A two-dimensional sheet-like Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst, a preparation method and application thereof

Abstract

The application discloses a two-dimensional sheet Bi2O2CO3 / Zn5(OH)6(CO3)2 composite photocatalyst, a preparation method and application. The technology aims to solve the problems of weak visible light absorption capacity and high electron-hole recombination rate of single basic zinc carbonate (Zn5(OH)6(CO3)2). In the application, Bi2O2CO3 dispersion liquid and Zn5(OH)6(CO3)2 precursor solution are reacted by hydrothermal reaction, two-dimensional sheet Bi2O2CO3 is introduced as a modifier, and by optimizing the mass ratio, the microstructure and interface characteristics of the composite material are effectively controlled, and the Bi2O2CO3 modified Zn5(OH)6(CO3)2 composite photocatalyst is successfully prepared. The visible light absorption efficiency of the basic zinc carbonate is effectively improved, the specific surface area is increased, and the recombination of the photo-generated electron-hole pairs is inhibited, and the charge separation efficiency is improved, so that the photocatalytic degradation performance of Zn5(OH)6(CO3)2 is significantly improved. The application expands the preparation and application technology of Zn5(OH)6(CO3)2-based materials, and the prepared photocatalyst shows good application potential in the field of environmental governance such as wastewater purification.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysts for the degradation of environmental pollutants, specifically a method for preparing a two-dimensional sheet-like basic zinc carbonate-based photocatalyst and its application in the degradation of tetracycline hydrochloride. Background Technology

[0002] In recent years, with the rapid development of modern industry, animal husbandry, and the medical industry, a large amount of pollutants have been continuously discharged into the natural environment, seriously threatening the balance of ecosystems and human health. Among these, antibiotic pollution in water bodies has become a major environmental problem of global concern. Tetracycline antibiotics, due to their broad-spectrum antibacterial properties and cost advantages, are widely used in animal husbandry, medical rehabilitation, and other fields. However, their abuse is widespread, making it difficult for traditional water treatment processes to effectively remove these antibiotics and their metabolites. They are frequently detected in municipal sewage outlets, wastewater treatment plant effluents, and natural water bodies, and the concentration of tetracycline substances in typical discharge source water phases is at a high level. Tetracycline hydrochloride, in particular, has a stable tetraphenylbenzene skeleton structure, making it extremely difficult to biodegrade naturally. Its persistent residue in water bodies has become one of the key problems that urgently need to be solved in the field of environmental governance worldwide. Therefore, the development of efficient and stable tetracycline hydrochloride removal technology has significant practical significance and application value for ensuring water environment safety and reducing ecological risks.

[0003] Zn5(OH)6(CO3)2 (basic zinc carbonate), a common inorganic functional material, is widely used in water purification due to its low preparation cost and good environmental compatibility. However, pure-phase basic zinc carbonate is a wide-bandgap semiconductor material, only responding to ultraviolet light with wavelengths less than 400 nm, and has no effective absorption of visible light. In its application for photocatalytic degradation of tetracycline hydrochloride, it suffers from significant technical shortcomings: extremely low visible light absorption efficiency, limited specific surface area, and highly efficient recombination of photogenerated electron-hole pairs. Ultimately, this results in photocatalytic activity that fails to meet the requirements for efficient tetracycline hydrochloride degradation in practical wastewater treatment, severely restricting its large-scale application and promotion in the field of water environment purification.

[0004] Modification of basic zinc carbonate has become a research hotspot to improve its photocatalytic performance. Bi₂O₂CO₃ (basic bismuth carbonate), as a typical bismuth-based photocatalytic material, possesses a unique two-dimensional layered crystal structure, a large specific surface area, and excellent visible light absorption characteristics. Its band gap is approximately 2.6-2.9 eV, enabling it to effectively utilize solar energy. Furthermore, it exhibits excellent chemical and thermal stability and can form heterojunction structures with other semiconductor materials, promoting the separation of photogenerated carriers, reducing recombination probability, and thus enhancing overall photocatalytic activity. Summary of the Invention

[0005] To address the technical deficiency of low visible light absorption efficiency in pure-phase basic zinc carbonate, this invention aims to provide a Bi₂O₂CO₃-modified basic zinc carbonate (Zn₅(OH)₆(CO₃)₂) photocatalyst, namely a heterojunction Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst. This heterojunction photocatalyst utilizes Bi₂O₂CO₃ to modify basic zinc carbonate. By controlling the composite structure of the two, the light absorption efficiency of basic zinc carbonate in the visible light region is effectively improved, its specific surface area is increased, and the recombination of photogenerated electron-hole pairs is suppressed, thereby significantly enhancing the photocatalytic degradation performance of Zn₅(OH)₆(CO₃)₂. Furthermore, this invention also provides a method for preparing this heterojunction Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst, and its application as a two-dimensional sheet-like basic zinc carbonate-based photocatalyst for the degradation of tetracycline hydrochloride.

[0006] The technical solution of the present invention is as follows: A method for preparing a two-dimensional sheet-like Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst, characterized by comprising the following steps: S1. Preparation of Bi2O2CO3 dispersion: Weigh Bi2O2CO3 powder, disperse it in deionized water, and obtain dispersion A after thorough dispersion; S2. Preparation of Zn5(OH)6(CO3)2 precursor solution: Weigh hexadecyltrimethylammonium bromide, zinc acetate, and urea respectively, and disperse them together in anhydrous ethanol. After stirring evenly, solution B is obtained. S3. Construction of Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst by hydrothermal reaction: Dispersion A and solution B were mixed and stirred continuously for 2–48 hours. The resulting mixed suspension was then transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction was completed, the resulting product was filtered, centrifuged, washed alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven to finally obtain the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst.

[0007] Furthermore, after mixing dispersion A and solution B in S3, the mixture was stirred continuously for 14 hours, and the concentration of Bi2O2CO3 was controlled between 5 g / L and 30 g / L.

[0008] Furthermore, the molar ratio of the three raw materials—hexadecyltrimethylammonium bromide, zinc acetate, and urea—in S2 is 1:1:1, and their concentration in solution B is 0.14 mol / L to 0.20 mol / L.

[0009] Furthermore, in S3, after the dispersion A and solution B are mixed, the volume ratio of anhydrous ethanol solvent is 80% and the volume ratio of deionized water is 20%.

[0010] Furthermore, in the hydrothermal reaction process of S3, the reaction temperature is carried out in three stages: in the first stage, the temperature is raised from 40°C to 140°C for 4 hours; in the second stage, the temperature is maintained at 140°C for 4 hours; in the third stage, the temperature is lowered from 140°C to 25°C for 6 hours, and the reaction is terminated after the temperature is lowered.

[0011] Furthermore, the drying temperature in S3 is 50°C, and the drying time is 24 hours.

[0012] Furthermore, the Bi2O2CO3 powder in S1 is prepared by the following method: S1.1 Weigh out bismuth ammonium citrate monohydrate and citric acid and disperse them in a mixed solution of deionized water and concentrated nitric acid with a volume ratio of 5:1. Sonicate until completely dissolved. Adjust the pH of the above mixed solution to 9 using sodium hydroxide solution. After stirring, obtain Bi2O2CO3 precursor solution. S1.2 The obtained Bi2O2CO3 precursor solution was transferred to a high-pressure reactor, sealed, and placed at 160℃ for hydrothermal reaction. After the reaction was completed, it was naturally cooled to room temperature. The resulting suspension was centrifuged to separate the precipitate. The precipitate was then washed alternately with deionized water and anhydrous ethanol. Finally, after drying, flower-like layered Bi2O2CO3 powder was obtained.

[0013] Furthermore, the molar ratio of bismuth ammonium citrate monohydrate to citric acid weighed in S1.1 is 1:0.42 ~ 1:8.35.

[0014] Two-dimensional sheet-like Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared according to the preparation method described above.

[0015] The application of the two-dimensional sheet-like Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst is characterized by its use in the photocatalytic purification of tetracycline hydrochloride, an antibiotic, in wastewater.

[0016] This invention utilizes a self-developed basic zinc carbonate precursor solution and Bi₂O₂CO₃ as a modifier to construct a Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst via hydrothermal reaction. The prepared Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst exhibits a wide visible light response range, high photogenerated carrier separation efficiency, and large specific surface area. The conduction and valence band positions of Bi₂O₂CO₃ match those of Zn₅(OH)₆(CO₃)₂, forming a heterojunction structure. The built-in electric field formed at the heterojunction interface effectively promotes the rapid separation and directional migration of photogenerated electron-hole pairs, significantly suppresses carrier recombination, and prolongs carrier lifetime, thereby improving the photocatalytic quantum efficiency. Zn5(OH)6(CO3)2, rich in hydroxyl and carbonate groups, exhibits a strong adsorption capacity for tetracycline hydrochloride, enriching the pollutant on the catalyst surface. Bi2O2CO3 provides highly efficient photocatalytic active sites, and the synergistic effect of both significantly improves degradation efficiency. Combining the strong visible light response of Bi2O2CO3, it extends the absorption efficiency of modified Zn5(OH)6(CO3)2 in the visible light region, effectively overcoming the shortcomings of low light absorption efficiency and insufficient catalytic activity of pure-phase basic zinc carbonate. This provides a novel and efficient photocatalytic material and technical approach for the efficient removal of tetracycline hydrochloride from water.

[0017] The preparation method described above successfully prepared three key technical elements of heterojunction Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalysts: first, the control of the molar ratio of raw materials in the basic zinc carbonate precursor solution; second, how to effectively promote the homogeneous mixing of the precursor solution; and third, the precise control of reaction conditions during the hydrothermal reaction to achieve effective modification of Zn5(OH)6(CO3)2 by Bi2O2CO3. During the hydrothermal reaction, by precisely controlling the molar ratio of raw materials in the basic zinc carbonate precursor solution, the solvent ratio of water to anhydrous ethanol, and the mixing of the precursor solution, the pH of the solution can be effectively controlled. By controlling the pH value, the controllability of the synthesis process is improved. Furthermore, by precisely controlling the reaction conditions through a specific solvent ratio of water to anhydrous ethanol during the hydrothermal reaction, the pH of the solution can be effectively controlled, and by controlling the pH value, the controllability of the synthesis process is improved. A suitable pH environment can suppress the hydrolysis rate of the precursor, avoid the formation of impurity phases, and ensure the simultaneous crystallization of Bi2O2CO3 and Zn5(OH)6(CO3)2 and the stable construction of the heterojunction. At the same time, precise control of pH can adjust the surface charge properties of the two components, reduce the interfacial energy, promote the formation of a tight interfacial bond between Bi2O2CO3 and Zn5(OH)6(CO3)2, enhance the synergistic effect of the heterojunction, and further improve the structural stability and photocatalytic performance of the composite photocatalyst, providing reliable technical support for its large-scale preparation and practical application. Attached Figure Description

[0018] Figure 1 The images show the XRD patterns of the Bi2O2CO3 powder prepared by Comparative Example 1, the Zn5(OH)6(CO3)2 powder prepared by Comparative Example 2, and the heterojunction Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared by Example 3.

[0019] Figure 2 The image shows a scanning electron microscope (SEM) image of the Bi₂O₂CO₃ powder prepared in Comparative Example 1.

[0020] Figure 3 The image shows a scanning electron microscope (SEM) image of the Zn5(OH)6(CO3)2 powder prepared as a control example 2.

[0021] Figure 4 The image shows a scanning electron microscope (SEM) image of the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared in Example 3.

[0022] Figure 5 The ultraviolet absorption spectra of the Bi2O2CO3 powder prepared in Example 1, the Zn5(OH)6(CO3)2 powder prepared in Example 2, and the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared in Example 3, after being irradiated with visible light for 30 minutes, show the degradation of the antibiotic tetracycline hydrochloride.

[0023] Figure 6 The graph shows a comparison of the rates at which the Bi2O2CO3 powder prepared in Comparative Example 1, the Zn5(OH)6(CO3)2 powder prepared in Comparative Example 2, and the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared in Example 3 degrade the antibiotic tetracycline hydrochloride under visible light irradiation.

[0024] Figure 7 The degradation diagrams show the degradation of tetracycline hydrochloride by Bi2O2CO3 / Zn5(OH)6(CO3)2-50 prepared in Example 1, Bi2O2CO3 / Zn5(OH)6(CO3)2-100 prepared in Example 2, Bi2O2CO3 / Zn5(OH)6(CO3)2-200 prepared in Example 3, and Bi2O2CO3 / Zn5(OH)6(CO3)2-300 prepared in Example 4 under visible light irradiation for 100 minutes.

[0025] Figure 8The XRD patterns are of the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalysts prepared in Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 3.

[0026] Figure 9 The image shows a scanning electron microscope (SEM) image of the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared in Comparative Example 3.

[0027] Figure 10 The image shows a scanning electron microscope (SEM) image of the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared in Comparative Example 4.

[0028] Figure 11 The image shows a scanning electron microscope (SEM) image of the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared in Comparative Example 5.

[0029] Figure 12 The UV absorption spectra of the Bi2O2CO3 / Zn5(OH)6(CO3)2 prepared in Comparative Example 3, Bi2O2CO3 / Zn5(OH)6(CO3)2 prepared in Comparative Example 4, Bi2O2CO3 / Zn5(OH)6(CO3)2 prepared in Comparative Example 5, Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared in Example 3, and the original antibiotic tetracycline hydrochloride solution after being irradiated with visible light for 10 minutes to degrade the antibiotic tetracycline hydrochloride. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of the present invention is not limited thereto. All technologies implemented based on the content of the present invention are within the scope of the present invention.

[0031] The raw materials used include bismuth ammonium citrate monohydrate, citric acid, hexadecyltrimethylammonium bromide, zinc acetate, and urea, which are commercially available analytical grade reagents produced by Sinopharm Chemical Reagent Co., Ltd.

[0032] Comparative Example 1: Preparation of Two-Dimensional Flower Cluster-Shaped Bi₂O₂CO₃ Photocatalyst 0.002 mol of bismuth ammonium citrate monohydrate and 0.167 mol of citric acid were weighed and dispersed in a mixed solution of 50 ml deionized water and 10 ml concentrated nitric acid. The solution was sonicated for 30 minutes until completely dissolved. The pH of the mixed solution was adjusted to 9 using a 10 mol / L sodium hydroxide solution, and the mixture was stirred continuously for 30 minutes. The resulting precursor solution was transferred to a 100 ml stainless steel autoclave with a polytetrafluoroethylene liner, sealed, and placed in an oven for hydrothermal reaction at 160 °C for 36 hours. After the reaction, the autoclave was allowed to cool naturally to room temperature. The resulting suspension was centrifuged, and the precipitate was collected. The precipitate was washed three times each with deionized water and anhydrous ethanol to remove residual ions and organic matter. Finally, the washed precipitate was dried in a vacuum drying oven at 45 °C for 12 hours to obtain a two-dimensional flower-like Bi₂O₂CO₃ powder sample.

[0033] like Figure 1 As shown, the positions of all diffraction peaks in the XRD diffraction pattern of the Bi₂O₂CO₃ powder prepared in Comparative Example 1 are consistent with the standard pattern (JCPDS: 41-1488), and no other diffraction peaks appear. This confirms that well-crystallized and phase-pure Bi₂O₂CO₃ was successfully obtained by the described preparation method. The microstructure of the prepared Bi₂O₂CO₃ powder is as follows. Figure 2 As shown, the Bi₂O₂CO₃ powder exhibits a three-dimensional flower-like structure formed by the self-assembly of two-dimensional nanosheets, with numerous pores on the surface. The 2 μm scale bar in the figure confirms that the size of individual assemblies ranges from submicron to several micrometers. This hierarchical nanoflower-like structure endows Bi₂O₂CO₃ with a large specific surface area, providing abundant surface active sites for the subsequent construction of heterojunction photocatalysts.

[0034] Comparative Example 2: Preparation of sheet-like Zn5(OH)6(CO3)2 photocatalyst 0.01 mol of hexadecyltrimethylammonium bromide, 0.01 mol of zinc acetate, and 0.01 mol of urea were dispersed in 40 ml of anhydrous ethanol and 10 ml of deionized water. The stirred mixture was transferred to a polytetrafluoroethylene reactor for high-pressure reaction. After the reaction, the resulting powder was filtered and centrifuged. To remove unreacted raw materials, the sample was washed three times with anhydrous ethanol and deionized water, respectively. The sample was then placed in a vacuum drying oven and dried at 45°C for 24 hours to prepare a sheet-like Zn5(OH)6(CO3)2. Its XRD diffraction pattern is shown below. Figure 1 As shown, the microstructure is as follows Figure 3 As shown, the Zn5(OH)6(CO3)2 has a loose, plate-like structure. Its XRD diffraction pattern is as follows. Figure 1As shown, all diffraction peaks perfectly match the standard basic zinc carbonate Zn5(OH)6(CO3)2 phase (JCPDS No. 19-1458), and the sharp peak shapes indicate that the obtained product has high crystallinity and high purity. The microstructure of the product is shown in the figure. Figure 3 As shown, the material exhibits a typical hierarchical structure: its basic building blocks are ultrathin nanosheets with a thickness of tens of nanometers. These nanosheets, as primary structures, further stack and extend along specific directions through a self-assembly process, ultimately forming two-dimensional sheet-like aggregates with a size of 1-3 micrometers. These sheet-like aggregates are not dense solids, but rather exhibit a loose, open petal-like or cauliflower-like three-dimensional morphology, with numerous voids and channels between the layers. This multi-level, porous structure constructed from two-dimensional nanosheets from bottom to top endows the material with a high specific surface area and abundant mass transport channels, providing sufficient active sites and reaction interfaces for its photocatalytic degradation of tetracycline hydrochloride.

[0035] Example 1: Preparation of Bi2O2CO3 modified Zn5(OH)6(CO3)2 photocatalyst Step 1: Prepare Bi2O2CO3 dispersion: Weigh 50mg of Bi2O2CO3 powder prepared in Example 1, disperse it in 10ml of deionized water, and obtain dispersion A after thorough dispersion.

[0036] Step 2: Prepare Zn5(OH)6(CO3)2 precursor solution: Weigh 3.64g of hexadecyltrimethylammonium bromide, 2.19g of zinc acetate, and 0.61g of urea. Disperse the above raw materials together in a mixed solution of 40ml anhydrous ethanol and 10ml deionized water. Stir well to obtain solution B.

[0037] Step 3: Mix dispersion A with solution B and stir continuously for 4 hours. Then, transfer the resulting mixed suspension to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is complete, filter the resulting product sequentially, centrifuge, and wash alternately with anhydrous ethanol and deionized water to remove unreacted raw materials and soluble impurities. Place the washed product in a vacuum drying oven and dry at 50°C for 24 hours to finally obtain the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst.

[0038] Example 2: Preparation of Bi2O2CO3 modified Zn5(OH)6(CO3)2 photocatalyst Step 1: Prepare Bi2O2CO3 dispersion: Weigh 100mg of Bi2O2CO3 powder prepared in Example 1, disperse it in 10ml of deionized water, and obtain dispersion A after thorough dispersion.

[0039] Step 2: Prepare Zn5(OH)6(CO3)2 precursor solution: Weigh 3.64g of hexadecyltrimethylammonium bromide, 2.19g of zinc acetate, and 0.61g of urea. Disperse the above raw materials together in a mixed solution of 40ml anhydrous ethanol and 10ml deionized water. Stir well to obtain solution B.

[0040] Step 3: Mix dispersion A with solution B and stir continuously for 4 hours. Then, transfer the resulting mixed suspension to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is complete, filter the resulting product sequentially, centrifuge, and wash alternately with anhydrous ethanol and deionized water to remove unreacted raw materials and soluble impurities. Place the washed product in a vacuum drying oven and dry at 50°C for 24 hours to finally obtain the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst.

[0041] Example 3: Preparation of Bi2O2CO3 modified Zn5(OH)6(CO3)2 photocatalyst Step 1: Prepare Bi2O2CO3 dispersion: Weigh 200mg of Bi2O2CO3 powder prepared in Example 1, disperse it in 10ml of deionized water, and obtain dispersion A after thorough dispersion.

[0042] Step 2: Prepare Zn5(OH)6(CO3)2 precursor solution: Weigh 3.64g of hexadecyltrimethylammonium bromide, 2.19g of zinc acetate, and 0.61g of urea. Disperse the above raw materials together in a mixed solution of 40ml anhydrous ethanol and 10ml deionized water. Stir well to obtain solution B.

[0043] Step 3: Mix dispersion A with solution B and stir continuously for 4 hours. Then, transfer the resulting mixed suspension to a high-pressure reactor lined with polytetrafluoroethylene (PTFE) for hydrothermal reaction. After the reaction is complete, the resulting product is sequentially filtered, centrifuged, and washed alternately with anhydrous ethanol and deionized water to remove unreacted raw materials and soluble impurities. The washed product is then placed in a vacuum drying oven and dried at 50°C for 24 hours to finally obtain the Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst. Its XRD diffraction pattern is shown below. Figure 1 As shown, it exhibits diffraction peaks for both Bi₂O₂CO₃ and Zn₅(OH)₆(CO₃)₂. The microstructure is as follows. Figure 4As shown, two-dimensional flower-like Bi₂O₂CO₃ particles are attached to the surface of sheet-like Zn₅(OH)₆(CO₃)₂. The Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst exhibits a multi-level composite structure. The main body is a large sheet-like structure, confirmed to be Zn₅(OH)₆(CO₃)₂, which provides the main substrate support framework. The key feature is that a large number of Bi₂O₂CO₃ microparticles with a size of hundreds of nanometers are tightly attached and uniformly distributed on the surface of the aforementioned sheet-like Zn₅(OH)₆(CO₃)₂. These Bi₂O₂CO₃ particles do not exist in isolation, but are assembled from even smaller nanosheets into flower-like or petal-like aggregates with a high specific surface area. This morphology clearly indicates that under the described preparation method, the two components, Bi₂O₂CO₃ and Zn₅(OH)₆(CO₃)₂, are not simply physically mixed, but form a tight heterojunction structure. This tight interfacial contact provides a channel for the efficient migration and separation of photogenerated carriers between the two phases, which is an important structural basis for the enhanced photocatalytic performance. This microstructure confirms that Bi2O2CO3 / Zn5(OH)6(CO3)2 has been successfully constructed.

[0044] Example 4: Preparation of Bi2O2CO3 modified Zn5(OH)6(CO3)2 photocatalyst Step 1: Prepare Bi2O2CO3 dispersion: Weigh 300mg of Bi2O2CO3 powder prepared in Example 1, disperse it in 10ml of deionized water, and obtain dispersion A after thorough dispersion.

[0045] Step 2: Prepare Zn5(OH)6(CO3)2 precursor solution: Weigh 3.64g of hexadecyltrimethylammonium bromide, 2.19g of zinc acetate, and 0.61g of urea. Disperse the above raw materials together in a mixed solution of 40ml anhydrous ethanol and 10ml deionized water. Stir well to obtain solution B.

[0046] Step 3: Mix dispersion A with solution B and stir continuously for 4 hours. Then, transfer the resulting mixed suspension to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is complete, filter the resulting product sequentially, centrifuge, and wash alternately with anhydrous ethanol and deionized water to remove unreacted raw materials and soluble impurities. Place the washed product in a vacuum drying oven and dry at 50°C for 24 hours to finally obtain the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst.

[0047] Example 5: Degradation of tetracycline hydrochloride by a Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst 10 mg of the Bi₂O₂CO₃ photocatalyst prepared in Example 1, the Zn₅(OH)₆(CO₃)₂ photocatalyst prepared in Example 2, and the Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ heterojunction photocatalyst prepared in Examples 1, 2, 3, and 4, and 50 ml of tetracycline hydrochloride solution (TC concentration of 20 mg / L) were taken respectively. After reacting in a dark room for 30 minutes to reach desorption equilibrium, the mixture was irradiated with a 300W xenon lamp. Samples were taken every 20 minutes, centrifuged, and tested using a Shimadzu UV2550 UV-Vis spectrophotometer to obtain the TC concentration changes at different degradation time points. Finally, the degradation rate was calculated based on the concentration changes. The results were compared with pure Bi₂O₂CO₃ and pure Zn₅(OH)₆(CO₃)₂. Figure 5 , Figure 6 As shown, Figure 5 As shown, the UV-Vis absorption spectrum of the tetracycline hydrochloride aqueous solution system was obtained after 30 minutes of visible light irradiation under the same conditions. The uncatalyzed original TC solution exhibited its characteristic absorption peak at approximately 357 nm. Compared with the TC solutions treated with pure Bi₂O₂CO₃ (Reference Example 1) and pure Zn₅(OH)₆(CO₃)₂ (Reference Example 2), the absorption intensity at the characteristic wavelength of 357 nm decreased, indicating that both solutions possess certain photocatalytic degradation activity. However, the TC solution treated with the Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ heterojunction photocatalyst (Example 3) showed the most significant attenuation of its characteristic absorption peak, and its absorption intensity was the lowest among the three catalytic experiments. This result directly proves that, within the same reaction time, the Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ heterojunction photocatalyst resulted in the most thorough degradation of TC, with a final degradation efficiency higher than any single-component catalyst. Figure 6Further quantitative analysis of the kinetic data of the degradation process was conducted, demonstrating the reaction rate constant obtained by fitting a pseudo-first-order kinetic model. The catalytic rate of pure Bi₂O₂CO₃ was approximately 0.0068 min⁻¹, and that of pure Zn₅(OH)₆(CO₃)₂ was approximately 0.0111 min⁻¹. However, the catalytic rate of the Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ heterojunction photocatalyst was significantly increased, reaching approximately 0.0138 min⁻¹. This data quantitatively indicates that: firstly, among single components, pure Zn₅(OH)₆(CO₃)₂ has a higher intrinsic activity than pure Bi₂O₂CO₃; secondly, the catalytic rate of the Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ heterojunction photocatalyst is not only approximately 1.24 times that of pure Zn₅(OH)₆(CO₃)₂, but also significantly higher than that of pure Bi₂O₂CO₃, proving that it has the fastest reaction rate. Experimental results show that, under the same test conditions, the heterojunction photocatalyst Bi2O2CO3 / Zn5(OH)6(CO3)2 of the present invention exhibits higher performance in visible light degradation of the antibiotic tetracycline hydrochloride.

[0048] The Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalysts prepared in Examples 1, 2, 3, and 4 all exhibited high performance in the visible light degradation of the antibiotic tetracycline hydrochloride, with degradation efficiencies all above 82%. Among them, the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalysts prepared in Examples 3 and 4 achieved a degradation rate of up to 99%.

[0049] Compare with Example 3 Step 1: Prepare Bi2O2CO3 dispersion: Weigh 200mg of Bi2O2CO3 powder prepared in Example 1, disperse it in 10ml of deionized water, and obtain dispersion A after thorough dispersion.

[0050] Step 2: Prepare Zn5(OH)6(CO3)2 precursor solution: Weigh 3.64g of hexadecyltrimethylammonium bromide, 2.19g of zinc acetate, and 0.61g of urea. Disperse the above raw materials together in a mixed solution of 20ml anhydrous ethanol and 10ml deionized water, and stir evenly to obtain solution B.

[0051] Step 3: Mix dispersion A with solution B and stir continuously for 4 hours. Then, transfer the resulting mixed suspension to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is complete, filter the resulting product sequentially, centrifuge, and wash alternately with anhydrous ethanol and deionized water to remove unreacted raw materials and soluble impurities. Place the washed product in a vacuum drying oven and dry at 50°C for 24 hours to finally obtain the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst.

[0052] Its XRD diffraction pattern is as follows Figure 8 As shown, compared with the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 3, the characteristic diffraction peaks of Zn5(OH)6(CO3)2 are very obvious, while the characteristic diffraction peaks of Bi2O2CO3 are relatively weak. The microstructure is as follows. Figure 9 As shown, there are almost no two-dimensional flower-like Bi2O2CO3 particles attached to the surface of the flaky Zn5(OH)6(CO3)2.

[0053] Compare with Example 4 Step 1: Prepare Bi2O2CO3 dispersion: Weigh 200mg of Bi2O2CO3 powder prepared in Example 1 and 2.19g of zinc acetate, disperse them in 10ml of deionized water, and obtain dispersion A after thorough dispersion.

[0054] Step 2: Prepare Zn5(OH)6(CO3)2 precursor solution: Weigh 3.64g of hexadecyltrimethylammonium bromide and 0.61g of urea, and disperse the above raw materials together in a mixed solution of 40ml anhydrous ethanol and 10ml deionized water. Stir well to obtain solution B.

[0055] Step 3: Mix dispersion A with solution B and stir continuously for 4 hours. Then, transfer the resulting mixed suspension to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is complete, filter the resulting product sequentially, centrifuge, and wash alternately with anhydrous ethanol and deionized water to remove unreacted raw materials and soluble impurities. Place the washed product in a vacuum drying oven and dry at 50°C for 24 hours to finally obtain the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst.

[0056] Its XRD diffraction pattern is as follows Figure 8 As shown, compared with the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 3, the characteristic diffraction peaks of Bi2O2CO3 are more obvious, while the characteristic diffraction peaks of Zn5(OH)6(CO3)2 are relatively weak. The microstructure is shown in the figure. Figure 10 As shown, there is almost no flaky Zn5(OH)6(CO3)2.

[0057] Compare with Example 5 Step 1: Prepare Bi2O2CO3 precursor solution: Weigh 0.36g of bismuth ammonium citrate monohydrate and 0.35g of citric acid, and disperse the above raw materials together in a mixed solution of 50ml deionized water and 10ml concentrated nitric acid. Adjust the pH of the mixed solution to 9 using a 10mol / L sodium hydroxide solution. After thorough dispersion, dispersion A is obtained.

[0058] Step 2: Prepare Zn5(OH)6(CO3)2 dispersion: Weigh 200mg of Zn5(OH)6(CO3)2 powder prepared in Example 2, disperse it in 10ml of deionized water, and stir evenly to obtain solution B.

[0059] Step 3: Dispersion A and solution B were mixed and stirred continuously for 4 hours. The resulting mixed suspension was then transferred to a high-pressure reactor lined with polytetrafluoroethylene (PTFE) for hydrothermal reaction at 160°C for 36 hours. After the reaction, the resulting product was sequentially filtered, centrifuged, and washed alternately with anhydrous ethanol and deionized water to remove unreacted raw materials and soluble impurities. The washed product was then placed in a vacuum drying oven and dried at 45°C for 24 hours to finally obtain the Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst.

[0060] Its XRD diffraction pattern is as follows Figure 8 As shown, compared with the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 3, the characteristic diffraction peaks of Bi2O2CO3 are very obvious, while the characteristic diffraction peaks of Zn5(OH)6(CO3)2 are relatively weak. The microstructure is as follows. Figure 11 As shown, there is a very small plate-like structure Zn5(OH)6(CO3)2, which cannot support Bi2O2CO3 particles.

[0061] Comparative Example 6: Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst for the degradation of tetracycline hydrochloride 100 mg of each of the following photocatalysts were taken: Bi2O2CO3 / Zn5(OH)6(CO3)2 prepared in Example 3, Bi2O2CO3 / Zn5(OH)6(CO3)2 prepared in Example 4, Bi2O2CO3 / Zn5(OH)6(CO3)2 prepared in Example 5, and Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst prepared in Example 3. Each photocatalyst was then reacted in a dark room for 30 minutes until desorption equilibrium was reached. Afterward, the mixture was irradiated with a 300W xenon lamp. Samples were taken every 10 minutes, centrifuged, and tested using a Shimadzu UV2550 UV-Vis spectrophotometer to obtain the TC concentration changes at different degradation time points. Finally, the degradation rate was calculated based on the concentration changes.

[0062] A comparison was made between the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 3 and Example 3, such as... Figure 12As shown, the degradation efficiency decreased by 16% after reacting under visible light for 10 minutes. The main reason is that the content of Bi2O2CO3 in the control example 3 decreased, which is consistent with the XRD and SEM results of the control example 3, resulting in the inability to form a Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst.

[0063] A comparison was made between the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 4 and the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 3, such as... Figure 12 As shown, the degradation efficiency decreased by 14% after reacting under visible light for 10 minutes. The main reason is that the content of Zn5(OH)6(CO3)2 in Control Example 4 decreased, which is consistent with the XRD and SEM results of Control Example 4, resulting in the inability to form Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst.

[0064] A comparison was made between the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 5 and the Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst of Example 3, such as... Figure 12 As shown, the degradation efficiency decreased by 67% after 10 minutes of reaction under visible light irradiation. The main reason is that the content of Zn5(OH)6(CO3)2 in control example 5 decreased, which is consistent with the XRD and SEM results of control example 4, resulting in the inability to form Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst.

[0065] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst, characterized in that, Includes the following steps: S1. Preparation of Bi2O2CO3 dispersion: Weigh Bi2O2CO3 powder, disperse it in deionized water, and obtain dispersion A after thorough dispersion; S2. Preparation of Zn5(OH)6(CO3)2 precursor solution: Weigh hexadecyltrimethylammonium bromide, zinc acetate, and urea respectively, and disperse them together in anhydrous ethanol. After stirring evenly, solution B is obtained. S3. Construction of Bi2O2CO3 / Zn5(OH)6(CO3)2 heterojunction photocatalyst by hydrothermal reaction: Dispersion A and solution B were mixed and stirred continuously for 2–48 hours. The resulting mixed suspension was then transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction was completed, the resulting product was filtered, centrifuged, washed alternately with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven to finally obtain the Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst.

2. The method for preparing the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 1, characterized in that, After mixing dispersion A and solution B in S3, the mixture is stirred continuously for 14 hours, and the concentration of Bi2O2CO3 is controlled between 5 g / L and 30 g / L.

3. The method for preparing the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 1, characterized in that, The molar ratio of the three raw materials, hexadecyltrimethylammonium bromide, zinc acetate, and urea, in S2 is 1:1:1, and their concentration in solution B is 0.14 mol / L to 0.20 mol / L.

4. The preparation method of the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 1, characterized in that, In S3, after dispersion A and solution B are mixed, anhydrous ethanol solvent accounts for 80% of the solution volume, and deionized water accounts for 20% of the solution volume.

5. The method for preparing the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 1, characterized in that, In the hydrothermal reaction process of S3, the reaction temperature is carried out in three stages: the first stage is to raise the temperature from 40°C to 140°C for 4 hours; the second stage is to keep the temperature at 140°C for 4 hours; the third stage is to lower the temperature from 140°C to 25°C for 6 hours, and the reaction is terminated after the temperature drop is completed.

6. The method for preparing the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 1, characterized in that, The drying temperature in S3 is 50°C, and the drying time is 24 hours.

7. The method for preparing the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 1, characterized in that, The Bi2O2CO3 powder in S1 is prepared by the following method: S1.1 Weigh out bismuth ammonium citrate monohydrate and citric acid and disperse them in a mixed solution of deionized water and concentrated nitric acid with a volume ratio of 5:

1. Sonicate until completely dissolved. Adjust the pH of the above mixed solution to 9 using sodium hydroxide solution. After stirring, obtain Bi2O2CO3 precursor solution. S1.2 The obtained Bi2O2CO3 precursor solution was transferred to a high-pressure reactor, sealed, and placed at 160℃ for hydrothermal reaction. After the reaction was completed, it was naturally cooled to room temperature. The resulting suspension was centrifuged to separate the precipitate. The precipitate was then washed alternately with deionized water and anhydrous ethanol. Finally, after drying, flower-like layered Bi2O2CO3 powder was obtained.

8. The method for preparing the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 7, characterized in that, The molar ratio of bismuth ammonium citrate monohydrate to citric acid weighed in S1.1 is 1:0.42 ~ 1:8.

35.

9. The two-dimensional sheet-like Bi2O2CO3 / Zn5(OH)6(CO3)2 photocatalyst prepared by the preparation method according to any one of claims 1-8.

10. The application of the two-dimensional sheet-like Bi₂O₂CO₃ / Zn₅(OH)₆(CO₃)₂ photocatalyst according to claim 9, characterized in that, Used for photocatalytic purification of tetracycline hydrochloride, an antibiotic, in wastewater within the visible light frequency domain.

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