Functionalized biochar material as well as preparation method and application thereof

Abstract

The invention provides a functional biochar material as well as a preparation method and application thereof. The functional biochar material comprises a biochar matrix and a functional interface layer constructed on the surface of the biochar matrix, the functional interface layer comprises complexed or coordinated active sites fixed on functional groups on the surface of the biochar; the complexation or coordination active sites are composed of multi-carboxyl chelating groups covalently fixed on the surface of the biochar and metal ions, metal oxides or metal hydroxides, and can be subjected to competitive complexation or coordination reconstruction under the action of multi-carboxyl organic acid molecules secreted by plant root systems, so that the reversible regulation and control of the chemical state of the interface is realized. The functionalized biochar material can be subjected to interface coordination reconstruction for multiple times along with the change of the concentration and variety of the plant rhizosphere organic acid, so that continuous regulation and control of nutrients or functional components among fixed, migrated and released states are realized, and the regulation and control behavior of the functionalized biochar material is more easily matched with the spatial and temporal distribution of the rhizosphere organic acid.

Description

Technical Field

[0001] This invention relates to the field of agricultural biotechnology, and in particular to a functionalized biochar material, its preparation method, and its application. Background Technology

[0002] Biochar, as a porous carbonaceous material, is widely used in agricultural fertilizer carriers and soil conditioners due to its large specific surface area and abundant surface functional groups. To improve the adsorption, fixation, or slow release capacity of biochar for nutrients, its surface is usually treated by chemical or physical modification methods.

[0003] Common technical solutions include introducing oxygen-containing functional groups such as carboxyl and hydroxyl groups onto the surface of biochar through acid treatment, alkali treatment, or salt solution impregnation, or loading metal ions and inorganic mineral components to enhance its adsorption capacity for nutrient molecules; after the modified biochar is applied to the soil, it relies on the adsorption-desorption balance of the material itself to achieve the slow release of nutrients.

[0004] The structure and chemical state of this type of biochar material remain largely stable after preparation, and its interaction in the soil environment depends primarily on the material's initial physicochemical properties. The aforementioned existing technology has at least the following shortcomings: 1. Modification is a static process and lacks environmental responsiveness. Once modified biochar enters the soil, its surface structure and functional group state remain basically fixed, making it impossible to adjust according to the dynamic changes in the plant rhizosphere environment, thus making it difficult to achieve precise nutrient release in specific areas or at specific stages.

[0005] 2. Limited match between nutrient release and plant needs. This type of technology mainly relies on the physical or chemical adsorption balance between materials and nutrients. The nutrient release process lacks a direct correlation with the actual absorption needs of plant roots, which can easily lead to problems such as low nutrient utilization or spatiotemporal mismatch.

[0006] Another category of existing technologies focuses on the application of environmentally responsive materials in agriculture or the environment, such as pH-responsive, ion-responsive, or temperature and humidity-responsive materials. These materials typically introduce reversible chemical bonds or stimulus-responsive groups, causing changes in their structure or properties in response to changes in external environmental conditions.

[0007] Material structural parameters (degree of crosslinking, porosity, membrane integrity) inevitably change over time, leading to a gradual drift in release behavior, mechanical properties, and response threshold. The material exhibits a "non-responsive / responsive" behavior, with intermediate states being difficult to maintain stably, and release or performance changes often occurring abruptly. The material may respond to any factor that causes changes in environmental parameters, resulting in non-targeted release or performance changes in relevant applications. After repeated stimulation, the response amplitude decreases, eventually transforming into irreversible structural changes or complete failure.

[0008] Environmentally responsive materials are often used to respond to changes in solution pH, salinity, or ion concentration to regulate the release or adsorption of substances. However, these materials are mostly polymers or inorganic-organic composites, and their response targets are typically changes in overall environmental parameters, rather than local signals generated by plant root activity. This existing technology still has the following shortcomings: Lack of specificity in response targets: Existing environmentally responsive materials typically use macroscopic parameters such as environmental pH and ionic strength as triggering conditions, making it difficult to distinguish between rhizosphere and non-rhizosphere regions and thus unable to achieve targeted responses to plant root activities.

[0009] In existing technologies, organic acids secreted by roots are mostly considered background factors affecting soil pH or nutrient migration, and there are no technical solutions that use them as triggers for material interface responses and to regulate material states. Furthermore, environmentally responsive materials often exist independently, with little integration with the porous structure and surface properties of biochar, making it difficult to fully utilize the carrier and interface advantages of biochar in agricultural applications.

[0010] Therefore, it is of great significance to develop a technology that can combine biochar and use root exudates as a response trigger signal. Summary of the Invention

[0011] This invention addresses the common problems in existing biochar materials used in agricultural applications, such as static modification methods, difficulty in sensing plant root activity, low matching degree between nutrient release and plant needs, and lack of rhizosphere-directed regulation capabilities. This invention proposes a functionalized biochar material with a root organic acid-responsive interface layer.

[0012] By constructing an interface layer on the surface of biochar that can selectively respond to organic acids secreted by plant roots, the interface layer undergoes structural or chemical state changes in the presence of rhizosphere organic acids, thereby achieving the directional release or regulation of nutrients or functional components in the rhizosphere region, improving nutrient utilization efficiency, and enhancing the coupling between biochar materials and plant root activities.

[0013] Specifically, the functionalized biochar material of the present invention includes a biochar matrix and a functional interface layer constructed on the surface of the biochar matrix; the functional interface layer is constructed on the pore walls or surface region of the biochar through in-situ generation; the functional interface layer contains complexing or coordination active sites fixed on the functional groups on the surface of the biochar; the complexing or coordination active sites are composed of polycarboxylic acid chelating groups covalently fixed on the surface of the biochar and metal ions or metal oxides (hydrides), and can undergo competitive complexation or coordination reconstruction under the action of polycarboxylic acid molecules secreted by plant roots.

[0014] The polycarboxylated organic acid molecules secreted by plant roots participate as competitive ligands in the interfacial chemical equilibrium regulation process of the functional interface layer. Through competitive complexation or coordination, the binding energy or binding mode between nutrients or functional components on the biochar surface and the functional interface layer is continuously changed, thereby regulating the fixation, migration or release behavior of nutrients or functional components on the biochar surface without relying on external coating degradation or overall environmental pH changes as triggering conditions.

[0015] The functional interface layer described in this application is constructed on the pore wall or surface region of biochar through in-situ generation. The functional phase (such as metal-organic coordination structure, metal oxide (hydride) active layer, etc.) "grows" on the pore wall / surface of biochar, forming an interface fusion / embedded combination with the carbon skeleton, and the active sites are distributed inside the pores.

[0016] Existing functional interface layers are usually used as outer coating layers, that is, forming a continuous film / shell (hydrogel, polymer, microcapsule shell, etc.) on the outer surface of particles. Essentially, it is "changing the outer structure → controlling diffusion / release".

[0017] The high utilization rate of active sites "deep into the pores" in this invention (something difficult to achieve with external coatings) is achieved through in-situ generation occurring on the pore walls / within the pores. Active sites are not simply piled on the outer surface, but distributed throughout the mesoporous / microporous channels. With the same amount of interfacial component, in-situ generation significantly increases the "proportion of effectively accessible sites," not simply by increasing the loading, but by improving site accessibility and utilization. External coatings often cover the pore openings with a membrane, which actually reduces the accessibility of sites within the pores.

[0018] In existing coating technologies, the organic acid first diffuses through the membrane, then swells / degrades, before reaching the interior, naturally introducing a lag. In contrast, the in-situ generation sites of this invention are located on the pore walls, allowing rhizosphere organic acids to directly engage in competitive / surface complexation once they enter the pores. This means the functional layer of this invention exhibits lower mass transfer resistance, resulting in a faster and more dynamic response to changes in rhizosphere organic acids, closely mirroring the spatiotemporal scale of the rhizosphere, rather than the "slow-then-fast" lag curve characteristic of coating technologies.

[0019] In existing coating technologies, during the response process, the coating layer (hydrogel / polymer) in the soil is affected by: salinity, calcium... 2+ / Mg 2+ Alternating wet and dry conditions, along with microbial degradation, lead to swelling-shrinkage fatigue, cracking, and detachment, causing drift in release patterns. The interfacial phase generated in situ in this invention is embedded within the carbon skeleton, maintaining its morphology independently of a high-water-content network structure. It maintains stable interfacial sites and repeatable responses in long-term soil environments, exhibiting better consistency in release / migration curves and significantly improved structural stability under wet-dry cycles and ionic strength fluctuations.

[0020] The outer coating layer often uses pH / swelling as the main effect, and tends to treat overall changes such as "acidification caused by inorganic acids" and "nitration-acidification" as trigger signals, resulting in non-selectivity. In this application, the in-situ generation sites are metal coordination centers or surface complexation sites, and the selectivity mainly comes from the differences in competitive complexation ability caused by the structural differences of organic acids.

[0021] Under the same pH conditions (each organic acid solution was adjusted and stabilized to pH 6.5 ± 0.1 by adding acid or alkali dropwise), different organic acids can still produce different degrees of interfacial reconstruction and binding state changes, thereby achieving true "molecular level" differential regulation, rather than "reacting to acid". This makes the interfacial selective regulation based on the differences in the molecular structure of organic acids clearer (reducing non-selective pH interference).

[0022] The in-situ generation sites in this application are located on the pore walls, and the pores themselves exhibit a local enrichment effect: rhizosphere organic acids and ions more easily form local concentration gradients within the pores. The material can form "local reaction micro-regions" within the pores, making competitive complexation / displacement more effective, resulting in stronger rhizosphere compatibility and higher unit mass regulation efficiency. The outer coating layer, due to its membrane barrier, weakens this micro-region effect.

[0023] The outer coating layer often separates "diffusion control" from "interfacial chemical sites," and the membrane layer shields adsorption / exchange sites. In-situ generation can achieve synergy of adsorption sites, coordination sites, and sustained-release binding sites on the same pore wall. That is, the same material in this application simultaneously possesses the ability to continuously regulate "immobilization / migration / release," rather than being limited to a single diffusion valve.

[0024] Furthermore, the polycarboxylic organic acid includes at least one organic acid secreted by plant roots.

[0025] Furthermore, the organic acid is selected from one or more of citric acid, oxalic acid, and malic acid.

[0026] Furthermore, the complexing or coordinating active sites include interfacial sites capable of forming multi-point coordination or chelation with polycarboxylic organic acids, and the interfacial sites are preferably distributed on the pore walls or inner surfaces of the biochar channels.

[0027] Furthermore, the complexing or coordinating active sites include metal ions, metal oxides, metal hydroxides, or combinations thereof.

[0028] Furthermore, metal ions, metal oxides, and metal hydroxides are fixed to the surface of biochar through coordination or chemical bonding with carboxyl, hydroxyl, or phenolic hydroxyl functional groups.

[0029] Metal ions, metal oxides, and metal hydroxides are fixed on the surface of biochar through coordination or chemical bonding with carboxyl, hydroxyl, or phenolic hydroxyl functional groups, thus achieving a stable connection between metal ions, metal oxides, and metal hydroxides and the biochar surface and solving the problem of adsorption instability caused by physical adsorption.

[0030] The competitive complexing or coordination between the organic acid molecule and the complexing or coordinating active site causes partial dissociation or reconstruction of the coordination structure in the functional interface layer.

[0031] The competitive complexing or coordination between the organic acid molecules and the complexing or coordinating active sites causes partial replacement, dissociation and reconstruction of the coordination structure in the functional interface layer. The process is a dynamic rearrangement process of the interface coordination structure. Within the usage conditions and time scale described in the embodiments of this application, the formation of the framework of the functional interface layer does not require degradation as a necessary condition, and no obvious degradation of the polymer shell or destruction of the film layer has been observed.

[0032] Under the conditions described in the embodiments of this application, no significant degradation was observed in the functional interface layer described in this application. Compared with response systems that rely on an outer coating layer, its advantages are as follows: A. More durable functionality and less performance drift (long-term consistency): Once the outer coating (such as hydrogel / microcapsule shell) degrades, its structure changes, and the release curve drifts over time. In this application, the interface layer is a "coordination rearrangement," the framework remains, and the regulatory logic does not depend on structural destruction. This application can still maintain a relatively stable regulatory pattern and repeatable response capability under long-term soil wet-dry cycles and ionic strength fluctuations.

[0033] B. Enables "multiple responses / cyclic control" (reversibility allows for repeated use): Degradation-type systems are often "one-time triggers"; the release ends when the shell breaks down. However, the system in this application allows for rearrangement when organic acids arrive and partial re-migration when organic acids recede. The material can be regulated in multiple rounds according to the pulsed changes of rhizosphere organic acids (different growth stages), rather than being exhausted in a single release.

[0034] C. Higher interface site utilization (avoiding site loss due to shell damage): Degradation leads to shell fragmentation, pore blockage, and loss of active components; the non-degradation rearrangement in this application preserves interfacial sites and maintains their accessibility. Under the same initial load, the number of long-term effective sites is higher, and the regulation efficiency per unit mass of material is more stable.

[0035] D. Fewer byproducts and ecological disturbance risks (particularly suitable for agricultural soils): Degradable shells can produce polymer fragments, small molecule debris, or swellings, which can affect soil porosity, microorganisms, or introduce additional organic loads. Under the conditions and timescales described in the embodiments of this application, the system of this application does not use degradation as the main pathway, and the byproducts are significantly reduced, thus reducing the non-targeted impacts on the rhizosphere microbial community and soil structure, which is especially advantageous in multi-season continuous application scenarios.

[0036] E. The response is more "refined" and closer to molecular recognition (rather than structural disintegration): Degradation involves macroscopic structural changes, often resulting in "on / off" releases. In contrast, the coordination rearrangement in this application involves molecular-level state regulation, allowing release / migration to vary continuously with organic acid concentration. This enables smoother, more tunable release / migration curves (not burst releases) and better matches the spatiotemporal distribution of rhizosphere organic acids.

[0037] F. Preparation and quality control are easier to standardize (advantage for industrial feasibility): Degradable shells are extremely sensitive to shell thickness and cross-linking degree, resulting in significant batch-to-batch variations. The coordination interface layer in this application is characterized by surface site density / metal center content, making it easier to define process windows and control quality. This also leads to better performance consistency across different batches, facilitating large-scale production.

[0038] The degree of competitive complexation or coordination varies with the type or concentration of polycarboxylated organic acids in the plant rhizosphere environment, and the interfacial chemical equilibrium regulation process can be partially or completely restored after the organic acid concentration decreases or disappears. That is, the functionalized biochar material of this application is reversible, and the transformation of nutrients or functional components on the biochar surface from a stable bound state to a migratable bound state or a release state is a continuous process. The functional interface layer does not rely on the structural destruction of the external coating layer or changes in the overall environmental pH to regulate the nutrients or functional components. The "continuously adjustable" aspect of this application refers to the fact that, under the action of plant-derived polycarboxylated organic acids, the degree of competitive complexation at the interface sites can continuously change with the type and concentration of organic acids, thereby continuously changing the binding energy and mobility of the surface-bound components, manifesting as continuous regulation of fixation / migration / release behavior. The "interfacial chemical state" of the functional interface layer of this application is continuously adjustable, realizing continuous adjustment of the "binding state and release flux of nutrients / functional components." Existing technologies often use pH changes or degradable bond breakage as triggering conditions, achieving "channel opening and closing" through membrane swelling / degradation. Therefore, the release behavior often exhibits thresholding and on / off characteristics. That is, the "continuously adjustable" technology described in this application differs in its regulatory mechanism from the thresholding and on / off release behavior based on membrane swelling or degradation.

[0039] This invention also provides a method for preparing the functionalized biochar material as described above, comprising the following steps: Step S1: Biochar matrix pretreatment; take the biochar matrix and wash it with deionized water and dry it to constant weight; further, take the powdered or granular biochar matrix, wash it with deionized water 2-5 times to remove soluble salts and floating ash; dry it at 60-90℃ to constant weight; to improve dispersibility, ultrasonically disperse the biochar in deionized water for 5-30 minutes.

[0040] Step S2: Perform surface oxidation treatment on the pretreated biochar matrix to introduce reactive oxygen-containing functional groups; the oxidation method is selected from one of hydrogen peroxide oxidation, dilute acid oxidation or ozone / air oxidation;

[0041] Further, hydrogen peroxide oxidation involves adding biochar to a 3-15 wt% hydrogen peroxide solution, stirring at room temperature or 40-70°C for 1-8 hours; filtering, washing until neutral, and drying.

[0042] Further, dilute acid oxidation involves adding biochar to a 0.5-3 mol / L dilute nitric acid or dilute hydrochloric acid solution, stirring at 40-80℃ for 0.5-4 hours, filtering, washing until neutral, and drying.

[0043] Furthermore, ozone / air oxidation involves treating the surface with ozone or air for 0.5-6 hours to increase the number of oxygen-containing functional groups.

[0044] The purpose of introducing reactive oxygen-containing functional groups on the surface of biochar matrix is ​​to obtain sufficient carboxyl / hydroxyl sites on the biochar surface to ensure the stable fixation of the subsequent "chelation site layer".

[0045] Step S3: "Using carboxyl activation-amine-carboxymethylation" to covalently fix the "chelate site layer" on the surface of biochar.

[0046] Step S4: Load the metal coordination center to form a "reconfigurable coordination center"; Step S41: Prepare metal salt solution: Furthermore, the metal ions are selected from Ca. 2+ Mg 2+ Fe 3+ Al 3+ Zn 2+ Mn 2+ One or more of the following; concentration 0.001–0.2 mol / L.

[0047] Step S42: Add the chelated biochar obtained in step S3 to the metal salt solution.

[0048] Furthermore, the solid-liquid ratio was 1:(10–50), and the mixture was stirred at room temperature for 0.5–6 hours.

[0049] Step S43: Adjust the pH of the solution to 5.5-8.0 (to ensure stable metal coordination rather than large-scale precipitation), and then stir for 0.5-2 hours.

[0050] Step S44: Filter, wash, and dry to obtain functionalized biochar material.

[0051] Further, step S44 involves filtration followed by washing with deionized water 2-5 times, each time for 1-10 minutes, until the concentration of metal ions in the washing solution is below 0.5-5 mg / L, and then drying at 60-90℃ for 6-24 hours to obtain functionalized biochar material.

[0052] Furthermore, the specific steps of step S3 are as follows: Step S31: Carboxyl activation. The pretreated biochar from step S2 is dispersed in a buffer solution, and then a carboxyl activator is added to activate the carboxyl groups on the surface of the biochar. After the reaction is complete, the biochar is filtered and washed.

[0053] Further, step S31 involves dispersing the pretreated biochar from step S2 in a buffer solution at a mass-to-volume ratio of 1:(10-50), wherein the pH of the buffer solution is 4.5-6.5; adding a carboxyl activator under stirring conditions, wherein the amount of carboxyl activator added is 0.1-5 times the mass of the biochar, or the concentration of the carboxyl activator in the reaction system is 0.05-0.5 mol / L; continuing to stir the reaction for 0.5-2 hours to activate the carboxyl groups on the surface of the biochar; filtering after the reaction is completed and rinsing once with the buffer solution.

[0054] Step S32: Add the activated biochar to a solution containing diamine or polyamine. After the reaction is complete, filter, wash 3-6 times, and dry to obtain amination biochar.

[0055] Further, in step S32, the activated biochar is added to a solution containing diamine or polyamine and stirred at room temperature for 2–12 h. After the reaction is complete, the mixture is filtered and washed 3–6 times with deionized water. The mass-to-volume ratio of biochar to deionized water is 1:(10–50). Each wash is stirred or shaken for 1–10 min. The washing is considered complete when the conductivity change between two adjacent washes is less than 10%. The biochar is then dried at 60–90 °C for 6–24 h until the mass is constant to obtain amination-modified biochar.

[0056] Furthermore, the washing process is considered complete when the change in conductivity between two consecutive wash solutions is less than 5%.

[0057] Furthermore, the activated biochar was added to ethylenediamine and diethylenetriamine, with the concentrations of ethylenediamine and diethylenetriamine being 0.1-5 mol / L.

[0058] Step S33: Carboxymethylation. The amination biochar obtained in step S32 is dispersed in an alkaline solution, and haloacetate is added to cause carboxymethylation of the amino groups. After the reaction is completed, the biochar is filtered, washed, and dried to obtain biochar with multiple carboxyl chelation sites on the surface.

[0059] Further, step S33 involves dispersing the amination biochar obtained in step S32 in an alkaline solution at a mass-to-volume ratio of 1:(10-50), controlling the pH of the system to be 9-12. The alkaline solution can be prepared from sodium hydroxide or sodium carbonate / sodium bicarbonate, and the concentration of the alkali is preferably 0.1-2.0 mol / L, or the pH can be maintained at 9-12 throughout the reaction by adding the alkaline solution dropwise. Under stirring conditions, a haloacetate is added as a carboxymethylating agent. The haloacetate is selected from sodium chloroacetate, sodium bromoacetate, or a combination thereof, and the amount added is 0.5-10 times the mass of the amination biochar. Subsequently, the reaction is stirred at 40-70°C for 1-8 hours to induce carboxymethylation of the amino groups. After the reaction is complete, filter the solution and wash it 1-3 times with dilute hydrochloric acid or dilute acetic acid, each time at a biochar mass-volume ratio of 1:(10-50), until the pH of the washing solution is 6-7. Then wash it 2-5 times with deionized water, each time for 1-10 minutes, until the pH of the washing solution is 6.5-7.5 and the conductivity tends to be stable. Finally, dry it at 60-90℃ for 6-24 hours until the mass is constant to obtain biochar with multiple carboxyl chelating sites on the surface.

[0060] Furthermore, the concentration of dilute hydrochloric acid or dilute acetic acid is 0.01-0.5 mol / L.

[0061] At this point, a "chelating site layer containing multiple carboxyl groups" is formed on the surface of the biochar, that is, a chelating group layer containing amine groups and multiple carboxyl groups, preferably iminodiacetic acid or nitrogen triacetic acid.

[0062] Furthermore, the preparation method also includes a step of preloading nutrients / functional components, the specific steps of which are as follows: Step S51: Disperse the functionalized biochar material from step S4 in a solution containing phosphate / ammonium nitrogen / potassium salt / trace element salt, and treat it under shaking conditions for 0.5-6 hours; Further, step S51 involves dispersing the functionalized biochar material from step S4 at a mass-to-volume ratio of 1:(10–100) in a solution containing phosphate / ammonium nitrogen / potassium salt / trace element salt, wherein the total ion concentration of the solution is 0.01–1.0 mol / L and the pH is 5.5–8.0.

[0063] Step S52: After the oscillation treatment is completed, the material is filtered, washed, and dried to obtain the preloaded "tunable bound state" functionalized biochar material.

[0064] Further, step S52 involves filtration after the oscillation treatment, followed by washing 2-5 times with deionized water or a low ionic strength buffer solution (pH 5.5-8.0), each wash lasting 1-10 minutes, with a solid-liquid ratio of 1:(10-50). The washing process is considered complete when the conductivity change between two consecutive washes is less than 10% and tends to stabilize. The material is then dried at 60-90℃ for 6-24 hours until the mass is constant, yielding the pre-loaded "tunable bound state" functionalized biochar material.

[0065] The function and principle of pre-loaded nutrients / functional components are as follows: by introducing nutrients or functional components into functionalized biochar materials, they form coordination bonds, surface complexes, or electrostatic adsorption with polycarboxyl chelate sites and metal coordination centers, thereby fixing them in a controllable bound state in the functional interface layer; under the action of polycarboxyl organic acids secreted by plant roots, organic acid molecules, as competing ligands, compete with the interface coordination centers for complexation or coordination reconstruction, changing the binding energy and existence form of nutrients or functional components, transforming them from a stable bound state to a migratable or releaseable state, so that nutrient release is regulated by the interface coordination state.

[0066] Furthermore, the mechanism of action of the "preloaded nutrients / functional components" is as follows: By introducing phosphate, ammonium nitrogen, potassium ions or trace element ions into functionalized biochar materials, they form coordination bonds, surface complexes or electrostatic adsorption states with the polycarboxyl chelate sites and metal coordination centers, thereby pre-fixing them at the material interface in the form of "tunable binding states".

[0067] The preloading process is not a simple physical adsorption, but rather a process in which nutrients or functional components participate in the coordination chemical equilibrium system of the functional interface layer, forming a bonded state coupled with the interface coordination structure.

[0068] Under the action of polycarboxylic organic acids secreted by plant roots, organic acid molecules, as competitive ligands, compete with the interfacial metal coordination centers for complexation or coordination reconstruction, thereby changing the binding energy and existing form of the nutrients or functional components, causing them to gradually change from a stable bound state to a migratory or release state.

[0069] Therefore, the pre-loaded nutrients / functional components are a necessary prerequisite for realizing the function of "interface coordination regulation → nutrient release regulation", and their role is as follows: (1) Construct a nutrient pool that can participate in interface coordination balance; (2) The nutrient release process is regulated by the interfacial coordination state, rather than simply by diffusion or dissolution; (3) Achieve coupling between nutrient release and dynamic changes in rhizosphere organic acids.

[0070] Furthermore, the washing process is considered complete when the change in conductivity between two consecutive wash solutions is less than 5%.

[0071] The present invention also provides an application of the functionalized biochar material as described above, wherein the functionalized biochar material is applied to agricultural soil to improve the compatibility of nutrients or functional components with the plant rhizosphere environment through interfacial chemical balance regulation.

[0072] Compared with existing technologies, the present invention has the following significant advantages: 1. Compared with existing technologies that rely on membrane degradation or swelling to control diffusion using an outer coating layer (hydrogel / microcapsule shell), this application constructs a functional interface layer in the pore wall or surface region of biochar through in-situ generation. This allows the interfacial active sites to be embedded and distributed within the pores, thereby significantly increasing the proportion of effective contactable sites with the same amount of interfacial components. At the same time, it avoids the mass transfer resistance and response hysteresis caused by the outer coating layer, making the interfacial chemical regulation of changes in plant rhizosphere organic acids faster and closer to the rhizosphere spatiotemporal scale. In addition, the in-situ generated interface layer forms a stable bond with the biochar framework, resulting in a more stable structure and less functional drift under soil wet-dry cycles, ionic strength fluctuations, and microbial activity. Furthermore, it can achieve differentiated regulation through competitive complexation / surface complexation caused by differences in organic acid molecular structure without relying on overall pH changes, reducing the non-selectivity problem of existing technologies.

[0073] 2. Unlike existing technologies that rely on coating degradation or membrane destruction to achieve release, the functional interface layer of this invention induces partial replacement and reconstruction of the coordination structure through competitive complexation at the organic acid interface, thereby regulating the chemical state of the interface without requiring interface layer degradation as a necessary condition. Therefore, under the expected use conditions, it can reduce structural instability and performance drift caused by shell degradation, exhibiting more durable regulation capability and better repeatability, while reducing the non-targeted impact of degradation byproducts on the soil environment, and facilitating a smoother, continuously adjustable fixation-migration-release behavior, thus improving the matching between material function and the spatiotemporal changes of rhizosphere organic acids.

[0074] 3. The "interfacial chemical state" of the functional interface layer in this application is continuously adjustable, achieving continuous adjustment of the "binding state and release flux of nutrients / functional components." Compared to existing technologies that rely on membrane degradation or swelling to control diffusion using an outer coating layer (hydrogel / microcapsule shell), this avoids burst release, resulting in smoother and more controllable release. It avoids the burst release phenomenon that easily occurs after triggering in existing on / off mechanisms. Continuous adjustment corresponds to the gradual shift of interfacial coordination equilibrium, making the release behavior more gradual and stable, the release curve smoother, reducing nutrient loss peaks, and improving utilization. This application is better suited to the spatiotemporal dynamics of the rhizosphere. Root secretion of organic acids is "pulsating / gradual," not just on or off. It is continuously adjustable and can respond stepwise to changes in concentration, making the material behavior closer to the actual needs of plants. This application has stronger selectivity, reducing non-selective triggering, while pH triggering responds to various acidifications. This application uses the "degree of competitive complexation of organic acids" as a control quantity, which is closer to "molecular recognition," reducing false triggering caused by changes in non-target environments. The interface layer of this application does not rely on degradation, resulting in better durability and repeatability; the continuous adjustability of this application allows for multiple rounds of rearrangement / regression, with minimal performance drift and repeatability over multiple seasons.

[0075] 4. Because the degree of interfacial coordination reconstruction can continuously change with the type and concentration of organic acids, the material of this invention exhibits smooth and gradual regulatory behavior during fixation, migration, and release, rather than thresholding or abrupt release. This helps reduce the risk of instantaneous loss of nutrients or functional components and improves utilization efficiency. This invention uses the competitive complexation between plant-derived polycarboxylic organic acids and interfacial coordination sites as the regulatory basis, rather than solely relying on overall environmental parameters such as pH and ionic strength. Therefore, it can distinguish the differences in the effects of different organic acids under the same or similar pH conditions, reducing non-selective responses caused by inorganic acidification, microbial metabolism, or changes in moisture.

[0076] 5. The regulation process of this invention does not involve the degradation of the polymer shell or outer coating material, reducing the risk of potential degradation debris or byproducts entering the environment, making it particularly suitable for applications with high ecological safety requirements, such as agricultural soils. This invention achieves functional regulation through the density of interfacial coordination sites and the content of metal centers. Compared to existing technologies that rely on the thickness of the outer coating or the degree of cross-linking, it is easier to control the process and conduct quality inspection, resulting in products with high batch consistency and suitability for industrial production. Attached Figure Description

[0077] Figure 1 This is the response of the functionalized biochar phosphorus release to the citric acid concentration in Example 1; Figure 2 The difference in the release of different organic acids and phosphorus under the same pH conditions in Example 1; Figure 3Example 2 compares soil phosphorus levels during the maize growing season using functional biochar, ordinary biochar, and coated fertilizer. Detailed Implementation

[0078] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the technical solutions of the present invention will be further described below in conjunction with implementation examples.

[0079] Example 1 This embodiment provides a method for preparing functionalized biochar materials, including the following steps: Step S1: Take corn stalks as biochar raw material, chop the corn stalks to a length of 1-3cm, and weigh them according to the amount of material to be fed in a single batch; wash them 3 times with deionized water, with the mass-volume ratio of corn stalks to deionized water being 1:10, and stir or soak for 10 minutes each time; after washing, dry them at 80℃ for 15 hours to obtain pretreated biochar for later use.

[0080] Step S2: Add the pretreated biochar from step S1 to a 5 wt% hydrogen peroxide solution and disperse it at a solid-liquid ratio of 1:30. Stir the mixture at 500 rpm for 4 h at 60 °C. After the reaction, filter the mixture and wash it with deionized water 4 times for 10 min each time until the pH of the washing solution is 7. Then dry it at 90 °C for 15 h to obtain biochar with oxygen-containing functional groups on its surface.

[0081] Step S3: "Using carboxyl activation-amine-carboxymethylation" to covalently fix a "chelate site layer" on the surface of biochar; Step S31: The biochar with oxygen-containing functional groups on its surface, after treatment in step S2, is dispersed in a 2-(N-morpholine)ethanesulfonic acid (MES) buffer solution at a mass-to-volume ratio of 1:30, wherein the buffer solution has a pH of 6; 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) are added under stirring, wherein the amount of EDC added is 2.5 times the mass of the biochar, and the amount of NHS added is 1.2 times the molar amount of the carbodiimide; the reaction is carried out at 25°C and 50 rpm for 1.5 h to activate the carboxyl groups on the surface of the biochar; after the reaction is completed, the mixture is filtered and quickly rinsed once with a MES buffer solution at a mass-to-volume ratio of 1:20 (pH 5); Step S32: Add the activated biochar from step S31 to a 5 mol / L ethylenediamine solution and disperse it at a biochar to ethylenediamine solution mass-to-volume ratio of 1:30. Stir at 500 rpm for 10 h at 30 °C. After the reaction, filter and wash five times with deionized water at a biochar to deionized water mass-to-volume ratio of 1:30, with each wash lasting 10 min under stirring or shaking. The washing is considered complete when the conductivity change between two consecutive washes is less than 5%. Then dry at 90 °C for 20 h to obtain amination-modified biochar. Step S33: The amination biochar obtained in step S32 is dispersed in a 1.0 mol / L sodium hydroxide solution at a mass-to-volume ratio of 1:30, and the pH of the system is controlled at 10. Sodium bromoacetate is added under stirring, and the amount of sodium bromoacetate added is 5 times the mass of the amination biochar. The reaction is then stirred at 60℃ for 5 h to induce carboxymethylation of the amino groups. After the reaction is complete, the mixture is filtered and washed twice with 0.5 mol / L dilute hydrochloric acid (each time at a solid-liquid ratio of 1:20) until the pH of the washing solution is 7. Then, it is washed three times with deionized water (each time for 10 min, solid-liquid ratio of 1:20) until the pH of the washing solution is 7 and the change in conductivity between two adjacent washing solutions is less than 5%. Finally, the mixture is dried at 90℃ for 20 h to obtain biochar with carboxymethyl chelation sites.

[0082] Step S4: Load the metal coordination center to form a "reconfigurable coordination center"; Step S41: Prepare 0.05 mol / L Fe 3+ Salt solution: Step S42: Add the chelated biochar obtained in step S3 to the metal salt solution. Step S43: Adjust the pH of the solution to 6.5, and then stir for 2 hours; Step S44: After the reaction is complete, filter the solution and wash it three times with deionized water. Each wash is performed for 10 minutes under stirring or shaking conditions. The mass-volume ratio of biochar to deionized water is 1:30. The washing is considered complete when the metal ion concentration in the two adjacent washes changes by less than 5%. Dry the solution at 90°C for 20 hours to obtain the functionalized biochar material.

[0083] Step S5: Preload phosphorus source; The functionalized biochar material obtained in step S4 was dispersed in KH2PO4 solution and treated under shaking conditions for 2 hours; then filtered, washed, and dried to obtain the phosphorus-loaded functionalized biochar material.

[0084] 0.50 g of the pre-loaded phosphorus functionalized biochar material prepared in step S5 of Example 1 was weighed and added to 50 mL of citric acid solutions of different concentrations (citric acid concentrations were 0, 0.1, 0.25, 0.5, 1.0, 2.0, and 5.0 mmol / L; the pH of the solution was adjusted to 6.5 ± 0.1). The reaction was carried out at 25℃ and 200 rpm for 24 h with shaking. After the reaction was completed, the phosphorus content in the solution was measured. Figure 1 As shown, the results indicate that the cumulative release of phosphorus in the material gradually increases with the increase of citric acid concentration, and the release-concentration relationship shows a continuous trend.

[0085] 0.50 g of the pre-loaded phosphorus functionalized biochar material prepared in step S5 of Example 1 was weighed and added to 50 mL of solutions containing different organic acids, namely citric acid, oxalic acid, and malic acid, each with a concentration of 1.0 mmol·L⁻¹. -1 The solution pH was adjusted to 6.5 ± 0.1, and the reaction was carried out with shaking at 25℃ for 24 h. After the reaction, the amount of phosphorus released from the solution was measured to compare the effects of different organic acids on the phosphorus release behavior of functionalized biochar materials under the same pH conditions. Figure 2 As shown, under the same pH conditions, the degree of nutrient release induced by different organic acids varies significantly; the release is highest under citric acid conditions, followed by oxalic acid, and lowest under malic acid conditions; the release shows a continuous upward trend with increasing organic acid concentration. These results indicate that the response mechanism of the material of this invention does not solely depend on pH changes, but is based on the difference in competitive complexation ability between organic acid molecules and interfacial coordination sites, achieving differentiated and continuously adjustable regulation of organic acids from different plant sources.

[0086] Example 2 This embodiment provides an application of the functionalized biochar material prepared in Example 1. The functionalized biochar material is applied to agricultural soil to achieve a stable supply of nutrients such as phosphorus during crop growth and reduce the risk of nutrient loss.

[0087] 1. Soil and Materials (1) Soil: Take 20cm of topsoil from a farmland, remove plant residues and stones, air dry naturally, pass through a 2mm sieve and mix well for later use.

[0088] (2) Functionalized biochar material: The functionalized biochar material prepared in Example 1 was ground and sieved to make the particle size 0.25-1.00 mm.

[0089] 2. Application and Cultivation (1) Potting and application: Weigh 15.0 kg of air-dried soil per pot and place it in a plastic pot. Add functional biochar material at 1.0% (w / w) of soil mass, i.e., 150 g per pot, and mix it thoroughly with the soil.

[0090] (2) Standardization of basic fertilizer: In order to eliminate the influence of differences in nitrogen and potassium, urea and potassium sulfate were added as basic fertilizers in all treatments at the same application rate; phosphorus input was controlled according to the principle of "standardization of phosphorus equivalent" (i.e., the amount of phosphorus input in each treatment was kept consistent to ensure that the comparison only reflects the differences in the controlled release mechanism of the materials).

[0091] (3) Moisture content control: Add deionized water to adjust the soil moisture content to 65%±5% of field capacity, and maintain it by weighing and replenishing water during the experiment.

[0092] (4) Crop planting: Using corn as the indicator crop, sow 3 seeds per pot, and thin out 1 seedling after emergence; cultivate at 25±2℃ under natural light conditions.

[0093] 3. Sampling and Measurement (1) Sampling period: Soil samples were collected during the jointing, tasseling and grain filling stages of maize.

[0094] (2) Available phosphorus in soil: Olsen-P in soil (mg·kg) was determined. -1 ).

[0095] (3) Phosphorus loss from leachate: After each watering, leachate was collected, and the cumulative amount of phosphorus loss in leachate during the three stages of “post-sowing – jointing, jointing – tasseling, and tasseling – grouting” (mg / pot) was calculated.

[0096] (4) Material recovery and stability observation: After the cultivation was completed at the end of the grouting period, the potting soil was air-dried and the material particles were sieved to recover the material. The appearance and integrity of the recovered material were recorded, the recovered mass was weighed, and the mass loss rate was calculated.

[0097] The determination of available phosphorus in the soil and phosphorus loss through leachate is as follows: 1) Sample preparation (1) The soil sample was air-dried after collection.

[0098] (2) After gently grinding in a mortar, pass through a 2mm sieve and mix well for later use; if it is necessary to improve repeatability, a portion of the sample can be passed through a 20-mesh sieve for chemical analysis.

[0099] (3) Record the soil moisture content before measurement (the 105℃ drying method can be used), and convert the result to air-dried soil.

[0100] 2) Reagent preparation (1) 0.5 mol·L -1NaHCO3 extractant (pH 8.5): Weigh out NaHCO3 to prepare a 0.5 mol·L⁻¹ solution. -1 The solution was prepared by adjusting the pH to 8.5 using NaOH solution.

[0101] (2) Activated carbon (optional): used for decolorization (suitable for samples with high organic matter content or darker extract color).

[0102] (3) Phosphorus standard solution: Prepare a series of standard solutions (e.g., 0, 0.2, 0.5, 1.0, 2.0, 5.0 mg·L⁻¹) using KH₂PO₄. -1 (in P).

[0103] (4) Colorimetric reagent: Molybdenum-antimony colorimetric method: Prepare the acidic ammonium molybdate-potassium antimony tartrate mixed reagent and ascorbic acid reducing agent according to the conventional method (or use a ready-made commercial kit and indicate "prepare according to the instructions").

[0104] 3) Extraction (1) Weigh 2.50g (accurate to 0.01g) of air-dried and sieved soil sample into a 100mL stoppered conical flask.

[0105] (2) Add 50.0 mL of 0.5 mol·L⁻¹ -1 NaHCO3 (pH 8.5) extractant (liquid-solid ratio 20:1).

[0106] (3) Place it on a constant temperature oscillator and oscillate at 25°C and 200 rpm for 30 min.

[0107] (4) Filter immediately after shaking: use quantitative filter paper for filtration; if the extract is turbid, let it stand first and then filter the supernatant. If necessary, use a 0.45μm microporous membrane for further clarification.

[0108] (5) (Optional decolorization step) If the extract is obviously colored: add 1.0g of activated carbon to the extraction system, shake for 2 minutes and then filter.

[0109] 4) Determination (colorimetric method) (1) Take V mL of the clear filtrate (usually 5.00 mL or 10.00 mL) into a colorimetric tube.

[0110] (2) Add molybdenum antimony anti-coloring reagent and ascorbic acid reducing agent (or add composite coloring agent), mix well and develop color at room temperature in the dark for 10–20 min.

[0111] (3) Measure the absorbance at a wavelength of 880 nm using a spectrophotometer, and convert the concentration C (mg·L) of P in the extract using a standard curve. -1 ).

[0112] 5) Calculation of Results Soil Olsen-P (mg·kg) -1 Calculate using the following formula: Olsen-P=C×V / m in: C: P concentration in the extract (mg·L) -1 ); V: Volume of extraction liquid (L, 0.050L in this example); m: Soil sample mass (kg, 0.00250 kg in this example).

[0113] Comparative Example 1 This comparative example refers to Example 2, except that the material applied to the soil is untreated biochar.

[0114] The untreated biochar was a basic biochar obtained from the same source and under the same pyrolysis conditions as the biochar used in Example 1. It only underwent step S1 (biochar matrix pretreatment) in Example 1, i.e., crushing and sieving (particle size 0.25–1.00 mm) and washing with deionized water until the conductivity of the washing solution tended to stabilize, and then drying for later use. It did not further perform the steps S2 (surface oxidation to introduce oxygen-containing functional groups), S3 (carboxyl activation-amineization-carboxymethylation to construct chelate site layer), S4 (metal coordination center loading), and S4 (preloading phosphorus source) in Example 1.

[0115] In this comparative example, to ensure consistency with the phosphorus input in Example 1, an exogenous phosphorus source was supplemented according to the principle of "phosphorus equivalent consistency". Specifically, the total phosphorus content (in mg·g) of the functionalized biochar material prepared in step S5 of Example 1 was determined in advance. -1 The total phosphorus input per unit of soil was calculated based on the actual application rate. In Comparative Example 1, soluble phosphorus sources were supplemented in equal amounts while applying untreated biochar, preferably potassium dihydrogen phosphate or monoammonium phosphate, to ensure that the total phosphorus input per unit of soil remained consistent with that in Example 1. The application rate, cultivation conditions, and sampling and measurement methods were the same as in Example 2.

[0116] Comparative Example 2 This comparative example refers to Example 2, the difference being that the material applied to the soil is a polymer-coated slow-release phosphate fertilizer granule with a continuous outer coating layer. The slow-release material is a coated slow-release phosphate fertilizer using existing conventional technology, and its granule structure includes: a phosphate fertilizer core material, which is monoammonium phosphate or diammonium phosphate; and a continuous polymer coating layer covering the outer surface of the core material, which is an outer coating layer formed of polyurethane material.

[0117] The coated slow-release phosphate fertilizer releases nutrients through the diffusion / osmotic resistance of the coating layer to water and dissolved phosphorus. Its release behavior is mainly controlled by the thickness and integrity of the coating layer, belonging to a slow-release mechanism dependent on diffusion control of the outer coating layer. The phosphorus application rate in Comparative Example 2 was calculated using the same phosphorus equivalent as in Example 2; all other application rates, cultivation conditions, and sampling and measurement methods were the same as in Example 2.

[0118] Figure 3 The functionalized biochar material described in Example 2 demonstrates its effect on maintaining the dynamics of available phosphorus in the soil and regulating phosphorus leaching loss during the crop growth period, and is compared with untreated biochar and coated slow-release material.

[0119] Dynamic changes of available phosphorus (Olsen-P) in soil during the growing season, as follows Figure 3 The results from A show that, during the three key growth stages of maize—jointing, tasseling, and grain-filling—there were significant differences in the changing trends of soil Olsen-P content under different material treatments.

[0120] Example 2: The functionalized biochar treatment maintained a high Olsen-P level throughout the entire growth period, with only a slow decreasing trend as the growth progressed. In Comparative Example 1, the untreated biochar treatment resulted in a generally low Olsen-P content in the soil, with a significant decrease as the growth period progressed. In Comparative Example 2, the coated slow-release material showed a high Olsen-P level in the early growth stage, but it decreased significantly over time, approaching the level of the untreated biochar during the grain-filling stage. These results indicate that the material in Example 2 can consistently maintain a plant-available phosphorus level in the soil throughout the crop's growth period, while untreated biochar struggles to provide effective phosphorus slow-release support, and the coated slow-release material suffers from release degradation over time.

[0121] Figure 3 In this context, B represents the cumulative amount of phosphorus loss in the leachate over the period. Figure 3 B in the figure shows the cumulative phosphorus loss in the leachate under different treatment conditions during the three stages: post-sowing to jointing stage, jointing to tasseling stage, and tasseling to grouting stage.

[0122] In Example 2, the phosphorus loss from the functionalized biochar treatment was low at all stages, and the changes between stages were gradual; in Comparative Example 1, the phosphorus loss from untreated biochar was slightly lower than that in Example 2, but its available phosphorus level in the soil was significantly lower (e.g., ...). Figure 3 (As shown in A in the figure); Comparative Example 2 showed a significant peak in phosphorus loss in the coating slow-release material from sowing to jointing stage. Although the loss decreased thereafter, the overall phosphorus loss was significantly higher than that of the other two treatments. This result indicates that the coating slow-release material is prone to causing a high risk of phosphorus loss in the early stages of crop growth, while the material in Example 2 can maintain the available phosphorus supply in the soil while suppressing leaching loss.

[0123] comprehensive Figure 3 As can be seen from A and B in the figures: although untreated biochar has a low phosphorus loss, it is difficult to maintain the available phosphorus level in the soil; the outer membrane slow-release material has a strong release in the early stage, resulting in significant phosphorus loss in the early growth stage and a decline in phosphorus supply capacity in the later stage; the functionalized biochar material in Example 2, while maintaining a high Olsen-P level, significantly reduced phosphorus leaching loss in the early growth stage and throughout the entire growth period, showing the regulatory characteristics of "balancing phosphorus supply stability and environmental safety".

[0124] The results show that, under the conditions of the aforementioned embodiments and comparative experiments, the material of the present invention can exhibit nutrient regulation characteristics that match the rhizosphere environment, making it suitable for application in agricultural soils.

[0125] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A functionalized biochar material, characterized in that, The functionalized biochar material includes a biochar matrix and a functional interface layer constructed on the surface of the biochar matrix; the functional interface layer is constructed in situ on the pore walls or surface region of the biochar; the functional interface layer contains complexing or coordination active sites fixed on the functional groups on the surface of the biochar; the complexing or coordination active sites are composed of polycarboxylic acid chelating groups covalently fixed on the surface of the biochar and metal ions, metal oxides or metal hydroxides, and can undergo competitive complexation or coordination reconstruction under the action of polycarboxylic acid molecules secreted by plant roots.

2. The functionalized biochar material according to claim 1, characterized in that, The polycarboxylic organic acids include at least one organic acid secreted by plant roots.

3. The functionalized biochar material according to claim 2, characterized in that, The organic acid is selected from one or more of citric acid, oxalic acid, and malic acid.

4. The functionalized biochar material according to claim 1, characterized in that, The complexing or coordinating active sites include interfacial sites capable of forming multi-point coordination or chelation with polycarboxylic organic acids.

5. The functionalized biochar material according to claim 4, characterized in that, The complexing or coordinating active sites include metal ions, metal oxides, metal hydroxides, or combinations thereof.

6. The functionalized biochar material according to claim 5, characterized in that, Metal ions, metal oxides, and metal hydroxides are fixed on the surface of biochar through coordination or chemical bonding with carboxyl, hydroxyl, or phenolic hydroxyl functional groups.

7. The method for preparing the functionalized biochar material according to any one of claims 1-6, characterized in that, Includes the following steps: Step S1: Biochar matrix pretreatment; Take the biochar matrix and wash it with deionized water and dry it to constant weight; Step S2: Perform surface oxidation treatment on the pretreated biochar matrix to introduce reactive oxygen-containing functional groups; the oxidation method is selected from one of hydrogen peroxide oxidation, dilute acid oxidation or ozone / air oxidation; Step S3: "Using carboxyl activation-amine-carboxymethylation" to covalently fix the "chelate site layer" on the surface of biochar; Step S4: Load the metal coordination center to form a "reconfigurable coordination center"; Step S41: Prepare metal salt solution: Step S42: Add the chelated biochar obtained in step S3 to the metal salt solution; Step S43: Adjust the pH of the solution to 5.5-8.0, and then stir for 0.5-2 hours; Step S44: Filter, wash, and dry to obtain functionalized biochar material.

8. The method according to claim 7, characterized in that, The specific steps of step S3 are as follows: Step S31: Disperse the pretreated biochar from step S2 in a buffer solution, then add a carboxyl activator to activate the carboxyl groups on the surface of the biochar. After the reaction is complete, filter and wash. Step S32: Add the activated biochar to a solution containing diamine or polyamine. After the reaction is complete, filter, wash 3-6 times, and dry to obtain amination biochar. Step S33: Disperse the amination biochar obtained in step S32 in an alkaline solution, add haloacetate to cause carboxymethylation of the amino groups; after the reaction is completed, filter, wash and dry to obtain biochar with multiple carboxyl chelation sites on the surface.

9. The method according to claim 7, characterized in that, It also includes a step of preloading nutrients / functional components, the specific steps of which are as follows: Step S51: Disperse the functionalized biochar material from step S4 in a solution containing phosphate / ammonium nitrogen / potassium salt / trace element salt, and treat it under shaking conditions for 0.5-6 hours; Step S52: After the oscillation treatment is completed, filter, wash and dry to obtain the preloaded "tunable bound state" functionalized biochar material.

10. The application of the functionalized biochar material according to any one of claims 1-6, characterized in that, The functionalized biochar material is applied to agricultural soil.

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