CBO / BVO / BMO heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalysts, in particular to a CBO / BVO / BMO heterojunction photocatalyst as well as a preparation method and application thereof. The preparation method of the CBO / BVO / BMO heterojunction photocatalyst comprises the following steps: uniformly mixing a Bi source, a V source and CuBi2O4 with a solvent, and then carrying out hydrothermal reaction to obtain a CuBi2O4 / BiVO4 composite material; and uniformly mixing a Bi source, a Mo source and the CuBi2O4 / BiVO4 composite material with a solvent, and then carrying out solvothermal reaction to obtain the CBO / BVO / BMO heterojunction photocatalyst. Compared with monomer catalysts (CuBi2O4, BiVO4 and Bi2MoO6), the conduction band and valence band of the CBO / BVO / BMO heterojunction photocatalyst are changed, the visible light absorption range is widened, the photon-generated carrier separation efficiency is enhanced, and the photocatalytic degradation effect on tetracycline hydrochloride is good.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, and in particular to a CBO / BVO / BMO heterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] Tetracycline hydrochloride (TC) is a widely used antibiotic. Its residues in the aquatic environment may not only lead to the spread of resistance genes but also have adverse effects on the ecosystem. Photocatalysis, as an advanced oxidation technology, can utilize photogenerated carriers to generate strong oxidizing free radicals such as hydroxyl radicals (·OH) and superoxide radicals (·O2). - Photocatalytic degradation of tetracycline hydrochloride involves the use of photocatalysts to degrade organic pollutants. In the process of photocatalytic degradation of tetracycline hydrochloride, the photocatalyst generates electron-hole pairs by absorbing light energy. These charge carriers can then undergo redox reactions with tetracycline hydrochloride molecules adsorbed on the catalyst surface, thereby achieving its degradation.

[0003] In the research on photocatalytic degradation of tetracycline hydrochloride, developing high-performance photocatalysts is key to improving degradation efficiency. Currently, single metal oxide photocatalysts are widely studied, but they have significant limitations: firstly, single photocatalysts have a narrow visible light absorption range, resulting in low solar energy utilization; secondly, photogenerated electrons and holes recombine readily, leading to low carrier separation efficiency, which in turn limits the improvement of photocatalytic activity. Furthermore, some single photocatalysts exhibit poor chemical stability and recyclability, making it difficult to meet practical application requirements.

[0004] To overcome the shortcomings of single photocatalysts, the construction of heterojunction photocatalysts has become a research hotspot in recent years. By combining two or more semiconductor materials to form a heterojunction, the band structure of the photocatalyst can be optimized, the visible light absorption range can be broadened, and a built-in electric field can be constructed using the energy level differences between semiconductors to promote the separation and migration of photogenerated carriers, thereby significantly improving photocatalytic performance. However, existing heterojunction photocatalysts (such as binary heterojunctions) still suffer from problems such as insufficient carrier separation efficiency, limited generation of active species, and poor adaptability to complex aquatic environments when degrading tetracycline hydrochloride. Their degradation efficiency and stability still have considerable room for improvement.

[0005] Therefore, developing a novel heterojunction photocatalyst with a wide visible light response range, high carrier separation efficiency, excellent degradation activity and stability for the efficient degradation of tetracycline hydrochloride in the aquatic environment is of great practical significance and application value for solving antibiotic pollution problems and protecting the ecological environment. Summary of the Invention

[0006] Based on the above, this invention proposes a CBO / BVO / BMO heterojunction photocatalyst, its preparation method, and its application, providing a new technical solution for the efficient removal of tetracycline hydrochloride from the aquatic environment.

[0007] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing a CBO / BVO / BMO heterojunction photocatalyst, comprising the following steps: Step 1: Mix Bi source, V source and CuBi2O4 with solvent, and then carry out hydrothermal reaction to obtain CuBi2O4 / BiVO4 composite material. Step 2: Mix the Bi source, Mo source, and CuBi2O4 / BiVO4 composite material with a solvent, and then carry out a solvothermal reaction to obtain a CBO / BVO / BMO heterojunction photocatalyst.

[0008] In a preferred embodiment of the present invention, in step 1, the Bi source is Bi(NO3)3·5H2O; the V source is NH4VO3; the molar ratio of the Bi source to the V source is 1:1; and the solvent is a mixture of ethylene glycol and water in a volume ratio of 1:2 to 2:1.

[0009] In step 1, a mixture of ethylene glycol and water with a volume ratio of 1:2 to 2:1 is used as the solvent. This is to utilize the high viscosity of ethylene glycol to slow down the nucleation and growth rate of BiVO4, resulting in monoclinic scheelite phase BiVO4 with uniform particle size and high crystallinity. If the volume ratio of ethylene glycol to water is lower than this ratio, the solvent viscosity is lower, the crystal growth rate is faster, but the particle size uniformity is slightly worse. If the volume ratio of ethylene glycol to water is higher than this ratio, the solvent viscosity is too high, which can easily lead to excessive particle agglomeration.

[0010] In a preferred embodiment of the present invention, in step 1, the temperature of the hydrothermal reaction is 150-180°C and the time is 10-16 hours.

[0011] In step 1, the core purpose of limiting the hydrothermal reaction temperature to 150-180 ℃ and the time to 10-16 h is to ensure that the monoclinic BiVO4 phase fully crystallizes, forms a regular morphology, and possesses excellent photocatalytic activity. Too high a temperature will destroy the crystal structure of the monoclinic phase, causing it to transform into the thermodynamically more stable but non-catalytically active tetragonal or zircon phase. Too low a temperature will prevent the precursor from fully crystallizing, resulting in a product that is predominantly amorphous or semi-crystalline, with numerous lattice defects, high photogenerated carrier recombination rates, and extremely low photocatalytic activity. Too long a reaction time will allow the Oswald ripening process to continue, leading to complete dissolution of small crystals, increased particle size of large crystals, decreased specific surface area, and fewer active sites. Too short a reaction time will only result in the precursor completing preliminary nucleation without entering the crystal growth stage, resulting in a product that is predominantly amorphous precursor with no catalytic activity.

[0012] Step 1, after the hydrothermal reaction is completed, also includes the steps of centrifuging to collect the solid product and drying it.

[0013] In a preferred embodiment of the present invention, the mass percentage of CuBi2O4 in the CuBi2O4 / BiVO4 composite material is 3% to 13%.

[0014] In a preferred embodiment of the present invention, in step 2, the Bi source is Bi(NO3)3·5H2O; the Mo source is Na2MoO4; and the molar ratio of the Bi source to the Mo source is 2:1.

[0015] In a preferred embodiment of the present invention, in step 2, the solvent is a mixture of ethylene glycol and ethanol in a volume ratio of 1:2 to 2:1.

[0016] In step 2, the solvent is limited to a mixture of ethylene glycol and ethanol in a volume ratio of 1:2 to 2:1 for the following reasons: the upper limit of the solvothermal reaction temperature is determined by the boiling point of the solvent, and ethylene glycol has a high boiling point (197°C). o C), ethanol has a low boiling point (78). o (c) A volume ratio of ethylene glycol to ethanol of 1:2 to 2:1 can control the reaction temperature at 150-180°C. o The optimal range for C is needed to balance the crystallinity and morphological uniformity of Bi₂MoO₆. If the ethylene glycol ratio is too high, the solvent polarity and viscosity increase significantly, leading to excessively high precursor solubility, slower ion diffusion, and a tendency to form amorphous products. Conversely, an excessively high ethanol ratio reduces solvent polarity, hindering the effective dissolution of the metal salt precursor and resulting in a large number of undissolved solid particles in the system.

[0017] In a preferred embodiment of the present invention, in step 2, the temperature of the solvothermal reaction is 150-180 °C and the time is 10-16 h.

[0018] In the solvothermal synthesis of Bi₂MoO₆, the solvothermal reaction temperature was selected as 150-180°C. oC. The reaction time is 10-16 hours, aiming to achieve a product with complete crystal structure, uniform morphology, and excellent photocatalytic activity. Too high or too low a temperature, or too long or too short a reaction time, will disrupt the equilibrium of crystal growth and adversely affect the product. Too high a temperature accelerates disordered ion collisions, leading to uncontrolled growth and the formation of coarse-grained, incompletely shaped crystals. Too low a temperature fails to meet the activation energy requirements for crystal phase formation, resulting in amorphous or low-crystallinity products. Too long a reaction time causes dissolution and recrystallization of active crystal faces, reducing the proportion of highly active crystal faces. Too short a reaction time results in incomplete phase transformation, preventing the intermediate from fully converting into the Bi₂MoO₆ crystal phase.

[0019] Step 2, after the solvothermal reaction is completed, also includes washing and drying the obtained product.

[0020] In a preferred embodiment of the present invention, the mass percentage of CuBi2O4 / BiVO4 composite material in the CBO / BVO / BMO heterojunction photocatalyst is 10%~30%.

[0021] This invention does not impose any particular limitation on the source of each raw material, which can be obtained by preparation methods well known to those skilled in the art or through commercial channels.

[0022] The second technical solution of the present invention is a CBO / BVO / BMO heterojunction photocatalyst prepared by the above preparation method.

[0023] The third technical solution of the present invention is the application of the above-mentioned CBO / BVO / BMO heterojunction photocatalyst in the photocatalytic degradation of pollutants, wherein the pollutant is tetracycline hydrochloride.

[0024] Compared with the prior art, the present invention has the following beneficial effects: This invention successfully prepared a CBO / BVO / BMO heterojunction photocatalyst. Experimental results on the photocatalytic degradation of tetracycline hydrochloride (TC) showed that the CBO / BVO / BMO heterojunction photocatalyst exhibited stronger photocatalytic activity than the pure monomer materials (CuBi₂O₄, BiVO₄, and Bi₂MoO₆). Compared with the monomer catalysts (CuBi₂O₄, BiVO₄, and Bi₂MoO₆), the CBO / BVO / BMO heterojunction photocatalyst exhibited changes in both its conduction and valence bands, broadening the visible light absorption range and enhancing the separation efficiency of photogenerated carriers. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the synthesis of CuBi2O4.

[0027] Figure 2 This is a schematic diagram of the synthesis of CuBi2O4 / BiVO4.

[0028] Figure 3 This is a schematic diagram of the synthesis of CuBi2O4 / BiVO4 / Bi2MoO6.

[0029] Figure 4 (a) XRD spectra and (b) FTIR spectra of CBO, BVO, BMO and 20% CBO / BVO / BMO.

[0030] Figure 5 SEM images of (a) CBO, (b) BVO, (c) BMO and (d) 20% CBO / BVO / BMO samples, TEM image of (e) 20% CBO / BVO / BMO sample, HR-TEM image of 20% CBO / BVO / BMO, and TEM elemental mapping image and EDS image of 20% CBO / BVO / BMO.

[0031] Figure 6 The following are XPS full spectrum, Bi 4f fine spectrum, Mo 3d fine spectrum, Cu 2p fine spectrum, V 2p fine spectrum, and O 1s fine spectrum of the 20% CBO / BVO / BMO sample.

[0032] Figure 7 Nitrogen adsorption-desorption isotherms and pore sizes for CBO, BVO, BMO, and CBO / BVO / BMO.

[0033] Figure 8 (a) Photocatalytic degradation efficiency of CBO, BVO, BMO and 20% CBO / BVO / BMO, (c) simulated kinetic curves, (d) photocatalytic efficiency of different proportions of CBO / BVO / BMO, (e) stability test of 20% CBO / BVO / BMO, and (f) effect of 20% CBO / BVO / BMO catalyst dosage on photocatalytic degradation efficiency.

[0034] Figure 9The effects of (a) cations on the degradation of tetracycline hydrochloride, (b) anions on the degradation of tetracycline hydrochloride, and (c) the effects of tetracycline hydrochloride in different water matrixes.

[0035] Figure 10 Transient fluorescence spectra of (a) CBO, BVO, BMO and 20% CBO / BVO / BMO, (b) photocurrent response plots, and (c) electrochemical impedance spectroscopy.

[0036] Figure 11 The images show (a) UV-vis DRS spectra of CBO, BVO, BMO and CBO / BVO / BMO, (b) Tauc plots, (c) Mott-Schottky plots of CBO, (d) BVO and (e) BMO, and (f) schematic diagrams of the band structures of CBO, BVO and BMO.

[0037] Figure 12 (a) Electron paramagnetic resonance spectrum of a free radical trapping experiment; (b) DMPO–·O2 - And (c)DMPO–·OH.

[0038] Figure 13 The diagrams show (a) the Z-type mechanism, (b) the II-type mechanism, and (c) the CBO / BVO / BMO photocatalytic mechanism.

[0039] Figure 14 Band structures calculated for DFT: (a) CBO, (b) BVO and (c) BMO; charge density distribution plots: (d) CBO, (e) BVO and (f) BMO.

[0040] Figure 15 Degradation pathway of tetracycline hydrochloride by 20% CBO / BVO / BMO photocatalyst.

[0041] Figure 16 To evaluate the toxicity of photocatalytic degradation intermediates using the TEST toxicity analysis software, (a) oral LD50 in rats was determined. 50 (b) Oral LD50 of large fleas 50 (c) Developmental toxicity and (d) Mutagenicity. Detailed Implementation

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0045] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0046] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0047] Unless otherwise specified, the "%" in this invention refers to a percentage by mass.

[0048] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1 1.1 Preparation of photocatalysts 1.1.1 Preparation of CuBi2O4 CuBi₂O₄ nanoparticles were synthesized using a liquid-phase precipitation and high-temperature calcination method: First, 0.89 g of Bi(NO₃)₃·5H₂O was dissolved in 1 mL of deionized water containing 10% HNO₃, which facilitated the dissolution of Bi(NO₃)₃·5H₂O. Then, 0.156 g of CuCl₂·2H₂O was dissolved in 30 mL of deionized water in another beaker. The two solutions were then thoroughly mixed, and 0.5 mL of 1M NaOH solution was added dropwise at room temperature, with continuous stirring using a magnetic stirrer for 3 h. Subsequently, the mixture was transferred to a 100 mL autoclave lined with polytetrafluoroethylene and heated in a drying oven at 180 °C for 24 h. After cooling, the resulting precipitate was centrifuged and washed three times with water and ethanol. The product was then dried overnight at 80 °C. After drying, the material was ground into uniformly sized particles and calcined in a muffle furnace at 400 °C for 2 h. After natural cooling to room temperature, CuBi2O4 was obtained and labeled as CBO.

[0051] 1.1.2 Preparation of BiVO4 and CuBi2O4 / BiVO4 BiVO4 was prepared by a solvothermal method: Bi(NO3)3·5H2O and NH4VO3 were dissolved in a mixed solvent (ethylene glycol:water volume ratio 2:1) at a molar ratio of 1:1 (the amount of mixed solvent was sufficient to fully dissolve Bi(NO3)3·5H2O and NH4VO3), and sonicated for 45 min to ensure complete dissolution. The solution was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave and heated in a drying oven at 160 °C for 12 h. Finally, the product was collected by centrifugation, washed several times, and dried at 60 °C for 6 h to obtain BiVO4, labeled as BVO.

[0052] CuBi₂O₄ / BiVO₄ was prepared by a solvothermal method: Bi(NO₃)₃·5H₂O and NH₄VO₃ were dissolved in a mixed solvent (ethylene glycol:water volume ratio 2:1) at a molar ratio of 1:1. Then, different amounts of the above-mentioned CuBi₂O₄ were added (the amount of mixed solvent was sufficient to fully dissolve Bi(NO₃)₃·5H₂O, NH₄VO₃, and CuBi₂O₄). The mixture was ultrasonicated for 45 min to ensure thorough and uniform dispersion. The mixture was then transferred to a 100 mL polytetrafluoroethylene-lined autoclave and heated in a drying oven at 160 °C for 12 h. Finally, the product was collected by centrifugation, washed several times, and dried at 60 °C for 6 h to obtain the CuBi₂O₄ / BiVO₄ composite material, labeled CBO / BVO. The CBO / BVO prepared with different amounts of CuBi2O4 are labeled as 3%CBO / BVO, 5%CBO / BVO, 7%CBO / BVO, 9%CBO / BVO, 11%CBO / BVO and 13%CBO / BVO (where percentage refers to the mass percentage of CuBi2O4 in CBO / BVO).

[0053] 1.1.3 Preparation of Bi2MoO6 and CuBi2O4 / BiVO4 / Bi2MoO6 Bi₂MoO₆ was synthesized via a direct solvothermal method: 1.94 g Bi(NO₃)₃·5H₂O and 0.412 g Na₂MoO₄ were dissolved in 50 mL of a mixed solvent (ethylene glycol to ethanol, volume ratio 1:1) under magnetic stirring. The mixture was stirred until the solution became clear and transparent, and stirring was continued for 1 h. The solution was then transferred to a 100 mL autoclave and maintained at 160 °C for 12 h. Finally, impurities adhering to the material were thoroughly washed away with distilled water and anhydrous ethanol, and the sample was dried in an oven at 70 °C to obtain a pure Bi₂MoO₆ sample, labeled BMO.

[0054] CuBi₂O₄ / BiVO₄ / Bi₂MoO₆ was synthesized via a direct solvothermal method: 1.94 g Bi(NO₃)₃·5H₂O and 0.412 g Na₂MoO₄ were dissolved in 50 mL of a mixed solvent (ethylene glycol to ethanol, volume ratio 1:1) under magnetic stirring. The mixture was stirred until the solution became clear and transparent, and then different amounts of 7% CBO / BVO powder were added and stirring continued for 1 h. The mixture was then transferred to a 100 mL autoclave and maintained at 160 °C for 12 h. Finally, the impurities adhering to the material were thoroughly washed away with distilled water and anhydrous ethanol, and then dried in an oven at 70 °C to obtain a series of CuBi2O4 / BiVO4 / Bi2MoO6 samples with different CBO / BVO contents, labeled as 10%CBO / BVO / BMO, 15%CBO / BVO / BMO, 20%CBO / BVO / BMO, 25%CBO / BVO / BMO and 30%CBO / BVO / BMO (where percentage refers to the mass percentage of 7%CBO / BVO in CBO / BVO / BMO).

[0055] 1.2 Structural and Morphological Analysis The prepared CBO, BVO, BMO, and 20% CBO / BVO / BMO were characterized by X-ray diffraction (XRD). The XRD patterns of all samples are shown below. Figure 4As shown in Figure a, the main diffraction peaks of pure CBO nanoparticles are located at 2θ = 32.6°, 33.7°, 36.7° and 46.8°, which are consistent with the diffraction peak positions of the standard card PDF#47-0096 of CuBi2O4. They belong to the (102), (310), (311), (321) and (411) crystal planes of CBO, respectively, indicating that CBO nanoparticles were successfully prepared. The main diffraction peaks of pure BVO nanoparticles are located at 2θ = 15.1°, 18.9°, 28.9°, 30.5°, 47.3°, 53.0°, 53.4° and 58.5°, which correspond to the crystal planes of BiVO4 as (020), (110), (011), (121), (040), (042), (222), (310) and (321), respectively. The corresponding values ​​and main characteristic peak positions can be found on the BiVO4 standard card PDF#14-0688, indicating that BiVO4 nanoparticles have been successfully prepared. In addition, the main diffraction peaks of pure BMO are located at 28.3°, 32.6°, 46.7°, 55.5°, and 58.4°, which correspond to the Bi2MoO6 PDF#21-0102 standard card, corresponding to the (131), (002), (202), (133), and (262) crystal planes, respectively, indicating that BMO nanoparticles were successfully prepared. In the XRD pattern of the CBO / BVO / BMO heterojunction, diffraction peaks of CBO, BVO, and BMO can be observed simultaneously, indicating that the CBO / BVO / BMO ternary composite photocatalyst was successfully prepared. Furthermore, the diffraction peaks of the CBO / BVO / BMO heterojunction are similar to those of BMO, while only the diffraction peak at 2θ=58.5° can be observed for CBO. This may be because the CBO content is relatively limited and difficult to observe, or because excessive mechanical stirring during the synthesis process damaged the CBO crystal planes. The characteristic peaks of BVO at 2θ = 15.1°, 28.9°, 47.3° and 53.4° disappeared, which may be due to the coverage by BMO nanosheets.

[0056] Fourier transform infrared spectroscopy (FTIR) was used to further examine the functional groups and chemical structures of CBO, BVO, BMO, and CBO / BVO / BMO ternary composite photocatalysts, such as... Figure 4 As shown in b, at 522 cm -1 The weak peak at 712 cm⁻¹ corresponds to the bending vibration of Bi-O; for the BVO sample, the peak at 712 cm⁻¹ corresponds to the bending vibration of Bi-O. -1 The peak position at 728 cm⁻¹ corresponds to the symmetric tensile vibration of VO, indicating the presence of VO bonds; for the BMO sample, the peak position at 728 cm⁻¹ corresponds to the symmetric tensile vibration of VO, indicating the presence of VO bonds; -1 The sharp peak at this point is related to the vibration of equatorial oxygen atoms within the MoO6 octahedron, and is attributed to the asymmetric stretching of Mo-O. However, for the 797 cm⁻¹... -1 and 842 cm -1The peaks appearing at these positions correspond to the asymmetric and symmetric stretching vibrations of the Mo-O vibration at the apex oxygen atom, respectively. Characteristic peaks of the CBO and BMO monomers can be clearly observed in the CBO / BVO / BMO ternary composite sample, with BVO at 712 cm⁻¹. -1 The characteristic peaks at 728 cm⁻¹ and BMO at 728 cm⁻¹ -1 The characteristic peaks at 728 cm⁻¹ interact with each other, causing the ternary composite sample to exhibit this characteristic peak at 728 cm⁻¹. -1 The characteristic peak intensity at that location decreases.

[0057] The surface morphology of the samples, including particle size, shape, distribution, surface roughness, and crystal structure, was analyzed by scanning and transmission electron microscopy. Figure 5 Figure a shows a SEM image of the CBO sample, reflecting the morphology of the spherical CBO nanoparticles. The CBO nanoparticles synthesized via liquid-phase precipitation and high-temperature calcination exhibit a smoother surface than those prepared without calcination, and the size of these particles is mainly concentrated in the 50-100 nm range. Figure 5 As can be seen from b, BVO exhibits an irregularly stacked, sheet-like spherical structure with numerous pores on its surface, which facilitates the adhesion of other nanoparticles. Figure 5 Image c shows a SEM image of the BMO sample, revealing a spindle-shaped structure with numerous small protrusions that roughen the surface, facilitating the formation of heterojunctions with other substances. Figure 5 As shown in Figure d, after the three materials are combined, CBO and BVO are deposited on the BMO surface in the form of small particles. Compared with pure BMO, the surface of the ternary composite sample is rugged due to the decoration of CBO and BVO, which can effectively increase its specific surface area and expose more surface active sites to participate in the photocatalytic reaction.

[0058] The structure of the 20% CBO / BVO / BMO ternary composite sample was further investigated using transmission electron microscopy, such as... Figure 5 As shown in Figure e, the morphology of the ternary composite sample is a combination of sheet-like structures and nanoparticle clusters. Combined with SEM images, it can be seen that BMO is encapsulated within the sheet-like structure, which is a BVO structure, and the nanoparticles are CBO scattered within the gaps of the BVO. TEM images confirm the tight bonding between CBO, BVO, and BMO in the ternary composite sample. Figure 5As shown in Figure f, the lattice fringes of the material are clearly visible in the HR-TEM image. Measuring the spacing of the lattice fringes reveals that the 0.22 nm, 0.29 nm, and 0.31 nm lattice fringes correspond to the (321) plane of CBO, the (310) plane of BVO, and the (262) plane of BMO, respectively. The adjacent crystal planes indicate that heterojunctions are formed at the CBO / BVO and BVO / BMO interfaces. Combined with energy dispersive spectroscopy (EDS), chemical composition information can be obtained simultaneously to understand the elemental composition and distribution of the material, such as... Figure 5 As shown in Figure g, the CBO / BVO / BMO ternary composite sample clearly contains Bi, Mo, V, Cu, and O elements and their respective content ratios (Table 1), which is consistent with the XRD results. These results indicate that the CBO / BVO / BMO heterojunction photocatalyst was successfully prepared, and the tight bonding between CBO / BVO and BVO / BMO is beneficial for the formation of the heterojunction, accelerating electron transfer in photocatalysis.

[0059] Table 1. Content ratio of each element in 20% CBO / BVO / BMO

[0060] The chemical composition and valence states of the elements were analyzed using X-ray photoelectron spectroscopy (XPS). The C 1s peak was derived from an external source and used for calibration. Figure 6 In the image, 'a' represents the full spectrum of CBO, BVO, BMO, and 20% CBO / BVO / BMO, showing the presence of elements such as Bi, Mo, Cu, V, and O in the composite material. This confirms the presence of CBO, BVO, and BMO in the composite material. Figure 6 In b, it can be observed that Bi's 4f 7 / 2 and Bi 4f 5 / 2 The characteristic peak positions of the orbital are approximately between 159 eV and 164 eV, similar to Bi. 3+ Consistent. For the fine spectrum of Mo 3d ( Figure 6 c), Mo 3d in BMO samples 3 / 2 and Mo 3d 5 / 2 The peak positions are at 231.5 and 228.3 eV. From Figure 6 As can be seen from d, the peaks at 949.1 eV and 937.4 eV belong to Cu 2p. 3 / 2 and Cu 2p 1 / 2 Furthermore, the peaks at 942.6 and 928.4 eV attributable to Cu 2p suggest the presence of divalent copper in the heterojunction. The two characteristic peaks at 520.1 and 512.7 eV belong to the 2p of V ions. 3 / 2 and 2p 1 / 2 ( Figure 6 (e). In Figure 6In the O 1s spectrum, the broad asymmetric peak can be divided into three peaks with binding energies around 529, 528, and 526 eV, respectively. This is attributed to lattice oxygen, surface hydroxyl groups, and absorbed water reduction. By comparing pure CBO, BVO, and BMO semiconductor materials, the binding energies of the major elements in the 20% CBO / BVO / BMO composite sample shift slightly to lower values, resulting in changes in the electron density at the interfaces of the three semiconductors. The electron transfer leads to strong interactions between them, enabling the formation of a CBO / BVO / BMO heterojunction.

[0061] Specific surface area and carrier separation efficiency are core factors for improving the photocatalytic performance of materials. Increasing the specific surface area provides more active sites, thereby enhancing the material's light absorption and utilization efficiency; while efficient carrier separation is key to the effective utilization of photogenerated electrons and holes, directly affecting the rate and effect of the photocatalytic reaction. This study measured the nitrogen adsorption-desorption isotherms of CBO, BVO, BMO, and a 20% CBO / BVO / BMO ternary composite photocatalyst. Figure 7 (a) It can be observed that these catalytic materials all exhibit type IV isotherms and H3 hysteresis loops. This result indicates that all catalysts possess a layered mesoporous structure characterized by capillary condensation, which is consistent with the structural properties of the materials. Figure 7 (b) This layered mesoporous structure not only provides a large specific surface area, increasing the contact area between the material and the reactants, but also effectively promotes the separation and transport of charge carriers, thus playing a key role in photocatalytic reactions and improving their photocatalytic performance.

[0062] Based on the adsorption-desorption isotherms, the specific surface areas (Table 2) of the CBO, BVO, BMO, and 20% CBO / BVO / BMO catalysts were found to be 8.9074 m². 2 / g、2.3272 m 2 / g, 50.413 m 2 / g and 17.442 m 2 / g, with pore volumes of 0.0795 cm³. 3 / g, 0.0127 cm 3 / g, 0.2069 cm 3 / g and 0.1503 cm 3 / g. Analysis results indicate that among individual catalysts, BMO exhibits the highest BET surface area and pore volume, primarily attributed to its spherical structure composed of smaller particles, which provides more active sites and reaction locations. In contrast, CBO and BVO show lower BET surface area and pore volume, likely due to their larger structural frameworks, which limit the increase in specific surface area and pore volume. Figure 7Figure b shows the pore size distribution of the corresponding samples. The large difference in pore size between samples indicates that their morphologies are significantly different, which is consistent with the results of scanning electron microscopy.

[0063] Furthermore, when CBO and BVO form composites with BMO, their BET surface area and pore volume decrease, indicating that the mesopores within BMO may be blocked due to close interactions with other semiconductors. This close interaction not only reduces pore volume but may also affect the specific surface area of ​​the material. However, this close interaction between semiconductors helps promote carrier transfer and separation, thereby improving photocatalytic performance. This suggests that although the specific surface area and pore volume are reduced in CBO / BVO / BMO composites, the interactions between semiconductors play a crucial role in enhancing photocatalytic performance.

[0064] Table 2 Specific surface area and average pore size of CBO, BVO, BMO and CBO / BVO / BMO

[0065] 1.3 Evaluation of photocatalytic performance The photocatalytic performance of monomeric and composite photocatalysts under visible light (400 nm < λ < 780 nm) was evaluated by measuring the degradation of tetracycline hydrochloride. Figure 8 As shown in Figure a, the removal efficiency of tetracycline hydrochloride varies significantly under different photocatalysts. Under dark conditions, pure BMO and the composite 20% CBO / BVO / BMO exhibit highly efficient adsorption performance for tetracycline, mainly due to the large specific surface area of ​​BMO (50.4130 m²). 2 The Cu²⁺ pore size (16.4164 nm) allows it to effectively capture and adsorb tetracycline. In contrast, CBO, BVO, and 7% CBO / BVO show relatively low adsorption capacities for tetracycline. Notably, CBO still exhibits a higher adsorption capacity for tetracycline than BVO and CBO / BVO, which may be due to the Cu²⁺ content. 2+ It forms a stable complex with tetracycline. For example... Figure 8As shown in Figure b, the degradation rates of tetracycline hydrochloride after 120 min of visible light irradiation by pure CBO, BVO, and BMO were 12.28%, 14.32%, and 15.72%, respectively. The relatively low photocatalytic efficiency of these single catalysts can be attributed to the rapid recombination of photogenerated electron-hole pairs. In contrast, the composite material of CBO, BVO, and BMO significantly improved the photocatalytic activity. Experimental screening revealed that the 7 wt% CBO and BVO composite material exhibited the highest degradation efficiency, with a tetracycline hydrochloride degradation rate of 41.06%. To further improve the effective separation of electrons and holes, a heterojunction was constructed by introducing BMO into the CBO / BVO matrix, thereby significantly enhancing the degradation performance. The degradation efficiency of the CBO / BVO and BMO composite materials showed an increasing trend with increasing CBO / BVO mass fraction. The degradation efficiency of the CBO / BVO and BMO composite materials increased with increasing CBO / BVO mass fraction, reaching an optimal degradation efficiency of 81.36% when the CBO / BVO mass fraction was 20%. Figure 8 In the diagram, d represents the values ​​of 10% CBO / BVO / BMO, 15% CBO / BVO / BMO, 20% CBO / BVO / BMO, 25% CBO / BVO / BMO, and 30% CBO / BVO / BMO, respectively. However, once the CBO / BVO mass fraction exceeds this ratio, further increasing its content leads to a decrease in degradation efficiency. This is mainly because excessive CBO / BVO completely blocks the pores of BMO, thereby reducing the effective reaction sites of the photocatalyst.

[0066] The degradation kinetics of tetracycline conform to a pseudo-first-order kinetic model. To compare the photocatalytic activity kinetic data of samples, a pseudo-first-order reaction model can be used: In the formula, k is the first-order kinetic rate constant; C is the instantaneous concentration of tetracycline hydrochloride at illumination time t; and C0 is the initial concentration of tetracycline hydrochloride. Figure 8 The data in Figure c show that the photodegradation rate constants (k) for CBO, BVO, BMO, CBO / BVO, and CBO / BVO / BMO are 0.00163, 0.00169, 0.00166, 0.00361, and 0.00753 min, respectively. -1 To test the stability and reproducibility of the synthesized CBO / BVO / BMO composite photocatalyst, multiple repeated experiments were conducted. Figure 8 The experiment demonstrated the continuous photocatalytic degradation of the CBO / BVO / BMO composite catalyst. After four cycles, the catalyst maintained good degradation activity for tetracycline hydrochloride, indicating that the composite catalyst has good photocatalytic performance and cycling performance. Figure 8The figure shows the effect of different amounts of CBO / BVO / BMO catalyst added on the photocatalytic degradation performance of tetracycline hydrochloride (by adding CBO / BVO / BMO catalyst to 100 mL of 20 mg·L⁻¹). -1 The photocatalytic degradation performance was tested in a tetracycline hydrochloride solution under the following conditions: visible light irradiation and catalyst dosage of 30 mg. The higher the dosage of CBO / BVO / BMO added, the faster the degradation rate. This is attributed to the increased number of active sites in the system due to the addition of photocatalyst. However, this increase is not unlimited. The activity begins to decrease when the photocatalyst dosage exceeds 0.8 g / L. This is because excessive catalyst addition may lead to catalyst aggregation, reducing the exposure of active sites and preventing sufficient contact between organic pollutants and active sites, thus decreasing catalytic activity.

[0067] 1.4 The Influence of Environmental Factors on Photocatalytic Degradation In addition, the effects of inorganic ions in the environment and different water matrix on the degradation of tetracycline hydrochloride were investigated (test conditions: 100 mL of tetracycline hydrochloride at a concentration of 20 mg·L⁻¹). -1 Photocatalytic degradation was carried out in water containing 0.01 mol / L of cations and anions and deionized water as the solvent, with 30 mg of a 20% CBO / BVO / BMO composite catalyst added. The photocatalytic degradation conditions were: a 300 W xenon lamp visible light source at a distance of 15 cm and a temperature of 25°C. o C. The time is 2 hours. (For example...) Figure 9 As shown in a, Na + K + Ca 2+ and Mg 2+ Ions have a significant impact on the uniformity of suppression, with K being the most prominent. + and Mg 2+ Cl - HCO3 - SO4 2- It also affects its degradation. Figure 9 (b) , but the effect of cations is not as great as that of anions on tetracycline hydrochloride. SO4 2- >Cl - >HCO3 - SO4 2- The inhibition effect is obvious, SO4 2- Has the ability to clear h + Due to the properties of ·OH, SO4 2-The addition of [a specific ingredient] severely inhibited the degradation of tetracycline hydrochloride. Four different water sources (distilled water, mineral water, tap water, and Songhua River water) were selected for the photocatalytic degradation of tetracycline hydrochloride. The results showed that, compared with distilled water, tap water and mineral water had a significant inhibitory effect on the photocatalytic degradation of tetracycline hydrochloride. Figure 9 (c) This inhibition may stem from certain specific ions present in mineral water and tap water. These ions can interact with active species generated during photocatalysis, such as holes (h + ) and hydroxyl radicals (·OH) react. When these ions react with h + When combined with ·OH, it consumes some of the active species, thereby reducing their opportunities to interact with tetracycline hydrochloride molecules. Ultimately, this competitive reaction inhibits the activity of the photocatalyst, thus reducing the photocatalytic degradation efficiency of tetracycline hydrochloride.

[0068] 1.5 Optical Absorption and Band Position Analysis In the process of photocatalytic degradation of pollutants, the recombination of electrons and photogenerated holes in semiconductor photocatalysis leads to a reduction in the number of electrons that transition to the CB phase and participate in the degradation reaction, thus weakening the redox capacity of the system. To further investigate the separation and transfer of photogenerated carriers in a 20% CBO / BVO / BMO heterojunction, PL spectroscopy, transient fluorescence, transient photocurrent response, and EIS were performed.

[0069] Figure 10 In Figure 'a', the fluorescence spectra of CBO, BVO, BMO, and 20% CBO / BVO / BMO are shown. All materials exhibit significant photoluminescence intensity in the 500-630 nm range. However, the photoluminescence intensity of the composite material CBO / BVO / BMO is significantly higher. - and h + The recombined CBO, BVO, and BMO layers exhibited significantly lower emission peak intensities than the three pure samples. In the composite material, the tight bonds between the CBO, BVO, and BMO layers allow electrons to shuttle between them, maintaining the activity of both active electrons and holes. This reduces the recombination probability of electron-hole pairs and improves the separation efficiency of photogenerated carriers. This efficient electron-hole dissociation not only enhances the photocatalytic activity of the material but also extends the carrier lifetime, resulting in better performance in photocatalytic reactions.

[0070] The stronger the photocurrent intensity, the higher the separation efficiency of photogenerated carriers, which in turn means stronger photocatalytic activity. Figure 10In this study, the instantaneous photocurrent of three pure samples (CBO, BVO, and BMO) and a composite sample (20% CBO / BVO / BMO) was measured to further investigate the photogenerated charge recombination. Under 300 W xenon lamp irradiation, four light-dark cycle tests showed that the composite photocatalyst could generate a higher photocurrent density in the presence of light than the CBO, BVO, and BMO samples. This indicates that the ternary composite material has better photocurrent response performance, consistent with the results of the previous activity analysis experiments on the degradation of tetracycline hydrochloride. Figure 10 In the diagram, 'c' corresponds to the EIS plot. It can be seen that the radius of the composite sample 20% CBO / BVO / BMO is the smallest compared to the radii of the three pure samples CBO, BVO, and BMO. This indicates that they have lower charge transfer impedance and longer electron lifetime, thus enabling more effective separation of electron-hole pairs (electron-hole pairs). - -h + This confirms the advantages of composite samples in charge separation and transfer.

[0071] UV-vis DRS was performed to characterize the optical properties of CBO, BVO, and BMO, further exploring the reasons for the enhanced photocatalytic activity after recombination. Figure 11 As shown in Figure a, the absorption edges of CBO, BVO, and BMO are 400, 459, and 533 nm, respectively. The absorption edge of CBO / BVO / BMO is 563 nm. Compared with CBO, BVO, and BMO, the absorption of the composite material exhibits a redshift, showing stronger light absorption than the pure monomers. This indicates that the construction of the heterojunction enhances the absorption of visible light by the material, giving it a higher light-harvesting ability. The band gap (Eg) of the semiconductor is calculated by the following formula: in, It is the light absorption coefficient; It is Planck's constant; Where is the photon frequency; A is the proportionality constant; Eg is the semiconductor bandgap energy. All three monomers are indirect semiconductors, therefore n is taken as 2 in this formula. Figure 11 From b, we can calculate that the band gap of CBO is 2.92 eV, the band gap of BVO is 2.49 eV, and the band gap of BMO is 2.52 eV.

[0072] The conduction band (CB) of CBO, BVO, and BMO materials was determined using the Mott-Schottky test. Figure 11 As shown in Figure c, a negative slope in the Mott-Schottky curve indicates a p-type semiconductor, therefore CBO is a p-type semiconductor. BVO and BMO are both n-type semiconductors because their Mott-Schottky curves have positive slopes. To obtain the flat band potential (E) of the material... fb ), use the following formula: in, Here, e represents space capacitance; e represents electron charge. and These are the dielectric constants of semiconductors and vacuum, respectively. For charge density; E and E fb εe and εb represent the electromotive force and the pack potential, respectively; k is the Boltzmann constant; T is the temperature. Compared with Ag / AgCl, the Eo of CBO, BVO, and BMO are... fb The values ​​are 0.6, -0.59, and -0.86 eV, respectively, and 0.8, -0.39, and -0.66 eV relative to NHE (pH=7). Generally, for p-type semiconductors, it is considered that E... VB =E fb +0.1V; for n-type semiconductors, E CB =E fb -0.1V. This means that the CBO's E VB The NHE estimate is 0.9 eV, while the EV values ​​for BVO and BMO are... CB The estimated values ​​are -0.49 eV and -0.76 eV, respectively.

[0073] 1.6 Photocatalytic Mechanism Analysis To investigate the key free radicals involved in the degradation of tetracycline hydrochloride by the 20% CBO / BVO / BMO composite catalyst, a series of free radical capture experiments were conducted, followed by electron paramagnetic resonance (ESR) characterization to identify the active species involved in the photocatalytic degradation process. The study incorporated scavenging agents: TEMPO, EDTA-2Na, isopropanol (IPA), and L-histidine, which were used to capture superoxide radicals (·O2). - ), hole (h + ), hydroxyl radicals (·OH) and singlet oxygen ( 1 O2). For example Figure 12 As shown in Figure a, without the addition of a free radical scavenger, the photocatalytic degradation efficiency of tetracycline (TC) by the composite catalyst reached 81.36%. This high degradation efficiency indicates that, without external interference, the CBO / BVO / BMO composite catalyst can fully utilize photogenerated carriers and effectively promote the degradation reaction of tetracycline hydrochloride. After adding 0.5 mg of L-histidine, the photocatalytic degradation efficiency of TC decreased to 65.21%, indicating that L-histidine captured some active species, thereby reducing their chances of reacting with tetracycline hydrochloride molecules. However, singlet oxygen (… 1 O2 is not a major active species in photocatalysis. DMPO was used as a radical scavenger for ESR of CBO / BVO / BMO to further verify this. -The formation of ·OH. Under conditions without light, DMPO–·O2… - ( Figure 12 (b) and DMPO–·OH ( Figure 12 c) There is no obvious peak; as the duration of illumination increases, the typical 1:1:1:1 O2 ratio increases. - The characteristic peaks and the ·OH characteristic peak in a 1:2:2:1 ratio became increasingly prominent. Therefore, the ESR test results confirmed the presence of ·O2. - ·OH and ·OH play important roles in the photodegradation reaction.

[0074] Based on the results of free radical capture experiments, a possible mechanism for the degradation of tetracycline hydrochloride by the CBO / BVO / BMO composite catalyst under visible light is proposed. According to the band structures of CBO, BVO, and BMO, CBO and BVO combine to form a Z-type heterojunction (…). Figure 13 (a) BVO and BMO combine to form a type II heterojunction ( Figure 13 (b) In the BVO and BMO heterojunction, the conduction band of BVO is lower than that of BMO, forming a built-in electric field that facilitates electron transfer. This electric field promotes the migration of photogenerated electrons from BMO to BVO, while retaining holes in the valence band of BVO, thus effectively separating electrons and holes. A schematic diagram of its degradation of tetracycline hydrochloride is shown in Figure 13c. When visible light irradiates the catalyst surface, photogenerated electrons and holes in BVO separate. Since the band gaps of BVO and BMO are similar, holes from BVO transfer to the valence band (VB) of BMO, while electrons from BMO transfer to the conduction band (CB) of BVO. The type II heterojunction electron transfer suppresses the recombination of photogenerated carriers. Meanwhile, electrons from BVO recombine with holes in CBO, resulting in a larger band gap. This makes the valence band of the catalyst more positive and the conduction band more negative. The photocatalyst after recombination has stronger oxygen activation ability and can also induce the generation of ·OH, rapidly initiating the degradation of tetracycline hydrochloride.

[0075] Models of CBO, BVO, and BMO were constructed and optimized using CASTEP. The band structures of CBO, BVO, and BMO in the Brillouin zone were plotted using the GGA function. The band gap is the distance from the top of the valence band to the bottom of the conduction band; electrons must cross the band gap to be excited. For example... Figure 14As shown in Figure ac, the Fermi levels of CBO, BVO, and BMO are all above their conduction bands, indicating that all three materials are semiconductors. Without external electric field interference, their conduction and valence bands are in a stable, unoccupied state. Different band gaps result in different bandgap values. A larger bandgap makes conduction band excitation more difficult, leading to lower intrinsic carrier concentration and conductivity. Simulations show that the bandgap for CBO is 1.037 eV, lower than the experimental value; the bandgap for BVO is 2.334 eV, close to the experimental value; and the bandgap for BMO is 2.360 eV, slightly lower than the experimental value. A certain deviation exists between theoretical and actual values, which is a common characteristic of DFT calculations.

[0076] Density of states (DOS) is a crucial physical quantity describing the distribution of electronic states in solid materials, reflecting the number of states that electrons can occupy at a specific energy level. As a function of energy, this quantity is closely related to the density of electronic states per unit volume. In solid-state physics, DOS is essential for understanding the electrical properties of materials, especially in defining the macroscopic properties of conductive materials. Accurate calculation of DOS allows for a detailed depiction of how electronic states change with energy, thereby determining the band structure characteristics of semiconductor materials, including the width of band gaps and interband regions. This analysis has significant theoretical and practical implications for revealing the conductivity mechanism, carrier mobility, and electronic transition characteristics of materials. To further explore the electronic structure of materials, projected density of states (PDOS) calculations were performed on all the materials studied. These calculations help determine the electron distribution within the conduction and valence bands, as well as the differences between different semiconductor materials. Figure 14 The results in ef show the density of states distribution of the material, where the density of states near the Fermi level is close to zero, but not absolutely zero. This indicates that most crystalline materials exhibit semiconductor properties, although metallic properties are also significant in some cases. The two non-zero spikes observed on either side of the Fermi level, based on the concept of a pseudogap, reveal a significant bandgap within the material. The existence of this bandgap further confirms the strong covalent bonding of the system, i.e., electrons form highly stable covalent bonds between atoms, thus affecting the material's electrical properties. The results show the densities of states for CBO, BVO, and BMO, indicating that near the Fermi level, the p-orbital electronic density of states contributes the most to the total density of states.

[0077] 1.7 Photocatalytic Degradation Pathway Analysis of Tetracycline Hydrochloride To better investigate the degradation pathway of tetracycline hydrochloride, LC-MS was used to identify the intermediate products after degradation (Table 3), and further validation of the intermediate products was performed using secondary mass spectrometry. Fourteen organic compounds were detected as intermediate products during the degradation of tetracycline hydrochloride, such as... Figure 15 As shown, four possible degradation pathways are proposed based on these intermediate products.

[0078] In pathway I, tetracycline hydrochloride (TC) molecules are fragmented into P1 (m / z=371) through deamination and dehydroxylation reactions, then P2 (m / z=278) is formed through dehydration and deamination reactions. P2 (m / z=278) undergoes ring cleavage to form P3 (m / z=204), and P4 (m / z=149) is formed through further dealkylation. A reduction reaction removes the double bond and hydroxyl group from the ring to give P5 (m / z=133). In pathway II, tetracycline hydrochloride (TC) molecules lose the alkyl group on the nitrogen atom through demethylation, and are subsequently cleaved to produce more smaller molecules that are then mineralized. In pathway III, tetracycline hydrochloride (TC) loses a water molecule through dehydration to form P7 (m / z=398). P7 (m / z=398) then undergoes hydroxylation to form P8 (m / z=310). P8 (m / z=310) can proceed along two pathways: it can undergo hydroxylation to form P9 (m / z=299), followed by ring-opening to form P10 (m / z=265), and finally ring cleavage to form P11 (m / z=167); or it can directly undergo continuous ring-opening reactions from P8 (m / z=310) to form P11 (m / z=167). In pathway IV, an unsaturated bond on the tetracycline hydrochloride ring is attacked by a free radical, resulting in the removal of a hydroxyl group to form P12 (m / z=167). Dealkylation forms P13 (m / z=302), and continuous dehydroxylation, decarbonylation, and ring cleavage yield P14 (m / z=275). These intermediates exhibit different chemical properties and toxicity during degradation, but ultimately mineralize into CO2 and H2O through further degradation reactions.

[0079] Table 3. LC-MS analysis of effective intermediate compounds of tetracycline hydrochloride degraded by CBO / BVO / BMO

[0080] This invention utilizes a toxicity assessment software tool (TEST) to comprehensively evaluate the toxicity of tetracycline (TC) and its 11 degradation intermediates (P1-P14) generated during photocatalytic degradation. Based on the structural formula of the chemical substances, oral LD50 was determined. 50 The median lethal dose (LD50) was used to predict the acute toxicity of TC and P1-P13 in rats (TEST is not applicable to P14). This method is effective in assessing the acute toxic effects of compounds on organisms. The oral LD50 of TC in rats... 50 The concentration was 1510 mg / kg, indicating low acute toxicity. Except for P5 and P6, all intermediates showed higher toxicity than TC (total toxicity). Figure 16(a) This indicates that the toxicity of intermediates increases during photocatalytic degradation, but the toxicity of the final product remains lower than TC. Many intermediates exhibit significantly increased developmental toxicity during degradation. Figure 16 (c). This suggests that although the toxicity of TC decreases during photocatalytic degradation, certain intermediates may have adverse effects on the development of organisms. Figure 16 The mutagenicity of TC was assessed throughout the degradation process, revealing changes in its mutagenic potential. This indicates that photocatalytic degradation not only affects the toxicity of TC but may also alter its mutagenicity. Although the toxicity of most intermediates decreased with photocatalytic degradation, some degree of toxicity remained. This suggests that while photocatalytic degradation is effective, not all intermediate toxicities can be completely eliminated. To mitigate the environmental threat posed by these intermediates, it is recommended to extend the duration of the photocatalytic degradation process. This could further reduce the concentration of intermediates and decrease their potential environmental risks.

[0081] This invention successfully prepared a CBO / BVO / BMO heterojunction photocatalyst by adjusting the input ratio of CBO, BVO, and BMO. Experimental results on the photocatalytic degradation of tetracycline hydrochloride (TC) showed that the CBO / BVO / BMO heterojunction photocatalyst exhibited stronger photocatalytic activity than the individual monomer materials (CBO, BVO, and BMO). The influence of the composite heterojunction on the separation of photogenerated carriers was investigated in depth, and a reasonable photocatalytic reaction mechanism was proposed. The analysis results are as follows: (1) Using CBO, BVO and BMO monomers as the framework, a CBO / BVO / BMO ternary heterojunction was constructed by hydrothermal method. Using tetracycline hydrochloride as the target degradation product, the experimental results showed that the CBO / BVO / BMO composite heterojunction exhibited excellent photocatalytic activity for tetracycline hydrochloride.

[0082] (2) The successful construction of the CBO / BVO / BMO ternary heterojunction was confirmed by characterization methods such as XRD, FT-IR, SEM, TEM, XPS and BET. The separation of photogenerated carriers in the composite heterojunction catalyst was analyzed by UV-vis and PL photoelectrochemical tests. Compared with the single catalyst, the conduction band and valence band of the composite catalyst were changed, which broadened the range of visible light absorption and enhanced the separation efficiency of photogenerated carriers.

[0083] (3) The active species that play a role in the reaction can be identified through free radical capture experiments. This indicates that hydroxyl radicals (·OH) and holes (h) + ) and superoxide radicals (·O2) - It played a certain role in the degradation process, and a reasonable photocatalytic reaction mechanism diagram was drawn.

[0084] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a CBO / BVO / BMO heterojunction photocatalyst, characterized in that, Includes the following steps: Step 1: Mix Bi source, V source and CuBi2O4 with solvent, and then carry out hydrothermal reaction to obtain CuBi2O4 / BiVO4 composite material. Step 2: Mix the Bi source, Mo source, and CuBi2O4 / BiVO4 composite material with a solvent, and then carry out a solvothermal reaction to obtain a CBO / BVO / BMO heterojunction photocatalyst.

2. The preparation method of the CBO / BVO / BMO heterojunction photocatalyst according to claim 1, characterized in that, In step 1, the Bi source is Bi(NO3)3·5H2O; the V source is NH4VO3; the molar ratio of the Bi source to the V source is 1:1; and the solvent is a mixture of ethylene glycol and water in a volume ratio of 1:2 to 2:

1.

3. The method for preparing the CBO / BVO / BMO heterojunction photocatalyst according to claim 1, characterized in that, In step 1, the hydrothermal reaction is carried out at a temperature of 150-180 ℃ for a time of 10-16 h.

4. The method for preparing the CBO / BVO / BMO heterojunction photocatalyst according to claim 1, characterized in that, The mass percentage of CuBi2O4 in the CuBi2O4 / BiVO4 composite material is 3%~13%.

5. The method for preparing the CBO / BVO / BMO heterojunction photocatalyst according to claim 1, characterized in that, In step 2, the Bi source is Bi(NO3)3·5H2O; the Mo source is Na2MoO4; and the molar ratio of the Bi source to the Mo source is 2:

1.

6. The method for preparing the CBO / BVO / BMO heterojunction photocatalyst according to claim 1, characterized in that, In step 2, the solvent is a mixture of ethylene glycol and ethanol in a volume ratio of 1:2 to 2:

1.

7. The method for preparing the CBO / BVO / BMO heterojunction photocatalyst according to claim 1, characterized in that, In step 2, the temperature of the solvothermal reaction is 150-180 °C, and the time is 10-16 h.

8. The method for preparing the CBO / BVO / BMO heterojunction photocatalyst according to claim 1, characterized in that, The mass percentage of CuBi2O4 / BiVO4 composite material in the CBO / BVO / BMO heterojunction photocatalyst is 10%~30%.

9. A CBO / BVO / BMO heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the CBO / BVO / BMO heterojunction photocatalyst as described in claim 9 in the photocatalytic degradation of pollutants, characterized in that, The pollutant is tetracycline hydrochloride.

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