An LDH@MIL-Fe core-shell composite material, a preparation method and application thereof

Abstract

This invention relates to the field of environmental pollution control and functional materials technology, and discloses an LDH@MIL-Fe core-shell composite material, its preparation method, and its application. The LDH@MIL-Fe core-shell composite material uses LDH as the core and MIL-Fe as the shell; the general formula of LDH is [M... 2+ 1‑x M 3+ x (OH)2] x+ (A n‑ ) x / n •mH2O; the MIL-Fe is Fe 3+ The MIL-Fe core serves as the metal center, and its organic ligands are one or more of terephthalic acid, trimesic acid, 2-aminoterephthalic acid, and fumaric acid. This invention constructs an LDH@MIL-Fe core-shell composite material, forming a heterogeneous structure with LDH as the core and MIL-Fe as the shell, achieving interfacial synergistic effects between LDH and MIL-Fe. Through the synergistic effect of photocatalysis and persulfate activation, it achieves highly efficient degradation of organic pollutants and exhibits good stability and recyclability. Even after multiple cycles, the material maintains a high degradation efficiency.

Description

Technical Field

[0001] This invention relates to the field of environmental pollution control and functional materials technology, and in particular to an LDH@MIL-Fe core-shell composite material, its preparation method, and its application. Background Technology

[0002] With rapid industrialization and urbanization, large quantities of recalcitrant organic pollutants, such as antibiotics, dyes, and perfluorinated compounds, are entering water bodies. These pollutants are typically characterized by high toxicity, persistence, and bioaccumulation, making them difficult to remove effectively using traditional water treatment methods. Conventional treatment technologies, such as adsorption, coagulation, and biodegradation, have limited removal efficiency for these pollutants and cannot meet increasingly stringent discharge requirements. Therefore, developing efficient pollutant removal technologies is of great significance.

[0003] Advanced oxidation technologies (AOCs) have garnered significant attention in water treatment due to their ability to rapidly degrade pollutants by generating highly reactive species with strong oxidizing capabilities. Among these, photocatalytic activation of persulfate systems utilizes photogenerated electrons and holes to further activate persulfate, generating sulfate radicals and other reactive species, thereby degrading organic pollutants. This system exhibits a high redox potential, a long half-life, and a wide applicable pH range, thus demonstrating promising application prospects. However, existing photocatalytic activation of persulfate systems still face certain limitations in practical applications.

[0004] Traditional photocatalytic materials typically have large band gaps, enabling them to respond only to ultraviolet light and resulting in low solar energy utilization efficiency. In the absence of light, photocatalytic reactions are difficult to occur, preventing the system from operating continuously. Furthermore, even with material modification to extend the visible light response range, the problems of rapid photogenerated carrier recombination rates and low quantum efficiency persist, thus limiting the activation efficiency of persulfate.

[0005] In the activation of persulfate, commonly used iron-based materials rely on Fe. 3+ / Fe 2+ The activation process is achieved through cyclical processes. Taking iron-based metal-organic frameworks as an example, they possess a large specific surface area and abundant active sites, but exhibit poor stability in aqueous solutions, readily undergoing ligand hydrolysis, leading to Fe... 3+ Leaching not only reduces the recyclability of materials but may also cause secondary pollution. Simultaneously, Fe... 3+ To Fe 2+ The conversion rate is slow, and there is a cycle blockage, which in turn affects the continuous activation ability of persulfate.

[0006] Layered bimetallic hydroxides possess a layered structure and good structural tunability, giving them a certain foundation for application in photocatalysis. Their layered structure helps suppress recombination of photogenerated carriers, but their visible light absorption is weak, and they lack efficient active sites for activating persulfate. Therefore, when used alone, it is difficult to achieve synergistic enhancement of photocatalysis and persulfate activation.

[0007] Furthermore, existing photocatalytic-persulfate systems face insufficient resistance to interference in real-world water environments. Anions and other interfering substances commonly found in water readily react with active species, reducing catalytic efficiency; and the system's mineralization capacity for complex, recalcitrant organic pollutants still needs improvement. Simultaneously, the preparation of some composite catalytic materials requires high temperature and pressure or complex template agents, resulting in demanding process conditions, high preparation costs, and hindering large-scale applications.

[0008] In recent years, core-shell composite materials have become an important approach to improving material properties due to their ability to combine the advantages of different components and produce synergistic effects. For example, constructing a composite structure using layered bimetallic hydroxides as the core material and metal-organic frameworks as the shell can, on the one hand, utilize the layered structure to suppress photogenerated carrier recombination, and on the other hand, the shell provides active sites to promote the activation of persulfate. Simultaneously, the core structure provides a certain degree of protection to the shell, contributing to improved material stability. Furthermore, the core-shell interface may promote electron transfer and accelerate Fe... 3+ / Fe 2+ This cycle improves synergistic catalytic efficiency.

[0009] However, existing research on the use of LDH@MIL-Fe core-shell structured materials for photocatalytic activation of persulfate systems is still limited, and problems exist such as weak interfacial bonding, unclear synergistic mechanisms, and insufficient catalytic activity under no-light conditions. Therefore, it is necessary to develop a structurally stable LDH@MIL-Fe core-shell composite material with significant interfacial synergistic effects and the ability to achieve effective degradation under different conditions, in order to improve the application effect of photocatalytic activation of persulfate systems in practical water treatment. Summary of the Invention

[0010] The purpose of this invention is to address the shortcomings of existing technologies by proposing an LDH@MIL-Fe core-shell composite material, its preparation method, and its applications.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] An LDH@MIL-Fe core-shell composite material, wherein the LDH@MIL-Fe core-shell composite material has LDH as the core and MIL-Fe as the shell; the general formula of LDH is [M 2+ 1-x M3+ x (OH)2] x+ (A n- ) x / n •mH2O, where M 2+ Zn 2+ Co 2+ Ni 2+ One or more of them, M 3+ For Al 3+ Fe 3+ One or more of them, A n- NO 3- Cl - CO3 2- One or more of the following, 0.2≤x≤0.33, 0.5≤m≤4; the MIL-Fe is Fe 3+ The MIL-Fe is a metal center, and its organic ligand is one or more of terephthalic acid, pyromellitic acid, 2-aminoterephthalic acid, and fumaric acid.

[0013] Preferably, the organic ligand of the MIL-Fe is fumaric acid.

[0014] Preferably, the mass ratio of LDH to MIL-Fe in the LDH@MIL-Fe core-shell composite material is 1:1.3-1:2.

[0015] Preferably, the LDH has a particle size of 50-200 nm, an interlayer spacing of 0.7-0.8 nm, and a morphology of flake, rod, or flower.

[0016] A method for preparing the LDH@MIL-Fe core-shell composite material as described above includes the following steps:

[0017] Step 1: Dissolve stannous chloride dihydrate in ethylene glycol to obtain solution A; dissolve aluminum sulfate octadechydrate in deionized water to obtain solution B; dissolve zinc sulfate heptahydrate in deionized water to obtain solution C; dissolve urea in deionized water to obtain solution D; mix solutions A, B, C, and D, and then ultrasonically and magnetically stir to obtain mixed solution E; transfer mixed solution E to a polytetrafluoroethylene-lined reactor and allow it to stand at 200°C for hydrothermal reaction for 24 h; after the reaction, the first precipitate obtained is centrifuged, washed, and dried to obtain LDH;

[0018] Step 2: Dissolve fumaric acid in ethanol, and after ultrasonic treatment and magnetic stirring, add LDH obtained in Step 1. Then, ultrasonic treatment and magnetic stirring are performed again to allow LDH and fumaric acid to be fully adsorbed and mixed to obtain solution F. Dissolve ferric chloride hexahydrate in deionized water, and after ultrasonic treatment and magnetic stirring, obtain solution G. Slowly add solution G dropwise to solution F under continuous magnetic stirring, and continue magnetic stirring for 24 h. After the reaction is completed, the second precipitate obtained is centrifuged, washed and dried to obtain LDH@MIL-Fe core-shell composite material.

[0019] Preferably, in step 1, the precipitate obtained after the reaction is washed with anhydrous ethanol and deionized water and then dried at 60°C for 12 h.

[0020] Preferably, in step 2, the second precipitate obtained after the reaction is completed is washed with anhydrous ethanol and deionized water and then dried at 70°C for 12 h.

[0021] Preferably, the LDH is tin-doped zinc-aluminum hydrotalcite, and the LDH has a hydroxyl-bridged interface with MIL-Fe.

[0022] Such as the application of the LDH@MIL-Fe core-shell composite material mentioned above in the photocatalytic activation of persulfate for the degradation of organic pollutants.

[0023] Preferably, the persulfate is potassium persulfate or sodium persulfate.

[0024] Preferably, the organic pollutant is an antibiotic, dye, or persistent organic pollutant.

[0025] Preferably, the antibiotic is tetracycline.

[0026] Preferably, in the application, the core-shell composite material is activated under light irradiation to degrade organic pollutants using persulfate.

[0027] Preferably, in the application, the core-shell composite material is activated under dark conditions to degrade organic pollutants using persulfate.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention constructs an LDH@MIL-Fe core-shell composite material, forming a heterostructure with LDH as the core and MIL-Fe as the shell, thereby achieving interfacial synergy between LDH and MIL-Fe. In terms of composition, by controlling the mass ratio of LDH to MIL-Fe to be 1:1.3-1:2 and forming interfacial characteristic structures, a foundation is provided at the material level for subsequent catalytic reactions.

[0030] This invention achieves efficient degradation of organic pollutants through the synergistic effect of photocatalysis and persulfate activation. The LDH@MIL-Fe core-shell composite material in this synergistic system effectively improves degradation efficiency, exhibiting a significantly higher degradation rate compared to LDH alone. In treating a 20 mg / L tetracycline aqueous solution, it achieves a 95.9% removal rate within 30 minutes, demonstrating high catalytic activity.

[0031] The material described in this invention exhibits good stability and recyclability. Even after multiple cycles, the material maintains a high degradation efficiency; after five cycles, its degradation efficiency remains above 87%, indicating good stability during long-term operation.

[0032] The LDH@MIL-Fe core-shell composite material described in this invention can effectively degrade organic pollutants under both light and dark conditions. Even in the dark, high degradation efficiency can still be achieved through the activation effect of persulfate; for example, when treating tetracycline, its degradation efficiency can remain above 80%, demonstrating the material's applicability under different environmental conditions.

[0033] This invention achieves synergistic enhancement of photocatalysis and persulfate activation through a core-shell structure design. The LDH core inhibits photogenerated carrier recombination, while the MIL-Fe shell provides active sites and promotes electron transfer through interfacial interactions, thereby improving the activation efficiency of persulfate and enhancing the generation of active species.

[0034] This invention utilizes the protective effect of the LDH core on the MIL-Fe shell, which helps reduce the hydrolysis of MIL-Fe and Fe in the aqueous environment. 3+ The leaching process reduces the risk of secondary pollution, while also enhancing the structural and mechanical stability of the material and extending its service life.

[0035] The material described in this invention exhibits a certain degree of resistance to interference in complex aquatic environments. Through a synergistic catalytic mechanism, it enhances the selectivity of active species and reduces the impact of common anions and other interfering substances on the degradation process, thereby improving the treatment efficiency of recalcitrant organic pollutants in actual water bodies.

[0036] This invention also provides a method for preparing LDH@MIL-Fe core-shell composite materials that is relatively simple, low-cost, and easy to scale up. This method does not require high temperature and high pressure or complex template agents, the reaction conditions are relatively mild, and the operation process is simple, which is conducive to practical application.

[0037] In summary, this invention achieves synergistic enhancement of photocatalysis and persulfate activation by constructing an LDH@MIL-Fe core-shell composite material, which has good application prospects in the field of organic pollutant degradation. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the morphological characteristics of LDH;

[0039] Figure 2 A schematic diagram showing the morphological characteristics of the LDH@MIL-Fe core-shell composite material;

[0040] Figure 3 A schematic diagram showing the morphological characteristics of MIL-Fe;

[0041] Figure 4 A schematic diagram comparing the ability of LDH, MIL-Fe and LDH@MIL-Fe core-shell composites to degrade tetracycline under photocatalytically activated persulfate conditions;

[0042] Figure 5 A comparative schematic diagram showing the ability of LDH, MIL-Fe and LDH@MIL-Fe core-shell composite materials to activate persulfate and degrade tetracycline under dark conditions;

[0043] Figure 6 A schematic diagram illustrating the effect of different initial persulfate concentrations on tetracycline degradation efficiency;

[0044] Figure 7 This is a schematic diagram illustrating the effect of common anions on the photocatalytic activation of persulfate degradation of tetracycline in LDH@MIL-Fe core-shell composite materials.

[0045] Figure 8 This is a schematic diagram of the free radical capture experimental results of LDH@MIL-Fe core-shell composite material in a photocatalytically activated persulfate degradation system for tetracycline.

[0046] Figure 9 This is a schematic diagram illustrating the cyclic stability of the LDH@MIL-Fe core-shell composite material. Detailed Implementation

[0047] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the technical solution of this invention is described in detail below, but this should not be construed as limiting the scope of implementation of this invention. Unless otherwise specified, the methods used in this invention are conventional methods in this technical field. In this invention, materials, reagents, or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0048] In one embodiment, the present invention proposes an LDH@MIL-Fe core-shell composite material, wherein the LDH@MIL-Fe core-shell composite material has LDH as the core and MIL-Fe as the shell; the general formula of LDH is [M 2+ 1-x M 3+x (OH)2] x+ (A n- ) x / n •mH2O, where M 2+ Zn 2+ Co 2+ Ni 2+ One or more of them, M 3+ For Al 3+ Fe 3+ One or more of them, A n- NO 3- Cl - CO3 2- One or more of the following, 0.2≤x≤0.33, 0.5≤m≤4; the MIL-Fe is Fe 3+ The MIL-Fe is a metal center, and its organic ligand is one or more of terephthalic acid, pyromellitic acid, 2-aminoterephthalic acid, and fumaric acid.

[0049] In a preferred embodiment of the present invention, the organic ligand of the MIL-Fe is fumaric acid.

[0050] In a preferred embodiment of the present invention, the mass ratio of LDH to MIL-Fe in the LDH@MIL-Fe core-shell composite material is 1:1.3-1:2.

[0051] In a preferred embodiment of the present invention, the LDH has a particle size of 50-200 nm, an interlayer spacing of 0.7-0.8 nm, and a morphology of flake, rod, or flower.

[0052] In one embodiment, the present invention provides a method for preparing the LDH@MIL-Fe core-shell composite material as described above, comprising the following steps:

[0053] Step 1: Dissolve stannous chloride dihydrate in ethylene glycol to obtain solution A; dissolve aluminum sulfate octadechydrate in deionized water to obtain solution B; dissolve zinc sulfate heptahydrate in deionized water to obtain solution C; dissolve urea in deionized water to obtain solution D; mix solutions A, B, C, and D, and then ultrasonically and magnetically stir to obtain mixed solution E; transfer mixed solution E to a polytetrafluoroethylene-lined reactor and allow it to stand at 200°C for hydrothermal reaction for 24 h; after the reaction, the first precipitate obtained is centrifuged, washed, and dried to obtain LDH;

[0054] Step 2: Dissolve fumaric acid in ethanol, and after ultrasonic treatment and magnetic stirring, add LDH obtained in Step 1. Then, ultrasonic treatment and magnetic stirring are performed again to allow LDH and fumaric acid to be fully adsorbed and mixed to obtain solution F. Dissolve ferric chloride hexahydrate in deionized water, and after ultrasonic treatment and magnetic stirring, obtain solution G. Slowly add solution G dropwise to solution F under continuous magnetic stirring, and continue magnetic stirring for 24 h. After the reaction is completed, the second precipitate obtained is centrifuged, washed and dried to obtain LDH@MIL-Fe core-shell composite material.

[0055] In a preferred embodiment of the present invention, in step 1, the precipitate obtained after the reaction is washed with anhydrous ethanol and deionized water and then dried at 60°C for 12 h.

[0056] In a preferred embodiment of the present invention, in step 2, the second precipitate obtained after the reaction is completed is washed with anhydrous ethanol and deionized water and then dried at 70°C for 12 h.

[0057] In a preferred embodiment of the present invention, the LDH is tin-doped zinc-aluminum hydrotalcite, and the LDH and MIL-Fe have hydroxyl-bridged interface features.

[0058] In one embodiment, the present invention proposes the application of the LDH@MIL-Fe core-shell composite material as described above in the photocatalytic activation of persulfate degradation of organic pollutants.

[0059] In a preferred embodiment of the present invention, the persulfate is potassium persulfate or sodium persulfate.

[0060] In a preferred embodiment of the present invention, the organic pollutant is an antibiotic, dye, or persistent organic pollutant.

[0061] In a preferred embodiment of the present invention, the antibiotic is tetracycline.

[0062] In a preferred embodiment of the present invention, the core-shell composite material is activated by persulfate degradation of organic pollutants under light irradiation.

[0063] In a preferred embodiment of the present invention, the core-shell composite material is activated under dark conditions to degrade organic pollutants using persulfate.

[0064] The LDH@MIL-Fe core-shell composite material of the present invention adopts a core-shell structure design, with LDH as the core and MIL-Fe as the shell, and the two form a synergistic catalytic system through interfacial interaction.

[0065] In photocatalysis, the LDH core has a layered structure, which helps suppress the recombination of photogenerated carriers. Simultaneously, by controlling the composition of metal ions in the LDH, the band gap of the material can be adjusted, thereby expanding its photoresponse range. The MIL-Fe shell exhibits excellent visible light absorption, and its porous structure enhances light scattering, improving light energy utilization efficiency.

[0066] During the persulfate activation process, Fe in the MIL-Fe shell 3+ The active site can directly participate in the activation of persulfate, generating sulfate radicals. Simultaneously, photogenerated electrons produced by the LDH nucleus under light conditions can convert Fe... 3+ Reduced to Fe 2+ This accelerates Fe 3+ / Fe 2+ The cycle further promotes the activation of persulfate, generating reactive species such as hydroxyl radicals, sulfate radicals, and singlet oxygen.

[0067] Through the interface formed by the core-shell structure described above, an electron transport channel can be formed between the LDH core and the MIL-Fe shell, promoting the electron transfer process, suppressing the recombination of photogenerated carriers, and accelerating the Fe... 3+ / Fe 2+ Cyclic reactions are achieved to synergistically enhance photocatalysis and persulfate activation. Furthermore, the layered structure of the LDH core provides some protection to the MIL-Fe shell, helping to reduce its hydrolysis in aqueous solution and Fe... 3+ The dissolution of LDH improves the structural stability of the material. Furthermore, LDH and Mil-Fe form a bonded structure through interfacial interactions.

[0068] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0069] Example 1: All required chemical reagents were of analytical grade. Among them, stannous chloride dihydrate (SnCl2·2H2O), aluminum sulfate octadechydrate (Al2(SO4)3·18H2O), zinc sulfate heptahydrate (ZnSO4·7H2O), urea (CH4N2O), ethylene glycol, fumaric acid, and anhydrous ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd., ferric chloride hexahydrate (FeCl3·6H2O) was purchased from Tianjin Damao Chemical Reagent Partnership (Limited Partnership), and tetracycline (TCH) was purchased from Sangon Biotech (Shanghai) Co., Ltd. All experiments used deionized water.

[0070] First, weigh a precise mass of analytical grade stannous chloride dihydrate solid using a precise balance, ensuring accuracy. Add the weighed solid to a clean beaker, add an appropriate amount of ethylene glycol as a solvent, and gently stir with a glass rod until the solid is completely dissolved. During the dissolution process, ensure no solid residue remains to guarantee accurate solution concentration. After complete dissolution, transfer the solution to a 10 mL volumetric flask, and wash the beaker several times with ethylene glycol, transferring the washings to the volumetric flask to ensure complete solute transfer. Then, dilute to the mark with ethylene glycol, shake thoroughly to ensure homogeneity, and obtain a clear solution with a concentration of 0.75 mol / L, labeled as solution A.

[0071] Using deionized water as the solvent, prepare a 0.37 mol / L aqueous solution of aluminum sulfate octahydrate in a 100 mL volumetric flask. Weigh an appropriate amount of aluminum sulfate octahydrate solid into a beaker, add a small amount of deionized water, and stir with a glass rod to gradually dissolve it. To accelerate complete dissolution, sonication can be performed appropriately. After complete dissolution, transfer the solution to a 100 mL volumetric flask, and wash the beaker and glass rod several times with deionized water. Transfer the washings to the volumetric flask as well, and then dilute to the mark with deionized water. Shake thoroughly to obtain solution B.

[0072] Following the same method, accurately weigh an appropriate amount of zinc sulfate heptahydrate crystals and add them to a beaker. Add an appropriate amount of deionized water and stir until completely dissolved. Observe for any undissolved solid particles during the dissolution process to ensure accurate solution concentration. After complete dissolution, transfer the solution to a 100 mL volumetric flask and wash the beaker and glass rod several times with deionized water. Transfer the washings to the volumetric flask as well. Finally, dilute to the mark with deionized water and shake thoroughly to obtain 100 mL of a colorless and transparent aqueous solution with a concentration of 3.2 mol / L, labeled as solution C.

[0073] Prepare a urea solution in another 100 mL volumetric flask. First, dissolve the urea in a beaker with a small amount of deionized water. After ensuring that the urea is completely dissolved, transfer the solution to the volumetric flask. Continue to add deionized water to near the mark, and then slowly add deionized water to the mark using a dropper. Shake thoroughly to mix the solution evenly, and you will get a urea solution with a concentration of 3.8 mol / L, labeled as solution D.

[0074] Take 10 mL of solution A, 15 mL of solution B, 8.5 mL of solution C, and 39 mL of solution D, and add them sequentially to a 100 mL beaker. After sonication for 10 min and stirring for 10 min, a mixed solution E is obtained. Transfer mixed solution E to a 100 mL polytetrafluoroethylene-lined reactor and place it in a muffle furnace. Allow it to stand at 200 °C for 24 h for hydrothermal reaction. After the reaction, allow it to cool naturally to room temperature. Remove the supernatant and transfer the precipitate to a 50 mL centrifuge tube. Centrifuge at 3000 × g for 5 min to remove the supernatant. Then add 30 mL of anhydrous ethanol and wash with shaking for 5 min, followed by centrifugation at 3000 × g for 5 min. Repeat the above process of washing with deionized water (shaking for 5 min) and centrifugation (3000 × g, 5 min) 3-5 times. Finally, the precipitate was dried in a 60℃ electric heating oven for 12 h to obtain tin-doped zinc aluminum hydrotalcite (Sn:Zn:Al=3.6:1.47:0.1), labeled as LDH, and stored at room temperature in the dark for later use.

[0075] 115 mg of fumaric acid was dissolved in 50 mL of ethanol, sonicated for 5 min, and magnetically stirred for 10 min. Then, 200 mg of the prepared LDH was added, and sonication was continued for 15 min, followed by magnetic stirring for 30 min to ensure complete adsorption and mixing of LDH and fumaric acid, yielding solution F. 270 mg of ferric chloride hexahydrate was dissolved in 50 mL of deionized water, sonicated for 5 min, and magnetically stirred for 5 min, yielding solution G. Solution G was then slowly added dropwise to solution F under continuous magnetic stirring, and the reaction was continued with magnetic stirring for 24 h.

[0076] After the reaction, the mixture was allowed to settle naturally for 30 min. The supernatant was removed, and the precipitate was transferred to a 50 mL centrifuge tube and centrifuged at 3000×g for 5 min. Subsequently, the mixture was washed sequentially with anhydrous ethanol and deionized water, shaking for 5 min each time and centrifuged at 3000×g for 5 min. The final precipitate was transferred to a 70℃ electrically heated drying oven and dried for 12 h. The resulting LDH@MIL-Fe core-shell composite material was then stored at room temperature for later use. Furthermore, following the above material preparation procedure, pure MIL-Fe material can be prepared without the addition of LDH.

[0077] The morphology of LDH, LDH@MIL-Fe core-shell composite material and MIL-Fe prepared in Example 1 was characterized and analyzed.

[0078] The prepared LDH exhibits a typical layered bimetallic hydroxide morphology, appearing as irregular plate-like and rod-like aggregates with relatively rough edges. A distinct layered stacking structure is observed on the surface, and the overall morphology is loose and porous. Figure 1 As shown.

[0079] The LDH@MIL-Fe core-shell composite material exhibits the morphology of the composite material after loading MIL-Fe onto the LDH surface. Fine MIL-Fe particles are observed to be uniformly distributed on the lamellar structure of the LDH substrate, forming a core-shell composite structure. This composite material maintains the basic framework of the LDH, while its surface roughness is significantly increased, and the bonding between particles is relatively tight, indicating that MIL-Fe was successfully loaded onto the LDH surface. Figure 2 As shown.

[0080] In contrast, MIL-Fe exhibits typical morphological characteristics of metal-organic framework materials, displaying a relatively regular bulk crystal structure, uniform particle size, smooth surface, clear crystal edges, and good particle dispersion, exhibiting polyhedral crystal structure characteristics, such as... Figure 3 As shown.

[0081] The above results indicate that the LDH@MIL-Fe core-shell composite material combines the structural features of both LDH and MIL-Fe materials, which is beneficial for providing more active sites and maintaining good structural stability.

[0082] In the performance test of photocatalytic activation of persulfate for the degradation of organic pollutants, a 300 W xenon lamp light source equipped with a <420 nm filter was used for irradiation. This xenon lamp light source was purchased from Beijing PLS-SXE300+UV Technology Co., Ltd. This filter allows light in the wavelength range of 420 nm to 780 nm to pass through. The LDH, MIL-Fe, and LDH@MIL-Fe core-shell composite materials prepared in Example 1 were dispersed in a system containing persulfate, and the degradation effect on tetracycline in aqueous solution was evaluated.

[0083] In a typical experiment, 100 mL of a 20 mg / L tetracycline aqueous solution was added to a photocatalytic reactor, along with 10 mg of photocatalyst and 0.2 mM persulfate. During the photocatalytic reaction, 1 mL of the suspension was taken at regular intervals, filtered through a 0.22 μm filter membrane, and immediately transferred to a liquid chromatography vial containing methanol quencher. The tetracycline concentration was then detected using high-performance liquid chromatography (HPLC). To ensure the reliability of the experimental results, all experiments were repeated three times.

[0084] The prepared LDH, MIL-Fe, and LDH@MIL-Fe core-shell composite materials were used to treat tetracycline wastewater, and the experimental results are as follows: Figure 4 As shown, in a 100 mL, 20 mg / L tetracycline system, after 30 min of reaction, the efficiencies of LDH, MIL-Fe, and LDH@MIL-Fe core-shell composite materials in activating persulfate for tetracycline degradation under visible light were 62%, 70.6%, and 95.9%, respectively. In contrast, in a system with only 0.2 mM persulfate, the degradation efficiency after 30 min of irradiation was 60.7%. These results indicate that the LDH@MIL-Fe core-shell composite material exhibits good synergistic catalytic performance in the photocatalytic activation of persulfate degradation systems.

[0085] Furthermore, the degradation effect of the prepared materials on tetracycline was investigated under dark conditions. LDH, MIL-Fe, and LDH@MIL-Fe core-shell composites were used in tetracycline degradation experiments under dark conditions. The experimental results are as follows: Figure 5 As shown, after 30 min of reaction, the degradation efficiencies of LDH, MIL-Fe, and LDH@MIL-Fe core-shell composite materials for 20 mg / L tetracycline were 61.5%, 64.5%, and 80%, respectively. These results indicate that the LDH@MIL-Fe core-shell composite material still exhibits good pollutant degradation ability under dark conditions, which is beneficial for improving the applicability of the degradation system in practical applications.

[0086] The effect of different initial persulfate concentrations on the photocatalytic activation efficiency of LDH@MIL-Fe core-shell composites for tetracycline degradation by persulfate was further investigated. Experimental results are as follows: Figure 6 As shown, the tetracycline degradation efficiency significantly improved when the persulfate concentration increased from 0.1 mM to 0.2 mM. Further increases in concentration to 0.3 mM and 0.4 mM accelerated the degradation rate, but the final degradation efficiency remained relatively similar to that at 0.2 mM. These results demonstrate that rapid tetracycline degradation can be achieved even at relatively low persulfate concentrations, showcasing economic efficiency.

[0087] Anions commonly found in natural water bodies may influence the photocatalytic activation of persulfate degradation systems. Cl- was selected. - SO4 2- HCO3 - and PO4 3- As a representative anion, its effect on the degradation system of LDH@MIL-Fe core-shell composite material was investigated. Figure 7The study demonstrated that, under the conditions of the aforementioned anions, the LDH@MIL-Fe core-shell composite material treated 100 mL and 20 mg / L tetracycline solutions with degradation efficiencies of 97.1%, 93.9%, 95.5%, and 87.2%, respectively. The results indicate that the material maintains good degradation performance under different anion conditions.

[0088] To further clarify the mechanism of tetracycline degradation by the LDH@MIL-Fe core-shell composite material in the photocatalytic activation of the persulfate system, free radical scavenging experiments were conducted. p-benzoquinone was added to the system as a superoxide radical scavenger, triethanolamine as a hole scavenger, methanol as a hydroxyl radical and sulfate radical scavenger, tert-butanol as a hydroxyl radical scavenger, and L-histidine as a singlet oxygen scavenger, respectively. The experimental results are as follows: Figure 8 As shown, after adding the aforementioned scavenging agents, the degradation efficiency of tetracycline decreased to 76.7%, 44.9%, 66.9%, 91.2%, and 95.9%, respectively. The addition of triethanolamine and p-benzoquinone significantly reduced the degradation efficiency, indicating that superoxide radicals and holes are the main reactive species in the system. The addition of methanol further inhibited the degradation efficiency, demonstrating the important role of sulfate radicals in the reaction. These results indicate that the key reactive species in this system include superoxide radicals, holes, and sulfate radicals.

[0089] To evaluate the stability of the prepared LDH@MIL-Fe core-shell composite material during recycling, cyclic experiments were conducted under the same experimental conditions, such as... Figure 9 As shown in the figure. After each reaction, the used material was recovered, washed, dried, and 10 mg was weighed again for the next round of reaction. It was added to 100 mL of a 20 mg / L tetracycline solution for photocatalytic degradation testing. The experimental results showed that after five consecutive cycles, the tetracycline degradation efficiency of the LDH@MIL-Fe core-shell composite material remained above 87% in the fifth experiment. The slight decrease in degradation efficiency may be related to the residue of some intermediate products on the material surface, which may have a certain impact on the active sites. Overall, the LDH@MIL-Fe core-shell composite material exhibits good cycling stability.

[0090] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An LDH@MIL-Fe core-shell composite material, characterized in that, The LDH@MIL-Fe core-shell composite material uses LDH as the core and MIL-Fe as the shell; the general formula of LDH is [M 2+ 1-x M 3+ x (OH)2] x+ (A n- ) x / n •mH2O, where M 2+ Zn 2+ Co 2+ Ni 2+ One or more of them, M 3+ For Al 3+ Fe 3+ One or more of them, A n- NO 3- Cl - CO3 2- One or more of the following, 0.2≤x≤0.33, 0.5≤m≤4; The MIL-Fe uses Fe 3+ It is a metal center, and its organic ligands are one or more of terephthalic acid, pyromellitic acid, 2-aminoterephthalic acid, and fumaric acid.

2. The LDH@MIL-Fe core-shell composite material according to claim 1, characterized in that, The mass ratio of LDH to MIL-Fe in the LDH@MIL-Fe core-shell composite material is 1:1.3-1:

2.

3. The LDH@MIL-Fe core-shell composite material according to claim 1, characterized in that, The LDH has a particle size of 50-200 nm, an interlayer spacing of 0.7-0.8 nm, and a morphology of flake, rod, or flower.

4. A method for preparing the LDH@MIL-Fe core-shell composite material as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Dissolve stannous chloride dihydrate in ethylene glycol to obtain solution A; dissolve aluminum sulfate octadechydrate in deionized water to obtain solution B; dissolve zinc sulfate heptahydrate in deionized water to obtain solution C; Dissolve urea in deionized water to obtain solution D; Solutions A, B, C, and D are mixed, and then subjected to ultrasonic treatment and stirring to obtain mixed solution E; The mixed solution E was transferred to a reaction vessel for static hydrothermal reaction. After the reaction was completed, the first precipitate was centrifuged, washed and dried to obtain LDH. Step 2: Dissolve the organic ligand in ethanol, sonicate and stir, then add the LDH obtained in Step 1, sonicate and stir again to fully adsorb and mix the LDH with the organic ligand to obtain solution F; Ferric chloride hexahydrate was dissolved in deionized water, and the solution was obtained by ultrasonic treatment and stirring. Add solution G dropwise into solution F under continuous stirring, and continue stirring to react; After the reaction was completed, the second precipitate was centrifuged, washed and dried to obtain the LDH@MIL-Fe core-shell composite material.

5. The preparation method according to claim 4, characterized in that, In step 1, the mixed solution E is transferred to a reaction vessel and allowed to stand at 200°C for hydrothermal reaction for 24 h; after the reaction is completed, the first precipitate is washed with anhydrous ethanol and deionized water and then dried at 60°C for 12 h.

6. The preparation method according to claim 4, characterized in that, In step 2, solution G is added dropwise to solution F under continuous stirring, and the reaction is continued for 24 h. After the reaction is completed, the second precipitate is washed with anhydrous ethanol and deionized water and then dried at 70 °C for 12 h.

7. The preparation method according to claim 4, characterized in that, In step 2, the organic ligand is fumaric acid.

8. The application of the LDH@MIL-Fe core-shell composite material as described in any one of claims 1-3 in the photocatalytic activation of persulfate for the degradation of organic pollutants.

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