A single-atom covalent organic framework material with adjustable iron loading, its preparation method, and a method for sulfamethoxazole degradation.

Abstract

This invention discloses a single-atom covalent organic framework material with adjustable iron loading, its preparation method, and a method for the degradation of sulfamethoxazole. Using COFs containing bipyridine groups as a framework provides anchoring points for iron loading. By controlling the amount of iron precursor added, the iron loading can be adjusted, successfully controlling the degradation pathway to nearly 100% high-valence iron. Furthermore, after calcination, the spin state of iron is altered, improving the PMS utilization rate and electron transport efficiency of the iron sites, thereby significantly enhancing the degradation efficiency of new pollutants. The preparation process has core advantages such as simplified equipment, easy operation, and low production cost. While adhering to the concept of green synthesis, it also possesses outstanding environmental compatibility, socio-economic value, and feasibility for industrial-scale production.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework materials technology, specifically relating to a single-atom covalent organic framework material with adjustable iron loading and its preparation method, as well as a sulfamethoxazole degradation method. Background Technology

[0002] With the increasing consumption of chemicals such as pharmaceuticals, pesticides, and personal care products, wastewater containing emerging pollutants such as persistent organic pollutants (POPs), endocrine disruptors, antibiotics, and microplastics is gradually becoming a significant source of water pollution. Worryingly, these emerging pollutants are persistent in the environment, difficult to remove through natural means, and also exhibit biotoxicity and bioaccumulation, thus posing a significant risk to the ecological environment and human health.

[0003] Advanced oxidation technologies based on persulfate monophosphate (PMS) activation are ideal solutions for removing the aforementioned new pollutants. The oxidant PMS used in this approach has advantages such as strong oxidizing power, low cost, ease of transportation, mild application conditions, diverse activation methods, and wide application range. In the pathways for PMS-activated degradation of organic pollutants, they are mainly divided into free radical and non-free radical reactive oxygen species (ROSs). Free radical ROSs have strong oxidizing power but poor selectivity and weak resistance to interference; while non-free radical ROSs have high pollutant selectivity and strong resistance to interference, but weak oxidizing power, and the products are sometimes more toxic than the pollutants themselves. The diversity of new pollutant degradation pathways depends on the specific conditions of the activation reaction system. The core of controlling new pollutant degradation pathways lies in preparing high-performance catalytic materials, and the analytical model is a catalyst with a clear structure.

[0004] Single-atom catalysts (SACs) possess the highest atom utilization efficiency and a nearly uniform coordination environment, which is also tunable. Their oxidation capacity is closely related to the coordination environment, and their oxidation behavior can be modulated by changing the type of metal active center, the short-range coordination environment, the long-range coordination environment, and the support. Therefore, single-atom catalysts are currently the best candidate materials for Fenton-like catalytic reactions, and iron-based single-atom catalysts (Fe SACs) have attracted widespread attention due to their low cost and environmental friendliness. However, currently, Fe SACs rely on high-temperature pyrolysis for preparation, typically requiring calcination at 700-1000℃, and the preparation conditions are stringent, making large-scale production difficult. Under high-temperature conditions, the catalyst undergoes pyrolysis or carbonization, generating undefined sites, making structural analysis difficult and hindering the elucidation of the PMS activation mechanism. Therefore, it is necessary to provide novel iron single-atom-based catalysts to achieve the degradation of new pollutants. Summary of the Invention

[0005] For the reasons mentioned above, the first objective of this invention is to provide a single-atom covalent organic framework material with adjustable iron loading, a COFs with pyrene and bipyridine as the main groups, wherein the two nitrogen atoms on the bipyridine provide a clear anchoring site for iron, and the COFs are uniformly loaded with single-atom iron; thus, it has excellent catalytic performance.

[0006] The second objective of this invention is to provide a method for preparing single-atom covalent organic framework materials with adjustable iron loading. Using bipyridine-containing COFs as raw materials, after loading an iron-containing compound and followed by calcination, iron atoms are introduced into the COF structure, significantly improving the catalytic activity of the covalent organic framework material. By controlling the amount of iron precursor compound added, the iron loading in the covalent organic framework material can be adjusted, thereby enhancing catalytic performance. The preparation method is simple, requiring no complex reaction processes or harsh reaction conditions.

[0007] The third objective of this invention is to provide a method for degrading sulfamethoxazole, in which a single-atom covalent organic framework material with adjustable iron loading is used as a catalyst to activate persulfate to degrade sulfamethoxazole in aqueous solution, enabling efficient degradation of sulfamethoxazole in actual water bodies under room temperature conditions.

[0008] The first objective of this invention can be achieved by adopting the following technical solution:

[0009] A single-atom covalent organic framework material with adjustable iron loading comprises a covalent organic framework material of Formula II and loaded iron ions; wherein the iron ions are connected to two nitrogen atoms on the bipyridine group in the covalent organic framework material of Formula II.

[0010]

[0011] Furthermore, the mass of the iron load is 0.5%–2.5% of the mass of the monoatomic covalent organic framework material with adjustable iron loading.

[0012] The second objective of this invention can be achieved by adopting the following technical solution:

[0013] A method for preparing a single-atom covalent organic framework material with adjustable iron loading, formula The covalent organic framework shown in II reacts with the iron precursor compound in a solvent; after the reaction is complete, solid-liquid separation is performed to obtain a solid intermediate product.

[0014] The intermediate product was calcined to obtain the single-atom covalent organic framework material with adjustable iron loading.

[0015] Furthermore, the iron precursor compound is one or a combination of two or more of ferric sulfate, ferrous sulfate, ferric nitrate, ferrous acetate, ferric acetate, ferrous chloride, ferric chloride, ferric acetylacetone, or ferrous acetylacetone.

[0016] Furthermore, the solvent is methanol.

[0017] Furthermore, the mass of the iron precursor compound is 5%-40% of the total mass of the covalent organic framework material and the iron precursor compound shown in Formula II.

[0018] Furthermore, the conditions for the self-assembly reaction are: 20-30℃, stirring at 150-250 r / min for 12-18 h.

[0019] Furthermore, the calcination is carried out in an inert gas atmosphere; the calcination temperature is 350-450℃; and the calcination time is 1-5 hours.

[0020] Furthermore, the covalent organic framework material shown in Formula II is prepared by a solvothermal reaction of 1,3,6,8-tetra-(p-aminophenyl)-pyrene and 2,2'-bipyridine-5,5'-dicarboxaldehyde.

[0021] Furthermore, it also includes an activation step: after the solvothermal reaction product is dried, it is activated at 140-150℃ under an argon atmosphere.

[0022] The third objective of this invention can be achieved by adopting the following technical solution:

[0023] A method for degrading sulfamethoxazole involves using a monoatom covalent organic framework material with adjustable iron loading as a catalyst to activate persulfate and degrade sulfamethoxazole in an aqueous solution.

[0024] Furthermore, the concentration ratio of the iron-loadable monoatom covalent organic framework material to persulfate in aqueous solution is 0.2 g / L:(0.5-2) mmol / L.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The iron-loadable single-atom covalent organic framework material of this application is a COF with pyrene and bipyridine as the main groups. The two nitrogen atoms on the bipyridine provide clear anchoring sites for iron, thus enabling the loading of an appropriate amount of single-atom iron. This covalent organic framework material acts as a catalyst to activate persulfate degradation of sulfamethoxazole. The degradation pathway is as follows: 1 O2 and Fe IV =O coexistence or Fe IV =O plays a dominant role, significantly enhancing degradation activity.

[0027] 2. The method for preparing the iron-loadable single-atom covalent organic framework material of this application uses COFs containing bipyridine groups as raw materials. It utilizes the dinitrogen atom pair of bipyridine to achieve loading, and after calcination, iron atoms are introduced into the COF structure. The preparation method is simple and does not require complex reaction processes or harsh reaction conditions. Furthermore, the catalytic performance can be altered by controlling the amount of iron precursor compound added, thereby regulating the iron loading in the covalent organic framework material.

[0028] 3. The sulfamethoxazole degradation method of the present invention uses a single-atom covalent organic framework material with adjustable iron loading as a catalyst to activate persulfate in aqueous solution to degrade sulfamethoxazole. When the Fe precursor addition ratio is increased from 10% to 30%, the degradation pathway changes from... 1 O2 and Fe IV =O coexistence transforms into all being Fe IV =O, which can achieve nearly 100% degradation of sulfamethoxazole in a relatively short time. Attached Figure Description

[0029] Figure 1 XRD patterns of the frame materials of Examples 1, 3 and Comparative Example 1;

[0030] Figure 2 The TGA thermogravimetric curves of the frame materials in Examples 1 and 3 are shown.

[0031] Figure 3 Transmission electron microscopy (TEM) image of the framework material prepared in Example 3;

[0032] Figure 4 The elemental distribution mapping diagram of the framework material prepared in Example 3;

[0033] Figure 5 The graph shows the efficiency of SMZ degradation by the framework materials of Examples 1, 3, Comparative Examples 1 and 2.

[0034] Figure 6 The graph shows the efficiency of Fe-BPY in degrading SMZ with different iron loadings in Examples 2-6.

[0035] Figure 7 The graph shows the different degradation pathways of SMZ by 10% Fe-BPY prepared in Example 3.

[0036] Figure 8 The graph shows the degradation effects of 30% Fe-BPY on SMZ via different pathways, as prepared in Example 5.

[0037] Figure 9 The graph shows the effect of 30% Fe-BPY prepared in Example 5 on the degradation of SMZ in actual water.

[0038] Figure 10 This is a schematic diagram of the molecular structure of the single-atom covalent organic framework material with adjustable iron loading according to this application. Detailed Implementation

[0039] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0040] Sulfonamides (SAs) are among the most common antibacterial antibiotics, possessing a broad antibacterial spectrum, simple structure, stable properties, and good water solubility. They are widely used in animal husbandry, aquaculture, and the prevention and treatment of human and animal diseases. SAs in the environment can harm plants, animals, humans, and microorganisms. Long-term exposure to SAs significantly impacts the growth and development of aquatic plants, animals, and algae. Sulfamethoxazole (SMZ) solutions drastically reduce the hatching rate, survival rate, activity level, and body size of zebrafish. Furthermore, plants and animals exposed to SAs for extended periods contain large amounts of SA residues. When ingested by humans, these residues undergo hepatic acetylation, producing large amounts of insoluble acesulfame potassium, which can damage the urinary system and liver and kidney function. Free SAs can also cause gastrointestinal diseases, blood disorders, and allergic reactions. Long-term contact between microorganisms and SAs and some of their transformation products can lead to gene mutations and the development of antibiotic resistance genes. SMZ residues have adverse effects on ecological health, contributing to the spread of antibiotic resistance genes and exhibiting toxicity to non-target organisms.

[0041] The microenvironmental regulation of the metal active sites in single-atom catalysts significantly impacts catalyst activity and selectivity, leading to differences in catalytic reaction efficiency or mechanisms. This provides crucial reference for the rational design of highly efficient single-atom catalysts for the removal of recalcitrant organic pollutants from water. Currently, the activation of PMS with iron-based single-atom catalysts for organic pollutant degradation typically focuses on regulating its coordination microenvironment, neglecting the influence of iron single-atom loading on catalytic activity. Therefore, the relationship between loading and catalyst activity requires further investigation to understand its connection. High iron loading tends to lead to agglomeration, forming iron nanoparticles, which hinders the analysis of material structure and degradation mechanisms. Conversely, low metal loading may result in some anchoring sites not being fully fixed, failing to achieve efficient removal of new pollutants or failing to reach optimal catalyst activity. Therefore, regulating the iron atom loading is particularly important.

[0042] Iron-based single-atom catalysts require stringent preparation conditions, typically relying on high-temperature pyrolysis and calcination at 700-1000℃. Under these high temperatures, the catalyst undergoes pyrolysis or carbonization, generating undefined sites. Covalent organic frameworks (COFs), a class of crystalline polymers composed of organic ligands linked by covalent bonds, offer advantages such as resolvable structures, stability, and recyclability. Furthermore, COFs possess well-defined and usable active sites. Loading a series of functional groups onto the COF framework allows transition metals to be loaded at specific sites with atomic precision, forming COF-supported single-atom catalysts (COFs-SACs) with well-defined structures. The precisely identifiable structure of COFs facilitates the resolving of the coordination environment of COFs-SACs. Therefore, single-atom COFs provide an ideal model for elucidating the degradation mechanisms of novel pollutants.

[0043] Therefore, this application provides a single-atom covalent organic framework material with adjustable iron loading, its preparation method, and a method for sulfamethoxazole degradation.

[0044] A single-atom covalent organic framework material (Fe-BPY-COFs) with adjustable iron loading comprises a covalent organic framework material of Formula II and loaded iron ions; wherein the iron ions are connected to two nitrogen atoms on the bipyridine group in the covalent organic framework material of Formula II.

[0045]

[0046] This application uses a covalent organic framework material with the structure shown in Formula II as raw material, wherein the bipyridine group is the anchoring site for iron atom loading, which can achieve precise control of the coordination microenvironment of iron single atoms; since the molar concentration of the bipyridine unit in the covalent organic framework material with the structure shown in Formula II is constant, the iron loading can be controlled by adjusting the addition concentration of Fe precursor and covalent organic framework.

[0047] As one embodiment, the iron-load-adjustable single-atom covalent organic framework material of this application is shown in Formula I: Figure 10 .

[0048]

[0049] As one implementation, the mass of the loaded iron is 0.5%-2.5% of the mass of the monoatomic covalent organic framework material with adjustable iron loading.

[0050] When the iron-loadable single-atom covalent organic framework material of this application is activated by persulfate (PMS) to degrade sulfamethoxazole (SMZ), for the Fe-BPY / PMS system with an iron loading of 1%, there is still... 1O2. When more iron atoms are anchored at the anchoring point, the degradation pathway changes from... 1 O2 and Fe IV =O coexistence transforms into all being Fe IV =O (e.g., load is 1.7%), while Fe IV =O has a relatively high oxidizing power 1 High O2 levels significantly enhance degradation activity.

[0051] This application also provides a method for preparing a single-atom covalent organic framework material with adjustable iron loading, characterized in that...

[0052] The covalent organic framework shown in Formula II reacts with the iron precursor compound in a solvent; after the reaction is completed, solid-liquid separation is performed to obtain a solid intermediate product.

[0053] The intermediate product was calcined to obtain the single-atom covalent organic framework material with adjustable iron loading.

[0054] As one implementation method, the specific process is as follows:

[0055] (1) The iron precursor compound was dissolved in a solvent to obtain the first reaction solution;

[0056] (2) The covalent organic framework shown in Formula II is stirred and mixed with the first reaction solution, then the solid is separated, washed, and dried to obtain a solid intermediate product;

[0057] (3) After calcining the solid intermediate product, a single-atom covalent organic framework material with adjustable iron loading is obtained.

[0058] As one implementation method, step (1) dissolution is ultrasonic dissolution and mixing, with an ultrasonic temperature of 20℃-30℃ and an ultrasonic time of 5-10min.

[0059] In one embodiment, the iron precursor compound is one or a combination of two or more of ferrous sulfate, ferrous sulfate, ferrous nitrate, ferrous acetate, ferrous acetate, ferrous chloride, ferric chloride, ferric acetylacetone, or ferrous acetylacetone.

[0060] In one embodiment, the solvent is methanol.

[0061] As one embodiment, the mass of the iron precursor compound is 5%-40% of the total mass of the covalent organic framework material shown in Formula II and the iron precursor compound.

[0062] As one implementation method, the conditions for the self-assembly reaction are: 20-30°C, stirring at 150-250 r / min for 12-18 h.

[0063] In one embodiment, the washing in step (3) is done with methanol; and the drying is done at 60-80°C for 3-6 hours.

[0064] In one embodiment, calcination is carried out under an inert gas atmosphere; the calcination temperature is 350-450°C; and the calcination time is 1-5 hours. In this embodiment, the solid intermediate product is placed in a quartz boat and then placed in a tube furnace for calcination under an argon atmosphere. This low-temperature self-assembly method preserves the original structure of the covalent organic framework material with bipyridine unit structure to the greatest extent, anchoring iron atoms on the bipyridine units and creating a clear coordination environment.

[0065] As one embodiment, the covalent organic framework material shown in Formula II is prepared by a solvothermal reaction of 1,3,6,8-tetra-(p-aminophenyl)-pyrene and 2,2'-bipyridine-5,5'-dicarboxaldehyde.

[0066] In one embodiment, the molar ratio of 1,3,6,8-tetra-(p-aminophenyl)-pyrene to 2,2'-bipyridine-5,5'-dicarboxaldehyde is 1:(2-2.2).

[0067] In one embodiment, the solvent for the solvothermal reaction is a mixture of 1,4-dioxane and 1,3,5-trimethylbenzene. In this embodiment, the volume ratio of 1,4-dioxane to 1,3,5-trimethylbenzene is 1:(0.2-5).

[0068] In one embodiment, the solvothermal reaction is carried out in the presence of acetic acid; in a preferred embodiment, the concentration of acetic acid is 3 mol / L; and the amount added is 5%-30% of the solvent volume.

[0069] As one embodiment, the molar-volume ratio of 1,3,6,8-tetra-(p-aminophenyl)-pyrene to the solvent is 1 mmol:(10-50 mL).

[0070] As one implementation method, the solvothermal reaction conditions are 110-130℃ for 12-96 hours.

[0071] As one embodiment, it also includes an activation step: after the solvothermal reaction product is dried, it is activated at 140-150°C under an argon atmosphere.

[0072] This application also provides a method for the degradation of sulfamethoxazole, in which a single-atom covalent organic framework material with adjustable iron loading is used as a catalyst to activate persulfate and degrade sulfamethoxazole in aqueous solution.

[0073] As one implementation method, Fe-BPY-COFs were dispersed in an aqueous SMZ solution, and the mixture was magnetically stirred at room temperature until adsorption-desorption equilibrium was reached. Then, persulfate solution was added to react.

[0074] As one implementation method, the water is tap water, lake water, or Pearl River water.

[0075] As one implementation method, the concentration ratio of the iron-loadable monoatom covalent organic framework material to persulfate in aqueous solution is 0.2 g / L:(0.5-2) mmol / L.

[0076] The following specific examples will provide further details.

[0077] Example 1

[0078] 0.15 mmol of 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 0.3 mmol of 2,2'-bipyridine-5,5'-dicarboxaldehyde, 1.5 mL of 1,4-dioxane, and 1.5 mL of 1,3,5-trimethylbenzene were added to a Pyrex tube and mixed thoroughly. After sonication for 10-15 min, 0.5 mL of 3M acetic acid was added to the tube. After thorough mixing for 15 min, the Pyrex tube was sealed and rapidly frozen in a liquid N2 bath. After three freeze-pump-thaw cycles for degassing, the reaction was heated at 120 °C for 72 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by filtration and washed with acetone and tetrahydrofuran. The mixture was dried under vacuum at 80 °C and activated in a sub-atmosphere at 150 °C to obtain a covalent organic framework material with the structure shown in Formula II, named BPY-COFs.

[0079] Example 2

[0080] 5 mg of ferric chloride was dissolved in 20 mL of anhydrous methanol and sonicated at 30 °C for 5 min. 95 mg of the covalent organic framework material BPY-COFs with the structure shown in Formula II was added. The mixture was stirred at 200 r / min at room temperature for 12 h. The solid was then separated, washed 3-5 times with anhydrous methanol, dried at 60-80 °C for 3-6 h, and calcined at 350 °C under inert conditions for 2 h to obtain a single-atom covalent organic framework material with adjustable iron loading, named 5%Fe-BPY. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Fe loading was 0.5952%.

[0081] Example 3

[0082] 10 mg of ferric chloride was dissolved in 20 mL of anhydrous methanol and sonicated at 30 °C for 5 minutes. 90 mg of the covalent organic framework material BPY-COFs with the structure shown in Formula II was added. The mixture was stirred at 150 r / min at room temperature for 12 h. The solid was then separated, washed 3-5 times with anhydrous methanol, dried at 60-80 °C for 3-6 h, and calcined at 400 °C under inert conditions for 2 h to obtain a single-atom covalent organic framework material with adjustable iron loading, named 10%Fe-BPY. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Fe loading was 0.9915%.

[0083] Example 4

[0084] 20 mg of ferric chloride was dissolved in 20 mL of anhydrous methanol and sonicated at 25 °C for 8 min. 80 mg of the covalent organic framework material BPY-COFs with the structure shown in Formula II was added. The mixture was stirred at 250 r / min at room temperature for 18 h. The solid was then separated, washed 3-5 times with anhydrous methanol, dried at 60-80 °C for 3-6 h, and calcined at 400 °C under inert conditions for 2 h to obtain a single-atom covalent organic framework material with adjustable iron loading, named 20%Fe-BPY. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Fe loading was 1.3082%.

[0085] Example 5

[0086] 30 mg of ferric chloride was dissolved in 20 mL of anhydrous methanol and sonicated at 25 °C for 5 min. 70 mg of the covalent organic framework material BPY-COFs with the structure shown in Formula II was added. The mixture was stirred at 175 r / min at room temperature for 124 h. The solid was then separated, washed 3-5 times with anhydrous methanol, dried at 60-80 °C for 3-6 h, and calcined at 375 °C under inert conditions for 4 h to obtain a single-atom covalent organic framework material with adjustable iron loading, named 30%Fe-BPY. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Fe loading was 1.6986%.

[0087] Example 6

[0088] 40 mg of ferric chloride was dissolved in 20 mL of anhydrous methanol and sonicated at 27 °C for 8 min. 60 mg of the covalent organic framework material BPY-COFs with the structure shown in Formula II was added. The mixture was stirred at 220 r / min at room temperature for 15 h. The solid was then separated, washed 3-5 times with anhydrous methanol, dried at 60-80 °C for 3-6 h, and calcined at 400 °C under inert conditions for 1.5 h to obtain a single-atom covalent organic framework material with adjustable iron loading, named 40%Fe-BPY. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Fe loading was 2.4402%.

[0089] Comparative Example 1

[0090] The difference between Comparative Example 1 and Example 3 is that Comparative Example 1 was not calcined; all other methods and steps were the same as in Example 3, and it was named 10% Fe-BPY (uncalcined). Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Fe loading was 0.8639%.

[0091] Comparative Example 2

[0092] The BPY-COFs prepared in Example 1 were calcined at 400℃ for 2 hours to obtain a covalent organic framework material, which was named BPY-COFs (calcined).

[0093] Material characterization:

[0094] (1) X-ray powder diffraction tests were performed on the BPY-COFs prepared in Example 1, the 10% Fe-BPY-COFs prepared in Example 3, and the Fe-BPY-COFs (uncalcined) prepared in Comparative Example 1. The X-ray powder diffraction patterns are shown below. Figure 1 As shown.

[0095] from Figure 1 It can be seen that the three different materials share the same main framework.

[0096] (2) The BPY-COFs prepared in Example 1 and the 10% Fe-BPY prepared in Example 3 were subjected to TGA testing, and their thermogravimetric (TG) curves are shown below. Figure 2 As shown.

[0097] from Figure 2 As can be seen, the BPY-COFs prepared in Example 1 and the 10% Fe-BPY prepared in Example 3 both have good high-temperature stability. The weight loss of BPY-COFs before 450℃ does not involve structural changes. Therefore, the low-temperature assisted synthesis temperature is determined to be 350-400℃ when calcining is performed.

[0098] (3) The 10% Fe-BPY prepared in Example 3 was subjected to TEM detection, and the TEM image is shown below. Figure 3 As shown in the figure, the Fe element distribution mapping diagram is as follows: Figure 4 As shown.

[0099] As can be seen from the figure, Fe atoms are uniformly distributed in the framework material.

[0100] Performance test for degradation of sulfamethoxazole (SMZ):

[0101] (1) 10 mg of catalyst was dispersed in 50 mL of SMZ solution, with an SMZ concentration of 5 mg / L and an initial pH of 7.0. The pH was not adjusted during the experiment, and the experimental temperature was room temperature (25℃). The catalyst was sonicated for 1 min to achieve complete dispersion. The mixture was then magnetically stirred at 300 rpm for 15 min until adsorption-desorption equilibrium was reached. Then, 2 mM persulfate solution was added to initiate the reaction. 1 mL samples were taken at set time intervals. Immediately after sampling, 20 μL of sodium thiosulfate solution was added to the sample to terminate the reaction. The sample was filtered using a 0.22 μm filter to obtain the test sample. The concentration of SMZ in the sample was determined by high performance liquid chromatography (HPLC). The degradation efficiency is shown in the figure below. Figure 6 As shown. The catalysts are 10% Fe-BPY prepared in Example 3, BYP-COFs prepared in Example 1, Fe-BPY (uncalcined) prepared in Comparative Example 1, and BYP-COFs (calcined) prepared in Comparative Example 2, respectively.

[0102] Figure 5 In the study, BPY-COFs failed to rapidly degrade SMZ regardless of whether calcination was performed or not, while SMZ was significantly degraded in both calcined and uncalcined Fe-BPY catalysts. This indicates that the loading of iron atoms is the reason for the significant improvement in catalyst degradation performance. Furthermore, calcined Fe-BPY showed a substantial increase in degradation efficiency compared to uncalcined Fe-BPY, achieving 100% degradation of SMZ within 120 minutes, clearly demonstrating high catalytic performance after calcination. Combined with thermogravimetric results, it was confirmed that the structure of BPY-COFs remained stable at 400℃, without pyrolysis or carbonization, and without the generation of undefined sites. Therefore, the iron single-atom catalyst obtained by this preparation method has a stable and resolvable structure. Thus, the improved catalytic performance may be due to the change in the spin state of iron caused by calcination, enabling it to efficiently transport electrons and utilize PMS.

[0103] (2) 10 mg of catalyst was dispersed in 50 mL of SMZ solution, with an SMZ concentration of 5 mg / L and an initial pH of 7.0. The pH was not adjusted during the experiment, and the experimental temperature was room temperature (25℃). The catalyst was sonicated for 1 min to achieve complete dispersion. The mixture was then magnetically stirred at 300 rpm for 15 min until adsorption-desorption equilibrium was reached. Then, 2 mM persulfate solution was added to initiate the reaction. 1 mL samples were taken at set time intervals. Immediately after sampling, 20 μL of sodium thiosulfate solution was added to the sample to terminate the reaction. The sample was filtered using a 0.22 μm filter to obtain the test sample. The concentration of SMZ in the sample was determined by high-performance liquid chromatography (HPLC). The degradation efficiency is shown in the figure below. Figure 6 As shown. The catalysts are 5% Fe-BPY prepared in Example 2, 10% Fe-BPY prepared in Example 3, 20% Fe-BPY prepared in Example 4, 30% Fe-BPY prepared in Example 5, and 40% Fe-BPY prepared in Example 6, respectively.

[0104] from Figure 6 It can be seen that when the Fe precursor addition ratio is between 5% and 30%, the iron loading is positively correlated with the degradation efficiency. However, when the Fe precursor addition ratio exceeds 40%, the iron loading and degradation efficiency show a negative correlation. This is because when the Fe precursor addition exceeds 30%, some metal nanoclusters may form, leading to a decrease in catalytic performance. Therefore, excessively high iron loading does not necessarily result in higher degradation efficiency, and the regulation of the metal loading of single-atom catalysts is essential.

[0105] (3) In the PMS-based activation degradation pathway of organic pollutants, the main types are free radical and non-free radical reactive oxygen species (ROSs). Free radical ROSs have strong oxidizing power but poor selectivity and weak anti-interference ability; while non-free radical ROSs have high pollutant selectivity and strong anti-interference ability but weak oxidizing power, and the toxicity of the products is sometimes higher than that of the pollutants. Therefore, targeted regulation of the degradation pathway can achieve efficient and safe degradation of pollutants. However, most current research focuses on the regulation of the metal coordination environment, while the influence of metal loading on the degradation pathway remains to be studied. In order to reveal the different catalytic behaviors and the intrinsic mechanism of selective degradation of Fe-BPY with different loadings, 10% Fe-BPY and 30% Fe-BPY with large activity differences were selected as representatives. A series of quenching experiments were conducted to explore the activation pathway of PMS on the two catalysts to determine the types of reactive oxygen species (ROSs) that play a dominant role in the two Fe-BPY / PMS systems.

[0106] The degradation experiments were conducted using 10% Fe-BPY prepared in Example 3 and 30% Fe-BPY prepared in Example 5 as catalysts, respectively. Potassium thiocyanate (KSCN) was used as a masking agent for the metal sites, and the experimental group without potassium thiocyanate was used as a control to determine the active sites of the catalytic reaction; the results are as follows. Figure 7 and Figure 8 As shown;

[0107] The addition of potassium thiocyanate resulted in virtually no degradation, indicating that the active centers of both the 10% Fe-BPY and 30% Fe-BPY catalysts are Fe atoms.

[0108] Methanol (MeOH), furfuryl alcohol (FFA), p-benzoquinone (p-BQ), and dimethyl sulfoxide (PMSO) were used as ·OH and ·OH groups, respectively. 1 O2, and Fe IV =O quencher; by capturing ROSs with the quencher, the inhibitory effect of the Fe-BPY / PMS system on pollutant oxidation was observed; the results are as follows Figure 7 and Figure 8 As shown.

[0109] FFA and PMSO had a strong inhibitory effect on SMZ degradation in the 10% Fe-BPY / PMS system, while MeOH and p-BQ had almost no effect, indicating that... 1 O2 and Fe IV =O is the main ROS species in the 10% Fe-BPY / PMS system. For the 30% Fe-BPY / PMS system, quenching experiments showed that the addition of MeOH, TBA, and FFA had no effect on the degradation of SMZ, indicating that ·OH and... 1 O2 and It is not ROSs in the system. However, the addition of PMSO has a significant inhibitory effect on the degradation of pollutants, which may be due to the capture of Fe in the PMSO system. IV =O, which inhibits the degradation of SMZ by the 30% Fe-BPY / PMS system. Therefore, based on the above quenching experimental results, it can be demonstrated that Fe in the Fe-BPY-COFs / PMS system... IV =O plays a crucial role in the degradation of SMZ, while for the 10% Fe-BPY / PMS system, there is still... 1 O2. Therefore, different loading amounts of iron atoms affect the degradation pathway; when more iron atoms are anchored at the anchoring points, the degradation pathway changes from... 1 O2 and Fe IV =O coexistence transforms into all being Fe IV =O, while FeIV =O has a relatively high oxidizing power 1 The high O2 content is also the reason for the significant increase in degradation activity.

[0110] (4) In laboratory experiments, ultrapure water was used. However, in actual water bodies, the presence of multiple coexisting ionic salts and complex water matrices greatly interferes with the degradation performance of the catalyst, which is a bottleneck for the practical application of the catalyst. In this embodiment, tap water, Pearl River water, and lake water were used as typical examples of actual water bodies to degrade SMZ and to study the degradation performance of the prepared catalyst (30% Fe-BPY) with the highest activity in actual water bodies.

[0111] The specific implementation conditions were as follows: 10 mg of the 30% Fe-BPY catalyst prepared in Example 5 was dispersed in 50 mL of actual water solution, with a SMZ concentration of 5 mg / L. The pH was not adjusted during the experiment, and the experimental temperature was room temperature (25°C). The catalyst was sonicated for 1 min to achieve complete dispersion. The mixture was then magnetically stirred at 300 rpm for 15 min until adsorption-desorption equilibrium was reached. Then, 2 mM persulfate solution was added to initiate the reaction. 1 mL samples were taken at set time intervals. Immediately after sampling, 20 μL of sodium thiosulfate solution was added to the sample to terminate the reaction. The sample was filtered using a 0.22 μm filter to obtain the test sample. The concentration of SMZ in the sample was determined by high-performance liquid chromatography (HPLC). The degradation effect of SMZ was as follows: Figure 9 As shown, 30% Fe-BPY can resist the influence of water matrix in actual water bodies and has good potential for practical application.

[0112] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A single-atom covalent organic framework material with adjustable iron loading, characterized in that, The invention comprises a covalent organic framework material of Formula II and a loaded iron ion; the iron ion is connected to two nitrogen atoms on the bipyridine group in the covalent organic framework material of Formula II. ； The method for preparing the iron-load-adjustable single-atom covalent organic framework material includes the following steps: The covalent organic framework shown in Formula II and the iron precursor compound undergo a self-assembly reaction in a solvent; after the reaction is completed, solid-liquid separation is performed to obtain a solid intermediate product; the mass of the iron precursor compound is 5%-40% of the total mass of the covalent organic framework material shown in Formula II and the iron precursor compound; the conditions for the self-assembly reaction are: 20-30℃, stirring at 150-250 r / min for 12-18 h. The intermediate product was calcined to obtain the single-atom covalent organic framework material with adjustable iron loading. Calcination is carried out in an inert gas atmosphere; the calcination temperature is 350-450℃; and the calcination time is 1-5 hours.

2. The iron-load-adjustable single-atom covalent organic framework material according to claim 1, characterized in that, The mass of the iron load is 0.5%-2.5% of the mass of the monoatomic covalent organic framework material with adjustable iron loading.

3. A method for preparing a single-atom covalent organic framework material with adjustable iron loading as described in claim 1 or 2, characterized in that, The covalent organic framework shown in Formula II reacts with the iron precursor compound in a solvent; after the reaction is completed, solid-liquid separation is performed to obtain a solid intermediate product. The intermediate product was calcined to obtain the single-atom covalent organic framework material with adjustable iron loading.

4. The method for preparing the iron-load-adjustable single-atom covalent organic framework material according to claim 3, characterized in that, The iron precursor compound is one or a combination of two or more of the following: ferrous sulfate, ferrous sulfate, ferrous nitrate, ferrous acetate, ferrous acetate, ferrous chloride, ferric chloride, ferric acetylacetone, or ferrous acetylacetone. The solvent is methanol.

5. The method for preparing the iron-load-adjustable single-atom covalent organic framework material according to claim 3, characterized in that, The covalent organic framework material shown in Formula II was prepared by a solvothermal reaction of 1,3,6,8-tetra-(p-aminophenyl)-pyrene and 2,2'-bipyridine-5,5'-dicarboxaldehyde.

6. The method for preparing the iron-load-adjustable single-atom covalent organic framework material according to claim 5, characterized in that, It also includes an activation step: after the solvothermal reaction product is dried, it is activated at 140-150℃ under an argon atmosphere.

7. A method for degrading sulfamethoxazole, characterized in that, The iron-load-adjustable single-atom covalent organic framework material of claim 1 is used as a catalyst to activate persulfate in aqueous solution to degrade sulfamethoxazole.

8. The method according to claim 7, characterized in that, The iron-load-adjustable single-atom covalent organic framework material of claim 1 has a concentration ratio of 0.2 g / L to (0.5-2) mmol / L in aqueous solution with respect to persulfate.

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