Blue-green algae-based activated carbon loaded heterogeneous Fenton catalyst, preparation method and application

Abstract

The invention relates to a blue-green algae-based activated carbon loaded heterogeneous Fenton catalyst, a preparation method and application. The preparation method of the blue-green algae-based activated carbon loaded heterogeneous Fenton catalyst comprises the following steps: S1, preparing blue-green algae-based activated carbon: mixing blue-green algae powder with an activating agent, carrying out thermochemical activation treatment, cooling to room temperature, and carrying out acid pickling and drying on obtained black solid powder to obtain the blue-green algae-based activated carbon; and S2, loading an iron-based catalyst: mixing the prepared blue-green algae-based activated carbon and iron salt in an organic solvent, performing ultrasonic dispersion, drying, and performing pyrolysis treatment to obtain the blue-green algae-based activated carbon loaded heterogeneous Fenton catalyst. The prepared nitrogen-doped activated carbon carrier can effectively promote circulation of Fe < 3 + > / Fe < 2 + >, and the catalyst shows extremely high degradation efficiency in combination with the enrichment effect of the large specific surface area on pollutants.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, specifically to a cyanobacteria-based activated carbon supported heterogeneous Fenton catalyst, its preparation method, and its application. Background Technology

[0002] Cyanobacteria, single-celled organisms widely found in lakes, reservoirs, and other aquatic bodies, can proliferate on a large scale when temperature and nutrients are suitable, forming an algal bloom. Cyanobacterial blooms not only disrupt the ecological balance of aquatic bodies, but the algal toxins produced by their metabolism can also harm human health through the food chain. The harmless treatment and resource utilization of the large amounts of cyanobacteria produced each year is a crucial issue facing the field of environmental protection, as conventional treatment methods often suffer from problems such as long treatment cycles and high difficulty.

[0003] Meanwhile, the widespread use of antibiotics in medicine, animal husbandry, and aquaculture has led to their residues becoming a typical emerging pollutant in water bodies. Antibiotics and their metabolites are biotoxic and difficult to remove effectively using conventional water treatment processes, posing a potential threat to the ecological environment and human health.

[0004] Advanced oxidation technologies (AOPs) are an effective means of degrading recalcitrant organic pollutants in water bodies. Among them, the Fenton process utilizes Fe... 2+ Catalyzing H2O2 to generate highly reactive hydroxyl radicals (·OH) can completely mineralize pollutants. However, the traditional homogeneous Fenton process has two inherent drawbacks: first, its optimal reaction pH range is extremely narrow, usually limited to a strongly acidic environment of 2.5-3.5; second, the reaction produces a large amount of iron-containing sludge, increasing the difficulty and cost of subsequent treatment.

[0005] To overcome the aforementioned drawbacks, heterogeneous Fenton catalysts have emerged. They immobilize iron-based active species on a support, making the catalyst easier to separate and recover, and broadening the pH range applicable to the reaction. Nevertheless, existing heterogeneous Fenton catalysts still generally suffer from several technical bottlenecks. For example, compared to homogeneous Fenton catalysts, their efficiency in generating reactive oxygen species is typically lower, leading to unsatisfactory degradation rates; during the reaction, the supported active metal components are prone to leaching and loss, which not only reduces the catalyst's stability and lifespan but may also cause secondary metal ion contamination.

[0006] Therefore, developing a heterogeneous Fenton catalyst that has widely available raw materials, low cost, simple preparation process, high catalytic activity, high stability and wide applicable pH range is a technical problem that urgently needs to be solved in the current water treatment technology field. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of existing heterogeneous Fenton catalysts, such as complex preparation, low activity, easy metal loss and dependence on specific raw materials, and to provide a cyanobacteria-based activated carbon supported heterogeneous Fenton catalyst with simple process, low cost, high catalytic activity and environmental friendliness.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A method for preparing a heterogeneous Fenton catalyst supported on cyanobacteria-based activated carbon, the method comprising the following steps:

[0010] S1. Preparation of cyanobacteria-based activated carbon: Mix cyanobacteria powder with an activator, and then heat it to 500-800 ℃ at a rate of 5-15℃ / min under an inert atmosphere for thermochemical activation treatment. The thermochemical activation time is 1-3 h. Cool to room temperature, acid wash the obtained black solid powder, and dry it to obtain cyanobacteria-based activated carbon.

[0011] The mass ratio of the activator to the cyanobacteria powder is 0.75-2.5:1;

[0012] S2, Supported iron-based catalyst: The cyanobacterial-based activated carbon obtained in step S1 is ultrasonically dispersed with iron salt in a solvent, stirred and mixed at 400-500 r / min for 5-8 h at 60±5 ℃, dried at 80±5 ℃, and then heated to 190-280 ℃ at a rate of 5-15 ℃ / min for 60 min-180 min for pyrolysis treatment. The obtained product is washed with acetone or ethanol until the supernatant is colorless, and dried to obtain the cyanobacterial-based activated carbon supported heterogeneous Fenton catalyst.

[0013] The mass ratio of cyanobacteria-based activated carbon to iron salt is 1:9-9:1.

[0014] Preferably, the activator in step S1 is selected from one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, potassium bicarbonate, and zinc chloride. The inventors have found that using zinc chloride as the activator provides mild activation conditions, better preserves nitrogen in the cyanobacteria matrix, and is beneficial for subsequent catalytic reactions.

[0015] This invention utilizes the type of activator to regulate the pore structure and nitrogen retention rate of cyanobacteria-based activated carbon. The inventors discovered that when potassium hydroxide is used as the activator, it primarily forms micropores, but requires a high activation temperature, resulting in significant nitrogen loss and a low yield of activated carbon. Zinc chloride, on the other hand, has milder activation conditions, forms larger pores than potassium hydroxide, and retains nitrogen better while achieving a higher yield.

[0016] Preferably, in step S1, the conditions for thermochemical activation treatment are: a heating rate of 5-15 ℃ / min, a thermochemical activation temperature of 500-800 ℃, and a thermochemical activation time of 1-3 h.

[0017] Through extensive experimentation, the inventors discovered that the thermochemical activation temperature is crucial in determining the pore structure and surface chemical properties of activated carbon. At relatively low temperatures (such as 400 °C in Comparative Example 1), thermochemical activation is insufficient, resulting in poor pore development, a small specific surface area, and consequently, insufficient adsorption and enrichment capacity for pollutants, leading to low catalytic efficiency. Temperatures above 800 °C cause the already formed microporous structure to collapse, reducing the specific surface area and causing significant leakage of naturally occurring nitrogen from cyanobacteria, weakening its promoting effect on iron ion electron transfer, which is also detrimental to catalysis. Therefore, controlling the thermochemical activation temperature between 500-800 °C, especially around 600 °C, is key to achieving the optimal balance between ensuring a high specific surface area and retaining effective nitrogen content.

[0018] Preferably, before step S1, the cyanobacteria are dried at 30-90 °C, pulverized, and passed through a 40-mesh sieve to obtain the cyanobacteria powder. This pretreatment step ensures uniform particle size of the raw material, which is beneficial for the uniformity of the subsequent thermochemical activation reaction.

[0019] The specific method for preparing cyanobacteria powder is as follows: Filter out impurities such as leaves and aquatic plant roots from the cyanobacteria solution using a mesh sieve. Rinse the filtered material with clean water and then sieve it again. Dry the cyanobacteria at room temperature under ventilation, then transfer it to an oven at 30-90 ℃ for further drying. The resulting dried cyanobacteria lumps are crushed using a high-speed pulverizer, passed through a 40-mesh sieve, and collected as cyanobacteria powder. A more preferred drying temperature is 50-80 ℃.

[0020] Preferably, in step S1, the acid washing method is as follows: the black solid powder is washed with a 10±5 wt% HCl solution, and then repeatedly rinsed with deionized water until the solution is neutral. The purpose is to remove residual activator and inorganic ash to avoid the influence of acid radicals on subsequent catalyst loading.

[0021] Preferably, the iron salt in step S2 is ferric chloride hexahydrate, and the solvent is anhydrous ethanol. Ethanol, as a solvent, has the advantages of moderate boiling point, good solubility, and easy evaporation, which facilitates the uniform dispersion of the iron salt precursor on the inner and outer surfaces of the activated carbon.

[0022] Preferably, the mass ratio of ferric chloride hexahydrate to cyanobacteria-based activated carbon in step S2 is 7:3 to 3:7.

[0023] The catalyst loading directly affects the number and dispersion of catalytic active sites. Too low a loading (e.g., the iron salt to activated carbon ratio of 1:9 in Comparative Example 2) results in insufficient active sites, leading to low catalytic efficiency and slow degradation rates. Too high a loading (e.g., the ratio of 9:1 in Comparative Example 3) causes iron species to easily agglomerate during heat treatment, forming large particles that clog the pores of the activated carbon and trap many active sites inside, preventing them from contacting the reactants, thus reducing overall catalytic activity. Therefore, controlling the mass ratio within the range of 7:3 to 3:7 ensures the formation of highly dispersed, uniformly sized active sites on the activated carbon support, maximizing catalytic efficiency.

[0024] Preferably, the pyrolysis heating rate in step S2 is 5-15 ℃ / min, the pyrolysis temperature is 190-280 ℃, and the holding time is 1-3h.

[0025] This step is crucial for the in-situ generation of iron-based active species. If the temperature is too low, ferric chloride cannot be effectively decomposed into catalytically active oxides or hydroxyl oxides; if the temperature is too high, it may damage the already formed activated carbon structure and exacerbate the aggregation of active species. Controlling the temperature within the relatively mild range of 190-280 ℃ allows for the conversion of iron salts into highly efficient catalytically active species without damaging the support structure.

[0026] Preferably, the method specifically includes:

[0027] S1. Zinc chloride and cyanobacteria powder are mixed at a mass ratio of 1.5:1, and then thermochemical activation is carried out by heating to 600℃ at a rate of 10℃ / min under a nitrogen atmosphere.

[0028] S2. The cyanobacteria-based activated carbon obtained in step S1 and ferric chloride hexahydrate were ultrasonically dispersed in ethanol at a mass ratio of 3:7 for 20 min. The mixture was stirred and mixed at 60±5 ℃ for 6 h, dried at 80 ℃, and then pyrolyzed at 220 ℃ at a rate of 10 ℃ / min for 120 min. The product was washed with acetone or ethanol until the supernatant was colorless and dried to obtain a heterogeneous Fenton catalyst supported on cyanobacteria-based activated carbon.

[0029] A heterogeneous Fenton catalyst supported on cyanobacteria-based activated carbon, prepared by the method described in this invention, exhibits excellent physical properties. In a preferred embodiment, its specific surface area is 1000-1200 m². 2 / g, pore volume 0.6-0.9 cm³ 3 / g.

[0030] An application of the catalyst described in this invention in the degradation of antibiotics in water. The catalyst described in this invention, in the catalytic degradation of antibiotics, should be carried out in the presence of hydrogen peroxide or potassium persulfate, and exhibits good degradation effects on antibiotic pollutants such as tetracycline hydrochloride and norfloxacin cyclophosphamide.

[0031] The beneficial effects of this invention are:

[0032] This invention creatively utilizes harmful cyanobacteria harvested from eutrophic waters as raw materials, achieving high-value resource utilization of waste biomass, which aligns with the green chemistry concept of "treating waste with waste." Employing a simple two-step impregnation-pyrolysis method, it requires no complex equipment or stringent conditions, facilitating large-scale production and significantly reducing catalyst preparation costs.

[0033] This invention utilizes the naturally nitrogen-rich characteristics of cyanobacteria to prepare a nitrogen-doped activated carbon support that can effectively promote Fe production. 3+ / Fe 2+ The cyclical nature of the catalyst, combined with its large specific surface area and its enrichment effect on pollutants, results in extremely high degradation efficiency (88.9% removal rate in 5 minutes in Example 1) and excellent reusability stability.

[0034] The catalyst described in this invention is active over a wide pH range, overcoming the drawback of the traditional Fenton process requiring a strong acid environment, and has a low iron ion dissolution rate, thus avoiding secondary pollution problems. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the AC-X preparation process;

[0036] Figure 2 These are (a) adsorption-desorption curves and (b) pore size distribution curves of AC-X;

[0037] Figure 3 These are SEM images of (a) AC-5, (b) AC-6, (c) AC-7 and (d) AC-8 at 1k (low) and 10k (high) magnification.

[0038] Figure 4 This is the preparation process of the FZAC composite catalyst;

[0039] Figure 5 These are SEM images and XRD patterns of FZAC with different amounts of FeCl3·6H2O;

[0040] Figure 6 The degradation performance of FZAC at different initial pH values;

[0041] Figure 7 It is the repeatable cyclic stability of FZAC in degrading tetracycline hydrochloride. Detailed Implementation

[0042] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0043] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0044] Unless otherwise specified, the reagents used in the following examples can be purchased from a regular biochemical reagent store.

[0045] Preparation of cyanobacteria powder: Leaves, aquatic plant roots and stems and other impurities in the cyanobacteria solution were filtered out by a mesh screen. The filtered material was rinsed with clean water and then screened. After screening, it was dried at room temperature and in a ventilated place for 72 h. Then it was placed in a 70 ℃ oven and dried for 72 h. Finally, it was crushed by a high-speed pulverizer and collected as cyanobacteria powder after passing through a 40 mesh screen.

[0046] Example 1

[0047] Step 1: Zinc chloride and cyanobacteria powder were added at a mass ratio (zinc-to-algae ratio) of 1.5:1 and ground until fully mixed. The treated cyanobacteria powder was placed in a horizontally placed tube furnace and heated to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere (flow rate 0.2 L / min). After thermochemical activation for 1.5 h, the mixture was cooled to room temperature. The black solid powder was taken out and mixed with 10 wt% HCl solution and stirred on a magnetic stirrer at 400 r / min for 24 h. The solid powder was then repeatedly washed with deionized water until neutral. The solid powder was dried in an oven at 105 °C to constant weight to obtain cyanobacteria-based activated carbon.

[0048] Step 2: Preparation of the iron-based catalyst / cyanobacteria activated carbon composite material: FeCl3·6H2O and activated carbon were weighed at a mass ratio of 7:3. The FeCl3·6H2O and activated carbon were dispersed in 30 mL of ethanol, sonicated for 20 min, and continuously stirred in a water bath at 60 ℃ and 400 r / min for 6 h. The mixture was then dried in an oven at 80 ℃ for 2 h. After being transferred to a corundum boat, the mixture was placed in a muffle furnace and heated to 220 ℃ at a rate of 10 ℃ / min for 120 min. After natural cooling, the resulting product was washed with acetone or ethanol until the supernatant was colorless. The product was then dried in an oven at 60 ℃ to obtain a solid powder, which was the iron-based catalyst / cyanobacteria activated carbon composite material (FZAC).

[0049] The specific surface area of ​​the cyanobacteria-based activated carbon was calculated using the BET method, and the activated carbon prepared by this method had a specific surface area of ​​1158 m². 2 / g; pore size distribution was obtained by NLDFT method, and the calculated pore volume of activated carbon was 0.82 cm³. 3 / g, with an average pore size of 2.84 nm.

[0050] Tetracycline hydrochloride aqueous solution was used to simulate dye wastewater, and the catalytic activity was evaluated by assessing the degradation performance of tetracycline hydrochloride. The concentration of the tetracycline hydrochloride solution was determined using a UV-Vis spectrophotometer. The specific operating steps are as follows:

[0051] (1) Plot the standard curve for tetracycline hydrochloride solution;

[0052] (2) Antibiotic degradation experimental parameters: 100 mL of 40 mg / L antibiotic aqueous solution and 5 mg of iron-based catalyst / cyanobacterial activated carbon composite material were added to a quartz cup and wrapped with tin foil to protect it from light. After adding a magnetic stir bar, the conical flask was placed in a water bath at 40 °C and the solution was magnetically stirred at 180 rpm. After adsorption equilibrium was reached, 40 mmol / L (0.4 mL) of hydrogen peroxide was added.

[0053] (3) Absorbance measurement: The absorbance was measured by spectrophotometry. Every 5 minutes, the supernatant was taken out, filtered through a 0.22 μm needle filter, and added to a cuvette with a 1 cm optical path. Deionized water was used as a blank reference, and the absorbance of the tetracycline hydrochloride solution was measured at the absorption wavelength near 357 nm using an ultraviolet spectrophotometer.

[0054] After the degradation experiment, the cyanobacteria-based activated carbon was centrifuged and washed with methanol solution. The degradation experiment was repeated five times to evaluate the stability of the catalytic performance. After 5 minutes of catalytic reaction, the removal rate of tetracycline hydrochloride reached 88.9%, and after 10 minutes of degradation equilibrium, the removal rate reached 92.9%. After repeating the experiment five times, the removal rate of tetracycline hydrochloride still reached 91.9%, indicating that the cyanobacteria-based activated carbon material has excellent catalytic performance.

[0055] Comparative Example 1

[0056] Step 1: Zinc chloride and cyanobacteria powder were added at a mass ratio (zinc-to-algae ratio) of 1.5:1 and ground until fully mixed. The treated cyanobacteria powder was placed in a horizontally placed tube furnace and heated to 400 °C at a rate of 10 °C / min under a nitrogen atmosphere (flow rate 0.2 L / min). After thermochemical activation for 1.5 h, the mixture was cooled to room temperature. The black solid powder was taken out and mixed with 10 wt% HCl solution and stirred on a magnetic stirrer at 400 r / min for 24 h. The solid powder was then repeatedly washed with deionized water until neutral. The solid powder was dried in an oven at 105 °C to constant weight to obtain cyanobacteria-based activated carbon.

[0057] Step 2: Preparation of the iron-based catalyst / cyanobacteria activated carbon composite material: FeCl3·6H2O and activated carbon were weighed at a mass ratio of 7:3. The FeCl3·6H2O and activated carbon were then dispersed in 30 mL of ethanol. The mixture was sonicated for 20 min and continuously stirred at 60 ℃ and 400 r / min for 6 h. The mixture was then dried in an oven at 80 ℃ for 2 h. After being transferred to a corundum boat, the mixture was placed in a muffle furnace and heated to 220 ℃ at a rate of 10 ℃ / min, and held at that temperature for 120 min. The resulting product was washed with acetone or ethanol until the supernatant was colorless. The product was then dried in an oven at 60 ℃ to obtain a solid powder, which was the iron-based catalyst / cyanobacteria activated carbon composite material.

[0058] Using the same antibiotic degradation and adsorption experimental conditions as in Example 1, the removal rate of tetracycline hydrochloride was 61.6% after 5 min, and it took 20 min to reach the antibiotic adsorption and degradation equilibrium, with a removal rate of 72.4%.

[0059] Comparative Example 2

[0060] Step 1: Zinc chloride and cyanobacteria powder were added at a mass ratio (zinc-to-algae ratio) of 1.5:1 and ground until fully mixed. The treated cyanobacteria powder was placed in a horizontally placed tube furnace and heated to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere (flow rate 0.2 L / min). After thermochemical activation for 1.5 h, the mixture was cooled to room temperature. The black solid powder was taken out and mixed with 10 wt% HCl solution and stirred on a magnetic stirrer at 400 r / min for 24 h. The solid powder was then repeatedly washed with deionized water until neutral. The solid powder was dried in an oven at 105 °C to constant weight to obtain cyanobacteria-based activated carbon.

[0061] Step 2: Preparation of the iron-based catalyst / cyanobacteria activated carbon composite material: FeCl3·6H2O and activated carbon were weighed at a mass ratio of 1:9. The FeCl3·6H2O and activated carbon were dispersed in 30 ml of ethanol and sonicated for 20 min. The mixture was then continuously stirred for 6 h at 60 ℃ and 400 r / min, and dried in an oven at 80 ℃ for 2 h. The mixture was transferred to a corundum boat and placed in a muffle furnace, then heated to 220 ℃ at a rate of 10 ℃ / min and held for 120 min. The resulting product was washed with acetone or ethanol until the supernatant was colorless, and then dried in an oven at 60 ℃ to obtain a solid powder, which was the iron-based catalyst / cyanobacteria activated carbon composite material.

[0062] Using the same experimental conditions for antibiotic degradation and adsorption as in Example 1, it took 55 minutes to reach antibiotic adsorption and degradation equilibrium, with a removal rate of 61.4%.

[0063] Comparative Example 3

[0064] Step 1: Zinc chloride and cyanobacteria powder were added at a mass ratio (zinc-to-algae ratio) of 1.5:1 and ground until fully mixed. The treated cyanobacteria powder was placed in a horizontally placed tube furnace and heated to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere (flow rate 0.2 L / min). After thermochemical activation for 1.5 h, the mixture was cooled to room temperature. The black solid powder was taken out and mixed with 10 wt% HCl solution and stirred on a magnetic stirrer at 400 r / min for 24 h. The solid powder was then repeatedly washed with deionized water until neutral. The solid powder was dried in an oven at 105 °C to constant weight to obtain cyanobacteria-based activated carbon.

[0065] Step 2: Preparation of the iron-based catalyst / cyanobacteria activated carbon composite material: FeCl3·6H2O and activated carbon were weighed at a mass ratio of 9:1. The FeCl3·6H2O and activated carbon were dispersed in 30 ml of ethanol and sonicated for 20 min. The mixture was then continuously stirred for 6 h at 60 ℃ and 400 r / min, and dried in an oven at 80 ℃ for 2 h. The mixture was transferred to a corundum boat and placed in a muffle furnace, then heated to 220 ℃ at a rate of 10 ℃ / min and held for 120 min. The resulting product was washed with acetone or ethanol until the supernatant was colorless, and then dried in an oven at 60 ℃ to obtain a solid powder, which was the iron-based catalyst / cyanobacteria activated carbon composite material.

[0066] Using the same experimental conditions for antibiotic degradation and adsorption as in Example 1, it took 30 minutes to reach antibiotic adsorption and degradation equilibrium, and the removal rate was only 53.4%.

[0067] Example 2: Single-factor experiment to investigate thermochemical activation temperature

[0068] After being washed and screened, the cyanobacteria were dried at room temperature and in a ventilated environment for 72 hours, then further dried in a 70°C oven for 72 hours. Finally, they were crushed using a high-speed pulverizer and collected as cyanobacteria powder after passing through a 40-mesh sieve. A schematic diagram of the AC-X preparation process is shown below. Figure 1 As shown.

[0069] Zinc chloride and cyanobacteria powder were weighed at a mass ratio of 1.5:1 (zinc-to-algae ratio for short), mixed, and ground thoroughly until homogeneous. The pretreated cyanobacteria powder was then placed in a horizontal tube furnace and heated at a programmed rate of 10 °C / min under a nitrogen atmosphere (nitrogen flow rate 0.2 L / min) to four target temperatures: 500 °C, 600 °C, 700 °C, and 800 °C. Thermochemical activation was maintained at these temperatures for 1.5 h, followed by natural cooling to room temperature. After cooling, the black solid powder was removed from the tube furnace and mixed with a 10 wt% hydrochloric acid solution. The mixture was then stirred continuously at 400 r / min for 24 h using a magnetic stirrer. After stirring, the solid powder was repeatedly rinsed with deionized water until the washing solution was neutral. Finally, the neutral solid powder is placed in an oven at 105 ℃ and dried to constant weight to obtain cyanobacteria-based activated carbon AC-X (X represents the activation temperature, which is 1 / 100 of the activation temperature and takes values ​​of 5, 6, 7 and 8).

[0070] Activation temperature directly affects the specific surface area and pore structure of AC-X. The nitrogen adsorption-desorption curves of AC-X were obtained using the nitrogen adsorption method, and the pore size distribution of AC-X was calculated using the BET model. The results are as follows: Figure 2 As shown. By Figure 2 (a) It can be seen that the nitrogen adsorption-desorption curves of all samples are mixed type I and type IV adsorption curves. In the low-pressure region (relative pressure < 0.3), the nitrogen adsorption capacity of AC-X increases rapidly, indicating that AC-X has a certain amount of micropores (pore size < 1 nm). Among them, AC-6 and AC-7 have the largest low-pressure adsorption capacity, while AC-5 has the smallest low-pressure adsorption capacity, indicating that the pore volume of the micropores of AC-6 and AC-7 is larger than that of AC-5. In the medium-pressure region (0.3 < relative pressure < 0.9), the nitrogen adsorption capacity increases slowly with increasing pressure, and capillary condensation occurs in all samples. The presence of H4 type hysteresis loops in AC-X is observed, indicating that all samples contain a certain amount of mesoporous structure. Under high pressure, nitrogen adsorbs on the gaps and macropores of AC, leading to an increase in adsorption capacity. However, no significant increase in adsorption capacity was observed in all samples in the high-pressure region where the relative pressure is close to 1, indicating that there is no macroporous structure in all samples. Figure 2 (b) It can be seen that the pore size distribution of AC-X is concentrated in the range of 0-2 nm, which further illustrates that AC-X activated by ZnCl2 has abundant microporous structure and a certain number of mesoporous structures.

[0071] The structural characteristics of AC-X, such as micropore volume, specific surface area, and total volume, which are closely related to its adsorption capacity, were calculated, and the results are shown in Table 1.

[0072] Table 1. Micropore volume, specific surface area, and total volume of AC-X

[0073] Depend on Figure 2 As shown in Table 1, due to the low activation temperature and incomplete activation, AC-5 has the smallest specific surface area, which is unfavorable for the catalytic degradation reaction. With the activation temperature increased to 600 °C, the sample's specific surface area reached 726.7 m². 2 / g gradually increased to 1158.4 m 2 / g. At an activation temperature of 700 ℃, the specific surface area of ​​AC-7 is 1112.3 m². 2 When the specific surface area of ​​AC-8 is further increased to 800 °C, the surface area decreases to 1019.3 m² / g. 2 At lower activation temperatures, molten ZnCl2 cannot acquire sufficient energy to diffuse uniformly into the cyanobacterial powder, resulting in slow activation, low activation degree, and insufficient development of the AC-5 pore structure and low specific surface area. With increasing activation temperature, ZnCl2 interacts with the oxygen-containing functional groups of the cyanobacterial powder, promoting dehydration and dehydrogenation reactions. This releases hydrogen and oxygen from the cyanobacterial precursor as water vapor, leading to carbon chain aromatization and the formation of a pore structure, thus increasing the specific surface area and micropore volume. When the temperature is further increased to 800 °C, the high temperature provides the system with sufficient energy, resulting in an excessively rapid activation reaction rate. Simultaneously, intermediate products volatilize from the system, causing the micropores of AC-8 to collapse and merge, further reducing the specific surface area.

[0074] The microstructure of AC-X was characterized using SEM, and the results are as follows: Figure 3 As shown, when the activation temperature is 500 ℃, AC-5 is relatively smooth overall, with fewer surface pores and low porosity. As the activation temperature increases from 500 ℃ to 700 ℃, richer pore structures are observed on the surfaces of AC-6 and AC-7. This is related to the increased activity of the activator ZnCl2 at high temperatures; at high temperatures, ZnCl2 flows violently within the carbon layer, thus forming a richer pore structure in AC. However, when the temperature continues to rise to 800 ℃, which is higher than the boiling point of ZnCl2, ZnCl2 mainly flows between the carbon layers in a gaseous state. Excessively high activation temperatures lead to pore collapse, resulting in a rougher morphology and an increase in large pore structures on AC-8.

[0075] In this experiment, AC-6 exhibited the best catalytic degradation performance because it has the highest specific surface area and a good pore structure.

[0076] Example 3: Effect of FeCl3·6H2O dosage on the microstructure of FZAC

[0077] A composite catalyst of iron-based catalyst and cyanobacterial activated carbon (FZAC) is prepared as follows: Figure 4 As shown, the specific steps are:

[0078] Step 1: Zinc chloride and cyanobacteria powder were added at a mass ratio (zinc-to-algae ratio) of 1.5:1 and ground until fully mixed. The treated cyanobacteria powder was placed in a horizontally placed tube furnace and heated to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere (flow rate 0.2 L / min). After thermochemical activation for 1.5 h, the mixture was cooled to room temperature. The black solid powder was taken out and mixed with 10 wt% HCl solution and stirred on a magnetic stirrer at 400 r / min for 24 h. The solid powder was then repeatedly washed with deionized water until neutral. The solid powder was dried in an oven at 105 °C to constant weight to obtain cyanobacteria-based activated carbon.

[0079] Step 2: Preparation of iron-based catalyst / cyanobacteria activated carbon composite material: FeCl3·6H2O and activated carbon were weighed at mass ratios of 0:1, 2:11, 3:7, 5:5, 7:3, 11:2, and 1:0, respectively. Except for the 0:1 and 1:0 mass ratios, the remaining FeCl3·6H2O and activated carbon were dispersed in 30 mL of ethanol, sonicated for 20 min, and continuously stirred at 60 ℃ and 400 r / min for 6 h. Then, the mixture was dried in an oven at 80 ℃ for 2 h. After being transferred to a corundum boat, it was placed in a muffle furnace and heated to 220 ℃ at a rate of 10 ℃ / min for 120 min. The resulting product was washed with acetone or ethanol until the supernatant was colorless, and then dried in an oven at 60 ℃ to obtain the FZAC catalyst. Based on the mass ratios of FeCl3·6H2O to ZAC (1:0, 2:11, 3:7, 5:5, 7:3, 2:11, and 0:1), the resulting catalysts were named FeOCl, FZAC-0.15, FZAC-0.3, FZAC-0.5, FZAC-0.7, FZAC-0.85, and ZAC, respectively.

[0080] The effect of the mass ratio of FeCl3·6H2O to ZAC on the microstructure of FZAC was obtained by SEM and XRD analysis. Figure 5ZAC has a rough surface with pores of varying sizes, exhibiting a rich pore structure. The sheet-like FeOCl structures stack up to form a blocky shape with a small specific surface area, limiting the contact area with pollutants. Combining FeOCl with the ZAC support does not result in significant structural changes on the surface, and the characteristic FeOCl diffraction peaks are not obvious. The surface morphology is similar to ZAC, and this ratio of composite has no effect on the surface morphology. A small amount of mixed sheet-like and cubic structures were found on the surface of FZAC-0.5; the surface of FZAC-0.7 exhibits the porous structure of AC, while the structure of the supported material completely transforms into sheet-like FeOCl, successfully loading the target catalyst onto the surface; on the surface of FZAC-0.85, FeOCl undergoes supersaturated growth, and the characteristic FeOCl diffraction peaks completely cover the characteristic peaks of ZAC. The sheet-like structure completely covers the ZAC pores and is tightly stacked, reducing its effective contact area with pollutants.

[0081] This study shows that by adjusting the mass ratio of FeCl3·6H2O to ZAC, the spatial distribution of FeCl3·6H2O on the support surface and in the pores can be precisely controlled, thereby controlling the phase composition of its pyrolysis products and optimizing the morphology of FZAC. Among them, the microstructure of FZAC-0.7 is most suitable for catalytic requirements and exhibits the best performance.

[0082] Example 4

[0083] Step 1: Zinc chloride and cyanobacteria powder were added at a mass ratio (zinc-to-algae ratio) of 1.5:1 and ground until fully mixed. The treated cyanobacteria powder was placed in a horizontally placed tube furnace and heated to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere (flow rate 0.2 L / min). After thermochemical activation for 1.5 h, the mixture was cooled to room temperature. The black solid powder was taken out and mixed with 10 wt% HCl solution and stirred on a magnetic stirrer at 400 r / min for 24 h. The solid powder was then repeatedly washed with deionized water until neutral. The solid powder was dried in an oven at 105 °C to constant weight to obtain cyanobacteria-based activated carbon.

[0084] Step 2: Preparation of the iron-based catalyst / cyanobacteria activated carbon composite material: FeCl3·6H2O and activated carbon were weighed at a 1:1 mass ratio, dispersed in 30 mL of ethanol, sonicated for 20 min, and continuously stirred at 60 ℃ and 400 r / min for 6 h. Then, it was dried in an oven at 80 ℃ for 2 h. The mixture was transferred to a corundum boat and placed in a muffle furnace, then heated to 220 ℃ at a rate of 10 ℃ / min and held for 120 min. The resulting product was washed with acetone or ethanol until the supernatant was colorless, and dried in an oven at 60 ℃ to obtain a solid powder, which is the iron-based catalyst / cyanobacteria activated carbon composite material.

[0085] Using the same antibiotic degradation and adsorption experimental conditions as in Example 1, the removal rate of tetracycline hydrochloride was 75.4% after 5 min, and it took 30 min to reach the antibiotic adsorption and degradation equilibrium, with a removal rate of 85.4%.

[0086] Application example: catalytic degradation experiment

[0087] A tetracycline hydrochloride solution of a certain concentration was prepared in a 250 mL Erlenmeyer flask and wrapped with aluminum foil to protect it from light. A magnetic stir bar was added, and the flask was placed in a water bath at the corresponding temperature. The solution was magnetically stirred at 200 r / min. When the solution temperature reached the set experimental temperature, a certain amount of FZAC was immediately added, and the dark adsorption experiment was initiated, with the time recorded as -30 min. After dark adsorption was complete, the test solution was filtered through a 0.22 μm filter membrane and injected into a cuvette with a 1 cm range. The absorbance was measured using a UV-Vis spectrophotometer, and the concentration of the test solution at that moment was calculated using a standard curve, recorded as min 0. Subsequently, a certain amount of H2O2 solution was added, and samples were taken at corresponding time intervals after timing began, recording the absorbance at 357 nm until degradation was complete.

[0088] 1. Effect of pH on FZAC degradation performance

[0089] For Fenton-like reaction systems, the heterogeneous catalytic efficiency is significantly correlated with the solution pH. Traditional homogeneous Fenton technology is limited by its narrow pH applicability, while heterogeneous systems can achieve a wider pH adaptability by controlling the catalyst surface properties. Under conditions of 100 mg / L catalyst FZAC, 40 mg / L contaminant concentration, and 40 mM H2O2 concentration, a comparison of tetracycline hydrochloride degradation experiments under initial pH values ​​of 3, 4, 6, and 8 revealed… Figure 6The degradation efficiency initially increased and then decreased with pH during the initial reaction stage (2.5 min), with degradation rates of 45.2% (pH=3), 79.9% (pH=4), 73.5% (pH=6), and 46.2% (pH=8). The initial rate was significantly lower under alkaline conditions (pH=8), mainly due to two synergistic effects: firstly, H2O2 tends to spontaneously decompose into H2O and O2 in alkaline media, rather than generating reactive oxygen species (such as ·OH) through a Fenton-like pathway; secondly, stable hydroxy-iron complexes form on the surface of the iron-based catalyst, covering the active sites and hindering the effective Fe(II) / Fe(III) cycle, thus inhibiting the catalytic reaction kinetics. Notably, despite the differences in initial reaction rates, the final degradation rate remained above 90% after 30 min in the pH range of 3-8, revealing the ZAC catalyst's ability to maintain highly efficient H2O2 activation in acidic to weakly alkaline environments. This wide pH adaptability may be related to the surface charge state of the heterogeneous catalyst. Under acidic conditions, the protonation of pollutant molecules enhances adsorption, while under weakly alkaline conditions, the partially deprotonated form may be more conducive to free radical attack. Compared to the stringent requirements of traditional Fenton reactions for strongly acidic conditions, the FZAC catalyst has successfully overcome the pH limitation, demonstrating its application potential in practical water remediation.

[0090] 2. Repeatability and stability of FZAC catalyst

[0091] The cyclic stability and reusability of the catalyst are core evaluation indicators for its engineering applications. Four consecutive cycle experiments were conducted (FZAC catalyst dosage: 100 mg / L, pollutant concentration: 40 mg / L, H2O2 concentration: 40 mM), with each cycle lasting 60 min, including 30 min of adsorption and 30 min of degradation. After degradation, the FZAC material was separated and recovered, then vacuum dried at 60 °C for further repeated experiments. Figure 7 As shown, the adsorption and degradation efficiency of FZAC for the target pollutant decreased slightly with increasing cycle number. The initial degradation rate was 95.5%, and after four cycles, the degradation efficiency dropped to 92.3%, a decrease of only 3.2%, indicating that the catalyst possesses good structural stability. The slight decrease in degradation efficiency may be due to the adsorption behavior of pollutant degradation intermediates on the catalyst surface, which partially hinders the adsorption of pollutants, leading to a decrease in adsorption rate and reduced pollutant enrichment. It may also hinder the contact between the active sites and the oxidant. Furthermore, the Fe on the FZAC surface during the reaction... 3+The trace leaching leads to a reduction in surface active sites. Nevertheless, the overall performance degradation of the catalyst is controllable, and the core structure does not suffer irreversible damage, fully verifying its long-term stability and cyclic applicability in heterogeneous catalytic systems, and providing technical support for its application in practical wastewater treatment scenarios.

[0092] In summary, comparing Comparative Example 1 (400 ℃) with Example 1 (600 ℃), the only variable was the thermochemical activation temperature, yet the effect showed a precipitous drop: the removal rate was only 61.6% after 5 minutes, and the final removal rate was only 72.4%. This proves that not all thermochemical activation temperatures can yield high-performance carriers; below a certain critical temperature (such as 400 ℃), the activated carbon pore structure is not fully developed, and the purpose of this invention cannot be achieved.

[0093] Data from Example 2 shows that good catalytic performance (removal rate >85% in 5 minutes) can be obtained when the thermochemical activation temperature is in the range of 500-800 °C, but the performance peak occurs around 600 °C. When the temperature rises to 800 °C, the specific surface area and pore volume begin to decrease (10¹⁹ m²). 2 / g, 0.65 cm 3 ( / g), and the performance is also slightly reduced accordingly.

[0094] Regarding the iron salt / activated carbon ratio, Comparative Example 2 (Fe:AC = 1:9, too low loading) achieved a final removal rate of only 61.4%, significantly lower than Example 1 (Fe:AC = 7:3). This demonstrates that the catalyst requires a certain loading to function effectively. Comparative Example 3 (Fe:AC = 9:1, too high loading) achieved a final removal rate of only 53.4%, even worse than with a low loading. This indicates that more catalyst does not necessarily lead to better results, strongly suggesting that excessive loading can cause active species to aggregate and clog pores, thus reducing catalytic efficiency. Example 4 (Fe:AC = 1:1, i.e., 5:5) showed a better removal rate (85.4%) than the comparative examples, but worse than Example 1.

Claims

1. A method for preparing a heterogeneous Fenton catalyst supported on cyanobacteria-based activated carbon, characterized in that, The method includes the following steps: S1. Preparation of cyanobacteria-based activated carbon: Mix cyanobacteria powder with an activator, and then heat to 500-800 ℃ at a rate of 5-15 ℃ / min under an inert atmosphere for thermochemical activation treatment for 1-3 h. Cool to room temperature, acid wash the obtained black solid powder, and dry it to obtain cyanobacteria-based activated carbon. The mass ratio of the activator to the cyanobacteria powder is 0.75-2.5:1; S2, Supported iron-based catalyst: The cyanobacterial-based activated carbon obtained in step S1 is ultrasonically dispersed with iron salt in a solvent, stirred and mixed at 400-500 r / min for 5-8 h at 60±5 ℃, dried at 80±5 ℃, and then heated to 190-280 ℃ at a rate of 5-15 ℃ / min for 60 min-180 min for pyrolysis treatment. The obtained product is washed with acetone or ethanol until the supernatant is colorless, and dried to obtain the cyanobacterial-based activated carbon supported heterogeneous Fenton catalyst. The mass ratio of cyanobacteria-based activated carbon to iron salt is 1:9-9:

1.

2. The preparation method according to claim 1, characterized in that: The activator mentioned in step S1 is selected from one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, potassium bicarbonate, and zinc chloride.

3. The preparation method according to claim 1, characterized in that: In step S1, the conditions for thermochemical activation treatment are: heating rate of 5-15 ℃ / min, thermochemical activation temperature of 500-800 ℃, and thermochemical activation time of 1-3 h.

4. The preparation method according to claim 1, characterized in that: In step S1, the acid washing method is as follows: the black solid powder is washed with 10±5 wt% HCl solution, and then the solid powder is repeatedly rinsed with deionized water until the solution is neutral.

5. The preparation method according to claim 1, characterized in that: The iron salt mentioned in step S2 is ferric chloride hexahydrate, and the solvent is anhydrous ethanol.

6. The preparation method according to claim 1 or 5, characterized in that: In step S2, the mass ratio of ferric chloride hexahydrate to the cyanobacteria-based activated carbon is 7:3 to 3:

7.

7. The preparation method according to claim 1, characterized in that: The pyrolysis heating rate in step S2 is 5-15℃ / min, the pyrolysis temperature is 190-280℃, and the holding time is 1-3 h.

8. The preparation method according to claim 1, characterized in that, The method specifically includes: S1. Zinc chloride and cyanobacteria powder are mixed at a mass ratio of 1.5:1, and then thermochemical activation is carried out by heating to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere. S2. The cyanobacteria-based activated carbon obtained in step S1 and ferric chloride hexahydrate were ultrasonically dispersed in ethanol at a mass ratio of 3:7 for 20 min. The mixture was stirred and mixed at 60±5 ℃ for 6 h, dried at 80 ℃, and then pyrolyzed at 220 ℃ at a rate of 10 ℃ / min for 120 min. The product was washed with acetone or ethanol until the supernatant was colorless and dried to obtain a heterogeneous Fenton catalyst supported on cyanobacteria-based activated carbon.

9. A cyanobacteria-based activated carbon supported heterogeneous Fenton catalyst prepared by the method of any one of claims 1-8.

10. The application of the catalyst of claim 9 in the degradation of antibiotics in water.

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