Soil amendment based on cyclodextrin and biochar and method for its preparation

Abstract

The application belongs to the technical field of soil remediation, and specifically discloses a soil remediation agent based on cyclodextrin and biochar and a preparation method thereof. The remediation agent is prepared by using biochar as a base carrier, in-situ loading of magnetic nanoparticles, formation of a composite polymer through beta-cyclodextrin, and complexation with 1-(2-pyridylazo)-2-naphthol. The mass ratio of 1-(2-pyridylazo)-2-naphthol to the composite polymer is 1:15-1:25. The soil remediation agent based on cyclodextrin and biochar and the preparation method thereof are used to construct a four-dimensional synergistic remediation system, and the multi-level pore structure improves the adsorption capacity and the specific chelation improves the solidification stability. The average stabilization rate of the composite heavy metal reaches 96.8%, which is 3%-20% higher than that of traditional materials. The heavy metal desorption rate is less than or equal to 2.1%, and the long-acting solidification effect is excellent.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to soil remediation agents based on cyclodextrin and biochar and their preparation methods. Background Technology

[0003] β-Cyclodextrin possesses a unique hydrophobic cavity structure, good biocompatibility, and modifiability. It is often used to prepare insoluble polymer resins via epichlorohydrin crosslinking and is widely applied in the field of pollutant adsorption. However, traditional single β-cyclodextrin polymers have limited specific surface area and simple pore structure, exhibiting only weak physical adsorption and hydroxyl coordination for heavy metal ions. They have poor chelation stability and are highly susceptible to interference from soil pH, organic matter, and ionic strength. Furthermore, the materials cannot be recycled and reused, resulting in high single-use costs, easy soil residue, and limited long-term remediation effects.

[0004] Biochar possesses advantages such as a hierarchical porous structure, ultra-large specific surface area, abundant surface functional groups, inexpensive and readily available raw materials, and environmental friendliness, making it an ideal carrier material for soil remediation. It can immobilize heavy metals through physical adsorption and surface functional group coordination. However, single biochar has weak specific chelation ability for heavy metals and poor remediation selectivity. Magnetic iron oxide nanoparticles possess excellent superparamagnetism, enabling rapid magnetic separation and recovery of materials, solving the industry pain points of residual remediation agents and non-reusability. However, single magnetic particles are prone to agglomeration, have low adsorption capacity, and poor stability.

[0005] Currently, there is no soil remediation solution that combines biochar carriers, magnetic nanoparticles, and β-cyclodextrin polymers. Traditional composite processes suffer from drawbacks such as magnetic particle agglomeration, weak synergistic effects among multiple components, and poor recovery stability. Therefore, this invention innovatively employs an in-situ composite process to construct a synergistic remediation system, addressing the technical pain points of existing materials, such as low adsorption capacity, lack of recyclability, poor stability, weak selectivity, and susceptibility to secondary pollution. Summary of the Invention

[0006] The purpose of this invention is to provide a soil remediation agent based on cyclodextrin and biochar and its preparation method, which solves the problems of low adsorption capacity, weak heavy metal chelation ability, inability to recycle and reuse remediation agents, poor remediation stability, and poor compatibility with composite heavy metals in traditional cyclodextrin materials, and achieves efficient, long-lasting, recyclable, and low-cost solidification and remediation of various soil heavy metals.

[0007] To achieve the above objectives, this invention provides a soil remediation agent based on cyclodextrin and biochar. The agent uses biochar as a substrate carrier, loads magnetic nanoparticles in situ, forms a composite polymer with β-cyclodextrin, and then complexes it with 1-(2-pyridineazo)-2-naphthol. The mass ratio of 1-(2-pyridineazo)-2-naphthol to the composite polymer is 1:15 to 1:25.

[0008] Preferably, the raw materials for biochar synthesis are one or more of the following: corn stalks, sycamore leaves, palm fiber, rice husks, and sawdust.

[0009] Preferably, the magnetic nanoparticles are magnetic iron oxide nanoparticles.

[0010] This invention also provides a method for preparing a soil remediation agent based on cyclodextrin and biochar, comprising the following steps: Step 1, Biochar Pretreatment: Grind and sieve the biochar, then acidify, wash with water, dry and activate it to obtain modified biochar for later use. Step 2, β-cyclodextrin alkaline swelling pretreatment: Add β-cyclodextrin to a 30%~35% sodium hydroxide aqueous solution, add modified biochar, stir at a constant temperature to swell and disperse, and obtain a uniform mixed suspension; Step 3, in-situ loading of magnetic nanoparticles: Iron salt precursor is added to the suspension and stirred at a constant temperature to generate magnetite magnetic nanoparticles in situ, which are uniformly loaded on the surface of the biochar and cyclodextrin system. Step 4, cross-linking polymerization reaction: Epichlorohydrin is slowly added dropwise to the mixed system loaded with magnetic nanoparticles, and cross-linking polymerization is carried out by stirring under controlled temperature. After the reaction is completed, the mixture is cooled, neutralized, filtered, washed, dried, ground and sieved to obtain a magnetic biochar / β-cyclodextrin composite polymer. Step 5, 1-(2-pyridineazo)-2-naphthol host-guest inclusion complexation modification: The composite polymer is dispersed in an ethanol-water mixed solution, and 1-(2-pyridineazo)-2-naphthol powder is added. The mixture is stirred at a constant temperature in the dark to carry out the inclusion reaction. After the reaction is completed, the mixture is centrifuged, washed, and vacuum dried to obtain the target composite repair agent.

[0011] Preferably, in step 1, the biochar is passed through a 100-200 mesh sieve, acidified and soaked in 0.5 mol / L dilute nitric acid for 4-6 hours, washed with deionized water until neutral, and dried at 60°C for 10-12 hours to complete the activation.

[0012] Preferably, in step 2, the ratio of β-cyclodextrin to sodium hydroxide aqueous solution is 1g:4~6mL, the amount of biochar added is 15%~30% of the mass of β-cyclodextrin, the pretreatment temperature is 25~30℃, and the stirring time is 22~26h.

[0013] Preferably, in step 3, the iron salt precursor is a mixture of ferric chloride hexahydrate and ferrous chloride tetrahydrate in a molar ratio of 2:1, the total iron salt mass is 20%~35% of the β-cyclodextrin mass, the reaction temperature is 40~50℃, the reaction is stirred for 1.5~2.5h, and nitrogen protection is maintained throughout the process.

[0014] Preferably, in step 4, the epichlorohydrin dropping rate is 0.8~1.2 mL / min, the polymerization reaction temperature is 55~65℃, and the reaction time is 4~6 h; neutralization is achieved by adjusting the pH to 6.8~7.2 with dilute hydrochloric acid, and washing is performed 3~5 times each with deionized water and anhydrous ethanol.

[0015] Preferably, in step 4, the molar ratio of epichlorohydrin to β-cyclodextrin is 8:1 to 12:1.

[0016] Preferably, in step 5, the volume ratio of ethanol to deionized water in the ethanol-water mixed solution is 3:7~5:5, the dispersion solid-liquid ratio is 1g:8~12mL, the inclusion reaction temperature is 40~50℃, and the stirring time in the dark is 3~5h.

[0017] The advantages and beneficial effects of the above-mentioned soil remediation agent based on cyclodextrin and biochar and its preparation method are as follows: 1. This invention constructs a four-dimensional integrated composite system consisting of a porous biochar carrier, magnetic iron oxide nanoparticles, β-cyclodextrin cavities, and 1-(2-pyridineazo)-2-naphthol (PAN) specific chelation, which breaks through the performance limitations of traditional single-component and two-component materials, and simultaneously achieves efficient adsorption, specific chelation, in-situ enrichment and rapid recovery of heavy metals, thereby achieving a qualitative improvement in remediation performance.

[0018] 2. This invention uses a liquid-phase in-situ synthesis method to load magnetic nanoparticles onto the surface of a biochar-cyclodextrin framework, effectively solving the problem of magnetic particle agglomeration. The particles are uniformly dispersed, firmly bonded, and have strong magnetic stability. They show no significant desorption after multiple cycles and have stable magnetic recovery efficiency.

[0019] 3. This invention relies on the natural multi-level porous structure of biochar and couples the cross-linked pores of cyclodextrin polymer to construct hierarchical interconnected channels, which greatly improves the specific surface area and heavy metal adsorption capacity of the material, provides sufficient active sites for PAN immobilization and heavy metal complexation, and significantly enhances the ability to resist interference from complex soil environments.

[0020] 4. This invention endows the remediation agent with excellent superparamagnetism. After the remediation is completed, it can be quickly separated and recycled by an external magnetic field, solving the problems of soil residue, single use, and secondary pollution of traditional remediation agents. The material has good recyclability and significantly reduces the remediation cost.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a comparison chart of the heavy metal stabilization rates of the embodiments and comparative examples of the present invention; Figure 2 Soil Pb after remediation in embodiments and comparative examples of the present invention 2+Content comparison chart; Figure 3 The soil Cd after remediation in the embodiments and comparative examples of the present invention 2+ Content comparison chart; Figure 4 Soil Cu after remediation in embodiments and comparative examples of the present invention 2+ Content comparison chart; Figure 5 The soil Zn after remediation in the embodiments and comparative examples of the present invention 2+ Content comparison chart. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0025] The following examples are not intended to limit the invention, but are only for illustration. Unless otherwise specified, the experimental methods used in the following examples are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0026] Example 1 The soil remediation agent based on cyclodextrin and biochar is prepared by using biochar as a substrate carrier to load magnetic nanoparticles in situ, forming a composite polymer through β-cyclodextrin, and then complexing it with 1-(2-pyridineazo)-2-naphthol; the mass ratio of 1-(2-pyridineazo)-2-naphthol (PAN) to the composite polymer is 1:15~1:25.

[0027] The raw materials for biochar synthesis are sycamore leaves, corn stalks, and palm fiber.

[0028] The magnetic nanoparticles are magnetic iron oxide nanoparticles.

[0029] The preparation method of soil remediation agent based on cyclodextrin and biochar includes the following steps: Step 1, Biochar Pretreatment: The biochar was pulverized and passed through a 150-mesh standard sieve. It was then acidified with 0.5 mol / L dilute nitric acid at room temperature for 5 hours to remove surface ash and impurities. Subsequently, it was repeatedly washed with deionized water until the washing solution was neutral. It was then dried in a vacuum drying oven at 60℃ for 12 hours, cooled, and sealed for storage to obtain activated modified biochar for later use. This process enriches the oxygen-containing functional groups on the biochar surface, improving its binding stability with cyclodextrin and magnetic particles.

[0030] Step 2, β-Cyclodextrin alkaline swelling pretreatment: Add β-cyclodextrin powder to a 32% NaOH aqueous solution at a material-to-liquid ratio of 1g:5mL, and add activated biochar at a ratio of 22% of the β-cyclodextrin mass. Place the mixture in a 28℃ constant temperature magnetic stirrer and stir at a constant speed of 200r / min for 24h to allow the β-cyclodextrin to fully swell and the hydroxyl groups to be activated. At the same time, the biochar is uniformly dispersed in the system to form a stable and homogeneous suspension mixture.

[0031] Step 3, In-situ loading of magnetic nanoparticles: The system was heated to 45°C and nitrogen gas was introduced throughout the process to prevent oxidation by air. Ferric chloride hexahydrate and ferrous chloride tetrahydrate (molar ratio 2:1) were weighed according to the ratio of the total mass of iron salt to 28% of the mass of β-cyclodextrin and added slowly in batches to the mixed suspension. The mixture was stirred at a constant temperature of 300 r / min for 2 h. Superparamagnetic iron oxide nanoparticles were generated through in-situ co-precipitation reaction and uniformly loaded on the surface of biochar and β-cyclodextrin framework without agglomeration.

[0032] Step 4, Crosslinking Polymerization: The mixture of magnetic particles was heated to 60℃ and stirred at a constant temperature (250 r / min). Epichlorohydrin was slowly added dropwise using a constant pressure dropping funnel at a rate controlled at 1.0 mL / min, with a precise molar ratio of β-cyclodextrin to epichlorohydrin of 1:10. After the addition was complete, the mixture was kept at a constant temperature for 5 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The pH of the system was slowly neutralized to 7.0 using 0.5 mol / L dilute hydrochloric acid, and allowed to settle for 2 h. The solid product was separated by filtration and washed 4 times with deionized water and 3 times with anhydrous ethanol to remove unreacted monomers, residual crosslinking agents, free iron salts, and inorganic salt impurities. The washed solid was dried in a vacuum drying oven at 60℃ for 12 h, ground, and passed through a 100-mesh standard sieve to obtain a black, loose magnetic biochar / β-cyclodextrin composite polymer resin, which was sealed and stored for later use.

[0033] Step 5, 1-(2-pyridineazo)-2-naphthol host-guest inclusion complexation modification: Prepare an anhydrous ethanol-deionized water mixed solvent with a volume ratio of 4:6. Disperse the composite polymer resin in the mixed solvent at a solid-liquid ratio of 1g:10mL and ultrasonically disperse for 10min (300W) to form a uniform suspension. Add PAN powder at a mass ratio of PAN to composite polymer resin of 1:20, seal and protect from light, and stir at 45℃ and 300r / min for 4h to complete the host-guest inclusion complexation reaction. After the reaction, centrifuge at 8000r / min for 10min, collect the solid precipitate, wash twice with anhydrous ethanol to remove unencapsulated free PAN on the surface. Vacuum dry at 45℃ for 8h, grind through a 100-mesh sieve, and finally obtain a black-orange magnetic biochar / β-cyclodextrin polymer-PAN composite repair agent.

[0034] Example 2 Soil remediation agents based on cyclodextrin and biochar are prepared by using biochar as a substrate carrier to load magnetic nanoparticles in situ, forming a composite polymer through β-cyclodextrin, and then complexing it with 1-(2-pyridineazo)-2-naphthol; the mass ratio of 1-(2-pyridineazo)-2-naphthol to the composite polymer is 1:15~1:25.

[0035] The raw materials for biochar synthesis are corn stalks and rice husks.

[0036] The magnetic nanoparticles are magnetic iron oxide nanoparticles.

[0037] The preparation method of soil remediation agent based on cyclodextrin and biochar includes the following steps: Step 1, Biochar Pretreatment: After crushing the biochar, pass it through a 180-mesh standard sieve. Acidify and soak it in 0.5mol / L dilute nitric acid at room temperature for 4 hours to remove ash and impurities from the surface of the biochar. Then wash it repeatedly with deionized water until the washing solution is neutral. Place it in a vacuum drying oven at 60℃ and dry it for 10 hours. After cooling, seal and store it to obtain activated modified biochar for later use.

[0038] Step 2, β-Cyclodextrin alkaline swelling pretreatment: Add β-cyclodextrin powder to a 35% NaOH aqueous solution at a material-to-liquid ratio of 1g:4mL, and add activated biochar at a ratio of 15% of the β-cyclodextrin mass. Place the mixture in a 25℃ constant temperature magnetic stirrer and stir at a constant speed of 200r / min for 22h to allow the β-cyclodextrin to fully swell and the hydroxyl groups to be activated. At the same time, the biochar is uniformly dispersed in the system to form a stable and homogeneous suspension mixture.

[0039] Step 3, In-situ loading of magnetic nanoparticles: The system was heated to 40°C and nitrogen gas was introduced throughout the process to prevent oxidation by air. Ferric chloride hexahydrate and ferrous chloride tetrahydrate (molar ratio 2:1) were weighed according to the ratio of the total mass of iron salt to 33% of the mass of β-cyclodextrin and added slowly in batches to the mixed suspension. The mixture was stirred at a constant temperature of 300 r / min for 1.5 h. Superparamagnetic iron oxide nanoparticles were generated through in-situ co-precipitation reaction and uniformly loaded on the surface of biochar and β-cyclodextrin framework without agglomeration.

[0040] Step 4, Crosslinking Polymerization: The mixture of magnetic particles was heated to 55℃ and stirred at a constant temperature (250 r / min). Epichlorohydrin was slowly added dropwise using a constant pressure dropping funnel at a rate controlled at 1.2 mL / min, with a precise molar ratio of β-cyclodextrin to epichlorohydrin of 1:12. After the addition was complete, the mixture was kept at a constant temperature for 6 hours for polymerization. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The pH of the system was slowly neutralized to 7.2 using 0.5 mol / L dilute hydrochloric acid, and allowed to settle for 2 hours. The solid product was separated by filtration and washed 5 times with deionized water and 3 times with anhydrous ethanol to remove unreacted monomers, residual crosslinking agents, free iron salts, and inorganic salt impurities. The washed solid was dried in a vacuum drying oven at 60℃ for 12 hours, ground, and passed through a 100-mesh standard sieve to obtain the magnetic biochar / β-cyclodextrin composite polymer resin, which was then sealed and stored for later use.

[0041] Step 5, 1-(2-pyridineazo)-2-naphthol host-guest inclusion complexation modification: Prepare an anhydrous ethanol-deionized water mixed solvent with a volume ratio of 5:5. Disperse the composite polymer resin in the mixed solvent at a solid-liquid ratio of 1g:12mL and ultrasonically disperse for 10min (300W) to form a uniform suspension. Add PAN powder at a mass ratio of PAN to composite polymer resin of 1:20, seal and protect from light, and stir at 40℃ and 300r / min for 5h to complete the host-guest inclusion complexation reaction. After the reaction, centrifuge at 8000r / min for 10min, collect the solid precipitate, wash twice with anhydrous ethanol to remove unencapsulated free PAN on the surface. Vacuum dry at 45℃ for 8h, grind through a 100-mesh sieve, and finally obtain the magnetic biochar / β-cyclodextrin polymer-PAN composite repair agent.

[0042] Example 3 Soil remediation agents based on cyclodextrin and biochar are prepared by using biochar as a substrate carrier to load magnetic nanoparticles in situ, forming a composite polymer through β-cyclodextrin, and then complexing it with 1-(2-pyridineazo)-2-naphthol; the mass ratio of 1-(2-pyridineazo)-2-naphthol to the composite polymer is 1:15~1:25.

[0043] The raw material for the synthesis of biochar is sawdust.

[0044] The magnetic nanoparticles are magnetic iron oxide nanoparticles.

[0045] The preparation method of soil remediation agent based on cyclodextrin and biochar includes the following steps: Step 1, Biochar Pretreatment: After crushing the biochar, pass it through a 110-mesh standard sieve. Acidify and soak it in 0.5mol / L dilute nitric acid at room temperature for 6 hours to remove ash and impurities from the surface of the biochar. Then wash it repeatedly with deionized water until the washing solution is neutral. Place it in a vacuum drying oven at 60℃ and dry it for 12 hours. After cooling, seal and store it to obtain activated modified biochar for later use.

[0046] Step 2, β-Cyclodextrin alkaline swelling pretreatment: Add β-cyclodextrin powder to a 30% NaOH aqueous solution at a material-to-liquid ratio of 1g:6mL, and add activated biochar at a ratio of 30% of the β-cyclodextrin mass. Place the mixture in a 25℃ constant temperature magnetic stirrer and stir at a constant speed of 200r / min for 26h to allow the β-cyclodextrin to fully swell and the hydroxyl groups to be activated. At the same time, the biochar is uniformly dispersed in the system to form a stable and homogeneous suspension mixture.

[0047] Step 3, In-situ loading of magnetic nanoparticles: The system was heated to 50°C and nitrogen gas was introduced throughout the process to prevent oxidation by air. Ferric chloride hexahydrate and ferrous chloride tetrahydrate (molar ratio 2:1) were weighed according to the ratio of the total mass of iron salt to 22% of the mass of β-cyclodextrin and added slowly in batches to the mixed suspension. The mixture was stirred at a constant temperature of 300 r / min for 2.5 h. Superparamagnetic iron oxide nanoparticles were generated through in-situ co-precipitation reaction and uniformly loaded on the surface of biochar and β-cyclodextrin framework without agglomeration.

[0048] Step 4, Crosslinking Polymerization: The mixture of magnetic particles was heated to 65℃ and stirred at a constant temperature (250 r / min). Epichlorohydrin was slowly added dropwise using a constant pressure dropping funnel at a rate of 0.8 mL / min, with a precise molar ratio of β-cyclodextrin to epichlorohydrin of 1:8. After the addition was complete, the mixture was kept at a constant temperature for 6 hours for polymerization. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The pH of the system was slowly neutralized to 6.8 using 0.5 mol / L dilute hydrochloric acid, and allowed to settle for 2 hours. The solid product was separated by filtration and washed four times with deionized water and four times with anhydrous ethanol to remove unreacted monomers, residual crosslinking agents, free iron salts, and inorganic salt impurities. The washed solid was dried in a vacuum drying oven at 60℃ for 12 hours, ground, and passed through a 100-mesh standard sieve to obtain the magnetic biochar / β-cyclodextrin composite polymer resin, which was then sealed and stored for later use.

[0049] Step 5, 1-(2-pyridinium azo)-2-naphthol host-guest inclusion complexation modification: Prepare an anhydrous ethanol-deionized water mixed solvent with a volume ratio of 5:6. Disperse the composite polymer resin in the mixed solvent at a solid-liquid ratio of 1g:8mL and ultrasonically disperse for 10min (300W) to form a uniform suspension. Add PAN powder at a mass ratio of PAN to composite polymer resin of 1:15, seal and protect from light, and stir at 50℃ and 300r / min for 3h to complete the host-guest inclusion complexation reaction. After the reaction, centrifuge at 8000r / min for 10min, collect the solid precipitate, wash twice with anhydrous ethanol to remove unencapsulated free PAN on the surface. Vacuum dry at 45℃ for 8h, grind through a 100-mesh sieve, and finally obtain the magnetic biochar / β-cyclodextrin polymer-PAN composite repair agent.

[0050] Comparative Example 1 Commercially available β-cyclodextrin powder was used directly as the repair material.

[0051] Comparative Example 2 Unlike Example 1, this example uses a β-cyclodextrin polymer-PAN repair agent and does not include biochar or magnetic nanoparticles. All other aspects are the same as in Example 1.

[0052] Comparative Example 3 Unlike Example 1, this example only combines biochar and β-cyclodextrin polymer, without loading magnetic particles or undergoing PAN chelation modification. All other aspects are the same as in Example 1.

[0053] Comparative Example 4 Unlike Example 1, this example only loads magnetic particles with a β-cyclodextrin polymer composite, without adding biochar or performing PAN modification. All other aspects are the same as in Example 1.

[0054] Comparative Example 5 Biochar, magnetic iron oxide particles, β-cyclodextrin polymer, and PAN powder were simply physically mixed in the same proportions as in Example 1, without in-situ compounding or isothermal encapsulation processes. All other aspects were consistent with Example 1.

[0055] Comparative Example 6 Only activated biochar was used as the remediation material.

[0056] The performance of the repair agents from Examples 1-3 and Comparative Examples 1-6 was tested. The test results are shown in Tables 1 and 2.

[0057] Topsoil contaminated with complex heavy metals (0-20 cm) from farmland was collected, air-dried, ground, and sieved through a 2 mm sieve to remove impurities such as stones and plant debris, thus preparing the test soil. Initial heavy metal content: Pb 2+ 486.3 mg / kg, Cd 2+2.85 mg / kg, Cu 2+ 212.7 mg / kg, Zn 2+ 358.4 mg / kg, soil texture is loam.

[0058] 100g of test soil was weighed and placed in a petri dish. 5wt% of the remediation agents from each example and comparative example were added, and the mixture was stirred evenly. The soil moisture content was adjusted to 25%, and the soil was cured at room temperature in the dark for 15 days. After curing, the leaching concentration of heavy metals in the soil was determined using the TCLP toxicity leaching method, and the heavy metal stabilization rate was calculated. Simultaneously, the PAN retention rate, magnetic recovery rate, and average remediation efficiency after 5 cycles were measured for each group of materials. Three parallel samples were set up for each experiment, and the average value was taken to eliminate experimental error.

[0059] Table 1 Test Results

[0060] Compared to traditional cyclodextrin-PAN materials that lack biochar and are non-magnetic (Comparative Example 2, stabilization rate 93.9%), the stabilization rate of Example 1 was increased to 96.8% (e.g., ...). Figure 1 As shown in the figure), the repair efficiency of single biochar and single magnetic modified material is much lower than that of the composite system in Example 1, which proves that there is a significant synergistic effect between the multi-level adsorption of biochar, magnetic enrichment, cyclodextrin immobilization and PAN chelation, and it is not a simple superposition of performance.

[0061] The four-component physical hybrid material (Comparative Example 5) had a PAN retention rate of only 71.3% and a repair efficiency of 81.2%, which is far lower than the material prepared by the in-situ composite process in Example 1. This proves that the in-situ loading and covalent / non-covalent composite process of the present invention can effectively improve the component binding stability, avoid the loss of active components, and ensure long-term repair performance.

[0062] The composite remediation agent of this invention has a magnetic recovery rate of up to 96.8%, and the remediation efficiency remains above 89.2% after 5 cycles. In contrast, traditional non-magnetic materials cannot be recycled after a single use and become ineffective directly. This invention completely solves the industry pain points of traditional soil remediation agents, such as single-use, residual pollution, and high cost.

[0063] The introduction of biochar significantly increases the specific surface area and pore utilization of the material, providing more active sites for heavy metal adsorption and PAN immobilization. Compared with the system without biochar, the adsorption capacity and stabilization rate are significantly improved, and the ability to resist interference from complex soil environments is greatly enhanced.

[0064] Under the formulation and process parameters of Example 1, the PAN retention rate, repair efficiency, magnetic recovery performance, and cycle stability of the material are all better than those of Examples 2 and 3, which verifies that the biochar doping amount, magnetic loading amount, and reaction parameters specified in this invention are within the optimal range, and the process has good repeatability and strong parameter controllability.

[0065] Note: All data are averages of 3 parallel experiments. The heavy metal residue content is the content of leached available form by TCLP. The lower the value, the lower the toxicity of heavy metals in the soil and the better the remediation effect. The blank group is the original contaminated soil without any remediation agent.

[0066] After remediation in Example 1, the effective residual amounts of the four heavy metals were significantly reduced, with removal rates exceeding 96% for all four. Compared to traditional cyclodextrin-PAN materials without biochar or magnetism (Comparative Example 2), the residual content of each heavy metal was lower, and the remediation precision was higher. This is far superior to comparative examples such as pure cyclodextrin, pure biochar, and single magnetic materials, fully demonstrating that there is a significant synergistic effect between biochar multi-level adsorption, magnetic enrichment, cyclodextrin immobilization, and PAN chelation, rather than a simple additive effect.

[0067] The residual content of each heavy metal after repair by the four-component physical mixture material (Comparative Example 5) was significantly higher than that in Example 1, especially Pb. 2+ Cd 2+ Cu 2+ Zn 2+ The residual amounts reached 91.99 mg / kg (e.g. Figure 2 As shown), 0.54 mg / kg (as shown) Figure 3 As shown), 39.30 mg / kg (as shown) Figure 4 (as shown), 67.82 mg / kg (as shown) Figure 5 As shown in the figure, the heavy metal stabilization rate is only 81.2%, and the PAN retention rate is only 71.3%. This fully demonstrates that the in-situ loading and integrated composite process of this invention can firmly fix the active components, avoid PAN loss, magnetic particle agglomeration, and desorption failure of each component, and significantly improve the specific chelation and curing effect of heavy metals. Simple physical mixing cannot achieve multi-level synergistic repair effect.

[0068] Example 1 shows that the composite remediation agent has a magnetic recovery rate of up to 96.8%, and the remediation efficiency remains above 89.2% after 5 cycles. The residual heavy metal content in the remediated soil after repeated use is still far lower than that in the comparative examples. In contrast, traditional non-magnetic materials (Comparative Examples 1, 2, 3, and 6) cannot be recycled after a single use and become ineffective directly. After remediation, the heavy metal leaching content is high and prone to rebound. This completely solves the industry pain points of traditional soil remediation agents, such as single use, residual pollution, poor long-term effectiveness, and high cost.

[0069] Compared to the magnetic cyclodextrin system without biochar (Comparative Example 4), the content of four heavy metal residues was significantly reduced after remediation in Example 1, demonstrating that the multi-level porous structure of biochar can effectively increase the specific surface area of ​​the material, enrich free heavy metal ions in the soil, provide sufficient reaction sites for PAN-specific chelation, synergistically reduce the content of available heavy metals in the soil, significantly improve the ability to resist interference from complex soil environments, and has extremely strong adaptability to multiple complex heavy metal pollution.

[0070] Therefore, this invention employs the aforementioned soil remediation agent based on cyclodextrin and biochar and its preparation method to construct a four-dimensional synergistic remediation system. The multi-level porous structure enhances adsorption capacity, and specific chelation improves solidification stability. The average stabilization rate for composite heavy metals reaches 96.8%, an improvement of 3%~20% compared to traditional materials, with a heavy metal desorption rate ≤2.1%, demonstrating excellent long-lasting solidification performance. The in-situ loaded superparamagnetic nanoparticles enable rapid magnetic separation and recovery of the remediation agent, with a room temperature magnetic recovery rate ≥95%. Even after 5 cycles of use, it maintains excellent remediation performance, significantly reducing the cost of soil remediation consumables and avoiding material residue in the soil.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A soil remediation agent based on cyclodextrin and biochar, characterized in that: The composite polymer was prepared by in-situ loading magnetic nanoparticles onto biochar as a substrate carrier, then forming a composite polymer with β-cyclodextrin, and finally complexing it with 1-(2-pyridineazo)-2-naphthol; the mass ratio of 1-(2-pyridineazo)-2-naphthol to the composite polymer was 1:15~1:

25.

2. The soil remediation agent based on cyclodextrin and biochar according to claim 1, characterized in that: The raw materials for biochar synthesis are one or more of the following: corn stalks, sycamore leaves, palm fiber, rice husks, and sawdust.

3. The soil remediation agent based on cyclodextrin and biochar according to claim 1, characterized in that: The magnetic nanoparticles are magnetic iron oxide nanoparticles.

4. The method for preparing the soil remediation agent based on cyclodextrin and biochar according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1, Biochar Pretreatment: Grind and sieve the biochar, then acidify, wash with water, dry and activate it to obtain modified biochar for later use. Step 2, β-cyclodextrin alkaline swelling pretreatment: Add β-cyclodextrin to a 30%~35% sodium hydroxide aqueous solution, add modified biochar, stir at a constant temperature to swell and disperse, and obtain a uniform mixed suspension; Step 3, in-situ loading of magnetic nanoparticles: Iron salt precursor is added to the suspension and stirred at a constant temperature to generate magnetite magnetic nanoparticles in situ, which are uniformly loaded on the surface of the biochar and cyclodextrin system. Step 4, cross-linking polymerization reaction: Epichlorohydrin is slowly added dropwise to the mixed system loaded with magnetic nanoparticles, and cross-linking polymerization is carried out by stirring under controlled temperature. After the reaction is completed, the mixture is cooled, neutralized, filtered, washed, dried, ground and sieved to obtain a magnetic biochar / β-cyclodextrin composite polymer. Step 5, 1-(2-pyridineazo)-2-naphthol host-guest inclusion complexation modification: The composite polymer is dispersed in an ethanol-water mixed solution, and 1-(2-pyridineazo)-2-naphthol powder is added. The mixture is stirred at a constant temperature in the dark to carry out the inclusion reaction. After the reaction is completed, the mixture is centrifuged, washed, and vacuum dried to obtain the target composite repair agent.

5. The method for preparing the soil remediation agent based on cyclodextrin and biochar according to claim 4, characterized in that: In step 1, the biochar is passed through a 100-200 mesh sieve, acidified and soaked in 0.5 mol / L dilute nitric acid for 4-6 hours, washed with deionized water until neutral, and dried at 60℃ for 10-12 hours to complete the activation.

6. The method for preparing the soil remediation agent based on cyclodextrin and biochar according to claim 4, characterized in that: In step 2, the ratio of β-cyclodextrin to sodium hydroxide aqueous solution is 1g:4~6mL, the amount of biochar added is 15%~30% of the mass of β-cyclodextrin, the pretreatment temperature is 25~30℃, and the stirring time is 22~26h.

7. The method for preparing the soil remediation agent based on cyclodextrin and biochar according to claim 4, characterized in that: In step 3, the iron salt precursor is a mixture of ferric chloride hexahydrate and ferrous chloride tetrahydrate in a molar ratio of 2:

1. The total iron salt mass is 20% to 35% of the β-cyclodextrin mass. The reaction temperature is 40 to 50°C, and the reaction is stirred for 1.5 to 2.5 hours under nitrogen protection throughout.

8. The method for preparing the soil remediation agent based on cyclodextrin and biochar according to claim 4, characterized in that: In step 4, the epichlorohydrin dropping rate is 0.8~1.2 mL / min, the polymerization reaction temperature is 55~65℃, and the reaction time is 4~6 h. Neutralization is achieved by adjusting the pH to 6.8~7.2 with dilute hydrochloric acid, and washing is performed 3~5 times each with deionized water and anhydrous ethanol.

9. The method for preparing the soil remediation agent based on cyclodextrin and biochar according to claim 4, characterized in that: In step 4, the molar ratio of epichlorohydrin to β-cyclodextrin is 8:1 to 12:

1.

10. The method for preparing the soil remediation agent based on cyclodextrin and biochar according to claim 4, characterized in that: In step 5, the volume ratio of ethanol to deionized water in the ethanol-water mixed solution is 3:7~5:5, the dispersion solid-liquid ratio is 1g:8~12mL, the inclusion reaction temperature is 40~50℃, and the stirring time is 3~5h in the dark.

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