A magnetic biochar composite semiconductor photocatalyst, preparation method thereof and application thereof

Abstract

The present invention relates to the field of chemical application technology, and more specifically to a magnetic biochar composite semiconductor photocatalyst, its preparation method, and its application. This invention incorporates potassium ferrate as a ferromagnetic raw material during the raw material stage to impart magnetic separation properties to the catalytic material, facilitating subsequent efficient degradation. The magnetic treatment process significantly improves the BET of the final composite photocatalyst material, ensuring that the resulting degradation material possesses superior degradation performance. Furthermore, the addition of an invasive species extract during the raw material stage ensures uniform distribution of the semiconductor metal oxides on the biochar surface, enhancing the overall photodegradation performance of the final product.

Description

Technical Field

[0001] The present invention relates to the field of chemical application technology, and in particular to a magnetic biochar composite semiconductor photocatalyst, a preparation method and application thereof. Background Art

[0002] The current use of advanced oxidation processes (AOPs) to treat organic pollutants is affected by the rapid recombination of photogenerated electron-hole pairs. Among the solutions, one of the most explored strategies is doping. Studies have shown that the photocatalytic activity of carbon materials as carriers of composite semiconductor photocatalysts can be effectively enhanced and can be used to degrade various organic pollutants in wastewater. In recent years, biochar as a carbon material has gradually come into people's attention, and biochar / metal oxide nanocomposites have gradually been used to degrade organic pollutants.

[0003] Existing technologies use plant-based biochar-loaded semiconductor photocatalysts to degrade organic pollutants. While environmentally friendly and low-cost, the photocatalysts are difficult to recover during the degradation process and there is a risk of metal oxide leaching from the semiconductor, compromising the practical performance of the final product. Therefore, designing an organic pollutant treatment system that is simple to prepare and apply, highly efficient, and pollution-free is a pressing technical challenge. Summary of the Invention

[0004] In response to the above problems, the present invention provides a magnetic biochar composite semiconductor photocatalyst, its preparation method and application. The present invention uses biomass of invasive plant species, such as Spartina alterniflora, as raw materials, has low cost, and the prepared composite magnetic biochar semiconductor photocatalyst is environmentally friendly and has no secondary pollution, can be efficiently recycled, and has significant degradation performance.

[0005] A method for preparing a magnetic biochar composite semiconductor photocatalyst comprises the following steps:

[0006] (1) Preparation of biochar: The pretreated invasive species powder is placed in a tube furnace and nitrogen is introduced to obtain biochar through a high-temperature oxygen-free hybridization step;

[0007] (2) Preparation of zinc oxide nanoparticle precursor: 0.02 mol / L zinc acetate dihydrate solution was prepared, polyvinyl pyrrolidone (PVP) was added thereto, and then the invasive species extract and 0.4 mol / L NaOH solution were added to generate zinc oxide nanoparticle precursor solution by sol-gel method;

[0008] (3) Preparation of a solid precursor: Potassium ferrate and the biochar prepared in step (1) are used as raw materials, added to the zinc oxide nanoparticle precursor solution in step (2), and centrifuged and dried to obtain a solid precursor;

[0009] (4) Preparation of magnetic biochar composite zinc oxide nanoparticles: The solid precursor prepared in step (3) is placed in a tube furnace and prepared in a high temperature and oxygen-free state by a one-step carbonization method to obtain a magnetic biochar composite semiconductor photocatalyst.

[0010] In some embodiments of the present invention, the alien invasive species in step (1) is selected from one or more combinations of coastal mudflat halophytes such as Radix Isatidis, Hippophae Rhamnoides, Sophora flavescens, Silybum marianum, Portulaca oleracea, Mangrove, and Spartina alterniflora, preferably Spartina alterniflora.

[0011] Due to the influence of extreme natural conditions such as seawater stress, coastal mudflat saline plants have high levels of reducing components such as flavonoids in their bodies, which play the role of dispersants and reducing agents when preparing semiconductor metal oxides by the sol-gel method and loading them onto biochar.

[0012] In some embodiments of the present invention, the pretreatment in step (1) includes a simple water washing treatment, drying and crushing steps; preferably, the pretreatment in step (1) includes repeatedly washing the freshly collected invasive alien species with distilled water three times, placing it in an oven at 60°C for 8 hours to constant weight, then crushing the dried invasive alien species into powder, sieving it (80 mesh), and placing it in a glass bottle and sealing it for use.

[0013] In some embodiments of the present invention, the high-temperature oxygen-free hybridization step in step (1) includes: evenly placing the invasive alien species powder in a quartz crucible, placing it in a tube furnace and introducing nitrogen (purity of 99.999%) at a flow rate of 100 mL / min, adjusting the tube furnace to 200°C and maintaining it for 30 minutes, then heating it to a high temperature of 700-900°C and maintaining it for 2 hours, cooling it after the pyrolysis is completed, stopping the introduction of nitrogen after it drops to room temperature, and taking out the carbonized material after cooling to room temperature to obtain biochar.

[0014] In some embodiments of the present invention, the heating rate of the tubular furnace in step (1) is 5°C / min, and the high temperature is preferably 800°C; after the pyrolysis is completed, the temperature is lowered at a rate of 5°C / min, and the nitrogen is stopped after it drops to room temperature; the sieve size of the carbonized material is 100 mesh.

[0015] The heating process in step (1) is maintained at 200° C. for 30 minutes, the purpose of which is to remove some impurities in the biomass in order to obtain a better carbonized product.

[0016] In some embodiments of the present invention, the invasive alien species extract in step (2) is used to extract reducing components in the invasive alien species. Its specific preparation process is as follows: weigh the pretreated invasive alien species powder and place it in a clean container, slowly add a 95% ethanol reagent along a glass rod, then wrap the beaker with tin foil, place it in a water bath at 80°C in the dark for 2 hours, centrifuge the solution at 4000 r / min for 2 minutes, and the supernatant is the invasive alien species extract. The invasive alien species extract is kept warm at 80°C for standby use; the mass ratio of the pretreated invasive alien species powder to 95% ethanol is 1:100.

[0017] In some embodiments of the present invention, the volume-to-weight ratio of the 0.02 mol / L zinc acetate dihydrate solution to polyvinylpyrrolidone (PVP) in step 2) is 200 ml:0.1 g; the volume ratio of the 0.02 mol / L zinc acetate dihydrate to the invasive alien species extract is 2:1; and the volume ratio of the 0.02 mol / L zinc acetate dihydrate to the 0.4 mol / L NaOH solution is 2:1.

[0018] The zinc oxide nanoparticle precursor solution preparation process of the present invention utilizes the reducing components in the extract of the invasive alien species to act as a reducing agent and dispersant, and a nanometer-scale unit dispersion is obtained by stirring. The molecules are cross-linked with each other through chemical bonds, hydrogen bonds, van der Waals forces, etc. to obtain a complex precursor solution.

[0019] In some embodiments of the present invention, in step (3): the mass ratio of the potassium ferrate to the biochar is 1.98:1; the weight-to-volume ratio of the biochar to the zinc oxide nanoparticle precursor solution is 1 g:200 ml; when added to the zinc oxide nanoparticle precursor solution, the mixture is stirred at 80° C. for 5 h; the centrifugal speed is 8000 r / min; and the obtained sample is dried in an oven at 60° C. overnight.

[0020] In some embodiments of the present invention, the conditions for high-temperature carbonization in step (4) are as follows: nitrogen (purity of 99.999%) is introduced into the tubular furnace at a flow rate of 100 mL / min, the tubular furnace is adjusted to a heating rate of 5°C / min to 200°C and maintained for 30 minutes, then the temperature is raised to a high temperature of 700-900°C and maintained for 2 hours, and after the pyrolysis is completed, the temperature is lowered at a rate of 5°C / min, and the nitrogen is stopped after it drops to room temperature. After cooling to room temperature, the carbonized material is taken out and sieved (100 mesh), washed with deionized water until neutral, and dried in an oven at 60°C overnight; the high temperature is preferably 800°C.

[0021] Among them, the one-step carbonization method described in step 4) of the present invention is that magnetization and loading are carried out simultaneously. At high temperature, potassium ferrate generates potassium hydroxide. Potassium hydroxide is an activator that can achieve the purpose of "pore formation" on the surface of the biochar material. The larger pore size structure is conducive to the loading of zinc oxide nanoparticles and the adsorption of organic pollutants by the prepared composite material.

[0022] On the other hand, the present invention provides a magnetic biochar composite semiconductor photocatalyst prepared by the above method.

[0023] This invention incorporates potassium ferrate as a ferromagnetic raw material during the raw material stage, imparting magnetic separation properties to the catalytic material, facilitating subsequent efficient degradation. The magnetic treatment process significantly improves the BET value of the final composite photocatalyst material, ensuring that the resulting degradable material possesses superior degradation performance. Furthermore, the addition of an invasive species extract during the raw material stage ensures uniform distribution of the semiconductor metal oxides on the biochar surface, enhancing the overall photodegradation performance of the final product.

[0024] In another aspect, the present invention provides an application of the magnetic biochar composite semiconductor photocatalyst prepared by the above method in degrading organic pollutants.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention uses an invasive alien plant as a raw material, improves the practical performance of the photocatalytic degradation material by adding a magnetic precursor, and synchronizes the magnetization of the composite material with the loading of zinc oxide nanoparticles, thereby fully utilizing the pore structure of the biochar itself and the "pore-forming" performance of the potassium hydroxide activator, increasing the embedding loading position of the zinc oxide nanoparticles, and at the same time, the addition of the ferromagnet can effectively inhibit the leaching of the nano zinc oxide particles during use, thereby improving the excellent performance of the photocatalytic composite material; during the photocatalytic degradation process, the composite material has a large number of active adsorption sites on the surface to adsorb organic pollutant molecules, and under visible light conditions, the semiconductor photocatalyst in the composite material works to degrade the organic pollutants into non-polluting small molecules, so that the composite material can repeatedly adsorb pollutant molecules, thereby improving the sustainable use performance of the composite material, and at the same time, the ferromagnetism of the material enables efficient recycling, avoiding secondary pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the standard curve diagram in the application example.

[0028] Figure 2 These are SEM photos of the magnetic Spartina alterniflora biochar composite semiconductor photocatalyst prepared in Example 1 at different magnifications.

[0029] Figure 3 This is the UV-visible absorption spectrum of malachite green (MG) liquid for photocatalytic degradation of organic pollutants in Example 1. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0031] The pretreatment of the Spartina alterniflora powder in the present invention is as follows: freshly collected Spartina alterniflora is repeatedly washed three times with distilled water, and then placed in an oven and dried at 60° C. for 8 hours to constant weight. The dried Spartina alterniflora is then crushed into powder and sieved (80 mesh). The pretreated Spartina alterniflora powder is placed in a glass bottle and sealed for later use.

[0032] The present invention provides a Spartina alterniflora extract: pretreated Spartina alterniflora powder is weighed and placed in a 1L clean beaker. 95% ethanol is slowly added along a glass rod, wherein the mass ratio of solid powder to ethanol is 1g:100ml. The beaker is then wrapped with tin foil and placed in a water bath at 80°C in the dark for 2 hours. The solution is then centrifuged at 4000 rpm for 2 minutes to obtain a supernatant, which is the Spartina alterniflora extract. The supernatant is then kept at 80°C for later use.

[0033] Example 1

[0034] (1) The pretreated Spartina alterniflora powder was evenly placed in a quartz crucible, placed in a tube furnace and introduced nitrogen (purity of 99.999%) at a flow rate of 100 mL / min, and the tube furnace was adjusted to increase the temperature to 200°C at a rate of 5°C / min and maintained for 30 min, then increased to 800°C and maintained for 2 h. After the pyrolysis was completed, the temperature was lowered at a rate of 5°C / min until it reached room temperature, and the introduction of nitrogen was stopped. After cooling to room temperature, the carbonized material was taken out and sieved (100 mesh) to obtain Spartina alterniflora biochar;

[0035] (2) Prepare 0.02 mol / L zinc acetate dihydrate, take 200 ml of 0.02 mol / L zinc acetate dihydrate and slowly pour it into a 500 mL beaker along a glass rod, place the beaker in a constant temperature magnetic stirrer at 80 ° C, and after the temperature in the beaker reaches 80 ° C, first add 0.1 g of polyvinyl pyrrolidone (PVP), and after the PVP is completely dissolved, slowly add 100 ml of Spartina alterniflora extract along the glass rod, stir for 1 hour, add 100 ml of 0.4 mol / L NaOH solution and continue stirring for 2 hours to generate a complex, which is the zinc oxide nanoparticle precursor solution;

[0036] (3) Weighing 3.96 g of potassium ferrate (K2FeO4) and 2 g of Spartina alterniflora biochar, adding them to 400 ml of the zinc oxide nanoparticle precursor solution synthesized in step 2), stirring at 80 ° C for 5 h, centrifuging the mixed liquid at 8000 r / min for 5 min, and then drying the obtained sample in an oven at 60 ° C overnight to obtain a solid precursor;

[0037] (4) The solid precursor obtained in step 3) was placed in a tube furnace and nitrogen (purity of 99.999%) was introduced at a flow rate of 100 mL / min. The tube furnace was adjusted to heat up to 200°C at a rate of 5°C / min and maintained for 30 min, then heated to 800°C and maintained for 2 h. After the pyrolysis was completed, the temperature was lowered at a rate of 5°C / min. When the temperature dropped to room temperature, the nitrogen introduction was stopped. After cooling to room temperature, the carbonized material was taken out and sieved (100 mesh), washed with deionized water until neutral, and dried in an oven at 60°C overnight to prepare solid material 1.

[0038] Example 2

[0039] The preparation process is the same as that of Example 1, except that potassium ferrate is not added in step (3), and solid material 2 is prepared.

[0040] Example 3

[0041] (1) The powder of Spartina alterniflora was evenly placed in a quartz crucible, placed in a tube furnace and introduced nitrogen (purity of 99.999%) at a flow rate of 100 mL / min. The tube furnace was set to heat up to 200°C at a rate of 5°C / min and maintained for 30 min, then heated to 800°C and maintained for 2 h. After the pyrolysis was completed, the temperature was lowered at a rate of 5°C / min until it reached room temperature, and the introduction of nitrogen was stopped. After cooling to room temperature, the carbonized material was taken out and sieved (100 mesh) to obtain Spartina alterniflora biochar;

[0042] (2) Weighed potassium ferrate (K2Fe04) and Spartina alterniflora biochar were added to deionized water at a mass ratio of 1.98:1. In particular, for the convenience of verification, deionized water was used instead of zinc acetate dihydrate and Spartina alterniflora extract in Example 1. After stirring at 80°C for 5 hours, the mixed liquid was centrifuged at 8000 r / min for 5 minutes, and then the obtained sample was dried in an oven at 60°C overnight to obtain a solid powder;

[0043] (3) The obtained solid powder was placed in a tube furnace and nitrogen (purity of 99.999%) was introduced at a flow rate of 100 mL / min. The tube furnace was adjusted to heat up to 200°C at a rate of 5°C / min and maintained for 30 min, then heated to 800°C and maintained for 2 h. After the pyrolysis was completed, the temperature was lowered at a rate of 5°C / min. After it dropped to room temperature, the nitrogen was stopped. After cooling to room temperature, the carbonized material was taken out and sieved (100 mesh), washed with deionized water until neutral, and dried in an oven at 60°C overnight to prepare solid material 3.

[0044] Example 4

[0045] The preparation process is the same as that of Example 1, except that polyvinyl pyrrolidone (PVP) is not added in step (2), and solid material 4 is prepared.

[0046] Example 5

[0047] The preparation process is the same as that of Example 1, except that in step (4), the temperature is increased to 200°C at a rate of 5°C / min and maintained for 30 minutes, and then increased to 700°C and maintained for 2 hours to prepare solid material 5.

[0048] Example 6

[0049] The preparation process is the same as that of Example 1, except that in step (4), the temperature is increased to 200°C at a rate of 5°C / min and maintained for 30 minutes, and then increased to 900°C and maintained for 2 hours to prepare solid material 6.

[0050] Comparative Example 1

[0051] Accurately prepare 0.02mol / L zinc acetate dihydrate (C4H6O4Zn2H20), take 200ml of 0.02mol / L zinc acetate dihydrate and slowly pour it into a 500mL beaker along a glass rod. After the temperature in the beaker reaches 80°C, first add 0.1g of polyvinyl pyrrolidone (PVP). After the PVP is completely dissolved, slowly add 100ml of Spartina alterniflora extract along the glass rod. After stirring for 1h, add 100ml of 0.4mol / L NaOH solution and continue stirring for 2h to generate a complex, which is the zinc oxide nanoparticle precursor solution. Then the precursor solution is centrifuged and dried. The dried sample is placed in a tubular furnace and annealed at 400°C with high-purity nitrogen gas (99.999%) at a flow rate of 80mL / min to obtain solid material 7 zinc oxide nanoparticles.

[0052] Application Examples

[0053] All photocatalytic degradation experiments of the present invention were carried out in an XPA-7 photochemical reactor. 0.04 g of the solid material prepared in each Example 1-6 was accurately weighed and added to 100 mL of a 200 mg / L malachite green (MG) standard solution. The mixture was magnetically stirred for 30 min under dark reaction conditions until the system reached a stable state. Then, a xenon lamp (power of 300 W) was turned on for illumination. A sample of the degradation solution (2 mL) was collected at equal intervals in a centrifuge tube and centrifuged at 8000 r / min for 2 min. The absorbance of the supernatant was measured at a wavelength of 617 nm (MG maximum absorption wavelength) using an ultraviolet-visible diffuse reflectance spectrometer. The concentration was converted using the standard curve formula (1). Three sets of experiments were repeated to determine the measurement results, and the solid material 7 zinc oxide nanoparticles prepared in Comparative Example 1 was used as a reference.

[0054] 1) Prepare MG standard solution:

[0055] Accurately weigh 0.2 g of MG powder into a 1 L volumetric flask, then add distilled water to the mark, shake repeatedly, and place in a dark place until use to obtain a 200 mg / L MG standard solution.

[0056] 2) Draw the standard curve of MG:

[0057] In a 20mL colorimetric tube, measure 5.000mL, 2.500mL, 1.250mL, and 0.625mL of the prepared 200mg / L MG standard solution, dilute to 20mL with deionized water, and let it stand until it stabilizes. Measure the absorbance of the prepared MG solution at different concentration gradients at the MG maximum absorption wavelength of 617nm, draw a standard curve, and then calculate the concentration of the subsequent degradation solution. Figure 1 As shown, the correlation coefficient of the standard curve is R 2 =99.87, formula (1) is Y=0.053X-0.022.

[0058] 3) The MG solution removal rate is calculated using formula (2):

[0059] D(%)=(C0-Ct) / C0×100%

[0060] Where D (%) is the removal rate of the prepared sample, C0 is the initial concentration of MG, and Ct is the concentration at the interval reaction time point.

[0061] The BET values of the solid materials prepared in Examples 1-6 and Comparative Example 1, as well as the photocatalytic degradation data of MG by the solid materials, are listed in Table 1 below.

[0062] Table 1

[0063]

[0064] By comparing Example 1 with Comparative Example 1 and Examples 2-4, it can be found that in the preparation process of the present invention, the addition of potassium ferrate can significantly improve the BET value of the composite material, thereby improving the composite material's ability to adsorb organic pollutants, and the final photocatalytic degradation efficiency is also significantly improved; when polyvinyl pyrrolidone (PVP) is used, it has little effect on the BET value of the preparation of the magnetic Spartina alterniflora biochar composite semiconductor photocatalyst, but has an effect on its photocatalytic degradation rate.

[0065] By comparing Example 1, Example 5 and Example 6, it can be found that when subjected to high-temperature oxygen-free treatment, BET is smaller at lower temperatures, but decreases when the temperature reaches 900°C. This may be due to the fact that the pore size of the biochar surface collapses due to the high temperature, resulting in a decrease in BET.

[0066] It is worth noting that, based on the above-mentioned design, in order to solve the same technical problem, even if some insubstantial changes or modifications are made to the present invention, the essence of the technical solution adopted is still the same as that of the present invention, and therefore it should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic biochar composite semiconductor photocatalyst, characterized in that The following steps are involved: (1) Preparation of biochar: The pretreated invasive species powder is placed in a tube furnace and nitrogen is introduced to obtain biochar through a high-temperature oxygen-free hybridization step; (2) Preparation of zinc oxide nanoparticle precursor: 0.02 mol / L zinc acetate dihydrate solution was prepared, polyvinyl pyrrolidone was added thereto, and then the invasive species extract and 0.4 mol / L NaOH solution were added to generate zinc oxide nanoparticle precursor solution by sol-gel method; (3) Preparation of a solid precursor: Potassium ferrate and the biochar prepared in step (1) are added to the zinc oxide nanoparticle precursor solution prepared in step (2) above, and centrifuged and dried to obtain a solid precursor; (4) Preparation of magnetic biochar composite zinc oxide nanoparticles: The solid precursor prepared in step (3) is placed in a tube furnace and prepared at high temperature and in an oxygen-free state by a one-step carbonization method to obtain a magnetic biochar composite semiconductor photocatalyst; the invasive alien species in step (1) is Spartina alterniflora; The preparation process of the invasive alien species extract in step (2) is as follows: weigh the pretreated invasive alien species powder and place it in a clean container; slowly add a 95% ethanol reagent along a glass rod; then wrap the beaker with tin foil; place it in a water bath at 80°C in the dark for 2 hours; centrifuge the solution at 4000 r / min for 2 minutes; and the supernatant is the invasive alien species extract; the mass ratio of the pretreated invasive alien species powder to 95% ethanol is 1g:100ml.

2. The method for preparing a magnetic biochar composite semiconductor photocatalyst according to claim 1, characterized in that The pretreatment in step (1) includes simple water washing, drying and crushing steps; specifically, the freshly collected invasive alien species are repeatedly washed three times with distilled water, placed in an oven at 60°C for 8 hours to constant weight, and then the dried invasive alien species are crushed into powder, sieved to 80 mesh, placed in a glass bottle, and sealed for use.

3. The method for preparing a magnetic biochar composite semiconductor photocatalyst according to claim 1, characterized in that The high-temperature oxygen-free hybridization step in step (1) includes: evenly placing the invasive alien species powder in a quartz crucible, placing it in a tubular furnace and introducing nitrogen, wherein the nitrogen purity reaches 99.999% and the flow rate is 100 mL / min, adjusting the tubular furnace to heat up to 200°C and maintain for 30 minutes, then heating to a high temperature of 700-900°C and maintaining for 2 hours, cooling after the pyrolysis is completed, stopping the introduction of nitrogen after it drops to room temperature, cooling to room temperature, taking out the carbonized material and sieving to obtain biochar; the tubular furnace heating rate is 5°C / min; after the pyrolysis is completed, the temperature is cooled at a rate of 5°C / min, and the introduction of nitrogen is stopped after it drops to room temperature; the sieve size of the carbonized material when sieving is 100 mesh.

4. The method for preparing a magnetic biochar composite semiconductor photocatalyst according to claim 1, characterized in that In the step 2), the volume-to-weight ratio of the 0.02 mol / L zinc acetate dihydrate solution to polyvinyl pyrrolidone is 200 ml:0.1 g; the volume ratio of the 0.02 mol / L zinc acetate dihydrate solution to the invasive alien species extract is 2:1; and the volume ratio of the 0.02 mol / L zinc acetate dihydrate solution to the 0.4 mol / L NaOH solution is 2:

1.

5. The method for preparing a magnetic biochar composite semiconductor photocatalyst according to claim 1, characterized in that In step (3), the mass ratio of potassium ferrate to biochar is 1.98:1; the weight volume ratio of the biochar to the zinc oxide nanoparticle precursor solution is 1 g:200 ml; when added to the zinc oxide nanoparticle precursor solution, stirring is carried out at 80° C. for 5 h; the centrifugal speed is 8000 r / min; and the obtained sample is dried in an oven at 60° C. overnight.

6. The method for preparing a magnetic biochar composite semiconductor photocatalyst according to claim 1, characterized in that The conditions of the high-temperature oxygen-free step in step (4) are as follows: nitrogen is introduced into the tubular furnace, the purity of the nitrogen reaches 99.999%, and the flow rate is 100 mL / min. The tubular furnace is adjusted to increase the temperature to 200°C at a rate of 5°C / min and maintained for 30 minutes, then the temperature is increased to a high temperature of 700-900°C and maintained for 2 hours. After the pyrolysis is completed, the temperature is lowered at a rate of 5°C / min. After the temperature drops to room temperature, the nitrogen is stopped. After cooling to room temperature, the carbonized material is taken out and sieved to 100 mesh, washed with deionized water until neutral, and dried in an oven at 60°C overnight.

7. The magnetic biochar composite semiconductor photocatalyst prepared by the method according to any one of claims 1 to 6.

8. Use of the magnetic biochar composite semiconductor photocatalyst as claimed in claim 7 in the degradation of organic pollutants.

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