Iron modified biochar as well as preparation method and application thereof

Abstract

The invention relates to the technical field of iron modified biochar, in particular to iron modified biochar as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing tea stem powder with FeCl3. 6H2O, and sequentially drying and pyrolyzing to obtain the iron modified biochar. According to the preparation method, tea stem powder and solid FeCl3 are ground and mixed and then directly pyrolyzed to prepare the iron modified biochar, and the preparation method has sustainability, low cost and workability. The tea stems are selected as the biochar precursor, the source is wide, the cost is low, the concept of treating waste with waste is met, the tea stems are loose in texture, the pretreatment energy consumption is low, the method is suitable for large-scale production, and the prepared iron-modified biochar has the excellent anti-organism removal rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of iron modified biochar, in particular to an iron modified biochar and a preparation method and application thereof. BACKGROUND

[0002] The main sources of antibiotics in surface water mainly include the following aspects: effluent containing antibiotic residues discharged by sewage treatment plants; tail water discharged after livestock and poultry breeding or aquaculture activities; wastewater discharged by pharmaceutical enterprises. According to the surface water detection report, 7 kinds of antibiotics represented by amoxicillin have been detected in the surface water in China, and the concentration of amoxicillin (AMX) antibiotic is the highest. The current status of water body antibiotic pollution is serious, the types of antibiotic pollution are various, the pollution concentration is high, and the antibiotics exist in various water bodies, which is harmful to the environment and human health. Therefore, it is urgent to find a suitable method for treating water body antibiotic pollution.

[0003] At present, the methods for removing antibiotics in water bodies can be divided into three categories: physical, chemical and biological technologies. The physical treatment method is mainly based on the adsorption principle, and this method has the advantages of economic environmental protection and simple operation, and has been widely used in recent years to remove antibiotic pollutants in water. The main adsorption materials include activated carbon and some new composite materials. Chemical technology includes ion exchange technology and advanced oxidation technology, but these methods have high operating costs and may also cause secondary pollution. Biological technology includes microbial method and plant method. The microbial method is to treat antibiotics by microorganisms, including aerobic treatment, anaerobic treatment, anaerobic / aerobic combined treatment process, etc. As shown in the Chinese patent with publication number CN117550753A, a coagulation reaction zone, a pre-sedimentation tank, an efficient sedimentation tank, an ozone gas distribution zone, an ozone oxidation tank, a primary anoxic tank, a primary aerobic tank, a secondary anoxic tank, a secondary aerobic tank and a disinfection tank are sequentially arranged for water treatment. However, the residual antibiotics can have toxic side effects on aerobic microorganisms, inhibiting their treatment effect, and there are also disadvantages of difficulty in domestication and instability. The plant method is to absorb and degrade antibiotic residues in water bodies by aquatic plants. The disadvantage is that it only has a high removal rate for specific antibiotics, has a small application range, and may produce resistant genes, resulting in a decrease in removal efficiency.

[0004] Therefore, physical technology has obvious advantages in adsorbing and removing antibiotics, and exploring an effective physical treatment method for amoxicillin antibiotics in water bodies is conducive to pollution control. SUMMARY

[0005] The technical problem to be solved by the present application is to provide an iron modified biochar which can effectively remove amoxicillin in water bodies, and a preparation method and application thereof.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is: a preparation method of iron modified biochar, comprising the following steps: mixing tea stem powder and FeCl3·6H2O, and sequentially performing drying and pyrolysis to obtain iron modified biochar.

[0007] Another technical scheme adopted by the present application is: the iron modified biochar prepared by the above preparation method of iron modified biochar.

[0008] Still another technical scheme adopted by the present application is: the application of the above iron modified biochar in removing amoxicillin in water bodies.

[0009] The present application has the beneficial effects that: the preparation method of the present application directly pyrolyzes the mixture of tea stem powder and solid FeCl3 to prepare iron modified biochar, which has sustainability, low cost and easy processability. The tea stem is selected as the biochar precursor, which is widely available and low in cost, in line with the concept of "waste treatment with waste", and the tea stem has loose texture, low pretreatment energy consumption, and is suitable for large-scale production. The prepared iron modified biochar has excellent antibio removal rate. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 SEM images of BC and FeCl3-BC in the embodiments of the present application; Figure 2 N2 adsorption / desorption and pore size distribution curves of BC and FeCl3-BC in the embodiments of the present application; Figure 3 Statistical graphs of removal rates of AMX by BC and FeCl3-BC at different pyrolysis temperatures in the embodiments of the present application; Figure 4 Statistical graphs of removal rates of AMX by FeCl3-BC at different adsorption times in the embodiments of the present application; Figure 5 Statistical graphs of removal rates and adsorption capacities of AMX by FeCl3-BC at different dosages in the embodiments of the present application; Figure 6 Statistical graphs of AMX adsorption effect and isoelectric potential of FeCl3-BC at different solution pH values in the embodiments of the present application; Figure 7 Statistical graphs of AMX adsorption capacity and adsorption capacity of FeCl3-BC at different initial mass concentrations and adsorption temperatures of AMX in the embodiments of the present application; Figure 8 Pseudo-first-order kinetic fitting model and pseudo-second-order kinetic model graphs of FeCl3-BC for AMX in the embodiments of the present application; Figure 9 Intraparticle diffusion fitting model graph of FeCl3-BC for AMX in the embodiments of the present application; Figure 10 This is a fitting graph of the experimental data of AMX adsorption by FeCl3-BC using the Langmuir isotherm adsorption model in the embodiments of the present invention; Figure 11 This is a fitting graph of the Freundlich isotherm adsorption model for the experimental data of FeCl3-BC adsorption of AMX in the embodiments of the present invention; Figure 12 This is a fitting graph of the experimental data of FeCl3-BC adsorption of AMX by the Temkin isotherm adsorption model in the embodiments of the present invention; Figure 13 The diagram shows the regeneration performance and hysteresis regression line of FeCl3-BC in this embodiment of the invention. Detailed Implementation

[0011] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0012] A method for preparing iron-modified biochar includes the following steps: mixing tea stem powder with FeCl3·6H2O, and then drying and pyrolyzing the mixture sequentially to obtain iron-modified biochar.

[0013] As can be seen from the above description, the preparation method of the present invention, which selects tea stems as biochar precursors, has the following advantages: 1) Tea stems themselves have fiber bundles and vascular bundle structures, and after carbonization, they easily form a hierarchical pore structure of micropores-mesopores-macropores, providing up to 500~1000 μm 2 1) The high specific surface area of ​​tea stems (<5%) facilitates the physical adsorption and diffusion of pollutants such as amoxicillin. 2) Tea stems have a low ash content (<5%), resulting in less pore blockage after carbonization. Compared with precursors such as rice husks / straws with ash content >10%, tea stems have a higher specific surface area retention rate. 3) Tea stems are rich in cellulose, hemicellulose, and lignin. After carbonization, they retain a large number of oxygen-containing functional groups such as -COOH and -OH, which can specifically adsorb polar organic compounds such as amino / carboxyl groups in amoxicillin through hydrogen bonding and electrostatic interactions. 4) Tea stems contain natural nitrogen elements such as protein and theanine. During carbonization, they form pyridine nitrogen / graphite nitrogen, which enhances surface polarity and catalytic activity, promoting the activation and degradation of pollutants by persulfate. 5) Natural minerals in tea stems, such as potassium, calcium, and magnesium, form metal oxides or carbonates after carbonization, which can serve as catalytic sites (e.g., CaO promotes the hydrolysis of antibiotics).

[0014] This invention involves grinding and mixing tea stem powder with solid FeCl3, followed by direct pyrolysis, resulting in a more uniform iron distribution. Compared to traditional impregnation methods, this non-impregnation method for preparing FeCl3-modified tea stem biochar has the following significant advantages: 1) Simplified process and reduced cost. 2) Improved iron loading uniformity; solution methods are prone to uneven iron loading and localized agglomeration due to uneven pore distribution in tea stems. 3) The non-impregnation method reduces the damage to the original pores of the tea stems by the liquid, preserving more hierarchical pores. 4) High-temperature in-situ reduction: direct pyrolysis of FeCl3 generates highly active Fe... 0 / Fe3O4, to avoid Fe in the impregnation method 3+ 5) Avoid oxidation: Fe during the impregnation drying process. 2+ Easily oxidized to Fe 3+ The impregnation-free method completes the reduction in one step in an inert atmosphere. 6) Environmental friendliness and reduced wastewater discharge: The impregnation-free method produces no FeCl3 waste liquid, reducing treatment costs. 7) Reduced energy consumption: By eliminating the drying process, carbonization energy consumption is reduced by 20-40%, making it suitable for large-scale production and applicable as an adsorbent for wastewater treatment.

[0015] Furthermore, the preparation method of tea stem powder is as follows: after washing the tea stems, they are dried and then pulverized.

[0016] Furthermore, the tea stem is at least one of green tea, black tea, oolong tea, white tea, yellow tea, and dark tea.

[0017] Furthermore, the mass ratio of tea stem powder to FeCl3·6H2O is 1:0.8~1.2.

[0018] As described above, if the mass ratio of tea stem powder to FeCl3·6H2O is too low, the iron loading is insufficient, and the adsorption capacity is limited; if it is too high, the iron particles will excessively aggregate, forming Fe3O4 / Fe. 3 C clusters reduce adsorption efficiency by 30% when the surface activity mass ratio is reduced to 1:1.5.

[0019] Furthermore, the pyrolysis conditions are: pyrolysis at 700~900℃ under an inert atmosphere.

[0020] As can be seen from the above description, the pyrolysis temperature determines the carbon skeleton structure and the iron species transformation pathway.

[0021] Furthermore, the inert atmosphere is nitrogen. Furthermore, the nitrogen gas permeation rate is 180~220 mL / min.

[0022] As can be seen from the above description, the nitrogen flow rate affects the pyrolysis rate and the release of volatiles. Therefore, the preferred nitrogen flow rate is 180~220 mL / min.

[0023] Furthermore, the pyrolysis products are washed and dried sequentially to obtain iron-modified biochar.

[0024] Furthermore, the washing method is as follows: first wash with anhydrous ethanol, then wash with ultrapure water.

[0025] As can be seen from the above description, anhydrous ethanol is first used for washing to selectively remove unreacted FeCl3 and organic impurities, avoiding the hydrolysis of iron salts during water washing.

[0026] Another technical solution adopted in this invention is: iron-modified biochar prepared by the above-mentioned method for preparing iron-modified biochar.

[0027] Another technical solution adopted in this invention is the application of the above-mentioned iron-modified biochar in the removal of amoxicillin from water.

[0028] As can be seen from the above description, the main mechanism by which the iron-modified biochar of the present invention removes amoxicillin from water is: Fe 3+ The Fe(OH)3 colloid generated by hydrolysis forms positively charged ≡Fe—OH2 at pH < 7. + It interacts with amoxicillin's -COO- through electrostatic action. - It binds to and adsorbs amoxicillin.

[0029] Furthermore, the amount of iron-modified biochar added is 0.67~2.67 g / L.

[0030] As described above, increasing the amount of adsorbent provides more active adsorption sites for amoxicillin, effectively increasing the contact area between the adsorbent and amoxicillin, thereby improving the adsorption efficiency of AMX. However, too many adsorption sites can easily create vacancy states, leading to a decrease in adsorption capacity. Therefore, the preferred addition amount of iron-modified biochar is 0.67~2.67 g / L.

[0031] Furthermore, the pH of the water body is 3 to 6.1.

[0032] As can be seen from the above description, the iron-modified biochar of the present invention is pH sensitive, and under neutral / alkaline conditions, Fe... 3+ It is prone to sedimentation and failure.

[0033] The tea stems used in the following examples were obtained from Qing Shi Yan Tea Factory in Wuyishan. The tea stems were obtained after processing rock tea. The main experimental instruments used are shown in Table 1, and the main reagents are shown in Table 2.

[0034] Table 1

[0035] Table 2-2

[0036] Note: Ultrapure water was used in the experiment. Example 1 of the present invention is a method for preparing iron-modified biochar, comprising the following steps: S1: Tea stem pretreatment Before conducting the experiment, the tea stems were thoroughly washed with ultrapure water to remove dust and impurities. The washed tea stems were then dried in an 80℃ oven to remove all moisture. After complete drying, they were pulverized in a grinder and then sieved through a 100-mesh standard sieve to ensure uniform particle size. Finally, the sieved tea stem powder was placed in sealed bags and stored in a dry environment for use in subsequent experiments.

[0037] Preparation of S3: FeCl3-BC Tea stem powder and FeCl3·6H2O were mixed at a 1:1 mass ratio and thoroughly ground. The mixture was then dried in an oven to remove excess moisture and placed in a quartz boat. The boat was then placed in a tube furnace, and nitrogen gas was introduced at a rate of 200 mL / min for 15 minutes to remove oxygen. The heating program was then initiated, and under nitrogen protection, the temperature was increased from room temperature to 800℃ at a rate of 5℃ / min, and maintained for 2 hours to allow for complete pyrolysis of the tea stem powder. After pyrolysis, the tube furnace was allowed to cool completely before removing the quartz boat. The product from the boat was poured into a beaker, anhydrous ethanol was added, and the mixture was washed three times in an ultrasonic cleaner. Then, ultrapure water was added, and the mixture was washed four times in an ultrasonic cleaner. After washing, the mixture was dried in a 60℃ oven. After drying, it was ground finely using an agate mortar and pestle and passed through a 100-mesh sieve to obtain iron-modified biochar, denoted as FeCl3-BC. Finally, the sieved FeCl3-BC was placed in a sealed bag and stored in a dry environment for subsequent experiments.

[0038] Comparative Example 1 of this invention is: a method for preparing tea stem biochar (BC), the steps of which are as follows: Ten g of tea stem powder prepared in previous experiments was placed in a quartz boat and then placed in a tube furnace. Nitrogen gas was introduced and the aeration rate was adjusted to 200 mL / min. Aeration was maintained for 15 minutes to remove oxygen from the tube furnace. Then, the heating program was started. Under nitrogen protection, the temperature was increased to 800℃ from room temperature at a rate of 5℃ / min and held for 2 hours to allow the tea stem powder to fully pyrolyze. After pyrolysis, the tube furnace was allowed to cool completely before the quartz boat was removed. The product in the quartz boat is tea stem biochar, denoted as BC. To facilitate subsequent experiments and applications, the prepared BC was ground in a mortar and sieved through a 100-mesh sieve to ensure uniform particle size. Finally, the sieved BC was placed in a sealed bag and stored under dry conditions for use in subsequent experiments.

[0039] The following tests were performed on the FeCl3-BC and BC prepared in Example 1 and Comparative Example 1: 1. Characterization of the properties of modified biochar samples To comprehensively analyze the performance evolution of the material samples before and after composite processing, a systematic study was conducted using a fully automated surface area and porosity analyzer (BET). The specific surface area, total pore volume, and average pore size of both unmodified tea stem biochar and ferric chloride-modified tea stem biochar were precisely measured and analyzed. Simultaneously, scanning electron microscopy (SEM) was used to meticulously observe the subtle changes in the surface morphology of both unmodified and ferric chloride-modified tea stem biochar. Furthermore, a vibrating sample magnetometer (VSM) was applied to measure the magnetic properties of the material samples and evaluate their magnetic characteristics.

[0040] 1.1 SEM See Figure 1 ,in Figure 1 (a) is the SEM image of BC. Figure 1 (b) is a SEM image of FeCl3-BC. From Figure 1 (a) As can be seen, the unmodified biochar (BC) has a smooth surface, uniform texture, and a dense overall structure. And... Figure 1 (b) It is evident that the surface of the iron-modified biochar becomes rough and irregular, with clearly visible protrusions and granular structures of varying sizes. This indicates that the iron element successfully attaches and forms aggregates or loaded particles, effectively increasing the specific surface area of ​​the biochar. Furthermore, numerous micropores are found on the surface of FeCl3-BC, providing ample adsorption sites and creating favorable conditions for the adsorption of AMX by FeCl3-BC.

[0041] 1.2 BET The pore parameters of BC and FeCl3-BC are shown in Table 3. From the table, the specific surface areas of BC and FeCl3-BC are 109.702 m². 2 / g and 563.267m 2 / g, with a total pore volume of 0.0502cm³. 3 / g and 0.2704cm 3 / g, with micropore volumes of 0.0420 cm³. 3 / g and 0.2261cm 3 / g, with average pore sizes of 1.831nm and 1.920nm respectively. This indicates that the specific surface area, total pore volume, and micropore volume of the modified biochar are about 5 times that of the unmodified biochar, proving that iron-modified biochar has a significant effect.

[0042] The specific surface area and pore size distribution of BC and FeCl3-BC were analyzed using N2 adsorption-desorption curves. The analyzed structures are shown in [see attached diagram].Figure 2 ,in Figure 2 (a) shows the N2 adsorption-desorption curve. Figure 2 (b) shows the aperture distribution curve. (From...) Figure 2 (a) It can be seen that the adsorption capacity increases rapidly at lower relative pressures, indicating that FeCl3-BC has many micropores. A hysteresis phenomenon occurs when the relative pressure reaches 0.45, indicating the presence of mesoporous structures. Therefore, the adsorption isotherm of FeCl3-BC is type IV. Figure 2 (b) It can be seen that the pore size of FeCl3-BC is mainly concentrated between 0 and 20 nm, indicating that FeCl3-BC has a microporous-mesoporous structure. ] This is consistent with the conclusions drawn from the N2 adsorption / desorption curves. Therefore, it can be concluded that FeCl3-BC possesses a porous structure with micropores and mesopores, as well as a large specific surface area, providing numerous adsorption sites for AMX.

[0043] Table 3

[0044] 2. Adsorption performance experiment of FeCl3-BC for amoxicillin 2.1 Preparation of amoxicillin standard solution and plotting of standard curve Accurately weigh 1000 mg of amoxicillin (AMX) and dissolve it in 1 L of ultrapure water to prepare a 1000 mg / L AMX stock solution, which was then stored in a light-protected environment. Using a pipette, accurately measure a certain amount of the AMX stock solution and add it to 50 mL colorimetric tubes, diluting with ultrapure water to prepare AMX solutions with concentrations of 0 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, 80 mg / L, and 100 mg / L, and mix thoroughly. Then, using a UV spectrophotometer, measure the absorbance of the prepared AMX solutions at a specific wavelength of 230 nm. Plot a standard curve of the AMX standard solutions based on the measured data to provide an accurate reference for subsequent quantitative analysis.

[0045] 2.2 Amoxicillin Adsorption Experiment This experiment employed a controlled variable method to investigate the adsorption performance of FeCl3-BC for AMX. 30 mL of AMX solution of a specific concentration was added to a 100 mL Erlenmeyer flask, along with a certain mass of FeCl3-BC. The flask was sealed and placed in a constant-temperature shaking incubator at 200 rpm and 30 °C for adsorption experiments (three parallel experiments were performed). After the adsorption process was complete, the solution was extracted using a syringe and finely filtered using a 0.22 μm microporous membrane to avoid measurement errors caused by FeCl3-BC particles. Subsequently, the absorbance of the AMX solution after adsorption by FeCl3-BC was measured using a UV spectrophotometer, and the measured data were substituted into the AMX standard curve to calculate the solution concentration. To evaluate the adsorption effect of FeCl3-BC on AMX, and to further understand the adsorption mechanism and optimal adsorption conditions of FeCl3-BC for AMX, this experiment systematically measured various factors including different temperatures, initial concentrations, pH values, adsorption times, and dosages.

[0046] Adsorption capacity Q e The formulas for calculating (mg / g) and removal rate η (%) are shown in Equations (1) and (2).

[0047] Equation (1); Equation (2); In the above formula: C o —Initial solution concentration, mg / L; C e —Concentration of solution at adsorption equilibrium, mg / L; V—Volume of adsorbed solution, L; W—Mass of adsorbent, g.

[0048] 2.3 Effect of pyrolysis temperature By changing the pyrolysis temperature as a single variable, FeCl3-BC and BC were obtained under different pyrolysis temperatures. Adsorption experiments were then conducted on them. (See...) Figure 3 ,Depend on Figure 3 It can be seen that iron-modified biochar with a pyrolysis temperature of 800℃ has the best adsorption effect on amoxicillin in water (up to 95%). The adsorption efficiency of iron-modified biochar at 800℃ is greater than that of iron-modified biochar at 600℃, which is greater than that of raw biochar at 800℃, which is greater than that of raw biochar at 600℃.

[0049] 2.4 Effect of Adsorption Time Prepare nine 100mL Erlenmeyer flasks. Add 30mL of 100mg / L AMX solution and 100mg of FeCl3-BC to each flask. Shake in a constant temperature shaker in the dark at 30℃, 200r / min, and at the natural pH for 1h, 3h, 5h, 8h, 10h, 12h, 16h, 24h, and 48h, respectively. After shaking, remove the flasks and filter the solutions through a 0.22μm filter to obtain FeCl3-BC. Measure the absorbance using a UV spectrophotometer (230nm) and calculate the removal rate and adsorption capacity.

[0050] Figure 4 The effect of different adsorption times on the AMX removal efficiency of FeCl3-BC was demonstrated. The results showed that the adsorption of AMX by FeCl3-BC reached equilibrium at approximately 5 hours, with an AMX removal efficiency as high as 95% and an adsorption capacity of approximately 28.5 mg / g. The adsorption of AMX by FeCl3-BC was relatively rapid in the first three hours, possibly because the adsorbent surface had a large number of effective adsorption sites at this time. With further increase in adsorption time, the AMX removal rate eventually tended to equilibrium due to the decrease in adsorption sites. Therefore, 5 hours was selected as the equilibrium time for the adsorption reaction.

[0051] 2.5 Impact of Dosage Prepare ten 100mg Erlenmeyer flasks. Add 30mL of 100mg / L AMX solution to each flask, and then add 20mg, 40mg, 60mg, 80mg, 100mg, 120mg, 140mg, 160mg, 180mg, and 200mg of FeCl3-BC, respectively. Incubate at 30℃, 200rpm, and at ambient pH in a constant-temperature shaking incubator in the dark for 5 hours. After incubation, remove the flasks, filter the solutions using a 0.22μm filter, and then measure the absorbance using a UV spectrophotometer (230nm). Calculate the removal rate and adsorption capacity.

[0052] Figure 5 The effect of adsorbent dosage on AMX removal rate. Figure 5 It can be seen that when the dosage increased from 0.67 g / L to 2.67 g / L, the removal rate of AMX increased significantly (from 40.30% to 95%), but the adsorption capacity decreased continuously (from 60.45 mg / g to 35.79 mg / g). This may be because the increased amount of adsorbent provides more active adsorption sites for AMX, effectively increasing the contact area between the adsorbent and AMX, thereby effectively improving the adsorption efficiency of AMX. ]When the AMX content remains constant, excessive adsorption sites easily become vacant (difficult to utilize), leading to a decrease in adsorption capacity. When the FeCl3-BC dosage increases from 2.67 g / L to 6.67 g / L, the adsorption of AMX gradually approaches equilibrium. Therefore, 2.67 g / L is selected as the optimal dosage.

[0053] 2.6 Effect of pH To investigate the effect of pH on the adsorption process, five 100 mL Erlenmeyer flasks were prepared, and 30 mL of 100 mg / L amoxicillin solution was added to each flask. The pH of the AMX solution in the Erlenmeyer flasks was adjusted to 3, 4, 6, 7, 9, and 11 using 0.1 mol / L NaOH and 0.1 mol / L HCl solutions, respectively. Then, 80 mg of FeCl3-BC was added. The flasks were placed in a constant temperature shaking incubator at 30 °C and 200 rpm for 5 hours in the dark. After shaking, the solutions were filtered through a 0.22 μm filter, and the absorbance was measured using a UV spectrophotometer (230 nm). The removal rate and adsorption capacity were calculated.

[0054] Zero-point potential (pH) of FeCl3-BC pzc The drift potential method was used for determination: Eight 100 mL Erlenmeyer flasks were filled with 30 mL of 0.01 mol / L CaCl2 solution, and the pH values ​​were adjusted to 4, 5, 6, 7, 8, 9, 10, and 11 respectively using 0.1 mol / L NaOH and 0.1 mol / L HCl solutions. 80 mg of FeCl3-BC was added, and the mixture was shaken in a constant temperature shaking incubator at 30℃ and 200 r / min in the dark for 24 h for adsorption. After the adsorption was completed, the solution was removed and filtered through a 0.22 μm filter. The final pH of the filtrate was measured. A curve was plotted with the initial pH as the abscissa and ΔpH as the ordinate. The intersection of the curve and the abscissa ΔpH = 0 is the zero-point potential (pH value) of the material sample. pzc ).

[0055] The effect of solution pH on AMX adsorption and the isopotential study of FeCl3-BC are shown in [reference needed]. Figure 6 ,in Figure 6 (a) shows the effect of solution pH on the adsorption performance of the material. Figure 6(a) The isoelectric effect of solution pH on FeCl3-BC. When the pH of the AMX solution is between 3.0 and 6.1, the removal efficiency of FeCl3-BC for AMX increases with increasing pH. At pH = 6.1, the removal efficiency of FeCl3-BC for AMX reaches a maximum of 95%, with an adsorption capacity of approximately 35.79 mg / g. When the pH of the AMX solution is between 6.1 and 11, the removal efficiency of FeCl3-BC for AMX gradually decreases with increasing pH. At pH = 11, the removal efficiency of FeCl3-BC for AMX is only 66.74%, a decrease of 28.71% compared to the highest removal efficiency. This indicates that the adsorption efficiency of FeCl3-BC is greatly affected by strong acid and strong base environments, but less affected by weak acid, neutral, and weak base environments.

[0056] Figure 6 (b) shows the zero-point potential (pH) of FeCl3-BC. pzc The study results showed that FeCl3-BC is positively charged when pH < 5.32 and negatively charged when pH > 5.32. Normally, when pH > 5.32... pzc At certain times, it is conducive to the adsorption of cations, while at certain times, pH is favorable. <pH pzc This is conducive to the adsorption of anions. When the pH of the AMX solution is less than 2.7, AMX is more likely to be used for adsorption. + It exists in the form of AMX; when pH is greater than 7.5. - It exists in the form of -COO; when the pH is between 2.7 and 7.5, it exists due to the presence of -COO. — and —NH3 + Therefore, using AMX ± FeCl3-BC exists in a specific form, and is positively charged at pH < 5.32 and negatively charged at pH > 5.32. Therefore, when pH is less than 2.7, the positively charged FeCl3-BC reacts with AMX. + Mutual repulsion leads to decreased adsorption performance. When pH > 7.5, negatively charged FeCl3-BC and AMX... - Mutual repulsion leads to reduced adsorption performance. When the pH is between 2.7 and 7.5, FeCl3-BC, which carries both charges, reacts with -COO in the AMX solution. — and —NH3 +Mutual attraction leads to high adsorption efficiency. Additionally, in acidic environments, amoxicillin exists in molecular form, resulting in stronger adsorption with biochar. Another possibility is that protonation occurs on the biochar surface under acidic conditions, increasing the positive charge and forming hydrogen bonds with electron-rich elements such as O and N in amoxicillin, thus accelerating adsorption. However, under strongly alkaline conditions, the phenolic hydroxyl and carboxyl groups of amoxicillin dissociate and become negatively charged, repelling the -COOH functional groups on the biochar surface and reducing adsorption efficiency. In summary, FeCl3-BC exhibits high adsorption performance in weakly acidic, neutral, and weakly alkaline environments. To demonstrate the material's maximum adsorption performance, subsequent experiments used pH=6.1 as the optimal parameter.

[0057] 2.7 Effects of initial AMX concentration and temperature 30 mL of AMX solutions with concentrations of 10 mg / L, 50 mg / L, 100 mg / L, 300 mg / L, 500 mg / L, 700 mg / L, and 900 mg / L were added to Erlenmeyer flasks. 80 mg of FeCl3-BC was added simultaneously. The flasks were placed in a constant-temperature shaking incubator, and different adsorption temperatures (15℃, 30℃, and 45℃) were set. Under natural pH conditions, the shaking speed was set to 200 rpm, and the mixture was shaken in the dark for 5 hours. After shaking, the solutions were filtered through a 0.22 μm filter, and the absorbance was measured using a UV spectrophotometer (230 nm). The removal rate and adsorption capacity were calculated based on this data.

[0058] Figure 7 This indicates the variation in the adsorption capacity of FeCl3-BC under different adsorption temperatures and AMX concentrations. At three different temperatures, the change in the adsorption capacity of FeCl3-BC exhibits two stages. The first stage: from AMX concentration of 10 mg / L to 300 mg / L, the adsorption capacity increases rapidly, possibly because the increased AMX concentration facilitates contact between FeCl3-BC and AMX, allowing for full utilization of the adsorption sites of FeCl3-BC. The second stage: when the AMX concentration is from 300 mg / L to 500 mg / L, the increase in the adsorption capacity of FeCl3-BC tends to reach equilibrium, possibly because the adsorption sites of FeCl3-BC have essentially reached saturation, thus inhibiting the increase in adsorption capacity. Furthermore, with increasing reaction temperature, it is evident that the adsorption capacity of FeCl3-BC for AMX also continuously increases. Therefore, the adsorption of AMX by FeCl3-BC is an entropy-increasing process and is an endothermic reaction.

[0059] 3. Adsorption kinetics Adsorption kinetics is an important tool for studying the change of adsorption rate over time and is of great significance for evaluating the adsorption performance of adsorbents. This invention uses pseudo-first-order, pseudo-second-order, and intraparticle diffusion models to fit and analyze experimental data, gaining a deeper understanding of the kinetic characteristics of the adsorption process of AMX by FeCl3-BC. The relevant experimental equations are as follows: (1) Quasi-first-order dynamic model Equation (3); In the above formula: Q t —The amount of adsorption at time t, mg / g; Q e —Adsorption capacity at equilibrium, mg / g; k1—Adsorption rate constant in the pseudo-first-order adsorption kinetic equation; t—Adsorption time, min.

[0060] (2) Quasi-second-order dynamic model Equation (4); In the above formula: t—adsorption time, min; Q t — The amount of adsorption at time t, mg / g; k2 — The adsorption rate constant of the pseudo-second-order kinetic equation; Q e —Adsorption capacity at equilibrium, mg / g.

[0061] This experiment used pseudo-first-order and pseudo-second-order dynamic models to fit and analyze the experimental data. Table 4 shows the fitted data. Figure 8 This is the fitting result.

[0062] The results in Table 4 show that the pseudo-second-order kinetic model is significantly better than the pseudo-first-order kinetic model in terms of fitting performance. The R-squared value of the pseudo-second-order kinetic model... 2 The value is as high as 0.9999, while the R-value of the quasi-first-order dynamic model is... 2 The value was only 0.5995, indicating a poor fit. Furthermore, the theoretical equilibrium adsorption capacity (28.63 mg / g) calculated using the pseudo-second-order kinetic model was in good agreement with the experimentally measured equilibrium adsorption capacity, demonstrating the model's high accuracy in predicting the adsorption behavior of FeCl3-BC for AMX. Therefore, using the pseudo-second-order kinetic model to describe the adsorption experiment has greater applicability and accuracy when exploring the kinetic mechanism of this adsorption process; thus, the pseudo-second-order kinetic model was chosen as the theoretical support. It can be concluded that the adsorption of AMX by FeCl3-BC is a physicochemical adsorption process, mainly controlled by pore filling, covalent bond formation, and electron exchange.

[0063] Table 4

[0064] (3) Intraparticle diffusion model Equation (5); In the above formula: Q t —Adsorption amount at time t, mg / g; t—Adsorption time, min; k3—Adsorption rate constant of the intraparticle diffusion model equation; C—Constant.

[0065] To clarify the diffusion mechanism of AMX particles adsorbed on FeCl3-BC, this invention applied an intraparticle diffusion model to verify the experimental data in detail. (See Table 5 and...) Figure 9 As can be seen, according to the intraparticle diffusion model, the adsorption process can be divided into two linear stages. The first stage, from 0 to 300 minutes, is called the membrane diffusion stage, and the goodness of fit R during this stage is... 2 The result is 0.94771. The second stage, from 300 to 2880 minutes, is called intraparticle diffusion, and the goodness of fit R during this stage is 0.94771. 2 The value is 0.94197. When K1 > K2, this is because amoxicillin molecules diffuse into the pores of the adsorbent material, leading to an increase in diffusion resistance. The boundary layer C1 < C2 indicates that amoxicillin diffuses relatively quickly on the surface of the adsorbent material, and the main rate-limiting factor in the adsorption process is intraparticle diffusion. Since the adsorption rate constant K1 > K2, the adsorption rate of FeCl3-BC is initially fast and then slows down.

[0066] Table 5

[0067] 4. Adsorption isotherm Adsorption isotherms are commonly used to describe the relationship between the adsorption amount and concentration of an adsorbent. This experiment selected the Langmuir, Freundlich, and Temkin equations to describe the adsorption isotherm process. The relevant equations are shown below: (1) The Langmuir isothermal adsorption model assumes that the adsorption process is mainly monolayer adsorption, K L The larger the size, the stronger the adsorption capacity.

[0068] The equation is: Equation (6); In the above formula: Q e —Equilibrium adsorption capacity, mg / g; C e —Adsorption equilibrium concentration, mg / L; Q m —Saturated adsorption capacity, mg / g; K L —Equilibrium constant of the Langmuir isotherm adsorption equation.

[0069] (2) In order to better analyze the Langmuir-type isotherm equation, the adsorption strength R is introduced. L .

[0070] The calculation formula is: Equation (7); In the above formula: K L —Langmuir type isothermal adsorption equation constant; C0—initial solution concentration, mg / L.

[0071] If R L A value greater than 1 indicates that adsorption is unfavorable; if 0... <R L A value less than 1 indicates good adsorption performance.

[0072] (3) The Freundlich isothermal adsorption model is based on the assumption of multilayer adsorption and assumes that there are complex and diverse interactions between the adsorbate and the adsorbent.

[0073] The equation is: Equation (8); In the above formula: Qe—equilibrium adsorption capacity, mg / g; 1 / n—characteristic parameter of Freundlich isotherm; K F —Freundlich isothermal adsorption equation equilibrium constant; Ce—adsorption equilibrium concentration, mg / L.

[0074] (4) The Temkin-type isothermal adsorption model is a theoretical framework that reflects the adsorption phenomenon. This model describes the complex interaction between the adsorbent and the adsorbate and reveals that the adsorption heat of molecules decreases linearly with the increase of surface coverage during the adsorption process.

[0075] The equation is: Equation (9); In the above formula: Q e —The amount of adsorption at which adsorption reaches equilibrium, mg / g; C e —The concentration of adsorbate at equilibrium, mg / L; α—The adsorption coefficient in the Temkin-type isotherm equation, which is related to the heat of adsorption; K T —Adsorption coefficient of the Temkin-type isothermal adsorption equation.

[0076] In this experiment, three isothermal adsorption models—Langmuir, Freundlich, and Temkin—were selected to fit the experimental data of FeCl3-BC adsorption of AMX, as shown in Table 8. Figures 10~12 Based on the fitting results in Table 6, R1 is... 2 >R3 2 >R2 2This indicates that the L-type adsorption isotherm equation can accurately describe the adsorption process of AMX by FeCl3-BC in aqueous solution, and also shows that the adsorption of AMX by FeCl3-BC follows a monolayer adsorption mechanism, which is basically consistent with the research results of Chen Yongliang et al. Through fitting analysis of the L-type adsorption isotherm equation, R0 was obtained. L The values ​​fall within the range of 0 to 1, clearly demonstrating the excellent adsorption performance of FeCl3-BC for AMX, with a maximum theoretical saturation adsorption capacity of 82.56 mg / g. Furthermore, fitting analysis using the F-type isotherm adsorption model revealed that the characteristic parameter 1 / n of the F-type isotherm at three different temperatures is around 0.3 (all less than 1), further proving the good adsorption performance of FeCl3-BC for AMX. The R-values ​​of the characteristic T-type isotherm equations at three different temperatures are also shown. 2 All values ​​are greater than 0.9, indicating that as the coverage of AMX by FeCl3-BC increases, the adsorption heat decreases linearly.

[0077] Table 6

[0078] 5. Adsorption Thermodynamics Analyzing adsorption thermodynamics helps us understand the driving forces and directions of the adsorption process. The ΔG of the adsorption process can be calculated using the van der Rohe equation and the Gibbs-Helmholtz equation. 0 ΔH 0 and ΔS 0 Isothermodynamic parameters.

[0079] The equation is: Equation (10); Equation (11); In the above formula: ΔG 0 —Gibbs free energy, change in kJ / mol; R —ideal gas constant, (8.314 J·mol) -1 ·K -1 T—absolute temperature; Q—reaction entropy; K 0 —Standard equilibrium constant; ∆H 0 —Standard enthalpy change, kJ / mol; ∆S 0 —Standard entropy change, J / (mol·K).

[0080] According to research, when the adsorption process conforms to the Langmuir equation or the Freundlich equation, the equilibrium constant of the adsorption isotherm equation can be used to replace the standard equilibrium constant K of the reaction. 0 .

[0081] The isothermal thermodynamic fitting results are shown in Table 7. From Table 7, we can see that ΔG 0The entropy is greater than zero at 15℃, 30℃, and 45℃, and gradually decreases with increasing temperature. This indicates that the reaction is non-spontaneous, but the spontaneity gradually increases with increasing temperature. The fact that ΔH is greater than zero indicates that the reaction is endothermic. Under high-temperature conditions, the system more easily obtains the necessary heat from the environment, thus favoring the reaction. The fact that ΔS is greater than zero indicates that the disorder of the system increases during the reaction. Increased entropy favors the reaction because it lowers the activation barrier, making the reaction easier to occur. In summary, the adsorption of AMX solution by FeCl3-BC is an entropy-increasing, endothermic, and non-spontaneous adsorption process.

[0082] Table 7

[0083] 6. Reuse Performance Study To evaluate the reusability of FeCl3-BC, the following tests were conducted. 30 mL of 100 mg / L AMX solution was added to a 100 mL Erlenmeyer flask, along with 80 mg of FeCl3-BC. The temperature of the constant-temperature shaking incubator was set to 30 °C, the rotation speed to 200 r / min, and the pH of the AMX solution was maintained at its natural value. After adsorption for 5 hours, the absorbance of the AMX solution was measured. After completing the above operations, FeCl3-BC was filtered out and dried in a 60 °C constant-temperature drying oven. The dried FeCl3-BC (80 mg) was added to a 100 mL Erlenmeyer flask, along with 20 mL of ethanol. Desorption was performed for 5 hours under the same conditions (30 °C, 200 r / min, natural pH). After desorption, FeCl3-BC was filtered out and dried in a 60 °C constant-temperature drying oven. The treated FeCl3-BC was then used again in the AMX adsorption experiment, and the change in its adsorption effect was measured. The reusability of FeCl3-BC was evaluated by comparing the differences in adsorption effects after multiple adsorption-desorption cycles.

[0084] Investigating the recyclability of adsorbents is crucial for the economic efficiency and practical application of materials. This experiment used anhydrous ethanol as the regenerator to desorb FeCl3-BC that had adsorbed AMX, and the performance of the regenerated material was tested. The regeneration performance graph and hysteresis regression line of FeCl3-BC are shown in [Figure number missing]. Figure 13 ,in Figure 13 (a) is a graph showing the regeneration performance of FeCl3-BC. Figure 13 (b) is the hysteresis loop of FeCl3-BC. For example... Figure 13As shown in (a), after four cycles, the removal rate of AMX by FeCl3-BC decreased from 99.27% ​​to 66.95%. This may be because a small amount of AMX remained undesorbed from FeCl3-BC during the desorption process, reducing the number of adsorption sites and thus lowering the removal rate. In conclusion, FeCl3-BC exhibits good reusability.

[0085] As shown in the hysteresis curve in 13(b), the saturation magnetic field of FeCl3-BC can reach 40.37 emu / g, indicating that FeCl3-BC has good magnetic properties, which makes it easy to separate by magnetic attraction. Therefore, when recycling materials, FeCl3-BC can be easily separated from water by magnetic attraction, which is beneficial for its subsequent recycling.

[0086] Embodiment 2 of the present invention is as follows: The only difference between Example 2 and Example 1 is that the mass ratio of tea stem powder to FeCl3·6H2O is 1:0.8; the nitrogen gas flow rate during pyrolysis is 180 mL / min; and the pyrolysis temperature is 700℃. Embodiment 3 of the present invention is as follows: The only difference between Example 3 and Example 1 is that the mass ratio of tea stem powder to FeCl3·6H2O is 1:1.2; the nitrogen gas flow rate during pyrolysis is 220 mL / min; and the pyrolysis temperature is 900℃. Embodiment 4 of the present invention is as follows: The only difference between Example 4 and Example 1 is that the mass ratio of tea stem powder to FeCl3·6H2O is 1:0.9; the nitrogen gas flow rate during pyrolysis is 185 mL / min; and the pyrolysis temperature is 750℃. Embodiment 5 of the present invention is as follows: The only difference between Example 5 and Example 1 is that the mass ratio of tea stem powder to FeCl3·6H2O is 1:1.1; the nitrogen gas flow rate during pyrolysis is 210 mL / min; and the pyrolysis temperature is 850℃. Example 6 of the present invention is: iron-modified biochar prepared by the preparation method of Example 1.

[0087] Example 7 of the present invention is: the application of iron-modified biochar of Example 1 in the removal of amoxicillin from water. The amount of iron-modified biochar added is 2.67 g / L and the pH of the water is 6.1.

[0088] Example 8 of the present invention is as follows: The only difference between Example 8 and Example 1 is that the tea stems are from Songxi County, Nanping City. The iron-modified biochar prepared showed a 95% removal rate of amoxicillin in water under the following conditions: iron-modified biochar dosage of 2.67 g / L, AMX solution concentration of 100 mg / L, pH of 6.1, and temperature of 30℃.

[0089] Embodiment 9 of the present invention is as follows: The only difference between Example 9 and Example 1 is that the tea stems are green tea stems, which are from Qing Shi Jun De Tea Factory in Wuyishan. The iron-modified biochar prepared has a removal rate of 94.3% for amoxicillin in water under the following conditions: iron-modified biochar dosage is 2.67 g / L, AMX solution concentration is 100 mg / L, pH is 6.1, and temperature is 30℃.

[0090] In summary, the iron-modified biochar, its preparation method, and its applications provided by this invention have the following advantages: 1. Using tea stems as a biochar precursor can provide up to 500~1000m 2 With a high specific surface area of ​​ / g and a high specific surface area retention rate, it can specifically adsorb polar organic compounds such as amino / carboxyl groups in amoxicillin through hydrogen bonding and electrostatic interactions. It can promote the activation and degradation of pollutants by persulfate and can also serve as a catalytic site, which is beneficial to the physical adsorption and diffusion of pollutants such as amoxicillin.

[0091] 2. FeCl3-modified tea stem biochar was prepared using a non-impregnation method. The process is simple, cost-effective, and produces good uniformity while retaining more graded pores and activity.

[0092] 3. Iron-modified biochar with a pyrolysis temperature of 800℃ showed the best adsorption effect on AMX. Under the conditions of iron-modified biochar dosage of 2.67 g / L, AMX solution concentration of 100 mg / L, pH of 6.1, and temperature of 30℃, iron-modified biochar reached adsorption equilibrium for AMX within 5 hours, with a removal rate as high as 95%.

[0093] 4. The adsorption mechanism of iron-modified biochar for AMX is electrostatic adsorption and hydrogen bonding. The adsorption process is more consistent with the description of the second-order kinetic model. Qm reaches 82.56 mg / g at 318 K. The adsorption of AMX by iron-modified biochar is an endothermic, non-spontaneous and entropy-increasing process.

[0094] 5. Iron-modified biochar adsorbents have good recyclability, and their magnetic separation properties make them easy to separate and recover from water bodies in practical applications.

[0095] 6. The pore structure of iron-modified biochar is a mixed microporous-mesoporous structure with abundant adsorption sites.

[0096] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention's specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing iron-modified biochar, characterized in that, Includes the following steps: Tea stem powder was mixed with FeCl3·6H2O, and then dried and pyrolyzed sequentially to obtain iron-modified biochar.

2. The method for preparing iron-modified biochar according to claim 1, characterized in that, The mass ratio of the tea stem powder to FeCl3·6H2O is 1:0.8~1.

2.

3. The method for preparing iron-modified biochar according to claim 1, characterized in that, The pyrolysis conditions are: pyrolysis at 700~900℃ under an inert atmosphere.

4. The method for preparing iron-modified biochar according to claim 3, characterized in that, The nitrogen gas flow rate is 180~220 mL / min.

5. The method for preparing iron-modified biochar according to claim 1, characterized in that, The pyrolysis products were washed and dried sequentially to obtain iron-modified biochar.

6. The method for preparing iron-modified biochar according to claim 5, characterized in that, The washing method is as follows: first wash with anhydrous ethanol, then wash with ultrapure water.

7. Iron-modified biochar prepared by the method of any one of claims 1-6.

8. The application of iron-modified biochar as described in claim 7 in the removal of amoxicillin from water.

9. The application according to claim 8, characterized in that, The amount of iron-modified biochar added is 0.67~2.67 g / L.

10. The application according to claim 8, characterized in that, The pH of the water body is 3 to 6.1.

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