Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater and preparation method thereof

Abstract

The present invention discloses a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater and a preparation method thereof. 2+ and Co 2+ The mixture was mixed and 2-methylimidazole was added to form ZIF-8 and ZIF-67 encapsulated therein. The resulting product was then mixed with iron phthalocyanine to obtain Fe-Co-ZIF. The Fe-Co-ZIF was further converted to Fe-Co-N@C by pyrolysis. The difference between the two metal active centers in the Fe-Co-Nx structure results in an asymmetric distribution of electron density for the nitrogen atoms. Furthermore, the atomically dispersed Fe and Co atoms create a uniform catalyst particle size, giving Fe-Co-N@C higher catalytic activity than single-metal catalysts. Its first-stage reaction rates are 1.41 times and 2.93 times those of Fe and Co single-metal catalysts, respectively.

Description

Technical Field

[0001] The present invention relates to the fields of chemical materials and pollutant treatment, and in particular to a method for preparing a Co-doped Fe-Co-N@C catalytic material and a method for using the same for advanced oxidation treatment of wastewater. Background Art

[0002] Advanced oxidation treatment technology is an efficient and promising wastewater treatment technology that can be used to treat a variety of polluted water bodies. Compared with traditional advanced oxidation technologies (such as Fe 2+ The degradation of refractory organic compounds (AOPs) using technologies such as UV / H2O2 and UV / H2O2, and persulfate technology offer numerous advantages and hold great promise for future applications in environmental remediation. Heterogeneous catalysts, in particular, have garnered significant attention in recent years for the advanced oxidation degradation of organic compounds due to their high catalytic efficiency, excellent stability, and ease of recycling.

[0003] At present, many studies have shown that doping Fe-SACs into carbonitride materials can achieve good PMS activation performance, and in most studies, isolated single Fe-N4 molecules are considered to be the active sites that play a major role. However, the symmetrical Fe-N4 structure, due to its strong intermediate adsorption capacity, will cause shielding of the active sites, resulting in a decrease in overall activity (Engineering Unsymmetrically Coordinated Fe Sites via HeteroatomPairs Synergetic Contribution for Efficient Oxygen Reduction. Small, 2023: 2304303.). Asymmetric coordination structures show great potential in regulating the adsorption of reaction intermediates at active sites, for example. For example, Zhang et al. found that the coordination of S in FeN4S1 and CoN3S1 leads to asymmetric coordination of the metal center, forming a polarization electric field centered on Fe, which triggers a lower intermediate energy barrier and improves catalytic activity (Uniform N-Coordinated Single-Atomic Iron Sites Dispersed in Porous Carbon Framework to Activate PMS for Efficient BPA Degradation via High-Valent Iron-Oxo Species). Therefore, it is of great practical significance to prepare new Fe-NC catalysts with asymmetric coordination structures to enhance their catalytic activity. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology and solve the problem that the intermediate products of traditional Fe-N catalysts are too strongly adsorbed on the active sites due to the symmetrical coordination structure, thereby limiting the catalytic activity, the purpose of the present invention is to provide a Co-doped Fe-Co-N@C catalyst and a preparation method thereof, and to provide a method for using the catalyst material for advanced oxidation treatment of wastewater.

[0005] Therefore, the present invention successfully prepared a novel asymmetric coordinated bimetallic single-atom catalyst (i.e., Fe-Co-N@C) through a three-step process of metal-organic framework formation and post-coordination. The post-coordination method can not only maintain the N coordination, but also adjust the asymmetric electronic structure of the Co metal atom through the post-coordinated Fe atom. x The Fe atoms in the coordination structure have a higher electron density than those in the Fe-N4 structure. The Fe-Co bimetallic co-coordination enhances the polarization electric field strength at the Fe-N and Co-N sites, resulting in stronger PMS adsorption and electron-donating abilities, and thus higher catalytic activity. Furthermore, compared to some currently available Fe and Co metal catalysts, the catalyst of the present invention has a more uniform shape and a fuller particle size. The synergistic coordination of the Fe and Co bimetallics, combined with the low metal loading, effectively reduces metal ion leaching. This solves the problem of fewer active sites and weak PMS adsorption in nanoparticle catalysts, enabling efficient removal of organic pollutants in water.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0007] A method for preparing a Co-doped Fe-Co-N@C catalyst comprises the following steps:

[0008] S1. Synthesize Zn-Co-ZIF precursor. The specific steps are as follows:

[0009] (1) Dissolve zinc nitrate hexahydrate and cobalt nitrate hexahydrate in methanol and mark it as solution A;

[0010] (2) Dissolve 2-methylimidazole in methanol in another beaker and label it as solution B;

[0011] (3) Stir solutions A and B separately with a glass rod. After they are completely dissolved, pour solution B into solution A and stir on a magnetic stirrer for 1 to 4 hours. After stirring, let the solution stand for 12 to 24 hours, wash with methanol, centrifuge and precipitate, and then vacuum dry at 60 to 80 ° C for 12 to 24 hours to obtain a Zn-Co-ZIF precursor.

[0012] S2. Mix the Zn-Co-ZIF precursor with iron phthalocyanine to obtain Fe-Co-MOF. The specific steps are as follows:

[0013] The obtained Zn-Co-ZIF precursor was dispersed in a beaker with 20-40 mL of N,N-dimethylformamide (DMF), and then 10-30 mg of iron phthalocyanine was added to the turbid solution. The solution was dissolved by ultrasonication for 5 minutes and heated and stirred at 60-80 ° C on a magnetic stirrer for 1-4 hours. Finally, the precipitate was collected by centrifugation and vacuum dried at 80 ° C to obtain Fe-Co-MOF.

[0014] S3, Zn in Fe-Co-MOF was removed by high temperature pyrolysis. 2+ After evaporation, Fe atoms and Co atoms will form coordination with N atoms in the cavity of the ZIF framework, thereby obtaining Fe-Co-N@C catalyst. The specific operation is as follows:

[0015] The obtained Fe-Co-MOF was placed in a quartz boat, which was then placed in a tube furnace. Nitrogen was then introduced into the tube furnace. Under these conditions, the temperature was increased to 700-900°C at a heating rate of 2-10°C / min and maintained for 2-4 hours. After the tube furnace cooled down, the sample was taken out, washed with methanol, and dried in a vacuum drying oven at 60-80°C for 12-24 hours to obtain a Fe-Co-N@C catalyst.

[0016] Preferably, in step S1 (1), the molar ratio of zinc nitrate hexahydrate to cobalt nitrate hexahydrate is 20 to 50:1, preferably 35:1.

[0017] Preferably, in step S1 (1), the molar ratio of zinc nitrate hexahydrate to methanol is 1:70-150, preferably 1:120; the molar ratio of cobalt nitrate hexahydrate to methanol is 1:3000-4500, preferably 1:3500.

[0018] Preferably, in step S1 (2), the molar ratio of 2-methylimidazole to methanol is 1:10 to 50, preferably 1:35.

[0019] Further preferably, in step S1 (3), the stirring time is 2 hours.

[0020] Further preferably, in step S1 (3), the static aging time is 12 hours.

[0021] Further preferably, in step S1 (3), the vacuum drying temperature is 60° C., and the vacuum drying time is 12 h.

[0022] More preferably, in step S2, the mass ratio of Zn-Co-ZIF to iron phthalocyanine is 15 to 50:1, preferably 35:1.

[0023] In step S2 , the organic solvent is a solvent that can interact with the π electron system on the phthalocyanine ring, such as N,N-dimethylformamide (DMF).

[0024] Preferably, the heating rate in step S3 is 5° C.; the calcination temperature is 800° C.; and the calcination time is 3 h.

[0025] Further preferably, in step S3, the temperature of the tube furnace is lowered to room temperature at a rate of 5°C / min.

[0026] Further preferably, in step S3, the vacuum drying temperature is 60° C., and the vacuum drying time is 12 h.

[0027] The present invention provides a Co-doped Fe-Co-N@C catalyst prepared by the synthesis method, which uses a porous carbon material as a carrier, and the surface and interior of the carrier are a coordination structure of iron, cobalt metal atoms and nitrogen atoms. The porous carbon material structure is a prismatic dodecahedron, and the carrier has a microporous structure with a pore diameter of 1-2 nm.

[0028] The present invention also provides a method for applying the Co-doped Fe-Co-N@C catalyst to the advanced oxidation treatment of wastewater, wherein Fe-Co-N@C catalyst powder is added to a solution containing a certain concentration of target organic pollutants, and then a certain amount of oxidant is immediately added to react.

[0029] Further preferably, the dosage of the Fe-Co-N@C catalyst is 0.1-1 g / L.

[0030] More preferably, the concentration of the organic pollutants is 5 to 20 mg / L.

[0031] More preferably, the oxidant is at least one of potassium persulfate, sodium persulfate, sodium persulfate and potassium persulfate.

[0032] Further preferably, the mass ratio of the Fe-Co-N@C catalyst to the oxidant is 1:3-12.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] (1) When introducing Fe, the present invention utilizes N,N-dimethylformamide (DMF), a solvent that can interact with the π electron system on the phthalocyanine ring, to generate a dipole-induced dipole interaction with the π electron system, thereby enhancing the molecular binding between the single-molecule iron phthalocyanine and the Zn-Co-ZIF, and obtaining Fe / Co single-atom dispersed Fe-Co-ZIF, thereby solving the problem in the prior art that iron phthalocyanine is insoluble, unevenly doped, resulting in the production of iron clusters, and the inability to form an effective single-atom Fe / Co cooperative coordination structure. In the prior art, methanol is generally used as an organic solvent to mix Fe and Zn-Co-ZIF. Solvents such as methanol do not interact with iron phthalocyanine, and iron phthalocyanine does not dissolve, so it causes Fe to easily agglomerate on the Zn-Co-ZIF, and an effective single-atom Fe / Co cooperative coordination structure cannot be generated.

[0035] (2) The present invention prepared Fe-Co-N@C catalyst by pyrolysis of Fe and Co co-doped ZIF nanomaterials. When the obtained Fe-Co-N@C was used to activate PMS to degrade organic pollutants, it was found that Fe-Co-N x Coordination structure ratio FeN x and CoN x The prepared Fe-Co-N@C exhibited superior catalytic performance, benefiting from the synergistic effect of the asymmetric coordination of single-atom Fe and Co atoms. The catalyst achieved a peak pollutant removal efficiency of 92.5% within 60 minutes, with calculated reaction rates 1.41 and 2.93 times those of the Fe-N@C and Co-N@C catalysts, respectively. Furthermore, Fe-Co-N@C exhibited excellent catalytic activity over a wide pH range of 2.0 to 10.0, suggesting promising applications in wastewater treatment.

[0036] (3) The Fe-Co-N@C catalyst preparation method proposed in the present invention has simple equipment, mild reaction conditions, easy process control, and the metal is distributed in the form of single atoms. It has extremely high atomic utilization and does not require the addition of toxic and harmful reagents, which facilitates the industrialization and engineering application of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Scanning electron microscopy, transmission electron microscopy, HAADF and MAPPING images of Fe-Co-N@C synthesized in Example 1 of the present invention, Fe-N@C in Comparative Example 1, and Co-N@C in Comparative Example 2.

[0038] Figure 2 This is the X-ray photoelectron spectrum of Fe-Co-N@C synthesized in Example 1 of the present invention.

[0039] Figure 3The degradation effects of Fe-Co-N@C of Example 1 of the present invention, Fe-N@C of Comparative Example 1, and Co-N@C of Comparative Example 2 are compared.

[0040] Figure 4 The figure shows the comparison of the degradation effects of the Fe-Co-N@C catalyst under different catalyst dosage conditions of the present invention.

[0041] Figure 5 The figure shows the comparison of the degradation effects of the Fe-Co-N@C catalyst under different oxidant dosage conditions of the present invention.

[0042] Figure 6 The degradation effects of the Fe-Co-N@C catalyst synthesized in the present invention are compared under different initial pH conditions.

[0043] Figure 7 This is an evaluation of the recycling performance of the Fe-N / O@C catalyst synthesized in the present invention.

[0044] Figure 8 This is a comparison chart of the XPS spectra of C1s and N1s of the Fe-N / O@C catalyst synthesized in the present invention before and after the reaction.

[0045] Table 1 compares the N1s XPS fitting results of Fe-Co-N@C synthesized in Example 1 of the present invention, Fe-N@C in Comparative Example 1, and Co-N@C in Comparative Example 2.

[0046] Table 2 compares the XPS fitting results of C1s and N1s of Fe-Co-N@C synthesized in Example 1 of the present invention before and after the reaction. DETAILED DESCRIPTION

[0047] The following is a further description of specific embodiments of the present invention. It should be noted that the description of the embodiments is intended to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0048] Example 1

[0049] Solution A was prepared by adding 3.57 g of Zn(NO₃)₂·6H₂O and 0.1 g of Co(NO₃)₂·6H₂O to 60 mL of methanol and sonicating until dissolved. Solution B was prepared by adding 3.84 g of 2-methylimidazole to 60 mL of methanol and sonicating until dissolved. The two solutions were then mixed, stirred at room temperature for 2 h, and allowed to settle for 12 h. The precipitate was collected by centrifugation and dried in a vacuum oven at 60°C for 12 h to obtain Zn-Co-ZIF. 0.5 g of Zn-Co-ZIF was dispersed in 30 mL of N,N-dimethylformamide (DMF). Then, 15 mg of iron phthalocyanine was added to the turbid solution, sonicated for 5 min, and then heated and stirred at 80°C for 2 h. The precipitate was collected by centrifugation and dried in a vacuum oven at 80°C to obtain Fe-Co-MOF. The dried Fe-Co-MOF was placed in a quartz boat and calcined in a tube furnace at 800°C for 3 h at a heating rate of 5°C / min under a nitrogen atmosphere. The calcined product was ground to obtain Fe-Co-N@C.

[0050] Comparative Example 1

[0051] Solution A was prepared by adding 3.57 g of Zn(NO₃)₂·6H₂O to 60 mL of methanol and sonicating until dissolved. Solution B was prepared by adding 3.84 g of 2-methylimidazole to 60 mL of methanol and sonicating until dissolved. The two solutions were then mixed, stirred at room temperature for 2 h, and allowed to settle for 12 h. The precipitate was collected by centrifugation and dried in a vacuum oven at 60°C for 12 h to obtain Zn-ZIF. 0.5 g of Zn-Co-ZIF was dispersed in 30 mL of N,N-dimethylformamide (DMF). Then, 0.115 g of iron phthalocyanine was added to the turbid solution, sonicated for 5 min, and then heated and stirred at 80°C for 2 h. The precipitate was collected by centrifugation and dried in a vacuum oven at 80°C to obtain Fe-Zn-MOF. The dried Fe-Zn-MOF was placed in a quartz boat and calcined in a tube furnace at 800°C for 3 h at a heating rate of 5°C / min under a nitrogen atmosphere. The calcined product was ground to obtain Fe-N@C.

[0052] Comparative Example 2

[0053] Solution A was prepared by adding 3.57 g of Zn(NO₃)₂·6H₂O and 0.115 g of Co(NO₃)₂·6H₂O to 60 mL of methanol and sonicating until dissolved. Solution B was prepared by adding 3.84 g of 2-methylimidazole to 60 mL of methanol and sonicating until dissolved. The two solutions were then mixed, stirred at room temperature for 2 h, and allowed to settle for 12 h. The precipitate was collected by centrifugation and dried in a vacuum oven at 60°C for 12 h to obtain Zn-Co-ZIF. 0.5 g of Zn-Co-ZIF was dispersed in 30 mL of N,N-dimethylformamide (DMF), sonicated for 5 min, and then heated and stirred at 80°C for 2 h. The precipitate was collected by centrifugation and dried in a vacuum oven at 80°C to obtain Zn-Co-MOF. The dried Zn-Co-MOF was placed in a quartz boat and calcined in a tube furnace at 800°C for 3 h at a heating rate of 5°C / min under a nitrogen atmosphere. The calcined product was ground to obtain Co-N@C.

[0054] The SEM and TEM images of the prepared catalysts are shown in Figure 2. Figure 1 As shown, Fe-N@C and Co-N@C maintain the complete regular dodecahedral rhombus structure ( Figure 1 (b1) and (c1)), the surface is smooth and the crystals are full. In contrast, the surface of Fe-Co-N@C becomes rough ( Figure 1 (a1)), while wrinkles appear at the edge of the crystal, and carbon nanotubes are also produced. In addition, Fe-Co-N@C shows the most serious surface collapse and the thinnest carbon wall. This is because iron phthalocyanine decomposes into free Fe atoms when calcined at 800℃. These free Fe atoms, together with Co, occupy the defect sites formed by the pyrolysis of Zn at high temperature and form coordination with N. HAADF-STEM images show that ( Figure 1 (a2), (b2) and (c2)), no metal nanoparticles or metal oxide nanoparticles can be observed in Fe-N@C, Co-N@C and Fe-Co-N@C. At the same time, the energy dispersive X-ray (MAPPING) spectrum ( Figure 1 (a4), (b4) and (c4)) also show that Fe, Co, C and N species are uniformly distributed in the carbon matrix, which confirms that Fe and Co exist in an atomically dispersed state.

[0055] By X-ray photoelectron spectroscopy (XPS, Figure 2 ) The internal structures of the Fe-Co-N@C, Fe-N@C and Co-N@C catalysts synthesized in Example 1 were further analyzed. The C1s fine spectra of the three materials ( Figure 2 There are four types of characteristic peaks in (a) corresponding to CC sp 2(284.7eV), CO / CN (285.8eV), C=O (288.3eV) and π-π* (291.0eV). The fine spectrum of N 1s ( Figure 2 (b) can be divided into four characteristic peaks. The peak at 398.3 eV is attributed to pyridinic N / MN (M is Fe and Co). Compared to Fe-N@C and Co-N@C, Fe-Co-N@C is slightly offset and lies between the two, indicating that pyridinic N is bound to Fe and Co atoms in the form of coordination bonds. The characteristic peaks at 399.4 eV, 400.8 eV, and 402.5 eV are attributed to pyrrolic N, graphitic N, and oxidized N, respectively. Table 1 compares the relative content of various N species in the three catalytic materials. Fe-Co-N@C has higher contents of pyrrolic N and graphitic N, which is beneficial for improving pollutant adsorption performance. Figure 2 (c) Comparison of Fe 2p spectra of Fe-Co-N@C and Fe-N@C. The peaks near 712.5 eV and 723.6 eV correspond to Fe 2p 3 / 2 and Fe 2p 1 / 2 , it can be seen that the Fe peak of Fe-Co-N@C has an obvious negative shift. Figure 2 (d) Comparison of the Co2p spectra of Fe-Co-N@C and Co-N@C. 779.7 eV and 797.0 eV belong to Co 2p, respectively. 3 / 2 and Co 2p 1 / 2 The Co peak of Fe-Co-N@C also exhibits a negative shift. Changes in XPS binding energy often indicate changes in electron density; a decrease in binding energy indicates an increase in electron density. Therefore, the coordination of the two metal atoms may increase the polarization field strength of the charge-rich centers on both metals, leading to superior catalytic performance.

[0056] Table 1 N1s fitting results of Fe-Co-N@C, Co-N@C and Fe-N@C

[0057]

[0058] Example 2

[0059] In this example, the Fe-Co-N@C of Example 1, the Fe-N@C of Comparative Example 1, and the Co-N@C of Comparative Example 2 were used to degrade a target organic pollutant (bisphenol AF, BPAF) to evaluate their catalytic performance. The specific procedures were as follows: Each of the Fe-Co-N@C of Example 1, the Fe-N@C of Comparative Example 1, and the Co-N@C of Comparative Example 2 was added to a solution containing 10 mg / L of the target organic pollutant, followed by the addition of 0.6 g / L of PMS.

[0060] like Figure 3As shown in (a), it can be seen that the removal rate of BPAF by adsorption alone is limited, and the adsorption removal rate after 60 minutes is only 4.5-6.7%. The removal rate of BPAF by PMS alone within 60 minutes is 3.2%, which shows that in the absence of a catalyst, PMS can hardly achieve degradation by self-decomposition to produce ROS. When the catalyst and PMS are added at the same time, the removal rate of BPAF is greatly improved. The removal rates of BPAF in the three catalyst systems after 60 minutes of reaction are 56.5%, 79.2% and 88.3%, respectively. Fe-Co-N@C shows the best catalytic performance. By comparing the pseudo-first-order kinetic constants ( Figure 3 (b)) It can be seen that the k of Fe-Co-N@C / PMS system is 2.93 times and 1.41 times that of Co-N@C / PMS and Fe-N@C / PMS, respectively. This is due to the bimetallic coordination of Fe-Co-N x The change in the site electron configuration breaks the inertness brought about by the symmetrical structure of Fe-N4 and Co-N4.

[0061] Example 3

[0062] In order to further evaluate the effect of catalyst dosage on the degradation of BPAF by Fe-Co-N@C / PMS system. According to the preparation method of Example 1, the synthesized Fe-Co-N@C catalyst was added to 100 mL of BPAF solution and reacted in a 250 mL blue-capped bottle. The control conditions for the reaction were that the pollutant concentration was 10 mg / L and the peroxymonosulfate (PMS) concentration was 0.6 g / L. The catalyst dosage range was 0.1 to 0.4 g / L. Figure 4 As shown in the figure, when the catalyst concentration increased from 0.1g / L to 0.2g / L, the BPAF removal rate increased from 43.9% to 89.8%. When the catalyst concentration was further increased to 0.4g / L, the removal rate reached 94.6%, achieving complete removal of BPAF. However, the improvement in reaction rate was not very significant. This is because more catalysts increase the number of active sites and the activation efficiency of PMS is higher, thus generating more reactive oxygen species (ROS) to degrade BPAF. However, when the active sites are excessive, not all sites can fully contact PMS due to the limited concentration of PMS, resulting in the inability to further increase the reaction rate.

[0063] Example 4

[0064] To further evaluate the effect of catalyst dosage on the degradation of BPAF by the Fe-Co-N@C / PMS system, the synthesized Fe-Co-N@C catalyst was added to 100 mL of BPAF solution in a 250 mL blue-capped bottle according to the preparation method of Example 1. The reaction was carried out under the control conditions of a pollutant concentration of 10 mg / L and a catalyst dosage of 0.3 g / L. The PMS concentration range was 0.3 to 1.2 g / L. Figure 5 As shown in the figure, as the PMS dosage increased from 0.3 g / L to 0.9 g / L, the BPAF removal rate also increased from 75.7% to 92.5%. This is because the increase in PMS dosage promoted the production of more ROS, thereby improving the degradation rate of BPAF. When the PMS dosage was further increased to 1.2 g / L, the reaction rate of the system only increased slightly, while the BPAF removal rate dropped to 91.8%. This is because the excessive addition of PMS will generate a large number of free radicals in a short period of time, triggering the self-quenching of free radicals and resulting in a decrease in the final removal rate.

[0065] Example 5

[0066] In order to further analyze the effect of Fe-N / O@C material on the activation performance of PMS under different initial pH conditions. The Fe-Co-N@C catalyst prepared in Example 1 was added to BPAF solutions with initial pH = 2.0, 6.0, 8.0, and 10.0, respectively, and reacted in a 250mL blue-capped bottle. The control conditions for the reaction were catalyst dosage of 0.1g / L, pollutant concentration of 10mg / L, and peroxymonosulfate (PMS) concentration of 0.6g / L. Figure 6 As shown in the figure, within the acidic range of initial pH = 2 to 6, the removal rate of BPAF by the Fe-Co-N@C / PMS system is 91.3-92.9%, and the best removal rate is achieved at pH = 4. Without additional acid or alkali, the initial pH of the solution is about 8, at which time the removal rate of BPAF is 89.8%. When the initial pH is further increased to a strong alkaline state, the removal rate decreases slightly, but still remains at 86.2%, which may be due to the presence of HSO5 - Under alkaline conditions, it is easy to dissociate into SO5 2- , its oxidation ability is relatively weak. However, overall, the Fe-Co-N@C / PMS system can maintain a high BPAF removal rate in a relatively wide pH range, which is sufficient to prove that Fe-Co-N@C has potential in practical applications.

[0067] Example 6

[0068] In order to further investigate the cyclic stability of Fe-Co-N@C materials, the Fe-Co-N@C catalyst prepared in Example 1 was subjected to a cyclic experiment for removing organic pollutants. Figure 7 As shown, after each reaction, the catalyst can be reused by simple solid-liquid separation and drying without further treatment. Fe-Co-N@C can still maintain an 80% removal rate after three cycles, indicating that the prepared catalyst has good cyclic stability.

[0069] Example 7

[0070] We performed XPS characterization on the catalyst materials before and after the reaction to analyze the catalytic mechanism in the system. Figure 8 As shown in Table 2, overall, the types of characteristic peaks in the C1s and N1s fine spectra of Fe-Co-N@C before and after the reaction do not change, but their corresponding binding energies change. Figure 8 (a) It can be found that after the reaction, the binding energies of CO / CN (286.2eV) and C=O (288.4eV) increased by 0.4eV and 0.1eV respectively. The increase in binding energy means that these sites act as electron donors, while the binding energy of the π-π* site changes greatly (1.5eV). This is because this site is likely to bind to BPAF and its byproducts (mainly byproducts containing benzene rings), undergoing electronic interactions, which leads to an increase in binding energy. Compared with the fine spectrum of N1s ( Figure 8 (b) We can find that the binding energy of the characteristic peak corresponding to pyridinic N / MN (398.2 eV) increases by 0.1 eV, while the binding energies corresponding to the characteristic peaks of pyrrolic N (399.1 eV) and graphitic N (400.4 eV) decrease by 0.3 eV and 0.4 eV, respectively, indicating that the pyridinic N / MN site acts as an electron donor, while pyrrolic N and graphitic N participate in the reaction as electron acceptors.

[0071] Table 2 Fitting results of C1s and N1s before and after the reaction of Fe-Co-N@C

[0072]

[0073] Finally, it should be noted that the above embodiments are merely preferred implementations of the present invention and are intended only to explain the present invention, not to limit the present invention. Those skilled in the art will appreciate that they may modify the technical solutions described in the above embodiments or substitute equivalent features for some of the technical features. Any changes, substitutions, and modifications made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater, characterized in that: The following steps are involved: S1. Preparation of solution A: Add zinc nitrate hexahydrate and cobalt nitrate hexahydrate to methanol and sonicate until dissolved. Preparation of solution B: Add 2-methylimidazole to methanol and sonicate until dissolved. Then, mix the two solutions, stir at room temperature, and let them settle. Finally, collect the precipitate by centrifugation and dry it in a vacuum oven to obtain Zn-Co-ZIF. S2. Zn-Co-ZIF is dispersed in N,N-dimethylformamide (DMF), and then iron phthalocyanine is added to the turbid solution, dissolved by ultrasonication, and then stirred under heating conditions. Finally, the precipitate is collected by centrifugation and dried in a vacuum drying oven to obtain Fe-Co-MOF. S3. The obtained Fe-Co-MOF precursor is placed in a quartz boat, which is then placed in a tube furnace. Nitrogen is then introduced into the tube furnace, and the temperature is increased for calcination. The obtained calcined product is cooled and ground to obtain Fe-Co-N@C.

2. The method for preparing a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater according to claim 1, characterized in that: In step S1, the molar ratio of zinc nitrate hexahydrate to methanol is 1:70-150; the molar ratio of cobalt nitrate hexahydrate to methanol is 1:3000-4500; and the molar ratio of 2-methylimidazole to methanol is 1:10-50.

3. The method for preparing a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater according to claim 1, characterized in that: In step S1, the stirring time is 1 to 4 hours; the static sedimentation time is 12 to 24 hours.

4. The method for preparing a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater according to claim 1, characterized in that: In step S1, the vacuum drying temperature is 60-80° C., and the vacuum drying time is 12-24 hours.

5. The method for preparing a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater according to claim 1, characterized in that: In step S2, the mass ratio of the iron phthalocyanine to the Zn-Co-ZIF is 1:15 to 1:50; the amount of N,N-dimethylformamide (DMF) added is 20 to 40 mL, and the temperature of stirring and heating is limited to 60 to 80°C.

6. The method for preparing a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater according to claim 1, characterized in that: In step S3, the heating rate is 2-10°C / min; the calcination temperature is 700-900°C, and the calcination time is 2-4h.

7. The method for preparing a Co-doped Fe-Co-N@C catalyst for advanced oxidation treatment of wastewater according to claim 1, characterized in that: In step S3, the temperature of the tube furnace is lowered to room temperature at a rate of 2-10°C / min.

8. A Co-doped Fe-Co-N@C catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: A porous carbon material is used as a carrier, and the surface and interior of the carrier are coordination structures of iron, cobalt metal atoms and nitrogen atoms. The porous carbon material structure is a prismatic dodecahedron, and the metal is distributed in the form of single atoms.

9. Use of a Co-doped Fe-Co-N@C catalyst according to claim 8 in removing organic pollutants in water using advanced oxidation technology, characterized in that: Co-doped Fe-Co-N@C catalyst powder is added to a solution containing target organic pollutants, and an oxidant is immediately added to react. The oxidant is at least one of potassium persulfate, sodium persulfate, sodium persulfate, and potassium persulfate.

10. The use according to claim 9, characterized in that The dosage of the Fe-Co-N@C catalyst is 0.1-1 g / L; the concentration of the organic pollutants is 5-20 mg / L; and the mass ratio of the Fe-Co-N@C catalyst to the oxidant is 1:2-10.

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