A self-grown carbon magnetic framework nanoneedle material, its preparation method and application

Abstract

This invention provides a self-grown carbon magnetic framework nanoneedle material, its preparation method, and its application, belonging to the field of wastewater, sediment, and soil remediation technology. The method includes the following steps: ultrasonically dispersing nano-carbon materials and non-ionic polymeric organic compounds, then adding magnetic materials and an organic framework solution to directionally grow a carbon magnetic framework precursor; oxidizing the precursor at high temperature to obtain self-grown carbon magnetic framework nanoneedles; and combining the nanoneedles with a substrate electrode to form a self-grown carbon magnetic framework nanoneedle cathode. This invention uses self-grown carbon magnetic framework nanoneedles as a cathode, utilizing their structural characteristics and excellent electrochemical performance to promote pollutant adsorption and the enrichment of dehalogenating bacteria, providing an excellent reducing environment for the removal of chlorinated organic compounds, providing in-situ electron donors, and accelerating electron transfer from the electrode to the dehalogenating bacteria, thereby improving the removal efficiency of chlorinated organic compounds.

Description

Technical Field

[0001] This invention relates to the field of wastewater, sediment and soil remediation technology, and in particular to a self-grown carbon magnetic framework nanoneedle material, its preparation method and its application in degrading chlorinated organic compounds. Background Technology

[0002] Chlorinated organic compounds, as important organic solvents and product intermediates, are widely used in the pesticide, pharmaceutical, and paper industries. Chlorophenols, as typical representatives, are extremely toxic and persistent. Besides their carcinogenic, teratogenic, and mutagenic effects, they can also damage the immune system, posing significant health risks with prolonged exposure. Low-chlorinated phenols are mainly found in industrial wastewater, while high-chlorinated phenols are primarily concentrated in sludge, resulting in widespread pollution and making their remediation crucial.

[0003] Existing methods for removing chlorinated organic compounds from water include using carbon nanotubes to adsorb chlorides, constructing microbial electrolysis cells using carbon felts to remove organochlorine pollution, and adding noble metal-modified electrodes or rare metal-modified electrodes to degrade chlorides. While carbon nanotubes are readily available as adsorbents, they suffer from difficulties in material separation and poor recyclability. Microbial electrolysis cells using carbon felts, while simple in construction, suffer from incomplete removal and long removal cycles. Adding noble metal-modified electrodes or rare metal-modified electrodes to degrade chlorides yields significant removal effects, but is costly and may introduce harmful ions to microorganisms.

[0004] Microbial reductive dechlorination is a major approach to degrading chlorinated organic compounds. Microbial electrolysis cell (MEC) technology can significantly improve the removal rate and speed of chlorinated organic compounds by microorganisms while maintaining the safety and effectiveness of microbial degradation techniques. This performance improvement largely depends on electrode materials that can meet specific requirements under particular operating conditions.

[0005] The presence of magnetic materials facilitates the reduction of hydrogen evolution overpotential, and there is a close relationship between magnetic materials, particularly transition metals, and genes associated with anaerobic reductive dechlorination enzymes. Hydrogenases are responsible for catalyzing the conversion of H₂ to H₂. +The genome of *Desulfitobacterium frappieri* encodes multiple [Ni-Fe] hydrogenase genes and Ni-dependent hydrogenase genes, releasing electrons. Studies have revealed that the ortho-reductive dechlorination enzyme of *Desulfitobacterium dehalogenans* contains a [4Fe-4S], [3Fe-4S], and a Co cofactor. A reductive dehalogenase for 3,5-dichlorophenol was isolated from *Desulfitobacterium frappieri* PCP-1, and the corresponding CprA-type reductive dehalogenase gene encodes the open reading frame cprA5, whose product has two [Fe-S] binding sites. Therefore, it is reasonable to infer that the presence of magnetic materials in anaerobic systems plays a positive role in the degradation of chlorinated organic matter.

[0006] However, magnetic materials in anaerobic systems are mostly distributed in ionic form within the contaminated medium, making them prone to loss and unstable. Utilizing magnetic materials coupled with nano-carbon materials to form carbon magnetic materials for immobilizing metallic materials and modifying electrodes is an important research direction. Organic framework materials and magnetic metal ions can undergo molecular rearrangement under thermodynamic equilibrium conditions, spontaneously growing into a three-dimensional needle-like plutonium structure. This three-dimensional plutonium structure, along with abundant catalytic sites, facilitates the adsorption of chlorinated organic compounds and microorganisms, promoting uniform contact between the catalyst, microorganisms, and pollutants, and facilitating the sustained catalytic reaction.

[0007] However, as an electrode material, the conductivity of magnetic materials needs further improvement, thus maintaining their original topological structure. Currently, most publicly available catalytic materials promote charge transfer from the electrode to the catalyst by adding carbon black. However, the contact area between the catalyst and conductive carbon is often unsatisfactory, and the uneven mixing further affects its efficiency. These factors significantly reduce the utilization rate of the active sites of the electrocatalyst, hindering subsequent activation and catalytic conversion. Organically coupling magnetic materials with carbon materials to form a dense, uniform, integrated catalyst, avoiding the introduction of conductive carbon black, and thus improving the material's application pathways and performance, is a pressing technological improvement. Summary of the Invention

[0008] To address the aforementioned problems in existing technologies, this invention provides a self-grown carbon magnetic framework nanoneedle material, its preparation method, and its application in degrading chlorinated organic compounds. This invention uses self-grown carbon magnetic framework nanoneedles as a cathode, leveraging their structural characteristics and excellent electrochemical performance to promote the adsorption of pollutants and the enrichment of dehalogenating bacteria. This provides an excellent reducing environment for the degradation of organochlorophenols, provides in-situ electron donors, and accelerates electron transfer from the electrode to the dehalogenating bacteria, thereby improving the removal efficiency of chlorinated organic compounds.

[0009] The technical solution of the present invention is as follows:

[0010] A self-grown carbon magnetic framework nanoneedle material, the preparation method of which includes the following steps:

[0011] S1. Preparation of precursor: Nano-carbon materials and non-ionic polymeric organic compounds are ultrasonically dispersed in an ultrasonic dispersion liquid, and then magnetic metal salts, organic framework solutions and alkaline solutions are added to react and obtain the precursor.

[0012] Preferably, in step S1, the nano-carbon material and the non-ionic polymeric organic compound are placed in an ultrasonic dispersion liquid for ultrasonic dispersion, and the ultrasonic dispersion time is 15-30 min; then, magnetic metal salt, organic framework solution and alkaline solution are added for mixing and stirring, so that the raw materials are mixed more uniformly; further, the stirring time is 30-60 min.

[0013] S2. Preparation of self-grown carbon magnetic framework nanoneedle material: The precursor is oxidized at high temperature to obtain self-grown carbon magnetic framework nanoneedle material.

[0014] Preferably, after heating-assisted self-growth in step S1, the product is centrifuged and washed to purify it, and finally dried to obtain self-grown carbon magnetic framework nanoneedle material.

[0015] Preferably, the carbon nanomaterial in step S1 includes one or a mixture of two types of multi-walled carbon nanotubes or single-walled carbon nanotubes; the non-ionic polymeric organic compound is polyvinylpyrrolidone.

[0016] Preferably, the ultrasonic dispersion solution in step S1 is one of N,N-dimethylformamide, methanol, and ethanol; the mass ratio of the carbon nanomaterial, the nonionic polymeric organic compound, and the ultrasonic dispersion solution is 1:(5-10):(25-680).

[0017] Preferably, the magnetic metal salt in step S1 includes nickel metal salt and iron metal salt;

[0018] More preferably, the nickel metal salt can be selected from, but is not limited to, nickel nitrate, nickel chloride, and nickel acetate; the iron metal salt can be selected from, but is not limited to, ferric chloride and ferric nitrate.

[0019] Preferably, the alkaline solution may be a sodium hydroxide solution; the concentration of the alkaline solution is 0.3-0.5 mol / L.

[0020] Preferably, the organic framework solution is a solution of terephthalic acid or 2-aminoterephthalic acid in N,N-dimethylformamide;

[0021] Preferably, the molar concentration of the organic framework solution is 0.08-0.12 mol / L; the volume ratio of the organic framework solution to the alkaline solution is (5-7):1;

[0022] More preferably, the volume ratio of the organic framework solution to the alkaline solution is 6:1.

[0023] Preferably, the molar concentration of the iron metal salt in the organic framework solution is 0.1-0.15 mol / L; the molar ratio of nickel ions to iron ions in the nickel metal salt and the iron metal salt is 1:1-1:2.

[0024] Preferably, the mass ratio of the magnetic metal salt to the carbon nanomaterial in step S1 is 7:1-8:1.

[0025] Preferably, the reaction in step S1 is a heating-assisted self-growth process, with a reaction temperature of 100-110℃ and a reaction time of 15-20h.

[0026] Preferably, the high-temperature oxidation in step S2 is carried out at a temperature of 450-650°C for 3-6 hours.

[0027] This invention also provides a self-grown carbon magnetic framework nanoneedle cathode, the preparation method of which includes the following steps:

[0028] The prepared self-grown carbon magnetic framework nanoneedle material, ethanol, deionized water and polytetrafluoroethylene emulsion were mixed to form a slurry, which was then coated on the substrate electrode. After filtration, drying and calcination, the cathode of the electrolytic cell was obtained.

[0029] Preferably, the mass of each component of the slurry is as follows: 0.1g of self-grown carbon magnetic framework nanoneedle material, 0.7mL of ethanol, 0.7mL of deionized water, and 180μL of polytetrafluoroethylene emulsion; the coating concentration is 2-4mg of self-grown carbon magnetic framework nanoneedle material per square centimeter; the calcination temperature is 360℃, and the calcination time is 1-3h.

[0030] More preferably, the substrate electrode includes, but is not limited to, carbon felt, nickel foam, copper foam, and nickel foam.

[0031] The present invention further provides an application of the self-grown carbon magnetic framework nanoneedle cathode, namely, using the self-grown carbon magnetic framework nanoneedle cathode in a microbial electrolysis cell to remove chlorinated organic matter.

[0032] The beneficial technical effects of this invention are as follows:

[0033] 1. This invention constructs a self-grown carbon magnetic framework nanoneedle-modified electrode as the cathode using magnetic materials as the core. The combination of carbon nanomaterials and magnetic materials reduces the reactor's internal resistance to migration, improving the conductivity of the magnetic materials while maintaining the original topological structure. This invention utilizes economical and readily available catalytic materials that are microbiologically friendly, significantly improving the electrode's hydrogen evolution activity and conductivity. This facilitates pollutant adsorption and the enrichment of dehalogenating bacteria, providing an excellent reducing environment for the degradation of chlorinated organic compounds and providing a pathway for electron transfer from the electrode to the dehalogenating bacteria, thereby enhancing the removal efficiency of chlorinated organic compounds.

[0034] 2. Compared with existing weak magnetic materials, this invention introduces carbon nanomaterials in the presence of polyvinylpyrrolidone (PVP). The presence of PPVP imparts hydrophilicity to the carbon nanomaterials, resulting in a more uniform distribution in solution. Compared with traditional processes, this avoids the increased time costs and material losses caused by prolonged ultrasound, greatly enhancing its bonding with precursor materials and giving the electrode material better conductivity. It also avoids the uneven catalyst distribution caused by the physical-mechanical mixing of the catalyst and conductive carbon black in the later stages, thus facilitating mass transfer in the system.

[0035] 3. Compared with existing electrode materials, this invention can regulate the catalytic function by changing the addition ratio of nickel magnetic material and ferromagnetic material. Nickel magnetic material has superior hydrogen evolution performance, which is conducive to the in-situ generation of electron donors, while ferromagnetic material has superior electrochemical mass transfer performance, which is conducive to reducing internal reaction resistance, providing a favorable environment for electron transfer and reduction, and reducing system energy consumption. Changing the addition ratio makes it applicable to more diverse scenarios and more universal.

[0036] 4. In summary, compared with existing publicly available technologies, this invention exhibits significantly higher efficiency and stability. Carbon materials are widely used due to their excellent biocompatibility, unique chemical properties, high physical strength, low cost, and lack of secondary pollution. Metallic materials demonstrate excellent conductivity, facilitating the smooth transfer of electrons from the circuit to the electrode surface. Metal-coupled carbon-based biocathodes can improve dechlorination performance. Treatment using the method of this invention can effectively increase the removal rate and efficiency of chlorinated organic compounds. Attached Figure Description

[0037] Figure 1 SEM images of (A) the self-grown carbon magnetic framework nanoneedle precursor and (B) the self-grown carbon magnetic framework nanoneedle material prepared in Example 1.

[0038] Figure 2 AC impedance curves of self-grown carbon magnetic framework nanoneedle electrode and traditional MEC blank group electrode.

[0039] Figure 3The cyclic voltammetric curves are shown for the self-grown carbon magnetic framework nanoneedle electrode and the conventional MEC blank group electrode. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0041] Example 1:

[0042] This embodiment provides a method for preparing a self-grown carbon magnetic framework nanoneedle cathode, including the following steps:

[0043] (1) Activation of multi-walled carbon nanotubes: 350 mg of multi-walled carbon nanotubes were added to 160 mL of H2SO4 / HNO3 solution and heated in a water bath at 80 °C for 3 h. After activation, the nanotubes were washed and dried for later use.

[0044] (2) Synthesis of self-grown carbon magnetic framework nanoneedle precursor: 350 mg of multi-walled carbon nanotubes obtained in step (1) and 1750 mg of polyvinylpyrrolidone were dissolved in 250 mL of N,N-dimethylformamide solution and sonicated at room temperature for 30 min to obtain solution A.

[0045] Add 0.96g Ni(NO3)2·6H2O, 1.81g FeCl3·6H2O, 100mL of N,N-dimethylformamide solution of 0.12mol / L terephthalic acid, and 20mL of NaOH solution to solution A, and stir at room temperature for 30min to obtain solution B;

[0046] Solution B was subjected to hydrothermal reaction at 100℃ for 15 h, washed three times with methanol and dried to obtain the precursor of self-grown carbon magnetic framework nanoneedles.

[0047] (3) Synthesis of self-grown carbon magnetic framework nanoneedles: The self-grown carbon magnetic framework nanoneedle precursor obtained in step (2) is placed in a quartz container and oxidized at 450°C for 6 hours in an air atmosphere to obtain self-grown carbon magnetic framework nanoneedle material, also known as self-grown carbon magnetic framework nanoneedle catalyst.

[0048] (4) Cathode preparation: The substrate electrode is a 4cm×4cm carbon felt. 32mg of the self-grown carbon magnetic framework nanoneedle catalyst obtained in step (3), 0.224mL of ethanol, 0.224mL of deionized water, and 0.0576mL of polytetrafluoroethylene emulsion are mixed to form a slurry. After shaking, the slurry is quickly coated onto the substrate electrode. After filtration and drying, it is calcined in air at 360℃ for 1h to obtain a self-grown carbon magnetic framework nanoneedle modified cathode.

[0049] The purpose of adding polyvinylpyrrolidone to multi-walled carbon nanotubes in step (2) is to modify the hydrophobic multi-walled carbon nanotubes, which are not conducive to dispersion in solvents, into hydrophilic multi-walled carbon nanotubes, which are easier to disperse in solvents, avoid the increased time cost and material loss caused by long-term ultrasound, and facilitate their combination with the precursor.

[0050] Step (3) involves high-temperature oxidation at 450℃. The purpose is to ensure that the multi-walled carbon nanotube structure is preserved and does not collapse, provided that the precursor is fully oxidized.

[0051] The purpose of step (4) is to ensure that the catalyst is uniformly and firmly loaded on the surface of the substrate electrode.

[0052] The SEM characterization of the self-grown carbon magnetic framework nanoneedle precursor prepared in step (2) of this embodiment is as follows: Figure 1 As shown in (A), the carbon magnetic framework nanoneedle precursor has spindle-shaped ends and a rod-shaped middle section with a relatively smooth surface. The carbon nanomaterials are uniformly distributed around it.

[0053] The SEM characterization of the self-grown carbon magnetic framework nanoneedles prepared in step (4) of this embodiment is as follows: Figure 1 As shown in (B), the morphology remains largely unchanged after calcination, but the surface becomes rough. The rough surface facilitates the adsorption of chlorinated organic pollutants and the attachment of microorganisms, thereby increasing the contact area and reducing mass transfer resistance.

[0054] Application Example 1:

[0055] The cathode modified with the self-grown carbon magnetic framework nanoneedles prepared in Example 1 improved the 2,4,6-TCP removal rate in a microbial electrolysis cell system.

[0056] Degradation experiments were conducted in batches. In a 250 mL microbial electrolysis reactor, 30 mL of 650 ppm ethanol solution of 2,4,6-TCP, 50 g of granular sludge (from the secondary sedimentation tank of a sewage treatment plant in Anhui), 30 mL of anaerobic substrate culture medium, and 90 mL of deionized water were added respectively. The reactor was kept at a constant temperature of 37 °C and the shaking speed was 120 rpm. The anode electrode was a carbon brush, and the cathode was the self-grown carbon magnetic framework nanoneedle cathode prepared in Example 1. The applied voltage was 0.6 V and the external resistance was 10 Ω.

[0057] After a certain reaction time, a certain amount of supernatant was taken, filtered through a 0.22 μm filter membrane, diluted, and the concentration of 2,4,6-TCP was determined. The experiment showed that using the cathode of this invention, the removal rate reached 14.39% after 16 hours; after 120 hours, 2,4,6-TCP was undetectable, and the removal rate of the target pollutant reached 100%. The first-order kinetic constant of the degradation reaction was k = 0.0162 h⁻¹. -1 .

[0058] Comparative Example 1: A comparative experiment using traditional anaerobic degradation and the present invention.

[0059] The experimental procedures are as follows: Degradation experiments were conducted in batches. In a 250 mL reactor, 30 mL of 650 ppm ethanol solution of 2,4,6-TCP was added, followed by 50 g of granular sludge, 30 mL of culture medium, and 90 mL of deionized water. The reactor was then incubated at 37°C with a shaking speed of 120 rpm. After a certain reaction time, a portion of the supernatant was taken, filtered through a 0.22 μm filter membrane, diluted, and the concentration of 2,4,6-TCP was determined.

[0060] Experiments showed that, under traditional anaerobic degradation, the removal rate of 2,4,6-TCP was 0.5% after 16 hours, and 86.2% after 120 hours. The first-order kinetic constant of the degradation reaction was k = 0.0113 h. -1 After treatment using the method of Example 1 of this invention, the removal rate after 16 hours of testing was 30 times that of the anaerobic degradation group, and after 120 hours of testing, the removal rate reached 100%, an increase of 13.8%. The first-order kinetic constant of the degradation reaction was 1.43 times that of the traditional anaerobic group, indicating an improvement in its degradation rate.

[0061] Comparative Example 2: A comparative experiment using a traditional MEC system and the present invention.

[0062] The experimental procedures are as follows: Degradation experiments were conducted in batches. In a 250 mL reactor, 30 mL of 650 ppm ethanol solution of 2,4,6-TCP was added, followed by 50 g of granular sludge, 30 mL of culture medium, and 90 mL of deionized water. The reactor was incubated at 37°C with a shaking speed of 120 rpm. A carbon brush was used as the anode electrode, and a 4 cm × 4 cm blank carbon felt electrode without catalyst was used as the cathode electrode. After a certain reaction time, a certain amount of supernatant was taken, filtered through a 0.22 μm filter membrane, diluted, and the concentration of 2,4,6-TCP was determined.

[0063] Experiments showed that the traditional MEC system achieved a 2.9% removal rate of 2,4,6-TCP after 16 hours of testing and an 86.9% removal rate after 120 hours of testing, with a first-order kinetic constant k = 0.0127 h. -1 After treatment using the method of Example 1 of this invention, the removal rate after 16 hours of testing was 4.8 times that of the traditional MEC group, and after 120 hours of testing, the removal rate reached 100%, an increase of 13.1%. The first-order kinetic constant of the degradation reaction was 1.28 times that of the traditional MEC group, indicating an improvement in its degradation rate.

[0064] Depend on Figure 2 As can be seen, the AC impedance curves of both the self-grown carbon magnetic framework nanoneedle experimental group electrode and the traditional MEC blank group electrode consist of a semicircle in the high-frequency region and a sloping line in the low-frequency region. The former is related to charge transfer impedance, while the latter is related to ion diffusion. It can be clearly observed that the semicircle diameter of the self-grown carbon magnetic framework nanoneedle experimental group electrode is much smaller than that of the blank control group, indicating that the self-grown carbon magnetic framework nanoneedle experimental group electrode has a smaller charge transfer impedance.

[0065] To more intuitively compare the magnitudes of the charge transfer impedances of the two, their curves are fitted with an equivalent circuit. Figure 2 (Small diagram). R in the equivalent circuit s R represents the ohmic impedance related to electron transport and ion transport in the electrolyte. ct The impedance related to charge transport, W, is related to the solid-state diffusion of ions within the active material. Through fitting, the Re of the self-grown carbon magnetic framework nanoneedle experimental electrode group was obtained. s R ct The values ​​were 2.08 and 25.27 Ω, respectively. The R0 value for the blank control group was... s R ct The values ​​are 3.73 and 32.99 Ω, respectively. It is evident that the addition of the catalyst increases the conductivity of the material, promotes ion transport, and reduces charge transfer resistance.

[0066] Depend on Figure 3As can be seen, the cyclic voltammetric characteristic curves of the self-grown carbon magnetic framework nanoneedles experimental group have a larger enclosed area and a more symmetrical shape compared with the traditional MEC blank group. Furthermore, a reduction peak appears at approximately 0.6 V, indicating that the material has a stronger electron storage capacity, better redox reversibility, and superior electrocatalytic activity.

[0067] Comparative Example 3:

[0068] In existing technologies, studies using stainless steel composite carbon materials as cathodes have shown a removal rate of 86.9% for 100 ppm 4-chlorophenol after 168 hours, compared to 58.5% for carbon brush cathodes, 49.4% for graphite particle cathodes, and 11.4% for stainless steel cathodes. Under an applied voltage of 600 mV, a Ru / Fe-biocathode removed 5 ppm of chlorinated organic compounds in 4 days with a removal rate of 96.3%, while this invention can remove 100% of 650 mg / L of chlorinated organic compounds in 5 days, demonstrating a more significant removal effect and a larger removal capacity.

[0069] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, and for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the specific details without departing from the general concept defined by the claims and their equivalents.

Claims

1. An application of a self-grown carbon magnetic framework nanoneedle cathode, characterized in that, The self-grown carbon magnetic framework nanoneedle cathode was used in a microbial electrolysis cell to remove chlorinated organic matter. The method for preparing the self-grown carbon magnetic framework nanoneedle cathode includes the following steps: A slurry was prepared by self-grown carbon magnetic framework nanoneedle material, ethanol, deionized water and polytetrafluoroethylene emulsion, and then coated onto the substrate electrode. After filtration, drying and calcination, the cathode of the electrolytic cell was obtained. The preparation method of the self-grown carbon magnetic framework nanoneedle material includes the following steps: S1. Preparation of precursor: Carbon nanomaterials and nonionic polymeric organic compounds are ultrasonically dispersed in an ultrasonic dispersion solution, and then magnetic metal salts, organic framework solutions and alkaline solutions are added to react and obtain the precursor; the self-grown carbon magnetic framework nanoneedle precursor has spindle-shaped ends and a rod-shaped middle, with a relatively smooth surface and carbon nanomaterials uniformly distributed around it; the carbon nanomaterials are multi-walled carbon nanotubes. S2. Preparation of self-grown carbon magnetic framework nanoneedle material: The precursor is oxidized at high temperature to obtain self-grown carbon magnetic framework nanoneedle material; the morphology of the self-grown carbon magnetic framework nanoneedles is unchanged, only the surface becomes rough; The magnetic metal salt in step S1 includes nickel metal salt and iron metal salt; the organic framework solution is terephthalic acid or N,N-dimethylformamide solution of 2-aminoterephthalic acid; the alkaline solution is sodium hydroxide solution. The molar concentration of the organic framework solution is 0.08-0.12 mol / L; the volume ratio of the organic framework solution to the alkaline solution is (5-7):1; The molar concentration of the iron metal salt in the organic framework solution is 0.1-0.15 mol / L; the molar ratio of nickel ions to iron ions in the nickel metal salt and the iron metal salt is 1:1-1:2; The high-temperature oxidation in step S2 is carried out at a temperature of 450-650℃ for 3-6 hours. High-temperature oxidation can preserve the multi-walled carbon nanotube structure without collapsing, provided that the precursor is fully oxidized.

2. The application according to claim 1, characterized in that, The nonionic high-molecular-weight organic compound mentioned in step S1 is polyvinylpyrrolidone.

3. The application according to claim 1, characterized in that, The ultrasonic dispersion solution in step S1 is one of N,N-dimethylformamide, methanol, and ethanol; the mass ratio of the carbon nanomaterial, nonionic polymeric organic compound, and ultrasonic dispersion solution is 1:(5-10):(25-680).

4. The application according to claim 1, characterized in that, The mass ratio of the magnetic metal salt to the carbon nanomaterial in step S1 is 7:1-8:

1.

5. The application according to claim 1, characterized in that, The reaction described in step S1 is a heating-assisted self-growth process, with a reaction temperature of 100-110℃ and a reaction time of 15-20h.

6. The application according to claim 1, characterized in that: The amounts of each component in the slurry are as follows: 0.1 g of self-grown carbon magnetic framework nanoneedle material, 0.7 mL of ethanol, 0.7 mL of deionized water, and 180 μL of polytetrafluoroethylene emulsion; the coating concentration is 2-4 mg of self-grown carbon magnetic framework nanoneedle material per square centimeter; the calcination temperature is 360℃, and the calcination time is 1-3 h.

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