A dogtail grass silicon-rich-vessel structure-based directional activation modified biochar, a preparation method and applications thereof

Abstract

The application belongs to the field of environmental functional materials and advanced treatment technology of antibiotic wastewater, and particularly relates to a directional activation modified biochar based on a silicon-rich dogtail grass vascular bundle structure, a preparation method and application thereof; the preparation method comprises the following steps: washing and drying dogtail grass, and then crushing and sieving; immersing dogtail grass powder in a KOH solution to initiate pre-activation, and then drying after the immersion; pyrolyzing the sample after the immersion in an inert atmosphere; and finally, sequentially performing pickling, water washing, drying, crushing and sieving on the sample after the pyrolysis to obtain the directional activation modified biochar. The application has the advantages of simple preparation process and low cost; the prepared material has a high specific area, is mainly mesoporous, and is rich in oxygen-containing functional groups on the surface, and can be used as a high-selectivity and high-capacity tetracycline adsorption material which can maintain stable adsorption performance in a wide pH range. The application realizes the dual goals of "waste resource utilization-antibiotic deep purification", and has strong industrialization value and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and advanced treatment technology of antibiotic wastewater. Specifically, it relates to a directionally activated modified biochar based on the silicon-rich vascular bundle structure of foxtail grass, its preparation method, and its application. Background Technology

[0002] Tetracycline (TC), a broad-spectrum antibiotic, is widely used in clinical medicine, livestock and poultry farming, and aquaculture due to its significant antibacterial effects and low price. In my country, tetracycline antibiotics account for more than 30% of the total annual antibiotic usage. Because of its poor biodegradability (half-life of several months to several years), large amounts of unmetabolized tetracycline enter aquatic environments through wastewater discharge and manure application to farmland, making it one of the most frequently detected and highest-concentrated antibiotics in water bodies. Tetracycline residues not only disrupt the structure of aquatic microbial communities but also induce the generation and spread of drug-resistant genes, threatening human health through bioaccumulation in the food chain. This has become a major environmental and public health problem that urgently needs to be addressed.

[0003] Currently, the main technologies for tetracycline removal from water bodies include advanced oxidation, membrane separation, microbial degradation, and adsorption, but all of them have significant drawbacks:

[0004] ① Advanced oxidation processes (AOPs): These processes require a large amount of oxidants (such as ozone and hydrogen peroxide) or rely on auxiliary energy such as ultraviolet light and ultrasound. They have extremely high energy consumption and operating costs, and are prone to producing intermediate products with unknown toxicity, posing a risk of secondary pollution.

[0005] ② Membrane separation technology: Membrane modules have high investment costs, are prone to membrane fouling during operation, require frequent cleaning and maintenance, and the concentrated liquid is difficult to dispose of, making it difficult to apply on a large scale;

[0006] ③ Microbial degradation method: The degradation cycle is long (usually >7 days), sensitive to environmental conditions (pH, temperature, dissolved oxygen), and has extremely low treatment efficiency for high-concentration tetracycline wastewater (>100 mg / L);

[0007] ④ Adsorption method: Due to its simple operation, low cost, and lack of secondary pollution, it has become the most promising technology. However, existing adsorption materials have a core bottleneck—the adsorption capacity of commercial activated carbon is limited (saturated adsorption capacity 80~150 mg·g). -1 ), regeneration is difficult; conventional biochar has a low specific surface area (<300 m²), 2 ·g -1 Due to its underdeveloped pore structure and few surface-active functional groups, the adsorption capacity for tetracycline is typically below 100 mg·g⁻¹. -1 This makes it difficult to meet the needs of in-depth processing.

[0008] Further analysis reveals two key flaws in existing biochar preparation technologies: first, the lack of targeted activation schemes tailored to the inherent structural characteristics of biomass, and the blind adoption of general activation processes, which fails to fully realize the structural potential of biomass; second, the lack of in-depth research on the synergistic mechanism between biomass components and activators, resulting in low efficiency in the construction of pore structures and active sites.

[0009] foxtail grass ( Setaria viridis Foxtail grass, an annual weed of the Poaceae family, is widely distributed and grows rapidly in my country, with an annual biomass of 5-8 tons per acre. It is an abundant and extremely low-cost source of agricultural waste biomass. Currently, foxtail grass is only used for feed, compost, or direct incineration; its unique structural and component advantages have not yet been developed and utilized.

[0010] (1) Vascular bundle structure: The vascular bundles in the stem of foxtail grass are arranged in a regular and orderly manner, forming a natural layered microchannel network, which provides a natural template for the directional construction of a porous system with excellent connectivity;

[0011] (2) Silicon-rich characteristics and high cellulose content: The epidermal cells of foxtail grass are rich in silicates (SiO2 content 3~6%) and cellulose content 35~45%. The synergistic effect of silicates and cellulose provides unique conditions for pore expansion and introduction of active sites during the activation process.

[0012] However, existing technologies lack research on the preparation of high-performance tetracycline adsorbents using the silica-rich vascular bundle structure of *Setaria viridis*, and no targeted activation technology for this type of biomass has been developed. Therefore, developing a targeted activation method based on the natural structural advantages of *Setaria viridis* to prepare modified biochar with high specific surface area, well-developed mesoporous structure, and abundant active sites is of significant theoretical and industrial value for overcoming the performance bottlenecks of existing adsorbent materials and achieving advanced treatment of tetracycline wastewater. Summary of the Invention

[0013] Existing tetracycline adsorbents (commercial activated carbon, conventional biochar) have low adsorption capacity (typically <100 mg·g). -1This invention addresses the technical shortcomings of traditional biochar, such as unreasonable pore structure, insufficient active sites, and incomplete activation processes that fail to fully utilize the inherent structural advantages of biomass. It aims to provide a method for the preparation of directionally activated modified biochar based on the silicon-rich vascular bundle structure of *Setaria viridis*, along with its applications. This invention utilizes the natural silicon-rich properties and layered vascular bundle structure of *Setaria viridis* to construct an adsorbent material through directional activation with KOH. The preparation process is simple and low-cost. The resulting material has a high specific area, is primarily mesoporous, and has a surface rich in oxygen-containing functional groups. It can be used as a highly selective and high-capacity tetracycline adsorbent, maintaining stable adsorption performance over a wide pH range. The raw material for this invention is widely distributed agricultural waste. The preparation process is simple and low-cost, with excellent adsorption performance and no secondary pollution. It achieves the dual goals of "waste resource utilization and deep antibiotic purification," and is suitable for the efficient treatment of tetracycline-containing wastewater from pharmaceutical, aquaculture, and hospital industries, possessing significant industrial value and application prospects.

[0014] The specific technical solution of the present invention is as follows.

[0015] This invention provides a method for preparing directionally activated modified biochar based on the silicon-rich vascular bundle structure of *Setaria viridis*, comprising the following steps:

[0016] (1) Wash and dry the foxtail grass, then crush and sieve it to obtain foxtail grass powder.

[0017] (2) Soak the foxtail grass powder in a KOH solution with a concentration of 1.5~2.5 mol / L for 20~28h to allow KOH to fully penetrate into the vascular bundle channels and silicate gaps of the foxtail grass and initiate pre-activation; after soaking, take out the sample and dry it.

[0018] (3) In an inert atmosphere, the impregnated sample obtained in step (2) is pyrolyzed at a temperature of 550~650 ℃. During the pyrolysis process, KOH undergoes decarboxylation and cross-linking reaction with cellulose in foxtail grass, and at the same time undergoes synergistic etching reaction with silicate to form a lamellar mesoporous-microporous composite structure. After the pyrolysis is completed, it is naturally cooled.

[0019] (4) First, acid wash is used to remove potassium salt and silicate residues in the pyrolysis sample, then it is washed with deionized water, and finally dried, crushed and sieved to obtain oxygen-containing functional groups-oriented activated modified biochar based on the silicon-rich vascular bundle structure of foxtail grass with hydroxyl, carboxyl and ether bonds on the surface.

[0020] In this invention, in step (1), the particles are crushed to a particle size of 0.2~1.0 mm and passed through a 50-mesh sieve.

[0021] In this invention, in step (2), the soaking time is 20-28 h, the drying temperature is 75-85℃, and the drying time is 20-30 h. In a specific embodiment, the KOH solution concentration is 2 mol / L, the soaking time is 24 h, the drying temperature is 80℃, and the drying time is 24 h.

[0022] In this invention, in step (3), the inert atmosphere is nitrogen or argon, with a flow rate of 0.2~1.0 L / min; during pyrolysis, the temperature is increased to the pyrolysis temperature at a rate of 8~12 ℃ / min, and the pyrolysis time is 1~4 h; preferably, the pyrolysis temperature is 580~620℃, and the pyrolysis time is 1.5-2.5 h. In a specific embodiment, the heating rate is 10℃ / min, the pyrolysis temperature is 600℃, and the pyrolysis time is 2 h.

[0023] In this invention, in step (4), the sample is acid-washed with 0.5~2 mol / L hydrochloric acid or sulfuric acid; washed with deionized water until neutral; dried at 75-85℃ and then pulverized through a 200-mesh sieve.

[0024] This invention also provides a directionally activated modified biochar based on the silica-rich vascular bundle structure of *Setaria viridis* prepared by the above-mentioned method. It exhibits a directional lamellar or stacked morphology of the *Setaria viridis* vascular bundle structure, with multi-level pore distribution and excellent connectivity, facilitating efficient channels for tetracycline molecule diffusion and adsorption; its specific surface area is ≥500 m². 2 ·g -1 The total pore volume is 0.4~1.2 cm³. 3 ·g -1 The average pore size is 2–6 nm, with mesopores accounting for ≥60%; the layer thickness is 5–20 nm, and the interlayer spacing is 3–8 nm. Preferably, the total pore volume is 0.5–1.2 cm³. 3 ·g -1 The average pore size is 2.5~5 nm; its mesoporous-dominated pore system can better match the size of tetracycline molecules (about 1.5 nm × 0.8 nm), reducing mass transfer resistance.

[0025] Furthermore, this invention provides an application of the above-mentioned directed activation modified biochar based on the silicon-rich vascular bundle structure of *Setaria viridis* in the adsorption and removal of tetracycline in water; the water includes pharmaceutical wastewater, aquaculture wastewater, hospital wastewater, and surface water contaminated with tetracycline, with an initial tetracycline concentration of 5-200 mg / L; the dosage of modified biochar is 0.1-3.0 g / L, and the initial pH of the adsorption system is 3-9; preferably, the initial tetracycline concentration is 50-200 mg / L; the dosage of modified biochar is 1-1.5 g / L; the initial pH of the adsorption system is 3-7; and the adsorption time is 60-180 min, at which point the tetracycline removal rate is above 95%.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] ① For the first time, the dual advantages of the silicon-rich and vascular bundle structure of foxtail grass were utilized to transform agricultural waste into high-performance adsorption materials through targeted activation, which not only realized the resource utilization of waste, but also broke through the technical bottleneck of "low structural utilization rate" of existing biochar.

[0028] ② A synergistic activation mechanism between KOH, silicates, and cellulose was constructed to form a directional preparation process of "impregnation-pyrolysis-purification". This process requires no complex equipment, the process parameters are easy to control, it is suitable for large-scale production, and the raw material cost is reduced by more than 60% compared with commercial activated carbon.

[0029] ③ Modified biochar with a specific surface area ≥ 500 m² 2 ·g -1 It can reach 728 m 2 ·g -1 Tetracycline saturated adsorption capacity ≥350 mg·g -1 It has an efficiency more than 3 times higher than conventional biochar and 2 to 4 times higher than commercial activated carbon; at a dosage of 0.5 to 1.5 g·L⁻¹ -1 It maintains high adsorption efficiency in a wide pH range (3~9) and high-concentration wastewater (tetracycline initial concentration 200 mg / L), with a removal rate of ≥95% within 3 h, solving the problems of "low adsorption capacity and poor pH adaptability" of existing materials;

[0030] ④ It is easy to operate, requires low dosage, and causes no secondary pollution. It is suitable for the deep treatment of various types of tetracycline-containing wastewater from pharmaceutical, aquaculture, and hospital industries. It can also be used for emergency treatment of polluted surface water, and has broad prospects for industrialization. Attached Figure Description

[0031] Figure 1 The images are scanning electron microscope (SEM) images of biochar before and after modification; a) is the unmodified biochar BC of Example 1, and b) is the modified biochar KBC of Example 2.

[0032] Figure 2 Fourier transform infrared spectra of biochar before and after adsorption (KBC+TC represents after adsorption, KBC represents before adsorption).

[0033] Figure 3 The adsorption kinetics curves of tetracycline on biochar before and after modification are shown.

[0034] Figure 4 The effect of different pH values ​​on the adsorption performance of KBC. Detailed Implementation

[0035] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] This invention provides a method for preparing directionally activated modified biochar based on the silicon-rich vascular bundle structure of *Setaria viridis*, comprising four core steps: raw material pretreatment, directional impregnation with KOH, synergistic pyrolysis activation, and purification post-treatment. The method achieves the directional transformation of the natural structure of *Setaria viridis* into a highly efficient adsorption structure by synergistically matching the KOH concentration, impregnation time, and pyrolysis parameters. This invention fully leverages the dual advantages of the silicon-rich characteristics and layered vascular bundle structure of *Setaria viridis*, utilizing the synergistic reaction between KOH and silicates and cellulose in *Setaria viridis* to directionally etch and form a layered mesoporous-microporous composite pore system. Simultaneously, a large number of active functional groups such as hydroxyl and carboxyl groups are introduced, constructing an adsorption system of "layered mesoporous-microporous composite structure + highly active oxygen-containing functional groups." The specific technical solution is as follows.

[0037] (I) Precise utilization of the natural structure and components of foxtail grass

[0038] This study is the first to clearly identify the core advantages of foxtail grass as a raw material for adsorption materials, and the synergistic effect of its structure and components provides a natural basis for the preparation of high-performance biochar.

[0039] ① Template effect of vascular bundle structure: The regularly arranged vascular bundles in the stem of foxtail grass form natural microchannels. When impregnated with KOH, they can penetrate in a directional manner along the channels. During pyrolysis, KOH selectively etches the vascular bundle walls, transforming the natural microchannels into directionally arranged lamellar pores, which greatly improves pore connectivity and mass transfer efficiency.

[0040] ② Synergistic activation effect of silicon-rich properties: The silicates in foxtail grass undergo a synergistic reaction during the pyrolysis of KOH:

[0041] SiO2+ 2KOH → K2SiO3+ H2O (1)

[0042] K2SiO3+ CO2→ K2CO3+ SiO2 (2)

[0043] The above reaction continuously expands the pores and increases the proportion of mesopores through the "etching-generating-re-etching" process. On the other hand, the generated potassium salt can act as a catalyst to promote the decarboxylation and cross-linking of cellulose and increase the number of surface active functional groups.

[0044] ③ High cellulose content ensures a sufficient carbon source: 35-45% cellulose content provides sufficient carbon source for biochar, ensuring the stability of the activated carbon skeleton and preventing pore collapse.

[0045] (ii) Collaborative optimization of targeted activation parameters

[0046] By systematically studying the synergistic effects of KOH concentration, impregnation time, pyrolysis temperature, and heating rate, a targeted activation process was developed to precisely control the structure and properties of biochar.

[0047] ① Optimization of KOH concentration and immersion time: Use 1.5~2.5 mol / L KOH solution and immerse for 20~28 h at a solid-liquid ratio of 1:12~1:18. This parameter combination can ensure that KOH can fully penetrate into the gap between the vascular bundle and the silicate, while avoiding excessive etching due to excessive KOH.

[0048] ② Precise control of pyrolysis process: Under an inert atmosphere, the temperature is increased to 550~650 ℃ at a rate of 8~12 ℃ / min, and pyrolysis is carried out for 1.5~2.5 h. The slow heating rate can avoid the collapse caused by the rapid expansion of the pore structure. The optimal pyrolysis temperature can achieve full carbonization of cellulose and efficient etching of silica, balancing the specific surface area and pore stability;

[0049] ③ Post-purification treatment: acid washing removes potassium salt and silicate residues, and water washing is performed until the conductivity is <10 μS / cm to ensure that the surface active sites are not covered by impurities.

[0050] (III) Synergistically Optimized Adsorption System

[0051] The modified biochar prepared by this invention has unique structural and performance advantages, forming a synergistic adsorption mechanism of "physical adsorption + chemical adsorption":

[0052] ① Advantages of physical adsorption: specific surface area ≥ 500 m² 2 ·g -1 Mesoporous components account for ≥60%, with a total pore volume of 0.4~1.2 cm³. 3 ·g -1 With a sheet thickness of 5~20 nm and an interlayer spacing of 3~8 nm, its unique layered mesoporous structure provides ample adsorption sites, significantly reducing the mass transfer resistance during the adsorption process.

[0053] ② Advantages of chemisorption: The surface is rich in oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH), which can synergistically enhance the adsorption affinity through hydrogen bonding (-OH with amino and carbonyl groups in tetracycline molecules), π-π conjugation (carbon skeleton with tetracycline aromatic ring), and electrostatic interaction (carboxyl group dissociates and interacts with tetracycline cations).

[0054] ③Comprehensive performance advantages: Saturated adsorption capacity ≥350 mg·g -1 It is 3.8 times better than unmodified biochar and 2 to 4 times better than commercial activated carbon, and maintains stable performance over a wide pH range of 3 to 9.

[0055] Example 1 Preparation of unmodified biochar BC

[0056] Fresh foxtail grass was taken, impurities were removed, and it was washed three times with deionized water. It was dried at 80℃ for 24 h, pulverized, and passed through a 50-mesh sieve. 100 g of foxtail grass powder was placed in a tube furnace and pyrolyzed at 600℃ for 2 h under nitrogen flow protection at a rate of 0.5 L / min and a temperature increase of 10℃ / min. After cooling, it was washed three times with 1 mol / L hydrochloric acid and then washed with deionized water until the conductivity was <10 μS / cm. After drying at 80℃, it was passed through a 200-mesh sieve to obtain unmodified biochar BC. Figure 1 a) A scanning electron microscope (SEM) image of unmodified biochar BC. As shown in the figure, the surface of unmodified biochar BC is dense with few pores. The specific surface area and porosity of unmodified biochar BC, as measured by an automated surface area and porosity analyzer (BELSORP-MAX, Micromeritics, USA), is BET 216 m². 2 ·g -1 Total pore volume: 0.18 cm³ 3 ·g -1 The saturated adsorption capacity for tetracycline was 87.2 mg·g. -1 .

[0057] Example 2 Preparation of the modified biochar KBC of the present invention

[0058] Take the foxtail grass powder prepared in Example 1, add 2 mol / L KOH solution, and soak at room temperature for 24 h, stirring once every 6 h to ensure uniform soaking. Then dry at 80℃ for 24 h. Place the material in a tube furnace, with nitrogen flow rate of 0.5 L / min, and heat to 600℃ at 10℃ / min, and keep at a constant temperature for 2 h for pyrolysis. After cooling, wash three times with 1 mol / L hydrochloric acid (soaking for 30 min each time) to remove potassium salt and silicate residues. Then rinse repeatedly with deionized water until the conductivity is <10 μS / cm. Dry at 80℃ for 24 h, pulverize and pass through a 200-mesh sieve to obtain KOH modified foxtail grass biochar KBC. Figure 1 b) SEM image of modified biochar KBC. As shown in the figure, modified biochar KBC exhibits a lamellar stacked structure and well-developed pores. The specific surface area was measured to be 728 m² using a fully automated specific surface area and porosity analyzer (BELSORP-MAX, Micromeritics, USA). 2 ·g -1 Total pore volume: 0.68 cm³ 3 ·g -1 The average pore size is 3.8 nm, the mesoporous content is 65%, the sheet thickness is 8-15 nm, and the saturated adsorption capacity for tetracycline is 420.6 mg·g. -1 .

[0059] Example 3: Comparison of adsorption performance of biochar before and after modification

[0060] Take 50 mL of 50 mg / L tetracycline solution and place it in a 100 mL stoppered conical flask. Add 50 mg of BC (Example 1) and KBC (Example 2) respectively, adjust the pH of the system to 3, and shake for adsorption in a constant temperature shaker at 25℃ and 200 r / min. Take a sample after 180 min, filter it through a 0.22 μm filter membrane, and determine the residual concentration of tetracycline by high performance liquid chromatography (HPLC).

[0061] Figure 2 Fourier transform infrared (FT-IR) spectra of biochar before and after adsorption (KBC+TC after adsorption, KBC before adsorption); the FT-IR curves show that the functional group characteristic peaks of KBC+TC are enhanced to varying degrees compared with KBC, which reflects that the degree of aromatization of the material is significantly improved.

[0062] Figure 3 The figure shows the adsorption kinetics curves of tetracycline on biochar before and after modification. As shown, the results indicate that the removal rate of BC was only 42.1% at 180 min, with an adsorption capacity of 26.8 mg·g⁻¹. -1 KBC removal rate reached 98.3% after 180 min, and the removal rate and adsorption capacity of KBC were 2.38 times and 2.71 times that of BC, respectively.

[0063] Example 4: Effect of dosage on KBC adsorption efficiency

[0064] Take 50 mL of 50 mg / L tetracycline solution and add 5 mg, 10 mg, 25 mg, 40 mg, 45 mg, 50 mg, and 100 mg of KBC (corresponding to dosages of 0.1, 0.2, 0.5, 0.8, 0.9, 1.0, and 2.0 g / L, respectively). Incubate at 25℃, pH=5, and 200 r / min for 6 h with shaking adsorption. Results show that when the dosage increases from 0.1 g / L to 2 g / L, the removal rate increases from 1.8% to 99.8%; the removal rate reaches over 99% when the dosage is ≥1.0 g / L; and the increase in removal rate slows down after the dosage exceeds 1 g / L (from 99.6% to 99.8%). This indicates that the modified biochar of this invention has a low dosage and significant cost advantage.

[0065] Example 5: Wide pH Range Adaptability Test

[0066] Take 50 mL of 50 mg / L tetracycline solution, adjust the pH to 3-9 with hydrochloric acid or sodium hydroxide, add 50 mg KBC, and shake to adsorb for 6 h at 25℃ and 200 r / min. Figure 4The effect of different pH values ​​on the adsorption performance of KBC was investigated. The results showed that as the pH increased from 3 to 7, the removal rate decreased from 96.5% to 91.6%; when the pH continued to increase from 7 to 9, the removal rate fluctuated at pH=8 and eventually decreased to 89.9%. Correspondingly, the equilibrium adsorption capacity... Qe The adsorption capacity of KBC decreased slowly from 48.2 mg / g to 44.9 mg / g as pH increased, indicating that KBC maintains stable adsorption performance over a wide pH range (3-9) and is suitable for the treatment of tetracycline wastewater under different water quality conditions.

[0067] Example 6: Performance Comparison with Commercial Activated Carbon

[0068] Take commercially available coconut shell activated carbon (specific surface area 1050 m²) 2 ·g -1 Tetracycline saturated adsorption capacity: 128 mg·g -1 A comparative test was conducted with KBC of the present invention: 50 mL of 200 mg / L tetracycline solution was taken, and 50 mg of coconut shell activated carbon and KBC were added respectively. Adsorption was carried out by shaking at 25℃ and 200 r / min for 24 h. The results showed that the removal rate of coconut shell activated carbon was 62.3%, and the saturated adsorption capacity was 124.6 mg·g⁻¹. -1 The removal rate of KBC was 87.5%, and the saturated adsorption capacity was 350.2 mg·g⁻¹. -1 The adsorption capacity is 1.8 times higher than that of commercial activated carbon, which fully demonstrates the performance advantages of the modified biochar of this invention.

[0069] The above embodiments fully verify that the present invention successfully prepared high-performance modified biochar through the directional activation of the silicon-rich vascular bundle structure of foxtail grass. Its adsorption capacity, pH adaptability and treatment efficiency are significantly better than those of existing adsorption materials. The process is simple and low-cost, providing a brand-new technical solution for the deep treatment of tetracycline wastewater and has important industrial application value.

Claims

1. The application of a directionally activated modified biochar based on the silicon-rich vascular bundle structure of *Setaria viridis* in the adsorption and removal of tetracycline in water, characterized in that, The initial pH of the adsorption system is 3-9; the preparation method of directionally activated modified biochar based on the silica-rich vascular bundle structure of *Setaria viridis* includes the following steps: (1) Wash and dry the foxtail grass, then crush and sieve it to obtain foxtail grass powder. (2) Soak the foxtail grass powder in a KOH solution with a concentration of 1.5~2.5 mol / L for 20~28 h to allow KOH to fully penetrate into the vascular bundle channels and silicate gaps of the foxtail grass and initiate pre-activation; after soaking, take out the sample and dry it. (3) In an inert atmosphere, the impregnated sample obtained in step (2) is pyrolyzed at a temperature of 550~650℃; during the pyrolysis process, KOH undergoes decarboxylation and cross-linking reaction with cellulose in foxtail grass, and at the same time undergoes synergistic etching reaction with silicate to form a lamellar mesoporous-microporous composite structure; after the pyrolysis is completed, it is naturally cooled. (4) First, acid washing is used to remove potassium salt and silicate residues from the pyrolysis sample. Then, the sample is washed with deionized water, and finally dried, pulverized, and sieved to obtain oxygen-containing functional groups-oriented activated modified biochar with a surface rich in hydroxyl, carboxyl, and ether bonds based on the silicon-rich vascular bundle structure of *Setaria viridis*. Among them: In step (3), the temperature is increased to the pyrolysis temperature at a heating rate of 8~12 ℃ / min, and the pyrolysis time is 1~4 h.

2. The application according to claim 1, characterized in that, In step (1), the particles are crushed to a particle size of 0.2~1.0 mm and passed through a 50-mesh sieve.

3. The application according to claim 1, characterized in that, In step (2), the drying temperature is 75-85℃ and the drying time is 20-30h.

4. The application according to claim 1, characterized in that, In step (3), the inert atmosphere is nitrogen or argon, and the flow rate is 0.2~1.0 L / min.

5. The application according to claim 1, characterized in that, In step (3), the pyrolysis temperature is 580~620℃ and the pyrolysis time is 1.5~2.5 h.

6. The application according to claim 1, characterized in that, In step (4), the sample is acid-washed with 0.5~2 mol / L hydrochloric acid or sulfuric acid; the sample is washed with deionized water until neutral.

7. The application according to claim 1, characterized in that, The directional activated modified biochar based on the silicon-rich vascular bundle structure of foxtail grass exhibits a directional lamellar or stacked morphology of the foxtail grass vascular bundle structure, with multi-level pore distribution and excellent connectivity.

8. The application according to claim 1, characterized in that, Directionally activated modified biochar based on the silicon-rich vascular bundle structure of *Setaria viridis* has a specific surface area ≥500 m². 2 ·g -1 The total pore volume is 0.4~1.2 cm³. 3 ·g -1 The average pore size is 2~6 nm, and the mesopore ratio is ≥60%; the layer thickness is 5~20 nm, and the interlayer spacing is 3~8 nm.

9. The application according to claim 1, characterized in that, The water bodies include pharmaceutical wastewater, aquaculture wastewater, hospital wastewater, and surface water bodies contaminated with tetracycline, with an initial tetracycline concentration of 5-200 mg / L.

10. The application according to claim 1, characterized in that, The dosage of modified biochar is 0.1~3.0 g / L.

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