Heteroatom-doped hierarchical porous carbon nanospheres and preparation method thereof

Abstract

The application relates to a kind of heteroatom doped multi-level pore carbon nanospheres and a preparation method thereof, and belongs to the technical field of new nano materials.The method is to use aromatic amine derivative as nitrogen source, simultaneously use cationic surfactant and silicon dioxide generated by hydrolysis of silicate as soft and hard template agent, in-situ co-assemble polymer nanospheres by polymerization of aromatic amine derivative and silicon dioxide generated by hydrolysis of silicate, further remove hard template by high-temperature pyrolysis under inert atmosphere and hydrofluoric acid etching, to obtain heteroatom doped multi-level pore carbon nanospheres with microporous-mesoporous-macroporous pore structure, which can be further activated to increase its porosity.The method overcomes the shortcomings that pore structure of carbon material prepared by using only soft template is easy to collapse and hard template needs to be prepared in advance, and has the advantages of mild conditions, easy-to-obtain raw materials and low cost.Heteroatom doped multi-level pore carbon nanospheres prepared by the method have microporous-mesoporous-macroporous multi-level pore structure, high porosity and uniform distribution of heteroatoms.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new nanomaterials, and particularly relates to a heteroatom-doped multi-level porous carbon nanosphere and a preparation method thereof. BACKGROUND

[0002] Porous carbon materials are widely used in adsorption, catalysis, medicine, energy storage and conversion, etc. due to their high specific surface area and porosity, good chemical stability and excellent electrical conductivity. Functionalization of pure carbon materials can adjust the relationship between structure and performance while maintaining their inherent properties, giving them more application value. Doping heteroatoms into the graphite framework to adjust the properties of carbon materials has become an important topic. Nitrogen atom doping can improve the electrical conductivity and wettability of carbon materials, improve the electrochemical performance of carbon materials, and also enhance the interaction between the surface of carbon materials and acid gas molecules, improve the performance of carbon materials in acid gas adsorption, and also improve the interaction between the supported metal and the carbon material, avoiding aggregation or sintering into larger particles, and improving the catalytic performance of the supported metal carbon material catalyst.

[0003] Porous carbon materials can be divided into microporous (pore size less than 2 nm), mesoporous (pore size between 2-50 nm) and macroporous (pore size greater than 50 nm) carbon materials according to pore size. Although microporous carbon materials are widely used in industry, their microporous channels are small and poorly connected, limiting their adsorption and mass transfer of organic electrolytes and macromolecular polymers. Macroporous carbon materials have large pore sizes and good connectivity, which can improve the diffusion of molecules in liquids or gases and the mass transfer efficiency in the reaction process, and their pore size can be precisely controlled within the macroporous size range, but their relatively low specific surface area and pore volume limit their application. The pore structure of mesoporous carbon materials is better than that of microporous carbon materials, and their specific surface area is higher than that of macroporous carbon materials, which has greater structural advantages. However, the specific surface area of mesoporous carbon materials is much smaller than that of microporous carbon materials and the mass transfer efficiency is lower than that of macroporous carbon materials, which also limits their application prospects to some extent. How to combine the advantages of various pore sizes and avoid their disadvantages is a problem that needs to be solved.

[0004] Hierarchical porous carbon materials have two or more than two pore structures, which have a bright application prospect in the fields of catalysis, adsorption, separation and energy storage and conversion. In the field of supercapacitors, the presence of hierarchical porous structure makes the pores that are difficult for electrolyte to enter to be utilized, improving the energy storage performance of electrode materials. In the field of electrocatalysis of fuel cells, the mutual connection of hierarchical porous structure promotes mass transfer and diffusion, making the active sites of catalysts more fully exposed and improving the catalytic activity of catalysts. In the field of adsorption, hierarchical porous structure solves the problem of low adsorption capacity of macroporous adsorbents due to few adsorption sites, and relieves the adsorption resistance of adsorbate in micropores and mesopores due to small pore size, improving the adsorption capacity and adsorption rate of adsorbents. Therefore, the synthesis method of hierarchical porous carbon materials is one of the current research hotspots.

[0005] The template method is a method widely used for preparing hierarchical porous carbon materials at present, which can be generally divided into soft template method and hard template method. The soft template method generally utilizes the ordered co-assembly of surfactants and organic carbon source precursors, and then removes the template by high-temperature carbonization, so that the prepared pore structure is mainly microporous. The advantage of the soft template method is that the structure can be flexibly regulated by changing the solution properties or environmental temperature, but the morphology of the prepared material is poor and the pore structure is easy to collapse. The hard template method is to composite carbon precursors and hard templates, and then use acid and alkali etching after carbonization, so that the prepared material is mainly a composite porous carbon material with mesopores and macropores. The advantage of the hard template method is that the structure and morphology of the template are fine and controllable, but a large amount of hard templates need to be prepared first, and the process is relatively complex. How to overcome the shortcomings of the soft and hard template methods is one of the keys to preparing porous carbon materials with excellent pore structure. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of nitrogen atom doped carbon nanospheres with hierarchical pore structure of microporous-mesoporous-macroporous by combining soft and hard templates, which combines the advantages of microporous, mesoporous and macroporous carbon materials, overcomes the shortcomings of easy collapse of pore structure of carbon materials prepared by only using soft template and the need to prepare hard template in advance, and improves the application performance.

[0007] To achieve the above object, the application provides a preparation method of heteroatom-doped multi-level porous carbon nanospheres, which comprises the following steps: dissolving aromatic amine derivatives and cationic surfactants in a mixed solvent of water and ethanol; wherein the concentration of the aromatic amine derivatives is 0.03-0.14 mol / L, and the concentration of the cationic surfactant solution is greater than 0 and less than 0.08 mol / L; adding an ammonia solution to the above system and stirring uniformly; the volume ratio of the ammonia solution to the mixed solvent is (1-11):2700; simultaneously adding a silicate and formaldehyde to the above system and stirring to obtain polymer nanospheres; wherein the volume ratio of the silicate to the mixed solvent is (48-84):270, and the volume ratio of the formaldehyde to the mixed solvent is (1-4):270; carbonizing the polymer nanospheres in an inert gas atmosphere to obtain silicon-heteroatom-doped carbon nanospheres; etching the silicon-heteroatom-doped carbon nanospheres with hydrofluoric acid to obtain heteroatom-doped multi-level porous carbon nanospheres; and activating the heteroatom-doped multi-level porous carbon nanospheres with an activating agent to obtain activated heteroatom-doped multi-level porous carbon nanospheres.

[0008] Specifically, the preparation method of the heteroatom-doped multi-level porous carbon nanospheres comprises the following steps:

[0009] (1) dissolving aromatic amine derivatives and cationic surfactants in a mixed solvent of water and ethanol; wherein the concentration of the aromatic amine derivatives is 0.03-0.14 mol / L, and the concentration of the cationic surfactant solution is greater than 0 and less than 0.08 mol / L;

[0010] (2) adding an ammonia solution to the above system and stirring uniformly; the volume ratio of the ammonia solution to the mixed solvent is (1-11):2700;

[0011] (3) simultaneously adding a silicate and formaldehyde to the above system and stirring to obtain polymer nanospheres; wherein the volume ratio of the silicate to the mixed solvent is (48-84):270, and the volume ratio of the formaldehyde to the mixed solvent is (1-4):270

[0012] (4) carbonizing the polymer nanospheres in an inert gas atmosphere to obtain silicon-heteroatom-doped carbon nanospheres;

[0013] (5) etching the silicon-heteroatom-doped carbon nanospheres with hydrofluoric acid to obtain heteroatom-doped multi-level porous carbon nanospheres; and (6) activating the heteroatom-doped multi-level porous carbon nanospheres with an activating agent to obtain activated heteroatom-doped multi-level porous carbon nanospheres.

[0014] The aromatic amine derivative in step (1) is selected from one or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, aniline, 2,4-diaminobenzenesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, 3,5-diaminobenzoic acid, p-aminobenzoic acid, o-aminobenzoic acid, m-aminobenzoic acid or p-aminophenol; the cationic surfactant is selected from one or more of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, octadecyltrimethylammonium bromide or octadecyltrimethylammonium chloride; the reaction temperature is 30-70 DEG C; and the volume ratio of water to ethanol in the solvent is 6:1-2:5.

[0015] The stirring rate in step (3) is 500-900 rpm.

[0016] The carbonization condition in step (4) is that the carbonization temperature is 700-900 DEG C under an inert gas atmosphere.

[0017] The activating agent in step (6) is a chemical activating agent selected from potassium bicarbonate, potassium carbonate, potassium hydroxide, potassium oxalate, sodium carbonate or sodium bicarbonate; the mass ratio of the heteroatom-doped multi-level porous carbon nanosphere to the activating agent is 0-1:4; and the activation temperature is 700-900 DEG C.

[0018] A heteroatom-doped multi-level porous carbon nanosphere is prepared by the above method.

[0019] The above method uses aromatic amine derivatives, formaldehyde, silicate ester, cationic surfactant and the like as basic materials, and a mixed solvent of water and ethanol as a reaction system. The pH of the system can affect the rate of reaction of the aromatic amine derivatives and formaldehyde to generate polymers, and also affect the rate of hydrolysis of the silicate ester to generate silica particles. The amounts of the aromatic amine derivatives, formaldehyde, silicate ester, cationic surfactant and ammonia in the system are mutually restricted, and by adjusting the amounts of these materials in the system and changing the system environment, such as temperature, stirring rate and solvent ratio, the morphology of the heteroatom-doped multi-level porous carbon nanosphere can be controlled. The carbonization temperature in the carbonization process, the type of activating agent in the activation process, the mass ratio of the heteroatom-doped multi-level porous carbon nanosphere to the activating agent and the activation temperature can be controlled to further increase the porosity.

[0020] The heteroatom-doped multi-level porous carbon nanosphere obtained by the above method has a micropore-mesopore-macropore multi-level porous structure, the heteroatoms are uniformly distributed, and the maximum specific surface area after activation is 1690 m 2 / g.

[0021] The present application has the following advantages:

[0022] 1. The present application deviates from the traditional method of using a single hard template agent or soft template agent, adopts a combination of soft and hard templates, and the silicate is directly hydrolyzed in the system to produce silica particles, so there is no need to prepare a hard template in advance, and the disadvantage of easy collapse of the pore structure of the carbon material prepared by using only a soft template agent is overcome.

[0023] 2. The present application has low raw material and template agent usage, low price, and high yield. The morphology of the heteroatom-doped multi-level pore carbon nanospheres can be controlled by adjusting the concentration of the aromatic amine derivative and the cationic surfactant solution, the amount of ammonia solution, the amount of silicate, and the amount of formaldehyde in the system, as well as the reaction temperature, stirring rate, and solvent ratio of water to ethanol. Furthermore, the porosity of the heteroatom-doped multi-level pore carbon nanospheres can be further increased by controlling the carbonization temperature, the type of activating agent, the mass ratio of the heteroatom-doped multi-level pore carbon nanospheres to the activating agent, and the activation temperature.

[0024] 3. The heteroatom-doped multi-level pore carbon nanospheres prepared by the present application have uniform heteroatom distribution and a multi-level pore structure of micropores-mesopores-macropores, and the maximum specific surface area after activation reaches 1690 m 2 / g. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 SEM image of the heteroatom-doped multi-level pore carbon nanospheres after 700°C carbonization and 10% HF treatment by the method of the present application.

[0026] Figure 2 TEM image of the heteroatom-doped multi-level pore carbon nanospheres prepared by the method of the present application at different stirring speeds.

[0027] Figure 3 TEM image of the heteroatom-doped multi-level pore carbon nanospheres prepared by the method of the present application with different water / ethanol solvent ratios.

[0028] Figure 4 TEM image of the heteroatom-doped multi-level pore carbon nanospheres prepared by the method of the present application with different amounts of cetyltrimethylammonium bromide.

[0029] Figure 5 TEM image of the heteroatom-doped multi-level pore carbon nanospheres prepared by the method of the present application with different amounts of tetraethyl orthosilicate.

[0030] Figure 6 TEM image of the heteroatom-doped multi-level pore carbon nanospheres prepared by the method of the present application with different amounts of m-phenylenediamine.

[0031] Figure 7 TEM image of the heteroatom-doped multi-level pore carbon nanospheres prepared by the method of the present application with different amounts of formaldehyde.

[0032] Figure 8TEM images of the heteroatom-doped multi-level porous carbon nanospheres prepared by the method of the present application with different amounts of ammonia.

[0033] Figure 9 Nitrogen adsorption-desorption curves and pore size distribution comparison chart of the heteroatom-doped multi-level porous carbon nanospheres prepared by the method of the present application with different amounts of ammonia.

[0034] Figure 10 Nitrogen adsorption-desorption curves and pore size distribution comparison chart of the heteroatom-doped multi-level porous carbon nanospheres prepared by the method of the present application with different amounts of ammonia after 700℃ activation.

[0035] Figure 11 Electrochemical performance of the heteroatom-doped porous carbon nanospheres prepared by the method of the present application before and after activation under a three-electrode system with different mass ratios of sample and potassium bicarbonate.

[0036] Figure 12 Electrochemical performance of the heteroatom-doped porous carbon nanospheres prepared by the method of the present application under a three-electrode system after carbonization at different temperatures and activation at 800℃.

[0037] Figure 13 Electrochemical performance of the heteroatom-doped porous carbon nanospheres prepared by the method of the present application under a three-electrode system after activation at different temperatures using different activators.

[0038] Figure 14 Electrochemical performance of the heteroatom-doped multi-level porous carbon nanospheres prepared by the method of the present application with different amounts of ammonia after 700℃ activation under a three-electrode system. DETAILED DESCRIPTION

[0039] The following non-limiting examples can enable those of ordinary skill in the art to more fully understand the present application, but are not intended to limit the present application in any way.

[0040] In the following examples, the test methods described are the conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0041] Example 1

[0042] Dissolve 0.2 g (0.0005 mol) of cetyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine in a mixed solution of 19 mL of water and 8 mL of ethanol, add 80 μL of 25% ammonia water, and stir at a temperature of 30℃ and a stirring speed of 500 rpm until the solution is uniform and transparent. Add 0.72 mL of tetraethyl silicate and 0.3 mL of formaldehyde aqueous solution, stir for 6 h, centrifuge, wash with 20% ethanol solution, and dry. Then, grind the sample into a powder and transfer it to a tube furnace, heat it to 100℃ at a rate of 10℃ / min under a nitrogen atmosphere, and then heat it to 800℃ at a rate of 1℃ / min under a nitrogen atmosphere, and then cool it to room temperature at a rate of 10℃ / min under a nitrogen atmosphere, and then cool it to room temperature under a nitrogen atmosphere. -1 heat it to 100℃ at a rate of 10℃ / min under a nitrogen atmosphere, and then heat it to 800℃ at a rate of 1℃ / min under a nitrogen atmosphere, and then cool it to room temperature at a rate of 10℃ / min under a nitrogen atmosphere, and then cool it to room temperature under a nitrogen atmosphere.-1 Heated to 350℃, kept for 2h, then heated to 1℃ / min -1 Heated to 800℃, kept for 2h. After cooling to room temperature, the sample was transferred to a 25mL centrifuge tube, 10mL of 10% HF was added, bubbles were generated, stirred overnight at 300rpm, after centrifugation, washed with deionized water, dried and collected for scanning electron microscopy characterization. Figure 1 SEM images of heteroatom doped hierarchical porous carbon nanospheres after 700℃ carbonization and treated with 10% HF. As can be seen from the figure, the heteroatom doped hierarchical porous carbon nanospheres exhibit a surface walnut kernel-like structure with cavities.

[0043] Example 2

[0044] 0.2g (0.0005mol) of cetyltrimethylammonium bromide and 0.2g (0.0018mol) of m-phenylenediamine were dissolved in a mixed solution of 19mL of water and 8mL of ethanol, 80μL of 25% ammonia water was added, the solution was stirred at 500rpm, 700rpm and 900rpm at 30℃ until it was uniform and transparent. 0.72mL of tetraethyl silicate and 0.3mL of formaldehyde aqueous solution were added, stirred for 6h, after centrifugation, washing, drying, the sample was transferred to a tube furnace, carbonized and etched at 800℃ under nitrogen atmosphere, and then characterized by transmission electron microscopy. Figure 2 TEM images of heteroatom doped hierarchical porous carbon nanospheres prepared at 500rpm, 700rpm and 900rpm stirring speeds, respectively. As can be seen from the figure, as the stirring speed increases, the internal cavities of the heteroatom doped hierarchical porous carbon nanospheres decrease and the spherical structure tends to be uneven.

[0045] Example 3

[0046] 0.2g (0.0005mol) of cetyltrimethylammonium bromide and 0.2g (0.0018mol) of m-phenylenediamine were dissolved in a mixed solution of 19mL of water and 8mL of ethanol, 80μL of 25% ammonia water was added, the solution was stirred at 500rpm, 700rpm and 900rpm at 30℃ until it was uniform and transparent. 0.72mL of tetraethyl silicate and 0.3mL of formaldehyde aqueous solution were added, stirred for 6h, after centrifugation, washing, drying, the sample was transferred to a tube furnace, carbonized and etched at 800℃ under nitrogen atmosphere, and then characterized by transmission electron microscopy. Figure 3 TEM images of heteroatom doped hierarchical porous carbon nanospheres prepared at 500rpm, 700rpm and 900rpm stirring speeds, respectively. As can be seen from the figure, as the stirring speed increases, the internal cavities of the heteroatom doped hierarchical porous carbon nanospheres decrease and the spherical structure tends to be uneven.

[0047] Example 4

[0048] 0 g (0 mol), 0.2 g (0.0005 mol), 0.4 g (0.0011 mol) and 0.8 g (0.0022 mol) cetyltrimethylammonium bromide, 0.2 g (0.0018 mol) m-phenylenediamine were dissolved in 19 mL water and 8 mL ethanol mixed solution, 80 μL 25% ammonia water was added, the solution was stirred to uniform transparency at 30°C temperature and 500 rpm stirring speed. 0.72 mL tetraethyl silicate and 0.3 mL formaldehyde aqueous solution were added, stirred for 6 h, after centrifugation, washing, drying, the sample was transferred to a tube furnace, carbonized at 800°C under nitrogen atmosphere and etched, then characterized by transmission electron microscopy. Figure 4 TEM images of heteroatom doped hierarchical porous carbon nanospheres prepared with a-d respectively 0 g (0 mol), 0.2 g (0.0005 mol), 0.4 g (0.0011 mol) and 0.8 g (0.0022 mol) cetyltrimethylammonium bromide, from the figure, with the increase of cetyltrimethylammonium bromide, the heteroatom doped hierarchical porous carbon nanospheres changed from solid small particle to nanospheres with internal cavity and then to solid nanospheres.

[0049] Example 5

[0050] 0.2 g (0.0005 mol) cetyltrimethylammonium bromide, 0.2 g (0.0018 mol) m-phenylenediamine were dissolved in 19 mL water and 8 mL ethanol mixed solution, 80 μL 25% ammonia water was added, the solution was stirred to uniform transparency at 30°C temperature and 500 rpm stirring speed. 0.48 mL, 0.60 mL, 0.72 mL and 0.84 mL tetraethyl silicate and 0.3 mL formaldehyde aqueous solution were added, stirred for 6 h, after centrifugation, washing, drying, the sample was transferred to a tube furnace, carbonized at 800°C under nitrogen atmosphere and etched, then characterized by transmission electron microscopy. Figure 5 TEM images of heteroatom doped hierarchical porous carbon nanospheres prepared with a-d respectively 0.48 mL, 0.60 mL, 0.72 mL and 0.84 mL tetraethyl silicate, from the figure, with the increase of tetraethyl silicate, the heteroatom doped hierarchical porous carbon nanospheres changed from a small amount of internal cavity to multiple cavity structure and then to solid structure.

[0051] Example 6

[0052] TEM images of heteroatom-doped hierarchical porous carbon nanospheres prepared with different amounts of m-phenylenediamine (a-c) and formaldehyde (a-d). The TEM images show that the heteroatom-doped hierarchical porous carbon nanospheres change from small cavities with a uniform structure to large cavities with an open structure as the amount of m-phenylenediamine increases, and change from small nanospheres with a radial shell to nanospheres with an internal cavity and then to solid nanospheres as the amount of formaldehyde increases. Figure 6 TEM images of heteroatom-doped hierarchical porous carbon nanospheres prepared with different amounts of m-phenylenediamine (a-c) and formaldehyde (a-d). The TEM images show that the heteroatom-doped hierarchical porous carbon nanospheres change from small cavities with a uniform structure to large cavities with an open structure as the amount of m-phenylenediamine increases, and change from small nanospheres with a radial shell to nanospheres with an internal cavity and then to solid nanospheres as the amount of formaldehyde increases.

[0053] Example 7

[0054] TEM images of heteroatom-doped hierarchical porous carbon nanospheres prepared with different amounts of m-phenylenediamine (a-c) and formaldehyde (a-d). The TEM images show that the heteroatom-doped hierarchical porous carbon nanospheres change from small cavities with a uniform structure to large cavities with an open structure as the amount of m-phenylenediamine increases, and change from small nanospheres with a radial shell to nanospheres with an internal cavity and then to solid nanospheres as the amount of formaldehyde increases. Figure 7 TEM images of heteroatom-doped hierarchical porous carbon nanospheres prepared with different amounts of m-phenylenediamine (a-c) and formaldehyde (a-d). The TEM images show that the heteroatom-doped hierarchical porous carbon nanospheres change from small cavities with a uniform structure to large cavities with an open structure as the amount of m-phenylenediamine increases, and change from small nanospheres with a radial shell to nanospheres with an internal cavity and then to solid nanospheres as the amount of formaldehyde increases.

[0055] Example 8

[0056] 0.2 g (0.0005 mol) of cetyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine were dissolved in a mixed solution of 19 mL of water and 8 mL of ethanol, 20 μL, 40 μL, 60 μL, 80 μL, 90 μL and 110 μL of 25% ammonia water were added, and the solution was stirred at a temperature of 30°C and a rotation speed of 500 rpm until it became uniformly transparent. 0.72 mL of tetraethyl silicate and 0.3 mL of an aqueous formaldehyde solution were added, and the mixture was stirred for 6 h. After centrifugation, washing and drying, the sample was transferred to a tube furnace, carbonized at 800°C under a nitrogen atmosphere, and etched. The sample was then subjected to a nitrogen adsorption / desorption experiment at a temperature of -196°C. Figure 8 FIGS. 11A to 11F are TEM images of heteroatom-doped hierarchical porous carbon nanospheres prepared using different amounts of 25% ammonia water, and it can be seen from the images that as the amount of ammonia water increases, the heteroatom-doped hierarchical porous carbon nanospheres change from solid nanoparticles to nanospheres with small cavities and then to irregular nanoparticles.

[0057] Example 9

[0058] 0.2 g (0.0005 mol) of cetyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine were dissolved in a mixed solution of 19 mL of water and 8 mL of ethanol, 10 μL, 20 μL, 40 μL and 60 μL of 25% ammonia water were added, and the solution was stirred at a temperature of 30°C and a rotation speed of 500 rpm until it became uniformly transparent. 0.72 mL of tetraethyl silicate and 0.3 mL of an aqueous formaldehyde solution were added, and the mixture was stirred for 6 h. After centrifugation, washing and drying, the sample was transferred to a tube furnace, carbonized at 800°C under a nitrogen atmosphere, and etched. The sample was then subjected to a nitrogen adsorption / desorption experiment at a temperature of -196°C. Figure 9 FIGS. 12A and 12B are nitrogen adsorption / desorption curves and BJH pore size distribution graphs of heteroatom-doped hierarchical porous carbon nanospheres prepared using different amounts of 25% ammonia water, and it can be seen from the graphs that NHCS-80 has the largest adsorption amount and its pore size is mainly distributed at -115 nm.

[0059] Example 10

[0060] 0.2 g (0.0005 mol) of hexadecyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine were dissolved in a mixture of 19 mL of water and 8 mL of ethanol. 10 μL, 20 μL, 40 μL, and 60 μL of 25% ammonia solution were added, and the mixture was stirred at 500 rpm at 30 °C until the solution became homogeneous and transparent. 0.72 mL of tetraethyl silicate and 0.3 mL of formaldehyde aqueous solution were added, and the mixture was stirred for 6 h. After centrifugation, washing, and drying, the sample was transferred to a tube furnace and carbonized and etched at 800 °C. The sample was then mixed with potassium bicarbonate at a mass ratio of 1:3 and heated under a nitrogen atmosphere at 10 °C for [time missing]. -1 The temperature was increased to 500℃ at a rate of [temperature], and then increased at a rate of 5℃ / min. -1 The sample was heated to 700℃ at a rising rate and held for 1 hour. After naturally cooling to room temperature, the sample was collected, washed with hydrochloric acid and deionized water until neutral, and then dried. Samples with a mass of 100 mg or more activated at 700℃ were degassed at 200℃ for 6 hours, and then subjected to nitrogen adsorption-desorption experiments at ~196℃. Figure 10 In Figures a and b, nitrogen adsorption-desorption curves and BJH pore size distribution diagrams of heteroatom-doped hierarchical porous carbon nanospheres prepared with 10 μL, 20 μL, 40 μL and 60 μL of 25% ammonia water respectively after activation at 700℃ are shown. As can be seen from the figure, the activated NHCS-80 has the maximum adsorption capacity, and its pore size is mainly distributed in the range of ~58 nm.

[0061] Example 11

[0062] 0.2 g (0.0005 mol) of hexadecyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine were dissolved in a mixture of 19 mL of water and 8 mL of ethanol. 60 μL of 25% ammonia solution was added, and the mixture was stirred at 500 rpm at 30 °C until the solution became homogeneous and transparent. 0.72 mL of tetraethyl silicate and 0.3 mL of formaldehyde aqueous solution were added, and the mixture was stirred for 6 h. After centrifugation, washing, and drying, the sample was transferred to a tube furnace and carbonized and etched at 800 °C. The sample was then mixed with potassium bicarbonate at mass ratios of 1:2, 1:3, and 1:4 and activated at 700 °C under a nitrogen atmosphere. Figure 11 The figure shows the electrochemical performance of heteroatom-doped hierarchical porous carbon nanospheres before activation and activated with potassium bicarbonate at different mass ratios in a three-electrode system. As can be seen from the figure, the heteroatom-doped hierarchical porous carbon nanospheres activated with potassium bicarbonate at a mass ratio of 1:4 exhibit the highest electrochemical performance.

[0063] Example 12

[0064] Dissolve 0.2 g (0.0005 mol) of cetyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine in a mixed solution of 19 mL of water and 8 mL of ethanol, add 60 μL of 25% ammonia water, and stir the solution at a temperature of 30°C and a rotation speed of 500 rpm until it becomes uniformly transparent. Add 0.72 mL of tetraethyl silicate and 0.3 mL of an aqueous formaldehyde solution, stir for 6 h, and then transfer the sample to a tube furnace after centrifugation, washing, and drying. Carbonize and etch the sample at 700°C, 750°C, 800°C, 850°C, and 900°C. Mix the sample with potassium bicarbonate at a mass ratio of 1:3, and activate at 800°C under a nitrogen atmosphere. Figure 12 To investigate the electrochemical performance of the heteroatom-doped hierarchical porous carbon nanospheres carbonized at different temperatures and activated at 800°C in a three-electrode system, it can be seen from the figure that the heteroatom-doped hierarchical porous carbon nanospheres carbonized at 700°C and activated at 800°C exhibit the highest electrochemical performance.

[0065] Example 13

[0066] Dissolve 0.2 g (0.0005 mol) of cetyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine in a mixed solution of 19 mL of water and 8 mL of ethanol, add 60 μL of 25% ammonia water, and stir the solution at a temperature of 30°C and a rotation speed of 500 rpm until it becomes uniformly transparent. Add 0.72 mL of tetraethyl silicate and 0.3 mL of an aqueous formaldehyde solution, stir for 6 h, and then transfer the sample to a tube furnace after centrifugation, washing, and drying. Carbonize and etch the sample at 700°C, 750°C, 800°C, 850°C, and 900°C. Mix the sample with potassium bicarbonate at a mass ratio of 1:3, and activate at 800°C under a nitrogen atmosphere. Figure 13 To investigate the electrochemical performance of the heteroatom-doped hierarchical porous carbon nanospheres carbonized at different temperatures and activated at 800°C in a three-electrode system, it can be seen from the figure that the heteroatom-doped hierarchical porous carbon nanospheres carbonized at 700°C and activated at 800°C exhibit the highest electrochemical performance.

[0067] Example 14

[0068] Dissolve 0.2 g (0.0005 mol) of cetyltrimethylammonium bromide and 0.2 g (0.0018 mol) of m-phenylenediamine in a mixed solution of 19 mL of water and 8 mL of ethanol, add 60 μL of 25% ammonia water, and stir the solution at a temperature of 30°C and a rotation speed of 500 rpm until it becomes uniformly transparent. Add 0.72 mL of tetraethyl silicate and 0.3 mL of an aqueous formaldehyde solution, stir for 6 h, and then transfer the sample to a tube furnace after centrifugation, washing, and drying. Carbonize and etch the sample at 700°C, 750°C, 800°C, 850°C, and 900°C. Mix the sample with potassium bicarbonate at a mass ratio of 1:3, and activate at 800°C under a nitrogen atmosphere. Figure 14The electrochemical performance of the heteroatom-doped multi-level porous carbon nanospheres prepared under 10 μL, 20 μL, 40 μL and 60 μL of 25% ammonia dosage after 700 ℃ activation in a three-electrode system is shown in the figure, and it can be seen that the heteroatom-doped multi-level porous carbon nanospheres prepared under 40 μL of 25% ammonia dosage exhibit the highest electrochemical performance.

[0069] For any person skilled in the art, many possible changes and modifications or equivalent embodiments of the technical solutions of the present application can be made to the technical content disclosed above without departing from the scope of the technical solutions of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application should still fall within the scope of protection of the technical solutions of the present application.

Claims

1. A method for preparing a heteroatom-doped hierarchical porous carbon nanosphere, characterized in that, The method comprises the following steps: 0.2 g of cetyltrimethylammonium bromide and 0.2 g of m-phenylenediamine are dissolved in a mixed solution of 19 mL of water and 8 mL of ethanol, 40 μL of 25% ammonia water is added, the solution is stirred at 30°C and a rotation speed of 500 rpm until it is uniformly transparent; meanwhile, 0.72 mL of tetraethyl silicate and 0.3 mL of formaldehyde aqueous solution are added, and the stirring is continued for 6 h; after centrifugation, washing and drying, the sample is transferred to a tube furnace, carbonized and etched at 800°C. The sample is uniformly mixed with potassium bicarbonate at a mass ratio of 1:3, heated to 500°C at a rate of 10°C / min under a nitrogen atmosphere, heated to 700°C at a rate of 5°C / min, kept for 1 h, naturally cooled to room temperature, and then collected; after washing with hydrochloric acid and deionized water until neutral, the sample is dried to obtain a heteroatom-doped hierarchical porous carbon nanosphere.

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