A zinc-iron layered double hydroxide composite material supported on biochar, and a preparation method and application thereof

Abstract

The application relates to a biochar loaded zinc-iron layered double metal oxide composite material and a preparation method and application thereof, and belongs to the technical field of adsorption and separation. The preparation method of the biochar loaded zinc-iron layered double metal oxide composite material comprises four steps of preparing cross-linked coated melamine cyanurate, preparing a precursor mixed solution, preparing a precursor and carbonizing. The obtained biochar loaded zinc-iron layered double metal oxide composite material has a very high adsorption capacity for tetracycline antibiotic pollutants under the conditions of wide pH value fluctuation range and high-concentration impurity ions.

Description

Technical Field

[0001] This invention relates to a biochar-supported zinc-iron layered bimetallic oxide composite material, its preparation method, and its application, belonging to the field of adsorption separation technology. Background Technology

[0002] Antibiotics are widely used in medical and agricultural production to treat bacterial infections and inhibit microorganisms. However, antibiotic residues in antibiotic-treated wastewater pose a threat to the aquatic environment and human health, even inducing the emergence of drug-resistant bacteria and ultimately leading to the transfer and spread of antibiotic-resistant genes. This severely damages the natural bacterial ecosystem and poses a potentially serious threat to the ecological environment and human health. Unfortunately, existing water treatment processes for completely removing antibiotics are generally very costly, require sophisticated equipment, and are economically inefficient. Adsorption methods utilize porous materials to adsorb pollutants in wastewater, achieving pollutant removal through separation. Compared to other separation methods, adsorption is simple to operate, efficient, low-cost, and widely applicable, without producing any byproducts, making it a promising candidate for water treatment. Biochar, in particular, has advantages such as abundant raw material resources and low production costs, making it a promising candidate for wastewater treatment. Biochar is a porous material with high carbon content, prepared from biomass raw materials such as agricultural and forestry waste under pyrolysis conditions. Due to its large specific surface area, abundant functional groups, and well-developed pore structure, it can be used as an adsorbent to remove antibiotic pollutants from water. However, biochar has limited adsorption sites, resulting in a limited adsorption capacity for antibiotic pollutants. Therefore, improving the adsorption effect of biochar to better apply it to the treatment of antibiotic-contaminated wastewater is essential. Generally, using magnetic materials, acids or alkalis, steam, nano-metal oxides or hydroxides, and atomically doped modified biochar can effectively improve the adsorption of antibiotic pollutants in water by biochar.

[0003] Layered bimetallic hydroxides (LDHs) are nanomaterials with unique ion exchange properties and stability, often used as adsorbents to remove target pollutants from the environment. However, their poor dispersibility leads to low adsorption capacity. Therefore, selecting a suitable support to uniformly disperse LDHs can effectively improve their adsorption performance. Existing research has shown that biochar can serve as a support, effectively improving the dispersibility of LDHs and promoting the adsorption of antibiotic pollutants in water by biochar-supported LDHs.

[0004] Chinese patent CN115282927 A discloses a zero-valent manganese biochar composite material (BC) prepared using sugarcane bagasse biochar and zero-valent manganese as raw materials via sodium borohydride reduction. nZVMn), and provides BC The preparation method of nZVMn and its application in the removal of tetracycline from water. The patented BZ... The maximum adsorption capacity of nZVMn for tetracycline antibiotic pollutants in water can reach 1214.138 mg / g, indicating a significant and intuitive improvement in adsorption capacity after biochar is loaded with active metal compounds. However, the test data disclosed in the patent shows that BC... The adsorption of tetracycline antibiotic pollutants by nZVMn is significantly inhibited by calcium and magnesium ions, and the inhibitory effect is significantly enhanced with the increase of calcium and magnesium ion concentration.

[0005] Chinese patent CN114433020A discloses a biochar-based composite material for fixing zero-valent iron and its application in removing tetracycline from water. The method involves adding hematite and biomass to deionized water, stirring thoroughly, and then ultrasonically treating the mixture. After drying, the mixture is pyrolyzed in a tubular furnace at 700-900℃, with nitrogen as the protective carrier gas throughout the process. The pyrolyzed material is then washed with ethanol and deionized water, respectively, and dried in a vacuum oven to obtain the BC / ZVI composite material. While the biochar-based composite material obtained by this patent exhibits a relatively high adsorption capacity for tetracycline, its adsorption capacity is significantly affected by pH; when the pH value exceeds 9, the adsorption capacity decreases substantially.

[0006] As can be seen above, biochar-supported metal or metal compound materials still have prominent problems in adsorbing antibiotic pollutants, such as the adsorption capacity being greatly affected by pH value and interference from impurity ions in the aqueous phase. Therefore, it is urgent to develop new biochar-supported active metal compound composite materials to expand the tolerance range of modified biochar for adsorbing and removing antibiotic pollutants in water and improve the applicability of adsorption materials. Summary of the Invention

[0007] To address the shortcomings of the existing technologies, this invention provides a biochar-supported zinc-iron layered bimetallic oxide composite material, its preparation method, and its application, achieving the following objectives: by modifying biochar and supporting it with zinc-iron layered bimetallic oxide, a composite material with high adsorption capacity for antibiotic pollutants in water under conditions of wide pH fluctuation range and high concentration of impurity ions is prepared.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A biochar-supported zinc-iron layered bimetallic oxide composite material, its preparation method and application, wherein the biochar-supported zinc-iron layered bimetallic oxide composite material is a microporous material with biochar as the matrix and zinc-iron layered bimetallic oxide uniformly distributed on the inner and outer pore wall surfaces of the biochar matrix. The preparation method of the biochar-supported zinc-iron layered bimetallic oxide composite material includes four steps: preparing cross-linked coated melamine cyanurate, preparing a precursor mixture, preparing a precursor, and carbonization. The following are further improvements to the above technical solution: Step 1: Preparation of cross-linked melamine cyanurate Melamine, cyanuric acid, and deionized water were placed in a reaction vessel and heated to the reaction temperature under low-speed stirring. After the reaction was complete, the stirring rate was increased, and then polyethyleneimine aqueous solution was added. After stirring evenly, tannic acid aqueous solution was added dropwise. After the addition was complete, the reaction was continued until complete. After filtration, washing, and drying, cross-linked melamine cyanurate was obtained. The mass concentration of polyethyleneimine in the polyethyleneimine aqueous solution is 5-15 wt%. The mass concentration of tannic acid in the tannic acid aqueous solution is 10~20wt%; The mass ratio of melamine, cyanuric acid, deionized water, polyethyleneimine aqueous solution, and tannic acid aqueous solution is 20~80:30~110:550~1300:30~90:40~110; The low-speed stirring has a stirring rate of 400~850 rpm. The reaction temperature is 60~85℃; After the reaction is complete, increase the stirring rate. The reaction time is 3.5 to 5 hours, and the stirring rate is 1100 to 1800 rpm. After the mixture is thoroughly mixed, the mixing time is 1 to 3.5 hours. The tannic acid aqueous solution is added at a rate of 20-120 g / min. The reaction continues until complete, with a reaction time of 3 to 6 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 6.5-6.8. The drying process involves a drying temperature of 70-95℃ and a drying time of 9-15 hours.

[0009] Step 2: Preparation of precursor mixture Tomato straw biomass powder, iron salt, zinc salt, cross-linked melamine cyanurate, complexing agent, and deionized water are placed in a mixing vessel, stirred, and ultrasonically dispersed to obtain a composite salt solution. Then, anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water are mixed to obtain an activator solution. The activator solution is then added dropwise to the composite salt solution under low-speed stirring. After the addition is complete, the temperature is raised to the reaction temperature, and the reaction is carried out under low-speed stirring until it is complete to obtain a precursor mixture. The tomato straw biomass powder is prepared by washing the tomato straw biomass with deionized water, then crushing it, drying it at 85~95℃ for 13~20 hours, and then sieving it to obtain powder with a particle size of 800~1200 mesh. The iron salt is one or a mixture of any two or more of ferric chloride, ferric sulfate, and ferric nitrate in any mass ratio. The zinc salt is one or a mixture of any two or more of zinc chloride, zinc sulfate, and zinc nitrate in any mass ratio. The complexing agent is one or a mixture of any two or more of the following in any mass ratio: tetrasodium glutamate diacetate, tetrasodium iminodisuccinate, ethylenediaminetetrapropionic acid, hypozoxytriacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, and 1,2-cyclohexanediaminetetraacetic acid. The tetraborate is one or a mixture of any two or more of sodium tetraborate, potassium tetraborate, and ammonium tetraborate in any mass ratio. The mass ratio of the tomato straw biomass powder, iron salt, zinc salt, cross-linked coated melamine cyanurate, complexing agent, and deionized water is 50~200:8~20:4~15:6~25:1~4:360~650. The mass ratio of anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water is 15~50:10~40:2~8:200~600; The activator solution is added dropwise to the composite salt solution at a rate of 30-100 g / min. The low-speed stirring has a stirring rate of 600~1000 rpm; The reaction temperature is 65~80℃; The reaction is expected to be complete within 1 to 3.5 hours.

[0010] Step 3: Preparation of precursor The precursor mixture was transferred into a hydrothermal reactor, and after the hydrothermal reaction was completed, it was centrifuged and dried to obtain the precursor. The hydrothermal reaction is carried out at a temperature of 110~150℃ for a time of 20~30 hours. The drying process involves a drying temperature of 60-85℃ and a drying time of 15-30 hours.

[0011] Step 4, Carbonization The precursor was placed in a carbonization furnace and heated to 470-600℃ at a rate of 3-5℃ / min under nitrogen protection at a flow rate of 20-120 mL / min. The mixture was then carbonized at a constant temperature for 2-3.5 hours, and the nitrogen protection was reduced to room temperature to obtain a biochar-supported zinc-iron layered bimetallic oxide composite material.

[0012] Compared with the prior art, the present invention achieves the following beneficial effects: 1. This invention utilizes tomato straw biomass powder and, through a combination of hydrothermal synthesis and low-temperature carbonization, obtains a biochar-supported zinc-iron layered bimetallic oxide composite material with high tetracycline adsorption capacity under conditions of wide pH fluctuation range and high concentration of impurity ions. 2. To simultaneously achieve the dual objectives of controlling the pore size distribution and structure of biochar and incorporating nitrogen into it, this invention designs a process for cross-linking and coating melamine cyanurate with tannic acid and polyethyleneimine. Melamine cyanurate plays two main roles: first, by incorporating nitrogen into biochar due to its high nitrogen content to increase the polarity of the pore walls; and second, by promoting micropore formation through its thermal decomposition. However, melamine cyanurate has a high nitrogen content and very low residual carbon content, resulting in relatively rapid thermal decomposition and a tendency to create large-pore structures with excessively large pore sizes. Therefore, cross-linking and coating with tannic acid and polyethyleneimine utilizes the high aromatic ring content and high residual carbon content of tannic acid to delay the rapid thermal decomposition of melamine cyanurate to a certain extent (during carbonization, the thermal decomposition of tannic acid easily forms a dense carbon layer, thus delaying the thermal decomposition of melamine cyanurate). 3. This invention promotes the uniform distribution and good dispersion of zinc and iron on the biochar matrix by adding highly efficient complexing agents containing amino and carboxyl groups. The basic principle is that these complexing agents can be fully dissolved and dispersed in the aqueous phase and contain polar functional groups such as amino or carboxyl groups, which enable them to be uniformly adsorbed on tomato straw biomass powder. In this way, the complexed metal ions can also be uniformly adsorbed on the surface of tomato straw biomass powder. During hydrothermal synthesis and carbonization, the uniform adsorption and good dispersion driven by the complexing agent will help prevent the thermal migration of metals and further agglomeration, thereby ensuring the good dispersion of zinc and iron during the hydrothermal synthesis process and the subsequent carbonization heating process, and ultimately promoting the uniform loading of zinc-iron layered bimetallic oxides on biochar. 4. In this invention, sodium tetraborate, potassium tetraborate, and ammonium tetraborate are used to activate and pore-form biochar during the carbonization process. The decomposition temperature of borates is relatively low, which can fully decompose at a lower carbonization temperature and form micropores with smaller pore sizes. In addition, the boron element introduced by borates can enhance the polarity of the biochar matrix, thereby improving the adsorption performance of tetracycline on the biochar-supported zinc-iron layered bimetallic oxide composite material. Attached Figure Description

[0013] Figure 1 The image shows a 1000x magnified scanning electron microscope image of the surface of the biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Example 1. Figure 2 The image shows a scanning electron microscope (SEM) image of the cross-section of the biochar obtained in Comparative Example 1 that is not loaded with zinc-iron layered bimetallic oxides, magnified 5000 times. Figure 3Fourier transform infrared spectra of the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Example 1 and Comparative Example 1. Figure 4 X-ray spectra of the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Example 1 and Comparative Example 1; Figure 5 The removal rates of tetracycline hydrochloride by the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 under different dosages are shown. Figure 6 The removal rates of tetracycline hydrochloride by the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 at different pH values. Figure 7 The adsorption capacity of tetracycline hydrochloride for the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 at different CaCl2 concentrations is shown. Figure 8 The adsorption capacity of tetracycline hydrochloride for the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 at different NaCl concentrations is shown. Figure 9 The removal rate of tetracycline hydrochloride by the biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Example 1 at different initial concentrations of tetracycline hydrochloride. Figure 10 The cycling performance of the biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Examples 1-3 for the adsorption of tetracycline hydrochloride. Detailed Implementation

[0014] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0015] Example 1: A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material Step 1: Preparation of cross-linked melamine cyanurate Melamine, cyanuric acid, and deionized water were placed in a reaction vessel and heated to the reaction temperature under low-speed stirring. After the reaction was complete, the stirring rate was increased, and then polyethyleneimine aqueous solution was added. After stirring evenly, tannic acid aqueous solution was added dropwise. After the addition was complete, the reaction was continued until complete. After filtration, washing, and drying, cross-linked melamine cyanurate was obtained. The mass concentration of polyethyleneimine in the polyethyleneimine aqueous solution is 11 wt%. The mass concentration of tannic acid in the tannic acid aqueous solution is 14 wt%. The mass ratio of melamine, cyanuric acid, deionized water, polyethyleneimine aqueous solution, and tannic acid aqueous solution is 65:89:860:50:70. The low-speed stirring has a stirring rate of 700 rpm; The reaction temperature is 80°C; After the reaction is complete, increase the stirring rate. The reaction time is 4 hours and the stirring rate is 1600 rpm. After the mixture is thoroughly mixed, the mixing time is 3 hours. The tannic acid aqueous solution was added at a rate of 90 g / min. The reaction continues until complete, with a reaction time of 5 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 6.7. The drying process was carried out at a temperature of 90°C for 13 hours.

[0016] Step 2: Preparation of precursor mixture Tomato straw biomass powder, iron salt, zinc salt, cross-linked melamine cyanurate, complexing agent, and deionized water are placed in a mixing vessel, stirred, and ultrasonically dispersed to obtain a composite salt solution. Then, anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water are mixed to obtain an activator solution. The activator solution is then added dropwise to the composite salt solution under low-speed stirring. After the addition is complete, the temperature is raised to the reaction temperature, and the reaction is carried out under low-speed stirring until it is complete to obtain a precursor mixture. The tomato straw biomass powder is prepared by washing the tomato straw biomass with deionized water, then crushing it, drying it at 90°C for 17 hours, and then sieving it to obtain powder with a particle size of 1000 mesh. The iron salt is ferric chloride; The zinc salt is zinc chloride; The complexing agent is tetrasodium diglutamate; The tetraborate is sodium tetraborate; The mass ratio of the tomato straw biomass powder, iron salt, zinc salt, cross-linked melamine cyanurate, complexing agent, and deionized water is 130:14:9:19:3:560. The mass ratio of anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water is 30:26:6:360; The activator solution is added dropwise to the composite salt solution at a rate of 70 g / min. The low-speed stirring is at a stirring rate of 850 rpm. The reaction temperature is 70°C; The reaction is to be completed within 3 hours.

[0017] Step 3: Preparation of precursor The precursor mixture was transferred into a hydrothermal reactor, and after the hydrothermal reaction was completed, it was centrifuged and dried to obtain the precursor. The hydrothermal reaction was carried out at a temperature of 120°C for 27 hours. The drying process is carried out at a temperature of 80°C for 25 hours.

[0018] Step 4, Carbonization The precursor was placed in a carbonization furnace and heated to 530°C at a rate of 4°C / min under nitrogen protection at a flow rate of 90 mL / min. The mixture was then carbonized at this temperature for 3 hours, and the nitrogen protection was reduced to room temperature to obtain a biochar-supported zinc-iron layered bimetallic oxide composite material.

[0019] Example 2: A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material Step 1: Preparation of cross-linked melamine cyanurate Melamine, cyanuric acid, and deionized water were placed in a reaction vessel and heated to the reaction temperature under low-speed stirring. After the reaction was complete, the stirring rate was increased, and then polyethyleneimine aqueous solution was added. After stirring evenly, tannic acid aqueous solution was added dropwise. After the addition was complete, the reaction was continued until complete. After filtration, washing, and drying, cross-linked melamine cyanurate was obtained. The polyethyleneimine aqueous solution contains 5 wt% polyethyleneimine. The mass concentration of tannic acid in the tannic acid aqueous solution is 10 wt%. The mass ratio of melamine, cyanuric acid, deionized water, polyethyleneimine aqueous solution, and tannic acid aqueous solution is 20:30:550:30:40. The low-speed stirring has a stirring rate of 400 rpm; The reaction temperature is 60°C; After the reaction is complete, increase the stirring rate. The reaction time is 3.5 hours and the stirring rate is 1100 rpm. After the mixture is thoroughly mixed, the mixing time is 1 hour. The tannic acid aqueous solution was added at a rate of 20 g / min. The reaction continues until complete, with a reaction time of 3 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 6.5. The drying process is carried out at a temperature of 70°C for 15 hours.

[0020] Step 2: Preparation of precursor mixture Tomato straw biomass powder, iron salt, zinc salt, cross-linked melamine cyanurate, complexing agent, and deionized water are placed in a mixing vessel, stirred, and ultrasonically dispersed to obtain a composite salt solution. Then, anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water are mixed to obtain an activator solution. The activator solution is then added dropwise to the composite salt solution under low-speed stirring. After the addition is complete, the temperature is raised to the reaction temperature, and the reaction is carried out under low-speed stirring until it is complete to obtain a precursor mixture. The tomato straw biomass powder is prepared by washing the tomato straw biomass with deionized water, then crushing it, drying it at 85°C for 20 hours, and then sieving it to obtain powder with a particle size of 800 mesh. The iron salt is ferric sulfate; The zinc salt is zinc sulfate; The complexing agent is tetrasodium iminodisuccinate; The tetraborate is potassium tetraborate; The mass ratio of the tomato straw biomass powder, iron salt, zinc salt, cross-linked coated melamine cyanurate, complexing agent, and deionized water is 50:8:4:6:1:360. The mass ratio of anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water is 15:10:2:200. The activator solution is added dropwise to the composite salt solution at a rate of 30 g / min. The low-speed stirring has a stirring rate of 600 rpm; The reaction temperature is 65°C; The reaction is to be completed within 1 hour.

[0021] Step 3: Preparation of precursor The precursor mixture was transferred into a hydrothermal reactor, and after the hydrothermal reaction was completed, it was centrifuged and dried to obtain the precursor. The hydrothermal reaction was carried out at a temperature of 110°C for 30 hours. The drying process is carried out at a temperature of 60°C for 30 hours.

[0022] Step 4, Carbonization The precursor was placed in a carbonization furnace and heated to 470°C at a rate of 3°C / min under nitrogen protection at a flow rate of 20 mL / min. The mixture was then carbonized at this temperature for 3.5 hours, and the nitrogen protection was reduced to room temperature to obtain a biochar-supported zinc-iron layered bimetallic oxide composite material.

[0023] Example 3: A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material Step 1: Preparation of cross-linked melamine cyanurate Melamine, cyanuric acid, and deionized water were placed in a reaction vessel and heated to the reaction temperature under low-speed stirring. After the reaction was complete, the stirring rate was increased, and then polyethyleneimine aqueous solution was added. After stirring evenly, tannic acid aqueous solution was added dropwise. After the addition was complete, the reaction was continued until complete. After filtration, washing, and drying, cross-linked melamine cyanurate was obtained. The polyethyleneimine aqueous solution contains 15 wt% polyethyleneimine. The mass concentration of tannic acid in the tannic acid aqueous solution is 20 wt%. The mass ratio of melamine, cyanuric acid, deionized water, polyethyleneimine aqueous solution, and tannic acid aqueous solution is 80:110:1300:90:110; The low-speed stirring is at a stirring rate of 850 rpm. The reaction temperature is 85°C; After the reaction is complete, increase the stirring rate. The reaction time is 5 hours and the stirring rate is 1800 rpm. After the mixture is thoroughly mixed, the mixing time is 3.5 hours. The tannic acid aqueous solution was added at a rate of 120 g / min. The reaction continues until complete, with a reaction time of 6 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 6.8. The drying process was carried out at a temperature of 95°C for 9 hours.

[0024] Step 2: Preparation of precursor mixture Tomato straw biomass powder, iron salt, zinc salt, cross-linked melamine cyanurate, complexing agent, and deionized water are placed in a mixing vessel, stirred, and ultrasonically dispersed to obtain a composite salt solution. Then, anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water are mixed to obtain an activator solution. The activator solution is then added dropwise to the composite salt solution under low-speed stirring. After the addition is complete, the temperature is raised to the reaction temperature, and the reaction is carried out under low-speed stirring until it is complete to obtain a precursor mixture. The tomato straw biomass powder is prepared by washing the tomato straw biomass with deionized water, then crushing it, drying it at 95°C for 13 hours, and then sieving it to obtain powder with a particle size of 1200 mesh. The iron salt is ferric nitrate; The zinc salt is zinc nitrate; The complexing agent is ethylenediaminetetrapropionic acid; The tetraborate is ammonium tetraborate; The mass ratio of the tomato straw biomass powder, iron salt, zinc salt, cross-linked melamine cyanurate, complexing agent, and deionized water is 200:20:15:25:4:650. The mass ratio of anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water is 50:40:8:600. The activator solution is added dropwise to the composite salt solution at a rate of 100 g / min. The low-speed stirring has a stirring rate of 1000 rpm; The reaction temperature is 80°C; The reaction is to be complete within 3.5 hours.

[0025] Step 3: Preparation of precursor The precursor mixture was transferred into a hydrothermal reactor, and after the hydrothermal reaction was completed, it was centrifuged and dried to obtain the precursor. The hydrothermal reaction was carried out at a temperature of 150°C for 20 hours. The drying process involves a drying temperature of 85°C and a drying time of 15 hours.

[0026] Step 4, Carbonization The precursor was placed in a carbonization furnace and heated to 600°C at a rate of 5°C / min under nitrogen protection at a flow rate of 120 mL / min. The mixture was then carbonized at a constant temperature for 2 hours, and the nitrogen protection was reduced to room temperature to obtain a biochar-supported zinc-iron layered bimetallic oxide composite material.

[0027] Example 4: A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material Step 1 is the same as in Example 1; Step 2: Preparation of precursor mixture The complexing agent is hyponitrotriacetic acid; Steps 3 and 4 are the same as in Example 1.

[0028] Example 5: A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material Step 1 is the same as in Example 1; Step 2: Preparation of precursor mixture The complexing agent is diethylenetriaminepentaacetic acid; Steps 3 and 4 are the same as in Example 1.

[0029] Example 6: A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material Step 1 is the same as in Example 1; Step 2: Preparation of precursor mixture The complexing agent is ethylenediaminetetraacetic acid; Steps 3 and 4 are the same as in Example 1.

[0030] Example 7: A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material Step 1 is the same as in Example 1; Step 2: Preparation of precursor mixture The complexing agent is 1,2-cyclohexanediaminetetraacetic acid; Steps 3 and 4 are the same as in Example 1.

[0031] Comparative Example 1: Based on Example 1, in step 2, the preparation of the precursor mixture was carried out without the addition of iron salts or zinc salts, i.e., only biochar was prepared without loading zinc-iron layered bimetallic oxides. The specific operation is as follows: Step 1 is the same as in Example 1; Step 2: Preparation of precursor mixture Based on Example 1, 14 parts iron salt, 9 parts zinc salt, and 3 parts complexing agent were replaced with 26 parts tomato straw biomass powder in equal amounts, and other operations were the same as in Example 1; Steps 3 and 4 are the same as in Example 1.

[0032] Comparative Example 2: Based on Example 1, in step 1, the preparation of cross-linked coated melamine cyanurate, cross-linking coating was not performed, and melamine cyanurate was obtained directly. The specific operation is as follows: Step 1: Preparation of melamine cyanurate Melamine, cyanuric acid, and deionized water are placed in a reaction vessel and heated to the reaction temperature under low-speed stirring. After the reaction is complete, the mixture is filtered, washed, and dried to obtain melamine cyanurate. The mass ratio of melamine, cyanuric acid, and deionized water is 65:89:860. The low-speed stirring has a stirring rate of 700 rpm; The reaction temperature is 80°C; After the reaction is complete, the reaction time is 4 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 6.7. The drying process was carried out at a temperature of 90°C for 13 hours.

[0033] Step 2: Preparation of precursor mixture Based on Example 1, 19 parts of cross-linked coated melamine cyanurate were replaced with an equal amount of 19 parts of melamine cyanurate, and other operations were the same as in Example 1; Steps 3 and 4 are the same as in Example 1.

[0034] Comparative Example 3: Based on Example 1, in step 2, preparing the precursor mixture, no complexing agent was added. Instead, 3 parts of complexing agent were replaced with 3 parts of deionized water in equal amounts. The specific operation is as follows: Step 1 is the same as in Example 1; Step 2: Preparation of precursor mixture Based on Example 1, replace 3 parts of complexing agent with 3 parts of deionized water in equal amounts, and perform the other operations as in Example 1; Steps 3 and 4 are the same as in Example 1.

[0035] Comparative Example 4: Based on Example 1, in step 2, preparing the precursor mixture, tetraborate was not added; instead, 4 parts of tetraborate were replaced with 6 parts of deionized water. The specific operation is as follows: Step 1 is the same as in Example 1; Step 2: Preparation of precursor mixture Based on Example 1, replace 4 parts of tetraborate with 6 parts of deionized water, and perform the other operations as in Example 1; Steps 3 and 4 are the same as in Example 1.

[0036] Performance characterization of biochar-supported zinc-iron layered bimetallic oxide composites and their application in the adsorption and removal of antibiotic pollutants in water (using tetracycline hydrochloride as a typical pollutant as the test sample): 1. Field emission scanning electron microscopy characterization: The biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Example 1 and Comparative Example 1 were characterized by scanning electron microscopy to compare the morphological changes before and after loading with zinc-iron layered bimetallic oxide. 2. Fourier transform infrared spectroscopy: Fourier transform infrared spectroscopy was performed on the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Example 1 and Comparative Example 1 to compare the changes in functional groups before and after loading with zinc-iron layered bimetallic oxide. 3. X-ray diffraction: X-ray diffraction was used to characterize the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Example 1 and Comparative Example 1 to evaluate whether the biochar was successfully loaded with zinc-iron layered bimetallic oxide and the morphological composition of the oxide. 4. Removal rate of tetracycline hydrochloride at different dosages: Tetracycline hydrochloride stock solution (500 mg / L) was diluted to prepare a tetracycline hydrochloride sample solution with an initial concentration (C0) of 50 mg / L. Then, the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were added to conical flasks containing 100 mL of tetracycline hydrochloride sample solution at dosages of 0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.4 g / L, and 1.6 g / L, respectively. After placing the conical flask on a constant-temperature shaker at 180 rpm and 25°C for 24 hours, adsorption-desorption equilibrium was reached, achieving saturated adsorption of tetracycline hydrochloride by the biochar-supported zinc-iron layered bimetallic oxide composite material in the sample solution. The remaining adsorbent material in the sample was removed by passing the sample through a 0.45 µm nylon filter membrane. The concentration C of tetracycline hydrochloride in the remaining sample solution was measured using a UV spectrophotometer. t According to the formula: R = (C0 - C) t The removal rate of tetracycline hydrochloride in the sample solution was calculated using the ratio of 0 to 100% for different dosages of biochar-supported zinc-iron layered bimetallic oxide composite material. 5. Removal rate of tetracycline hydrochloride at different pH values: Tetracycline hydrochloride sample solutions with an initial concentration C0 of 50 mg / L were adjusted to pH 3, 4, 6, 7, 9, and 11 using hydrochloric acid and sodium hydroxide. Then, biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were added at a dosage of 1.0 g / L. Following the specific procedures described in section 4 above, the concentration C of tetracycline hydrochloride in the sample solution after saturated adsorption was measured. t The removal rate of tetracycline hydrochloride at different pH values ​​was calculated using the same formula. 6. Adsorption capacity of tetracycline hydrochloride at different CaCl2 concentrations: Tetracycline hydrochloride sample solutions with an initial concentration C0 of 50 mg / L were prepared by adding CaCl2 to CaCl2 concentrations of 25 mmol / L, 50 mmol / L, 75 mmol / L, and 100 mmol / L. Then, biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were added at a dosage of 1.0 g / L. Following the specific procedures described in section 4 above, the concentration C of tetracycline hydrochloride in the sample solution after saturated adsorption was tested. t According to the formula: q = (C0 - C t The adsorption capacity of tetracycline hydrochloride at different CaCl2 concentrations is calculated by q × V / m, where q is in mg / g, V is the volume of the tetracycline hydrochloride sample solution, and m is the mass of the biochar-supported zinc-iron layered bimetallic oxide composite material. 7. Adsorption capacity of tetracycline hydrochloride at different NaCl concentrations: Tetracycline hydrochloride sample solution with an initial concentration C0 of 50 mg / L was prepared by adding NaCl to prepare tetracycline hydrochloride sample solutions with NaCl concentrations of 25 mmol / L, 50 mmol / L, 75 mmol / L, and 100 mmol / L. Then, the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were added at a dosage of 1.0 g / L. Following the specific operation in Section 6 above, the adsorption capacity of tetracycline hydrochloride at different NaCl concentrations was tested and calculated. 8. Removal rate of tetracycline hydrochloride by biochar-supported zinc-iron layered bimetallic oxide composite material under different initial tetracycline hydrochloride concentrations: Tetracycline hydrochloride sample solutions with initial concentrations of 10 mg / L, 25 mg / L, 50 mg / L, 75 mg / L, and 100 mg / L were prepared. The biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Example 1 was then added at a dosage of 1.0 g / L. Following the specific procedures described in section 4 above, the concentration C of tetracycline hydrochloride in the sample solution was tested after 5 min, 10 min, 30 min, 60 min, 90 min, and 120 min of feeding. t The removal rate of tetracycline hydrochloride at different initial concentrations was calculated using the same formula at different time intervals. 9. Cyclic performance of tetracycline hydrochloride adsorption by biochar-supported zinc-iron layered bimetallic oxide composite material: The biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Examples 1-3 was added at a dosage of 1.0 g / L to a conical flask containing 100 mL of tetracycline hydrochloride sample solution (initial concentration C0 was 50 mg / L). The conical flask was placed on a constant temperature shaker at 180 rpm and 25 °C for 24 h until adsorption-desorption equilibrium was reached, achieving saturated adsorption of tetracycline hydrochloride by the biochar-supported zinc-iron layered bimetallic oxide composite material in the sample solution. The remaining adsorbent material in the sample was removed by passing the sample through a 0.45 µm nylon filter membrane. The concentration Ct of tetracycline hydrochloride in the remaining sample solution was measured using a UV spectrophotometer. The concentration was calculated using the formula: q = (C0 - Ct) / (Ct + ... t The adsorption capacity of the biochar-supported zinc-iron layered bimetallic oxide composite material for tetracycline hydrochloride in the sample solution was calculated by using V / m. The biochar-supported zinc-iron layered bimetallic oxide composite material was regenerated with 0.1 mol / L NaOH solution. After regeneration, the above adsorption process was repeated, and the adsorption capacity was measured after 5 cycles.

[0037] Appendix Figure 1 The biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Example 1 is shown in a 1000x magnified scanning electron microscope image. Figure 2 The two images are scanning electron microscope (SEM) images of the cross-section of the biochar without zinc-iron layered bimetallic oxide loading obtained in Comparative Example 1, magnified 5000 times. (The images are attached.) Figure 1 The surface roughness is higher due to the in-situ growth of zinc-iron layered bimetallic oxides onto the surface of biochar.

[0038] Appendix Figure 3 These are the Fourier transform infrared spectra of the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Example 1 and Comparative Example 1. The spectrum for Comparative Example 1 is at 3404.9 cm⁻¹. -1The peak at this location represents the stretching vibration of oxygen-hydrogen bonds or nitrogen-hydrogen bonds on the -OH or -NH- functional groups in biochar. This peak was blue-shifted to 3426.2 cm⁻¹ in Example 1. -1 The presence of this component indicates an increase in -OH or -NH- functional groups after loading with zinc-iron layered bimetallic oxide. Similarly, in Comparative Example 1, the concentration at 1428.4 cm⁻¹... -1 The absorption peak at that point corresponds to the stretching vibration of the C-C bond in the aromatic ring, and in Example 1, it also blue-shifted to 1455.2 cm⁻¹. -1 This also indicates that after loading with zinc-iron layered bimetallic oxide, the number of polar functional groups around the C-C bonds of the aromatic ring (hydroxyl, carbonyl, carboxyl, etc. introduced due to the loading with zinc-iron layered bimetallic oxide) increases. Comparative Example 1 shows an increase at 874.9 cm⁻¹. -1 The absorption peak at that point is the CH bending vibration peak in the fatty chain; in Example 1, this peak was blue-shifted to 874.9 cm⁻¹. -1 Furthermore, the intensity is slightly weakened because the CH bonds in the aliphatic chain have relatively weak bond energies and are easily oxidized into polar groups by oxygen-containing functional groups during hydrothermal reactions or carbonization. Moreover, during carbonization, the surrounding supported metal oxides have a catalytic effect, causing some oxygen-containing polar groups to be catalytically decomposed and carbonized away, leading to a blue shift and weakening of the peak. Compared to Comparative Example 1, Example 1 shows a lower intensity at 531 cm⁻¹. -1 and 460.1cm -1 The two newly added characteristic peaks with relatively high intensity correspond to the characteristic peaks of hydroxyl groups (Zn-OH or Fe-OH) that are tightly adsorbed and bound to Zn and Fe on the Zn and Fe layered bimetallic oxides. These two newly added characteristic peaks also fully demonstrate that zinc-iron layered bimetallic oxides have been successfully loaded onto biochar.

[0039] Appendix Figure 4 The X-ray spectra of the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Example 1 and Comparative Example 1 are shown. As can be seen from the spectra, compared with the standard spectra of ZnO and Fe2O3, Example 1 almost completely covers the characteristic peaks corresponding to the two oxides, while Comparative Example 1 does not have these characteristic peaks. This indicates that zinc-iron layered bimetallic oxides were successfully loaded onto the biochar. In addition, the characteristic peaks of amorphous carbon in Comparative Example 1 are significantly weaker in Example 1, which also indicates that zinc-iron layered bimetallic oxides are relatively uniformly loaded on the surface of the biochar. This uniform loading can also be regarded as the zinc-iron layered bimetallic oxides coating the surface of the biochar. This coating layer significantly weakens the intensity of the characteristic peaks of amorphous carbon in the XRD spectrum of Example 1.

[0040] Appendix Figure 5The removal rates of tetracycline hydrochloride from the biochar-supported zinc-iron layered bimetallic oxide composite materials obtained in Examples 1-3 and Comparative Examples 1-4 were compared under different dosages. In Examples 1-3, the removal rate was generally above 95% when the dosage was above 1.0 g / L. However, the removal rate of Comparative Example 1 was the lowest, and its removal rate was much lower than that of Examples 1-3 and Comparative Examples 2-4 at all dosages. This may be because biochar without zinc-iron layered bimetallic oxide has fewer active adsorption sites on its inner and outer surfaces, making it difficult to achieve a high removal rate. In Comparative Example 2, no cross-linked melamine cyanurate was prepared. Instead, melamine cyanurate was added during the biochar precursor preparation stage. The main functions of adding melamine cyanurate are twofold: first, its high nitrogen content allows for nitrogen doping into the biochar, increasing the polarity of the internal pore walls; second, its thermal decomposition promotes micropore formation. However, melamine cyanurate has a high nitrogen content and very low residual carbon content, resulting in relatively rapid thermal decomposition and a tendency to create large-pore structures. Therefore, cross-linking with tannic acid and polyethyleneimine utilizes the high aromatic ring content and high residual carbon content of tannic acid to delay the rapid thermal decomposition of melamine cyanurate to some extent (the thermal decomposition of tannic acid during carbonization easily forms a dense carbon layer, thus delaying the thermal decomposition of melamine cyanurate). The significant decrease in the adsorption and removal rate of tetracycline hydrochloride in Comparative Example 2 indicates that cross-linking with tannic acid and polyethyleneimine is effective. The melamine coating likely inhibited the formation of macroporous structures, thereby enhancing adsorption by promoting the formation of more micropores. In Comparative Example 3, without the addition of a complexing agent, the adsorption and removal rate of tetracycline hydrochloride also decreased significantly. This may be because the complexing agent can promote the uniform dispersion and distribution of zinc and iron metals within the biochar matrix, thus significantly improving the adsorption performance of the final composite material. In Comparative Example 4, the absence of tetraborate during the preparation of the biochar precursor also resulted in a significant decrease in the adsorption and removal rate of tetracycline hydrochloride. This may be because borates such as sodium tetraborate, potassium tetraborate, and ammonium tetraborate play a certain pore-forming role during carbonization due to thermal decomposition. Alternatively, it may be because the boron element introduced by the borates can enhance the polarity of the biochar matrix, thereby improving the adsorption performance of tetracycline on the biochar-supported zinc-iron layered bimetallic oxide composite material.

[0041] Figure 6The figures show the removal rates of tetracycline hydrochloride at different pH values ​​for the zinc-iron layered bimetallic oxide composite materials supported on biochar obtained in Examples 1-3 and Comparative Examples 1-4. As can be seen from the figures, the removal rate of tetracycline hydrochloride in Examples 1-3 decreased to about 90% at lower pH values, but gradually increased with increasing pH. When the pH was greater than 7, the removal rate decreased slightly, but still remained above 90%. This indicates that the large-scale fluctuation of pH had a limited negative impact on the removal rate. This may be because the loading of Zn and Fe metals enhanced the adsorption force between tetracycline hydrochloride and the biochar matrix. Although the electrostatic adsorption force between tetracycline hydrochloride and the biochar surface changed drastically at lower or higher pH values, the strong adsorption effect of the zinc-iron layered bimetallic oxide offset this drastic change. In addition, the doping of nitrogen in the biochar may also have played a certain role in enhancing adsorption, because the positively charged tetracycline has a very strong electrostatic binding force with the electronegative nitrogen atoms in the biochar. This strong electrostatic effect to some extent offset the adverse effects of drastic pH changes. Furthermore, in Comparative Example 1, which did not have zinc-iron layered bimetallic oxide loaded, the adsorption of tetracycline hydrochloride was greatly affected by pH value. This may be mainly because the biochar surface of Comparative Example 1 was not loaded with zinc-iron layered bimetallic oxide. Comparative Example 2, which did not have melamine cyanurate cross-linking coating, also had difficulty maintaining a high removal rate of tetracycline hydrochloride over a wide pH range. This may be due to insufficient nitrogen doping or excessive increase in micropore size caused by the rapid thermal decomposition of melamine cyanurate. The lack of complexing agent in Comparative Example 3 also caused uneven distribution of zinc-iron layered bimetallic oxide, affecting the removal rate over a wide pH range. The removal rate of Comparative Example 4 fluctuated greatly with pH value, possibly due to the lack of the activating pore-forming effect and polarity enhancement effect of tetraborate.

[0042] Appendix Figure 7 and attached Figure 8 The figures show the adsorption capacities of tetracycline hydrochloride on biochar-supported zinc-iron layered bimetallic oxide composites obtained in Examples 1-3 and Comparative Examples 1-4, respectively, under different CaCl2 and NaCl concentrations. Comparing these two figures overall, the effect of NaCl concentration variation on adsorption capacity is significantly less than that of CaCl2 concentration variation. This aligns with the general rule for tetracycline adsorption on biochar-supported metal compound composites; calcium ions are divalent metal ions with significantly larger ionic radii than monovalent sodium ions. Compared to sodium ions, divalent calcium ions are more likely to occupy more adsorption sites, resulting in a greater impact on tetracycline adsorption. However, from... Figure 7Based on the test results, compared with the other four comparative examples, Examples 1-3, at the highest calcium ion concentration of 100 mmol / L, still maintained an adsorption capacity of about 900 mg / g for tetracycline hydrochloride. This indicates that the biochar-supported zinc-iron layered bimetallic oxide composite material obtained in this invention can effectively shield the adsorption site occupancy effect caused by high concentrations of calcium ions. This may be because the negative charge radii of zinc and iron in the zinc-iron layered bimetallic oxide are relatively large. After calcium ions occupy a certain number of adsorption sites, the negative charge adsorption radius still retains a certain electrostatic attraction, and can still effectively adsorb a certain amount of tetracycline hydrochloride. Macroscopically, this is manifested as a very small decrease in adsorption capacity at higher calcium ion concentrations.

[0043] Appendix Figure 9 The removal rate of tetracycline hydrochloride by the biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Example 1 was investigated under different initial tetracycline hydrochloride concentrations. Overall, when the initial tetracycline hydrochloride concentration was below 25 mg / L, Example 1 achieved a near 100% removal rate of tetracycline hydrochloride within 40 minutes. When the initial tetracycline hydrochloride concentration reached 50 mg / L, the removal rate of tetracycline hydrochloride in Example 1 also exceeded 95%. When the initial tetracycline hydrochloride concentration increased to 75 and 100 mg / L, the removal rate of tetracycline hydrochloride was still maintained above 75%. This indicates that the biochar-supported zinc-iron layered bimetallic oxide composite material obtained in this invention has excellent effects on treating wastewater with high concentrations of tetracycline hydrochloride.

[0044] Figure 10 The biochar-supported zinc-iron layered bimetallic oxide composite material obtained in Examples 1-3 exhibits excellent cyclic regeneration performance for the adsorption of tetracycline hydrochloride. After 5 cycles of adsorption, the adsorption capacity can still be maintained above 900 mg / g, which fully demonstrates that the biochar-supported zinc-iron layered bimetallic oxide composite material obtained in this invention has excellent cyclic regeneration performance for the adsorption of tetracycline hydrochloride.

[0045] 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. A method for preparing a biochar-supported zinc-iron layered bimetallic oxide composite material, characterized in that: The preparation method of the biochar-supported zinc-iron layered bimetallic oxide composite material includes four steps: preparing cross-linked coated melamine cyanurate, preparing a precursor mixture, preparing a precursor, and carbonization. The preparation of cross-linked coated melamine cyanurate involves placing melamine, cyanuric acid, and deionized water into a reaction vessel, heating to the reaction temperature under low-speed stirring, increasing the stirring rate after the reaction is complete, adding a polyethyleneimine aqueous solution, stirring evenly, then adding a tannic acid aqueous solution dropwise, continuing the reaction until complete after the addition is finished, and then filtering, washing, and drying to obtain cross-linked coated melamine cyanurate. The reaction temperature is 60~85℃; The preparation of the precursor mixture involves placing tomato straw biomass powder, iron salt, zinc salt, cross-linked melamine cyanurate, complexing agent, and deionized water into a mixing vessel, stirring and ultrasonically dispersing to obtain a composite salt solution, then mixing anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water to obtain an activator solution, and then adding the activator solution dropwise to the composite salt solution under low-speed stirring. After the addition is complete, the temperature is raised to the reaction temperature, and the mixture is stirred at low speed until the reaction is complete to obtain the precursor mixture. The iron salt is one or a mixture of any two or more of ferric chloride, ferric sulfate, and ferric nitrate in any mass ratio. The zinc salt is one or a mixture of any two or more of zinc chloride, zinc sulfate, and zinc nitrate in any mass ratio. The complexing agent is one or a mixture of any two or more of the following in any mass ratio: tetrasodium glutamate diacetate, tetrasodium iminodisuccinate, ethylenediaminetetrapropionic acid, hypozoxytriacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, and 1,2-cyclohexanediaminetetraacetic acid. The tetraborate is one or a mixture of any two or more of sodium tetraborate, potassium tetraborate, and ammonium tetraborate in any mass ratio; The reaction temperature is 65~80℃; The reaction is to be completed within 1 to 3.5 hours. The precursor preparation involves transferring the precursor mixture into a hydrothermal reactor, and after the hydrothermal reaction is completed, centrifuging and drying are performed to obtain the precursor. The hydrothermal reaction is carried out at a temperature of 110~150℃ for a time of 20~30 hours. The carbonization process involves placing the precursor in a carbonization furnace and heating it to 470-600°C at a rate of 3-5°C / min under nitrogen protection at a flow rate of 20-120 mL / min. The mixture is then carbonized at this constant temperature for 2-3.5 hours, followed by cooling to room temperature under nitrogen protection, to obtain a biochar-supported zinc-iron layered bimetallic oxide composite material.

2. The method for preparing the biochar-supported zinc-iron layered bimetallic oxide composite material according to claim 1, characterized in that: The mass concentration of polyethyleneimine in the polyethyleneimine aqueous solution is 5-15 wt%. The mass concentration of tannic acid in the tannic acid aqueous solution is 10~20wt%; The mass ratio of melamine, cyanuric acid, deionized water, polyethyleneimine aqueous solution, and tannic acid aqueous solution is 20~80:30~110:550~1300:30~90:40~110.

3. The method for preparing the biochar-supported zinc-iron layered bimetallic oxide composite material according to claim 1, characterized in that: The mass ratio of the tomato straw biomass powder, iron salt, zinc salt, cross-linked coated melamine cyanurate, complexing agent, and deionized water is 50~200:8~20:4~15:6~25:1~4:360~650. The mass ratio of anhydrous sodium carbonate, sodium hydroxide, tetraborate, and deionized water is 15~50:10~40:2~8:200~600.

4. The biochar-supported zinc-iron layered bimetallic oxide composite material prepared by any one of the preparation methods according to claims 1-3, characterized in that: The biochar-supported zinc-iron layered bimetallic oxide composite material is a microporous material with biochar as the matrix and zinc-iron layered bimetallic oxide uniformly distributed on the inner and outer pore walls of the biochar matrix.

5. The application of the biochar-supported zinc-iron layered bimetallic oxide composite material according to claim 4, characterized in that: The biochar-supported zinc-iron layered bimetallic oxide composite material is used for the adsorption and removal of tetracycline hydrochloride.

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