Magnetic biochar based on eucalyptus residue tannin directional grafting, and preparation method and application thereof

Abstract

The application provides a magnetic biochar based on eucalyptus residue tannin directional grafting and a preparation method and application thereof, wherein the magnetic biochar based on eucalyptus residue tannin directional grafting comprises: magnetic biochar, the magnetic biochar comprises magnetic iron particles and biochar, wherein the magnetic iron particles are loaded on the biochar; and tannin, the tannin is grafted on the biochar to adsorb ammonium nitrogen in soil. The magnetic biochar can solve the problems of serious nitrogen loss, poor porosity, high heavy metal content and the like of acid soil.

Description

Technical Field

[0001] This application relates to the field of biochar technology, and in particular to a magnetic biochar based on eucalyptus residue tannin directional grafting, its preparation method, and its application. Background Technology

[0002] Acidic soils present numerous problems. On the one hand, they accelerate the leaching and loss of ammonium nitrogen, promote nitrification, and exacerbate nitrogen gaseous loss, resulting in low fertilizer utilization and significant agricultural non-point source pollution. On the other hand, they can significantly activate the activity of heavy metals such as cadmium and lead in the soil, which are easily accumulated by crops and transferred along the food chain, endangering agricultural product safety and ecological health. Furthermore, these soils are generally heavy and clayey with poor porosity, resulting in weak overall aeration and water permeability and insufficient water and fertilizer retention capacity. This easily hinders crop root growth, leading to a continuous decline in soil fertility over the long term, severely restricting stable crop yields and income growth and sustainable agricultural development in the region. Summary of the Invention

[0003] In view of this, the purpose of this application is to propose a magnetic biochar based on eucalyptus residue tannin directional grafting, its preparation method and application, in order to solve the problems of severe nitrogen loss, poor porosity and high heavy metal content in acidic soils.

[0004] To achieve the above objectives, this application provides a magnetic biochar based on eucalyptus residue tannin-directed grafting, comprising:

[0005] Magnetic biochar, comprising magnetic iron particles and biochar, wherein the magnetic iron particles are loaded onto the biochar; Tannins grafted onto the biochar to adsorb ammonium nitrogen from the soil.

[0006] Optionally, the tannins are grafted onto the magnetic biochar using a crosslinking agent, which includes one or more of glutaraldehyde, epichlorohydrin, or ethylenediamine.

[0007] Based on the same inventive concept, this disclosure provides a method for preparing magnetic biochar based on eucalyptus residue tannin-directed grafting, comprising: The magnetic iron particles are loaded onto the biochar to obtain the magnetic biochar; The tannins are grafted onto the magnetic biochar to obtain the magnetic biochar based on eucalyptus residue tannin directional grafting.

[0008] Optionally, the grafting of the tannins onto the biochar to obtain the magnetic biochar based on the directional grafting of eucalyptus residue tannins includes: A cross-linking agent is added to the tannin extract, the pH is adjusted to 4-6, and the extract is activated at 40-60℃ for 30-60 min to obtain an activated solution, wherein the tannin extract is rich in the tannin. The magnetic biochar was added to the activation solution and stirred at 50-70°C for 2-5 hours to obtain the magnetic biochar based on directional grafting of eucalyptus residue tannin.

[0009] Optionally, the preparation of the tannin extract and the biochar includes: Eucalyptus residue was added to the solution, extracted by ultrasound, and separated by filtration to obtain the tannin extract and extraction residue. The extracted residue was carbonized under a nitrogen atmosphere to obtain the biochar.

[0010] Optionally, the step of carbonizing the extraction residue under a nitrogen atmosphere to obtain the biochar includes: The extracted residue was pre-carbonized at a low temperature of 300-400℃ under a nitrogen atmosphere, and then carbonized at a high temperature of 500-600℃ to obtain the biochar.

[0011] Optionally, the preparation of the magnetic biochar includes: The biochar was dispersed in an iron salt solution and stirred in a water bath at 60-80°C for 2-4 hours. The pH was adjusted to 8-10, and stirring was continued for 1-2 hours. The biochar was then separated, washed, and dried to obtain the magnetic biochar.

[0012] Optionally, the iron salt solution is Fe 2+ and Fe 3+ A mixed solution, wherein the Fe 2+ With the Fe 3+ The molar ratio is 1:(1-2), and the total iron concentration in the iron salt solution is 0.2-0.8 mol / L.

[0013] Based on the same inventive concept, this disclosure also provides a magnetic biochar based on eucalyptus residue tannin directional grafting for adsorbing ammonium nitrogen in acidic soil.

[0014] Based on the same inventive concept, this disclosure also provides a soil conditioner, including the above-mentioned magnetic biochar based on directional grafting of eucalyptus residue tannin.

[0015] Based on the same inventive concept, this disclosure also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable by the processor, wherein the processor implements the method described above when executing the computer program.

[0016] As can be seen from the above, the magnetic biochar based on eucalyptus residue tannin-directed grafting provided in this application includes: magnetic biochar, which comprises magnetic iron particles and biochar, wherein the magnetic iron particles are loaded onto the biochar; and tannin, which is grafted onto the biochar to adsorb ammonium nitrogen in the soil. The biochar in the above-mentioned magnetic biochar not only provides a stable loading matrix for the magnetic iron particles and tannin, but also improves soil permeability and water retention through its porous structure, while adsorbing free heavy metal ions, thus helping to alleviate soil heavy metal pollution. The magnetic iron particles on the surface and in the pores of the magnetic biochar endow the biochar with magnetic responsiveness, allowing for rapid recovery through magnetic separation after crop harvest, avoiding the adverse effects of long-term magnetic biochar residue on soil physicochemical properties. The tannin grafted onto the biochar surface, due to its rich content of ortho-phenolic hydroxyl groups, can efficiently adsorb NH4 in the soil through complexation. + Furthermore, its antioxidant activity inhibits nitrification, reduces nitrogen gaseous loss, and solves the problem of severe nitrogen loss in acidic soils. In addition, the iron atoms on the magnetic iron particles form stable five-membered ring chelates with the ortho-phenolic hydroxyl groups of the aromatic components in tannins, which significantly enhances the binding strength and stability of the tannin graft layer. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments.

[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0019] Acidic soils are widely distributed in southern my country and are one of the main soil types faced in agricultural production. Their inherent physicochemical defects and accompanying pollution problems severely restrict sustainable agricultural development and the improvement of soil ecological environment quality. Acidic soils have a high concentration of hydrogen ions, which easily leads to an imbalance in the transformation of nitrogen forms in the soil, particularly ammonium nitrogen (NH4+). +It is easy to lose fertilizer through leaching and nitrification. In particular, nitrogen oxides (such as NO and N2O) produced during nitrification will escape in gaseous form, which not only reduces the utilization rate of fertilizer and increases agricultural production costs, but also causes air pollution, exacerbates the greenhouse effect, and becomes one of the important sources of agricultural non-point source pollution.

[0020] At the same time, in acidic soil environments, the activity of heavy metal ions (such as lead, cadmium, copper, zinc, etc.) is significantly enhanced, making them more likely to be released from the soil solid phase into the liquid phase. After being absorbed and accumulated by crops, they not only inhibit crop growth and reduce crop yield and quality, but also threaten human health through the food chain. Heavy metal pollution has become a key and difficult issue in the remediation of acidic soils.

[0021] In addition, acidic soils generally have problems such as heavy texture and poor pore structure, resulting in poor soil aeration and water retention, a harsh root growth environment, which in turn affects the crop's absorption and utilization of water and nutrients, further exacerbating the predicament of soil fertility decline and agricultural production efficiency reduction.

[0022] In response to the problems of severe nitrogen loss, heavy metal pollution, and poor aeration and water retention in acidic soils, this application proposes a magnetic biochar based on directional grafting of eucalyptus residue tannin, its preparation method, and its application.

[0023] The embodiments of this application will be described in detail below.

[0024] A magnetic biochar based on eucalyptus residue tannin-directed grafting, comprising: Magnetic biochar, comprising magnetic iron particles and biochar, wherein the magnetic iron particles are loaded onto the biochar; Tannins grafted onto the biochar to adsorb ammonium nitrogen from the soil.

[0025] In this embodiment, the biochar in the magnetic biochar not only provides a stable loading matrix for magnetic iron particles and tannins, but also improves soil permeability and water retention through its porous structure, while adsorbing free heavy metal ions to help alleviate soil heavy metal pollution. The magnetic iron particles on the surface and in the pores of the magnetic biochar endow it with magnetic responsiveness, allowing for rapid recovery via magnetic separation after crop harvest, thus avoiding the adverse effects of long-term magnetic biochar residue on soil physicochemical properties. Tannins grafted onto the biochar surface, due to their rich content of ortho-phenolic hydroxyl groups, can efficiently adsorb NH4 from the soil through complexation. + Furthermore, its antioxidant activity inhibits nitrification, reduces nitrogen gaseous loss, and solves the problem of severe nitrogen loss in acidic soils. In addition, the iron atoms on the magnetic iron particles form stable five-membered ring chelates with the ortho-phenolic hydroxyl groups of the aromatic components in tannins, which significantly enhances the binding strength and stability of the grafted layer.

[0026] In some embodiments, the tannins are grafted onto the magnetic biochar using a crosslinking agent, which includes one or more of glutaraldehyde, epichlorohydrin, or ethylenediamine.

[0027] In this embodiment, tannins are directionally grafted onto the surface of magnetic biochar using crosslinking agents such as glutaraldehyde, epichlorohydrin, or ethylenediamine. Compared to physical adsorption, this significantly improves the binding strength between tannins and biochar. The crosslinking agent can form stable chemical bridges between the tannin molecules and the magnetic biochar surface. This prevents tannin loss in acidic soil leaching environments, ensuring long-term nitrogen adsorption capacity. Furthermore, it can regulate the spatial arrangement of the tannin graft layer, increasing the exposure of ortho- and ortho-phenolic hydroxyl groups and enhancing NH4+ adsorption. + This improves the complexation adsorption efficiency while avoiding tannin aggregation, ensuring full utilization of the active sites on the material surface, and providing a stable and efficient reaction interface for subsequent nitrogen adsorption reactions.

[0028] Based on the same inventive concept, this disclosure provides a method for preparing the above-mentioned magnetic biochar based on directional grafting of eucalyptus residue tannins, comprising: The magnetic iron particles are loaded onto the biochar to obtain the magnetic biochar; The tannins are grafted onto the magnetic biochar to obtain the magnetic biochar based on the directional grafting of eucalyptus residue tannins. This preparation method has the beneficial effects of the above-described examples of magnetic biochar based on the directional grafting of eucalyptus residue tannins, which will not be repeated here.

[0029] In some embodiments, grafting the tannins onto the biochar to obtain the magnetic biochar based on eucalyptus residue tannin directional grafting includes: A cross-linking agent is added to the tannin extract, the pH is adjusted to 4-6, and the extract is activated at 40-60℃ for 30-60 min to obtain an activated solution, wherein the tannin extract is rich in the tannin. The magnetic biochar was added to the activation solution and stirred at 50-70°C for 2-5 hours to obtain the magnetic biochar based on directional grafting of eucalyptus residue tannin.

[0030] In this embodiment, an acidic activation environment with a pH of 4-6 activates the phenolic hydroxyl groups of tannins while preventing tannins from becoming ineffective due to excessive acid hydrolysis. An activation temperature of 40-60°C promotes the full integration of the crosslinking agent and tannins, enhancing the stability of the grafted precursor. The subsequent reaction temperature of 50-70°C accelerates the chemical bonding between the crosslinking agent and magnetic biochar, shortening the reaction cycle and ensuring the uniformity of tannin grafting. This process forms a dense and firmly bonded tannin graft layer on the surface of the magnetic biochar, ensuring resistance to NH4+. + High adsorption capacity and stability.

[0031] In some embodiments, the preparation of the tannin extract and the biochar includes: Eucalyptus residue was added to the solution, extracted by ultrasound, and separated by filtration to obtain the tannin extract and extraction residue. The extracted residue was carbonized under a nitrogen atmosphere to obtain the biochar.

[0032] In this embodiment, biochar is prepared by carbonizing the residue after ultrasonic extraction of tannins from eucalyptus residue under a nitrogen atmosphere, thereby achieving high-value utilization of agricultural waste. Ultrasonic extraction can efficiently separate tannins from eucalyptus residue, maximizing the extraction of active ingredients for nitrogen adsorption. The extraction residue retains the natural porous fibrous structure of eucalyptus residue, which, after nitrogen carbonization, forms a rich pore structure and abundant oxygen-containing functional groups. This provides sufficient loading sites for magnetic nanoparticles and enhances the soil-improving ability of biochar itself—improving the aeration and water retention of acidic soil through the pore structure, and adsorbing heavy metal ions and nitrogen through functional groups, thereby reducing material preparation costs while improving overall environmental benefits.

[0033] In some embodiments, carbonizing the extraction residue under a nitrogen atmosphere to obtain the biochar includes: The extracted residue was pre-carbonized at a low temperature of 300-400℃ under a nitrogen atmosphere, and then carbonized at a high temperature of 500-600℃ to obtain the biochar.

[0034] In this embodiment, a segmented process of low-temperature pre-carbonization at 300-400℃ and high-temperature carbonization at 500-600℃ is employed to precisely control the structure and properties of the biochar. Low-temperature pre-carbonization removes volatile substances from the extraction residue, preserving the complete porous framework structure and preventing pore collapse caused by direct high-temperature carbonization. High-temperature carbonization further carbonizes residual organic matter, forming a stable carbon framework and enriching surface functional groups. This process can produce biochar with a well-developed pore structure, large specific surface area, and strong chemical stability, providing an excellent carrier for subsequent magnetic material loading and tannin grafting. This ensures that the biochar possesses both good structural support and adsorption capacity in the soil, while also improving its corrosion resistance and extending the material's service life in the soil.

[0035] In some embodiments, the preparation of the magnetic biochar includes: The biochar was dispersed in an iron salt solution and stirred in a water bath at 60-80°C for 2-4 hours. The pH was adjusted to 8-10, and stirring was continued for 1-2 hours. The biochar was then separated, washed, and dried to obtain the magnetic biochar.

[0036] In this embodiment, a water bath environment of 60-80℃ can accelerate the dispersion of iron salts in the pores of biochar; alkaline pH conditions can promote the hydrolysis of iron ions to generate Fe(OH)2 and Fe(OH)3 precursors, which are then converted into stable magnetic iron oxides (such as Fe3O4) and combine with functional groups on the surface of biochar to form a robust loading structure. This process can prepare magnetic biochar with strong magnetic responsiveness and good dispersibility, ensuring the high efficiency of subsequent magnetic separation and recovery, and enhancing the adsorption and fixation capacity of heavy metal ions by relying on the synergistic effect of magnetic particles. At the same time, it provides chemical anchors for tannin grafting, improving the overall composite stability of the material.

[0037] In some embodiments, the iron salt solution is Fe 2+ and Fe 3+ A mixed solution, wherein the Fe 2+ With the Fe 3+ The molar ratio is 1:(1-2), and the total iron concentration in the iron salt solution is 0.2-0.8 mol / L.

[0038] In this embodiment, Fe is limited 2+ with Fe 3+ A molar ratio of 1:(1-2) and a total iron concentration of 0.2-0.8 mol / L are key parameters for regulating the structure and properties of magnetic biochar. 2+ with Fe 3+ A molar ratio of 1:(1-2) conforms to the optimal ratio for preparing magnetic iron oxides by co-precipitation, ensuring the Fe... 2+ with Fe 3+ The reaction process generates high-purity, crystal-stable magnetic particles, avoiding particle crystal defects caused by single-valence iron ions. A total iron concentration of 0.2-0.8 mol / L balances loading and dispersibility; too low a concentration leads to insufficient magnetic particle loading and weak magnetic response, while too high a concentration easily causes particle agglomeration and blockage of biochar pores. Under the above ratio, magnetic biochar with strong magnetism, uniform dispersion, and intact pores can be prepared, ensuring that the material can efficiently adsorb nitrogen and heavy metals in the soil and can be rapidly recovered through magnetic separation for recycling.

[0039] Based on the same inventive concept, this disclosure also provides a magnetic biochar based on eucalyptus residue tannin-directed grafting for adsorbing ammonium nitrogen in acidic soils, which can significantly reduce NH4 in the soil. + This reduces leaching losses and nitrification gaseous loss, thus improving the utilization rate of fertilizer nitrogen.

[0040] Based on the same inventive concept, this disclosure also provides a soil conditioner, comprising the aforementioned magnetic biochar based on eucalyptus residue tannin-directed grafting. This soil conditioner possesses the beneficial effects of the aforementioned embodiments of magnetic biochar based on eucalyptus residue tannin-directed grafting, which will not be elaborated further here.

[0041] The above embodiments are described below with reference to specific examples and comparative examples.

[0042] Example 1 A method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins, comprising: S1: Eucalyptus bark and eucalyptus sawdust were mixed at a mass ratio of 1:2, dried at 80℃ until the moisture content was 6%, and then pulverized through a 100-mesh sieve to obtain eucalyptus residue powder. Testing revealed that the tannin content in the eucalyptus residue powder was 12.5%.

[0043] S2: Take 100g of eucalyptus residue powder, add 1000mL of 60% ethanol aqueous solution, extract for 2 hours at 50℃ and ultrasonic power of 300W, filter and separate to obtain tannin extract (tannin content about 22 g / L) and extraction residue (about 65g).

[0044] S3: Place the extracted residue in a tube furnace and, under nitrogen protection, heat it to 350°C at 8°C / min and hold it for 1.5 hours for low-temperature pre-carbonization; continue to heat it to 550°C at 5°C / min and hold it for 2 hours for high-temperature carbonization; after natural cooling, biochar (about 28g) is obtained.

[0045] S4: Take 20g of biochar and disperse it in 300mL of a mixed iron salt solution (FeSO4·7H2O and FeCl3·6H2O, Fe... 2+ With the Fe 3+ The molar ratio of the two components was 1:1.5, and the total iron concentration was 0.5 mol / L. The mixture was stirred in a 70°C water bath for 3 hours. 2 mol / L NaOH solution was slowly added to adjust the pH to 9.0, and stirring continued for 1.5 hours. The mixture was then magnetically separated, washed with deionized water until neutral, and dried at 80°C to obtain magnetic biochar (approximately 24 g).

[0046] S5: The tannin extract obtained in step S2 was concentrated under reduced pressure to 1 / 4 of its original volume (approximately 250 mL), 2.5 mL of glutaraldehyde (25% aqueous solution) was added, and the pH was adjusted to 5.0 with acetic acid. The mixture was then activated at 50°C for 45 minutes. The magnetic biochar obtained in step S4 was added to the above activation solution, and the mixture was stirred at 60°C for 3 hours to allow tannins to be grafted onto the surface of the magnetic biochar via a crosslinking agent. After the reaction, the mixture was washed with deionized water until neutral and dried at 70°C to obtain magnetic biochar (approximately 26 g) based on eucalyptus residue tannin-directed grafting. This magnetic biochar based on eucalyptus residue tannin-directed grafting comprises: magnetic biochar, which includes magnetic iron particles and biochar, wherein the magnetic iron particles are loaded onto the biochar; and tannins, which are grafted onto the biochar via a crosslinking agent to adsorb ammonium nitrogen from the soil.

[0047] Material characterization was performed on the magnetic biochar based on eucalyptus residue tannin-directed grafting prepared in Example 1. XRD patterns showed the simultaneous presence of broad diffraction peaks of biochar, characteristic diffraction peaks of Fe3O4 (2θ≈30.1°, 35.5°, 43.1°, 57.0°, 62.6°), and characteristic peaks after tannin grafting, proving that tannin was successfully grafted onto the magnetic biochar. SEM images showed that the biochar surface was loaded with spherical Fe3O4 nanoparticles with a uniform particle size distribution of 20-50 nm, and a uniform film-like coating layer appeared on the surface after tannin grafting. BET specific surface area: 298 m² for biochar. 2 / g, magnetic biochar is 265 m 2 / g, the magnetic biochar grafted with tannins has a content of 326 m 2 The tannin grafting density of 18.6 emu / g indicates that the tannin grafting did not significantly block the pores; instead, the surface modification increased the specific surface area. VSM magnetic property testing showed a saturation magnetization of 18.6 emu / g and coercivity approaching zero, exhibiting typical superparamagnetic characteristics, allowing for efficient separation under an applied magnetic field. Elemental analysis (ICP-OES) revealed an iron content of 12.3 wt%. Surface phenolic hydroxyl content determination (Folin-Ciocalteu method) showed a surface phenolic hydroxyl content of 3.4 mmol / g.

[0048] Example 2 A method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins, comprising: S1: Take a dried eucalyptus bark sample, crush it through a 60-mesh sieve to obtain eucalyptus residue powder.

[0049] S2: Take 100g of eucalyptus residue powder, add 800mL of 50% ethanol aqueous solution, extract for 3 hours at 40℃ and ultrasonic power of 200W, filter and separate to obtain tannin extract and extraction residue.

[0050] S3: Under nitrogen protection, the extraction residue is heated to 300℃ at 5℃ / min and held for 2 hours for low-temperature pre-carbonization; then the temperature is further increased to 500℃ at 5℃ / min and held for 3 hours for high-temperature carbonization to obtain biochar.

[0051] S4: Disperse biochar in a mixed solution of iron salts (Fe 2+ and Fe 3+ The molar ratio of the two components was 1:1, and the total iron concentration was 0.2 mol / L. The mixture was stirred in a 60°C water bath for 4 hours, and then an alkaline solution was added to adjust the pH to 8.0. The mixture was stirred for another 2 hours, and then separated, washed, and dried to obtain magnetic biochar.

[0052] S5: Concentrate the tannin extract, add epichlorohydrin (crosslinking agent), adjust the pH to 4.0, and activate at 40℃ for 60 minutes to obtain an activated solution; add magnetic biochar to the activated solution, stir and react at 50℃ for 5 hours, wash and dry to obtain magnetic biochar based on directional grafting of eucalyptus residue tannin.

[0053] Material characterization was performed on the magnetic biochar based on directional grafting of eucalyptus residue tannins prepared in Example 2: XRD and FTIR characterization confirmed that Fe3O4 and tannins coexist stably in biochar without significant phase disruption. BET specific surface area: 280 m² / g; saturation magnetization: 12.5 emu / g; surface phenolic hydroxyl content: 2.5 mmol / g.

[0054] Example 3 A method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins, comprising: S1: Take a dry sample of eucalyptus wood chips, crush them through a 200-mesh sieve, and obtain eucalyptus residue powder.

[0055] S2: Take 100g of eucalyptus residue powder, add 1500mL of 70% ethanol aqueous solution, extract for 1 hour at 60℃ and ultrasonic power of 400W, filter and separate to obtain tannin-rich extract and extraction residue.

[0056] S3: Under nitrogen protection, the extraction residue is heated to 400℃ at 10℃ / min and held for 1 hour for low-temperature pre-carbonization; then the temperature is further increased to 600℃ at 10℃ / min and held for 2 hours for high-temperature carbonization to obtain biochar.

[0057] S4: Disperse biochar in a mixed solution of iron salts (Fe 2+ and Fe 3+ The molar ratio of the two components was 1:2, and the total iron concentration was 0.8 mol / L. The mixture was stirred in an 80℃ water bath for 2 hours, and the pH was adjusted to 10.0 by adding alkali solution. The mixture was stirred for another hour, and then separated, washed, and dried to obtain magnetic biochar.

[0058] S5: Concentrate the tannin extract, add ethylenediamine, adjust the pH to 6.0, and activate at 60℃ for 30 minutes to obtain an activated solution; add magnetic biochar to the activated solution, stir and react at 70℃ for 2 hours, wash and dry to obtain magnetic biochar based on directional grafting of eucalyptus residue tannin.

[0059] Material characterization was performed on the magnetic biochar based on directional grafting of eucalyptus residue tannins prepared in Example 3: BET specific surface area: 380 m² 2 / g; Saturation magnetization: 28.6 emu / g; Surface phenolic hydroxyl content: 4.2 mmol / g.

[0060] Comparative Example 1 The preparation process of a biochar includes: S1: Mix eucalyptus bark and eucalyptus sawdust in a mass ratio of 1:2, dry at 80℃ to a moisture content of 6%, and pulverize through a 100-mesh sieve to obtain eucalyptus residue powder.

[0061] S2: Eucalyptus residue powder is placed in a tube furnace and heated to 350°C at 8°C / min under nitrogen protection, and held for 1.5 hours for low-temperature pre-carbonization; then heated to 550°C at 5°C / min and held for 2 hours for high-temperature carbonization, and obtained biochar after natural cooling.

[0062] The difference between Comparative Example 1 and Example 1 is that the biochar obtained was not loaded with magnetic iron particles and was not grafted with tannins.

[0063] Comparative Example 2 The preparation process of a magnetic biochar includes: S1: Mix eucalyptus bark and eucalyptus sawdust in a mass ratio of 1:2, dry at 80℃ to a moisture content of 6%, and pulverize through a 100-mesh sieve to obtain eucalyptus residue powder.

[0064] S2: Eucalyptus residue powder is placed in a tube furnace and heated to 350°C at 8°C / min under nitrogen protection, and held for 1.5 hours for low-temperature pre-carbonization; then heated to 550°C at 5°C / min and held for 2 hours for high-temperature carbonization, and obtained biochar after natural cooling.

[0065] S3: Take 20g of biochar and disperse it in 300mL of a mixed iron salt solution (FeSO4·7H2O and FeCl3·6H2O, Fe... 2+ With the Fe 3+ The molar ratio of the two components was 1:1.5, and the total iron concentration was 0.5 mol / L. The mixture was stirred in a 70℃ water bath for 3 hours. 2 mol / L NaOH solution was slowly added to adjust the pH to 9.0, and stirring continued for 1.5 hours. The mixture was then magnetically separated, washed with deionized water until neutral, and dried at 80℃ to obtain magnetic biochar.

[0066] The difference between Comparative Example 2 and Example 1 is that the biochar obtained was only loaded with magnetic iron particles and was not grafted with tannins.

[0067] Comparative Example 3 A method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins, comprising: S1: Mix eucalyptus bark and eucalyptus sawdust in a mass ratio of 1:2, dry at 80℃ to a moisture content of 6%, and pulverize through a 100-mesh sieve to obtain eucalyptus residue powder.

[0068] S2: Take 100g of eucalyptus residue powder, add 1000mL of 60% ethanol aqueous solution, extract for 2 hours at 50℃ and ultrasonic power of 300W, filter and separate to obtain tannin extract (tannin content of about 22 g / L) and extraction residue.

[0069] S3: Place the extracted residue in a tube furnace and, under nitrogen protection, heat it to 350°C at 8°C / min and hold it for 1.5 hours for low-temperature pre-carbonization; continue to heat it to 550°C at 5°C / min and hold it for 2 hours for high-temperature carbonization, and obtain biochar after natural cooling.

[0070] S4: The tannin extract obtained in step S2 was concentrated under reduced pressure to 1 / 4 of its original volume (approximately 250 mL), and 2.5 mL of glutaraldehyde (25% aqueous solution) was added. The pH was adjusted to 5.0 with acetic acid, and the mixture was activated at 50°C for 45 minutes. The biochar obtained in step S3 was added to the above activation solution, and the mixture was stirred at 60°C for 3 hours to allow tannins to be grafted onto the surface of the magnetic biochar via a crosslinking agent. After the reaction, the biochar was washed with deionized water until neutral and dried at 70°C to obtain biochar based on the directional grafting of eucalyptus residue tannins.

[0071] The difference between Comparative Example 3 and Example 1 is that the biochar obtained was only grafted with tannins and was not loaded with magnetic iron particles.

[0072] The biochar prepared in Example 1 and Comparative Examples 1-3 were subjected to performance tests.

[0073] (1) Test soil: Typical acidic red soil from southern China was collected, with a sampling depth of 0-20 cm in the topsoil layer. After sampling, impurities such as stones and plant residues were removed from the soil, and the soil was air-dried and then sieved through a 2 mm sieve for later use. Based on previous measurements, the basic physicochemical properties of the soil are as follows: pH=4.8, organic matter 18.5 g / kg, and available nitrogen 85 mg / kg.

[0074] (2) Test materials: Example 1 Material: TM-BC (magnetic biochar based on directional grafting of eucalyptus residue tannins). Comparative Example 1 Material: BC (Biochar without magnetic iron particles and without grafted tannins). Comparative Example 2 Material: M-BC (biochar loaded only with magnetic iron particles, without grafted tannins); Comparative Example 3 Material: T-BC (Biochar grafted with only tannins, without magnetic iron particles loaded). All materials were ground through a 100-mesh sieve, dried, sealed, and stored for later use.

[0075] (3) Test crops: Corn seedlings (variety: Zhengdan 958) were selected. The seeds were plump and uniform in size. After being disinfected with 5% sodium hypochlorite solution for 10 minutes, they were rinsed with deionized water and placed in a 25℃ constant temperature incubator to germinate. Seedlings with uniform germination were selected for pot experiments.

[0076] (4) Experimental grouping This experiment consisted of 5 treatment groups, with 3 replicates in each group to ensure the reliability of the experimental data. The specific groupings are as follows: Treatment Group 1: Add material from Example 1 (TM-BC) at a rate of 2% of the soil weight; Treatment Group 2: Add material (BC) from Comparative Example 1 at a rate of 2% of the soil weight; Treatment group 3: Add material (M-BC) from Comparative Example 2 at a rate of 2% of the soil weight; Treatment group 4: Add material (T-BC) from Comparative Example 3 at a rate of 2% of the soil weight; Treatment group 5: Blank control (CK), with no added improvement materials.

[0077] (5) Cultivation conditions For each replicate, 1 kg of air-dried and sieved soil was placed in a 2 L plastic culture dish. The corresponding amendments were accurately added according to the group design, and the mixture was thoroughly stirred manually. Urea (200 mg N / kg) was added as a nitrogen source. Soil moisture content in all treatment groups was adjusted to 70% of field capacity. The culture dishes were placed in a 25℃ constant temperature incubator for 45 days, with good ventilation maintained during the incubation period, and water lost through evaporation replenished periodically.

[0078] (6) Sampling and testing Soil samples were taken on days 7, 15, 30, and 45 of cultivation to measure soil pH and NH4. + Content, NO3 - Content and N2O emission flux. Maize biomass was measured after cultivation. NH4 + and NO3 - Content: Determined using a flow injection analyzer after extraction with 2 mol / L KCl solution. N2O emission flux: Determined using a static chamber-gas chromatography method.

[0079] (7) Magnetic recovery performance test After cultivation, soil samples from treatment group 1 were dispersed in water, and magnetic biochar was separated under an applied magnetic field (magnetic field strength 0.2 T). The recovery rate was calculated. The recovered magnetic biochar was regenerated with 0.1 mol / L NaOH solution, and the regenerated biochar's resistance to NH4+ was determined. + Adsorption performance.

[0080] The experimental results are shown in Table 1: Table 1. Effects of different treatment groups on nitrogen form and N2O emissions in acidic soils (after 45 days of incubation).

[0081] Data show that treatment group 1 (TM-BC) significantly improved acidic red soil compared to other treatment groups: soil pH increased from an initial 4.8 to 6.1, a 24.5% increase compared to the control group; soil NH4... + The content reached 68.4 mg / kg, which was 2.4 times that of the control group; NO3 - The nitrogen content decreased to 42.6 mg / kg, a reduction of 31.8% compared to the control group, indicating a significant reduction in nitrogen leaching loss; the cumulative N2O emissions decreased by 53.7% compared to the control group, indicating a significant effect in greenhouse gas emission reduction; and the maize biomass reached 12.8 g / pot, nearly twice that of the control group.

[0082] Treatment group 2 (BC, biochar without magnetic iron particles, ungrafted tannins) lacked tannin grafting and magnetic loading, resulting in low NH4 content. + It has a weak ability to retain NO3. - The content is high, and the risk of nitrogen loss is significant.

[0083] Soil NH4 in treatment group 1 (TM-BC, loaded with magnetic iron + grafted tannin) + The concentration reached 68.4 mg / kg, with cumulative N2O emissions of only 3.8 mg·N / kg and maize biomass of 12.8 g / pot; while treatment group 4 (T-BC, unloaded with magnetic iron + grafted tannins only) had NH4 content of 68.4 mg / kg, with cumulative N2O emissions of only 3.8 mg·N / kg and maize biomass of only 12.8 g / pot; + The tannin content was 60.5 mg / kg, 13.1% lower than treatment group 1; cumulative N2O emissions were 4.5 mg·N / kg, 18.4% higher than treatment group 1; and maize biomass was 11.2 g / pot, 12.5% ​​lower than treatment group 1. The only variable between the two groups was whether or not magnetic iron was loaded. The performance difference directly confirms the key enhancing effect of magnetic iron on the tannin effect: Fe³⁺ on the surface of the nanoparticle iron. + It can act as a chemical anchor, forming a stable five-membered ring chelate with the ortho-phenolic hydroxyl groups of flavonoid polyphenols in tannins, significantly enhancing the binding strength and stability of the tannin graft layer, preventing tannins from falling off and being lost in acidic soil environments, and ensuring the long-term effectiveness and efficacy of tannin active sites.

[0084] Meanwhile, compared with the magnetic biochar group without tannin grafting (treatment group 3, M-BC), the NH4 content of treatment group 1 was lower. +The content increased by 29.5%, N2O emissions decreased by 26.9%, and maize biomass increased by 33.3%, further verifying that tannin is the core functional layer for nitrogen regulation, while magnetic iron achieved a 1+1>2 improvement effect by improving tannin stability and strengthening adsorption synergy.

[0085] Magnetic recovery performance test results: The recovery rate of magnetic biochar in treatment group 1 reached 86.5%; after regeneration, NH4... + The adsorption capacity was 82.3% of the original adsorption capacity, indicating that the magnetic biochar of the present invention has good recyclability and regeneration performance.

[0086] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application is limited to these examples; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0087] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description.

[0088] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the claims of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A magnetic biochar based on directional grafting of eucalyptus residue tannins, characterized in that, include: Magnetic biochar, comprising magnetic iron particles and biochar, wherein the magnetic iron particles are loaded onto the biochar; Tannins grafted onto the biochar to adsorb ammonium nitrogen from the soil.

2. The magnetic biochar based on eucalyptus residue tannin-directed grafting according to claim 1, characterized in that, The tannins are grafted onto the magnetic biochar using a crosslinking agent, which includes one or more of glutaraldehyde, epichlorohydrin, or ethylenediamine.

3. A method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins as described in any one of claims 1-2, characterized in that, include: The magnetic iron particles are loaded onto the biochar to obtain the magnetic biochar; The tannins are grafted onto the magnetic biochar to obtain the magnetic biochar based on eucalyptus residue tannin directional grafting.

4. The method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins according to claim 3, characterized in that, The process of grafting the tannins onto the biochar to obtain the magnetic biochar based on eucalyptus residue tannin directional grafting includes: A cross-linking agent is added to the tannin extract, the pH is adjusted to 4-6, and the extract is activated at 40-60℃ for 30-60 min to obtain an activated solution, wherein the tannin extract is rich in the tannin. The magnetic biochar was added to the activation solution and stirred at 50-70°C for 2-5 hours to obtain the magnetic biochar based on directional grafting of eucalyptus residue tannin.

5. The method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins according to claim 4, characterized in that, The preparation of the tannin extract and the biochar includes: Eucalyptus residue was added to the solution, extracted by ultrasound, and separated by filtration to obtain the tannin extract and extraction residue. The extracted residue was carbonized under a nitrogen atmosphere to obtain the biochar.

6. The method for preparing magnetic biochar according to claim 5, characterized in that, The step of carbonizing the extraction residue under a nitrogen atmosphere to obtain the biochar includes: The extracted residue was pre-carbonized at a low temperature of 300-400℃ under a nitrogen atmosphere, and then carbonized at a high temperature of 500-600℃ to obtain the biochar.

7. The method for preparing magnetic biochar based on directional grafting of eucalyptus residue tannins according to claim 3, characterized in that, The preparation of the magnetic biochar includes: The biochar was dispersed in an iron salt solution and stirred in a water bath at 60-80°C for 2-4 hours. The pH was adjusted to 8-10, and stirring was continued for 1-2 hours. The biochar was then separated, washed, and dried to obtain the magnetic biochar.

8. The method for preparing magnetic biochar according to claim 7, characterized in that, The iron salt solution is Fe 2+ and Fe 3+ A mixed solution, wherein the Fe 2+ With the Fe 3+ The molar ratio is 1:(1-2), and the total iron concentration in the iron salt solution is 0.2-0.8 mol / L.

9. A magnetic biochar based on eucalyptus residue tannin-directed grafting for adsorbing ammonium nitrogen in acidic soils.

10. A soil conditioner, characterized in that, Including the magnetic biochar based on directional grafting of eucalyptus residue tannin as described in any one of claims 1-2.

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