Modified MOF materials, their preparation methods and applications, and methods for CO2 adsorption and capture.

Abstract

This invention relates to the field of MOF material modification / modification, and discloses a modified MOF material, its preparation method and application, and a method for CO2 adsorption and capture. A method for preparing a modified MOF material includes the following steps: (1) subjecting a MOF precursor solution to a solution containing a modifying component via hydrothermal reaction to obtain a solid product, wherein the MOF precursor solution includes a solvent, an organic ligand, and a metal precursor; (2) drying the solid product obtained in step (1); wherein the modifying component is selected from at least one of Group VB metal elements. The modified MOF material prepared by this method exhibits high hydrothermal stability and can enhance its cycle stability for CO2 adsorption under real flue gas humidity conditions.

Description

Technical Field

[0001] This invention relates to the field of MOF material modification, specifically to a modified MOF material, its preparation method and application, and a method for CO2 adsorption and capture. Background Technology

[0002] Traditional coal-fired power plants, due to their low flue gas pressure and low CO2 concentration, typically employ chemical absorption as their post-combustion capture process. This method utilizes alkaline amine solutions to capture CO2 through chemical reactions, exhibiting good selectivity and absorption rates. However, the long-term operation of alkaline solvents corrodes equipment and pipelines, and the amine solution itself undergoes thermal and oxidative degradation. Furthermore, the desorption process requires overcoming the latent and sensible heat of the solvent, consuming large amounts of steam, increasing equipment investment costs and safety risks, resulting in significant amine loss and high energy consumption. To overcome these drawbacks, those skilled in the art have researched and developed solid-state adsorption methods for CO2 removal. These methods can absorb CO2 under low partial pressure and low concentration conditions, exhibiting low corrosivity to equipment and low regeneration temperatures. They have been extensively studied in the fields of flue gas CO2 removal and direct carbon capture in air, and are expected to become a new generation of CO2 capture technology.

[0003] MOFs (Metal-Organic Fabrics) are solid adsorbent materials with high specific surface area, high porosity, and highly tunable structure. They are formed by the self-assembly of metal ions or metal clusters with organic ligands, and are porous polymers that combine the characteristics of inorganic and organic materials. Due to their unique structure and chemical properties, MOFs are widely used in gas separation, especially in CO2 capture. From the perspective of adsorption mechanism, they can be divided into physical adsorption and chemical adsorption. Physical adsorption mainly utilizes the sieving effect of pore size and the van der Waals forces between CO2 and the material's pores, while chemical adsorption utilizes the acidity of CO2, allowing it to react chemically with the amine functional groups in the material and be adsorbed. Generally, chemical adsorption is more suitable for capturing low partial pressure and low concentration CO2, offering higher selectivity and faster adsorption rates.

[0004] In MOFs (Metal-Organic Facility), the interaction between metal ions or metal clusters and organic linkers is primarily coordination, and the forces are relatively weak. When encountering polar molecules, these molecules can disrupt the coordination bonds in the MOF framework, leading to structural collapse and affecting adsorption and separation performance. Water is a widely present component in flue gas and even air. As a polar molecule, moisture has a significant impact on the structural stability and adsorption performance of MOF materials. Most reported MOF materials exhibit poor hydrothermal stability, and their structures are prone to collapse under real flue gas humidity or air humidity conditions, affecting adsorption performance, increasing material and operating costs, and limiting the commercial application of MOFs. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of competitive adsorption of water vapor in the feed gas, structural collapse, and poor material cycle stability encountered by traditional MOF materials in flue gas CO2 removal and direct carbon capture. This invention provides a modified MOF material, its preparation method, its application, and a method for CO2 adsorption and capture. The modified MOF material prepared by this method exhibits high hydrothermal stability, which enhances its cycle stability for CO2 adsorption under real flue gas humidity conditions.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing modified MOF materials, the method comprising the following steps: (1) The precursor solution of MOFs is subjected to hydrothermal reaction with a solution containing modified components to obtain a solid product. The precursor solution of MOFs includes a solvent, an organic ligand and a metal precursor. (2) Dry the solid product obtained in step (1); The modified component is selected from at least one of the group VB metal elements.

[0007] Preferably, the method for preparing the solution containing the modified component includes: dissolving the hydrated oxide of the modified component in an aqueous hydrogen peroxide solution.

[0008] Preferably, the method for preparing the hydrated oxide of the modified component includes: S1. Melt-calcining the oxide and alkali of the modified component; S2. Dissolve the molten roasted product of S1 in water to obtain a slurry; perform solid-liquid separation on the slurry to obtain a liquid material; S3. Adjust the pH of the liquid material to 4-6, and then dry it.

[0009] The second aspect of the present invention provides a modified MOF material prepared by the preparation method described in the first aspect.

[0010] A third aspect of the present invention provides an application of the modified MOFs material described in the second aspect in CO2 adsorption.

[0011] The fourth aspect of the present invention provides a method for CO2 adsorption and capture, the method comprising: sending a CO2-containing feed gas into a reactor to contact and adsorb it with a modified MOFs material; after the adsorption is completed, sending an inert gas into the reactor to contact and desorb it with the CO2-adsorbed modified MOFs material. The modified MOFs material is the modified MOFs material described in the second aspect.

[0012] The beneficial effects of the present invention through the above technical solution include: The modified MOFs material prepared by the preparation method provided in this invention not only improves the hydrothermal stability of the material and enhances its cycle stability for CO2 adsorption under real flue gas humidity conditions, but also introduces open metal sites to promote CO2 adsorption. Attached Figure Description

[0013] Figure 1 The cycling performance diagrams are of Nb-MIL-101(Cr) in Example 1 of the present invention and MIL-101(Cr) in Comparative Example 1. Figure 2 The cycling performance diagrams are of Nb-MIL-101(Al) in Example 2 and MIL-101(Al) in Comparative Example 2. Figure 3 The cycling performance diagrams are of Nb-MOF-808 in Example 3 and MOF-808 in Comparative Example 3 of the present invention. Figure 4 The cycling performance diagrams are of Ta-MOF-808 in Example 4 and MOF-808 in Comparative Example 4 of the present invention. Figure 5 The cycling performance diagrams are of Ta-ZIF-8 in Example 5 and ZIF-8 in Comparative Example 5 of the present invention. Figure 6 The cycling performance diagrams are for Nb-MIL-101(Cr) in Example 1 and Nb-MIL-101(Cr)-s in Example 6 of this invention. Figure 7 The diagram shows the cycle performance of Nb-MIL-101(Cr) in Example 1 of the present invention and s-Nb-MIL-101(Cr) in Comparative Example 6. Detailed Implementation

[0014] 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.

[0015] The first aspect of this invention provides a method for preparing modified MOF materials, the method comprising the following steps: (1) The precursor solution of MOFs is subjected to hydrothermal reaction with a solution containing modified components to obtain a solid product. The precursor solution of MOFs includes a solvent, an organic ligand and a metal precursor. (2) Dry the solid product obtained in step (1); The modified component is selected from at least one of the group VB metal elements.

[0016] The preparation method provided by this invention involves a hydrothermal reaction between the precursor solution of MOFs and the modified component, which exists in a solution containing the modified component. This process is more conducive to improving the stability of the material, maintaining its adsorption performance under real flue gas humidity conditions, enhancing the cycle stability of the material, reducing the consumption cost of the material, and saving operating expenses. It has significant practical implications for the fields of flue gas CO2 removal and direct carbon capture in air.

[0017] The present invention has a wide range of choices for the group VB metal elements, and preferably, the modified component is niobium and / or tantalum.

[0018] According to the present invention, preferably, the method for preparing the solution containing the modified component includes: dissolving the hydrated oxide of the modified component in an aqueous hydrogen peroxide solution.

[0019] The present invention does not particularly limit the amount of the hydrogen peroxide aqueous solution used, as long as a clear solution containing the modified component is obtained. Preferably, the mass ratio of the hydrated oxide of the modified component to the hydrogen peroxide aqueous solution is 1:5-15.

[0020] According to the present invention, preferably, the concentration of the hydrogen peroxide aqueous solution is 10-40 wt%. The hydrogen peroxide aqueous solution can be obtained commercially.

[0021] Preferably, the dissolution is carried out under stirring conditions.

[0022] The present invention does not impose any particular limitation on the stirring conditions, which can be appropriately selected according to the specific circumstances, with the aim of accelerating the uniform mixing of the two.

[0023] According to the present invention, preferably, the method for preparing the hydrated oxide of the modified component includes: S1. Melt-calcining the oxide and alkali of the modified component; S2. Dissolve the molten roasted product of S1 in water to obtain a slurry; perform solid-liquid separation on the slurry to obtain a liquid material; S3. Adjust the pH of the liquid material to 4-6, and then dry it.

[0024] The hydrated oxide-modified MOFs material prepared by the method described in this invention is beneficial for incorporating Group VB metal elements into the MOF framework from an atomic perspective, making the doping more uniform. At the same time, it facilitates electron transfer with MOF metal nodes in atomic form, promoting interaction with CO2.

[0025] According to the present invention, preferably, the melting and calcining conditions in S1 include: a temperature of 300-800℃, specifically 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, and any two of these values ​​forming a range, preferably 500-600℃; and a time of 5-12h, specifically 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, and any two of these values ​​forming a range, preferably 5-10h.

[0026] According to the present invention, preferably, the molar ratio of the oxide to the alkali of the modified component is 1:8-12, specifically 1:8, 1:8.5, 1:9, 1:9.5, 1:10, 1:10.5, 1:11, 1:11.5, 1:12, and a range of any two of these values.

[0027] The present invention allows for a wide range of choices of the type of alkali. Preferably, the alkali is a strong alkali, and more preferably sodium hydroxide and / or potassium hydroxide.

[0028] The present invention does not have a particular limitation on the amount of water used in S2, as long as it is sufficient to dissolve the molten roasted product of S1.

[0029] The present invention does not impose any particular limitation on the solid-liquid separation described in S2, and conventional technical means in the art can be used.

[0030] According to the present invention, preferably, pH is adjusted by an acid in S3, wherein the acid is preferably selected from organic acids, more preferably selected from at least one of acetic acid, propionic acid and malic acid.

[0031] Preferably, the method for preparing the hydrated oxide of the modified component further includes: in S3, adjusting the pH of the liquid material to 4-6, and then performing solid-liquid separation and drying in sequence.

[0032] The present invention does not impose any particular limitation on the solid-liquid separation described in S3, and conventional technical means in the art can be used.

[0033] The present invention does not have any particular limitation on the drying described in S3, and it can be carried out with reference to conventional methods in the art.

[0034] This invention does not impose any particular limitations on the types and amounts of substances in the precursor solution of the MOFs. The conventional methods in the art can be used to obtain various common MOFs materials.

[0035] The present invention has a wide range of choices for the organic ligands. Preferably, the organic ligands are selected from at least one of terephthalic acid, trimesic acid, 2-methylimidazole and 2,5-dihydroxyterephthalic acid.

[0036] The present invention has a wide range of metal types that can be selected from the metal precursor. Preferably, the metal in the metal precursor is selected from at least one of chromium, aluminum, iron, zirconium, zinc, copper and magnesium.

[0037] The present invention allows for a wide range of choices for the metal precursor, as long as it contains the aforementioned metals. Preferably, the metal precursor is selected from at least one of the sulfate, nitrate, and chloride of a metal.

[0038] The present invention does not impose any particular limitation on the type of solvent, and any conventional choice in the art can be made. Preferably, the solvent is selected from at least one of sodium acetate, N,N-dimethylformamide, methanol, ethanol, acetone, and acetonitrile.

[0039] The present invention does not have a particular limitation on the amount of solvent used, and can be carried out with reference to conventional methods in the art, which will not be described in detail here.

[0040] According to the present invention, preferably, the molar ratio of the organic ligand to the metal precursor is 0.2-5:1.

[0041] According to the present invention, preferably, the molar ratio of the modified component to the metal precursor in the solution containing the modified component is 1:10-25, specifically 1:10, 1:10.5, 1:11, 1:11.5, 1:12, 1:12.5, 1:13, 1:13.5, 1:14, 1:14.5, 1:15, 1:15.5, 1:16, 1:16.5, 1:17, 1:17.5, 1:18, 1:18.5, 1:19, 1:19.5, 1:20, 1:21, 1:21.5, 1:22, 1:22.5, 1:23, 1:23.5, 1:24, 1:24.5, 1:25, and a range of any two of these values, preferably 1:12-20. By adopting this preferred embodiment, the modified metal elements can better transfer electrons with the MOF metal nodes without affecting the overall MOF framework structure.

[0042] The present invention does not have any particular limitation on the method of adding the MOF precursor solution and the modified component solution in step (1), as long as they are mixed evenly. According to a preferred embodiment of the present invention, the modified component solution is added to the MOF precursor solution.

[0043] According to a preferred embodiment of the present invention, the solution containing the modified component is added dropwise to the precursor solution of MOFs, and then stirred to ensure thorough mixing. The present invention does not impose particular limitations on the stirring conditions, which can be appropriately selected according to specific circumstances to accelerate uniform mixing.

[0044] According to the present invention, preferably, the conditions for the hydrothermal reaction in step (1) include: a temperature of 150-260℃, specifically 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, and any two of these values ​​forming a range, preferably 160-220℃; and a time of 10-30h, specifically 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h, 30h, and any two of these values ​​forming a range, preferably 12-24h. Using this preferred embodiment, the modified MOF has a higher yield and a more stable structure.

[0045] Preferably, the preparation method of the modified MOFs material further includes: performing solid-liquid separation and washing on the hydrothermal reaction product obtained in step (1) to obtain a solid product. The present invention does not impose any particular limitation on the solid-liquid separation, and conventional techniques in the art can be used.

[0046] The present invention does not have any particular limitation on the washing method, and it can be carried out with reference to conventional methods in the art.

[0047] The present invention does not have any particular limitation on the drying in step (2), and can be carried out with reference to conventional methods in the art.

[0048] The second aspect of the present invention provides a modified MOF material prepared by the preparation method described in the first aspect.

[0049] According to the present invention, preferably, the MOFs material in the modified MOFs material is selected from at least one of MIL-101(Cr), MIL-101(Al), MIL-101(Fe), MOF-808(Zr), ZIF-8(Zn), MOF-74(Mg), MOF-74(Zn) and MOF-74(Cu).

[0050] A third aspect of the present invention provides an application of the modified MOFs material described in the second aspect in CO2 adsorption.

[0051] The modified MOFs material described in this invention is suitable for CO2 adsorption, especially for absorption or capture devices for low partial pressure CO2, such as industrial waste gas treatment, flue gas CO2 removal, and direct carbon capture of air.

[0052] The fourth aspect of the present invention provides a method for CO2 adsorption and capture, the method comprising: sending a CO2-containing feed gas into a reactor to contact and adsorb it with a modified MOFs material; after the adsorption is completed, sending an inert gas into the reactor to contact and desorb it with the CO2-adsorbed modified MOFs material. The modified MOFs material is the modified MOFs material described in the second aspect.

[0053] According to the present invention, preferably, the inlet flow rate of CO2-containing feed gas is 5-50 mL / min, more preferably 10-35 mL / min, relative to 1g of modified MOFs material.

[0054] According to the present invention, preferably, the adsorption temperature is 20-50°C, more preferably 35-45°C.

[0055] According to the present invention, preferably, the desorption temperature is 80-120°C, more preferably 90-110°C.

[0056] The method described in this invention is suitable for processing CO2-containing feed gas with low CO2 content. Preferably, the CO2 volume content in the CO2-containing feed gas is 1-15%.

[0057] The modified MOFs material prepared by the method provided in this invention exhibits high hydrothermal stability, which enhances its cyclic stability in adsorbing CO2 under real flue gas humidity conditions. Therefore, the method of this invention can treat not only conventional anhydrous CO2-containing feed gas, but also CO2-containing feed gas containing water. According to this invention, preferably, the CO2-containing feed gas also contains water vapor, and the volume content of the water vapor is preferably 20-50%.

[0058] This invention does not particularly limit the source of the CO2-containing feed gas, and it can be CO2-containing feed gas obtained by various means, such as industrial waste gas, flue gas, or air generated by ammonia synthesis unit. Preferably, the CO2-containing feed gas comes from flue gas or air.

[0059] The method described in this invention is applicable to different devices for adsorbing CO2, such as fixed bed devices, fluidized bed devices, and moving bed devices.

[0060] The present invention will be described in detail below through embodiments.

[0061] In the following examples, niobium oxide is a commercially available product from Shanghai Maclean Biochemical Technology Co., Ltd., with product number N814705; Tantalum oxide is a commercially available product from Shanghai Aladdin Biochemical Technology Co., Ltd., with the product number T431843.

[0062] Example 1 (1) The preparation process of hydrated niobium oxide is as follows: Niobium oxide and potassium hydroxide in a molar ratio of 1:10 were melt-calcined at 550°C for 8 hours, then dissolved in water and filtered to obtain a liquid material. The pH of the liquid material was adjusted to 5 with acetic acid, and then filtered and dried to obtain hydrated niobium oxide.

[0063] (2) The method for modifying MIL-101(Cr) is as follows: First, prepare 300 mL of 0.05 M sodium acetate solution, then add 9.84 g of terephthalic acid and 24 g of chromium nitrate nonahydrate, stir well to obtain the precursor solution of MOFs. Take 4 g of hydrated niobium oxide obtained in step (1) into a beaker, add 40 g of hydrogen peroxide (concentration 30 wt%) and stir until clear. Add the niobium-containing clear solution dropwise to the MOFs precursor solution, wherein the molar ratio of niobium in the niobium-containing clear solution to chromium in the MOFs precursor solution is 1:15. Stir well, then transfer to a hydrothermal reactor and react at 200℃ for 12 h. After the reaction is completed, filter, wash and dry to obtain modified MIL-101(Cr), labeled as Nb-MIL-101(Cr).

[0064] (3) The CO2 adsorption and desorption process is as follows: Five g of Nb-MIL-101(Cr) was placed in a constant-temperature zone within a quartz glass tube. The quartz tube was surrounded by an electric heating device and insulation material, and the adsorption temperature was controlled at 45°C. One end of the quartz tube was connected to the inlet, and the other end to the outlet. The feed gas was a 15% / 85% (v / v) CO2 / N2 mixture. This feed gas was first humidified to 25% by a humidity generator, then its flow rate was controlled at 120 mL / min by a flow meter and regulating valve, and finally flowed out from the other end of the quartz tube through the adsorbent material. Both ends of the quartz tube were equipped with gas detection devices and flow detection devices to monitor the gas concentration and flow rate in real time. The adsorption process was complete when the CO2 concentration at the outlet no longer changed. After adsorption was complete, N2 was introduced into the other end of the quartz tube for backflushing, while the desorption temperature was controlled at 100°C. The desorption process was complete when the CO2 concentration in the outflowing gas no longer changed. Based on the recorded data, the relationship between CO2 adsorption and time, as well as the relationship between CO2 desorption and time, can be obtained. By repeating the above adsorption and desorption process, the adsorption-desorption cycle curves of the modified MIL-101(Cr) can be obtained, thus revealing the cyclic stability characteristics of the material.

[0065] Example 2 (1) The preparation process of hydrated niobium oxide is as follows: Niobium oxide and potassium hydroxide in a molar ratio of 1:10 were melt-calcined at 500°C for 10 hours, then dissolved in water and filtered to obtain a liquid material. The pH of the liquid material was adjusted to 5.5 with acetic acid, and then filtered and dried to obtain hydrated niobium oxide.

[0066] (2) The method for modifying MIL-101(A1) is as follows: First, prepare 300 mL of 0.05 M sodium acetate solution, then add 9.84 g of terephthalic acid and 12.78 g of aluminum nitrate nonahydrate, stir evenly to obtain the precursor solution of MOFs. Take 4 g of hydrated niobium oxide prepared in step (1) into a beaker, add 42 g of hydrogen peroxide (concentration 30 wt%) and stir until clear. Add the clear niobium-containing solution dropwise to the precursor solution of MOFs, wherein the molar ratio of niobium in the clear niobium-containing solution to aluminum in the precursor solution of MOFs is 1:15. Stir evenly, then transfer the mixed solution to a hydrothermal reactor and react at 200℃ for 12 h. After the reaction is completed, filter, wash and dry to obtain modified MIL-101(Cr), labeled as Nb-MIL-101(Al).

[0067] (3) The CO2 adsorption and desorption process is as follows: Five g of Nb-MIL-101(Al) was placed in a constant-temperature zone within a quartz glass tube. The quartz tube was surrounded by an electric heating device and insulation material, and the adsorption temperature was controlled at 45°C. One end of the quartz tube was connected to the inlet, and the other end to the outlet. The feed gas was a 15% / 85% (v / v) CO2 / N2 mixture. This feed gas was first humidified to 25% by a humidity generator, then its flow rate was controlled at 120 mL / min by a flow meter and regulating valve, and finally flowed out from the other end of the quartz tube through the adsorbent material. Both ends of the quartz tube were equipped with gas detection devices and flow detection devices to monitor the gas concentration and flow rate in real time. The adsorption process was complete when the CO2 concentration at the outlet no longer changed. After adsorption was complete, N2 was introduced into the other end of the quartz tube for backflushing, while the desorption temperature was controlled at 100°C. The desorption process was complete when the CO2 concentration in the outflowing gas no longer changed. Based on the recorded data, the relationship between CO2 adsorption and time, as well as the relationship between CO2 desorption and time, can be obtained. By repeating the above adsorption and desorption process, the adsorption-desorption cycle curves of modified MIL-101(Al) can be obtained, thus revealing the cyclic stability characteristics of the material.

[0068] Example 3 The preparation process of hydrated niobium oxide is as follows: Niobium oxide and sodium hydroxide in a molar ratio of 1:10 are melt-calcined at 600℃ for 8 hours, then dissolved in water and filtered to obtain a liquid material. The pH of the liquid material is adjusted to 5 with acetic acid, and then filtered and dried to obtain hydrated niobium oxide.

[0069] (2) The method for modifying MIL-101(Fe) is as follows: First, prepare 300 mL of 0.05 M sodium acetate solution, then add 9.84 g of terephthalic acid and 14.5 g of ferric nitrate nonahydrate, and stir until homogeneous to obtain the precursor solution of MOFs. Take 4 g of hydrated niobium oxide prepared in step (1) into a beaker, add 43 g of hydrogen peroxide (concentration 30 wt%) and stir until clear. Slowly add the niobium-containing clear solution to the MOFs precursor solution, wherein the molar ratio of niobium in the niobium-containing clear solution to iron in the MOFs precursor solution is 1:15. Stir until homogeneous, then transfer to a hydrothermal reactor and react at 200℃ for 12 h. After the reaction is complete, filter, wash and dry to obtain modified MIL-101(Fe), labeled as Nb-MIL-101(Fe).

[0070] (3) The CO2 adsorption and desorption process is as follows: Five g of Nb-MIL-101(Fe) was placed in a constant-temperature zone within a quartz glass tube. The quartz tube was surrounded by an electric heating device and insulation material, and the adsorption temperature was controlled at 45°C. One end of the quartz tube was connected to the inlet, and the other end to the outlet. The feed gas was a 15% / 85% (v / v) CO2 / N2 mixture. This feed gas was first humidified to 25% by a humidity generator, then its flow rate was controlled at 120 mL / min by a flow meter and regulating valve, and finally flowed out from the other end of the quartz tube through the adsorbent material. Both ends of the quartz tube were equipped with gas detection devices and flow detection devices to monitor the gas concentration and flow rate in real time. The adsorption process was complete when the CO2 concentration at the outlet no longer changed. After adsorption was complete, N2 was introduced into the other end of the quartz tube for backflushing, while the desorption temperature was controlled at 100°C. The desorption process was complete when the CO2 concentration in the outflowing gas no longer changed. Based on the recorded data, the relationship between CO2 adsorption and time, as well as the relationship between CO2 desorption and time, can be obtained. By repeating the above adsorption and desorption process, the adsorption-desorption cycle curves of modified MIL-101(Fe) can be obtained, thus revealing the cyclic stability characteristics of the material.

[0071] Example 4 (1) The preparation process of hydrated tantalum oxide is as follows: Tantalum oxide and potassium hydroxide in a molar ratio of 1:8.5 were melt-calcined at 500°C for 8 hours, then dissolved in water and filtered to obtain a liquid material. The pH of the liquid material was adjusted to 4.5 with acetic acid, and then filtered and dried to obtain hydrated tantalum oxide.

[0072] (2) The method for modifying MOF-808 is as follows: First, 13.98 g of ZrCl4 and 4.2 g of trimesic acid were mixed and stirred in 300 mL of DMF solution to obtain a precursor solution of MOFs. 4 g of hydrated tantalum oxide prepared in step (1) was placed in a beaker, and 40 g of hydrogen peroxide (30 wt%) was added and stirred until clear. The clear solution containing tantalum was added dropwise to the precursor solution of MOFs. The molar ratio of tantalum in the clear solution containing tantalum to Zr in the precursor solution of MOFs was 1:13. The mixture was stirred evenly and then transferred to a hydrothermal reactor. The reaction was carried out at 180 °C for 12 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified MOF-808, labeled as Ta-MOF-808.

[0073] (3) The CO2 adsorption and desorption process is as follows: 5 g of Ta-MOF-808 was placed in the isothermal zone of a quartz glass tube. The quartz tube was surrounded by an electric heating device and insulation material, and the adsorption temperature was controlled at 45℃. One end of the quartz tube was connected to the gas inlet, and the other end was connected to the exhaust port. The feed gas was a 15% / 85% (v / v) CO2 / N2 mixture. This feed gas was first passed through a humidity generator to adjust the humidity to 25%, and then the flow rate was controlled at 120 mL / min by a flow meter and regulating valve. Finally, it flowed out from the other end of the quartz tube through the adsorbent material. Both ends of the quartz tube were equipped with gas detection devices and flow detection devices to monitor the gas concentration and flow rate in real time. The adsorption process was complete when the CO2 concentration at the outlet no longer changed. After adsorption was completed, N2 was introduced into the other end of the quartz tube for backflushing, while the desorption temperature was controlled at 100℃. The desorption process was complete when the CO2 concentration in the outflowing gas no longer changed. Based on the recorded data, the relationship between CO2 adsorption and time, as well as the relationship between CO2 desorption and time, can be obtained. By repeating the above adsorption and desorption process, the adsorption-desorption cycle curves of the modified MOF-808 can be obtained, thus revealing the cyclic stability characteristics of the material.

[0074] Example 5 (1) The preparation process of hydrated tantalum oxide is as follows: Tantalum oxide and sodium hydroxide in a molar ratio of 1:11 were melt-calcined at 500°C for 8 h, then dissolved in water and filtered to obtain a liquid material. The pH of the liquid material was adjusted to 5 with acetic acid, and then filtered and dried to obtain hydrated tantalum oxide.

[0075] (2) The method for modifying ZIF-8 is as follows: Take 20 g of zinc nitrate hexahydrate and 5 g of 2-methylimidazole in 300 mL of DMF solution, mix and stir to obtain the precursor solution of MOFs. Take 4 g of hydrated tantalum oxide prepared in step (1) in a beaker, add 41 g of hydrogen peroxide (concentration 30wt%) and stir until clear. Add the clear solution containing tantalum dropwise to the precursor solution of MOFs, wherein the molar ratio of tantalum element in the clear solution containing tantalum to zinc element in the precursor solution of MOFs is 1:18. Stir evenly, then transfer the mixed solution to a hydrothermal reactor and react at 160℃ for 12 h. After the reaction is completed, filter, wash and dry to obtain modified ZIF-8, labeled as Ta-ZIF-8.

[0076] (3) The CO2 adsorption and desorption process is as follows: Five g of Ta-ZIF-8 was placed in a constant-temperature zone within a quartz glass tube. The quartz tube was surrounded by an electric heating device and insulation material, and the adsorption temperature was controlled at 45°C. One end of the quartz tube was connected to the inlet, and the other end to the outlet. The feed gas was a 15% / 85% (v / v) CO2 / N2 mixture. This feed gas was first humidified to 25% by a humidity generator, then its flow rate was controlled at 120 mL / min by a flow meter and regulating valve, and finally flowed out from the other end of the quartz tube through the adsorbent material. Both ends of the quartz tube were equipped with gas detection devices and flow detection devices to monitor the gas concentration and flow rate in real time. The adsorption process was complete when the CO2 concentration at the outlet no longer changed. After adsorption, N2 was introduced into the other end of the quartz tube for backflushing, while the desorption temperature was controlled at 100°C. The desorption process was complete when the CO2 concentration in the outflowing gas no longer changed. The relationship between CO2 adsorption and desorption over time can be obtained from the recorded data. By repeating the above adsorption and desorption process, the adsorption-desorption cycle curve of the modified ZIF-8 can be obtained, and the cycle stability characteristics of the material can be obtained.

[0077] Example 6 The procedure was carried out according to Example 1, except that the preparation process of hydrated niobium oxide was omitted. Specifically, it included: The method for modifying MIL-101(Cr) is as follows: First, prepare 300 mL of 0.05 M sodium acetate solution, then add 9.84 g of terephthalic acid and 24 g of chromium nitrate nonahydrate, and stir until homogeneous to obtain the precursor solution of MOFs. Take 4 g of niobium oxide in a beaker, add 40 g of hydrogen peroxide (30 wt%), and stir until clear. Add the clear niobium-containing solution dropwise to the MOF precursor solution, stir until homogeneous, and then transfer to a hydrothermal reactor. React at 200 °C for 12 h. After the reaction, filter, wash, and dry to obtain modified MIL-101(Cr), labeled as Nb-MIL-101(Cr)-s.

[0078] Comparative Example 1 (1) The method for MIL-101(Cr) is as follows: Prepare 300 mL of 0.05 M sodium acetate solution, then add 9.84 g of terephthalic acid and 24 g of chromium nitrate nonahydrate, and stir until homogeneous to obtain a precursor solution of MOFs. Transfer the obtained MOF precursor solution to a hydrothermal reactor and react at 200 °C for 12 h. After the reaction is complete, filter, wash, and dry to obtain MIL-101(Cr).

[0079] CO2 The adsorption-desorption process was carried out according to the method of Example 1. Comparative Example 2 (1) The specific preparation process of MIL-101(Al) is as follows: Prepare 300 mL of 0.05 M sodium acetate solution, then add 9.84 g of terephthalic acid and 12.78 g of hydrated aluminum nitrate, and stir until homogeneous to obtain a precursor solution of MOFs. Transfer the MOF precursor solution to a hydrothermal reactor and react at 200 °C for 12 h. After the reaction is complete, filter, wash, and dry to obtain MIL-101(Al).

[0080] (2) The CO2 adsorption and desorption process was carried out according to the method in Example 2.

[0081] Comparative Example 3 (1) The specific preparation process of MIL-101(Fe) is as follows: First, prepare 300 mL of 0.05 M sodium acetate solution, then add 9.84 g of terephthalic acid and 14.5 g of ferric nitrate nonahydrate, and stir until homogeneous to obtain a precursor solution of MOFs. Transfer the obtained MOF precursor solution to a hydrothermal reactor and react at 200 °C for 12 h. After the reaction is complete, filter, wash, and dry to obtain MIL-101(Fe).

[0082] (2) The CO2 adsorption and desorption process was carried out according to the method in Example 3.

[0083] Comparative Example 4 (1) The specific preparation process of MOF-808 is as follows: First, 13.98 g of ZrCl4 and 4.2 g of trimesic acid were added to 300 mL of DMF solution and mixed thoroughly to obtain a precursor solution of MOFs. The obtained MOF precursor solution was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain MOF-808.

[0084] (2) The CO2 adsorption and desorption process was carried out according to the method in Example 4.

[0085] Comparative Example 5 (1) The specific preparation process of ZIF-8 is as follows: 20 g of zinc nitrate hexahydrate and 5 g of 2-methylimidazole were mixed and stirred in 300 mL of DMF solution to obtain a precursor solution of MOFs. The obtained precursor solution of MOFs was transferred to a hydrothermal reactor and reacted at 160 °C for 12 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain ZIF-8.

[0086] (2) The CO2 adsorption and desorption process was carried out according to the method in Example 5.

[0087] Comparative Example 6 The procedure is carried out according to the method of Example 1, except that... (1) The method for modifying MIL-101(Cr) is as follows: First, prepare 300 mL of sodium acetate solution with a concentration of 0.05 M, then add 9.84 g of terephthalic acid and 24 g of chromium nitrate nonahydrate, stir evenly, and obtain the precursor solution of MOFs. Take the hydrated niobium oxide obtained in step (1) and add it to the precursor solution of MOFs, wherein the molar ratio of niobium element in hydrated niobium oxide to chromium element in the precursor solution of MOFs is 1:15. Stir evenly, then transfer it to a hydrothermal reactor and react at 200℃ for 12 h. After the reaction is completed, filter, wash and dry to obtain modified MIL-101(Cr), labeled as s-Nb-MIL-101(Cr).

[0088] (2) The CO2 adsorption and desorption process was carried out according to the method in Example 1.

[0089] In the above embodiments and comparative examples, Figure 1 The cycling performance diagrams are of Nb-MIL-101(Cr) in Example 1 of the present invention and MIL-101(Cr) in Comparative Example 1. Figure 2 The cycling performance diagrams are of Nb-MIL-101(Al) in Example 2 and MIL-101(Al) in Comparative Example 2. Figure 3The cycling performance diagrams are of Nb-MOF-808 in Example 3 and MOF-808 in Comparative Example 3 of the present invention. Figure 4 The cycling performance diagrams are of Ta-MOF-808 in Example 4 and MOF-808 in Comparative Example 4 of the present invention. Figure 5 The cycling performance diagrams are of Ta-ZIF-8 in Example 5 and ZIF-8 in Comparative Example 5 of the present invention. Figure 6 The cycling performance diagrams are for Nb-MIL-101(Cr) in Example 1 and Nb-MIL-101(Cr)-s in Example 6 of this invention. Figure 7 The diagram shows the cycle performance of Nb-MIL-101(Cr) in Example 1 of the present invention and s-Nb-MIL-101(Cr) in Comparative Example 6.

[0090] pass Figure 1-7 As can be seen from the comparison of cycling performance, the cycling performance of MOF materials such as MIL-101(Cr), MIL-101(Al), MOF-808, and ZIF-8 is greatly improved after modification using the method of this embodiment. After five cycles, the adsorption capacity of the material remains almost unchanged, which fully demonstrates that the modified MOF material prepared by this embodiment has high hydrothermal stability. Moreover, the initial adsorption capacity of the material also increases, mainly due to the charge transfer between Nb / Ta and the central metal atoms of the metal nodes in the MOF structure, which promotes the adsorption of CO2 by the metal sites.

[0091] 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 method for preparing a modified MOF material, characterized in that, The method includes the following steps: (1) The precursor solution of MOFs is subjected to hydrothermal reaction with a solution containing modified components to obtain a solid product. The precursor solution of MOFs includes a solvent, an organic ligand and a metal precursor. (2) Dry the solid product obtained in step (1); The modified component is selected from at least one of the group VB metal elements.

2. The method according to claim 1, wherein, The modified component is niobium and / or tantalum; Preferably, the method for preparing the solution containing the modified component includes: dissolving the hydrated oxide of the modified component in an aqueous hydrogen peroxide solution; Preferably, the mass ratio of the hydrated oxide of the modified component to the aqueous hydrogen peroxide solution is 1:5-15; Preferably, the concentration of the hydrogen peroxide aqueous solution is 10-40 wt%.

3. The method according to claim 2, wherein, The method for preparing the hydrated oxide of the modified component includes: S1. Melt-calcining the oxide and alkali of the modified component; S2. Dissolve the molten roasted product of S1 in water to obtain a slurry; perform solid-liquid separation on the slurry to obtain a liquid material; S3. Adjust the pH of the liquid material to 4-6, and then dry it.

4. The method according to claim 3, wherein, The conditions for melt roasting described in S1 include: a temperature of 300-800℃, preferably 500-600℃; and a time of 5-12h, preferably 5-10h. Preferably, the molar ratio of the oxide to the alkali of the modified component is 1:8-12; Preferably, the alkali is sodium hydroxide and / or potassium hydroxide; Preferably, pH is adjusted using an acid in S3, wherein the acid is preferably selected from organic acids, more preferably from at least one of acetic acid, propionic acid and malic acid.

5. The method according to any one of claims 1-4, wherein, The molar ratio of the organic ligand to the metal precursor is 0.2-5:1; Preferably, the organic ligand is selected from at least one of terephthalic acid, trimesic acid, 2-methylimidazole and 2,5-dihydroxyterephthalic acid; Preferably, the metal in the metal precursor is selected from at least one of chromium, aluminum, iron, zirconium, zinc, copper and magnesium; Preferably, the solvent is selected from at least one of sodium acetate, N,N-dimethylformamide, methanol, ethanol, acetone and acetonitrile.

6. The method according to any one of claims 1-5, wherein, The molar ratio of the modified component to the metal precursor in the solution containing the modified component is 1:10-25, preferably 1:12-20, based on elemental composition. Preferably, the conditions for the hydrothermal reaction in step (1) include: a temperature of 150-260℃, preferably 160-220℃; and a time of 10-30 h, preferably 12-24 h.

7. A modified MOF material prepared by the preparation method according to any one of claims 1-6; Preferably, the MOFs material in the modified MOFs material is selected from at least one of MIL-101(Cr), MIL-101(Al), MIL-101(Fe), MOF-808(Zr), ZIF-8(Zn), MOF-74(Mg), MOF-74(Cu), and MOF-74(Zn).

8. The application of the modified MOFs material according to claim 7 in CO2 adsorption.

9. A method for CO2 adsorption and capture, the method comprising: CO2-containing feed gas is fed into the reactor to contact and adsorb with the modified MOFs material. After adsorption, inert gas is fed into the reactor to contact and desorb with the CO2-adsorbed modified MOFs material. The modified MOFs material is the modified MOFs material according to claim 7.

10. The method according to claim 9, wherein, The inlet flow rate of CO2-containing feed gas is 5-50 mL / min, preferably 10-35 mL / min, relative to 1g of modified MOF material; Preferably, the adsorption temperature is 20-50℃, more preferably 35-45℃; Preferably, the desorption temperature is 80-120℃, more preferably 90-110℃; Preferably, the volume content of CO2 in the CO2-containing feed gas is 1-15%; Preferably, the CO2-containing feed gas also contains water vapor, and the volume content of the water vapor is preferably 20-50%. Preferably, the CO2-containing raw material gas comes from flue gas or air.

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