Mofs and porous carbon composites, methods of making and using the same

Abstract

This invention relates to the field of novel composite materials, and discloses a MOFs-porous carbon composite material, its preparation method, and its applications. The composite material comprises a metal-organic framework (MOF) material and porous carbon incorporated within the MOF material; the MOF material is ZIF-8; and the mass ratio of the MOF material to the porous carbon is 1:0.5-2. The MOFs-porous carbon composite material provided by this invention exhibits high CO2 content. 2 Its adsorption capacity and selectivity allow it to capture CO from flue gas. 2 It has the advantages of large adsorption capacity, high selectivity and recyclability, and can be applied to industrial waste gas treatment, with broad application prospects and market value.

Description

MOFs and porous carbon composites, their preparation methods and applications Technical Field

[0001] This invention relates to the field of novel composite materials, specifically to a MOF and porous carbon composite material, its preparation method, and its application. Background Technology

[0002] Industrial combustion and other high-temperature processes release large amounts of carbon dioxide, which accumulates excessively in the atmosphere, exacerbating the greenhouse effect. Therefore, the development of efficient carbon dioxide capture technologies is urgently needed.

[0003] Currently, traditional CO2 capture technologies mainly include absorption-desorption, membrane separation, and chemical absorption. However, these technologies suffer from drawbacks such as high cost, complex operation, high energy consumption, and poor CO2 selectivity, which limit their widespread adoption and promotion in industrial applications.

[0004] Metal-organic frameworks (MOFs) are considered the most promising adsorbent materials, exhibiting high CO2 adsorption capacity under high pressure, but they suffer from low adsorption capacity and poor selectivity at ambient pressure. Porous carbon materials have gained attention due to their advantages such as light weight, strong thermal stability, and low cost, but they have poor selectivity for CO2 adsorption, and the preparation process of high specific surface area porous carbon is complex.

[0005] Therefore, the research and development of new high-adsorption materials is of great practical significance and research value for CO2 adsorption. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low adsorption capacity and poor adsorption selectivity of existing adsorbent materials when capturing CO2, and to provide a MOFs-porous carbon composite material, its preparation method, and its applications. The MOFs-porous carbon composite material prepared by the method provided in this invention has a highly ordered pore structure and good chemical stability. It can capture CO2 in flue gas and has high CO2 adsorption and selectivity, as well as advantages such as recyclability and high stability.

[0007] To achieve the above objectives, a first aspect of the present invention provides a MOFs-porous carbon composite material, wherein the composite material comprises a metal-organic framework material and porous carbon incorporated therein; the metal-organic framework material is ZIF-8; and the mass ratio of the metal-organic framework material to the porous carbon is 1:0.5-2.

[0008] A second aspect of this invention provides a method for preparing MOFs-porous carbon composite materials, the method comprising:

[0009] (1) Mix metal-organic framework materials and porous carbon precursors to obtain a hybrid material;

[0010] (2) The mixed material is heat-treated to obtain a MOFs-porous carbon composite;

[0011] (3) The composite is subjected to surface modification treatment to obtain MOFs and porous carbon composite material.

[0012] A third aspect of the present invention provides a MOFs-porous carbon composite material prepared by the method described in the second aspect above.

[0013] The fourth aspect of the present invention provides an application of the MOFs and porous carbon composite materials described in the first or third aspect above in the carbon dioxide capture technology in flue gas.

[0014] Through the above technical solution, the present invention can achieve the following technical effects:

[0015] (1) In this invention, MOFs and porous carbon precursors are used as raw materials to prepare MOFs and porous carbon composite materials. Since MOFs have highly ordered pore structure and micropores with precise size and shape, and can produce good synergistic effect with porous carbon, the prepared composite material exhibits a large adsorption capacity.

[0016] (2) The MOFs and porous carbon composite material provided by the present invention adds MOFs and porous carbon precursors at the same time during the preparation process. The resulting composite material has a small pore size and a high specific surface area. After multiple adsorption and regeneration, it can still maintain a highly ordered pore structure, and has high stability and recyclability.

[0017] (3) The MOFs and porous carbon composite material provided by the present invention introduces porous carbon and combines it with MOFs in the form of carbon material during the heat treatment process to form a porous structure. This not only gives the composite material additional pore structure and surface area, but also enhances the adsorption and selectivity of CO2.

[0018] (4) The MOFs and porous carbon composite materials provided by the present invention are suitable for capturing CO2 in flue gas at higher temperatures. The method is simple, easy to operate, and has low operating costs, and can be used for industrial mass production. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The first aspect of the present invention provides a MOFs and porous carbon composite material, wherein the composite material comprises a metal-organic framework material and porous carbon incorporated in the metal-organic framework material; the metal-organic framework material is ZIF-8; and the mass ratio of the metal-organic framework material to the porous carbon is 1:0.5-2.

[0021] In this invention, the composite material consists of a metal-organic framework (MOF) and porous carbon incorporated within the MOF. The MOF has a highly ordered pore structure. By introducing porous carbon, which is combined with MOFs in the form of carbon materials, the morphology of the resulting composite material is not particularly limited. The MOF particles and porous carbon precursor particles can exist in the composite material in the form of contact, coating, or embedding. Compared with MOF materials, the composite material has more pores, a larger specific surface area, and more active sites. After multiple adsorptions and regenerations, it still has a highly ordered pore structure and will not be significantly damaged or deactivated. It has high stability and recyclability, and can be used for CO2 capture in flue gas at higher temperatures, with more efficient adsorption and selectivity.

[0022] In this invention, the mass ratio of the metal-organic framework material to porous carbon is 1:0.5-2, which can be any value within the range of 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, and any two of these values. Satisfying this range is beneficial for the composite material to have more efficient adsorption and selectivity in the CO2 adsorption process, as well as higher stability and recyclability.

[0023] In some embodiments of the present invention, preferably, the composite material has an average pore size of 0.2-0.5 nm and a specific surface area of ​​800-1200 m². 2 / g. In this invention, the specific surface area of ​​the composite material was determined using the nitrogen adsorption method (BET method); the average pore size was determined using a pore size distribution analyzer.

[0024] In some embodiments of the present invention, preferably, the composite material further comprises modifying functional groups attached to the metal-organic framework material and the porous carbon surface; the modifying functional groups are selected from at least one of hydroxyl, amino and carbonyl groups.

[0025] In some embodiments of the present invention, preferably, the content of the modified functional groups in the composite material is 0.1-0.5 wt%.

[0026] In this invention, by modifying the surface of the composite to increase the number of hydroxyl, carboxyl, and basic groups on the surface of the composite, it is beneficial to improve the chemical reactivity of the composite material surface and enhance the adsorption and selectivity of CO2.

[0027] In some embodiments of the present invention, preferably, the ZIF-8 has a pore size of 0.34-0.36 nm, an average particle size of 10-100 nm, and a specific surface area of ​​1200-1600 m². 2 / g.

[0028] In this invention, controlling the pore size, average particle size, and specific surface area of ​​the ZIF-8 material within the aforementioned ranges is beneficial for the composite material to exhibit more efficient adsorption and selectivity during CO2 adsorption, as well as higher stability and recyclability. Furthermore, in this invention, the ZIF-8 material possesses a specific crystal structure, in which metal ions and organic ligands are arranged in precise proportions and configurations, endowing the ZIF-8 material with a highly ordered pore structure. This structure is commercially available, for example, from Shanghai Chuangsai Technology Co., Ltd.

[0029] A second aspect of the present invention provides a method for preparing MOFs-porous carbon composite materials, characterized in that the method comprises:

[0030] (1) Mix metal-organic framework materials and porous carbon precursors to obtain a hybrid material;

[0031] (2) The mixed material is heat-treated to obtain a MOFs-porous carbon composite;

[0032] (3) The composite is subjected to surface modification treatment to obtain MOFs and porous carbon composite material.

[0033] In some embodiments of the present invention, preferably, in step (1), the mass ratio of the metal-organic framework material to the porous carbon precursor is 1:0.5-2.

[0034] In this invention, by adjusting the mass ratio of MOFs materials and porous carbon precursors, the composite material can exhibit more efficient adsorption and selectivity during CO2 adsorption, as well as higher stability and recyclability.

[0035] In some embodiments of the present invention, preferably, in step (1), the porous carbon precursor is polystyrene; the weight-average molecular weight of the polystyrene is 30,000-80,000 g / mol.

[0036] In this invention, in step (1), the porous carbon precursor is polystyrene, preferably solid polystyrene particles. Its morphology is not particularly limited, as long as it can be combined with MOFs material in the form of carbon material. For example, it can be granular, powdered, or spherical. The diameter of polystyrene is 50-1000 nm. In addition, polystyrene can be obtained commercially, for example, it can be purchased from Hubei Yunmei Technology Co., Ltd.

[0037] In some embodiments of the present invention, preferably, the metal-organic framework material is ZIF-8; the ZIF-8 has a pore size of 0.34-0.36 nm, an average particle size of 10-100 nm, and a specific surface area of ​​1200-1600 m². 2 / g. In this invention, the description of ZIF-8 is as described above and will not be repeated here.

[0038] In some embodiments of the present invention, preferably, in step (2), the heat treatment is carried out in the presence of a protective gas, preferably nitrogen, and the flow rate of the nitrogen gas stream is 50-80 mL / min; the target temperature of the heat treatment is 400-600℃, and the holding time is 2-6 h, preferably 3-5 h.

[0039] In this invention, the heat treatment process causes some carbon atoms in the porous carbon material to vaporize, thereby gradually forming a well-developed pore structure, which can improve the material's ability to adsorb gases.

[0040] In this invention, the flow rate of the inert gas introduced during the heat treatment process needs to be strictly controlled within the aforementioned range. This ensures that the inert atmosphere can effectively cover the material surface and maintain a stable atmospheric environment. A flow rate that is too low may result in an uneven atmosphere, failing to effectively protect the material; a flow rate that is too high may cause atmospheric disturbance or loss of material particles.

[0041] In this invention, controlling the target temperature and treatment time within the aforementioned range is beneficial for the composite material to possess a highly ordered pore structure, resulting in more efficient adsorption and selectivity. If the target temperature is too low, the desired treatment effect cannot be achieved; if the temperature is too high, the structure will be damaged, causing pore collapse and hindering gas adsorption. Furthermore, if the heat treatment time is too short, the desired effect of optimizing the pore structure of the porous carbon material cannot be achieved; if the time is too long, the material yield will be low, and the framework will easily collapse, failing to maintain the porous morphology effectively.

[0042] According to some embodiments of the present invention, preferably, in step (3), the surface modification process includes: holding the composite at the target temperature for 2-5 hours in the presence of hydrofluoric acid or a mixture containing ammonia; the concentration of the hydrofluoric acid is 10-20 wt%; the mixture includes ammonia and nitrogen; and the concentration of ammonia in the mixture is 0.5-1 wt%.

[0043] In this invention, the introduction of hydrofluoric acid increases the content of hydroxyl and carboxyl groups on the surface of the composite, while the introduction of an ammonia-containing gas mixture introduces basic groups onto the surface of the composite, thereby enhancing the chemical reactivity of the composite surface and improving its adsorption and selectivity for CO2. Furthermore, in this invention, ammonia provides a large number of Lewis basic sites, which is beneficial for the adsorption of CO2 (an acidic gas molecule), but has no significant effect on N2, thus improving the selectivity of the composite material. Moreover, this preparation method is simple, requires minimal equipment, and can be used for large-scale industrial production.

[0044] A third aspect of the present invention provides a MOFs-porous carbon composite material prepared by the method described in the second aspect above.

[0045] The fourth aspect of the present invention provides an application of the MOFs and porous carbon composite materials described in the first or third aspect above in the carbon dioxide capture technology in flue gas.

[0046] The present invention will be described in detail below through embodiments.

[0047] Specific surface area was determined using the nitrogen adsorption method (BET method);

[0048] The average pore size was measured using a pore size distribution instrument (pore size distribution analyzer);

[0049] The CO2 adsorption capacity was determined using a gas adsorption analyzer (mass spectrometry at ambient pressure).

[0050] Example 1

[0051] (1) Mix 15g of ZIF-8 and 15g of polystyrene (weight average molecular weight of 50000g / mol) to obtain a mixed material;

[0052] (2) The above-mentioned mixed material was transferred to a high-temperature furnace and heat-treated in a nitrogen atmosphere. The nitrogen flow rate was controlled at 50 mL / min, the temperature was raised to 500 °C, and the reaction was kept at a constant temperature for 5 h to obtain MOFs and porous carbon composites.

[0053] (3) The obtained composite was surface modified by introducing a mixed gas containing 1 wt% ammonia and keeping it at 500°C for 4 hours. Then it was cooled to room temperature to obtain the surface-modified MOFs and porous carbon composite material, which was denoted as MOF-1.

[0054] The BET of MOF-1 was determined to be 900m. 2 The surface has an average pore size of 0.4 nm and a surface-modified amino group content of 0.5 wt%. At 298 K and 1 atm, MOF-1 exhibits a CO2 adsorption capacity of 3.6 mmol / g and a CO2 selectivity greater than 98%. Even after 10 cycles, it still demonstrates good CO2 adsorption performance and selectivity.

[0055] Example 2

[0056] (1) Mix 10g of ZIF-8 and 20g of polystyrene (weight average molecular weight of 50000g / mol) to obtain a mixed material;

[0057] (2) The above-mentioned mixed material was transferred to a high-temperature furnace and heat-treated in a nitrogen atmosphere. The nitrogen flow rate was controlled at 50 mL / min. The temperature was raised to 600 °C and the reaction was kept at a constant temperature for 3 h to obtain MOFs and porous carbon composites.

[0058] (3) The obtained composite was surface modified by introducing a mixed gas containing 0.5 wt% ammonia and keeping it at 600°C for 3 hours. Then it was cooled to room temperature to obtain the surface-modified MOFs and porous carbon composite material, which was denoted as MOF-2.

[0059] The specific surface area of ​​MOF-2 was measured to be 1200 m². 2 The surface has an average pore size of 0.3 nm and a surface-modifying amino group content of 0.4 wt%. At 298 K and 1 atm, MOF-2 exhibits a CO2 adsorption capacity of 3.5 mmol / g and a CO2 selectivity greater than 98%.

[0060] Example 3

[0061] (1) Mix 20g of ZIF-8 and 10g of polystyrene (weight average molecular weight of 50000g / mol) to obtain a mixed material;

[0062] (2) The above-mentioned mixed material was transferred to a high-temperature furnace and heat-treated in a nitrogen atmosphere. The nitrogen flow rate was controlled at 50 mL / min, the temperature was raised to 500 °C, and the reaction was kept at a constant temperature for 4 h to obtain MOFs and porous carbon composites.

[0063] (3) The obtained composite was surface modified by introducing a mixed gas containing 0.5 wt% ammonia and keeping it at 500°C for 4 hours. Then it was cooled to room temperature to obtain the surface-modified MOFs and porous carbon composite material, which was denoted as MOF-3.

[0064] The specific surface area of ​​MOF-3 was determined to be 700 m².2 The surface has an average pore size of 0.4 nm and a surface-modifying amino group content of 0.4 wt%. At 298 K and 1 atm, MOF-3 exhibits a CO2 adsorption capacity of 3.2 mmol / g and a CO2 selectivity greater than 96%.

[0065] Example 4

[0066] (1) Mix 15g of ZIF-8 and 15g of polystyrene (weight average molecular weight of 50000g / mol) to obtain a mixed material;

[0067] (2) The above-mentioned mixed material was transferred to a high-temperature furnace and heat-treated in a nitrogen atmosphere. The nitrogen flow rate was controlled at 50 mL / min. The temperature was raised to 400 °C and the reaction was kept at a constant temperature for 6 h to obtain MOFs and porous carbon composites.

[0068] (3) The obtained composite was surface modified by introducing a mixed gas containing 0.5 wt% ammonia and keeping it at 400°C for 4 hours. Then it was cooled to room temperature to obtain the surface-modified MOFs and porous carbon composite material, which was denoted as MOF-4.

[0069] The specific surface area of ​​MOF-4 was determined to be 1000 m². 2 The surface has an average pore size of 0.4 nm and a surface-modifying amino group content of 0.3 wt%. At 298 K and 1 atm, MOF-4 exhibits a CO2 adsorption capacity of 2.7 mmol / g and a CO2 selectivity greater than 97%.

[0070] Example 5

[0071] (1) Mix 15g of ZIF-8 and 15g of polystyrene (weight average molecular weight of 50000g / mol) to obtain a mixed material;

[0072] (2) The above-mentioned mixed material was transferred to a high-temperature furnace and heat-treated in a nitrogen atmosphere. The nitrogen flow rate was controlled at 50 mL / min, the temperature was raised to 500 °C, and the reaction was kept at a constant temperature for 4 h to obtain MOFs and porous carbon composites.

[0073] (3) The obtained composite was surface modified by introducing a mixed gas containing 0.5 wt% ammonia and keeping it at 500°C for 4 hours. Then it was cooled to room temperature to obtain the surface-modified MOFs and porous carbon composite material, which was denoted as MOF-5.

[0074] The specific surface area of ​​MOF-5 was determined to be 800 m². 2The surface has an average pore size of 0.5 nm and a surface-modifying amino group content of 0.3 wt%. At 298 K and 1 atm, MOF-5 exhibits a CO2 adsorption capacity of 2.5 mmol / g and a CO2 selectivity greater than 95%.

[0075] Example 6

[0076] (1) Mix 15g of ZIF-8 and 25g of polystyrene (weight average molecular weight of 50000g / mol) to obtain a mixed material;

[0077] (2) The above-mentioned mixed material was transferred to a high-temperature furnace and heat-treated in a nitrogen atmosphere. The nitrogen flow rate was controlled at 50 mL / min. The temperature was raised to 400 °C and the reaction was kept at a constant temperature for 5 h to obtain MOFs and porous carbon composites.

[0078] (3) The obtained composite was surface modified by introducing a mixed gas containing 0.5 wt% ammonia and keeping it at 400°C for 4 hours. Then it was cooled to room temperature to obtain the surface-modified MOFs and porous carbon composite material, which was denoted as MOF-6.

[0079] The specific surface area of ​​MOF-6 was measured to be 1000 m². 2 The surface has an average pore size of 0.4 nm and a surface-modifying amino group content of 0.2 wt%. At 298 K and 1 atm, MOF-6 exhibits a CO2 adsorption capacity of 2 mmol / g and a CO2 selectivity greater than 90%.

[0080] Example 7

[0081] (1) Mix 15g of ZIF-8 and 18g of polystyrene (weight average molecular weight of 50000g / mol) to obtain a mixed material;

[0082] (2) The above-mentioned mixed material was transferred to a high-temperature furnace and heat-treated in a nitrogen atmosphere. The nitrogen flow rate was controlled at 50 mL / min, the temperature was raised to 550 °C, and the reaction was kept at a constant temperature for 2 h to obtain MOFs and porous carbon composites.

[0083] (3) The obtained composite was surface modified by introducing a mixed gas containing 0.5 wt% ammonia and keeping it at 550°C for 3 hours. Then it was cooled to room temperature to obtain the surface-modified MOFs and porous carbon composite material, which was denoted as MOF-7.

[0084] The specific surface area of ​​MOF-7 was determined to be 700 m². 2The surface has an average pore size of 0.6 nm and a surface-modified amino group content of 0.1 wt%. At 298 K and 1 atm, MOF-7 exhibits a CO2 adsorption capacity of 1.5 mmol / g and a CO2 selectivity greater than 92%.

[0085] Comparative Example 1

[0086] The preparation method of Example 1 is the same as that of Example 1, except that polystyrene is not added in step (1); the surface-modified MOFs and porous carbon composite material is finally obtained, which is denoted as MOF-8.

[0087] The specific surface area of ​​MOF-8 was measured to be 550 m². 2 The surface has an average pore size of 0.2 nm and a surface-modified amino group content of 0.1 wt%. At 298 K and 1 atm, MOF-8 exhibits a CO2 adsorption capacity of 1.3 mmol / g and a CO2 selectivity greater than 82%.

[0088] Comparative Example 2

[0089] The preparation method of Example 1 was followed, except that no surface modification was performed. The other steps were the same as in Example 1, and the MOFs and porous carbon composite was finally obtained, which was denoted as MOF-9.

[0090] The specific surface area of ​​MOF-9 was measured to be 1240 m². 2 The average pore size is 0.6 nm. At 298 K and 1 atm, MOF-9 exhibits a CO2 adsorption capacity of 1.2 mmol / g and a CO2 selectivity greater than 75%.

[0091] The results above show that the MOFs-porous carbon composite material prepared in this invention has high adsorption capacity and selectivity. Examples 1-7 demonstrate that controlling the mass ratio of MOFs to polystyrene within the range defined in this invention results in a composite material with higher adsorption capacity and greater adsorption selectivity, leading to better CO2 adsorption. In Comparative Example 1, the absence of polystyrene resulted in a smaller specific surface area and pore size of the ZIF-8 porous carbon material, leading to lower adsorption capacity and poorer adsorption selectivity. Comparative Example 2, lacking surface modification treatment, resulted in a MOFs-porous carbon composite with lower CO2 adsorption capacity and selectivity. The effects of this invention can only be achieved by controlling the mass ratio of ZIF-8 to polystyrene within the range defined in this invention and meeting the conditions for heat treatment and surface modification.

[0092] The MOFs-porous carbon composite material described in this invention has a high specific surface area, high adsorption capacity and high selectivity for CO2, can be recycled and has high stability, and the preparation process is simple, the product does not require further washing treatment, and has high economic benefits.

[0093] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite material of MOFs and porous carbon, characterized in that, The composite material comprises a metal-organic framework material and porous carbon incorporated therein; the metal-organic framework material is ZIF-8; the mass ratio of the metal-organic framework material to the porous carbon is 1:0.5-2; the composite material is prepared by mixing the metal-organic framework material and the porous carbon precursor, followed by heat treatment and surface modification; the porous carbon precursor is polystyrene; the composite material contains modifying functional groups attached to the surfaces of the metal-organic framework material and the porous carbon, wherein the modifying functional groups are selected from at least one of hydroxyl, amino, and carbonyl groups.

2. The composite material according to claim 1, wherein, The composite material has an average pore size of 0.2-0.5 nm and a specific surface area of ​​800-1200 m². 2 / g.

3. The composite material according to claim 1, wherein, In the composite material, the content of the modified functional group is 0.1-0.5 wt%.

4. The composite material according to claim 1, wherein, The ZIF-8 has a pore size of 0.34-0.36 nm, an average particle size of 10-100 nm, and a specific surface area of ​​1200-1600 m². 2 / g.

5. A method for preparing MOFs-porous carbon composite materials, characterized in that, The method includes: (1) mixing a metal-organic framework material and a porous carbon precursor to obtain a mixed material; the porous carbon precursor is polystyrene; the metal-organic framework material is ZIF-8; (2) heat-treating the mixed material to obtain a MOFs-porous carbon composite; (3) surface-modifying the composite to obtain a MOFs-porous carbon composite material; the composite material contains modifying functional groups attached to the surface of its metal-organic framework material and porous carbon, wherein the modifying functional groups are selected from at least one of hydroxyl, amino and carbonyl groups.

6. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of the metal-organic framework material to the porous carbon precursor is 1:0.5-2.

7. The preparation method according to claim 5, characterized in that, The weight-average molecular weight of the polystyrene is 30,000-80,000 g / mol.

8. The preparation method according to claim 5, characterized in that, The ZIF-8 has a pore size of 0.34-0.36 nm, an average particle size of 10-100 nm, and a specific surface area of ​​1200-1600 m². 2 / g.

9. The preparation method according to claim 5, characterized in that, In step (2), the heat treatment is carried out in the presence of a protective gas.

10. The preparation method according to claim 9, characterized in that, The protective gas is nitrogen, and the nitrogen gas flow rate is 50-80 mL / min.

11. The preparation method according to claim 5, characterized in that, The target temperature for the heat treatment is 400-600℃, and the holding time is 2-6 hours.

12. The preparation method according to claim 11, characterized in that, In step (3), the surface modification process includes: keeping the composite at the target temperature for 2-5 hours in the presence of hydrofluoric acid or a mixture containing ammonia.

13. The preparation method according to claim 12, characterized in that, The concentration of the hydrofluoric acid is 10-20 wt%.

14. The preparation method according to claim 12, characterized in that, The mixed gas includes ammonia and nitrogen.

15. The preparation method according to claim 14, characterized in that, The concentration of ammonia in the mixture is 0.5-1 wt%.

16. The MOFs-porous carbon composite material prepared by the preparation method according to any one of claims 5-15.

17. The application of the MOFs and porous carbon composite materials according to any one of claims 1-4 in the carbon dioxide capture technology in flue gas.