A method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on silane coupling agent

Abstract

The application relates to a method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on a silane coupling agent and belongs to the field of environmental protection. The method combines a soft template and a hard template and is assisted by physical activation, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane is introduced into the system as a structure directing agent, a pore forming agent and a nitrogen source, and nitrogen-doped hollow hierarchical porous carbon spheres are prepared in one step. The specific surface area of the prepared material is as high as 1716.75 m 2 / g. The N-(2-aminoethyl)-3-aminopropyl trimethoxysilane can not only serve as a nitrogen source, but also promote the formation of pores in the process of synthesizing the carbon material. The adsorption amount of CO2 can reach 5.11 mmol / g under the conditions of 0 DEG C and 1 bar. The method has the advantages of simple process, low energy consumption, easy modification, high raw material utilization rate, easy availability, easy industrial application, etc. The prepared carbon material has great application potential in carbon dioxide capture before and after combustion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental protection, and particularly relates to a method for preparing nitrogen-doped hollow hierarchical porous carbon spheres. BACKGROUND

[0002] According to data published by the Global Real-Time Carbon Data website, the total global carbon emissions in 2020 were 33.46 Gt, and the total global carbon emissions in 2022 were 36.11 Gt, with a growth rate of 7.92% in two years. A large amount of carbon dioxide is emitted by key industries, leading to increasingly obvious greenhouse effects and gradually deteriorating global climate. In order to alleviate this problem, among four carbon capture and storage (CCUS) technologies, the solid adsorbent adsorption technology is considered an effective technology for separating carbon dioxide from flue gas, and the most representative solid adsorbent is a porous carbon material. The porous carbon material is widely studied due to its rich pore structure, good water / thermal stability, good acid / base resistance, adjustable pore structure and low cost. Controlling the pore structure of the porous carbon material and adjusting the basic adsorption sites of the carbon material are key factors for effective utilization of the carbon material.

[0003] Patent CN113285082A discloses a method for preparing nitrogen-doped hollow carbon spheres, which mainly includes four steps: 1) synthesizing an ATRP initiator with chlorosilane; 2) surface modification of nano-SiO2 with the ATRP initiator; 3) coating of the SiO2 precursor with a polydimethylaminoethyl methacrylate (PDMAEMA) macromolecular initiator; and 4) preparation of styrene (PS) coated SiO2-g-PDMAEMA. The patent has the following disadvantages: (1) the preparation process is complex, and the raw materials are highly toxic; and (2) the method has high requirements for process equipment.

[0004] Patent CN112301361A discloses a method for preparing hollow nitrogen-doped porous carbon. The patent has the following disadvantages: the preparation process is relatively complicated, and the sample preparation period is long.

[0005] In view of the above-mentioned defects in the prior art method, the application provides a simple and economical synthesis method. The method uses economically available resorcinol and formaldehyde solution as a carbon source, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane (KH-792) as a structure directing agent, a nitrogen source and a pore-forming agent, and synthesizes hollow hierarchical porous carbon spheres. Compared with other existing methods, the method only needs to add one silane coupling agent to achieve the triple effects of constructing a hollow structure, forming hierarchical pores and doping nitrogen. The method has the advantages of simple operation process, low energy consumption, easy modification, high raw material utilization rate, economic availability and easy industrial scale application. The carbon spheres prepared by the method have rich pore structure and nitrogen source, and therefore have relatively good CO2 adsorption performance. SUMMARY

[0006] In order to overcome the above-mentioned defects in the prior art, the purpose of the present application is to provide a simple and economical preparation method of hollow hierarchical porous carbon spheres. The method uses N-(2-aminoethyl)-3-aminopropyl trimethoxysilane as a structure directing agent, a nitrogen source and a pore-forming agent, and a resorcinol and formaldehyde solution as a carbon source to synthesize hollow hierarchical porous carbon spheres.

[0007] A method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on a silane coupling agent, comprising the following steps:

[0008] (1) Add deionized water and anhydrous ethanol to a beaker, the volume ratio of ethanol to water is 2:33, and stir for 2-30 min to mix uniformly;

[0009] (2) Add a 31% mass fraction of silica sol and N-(2-aminoethyl)-3-aminopropyl trimethoxysilane to the mixture of (1) above, the volume ratio of the former to the latter is 4:5, and stir for 10-60 min;

[0010] (3) Add 25% mass fraction of ammonia water to the mixture of (2) above, the volume ratio of ammonia water to alcohol water is 1:140, and stir for 2-300 min to mix uniformly;

[0011] (4) Add resorcinol to the mixed solution of (3) above and stir. After it is dissolved, add 37% mass fraction of formaldehyde solution to the solution, the mass ratio of resorcinol to formaldehyde solution is 2:3, and continuously stir at 60℃±10℃ water bath condition for 12-72h, the speed of the magnetic stirrer is set to 200-600r / min.

[0012] (5) Centrifuge the reaction solution of (4) above at a speed of 5000-10000r / min to obtain a solid product, cross-wash the solid product with deionized water and ethanol for 3 times, and dry the solid product at 20-100℃ for 5-30h after centrifugation;

[0013] (6) Put the solid product obtained in (5) above into a gas furnace, heat to 400-500℃ at a heating rate of 1-10℃ / min in N2 atmosphere, keep for 1-5h, then restore the heating rate to 600-800℃ at a heating rate of 1-10℃ / min, keep for 1-5h, and then naturally cool down;

[0014] (7) Soak the solid product obtained in (6) above with 5wt%-50wt% hydrofluoric acid for 12-24h, then wash with deionized water and dry to obtain nitrogen-doped hollow hierarchical porous carbon microspheres.

[0015] (8) Put the ceramic boat containing the sample of the above (7) into a tube furnace, heat to 600-900℃ at a heating rate of 5-20℃ / min, after reaching the specified temperature, introduce the activation gas CO2(≥99.5%) into the tube furnace, the CO2 gas flow rate is 50-150cm 3 / min, maintain for 1-5h, then switch back to nitrogen to prevent further activation during the cooling process.

[0016] A method for preparing nitrogen-doped hollow carbon spheres based on a silane coupling agent, the technical method is as follows:

[0017] (1) Add 66ml of deionized water, 4ml of anhydrous ethanol into a beaker, stir for 5-10min to make them mix evenly;

[0018] (2) Add 0.8ml of 31% mass fraction silica sol and 0.1ml of N-(2-aminoethyl)-3-aminopropyl trimethoxysilane into the mixed solution of the above (1) in sequence, stir for 30min;

[0019] (3) Add 0.5ml of 25% mass fraction ammonia water into the mixed solution of the above (2), stir for 5min to make them mix evenly;

[0020] (4) Add 0.5g of resorcinol into the mixed solution of the above (3) and stir. After it is dissolved, add 0.7g of 37% mass fraction formaldehyde solution into the solution, and continuously stir under the condition of 60℃±10℃ water bath for 24-48h, the speed of the magnetic stirrer is set to 200-300r / min.

[0021] (5) Centrifuge the reaction solution of the above (4) at a speed of 5000-10000r / min to obtain solid product, cross wash with deionized water and ethanol for 3 times, dry the solid product at 80℃ for 8-16h after centrifugation;

[0022] (6) Put the solid product obtained in the above (5) into a gas atmosphere furnace, heat to 450℃ at a heating rate of 2℃ / min under N2 atmosphere, maintain for 2h, then restore the heating rate to 800℃ at a heating rate of 1℃ / min, maintain for 3h, then naturally cool down;

[0023] (7) Soak the solid product obtained in the above (6) with 10wt% hydrofluoric acid for 10-40h, then wash with deionized water and dry, to obtain nitrogen-doped hollow hierarchical porous carbon microspheres.

[0024] (8) Put the ceramic boat containing the sample of the above (7) into a tube furnace, heat to 600-900℃ at a heating rate of 5-20℃ / min, after reaching the specified temperature, introduce the activation gas CO2(≥99.5%) into the tube furnace, the CO2 gas flow rate is 50-150cm3 The gas flow rate was maintained at 0.5 min for 3 hours, then switched back to nitrogen to prevent further activation during the cooling process.

[0025] In the aforementioned method for preparing nitrogen-doped hollow hierarchical carbon spheres, in step (2), the amount of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane added is 0.1-1.0 ml;

[0026] In the aforementioned method for preparing nitrogen-doped hollow hierarchical carbon spheres, the stirring speed in steps (1), (2), and (3) is 200–500 r / min.

[0027] Compared with the prior art, the technical advantages of this invention are as follows:

[0028] 1. This invention uses N-(2-aminoethyl)-3-aminopropyltrimethoxysilane as a structure directing agent, pore-forming agent and nitrogen source, which can be used for multiple purposes, greatly simplifying the preparation steps, reducing the preparation cost and making it easy to realize industrial production.

[0029] 2. Current preparation methods often require the use of high-pressure equipment, such as hydrothermal reaction apparatus, which places certain demands on the equipment. The method used in this invention does not require hydrothermal treatment, thus easily reducing manufacturing costs.

[0030] 3. The porous carbon sphere material prepared by this technique can achieve a specific surface area of ​​up to 1716.75 m². 2 / g, pore volume 1.70cm³ 3 With a nitrogen content of 3.82%, the CO2 adsorption capacity of the carbon material reaches 5.11 mmol / g at 0℃ and 1 bar. At 25℃ and 1 bar, the CO2 adsorption capacity reaches 3.00 mmol / g. Compared with the solid carbon spheres in the comparative example, the specific surface area is increased by 253.11%, the pore volume by 553.85%, and the CO2 adsorption capacity is increased by 43.54% at 0℃ and 1 bar. These data fully demonstrate the advanced nature of this technology in preparing porous hollow carbon materials, facilitating industrial production and bringing significant socio-economic benefits. Attached Figure Description

[0031] Figure 1 The actual morphology of the sample during the experiment;

[0032] Figure 2 (a) and (b) are SEM images of the comparative example and Example 5, respectively; (c) and (d) are TEM images of the comparative example and Example 5, respectively.

[0033] Figure 3 CO2 adsorption curves for comparative examples and Example 6;

[0034] Figure 4 EDS spectrum of Example 6; Detailed Implementation

[0035] The following provides a clear and complete description of the solutions in the embodiments of the present invention, as well as a presentation of some characterization results.

[0036] In the following examples, the ammonia solution is 25% by mass. The formaldehyde solution is 37% by mass.

[0037] Example 1

[0038] Add 66 ml of deionized water and 4 ml of anhydrous ethanol to a beaker and stir at 400 rpm for 5 min until homogeneous. Then, while stirring, add 0.8 ml of silica sol and 0.1 ml of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to the ethanol-water mixture, stirring at 400 rpm for 30 min. Next, add 0.5 ml of ammonia water and stir at 400 rpm for 5 min until homogeneous. Finally, add 0.5 g of resorcinol to the solution and stir at 400 rpm. After it dissolves, add 0.763 g of formaldehyde solution and stir continuously in a 60°C water bath for 24 h, with the magnetic stirrer speed set to 200 rpm. Then, centrifuge the reaction solution at 5000 rpm to obtain a solid product, wash three times alternately with deionized water and ethanol, centrifuge, and dry the solid product at 80°C for 12 h. The obtained solid product was then placed in an atmosphere furnace and heated to 450℃ at a rate of 2℃ / min in a N2 atmosphere, held for 2 h, and then the temperature was increased to 800℃ at a rate of 1℃ / min and held for 3 h, followed by natural cooling. After cooling, it was soaked in 10wt% hydrofluoric acid for 24 h, then washed with deionized water and dried to obtain nitrogen-doped hollow hierarchical porous carbon microspheres. The CO2 adsorption performance was tested at 0℃ and 1 bar, and the adsorption capacity was 2.55 mmol / g.

[0039] Example 2

[0040] Add 66 ml of deionized water and 4 ml of anhydrous ethanol to a beaker and stir at 400 rpm for 5 min until homogeneous. Then, while stirring, add 0.8 ml of silica sol and 0.2 ml of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to the ethanol-water mixture, stirring at 400 rpm for 30 min. Next, add 0.5 ml of ammonia water and stir at 400 rpm for 5 min until homogeneous. Finally, add 0.5 g of resorcinol to the solution and stir at 400 rpm. After it dissolves, add 0.763 g of formaldehyde solution and stir continuously for 24 h in a 60°C water bath with a magnetic stirrer at 200 rpm. Then, centrifuge the reaction solution at 5000 rpm to obtain a solid product, wash three times alternately with deionized water and ethanol, centrifuge, and dry the solid product at 80°C for 12 h. The obtained solid product was then placed in an atmosphere furnace and heated to 450℃ at a rate of 2℃ / min in a N2 atmosphere, held for 2 h, and then the temperature was increased to 800℃ at a rate of 1℃ / min and held for 3 h, followed by natural cooling. After cooling, it was soaked in 10wt% hydrofluoric acid for 24 h, then washed with deionized water and dried to obtain nitrogen-doped hollow hierarchical porous carbon microspheres. The CO2 adsorption performance was tested at 0℃ and 1 bar, and the adsorption capacity was 2.84 mmol / g.

[0041] Example 3

[0042] Add 66 ml of deionized water and 4 ml of anhydrous ethanol to a beaker and stir at 400 rpm for 5 min until homogeneous. Then, while stirring, add 0.8 ml of silica sol and 0.3 ml of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to the ethanol-water mixture, stirring at 400 rpm for 30 min. Next, add 0.5 ml of ammonia water and stir at 400 rpm for 5 min until homogeneous. Finally, add 0.5 g of resorcinol to the solution and stir at 400 rpm. After it dissolves, add 0.763 g of formaldehyde solution and stir continuously in a 60°C water bath for 24 h, with the magnetic stirrer set to 300 rpm. Then, centrifuge the reaction solution at 5000 rpm to obtain a solid product, wash three times alternately with deionized water and ethanol, centrifuge, and dry the solid product at 80°C for 12 h. The obtained solid product was then placed in an atmosphere furnace and heated to 450℃ at a rate of 2℃ / min in a N2 atmosphere, held for 2 h, and then the temperature was increased to 800℃ at a rate of 1℃ / min and held for 3 h, followed by natural cooling. After cooling, it was soaked in 10wt% hydrofluoric acid for 24 h, then washed with deionized water and dried to obtain nitrogen-doped hollow hierarchical porous carbon microspheres. The CO2 adsorption performance was tested at 0℃ and 1 bar, and the adsorption capacity was 2.98 mmol / g.

[0043] Example 4

[0044] Add 66 ml of deionized water and 4 ml of anhydrous ethanol to a beaker and stir at 400 rpm for 5 min until homogeneous. Then, while stirring, add 0.8 ml of silica sol and 0.4 ml of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to the ethanol-water mixture, stirring at 400 rpm for 30 min. Next, add 0.5 ml of ammonia water and stir at 400 rpm for 5 min until homogeneous. Finally, add 0.5 g of resorcinol to the solution and stir at 400 rpm. After it dissolves, add 0.763 g of formaldehyde solution and stir continuously in a 60°C water bath for 24 h, with the magnetic stirrer set to 200 rpm. Then, centrifuge the reaction solution at 5000 rpm to obtain a solid product, wash three times alternately with deionized water and ethanol, centrifuge, and dry the solid product at 80°C for 12 h. The obtained solid product was then placed in an atmosphere furnace and heated to 450℃ at a rate of 2℃ / min in a N2 atmosphere, held for 2 h, and then the temperature was increased to 800℃ at a rate of 1℃ / min and held for 3 h, followed by natural cooling. After cooling, it was soaked in 10wt% hydrofluoric acid for 24 h, then washed with deionized water and dried to obtain nitrogen-doped hollow hierarchical porous carbon microspheres. The CO2 adsorption performance was tested at 0℃ and 1 bar, and the adsorption capacity was 3.70 mmol / g.

[0045] Example 5

[0046] Add 66 ml of deionized water and 4 ml of anhydrous ethanol to a beaker and stir at 400 rpm for 5 min until homogeneous. Then, while stirring, add 0.8 ml of silica sol and 0.5 ml of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to the ethanol-water mixture, stirring at 400 rpm for 30 min. Next, add 0.5 ml of ammonia water and stir at 400 rpm for 5 min until homogeneous. Finally, add 0.5 g of resorcinol to the solution and stir at 400 rpm. After it dissolves, add 0.763 g of formaldehyde solution and stir continuously in a 60°C water bath for 24 h, with the magnetic stirrer speed set to 300 rpm. Then, centrifuge the reaction solution at 5000 rpm to obtain a solid product, wash three times alternately with deionized water and ethanol, centrifuge, and dry the solid product at 80°C for 12 h. The obtained solid product was then placed in an atmosphere furnace and heated to 450℃ at a rate of 2℃ / min in a N2 atmosphere, held for 2 h, and then the temperature was increased to 800℃ at a rate of 1℃ / min and held for 3 h, followed by natural cooling. After cooling, it was soaked in 10wt% hydrofluoric acid for 24 h, then washed with deionized water and dried to obtain nitrogen-doped hollow hierarchical porous carbon microspheres. The CO2 adsorption performance was tested at 0℃ and 1 bar, and the adsorption capacity was 3.92 mmol / g.

[0047] Example 6

[0048] Add 66 ml of deionized water and 4 ml of anhydrous ethanol to a beaker and stir at 400 rpm for 5 min until homogeneous. Then, while stirring, add 0.8 ml of silica sol and 1 ml of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to the ethanol-water mixture, stirring at 400 rpm for 30 min. Next, add 0.5 ml of ammonia water and stir at 400 rpm for 5 min until homogeneous. Finally, add 0.5 g of resorcinol to the solution and stir at 400 rpm. After it dissolves, add 0.763 g of formaldehyde solution and stir continuously in a 60°C water bath for 24 h, with the magnetic stirrer set to 300 rpm. Then, centrifuge the reaction solution at 5000 rpm to obtain a solid product, wash three times alternately with deionized water and ethanol, centrifuge, and dry the solid product at 80°C for 12 h. The obtained solid product was then placed in an atmosphere furnace and heated to 450°C at a rate of 2°C / min in a N2 atmosphere, held for 2 hours, then the temperature was increased to 800°C at a rate of 1°C / min and held for 3 hours, followed by natural cooling. After cooling, it was soaked in 10wt% hydrofluoric acid for 24 hours, then washed with deionized water and dried to obtain nitrogen-doped hollow hierarchical porous carbon microspheres. A ceramic boat containing the above sample was placed in a tube furnace, and nitrogen gas was flowed at a heating rate of 10°C / min to 850°C. After reaching the specified temperature, the activation gas CO2 was introduced into the tube furnace (50 cm²). 3 The gas was held at 0°C and 1 bar for 3 hours, then switched back to nitrogen to prevent further activation during cooling. The CO2 adsorption performance was tested at 0°C and 1 bar, and the adsorption capacity was 5.11 mmol / g.

[0049] Comparative Example 1

[0050] Add 66 ml of deionized water and 4 ml of anhydrous ethanol to a beaker, and stir at 400 rpm for 5 minutes until homogeneous. Then, while stirring, add 0.5 ml of ammonia to the ethanol-water mixture, and stir at 400 rpm for 5 minutes until homogeneous. Finally, add 0.5 g of resorcinol to the solution and stir at 400 rpm. After it dissolves, add 0.763 g of formaldehyde solution to the solution, and stir continuously for 24 hours in a 60°C water bath with the magnetic stirrer speed set to 200-300 rpm. Then, centrifuge the reaction solution at 5000 rpm to obtain a solid product, wash three times alternately with deionized water and ethanol, centrifuge, and dry the solid product at 80°C for 12 hours. The obtained solid product was then placed in an atmosphere furnace and heated to 450℃ in a N2 atmosphere at a heating rate of 2℃ / min, held for 2 hours, and then the temperature was increased to 800℃ at a rate of 1℃ / min, held for 3 hours, and then allowed to cool naturally to obtain phenolic resin carbon microspheres. The CO2 adsorption performance was tested at 0℃ and 1 bar, and the adsorption capacity was 3.56 mmol / g.

[0051] The results of the examples and comparative data are compared as follows:

[0052] The table above shows the specific surface area, pore structure parameters, adsorption capacity, and nitrogen content of the comparative and exemplary samples. As can be seen from the table, the carbon spheres prepared using the simple and economical synthesis method provided by this invention possess abundant pore structure and nitrogen source. The specific surface area of ​​the exemplary samples is higher than that of the comparative samples, and the specific surface area of ​​the exemplary samples shows a continuous increasing trend with increasing KH-792 content. The highest specific surface area among the exemplary samples is 1716.75 m². 2 The optimal CO2 adsorption capacity was 5.11 mmol / g. Compared to the comparative example, the specific surface area increased by 253.11%, and the pore volume increased by 553.85% under the conditions of 0℃ and 1 bar.

[0053]

[0054] The CO2 adsorption capacity was increased by 43.54%, indicating that the hollow nitrogen-doped carbon microspheres prepared by this method have excellent structure and performance.

[0055] Based on the data shown in the attached figure, Figure 1 The images show the actual state of the sample at various stages during the experiment, mainly divided into the polymerization stage and the carbonization stage. After the polymerization reaction, the sample was reddish-brown; after high-temperature carbonization, the sample turned black.

[0056] Figure 2The microstructure was characterized, with (a) and (c) being comparative examples, and (b) and (d) being examples 5. Observing Figure (a), it can be seen that the carbon spheres have a particle size of approximately 437.6 nm, a smooth surface, and good dispersibility. Figure (c) also shows that the obtained carbon spheres are dense and uniform, without obvious cavity formation. Observing Figure (b), it was found that the carbon spheres have a very small particle size, with an average particle size of only about 40.6 nm, and the surface morphology of the carbon spheres is relatively rough. Figure (d) shows, via TEM, that the prepared carbon spheres have very obvious cavities. Measurements of the cavities revealed that their diameter is approximately 11.3 nm, close to the size of the added silica sol, indicating that this method successfully prepared hollow nitrogen-doped carbon microspheres.

[0057] Figure 3 The figures show the CO2 adsorption curves for the comparative example and Example 6. At 0°C and 1 bar, the CO2 adsorption capacity of the comparative example was only 3.56 mmol / g, while the CO2 adsorption capacity of the example reached 5.11 mmol / g, representing an increase of 43.54%. Furthermore, as the pressure increased, the adsorption capacity of the comparative example gradually slowed down, while the adsorption capacity of the example did not show a depletion trend, predicting that the example sample would exhibit superior adsorption performance under high pressure. The outstanding CO2 adsorption performance of the example sample is attributed to its rich microporous structure and high nitrogen content, which are key factors affecting CO2 adsorption performance.

[0058] Figure 4 The results are from the EDS analysis of Example 6. The results show that the hollow carbon spheres mainly contain three elements: C, O, and N, with a nitrogen content of 4.82%.

[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 nitrogen-doped hollow hierarchical porous carbon spheres based on silane coupling agents, comprising the following steps: (1) Add deionized water and anhydrous ethanol to a beaker. The volume ratio of ethanol to water is 2:

33. Stir for 2-30 minutes to mix them evenly. (2) Add silica sol and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane with a mass fraction of 31% to the mixture in (1) above, with a volume ratio of 4:5 between the former and the latter, and stir for 10-60 min. (3) Add 25% ammonia water to the mixture in (2) above. The volume ratio of ammonia water to alcohol to water is 1:

140. Stir for 2-300 minutes to mix it evenly. (4) Add resorcinol to the mixed solution of (3) above and stir. After it dissolves, add formaldehyde with a mass fraction of 37% to the solution. The mass ratio of resorcinol to formaldehyde is 2:

3. Stir continuously for 12-72 hours under water bath conditions of 60℃±10℃. The speed of the magnetic stirrer is set to 200-600r / min. (5) Centrifuge the reaction solution of (4) above at a speed of 5000-10000 r / min to obtain a solid product, wash it three times with deionized water and ethanol, and then dry the solid product at 20-100℃ for 5-30 h after centrifugation. (6) The solid product obtained in (5) above is placed into an atmosphere furnace and heated to 400-500°C in N2 atmosphere at a heating rate of 1-10°C / min, and held for 1-5 hours. Then, the temperature is restored to 600-800°C at a heating rate of 1-10°C / min, and held for 1-5 hours. Then, the temperature is allowed to drop naturally. (7) Soak the solid product obtained in (6) above in 5wt%-50wt% hydrofluoric acid for 12-24h, then wash with deionized water and dry to obtain nitrogen-doped hollow hierarchical porous carbon microspheres. (8) Place the ceramic boat containing the sample from (7) above into a tube furnace and heat it to 600-900℃ at a heating rate of 5-20℃ / min. After reaching the specified temperature, introduce the activation gas CO2 into the tube furnace at a flow rate of 50-150 cm⁻¹. 3 Maintain at 0.5 min for 1-5 hours, then switch back to nitrogen to prevent further activation during cooling.

2. The method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on silane coupling agents as described in claim 1, characterized in that... In step (4), continuous stirring is required for 24-48 hours under a water bath at 60℃±10℃, and the speed of the magnetic stirrer is set to 200~300r / min.

3. The method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on silane coupling agents as described in claim 1, characterized in that... In step (5), the centrifuged solid product needs to be dried at 80°C for 8-16 hours.

4. The method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on silane coupling agents as described in claim 1, characterized in that... In step (6), the temperature needs to be raised to 450°C in an N2 atmosphere at a heating rate of 2°C / min and held for 2 hours. Then, the temperature is raised to 800°C at a heating rate of 1°C / min and held for 3 hours, followed by natural cooling.

5. The method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on silane coupling agents as described in claim 1, characterized in that... In step (7), the sample is soaked in hydrofluoric acid for 24 hours.

6. The method for preparing nitrogen-doped hollow hierarchical porous carbon spheres based on silane coupling agents as described in claim 1, characterized in that... In step (8), the temperature needs to be heated to 850°C at a heating rate of 10°C / min.

7. The application of nitrogen-doped hollow hierarchical porous carbon spheres prepared by the method according to any one of claims 1-6 in solid carbon dioxide adsorbents.

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