Porous material, preparation method thereof and application of porous material in air trapping of carbon dioxide

Abstract

The invention relates to the technical field of direct air trapping of carbon dioxide, and provides a porous material, a preparation method and application in air trapping of carbon dioxide, the material comprises a graphite felt / gamma-alumina composite material and polyethyleneimine chemically loaded on the surface of the graphite felt / gamma-alumina composite material; the graphite felt / gamma-aluminum oxide composite material comprises a graphite felt framework and gamma-aluminum oxide loaded on the surface and in pore channels of the graphite felt framework in situ; the gamma-aluminum oxide is generated by calcining and pyrolyzing boehmite, the boehmite is generated in situ through hydrothermal reaction of aluminum nitrate and urea on the surface and in pore channels of a graphite felt framework, the graphite felt is used as the framework, the gamma-aluminum oxide is used as an active loading substrate, and the polyethyleneimine is used as a CO2 adsorption functional component. The three components are synergistic and are driven by sunlight to efficiently and directly capture CO2 from air, so that the problems of low mass transfer efficiency, low desorption rate, high regeneration energy consumption and poor mechanical stability of a traditional material are solved.

Description

Technical Field

[0001] This invention relates to the field of direct air capture of carbon dioxide technology, and more specifically, to a porous material, its preparation method, and its application in air capture of carbon dioxide. Background Technology

[0002] In the process of advancing the global carbon neutrality goal, carbon-negative technologies have become key to removing dispersed CO2 from the atmosphere. CCUS technology can only capture high concentrations of CO2 from industrial stationary emission sources, relying on fixed industrial facilities and having limited site selection; while direct air capture (DAC) technology does not rely on stationary emission sources, can directly capture low concentrations of CO2 in the atmosphere of about 420 ppm, is flexible in deployment, can cover non-point source emission areas, and is the core technology for achieving carbon-negative emissions.

[0003] Currently, DAC technology faces two major bottlenecks: one is the adsorption stage, where traditional adsorption materials suffer from low adsorption capacity, slow adsorption kinetics, and poor stability in humid environments; the other is the desorption stage, where the desorption rate is slow, energy consumption is high, and existing materials are difficult to efficiently couple with clean energy-driven methods.

[0004] For example, the organic amine functionalized macroporous alumina CO2 adsorbent disclosed in Chinese invention patent CN106890621A is in powder or granular form, with high mass transfer resistance and poor stability. It is only suitable for industrial flue gas capture and cannot be adapted to the high-flow-rate, low-concentration air treatment in DAC scenarios. It is also difficult to integrate with photothermal regeneration systems. The carbon dioxide adsorbent disclosed in Chinese invention patent application CN202510074595.3 is also in powder form. It relies on external heat sources for regeneration, has high energy consumption, cannot utilize solar energy, lacks a self-supporting macroscopic structure, has insufficient mechanical strength, and has poor reliability in engineering applications. Chinese invention patent application CN120155047A adopts the liquid amine absorption method. The system is complex, relies on precision pipelines, the amine liquid is easily degraded and volatilized, the maintenance cost is high, the gas-liquid mass transfer efficiency is limited, and the energy loss during the desorption process is large.

[0005] In addition, although two-dimensional nanomaterials such as graphene have high specific surface area and photothermal potential, they lack self-supporting macroscopic three-dimensional structures, are prone to stacking of layers leading to a sharp increase in mass transfer resistance, insufficient mechanical strength, and high cost of large-scale production. They cannot meet the requirements of DAC technology for high throughput, low energy consumption, and long-term stable operation. Therefore, developing a structured composite adsorption material with high adsorption performance, low energy consumption solar regeneration, and good mechanical stability has become the key to the industrial application of DAC technology. Summary of the Invention

[0006] In view of this, the present invention provides a porous material and its preparation method and its application in air capture of carbon dioxide. The material uses graphite felt as a skeleton, γ-alumina as an active support substrate, and polyethyleneimine as a CO2 adsorption functional component. The three components work synergistically to achieve efficient direct air capture of CO2, solving the problems of low mass transfer efficiency, slow desorption rate, high regeneration energy consumption, and poor mechanical stability of traditional materials. Finally, it achieves an adsorption capacity of 1.15 mmol / g for low concentration CO2, completes desorption within 2 minutes under solar energy drive, and reduces the desorption temperature by 7°C.

[0007] The technical solution of this invention is as follows: In a first aspect, the present invention provides a porous material comprising a graphite felt / γ-alumina composite material and polyethyleneimine chemically loaded on the surface of the graphite felt / γ-alumina composite material; The graphite felt / γ-alumina composite material includes a graphite felt skeleton and γ-alumina in situ loaded on the surface and in the pores of the graphite felt skeleton; The γ-alumina is generated by calcination and pyrolysis of boehmite, which is generated in situ by hydrothermal reaction of aluminum nitrate and urea on the surface and in the pores of the graphite felt skeleton.

[0008] Furthermore, the polyethyleneimine is loaded by impregnation at a concentration of 150-250 mg / mL. -1 .

[0009] Furthermore, the mass ratio of the polyethyleneimine to the graphite felt / γ-alumina composite material is (0.02-0.1):1.

[0010] Furthermore, the molar ratio of aluminum nitrate to urea is 1:(2-3); the mass ratio of graphite felt to aluminum nitrate is 1:(1-2).

[0011] Secondly, based on the same inventive concept, the present invention provides a method for preparing the porous material according to any one of the first aspects, comprising the following steps: S1. Pretreatment of graphite felt: Aluminum nitrate and urea are dissolved in deionized water to obtain a precursor solution; the pretreated graphite felt is immersed in the precursor solution, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated and kept at the temperature for 8-12 hours, cooled and rinsed with deionized water, dried and then calcined to obtain graphite felt / γ-alumina composite material. S2. Polyethyleneimine is dissolved in anhydrous ethanol to obtain a polyethyleneimine solution. The graphite felt / γ-alumina composite material is immersed in the polyethyleneimine solution, washed with anhydrous ethanol, and dried to obtain the porous material.

[0012] Furthermore, the pretreatment of graphite felt in step S1 specifically includes: ultrasonically cleaning the graphite felt in a mixture of ethanol and deionized water for 10-20 minutes at 40-50 kHz, and drying it at 50-70°C for 8-12 hours.

[0013] Furthermore, in step S1, the filling degree of the high-pressure reactor is 65%-80%.

[0014] Furthermore, in step S1, after transferring the material to the high-pressure reactor lined with polytetrafluoroethylene, the heating temperature is 160-180℃, and the heating rate is 5-10℃ / min; the drying temperature is 40-60℃, and the drying time is 8-12h; the calcination temperature is 500-600℃, and the calcination time is 2-4h.

[0015] Further, the concentration of the polyethyleneimine solution in step S2 is 150-250 mg·mL. -1 The soaking time is 18-24 hours; the drying temperature is 40-60℃.

[0016] Thirdly, based on the same inventive concept, the present invention provides the application of the porous material described in any one of the first aspects or the porous material prepared by any one of the second aspects in direct air capture of CO2.

[0017] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: 1. The high specific surface area of ​​γ-alumina and the high CO2 affinity of polyethyleneimine work synergistically, combined with the low-resistance mass transfer channels of graphite felt, so that the material can adsorb 1.15 mmol / g of low concentration CO2 of 420 ppm. The adsorption is fast and can reach adsorption saturation within 72 min, which can meet the needs of capturing large flow rates of low concentration air.

[0018] 2. The photothermal conversion and thermal conductivity of graphite felt, combined with the in-situ heat transfer of γ-alumina and polyethyleneimine, enable CO2 desorption to be completed in ≤2 minutes and the desorption temperature to be reduced by 7°C under simulated sunlight irradiation. This achieves a green and low-carbon regeneration process without the need for fossil fuels.

[0019] 3. The skeletal support of graphite felt, combined with the tight bond between γ-alumina and polyethyleneimine, ensures that the material does not pulverize or wear after adsorption-desorption, thus meeting the engineering requirements for long-term stable operation of DAC technology.

[0020] 4. The integrated structural design avoids dust pollution and uneven filling of powder materials, has a small bed pressure drop, can be modularly deployed, and is compatible with DAC equipment in different scenarios, reducing the difficulty of engineering applications and maintenance costs. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a SEM image of the product in Embodiment 1 of the present invention; Figure 2 This is a graph showing the direct air adsorption carbon dioxide adsorption curves of the products in the embodiments and comparative examples of the present invention; Figure 3 This is a graph showing the amount of carbon dioxide adsorbed by direct air adsorption in the embodiments and comparative examples of the present invention; Figure 4 This is a graph showing the direct air adsorption carbon dioxide desorption curves of the embodiments and comparative examples of the present invention; Figure 5 This is a TPD curve diagram of the product in Embodiment 1 of the present invention; Figure 6 This is a TPD curve of the product in Comparative Example 1 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0025] To address the technical problems existing in the prior art, according to one aspect of the embodiments of this disclosure, a porous material is provided, comprising a graphite felt / γ-alumina composite material and polyethyleneimine chemically loaded on the surface of the graphite felt / γ-alumina composite material; The graphite felt / γ-alumina composite material includes a graphite felt skeleton and γ-alumina loaded in situ on the surface and in the pores of the graphite felt skeleton; γ-alumina is generated by calcination and pyrolysis of boehmite, which is generated in situ through hydrothermal reaction of aluminum nitrate and urea on the surface and in the pores of the graphite felt skeleton.

[0026] It is worth noting that direct air adsorption (DAC) technology refers to the process of directly capturing CO2 at extremely low concentrations (approximately ~420 ppm) from ambient air using specific chemical or physical adsorbents. Its core lies in developing adsorbent materials that exhibit high selectivity for CO2, high adsorption capacity, and easy regeneration.

[0027] Graphite felt is a high-performance carbon material obtained by high-temperature graphitization of carbon felt. It possesses high carbon content, excellent high-temperature stability and corrosion resistance, and is lightweight and flexible, exhibiting both thermal conductivity and good photothermal conversion properties, making it suitable as a framework substrate for composite adsorbent materials. By loading active components onto its surface, structured adsorbents with rapid mass transfer channels and highly efficient thermally conductive networks can be constructed, significantly improving CO2 adsorption-desorption kinetics. Combined with in-situ heating design, low-energy thermal regeneration can also be achieved, meeting the requirements of direct air capture for long-term operation of adsorbent materials.

[0028] γ-alumina is a common porous inorganic material with high specific surface area, good thermal stability and abundant surface hydroxyl groups. The hydroxyl groups on its surface can serve as active sites or be used for further functionalization.

[0029] Polyethyleneimine (PEI) is a polymer rich in amino groups (-NH2). Amino groups have a high affinity for CO2 molecules and can undergo reversible chemical reactions. Therefore, PEI is used as an amino modifier loaded onto porous materials to improve their CO2 adsorption performance.

[0030] Based on the above material properties, this invention introduces a three-dimensional mesh graphite felt as the core framework. The through-holes of the graphite felt provide a low-resistance, high-speed flow path for the gas, greatly improving the gas-solid contact efficiency and mass transfer kinetics. Its framework provides stable mechanical support for the active alumina and amine groups, fundamentally avoiding material pulverization and ensuring the structural integrity and stability of long-term operation, making the material itself a durable, independently usable structured adsorption module.

[0031] In addition, the graphite felt skeleton can serve as a highly efficient photothermal converter, rapidly and uniformly converting light energy into heat energy under illumination and directly transferring it to the amine-functionalized active alumina loaded on it. This enables the material to achieve in-situ, efficient solar-driven regeneration, and the addition of graphite felt can significantly reduce the desorption temperature of the material, saving energy.

[0032] It should be noted that, in the existing technology, although two-dimensional nanomaterials such as graphene have been widely studied due to their high specific surface area and photothermal potential, they lack a self-supporting macroscopic three-dimensional structure. When used for adsorption, the stacking of sheets can easily lead to a sharp increase in mass transfer resistance and excessive pressure drop in the bed, which cannot meet the high-throughput processing requirements of direct air capture (DAC) for large flow rates and low concentrations of gases. At the same time, their mechanical strength is insufficient, and they are prone to pulverization during long-term operation, resulting in the loss of active components. Furthermore, the cost of large-scale production and processing technology also restrict their engineering applications.

[0033] Therefore, graphene has inherent defects in terms of macroscopic structure, mass transfer performance, mechanical stability, and engineering cost. Based on this, the present invention selects graphite felt as the skeleton of the composite material to solve the above problems. Graphite felt has a pre-formed, highly interconnected three-dimensional network structure, providing a direct, low-resistance flow channel for gas, fundamentally optimizing mass transfer dynamics. As a flexible carbon fiber felt, it has excellent mechanical strength and resilience, providing durable and stable support for active components. Simultaneously, its three-dimensional network is more conducive to uniform light absorption and heat diffusion, achieving efficient in-situ photothermal regeneration and overcoming the core bottleneck of graphene and other materials in DAC applications.

[0034] In some examples, polyethyleneimine was loaded by impregnation at a concentration of 150-250 mg / mL. -1 .

[0035] In some examples, the mass ratio of polyethyleneimine to graphite felt / γ-alumina composite material is (0.02-0.1):1.

[0036] In some examples, the molar ratio of aluminum nitrate to urea is 1:(2-3); the mass ratio of graphite felt to aluminum nitrate is 1:(1-2).

[0037] According to another aspect of the embodiments of this application, a method for preparing a porous material is also provided, comprising the following steps: S1. Pretreatment of graphite felt: Aluminum nitrate and urea are dissolved in deionized water to obtain a precursor solution; the pretreated graphite felt is immersed in the precursor solution, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated and kept at the temperature for 8-12 hours, cooled and rinsed with deionized water, dried and then calcined to obtain graphite felt / γ-alumina composite material. S2. Polyethyleneimine is dissolved in anhydrous ethanol to obtain a polyethyleneimine solution. The graphite felt / γ-alumina composite material is immersed in the polyethyleneimine solution, washed with anhydrous ethanol, and dried to obtain a porous material.

[0038] In some examples, the pretreatment of graphite felt in step S1 specifically includes: ultrasonically cleaning the graphite felt in a mixture of ethanol and deionized water at 40-50 kHz for 10-20 min, and drying it at 50-70℃ for 8-12 h.

[0039] In some examples, the high-pressure reactor is filled to 65%-80% in step S1.

[0040] In some examples, after the transfer to the polytetrafluoroethylene-lined high-pressure reactor in step S1, the heating temperature is 160-180℃, the heating rate is 5-10℃ / min; the drying temperature is 40-60℃, the drying time is 8-12h; and the calcination temperature is 500-600℃, the calcination time is 2-4h.

[0041] In some examples, the concentration of the polyethyleneimine solution in step S2 is 150-250 mg / mL. -1 The soaking time is 18-24 hours; the drying temperature is 40-60℃.

[0042] According to another aspect of the embodiments of this application, the application of the porous material described in any of the first aspects or the porous material prepared by any of the preparation methods described in any of the second aspects in direct air capture of CO2 is also provided.

[0043] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0044] Example 1 This embodiment 1 provides a porous material and its preparation method. The preparation method includes the following steps: S1. Graphite felt was ultrasonically cleaned in a mixture of ethanol and deionized water at 40 kHz for 15 min and dried at 60 °C for 10 h. 0.2 g of aluminum nitrate and 0.1 g of urea were stirred and dissolved in 35 mL of deionized water to obtain a precursor solution. 0.2 g of pretreated graphite felt was immersed in the precursor solution and transferred to a high-pressure reactor with a 70% polytetrafluoroethylene liner. The temperature was increased to 170 °C at a rate of 5 °C / min and held for 10 h. After cooling, the mixture was rinsed three times with deionized water, dried at 50 °C for 10 h, and then calcined at 550 °C for 3 h to obtain a graphite felt / γ-alumina composite material. S2. Dissolve 2.5 g of polyethyleneimine in 10 mL of anhydrous ethanol to obtain a concentration of 250 mg / mL. -1The graphite felt / γ-alumina composite material was immersed in a polyethyleneimine solution for 20 hours, washed three times with anhydrous ethanol, and dried at 50°C for 10 hours to obtain a porous material.

[0045] The SEM image of the product obtained in Example 1 is as follows: Figure 1 As shown.

[0046] Example 2 This embodiment 2 provides a porous material and its preparation method. The preparation method is basically the same as that in embodiment 1, except that the amount of graphite felt used is 0.1g.

[0047] Example 3 This embodiment 3 provides a porous material and its preparation method. The preparation method is basically the same as that in embodiment 1, except that the amount of polyethyleneimine used is 1.5g.

[0048] Comparative Example 1 Comparative Example 1 provides a composite material and its preparation method, which are basically the same as those in Example 1, except that the graphite felt was not immersed in the precursor solution to verify the technical effect of using it as an amine-functionalized active alumina material.

[0049] Comparative Example 2 Comparative Example 2 provides a composite material and its preparation method, which are basically the same as those in Example 1, except that polyethyleneimine was not added, in order to verify the technical effect of using it as a graphite felt composite active alumina material.

[0050] To better understand this invention, the adsorption and desorption performance of the materials in the embodiments and comparative examples were tested. The test steps are as follows: S1. System pretreatment: The test material is placed in a fixed-bed reactor and the reaction system is purged with dry argon gas at a flow rate of 200 mL / min at 25°C for 30 minutes until the CO2 concentration at the reactor outlet drops below the detection limit of the gas analyzer, so as to eliminate the interference of background CO2 in the environment and the system. S2. Adsorption Test: Simulated air at a flow rate of 50 mL / min was introduced into the pretreated reactor, which had a quartz window for light irradiation and controlled relative humidity of the gas. During this process, the CO2 concentration changes in the reactor outlet gas flow were monitored and recorded in real time using a high-resolution infrared gas analyzer (sensitivity: 0.001%vol, response time ≤90 seconds), and the dynamic adsorption capacity of the material was calculated accordingly. S3. Desorption Test: After adsorption saturation, switch to dry argon gas at a flow rate of 400 mL / min for purging until the CO2 concentration in the system approaches zero. Then, use a solar simulator (0.566 W / cm²) to... 2 As a light source, it irradiates the materials inside the reactor, triggering and accelerating the release process of the captured CO2; at the same time, the gas analyzer is used to monitor and record the instantaneous concentration and cumulative release of CO2 during the light-triggered desorption process. S4. Calculate the adsorption and desorption amounts of the material according to the formulas shown below: Formula for calculating adsorption capacity: Formula for calculating desorption amount: In the formula, q s q d CO2 adsorption and desorption capacities are represented by mmol / g, Q by airflow rate (mL / min), and C0 and C by inlet and outlet carbon dioxide concentrations (vol%), respectively. Breakthrough time t b and adsorption equilibrium time t s h; m is the adsorbent mass, g; V m T is the molar volume of the gas, 22.4 L / mol; T0 is the temperature under standard conditions, 273 K; T is the desorption temperature, K.

[0051] S5. TPD (Temperature Programmed Desorption) Test: The amine-functionalized graphite felt composite active alumina and amine-functionalized active alumina materials obtained in Example 1 and Comparative Example 1 were subjected to TPD test. During this process, the desorption temperature range was set to 25℃-140℃ and the heating rate was 5℃ / min.

[0052] The adsorption curves of the examples and comparative examples were obtained by calculating using the above formula. Figure 2 As shown, the adsorption amounts of the examples and comparative examples are as follows: Figure 3 As shown, the desorption curves of the embodiments and comparative examples are as follows. Figure 4 As shown, the TPD test results of amine-functionalized graphite felt composite activated alumina (Example 1) are as follows. Figure 5 As shown, the TPD test results of the amine-functionalized active alumina material (Comparative Example 1) are as follows. Figure 6 As shown.

[0053] Table 1 shows the adsorption and desorption time data of the materials in Examples 1-3 and Comparative Examples 1-2: Table 1 Adsorption capacity and desorption time data Depend on Figure 3As shown in Table 1, the CO2 adsorption capacity of the material of this invention reaches 1.15 mmol / g, while the CO2 adsorption capacity of the amine-functionalized activated alumina material in Comparative List 1 is only 0.56 mmol / g, and the CO2 adsorption capacity of the graphite felt composite activated alumina material in Comparative List 2 is only 0.1 mmol / g. This is precisely because the addition of graphite felt composite material optimizes the pore structure, improves the carbon dioxide mass transfer efficiency, and ultimately significantly increases the adsorption capacity of the material. (From Table 1, ...) Figure 5 and Figure 6 It can be seen that the material of the present invention can complete desorption in 85 seconds after being composited with graphite felt, and the initial desorption temperature is only 50°C, while the amine-functionalized active alumina material in Comparative Example 1 takes 500 seconds to complete desorption and the initial desorption temperature is 57°C. This is because the addition of graphite felt composite significantly optimizes the desorption rate and desorption temperature of the material.

[0054] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0055] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A porous material, characterized in that, Includes a graphite felt / γ-alumina composite material and polyethyleneimine chemically loaded on the surface of the graphite felt / γ-alumina composite material; The graphite felt / γ-alumina composite material includes a graphite felt skeleton and γ-alumina in situ loaded on the surface and in the pores of the graphite felt skeleton; The γ-alumina is generated by calcination and pyrolysis of boehmite, which is generated in situ by hydrothermal reaction of aluminum nitrate and urea on the surface and in the pores of the graphite felt skeleton.

2. The material according to claim 1, characterized in that, The polyethyleneimine is loaded in an impregnated manner, the loading concentration being 150-250 mg mL -1 .

3. The material according to claim 1, characterized in that, The mass ratio of the polyethyleneimine to the graphite felt / γ-alumina composite material is (0.02-0.1):

1.

4. The material according to claim 1, characterized in that, The molar ratio of aluminum nitrate to urea is 1:(2-3); the mass ratio of graphite felt to aluminum nitrate is 1:(1-2).

5. A method for preparing a porous material according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Pretreatment of graphite felt: aluminum nitrate and urea are dissolved in deionized water by stirring to obtain a precursor solution; The pretreated graphite felt was immersed in the precursor solution, transferred to a high-pressure reactor lined with polytetrafluoroethylene, heated and held for 8-12 hours, cooled and rinsed with deionized water, dried and then calcined to obtain the graphite felt / γ-alumina composite material. S2. Polyethyleneimine is dissolved in anhydrous ethanol to obtain a polyethyleneimine solution. The graphite felt / γ-alumina composite material is immersed in the polyethyleneimine solution, washed with anhydrous ethanol, and dried to obtain the porous material.

6. The method according to claim 5, characterized in that, The pretreatment of graphite felt in step S1 specifically includes: ultrasonically cleaning the graphite felt in a mixture of ethanol and deionized water for 10-20 minutes at 40-50 kHz, and drying it at 50-70℃ for 8-12 hours.

7. The method according to claim 5, characterized in that, In step S1, the filling degree of the high-pressure reactor is 65%-80%.

8. The method according to claim 5, characterized in that, In step S1, after the material is transferred to a high-pressure reactor lined with polytetrafluoroethylene, the heating temperature is 160-180℃ and the heating rate is 5-10℃ / min; the drying temperature is 40-60℃ and the drying time is 8-12h; the calcination temperature is 500-600℃ and the calcination time is 2-4h.

9. The method according to claim 5, characterized in that, The concentration of the polyethyleneimine solution in the step S2 is 150-250 mg·mL -1 ; the dipping time is 18-24 h; and the drying temperature is 40-60℃.

10. The use of a porous material according to any one of claims 1-4 in direct air capture of CO2.

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