Preparation method of confined carbon film electrode and application thereof

Abstract

The present application relates to the technical field of water treatment, in particular to a preparation method of a confined carbon film electrode and application thereof. The advanced oxidation technology is a free radical oxidation system mainly with hydroxyl radicals and sulfate radicals. When degrading persistent organic pollutants, the hydroxyl radicals and sulfate radicals are easily consumed by chain reaction with anions in water and also produce toxic byproducts. In view of the above problems, the present application provides a confined carbon film electrode which is formed by depositing Fe2O3 / CNTs composite material on the surface of a microporous filter membrane to form a membrane electrode. The Fe2O3 / CNTs composite material is to confine iron oxide nanoparticles on the sidewall of the hollow pipe of carboxyl functionalized CNTs. The present application combines electrocatalysis technology and membrane separation technology, can more efficiently remove harmful substances such as persistent organic pollutants and heavy metals in water, and has higher water purification efficiency compared with the single electrocatalysis technology and membrane separation technology.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a method for preparing a confined carbon film electrode and its application. Background Technology

[0002] Persistent organic pollutants (POPs) are distributed in water bodies, soil, and air in my country, with the aquatic environment being the primary carrier of POPs. Traditional water treatment processes are generally ineffective in removing these POPs, while advanced oxidation technologies (AOs) exhibit excellent degradation capabilities by generating hydroxyl radicals; however, they are susceptible to the influence of water composition and environmental factors.

[0003] Compared to radical oxidation systems in advanced oxidation technologies, which are dominated by hydroxyl and sulfate radicals, non-radical substances, such as singlet oxygen, are more effective. 1 O2 is considered to have excellent resistance to environmental substrate interference and a wide pH adaptability, making it more suitable for treating complex wastewater. Hydroxyl radicals and sulfate radicals may be consumed in chain reactions with anions in water, or even produce toxic byproducts. However, those with electrophilic properties... 1 O2 exhibits good selectivity for electron-rich organic pollutants and is insensitive to anions.

[0004] Electrocatalytic membrane filtration technology is considered one of the most promising technologies in next-generation water treatment. Electrocatalysis can easily synthesize key precursors for in-situ generation of singlet oxygen. With the support of an electric field, effective activation of the precursors can be achieved, and... 1 O2 generation. Electrocatalytic membrane filtration technology can effectively remove pollutants at high flux under low transmembrane pressure, thus being significantly superior to traditional membrane filtration technologies that rely solely on physical retention mechanisms. This integration of electrocatalysis and membrane filtration results in excellent water treatment efficiency.

[0005] In conventional electrocatalytic systems, the oxygen evolution reaction at the anode is generally considered a side reaction that does not contribute to the degradation of organic matter and is a major factor reducing overall current efficiency. The generation of H2O2 via the two-electron oxygen reduction reaction (ORR) at the cathode has become a promising synthetic method. In electrocatalytic systems, H2O2 is synthesized... 1 One of the key precursors of O2, therefore, by using oxygen as a recyclable resource to supply the cathode to generate H2O2 in situ through a two-electron oxygen reduction reaction, the risks of storing, transporting and utilizing hydrogen peroxide are avoided.

[0006] Numerous studies have shown that carbon nanotubes are the source of... 1 Effective electrode materials for H2O2, a key precursor of O2, are urgently needed. Therefore, there is an urgent need to develop novel electrode materials and stable electrocatalytic reactors capable of selectively and effectively degrading persistent organic pollutants in real-world water conditions. SUMMARY

[0007] The prior art has the problem that the advanced oxidation technology is a free radical oxidation system mainly with hydroxyl radicals and sulfate radicals, and the hydroxyl radicals and sulfate radicals are easily consumed by chain reaction with anions in water when degrading persistent organic pollutants, and toxic byproducts are also produced.

[0008] Preferably, the preparation method of the Fe2O3 / CNTs composite material comprises the following steps:

[0009] S1, acid bath reflux,

[0010] The carbon nanotubes are acid treated to introduce carboxyl groups on the surface of the carbon nanotubes to obtain carboxylated carbon nanotubes;

[0011] S2, centrifugal water washing to neutral,

[0012] The carboxylated carbon nanotubes obtained in step S1 are placed in ultrapure water and centrifugally washed to neutral, and the obtained solid product is freeze-dried to obtain carboxylated carbon nanotube powder;

[0013] S3, obtaining an iron precursor solution,

[0014] The ferric nitrate is dispersed in 15-25 mL of acetone and uniformly ultrasonically dispersed to obtain an iron precursor solution, and the mass percentage content of Fe element in the iron precursor solution is 3-15%;

[0015] S4, obtaining a carbon nanotube iron precursor solution,

[0016] 200 mg of carboxylated carbon nanotube powder is added to the iron precursor solution and uniformly dispersed and stirred;

[0017] S5, obtaining iron-doped carbon nanotubes,

[0018] The carbon nanotube iron precursor solution obtained in step S4 is stirred at room temperature to volatilize the solvent until only solid powder is left, and iron-doped carbon nanotubes are obtained;

[0019] S6, the iron-doped carbon nanotubes obtained in step S5 are placed at 140-150 DEG C for air blowing drying for 10-12 h, and then ground to the required particle size to obtain CNT confined Fe2O3 powder;

[0020] S7, dispersing the CNT-confined Fe2O3 powder obtained in step S6 in 40 mL of an organic solvent, and uniformly ultrasonically dispersing to obtain a CNT-confined Fe2O3 suspension, wherein the mass concentration of the CNT-confined Fe2O3 powder in the organic solvent is 1.25 ± 0.05 mg / mL;

[0021] S8, forming an active coating layer on the surface of a microporous filter membrane by vacuum filtration of the CNT-confined Fe2O3 suspension obtained in step S7, wherein the thickness of the active coating layer is 1-100 μm, and finally washing the surface of the active coating layer with ultrapure water to remove the organic solvent, and drying at room temperature to obtain a confined carbon film electrode.

[0022] Preferably, step S1 is performed according to the following steps:

[0023] The multi-walled carbon nanotubes and concentrated nitric acid are added to a reactor for reflux stirring reaction for 12-14 h to obtain carboxylated carbon nanotubes, wherein the volume-to-mass ratio of the multi-walled carbon nanotubes to concentrated nitric acid is 2 mg: 1 mL, and the reflux stirring temperature is 140-160 °C.

[0024] Preferably, the temperature for freeze-drying in step S2 is -60 °C, and the freeze-drying time is 18-24 h.

[0025] Preferably, the average particle size of the CNT-confined Fe2O3 powder is 1-10 μm.

[0026] Preferably, the organic solvent in step S7 comprises at least one of N-methylpyrrolidone and ethanol.

[0027] Preferably, the carbon nanotubes are multi-walled carbon nanotubes.

[0028] Preferably, the multi-walled carbon nanotubes have 2-50 coaxial layers.

[0029] Preferably, the thickness of the microporous filter membrane is 0.15 ± 0.05 mm.

[0030] The thickness of the microporous filter membrane is 0.15 ± 0.02 mm.

[0031] Preferably, the microporous filter membrane has a porosity of 70-80% and a pore size of 0.45 ± 0.05 μm.

[0032] The present application has the following advantages:

[0033] (1) The present application combines electro-catalysis technology and membrane separation technology, and can more efficiently remove harmful substances such as persistent organic pollutants and heavy metals in water, and has higher water purification efficiency than single electro-catalysis technology and membrane separation technology.

[0034] (2) Compared with the traditional water treatment technology, the system does not need to add chemical agents, avoids secondary pollution, can save resources and energy, and has good environmental protection benefits;

[0035] (3) Unlike the traditional carbon nanotube inorganic electrocatalytic membrane in-situ generating H2O2, the confined carbon film electrode has a unique nanometer confined microstructure, and by combining carboxylated carbon nanotubes and iron oxide nanoparticles as cathode materials, non-free radical substances are generated in-situ 1 O2, and using 1 O2 to degrade persistent organic pollutants in actual wastewater;

[0036] (4) The present application solves the problem of oxygen evolution side reaction in traditional electrocatalytic technology, and uses oxygen to generate H2O2 through two-electron oxygen reduction, and then generates 1 O2 through the divalent iron / ferric iron cycle acceleration mechanism, which is a micro-resource recycling process;

[0037] (5) The present application uses a peristaltic pump to drive water flow, and forces the wastewater to pass through the anode and the cathode in sequence to improve the mass transfer rate, thereby improving the total reaction kinetics of pollutant degradation and enhancing the degradation effect of pollutants;

[0038] (6) The present application adopts a multi-port design and a two-way valve switch control, which makes the operation more flexible and convenient, can adjust the switch and flow according to the actual situation, and improves the accuracy and controllability of the operation;

[0039] (7) The present application is made of high-quality organic glass material, which can visualize the internal working condition of the membrane electrode reactor, has excellent chemical stability and corrosion resistance, can ensure long-term stable operation of the reactor, and reduce maintenance and replacement costs.

[0040] DRAWINGS

[0041] Figure 1 SEM diagram of the confined carbon film electrode obtained in Example 1.

[0042] Figure 2 TEM diagram of the confined carbon film electrode obtained in Example 1.

[0043] Figure 3 Structure diagram of the water purification membrane reactor used in the present application.

[0044] Figure 4 Assembled structure diagram of the membrane assembly in the water purification membrane reactor used in the present application.

[0045] Figure 5 Comparison diagram of the degradation effect of the water purification membrane electrode reactor obtained in Examples 1-3 on acetaminophen. DETAILED DESCRIPTION

[0046] The application will be described in detail below in conjunction with the examples. It should be understood that the following examples are merely illustrative of the embodiments of the application, but are not intended to limit the scope of the application.

[0047] The carbon nanotubes used in the following examples of the application are multi-walled carbon nanotubes, which are purchased from Sichuan Reclamation Technology Development Co., Ltd., and the item number is KY20240611093.

[0048] The microporous filter membrane used in the preparation of the confined carbon film electrode in the following examples of the application is a polytetrafluoroethylene hydrophilic filter membrane, with a thickness of 0.15 μm, a porosity of 80%, and a pore size of 0.45 μm, which is purchased from Hangzhou Micron Technology Co., Ltd.

[0049] The stainless steel mesh used in the application has a thickness of 1 mm.

[0050] The carbon fiber felt film electrode has a thickness of 2 mm.

[0051] The polytetrafluoroethylene gasket has a thickness of 2 mm.

[0052] The polytetrafluoroethylene filter membrane has a thickness of 0.15 mm.

[0053] The titanium mesh has a thickness of 1 mm.

[0054] The mass concentration of the concentrated nitric acid used in the following examples of the application is 68%.

[0055] The acid bath reflux temperature in the following examples of the application is 150°C.

[0056] Example 1

[0057] A confined carbon film electrode is prepared by the following method:

[0058] S1, acid bath reflux,

[0059] The multi-walled carbon nanotubes and concentrated nitric acid are added to a reactor for reflux stirring reaction for 14 h, to obtain carboxylated carbon nanotubes, wherein the volume-to-mass ratio of the multi-walled carbon nanotubes to concentrated nitric acid is 2 mg: 1 mL;

[0060] S2, centrifugal water washing to neutral,

[0061] The carboxylated carbon nanotubes obtained in step S1 are placed in ultrapure water for centrifugal washing to neutral, and the obtained solid product is freeze-dried, with a freeze-drying temperature of -60°C and a freeze-drying time of 24 h, to obtain carboxylated carbon nanotube powder;

[0062] S3, obtaining an iron precursor solution,

[0063] Fe(NO3)3.9H2O was dispersed in 20 mL of acetone and ultrasonically dispersed to obtain an iron precursor solution, the mass percentage of Fe in the iron precursor solution was 10%;

[0064] S4, obtaining a carbon nanotube iron precursor solution,

[0065] 200 mg of carboxylated carbon nanotube powder was added to the iron precursor solution and uniformly dispersed by stirring;

[0066] S5, obtaining iron-doped carbon nanotubes,

[0067] The carbon nanotube iron precursor solution obtained in step S4 was stirred at room temperature to evaporate the solvent until only solid powder was left, i.e. iron-doped carbon nanotubes were obtained;

[0068] S6, the iron-doped carbon nanotubes obtained in step S5 were subjected to air drying at 140°C for 12 h, and then ground to the desired particle size, i.e. CNT-confined Fe2O3 powder was obtained, the average particle size of the CNT-confined Fe2O3 powder was 10 μm;

[0069] S7, the CNT-confined Fe2O3 powder obtained in step S6 was dispersed in 40 mL of N-methyl pyrrolidone and ultrasonically dispersed to obtain a CNT-confined Fe2O3 suspension, the mass concentration of the CNT-confined Fe2O3 powder in the organic solvent was 1.25 mg / mL.

[0070] S8, the CNT-confined Fe2O3 suspension obtained in step S7 was formed into an active coating on the surface of a microporous filter membrane by vacuum filtration, the thickness of the active coating was 1 μm, and finally the organic solvent on the surface of the active coating was removed by washing with ultrapure water, and after drying at room temperature, a confined carbon film electrode was obtained.

[0071] The confined carbon film electrode obtained in Example 1 was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The test conditions were as follows: an FEI-F50 field emission scanning electron microscope (FE-SEM) was used to obtain SEM images, and the operating acceleration voltage was 20 kV. A JEM-2100 field emission transmission electron microscope (FE-TEM) was used to capture high-angle dark field scanning transmission electron microscopy (HADFTEM) images, and the operation was carried out at an acceleration voltage of 200 kV.

[0072] The SEM image of the confined carbon film electrode obtained in Example 1 is shown in FIG. 1 of the accompanying drawings, and the CNT-confined Fe2O3 powder is uniformly distributed on the surface of the PTFE filter membrane. Figure 1

[0073] The TEM image of the confined carbon film electrode obtained in Example 1 is shown in FIG. 2 of the accompanying drawings. Figure 2 ​​

[0074] Example 2

[0075] A confined carbon film electrode is prepared by the following method:

[0076] S1, acid bath reflux,

[0077] Multi-walled carbon nanotubes and concentrated nitric acid are added to a reactor for reflux stirring reaction for 14 h, and carboxylated carbon nanotubes are obtained, wherein the volume-mass ratio of the multi-walled carbon nanotubes to the concentrated nitric acid is 2 mg: 1 mL;

[0078] S2, centrifugal water washing to neutral,

[0079] The carboxylated carbon nanotubes obtained in step S1 are centrifugally washed to neutral in ultrapure water, and the obtained solid product is freeze-dried at a temperature of -60°C for 24 h, and carboxylated carbon nanotube powder is obtained;

[0080] S3, obtaining an iron precursor solution,

[0081] Iron nitrate nonahydrate is dispersed in 20 mL of acetone and uniformly ultrasonically dispersed to obtain an iron precursor solution, and the mass percentage of Fe element in the iron precursor solution is 3%;

[0082] S4, obtaining a carbon nanotube iron precursor solution,

[0083] 200 mg of the carboxylated carbon nanotube powder is added to the iron precursor solution and uniformly dispersed and stirred;

[0084] S5, obtaining iron-doped carbon nanotubes,

[0085] The carbon nanotube iron precursor solution obtained in step S4 is stirred at room temperature to volatilize the solvent until only solid powder is left, and iron-doped carbon nanotubes are obtained;

[0086] S6, the iron-doped carbon nanotubes obtained in step S5 are subjected to air blowing drying at 140°C for 12 h, and then ground to a desired particle size, and CNT confined Fe2O3 powder is obtained, wherein the average particle size of the CNT confined Fe2O3 powder is 10 μm;

[0087] S7, the CNT confined Fe2O3 powder obtained in step S6 is dispersed in 40 mL of N-methyl pyrrolidone and uniformly ultrasonically dispersed, and CNT confined Fe2O3 suspension is obtained, wherein the mass concentration of the CNT confined Fe2O3 powder in the organic solvent is 1.25 mg / mL.

[0088] S8, the CNT confined Fe2O3 suspension obtained in step S7 is formed into an active coating on the surface of a microporous filter membrane by vacuum suction filtration, the thickness of the active coating is 1 μm, and finally the active coating surface is rinsed with ultrapure water to remove organic solvents, and after drying at room temperature, a confined carbon film electrode is obtained.

[0089] Example 3

[0090] A confined carbon film electrode is prepared by the following method:

[0091] S1, acid bath reflux,

[0092] Multi-walled carbon nanotubes and concentrated nitric acid are added to a reactor for reflux stirring reaction for 14 h, to obtain carboxylated carbon nanotubes, the volume-mass ratio of the multi-walled carbon nanotubes to the concentrated nitric acid being 2 mg: 1 mL;

[0093] S2, centrifugal water washing to neutral,

[0094] The carboxylated carbon nanotubes obtained in step S1 are placed in ultrapure water for centrifugal washing to neutral, and the obtained solid product is freeze-dried, the freeze-drying temperature being -60°C, and the freeze-drying time being 24 h, to obtain carboxylated carbon nanotube powder;

[0095] S3, obtaining an iron precursor solution,

[0096] Iron nitrate nonahydrate is dispersed in 20 mL of acetone and uniformly ultrasonically dispersed to obtain an iron precursor solution, the mass percentage content of Fe element in the iron precursor solution being 15%;

[0097] S4, obtaining a carbon nanotube iron precursor solution,

[0098] 200 mg of carboxylated carbon nanotube powder is added to the iron precursor solution and uniformly dispersed and stirred;

[0099] S5, obtaining iron-doped carbon nanotubes,

[0100] The carbon nanotube iron precursor solution obtained in step S4 is stirred at room temperature to volatilize the solvent until only solid powder is left, to obtain iron-doped carbon nanotubes;

[0101] S6, the iron-doped carbon nanotubes obtained in step S5 are placed in a blast drying oven at 140°C for 12 h, and then ground to the required particle size, to obtain CNT confined Fe2O3 powder, the average particle size of the CNT confined Fe2O3 powder being 10 μm;

[0102] S7. Disperse the CNT-confined Fe2O3 powder obtained in step S6 in 40 mL of N-methylpyrrolidone and ultrasonically disperse it evenly to obtain a CNT-confined Fe2O3 suspension. The mass concentration of the CNT-confined Fe2O3 powder in the organic solvent is 1.25 mg / mL.

[0103] S8. The CNT-confined Fe2O3 suspension obtained in step S7 is used to form an active coating on the surface of a microporous filter membrane by vacuum filtration. The thickness of the active coating is 1 μm. Finally, the organic solvent on the surface of the active coating is removed by rinsing with ultrapure water. After drying at room temperature, the confined carbon film electrode is obtained.

[0104] Comparative Example 1 is the same as Example 1, except that the organic solvent in step S7 of Comparative Example 1 is ethanol.

[0105] Comparative Example 2 is the same as Example 1, except that the acid bath reflux step in Comparative Example 2 is as follows:

[0106] Multi-walled carbon nanotubes and concentrated nitric acid were added to a reactor and refluxed and stirred for 5 hours. The acid bath reflux temperature was 5 hours to obtain carboxylated carbon nanotubes. The volume-to-mass ratio of the multi-walled carbon nanotubes to concentrated nitric acid was 2 mg: 1 mL.

[0107] Performance testing

[0108] The confined carbon film electrodes obtained in Examples 1-3 and Comparative Example 1 of this invention were used to conduct degradation experiments on solutions containing acetaminophen. The experimental results are shown in Tables 1 and 2.

[0109] First, prepare the solution to be degraded by adding organic pollutants and sodium sulfate electrolyte to water and stirring until homogeneous. The mass concentration of the organic pollutants in the water is 5 mg / L, and the mass concentration of the sodium sulfate in the water is 50 mmol / L.

[0110] The confined carbon film electrodes obtained in Examples 1-3 of this invention are used as the cathodes of the water purification membrane electrode reactor, and the carbon fiber felt film electrode is used as the anode. The solution to be degraded is used as the electrolyte of the water purification membrane electrode reactor. The structure of the water purification membrane reactor is as shown in the appendix to the specification. Figure 3 As shown. The assembly structure of the membrane module in the water purification membrane reactor is as shown in the attached instruction manual. Figure 4 As shown, from top to bottom, the components are: PTFE gasket, stainless steel mesh, carbon fiber felt membrane electrode, PTFE gasket, PTFE filter membrane, confined carbon membrane electrode, titanium mesh, and PTFE gasket. The membrane module in the water purification membrane reactor is clamped by the top and bottom plates of the water purification membrane reactor. The diameter of the membrane module is 30mm.

[0111] The middle part of the top plate of the water purification membrane reactor contains a large cylindrical cavity and a small cylindrical cavity. The large cylindrical cavity is located above the small cylindrical cavity. The axis of the large cylindrical cavity coincides with that of the small cylindrical cavity. The adjacent end faces of the large cylindrical cavity and the small cylindrical cavity are tightly sealed to each other. The large cylindrical cavity and the small cylindrical cavity are integrally formed. A small hole is formed in the bottom end face of the large cylindrical cavity. The diameter of the small hole is 4 mm. The large cylindrical cavity and the small cylindrical cavity are in communication with each other through the small hole. The upper end of the small cylindrical cavity is open. The lower end of the small cylindrical cavity is open. Each horizontal cross section of the small cylindrical cavity along its axis is a hollow circle. The inner diameter of the hollow circle is equal to the diameter of the membrane assembly.

[0112] The bottom plate of the water purification membrane reactor is completely the same as the top plate of the water purification membrane reactor. The adjacent end faces of the small cylindrical cavities in the top plate and the bottom plate of the water purification membrane reactor are tightly sealed to each other. When installed, the centers of the adjacent end faces of the small cylindrical cavities in the top plate and the bottom plate of the water purification membrane reactor are collinear. The small cylindrical cavities in the top plate and the bottom plate of the water purification membrane reactor are tightly sealed to each other to form a sealed cavity. The filter membrane assembly is tightly sealed in the sealed cavity formed by the small cylindrical cavities in the top plate and the bottom plate of the water purification membrane reactor.

[0113] The membrane spacing between the cathode and the anode in the water purification membrane electrode reactor is 2.15 mm.

[0114] During the test, the anode and the cathode of the water purification membrane electrode reactor are connected to an external direct-current stabilized power supply. The voltage is 2 V. Under the action of forced convection mass transfer of the peristaltic pump, oxygen generated by the oxygen evolution reaction of the anode is transported to the limited carbon film electrode together with the electrolyte. H2O2 is generated by the two-electron oxygen reduction reaction at the cathode. Then, Fe3+ / Fe2+ is generated on the surface of the limited carbon film electrode. 1 O2. Non-radical substance 1 O2 can convert persistent organic pollutants acetaminophen in water into harmless small molecular substances such as carbon dioxide and water. During the experiment, the electrolyte continuously and continuously penetrates the membrane assembly from the cylindrical cavity of the top plate of the water purification membrane electrode reactor and is pumped into the cylindrical cavity of the bottom plate of the water purification membrane electrode reactor. The flow rate of the electrolyte is 4 mL / min. The volume of the electrolyte treated by the water purification membrane electrode reactor is 200 mL. The degradation effect of the water purification membrane electrode reactor obtained in Examples 1-3 on acetaminophen is shown in the accompanying drawings. Figure 5

[0115] Comparative Example 3 is the same as Example 1, except that no external electric field is applied during the test of Comparative Example 3.

[0116] The calculation formula of the degradation rate of acetaminophen in the electrolyte is as follows:

[0117] ​Degradation rate (%) = ((initial mass concentration of acetaminophen - mass concentration of acetaminophen after treatment) / initial mass concentration of acetaminophen) x 100%.

[0118] Table 1

[0119] Test item Degradation rate (%), paracetamol Example 1 97.4 Example 2 50.2 Example 3 64.9 Comparative Example 1 81.6 Comparative Example 2 48.5 Comparative Example 3 12.4

[0120] Table 2

[0121] Test item Degradation rate (%), methylene blue Example 1 100％ Example 2 76.2％ Example 3 83.6％ Comparative Example 1 86.5％ Comparative Example 2 88.8％ Comparative Example 3 20.3％

[0122] The above-described embodiments according to the present application are merely intended to illustrate the present application, and the related skilled in the art can make various changes and modifications without departing from the technical idea of the present application. The technical scope of the present application is not limited to the above-described embodiments, and must be determined by the scope of the claims.

Claims

1. A confined carbon film electrode, characterized in that, It is a membrane electrode formed by depositing Fe2O3 / CNTs composite material on the surface of a microporous filter membrane. The Fe2O3 / CNTs composite material confines iron oxide nanoparticles on the hollow channel sidewall of carboxyl-functionalized CNTs. The iron oxide nanoparticles and the carboxyl groups on the hollow channel sidewall of CNTs form coordination chemical bonds. The preparation method of the Fe2O3 / CNTs composite material includes the following steps: S1, acid bath reflux. Carbon nanotubes are treated with acid to introduce carboxyl groups on their surface, resulting in carboxylated carbon nanotubes. S2. Centrifuge and wash with water until neutral. The carboxylated carbon nanotubes obtained in step S1 were centrifuged and washed in ultrapure water until neutral, and the obtained solid product was freeze-dried to obtain carboxylated carbon nanotube powder. S3. Obtain the iron precursor solution. Ferric nitrate was dispersed in 15-25 mL of acetone and ultrasonically dispersed to obtain an iron precursor solution, wherein the mass percentage of Fe in the iron precursor solution was 10%. S4. Obtain the carbon nanotube iron precursor solution. Add 200 mg of carboxylated carbon nanotube powder to the iron precursor solution and disperse and stir evenly; S5. Obtain iron-doped carbon nanotubes. The iron precursor solution of carbon nanotubes obtained in step S4 is stirred at room temperature to evaporate the solvent until the solvent is completely evaporated and only solid powder remains, thus obtaining iron-doped carbon nanotubes. S6. Place the iron-doped carbon nanotubes obtained in step S5 at 140-150℃ for 10-12 hours of forced air drying, and then grind them to the required particle size to obtain CNT-confined Fe2O3 powder. S7. Disperse the CNT-confined Fe2O3 powder obtained in step S6 in 40 mL of organic solvent and ultrasonically disperse it evenly to obtain a CNT-confined Fe2O3 suspension. The mass concentration of the CNT-confined Fe2O3 powder in the organic solvent is 1.25 ± 0.05 mg / mL. S8. The CNT-confined Fe2O3 suspension obtained in step S7 is used to form an active coating on the surface of a microporous filter membrane by vacuum filtration. The thickness of the active coating is 1-100 μm. Finally, the organic solvent on the surface of the active coating is removed by rinsing with ultrapure water. After drying at room temperature, the confined carbon film electrode is obtained. The acid bath reflux involves adding multi-walled carbon nanotubes and concentrated nitric acid to the reactor and refluxing and stirring for 12-14 hours. The organic solvent mentioned in step S7 includes at least one of N-methylpyrrolidone and ethanol.

2. The confined carbon film electrode according to claim 1, characterized in that, Step S1 is performed as follows: Multi-walled carbon nanotubes and concentrated nitric acid are added to a reactor and refluxed and stirred to obtain carboxylated carbon nanotubes. The volume-to-mass ratio of the multi-walled carbon nanotubes to concentrated nitric acid is 2 mg: 1 mL, and the reflux stirring temperature is 140-160 °C.

3. The confined carbon film electrode according to claim 1, characterized in that, In step S2, the freeze-drying temperature is -60℃ and the freeze-drying time is 18-24h.

4. A confined carbon film electrode according to claim 1, characterized in that, The average particle size of the CNT-confined Fe2O3 powder is 1-10 μm.

5. A confined carbon film electrode according to claim 1, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes.

6. A confined carbon film electrode according to claim 5, characterized in that, The number of coaxial layers of the multi-walled carbon nanotubes is 2-50.

7. A confined carbon film electrode according to claim 1, characterized in that, The thickness of the microporous filter membrane is 0.15±0.02mm.

8. A confined carbon film electrode according to claim 7, characterized in that, The microporous filter membrane has a porosity of 70-80% and a pore size of 0.45±0.05μm.

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