A bifunctional layered structured biochar-based composite material for acidic soil and a method of preparing the same

Abstract

This invention provides a bifunctional layered biochar-based composite material for acidic soils and its preparation method. The bifunctional layered biochar-based composite material comprises: a biochar carrier; an alkaline ion slow-release core loaded in the internal pores of the biochar carrier for slowly releasing alkaline ions in an acidic soil environment to transform the soil environment from acidic to neutral; and a trace element organic framework loaded on the surface of the biochar carrier for releasing trace elements when the soil environment changes from neutral to acidic. This bifunctional layered biochar-based composite material solves the problem of the time-dependent disconnect between pH regulation and nutrient supply in acidic soils, ultimately achieving the dual goals of long-term acid suppression and precise fertilization in acidic soils.

Description

Technical Field

[0001] This application relates to the field of biochar technology, and in particular to a bifunctional layered biochar-based composite material for acidic soils and its preparation method. Background Technology

[0002] Acidic soils are a significant low-yield soil type in southern my country. Low pH, high aluminum toxicity, and micronutrient deficiency are the three major obstacles limiting crop growth. Current technologies often involve simply mixing substances that increase pH and release micronutrients, which may lead to a disconnect between pH adjustment and nutrient supply in time, failing to fundamentally solve the problem of coexisting re-acidification and nutrient deficiency. Summary of the Invention

[0003] In view of this, the purpose of this application is to propose a bifunctional layered biochar-based composite material for acidic soil and its preparation method, so as to solve the problem that existing materials are out of sync with pH regulation and nutrient supply in acidic soil in time, and cannot fundamentally solve the problem of coexistence of re-acidification and nutrient deficiency.

[0004] To achieve the above objectives, this application provides a bifunctional layered biochar-based composite material for acidic soils, comprising:

[0005] Biochar carrier; An alkaline ion slow-release core is loaded in the internal pores of the biochar carrier to slowly release alkaline ions in an acidic soil environment, thereby transforming the acidic soil environment into a neutral environment. A trace element organic framework, loaded on the surface of the biochar carrier, is used to release trace elements when the soil environment changes from neutral to acidic.

[0006] Optionally, the alkaline ion-releasing core comprises a magnesium-aluminum layered double hydroxide, wherein the magnesium-aluminum layered double hydroxide is composed of Mg 2+ With Al 3+ It forms a layered framework, with CO3 embedded in the interlayer voids. 2- And the Mg 2+ With the Al 3+ The molar ratio is (2:1) - (4:1).

[0007] Optionally, the trace element organic framework includes a metal-organic framework and trace elements, wherein the trace elements are loaded on the metal-organic framework, and the trace elements include boron and zinc. The metal-organic framework is a zeolite imidazole ester framework material or a Lavoisier framework material.

[0008] Optionally, the biochar carrier is made from seaweed raw material through pyrolysis.

[0009] Optionally, the seaweed raw material includes one or more of Ulva perforatum, Sargassum fusiforme, and Ulva prolifera.

[0010] Optionally, the alkaline ion slow-release core accounts for 15%-35% of the total weight of the bifunctional layered biochar-based composite material, and the trace element organic framework accounts for 3%-12% of the total weight of the bifunctional layered biochar-based composite material.

[0011] Based on the same inventive concept, this disclosure also provides a method for preparing a bifunctional layered biochar-based composite material for acidic soils, comprising: Preparation of biochar carriers; The alkaline ion slow-release core is loaded in the internal pores of the biochar carrier to slowly release alkaline ions in an acidic soil environment, thereby transforming the acidic soil environment into a neutral environment. A trace element organic framework is loaded onto the surface of the biochar carrier to obtain the bifunctional layered biochar-based composite material, wherein the trace element organic framework is released from the surface of the biochar carrier when the soil changes from a neutral environment to an acidic environment.

[0012] Optionally, loading the alkaline ion-releasing core into the internal pores of the biochar support includes: The biochar carrier was dispersed in water, magnesium and aluminum salts were added, and alkaline solution was added dropwise to maintain the pH of the solution at 9-11. The solution was hydrothermally aged at 60-90℃ for 6-24 hours. After cooling, the solid was collected by centrifugation, washed until neutral, and then dried to obtain a biochar carrier loaded with an alkaline ion slow-release core.

[0013] Optionally, loading the trace element organic framework onto the surface of the biochar support includes: A biochar support loaded with a basic ion slow-release core was added to a solvent containing a zinc source, an organic ligand, and a boron source, and reacted at 25-85°C for 6-24 hours to load a trace element organic framework onto the surface of the biochar support. After the reaction, the product was collected by centrifugation, washed, and dried to obtain the bifunctional layered biochar-based composite material.

[0014] Based on the same inventive concept, this disclosure also provides a soil conditioner, including the bifunctional layered biochar-based composite material described in any of the above claims.

[0015] As described above, the dual-functional layered biochar-based composite material provided in this application comprises a biochar carrier, an alkaline ion slow-release core, and a trace element organic framework. The biochar carrier provides a stable loading substrate for the alkaline ion slow-release core and the trace element organic framework. Its porous structure enhances soil permeability and water retention, while also adsorbing some free heavy metal ions, thus helping to alleviate soil pollution. The alkaline ion slow-release core is loaded within the pores of the biochar, avoiding direct and rapid contact with the soil, achieving a slow release of alkaline ions. This gradually adjusts the pH of acidic soil to neutral, avoiding the rapid pH rise and fall caused by the rapid release of alkali from traditional lime-based materials, reducing stimulation to crop roots, and simultaneously inhibiting Al³⁺. + Toxicity to crops. The micronutrient organic framework is loaded on the surface of biochar, maintaining structural stability when the soil is neutral, without redundant release of micronutrients. It precisely dissociates and releases micronutrients such as zinc and boron only when the soil becomes acidic, compensating for the loss of micronutrients caused by acidification. In this embodiment, the alkaline ion slow-release core and the micronutrient organic framework form a close functional synergy: the alkaline ion slow-release core maintains the soil in a neutral and stable state, and the original micronutrients in the soil can exist stably and are not easily lost under neutral conditions, without the need for additional replenishment. Therefore, the micronutrient organic framework remains silent and does not release fertilizer at this time. When the soil shows a tendency to become acidic, the acidic environment will trigger the precise dissociation of the micronutrient organic framework, releasing micronutrients such as zinc and boron to compensate for the loss of micronutrients caused by acidification. The alkaline ion slow-release core and the micronutrient organic framework work together to match the micronutrient change pattern of neutral stability and acidification loss in acidic soil, ultimately achieving the dual goals of long-term acid suppression and precise fertilization in acidic soil. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram illustrating the preparation method of a bifunctional layered biochar-based composite material according to an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0019] 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.

[0020] As mentioned in the background, acidic soil is one of the most widespread and far-reaching low-yield soil types in southern my country, covering more than 60% of the arable land area in the south. It severely restricts the yield and quality improvement of major crops such as rice, corn, and vegetables. The core problems of this type of soil are mainly manifested in low pH, high aluminum toxicity, and micronutrient deficiency.

[0021] Low pH environments pose a particularly significant direct threat to crops. Low pH environments inhibit root development, and acidic conditions disrupt the proton gradient balance of root cells, leading to root tip necrosis, reduced lateral root germination, and a significant reduction in root absorption area. Even if a certain amount of nutrients are present in the soil, they are difficult for crops to effectively absorb. Low pH also affects the synthesis and stability of chlorophyll in crop photosynthesis, resulting in leaf yellowing and decreased photosynthetic efficiency. At the same time, it inhibits respiration and substance transport, causing crops to grow slowly, weaken their resistance, and become more susceptible to pests and diseases.

[0022] When soil pH remains below 5.5 for an extended period, aluminum will be activated and released from soil minerals, exchanging for Al³⁺. + It exists in the form of a substance whose strong toxicity can damage the cell membrane structure of crop roots, inhibiting root elongation and nutrient absorption.

[0023] More importantly, soil pH directly determines the retention and supply efficiency of micronutrients: when soil pH is adjusted to the neutral range (5.5-6.5), the chemical forms of essential micronutrients such as zinc, boron, and molybdenum are more stable, less likely to be excessively adsorbed by soil colloids, and less likely to be leached away by rainwater. They can remain in the soil in an effective state to meet the normal growth needs of crops, and there is no need to supplement micronutrients at this time. However, when the soil shows a tendency to re-acidify (pH drops below 5.5), micronutrients will be converted back into free or easily leached forms and rapidly lost due to leaching caused by the rainy weather in the south. At the same time, root damage caused by low pH will further reduce the crop's ability to absorb micronutrients. This is precisely the critical point when crops need to supplement micronutrients the most.

[0024] Existing technologies addressing the aforementioned problems are mostly limited to the simple physical mixing and application of pH-regulating substances (such as lime and ordinary biochar) with micronutrient fertilizers (such as zinc and boron fertilizers), simultaneously introducing acid-suppressing substances and micronutrients in one application. While this approach seems to solve both acidity and nutrient deficiency issues, it has inherent flaws. When the soil is adjusted to neutral, there is no need for additional micronutrient supplementation (the available micronutrients in the soil are sufficient). However, the mixed micronutrients are either fixed by neutral soil colloids and cannot be utilized, or they are slowly lost due to the lack of necessary controlled-release mechanisms, resulting in nutrient waste. Furthermore, when the soil becomes acidic again, micronutrients begin to be lost in large quantities, and crops urgently need nutrient replenishment, the previously mixed micronutrients have been depleted or converted into ineffective forms, failing to respond promptly to the demand. This leads to crops suffering from both the direct harm of low pH and micronutrient deficiency under acidic stress, making it difficult to fundamentally achieve long-term improvement of acidic soils.

[0025] To address the aforementioned issues, this application provides a bifunctional layered biochar-based composite material for acidic soils and its preparation method.

[0026] The following is in conjunction with the appendix Figure 1 The embodiments of this application will be described in detail below.

[0027] In some embodiments, a bifunctional layered biochar-based composite material for acidic soils comprises: Biochar carrier; An alkaline ion slow-release core is loaded in the internal pores of the biochar carrier to slowly release alkaline ions in an acidic soil environment, thereby transforming the acidic soil environment into a neutral environment. A trace element organic framework, loaded on the surface of the biochar carrier, is used to release trace elements when the soil environment changes from neutral to acidic.

[0028] In this embodiment, the bifunctional layered biochar-based composite material includes a biochar carrier, an alkaline ion slow-release core, and a trace element organic framework. The biochar carrier provides a stable loading substrate for the alkaline ion slow-release core and the trace element organic framework. Its porous structure enhances soil permeability and water retention, while also adsorbing some free heavy metal ions, thus helping to alleviate soil pollution. The alkaline ion slow-release core is loaded within the pores of the biochar, avoiding direct and rapid contact with the soil, achieving a slow release of alkaline ions. This gradually adjusts the pH of acidic soil to neutral, avoiding the rapid pH fluctuations caused by the rapid release of alkali from traditional lime-based materials, reducing stimulation to crop roots, and simultaneously inhibiting Al³⁺. + Toxicity to crops. The micronutrient organic framework is loaded on the surface of biochar, maintaining structural stability when the soil is neutral, without redundant release of micronutrients. It precisely dissociates and releases micronutrients such as zinc and boron only when the soil becomes acidic, compensating for the loss of micronutrients caused by acidification.

[0029] In this embodiment, the alkaline ion slow-release core and the trace element organic framework form a close functional synergy: the alkaline ion slow-release core maintains the soil in a neutral and stable state, and the original trace elements in the soil can exist stably and are not easily lost in a neutral environment, without the need for additional replenishment. Therefore, the trace element organic framework remains silent and does not release fertilizer at this time. When the soil shows a tendency to re-acidify, the re-acidification environment will trigger the precise dissociation of the trace element organic framework, releasing trace elements such as zinc and boron to make up for the trace element loss caused by re-acidification. The alkaline ion slow-release core and the trace element organic framework work together to match the change pattern of trace elements in acidic soils, which are stable in neutral conditions and lost in re-acidification, and finally achieve the dual goals of long-term acid suppression and precise fertilizer supply in acidic soils.

[0030] In some embodiments, the alkaline ion-releasing core comprises a magnesium-aluminum layered double hydroxide, wherein the magnesium-aluminum layered double hydroxide is composed of Mg 2+ With Al 3+ It forms a layered framework, with CO3 embedded in the interlayer voids. 2- And the Mg 2+ With the Al 3+ The molar ratio is (2:1) - (4:1).

[0031] In this embodiment, the alkaline ion-releasing core comprises a magnesium-aluminum layered double hydroxide, which is an anionic layered material with CO3 intercalated between the layers. 2- It can react with H in the soil + The reaction produces HCO3 - CO2, and OH released by synergistic layer dissociation - Achieving dual acid neutralization results in a longer-lasting acid suppression effect; wherein, the Mg... 2+ With the Al 3+The molar ratio is (2:1)-(4:1), and this ratio range can ensure the stability of the magnesium-aluminum layered double hydroxide layered structure. If this ratio is too high (Al...), it will cause problems. 3+ Insufficient Al content leads to weakened interlayer bonding, making the material prone to decomposition and unable to release alkali effectively over a long period; too low an Al content results in... 3+ Excessive amounts of magnesium-aluminum layered double hydroxides can lead to excessively high charge density in the layers, making the structure prone to collapse and potentially increasing the risk of aluminum toxicity. Magnesium-aluminum layered double hydroxides at this ratio can slowly dissociate and release alkali in acidic environments while maintaining structural stability in neutral environments, thus avoiding excessive alkali release.

[0032] In some embodiments, the trace element organic framework includes a metal-organic framework and trace elements, wherein the trace elements are loaded on the metal-organic framework, and the trace elements include boron and zinc. The metal-organic framework is a zeolite imidazolate framework or a Lavoisier framework.

[0033] In this embodiment, zinc and boron were selected as the core trace elements, both of which are essential for crop growth. Zinc participates in chlorophyll synthesis and enzyme activity regulation, alleviating leaf yellowing under acid stress; boron enhances cell wall stability and resists aluminum toxicity damage to roots caused by re-acidification. The synergistic supplementation of these two elements can significantly improve the crop's resistance to acid stress. This embodiment also limits the MOF (metal-organic framework) to zeolite imidazolium ester (ZIFs) or Lavoirian framework (MILs) materials, such as zeolite imidazolium ester framework material-8 and Lavoirian framework material-101 ​​from the Materials Research Institute. Both possess excellent pH response characteristics and porous loading capacity: ZIFs materials easily break coordination bonds in acidic environments, allowing for rapid release of trace elements in response to re-acidification signals; MILs materials exhibit stronger chemical stability, are adaptable to more complex soil environments, and have larger pore volumes, increasing the trace element loading capacity.

[0034] In some embodiments, the biochar carrier is made from seaweed raw material through pyrolysis.

[0035] In this embodiment, seaweed was selected as the raw material for preparing biochar carriers. Compared with traditional raw materials such as straw and sawdust, this significantly improves the performance and environmental value of biochar carriers. Firstly, seaweed (such as Ulva perforatum, Sargassum fusiforme, and Ulva prolifera) is rich in organic components such as polysaccharides and proteins. The biochar formed after pyrolysis has a richer pore structure and surface functional groups (such as hydroxyl and carboxyl groups). This not only enhances the loading capacity of the basic core and MOF framework and improves the material binding stability, but also adsorbs free Al from the soil through surface functional groups. 3+Firstly, it can further alleviate aluminum toxicity; secondly, seaweed resources are abundant, especially green algae such as Ulva prolifera which often grow explosively. Using them as raw materials to prepare biochar can realize the resource utilization of waste, reduce the material preparation cost, and at the same time reduce the impact of seaweed accumulation on the ecological environment; thirdly, seaweed-based biochar has a high content of basic ions and has a certain degree of weak alkalinity, which can help the alkaline core neutralize soil acidity and improve acid suppression efficiency.

[0036] In some embodiments, the seaweed raw material includes one or more of Ulva perforatum, Sargassum fusiforme, and Ulva prolifera.

[0037] In this embodiment, the seaweed raw material includes one or more of Ulva pertusa, Sargassum fusiforme, and Ulva prolifera. All three are widely distributed seaweed species along the coast of my country, making them readily available. Each of the three has its own advantages in composition and structure. Ulva pertusa has a high cellulose content, and its biochar after pyrolysis has a more regular pore structure and strong load stability. Sargassum fusiforme is rich in potassium, calcium, and other basic ions, resulting in a more significant acid-suppressing effect. Ulva prolifera has a fast growth rate, high yield, and the lowest raw material cost. The three can be used individually or in combination, allowing for flexible adjustments based on the cost and performance requirements of soil improvement: for example, Sargassum fusiforme can be chosen as the main material to enhance the acid-suppressing effect for extremely acidic soils; Ulva pertusa can be chosen as the main material for scenarios requiring high load capacity; and Ulva prolifera can be chosen as the main material for large-scale, low-cost improvement needs, thus broadening the application scenarios of the composite material.

[0038] In some embodiments, the alkaline ion-releasing core accounts for 15%-35% of the total weight of the bifunctional layered biochar-based composite material, and the trace element organic framework accounts for 3%-12% of the total weight of the bifunctional layered biochar-based composite material.

[0039] In this embodiment, when the alkaline ion slow-release core accounts for less than 15% of the total weight of the bifunctional layered biochar-based composite material, the release of alkaline ions is insufficient, making it impossible to effectively adjust acidic soil to neutral and inhibit re-acidification in the long term. When the proportion is higher than 35%, it not only increases the material preparation cost but may also lead to excessive release of alkaline ions, causing the soil pH to be too high, which in turn fixes trace elements and affects crop growth. When the trace element organic framework accounts for less than 3% of the total weight of the bifunctional layered biochar-based composite material, the amount of trace elements released during re-acidification is insufficient and cannot alleviate nutrient deficiency symptoms. When the proportion is higher than 12%, it will not only waste trace elements but may also cause nutrient antagonism due to excessive release during re-acidification (such as excessive zinc inhibiting iron absorption).

[0040] Based on the same inventive concept, such as Figure 1 As shown, this disclosure also provides a method for preparing a bifunctional layered biochar-based composite material for acidic soils, comprising: S100: Preparation of biochar carrier; S200: The alkaline ion slow-release core is loaded in the internal pores of the biochar carrier to slowly release alkaline ions in an acidic soil environment, so as to transform the acidic soil environment into a neutral environment. S300: A trace element organic framework is loaded onto the surface of the biochar carrier to obtain the bifunctional layered biochar-based composite material, wherein the trace element organic framework is released from the surface of the biochar carrier when the soil changes from a neutral environment to an acidic environment.

[0041] In some embodiments, loading the alkaline ion-releasing core into the internal pores of the biochar support includes: The biochar carrier was dispersed in water, magnesium and aluminum salts were added, and alkaline solution was added dropwise to maintain the pH of the solution at 9-11. The solution was hydrothermally aged at 60-90℃ for 6-24 hours. After cooling, the solid was collected by centrifugation, washed until neutral, and then dried to obtain a biochar carrier loaded with an alkaline ion slow-release core.

[0042] In this embodiment, biochar was dispersed in water and magnesium aluminum salt was added. The pH was then adjusted to 9-11 by adding alkaline solution. This pH range is the optimal condition for the in-situ synthesis of MgAl-LDHs (magnesium aluminum layered double hydroxides), which can promote the synthesis of MgAl-LDHs. 2+ With Al 3+ Uniform precipitation within the pores of biochar forms a structurally complete layered double hydroxide, avoiding product impurities caused by excessively high or low pH. Hydrothermal aging at 60-90℃ and for 6-24 hours promotes the growth and crystal formation of MgAl-LDHs crystals, enhancing the stability of the layered structure and strengthening the long-term alkali release capacity. Too low a temperature or too short a time will result in insufficient crystal growth and structural instability; too high a temperature or too long a time will increase energy consumption and costs.

[0043] In some embodiments, loading the trace element organic framework onto the surface of the biochar support includes: A biochar support loaded with a basic ion slow-release core was added to a solvent containing a zinc source, an organic ligand, and a boron source, and reacted at 25-85°C for 6-24 hours to load a trace element organic framework onto the surface of the biochar support. After the reaction, the product was collected by centrifugation, washed, and dried to obtain the bifunctional layered biochar-based composite material.

[0044] In this embodiment, a zinc source, an organic ligand, and a boron source are simultaneously added to the reaction system, enabling the one-step synthesis of the MOF framework and the loading of trace elements. The zinc source, acting as the metal center of the MOF framework, coordinates with the organic ligand to form the MOF skeleton, while the boron source is loaded into the MOF channels through physical adsorption or weak chemical interaction. This simplifies the process steps and improves the uniformity of trace element loading. The reaction temperature range of 25-85℃ is suitable for the synthesis requirements of different types of MOFs, and the reaction time of 6-24 hours ensures sufficient growth of the MOF framework, forming a complete porous structure and ensuring the loading capacity.

[0045] Based on the same inventive concept, this disclosure also provides a soil conditioner, including the bifunctional layered biochar-based composite material described in any of the above claims, and having the beneficial effects of the bifunctional layered biochar-based composite material embodiments, which will not be repeated here.

[0046] The above embodiments are illustrated below with reference to specific examples.

[0047] The raw materials and pharmaceuticals used in this embodiment are all commercially available products.

[0048] Example 1 A method for preparing a bifunctional layered biochar-based composite material for acidic soils, comprising: S1: Fresh samples of Ulva perforatum were taken, washed three times with deionized water to remove salt and impurities, and dried at 80℃ to constant weight. The dried seaweed was pulverized and passed through a 60-mesh sieve. 50g of seaweed powder was placed in a tube furnace and heated to 500℃ at 5℃ / min under a nitrogen atmosphere and held for 2 hours. After pyrolysis, it was naturally cooled to room temperature to obtain a biochar carrier (labeled BC-1), which was then ground and passed through a 100-mesh sieve for later use. S2: Weigh 5.0 g of BC-1 and disperse it in 200 mL of deionized water. Sonicate the solution for 30 minutes to ensure complete dispersion, obtaining a biochar suspension. Prepare a mixed salt solution: Dissolve 0.06 mol of Mg(NO3)2·6H2O and 0.02 mol of Al(NO3)3·9H2O in 100 mL of deionized water (Mg / Al = 3:1). Slowly add the mixed salt solution dropwise to the biochar suspension while stirring, simultaneously adding 2 mol / L NaOH solution to maintain the pH at 10. After the addition is complete, transfer the mixture to a hydrothermal reactor and age it at 80 °C for 12 hours. After cooling, centrifuge to collect the solid, wash with deionized water until neutral, and dry at 80 °C to obtain the biochar support loaded with MgAl-LDHs (labeled BC-LDH-1). S3: 2.0 g of BC-LDH-1 was impregnated in 100 mL of methanol solution containing 2-methylimidazole (8.0 g), zinc nitrate (Zn(NO3)2·6H2O, 4.0 g) and H3BO3 (4.0 g). The mixture was stirred at 30 °C for 12 hours. After the reaction was completed, the product was collected by centrifugation, washed three times with methanol, and dried under vacuum at 60 °C to obtain a bifunctional layered biochar-based composite material (labeled as BC-LDH-ZIF-1).

[0049] Material characterization of BC-LDH-ZIF-1 was performed.

[0050] XRD patterns show that BC-LDH-ZIF-1 contains broad diffraction peaks of biochar, characteristic layered peaks of LDHs (layered double hydroxides) (2θ ≈ 11.6°, 23.4°), and characteristic peaks of ZIF-8 (zeolite imidazolium ester skeleton-8) (2θ ≈ 7.4°, 12.8°), proving that the three-layer structure was successfully constructed.

[0051] SEM images show that the biochar surface is covered with nanosheet-like LDHs and typical rhombic dodecahedral ZIF-8 particles, which are evenly distributed.

[0052] BET specific surface area: BC-1 is 320 m² / g, BC-LDH-1 is 285 m² / g, and BC-LDH-ZIF-1 is 510 m² / g, indicating that MOF loading significantly improves the porosity of the material.

[0053] Elemental analysis (ICP-OES): Zn loading was 4.2 wt%, and B loading was 2.0 wt%.

[0054] Thermogravimetric analysis (TGA) was used to determine the thermal weight loss behavior of the composite material. By comparing the weight loss curves of the biochar support, the biochar intermediate loaded with LDHs, and the final composite material, the mass fractions of alkaline ion slow-release core (MgAl-LDHs) and trace element organic framework (ZIF-8) in the composite material were calculated: In BC-LDH-ZIF-1, alkaline ion slow-release core (MgAl-LDHs) accounted for 25% of the total weight of the composite material, and trace element organic framework (ZIF-8) accounted for 8% of the total weight of the composite material.

[0055] Example 2 A method for preparing a bifunctional layered biochar-based composite material for acidic soils, comprising: S1: Take a dried sample of Sargassum fusiforme, crush it through a 60-mesh sieve, and then pyrolyze it at 450℃ for 3 hours under nitrogen protection to obtain seaweed biochar (BC-2). S2: Weigh 5.0 g of BC-2 and disperse it in 200 mL of deionized water. Sonicate the solution for 30 minutes to ensure complete dispersion, obtaining a biochar suspension. Prepare a mixed salt solution: Dissolve 0.04 mol of Mg(NO3)2·6H2O and 0.02 mol of Al(NO3)3·9H2O in 100 mL of deionized water (Mg / Al = 2:1). Slowly add the mixed salt solution dropwise to the biochar suspension while stirring, simultaneously adding 2 mol / L NaOH solution to maintain the pH of the system at 9.5. After the addition is complete, transfer the mixture to a hydrothermal reactor and age it at 70 °C for 18 hours. After cooling, centrifuge to collect the solid, wash with deionized water until neutral, and dry at 80 °C to obtain a biochar support loaded with MgAl-LDHs (labeled BC-LDH-2). S3: BC-LDH-2 was added to a DMF solution containing Zn(NO3)2, H3BO3 and trimellitic acid. The solution contained trimellitic acid (8.0 g), zinc nitrate (Zn(NO3)2·6H2O, 4.0 g) and H3BO3 (4.0 g). The mixture was reacted at 85 °C for 24 hours to obtain a bifunctional layered biochar-based composite material, denoted as BC-LDH-MOF-2.

[0056] Material characterization of BC-LDH-MOF-2 was performed.

[0057] Characterization by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed that layered hydrogen hydroxides (LDHs) and metal-organic frameworks (MOFs) coexist stably in the composite material without significant phase destruction or structural collapse. Elemental analysis results show that the Zn loading in the composite material is 3.8 wt%, the B loading is 1.2 wt%, and the target element loading is uniform and reaches the expected level. pH response release performance tests show that the material has significant acid response release characteristics: in a buffer system with pH=5.0, the cumulative release rates of Zn and B elements over 24 hours are as high as 68% and 55%, respectively, while in a neutral buffer system with pH=7.0, the cumulative release rates of both over 24 hours are less than 10%, demonstrating a good pH-targeted release effect.

[0058] Thermogravimetric analysis (TGA) determined that the alkaline ion slow-release core (MgAl-LDHs) in BC-LDH-ZIF-1 accounted for 15% of the total weight of the composite material, and the trace element organic framework (ZIF-8) accounted for 12% of the total weight of the composite material.

[0059] Example 3 A method for preparing a bifunctional layered biochar-based composite material for acidic soils, comprising: S1: Take a dried sample of seaweed, crush it through a 60-mesh sieve, and then pyrolyze it at 300℃ for 4 hours under nitrogen protection to obtain seaweed biochar (BC-3). S2: Weigh 5.0 g of BC-3 and disperse it in 200 mL of deionized water. Sonicate the solution for 30 minutes to ensure complete dispersion, obtaining a biochar suspension. Prepare a mixed salt solution: Dissolve 0.08 mol of Mg(NO3)2·6H2O and 0.02 mol of Al(NO3)3·9H2O in 100 mL of deionized water (Mg / Al = 4:1). Slowly add the mixed salt solution dropwise to the biochar suspension while stirring, simultaneously adding 2 mol / L NaOH solution to maintain the pH at 11. After the addition is complete, transfer the mixture to a hydrothermal reactor and age it at 90 °C for 6 hours. After cooling, centrifuge to collect the solid, wash with deionized water until neutral, and dry at 80 °C to obtain a biochar support loaded with MgAl-LDHs (labeled BC-LDH-3). S3: BC-LDH-3 was added to a DMF solution containing Zn(NO3)2, H3BO3 and trimellitic acid. The solution contained trimellitic acid (8.0 g), zinc nitrate (Zn(NO3)2·6H2O, 4.0 g) and H3BO3 (4.0 g). The mixture was reacted at 25 °C for 6 hours to obtain a bifunctional layered biochar-based composite material, denoted as BC-LDH-MOF-3.

[0060] Material characterization of BC-LDH-MOF-3 was performed.

[0061] Thermogravimetric analysis (TGA) determined that the alkaline ion slow-release core (MgAl-LDHs) in BC-LDH-ZIF-1 accounted for 35% of the total weight of the composite material, and the trace element organic framework (ZIF-8) accounted for 3% of the total weight of the composite material.

[0062] The pore structure of the material was characterized by specific surface area testing. The specific surface area of ​​BC-LDH-MOF-3 was measured to be 480 m² / g, which shows that it has excellent porous structure advantages.

[0063] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that only step S1 is performed to obtain BC-1.

[0064] Comparative Example 2 Biochar support BC-1 was prepared according to the method in step S1 of Example 1; Referring to the raw material ratio of 0.06 mol Mg(NO3)2·6H2O, 0.02 mol Al(NO3)3·9H2O, and 2 mol / L NaOH solution adjusted to pH=10 in step S2 of Example 1, the biochar carrier addition step was omitted. The mixed salt solution was directly mixed with the NaOH solution and transferred to a hydrothermal reactor. It was aged at 80°C for 12 hours, followed by centrifugation, washing, and drying at 80°C to prepare MgAl-CO3 type LDHs powder. Referring to the raw material ratio in step S3 of Example 1 (8.0 g of 2-methylimidazole, 4.0 g of zinc nitrate, 4.0 g of boric acid, and 100 mL of methanol), the BC-LDH-1 carrier addition step was omitted. The two raw materials were directly dissolved in methanol and stirred at 30 °C for 12 hours. Subsequently, after centrifugation, washing with methanol three times, and vacuum drying at 60 °C, ZIF-8 powder was prepared. Based on the actual mass ratio of each component in Example 1 (i.e., the mass percentage of BC-1, MgAl-LDHs, and ZIF-8 in the final BC-LDH-ZIF-1 composite material), accurately weigh the BC-1 powder, MgAl-CO3 type LDHs powder, and ZIF-8 powder prepared above, place them in a high-speed mixer, and mechanically mix them at 200 r / min for 30 minutes at room temperature to ensure that the three components are mixed evenly, and obtain a physically mixed sample, labeled as Mix-1.

[0065] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that only steps S1 and S2 are performed to obtain BC-LDH-1.

[0066] The biochar prepared in Example 1 and Comparative Examples 1-3 were subjected to performance tests.

[0067] (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 (acidic), exchangeable aluminum content is 2.1 cmol / kg, available Zn content is 0.8 mg / kg, and available B content is 0.2 mg / kg.

[0068] (2) Test materials: Example 1 Material: BC-LDH-ZIF-1 (bifunctional layered biochar-based composite material). Comparative Example 1 Material: BC-1 (biochar carrier); Comparative Example 2 Material: Mix-1 (a physical mixture of BC-1, MgAl-CO3 type LDHs, and ZIF-8); Comparative Example 3 Material: BC-LDH-1 (Biochar support loaded with MgAl-LDHs). All materials were ground through a 100-mesh sieve, dried, sealed, and stored for later use.

[0069] (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.

[0070] (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 (BC-LDH-ZIF-1) at a rate of 1% of the soil weight (i.e., 10g of material per 1kg of soil). Treatment Group 2: Add material from Comparative Example 1 (BC-1) at a rate of 1% of the soil weight; Treatment group 3: Add material (Mix-1) from Comparative Example 2 at a rate of 1% of the soil weight; Treatment group 4: Add material (BC-LDH-1) from Comparative Example 3 at a rate of 1% of the soil weight; Treatment group 5: Blank control (CK), with no added improvement materials.

[0071] (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 amendment material was accurately added according to the group design, and the mixture was thoroughly mixed manually. The soil moisture content of all treatment groups was adjusted to 60% of field capacity (moisture was controlled by weighing, and water lost through evaporation was replenished periodically). The culture dishes were placed in a 25℃ constant temperature incubator for constant temperature incubation, and good ventilation was maintained during the incubation period.

[0072] (6) Sampling time Sampling was conducted on days 7, 30, 60, and 90 of cultivation. Soil samples were collected from each cultivation pot using a five-point sampling method. After removing impurities, relevant indicators were measured immediately. Crop growth indicators for pot-assisted experiments were measured simultaneously on day 60 of cultivation.

[0073] (7) Test method Soil pH: Determined by potentiometric method. Weigh 5g of air-dried soil sample and place it in a 50mL centrifuge tube. Add deionized water at a soil-to-water ratio of 1:2.5 (m:v). Shake for 30min and let stand for 30min. Measure the pH of the supernatant using a pH meter. Each sample was measured in triplicate, and the average value was taken.

[0074] Exchangeable aluminum content: determined by potassium chloride extraction-aluminum reagent colorimetric method. Weigh 2g of air-dried soil sample into a 100mL Erlenmeyer flask, add 20mL of 1mol / L KCl solution, shake for 1h, filter, take 5mL of filtrate into a 50mL volumetric flask, add aluminum reagent colorimetric reagent, dilute to the mark, shake well, let stand for 20min, and measure the absorbance at 530nm wavelength on a spectrophotometer. Calculate the exchangeable aluminum content according to the standard curve.

[0075] Available Zn and available B content: determined by DTPA extraction-ICP-OES method. 10g of air-dried soil sample was weighed and placed in a 250mL Erlenmeyer flask, 50mL of DTPA extraction solution was added, the mixture was shaken for 2h and then filtered. The filtrate was collected and the contents of available Zn and available B in the filtrate were determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0076] (8) Potted plant-assisted experiment: After 60 days of cultivation, the corn plants were carefully removed, rinsed with deionized water, and the following growth indicators were measured: Plant height: The height from the base of the plant to the growing point was measured using a ruler, accurate to 0.1 cm; Root length: The length from the base of the main root to the root tip is measured using a ruler, accurate to 0.1 cm; Biomass: The plants were divided into above-ground parts (stems and leaves) and underground parts (roots), and were placed in an oven at 105℃ for 30 minutes to blanch them. Then they were dried at 80℃ to constant weight, and the dry weight was measured using an electronic balance to an accuracy of 0.1g.

[0077] The specific experimental results are shown in the table below: Table 1. Comparison of experimental results for treatment groups 1-5

[0078] Based on the experimental data of maize seedlings cultured for 90 days in Table 1, it can be seen that the bifunctional layered biochar-based composite material (BC-LDH-ZIF-1, treatment group 1) showed significantly better improvement effects on acidic red soil in southern China than other treatments and the blank control. Regarding soil pH regulation and acidification mitigation, this material increased the soil pH from an initial 4.8 to 6.2, while reducing the exchangeable aluminum content to 0.4 cmol / kg. Compared to the blank control (pH=4.8, exchangeable aluminum 2.1 cmol / kg), it achieved a 29% increase in pH and an 81% reduction in aluminum toxicity, demonstrating a far superior effect in mitigating aluminum toxicity in acidic red soil compared to biochar alone (treatment group 2), physical mixtures (treatment group 3), and biochar loaded only with LDHs (treatment group 4). In terms of nutrient supply, treatment group 1 achieved available Zn and available B contents of 5.8 mg / kg and 0.9 mg / kg, respectively, which is significantly lower than the blank control (0.8 mg / kg, 0.2 mg / kg, 0.9 ... The effective Zn and B content was 7.25 times and 4.5 times higher than that of the control group (6.3 g / kg), respectively, fully leveraging the pH-responsive release characteristics to achieve efficient nutrient supply in acidic soils. The corresponding crop growth performance was also more outstanding, with maize biomass (12.5 g / pot) nearly twice that of the control group (6.3 g / pot), significantly higher than other treatment groups. The physical mixture (Mix-1) in Comparative Example 2, lacking the structural synergy of LDHs and MOFs, could neither maintain soil pH for a long time (pH only 5.8 after 90 days of cultivation) nor achieve targeted nutrient release. Nutrients were easily lost during water runoff, resulting in effective Zn and B content of only 3.2 mg / kg and 0.5 mg / kg, respectively. Overall, BC-LDH-ZIF-1, through the synergistic effect of LDHs, MOFs, and biochar, simultaneously achieved pH regulation, aluminum toxicity mitigation, and precise nutrient supply in acidic red soils, with a comprehensive improvement effect far superior to single materials or physical mixtures.

[0079] 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.

[0080] While specific details have been set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that embodiments of this application may be practiced without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0081] 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. The embodiments of this application are intended to cover all such substitutions, modifications, and variations falling 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 bifunctional layered biochar-based composite material for acidic soils, characterized in that, include: Biochar carrier; An alkaline ion slow-release core is loaded in the internal pores of the biochar carrier to slowly release alkaline ions in an acidic soil environment, thereby transforming the acidic soil environment into a neutral environment. A trace element organic framework, loaded on the surface of the biochar carrier, is used to release trace elements when the soil environment changes from neutral to acidic.

2. The bifunctional layered biochar-based composite material according to claim 1, characterized in that, The alkaline ion-releasing core comprises a magnesium-aluminum layered double hydroxide, which is composed of Mg... 2+ With Al 3+ It forms a layered framework, with CO3 embedded in the interlayer voids. 2- And the Mg 2+ With the Al 3+ The molar ratio is (2:1) - (4:1).

3. The bifunctional layered biochar-based composite material according to claim 1, characterized in that, The trace element organic framework includes a metal-organic framework and trace elements, wherein the trace elements are loaded on the metal-organic framework, and the trace elements include boron and zinc. The metal-organic framework is a zeolite imidazolate framework material or a Lavoisier framework material.

4. The bifunctional layered biochar-based composite material according to claim 1, characterized in that, The biochar carrier is made from seaweed raw material through pyrolysis.

5. The bifunctional layered biochar-based composite material according to claim 4, characterized in that, The seaweed raw materials include one or more of the following: Ulva perforatum, Sargassum fusiforme, and Ulva prolifera.

6. The bifunctional layered biochar-based composite material according to claim 1, characterized in that, The alkaline ion slow-release core accounts for 15%-35% of the total weight of the bifunctional layered biochar-based composite material, and the trace element organic framework accounts for 3%-12% of the total weight of the bifunctional layered biochar-based composite material.

7. A method for preparing a bifunctional layered biochar-based composite material for acidic soils, characterized in that, include: Preparation of biochar carriers; The alkaline ion slow-release core is loaded in the internal pores of the biochar carrier to slowly release alkaline ions in an acidic soil environment, thereby transforming the acidic soil environment into a neutral environment. A trace element organic framework is loaded onto the surface of the biochar carrier to obtain the bifunctional layered biochar-based composite material, wherein the trace element organic framework is released from the surface of the biochar carrier when the soil changes from a neutral environment to an acidic environment.

8. The preparation method according to claim 7, characterized in that, The method of loading the alkaline ion-releasing core into the internal pores of the biochar support includes: The biochar carrier was dispersed in water, magnesium and aluminum salts were added, and alkaline solution was added dropwise to maintain the pH of the solution at 9-11. The solution was hydrothermally aged at 60-90℃ for 6-24 hours. After cooling, the solid was collected by centrifugation, washed until neutral, and then dried to obtain a biochar carrier loaded with an alkaline ion slow-release core.

9. The preparation method according to claim 8, characterized in that, The process of loading a trace element organic framework onto the surface of the biochar carrier includes: A biochar support loaded with a basic ion slow-release core was added to a solvent containing a zinc source, an organic ligand, and a boron source, and reacted at 25-85°C for 6-24 hours to load a trace element organic framework onto the surface of the biochar support. After the reaction, the product was collected by centrifugation, washed, and dried to obtain the bifunctional layered biochar-based composite material.

10. A soil conditioner, characterized in that, Including the bifunctional layered biochar-based composite material according to any one of claims 1-6.

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