A dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material and a preparation method thereof

Abstract

The application discloses a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material and a preparation method thereof, relates to the technical field of electrode materials, and comprises the following steps: immersing wood precursors in an ethanol solution containing an iron-based catalyst precursor and polyvinylpyrrolidone, and drying the wood precursors to obtain catalyst-loaded wood precursors; placing the catalyst-loaded wood precursors and dicyandiamide in a reactor; and performing acid pickling on the product to obtain the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material. The application realizes the construction of a three-dimensional penetrating conductive network of nitrogen-doped carbon nanotubes, the synergistic formation of a hierarchical porous structure of micropores-mesopores-macropores, and the efficient co-doping of nitrogen / oxygen heteroatoms in the carbonized wood skeleton simultaneously, reduces energy consumption and safety risks, realizes the unification of high-quality loading, high specific capacitance, excellent rate performance and super-long cycle life, and provides a brand-new technical path for the development of high-performance wood-based supercapacitor electrode materials.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material and its preparation method. Background Technology

[0002] With the continuous growth of global energy demand and the increasing depletion of fossil fuels, the development of efficient, clean, and renewable energy storage and conversion technologies has become a current research hotspot. Supercapacitors, as a novel energy storage device situated between traditional capacitors and secondary batteries, have shown broad application prospects in portable electronic devices, new energy vehicles, and smart grids due to their advantages such as high power density, long cycle life, fast charge / discharge rates, and wide operating temperature range. Electrode materials are one of the key factors determining the performance of supercapacitors. Among them, porous carbon materials, due to their high specific surface area and excellent... The high conductivity and excellent chemical stability of dicyandiamide make it the preferred material for preparing supercapacitor electrodes. Recent studies have attempted to grow nitrogen-doped carbon nanotubes in carbonized wood using dicyandiamide as the nitrogen source. However, these studies primarily focus on the growth of carbon nanotubes and nitrogen doping, without systematically revealing the stepwise mediating role of dicyandiamide in the pre-carbonization and carbonization stages, the synergistic regulatory mechanism of the micropore-mesopore-macropore hierarchical structure, or achieving strong interfacial bonding between the carbon nanotube network and the wood skeleton, as well as optimizing nitrogen / oxygen co-doping under high-quality loading. Therefore, there is still significant room for improvement in specific capacitance, rate performance, and cycle life. In recent years, biomass derivatives... Carbonized materials have attracted widespread attention due to their wide availability, renewability, low cost, and environmental friendliness, especially natural wood. Wood possesses a unique three-dimensional anisotropic structure containing numerous micron-sized channels vertically aligned along the growth direction. These channels are retained after carbonization and can serve as electrolyte reservoirs and rapid ion transport channels, making carbonized wood an ideal precursor for constructing self-supporting, binder-free, high-quality loaded thick electrodes. However, directly carbonized wood electrodes typically suffer from underdeveloped pore structures, insufficient active sites, and low utilization of micron-sized vertical channels, leading to limitations in their electrical properties. The capacitance performance is far lower than theoretical expectations, making it difficult to meet the application requirements of high-performance energy storage devices. To overcome these shortcomings, researchers have made various attempts. On the one hand, they have post-treated carbonized wood through physical or chemical activation to increase its specific surface area and pore volume. Physical activation is usually energy-intensive and time-consuming, while chemical activation requires a large amount of highly corrosive activating agents, which can easily damage the macroscopic structure of the wood and corrode the equipment. On the other hand, they have introduced carbon nanomaterials with excellent conductivity, such as carbon nanotubes and graphene, into the channels of carbonized wood to improve the space utilization of the channels and the overall conductivity of the electrodes.

[0003] However, current common solutions have many drawbacks, including: existing technologies for the preparation of carbonized wood-based composite electrode materials generally involve cumbersome multi-step chemical vapor deposition processes, high energy consumption and involvement of hazardous gases; pore structure control relies on additional physical or chemical activation, leading to structural damage and equipment corrosion; active materials are not firmly bonded to the carbon skeleton through physical filling, affecting cycle stability; heteroatom doping and carbon nanotube construction are not synchronized and require additional carbon sources; and it is difficult to achieve the synergistic construction of micropores, mesopores and macropores and the optimization of nitrogen / oxygen co-doping under high-quality loading, which limits the further improvement of the specific capacitance, rate performance and cycle life of electrode materials. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above-mentioned dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material and its preparation method, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to provide a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material and its preparation method. This invention addresses the common problems in the preparation of carbonized wood-based composite electrode materials, such as the cumbersome multi-step chemical vapor deposition process, high energy consumption and involvement of hazardous gases, pore structure control relying on additional physical or chemical activation leading to structural damage and equipment corrosion, weak bonding between active materials and the carbon skeleton through physical filling affecting cycle stability, asynchronous heteroatom doping and carbon nanotube construction requiring additional carbon sources, and difficulty in achieving the synergistic construction of micropores, mesopores, and macropores and optimization of nitrogen / oxygen co-doping under high-quality loading. These problems limit further improvements in the specific capacitance, rate performance, and cycle life of electrode materials.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, embodiments of the present invention provide a method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material, comprising: cutting wood and immersing it in an ethanol solution containing an iron-based catalyst precursor and polyvinylpyrrolidone; loading the iron-based catalyst precursor by a vacuum-assisted impregnation method; and drying it to obtain a catalyst-loaded wood precursor; placing the catalyst-loaded wood precursor and dicyandiamide in a reactor and performing a one-step chemical vapor deposition reaction under an inert gas atmosphere at a reaction temperature of 700–1000°C; after the reaction, acid washing the product to remove exposed iron-based nanoparticles; and drying the acid-washed product to obtain the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material.

[0008] As a preferred embodiment of the preparation method of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, wherein: the wood is selected from one or more of linden, pine, paulownia or balsa wood, and the thickness of the wood after cutting is 0.5–2 mm; the iron-based catalyst precursor is selected from at least one of ferric nitrate, ferric chloride or ferric sulfate, and the concentration of the iron-based catalyst precursor in the ethanol solution is 50–300 mM; the concentration of polyvinylpyrrolidone in the ethanol solution is 1–5 mg / mL.

[0009] As a preferred embodiment of the preparation method of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, the vacuum-assisted impregnation method includes: immersing the wood in the ethanol solution, placing it in a vacuum drying oven, evacuating to -0.08 to -0.1 MPa, maintaining for 10 to 30 minutes, restoring to normal pressure, and repeating the vacuum-normal pressure cycle 2 to 5 times to allow the solution to fully penetrate into the vertical channels of the wood.

[0010] As a preferred embodiment of the preparation method of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, the one-step chemical vapor deposition reaction includes: firstly, heating to 240–280°C at a heating rate of 1–5°C / min and holding for 1–3 hours for pre-carbonization treatment, and then heating to 700–1000°C at a heating rate of 1–5°C / min and holding for 1–3 hours for carbonization treatment.

[0011] As a preferred embodiment of the preparation method of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, the pre-carbonization treatment temperature is 260℃ and the holding time is 2 hours; the carbonization treatment temperature is 800℃ and the holding time is 2 hours, and the heating rate is 2℃ / min.

[0012] As a preferred embodiment of the preparation method of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, wherein: the mass ratio of dicyandiamide to the wood precursor supported by the catalyst is 5:1; the purity of the dicyandiamide is not less than 99%; the concentration of the dilute hydrochloric acid solution is 0.5–2 M, and the soaking time is 6–24 hours.

[0013] As a preferred embodiment of the preparation method of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, wherein: the drying is performed by vacuum drying at 50–80°C for 6–12 hours; the resulting composite material has a mass loading of 40–60 mg / cm², a specific surface area of ​​200–500 m² / g, a nitrogen content of 2–10 at%, and an oxygen content of 5–15 at%.

[0014] Secondly, to further solve the above-mentioned technical problems, the present invention provides a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material, comprising: a carbonized wood skeleton having micron-sized channels arranged perpendicularly along the growth direction; a nitrogen-doped carbon nanotube network grown in situ on the inner wall and surface of the micron-sized channels of the carbonized wood skeleton, forming a three-dimensional through-conductive network; the composite material has a hierarchical porous structure, including micropores, mesopores and macropores formed by the micron-sized channels, and contains nitrogen heteroatom functional groups and oxygen heteroatom functional groups.

[0015] As a preferred embodiment of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, wherein the nitrogen-doped carbon nanotube is a bamboo-like multi-walled carbon nanotube structure with a diameter of 10–50 nm.

[0016] As a preferred embodiment of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material of the present invention, wherein: the mass loading of the composite material is 40–60 mg / cm², and the specific surface area is 200–500 m² / g; the nitrogen element exists in the form of pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen or nitrogen oxide, and the oxygen element exists in the form of quinone group, phenolic hydroxyl group or carboxyl group.

[0017] The beneficial effects of this invention are as follows: This invention utilizes a dicyandiamide-mediated one-step chemical vapor deposition method to simultaneously achieve the construction of a three-dimensional through-hole conductive network of nitrogen-doped carbon nanotubes, the synergistic formation of a hierarchical porous structure of micropores, mesopores, and macropores, and the efficient co-doping of nitrogen / oxygen heteroatoms in a carbonized wood skeleton. The resulting composite material has a mass loading of 40–60 mg / cm² and a specific surface area of ​​200–500 m² / g, and can be directly used as a self-supporting electrode. This method integrates catalyst loading, wood carbonization, carbon nanotube growth, and heteroatom doping into a single high-temperature process, eliminating the need for additional activators and reducing gases, significantly simplifying the process and reducing energy consumption and safety risks. Benefiting from the synergistic effect of the three-dimensional conductive network, hierarchical porous structure, and nitrogen / oxygen functional groups, this electrode exhibits an areal capacitance exceeding 5000 mF / cm² at a current density of 5 mA / cm² and a specific capacitance of 300 mF / cm² at a current density of 300 mF / cm². Maintaining a capacitance retention rate of over 60% even at high current densities of mA / cm², and with a retention rate of no less than 90% after 30,000 charge-discharge cycles, this invention achieves a unified approach of high-quality load, high specific capacitance, excellent rate performance, and ultra-long cycle life. This provides a novel technical path for the development of high-performance wood-based supercapacitor electrode materials. Compared to existing reports using dicyandiamide or melamine, this invention, through precise control of the mass ratio of dicyandiamide to wood precursor (5:1) and a two-stage heating process of pre-carbonization / carbonization, achieves for the first time tunable micropore-mesopore-macropore ratio, optimized spatial distribution of nitrogen / oxygen co-doping sites, and strong interfacial bonding between the carbon nanotube network and the wood skeleton in a carbonized wood skeleton. This results in an areal specific capacitance exceeding 5000 mF / cm² and a rate retention rate of over 60% at 300 mA / cm² even at ultra-high mass loads of 40–60 mg / cm², significantly outperforming similar materials in published literature. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments 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. Wherein: Figure 1 This is a flowchart illustrating the implementation of the present invention in Example 1. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0021] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0022] Example 1 Reference Figure 1 This is the first embodiment of the present invention, which provides a method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material, comprising the following steps: S1: After cutting the wood, it is immersed in an ethanol solution containing an iron-based catalyst precursor and polyvinylpyrrolidone. The iron-based catalyst precursor is loaded by vacuum-assisted impregnation and dried to obtain the catalyst-loaded wood precursor.

[0023] Preferably, the wood is selected from one or more of linden, pine, paulownia or balsa wood, and the thickness of the wood after cutting is 0.5–2 mm; the iron-based catalyst precursor is selected from at least one of ferric nitrate, ferric chloride or ferric sulfate, and the concentration of the iron-based catalyst precursor in the ethanol solution is 50–300 mM; the concentration of polyvinylpyrrolidone in the ethanol solution is 1–5 mg / mL.

[0024] Furthermore, the vacuum-assisted impregnation method includes: immersing the wood in an ethanol solution, placing it in a vacuum drying oven, evacuating to -0.08 to -0.1 MPa, maintaining it for 10 to 30 minutes, restoring it to normal pressure, and repeating the vacuum-normal pressure cycle 2 to 5 times to allow the solution to fully penetrate the vertical channels of the wood.

[0025] Specifically, in this step, polyvinylpyrrolidone (PVP) acts as a dispersant and stabilizer; the polar groups in its molecule can react with iron-based catalyst precursors (such as Fe). 3+ The PVP forms a coordination effect to prevent catalyst particle agglomeration. At the same time, PVP can interact with oxygen-containing functional groups in wood through hydrogen bonds to achieve uniform loading of the catalyst on the inner wall of the wood pores. The vacuum-assisted impregnation method uses multiple vacuum-atmospheric pressure cycles to drive the solution to repeatedly enter and exit the vertical channels of the wood by pressure difference, ensuring that the catalyst precursor can fully penetrate into the depth of the wood's micron-level channels, laying the foundation for the uniform growth of carbon nanotubes.

[0026] S2: The catalyst-loaded wood precursor and dicyandiamide are placed in a reactor and subjected to a one-step chemical vapor deposition reaction under an inert gas atmosphere at a reaction temperature of 700–1000℃.

[0027] Preferably, the one-step chemical vapor deposition reaction includes: firstly, heating to 240–280°C at a heating rate of 1–5°C / min and holding for 1–3 hours for pre-carbonization treatment, and then heating to 700–1000°C at a heating rate of 1–5°C / min and holding for 1–3 hours for carbonization treatment.

[0028] Specifically, the pre-carbonization treatment temperature is 260℃, and the holding time is 2 hours; the carbonization treatment temperature is 800℃, the holding time is 2 hours, and the heating rate is 2℃ / min.

[0029] Furthermore, the mass ratio of dicyandiamide to the catalyst-supported wood precursor is 5:1; the purity of dicyandiamide is not less than 99%; the concentration of the dilute hydrochloric acid solution is 0.5–2 M, and the soaking time is 6–24 hours.

[0030] Specifically, the reactor is a tubular furnace. Dicyandiamide is placed upstream in the gas flow direction, and the catalyst-loaded wood precursor is placed downstream. An inert gas (nitrogen or argon) flows from upstream to downstream at a flow rate of 50–200 sccm. During the heating process, dicyandiamide first undergoes thermal decomposition in the pre-carbonization stage at 240–280℃, releasing carbon- and nitrogen-containing active species (such as ammonia and cyanamide compounds). These active species diffuse with the gas flow to the surface and pores of the wood precursor. When the temperature is further raised to 700–1000℃, the iron-based catalyst precursor is reduced to iron-based nanoparticles. These nanoparticles act as catalysts, adsorbing carbon atoms produced by the decomposition of dicyandiamide and catalyzing the growth of carbon nanotubes through a "tip growth" mechanism. At the same time, the nitrogen-containing species produced by the decomposition of dicyandiamide replace carbon atoms in the carbon framework at high temperatures, achieving nitrogen doping.

[0031] Furthermore, acid washing is performed using a 0.5–2 M dilute hydrochloric acid solution for 6–24 hours to remove iron-based nanoparticles exposed on the outside of carbon nanotubes. Iron-based nanoparticles encapsulated at the tips of carbon nanotubes cannot be removed by acid washing because they are wrapped in a carbon layer. However, the presence of these iron-based nanoparticles does not affect the electrochemical performance of the material and can instead be used as magnetic functional components for specific applications.

[0032] It should be noted that the reaction of dicyandiamide is mediated in two steps during the heating process: (1) During the pre-carbonization stage at 240–280℃, dicyandiamide undergoes thermal decomposition, releasing carbon- and nitrogen-containing active species such as ammonia and cyanamide compounds. These species diffuse into the vertical channels of wood and are initially adsorbed on the surface of the iron-based catalyst precursor. (2) During the carbonization stage at 700–1000℃, the iron-based catalyst precursor is reduced to iron-based nanoparticles, and the active species adsorbed on its surface decomposes into carbon atoms, which catalyze the growth of carbon nanotubes through the "tip growth" mechanism. At the same time, the nitrogen atoms in the active species replace the carbon atoms in the carbon skeleton, achieving nitrogen doping. In this process, dicyandiamide serves as a carbon source, nitrogen source, and mediator, avoiding the introduction of additional carbon sources and reducing gases. Furthermore, the gases produced by its decomposition have a mild etching effect on the wood skeleton. In conjunction with the template effect of iron-based nanoparticles, a hierarchical porous structure of micropores (<2 nm), mesopores (2–50 nm), and primary macropores (>50 nm) is simultaneously formed in the carbonized wood skeleton.

[0033] S3: After the reaction is complete, the product is acid-washed to remove the exposed iron-based nanoparticles.

[0034] Preferably, pickling is performed using a dilute hydrochloric acid solution with a concentration of 0.5–2 M, and the soaking time is 6–24 hours.

[0035] Furthermore, during the pickling process, the reacted composite material is immersed in a dilute hydrochloric acid solution and left to stand at room temperature or stirred slightly to allow the acid to fully contact the surface of the composite material and dissolve the exposed iron-based nanoparticles. After pickling, it is repeatedly rinsed with deionized water until the washing solution is neutral to remove residual hydrochloric acid and dissolved iron ions.

[0036] Specifically, the purpose of acid washing is to remove iron-based nanoparticles that are not encapsulated within the carbon nanotubes, thus preventing them from interfering with subsequent electrochemical tests. Iron-based nanoparticles encapsulated at the carbon nanotube tips due to the "tip growth" mechanism are wrapped in a carbon layer and cannot come into contact with the acid, thus remaining intact. These retained iron-based nanoparticles can serve as magnetic components, playing a role in applications related to magnetic properties.

[0037] S4: Dry the acid-washed product to obtain dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material.

[0038] Preferably, the drying is performed by vacuum drying at 50–80°C for 6–12 hours; the resulting composite material has a mass load of 40–60 mg / cm², a specific surface area of ​​200–500 m² / g, a nitrogen content of 2–10 at%, and an oxygen content of 5–15 at%.

[0039] Specifically, vacuum drying is carried out in a vacuum drying oven, with the drying temperature controlled between 50 and 80°C to avoid high temperatures damaging the heteroatom functional groups in the material. The dried composite material can be used directly as a self-supporting electrode without the need to add any binder or conductive agent.

[0040] Furthermore, the microstructure characteristics of the resulting composite material are as follows: the carbonized wood skeleton retains the micron-sized channels (approximately 20–50 μm in diameter) that are vertically arranged along the growth direction of natural wood, with numerous pits distributed on the channel walls; nitrogen-doped carbon nanotubes grow uniformly on the inner and outer surfaces of the channels, forming a three-dimensional through-conductive network; the carbon nanotubes have a bamboo-like multi-walled structure with a diameter of 10–50 nm, and some iron-based nanoparticles are encapsulated at the tips of the carbon nanotubes; the composite material simultaneously possesses a hierarchical porous structure of micropores (<2 nm, formed by etching of iron-based nanoparticles), mesopores (2–50 nm, formed by interwoven carbon nanotube networks), and macropores (>50 nm, composed of the original channels of wood).

[0041] In summary, this invention utilizes a dicyandiamide-mediated one-step chemical vapor deposition method to simultaneously achieve the construction of a three-dimensional through-hole conductive network of nitrogen-doped carbon nanotubes, the synergistic formation of a hierarchical porous structure of micropores, mesopores, and macropores, and the efficient co-doping of nitrogen / oxygen heteroatoms in a carbonized wood framework. The resulting composite material exhibits a high mass loading of 40–60 mg / cm² and a specific surface area of ​​200–500 m² / g, making it directly usable as a self-supporting electrode. This method integrates catalyst loading, wood carbonization, carbon nanotube growth, and heteroatom doping into a single high-temperature process, eliminating the need for additional activators and reducing gases, significantly simplifying the process and reducing energy consumption and safety risks. Benefiting from the synergistic effect of the three-dimensional conductive network, hierarchical porous structure, and nitrogen / oxygen functional groups, this electrode achieves an areal capacitance exceeding 5000 mF / cm² at a current density of 5 mA / cm² and a specific capacitance of 300 mF / cm² at a current density of 300 mF / cm². Maintaining a capacitance retention rate of over 60% even at high current densities of mA / cm², and with a retention rate of no less than 90% after 30,000 charge-discharge cycles, this invention achieves a unified approach of high-quality load, high specific capacitance, excellent rate performance, and ultra-long cycle life. This provides a novel technical path for the development of high-performance wood-based supercapacitor electrode materials. Compared to existing reports using dicyandiamide or melamine, this invention, through precise control of the mass ratio of dicyandiamide to wood precursor (5:1) and a two-stage heating process of pre-carbonization / carbonization, achieves for the first time tunable micropore-mesopore-macropore ratio, optimized spatial distribution of nitrogen / oxygen co-doping sites, and strong interfacial bonding between the carbon nanotube network and the wood skeleton in a carbonized wood skeleton. This results in an areal specific capacitance exceeding 5000 mF / cm² and a rate retention rate of over 60% at 300 mA / cm² even at ultra-high mass loads of 40–60 mg / cm², significantly outperforming similar materials in published literature.

[0042] Example 2, an embodiment of the present invention, provides a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material, comprising: a carbonized wood skeleton having micron-sized channels arranged perpendicularly along the growth direction; a nitrogen-doped carbon nanotube network grown in situ on the inner wall and surface of the micron-sized channels of the carbonized wood skeleton, forming a three-dimensional through-conductive network; the composite material has a hierarchical porous structure, including micropores, mesopores and macropores composed of micron-sized channels, and contains nitrogen heteroatom functional groups and oxygen heteroatom functional groups.

[0043] Furthermore, the nitrogen-doped carbon nanotubes have a bamboo-like multi-walled carbon nanotube structure with a diameter of 10–50 nm.

[0044] Specifically, the composite material has a mass load of 40–60 mg / cm² and a specific surface area of ​​200–500 m² / g; nitrogen exists in the form of pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen or nitrogen oxide, and oxygen exists in the form of quinone groups, phenolic hydroxyl groups or carboxyl groups.

[0045] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material, characterized in that: include: After the wood is cut, it is immersed in an ethanol solution containing an iron-based catalyst precursor and polyvinylpyrrolidone. The iron-based catalyst precursor is loaded by a vacuum-assisted impregnation method and dried to obtain a catalyst-loaded wood precursor. The wood precursor with the supported catalyst and dicyandiamide were placed in a reactor and subjected to a one-step chemical vapor deposition reaction under an inert gas atmosphere at a reaction temperature of 700–1000 °C. After the reaction was completed, the product was acid washed to remove the exposed iron-based nanoparticles. The acid-washed product was dried to obtain the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material.

2. The method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material as described in claim 1, characterized in that: The wood is selected from one or more of linden, pine, paulownia or balsa wood, and the thickness of the wood after cutting is 0.5–2 mm; the iron-based catalyst precursor is selected from at least one of ferric nitrate, ferric chloride or ferric sulfate, and the concentration of the iron-based catalyst precursor in the ethanol solution is 50–300 mM; the concentration of polyvinylpyrrolidone in the ethanol solution is 1–5 mg / mL.

3. The method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material as described in claim 1, characterized in that: The vacuum-assisted impregnation method includes: immersing the wood in the ethanol solution, placing it in a vacuum drying oven, evacuating to -0.08 to -0.1 MPa, maintaining for 10–30 minutes, restoring to normal pressure, and repeating the vacuum-normal pressure cycle 2–5 times to allow the solution to fully penetrate the vertical channels of the wood.

4. The method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material as described in claim 1, characterized in that: The one-step chemical vapor deposition reaction includes: first, heating to 240–280°C at a heating rate of 1–5°C / min and holding for 1–3 hours for pre-carbonization treatment, and then heating to 700–1000°C at a heating rate of 1–5°C / min and holding for 1–3 hours for carbonization treatment.

5. The method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material as described in claim 4, characterized in that: The pre-carbonization treatment is performed at a temperature of 260°C for 2 hours; the carbonization treatment is performed at a temperature of 800°C for 2 hours, with a heating rate of 2°C / min.

6. The method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material as described in claim 1, characterized in that: The mass ratio of dicyandiamide to the wood precursor supported by the catalyst is 5:1; the purity of the dicyandiamide is not less than 99%; the concentration of the dilute hydrochloric acid solution is 0.5–2 M, and the soaking time is 6–24 hours.

7. The method for preparing a dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material as described in claim 1, characterized in that: The drying process involves vacuum drying at 50–80°C for 6–12 hours; the resulting composite material has a mass loading of 40–60 mg / cm², a specific surface area of ​​200–500 m² / g, a nitrogen content of 2–10 at%, and an oxygen content of 5–15 at%.

8. A dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material, prepared according to the preparation method of the dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material according to any one of claims 1 to 7, characterized in that: include, Carbonized wood skeleton, which has micron-sized channels arranged perpendicularly along the growth direction; Nitrogen-doped carbon nanotube networks are grown in situ on the inner walls and surface of the micron-scale channels of the carbonized wood skeleton, forming a three-dimensional through-conductive network. The composite material has a hierarchical porous structure, including micropores, mesopores and macropores formed by the micron-level channels, and contains nitrogen heteroatom functional groups and oxygen heteroatom functional groups.

9. The dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material according to claim 8, characterized in that: The nitrogen-doped carbon nanotubes have a bamboo-like multi-walled carbon nanotube structure with a diameter of 10–50 nm.

10. The dicyandiamide-mediated nitrogen-doped carbon nanotube / carbonized wood composite material according to claim 8, characterized in that: The composite material has a mass loading of 40–60 mg / cm² and a specific surface area of ​​200–500 m² / g; the nitrogen element exists in the form of pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen or nitrogen oxide, and the oxygen element exists in the form of quinone group, phenolic hydroxyl group or carboxyl group.

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