LaFeO3 / Bi4Ti3O12 composite photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a LaFeO3 / Bi4Ti3O12 composite photocatalyst as well as a preparation method and application thereof, the composite photocatalyst is of a heterostructure formed by LaFeO3 and Bi4Ti3O12 through interface chemical bonding, and the heterostructure takes a lattice matched with LaFeO3 and Bi4Ti3O12 as a structural basis; the preparation method comprises the following steps: synthesizing LaFeO3 by a hydrothermal method, and depositing LaFeO3 nanoparticles on the surface of Bi4Ti3O12 by the hydrothermal method to prepare the LaFeO3 / Bi4Ti3O12 composite material, the LaFeO3 / Bi4Ti3O12 recoverable photocatalytic material provided by the invention solves the double pain points of insufficient degradation performance and high recovery difficulty of a traditional photocatalyst in organic pollutant treatment, and through material structure design and performance synergy, the photocatalytic material has the advantages of simple preparation process and low cost, and is suitable for industrial production. The integration of'efficient degradation 'and'convenient recovery' is realized.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture water treatment engineering, specifically relating to a LaFeO3 / Bi4Ti3O 12 Composite photocatalysts, their preparation methods, and applications. Background Technology

[0002] In recent years, with the continuous expansion of industrialized aquaculture, antibiotic residues in aquaculture wastewater have gradually become a new type of pollutant worthy of attention. Tetracycline (TC) is widely used due to its low cost and broad antibacterial spectrum, but its environmental residues and impacts cannot be ignored. Studies show that approximately 60%–90% of tetracycline enters the aquatic environment unchanged through feces and urine, not only exerting continuous selective pressure on aquatic microbial communities but also potentially exacerbating the spread of antibiotic resistance genes (ARGs), posing a potential threat to ecological security and public health.

[0003] Currently, common technologies for treating tetracycline in water include direct photolysis, ozonation, membrane separation, adsorption, and biodegradation. However, these methods all have certain limitations: direct photolysis is susceptible to competitive absorption of photons by coexisting pollutants in the water and may generate more toxic intermediates; ozonation technology has high operating costs and limited ability to completely mineralize tetracycline, usually requiring combination with other processes; membrane treatment technology can effectively retain pollutants, but faces problems such as high energy consumption, membrane fouling, and frequent replacement of membrane modules; adsorption methods, although simple to operate and rapid in reaction, cannot achieve complete degradation of pollutants, and there is a risk of secondary release after adsorption saturation.

[0004] Among various advanced processing technologies, semiconductor-based photocatalytic advanced oxidation processes stand out due to their ability to utilize sunlight to drive reactions and generate highly reactive oxidizing species (such as ·OH, h₂). + O2 - (etc.), and achieve deep mineralization of organic pollutants, which is considered one of the most promising treatment methods. Among many photocatalytic materials, layered bismuth-based materials (such as Bi4Ti3O) are particularly promising. 12 With its unique Aurivillius crystal structure, [Bi2O2] 2+ The spontaneous polarization effect caused by the alternating arrangement of bilayer and titanate layers, and the resulting efficient separation capability of photogenerated carriers, has attracted widespread research attention. However, in practical aquaculture wastewater treatment scenarios, this type of material still faces the following technical bottlenecks: 1. High photogenerated carrier recombination rate: single Bi4Ti3O 121. Limited separation efficiency of photogenerated electron-hole pairs in the material leads to low quantum yield, restricting its catalytic degradation performance; 2. Insufficient visible light utilization: Its band gap width is approximately 3.2 eV, mainly responding to the ultraviolet region, with weak utilization of the visible light portion of the solar spectrum; 3. Difficulty in recycling and risk of secondary pollution: Nanoscale powder catalysts are difficult to completely separate from water bodies after use, not only causing catalyst loss and difficulty in reuse, but also potentially leading to nanoparticle residues and ecotoxicity issues. Currently, bismuth-based catalysts generally face two major bottlenecks in practical applications: First, the recycling is difficult, as most bismuth-based materials are nanoscale particles (such as Bi4Ti3O). 12 Bismuth nanosheets and Bi2O3 nanoparticles are highly dispersed and non-magnetic, requiring energy-intensive separation methods such as centrifugation and filtration, making them impractical for aquaculture wastewater treatment. Secondly, they suffer from low carrier separation efficiency, and the bandgap of single bismuth-based semiconductors is relatively narrow (e.g., Bi4Ti3O3). 12 (With a band gap of 3.29 eV), photogenerated electron-hole pairs easily recombine, leading to a limited rate of antibiotic degradation.

[0005] In the research on improving the photocatalytic performance of bismuth-based materials, constructing heterojunctions, element doping, and surface modification are the current mainstream optimization strategies. However, existing systems still have bottlenecks such as insufficient structural stability, narrow spectral response range, and environmentally unfriendly synthesis processes.

[0006] For example, the LaFeO3 / BiOBr composite catalyst, although it inhibits photogenerated carrier recombination through a Z-type charge transfer pathway and shows good degradation effect on low concentrations of 5 mg / L Rhodamine B, has strong van der Waals forces between BiOBr sheets and lacks an effective repulsion mechanism. It is very easy for them to stack and aggregate face-to-face, forming micron-sized aggregates of 0.7~2.2 μm, resulting in insufficient exposure of active sites. At the same time, its synthesis process requires the use of organic solvents such as methanol and glacial acetic acid and adopts a multi-step high-temperature process, which not only has high energy consumption but also brings significant environmental pressure, making it difficult to adapt to the needs of industrial-scale production. The LaFeO3 / Bi2WO6 Z-type heterojunction constructed by a simple solvothermal method exhibits photocatalytic performance 20 times and 10 times that of pure LaFeO3 and Bi2WO6, respectively, demonstrating certain application potential. However, it still has significant drawbacks: UV-VisDRS data shows that its band gap is as wide as 2.76 eV, far exceeding the 2.24 eV of the LFO / BTO composite material in this application, making it unable to respond to visible light with wavelengths >500 nm (accounting for more than 50% of the solar energy spectrum), thus limiting solar energy utilization; regarding chemical stability, W in Bi2WO6... 6+ Easily reduced to W by photogenerated electrons 5+This leads to the reconstruction of lattice oxygen vacancies, resulting in weakened interfacial bonding in the heterojunction and a continuous decline in catalyst activity. Although the BiOBr / FeWO4Ⅱ type heterojunction synthesized via a solvothermal method broadens the photoresponse range with the help of FeWO4, achieving a 90.4% degradation rate of doxycycline within 1 hour, the band gap of this composite material (4:1 ratio) is 2.46 eV, still wider than the 2.24 eV of LFO / BTO, resulting in lower solar energy utilization. In practical applications, it requires high-power xenon lamps for illumination, leading to high energy consumption and making it unsuitable for natural light environments.

[0007] When TiO2-based materials are used to remove antibiotics from aquaculture wastewater, pure anatase TiO2 has a band gap of 3.2 eV, meaning it can only respond to ultraviolet light. After N and P co-doping modification, its band gap shrinks to 2.67-2.78 eV, achieving visible light response, but it can only absorb wavelengths ≤445 nm. This wavelength range accounts for only about 5% of the solar spectrum, resulting in low utilization of natural light. Bi4Ti3O... 12 The band gap of the / TiO2 heterojunction material is 2.79-2.96 eV, and its optical response range is similar to that of N and P co-doped TiO2, but it is still limited to short wavelength visible light.

[0008] Patent 2018110206475 prepared Bi4Ti3O via an ion doping pathway. 12 –LaFeO3 solid solution. The essence of a solid solution is a homogeneous mixture at the atomic / molecular scale, i.e., La… 3+ Fe 3+ Ions enter Bi4Ti3O 12 Substitution of some original ions in the crystal lattice (such as Bi) 3+ or Ti 4+ This results in the formation of a new phase with uniform composition and simple structure, where the properties of its components are diluted with each other, and the magnetic properties of LaFeO3 and Bi4Ti3O are also affected. 12 When the ferroelectricity of the metal is destroyed, its key functional properties such as magnetism and ferroelectricity are often "diluted" or even disappear, making it difficult to simultaneously meet the dual requirements of efficient catalysis and convenient recycling.

[0009] The paper "Preparation and promising application of novel LaFeO3 / BiOBrheterojunction photocatalysts for photocatalytic and photo-Fenton removal of dyes" focuses on exploring the heterojunction mechanism and studying the dye degradation performance, representing typical basic research. Rhodamine B, often used as a model pollutant in the literature, can generally be effectively removed through a combination of processes such as flocculation, adsorption, and advanced oxidation. Its treatment technology is relatively mature, and it is not a top-tier pollutant known for its "trace amounts, persistence, and high ecological risk."

[0010] Therefore, it is of great significance to develop a photocatalytic material with broad spectral response, high catalytic activity, good stability, and convenient magnetic recovery function for the deep purification of antibiotic pollutants in aquaculture wastewater. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a LaFeO3 / Bi4Ti3O 12 Composite photocatalysts and their preparation methods, along with their application in controlling antibiotic pollution in aquaculture wastewater, are used to overcome the shortcomings of existing photocatalytic materials, such as low visible light utilization efficiency, high carrier recombination rate, difficulty in recycling, and poor resistance to water body interference.

[0012] The LaFeO3 / Bi4Ti3O provided by this invention 12 Composite photocatalysts, constructed by combining LaFeO3 and Bi4Ti3O 12 The heterojunction structure between them synergistically regulates the energy band and surface properties of the material, and utilizes the inherent magnetism of LaFeO3 to achieve rapid separation and recycling of the material after use.

[0013] Specifically, the LaFeO3 / Bi4Ti3O provided by this invention 12 The composite photocatalyst is composed of LaFeO3 and Bi4Ti3O 12 The heterostructure is formed through interfacial chemical bonding, with LaFeO3 and Bi4Ti3O4 as the main components. 12 The matched lattice serves as the structural basis.

[0014] During high-temperature synthesis, interfacial atoms achieve a transformation from physical mixing to chemical bonding by forming oxygen bridges with covalent-ionic hybrid characteristics, accompanied by significant orbital hybridization. This robust interfacial bonding not only enhances the physical stability of the heterojunction but, more importantly, reconstructs the interfacial electronic structure, inducing a strong built-in electric field. This lays an indispensable microscopic foundation for efficient charge separation, precise bandgap control, and overall improvement in photocatalytic performance. This bonding method effectively resists magnetic field adsorption and water scouring forces during the recycling process, preventing the shedding of active components. The constructed material is Bi4Ti3O. 12 The LaFeO3 heterojunction composite material maintains the independent chemical composition and crystal structure of each component, achieving physical contact and chemical bonding only through the interface. The synthesis route in this application also reflects this difference: LaFeO3 nanoparticles and Bi4Ti3O4 nanoparticles are first prepared separately. 12 Then, through a secondary process, the two are bonded at the interface. This "stepwise synthesis-interface bonding" strategy aims to solve the bottleneck that the solid solution route cannot overcome: the independent retention and synergistic enhancement of functional properties.

[0015] The core of heterojunction design lies in utilizing precise band matching and controllable charge transfer mechanisms (such as the Z-type mechanism) at the interface to significantly improve the separation efficiency of photogenerated carriers while fully preserving the intrinsic properties of each component. For example, the magnetism of LaFeO3 is retained, thus achieving efficient magnetic recovery of the material; Bi4Ti3O 12 Its ferroelectricity is also maintained, and its spontaneous polarization built-in electric field can further promote charge separation.

[0016] Furthermore, LaFeO3 and Bi4Ti3O 12 The molar ratio is 2.2:1.

[0017] Furthermore, LaFeO3 is an orthorhombic crystal system (PDF#37-1493); Bi4Ti3O 12 It belongs to the tetragonal crystal system, PDF#35-0795.

[0018] Choose the orthorhombic LaFeO3 (LFO) and the tetragonal Bi4Ti3O 12 (BTO) heterojunctions are based on a deep complementary design in terms of structure and function, specifically reflected in the following two aspects: (1) Structural homology ensures interface lattice matching: Both LFO and BTO are derived from the perovskite structural framework. LFO, as a standard perovskite (ABO3), exhibits a thermodynamically stable orthorhombic phase due to lattice distortion; BTO belongs to the Aurivillius phase, and its main body consists of three layers of perovskite units (Bi2Ti3O4). 10 ) 2-This shared structural gene provides the basis for achieving low lattice mismatch and atomic-level "seamless connection" at the interface between the two.

[0019] (2) Ferroelectric-antiferromagnetic synergistic charge separation: The orthorhombic LFO (PDF#37-1493) is chosen to maintain its antiferromagnetic ground state. Under this specific symmetry, the tilt and rotation modes of the FeO6 octahedron can generate a specific magnetic order, which is the structural "cornerstone" of the material's magnetism; the tetragonal BTO (PDF#35-0795) is chosen to utilize the strong spontaneous polarization induced by its non-centrosymmetric structure. This polarization forms a strong built-in electric field at the heterojunction interface, which can effectively drive the reverse migration of photogenerated electrons and holes, greatly suppress their recombination, and continuously provide active charge carriers for surface catalytic reactions.

[0020] The combination of LFO and BTO at the interface not only achieves structural stability through lattice matching, but also constructs a fully functional catalytic system at the microscopic level through the interaction of ferroelectric polarization and antiferromagnetic order: the polarization field of BTO solves the problem of "separation efficiency" of photogenerated carriers, while the interface coupling may further induce novel magnetoelectric effects, providing a potential path for the "recovery and regeneration" of catalysts.

[0021] The present invention also provides a LaFeO3 / Bi4Ti3O as described above. 12 The preparation method of the composite photocatalyst includes the following steps: Step S1: Hydrothermal synthesis of LaFeO3; Step S2: Deposit LaFeO3 nanoparticles onto Bi4Ti3O4 using a hydrothermal method. 12 Surface preparation of LaFeO3 / Bi4Ti3O 12 Composite materials.

[0022] Furthermore, the specific steps of step S1 are as follows: Step S11: Take La(NO3)3·6H2O and Fe(NO3)3·9H2O, add them to a mixed solvent composed of ethylene glycol (EG) and ethanol (EtOH), and stir the resulting mixture with a magnetic stirrer to form a homogeneous precursor solution; Step S12: Transfer the precursor solution obtained in step S11 to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and react at 170-190℃ for 20-28 hours. Step S13: After the reaction is complete, allow the mixture to cool naturally to room temperature, collect the precipitate and wash it; dry the washed product in an oven at 60-80℃ for 6-12 hours to obtain the LaFeO3 powder precursor. Step S14: Place the powdered precursor obtained in step S13 into a muffle furnace and calcine it in an air atmosphere at 750-850℃ for 3-5 hours to obtain the final product LaFeO3 nanoparticles.

[0023] Furthermore, in step S11, the molar ratio of La(NO3)3·6H2O and Fe(NO3)3·9H2O is 0.9:1-1.1:1; the volume of the mixed solvent composed of ethylene glycol and ethanol is 30-50 mL, and the volume ratio of ethylene glycol to ethanol is 8.5:1.5-9.5:0.5; the magnetic stirrer is stirred at a speed of 400-700 rpm for 50-90 minutes; in step S13, the precipitate is washed 6-8 times alternately with 20-40 mL of deionized water and 20-40 mL of ethanol as washing agents.

[0024] Furthermore, the specific steps of step S2 are as follows: Step S21: Place C 16 H 36 Add O4Ti to 25-35 mL of NaOH solution and stir on a magnetic stirrer at 300-600 rpm for 20-40 minutes. Step S22: Add Bi(NO3)3·5H2O to the above solution and continue stirring for 20-40 minutes. The resulting solution is denoted as solution A. Step S23: Add the LaFeO3 nanoparticle solution obtained in step S14 with a concentration of 10.0-12.5 g / L to solution A, and then stir at 400-700 rpm for 50-90 minutes; solution A is for preparing Bi4Ti3O 12 The precursor solution, after hydrothermal treatment, formed a crystalline precipitate Bi4Ti3O. 12 ; Step S24: Transfer the mixed solution obtained in step S23 to a hydrothermal reactor with an 80-120 mL polytetrafluoroethylene liner and react at 170-190°C for 18-24 hours. Step S25: Allow the reactor to cool naturally to room temperature; collect and wash the precipitate; then dry the product at 60-80℃ for 8-16 hours to finally obtain LaFeO3 / Bi4Ti3O 12 Composite materials.

[0025] Furthermore, in step S21, the concentration of the NaOH solution is 2.5-3.5 mol / L; C 16 H 36 The amount of O4Ti used is 0.7-1.0 mL; the amount of Bi(NO3)3·5H2O used in step S22 is 1.4-1.8 g; in step S25, the precipitate is washed 3-5 times alternately with 30-50 mL of deionized water and 30-50 mL of ethanol as washing agents.

[0026] LaFeO3 materials prepared under sintering conditions of 750-850℃ exhibit the highest saturation magnetization, demonstrating excellent magnetic field response performance, which is beneficial for achieving efficient capture and recovery of the material through an external magnetic field. LaFeO3-based catalysts possess typical soft magnetic properties (coercivity approximately 122 Oe, remanence approximately 0.0022 emu / g), which is a key advantage for achieving efficient magnetic recovery. This characteristic not only enables rapid separation of the material in an external magnetic field, but also, due to the near-zero remanence, effectively avoids particle agglomeration caused by residual magnetism, thereby simplifying the recovery process and maintaining the physical integrity of the catalyst.

[0027] Bi4Ti3O 12 For a stable perovskite structure, Ti 4+ It is chemically inert, not easily reduced, and can maintain its structural integrity even under long-term light exposure. By combining it with LaFeO3, it successfully solves the core drawbacks of LaFeO3 / Bi2WO6, namely "narrow spectral response and insufficient stability".

[0028] This application specifies in detail that the composite photocatalyst is composed of LaFeO3 and Bi4Ti3O 12 The heterostructure is formed through interfacial chemical bonding, with LaFeO3 and Bi4Ti3O4 as the main components. 12 A matched crystal lattice serves as the structural basis. Further detailed specifications are applied to the process parameters; any deviation from the molar ratio, crystal phase, or key process parameters will lead to weakened magnetic properties, a narrowed optical response range, or the appearance of impurity phases such as Bi₂O₃ and Fe₂O₃ at the heterojunction interface, thus affecting performance.

[0029] This application employs a one-step sol-hydrothermal method to prepare LaFeO3 / Bi4Ti3O 12 Composite materials, using water as the main solvent, possess both the advantages of being green and environmentally friendly and having low energy consumption, and Bi4Ti3O 12 Its ferroelectric properties can generate electrostatic repulsion, effectively resisting the tight stacking of sheets, and making it easier to form nanosheets or ultrathin layered structures with excellent dispersion. This can fully expose active sites and greatly improve carrier separation efficiency.

[0030] LaFeO3 / Bi4Ti3O 12 The composite material, through a synergistic design of "perovskite structure + ferroelectric properties + heterojunction," specifically addresses the core bottleneck of existing bismuth-based catalytic systems. (Bi4Ti3O) 12The ferroelectric built-in electric field of LaFeO3 can directionally drive carrier separation, significantly reducing the recombination rate; the p-type semiconductor properties of LaFeO3 can broaden the spectral response range and possess high saturation magnetization, enabling efficient material recovery; the combination of the two forms a comprehensive advantage of "high catalytic activity + broad spectral response + long-term stability + easy recovery", which is more suitable for the application requirements of actual water treatment scenarios. Bi4Ti3O 12 Belonging to the Aurivillius structure, its valence band is formed by the hybridization of Bi6s and O2p orbitals. Compared to BiOX materials with the Sillén structure, the Aurivillius structure exhibits significant spontaneous polarization characteristics, enabling the formation of a strong built-in electric field within the material. This electric field not only effectively promotes the separation of photogenerated electron-hole pairs but also enhances the migration ability of holes to the catalyst surface, thereby significantly improving the oxidation activity and charge transport efficiency of the material. Iron-based perovskite composite oxide LaFeO3, as a typical p-type semiconductor, is suitable for large-scale preparation due to its relatively narrow band gap (approximately 2.19 eV), unique magnetism, easily tunable microstructure, and easier recycling. This method is simple, mild, and does not use toxic organic solvents.

[0031] The present invention also provides a LaFeO3 / Bi4Ti3O as described above. 12 Application of composite photocatalysts in tetracycline degradation.

[0032] Furthermore, the specific steps of the application are: to apply the LaFeO3 / Bi4Ti3O 12 The composite photocatalyst was added to a tetracycline solution with a concentration of 10-80 mg / L to form a mixed system. The mixed system was then magnetically stirred in the dark for 20-60 minutes to ensure that the catalyst and pollutant reached adsorption-desorption equilibrium. Subsequently, under continuous stirring, the mixed system was irradiated with visible light from a 300W xenon lamp equipped with a λ>420nm filter for 60-150 minutes to complete the photocatalytic degradation reaction.

[0033] Compared with the prior art, the present invention has the following outstanding features and advantages: 1. The LaFeO3 / Bi4Ti3O of the present invention 12 Recyclable photocatalytic materials solve the dual pain points of traditional photocatalysts (such as TiO2-based materials) in the treatment of organic pollutants (especially antibiotics in aquaculture wastewater) – namely, "insufficient degradation performance" and "difficult recycling". Through material structure design and performance synergy, "efficient degradation" and "convenient recycling" are integrated.

[0034] 2. LaFeO3 / Bi4Ti3O 12The design focuses on performance enhancement and solving catalyst recovery problems to avoid secondary pollution and resource waste: ① broadening the photoresponse range and improving the utilization rate of natural light; ② suppressing carrier recombination and enhancing activity (h + , ·OH) species generation; ③ Enhanced anti-interference ability, adaptable to complex wastewater matrix, LaFeO3 / Bi4Ti3O 12 Utilizing 500-620nm long-wavelength visible light avoids the absorption range of colored substances, minimizing interference from light competition; ④ Introducing magnetic components enables low-cost and rapid separation: LaFeO3 itself possesses weak magnetism (saturation magnetization 1.2-2.0 emu / g), and reacts with Bi4Ti3O 12 After fusion, the magnetic properties are retained and the photocatalytic activity is not affected; ⑤ Optimize the structural stability of the material to ensure its recyclability: LaFeO3 and Bi4Ti3O 12 The material forms a stable heterogeneous structure through chemical bonding, rather than physical mixing, thus avoiding the shedding of active components during the recycling process (magnetic separation, water rinsing). Experiments show that after five cycles of tetracycline degradation, the material still maintains a degradation rate of over 85%.

[0035] 3. LaFeO3 and Bi4Ti3O 12 After four cycles of tetracycline degradation, the constructed composite material maintained an antibiotic degradation rate of over 85%, with a performance decline of less than 15%. In contrast, traditional N / P co-doped TiO2 only required three cycles, resulting in a degradation rate that dropped from over 90% to below 65%, demonstrating a significant difference in cycle stability. Furthermore, the stable heterojunction structure inhibits metal ion leaching, preventing secondary pollution of water bodies by metal ions and reducing performance degradation due to component loss. This extends the material's lifespan, reduces catalyst replacement frequency and resource consumption, further highlighting the technology's environmental friendliness and sustainability.

[0036] 4. Low preparation threshold and controllable cost, suitable for large-scale engineering applications: LaFeO3 / Bi4Ti3O 12 The preparation method is a sol-hydrothermal method, which is simple and efficient. It does not require complex equipment such as high-temperature flames and precision atomization. It only requires mixing precursors such as lanthanum nitrate, ferric nitrate, and tetrabutyl titanate in proportion to prepare a solution, and then completing the synthesis through a low-temperature hydrothermal reaction (hot water temperature 180-200℃, reaction time 20h). The operation process is easy to standardize, which greatly reduces the technical threshold for production.

[0037] 5. All precursors used are mass-produced raw materials in the chemical industry – lanthanum nitrate (99% purity, market price approximately 150 RMB / kg), ferric nitrate (98% purity, approximately 50 RMB / kg), and tetrabutyl titanate (99% purity, approximately 80 RMB / kg). Not only is the purity easily met, but the price is also only that of Bi4Ti3O. 12The cost of the high-purity bismuth nitrate used in TiO2 is only 1 / 3 to 1 / 10 of the cost (approximately 500 RMB / kg), resulting in a significant advantage in raw material cost. This combination of "simplified process + low-cost raw materials" allows for easy mass production at the ton level, perfectly meeting the needs of scenarios such as aquaculture wastewater treatment, which have high requirements for technological scale and engineering, and providing economic support for the implementation of the technology.

[0038] 6. The inherent weak magnetism of LaFeO3 (saturation magnetization 1.2-2.0 emu / g) in conjunction with Bi4Ti3O 12 The composite material is completely preserved, and through the heterojunction interface chemical bonding design, there is no interference between magnetic properties and photocatalytic activity. After the aquaculture wastewater treatment is completed, there is no need for the high-speed centrifugation (≥8000rpm, high energy consumption) or easily clogged ultrafiltration membrane filtration required by traditional TiO2-based materials. Only an external magnetic field of 0.1-0.3T is needed, and the material can be rapidly separated by sedimentation within 5-10 minutes, with a recovery efficiency of over 95%, far exceeding the efficiency of traditional centrifugal separation (about 70%). In terms of operating costs, the energy consumption of magnetic field separation is only 1 / 5 of that of centrifugal separation, and there is no need for frequent equipment maintenance (such as replacing filter membranes and repairing centrifuge units), reducing operating labor costs. This "low energy consumption + easy operation" recovery method solves the core pain points of "difficult recovery and expensive recovery" of photocatalytic materials in wastewater treatment, significantly improving the practicality and economy of the technology application.

[0039] 7. LaFeO3 / Bi4Ti3O 12 Composite materials are designed to balance structural and functional advantages; their sheet-like or block-like structures reduce the risk of particle dispersion and loss; more importantly, the LaFeO3 component possesses weak magnetic properties (saturation magnetization of 1.2-2.0 emu / g), allowing for rapid separation without complex equipment using only an external magnetic field, achieving a separation efficiency exceeding 95%, while also being energy-efficient and free from filter clogging issues. This "easy separation, low cost" characteristic perfectly meets the practical needs of aquaculture wastewater treatment for both economy and convenience, while simultaneously reducing the risk of secondary pollution caused by material loss at the source. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the synthesis process of LFO / BTO composite materials; Figure 2 In the embodiments of the present invention, LaFeO3 (LFO) and Bi4Ti3O are used. 12 (a) UV-Vis absorption spectra of (BTO) and LFO / BTO composite materials and their corresponding first derivative curves (b); Figure 3 XRD patterns of LFO, BTO, and LFO / BTO composite materials; Figure 4 Surface morphology and microstructure diagrams of LFO and BTO materials; Figure 5 The surface morphology and microstructure of the LFO / BTO composite material are shown in the diagram. Figure 6 The energy spectrum of the LFO / BTO composite material is shown below. Figure 7 This is a uniform distribution diagram of the elements La, O, Fe, Zn, C, and N; Figure 8 The X-ray photoelectron spectra of LFO / BTO composite materials are shown, where (a) is the full spectrum and (b) to (f) are high-resolution spectra of La-3d, Fe-2p, O-1s, Bi-4f and Ti-2p, respectively. Figure 9 Photoluminescence spectra of BTO, LFO, and LFO / BTO composite materials; Figure 10 (a) Comparison of tetracycline removal by LFO, BTO and LFO / BTO composite material, (b) Corresponding reaction kinetic curves; Figure 11 The tetracycline removal effect of LFO / BTO composite material under different (a) catalyst dosages and (b) reaction kinetic curves under the corresponding conditions are shown. Figure 12 The tetracycline removal effect of LFO / BTO composite material under different initial tetracycline concentrations (a) and (b) reaction kinetic curves under the corresponding conditions are shown. Figure 13 The tetracycline removal efficiency of LFO / BTO composite material under different solution pH conditions (a) and reaction kinetic curves under the corresponding conditions (b) are shown. Figure 14 The tetracycline removal efficiency of LFO / BTO composite material under (a) different inorganic anions and (c) humic acid, and (b) and (d) are the reaction kinetic curves under the corresponding conditions; Figure 15 (a) Results of the cycle stability test of LFO / BTO composite material; (b) Comparison of X-ray diffraction patterns of the material before and after photocatalytic reaction. Figure 16 This is a schematic diagram of the free radical trapping experiment and electron paramagnetic resonance test results in an embodiment of the present invention; Figure 16 (a) Comparison of the degradation efficiency of tetracycline in the presence of different free radical scavengers; Figure 16 (b) shows the electron paramagnetic resonance spectrum of the DMPO-•OH adduct, comparing the signal intensity under dark conditions and 5 minutes of illumination. Figure 16 (c) is TEMPO-h+ The electron paramagnetic resonance spectrum of the adduct shows the signal changes in the dark state and after 5 minutes of visible light irradiation. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The technical solutions of the present invention will be further described below with reference to implementation examples.

[0042] The optical properties and photogenerated charge behavior of photocatalytic materials were analyzed and evaluated using ultraviolet-visible light (UV-VisDRS, Shimadzu UV-3600iPlus, Japan). In the following examples, X-ray diffraction (XRD, Rigaku Smart Lab SE, Japan) was used to analyze the phase composition and crystal structure of the samples; scanning electron microscopy (SEM, ZEISG Gemini SEM300, Germany) was used to observe the surface morphology and microstructure of the composite material; X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, USA) was used to determine the elemental composition and chemical state of the material surface; Edinburgh FLS1000 fluorescence spectrometer was used to reveal the separation and recombination efficiency of photogenerated charges; and electron paramagnetic resonance spectroscopy (EPR) was used to detect any possible free radicals or defect centers in the samples.

[0043] In the examples, lanthanum nitrate hexahydrate (La(NO3)3·6H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and tetrabutyl titanate (C 16 H 36 The reagents used in the experiment, including O4Ti, bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), ethylene glycol (EG), anhydrous ethanol (EtOH), sodium hydroxide (NaOH), disodium oxalate tetraacetate (EDTA-2Na), p-benzoquinone (BQ), isopropanol (IPA), and tetracycline (TC), are all analytical grade and require no further treatment before use.

[0044] Example 1 This embodiment provides a LaFeO3 / Bi4Ti3O 12 Preparation methods of composite photocatalysts, such as Figure 1 As shown, the specific steps are as follows: Step S1, hydrothermal synthesis of LaFeO3, the specific steps are as follows: Step S11: Add 4 mmol of La(NO3)3·6H2O and 4 mmol of Fe(NO3)3·9H2O to a mixed solvent consisting of ethylene glycol (EG) and ethanol (EtOH), wherein the volume of the mixed solvent is 40 mL and the volume ratio of EG to EtOH is 8.5:1; stir the resulting mixture vigorously at 500 rpm for 60 minutes on a magnetic stirrer to form a homogeneous precursor solution; Step S12: Transfer the precursor solution obtained in step S11 to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and react at 180°C for 24 hours. Step S13: After the reaction is complete, the mixture is allowed to cool naturally to room temperature. The precipitate is collected and washed 6 times alternately with 30 mL of deionized water and 30 mL of ethanol. The washed product is then dried in an oven at 60 °C for 12 hours to obtain a powdered LaFeO3 precursor. Step S14: Place the LaFeO3 powder precursor obtained in step S13 into a muffle furnace and calcine it at 800°C in air for 4 hours to obtain the final product, LaFeO3 nanoparticles.

[0045] Step S2, Bi4Ti3O 12 The synthesis was carried out via a solvothermal method, and the specific steps are as follows: Step S21, add 0.85 mL of C 16 H 36 O4Ti was added to 30 mL of sodium hydroxide solution (3 mol / L) and stirred at 600 rpm for 30 minutes on a magnetic stirrer. Step S22: Add 1.61g of Bi(NO3)3·5H2O to the solution and stir until completely dissolved; transfer the mixture to a 100mL polytetrafluoroethylene-lined autoclave and react at 180°C for 20 hours. Step S23: After the reaction is complete, the autoclave is allowed to cool naturally to room temperature. The resulting precipitate is collected and washed five times alternately with 40 mL of deionized water and 40 mL of ethanol. The product is then dried at 80 °C for 12 hours to obtain Bi4Ti3O. 12 Nanoparticles.

[0046] Step S3: Deposit LaFeO3 nanoparticles onto Bi4Ti3O4 using a hydrothermal method. 12 Surface preparation of LaFeO3 / Bi4Ti3O 12 Composite materials, the specific steps are as follows: Step S31: Add 0.85mLC 16 H 36O4Ti (tetrabutyl titanate) was added to 30 mL of 3 mol / L NaOH solution and stirred at 600 rpm for 30 minutes on a magnetic stirrer. Step S32: Add 1.61g of Bi(NO3)3·5H2O to the above solution and continue stirring for 30 minutes until completely dissolved. The resulting solution is denoted as solution A. Step S33: Add 1.81g of the LaFeO3 nanoparticles prepared in step S14 to 20ml of solution B made of deionized water, add solution B to solution A, and stir at 700rpm for 60 minutes to mix them thoroughly. Step S34: Transfer the mixed solution obtained in step S23 to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor and react at 180 °C for 20 hours. Step S35: Allow the reactor to cool naturally to room temperature, collect the precipitate, and wash it 5 times alternately with 40 mL of deionized water and 40 mL of ethanol as washing agents; then dry the product at 80 °C for 12 hours to finally obtain LaFeO3 / Bi4Ti3O 12 Composite material, denoted as LFO / BTO composite material.

[0047] The LaFeO3 / Bi4Ti3O prepared in this embodiment 12 Composite photocatalytic materials, which are constructed by combining LaFeO3 and Bi4Ti3O 12 The heterojunction structure between them enables synergistic control of the material's band structure.

[0048] To characterize its optical performance, the following test methods were used: UV-Vis Diffuse Reflectance Spectroscopy: The sample was tested using a UV-Vis spectrophotometer equipped with an integrating sphere attachment. The specific steps are as follows: First, turn on the instrument and integrating sphere attachment and preheat for 20 minutes. Then, set the wavelength range to 200-1000 nm, the scan speed to medium, the data interval to 1 nm, the photometric mode to diffuse reflectance (R%), and the slit width to 2.0 nm. After baseline correction using a barium sulfate standard white plate as a reference, LaFeO3 and Bi4Ti3O2 were tested. 12 and LaFeO3 / Bi4Ti3O 12 Composite material powder samples were loaded into the sample cell and flattened to cover the test window. Diffuse reflectance spectra in the wavelength range of 200–1000 nm were collected at room temperature. Finally, the Kubelka-Munk function was used to process the obtained data and calculate the optical band gap of the material.

[0049] Figure 2 In this embodiment, LaFeO3 (LFO) and Bi4Ti3O are used. 12The UV-Vis absorption spectra of (BTO) and LFO / BTO composites and their corresponding first derivative curves; such as Figure 2 (a) The optical properties and photogenerated charge behavior of photocatalytic materials were analyzed and evaluated using ultraviolet-visible light (UV-VisDRS, Shimadzu UV-3600iPlus, Japan), reflecting the absorption capacity of three materials for different wavelengths of light. Compared with single Bi4Ti3O4... 12 Compared to (BTO), LaFeO3 / Bi4Ti3O 12 The reflectivity of the (LFO / BTO) composite material significantly decreases in the 400–800 nm wavelength range, and its reflectivity is similar to that of LaFeO3 (LFO), indicating that the introduction of LFO effectively enhances the composite material's absorption of visible light. Figure 2 (b) Further, the first derivative curves of the DRS spectra of each sample are shown. These are used to accurately determine the absorption edge position and optical band gap of each material. The wavelength corresponding to the peak of the curve is the absorption edge of the material.

[0050] According to formula (1): (1); Where λ is the wavelength corresponding to the absorption edge, the calculations show that: the absorption edge of pure BTO is located at 375.92 nm, with a band gap of 3.29 eV; the absorption edge of pure LFO is located at 564.98 nm, with a band gap of 2.19 eV; while the absorption edge of the LFO / BTO composite material is red-shifted to 554.72 nm, with a band gap of 2.24 eV (see...). Figure 2 (b) The above results demonstrate that a heterojunction structure was successfully formed between LFO and BTO, and a synergistic effect was achieved through band matching, reducing the band gap of the composite material to 2.24 eV. As shown in the figure, the photoresponse range of this composite material extends to the long-wave visible light region of 500–620 nm, effectively covering the long-wave visible light with a higher energy proportion in the solar spectrum. This wavelength range effectively avoids the main absorption range of common colored substances such as algae and humic substances, thus significantly reducing interference from the background color of the water body when treating colored systems such as aquaculture wastewater. Even in complex water quality environments, the material of this invention can still stably capture the long-wave visible light component in natural light, and its light absorption stability is significantly better than that of traditional TiO2-based materials, providing a reliable guarantee for achieving continuous and efficient photocatalytic reactions.

[0051] The microstructural basis for this performance improvement can be found in... Figure 3 The system was revealed by XRD characterization. The XRD test was performed according to the following steps: Take an appropriate amount of LaFeO3 / Bi4Ti3O 12The composite powder sample was placed in a clean sample cell, and its surface was flattened to be flush with the edge of the sample cell using a glass slide. No additional grinding was performed during the process to maintain the original crystalline state of the sample. An X-ray diffractometer equipped with a CuKα radiation source (λ=1.5406Å) was used, with the tube voltage set to 40kV and the tube current to 40mA. Data acquisition was performed within the range of 10°–80° (2θ) at a scanning speed of 10° / min, a step size of 0.02°, and a receiving slit of 0.3mm. The instrument was preheated for 15 minutes before testing to ensure the stability of the X-ray tube. All measurements were performed at room temperature. The obtained data were processed using Jade software and compared with standard PDF cards (LaFeO3:PDF#37-1493, Bi4Ti3O). 12 Compare with PDF#35-0795 to confirm the crystal structure and phase purity.

[0052] XRD patterns show that the characteristic diffraction peaks of LFO and BTO perfectly match those of the standard cards (LFO: PDF#37-1493; BTO: PDF#35-0795), with no impurity peaks, indicating that both phases possess high crystallinity and purity, maintaining the integrity of their respective lattice structures after compositing. More importantly, the lattice constant mismatch between their core crystal planes is far below the 5% "lattice matching critical value," indicating that LFO and BTO can achieve a low-defect "seamless connection" at the interface, forming a continuous crystal structure. This structural feature of "pure phase high crystallinity—low lattice mismatch—uniform interface contact" constitutes a complete microscopic chain for the synergistic regulation of the LFO / BTO heterojunction. Based on this, LFO and BTO form a stable interface through lattice matching, and reconstruct the band structure through orbital hybridization, achieving a band gap narrowing to 2.24 eV; simultaneously, oxygen vacancy defects introduce intermediate energy levels, combined with the band broadening effect caused by ferroelectric polarization, jointly extending the optical response to ≤620 nm. Furthermore, the synergistic effect of charge transfer and the ferroelectric built-in electric field effectively ensures the efficient separation of photogenerated carriers under narrow bandgap conditions. Ultimately, this composite material achieves a significant improvement in overall performance in terms of broad spectral response, high charge separation efficiency, and strong catalytic activity. This wider light response range eliminates the need for artificial light sources, making it more suitable for the practical needs of "natural light-driven" scenarios in aquaculture wastewater treatment, significantly improving the flexibility and economy of the technology application.

[0053] Figures 4 to 7 Scanning electron microscope images clearly show LaFeO3 and Bi4Ti3O 12The microstructure and structural characteristics of the composite material were investigated. The specific testing steps using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were as follows: An appropriate amount of powder sample was uniformly adhered to a conductive adhesive and sputter-coated with gold, then placed in the SEM sample chamber. A representative field of view was selected, and secondary electron signals were acquired at different magnifications to obtain images of the sample's microstructure. Subsequently, to verify the elemental distribution in the composite material, an EDS was used to perform a surface scan of the selected area, focusing on detecting the spatial distribution of four elements: La, Fe, Bi, and Ti.

[0054] like Figure 4 As shown in a, pure-phase LaFeO3 is composed of smooth and uniform elliptical nanoparticles with an average particle size of about 60 nanometers. Figure 4 b shows Bi4Ti3O 12 Microsphere structures were formed through the self-assembly of regular nanosheets. Figure 5 a and 5b demonstrate the interaction between LaFeO3 and Bi4Ti3O 12 The morphological characteristics of the composite are as follows: LaFeO3 nanoparticles are uniformly dispersed in Bi4Ti3O 12 Microsphere surface. Figure 6 LaFeO3 / Bi4Ti3O 12 The energy dispersive spectroscopy (EDS) spectrum showed that the mass percentages of La, Bi, O, Ti, and Fe in the material were 43.9%, 28.1%, 17.2%, 7.7%, and 3.0%, respectively. The uniform distribution of elements such as La, O, Fe, Zn, C, and N in the SEM-EDS analysis was also observed. Figure 7 Visually presented. These results confirm the LaFeO3 / Bi4Ti3O 12 Successful preparation of composite materials.

[0055] Next, X-ray photoelectron spectroscopy (XPS) analysis was performed to determine the elemental composition and chemical valence state of LFO / BTO. LaFeO3 / Bi4Ti3O 12 XPS testing of heterojunctions requires first uniformly coating the purified and dried powder sample onto a conductive adhesive, using monochromatic Al Kα rays as the excitation source, within a range ≤1×10⁻⁶. -9 Under a high vacuum environment of mbar, a full-spectrum scan in the range of 0–1200 eV was first performed with a flux of 100 eV and a step size of 1 eV to qualitatively confirm the presence of elements such as Bi, Ti, Fe, La, and O. Then, for each characteristic element, a high-resolution scan was performed with a flux of 20–30 eV and a step size of 0.05 eV. The chemical valence state and atomic ratio of the elements were analyzed by fitting standard binding energy data, supplemented by pure phase LaFeO3 and Bi4Ti3O 12 By comparing samples, the surface electronic structure and interface interaction of the heterojunction were ultimately revealed.

[0056] The results are as follows Figure 8 As shown. The spectrum was calibrated using the C 1s peak (binding energy 284.80 eV). The complete scan spectrum ( Figure 8 (a) clearly confirms the presence of five elements: Bi, Ti, O, La, and Fe in the composite material. High-resolution La-3dXPS spectra are shown below. Figure 8 As shown in (b), four characteristic peaks are displayed. The peaks with binding energies of 834.33 eV and 838.08 eV correspond to the main peak and satellite peak of La⁻³d⁵ / ², respectively. The peaks with binding energies of 851.21 eV and 855.13 eV correspond to the main peak and satellite peak of La⁻³d³ / ², respectively. The calculated spin-orbit splitting energy of the La 3d orbital is 16.88 eV. The high-resolution Fe 2p XPS spectrum is shown below. Figure 8 As shown in (c), in the Fe 2p region, the peaks with binding energies of 710.00 eV and 711.45 eV correspond to Fe, respectively. 2+ and Fe 3+ The Fe 2p3 / 2 orbital signal. These mixed valence states significantly suppress electron-hole recombination. The peak with a binding energy of 724.23 eV corresponds to the Fe 2p1 / 2 orbital signal, and a distinct satellite peak (labeled "sat.") is observed between the Fe 2p3 / 2 and Fe 2p1 / 2 peaks. In the O 1s region ( Figure 8 In (d), the peaks with binding energies of 529.50 eV, 530.00 eV, and 531.51 eV correspond to lattice oxygen (O1) and oxygen vacancy (O2), respectively. v ) and adsorbed oxygen (O a High-resolution Bi-4f XPS spectrum as follows Figure 8 As shown in (e), the peak with a binding energy of 158.97 eV corresponds to the Bi-4f7 / 2 orbital, while the peak with a binding energy of 164.31 eV corresponds to the Bi-4f5 / 2 orbital. The binding energy difference between these two peaks is 5.34 eV, consistent with the Bi-4f5 / 2 orbital. 3+ The typical peak splitting mode indicates that bismuth in the material is mainly in the form of Bi. 3+ The form exists. High-resolution Ti 2p XPS spectra are as follows: Figure 8 As shown in (f), Ti 4+ The characteristic peaks are clearly visible, with the peaks at 457.86 eV and 464.30 eV corresponding to the Ti 2p3 / 2 and Ti 2p1 / 2 orbitals, respectively. Additionally, an extra peak appears at 466.30 eV. This phenomenon arises from the partial overlap between the Bi 4d3 / 2 peak and the Ti 2p orbital peak due to their similar binding energies, resulting in the observed extra peak.

[0057] Photoluminescence (PL) spectroscopy is commonly used to characterize charge transfer in semiconductors. The testing procedure is as follows: The powder sample to be tested is evenly spread on the sample stage, and a xenon lamp with a wavelength of 325 nm is used as the excitation source. The excitation slit width is set to 2.0 nm, and the emission slit width is 1.5 nm. Fluorescence emission spectra in the wavelength range of 300-900 nm are collected at room temperature.

[0058] like Figure 9 As shown, BTO exhibits the strongest photoluminescence PL peak, indicating its highest electron-hole recombination rate. In contrast, the BTO / LFO composite material shows the weakest PL intensity, suggesting superior charge separation efficiency. This improvement stems from the heterojunction interface between BTO and LFO, which effectively achieves spatial separation of charge carriers, thereby significantly enhancing photocatalytic activity.

[0059] Example 2 This embodiment provides the LaFeO3 / Bi4Ti3O prepared in Example 1. 12 Application of (LFO / BTO) composite material in the degradation of tetracycline (TC). The specific steps of the application are: separately combining single LaFeO3 (LFO) and Bi4Ti3O3. 12 (BTO) and the LaFeO3 / Bi4Ti3O prepared in Example 1 12 The composite photocatalyst was added to a 20 mg / L tetracycline solution to form a mixed system, with a catalyst dosage of 1.6 g / L. The mixed system was magnetically stirred for 30 minutes in the dark, with an initial pH of 8.0, to ensure that the catalyst and pollutant reached adsorption-desorption equilibrium. Subsequently, under continuous stirring, the mixed system was irradiated with visible light from a 300W xenon lamp equipped with a λ > 420 nm filter for 120 minutes to complete the photocatalytic degradation reaction.

[0060] Figure 10 (a) Comparison of the removal effects of LFO, BTO and LFO / BTO composite material on tetracycline. Figure 10 (b) The corresponding reaction kinetics curve; After 30 minutes of dark reaction, the adsorption removal rates of TC by LFO, BTO, and LFO / BTO were 10%, 6%, and 33%, respectively. The LFO / BTO composite material exhibited significantly higher adsorption capacity, which is related to its superior texture properties. As shown in Table S1, the BET specific surface area of ​​LFO / BTO is 20.91 m². 2 / g, pore volume is 0.14cm³ 3 / g, all higher than LFO (15.23m 2 / g) and BTO (10.20m 2 / g). Adsorption reached equilibrium within 30 minutes.

[0061] Table S1 Specific surface area, pore size, and pore volume of materials ; Photocatalytic degradation performance: After 120 minutes of visible light irradiation, the removal rates of TC by BTO, LFO, and LFO / BTO were 44%, 66%, and 95%, respectively. The LFO / BTO composite material exhibited the best photocatalytic performance. The weaker performance of BTO may be attributed to its wide band gap (3.29 eV) and high recombination rate of photogenerated electron-hole pairs.

[0062] Reaction kinetic analysis: based on Figure 10 (b) shows the first-order reaction kinetics fitting results, indicating a reaction rate constant of 0.0230 min for the LFO / BTO composite material. -1 The values ​​were LFO (0.0086 min). -1 ) and BTO (0.0049min -1 The results showed that the LFO and BTO heterojunction structure effectively promoted the separation and migration of photogenerated carriers, thereby significantly improving the photocatalytic performance.

[0063] In this embodiment, the LFO / BTO composite material achieves a TC removal rate (95%) that is superior to or equivalent to that of several previously reported materials. For example, Gan et al. developed a g-C3N4 / BaTiO3 / PVDF photocatalytic-membrane coupling system that achieved a TC removal rate of 90.63%; Zhang et al. constructed an S-type BaTiO3 / g-C3N4 heterojunction that achieved a removal rate of 91.88%. This composite material maintains high performance while having a simpler preparation method and requiring no additional membrane separation or complex synthesis processes.

[0064] Therefore, the LFO / BTO composite material prepared in this invention has excellent adsorption and photocatalytic synergistic performance. Its high efficiency in degrading tetracycline under visible light is mainly attributed to the improved carrier separation efficiency brought about by the heterojunction structure, as well as its superior specific surface area and pore structure.

[0065] Example 3 This embodiment refers to Embodiment 2. The difference between this embodiment and Embodiment 2 is that in this embodiment, the catalyst is added to tetracycline solutions with concentrations of 10, 20, 30, 40, and 50 mg / L to form a mixed system. The catalyst dosage is 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.6 g / L.

[0066] 1. Effect of catalyst dosage like Figure 11As shown in (a), with the catalyst dosage increasing from 0.2 g / L to 1.6 g / L, the TC removal rate increased from 22% to 95%, and the reaction rate constant increased from 0.00149 min. -1 Increased to 0.0230 min -1 ( Figure 11 (b) When the dosage was further increased to 2.0 g / L, the removal rate did not show a significant improvement (96%), which is presumably due to the catalyst overload causing agglomeration, resulting in a reduction of active sites and a light-blocking effect. Therefore, the preferred catalyst dosage is 1.6 g / L.

[0067] 2. Effect of initial TC concentration The effect of different initial TC concentrations (10–50 mg / L) on degradation efficiency was investigated under the conditions of catalyst dosage of 1.6 g / L and reaction time of 120 minutes. Figure 12 As shown in (a), the removal efficiency gradually decreases with increasing TC concentration. When the concentration is below 20 mg / L, the removal rate exceeds 90%; when the concentration rises to 50 mg / L, the removal rate drops to 44%. The reaction rate constant also decreases from 0.0230 min at 10 mg / L. -1 The concentration decreased significantly to 50 mg / L at 0.00351 min. -1 ( Figure 12 b). This phenomenon is attributed to: (1) the limited number of active sites at a fixed catalyst dosage; and (2) the occupation of surface active sites by degradation intermediates. The results show that LFO / BTO exhibits the best removal effect when the TC concentration is not higher than 20 mg / L.

[0068] 3. Effect of solution pH A series of 10 mg / L tetracycline solutions with pH values ​​of 3.0, 5.0, 7.0, 8.0, 9.0, and 11.0 were prepared. Degradation experiments were performed at each pH condition according to the test method described in Example 2. Figure 13 (a) The results showed that the removal rate was highest (95%) at pH 7–8, with a reaction rate constant of 0.023 min. -1 Under these conditions, TC uses TCH. - TC 2- It exists in anionic form and readily adsorbs onto the catalyst surface via electrostatic attraction. Under acidic conditions (pH 3–5), TC mainly exists as TCH3. + The form exists, and Cl - (From hydrochloric acid acidification) may consume •OH to generate ClO•, leading to a decrease in removal rate (approximately 80% at pH 5). Under strongly alkaline conditions (pH 11), the removal rate drops to 68%, with a reaction rate constant of 0.00434 min. -1 Figure 13(b) is attributed to the electrostatic repulsion between TC anions and the negatively charged catalyst surface, which exhibits stable and efficient degradation capabilities over a wide pH range of 5.0–9.0.

[0069] Example 4 This embodiment tested the effects of common water components on the composite material in the degradation of tetracycline (TC). The specific steps are the same as in Example 2. Under optimal conditions (catalyst 1.6 g / L, pH 8, TC 10 mg / L), this embodiment evaluated the effects of inorganic anions (5 mmol / L) and humic acid on the degradation process. NaCl, Na₂SO₄, NaHCO₃, NaNO₂, and NaH₂PO₄ at concentrations of 5 mM were added to simulate the presence of Cl₂. - SO4 2- HCO3 - NO2 - H2PO4 - Coexisting ions and complex water bodies containing humic acid.

[0070] Test results: such as Figure 14 As shown in (a), Cl - With NO2 - It has a slight effect on the removal rate, or even slightly promotes it; H2PO4 - The inhibition effect was strongest, reducing the removal rate to 68%. The anion inhibition order was: H2PO4. - SO4 2- >HCO3 - This may stem from its complexation with metal ions on the catalyst surface, alteration of the band structure, and competition for active sites. The reaction rate trend is consistent with the removal rate. Figure 14 (b)). For example Figure 14 (c) and Figure 14 As shown in (d), low concentrations of HA (4 mg / L) had no significant effect on the removal rate; however, when the concentration increased to 8–16 mg / L, both the removal rate and the reaction rate decreased significantly. HA inhibits the photocatalytic process by shielding the active sites through its light absorption properties and surface functional groups (such as carboxyl and phenolic hydroxyl groups).

[0071] Example 5 This embodiment focuses on the photocatalytic cycle stability test of the composite material prepared in Example 1. To verify the cycle stability of the material, the following experiments were conducted: Test method: An integrated continuous treatment process was adopted, consisting of "photocatalytic reaction (natural light irradiation) - magnetic field separation (0.1-0.3T, separation time 5-10 min) - material regeneration (deionized water washing, reusable more than 5 times)". The separated catalyst can be directly reused for the treatment of the next batch of wastewater after a simple rinse with deionized water. 40 mg of LaFeO3 / Bi4Ti3O2 prepared in Example 1 was added to 25 mL of a 10 mg / L tetracycline solution. 12 Composite material (catalyst concentration 1.6 g / L). First, the mixture was magnetically stirred in the dark for 30 minutes to reach adsorption-desorption equilibrium. Then, under continuous stirring, the mixture was irradiated with a 300 W xenon lamp equipped with a λ>420 nm filter for 120 minutes.

[0072] Cyclic Process: After each photocatalytic reaction, a 0.2T NdFeB permanent magnet was used to adsorb the catalyst onto the outside of the reaction vessel for 5 minutes, separating the catalyst from the solution. After pouring out the supernatant, the catalyst adsorbed on the vessel wall was gently washed with deionized water to remove surface residues. Subsequently, 25 mL of fresh 10 mg / L tetracycline solution was added, and the above dark adsorption and photocatalytic degradation steps were repeated, for a total of 4 cycles.

[0073] Comparative Example: Parallel cyclic testing was performed on traditional N / P co-doped TiO2 materials under the same test conditions.

[0074] Test results: The results are as follows Figure 15 As shown. Figure 15 (a) shows the change in TC removal performance after four cycles. After four cycles, the TC removal rate decreased slightly from the initial 95% to 90%, indicating that its catalytic activity remained good. To further verify the structural stability, we performed XRD characterization on the catalyst after four cycles. Figure 15 (b) The characteristic diffraction peak positions of the composite material did not shift significantly, and the peak intensity did not decrease significantly, proving that its crystal structure remained intact. In summary, this composite material not only has excellent recycling performance but also exhibits good structural stability, providing important support for practical applications. In contrast, the N / P co-doped TiO2 material of the comparative example had a degradation rate of 92% after the first cycle, but after three cycles, the degradation rate dropped sharply to 62%, resulting in severe performance degradation, far inferior to the material of this invention.

[0075] Economic evaluation: Based on the advantages of long-term catalyst stability, low energy consumption of magnetic field separation and the elimination of frequent material replacement, the overall processing cost of this integrated process can be reduced by more than 60% compared with traditional TiO2-based materials that require frequent replacement and are difficult to separate, demonstrating significant economic and engineering application value.

[0076] Example 6 To clarify LaFeO3 / Bi4Ti3O 12 The active species that play a major role in the photocatalytic degradation of tetracycline (TC) by the (LFO / BTO) composite material are analyzed in this embodiment through free radical capture experiments and electron paramagnetic resonance (EPR) tests.

[0077] 1. Free radical capture experiment Under optimal reaction conditions (catalyst dosage 1.6 g / L, initial TC concentration 10 mg / L, pH 8.0), the following scavenging agent was added to the reaction system: p-benzoquinone (BQ) was used to scaveng superoxide radicals (·O2). - ); Disodium ethylenediaminetetraacetate (EDTA-2Na) is used to capture photogenerated holes (h + Ethanol (ETOH) is used to capture hydroxyl radicals (·OH).

[0078] Experimental results are as follows Figure 16 As shown in (a), after the addition of BQ, the TC removal rate decreased slightly from 95% to 93%, indicating that the O2 removal rate decreased. - Its contribution to the degradation process is relatively small. After adding EDTA-2Na or ETOH alone, the TC removal rate decreased to 74% and 82%, respectively, indicating that h... + ·OH is the main active species in the catalytic process.

[0079] 2. Electron paramagnetic resonance analysis To further verify the above results, an EPR test was conducted. Figure 16 (b) shows the EPR spectra of the DMPO-·OH adduct in the dark and after 5 minutes of illumination. A distinct characteristic peak of DMPO-·OH was observed after illumination, indicating the formation of ·OH in the system. Figure 16 (c) is TMPO-h + The EPR spectra of the adduct under the same conditions show that the intensity of the characteristic signal is significantly weakened after illumination compared to the dark state, indicating the presence of a large number of photogenerated holes during the reaction. Conclusion: The free radical capture experiment and EPR test results jointly confirm that the dominant active species in the photocatalytic reaction system described in this invention is the photogenerated hole (h + ) and hydroxyl radicals (·OH), superoxide radicals (·O2) - The effect of [the catalyst] is relatively limited. This conclusion provides experimental evidence for elucidating the photocatalytic reaction mechanism of LFO / BTO composite materials.

[0080] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A LaFeO3 / Bi4Ti3O 12 Composite photocatalyst, characterized in that: The composite photocatalyst is composed of LaFeO3 and Bi4Ti3O 12 The heterostructure is formed through interfacial chemical bonding, with LaFeO3 and Bi4Ti3O4 as the main components. 12 The matched lattice serves as the structural basis.

2. The LaFeO3 / Bi4Ti3O3 according to claim 1 12 Composite photocatalyst, characterized in that: LaFeO3 and Bi4Ti3O 12 The molar ratio is 2.2:

1.

3. The LaFeO3 / Bi4Ti3O3 according to claim 1 12 Composite photocatalyst, characterized in that: LaFeO3 is an orthorhombic crystal system, PDF#37-1493; Bi4Ti3O 12 It belongs to the tetragonal crystal system, PDF#35-0795.

4. The LaFeO3 / Bi4Ti3O3 according to any one of claims 1-3 12 A method for preparing a composite photocatalyst, characterized in that, Includes the following steps: Step S1: Hydrothermal synthesis of LaFeO3; Step S2: Deposit LaFeO3 nanoparticles onto Bi4Ti3O4 using a hydrothermal method. 12 Surface preparation of LaFeO3 / Bi4Ti3O 12 Composite materials.

5. The preparation method according to claim 4, characterized in that, The specific steps of step S1 are as follows: Step S11: Take La(NO3)3·6H2O and Fe(NO3)3·9H2O, add them to a mixed solvent composed of ethylene glycol and ethanol, and stir the resulting mixture with a magnetic stirrer to form a homogeneous precursor solution. Step S12: Transfer the precursor solution obtained in step S11 to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and react at 170-190℃ for 20-28 hours. Step S13: After the reaction is complete, allow the mixture to cool naturally to room temperature, collect the precipitate and wash it; dry the washed product in an oven at 60-80℃ for 6-12 hours to obtain the LaFeO3 powder precursor. Step S14: Place the powdered precursor obtained in step S13 into a muffle furnace and calcine it in an air atmosphere at 750-850℃ for 3-5 hours to obtain the final product LaFeO3 nanoparticles.

6. The preparation method according to claim 5, characterized in that, In step S11, the molar ratio of La(NO3)3·6H2O and Fe(NO3)3·9H2O is 0.9:1-1.1:1; the volume of the mixed solvent composed of ethylene glycol and ethanol is 30-50 mL, and the volume ratio of ethylene glycol to ethanol is 8.5:1.5-9.5:0.5; the magnetic stirrer is stirred at a speed of 400-700 rpm for 50-90 minutes; in step S13, the precipitate is washed 6-8 times alternately with 20-40 mL of deionized water and 20-40 mL of ethanol as washing agents.

7. The preparation method according to claim 4, characterized in that, The specific steps of step S2 are as follows: Step S21: Place C 16 H 36 Add O4Ti to 25-35 mL of NaOH solution and stir on a magnetic stirrer at 300-600 rpm for 20-40 minutes. Step S22: Add Bi(NO3)3·5H2O to the above solution and continue stirring for 20-40 minutes. The resulting solution is denoted as solution A. Step S23: Add the LaFeO3 nanoparticle solution obtained in step S14 with a concentration of 10.0-12.5 g / L to solution A, and then stir at a speed of 400-700 rpm for 50-90 minutes. Step S24: Transfer the mixed solution obtained in step S23 to a hydrothermal reactor with an 80-120 mL polytetrafluoroethylene liner and react at 170-190 °C for 18-24 hours. Step S25: Allow the reactor to cool naturally to room temperature; collect and wash the precipitate; then dry the product at 60-80℃ for 8-16 hours to finally obtain LaFeO3 / Bi4Ti3O 12 Composite materials.

8. The preparation method according to claim 7, characterized in that, In step S21, the concentration of the NaOH solution is 2.5-3.5 mol / L; C 16 H 36 The amount of O4Ti used is 0.7-1.0 mL; the amount of Bi(NO3)3·5H2O used in step S22 is 1.4-1.8 g; in step S25, the precipitate is washed 3-5 times alternately with 30-50 mL of deionized water and 30-50 mL of ethanol as washing agents.

9. The LaFeO3 / Bi4Ti3O3 according to any one of claims 1-8 12 Application of composite photocatalysts in tetracycline degradation.

10. The application according to claim 9, characterized in that, The specific steps of the application are: to use the LaFeO3 / Bi4Ti3O 12 The composite photocatalyst is added to a tetracycline solution with a concentration of 10-80 mg / L to form a mixed system. The mixed system is magnetically stirred in the dark for 20-60 minutes. Under continuous stirring, a 300W xenon lamp equipped with a λ>420nm filter is used to provide visible light to the mixed system for 60-150 minutes to complete the photocatalytic degradation reaction.

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