High-nitrogen-doped coconut shell activated carbon, preparation method and application thereof

Abstract

This invention discloses a high-nitrogen-doped coconut shell activated carbon, its preparation method, and its applications. The preparation method includes: crushing and sieving coconut shell carbonized material to obtain carbonized material powder; subjecting the carbonized material powder to plasma surface pretreatment in an air atmosphere; dispersing the plasma-pretreated carbonized material in water and adding a polyamine reagent for reflux reaction to obtain nitrogen-doped carbonized material; mixing the nitrogen-doped carbonized material with a eutectic salt for gradient activation treatment; and then washing, acid washing, water washing, and drying the activated product to obtain high-nitrogen-doped coconut shell activated carbon. The preparation method of this invention has high nitrogen doping efficiency, mild activation conditions, is energy-saving and environmentally friendly, and can achieve synergistic optimization of the pore size and nitrogen doping of biomass activated carbon. The resulting activated carbon has both high nitrogen content and high specific surface area, and exhibits excellent CO2 adsorption performance.

Description

Technical Field

[0001] This invention belongs to the field of carbon capture and porous carbon material preparation technology. Specifically, this invention relates to a high-nitrogen-doped coconut shell activated carbon, its preparation method, and its application. Background Technology

[0002] With accelerated industrialization, the combustion of fossil fuels has led to a continuous increase in CO2 emissions, becoming a major driver of global climate change. Therefore, efficient and economical CO2 capture technologies are crucial for achieving carbon emission reduction. Among numerous CO2 capture technologies, porous solid-state adsorption has attracted widespread attention due to its advantages such as low energy consumption, simple operation, and recyclable adsorbents. Porous carbon materials, with their high specific surface area, rich pore structure, and good stability, have become ideal adsorbents. Biomass activated carbon has abundant raw materials, simple preparation methods, and is renewable and recyclable. It also offers high controllability in pore structure improvement and surface functionalization, easily forming well-developed micropores, making it an excellent adsorbent for carbon dioxide capture. However, traditional biomass activated carbon mainly relies on physical adsorption, and its adsorption capacity is limited by specific surface area and micropore volume, making it difficult to meet the industrial requirements for ultra-high CO2 adsorption.

[0003] Introducing nitrogen-containing functional groups into biochar materials can significantly enhance CO2 adsorption capacity. Nitrogen atom doping can alter the electron distribution of carbon materials, generating alkaline sites, enhancing the interaction with acidic CO2, and improving adsorption selectivity and active site density. However, current methods for preparing nitrogen-doped porous biochar suffer from problems such as uneven doping, low nitrogen content, cumbersome procedures, or high costs, resulting in low doping efficiency and difficulty in achieving high nitrogen content and uniform distribution. Therefore, developing a simple, low-cost method for preparing biochar materials with uniform nitrogen doping and high nitrogen content, possessing both a well-developed pore structure and abundant nitrogen-containing functional groups, is key to overcoming the technological bottleneck in preparing porous carbon with high CO2 adsorption performance.

[0004] Chinese patent CN119191288A discloses a high-nitrogen-doped layered porous bayberry kernel-based activated carbon and its preparation method. The bayberry kernels are washed, dried, crushed, and sieved. They are then impregnated with nitric acid for pre-oxidation treatment. A nitrogen source is mixed with a potassium activator, heated and stirred in deionized water, dried, and then calcined and activated in a mixed atmosphere of nitrogen and ammonia. The activated carbon product is obtained after acid washing and verification. However, this process has significant drawbacks: the pre-oxidant used is nitric acid, which poses safety risks and requires extremely high-performance equipment, making it unsuitable for industrial applications. Furthermore, the direct mixing of uncarbonized raw materials with the nitrogen source leads to substantial nitrogen loss during high-temperature activation, resulting in resource waste. The ammonia used in activation is highly corrosive and toxic, placing extremely high demands on reaction equipment, increasing equipment costs and safety hazards, and hindering industrial scale-up and safe production. Chinese patent CN108499532A discloses a method for preparing nitrogen-doped activated carbon from waste fruit shells pre-oxidized with hydrogen peroxide. First, the pre-treated waste fruit shells are mixed with distilled water and stirred hydrothermally to obtain a carbon precursor. This precursor is then sequentially mixed with hydrogen peroxide, urea, and alkali metal oxalate to obtain a pre-activation suspension. The suspension is then subjected to drying, grinding, calcination, washing, and drying steps to obtain the nitrogen-doped activated carbon adsorbent. While this method is effective in nitrogen doping, the process is relatively complex, requires sophisticated equipment, and is costly, making it difficult to widely apply industrially.

[0005] In summary, the development of a simple, safe, and low-cost biomass porous carbon preparation method that can simultaneously achieve high nitrogen doping rate and well-developed pore structure is of significant scientific value and promising application prospects, as it breaks through the technical bottleneck of ultra-high CO2 adsorption performance. Summary of the Invention

[0006] This invention aims to at least partially address one of the technical problems in related technologies. Therefore, embodiments of this invention propose a high-nitrogen-doped coconut shell activated carbon, its preparation method, and its applications.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, embodiments of the present invention provide a method for preparing high-nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material is crushed and sieved to obtain carbonized material powder; (2) The carbonized powder is subjected to plasma surface pretreatment in an air atmosphere; (3) Disperse the plasma pretreated carbon material in water, add polyamine reagent, reflux reaction, and then filter, wash and dry to obtain nitrogen-doped carbon material; (4) The nitrogen-doped carbon material is mixed with a eutectic salt and subjected to gradient activation treatment; (5) The activated product obtained in step (4) is sequentially rinsed, acid-washed, water-washed and dried to obtain the high-nitrogen doped coconut shell activated carbon.

[0009] The method for preparing high-nitrogen-doped coconut shell activated carbon in this invention enhances nitrogen doping efficiency through plasma pretreatment and chemical grafting processes, and then reduces nitrogen loss through low-temperature activation assisted by eutectic salt. At the same time, the activation process constructs a well-developed pore structure dominated by micropores, which synergistically enhances CO2 adsorption capacity. The final activated carbon exhibits high nitrogen content and high CO2 adsorption performance.

[0010] In some embodiments, in step (1), the mesh size of the carbonized powder is 200-325 mesh.

[0011] In some embodiments, in step (2), the power of the plasma surface pretreatment is 100~300W and the treatment time is 10~30min.

[0012] In some embodiments, in step (3), the polyamine reagent includes at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine; And / or, the mass ratio of plasma pretreated carbonized material to the polyamine reagent is 1:(0.5~3).

[0013] In some embodiments, in step (3), the reaction temperature of the reflux reaction is 60~120℃ and the reaction time is 2~12h; And / or, the drying temperature is 70~120℃, and the drying time is 10~24h.

[0014] In some embodiments, in step (4), the eutectic salt includes at least one of Na2CO3-K2CO3 eutectic salt, KHCO3-KCl eutectic salt, ZnCl2-KCl eutectic salt, and NaCl-KCl eutectic salt; And / or, the mass ratio of the nitrogen-doped carbon material to the eutectic salt is 1:(1~5).

[0015] In some embodiments, in step (4), the gradient activation process is as follows: under the protection of an inert atmosphere, the mixture of the nitrogen-doped carbon material and the eutectic salt is first heated to 300-400°C at a heating rate of 2-5°C / min and held for 0.5-1h; then the temperature is further increased to 450-650°C at a heating rate of 5-10°C / min and held for 1-2h.

[0016] In some embodiments, in step (5), the acid solution used in the pickling includes at least one of hydrochloric acid, sulfuric acid, and glacial acetic acid, the volume concentration of the acid solution is 5% to 30%, the pickling temperature is room temperature to 80°C, and the pickling time is 10 to 60 minutes. And / or, the drying temperature is 70~120℃, and the drying time is 12~24h.

[0017] Secondly, embodiments of the present invention also propose a high-nitrogen-doped coconut shell activated carbon, which is prepared by the preparation method described in the first aspect.

[0018] Thirdly, embodiments of the present invention also propose an application of high-nitrogen-doped coconut shell activated carbon as described in the second aspect, wherein the high-nitrogen-doped coconut shell activated carbon is used to adsorb carbon dioxide.

[0019] The advantages and beneficial effects of the embodiments of the present invention are as follows: (1) Significantly improved nitrogen doping efficiency: In this embodiment of the invention, the coconut shell carbonized material is first subjected to plasma treatment to introduce oxygen-containing functional groups, which provide grafting anchors for nitrogen doping. Then, the nitrogen doping process is stripped from the high-temperature activation by chemical grafting and completed under mild liquid phase conditions, which greatly improves the nitrogen retention rate. The nitrogen content of the final activated carbon product is more than 5%. (2) Mild activation conditions, energy saving and environmental protection: The embodiments of the present invention adopt a eutectic salt-assisted activation process, which has a lower activation temperature and does not require a high temperature and high pressure environment. The reaction conditions are milder, and there is no need to use strong corrosive activators such as KOH. The process is more environmentally friendly, has lower equipment requirements, and is easier to achieve large-scale production. Moreover, the molten salt can be recycled, saving resources.

[0020] (3) Synergistic optimization of pore size and nitrogen doping: In this embodiment of the invention, nitrogen element is efficiently fixed by chemical grafting, and then low-temperature activation is assisted by eutectic salt, which can avoid the loss of nitrogen element at high temperature. At the same time, the pore structure is fully developed, and the final activated carbon product has both high nitrogen content and high specific surface area, and exhibits excellent CO2 adsorption performance. Attached Figure Description

[0021] Figure 1 The diagram shows the CO2 adsorption performance of coconut shell activated carbon prepared in Examples 1-5 of this invention, commercial activated carbon, and activated carbon in Comparative Examples 1-4. Detailed Implementation

[0022] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] In this invention, when a value is described as a range, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as specific numerical values ​​falling within that range, regardless of whether specific numerical values ​​or specific subranges are explicitly specified.

[0024] In this invention, the terms “comprising” and “including” and their various variations mean that other elements or wholes may be included but are not specifically described.

[0025] In this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0026] In a first aspect, embodiments of the present invention provide a method for preparing high-nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) Grinding raw materials: The coconut shell carbonized material is crushed and sieved to obtain carbonized material powder; (2) Plasma pretreatment: The carbonized powder is subjected to plasma surface pretreatment in an air atmosphere; (3) Chemical grafting of nitrogen doping: The plasma pretreated carbonized material is dispersed in water, and polyamine reagents are added. The mixture is then subjected to reflux reaction, filtered, washed with water, and dried to obtain nitrogen-doped carbonized material. (4) Eutectic salt-assisted low-temperature gradient activation: The nitrogen-doped carbon material is mixed with eutectic salt and subjected to gradient activation treatment; (5) Post-processing: The activated product obtained in step (4) is sequentially rinsed, acid-washed, water-washed and dried to obtain the high-nitrogen doped coconut shell activated carbon.

[0027] This invention couples three key technologies: "plasma surface activation pretreatment, surface chemical grafting nitrogen doping, and eutectic salt-assisted low-temperature gradient activation," fundamentally reconstructing the traditional process framework for nitrogen-doped activated carbon. Plasma pretreatment introduces abundant oxygen-containing functional groups as grafting anchors, followed by chemical grafting to achieve efficient and uniform nitrogen introduction. Then, a low-temperature eutectic salt-assisted gradient activation process is used, achieving bidirectional development of pore structure and surface nitrogen-containing functional groups at temperatures far lower than traditional activation processes. This results in activated carbon with both high nitrogen content and high specific surface area, exhibiting excellent CO2 adsorption performance.

[0028] In some embodiments, in step (1), the mesh size of the carbonized powder is 200-325 mesh.

[0029] It should be noted that the coconut shell carbonized material used in step (1) of the preparation method of the present invention can be directly purchased from the market, for example, it can be purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd., Wenchang City East Suburb Coconut Activated Carbon Factory, Suzhou Yituolian International Trade Co., Ltd., etc.

[0030] In some embodiments, in step (2), the plasma surface pretreatment is performed at room temperature and pressure, and the power of the plasma surface pretreatment is 100~300W, and the treatment time is 10~30min. By performing plasma surface pretreatment on the carbonized powder, oxygen-containing functional groups are introduced onto its surface. These oxygen-containing functional groups can serve as active anchors in the subsequent chemical grafting nitrogen doping process, thereby significantly improving the binding efficiency with the nitrogen source (polyamine reagent) and the amount of nitrogen incorporated.

[0031] In some embodiments, in step (3), the polyamine reagent includes at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine; And / or, the mass ratio of plasma pretreated carbonized material to the polyamine reagent is 1:(0.5~3).

[0032] In step (3) of this embodiment, nitrogen doping is chemically grafted onto plasma pretreated carbon material using polyamine reagents. The nitrogen-containing functional groups in the polyamine reagents will undergo a condensation reaction with the abundant oxygen-containing functional groups on the surface of the plasma pretreated carbon material, thereby fixing nitrogen atoms to the carbon skeleton surface and achieving effective doping of nitrogen.

[0033] Furthermore, the embodiments of this invention use polyamine reagents as nitrogen sources for nitrogen doping, which has the following advantages: 1) Polyamine reagents have high grafting activity with plasma pretreated carbonized materials. They can form stable covalent bonds through amidation reaction, making nitrogen doping more stable and nitrogen utilization efficiency higher. In contrast, traditional nitrogen sources (such as urea and melamine) mainly achieve nitrogen doping by releasing ammonia during pyrolysis, resulting in lower nitrogen utilization efficiency.

[0034] 2) Matching with subsequent activation processes: Polyamine reagents are stable at 60~120℃ with almost no decomposition loss, and nitrogen atoms are firmly bound to the carbon skeleton surface after covalent grafting; while the subsequent activation temperature in the embodiments of the present invention is lower, further reducing the loss of nitrogen elements; while traditional nitrogen sources need to be pyrolyzed at higher temperatures (>500℃) first.

[0035] 3) The polyamine reagents used in the embodiments of the present invention do not produce harmful gases during nitrogen doping and do not require special equipment such as high temperature, high pressure and corrosion resistance.

[0036] In some embodiments, in step (3), the reaction temperature of the reflux reaction is 60~120℃ and the reaction time is 2~12h; And / or, the drying temperature is 70~120℃, and the drying time is 10~24h.

[0037] In some embodiments, in step (4), the eutectic salt includes at least one of Na2CO3-K2CO3 eutectic salt, KHCO3-KCl eutectic salt, ZnCl2-KCl eutectic salt, and NaCl-KCl eutectic salt; And / or, the mass ratio of the nitrogen-doped carbon material to the eutectic salt is 1:(1~5).

[0038] The embodiments of this invention use eutectic salts, which have the following advantages: Firstly, they can lower the melting temperature and form a uniform liquid phase environment: the eutectic salt system has a lower eutectic point, which can form a uniform molten liquid phase at a lower temperature, promoting the uniformity of mass transfer and activation reactions, and facilitating the synergistic development of micropores and mesopores; secondly, they can also regulate the pore structure distribution: by selecting different combinations of cations and anions, the polarity and diffusion behavior of the molten salt can be controlled, thereby achieving fine control of the pore size distribution; in addition, the use of eutectic salts can also reduce the volatilization loss of nitrogen at high temperatures: during the activation process, the eutectic salt can form a uniform liquid protective layer on the surface of the carbon material, inhibiting the decomposition and volatilization of nitrogen-containing functional groups at high temperatures, thereby improving the nitrogen retention rate.

[0039] In some embodiments, the gradient activation process in step (4) is as follows: Under an inert atmosphere, the mixture of nitrogen-doped carbon material and eutectic salt is first heated to 300-400°C at a heating rate of 2-5°C / min and held for 0.5-1h for low-temperature pre-activation. During this stage, the eutectic salt begins to melt and uniformly coat the material surface, initially forming a liquid reaction medium, which promotes the stabilization of nitrogen-containing functional groups on the material surface, thereby reducing nitrogen loss in subsequent high-temperature treatment. Then, the temperature is further increased to 450-650°C at a heating rate of 5-10°C / min and held for 1-2h for high-temperature main activation. During this stage, the eutectic salt fully activates the carbon skeleton, etches amorphous carbon, and generates abundant micropores and mesopores. Through gradient activation, the synergistic effect of "nitrogen fixation first, pore formation later" is achieved, which avoids the problems of large-scale nitrogen volatilization and pore structure collapse in traditional one-step high-temperature activation.

[0040] Existing technologies mostly employ nitrogen source solid-state mixed heat treatment processes or ammonia activation processes for nitrogen doping. However, physical or chemical activation processes involve high heat treatment temperatures, which can easily lead to nitrogen loss. This invention, however, utilizes a synergistic process of chemical grafting nitrogen doping and eutectic salt-assisted low-temperature activation. The chemical grafting nitrogen doping is performed under mild liquid-phase conditions, allowing for a full reaction between the oxidized and nitrogen-containing structures, significantly improving nitrogen retention. Simultaneously, eutectic salt-assisted low-temperature activation lowers the activation temperature by 100-200°C, further reducing nitrogen loss during high-temperature heat treatment and simultaneously achieving full porosity development.

[0041] In some embodiments, in step (5), the acid solution used in the pickling includes at least one of hydrochloric acid, sulfuric acid, and glacial acetic acid, the volume concentration of the acid solution is 5% to 30%, the pickling temperature is room temperature to 80°C, and the pickling time is 10 to 60 minutes. And / or, the drying temperature is 70~120℃, and the drying time is 12~24h.

[0042] Secondly, embodiments of the present invention also propose a high-nitrogen-doped coconut shell activated carbon, which is prepared by the preparation method described in the first aspect.

[0043] In some embodiments, the nitrogen content in the high-nitrogen-doped coconut shell activated carbon is ≥5wt%.

[0044] Thirdly, embodiments of the present invention also propose an application of high-nitrogen-doped coconut shell activated carbon as described in the second aspect, wherein the high-nitrogen-doped coconut shell activated carbon is used to adsorb carbon dioxide.

[0045] The following are non-limiting embodiments and comparative examples of the present invention. It should be noted that the schemes in the comparative examples are not prior art, but are only set up for comparison with the schemes in the embodiments, and are not intended to limit the present invention. Unless otherwise stated, all raw materials used in the embodiments and comparative examples are conventional commercially available products, or can be prepared by known methods.

[0046] Example 1 This embodiment provides a method for preparing high-nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd., with ash content of 3.96%, volatile matter of 16.91%, total moisture of 3.89wt% (dry basis), and carbon content of 86.39%) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Place the carbonized powder in a low-temperature plasma reactor and perform plasma surface pretreatment on the carbonized powder for 15 min under air atmosphere, normal temperature and pressure conditions, and power conditions of 100W. (3) Take 10g of plasma pretreated carbon material and disperse it in 100mL of deionized water, add 15g of ethylenediamine, reflux and stir at 80℃ for 8h, filter and wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbon material. (4) Mix the above nitrogen-doped carbonized material with ZnCl2-KCl eutectic salt at a mass ratio of 1:3. Then, under the protection of nitrogen atmosphere, raise the temperature from room temperature to 350℃ at a heating rate of 3℃ / min and hold for 1h. Then, raise the temperature from 350℃ to 600℃ at a heating rate of 5℃ / min and hold for 2h. (5) After cooling the activated product obtained in step (4), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain high nitrogen doped coconut shell activated carbon.

[0047] Example 2 This embodiment provides a method for preparing high-nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) The carbonized powder was placed in a low-temperature plasma reactor and subjected to plasma surface pretreatment for 10 min at a power of 200W under air atmosphere, normal temperature and pressure conditions. (3) Take 10g of plasma pretreated carbon material and disperse it in 100mL of deionized water, add 15g of ethylenediamine, reflux and stir at 80℃ for 8h, filter and wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbon material. (4) Mix the above nitrogen-doped carbonized material with ZnCl2-KCl eutectic salt at a mass ratio of 1:3. Then, under the protection of nitrogen atmosphere, raise the temperature from room temperature to 350℃ at a heating rate of 3℃ / min and hold for 1h. Then, raise the temperature from 350℃ to 600℃ at a heating rate of 5℃ / min and hold for 2h. (5) After cooling the activated product obtained in step (4), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain high nitrogen doped coconut shell activated carbon.

[0048] Example 3 This embodiment provides a method for preparing nitrogen-doped coconut shell activated carbon, including the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Place the carbonized powder in a low-temperature plasma reactor and perform plasma surface pretreatment on the carbonized powder for 15 min under air atmosphere, normal temperature and pressure conditions, and power conditions of 100W. (3) Take 10g of plasma pretreated carbon material and disperse it in 100mL of deionized water, add 30g of triethylenetetramine, reflux and stir at 80℃ for 8h, filter, wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbon material. (4) Mix the above nitrogen-doped carbonized material with ZnCl2-KCl eutectic salt at a mass ratio of 1:3. Then, under the protection of nitrogen atmosphere, raise the temperature from room temperature to 350℃ at a heating rate of 3℃ / min and hold for 1h. Then, raise the temperature from 350℃ to 600℃ at a heating rate of 5℃ / min and hold for 2h. (5) After cooling the activated product obtained in step (4), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain nitrogen-doped coconut shell activated carbon.

[0049] Example 4 This embodiment provides a method for preparing high-nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Place the carbonized powder in a low-temperature plasma reactor and perform plasma surface pretreatment on the carbonized powder for 15 min under air atmosphere, normal temperature and pressure conditions, and power conditions of 100W. (3) Take 10g of plasma pretreated carbon material and disperse it in 100mL of deionized water, add 15g of ethylenediamine, reflux and stir at 80℃ for 8h, filter and wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbon material. (4) Mix the above nitrogen-doped carbonized material with Na2CO3-K2CO3 eutectic salt at a mass ratio of 1:2. Then, under the protection of nitrogen atmosphere, raise the temperature from room temperature to 350℃ at a heating rate of 3℃ / min and hold for 1h. Then, raise the temperature from 350℃ to 600℃ at a heating rate of 5℃ / min and hold for 2h. (5) After cooling the activated product obtained in step (4), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain high nitrogen doped coconut shell activated carbon.

[0050] Example 5 This embodiment provides a method for preparing high-nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Place the carbonized powder in a low-temperature plasma reactor and perform plasma surface pretreatment on the carbonized powder for 15 min under air atmosphere, normal temperature and pressure conditions, and power conditions of 100W. (3) Take 10g of plasma pretreated carbon material and disperse it in 100mL of deionized water, add 15g of ethylenediamine, reflux and stir at 80℃ for 8h, filter and wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbon material. (4) Mix the above nitrogen-doped carbonized material with ZnCl2-KCl eutectic salt at a mass ratio of 1:3. Then, under the protection of nitrogen atmosphere, first raise the temperature from room temperature to 300℃ at a heating rate of 2℃ / min and hold for 0.5h; then raise the temperature from 300℃ to 650℃ at a heating rate of 5℃ / min and hold for 1.5h. (5) After cooling the activated product obtained in step (4), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain high nitrogen doped coconut shell activated carbon.

[0051] Comparative Example 1 This comparative example provides a method for preparing nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Take 10g of carbonized material powder and disperse it in 100mL of deionized water, add 15g of ethylenediamine, reflux and stir at 80℃ for 8h, filter, wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbonized material. (3) Mix the above nitrogen-doped carbonized material with ZnCl2-KCl eutectic salt at a mass ratio of 1:3. Then, under the protection of nitrogen atmosphere, raise the temperature from room temperature to 350℃ at a heating rate of 3℃ / min and hold for 1h. Then, raise the temperature from 350℃ to 600℃ at a heating rate of 5℃ / min and hold for 2h. (4) After cooling the activated product obtained in step (3), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain nitrogen-doped coconut shell activated carbon.

[0052] Comparative Example 2 This comparative example provides a method for preparing nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Place the carbonized powder in a low-temperature plasma reactor and perform plasma surface pretreatment on the carbonized powder for 15 min under air atmosphere, normal temperature and pressure conditions, and power conditions of 100W. (3) Take 10g of plasma pretreated carbonized material and 30g of urea and disperse them in 100mL of deionized water. Stir at room temperature for 8h and then dry at 120℃ for 12h to obtain nitrogen-doped carbonized material. (4) Mix the above nitrogen-doped carbonized material with ZnCl2-KCl eutectic salt at a mass ratio of 1:3. Then, under the protection of nitrogen atmosphere, raise the temperature from room temperature to 350℃ at a heating rate of 3℃ / min and hold for 1h. Then, raise the temperature from 350℃ to 600℃ at a heating rate of 5℃ / min and hold for 2h. (5) After cooling the activated product obtained in step (4), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain nitrogen-doped coconut shell activated carbon.

[0053] Comparative Example 3 This comparative example provides a method for preparing nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Place the carbonized powder in a low-temperature plasma reactor and perform plasma surface pretreatment on the carbonized powder for 15 min under air atmosphere, normal temperature and pressure conditions, and power conditions of 100W. (3) Take 10g of plasma pretreated carbon material and disperse it in 100mL of deionized water, add 15g of ethylenediamine, reflux and stir at 80℃ for 8h, filter and wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbon material. (4) Mix the above nitrogen-doped carbonized material with KOH at a mass ratio of 1:3. Then, under the protection of nitrogen atmosphere, heat the mixture from room temperature to 800℃ at a heating rate of 5℃ / min and keep it at that temperature for 2 hours. (5) After cooling the activated product obtained in step (4), it is acid-washed with 5% volume fraction dilute hydrochloric acid at room temperature for 15 min, then washed with deionized water until the solution is neutral, and finally dried at 110℃ for 12 h to obtain nitrogen-doped coconut shell activated carbon.

[0054] Comparative Example 4 This comparative example provides a method for preparing nitrogen-doped coconut shell activated carbon, comprising the following steps: (1) The coconut shell carbonized material (purchased from Pingluo County Xuanzhong Activated Carbon Co., Ltd.) was crushed and sieved to 200 mesh to obtain carbonized material powder; (2) Place the carbonized powder in a low-temperature plasma reactor and perform plasma surface pretreatment on the carbonized powder for 15 min under air atmosphere, normal temperature and pressure conditions, and power conditions of 100W. (3) Take 10g of plasma pretreated carbon material and disperse it in 100mL of deionized water, add 15g of ethylenediamine, reflux and stir at 80℃ for 8h, filter and wash three times with 100mL of deionized water, and dry at 80℃ for 12h to obtain nitrogen-doped carbon material. (4) The above nitrogen-doped carbonized material and ZnCl2-KCl eutectic salt are thoroughly mixed at a mass ratio of 1:3. Then, the mixture is heated directly from room temperature to 600℃ at a heating rate of 5℃ / min under nitrogen atmosphere protection and kept at the temperature for 2h. (5) After cooling the activated product obtained in step (4), wash it with 100 mL of deionized water to remove the residual molten salt, then acid wash it with 5% volume fraction of dilute hydrochloric acid at room temperature for 15 min, then wash it with deionized water until the solution is neutral, and finally dry it at 110℃ for 12 h to obtain high nitrogen doped coconut shell activated carbon.

[0055] The pore structure parameters (specific surface area, pore volume), nitrogen content, and carbon dioxide adsorption capacity of the activated carbon prepared in Examples 1-5 and Comparative Examples 1-4, as well as commercial activated carbon, were tested, and the results are shown in Table 1; and the carbon dioxide adsorption capacity under different adsorption pressures is shown in Table 1. Figure 1 As shown.

[0056] Table 1 Performance of activated carbon in the examples and comparative examples

[0057] As can be seen from Table 1, the activated carbon prepared in this embodiment of the invention has significantly higher nitrogen content and CO2 adsorption capacity than commercial activated carbon and activated carbon prepared in the comparative example. This demonstrates that the present invention, through plasma treatment combined with chemical grafting, can improve nitrogen doping efficiency and effect, and further reduces nitrogen loss through a eutectic salt-assisted low-temperature gradient activation process. This effectively addresses the challenge of simultaneously achieving a well-developed pore structure and abundant nitrogen-containing functional groups, significantly enhancing the CO2 capture performance of the activated carbon.

[0058] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing high-nitrogen-doped coconut shell activated carbon, characterized in that, Includes the following steps: (1) The coconut shell carbonized material is crushed and sieved to obtain carbonized material powder; (2) The carbonized powder is subjected to plasma surface pretreatment in an air atmosphere; (3) Disperse the plasma pretreated carbon material in water, add polyamine reagent, reflux reaction, and then filter, wash and dry to obtain nitrogen-doped carbon material; (4) The nitrogen-doped carbon material is mixed with a eutectic salt and subjected to gradient activation treatment; (5) The activated product obtained in step (4) is sequentially rinsed, acid-washed, water-washed and dried to obtain the high-nitrogen doped coconut shell activated carbon.

2. The method for preparing high-nitrogen-doped coconut shell activated carbon according to claim 1, characterized in that, In step (1), the carbonized powder has a mesh size of 200-325.

3. The method for preparing high-nitrogen-doped coconut shell activated carbon according to claim 1, characterized in that, In step (2), the power during plasma surface pretreatment is 100~300W and the treatment time is 10~30min.

4. The method for preparing high-nitrogen-doped coconut shell activated carbon according to claim 1, characterized in that, In step (3), the polyamine reagent includes at least one of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine; And / or, the mass ratio of plasma pretreated carbonized material to the polyamine reagent is 1:(0.5~3).

5. The method for preparing high-nitrogen-doped coconut shell activated carbon according to claim 1, characterized in that, In step (3), the reflux reaction temperature is 60~120℃ and the reaction time is 2~12h; And / or, the drying temperature is 70~120℃, and the drying time is 10~24h.

6. The method for preparing high-nitrogen-doped coconut shell activated carbon according to claim 1, characterized in that, In step (4), the eutectic salt includes at least one of Na2CO3-K2CO3 eutectic salt, KHCO3-KCl eutectic salt, ZnCl2-KCl eutectic salt, and NaCl-KCl eutectic salt; And / or, the mass ratio of the nitrogen-doped carbon material to the eutectic salt is 1:(1~5).

7. The method for preparing high-nitrogen-doped coconut shell activated carbon according to claim 1, characterized in that, In step (4), the gradient activation process is as follows: under the protection of an inert atmosphere, the mixture of the nitrogen-doped carbon material and the eutectic salt is first heated to 300-400℃ at a heating rate of 2-5℃ / min and held for 0.5-1h; then the temperature is further increased to 450-650℃ at a heating rate of 5-10℃ / min and held for 1-2h.

8. The method for preparing high-nitrogen-doped coconut shell activated carbon according to claim 1, characterized in that, In step (5), the acid solution used in the pickling includes at least one of hydrochloric acid, sulfuric acid, and glacial acetic acid, the volume concentration of the acid solution is 5% to 30%, the pickling temperature is room temperature to 80°C, and the pickling time is 10 to 60 minutes. And / or, the drying temperature is 70℃~120℃, and the drying time is 12~24h.

9. A high-nitrogen-doped coconut shell activated carbon, characterized in that, The high-nitrogen-doped coconut shell activated carbon is prepared by the preparation method according to any one of claims 1-8.

10. An application of the high-nitrogen-doped coconut shell activated carbon as described in claim 9, characterized in that, The high-nitrogen-doped coconut shell activated carbon was used to adsorb carbon dioxide.

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