A quantum dot modified weak magnetic s-type heterojunction photocatalyst ZnIn2S4 / alpha-Fe2O3, a preparation method and application thereof

Abstract

This invention belongs to the field of antibiotic wastewater treatment technology, specifically relating to a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3, its preparation method, and its application. The preparation method of this quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 is as follows: zinc salt, indium salt, and sulfur source are added to water to prepare a homogeneous solution; then α-Fe2O3 nanoparticles are added, and the mixture is heated at 30-90℃ for 1-6 hours to allow ZnIn2S4 to grow in situ on α-Fe2O3. After washing and drying, the product is obtained. This invention employs a simple solvothermal combined with a mild water bath chemical in-situ growth technique to synthesize a low-cost, easily magnetically recoverable, universally applicable, and highly efficient antibiotic removal weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3.

Description

Technical Field

[0001] This invention belongs to the field of antibiotic wastewater treatment technology, specifically relating to a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3, its preparation method, and its application. Background Technology

[0002] With the rapid development of the world and my country's economy, the pharmaceutical industry has continued to expand, and the production and application of antibiotics have become increasingly widespread. Since the advent of nalidixic acid in 1962, quinolone antibiotics have developed into broad-spectrum, highly effective, and low-toxicity anti-infective chemotherapy drugs. However, the extensive use and even abuse of antibiotics not only easily leads to liver and kidney damage and neurotoxicity in humans, but also increases bacterial resistance, resulting in "superbugs" that endanger human life and health. At the same time, due to their stable chemical structure, antibiotics are difficult to degrade in the natural environment. As a major antibiotic producer, my country's wastewater discharge from related enterprises is enormous, becoming a significant source of water pollution and posing a serious challenge to the ecological environment. Therefore, the development of efficient and economical antibiotic wastewater treatment technologies is urgently needed.

[0003] Antibiotic wastewater is typically characterized by high organic matter concentration and large fluctuations in water quality and quantity, making it one of the most difficult industrial wastewaters to treat. Existing treatment methods mainly include biological methods, electrochemical methods, adsorption methods, and advanced oxidation technologies. Among these, biological methods are relatively inexpensive but have long treatment cycles, and high concentrations of antibiotics can inhibit microbial activity; adsorption or membrane filtration methods only achieve physical enrichment of pollutants, failing to achieve complete degradation and easily causing secondary pollution; electrochemical methods are inefficient and energy-intensive when treating low-concentration wastewater. Photocatalysis technology utilizes sunlight to excite semiconductors to generate photogenerated electron-hole pairs, which then react with dissolved oxygen or water molecules in the water to generate hydroxyl radicals (•OH) and superoxide radicals (•O2). - Reactive oxygen species such as silver phosphate / bismuth sulfide / bismuth oxide can be used to achieve deep mineralization of antibiotic molecules. This technology shows broad application prospects due to its advantages such as low energy consumption, thorough degradation, and environmental friendliness. For example, Liu Zhifeng et al. achieved good results in treating antibiotics using a silver phosphate / bismuth sulfide / bismuth oxide dual Z-type photocatalyst, but the treatment cycle was long, and the recovery of powdered catalysts was difficult in practical industrial applications.

[0004] Current Type-II (staggered) heterojunction catalysts feature an alternating band structure, with the conduction and valence bands of the two semiconductors positioned at different elevations. Upon photoexcitation, electrons migrate from the semiconductor with the higher conduction band to the semiconductor with the lower one, while holes migrate in the opposite direction. However, the redox capability of photogenerated carriers in traditional Type-II heterojunctions is weakened. Z-type heterojunction catalysts mimic natural photosynthesis, achieving electron transport through conductive media (such as noble metals or carbon materials) or direct contact. Currently, the core problem of Z-type heterojunctions—the contradiction between the electron transfer path and the thermodynamically spontaneous process—remains unresolved.

[0005] Based on this, the present invention constructs an S-type heterojunction photocatalyst that is easy to magnetically separate and recover, has high photocatalytic performance, good stability and good degradation universality, and is expected to be widely used in the treatment of industrial antibiotic wastewater. Summary of the Invention

[0006] One objective of this invention is to provide a method for preparing a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3. This preparation method is simple and operates under mild conditions, exhibiting excellent degradation effects on various antibiotics. The catalyst is weakly magnetic and easily recoverable, providing a novel solution for the treatment of industrial antibiotic wastewater and demonstrating significant practical application potential.

[0007] The second objective of this invention is to provide a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3. This invention uses weakly magnetic α-Fe2O3 as a substrate and constructs an S-type heterojunction photocatalyst through in-situ growth of ZnIn2S4 quantum dots. This S-type heterojunction photocatalyst exhibits high activity in degrading antibiotics, good stability, and easy magnetic separation and recovery. It also demonstrates good degradation effects on quinolone antibiotics such as norfloxacin, levofloxacin, and oxytetracycline hydrochloride, exhibiting good degradation versatility.

[0008] The third objective of this invention is to provide an application of a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3.

[0009] To achieve the aforementioned primary objective, the present invention adopts the following technical solution: A method for preparing a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 includes the following steps: Zinc salt, indium salt, and sulfur source were added to water to prepare a homogeneous solution. Then, α-Fe2O3 nanoparticles were added and the mixture was heated at 30~90℃ for 1~6 h to allow ZnIn2S4 to grow in situ on α-Fe2O3. After washing and drying, the S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 was obtained.

[0010] More preferably, the heating reaction is carried out at a temperature of 50-70°C for 3-5 hours.

[0011] Preferably, the molar ratio of the zinc salt, indium salt, sulfur source, and α-Fe2O3 nanoparticles is 1:(1.6~2):(3.9~5.10):(0.5~2), and the ratio of the zinc salt to water is 1 mmol:100 mL.

[0012] More preferably, the molar ratio of the zinc salt, indium salt, sulfur source, and α-Fe2O3 nanoparticles is 1:(1.6~1.62):(5~5.09):(0.5~1).

[0013] Preferably, the zinc salt is any one of zinc chloride, zinc nitrate, zinc acetate, or zinc formate; the indium salt is any one of indium chloride, indium nitrate, indium acetate, or indium formate; and the sulfur source is any one of thioacetamide, thiourea, or sodium sulfide.

[0014] This invention uses weakly magnetic α-Fe2O3 as a substrate and constructs an S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 by in-situ growth of ZnIn2S4 quantum dots onto α-Fe2O3: (1) α-Fe2O3, as a narrow bandgap (~2.1 eV) n-type semiconductor, has the advantages of strong visible light response, high stability, weak magnetism and low cost; ZnIn2S4 is a typical chalcogenide layered compound with good visible light absorption and suitable band position. Constructing an S-type heterojunction by combining α-Fe2O3 and ZnIn2S4 can not only broaden the spectral response range, but also effectively promote the spatial separation of photogenerated carriers, thereby retaining holes and electrons with strong oxidizing and reducing properties to significantly improve photocatalytic degradation activity.

[0015] (2) The present invention strictly controls the order in which ZnIn2S4 is loaded onto α-Fe2O3. The preparation method described in the present invention ensures that ZnIn2S4 quantum dots are grown in situ on α-Fe2O3, thereby constructing an S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 (IS / FO).

[0016] Because ZIS quantum dots are very small and easily aggregate, and their visible light absorption is significantly worse than that of α-Fe2O3, adjusting the loading order, i.e., using a hydrothermal method to uniformly grow α-Fe2O3 on aggregated ZIS nanoparticles, can easily cause a shading effect, affecting the light absorption of ZIS and greatly reducing the number of photogenerated carriers in the FO / IS composite under illumination.

[0017] (3) The present invention controls the molar ratio of zinc salt and α-Fe2O3 nanoparticles so that the molar ratio of zinc salt to α-Fe2O3 is 1:(0.5~2), preferably, the molar ratio of zinc salt to α-Fe2O3 is 1:(0.5~1).

[0018] (4) To address the issues of weakened redox capability of photogenerated carriers in traditional type II heterojunctions and theoretical controversies surrounding the charge transport path in traditional type Z heterojunctions, the ZnIn2S4 / α-Fe2O3 (IS / FO) photocatalyst of this invention is an S-type heterojunction. The S-type heterojunction consists of a reduced photocatalyst (RP) and an oxidized photocatalyst (OP), with a difference in their Fermi levels. Upon contact, electrons spontaneously flow from RP to OP until the Fermi level reaches equilibrium, thereby forming a built-in electric field at the interface pointing from RP to OP, inducing the OP band to bend downwards and the RP band to bend upwards. Under illumination, the built-in electric field, band bending, and Coulomb attraction work together to promote the recombination of electrons with weaker reducing ability in the OP conduction band and holes with weaker oxidizing ability in the RP valence band at the interface, while electrons with stronger reducing ability in the RP conduction band and holes with stronger oxidizing ability in the OP valence band are retained. This unique charge transfer mechanism achieves a dual core advantage: on the one hand, it effectively suppresses bulk recombination of photogenerated carriers through spatial separation; on the other hand, while retaining strong redox capabilities, it avoids the drawback of carrier redox potential decay in type II heterojunctions.

[0019] (5) Controlling the water bath temperature and water bath reaction time in the catalyst preparation process in this invention: The ZIS in the catalyst prepared by this invention is a quantum dot of about 10 nm. Compared with the high temperature hydrothermal method, the ZIS prepared by this invention has a smaller particle size, a shorter water bath reaction time, milder reaction conditions, and a simpler preparation method.

[0020] Preferably, the preparation process of the α-Fe2O3 nanoparticles is as follows: FeCl3·6H2O and NaC2H3O2 are added to a mixture of ethanol and water, subjected to hydrothermal reaction, cooled to room temperature, washed and dried to obtain the nanoparticles.

[0021] Preferably, the molar ratio of FeCl3·6H2O to NaC2H3O2 is (2~3):1, the volume ratio of FeCl3·6H2O to the mixed solution is 1 mmol:15 mL, and the hydrothermal reaction temperature is 90~190℃, and the time is 9~20 h.

[0022] More preferably, the hydrothermal reaction is carried out at a temperature of 90~180℃ for a time of 12~18 h.

[0023] In this invention, weakly magnetic α-Fe₂O₃ is used as the substrate, which is particularly suitable for real-world wastewater treatment scenarios compared to strongly magnetic materials (such as Fe₃O₄). Metal agitators are commonly used in actual wastewater treatment processes, and these agitators themselves have a certain magnetic adsorption capacity. If the catalyst is too magnetic, it is easily adsorbed in large quantities onto the agitator, which will seriously affect the photocatalytic degradation efficiency and make it difficult to meet the requirements of continuous industrial treatment. In contrast, α-Fe₂O₃ has mild magnetic properties and is not easily adsorbed by the agitator. It can be stably suspended and uniformly dispersed in the wastewater system, ensuring sufficient contact between the catalyst and pollutants in the wastewater, thus better meeting the continuous operation requirements of actual wastewater treatment.

[0024] At the same time, it also ensures that the S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 has better recovery convenience in practice.

[0025] To achieve the second objective mentioned above, the present invention adopts the following technical solution: A quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 was prepared using the preparation method described in the first objective.

[0026] To achieve the third objective mentioned above, the present invention adopts the following technical solution: The application of a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst, ZnIn2S4 / α-Fe2O3, for the photocatalytic degradation of antibiotic pollutants in water.

[0027] Preferably, the antibiotic contaminant is tetracycline, norfloxacin, levofloxacin, or oxytetracycline hydrochloride.

[0028] Preferably, the concentration of antibiotic pollutants in the water is 10~90 mg / L, and the addition ratio of the S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 in the water is 0.5~1 g / L.

[0029] Preferably, the light intensity of the photocatalytic degradation is 300~500 mW / cm². 2 The temperature is 25~45℃ and the time is 10~60 min.

[0030] The S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 described in this invention is mixed with antibiotic water and stirred at a speed of 500~1200 rpm in the dark to reach adsorption equilibrium. Then, a photocatalytic reaction is carried out under light to complete the degradation of antibiotics.

[0031] Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention synthesizes a quantum dot-modified S-type heterojunction photocatalyst, ZnIn2S4 / α-Fe2O3, using a solvothermal reaction followed by in-situ chemical growth under mild conditions. Specifically, weakly magnetic α-Fe2O3 nanoparticles prepared by hydrothermal method are added to a solvent along with appropriate amounts of zinc salt, indium salt, and sulfur source, and dispersed uniformly. Under mild conditions, ZnIn2S4 quantum dots are generated in situ, forming a compact S-type heterojunction structure with the α-Fe2O3 catalyst. This method is simple to operate, has mild reaction conditions, and is low in cost. The resulting photocatalyst exhibits good degradation effects on antibiotics, providing a new solution for the treatment of industrial antibiotic wastewater and showing broad application prospects.

[0032] 2. This invention uses weakly magnetic α-Fe2O3 as a substrate and constructs a low-cost, easily magnetically separated and recovered, highly stable, and widely applicable S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 by in-situ growing ZnIn2S4 quantum dots on α-Fe2O3. It is expected to be widely used in the treatment of industrial antibiotic wastewater.

[0033] 3. The quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 synthesized in this invention is particularly sensitive to light and exhibits good stability in the degradation of antibiotics under visible light. Except for a slightly lower degradation rate for norfloxacin, it has good degradation effects on levofloxacin, oxytetracycline hydrochloride, and tetracycline, with degradation rates exceeding 70%.

[0034] 4. The quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 synthesized in this invention has weak magnetic properties, providing a new idea and method for the development of efficient catalyst recycling, and has great practical application prospects in the field of photocatalytic treatment of antibiotic wastewater. Attached Figure Description

[0035] Figure 1 This is a comparison of the degradation activities of quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 on tetracycline prepared by different water bath temperatures, reaction times, and molar ratios of zinc salt to α-Fe2O3 according to the present invention. Figure 2 This is a TEM image of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of the present invention. Figure 3 The image shows the magnetic properties of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of this invention. Figure 4This is a free radical capture activity diagram of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of the present invention for the degradation of tetracycline; wherein Figure 4 Figure a shows the tetracycline degradation rate of the catalyst with or without different free radical scavengers. Figure 4 b shows the photodegradation activity of tetracycline solution with or without different free radical scavengers; Figure 5 The Mott-Schottky curves of ZnIn2S4 and α-Fe2O3 at 500 Hz, 1000 Hz and 1500 Hz are shown, where 5(a) and 5(b) correspond to α-Fe2O3 and ZnIn2S4, respectively. Figure 6 (a) and (b) are the UV-Vis diffuse reflectance absorption diagrams and Tauc curves of the quantum dot-modified S-type heterojunction photocatalysts ZnIn2S4 / α-Fe2O3, α-Fe2O3 and ZnIn2S4 obtained in Example 4 of the present invention, respectively. Figure 7 XPS spectra of quantum dot-modified S-type heterojunction photocatalysts ZnIn2S4 / α-Fe2O3, α-Fe2O3 and ZnIn2S4 obtained in Example 4 of the present invention; Figure 8 This is a diagram illustrating the photocatalytic mechanism of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of this invention. Figure 9 The catalytic activity and catalytic adaptability results of the S-type heterojunction photocatalyst of this invention are as follows: Figure 9 (a) is a comparison diagram of the degradation activity of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of the present invention and the catalysts of Comparative Examples 1 to 3 on tetracycline. Figure 9 (b) The photodegradation activity of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of the present invention for various antibiotics; Figure 10 The image shows the change in absorbance over time of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of this invention during the degradation of tetracycline. Detailed Implementation

[0036] The technical solution of the present invention will be further explained below with reference to specific embodiments, comparative examples, experimental examples and accompanying drawings.

[0037] Unless otherwise specified, the raw materials and preparation methods used in the following examples, comparative examples, and experimental cases are all conventional materials and techniques in the art.

[0038] Example 1 (1) FeCl3·6H2O and NaC2H3O2 were mixed at a molar ratio of 3:1 and then added to a mixture of ethanol and distilled water (volume ratio of ethanol to distilled water was 6:1). The mixture was stirred until completely dissolved, with the volume ratio of FeCl3·6H2O to the mixture being 1 mmol: 15 mL. The resulting solution was transferred to a polytetrafluoroethylene reactor and placed in an electric heating drying oven at 180 °C for 18 h. After cooling to room temperature, the mixture was washed several times alternately with distilled water and anhydrous ethanol, and then dried in an oven at 60 °C for later use, thus obtaining α-Fe2O3 nanoparticles. The sample was named α-Fe2O3.

[0039] (2) Prepare a homogeneous solution by mixing Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea with deionized water, wherein the molar ratio of Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea is 1:1.62:5.09, and the volume ratio of Zn(NO3)2·6H2O to deionized water is 1 mmol:100 mL. After the solution becomes clear, add α-Fe2O3 prepared in step (1), wherein the molar ratio of Zn(NO3)2·6H2O to α-Fe2O3 is 1:1. Stir to disperse the solution evenly. Then place the resulting solution in a water bath and heat it to 30℃, 50℃, 70℃, and 90℃ respectively, and keep it at the temperature for 3 h. After the reaction is complete, wash the sample and dry it in a 60℃ oven to obtain ZnIn2S4 / α-Fe2O3 (IS / FO).

[0040] Degradation rate test: Photocatalysts obtained at different reaction temperatures were added to 100 mL of water containing 50 mg / L tetracycline. The addition ratio of IS / FO photocatalyst was 0.5 g / L. The mixture was stirred in the dark for 30 min to reach adsorption and desorption equilibrium. The photocatalytic degradation experiment was conducted under irradiation with a 300 W xenon lamp equipped with a 400 nm cutoff filter, with a light intensity of 345 mW / cm². 2 At specific time intervals, 3 mL of the degraded solution was taken, centrifuged thoroughly, and the supernatant was collected. After filtration through a 0.22 μm filter, the absorbance of the solution was measured at the characteristic wavelength of the pollutant using a UV-Vis spectrophotometer. The degradation rate of tetracycline by the S-type heterojunction photocatalyst IS / FO obtained under different conditions was calculated. The results are as follows: Figure 1 As shown in (a).

[0041] Analysis: The degradation rate is highest when the isothermal reaction temperature is 70℃.

[0042] Example 2 Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea were mixed with deionized water to form a homogeneous solution, wherein the molar ratio of Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea was 1:1.62:5.09, and the volume ratio of Zn(NO3)2·6H2O to deionized water was 1 mmol:100 mL. After the solution became clear, α-Fe2O3 prepared according to step (1) of Example 1 was added, with a molar ratio of Zn(NO3)2·6H2O to α-Fe2O3 of 1:1. The mixture was stirred to disperse the solution evenly. The resulting solution was then placed in a water bath and heated to 70°C and reacted at this temperature for 1.5 h, 3 h, 4.5 h, and 6 h, respectively. After the reaction was completed, the sample was washed and dried in a 60°C oven to obtain ZnIn2S4 / α-Fe2O3 (IS / FO).

[0043] Referring to the aforementioned degradation rate test method, the visible light degradation activity of the S-type heterojunction photocatalyst IS / FO obtained at different reaction times was tested, and the results are as follows: Figure 1 As shown in (b).

[0044] Analysis: The degradation rate was highest when the isothermal reaction time was 3 hours.

[0045] Example 3 Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea were mixed with deionized water to prepare a homogeneous solution, wherein the molar ratio of Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea was 1:1.62:5.09, and the volume ratio of Zn(NO3)2·6H2O to deionized water was 1 mmol:100 mL. After the solution became clear, α-Fe2O3 prepared according to step (1) of Example 1 was added, and the mixture was stirred to disperse it evenly. The resulting homogeneous solution was then placed in a water bath and heated to 70°C and reacted at this temperature for 3 h. After the reaction was completed, the sample was washed and dried in an oven at 60°C to obtain ZnIn2S4 / α-Fe2O3 (IS / FO), wherein the molar ratio of Zn(NO3)2·6H2O to α-Fe2O3 was changed to 0.5:1, 1:1, 1.5:1, and 2:1.

[0046] Referring to the aforementioned degradation rate test method, the visible light degradation activity of the S-type heterojunction photocatalyst IS / FO obtained with different molar ratios of ZnIn2S4 and α-Fe2O3 was tested, and the results are as follows: Figure 1 As shown in (c).

[0047] Analysis: The degradation rate is highest when the molar ratio of Zn(NO3)2·6H2O to α-Fe2O3 is 1:1.

[0048] In conclusion, Figure 1 (ac) are comparative graphs showing the visible light degradation activity of the S-type heterojunction photocatalyst IS / FO prepared in this invention on tetracycline under different reaction temperatures, reaction times, and molar ratios of ZnIn2S4 and α-Fe2O3. The results show that key process parameters such as water bath reaction temperature, water bath reaction time, and the molar ratio of ZnIn2S4 to α-Fe2O3 significantly affect the particle size of ZnIn2S4, the ratio of the two components in the heterojunction, and the photogenerated carrier density. Ultimately, this leads to significant differences in the tetracycline degradation performance of the S-type heterojunction photocatalyst IS / FO prepared in this invention.

[0049] Example 4 Example 4 is based on the experimental results of Examples 1-3. The optimal reaction temperature, reaction time, and molar ratio of ZnIn2S4 to α-Fe2O3 were selected, and other parameters were the same as in Example 1. Specifically, the molar ratio of Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea was controlled at 1:1.62:5.09, and the molar ratio of Zn(NO3)2·6H2O to α-Fe2O3 was 1:1. The solution after adding α-Fe2O3 was placed in a water bath and heated to 70°C for 3 hours. After the reaction, the sample was washed and dried in a 60°C oven to obtain the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 (IS / FO).

[0050] Comparative Example 1 The difference between Comparative Example 1 and Example 4 is that step (2) is omitted, that is, pure α-Fe2O3 is prepared.

[0051] Comparative Example 2 The difference between Comparative Example 2 and Example 4 is that step (1) is omitted and α-Fe2O3 is not added in step (2), thus pure ZnIn2S4 is prepared.

[0052] Comparative Example 3 Comparative Example 3 provides an FO / IS catalyst, and the preparation steps are as follows: (1) Prepare a homogeneous solution by mixing Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea with deionized water, wherein the molar ratio of Zn(NO3)2·6H2O, In(NO3)3·4H2O, and thiourea is 1:1.62:5.09, and the volume ratio of Zn(NO3)2·6H2O to deionized water is 1 mmol:100 mL. Then, heat the resulting homogeneous solution in a water bath to 70 °C and maintain the temperature for 3 h. After the reaction is complete, wash the sample and dry it in a 60 °C oven for later use. The sample is named ZnIn2S4.

[0053] (2) FeCl3·6H2O and NaC2H3O2 were added to a mixture of ethanol and distilled water (volume ratio of ethanol to distilled water was 6:1) at a molar ratio of 3:1, and stirred until completely dissolved. The volume ratio of FeCl3·6H2O to the mixture was 1 mmol: 15 mL. ZnIn2S4 prepared according to the above method was then added, with a molar ratio of FeCl3·6H2O to ZnIn2S4 of 2:1. The mixture was stirred for 30 min. The resulting suspension was transferred to a polytetrafluoroethylene reactor and placed in an electric heating drying oven at 180 °C for 18 h. After cooling to room temperature, the mixture was washed several times alternately with distilled water and anhydrous ethanol, and then dried in an oven at 60 °C to obtain FO / IS.

[0054] Experimental Example 1: Structural Characterization 1. The specific surface area, pore size, and pore volume parameters of the pure α-Fe2O3 prepared in Comparative Example 1, the pure ZnIn2S4 (ZIS) prepared in Comparative Example 2, and the ZnIn2S4 / α-Fe2O3 (IS / FO) prepared in Example 4 are shown in Table 1.

[0055] Table 1. Specific surface area, pore size, and pore volume parameters of various catalysts 2. TEM image of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4, as shown. Figure 2 As shown, where Figure 2 (a) is a TEM image of ZnIn2S4 / α-Fe2O3 on a 500 nm scale. Figure 2 (b) is a TEM image of ZnIn2S4 / α-Fe2O3 on a 10 nm scale.

[0056] from Figure 2 The TEM clearly shows the lattice fringes of ZnIn2S4 and α-Fe2O3, and the ZnIn2S4 quantum dots are spherical and densely grown on the α-Fe2O3 cube.

[0057] Experimental Example 2 Figure 3 These are adsorption photographs of α-Fe2O3 (Comparative Example 1) and S-type heterojunction photocatalyst IS / FO (Example 4) by strong magnets, respectively, demonstrating that the catalyst prepared in this invention has weak magnetic properties, which is very beneficial for catalyst recovery in actual industrial antibiotic wastewater treatment.

[0058] Experimental Example 3: Free Radical Scavenging Experiment To investigate the free radical scavenging activity of the S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 in the degradation of tetracycline, ascorbic acid (AA) was used to capture •O2. - Ammonium oxalate (AO) is used to capture h + Isopropanol (IPA) is used to capture •OH. The specific test method is as follows: The S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 was added to 100 mL of water containing 50 mg / L tetracycline. The addition ratio of the S-type heterojunction photocatalyst was 0.5 g / L. Different free radical scavengers were also added, and the mixture was stirred in the dark for 30 min to reach adsorption and desorption equilibrium. The photocatalytic degradation experiment was conducted under irradiation with a 300 W xenon lamp equipped with a 400 nm cutoff filter, with a light intensity of 345 mW / cm². 2 At specific time intervals, 3 mL of the degradation solution was taken, centrifuged thoroughly, and the supernatant was collected. After filtration through a 0.22 μm filter, the absorbance of the solution was measured at the characteristic wavelength of the pollutant using a UV-Vis spectrophotometer. The change in absorbance of the tetracycline solution with irradiation time was recorded. Additionally, the tetracycline degradation activity of the catalyst was statistically analyzed with and without different free radical scavengers, as shown in the graph. Figure 4 As shown, where Figure 4 (a) Graph showing the tetracycline degradation rate of the catalyst with or without different free radical scavengers. Figure 4 (b) Graph showing the photodegradation activity of tetracycline solution with or without different free radical scavengers.

[0059] from Figure 4 It is evident from (a) and 4(b) that the degradation rate with the addition of IPA was 56.40%, with the addition of ascorbic acid (AA) it was 59.79%, and with the addition of AO it was 50.62%. Compared with the absence of free radical scavengers, the degradation rate of tetracycline decreased significantly after the addition of IPA, AA, and AO, indicating that •OH and •O2 are present in the visible light photocatalytic degradation of tetracycline. - h + They all play a role. Their contribution order to the photocatalytic degradation of tetracycline is h. + > • OH> • O2 - .

[0060] Experimental Example 4: Photocatalytic Mechanism To investigate the photocatalytic mechanism of the S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 of this invention, electrochemical tests were performed on α-Fe2O3 (Comparative Example 1) and ZnIn2S4 (Comparative Example 2). The Mott-Schottky curves of α-Fe2O3 and ZnIn2S4 at 500Hz, 1000Hz, and 1500Hz are shown below. Figure 5 As shown, where Figure 5 (a) and (b) correspond to α-Fe₂O₃ (Comparative Example 1) and ZnIn₂S₄ (Comparative Example 2), respectively. The UV-Vis diffuse reflectance absorption spectra of the S-type heterojunction photocatalyst ZnIn₂S₄ / α-Fe₂O₃ (IS / FO) (Example 4), pure α-Fe₂O₃, and pure ZnIn₂S₄ (ZIS) are shown below. Figure 6 As shown, Figure 6 (a) and (b) represent the UV-Vis diffuse reflectance absorption spectra and Tauc curves of each catalyst, respectively. XPS values ​​for the S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 (IS / FO), pure α-Fe2O3, and pure ZnIn2S4 (ZIS) are shown below. Figure 7 As shown, Figure 7 (ae) are high-resolution spectra of Fe 2p, O 1s, Zn 2p, In 3d, and S 2p, respectively.

[0061] according to Figure 5 The Mott-Schottky curves of α-Fe₂O₃ and ZnIn₂S₄ show that the conduction band potentials of the catalysts α-Fe₂O₃ and ZnIn₂S₄ are approximately -0.94 eV (vs. NHE) and -0.83 eV (vs. NHE), respectively. Further analysis using... Figure 6 The band gap E of catalysts α-Fe2O3 and ZnIn2S4 was estimated from the UV-Vis diffuse reflectance absorption diagram. g The values ​​are 1.95 eV and 2.14 eV, respectively. Therefore, it can be determined that... Figure 8 The positions of the conduction band and valence band of α-Fe2O3 and ZnIn2S4 are shown.

[0062] from Figure 7The XPS analysis of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 clearly shows that, compared to pure α-Fe2O3, the Fe 2p and O 1s peaks in the S-type heterojunction photocatalyst IS / FO shift towards higher binding energies, indicating that α-Fe2O3 in the IS / FO catalyst loses electrons. Conversely, compared to pure ZnIn2S4, the Zn 2p, In3d, and S 2p peaks in the IS / FO catalyst shift towards lower binding energies, indicating that ZnIn2S4 in the IS / FO composite gains electrons. This phenomenon indicates spontaneous electron transfer at the heterojunction interface, consistent with the electron migration trend from α-Fe2O3 (lower work function) to ZnIn2S4 (higher work function) under thermodynamic equilibrium. This results in the α-Fe2O3 surface becoming positively charged due to electron loss, and the ZnIn2S4 (ZIS) surface becoming negatively charged due to electron acceptance. This establishes a built-in electric field pointing from α-Fe₂O₃ towards ZIS. When excited by visible light, photogenerated electrons in the conduction band of ZnIn₂S₄ are directionally transferred to α-Fe₂O₃ under the drive of the built-in electric field. Simultaneously, holes in the valence band of α-Fe₂O₃ migrate to ZnIn₂S₄ and recombine at the contact interface. This allows the holes in the valence band of ZnIn₂S₄ and the electrons in the conduction band of α-Fe₂O₃ to retain high oxidation and reduction capabilities, respectively, ultimately forming a spatially separated S-type charge transfer path (see...). Figure 8 ).

[0063] Because the conduction band potential of α-Fe2O3 is higher than that of O2 / •O2 - Since the potential is more negative, electrons in the conduction band of α-Fe₂O₃ can reduce dissolved oxygen captured on the catalyst surface to •O₂. - This allows organic pollutants to be decomposed into non-toxic and harmless small molecules. The valence band potential of ZnIn2S4 (1.31 eV) is lower than that of H2O / •OH (+2.38 eV). Under light irradiation, the holes in the valence band of ZnIn2S4 cannot directly oxidize water to •OH, but they can directly oxidize organic pollutants. Furthermore, the intermediate product hydrogen peroxide in the catalytic system also generates a large amount of •OH during decomposition, thus degrading organic pollutants into small molecules. In summary, the S-type heterojunction in the IS / FO composite provides a faster separation and transfer pathway for photogenerated carriers, effectively promoting the degradation reaction on the photocatalyst surface and enabling more efficient degradation of various antibiotics. Figure 8 The S-type heterojunction catalytic mechanism is shown.

[0064] Experimental Example 5: Photocatalytic Degradation Performance of Antibiotics To evaluate the photodegradation activity and general applicability of the catalysts obtained in Example 4 and Comparative Examples 1-3 of this invention for antibiotics, the following experiments were conducted: The catalysts obtained in Example 4 and Comparative Examples 1-3 were added to antibiotic wastewater with a tetracycline concentration of 50 mg / L. The addition ratio of each catalyst group was 0.5 g / L, and the mixture was stirred at 1000 rpm until homogeneous. The specific experimental method was the same as in Example 3, except that a free radical scavenger was not added. The tetracycline degradation activity results of the catalysts of Example 4, Comparative Examples 1, 2, and 3 after irradiation with visible light for 60 min are as follows. Figure 9 As shown in (a).

[0065] Depend on Figure 9 It is known that the degradation rate of tetracycline in the blank sample was 0 when only light was applied without a catalyst, indicating that tetracycline is stable and not easily photodegraded. Compared with single pure catalysts (ZIS and α-Fe2O3), the S-type heterojunction catalysts IS / FO and FO / IS showed better tetracycline degradation effects, indicating that the S-type heterojunction structure plays a significant role in the photocatalytic process. However, the photocatalytic activity of IS / FO was significantly better than that of FO / IS, indicating that the catalyst preparation process has a significant impact on the activity of the S-type heterojunction catalyst. It is speculated that this may be because ZIS quantum dots are very small and easily aggregate, and their visible light absorption capacity is significantly worse than that of α-Fe2O3. Therefore, the hydrothermal method of uniformly growing α-Fe2O3 on aggregated ZIS nanoparticles easily causes a shading effect, affecting the light absorption of ZIS and greatly reducing the number of photogenerated carriers in the FO / IS composite under illumination.

[0066] also, Figure 9 (b) Except for norfloxacin, the S-type heterojunction photocatalyst IS / FO showed a degradation rate of over 70% for levofloxacin, oxytetracycline hydrochloride and tetracycline after 50 min of illumination, indicating that the S-type heterojunction catalyst of the present invention has good universality for antibiotic degradation.

[0067] Figure 10 The image shows the change in absorbance over time of the quantum dot-modified S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 obtained in Example 4 of this invention during the degradation of tetracycline.

[0068] Figure 10 During the dark-state adsorption-desorption equilibrium before illumination, the absorption peak of tetracycline did not shift significantly under the action of the ZnIn2S4 / α-Fe2O3 catalyst, indicating that the dark-state adsorption process did not change the structure of tetracycline. However, after 10-20 min of illumination, the absorbance of the tetracycline solution decreased sharply at a wavelength of approximately 357 nm, and the position of the absorption peak shifted significantly with the extension of illumination time, indicating that the catalyst effectively degraded tetracycline.

[0069] The above are merely preferred embodiments of the present invention and are not limited to the examples described above. Those skilled in the art will recognize that various modifications and variations can be made based on the principles of the present invention. Any modifications or improvements made should be considered within the scope of protection of the present invention.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3, characterized in that, Includes the following steps: Zinc salt, indium salt, and sulfur source were added to water to prepare a homogeneous solution; then α-Fe2O3 nanoparticles were added, and the mixture was heated at 30~90℃ for 1~6 h to allow ZnIn2S4 to grow in situ on α-Fe2O3. After washing and drying, the S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 was obtained.

2. The method for preparing a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 1, characterized in that, The molar ratio of the zinc salt, indium salt, sulfur source, and α-Fe2O3 nanoparticles is 1:(1.6~2):(3.9~5.10):(0.5~2), and the ratio of the zinc salt to water is 1 mmol:100 mL.

3. The method for preparing a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 1, characterized in that, The zinc salt is any one of zinc chloride, zinc nitrate, zinc acetate, or zinc formate. The indium salt is any one of indium chloride, indium nitrate, indium acetate, or indium formate. The sulfur source is any one of thioacetamide, thiourea, or sodium sulfide.

4. The method for preparing a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 1, characterized in that, The preparation process of the α-Fe2O3 nanoparticles is as follows: FeCl3·6H2O and NaC2H3O2 are added to a mixture of ethanol and water, and a hydrothermal reaction is carried out. After cooling to room temperature, the nanoparticles are washed and dried to obtain the final product.

5. The method for preparing a quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 4, characterized in that, The molar ratio of FeCl3·6H2O to NaC2H3O2 is (2~3):1, and the volume ratio of FeCl3·6H2O to the mixed solution is 1 mmol:15 mL; the hydrothermal reaction temperature is 90~180℃, and the time is 12~18 h.

6. A quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The application of the quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 6, characterized in that, Used for photocatalytic degradation of antibiotic pollutants in water.

8. The application of the quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 7, characterized in that, The antibiotic contaminants are tetracycline, norfloxacin, levofloxacin, or oxytetracycline hydrochloride.

9. The application of the quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 7, characterized in that, The concentration of antibiotic pollutants in the water body is 10~90 mg / L, and the addition ratio of S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 in the water body is 0.5~1 g / L.

10. The application of the quantum dot-modified weakly magnetic S-type heterojunction photocatalyst ZnIn2S4 / α-Fe2O3 according to claim 7, characterized in that, The light intensity for the photocatalytic degradation is 300~500 mW / cm². 2 The temperature is 25~45℃ and the time is 10~60 min.

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