Porous carbon material with adjustable pore size and preparation method and application thereof

Abstract

The present application relates to a kind of pore size adjustable control porous carbon material and its preparation method and application.In phenol source, alkali solution is stirred, then heated to 60-90 ℃, after adding aldehyde source solution, stirring, cooling to room temperature, add acid solution to adjust the mixture to neutral, obtain phenolic resin oligomer solution;Water is evaporated, low carbon alcohol is added, and phenolic low carbon alcohol solution is prepared;Preparation of silica sol, wherein the particle size of silica particle is controlled by adjusting pH value;Phenolic low carbon alcohol solution and silica sol are mixed and stirred at 35-45 ℃, then washed, filtered, dried, to obtain silica-phenolic resin composite carbon source;Carbonization treatment is carried out on silica-phenolic resin composite carbon source, to obtain carbonized product with carbon skeleton and SiO2 template;Wet etching treatment is carried out on carbonized product, and SiO2 template is selectively etched away, so that hole is formed in the position occupied by SiO2 particle, then washed, filtered, dried, to obtain porous carbon material with adjustable pore size.

Description

Technical Field

[0001] This invention relates to the field of porous carbon material preparation technology, and in particular to a porous carbon material with tunable pore size, its preparation method, and its application. Background Technology

[0002] With the advancement of science and technology and the development of industry, people have increasingly higher requirements for material performance. Among many new materials, porous carbon materials have attracted much attention due to their unique structure and excellent performance. Porous carbon materials are carbon materials with a highly developed pore structure, and their pore size, distribution, and morphology have a significant impact on the material's properties. By controlling the pore size, porous carbon materials with different pore structures can be prepared to meet the needs of different fields.

[0003] Microporous carbon materials are carbonaceous materials with abundant micropores, typically with pore sizes less than 2 nm. Due to their unique pore structure and excellent physicochemical properties, these materials exhibit broad application potential in fields such as gas adsorption and separation, energy storage, catalyst supports, environmental protection, and biomedicine. Microporous carbon materials not only possess high specific surface area, good electrical conductivity, and thermal stability, but also demonstrate outstanding adsorption performance and catalytic activity. Mesoporous carbon materials have pore sizes between 2 and 50 nm, and are commonly prepared using template methods. They are suitable for applications requiring the transport of larger molecules or ions, such as catalyst supports and the adsorption and release of biomolecules. Macroporous carbon materials have pore sizes greater than 50 nm, suitable for applications requiring rapid mass transfer and low pressure drop, such as fluid filtration and electrode materials. Different pore sizes correspond to different applications, thus necessitating the preparation of porous carbon materials with varying pore sizes. Common preparation methods include activation methods and hard template methods. Hard template methods typically use nano-silica as a hard template. The smaller the particle size, the more expensive it is. Furthermore, silica tends to aggregate during dispersion, leading to uneven pore size dispersion, which affects the electrochemical performance of the material and consequently the overall performance of the battery.

[0004] Zhou et al. directly used nano-silica sol as a hard template and prepared mesoporous carbon spheres with tunable pore sizes of 7-22 nm using a spray drying method (Zhou Jianguo, Research on the Preparation of Mesoporous / Hollow Carbon Microspheres by Spray Drying and Their Applications [D] East China University of Science and Technology, 2016). However, the strong van der Waals forces between nano-silica particles make dispersion in solvents difficult to solve, leading to agglomeration and resulting in larger and less uniform pore sizes in subsequent porous carbon materials. Furthermore, nano-silica sol is expensive and not suitable for large-scale industrial production.

[0005] Therefore, developing a method for preparing porous carbon materials with a relatively concentrated pore size distribution can not only maximize the advantages of different pore sizes and meet different needs, but also provide strong support for further optimizing the electrochemical performance of porous carbon materials. This is a key issue that urgently needs to be addressed in the current research field. Summary of the Invention

[0006] This invention aims to provide a porous carbon material with tunable pore size, its preparation method, and its applications, overcoming problems such as difficult template dispersion, uneven pore size, complex preparation process, and limited electrochemical performance of carbon materials in existing technologies. By introducing silica sol with controllable particle size as a hard template, and combining it with phenolic resin oligomers, followed by carbonization and etching, the controllable construction of a porous structure is achieved. This results in a porous carbon material with uniform pore size distribution, high specific surface area, and excellent cycle stability, making it particularly suitable for energy storage materials, lithium-ion battery anodes, and other fields.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing porous carbon materials with tunable pore size, comprising:

[0008] Add the phenol source to a container at 25-50℃, then add the first alkali solution and stir. Then raise the temperature to 60-90℃, add the aldehyde source solution and stir. Finally, cool to room temperature and add the first acid solution to adjust the mixture to neutral to obtain a phenolic resin oligomer solution.

[0009] The water in the phenolic resin oligomer solution is evaporated, and then a low-carbon alcohol is added to prepare a phenolic low-carbon alcohol solution; wherein the low-carbon alcohol includes any one of methanol, ethanol, propanol, and butanol.

[0010] A second acid solution or a second alkali solution is added to a silicate solution to adjust the pH value of the silicate solution to between 4.0 and 10.0, thereby preparing a silica sol; the silica sol comprises colloidal silica particles, wherein the particle size of the silica particles is controlled by adjusting the pH value.

[0011] The phenolic low-carbon alcohol solution and the silica sol are mixed and stirred at 35-45°C to obtain a mixture. The mixture is then washed, filtered, and dried to obtain a silica-phenolic resin composite carbon source. In the silica-phenolic resin composite carbon source, the silica particles are uniformly dispersed.

[0012] Under an inert atmosphere, the silica-phenolic resin composite carbon source is carbonized to obtain a carbonized product with a carbon skeleton and a SiO2 template; wherein, the carbon skeleton is a three-dimensional continuous carbon skeleton formed by the pyrolysis of phenolic resin oligomers, forming a continuous conductive network; and SiO2 particles are uniformly dispersed between the carbon skeleton as templates.

[0013] The carbonized product is subjected to wet etching with an etching solution. Through the wet etching process, the SiO2 template is selectively etched away, thereby forming pores in the positions occupied by the SiO2 particles. After washing, filtering and drying, the porous carbon material with adjustable pore size is obtained.

[0014] Preferably, the phenol source includes one of phenol, resorcinol, phloroglucinol, cashew phenol, m-aminophenol, 3-aminophenol, cresol, nonylphenol, octylphenol, and xylenol;

[0015] The aldehyde source solution includes one or more of formaldehyde, terephthalaldehyde, acetaldehyde, and furfural;

[0016] The first alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution;

[0017] The first acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, nitric acid solution, acetic acid solution, and citric acid solution;

[0018] The silicate solution includes either a sodium silicate solution or a potassium silicate solution.

[0019] The second alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution;

[0020] The second acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, and nitric acid solution;

[0021] The etching solution includes one of the following: HF solution, NaOH solution, or KOH solution.

[0022] Preferably, the step of adding the first acid solution to adjust the mixture to neutral specifically involves adding the first acid solution to adjust the mixture to pH = 7.0 ± 0.5.

[0023] Preferably, the step of evaporating the water from the phenolic resin oligomer solution and then adding a low-carbon alcohol to prepare a phenolic low-carbon alcohol solution specifically includes:

[0024] The water in the phenolic resin oligomer solution is evaporated using any one of the following evaporation methods: rotary evaporation, reduced pressure evaporation, water bath evaporation, or hot plate evaporation.

[0025] The phenolic low-carbon alcohol solution was prepared by adding low-carbon alcohol at a ratio of 20-30 wt.% of the phenolic resin oligomer in the solution.

[0026] Preferably, the execution order of preparing the silica sol and the phenolic low-carbon alcohol solution includes: first preparing the silica sol and then preparing the phenolic low-carbon alcohol solution; or, preparing the silica sol and preparing the phenolic low-carbon alcohol solution are performed simultaneously; or, the phenolic low-carbon alcohol solution is prepared first and then the silica sol is prepared.

[0027] Preferably, the carbonization process includes: heating from room temperature to 600-900°C at a heating rate of 2-10°C / min, and holding at that temperature for 1-8 hours.

[0028] Preferably, the method for wet etching the carbonized product using an etching solution includes: immersing the carbonized product in the etching solution and performing wet etching.

[0029] The washing process involves using deionized water until the solution is neutral.

[0030] The drying temperature is 80-110℃.

[0031] More preferably, the method of wet etching the carbonized product with an etching solution further includes: magnetic stirring while immersing for 0.5-24 hours.

[0032] Secondly, embodiments of the present invention provide a porous carbon material with tunable pore size prepared by the preparation method described in the first aspect above.

[0033] Thirdly, the present invention provides an application of a porous carbon material with tunable pore size prepared by the preparation method described in the first aspect above, wherein the porous carbon material is used as an electrode material, separator material, or coating material in a secondary battery.

[0034] The method for preparing porous carbon materials with tunable pore size provided in this invention involves hydrolyzing a silica solution under controlled pH conditions to generate silica sol with tunable particle size, and then uniformly compounding it with phenolic resin oligomers in a low-carbon alcohol system. Following carbonization and template etching, a porous carbon material with a three-dimensional continuous carbon framework and tunable pore size structure is successfully constructed. This method features a simple process flow and mild preparation conditions, avoiding problems such as poor dispersion and non-uniform pore structure associated with traditional solid templates. While improving the controllability of pore size, it also significantly increases the specific surface area of ​​the porous carbon material, facilitating rapid diffusion and effective storage of metal ions. This effectively enhances the electrochemical performance of porous carbon materials in energy storage devices, demonstrating good controllability and promising prospects for industrial application. Attached Figure Description

[0035] Figure 1 A flowchart illustrating a method for preparing porous carbon materials with tunable pore size provided in an embodiment of the present invention;

[0036] Figure 2 This is a scanning electron microscope (SEM) image of the porous carbon material with adjustable pore size prepared in Example 1 of the present invention;

[0037] Figure 3 This is a pore size distribution diagram of the porous carbon material with adjustable pore size prepared in Example 1 of the present invention;

[0038] Figure 4 This is a pore size distribution diagram of the porous carbon material prepared in Comparative Example 1 of the present invention;

[0039] Figure 5 This is a pore size distribution diagram of the porous carbon material prepared in Comparative Example 2 of the present invention;

[0040] Figure 6 This is a pore size distribution diagram of the porous carbon material prepared in Comparative Example 3 of the present invention. Detailed Implementation

[0041] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0042] This invention provides a porous carbon material with tunable pore size and its preparation method.

[0043] Figure 1 This is a flowchart of a method for preparing porous carbon materials with adjustable pore size provided in an embodiment of the present invention. The following section will first refer to... Figure 1 The preparation method proposed in this invention will be described.

[0044] like Figure 1 The main steps in the preparation method of porous carbon materials with tunable pore size include:

[0045] Step 110: Add the phenol source to a container at 25-50℃, then add the first alkali solution and stir. Then raise the temperature to 60-90℃, add the aldehyde source solution and stir. Finally, cool to room temperature, add the first acid solution to adjust the mixture to neutral, and obtain the phenolic resin oligomer solution.

[0046] Among them, the phenolic source includes one of the following: phenol, resorcinol, phloroglucinol, cashew nut shell, m-aminophenol, 3-aminophenol, cresol, nonylphenol, octylphenol, and xylenol;

[0047] The aldehyde source solution includes one or more of formaldehyde, terephthalaldehyde, acetaldehyde, and furfural;

[0048] The first alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution;

[0049] The first acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, nitric acid solution, acetic acid solution, and citric acid solution;

[0050] Adjust the mixture to neutral by adding the first acid solution. Specifically, after adding the first acid solution, adjust the pH of the mixture to 7.0 ± 0.5.

[0051] In this step, under alkaline conditions, the phenolic source and the aldehyde source solution (using formaldehyde as an example) undergo a nucleophilic addition reaction to form a hydroxymethylphenol intermediate. This is followed by a condensation reaction to form a phenolic resin oligomer with a certain degree of polymerization. By controlling the temperature and reaction time, the degree of condensation can be effectively adjusted to obtain a liquid oligomeric phenolic resin system suitable for subsequent compounding. After the reaction is complete, the pH is adjusted to neutral by adding an acid solution to terminate the reaction and stabilize the resulting phenolic resin oligomer solution.

[0052] Preferably, the stirring time for adding the first alkaline solution is 10–30 min, and the temperature is preferably 40–50 °C to ensure that the system is fully alkalized. If the temperature is too low, the phenol source will precipitate locally or be unevenly dispersed, which is not conducive to dispersion. If the temperature is too high, the condensation reaction may be induced prematurely, forming an unstable intermediate polymer.

[0053] Preferably, the aldehyde source solution is added slowly dropwise, and the reaction is carried out at a temperature of 60-90°C for 60-120 minutes to promote the condensation reaction. Finally, the first acid solution is added to adjust the pH of the mixture to neutral. Optionally, stirring is continued for 10-20 minutes after the first acid solution is added to terminate the reaction and achieve stabilization.

[0054] It should be noted that the reaction time can be adjusted appropriately according to the amount of reactants. When the reactant concentration is high, the effective collision frequency in the system increases, the reaction rate is relatively faster, and the reaction time can be appropriately shortened; however, at the same time, the system viscosity increases, which may restrict diffusion in the later polycondensation process, requiring comprehensive control of temperature and target degree of polymerization. Conversely, when the reactant concentration is low, the reaction rate decreases, and the reaction time should be appropriately extended to ensure sufficient polycondensation. Therefore, there is a certain correlation between reaction time and reactant concentration, and those skilled in the art can optimize the settings based on the actual system parameters and commonly used techniques in the field during actual implementation.

[0055] Step 120: Evaporate the water in the phenolic resin oligomer solution, and then add low-carbon alcohol to prepare a phenolic low-carbon alcohol solution.

[0056] Specifically, water evaporation can be carried out using any of the following evaporation methods: rotary evaporation, reduced pressure evaporation, water bath evaporation, or hot plate evaporation.

[0057] The added low-carbon alcohols include any one of methanol, ethanol, propanol, and butanol; the amount of low-carbon alcohol added is based on the ratio of the phenolic resin oligomer to the mass concentration of the phenolic low-carbon alcohol solution after addition being 20-30 wt.%.

[0058] If the mass concentration of phenolic resin oligomers in the phenolic low-carbon alcohol solution exceeds 30 wt.%, the solution viscosity will increase significantly. When compounded with silica sol, further cross-linking reactions easily occur between the phenolic oligomers, leading to rapid gelation of the system. This is detrimental to the uniform doping and dispersion of silica particles, potentially affecting the uniformity of the composite structure and the control of the pore structure. Conversely, if the mass concentration of phenolic resin oligomers is below 20 wt.%, insufficient carbon precursor content will result in difficulty in forming a complete three-dimensional continuous carbon framework structure after carbonization. Simultaneously, the reduced coating degree of the silica template will cause problems such as pore structure collapse, pore wall discontinuity, or reduced conductivity, thereby weakening the mechanical strength and electrochemical performance of the final porous carbon material. Therefore, in this invention, the mass concentration of phenolic oligomers is preferably controlled at 20–30 wt.% to balance dispersibility, structural integrity, and the construction of a conductive network, ensuring the acquisition of porous carbon materials with good pore structure control and performance.

[0059] Step 130: Add a second acid solution or a second alkali solution to the silicate solution to adjust the pH value of the silicate solution to between 4.0 and 10.0, and prepare silica sol.

[0060] Specifically, silica sol includes colloidal silica particles.

[0061] The silicate solution includes either sodium silicate solution or potassium silicate solution.

[0062] The second alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution;

[0063] The second acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, and nitric acid solution.

[0064] In this step, the particle size of the silica particles is controlled by adjusting the pH value, as further explained below:

[0065] This invention induces hydrolysis and condensation reactions in silicates by introducing a second acid or alkali solution into a silicate solution to adjust the pH of the system to the range of 4.0-10.0, thereby forming a colloidal silica sol. This process mainly involves the hydrolysis of silicate ions to generate monomeric silicic acid and subsequent polymerization and condensation reactions, producing a stable Si-O-Si bond network structure, which gradually forms nanoscale colloidal particles.

[0066] The rates of hydrolysis and condensation differ significantly under different pH conditions, thus affecting the growth mechanism and particle size distribution of silica particles. Under slightly acidic conditions (pH = 4-6), the hydrolysis rate is faster and the condensation rate is relatively slower, which is conducive to the formation of colloidal particles with smaller particle size and better dispersibility. Under neutral or slightly alkaline conditions (pH = 7-10), the condensation rate is accelerated, the colloidal particle size gradually increases, the interparticle interaction is enhanced, and it is easy to form larger or more compact SiO2 particles.

[0067] Therefore, in practical implementation, the target pH value to be controlled can be determined according to the actual needs of pore size, thereby enabling controllable adjustment of silica particle size and laying the foundation for subsequent adjustment of the pore size of porous carbon materials.

[0068] The execution order of steps 110-120 and step 130 can be arbitrary or simultaneous. That is, the execution order of preparing silica sol and preparing phenolic low-carbon alcohol solution includes preparing silica sol first and then preparing phenolic low-carbon alcohol solution, or preparing silica sol and preparing phenolic low-carbon alcohol solution simultaneously, or preparing phenolic low-carbon alcohol solution first and then preparing silica sol.

[0069] Step 140: Mix the phenolic low-carbon alcohol solution with silica sol at 35-45℃ to obtain a mixture. Wash, filter and dry the mixture to obtain a silica-phenolic resin composite carbon source.

[0070] In this step, a mixture is obtained by mixing and stirring a phenolic low-carbon alcohol solution with a silica sol at 35-45°C. This allows phenolic oligomers to be adsorbed onto the silica surface through hydrogen bonding or van der Waals forces, while some phenolic molecules permeate into the gaps between the sol particles, forming a composite structure. During this process, no significant chemical cross-linking reaction occurs in the system. After washing, filtering, and drying, the resulting mixture forms a silica-phenolic resin composite carbon source with good dispersibility and interfacial bonding. In the silica-phenolic resin composite carbon source, the silica particles are uniformly dispersed.

[0071] The uniform dispersion of silica particles is mainly due to the following two aspects: First, the particles in the silica sol are in a colloidal state, with controllable particle size during the previous preparation process and surface charge, exhibiting high dispersion stability and being less prone to aggregation. Second, the hydroxyl groups in the phenolic oligomers can physically adsorb onto the silica surface through hydrogen bonds or van der Waals forces, thereby achieving a "coating" distribution and stable fixation of the silica particles during mixing and stirring, preventing their aggregation. Therefore, the highly uniform spatial distribution of silica provides a foundation for the uniformity of pore size distribution after subsequent carbonization and etching.

[0072] Step 150: Under an inert atmosphere, the silica-phenol resin composite carbon source is carbonized to obtain a carbonized product with a carbon skeleton and a SiO2 template.

[0073] The carbon skeleton is a three-dimensional continuous carbon skeleton formed by the pyrolysis of phenolic resin oligomers, forming a continuous conductive network; SiO2 particles are uniformly dispersed between the carbon skeleton as templates.

[0074] The carbonization process includes heating from room temperature to 600-900℃ at a heating rate of 2-10℃ / min and holding at that temperature for 1-8 hours.

[0075] This step, by controlling the heating rate at 2–10℃ / min, effectively avoids material structural damage caused by localized thermal stress and ensures that the phenolic resin oligomers slowly release small molecules (such as H2O, CO2, CH4, etc.) during pyrolysis, gradually transforming into carbonaceous materials. The controllable heating rate helps form a structurally stable carbon framework while reducing agglomeration or cracking during thermal polycondensation.

[0076] When the temperature is raised to 600-900℃ and kept constant for 1-8 hours, the phenolic oligomers complete the transformation from an amorphous organic structure to an amorphous carbon structure with a low degree of graphitization, forming a conductive carbon skeleton with a three-dimensional continuous structure and good electronic conductivity.

[0077] Throughout the carbonization process, SiO2 particles are uniformly embedded in the carbon skeleton as hard templates, without participating in the pyrolysis reaction, maintaining their original particle size and dispersion state. This ensures that the pores formed after subsequent etching maintain consistency in size and distribution, thereby obtaining porous carbon materials with uniform pore size and high specific surface area.

[0078] Step 160: The carbonized product is subjected to wet etching with an etching solution. Through wet etching, the SiO2 template is selectively etched away, thereby forming pores in the positions occupied by the SiO2 particles. After washing, filtering and drying, a porous carbon material with adjustable pore size is obtained.

[0079] The method of wet etching of carbonized products using an etching solution includes: immersing the carbonized products in an etching solution and performing wet etching; preferably, magnetic stirring can also be performed during immersion, and the uniformly dispersed SiO2 template in the carbonized products can be selectively removed by wet etching, thereby forming a regular pore structure in its original position and obtaining a porous carbon material with adjustable pore size.

[0080] Specifically, the etching solution can be selected from any one of hydrofluoric acid (HF) solution, sodium hydroxide (NaOH) solution, or potassium hydroxide (KOH) solution. Among them, HF solution can directly react with SiO2 to generate soluble hexafluorosilicic acid (H2SiF6); alkaline solutions such as NaOH or KOH can convert SiO2 into soluble silicates through reaction, thereby achieving efficient etching of SiO2 templates.

[0081] The wet etching method involves fully immersing the carbide products in the aforementioned etching solution, preferably under magnetic stirring conditions, for 0.5-24 hours. Magnetic stirring further enhances the contact efficiency between the etching solution and the carbide products, accelerating the removal reaction process of the SiO2 template.

[0082] After etching, the obtained porous carbon material is repeatedly washed with deionized water until the washing solution is neutral to remove residual etching byproducts. After washing, it is dried at a temperature of 80-110℃, preferably for 6-12 hours, to fully remove adsorbed moisture, maintain the stability of the material's pore structure, and prevent thermal collapse.

[0083] The porous carbon material prepared by the above-described preparation method of the present invention has a tunable pore size distribution with a main pore size ranging from 0.5 to 100 nm. Specifically, the lower the pH value of the silicate solution in step 130, the smaller the main pore size of the obtained porous carbon material; conversely, the higher the pH value, the larger the main pore size. The prepared porous carbon material can be used as an electrode material, separator material, or coating material in secondary batteries.

[0084] Summarizing the above process, taking phenol, formaldehyde, and sodium silicate as phenol source, aldehyde source solution, and silicate as examples, the pore size control mechanism of this invention is as follows:

[0085] Phenol can undergo an addition reaction with formaldehyde under alkaline conditions, followed by condensation and polymerization. When acid is added to a sodium silicate (Na₂SiO₃) solution, a hydrolysis reaction occurs, in which sodium silicate reacts with hydrogen ions (H⁺) in water. + They combine to form silicic acid (H₂SiO₃) and the corresponding salt. Here, H… + It originates from acid, and it reacts with silicate ions (SiO3) in sodium silicate. 2- Sodium silicate combines with water to form silicic acid (H₂SiO₃), which is insoluble in water. Because silicic acid has very low solubility in water, it readily precipitates out of the solution as a precipitate. This precipitate is silicon dioxide (SiO₂), but it usually exists in a hydrated form, such as SiO₂·nH₂O (where n represents the number of water molecules). In water, sodium silicate completely ionizes to form metasilicate (SiO₃²⁻). 2- ) and sodium ions (Na +Under alkaline conditions, sodium silicate undergoes a hydrolysis reaction with water to produce silicic acid (H₂SiO₃) and sodium hydroxide (NaOH). This is because under alkaline conditions, hydroxide ions (OH⁻) are produced. - A higher concentration of H₂SiO₃ inhibits further hydrolysis of silicic acid (H₂SiO₃), causing the reaction to proceed in the reverse direction, i.e., towards the formation of sodium silicate (Na₂SiO₃).

[0086] The particle size of silica produced by the hydrolysis of sodium silicate solution changes with increasing pH. Specifically, at lower pH values ​​(e.g., under acidic conditions), the hydrolysis of sodium silicate is faster, but the resulting silica particles are smaller. This is because the higher hydrogen ion concentration under acidic conditions promotes the combination of silicate ions with hydrogen ions, but also accelerates the condensation and precipitation of silicic acid, resulting in smaller particles. As the pH increases (e.g., under alkaline conditions), the hydrolysis rate of sodium silicate slows down, and the resulting silica particles gradually increase in size. This is because under alkaline conditions, the concentration of hydroxide ions increases, and they combine with silicate ions to form more stable silicate ions, thus slowing down the condensation and precipitation of silicic acid. In summary, the particle size of silica produced by the hydrolysis of sodium silicate solution gradually increases with increasing pH, but the specific trend and extent of this change depend on the combined effects of multiple factors. The reaction principle for synthesizing porous carbon involves complex chemical reactions and physical processes, such as material proportions and preparation procedures. By precisely controlling the synergistic effect of various factors, porous carbon materials with tunable pore size and excellent performance can be prepared.

[0087] In this invention, silica sol generated by the hydrolysis of sodium silicate solution serves as a hard template, replacing the solid silica particles synthesized by the traditional gas-phase method. This effectively overcomes the problems of poor dispersibility and easy agglomeration of the latter during the composite process, significantly improving the uniformity and stability of the system. The method is simple to operate, easy to control, and has strong process feasibility. By adjusting the solution pH to 4.0-10.0, the silica particle size distribution during the hydrolysis process can be precisely controlled, thereby achieving the control of different pore sizes after carbonization and obtaining porous carbon materials with high specific surface area and hierarchical pore structure. Because silica can be uniformly deposited in the phenolic carbon precursor system in the sol state, the aggregation problem of nano-SiO2 templates during carbonization is avoided. Therefore, the pore distribution formed after etching is more uniform, which is beneficial for the construction of ion / electrolyte diffusion and rapid transport channels.

[0088] In summary, the proposed method not only improves the structural controllability and repeatability of porous carbon materials, but also helps to enhance the specific capacity, rate performance, and cycle stability of porous carbon materials in electrochemical applications, and has broad application prospects.

[0089] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0090] Example 1

[0091] This embodiment provides a method for preparing porous carbon materials with adjustable pore size, specifically including the following steps:

[0092] Step 1: Add 8g of melted phenol to a three-necked flask at 45℃, then add 10mL of 0.2M NaOH solution and stir for 20min to mix evenly; then slowly add 13.76g of formaldehyde solution (37wt.%), stir at 78℃ for 60min to obtain the reactant. After the reactant is cooled to room temperature, adjust the pH to neutral (pH=7.0±0.5) with 0.2M HCl aqueous solution and continue stirring for 15min to obtain a phenolic resin oligomer solution.

[0093] Step 2: The phenolic resin oligomer solution obtained in Step 1 is prepared by rotary evaporation to evaporate the water in the solution, and then ethanol is added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%.

[0094] Step 3: Mix 7.5g sodium silicate (Si O2 27wt.%), 22.5g water and an appropriate amount of 0.50M H2SO4 aqueous solution, adjust the pH of the sodium silicate solution to 4.0 with H2SO4 aqueous solution, stir at room temperature for 30min to form a silica sol with colloidal silica particles.

[0095] Step 4: Add the silica sol with pH value of 4.0 obtained in Step 3 to 10g of the phenolic ethanol solution obtained in Step 2 at 40℃, stir for 1h, then vacuum filter, wash 3 times with deionized water until the washing solution is neutral, and dry at 100℃ for 10h to obtain silica-phenolic resin composite carbon source.

[0096] Step 5: Carbonize the silica-phenol resin composite carbon source obtained in step 4 in a tube furnace, purge with nitrogen gas at a flow rate of 5 L / min, and raise the temperature at a rate of 5 °C / min from room temperature to 800 °C. Hold at this temperature for 2 hours to obtain the carbonized product.

[0097] Step 6: Wet etching of the carbonized product with hydrofluoric acid, magnetic stirring for 24 hours, then repeatedly washing with deionized water until the washing solution is neutral, and drying at 80°C for 8 hours to finally obtain a finished porous carbon material with adjustable pore size.

[0098] The scanning electron microscope (SEM) image of the porous carbon material with adjustable pore size prepared in this embodiment is shown below. Figure 2 As shown, the pore size distribution of the tunable porous carbon material is as follows: Figure 3 As shown.

[0099] Example 2

[0100] This embodiment provides a method for preparing porous carbon materials with adjustable pore size, specifically including the following steps:

[0101] Step 1: Add 8g of melted phenol to a three-necked flask at 45℃, then add 10mL of 0.2M NaOH solution and stir for 20min to mix evenly; then slowly add 13.76g of formaldehyde solution (37wt.%), stir at 78℃ for 60min to obtain the reactant. After the reactant is cooled to room temperature, adjust the pH to neutral (pH=7.0±0.5) with 0.2M HCl aqueous solution and continue stirring for 15min to obtain a phenolic resin oligomer solution.

[0102] Step 2: The phenolic resin oligomer solution obtained in Step 1 is prepared by rotary evaporation to evaporate the water in the solution, and then ethanol is added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%.

[0103] Step 3: Mix 7.5g sodium silicate (Si O2 27wt.%), 22.5g water and an appropriate amount of 0.50M H2SO4 aqueous solution, adjust the pH of the sodium silicate solution to 5.0 with H2SO4 aqueous solution, stir at room temperature for 30min to form a silica sol with colloidal silica particles.

[0104] Step 4: Add the silica sol with pH value of 5.0 obtained in step 3 to 10g of the phenolic ethanol solution obtained in step 2 at 40℃, stir for 1h, then vacuum filter, wash 3 times with deionized water until the washing solution is neutral, and dry at 100℃ for 10h to obtain silica-phenolic resin composite carbon source.

[0105] Step 5: Carbonize the silica-phenol resin composite carbon source obtained in step 4 in a tube furnace, purge with nitrogen gas at a flow rate of 5 L / min, and raise the temperature at a rate of 5 °C / min from room temperature to 800 °C. Hold at this temperature for 2 hours to obtain the carbonized product.

[0106] Step 6: Wet etching of the carbonized product with hydrofluoric acid, magnetic stirring for 24 hours, then repeatedly washing with deionized water until the washing solution is neutral, and drying at 80°C for 8 hours to finally obtain a finished porous carbon material with adjustable pore size.

[0107] Example 3

[0108] This embodiment provides a method for preparing porous carbon materials with adjustable pore size, specifically including the following steps:

[0109] Step 1: Add 8g of melted phenol to a three-necked flask at 45℃, then add 10mL of 0.2M NaOH solution and stir for 20min to mix evenly; then slowly add 13.76g of formaldehyde solution (37wt.%), stir at 78℃ for 60min to obtain the reactant. After the reactant is cooled to room temperature, adjust the pH to neutral (pH=7.0±0.5) with 0.2M HCl aqueous solution and continue stirring for 15min to obtain a phenolic resin oligomer solution.

[0110] Step 2: The phenolic resin oligomer solution obtained in Step 1 is prepared by rotary evaporation to evaporate the water in the solution, and then ethanol is added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%.

[0111] Step 3: Mix 7.5g sodium silicate (Si O2 27wt.%), 22.5g water and an appropriate amount of 0.50M NaOH aqueous solution, adjust the pH of the sodium silicate solution to 8.0 with NaOH aqueous solution, stir at room temperature for 30min to form a silica sol with colloidal silica particles;

[0112] Step 4: Add the silica sol with pH value of 8.0 obtained in step 3 to 10g of the phenolic ethanol solution obtained in step 2 at 40℃, stir for 1h, then vacuum filter, wash 3 times with deionized water until the washing solution is neutral, and dry at 100℃ for 10h to obtain silica-phenolic resin composite carbon source.

[0113] Step 5: Carbonize the silica-phenol resin composite carbon source obtained in step 4 in a tube furnace, purge with nitrogen gas at a flow rate of 5 L / min, and raise the temperature at a rate of 5 °C / min from room temperature to 800 °C. Hold at this temperature for 2 hours to obtain the carbonized product.

[0114] Step 6: Wet etching of the carbonized product with hydrofluoric acid, magnetic stirring for 24 hours, then repeatedly washing with deionized water until the washing solution is neutral, and drying at 80°C for 8 hours to finally obtain a finished porous carbon material with adjustable pore size.

[0115] Example 4

[0116] This embodiment provides a method for preparing porous carbon materials with adjustable pore size, specifically including the following steps:

[0117] Step 1: Add 8g of melted phenol to a three-necked flask at 45℃, then add 10mL of 0.2M NaOH solution and stir for 20min to mix evenly; then slowly add 13.76g of formaldehyde solution (37wt.%), stir at 78℃ for 60min to obtain the reactant. After the reactant is cooled to room temperature, adjust the pH to neutral (pH=7.0±0.5) with 0.2M HCl aqueous solution and continue stirring for 15min to obtain a phenolic resin oligomer solution.

[0118] Step 2: The phenolic resin oligomer solution obtained in Step 1 is prepared by rotary evaporation to evaporate the water in the solution, and then ethanol is added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%.

[0119] Step 3: Mix 7.5g sodium silicate (Si O2 27wt.%), 22.5g water and an appropriate amount of 0.50M NaOH aqueous solution, adjust the pH of the sodium silicate solution to 9.0 with NaOH aqueous solution, stir at room temperature for 30min to form a silica sol with colloidal silica particles.

[0120] Step 4: Add the silica sol with pH value of 9.0 obtained in step 3 to 10g of the phenolic ethanol solution obtained in step 2 at 40℃, stir for 1h, then vacuum filter, wash 3 times with deionized water until the washing solution is neutral, and dry at 100℃ for 10h to obtain silica-phenolic resin composite carbon source.

[0121] Step 5: Carbonize the silica-phenol resin composite carbon source obtained in step 4 in a tube furnace, purge with nitrogen gas at a flow rate of 5 L / min, and raise the temperature at a rate of 5 °C / min from room temperature to 800 °C. Hold at this temperature for 2 hours to obtain the carbonized product.

[0122] Step 6: Wet etching of the carbonized product with hydrofluoric acid, magnetic stirring for 24 hours, then repeatedly washing with deionized water until the washing solution is neutral, and drying at 80°C for 8 hours to finally obtain a finished porous carbon material with adjustable pore size.

[0123] Example 5

[0124] This embodiment provides a method for preparing porous carbon materials with adjustable pore size, specifically including the following steps:

[0125] Step 1: Add 8g of melted phenol to a three-necked flask at 45℃, then add 10mL of 0.2M NaOH solution and stir for 20min to mix evenly; then slowly add 13.76g of formaldehyde solution (37wt.%), stir at 78℃ for 60min to obtain the reactant. After the reactant is cooled to room temperature, adjust the pH to neutral (pH=7.0±0.5) with 0.2M HCl aqueous solution and continue stirring for 15min to obtain a phenolic resin oligomer solution.

[0126] Step 2: The phenolic resin oligomer solution obtained in Step 1 is prepared by rotary evaporation to evaporate the water in the solution, and then ethanol is added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%.

[0127] Step 3: Mix 5.5g potassium silicate (SiO2 27wt.%), 22.5g water and an appropriate amount of 1M HCl aqueous solution. Adjust the pH of the potassium silicate solution to 4.5 with the HCl aqueous solution. Stir at room temperature for 30 minutes to form a silica sol with colloidal silica particles.

[0128] Step 4: Add the silica sol with pH value of 4.5 obtained in step 3 to 10g of the phenolic ethanol solution obtained in step 2 at 40℃, stir for 1h, then vacuum filter, wash 3 times with deionized water until the washing solution is neutral, and dry at 100℃ for 10h to obtain silica-phenolic resin composite carbon source.

[0129] Step 5: Carbonize the silica-phenol resin composite carbon source obtained in step 4 in a tube furnace, purge with nitrogen gas at a flow rate of 5 L / min, and raise the temperature at a rate of 5 °C / min from room temperature to 800 °C. Hold at this temperature for 2 hours to obtain the carbonized product.

[0130] Step 6: Wet etching of the carbonized product with hydrofluoric acid, magnetic stirring for 24 hours, then repeatedly washing with deionized water until the washing solution is neutral, and drying at 80°C for 8 hours to finally obtain a finished porous carbon material with adjustable pore size.

[0131] Comparative Example 1

[0132] The execution method of this comparative example is basically the same as that of Example 1, except that sodium silicate in step 3 is replaced with sodium metasilicate.

[0133] The pore size distribution diagram of the porous carbon material prepared in Comparative Example 1 is shown in Figure 1. Figure 4 As shown.

[0134] Comparative Example 2

[0135] The execution method of this comparative example is basically the same as that of Example 1, except that the sulfuric acid aqueous solution in step 3 is replaced with acetic acid aqueous solution.

[0136] The pore size distribution diagram of the porous carbon material prepared in Comparative Example 2 is shown in Figure 2. Figure 5 As shown.

[0137] Comparative Example 3

[0138] The execution method of this comparative example is basically the same as that of Example 1. The difference is that step 3 is not performed. In step 4, nano-silica (with a particle size of about 7 nm) prepared by conventional vapor deposition is directly added to 10 g of the phenolic ethanol solution obtained in step 2 at 40°C.

[0139] The pore size distribution diagram of the porous carbon material prepared in Comparative Example 3 is shown in Figure 3. Figure 6 As shown.

[0140] The products obtained in Examples 1-5 and Comparative Examples 1-3 were tested for specific surface area, pore size and pore volume using static capacity nitrogen adsorption method. The test results are shown in Table 1.

[0141] Table 1 shows the test results of Examples 1-5 and Comparative Examples 1-3.

[0142]

[0143]

[0144] As shown in Table 1, the comparison between Comparative Example 3 and Examples 1-5 shows that using silica sol obtained by hydrolysis of silicate solution as a template can yield porous carbon materials with a larger specific surface area.

[0145] Depend on Figure 3 (Example 1) and Figure 6 (Comparative Example 3) shows that the porous carbon prepared using silica sol with added silicate (Example 1) as a hard template has a uniform pore size distribution, avoiding the uneven pore size distribution caused by the agglomeration of nano-silica particles due to strong van der Waals forces during the dispersion process of traditional silica templates. The silica sol, due to its lower concentration, avoids this problem, ensuring that silica particles are uniformly dispersed in the carbon matrix, thereby guaranteeing the concentration of the porous carbon pore size distribution.

[0146] Depend on Figure 3 (Example 1) and Figure 4 As can be seen from Comparative Example 1, metasilicate (Comparative Example 1) is a dimer or trimer of silicate. The hydrolysis process is slow, resulting in larger and uneven silica particles, which leads to uneven pore size distribution in subsequent porous carbon materials.

[0147] As shown in Table 1, Comparative Example 2 and Example 1, using a strong acid solution to provide hydrogen ions and creating a pH environment of 4-5 for the hydrolysis of sodium silicate can yield porous carbon materials with a larger specific surface area. Compared to weak organic acids, strong acids completely ionize in aqueous solution, resulting in a faster hydrolysis reaction of sodium silicate and smaller silica particles. This is because the higher hydrogen ion concentration promotes the combination of silicate ions with hydrogen ions, but it also accelerates the condensation and precipitation process of silicic acid, leading to smaller particles and thus increasing the pore volume of the carbon material.

[0148] Depend on Figure 3 (Example 1) and Figure 5 As shown in Comparative Example 2, the organic weak acid (Comparative Example 2) partially ionizes in aqueous solution, resulting in a low hydrogen ion concentration. This slows down the hydrolysis rate of sodium silicate, causing the generated silica particles to gradually increase in size and leading to uneven pore size distribution in the subsequent porous carbon. This is because under alkaline conditions, the concentration of hydroxide ions increases, and they combine with silicate ions to form more stable silicate ions, thereby slowing down the condensation and precipitation rate of silicic acid.

[0149] The method for preparing porous carbon materials with tunable pore size provided in this invention involves hydrolyzing a silica solution under controlled pH conditions to generate silica sol with tunable particle size, and then uniformly compounding it with phenolic resin oligomers in a low-carbon alcohol system. Following carbonization and template etching, a porous carbon material with a three-dimensional continuous carbon framework and tunable pore size structure is successfully constructed. This method features a simple process flow and mild preparation conditions, avoiding problems such as poor dispersion and non-uniform pore structure associated with traditional solid templates. While improving the controllability of pore size, it also significantly increases the specific surface area of ​​the porous carbon material, facilitating rapid diffusion and effective storage of metal ions. This effectively enhances the electrochemical performance of porous carbon materials in energy storage devices, demonstrating good controllability and promising prospects for industrial application.

[0150] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing porous carbon materials with tunable pore size, characterized in that, The preparation method includes: Add the phenol source to a container at 25-50℃, then add the first alkali solution and stir. Then raise the temperature to 60-90℃, add the aldehyde source solution and stir. Finally, cool to room temperature and add the first acid solution to adjust the mixture to neutral to obtain a phenolic resin oligomer solution. The water in the phenolic resin oligomer solution is evaporated, and then a low-carbon alcohol is added to prepare a phenolic low-carbon alcohol solution; wherein the low-carbon alcohol includes any one of methanol, ethanol, propanol, and butanol. A second acid solution or a second alkali solution is added to a silicate solution to adjust the pH value of the silicate solution to between 4.0 and 10.0, thereby preparing a silica sol; the silica sol comprises colloidal silica particles, wherein the particle size of the silica particles is controlled by adjusting the pH value. The phenolic low-carbon alcohol solution and the silica sol are mixed and stirred at 35-45°C to obtain a mixture. The mixture is then washed, filtered, and dried to obtain a silica-phenolic resin composite carbon source. In the silica-phenolic resin composite carbon source, the silica particles are uniformly dispersed. Under an inert atmosphere, the silica-phenolic resin composite carbon source is carbonized to obtain a carbonized product with a carbon skeleton and a SiO2 template; wherein, the carbon skeleton is a three-dimensional continuous carbon skeleton formed by the pyrolysis of phenolic resin oligomers, forming a continuous conductive network; and SiO2 particles are uniformly dispersed between the carbon skeleton as templates. The carbonized product is subjected to wet etching with an etching solution. Through the wet etching process, the SiO2 template is selectively etched away, thereby forming pores in the positions occupied by the SiO2 particles. After washing, filtering and drying, the porous carbon material with adjustable pore size is obtained.

2. The preparation method according to claim 1, characterized in that, The phenol source includes one of the following: phenol, resorcinol, phloroglucinol, cashew nut shell, m-aminophenol, 3-aminophenol, cresol, nonylphenol, octylphenol, and xylenol; The aldehyde source solution includes one or more of formaldehyde, terephthalaldehyde, acetaldehyde, and furfural; The first alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution; The first acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, nitric acid solution, acetic acid solution, and citric acid solution; The silicate solution includes either a sodium silicate solution or a potassium silicate solution. The second alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution; The second acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, and nitric acid solution; The etching solution includes one of the following: HF solution, NaOH solution, or KOH solution.

3. The preparation method according to claim 1, characterized in that, The step of adding the first acid solution to adjust the mixture to neutrality specifically involves adding the first acid solution to adjust the mixture to pH = 7.0 ± 0.

5.

4. The preparation method according to claim 1, characterized in that, The step of evaporating the water from the phenolic resin oligomer solution and then adding a low-carbon alcohol to prepare a phenolic low-carbon alcohol solution specifically includes: The water in the phenolic resin oligomer solution is evaporated using any one of the following evaporation methods: rotary evaporation, reduced pressure evaporation, water bath evaporation, or hot plate evaporation. The phenolic low-carbon alcohol solution was prepared by adding low-carbon alcohol at a ratio of 20-30 wt.% of the phenolic resin oligomer in the solution.

5. The preparation method according to claim 1, characterized in that, The execution order of preparing silica sol and preparing phenolic low-carbon alcohol solution includes: first preparing silica sol and then preparing phenolic low-carbon alcohol solution; or, preparing silica sol and preparing phenolic low-carbon alcohol solution simultaneously; or, preparing phenolic low-carbon alcohol solution first and then preparing silica sol.

6. The preparation method according to claim 1, characterized in that, The carbonization process includes: heating from room temperature to 600-900°C at a heating rate of 2-10°C / min, and holding at that temperature for 1-8 hours.

7. The preparation method according to claim 1, characterized in that, The method for wet etching the carbonized product using an etching solution includes: immersing the carbonized product in the etching solution and performing wet etching; The washing process involves using deionized water until the solution is neutral. The drying temperature is 80-110℃.

8. The preparation method according to claim 7, characterized in that, The method for wet etching the carbonized product using an etching solution further includes: magnetic stirring during immersion for 0.5-24 hours.

9. A porous carbon material with tunable pore size prepared by any of the preparation methods described in claims 1-7.

10. An application of a porous carbon material with tunable pore size prepared by any one of the preparation methods according to claims 1-7, characterized in that, The porous carbon material is used in electrode materials, separator materials, or coating materials for secondary batteries.

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