Iron monatomic catalyst, preparation method and application thereof

Abstract

The application relates to an iron monatomic catalyst as well as a preparation method and application thereof, relates to the technical field of environmental functional materials, and discloses the iron monatomic catalyst, which comprises a nitrogen-doped carbon carrier with a stacked sheet structure; nitrogen atoms and carbon atoms of the nitrogen-doped carbon carrier form a Fe-N3C1 coordination structure with iron monatomic active centers; and the atomic concentration of the iron monatomic catalyst is 0.1-0.5 at%. The iron monatomic catalyst has the characteristics of high ozone catalytic oxidation activity, high stability and low metal ion leaching, can remove disinfection by-product precursor substances in the ozone catalytic oxidation pretreatment of drinking water, and can inhibit the formation of nitrogen-containing disinfection by-products in the subsequent disinfection process.

Description

Technical Field

[0001] This application relates to the field of environmental functional materials technology, and in particular to an iron single-atom catalyst, its preparation method, and its application. Background Technology

[0002] Chlorination disinfection is a core process for ensuring the safety of drinking water supply. However, during chlorination, naturally occurring organic substances in the water can react with disinfectants to generate disinfection byproducts such as trihalomethanes and haloacetic acids, which pose a threat to human health. The national standard GB 5749-2022, "Standards for Drinking Water Quality," has clearly stipulated limits for the content of common carbonaceous disinfection byproducts such as trihalomethanes and haloacetic acids. However, recent studies have found that nitrogenous disinfection byproducts (N-DBPs) are more biotoxic than carbonaceous disinfection byproducts (C-DBPs). Therefore, controlling the formation of nitrogenous disinfection byproducts is of great significance for improving drinking water quality and ensuring drinking water safety.

[0003] Currently, ozone oxidation technology is widely used in drinking water pretreatment to control the generation of disinfection byproducts during subsequent disinfection. To improve ozone oxidation efficiency, catalysts are often used in conjunction with ozone. The catalytic effect of catalysts significantly improves ozone mass transfer efficiency and interfacial contact time, enhancing ozone utilization efficiency in the liquid phase and reducing reaction energy consumption. Transition metal oxides are widely used as catalysts in ozone catalytic oxidation technology, with manganese dioxide being a common example. While manganese dioxide catalysts have a certain ability to promote ozone decomposition, their limited surface active sites and clustered state restrict ozone activation efficiency. Furthermore, manganese dioxide catalysts are prone to manganese ion leaching during ozone catalytic oxidation, leading to catalyst inactivation and secondary environmental pollution, thus limiting their long-term use. Therefore, although transition metal oxide catalysts possess a certain ozone decomposition capacity, they still face problems such as insufficient catalytic efficiency, low density of active sites, poor catalyst stability, and secondary environmental pollution caused by metal ion leaching, making them unsuitable for drinking water pretreatment processes.

[0004] In recent years, single-atom catalysts have attracted widespread attention due to their near 100% atom utilization efficiency and excellent catalytic performance in ozone catalysis. However, existing ozone-combined single-atom catalyst applications mainly focus on the degradation of organic pollutants in industrial / domestic wastewater. For example, patent application CN120586877A proposes a method for preparing a highly loaded iron single-atom catalyst and an advanced oxidation technology for treating organic wastewater, which uses Fe... 3+The highly loaded Fe-SAC catalyst, assembled into a macromolecular organic framework, was added to wastewater containing organic pollutants. With the addition of an oxidant, it underwent heterogeneous advanced oxidation degradation, effectively removing various pollutants such as phenols, dyes, and pharmaceuticals. However, single-atom catalysts generally suffer from poor stability and the risk of metal ion leaching. No research has been reported on controlling the content of disinfection byproduct precursors in drinking water and inhibiting the formation of subsequent nitrogen-containing disinfection byproducts. Therefore, developing a single-atom catalyst with high ozone catalytic oxidation activity, high stability, and no risk of metal ion leaching to improve the removal efficiency of disinfection byproduct precursors and control the formation of nitrogen-containing disinfection byproducts during subsequent disinfection is of great significance for improving drinking water quality and ensuring drinking water safety. Summary of the Invention

[0005] The purpose of this invention is to overcome the existing defects and shortcomings and provide an iron single-atom catalyst with high ozone catalytic oxidation activity, high stability and low metal ion leaching. It can remove disinfection byproduct precursors in ozone catalytic oxidation pretreatment of drinking water and inhibit the formation of nitrogen-containing disinfection byproducts in subsequent disinfection processes.

[0006] Another object of the present invention is to provide a method for preparing an iron single-atom catalyst.

[0007] Another objective of this invention is to provide an application of a mixed iron single-atom catalyst in ozone catalytic oxidation, particularly in the pretreatment process for water chlorination disinfection.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects an iron single-atom catalyst, comprising a nitrogen-doped carbon support with a stacked sheet structure, wherein the nitrogen atoms and carbon atoms of the nitrogen-doped carbon support form a Fe-N3C1 coordination structure with the iron single-atom active center; and the atomic concentration of the iron single atoms in the iron single-atom catalyst is 0.1-0.5 at.

[0009] The catalyst of this invention constructs a single-atom catalyst with a specific Fe-N3Cl coordination structure by anchoring iron atoms in a nitrogen-doped carbon substrate. This specific structure enhances the electronic interaction between the iron single-atom catalytic active center and the nitrogen-doped carbon substrate, optimizes the electronic structure of the iron single-atom catalytic active center, thereby maximizing the utilization of the inherent catalytic ability of the central iron atom, regulating the electron density of the iron atom, promoting the dissociation of ozone in the iron single-atom catalytic active center to form highly reactive oxygen species such as surface atomic oxygen and surface peroxide with high redox potential, and increasing the generation rate of free radicals such as hydroxyl radicals and singlet oxygen, thereby achieving the removal of disinfection byproduct precursors in water and inhibiting the formation of nitrogen-containing disinfection byproducts in subsequent disinfection processes.

[0010] Furthermore, the specific iron single-atom concentration in the iron single-atom catalyst helps to avoid the phenomenon of metal particle agglomeration, optimizes the active center structure of the catalyst, maintains high atomic utilization efficiency of the central iron element, and avoids the metal dissolution problem that exists during the use of transition metal oxide catalysts.

[0011] In some embodiments, the concentration of the iron single atoms in the iron single-atom catalyst can be a range of 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any combination thereof.

[0012] Preferably, the atomic concentration of the iron single atoms in the iron single atom catalyst is 0.25-0.3 at.

[0013] In some embodiments, the hybrid boron carbon-nitrogen catalyst also has a graphite microcrystalline structure, which has graphite (002) and (101) crystal planes at 2θ of 26° ± 0.5° and 44° ± 0.5°, respectively, in the X-ray diffraction pattern. The abundance of graphite microcrystals implies a rich defect structure in the substrate of the iron single-atom catalyst, providing suitable coordination conditions for the coordination of iron single atoms.

[0014] This invention protects a method for preparing an iron single-atom catalyst, comprising the following steps: Ferrous salt, dicyandiamide, and polydentate carboxylic acid ligand were ball-milled and mixed evenly, and then calcined at 750–850 °C for 2.5–4 h in an inert atmosphere to obtain the iron single-atom catalyst. The mass ratio of the ferrous salt to the nitrogen-containing carbon source is (0.005-0.02):10.

[0015] The preparation method of this invention is simple, the raw material cost is low, and the elements used do not contain precious metals, making it suitable for industrial production and possessing good industrial prospects. The prepared catalyst material is a solid powder, which is easy to recycle and regenerate, has stable and excellent structural properties, and is an environmentally friendly material with the advantages of not producing toxic byproducts and being green and environmentally friendly.

[0016] This preparation method involves calcining a compound of ferrous salt, nitrogen-containing carbon source, and multidentate carboxylic acid ligand at a specific temperature to form a single-atom structure with specific coordination. This method can regulate the distribution of iron, inhibit the aggregation of iron atoms during calcination, improve stability, and reduce the risk of metal ion leaching.

[0017] It is important to note that calcination temperature has a significant impact on the formation of the iron atom coordination structure in iron single-atom catalysts. During calcination, the metal ions generated from the pyrolysis of ferrous salts coordinate with the substrate formed by the thermal decomposition of nitrogen-containing carbon sources under the synergistic effect of polydentate carboxylic acid ligands. Iron elements are anchored atomically within the defects of the substrate formed by the thermal decomposition of nitrogen-containing carbon sources, ultimately forming an iron single-atom catalyst with an Fe-N3C1 coordination structure. When the calcination temperature is too high, a large amount of nitrogen in the substrate is easily lost, affecting the stability of the Fe-N3C1 coordination structure; when the calcination temperature is too low, excessive carbon source will cover the catalyst surface, affecting the exposure of defects in the substrate coordinated with iron ions, ultimately affecting the catalytic activity of the catalyst. Controlling the temperature at a suitable level is beneficial for the formation of the coordination structure of iron single-atom catalysts and avoids the aggregation of iron nanoparticles.

[0018] Preferably, the calcination temperature is 780–820°C, more preferably 795–805°C.

[0019] Preferably, the heating rate of the calcination is 3-7℃ / min, more preferably 4-6℃ / min.

[0020] In some embodiments, the ferrous salt is selected from at least one of ferrous chloride, ferrous sulfate, and ferrous acetate.

[0021] In some embodiments, the polydentate carboxylic acid ligand is selected from at least one of pyromellitic acid, terephthalic acid, and pyromellitic tetracarboxylic acid.

[0022] In some embodiments, the mass ratio of the ferrous salt to the polydentate carboxylic acid ligand is (0.005-0.02):1.

[0023] This invention protects the application of the iron single-atom catalyst described herein or the iron single-atom catalyst obtained by the preparation method in ozone catalytic oxidation.

[0024] In some embodiments, ozone catalytic oxidation is used as a pretreatment process for water chlorination disinfection, which is used to remove nitrogen-containing organic matter in the water to inhibit the generation of nitrogen-containing disinfection byproducts during chlorination disinfection.

[0025] In some embodiments, the pretreatment process conditions are: ozone concentration of 500~1200ppm and iron single-atom catalyst dosage of 0.1~0.7g / L.

[0026] In some embodiments, the chlorination disinfection is chloramine disinfection.

[0027] In some embodiments, the nitrogen-containing organic matter in the water includes amino acids, specifically asparagine. Specifically, the concentration of the asparagine in the water is 0.01-0.3 mmol / L.

[0028] Specifically, the nitrogen-containing disinfection byproducts include dichloroacetamide.

[0029] Compared with the prior art, the beneficial effects of the present invention are: This invention provides an iron single-atom catalyst, which constructs a single-atom catalyst with a specific Fe-N3C1 coordination structure by anchoring iron atoms in a nitrogen-doped carbon substrate. This specific structure enhances the electronic interaction between the iron single-atom catalytic active center and the nitrogen-doped carbon substrate, optimizes the electronic structure of the iron single-atom catalytic active center, thereby maximizing the utilization of the inherent catalytic ability of the central iron atom, regulating the electron density of the iron atom, promoting the dissociation of ozone in the iron single-atom catalytic active center to form highly reactive oxygen species such as surface atomic oxygen and surface peroxide with high redox potential, and increasing the generation rate of free radicals such as hydroxyl radicals and singlet oxygen, thereby achieving the removal of disinfection byproduct precursors in water and inhibiting the formation of nitrogen-containing disinfection byproducts in subsequent disinfection processes. Attached Figure Description

[0030] Figure 1 These are transmission electron microscope and scanning electron microscope images of the iron single-atom catalyst from Example 1; wherein, Figure 1 a is a transmission electron microscope image of Example 1; Figure 1 b is a scanning electron microscope image of Example 1.

[0031] Figure 2 Wide-angle X-ray diffraction patterns of the catalysts of Example 1 and Comparative Example 1.

[0032] Figure 3 The image shows the energy-dispersive X-ray spectrum of the iron single-atom catalyst in Example 1; wherein, Figure 3 a is the energy dispersive X-ray spectrum of the catalyst in Example 1, including C, N and Fe elements; Figure 3 b is the C element energy dispersive X-ray spectrum of the catalyst; Figure 3 c is the N element energy dispersive X-ray spectrum of the catalyst; Figure 3 d is the Fe elemental energy dispersive X-ray spectrum of the catalyst.

[0033] Figure 4 The image shows the in-situ Raman spectrum of the iron single-atom catalyst in Example 1 under ozone conditions. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0035] Example 1 An iron single-atom catalyst includes a nitrogen-doped carbon support with a stacked sheet structure and an iron atom active center anchored on the support in the form of a single atom, wherein the nitrogen atoms and carbon atoms of the nitrogen-doped carbon support form an Fe-N3C1 coordination structure with the iron single-atom active center.

[0036] The preparation method of the iron single-atom catalyst includes the following steps: S1. After initially mixing 0.0068g of ferrous chloride, 0.5g of trimesic acid and 5g of dicyandiamide, put them into a ball mill jar and then ball mill them at 600rpm for 2 hours to make the raw materials uniformly mixed.

[0037] S2, the raw material powder obtained in step S1 is placed in a tube furnace and calcined at 800°C under N2 atmosphere for 3 hours. After calcination, it is naturally cooled to room temperature to obtain a black solid powder, which is the iron single-atom catalyst; the iron single-atom catalyst is denoted as Fe-N3.

[0038] Example 2 An iron single-atom catalyst differs from Example 1 in that the mass ratio of ferrous chloride, trimesic acid, and dicyandiamide in the preparation method of this example is 0.0075:0.5:5.

[0039] Example 3 An iron single-atom catalyst, which differs from Example 1 in that the calcination temperature in the preparation method of this example is 820°C.

[0040] Example 4 The application of a combination of an iron single-atom catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of the iron single-atom catalyst from Example 1 (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 500 ppm ozone using an ozone generator and introduce the ozone into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0041] Example 5 The application of a combination of an iron single-atom catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of the iron single-atom catalyst from Example 1 (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 800 ppm ozone using an ozone generator and introduce it into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0042] Example 6 The application of a combination of an iron single-atom catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of the iron single-atom catalyst from Example 1 (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 1000 ppm ozone using an ozone generator and introduce the ozone into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0043] Example 7 The application of a combination of an iron single-atom catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of the iron single-atom catalyst from Example 1 (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 1200 ppm ozone using an ozone generator and introduce the ozone into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0044] Example 8 The application of a combination of iron single-atom catalyst and ozone in the pretreatment of water for chlorination disinfection differs from Example 6 in that the amount of iron single-atom catalyst added in this example is 10 mg.

[0045] Example 9 The application of a combination of iron single-atom catalyst and ozone in the pretreatment of water for chlorination disinfection differs from Example 6 in that the amount of iron single-atom catalyst added in this example is 50 mg.

[0046] Example 10 The application of a combination of iron single-atom catalyst and ozone in the pretreatment of water for chlorination disinfection differs from Example 6 in that the amount of iron single-atom catalyst added in this example is 70 mg.

[0047] Comparative Example 1 An application of a combination of manganese dioxide catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of commercial manganese dioxide catalyst (Aladdin) (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 500 ppm ozone using an ozone generator and introduce ozone into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0048] Comparative Example 2 An application of a combination of manganese dioxide catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of commercial manganese dioxide catalyst (Aladdin) (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 800 ppm ozone using an ozone generator and introduce ozone into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0049] Comparative Example 3 An application of a combination of manganese dioxide catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of commercial manganese dioxide catalyst (Aladdin) (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 1000 ppm ozone using an ozone generator and introduce ozone into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0050] Comparative Example 4 An application of a combination of manganese dioxide catalyst and ozone in the pretreatment of water for chlorination disinfection includes the following steps: Take 30 mg of commercial manganese dioxide catalyst (Aladdin) (catalyst concentration 0.3 g / L) and place it in the constructed catalytic reaction system. Introduce water with an asparagine concentration of 0.1 mmol / L. Generate 1200 ppm ozone using an ozone generator and introduce ozone into the catalytic reaction system at a flow rate controlled at 200 mL / min. -1 The temperature of the entire reaction system was controlled at a constant 25℃, and the reaction time was 60 minutes.

[0051] Comparative Example 5 The application of a combination of manganese dioxide catalyst and ozone in the pretreatment of water for chlorination disinfection differs from Comparative Example 3 in that the amount of manganese dioxide catalyst added in this comparative example is 10 mg.

[0052] Comparative Example 6 The application of a combination of manganese dioxide catalyst and ozone in the pretreatment of water for chlorination disinfection differs from Comparative Example 3 in that the amount of manganese dioxide catalyst added in this comparative example is 50 mg.

[0053] Comparative Example 7 The application of a combination of manganese dioxide catalyst and ozone in the pretreatment of water for chlorination disinfection differs from Comparative Example 3 in that the amount of manganese dioxide catalyst added in this comparative example is 70 mg.

[0054] Performance testing 1. Microscopic morphology characterization The microstructure of the sample from Example 1 was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results are as follows: Figure 1 As shown.

[0055] from Figure 1 As can be seen, the iron single-atom catalyst of Example 1 exhibits a plate-like structure with a rough surface and a cluster-like stacked structure, which indicates that abundant pores and edge active sites are formed during the synthesis of the iron single-atom catalyst.

[0056] 2. XRD characterization The samples from Example 1 and Comparative Example 1 were subjected to X-ray diffraction (XRD) analysis, and the wide-angle X-ray diffraction patterns obtained are shown below. Figure 2 As shown.

[0057] from Figure 2 It can be seen that the iron single-atom catalyst in Example 1 exhibits two distinct broadened diffraction peaks near 26° and 44°, corresponding to the (002) and (101) crystal planes of graphite. The presence of the (002) and (101) crystal planes indicates that there are abundant defect structures in the substrate of the iron single-atom catalyst, and these abundant defect structures provide suitable coordination conditions for the coordination of iron single atoms.

[0058] Furthermore, no Fe crystallization diffraction peaks were detected in the XRD pattern, indicating that Fe may be anchored in the substrate in the form of single atoms, or there may be nanoparticle aggregation below the XRD detection limit. Combined with the Fe elemental distribution in the subsequent EDS pattern, it was determined that no Fe nanoparticle aggregation had formed, thus confirming that Fe in the catalyst of this invention was successfully anchored in the substrate in the form of single atoms.

[0059] The wide-angle X-ray diffraction pattern of Comparative Example 1 shows clear diffraction peaks. The positions and relative intensities of the main diffraction peaks are highly consistent with the manganese dioxide standard card (number: PDF#44-0141) in the database, proving that the catalyst of Comparative Example 1 has high purity.

[0060] 3. EDS characterization The energy dispersive X-ray spectra (EDS) obtained from the sample detection in Example 1 are as follows: Figure 3 As shown.

[0061] from Figure 3 It can be seen that C, N, and Fe, these three different elements, coexist and are uniformly distributed on the catalyst surface in Example 1. Simultaneously, the energy-dispersive X-ray spectrum of Fe was observed (…). Figure 3 d) It was found that the iron element was uniformly dispersed throughout the catalyst support, and no obvious local agglomeration of iron element was observed, confirming that the iron element had been successfully anchored in the nitrogen-doped carbon substrate and formed a stable coordination structure with the substrate.

[0062] 4. XPS characterization The X-ray photoelectron spectroscopy analysis data obtained from the sample detection in Example 1 are shown in Table 1.

[0063] Table 1

[0064] The results show that the support for the iron single-atom catalyst in Example 1 is a highly nitrogen-doped carbon material, and the binding energy of N indicates that it is mainly in the form of pyridine nitrogen, which is conducive to the formation of Fe-N. x The structure, and the Fe loading in the iron single-atom catalyst is 0.28 at.

[0065] 5. In-situ Raman test The catalyst of Example 1 was tested using Raman spectroscopy under 1000 ppm ozone conditions. The in-situ Raman spectrum obtained is shown below. Figure 4 As shown.

[0066] from Figure 4 It can be seen that, under ozone conditions, the iron single-atom catalyst described in this invention exhibits a high performance at 800 cm⁻¹ in the in-situ Raman spectrum. -1 and 1000cm -1 Characteristic peaks belonging to surface atomic oxygen and surface peroxide species were observed at the respective locations.

[0067] The results show that ozone on the surface of the iron single-atom catalyst described in this invention is effectively activated, and surface atomic oxygen and surface peroxide species are generated on the catalyst surface, which in turn generate free radicals with high redox potentials such as hydroxyl radicals and singlet oxygen. This can be used to achieve efficient removal of asparagine and regulate the generation of dichloroacetamide in the subsequent chloramine disinfection process.

[0068] 6. Optimal Ozone Concentration Test The catalytic efficiency of the asparagine-containing water bodies treated by the pretreatment processes of Examples 4-7 and Comparative Examples 1-4 is shown in Table 2.

[0069] The catalytic efficiency is measured by the degradation rate of asparagine in the aqueous solution. The degradation rate is calculated using the formula: (1-C / C0)×100%, where C0 is the initial concentration of asparagine and C is the concentration of asparagine after ozone catalytic oxidation.

[0070] Catalytic efficiency testing method: The initial concentration of asparagine (C0) and the concentration of asparagine after ozone catalytic oxidation (C) were determined using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS). The chromatographic portion of the HPLC-MS / MS was performed using EC-C. 18 The chromatographic column was 100×2.1mm×1.9μm, with a column temperature set to 30℃ and an injection volume of 5μL. Mobile phase A was water containing 0.1% formic acid, and mobile phase B was acetonitrile. The mobile phase flow rate was 0.3mL / min, and a gradient elution program was used: 0-2 min, 5%→20%B; 2-2.5 min, 20%→95%B; 2.5-3 min, 95%B; 3-3.1 min, 95%→5%B. In the high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS) section, multiple reaction ion (MRI) scanning mode was set, and specific asparagine precursor ions (mother ion mass-to-charge ratio of 133.1) and characteristic fragment ions (daughter ion MRI of 74.1) were selected for detection.

[0071] Table 2 Optimal Ozone Concentration Test Results

[0072] As can be seen from Table 2, the iron single-atom catalyst of the present invention has higher catalytic efficiency for asparagine than that of manganese dioxide catalyst at different ozone concentrations.

[0073] Specifically, when the ozone concentration was 500 ppm, the catalytic efficiency of Example 4 was 29%, an improvement of 52.6% compared to Comparative Example 1; when the ozone concentration increased to 800 ppm, the catalytic efficiency of Example 5 was 20%, an improvement of 33.3% compared to Comparative Example 2; when the ozone concentration increased to 1000 ppm, the catalytic efficiency of Example 6 reached 42%, while Comparative Example 3 only had 18% catalytic efficiency, making Example 6 2.3 times more efficient than Comparative Example 3; when the ozone concentration continued to increase to 1200 ppm, compared to the 1000 ppm ozone concentration condition, the catalytic efficiency of Example 7 and Comparative Example 4 improved slightly, but the improvement was not significant. Considering the minimum amount of raw materials added, the optimal ozone concentration was determined to be 1000 ppm.

[0074] It is worth noting that when the ozone concentration increased from 500 ppm to 1000 ppm, the catalytic efficiency of the iron single-atom catalyst increased, demonstrating excellent ozone catalytic oxidation ability. This indicates that the iron single-atom catalyst in Example 1 promotes the generation of active oxygen species under high ozone concentrations. The catalytic efficiency of the manganese dioxide catalyst was consistently less than 20% at ozone concentrations of 500-1000 ppm, showing insensitivity to changes in ozone concentration, reflecting the limited catalytic ability of the manganese dioxide catalyst for asparagine.

[0075] The catalytic efficiency of the iron single-atom catalysts in Examples 2-3 at an ozone concentration of 1000 ppm is comparable to that in Example 1, and will not be repeated here.

[0076] 7. Optimal catalyst dosage test The catalytic efficiency of the asparagine-containing water bodies treated by the pretreatment processes of Examples 6, 8-10 and Comparative Examples 3, 5-7 is shown in Table 3.

[0077] Table 3 Optimal catalyst dosage test results

[0078] As shown in Table 2, the catalytic efficiency of the iron single-atom catalyst in Example 1 exhibits a trend of first increasing and then decreasing with different catalyst dosages, indicating an optimal catalyst dosage window. The optimal catalyst dosage for the iron single-atom catalyst is 0.03 g, achieving the highest catalytic efficiency of 42%. The catalytic efficiency of Example 10 decreased with excessive catalyst dosage, possibly due to the shielding of active sites, leading to reduced contact efficiency between ozone and the catalyst and consequently a decrease in overall catalytic efficiency. The manganese dioxide catalyst exhibits low catalytic efficiency and is insensitive to changes in catalyst dosage. These results demonstrate that the iron single-atom catalyst of this invention requires only a small dosage to achieve maximum catalytic efficiency, avoiding waste and additional costs associated with excessive catalyst dosage.

[0079] 8. Test on the amount of sterilization byproducts generated after catalysis Chloramine disinfection experiments were conducted using simulated solutions containing 0.1 mmol / L asparagine, prepared using the pretreatment processes of Example 6 and Comparative Example 3. Simultaneously, a simulated solution pretreated with 1000 pmm ozone served as the ozone control group, while a simulated solution without any pretreatment served as the blank group. The test results of the chloramine disinfection experiment are expressed as the amount of dichloroacetamide generated at different times, and the results are shown in Table 4.

[0080] The specific procedure for the chloramine disinfection experiment is as follows: Mix 2 mmol / L chloramine solution, pretreated 0.1 mmol / L asparagine simulated solution and 0.2 mol / L phosphate buffer solution, and then bring the volume to 100 mL with ultrapure water.

[0081] The prepared solution was placed in the dark at 25°C for reaction. After 24h, 48h, 72h and 96h of reaction, a portion of the solution was taken out, and ascorbic acid solution was added to terminate the reaction. The amount of dichloroacetamide produced was then measured.

[0082] The method for detecting the amount of disinfection byproduct dichloroacetamide was as follows: Gas chromatography-tandem mass spectrometry (GC-MS / MS) was used. The chromatographic section of the GC-MS / MS used an HP-5 MS UI column (30m × 0.25mm × 0.25μm), with an injection port temperature set to 180℃ and an injection volume of 1μL. Nitrogen was used as the carrier gas at a flow rate of 1mL / min. A programmed temperature ramp was executed: initial temperature 40℃, hold for 10 min, ramp to 150℃ at a rate of 40℃ / min, hold for 5 min, ramp to 250℃ at a rate of 40℃ / min, and hold for 3 min. The mass spectrometry section of the GC-MS / MS used an EI ion source at a temperature of 230℃, an electron impact energy of 70 eV, and a quadrupole temperature of 150℃.

[0083] Table 4. Test results of the amount of dichloroacetamide generated as a disinfection byproduct.

[0084] As shown in Table 4, the blank group without any pretreatment had a high concentration of dichloroacetamide, a disinfection byproduct, after subsequent chloramine disinfection. The control group, which underwent ozone pretreatment, had a dichloroacetamide removal rate of less than 30%. After the process in Example 6, the formation of dichloroacetamide was significantly inhibited during subsequent chloramine disinfection, and the inhibitory effect further increased with prolonged disinfection time. Compared to the blank group, the removal rate of dichloroacetamide remained between 45% and 50%. In contrast, with the pretreatment in Comparative Example 3, the concentration of dichloroacetamide remained consistently high, and the removal rate of dichloroacetamide was less than 30% compared to the blank group.

[0085] The results showed that, compared with commercial manganese dioxide catalysts, the amount of dichloroacetamide generated during the ozone catalytic oxidation of asparagine using the iron single-atom catalyst described in this invention was reduced by more than 30%, and the amount of dichloroacetamide generated further decreased with the extension of disinfection time.

[0086] Therefore, the iron single-atom catalyst described in this invention can remove asparagine while also controlling the generation of subsequent disinfection byproducts, and has important practical application value.

[0087] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A single-atom iron catalyst, characterized in that, The nitrogen-doped carbon support includes a stacked sheet-like structure, wherein the nitrogen atoms and carbon atoms of the nitrogen-doped carbon support form a Fe-N3C1 coordination structure with iron single-atom active centers; the iron single atoms have an atomic concentration of 0.1-0.5 at in the iron single-atom catalyst.

2. The iron single-atom catalyst according to claim 1, characterized in that, The hybrid boron carbon-nitrogen catalyst also has a graphite microcrystalline structure, which has graphite (002) and (101) crystal planes at 2θ of 26°±0.5° and 44°±0.5° in the X-ray diffraction pattern, respectively.

3. A method for preparing the iron single-atom catalyst according to claim 1 or 2, characterized in that, Includes the following steps: Ferrous salt, dicyandiamide, and polydentate carboxylic acid ligand were ball-milled and mixed evenly, and then calcined at 750–850 °C for 2.5–4 h in an inert atmosphere to obtain the iron single-atom catalyst. The mass ratio of the ferrous salt to dicyandiamide is (0.005-0.02):

10.

4. The method for preparing the iron single-atom catalyst according to claim 3, characterized in that, The ferrous salt is selected from at least one of ferrous chloride, ferrous sulfate, and ferrous acetate.

5. The method for preparing the iron single-atom catalyst according to claim 3, characterized in that, The polydentate carboxylic acid ligand is selected from at least one of pyromellitic acid, terephthalic acid, and pyromellitic tetracarboxylic acid.

6. The method for preparing the iron single-atom catalyst according to claim 3, characterized in that, The mass ratio of the ferrous salt to the polydentate carboxylic acid ligand is (0.005-0.02):

1.

7. The application of an iron single-atom catalyst according to claim 1 or 2 or an iron single-atom catalyst obtained by any one of claims 3-6 in ozone catalytic oxidation.

8. The application according to claim 7, characterized in that, The ozone catalytic oxidation is used as a pretreatment process for water chlorination disinfection. The pretreatment process is used to remove nitrogen-containing organic matter in the water to inhibit the generation of nitrogen-containing disinfection byproducts during chlorination disinfection.

9. The application according to claim 8, characterized in that, The pretreatment process conditions are as follows: ozone concentration of 500~1200ppm and iron single-atom catalyst dosage of 0.1~0.7g / L.

10. The application according to claim 8, characterized in that, The chlorination disinfection mentioned is chloramine disinfection.

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