Magnetic porous shell-tussah silk functionalized biochar and preparation method thereof

Abstract

This application relates to the field of environmental functional technology and discloses a magnetic porous chitosan-functionalized biochar and its preparation method. The material is prepared by solid-phase synthesis from a pre-carbonized biochar precursor, chitosan, organic acid iron salt, and sodium bicarbonate. The method includes: ball milling the raw materials to obtain an ultrafine composite powder, placing it in a constant temperature and humidity environment for moisture-induced solid-phase aging to allow the components to assemble at the interface; subsequently, subjecting it to restricted pyrolysis and in-situ magnetization under an inert atmosphere, and finally washing and drying to obtain the target product. This invention employs a solid-phase mechanochemical process combined with moisture aging, avoiding pore blockage caused by liquid-phase impregnation and inhibiting nitrogen loss during pyrolysis through coordination. The obtained product has a well-developed mesoporous structure, high nitrogen doping content, and rapid magnetic response characteristics, exhibiting excellent adsorption capacity, kinetic rate, and cycling stability for heavy metals and antibiotics.

Description

Technical Field

[0001] This invention relates to the field of environmental functional technology, specifically to a magnetic porous chitosan-functionalized biochar and its preparation method. Background Technology

[0002] Biochar, due to its porous structure and wide availability of raw materials, is widely used in aquatic environment remediation. However, virgin biochar has a relatively scarce surface functional group, resulting in limited adsorption capacity and selectivity for complex pollutants such as heavy metal ions and antibiotics. In recent years, antibiotic pollution (such as tetracycline) in aquatic environments has become increasingly serious. Compared to the smaller heavy metal ions, antibiotic molecules such as tetracycline have a larger spatial volume, making it difficult for traditional microporous biochar to penetrate the pores, easily leading to steric hindrance. Furthermore, the complex molecular structure of these pollutants necessitates not only extensive pore filling of the material but also an abundance of oxygen- and nitrogen-containing functional groups on the adsorbent surface to achieve specific binding through various mechanisms such as hydrogen bonding, coordination, or π-π stacking effects. Due to the lack of targeted functional groups and suitable mesoporous channels, virgin biochar is ill-suited to meet the demand for efficient antibiotic removal in aquatic environments.

[0003] Utilizing chitosan, a natural polymer rich in amino and hydroxyl groups, to modify the surface of biochar is a common strategy to enhance its adsorption performance for heavy metals and antibiotics. The preparation of chitosan-modified biochar mainly relies on the liquid-phase impregnation method. This process typically involves dissolving chitosan in a dilute acid solvent, mixing it with biochar, impregnating it, and then drying, cross-linking, or pyrolyzing it. This wet process has significant limitations in practical applications. Due to the high viscosity of the chitosan solution, during solvent evaporation, chitosan tends to form a dense gel film or continuous coating on the biochar surface. This physical coating often blocks the abundant micropores and mesopores of the biochar itself, leading to a significant decrease in the specific surface area of ​​the modified material. This pore blockage is particularly detrimental to antibiotic molecules that require large diffusion channels, severely increasing the mass transfer resistance of pollutants diffusing into the material and thus limiting the improvement of adsorption efficiency. Furthermore, the liquid-phase method involves the use of large amounts of acidic solvents and subsequent processing, and the dissolved polymer chains are difficult to achieve uniform and highly dispersed loading on the matrix surface.

[0004] To impart chemical stability to composite materials in water treatment environments, high-temperature pyrolysis is typically required. However, during traditional pyrolysis, the nitrogen-containing functional groups in the chitosan molecular chain exhibit poor thermal stability, readily decomposing at high temperatures and volatilizing into gaseous form. This results in a low nitrogen doping content in the final carbon material, significant loss of active adsorption sites, and a loss of the material's ability to form strong interactions with antibiotic molecules. Furthermore, powdered biochar adsorbents face challenges in solid-liquid separation and high recycling costs in practical applications. While introducing magnetic media can solve the separation problem, existing co-precipitation or simple mixed magnetization processes often lead to the easy aggregation and exposure of magnetic particles. Under acidic regeneration elution conditions, iron components are easily dissolved and lost, thus reducing the adsorbent's cycle life and stability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a magnetic porous chitosan-functionalized biochar and its preparation method, which solves the problem that existing chitosan-modified biochar preparation processes mostly employ liquid-phase impregnation, which has the drawback of chitosan easily gelling and clogging the pores of biochar during solvent removal.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a magnetic porous chitosan-functionalized biochar, which adopts the following technical solution: A magnetic porous chitosan-functionalized biochar is made from the following raw materials in parts by weight: 100 parts of pre-carbonized biochar precursor, 50-150 parts of chitosan powder, 40-80 parts of organic acid iron salt, and 100-200 parts of sodium bicarbonate.

[0007] By employing the above technical solution, this invention utilizes solid raw materials in a specific ratio to prepare functionalized biochar via a solid-phase synthesis route. Specifically, the pre-carbonized biochar precursor serves as a carbon skeleton carrier, providing a basic specific surface area and a stable carbon structure; chitosan powder acts as both a nitrogen and carbon source, providing nitrogen-containing functional groups after pyrolysis; organic acid iron salts are converted in situ into magnetic iron oxide or zero-valent iron particles during pyrolysis, endowing the material with magnetic separation properties; sodium bicarbonate acts as an auxiliary agent, decomposing to generate gas during pyrolysis to create pores and regulate the pH of the microenvironment during preparation. The synergistic effect of these components results in a final product with a well-developed pore structure, high nitrogen doping content, and rapid magnetic response, solving the problems of pore blockage and difficult recovery.

[0008] Preferably, the organic ferric acid salt is one or a combination of several of ferric citrate, ferrous gluconate, ferric gluconate, and ferrous citrate. Compared with inorganic strong acid ferric salts, organic ferric acid salts have weaker hydrolytic acidity, can coexist with sodium bicarbonate during the humid aging stage without undergoing a violent acid-base neutralization reaction, maintain the integrity of the precursor structure, and the organic acid anions can serve as auxiliary carbon sources to participate in the construction of the carbon skeleton during pyrolysis.

[0009] Preferably, the pre-carbonized biochar precursor is a product obtained by pyrolysis of lignocellulosic biomass at 300-400℃ for 1.0-2.0 hours under an inert atmosphere. The low-temperature pre-carbonization process removes unstable volatiles from the biomass and initially constructs carbon pores, which is beneficial for the loading of chitosan and iron sources in subsequent mechanochemical processes.

[0010] Preferably, the lignocellulosic biomass includes one or more of fruit trees, pine trees, straw, rice husks, or sawdust.

[0011] Secondly, the present invention provides a method for preparing magnetic porous chitosan-functionalized biochar, employing the following technical solution: A method for preparing magnetic porous chitosan-functionalized biochar includes the following steps: S1: Solid-phase mechanochemical grafting: The raw materials are mixed evenly and then ball-milled to obtain ultrafine composite powder; S2: Moisture-induced solid-phase aging: The ultrafine composite powder obtained in S1 is placed in a constant temperature and humidity environment for static aging, and the powder adsorbs the environmental moisture to induce interfacial chemical assembly. S3: Restricted pyrolysis and magnetization: The powder aged by S2 is subjected to high-temperature pyrolysis under an inert atmosphere; S4: Product purification and recovery: The obtained product is washed, magnetically separated, and dried to obtain the target product.

[0012] By employing the above technical solution, this invention utilizes a synergistic process of mechanochemical dispersion, moisture-induced assembly, and limited pyrolysis to achieve the grafting and structural regulation of functional components on the surface of biochar. The specific reaction mechanism and process are as follows: The first stage (solid-phase mechanochemical grafting): Under the shearing and impact of mechanical ball milling, the biochar precursor, chitosan, organic acid iron salt, and sodium bicarbonate are refined and mixed. The mechanical force generated by ball milling induces defect sites and active surfaces on the particle surface, promoting the physical entanglement and adsorption of chitosan molecular chains with the biochar matrix, thus avoiding the uneven distribution caused by solvent surface tension in the liquid phase method.

[0013] The second stage (moisture-induced solid-phase aging): The composite powder is placed in a constant temperature and humidity environment. Sodium bicarbonate adsorbs water molecules in the environment, forming a trace alkaline liquid film microenvironment on the surface of the powder particles. This alkaline liquid film microenvironment induces the following interfacial chemical evolution: Sodium bicarbonate undergoes micro-hydrolysis to produce hydroxide ions, which neutralize the protons on the amino groups of chitosan, promoting the extension of the chitosan molecular chains and the exposure of the amino groups.

[0014] Organic acid iron salts undergo slow hydrolysis under slightly humid conditions, and the resulting iron species complex with the amino and hydroxyl groups of chitosan through coordination bonds.

[0015] This gas-solid interface reaction avoids the loss and aggregation of chitosan caused by excessive solvent in the liquid phase method, and fixes the iron source and chitosan on the surface of biochar in the form of a coordination complex, laying the foundation for the structural evolution in subsequent pyrolysis.

[0016] The third stage (limited pyrolysis and magnetization): Under a high-temperature inert atmosphere, the precursor undergoes structural reorganization. Sodium bicarbonate begins to decompose at around 200°C, releasing carbon dioxide and water vapor. The gas generated in situ penetrates the carbonized layer of chitosan, forming mesoporous channels inside the material and preventing pore blockage caused by chitosan carbonization and coking.

[0017] As the temperature rises to 700-850℃, the organic acid iron salts decompose and are reduced by the surrounding carbon matrix and decomposition atmosphere, generating in situ nano-sized iron(III) oxide or zero-valent iron particles, which are dispersed in the carbon skeleton.

[0018] Chitosan undergoes aromatization at high temperatures, allowing nitrogen atoms to be in-situ doped into the carbon lattice, forming active sites such as pyridine nitrogen and graphitic nitrogen. Thanks to the coordination fixation during the aging stage, nitrogen volatilization loss is reduced, improving the nitrogen doping efficiency of the final product.

[0019] Preferably, in step S1, the ball milling conditions are: a ball-to-material mass ratio of 20:1 to 40:1, a ball milling speed of 400 to 600 rpm, and a ball milling time of 2.0 to 4.0 hours. These parameter ranges ensure that the material is sufficiently refined without damaging the basic structure of the carbon skeleton.

[0020] Preferably, in step S2, the relative humidity (RH) of the constant temperature and humidity environment is 70%-85%, the temperature is 40-55℃, and the aging time is 12-24 hours; and no liquid water is added directly during the aging process. These conditions control the thickness of the interfacial liquid film, ensuring that the interfacial reaction occurs while preventing the material from deliquescing and clumping.

[0021] Preferably, in step S3, the pyrolysis process includes two heating stages: the first stage involves heating to 200°C at a rate of 10°C / min and holding at that temperature for 30 minutes; the second stage involves heating to 700-850°C at a rate of 10°C / min and holding at that temperature for 1.5-3.0 hours. The first stage of holding at that temperature coincides with the decomposition temperature range of sodium bicarbonate, ensuring the pore-forming process proceeds; the second stage of high-temperature treatment ensures the degree of graphitization and the reduction and crystallization of iron species.

[0022] Preferably, in step S4, the washing involves repeatedly washing with deionized water until the pH of the filtrate is neutral, during which solid-liquid separation is performed using an external magnetic field. Step S4 removes and decomposes residual sodium salts and impurities, and opens up the microporous structure.

[0023] Preferably, the preparation method of the pre-carbonized biochar precursor is as follows: dry biomass raw material is placed in a tube furnace, heated to 300-400℃ at a heating rate of 10℃ / min under nitrogen protection, kept at a constant temperature for 1.0-2.0 hours, and then ground and sieved after natural cooling.

[0024] This invention provides a magnetic porous chitosan-functionalized biochar and its preparation method. It has the following beneficial effects: 1. This invention employs solid-phase mechanochemical ball milling combined with in-situ sodium bicarbonate pore-forming technology, avoiding the biochar pore blockage problem caused by chitosan dissolution-regelation in traditional liquid-phase impregnation methods. During pyrolysis, sodium bicarbonate decomposes and releases carbon dioxide and water vapor, constructing abundant mesoporous channels within the dense chitosan carbonized layer, thereby increasing the specific surface area of ​​the material. This open, multi-level pore structure reduces liquid-phase mass transfer resistance and significantly enhances the adsorption kinetics rate of pollutants on the material.

[0025] 2. This invention introduces a moisture-induced solid-phase aging step, which utilizes trace amounts of adsorbed water to construct an interfacial reaction environment, promoting the deprotonation of chitosan amino groups and their coordination complexation with iron ions. This coordination enhances the thermal stability of the organic precursor and inhibits the volatilization loss of nitrogen during pyrolysis, thereby increasing the doping amount of active nitrogen species such as pyridine nitrogen and graphitic nitrogen in the final product, and enhancing the material's coordination ability for heavy metal ions and its affinity for organic pollutants.

[0026] 3. This invention selects organic acid iron salts as magnetic precursors, which are converted in situ into uniformly dispersed magnetic iron oxide or zero-valent iron particles under restricted reduction pyrolysis conditions. The carbon skeleton's coating effect on the magnetic particles endows the material with magnetic response properties, realizing rapid solid-liquid separation after adsorption. At the same time, it prevents the dissolution and loss of magnetic components in the acidic regeneration environment, ensuring the structural stability and adsorption performance of the material in multiple cycles of use. Attached Figure Description

[0027] Figure 1This is a flowchart of the method of the present invention; Figure 2 This is a morphological structure analysis diagram of the target product obtained in Example 3 of the present invention; Figure 3 This is a surface elemental analysis diagram of the target product obtained in Example 3 of the present invention; Figure 4 The images show the FTIR, XRD, thermogravimetric analysis, and magnetic intensity analysis of the target product obtained in Example 3 of this invention. Detailed Implementation

[0028] The technical solutions in 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.

[0029] Please see the appendix Figure 1 - Appendix Figure 4 This invention provides a magnetic porous chitosan-functionalized biochar and its preparation method.

[0030] raw material: Applewood is obtained from agricultural pruning waste. After being peeled, washed with deionized water to remove dirt and sand, it is naturally air-dried, crushed and sieved using a pulverizer, and the wood chips with a particle size between 0.15mm and 0.25mm are selected as biomass raw materials for future use.

[0031] Chitosan, degree of deacetylation ≥90.0%, viscosity 100 mPa·s to 200 mPa·s; ferric citrate, iron content 16.5% to 18.5%; ferrous gluconate, purity ≥98.0%; sodium bicarbonate, purity ≥99.5%; anhydrous ferric chloride, purity ≥97.0%; tetracycline hydrochloride, purity ≥98.0%; lead nitrate, purity ≥99.0%; cadmium nitrate, purity ≥99.0%.

[0032] Preparation Example 1: This preparation example provides a pre-carbonized biochar precursor (denoted as BC-Pre-1), including the following steps: Dry applewood powder was placed in a quartz boat in a tube furnace, and high-purity nitrogen was introduced at a flow rate of 20 mL / min to purge the air from the furnace. The temperature was increased from room temperature to 300°C at a rate of 10°C / min and held at 300°C for 1 hour. After pyrolysis, the powder was naturally cooled to room temperature under nitrogen protection. The product was then removed, ground, and passed through a 100-mesh sieve to obtain the final product.

[0033] Preparation Example 2: This preparation example provides a pre-carbonized biochar precursor (denoted as BC-Pre-2), including the following steps: Dry applewood powder was placed in a quartz boat in a tube furnace, and high-purity nitrogen was introduced at a flow rate of 20 mL / min to purge the air from the furnace. The temperature was increased from room temperature to 400°C at a rate of 10°C / min and held at 400°C for 2.0 hours. After pyrolysis, the powder was naturally cooled to room temperature under nitrogen protection. The product was then removed, ground, and passed through a 100-mesh sieve to obtain the final product.

[0034] Preparation Example 3: This preparation example provides a pre-carbonized biochar precursor (denoted as BC-Pre-3), including the following steps: Dry applewood powder was placed in a quartz boat in a tube furnace, and high-purity nitrogen was introduced at a flow rate of 20 mL / min to purge the air from the furnace. The temperature was increased from room temperature to 350°C at a rate of 10°C / min and held at 350°C for 1.5 hours. After pyrolysis, the powder was naturally cooled to room temperature under nitrogen protection. The product was then removed, ground, and passed through a 100-mesh sieve to obtain the final product. Example 1

[0035] This embodiment provides a magnetic porous chitosan-functionalized biochar based on mechanochemical synergistic moisture aging, including the following steps: (1) Solid-phase mechanochemical grafting: Weigh 100g of the pre-carbonized biochar precursor (BC-Pre-3) prepared in Preparation Example 3, 100g of chitosan powder, 60g of ferric citrate and 150g of sodium bicarbonate; after mixing the above materials evenly, load them into the zirconium jar of the planetary ball mill, add zirconium grinding balls with a diameter of 5-15mm, and control the ball-to-material mass ratio at 30:1; ball mill at 500rpm for 3.0 hours, with the running mode being 15 minutes of operation followed by a 5-minute pause, to obtain ultrafine composite powder.

[0036] (2) Moisture-induced solid-phase aging: Take out the composite powder obtained in step (1), spread it evenly in a clean petri dish, with a layer thickness of about 0.8 cm; place it in a constant temperature and humidity chamber, set the relative humidity (RH) to 80% and the temperature to 45℃, and let it stand for aging for 18 hours; during this process, no liquid water is added, and the powder is used to adsorb environmental moisture to induce interfacial chemical assembly.

[0037] (3) Restricted pyrolysis and magnetization: The aged powder was transferred to a tube furnace and heated to 200°C at a rate of 10°C / min under a nitrogen atmosphere (flow rate 200 mL / min) and held for 30 minutes. Then, the temperature was increased to 800°C at a rate of 10°C / min and pyrolyzed at 800°C for 2.0 hours. After the pyrolysis was completed, the powder was naturally cooled to room temperature.

[0038] (4) Product purification and recovery: The obtained product is first washed repeatedly with deionized water until the pH value of the filtrate is neutral (pH≈7.0). During this period, the solid is magnetically separated and recovered using an external magnet. Finally, the solid is dried in a vacuum drying oven at 60℃ for 12 hours, ground and sieved to obtain the target product. Example 2

[0039] This embodiment provides a magnetic porous chitosan-functionalized biochar based on mechanochemical synergistic moisture aging, including the following steps: (1) Solid-phase mechanochemical grafting: Weigh 100g of the pre-carbonized biochar precursor (BC-Pre-1) prepared in Example 1, 50g of chitosan powder, 40g of ferric citrate and 100g of sodium bicarbonate; mix the above materials evenly and put them into the zirconium jar of the planetary ball mill, add zirconium grinding balls with a diameter of 5-15mm, and control the ball-to-material mass ratio at 20:1; ball mill at 400rpm for 2.0 hours, with the running mode being 5 minutes paused every 15 minutes to obtain ultrafine composite powder.

[0040] (2) Moisture-induced solid-phase aging: Take out the composite powder obtained in step (1), spread it evenly in a clean petri dish, with a layer thickness of about 0.5 cm; place it in a constant temperature and humidity chamber, set the relative humidity (RH) to 70% and the temperature to 40℃, and let it stand for aging for 12 hours; during this process, no liquid water is added, and the powder is used to adsorb environmental moisture to induce interfacial chemical assembly.

[0041] (3) Restricted pyrolysis and magnetization: The aged powder was transferred to a tube furnace and heated to 200°C at a rate of 10°C / min under a nitrogen atmosphere (flow rate 20 mL / min) and held for 30 minutes. Then, the temperature was increased to 700°C at a rate of 10°C / min and pyrolyzed at 700°C for 1.5 hours. After the pyrolysis was completed, the powder was naturally cooled to room temperature.

[0042] (4) Product purification and recovery: The obtained product is first washed repeatedly with deionized water until the pH value of the filtrate is neutral (pH≈7.0). During this period, the solid is magnetically separated and recovered using an external magnet. Finally, the solid is dried in a vacuum drying oven at 60℃ for 24 hours, ground and sieved to obtain the target product. Example 3

[0043] This embodiment provides a magnetic porous chitosan-functionalized biochar based on mechanochemical synergistic moisture aging, including the following steps: (1) Solid-phase mechanochemical grafting: Weigh 100g of the pre-carbonized biochar precursor (BC-Pre-2) prepared in Preparation Example 2, 150g of chitosan powder, 80g of ferric citrate and 200g of sodium bicarbonate; after mixing the above materials evenly, load them into the zirconium jar of the planetary ball mill, add zirconium grinding balls with a diameter of 5-15mm, and control the ball-to-material mass ratio at 40:1; ball mill at 600rpm for 4.0 hours, with the running mode being 15 minutes of operation followed by a 5-minute pause, to obtain ultrafine composite powder.

[0044] (2) Moisture-induced solid-phase aging: Take out the composite powder obtained in step (1), spread it evenly in a clean petri dish, with a layer thickness of about 1.0 cm; place it in a constant temperature and humidity chamber, set the relative humidity (RH) to 85% and the temperature to 55℃, and let it stand for aging for 24 hours; during this process, no liquid water is added, and the powder is used to adsorb environmental moisture to induce interfacial chemical assembly.

[0045] (3) Restricted pyrolysis and magnetization: The aged powder was transferred to a tube furnace and heated to 200°C at a rate of 10°C / min under a nitrogen atmosphere (flow rate 200 mL / min) and held for 30 minutes. Then, the temperature was increased to 850°C at a rate of 10°C / min and pyrolyzed at 850°C for 3.0 hours. After the pyrolysis was completed, the powder was naturally cooled to room temperature.

[0046] (4) Product purification and recovery: The obtained product is first washed repeatedly with deionized water until the pH value of the filtrate is neutral (pH≈7.0). During this period, the solid is magnetically separated and recovered using an external magnet. Finally, the solid is dried in a vacuum drying oven at 80℃ for 12 hours, ground and sieved to obtain the target product. Example 4

[0047] This embodiment provides a magnetic porous chitosan-functionalized biochar based on mechanochemical synergistic moisture aging. The difference between this embodiment and Embodiment 1 lies only in the change of the iron source, including the following steps: (1) Solid-phase mechanochemical grafting: Weigh 100g of the pre-carbonized biochar precursor (BC-Pre-3) prepared in Preparation Example 3, 100g of chitosan powder, 60g of ferrous gluconate and 150g of sodium bicarbonate; after mixing the above materials evenly, load them into the zirconium jar of the planetary ball mill, add zirconium grinding balls with a diameter of 5-15mm, and control the ball-to-material mass ratio at 30:1; ball mill at 500rpm for 3.0 hours, with the running mode being 15 minutes of operation followed by a 5-minute pause, to obtain ultrafine composite powder.

[0048] (2) Moisture-induced solid-phase aging: Take out the composite powder obtained in step (1), spread it evenly in a clean petri dish, with a layer thickness of about 0.8 cm; place it in a constant temperature and humidity chamber, set the relative humidity (RH) to 80% and the temperature to 45℃, and let it stand for aging for 18 hours; during this process, no liquid water is added, and the powder is used to adsorb environmental moisture to induce interfacial chemical assembly.

[0049] (3) Restricted pyrolysis and magnetization: The aged powder was transferred to a tube furnace and heated to 200°C at a rate of 10°C / min under a nitrogen atmosphere (flow rate 200 mL / min) and held for 30 minutes. Then, the temperature was increased to 800°C at a rate of 10°C / min and pyrolyzed at 800°C for 2.0 hours. After the pyrolysis was completed, the powder was naturally cooled to room temperature.

[0050] (4) Product purification and recovery: The obtained product is first washed repeatedly with deionized water until the pH value of the filtrate is neutral (pH≈7.0). During this period, the solid is magnetically separated and recovered using an external magnet. Finally, the solid is dried in a vacuum drying oven at 60℃ for 12 hours, ground and sieved to obtain the target product.

[0051] Comparative Example 1: Compared with Example 1, the difference is that step (2) moisture-induced solid-phase aging is omitted, and the composite powder obtained by ball milling in step (1) is directly fed into a tube furnace for restricted pyrolysis and magnetization in step (3). The rest are the same.

[0052] Comparative Example 2: Compared with Example 1, the difference is that the traditional liquid-phase impregnation method is used instead of the solid-phase mechanochemical and aging process of the present invention. The specific operation is as follows: 100g of chitosan is dissolved in 1000mL of 2% acetic acid solution, and 60g of ferric citrate, 150g of sodium bicarbonate and 100g of pre-carbonized biochar (BC-Pre-3) are added in sequence. The mixture is magnetically stirred at room temperature for 6 hours, and then dried at 80°C to remove moisture. The resulting dry solid is directly subjected to the pyrolysis in step (3), and the rest is the same.

[0053] Comparative Example 3: Compared with Example 1, the difference is that sodium bicarbonate was not added to the raw materials in step (1). Biochar, chitosan and ferric citrate were mixed and ball-milled according to the proportion of Example 1 and then subjected to subsequent processing. All other aspects were the same.

[0054] Comparative Example 4: Compared with Example 1, the difference is that in step (1), 60g of ferric citrate was replaced with an equimolar amount of anhydrous ferric chloride (FeCl3), and all other steps were the same.

[0055] Comparative Example 5: Compared with Example 1, the difference is that no modification treatment was performed. The pre-carbonized biochar precursor (BC-Pre-3) obtained in Preparation Example 3 was directly placed in a tube furnace and pyrolyzed according to the same heating program and atmosphere conditions as in step (3). All other aspects were the same.

[0056] Test Example 1: Basic Physicochemical Properties and Process Feasibility Test To verify the feasibility of the preparation process and the basic physicochemical characteristics of the product, the physicochemical properties of the samples obtained in Examples 1-4 and Comparative Examples 1-5 were tested. First, the yield was calculated, and the total mass of the solid raw materials input during the preparation process and the mass of the final product obtained after washing and drying were recorded, and the ratio between the two was calculated. The mass percentages of carbon, hydrogen, and nitrogen in the samples were determined using an elemental analyzer. The iron loading was determined using an acid digestion method. The sample was weighed and digested in a microwave digester with aqua regia. After volume adjustment, the iron ion concentration in the solution was determined by inductively coupled plasma atomic emission spectrometry and converted to the unit mass loading. The magnetic separation performance was tested as follows: 100 mg of sample was dispersed in 100 mL of deionized water and ultrasonically dispersed for 5 minutes. A neodymium iron boron magnet with a surface magnetic field strength of 3000 Gauss was placed in the middle of the outer wall of the container, and the time required for the suspension to change from turbid to clear was recorded.

[0057] The test data for each sample are shown in the table below: Table 1 shows the basic physicochemical property test data of each embodiment and comparative sample.

[0058] Sample number Yield (%) Nitrogen content (N, wt%) Iron loading (Fe, mg / g) Magnetic separation time (s) Example 1 31.4 4.82 76.5 18 Example 2 29.8 3.15 54.2 25 Example 3 34.2 5.67 88.9 14 Example 4 32.1 4.65 72.8 21 Comparative Example 1 30.9 3.54 75.1 32 Comparative Example 2 27.5 3.92 70.4 28 Comparative Example 3 51.6 4.10 62.3 24 Comparative Example 4 21.3 1.88 68.7 85 Comparative Example 5 88.5 0.32 0.15 >600 (non-magnetic) Based on the data in Table 1 and the experimental phenomena, the analysis is as follows: A comparison of the data from Example 1 and Comparative Example 1 shows that after adding the moisture-induced solid-phase aging step, the nitrogen content of the material increased from 3.54% to 4.82%. This difference indicates that during the aging stage, the micro-liquid film environment formed by the moisture absorption of the powder promotes the function of sodium bicarbonate, creating a locally alkaline environment that facilitates the deprotonation of chitosan amino groups and their coordination with the biochar matrix and iron ions, thereby reducing nitrogen volatilization during pyrolysis.

[0059] The comparison between Example 1 and Comparative Example 4 shows that the acidity or alkalinity of the iron source affects the formation of the material structure. Comparative Example 4 used anhydrous ferric chloride, and its yield (21.3%) and nitrogen content (1.88%) were both lower than those of Example 1, with the magnetic separation time extended to 85 seconds. This is because the strongly acidic environment generated by the hydrolysis of ferric chloride reacted with sodium bicarbonate during the aging stage, releasing gas and disrupting the precursor assembly structure, leading to chitosan degradation and iron species aggregation. The organic iron salt used in the examples maintained chemical stability during the aging stage.

[0060] Comparative Example 3, without the addition of sodium bicarbonate, showed a higher yield (51.6%) than Example 1 (31.4%). The difference in yield stemmed from the removal of sodium bicarbonate as a sacrificial template agent during pyrolysis and subsequent washing, indicating that the lower yield in the examples corresponded to effective removal of the pore-forming agent. All examples samples achieved magnetic separation within 25 seconds, demonstrating that mechanochemical dispersion combined with reductive pyrolysis converts organic iron salts into magnetically responsive iron species.

[0061] Test Example 2: Characterization of Material Morphology and Physicochemical Structure Morphological analysis of the target product obtained in Example 3 by scanning electron microscopy (SEM) showed that (e.g.) Figure 2 As shown in the figure, after introducing magnetic components, the product surface retained a porous structure and a large number of nanoparticles appeared, indicating that the synergistic optimization of magnetic loading and porous structure can balance functionality and structural stability. Figure 3 As shown, the surface of the target product obtained in Example 3 exhibits a uniform elemental distribution of C, O, N, and Fe, further confirming the successful loading of iron oxides. The pore structure parameters of the target product obtained in Example 3 are shown in Table 2. Table 2 Pore structure analysis of adsorbents SABET(m² / g) SAmic(m² / g) SAex(m² / g) Vtot(cm³ / g) Vmic(cm³ / g) Dava(nm) 398.5 365.4 33.1 0.108 0.040 4.389 Note: SABET, SAmic, and SAex represent the BET specific surface area, micropore area, and external surface area of ​​the adsorbent, respectively; Vtot and Vmic represent the total pore volume and micropore volume, respectively; Dava represents the average pore size of the adsorbent.

[0062] Infrared spectroscopy analysis revealed a broad peak (OH stretching vibration) at 3200-3600 cm⁻¹, indicating the presence of hydroxyl groups on the surface. A weak C=C aromatic ring vibration peak or NH bending vibration peak was observed near 1620 cm⁻¹. Simultaneously, a CO₃²⁻ vibration peak appeared in the 1420 cm⁻¹ region, indicating the presence of a large amount of carbonate in the sample. This is beneficial for mineral precipitation during heavy metal removal and promotes the solidification of heavy metals. Furthermore, the peak at 1100 cm⁻¹ was attributed to a CO / CN peak. The peak at 880 cm⁻¹ was due to the out-of-plane bending vibration of carbonate. The presence of Fe-O vibration in the 570 cm⁻¹ region confirmed that the introduction of iron oxides increased the number of O-containing groups.

[0063] XRD pattern of the target product obtained in Example 3 ( Figure 4(b) shows the crystal structure characteristics of the sample at different diffraction angles (2θ range 5°–90°), revealing characteristic peak positions of CaCO3 and SiO2. In this XRD pattern, typical diffraction peaks belonging to the graphitic carbon (002) crystal plane can be observed in the range of 2θ≈20°–30°, indicating the presence of a highly crystalline graphitized carbon structure in the sample. After magnetization, new characteristic peaks belonging to γ-Fe2O3 (maghemite) were added (2θ≈30.24°, 35.63°, 43.28°, and 62.93°), whose peak positions are consistent with standard diffraction data (PDF#39-1346).

[0064] TG analysis of the target product obtained in Example 3 showed that its thermal decomposition process exhibited staged characteristics. All samples showed desorption of adsorbed water and trace volatile components in the initial stage (room temperature to 200°C). A mass change step appeared around 420°C, presumably related to the pyrolysis behavior of residual chitosan. Subsequently, common pyrolysis characteristics were observed in the 700°C range, mainly due to the further pyrolysis of residual cellulose, hemicellulose, lignin, or carbonate minerals in the biochar. A unique thermal response was exhibited in the high-temperature range (900°C), and its mass abrupt change can be attributed to the thermal decomposition reaction of γ-Fe₂O₃ nanoparticles. The final residual mass percentage of the product in Example 3 was 72.65%, indicating that the material system as a whole possesses excellent thermal stability. According to VSM analysis, the coercivity and remanence of the product in Example 3 were almost zero, and no obvious hysteresis loop was observed. The saturation magnetization was 7.62 emu / g, indicating that it could be successfully separated from water under the action of an applied magnetic field, which has economic benefits in practical applications.

[0065] Test Example 3: Comparison Test of Adsorption Performance and Stability Experimental steps The pollutant removal performance of the samples prepared in Examples 1-4 and Comparative Examples 1-5 was evaluated. First, the saturated adsorption capacity was determined. Lead nitrate solutions with concentrations ranging from 50-400 mg / L and tetracycline hydrochloride solutions with concentrations ranging from 50-500 mg / L were prepared, and the pH was adjusted to 5.0 ± 0.1. 20 mg of the sample was accurately weighed and placed in a 50 mL centrifuge tube, and 25 mL of the pollutant solution was added. The mixture was shaken at 25°C and 150 rpm for 24 hours. After centrifugation, the supernatant was filtered through a 0.22 μm filter membrane. The lead ion concentration in the filtrate was determined using atomic absorption spectrometry, and the tetracycline concentration was determined using a UV-Vis spectrophotometer at 357 nm. The maximum saturated adsorption capacity was calculated using the Langmuir model. Next, adsorption kinetics were tested. 0.8 g / L of adsorbent was added to solutions with an initial concentration of 200 mg / L. Samples were taken at different time points from 5 min to 1440 min, and the time required to reach 90% equilibrium adsorption was recorded. Finally, a cycle regeneration stability test was conducted. Taking lead ion adsorption as an example, the sample after adsorption saturation was desorbed with 0.1 mol / L HCl solution, washed with deionized water until neutral, dried, and then adsorbed again. This process was repeated 5 times, and the adsorption capacity retention rate after the 5th cycle was calculated.

[0066] The adsorption performance and cycle stability test data of each sample are shown in the table below: Table 3 Adsorption performance and cycle stability data of each sample for heavy metals and organic pollutants. Sample number Pb²⁺ saturated adsorption capacity (mg / g) TC saturated adsorption capacity (mg / g) Kinetic equilibrium time (t, 90%) (Pb²⁺, min) Retention rate (%, Pb²⁺) after 5 cycles Example 1 186.4 248.7 45 89.2 Example 2 162.3 215.6 50 85.4 Example 3 191.8 255.3 40 88.7 Example 4 178.5 239.1 48 87.5 Comparative Example 1 125.4 168.2 75 68.3 Comparative Example 2 142.1 176.5 140 54.1 Comparative Example 3 68.9 95.4 110 72.6 Comparative Example 4 45.2 62.8 180 35.4 Comparative Example 5 23.6 38.1 240 - Based on the data in Table 3 and the material properties, the analysis is as follows: The saturated adsorption capacities of Pb²⁺ and tetracycline in Example 1 were 186.4 mg / g and 248.7 mg / g, respectively, which were higher than those in Comparative Example 1 (125.4 mg / g and 168.2 mg / g). The data indicate that the moisture aging process promoted the dispersion of chitosan on the biochar surface and the retention of functional groups, thereby increasing the density of effective adsorption sites. After five adsorption-desorption cycles, Example 1 maintained an adsorption capacity retention rate of 89.2%, higher than the 68.3% in Comparative Example 1, indicating that the aging process enhanced the interfacial bonding stability between the active component and the matrix.

[0067] Compared to the liquid-phase impregnation method of Comparative Example 2, the adsorption kinetic equilibrium time of Example 1 (45 min) was significantly shorter than that of Comparative Example 2 (140 min). Samples prepared by the liquid-phase method are prone to pore blockage due to solvent evaporation, increasing internal mass transfer resistance. This invention employs solid-phase ball milling combined with sodium bicarbonate pore-forming to construct a pore structure conducive to mass transport. Comparative Example 2 exhibited poor cycle stability (54.1%), indicating that the physically attached active layer is easily detached during acid washing.

[0068] Comparative Example 3, without the addition of sodium bicarbonate, exhibited a low adsorption capacity (Pb²⁺ 68.9 mg / g). The gas produced during the pyrolysis of sodium bicarbonate acts as a pore-expanding agent; the lack of sodium bicarbonate resulted in insufficient specific surface area and contact sites. Comparative Example 4, using a strongly acidic iron source, showed a significant decrease in adsorption performance (Pb²⁺ 45.2 mg / g), indicating that the strong acid environment disrupted the active functional groups such as amino groups of chitosan, leading to a loss of coordination ability. The data from these examples confirm the comprehensive effect of the mechanochemical synergistic aging process in improving adsorption capacity, rate, and cycle stability.

[0069] Test Example 4: Theoretical Simulation Analysis of Adsorption Mechanism To further elucidate the efficient removal mechanism of antibiotics (tetracycline) and heavy metals by the material of this invention at the molecular orbital level, the electron transfer capability of the material system was quantitatively characterized using spin polarized molecular orbital theory (DFT). Figure 2 As shown, the HOMO-LUMO band gap of the original graphene is 2.64 eV, indicating a high electron migration barrier.

[0070] Simulation results show that the band gap is significantly reduced after functionalization with -OH, -COOH, -NH2, and -CO-Fe-OH groups using the process of this invention. Among these, the -CO-Fe-OH group... The narrowing to 0.51 eV indicates a significant improvement in orbital energy level matching, effectively reducing the energy barrier for interface charge transfer.

[0071] Further quantitative analysis of the adsorption energy revealed that the functionalized groups exhibited extremely strong affinity for tetracycline (TC). Specifically, the adsorption energy of the hydroxyl group (-OH) for TC was as high as -36.14 eV, the amino group (-NH2) had an adsorption energy of -22.70 eV, and the iron oxide (O-Fe-OH) group had an adsorption energy of -21.09 eV. This indicates that the high-density active nitrogen / oxygen functional groups retained on the biochar surface through the solid-phase mechanochemical synergistic moisture aging process of this invention can specifically capture antibiotic molecules through strong hydrogen bonds and coordination interactions.

[0072] Regarding heavy metal adsorption, the -OH group exhibits the best adsorption energy for Pb²⁺ (-22.03 eV), while the -NH₂ group shows a specific interaction with Cu²⁺ (adsorption energy -7.30 eV). The theoretical calculation results above are in high agreement with the experimental data in Test Example 2, which confirms the great potential of the material of this invention in the treatment of antibiotic wastewater from a microscopic perspective.

[0073] 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.

Claims

1. A magnetic porous chitosan-functionalized biochar, characterized in that, It is made from the following raw materials in parts by weight: 100 parts of pre-carbonized biochar precursor, 50-150 parts of chitosan powder, 40-80 parts of organic acid iron salt and 100-200 parts of sodium bicarbonate.

2. The magnetic porous chitosan-functionalized biochar according to claim 1, characterized in that, The organic ferric acid salt is one or a combination of several of ferric citrate, ferrous gluconate, ferric gluconate, and ferrous citrate.

3. The magnetic porous chitosan-functionalized biochar according to claim 1, characterized in that, The pre-carbonized biochar precursor is a product obtained by pyrolysis of lignocellulosic biomass at a low temperature of 300-400℃ for 1.0-2.0 hours under an inert atmosphere.

4. The magnetic porous chitosan-functionalized biochar according to claim 3, characterized in that, The lignocellulosic biomass includes one or more of the following: fruit trees, pine trees, straw, rice husks, or sawdust.

5. A method for preparing magnetic porous chitosan-functionalized biochar according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Solid-phase mechanochemical grafting: The raw materials are mixed evenly and then ball-milled to obtain ultrafine composite powder; S2: Moisture-induced solid-phase aging: The ultrafine composite powder obtained in S1 is placed in a constant temperature and humidity environment for static aging, and the powder adsorbs the environmental moisture to induce interfacial chemical assembly. S3: Restricted pyrolysis and magnetization: The powder aged by S2 is subjected to high-temperature pyrolysis under an inert atmosphere; S4: The obtained product is washed, magnetically separated, and dried to obtain the target product.

6. The method for preparing magnetic porous chitosan-functionalized biochar according to claim 5, characterized in that, In step S1, the ball milling conditions are: ball-to-material mass ratio of 20:1-40:1, ball milling speed of 400-600 rpm, and ball milling time of 2.0-4.0 hours.

7. The method for preparing magnetic porous chitosan-functionalized biochar according to claim 5, characterized in that, In step S2, the relative humidity (RH) of the constant temperature and humidity environment is 70%-85%, the temperature is 40-55℃, and the static aging time is 12-24 hours; and no liquid water is added directly during the aging process.

8. The method for preparing magnetic porous chitosan-functionalized biochar according to claim 5, characterized in that, In step S3, the pyrolysis process includes two heating programs: the first stage heats up to 200℃ at a rate of 10℃ / min and holds for 30 minutes; the second stage heats up to 700-850℃ at a rate of 10℃ / min and holds for 1.5-3.0 hours.

9. The method for preparing magnetic porous chitosan-functionalized biochar according to claim 5, characterized in that, In step S4, the washing involves repeatedly washing with deionized water until the pH of the filtrate is neutral, during which solid-liquid separation is performed in conjunction with an external magnetic field.

10. The method for preparing magnetic porous chitosan-functionalized biochar according to claim 5, characterized in that, The preparation method of the pre-carbonized biochar precursor is as follows: dry biomass raw material is placed in a tube furnace and heated to 300-400℃ at a heating rate of 10℃ / min under nitrogen protection, and kept at a constant temperature for 1.0-2.0 hours. After natural cooling, it is ground and sieved.

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