Magnetic charcoal / silver phosphate composite material and preparation method thereof

Abstract

The invention provides a preparation method of a magnetic biochar / silver phosphate composite material, which comprises the following steps: step S1, biomass template pretreatment: selecting biomass as a template, cleaning in at least one of an acid solution, an alkali solution and a buffer solution, and performing low-temperature freezing and slicing to obtain the biomass template; step S2, preparing magnetic biochar: preparing the biomass template prepared in the step S1 by a one-pot method to obtain the magnetic biochar; and S3, preparing the magnetic biochar / silver phosphate composite material: performing surface modification on the magnetic biochar prepared in the step S2 by adopting a modifier containing an organic anion group, and performing induced precipitation on the magnetic biochar subjected to surface modification to obtain the magnetic biochar / silver phosphate composite material. The magnetic charcoal / silver phosphate composite material provided by the embodiment of the invention is high in photocatalytic activity, good in stability, easy to recover, good in circularity, low in cost and green in process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic materials, and particularly relates to a magnetic biochar / silver phosphate composite material and a preparation method thereof. BACKGROUND

[0002] The problem of antibiotic drug (such as norfloxacin, tetracycline, etc.) residues in the environment is serious. Traditional treatment methods such as adsorption method only transfer pollutants, and the efficiency of biological degradation method is low due to the antibiotic inhibition. Although the photocatalytic technology in the advanced oxidation method has a mild condition, the core photocatalyst such as silver phosphate (Ag3PO4) has defects such as serious photo-corrosion, small specific surface area and difficult recovery. The existing improvement schemes include: (1) Ag3PO4 is combined with metal / metal oxide (such as Ag / Ag3PO4, Ag3PO4 / ZnO): this scheme partially improves the stability, but the photocatalytic activity is not synergistically improved; (2) Ag3PO4 is combined with carbon material (such as graphene oxide / Ag3PO4): the cost is high, and the preparation process of the carbon material (such as carbon nanotube) is complex. Therefore, the existing technology cannot balance the photocatalytic activity, stability, low cost and easy recovery. SUMMARY

[0003] To solve at least one technical problem in the prior art, the application provides a magnetic biochar / silver phosphate composite material and a preparation method thereof, which has high photocatalytic activity and low cost. To achieve the above technical purpose, the technical scheme adopted by the embodiments of the application is as follows: In a first aspect, the application provides a preparation method of a magnetic biochar / silver phosphate composite material, which includes the following steps: Step S1, biomass template pretreatment: selecting biomass as a template, washing in at least one of an acid solution, an alkali solution and a buffer solution, and then freezing at low temperature and slicing to obtain the biomass template; Step S2, preparation of magnetic biochar: preparing the magnetic biochar by one-pot method using the biomass template prepared in step S1; Step S3, preparation of magnetic biochar / silver phosphate composite material: modifying the magnetic biochar prepared in step S2 by using a modifier containing an organic anion group, and then inducing the magnetic biochar after surface modification to deposit to obtain the magnetic biochar / silver phosphate composite material.

[0004] Further, in step S1, the biomass includes pollen and / or lignocellulose biomass. And / or, the lignocellulose biomass includes at least one of plant leaves, straw, algae and biological cellulose. And / or, the plant leaves include at least one of C3 plants and C4 plants. And / or, the straw includes the straw of the Gramineae; And / or, the algae includes the Spirulina.

[0005] And / or, the acid solution includes hydrochloric acid, and the concentration of the hydrochloric acid is 0.05-0.2 mol / L; And / or, the alkali solution includes sodium hydroxide, and the concentration of the sodium hydroxide is 0.05-0.2 mol / L; And / or, the buffer solution includes the phosphate buffer, and the pH of the phosphate buffer is 7.0-7.8; And / or, the temperature of the low-temperature freezing is -196 to -70℃, and the time is 1-5 min; And / or, the low-temperature freezing includes immersing the biomass into a low-temperature fixing agent, and then performing a quick freezing treatment in liquid nitrogen and / or a freezing microtome; the low-temperature fixing agent includes 3.5-4.5% of paraformaldehyde and / or 0.05-0.15% of succinic acid in terms of mass fraction; And / or, the thickness of the section is 10-30 µm.

[0006] Further, in the step S2, the one-pot method includes an impregnation-pyrolysis method, and the impregnation-pyrolysis method includes: immersing 0.5-3 g of the biomass template prepared in the step S1 into 50-200 mL of a precursor solution for 2-12 h, then taking out the biomass template, drying the biomass template, and performing a thermal decomposition under a limited oxygen condition with an oxygen concentration less than 5% for 1-5 h, wherein the thermal decomposition temperature is 300-800℃, and the heating rate is 2-5℃ / min; after cooling, the biomass template is taken out and cleaned to obtain the magnetic biochar; And / or, the one-pot method includes a hydrothermal method, and the hydrothermal method includes: mixing 0.5-3 g of the biomass template prepared in the step S1 with 50-200 mL of a precursor solution, and placing the mixture into a high-pressure reaction kettle to perform a hydrothermal reaction, wherein the temperature of the hydrothermal reaction is 160-300℃, and the time is 10-15 h; after the reaction, the mixture is cooled, taken out, and cleaned to obtain the magnetic biochar; And / or, the one-pot method includes a microwave catalytic conversion method, and the microwave catalytic conversion method includes: mixing 0.5-3 g of the biomass template prepared in the step S1 with 10-100 mL of a first activator and immersing for 1-12 h, then adding 50-200 mL of a precursor solution, and placing the mixture into a microwave device to perform a reaction, wherein the power of the microwave device is set to 300-700 w, and the reaction time is 20-30 min; after the reaction, the mixture is cooled, taken out, and cleaned to obtain the magnetic biochar.

[0007] Further, the precursor solution includes iron salt and zinc salt. And / or, the iron salt includes at least one of potassium ferrate, ferric nitrate, and ferric chloride; And / or, the zinc salt includes at least one of zinc acetate, zinc nitrate, and zinc chloride; And / or, the concentration of the precursor solution is 0.01–0.5 mol / L; And / or, the molar ratio of the iron salt to the zinc salt is (1.8–2.2):1; And / or, the first activator includes at least one of zinc chloride, phosphoric acid, and potassium hydroxide; And / or, the concentration of the first activator is 0.1 to 2.0 mol / L.

[0008] Furthermore, the soaking temperature is 15–80°C; And / or, the drying includes vacuum drying, wherein the drying temperature is 55-65°C and the drying time is 8-15 hours; And / or, the cooling includes cooling to 15–25°C under N2 protection. And / or, the cleaning includes magnetic separation cleaning, which involves using a magnet to attract the contents of the container while removing the supernatant; And / or, the cleaning includes cleaning to a pH value of 6.5 to 7.5.

[0009] Further, in step S3, the organic anionic group includes at least one of a carboxylic acid group, a sulfonic acid group, and an amino group; And / or, the modifier containing an organic anionic group includes at least one of ammonium hydroxide, ammonia, citric acid, and aminosulfonic acid.

[0010] Further, in step S3, the surface modification includes: activating the magnetic biochar in 10-100 mL of a second activator, then adding ammonium hydroxide with a concentration of 0.5-1.5% (w / v) and a volume of 50-100 mL and reacting for 0.5-2 h, wherein the mass ratio of the second activator to the magnetic biochar is 1:1-5:1, and finally treating it in a treatment solution to obtain the surface-modified magnetic biochar; And / or, the surface modification includes: placing the magnetic biochar in a tube furnace and introducing ammonia and nitrogen into the tube furnace, reacting at 300-600°C for 1-4 hours to obtain the surface-modified magnetic biochar; And / or, the surface modification includes: activating the magnetic biochar in 10-100 mL of a second activator, then adding citric acid at a concentration of 0.5-1.5% (w / v) and a volume of 50-100 mL and reacting for 0.5-2 h, wherein the mass ratio of citric acid to the magnetic biochar is 1:1-3:1, to obtain the surface-modified magnetic biochar; Further, the treatment solution is prepared by dissolving sodium dithionite in glacial acetic acid, wherein the concentration of sodium dithionite is 0.5-1.5% (w / v) and the treatment time is 0.5-2 h; And / or, the volume ratio of ammonia to nitrogen is 1:4 to 1:10; And / or, the ammonia gas flow rate is 50–200 mL / min; And / or, the nitrogen gas flow rate is 50–200 mL / min; And / or, the second activator includes glutaraldehyde and / or epichlorohydrin; And / or, the concentration of the second activator is 1-5%; And / or, the pH of the second activator is 8 to 10; And / or, the activation temperature in the second activator is 15-25°C, and the activation time is 1-2 hours.

[0011] Further, in step S3, the induced precipitation includes: dispersing the surface-modified magnetic biochar in a silver nitrate solution with a concentration of 0.05–0.2 mol / L and a volume of 20–70 mL, adjusting the pH to 7–9 with a second alkaline solution, adding a disodium hydrogen phosphate solution with a concentration of 0.05–0.2 mol / L and a volume of 20–70 mL, and reacting at 25–80 °C for 1–3 h to obtain the magnetic biochar / silver phosphate composite material; The second alkaline solution includes at least one of sodium hydroxide and ammonia water.

[0012] Secondly, embodiments of the present invention also provide a magnetic biochar / silver phosphate composite material prepared by the above-described preparation method.

[0013] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: (1) The magnetic biochar / silver phosphate composite material provided in this embodiment of the invention utilizes the natural hierarchical structure of biomass templates to replace artificial templates, avoiding secondary pollution. Biochar raw materials (such as plant straw and algae) are widely available and inexpensive, significantly reducing the cost of composite materials. The "one-pot" preparation method avoids the template removal step, making the process simple and easy to operate. The introduction of magnetic biochar enables the composite material to achieve high adsorption, high conductivity and magnetic separation characteristics. The "surface modification-induced precipitation" method achieves uniform distribution of Ag3PO4 on the surface of magnetic biochar, optimizes the band structure and enhances resistance to photocorrosion. The introduction of ZnFe2O4 imparts magnetism to the material, allowing for rapid separation with an external magnetic field. After 7 cycles, the degradation efficiency still reaches over 86%.

[0014] (2) The magnetic biochar / silver phosphate composite material provided in the embodiments of the present invention has high photocatalytic activity, good stability, easy recovery and good recyclability, low cost and green process. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] Furthermore, it should be understood that after reading the contents disclosed in this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the protection scope defined by this invention.

[0017] In a first aspect, embodiments of the present invention provide a method for preparing a magnetic biochar / silver phosphate composite material, comprising the following steps: Step S1, Biomass template pretreatment: Select biomass as template, wash it in at least one of acid solution, alkaline solution, and buffer solution, and then freeze and slice it at low temperature to obtain biomass template; Step S2, Preparation of magnetic biochar: The biomass template obtained in step S1 is used to prepare the magnetic biochar (Biochar-ZnFe2O4) in a one-pot process. Step S3, preparation of magnetic biochar / silver phosphate composite material: The magnetic biochar obtained in step S2 is surface modified with a modifier containing organic anionic groups, and then the surface-modified magnetic biochar is induced to precipitate to obtain magnetic biochar / silver phosphate composite material (Biochar-ZnFe2O4 / Ag3PO4).

[0018] Further, in step S1, the biomass includes pollen and / or lignocellulosic biomass; And / or, the lignocellulosic biomass includes at least one of plant leaves, straw, algae, and biocellulose; And / or, the plant leaves include at least one of C3 plants and C4 plants; And / or, the straw includes the straw of grasses; And / or, the algae include Spirulina.

[0019] And / or, the acid solution includes hydrochloric acid, wherein the concentration of the hydrochloric acid (HCl) is 0.05–0.2 mol / L; And / or, the alkaline solution includes sodium hydroxide, wherein the concentration of the sodium hydroxide (NaOH) is 0.05–0.2 mol / L; And / or, the buffer solution comprises phosphate buffer, wherein the phosphate buffer (PBS) has a pH of 7.0 to 7.8; And / or, the cryogenic freezing temperature is -196 to -70°C, and the time is 1 to 5 minutes; And / or, the cryogenic freezing includes immersing biomass in a cryogenic fixative and then rapidly freezing it in liquid nitrogen and / or a cryostat; the cryogenic fixative comprises, by mass fraction, 3.5 to 4.5% paraformaldehyde and / or 0.05 to 0.15% succinic acid; And / or, the thickness of the slice is 10–30 µm.

[0020] It should be noted that this application uses natural biomass with a multi-dimensional hierarchical structure as a template. The loose and porous structure is beneficial to the final use effect of the material. It uses acid, alkali or buffer solution to clean the biomass to remove impurities such as pigments.

[0021] Further, in step S2, the one-pot method includes an impregnation-pyrolysis method, which includes: soaking 0.5-3g of the biomass template obtained in step S1 in 50-200mL of precursor solution for 2-12h, then taking out the biomass template, drying the biomass template, and carrying out thermal decomposition for 1-5h under oxygen-limited conditions with an oxygen concentration of less than 5%, wherein the thermal decomposition temperature is 300-800℃ and the heating rate is 2-5℃ / min, for example, the temperature can be 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, etc., and the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, etc., after cooling, taking it out and washing it to obtain the magnetic biochar; And / or, the one-pot method includes a hydrothermal method, which includes: mixing 0.5-3g of the biomass template obtained in step S1 with 50-200mL of precursor solution, and placing it in a high-pressure reactor for hydrothermal reaction. The hydrothermal reaction temperature is 160-300℃ and the time is 10-15h. For example, the temperature can be 160℃, 200℃, 250℃, 300℃, etc. After the reaction, the mixture is cooled, removed, and washed to obtain the magnetic biochar. And / or, the one-pot method includes a microwave catalytic conversion method, which includes: mixing 0.5-3g of the biomass template obtained in step S1 with 10-100mL of the first activator and soaking for 1-12 hours, then adding 50-200mL of the precursor solution and placing it in a microwave device for reaction, setting the power of the microwave device to 300-700W, for example, the power can be 300W, 400W, 500W, 600W, 700W, etc., the reaction time to 20-30 minutes, cooling after reaction, taking it out and washing it to obtain the magnetic biochar.

[0022] It should be noted that the preparation of the magnetic biochar in step S2 of this application can be carried out using any one of the one-pot methods, or a combination of any two or three methods. The biomass template is loose and porous. By adjusting any parameter in the precursor solution, the deposition rate and amount of ions in the precursor solution on the biomass template can be adjusted, which is beneficial for various precursors to penetrate into the interior of the biomass template.

[0023] Furthermore, the precursor solution includes iron salts and zinc salts; And / or, the iron salt includes at least one of potassium ferrate, ferric nitrate, and ferric chloride; And / or, the zinc salt includes at least one of zinc acetate, zinc nitrate, and zinc chloride; And / or, the concentration of the precursor solution is 0.01 to 0.5 mol / L, for example, it can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc.; And / or, the molar ratio of the iron salt to the zinc salt is (1.8 to 2.2):1, for example, the ratio can be 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, etc.; And / or, the first activator includes at least one of zinc chloride (ZnCl2), phosphoric acid (H3PO4), and potassium hydroxide (KOH); And / or, the concentration of the first activator is 0.1 to 2.0 mol / L, for example, it can be 0.1 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, etc.

[0024] Furthermore, the soaking temperature is 15–80°C; And / or, the drying includes vacuum drying, wherein the drying temperature is 55-65°C and the drying time is 8-15 hours; And / or, the cooling includes cooling to 15–25°C under N2 protection. And / or, the cleaning includes magnetic separation cleaning, which involves using a magnet to attract the contents of the container while removing the supernatant; And / or, the cleaning includes cleaning to a pH value of 6.5 to 7.5.

[0025] In this application, the drying process employs extremely low temperature drying to avoid residual moisture in the magnetic biochar, which could affect pyrolysis and facilitate the preparation of the layered magnetic biochar structure. The magnetic separation cleaning process ensures the purity of the product, guarantees the absence of impurities, and protects the structural integrity of the product. Cleaning to a neutral pH ensures the surface charge neutrality of the magnetic biochar, preventing any impact on the subsequent preparation of composite materials.

[0026] Further, in step S3, the organic anionic group includes at least one of a carboxylic acid group, a sulfonic acid group, and an amino group; And / or, the modifier containing an organic anionic group includes at least one of ammonium hydroxide, ammonia, citric acid, and aminosulfonic acid.

[0027] Further, in step S3, the surface modification includes: activating the magnetic biochar in 10-100 mL of a second activator, then adding ammonium hydroxide with a concentration of 0.5-1.5% (w / v) and a volume of 50-100 mL and reacting for 0.5-2 h, wherein the mass ratio of the second activator to the magnetic biochar is 1:1-5:1, and finally treating it in a treatment solution to obtain the surface-modified magnetic biochar; And / or, the surface modification includes: placing the magnetic biochar in a tube furnace and introducing ammonia and nitrogen into the tube furnace, reacting at 300-600°C for 1-4 hours, for example, the temperature can be 300°C, 400°C, 500°C, 600°C, etc., to obtain the surface-modified magnetic biochar. And / or, the surface modification includes: activating the magnetic biochar in 10-100 mL of a second activator, then adding citric acid at a concentration of 0.5-1.5% (w / v) and a volume of 50-100 mL and reacting for 0.5-2 h, wherein the mass ratio of citric acid to the magnetic biochar is 1:1-3:1, to obtain the surface-modified magnetic biochar.

[0028] The surface of the magnetic biochar is modified with the modifier containing anionic groups, which facilitates the subsequent induction or promotion of uniform distribution and deposition of Ag3PO4 crystals on the surface of the magnetic biochar. The hydrophilicity of the magnetic biochar is improved after modification with the modifier, and the Ag⁺ adsorption rate is increased by 25%.

[0029] Further, the treatment solution is prepared by dissolving sodium dithionite in glacial acetic acid, wherein the concentration of sodium dithionite is 0.5-1.5% (w / v) and the treatment time is 0.5-2 h; And / or, the volume ratio of ammonia to nitrogen is 1:4 to 1:10, for example, it can be 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.; And / or, the ammonia gas flow rate is 50 to 200 mL / min, for example, it can be 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, etc.; And / or, the nitrogen gas flow rate is 50 to 200 mL / min, for example, it can be 50 mL / min, 100 mL / min, 150 mL / min, 200 mL / min, etc.; And / or, the second activator includes glutaraldehyde and / or epichlorohydrin; And / or, the concentration of the second activator is 1 to 5%, for example, it can be 1%, 2%, 3%, 4%, 5%, etc.; And / or, the pH of the second activator is 8 to 10, for example, it can be 8, 8.5, 9, 9.5, 10, etc.; And / or, the activation temperature in the second activator is 15-25°C, and the activation time is 1-2 hours.

[0030] Further, in step S3, the induced precipitation includes: dispersing the surface-modified magnetic biochar in a silver nitrate (AgNO3) solution with a concentration of 0.05–0.2 mol / L and a volume of 20–70 mL, adjusting the pH to 7–9 with a second alkaline solution, adding a disodium hydrogen phosphate (Na2HPO4) solution with a concentration of 0.05–0.2 mol / L and a volume of 20–70 mL, and reacting at 25–80 °C for 1–3 h to obtain the magnetic biochar / silver phosphate composite material (Biochar-ZnFe2O4 / Ag3PO4 composite material). The second alkaline solution includes at least one of sodium hydroxide (NaOH) and ammonia (NH3·H2O).

[0031] The concentration of NaOH is 0.5–1.0 mol / L, and the concentration of NH3·H2O is 25–28%.

[0032] Secondly, embodiments of the present invention also provide a magnetic biochar / silver phosphate composite material prepared by the above-described preparation method.

[0033] In the following specific embodiments, operations not specified under certain conditions are performed under standard conditions or conditions recommended by the manufacturer. All raw materials without specified manufacturers and specifications are commercially available products.

[0034] Example 1 A method for preparing a magnetic biochar / silver phosphate composite material includes the following steps: Step S1, Biomass template pretreatment: Select corn leaves as biomass, rinse with deionized water, soak in 0.1 mol / L NaOH, then take them out and freeze at -80℃ for 1 min, and cut them into slices with a thickness of 20 μm to obtain the biomass template; Step S2, Preparation of magnetic biochar: A precursor solution of ZnFe2O4 was prepared using ferric nitrate (Fe(NO3)3) and zinc nitrate (Zn(NO3)2), with a molar ratio of Fe(NO3)3 to Zn(NO3)2 of Fe:Zn = 2:1, and the concentration of the precursor solution was 0.5 mol / L. 2g of the biomass template obtained in step S1 was placed in 100mL of the precursor solution and soaked at 25℃ for 10h. Then, it was removed and dried under vacuum at 60℃ for 12h. Then, it was placed in a tube furnace and pyrolyzed at 300℃ for 2h under N2 protection. After that, it was cooled to room temperature under N2 protection and subjected to magnetic separation and ultrasonic washing until the pH value was 7 to obtain Biochar-ZnFe2O4. Step S3, preparation of magnetic biochar / silver phosphate composite material: The magnetic biochar obtained in step S2 was activated at 20°C in glutaraldehyde (pH 9, concentration 3%, volume 50 mL) for 2 h, followed by the addition of ammonium hydroxide (1% (w / v), volume 50 mL) for 2 h, and then treated with sodium dithionite-glacial acetic acid solution (1% (w / v)) for 1 h to obtain surface-modified magnetic biochar; The surface-modified magnetic biochar was dispersed in 50 mL of 0.1 mol / L AgNO3 solution, the pH of the solution was adjusted to 7 using sodium hydroxide, and then 50 mL of 0.1 mol / L Na2HPO4 solution was added, and the reaction was carried out at 25°C for 1 h to obtain the Biochar-ZnFe2O4 / Ag3PO4 composite material.

[0035] Example 2 A method for preparing a magnetic biochar / silver phosphate composite material includes the following steps: Step S1, Biomass template pretreatment: Wheat straw is selected as biomass, rinsed with deionized water, soaked in 0.1 mol / L HCl, then taken out and frozen at -80℃ for 1 min, and cut into slices with a thickness of 20 μm to obtain the biomass template; Step S2, Preparation of magnetic biochar: A precursor solution of ZnFe2O4 is prepared using ferric chloride (FeCl3) and zinc chloride (ZnCl2), with a molar ratio of FeCl3 to ZnCl2 of Fe:Zn = 2:1 and a concentration of 0.3 mol / L. 2 g of the biomass template obtained in step S1 is placed in 100 mL of the precursor solution and reacted in a high-pressure reactor at 230 °C for 6 h. The mixture is then removed, dried under vacuum at 60 °C for 12 h, cooled to room temperature under N2 protection, and subjected to magnetic separation and ultrasonic washing until the pH value reaches 7 to obtain the Biochar-ZnFe2O4. Step S3, preparation of magnetic biochar / silver phosphate composite material: The magnetic biochar obtained in step S2 is activated at 20°C in glutaraldehyde (pH 9, concentration 3%, volume 50mL) for 2 hours, followed by the addition of citric acid (1% w / v, volume 50mL) for 2 hours to obtain surface-modified magnetic biochar; the surface-modified magnetic biochar is dispersed in 50mL of 0.1mol / L AgNO3 solution, the pH of the solution is adjusted to 8 using sodium hydroxide, and then 50mL of 0.1mol / L Na2HPO4 solution is added, and the reaction is carried out at 50°C for 2 hours to obtain Biochar-ZnFe2O4 / Ag3PO4 composite material.

[0036] Example 3 A method for preparing a magnetic biochar / silver phosphate composite material includes the following steps: Step S1, Biomass template pretreatment: Spirulina was selected as biomass, rinsed with deionized water, soaked and rinsed in PBS with a pH of 7.4, then taken out and frozen at -80℃ for 1 min, and cut into slices with a thickness of 20 μm to obtain the biomass template; Step S2, Preparation of magnetic biochar: A precursor solution of ZnFe2O4 was prepared using potassium ferrate (K2FeO4) and zinc acetate (Zn(CH3COO)2), with a molar ratio of Fe:Zn of K2FeO4 to Zn(CH3COO)2 of 2:1. The concentration of the precursor solution was 0.4 mol / L. 2 g of the biomass template obtained in step S1 was added to 60 mL of KOH with a concentration of 1 mol / L and mixed and soaked for 6 h. Then, 100 mL of the precursor solution was added and the mixture was placed in a microwave device for reaction. The power of the microwave device was set to 700 W and the time to 25 min. The mixture was then removed and dried under vacuum at 60 °C for 12 h. After being cooled to room temperature under N2 protection, it was subjected to magnetic separation and ultrasonic washing until the pH value was 7 to obtain Biochar-ZnFe2O4. Step S3, Preparation of magnetic biochar / silver phosphate composite material: The magnetic biochar obtained in step S2 is activated at 20°C in glutaraldehyde (pH 9, concentration 3%, volume 50mL) for 2 hours. Then, 1% (w / v) aminosulfonic acid (volume 50mL) is added and reacted for 2 hours to obtain surface-modified magnetic biochar. The surface-modified magnetic biochar is dispersed in 50mL of 0.1mol / L AgNO3 solution, and the pH of the solution is adjusted to 9 using sodium hydroxide. Then, 50mL of 0.1mol / L Na2HPO4 solution is added, and the reaction is carried out at 80°C for 3 hours to obtain the Biochar-ZnFe2O4 / Ag3PO4 composite material.

[0037] Comparative Example 1 A method for preparing an Ag3PO4 photocatalyst, comprising: 50 mL of 0.1 mol / L AgNO3 solution and 50 mL of 0.1 mol / L Na2HPO4 solution were mixed and stirred at room temperature for 1 h. After filtration, washing and drying, Ag3PO4 photocatalyst was obtained.

[0038] Comparative Example 2 A method for preparing an Ag3PO4 / ZnO composite material, comprising: 50 mL of 0.1 mol / L AgNO3 solution and 50 mL of 0.1 mol / L Na2HPO4 solution were mixed, and then 1.7 g of ZnO nanoparticles were co-precipitated with AgNO3 / Na2HPO4. After stirring at room temperature for 1 h, the mixture was filtered, washed and dried to obtain Ag3PO4 / ZnO composite material.

[0039] Comparative Example 3 The preparation of an Ag3PO4 / graphene composite material includes: Graphene oxide (GO) was mixed with 50 mL of Ag3PO4 at a concentration of 5 mg / mL using ultrasound assistance. The amount of GO added was 8% of the mass fraction of Ag3PO4. The mixture was reacted at 180 °C for 6 h. After filtration, washing and drying, the GO / Ag3PO4 composite material was obtained.

[0040] Application Examples This application example evaluates the visible light catalytic activity, stability, and magnetic properties of the Biochar-ZnFe2O4 / Ag3PO4 composite material provided in Examples 1-3, the Ag3PO4 photocatalyst provided in Comparative Example 1, the Ag3PO4 / ZnO composite material provided in Comparative Example 2, and the Ag3PO4 / graphene composite material provided in Comparative Example 3. Specifically: Visible light catalytic activity: The photocatalytic reaction was tested using a BL-GHX-V type photocatalytic reaction device. The test conditions were as follows: a xenon lamp was used as the visible light source, with wavelengths below 420 nm filtered out. Antibiotics (norfloxacin, amoxicillin, ciprofloxacin, tetracycline hydrochloride, etc.) were selected as the target pollutants for degradation. Representative antibiotics with stable aromatic and heterocyclic rings (hereinafter referred to as typical antibiotics) were selected as the treatment targets. Under visible light irradiation, the degradation rate of typical antibiotics (i.e., the percentage of substrate amount after reaction to that before reaction per unit time) and mineralization (i.e., total organic carbon (TOC) removal rate) were used as indicators to evaluate the photocatalytic activity of the magnetic biochar / silver phosphate composite material. Simultaneously, the Langmuir-Hinshelwood model was used to investigate the photocatalytic reaction kinetic constant of the composite material, and its photocatalytic activity was evaluated based on the magnitude of the kinetic constant.

[0041] Stability: Under visible light irradiation, the degradation rate and mineralization of typical antibiotics were used as indicators. Through recycling experiments, the magnetic biochar / silver phosphate composite material was separated and collected after each use, dried, and reused. With the increase of recycling times, the stability of the composite material was comprehensively analyzed by combining the test results of antibiotic removal rate and mineralization.

[0042] Magnetic properties: The hysteresis loop of the composite material samples was measured using a vibrating sample magnetometer (VSM), and the magnetic properties of the magnetic biochar / silver phosphate composite material were evaluated by analyzing the hysteresis loop spectrum.

[0043] The performance of the Biochar-ZnFe2O4 / Ag3PO4 composite material provided in Examples 1-3, the Ag3PO4 photocatalyst provided in Comparative Example 1, the Ag3PO4 / ZnO composite material provided in Comparative Example 2, and the Ag3PO4 / graphene composite material provided in Comparative Example 3 are summarized in Table 1 below.

[0044] Table 1. Performance test results of the products prepared in Examples 1-3 and Comparative Examples 1-3 As shown in Table 1, among the composite materials prepared according to the prior art in Comparative Examples 1-3, the Ag3PO4 photocatalyst prepared in Comparative Example 1 and the Ag3PO4 / ZnO composite material prepared in Comparative Example 2 have similar degradation efficiencies for methyl orange, both of which are very low and have poor stability, and lose activity after cycling. Although the Ag3PO4 / graphene composite material prepared in Comparative Example 3 has a degradation rate that can be increased by up to 80%, the preparation of graphene is complex and costly, and the cycling performance is poor, resulting in unsatisfactory effects.

[0045] The Biochar-ZnFe2O4 / Ag3PO4 composite material prepared in Example 1 of this application, with norfloxacin as the target pollutant, was degraded for 120 minutes in a BL-GHX-V type photoreactor. The degradation rate reached 92% and the TOC removal rate was 85%. After 5 cycles, the degradation rate remained at 88%. VSM testing showed a magnetic separation recovery rate of 95%. Compared with Comparative Example 1, it can be seen that the larger specific surface area and microporous structure of magnetic biochar provide more active sites for the reaction. Its conductivity promotes the separation of photogenerated electron-hole pairs, which increases the degradation efficiency of antibiotics to more than twice that of pure Ag3PO4. The Biochar-ZnFe2O4 / Ag3PO4 composite material prepared in Example 2 achieved a degradation rate of 94% with amoxicillin as the target pollutant. The Biochar-ZnFe2O4 / Ag3PO4 composite material prepared in Example 3 achieved a degradation rate of 90% and a mineralization of 88% with ciprofloxacin as the target pollutant. After 7 cycles, the degradation rate was 86% and the magnetic recovery rate was 93%. Among them, in the Biochar-ZnFe2O4 / Ag3PO4 composite materials provided in Examples 1-3 of this application, it can be seen that the cyclic degradation rate of the Biochar-ZnFe2O4 / Ag3PO4 composite materials prepared in this example is higher than 90%, and can still reach 85% after multiple cycles. The recovery rate can also reach more than 90%, with excellent overall performance, low cost, and great potential.

[0046] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a magnetic biochar / silver phosphate composite material, characterized in that, Includes the following steps: Step S1, Biomass template pretreatment: Select biomass as template, wash it in at least one of acid solution, alkaline solution, and buffer solution, and then freeze and slice it at low temperature to obtain biomass template; Step S2, Preparation of magnetic biochar: The magnetic biochar is obtained by preparing the biomass template obtained in step S1 using a one-pot method. Step S3, preparing magnetic biochar / silver phosphate composite material: the magnetic biochar obtained in step S2 is surface-modified with a modifier containing organic anionic groups, and then the surface-modified magnetic biochar is induced to precipitate to obtain magnetic biochar / silver phosphate composite material.

2. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 1, characterized in that, In step S1, the biomass includes pollen and / or lignocellulose biomass; And / or, the lignocellulosic biomass includes at least one of plant leaves, straw, algae, and biocellulose; And / or, the plant leaves include at least one of C3 plants and C4 plants; And / or, the straw includes the straw of grasses; And / or, the algae include Spirulina; And / or, the acid solution includes hydrochloric acid, the concentration of which is 0.05–0.2 mol / L; And / or, the alkaline solution includes sodium hydroxide, the concentration of which is 0.05–0.2 mol / L; And / or, the buffer solution comprises a phosphate buffer having a pH of 7.0 to 7.8; And / or, the cryogenic freezing temperature is -196 to -70°C, and the time is 1 to 5 minutes; And / or, the cryogenic freezing includes immersing biomass in a cryogenic fixative and then rapidly freezing it in liquid nitrogen and / or a cryostat; the cryogenic fixative comprises, by mass fraction, 3.5 to 4.5% paraformaldehyde and / or 0.05 to 0.15% succinic acid; And / or, the thickness of the slice is 10–30 µm.

3. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 1, characterized in that, In step S2, the one-pot method includes an impregnation-pyrolysis method, which includes: soaking 0.5-3g of the biomass template obtained in step S1 in 50-200mL of precursor solution for 2-12 hours, then taking out the biomass template, drying the biomass template, and carrying out thermal decomposition for 1-5 hours under oxygen-limited conditions with an oxygen concentration of less than 5%, wherein the thermal decomposition temperature is 300-800℃ and the heating rate is 2-5℃ / min, and after cooling, taking it out and washing it to obtain the magnetic biochar; And / or, the one-pot method includes a hydrothermal method, which includes: mixing 0.5-3g of the biomass template obtained in step S1 with 50-200mL of precursor solution, and placing it in a high-pressure reactor for hydrothermal reaction. The hydrothermal reaction is carried out at a temperature of 160-300℃ for 10-15h. After the reaction, the mixture is cooled, removed, and washed to obtain the magnetic biochar. And / or, the one-pot method includes a microwave catalytic conversion method, which includes: mixing 0.5-3g of the biomass template obtained in step S1 with 10-100mL of the first activator and soaking for 1-12 h, then adding 50-200mL of the precursor solution and placing it in a microwave device for reaction, setting the power of the microwave device to 300-700w and the reaction time to 20-30min, cooling after the reaction, removing and washing to obtain the magnetic biochar.

4. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 3, characterized in that, The precursor solution includes iron salts and zinc salts; And / or, the iron salt includes at least one of potassium ferrate, ferric nitrate, and ferric chloride; And / or, the zinc salt includes at least one of zinc acetate, zinc nitrate, and zinc chloride; And / or, the concentration of the precursor solution is 0.01–0.5 mol / L; And / or, the molar ratio of the iron salt to the zinc salt is (1.8–2.2):1; And / or, the first activator includes at least one of zinc chloride, phosphoric acid, and potassium hydroxide; And / or, the concentration of the first activator is 0.1 to 2.0 mol / L.

5. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 3, characterized in that, The soaking temperature is 15–80°C; And / or, the drying includes vacuum drying, wherein the drying temperature is 55-65°C and the drying time is 8-15 hours; And / or, the cooling includes cooling to 15–25°C under N2 protection; And / or, the cleaning includes magnetic separation cleaning, which involves using a magnet to attract the contents of the container while removing the supernatant; And / or, the cleaning includes cleaning to a pH value of 6.5 to 7.

5.

6. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 1, characterized in that, In step S3, the organic anionic group includes at least one of a carboxylic acid group, a sulfonic acid group, and an amino group; And / or, the modifier containing an organic anionic group includes at least one of ammonium hydroxide, ammonia, citric acid, and aminosulfonic acid.

7. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 1, characterized in that, In step S3, the surface modification includes: activating the magnetic biochar in 10-100 mL of a second activator, then adding ammonium hydroxide with a concentration of 0.5-1.5% (w / v) and a volume of 50-100 mL and reacting for 0.5-2 h, wherein the mass ratio of the second activator to the magnetic biochar is 1:1-5:1, and finally treating it in a treatment solution to obtain the surface-modified magnetic biochar; And / or, the surface modification includes: placing the magnetic biochar in a tube furnace and introducing ammonia and nitrogen into the tube furnace, reacting at 300-600°C for 1-4 hours to obtain the surface-modified magnetic biochar; And / or, the surface modification includes: activating the magnetic biochar in 10-100 mL of a second activator, then adding citric acid at a concentration of 0.5-1.5% (w / v) and a volume of 50-100 mL and reacting for 0.5-2 h, wherein the mass ratio of citric acid to the magnetic biochar is 1:1-3:1, to obtain the surface-modified magnetic biochar.

8. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 7, characterized in that, The treatment solution is prepared by dissolving sodium dithionite in glacial acetic acid, wherein the concentration of sodium dithionite is 0.5-1.5% (w / v) and the treatment time is 0.5-2 h. And / or, the volume ratio of ammonia to nitrogen is 1:4 to 1:10; And / or, the ammonia gas flow rate is 50–200 mL / min; And / or, the nitrogen gas flow rate is 50–200 mL / min; And / or, the second activator includes glutaraldehyde and / or epichlorohydrin; And / or, the concentration of the second activator is 1-5%; And / or, the pH of the second activator is 8 to 10; And / or, the activation temperature in the second activator is 15-25°C, and the activation time is 1-2 hours.

9. The method for preparing the magnetic biochar / silver phosphate composite material as described in claim 1, characterized in that, In step S3, the induced precipitation includes: dispersing the surface-modified magnetic biochar in a silver nitrate solution with a concentration of 0.05–0.2 mol / L and a volume of 20–70 mL, adjusting the pH to 7–9 with a second alkaline solution, adding a disodium hydrogen phosphate solution with a concentration of 0.05–0.2 mol / L and a volume of 20–70 mL, and reacting at 25–80 °C for 1–3 h to obtain the magnetic biochar / silver phosphate composite material; The second alkaline solution includes at least one of sodium hydroxide and ammonia water.

10. The magnetic biochar / silver phosphate composite material prepared by the method of any one of claims 1-9.

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