Preparation method and application of perilla leaf traditional Chinese medicine residue-based charcoal composite material

Abstract

The invention discloses a preparation method and application of a perilla leaf traditional Chinese medicine residue-based charcoal composite material. Belongs to the technical field of soil remediation materials. The method comprises the following three steps: by taking perilla leaf extraction residue as a raw material, performing pretreatment, performing gradient oxygen-limited cracking and preparing a finished product: firstly, air-drying the raw material until the water content is less than or equal to 15%, crushing and sieving with a 2mm sieve; nitrogen is introduced at the speed of 40-60 mL / min to serve as shielding gas, the temperature is increased to 180-220 DEG C at the speed of 8-12 DEG C / min to be cracked for 1-2 h, the temperature is continuously increased to 400-450 DEG C to be cracked for 3-6 h, and the temperature difference of two sections of cracking is larger than or equal And finally, quenching with nitrogen, crushing and sieving with a 0.15 mm sieve to obtain a finished product. The adsorption performance of the prepared biochar composite material on Pb < 2 + > and Cd < 2 + > is remarkably improved; and the preparation process is free of chemical addition, low in raw material cost and suitable for in-situ remediation of Pb < 2 + > and Cd < 2 + > contaminated soil, and resource utilization of the medical solid waste is achieved.

Description

Technical Field

[0001] This invention relates to the field of soil remediation materials technology, and more specifically to a method for preparing and applying a biochar composite material based on perilla leaf medicinal residue. Background Technology

[0002] With the rapid development of industrialization and intensive agriculture, soil heavy metal pollution has become an increasingly serious problem. Among them, Pb 2+ Cd 2+ Due to their high toxicity, poor mobility, and tendency to accumulate in soil over long periods, biochar not only damages soil physicochemical properties and inhibits plant growth and development, but also accumulates through the food chain, posing a serious threat to human health. Currently, biochar has become a research hotspot in the field of heavy metal contaminated soil remediation due to its advantages such as wide availability of raw materials, stable adsorption performance, and environmental friendliness.

[0003] In existing technologies, biochar raw materials used for heavy metal adsorption are mostly concentrated in traditional agricultural waste (such as cow dung, straw, rice husks, etc.), and are mostly prepared using single-temperature pyrolysis or strong acid-base chemical modification processes. These technologies have significant bottlenecks:

[0004] 1. Limited Adsorption Performance: Traditional agricultural waste contains limited amounts of lignin and polyphenolic active precursors. Single-temperature pyrolysis is insufficient to fully enrich oxygen-containing functional groups (phenolic hydroxyl and carboxyl groups), resulting in limited adsorption performance of biochar for Pb. 2+ The adsorption capacity is generally ≤60 mg / g, which is insufficient to meet the remediation needs of moderately to heavily contaminated soils.

[0005] 2. Coexistence of preparation cost and environmental risks: In order to improve adsorption performance, existing technologies often need to introduce chemical activators such as phosphoric acid and potassium hydroxide, which not only increases the preparation cost, but also easily causes secondary pollution due to activator residues.

[0006] 3. Poor batch stability of products: The composition of raw materials such as straw and cow dung fluctuates greatly due to the influence of place of origin and season, resulting in poor consistency of biochar performance and hindering large-scale application.

[0007] The traditional Chinese medicine industry generates tens of thousands of tons of perilla leaf residue annually. Currently, this type of pharmaceutical solid waste is mostly disposed of using extensive methods such as landfill and incineration. This not only occupies a large amount of land resources, but the residual volatile oil components, such as perillaldehyde, may also leach through the leachate, causing secondary pollution to the surrounding soil and water bodies. In fact, perilla leaf residue is rich in rosmarinic acid, flavonoids, and natural calcium and potassium minerals, possessing a natural advantage in preparing high-performance heavy metal adsorption biochar.

[0008] However, existing research on the resource utilization of perilla leaf residue has significant limitations: 1. Incompatible pyrolysis process: Directly applying a single-temperature pyrolysis process cannot effectively remove volatile oil impurities from perilla leaf residue, which can easily cause biochar pore blockage and result in insufficient exposure of oxygen-containing functional groups.

[0009] 2. The advantages of raw material components have not been fully explored: the existing technology has not made specific use of the high calcium characteristics of perilla leaf residue, and cannot enhance the adsorption effect through the precipitation effect of calcium and heavy metal ions. It has also not designed a gradient pyrolysis process to retain the active functional groups derived from rosmarinic acid.

[0010] 3. Deviation in Application Focus: Existing patents and literature mostly focus on the extraction of medicinal components from perilla leaf residue and the adsorption of dye wastewater. There is no evidence of using a gradient oxygen-limited pyrolysis process to prepare perilla leaf-based biochar and applying it to soil Pb removal. 2+ Cd 2+ Reports related to the repair.

[0011] In summary, developing a biochar preparation method that requires no chemical modification, has strong process adaptability, and can fully utilize the resource advantages of Perilla leaf residue is of great significance for promoting the resource utilization of pharmaceutical solid waste and the remediation of heavy metal contaminated soil. Summary of the Invention

[0012] In view of this, the present invention provides a method for preparing and applying a biochar composite material based on perilla leaf medicinal residue.

[0013] To address the bottlenecks in existing biochar preparation technologies, such as low adsorption capacity, reliance on chemical modification, and poor raw material uniformity, and to solve the technical defects in the resource utilization of perilla leaf residue (a traditional Chinese medicine residue), including volatile oil residue clogging pores, easy decomposition of rosmarinic acid at high temperatures, and ineffective utilization of natural calcium and potassium elements, this invention provides a perilla leaf residue-based biochar composite material and its gradient oxygen-limited pyrolysis preparation method. The core design concept of this invention is as follows: 1. A gradient temperature pyrolysis process is adopted to remove volatile oil impurities from perilla leaf residue in a targeted manner, while maximizing the retention of active functional groups.

[0014] 2. Fully utilize the natural high calcium and potassium properties of perilla leaf residue to enhance the adsorption effect of heavy metals through ion exchange and precipitation.

[0015] 3. Achieve green preparation without chemical additives, balancing adsorption performance and environmental safety.

[0016] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing a biochar composite material based on perilla leaf residue includes the following steps: (1) Raw material pretreatment: The residue of perilla leaf extraction is air-dried, crushed and sieved, and the sieve material is collected; (2) Gradient oxygen-limited pyrolysis: The undersize obtained in step (1) is placed in a tube furnace and nitrogen is introduced as a protective gas at a flow rate of 40-60 mL / min; the temperature is increased to 180-220 ℃ at a heating rate of 8-12 ℃ / min and isothermal pyrolysis is carried out for 1-2 h; the same heating rate is maintained and the temperature is increased to 400-450 ℃ and isothermal pyrolysis is carried out for 3-6 h; the temperature difference between the two pyrolysis stages is ≥200 ℃. (3) Cool the pyrolysis products to room temperature, crush them and pass them through a 0.15 mm standard sieve, and collect the sieve residue.

[0017] Furthermore, air-dry until the moisture content is ≤15%, then crush and pass through a 2 mm standard sieve.

[0018] Furthermore, in step (2), the first pyrolysis temperature is 200 ℃ and the second pyrolysis temperature is 420 ℃.

[0019] Furthermore, in step (2), the nitrogen flow rate is 50 mL / min and the heating rate is 10 ℃ / min.

[0020] Furthermore, in step (2), the isothermal time for the first pyrolysis stage is 1.5 h, and the isothermal time for the second pyrolysis stage is 4 h.

[0021] Furthermore, in step (3), the cooling is achieved by rapid cooling with nitrogen.

[0022] Application of the perilla leaf medicinal residue-based biochar composite material prepared by the above method in the remediation of heavy metal contaminated soil.

[0023] Furthermore, the heavy metals are Pb and Cd.

[0024] Furthermore, the application rate is 20~50 t / hm².

[0025] The biochar composite material prepared in this invention is effective against Pb. 2+ Cd 2+ Its high adsorption performance stems from a triple mechanism of action: "pore structure + functional group complexation + mineral synergy". 1. Removal of volatile oils and directional pore construction: Volatile oil impurities such as perillaldehyde are preferentially removed in the low-temperature range of 180~220 ℃, eliminating the risk of pore blockage; pyrolysis in the medium-temperature range of 400~450 ℃ forms a well-developed microporous-mesoporous structure, enabling the material's specific surface area to reach 20~80 m². 2 / g provides ample adsorption sites for heavy metal ions.

[0026] 2. Directed Retention of Active Oxygen-Containing Functional Groups: The gradient pyrolysis temperature range (180~220 ℃ / 400~450 ℃) avoids the drastic decomposition temperature of rosmarinic acid (171~175 ℃). Referring to studies on the thermal stability of phenolic substances (similar phenolic acids to rosmarinic acid typically decompose at 170~180 ℃), the low-temperature range (180~220 ℃) ​​of this invention not only prevents premature decomposition but also promotes the conversion of derivatives into active functional groups such as phenolic hydroxyl and carboxyl groups, resulting in a total oxygen-containing functional group content ≥3.0 mmol / g. Fourier transform infrared spectroscopy (FTIR) analysis shows that the material at 3420 cm⁻¹... -1 (hydroxyl group), 1650 cm -1 A distinct characteristic peak exists at the (carboxyl) group, indicating the adsorption of Pb. 2+ Cd 2+ The subsequent peak shift confirmed that the phenolic hydroxyl and carboxyl groups underwent a complexation reaction with heavy metal ions, thus achieving the target peak for Pb. 2+ Cd 2+ Highly efficient capture.

[0027] 3. Synergistic effect of natural calcium and potassium minerals: During the decomposition process, the calcium and potassium elements in perilla leaf residue are converted into minerals such as CaCO3 and K2CO3. On the one hand, these minerals can regulate soil pH, creating conditions for the precipitation of heavy metal ions; on the other hand, they can react with Pb... 2+ Cd 2+ Stable precipitates such as PbCO3 and CdCO3 are formed, and ion exchange with heavy metal ions occurs through surface hydroxyl groups, thus enhancing the adsorption effect through a dual effect. This mechanism is consistent with the industry consensus that 'mineral-based biochar enhances adsorption through a dual effect of precipitation and ion exchange'.

[0028] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved adsorption performance: The biochar composite material prepared in this invention significantly improves the adsorption performance of Pb. 2+ The adsorption capacity is ≥60 mg / g, which is 3.4% higher than that of traditional wood-based biochar (adsorption capacity of approximately 58 mg / g) in existing technologies; for Cd... 2+ The adsorption capacity is ≥30 mg / g, which is 64.3% higher than that of rice husk biochar (adsorption capacity of about 21.3 mg / g), and can meet the requirements of moderate to severe heavy metal polluted soil (Pb) in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB15618-2018). 2+ Content ≥300 mg / kg, Cd 2+ The remediation requirement is ≥1.5 mg / kg. The model was fitted using a pseudo-second-order kinetic model (R0.05). 2 ≥0.996) and Langmuir isotherm model fitting (R 2(≥0.989), confirming that the adsorption process is mainly chemical adsorption, with significant monolayer adsorption characteristics. This excellent performance is due to the triple action mechanism of "pore structure + functional group complexation + mineral synergy" mentioned above.

[0029] 2. Low production cost and environmentally friendly: The raw material is made from the residue of perilla leaves, a traditional Chinese medicine, which is a solid waste of medicine. This realizes the resource utilization of waste and the raw material cost is close to zero. At the same time, the gradient oxygen-limited pyrolysis process does not require high temperature (400~450 ℃), which reduces the energy consumption by more than 30% compared with the traditional biochar high-temperature carbonization of 600~800 ℃. No chemical activators are added throughout the process, avoiding secondary pollution caused by activator residues. In addition, the small amount of small molecule volatiles generated during the pyrolysis process can be collected by nitrogen purging, with no waste gas emission. The total production cost is ≤600 yuan / ton, which is more than 40% lower than the traditional straw biochar (production cost of about 1000 yuan / ton).

[0030] 3. Strong environmental adaptability: The gradient pyrolysis process can completely decompose the residual medicinal components and volatile oils in perilla leaf residue, with no risk of secondary pollution. After applying this material to soil remediation, the soil pH can be stabilized within the suitable range of 6.5-7.5, without disrupting the soil acid-base balance or affecting subsequent crop growth. Thermodynamic parameters show that the adsorption process ΔG 0 -15~-8 kJ / mol (spontaneous adsorption), ΔH 0 With a heat capacity of -40 to -20 kJ / mol (exothermic reaction), it is suitable for ambient temperature (15 to 35 °C) applications in in-situ soil remediation.

[0031] 4. This application targets the compositional characteristics of Perilla Leaf Residue and precisely removes residual impurities through gradient oxygen-limited pyrolysis. Compared with conventional biochar preparation methods, the adsorption performance is improved by more than 25%, realizing the high-value recycling and utilization of medicinal residue. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0033] Figure 1This is a process flow diagram of the present invention. In the diagram, "180-220℃ pyrolysis (1-2h)" corresponds to the "low-temperature devolatile oil removal" step of the present invention, which can directionally remove volatile oil impurities such as perilla ketone from the residue of perilla leaves; "400-450℃ pyrolysis (3-6h)" corresponds to the "medium-temperature pore formation and functional group preservation" step, which can form a well-developed pore structure and retain active functional groups such as phenolic hydroxyl and carboxyl groups; "40-60mL / min nitrogen" is a protective gas used to prevent the oxidation of raw materials and to promptly remove small molecule volatiles to prevent pore blockage.

[0034] Figure 2 To illustrate the adsorption of Pb by the perilla leaf-based biochar composite material in Experiment 2 of this invention. 2+ FTIR spectra.

[0035] Figure 3 This is a comparison chart of tobacco growth in different treatment groups, as well as the activity of enzymes related to the antioxidant system and the content of MDA in Experiment 3 of this invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0037] Example 1 Preparation of Perilla Leaf Residue-Based Biochar Composite Material 1. Raw material pretreatment: Take the perilla leaf extract residue provided by Hunan Times Sunshine Pharmaceutical Co., Ltd., add deionized water at a solid-liquid ratio of 1:5 (g / mL), stir and rinse 3 times (5 min each time) to remove residual extract and dust on the surface, air dry naturally until the moisture content is 12%, put it into a pulverizer to pulverize and pass it through a 2 mm standard sieve, and collect the sieve material for later use.

[0038] The specific components of the perilla leaf extract residue are: rosmarinic acid ≥ 0.8%, total flavonoids ≥ 1.2%, calcium ≥ 15 mg / g, potassium ≥ 20 mg / g, and lignin 25~30%.

[0039] 2. Gradient oxygen-limited pyrolysis: The pretreated undersize material was evenly spread in a quartz boat (5g / boat), placed in the constant temperature zone of a tube furnace, and nitrogen gas with a purity ≥99.99% was introduced as a protective gas. The furnace was first purged for 30 minutes to remove air, and then the nitrogen flow rate was controlled at 50 mL / min. The temperature was increased to 200 ℃ at a rate of 10 ℃ / min and pyrolyzed at a constant temperature for 1.5 h. The same heating rate was maintained and the temperature was increased to 420 ℃ and pyrolyzed at a constant temperature for 4 h. The temperature difference between the two pyrolysis stages was 220 ℃.

[0040] 3. Preparation of finished product: After pyrolysis, nitrogen gas is introduced to rapidly cool to room temperature. The product is then placed in a pulverizer and pulverized. It is then passed through a 0.15 mm standard sieve, and the sieve material is collected and packaged to obtain the perilla leaf medicinal residue-based biochar composite material.

[0041] Example 2 In step 2, the nitrogen flow rate is adjusted to 40 mL / min, and the rest of the operation is the same as in Example 1.

[0042] Example 3 In step 2, the nitrogen flow rate is adjusted to 60 mL / min, and the rest of the operation is the same as in Example 1.

[0043] Example 4 In step 2, the heating rate is adjusted to 8℃ / min, and the rest of the operation is the same as in Example 1.

[0044] Example 5 In step 2, the heating rate is adjusted to 12℃ / min, and the rest of the operation is the same as in Example 1.

[0045] Example 6 In step 2, the first stage of isothermal pyrolysis lasts for 1 hour, and the remaining operations are the same as in Example 1.

[0046] Example 7 In step 2, the first stage of isothermal pyrolysis lasts for 2 hours, and the remaining operations are the same as in Example 1.

[0047] Example 8 In step 2, the second stage of isothermal pyrolysis lasts for 3 hours, and the remaining operations are the same as in Example 1.

[0048] Example 9 In step 2, the second stage of isothermal pyrolysis lasts for 6 hours, and the remaining operations are the same as in Example 1.

[0049] Comparative Example 1 Step 2 employs a one-step pyrolysis method (heating to 420°C at a heating rate of 10°C / min for 4 hours, without introducing nitrogen, using an air atmosphere), with the remaining operations being the same as in Example 1.

[0050] Comparative Example 2 In step 2, nitrogen gas at a rate of 50 mL / min is introduced as a protective gas, and the temperature is increased to 380°C at a rate of 10°C / min for isothermal pyrolysis for 1.5 h. The temperature is then increased to 480°C at the same rate for isothermal pyrolysis for 4 h. The remaining operations are the same as in Example 1.

[0051] Comparative Example 3 Nitrogen gas was introduced at a rate of 50 mL / min as a protective gas, and the temperature was increased to 420°C at a rate of 10°C / min. The temperature was then maintained for continuous pyrolysis for 5.5 h (consistent with the total pyrolysis time of 1.5 h + 4 h = 5.5 h in Example 1). The remaining operations were the same as in Example 1.

[0052] Comparative Example 4 In step 2, the nitrogen flow rate is adjusted to 30 mL / min, and the rest of the operation is the same as in Example 1.

[0053] Comparative Example 5 In step 2, the heating rate is adjusted to 15℃ / min, and the rest of the operation is the same as in Example 1.

[0054] Comparative Example 6 In step 1, the moisture content of the raw materials is 20%, and the remaining operations are the same as in Example 1.

[0055] Comparative Example 7 In step 3, the sample is passed through a 0.2mm standard sieve; the remaining operations are the same as in Example 1.

[0056] Comparative Example 8 After the pyrolysis in step 3 is completed, the mixture is allowed to cool naturally (nitrogen quenching is cancelled), and the remaining operations are the same as in Example 1.

[0057] Comparative Example 9 Replace the raw material in step 1 with rice husks, and perform the remaining operations as in Example 1.

[0058] The specific contents of the core components of rice husk are: lignin 18~22%, cellulose 30~35%, ash 15~20%, calcium ≤2 mg / g, and potassium 8~12 mg / g.

[0059] Comparative Example 10 In step 2, the nitrogen flow rate is adjusted to 70 mL / min, and the rest of the operation is the same as in Example 1.

[0060] Comparative Example 11 In step 2, the heating rate is adjusted to 14℃ / min, and the rest of the operation is the same as in Example 1.

[0061] Comparative Example 12 Traditional wood biochar (purchased from Zhengzhou Dingyi Environmental Protection Technology Co., Ltd., for control purposes, particle size ≤0.15 mm).

[0062] Experiment 1 I. Physicochemical Performance Testing 1. Test subjects: Biochar composite materials prepared in Examples 1-9 and Comparative Examples 1-12.

[0063] 2. Testing Method: Oxygen-containing functional group content: determined by Boehm titration method, using 0.1 mol / L NaOH, Na2CO3, and NaHCO3 standard solutions respectively, and the total content of phenolic hydroxyl and carboxyl groups was calculated.

[0064] Specific surface area and pore structure: determined by BET nitrogen adsorption-desorption method. Before testing, the sample was degassed at 105 °C for 3 h. Adsorption-desorption experiments were carried out at liquid nitrogen temperature (-196 °C) using nitrogen as adsorbate.

[0065] Mineral element content: The content was determined by inductively coupled plasma mass spectrometry (ICP-MS). The sample was digested by microwave (nitric acid-hydrogen peroxide system, volume ratio 3:1) and then diluted to 25 mL for calcium and potassium content detection.

[0066] II. Heavy Metal Adsorption Performance Test 1. Test subjects: Biochar composite materials prepared in Examples 1-9 and Comparative Examples 1-12.

[0067] 2. Experimental materials: Adsorbent: All adsorbents should be dried at 105 °C for 2 h before use to remove adsorbed water.

[0068] Heavy metal solutions: Analytical grade Pb(NO3)2 and Cd(NO3)2 reagents were used to prepare Pb(NO3)2 and Cd(NO3)2 solutions with an initial concentration of 100 mg / L using deionized water. The pH was adjusted to 5.0 with 0.1 mol / L HNO3 or NaOH.

[0069] Experimental apparatus: constant temperature shaker, ICP-MS, volumetric flasks, stoppered centrifuge tubes, pH meter.

[0070] 3. Experimental methods: Add 0.05 g of each adsorbent to 25 mL of the corresponding heavy metal solution, place in a 25 ℃ constant temperature shaker, and shake at 150 r / min for 24 h until adsorption equilibrium is reached. After adsorption, filter the supernatant through a 0.45 μm filter membrane, determine the remaining heavy metal concentration by ICP-MS, and calculate the adsorption capacity according to the formula. Three parallel experiments were set up for each group, and significance analysis was performed using SPSS software (P<0.05).

[0071] q e =[(C0-C e )×V] / m, where, q e To balance the adsorption capacity, C0 is the initial concentration, C e To achieve equilibrium concentration, V is the solution volume and m is the adsorbent mass.

[0072] III. Test Results Table 1 Performance Test Results

[0073] Table 1 Appendix

[0074] The above results indicate that: The gradient oxygen-limited pyrolysis process parameters, the raw material of perilla leaf medicinal residue, and the soil pH range of 5.0-7.0 in this invention are all crucial to achieving high adsorption performance and remediation effect. Deviation from any step will lead to damage to the pore structure, decomposition of functional groups, or failure of the synergistic mechanism, fully demonstrating that the technical solution of this invention is a precise optimization targeting the core needs.

[0075] Gradient optimization experiments on core parameters such as nitrogen flow rate, heating rate, and pyrolysis time confirmed that the parameter range defined in this invention (nitrogen flow rate 40-60 mL / min, heating rate 8-12 °C / min, first-stage isothermal pyrolysis 1-2 h, second-stage isothermal pyrolysis 3-6 h) is the optimal range balancing adsorption performance, process feasibility, and economy. When the parameters deviate from this range, adsorption performance may decrease due to oxidation residues, pore blockage, or functional group decomposition, or the practical application value may be reduced due to increased energy consumption and cost.

[0076] The biochar composite material based on perilla leaf residue prepared in this invention has a positive effect on Pb. 2+ Cd 2+ The adsorption capacity of Pb is significantly higher than that of wood-based biochar prepared from other materials. 2+ The adsorption capacity was increased by 3.4% compared to traditional wood biochar (58 mg / g) and by 32.7% compared to rice husk biochar (45.2 mg / g); Cd 2+ The adsorption capacity was increased by 118.8% compared to traditional wood biochar (16 mg / g) and by 64.3% compared to rice husk biochar (21.3 mg / g). This advantage stems from a triple mechanism of action: porous structure, functional group complexation, and mineral synergy. The well-developed pores provide ample adsorption sites, phenolic hydroxyl and carboxyl groups complex with heavy metal ions, and calcium and potassium minerals form stable precipitates, all contributing to enhanced adsorption performance. Experiments showed that the adsorption effect was optimal at pH 5.0; adsorption decreased by 15%–20% after pH deviation, confirming the significant impact of pH on adsorption performance.

[0077] Experiment 2 Functional group characterization: Fourier transform infrared spectroscopy (FTIR) was used to analyze the adsorption of Pb on the biochar composite material based on perilla leaf residue prepared in Example 1. 2+ FTIR spectra of (100 mg / L), test range 4000-400 cm⁻¹-1 4 cm resolution -1 The changes in functional groups before and after adsorption were analyzed.

[0078] The results are as follows Figure 2 (To clearly display the hydroxyl group (3420cm)) - ¹), Carboxyl group (1650cm) - The characteristic peak shift (the core analysis object of this experiment) is only truncated to 1500~3500 cm⁻¹. - ¹The key wavenumber range is shown in the figure, with 3420cm. -1 The characteristic peak corresponds to the hydroxyl group (-OH), at 1650 cm⁻¹. -1 The characteristic peak corresponds to the carboxyl group (-COOH), which adsorbs Pb. 2+ The shift in the shape of the last two characteristic peaks confirms the interaction between hydroxyl, carboxyl, and Pb. 2+ Complexation reaction is one of the core mechanisms by which the biochar composite material based on perilla leaf residue of this invention efficiently adsorbs heavy metals.

[0079] Experiment 3 Laboratory potted plant in-situ restoration experiment 1. Experimental Materials Basic soil: Tobacco-specific seedling substrate (provided by Yongzhou Siyuan Agricultural Technology Co., Ltd., suitable for the growth needs of tobacco seedlings, and free from heavy metal pollution).

[0080] Repair materials: Perilla leaf medicinal residue-based biochar composite material prepared in Example 1, rice husk biochar prepared in Comparative Example 9, and traditional wood biochar in Comparative Example 12 (all with particle size ≤0.15 mm). All biochars were dried at 105 °C for 2 h before use to remove adsorbed water.

[0081] Test crop: Tobacco K326 seeds (purity ≥98%, germination rate ≥95%).

[0082] Heavy metal reagents: lead nitrate (analytical grade), cadmium acetate dihydrate (analytical grade).

[0083] Cultivation aids: MS medium, flower pots (15cm×10cm×12cm in diameter and height, with a drip tray at the bottom to prevent leakage).

[0084] 2. Experimental Design and Methods Group design: A total of 6 treatment groups were set up, with 5 replicates in each treatment group, and each pot containing 200g of spare tobacco seedling substrate.

[0085] Control group 1 (CK1): Seedling substrate (free of heavy metal pollution) + no biochar application; Control group 2 (CK2): Seedling substrate + heavy metal pollution (irrigation method) + no biochar application; Control group 3 (CK3): Seedling substrate + heavy metal pollution (irrigation method) + rice husk biochar (application rate 20 t / hm) 2 Based on a matrix bulk density of 1.3 g / cm³ 3 (Converted to 0.2kg of substrate per pot, the application rate per pot is 0.0052g). Control group 4 (CK4): Seedling substrate + heavy metal pollution (irrigation method) + traditional wood biochar (application rate 20 t / hm) 2 (0.0052g per pot) Experimental Group 1 (T1): Seedling substrate + heavy metal pollution (irrigation method) + perilla leaf medicinal residue-based biochar composite material (application rate 20 t / hm). 2 (0.0052g per pot) Experimental Group 2 (T2): Seedling substrate + heavy metal pollution (irrigation method) + perilla leaf medicinal residue-based biochar composite material (application rate 50 t / hm). 2 (0.013g per pot).

[0086] Heavy metal pollution simulation (irrigation method): Prepare heavy metal mother liquor according to the target pollution concentration (Pb). 2+ 200 mg / kg, Cd 2 + Calculate the required volume of mother liquor (50 mg / kg), dilute with deionized water to 200 mL, and evenly pour it into the seedling substrate of each contaminated group (40 mL per pot); the CK1 group is poured with the same amount of deionized water; after pouring, a small amount of deionized water is added every day to maintain the moisture content of the seedling substrate at 60%, and the substrate is balanced at room temperature for 30 days to ensure that the heavy metals are evenly distributed and stable in the seedling substrate.

[0087] Biochar application and sowing: According to the application amount of each group, the different biochars were evenly spread on the surface of the corresponding treatment group's seedling substrate and mixed with a sterile glass rod; CK1 and CK2 groups were mixed simultaneously without biochar application; 5g of MS medium was added to each pot as a nutrient substrate and mixed with the surface seedling substrate again; 3 tobacco K326 seeds were sown in each pot, covered with 0.5cm of sterile seedling substrate, and thoroughly watered (20 mL per pot). After emergence, the seedlings were thinned to 1 strong seedling per pot.

[0088] Greenhouse cultivation: Cultivate in an artificial climate chamber, controlling the temperature at 25±2 ℃, light intensity at 16 h / d (light intensity 30000lx), and relative humidity at 60%~70%, and water regularly with deionized water (10 mL every 3 days to avoid leakage).

[0089] Sampling and Measurement: 60 days after sowing, collect all tobacco-specific seedling substrate from each pot, mix thoroughly, and take a portion of the sample to determine the available Pb in the soil.2+ Cd 2+ Content (using DTPA extraction method: the extract was prepared as 0.005 mol / L DTPA-0.01 mol / L CaCl2-0.1 mol / L TEA buffer, liquid-to-solid ratio 10:1, shaken at 25 ℃ for 2 h, the supernatant was filtered through a 0.45 μm filter membrane and then analyzed by ICP-MS); 90 days after sowing, whole tobacco plants were harvested, and the fresh weight of the aboveground parts of the plants was measured. The tolerance coefficient (biomass of each treatment group / CK1 biomass) was calculated; Cd content of the aboveground parts of the plants was determined by ICP-MS. 2+ Content. Data were analyzed using SPSS 26.0 statistical software for one-way ANOVA, and multiple comparisons were performed using Duncan's new multiple range method (P<0.05). Data are expressed as mean ± standard deviation.

[0090] The methods used in this experiment to determine the activity of enzymes related to the antioxidant system and the content of MDA in tobacco seedlings are industry-standard methods, as detailed below: Superoxide dismutase (SOD): The activity was determined by the nitroblue tetrazolium (NBT) photoreduction method. One enzyme activity unit (U / g) was defined as the amount of enzyme that inhibited NBT photoreduction by 50%.

[0091] Peroxidase (POD): Determined by the guaiacol method, with a change of 0.01 OD470nm per minute as one enzyme activity unit (U / g).

[0092] Polyphenol oxidase (PPO): The activity was determined by the catechol method, with a change of 0.01 OD420nm per minute defined as one enzyme activity unit (U / g).

[0093] Malondialdehyde (MDA): Determined by the thiobarbituric acid (TBA) colorimetric method, and the result is expressed as nmol / g.

[0094] 3. Experimental Results Results chart 2 Figure 3 As shown.

[0095] Table 2 Results of in-situ restoration experiments with potted plants in the laboratory

[0096] 4. Results Analysis Soil remediation effect: Available Pb in soil from each biochar treatment group 2+ Cd 2+ The removal rates were significantly higher than those of the CK2 group, and the effects of the perilla leaf medicinal residue-based biochar composite material treatment groups (T1 and T2) far exceeded those of rice husk biochar (CK3) and traditional wood biochar (CK4). T1 group (20 t / hm) 2 Pb 2+ Cd2+ The removal rates were 50.1% and 57.9% higher than those of the CK3 group, respectively, and the T2 group (50 t / hm) was also higher. 2 The removal rate was further improved to over 78%. This advantage stems from the triple action mechanism of "pore structure + functional group complexation + mineral synergy" mentioned earlier—the well-developed pores adsorb available heavy metals in the soil, phenolic hydroxyl and carboxyl groups complex and fix them, and the CaCO3 and K2CO3 transformed from calcium and potassium minerals further form stable precipitates, all of which together improve the removal rate, proving that the adsorption and remediation performance of the perilla leaf medicinal residue-based biochar composite material is superior.

[0097] Seedling growth recovery: Heavy metal stress significantly inhibited tobacco seedling growth (the aboveground fresh weight of the CK2 group was only 42.1% of that of the CK1 group), while the application of biochar significantly improved seedling growth. The aboveground fresh weight of the T1 group increased by 34.8% and 29.2% compared with the CK3 and CK4 groups, respectively, and the fresh weight of the T2 group was close to that of the uncontaminated CK1 group, with a tolerance coefficient of 0.95. This indicates that the remediated tobacco-specific seedling substrate can significantly alleviate the growth inhibition of tobacco seedlings by heavy metals.

[0098] Seedling safety assurance: The heavy metal content in the aboveground parts of tobacco seedlings in the experimental group was significantly lower than that in the control biochar group. The Cd content in the aboveground parts of seedlings in the T1 group was significantly lower. 2+ The Cd content in group T2 was reduced by more than 60% compared to groups CK3 and CK4. 2+ The content is ≤0.04 mg / kg, indicating that biochar can not only repair the soil, but also effectively inhibit the absorption and accumulation of heavy metals by crop seedlings, providing a safety guarantee for subsequent growth.

[0099] Antioxidant system regulation: The treatment group with perilla leaf residue-based biochar composite material significantly enhanced the activity of antioxidant enzymes (SOD, POD, PPO) in tobacco seedlings, reduced MDA accumulation, and alleviated heavy metal-induced oxidative damage. This is closely related to the antioxidant properties of residual phenolic substances (rosmarinic acid, flavonoids) in perilla leaf residue. Simultaneously, after remediation, the pH of the tobacco-specific seedling substrate in each treatment group remained stable between 6.8 and 7.3, without disrupting the soil acid-base balance, providing a favorable environment for tobacco seedling growth.

[0100] Experiment 4 Adsorption kinetics and thermodynamics core verification 1. Experimental Materials and Methods Adsorbent: The biochar composite material based on perilla leaf residue prepared in Example 1 was dried at 105 °C for 2 h before use to remove adsorbed water.

[0101] Experimental conditions: Pb 2+ / Cd 2+Initial concentration 100 mg / L, solution pH=5.0, adsorbent dosage 0.05 g / 25 mL, constant temperature shaking speed 150 r / min.

[0102] Test methods: Kinetic experiments were conducted to record the residual heavy metal concentrations at different time points (0, 5, 10, 20, 30, 60, 120, 240, 480, 720 min). The adsorption temperature was 25 ℃. Samples taken at each time point were filtered through a 0.45 μm filter membrane and analyzed by ICP-MS. Thermodynamic experiments were conducted at three levels: 25 ℃, 35 ℃, and 45 ℃. The samples were oscillated for 24 h at each temperature until adsorption equilibrium was reached. After equilibrium, the samples were filtered and the concentrations were measured. The data were fitted using a pseudo-second-order kinetic model and a Langmuir isotherm model, and the thermodynamic parameters (ΔG) were calculated. 0 ΔH 0 ΔS 0 ).

[0103] 2. Core Experimental Results Table 3 Adsorption kinetics and thermodynamic results

[0104] 3. Conclusion The present invention relates to the biochar composite material based on perilla leaf residue for the treatment of Pb. 2+ Cd 2+ The adsorption conforms to the pseudo-second-order kinetic model (R). 2 ≥0.996), indicating that adsorption is mainly chemisorption. Combined with the previously mentioned effects of "porosity providing sufficient adsorption sites and calcium-potassium mineral synergistic precipitation," this constitutes a triple adsorption mechanism of "porosity + functional group complexation + mineral synergy." The Langmuir model fitting confirms excellent saturated adsorption capacity (Pb). 2+ ≥61.6 mg / g, Cd 2+ ≥32.7 mg / g). Thermodynamic parameters show ΔG 0 <0 (spontaneous adsorption), ΔH 0 <0 (exothermic reaction) indicates that the adsorption process can proceed spontaneously at room temperature, and that low temperature is more conducive to adsorption, which is fully suitable for the room temperature (15~35 ℃) application scenario of soil in-situ remediation, further confirming the effectiveness of the triple adsorption mechanism.

[0105] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0106] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a biochar composite material based on perilla leaf medicinal residue, characterized in that, Includes the following steps: (1) Raw material pretreatment: The residue of perilla leaf extraction is air-dried, crushed and sieved, and the sieve material is collected; (2) Gradient oxygen-limited pyrolysis: The undersize obtained in step (1) is placed in a tube furnace and nitrogen is introduced as a protective gas at a flow rate of 40-60 mL / min; the temperature is increased to 180-220 ℃ at a heating rate of 8-12 ℃ / min and isothermal pyrolysis is carried out for 1-2 h; the same heating rate is maintained and the temperature is increased to 400-450 ℃ and isothermal pyrolysis is carried out for 3-6 h; the temperature difference between the two pyrolysis stages is ≥200 ℃. (3) Cool the pyrolysis products to room temperature, crush them and pass them through a 0.15 mm standard sieve, and collect the sieve residue.

2. The preparation method according to claim 1, characterized in that, Air dry until the moisture content is ≤15%, then crush and pass through a 2 mm standard sieve.

3. The preparation method according to claim 1, characterized in that, In step (2), the first pyrolysis temperature is 200℃ and the second pyrolysis temperature is 420℃.

4. The preparation method according to claim 1, characterized in that, In step (2), the nitrogen flow rate is 50 mL / min and the heating rate is 10 ℃ / min.

5. The preparation method according to claim 1, characterized in that, In step (2), the isothermal time for the first pyrolysis stage is 1.5 h, and the isothermal time for the second pyrolysis stage is 4 h.

6. The preparation method according to claim 1, characterized in that, In step (3), the cooling is achieved by rapid cooling with nitrogen.

7. The application of the perilla leaf medicinal residue-based biochar composite material prepared by any of the preparation methods described in claims 1-6 in the remediation of heavy metal contaminated soil.

8. The application as described in claim 7, characterized in that, The heavy metals are Pb and Cd.

9. The application as described in claim 7, characterized in that, The application rate is 20~50 t / hm².

Images