Micro-mesoporous synergic ultra-high specific surface area porous carbon material, and preparation method and application thereof

Abstract

The application belongs to the field of energy storage materials, and provides a micro-mesopore synergistic ultrahigh specific surface area porous carbon material and a preparation method and application thereof. The application innovatively uses an ionic liquid containing imidazole cations and cyan group anions as a precursor, and successfully constructs a nitrogen-doped carbon matrix with regular structure and no ash content by virtue of the excellent molecular uniformity and self-nitrogen characteristics of the ionic liquid. Efficient etching is performed through a further chemical activation method of KOH, the pore volume distribution of micro-pores and mesopores is accurately controlled, an ideal hierarchical porous structure of "mesopore transmission and micropore storage" is formed, and excellent methane adsorption performance is finally realized. The methane storage capacity mass adsorption capacity reaches 0.41 g g ‑1 , the volume adsorption capacity reaches 250 cm 3 (STP)cm ‑3 .

Description

TECHNICAL FIELD

[0001] The application belongs to the field of energy storage materials, and provides a micro-mesopore synergistic ultrahigh specific surface area porous carbon material and a preparation method and application thereof. BACKGROUND

[0002] Carbon materials have excellent chemical and thermal stability and low cost, and the skeleton formed by carbon-carbon covalent bonds can withstand acid and alkali corrosion and high temperature above 300 DEG C. Porous carbon materials have ultrahigh specific surface area, adjustable hierarchical pore structure, and excellent chemical stability and conductivity, and have irreplaceable application value in key fields such as energy storage, environmental governance, and catalytic reaction, and have become one of the research hotspots in the field of material science. For example, in the field of methane molecular adsorption storage, methane is a clean and efficient energy carrier, and its safe and efficient storage is the core bottleneck for promoting the development of natural gas vehicles and distributed energy systems. The high specific surface area and hierarchical pore structure of porous carbon materials can significantly improve the methane storage capacity per unit mass / volume, and the micro-mesopore synergy can accelerate the diffusion rate of methane in the material, avoid the increase of mass transfer resistance caused by pore blockage during the adsorption / desorption process, and directly affect the charging and discharging efficiency and cycle stability of the methane storage system.

[0003] Although the prospects of porous carbon material adsorbents are broad, how to integrate ultrahigh specific surface area and optimized hierarchical pore structure into the carbon skeleton through precise design and controllable preparation is still a great challenge for current research. Traditional biomass or polymer precursors often have non-uniform structures, resulting in wide and uncontrollable pore distribution of the derived carbon materials. At present, the development of porous carbon materials is facing the bottleneck of specific surface area upper limit and tunable multi-level pore size structure, and the traditional preparation method is difficult to further break through the threshold of 3500 m² / g of specific surface area (the specific surface area of graphene is about 2630 m 2 / g). In order to pursue high specific surface area, conventional activation process is often used, but excessive activation will cause collapse of the pore structure, resulting in decrease of specific surface area instead of increase, and the preparation process is easy to introduce large pores (>50 nm), which seriously restricts the methane adsorption performance. Single micropore structure can provide high specific surface area, which is beneficial to realize the mass adsorption capacity of methane molecules, but it will limit the transmission rate of gas molecules due to narrow pore channel, and is not conducive to achieving the volume adsorption capacity.

[0004] In recent years, ionic liquids as a new type of precursor provide a new platform for the design of functionalized carbon materials. Ionic liquids are composed of organic cations and organic / inorganic anions, which have unique advantages such as molecular level designability, high carbon / nitrogen content, extremely low vapor pressure and excellent thermal stability. Not only does it ensure high carbon yield and inherent nitrogen element source, but its molecular uniformity also indicates that the derived carbon material may have a more uniform pore structure. However, direct carbonization of ionic liquids often fails to obtain a sufficiently developed pore structure. Therefore, how to use the direct carbonization of ionic liquids to obtain ultra-high specific surface area porous carbon materials and meet the application of methane molecular adsorption storage is a problem to be solved. SUMMARY

[0005] In view of the above problems, the present application uses an ionic liquid with imidazole cation and cyan-containing anion as a precursor, and is supplemented with chemical activation of KOH, to realize ultra-high specific surface area (4783.30 m² / g) while precisely controlling the micropore and mesopore pore volume distribution, forming an ideal hierarchical porous structure of "mesopore transmission and micropore storage", and finally realizing excellent methane adsorption performance.

[0006] Firstly, the present application provides a preparation method of micro-mesoporous synergistic ultra-high specific surface area porous carbon material, wherein the porous carbon material is prepared by carbonization and activation of a cyan-containing ionic liquid as a precursor at high temperature.

[0007] Preferably, the preparation method comprises the following steps:

[0008] (1) Dissolve imidazole cation and cyan-containing anion in water, introduce protective gas, and stir uniformly to form a mixed solution;

[0009] (2) Vacuum dry the mixed solution to form an ionic liquid;

[0010] (3) Carbonize the ionic liquid under N2 atmosphere to obtain derived carbon;

[0011] (4) Grind and mix the derived carbon and KOH powder in a mass ratio of 1:3-6, and activate under N2 atmosphere;

[0012] (5) Post-treat the mixture to obtain the porous carbon.

[0013] Preferably, in step (1), the imidazole cation is one or more of 1-ethyl-3-methylimidazole chloride (EMIm), 1-butyl-3-methylimidazole chloride (BMIm) and 1-decyl-3-methylimidazole chloride (Demim).

[0014] Preferably, in step (1), the cyano-containing anion is one or more of sodium dicyandiamide (DCA) and sodium tricyanomethanide (TCM).

[0015] Preferably, in step (2), the vacuum drying conditions are drying at 60-100℃ for 12-48 hours.

[0016] Preferably, in step (3), the carbonization conditions are carbonization at 700-900 °C for 1-4 hours.

[0017] Preferably, in step (4), the activation conditions are 700~900 °C for 1-4 h.

[0018] Preferably, in step (5), the post-treatment includes hydrochloric acid washing and water washing.

[0019] Preferably, it is composed of micropores of 0.5~2 nm and mesopores of 2~8 nm, with a specific surface area greater than 4500 m². 2 / g.

[0020] The porous carbon material prepared by this invention can be applied in methane molecule adsorption storage.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention innovatively employs an ionic liquid containing imidazole cations and cyano anions as a precursor. Leveraging its excellent molecular uniformity and self-containing nitrogen properties, a well-structured, ash-free nitrogen-doped carbon matrix was successfully constructed. Through efficient etching using a KOH chemical activation method, an ultra-high specific surface area (4783.30 m² / g) was achieved while precisely controlling the pore volume distribution of micropores and mesopores, forming an ideal hierarchical porous structure of "mesoporous transport and microporous storage," ultimately realizing superior methane adsorption performance. Its methane storage capacity and mass adsorption capacity reach 0.41 g g. -1 Volume adsorption capacity reaches 250 cm³ 3 (STP) cm -3 . Attached Figure Description

[0023] Figure 1 (A) is a scanning electron microscope image of the [BMIm][DCA] porous carbon material prepared in Example 1, and (B) is a transmission electron microscope image. The inset shows the selected diffraction.

[0024] Figure 2 The N2 adsorption-desorption isotherm of the [BMIm][DCA] porous carbon material prepared in Example 1 is shown in the inset as its pore size distribution curve.

[0025] Figure 3(A) is a scanning electron microscope image of the [BMIm][TCM] porous carbon material prepared in Example 2, and (B) is a transmission electron microscope image. The inset shows the selected diffraction.

[0026] Figure 4 The N2 adsorption-desorption isotherm of the [BMIm][TCM] porous carbon material prepared in Example 2 is shown in the inset as its pore size distribution curve.

[0027] Figure 5 The methane adsorption performance of the [BMIm][TCM] porous carbon material prepared in Example 2 is tested, including mass adsorption curves and volume adsorption curves. Detailed Implementation

[0028] It should be noted that the raw materials and instruments used in the embodiments are not specifically limited in their source; they can be purchased from the market or prepared according to conventional methods well known to those skilled in the art. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0029] This invention selects imidazole cations with different branch lengths (such as EMIm, BMIm, and Demim) and anions with different nitrogen contents (such as dicyanoamino [DCA] and tricyanomethane [TCM]) to precisely synthesize imidazole onium salts with specific structures and nitrogen contents. The synthesized imidazole onium salts are then subjected to high-temperature carbonization in a nitrogen atmosphere. By controlling the carbonization temperature, the decomposition and condensation of the anions and cations are gradually achieved, generating derived carbons with different nitrogen contents (10%~30%) and short-range ordered structures. Subsequently, KOH is used as an activator for high-temperature activation. By precisely controlling parameters such as the activation temperature (700~900℃), holding time (1~3 h), and the mass ratio of activator to derived carbon, porous carbon materials with a pore size distribution concentrated below 8 nm and dominated by micropores (<2 nm) are prepared.

[0030] Example 1

[0031] 5 mmol of 1-butyl-3-methylimidazolium chloride (BMIm) and sodium dicyandiamide (DCA) were dissolved in 30 ml of deionized water. N2 was introduced to isolate oxygen, and the mixture was magnetically stirred for more than 30 min to ensure uniform mixing. The clear solution was transferred to a vacuum oven and dried at 80 °C for about 24 h. The upper oily liquid was collected, avoiding the bottom NaCl crystals as much as possible. Alcohol was added, and the mixture was centrifuged at 8000 rpm for 3 min. The washing was repeated 3 times, and then the mixture was transferred to a vacuum oven and dried at 60 °C for about 12 h to obtain the [BMIm][DCA] ionic liquid. The concentrated [BMIm][DCA] ionic liquid was transferred to a ceramic boat and carbonized at 800 °C for 2 h in an N2 atmosphere at a heating rate of 10 °C / min. After natural cooling to room temperature, [BMIm][DCA] derived carbon was obtained.

[0032] [BMIm][DCA]-derived carbon and KOH powder were thoroughly ground and mixed in a 1:4 ratio. The mixed solid powder was transferred to a tube furnace and activated at 800 °C for 2 h under N2 atmosphere. The mixture after reaction was washed with 1M HCl and then rinsed with deionized water until neutral to obtain [BMIm][DCA] porous carbon material.

[0033] like Figure 1 As shown in (A) and (B), the porous carbon [BMIm][DCA] prepared by carbonizing [BMIm][DCA] ionic liquid at 800 °C for 2 h and activating it with KOH powder at a ratio of 1:4, has a rich pore structure on its surface as shown by scanning electron microscopy images. Transmission electron microscopy and selected diffraction images show that it has a directional structure with short-range order. Figure 2 The [BMIm][DCA] porous carbon exhibits a diameter as high as 3895.63 m. 2 The specific surface area is approximately 0.5 to 8 nm.

[0034] Example 2

[0035] 5 mmol of 1-butyl-3-methylimidazolium chloride (BMIm) and sodium tricyanomethanide (TCM) were dissolved in 30 ml of deionized water. N2 was introduced to isolate oxygen, and the mixture was magnetically stirred for more than 30 min to ensure uniform mixing. The clear solution was transferred to a vacuum oven and dried at 80 °C for about 24 h. The upper oily liquid was collected, avoiding the bottom NaCl crystals as much as possible. Alcohol was added, and the mixture was centrifuged at 8000 rpm for 3 min. The washing was repeated 3 times, and then the mixture was transferred to a vacuum oven and dried at 60 °C for about 12 h to obtain the [BMIm][TCM] ionic liquid. The concentrated [BMIm][TCM] ionic liquid was transferred to a ceramic boat and carbonized at 800 °C for 2 h in an N2 atmosphere at a heating rate of 10 °C / min. After natural cooling to room temperature, [BMIm][TCM] derived carbon was obtained.

[0036] [BMIm][TCM]-derived carbon and KOH powder were thoroughly ground and mixed in a 1:5 ratio. The mixed solid powder was then transferred to a tube furnace and activated at 800 °C for 2 h under N2 atmosphere. The mixture was washed with 1M HCl and then rinsed with deionized water until neutral to obtain [BMIm][TCM] porous carbon material.

[0037] like Figure 3 As shown, [BMIm][TCM] porous carbon was prepared by carbonizing [BMIm][TCM] ionic liquid at 800 °C for 2 h and activating it with KOH powder at a ratio of 1:5. Scanning electron microscopy images show that its surface has a rich pore structure, and the pores are smaller than those of [BMIm][DCA] porous carbon. Transmission electron microscopy and selective diffraction images show that it also has a short-range ordered directional structure. Figure 4 The [BMIm][DCA] porous carbon exhibits a high density of 4783.30 μm. 2 The specific surface area is approximately 0.5 to 8 nm.

[0038] The methane adsorption performance of the [BMIm][TCM] porous carbon obtained in Example 2 was tested, such as... Figure 5 As shown, its methane storage capacity adsorption capacity reaches 0.41 g g. -1 Volume adsorption capacity reaches 250 cm³ 3 (STP)cm -3 .

[0039] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a micro-mesoporous synergistic ultra-high specific surface area porous carbon material, characterized in that, The porous carbon material is prepared by carbonization and activation at high temperature using a cyano-containing ionic liquid as a precursor; the process includes the following steps: (1) Dissolve the imidazole cation and the cyano-containing anion in water, introduce a protective gas, and stir until a mixture is formed; (2) The mixture is vacuum dried to form an ionic liquid; (3) The above ionic liquid was carbonized under N2 atmosphere to obtain derived carbon; (4) The above-derived carbon and KOH powder are thoroughly ground and mixed in a mass ratio of 1:3~6, and then activated under N2 atmosphere; (5) The above mixture is post-processed to obtain the porous carbon, wherein In step (1), the imidazole cation is one or more of 1-ethyl-3-methylimidazolium chloride (EMIm), 1-butyl-3-methylimidazolium chloride (BMIm), and 1-decyl-3-methylimidazolium chloride (Demim), and the cyano-containing anion is one or more of sodium dicyandiamide (DCA) and sodium tricyanomethanide (TCM). In step (4), the activation conditions are 700~900 °C for 1-4 h.

2. The method for preparing a micro-mesoporous synergistic ultra-high specific surface area porous carbon material according to claim 1, characterized in that, In step (2), the vacuum drying conditions are drying at 60-100℃ for 12-48 hours.

3. The method for preparing a micro-mesoporous synergistic ultra-high specific surface area porous carbon material according to claim 1, characterized in that, In step (3), the carbonization conditions are 700-900 ℃ for 1-4 hours.

4. The method for preparing a micro-mesoporous synergistic ultra-high specific surface area porous carbon material according to claim 1, characterized in that, In step (5), the post-treatment includes hydrochloric acid washing and water washing.

5. A micro-mesoporous synergistic ultra-high specific surface area porous carbon material obtained by the preparation method according to claim 1, characterized in that, It consists of micropores of 0.5–2 nm and mesopores of 2–8 nm, with a specific surface area greater than 4500 m². 2 / g.

6. The application of the porous carbon material according to claim 5 in methane molecule adsorption storage.

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