Heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalytic degradation, in particular to a heterojunction photocatalyst as well as a preparation method and application thereof. The preparation method of the heterojunction photocatalyst comprises the following steps: respectively dissolving a Bi source and a V source in water to obtain a Bi source solution and a V source solution; mixing the Bi source solution and the V source solution to form a stable suspension; adding an alkaline solution into the stable suspension until a reaction system is neutral, and then carrying out hydrothermal reaction to obtain Bi2O3 / BiVO4; dispersing a Cd source in water to obtain a Cd source solution; and adding a sulfur source and the Bi2O3 / BiVO4 into the Cd source solution, carrying out ultrasonic treatment, and then carrying out heating reaction to obtain the heterojunction photocatalyst. The heterojunction photocatalyst (Bi2O3 / BiVO4 / CdS) prepared by the method disclosed by the invention shows excellent photocatalytic degradation activity on pollutants such as tetracycline hydrochloride and the like.

Description

Technical Field

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

[0002] Pollutants such as tetracycline hydrochloride, oxytetracycline, metronidazole, and cyproconazole are chemically stable and difficult to degrade. Long-term accumulation can disrupt the ecological balance and even harm human health through the food chain. Therefore, the development of efficient water pollutant degradation technologies is urgently needed. Photocatalytic degradation technology, with its advantages of being green, environmentally friendly, and producing no secondary pollution, has become one of the ideal means of treating organic pollutants. Its core lies in developing high-performance photocatalysts. Among many semiconductor photocatalysts, bismuth vanadate (BiVO4) has attracted much attention due to its unique band structure. Compared to traditional wide-bandgap semiconductors, BiVO4 exhibits excellent visible light response characteristics, effectively improving photon utilization efficiency. It also possesses structural stability and excellent environmental compatibility due to its chemically inert framework, and its surface structure is easily modified and controlled, showing broad application prospects in the field of pollutant degradation.

[0003] However, BiVO4, as a narrow bandgap semiconductor, inherently suffers from a high recombination rate of photogenerated electrons and holes. This problem severely limits its photocatalytic activity, making its degradation efficiency in practical wastewater treatment insufficient to meet requirements. To overcome this deficiency, researchers have attempted to optimize the photocatalytic performance of BiVO4 through various modification methods, such as constructing heterojunctions, elemental doping, and surface modification. Among these, heterostructure construction is an effective strategy to suppress photogenerated carrier recombination and broaden the photoresponse range. By combining BiVO4 with other semiconductor materials, the differences in the band structures of different materials can be utilized to construct charge separation channels, thereby improving the efficiency of the photocatalytic reaction.

[0004] However, existing composite catalysts still have many shortcomings: on the one hand, the charge separation efficiency and redox capacity of binary composite systems are limited, and the degradation efficiency of pollutants needs to be improved; on the other hand, the construction process of ternary composite systems is not yet mature, and some composite materials have problems such as loose interfacial bonding, poor charge transfer pathways, and insufficient stability. Moreover, their catalytic performance is easily affected in complex aquatic environments (such as the presence of anions and cations, and different water quality matrices). At the same time, the broad-spectrum degradation capacity for multiple pollutants and the toxicity control of intermediates during the degradation process still need further optimization.

[0005] Therefore, developing a BiVO4-based heterojunction photocatalyst with strong interfacial bonding, high charge separation efficiency, strong stability, and high efficiency in degrading various organic pollutants in complex environments, while clarifying its degradation mechanism and intermediate toxicity variation patterns, is of great significance for promoting the application of photocatalysis technology in practical water pollution control. Summary of the Invention

[0006] Based on the above, the present invention provides a heterojunction photocatalyst, its preparation method, and its application.

[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 heterojunction photocatalyst, comprising the following steps: Step 1: Dissolve Bi source and V source in water respectively to obtain Bi source solution and V source solution; mix Bi source solution and V source solution to form stable suspension; add alkaline solution to stable suspension until the reaction system is neutral, and then carry out hydrothermal reaction to obtain Bi2O3 / BiVO4; Step 2: Disperse the Cd source in water to obtain a Cd source solution; add a sulfur source and the Bi2O3 / BiVO4 to the Cd source solution, sonicate, and then heat to react to obtain the heterojunction photocatalyst.

[0008] In a preferred embodiment of the present invention, in step 1, the Bi source is Bi(NO3)3·5H2O; and the V source is NH4VO3.

[0009] In a preferred embodiment of the present invention, in step 1, the alkaline solution is 0.1-2 M NH3·H2O.

[0010] The reason why this invention limits the alkaline solution to 0.1-2 M NH3·H2O is as follows: other strong bases such as NaOH are not suitable for this invention. Because NH3·H2O has a mild alkalinity and the rate of pH increase is easily controlled, it can avoid product aggregation or impurity phase formation caused by excessively high local pH.

[0011] 0.1-2 M NH3·H2O is a low-concentration weak base. Compared to concentrated ammonia, its pH rise rate is more gradual, effectively avoiding the formation of impurities or product aggregation caused by local pH abrupt changes. Therefore, the concentration of ammonia used is limited to 0.1-2 M.

[0012] 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 h.

[0013] The reasons for limiting the hydrothermal reaction temperature and time to the above parameters in this invention are as follows: In the hydrothermal preparation of BiVO4, the core purpose of a temperature of 150-180 ℃ and a time of 10-16 h is to ensure that the monoclinic BiVO4 fully crystallizes, forms a regular morphology, and possesses excellent photocatalytic activity. Excessively high temperatures 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. If the temperature is too low, the precursor cannot be completely crystallized, and the product is mainly amorphous or semi-crystalline, with many lattice defects, high photogenerated carrier recombination rate, and extremely low photocatalytic activity. If the time is too long, the Oswald ripening process continues, small grains completely dissolve, large grains increase in size, specific surface area decreases, and active sites decrease. If the time is too short, the precursor only completes the initial nucleus formation and does not enter the crystal growth stage, and the product is mainly amorphous precursor with no catalytic activity.

[0014] Step 1 includes washing the obtained product and drying it after the hydrothermal reaction is completed.

[0015] In a preferred embodiment of the present invention, the mass fraction of Bi2O3 in the Bi2O3 / BiVO4 is 5% to 20%.

[0016] In step 1, the amounts of Bi source and V source are as follows: the amount of V source is fixed, and the amount of Bi source is slightly in excess compared to the "Bi source:V source molar ratio = 1:1"; the excess Bi source generates Bi2O3 under subsequent reaction conditions, and the amount of Bi source can ensure that the mass fraction of Bi2O3 in Bi2O3 / BiVO4 is 5%~20%.

[0017] In a preferred embodiment of the present invention, in step 2, the Cd source is CdCl2·2.5H2O; the sulfur source is thioacetamide; and the molar ratio of the Cd source to the sulfur source is 1:1.

[0018] In a preferred embodiment of the present invention, in step 2, the heating reaction temperature is 80-95 °C and the time is 1.5-3 h.

[0019] The reason why the heating reaction temperature and time are limited to the above parameters in this invention is as follows: Thioacetamide (TAA) itself is not a direct sulfur source, and needs to be hydrolyzed in aqueous solution to generate S. 2- At very low temperatures, TAA hydrolyzes slowly, and S... 2- Low release rate, compared to Cd 2+ The binding rate is slow, the precipitation reaction is incomplete, and the product yield is low. If the temperature is too high, TAA hydrolyzes too quickly, and S... 2- The concentration increases rapidly and readily reacts with Cd. 2+Rapid aggregation results in CdS particles with a wide particle size distribution, irregular morphology, and even amorphous structures. Under conditions of 80-95℃, the TAA hydrolysis rate is moderate, which is conducive to the formation of CdS with uniform particle size and good crystal structure. However, if the time is too short, CdS... 2+ With S 2- Rapid binding forms an amorphous CdS precursor. If the process is too prolonged, Ostwald ripening occurs, leading to a wider CdS particle size distribution and a reduction in its specific surface area and photocatalytic activity.

[0020] In a preferred embodiment of the present invention, the mass percentage of Bi2O3 / BiVO4 in the heterojunction photocatalyst is 5% to 25%.

[0021] In step 2, the ultrasonic treatment time is 1 hour. The purpose of ultrasonic treatment is to ensure that Bi₂O₃ / BiVO₄ is evenly dispersed, so as to facilitate the full binding of CdS to the Bi₂O₃ / BiVO₄ surface during the nucleation process. The liquid volume of the ultrasonic Bi₂O₃ / BiVO₄ is 50-100 mL, and the ultrasonic power is 80-120 W.

[0022] Step 2, after the heating reaction is completed, also includes the steps of centrifuging to collect the product and rinsing and drying the product.

[0023] The second technical solution of the present invention is a heterojunction photocatalyst prepared by the above-mentioned preparation method.

[0024] The third technical solution of the present invention is the application of the above-mentioned heterojunction photocatalyst in the photocatalytic degradation of pollutants, wherein the pollutants are tetracycline hydrochloride, oxytetracycline, metronidazole or cyproconazole.

[0025] Compared with the prior art, the present invention has the following beneficial effects: This invention employs an alkaline etching-assisted in-situ self-assembly strategy to successfully construct a Bi₂O₃ / BiVO₄ heterojunction system. The type II band arrangement induces the formation of a built-in electric field at the interface, driving photogenerated electrons to migrate towards the Bi₂O₃ conduction band, while holes accumulate in the BiVO₄ valence band. Based on this, a ternary composite system is constructed by loading CdS using interfacial charge-directed assembly technology, achieving gradient optimization of the band structure. The heterojunction photocatalyst (Bi₂O₃ / BiVO₄ / CdS) prepared using this method exhibits excellent photocatalytic degradation activity against pollutants such as tetracycline hydrochloride. Attached Figure Description

[0026] 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.

[0027] Figure 1 (a) XRD pattern and (b) FTIR pattern of different catalysts.

[0028] Figure 2 SEM images of (a) 10% Bi2O3 / BiVO4, (b) CdS and (c) 15% Bi2O3 / BiVO4 / CdS samples.

[0029] Figure 3 TEM images of (a) 10% Bi2O3 / BiVO4, (b) CdS, (c) 15% Bi2O3 / BiVO4 / CdS samples, and TEM-EDS mapping and corresponding mapping of Bi, V, O, Cd, and S elements for 15% Bi2O3 / BiVO4 / CdS.

[0030] Figure 4 XPS full spectra of (a) 10% Bi2O3 / BiVO4, CdS, and 15% Bi2O3 / BiVO4 / CdS samples, (b) Bi 4f, (c) V 2p, (d) O 1s, (e) Cd 3d, and (f) S 2p.

[0031] Figure 5 Nitrogen adsorption-desorption isotherms for 10% Bi₂O₃ / BiVO₄, CdS, and 15% Bi₂O₃ / BiVO₄ / CdS.

[0032] Figure 6 (a) and (b) the photocatalytic degradation efficiency of 10% Bi₂O₃ / BiVO₄, (c) the simulated kinetic curve, (d) and (e) the photocatalytic efficiency of 15% Bi₂O₃ / BiVO₄ / CdS, and (f) the simulated kinetic curve. Figure 7 Stability test of 15% Bi2O3 / BiVO4 / CdS.

[0033] Figure 8 (a) The effect of cations on the degradation of tetracycline hydrochloride, (b) The effect of anions on the degradation of tetracycline hydrochloride, and (c) The degradation efficiency of tetracycline hydrochloride in different water matrixes.

[0034] Figure 9 The degradation performance of 15% Bi2O3 / BiVO4 / CdS on different pollutants was evaluated.

[0035] Figure 10 (a) UV-Vis absorption spectrum, (b) Tauc curve, Mott-Schottky curve, (c) 10% Bi₂O₃ / BiVO₄ and (d) 15% Bi₂O₃ / BiVO₄ / CdS.

[0036] Figure 11 (a) transient photocurrent spectrum, (b) electrochemical impedance spectrum, (c) photoluminescence spectrum and (d) time-resolved photoluminescence spectrum of BiVO4, 10%Bi2O3 / BiVO4 and 15%Bi2O3 / BiVO4 / CdS.

[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 diagram shows the photocatalytic reaction mechanism of 15% Bi2O3 / BiVO4 / CdS.

[0039] Figure 14 Degradation pathway of tetracycline hydrochloride by 15% Bi2O3 / BiVO4 / CdS.

[0040] Figure 15 To evaluate the toxicity of photodegradation intermediates using a test, (a) oral LD50 in large fleas was determined. 50 (b) bioaccumulation factors, (c) mutagenicity and (d) developmental toxicity. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0045] 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.

[0046] Unless otherwise specified, the "%" in this invention refers to a percentage by mass.

[0047] 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.

[0048] 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.

[0049] Example 1 1.1 Photocatalyst preparation method 1.1.1 Preparation of BiVO4 and Bi2O3 / BiVO4 The in-situ synthesis of BiVO4 nanoparticles was performed as follows: 4.8507 g of Bi(NO3)3·5H2O and 1.1698 g of NH4VO3 were weighed using an analytical balance. The Bi(NO3)3·5H2O and NH4VO3 were placed in two beakers, and 25 mL of 2 M HNO3 solution (water as the solvent) was added to each beaker. The two solutions were then mixed to form a stable yellow suspension, which was maintained at 160 °C for 12 h to generate BiVO4.

[0050] Bi₂O₃ / BiVO₄ nanoparticles were synthesized in situ using a one-pot method. The specific steps were as follows: Bi(NO₃)₃·5H₂O and NH₄VO₃ were placed in two beakers. 2 M HNO₃ solution (water as the solvent, sufficient to fully dissolve both Bi(NO₃)₃·5H₂O and NH₄VO₃) was added to each beaker, keeping the amount of NH₄VO₃ constant. Bi(NO₃)₃·5H₂O was added at a molar ratio greater than 1:1. The two solutions were then mixed to form a stable yellow suspension. 1 M NH₃·H₂O solution was added dropwise to the yellow suspension, with continuous stirring for 30 min. The pH was adjusted to 7 to allow excess Bi(NO₃)₃·5H₂O to form Bi(OH)₃. The solution was then transferred to a 100 mL autoclave and maintained at 160 °C for 12 h. Finally, the nanoparticles were washed three times with deionized water and ethanol, and then dried overnight in an oven at 70 °C to obtain a series of x%Bi2O3 / BiVO4 nanoparticles (x=5, 10, 15 and 20). The percentage in x%Bi2O3 / BiVO4 refers to the mass percentage of Bi2O3 in Bi2O3 / BiVO4.

[0051] 1.1.2 Preparation of CdS and Bi2O3 / BiVO4 / CdS CdS was successfully synthesized using an aqueous electrostatic self-assembly technique. The specific steps are as follows: 50 mL of deionized water was added to a beaker, and 1 mmol of CdCl2·2.5H2O was ultrasonically dispersed in the 50 mL of deionized water. After complete dissolution, 1 mmol of thioacetamide was added, and the mixture was ultrasonically treated for 1 h. The beaker was then placed in water and heated at 90 °C for 2 h. The product was centrifuged, rinsed, and dried overnight at 70 °C to obtain CdS.

[0052] Bi₂O₃ / BiVO₄ / CdS was successfully synthesized using an aqueous electrostatic self-assembly technique. The specific steps are as follows: 50 mL of deionized water was added to a beaker. 1 mmol of CdCl₂·2.5H₂O was ultrasonically dispersed in the 50 mL of deionized water. After complete dissolution, 1 mmol of thioacetamide and different amounts of 10% Bi₂O₃ / BiVO₄ were added, and the mixture was ultrasonically treated for 1 h. The beaker was then placed in water and heated at 90 °C for 2 h. The product was centrifuged, rinsed, and dried overnight at 70 °C to obtain x%Bi₂O₃ / BiVO₄ / CdS (x = 5, 10, 15, 20, and 25). The percentage in x%Bi₂O₃ / BiVO₄ / CdS refers to the mass percentage of Bi₂O₃ / BiVO₄ in the total Bi₂O₃ / BiVO₄ / CdS.

[0053] 1.2 Structural and Morphological Analysis To investigate the crystal phase structure of the prepared photocatalytic material, X-ray diffraction was performed on the sample. Figure 1 Figure a shows the X-ray diffraction of BiVO4, 10%Bi2O3 / BiVO4, CdS and 15%Bi2O3 / BiVO4 / CdS samples. The main diffraction peaks of the BiVO4 monomer 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. These values ​​are consistent with the positions of the main characteristic peaks of the BiVO4 standard card PDF#14-0688. The diffraction peaks of in-situ grown Bi2O3 / BiVO4 are referenced from the standard card Bi2O3 (PDF#78-1633). The diffraction peaks at 2θ = 45.2°, 53.6°, and 56.2° correspond to the (220), (311), and (222) planes of Bi2O3, respectively. Furthermore, the in-situ formation of Bi2O3 did not change the crystal phase of BiVO4. The diffraction peaks of CdS mainly appear at 24.8°, 26.5°, 28.2°, 36.6°, 43.6°, 47.8°, 50.8°, 51.8°, 52.8°, and 58.3°, corresponding to the (100), (002), (101), (102), (110), (103), (200), (112), (201), and (202) planes, respectively. For the composite sample, diffraction peaks of both BiVO4 and CdS were observed, indicating that the Bi2O3 / BiVO4 / CdS composite material was successfully prepared. Furthermore, Fourier transform infrared spectroscopy (FT-IR) tests were performed on various samples. Figure 1 As shown in Figure b, the BiVO4 material at 742 cm⁻¹ -1 The characteristic peak of strong absorption at this point is attributed to VO4. 3- Antisymmetric stretching vibrations of the VO bond in Bi₂O₃ / BiVO₄ materials at 1364 and 1383 cm⁻¹ -1 Two characteristic peaks not found in BiVO4 appeared at the CdS concentration, corresponding to the vibrations of the O-Bi-O and Bi-O bonds; CdS showed peaks in the 500-4000 cm⁻¹ range. -1 No obvious characteristic peak was observed at 3480 cm⁻¹. -1 A weak peak appears at a certain point, corresponding to the stretching vibration peak of OH, which is related to the water adsorbed on the sample surface. Both VO and Bi-O bonds appear in the composite sample, but the intensity of the CdS binding peak is reduced.

[0054] To more intuitively observe the surface morphology of the synthesized material, the samples were tested using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The test results are as follows: Figure 2 As shown in ac, Figure 2 The scan images of 10% Bi₂O₃ / BiVO₄, CdS, and 15% Bi₂O₃ / BiVO₄ / CdS samples are shown in the image. The Bi₂O₃ / BiVO₄ samples are relatively well-formed, with Bi₂O₃ nanoparticles clearly visible growing on rod-shaped BiVO₄ particles. The CdS monomer, on the other hand, exhibits petal-shaped microspheres, clearly showing that these microspheres are composed of numerous nanosheets. When Bi₂O₃ / BiVO₄ and CdS are combined, their regular shapes are disrupted, leading to a reduction in the specific surface area of ​​the composite material. However, its layered stacked structure still effectively intercepts and reacts with pollutants.

[0055] High-resolution transmission electron microscopy was performed on the 15% Bi2O3 / BiVO4 / CdS sample to further analyze the morphology, structure and lattice fringes of the composite sample. Figure 3 Images ab in the figure represent Bi₂O₃ / BiVO₄ / CdS samples at different resolutions. The results are consistent with SEM results, indicating that Bi₂O₃ / BiVO₄ and CdS materials can be found in the composite sample. Figure 3 As shown in Figure c, the (040) crystal plane of BiVO4, the (220) crystal plane of Bi2O3, and the (0 4 0) crystal plane of CdS can be found in the Bi2O3 / BiVO4 / CdS sample. The spacing of the corresponding lattice fringes is 0.15, 0.25, and 0.17 nm, respectively. These lattice fringes are consistent with the XRD results, further demonstrating the successful preparation of the Bi2O3 / BiVO4 / CdS sample. To further analyze the distribution of each element, EDS mapping tests were performed on the sample. Figure 3 In the middle (d), the presence and uniform distribution of Bi, V, O, Cd and S elements can be seen, which is consistent with the results of SEM and TEM analysis.

[0056] X-ray photoelectron spectroscopy (XPS) is used to analyze the surface elemental composition and chemical state of materials. Figure 4 Figure 'a' shows the full spectrum of the composite samples of 10% Bi₂O₃ / BiVO₄, CdS, and 15% Bi₂O₃ / BiVO₄ / CdS. The 15% Bi₂O₃ / BiVO₄ / CdS composite sample exhibits a Bi 4f peak, a V 2p peak, an O 1s peak, a Cd 3d peak, and a S 2p peak, indicating that Bi, V, and O elements originate from Bi₂O₃ / BiVO₄; Cd and S elements originate from CdS, indicating successful binding of Bi₂O₃ / BiVO₄ and CdS, which is consistent with the mapping results in TEM. To determine the state of each element during the reaction, high-resolution XPS measurements were performed sequentially. Figure 4In the image, b represents the high-resolution XPS of Bi 4f from the 10% Bi₂O₃ / BiVO₄ and 15% Bi₂O₃ / BiVO₄ / CdS samples. The Bi 4f spectrum of the Bi₂O₃ / BiVO₄ / CdS sample shows two distinct peaks, representing Bi 4f. 5 / 2 (163.56 eV) and Bi 4f 7 / 2 (158.26 eV), compared to 10%Bi2O3 / BiVO4, the Bi peak shifts towards lower binding energy. Figure 4 The middle c shows distinct peaks at 523.59 eV and 516.56 eV in the V 2p spectrum, corresponding to V 2p, respectively. 3 / 2 and V 2p 1 / 2 Compared to Bi₂O₃ / BiVO₄, the V peak also shifts towards lower binding energies. The O 1s binding energies of the Bi₂O₃ / BiVO₄ / CdS samples are located at 533.24, 531.80, and 529.70 eV. Figure 4 (middle d). Cd 3d high-resolution spectrum as shown Figure 4 As shown in Figure e, Cd3d in CdS 3 / 2 and Cd 3d 1 / 2 The binding energies initially appear at 412.21 and 405.48 eV, but after recombination, the binding energies shift to 412.09 and 405.48 eV, resulting in a negative displacement of the orbital binding energy. For example... Figure 4 As shown in f, the S 2p of CdS 1 / 2 and S 2p 3 / 2 The binding energies appear at 160.94 and 159.02 eV, while the S 2p binding energies of the composite sample 15%Bi2O3 / BiVO4 / CdS are... 1 / 2 and S 2p 3 / 2 The binding energies shifted to 163.54 and 158.28 eV, respectively. A positive shift in orbital binding energy indicates a decrease in electron density, while a negative shift indicates an increase in electron density. The peak binding energies of the Bi4f, V 2p, and O 1s orbitals in the 15%Bi2O3 / BiVO4 / CdS composite material showed a slight negative shift compared to Bi2O3 / BiVO4, indicating electron migration at the composite heterojunction interface between Bi2O3 / BiVO4. XPS analysis revealed that after the 10%Bi2O3 / BiVO4 material was combined with CdS, a heterojunction interface was formed between the two, and electrons transferred from Bi2O3 / BiVO4 to CdS. Table 1 shows the content of various elements in the 15%Bi2O3 / BiVO4 / CdS sample. The amount of Bi was greater than that of V, indicating that Bi and V did not react in a 1:1 ratio and were completely converted into BiVO4. The excess Bi combined with O to form Bi2O3, proving the successful composite of Bi2O3 / BiVO4 nanoparticles.

[0057] Table 1. Content of different elements in 15% Bi₂O₃ / BiVO₄ / CdS samples

[0058] The surface properties of 10% Bi₂O₃ / BiVO₄, CdS, and 15% Bi₂O₃ / BiVO₄ / CdS samples were investigated using nitrogen adsorption-desorption isotherms. Figure 5 As shown in Table 2, the nitrogen adsorption-desorption isotherms of 10%Bi₂O₃ / BiVO₄, CdS, and 15%Bi₂O₃ / BiVO₄ / CdS are all Type IV isotherms, indicating that the prepared samples are all mesoporous structures. The calculated specific surface areas of 10%Bi₂O₃ / BiVO₄, CdS, and 15%Bi₂O₃ / BiVO₄ / CdS are 6.619, 15.600, and 5.888 m², respectively. 2 ·g -1 The average pore sizes were determined to be 14.567, 36.220, and 4.179 nm. These experimental results indicate that 10% Bi₂O₃ / BiVO₄ and CdS have relatively large specific surface areas and average pore sizes. The composite material exhibits a tighter bond, leading to a decrease in the specific surface area and average pore size of the composite sample. This suggests that the morphology of the composite sample changes, which is consistent with the SEM results.

[0059] Table 2. Specific surface area and average pore size of 10%Bi₂O₃ / BiVO₄, CdS, and 15%Bi₂O₃ / BiVO₄ / CdS

[0060] 1.3 Evaluation of photocatalytic performance Using tetracycline hydrochloride as the target pollutant, a 300 W xenon lamp was used to investigate the photocatalytic degradation of tetracycline hydrochloride in water by synthetic materials under visible light irradiation to evaluate the degradation activity of different catalysts. Figure 6 Figure 8a shows the photocatalytic degradation curves and bar graphs of tetracycline hydrochloride by BiVO4 and Bi2O3 nanoparticles with different contents. The results show that the generation of Bi2O3 improves the degradation activity of the catalyst; among them, 10% Bi2O3 / BiVO4 nanoparticles showed the highest degradation activity, reaching 44.18%, while the degradation rate of pure BiVO4 was only 14.32%. This indicates that Bi2O3 modification improves the degradation efficiency of BiVO4. As the Bi2O3 loading increases, the photocatalytic activity also increases. However, excessive Bi2O3 will reduce the photocatalytic activity, which may be because excessive Bi2O3 tends to agglomerate, which is not conducive to contact with BiVO4 and thus not conducive to the improvement of photocatalytic degradation activity.

[0061] Meanwhile, the fitting of the concentration change and time progression of the pollutant tetracycline hydrochloride during the degradation process follows the following reaction formula:

[0062] In the formula, k is the first-order kinetic rate constant; C is the instantaneous concentration of tetracycline hydrochloride after illumination time t; and C0 is the initial concentration of tetracycline hydrochloride. The kinetic fitting curve shows a good linear relationship, and the rate constant is as follows: Figure 6 As shown in Figure c, the k-value of 10% Bi₂O₃ / BiVO₄ nanoparticles is 0.00181 min⁻¹. -1 The k value is higher than that of other molar ratios, with the k value for 15% Bi₂O₃ / BiVO₄ being 0.00163 min. -1 The k-value for 20% Bi₂O₃ / BiVO₄ is 0.00138 min. -1 The k-value for 5% Bi₂O₃ / BiVO₄ is 0.00123 min. -1 The k-value for BiVO4 is 0.00118 min. -1 Consistent with the results of the photocatalytic degradation experiment, this indicates that Bi2O3 modification of BiVO4 can effectively improve the separation efficiency of photogenerated electrons and holes, and enhance photocatalytic activity.

[0063] However, the photocatalytic activity of Bi2O3 / BiVO4 particles fell far short of expectations. Therefore, a co-precipitation method was used to combine Bi2O3 / BiVO4 / CdS to form a heterojunction. The photocatalytic degradation activity of Bi2O3 / BiVO4 / CdS with different loadings in water was investigated. Figure 6 In the figure, d represents the degradation curves of tetracycline hydrochloride by different catalysts within 2 h. The degradation rate of 15% Bi₂O₃ / BiVO₄ / CdS reached 82.56%, which is 5.76 times that of BiVO₄ and 2.15 times that of CdS (38.37%), demonstrating excellent photocatalytic degradation activity. To further understand the photocatalytic reaction rate of tetracycline hydrochloride, the reaction kinetics of the photocatalytic process were studied using the Langmuir model. Fitting calculations showed that the 15% Bi₂O₃ / BiVO₄ / CdS had the highest rate constant for the degradation of tetracycline hydrochloride. Figure 6 (f), its value is 0.01471 min. -1 .

[0064] To evaluate the stability and reproducibility of the samples, a cyclic experiment was conducted on the degradation of tetracycline hydrochloride using 15% Bi₂O₃ / BiVO₄ / CdS. This involved collecting the used sample after each photocatalytic degradation experiment and then repeating the cycle for the next experiment. Figure 7As shown, after repeating the experiment four times, the 15% Bi2O3 / BiVO4 / CdS sample showed a significant decrease, which is presumably because CdS, as a sulfide, is easily photocorroded, thus leading to a decrease in its stability.

[0065] 1.4 The Influence of Environmental Factors on Photocatalytic Degradation When applying the catalyst to a real wastewater environment, the presence of various cations and anions in the wastewater can affect its activity. Therefore, this invention uses a 300 W xenon lamp as the visible light source and a 420 nm cutoff filter to systematically investigate the effects of different cations, anions, and water quality on the photocatalytic degradation activity of the catalyst. (The catalyst used was 15% Bi₂O₃ / BiVO₄ / CdS; the tetracycline wastewater volume was 100 mL; and the catalyst dosage was 30 mg.) Figure 8 As shown in Figure a, the effects of different cations on the degradation of tetracycline hydrochloride by the catalyst were investigated. Different cations (Na₂O₃, Na ... + K + Ca 2+ All of these have an inhibitory effect on photocatalytic efficiency, among which Ca... 2+ The inhibitory effect on photocatalytic activity is most significant, which may be due to Ca 2+ Having a large amount of charge, Ca 2+ It has a stronger ability to absorb electrons than other cations, and the reduction of electrons leads to ·O2 - The production rate decreased. For example... Figure 8 As shown in Figure b, the degree of inhibition of photocatalysis by anions is SO4. 2- >Cl - >HCO3 - SO4 2- SO4 has the strongest inhibitory effect on photocatalysis. 2- It can capture hydroxyl radicals and react with them to generate ·SO4. 2- , and Cl - It reacts with hydroxyl radicals to generate ·Cl - This further affects the catalytic reaction. To evaluate the influence mechanism of water matrix on the photocatalytic process, this invention selected four typical water environments—distilled water, mineral water, tap water, and Songhua River water—to conduct comparative experiments on tetracycline hydrochloride degradation. The results showed that, compared with the distilled water system with a single ionic composition, mineral water and tap water containing multiple inorganic ions exhibited a significant inhibitory effect on the degradation efficiency of pollutants. Figure 8 (c) This phenomenon is attributed to the competitive consumption between dissolved ions and photocatalytic active components in the water: on the one hand, cations occupy active sites on the catalyst surface through electrostatic adsorption, hindering the contact of pollutant molecules; on the other hand, anions and photogenerated holes (h +The active species undergoes an oxidation reaction and simultaneously exhibits a quenching effect with ·OH. This dual effect leads to a decrease in the effective concentration of the active species, thereby weakening the redox reaction kinetics between the active species and the target pollutant.

[0066] To investigate the degradation performance of the Bi2O3 / BiVO4 / CdS composite material for other organic pollutants, the photocatalytic activity of oxytetracycline, myclobutanil, and metronidazole was also tested (test conditions were as follows: light source: 300 W xenon lamp with a 420 nm cutoff filter; catalyst dosage: 30 mg; pollutant volume: 100 mL; pollutant concentration: 20 mg / L). Figure 9 As shown, under visible light irradiation, the composite photocatalyst achieved a degradation efficiency of 68.99% for oxytetracycline and 80.14% for cyazofamid within 2 hours, with a degradation rate as high as 87.98% for oxytetracycline. The results indicate that the Bi₂O₃ / BiVO₄ / CdS composite material exhibits excellent photocatalytic degradation effects on these three organic pollutants.

[0067] 1.5 Optical Absorption and Band Position Analysis like Figure 10 As shown in Figure a, the light absorption range of 15% Bi₂O₃ / BiVO₄ / CdS is expanded. The band gap value of the prepared sample was quantitatively estimated using the Kubelka-Munk method, based on... Figure 10 As shown in b ( ) 1 / 2 and( The relationship diagram was used to calculate the E values ​​of Bi₂O₃ / BiVO₄ and CdS. g The values ​​were 2.42 and 2.09 eV, respectively. The Mott-Schotty curves show that the slope of the linear portion of the sample is positive, exhibiting characteristics of an n-type semiconductor. The flat-band potentials of Bi₂O₃ / BiVO₄ and CdS were determined by extrapolating the intercept of the linear section from the Mott-Schotty curves (MS curves), and the measured flat-band potentials (E₂O₃ / BiVO₄ and CdS) were calculated. fb The conduction band and valence band values ​​are 0.14 and -1.18 eV, respectively. Based on the flat band potential and the band gap values ​​of the semiconductor photocatalytic materials, the conduction band and valence band positions of Bi2O3 / BiVO4 and CdS can be reasonably inferred. The conduction bands of Bi2O3 / BiVO4 and CdS are 0.04 and -1.28 eV, respectively; the valence bands of CdS are -2.36 and -3.37 eV, respectively.

[0068] To elucidate the photocatalytic activity, transient photocurrent response (it), electrochemical impedance spectroscopy (EIS), photoluminescence (PL), and time-resolved photoluminescence (TRPL) spectra of BiVO4, 10%Bi2O3 / BiVO4, and 15%Bi2O3 / BiVO4 / CdS composites were analyzed. Figure 11 As shown in Figure a, transient photocurrent response tests were performed on different samples. After four switching intermittent cycles, the photocurrent signal of the 15%Bi2O3 / BiVO4 / CdS composite material was the strongest, followed by the 10%Bi2O3 / BiVO4 composite material, and then BiVO4. The formation of heterojunctions in the 15%Bi2O3 / BiVO4 / CdS composite material reduced the recombination of photogenerated carriers, thus resulting in the strongest photocurrent density. Figure 11 Figure b corresponds to the EIS plot. EIS testing can further investigate the charge transfer of BiVO4, 10%Bi2O3 / BiVO4, and 15%Bi2O3 / BiVO4 / CdS. In the low-frequency region, the diagonal lines in the spectrum mainly reflect the diffusion impedance of ions on the electrode, i.e., the Wobbug impedance. Clearly, compared to BiVO4 and 10%Bi2O3 / BiVO4, the 15%Bi2O3 / BiVO4 / CdS composite material exhibits a similar and more compact semi-circular morphology in the mid-to-high frequency region, while showing a gentler slope in the low-frequency region. This indicates that the composite material has lower charge transfer impedance and a longer electron lifetime, thus achieving higher electron-hole pair separation efficiency and exhibiting superior photocatalytic degradation performance.

[0069] Figure 11 Figure c shows the photoluminescence (PL) spectra of different samples in the 420-700 nm range. The emission peak intensity of the composite material is lower than that of the two pure samples, indicating that the electronic interaction between BiVO4 and 10%Bi2O3 / BiVO4 within the heterojunction structure can largely suppress interband electron-hole transitions and reduce their rapid recombination rate. To more intuitively highlight the photoinduced charge carrier separation process, TRPL spectroscopy analysis can be performed. Figure 11 As shown in Figure d, the average fluorescent electronic lifetime (τ) of the 15% Bi₂O₃ / BiVO₄ / CdS composite material is... ave The photogenerated carrier lifetime of 15%Bi2O3 / BiVO4 is 0.1593 ns, which is longer than that of 10%Bi2O3 / BiVO4 (0.1478 ns) and BiVO4 (0.1410 ns). This means that the 15%Bi2O3 / BiVO4 / CdS composite material has a longer photogenerated carrier lifetime. Compared with pure BiVO4, the method of constructing a heterojunction is effective for charge separation.

[0070] 1.6 Analysis of photocatalytic degradation mechanism To verify the mechanism of photocatalytic reaction, such as Figure 12 In this study, TEMPO, L-Histidine, EDTA-2Na, and IPA were selected as free radical scavengers to participate in the degradation reaction, respectively capturing ·O2. - , 1 O2, h + The role of free radicals in the photocatalytic degradation process was investigated using ·OH free radicals. Without any free radical scavenging agent, the catalyst exhibited a degradation efficiency of 82.56% for tetracycline hydrochloride. When TEMPO was introduced into the reaction system, the degradation efficiency decreased to 61.41%, indicating that ·O2... - The photodegradation process was inhibited. The addition of L-Histidine to the reaction system reduced the removal rate of tetracycline hydrochloride to 58.74%, indicating that L-Histidine plays an important role in the degradation reaction system. EDTA-2Na had a more significant inhibitory effect on the photodegradation reaction, reducing the degradation efficiency to 51.33%. Furthermore, in the presence of IPA, the removal rate of tetracycline hydrochloride decreased to 77.33%, meaning that h + It plays a certain role in this system. Besides free radical capture experiments, ESR spectroscopy can be used to further investigate O2. - The role of ·OH in photocatalysis. ESR spectroscopy utilizes DMPO as an electron trap to detect the ·O2 content during the photocatalytic reaction of 15% Bi2O3 / BiVO4 / CdS. - The role played by ·OH. No ·O2 was received in a dark environment. - ( Figure 12 b) and ·OH ( Figure 12 The signal corresponding to c) in the middle. After the light was introduced, a signal intensity of 1:1:1:1 was detected in O2. - Characteristic peaks and ·OH characteristic peaks in a 1:2:2:1 ratio, and the ·O2 characteristic peaks increase with increasing illumination time. - The signals for ·OH are also continuously strengthening, indicating the generation of more oxidizing free radicals that play a significant role in the photocatalytic reaction. The ESR test results are consistent with the free radical capture experiment results, confirming the role of ·O2. - The presence of ·OH free radicals.

[0071] The interfacial transfer mechanism of electrons and holes generated by photoexcitation in a 15% Bi₂O₃ / BiVO₄ / CdS photocatalyst and the possible photocatalytic reaction mechanism were investigated. When visible light irradiates the surface of the composite photocatalyst material, electrons on the surface are excited. Due to the small difference between the conduction band and valence band positions of Bi₂O₃ and BiVO₄ and the tight bonding between the two components, electrons from BiVO₄ flow to Bi₂O₃, while holes on Bi₂O₃ are transferred to BiVO₄ driven by the built-in electric field. Due to the transfer of holes from Bi₂O₃, electrons in the conduction band jump to the nearest CdS valence band for recombination, which can be verified by XPS analysis. After the transfer of electrons and holes, strongly oxidizing holes and strongly reducing electrons appear on the surfaces of BiVO₄ and CdS materials, achieving their spatial distribution and improving the redox capacity of the material.

[0072] In the 15% Bi₂O₃ / BiVO₄ / CdS heterojunction system, the conduction band potential of CdS (CB = -1.08 eV) is sufficiently negative, allowing photogenerated electrons on CdS to react with dissolved oxygen to form ·O₂. - (E(O2 / ·O2) - = -0.33 eV (vs. NHE). Furthermore, the valence band potential of 10% Bi₂O₃ / BiVO₄ (VB = 2.00 eV) is sufficiently positive to degrade OH⁻. - Oxidized to ·OH (E (OH) - The concentration of ·OH (vs. NHE) is 1.99 eV, which is consistent with experimental results on free radical capture. This is due to the presence of ·O2. - ·OH free radicals have high redox activity and can attack tetracycline hydrochloride in solution, causing its molecules to break down.

[0073] 1.7 Pathway Analysis of Photocatalytic Degradation of Tetracycline Hydrochloride Intermediate products during the degradation process were detected using LC-MS to infer their possible degradation pathways. Based on different m / z peaks, 16 intermediate products were detected in the photocatalytic degradation system. Figure 14The mass spectrum of tetracycline hydrochloride (TC) shows a distinct peak at m / z=445. In pathway I, the methyl group on the N-chain is removed to form P1 (m / z=417), which is then deamidated to form P4 (m / z=340). The active radical attacks the carbonyl group and unsaturated double bond on the P4 ring to form P7 (m / z=273), and the hydroxyl group on the ring is removed to form P10 (m / z=240). Then, ring cleavage breaks the large π bond of the benzene ring to form P13 (m / z=196), followed by ring opening to form P15 (m / z=98). P16 (m / z=100) is obtained by the reduction of P15. In pathway II, a ring-opening reaction breaks the double bond to form P2 (m / z=283), which is further cleaved to form P5 (m / z=260). P5 undergoes an elimination reaction to add an unsaturated double bond to form P8 (m / z=240). P11 (m / z=176) is obtained through further ring cleavage, which continues to form P14 (m / z=148). Finally, the active free radical reduces the large π bond on the benzene ring to form P16 (m / z=100). In pathway III, demethylation, deamination, deamidation, and ring cleavage form P3 (m / z=272), followed by double bond opening and ring opening to form P6 (m / z=278). Further ring opening forms P9 (m / z=216), and finally phenol P12 (m / z=94) is formed. Subsequently, the intermediate can be further degraded to produce more small molecules and completely mineralized into CO2 and H2O.

[0074] Table 3. LC-MS analysis of effective intermediate compounds of tetracycline hydrochloride degraded by 15% Bi₂O₃ / BiVO₄ / CdS

[0075]

[0076] The toxicity of tetracycline hydrochloride (TC) and its intermediates was assessed using toxicity assessment software (TEST) and oral LD50 in large fleas. 50 Biological accumulation factors, developmental toxicity, and mutagenicity are used as evaluation criteria. For example... Figure 15 As shown in Figure a, the oral LD50 of TC in large fleas 50 The LD50 of intermediate products such as P3, P5, P6, P9, and P14 is 4.91 mol / L. 50 The value shows a downward trend, while the LD values ​​of other intermediate products... 50 The values ​​are all relatively large, with P10's LD being particularly high. 50 It has the highest potential value and the lowest toxicity. Therefore, it is essential to ensure that the intermediate products are completely degraded during the reaction process; otherwise, it will cause serious harm to large fleas. Figure 15Figure b shows the bioaccumulation factor of intermediate products. The bioaccumulation factor index decreases for most intermediates, with a few exceptions showing an increase. However, even after complete degradation, the index remains lower than the total toxicity (TC), indicating a gradually decreasing bioaccumulation potential and a low risk to the organism. Figure 15 From the perspective of intermediate c, except for TC, P1, P2, and P4 intermediates which have positive mutagenicity values, most intermediate products have mutagenicity values ​​in the negative mutagenicity range. From a developmental toxicity perspective, it is worrying that, except for intermediate P3, most intermediate products show significantly increased developmental toxicity. Figure 15 (d).

[0077] This invention employs an alkaline etching-assisted in-situ self-assembly strategy to successfully construct a Bi₂O₃ / BiVO₄ heterojunction system. The type II band arrangement induces the formation of a built-in electric field at the interface, driving photogenerated electrons to migrate to the Bi₂O₃ conduction band, while holes are enriched in the BiVO₄ valence band. Based on this, a ternary composite system is constructed by loading CdS using interfacial charge-directed assembly technology, achieving gradient optimization of the band structure. The catalytic efficiency of the composite photocatalyst is verified through photocatalytic degradation experiments. The material is discussed in detail using various testing methods, including XRD, FT-IR, XPS, BET, and photo / electrochemical testing. The effects of cations and anions and different water quality environments on the degradation of tetracycline hydrochloride by the composite photocatalyst are investigated using a controlled variable method. Based on the characterization results, the transfer of charge and holes in the composite heterojunction is rationally proposed, and the active free radicals playing an important role in the degradation process are identified. Finally, the intermediate products of tetracycline hydrochloride degradation are analyzed by LC-MS to deduce the degradation process. The analytical results are as follows: (1) SEM, TEM and EDS showed that Bi2O3 / BiVO4 and CdS and the composite material Bi2O3 / BiVO4 / CdS were successfully prepared. Bi2O3 nanoparticles grew on BiVO4 rod-shaped particles, while CdS monomers appeared as petal-shaped microspheres. The specific surface area of ​​the composite sample was reduced.

[0078] (2) Photodegradation experiments were conducted on pollutants such as tetracycline hydrochloride, oxytetracycline, metronidazole, and cyazofamid under visible light irradiation. The degradation rate of tetracycline hydrochloride by 15% Bi2O3 / BiVO4 / CdS was as high as 82.56%, which is 5.76 times that of BiVO4 and 2.15 times that of CdS (38.37%), showing excellent photocatalytic degradation activity.

[0079] (3) According to the test results of EIS, it curve, Mott-Schotty curve, PL and TRPL, the Bi2O3 / BiVO4 / CdS heterojunction photocatalyst has good photogenerated carrier separation efficiency and high charge transfer efficiency. This synergistic effect significantly improves the spatial separation efficiency of electron-hole and enhances the redox potential window through band position matching, ultimately forming a photocatalytic mechanism of "charge separation-directional migration-multiphase reaction" synergistic enhancement.

[0080] 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 heterojunction photocatalyst, characterized in that, Includes the following steps: Step 1: Dissolve Bi source and V source in water respectively to obtain Bi source solution and V source solution; mix Bi source solution and V source solution to form stable suspension; add alkaline solution to stable suspension until the reaction system is neutral, and then carry out hydrothermal reaction to obtain Bi2O3 / BiVO4; Step 2: Disperse the Cd source in water to obtain a Cd source solution; add a sulfur source and the Bi2O3 / BiVO4 to the Cd source solution and sonicate, then heat to react and obtain the heterojunction photocatalyst.

2. The method for preparing the 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.

3. The method for preparing the heterojunction photocatalyst according to claim 1, characterized in that, In step 1, the alkaline solution is 0.1-2M NH3·H2O.

4. The method for preparing the 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.

5. The method for preparing the heterojunction photocatalyst according to claim 1, characterized in that, The mass fraction of Bi2O3 in the Bi2O3 / BiVO4 is 5%~20%.

6. The method for preparing the heterojunction photocatalyst according to claim 1, characterized in that, In step 2, the Cd source is CdCl2·2.5H2O; the sulfur source is thioacetamide; and the molar ratio of the Cd source to the sulfur source is 1:

1.

7. The method for preparing the heterojunction photocatalyst according to claim 1, characterized in that, In step 2, the heating reaction is carried out at a temperature of 80-95 °C for 1.5-3 h.

8. The method for preparing the heterojunction photocatalyst according to claim 1, characterized in that, The mass percentage of Bi2O3 / BiVO4 in the heterojunction photocatalyst is 5%~25%.

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

10. The application of the heterojunction photocatalyst as described in claim 9 in the photocatalytic degradation of pollutants, characterized in that, The contaminants are tetracycline hydrochloride, oxytetracycline, metronidazole, or cyazofamid.

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