Nitrogen-doped carbon micropipes and a method for preparing the same

Abstract

The application provides a nitrogen-doped carbon micrometer tube and a preparation method thereof, and belongs to the technical field of carbon micrometer and nanometer material preparation. The nitrogen-doped carbon micrometer tube material is a hollow tubular structure, the diameter of the tube is 1-2 micrometers, the length of the tube is 5-15 micrometers, and the thickness of the tube wall is 10-50 nanometers. The preparation method comprises the following steps: firstly, a nitrogen-containing compound is heat-polymerized to prepare a nitrogen-containing solid carbon source; then, the nitrogen-containing solid carbon source is pyrolyzed at high temperature, and a carbon micrometer tube is catalytically grown on the surface of a metal catalyst through chemical vapor deposition of pyrolysis gas. The preparation method is simple in operation process, can be prepared on a large scale, and the obtained nitrogen-doped carbon micrometer tube has unique micro-nano structures and high nitrogen content, and has wide application prospects in the field of electrochemical energy storage.

Description

Technical Field

[0001] This invention relates to a nitrogen-doped carbon microtube and its preparation method, belonging to the field of carbon microtube preparation technology. Background Technology

[0002] Currently, carbon nanotubes have achieved remarkable success in various research fields due to their excellent electrical conductivity and outstanding stability. However, reports and research on carbon microtubes, which are micrometer-scale carbon tubes with similar structures and properties to carbon nanotubes, are quite rare. Due to their nanoscale size, carbon nanotubes exhibit strong van der Waals forces and π-π interactions, making them prone to aggregation. Furthermore, the tubes are often entangled, making dispersion in a matrix difficult. In addition, the small diameter of carbon nanotubes restricts the entry of larger molecules into their cavities, resulting in generally poor monodispersity and monooperability. The hollow portions of carbon nanotubes are frequently partially or completely blocked by products, leading to a series of problems in molecular transport and mass transfer. These unfavorable factors significantly reduce the practical application value of carbon nanotubes. In contrast, carbon microtubes have a significant diameter advantage compared to carbon nanotubes, showing broad application prospects in microelectronics and micromechanical devices, micro / nanoreactors, drug delivery, and micro / nanofluidics. However, since the activity of catalysts decreases with increasing particle size, the methods traditionally used to synthesize carbon nanotubes are not applicable to the synthesis of carbon microtubes. Currently, there is a huge challenge in the efficient and controllable synthesis of carbon microtubes.

[0003] Current methods for synthesizing carbon microtubes generally suffer from drawbacks such as demanding conditions and poor controllability. One method, disclosed in patent application CN110028066A, involves using corn silk as a biomass precursor to prepare porous carbon microtubes through carbonization and activation. However, this method cannot achieve controllable adjustment of the carbon microtube diameter, and the prepared carbon microtubes are hard carbon materials, making graphitization impossible. Another method, disclosed in patent application CN103387220B, involves synthesizing carbon microtubes using urea and ethylene glycol as carbon sources via a high-temperature, high-pressure method. However, this method suffers from high synthesis temperatures and pressures, resulting in extremely demanding synthesis conditions that hinder large-scale synthesis of carbon microtubes. Therefore, there is a need to provide a method for preparing carbon microtubes with mild and controllable synthesis conditions, namely, to reduce the synthesis temperature of carbon microtubes, synthesize them under normal pressure, and precisely control the diameter, crystallinity, and heteroatom doping of carbon microtubes, so as to achieve controllable, large-scale, and high-quality synthesis of carbon microtubes. Summary of the Invention:

[0004] To address the shortcomings of existing carbon microtube fabrication technologies, this invention provides a chemical vapor deposition-catalyzed, controllable synthesis method for nitrogen-doped carbon microtubes, enabling low-temperature, controllable, and large-scale synthesis. The introduction of nitrogen atoms alters the structure of the carbon matrix, generating more electrochemical / catalytic active sites and influencing the charge distribution to improve the conductivity of the carbon microtubes. Simultaneously, the introduction of nitrogen atoms also improves the surface wettability of the carbon microtubes. In summary, nitrogen doping endows carbon microtubes with superior physicochemical properties, improves their application performance, and significantly expands the application range of carbon microtubes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A nitrogen-doped carbon microtube, wherein the nitrogen-doped carbon microtube is a hollow tubular structure with a diameter of 0.7-2 μm, a length of 5-20 μm, and a wall thickness of 10-80 nm.

[0007] A method for preparing nitrogen-doped carbon microtubes, comprising the following steps: First, a nitrogen-containing solid carbon source is prepared by thermal polycondensation of a nitrogen-containing compound. Second, the nitrogen-containing solid carbon source and nickel powder are placed in the pyrolysis zone and vapor deposition reaction zone of a heating device, respectively. The nitrogen-containing solid carbon source is pyrolyzed at high temperature, and the pyrolysis gas catalyzes the growth of carbon microtubes on the surface of the nickel powder through chemical vapor deposition. Finally, the sample is removed after the reaction, added to a hydrochloric acid solution, and post-processed to obtain the nitrogen-doped carbon microtube material. Specifically, the method includes the following steps:

[0008] The first step is to prepare a nitrogen-containing solid carbon source:

[0009] The nitrogen-containing compound was placed in a covered corundum boat, transferred to a muffle furnace, heated from room temperature to 400-600℃, reacted for 2-6 hours, and the product was ground to obtain a powdered nitrogen-containing solid carbon source.

[0010] The second step involves fabricating nitrogen-doped carbon microtubes using chemical vapor deposition.

[0011] 2.1) Place the nitrogen-containing solid carbon source obtained in the first step into an open corundum boat container A; place the metallic nickel powder into an open corundum boat container B.

[0012] 2.2) Container A and Container B are placed in a quartz tube. The quartz tube is placed in a heating device, with Container A located in the pyrolysis zone of the heating device and Container B located in the vapor deposition reaction zone of the heating device.

[0013] 2.3) A carrier gas is introduced into the quartz tube, flowing from container A to container B. The pyrolysis zone and the vapor deposition reaction zone are heated to their final temperatures for isothermal reaction. The final temperature of the pyrolysis zone is 650-900℃, and the final temperature of the vapor deposition reaction zone is 700-1000℃. The isothermal reaction time is 30-240 minutes. After the reaction, the heating device is allowed to cool naturally to room temperature. During the reaction in step 2.3), the nitrogen-containing solid carbon source is pyrolyzed at high temperature to produce gaseous nitrogen-containing carbon molecules. Under the action of the carrier gas, the gaseous molecules come into contact with, dissolve, and gradually reach saturation with nickel powder. Subsequently, under the catalytic action of high temperature and nickel powder, carbon atoms connect and gradually diffuse and deposit, finally growing into nitrogen-doped carbon microtubes.

[0014] The third step involves removing the sample from container B and placing it in a beaker. Hydrochloric acid solution is then added, with a mass ratio of hydrochloric acid solution to the sample from container B of 100:1. The reaction is allowed to proceed for 24-48 hours. The mixture is then filtered, washed with water until the solution is neutral, and finally freeze-dried to obtain nitrogen-doped carbon microtube material.

[0015] Furthermore, in the first step, the nitrogen-containing compound is one or more of urea, thiourea, monocyanamide, dicyandiamide, dicyandiamide, melamine, and melamine chloride.

[0016] Furthermore, in step 2.1), the mass ratio of the nitrogen-containing solid carbon source to the nickel powder is 1:0.1-2. The particle size of the nickel powder is 100-300 nm.

[0017] Furthermore, in step 2.3), the carrier gas is one of nitrogen, argon, helium, methane, and ethylene.

[0018] Furthermore, the heating rate in the first step is 2-10℃ / min. In step 2.3), both the pyrolysis zone and the vapor deposition reaction zone are heated to the final temperature at a heating rate of 1-10℃ / min.

[0019] Furthermore, in the third step, the concentration of the hydrochloric acid solution is 2-8 mol / L. The freeze-drying temperature in the third step is -52℃, and the time is 24-72 hours.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The present invention achieves the preparation of high-purity nitrogen-doped carbon microtubes by using a strategy of solid carbon source pyrolysis chemical vapor deposition.

[0022] (2) The structure of nitrogen-doped carbon microtubes is adjustable. By adjusting the proportion of nitrogen-containing solid carbon source, the particle size of nickel powder, reaction temperature, isothermal time and other factors, the morphology, size and nitrogen content of hollow microtube structure can be controlled.

[0023] (3) The method of the present invention is simple to operate, easy to scale up, has mild and controllable reaction conditions, and uses a wide range of raw materials. The nitrogen-doped carbon microtubes prepared have broad application prospects in the field of electrochemical energy storage. Attached Figure Description

[0024] Figure 1 The image shown is a scanning electron microscope (SEM) image of the nitrogen-doped carbon microtube obtained in Example 1 of this invention.

[0025] Figure 2 The XRD pattern of the nitrogen-doped carbon microtube obtained in Example 1 of this invention;

[0026] Figure 3 The Raman spectrum of the nitrogen-doped carbon microtube obtained in Example 1 of this invention;

[0027] Figure 4 The N1s plot of the XPS spectrum of the nitrogen-doped carbon microtube obtained in Example 1 of this invention;

[0028] Figure 5 This is a scanning electron microscope image of the nitrogen-doped carbon microtube obtained in Example 2 of the present invention;

[0029] Figure 6 This is a scanning electron microscope image of the nitrogen-doped carbon microtube obtained in Example 3 of the present invention;

[0030] Figure 7 This is a scanning electron microscope image of the nitrogen-doped carbon microtube obtained in Example 4 of the present invention;

[0031] Figure 8 This is a scanning electron microscope image of the nitrogen-doped carbon microtube obtained in Example 5 of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0033] Example 1:

[0034] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0035] (1) Preparation steps of nitrogen-containing solid carbon source: Weigh melamine and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 550℃ at a rate of 10℃ / min, react for 4h, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0036] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly on the bottom of corundum boat container A, and spread 0.2g of metallic nickel powder with a particle size of 200nm evenly on the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0037] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0038] (4) The pyrolysis zone where container A is located is heated from room temperature to 800°C at a rate of 10°C / min, and the vapor deposition reaction zone where container B is located is heated to 800°C at a rate of 10°C / min. The reaction is kept at a constant temperature for 60 min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0039] (5) Take the sample out of container B, place it in a beaker, add 50 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0040] The nitrogen-doped carbon microtubes fabricated in this embodiment are shown in the scanning electron microscope as follows: Figure 1 As shown in the image, scanning electron microscopy reveals that the fabricated nitrogen-doped carbon microtubes possess a regular micro / nano structure. The microtubes have a diameter of 1 μm, a length of approximately 10 μm, and a wall thickness of 60 nm. XRD analysis of the nitrogen-doped carbon microtubes is also presented. Figure 2 As shown, distinct carbon characterization diffraction peaks are present, indicating that the precursor was successfully converted into carbon material under the catalysis of nickel powder. Raman analysis of the nitrogen-doped carbon microtubes, as shown... Figure 3 As shown, the Raman spectrum contains two characteristic peaks for carbon, I D / I G The low value indicates that the nitrogen-doped microtubes have a high degree of graphitization.

[0041] Figure 4 The N1s plot of the XPS spectrum of the nitrogen-doped carbon microtube prepared in this embodiment is fitted with three characteristic peaks, corresponding to pyridine nitrogen (~398.7 eV), pyrrole nitrogen (~399.7 eV), and graphitic nitrogen (~401.2 eV). This plot illustrates the presence of nitrogen atoms in the carbon microtube, and nitrogen doping was successfully achieved.

[0042] Example 2:

[0043] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0044] (1) Preparation steps of nitrogen-containing solid carbon source: weigh melamine and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 550°C at a rate of 10°C / min, react for 4 hours, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0045] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly on the bottom of corundum boat container A, and spread 1.0g of metallic nickel powder with a particle size of 200nm evenly on the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0046] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0047] (4) The pyrolysis zone where container A is located is heated from room temperature to 800°C at a rate of 10°C / min, and the vapor deposition reaction zone where container B is located is heated to 800°C at a rate of 10°C / min. The reaction is kept at a constant temperature for 60 min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0048] (5) Take the sample out of container B, place it in a beaker, add 45 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0049] The nitrogen-doped carbon microtubes fabricated in this embodiment are shown in the scanning electron microscope as follows: Figure 5 As shown, scanning electron microscopy reveals that the fabricated nitrogen-doped carbon microtubes have a regular micro / nano structure, with a diameter of 1.5 μm, a length of approximately 9 μm, and a wall thickness of 60 nm.

[0050] XRD analysis of nitrogen-doped carbon microtubes revealed distinct carbon-characteristic diffraction peaks, indicating that the precursor was successfully converted into carbon material under the catalysis of nickel powder. Raman analysis of the nitrogen-doped carbon microtubes showed two characteristic peaks for carbon in the Raman spectrum, I... D / I G The low value indicates that the nitrogen-doped microtubes have a high degree of graphitization. XPS analysis of the nitrogen-doped carbon microtubes showed that the presence of the N1s diffraction peak indicated successful nitrogen doping.

[0051] Example 3:

[0052] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0053] (1) Preparation steps of nitrogen-containing solid carbon source: weigh melamine and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 550°C at a rate of 10°C / min, react for 4 hours, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0054] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly at the bottom of corundum boat container A, and spread 2.0g of metallic nickel powder with a particle size of 200nm evenly at the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0055] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0056] (4) The pyrolysis zone where container A is located is heated from room temperature to 800°C at a rate of 10°C / min, and the vapor deposition reaction zone where container B is located is heated to 800°C at a rate of 10°C / min. The reaction is kept at a constant temperature for 60 min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0057] (5) Take the sample out of container B, place it in a beaker, add 40 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0058] The nitrogen-doped carbon microtubes fabricated in this embodiment are shown in the scanning electron microscope as follows: Figure 6 As shown, scanning electron microscopy reveals that the fabricated nitrogen-doped carbon microtubes have a regular micro / nano structure, with a diameter of 1.2 μm, a length of approximately 6 μm, and a wall thickness of approximately 60 nm.

[0059] XRD analysis of nitrogen-doped carbon microtubes revealed distinct carbon-characteristic diffraction peaks, indicating that the precursor was successfully converted into carbon material under the catalysis of nickel powder. Raman analysis of the nitrogen-doped carbon microtubes showed two characteristic peaks for carbon in the Raman spectrum, I... D / I G The low value indicates that the nitrogen-doped microtubes have a high degree of graphitization. XPS analysis of the nitrogen-doped carbon microtubes showed that the presence of the N1s diffraction peak indicated successful nitrogen doping.

[0060] Example 4:

[0061] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0062] (1) Preparation steps of nitrogen-containing solid carbon source: weigh melamine and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 550°C at a rate of 10°C / min, react for 4 hours, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0063] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly on the bottom of corundum boat container A, and spread 0.2g of metallic nickel powder with a particle size of 200nm evenly on the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0064] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0065] (4) The pyrolysis zone where container A is located is heated from room temperature to 700°C at a rate of 10°C / min, and the vapor deposition reaction zone where container B is located is heated to 700°C at a rate of 10°C / min. The reaction is kept at a constant temperature for 60 min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0066] (5) Take the sample out of container B, place it in a beaker, add 50 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0067] The nitrogen-doped carbon microtubes fabricated in this embodiment are shown in the scanning electron microscope as follows: Figure 7 As shown, scanning electron microscopy reveals that the fabricated nitrogen-doped carbon microtubes have a regular micro / nano structure, with a diameter of 0.7 μm, a length of approximately 20 μm, and a wall thickness of approximately 50 nm.

[0068] XRD analysis of the nitrogen-doped carbon microtubes revealed the presence of distinct carbon-characteristic diffraction peaks. Raman analysis of the nitrogen-doped carbon microtubes showed two characteristic carbon peaks in the Raman spectrum, both results indicating that the precursor was successfully converted into carbon material under the action of nickel metal powder. XPS analysis of the nitrogen-doped carbon microtubes showed the presence of the N1s diffraction peak, indicating successful nitrogen doping.

[0069] Example 5:

[0070] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0071] (1) Preparation steps of nitrogen-containing solid carbon source: weigh melamine and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 550°C at a rate of 10°C / min, react for 4 hours, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0072] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly on the bottom of corundum boat container A, and spread 0.2g of metallic nickel powder with a particle size of 200nm evenly on the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0073] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0074] (4) The pyrolysis zone where container A is located is heated from room temperature to 900°C at a rate of 10°C / min, and the vapor deposition reaction zone where container B is located is heated to 900°C at a rate of 10°C / min. The reaction is kept at a constant temperature for 60 min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0075] (5) Take the sample out of container B, place it in a beaker, add 50 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0076] The nitrogen-doped carbon microtubes fabricated in this embodiment are shown in the scanning electron microscope as follows: Figure 8 As shown, scanning electron microscopy reveals that the fabricated nitrogen-doped carbon microtubes have a regular micro / nano structure, with a diameter of 1 μm, a length of approximately 12 μm, and a wall thickness of approximately 70 nm.

[0077] XRD analysis of nitrogen-doped carbon microtubes revealed distinct carbon-characteristic diffraction peaks, indicating successful conversion of the precursor into carbon material under the action of a nickel metal catalyst. Raman analysis of the nitrogen-doped carbon microtubes showed two characteristic peaks for carbon in the Raman spectrum: I... D / I G The low value indicates that the nitrogen-doped microtubes have a high degree of graphitization, which is attributed to the excellent catalytic effect of nickel powder at high temperatures. XPS analysis of the nitrogen-doped carbon microtubes revealed the presence of an N1s diffraction peak, indicating successful nitrogen doping.

[0078] Example 6:

[0079] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0080] (1) Preparation steps of nitrogen-containing solid carbon source: weigh thiourea and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 550°C at a rate of 10°C / min, react for 4 hours, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0081] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly at the bottom of corundum boat container A, and spread 2.0g of metallic nickel powder with a particle size of 200nm evenly at the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0082] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0083] (4) The pyrolysis zone where container A is located is heated from room temperature to 900℃ at a rate of 10℃ / min, and the vapor deposition reaction zone where container B is located is heated to 1000℃ at a rate of 10℃ / min. The reaction is kept at a constant temperature for 100min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0084] (5) Take the sample out of container B, place it in a beaker, add 50 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0085] The nitrogen-doped carbon microtubes prepared in this embodiment have a diameter of 1 μm, a length of approximately 10 μm, and a wall thickness of approximately 80 nm. XRD analysis of the nitrogen-doped carbon microtubes revealed distinct carbon-characteristic diffraction peaks, indicating that the precursor was successfully converted into carbon material under the action of a nickel metal catalyst. Raman analysis of the nitrogen-doped carbon microtubes showed two characteristic peaks for carbon in the Raman spectrum, I... D / I G The low value indicates that the nitrogen-doped microtubes have a high degree of graphitization at high vapor deposition temperatures. XPS analysis of the nitrogen-doped carbon microtubes showed that the presence of the N1s diffraction peak indicated successful nitrogen doping.

[0086] Example 7:

[0087] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0088] (1) Preparation steps of nitrogen-containing solid carbon source: weigh urea and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 400℃ at a rate of 10℃ / min, react for 6h, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0089] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly on the bottom of corundum boat container A, and spread 4.0g of metallic nickel powder with a particle size of 200nm evenly on the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0090] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0091] (4) The pyrolysis zone where container A is located is heated from room temperature to 650°C at a rate of 10°C / min, and the vapor deposition reaction zone where container B is located is heated to 800°C at a rate of 10°C / min. The reaction is kept at a constant temperature for 30 min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0092] (5) Take the sample out of container B, place it in a beaker, add 50 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0093] The nitrogen-doped carbon microtubes prepared in this embodiment have a diameter of 1 μm, a length of approximately 5 μm, and a wall thickness of approximately 40 nm. XRD analysis of the nitrogen-doped carbon microtubes revealed the presence of distinct carbon-characteristic diffraction peaks. Raman analysis showed two characteristic carbon peaks in the Raman spectrum, both indicating that the precursor was successfully converted into carbon material under the influence of nickel metal powder. XPS analysis of the nitrogen-doped carbon microtubes showed the presence of the N1s diffraction peak, confirming successful nitrogen doping.

[0094] Example 8:

[0095] A method for preparing nitrogen-doped carbon microtubes includes the following steps:

[0096] (1) Preparation steps of nitrogen-containing solid carbon source: Weigh dicyandiamine and place it in a covered corundum boat, transfer it to a muffle furnace, heat it to 600℃ at a rate of 10℃ / min, react for 2h, grind the product to obtain a powdered nitrogen-containing solid carbon source.

[0097] (2) Spread 2.0g of nitrogen-containing solid carbon source powder evenly on the bottom of corundum boat container A, and spread 0.5g of metallic nickel powder with a particle size of 200nm evenly on the bottom of corundum boat container B. Place container A and container B inside the quartz tube.

[0098] (3) Place the quartz tube from (2) into the two-stage heating furnace, so that the inner container A and container B of the quartz tube are located in the pyrolysis zone and the vapor deposition reaction zone, respectively; introduce argon gas into the quartz tube, with container A containing nitrogen-containing solid carbon source powder located upstream of the carrier gas and container B containing metallic nickel powder located downstream of the carrier gas.

[0099] (4) The pyrolysis zone where container A is located is heated from room temperature to 650°C at a rate of 10°C / min, and the vapor deposition reaction zone where container B is located is heated to 800°C at a rate of 10°C / min. The reaction is kept at a constant temperature for 240 min. After the reaction is completed, the heating device is naturally cooled to room temperature.

[0100] (5) Take the sample out of container B, place it in a beaker, add 50 mL of 2 mol / L hydrochloric acid solution, react for 48 h to remove the nickel powder. Filter the sample after removing the nickel powder, wash with water until the solution is neutral, and finally freeze-dry at -52℃ for 72 h to obtain nitrogen-doped carbon microtube material.

[0101] The nitrogen-doped carbon microtubes prepared in this embodiment have a diameter of 1.2 μm, a length of approximately 20 μm, and a wall thickness of approximately 40 nm. XRD analysis of the nitrogen-doped carbon microtubes revealed the presence of distinct carbon-characteristic diffraction peaks. Raman analysis showed two characteristic carbon peaks in the Raman spectrum, both indicating that the precursor was successfully converted into carbon material under the influence of nickel metal powder. XPS analysis of the nitrogen-doped carbon microtubes showed the presence of an N1s diffraction peak, confirming successful nitrogen doping.

[0102] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for producing nitrogen-doped carbon microtubes, characterized by comprising the steps of: The preparation method comprises the following steps: ​ Firstly, a nitrogen-containing solid carbon source is prepared by thermal polycondensation of a nitrogen-containing compound; Secondly, the nitrogen-containing solid carbon source and metal nickel powder are respectively placed in a pyrolysis zone and a vapor deposition reaction zone of a heating device, the nitrogen-containing solid carbon source is pyrolyzed at high temperature, and the pyrolysis gas is chemically vapor deposited on the surface of the metal nickel powder to catalytically grow carbon microtubules; Finally, the product obtained after the reaction is added into a hydrochloric acid solution for post-treatment to obtain a nitrogen-doped carbon microtubule material. In the first step, the nitrogen-containing compound is one or more of urea, thiourea, cyanamide, dicyanamide, dicyandiamide, melamine and melamine chloride. In step 2.3), the carrier gas is one of nitrogen, argon and helium. The nitrogen-doped carbon microtubule is a hollow tubular structure, the diameter of the tube is 0.7-2 μm, the length of the tube is 5-20 μm, and the thickness of the tube wall is 10-80 nm. In step 2.1), the mass ratio of the nitrogen-containing solid carbon source to the metal nickel powder is 1:0.1-2, and the particle size of the metal nickel powder is 100-300 nm. In the first step, the heating rate is 2-10 ℃ / min; in step 2.3), the pyrolysis zone and the vapor deposition reaction zone are both heated to the final temperature at a heating rate of 1-10 ℃ / min. In the third step, the concentration of the hydrochloric acid solution is 2-8 mol / L; the freeze-drying temperature is-52 ℃, and the time is 24-72 h; the mass ratio of the hydrochloric acid solution to the sample is 100:1, and the reaction time is 24-48 h. ​ 2. The method for preparing a nitrogen-doped carbon microtube according to claim 1, characterized in that, ​ 3. The method for preparing a nitrogen-doped carbon microtube according to claim 1, characterized in that, ​ 4. The method for preparing a nitrogen-doped carbon microtube according to claim 1, characterized in that, ​

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