Nitrogen-doped graded porous carbon and preparation method thereof based on dual-template coupling in-situ activation method

Abstract

The invention provides nitrogen-doped graded porous carbon and a preparation method thereof based on a double-template coupling in-situ activation method, and belongs to the technical field of porous carbon material preparation. Through the coupling design of the synergistic effect of the double templates (the soft template and the degradable hard template) and in-situ gas-phase activation, the preparation method which is simple in process, green, environmentally friendly and capable of being popularized on a large scale is provided. According to the method, a macrostructure template, a mesostructure template and a chemical activator are combined into one through an ingenious process design, so that not only is the integrated construction of the nitrogen-doped hierarchical porous carbon material realized, but also the technical bottlenecks of difficulty in structural hierarchy construction, non-uniform nitrogen doping, complex process, poor environmental protection property and the like are solved.

Description

Technical Field

[0001] This invention relates to the field of porous carbon material preparation technology, and in particular to a nitrogen-doped hierarchical porous carbon and its preparation method based on a dual-template coupling in-situ activation method. Background Technology

[0002] Porous carbon materials are widely used due to their high specific surface area, tunable pore structure, and good electrical conductivity. Phenolic resins, as ideal precursors, have easily controllable molecular structure and crosslinking degree, and exhibit high carbon yield after carbonization.

[0003] Currently, common methods for preparing porous carbon include template methods and activation methods. Hard template methods (such as using silica nanospheres) can precisely replicate the morphology of the template to obtain ordered channels, but the subsequent template removal step (usually using hazardous chemicals such as hydrofluoric acid) is cumbersome, environmentally unfriendly, and costly. Soft template methods (such as using F127) can form ordered mesopores through self-assembly, but the control requirements for precursor molecular weight and synthesis conditions are extremely stringent, resulting in a narrow process window and difficulty in large-scale production. While the single KOH chemical activation method can create abundant micropores and obtain a high specific surface area, it easily leads to pore collapse and makes it difficult to form ordered mesoscopic or macroscopic structures. More importantly, the strong alkalinity of KOH severely corrodes equipment.

[0004] Furthermore, the inert surface chemistry of pure carbon materials limits their performance in electrochemical applications. Although nitrogen doping can improve wettability and pseudocapacitive properties through post-treatment, post-doping methods often suffer from problems such as uneven doping and low efficiency.

[0005] Therefore, developing a simple, environmentally friendly method for preparing phenolic resin-based porous carbon that can simultaneously and precisely control the hierarchical pore structure and surface chemical properties has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a nitrogen-doped hierarchical porous carbon and its preparation method based on a dual-template coupling in-situ activation method, in order to solve the above-mentioned technical problems.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing nitrogen-doped hierarchical porous carbon based on a dual-template coupled in-situ activation method, comprising the following steps: Step 1) Phenol, formaldehyde solution and water are mixed and reacted under the action of an alkaline catalyst to obtain phenolic resin solution, which serves as a carbon precursor; Step 2) Mix the phenolic resin solution, mesoporous template agent and melamine-formaldehyde resin aqueous solution in ethanol to obtain a mixed solution, and then slowly evaporate the solvent to obtain a solid product; Step 3) The obtained solid product is subjected to heat treatment, washing and drying in sequence to obtain nitrogen-doped hierarchical porous carbon.

[0008] Furthermore, in step 1), the mass concentration of the formaldehyde solution is 30-50%; The molar ratio of phenol to formaldehyde in the formaldehyde solution is 1:1~5; The molar ratio of phenol to alkaline catalyst is 1:0.01~0.15.

[0009] Furthermore, in step 1), the reaction is carried out under stirring, the reaction temperature is 50~100℃, and the reaction time is 40~80min; The alkaline catalyst includes sodium hydroxide, potassium hydroxide, or ammonia.

[0010] Furthermore, in step 2), the mass ratio of the phenolic resin solution to the mesoporous template agent is 1~3:0.1~1; The mass concentration of the melamine-formaldehyde resin aqueous solution is 30-70%; The mass ratio of phenolic resin in the phenolic resin solution to melamine-formaldehyde resin in the melamine-formaldehyde resin aqueous solution is 1:0.5~2; The mesoporous template agent includes block copolymer F127.

[0011] Furthermore, in step 2), the mixing is carried out under vigorous stirring for 3 to 6 hours.

[0012] Furthermore, in step 2), the temperature of the volatile solvent is 40~60℃ and the time is 30~45h.

[0013] Furthermore, in step 3), the heat treatment is a programmed temperature rise process, which includes two stages: low-temperature carbonization and high-temperature carbonization. The temperature for low-temperature carbonization is ≤600℃, the time for low-temperature carbonization is 2~5h, and the heating rate from room temperature to the temperature for low-temperature carbonization is 1~3℃ / min. The high-temperature carbonization temperature is 800~1000℃, the high-temperature carbonization time is 1~3h, and the heating rate is 5~8℃ / min when the temperature is raised from the low-temperature carbonization temperature to the high-temperature carbonization temperature.

[0014] Furthermore, in step 3), the drying temperature is 70~100℃ and the drying time is 10~15h.

[0015] This invention provides a nitrogen-doped hierarchical porous carbon prepared by the above method, wherein the nitrogen doping amount in the nitrogen-doped hierarchical porous carbon is 2~6 at.

[0016] Furthermore, the nitrogen-doped hierarchical porous carbon simultaneously contains micropores, mesopores, and macropores. The nitrogen-doped hierarchical porous carbon material has a specific surface area of ​​1500~2300 m². 2 / g.

[0017] The beneficial effects of this invention are: Integrated process: This invention innovatively selects melamine-formaldehyde resin (MF) as a thermally degradable hard template, an in-situ nitrogen doping source, and a gas-phase activator precursor, breaking through the cumbersome nature of traditional multi-step processes, achieving "one agent for three uses", reducing costs and improving efficiency.

[0018] Green and environmentally friendly: It eliminates the step of etching the template with hazardous chemicals such as hydrofluoric acid (HF) that must be used in the traditional hard template method. The MF template can be completely removed by heat treatment, which is environmentally friendly and has high production safety.

[0019] Excellent structure and superior performance: Through the synergistic effect of F127 soft template and MF hard template, a multi-level porous structure with micropores, mesopores, and macropores was successfully constructed. Micropores provide high specific surface area and a large number of active sites; ordered mesopores facilitate rapid ion transport; macropores act as ion buffers, shortening ion diffusion distances. This structure is conducive to constructing efficient ion and electron transport channels.

[0020] Uniform doping: The continuous release of gaseous NH3 ensures that nitrogen atoms are highly uniformly doped in the carbon framework, effectively improving the surface wettability and electrochemical activity of carbon materials.

[0021] Easy to scale up and mass-produce: This method has a simple process flow, mild conditions, and does not require complex and expensive post-processing, making it potential for large-scale industrial production. Detailed Implementation

[0022] This invention provides a method for preparing nitrogen-doped hierarchical porous carbon based on a dual-template coupled in-situ activation method, comprising the following steps: Step 1) Phenol, formaldehyde solution and water are mixed and reacted under the action of an alkaline catalyst to obtain phenolic resin solution, which serves as a carbon precursor; Step 2) Mix the phenolic resin solution, mesoporous template agent and melamine-formaldehyde resin aqueous solution in ethanol to obtain a mixed solution, and then slowly evaporate the solvent to obtain a solid product; Step 3) The obtained solid product is subjected to heat treatment, washing and drying in sequence to obtain nitrogen-doped hierarchical porous carbon.

[0023] In this invention, in step 1), the mass concentration of the formaldehyde solution is 30-50%, preferably 37%; The molar ratio of phenol to formaldehyde in the formaldehyde solution is 1:1 to 5, preferably 1:2 to 4; The molar ratio of phenol to alkaline catalyst is 1:0.01~0.15, preferably 1:0.08~0.13.

[0024] In this invention, in step 1), the reaction is carried out under stirring, the reaction temperature is 50~100℃, preferably 70~90℃, and the reaction time is 40~80min, preferably 60min; The alkaline catalyst includes sodium hydroxide, potassium hydroxide, or ammonia, preferably sodium hydroxide.

[0025] In this invention, in step 1), the phenolic resin is a first-order phenolic resin.

[0026] In this invention, in step 2), the mass ratio of the phenolic resin solution to the mesoporous template agent is 1~3:0.1~1, preferably 2:0.3~0.8; The mass concentration of the melamine-formaldehyde resin aqueous solution is 30-70%, preferably 50%; The mass ratio of phenolic resin in the phenolic resin solution to melamine-formaldehyde resin in the melamine-formaldehyde resin aqueous solution is 1:0.5~2, preferably 1:0.8~1.5; The mesoporous template agent is preferably a block copolymer F127.

[0027] In this invention, in step 2), the melamine-formaldehyde resin simultaneously serves as a thermally degradable hard template, a nitrogen dopant source, and a gas-phase activator precursor.

[0028] In this invention, in step 2), the mixing is carried out under vigorous stirring for 3 to 6 hours, preferably 4 to 5 hours.

[0029] In this invention, in step 2), the temperature of the volatile solvent is 40~60℃, preferably 50℃; the time is 30~45h, preferably 35~40h.

[0030] In this invention, in step 2), during the evaporation of the solvent, F127 and phenolic resin first undergo evaporation-induced synergistic self-assembly to form an ordered mesoscopic structure; at the same time, MF resin undergoes polymerization and curing to form nanoparticles, which are embedded in the F127 / phenolic resin composite structure.

[0031] In this invention, in step 3), the heat treatment is a programmed temperature rise process, which includes two stages: low-temperature carbonization and high-temperature carbonization. The preferred temperature for low-temperature carbonization is ≤600℃, and the preferred time for low-temperature carbonization is 2~5h, preferably 3~4h; when heating from room temperature to the low-temperature carbonization temperature, the heating rate is 1~3℃ / min, preferably 2℃ / min; The high-temperature carbonization temperature is 800~1000℃, preferably 900℃; the high-temperature carbonization time is 1~3h, preferably 2h; when the temperature is raised from the low-temperature carbonization temperature to the high-temperature carbonization temperature, the heating rate is 5~8℃ / min, preferably 6~7℃ / min.

[0032] In this invention, during the low-temperature carbonization, the F127 template and MF resin decompose. The decomposition of F127 leaves behind its replicated ordered mesoporous channels. The decomposition of MF resin generates gas, which on the one hand activates pore formation, and on the other hand achieves nitrogen doping.

[0033] In this invention, during the high-temperature carbonization, the carbon skeleton derived from phenolic resin is further graphitized, thereby improving the electrical conductivity and mechanical stability of the material.

[0034] In this invention, in step 3), the heat treatment is carried out under an inert atmosphere.

[0035] In this invention, in step 3), the drying temperature is 70~100℃, preferably 80~90℃; the drying time is 10~15h, preferably 12~14h.

[0036] This invention provides a nitrogen-doped hierarchical porous carbon prepared by the above method, wherein the nitrogen doping amount in the nitrogen-doped hierarchical porous carbon is 2~6 at%, preferably 3~5 at.

[0037] In this invention, the nitrogen-doped hierarchical porous carbon simultaneously contains micropores, mesopores, and macropores. In this invention, the pore size of the micropores is preferably 0.5~1nm, the pore size of the mesopores is preferably 3~4nm, and the pore size of the macropores is preferably 20~50nm.

[0038] The nitrogen-doped hierarchical porous carbon material has a specific surface area of ​​1500~2300 m². 2 / g, preferably 1800~2100m 2 / g.

[0039] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1

[0041] 0.1 mol phenol, 0.2 mol formaldehyde (37% formaldehyde solution) and 0.01 mol NaOH catalyst were mixed with 20 mL deionized water and stirred at 70 °C for 1 hour to obtain a phenolic resin solution, which was used as a carbon precursor. Take 2g of phenolic resin solution, 0.5g of Pluronic F127 and 2g of melamine-formaldehyde resin (added in the form of a 50% aqueous solution) and 10mL of ethanol, mix them, and stir vigorously for 4h to obtain a uniform and transparent mixed solution. The resulting mixed solution was poured into a petri dish and placed in an oven to evaporate the solvent at 50°C. After 36 hours, a pale yellow transparent film was obtained. This film was then heat-treated in a tube furnace. First, the temperature was increased to 350°C at a rate of 1°C / min under an argon atmosphere and held for 2 hours. Then, the temperature was increased to 900°C at a rate of 5°C / min and held for 1 hour. The film was then allowed to cool naturally to room temperature. The resulting solid product was washed sequentially with ethanol and deionized water to remove impurities. Finally, it was vacuum dried at 80°C for 12 hours to obtain nitrogen-doped hierarchical porous carbon, denoted as NPC-1.

[0042] Example 2

[0043] 0.1 mol phenol, 0.3 mol formaldehyde (37% formaldehyde solution), 0.08 mol NaOH catalyst, and 30 mL deionized water were mixed and stirred at 70°C for 1 hour to obtain a phenolic resin solution, which served as a carbon precursor. Take 2g of phenolic resin solution, 1g of Pluronic F127 and 1g of melamine-formaldehyde resin (MF, 50% aqueous solution) and 15mL of ethanol, mix them, and stir vigorously for 4h to obtain a uniform and transparent mixed solution. The resulting mixed solution was poured into a petri dish and placed in an oven to evaporate the solvent at 50°C. After 40 hours, a pale yellow transparent film was obtained. This film was then heat-treated in a tube furnace. First, the temperature was increased to 350°C at a rate of 1°C / min under an argon atmosphere and held for 2 hours. Then, the temperature was increased to 800°C at a rate of 8°C / min and held for 1 hour. The film was then allowed to cool naturally to room temperature. The resulting solid product was washed sequentially with ethanol and deionized water to remove impurities, and then vacuum dried at 80°C for 12 hours to obtain nitrogen-doped hierarchical porous carbon, denoted as NPC-2.

[0044] Example 3

[0045] 0.1 mol phenol, 0.5 mol formaldehyde (37% formaldehyde solution) and 0.15 mol NaOH catalyst were mixed with 30 mL deionized water and stirred at 70 °C for 1 hour to obtain a phenolic resin solution, which was used as a carbon precursor. Take 2g of phenolic resin solution, 2g of Pluronic F127 and 1.5g of melamine-formaldehyde resin (added in the form of a 50% aqueous solution) and 10mL of ethanol, mix them, and stir vigorously for 4h to obtain a uniform and transparent mixed solution. The resulting mixed solution was poured into a petri dish and placed in an oven to evaporate the solvent at 50°C. After 36 hours, a pale yellow transparent film was obtained. This film was then heat-treated in a tube furnace. First, the temperature was increased to 350°C at a rate of 1°C / min under an argon atmosphere and held for 2 hours. Then, the temperature was increased to 900°C at a rate of 5°C / min and held for 1 hour. The film was then allowed to cool naturally to room temperature. The resulting solid product was washed sequentially with ethanol and deionized water to remove impurities. Finally, it was vacuum dried at 80°C for 12 hours to obtain nitrogen-doped hierarchical porous carbon, denoted as NPC-3.

[0046] Comparative Example 1

[0047] Unlike Example 1, melamine-formaldehyde resin was not added in this comparative example, and the resulting product is denoted as C-1.

[0048] Performance testing

[0049] Characterization showed that the material NPC-1 obtained in Example 1 had the following properties: High specific surface area: BET specific surface area is 1250 m² 2 / g.

[0050] Hierarchical pore size distribution: The pore size distribution shows concentrated distributions at 0.5–1 nm (micropores), 3–4 nm (mesopores, from F127), and 20–50 nm (macropores, from MF), with microporosity of 85%–95%, mesoporosity of 2%–10%, and macroporosity of 1–5%. In contrast, the hierarchical pore size distribution of material C-1 obtained in Comparative Example 1 is as follows: microporosity ≤85%, mesoporosity ≥10%, and macroporosity ≥5%.

[0051] Nitrogen doping: XPS tests showed a nitrogen doping level of 4.5 at.

[0052] Electrochemical performance: At a current density of 1 A / g, its specific capacitance reaches 280 F / g, which is much higher than that of material C-1 in Comparative Example 1 (180 F / g), and the capacity retention rate is as high as 85% at a large current density of 10 A / g.

[0053] As can be seen from the above embodiments, the present invention provides a nitrogen-doped hierarchical porous carbon and its preparation method based on a dual-template coupled in-situ activation method. The preparation method of the present invention is simple and environmentally friendly. Through ingenious process design, this method integrates macroscopic structural templates, mesoscopic structural templates, and chemical activators into one, not only achieving the integrated construction of nitrogen-doped hierarchical porous carbon materials, but also solving technical bottlenecks such as difficulties in constructing hierarchical structures, uneven nitrogen doping, and complex and environmentally unfriendly processes, thus possessing significant industrial application value.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nitrogen-doped hierarchical porous carbon based on dual-template coupling in-situ activation, characterized in that, Includes the following steps: Step 1) Phenol, formaldehyde solution and water are mixed and reacted under the action of an alkaline catalyst to obtain phenolic resin solution, which serves as a carbon precursor; Step 2) Mix the phenolic resin solution, mesoporous template agent and melamine-formaldehyde resin aqueous solution in ethanol to obtain a mixed solution, and then slowly evaporate the solvent to obtain a solid product; Step 3) The obtained solid product is subjected to heat treatment, washing and drying in sequence to obtain nitrogen-doped hierarchical porous carbon.

2. The method for preparing nitrogen-doped hierarchical porous carbon based on dual-template coupling in-situ activation according to claim 1, characterized in that, In step 1), the mass concentration of the formaldehyde solution is 30-50%; The molar ratio of phenol to formaldehyde in the formaldehyde solution is 1:1~5; The molar ratio of phenol to alkaline catalyst is 1:0.01~0.

15.

3. A method for preparing nitrogen-doped hierarchical porous carbon based on a dual-template coupled in-situ activation method according to claim 1 or 2, characterized in that, In step 1), the reaction is carried out under stirring, the reaction temperature is 50~100℃, and the reaction time is 40~80min; The alkaline catalyst includes sodium hydroxide, potassium hydroxide, or ammonia.

4. The method for preparing nitrogen-doped hierarchical porous carbon based on dual-template coupling in-situ activation according to claim 3, characterized in that, In step 2), the mass ratio of the phenolic resin solution to the mesoporous template agent is 1~3:0.1~1; The mass concentration of the melamine-formaldehyde resin aqueous solution is 30-70%; The mass ratio of phenolic resin in the phenolic resin solution to melamine-formaldehyde resin in the melamine-formaldehyde resin aqueous solution is 1:0.5~2; The mesoporous template agent includes block copolymer F127.

5. A method for preparing nitrogen-doped hierarchical porous carbon based on a dual-template coupled in-situ activation method according to claim 1, 2, or 4, characterized in that, In step 2), the mixing is carried out under vigorous stirring for 3 to 6 hours.

6. The method for preparing nitrogen-doped hierarchical porous carbon based on dual-template coupling in-situ activation according to claim 5, characterized in that, In step 2), the temperature of the volatile solvent is 40~60℃ and the time is 30~45h.

7. A method for preparing nitrogen-doped hierarchical porous carbon based on a dual-template coupled in-situ activation method according to claim 4 or 6, characterized in that, In step 3), the heat treatment is a programmed temperature rise process, which includes two stages: low-temperature carbonization and high-temperature carbonization. The temperature for low-temperature carbonization is ≤600℃, the time for low-temperature carbonization is 2~5h, and the heating rate from room temperature to the temperature for low-temperature carbonization is 1~3℃ / min. The high-temperature carbonization temperature is 800~1000℃, the high-temperature carbonization time is 1~3h, and the heating rate is 5~8℃ / min when the temperature is raised from the low-temperature carbonization temperature to the high-temperature carbonization temperature.

8. The method for preparing nitrogen-doped hierarchical porous carbon based on dual-template coupling in-situ activation according to claim 7, characterized in that, In step 3), the drying temperature is 70~100℃ and the drying time is 10~15h.

9. The nitrogen-doped hierarchical porous carbon prepared by the method according to any one of claims 1 to 8, characterized in that, The nitrogen doping amount in the nitrogen-doped hierarchical porous carbon is 2~6 at.

10. The nitrogen-doped hierarchical porous carbon according to claim 9, characterized in that, The nitrogen-doped hierarchical porous carbon contains a structure that simultaneously contains micropores, mesopores, and macropores. The nitrogen-doped hierarchical porous carbon material has a specific surface area of ​​1500~2300 m². 2 / g.