Biochar-loaded nano zero-valent iron composite material as well as preparation method and application thereof

Abstract

The invention provides a biochar loaded nano zero-valent iron composite material as well as a preparation method and application thereof, and belongs to the technical field of comprehensive application of environmental protection and waste recycling. The method comprises the following steps: pyrolyzing and carbonizing a biochar raw material to prepare original biochar; the original biochar is washed with deionized water and then dried; then performing primary ball milling on the biochar and sodium alginate, and then performing secondary ball milling on the biochar and nano zero-valent iron to prepare the biochar loaded zero-valent iron composite material. The zero-valent iron loaded biochar composite material is prepared by adopting a directional ball milling method, and is used for activating persulfate to realize efficient removal of tetracycline hydrochloride in water. Zero-valent iron is loaded on biochar by adopting a step-by-step ball milling method, firstly, sodium alginate is used as a binder, and forms a colloidal layer on the surface of the material, so that the release speed of nano zero-valent iron in water can be effectively slowed down, and the capacity of the material for permanently activating persulfate in a water environment is enhanced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental protection and comprehensive application of waste resources, and particularly relates to a biochar loaded nano zero-valent iron composite material and a preparation method and application thereof. BACKGROUND

[0002] As the main environmental pollutants of medical waste water, livestock excretion and aquaculture drug residues, antibiotics present multi-dimensional characteristics of ecological hazards: not only weaken the primary productivity of water body by inhibiting the photosynthesis of algae, but also interfere with the reproductive endocrine function of fish, and even induce environmental bacteria to produce drug resistance genes (ARGs), accelerating the global spread of superbugs. Taking tetracycline hydrochloride (TCH) as an example, this broad-spectrum antibiotic with an annual use of more than 6000 tons, due to the incomplete biological metabolism, 30%-90% of the original drug enters the environment through excretion, and currently µg / L level residues (up to 45.7 µg / L) have been detected in global water bodies, and the accumulation amount in soil sediments reaches 0.8-4.3 mg / kg. Its high water solubility (300 mg / L) and persistence (half-life > 100 days) promote TCH to migrate through adsorption-desorption at the water-soil interface and be transmitted along the food chain. Studies have shown that 0.1 mg / L TCH exposure can cause damage to algal cell membrane lipid peroxidation, and the fish embryo malformation rate increases to 67% at a concentration of 1 mg / L; more seriously, when the environmental concentration is more than 0.5 mg / L, the abundance of drug resistance genes tetM and tetW increases by 300 times, significantly enhancing the multiple drug resistance of pathogenic bacteria. Given that TCH pollution has penetrated 76% of global freshwater ecosystems, developing efficient and low-cost pollution control technology has become a core breakthrough to block the transmission chain of drug resistance genes and maintain ecological safety.

[0003] Nano zero-valent iron (nZVI) is favored in environmental remediation due to its environmental and economic characteristics, especially in treating pollutants in groundwater and industrial wastewater. At the same time, biochar is a low-cost, waste resource utilization high-performance adsorbent and carrier, and some researchers use biochar combined with nZVI to effectively degrade organic pollutants through advanced oxidation process, providing a new method for environmental remediation. However, due to the easy aggregation and oxidation of nZVI in environmental treatment process, its practical application efficiency is limited. Through the treatment of surfactants or organic polymers, the dispersibility and stability can be improved.

[0004] High-energy ball milling is a material preparation method based on mechanochemical effects. It applies high-frequency impact, shearing, and friction to raw material powders using milling media (such as stainless steel balls or tungsten carbide balls), achieving atomic-level mixing and structural control. Studies have shown that when the milling intensity reaches a critical value, the average grain size of metal powders can be refined to below 20 nm, increasing the specific surface area by 3-5 times, thus significantly enhancing surface activity. Sodium alginate (SA) is a natural polysaccharide extracted from brown algae. This invention introduces SA as a green binder to construct a core-shell composite material. The mechanochemical effect of high-energy ball milling not only uniformly embeds nZVI particles into the mesoporous channels of biochar but also induces the formation of Fe-C heterostructures through plastic deformation of the carbon matrix, significantly enhancing electron transfer efficiency. The introduction of sodium alginate further overcomes the material's delay-response bottleneck—anchoring nZVI particles through chelation and inhibiting oxidative aggregation; simultaneously, the dynamic hydration layer of SA delays Fe dissolution through a hydrogen bond network and triggers self-healing functions under fluctuating pH conditions in wastewater. This strategy provides an efficient and low-consumption technical solution for antibiotic wastewater treatment through atomic-level dispersion via high-energy ball milling and interfacial regulation with sodium alginate. It also offers a new "mechanical-chemical" synergistic paradigm for the design of heterogeneous catalytic materials, promoting the engineering of advanced oxidation technologies and demonstrating significant application prospects. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing biochar-supported zero-valent iron composite materials using directional ball milling, and to apply this method to the removal of tetracycline hydrochloride from water by activated persulfate treatment. This invention utilizes mechanical ball milling with an organic polymer as a binder, taking sodium alginate as an example, to load zero-valent iron onto porous biochar. This effectively enhances the catalytic morphology of the composite material while preventing the aggregation and oxidation of nano-zero-valent iron, thus improving the material's stability and sustainable application. This method is not only low-cost, highly efficient, and pollution-free, but also uses widely available materials, has a simple preparation process, and is easy to scale up. In summary, this invention has promising application prospects, particularly in improving pollutant removal efficiency and reducing environmental remediation costs.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: a method for preparing a biochar-supported nano-zero-valent iron composite material, wherein the preparation of the biochar-supported nano-zero-valent iron composite material uses biochar as the core, sodium alginate as a binder, and nano-zero-valent iron is loaded on the surface, specifically including the following steps: (1) After pretreatment, the biomass raw material is pyrolyzed and carbonized in an inert gas atmosphere to obtain raw biochar; (2) Grind, wash, centrifuge and dry the raw biochar obtained in step (1) to obtain pretreated biochar; (3) The pretreated biochar obtained in step (2) is mixed with sodium alginate solution and subjected to preliminary ball milling; (4) Add nano-zero valent iron to the ball milling product of step (3) and perform secondary ball milling to obtain a viscous mixture; (5) The viscous mixture obtained in step (4) is dried and crushed to obtain the biochar-supported nano-zero-valent iron composite material.

[0007] The biomass raw materials are selected from agricultural and forestry waste, including at least one of peanut shells, straw, fruit shells or sawdust; The polysaccharide binder can be replaced with chitosan or carboxymethyl cellulose.

[0008] Preferably, in step (1): the inert gas is nitrogen or helium; the heating rate of the pyrolysis carbonization is 6-10℃ / min, preferably 10℃ / min; the pyrolysis carbonization temperature is 500-900℃, preferably 700℃; and the pyrolysis carbonization retention time is 1.5-2.5h, preferably 2h.

[0009] Preferably, in step (2): the water washing uses deionized water, and the mass-to-volume ratio of biochar to deionized water is 1g:5mL to 1g:20mL; the water washing stirring rate is 300-500r / min, and the stirring time is 18-24h; the centrifugation speed is 2000-5000r / min, preferably 3000r / min, and the centrifugation time is 3-5min; the drying temperature is 60-105℃, preferably 80℃.

[0010] Preferably, in step (3): the concentration of the sodium alginate solution is 1 g / L; the volume ratio of the pretreated biochar to the sodium alginate solution is 5:1 to 30:1, preferably 15:1; the rotation speed of the initial ball mill is 800 to 1800 r / min, preferably 1500 r / min; and the initial ball milling time is 5 to 15 min, preferably 5 min.

[0011] Preferably, in step (4): the particle size of the nano-zero valent iron is 100-300 nm; the mass ratio of the pretreated biochar to the nano-zero valent iron is 5:1-20:1, preferably 10:1; the rotation speed of the secondary ball mill is 800-1800 r / min, preferably 1500 r / min; and the secondary ball milling time is 5-15 min, preferably 5 min.

[0012] Further preferably, in step (5): the drying temperature is 80-105℃, preferably 85℃; the drying time is 18-24h; the crushing is carried out by mechanical grinding and passing through a 100-mesh sieve.

[0013] Another technical solution of the present invention is: a biochar-supported nano-zero-valent iron composite material prepared by the above method, wherein the composite material has a core-shell structure and nano-zero-valent iron is uniformly dispersed in the biochar mesoporous channels; The surface of the composite material is rich in Fe-C heterostructures, which enhances electron transfer efficiency. The composite material is stable in the pH range of 2 to 8, and the uniformly dispersed loading structure formed by the layered adhesion of organic polymers can slow down the rapid hydrolysis and aggregation of nano-zero valent iron.

[0014] To achieve the objective of this invention, another technical solution is also provided: the application of the above-mentioned biochar-supported nano-zero-valent iron composite material in the degradation of tetracycline hydrochloride in activated persulfate water, comprising the following steps: (1) Add the composite material and persulfate to a water body containing tetracycline hydrochloride; (2) React under stirring conditions for 30–120 min, preferably 60 min, to degrade tetracycline hydrochloride; (3) After the reaction is completed, the composite material is recovered by centrifugation for recycling. Specifically, the centrifugation is carried out by a high-speed centrifuge with centrifugation parameters of 2000-5000 r / min, preferably 3000 r / min. The supernatant liquid after centrifugation is poured out, and the composite material placed at the bottom of the centrifuge tube is rinsed with deionized water and placed in an oven to dry for the next recycling.

[0015] Preferably, the persulfate is potassium persulfate (K2S2O8), sodium persulfate (Na2S2O8), or ammonium persulfate ((NH4)2S2O8), with potassium persulfate being preferred; the concentration of the persulfate is 0.1–1 mM, preferably 0.5 mM; the initial concentration of the tetracycline hydrochloride is 5–100 mg / L, preferably 50 mg / L; and the mass ratio of the composite material to the tetracycline hydrochloride is 1:1–20:1, preferably 5:1.

[0016] More preferably, the free radicals generated by the activation of persulfate by the composite material include singlet oxygen free radicals, sulfate free radicals and hydroxyl free radicals; the removal rate of tetracycline hydrochloride by the composite material is ≥99.2% within 60 min; and the removal rate of tetracycline hydrochloride by the composite material is still ≥88.3% after 5 cycles of use.

[0017] Compared with the prior art, the present invention achieves the following technical effects: This invention utilizes a directional ball milling method to prepare a zero-valent iron-supported biochar composite material for the efficient removal of tetracycline hydrochloride from water by activating persulfate. Zero-valent iron is loaded onto biochar using a stepwise ball milling method. Sodium alginate is used as a binder, forming a gel-like layer on the material surface, which effectively slows down the release rate of nano-zero-valent iron in water, thereby enhancing the material's ability to persistently activate persulfate in an aquatic environment. This preparation method is simple, environmentally friendly, and easily scalable for industrial production. In summary, this invention not only provides a new approach to preparing environmentally functional materials to improve the removal efficiency of tetracycline hydrochloride from water, but also realizes the resource reuse of agricultural and forestry waste, possessing significant environmental and economic value.

[0018] The advantages of this invention are as follows: The biochar raw materials used in this invention are widely available, including inexpensive and readily available agricultural and forestry waste, which significantly reduces the economic cost of the synthetic materials. The directional ball milling method proposed in this invention is used to prepare biochar-supported zero-valent iron composite materials. The stepwise synthesis is carried out by ball milling, which is easy to industrialize and does not require the addition of additional compounds. The biochar-supported zero-valent iron composite material prepared by the directional ball milling method of this invention not only has the characteristics of large specific surface area and rich surface functional groups compared with traditional composite materials of this type, but also significantly improves the stability of the material and solves the problems of easy hydrolysis and agglomeration of zero-valent iron. In addition, the composite material also has certain adsorption performance for pollutants such as tetracycline hydrochloride in water. The biochar-supported zero-valent iron composite material prepared in this invention exhibits excellent persulfate activation efficiency, enabling rapid removal of tetracycline hydrochloride from water. Specifically, this material can remove 99.2% of tetracycline hydrochloride from water within 60 minutes. The synergistic effect of biochar and zero-valent iron enhances the active groups on the material surface, further improving the removal efficiency of tetracycline hydrochloride. Attached Figure Description

[0019] For ease of explanation, the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0020] Figure 1 This is a flowchart illustrating the preparation process of the biochar-supported nano-zero-valent iron composite material in this invention. Figure 2 Graphs showing the effects of different reaction systems on the removal of tetracycline hydrochloride; Figure 3 The image shows the XRD pattern of the composite material. Figure 4 These are images showing the effect of composite materials activating persulfate to degrade tetracycline hydrochloride under different factors; Figure 5 This is a diagram showing the effect of activated persulfate degrading tetracycline hydrochloride under multiple cycle experiments on composite materials. Detailed Implementation

[0021] The following are specific embodiments of the present invention, described in conjunction with the accompanying drawings, to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments. Specific details, such as particular configurations, are provided in the following description merely to aid in a comprehensive understanding of the embodiments of the present invention. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0023] Unless otherwise specified, the materials, practices, and experimental equipment involved in the embodiments of this invention are all commercially available products in the relevant chemical and biotechnology fields.

[0024] Example 1:

[0025] This invention relates to a method for preparing a biochar-supported nano-zero-valent iron composite material with activated persulfate, comprising the following steps: After collecting everyday waste peanut shells, the surface residue is washed off with deionized water, and then the shells are dried in an oven to remove excess moisture. The dried peanut shells are then pulverized using a pulverizer, and the pulverized shells are placed in a tube furnace for pyrolysis and carbonization. The heating rate is 10 °C / min, and heating is stopped once 700 °C is reached. The tube furnace temperature is then maintained at 700 °C for 2 hours. After the carbonization process is complete, the shells are allowed to cool naturally to room temperature to obtain raw peanut shell biochar.

[0026] Take 10 g of the raw biochar obtained in step (1) and add 100 mL of deionized water to a 150 mL beaker at a volume ratio of 10:1. Stir at 400 r / min for 2 h on a magnetic stirrer. Then, transfer the thoroughly washed black mixture to a 50 mL centrifuge tube and centrifuge at 3000 r / min for 5 min. Remove the centrifuge tube and pour off the supernatant. Use a wash bottle containing deionized water to wash the biochar at the bottom of the centrifuge tube into a petri dish. Then, place the petri dish containing the mixture of biochar and deionized water in an 80 °C oven to dry for 24 h. After drying, remove the petri dish and gently scrape off the raw biochar adhering to it with a spatula to obtain the water-washed and dried raw biochar.

[0027] Take 3 g of the dried raw biochar obtained in step (2). First, put 1.5 g of the biochar into the grinding jar of a high-energy ball mill. Then, add 1 mL of a 1 g / L sodium alginate solution to the surface of the raw biochar. Then, cover the surface with another 1.5 g of raw biochar. Set the high-energy ball mill to 1500 r / min and mill for 5 min. After milling, open the grinding jar and weigh out nano-zero ferric iron with a mass ratio of raw biochar to nano-zero ferric iron of (10:1). Add the nano-zero ferric iron to the grinding jar and cover the surface of the biochar with the biochar. Then, turn on the high-energy ball mill and set the speed to 1500 r / min and mill for 5 min. Use a spatula to gently scrape off the black viscous mixture adhering to the grinding jar and place it on a petri dish.

[0028] The black viscous mixture obtained in step (3) was placed in an 85°C oven for drying for 24 h. After drying, the petri dish was removed, and the black powder was gently scraped off with a spatula and stored in a sealed bag. Finally, the biochar-supported nano-zero-valent iron composite material prepared by stepwise ball milling was obtained.

[0029] A method for activating persulfate to degrade tetracycline hydrochloride in water using a biochar-supported nano-zero-valent iron composite material prepared by directional ball milling, comprising the following steps: First, persulfate is added to the water containing tetracycline hydrochloride. Then, biochar-supported nano-zero-valent iron composite material is added while stirring with a magnetic stirrer. The reaction pH is controlled between 2 and 8. The biochar-supported nano-zero-valent iron composite material activates the persulfate to generate singlet oxygen radicals, sulfate radicals, and hydroxyl radicals, which degrade the tetracycline hydrochloride in the water. The preferred pH is 3 to 6.

[0030] The amounts of biochar-supported nano-zero-valent iron composite material, persulfate, and tetracycline hydrochloride are 10–100 mg, 0.1–2 mM / L, and 5–100 mg / L, respectively; preferably 20 mg, 0.5 mM / L, and 50 mg / L.

[0031] The persulfate is one or more of Na2S2O8, K2S2O8, and (NH4)2S2O8, preferably K2S2O8.

[0032] The activation and degradation reaction time is greater than 30 to 120 minutes, preferably 60 minutes.

[0033] Example 2:

[0034] The biochar-supported nano-zero-valent iron composite material prepared in Example 1 was tested.

[0035] Biochar-supported nano-zero-valent iron composite material was added to a 150 mL beaker, and tetracycline hydrochloride at a concentration of 50 mg / L was added. The reaction volume was 100 mL, and deionized water was used as the solvent. The initial pH of the reaction was measured to be 4.03. Potassium persulfate was added at 0.5 mM / L, and nZVI-HBC at 0.2 g / L. The experiment was conducted in a magnetic stirrer at a stirring rate of 400 r / min at room temperature (25 ℃). Samples of 1 mL were taken at 0, 5, 10, 30, and 60 min, and the reaction was quenched with 1 µL of methanol (MeOH). The samples were filtered through a 0.22 μm filter membrane and analyzed by high-performance liquid chromatography (HPLC). A Syncronis column (250 × 4.6 mm, C18, 5 μm) was used, the detection wavelength was 355 nm, and a PDA detector was used. The tetracycline hydrochloride content was determined by HPLC.

[0036] Meanwhile, under the same experimental conditions, a control experiment was conducted by changing the added materials, as follows: 1) Only nano-zero valent iron was added to the system, and the amount of nano-zero valent iron added was 0.02 g / L; 2) Only 700BC was added to the system, and the amount of 700BC added was 0.2 g / L; 3) Nano-zero valent iron and 700BC were added to the system in a mixed manner, with the amount of nano-zero valent iron added being 0.02 g / L and the amount of 700BC added being 0.18 g / L; 4) The amount of potassium persulfate added to the system is 0.5 mM / L, and the amount of nano-zero valent iron added is 0.02 g / L; 5) Only potassium persulfate was added to the system at a concentration of 0.5 mM / L; 6) The amount of potassium persulfate added to the system is 0.5 mM / L, and the amount of 700BC added is 0.2 g / L; 7) The amount of potassium persulfate added to the system is 0.5 mM / L, and the amount of nZVI-HBC added is 0.2 g / L.

[0037] Changes in tetracycline hydrochloride removal rate are as follows: Figure 2 As shown, nZVI-HBC showed the highest and fastest efficiency in activating PDS to degrade TCH, with a removal rate of 99.2% for tetracycline hydrochloride after 60 min of reaction. Compared with nZVI, nZVI-HBC had a lower Fe content for the same mass, but a higher degradation rate and efficiency, indicating that nZVI-HBC was more efficient in activating PDS.

[0038] Figure 3The XRD patterns of pristine biochar (700 BC) and the biochar-supported nano-zero-valent iron composite (nZVI-HBC) are shown. The main characteristic peak of zero-valent iron is 2θ at 54.72°. The XRD pattern of pristine biochar (700 BC) shows a broad diffraction peak between 20 and 30°, indicating an amorphous graphite structure. The XRD pattern of the ball-milled biochar-supported nano-zero-valent iron composite (nZVI-HBC) shows numerous diffraction peaks, including those of Fe and SiO2. The SiO2 diffraction peak confirms the presence of quartz crystals in the biochar, and the 54.72° peak, a characteristic peak of Fe, is attributed to zero-valent iron, indicating successful loading of zero-valent iron onto the biochar.

[0039] Example 3:

[0040] Experiments were conducted on the biochar-supported nano-zero-valent iron composite material prepared in Example 1 under the influence of different factors.

[0041] Biochar-supported nano-zero-valent iron composite material was added to a 150 mL beaker, and tetracycline hydrochloride at a concentration of 50 mg / L was added. The reaction volume was 100 mL, and deionized water was used as the solvent. The initial pH of the reaction was measured to be 4.03. Potassium persulfate was added at 0.5 mM / L, and nZVI-HBC at 0.2 g / L. The experiment was conducted in a magnetic stirrer at a stirring rate of 500 r / min at room temperature. Samples of 1 mL were taken at 0, 5, 10, 30, and 60 min, and the reaction was quenched with 1 µL of methanol (MeOH). The samples were filtered through a 0.22 μm filter membrane and analyzed by high-performance liquid chromatography (HPLC). A Syncronis column (250 × 4.6 mm, C18, 5 μm) was used, the detection wavelength was 355 nm, and a PDA detector was used. The tetracycline hydrochloride content was determined by HPLC.

[0042] Figure 4 (a) The removal of tetracycline hydrochloride by potassium persulfate using biochar-supported nano-zero-valent iron composite material at different pH values. It can be seen that the degradation rate of tetracycline hydrochloride increases with decreasing pH, reaching its highest at pH 2 (99.2%). However, the removal rate of tetracycline hydrochloride is still 64.2% at pH 7. This indicates that the biochar-supported nano-zero-valent iron composite material prepared in Example 1 can effectively activate persulfate over a wide pH range, thus maintaining good removal capacity for tetracycline hydrochloride.

[0043] Figure 4 (b) The removal of tetracycline hydrochloride by potassium persulfate using biochar-supported nano-zero-valent iron composite material under the influence of different anions. It can be seen that the degradation rate of tetracycline hydrochloride increases in the presence of Cl... - SO4 2- NO3- The effect is minimal in the case of ions, especially in HCO3-. - The effect of ions reduced the degradation rate to 51.2%.

[0044] Figure 4 (c) The removal of tetracycline hydrochloride by potassium persulfate activated by biochar-supported nano-zero-valent iron under different water pollution conditions. It can be seen that the degradation rate of tetracycline hydrochloride is most affected by high-concentration aquaculture wastewater, with the composite material reducing the activation degradation rate of persulfate to 44.6%. However, the degradation rate of tetracycline hydrochloride in sewage treatment plant wastewater and river water remains above 78.4%. This indicates that the prepared biochar-supported nano-zero-valent iron can effectively activate persulfate under different water conditions, thus maintaining good removal capacity for tetracycline hydrochloride.

[0045] Example 4:

[0046] Cyclic tests were conducted on the biochar-supported nano-zero-valent iron composite material prepared in Example 1.

[0047] The prepared biochar-supported nano-zero-valent iron composite material was placed in a 250 mL Erlenmeyer flask. Tetracycline hydrochloride at a concentration of 50 mg / L was added, with a reaction volume of 100 mL and deionized water as the solvent. Potassium persulfate was added at 0.5 mM / L, and nZVI-HBC at 0.2 g / L. The experiment was conducted in a shaker at a shaking rate of 150 r / min, with each cycle lasting 30 min. After the reaction, the liquid in the Erlenmeyer flask was transferred to a 50 mL centrifuge tube and centrifuged at 3000 r / min for 5 min. After centrifugation, the supernatant was discarded, and the biochar composite material at the bottom was washed out using a wash bottle containing 50 mg / L tetracycline hydrochloride and poured into a 250 mL Erlenmeyer flask to start the next cycle. The experiment was repeated 5 times. The reaction temperature was room temperature. At 0, 5, 10, and 30 min, 1 mL samples were taken, and the reaction was quenched with 1 µL of methanol (MeOH). The samples were then filtered through a 0.22 μm filter membrane and analyzed by high performance liquid chromatography (HPLC). The chromatographic column was a Syncronis column (250 × 4.6 mm, C18, 5 μm), the detection wavelength was 355 nm, and the detector was a PDA detector. The tetracycline hydrochloride content was determined by high performance liquid chromatography.

[0048] Figure 5The results of a five-cycle experiment on the removal of tetracycline hydrochloride (TCH) from persulfate using the prepared biochar-supported nano-zero-valent iron composite material are presented. In the first reaction, after the addition of PDS, the TCH removal efficiency was 97.6%; after washing and recovery, the removal efficiency was 95.5% within 30 minutes in the second reaction; 94.5% in the third; 93.2% in the fourth; and 88.3% after the fifth recovery. The degradation of pollutants in the nZVI / HBC@PDS system mainly depends on the free radicals generated by catalytic activation, Fe... 0 Consumption and the accumulation of pollutants on the material lead to a slight decrease in performance, demonstrating good recycling value.

[0049] Example 5:

[0050] The biochar-supported nano-zero-valent iron composite material ① prepared in Example 1, the material ② prepared by ball milling zero-valent iron and biochar, and the composite material ③ prepared by mixing sodium alginate, biochar, and zero-valent iron were compared through cyclic tests.

[0051] The specific steps for preparing material ② by ball milling zero-valent iron and biochar are as follows: (1) Take 3 g of the raw biochar obtained in step (1) of Example 1 and place it in a ball mill jar; weigh the raw biochar and nano zero-valent iron with a mass ratio of (10:1) and add it to the ball mill jar, and ball mill it according to the previous ball milling conditions.

[0052] (2) Take out the above mixture and place it in an 85°C oven to dry for 24 h. After drying, take out the petri dish and use a spatula to gently scrape off the black powder into a sealed bag for storage to obtain material ②.

[0053] The composite material was prepared by mixing sodium alginate, biochar, and zero-valent iron. The specific steps are as follows: (1) Dissolve 2 g of sodium alginate in 100 mL of oxygen-free deionized water, heat to dissolve at 55°C, let stand for 60 min to remove air bubbles from the sol, and obtain a sodium alginate solution with a mass concentration of 2%. (2) Mix 1 g of nano-zero valent iron, 1 g of biochar and the obtained sodium alginate solution, stir evenly to obtain sodium alginate / biochar supported nano-zero valent iron blend SA / BC-nZVI. (3) Weigh 20 g of CaCl2 and dissolve it in 500 mL of ultrapure water to obtain a CaCl2 solution with a mass concentration of 4.0%. Take 100 mL of the obtained blend SA / BC-nZVI and add it dropwise to the prepared CaCl2 solution with a syringe to carry out cross-linking reaction. After reacting for 60 min, spherical sodium alginate / biochar co-supported nano zero-valent iron (SA / BC-nZVI microspheres) are obtained. (4) The spherical sodium alginate / biochar co-supported nano zero-valent iron obtained in step (3) was washed 5 times with ultrapure water and dried in a vacuum freeze dryer for 24 h to obtain sodium alginate / biochar co-supported nano zero-valent iron composite material ③.

[0054] The materials ①, ② and ③ prepared above were compared according to the cyclic test method described in Example 4.

[0055] Table 1 Cycle number Material 1 Material 2 Material 3 Degradation rate in the first cycle 97.6% 97.9% 85.8% Degradation rate in the second cycle 95.5% 40.8% 86.7% Degradation rate in the third cycle 94.5% 16.7% 85.2% Degradation rate in the fourth cycle 93.2% 10.7% 82.8% Degradation rate in the fifth cycle 88.3% 7.5% 83.3% Degradation rate in the sixth cycle 70.6% 3.6% 80.1% The final experimental results are shown in Table 1. The biochar-supported nano-zero-valent iron composite material ① prepared by directional ball milling has good repeatability. After the first four cycles, the degradation rate is still 93.2%, and then the degradation rate decreases rapidly, with a degradation rate of 70.6% in the sixth experiment. Material ② obtained by ball milling zero-valent iron with biochar without adding sodium alginate has a better effect in the first reaction, with a TCH removal rate of 97.9%, but its cycle performance is poor. It has decreased to 40.8% in the second reaction, and the removal rate is only 3.6% after the sixth experiment. The composite material ③ prepared by the mixing method also has a good effect in preventing the polymerization of zero-valent iron, but its iron release efficiency is lower than that of material ①. Although the TCH removal effect is stable, the degradation rate is still 80.1% after six cycles, but the highest degradation rate is 86.7%.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0057] This invention discloses a method for preparing biochar-supported nano-zero-valent iron composite material for activating persulfate degradation of tetracycline hydrochloride in water using directional ball milling, belonging to the field of water pollution remediation functional materials and treatment technology. The preparation method of this composite material includes the following steps: peanut shell raw materials are crushed and placed in a tube furnace under nitrogen atmosphere to prepare raw biochar at 700 °C using pyrolysis carbonization. The prepared biochar raw material is washed three times until pH neutral, centrifuged, and dried to obtain pretreated biochar. The biochar material is then pre-milled with an appropriate amount of sodium alginate solution in a ball mill jar, followed by secondary ball milling with nano-zero-valent iron. The resulting composite is then dried to obtain the biochar-supported nano-zero-valent iron composite material. This composite material can achieve highly efficient removal of tetracycline hydrochloride when activated by persulfate, with a removal rate of 99.2% after 60 min of reaction, and also exhibits significant recycling performance. The biochar-supported nano-zero-valent iron composite material proposed in this invention can efficiently activate persulfate to generate singlet oxygen radicals, sulfate radicals, and hydroxyl radicals over a wide pH range, significantly improving the removal efficiency of tetracycline hydrochloride. Furthermore, this technology is easy to operate, highly efficient, and environmentally friendly.

[0058] Those skilled in the art to which this application pertains may make various modifications or additions to the specific embodiments described, or adopt similar methods to replace them, without departing from the inventive concept of this application or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a biochar-supported nano-zero-valent iron composite material, characterized in that, Includes the following steps: (1) After pretreatment, the biomass raw material is pyrolyzed and carbonized in an inert gas atmosphere to obtain raw biochar; (2) Grind, wash, centrifuge and dry the raw biochar obtained in step (1) to obtain pretreated biochar; (3) The pretreated biochar obtained in step (2) is mixed with sodium alginate solution and subjected to preliminary ball milling; (4) Add nano-zero valent iron to the ball milling product of step (3) and perform secondary ball milling to obtain a viscous mixture; (5) The viscous mixture obtained in step (4) is dried and crushed to obtain the biochar-supported nano-zero-valent iron composite material.

2. The preparation method according to claim 1, characterized in that, In step (1): the inert gas is nitrogen or helium, the heating rate of the pyrolysis carbonization is 6-10℃ / min, the pyrolysis carbonization temperature is 500-900℃, and the pyrolysis carbonization retention time is 1.5-2.5h.

3. The preparation method according to claim 1, characterized in that, In step (2): the water washing uses deionized water, and the mass-volume ratio of biochar to deionized water is 1g:5mL to 1g:20mL; the water washing stirring rate is 300-500r / min, and the stirring time is 18-24h; the centrifugation speed is 2000-5000r / min, the centrifugation time is 3-5min, and the drying temperature is 60-105℃.

4. The preparation method according to claim 1, characterized in that, In step (3): the concentration of the sodium alginate solution is 1 g / L; the volume ratio of the pretreated biochar to the sodium alginate solution is 5:1 to 30:1; the rotation speed of the initial ball mill is 800 to 1800 r / min; and the initial ball milling time is 5 to 15 min.

5. The preparation method according to claim 1, characterized in that, In step (4): the particle size of the nano-zero valent iron is 100-300 nm; the mass ratio of the pretreated biochar to the nano-zero valent iron is 5:1-20:1; the rotation speed of the secondary ball mill is 800-1800 r / min; and the secondary ball milling time is 5-15 min.

6. The preparation method according to claim 1, characterized in that, In step (5): the drying temperature is 80-105℃; the drying time is 18-24h; the crushing is carried out by mechanical grinding and passing through a 100-mesh sieve.

7. A biochar-supported nano-zero-valent iron composite material prepared according to any one of claims 1 to 6, characterized in that: The composite material has a core-shell structure, with nano-zero-valent iron uniformly dispersed in the mesoporous channels of biochar. The surface of the composite material is rich in Fe-C heterostructures, which enhances electron transfer efficiency. The composite material is stable in the pH range of 2 to 8, and the uniformly dispersed loading structure formed by the layered adhesion of organic polymers can slow down the rapid hydrolysis and aggregation of nano-zero valent iron.

8. The application of the biochar-supported nano-zero-valent iron composite material according to claim 7 in the degradation of tetracycline hydrochloride in water bodies by activated persulfate, characterized in that, Includes the following steps: (1) Add the composite material and persulfate to a water body containing tetracycline hydrochloride; (2) React under stirring conditions for 30–120 min to degrade tetracycline hydrochloride; (3) After the reaction is complete, the composite material is recovered by centrifugation and recycled.

9. The application according to claim 8, characterized in that: The persulfate is potassium persulfate, sodium persulfate, or ammonium persulfate; The concentration of the persulfate is 0.1–1 mM; The initial concentration of the tetracycline hydrochloride is 5–100 mg / L; The mass ratio of the composite material to tetracycline hydrochloride is 1:1 to 20:

1.

10. The application according to claim 8, characterized in that: The free radicals generated by the activation of persulfate by the composite material include singlet oxygen free radicals, sulfate free radicals, and hydroxyl free radicals.

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