Nitrogen-doped carbon-based iron monatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-doped carbon-based iron monatomic catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts, the nitrogen-doped carbon-based iron monatomic catalyst with a hierarchical porous structure, namely an Fe-N4 monatomic catalyst (ITFeSA-N4), is constructed by adopting a strategy of taking inorganic salt as a template and assisting synergistic pyrolysis of nitrogen-containing ionic liquid and Fe-MOF. Inorganic salt is taken as a template, so that agglomeration of active sites can be effectively inhibited, a hierarchical pore structure is constructed, and the template removal process is simpler and more convenient due to excellent water solubility of the inorganic salt; the nitrogen-containing ionic liquid is used as a nitrogen source, the coordination environment of Fe-pyridine N4 can be accurately regulated and controlled, the structure can remarkably improve the Fe site electron cloud density (d-band center upward shift) and promote O-O bond dissociation (energy barrier reduction) in PMS, and meanwhile, the hierarchical pore channel structure can improve the O2 diffusion rate, so that ORR reaction kinetics is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and in particular to a nitrogen-doped carbon-based iron single-atom catalyst and a preparation method and application thereof. Background Art

[0002] The widespread spread of emerging organic pollutants in aquatic environments has attracted increasing attention, mainly including antibiotics, hormones, personal care products, pesticides, etc. Current treatment methods are insufficient to completely remove antibiotics, so antibiotics will eventually be discharged into the natural environment. Antibiotics are generally weakly toxic to organisms. Their main harm is to screen out microorganisms with resistance genes, allowing them to grow, migrate and spread preferentially, thereby negatively affecting the entire ecosystem. Advanced oxidation processes (AOPs) are increasingly attracting attention due to their simple operation, rapid reaction, green and efficient nature. In particular, advanced oxidation processes based on sulfate radicals (·SO4) are used to remove refractory organic pollutants in water. Sulfate radicals are usually produced by the heterogeneous activation of persulfates, especially persulfate (PMS), and are usually accompanied by the formation of hydroxyl radicals (·OH).

[0003] The oxygen reduction reaction (ORR) is a key reaction occurring on the cathode side of new energy devices such as fuel cells and metal-air batteries. While the reaction can proceed spontaneously from a thermodynamic perspective, its kinetics are extremely slow, severely limiting the energy conversion efficiency of these new energy devices. Adding a catalyst is one of the most effective methods for increasing the ORR reaction rate.

[0004] Whether it's the aforementioned sulfate radical degradation of organic pollutants or the catalytic oxygen reduction reaction, both involve the activation and conversion of O-O bonds in oxygen-containing species (PMS or O2) using catalysts. Traditional iron-based catalysts suffer from low atom utilization and high metal leaching, limiting their catalytic performance. Furthermore, iron-based catalysts can experience catalytic performance degradation over extended periods of time, and their catalytic stability is poor, hindering their practical application. In contrast, carbon-based materials offer advantages such as low cost, environmental friendliness, ease of preparation, and low metal leaching. However, their catalytic activity is generally low, and their effectiveness is often affected by surface structure and heterogeneous distribution of active sites. Further optimization is needed, such as through heteroatom doping, surface modification, and heat treatment to improve their catalytic performance. In recent years, single-atom catalysis has become a hot topic in the field of electrocatalysis. Its high density of active sites can exponentially enhance the catalytic activity of materials. As heterogeneous catalysts, single-atom catalysts not only enable catalyst separation and recovery, but also significantly improve atom utilization due to their fully exposed atomic interfaces. Their catalytic activity far exceeds that of nanoparticle catalysts, nearly matching that of homogeneous catalysis. However, due to the high surface free energy of individual atoms, once the precursor atoms are present in large quantities during the synthesis process, they tend to agglomerate and form nanoparticles, which affects catalytic activity. In addition, the precipitation of single-atom catalysts during catalytic reactions can also lead to reduced catalyst stability. Summary of the Invention

[0005] The present invention provides a nitrogen-doped carbon-based iron single-atom catalyst, its preparation method, and application, effectively resolving the technical issues of poor catalytic performance and catalytic stability of existing iron-based catalysts, carbon-based materials, and single-atom catalysts. The present invention employs an inorganic salt template-assisted synergistic pyrolysis strategy of nitrogen-containing ionic liquids and FeMOF nanoparticles to construct a nitrogen-doped carbon-based iron single-atom catalyst with a hierarchical porous structure. This catalyst not only promotes heterolytic cleavage of the O-O bond in PMS, but also enhances the O2 diffusion rate through the hierarchical pore structure, significantly improving the ORR reaction kinetics. This multi-scale control strategy of "pore structure-electronic properties-catalytic activity" not only provides new insights into the development of efficient environmental-energy dual-function catalysts, but also deepens our understanding of the structure-activity relationship of single-atom sites in redox reactions.

[0006] The first object of the present invention is to provide a method for preparing a nitrogen-doped carbon-based iron single-atom catalyst, comprising the following steps: Using an inorganic salt as a template and a nitrogen-containing ionic liquid as a nitrogen source, under a protective atmosphere, the inorganic salt is used to assist the synergistic pyrolysis of the nitrogen-containing ionic liquid and Fe-MOF nanoparticles. The Fe-MOF nanoparticles and the nitrogen-containing ionic liquid are carbonized, and the nitrogen atoms in the nitrogen-containing ionic liquid are doped into the carbon lattice of the carbonized Fe-MOF to obtain Fe-pyridine N4. The nitrogen atoms in the nitrogen-containing ionic liquid are used to regulate the coordination environment of Fe-pyridine N4, and the inorganic salt template is removed to obtain a nitrogen-doped carbon-based Fe single atom precursor.

[0007] The nitrogen-doped carbon-based Fe single-atom precursor is acid-etched to remove the iron nanoparticles in the nitrogen-doped carbon-based Fe single-atom precursor, thereby obtaining a nitrogen-doped carbon-based iron single-atom catalyst.

[0008] As a preferred embodiment, the mass ratio of the nitrogen-containing ionic liquid, the inorganic salt and the Fe-MOF nanoparticles is 10:5:0.1~5.

[0009] As a preferred embodiment, the nitrogen-containing ionic liquid is one or more of 1-ethyl-3-methylimidazolium acetate ([EMIm][N(CN)2]), 1-hexyl-3-methylimidazolium acetate ([HexMIm][N(CN)2]), and 1-hydroxyethyl-3-methylimidazolium acetate ([HydEMIm][N(CN)2]).

[0010] As a preferred embodiment, the Fe-MOF nanoparticles are one or more of MIL-100(Fe), MIL-88B(Fe), and MIL-101(Fe).

[0011] As a preferred embodiment, the inorganic salt is one or more of KCI, NaCl, CaCl2, K2SO4, Na2SO4, and CaSO4.

[0012] As a preferred embodiment, the acid etching is: immersing the nitrogen-doped carbon-based Fe single atom precursor in an inorganic acid solution with a concentration of 0.5 mol / L to 3 mol / L for 8 h to 24 h.

[0013] As a preferred embodiment, the pyrolysis temperature is 300° C. to 1200° C., and the pyrolysis time is 5 min to 5 h.

[0014] The second object of the present invention is to provide a nitrogen-doped carbon-based iron single-atom catalyst prepared by any of the preparation methods described above.

[0015] The third object of the present invention is to provide an application of the above-mentioned nitrogen-doped carbon-based iron single-atom catalyst in the degradation of organic pollutants.

[0016] The third object of the present invention is to provide an application of the above-mentioned nitrogen-doped carbon-based iron single-atom catalyst in catalyzing oxygen reduction reaction.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a preparation method of a nitrogen-doped carbon-based iron single-atom catalyst, which uses an inorganic salt as a template and a nitrogen-containing ionic liquid as a nitrogen source. Under a protective atmosphere, the inorganic salt is used to assist the coordinated pyrolysis of the nitrogen-containing ionic liquid and Fe-MOF nanoparticles. The Fe-MOF nanoparticles and the nitrogen-containing ionic liquid are carbonized, and the nitrogen atoms in the nitrogen-containing ionic liquid are doped into the carbon lattice of the carbonized Fe-MOF to obtain Fe-pyridine N4. The coordination environment of the Fe-pyridine N4 is regulated by the nitrogen atoms of the nitrogen-containing ionic liquid, and the inorganic salt template is removed to obtain a nitrogen-doped carbon-based Fe single-atom precursor; the nitrogen-doped carbon-based Fe single-atom precursor is acid-etched to remove the iron nanoparticles in the nitrogen-doped carbon-based Fe single-atom precursor to obtain a nitrogen-doped carbon-based iron single-atom catalyst. The present invention adopts an inorganic salt as a template to assist the coordinated pyrolysis of the nitrogen-containing ionic liquid and Fe-MOF to construct a nitrogen-doped carbon-based iron single-atom catalyst with a hierarchical porous structure, namely, Fe-N4 single-atom catalyst (ITFe SA -N4). Using inorganic salts as templates can effectively inhibit the aggregation of active sites and construct a multi-level pore structure. Its excellent water solubility also makes the template removal process easier. Using nitrogen-containing ionic liquids as nitrogen sources can accurately regulate the coordination environment of Fe-pyridinic N4. This structure can significantly increase the electron cloud density of the Fe site (upward shift of the d-band center) and promote the heterolytic cleavage of the O-O bond in PMS (reduced energy barrier). At the same time, the hierarchical pore structure can increase the O2 diffusion rate, thereby greatly improving the ORR reaction kinetics. The present invention develops a high-content pyridinic nitrogen and single-atom Fe-pyridinic N4 bifunctional carbon-based Fe single-atom catalyst with excellent pollutant degradation and ORR catalytic performance by precisely designing the Fe-N4 coordination microenvironment.

[0018] The multi-scale control strategy of "pore structure-electronic properties-catalytic activity" of the present invention not only provides new ideas for the development of efficient environmental-energy dual-functional catalysts, but also deepens the understanding of the structure-activity relationship of single-atom sites in oxidation-reduction reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a comparison chart of the relationship between time and degradation efficiency when the nitrogen-doped carbon-based iron single-atom catalysts of Examples 1, 2, and 4 of the present invention activate persulfate to degrade tetracycline.

[0020] Figure 2This is a comparison chart of the relationship between time and degradation efficiency when the nitrogen-doped carbon-based iron single-atom catalyst of Examples 3, 5, and 6 of the present invention activates persulfate to degrade tetracycline.

[0021] Figure 3 This is a comparison chart of the relationship between time and degradation efficiency when persulfate is activated to degrade tetracycline by the nitrogen-doped carbon-based iron single-atom catalyst of Example 1 of the present invention and the nitrogen-doped carbon-based catalyst of Comparative Example 1.

[0022] Figure 4 This is a comparison chart of the potential-current density curves corresponding to the nitrogen-doped carbon-based iron single-atom catalysts of Examples 1, 2, and 4 of the present invention during oxygen reduction catalysis.

[0023] Figure 5 This is a comparison chart of the time potential-current density curves corresponding to the nitrogen-doped carbon-based iron single-atom catalysts of Examples 3, 5, and 6 of the present invention during oxygen reduction catalysis.

[0024] Figure 6 This is a comparison diagram of the potential-current density curves corresponding to the nitrogen-doped carbon-based iron single-atom catalyst of Example 1 of the present invention and the nitrogen-doped carbon-based catalyst of Comparative Example 1 when activating oxygen reduction catalysis.

[0025] Figure 7 The adsorption configuration of the single-atom Fe-N4 site upon activation of PMS and its corresponding adsorption energy (E) obtained by DFT theoretical simulation in Example 1 of the present invention are shown in FIG. ads ) and OO bond length.

[0026] Figure 8 The adsorption configuration of the single-atom Fe-N4 site during the ORR reaction and its corresponding adsorption energy (E) obtained by DFT theoretical simulation in Example 1 of the present invention are shown in FIG. ads ) and OO bond length.

[0027] Figure 9 This is the HAADF-STEM image of the nitrogen-doped carbon-based iron single-atom catalyst in Example 1 of the present invention. The part circled in red in the figure is the iron single atom. DETAILED DESCRIPTION

[0028] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention is further described below with reference to specific examples and accompanying drawings. However, the examples are not intended to limit the present invention. The following experimental and detection methods are conventional methods unless otherwise specified; the reagents and raw materials are commercially available unless otherwise specified.

[0029] In view of the problems mentioned in the background technology of the present invention: First, traditional iron-based catalysts have the problems of low atomic utilization and strong metal leaching, which leads to limited catalytic performance. In addition, iron-based catalysts may experience catalytic performance decline during long-term reactions, and the stability of the catalytic reaction is poor, which affects its actual application effect. Second, the catalytic activity of carbon-based materials is generally low, and their catalytic effect is often affected by the surface structure and the uneven distribution of active sites. Third, in single-atom catalysts, due to the high surface free energy of individual atoms, once the precursor atom content is high during the synthesis process, it will tend to agglomerate and form nanoparticles, affecting the catalytic activity. Fourth, the precipitation of single-atom catalysts in catalytic reactions leads to reduced catalyst stability. Based on the above-mentioned technical problems, the present invention provides a nitrogen-doped carbon-based iron single-atom catalyst and its preparation method and application.

[0030] The technical solution of the present invention is analyzed and explained in detail below.

[0031] The present invention first provides a method for preparing a nitrogen-doped carbon-based iron single-atom catalyst, comprising the following steps: S1, using an inorganic salt as a template and a nitrogen-containing ionic liquid as a nitrogen source, under a protective atmosphere, the inorganic salt is used to assist the coordinated pyrolysis of the nitrogen-containing ionic liquid and Fe-MOF nanoparticles, the Fe-MOF nanoparticles and the nitrogen-containing ionic liquid are carbonized, and the nitrogen atoms in the nitrogen-containing ionic liquid are doped into the carbon lattice of the carbonized Fe-MOF to obtain Fe-pyridine N4, and the nitrogen atoms in the nitrogen-containing ionic liquid are used to regulate the coordination environment of Fe-pyridine N4, and the inorganic salt template is removed to obtain a nitrogen-doped carbon-based Fe single atom precursor.

[0032] S2, acid-etching the nitrogen-doped carbon-based Fe single-atom precursor to remove the iron nanoparticles in the nitrogen-doped carbon-based Fe single-atom precursor to obtain a nitrogen-doped carbon-based iron single-atom catalyst.

[0033] In the above technical scheme, the present invention adopts an inorganic salt as a template, assists the strategy of synergistic pyrolysis of nitrogen-containing ionic liquid and Fe-MOF, and constructs a nitrogen-doped carbon-based iron single-atom catalyst with a hierarchical porous structure. Using inorganic salt as a template can effectively inhibit the aggregation of active sites and construct a multi-level pore structure, and its excellent water solubility makes the template removal process simpler; using nitrogen-containing ionic liquid as a nitrogen source, the coordination environment of Fe-pyridine N4 can be accurately regulated. The structure can significantly improve the electron cloud density of the Fe site (upward shift of the d-band center) and promote the heterolytic cleavage of the OO bond in PMS (reduced energy barrier). At the same time, the hierarchical pore structure can increase the O2 diffusion rate, thereby greatly improving the ORR reaction kinetics. The present invention has developed a high content of pyridinic nitrogen and single-atom Fe-pyridine N4 by precisely designing the Fe-N4 coordination microenvironment, a bifunctional carbon-based Fe single-atom catalyst with excellent pollutant degradation and ORR catalytic performance.

[0034] It should be noted that mixing Fe-MOF nanoparticles with inorganic salt solution belongs to physical mixing, and the inorganic salt plays the role of a hard template. After drying and pyrolysis, the inorganic salt template is removed by water washing, which plays a role in pore formation and increasing the specific surface area of the material. During acid etching, the Fe element in the Fe-MOF will agglomerate and generate iron nanoparticles under the action of high temperature in the pyrolysis process. The role of acid etching is to etch away the iron nanoparticles to generate iron monomers.

[0035] In order to ensure that the final product catalyst is loaded with sufficient iron monomers, the mass ratio of the nitrogen-containing ionic liquid, inorganic salt and Fe-MOF nanoparticles is 10:5:0.1-5. For the amount of Fe-MOF nanoparticles, when the amount is too small, less than 0.1 defined here, there may be no Fe element in the product after acid etching, that is, all the iron nanoparticles or Fe elements are removed, and iron monomers cannot be formed. When the amount is too large, greater than 5 defined here, then in the precursor after pyrolysis, there will be a lot of iron nanoparticles, and the particles may be very large. In the subsequent acid etching, the iron nanoparticles cannot be completely removed, and finally iron monomers cannot be formed.

[0036] It should be noted that the nitrogen-containing ionic liquid is one or more of 1-ethyl-3-methylimidazolium acetate ([EMIm][N(CN)2]), 1-hexyl-3-methylimidazolium acetate ([HexMIm][N(CN)2]), and 1-hydroxyethyl-3-methylimidazolium acetate ([HydEMIm][N(CN)2]). The Fe-MOF nanoparticles are one or more of MIL-100(Fe), MIL-88B(Fe), and MIL-101(Fe). The inorganic salt is one or more of KCI, NaCl, CaCl2, K2SO4, Na2SO4, and CaSO4.

[0037] In order to regulate the loading amount of iron monomers of the nitrogen-doped carbon-based iron monomer catalyst, the acid etching is as follows: the nitrogen-doped carbon-based Fe monomer precursor is soaked in an inorganic acid solution with a concentration of 0.5 mol / L-3 mol / L for 8 h-24 h. Insufficient or excessive etching will reduce the content of iron monomers in the final product: insufficient etching will result in the presence of a large number of iron nanoparticles in the product after etching, and excessive etching will etch away some unstable iron monomers. Both of them will reduce the content of iron monomers, which will reduce the PMS activation performance and ORR catalytic performance of the catalyst.

[0038] To further improve the catalytic performance of the catalyst, the pyrolysis temperature is 300-1200℃, and the pyrolysis time is 5 min-5 h; more preferably 0.5 h-3 h. For the pyrolysis process in the technical solution of the present application, when the pyrolysis is insufficient, such as pyrolysis at 300℃ for less than 5 min, it will cause Fe-MOF and nitrogen-containing ionic liquid to be unable to be fully doped, unable to form carbonized products, and will seriously affect the performance of the catalyst. When excessive pyrolysis occurs, such as pyrolysis at 1200℃ for more than 5 h, it will cause Fe-MOF to be over-carbonized, which will reduce the catalytically active sites in the final product and also affect the doping of nitrogen elements in the nitrogen source.

[0039] The technical effects of the present application will be described below in conjunction with specific examples and comparative examples.

[0040] Example 1 A preparation method of a nitrogen-doped carbon-based iron monatomic catalyst, comprising the following steps: S1, first mix MIL-100(Fe) nanoparticles and a saturated aqueous solution of NaCl, freeze-dry to obtain a mixture, fully grind the mixture with nitrogen-containing ionic liquid 1-ethyl-3-methylimidazolium acetate [EMIm][N(CN)2], place it in a tube furnace, pyrolyze at 800℃ for 2 h under Ar atmosphere, cool to room temperature, remove excess NaCl template with deionized water to obtain a nitrogen-doped carbon-based Fe monatomic precursor, wherein the mass ratio of nitrogen-containing ionic liquid, NaCl and MIL-100(Fe) nanoparticles is 10:5:0.5.

[0041] S2, treat the nitrogen-doped carbon-based Fe monatomic precursor with 3 mol / L H2SO4 for 12 h, then wash with deionized water multiple times until the pH value of the filtrate reaches neutral to obtain a nitrogen-doped carbon-based Fe monatomic catalyst, denoted as ITFe SA -N4-1.

[0042] Example 2 A preparation method of a nitrogen-doped carbon-based iron monatomic catalyst, comprising the following steps: S1, first mix MIL-100(Fe) nanoparticles and a saturated aqueous solution of NaCl, freeze-dry to obtain a mixture, fully grind the mixture with nitrogen-containing ionic liquid 1-ethyl-3-methylimidazolium acetate [EMIm][N(CN)2], place it in a tube furnace, pyrolyze at 800℃ for 2 h under Ar atmosphere, cool to room temperature, remove excess NaCl template with deionized water to obtain a nitrogen-doped carbon-based Fe monatomic precursor, wherein the mass ratio of nitrogen-containing ionic liquid, NaCl and MIL-100(Fe) nanoparticles is 10:5:0.5.

[0043] S2, the nitrogen-doped carbon-based Fe single atom precursor was treated with H2SO4 at a concentration of 3 mol / L for 12 h, and then rinsed with deionized water several times until the pH value of the filtrate reached neutral, to obtain a nitrogen-doped carbon-based Fe single atom catalyst, which was recorded as ITFe SA -N4-2.

[0044] Example 3 A method for preparing a nitrogen-doped carbon-based iron single-atom catalyst comprises the following steps: S1. MIL-88B(Fe) nanoparticles and a saturated aqueous solution of NaSO4 were thoroughly mixed and freeze-dried to obtain a mixture. The mixture was then thoroughly ground with the nitrogen-containing ionic liquid 1-hydroxyethyl-3-methylimidazolium acetate [HydEMIm][N(CN)2]. The mixture was then heated to 700°C in a tube furnace under an Ar atmosphere and pyrolyzed for 2 hours. The mixture was then cooled to room temperature and the excess NaSO4 template was removed with deionized water to obtain a nitrogen-doped carbon-based Fe single-atom precursor. The mass ratio of the nitrogen-containing ionic liquid, NaSO4, and MIL-88B(Fe) nanoparticles was 10:5:1.

[0045] S2, the nitrogen-doped carbon-based Fe single atom precursor was treated with H2SO4 at a concentration of 3 mol / L for 12 h, and then rinsed with deionized water several times until the pH value of the filtrate reached neutral, to obtain a nitrogen-doped carbon-based Fe single atom catalyst, which was recorded as ITFe SA -N4-3.

[0046] Example 4 A method for preparing a nitrogen-doped carbon-based iron single-atom catalyst comprises the following steps: S1. MIL-88B(Fe) nanoparticles and a saturated aqueous solution of NaSO4 were thoroughly mixed and freeze-dried to obtain a mixture. The mixture was then thoroughly ground with the nitrogen-containing ionic liquid 1-hydroxyethyl-3-methylimidazolium acetate [HydEMIm][N(CN)2]. The mixture was then heated to 900°C in a tube furnace under an Ar atmosphere and pyrolyzed for 2 hours. The mixture was then cooled to room temperature and the excess NaSO4 template was removed with deionized water to obtain a nitrogen-doped carbon-based Fe single-atom precursor. The mass ratio of the nitrogen-containing ionic liquid, NaSO4, and MIL-88B(Fe) nanoparticles was 10:5:1.

[0047] S2, the nitrogen-doped carbon-based Fe single atom precursor was treated with 3 mol / L HCl for 8 h, and then rinsed with deionized water several times until the pH value of the filtrate reached neutral, to obtain a nitrogen-doped carbon-based Fe single atom catalyst, which was recorded as ITFe SA -N4-4.

[0048] Example 5 A method for preparing a nitrogen-doped carbon-based iron single-atom catalyst comprises the following steps: S1. MIL-101(Fe) nanoparticles and a saturated aqueous solution of NaSO4 were thoroughly mixed and freeze-dried to obtain a mixture. The mixture was then thoroughly ground with the nitrogen-containing ionic liquid 1-ethyl-3-methylimidazolium acetate [EMIm][N(CN)2]. The mixture was then heated to 800°C in a tube furnace under an Ar atmosphere and pyrolyzed for 2 hours. The mixture was then cooled to room temperature and the excess NaSO4 template was removed with deionized water to obtain a nitrogen-doped carbon-based Fe single-atom precursor. The mass ratio of the nitrogen-containing ionic liquid, NaSO4, and MIL-101(Fe) nanoparticles was 10:5:1.5.

[0049] S2, the nitrogen-doped carbon-based Fe single atom precursor was treated with 0.5 mol / L HCl for 24 h, and then rinsed with deionized water several times until the pH value of the filtrate reached neutral, to obtain a nitrogen-doped carbon-based Fe single atom catalyst, which was recorded as ITFe SA -N4-5.

[0050] Example 6 A method for preparing a nitrogen-doped carbon-based iron single-atom catalyst comprises the following steps: S1. MIL-101(Fe) nanoparticles and a saturated aqueous solution of CaCl2 were thoroughly mixed and freeze-dried to obtain a mixture. The mixture was then thoroughly ground with the nitrogen-containing ionic liquid 1-hexyl-3-methylimidazolium acetate [HexMIm][N(CN)2]. The mixture was then heated to 900°C in a tube furnace under an Ar atmosphere and pyrolyzed for 2 hours. The mixture was then cooled to room temperature and the excess CaCl2 template was removed with deionized water to obtain a nitrogen-doped carbon-based Fe single-atom precursor. The mass ratio of the nitrogen-containing ionic liquid, CaCl2, and MIL-101(Fe) nanoparticles was 10:5:0.5.

[0051] S2, the nitrogen-doped carbon-based Fe single atom precursor was treated with HNO3 at a concentration of 1.5 mol / L for 8 h, and then rinsed with deionized water several times until the pH value of the filtrate reached neutral, to obtain a nitrogen-doped carbon-based Fe single atom catalyst, which was recorded as ITFe SA -N4-6.

[0052] Example 7 A method for preparing a nitrogen-doped carbon-based iron single-atom catalyst comprises the following steps: S1. MIL-101(Fe) nanoparticles and a saturated aqueous solution of CaCl2 were thoroughly mixed and freeze-dried to obtain a mixture. The mixture was then thoroughly ground with the nitrogen-containing ionic liquid 1-hexyl-3-methylimidazolium acetate [HexMIm][N(CN)2]. The mixture was then heated to 300°C in a tube furnace under an Ar atmosphere and pyrolyzed for 2 hours. The mixture was then cooled to room temperature and the excess CaCl2 template was removed with deionized water to obtain a nitrogen-doped carbon-based Fe single-atom precursor. The mass ratio of the nitrogen-containing ionic liquid, CaCl2, and MIL-101(Fe) nanoparticles was 10:5:5.

[0053] S2, the nitrogen-doped carbon-based Fe single atom precursor was treated with HNO3 at a concentration of 1.5 mol / L for 8 h, and then rinsed with deionized water several times until the pH value of the filtrate reached neutral, to obtain a nitrogen-doped carbon-based Fe single atom catalyst, which was recorded as ITFe SA -N4-7.

[0054] Example 8 A method for preparing a nitrogen-doped carbon-based iron single-atom catalyst comprises the following steps: S1. MIL-100(Fe) nanoparticles and a saturated aqueous solution of CaCl2 were thoroughly mixed and freeze-dried to obtain a mixture. The mixture was then thoroughly ground with the nitrogen-containing ionic liquid 1-hexyl-3-methylimidazolium acetate [HexMIm][N(CN)2]. The mixture was then placed in a tube furnace and heated to 1200°C for 2 hours under an Ar atmosphere for pyrolysis. The mixture was then cooled to room temperature and the excess CaCl2 template was removed with deionized water to obtain a nitrogen-doped carbon-based Fe single-atom precursor. The mass ratio of the nitrogen-containing ionic liquid, CaCl2, and MIL-100(Fe) nanoparticles was 10:5:0.1.

[0055] S2, the nitrogen-doped carbon-based Fe single atom precursor was treated with HNO3 at a concentration of 1.5 mol / L for 8 h, and then rinsed with deionized water several times until the pH value of the filtrate reached neutral, to obtain a nitrogen-doped carbon-based Fe single atom catalyst, which was recorded as ITFe SA -N4-8.

[0056] In order to further illustrate the technical effects of the present invention, the present invention is also provided with comparative examples, as follows: Comparative Example 1 Compared with Example 1, the difference is that no Fe-MOF nanoparticles are added.

[0057] A method for preparing a nitrogen-doped carbon-based catalyst comprises the following steps: S1, firstly, grind the solid NaCl and the nitrogen-containing ionic liquid [EMIm][N(CN)2] thoroughly, place them in a tube furnace, pyrolyze at 800 DEG C for 2h under Ar atmosphere, and cool to room temperature. The mass ratio of the nitrogen-containing ionic liquid to NaCl is 2:1.

[0058] S2, treat the ionic liquid and NaCl precursor with 3 mol / L H2SO4 for 12h, then rinse with deionized water for multiple times until the pH value of the filtrate reaches neutral, to obtain a nitrogen-doped carbon-based catalyst, denoted as IT.

[0059] The performance of the nitrogen-doped carbon-based iron monatomic catalysts prepared in Examples 1-8 and the nitrogen-doped carbon-based catalyst prepared in Comparative Example 1 was detected, and the results are as follows.

[0060] Figure 1 The relationship between time and degradation efficiency of the nitrogen-doped carbon-based iron monatomic catalysts of Examples 1, 2 and 4 when activating PMS to degrade tetracycline was compared. Figure 1 It can be seen that the performance of the catalyst of Example 1 is better than that of the catalysts of Examples 4 and 2 in activating PMS to degrade tetracycline, indicating that the relatively low pyrolysis temperature (700 DEG C) and the relatively high MOF content of 10:5:2 in the preparation process of Example 2 are not conducive to improving the performance of the catalyst in activating PMS.

[0061] Figure 2 The relationship between time and degradation efficiency of the nitrogen-doped carbon-based iron monatomic catalysts of Examples 3, 5 and 6 when activating PMS to degrade tetracycline was compared. Figure 2 It can be seen that the performance of the catalyst of Example 5 is better than that of the catalysts of Examples 6 and 3 in activating PMS to degrade tetracycline.

[0062] Figure 3 The relationship between time and degradation efficiency of the nitrogen-doped carbon-based iron monatomic catalyst of Example 1 and the nitrogen-doped carbon-based catalyst of Comparative Example 1 when activating PMS to degrade tetracycline was compared. Figure 3 It can be seen that when only the catalyst of Example 1 is added without PMS, the degradation rate of tetracycline is the lowest, and the catalyst only plays the role of an adsorbent; when only PMS is added without the catalyst, PMS cannot generate enough active free radicals to degrade tetracycline; in addition, since no Fe-MOF nanoparticles are added in Comparative Example, the catalyst does not contain iron monatomic, resulting in poor degradation performance of the catalyst of Comparative Example.

[0063] Figure 4 The potential-current density curves of the nitrogen-doped carbon-based iron monatomic catalysts of Examples 1, 2 and 4 in oxygen reduction catalysis were compared. Figure 4 It can be seen that according to the half-wave potential, the ORR catalyst performance of Example 1 is better than that of the catalysts of Example 4 and Example 2, indicating that the relatively low pyrolysis temperature (700°C) and the relatively high MOF content of 10:5:2 in the preparation process of Example 2 are not conducive to improving the ORR performance of the catalyst.

[0064] Figure 5 The graph is a comparison of the potential-current density curves corresponding to the nitrogen-doped carbon-based iron single-atom catalysts of Examples 3, 5, and 6 of the present invention during oxygen reduction catalysis. Figure 5 It can be seen that the ORR performance of the catalyst of Example 5 is better than that of the catalysts of Example 6 and Example 3.

[0065] Figure 6 The figure is a comparison of the potential-current density curves corresponding to the activation of oxygen reduction catalysis by the nitrogen-doped carbon-based iron single atom catalyst of Example 1 of the present invention and the nitrogen-doped carbon-based catalyst of Comparative Example 1. Figure 6 It can be seen that since the comparative example does not contain Fe-MOF nanoparticles, the catalyst does not contain single iron atoms, resulting in poor ORR performance of the comparative example catalyst.

[0066] Figure 7 The adsorption configuration of the single-atom Fe-N4 site upon activation of PMS and its corresponding adsorption energy (E) obtained by DFT theoretical simulation in Example 1 of the present invention are shown in FIG. ads ) and OO bond length. Figure 7 It can be seen that the O-O bond length of PMS obtained through theoretical calculation simulation is 2.54Å, and the adsorption energy of PMS on the catalyst surface is -2.07eV, indicating that the catalyst can effectively lengthen the O-O bond length of PMS, which is conducive to the breakage of PMS to generate SO4 - ,The lower adsorption energy indicates that PMS is firmly adsorbed on the catalyst surface, which is beneficial to the subsequent activation of PMS.

[0067] Figure 8 The adsorption configuration of the single-atom Fe-N4 site during the ORR reaction and its corresponding adsorption energy (E) obtained by DFT theoretical simulation in Example 1 of the present invention are shown in FIG. ads ) and OO bond length. Figure 8 It can be seen that the OO bond length of oxygen obtained through theoretical calculation simulation is 1.29Å, and the adsorption energy of oxygen on the catalyst surface is -0.84eV, indicating that the catalyst can effectively lengthen the OO bond length of the reactant oxygen, which is beneficial to the next reduction reaction of oxygen. The lower adsorption energy indicates that the adsorption of oxygen on the catalyst surface is relatively firm, which is beneficial to the subsequent reduction of oxygen.

[0068] Table 1 Element contents of catalysts in different embodiments obtained by XPS test Table 2 N element content of different types of catalysts obtained by XPS analysis The “-” in Table 1 and Table 2 indicates that the value could not be determined.

[0069] The data in Tables 1 and 2 compare the elemental contents of C, N, and O in different catalysts. It can be seen that the catalysts with higher nitrogen contents have stronger catalytic activity, indicating that nitrogen doping of the catalyst will affect the performance; the catalysts with higher total contents of pyridinic N and Fe-N have stronger catalytic activity, indicating that by changing the preparation conditions, the contents of pyridinic N and Fe-N in the active sites can be increased, thereby improving the catalyst activity.

[0070] In summary, the present invention provides a catalyst that can not only efficiently activate PMS to rapidly degrade organic pollutants such as antibiotics, but also efficiently and stably catalyze ORR.

[0071] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a nitrogen-doped carbon-based iron single-atom catalyst, characterized in that: The following steps are involved: Using an inorganic salt as a template and a nitrogen-containing ionic liquid as a nitrogen source, the inorganic salt is used to assist the coordinated pyrolysis of the nitrogen-containing ionic liquid and Fe-MOF nanoparticles under a protective atmosphere. The Fe-MOF nanoparticles and the nitrogen-containing ionic liquid are carbonized, and the nitrogen atoms in the nitrogen-containing ionic liquid are doped into the carbon lattice of the carbonized Fe-MOF to obtain Fe-pyridine N4. The coordination environment of the Fe-pyridine N4 is regulated by the nitrogen atoms in the nitrogen-containing ionic liquid, and the inorganic salt template is removed to obtain a nitrogen-doped carbon-based Fe single atom precursor. The nitrogen-doped carbon-based Fe single-atom precursor is acid-etched to remove the iron nanoparticles in the nitrogen-doped carbon-based Fe single-atom precursor, thereby obtaining a nitrogen-doped carbon-based iron single-atom catalyst.

2. The method for preparing the nitrogen-doped carbon-based iron single-atom catalyst according to claim 1, characterized in that: The mass ratio of the nitrogen-containing ionic liquid, the inorganic salt and the Fe-MOF nanoparticles is 10:5:0.1-5.

3. The method for preparing the nitrogen-doped carbon-based iron single-atom catalyst according to claim 1, wherein: The nitrogen-containing ionic liquid is one or more of 1-ethyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, and 1-hydroxyethyl-3-methylimidazolium acetate.

4. The method for preparing the nitrogen-doped carbon-based iron single-atom catalyst according to claim 1, wherein: The Fe-MOF nanoparticles are one or more of MIL-100(Fe), MIL-88B(Fe), and MIL-101(Fe).

5. The method for preparing the nitrogen-doped carbon-based iron single-atom catalyst according to claim 1, wherein: The inorganic salt is one or more of KCI, NaCl, CaCl2, K2SO4, Na2SO4, and CaSO4.

6. The method for preparing the nitrogen-doped carbon-based iron single-atom catalyst according to claim 1, characterized in that: The acid etching is as follows: immersing the nitrogen-doped carbon-based Fe single atom precursor in an inorganic acid solution with a concentration of 0.5 mol / L to 3 mol / L for 8 hours to 24 hours.

7. The method for preparing the nitrogen-doped carbon-based iron single-atom catalyst according to claim 1, characterized in that: The pyrolysis temperature is 300° C. to 1200° C., and the pyrolysis time is 0.5 h to 3 h.

8. A nitrogen-doped carbon-based iron single-atom catalyst, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the nitrogen-doped carbon-based iron single-atom catalyst according to claim 8 in degrading organic pollutants.

10. Use of the nitrogen-doped carbon-based iron single-atom catalyst according to claim 8 in catalyzing an oxygen reduction reaction.

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