A cyanamide-based axially coordinated cobalt single-atom catalyst for persulfate activation, preparation method and application thereof

Abstract

The present invention discloses a cyanamide-based axially coordinated cobalt single-atom catalyst for persulfate activation, its preparation method, and application, belonging to the technical field of persulfate advanced oxidation. The catalyst is prepared by the following method: adding NH2CN and NaOH simultaneously to a CoCl2 solution, stirring the solution for reaction, washing, filtering, and drying after the reaction is complete to obtain the catalyst CoN4(NCN). The present invention uses a one-step precipitation method to synthesize a catalyst having an isolated Co site and cyanamide ([NCN] 2‑ ) coordination structure of the catalyst CoN4(NCN). This catalyst can be used in persulfate-activated advanced oxidation systems and can be used to deeply treat water contaminated with high concentrations of organic matter, improving its biodegradability. Furthermore, CoN4(NCN) exhibits remarkable stability and environmental adaptability, offering significant application prospects and value in the degradation of organic pollutants.

Description

Technical Field

[0001] The present invention belongs to the technical field of persulfate advanced oxidation, and in particular relates to a cyanamide-based axially coordinated cobalt single-atom catalyst for persulfate activation, a preparation method and application thereof. Background Art

[0002] Advanced oxidation processes (AOPs) are considered a promising wastewater treatment technology. They degrade organic pollutants by generating reactive oxygen species (ROS) through the activation of oxidants such as ozone (O₃), hydrogen peroxide (H₂O₂), peroxymonosulfate (PMS), and peroxydisulfate (PDS). The asymmetric structure of PMS molecules facilitates cleavage of the O-O bond, making them more susceptible to activation. Furthermore, PMS-based AOPs offer advantages such as the simultaneous generation of various ROS, pollutant removal via both free radical and non-radical pathways, and strong adaptability to a wide pH range. While there are many methods for activating PMS, such as metal catalysis, heat, microwaves, ultrasound, and light, metal catalysis has attracted widespread attention due to its advantages such as energy conservation, high efficiency, and ease of reuse. Currently, metal catalysts are generally classified as homogeneous and heterogeneous based on their form. However, due to the drawbacks of homogeneous catalysts, such as secondary pollution and a narrow pH range, the development of heterogeneous catalysts is gaining increasing attention.

[0003] In the past decade, the emergence of single-atom catalysts has opened up a new field for the development of heterogeneous catalysts. This type of catalyst fixes dispersed metal atoms on a support, which not only expands the active sites to the atomic level and maximizes the contact efficiency between the active sites and other molecules, but also provides tunable metal coordination and excellent metal-support interactions. In recent years, SACs have been applied to PMS-based AOPs to remove various organic pollutants and have shown excellent performance. In addition to effectively generating common free radicals (·OH, SO4 ·- 、O2 ·- ), SACs have also been shown to be effective against non-radical pathways, including highly selective generation of non-radical reactive species, such as 1 Direct electron transfer mediated by O2 and high-valent metal oxygen species (HVMO), or catalyst-PMS complex.

[0004] Among several non-free radical oxidation pathways, HVMO is a ROS that has only recently received attention. More and more studies have shown its important role in AOPs. HVMO has some unique advantages, including a longer lifespan (7-10s, compared to 10s for free radicals). -6 -10 -9s), excellent resistance to environmental background substances, higher steady-state concentration, strong oxidizing ability, and selectivity for electron-rich organic pollutants. Therefore, designing catalysts that can enhance the efficient and selective generation of HVMO is very promising in the field of water purification and will help further explore the formation mechanism of HVMO.

[0005] However, there are currently few catalysts that can activate PMS to specifically generate HVMO. This is because this process is challenged by the "oxygen wall" rule of transition metals, that is, "when the 3d orbital exceeds 4 electrons, the bonding between the transition metal and the terminal oxygen ligand is inhibited, and the metal-oxygen bond order is reduced because the d electrons occupy the π-antibonding orbital of the metal oxygen." This means that an effective way to overcome the "oxygen wall" is to reduce the three-dimensional orbital filling of the metal and provide more empty orbitals for the electrons from oxygen. Therefore, it is particularly important to design the electronic structure of the central atom. Therefore, finding a catalyst that can overcome the "oxygen wall" rule to promote the selective formation of HVMO during the activation of PMS has important application value. Summary of the Invention

[0006] The invention provides a catalyst for persulfate activation, wherein the catalyst is a cyanamide-based axially coordinated cobalt single-atom catalyst CoN4 (NCN).

[0007] The preparation method of the above catalyst CoN4 (NCN) comprises the following steps:

[0008] Add NH2CN and NaOH to the CoCl2 solution at the same time, stir and react, and after the reaction is completed, wash, filter and dry to obtain the product CoN4(NCN).

[0009] In the above-mentioned preparation method of the catalyst CoN4 (NCN), each raw material is selected from the following parts:

[0010] 10-500 parts of CoCl2 solution, 0.04-2.1 parts of NH2CN, 0.06-3.2 parts of NaOH;

[0011] When the component is a solid component, the portion number represents grams; when the component is a liquid component, the portion number represents milliliters; in actual application, the portion number can be enlarged or reduced proportionally.

[0012] In a specific embodiment, each raw material is selected from the following parts:

[0013] 50 parts of CoCl2 solution, 0.21 parts of NH2CN, and 0.32 parts of NaOH;

[0014] When the component is a solid component, the portion number represents grams; when the component is a liquid component, the portion number represents milliliters; in actual application, the portion number can be enlarged or reduced proportionally.

[0015] In the preparation method of the above-mentioned catalyst CoN4 (NCN), the concentration of the CoCl2 solution is selected from 2.4 to 120 g / L, preferably 12 g / L.

[0016] The present invention provides the use of the above catalyst CoN4 (NCN) in activating persulfate to degrade organic pollutants.

[0017] The present invention provides a catalytic membrane loaded with CoN4(NCN), namely, a CoN4(NCN) / PVDF membrane, wherein the catalytic membrane is prepared by the following method:

[0018] The catalyst CoN4(NCN) is dispersed in an organic solvent and stirred evenly to obtain a CoN4(NCN) solution; the CoN4(NCN) solution is then filtered onto a polyvinylidene fluoride membrane under vacuum pressure to achieve the loading of CoN4(NCN) on the polyvinylidene fluoride membrane; after drying, a CoN4(NCN) / PVDF membrane is obtained.

[0019] In the above-mentioned method for preparing the catalytic membrane, the organic solvent is ethanol.

[0020] In the above-mentioned method for preparing the catalytic membrane, the concentration of the CoN4 (NCN) solution is selected from 0.2 to 10 mg / mL, preferably 1 mg / mL.

[0021] The present invention provides a sewage treatment method, comprising the following steps:

[0022] The CoN4 (NCN) catalyst is mixed with persulfate and added to the sewage to achieve the degradation treatment of organic pollutants in the sewage.

[0023] In the above sewage treatment method, the concentration of the CoN4 (NCN) catalyst in the sewage is selected from 0.05 to 0.20 g / L, preferably 0.1 g / L; the concentration of the persulfate is selected from 0.25 to 2.00 mM, preferably 0.5 mM.

[0024] In the above sewage treatment method, the pH of the sewage should be adjusted to 5-11, preferably 11.

[0025] In the present invention, the persulfate is peroxymonosulfate (PMS).

[0026] In the present invention, the organic pollutants are selected from one or more of bisphenol A, methylene blue, enrofloxacin, phenol, and 4-bromophenol.

[0027] The beneficial effects of the present invention are:

[0028] The present invention adopts a one-step precipitation method to synthesize a novel nanostructured carbon nanotube with isolated Co sites and cyanamide ([NCN] 2- ) coordination structure of the catalyst CoN4 (NCN). This catalyst is a five-coordinated asymmetric cobalt single-atom catalyst with cyanamide groups coordinated in the axial direction. It can achieve the following effects through its asymmetric structure: (1) Precisely control the reaction site of the catalyst so that the catalyst can provide excellent selectivity for specific reactants or intermediates in complex reactions, avoiding the occurrence of ineffective or side reactions; (2) Regulate the electronic structure around the active center so that the electrons are in a state that is easier to flow, thereby increasing activity; (3) Introduce different types of ligands or functional groups into the catalyst to create a diverse reaction environment. This adjustability allows the catalyst to exhibit different performance under different reaction conditions, further broadening its scope of application.

[0029] Compared with traditional CoN4 and CoN5 catalysts, [NCN] 2- The strong cationic polarization ability of the cations combined with the axially asymmetric geometry leads to a higher degree of electron delocalization at the Co site, thereby effectively reducing the energy barrier for the generation of the active species Co(IV)=O.

[0030] In the present invention, the catalyst CoN4 (NCN) can be used in an advanced oxidation system based on persulfate activation to deeply treat water bodies polluted by high-concentration organic matter and improve its biodegradability.

[0031] In addition, CoN4 (NCN) also has significant stability and environmental adaptability, and has important application prospects and value in the field of organic pollutant degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The synthesis process of CoN4(NCN) (a), SEM images at different scales (b-d) and EDS-mapping image (e);

[0033] Figure 2 XRD spectrum (a), FT-IR spectrum (b) and Raman image (c) of CoN4(NCN);

[0034] Figure 3 Normalized Co element k-edge XANES spectrum (a), Fourier transform EXAFS spectrum of CoN4 (NCN) and standard sample (b), fitting results of Co k-edge EXAFS in CoN4 (NCN) in R space (c) and K space (d), wavelet transform results of Co foil (e), CoO (f), Co3O4 (g), CoN4 (NCN) (h);

[0035] Figure 4 Comparison of the activation performance of PMS by CoN4(NCN) and other common cobalt-based catalysts (a) and the decomposition rate of PMS by CoN4(NCN) and other common cobalt-based catalysts (b);

[0036] Figure 5 The effect of catalyst dosage on the performance of PMS activated by CoN4 (NCN) (a); the reaction rate constant of BPA degradation under different catalyst dosages (b); the effect of PMS concentration on the performance of PMS activated by CoN4 (NCN) (c); the reaction rate constant of BPA degradation under different PMS concentrations (d); the effect of pH on the performance of PMS activated by CoN4 (NCN) (e); the reaction rate constant of BPA degradation under different pH (f);

[0037] Figure 6 Continuously operating device based on CoN4(NCN) / PVDF membrane (a); Treatment effect of CoN4(NCN) / PVDF membrane continuously operating device on BPA and ion leaching concentration (b); SEM images of CoN4(NCN) / PVDF membrane (c-d);

[0038] Contact angle test results of CoN4(NCN) / PVDF membrane (e). DETAILED DESCRIPTION

[0039] In the present invention, the CoCl2 solution is prepared by dissolving CoCl2·6H2O in ionized water.

[0040] In the present invention, CoN4(NCN) represents the coordination structure of the material, that is, the central cobalt atom is coordinated with 4 N atoms, and is coordinated with NCN in the fifth direction, hence the name. Figure 1 The model structure constructed in (a) is consistent.

[0041] The other materials used in the present invention, unless otherwise stated, can be obtained through commercial channels. Unless otherwise specified, other terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art. The present invention will be further described in detail below with reference to specific examples and data. The following examples are merely for illustration of the present invention and are not intended to limit the scope of the present invention in any way.

[0042] Example 1

[0043] The catalyst CoN4 (NCN) was prepared as follows:

[0044] 0.21 g NH2CN and 0.32 g NaOH were added to 50 mL CoCl2 solution (12 g / L) at the same time, and the mixture was stirred for 1 h. After the reaction was completed, the mixture was washed with deionized water, filtered, and freeze-dried in vacuo to obtain the product CoN4 (NCN).

[0045] Figure 1 The synthesis process of CoN4(NCN) (a), SEM images at different scales (b~d) and EDS-mapping image (e) are shown.

[0046] Scanning electron microscopy (SEM) images (b-c) reveal the micromorphology of CoN4(NCN) as irregular particles. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) was used to examine the distribution of cobalt atoms (d). As shown in the image, the prominent bright spots can be attributed to dispersed single Co atoms. Energy dispersive spectroscopy (e) demonstrates the uniform distribution of C, N, and Co elements in the catalyst.

[0047] Figure 2 The XRD spectrum (a), FT-IR spectrum (b) and Raman image (c) of CoN4(NCN) are shown.

[0048] The X-ray diffraction (XRD) pattern of CoN4 (NCN) showed that no cobalt-related peaks were observed, indicating that no cobalt nanoparticles or cobalt oxides were produced. Functional group information can be obtained by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. In the ATR-FTIR spectrum, at 2112 cm -1 There is an obvious peak at [NCN] 2- Asymmetrical stretch. 1550cm -1 and 1410cm -1 The two peaks at 668 cm correspond to carbon-nitrogen bonds. -1 Another peak at 855 cm is characteristic of hydrocarbon vibrations. -1 and 2333cm -1 The two peaks at correspond to the stretching vibration modes of CN and C≡N, respectively. Figure 2 This indicates that the cobalt element in the material does not exist in the form of clusters or nanoparticles, and that [NCN] exists in the structure. 2- group.

[0049] Figure 3Shown are the normalized Co element k-edge XANES spectrum (a), Fourier transform EXAFS spectra of CoN4(NCN) and standard samples (b), fitting results of Co k-edge EXAFS in CoN4(NCN) in (c) R space and (d) K space, and wavelet transform results of (e) Co foil, (f) CoO, (g) Co3O4, and (h) CoN4(NCN).

[0050] X-ray absorption fine structure (XAFS) test was used to further explore the chemical state and coordination environment of Co element in CoN4 (NCN). The k-edge XANES spectrum of Co shows that the near-edge absorption energy of CoN4 (NCN) is between CoO and Co3O4 standard compounds, indicating that the valence state of Co in CoN4 (NCN) is between +2-+3. For the Fourier transform (FT) extended X-ray absorption fine structure (EXAFS) of CoN4 (NCN) and reference samples, the chemical state of Co element in CoN4 (NCN) is between +2-+3 and +3. In contrast, no obvious Co-Co bond was observed in CoN4(NCN), whereas A peak appears at , corresponding to the Co-N coordination. The peak at [NCN] 2- In addition, the k-space information is provided in the wavelet transform EXAFS (WT-EXAFS) spectrum. The results show that the k value of CoN4 (NCN) is The maximum intensity is at 1.5, which is caused by Co-N, while Co-Co and Co-O do not have the maximum intensity value. In addition, the k-edge EXAFS curve fitting results of Co show that there are 5 N atoms coordinated with Co in the first shell. In the second shell, the Co-C coordination information and distance are fitted to 4.8 and 1.5, respectively. This asymmetric structure can provide stronger electron transfer ability.

[0051] 1. Bisphenol A degradation performance test

[0052] This study aimed to evaluate the catalytic effect of CoN4 (NCN) on peroxymonosulfate (PMS).

[0053] The degradation experiment was carried out in a 250 mL container, stirred at 500 rpm at room temperature. 10 mg of CoN4 (NCN) or other catalyst (20 mg / L, pH = 6.3, without adjustment and buffer) was added to 100 mL of bisphenol A (BPA) solution. Subsequently, 0.5 mM PMS was added to the above solution, which marked the start of the degradation reaction. The reaction solution was sampled at regular intervals. The sample was then filtered with a 0.22 μm membrane filter and mixed with 50 μL of Na2S2O3 (150 mM) solution. The obtained sample was detected for BPA concentration using high-performance liquid chromatography (HPLC, LC-20, Shimadzu). The above experiments were carried out in triplicate. The degradation curve of the target pollutant was fitted using a pseudo-first-order model, and the apparent rate constant was calculated.

[0054] The test results are as follows Figure 4 As shown:

[0055] CoN4(NCN) had little adsorption effect on bisphenol A (BPA); when only PMS was present, BPA could not be degraded, indicating that the contribution of adsorption and PMS self-decomposition could be ignored. In contrast, in the CoN4(NCN) / PMS system, BPA was completely degraded within 5 min, and its kinetic constant (k app ) value is 1.17min -1 , which is much higher than other homogeneous (about 2 times) and heterogeneous (about 20 to 100 times) catalysts.

[0056] In addition, the PMS residual concentrations in different catalytic systems are as follows Figure 4 As shown in (b), CoN4(NCN) can activate 87.89% of PMS within 7 minutes, with the highest PMS utilization rate. 2+ , Co3O4, Co2O3, and CoO can only activate about 10 to 20% of PMS, resulting in a waste of oxidants.

[0057] The activation principle of CoN4 (NCN) on PMS is as follows:

[0058] First, PMS is adsorbed on the active site of the catalyst; then a single or double electron transfer occurs from the catalyst to the PMS; the electron transfer to the PMS causes the OO bond to break, generating OH and SO4 ·- , HVMO and other different active species.

[0059] 2. BPA degradation experiment under different operating parameters

[0060] The optimal catalyst dosage was investigated by varying the initial catalyst concentration, with four dosage gradients of 0.05 g / L, 0.1 g / L, 0.15 g / L, and 0.2 g / L. The optimal PMS dosage was also investigated by varying the initial PMS concentration, with five concentration gradients of 0.25 mM, 0.50 mM, 1.00 mM, 1.50 mM, and 2.00 mM. To investigate the effect of initial pH, the initial pH of the BPA solution was adjusted to 3.0, 5.0, 7.0, 9.0, and 11.0 using H2SO4 and NaOH. In all experiments, samples were taken at regular intervals and the BPA concentration was measured.

[0061] The test results are as follows Figure 5 As shown:

[0062] like Figure 5 (a) and Figure 5 As shown in (b), when 0.05 g / L CoN4(NCN) was introduced, 88.47% of BPA was degraded within 7 minutes. In contrast, when the catalyst concentration was increased to 0.10-0.20 g / L, BPA was completely removed within 5 minutes. This result shows that as the concentration of CoN4(NCN) increases, the degradation rate increases, and the kapp value increases from 0.28 min to 0.67 min. -1 Increased to 1.74 minutes -1 .

[0063] like Figure 5 (c) and Figure 5 As shown in (d), the degradation performance increases with increasing PMS concentration, as higher PMS concentrations generally produce more reactive oxygen species (ROS). However, when the PMS dosage reaches 1.00 mM or higher, the change in kapp is minimal, which may be due to the fact that the active sites are fully utilized and no more PMS is decomposed.

[0064] like Figure 5 (e) and Figure 5 As shown in (f), the activation energy is different at different pH values, so the initial pH value of the solution is a key factor affecting the catalytic activity. For CoN4(NCN), significant pH adaptability is shown in the degradation of BPA. In the pH range of 5 to 11, BPA can be almost completely degraded within 7 minutes, but when the initial pH is 3, the degradation rate drops to 87.02% and the kapp value drops to 0.28 minutes. -1 This phenomenon can be explained by the excess H + It consumes free radicals and promotes the leaching of metal ions in the system, thereby reducing the performance of the catalyst.

[0065] 3. Preparation and Application of Catalytic Membranes

[0066] Preparation of CoN4(NCN) / PVDF catalytic membrane:

[0067] 0.1 g of the catalyst CoN4(NCN) was dispersed in 100 mL of anhydrous ethanol, stirred vigorously for 30 minutes, and sonicated for 1 hour to obtain a uniformly dispersed solution (1 mg / mL, 100 mL). This solution was then filtered under vacuum pressure onto a polyvinylidene fluoride (PVDF) membrane to achieve CoN4(NCN) loading on the PVDF membrane. Finally, the CoN4(NCN) / PVDF membrane was dried at room temperature for 24 hours before use.

[0068] Continuous flow experiments:

[0069] Place the prepared catalytic membrane in the filter membrane holder, such as Figure 6 As shown in (a), a circulating pump was used to pump BPA simulated wastewater (10 mg / L) mixed with 1 mM PMS through the catalytic membrane device at a rate of 0.6 mL / min. Finally, samples were taken at intervals to detect the BPA concentration and the leached cobalt concentration in the samples.

[0070] The test results are as follows Figure 6 As shown:

[0071] like Figure 6 As shown in (b), a mixed solution containing 10 mg / L BPA and 1 mM PMS was passed through the catalytic membrane at a flow rate of 0.6 mL / min. After 6 hours of continuous operation, a BPA removal efficiency of 98.63% was maintained without the addition of PMS, demonstrating the ability of the catalytic membrane system to continuously and efficiently generate ROS.

[0072] like Figure 6 (c) and Figure 6 As shown in (d), the surface of the CoN4(NCN) / PVDF membrane remains intact.

[0073] like Figure 6 As shown in (e), the contact angle of CoN4(NCN) / PVDF membrane with water is 13.33°, indicating good hydrophilicity. This property facilitates effective contact between the catalyst and pollutants in water.

[0074] In addition, during the entire treatment process, the leaching concentration of Co in the CoN4(NCN) / PVDF membrane was always maintained at 10-30 μg / L, with significant safety and stability.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. Application of catalyst CoN4 (NCN) in the activation of persulfate to degrade organic pollutants; The catalyst CoN4 (NCN) is a cyanamide-axially coordinated cobalt single-atom catalyst, which is a five-coordinated asymmetric cobalt single-atom catalyst in which the cyanamide group is coordinated in the axial direction; The preparation method of the catalyst CoN4 (NCN) comprises the following steps: Add NH2CN and NaOH to the CoCl2 solution at the same time, stir and react, and after the reaction is completed, wash, filter and dry to obtain the product CoN4(NCN).

2. The use according to claim 1, characterized in that In the preparation method of the catalyst CoN4 (NCN), the raw materials are selected from the following parts: 10 to 500 parts of CoCl2 solution, 0.04 to 2.1 parts of NH2CN, and 0.06 to 3.2 parts of NaOH.

3. A catalytic membrane loaded with CoN4(NCN), characterized in that: The catalytic membrane is prepared by the following method: The catalyst CoN4(NCN) is dispersed in an organic solvent and stirred to obtain a CoN4(NCN) solution. The CoN4(NCN) solution is then filtered onto a polyvinylidene fluoride membrane under vacuum pressure to achieve the loading of CoN4(NCN) on the polyvinylidene fluoride membrane. After drying, a CoN4(NCN) / PVDF membrane is obtained. The catalyst CoN4 (NCN) is a cyanamide-axially coordinated cobalt single-atom catalyst, which is a five-coordinated asymmetric cobalt single-atom catalyst in which the cyanamide group is coordinated in the axial direction; The preparation method of the catalyst CoN4 (NCN) comprises the following steps: Add NH2CN and NaOH to the CoCl2 solution at the same time, stir and react, and after the reaction is completed, wash, filter and dry to obtain the product CoN4(NCN).

4. The catalytic membrane loaded with CoN4(NCN) according to claim 3, characterized in that In the preparation method of the catalyst CoN4 (NCN), the raw materials are selected from the following parts: 10 to 500 parts of CoCl2 solution, 0.04 to 2.1 parts of NH2CN, and 0.06 to 3.2 parts of NaOH.

5. The catalytic membrane loaded with CoN4(NCN) according to claim 3, characterized in that The organic solvent is ethanol; the concentration of the CoN4(NCN) solution is selected from 0.2 to 10 mg / mL.

6. A sewage treatment method, characterized in that: Here are the steps: The catalyst CoN4 (NCN) is mixed with persulfate and added to the sewage to achieve degradation of organic pollutants in the sewage; The catalyst CoN4 (NCN) is a cyanamide-axially coordinated cobalt single-atom catalyst, which is a five-coordinated asymmetric cobalt single-atom catalyst in which the cyanamide group is coordinated in the axial direction; The preparation method of the catalyst CoN4 (NCN) comprises the following steps: Add NH2CN and NaOH to the CoCl2 solution at the same time, stir and react, and after the reaction is completed, wash, filter and dry to obtain the product CoN4(NCN).

7. The sewage treatment method according to claim 6, characterized in that: The concentration of the catalyst CoN4 (NCN) in the sewage is selected from 0.05 to 0.20 g / L; the concentration of the persulfate is selected from 0.25 to 2.00 mM.

8. The sewage treatment method according to claim 6, characterized in that: The pH of the sewage is 5-11.

9. The sewage treatment method according to claim 6, characterized in that: The persulfate is peroxymonosulfate; the organic pollutant is selected from one or more of bisphenol A, methylene blue, enrofloxacin, phenol, and 4-bromophenol.

10. The sewage treatment method according to claim 6, characterized in that: In the preparation method of the catalyst CoN4 (NCN), the raw materials are selected from the following parts: 10 to 500 parts of CoCl2 solution, 0.04 to 2.1 parts of NH2CN, and 0.06 to 3.2 parts of NaOH.

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