Bi4O5Br2, pure ZnO, and Bi4O5Br2-ZnO composite photocatalysts;
[0028] Figure 5 The yield diagram of CO and CH4, the CO2 reduction products, of the Bi4O5Br2-ZnO composite photocatalyst;
[0029] Figure 6 This is a graph showing the stability test of the CO product after multiple cycles of experiments. Detailed Implementation
[0030] To make the technical means, features and effects of the present invention easier to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0031] 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.
[0032] Example 1
[0033] A method for preparing a Bi4O5Br2-ZnO composite photocatalyst includes the following steps:
[0034] S1: Dissolve 0.103g sodium bromide in 20mL deionized water, dissolve 1.94g Bi(NO3)3·5H2O in 40mL ethanol, then mix the two and stir to obtain solution A;
[0035] S2: Mix 4 mL of NH3·H2O ammonia solution with solution A, stir until homogeneous, and adjust the pH to 11 to obtain solution B;
[0036] S3: Add 0.0814 g of nano zinc oxide to solution B to obtain solution C;
[0037] S4: Transfer solution C to an autoclave and keep it at 170°C for 12 hours. After the reaction, cool to room temperature to obtain reaction product D.
[0038] S5: The reaction product D was centrifuged at 1400 r / min for 3 min, washed 5 times with anhydrous ethanol, and dried at 60℃ for 12 hours to obtain the Bi4O5Br2-ZnO composite photocatalyst.
[0039] In Example 1, the molar ratio of Bi(NO3)3·5H2O to ZnO in the Bi4O5Br2-ZnO composite photocatalyst is 1:1, so the composite photocatalyst is denoted as Bi4O5Br2-1ZnO.
[0040] Examples 2-4
[0041] By adjusting the amount of nano zinc oxide in Example 1, Bi4O5Br2-ZnO composite photocatalysts with molar ratios of Bi(NO3)3·5H2O to ZnO of 1:0.25, 1:0.5, and 1:2 were obtained, and were respectively denoted as Bi4O5Br2-0.25ZnO, Bi4O5Br2-0.5ZnO, and Bi4O5Br2-2ZnO;
[0042] Figure 1 The images show the XRD patterns of pure Bi4O5Br2, pure ZnO, and Bi4O5Br2-ZnO composite photocatalysts. The horizontal axis represents the diffraction angle (2θ), and the vertical axis represents the intensity of the diffraction peaks. Figure 1 As shown, the bismuth-rich oxyhalide has a monoclinic structure, and the zinc oxide has a hexagonal structure. The diffraction peaks of the composite heterojunction catalyst all contain the characteristic peaks of Bi4O5Br2 and ZnO, indicating that the Bi4O5Br2-ZnO composite photocatalyst was successfully prepared. As the proportion of ZnO decreases: (1) the diffraction peak intensity of Bi4O5Br2 at 2θ of 29.05° and 32.41° increases, indicating that Bi4O5Br2 mainly crystallizes or grows along the (303) and (120) crystal planes; (2) the diffraction peak intensity of Bi4O5Br2 at 2θ of 24.36° and 33.29° decreases, indicating that its crystallization or growth along the (310) and (501) crystal planes is inhibited. This is attributed to the interface formed by the introduced ZnO and Bi4O5Br2 hindering its crystallization or growth along the (310) and (501) crystal planes. Similarly, the diffraction peaks of ZnO at 2θ of 9.63° and 24.36° are weakened or even disappear, meaning that the crystallization or growth of ZnO along the (100) and (002) crystal planes is suppressed.
[0043] Figure 2 The image shows a scanning electron microscope image of pure Bi4O5Br2, as follows. Figure 2 As shown, pure Bi4O5Br2 is a petal that is self-assembled from nanosheets.
[0044] Figure 3 This is a scanning electron microscope image of the Bi4O5Br2 / 1-ZnO composite photocatalyst. Figure 3 As shown, ZnO nanoparticles are uniformly dispersed on the surface of two-dimensional nanosheet Bi4O5Br2, forming a heterojunction composite photocatalyst. This indicates that the introduction of ZnO did not change the morphology of Bi4O5Br2, but made the surface of Bi4O5Br2 rough. These rough surfaces can serve as active sites for carbon dioxide adsorption and reaction.
[0045] Figure 4The images show the UV-Vis absorption spectra of Bi4O5Br2, ZnO, and Bi4O5Br2-ZnO composite photocatalysts, where the horizontal axis represents wavelength and the vertical axis represents normalized absorbance (normalized1). Figure 4 As shown, the absorption edge of pure ZnO (383.7 nm) is in the ultraviolet spectral range (200–400 nm), while the absorption edge of pure Bi4O5Br2 (499.7 nm) is in the visible spectral range (400–800 nm). Compared with pure ZnO, the light absorption of the composite photocatalysts is red-shifted into the visible spectral range, with Bi4O5Br2–2ZnO having the largest light absorption edge at 729.9 nm.
[0046] The experimental data are shown in Table 1:
[0047] Table 1. Effect of the molar ratio of Bi(NO3)3·5H2O to ZnO on UV-Vis absorption.
[0048] Sample Mole ratio UV-Vis absorption edge (nm) Bi4O5Br2 1：0 499.7 Bi4O5Br2-0.25ZnO 1：0.25 450 Bi4O5Br2-0.5ZnO 1：0.5 483.8 <![CDATA[Bi4O5Br2-1ZnO]]> 1：1 469.1 <![CDATA[Bi4O5Br2-2ZnO]]> 1：2 729.9 ZnO 0：1 383.7
[0049] As shown in Table 1, the maximum light absorption edge of the sample Bi4O5Br2-2ZnO is 729.9 nm, which includes the ultraviolet light range of ZnO and the visible light range of Bi4O5Br2, and exhibits a red shift, thus achieving almost full-spectrum absorption of ultraviolet and visible light and improving the utilization rate of visible light.
[0050] Example 5
[0051] A method for preparing a Bi4O5Br2-ZnO composite photocatalyst includes the following steps:
[0052] S1: Dissolve 0.103g sodium bromide in 20mL deionized water, dissolve 1.94g Bi(NO3)3·5H2O in 40mL ethanol, then mix the two and stir to obtain solution A;
[0053] S2: Mix 4 mL of NH3·H2O ammonia solution with solution A, stir until homogeneous, and adjust the pH to 11 to obtain solution B;
[0054] S3: Add 0.1628g of nano zinc oxide to solution B to obtain solution C;
[0055] S4: Transfer solution C to an autoclave and keep it at 160°C for 13 hours. After the reaction, cool to room temperature to obtain reaction product D.
[0056] S5: The reaction product D was centrifuged at 1400 r / min for 5 min, washed 5 times with anhydrous ethanol, and dried at 60℃ for 13 hours to obtain the Bi4O5Br2-ZnO composite photocatalyst.
[0057] In Example 5, the molar ratio of Bi(NO3)3·5H2O to ZnO in the Bi4O5Br2-ZnO composite photocatalyst is 1:2, so the composite catalyst is denoted as Bi4O5Br2-2ZnO.
[0058] The prepared Bi4O5Br2-2ZnO composite photocatalyst was used for photocatalytic reduction of CO2, including the following steps:
[0059] S1: 12 mg of Bi4O5Br2-2ZnO composite photocatalyst was added to 12 g of anhydrous ethanol and ultrasonically vibrated for 3 h to obtain a catalyst suspension.
[0060] S2: Pour the catalyst suspension into a petri dish and dry it at 60°C to obtain a catalyst film;
[0061] S3: Place the catalyst film into a light-transmitting sealed reactor, fill it with CO2 and water vapor (molar ratio of approximately 1:11), seal the reactor, and react under sunlight for 1 hour.
[0062] After the reaction was completed, the composition of the gas in the reactor was analyzed. The main components were CO2, CO, O2 and CH4.
[0063] Examples 6-8
[0064] By adjusting the amount of nano zinc oxide in Example 5, Bi4O5Br2-ZnO composite photocatalysts with molar ratios of Bi(NO3)3·5H2O to ZnO of 1:0.25, 1:0.5, and 1:1 were obtained, and were respectively denoted as Bi4O5Br2-0.25ZnO, Bi4O5Br2-0.5ZnO, and Bi4O5Br2-1ZnO;
[0065] The prepared Bi4O5Br2-0.25ZnO, Bi4O5Br2-0.5ZnO, and Bi4O5Br2-1ZnO composite photocatalysts were then used for photocatalytic reduction of CO2, following the same steps as in Example 5.
[0066] Comparative Example 1
[0067] Compared to Example 5, pure Bi4O5Br2 was directly used for photocatalytic reduction of CO2.
[0068] Comparative Example 2
[0069] Compared to Example 5, pure ZnO was directly used for photocatalytic reduction of CO2.
[0070] Figure 5This graph shows the yields of CO and CH4, the CO reduction products, from pure Bi4O5Br2, pure ZnO, and a composite photocatalyst. The horizontal axis represents the type of composite catalyst, and the vertical axis represents the yield. Figure 5 As shown in Table 2, the yields of CO and CH4 exhibit nonlinear changes as the molar ratio of Bi(NO3)3·5H2O to ZnO in the Bi4O5Br2-ZnO composite photocatalyst decreases.
[0071] Table 2. Effects of the molar ratio of Bi(NO3)3·5H2O to ZnO on the yield and selectivity of photocatalytic CO2 reduction products CO and CH4.
[0072]
[0073] As shown in Table 2, the CO yields of pure Bi4O5Br2 and ZnO are 2.76 μmol·g, respectively. -1 ·h -1 and 1.74 μmol·g -1 ·h -1 The CH4 yields were 1.34 μmol·g. -1 ·h -1 and 0.67 μmol·g -1 ·h -1 The composite photocatalyst exhibited higher yields of both CO and CH4 than pure Bi4O5Br2 and ZnO. When the molar ratio of Bi4O5Br2 to ZnO was 1:2, the sample Bi4O5Br2 / 2-ZnO showed the highest CO yield of 8.43 μmol·g. -1 ·h -1 The highest corresponding CH4 yield was 2.56 μmol·g. -1 ·h -1 The selectivity of the catalyst for CO was 76.7%.
[0074] Example 9
[0075] A method for preparing a Bi4O5Br2-ZnO composite photocatalyst includes the following steps:
[0076] S1: Dissolve 0.103g sodium bromide in 20mL deionized water, dissolve 1.94g Bi(NO3)3·5H2O in 40mL ethanol, then mix the two and stir to obtain solution A;
[0077] S2: Mix 4 mL of NH3·H2O ammonia solution with solution A, stir until homogeneous, and adjust the pH to 11 to obtain solution B;
[0078] S3: Add 0.1628g of nano zinc oxide to solution B to obtain solution C;
[0079] S4: Transfer solution C to an autoclave and keep it at 180°C for 11 hours. After the reaction, cool to room temperature to obtain reaction product D.
[0080] S5: The reaction product D was centrifuged at 1400 r / min for 5 min, washed 5 times with anhydrous ethanol, and dried at 60℃ for 13 hours to obtain the Bi4O5Br2-ZnO composite photocatalyst.
[0081] In the example, the molar ratio of Bi(NO3)3·5H2O to ZnO in the Bi4O5Br2-ZnO composite photocatalyst is 1:2, so the composite catalyst is denoted as Bi4O5Br2-2ZnO;
[0082] The prepared Bi4O5Br2-2ZnO composite photocatalyst was used for photocatalytic reduction of CO2, including the following steps:
[0083] S1: 12 mg of Bi4O5Br2-2ZnO composite photocatalyst was added to 12 g of anhydrous ethanol and ultrasonically vibrated for 3 h to obtain a catalyst suspension.
[0084] S2: Pour the catalyst suspension into a petri dish and dry it at 60°C to obtain a catalyst film;
[0085] S3: Place the catalyst film into a light-transmitting sealed reactor, fill it with CO2 and water vapor (molar ratio of approximately 1:11), seal the reactor, and react for 1 hour under simulated sunlight.
[0086] After the reaction was completed, the composition of the gas in the reactor was analyzed. The main components were CO2, CO, O2 and CH4.
[0087] The reaction products in the reactor are discharged, replaced, and then CO2 and water vapor (molar ratio of approximately 1:11) are introduced. The reactor is then sealed and reacted under simulated sunlight for 1 hour. This process is repeated several times.
[0088] Figure 6 This is a graph showing the stability of CO produced by the sample Bi4O5Br2-2ZnO after multiple cycles. The horizontal axis represents the number of cycles, and the vertical axis represents the yield. Figure 6 As shown in Table 3, the photocatalytic decomposition of CO2 was repeated under simulated sunlight conditions.
[0089] Table 3. Effect of photocatalytic cycle number on CO yield.
[0090]
[0091]
[0092] As shown in Table 3, the number of cycles has little effect on the yield of CO produced by the photocatalytic reduction of CO2 by Bi4O5Br2-2ZnO. The yield of CO shows a slight decrease with the increase of the number of cycles.
[0093] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the substantive protection scope of the technical solution of the present invention.
Claims
1. A method for preparing a Bi4O5Br2-ZnO composite photocatalyst, characterized in that, Includes the following steps: S1: Mix an aqueous solution of sodium bromide with an ethanolic solution of bismuth nitrate pentahydrate and stir to obtain solution A; S2: Mix ammonia water with solution A and stir until homogeneous to obtain solution B; S3: Add nano zinc oxide to solution B to obtain solution C; S4: Transfer solution C to a high-pressure reactor for hydrothermal reaction. After the reaction is complete, cool to obtain reaction product D; S5: Centrifuge the reaction product D, wash it with anhydrous ethanol, and dry it to obtain the Bi4O5Br2-ZnO composite photocatalyst.
2. The preparation method of the Bi4O5Br2-ZnO composite photocatalyst as described in claim 1, characterized in that, The molar ratio of sodium bromide to bismuth nitrate pentahydrate in S1 is 1:
4.
3. The preparation method of the Bi4O5Br2-ZnO composite photocatalyst as described in claim 1, characterized in that, In S2, ammonia is used to adjust the pH of solution B to 11.
4. The preparation method of the Bi4O5Br2-ZnO composite photocatalyst as described in claim 1, characterized in that, The molar ratio of nano zinc oxide to bismuth nitrate pentahydrate in S3 is 0.25 to 2:
1.
5. The preparation method of the Bi4O5Br2-ZnO composite photocatalyst as described in claim 1, characterized in that, The hydrothermal reaction conditions described in S4 are a temperature of 160–180°C and a reaction time of 11–13 h.
6. A Bi4O5Br2-ZnO composite photocatalyst, characterized in that, The catalyst is prepared using the method described in any one of claims 1 to 5, wherein Bi4O5Br2 is in the form of flakes and ZnO is in the form of particles.
7. An application of a Bi4O5Br2-ZnO composite photocatalyst, characterized in that, Includes the following steps: S1: Disperse the Bi4O5Br2-ZnO composite photocatalyst according to claim 6 into anhydrous ethanol to obtain a catalyst suspension; S2: Pour the catalyst suspension into a petri dish and dry it to obtain a catalyst film; S3: Place the catalyst film into a light-transmitting sealed reactor, fill it with CO2 and water vapor, and react it under sunlight or simulated sunlight.