Hollow porous carbon and preparation method and application thereof

Abstract

The application discloses hollow porous carbon and a preparation method and application thereof, and the preparation method comprises the following steps: S1, preparing a carbon-based porous material; S2, immersing the carbon-based porous material in step S1 in an alkali solution, and heating and stirring, wherein the concentration of the alkali solution is 0.2-2.5 M, so as to obtain an etched hollow porous carbon base; S3, repeatedly cleaning the etched hollow porous carbon base in step S2 with water, and drying to obtain OMS; S4, dispersing the OMS in step S3 in a solvent, and adding polyethyleneimine (PEI), so as to obtain an OMS solution loaded with amine, wherein the mass ratio of the OMS and the polyethyleneimine is 1:0.5-0.9; and S5, removing the solvent in the OMS solution loaded with amine in step S4, and drying to obtain hollow porous carbon. The composite material obtained by the application exhibits excellent CO2 and H2O synchronous capture capacity.

Description

Technical Field

[0001] This invention relates to the field of porous carbon, and more particularly to a hollow porous carbon, its preparation method, and its applications. Background Technology

[0002] Carbon dioxide capture technology is a strategic means to address global climate change and achieve carbon neutrality. Among various capture schemes, carbon-based porous materials, with their excellent structural stability, superior mechanical strength, and significant water resistance, show great application potential in treating complex industrial flue gas or atmospheric environments containing water vapor.

[0003] Chinese patent application CN116116384A discloses a mixed amine-modified mesoporous silica solid adsorbent, its preparation method, and its application. The preparation method includes mixing tetraethylenepentamine and diethanolamine in an organic solvent, adding SBA-15, impregnating and stirring at room temperature, and drying to obtain the mixed amine-modified mesoporous silica solid adsorbent. The mixed amine-modified solid adsorbent prepared by this method can be used to directly capture carbon dioxide from the air, but its carbon dioxide capture efficiency needs improvement. Summary of the Invention

[0004] The present invention aims to provide a hollow porous carbon, its preparation method and application, which has excellent ability to simultaneously capture CO2 and H2O.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing hollow porous carbon includes the following steps:

[0007] S1. Prepare a carbon-based porous material, wherein the carbon-based porous material contains silicon-based components;

[0008] S2. The carbon-based porous material from step S1 is immersed in an alkaline solution and heated and stirred. The concentration of the alkaline solution is 0.2-2.5M to obtain an etched hollow porous carbon matrix.

[0009] S3. Clean and dry the etched hollow porous carbon substrate from step S2 to obtain OMS;

[0010] S4. Disperse the OMS from step S3 in a solvent, add polyethyleneimine, and stir to obtain an amine-loaded OMS solution. The mass ratio of OMS to polyethyleneimine is 1:0.5-0.9.

[0011] S5. Remove the solvent from the OMS solution containing the amine loaded in step S4 and dry to obtain hollow porous carbon.

[0012] This invention utilizes strong alkali etching to remove silicon-based components from materials, encapsulating polyethyleneimine molecules with high amine group density, abundant active sites, and low volatility within hollow porous carbon, thereby enhancing the simultaneous CO2 and H2O capture capability of hollow porous carbon.

[0013] The carbon-based porous materials in this invention include one or more of silicon-doped carbon materials, carbon / silicon oxide composite materials, and silicon carbide (SiC)-based porous materials.

[0014] According to embodiments of the present invention, the present invention can be further optimized, and the optimized technical solution is as follows:

[0015] In step S2, the concentration of the alkaline solution is 0.2-1.3 M; preferably, the concentration of the alkaline solution is 0.8-1.3 M. Alkaline solutions within this concentration range can achieve a greater degree of etching, preventing the hollow carbon spheres from collapsing and maintaining a greater number of mesopores.

[0016] Preferably, the alkaline solution is a NaOH solution.

[0017] In one preferred embodiment, in step S4, the mass ratio of OMS to polyethyleneimine is 1:60%-80%; preferably, the mass ratio of OMS to polyethyleneimine is 1:65%-75%. This mass ratio range allows the prepared hollow porous carbon to have superior simultaneous CO2 and H2O capture capabilities.

[0018] In one preferred embodiment, the mass-volume ratio of OMS to solvent in step S4 is 0.1-0.3 g: 10-30 mL.

[0019] In one preferred embodiment, the carbon-based porous material in step S1 can be purchased directly.

[0020] The preparation method of the carbon-based porous material in step S1 includes the following steps:

[0021] S11. Dissolve tetrapropyl silicate and ammonia in a solvent and stir to form a precursor solution;

[0022] S12. Mix the precursor solution from step S11 with resorcinol and formaldehyde, stir and react to obtain the product;

[0023] S13. Centrifuge, wash and dry the product obtained in step S12 to obtain OMS-Si;

[0024] S14. Calcine the OMS-Si obtained in step S13 under inert gas protection to obtain OMS-Si-C.

[0025] In one preferred embodiment, in step S14, the calcination temperature is 700-900℃, optionally, the calcination heating rate is 2-8℃ / min, and optionally, the calcination time is 2-4 h.

[0026] In one preferred embodiment, in step S11, the volume ratio of tetrapropyl silicate to ammonia is 5-9:2-4. The mass percentage of ammonia is 25%~28%.

[0027] In one preferred embodiment, in step S11, the solvent is a mixed solvent of anhydrous ethanol and deionized water with a volume ratio of 6-8:1, and the volume ratio of tetrapropyl silicate to the solvent is 7:70-90; in step S12, the mass-volume ratio of tetrapropyl silicate to resorcinol and formaldehyde contained in the precursor solution is 5-9 mL:0.2-0.4 g:0.5-0.7 mL.

[0028] In step S11, the stirring rate is 700-900 r / min and the stirring time is 20-40 min.

[0029] In step S12, the stirring time is 20-28 hours.

[0030] In step S13, the washing specifically involves washing with deionized water and anhydrous ethanol until the solution is clear. In step S13, the drying temperature is 70-90℃, and the drying time is 10-14 h.

[0031] In step S14, the inert gas is a nitrogen atmosphere.

[0032] In step S2, the heating temperature is 70-90℃ and the heating time is 10-14 h.

[0033] In step S3, the etched hollow porous carbon substrate from step S2 is repeatedly washed with water until the pH of the washing solution is 6-8; preferably neutral.

[0034] In step S3, the drying temperature is 50-70℃ and the drying time is 10-14 h.

[0035] The solvent in step S4 is one or more of anhydrous methanol and anhydrous ethanol.

[0036] To ensure sufficient diffusion and anchoring of organic amine molecules within the pores of the support, the stirring speed in step S4 is 400-1200 rpm, and the stirring time is 4-20 h. Preferably, the stirring speed in step S4 is 600-1000 rpm, and the stirring time is 6-18 h. More preferably, the stirring speed in step S4 is 700-900 rpm, and the stirring time is 8-16 h.

[0037] In step S5, the drying temperature is 50-70℃, and the drying time is 10-14 h. If the drying temperature is too low or the drying time is too short, the residual solvent will not be removed sufficiently, which may affect the pore opening and CO2 / H2O collection performance. If the drying temperature is too high or the drying time is too long, it may cause polyethyleneimine molecules to migrate, agglomerate, or reduce the activity of some amine groups, thereby affecting the stability of the material and its simultaneous collection ability.

[0038] Preferably, the molecular weight of PEI is 500-1200, and more preferably it is linear.

[0039] This invention also discloses a hollow porous carbon (OMS) prepared according to the described method. The hollow porous carbon has a particle size range of 400-600 nm, a shell size of 70-90 nm, and a specific surface area of ​​1100-1300 m². 2 / g, wherein the micropore size is 0.8-1 nm and the mesopore size is 9-11 nm.

[0040] The present invention also discloses the application of the hollow porous carbon described above in a material for simultaneous capture of CO2 and H2O.

[0041] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention encapsulates polyethyleneimine (PEI) molecules within hollow carbon spheres through physical confinement, achieving ultra-high amine loading while ensuring unobstructed external diffusion channels, thus significantly increasing amine loading. The resulting composite material exhibits excellent simultaneous CO2 and H2O capture capabilities. The composite material possesses abundant amine active sites, a good pore structure, and adaptability to water vapor environments, enabling simultaneous CO2 and H2O capture under water vapor conditions. The synergistic adsorption of H2O not only enhances the material's applicability to humid flue gas or moist air environments but also promotes the adsorption and conversion process of CO2 at amino sites, improving the material's capture efficiency and stability in complex atmospheres. Therefore, the hollow porous carbon composite material prepared by this invention has good application value and promotion prospects in carbon replenishment, air pollution control, industrial flue gas purification, and ecological protection engineering, and is particularly suitable for CO2 capture applications in complex industrial flue gas or atmospheric environments containing water vapor. Attached Figure Description

[0042] Figure 1 (a) Schematic diagram of the OMS material preparation process; (b) SEM; (c) TEM; (d) High magnification TEM.

[0043] Figure 2 Transmission electron microscope (TEM) images of OMS at different etching levels are shown, where (a) is OMS-0.5; (b) is OMS-1; and (c) is OMS-1.5.

[0044] Figure 3 The adsorption curves of the target product under 70% RH humidity conditions are shown in the examples and comparative examples.

[0045] Figure 4 The OMS-70PEI and OMS-1 absorb water to saturation before capturing carbon dioxide at 70% humidity and 3000ppm CO2.

[0046] Figure 5 Molecular dynamics simulation results of adsorption and diffusion behavior of mixed gases in OMS-70PEI with the OMS shell pore size set to 2.0 nm. (a) Molecular dynamics simulation of adsorption and diffusion behavior in OMS-70PEI with CO2 / H2O / N2 volume ratio = 5:2.5:92.5, time range 0~100 ns. (b) Number of H2O molecules adsorbed by the mixed gas in different regions of OMS-PEI (feed PEI, shell Carbon, hollow feed region). (c) Number of CO2 molecules adsorbed by the mixed gas in different regions of OMS-PEI (feed PEI, shell Carbon, hollow feed region). (d) Number of N2 molecules adsorbed by the mixed gas in different regions of OMS-PEI (feed PEI, shell Carbon, hollow feed region).

[0047] Figure 6 Molecular dynamics simulation results of adsorption and diffusion behavior of mixed gases in OMS-70PEI with an OMS shell pore size set to 4.0 nm. (a) Molecular dynamics simulation of adsorption and diffusion behavior in OMS-70PEI with CO2 / H2O / N2 volume ratio = 5:2.5:92.5, time range 0~100 ns. (b) Number of H2O molecules adsorbed by the mixed gas in different regions of OMS-PEI (feed PEI, shell Carbon, hollow feed region). (c) Number of CO2 molecules adsorbed by the mixed gas in different regions of OMS-PEI (feed PEI, shell Carbon, hollow feed region). (d) Number of N2 molecules adsorbed by the mixed gas in different regions of OMS-PEI (feed PEI, shell Carbon, hollow feed region).

[0048] Figure 7 This is the XPS elemental analysis diagram of the composite material in Example 2. Detailed Implementation

[0049] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0050] Synthesis of hollow carbon sphere OMS

[0051] First, 7 mL of tetrapropyl silicate and 3 mL of ammonia were accurately measured according to the experimental ratio and dissolved together in 70 mL of anhydrous ethanol and 10 mL of deionized water. The mixture was stirred continuously at 800 r / min for 30 min at room temperature to ensure thorough mixing and the formation of a homogeneous precursor solution. Then, 0.25 g of resorcinol and 0.56 mL of formaldehyde were added to the mixture, and the reaction was continued at 25 °C for 24 h with stirring. After the reaction was complete, the product was transferred to a centrifuge tube and washed with deionized water and anhydrous ethanol until clear. The product was then dried in a drying oven at 80 °C for 12 h. Finally, it was transferred to a tube furnace and heated to 800 °C at a heating rate of 5 °C / min under a nitrogen atmosphere, and calcined at this temperature for 3 h to obtain OMS-Si-C.

[0052] The obtained OMS-Si-C was immersed in a 1 M NaOH solution and reacted at a constant temperature of 80℃ with stirring for 12 h. The silicon-based components in the material were removed by etching with a strong base to construct a hollow structure. After the reaction was completed, the product was repeatedly washed with a large amount of deionized water until the pH of the washing solution was neutral. Then it was placed in a vacuum drying oven at 60℃ for 12 h to finally obtain OMS-1.

[0053] The obtained OMS-Si-C was immersed in a 0.5 M NaOH solution and reacted at a constant temperature of 80 °C with stirring for 12 h. The silicon-based components in the material were removed by etching with a strong base to construct a hollow structure. After the reaction was completed, the product was repeatedly washed with a large amount of deionized water until the pH of the washing solution was neutral. Then it was placed in a vacuum drying oven at 60 °C for 12 h to finally obtain OMS-0.5.

[0054] The obtained OMS-Si-C was immersed in a 1.5 M NaOH solution and reacted at a constant temperature of 80 °C with stirring for 12 h. The silicon-based components in the material were removed by etching with a strong base to construct a hollow structure. After the reaction was completed, the product was repeatedly washed with a large amount of deionized water until the pH of the washing solution was neutral. Then it was placed in a vacuum drying oven at 60 °C for 12 h to finally obtain OMS-1.5.

[0055] Example 1

[0056] 0.2 g of OMS-1 was dispersed in 20 mL of anhydrous methanol and sonicated to obtain a homogeneous suspension. Then, at room temperature, a linear PEI with a molecular weight of 800 (60 wt% loading, including 0.3 g of PEI) was added. The mixed suspension was continuously stirred at 800 rpm for 12 h at room temperature to ensure sufficient diffusion of the organic amine molecules and anchorage within the pores of the support. After the reaction was complete, the methanol solvent was removed under reduced pressure using a rotary evaporator. Finally, the resulting solid was placed in a vacuum oven and dried at 60 °C for 12 h to completely remove residual solvent, yielding the target product OMS-60PEI.

[0057] Example 2

[0058] The difference between this embodiment and Example 1 is that 70 wt% PEI was added. The mixed suspension was continuously stirred at 800 rpm for 12 h at room temperature to obtain the target product OMS-70PEI.

[0059] Example 3

[0060] The difference between this embodiment and Example 1 is that 80 wt% PEI was added. The mixed suspension was continuously stirred at 800 rpm for 12 h at room temperature to obtain the target product OMS-80PEI.

[0061] CO2 adsorption performance evaluation of the examples

[0062] The preparation process of hollow carbon spheres by OMS and the SEM and TEM images are shown below. Figure 1 As shown.

[0063] The etching degrees obtained by etching with different NaOH concentrations are as follows: Figure 2 As shown, the etching degree increases with increasing NaOH concentration, but when the concentration is greater than or equal to 1.5 M, the hollow carbon spheres collapse. Figure 2 -c). Structural collapse is detrimental to amine bonding, therefore higher concentrations were not investigated. Therefore, 0.2–1.3 M NaOH solutions were chosen for etching to achieve a greater etching depth while preventing the collapse of hollow carbon spheres and maintaining a higher degree of mesoporous structure. Subsequently, OMS-1 obtained from etching with 1 M NaOH was selected as the support for subsequent amine functionalization.

[0064] The CO2 adsorption performance of OMS-0.5, OMS-1.0, OMS-1.5 and the composite materials in Examples 1-3 (all used as adsorbents) was evaluated. The adsorbent loading amount was 100 mg (pretreated at 100℃ for 30 min), the adsorption pressure was 0~1 bar, and the adsorption temperature was 25℃, as shown in Table 1.

[0065] Table 1. CO2 adsorption capacity of materials in each embodiment and comparative example.

[0066]

[0067] OMS-Si-C does not adsorb CO2.

[0068] The H2O adsorption performance of OMS-1 and the products OMS-60PEI, OMS-70PEI, and OMS-80PEI from Examples 1-3 was evaluated. The adsorbent loading was 100 mg (pre-treated at 100°C for 30 min), the adsorption pressure was 1 bar, the adsorption temperature was 25°C, and the humidity was 70% RH. The results are as follows: Figure 3 As shown.

[0069] From Table 1 and Figure 3 It can be seen that the CO2 adsorption capacity of the amine-functionalized OMS-PEI composite material used for CO2 and H2O capture in this invention is greatly improved, and it also has water adsorption properties.

[0070] CO2 and H2O breakthrough adsorption tests were performed on OMS-1 and the target product OMS-70PEI from Example 2. The adsorption pressure was 1 bar, the adsorption temperature was 25°C, the CO2 concentration was 3000 ppm, and the humidity was 70% RH. Figure 4 As shown, OMS-70PEI exhibits excellent CO2 capture performance under low CO2 concentration conditions, and its CO2 adsorption performance increases from 1.43 mmol / g to 4.20 mmol / g in the presence of water.

[0071] Molecular dynamics was used to study the transport behavior of gas molecules in the OMS-PEI system. The gas molecules in the system included CO2, H2O, and N2. The initial configuration of the system was generated using PACKMOL software, and the system underwent energy minimization, NPT, and NVT simulations in sequence to ensure that each component had a reasonable spatial distribution in the initial state. Statistical analysis was performed on the molecular density, diffusion coefficient, and other properties within the system.

[0072] All molecular dynamics simulations were performed using GROMACS software in the NPT and NVT ensembles, with force field parameters for each component derived from the General Amber Force Field (GAFF). The geometries of gas and PEI molecules were optimized using Gaussian 16 software with the DFT method at the B3LYP / 6-31+G** level, and atomic point charges were fitted using Multiwfn software with the RESP method.

[0073] During the simulation, periodic boundary conditions were applied to the system in the X, Y, and Z directions. The steepest descent method was used to minimize the system's energy, eliminating unreasonable contacts in the initial structure. The system temperature was controlled at 25°C using the V-rescale coupling method to match experimental conditions, with a time constant of 0.1 ps. The cutoff distance for short-range van der Waals interactions and electrostatic interactions was set to 1.20 nm, while long-range electrostatic interactions were calculated using the Particle Mesh Ewald method. Furthermore, the carbon layer and the isolating helium plate were frozen to ensure the overall structural stability of the system. Data generated based on the above simulation settings were used for subsequent sampling and analysis. Visualization of the simulation trajectory and structural analysis were performed using VMD software, such as... Figure 5-6 As shown, the threshold effect of mass transfer channel size was further investigated to verify the adsorption energy absorption of CO2 / H2O.

[0074] like Figure 6 As shown, when the OMS shell pore size is set to 4.0 nm, it can be observed that most CO2 gradually diffuses into the hollow structure of the OMS and reacts with PEI. Almost all water molecules also enter the hollow structure of the OMS, where they undergo strong hydrogen bonding with the highly hydrophilic and amino-rich PEI molecular chains. This is followed by adsorption on the carbon layer surface in the OMS system with a 2 nm pore size (e.g., ...). Figure 5 The adsorption of CO2 (as shown in the figure) is transformed into internal PEI adsorption, which thermodynamically greatly promotes the bicarbonate reaction pathway between CO2 and amino groups. At this time, the adsorption of H2O mainly comes from the PEI molecules encapsulated in the internal hollow structure, which effectively promotes the co-adsorption of CO2 and H2O.

[0075] like Figure 7 As shown, according to the EDS-Mapping results of transmission electron microscopy, C, N, O and Si elements are abundant in the OMS-70PEI spherical structure, with the N signal distribution being relatively uniform, indicating that PEI is uniformly distributed in the OMS hollow structure.

[0076] The embodiments of the present invention have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention is not limited to the specific embodiments described above; these embodiments are merely illustrative and not limiting. Those skilled in the art, under the guidance of the present invention, can make many modifications without departing from the spirit and scope of the claims, and all such modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing hollow porous carbon, characterized in that, Includes the following steps: S1. Prepare a carbon-based porous material, wherein the carbon-based porous material contains silicon-based components; S2. The carbon-based porous material from step S1 is immersed in an alkaline solution and heated and stirred. The concentration of the alkaline solution is 0.2-2.5 M to obtain an etched hollow porous carbon matrix. S3. Clean and dry the etched hollow porous carbon substrate from step S2 to obtain OMS; S4. Disperse the OMS from step S3 in a solvent, add polyethyleneimine to obtain an amine-loaded OMS solution, with a mass ratio of OMS to polyethyleneimine of 1:0.5-0.9; S5. Remove the solvent from the OMS solution containing the amine loaded in step S4 and dry to obtain hollow porous carbon.

2. The method for preparing hollow porous carbon according to claim 1, characterized in that, In step S2, the concentration of the alkaline solution is 0.2-1.3M; preferably, the concentration of the alkaline solution is 0.8-1.3M.

3. The method for preparing hollow porous carbon according to claim 1, characterized in that, In step S4, the mass ratio of OMS to polyethyleneimine is 1:60%-80%; preferably, the mass ratio of OMS to polyethyleneimine is 1:65%-75%.

4. The method for preparing hollow porous carbon according to claim 1, characterized in that, In step S4, the mass-volume ratio of OMS to solvent is 0.1-0.3 g: 10-30 ml.

5. The method for preparing hollow porous carbon according to any one of claims 1-4, characterized in that, The preparation method of the carbon-based porous material in step S1 includes the following steps: S11. Dissolve tetrapropyl silicate and ammonia in a solvent and stir to form a precursor solution; S12. Mix the precursor solution from step S11 with resorcinol and formaldehyde, and stir to react; S13. Centrifuge, wash and dry the product obtained in step S12 to obtain OMS-Si; S14. Calcine the OMS-Si obtained in step S13 under inert gas protection to obtain OMS-Si-C.

6. The method for preparing hollow porous carbon according to claim 5, characterized in that, In step S14, the calcination temperature is 700-900℃, the calcination heating rate is 2-8℃ / min, and the calcination time is 2-4h.

7. The method for preparing hollow porous carbon according to claim 5, characterized in that, In step S11, the volume ratio of tetrapropyl silicate to ammonia is 5-9:2-4.

8. The method for preparing hollow porous carbon according to claim 5, characterized in that, In step S11, the solvent is a mixture of anhydrous ethanol and deionized water with a volume ratio of 6-8:1, and the volume ratio of tetrapropyl silicate to the solvent is 7:70-90; in step S12, the mass-volume ratio of tetrapropyl silicate, resorcinol and formaldehyde is 5-9 mL: 0.2-0.4 g: 0.5-0.7 mL.

9. A hollow porous carbon prepared by the preparation method according to any one of claims 1-8.

10. The application of the hollow porous carbon of claim 9 in a material for simultaneous capture of CO2 and H2O.

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