Method for constructing axial halogen coordination iron-based catalyst and application thereof

Abstract

The invention provides a method for constructing an axial halogen coordination iron-based catalyst and application of the axial halogen coordination iron-based catalyst, and belongs to the technical field of catalytic materials and environmental pollution control. The preparation method comprises the following steps: introducing amino to the surface of a multi-walled carbon nanotube to obtain a modified multi-walled carbon nanotube; iron tetracarboxyl phthalocyanine and the modified multi-walled carbon nanotubes are subjected to covalent grafting through an amidation reaction, and a precursor is obtained; mixing the precursor with a halogen-containing solid source and a nitrogen source, and carrying out temperature programming and segmented pyrolysis in an inert gas atmosphere to obtain a pyrolysis product; and carrying out acid pickling on the pyrolysis product. The core of the preparation method disclosed by the invention lies in a multi-step collaborative strategy of molecular isolation, interface bridging, gas phase migration, fixed-point capture and coordination regulation, so that ultrahigh monatomic dispersity is realized, and unification of high density and high dispersity is ensured; meanwhile, the electronic structure of the iron center is effectively optimized, and excellent intrinsic activity is shown.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials and environmental pollution control technology, specifically to a method for constructing axially halogen-coordinated iron-based catalysts and their applications. Background Technology

[0002] Advanced persulfate oxidation technology is widely used in the treatment of recalcitrant organic pollutants, and its effectiveness hinges on catalyst design. Iron-based catalysts (Fe-SACs) have become star materials in this field due to their near 100% atom utilization and uniform Fe-N4 active sites.

[0003] Currently, mainstream preparation methods such as "mixed pyrolysis" and "MOF derivatization" have inherent defects: uneven mixing of precursors leads to metal agglomeration; the migration of metal atoms during pyrolysis is uncontrollable, making it difficult to achieve both high loading and high dispersion at the same time; and the local coordination environment of the final active site (such as axial coordination) is difficult to precisely control, which limits its intrinsic activity.

[0004] In particular, studies using iron phthalocyanine (FePc) as a precursor often involve simply mixing it with a carbon support followed by pyrolysis. During this process, the strong π-π interactions between FePc molecules easily lead to their own aggregation. During pyrolysis, iron atoms inevitably agglomerate to form nanoparticles, violating the original intention of preparing single-atom catalysts. Therefore, developing a novel preparation method that can pre-suppress precursor aggregation, achieve in-situ fixation of metal atoms, and precisely control the final coordination environment is crucial to overcoming current technological bottlenecks.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for constructing axially halogen-coordinated iron-based catalysts and their applications. The core of the preparation method of this invention lies in a multi-step synergistic strategy of "molecular isolation-interfacial bridging-gas phase migration-site trapping-coordination regulation," which achieves ultra-high single-atom dispersion, ensuring a balance between high density and high dispersibility; at the same time, it effectively optimizes the electronic structure of the iron center, exhibiting superior intrinsic activity.

[0007] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted: This invention provides a method for constructing an axially halogen-coordinated iron-based catalyst, comprising the following steps: S1. Introduce amino groups on the surface of multi-walled carbon nanotubes to obtain modified multi-walled carbon nanotubes. S2. Tetracarboxylated phthalocyanine iron is covalently grafted with the modified multi-walled carbon nanotubes via an amidation reaction to obtain the precursor; S3. The precursor is mixed with a halogen-containing solid source and a nitrogen source, and then heated and pyrolyzed in stages under an inert gas atmosphere to obtain pyrolysis products. S4. The pyrolysis product is acid-washed to obtain an axially halogenated coordinated iron-based catalyst.

[0008] In S1, amino groups are covalently grafted onto the surface of multi-walled carbon nanotubes. This step is not a simple oxidation, but rather introduces an active functional group (-NH2) that can chemically react with subsequent steps, laying the foundation for "interfacial bridging". The S2 step is crucial, as it covalently links the carboxyl groups of tetracarboxylated iron phthalocyanine to the amino groups on multi-walled carbon nanotubes via an amidation reaction. This isolates each FePc molecule, fixing it firmly within the polymer chain and chemically preventing π-π stacking between FePc molecules. This achieves true molecular-level dispersion, resolving the aggregation problem at its source for generating single atoms.

[0009] C2N2 is produced during pyrolysis in S3. + Nitrogen-containing fragments, acting as an additional nitrogen source, help repair and form a more stable Fe-N4 structure during pyrolysis. NH4Cl: This is an innovative step; NH4Cl sublimates and decomposes into NH3 and HCl gases at 340℃. The HCl gas flows downstream with the carrier gas to the sample region. Gas-phase migration and trapping: The HCl gas interacts with phthalocyanine iron molecules, promoting the decomposition of FePc macromolecules on one hand, and on the other hand, Cl... - It may coordinate axially with the Fe atom at the center of the forming Fe-N4 site in the form of a gaseous ligand, forming a Cl-Fe-N4 structure.

[0010] In S4, acid washing is used to remove unstable species. These unstable species refer to two types: firstly, tetracarboxylated phthalocyanine iron molecules that failed to undergo the amidation reaction with the modified amino multi-walled carbon nanotubes and adhered to the tube wall; and secondly, small amounts of iron elements (possibly iron atoms, iron clusters, and iron nanoparticles) that may form on the multi-walled carbon nanotube wall after high-temperature pyrolysis calcination. Acid washing removes these un-amidated tetracarboxylated phthalocyanine iron molecules that failed to embed themselves into the multi-walled carbon nanotubes, as well as the adhering and easily lost iron elements, thus facilitating the formation of a truly monodisperse iron-based catalyst with a firmly embedded structure.

[0011] Preferably, step S1 specifically includes the following steps: Multi-walled carbon nanotubes were heated in a mixed acid and refluxed, then dispersed in anhydrous toluene. An excess of 3-aminopropyltriethoxysilane was added, and the mixture was refluxed under inert gas protection, cooled, washed, and dried to obtain modified multi-walled carbon nanotubes.

[0012] Preferably, the inert gas is argon; Preferably, the protection temperature is 100℃-120℃, and the protection time is 20h-28h; Preferably, the protection temperature is 110℃ and the protection time is 24h.

[0013] Preferably, the specific steps of S2 are as follows: S201. The modified multi-walled carbon nanotubes are dispersed in anhydrous N,N-dimethylformamide (DMF) to obtain a modified multi-walled carbon nanotube dispersion. S202, The tetracarboxylated phthalocyanine iron and 4-dimethylaminopyridine are then added to another portion of anhydrous N,N-dimethylformamide for activation, to obtain an activated tetracarboxylated phthalocyanine iron solution; S203. The activated tetracarboxylated phthalocyanine iron solution is added dropwise to the modified multi-walled carbon nanotube dispersion and stirred to react. After the reaction is completed, the mixture is washed and dried under vacuum to obtain the precursor.

[0014] Preferably, the activation conditions are: activation at room temperature for 20-40 minutes; Preferably, the activation condition is activation at room temperature for 30 minutes; Preferably, the room temperature is 15℃-30℃.

[0015] Preferably, the specific step of the stirring reaction in step S203 is to magnetically stir the reaction at 60°C for 36 hours.

[0016] Preferably, the segmented pyrolysis in step S3 specifically includes the following steps: Heat to 350℃-450℃ at a rate of 5℃ / min, and hold for 1-2 hours; Then, raise the temperature to 750℃-850℃ at the same rate and hold for 1.5h-3h.

[0017] Preferably, the segmented pyrolysis in step S3 specifically includes the following steps: Heat to 400℃ at a rate of 5℃ / min and hold for 1 hour; Then, the temperature was increased to 800℃ at the same rate and held for 2 hours.

[0018] Preferably, the mass ratio of the halogen-containing solid source to the nitrogen source is 4:(5-15). Preferably, the mass ratio of the halogen-containing solid source to the nitrogen source is 4:10.

[0019] Preferably, the halogen-containing solid source is ammonium halide; Preferably, the ammonium halide is either ammonium chloride or ammonium bromide; Preferably, the halogen-containing solid source is ammonium chloride.

[0020] Preferably, the nitrogen source provides a stable site for a nitrogen-rich environment; Preferably, the nitrogen source is dicyandiamine.

[0021] Preferably, the mixed acid is prepared by mixing sulfuric acid and nitric acid in a volume ratio of (2-5):1; Preferably, the sulfuric acid has a mass fraction of 98% and the nitric acid has a mass fraction of 68%.

[0022] The reflux temperature is 60℃-80℃; the reflux time is 3h-5h.

[0023] Preferably, the mixed acid is prepared by mixing sulfuric acid and nitric acid in a volume ratio of 3:1; The reflux temperature is 70°C; the reflux time is 4 hours.

[0024] Preferably, the specific steps of step S4 are as follows: The pyrolysis product obtained in S3 was dispersed in a 0.5 M H2SO4 solution, stirred and refluxed at 80 °C for 6 hours, then washed with deionized water until neutral, and dried under vacuum.

[0025] The present invention also provides an iron-based catalyst prepared by the above preparation method.

[0026] The present invention also provides an application of the above-mentioned iron-based catalyst in the persulfate advanced oxidation technology for degrading organic pollutants.

[0027] Preferably, the organic pollutant is an antibiotic pollutant.

[0028] Preferably, the persulfate is permonosulfate or perdisulfate.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The problem of precursor aggregation was solved, and ultra-high single-atom dispersion was achieved: A covalent grafting strategy chemically ensured atomic-level isolation of FePc molecules. Characterization by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed that iron in the final catalyst was distributed in a completely single-atom form, with almost no iron nanoparticles or clusters observed. Even with an iron loading as high as 3.5 wt%, extremely high dispersion was maintained, with a single-atom ratio exceeding 99%, completely overcoming the contradiction between high loading and high dispersion.

[0030] (2) Precise control of the coordination environment was achieved, resulting in ultra-high intrinsic activity: Compared with conventional Fe-N4 / C catalysts without axial coordination, the Cl-Fe-SACs / CNT catalyst prepared in this invention exhibits a higher apparent rate constant ( ) in the degradation of tetracycline hydrochloride (TCH) by activated persulfate (PMS). k obs The efficiency was increased by 2.56 times. This indicates that the axial Cl ligand effectively optimized the electronic structure of the Fe center and significantly reduced the reaction energy barrier.

[0031] (3) It possesses both excellent stability and mass transfer efficiency: The catalyst prepared by this invention has excellent structural and catalytic stability, and high saturation magnetization, which can be recovered by applying an external magnetic field; it also has a wide pH tolerance range and is universally applicable to different types of antibiotics. Attached Figure Description

[0032] Figure 1 Physical image of Cl-Fe-SACs / CNT catalyst; Figure 2 : HAADF-STEM characterization of Cl-Fe-SACs / CNT catalyst; Figure 3 Distribution diagrams of Cl-Fe-SACs / CNT elements, where A is the distribution diagram of Fe; B is the distribution diagram of O; C is the distribution diagram of N; and D is the distribution diagram of C. Figure 4 Magnetic characterization diagram of Cl-Fe-SACs / CNT catalyst; Figure 5 Comparison of the TCH degradation performance of Cl-Fe-SACs / CNT and Fe-SACs / CNT prepared by conventional mixed pyrolysis method with activated PMS; Figure 6 The rate constant of the reaction between Cl-Fe-SACs / CNT and conventional mixed pyrolysis method for Fe-SACs / CNT activation of PMS for TCH degradation ( k obs )Compare; Figure 7 Comparison of Fe dissolution concentration after reaction of Cl-Fe-SACs / CNT and Fe-SACs / CNT prepared by conventional mixed pyrolysis method; Figure 8 Evaluation of the degradation performance of Cl-Fe-SACs / CNTs on different types of antibiotics; Figure 9 Evaluation of the degradation effect of Cl-Fe-SACs / CNT under different pH conditions; Figure 10 XRD patterns of TCH before and after degradation by Cl-Fe-SACs / CNT; Figure 11 Evaluation of the cyclic stability and regenerability of Cl-Fe-SACs / CNT. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0034] Example 1 Step 1: Covalent grafting modification of multi-walled carbon nanotubes Pharmaceuticals: Multi-walled carbon nanotubes (MWCNTs), 3-aminopropyltriethoxysilane (APTES), anhydrous toluene.

[0035] step: 1) 5g of MWCNTs were refluxed at 70°C for 4 hours in 100ml of 98% H2SO4 / 68% HNO3 (3:1 v / v) to introduce carboxyl groups (-COOH) and obtain 4.5g of COOH-MWCNTs.

[0036] 2) Disperse 2.0g of COOH-MWCNTs in anhydrous toluene, add excess APTES, and reflux at 110℃ for 24 hours under argon protection.

[0037] 3) After cooling, the sample was repeatedly washed by centrifugation with ethanol and deionized water, and then dried under vacuum to obtain 1.8 g of NH2-MWCNTs.

[0038] Step 2: Constructing a "molecularly isolated" precursor Drugs: NH2-MWCNTs obtained in step one, iron tetracarboxylated phthalocyanine (FeTcPc), N,N-dicyclohexylcarbodiimide (DCC), 4-dimethylaminopyridine (DMAP), and N,N-dimethylformamide (DMF).

[0039] step: 1) Disperse 1.0 g of NH2-MWCNTs in anhydrous DMF to obtain an NH2-MWCNTs dispersion.

[0040] 2) Add 0.1g FeTcPc, 0.1g DCC (activator) and 0.05g DMAP (catalyst) to 50ml anhydrous DMF and activate at room temperature for 30 minutes.

[0041] 3) The activated FeTcPc solution was added dropwise to the above NH2-MWCNTs dispersion and the mixture was magnetically stirred at 60°C for 36 hours.

[0042] 4) After the reaction was completed, the FePc was thoroughly washed with anhydrous DMF and ethanol to remove the physically adsorbed FePc, and then dried under vacuum to obtain 0.8 g FeTcPc-g-MWCNTs.

[0043] Step 3: Halogen coordination engineering in the gas phase migration and site-specific capture process Drugs: FeTcPc-g-MWCNTs obtained in step two, a solid mixture of dicyandiamine (DCDA) and ammonium chloride (NH4Cl).

[0044] step: 1) Place 0.5g of FeTcPc-g-MWCNTs and 0.2g of DCDA / NH4Cl (mass ratio 10:4) mixed powder in ceramic boats. Place the DCDA / NH4Cl mixture upstream of the tube furnace and the sample downstream.

[0045] 2) Under an argon atmosphere, heat to the first temperature range (400℃) at a rate of 5℃ / min and hold for 1 hour.

[0046] 3) Then continue to heat up to the second temperature range (800℃) at a rate of 5℃ / min, and hold for 2 hours.

[0047] 4) Cool naturally to room temperature to obtain the pyrolysis products.

[0048] Step 4: Removal of Unstable Species and Purification Chemicals: The pyrolysis product obtained in step 3, and a 0.5 M H2SO4 solution.

[0049] Steps: The pyrolysis products were dispersed in a 0.5M H2SO4 solution, stirred and refluxed at 80°C for 6 hours, then washed with deionized water until neutral, and dried under vacuum to obtain the final catalyst Cl-Fe-SACs / CNT (0.35g).

[0050] A physical image of the catalyst is shown below. Figure 1 As shown; The HAADF-STEM characterization image of the catalyst is shown below. Figure 2 As shown, from Figure 2 It can be seen that the distribution of each element is relatively uniform; from Figure 3The mapping diagram of the catalyst shows that Fe, O, N and C are distributed relatively evenly on the multi-walled carbon nanotube matrix, especially Fe, which is distributed very evenly and no obvious agglomeration is observed. The prepared catalyst was characterized magnetically using a vibrating sample magnetometer (VSM), and the results are as follows: Figure 4 As shown, from Figure 4 The data shows that the catalyst has a saturation magnetization of 2.72 emu / g, and can be recovered by applying an external magnetic field.

[0051] Example 2 Step 1: Covalent grafting modification of CNTs Pharmaceuticals: MWCNTs, APTES, anhydrous toluene.

[0052] step: 1) 5g of MWCNTs were refluxed at 80°C for 5 hours in 100ml of 98% H2SO4 / 68% HNO3 (5:1 v / v) to introduce carboxyl groups (-COOH) and obtain 4.5g of COOH-MWCNTs.

[0053] 2) Disperse 2.0g of COOH-MWCNTs in anhydrous toluene, add excess APTES, and reflux at 110℃ for 24 hours under argon protection.

[0054] 3) After cooling, the sample was repeatedly washed by centrifugation with ethanol and deionized water, and then dried under vacuum to obtain 1.8 g of NH2-MWCNTs.

[0055] Step 2: Constructing a "molecularly isolated" precursor Chemicals: NH2-MWCNTs, FeTcPc, DCC, DMAP, and anhydrous DMF obtained in step one.

[0056] step: 1) Disperse 1.0 g of NH2-MWCNTs in anhydrous DMF to obtain an NH2-MWCNTs dispersion.

[0057] 2) Add 0.1g FeTcPc, 0.1g DCC (activator) and 0.05g DMAP (catalyst) to 50ml anhydrous DMF and activate at room temperature for 30 minutes.

[0058] 3) The activated FeTcPc solution was added dropwise to the above NH2-MWCNTs dispersion and the mixture was magnetically stirred at 60°C for 36 hours.

[0059] 4) After the reaction was completed, the FePc was thoroughly washed with anhydrous DMF and ethanol to remove the physically adsorbed FePc, and then dried under vacuum to obtain 0.8 g FeTcPc-g-MWCNTs.

[0060] Step 3: Halogen coordination engineering in the gas phase migration and site-specific capture process Drugs: FeTcPc-g-MWCNTs obtained in step two, a solid mixed powder of DCDA and NH4Cl.

[0061] step: 1) Place 0.75g of FeTcPc-g-MWCNTs and 0.2g of DCDA / NH4Cl (mass ratio 15:4) mixed powder in ceramic boats. Place the DCDA / NH4Cl mixture upstream of the tube furnace and the sample downstream.

[0062] 2) Under an argon atmosphere, the temperature is increased to the first temperature range (450℃) at a rate of 5℃ / min and held for 2 hours.

[0063] 3) Then continue to heat up to the second temperature range (850℃) at a rate of 5℃ / min, and hold for 3 hours.

[0064] 4) Cool naturally to room temperature to obtain the pyrolysis products.

[0065] Step 4: Removal of Unstable Species and Purification Chemicals: The pyrolysis product obtained in step 3, and a 0.5 M H2SO4 solution.

[0066] Steps: The pyrolysis products were dispersed in a 0.5 M H2SO4 solution, stirred and refluxed at 60 °C for 3 hours, then washed with deionized water until neutral, and dried under vacuum to obtain the final catalyst Cl-Fe-SACs / CNT (0.48 g).

[0067] Comparative Example 1: Traditional Hybrid Pyrolysis Method The specific steps of the traditional mixed pyrolysis method for preparing Fe-SACs / CNT composite catalysts are as follows: Pretreatment of multi-walled carbon nanotubes: (1) Place 5g of MWCNTs in 100ml of a mixed acid of 98% H2SO4 / HNO3 (3:1 v / v) and reflux at 70°C for 4 hours.

[0068] (2) After cooling, the sample was repeatedly centrifuged and washed with deionized water until neutral, and then dried under vacuum to obtain 4.8g of acidified CNTs (COOH-MWCNTs).

[0069] This step is only intended to introduce carboxyl groups to increase the hydrophilicity of the support and surface defects, but does not introduce chemically reactive functional groups (such as -NH2).

[0070] 2. Physically mixed precursors: (1) Take 2.0g of COOH-MWCNTs and disperse them in 100ml of anhydrous DMF.

[0071] (2) Add 0.1g FeTcPc directly to the above dispersion and stir for a period of time (6-12 hours) at room temperature or slightly above room temperature (60℃) so that FeTcPc is loaded onto the CNT surface through physical adsorption (mainly weak π-π interaction and physical adsorption force).

[0072] (3) After the reaction is complete, the solid is collected by filtration or centrifugation and washed with solvent to remove the FeTcPc molecules that are not firmly adsorbed. The solid is then dried under vacuum to obtain 1.8 g of FeTcPc / CNT physical mixture.

[0073] 3. Direct pyrolysis: (1) Take 0.5g of FeTcPc / CNT physical mixture and 0.2g of DCDA solid powder (used only as nitrogen source) and mix them in a mortar.

[0074] (2) Place the mixture in a single-temperature zone tube furnace, and under argon protection, directly raise it to 800°C at 5°C / min and keep it at that temperature for 2 hours.

[0075] This process lacks the introduction of gaseous ligands and has no dual-temperature zone design; it is a single heat treatment process.

[0076] Acid washing and purification: (1) The pyrolysis products after pyrolysis were stirred and refluxed at 80°C for 6 hours in 0.5 M H2SO4 solution.

[0077] (2) Wash with deionized water until neutral, and dry under vacuum to obtain 0.42g of catalyst prepared by conventional method, denoted as Fe-SACs / CNT (conventional).

[0078] Experimental Example 1: Comparison of the TCH degradation performance of Cl-Fe-SACs / CNT and Fe-SACs / CNT activated PMS prepared by conventional mixed pyrolysis method Experimental results are as follows Figure 5As shown, 0.01g of Cl-Fe-SACs / CNT and Fe-SACs / CNT prepared by the traditional mixed pyrolysis method were respectively used to activate 0.02g of persulfate (PMS) to degrade 100ml of tetracycline hydrochloride (TCH) with an initial concentration of 20 mg / L. After 75 minutes, the corresponding absorbance values ​​were measured at a wavelength of 355nm in a UV-Vis spectrophotometer, and the degradation rates were calculated. The removal rates were 94% and 59%, respectively. In terms of removal rate, Cl-Fe-SACs / CNT was 1.6 times that of Fe-SACs / CNT prepared by the traditional mixed pyrolysis method.

[0079] Experimental Example 2: Preparation of Fe-SACs / CNTs using Cl-Fe-SACs / CNTs via conventional mixed pyrolysis method to activate PMS and degrade TCH. k obs Compare Experimental results are as follows Figure 6 As shown, Cl-Fe-SACs / CNT and Fe-SACs / CNT prepared by conventional mixed pyrolysis method activate PMS to degrade TCH. k obs (Calculate the reaction rate constant based on this formula: ln) = - k obs t, where C is the initial concentration (20 mg / L), C0 is the concentration at time t, and t is the reaction time, are both 0.0448 min. -1 and 0.0175 min -1 In terms of reaction rate, Cl-Fe-SACs / CNT is 2.56 times faster than Fe-SACs / CNT produced by the conventional mixed pyrolysis method.

[0080] Experimental Example 3: Comparison of Fe dissolution concentration after reaction of Cl-Fe-SACs / CNT and Fe-SACs / CNT prepared by conventional mixed pyrolysis method Experimental results are as follows Figure 7 As shown, the Fe dissolution concentration after the reaction of Fe-SACs / CNT prepared by the conventional mixed pyrolysis method was 0.335 mg / L as determined by ICP-MS (water sample after the reaction was completed, i.e., 75 minutes after the reaction was completed). However, the Fe dissolution concentration after Cl-Fe-SACs / CNT degraded tetracycline hydrochloride was only 0.085 mg / L, and the metal dissolution rate was reduced by 75%, indicating that Cl-Fe-SACs / CNT has good stability.

[0081] Experimental Example 4: Evaluation of the degradation performance of Cl-Fe-SACs / CNTs on different types of antibiotics Experimental methods: The degradation of different antibiotics (lomefloxacin hydrochloride, norfloxacin, and penicillin) by Cl-Fe-SACs / CNT under the same conditions as the degradation of tetracycline hydrochloride was performed: 0.01 g of Cl-Fe-SACs / CNT was used to activate 0.02 g of PMS to degrade 100 ml of lomefloxacin hydrochloride, norfloxacin, and penicillin at an initial concentration of 20 mg / L. After 75 minutes, the absorbance was measured at 280 nm (applicable to lomefloxacin hydrochloride) using a UV-Vis spectrophotometer, and the degradation rate was calculated. The concentrations of norfloxacin and penicillin were determined by liquid chromatography.

[0082] Experimental results are as follows Figure 8 As shown, from Figure 8 It can be seen that the removal rates of tetracycline hydrochloride, lomefloxacin hydrochloride, norfloxacin, and penicillin by Cl-Fe-SACs / CNT at 75 minutes were 94%, 87%, 71%, and 84%, respectively, indicating that Cl-Fe-SACs / CNT has a good degradation effect on different types of antibiotics and has a certain degree of universality.

[0083] Experimental Example 5: Evaluation of the degradation effect of Cl-Fe-SACs / CNT under different pH conditions Experimental steps: The pH of 100 ml of 20 mg / L tetracycline hydrochloride was adjusted to 2, 3, 4, 6, 7, 8, 10, and 12 respectively using 0.1 mol / L HCl and 0.1 mol / L NaOH via dropper. The experimental method was the same as in Experiment 1.

[0084] Experimental results are as follows Figure 9 As shown in the figure, Cl-Fe-SACs / CNT exhibits good TCH degradation performance within a pH range of 3-10, indicating that the catalyst has a wide pH tolerance range.

[0085] Experimental Example 6: Stability Evaluation of Cl-Fe-SACs / CNT Structure The Cl-Fe-SACs / CNT catalyst before and after the reaction was measured by X-ray diffraction (XRD). The experimental results are as follows: Figure 10 As shown in the XRD pattern, the intensity of the Cl-Fe-SACs / CNT peaks did not decrease significantly before and after the degradation of TCH, and the position of the peaks did not shift significantly, indicating that the Cl-Fe-SACs / CNT catalyst has good structural stability before and after the reaction.

[0086] Experimental Example 7: Evaluation of Cyclic Stability and Regenerability of Cl-Fe-SACs / CNT Experimental steps: Fifteen 0.01g portions of Cl-Fe-SACs / CNT catalyst were used to perform the same experiment as in Example 1 on the degradation of tetracycline hydrochloride, which was recorded as one reaction. After filtration, washing, and drying, the above operation was repeated for each of the 15 portions of catalyst, which was recorded as two reactions. The same experiment was performed eight times, which was recorded as eight cycles.

[0087] Experimental results are as follows Figure 11 As shown in the figure, the Cl-Fe-SACs / CNT catalyst maintained a 78% removal rate after 8 cycles, indicating excellent cycle stability. Furthermore, a simple 2-hour incubation at 800℃ in an argon atmosphere increased the catalyst's TCH removal capacity to 85%, demonstrating good regenerability.

[0088] This invention: (1) A precursor construction strategy of "covalent grafting molecular isolation" is proposed: This invention abandons simple physical mixing and instead uses an amidation covalent reaction to firmly graft FeTcPc molecules onto aminated CNTs in monomolecular form. This method chemically eliminates the pre-agglomeration of FePc molecules caused by π-π stacking, providing a highly homogenized precursor for subsequent pyrolysis to generate high-density, highly dispersed single-atom catalysts. This is a crucial prerequisite for achieving high single-atom loading.

[0089] (2) Propose the "vapor phase migration-axial halogen coordination" engineering: This invention innovatively introduces NH4Cl as a gas-phase axial ligand source. During pyrolysis, the HCl gas produced by its decomposition flows to the reaction zone and participates in coordination in situ. This not only promotes the decomposition of the precursor and the formation of Fe-N4 sites, but also increases the probability of introducing Cl- ligands at their axial positions, constructing Cl-Fe-N4 active centers. This method of precisely controlling the electronic structure of single-atom centers through gas-phase chemistry is a core innovation for achieving ultra-high intrinsic activity of catalysts.

[0090] (3) Multifunctional pyrolysis atmosphere and "dual temperature zone" design: This invention designs a mixed auxiliary of DCDA and NH4Cl and a dual-temperature-zone pyrolysis process. DCDA provides stable sites in a nitrogen-rich environment, while NH4Cl provides gaseous ligands. The first temperature zone (400℃) is the critical window for NH4Cl decomposition and the action of the gaseous ligands; the second temperature zone (800℃) is used to complete carbonization and crystallization. This multi-component, temperature-zoned pyrolysis strategy works synergistically, is complex and ingenious, and greatly enhances the non-obviousness and inventiveness of the method.

[0091] (4) Innovation in catalyst structure and application mechanism: The resulting Cl-Fe-SACs / CNT catalyst exhibits excellent stability and selectivity in complex aquatic environments, providing a superior new material for solving practical wastewater problems. Its axial Cl ligands effectively modulate the electron density of the Fe centers, optimizing their adsorption energy for PMS and dominating a highly efficient non-radical oxidation pathway.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for constructing an axially halogen-ligating iron-based catalyst characterized in that, It comprises the following steps: S1, introducing amino groups on the surface of multi-walled carbon nanotubes to obtain modified multi-walled carbon nanotubes; S2, covalently grafting tetra-carboxylic phthalocyanine iron and the modified multi-walled carbon nanotubes through an amidation reaction to obtain a precursor; S3, mixing the precursor with a halogen-containing solid source and a nitrogen source, and pyrolyzing in stages under the atmosphere of an inert gas by programmed temperature rising to obtain a pyrolysis product; S4, acid washing the pyrolysis product to obtain an axial halogen-coordinated iron-based catalyst.

2. The method of claim 1, wherein the method is characterized by, The S1 step specifically comprises the following steps: The multi-walled carbon nanotubes are heated in mixed acid, refluxed, then dispersed in anhydrous toluene, an excess of 3-aminopropyltriethoxysilane is added, and the mixture is condensed and refluxed under the protection of an inert gas, cooled, washed, and dried to obtain modified multi-walled carbon nanotubes.

3. The method of claim 1, wherein the method is characterized by, The specific steps of S2 are as follows: S201, dispersing the modified multi-walled carbon nanotubes in anhydrous N,N-dimethylformamide to obtain a modified multi-walled carbon nanotube dispersion; S202, then adding the tetra-carboxylic phthalocyanine iron and 4-dimethylamino pyridine to another portion of anhydrous N,N-dimethylformamide to activate, obtaining an activated tetra-carboxylic phthalocyanine iron solution; S203, adding the activated tetra-carboxylic phthalocyanine iron solution dropwise to the modified multi-walled carbon nanotube dispersion and stirring to react, then washing, vacuum drying after the reaction to obtain a precursor.

4. The method of constructing an axial halogen-ligating iron-based catalyst according to claim 1, wherein, The staged pyrolysis in the S3 step specifically comprises the following steps: Rising the temperature to 350-450℃ at a rate of 5℃ / min, and keeping the temperature for 1-2h; Then rising the temperature to 750-850℃ at the same rate, and keeping the temperature for 1.5-3h.

5. The method for constructing an axial halogen-ligating iron-based catalyst according to claim 1, characterized by, The mass ratio of the halogen-containing solid source to the nitrogen source is 4: (5-15).

6. The method of constructing an axial halogen-ligating iron-based catalyst according to claim 5, wherein, The halogen-containing solid source is ammonium halide; The nitrogen source provides a nitrogen-rich environment stable site.

7. The method of claim 2, wherein the method is characterized by, The mixed acid is prepared by mixing sulfuric acid and nitric acid at a volume ratio of (2-5):1; The refluxing temperature is 60-80℃, and the refluxing time is 3-5h.

8. An iron-based catalyst prepared by the method of constructing an axial halogen-coordinated iron-based catalyst according to any one of claims 1-7.

9. The use of the iron-based catalyst according to claim 8 in the degradation of organic pollutants in persulfate advanced oxidation technology.

10. Use of the iron-based catalyst according to claim 9 for the degradation of organic pollutants in persulfate advanced oxidation technology, characterized in that, The organic pollutants are antibiotic pollutants.

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