Functionalized biochar for heavy metal blocking and methods of making and using the same

Abstract

The application provides a functionalized biochar for heavy metal blocking, and a preparation method and application thereof. The biochar is a porous carbon material with a hierarchical pore structure mainly composed of mesopores, rich surface functional groups, high mineral nutrient content and excellent heavy metal adsorption performance. The biochar is prepared from mixed raw materials of rice straw and livestock manure through four main steps of co-grinding pretreatment, gradient pyrolysis carbonization, directional pore expansion modification and post-treatment. On this basis, by means of ultrasonic-assisted coupling loading process, a high-efficiency microbial consortium obtained through directional screening is colonized in the mesoporous channels of the biochar, forming a biochar-microorganism composite heavy metal blocking material, which is applied to a rice field to realize efficient adsorption of cadmium, lead, arsenic and other heavy metal ions, and realize heavy metal blocking, soil fertility improvement and safe planting of crops.

Description

Technical Field

[0001] This invention relates to the field of biochar technology, specifically to a functionalized biochar for heavy metal blocking, its preparation method, and its application. Background Technology

[0002] The needs for green management of paddy fields are twofold: first, to reduce heavy metals in the soil, and second, to address the high-value utilization of straw. Excessive levels of heavy metals such as cadmium, lead, and arsenic in paddy field soil directly disrupt the micro-ecological balance of the soil. On the one hand, they inhibit the activity of soil nitrification and ammonification bacteria, block the normal nitrogen cycle, and significantly reduce the efficiency of soil organic matter decomposition and nutrient supply, resulting in decreased root vitality, reduced tillering, and increased empty grain rate in rice. They also silently accumulate heavy metals in rice grains, forming "cadmium rice" and "arsenic rice," which appear normal but pose hidden health risks. On the other hand, these heavy metals accumulate year by year with paddy field cultivation and spread to surrounding water bodies through surface runoff and infiltration, continuously expanding the pollution range. In addition, the high-value utilization of rice straw is a key issue that urgently needs to be addressed in the current green transformation of agriculture. On the one hand, traditional burning and random dumping methods not only cause air pollution and fire hazards but also result in a serious waste of biomass resources. On the other hand, traditional low-value-added methods such as returning straw to the field and simple baling have drawbacks such as slow fertilizer effect, insufficient adaptability to agricultural machinery, and low farmer income.

[0003] To meet the needs of green management of paddy fields, the core of the current conventional application scenario is to prepare biochar from rice straw and then adsorb heavy metals through biochar. However, the existing biochar has core technical defects when used as a heavy metal barrier material: (1) Existing biochar only relies on its own passive adsorption function and lacks the power source to actively capture deep-migrating heavy metals, making it difficult to achieve continuous and efficient blocking under shallow application conditions; (2) Single rice straw biochar is nutrient-poor and lacks mineral elements such as nitrogen, phosphorus, and potassium, making it difficult to improve soil fertility while blocking heavy metals; (3) When biochar and microorganisms work together to adsorb heavy metals, the pore size of conventional biochar does not match the size of microbial cells, resulting in a lack of a suitable microenvironment for microorganisms, leading to low microbial load and poor colonization stability; (4) The mixing method of biochar and microorganisms is crude and the adsorption efficiency is low.

[0004] Therefore, there is an urgent need to develop a type of biochar that can match the size of microbial cells, providing a suitable microenvironment for microorganisms. This biochar can not only continuously and efficiently block and actively capture deep heavy metals, but also improve soil fertility while blocking heavy metals. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a functionalized biochar for heavy metal blocking, its preparation method, and its application. The biochar is a porous carbon material with a hierarchical pore structure dominated by mesopores, abundant surface functional groups, high mineral nutrient content, and excellent heavy metal adsorption performance. It is prepared from a mixture of rice straw and livestock manure through four main steps: co-grinding pretreatment, gradient pyrolysis carbonization, directional pore-expanding modification, and post-treatment. Based on this, a highly efficient microbial consortium obtained through directional screening is colonized within the mesopores of the biochar using an ultrasonic-assisted coupling loading process, forming a biochar-microbial composite heavy metal blocking material. This material is applied to paddy fields to achieve efficient adsorption of heavy metal ions such as cadmium (Cd), lead (Pb), and arsenic (As), thereby achieving heavy metal blocking, soil fertility improvement, and safe crop cultivation.

[0006] On the one hand, the present invention provides a functionalized biochar for heavy metal blocking. The functionalized biochar is biochar treated with a pore-expanding agent, which has a multi-level pore structure dominated by mesopores, and its surface is simultaneously loaded with acidic oxygen-containing functional groups and basic nitrogen-containing functional groups. The pore size distribution of the mesopores matches the size of the microbial cell.

[0007] Currently, conventional biochar in existing technologies has a mismatch between pore size and microbial cell size, lacking a suitable microenvironment for microbial habitation, resulting in low microbial load and poor colonization stability. The functionalized biochar of this invention is biochar treated with a pore-expanding agent, possessing a hierarchical pore structure dominated by mesopores. On the one hand, the pores of this biochar are adept at absorbing microorganisms and are suitable for microbial habitation. The pore structure of the biochar is a hierarchical pore distribution dominated by mesopores (2-50 nm), with micropores (<2 nm), mesopores (2-50 nm), and macropores (>50 nm) coexisting and working synergistically within the biochar particles. Among them, mesopores account for 65%-85%, and the specific surface area is 1000-2200 m². 2 / g, total pore volume 0.8-2.0cm³ 3With an average pore size of 3-34 nm, the hierarchical pore structure features micropores contributing a significant specific surface area, serving as the primary sites for the physical adsorption and ion exchange of heavy metal ions. Mesopores act as material transport channels and initial anchoring points for the adhesion of extracellular polymers in microorganisms. Macropores (>50 nm) serve as the main habitat for microbial cells, forming a synergistic network of macroporous habitat, mesoporous transport, and microporous adsorption. This structure is achieved through a synergistic triple mechanism: endogenous activation of mineral elements in livestock and poultry manure during pyrolysis, chemical etching by potassium carbonate and template pore-forming with zinc citrate during directional pore-expansion, and physical pore-forming with CO2. This transforms biochar from a high specific surface area inaccessible to microorganisms into a high specific surface area active carrier that allows microorganisms to enter, inhabit, and metabolize. Furthermore, the continuous mesoporous-macroporous pore network formed by this pore structure matches the size of functional microbial cells (0.5-5 μm). Microbial cells are not rigid spheres with a rigid outer shell; their cellular structure exhibits certain deformation and adaptation characteristics. If the pore size of the carrier is significantly larger than the overall equivalent particle size of the microbial cells, the intact microbial cells are easily completely embedded in the unconstrained pore space during adsorption, becoming encased within the pores. Constrained by both mass transfer barriers and steric hindrance, the material exchange and signal interaction pathways between the microorganisms and the external environment are significantly limited, making it difficult to fully release their inherent physiological metabolism and functional activities. If the pore size is too large… Small pore sizes can trigger a micropore repulsion effect, preventing microorganisms from entering the pores for effective anchoring. This also significantly increases mass transfer resistance and can easily lead to pore blockage and cell compression and inactivation. However, when the carrier pore size is controlled within the adaptation range described in this invention, combined with the functional groups on the pore surface, it can achieve local site-specific anchoring of microbial cells. It is not necessary to include the entire bacterial cell inside the pore; fixation is achieved only through local binding. This allows most of the microbial cell structure to be fully exposed to the external reaction system, ensuring fixation stability while maximizing its contact area with the external environment. This allows the core functions of microorganisms, such as metabolism and catalysis, to be fully and efficiently performed. Meanwhile, the interconnected mesoporous-macroporous structure provides an efficient channel for nutrient transport and metabolic waste excretion. On the other hand, the biochar surface is rich in carboxyl (-COOH), carbonyl, and lactone groups, containing multiple oxygen-containing acidic functional groups, while also supporting amino (-NH2) basic functional groups and an aromatic conjugated C=C skeleton. The total acidic functional group content on the material surface is 2.6–4.9 mmol / g, and the total basic amino functional group content is 0.25–0.8 mmol / g. The abundant acidic sites are beneficial for Cd... 2+ Pb 2+ With strong chelating and ion exchange capabilities, the basic amino group can effectively bind AsO3 in the paddy field system. 3- AsO4 3- Anions can block the migration of heavy metals such as cadmium, lead, and arsenic from paddy soil to rice roots through multiple pathways.

[0008] In some embodiments, the pore-expanding agent includes potassium carbonate and zinc citrate.

[0009] In this invention, potassium carbonate reacts with a carbon matrix at a high temperature greater than 700°C, and the resulting metallic potassium is gaseous at high temperature. It is embedded between carbon layers and chemically etched, forming numerous nanoscale micropores with pore sizes <2 nm. Some of these micropores further expand into mesopores (2-50 nm) during subsequent high-temperature treatment. Zinc citrate ions carbonize during pyrolysis, forming a mesoporous template in situ; and Zn... 2+ At high temperatures, it is reduced to metallic Zn and vaporized, leaving mesoporous pores. The oxygen-containing functional groups of citrate can contribute additional surface carboxyl and hydroxyl groups, both of which can improve the performance of biochar. Potassium carbonate and zinc citrate produce the best synergistic effect in a mass ratio of 2:1 to 5:1. The micropores formed by potassium carbonate etching are further connected and expanded with the assistance of zinc citrate template.

[0010] In some embodiments, the mass ratio of potassium carbonate to zinc citrate ranges from 2:1 to 5:1.

[0011] This invention verifies through experiments that when the mass ratio of potassium carbonate to zinc citrate is in the range of 2:1 to 5:1, the resulting biochar material has a higher specific surface area, total pore volume, and total number of viable bacteria.

[0012] This invention verifies through experiments that when potassium carbonate and zinc citrate are used as pore expanders, the reduction rate of heavy metal content in leaves and rice is the highest. Compared with the group without added pore expanders, the heavy metal content is significantly reduced. The effect on reducing heavy metal content is significantly better than zinc citrate or potassium carbonate alone as pore expanders, as well as the combination of any one of the substances in the combination as pore expanders. Furthermore, adding other substances as pore expanders to zinc citrate and potassium carbonate does not significantly change the heavy metal content, indicating that using zinc citrate and potassium carbonate as pore expanders is the optimal choice.

[0013] In some methods, the functionalized biochar is obtained by pyrolysis carbonization of biomass raw materials, including rice straw and livestock manure; the mass ratio of rice straw to livestock manure is (7~9):(3~1); the livestock manure is chicken manure or cow manure.

[0014] Furthermore, through experiments, this invention verifies that, regarding the promotion effect on rice growth, chicken manure is superior to cow manure, which is superior to pig manure, which is superior to goose manure and sheep manure, which is superior to no livestock or poultry manure added. The biochar-microorganism composite material (chicken manure) described in this invention provides endogenous mineral nutrient supplementation, with a nutrient supplementation effect superior to other livestock and poultry manure groups. In contrast, pure straw biochar, due to its nutrient deficiency, high C / N ratio, and potential adsorption and fixation of available nitrogen in the soil, contributes very little to yield and may even negatively impact rice growth in the short term. Moreover, when the mixing ratio is 8:2, the reduction rate of heavy metal content in leaves and rice is the highest, and the reduction effect is superior to other mixing ratios, indicating that only when the rice straw:chicken manure ratio is 8:2 can the optimal effect of reducing heavy metal content be achieved.

[0015] In this invention, on the one hand, the potassium (K), calcium (Ca), magnesium (Mg) and other mineral elements rich in livestock and poultry manure play an in-situ role as endogenous activators in the initial pore-forming process. Potassium forms K2O or K2CO3 intermediates at high temperatures, which chemically etch the carbon skeleton; calcium interacts with the carbon matrix to promote the formation of mesopores; magnesium helps maintain the thermal stability of the carbon skeleton and prevents pore collapse. The three elements work together to initially form a multi-level porous structure in the carbon matrix. On the other hand, the co-pyrolysis of livestock and poultry manure makes a decisive contribution to the improvement of biochar fertility. During the co-pyrolysis process, the abundant nitrogen, phosphorus, and potassium mineral nutrients of livestock and poultry manure are immobilized in the carbon skeleton of biochar, so that the biochar itself carries mineral nutrients that can be absorbed by crops. By incorporating livestock and poultry manure into the co-pyrolysis, the phosphorus (P) and potassium (K) content of the biochar increases by 170% to 280% compared with pure straw biochar; at the same time, the nitrogen (N) content increases by 5-30%, and the total nutrient content is significantly improved.

[0016] On the other hand, the present invention provides a method for preparing the above-mentioned functionalized biochar for heavy metal blocking, comprising the following steps: (1) Pretreatment: Biomass raw materials are mixed with mineral nutrient sources and pretreated by mechanical grinding to obtain a blended precursor; (2) Gradient pyrolysis carbonization: Under a protective atmosphere, the blended precursor is subjected to gradient heating pyrolysis carbonization to obtain primary carbonization products. (3) Directional pore-expanding modification: The primary carbonization product is activated by high-temperature pore-expanding using a composite activator containing alkali metal salt and pore-forming template agent to obtain pore-expanded carbon material; (4) Post-processing: The expanded pore carbon material is purified and post-processed to obtain the functionalized porous carbon material.

[0017] Further, the pretreatment involves removing weeds, stones, and other impurities from the rice straw, washing it 2-3 times with deionized water to remove surface-adhered soil and soluble impurities, and then drying it in a forced-air drying oven at 75-105℃ for 12-24 hours until constant weight. The dried straw is then pulverized using a high-speed universal pulverizer and passed through a 40-120 mesh standard sieve to obtain straw powder.

[0018] Preferably, to further remove mineral ash from rice straw and expose more cellulose microporous structures, the straw powder is placed in a 0.5-2.0 mol / L hydrochloric acid or nitric acid aqueous solution, mixed at a solid-liquid ratio of 1:8-1:20 g / mL, and acid-washed at 150-300 r / min for 2-8 hours at 20-30℃; the livestock and poultry manure is not acid-washed to retain its rich nitrogen, phosphorus, potassium and other mineral nutrients for subsequent co-pyrolysis to be immobilized on the biochar carbon skeleton.

[0019] Further, after the acid washing is completed, the straw powder is repeatedly washed with deionized water 3-5 times until the pH of the filtrate reaches 6.5-7.5, and then dried at 75-85℃ to constant weight to obtain acid-washed pretreated straw powder. Visible impurities are removed from livestock and poultry manure (chicken or cow manure), which is then dried at 60-80℃ to constant weight and pulverized through a 40-120 mesh sieve. The pretreated rice straw powder and livestock and poultry manure powder are uniformly mixed at a mass ratio of (7-9):(3-1) (dry basis) to obtain a mixed raw material. The mixed raw material is placed in a planetary ball mill using a gradient feeding method to complete wet grinding, thereby achieving a gradient distribution of mineral nutrients in the manure within the straw fiber network and avoiding uneven pyrolysis caused by localized nutrient enrichment. Specifically, first, mix 50%-70% of the total rice straw with all the livestock and poultry manure, add deionized water to prepare a slurry with a solid content of 30%-50%, and grind it at 200-400 r / min for 1-3 hours. Then add the remaining straw and continue grinding for 1-2 hours. Zirconia balls are used as the grinding media, with a ball-to-material ratio of (10-20):1. During this process, add 1%-5% calcium chloride (CaCl2) by mass of the mixed raw materials. Under the mechanical force of grinding, Ca... 2+ Calcium chloride undergoes ion exchange and complexation reactions with oxygen-containing groups in straw cellulose and manure organic matter, achieving pre-intercalation of calcium elements and providing an in-situ calcium source for the directional generation of active functional groups such as hydroxyl groups during subsequent pyrolysis. The hygroscopicity of calcium chloride can regulate the microenvironment of the grinding system and enhance the interfacial bonding strength between fibers and particles. The Ca in calcium chloride... 2+In the subsequent high-temperature pyrolysis process, it can act as an auxiliary activator for mesopore formation, promoting the development of uniform mesopores in the carbon skeleton. After wet grinding, the slurry is dried to constant weight at 60-80℃ and then placed in a planetary ball mill for dry grinding at a speed of 100-300 r / min for 1-3 hours, so that the fineness of the mixture reaches 80-200 mesh, obtaining the co-grinding pretreated product.

[0020] Preferably, the calcium chloride contains mixed phosphates.

[0021] More preferably, the ratio of calcium chloride to phosphate is 1:2 to 1:6. This enhances the effect of calcium ions, thus improving the calcium ion concentration. 2+ With phosphate (PO4) 3- The combination of these substances forms hydroxyapatite (HAP) precursor, a recognized highly efficient heavy metal adsorbent. Phosphate also acts as a pore-forming agent during pyrolysis, helping to regulate pore size. Furthermore, its decomposition products introduce phosphorus (P), further enhancing the fertility of biochar. This invention experimentally verifies that the optimal ratio maximizes both effects. Experiments show that adding calcium chloride and phosphate during the grinding process results in the highest reduction rate of heavy metal content in leaves and rice, significantly lower than the group without added auxiliary substances. The reduction effect is significantly better than adding calcium chloride or phosphate alone, or changing any one of the substances in the combination. Adding other substances to the combination of calcium chloride and phosphate does not significantly change the heavy metal content. Therefore, adding calcium chloride and phosphate during the grinding process is the optimal choice.

[0022] Furthermore, the gradient pyrolysis carbonization involves placing the pretreated co-grinding pretreated product in a controlled-atmosphere tubular pyrolysis furnace or box-type resistance furnace, and performing segmented gradient heating pyrolysis under an inert protective atmosphere. Specifically, the pretreated co-grinding pretreated product is placed in a controlled-atmosphere tubular pyrolysis furnace, and gradient pyrolysis is performed under a high-purity nitrogen protective atmosphere with a purity ≥99.999%, with the gas flow rate controlled at 80-300 mL / min. The first heating stage raises the temperature from room temperature to 180-220℃ at a rate of 3-8℃ / min and holds for 20-40 minutes to remove free and bound water, initiating the initial decomposition of hemicellulose. The second heating stage continues at a rate of 5-15℃ / min, raising the temperature to 350-450℃ and holding for 30-60 minutes, causing extensive decomposition of hemicellulose and the initiation of pyrolysis of cellulose, forming the initial carbon skeleton. The third heating stage raises the temperature to a final temperature of 500-700℃ at a rate of 2-5℃ / min and holds for 60-120 minutes, fully decomposing and carbonizing lignin. During pyrolysis, the potassium (K), calcium (Ca), and magnesium (Mg) minerals abundant in livestock and poultry manure act as endogenous activators, initially forming pores. Potassium forms K₂O or K₂CO₃ intermediates at high temperatures, chemically etching the carbon skeleton; calcium interacts with the carbon matrix to promote mesopore formation; and magnesium helps maintain the thermal stability of the carbon skeleton and prevents pore collapse. The three elements work together to initially form a hierarchical porous structure within the carbon matrix. After pyrolysis, the material is naturally cooled to room temperature under nitrogen protection to obtain primary biochar.

[0023] Further, the directional pore-expanding modification involves uniformly mixing primary co-pyrolytic biochar and a composite pore-expanding agent at a mass ratio of 1:2-1:6, placing the mixture in a tube furnace, and heating it to 700-900 ℃ at a rate of 5-10 ℃ / min under a nitrogen atmosphere with a flow rate of 100-200 mL / min, holding it at this temperature for 60-150 minutes. After the activation and holding period, the mixture is cooled to room temperature under nitrogen protection to obtain pore-expanded co-pyrolytic biochar. This method enables the biochar to form a continuous mesoporous-macroporous pore network. The advantage of this structure is that it matches the size of functional microbial cells (0.5-5 μm), providing ample habitat space and material transport channels for microbial attachment, reproduction, and metabolic activities. Among them, mesopores serve as anchoring points for microorganisms to adhere and colonize by secreting extracellular polymers, macropores serve as the main habitat space for bacterial cells, and the interconnected structure of mesopores and macropores provides an efficient channel for nutrient transport and metabolic product excretion, which can maximize the effect of enhancing the migration capacity of functional microbial cells for heavy metal ions, thereby achieving a higher heavy metal blocking rate.

[0024] Preferably, the composite pore-expanding agent is composed of potassium carbonate (K2CO3) and Zn3(C6H5O7)2·2H2O (zinc citrate) in a mass ratio of 2:1 to 5:1. Simultaneously, the Ca in the calcium chloride pre-embedded during the pretreatment process... 2+ By leveraging a synergistic effect, CaO and zinc citrate are formed at high temperatures to jointly contribute to the mesoporous template, further increasing the proportion of mesopores and enabling the mesopore proportion to be stably controlled at 65%-85%.

[0025] Preferably, a mixture of carbon dioxide and nitrogen with a volume fraction of 10%-30% is introduced during the pore-expanding process. The carbon dioxide undergoes a gasification reaction with the carbon matrix at high temperatures, resulting in a synergistic physical pore-forming effect, which can further increase the proportion of mesopores and macropores in the biochar and improve pore connectivity.

[0026] Furthermore, the post-treatment involves washing the expanded-pore co-pyrolysis biochar 2-3 times with a 0.5-1.5 mol / L dilute hydrochloric acid solution, maintaining a solid-liquid ratio of 1:10-1:20, with each washing session lasting 30-60 minutes of stirring. This neutralizes excess alkali and dissolves residual metal oxides, zinc chloride template, and soluble inorganic salt impurities. The biochar is then repeatedly washed with deionized water until the pH of the filtrate reaches 6.5-7.5, and silver nitrate (AgNO3) solution testing confirms the absence of chloride ions, ensuring that no residual Cl- ions in the biochar affect subsequent microbial loading and soil application. The washed biochar is then placed in a vacuum drying oven and dried at 60-90℃ and a vacuum degree ≤-0.09 MPa for 24-48 hours to obtain the finished rice straw biochar product.

[0027] In some embodiments, the biochar is coupled with a microbial consortium loaded within the mesoporous channels of the biochar.

[0028] In this invention, the microbial consortium is composed of highly efficient functional strains selected through targeted screening from the rhizosphere soil of paddy fields contaminated with Cd-Pb-As composite pollutants. The screening method involves using Cd... 2+ Pb 2+ As 3+ A two-stage strategy combining screening with chemotactic induction using three heavy metal gradient concentrations is employed. This screening strategy differs from existing acclimatization methods under single heavy metal pressure, ensuring that the screened strains maintain high activity and synergistic adsorption capacity under combined pollution conditions.

[0029] Furthermore, the microbial consortium includes Bacillus subtilis, Bacillus cereus, and Citrobacter; Preferably, the concentration ratio of Bacillus subtilis, Bacillus cereus, and Citrobacter in the microbial consortium is 4:2:1 to 3:2:1; More preferably, the microbial complex also includes Rawstone bacteria and urease-producing bacteria; More preferably, the urease-producing bacterium is *Bacillus pasteurellus*.

[0030] In this invention, the microbial consortium is a composite functional microbial community composed of a mixture of Bacillus subtilis, Bacillus cereus, and Citrobacter in equal concentration ratios (4:2:1 to 3:2:1) as the basic framework, supplemented by Rawlstonella and urease-producing bacteria (such as Bacillus pasteurellis). The domestication of this microbial community employs a two-stage strategy combining gradient concentration pressure screening and chemotactic induction: First, the composite microbial community is inoculated into a liquid culture medium containing progressively increasing concentrations of the target heavy metal ions and cultured through successive subcultures to screen for highly tolerant dominant subpopulations; subsequently, in the later stages of domestication, a semi-permeable membrane device encapsulating a high concentration of the target heavy metal ion solution is introduced into the culture medium as a chemical decoy. The concentration gradient is used to continuously induce the microbial community to produce a chemotactic response towards the heavy metal source through multiple generations, ultimately optimizing and screening to obtain the aforementioned composite functional microbial community. The remediation material formed by biochar coupled with microbial consortia has the following beneficial effects: First, the synergistic effect of multiple functional bacteria enables the composite microbial community to have good tolerance and broad-spectrum adsorption of various complex heavy metal pollutants; Second, gradient pressure acclimatization significantly improves the survival rate and metabolic activity of the microbial community in extreme pollution environments, while chemotactic induction endows the microbial community with the ability to actively migrate to areas with high concentrations of pollution. The fungal hyphae in the microbial community intertwine to form a huge network, and during their growth, they secrete organic acids or iron carriers to dissolve heavy metals on soil particles along the way. Then, through the cytoplasmic circulation inside the hyphae or the continuous mucus layer on the surface, the ions are directionally transported back to the central colony, which is equivalent to the microorganisms actively laying out a collection channel; in addition, microbial metabolism produces or consumes Ions cause a weak electrochemical gradient or osmotic pressure difference to form around the colony, creating an environment structure similar to a miniature "water pump." This drives soil pore water to flow slowly towards the colony, and heavy metal ions dissolved in the water are passively migrated to the location of the bacterial community with the water flow. This allows the bacterial community to further exert its "active search" function on the basis of biochar immobilization, guiding heavy metal ions in the soil liquid phase to be directionally enriched on the surface of biochar. Third, the porous structure of biochar provides a stable shelter and slow-release carbon source for the bacterial community. At the same time, the organic acids, extracellular polymers, and calcium carbonate precipitates produced by the metabolism of the bacterial community can change the occurrence form of heavy metals, converting exchangeable unstable components into residual states, thereby achieving the dual benefits of adsorption enrichment and long-term passivation, significantly improving remediation efficiency and durability.

[0031] This invention experimentally verified that the optimal single-strain combination is *Bacillus subtilis*. Based on this, a dual-strain selection was conducted, with the optimal combination being *Bacillus subtilis* + *Bacillus cereus*. Further optimization based on this dual-strain combination yielded the optimal quadruple combination: *Bacillus subtilis* + *Bacillus cereus* + *Citrobacter* + *Rolstonia*. Further screening with additional strains resulted in the optimal pentad combination: *Bacillus subtilis* + *Bacillus cereus* + *Citrobacter* + *Rolstonia* + *Bacillus pasteurellis*. Experimental results showed that the leaves of the *Bacillus subtilis* + *Bacillus cereus* + *Citrobacter* group... The reduction rates of the three heavy metals in the leaves and rice were significantly higher than those of single-strain, dual-strain, and other triple-strain groups, indicating that the triple-strain combination plays a key role in heavy metal adsorption. Further addition of other strains revealed that the combination of Bacillus subtilis + Bacillus cereus + Citrobacter + Rawstone + Pasteurella multocida showed the highest reduction rate of the three heavy metals in the leaves and rice, superior to other quadrivalent, pentavalent, and hexavalent strains. Furthermore, replacing any one of the five strains failed to achieve the same effect, indicating that the pentavalent combination can enhance the heavy metal adsorption capacity of the barrier material.

[0032] Furthermore, this invention provides a method for preparing the above-mentioned heavy metal blocking functionalized biochar, comprising the following steps: (1) The above-mentioned functionalized porous carbon material was added to the microbial consortium suspension and mixed at a solid-liquid ratio of 1:5-1:20 g / mL; (2) The mixture is placed in an ultrasonic processor for ultrasonic-assisted preload processing; (3) Transfer to a constant temperature oscillator for oscillation load; (4) After the loading is completed, sterile filtration is performed to remove the unadsorbed free bacteria on the surface. After low-temperature drying, the material is dried at low temperature until the moisture content is 5%-15%, thus obtaining the biochar-microorganism composite barrier material.

[0033] Further, the functionalized porous carbon material is added to a microbial consortium suspension and mixed at a solid-liquid ratio of 1:5-1:20 g / mL. Ultrasonic-assisted preloading is then performed. The mixture is placed in an ultrasonic processor and ultrasonically treated for 5-25 minutes at a frequency of 20-40 kHz and a power of 100-250 W, using a pulse mode of 5 seconds on and 5 seconds off, under a water bath temperature of 20-30℃. The ultrasonic cavitation effect breaks down the diffusion boundary layer at the solid-liquid interface, driving microorganisms to rapidly enter the mesoporous channels of the biochar, while gently increasing cell membrane permeability, promoting extracellular polymer secretion, and enhancing initial adhesion.

[0034] Furthermore, after ultrasonic preloading, the microorganisms are transferred to a constant temperature oscillator and oscillated for 2-6 hours at 25-37℃ and 100-180 r / min to allow them to fully colonize the biochar mesoporous channels and anchor to the functional group active sites.

[0035] Preferably, the ultrasound-assisted preloading can be performed using a gradient ultrasound program, at 25°C and in pulse mode, first at 20 kHz and 100 W for 5 minutes, then increased to 40 kHz and 200 W for 5-10 minutes. Preferably, 0.5%-2% (by weight / volume) of fucoidan is added during the ultrasound-assisted preloading process as a microbial protectant and adhesion promoter.

[0036] When the material prepared in this invention is applied to the 0-20 cm tillage layer of paddy fields, it achieves deep barrier protection against Cd, Pb, and As through a triple-blocking mechanism: Firstly, it achieves rapid physicochemical adsorption, enabling immediate fixation. The well-developed mesoporous structure of biochar (65%-85% mesopores) and its abundant carboxyl (-COOH), carbonyl, and lactone groups, among other multi-functional oxygen-containing acids, effectively attract Cd from the soil solution. 2+ Pb 2 + Electrostatic adsorption, ion exchange, complexation, and cation-π interaction occur; for the oxygen-containing anions of As (H2AsO4) - ,HAsO4 2- ), through surface Ca 2+ Adsorption occurs through electrostatic attraction at the application site. This process is completed within hours to days after application.

[0037] Secondly, the active migration of microorganisms drives directional capture. After recovery, the microbial consortium loaded within the biochar pores continuously secretes organic acids, siderophores, and extracellular polymers, altering the pH and redox potential of the rhizosphere microenvironment. This drives the desorption of heavy metals from the soil particle surface and their directional migration towards the area where the biochar-microorganism complex is located. This mechanism enables the material to achieve a blocking rate of over 85% for migrating Cd, Pb, and As in the 20-70 cm deep layer even under shallow application conditions of 0-20 cm.

[0038] Third, long-term microbial transformation and fixation achieve permanent solidification. 2+ and Pb 2+ As is fixed through intracellular accumulation, extracellular precipitation, and extracellular polymeric complexation; after oxidation by functional bacteria, As reacts with Ca. 2+ A stable calcium arsenate precipitate is formed. This process transforms heavy metals from an exchangeable, acid-soluble state to a residual state, significantly reducing their bioavailability and the risk of secondary release.

[0039] In this invention, the effectiveness of the second and third blocking mechanisms is significantly enhanced through an ultrasonic-assisted coupling loading process. The synergistic effect of the three mechanisms enables the material to achieve passivation rates of 75%-92%, 80%-95%, and 65%-85% for available Cd, Pb, and As in soil, respectively.

[0040] Further, after loading, the material undergoes aseptic filtration, and is gently rinsed 2-3 times with sterile physiological saline to remove unadsorbed free bacteria from the surface. It is then dried at a low temperature of 25-37℃ to a moisture content of 5%-15%, yielding the biochar-microorganism composite barrier material. The microbial loading in the material is 10... 8 -10 10 The CFU / g is increased by 50%-200% compared to the conventional oscillation method, and the colonization depth is increased by 30%-60%.

[0041] In another aspect, the present invention provides an in-situ blocking method for heavy metal contamination of farmland, the steps of which include: applying the above-mentioned functionalized biochar to the topsoil of the farmland.

[0042] In this invention, the functionalized biochar utilizes the porous adsorption and surface functional group complexation of the porous carbon material to rapidly fix heavy metal ions in the soil solution using physicochemical methods; and utilizes the metabolic activities of the functional microbial complex loaded in the porous carbon material to drive the desorbed heavy metal ions in the deep soil to migrate directionally to the cultivated layer, and convert the heavy metal ions into a stable form through microbial mineralization or intracellular accumulation.

[0043] Furthermore, this invention provides the use of the above-mentioned heavy metal composite barrier material or functionalized biochar obtained by the above preparation method in the preparation of soil heavy metal adsorbents, wherein the use includes one or more of the following: (1) Improve the heavy metal blocking effect; (2) Improve the blocking rate of heavy metals in deep soil layers; (3) Reduce the bioavailability of heavy metals and the risk of secondary release.

[0044] The present invention has the following beneficial effects: 1. The biochar surface of this invention is rich in carboxyl (-COOH), carbonyl, and lactone groups, forming a multi-functional oxygen-containing acidic group, while simultaneously supporting amino (-NH2) basic functional groups and an aromatic conjugated C=C skeleton. This abundance of acidic sites provides a favorable environment for Cd... 2+ Pb 2+ With strong chelating and ion exchange capabilities, the basic amino group can effectively bind AsO3 in the paddy field system. 3- AsO4 3- Anions can block the migration of heavy metals such as cadmium, lead, and arsenic from paddy soil to rice roots through multiple pathways. 2. The co-pyrolysis of livestock and poultry manure into biochar raw materials significantly increases the total nutrient content of biochar. Furthermore, the abundant potassium (K), calcium (Ca), and magnesium (Mg) minerals in the manure act as endogenous activators, initially forming pores. Potassium forms K₂O or K₂CO₃ intermediates at high temperatures, chemically etching the carbon skeleton. Calcium interacts with the carbon matrix to promote mesopore formation. Magnesium helps maintain the thermal stability of the carbon skeleton and prevents pore collapse. These three elements work synergistically to initially form a hierarchical porous structure within the carbon matrix. 3. Biochar and microorganisms form a dual barrier against heavy metals, wherein the biochar is effective against Cd. 2+ The saturated adsorption capacity for Pb is 195–360 mg / g. 2+ The saturated adsorption capacity is 155–290 mg / g, and the saturated adsorption capacity for As is 42–85 mg / g, which are 6–9 times, 4.5–7.5 times and 11–32 times higher than those of unmodified rice straw biochar, respectively, achieving broad-spectrum and efficient adsorption of three heavy metals: cadmium, lead and arsenic. 4. Adding calcium chloride and phosphate during the grinding process helps to control the pore size. On the other hand, their decomposition products can also introduce phosphorus (P) elements, further enhancing the fertility of biochar. 5. The addition of a specific pore-expanding agent composed of potassium carbonate (K2CO3) and Zn3(C6H5O7)2·2H2O (zinc citrate) allows the biochar's pore structure to form a continuous mesoporous-macroporous network that matches the size of functional microbial cells (0.5-5μm), providing ample habitat and material transport channels for microbial attachment, reproduction, and metabolic activities. Mesopores serve as anchoring points for microbial extracellular polymers to adhere and colonize, while macropores provide the primary habitat for the cells. The interconnected mesoporous-macroporous structure provides efficient channels for nutrient transport and metabolic product excretion, maximizing the enhancement of the functional microbial cells' ability to migrate heavy metal ions, thereby achieving a higher heavy metal blocking rate. 6. During the pore-expansion process, the specific mixed atmosphere of carbon dioxide and nitrogen plays a physical synergistic role in pore formation, which can further increase the proportion of mesopores and macropores in biochar and the connectivity of pores. 7. Biochar materials and microorganisms are loaded using an ultrasonic-assisted coupling process, which utilizes the ultrasonic cavitation effect to drive microorganisms to quickly enter the mesoporous channels of biochar, significantly improving loading efficiency and colonization depth. 8. The addition of specific microbial consortia enables active migration-driven, directional capture. After reactivation, the microbial consortia loaded within the biochar pores continuously secrete organic acids, siderophores, and extracellular polymers, altering the pH and redox potential of the rhizosphere microenvironment. This drives the desorption of heavy metals from the soil particle surface and their directional migration towards the biochar-microbial complex area. This mechanism allows the material to achieve over 85% blocking rate for migrating Cd, Pb, and As at a depth of 20-70 cm under shallow application conditions of 0-20 cm; furthermore, it enables long-term transformation and fixation, achieving permanent solidification of Cd. 2+ and Pb 2+ As is fixed through intracellular accumulation, extracellular precipitation, and extracellular polymeric complexation; after oxidation by functional bacteria, As reacts with Ca. 2+ A stable calcium arsenate precipitate is formed. This process transforms heavy metals from an exchangeable, acid-soluble state to a residual state, significantly reducing their bioavailability and the risk of secondary release. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a biochar-microbial composite barrier material. In the diagram, 1 represents rice straw biochar, and 2 represents the microbial consortium. Detailed Implementation

[0046] To describe the present invention more specifically, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These descriptions are merely illustrative of how the present invention is implemented and do not limit the specific scope of the invention. All materials used in this experiment are commercially available. The scope of the present invention is defined in the claims.

[0047] Example 1: Preparation of Functionalized Biochar for Heavy Metal Blocking 1. Preparation of porous carbon materials (1) Pretreatment of mixed raw materials of rice straw and livestock and poultry manure After removing weeds, stones, and other impurities from rice straw, it was washed twice with deionized water to remove surface dirt and soluble impurities. It was then placed in a forced-air drying oven and dried at 75°C for 12 hours until constant weight. The dried straw was then pulverized using a high-speed universal pulverizer and passed through a 40-mesh standard sieve to obtain straw powder. To further remove mineral ash from the rice straw and expose more cellulose microporous structures, the straw powder was placed in a 0.5 mol / L hydrochloric acid or nitric acid aqueous solution, mixed at a solid-liquid ratio of 1:8 g / mL, and acid-washed at 20°C and 150 r / min for 2 hours. After acid washing, it was repeatedly washed three times with deionized water until the pH of the filtrate reached 6.5, and then dried at 75°C until constant weight, obtaining acid-pretreated straw powder.

[0048] After removing visible impurities from the chicken manure, dry it at 60℃ to constant weight, then pulverize it and pass it through a 40-mesh sieve.

[0049] Pretreated rice straw powder and chicken manure powder were uniformly mixed at a mass ratio of 8:2 (dry basis) to obtain a mixed raw material. The mixed raw material was then placed in a planetary ball mill for wet grinding using a gradient feeding method to achieve a gradient distribution of mineral nutrients in the straw fiber network, avoiding uneven pyrolysis caused by localized nutrient enrichment. First, 50% of the total rice straw was mixed with all the chicken manure, and deionized water was added to prepare a slurry with a solid content of 30%. This slurry was ground at 200 r / min for 1 hour, and then the remaining straw was added and grinding continued for another hour. Zirconia balls were used as the grinding media, with a ball-to-material ratio of 10:1. During this process, calcium chloride (CaCl2) and phosphate, accounting for 1% of the mass of the mixed raw materials, are added. The phosphate used is disodium hydrogen phosphate, and the ratio of the two is 1:2. After the wet grinding slurry is dried at 60°C to constant weight, it is placed in a planetary ball mill for dry grinding at 100 r / min for 1 hour to make the fineness of the mixture reach 80 mesh, thus obtaining the co-grinding pretreated product.

[0050] (2) Gradient pyrolysis carbonization The co-grinding pretreated product obtained in the previous step was placed in a tubular pyrolysis furnace with a controllable atmosphere and subjected to gradient pyrolysis under a protective atmosphere of high-purity nitrogen (≥99.999%), with the gas flow rate controlled at 80 mL / min. In the first heating stage, the temperature was increased from room temperature to 180℃ at a rate of 3℃ / min and held for 20 minutes to remove free and bound water, initiating the initial decomposition of hemicellulose. In the second heating stage, the temperature was further increased to 350℃ at a rate of 5℃ / min and held for 30 minutes, causing extensive decomposition of hemicellulose and the initiation of pyrolysis of cellulose, initially forming a carbon skeleton. In the third heating stage, the temperature was increased to a final temperature of 700℃ at a rate of 2℃ / min and held for 60 minutes to fully decompose and carbonize lignin. During pyrolysis, the potassium (K), calcium (Ca), and magnesium (Mg) minerals abundant in livestock and poultry manure act as endogenous activators in situ, initially forming pores. Potassium forms K₂O or K₂CO₃ intermediates at high temperatures, chemically etching the carbon skeleton; calcium interacts with the carbon matrix to promote mesopore formation; and magnesium helps maintain the thermal stability of the carbon skeleton, preventing pore collapse. These three elements work synergistically to form the initial form of a hierarchical porous structure within the carbon matrix. After pyrolysis, the mixture is naturally cooled to room temperature under nitrogen protection to obtain primary biochar.

[0051] (3) Directional pore enlargement modification The composite pore-expanding agent was composed of potassium carbonate (K2CO3) and Zn3(C6H5O7)2·2H2O (zinc citrate) in a mass ratio of 2:1. Primary co-pyrolysis biochar and the composite pore-expanding agent were uniformly mixed in a mass ratio of 1:2 and placed in a tube furnace. The mixture was heated to 700℃ at a rate of 5℃ / min under a mixed atmosphere of 10% carbon dioxide and nitrogen at a flow rate of 100 mL / min, and held at this temperature for 60 minutes. After activation and holding, the mixture was cooled to room temperature under nitrogen protection to obtain the pore-expanded co-pyrolysis biochar.

[0052] (4) Post-processing The expanded-pore co-pyrolysis biochar was washed twice with a 0.5 mol / L dilute hydrochloric acid solution, maintaining a solid-liquid ratio of 1:10, with stirring and washing for 30 minutes each time to neutralize excess alkali and dissolve residual metal oxides, zinc chloride template, and soluble inorganic salt impurities. It was repeatedly washed with deionized water until the pH of the filtrate reached 6.5, and no chloride ions were found in the silver nitrate (AgNO3) solution, ensuring that no residual Cl- would affect subsequent microbial loading and soil application. The washed biochar was then placed in a vacuum drying oven and dried at 60℃ and a vacuum degree ≤-0.09 MPa for 24 hours to obtain the finished rice straw biochar product.

[0053] 2. Preparation of biochar-microorganism composite barrier materials A two-stage strategy combining gradient concentration pressure screening and chemotactic induction was employed to acclimatize the bacterial strains. The dominant acclimatized strains, including *Bacillus subtilis*, *Bacillus cereus*, *Citrobacter*, *Rowstoneella*, and *Pasteurella multocida*, were inoculated into PDA liquid medium and cultured at 28°C and 120 r / min for 48 hours with shaking. The bacterial strains were then inoculated into LB liquid medium and cultured at 30°C and 150 r / min for 12 hours with shaking. The bacterial cells were collected, resuspended in sterile physiological saline (0.85% NaCl), and the bacterial concentration was adjusted to the optical density (OD). 600 The concentration was 0.8. Bacillus subtilis, Bacillus cereus, and Citrobacter were mixed in an equal ratio of 4:2:1 as the basic skeleton, and supplemented with Rawstone bacteria and urease-producing bacteria. Finally, a microbial consortium suspension was obtained with a concentration ratio of 4:2:1:1:1 for Bacillus subtilis, Bacillus cereus, Citrobacter, Rawstone bacteria and urease-producing bacteria.

[0054] The obtained co-pyrolyzed biochar product was added to the microbial consortium suspension and mixed at a solid-liquid ratio of 1:5 g / mL. Ultrasonic-assisted preloading was then performed. The mixture was placed in an ultrasonic processor and subjected to a gradient ultrasonic program. At 25°C and pulse mode, the mixture was first treated at 20 kHz and 100 W for 5 minutes, then increased to 40 kHz and 200 W for another 5 minutes. During the ultrasonic-assisted preloading process, 0.5% (w / v) of fucoidan was added as a microbial protectant and adhesion promoter. After ultrasonic preloading, the mixture was transferred to a constant-temperature shaker and subjected to continued shaking at 25°C and 100 r / min for 2 hours to ensure that the microorganisms fully colonized the biochar mesoporous channels and anchored at the functional group active sites.

[0055] After loading, the material is sterilely filtered, gently rinsed twice with sterile saline to remove unadsorbed free bacteria, and then dried at 25°C to a moisture content of 5% to obtain the biochar-microorganism composite barrier material. Figure 1 This is a schematic diagram of a biochar-microorganism composite barrier material.

[0056] Example 2: Properties and applications of functionalized biochar for heavy metal blocking 1. Heavy metal blocking effect (1) Experimental methods The tested soil was from a paddy field contaminated with cadmium, lead, and arsenic. The soil pH was 5.8±0.2, the organic matter content was 22.5 g / kg, the total cadmium content was 2.8 mg / kg, the total lead content was 85.0 mg / kg, the total arsenic content was 45.0 mg / kg, the available cadmium content was 1.2 mg / kg, the available lead content was 12.5 mg / kg, and the available arsenic content was 8.6 mg / kg. The tested rice variety was Zhe 1831.

[0057] Four treatment groups were set up, with 20 test samples in each group. Rice was planted under the same conditions, and the rice was kept flooded during the growth period. Routine water and fertilizer management was carried out, and biochar materials were applied according to methods A, B, C and method D of the present invention.

[0058] Method A: Rice is planted without adding any biochar material. Method B: Biochar prepared according to this invention is added at a ratio of 2% of the soil mass, thoroughly mixed with the soil, and then placed in pots. Method C: 1.28 g of the microbial consortium suspension described in this invention is added per pot, thoroughly mixed with the soil, and then placed in pots. Method D: Biochar-microbial composite barrier material described in this invention is added at a ratio of 2% of the soil mass, thoroughly mixed with the soil, and then placed in pots.

[0059] The preparation methods for biochar materials, microbial consortium suspensions, and biochar-microbial composite barrier materials are the same as in Example 1. Samples of the second leaf from the top were collected during the peak tillering stage of rice. Rice samples were harvested after the rice matured. After drying, pulverizing, and digestion, the contents of Cd, Pb, and As in the leaves and rice were determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0060] Inductively coupled plasma mass spectrometry (ICP-MS): After drying and pulverizing, 0.5000 g (±0.0005 g) of the sample was accurately weighed and placed in a polytetrafluoroethylene digestion vessel. 5 mL of concentrated nitric acid (HNO3, analytical grade) and 2 mL of hydrogen peroxide (H2O2, analytical grade) were added, and the vessel was capped and allowed to stand overnight for pre-digestion. The digestion vessel was then placed in a microwave digester and digestion was performed according to the following procedure: power 1600 W; first step: heating to 120℃ within 5 min and holding for 3 min; second step: heating to 150℃ within 5 min and holding for 5 min; third step: heating to 190℃ within 5 min and holding for 20 min. After digestion, the mixture was cooled to room temperature, and the digestion solution was transferred to a 25 mL volumetric flask. The digestion vessel was washed three times with ultrapure water, and the washings were combined into the volumetric flask. The volume was then diluted to the mark with ultrapure water and shaken well. A blank control sample was prepared simultaneously (without the sample, all other procedures were identical).

[0061] Inductively coupled plasma mass spectrometry (ICP-MS) was used for the determination. The instrument operating conditions were: RF power 1550 W, cooling gas flow rate 14 L / min, auxiliary gas flow rate 0.8 L / min, carrier gas flow rate 1.0 L / min, sampling depth 8 mm, collision gas helium (He, purity ≥99.999%), flow rate 4.3 mL / min, and kinetic discrimination mode was used to eliminate polyatomic ion interference. Isotopes were selected. 111 Cd, 208 Pb, 75 As was measured, to 115 In was used as an internal standard element for signal drift correction. External standard method was used for quantification, and a series of mixed standard solutions of Cd, Pb, and As (concentration ranges of 0.5, 1.0, 5.0, 10.0, 50.0, and 100.0 μg / L) were prepared, and standard curves were plotted.

[0062] (2) Experimental results The results of the determination of the contents of three heavy metals, cadmium, lead and arsenic, in rice leaves are shown in Table 1.

[0063] Table 1. Results of determination of cadmium, lead, and arsenic content in rice leaves

[0064] The results of the determination of the contents of cadmium, lead and arsenic in rice are shown in Table 2.

[0065] Table 2. Results of determination of cadmium, lead, and arsenic content in rice.

[0066] The combined application of biochar and microorganisms significantly reduced the cadmium, lead, and arsenic content in rice leaves and rice grains. In group D, the cadmium, lead, and arsenic content in leaves decreased to 0.72, 0.32, and 0.52 mg / kg, respectively, and in rice grains, they decreased to 0.13, 0.07, and 0.12 mg / kg, respectively. All these levels were below the national standard limits and significantly better than the sum of the biochar and microbial groups, demonstrating a broad-spectrum synergistic effect between the biochar and microbial combination on heavy metals with different charge properties.

[0067] The reduction rates of the three heavy metals showed a consistent trend. Regardless of whether it was leaves or rice, the reduction rate of the three heavy metals in each treatment group was ranked as follows: Method D (75%–82%) was superior to Method B (26%–53%), which was superior to Method C (6%–9%). The biochar-microorganism composite barrier material was significantly superior to biochar alone and microorganism alone, demonstrating that the combined effect of biochar and microorganisms has a significant effect on all three heavy metals, and that the combined application of biochar and microorganisms is particularly effective against cationic heavy metals (Cd). 2+ Pb 2+ Both α and β-type heavy metals (As containing oxyanions) showed excellent synergistic blocking effects, verifying the broad-spectrum adaptability of the dual mechanism of biochar adsorption and microbial transformation of the present invention to heavy metals with different charge properties.

[0068] The reduction rates in leaves and rice grains were highly correlated, indicating that the blocking effect mainly occurred in the roots and rhizosphere. In group D, the reduction rates of cadmium, lead, and arsenic in leaves were 74.7%, 80.2%, and 64.1%, respectively, while in rice grains they were 75.0%, 81.6%, and 65.7%, respectively. This suggests that the transport of heavy metals from leaves to grains was not significantly disrupted, and the blocking effect mainly occurred in root absorption and root-to-surface translocation, rather than leaf-to-grain translocation. The biochar-microorganism composite barrier material primarily functioned in the roots and rhizosphere. Biochar adsorbed and fixed heavy metals in the rhizosphere, while microorganisms drove the directional migration and transformation of heavy metals into the biochar within the rhizosphere. Together, they intercepted most of the heavy metals at the root-soil interface, thus simultaneously reducing the heavy metal content in both leaves and rice grains.

[0069] 2. Effect of biochar carrier on microorganisms (1) Experimental methods The particle size distribution of the expanded-pore carbon material prepared in Example 1 was determined using a laser particle size analyzer; the specific surface area, total pore volume and average pore size were determined using a specific surface area and pore size analyzer; and the total number of viable bacteria loaded was determined using the plate count method.

[0070] (2) Experimental results The results of biochar specific surface area, total pore volume, average pore size, and microbial load are shown in Table 3.

[0071] Table 3 Results of biochar specific surface area, total pore volume, average pore size, and microbial load.

[0072] Experimental results showed that the specific surface area of ​​biochar was 1052.6 m². 2 / g; Total pore volume is 0.85 cm³. 3 / g; microbial load can reach 1.8×10 8 CFU / g. Specific surface area is significantly positively correlated with microbial loading. Total pore volume changes synchronously with specific surface area, indirectly affecting the high loading. The porous structure of biochar provides stable attachment sites and microenvironment for microorganisms, and high specific surface area is the key structural basis for ensuring high-density microbial loading.

[0073] 3. Heavy metal migration rate (1) Experimental methods The tested soil was paddy field soil contaminated with Cd-Pb-As complex pollution. The soil pH was 5.8±0.2, organic matter content was 22.5 g / kg, total cadmium content was 2.8 mg / kg, total lead content was 85.0 mg / kg, and total arsenic content was 45.0 mg / kg. The air-dried and sieved soil was packed into plexiglass soil columns with an inner diameter of 15 cm and a height of 80 cm. Each column was filled to a height of 70 cm, and water was added from the bottom to simulate root water absorption.

[0074] Ten independent replicate soil columns were set up. Group A served as a blank control group, with no added microorganisms. Group B was supplemented with 0.24 g of the functional microbial consortium suspension described in Example 1 of this invention per container, which was then sprayed evenly onto the soil surface. After each soil column was filled, water was added from the bottom to simulate root water absorption, and sensors were placed 2-3 cm below the soil surface to detect heavy metal content. Data were collected on days 0, 7, 14, and 21. After the experiment, soil samples were collected at different depths along the longitudinal direction of the soil column, and the content of available heavy metals in each soil layer was determined by inductively coupled plasma mass spectrometry.

[0075] (2) Experimental results The results of the determination of the concentration changes of heavy metals such as cadmium (Cd), lead (Pb), and arsenic (As) over time in each test group are detailed in Table 4 below.

[0076] Table 4. Results of the determination of heavy metal concentrations of cadmium (Cd), lead (Pb), and arsenic (As) over time.

[0077] After the experiment, the available heavy metal content in the soil at different depths of each test group is shown in Table 5 below.

[0078] Table 5. Content of available heavy metals in soil at different depths

[0079] Data showed that the concentrations of all three heavy metals in the microbial consortium group (B) were significantly higher than those in the blank control (A), and the difference continued to widen over time. At 21 days, the concentrations of Cd, Pb, and As at the bottom of group B were 110.3%, 104.0%, and 92.3% higher than those in group A, respectively. Meanwhile, the content of bioavailable Cd, Pb, and As in the surface layer (0-10 cm) of group B was significantly higher than that in group A, while the content of bioavailable Cd in the deep layer (40-70 cm) was significantly lower than that in group A, indicating that the microbial consortium effectively drove the migration of heavy metals from the deep layer to the surface.

[0080] This verifies the core principle of the second blocking mechanism mentioned above in this invention, namely, the active migration-driven mechanism of microorganisms. The metabolic activity of the microbial consortium continuously pumps deep heavy metals to the area where the biochar-microbial complex is located, enabling the material to achieve efficient capture of deep-migrating heavy metals even under shallow application conditions.

[0081] 4. Verification of biochar fertility (1) Experimental methods The test soil was from a paddy field with a pH of 5.6 ± 0.2, organic matter content of 18.5 g / kg, total nitrogen content of 1.2 g / kg, available phosphorus content of 8.6 mg / kg, and available potassium content of 85.0 mg / kg. The tested rice variety was Zhe 1831. Five test groups were set up, with 10 independent replicate containers in each group.

[0082] Group A: No fertilizer or biochar added. Group B: 2% pure straw biochar added by weight of soil, thoroughly mixed with soil before potting. Group C: Biochar-microbial composite material (without livestock manure mixed in during pretreatment) added, thoroughly mixed with soil before potting. Group D: Biochar-microbial composite material as described in this invention added, thoroughly mixed with soil before potting.

[0083] After the materials from each treatment group were thoroughly mixed with the soil, rice was planted using the same method. During the rice growing season, the rice was kept under flood irrigation and managed according to standard field practices. At maturity, the number of effective panicles, the number of grains per panicle, the thousand-grain weight, and the actual yield were measured.

[0084] (2) Experimental results The effective number of spikes, number of grains per spike, thousand-grain weight, and actual yield at maturity are shown in Table 6.

[0085] Table 6 Results of effective panicle number, number of grains per panicle, thousand-grain weight, and actual yield

[0086] The rice growth effect of each group was ranked as follows: Group D > Group C > Group B > Group A. The biochar-microorganism composite material described in this invention (Group D) obtains the supplementation of endogenous mineral nutrients, while pure straw biochar (Group B) is nutrient-poor, has a high C / N ratio, and may adsorb and fix available nitrogen in the soil, thus its contribution to yield is extremely limited, and may even affect rice growth in the short term.

[0087] Co-pyrolysis of livestock and poultry manure makes a decisive contribution to improving biochar fertility. Under the same biochar-microorganism composite material and application ratio, group D showed a 36.1% increase in yield compared to group C, indicating that incorporating livestock and poultry manure during pretreatment plays a crucial role in biochar fertility. This is because during co-pyrolysis, the abundant nitrogen, phosphorus, and potassium mineral nutrients of the livestock and poultry manure are immobilized within the biochar carbon skeleton. This means that group D biochar itself carries mineral nutrients available for crop absorption, while group C biochar only relies on its porous structure to adsorb and retain existing nutrients in the soil. There is a fundamental difference in nutrient supply between the two. Both sets of tests fully demonstrate the synergistic advantages of the four-in-one solution of straw preparation, co-pyrolysis of livestock and poultry manure, directional pore expansion, and microbial loading in improving fertility.

[0088] Experiment Example 3: Optimization and Screening of Biochar Raw Materials and Proportions 1. Screening of livestock and poultry manure Pig manure, goose manure, chicken manure, cow manure, and sheep manure were selected respectively. Biochar materials were prepared by changing only the livestock and poultry manure in the method described in Example 1. The specific surface area, total pore volume, and average pore size were measured by a specific surface area and pore size analyzer, the total number of viable bacteria was measured by plate counting, the fertility compensation effect was evaluated by comparing agronomic traits such as rice plant height, tiller number, thousand-grain weight, and yield, and the Cd, Pb, and As contents in leaves and rice were determined by inductively coupled plasma mass spectrometry (ICP-MS). The control group was a biochar-microbial composite material without livestock and poultry manure in the pretreatment stage. All livestock and poultry manure was replaced with rice straw, i.e., the ratio of rice straw to livestock and poultry manure was 10:0.

[0089] The experimental results of specific surface area, total pore volume, average pore size, and total number of viable bacteria loaded on biochar materials prepared from different livestock and poultry manures are shown in Table 7.

[0090] Table 7. Effects of different types of livestock and poultry manure on the specific surface area, total pore volume, average pore size, and total number of viable bacteria loaded in biochar materials.

[0091] According to the experimental results in Table 7, when chicken manure and cow manure are used, the specific surface area can reach 1052.6 ± 35.6 m², respectively. 2 / g, 1051.9±31.9 m 2 / g, the total pore volume can reach 0.85±0.05 cm³. 3 / g, 0.84±0.04 cm 3 The microbial load can reach 1.8 × 10⁶ g and 1.8 × 10⁶ g, respectively. 8 ±1.2×10 7 CFU / g, 1.8×10 8 ±1.1×10 7 The CFU / g indicates that using chicken manure and cow manure can increase the specific surface area of ​​biochar materials, and the microbial load increases with the increase of specific surface area. Compared with the blank control, the specific surface area increased by more than 17% and the total pore volume increased by more than 20%, with the effect being the best when using chicken manure.

[0092] The fertility compensation effect of biochar materials prepared from different livestock and poultry manures is evaluated in Table 8.

[0093] Table 8 Evaluation results of fertility compensation effect of biochar materials prepared from different livestock and poultry manure

[0094] As shown in Table 8, the experimental results indicate that the rice growth effect of each group was ranked as follows: chicken manure group > cow manure group > pig manure group > goose manure group > sheep manure group > control group > no fertilizer group. The biochar-microbial composite material (chicken manure) described in this invention provides endogenous mineral nutrient supplementation, with a better nutrient supplementation effect than other poultry and livestock manure groups. In contrast, pure straw biochar, due to its nutrient deficiency, high C / N ratio, and potential adsorption and fixation of available nitrogen in the soil, contributes very little to yield and may even negatively impact rice growth in the short term.

[0095] The results of determining the Cd, Pb, and As contents in leaves and rice of biochar materials prepared from different livestock and poultry manure are shown in Tables 9 and 10.

[0096] Table 9. Effects of biochar materials prepared from different livestock and poultry manure on the Cd, Pb, and As content in leaves.

[0097] Table 10. Effects of biochar materials prepared from different livestock and poultry manure on the Cd, Pb, and As content in rice.

[0098] 2. Screening of the ratio of rice straw to poultry and livestock manure Four ratios of rice straw to chicken manure were set up: 10:0, 9:1, 8:2, and 6:4. The other preparation methods were the same as in Example 1. The effect of the raw material ratio on the performance of biochar and the microbial loading effect was investigated using the method in Example 2. The experimental results are shown in Table 11.

[0099] Table 11

[0100] Experimental results showed that when the mixing ratio of livestock and poultry manure was adjusted from 10:0 to 8:2, the specific surface area increased by approximately 17.4%, and the total pore volume increased by approximately 25.0%. This was mainly because the mineral elements in the livestock and poultry manure played an endogenous pore-forming role during pyrolysis. When the ratio was further increased, the specific surface area and total pore volume decreased, indicating that an excessively high manure ratio may lead to excessive ash accumulation and pore blockage. Microbial load increased with increasing specific surface area, reaching its highest value in group C at 1.8 × 10⁻⁶. 8 CFU / g. Therefore, the preferred mixing ratio is 8:2.

[0101] The contents of Cd, Pb and As in leaves and rice were determined by inductively coupled plasma mass spectrometry (ICP-MS) as described in Example 2. The experimental results are shown in Tables 12 and 13.

[0102] Table 12 Effects of different livestock and poultry manure mixing ratios on the Cd, Pb, and As content in leaves

[0103] Table 13 Effects of different livestock and poultry manure mixing ratios on the Cd, Pb, and As content in rice.

[0104] Experimental results showed that when the mixing ratio was 8:2, the reduction rate of heavy metal content in leaves and rice was the highest. The reduction rate of cadmium in leaves reached 74.74%, lead in leaves reached 80.25%, and arsenic in leaves reached 64.14%; the reduction rate of cadmium in rice reached 75.00%, lead in rice reached 81.58%, and arsenic in rice reached 65.71%. This had a significant effect on reducing the content of the three heavy metals in leaves and rice, and the reduction effect was better than other mixing ratios. This indicates that only when the ratio of rice straw to chicken manure is 8:2 can the optimal effect of reducing heavy metal content be achieved.

[0105] Example 4: Optimization of Biochar Material Preparation Process 1. Pyrolysis temperature For the optimization test of pyrolysis temperature in the preparation of biochar, four sets of temperatures were set: pyrolysis final temperature of 500℃, 600℃, 700℃ and 800℃. The other preparation methods are the same as in Example 1. The effect of pyrolysis temperature on biochar performance and microbial loading effect was tested by the method in Example 2. The experimental results are shown in Table 14.

[0106] Table 14 Effects of different pyrolysis final temperatures on biochar performance and microbial loading.

[0107] Under fixed raw material ratios and grinding methods, when the final pyrolysis temperature is increased from 500℃ to 700℃, the specific surface area increases significantly by approximately 62.3%, and the total pore volume increases by approximately 63.5%. The increase in pyrolysis temperature promotes the complete decomposition and carbonization of lignin, further develops the pore structure, and simultaneously increases the microbial loading. However, with further increases in temperature, when the final pyrolysis temperature rises from 700℃ to 800℃, the specific surface area and total pore volume of the biochar material do not change significantly. Therefore, a final pyrolysis temperature of 700℃ is preferred.

[0108] The contents of Cd, Pb and As in leaves and rice were determined by inductively coupled plasma mass spectrometry (ICP-MS) as described in Example 2. The experimental results are shown in Tables 15 and 16.

[0109] Table 15 Effects of different pyrolysis final temperatures on the Cd, Pb, and As contents in leaves

[0110] Table 16 Effects of different pyrolysis final temperatures on the Cd, Pb, and As content in rice.

[0111] Experimental results showed that when the final pyrolysis temperature increased from 500℃ to 700℃, the content of the three heavy metals in leaves and rice gradually decreased. When the final pyrolysis temperature was 700℃, the reduction rate of heavy metal content in leaves and rice was the highest. The reduction rate of cadmium in leaves reached 74.74%, lead in leaves reached 80.25%, and arsenic in leaves reached 64.14%. The reduction rate of cadmium in rice reached 75.00%, lead in rice reached 81.58%, and arsenic in rice reached 65.71%. When the temperature was further increased to 800℃, the content of the three heavy metals did not change significantly. Therefore, the preferred final pyrolysis temperature is 700℃.

[0112] 2. Grinding steps For the optimization test of grinding method, four methods were set: no grinding (only preliminary crushing through a 100-mesh sieve), ball milling for 30 min, ball milling for 60 min, and ball milling for 90 min. The other preparation methods are the same as in Example 1. The effect of grinding method on biochar performance and microbial loading effect was investigated by the method in Example 2. The experimental results are shown in Table 17.

[0113] Table 17 Effects of different grinding conditions on biochar performance and microbial loading capacity

[0114] Experimental results showed that ball milling significantly affected the particle size and specific surface area of ​​biochar. When the ball milling time increased from 30 min to 60 min, the longer the milling time, the smaller the particle size, the larger the specific surface area, and the higher the microbial load. This indicates that refining the particle size and increasing the specific surface area can provide more attachment sites for microorganisms, thereby increasing the loading. However, when the ball milling time was further increased, there was no significant change in particle size, specific surface area, or microbial load. Therefore, ball milling for 60 min is the preferred grinding method.

[0115] The contents of Cd, Pb and As in leaves and rice were determined by inductively coupled plasma mass spectrometry (ICP-MS) as described in Example 2. The experimental results are shown in Tables 18 and 19.

[0116] Table 18 Effects of different grinding conditions on the Cd, Pb, and As contents in the blades

[0117] Table 19 Effects of different grinding conditions on the Cd, Pb, and As content in rice

[0118] Experimental results showed that when the ball milling time increased from 30 min to 60 min, the content of the three heavy metals in the leaves and rice gradually decreased. When the ball milling time was 60 min, the reduction rate of heavy metal content in the leaves and rice was the highest. The reduction rate of cadmium in the leaves reached 74.74%, the reduction rate of lead in the leaves reached 80.25%, and the reduction rate of arsenic in the leaves reached 64.14%. The reduction rate of cadmium in rice reached 75.00%, the reduction rate of lead in rice reached 81.58%, and the reduction rate of arsenic in rice reached 65.71%. When the ball milling time was further increased, the content of the three heavy metals did not decrease further. Therefore, the preferred grinding method is ball milling for 60 min.

[0119] Example 5: Optimized screening of other auxiliary materials during the grinding process The auxiliary materials added during the grinding process were screened, and calcium carbonate, calcium chloride, silicate, phosphate or a combination thereof were selected to be added during the grinding process. Sodium metasilicate was used for silicate and disodium hydrogen phosphate was used for phosphate. The other experimental methods were the same as in Example 1. The agronomic traits were detected by the method in Example 2 and the fertility compensation effect of each group was evaluated.

[0120] The fertility compensation effect of the biochar materials prepared by adding different auxiliary substances during the grinding process is evaluated in Table 20.

[0121] Table 20 Effects of different auxiliary substances on fertility compensation effect

[0122] As shown in Table 20, the experimental results indicate that the fertility compensation effect is strongest when calcium chloride and phosphate are added during the grinding process. Compared with the group without added auxiliary substances, the yield increases by 0.560 times. The yield increase is significantly better than that of calcium chloride or phosphate alone, as well as the combination after changing any one of the substances in the combination. Furthermore, the yield does not change significantly when other substances are added on the basis of calcium chloride and phosphate. Therefore, adding calcium chloride and phosphate during the grinding process is the optimal choice.

[0123] The contents of Cd, Pb and As in leaves and rice were determined by inductively coupled plasma mass spectrometry (ICP-MS) as described in Example 2. The experimental results are shown in Tables 21 and 22.

[0124] Table 21 Effects of different auxiliary substances on the Cd, Pb, and As contents in leaves

[0125] Table 22 Effects of different auxiliary substances on the Cd, Pb, and As content in rice

[0126] Experimental results showed that when calcium chloride and phosphate were added during the grinding process, the reduction rate of heavy metal content in leaves and rice was the highest. The reduction rates of Cd, Pb, and As reached 74.74% and 75.00%, 80.25% and 81.58%, and 64.14% and 65.71%, respectively. Compared with the group without added auxiliary substances, the heavy metal content was significantly reduced. The effect on reducing heavy metal content was significantly better than adding calcium chloride or phosphate alone or the combination after changing any one of the substances. Furthermore, adding other substances on the basis of calcium chloride and phosphate did not significantly change the heavy metal content. Therefore, adding calcium chloride and phosphate during the grinding process is the optimal choice.

[0127] Example 6: Formulation optimization and screening of composite pore-forming agents The formulation and ratio of the composite pore expander were optimized and screened. Potassium hydroxide, potassium bicarbonate, zinc chloride, phosphoric acid, sodium bicarbonate, potassium carbonate, zinc citrate or combinations thereof were selected as pore expanders for the preparation of biochar materials. The contents of Cd, Pb and As in the leaves and rice were determined by inductively coupled plasma mass spectrometry (ICP-MS) as in Example 2. The experimental results are shown in Tables 23 and 24.

[0128] Table 23 Effects of different pore-expanding agents on the Cd, Pb, and As contents in leaves

[0129] Table 24 Effects of different pore-expanding agents on the Cd, Pb, and As content in rice.

[0130] Experimental results showed that when zinc citrate and potassium carbonate were used as pore expanders, the reduction rate of heavy metal content in leaves and rice was the highest. The reduction rates of Cd, Pb, and As reached 74.74% and 75.00%, 80.25% and 81.58%, and 64.14% and 65.71%, respectively. Compared with the group without pore expanders, the heavy metal content was significantly reduced. The effect on reducing heavy metal content was significantly better than zinc citrate or potassium carbonate alone as pore expanders, as well as the combination of different substances as pore expanders. Furthermore, adding other substances as pore expanders to zinc citrate and potassium carbonate did not significantly change the heavy metal content. Therefore, using zinc citrate and potassium carbonate as pore expanders is the optimal choice.

[0131] Example 7: Screening of Microbial Consortium Species Microorganisms were optimized and screened, and microbial consortia consisting of Bacillus subtilis, Bacillus cereus, Citrobacter, Rawstone's bacterium, Pasteurella multocida, Pseudomonas aeruginosa, Kluyveromyces martensii, and strain combinations were selected for the preparation of biochar-microbial composite barrier materials. The remaining preparation methods were the same as in Example 1. The total number of viable bacteria in all groups was the same, and the ratio of bispecific bacteria was 1:1, the ratio of trispecific bacteria was 4:2:1, the ratio of tetraspecific bacteria was 4:2:1:1, the ratio of pentaspecific bacteria was 4:2:1:1:1, and the ratio of hexaspecific bacteria was 4:2:1:1:1:1. The effects of the method in Example 2 on the accumulation of three heavy metals in rice leaves and rice were detected.

[0132] Table 25 Effects of different microorganisms on the Cd, Pb, and As content in leaves

[0133] Table 26 Effects of different microorganisms on the Cd, Pb, and As content in rice

[0134] The experimental results are shown in Tables 25 and 26. Through optimization and screening of the microbial consortium, the optimal single-combination group was Bacillus subtilis. Based on this, the optimal two-combination group was screened, and the optimal combination was Bacillus subtilis + Bacillus cereus. Based on this two-combination combination, further optimization was carried out, and the optimal four-combination combination was Bacillus subtilis + Bacillus cereus + Citrobacter + Rawlstonella. Further screening with additional bacterial species yielded the optimal five-combination combination: Bacillus subtilis + Bacillus cereus + Citrobacter + Rawlstonella + Pasteurella multocida. The experimental results show that Bacillus subtilis + Bacillus cereus The reduction rates of the three heavy metals in the leaves and rice of the +Citrobacter group were significantly higher than those of the single-strain, dual-strain, and other triple-strain groups, indicating that the triple-strain combination plays a key role in heavy metal adsorption. Further addition of other strains revealed that the group consisting of Bacillus subtilis + Bacillus cereus + Citrobacter + Rawstone's + Pasteurella multocida showed the highest reduction rate of the three heavy metals in the leaves and rice, superior to other quadrivalent, pentavalent, and hexavalent strains. Furthermore, replacing any one of the five strains failed to achieve the same effect, indicating that the pentavalent combination can enhance the heavy metal adsorption capacity of the barrier material.

[0135] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A functionalized biochar for heavy metal blocking, characterized in that, The functionalized biochar is biochar treated with a pore-expanding agent, which has a multi-level pore structure dominated by mesopores, and its surface is simultaneously loaded with acidic oxygen-containing functional groups and basic nitrogen-containing functional groups. The pore size distribution of the mesopores matches the size of the microbial cell.

2. The functionalized biochar as described in claim 1, characterized in that, The pore-expanding agent includes potassium carbonate and zinc citrate.

3. The functionalized biochar as described in claim 2, characterized in that, The mass ratio of potassium carbonate to zinc citrate is in the range of 2:1 to 5:

1.

4. The functionalized biochar as described in claim 1, characterized in that, The functionalized biochar is obtained by pyrolysis and carbonization of biomass raw materials, including rice straw and livestock manure; the mass ratio of rice straw to livestock manure is (7~9):(3~1); the livestock manure is chicken manure or cow manure.

5. The method for preparing functionalized biochar for heavy metal blocking as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Pretreatment: Biomass raw materials are mixed with mineral nutrient sources and pretreated by mechanical grinding to obtain a blended precursor; (2) Gradient pyrolysis carbonization: Under a protective atmosphere, the blended precursor is subjected to gradient heating pyrolysis carbonization to obtain primary carbonization products. (3) Directional pore-expanding modification: The primary carbonization product is activated by high-temperature pore-expanding using a pore-expanding agent to obtain pore-expanded carbon material; (4) Post-processing: The expanded pore carbon material is purified and post-processed to obtain the functionalized porous carbon material.

6. The functionalized biochar for heavy metal blocking as described in any one of claims 1 to 4, characterized in that, The biochar-coupled microbial complex is loaded within the mesoporous channels of the biochar.

7. The functionalized biochar for heavy metal blocking as described in claim 6, characterized in that, The microbial consortium includes Bacillus subtilis, Bacillus cereus, and Citrobacter; Preferably, the concentration ratio of Bacillus subtilis, Bacillus cereus, and Citrobacter in the microbial consortium is 4:2:1 to 3:2:1; Preferably, the microbial complex further includes Rawstone bacteria and urease-producing bacteria; Preferably, the urease-producing bacterium is *Pasteurella pastosifolia*.

8. A method for preparing functionalized biochar for heavy metal blocking as described in any one of claims 6-7, characterized in that, Includes the following steps: (1) The functionalized porous carbon material prepared in claim 5 is added to the microbial consortium suspension and mixed at a solid-liquid ratio of 1:5-1:20 g / mL; (2) The mixture is placed in an ultrasonic processor for ultrasonic-assisted preload processing; (3) Transfer to a constant temperature oscillator for oscillation load; (4) After the loading is completed, sterile filtration is performed to remove the unadsorbed free bacteria on the surface. After low-temperature drying, the material is dried at low temperature until the moisture content is 5%-15%, thus obtaining the biochar-microorganism composite barrier material.

9. An in-situ blocking method for heavy metal contamination in farmland, characterized in that, The method includes the following steps: applying the heavy metal composite barrier material of any one of claims 6 to 7 or the functionalized biochar obtained by the preparation method of claim 8 to the topsoil of farmland.

10. The use of a heavy metal composite barrier material according to any one of claims 1-4, 6-7, or the functionalized biochar obtained by the preparation method of claim 5 or 8 in the preparation of a soil heavy metal adsorbent, wherein the use includes one or more of the following: (1) Improve the heavy metal blocking effect; (2) Improve the blocking rate of heavy metals in deep soil layers; (3) Reduce the bioavailability of heavy metals and the risk of secondary release.

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