A nitrogen-doped composite carbon material for electro-catalytic oxidation treatment of medical wastewater and a preparation method and application thereof

Abstract

The application relates to a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater and a preparation method and application thereof, and belongs to the technical field of water treatment and carbon-based functional material. The preparation method comprises the following steps: S1, pretreating carbon nanotubes to obtain surface-activated carbon nanotubes; S2, mixing and dispersing coal pitch and the obtained surface-activated carbon nanotubes to prepare carbon nanotube / coal pitch composite precursors; S3, adding coal-based activated carbon and a nitrogen source into the carbon nanotube / coal pitch composite precursors, and uniformly mixing to obtain a composite mixture; S4, drying and pretreating the composite mixture; S5, pre-oxidizing the material treated in the step S4; S6, carbonizing the material treated in the step S5 under an inert atmosphere; and S7, activating the carbonized material to obtain the nitrogen-doped composite carbon material. The nitrogen-doped composite carbon material is applied to electrocatalytic oxidation removal of antibiotic pollutant wastewater.

Description

Technical Field

[0001] This invention belongs to the field of water treatment and carbon-based functional materials technology, specifically relating to a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, its preparation method, and its application. Background Technology

[0002] With the widespread use of antibiotics in medical, aquaculture, and pharmaceutical fields, the residues of antibiotic pollutants such as tetracycline, oxytetracycline, chlortetracycline, doxycycline, sulfonamides, and quinolones in medical wastewater, pharmaceutical wastewater, and aquaculture wastewater are becoming increasingly prominent. These pollutants typically possess stable molecular structures, are difficult to biodegrade, and have strong environmental persistence. If discharged directly into water bodies without effective treatment, they can easily lead to the accumulation of ecotoxicity and may induce the spread of drug-resistant bacteria and genes. Therefore, developing efficient, stable, and cost-effective antibiotic pollutant removal technologies is of great significance.

[0003] Currently, treatment methods for antibiotic-contaminated wastewater mainly include biological methods, adsorption methods, membrane separation methods, and advanced oxidation methods. Among these, biological methods are easily affected by the antibacterial effect of antibiotics, limiting their treatment efficiency; membrane separation methods, while possessing high retention capacity, suffer from severe membrane fouling and high operating costs; adsorption alone can achieve pollutant enrichment, but it essentially involves phase transfer of pollutants and is difficult to achieve complete degradation. Therefore, electrocatalytic oxidation technology, which can simultaneously achieve pollutant enrichment and in-situ degradation, is gradually gaining attention.

[0004] Carbon-based materials, due to their wide availability, good chemical stability, tunable conductivity, and easily controllable surface structure, have promising applications in wastewater treatment and electrochemistry. Existing patents demonstrate that carbon nanotubes can form composite precursors with coal tar pitch. Ultrasonic dispersion and heat treatment can improve the conductivity and structural properties of the resulting carbon materials, leading to carbon materials with good thermal conductivity, electrical conductivity, and reinforcing effects, which can be extended to applications such as electrodes. On the other hand, coal tar pitch, as a residue from coal tar distillation, features high carbon yield and low impurity content, making it a porous carbon precursor with application potential. In existing technologies, coal tar pitch can be pre-oxidized, carbonized, and activated to prepare porous carbon materials or spherical activated carbon, which can then be used in water treatment, for example, as a pollutant adsorption carrier or a substrate for composite catalytic materials. Related patents have shown that coal tar pitch-based spherical activated carbon composite materials can effectively adsorb suspended solids and pollutants in water, demonstrating a good foundation for applications in water treatment.

[0005] However, existing technologies still have some shortcomings. First, coal tar pitch molecules contain many polycyclic aromatic hydrocarbons, which easily accumulate during pyrolysis, hindering the formation of a well-developed porous structure. Simultaneously, due to the inherent viscosity of pitch particles, agglomeration easily occurs during traditional heat treatment, leading to incomplete pre-oxidation and further causing problems such as high-temperature foaming, structural damage, and decreased carbonization yield. Second, while single coal-based activated carbon possesses a high specific surface area and certain adsorption capacity, its use as an electrocatalytic oxidation electrode material still suffers from defects such as discontinuous conductive networks, limited electron transport efficiency, and insufficient interfacial active sites, making it difficult to balance pollutant enrichment capacity with electrocatalytic reaction efficiency. Third, existing composite materials based on coal tar pitch or activated carbon are mostly concentrated in adsorption, photocatalysis, energy storage, or structural materials, with relatively insufficient research on ternary composite electrocatalytic materials of carbon nanotubes / coal tar pitch / coal-based activated carbon for treating medical wastewater or antibiotic-contaminated wastewater.

[0006] Therefore, there is an urgent need to develop a composite carbon material that combines high conductivity, hierarchical porous structure, good structural stability and abundant surface active sites to achieve efficient adsorption and enrichment of medical wastewater or antibiotic-contaminated wastewater and synergistic removal by electrocatalytic oxidation. Summary of the Invention

[0007] The purpose of this invention is to provide a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, its preparation method, and its application, aiming to solve the following problems: ① Although existing single activated carbon materials have high specific surface area and certain pollutant adsorption capacity, their conductivity is relatively limited. When used as electrode materials for electrocatalytic oxidation, the electron transport path is discontinuous, making it difficult to fully meet the requirements of rapid charge transfer and efficient interfacial reaction. ② During the heat treatment process, existing coal tar pitch-based porous carbon materials are prone to agglomeration due to the stickiness of the pitch particles, leading to incomplete pre-oxidation and foaming at high temperatures, causing damage to the pore and crystal structures and reducing the carbonization yield. ③ Although existing carbon nanotube / pitch composite technology can improve conductivity and structural uniformity, most applications are concentrated in structural materials, energy storage materials, or thermal conductivity enhancement materials, and have not yet been combined with the porous adsorption function and nitrogen-containing active site regulation of coal-based activated carbon, making it difficult to simultaneously achieve pollutant adsorption and enrichment, rapid electron transport, and enhanced surface catalytic activity. ④ Existing water treatment composite materials based on coal tar pitch spherical activated carbon mostly focus on adsorption, sterilization or photocatalysis. For the electrocatalytic oxidation removal of medical wastewater or antibiotic pollutant wastewater, there is still a lack of a composite carbon material system that combines high conductivity, hierarchical porous structure, good stability and abundant active sites.

[0008] The preparation method of this invention includes mixing and dispersing pretreated carbon nanotubes with coal tar pitch to obtain a composite precursor, then adding coal-based activated carbon and a nitrogen source and mixing evenly. Following drying, pretreatment, pre-oxidation, inert atmosphere carbonization, and activation treatment, a nitrogen-doped composite carbon material is obtained. The prepared nitrogen-doped composite carbon material combines the conductive network of carbon nanotubes, the structural stability of coal tar pitch-derived carbon, and the porous adsorption characteristics of coal-based activated carbon. It also possesses nitrogen-containing active sites formed by the pyrolysis of the nitrogen source, effectively improving electron transport capacity, pollutant enrichment capacity, and surface reactivity. This composite carbon material can be used as an electrocatalytic oxidation electrode material for the treatment of medical wastewater or antibiotic-contaminated wastewater, achieving synergistic degradation through adsorption enrichment and electrocatalytic oxidation. The method is simple, uses readily available raw materials, and has low cost, showing promising application prospects.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater includes the following steps:

[0011] S1. Pre-treat carbon nanotubes to obtain surface-activated carbon nanotubes;

[0012] S2. Coal tar pitch is mixed and dispersed with the obtained surface-activated carbon nanotubes to prepare a carbon nanotube / coal tar pitch composite precursor.

[0013] S3. Add coal-based activated carbon and nitrogen source to the carbon nanotube / coal tar pitch composite precursor, and mix evenly to obtain a composite mixture.

[0014] S4. The composite mixture is dried and pretreated.

[0015] S5. Pre-oxidize the material after step S4.

[0016] S6. The material processed in step S5 is carbonized under an inert atmosphere.

[0017] S7. The carbonized material is activated to obtain nitrogen-doped composite carbon material.

[0018] Further, in step S1, the pretreatment of the carbon nanotubes is acid oxidation treatment, and the acid used is one or more of the following: nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid; the acid oxidation treatment temperature is 50-90℃, and the treatment time is 2-8 h; after acid oxidation treatment, the obtained carbon nanotubes are washed until neutral and then vacuum dried at 60-120℃ for 6-24 h to obtain surface-activated carbon nanotubes.

[0019] Further, in step S2, the mass ratio of coal tar pitch to carbon nanotubes is 100:(1-20); the carbon nanotubes are one or a combination of two or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes; the dispersion is achieved by one or a combination of two or more of ultrasonic dispersion, mechanical stirring, and ball milling; the dispersion medium used is one or a combination of two or more of ethanol, water, acetone, and N,N-dimethylformamide; and the amount of dispersion medium added is 5-30 mL / g based on the total mass of coal tar pitch and carbon nanotubes.

[0020] Further, in step S3, based on 100 parts by mass of coal tar pitch, the amount of coal-based activated carbon added is 20-200 parts by mass, and the amount of nitrogen source added is 10-100 parts by mass. The nitrogen source is one or a combination of two or more of melamine, urea, dicyandiamide, cyanamide, ammonium salt compounds, nitrogen-containing small organic molecule compounds, and nitrogen-containing conductive polymers; wherein the nitrogen-containing conductive polymer is polyaniline and / or polypyrrole.

[0021] Further, in step S4, the drying temperature is 60-120℃ and the drying time is 4-24 h; the pretreatment is carried out under an inert atmosphere, the pretreatment temperature is 180-300℃ and the holding time is 0.5-5 h.

[0022] Further, in step S5, the pre-oxidation treatment is carried out in an oxidizing atmosphere, the pre-oxidation temperature is 200-320℃, and the pre-oxidation time is 2-12 h; the oxidizing atmosphere is air, oxygen, or a mixture of air and oxygen.

[0023] Further, in step S6, the carbonization process is carried out in a segmented heating manner: first, the temperature is raised to 350-500℃ at a heating rate of 1-10℃ / min and held for 0.5-3 h, then the temperature is raised to 600-1000℃ at a heating rate of 1-10℃ / min and held for 0.5-5 h; the inert atmosphere is nitrogen, argon, or a mixture of the two.

[0024] Further, in step S7, the activation treatment is physical activation or chemical activation; the physical activation is carbon dioxide activation or steam activation, the activation temperature is 700-1000℃, the activation time is 0.5-10 h, and after physical activation, it is cooled to room temperature; the chemical activator is potassium hydroxide or potassium carbonate, the mass ratio of the chemical activator to the carbonized material is (0.5-4):1, the chemical activation temperature is 600-900℃, the chemical activation time is 0.5-5 h, after chemical activation, it is washed sequentially with 0.05-1.0 mol / L hydrochloric acid and deionized water until neutral, and dried at 60-120℃ for 6-24 h.

[0025] The present invention also provides a nitrogen-doped composite carbon material, which is prepared by the above-described preparation method; the one-dimensional conductive network composed of carbon nanotubes and the coal tar pitch-derived carbon skeleton are interwoven to form a conductive pathway, the coal-based activated carbon provides a microporous and / or mesoporous structure, and the material surface contains nitrogen-doped active sites that are decomposed by the nitrogen source and introduced into the carbon skeleton surface during the carbonization process, and the final carbonization temperature of the carbonization process is 600-1000℃.

[0026] The present invention also provides the application of the above-mentioned nitrogen-doped composite carbon material in the electrocatalytic oxidation treatment of medical wastewater or antibiotic-contaminated wastewater. The composite carbon material can be used as an anode active layer, a three-dimensional particle electrode filler, a supported electrode active component, or a conductive reaction medium.

[0027] The advantages of this invention over the prior art are:

[0028] 1. It possesses dual functions of adsorption enrichment and electrocatalytic oxidation. This invention introduces coal-based activated carbon into a composite system, giving the material a high specific surface area and abundant pore structure. It can first adsorb and enrich antibiotic pollutant molecules, and then achieve in-situ degradation through electrocatalytic oxidation, thereby overcoming the shortcomings of single adsorption methods that only achieve pollutant transfer.

[0029] 2. Excellent conductive network and high electron transport efficiency. This invention introduces carbon nanotubes to construct a continuous conductive network, which can effectively reduce the resistance to charge transfer inside the material and improve the problem of insufficient conductivity of traditional activated carbon electrodes.

[0030] 3. Good structural stability and high carbonization yield. This invention incorporates pretreatment and pre-oxidation steps, which can effectively alleviate the problems of adhesion, agglomeration, melting and foaming of coal tar pitch during high-temperature heat treatment, improve carbonization yield and maintain the integrity of the porous structure.

[0031] 4. Abundant surface active sites. This invention utilizes a nitrogen source to achieve in-situ nitrogen doping during heat treatment, which can introduce a variety of nitrogen-containing active sites on the surface of composite carbon materials, improve the electronic structure and enhance interfacial reactivity, thereby facilitating the electrocatalytic oxidation degradation of antibiotic pollutants.

[0032] 5. The process is simple, raw materials are widely available, and it is easy to promote. This invention uses coal tar pitch, coal-based activated carbon, carbon nanotubes, and a nitrogen source as the main raw materials, which are readily available. The preparation process mainly includes dispersion and compounding, drying pretreatment, pre-oxidation, carbonization, and activation. The required equipment can be conventional stirring devices, drying equipment, and controlled atmosphere heat treatment equipment. The process route is clear, the operating conditions are adjustable, and it is easy to carry out batch preparation and engineering scale-up. It also has the potential for application in the electrocatalytic oxidation treatment of medical wastewater or antibiotic-related pollutant wastewater.

[0033] In summary, the preparation method of nitrogen-doped composite carbon material (nitrogen-doped carbon nanotube / coal tar pitch / coal-based activated carbon composite carbon material) provided by this invention can effectively solve the problems of insufficient conductivity, poor structural stability and limited active sites of existing carbon-based electrocatalytic materials, and has good application value in the electrocatalytic oxidation removal of medical wastewater or antibiotic pollutant wastewater. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 The image shows a SEM image of the nitrogen-doped composite carbon material prepared using the method of the present invention.

[0036] Figure 2 The image shows an HRTEM image of a nitrogen-doped composite carbon material prepared using the method of this invention.

[0037] Figure 3 The diagram shows the adsorption capacity of the nitrogen-doped composite carbon material prepared using the preparation method of the present invention.

[0038] Figure 4 The pore size diagram is shown for the nitrogen-doped composite carbon material prepared using the preparation method of the present invention.

[0039] Figure 5 The image shows the CV diagram of the nitrogen-doped composite carbon material prepared using the preparation method of the present invention.

[0040] Figure 6 The image shows the LSV diagram of the nitrogen-doped composite carbon material prepared using the preparation method of the present invention.

[0041] Figure 7 This is a flowchart of the preparation method of the nitrogen-doped composite carbon material of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. However, it should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention. All equivalent substitutions, improvements, and variations made within the spirit and principles of this invention should fall within the scope of protection of this invention.

[0043] Specific implementation method one: as follows Figure 7As shown, this embodiment discloses a method for preparing a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, including the following steps:

[0044] S1. Pre-treat carbon nanotubes to obtain surface-activated carbon nanotubes. The pre-treatment method for the carbon nanotubes is acid oxidation treatment, using one or more of the following acids: nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid; the acid oxidation treatment temperature is 50-90℃, and the treatment time is 2-8 h; preferably, the acid oxidation treatment temperature is 60-70℃, and the treatment time is 3-5 h. After acid oxidation treatment, the obtained carbon nanotubes are washed until neutral and then vacuum dried at 60-120℃ for 6-24 h to obtain surface-activated carbon nanotubes.

[0045] S2. Coal tar pitch is mixed and dispersed with the obtained surface-activated carbon nanotubes to prepare a carbon nanotube / coal tar pitch composite precursor. The mass ratio of coal tar pitch to carbon nanotubes is 100:(1-20), preferably 100:(5-15). The carbon nanotubes are one or a combination of two or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes; the dispersion is achieved by one or a combination of two or more of ultrasonic dispersion, mechanical stirring, and ball milling; the dispersion medium is one or a combination of two or more of ethanol, water, acetone, and N,N-dimethylformamide. The amount of dispersion medium added is 5-30 mL / g, preferably 10-25 mL / g, based on the total mass of coal tar pitch and carbon nanotubes.

[0046] S3. Add coal-based activated carbon and a nitrogen source to the carbon nanotube / coal tar pitch composite precursor, and mix evenly to obtain a composite mixture. Based on 100 parts by weight of coal tar pitch, the amount of coal-based activated carbon added is 20-200 parts by weight, and the amount of nitrogen source added is 10-100 parts by weight. The nitrogen source is one or a combination of two or more of melamine, urea, dicyandiamide, cyanamide, ammonium salt compounds, nitrogen-containing small organic molecule compounds, and nitrogen-containing conductive polymers; wherein the nitrogen-containing conductive polymer is polyaniline and / or polypyrrole.

[0047] Preferably, the nitrogen source is one or a combination of two or more of melamine, urea, and dicyandiamide; preferably, based on 100 parts by weight of coal tar pitch, the amount of coal-based activated carbon added is 40-150 parts by weight, and the amount of nitrogen source added is 20-60 parts by weight.

[0048] S4. The composite mixture is dried and pretreated. The drying temperature is 60-120℃ and the drying time is 4-24 h; the pretreatment is carried out in an inert atmosphere (such as nitrogen atmosphere), the pretreatment temperature is 180-300℃ and the holding time is 0.5-5 h.

[0049] S5. The material processed in step S4 is subjected to pre-oxidation treatment. The pre-oxidation treatment is carried out in an oxidizing atmosphere, the pre-oxidation temperature is 200-320℃, and the pre-oxidation time is 2-12 h; the oxidizing atmosphere is air, oxygen, or a mixture of air and oxygen.

[0050] S6. The material processed in step S5 is carbonized under an inert atmosphere. The carbonization process is carried out in a segmented heating manner: first, the temperature is increased to 350-500℃ at a heating rate of 1-10℃ / min and held for 0.5-3 h, then the temperature is increased to 600-1000℃ at a heating rate of 1-10℃ / min and held for 0.5-5 h; the inert atmosphere is nitrogen, argon, or a mixture of the two.

[0051] S7. The carbonized material is activated to obtain nitrogen-doped composite carbon material (nitrogen-doped carbon nanotube / coal tar pitch / coal-based activated carbon composite carbon material). The activation treatment is physical activation or chemical activation; the physical activation is carbon dioxide activation or steam activation, the activation temperature is 700-1000℃, the activation time is 0.5-10 h, and the material is cooled to room temperature after physical activation; the chemical activator is potassium hydroxide or potassium carbonate, the mass ratio of the chemical activator to the carbonized material is (0.5-4):1, the chemical activation temperature is 600-900℃, the chemical activation time is 0.5-5 h, and after chemical activation, the material is washed sequentially with 0.05-1.0 mol / L hydrochloric acid and deionized water until neutral, and then dried at 60-120℃ for 6-24 h.

[0052] Specific Implementation Method 2: This implementation method discloses a nitrogen-doped composite carbon material. The composite carbon material is prepared by the preparation method described in Specific Implementation Method 1. The one-dimensional conductive network composed of carbon nanotubes is interwoven with the coal tar pitch-derived carbon skeleton to form a conductive pathway. Coal-based activated carbon provides microporous and / or mesoporous structures. The material surface contains nitrogen-doped active sites that are decomposed by the nitrogen source and introduced into the carbon skeleton surface during the carbonization process.

[0053] Specific Implementation Method 3: This implementation method discloses the application of the nitrogen-doped composite carbon material described in Specific Implementation Method 2 in the electrocatalytic oxidation treatment of medical wastewater or antibiotic-contaminated wastewater. The composite carbon material is used as an anode active layer, a three-dimensional particle electrode filler, a supported electrode active component, or a conductive reaction medium.

[0054] Medical wastewater or antibiotic-contaminated wastewater refers to wastewater that simulates antibiotics, pharmaceuticals, hospitals, livestock, or mixed organic wastewater containing antibiotic-contaminated pollutants. The antibiotic-contaminated pollutants include one or more of tetracycline, oxytetracycline, chlortetracycline, doxycycline, sulfonamides, and quinolones. Under the action of an external electric field, the composite carbon material degrades antibiotic-contaminated pollutants through the synergistic effect of adsorption enrichment and electrocatalytic oxidation.

[0055] Furthermore, the composite carbon material, after being combined with a binder and / or conductive additive, is loaded onto the surface of a titanium plate, graphite felt, carbon cloth, nickel foam, graphite plate, or conductive ceramic substrate to form an electrode; the binder is one or a combination of two or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; the conductive additive is one or a combination of two or more of acetylene black, conductive carbon black, graphite powder, and carbon nanotubes.

[0056] Furthermore, when the composite carbon material is used for electrocatalytic oxidation treatment of medical wastewater or antibiotic-contaminated wastewater, it combines the functions of pollutant adsorption and enrichment, rapid electron transfer, and enhanced surface reactivity to achieve efficient degradation of antibiotic-contaminated pollutants.

[0057] Specific implementation method four: such as Figure 7 As shown, this embodiment discloses a method for preparing a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, including the following steps:

[0058] S1, Carbon nanotube pretreatment

[0059] First, the carbon nanotubes undergo surface pretreatment to improve their dispersibility, surface activity, and compatibility with the coal tar pitch system. Preferably, an acidification treatment is used to introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups onto the surface of the carbon nanotubes, thereby enhancing their dispersion performance in the liquid phase system and promoting their interfacial bonding with coal tar pitch and coal-based activated carbon.

[0060] S2. Preparation of carbon nanotube / coal tar composite precursor

[0061] Coal tar pitch and pretreated carbon nanotubes are mixed at a mass ratio of 100:(1-20), preferably 100:(5-15), and dispersed in a dispersion medium to obtain a uniform carbon nanotube / coal tar pitch dispersion system. The dispersion medium is one or a combination of two or more of ethanol, water, acetone, and N,N-dimethylformamide; the amount of dispersion medium added is 5-30 mL / g, preferably 10-25 mL / g, based on the total mass of coal tar pitch and carbon nanotubes. The dispersion treatment can be achieved by one or a combination of two or more of ultrasonic dispersion, mechanical stirring, and ball milling; preferably, the ultrasonic dispersion time is 0.5-6 h, the mechanical stirring time is 0.5-6 h, and the ball milling time is 0.5-8 h. After dispersion, the dispersion medium is removed by vacuum distillation, heating to remove the solvent, or vacuum drying to obtain the carbon nanotube / coal tar pitch composite precursor.

[0062] S3, Introducing coal-based activated carbon and nitrogen source

[0063] Coal-based activated carbon and a nitrogen source are added to the above-mentioned carbon nanotube / coal tar composite precursor, and the mixture is thoroughly and uniformly mixed by ball milling, mechanical stirring, grinding, or wet dispersion to obtain a composite mixture. Based on 100 parts by weight of coal tar, the amount of coal-based activated carbon added is 20-200 parts by weight, and the amount of nitrogen source added is 10-100 parts by weight; preferably, the amount of coal-based activated carbon added is 40-150 parts by weight, and the amount of nitrogen source added is 20-60 parts by weight.

[0064] Coal-based activated carbon is used to provide a well-developed pore structure and a high specific surface area to enhance the adsorption and enrichment capacity for antibiotic pollutant molecules. A nitrogen source is used to introduce nitrogen-containing active sites such as pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen during subsequent carbonization treatment to improve the surface electronic structure and interfacial reactivity of the composite carbon material. The nitrogen source is one or a combination of two or more of melamine, urea, dicyandiamide, cyanamide, ammonium salt compounds, nitrogen-containing small organic molecule compounds, and nitrogen-containing conductive polymers; wherein the nitrogen-containing conductive polymer is polyaniline and / or polypyrrole. Preferably, the nitrogen source is one or a combination of two or more of melamine, urea, and dicyandiamide.

[0065] The mixing method can be selected according to the state of the material. When using ball milling, the ball milling speed can be 100-500 rpm and the ball milling time can be 0.5-8 h; when using mechanical stirring, the stirring time can be 0.5-6 h; when using grinding, the grinding time can be 0.5-3 h; when using wet dispersion, ethanol, water or a mixture thereof can be added as an auxiliary dispersion medium, and after mixing evenly, the auxiliary dispersion medium can be removed by drying.

[0066] S4. Drying and Pretreatment

[0067] The composite mixture is dried to remove the dispersion medium from the system. The drying temperature is 60-120℃, and the drying time is 4-24 h. Preferably, after drying, the resulting material is placed under an inert atmosphere for low-temperature pretreatment, wherein the inert atmosphere is nitrogen, argon, or a mixture of both; the low-temperature pretreatment temperature is 180-300℃, and the holding time is 0.5-5 h. Through drying and low-temperature pretreatment, residual dispersion medium and low-boiling-point components can be further removed, the mixing uniformity between carbon nanotubes, coal tar pitch, coal-based activated carbon, and nitrogen source can be improved, and a more stable precursor system can be provided for subsequent pre-oxidation treatment.

[0068] S5, Pre-oxidation treatment

[0069] The dried and pretreated material is placed in an oxidizing atmosphere for pre-oxidation treatment, wherein the oxidizing atmosphere is air, oxygen, or a mixture of air and oxygen; the pre-oxidation temperature is 200-320℃, and the pre-oxidation time is 2-12 h. Preferably, the pre-oxidation temperature is 250-280℃, and the pre-oxidation time is 5-8 h. Through pre-oxidation treatment, the coal tar pitch undergoes non-melting cross-linking, inhibiting melting flow, agglomeration, and foaming phenomena in the subsequent high-temperature carbonization stage, thereby improving the carbonization yield and helping to maintain a more complete porous structure and composite skeleton stability.

[0070] S6, carbonization treatment

[0071] The pre-oxidized material is placed in an inert atmosphere for carbonization treatment, wherein the inert atmosphere is nitrogen, argon, or a mixture of both. The carbonization treatment is preferably carried out using a staged heating method: first, the temperature is increased to 350-500℃ at a heating rate of 1-10℃ / min and held for 0.5-3 h to promote the slow release of low-molecular-weight volatiles and reduce the risk of cracking, foaming, and structural damage during high-temperature treatment; then, the temperature is further increased to 600-1000℃ at a heating rate of 1-10℃ / min and held for 0.5-5 h to fully carbonize the coal tar pitch and form a coal tar pitch-derived carbon skeleton, while simultaneously introducing nitrogen-containing species generated from the decomposition of the nitrogen source onto the surface of the carbon skeleton, forming nitrogen-doped active sites.

[0072] During carbonization, the one-dimensional conductive network formed by carbon nanotubes intertwines with the coal tar pitch-derived carbon framework, and together with coal-based activated carbon, forms a stable composite conductive framework. This composite structure is beneficial for improving the electron transport capability and structural stability of the material, and provides a basis for constructing a hierarchical porous structure in subsequent activation treatment. The holding temperature stage of 350-500℃ is an intermediate stabilization stage and is not considered the final carbonization temperature; the holding temperature stage of 600-1000℃ is the final carbonization stage, used to form a stable composite carbon framework and nitrogen-doped structure.

[0073] S7, Activation Treatment

[0074] The carbonized material is further activated to construct a more developed microporous, mesoporous, or hierarchical pore structure, thereby improving the material's specific surface area, pore volume, and contaminant enrichment capacity. The activation treatment employs either physical or chemical activation. Physical activation is performed using carbon dioxide or steam, at an activation temperature of 700-1000℃ and an activation time of 0.5-10 h. During physical activation, carbon dioxide or steam etches and expands the carbon framework at high temperatures, resulting in a richer pore structure within the material. After physical activation, the obtained material is cooled to room temperature and optionally washed with deionized water and dried.

[0075] The chemical activator is potassium hydroxide or potassium carbonate, and the mass ratio of the chemical activator to the carbonized material is (0.5-4):1. The chemical activation temperature is 600-900℃, and the chemical activation time is 0.5-5 h. After chemical activation, the material is washed sequentially with 0.05-1.0 mol / L hydrochloric acid and deionized water until neutral to remove residual inorganic salts, alkaline components, and soluble impurities. Then, it is dried at 60-120℃ for 6-24 h to obtain nitrogen-doped composite carbon material.

[0076] Through activation treatment, the pore structure in the material is further opened, and a synergistic effect is formed between the one-dimensional conductive network of carbon nanotubes, the carbon skeleton derived from coal tar pitch and the porous structure of coal-based activated carbon, which is conducive to improving the adsorption and enrichment capacity of pollutants, electrolyte wettability and interfacial reactivity.

[0077] Specific Embodiment Five: This embodiment discloses a method for constructing an electrode using a nitrogen-doped composite carbon material prepared by the method described in Specific Embodiment Four. The obtained nitrogen-doped composite carbon material is mixed with a binder and / or a conductive additive to form an electrode slurry or electrode mixture, which is then loaded onto the surface of a conductive substrate to obtain an electrocatalytic oxidation electrode.

[0078] The binder is one or a combination of two or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; the conductive additive is one or a combination of two or more of acetylene black, conductive carbon black, graphite powder, and carbon nanotubes; the conductive substrate is a titanium plate, graphite felt, carbon cloth, nickel foam, graphite plate, or conductive ceramic substrate.

[0079] Preferably, the mass ratio of the nitrogen-doped composite carbon material, the conductive additive, and the binder is (85-98):(0-10):(2-10); more preferably, it is (90-95):(3-5):5. When the conductive matrix itself has good conductivity and no additional conductive additive is needed, the mass ratio of the nitrogen-doped composite carbon material to the binder is (90-98):(2-10).

[0080] The electrode slurry's flowability can be adjusted by adding one or more of N-methylpyrrolidone, water, and ethanol in a mixture. The solvent content is 1-10 mL / g, based on the total mass of the nitrogen-doped composite carbon material, conductive additive, and binder. The electrode slurry can be loaded onto the conductive substrate surface by scraping, dripping, dipping, spraying, or rolling. After loading, it is dried at 60-120℃ for 4-24 h, and if necessary, pressed into a tablet to obtain the electrocatalytic oxidation electrode.

[0081] The electrocatalytic oxidation electrode can be used as an anode for the electrocatalytic oxidation treatment of medical wastewater or antibiotic-contaminated wastewater. Under the action of an external electric field, the one-dimensional conductive network of carbon nanotubes in the nitrogen-doped composite carbon material promotes electron transfer, the coal tar pitch-derived carbon framework helps maintain the stability of the electrode structure, the porous structure of coal-based activated carbon facilitates the adsorption and enrichment of pollutants, and the nitrogen-doped active sites enhance interfacial reactivity, thereby achieving the electrocatalytic oxidation degradation of antibiotic-contaminated pollutants.

[0082] Specific Implementation Method Six: This implementation method discloses the application of a nitrogen-doped composite carbon material prepared by the preparation method described in Specific Implementation Method Four as a three-dimensional particle electrode filler in an electrocatalytic oxidation reaction system.

[0083] When the nitrogen-doped composite carbon material is used to treat medical wastewater or antibiotic-contaminated wastewater, it can fill the space between the cathode and anode of a three-dimensional electrode reaction system and participate in electrocatalytic oxidation reactions as a conductive reaction medium or a three-dimensional particle electrode filler under an applied electric field. The microporous and / or mesoporous structure provided by coal-based activated carbon can adsorb and enrich antibiotic-contaminated pollutant molecules, the one-dimensional conductive network formed by carbon nanotubes can promote rapid electron transfer, and the coal tar pitch-derived carbon skeleton helps enhance the structural stability of the composite material. Simultaneously, the nitrogen-doped active sites introduced onto the carbon skeleton surface by the decomposition of the nitrogen source during carbonization can improve the electronic structure of the material surface and enhance interfacial reactivity.

[0084] Through the synergistic effect of adsorption enrichment, electron transfer and enhanced surface reactivity, the nitrogen-doped composite carbon material can promote the electrocatalytic oxidative degradation of target pollutants in medical wastewater or antibiotic wastewater.

[0085] Example 1

[0086] This embodiment discloses a method for preparing a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, comprising the following steps:

[0087] S1. Raw material pretreatment

[0088] Two g of multi-walled carbon nanotubes were added to 200 mL of a mixed acid solution, which was a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1; wherein the mass fraction of concentrated sulfuric acid was 95%-98% and the mass fraction of concentrated nitric acid was 65%-68%; and then the mixture was stirred and acidified at 60 °C for 4 h. After the reaction was completed, the mixture was repeatedly washed with deionized water until neutral, and then vacuum dried at 80 °C for 12 h to obtain the pretreated carbon nanotubes.

[0089] Preparation of S2, carbon nanotube / coal tar composite precursor

[0090] 20 g of coal tar pitch was mixed with the pretreated carbon nanotubes obtained in step S1 and added to 400 mL of anhydrous ethanol. After ultrasonic dispersion for 3 h, mechanical stirring was continued for 1 h to obtain a uniform suspension. The resulting suspension was then transferred to a vacuum distillation apparatus to remove ethanol at 110 °C. After natural cooling to room temperature, the mixture was pulverized and ground to obtain the carbon nanotube / coal tar pitch composite precursor.

[0091] S3, introduction of coal-based activated carbon and nitrogen source

[0092] 24 g of coal-based activated carbon and 8 g of melamine were added to the carbon nanotube / coal tar composite precursor obtained in step S2 and mixed evenly by ball milling at a speed of 300 rpm for 4 h to obtain a composite mixture. Melamine was used as a nitrogen source to introduce nitrogen-doped active sites during subsequent heat treatment.

[0093] S4. Drying and Pretreatment

[0094] The composite mixture obtained in step S3 was dried in a 90℃ drying oven for 10 h, and then transferred to a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 220℃ at a heating rate of 3℃ / min and held for 2 h to obtain the pretreated sample.

[0095] S5, Pre-oxidation treatment

[0096] The sample obtained in step S4 was placed in an air atmosphere and heated to 260°C at a heating rate of 2°C / min, held at that temperature for 6 hours, and then naturally cooled to room temperature to obtain a pre-oxidized sample.

[0097] S6, carbonization treatment

[0098] The pre-oxidized sample obtained in step S5 was placed in a tube furnace and heated to 450°C at a heating rate of 3°C / min and held for 1 h under the protection of high-purity nitrogen. Then, it was heated to 800°C at a heating rate of 3°C / min and held for 2 h. After cooling, the carbonized product was obtained.

[0099] S7, Activation Treatment

[0100] The carbonized product obtained in step S6 was activated at 850°C for 1.5 h in a CO2 atmosphere. After activation, it was naturally cooled to room temperature to obtain a nitrogen-doped carbon nanotube-coal tar pitch-coal-based activated carbon composite carbon material, which is referred to as the composite carbon material of Example 1.

[0101] The morphology and pore structure of the composite carbon material from Example 1 were characterized. Figure 1 It is evident that the obtained nitrogen-doped composite carbon material exhibits a relatively loose porous structure, which is beneficial for increasing the contact area between the material and pollutant molecules in wastewater. Figure 2 It is evident that the material possesses a carbonaceous framework and porous structure, indicating the formation of a composite carbon structure among carbon nanotubes, coal tar pitch-derived carbon, and coal-based activated carbon. Figure 3 It is evident that the obtained nitrogen-doped composite carbon material exhibits significant nitrogen adsorption-desorption behavior, indicating a rich porous structure within the material. Figure 4 It is evident that the obtained nitrogen-doped composite carbon material has a certain pore size distribution, indicating that the activation treatment can further open the pores and improve the accessibility of the pore structure of the material, which is beneficial to the adsorption, enrichment and mass transfer diffusion of antibiotic pollutants.

[0102] S8, Electrode Preparation

[0103] Take 0.90 g of the obtained composite carbon material, 0.05 g of acetylene black and 0.05 g of polyvinylidene fluoride, add them to 3 mL of N-methylpyrrolidone and stir to form a uniform slurry. Coat the obtained slurry uniformly onto the surface of the pretreated titanium plate and dry it at 80 °C for 10 h. Then, perform a pressing process to obtain the composite carbon electrode.

[0104] Example 2

[0105] This embodiment discloses a method for preparing a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, comprising the following steps:

[0106] S1. Raw material pretreatment

[0107] 3 g of multi-walled carbon nanotubes were added to 250 mL of 5% (w / w) dilute nitric acid solution and stirred at 70 °C for 4 h. After treatment, the nanotubes were washed with deionized water until neutral and then dried under vacuum at 100 °C for 8 h to obtain pretreated carbon nanotubes.

[0108] Preparation of S2, carbon nanotube / coal tar composite precursor

[0109] 20 g of coal tar pitch was mixed with the pretreated carbon nanotubes obtained in step S1 and added to 420 mL of anhydrous ethanol. The mixture was ultrasonically dispersed for 3 h and mechanically stirred for 1 h to obtain a homogeneous mixture. The solvent was then removed by vacuum distillation at 110 °C. After cooling and pulverizing, the carbon nanotube / coal tar pitch composite precursor was obtained.

[0110] S3, introduction of coal-based activated carbon and nitrogen source

[0111] 18 g of coal-based activated carbon and 6 g of melamine were added to the composite precursor obtained in step S2, and 20 mL of anhydrous ethanol was added as an auxiliary dispersion medium. The mixture was ball-milled for 5 h to obtain the composite mixture. Melamine was used as a nitrogen source to form nitrogen-doped active sites.

[0112] S4. Drying and Pretreatment

[0113] The composite mixture obtained in step S3 was dried at 85°C for 12 h, and then heated to 200°C at a heating rate of 2°C / min under a nitrogen atmosphere and held for 1.5 h to obtain the pretreated sample.

[0114] S5, Pre-oxidation treatment

[0115] The sample obtained in step S4 was heated to 250°C in air at a rate of 2°C / min and held for 8 hours to obtain a pre-oxidized sample.

[0116] S6, carbonization treatment

[0117] The pre-oxidized sample obtained in step S5 was placed in a tube furnace under nitrogen protection and heated to 500°C at a heating rate of 3°C / min, held for 1 h, then heated to 850°C and held for 2 h. After cooling, the carbonized product was obtained.

[0118] S7, Activation Treatment

[0119] The carbonized product obtained in step S6 was mixed with potassium hydroxide at a mass ratio of 1:2. The mixture was heated to 750°C at a heating rate of 5°C / min under a nitrogen atmosphere and held at this temperature for 1 h. After activation, the mixture was washed sequentially with 0.1 mol / L hydrochloric acid and deionized water until neutral, and then dried at 105°C for 8 h to obtain the nitrogen-doped composite carbon material, which is referred to as the composite carbon material of Example 2.

[0120] S8, Electrode Preparation

[0121] The composite carbon material obtained in step S7 of Example 2 was mixed with polytetrafluoroethylene emulsion at a mass ratio of 95:5 and then uniformly coated on the surface of graphite felt. The mixture was then dried at 80°C for 8 hours to obtain the composite carbon electrode.

[0122] Example 3

[0123] This embodiment discloses a method for preparing a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, comprising the following steps:

[0124] S1. Raw material pretreatment

[0125] 1.5 g of double-walled carbon nanotubes were added to 150 mL of concentrated nitric acid (65%-68% by mass) and refluxed at 50 °C for 3 h. After the reaction was complete, the mixture was filtered, washed with deionized water until neutral, and dried at 80 °C for 10 h to obtain activated carbon nanotubes.

[0126] Preparation of S2, carbon nanotube / coal tar composite precursor

[0127] 15 g of coal tar pitch was mixed with the activated carbon nanotubes obtained in step S1, and then added to 315 mL of anhydrous ethanol. The mixture was sonicated for 3 h and mechanically stirred for 1 h to obtain a uniform slurry. Subsequently, the ethanol was removed by vacuum distillation at 110 °C, and the slurry was cooled and pulverized to obtain the carbon nanotube / coal tar pitch composite precursor.

[0128] S3, introduction of coal-based activated carbon and nitrogen source

[0129] 22.5 g of coal-based activated carbon and 7.5 g of melamine were added to the composite precursor obtained in step S2. The mixture was first premixed in an agate mortar for 30 min, and then transferred to a ball mill and ball-milled at 250 rpm for 3 h to obtain a uniformly mixed composite material. Melamine was used as a nitrogen source in the subsequent pyrolysis nitrogen doping process.

[0130] S4. Drying and Pretreatment

[0131] The composite material obtained in step S3 was vacuum dried at 100℃ for 8 h, and then heated to 230℃ at a heating rate of 2℃ / min under a nitrogen atmosphere and held for 1 h to obtain the pretreated sample.

[0132] S5, Pre-oxidation treatment

[0133] The pretreated sample obtained in step S4 was transferred into an air atmosphere and heated to 280°C at a heating rate of 2°C / min, and held at that temperature for 5 h to obtain a pre-oxidized sample.

[0134] S6, carbonization treatment

[0135] The pre-oxidized sample obtained in step S5 was heated to 400℃ at a heating rate of 3℃ / min under nitrogen protection, held for 1 h, then heated to 900℃ and held for 1.5 h. After cooling, the carbonized sample was obtained.

[0136] S7, Activation Treatment

[0137] The carbonized sample obtained in step S6 was placed in a steam activation device and activated by passing steam through it at 900°C for 1 hour. After activation, it was naturally cooled to room temperature to obtain a nitrogen-doped composite carbon material, which is referred to as the composite carbon material of Example 3.

[0138] S8, Electrode Preparation

[0139] The composite carbon material obtained in step S7 of Example 3 was mixed with conductive carbon black and sodium carboxymethyl cellulose binder at a mass ratio of 92:3:5 to form a slurry, which was then coated on the surface of carbon cloth and dried at 70°C for 12 h to obtain a composite carbon electrode.

[0140] Comparative Example 1

[0141] A method for preparing a composite carbon material includes the following steps:

[0142] S1. Raw material pretreatment

[0143] This comparative example does not include carbon nanotubes. Weigh out 20 g of coal tar pitch for later use.

[0144] S2. Preparation of coal tar pitch precursor

[0145] Add 20 g of coal tar pitch to 400 mL of anhydrous ethanol and disperse mechanically for 1 h to obtain a coal tar pitch dispersion.

[0146] S3, introduction of coal-based activated carbon and nitrogen source

[0147] 24 g of coal-based activated carbon and 8 g of melamine were added to the coal tar pitch dispersion obtained in step S2, and the mixture was ultrasonicated for 1 h and then ball-milled for 4 h to obtain a uniformly mixed composite material. Melamine was used as the nitrogen source.

[0148] S4. Drying and Pretreatment

[0149] The composite material obtained in step S3 was dried at 90°C for 10 h, and then heated to 220°C at a heating rate of 3°C / min under a nitrogen atmosphere and held at that temperature for 2 h.

[0150] S5, Pre-oxidation treatment

[0151] The material (sample) obtained in step S4 was heated to 260°C in air at a heating rate of 2°C / min and held at that temperature for 6 hours.

[0152] S6, carbonization treatment

[0153] The material (sample) after pre-oxidation in step S5 was heated to 450°C at a heating rate of 3°C / min under a nitrogen atmosphere and held for 1 h. Then it was heated to 800°C and held for 2 h to obtain the carbonized product.

[0154] S7, Activation Treatment

[0155] The carbonized product obtained in step S6 was activated at 850°C for 1.5 h in a CO2 atmosphere. After activation, it was naturally cooled to room temperature to obtain a control material without added carbon nanotubes.

[0156] S8, Electrode Preparation

[0157] Following the electrode preparation method in Example 1, the undoped nitrogen-containing comparative material was prepared into a composite carbon electrode for subsequent performance comparison.

[0158] Comparative Example 2

[0159] A method for preparing a composite carbon material includes the following steps:

[0160] S1. Raw material pretreatment

[0161] Two g of multi-walled carbon nanotubes were pretreated with mixed acid according to the method in Example 1, and then washed, dried and used for later use.

[0162] Preparation of S2, carbon nanotube / coal tar composite precursor

[0163] 20 g of coal tar pitch was mixed with carbon nanotubes pretreated in step S1, added to 400 mL of anhydrous ethanol, ultrasonically dispersed for 3 h and mechanically stirred for 1 h, and then the ethanol was removed at 110 °C to obtain the carbon nanotube / coal tar pitch composite precursor.

[0164] S3, Introduction of coal-based activated carbon

[0165] This comparative example does not include a nitrogen source, specifically melamine. 24 g of coal-based activated carbon was added to the composite precursor obtained in step S2, and the mixture was ball-milled for 4 h to obtain the composite mixture.

[0166] S4. Drying and Pretreatment

[0167] The composite mixture obtained in step S3 was dried at 90°C for 10 h, and then heated to 220°C at a heating rate of 3°C / min under a nitrogen atmosphere and held for 2 h.

[0168] S5, Pre-oxidation treatment

[0169] The material (sample) obtained in step S4 was heated to 260°C in air at a heating rate of 2°C / min and held at that temperature for 6 hours.

[0170] S6, carbonization treatment

[0171] The material (sample) obtained in step S5 is heated to 450°C at a heating rate of 3°C / min under a nitrogen atmosphere, held for 1 h, and then heated to 800°C and held for 2 h.

[0172] S7, Activation Treatment

[0173] The carbonized product obtained in step S6 was activated at 850°C for 1.5 h in a CO2 atmosphere. After activation, it was naturally cooled to room temperature to obtain the nitrogen-free control material.

[0174] S8, Electrode Preparation

[0175] Following the electrode preparation method in Example 1, the undoped nitrogen-containing comparative material was prepared into a composite carbon electrode for subsequent performance comparison.

[0176] Comparative Example 3

[0177] A method for preparing a composite carbon material includes the following steps:

[0178] S1. Raw material pretreatment

[0179] Two g of multi-walled carbon nanotubes were pretreated with mixed acid according to the method in Example 1, and then washed, dried and used for later use.

[0180] Preparation of S2, carbon nanotube / coal tar composite precursor

[0181] 20 g of coal tar pitch was mixed with pretreated carbon nanotubes and added to 400 mL of anhydrous ethanol. The mixture was ultrasonically dispersed for 3 h and mechanically stirred for 1 h. The ethanol was then removed at 110 °C to obtain the carbon nanotube / coal tar pitch composite precursor.

[0182] S3, introduction of coal-based activated carbon and nitrogen source

[0183] 24 g of coal-based activated carbon and 8 g of melamine were added to the composite precursor obtained in step S2, and the mixture was ball-milled for 4 h to obtain a composite mixture. Melamine was used as the nitrogen source.

[0184] S4. Drying and Pretreatment

[0185] The composite mixture obtained in step S3 was dried at 90°C for 10 h, and then heated to 220°C at a heating rate of 3°C / min under a nitrogen atmosphere, and held at that temperature for 2 h.

[0186] S5, carbonization treatment

[0187] This comparative example does not undergo pre-oxidation treatment. The material (sample) after pretreatment in step S4 is placed directly under a nitrogen atmosphere and heated to 450°C at a heating rate of 3°C / min, held for 1 h, and then heated to 800°C and held for 2 h to obtain the carbonized product.

[0188] S6, Activation Treatment

[0189] The carbonized product obtained in step S5 was activated at 850°C for 1.5 h in a CO2 atmosphere. After activation, it was naturally cooled to room temperature to obtain the unoxidized control material.

[0190] S7, Electrode Preparation

[0191] Following the electrode preparation method in Example 1, the unoxidized comparative material was prepared into a composite carbon electrode for subsequent performance comparison.

[0192] Application Example 1

[0193] A planar electrocatalytic reactor was assembled using the composite carbon electrode prepared in Example 1 as the anode and a stainless steel plate as the cathode. The electrochemical performance of the composite carbon electrode prepared in Example 1 was further tested. Figure 5 As can be seen, the obtained composite carbon electrode exhibits a significant cyclic voltammetric response within the test potential range, indicating that the electrode possesses certain interfacial electrochemical activity. Figure 6 As can be seen, the obtained composite carbon electrode exhibits a significant linear sweep voltammetric response, indicating that it can generate an effective current response under an applied electric field, which is beneficial for promoting charge transfer and interfacial electrocatalytic oxidation reactions. 200 mL of tetracycline-simulated wastewater with a concentration of 50 mg / L was taken, and 0.05 mol / L Na₂SO₄ was added as a supporting electrolyte. The initial pH of the solution was adjusted to 6.5, and the electrode spacing was controlled at 2 cm. The electrode was then subjected to an electric field at 10 mA / cm² at room temperature. 2 A constant current electrocatalytic reaction was carried out at a current density of 60 min.

[0194] Every 10 minutes during the reaction, 5 mL samples were taken and filtered through a 0.45 μm filter membrane. The tetracycline concentration was then measured using a UV-Vis spectrophotometer or high-performance liquid chromatography. The results showed that the tetracycline concentration gradually decreased with increasing reaction time, indicating that the composite carbon electrode prepared in Example 1 has good electrocatalytic oxidation removal capacity for tetracycline. Tetracycline, as a typical antibiotic pollutant, can be used to characterize the treatment effect of the composite carbon material of this invention on antibiotic-polluting wastewater.

[0195] Application Example 2

[0196] The composite carbon electrode prepared in Example 2 was used as the anode, and the graphite plate was used as the cathode to assemble an electrocatalytic reactor. 500 mL of pretreated actual medical wastewater was taken, and tetracycline was added to it to make its initial concentration 30 mg / L. The electrode spacing was controlled at 2.5 cm, and the reaction was carried out at a constant voltage of 5 V at room temperature for 90 min.

[0197] Samples were taken every 15 minutes during the reaction to measure tetracycline concentration, COD, and changes in UV absorption spectra. The results showed that the composite carbon electrode still exhibited good tetracycline degradation ability in complex medical wastewater systems and demonstrated a certain degree of organic matter mineralization, indicating that the composite carbon material of this invention is suitable for the electrocatalytic oxidation removal of typical antibiotic pollutants in medical wastewater.

[0198] Application Example 3

[0199] The composite carbon electrode prepared in Example 1 was used for cycle stability testing. After completing one electrocatalytic oxidation reaction of tetracycline simulated wastewater under the conditions described in Example 1, the electrode was removed, rinsed with deionized water, and dried at 60°C for 2 h before the next reaction. This process was repeated for 5 cycles.

[0200] The tetracycline removal rate was measured after each cycle, and the changes in electrode surface morphology were observed. The results showed that the composite carbon electrode maintained good treatment performance after multiple cycles, indicating that the nitrogen-doped carbon nanotube / coal tar pitch / coal-based activated carbon composite carbon material has good structural stability and reusability.

[0201] Application Example 4

[0202] Electrocatalytic oxidation of 50 mg / L tetracycline-simulated wastewater was performed using electrodes prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively, under the same conditions. The reaction conditions were: reaction liquid volume 200 mL, supporting electrolyte Na₂SO₄ concentration 0.05 mol / L, electrode spacing 2 cm, and current density 10 mA / cm². 2 The initial pH was 6.5, and the reaction time was 60 min.

[0203] The tetracycline removal effects of different electrodes at the same time were compared. The results showed that the composite carbon electrode obtained in Example 1 had a better treatment effect than the comparative electrodes. Among them, Comparative Example 1 had weaker electron transport ability due to the lack of carbon nanotube conductive network; Comparative Example 2 had insufficient surface reactivity due to the lack of nitrogen doping sites introduced by nitrogen source; and Comparative Example 3 had lower overall performance than Example 1 due to the omission of the pre-oxidation step, which reduced the stability of the material structure.

[0204] Unless otherwise specified, all raw materials used in this invention are commercially available. The carbon nanotubes used can be single-walled, double-walled, or multi-walled carbon nanotubes; the coal tar pitch used is preferably medium-temperature coal tar pitch, high-temperature coal tar pitch, or modified coal tar pitch; the coal-based activated carbon used is preferably powdered or granular coal-based activated carbon; the nitrogen source used is one or a combination of two or more of melamine, urea, dicyandiamide, cyanamide, ammonium salt compounds, nitrogen-containing small organic molecule compounds, and nitrogen-containing conductive polymers; wherein the nitrogen-containing conductive polymer is polyaniline and / or polypyrrole. In a specific embodiment, analytical grade melamine is preferably used as the nitrogen source.

[0205] In this invention, the low-temperature pretreatment in step S4, the pre-oxidation treatment in step S5, the carbonization treatment in step S6, and the activation treatment in step S7 can all be carried out using heat treatment equipment. The heat treatment equipment can be a tube furnace, box furnace, rotary furnace, fluidized bed furnace, or other heat treatment device capable of providing appropriate atmosphere and temperature program control. Steps S4 and S6 can be carried out under an inert atmosphere such as nitrogen, argon, or a mixture of both; step S5 can be carried out under an oxidizing atmosphere such as air, oxygen, or a mixture of air and oxygen; and step S7 can be carried out under carbon dioxide, water vapor, or an inert atmosphere, depending on the activation method.

[0206] In this invention, carbon nanotubes are used to construct a continuous conductive network, coal tar pitch is used to provide a high-carbon-yield carbon source and form a composite carbon framework, coal-based activated carbon is used to provide a well-developed pore structure and pollutant adsorption sites, and a nitrogen source is used to introduce nitrogen-containing active sites during heat treatment to improve the surface electronic structure and electrocatalytic activity of the composite carbon material. By synergistically combining the above components and sequentially performing dispersion, pretreatment, pre-oxidation, carbonization, and activation steps, a nitrogen-doped composite carbon material with conductivity, pore structure, and surface activity can be obtained and applied to the electrocatalytic oxidation removal of medical wastewater or antibiotic-containing pollutant wastewater.

Claims

1. A method for preparing a nitrogen-doped composite carbon material for electrocatalytic oxidation treatment of medical wastewater, characterized in that: Includes the following steps: S1. Pre-treat carbon nanotubes to obtain surface-activated carbon nanotubes; S2. Coal tar pitch is mixed and dispersed with the obtained surface-activated carbon nanotubes to prepare a carbon nanotube / coal tar pitch composite precursor. S3. Add coal-based activated carbon and nitrogen source to the carbon nanotube / coal tar pitch composite precursor, and mix evenly to obtain a composite mixture. S4. The composite mixture is dried and pretreated. S5. Pre-oxidize the material after step S4. S6. The material processed in step S5 is carbonized under an inert atmosphere. S7. The carbonized material is activated to obtain nitrogen-doped composite carbon material.

2. The preparation method according to claim 1, characterized in that: In step S1, the pretreatment of the carbon nanotubes is acid oxidation treatment, and the acid used is one or more of the following: nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid. The acid oxidation treatment temperature is 50-90℃, and the treatment time is 2-8h. After acid oxidation treatment, the obtained carbon nanotubes are washed until neutral and then vacuum dried at 60-120℃ for 6-24h to obtain surface-activated carbon nanotubes.

3. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of coal tar pitch to carbon nanotubes is 100:(1-20); the carbon nanotubes are one or a combination of two or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes; the dispersion is achieved by one or a combination of two or more of ultrasonic dispersion, mechanical stirring, and ball milling; the dispersion medium used is one or a combination of two or more of ethanol, water, acetone, and N,N-dimethylformamide; the amount of dispersion medium added is 5-30 mL / g based on the total mass of coal tar pitch and carbon nanotubes.

4. The preparation method according to claim 1, characterized in that: In step S3, based on 100 parts by weight of coal tar pitch, the amount of coal-based activated carbon added is 20-200 parts by weight, and the amount of nitrogen source added is 10-100 parts by weight. The nitrogen source is one or a combination of two or more of melamine, urea, dicyandiamide, cyanamide, ammonium salt compounds, nitrogen-containing small organic molecule compounds, and nitrogen-containing conductive polymers; wherein the nitrogen-containing conductive polymer is polyaniline and / or polypyrrole.

5. The preparation method according to claim 1, characterized in that: In step S4, the drying temperature is 60-120℃ and the drying time is 4-24 h; the pretreatment is carried out under an inert atmosphere, the pretreatment temperature is 180-300℃ and the holding time is 0.5-5 h.

6. The preparation method according to claim 1, characterized in that: In step S5, the pre-oxidation treatment is carried out in an oxidizing atmosphere, the pre-oxidation temperature is 200-320℃, and the pre-oxidation time is 2-12 h. The oxidizing atmosphere is air, oxygen, or a mixture of air and oxygen.

7. The preparation method according to claim 1, characterized in that: In step S6, the carbonization process is carried out in a segmented heating manner: first, the temperature is raised to 350-500℃ at a heating rate of 1-10℃ / min and held for 0.5-3 h, then the temperature is raised to 600-1000℃ at a heating rate of 1-10℃ / min and held for 0.5-5 h; the inert atmosphere is nitrogen, argon or a mixture of the two.

8. The preparation method according to claim 1, characterized in that: In step S7, the activation treatment is physical activation or chemical activation; the physical activation is carbon dioxide activation or steam activation, the activation temperature is 700-1000℃, the activation time is 0.5-10 h, and after physical activation, it is cooled to room temperature; the chemical activator is potassium hydroxide or potassium carbonate, the mass ratio of the chemical activator to the carbonized material is (0.5-4):1, the chemical activation temperature is 600-900℃, the chemical activation time is 0.5-5 h, after chemical activation, it is washed sequentially with 0.05-1.0 mol / L hydrochloric acid and deionized water until neutral, and dried at 60-120℃ for 6-24 h.

9. A nitrogen-doped composite carbon material, characterized in that: The composite carbon material is prepared by the preparation method described in any one of claims 1-8. The one-dimensional conductive network composed of carbon nanotubes is interwoven with the coal tar pitch-derived carbon skeleton to form a conductive pathway. Coal-based activated carbon provides microporous and / or mesoporous structures. The material surface contains nitrogen-doped active sites that are decomposed by the nitrogen source and introduced into the carbon skeleton surface during the carbonization process.

10. The application of the nitrogen-doped composite carbon material according to claim 9 in the electrocatalytic oxidation treatment of medical wastewater or antibiotic-contaminated wastewater, characterized in that: The composite carbon material is used as an anode active layer, a three-dimensional particle electrode filler, a supported electrode active component, or a conductive reaction medium.

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