Preparation and water treatment application of A-site defect oxygen-enriched vacancy ZnFe2O4

Abstract

The invention relates to the technical field of environmental catalysis and water pollution control, and discloses preparation and water treatment application of A-site defect oxygen-enriched vacancy ZnFe2O4, which comprises the following steps: dissolving a zinc salt, an iron salt, an organic ligand and a structure-directing agent in a mixed solvent, and controlling the molar ratio of the zinc salt to the iron salt to be less than 1: 2; carrying out solvothermal reaction on the precursor solution, carrying out solid-liquid separation, and drying to obtain a bimetallic MOF precursor; and carrying out high-temperature calcination on the bimetallic MOF precursor, and cooling to obtain the A-site defect oxygen-enriched vacancy ZnFe2O4. A-site defects are introduced into crystal lattices in the pyrolysis conversion process of the metal organic framework derivative by controlling the feeding molar ratio of zinc salt to iron salt in a precursor mixed solution to be smaller than the stoichiometric ratio of a spinel structure; lattice distortion induces oxygen vacancies to be generated on the surface and in the catalyst, and the problems that the defect concentration is low and difficult to control in an existing conventional preparation process are solved.

Description

Technical Field

[0001] This invention relates to the field of environmental catalysis and water pollution control technology, specifically to the preparation and water treatment application of ZnFe2O4 with A-site defect oxygen-rich vacancy. Background Technology

[0002] With the acceleration of industrialization, the effective degradation of organic pollutants in water bodies has become an important issue in environmental governance. Advanced oxidation technologies based on sulfate radicals have attracted much attention due to their strong oxidizing power and wide applicability. Among numerous persulfate-activated catalysts, magnetic nano-spinel ferrites have shown great application potential in environmental catalytic water treatment due to their excellent magnetic separation performance, high catalytic activity, and chemical stability. The catalytic activity of spinel-type ferrites is highly dependent on the occupancy of metal ions in their crystal structure; precise regulation of their electronic structure is crucial for enhancing the redox capacity of the system.

[0003] In recent years, researchers have developed various modification methods to further enhance the catalytic performance of spinel ferrites. Among existing technologies, elemental doping or composite modification to regulate the electronic structure of materials has become a common approach to improve their catalytic performance. On one hand, researchers introduce lattice distortion and adjust the electronic density of states by doping rare earth elements or transition metals into the lattice sites of ferrites, aiming to enhance the activation efficiency for persulfate. On the other hand, existing technologies also attempt to use bimetallic metal-organic frameworks as precursors, obtaining ferrite-based composite materials through high-temperature calcination, aiming to utilize their porous structure to improve the accessibility of pollutant adsorption and catalytic sites.

[0004] Existing preparation methods struggle to achieve precise and directional control of metal atom vacancies, especially critical A-site defects, when modulating the electronic structure of spinel ferrites. Traditional doping modification or conventional solid-state calcination processes typically only create random and extremely low-concentration common defects on the material surface, failing to induce a large number of oxygen-rich vacancy structures necessary for efficient persulfate activation at the crystal lattice level. This lack of intrinsic defect-oriented control methods directly results in a severe shortage of effective active sites on the surface of existing ferrite catalysts, leading to high electron transfer resistance. When treating wastewater containing organic pollutants, conventional catalysts encounter technical bottlenecks in their activation efficiency for persulfate, resulting in slow overall degradation rates and difficulty in achieving substantial breakthroughs in catalytic performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing and applying A-site defect-enriched oxygen vacancy-rich ZnFe2O4 to water treatment. This method solves the problem that existing traditional methods are difficult to control the concentration and distribution of A-site zinc vacancies, resulting in limited improvement in catalytic activity and poor reproducibility.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing ZnFe2O4 with A-site defects and oxygen-rich vacancies, comprising the following steps: Zinc salt, iron salt, organic ligand and structure directing agent are dissolved in a mixed solvent, and the molar ratio of zinc salt to iron salt is controlled to be less than 1:2. After uniform mixing, a precursor solution is obtained. The precursor solution was subjected to a solvothermal reaction, and after solid-liquid separation and drying, a bimetallic MOF precursor was obtained. The bimetallic MOF precursor was calcined at high temperature and then cooled to obtain the oxygen-rich vacancy ZnFe2O4 with A-site defects.

[0007] Preferably, the zinc salt is zinc nitrate hexahydrate, the iron salt is ferric nitrate nonahydrate, the organic ligand is trimesic acid, the structure directing agent is polyvinylpyrrolidone, and the mixed solvent is composed of N,N-dimethylformamide and deionized water.

[0008] Preferably, the molar ratio of the zinc salt to the iron salt is 0.5:2 to 0.95:2, and the volume ratio of N,N-dimethylformamide to deionized water in the mixed solvent is 1:2 to 1:1.

[0009] Preferably, the temperature of the solvothermal reaction is 150°C to 180°C, and the time is 12 hours to 24 hours; the drying operation is carried out under vacuum drying at 60°C to 80°C.

[0010] Preferably, the atmosphere for high-temperature calcination is an air atmosphere or an inert atmosphere, the heating rate is 2℃ / min to 5℃ / min, the calcination temperature is 500℃ to 800℃, and the holding time is 2 hours to 4 hours.

[0011] A water treatment application method includes the following steps: The catalyst and persulfate are added simultaneously to wastewater containing organic pollutants; The catalytic degradation reaction was carried out under stirring conditions; After the reaction is complete, an external magnetic field is applied to separate the spent catalyst.

[0012] Preferably, the initial concentration of the target organic pollutant in the wastewater is between 10 mg / L and 50 mg / L.

[0013] Preferably, the catalyst is added at a rate of 0.5 g / L to 2.0 g / L, and the mass ratio of the catalyst to the persulfate is 1:0.5 to 1:2.

[0014] Preferably, the temperature of the catalytic degradation reaction is 15°C to 40°C, the initial pH of the wastewater is 3.0 to 11.0, and the reaction time is 30 minutes to 120 minutes.

[0015] Preferably, after separating the spent catalyst, a catalyst cleaning and regeneration step is also included: the separated spent catalyst is washed with deionized water and anhydrous ethanol respectively, and then vacuum dried at 60°C to 80°C to obtain the regenerated catalyst.

[0016] This invention provides a method for preparing oxygen-rich ZnFe2O4 with A-site defects and its application in water treatment. It offers the following advantages: 1. This invention introduces A-site defects into the lattice during the pyrolysis conversion of metal-organic framework derivatives by controlling the molar ratio of zinc salt to iron salt in the precursor mixed solution to be less than the stoichiometric ratio of spinel structure 1:2. The lattice distortion induces oxygen vacancies on the catalyst surface and inside, solving the problem of low defect concentration and difficulty in controlling it in existing conventional preparation processes.

[0017] 2. The A-site defect oxygen-rich vacancy ZnFe2O4 nanocatalyst prepared by this invention has electron transfer capability; the surface oxygen vacancy serves as an active site, reducing the electron transfer resistance between the catalyst and persulfate, thereby activating the persulfate and improving the catalytic degradation rate of organic pollutants in water treatment applications.

[0018] 3. The nano-ZnFe2O4 material provided by this invention serves as a heterogeneous catalyst. The oxygen vacancies on the surface reduce the electron transfer resistance between the material and persulfate, thereby improving the activation efficiency of persulfate and achieving the degradation of organic pollutants. At the same time, the material is magnetic, and solid-liquid separation can be achieved by applying an external magnetic field after the reaction. In multiple cycles of use, it inhibits the leaching of metal ions, maintains structural stability, and reduces the operating cost of water treatment. Attached Figure Description

[0019] Figure 1 This is a SEM image of the A-site defect ZnFe2O4 of the present invention; Figure 2 This invention compares the degradation efficiency and adsorption effect of A-site defective ZnFe2O4 and ZnFe2O4 catalyst on sulfamethoxazole with the oxidation effect of PMS alone. Figure 3 This is a schematic diagram of the preparation process steps of the present invention; Figure 4 The figure shows the electron paramagnetic resonance (EPR) characterization results of this invention. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0022] The CAS number for zinc nitrate hexahydrate is 10196-18-6; The CAS number for ferric nitrate nonahydrate is 7782-61-8; The chemical name of pyromellitic acid is 1,3,5-phenyltricarboxylic acid, the CAS number is 554-95-0, and the purity is analytical grade. Polyvinylpyrrolidone (PVP) is a structure-directing polymer compound with N-vinylpyrrolidone as its repeating unit. The K30 specification with an average molecular weight of approximately 40,000 was selected. The CAS number is 9003-39-8, and the purity is analytical grade. The molecular formula of N,N-dimethylformamide (DMF) is C3H7NO, the CAS number is 68-12-2, and the purity is analytical grade. The molecular formula of anhydrous ethanol is C2H6O, the CAS number is 64-17-5, and the purity is analytical grade. The persulfate source was potassium persulfate complex salt (2KHSO5·KHSO4·K2SO4), CAS number 70693-62-8, and the purity was analytical grade. The chemical name of sulfamethoxazole is 4-amino-N-(5-methyl-3-isoxazolyl)benzenesulfonamide, CAS number is 72-14-0, and its purity is analytical grade. The chemical name of acetaminophen is N-(4-hydroxyphenyl)acetamide, CAS number is 103-90-2, and its purity is analytical grade. The deionized water was prepared in the laboratory and its resistivity was not less than 18.2 MΩ·cm.

[0023] Preparation Example 1: See Appendix Figure 3 This preparation example provides A-site defect Zn 0.9 The preparation method of Fe2O4 nanocatalyst includes the following steps: (1) Weigh 0.2678 g of 0.9 mmol zinc nitrate hexahydrate and 1.212 g of 2.0 mmol ferric nitrate nonahydrate, dissolve them in 70 mL of a mixed solvent of N,N-dimethylformamide and deionized water with a volume ratio of 12:23, and stir magnetically for 30 minutes. (2) Add 0.3152 g of 1.5 mmol pyromellitic acid and 3.0 g of polyvinylpyrrolidone to the above solution, and continue to stir magnetically for 1 hour until completely dissolved to obtain a mixed solution; (3) The mixed solution was transferred into a 100 ml high-pressure reactor with a polytetrafluoroethylene liner, sealed, and then subjected to a solvothermal reaction in an oven at 170°C for 24 hours. (4) After the reaction is completed, the mixture is allowed to cool naturally to room temperature. The precipitate is collected by centrifugation and washed three times with anhydrous ethanol and deionized water respectively. The precipitate is then dried in a vacuum drying oven at 70°C for 12 hours to obtain the bimetallic MOF precursor. (5) The bimetallic MOF precursor was placed in a muffle furnace and heated to 700°C at a rate of 2°C / min in air atmosphere. It was calcined at a constant temperature for 3 hours and then naturally cooled to room temperature before grinding to obtain black nanopowder with A-site defects, which was denoted as catalyst C-0.9.

[0024] Preparation Example 2: This preparation example provides A-site defective Zn 0.5 The preparation method of Fe2O4 nanocatalyst includes the following steps: (1) Weigh 0.5 mmol zinc nitrate hexahydrate and 2.0 mmol ferric nitrate nonahydrate, dissolve them in 70 mL of a mixed solvent of N,N-dimethylformamide and deionized water in a volume ratio of 1:2, and stir magnetically for 30 minutes; (2) Add 1.5 mmol of pyromellitic acid and 3.0 g of polyvinylpyrrolidone to the above solution and continue to stir magnetically for 1 hour until completely dissolved to obtain a mixed solution; (3) The mixed solution was transferred into a 100 ml high-pressure reactor with a polytetrafluoroethylene liner, sealed, and then subjected to a solvothermal reaction in an oven at 150 °C for 12 hours. (4) After the reaction is completed, the mixture is allowed to cool naturally to room temperature. The precipitate is collected by centrifugation and washed three times with anhydrous ethanol and deionized water respectively. The precipitate is then dried in a vacuum drying oven at 60°C for 12 hours to obtain the bimetallic MOF precursor. (5) The bimetallic MOF precursor was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min in air atmosphere. It was calcined at a constant temperature for 2 hours and then naturally cooled to room temperature before grinding to obtain black nanopowder with A-site defects, which was denoted as catalyst C-0.5.

[0025] Preparation Example 3: This preparation example provides A-site defective Zn 0.95 The preparation method of Fe2O4 nanocatalyst includes the following steps: (1) Weigh 0.95 mmol zinc nitrate hexahydrate and 2.0 mmol ferric nitrate nonahydrate, dissolve them in 70 mL of a 1:1 mixture of N,N-dimethylformamide and deionized water, and stir magnetically for 30 minutes. (2) Add 1.5 mmol of pyromellitic acid and 3.0 g of polyvinylpyrrolidone to the above solution and continue to stir magnetically for 1 hour until completely dissolved to obtain a mixed solution; (3) The mixed solution was transferred into a 100 ml high-pressure reactor with a polytetrafluoroethylene liner, sealed, and then subjected to a solvothermal reaction in an oven at 180°C for 24 hours. (4) After the reaction is completed, the mixture is allowed to cool naturally to room temperature. The precipitate is collected by centrifugation and washed three times with anhydrous ethanol and deionized water respectively. The precipitate is then dried in a vacuum drying oven at 80°C for 12 hours to obtain the bimetallic MOF precursor. (5) The bimetallic MOF precursor was placed in a tube furnace and heated to 800°C at a rate of 2°C / min under an argon atmosphere. It was calcined at a constant temperature for 4 hours and then naturally cooled to room temperature before grinding to obtain black nanopowder with A-site defects, which was denoted as catalyst C-0.95.

[0026] Preparation Example 4: This preparation example provides A-site defective Zn 0.7 The preparation method of Fe2O4 nanocatalyst includes the following steps: (1) Weigh 0.7 mmol zinc nitrate hexahydrate and 2.0 mmol ferric nitrate nonahydrate, dissolve them in 70 mL of a mixed solvent of N,N-dimethylformamide and deionized water in a volume ratio of 3:5, and stir magnetically for 30 minutes; (2) Add 1.5 mmol of pyromellitic acid and 3.0 g of polyvinylpyrrolidone to the above solution and continue to stir magnetically for 1 hour until completely dissolved to obtain a mixed solution; (3) The mixed solution was transferred into a 100 ml high-pressure reactor with a polytetrafluoroethylene liner, sealed, and then subjected to a solvothermal reaction in an oven at 160 °C for 18 hours. (4) After the reaction is completed, the mixture is allowed to cool naturally to room temperature. The precipitate is collected by centrifugation and washed three times with anhydrous ethanol and deionized water respectively. The precipitate is then dried in a vacuum drying oven at 70°C for 12 hours to obtain the bimetallic MOF precursor. (5) The bimetallic MOF precursor was placed in a muffle furnace and heated to 600°C at a rate of 3°C / min in air atmosphere. It was calcined at a constant temperature for 3 hours and then naturally cooled to room temperature before grinding to obtain black nanopowder with A-site defects, which was denoted as catalyst C-0.7.

[0027] Example 1: This example provides a defect Zn at position A. 0.9 The application of Fe2O4 nanocatalysts in the degradation of sulfamethoxazole includes the following steps: Measure 100 mL of sulfamethoxazole solution with a concentration of 20 mg / L and a pH of 7, add 0.1 g of catalyst C-0.9 obtained in Preparation Example 1 and 0.1 g of persulfate, and stir magnetically at room temperature for 60 minutes; after the reaction is completed, apply an external magnetic field to separate the waste catalyst. The prepared catalyst C-0.9 was characterized by scanning electron microscopy, and its microstructure is shown in the attached figure. Figure 1 As shown, porous nanoparticles with abundant defect distribution are aggregated. The concentration of sulfamethoxazole in the solution after the reaction was measured by high performance liquid chromatography, and the degradation rate after 60 minutes was calculated to be 78%.

[0028] Comparative Example 1: This comparative example provides the preparation of a defect-free ZnFe2O4 catalyst and its application in the degradation of sulfamethoxazole, including the following steps: The ZnFe2O4 catalyst was prepared under the conditions of Preparation Example 1, except that the amount of zinc nitrate hexahydrate was changed to 1.0 mmol, while the amount of ferric nitrate nonahydrate was kept constant at 2.0 mmol. The resulting product was designated as catalyst C-1. 100 mL of a sulfamethoxazole solution with a concentration of 20 mg / L and a pH of 7 was taken, and 0.1 g of catalyst C-1 and 0.1 g of persulfate were added. The mixture was magnetically stirred at room temperature for 60 minutes. The concentration of sulfamethoxazole in the solution after the reaction was measured by high performance liquid chromatography, and the degradation rate after 60 minutes was calculated to be 56%.

[0029] Example 2: This example provides a defect Zn at position A. 0.9 The adsorption of sulfamethoxazole by Fe2O4 nanocatalyst was tested individually, including the following steps: 100 mL of a sulfamethoxazole solution with a concentration of 20 mg / L and a pH of 7 was taken, and only 0.1 g of the catalyst C-0.9 obtained in Preparation Example 1 was added. The solution was magnetically stirred at room temperature for 60 minutes. The concentration of sulfamethoxazole in the solution was measured by high performance liquid chromatography, and the adsorption rate after 60 minutes was calculated to be 1%, proving that catalyst C-0.9 had no significant adsorption and removal effect on its own.

[0030] Comparative Example 2: This comparative example provides a test of the adsorption effect of a defect-free ZnFe2O4 catalyst on sulfamethoxazole, including the following steps: 100 mL of a sulfamethoxazole solution with a concentration of 20 mg / L and a pH of 7 was taken, and only 0.1 g of catalyst C-1 obtained in Comparative Example 1 was added. The solution was magnetically stirred at room temperature for 60 minutes. The concentration of sulfamethoxazole in the solution was measured by high performance liquid chromatography, and the adsorption rate after 60 minutes was calculated to be 1%, proving that catalyst C-1 had no significant adsorption and removal effect on its own.

[0031] Comparative Example 3: This comparative example provides a test of the oxidation effect of sulfate alone on sulfamethoxazole, including the following steps: 100 mL of a sulfamethoxazole solution with a concentration of 20 mg / L and a pH of 7 was taken, and only 0.1 g of persulfate was added. The mixture was magnetically stirred at room temperature for 60 minutes. The concentration of sulfamethoxazole in the solution was measured by high performance liquid chromatography, and the degradation rate after 60 minutes was calculated to be 1%, proving that persulfate had no significant effect on removal by oxidation alone.

[0032] Based on the test results of Examples 1 and 2, as well as Comparative Examples 1 to 3, the degradation efficiency and adsorption effect of each system on sulfamethoxazole are compared in the attached figure. Figure 2 As shown; via appendix Figure 2 The direct comparison proves that the A-site defect Zn prepared by this invention 0.9 The degradation efficiency of Fe2O4 catalyst synergistically with persulfate is significantly better than that of defect-free catalyst systems and single adsorption or single oxidation systems.

[0033] Example 3: This example provides a defect Zn at site A. 0.9 The degradation application of Fe2O4 nanocatalysts under a wide pH adaptability includes the following steps: Four 100 mL aliquots of sulfamethoxazole solution with a concentration of 20 mg / L were taken and their initial pH values ​​were adjusted to 3, 5, 9, and 11, respectively. 0.1 g of catalyst C-0.9 obtained in Preparation Example 1 and 0.1 g of persulfate were added to each solution, and the mixtures were magnetically stirred at room temperature for 60 minutes. The concentration of sulfamethoxazole in each solution after the reaction was measured using high-performance liquid chromatography (HPLC). The degradation rates after 60 minutes were calculated to be 71%, 75%, 83%, and 89%, respectively, under the initial pH values ​​of 3, 5, 9, and 11.

[0034] Example 4: This example provides a defect Zn at site A. 0.5 The application of Fe2O4 nanocatalysts in the degradation of sulfamethoxazole includes the following steps: 100 mL of a sulfamethoxazole solution with a concentration of 10 mg / L and a pH of 7 was taken, and 0.05 g of the catalyst C-0.5 obtained in Preparation Example 2 and 0.025 g of persulfate were added. The mixture was stirred magnetically at room temperature for 30 minutes. After the reaction was completed, an external magnetic field was applied to separate the spent catalyst. The concentration of sulfamethoxazole in the solution after the reaction was measured by high performance liquid chromatography. The results showed that the catalytic system had a significant degradation effect on sulfamethoxazole.

[0035] Example 5: This example provides a defect Zn at site A. 0.95 The application of Fe2O4 nanocatalysts in the degradation of sulfamethoxazole includes the following steps: 100 mL of a sulfamethoxazole solution with a concentration of 50 mg / L and a pH of 7 was taken, and 0.2 g of the catalyst C-0.95 obtained in Preparation Example 3 and 0.4 g of persulfate were added. The mixture was magnetically stirred at room temperature for 120 minutes. After the reaction was completed, an external magnetic field was applied to separate the spent catalyst. The concentration of sulfamethoxazole in the solution after the reaction was measured by high performance liquid chromatography. The system was found to maintain stable catalytic oxidation performance under high concentration of pollutants.

[0036] Application Example 1: This application example provides a defect Zn at position A. 0.9 The application of Fe2O4 nanocatalysts in magnetic separation and recycling in water treatment processes includes the following steps: (1) Measure 100 ml of sulfamethoxazole wastewater with a concentration of 20 mg / L, add 0.1 g of catalyst C-0.9 obtained in Preparation Example 1 and 0.1 g of persulfate, and stir magnetically at room temperature for 60 minutes; (2) After the reaction is complete, stop stirring and apply a magnetic field to the outside of the reaction vessel so that the suspended catalyst powder is rapidly enriched and settled within 3 minutes. Pour out the supernatant to complete the solid-liquid separation. (3) The collected waste catalyst was washed three times with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 70°C to obtain the regenerated catalyst. (4) The regenerated catalyst is directly added to the next batch of sulfamethoxazole wastewater degradation cycle, and the above steps (1) to (3) are repeated a total of five times; High-performance liquid chromatography (HPLC) analysis showed that after five water treatment cycles, the degradation rate of sulfamethoxazole by the catalyst did not decrease significantly, and the dissolution of iron and zinc ions in the solution was extremely low, proving that the material has excellent structural stability and practical application value in water treatment engineering.

[0037] See appendix Figure 4 Electron paramagnetic resonance (EPR) characterization results indicate that the introduction of A-site defects makes Zn 0.9 The oxygen vacancy content on the Fe2O4 surface was significantly increased.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing ZnFe2O4 with oxygen-rich vacancies at A-site defects, characterized in that, Includes the following steps: Zinc salt, iron salt, organic ligand and structure directing agent are dissolved in a mixed solvent, and the molar ratio of zinc salt to iron salt is controlled to be less than 1:

2. After uniform mixing, a precursor solution is obtained. The precursor solution was subjected to a solvothermal reaction, and after solid-liquid separation and drying, a bimetallic MOF precursor was obtained. The bimetallic MOF precursor was calcined at high temperature and then cooled to obtain the oxygen-rich vacancy ZnFe2O4 with A-site defects.

2. The method for preparing ZnFe2O4 with A-site defects and oxygen-rich vacancies according to claim 1, characterized in that: The zinc salt is zinc nitrate hexahydrate, the iron salt is ferric nitrate nonahydrate, the organic ligand is trimesic acid, the structure directing agent is polyvinylpyrrolidone, and the mixed solvent is composed of N,N-dimethylformamide and deionized water.

3. The method for preparing ZnFe2O4 with A-site defects and oxygen-rich vacancies according to claim 2, characterized in that: The molar ratio of the zinc salt to the iron salt is 0.5:2 to 0.95:2, and the volume ratio of N,N-dimethylformamide to deionized water in the mixed solvent is 1:2 to 1:

1.

4. The method for preparing ZnFe2O4 with A-site defects and oxygen-rich vacancies according to claim 1, characterized in that: The solvothermal reaction is carried out at a temperature of 150°C to 180°C for 12 to 24 hours; the drying operation is carried out under vacuum at a temperature of 60°C to 80°C.

5. The method for preparing ZnFe2O4 with A-site defects and oxygen-rich vacancies according to claim 1, characterized in that: The high-temperature calcination atmosphere is air or inert atmosphere, the heating rate is 2℃ / min to 5℃ / min, the calcination temperature is 500℃ to 800℃, and the holding time is 2 hours to 4 hours.

6. A water treatment application method, using A-site defect oxygen-rich vacancy ZnFe2O4 obtained by the method for preparing A-site defect oxygen-rich vacancy ZnFe2O4 according to any one of claims 1 to 5 as a catalyst, characterized in that, Includes the following steps: The catalyst and persulfate are added simultaneously to wastewater containing organic pollutants; The catalytic degradation reaction was carried out under stirring conditions; After the reaction is complete, an external magnetic field is applied to separate the spent catalyst.

7. A water treatment application method according to claim 6, characterized in that: The initial concentration of the target organic pollutant in the wastewater is between 10 mg / L and 50 mg / L.

8. A water treatment application method according to claim 6, characterized in that: The catalyst is added at a rate of 0.5 g / L to 2.0 g / L, and the mass ratio of the catalyst to the persulfate is 1:0.5 to 1:

2.

9. A water treatment application method according to claim 6, characterized in that: The catalytic degradation reaction is carried out at a temperature of 15°C to 40°C, the initial pH of the wastewater is 3.0 to 11.0, and the reaction time is 30 minutes to 120 minutes.

10. A water treatment application method according to claim 6, characterized in that: After separating the spent catalyst, the process also includes a catalyst cleaning and regeneration step: the separated spent catalyst is washed with deionized water and anhydrous ethanol respectively, and then vacuum dried at 60°C to 80°C to obtain the regenerated catalyst.

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