A modified biochar for remediating long-lasting pesticide contaminated water bodies and soils and a method of making the same

Abstract

The present application belongs to the field of pesticide pollution remediation, and provides a preparation method of modified biochar, comprising the following steps: (1) preparing an alkali solution with a certain volume; (2) weighing plant starch and stirring and dispersing the starch in the alkali solution to obtain a starch dispersion liquid; (3) mixing a crosslinking agent with the remaining alkali solution, and then adding the mixture into the starch dispersion liquid dropwise, and stirring and reacting under constant temperature to obtain a reaction liquid; (4) adding soluble iron salt and alkaline potassium salt into the reaction liquid in sequence, and continuing to stir and react to obtain a mixture; (5) drying the obtained mixture to form a solid; and (6) placing the dried solid into a tube furnace, and pyrolyzing and carbonizing the solid under a nitrogen atmosphere at high temperature, and then performing acid pickling and drying to obtain starch-based modified biochar. The starch-based modified biochar prepared through chemical crosslinking modification and metal salt loading synergistic modification is suitable for remediation of long-acting herbicide contaminated water bodies and soil, and also has the effect of improving soil acidity.

Description

Technical Field

[0001] This invention belongs to the field of pesticide pollution remediation, and particularly relates to a modified biochar for remediating water bodies and soil contaminated by long-acting pesticides and its preparation method. Background Technology

[0002] In recent years, long-acting herbicides have been widely used in agricultural production management due to their strong systemic properties and long residual effect. For example, varieties such as nicosulfuron, imidacloprid, and atrazine can effectively suppress weed growth and increase crop yield. However, these herbicides are difficult to degrade in soil and aquatic environments, easily undergoing leaching and migration, leading to long-term cumulative residues. This damages soil microbial diversity, reduces soil fertility and ecological stability, affects crop rhizosphere health, and poses potential risks to aquatic ecosystems and human health. Therefore, long-acting herbicide pollution has become a crucial issue that urgently needs to be addressed for sustainable agricultural development and environmental safety management.

[0003] Currently, remediation technologies for long-acting herbicide pollution mainly include physical adsorption, chemical degradation, and bioremediation. While physical adsorption is simple to operate, it has limited adsorption capacity, is prone to desorption and re-contamination, and has high waste disposal costs. Chemical oxidation degradation is highly efficient, but the process is expensive, energy-intensive, and may pose a risk of secondary pollution. Bioremediation, while environmentally friendly, has a long cycle and high environmental requirements, making it difficult to rapidly promote and apply in large-scale pollution scenarios.

[0004] Biochar is a porous carbon material prepared by the pyrolysis and carbonization of biomass. It possesses advantages such as large specific surface area, well-developed pore structure, abundant oxygen-containing functional groups on the surface, good chemical stability, wide availability of raw materials, and low cost, and has shown promising application prospects in environmental pollution remediation and soil improvement. Natural biochar mainly removes organic pollutants through mechanisms such as surface adsorption, ion exchange, and complexation. However, its single adsorption capacity and degradation efficiency remain limited for structurally stable and recalcitrant long-acting herbicides.

[0005] Therefore, there is an urgent need to develop a green remediation material that is abundant in resources, low in cost, environmentally friendly, and renewable, which can effectively remove long-lasting herbicide residues and improve soil health at the same time. Summary of the Invention

[0006] This invention aims to address the shortcomings of existing technologies by providing a modified biochar for remediating water and soil contaminated by long-acting pesticides, and its preparation method. The starch-based modified biochar prepared by this invention not only efficiently removes pollutants from long-acting herbicides, but also improves soil physicochemical properties by regulating soil pH, providing a porous structure, enhancing cation exchange capacity, providing a habitat for soil microorganisms, and increasing soil microbial activity. This promotes the decomposition of organic pollutants and nutrient transformation, ultimately improving crop health and sustainable agricultural production. Therefore, developing this starch-based modified biochar with synergistic pollution remediation and soil improvement functions has significant research value and practical application prospects.

[0007] To address the above problems, the present invention provides the following technical solution: A method for preparing modified biochar includes the following steps: (1) Prepare a certain volume of alkaline solution; preferably, weigh 60 mg of sodium hydroxide and 1.5 g of sodium chloride and dissolve them in 50 mL of primary water to prepare an alkaline solution; (2) Weigh out the plant starch and stir it into 60-75% of the total volume of the prepared alkaline solution to obtain a starch dispersion. (3) After mixing the crosslinking agent with the remaining alkaline solution, slowly add it dropwise to the starch dispersion above, and stir under constant temperature to carry out the crosslinking reaction to obtain the reaction solution; (4) Add soluble iron salt and basic potassium salt to the above reaction solution in sequence, and continue to stir the reaction for 20-40 min under water bath conditions of 80-90℃ to obtain a mixture; (5) Place the resulting mixture in an electric oven and dry it to form a solid; (6) The dried solid is placed in a tube furnace and pyrolyzed and carbonized at high temperature under nitrogen atmosphere. After cooling, the solid is taken out and acid-washed for 1-3 hours. Then it is washed with deionized water until neutral and finally dried for later use to obtain starch-based modified biochar.

[0008] In the modified biochar preparation method described above, in step (2), the plant starch is selected from one or more of cereal starch, tuber starch, and legume starch. Cereal starches include corn starch, wheat starch, and rice starch; tuber starches include potato starch, cassava starch, and sweet potato starch; and legume starches include pea starch and mung bean starch. Preferably, the plant starch is selected from corn starch. Compared to tuber starch, which contains phosphate groups and is prone to excessive swelling and thickening in alkaline solutions, and wheat starch, which easily forms lipid complexes, corn starch has a suitable linear / branched chain ratio and excellent rheological stability. This not only ensures the uniform dispersion of the crosslinking agent but also eliminates the interference of impurities on the coordination of iron ions. At the same time, its crosslinking backbone exhibits a unique mesoporous derivatization advantage under potassium salt activation, and its pore size distribution is highly matched with the kinetic diameter of the long-acting herbicide macromolecule, thereby significantly improving the adsorption rate and capacity of the material. In the modified biochar preparation method described above, in step (3), the crosslinking agent is selected from one or more of haloalkylene oxides, dihaloalcohols, and other haloalcohols.

[0009] In the modified biochar preparation method described above, in step (3), the crosslinking agent is selected from halogenated epoxy alkanes, specifically epichlorohydrin, epibromopropane, epifluoropropane, and 1,2-epoxy-4-chlorobutane. Most preferably, in step (3), the crosslinking agent is selected from epichlorohydrin. Under these conditions, on the one hand, compared to the defects of carbon-fluorine bonds being extremely difficult to remove and carbon-bromine bonds being easily hydrolyzed by side reactions, epichlorohydrin has better reaction kinetics, achieving efficient and controllable etherification crosslinking under mild alkaline conditions; on the other hand, the glycerol diether bridge structure (-O-CH2-CH(OH)-CH2-O-) formed by its crosslinking enhances the starch's resistance to high-temperature melting collapse while introducing a large number of new secondary hydroxyl groups (-OH) in situ. These newly added polar groups provide abundant and efficient coordination sites for the subsequent complexation deposition of iron ions, thus playing a key synergistic role in the pyrolysis and loading steps. Furthermore, epichlorohydrin, as an inexpensive bulk chemical, significantly improves the economic feasibility of the process.

[0010] In the modified biochar preparation method described above, the crosslinking reaction temperature in step (3) is 40–60℃, and the reaction time is 2–4 h. This invention strictly controls the crosslinking reaction temperature at 40–60℃ and the reaction time at 2–4 h to achieve the optimal balance between reaction kinetics and side reaction inhibition. If the temperature is below 40℃ or the time is less than 2 h, the epichlorohydrin ring-opening etherification is insufficient, resulting in a low crosslinking density, making it impossible to construct a three-dimensional polymer network sufficient to resist subsequent high-temperature carbonization shrinkage. If the temperature is above 60℃ or the time exceeds 4 h, epichlorohydrin will undergo a violent hydrolysis side reaction in an alkaline system to generate glycerol, causing ineffective consumption of the crosslinking agent. Furthermore, excessively high temperatures or excessively long reaction times (>4 h) easily trigger alkaline degradation of starch molecular chains. Therefore, this mild reaction window ensures both the density and stability of the crosslinking network and maximizes the utilization rate of the crosslinking agent, laying a structural foundation for the subsequent formation of a high specific surface area porous carbon skeleton.

[0011] In the modified biochar preparation method described above, in step (4), the soluble iron salt is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate. Preferably, in step (4), the soluble iron salt is selected from ferric chloride hexahydrate, which has significant synergistic modification advantages compared to ferric nitrate and ferric sulfate. First, during the high-temperature carbonization stage, the strong oxidizing properties of nitrate ions easily lead to excessive ablation of the carbon skeleton and pore collapse, while sulfate ions easily induce sulfur poisoning and mask active sites; while chloride ions are not only mild in nature, but can also act as an in-situ pore-forming agent during volatilization, synergistically enriching the hierarchical pore structure of the carbon skeleton, and effectively inhibiting the aggregation of iron nanoparticles at high temperatures. Second, the crystal water inherent in ferric chloride hexahydrate plays a "slow-release permeation" role during the mild drying process, avoiding the rapid crystallization and precipitation of iron salt on the surface, and promoting the deep and uniform colonization of iron ions in the three-dimensional network of cross-linked starch. This excellent dispersibility and structural integrity provide the maximum active center for the efficient adsorption and catalytic degradation of long-acting herbicides in the final material. In the modified biochar preparation method described above, in step (4), the alkaline potassium salt is selected from one or more of potassium carbonate, potassium bicarbonate, and potassium hydroxide. Preferably, in step (4), the alkaline potassium salt is selected from potassium carbonate. Under these conditions, it has multiple synergistic advantages compared to potassium hydroxide and potassium bicarbonate. First, in the metal loading stage, potassium carbonate provides a mild alkaline buffer environment, avoiding the instantaneous and violent precipitation and aggregation of iron ions caused by strong alkalis (such as potassium hydroxide), and realizing the uniform molecular-level deposition of iron-based complexes in the starch network. Second, in the high-temperature carbonization stage, potassium carbonate, as a mild chemical activator, avoids excessive ablation of the carbon skeleton and can precisely etch a highly developed hierarchical porous structure in situ. Finally, the potassium carbonate and its derivatives remaining in the biochar endow the material with a long-lasting and mild alkaline buffering capacity. In practical applications, it can not only efficiently fix pollutants, but also safely and effectively neutralize soil acidity, regulate pH value, and improve the rhizosphere microecology of crops, achieving the dual effects of pollution remediation and soil improvement. In the modified biochar preparation method described above, in step (4), the mass ratio of the soluble iron salt to the alkaline potassium salt is (0.5–1):1. Under this condition, the aim is to achieve a synergistic balance between "high dispersion of metal active sites" and "perfect development of porous carbon framework". If the ratio is less than 0.5:1, excessive potassium salt will cause excessive ablation of the carbon framework and pore collapse at high temperature, and the density of iron-based catalytic active centers will be insufficient, weakening the degradation efficiency; if the ratio is greater than 1:1, the activation and pore-forming power of potassium salt will be insufficient, resulting in a low specific surface area of ​​the material, and the excessive iron source will exceed the confined coordination capacity of the cross-linked network, which will easily cause severe aggregation and blockage of pores at high temperature. At the same time, the residual alkaline buffering capacity of the material will decrease, which is not conducive to the subsequent improvement of soil acidity. Preferably, in step (4), the mass ratio of the soluble iron salt to the alkaline potassium salt is 0.5:1, which maximizes the uniform dispersion of iron nanoparticles and the perfect formation of hierarchical pores.

[0012] In the modified biochar preparation method described above, in step (5), the drying conditions are as follows: the obtained mixture is placed in an electric heating oven at 30-60℃ and dried for 24-48 hours until the moisture is completely evaporated and a dry solid is formed. Under these conditions, the limitations of conventional high-temperature rapid drying that easily damages the microstructure of the material are overcome. First, the slow dehydration at low temperature effectively regulates the crystallization kinetics of the system, avoiding the "surface crusting" and agglomeration of metal salts caused by violent evaporation of moisture, and ensuring that iron ions and potassium ions are deeply and uniformly anchored in the three-dimensional network of cross-linked starch under capillary action. Second, the gentle temperature gradient prevents the tearing and damage of the fragile cross-linked network caused by the boiling of internal moisture, and preserves the rudimentary form of highly interconnected pores. Finally, the treatment for 24-48 hours ensures the complete removal of deep-bound water, fundamentally preventing the "skeleton bursting" and pore collapse caused by the instantaneous vaporization and expansion of moisture during subsequent pyrolysis at 700℃. This drying process, with its extremely low energy consumption, provides an indispensable structural guarantee for the formation of high specific surface area and highly dispersed metal sites. In the modified biochar preparation method described above, step (6) involves heating at a rate of 10°C / min under a nitrogen atmosphere. Under these conditions, the aim is to achieve the optimal thermodynamic balance between the gradual evolution of the carbon skeleton and the metal phase transition. If the heating rate is too fast, the volatiles inside the precursor will be released violently in a short time, and the huge gas pressure will easily cause disordered rupture and pore collapse of the starch crosslinked skeleton. Furthermore, the excessive kinetic energy of iron atoms will easily lead to agglomeration and sintering. If the heating rate is too slow, it will not only significantly increase the time cost and process energy consumption, but also easily lead to secondary deposition of pyrolysis tar and blockage of the pores. The moderate heating rate of 10°C / min ensures that the crosslinked network undergoes a gradual pyrolysis reaction, allowing the volatile gases to escape gently and play a gentle "in-situ pore-forming" role. At the same time, it provides a sufficient reaction window for potassium salt etching and uniform reduction of iron ions. Finally, under the premise of ensuring economy, a modified biochar with a stable skeleton, well-developed pores, and highly dispersed metal sites was successfully constructed.

[0013] In the modified biochar preparation method described above, in step (6), the high-temperature pyrolysis carbonization temperature is 600-800 ℃, and the pyrolysis time is 0.5-2 h. Under these conditions, the thermodynamic equilibrium of carbon skeleton activation, functional group evolution, and metal phase transformation is precisely controlled. If the temperature is below 600 ℃ or the time is insufficient, carbonization and potassium salt activation will be incomplete, making it difficult to develop rich hierarchical pores. If the temperature is above 800 ℃ or the time is too long, it will lead to excessive ablation of the carbon skeleton and collapse of pores, decomposition and loss of a large number of surface polar oxygen-containing functional groups, and it is very easy to cause severe thermal sintering and agglomeration of iron nanoparticles, resulting in a significant reduction in catalytic active sites. Preferably, in step (6), the high-temperature pyrolysis carbonization temperature is 700°C and the pyrolysis time is 1 hour. Under these preferred conditions, not only is the optimal in-situ etching and pore-forming effect of potassium carbonate stimulated and the oxygen-containing defects on the surface preserved to the maximum extent, but also the efficient reduction and extreme dispersion of the iron-based active center are achieved through appropriate thermodynamic conditions. Thus, while ensuring low energy consumption, the material is endowed with the best long-lasting herbicide adsorption and catalytic degradation performance.

[0014] The starch used in this invention is a renewable, inexpensive, and widely available natural high-molecular-weight carbohydrate. It can flexibly utilize agricultural by-product starch or expired commercial starch, achieving the resource utilization of waste. Alkali-catalyzed epichlorohydrin crosslinking modification introduces more hydrophilic and active functional groups, enhancing the stability and functionalization potential of the starch molecular chain. Furthermore, by combining with metal salt complexation deposition, uniformly distributed metal oxide components and a well-developed porous carbon framework are generated during subsequent high-temperature carbonization, significantly increasing the specific surface area, surface functional group content, and metal active sites of the biochar.

[0015] This invention provides a method for preparing modified biochar, using widely available, low-cost, and renewable plant starch as the carbon source. First, under an alkaline catalytic system, epichlorohydrin is used to crosslink with the hydroxyl groups on the starch molecular chain via ring-opening etherification, constructing a stable three-dimensional polymer network. This not only prevents the collapse of the carbon skeleton at high temperatures but also provides abundant steric hindrance and coordination sites for subsequent metal anchoring. Subsequently, ferric chloride hexahydrate and potassium carbonate are introduced. Iron ions achieve uniform colonization through strong complexation with oxygen-containing functional groups. During the high-temperature carbonization stage, potassium carbonate etches the carbon skeleton in situ, generating well-developed hierarchical channels (micro / mesopores) and synergistically inhibiting the aggregation of iron nanoparticles. The resulting multifunctional modified biochar possesses a large specific surface area, abundant polar oxygen-containing defects, and highly dispersed iron-based active centers. In terms of remediation mechanism, this biochar exhibits excellent targeted adsorption and accumulation capabilities for long-acting herbicides such as nicosulfuron, imidazoline, and atrazine through a strong "pore-filling" effect, hydrogen bonding, and π–π interactions. Simultaneously, its iron-active sites promote local redox reactions, accelerating the desorption and degradation of herbicide molecules. Furthermore, its abundant pores and released alkaline buffer components effectively neutralize soil acidity, improve the microecology, and provide a high-quality habitat for crop roots, demonstrating significant application value in agricultural non-point source pollution control and soil health management.

[0016] Based on the same inventive concept, this invention provides modified biochar prepared by the modified biochar preparation method described above.

[0017] Based on the same inventive concept, this invention provides modified biochar prepared by the method described above, or the use of the modified biochar described above, for the remediation of water and soil contaminated by long-acting pesticides. Preferably, the pesticide contamination is any one of nicosulfuron, imidazoline, and atrazine.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention utilizes starch as the main carbon source, which is widely available, inexpensive, and renewable. It can flexibly utilize agricultural by-product starch or commercially available starch that has exceeded its shelf life, thereby achieving high-value utilization of waste resources, reducing production costs, and minimizing environmental burden. Through alkaline-catalyzed epichlorohydrin crosslinking modification, starch molecules are endowed with a good three-dimensional network structure and functional group density, which improves chemical stability and the uniformity of subsequent composite modification, forming a carbon-based precursor with abundant pores, high functional group content, and stable structure, laying the foundation for high-performance environmental remediation materials.

[0019] (2) In the preparation process, ferric chloride hexahydrate and potassium carbonate are introduced. By using synergistic steps such as complexation deposition, ion exchange and high-temperature carbonization, metal ions are highly uniformly distributed and stably embedded in the porous carbon skeleton, which significantly improves the specific surface area, pore structure and metal active site content of biochar, enhances the adsorption and complexation degradation performance of long-acting herbicides, and is conducive to the efficient removal of typical pollutants such as nicosulfuron, imidazoline and atrazine.

[0020] (3) The starch-based modified biochar prepared by the present invention not only has excellent pesticide pollution remediation performance, but also achieves multiple improvement effects in the soil, including increasing cation exchange capacity, buffering soil acidity, adjusting pH value, providing a porous habitat for soil microorganisms, promoting microbial activity and accelerating the decomposition and transformation of organic pollutants, and ultimately improving crop root development and healthy growth.

[0021] (4) The preparation method of the present invention is mild and environmentally friendly, avoids high energy consumption or secondary pollution, is suitable for large-scale production, conforms to the concept of green circular economy, and is an efficient environmental remediation and soil improvement technology that achieves a win-win situation for ecology and economy. It has important application value and promotion prospects. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the surface of the original corn starch biochar material (CS) in Comparative Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the surface of the cross-linked starch biochar material (ECS) of Comparative Example 2 of the present invention; Figure 3 This is a scanning electron microscope image of the surface of the starch-based modified biochar material in Example 1 of the present invention; Figure 4 The kinetic comparison of the adsorption and removal rate of nicosulfuron in water by starch-based modified biochar (FKECS) prepared in Example 1 of this invention with that of Comparative Examples 1 and 2 (CS, ECS) is shown in the figure. Figure 5 This is a comparison chart of the removal rate of nicosulfuron in the soil and the soil pH improvement effect of different treatment groups (CK, CS, FKECS) on the 21st day of remediation in Example 1 of the present invention. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0026] Example 1: A method for preparing modified biochar includes the following steps: (1) Weigh 60 mg of sodium hydroxide and 1.5 g of sodium chloride and dissolve them in 50 mL of primary water to prepare an alkaline solution; (2) Weigh 5g of corn starch and disperse it in 37.5mL of prepared alkaline solution under 50℃ water bath conditions with magnetic stirrer at 100rpm to obtain starch dispersion; (3) Accurately transfer 21 μL of epichlorohydrin and mix it with the remaining alkali solution, then slowly add it dropwise to the starch dispersion above. The dropwise addition is completed within 3 min. Stir the reaction under constant temperature for 3 h to obtain the reaction solution. (4) Add 0.5g of ferric chloride hexahydrate (FeCl3·6H2O) and 1g of potassium carbonate (K2CO3) to the above reaction solution in sequence, and continue to stir the reaction for 30min under a water bath at 90℃ to obtain a mixture; (5) Place the resulting mixture in an electric oven and dry it at 45°C for 24 hours until the moisture is completely evaporated and a solid is formed; (6) The dried solid was placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min under a nitrogen atmosphere. The solid was pyrolyzed and carbonized at 700°C for 1 hour. After cooling, the solid was removed and soaked in 1 mol / L hydrochloric acid solution for 3 hours. Then it was washed with deionized water until neutral and finally dried for later use. Starch-based modified biochar was obtained and named FKECS.

[0027] Comparative Example 1: A method for preparing biochar includes the following steps: (1) Measure 50 mL of Grade I water; (2) Weigh 5g of corn starch and disperse it in 50mL of water at 100rpm under a 50℃ water bath using a magnetic stirrer; (3) Stir the reaction under constant temperature for 3.5 h to obtain the reaction solution; (4) Place the obtained reaction solution in an electric heating oven and dry it at 45°C for 24 hours until the water is completely evaporated and a solid is formed; (5) The dried solid was placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min under a nitrogen atmosphere. The solid was pyrolyzed and carbonized at 700°C for 1 hour. After cooling, the solid was taken out and soaked in 1 mol / L hydrochloric acid solution for 3 hours. Then it was washed with deionized water until neutral and finally dried for later use. The biochar was obtained and named CS.

[0028] Comparative Example 2: A method for preparing biochar includes the following steps: (1) Weigh 60 mg of sodium hydroxide and 1.5 g of sodium chloride and dissolve them in 50 mL of primary water to prepare an alkaline solution; (2) Weigh 5g of corn starch and disperse it in 37.5mL of prepared alkaline solution under 50℃ water bath conditions with magnetic stirrer at 100rpm to obtain starch dispersion; (3) Accurately transfer 21 μL of epichlorohydrin and mix it with the remaining alkali solution, then slowly add it dropwise to the starch dispersion above. The dropwise addition is completed within 3 min. Stir the reaction under constant temperature for 3.5 h to obtain the reaction solution. (4) Place the obtained reaction solution in an electric heating oven and dry it at 45°C for 24 hours until the water is completely evaporated and a solid is formed; (5) The dried solid was placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min under a nitrogen atmosphere. The solid was pyrolyzed and carbonized at 700°C for 1 hour. After cooling, the solid was taken out and soaked in 1 mol / L hydrochloric acid solution for 3 hours. Then it was washed with deionized water until neutral and finally dried for later use. The biochar was obtained and named ECS.

[0029] Test Example 1: Figure 1 This is a scanning electron microscope image of the surface of the original corn starch biochar material (CS) in Comparative Example 1 of this invention. Figure 1 It can be seen that its surface is relatively flat and dense with few pores, indicating that the carbon skeleton structure of the unmodified system is closed and the number of micropores and mesopores is limited.

[0030] Figure 2 This is a scanning electron microscope (SEM) image of the surface of the cross-linked starch biochar (ECS) material in Comparative Example 2 of this invention. Figure 2 It can be seen that obvious lamellar cracks and crevices appear on the surface of the material, and the number of pores increases, indicating that the epichlorohydrin crosslinking reaction promotes the breaking and rearrangement of starch molecular chains, laying the foundation for the formation of a porous carbon skeleton by subsequent pyrolysis.

[0031] Figure 3 This is a scanning electron microscope (SEM) image of the surface of the starch-based modified biochar material in Example 1 of the present invention. Figure 3It can be seen that its surface has a more developed porous structure, forming a three-dimensional interconnected pore network, with a significant increase in sheet-like cracks and open pore size. This fully demonstrates that epichlorohydrin crosslinking and metal salt complex deposition produced a significant synergistic porosification effect during the carbonization process.

[0032] from Figure 1 , Figure 2 , Figure 3 The SEM images clearly show that the modification steps of this invention effectively improve the pore structure of starch-based biochar. The CS sample has fewer and denser pores, while the ECS sample exhibits more delamination and gaps after epichlorohydrin crosslinking. The FKECS sample, under the synergistic modification of epichlorohydrin and metal complexation, displays the richest and most continuous three-dimensional pore network structure. This hierarchical pore structure is beneficial for increasing the specific surface area and the number of exposed functional groups, thereby enhancing the adsorption performance for long-acting herbicide molecules, fully demonstrating the innovation and superiority of the preparation method of this invention.

[0033] Table 1. Specific surface area, pore volume, and average pore diameter of different materials

[0034] Table 1 shows the specific surface area, pore volume, and average pore size of different materials. As can be seen from Table 1, the modification gradually increased the specific surface area and pore volume, while simultaneously regulating the pore size distribution, resulting in a richer and more developed porous structure. The specific surface area of ​​ECS is approximately 47 times that of CS, while that of FKECS is approximately 83 times that of CS. At the same time, the pore volume of FKECS is approximately 65 times higher than that of CS, indicating that the synergistic modification of epichlorohydrin crosslinking and metal complexation effectively constructs a richer porous structure, which is beneficial for improving the adsorption capacity for pollutants.

[0035] Test Example 2: This test example tested the adsorption and removal performance of the starch-based modified biochar (FKECS) prepared in the embodiments of the present invention on long-acting herbicides (taking nicosulfuron as an example) in water, and compared it with the unmodified starch biochar (CS) of Comparative Example 1 and the biochar (ECS) crosslinked only by epichlorohydrin of Comparative Example 2.

[0036] 1. Experimental Method: A simulated polluted water sample with a concentration of 20 mg / L nicosulfuron was prepared. 8 mg of CS, ECS, and FKECS samples were weighed and placed in 50 mL brown glass tubes, and 30 mL of the simulated polluted water sample was added. The pH of the solution was adjusted to 7.0 ± 0.2 with 0.1 mol / L HCl or NaOH solution. The brown glass tubes were placed in a constant-temperature shaker and the reaction was carried out at 25℃ and 180 rpm in the dark. Samples were taken at 10 min, 30 min, 60 min, 120 min, and 240 min of reaction, filtered through a 0.22 μm filter membrane, and the residual concentration of nicosulfuron in the filtrate was determined using high-performance liquid chromatography (HPLC), and the removal rate R was calculated. The removal effects of different materials on nicosulfuron are shown in Table 2.

[0037]

[0038] In the formula: R is the removal rate of nicosulfuron (%); C0 is the initial concentration of nicosulfuron in the water sample (mg / L); C t The residual concentration (mg / L) of nicosulfuron in the filtrate at time t (when the sample was taken) during the reaction.

[0039] Table 2. Removal effect of different materials on nicosulfuron

[0040] 2. Experimental Results and Analysis: Experimental results, as shown in Table 2, indicate that unmodified starch biochar (CS) has limited adsorption capacity for herbicides due to its underdeveloped pore structure, with an equilibrium removal rate of only about 5.3%. While the ECS sample crosslinked only with epichlorohydrin showed an increased specific surface area and a removal rate of approximately 8.5%, its adsorption rate was slow. In contrast, the FKECS prepared in this invention achieved a removal rate of over 94.2% within 60 minutes, demonstrating extremely rapid adsorption kinetics and excellent removal capacity. This is attributed to the synergistic effect of epichlorohydrin crosslinking and metal salt complex deposition, which constructed a well-developed hierarchical pore structure and abundant surface active sites during high-temperature carbonization.

[0041] Example 3: This embodiment investigated the remediation effect of starch-based modified biochar (FKECS) on soil contaminated by long-acting herbicides and its effect on improving the physical and chemical properties of the soil.

[0042] 1. Experimental Method: Topsoil (0-20 cm) from farmland was collected, air-dried, and then sieved through a 2 mm sieve. Nicosulfuron standard was dissolved in HPLC-grade acetonitrile to prepare a 1000 mg / L standard stock solution. Based on the total mass of the experimental soil, the calculated volume of stock solution was accurately transferred, diluted with an appropriate amount of deionized water, and then evenly sprayed onto the soil surface using a sprayer. After continuous mixing and allowing the solvent to evaporate naturally, simulated contaminated soil with an initial contamination concentration of 5 mg / kg was prepared. The contaminated soil was then divided into three treatment groups: CK group: No remediation materials added (natural degradation control); CS group: with 1% (w / w) of unmodified starch biochar from Comparative Example 1; FKECS group: Starch-based modified biochar prepared by adding 1% (w / w) of the starch-based modified biochar prepared in Example 1.

[0043] After thoroughly mixing the soil samples from each group, they were placed in plastic basins, and the soil moisture content was adjusted to 60% of field capacity. The basins were then incubated in the dark at room temperature (25 ± 2 ℃). Samples were taken on days 7, 14, and 21 of incubation. The determination method was as follows: 10.0 g of the soil sample was accurately weighed and placed in a 50 mL polytetrafluoroethylene centrifuge tube. 20 mL of acetonitrile extraction solution containing 1% (v / v) acetic acid was added. The centrifuge tube was placed in a constant-temperature shaker and extracted at 200 rpm for 30 min at room temperature. After extraction, the centrifuge tube was placed in a high-speed refrigerated centrifuge and centrifuged at 4000 rpm for 10 min. The supernatant was accurately aspirated, filtered through a 0.22 μm organic microporous membrane (such as a PTFE membrane), and injected into a vial. Herbicide residues were determined using liquid chromatography-mass spectrometry (LC-MS). Meanwhile, another 10.0 g of soil sample from day 21 was placed in a beaker, and 25.0 mL of deionized water was added (i.e., according to a water-soil liquid-solid ratio of 2.5:1 mL / g). After stirring vigorously for 1 min, the sample was allowed to stand for 30 min, and the soil pH value of the supernatant was measured using a high-precision pH meter.

[0044] Table 3. Degradation and removal of nicosulfuron in soil and changes in soil pH

[0045] 2. Experimental Results and Analysis: As shown in Table 3, under natural conditions (CK group), the long-acting herbicide degrades slowly, with a removal rate of only 25.4% after 21 days, and the soil is acidic (pH 5.2), which is unfavorable for crop growth. Using the CS group (Comparative Example 1), the removal rate after 21 days is only 45.2%, and the soil is also acidic (pH 5.4). However, after adding FKECS, the removal rate on day 21 is as high as 96.2%, significantly better than ordinary biochar (CS group). This indicates that FKECS not only immobilizes pollutants through strong physical adsorption, but its loaded active metal component (Fe) may also participate in the catalytic degradation process, accelerating the elimination of herbicides. Furthermore, after adding FKECS, the soil pH increased from 5.2 to 6.6, effectively neutralizing soil acidity. This is because potassium carbonate (K2CO3) was introduced during the preparation of FKECS, giving the material alkaline buffering capacity. This verifies that the material of this invention has the dual function of improving soil acidity and optimizing the soil microenvironment while remediating pollution.

[0046] Figure 4 This is a kinetic comparison of the adsorption and removal rate of nicosulfuron in water by the starch-based modified biochar (FKECS) prepared in Example 1 of this invention, and Comparative Examples 1 and 2 (CS, ECS), over time. Figure 4 As can be seen from the kinetic comparison of the adsorption and removal rates of nicosulfuron in water by the starch-based modified biochar (FKECS) prepared in Example 1 of this invention with those of Comparative Examples 1 and 2 (CS, ECS), it can be seen that the adsorption kinetics of the unmodified starch biochar (CS) and the cross-linked biochar (ECS) for the herbicide are very slow, with removal rates of only about 5.3% and 8.5% respectively at 240 min. In contrast, the modified biochar (FKECS) prepared in Example 1 exhibits extremely excellent adsorption kinetic characteristics, with the removal rate rapidly jumping to 78.4% within the first 10 min of the reaction, exceeding 94.2% at 60 min, and finally achieving near-complete removal of 98.9% at 240 min. This indicates that the synergistic effect of epichlorohydrin cross-linking and metal salt complex deposition effectively constructs a well-developed hierarchical pore structure and abundant surface active sites, achieving rapid and efficient capture of pollutants.

[0047] Figure 5 This is a comparison chart showing the removal rate of nicosulfuron in the soil and the soil pH improvement effect of different treatment groups (CK, CS, FKECS) on day 21 of remediation in Example 1 of the present invention. Figure 5As can be seen from the comparison chart of the removal rate of nicosulfuron in the soil and the soil pH improvement effect of different treatment groups (CK, CS, FKECS) on the 21st day of remediation in Example 3 of this invention, the degradation of long-acting herbicides is extremely slow under natural control conditions (CK group), with a removal rate of only 25.4% after 21 days. Although the removal rate was increased to 45.2% by adding ordinary starch biochar of Comparative Example 1 (CS group), the remediation effect was still limited. However, the soil with the modified biochar of this invention (FKECS group) showed a removal rate as high as 96.2% on the 21st day, demonstrating a significant advantage in pollution remediation. Meanwhile, from... Figure 5 It can be seen that the FKECS treatment group significantly increased the original acidic soil pH (5.2) to 6.6, effectively neutralizing the soil acidity. This indicates that FKECS not only efficiently immobilizes pollutants, but its loaded metal active components may also participate in the catalytic degradation process.

[0048] It should be noted that the specific embodiments are merely representative examples of the present invention, and the technical solution of the present invention is obviously not limited to the above embodiments, and there can be many variations. Those skilled in the art who obtain the present invention based on its explicit disclosure or without objection from the written description should consider it to be within the scope of protection of this patent.

Claims

1. A method for preparing modified biochar, characterized in that, Includes the following steps: (1) Prepare a certain volume of alkaline solution; (2) Weigh out the plant starch and stir it to disperse it in 60-75% of the total volume of the prepared alkaline solution to obtain a starch dispersion. (3) After mixing the crosslinking agent with the remaining alkaline solution, slowly add it dropwise to the starch dispersion above, and stir under constant temperature to carry out the crosslinking reaction to obtain the reaction solution; (4) Add soluble iron salt and basic potassium salt to the above reaction solution in sequence, and continue to stir the reaction for 20-40 min under water bath conditions of 80-90℃ to obtain a mixture; (5) Place the resulting mixture in an electric oven and dry it to form a solid; (6) The dried solid is placed in a tube furnace and pyrolyzed and carbonized at high temperature under nitrogen atmosphere. After cooling, the solid is taken out and acid-washed for 1-3 hours. Then it is washed with deionized water until neutral and finally dried for later use to obtain starch-based modified biochar.

2. The method for preparing modified biochar according to claim 1, characterized in that, In step (2), the plant starch is selected from one or more of cereal starch, potato starch, and legume starch.

3. The method for preparing modified biochar according to claim 1, characterized in that, In step (3), the crosslinking agent is selected from one or more of haloalkylene oxides, dihaloalcohols, and other haloalcohols.

4. The method for preparing modified biochar according to claim 3, characterized in that, In step (3), the crosslinking agent is selected from haloepoxyalkanes, and the haloepoxyalkanes are any one of epichlorohydrin, epibromopropane, epifluoropropane, and 1,2-epoxy-4-chlorobutane.

5. The method for preparing modified biochar according to claim 1, characterized in that, In step (4), the soluble iron salt is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate.

6. The method for preparing modified biochar according to claim 5, characterized in that, In step (4), the alkaline potassium salt is selected from one or more of potassium carbonate, potassium bicarbonate, and potassium hydroxide.

7. The method for preparing modified biochar according to claim 6, characterized in that, In step (4), the mass ratio of the soluble iron salt to the alkaline potassium salt is (0.5–1):

1.

8. The method for preparing modified biochar according to claim 6, characterized in that, In step (6), the temperature of the high-temperature pyrolysis carbonization is 600-800℃, and the pyrolysis time is 0.5-2 h.

9. Modified biochar prepared by the method for preparing modified biochar according to any one of claims 1-8.

10. The use of the modified biochar prepared by the method of any one of claims 1-8, or the modified biochar as described in claim 9, characterized in that, The intended use is for remediating water bodies and soil contaminated by long-acting pesticides.

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