A process for the construction of an axial halogen-ligated iron-based catalyst and uses thereof

Abstract

The application provides a method for constructing an axial halogen coordination iron-based catalyst and application thereof, and belongs to the field of catalytic materials and environmental pollution control technology. The preparation method comprises the following steps: introducing an amino group on the surface of a multi-walled carbon nanotube to obtain modified multi-walled carbon nanotubes; covalently grafting iron tetracarboxy phthalocyanine and the modified multi-walled carbon nanotubes through an amidation reaction to obtain a precursor; mixing the precursor with a halogen-containing solid source and a nitrogen source, and performing programmed temperature rising and segmented pyrolysis under the atmosphere of an inert gas to obtain a pyrolysis product; and performing acid pickling on the pyrolysis product. The core of the preparation method is a multi-step synergistic strategy of "molecular isolation-interface bridging-gas phase migration-site specific capture-coordination regulation", which realizes ultrahigh single-atom dispersion, guarantees the unity of high density and high dispersion, and effectively optimizes the electronic structure of the iron center, thereby exhibiting superior intrinsic activity.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of catalytic materials and environmental pollution control technology, and particularly belongs to a method for constructing an axial halogen-coordinated iron-based catalyst and application thereof. BACKGROUND

[0002] The persulfate advanced oxidation technology is widely applied in the field of treating refractory organic pollutants, and the core of its efficiency is the design of catalysts. The iron-based catalyst (Fe-SACs) has become a star material in this field due to its nearly 100% atom utilization rate and uniform Fe-N4 active sites.

[0003] At present, the mainstream preparation methods such as “mixed pyrolysis method” and “MOF derivation method” have inherent defects: the uneven mixing of precursors leads to metal aggregation; the uncontrolled migration of metal atoms during pyrolysis makes it difficult to achieve high loading and high dispersion at the same time; and the local coordination environment (such as axial coordination) of the final active site is difficult to accurately control, which limits its intrinsic activity.

[0004] In particular, the work using iron phthalocyanine (FePc) as a precursor directly mixes it with a carbon carrier and then pyrolyzes it. In this process, the strong π-π interaction between FePc molecules easily leads to their own accumulation, and the iron atoms will inevitably aggregate to form nanoparticles during pyrolysis, which goes against the original intention of preparing single-atom catalysts. Therefore, developing a new preparation method that can prevent precursor aggregation, achieve in-situ fixation of metal atoms, and accurately control the final coordination environment is the key to breaking through the current technical bottleneck.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to provide a method for constructing an axial halogen-coordinated iron-based catalyst and application thereof. The core of the preparation method of the present application is a multi-step synergistic strategy of “molecular isolation-interface bridging-gas phase migration-site-specific capture-coordination regulation”, which achieves ultra-high single-atom dispersion, ensures the unity of high density and high dispersion, and effectively optimizes the electronic structure of the iron center, showing superior intrinsic activity.

[0007] In order to achieve the above purpose of the present application, the following technical solutions are adopted:

[0008] The present application provides a method for constructing an axial halogen-coordinated iron-based catalyst, comprising the following steps:

[0009] S1, introducing amino groups on the surface of multi-walled carbon nanotubes to obtain modified multi-walled carbon nanotubes;

[0010] S2, covalently grafting iron tetracarboxy phthalocyanine and the modified multi-walled carbon nanotubes through an amidation reaction to obtain a precursor;

[0011] S3, mixing the precursor with a halogen-containing solid source and a nitrogen source, programmed temperature rising and stepwise pyrolysis under the atmosphere of inert gas to obtain a pyrolysis product;

[0012] S4, acid washing the pyrolysis product to obtain an axial halogen-coordinated iron-based catalyst.

[0013] In S1, the amino group is covalently grafted on the surface of the multi-walled carbon nanotube. This step is not simple oxidation, but introduces an active functional group (-NH2) which can chemically react with the subsequent steps, laying the foundation for "interface bridging";

[0014] S2 is a key step. The carboxyl group of the tetracarboxy phthalocyanine iron is covalently connected to the amino group on the multi-walled carbon nanotube through an amidation reaction. This makes each FePc molecule "isolated" and fixed on the polymer chain, completely avoiding π-π stacking between FePc molecules from a chemical point of view, and achieving true "molecular level" dispersion, solving the agglomeration problem at the source for generating single atoms.

[0015] C2N2 + fragments, as an additional nitrogen source, help to repair and form more stable Fe-N4 structures during pyrolysis. NH4Cl: This is an innovative step. NH4Cl sublimates into NH3 and HCl gas at 340℃. HCl gas flows with the carrier gas to the downstream sample area. Gas phase migration and capture: HCl gas interacts with phthalocyanine iron molecules, on the one hand promoting the decomposition of FePc macromolecules, on the other hand, Cl - may form a Cl-Fe-N4 structure by axially coordinating with the Fe atom at the center of the Fe-N4 site being formed in the form of a gas phase ligand.

[0016] In S4, acid washing is used to remove unstable species. The unstable species here refer to two aspects: one is the tetracarboxy phthalocyanine iron molecules that fail to attach to the tube wall through amidation reaction with the modified amino multi-walled carbon nanotube, and the other is a small amount of iron elements (possibly iron atoms, iron clusters and iron nanoparticles) that may be formed on the multi-walled carbon nanotube wall after high-temperature pyrolysis calcination. Acid washing can remove these tetracarboxy phthalocyanine iron that fails to embed in the multi-walled carbon nanotube through amidation reaction and the iron elements that are easy to lose and hang on the wall, which is beneficial to the formation of a truly monodisperse iron-based catalyst with a firm embedded structure.

[0017] Preferably, the S1 step specifically comprises the following steps:

[0018] The multi-walled carbon nanotubes are heated in mixed acid, refluxed, then dispersed in anhydrous toluene, an excess of 3-aminopropyl triethoxysilane is added, and the mixture is condensed and refluxed under inert gas protection, cooled, washed, and dried to obtain modified multi-walled carbon nanotubes.

[0019] Preferably, the inert gas is argon;

[0020] Preferably, the protection temperature is 100-120℃, and the protection time is 20-28h.

[0021] Preferably, the protection temperature is 110℃, and the protection time is 24h.

[0022] Preferably, the specific steps of S2 are as follows:

[0023] S201. The modified multi-walled carbon nanotubes are dispersed in anhydrous N,N-dimethylformamide (DMF) to obtain a modified multi-walled carbon nanotube dispersion;

[0024] S202. The tetracarboxy phthalocyanine iron and 4-dimethylamino pyridine are then added to another portion of anhydrous N,N-dimethylformamide and activated to obtain an activated tetracarboxy phthalocyanine iron solution;

[0025] S203. The activated tetracarboxy phthalocyanine iron solution is added dropwise to the modified multi-walled carbon nanotube dispersion and stirred to react. After the reaction is completed, the product is washed and vacuum dried to obtain a precursor.

[0026] Preferably, the activation condition is 20-40min at room temperature.

[0027] Preferably, the activation condition is 30min at room temperature.

[0028] Preferably, the room temperature is 15-30℃.

[0029] Preferably, the specific step of stirring in S203 is magnetic stirring at 60℃ for 36h.

[0030] Preferably, the stepwise pyrolysis in S3 specifically includes the following steps:

[0031] Ramp up at a rate of 5℃ / min to 350-450℃ and hold for 1-2h;

[0032] Then ramp up at the same rate to 750-850℃ and hold for 1.5-3h.

[0033] Preferably, the stepwise pyrolysis in S3 specifically includes the following steps:

[0034] Ramp up at a rate of 5℃ / min to 400℃, and keep for 1h;

[0035] Then ramp up at the same rate to 800℃, and keep for 2h.

[0036] Preferably, the mass ratio of the halogen-containing solid source to the nitrogen source is 4:(5-15);

[0037] Preferably, the mass ratio of the halogen-containing solid source to the nitrogen source is 4:10.

[0038] Preferably, the halogen-containing solid source is ammonium halide;

[0039] Preferably, the ammonium halide is any one of ammonium chloride or ammonium bromide;

[0040] Preferably, the halogen-containing solid source is ammonium chloride.

[0041] Preferably, the nitrogen source provides a nitrogen-rich environment stable site;

[0042] Preferably, the nitrogen source is dicyanediamine.

[0043] Preferably, the mixed acid is prepared by mixing sulfuric acid and nitric acid at a volume ratio of (2-5):1;

[0044] Preferably, the mass fraction of the sulfuric acid is 98%, and the mass fraction of the nitric acid is 68%.

[0045] The temperature of the reflux is 60℃-80℃; the reflux time is 3h-5h.

[0046] Preferably, the mixed acid is prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1;

[0047] The temperature of the reflux is 70℃; the reflux time is 4h.

[0048] Preferably, the specific steps of the S4 step are:

[0049] The pyrolysis product obtained in S3 is dispersed in a 0.5M H2SO4 solution, stirred at 80℃ for reflux for 6 hours, then washed to neutral with deionized water, and vacuum dried.

[0050] The application also provides an iron-based catalyst prepared by the above preparation method.

[0051] The application also provides an application of the above iron-based catalyst in degrading organic pollutants in a persulfate advanced oxidation technology.

[0052] Preferably, the organic pollutants are antibiotic pollutants.

[0053] Preferably, the persulfate salt is a permonosulfate salt or a perdisulfate salt.

[0054] Compared with the prior art, the present application has the beneficial effects that:

[0055] (1) The problem of precursor agglomeration is solved, and ultra-high monatomic dispersion is achieved:

[0056] By covalent grafting strategy, the atomic level isolation of FePc molecules is chemically ensured. The high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) characterization confirms that the iron element in the final catalyst is distributed in the form of complete single atom, and almost no iron nanoparticles or clusters are observed. Even if the iron loading is as high as 3.5 wt%, the ultra-high dispersion can still be maintained, and the single atom ratio is more than 99%, completely overcoming the contradiction between high loading and high dispersion.

[0057] (2) The precise regulation of coordination environment is achieved, and ultra-high intrinsic activity is obtained:

[0058] Compared with the traditional Fe-N4 / C catalyst without axial coordination, the Cl-Fe-SACs / CNT catalyst prepared by the present application has a 2.56-fold increase in the apparent reaction rate constant (kapp) in the reaction of activating permonosulfate (PMS) to degrade tetracycline hydrochloride (TCH). This indicates that the axial Cl ligand effectively optimizes the electronic structure of the Fe center, significantly reducing the reaction energy barrier. k obs

[0059] (3) Excellent stability and mass transfer efficiency:

[0060] The catalyst prepared by the present application has excellent structural stability and catalytic stability, and has a high saturation magnetization, which can be recovered by applying an external magnetic field; at the same time, it has a wide pH tolerance range and universality for different types of antibiotics. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 : Cl-Fe-SACs / CNT catalyst real object picture;

[0062] Figure 2 : Cl-Fe-SACs / CNT catalyst HAADF-STEM characterization picture;

[0063] Figure 3 : Cl-Fe-SACs / CNT element distribution picture, wherein A is the distribution picture of Fe element; B is the distribution picture of O element; C is the distribution picture of N element; D is the distribution picture of C element;

[0064] Figure 4 : Cl-Fe-SACs / CNT catalyst magnetic characterization picture;​

[0065] Figure 5 Comparison of Cl-Fe-SACs / CNT and traditional mixed pyrolysis method Fe-SACs / CNT activated PMS degradation TCH performance;

[0066] Figure 6 Comparison of Cl-Fe-SACs / CNT and traditional mixed pyrolysis method Fe-SACs / CNT activated PMS degradation TCH reaction rate constant (k) k obs

[0067] Figure 7 Comparison of Cl-Fe-SACs / CNT and traditional mixed pyrolysis method Fe-SACs / CNT reaction after Fe dissolution concentration;

[0068] Figure 8 Evaluation of Cl-Fe-SACs / CNT degradation performance of different types of antibiotics;

[0069] Figure 9 Evaluation of Cl-Fe-SACs / CNT degradation effect under different pH conditions;

[0070] Figure 10 XRD pattern of Cl-Fe-SACs / CNT before and after degradation of TCH;

[0071] Figure 11 Evaluation of Cl-Fe-SACs / CNT cycle stability and regeneration. DETAILED DESCRIPTION

[0072] The technical solutions of the present application will be described clearly and completely in combination with the specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application. The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are all conventional products that can be purchased on the market.

[0073] Example 1

[0074] Step one: covalent grafting modification of multi-walled carbon nanotubes

[0075] Drugs: multi-walled carbon nanotubes (MWCNTs), 3-aminopropyl triethoxysilane (APTES), anhydrous toluene.

[0076] ​Procedure:

[0077] 1) 5 g MWCNTs were refluxed in 100 ml of 98% H2SO4 / 68% HNO3(3:1 v / v) at 70 °C for 4 h to introduce carboxyl groups (-COOH) to obtain 4.5 g of COOH-MWCNTs.

[0078] 2) 2.0 g of COOH-MWCNTs were dispersed in anhydrous toluene and excess APTES was added. The mixture was refluxed at 110 °C for 24 h under argon.

[0079] 3) After cooling, the mixture was repeatedly washed with ethanol and deionized water by centrifugation and dried under vacuum to obtain 1.8 g of NH2-MWCNTs.

[0080] Step two: Construction of "molecular isolation" type precursor

[0081] Materials: NH2-MWCNTs obtained in step one, iron tetracarboxy phthalocyanine (FeTcPc), N,N-dicyclohexyl carbodiimide (DCC), 4-dimethylamino pyridine (DMAP), N,N-dimethyl formamide (DMF).

[0082] Procedure:

[0083] 1) 1.0 g of NH2-MWCNTs were dispersed in anhydrous DMF to obtain a NH2-MWCNTs dispersion.

[0084] 2) 0.1 g of FeTcPc, 0.1 g of DCC (activator) and 0.05 g of DMAP (catalyst) were added to 50 ml of anhydrous DMF and activated at room temperature for 30 min.

[0085] 3) The activated FeTcPc solution was added dropwise to the above NH2-MWCNTs dispersion and the mixture was stirred magnetically at 60 °C for 36 h.

[0086] 4) After the reaction was completed, the mixture was washed thoroughly with anhydrous DMF and ethanol to remove physically adsorbed FePc and dried under vacuum to obtain 0.8 g of FeTcPc-g-MWCNTs.

[0087] Step three: Halogen coordination engineering in the process of gas phase migration and site-specific capture

[0088] Materials: FeTcPc-g-MWCNTs obtained in step two, a mixture of solid dicyandiamide (DCDA) and ammonium chloride (NH4Cl) powder.

[0089] Procedure:

[0090] 1) Place 0.5g of FeTcPc-g-MWCNTs and 0.2g of DCDA / NH4Cl (mass ratio 10:4) mixed powder in porcelain boats. Place the DCDA / NH4Cl mixture upstream of the tube furnace and the sample downstream.

[0091] 2) Under an argon atmosphere, heat to the first temperature range (400℃) at a rate of 5℃ / min and hold for 1 hour.

[0092] 3) Then continue to heat up to the second temperature range (800℃) at a rate of 5℃ / min, and hold for 2 hours.

[0093] 4) Cool naturally to room temperature to obtain the pyrolysis products.

[0094] Step 4: Removal of Unstable Species and Purification

[0095] Chemicals: The pyrolysis product obtained in step three, and a 0.5 M H2SO4 solution.

[0096] Steps: The pyrolysis products were dispersed in 0.5M H2SO4 solution, stirred and refluxed at 80℃ 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).

[0097] A physical image of the catalyst is shown below. Figure 1 As shown;

[0098] 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;

[0099] from Figure 3 The 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.

[0100] 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.

[0101] Example 2

[0102] Step 1: Covalent grafting modification of CNTs

[0103] Pharmaceuticals: MWCNTs, APTES, anhydrous toluene.

[0104] step:

[0105] 1) 5 g MWCNTs were refluxed in 100 ml of 98% mass fraction H2SO4 / 68% mass fraction HNO3(5:1 v / v) at 80°C for 5 hours to introduce carboxyl groups (-COOH), obtaining 4.5 g of COOH-MWCNTs.

[0106] 2) 2.0 g of COOH-MWCNTs were dispersed in anhydrous toluene, and an excess of APTES was added, and refluxed at 110°C under argon protection for 24 hours.

[0107] 3) After cooling, repeated centrifugal washing with ethanol and deionized water, and vacuum drying, 1.8 g of NH2-MWCNTs were obtained.

[0108] Step two: construction of a "molecular isolation" type precursor

[0109] Medicines: NH2-MWCNTs obtained in step one, FeTcPc, DCC, DMAP, anhydrous DMF.

[0110] Step:

[0111] 1) 1.0 g of NH2-MWCNTs were dispersed in anhydrous DMF to obtain a NH2-MWCNTs dispersion.

[0112] 2) 0.1 g of FeTcPc, 0.1 g of DCC (activator) and 0.05 g of DMAP (catalyst) were added to 50 ml of anhydrous DMF, and activated at room temperature for 30 minutes.

[0113] 3) The activated FeTcPc solution was added dropwise to the above-mentioned NH2-MWCNTs dispersion, and the reaction was carried out at 60°C under magnetic stirring for 36 hours.

[0114] 4) After the reaction was completed, anhydrous DMF and ethanol were used for thorough washing to remove physically adsorbed FePc, and vacuum drying, obtaining 0.8 g of FeTcPc-g-MWCNTs.

[0115] Step three: halogen coordination engineering in the process of gas phase migration and site-specific capture

[0116] Medicines: FeTcPc-g-MWCNTs obtained in step two, mixed powder of solid DCDA and NH4Cl.

[0117] Step:

[0118] 1) 0.75 g of FeTcPc-g-MWCNTs and 0.2 g of a mixed powder of DCDA / NH4Cl (mass ratio 15:4) were respectively placed in a porcelain boat, and the DCDA / NH4Cl mixture was placed upstream of the tube furnace, and the sample was placed downstream.

[0119] 2) Under argon atmosphere, the temperature was raised to the first temperature stage (450 °C) at a rate of 5 °C / min and held for 2 hours.

[0120] 3) Then the temperature was continued to be raised to the second temperature stage (850 °C) at a rate of 5 °C / min and held for 3 hours.

[0121] 4) The pyrolysis product was cooled to room temperature naturally to obtain the pyrolysis product.

[0122] Step four: removal of unstable species and purification

[0123] Medicine: the pyrolysis product obtained in step three, 0.5 M H2SO4 solution.

[0124] Step: the pyrolysis product was dispersed in 0.5 M H2SO4 solution, stirred at 60 °C for 3 hours, then washed to neutral with deionized water, and vacuum dried to obtain the final catalyst Cl-Fe-SACs / CNT (0.48 g).

[0125] Comparative example 1: traditional mixed pyrolysis method

[0126] The specific steps of the traditional mixed pyrolysis method for preparing Fe-SACs / CNT composite catalyst are as follows:

[0127] Multi-walled carbon nanotube pretreatment:

[0128] (1) 5 g of MWCNTs were refluxed in 100 ml of a mixed acid of mass fraction 98% H2SO4 / mass fraction HNO3 (3:1 v / v) at 70 °C for 4 hours.

[0129] (2) After cooling, repeatedly centrifugal washed with deionized water to neutral, and vacuum dried to obtain 4.8 g of acid-treated CNTs (COOH-MWCNTs).

[0130] This step is only intended to introduce carboxyl groups to increase the hydrophilicity and surface defects of the carrier, but does not introduce active functional groups (such as -NH2) that can undergo chemical reactions.

[0131] 2. Physical mixing of precursors:

[0132] (1) 2.0 g of COOH-MWCNTs were dispersed in 100 ml of anhydrous DMF.

[0133] (2) 0.1 g of FeTcPc was directly added to the above dispersion, and stirred at room temperature or slightly higher than room temperature (60 °C) for a period of time (6-12 hours) to allow FeTcPc to be loaded on the surface of CNTs through physical adsorption (mainly weak π-π interaction and physical adsorption force).

[0134] (3) After the reaction, the solid was collected by filtration or centrifugation and washed with solvent to remove the unfirmly adsorbed FeTcPc molecules, and vacuum dried to obtain 1.8 g of FeTcPc / CNT physical mixture.

[0135] 3. Direct pyrolysis:

[0136] (1) 0.5 g of FeTcPc / CNT physical mixture was simply physically mixed with 0.2 g of DCDA solid powder (only as nitrogen source) in a mortar.

[0137] (2) The mixture was placed in a single-temperature-zone tube furnace and directly raised to 800°C at 5°C / min under argon protection, and kept for 2 hours.

[0138] This process lacks the introduction of gas-phase ligands and has no double-temperature-zone design, and is a single heat treatment process.

[0139] Acid washing purification:

[0140] (1) The pyrolysis product after pyrolysis was stirred in a 0.5 M H2SO4 solution at 80°C for 6 hours.

[0141] (2) Washed to neutral with deionized water and vacuum dried to obtain 0.42 g of the catalyst prepared by the traditional method, denoted as Fe-SACs / CNT (traditional).

[0142] Experimental Example 1: Comparison of the performance of Cl-Fe-SACs / CNT and traditional mixed pyrolysis Fe-SACs / CNT in activating PMS to degrade TCH

[0143] The experimental results are shown in Figure 5 , 0.01 g of Cl-Fe-SACs / CNT and traditional mixed pyrolysis Fe-SACs / CNT were respectively used to activate 0.02 g of persulfate (PMS) to degrade 100 ml of tetracycline hydrochloride (TCH) with an initial concentration of 20 mg / L, and the absorbance value at 355 nm was measured in an ultraviolet-visible spectrophotometer after 75 minutes, and the degradation rate was calculated. The removal rates were 94% and 59%, respectively, and the removal rate of Cl-Fe-SACs / CNT was 1.6 times that of traditional mixed pyrolysis Fe-SACs / CNT.

[0144] Experimental Example 2: Comparison of the performance of Cl-Fe-SACs / CNT and traditional mixed pyrolysis Fe-SACs / CNT in activating PMS to degrade TCH k obs Comparison

[0145] The experimental results are shown in Figure 6As shown, the Cl-Fe-SACs / CNT and the traditional mixed pyrolysis Fe-SACs / CNT activated PMS to degrade TCH k obs ln = - k obs t, where C is the initial concentration (20 mg / L), Co is the concentration after the reaction proceeds for t time, and t is the reaction time) were 0.0448 min -1 and 0.0175 min -1 , i.e. the reaction rate of Cl-Fe-SACs / CNT was 2.56 times that of the traditional mixed pyrolysis Fe-SACs / CNT.

[0146] Experimental Example 3: Comparison of Fe dissolution concentration after reaction of Cl-Fe-SACs / CNT and traditional mixed pyrolysis Fe-SACs / CNT

[0147] As shown in the experimental results Figure 7 , the Fe dissolution concentration after reaction of the traditional mixed pyrolysis Fe-SACs / CNT was 0.335 mg / L (water sample after reaction, i.e. reaction proceeded for 75 minutes) determined by ICP-MS, while the Fe dissolution concentration after degradation of tetracycline hydrochloride by Cl-Fe-SACs / CNT was only 0.085 mg / L, and the metal dissolution rate was reduced by 75%, indicating that Cl-Fe-SACs / CNT has good stability.

[0148] Experimental Example 4: Evaluation of degradation performance of Cl-Fe-SACs / CNT on different types of antibiotics

[0149] Experimental method:

[0150] The conditions for degradation of different antibiotics (lomefloxacin hydrochloride, norfloxacin, penicillin) by Cl-Fe-SACs / CNT were the same as those for degradation of tetracycline hydrochloride, i.e. 0.01 g of Cl-Fe-SACs / CNT was respectively activated by 0.02 g of PMS to degrade 100 ml of lomefloxacin hydrochloride, norfloxacin, and penicillin with an initial concentration of 20 mg / L, and after 75 minutes, the corresponding absorbance was measured at a wavelength of 280 nm (suitable for lomefloxacin hydrochloride) in a UV-visible spectrophotometer to calculate the degradation rate. The concentrations of norfloxacin and penicillin were determined by liquid chromatography.

[0151] As shown in the experimental results Figure 8 , from Figure 8It can be seen that the removal rates of tetracycline hydrochloride, lomefloxacin hydrochloride, norfloxacin and penicillin by Cl-Fe-SACs / CNT are 94%, 87%, 71% and 84% respectively at 75 minutes, which indicates that Cl-Fe-SACs / CNT has good degradation effect on different types of antibiotics and has certain universality.

[0152] Experimental Example 5: Evaluation of degradation effect of Cl-Fe-SACs / CNT under different pH conditions

[0153] Experimental procedure:

[0154] 100ml of 20mg / L tetracycline hydrochloride was adjusted to pH 2, 3, 4, 6, 7, 8, 10 and 12 by 0.1mol / L HCl and 0.1mol / L NaOH respectively by using a rubber bulb dropper. The experimental method is the same as that of Experimental Example 1.

[0155] The experimental results are shown in Figure 9 From the figure, it can be seen that Cl-Fe-SACs / CNT has good effect on degrading TCH in the pH range of 3-10, which indicates that the catalyst has a wide pH tolerance range.

[0156] Experimental Example 6: Evaluation of structural stability of Cl-Fe-SACs / CNT

[0157] The Cl-Fe-SACs / CNT catalyst before and after reaction was measured by X-ray diffraction (XRD). The experimental results are shown in Figure 10 From the XRD spectrum, it can be seen that the intensity of the peak does not decrease significantly and the position of the peak does not shift significantly before and after degrading TCH, which indicates that the Cl-Fe-SACs / CNT catalyst has good structural stability before and after reaction.

[0158] Experimental Example 7: Evaluation of cycle stability and regeneration of Cl-Fe-SACs / CNT

[0159] Experimental procedure:

[0160] 15 portions of 0.01g of Cl-Fe-SACs / CNT catalyst were taken to degrade tetracycline hydrochloride as in Experimental Example 1, which is recorded as reaction 1 time. After the 15 portions of the catalyst after reaction were filtered, washed and dried, the above operation was repeated, which is recorded as reaction 2 times, and the same experiment was carried out for 8 times in turn, which is recorded as cycle 8 times.

[0161] The experimental results are shown in Figure 11As shown in the figure, it can be seen from the figure that the Cl-Fe-SACs / CNT catalyst still maintains 78% removal rate after 8 cycles, indicating that the catalyst has excellent cycle stability. In addition, the catalyst removal TCH capacity can be improved to 85% after simple 800℃ argon atmosphere for 2h, indicating that the catalyst has good reproducibility.

[0162] The present application:

[0163] (1) Propose a "covalent grafting molecular isolation" precursor construction strategy:

[0164] The present application discards simple physical mixing, and firmly grafts FeTcPc molecules in a single molecule form on the aminated CNT through amide covalent reaction. The method completely eliminates the pre-agglomeration of FePc molecules caused by π-π stacking from the chemical aspect, and provides a highly uniform precursor for subsequent pyrolysis to generate high-density and high-dispersion single-atom catalyst, which is a key prerequisite for realizing high-load single atom.

[0165] (2) Propose a "gas phase migration-axial halogen coordination" project:

[0166] The present application innovatively introduces NH4Cl as a gas phase axial ligand source. In the pyrolysis process, the HCl gas generated 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 introduces Cl-ligands at its axial position with a higher probability, thereby constructing Cl-Fe-N4 active centers. This method of precisely regulating the electronic structure of single-atom centers through gas phase chemistry is a core innovation to realize ultra-high intrinsic activity of the catalyst.

[0167] (3) Multifunctional pyrolysis atmosphere and "double temperature zone" design:

[0168] The present application designs a mixed auxiliary agent of DCDA and NH4Cl and a double temperature zone pyrolysis process. DCDA provides a nitrogen-rich environment to stabilize the site, and NH4Cl provides a gas phase ligand. The first temperature section (400℃) is a key window for NH4Cl decomposition and gas phase ligand action; the second temperature section (800℃) is used for completing carbonization and crystallization. The synergistic effect of this multi-component, temperature zone pyrolysis strategy is complex and delicate, greatly enhancing the non-obviousness and creativity of the method.

[0169] (4) Catalyst structure and application mechanism innovation:

[0170] The finally obtained Cl-Fe-SACs / CNT catalyst has axial Cl ligand which can effectively adjust the electron density of Fe center, optimize the adsorption energy of PMS and lead to a high efficient non-radical oxidation path. The catalyst shows excellent stability and selectivity in complex water body background, providing a new material with superior performance for solving practical wastewater problems.

[0171] Finally, it should be noted that: the above examples are used to illustrate the technical solutions of the present application, but not limited to them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for constructing an axially halogenated coordinated iron-based catalyst, characterized in that, Includes 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. The halogen-containing solid source is ammonium chloride; The nitrogen source provides a stable site in a nitrogen-rich environment, and the nitrogen source is dicyandiamine; The segmented pyrolysis in 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. The specific steps of S2 are as follows: S201. The modified multi-walled carbon nanotubes are dispersed in anhydrous N,N-dimethylformamide 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.

2. The method for constructing an axially halogenated coordinated iron-based catalyst according to claim 1, characterized in that, 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.

3. The method for constructing an axially halogenated coordinated iron-based catalyst according to claim 1, characterized in that, The mass ratio of the halogen-containing solid source to the nitrogen source is 4:(5-15).

4. The method for constructing an axially halogenated coordinated iron-based catalyst according to claim 2, characterized in that, The mixed acid is prepared by mixing sulfuric acid and nitric acid in a volume ratio of (2-5):1; The reflux temperature is 60℃-80℃; the reflux time is 3h-5h.

5. An iron-based catalyst prepared by the method for constructing an axially halogenated coordinated iron-based catalyst as described in any one of claims 1-4.

6. The application of the iron-based catalyst as described in claim 5 in the degradation of organic pollutants in persulfate advanced oxidation technology.

7. The application of the iron-based catalyst according to claim 6 in the degradation of organic pollutants in persulfate advanced oxidation technology, characterized in that, The organic pollutant is an antibiotic.

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