Preparation method of magnetic magnesium-iron co-modified biochar and application of magnetic magnesium-iron co-modified biochar in lead ion adsorption

Abstract

The application discloses a preparation method of magnetic magnesium-iron co-modified biochar and application of the magnetic magnesium-iron co-modified biochar in lead ion adsorption, and belongs to the technical field of environmental functional materials. The prepared magnetic magnesium-iron co-modified biochar adsorbent can effectively improve the maximum adsorption capacity of biochar for lead ions Pb (II) by increasing the surface roughness of the biochar adsorbent, successfully loading Mg and Fe onto the surface of corn straw, and the biochar has magnetism and excellent separation and recovery performance, can be efficiently recovered from a solution and reused, and the adsorption process follows a quasi-second-order kinetic model and a Langmuir adsorption model; the main mechanism of the adsorption process is electrostatic attraction, H-bond adsorption, pi-pi interaction, surface complexation and ion exchange, the adsorption efficiency for lead ions Pb (II) is effectively improved, and an efficient, low-cost and environment-friendly solution for lead pollution treatment is provided.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, specifically referring to a method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption. Background Technology

[0002] Lead ions (Pb(II)) in water resources are highly toxic, and even trace amounts can cause health problems. Moreover, lead ions are difficult to excrete from the body and have bioaccumulation properties. Long-term exposure can cause headaches, diarrhea, liver disorders, and nervous system damage. Therefore, it is particularly important to adopt green and environmentally friendly methods to remove lead ions from water.

[0003] Methods for removing heavy metals from water include evaporation, adsorption, membrane separation, biological treatment, and chemical precipitation. Among these, adsorption is widely used due to its low cost, ease of operation, and environmental friendliness. Biochar has a strong lead ion adsorption capacity. Biochar made from agricultural waste such as corn stalks has been proven to be a highly efficient, low-cost, and environmentally friendly heavy metal adsorbent. However, traditional biochar adsorption materials suffer from problems such as low specific surface area, underdeveloped pore structure, and insufficient surface functional groups, resulting in insufficient adsorption efficiency for heavy metals. Existing modification technologies mostly use single metal modification, which has limited improvement in adsorption capacity, and the materials are difficult to recycle, easily causing secondary pollution. Summary of the Invention

[0004] In response to the above situation and to overcome the shortcomings of the existing technology, this invention provides a method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption. This method effectively solves the problems of low adsorption efficiency and difficult separation of lead ions in biochar made from corn stalks currently on the market, and provides an efficient, low-cost, and environmentally friendly solution for lead pollution control.

[0005] The technical solution adopted in this invention is as follows: This invention proposes a method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption, comprising the following preparation steps:

[0006] Corn stalks were crushed, washed to remove impurities, dried, ground, and sieved to obtain unmodified biochar (BC). The unmodified biochar was soaked in citric acid, dried, washed until neutral, and then pyrolyzed in a muffle furnace to obtain acid-modified biochar (HBC). The acid-modified biochar was ultrasonically mixed with MgCO3 and Fe3O4, and a modified lignin-silk peptide complex was added. The mixture was then transferred to a high-pressure reactor for high-pressure reaction. The product was washed with anhydrous ethanol and deionized water and dried to obtain magnetic magnesium-iron co-modified biochar (MBC).

[0007] Furthermore, the preparation of the modified lignin-silk peptide complex includes the following steps:

[0008] Silk fibroin was dissolved in LiBr solution, and trypsin was added to hydrolyze and retain the fraction with a molecular weight cutoff of 500-1000 Da. The silk peptide fragments were separated and collected, and then freeze-dried for later use. In a sodium lignin sulfonate-borate buffer solution, ethyl gallate and laccase were added to react and generate a quinone graft structure. ZnCl2 solution was added dropwise to form a blue metal complex precipitate. The resulting product was mixed with deionized water, sonicated at 4°C, and then rapidly freeze-dried to obtain a powdered modified lignin-silk peptide complex.

[0009] Furthermore, the concentration of citric acid is 0.8-1.5 mol / L.

[0010] Furthermore, the citric acid soaking time is 12-36 hours.

[0011] Furthermore, the pyrolysis heating rate of the muffle furnace is 8-15℃ / min.

[0012] Furthermore, the mass ratio of the acid-modified biochar to MgCO3 and Fe3O4 is (3-5):(3-5):1.

[0013] Furthermore, the mass ratio of the trypsin to the substrate is 1:(45-55).

[0014] Furthermore, the molar ratio of ZnCl2 to gallic acid is 1:2.

[0015] Furthermore, the mass ratio of the silk fibroin peptide to the blue metal complex precipitate is 1:(2.5-3.5).

[0016] Furthermore, magnetic magnesium-iron co-modified biochar was added to a lead ion aqueous solution at a mass ratio of 1:1000.

[0017] The beneficial effects achieved by the present invention using the above structure are as follows:

[0018] This paper proposes a method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption. The biochar exhibits a loose, rough and porous structure on its surface, which can remove Pb(II) from aqueous solution. Mg and Fe are loaded on the biochar made from corn straw in the form of oxides, which significantly improves the maximum adsorption capacity for Pb(II).

[0019] The adsorption process of magnetic magnesium-iron co-modified biochar simultaneously follows the pseudo-secondary, intraparticle diffusion, and Langmuir models, indicating that chemisorption on a homogeneous monolayer is the main adsorption mechanism. This biochar achieves Pb(II) adsorption through multiple mechanisms, including electrostatic attraction, H-bond adsorption, π-π interaction, surface complexation, and ion exchange, effectively improving the adsorption efficiency of Pb(II). Furthermore, this biochar is easy to separate and reuse, and can maintain its effectiveness after multiple cycles.

[0020] By adding the modified lignin-silk peptide complex, the grain size of the loaded Mg / Fe oxide is limited to below 60 nm, allowing the metal oxide to form a monolayer covering on the biochar surface, increasing the number of Pb(II) binding sites per unit area, improving structural stability, and thus enhancing the adsorption capacity of biochar for Pb(II). The phenolic hydroxyl groups in lignin are anchored to the crystal face of Fe3O4 through hydrogen bonds, and the sulfonic acid groups generate a negative potential, preventing particle aggregation through electrostatic repulsion. The arginine guanidine groups in the tripeptide sequence of the silk peptide component capture magnesium / iron ions in the solution through strong electrostatic interaction, and the predetermined sites promote uniform nucleation. The phenolic hydroxyl groups (-OH) and carboxyl groups (-COOH) provide additional Pb(II) binding sites, further enhancing the adsorption capacity for Pb(II).

[0021] In summary, this biochar exhibits superior adsorption capacity and excellent regeneration potential, making it a promising, cost-effective, and environmentally friendly Pb(II) adsorbent. Attached Figure Description

[0022] Figure 1 The images show SEM images of a magnetic magnesium-iron co-modified biochar proposed in this invention. Figures a, b, and c are SEM images of unmodified biochar (BC), acid-modified biochar (HBC), and magnetic magnesium-iron co-modified biochar (MBC), respectively. Figures d, e, f, g, h, and i are elemental images of Mg, Al, Fe, C, Ca, and O, respectively.

[0023] Figure 2 This is a bar chart illustrating the effect of biochar dosage on the adsorption capacity of a magnetic magnesium-iron co-modified biochar proposed in this invention.

[0024] Figure 3 This is a fitted curve showing the effect of contact time between the biochar and Pb(II) on Pb(II) in a magnetic magnesium-iron co-modified biochar proposed in this invention.

[0025] Figure 4 The effect of the initial concentration of Pb(II) on the adsorption capacity of a magnetic magnesium-iron co-modified biochar proposed in this invention is shown in (a) and the adsorption isotherm fitting curves of Pb(b, c).

[0026] Figure 5This is a bar chart of the regeneration cycle of magnetic magnesium-iron co-modified biochar proposed in this invention. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1: A method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption.

[0029] To prepare a modified lignin-silk fibroin complex, 10g of silk fibroin was dissolved in 0.1M LiBr solution, and trypsin was added at a mass ratio of 1:45. The mixture was hydrolyzed at 37℃ for 2h, and the molecular weight cutoff of 500-1000 Da was retained. The silk fibroin peptide fragments were separated and collected, and then freeze-dried for later use. In a sodium lignin sulfonate-borate buffer solution, 2g of ethyl gallate and 500U of laccase were added to generate a quinone graft structure. A 0.1M ZnCl2 solution was added dropwise to form a blue metal complex precipitate. 1g of silk fibroin peptide and 2.5g of the blue metal complex precipitate were mixed in deionized water, sonicated at 4℃ for 15min, and then rapidly freeze-dried to obtain a powdered modified lignin-silk fibroin complex.

[0030] Corn stalks were crushed and washed to remove surface impurities, then thoroughly dried at 80℃ to reduce the impact of moisture content on subsequent processes. After drying, they were ground and then sieved through a 60-mesh standard sieve for particle size control, yielding unmodified biochar base material (BC). 20g of the unmodified biochar sample was soaked in a 0.8mol / L citric acid solution for 12 hours. This step effectively activated surface functional groups. The modified material was dried and repeatedly washed until a neutral pH was reached. It was then transferred to a muffle furnace for pyrolysis, with a heating rate of 8℃ / min, and held at a constant temperature of 500℃ for 3 hours to complete the preparation of acid-modified biochar, yielding acid-modified biochar (HBC). In the final stage, 1g of acid-modified biochar was mixed with MgCO3 and 0.3g of Fe3O4, and 2... wt% modified lignin-silk peptide complex was uniformly dispersed by ultrasound for 30 min, and then reacted in a high-pressure reactor at 150℃ for 5 h. The product was thoroughly washed with anhydrous ethanol and deionized water, and finally dried in an oven at 80℃ to obtain magnetic magnesium-iron co-modified biochar (MBC) for subsequent applications.

[0031] Example 2: A method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption.

[0032] To prepare a modified lignin-silk fibroin complex, 10g of silk fibroin was dissolved in 0.1M LiBr solution, and trypsin was added at a mass ratio of 1:50 (enzyme to substrate). The mixture was hydrolyzed at 37℃ for 2h, and the molecular weight cutoff of 500-1000 Da was retained. The silk fibroin peptide fragments were separated and collected, and then freeze-dried for later use. In a sodium lignin sulfonate-borate buffer solution, 2g of ethyl gallate and 500U of laccase were added to generate a quinone graft structure. A 0.1M ZnCl2 solution was added dropwise to form a blue metal complex precipitate. 1g of silk fibroin peptide and 3g of the blue metal complex precipitate were mixed in deionized water, sonicated at 4℃ for 15min, and then rapidly freeze-dried to obtain a powdered modified lignin-silk fibroin complex.

[0033] Corn stalks were crushed and washed to remove surface impurities, then thoroughly dried at 80℃ to reduce the impact of moisture content on subsequent processes. After drying, they were ground and then sieved through a 60-mesh standard sieve for particle size control, yielding unmodified biochar base material (BC). 20g of the unmodified biochar sample was soaked in a 1.2mol / L citric acid solution for 24 hours. This step effectively activated surface functional groups. The modified material was dried and repeatedly washed until a neutral pH was reached. It was then transferred to a muffle furnace for pyrolysis, with a heating rate of 10℃ / min, and held at a constant temperature of 500℃ for 2 hours to complete the preparation of acid-modified biochar, yielding acid-modified biochar (HBC). In the final stage, 1g of acid-modified biochar was mixed with MgCO3 and 0.25g of Fe3O4, and 2... wt% modified lignin-silk peptide complex was uniformly dispersed by ultrasound for 30 min, and then reacted in a high-pressure reactor at 150℃ for 5 h. The product was thoroughly washed with anhydrous ethanol and deionized water, and finally dried in an oven at 80℃ to obtain magnetic magnesium-iron co-modified biochar (MBC) for subsequent applications.

[0034] Example 3: A method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption.

[0035] To prepare a modified lignin-silk fibroin complex, 10g of silk fibroin was dissolved in 0.1M LiBr solution, and trypsin was added at a mass ratio of 1:55. The mixture was hydrolyzed at 37℃ for 2h, and the molecular weight cutoff of 500-1000 Da was retained. The silk fibroin peptide fragments were separated and collected, and then freeze-dried for later use. In a sodium lignin sulfonate-borate buffer solution, 2g of ethyl gallate and 500U of laccase were added to generate a quinone graft structure. A 0.1M ZnCl2 solution was added dropwise to form a blue metal complex precipitate. 1g of silk fibroin peptide and 3.5g of the blue metal complex precipitate were mixed in deionized water, sonicated at 4℃ for 15min, and then rapidly freeze-dried to obtain a powdered modified lignin-silk fibroin complex.

[0036] Corn stalks were crushed and washed to remove surface impurities, then thoroughly dried at 80℃ to reduce the impact of moisture content on subsequent processes. After drying, they were ground and then sieved through a 60-mesh standard sieve for particle size control, yielding unmodified biochar base material (BC). 20g of the unmodified biochar sample was soaked in a 1.5mol / L citric acid solution for 36h. This step effectively activated surface functional groups. The modified material was dried and repeatedly washed until a neutral pH was reached. It was then transferred to a muffle furnace for pyrolysis, with a heating rate of 15℃ / min, and finally held at a constant temperature of 500℃ for 1.5h to complete the preparation of acid-modified biochar, yielding acid-modified biochar (HBC). In the final stage, 1g of acid-modified biochar was mixed with MgCO3 and 0.2g of Fe3O4, and 2... wt% modified lignin-silk peptide complex was uniformly dispersed by ultrasound for 30 min, and then reacted in a high-pressure reactor at 150℃ for 5 h. The product was thoroughly washed with anhydrous ethanol and deionized water, and finally dried in an oven at 80℃ to obtain magnetic magnesium-iron co-modified biochar (MBC) for subsequent applications.

[0037] Comparative Example 1: Corn stalk raw material was crushed and then washed to remove surface impurities. It was then fully dried at 80°C to reduce the impact of the raw material's moisture content on subsequent processes. After drying, it was ground and then sieved through a 60-mesh standard sieve for particle size control to obtain unmodified biochar base material (BC).

[0038] Comparative Example 2: Corn stalk raw material was crushed and then washed to remove surface impurities. It was then fully dried at 80℃ to reduce the impact of raw material moisture content on subsequent processes. After drying, it was ground and then sieved through a 60-mesh standard sieve for particle size control to obtain unmodified biochar base material (BC). 20g of the unmodified biochar sample was soaked in a 1.5mol / L citric acid solution for 36h. This step effectively activated the surface functional groups. The modified material was dried and repeatedly washed until it reached a neutral pH. It was then transferred to a muffle furnace for pyrolysis reaction. The heating rate was set at 15℃ / min, and finally, it was kept at a constant temperature of 500℃ for 1.5h to complete the preparation process of acid-modified biochar and obtain acid-modified biochar (HBC).

[0039] Experimental Example 1: The appearance morphology of the sample was measured using scanning electron microscopy-energy dispersive spectroscopy (SEM-Mapping), and the distribution of the material composition was observed; the surface area and pore structure of the material were measured using a surface area analyzer (BET).

[0040] The results are as follows Figure 1 As shown, compared with unmodified corn stalk biochar, the corn stalk with modified lignin-silk peptide complex has larger pores, a rougher surface, and a larger specific surface area. The elemental diagram shows the presence of Fe and Mg elements, and MgO particles are clearly visible. These results indicate that Mg and Fe were successfully loaded onto the surface of corn stalk, increasing its specific surface area and obtaining more active sites, thereby improving its adsorption capacity for Pb(II).

[0041] Experimental Example 2: 20 mL of a 100 mg / L Pb(II) solution and 0.02 g of adsorbent were placed in a 50 mL Erlenmeyer flask, and the pH was adjusted to 6. Adsorption experiments were conducted using a constant-temperature shaker at 298 K and 180 rpm to investigate the effect of adsorbent dosage (5-50 g / L) on adsorption. After the experiment, samples were taken to measure the Pb(II) concentration. Three average experiments were performed, and the average value was taken. The adsorption capacity (Equation 1) and removal rate (Equation 2) were calculated using the following formulas:

[0042]

[0043] In the formula: R is the removal rate, in %; C0 is the initial concentration of heavy metal, in mg / L; C is the remaining concentration of heavy metal in the solution after adsorption equilibrium, in mg / L; q is the adsorption amount, in mg / g; V is the solution volume, in mL; and m is the mass of the adsorbent, in mg.

[0044] The adsorption capacity of biochar for Pb(II) was tested through intermittent adsorption experiments, and the results are as follows: Figure 2As shown, when the adsorbent dosage increased to 10 mg / L, the adsorption capacity of MBC, HBC, and BC for Pb(II) reached its maximum, at 95.54 mg / g, 71.40 mg / g, and 61.42 mg / g, respectively. Among them, the magnetic magnesium-iron co-modified biochar (MBC) was significantly more effective than unmodified BC and unmodified HBC, indicating that with the increase of adsorbent dosage, the number of active sites increased, significantly improving the removal rate of Pb(II). When the adsorbent dosage continued to increase to 50 mg / L, the adsorption capacity gradually decreased, indicating that at high dosages, adsorbent particle aggregation reduced the surface area. Therefore, it was concluded that magnetic magnesium-iron co-modified biochar (MBC) had the best Pb(II) removal effect, and considering both adsorption capacity and economic cost, 10 mg / L was the optimal dosage.

[0045] Experimental Example 3: 0.02 g of magnetic magnesium-iron co-modified biochar (MBC) was weighed into a 50 mL Erlenmeyer flask, and 20 mL of a 100 mg / L Pb(II) solution was added. The Erlenmeyer flask was placed in a constant temperature shaker at 25 °C with a rotation speed of 180 r / min and a pH of 6. The concentration of Pb(II) was measured by atomic absorption spectrometry at 5, 10, 30, 60, 90, 120 and 150 min. Three average experiments were conducted, and the average value was taken. The adsorption mechanism of modified biochar on Pb(II) was investigated using a pseudo-first-order kinetic model (Equation 3), a pseudo-second-order kinetic model (Equation 4) and an intraparticle diffusion model (Equation 5).

[0046]

[0047]

[0048] In the formula: qt is the amount of heavy metal adsorbed by the modified biochar at time t, in mg / g; t is the adsorption time, in min; k1 is the adsorption rate constant, in min; k2 is the adsorption rate constant, in g / (mg·min); Kdi is the intraparticle diffusion constant, in mg / g·min. 1 / 2 Ci is the boundary layer constant.

[0049] Table 1. Dynamic Fitting Parameters

[0050]

[0051] Adsorption kinetics experiments were conducted to investigate the adsorption capacity of Pb(II) on different biochars using pseudo-first-order kinetics, pseudo-second-order kinetics, and intraparticle diffusion models. Table 1 shows that the R1 value of the pseudo-second-order kinetics is... 2 All values ​​were higher than the pseudo-first-order kinetics, indicating that the adsorption of Pb(II) by biochar products at each stage in this invention was mainly chemisorption; such as Figure 3As shown, the adsorption of Pb(II) by all biochars showed a trend of rapid adsorption followed by equilibrium, and the equilibrium was basically reached within 150 min. All biochars showed adsorption effect, and the adsorption effect showed that MBC was the best, followed by HBC, and BC was the weakest. This indicates that the final product, magnetic magnesium-iron co-modified biochar (MBC), has the best adsorption effect on Pb(II).

[0052] Experimental Example 4: 0.02 g of adsorbent was added to 20 mL of Pb(II) solutions with mass concentrations of 20 mg / L, 40 mg / L, 60 mg / L, 80 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 350 mg / L, 400 mg / L, and 450 mg / L. The solution was shaken at 298 K with pH 6 at 180 r / min for 120 min. After the experiment, samples were taken to measure the concentration of Pb(II). Three average experiments were conducted, and the average value was taken. The results were then fitted using the Langmuir model (Equation 6) and the Freundlich model (Equation 7).

[0053]

[0054] In the formula: qm is the maximum adsorption capacity, in mg / g; KL is the Langmuir adsorption equilibrium constant; KF is the Freundlich adsorption equilibrium constant; and n is the Freundlich constant.

[0055] Table 2 Adsorption isotherm fitting parameters

[0056]

[0057] The experimental data were fitted using the Langmuir isotherm model and the Freundlich isotherm model, such as Figure 4 As shown in Table 2, the Langmuir isotherm model reflects the monolayer adsorption effect of pollutants on homogeneous adsorbents, while the Freundlich isotherm model typically reflects the multilayer adsorption effect of pollutants on homogeneous adsorbents. Both models show good fitting results, with the Langmuir isotherm model showing a higher R-value. 2 The values ​​are all higher than those of the Freundlich isotherm model, indicating that the Langmuir isotherm model can better explain the process of Pb(II) removal from groundwater by biochar, and that this process belongs to homogeneous monolayer chemisorption. According to the Langmuir fitting data, the n values ​​of the three adsorbents are all greater than 1, indicating that each biochar is conducive to the Pb(II) adsorption process. The maximum adsorption capacities of MBC, HBC, and BC for Pb(II) are 578.381 mg / g, 466.078 mg / g, and 364.704 mg / g, respectively, with MBC having a much larger adsorption capacity than HBC and BC. Figure 4As shown, the adsorption of Pb(II) on all biochars increased with the increase of the initial Pb(II) concentration, and then gradually reached a plateau. The maximum adsorption capacity of MBC, HBC and BC for Pb(II) was 253.6 mg / g, 191.2 mg / g and 167.9 mg / g, respectively, which proves that the adsorption effect of magnetic magnesium iron co-modified biochar (MBC) is the best.

[0058] Example 5: The dried adsorbed material was shaken with 0.1 mol / L HCl at room temperature for 30 min, washed with distilled water until neutral, dried, and the adsorption effect was tested again. The adsorption-desorption experiment was repeated five times, and three parallel experiments were conducted. The average value was taken.

[0059] The results of the regeneration experiment are as follows Figure 5 As shown, after five cycles, the adsorption capacity of magnetic magnesium-iron co-modified biochar (MBC) for Pb(II) decreased from 99.51 mg / g to 86.95 mg / g. The rate of decrease in adsorption capacity after the reaction was slow, and it still had a high adsorption capacity after five cycles. The results indicate that magnetic magnesium-iron co-modified biochar has good recyclability.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0061] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A magnetic magnesium-iron co-modified biochar, characterized in that: The preparation of magnetic magnesium-iron co-modified biochar includes the following steps: Corn stalks were crushed, washed to remove impurities, dried, ground, and sieved to obtain unmodified biochar BC. The unmodified biochar was soaked in citric acid, dried, washed until neutral, and then pyrolyzed in a muffle furnace to obtain acid-modified biochar HBC. The acid-modified biochar was ultrasonically mixed with MgCO3 and Fe3O4, and a modified lignin-silk peptide complex was added. The mixture was then transferred to a high-pressure reactor for high-pressure reaction. The product was washed with anhydrous ethanol and deionized water and dried to obtain magnetic magnesium-iron co-modified biochar MBC. The preparation of the modified lignin-silk peptide complex includes the following steps: Silk fibroin was dissolved in LiBr solution, and trypsin was added to hydrolyze and retain the fraction with a molecular weight cutoff of 500-1000 Da. Silk fibroin peptide fragments were separated and collected, and then freeze-dried for later use. In a sodium lignosulfonate-borate buffer solution, ethyl gallate and laccase were added to react and generate a quinone graft structure. ZnCl2 solution was added dropwise to form a blue metal complex. The obtained silk fibroin peptide fragments and the blue metal complex were mixed in deionized water, sonicated at 4°C, and then rapidly freeze-dried to obtain a powdered modified lignin-silk fibroin peptide complex. The molar ratio of ZnCl2 to ethyl gallate is 1:2; The mass ratio of the silk fibroin peptide to the blue metal complex precipitate is 1:

3.

2. The magnetic magnesium-iron co-modified biochar according to claim 1, characterized in that: The concentration of citric acid is 0.8-1.5 mol / L.

3. The magnetic magnesium-iron co-modified biochar according to claim 2, characterized in that: The citric acid soaking time is 12-36 hours.

4. The magnetic magnesium-iron co-modified biochar according to claim 3, characterized in that: The heating rate of the muffle furnace pyrolysis is 8-15℃ / min.

5. The magnetic magnesium-iron co-modified biochar according to claim 4, characterized in that: The mass ratio of the acid-modified biochar to MgCO3 and Fe3O4 is (3-5):(3-5):

1.

6. The magnetic magnesium-iron co-modified biochar according to claim 5, characterized in that: The mass ratio of trypsin to silk fibroin is 1:(45-55).

7. The application of any one of the magnetic magnesium-iron co-modified biochars according to claims 1-6 in lead ion adsorption, characterized in that: Magnetic magnesium-iron co-modified biochar was added to a lead ion aqueous solution at a mass ratio of 1:1000.

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