A biochar-based fe monatomic catalyst, and a preparation method and application thereof

Abstract

This invention provides a biochar-based Fe single-atom catalyst, its preparation method, and its application. The preparation method includes the following steps: calcining shrimp shells under a nitrogen or inert gas atmosphere to obtain biochar, followed by acid washing, cleaning, and drying to obtain biochar SO; dissolving melamine and cyanuric acid in DMSO to obtain solution A and solution B; dissolving ferric citrate in solution A and then adding it to solution B; stirring and reacting; filtering, washing, and drying to obtain supramolecular polymer MCA; mixing the obtained SO and MCA at a mass ratio of 1:0.25~1, grinding, and then co-pyrolyzing at 450-750℃ for 1-5 hours under a nitrogen or inert gas atmosphere, followed by cooling. The technical solution of this invention exhibits high catalytic activity, can efficiently catalyze the rapid degradation of aniline by PMS, is low in cost, has minimal environmental impact, and is safe, showing great application potential in the treatment of aniline-related wastewater.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a biochar-based Fe single-atom catalyst, its preparation method, and its application. Background Technology

[0002] The threat posed by aniline pollution in groundwater to human and ecological health cannot be ignored, and effective treatment of aniline in water is of great significance. At present, the technologies for treating aniline in water mainly include three categories: physical methods, biological methods, and chemical methods. Among them, chemical methods include photocatalytic degradation, electrocatalytic degradation, homogeneous catalyst catalytic degradation, and heterogeneous catalyst catalytic degradation. Among them, (1) photocatalytic degradation mainly occurs in the light-transmitting layer, and photocatalytic degradation of organic matter in the surface layer of water. Studies have found that light sources, media, heavy metal ions, nitric acid, and nitrite can all affect photodegradation. Photocatalysis mainly occurs in the light-transmitting layer, and photocatalytic degradation of organic matter in the surface layer of water. Studies have found that light sources, media, heavy metal ions, nitric acid, and nitrite can all affect photodegradation. (2) Electrocatalytic degradation is a method that uses anodic action to directly decompose organic matter or uses anodic reaction to form hydroxyl groups, which give it a high oxidizing ability, thereby partially mineralizing it and forming small organic or inorganic molecules. Essentially, it is a reaction involving the transfer of electrons in opposite directions at the solid-liquid interface. The solid-liquid interface area, electrode potential, and the morphology and concentration of species on the electrode surface play an important role in the electrochemical reaction rate. (3) Catalytic degradation by catalysts includes both homogeneous and heterogeneous catalysts. The earliest developed system was the homogeneous system, which utilizes only radiation, heating, ultrasound, alkali, or transition metal ions for catalytic reaction. Homogeneous catalysts have the advantages of highly uniform active sites, extremely high metal utilization, and strong catalytic activity. (4) Heterogeneous systems are superior to homogeneous systems because (a) solid heterogeneous catalysts can be easily separated from treated water and reused; (b) there is no need to remove dissolved metals from treated water for secondary treatment; and (c) they are more tolerant of operating conditions. There are many types of heterogeneous catalysts, which can be classified into bulk catalysts, nanoparticle catalysts, nanocluster catalysts, and single-atom catalysts according to metal size. Bulk catalysts and nanocatalysts have inherent drawbacks: (1) low utilization of metal atoms, with only surface or subsurface atoms participating in the catalytic process; (2) nanoparticles are heterogeneous in size, morphology, composition, and interaction with the support, resulting in various adsorption configurations for reactants, often leading to side reactions. On the other hand, the heterogeneity of nanocatalysts also hinders the understanding of the structure-activity relationship of heterogeneous catalysis and the design and development of highly efficient catalysts. Against this backdrop, a heterogeneous catalyst with a theoretical atom utilization rate close to 100% and a nearly homogeneous structure—the single-atom catalyst—has emerged.

[0003] While physical methods can treat large quantities of wastewater and are simple in process, they involve cumbersome pretreatment, high costs, and secondary pollution. They also cannot effectively reduce the toxicity of pollutants and cannot be directly used for treating organic wastewater; however, they can be used as pretreatment in wastewater treatment processes. Biological oxidation of organic pollutants requires 15 to 20 days, during which daily monitoring is necessary to maintain favorable environmental conditions for microbial growth. The effectiveness of biological processes depends on the type of substrate available to the microorganisms. Therefore, biological treatment is challenging for toxic compounds such as aniline and their derivatives. Photocatalytic materials have a narrow absorption range for ultraviolet light. While the bandgap of photocatalytic materials can be expanded through modification using different techniques, the overall photocatalytic quantum utilization rate remains low, and the degradation efficiency is also affected by the catalyst properties. Some wastewaters (such as dyeing and printing wastewater, papermaking wastewater, and leather tanning wastewater) have high chroma and many impurities, hindering light penetration and severely impacting photocatalytic oxidation. Furthermore, to improve reaction rates, currently used high-efficiency catalysts are mostly nanoparticles with small particle sizes, making recovery difficult. Electrocatalytic degradation technology has limited applicability on a small scale, high operational requirements, and high operating costs, restricting its widespread application in wastewater treatment. Homogeneous catalysts have complex preparation processes, high costs, and short lifespans, limiting their application in the environmental field. Summary of the Invention

[0004] To address the above technical problems, this invention discloses a biochar-based Fe single-atom catalyst, its preparation method, and its application. It can efficiently activate PMS to degrade aniline, improve degradation efficiency, and can be used in wastewater treatment containing aniline pollutants.

[0005] The technical solution adopted by this invention is as follows:

[0006] A method for preparing a biochar-based Fe single-atom catalyst includes the following steps:

[0007] Step S1: Calcine shrimp shells under a nitrogen or inert gas atmosphere to obtain biochar, then acid wash, clean and dry to obtain shrimp shell biochar, labeled as SO;

[0008] In step S2, melamine and cyanuric acid are dissolved in DMSO to obtain solution A and solution B. Iron salt is dissolved in solution A and then poured into solution B. The mixture is stirred and reacted, filtered, washed and dried to obtain a supramolecular polymer Fe-SOFs that confines iron in a hexagonal cavity to prevent its aggregation, labeled as MCA.

[0009] Step S3: The obtained shrimp shell biochar SO and supramolecular polymer Fe-SOFs MCA are mixed at a mass ratio of 1:0.25~1, ground, and then heated to 450-650℃ and kept at that temperature for 1-5h under a nitrogen or inert gas atmosphere for co-pyrolysis. After cooling, the biochar-based Fe single-atom catalyst Fe-MCA@SS is obtained.

[0010] This technical solution uses shrimp shell biochar as a support and co-pyrolyzes it with MCA to obtain a catalyst. Fe exists in the catalyst in the form of single atoms, and these Fe atoms are coordinated with N, possessing single-atom Fe-pyridine N4 sites. This catalyst exhibits superior catalytic activation ability for PMS, efficiently catalyzing the degradation of aniline from potassium persulfate (PMS); furthermore, this catalyst demonstrates better environmental adaptability and causes less environmental damage.

[0011] As a further improvement of the present invention, in step S1, the calcination temperature is 380~450℃ and the calcination time is 1-3h. Further, the calcination temperature is 400℃ and the calcination time is 2h.

[0012] As a further improvement of the present invention, in step S1, acid washing is performed with dilute sulfuric acid for 0.5-3 hours, followed by washing multiple times with pure water and vacuum drying. Further, the concentration of the dilute sulfuric acid is 1 mol / L, the washing time is 2 hours, and the vacuum drying temperature is 55-65℃.

[0013] As a further improvement of the present invention, in step S2, the iron salt is ferric citrate, the mass ratio of ferric citrate to melamine / cyanuric acid is 1:4-200, and the mass ratio of melamine to cyanuric acid is 1:1. Further, the mass ratio of ferric citrate to melamine / cyanuric acid is 1:4 / 6 / 10 / 20 / 200.

[0014] As a further improvement of the present invention, in step S2, an organic filter membrane is used for filtration, followed by washing with pure water multiple times and vacuum drying at 55-65°C.

[0015] As a further improvement of the present invention, in step S3, the heating rate is 2-5℃ / min; the holding time is 4h. Further, the heating rate is 2.3℃ / min.

[0016] As a further improvement of the present invention, in step S3, the material is ground and then passed through a 100-mesh sieve.

[0017] As a further improvement of the present invention, in step S3, the mass ratio of SO to MCA is 1:1.

[0018] The present invention also discloses a biochar-based Fe single-atom catalyst, which is prepared by any of the above-described methods for preparing biochar-based Fe single-atom catalysts.

[0019] The present invention also discloses the application of the biochar-based Fe single-atom catalyst described above for catalyzing the treatment of wastewater containing aniline with potassium persulfate.

[0020] As a further improvement of the present invention, the amount of the biochar-based Fe single-atom catalyst is 20-50% of the mass of potassium persulfate.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The technical solution of this invention features high atom utilization and high catalytic activity, enabling efficient catalysis of PMS for rapid degradation of aniline. It drastically reduces aniline content within 5 minutes, achieves high TOC removal rate, exhibits excellent pH adaptability and good environmental adaptability, is low-cost, causes minimal environmental damage, and is safe and efficient, demonstrating significant application potential in aniline wastewater treatment. Furthermore, the preparation method is simple, inexpensive, and has a long lifespan. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing a biochar-based Fe single-atom catalyst according to the present invention.

[0024] Figure 2 These are the X-ray energy spectrum and transmission electron microscopy image of Embodiment 1 of the present invention, wherein (a) is a transmission electron microscopy image and (b) is an X-ray energy spectrum.

[0025] Figure 3 This is the Fourier transform spectrum derived from the fine structure of extended X-ray absorption in Embodiment 1 of the present invention.

[0026] Figure 4 This is the Fourier transform-X-ray absorption fine structure fitting curve of Embodiment 1 of the present invention.

[0027] Figure 5 This is a comparison chart of the aniline residual rate between Example 1 and the comparative example of the present invention.

[0028] Figure 6 This is a comparison of the aniline residual rate at different pH values ​​in Example 1 of the present invention.

[0029] Figure 7 This refers to the residual rate in simulated aniline wastewater in Example 1 of the present invention.

[0030] Figure 8 These are the aniline degradation rate results from Examples 2-4 of this invention.

[0031] Figure 9 This is a comparison of the effects of Example 1 of the present invention and catalysts prepared from other biomass on the catalytic degradation of aniline by PMS. Detailed Implementation

[0032] The preferred embodiments of the present invention will be described in further detail below.

[0033] A method for preparing a biochar-based Fe single-atom catalyst, such as... Figure 1 As shown, it includes the following steps:

[0034] Step S1: Calcine shrimp shells under a nitrogen atmosphere to obtain biochar. Acid wash with dilute sulfuric acid for 0.5-3 hours, then wash with pure water multiple times and vacuum dry to obtain shrimp shell biochar, labeled as SO.

[0035] In step S2, melamine and cyanuric acid are dissolved in DMSO to obtain solution A and solution B. Ferric citrate is dissolved in solution A and then poured into solution B. The mixture is stirred and reacted, filtered, washed and dried to obtain a supramolecular polymer Fe-SOFs that confines iron in a hexagonal cavity to prevent its aggregation, labeled as MCA.

[0036] Step S3: The obtained shrimp shell biochar SO and supramolecular polymer Fe-SOFs MCA are mixed at a mass ratio of 1:0.25~1, ground, and then heated to 450-650℃ and kept at that temperature for 1-5h under a nitrogen or inert gas atmosphere for co-pyrolysis. After cooling, the biochar-based Fe single-atom catalyst Fe-MCA@SS is obtained.

[0037] In step S1, the calcination temperature is 380~450℃, and the calcination time is 1-3h. Further, the calcination temperature is 400℃, and the calcination time is 2h.

[0038] Furthermore, the concentration of the dilute sulfuric acid is 1 mol / L, and the washing time is 2 hours; the vacuum drying temperature is 55-65℃.

[0039] In step S2, the mass ratio of ferric citrate to melamine / cyanuric acid is 1:4-200, and the mass ratio of melamine to cyanuric acid is 1:1. Further, the mass ratio of ferric citrate to melamine / cyanuric acid is 1:4 / 6 / 10 / 20 / 200.

[0040] In step S2, an organic filter membrane is used for filtration, followed by washing with pure water multiple times and vacuum drying at 55-65℃.

[0041] In step S3, the mass ratio of SO to MCA is 1:1.

[0042] Further, in step S3, the heating rate is 2-5℃ / min; the holding time is 4h. Further, the heating rate is 2.3℃ / min. In step S3, the material is ground and then passed through a 100-mesh sieve.

[0043] The following description uses specific examples to illustrate the point. Example

[0044] A biochar-based Fe single-atom catalyst is prepared using the following steps:

[0045] First, shrimp shells were placed in a tube furnace and calcined at 400°C under a N2 atmosphere for 2 h to obtain biochar. The ground biochar was washed with 1 mol / L H2SO4 at room temperature for 2 h, then washed three times with pure water, and dried under vacuum at 60 °C to obtain SO.

[0046] The obtained biochar (labeled SO) was placed in a tube furnace and heated to 550°C at a rate of 2.3 °C / min in a N2 atmosphere, and held for 4 h. After cooling to room temperature, the solid was thoroughly ground and sieved to obtain pure biochar SS for subsequent comparative experiments.

[0047] 5 g of melamine / cyanuric acid was dissolved in DMSO to obtain solution A / B. 0.5 g of ferric citrate was dissolved in solution A, and the mixture was stirred for 30 min. Then, solution B was gradually poured into solution A, and the mixture was stirred for another 30 min to obtain a yellow solid. The yellow solid was then filtered through an organic filter membrane, washed three times with pure water, and dried in a vacuum oven at 60 °C. As a result, supramolecular organic frameworks (Fe-SOFs), or MCA, were obtained, which confine iron within hexagonal cavities to prevent its aggregation.

[0048] In addition, MCA was placed in a tube furnace and heated to 550 °C at a rate of 2.3 °C / min in a N2 atmosphere for 4 hours. After cooling to room temperature, the solid was thoroughly ground and passed through a 100-mesh sieve to obtain Fe-MCA, which was used for subsequent comparative experiments.

[0049] Before co-pyrolysis, SO and MCA were mixed in a 1:1 mass ratio and cooled to room temperature. The solid was then thoroughly ground and passed through a 100-mesh sieve. The resulting solid was labeled Fe-MCA. The obtained Fe-MCA compound was placed in a tube furnace and heated to 550°C at a rate of 2.3°C / min under a N2 atmosphere, and held for 4 hours. After cooling to room temperature, the solid was thoroughly ground and sieved to obtain the target catalyst, labeled Fe-MCA@SS. It was then harvested and stored in a drying oven.

[0050] The X-ray energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) images of the catalyst obtained in this embodiment are as follows: Figure 2 As shown, the uniform distribution of Fe element indicates that Fe does indeed exist in Fe-MCA@SS. Transmission electron microscopy results show that no crystalline Fe species, such as aggregated clusters or nanoparticles, are present on the surface of Fe-MCA@SS. Therefore, Fe likely exists in Fe-MCA@SS in single-atom form. The Fourier transform spectrum derived from the extended X-ray absorption fine structure is shown below. Figure 3 As shown, Fe-MCA@SS exhibits only one main peak around 1.5 Å, attributed to the Fe-N scattering pathway. Furthermore, Fe-O (1.6 Å) detected in FeO and Fe-Fe (2.2 Å) detected in Fe foil are not present in Fe-MCA@SS; simultaneously, combined with... Figure 4 The wavelet transform-X-ray absorption fine structure fitting curves show only one intensity maximum of ~4.5 Å⁻¹, indicating that Fe atoms are coordinated with N. Furthermore, the coordination number of Fe in Fe-MCA@SS is 4.0, and the average bond length is 1.997 Å. The formation energy (E0) of the Fe−pyridine N₄ configuration is... form The smaller configuration (1.207 eV) compared to Fe−pyrrole N4 (3.783 eV) indicates that the Fe atom tends to bind with pyridine N. In summary, the above analytical results confirm the presence of a single-atom Fe−pyridine N4 site in Fe-MCA@SS. Example 2

[0051] A biochar-based Fe single-atom catalyst is prepared using the following steps:

[0052] First, shrimp shells were placed in a tube furnace and calcined at 400°C under a N2 atmosphere for 2 h to obtain biochar. The ground biochar was washed with 1 mol / L H2SO4 at room temperature for 0.5 h, then washed three times with pure water, and dried under vacuum at 60 °C to obtain SO.

[0053] 5 g of melamine / cyanuric acid was dissolved in DMSO to obtain solution A / B. 0.05 g of ferric citrate was dissolved in solution A, and the mixture was stirred for 30 min. Then, solution B was gradually poured into solution A, and the mixture was stirred for another 30 min to obtain a yellow solid. The yellow solid was then filtered through an organic filter membrane, washed three times with pure water, and dried in a vacuum oven at 60 °C. As a result, supramolecular organic frameworks (Fe-SOFs), or MCA, were obtained, which confine iron within hexagonal cavities to prevent its aggregation.

[0054] Before co-pyrolysis, SO and MCA were mixed at a mass ratio of 1:0.75 and cooled to room temperature. The solid was then thoroughly ground and passed through a 100-mesh sieve. The resulting solid was labeled Fe-MCA. The obtained Fe-MCA compound was placed in a tube furnace and heated to 450°C at a rate of 2°C / min in a N2 atmosphere, and held for 5 hours. After cooling to room temperature, the solid was thoroughly ground and sieved to obtain the target catalyst, labeled Fe-MCA@SS2. It was then harvested and stored in a drying oven. Example 3

[0055] A biochar-based Fe single-atom catalyst is prepared using the following steps:

[0056] First, shrimp shells were placed in a tube furnace and calcined at 400°C under a N2 atmosphere for 2 h to obtain biochar. The ground biochar was washed with 1 mol / L H2SO4 at room temperature for 3 h, then washed three times with pure water, and dried under vacuum at 60 °C to obtain SO.

[0057] 5 g of melamine / cyanuric acid was dissolved in DMSO to obtain solution A / B. 2.5 g of ferric citrate was dissolved in solution A, and after stirring for 30 min, solution B was gradually poured into solution A, and the mixture was stirred for another 30 min to obtain a yellow solid. The yellow solid was then filtered through an organic filter membrane, washed three times with pure water, and dried in a vacuum oven at 60 °C. As a result, supramolecular organic frameworks (Fe-SOFs), i.e., MCA, were obtained, which confine iron within hexagonal cavities to prevent its aggregation.

[0058] Before co-pyrolysis, SO and MCA were mixed at a mass ratio of 1:0.5 and cooled to room temperature. The solid was then thoroughly ground and passed through a 100-mesh sieve. The resulting solid was labeled Fe-MCA. The obtained Fe-MCA compound was placed in a tube furnace and heated to 650°C at a rate of 5°C / min in a N2 atmosphere, and held for 1 hour. After cooling to room temperature, the solid was thoroughly ground and sieved to obtain the target catalyst, labeled Fe-MCA@SS3. It was then harvested and stored in a drying oven. Example 4

[0059] A biochar-based Fe single-atom catalyst is prepared using the following steps:

[0060] First, shrimp shells were placed in a tube furnace and calcined at 400°C under a N2 atmosphere for 2 h to obtain biochar. The ground biochar was washed with 1 mol / L H2SO4 at room temperature for 2 h, then washed three times with pure water, and dried under vacuum at 60 °C to obtain SO.

[0061] 5 g of melamine / cyanuric acid was dissolved in DMSO to obtain solution A / B. 0.5 g of ferric citrate was dissolved in solution A, and the mixture was stirred for 30 min. Then, solution B was gradually poured into solution A, and the mixture was stirred for another 30 min to obtain a yellow solid. The yellow solid was then filtered through an organic filter membrane, washed three times with pure water, and dried in a vacuum oven at 60 °C. As a result, supramolecular organic frameworks (Fe-SOFs), or MCA, were obtained, which confine iron within hexagonal cavities to prevent its aggregation.

[0062] Before co-pyrolysis, SO and MCA were mixed at a mass ratio of 1:0.25 and cooled to room temperature. The solid was then thoroughly ground and passed through a 100-mesh sieve. The resulting solid was labeled Fe-MCA. The obtained Fe-MCA compound was placed in a tube furnace and heated to 550°C at a rate of 2.3°C / min in a N2 atmosphere, and held for 4 hours. After cooling to room temperature, the solid was thoroughly ground and sieved to obtain the target catalyst, labeled Fe-MCA@SS4. It was then harvested and stored in a drying oven.

[0063] The catalysts obtained in Examples 2-4 were tested, and the results showed that the catalysts in Examples 2-4 had single-atom Fe-pyridine N4 sites.

[0064] The catalysts from Examples 1-4 were used to conduct catalytic degradation experiments of aniline using PMS. The aniline degradation experiments were carried out in 50 mL of deionized aniline aqueous solution. The 50 mL aniline solution (concentration 10 mg / L) was magnetically stirred at room temperature. 0.01 g of catalyst was dispersed in the aniline solution, and the reaction was initiated after adding 0.25 mL of potassium persulfate (PMS, 100 g / L). At regular intervals, 1.0 mL of the reaction solution was taken, quenched with 10 μL of sodium thiosulfate (50 g / L), and filtered through a 0.22 µm polytetrafluoroethylene membrane.

[0065] Meanwhile, aniline degradation experiments were conducted under the above conditions using PMS without catalyst, supramolecular polymer (Fe-MCA obtained in Example 1) + PMS, and pure biochar (SS obtained in Example 1) + PMS as comparative examples.

[0066] The aniline residual rates of Example 1 and the comparative example are as follows: Figure 5As shown, PMS alone can only degrade about 22.5% of aniline after 15 min of reaction. Even with the simultaneous addition of SS and PMS, only 38% of aniline is eliminated, while the Fe-MCA + PMS system removes only about 13% of aniline. Conversely, Fe-MCA@SS + PMS causes a sharp reduction in aniline content within 5 min, and this process follows the pseudo-first-order kinetic model well, with a rate constant of 0.58 min. -1 (Approximately 22 times larger than SS, and 72.5 times larger than Fe-MCA), indicating that Fe-MCA@SS can efficiently activate PMS to degrade aniline. The aniline degradation rate results for Examples 2-4 are as follows... Figure 8 As shown, in Examples 2 to 4, the degradation rate of aniline can reach more than 40% within 2 minutes.

[0067] The catalyst from Example 1 was used in degradation experiments with PMS on aniline solutions at different pH values. These degradation experiments were conducted in 50 mL aniline solutions. 50 mL aniline solutions (10 mg / L concentration) with pH values ​​of 3, 5, 7, 9, and 11 were prepared and magnetically stirred at room temperature. 0.01 g of catalyst was dispersed in the aniline solution, and 0.25 mL of potassium persulfate (PMS, 100 g / L) was added to initiate the reaction. At regular intervals, 1.0 mL of the reaction solution was taken, quenched with 10 μL of sodium thiosulfate (50 g / L), and filtered through a 0.22 µm polytetrafluoroethylene membrane.

[0068] The obtained aniline residual rate results are as follows Figure 6 As shown, even at pH 3, the degradation of aniline was only slightly inhibited, and it was still completely degraded within 15 minutes of the reaction. In other words, Fe-MCA@SS exhibits excellent pH adaptability.

[0069] Furthermore, the catalyst of Example 1 was tested in simulated aniline wastewater. The degradation experiment was carried out in 50 mL of aniline wastewater (concentration of 10 mg / L), and the specific steps were the same as before.

[0070] The residual rate of aniline obtained in simulated aniline-containing groundwater wastewater is as follows: Figure 7 As shown, Fe-MCA@SS in Example 1 can also effectively catalyze the degradation of aniline after 15 min, with a TOC removal rate of nearly 50%, further verifying the excellent catalytic performance of Fe-MCA@SS and its practical application value for aniline wastewater.

[0071] Overall, Fe-MCA@SS exhibits good environmental adaptability and causes minimal environmental damage, making it a safe and efficient method for treating aniline wastewater.

[0072] Based on Example 1, other biomass was used as a comparison, such as onion, spirulina, wood ear fungus, tea leaves, rapeseed, and wheat straw, with the specific steps being the same as in Example 1. The obtained catalysts were used to catalyze the aniline degradation of PMS according to the aforementioned method. The aniline degradation experiment was conducted in a 50 mL aniline solution, with the 50 mL aniline solution (concentration 10 mg / L) being magnetically stirred at room temperature. 0.01 g of catalyst was dispersed in the aniline solution, and 0.25 mL of potassium persulfate (PMS, 100 g / L) was added before the reaction began. Every so often, 1.0 mL of the reaction solution was taken, quenched with 10 μL of sodium thiosulfate (50 g / L), and filtered through a 0.22 µm polytetrafluoroethylene membrane. The aniline degradation rate data of PMS catalyzed by the catalysts obtained using other biomass and the catalyst prepared from shrimp shells in Example 1 are as follows: Figure 9 As shown, the catalyst prepared from shrimp shells in Example 1 achieved a 60% aniline degradation rate after 60 minutes, which is far higher than that of other biomass-based catalysts.

[0073] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. The application of a biochar-based Fe single-atom catalyst, characterized in that: It is used to catalyze the treatment of wastewater containing aniline with potassium persulfate. The preparation method of the biochar-based Fe single-atom catalyst includes the following steps: Step S1: Calcine the shrimp shells in a nitrogen or inert gas atmosphere to obtain biochar, then acid wash, clean and dry to obtain shrimp shell biochar. Step S2: Melamine and cyanuric acid are dissolved in DMSO to obtain solution A and solution B. Iron salt is dissolved in solution A and then poured into solution B. The mixture is stirred and reacted, filtered, washed and dried to obtain the supramolecular polymer Fe-SOFs that confines iron in a hexagonal cavity. Step S3: The obtained shrimp shell biochar and supramolecular polymer Fe-SOFs are mixed at a mass ratio of 1:0.25~1, ground, and then heated to 450-650℃ and kept at the temperature for 1-5h under a nitrogen or inert gas atmosphere for co-pyrolysis. After cooling, biochar-based Fe single-atom catalyst is obtained. In step S1, the calcination temperature is 380~450℃ and the calcination time is 1-3h; in step S2, the iron salt is ferric citrate, the mass ratio of ferric citrate to melamine / cyanuric acid is 1:4-200, and the mass ratio of melamine to cyanuric acid is 1:

1.

2. The application of the biochar-based Fe single-atom catalyst according to claim 1, characterized in that: The amount of the biochar-based Fe single-atom catalyst used is 20-50% of the mass of potassium persulfate.

3. The application of the biochar-based Fe single-atom catalyst according to claim 1, characterized in that: In step S1, acid washing is performed with dilute sulfuric acid for 0.5 to 3 hours, followed by washing with pure water multiple times and vacuum drying.

4. The application of the biochar-based Fe single-atom catalyst according to claim 3, characterized in that: In step S2, an organic filter membrane is used for filtration, followed by washing with pure water multiple times and vacuum drying at 55-65℃.

5. The application of the biochar-based Fe single-atom catalyst according to claim 1, characterized in that: In step S3, the material is ground and then passed through a 100-mesh sieve.

6. The application of the biochar-based Fe single-atom catalyst according to claim 5, characterized in that: In step S3, the heating rate is 2-5℃ / min; the holding time is 4h; and in step S3, the mass ratio of the shrimp shell biochar to the supramolecular polymer Fe-SOFs is 1:1.

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