A metal organic framework co2 adsorbent material and a method of making the same

Abstract

The application relates to the technical field of metal organic framework porous adsorbing materials, in particular to a metal organic framework CO2 adsorbing material and a preparation method thereof. 2+ The mass fraction of Ca 2+ is 8-16% based on the total mass of the material; acidized multi-walled carbon nanotubes are uniformly loaded on the surface of the material, and the mass fraction of the acidized multi-walled carbon nanotubes is 0.5-1.5% based on the total mass of the material; the material has a multi-stage pore structure, the proportion of micropore structure with a size of 0.8-1.2 nm in the pore structure is 62-68%, and the material has excellent CO2 adsorbing performance and long-period cycle performance.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework porous adsorption materials, specifically to a metal-organic framework CO2 adsorption material and its preparation method. Background Technology

[0002] Carbon dioxide is the core gas contributing to the greenhouse effect. With industrialization and the massive consumption of fossil fuels, atmospheric carbon dioxide emissions have continued to rise, causing the global average surface temperature to increase by about 1°C compared to pre-industrial levels. To limit the temperature rise to within 1.5°C, carbon capture, utilization, and storage (CCUS) is the core technological pathway to achieve this goal, with carbon capture being the most critical link in the CCUS chain. Existing carbon capture methods include absorption, membrane separation, cryogenic separation, and adsorption. The first three technologies generally suffer from drawbacks such as high energy consumption, high operating costs, and the potential for secondary pollution. Adsorption, with its advantages of low energy consumption, environmental friendliness, and excellent gas separation selectivity, has become a decarbonization technology with great industrial potential.

[0003] Traditional solid adsorbents mainly include porous materials such as activated carbon and zeolite molecular sieves. Activated carbon mainly relies on physical adsorption, resulting in low carbon dioxide adsorption capacity and separation selectivity, and its surface has few active sites. Zeolite molecular sieves have regular pores, but their adsorption performance decreases sharply at high temperatures, with carbon dioxide adsorption approaching zero at 200°C. At the same time, zeolite is highly hydrophilic, and water vapor in the flue gas competes with carbon dioxide for adsorption, significantly reducing the effective adsorption capacity. Both are difficult to apply on a large scale in flue gas decarbonization scenarios.

[0004] Metal-organic frameworks (MOFs) possess advantages such as tunable pore size, high specific surface area, abundant metal active sites, and low regeneration energy consumption, making them popular materials for next-generation carbon capture technologies. Cu-BTC, a type of MOF, is the most widely used solid adsorbent material due to its well-developed pores and abundant Lewis acidic unsaturated metal sites on its surface, exhibiting a strong affinity for carbon dioxide. However, pure Cu-BTC has significant drawbacks: its strong hydrophilicity makes the crystal framework prone to hydrolysis and collapse in humid environments; its poor thermal stability leads to framework decomposition at high temperatures; and repeated adsorption-desorption cycles result in pore structure damage and continuous loss of active sites, leading to poor recyclability.

[0005] Existing modification methods for optimizing Cu-BTC performance mainly fall into two categories: metal ion doping and carbon-based material composites. Metal ion doping can introduce novel metal active sites and optimize the material's pore structure; carbon nanotube composites can improve mass transfer efficiency and enhance cycle durability. Most current publicly available research only employs metal ion doping or carbon nanotube composites alone to modify Cu-BTC.

[0006] Using Ca 2+There are few technical solutions that combine in-situ doping with acidified carbon nanotubes to synergistically improve carbon dioxide adsorption capacity and cycle stability. Single modification methods cannot simultaneously meet the requirements of high adsorption capacity and long-term cycle use.

[0007] In summary, there is an urgent need for a metal-organic framework CO2 adsorbent material that combines high adsorption capacity with long cycle performance. Summary of the Invention

[0008] The present invention aims to solve the technical problem of how to provide a metal-organic framework CO2 adsorbent material that has both high adsorption capacity and long cycle performance.

[0009] To achieve the above objectives, a first aspect of the present invention provides a metal-organic framework CO2 adsorbent material, wherein the material is a Cu-BTC modified material, and the Cu-BTC crystal is doped with Ca. 2+ Based on the total mass of the material, Ca 2+ The mass fraction is 8-16%;

[0010] The material surface is uniformly loaded with acidified multi-walled carbon nanotubes, and the mass fraction of acidified multi-walled carbon nanotubes is 0.5% to 1.5% based on the total mass of the material.

[0011] The material has a hierarchical porous structure, with micropores of 0.8~1.2 nm accounting for 62~68% of the total porous structure.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned metal-organic framework CO2 adsorbent material, comprising the following steps:

[0013] S1. Immerse multi-walled carbon nanotubes in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid, stir for the first time, wash with deionized water, and dry for the first time to obtain acidified multi-walled carbon nanotubes.

[0014] S2. Copper nitrate trihydrate, calcium acetate monohydrate and deionized water are mixed to obtain a metal ion solution. 1,3,5-benzenetricarboxylic acid and anhydrous ethanol are mixed to obtain an organic ligand solution. The metal ion solution and the organic ligand solution are mixed, sonicated and stirred for a second time to obtain a precursor mixture.

[0015] S3. The acidified multi-walled carbon nanotubes obtained in step S1 are mixed with the precursor mixture obtained in step S2, and subjected to hydrothermal reaction, cooling, washing, and second drying to obtain the metal-organic framework CO2 adsorbent material.

[0016] The beneficial effects of this invention are as follows:

[0017] (1) In the CO2 adsorption material provided by the present invention, Ca 2+Doping modulates MOF crystals, adding Lewis acidic adsorption sites, while acidified carbon nanotubes introduce carboxyl polar sites and simultaneously build interconnected mass transfer channels. The two work synergistically, resulting in a 31.5% increase in carbon dioxide adsorption capacity compared to the original Cu-BTC sample.

[0018] (2) The Ca provided by the present invention 2+ By strengthening the crystal framework structure through dual modification with acidified carbon nanotubes, the thermal decomposition temperature of the material is increased, and the channels are less prone to irreversible collapse during multiple cycles, which greatly improves the drawback of poor cycling stability of traditional Cu-BTC.

[0019] (3) The preparation method provided by the present invention adopts a one-step in-situ solvothermal path, and conventional chemical raw materials can be used to complete the preparation. The reaction conditions are mild and the scale-up production is relatively easy. The temperature required for the regeneration stage is relatively low, and the overall operating energy consumption is small, which is suitable for flue gas decarbonization scenarios in power plants, metallurgy, and cement industries. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation process of the metal-organic framework CO2 adsorbent material of the present invention;

[0021] Figure 2 This is a schematic diagram of the apparatus used for evaluating the performance of the adsorption material of the present invention;

[0022] Figure 3 X-ray diffraction patterns of the adsorbent materials prepared in Comparative Examples 1, 2, and 1, and the adsorbent material of Example 1 after cycling test.

[0023] Figure 4 The images are scanning electron microscope (SEM) images of Comparative Example 1, Comparative Example 2, Example 1, and Example 1 after cyclic testing. In the images, a and b are Comparative Example 1, c and d are Comparative Example 2, e and f are Example 1, and g and h are SEM images of Example 1 after cyclic testing.

[0024] Figure 5 The bar chart shows the carbon dioxide saturated adsorption capacity of the adsorbent material in Example 1.

[0025] Figure 6 This is a bar chart showing the capacity change of the adsorbent material in Example 1 after 7 adsorption-desorption cycles;

[0026] Figure 7 This is a schematic diagram of the carbon dioxide synergistic adsorption mechanism of the metal-organic framework CO2 adsorption material of the present invention. Detailed Implementation

[0027] 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.

[0028] The purpose of this invention is to provide a calcium ion-doped and acidified carbon nanotube composite modified Cu-BTC adsorbent material and its preparation method, in order to solve the problems of low adsorption capacity of pure Cu-BTC, insufficient thermal stability, easy collapse of the framework during cycling, and limited optimization range of single modification in the existing technology.

[0029] The first aspect of this invention provides a metal-organic framework CO2 adsorbent material, wherein the material is a Cu-BTC modified material, and the Cu-BTC crystal is doped with Ca. 2+ Based on the total mass of the material, Ca 2+ The mass fraction is 8-16%;

[0030] The material surface is uniformly loaded with acidified multi-walled carbon nanotubes, and the mass fraction of acidified multi-walled carbon nanotubes is 0.5% to 1.5% based on the total mass of the material.

[0031] The material has a hierarchical porous structure, with micropores of 0.8~1.2 nm accounting for 62~68% of the total porous structure.

[0032] In this invention, the metal-organic framework CO2 adsorbent is a calcium ion-doped acidified carbon nanotube composite modified Cu-BTC carbon dioxide adsorbent, specifically a Cu-BTC metal-organic framework material with in-situ Ca doping. 2+ Acidified multi-walled carbon nanotubes are loaded onto the outside of the crystal.

[0033] In this invention, after the metal-organic framework CO2 adsorbent material is saturated with adsorption, it is dried in a vacuum environment at 100°C for 5 hours to complete desorption and regeneration, and can be recycled.

[0034] In this invention, the acidified multi-walled carbon nanotubes are rich in carboxyl oxygen-containing functional groups on their surface after acidification treatment.

[0035] According to the present invention, the BET specific surface area of ​​the material is 1200~1340 m². 2 / g, pore volume 0.5~0.6 cm³ 3 / g.

[0036] According to the present invention, under the conditions of 25°C and an inlet flow rate of 20 mL / min, the CO2 adsorption capacity is 2.96~3.17 mmol / g.

[0037] In this invention, the CO2 adsorption capacity of the material is increased by up to 31.5% compared to that of pure Cu-BTC.

[0038] According to the present invention, after seven adsorption-desorption cycles, the material retains 70-75% of its initial CO2 adsorption capacity.

[0039] According to the present invention, the thermal decomposition temperature of the material is 300~370℃.

[0040] In this invention, the thermal decomposition temperature of the material is higher than that of pure Cu-BTC, thus improving its thermal stability.

[0041] A second aspect of the present invention provides a method for preparing the above-mentioned metal-organic framework CO2 adsorbent material, comprising the following steps:

[0042] S1. Immerse multi-walled carbon nanotubes in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid, stir for the first time, wash with deionized water, and dry for the first time to obtain acidified multi-walled carbon nanotubes.

[0043] S2. Copper nitrate trihydrate, calcium acetate monohydrate and deionized water are mixed to obtain a metal ion solution. 1,3,5-benzenetricarboxylic acid and anhydrous ethanol are mixed to obtain an organic ligand solution. The metal ion solution and the organic ligand solution are mixed, sonicated and stirred for a second time to obtain a precursor mixture.

[0044] S3. The acidified multi-walled carbon nanotubes obtained in step S1 are mixed with the precursor mixture obtained in step S2, and subjected to hydrothermal reaction, cooling, washing, and second drying to obtain the metal-organic framework CO2 adsorbent material.

[0045] According to the present invention, in step S1, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:2~4.

[0046] According to the present invention, the mass ratio of the multi-walled carbon nanotubes to the volume ratio of the mixed acid solution is 1:30~50.

[0047] In this invention, the concentrated sulfuric acid has a mass fraction of 98%, and the concentrated nitric acid has a mass fraction of 68%.

[0048] In this invention, the purity of the multi-walled carbon nanotubes is ≥95%.

[0049] According to the present invention, the conditions for the first stirring include stirring at 40~60°C for 20~24 hours.

[0050] According to the present invention, the deionized water is washed until neutral.

[0051] According to the present invention, the conditions for the first drying include: vacuum drying at 50~70°C for 20~24 hours.

[0052] According to the present invention, in step S2, the mass ratio of copper nitrate trihydrate, calcium acetate monohydrate and deionized water is 1:0.08~0.16:22~26.

[0053] According to the present invention, the mass ratio of 1,3,5-benzenetricarboxylic acid to the volume ratio of anhydrous ethanol is 1:46~50.

[0054] According to the present invention, the volume ratio of the metal ion solution to the organic ligand solution is 1:0.9~1.1.

[0055] According to the present invention, the conditions for ultrasound include: ultrasound time of 25 to 35 minutes.

[0056] According to the present invention, the conditions for the second stirring include: a stirring time of 0.8 to 1.2 hours.

[0057] According to the present invention, in step S3, the mass ratio of the acidified multi-walled carbon nanotubes to the volume ratio of the precursor mixture is 1:6000~12000.

[0058] According to the present invention, in step S3, the conditions for the hydrothermal reaction include: reacting at 110~130℃ for 14~18h.

[0059] According to the present invention, in step S3, the cooling conditions include: natural cooling to 20~30°C.

[0060] In this invention, the washing in step S3 can be performed by washing the solid product after the hydrothermal reaction three times using a mixed solvent of anhydrous ethanol and deionized water.

[0061] According to the present invention, the conditions for the second drying include: vacuum drying at 90~110°C for 22~26 hours.

[0062] According to the present invention, the material is activated before adsorbing CO2, and the activation conditions include: vacuum heating at 90~110℃ for 4~6 hours.

[0063] Test methods

[0064] Performance evaluation of adsorption materials

[0065] The actual adsorbent material was placed in a fixed bed device to carry out dynamic CO2 adsorption tests. The standard adsorption conditions were an adsorption temperature of 25℃ and a simulated flue gas inlet flow rate of 20 mL / min. After saturation, the material was vacuum dried at 100℃ for 5 hours to complete desorption and regeneration. The capacity retention rate was recorded after 7 cycles.

[0066] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. All other embodiments implemented by those skilled in the art based on the embodiments of the present invention without creative improvements are within the protection scope of the present invention.

[0067] The reagents used in the examples and comparative examples are conventional reagents in the art and are all commercially available.

[0068] Example 1

[0069] Take 0.015g of 95% pure multi-walled carbon nanotubes and prepare a mixed acid solution with 98% concentrated sulfuric acid and 68% concentrated nitric acid in a volume ratio of 3:1. The mass ratio of multi-walled carbon nanotubes to the volume ratio of the mixed acid solution is 1:40. Acidify by stirring at 50℃ for 24h. Wash with deionized water until the filtrate is neutral. Dry under vacuum at 60℃ for 24h to obtain acidified multi-walled carbon nanotubes.

[0070] Weigh 2.5g of copper nitrate trihydrate and dissolve it in 60mL of deionized water. Add 0.35g of calcium acetate monohydrate and stir to dissolve. Then dissolve 1.25g of 1,3,5-benzenetricarboxylic acid in 60mL of anhydrous ethanol. Mix the two solutions in a 1:1 volume ratio and sonicate for 30min and stir magnetically for 1h to prepare a homogeneous precursor mixture.

[0071] Acidified multi-walled carbon nanotubes were added to the precursor mixture and fully dispersed. The volume ratio of the precursor mixture to the mass ratio of the acidified multi-walled carbon nanotubes was 8000:1. The mixture was then transferred to a lined reactor and reacted solvothermically at 120°C for 16 hours, followed by natural cooling. The product was washed three times with an ethanol-water mixed solvent and dried under vacuum at 100°C for 24 hours to obtain the metal-organic framework CO2 adsorbent material A1, denoted as Ca-Cu-BTC@1CNT.

[0072] Cu-BTC crystal is doped with Ca 2+ The mass fraction of the material is 14%, the mass fraction of acidified multi-walled carbon nanotubes uniformly loaded on the surface is 1%, the microporous structure of 0.8~1.2 nm accounts for 65% of the pore structure, and the BET specific surface area is 1338.3 m². 2 / g, pore volume 0.56 cm³ 3 / g, thermal decomposition temperature is 370℃.

[0073] Before the adsorption test, the metal-organic framework CO2 adsorbent material A1 was activated in vacuum at 100℃ for 5 hours.

[0074] At 25℃ and 20mL / min atmospheric pressure, the CO2 adsorption capacity was 3.17 mmol / g, and after 7 adsorption-desorption cycles, the capacity retained 72% of the initial value.

[0075] Example 2

[0076] Take 0.015g of 95% pure multi-walled carbon nanotubes and prepare a mixed acid solution with 98% concentrated sulfuric acid and 68% concentrated nitric acid in a volume ratio of 2:1. The mass ratio of multi-walled carbon nanotubes to the volume ratio of the mixed acid solution is 1:30. Acidify by stirring at 40℃ for 20h. Wash with deionized water until the filtrate is neutral. Dry under vacuum at 50℃ for 20h to obtain acidified multi-walled carbon nanotubes.

[0077] Weigh 2.5g of copper nitrate trihydrate and dissolve it in 60mL of deionized water. Add 0.2g of calcium acetate monohydrate and stir to dissolve. Then dissolve 1.25g of 1,3,5-benzenetricarboxylic acid in 60mL of anhydrous ethanol. Mix the two solutions in a 1:1 volume ratio and sonicate for 30min and magnetically stir for 1h to prepare a homogeneous precursor mixture.

[0078] Acidified multi-walled carbon nanotubes were added to the precursor mixture and fully dispersed. The volume ratio of the precursor mixture to the mass ratio of the acidified multi-walled carbon nanotubes was 12000:1. The mixture was then transferred to a lined reactor and subjected to a lyothermal reaction at 120°C for 16 hours, followed by natural cooling. The product was washed three times with an ethanol-water mixed solvent and then vacuum dried at 100°C for 24 hours to obtain metal-organic framework CO2 adsorbent material A2.

[0079] Cu-BTC crystal is doped with Ca 2+ The mass fraction of the material is 8%, the mass fraction of acidified multi-walled carbon nanotubes uniformly loaded on the surface is 0.5%, the microporous structure of 0.8~1.2 nm accounts for 62% of the pore structure, and the BET specific surface area is 1304.1 m². 2 / g, pore volume 0.57 cm³ 3 / g, thermal decomposition temperature is 310℃.

[0080] Before the adsorption test, the metal-organic framework CO2 adsorbent material A2 was activated in vacuum at 100℃ for 5 hours.

[0081] At 25℃ and 20mL / min atmospheric pressure, the CO2 adsorption capacity was 2.96 mmol / g, and after 7 adsorption-desorption cycles, the capacity retained 70% of the initial value.

[0082] Example 3

[0083] Take 0.015 g of 95% pure multi-walled carbon nanotubes and prepare a mixed acid solution with 98% concentrated sulfuric acid and 68% concentrated nitric acid in a volume ratio of 4:1. The mass ratio of multi-walled carbon nanotubes to the volume ratio of the mixed acid solution is 1:50. Acidify by stirring at 60℃ for 24 h, wash with deionized water until the filtrate is neutral, and vacuum dry at 70℃ for 24 h to obtain acidified multi-walled carbon nanotubes.

[0084] Weigh 2.5g of copper nitrate trihydrate and dissolve it in 60mL of deionized water. Add 0.4g of calcium acetate monohydrate and stir to dissolve. Then dissolve 1.25g of 1,3,5-benzenetricarboxylic acid in 60mL of anhydrous ethanol. Mix the two solutions in a 1:1 volume ratio and sonicate for 30min and stir magnetically for 1h to prepare a homogeneous precursor mixture.

[0085] Acidified multi-walled carbon nanotubes were added to the precursor mixture and fully dispersed. The volume ratio of the precursor mixture to the mass ratio of the acidified multi-walled carbon nanotubes was 6000:1. The mixture was then transferred to a lined reactor and reacted solvothermically at 120°C for 16 hours, followed by natural cooling. The product was washed three times with an ethanol-water mixed solvent and vacuum dried at 100°C for 24 hours to obtain metal-organic framework CO2 adsorbent material A3.

[0086] Cu-BTC crystal is doped with Ca 2+ The mass fraction of the material is 16%, the mass fraction of acidified multi-walled carbon nanotubes uniformly loaded on the surface is 1.5%, the microporous structure of 0.8~1.2 nm accounts for 60% of the pore structure, and the BET specific surface area is 1240 m². 2 / g, pore volume 0.56cm 3 / g, thermal decomposition temperature is 330℃.

[0087] Before the adsorption test, the metal-organic framework CO2 adsorbent material A3 was activated in vacuum at 100℃ for 5 hours.

[0088] At 25℃ and 20mL / min atmospheric pressure, the CO2 adsorption capacity was 3.08 mmol / g, and after 7 adsorption-desorption cycles, the capacity retained 68% of the initial value.

[0089] Comparative Example 1

[0090] Weigh 2.5g of copper nitrate trihydrate and dissolve it in 60mL of deionized water. Then dissolve 1.25g of 1,3,5-benzenetricarboxylic acid in 60mL of anhydrous ethanol. Mix the two solutions in a 1:1 volume ratio and sonicate for 30min and magnetically stir for 1h to prepare a homogeneous precursor mixture.

[0091] The precursor mixture was transferred to a lined reactor and reacted solvothermically at 120°C for 16 hours, followed by natural cooling. The product was washed three times with an ethanol-water mixed solvent and dried under vacuum at 100°C for 24 hours to obtain pure Cu-BTC adsorbent D1, denoted as Cu-BTC.

[0092] The specific surface area of ​​D1 is 990.6 m². 2 / g, under the same working conditions, the CO2 adsorption capacity is 2.41mmol / g. After multiple cycles, the crystal channels collapse over a large area, the adsorption capacity decreases by more than 40%, and the thermal decomposition temperature is 310℃.

[0093] Comparative Example 2

[0094] Weigh 2.5g of copper nitrate trihydrate and dissolve it in 60mL of deionized water. Add 0.35g of calcium acetate monohydrate and stir to dissolve. Then dissolve 1.25g of 1,3,5-benzenetricarboxylic acid in 60mL of anhydrous ethanol. Mix the two solutions in a 1:1 volume ratio and sonicate for 30min and stir magnetically for 1h to prepare a homogeneous precursor mixture.

[0095] The precursor mixture was transferred to a lined reactor and reacted solvothermically at 120°C for 16 h, followed by natural cooling. The product was washed three times with an ethanol-water mixed solvent and dried under vacuum at 100°C for 24 h to obtain metal-organic framework CO2 adsorbent material D2, denoted as 14%Ca-Cu-BTC.

[0096] The CO2 adsorption capacity of D2 was measured to be 2.95 mmol / g. Lacking the buffer protection of the carbon nanotube framework, the pores are easily damaged during the recycling process, and the stability is significantly weaker than that of the metal-organic framework CO2 adsorbent material in Example 1.

[0097] Comparative Example 3

[0098] The preparation method of Example 1 was followed, except that the volume ratio of the precursor mixture to the mass ratio of the acidified multi-walled carbon nanotubes was 5500:1, and the highly acidified multi-walled carbon nanotube doped adsorbent D3 was prepared, denoted as Ca-Cu-BTC@1.5CNT, with a mass fraction of 1.64% for the acidified multi-walled carbon nanotubes.

[0099] Excessive carbon nanotubes agglomerate and block the micropores of the material, reducing the D3 specific surface area to 1245.6 m². 2 / g, CO2 saturated adsorption capacity decreased to 2.85 mmol / g.

[0100] Comparative Example 4

[0101] Following the preparation method of Example 1, except that 0.42 g of calcium acetate monohydrate was added to prepare the high-calcium-doped adsorbent D4. The Ca in D4... 2+ The mass fraction is 17%.

[0102] Excess Ca 2+ It will disrupt the original coordination crystal framework of Cu-BTC, and the specific surface area of ​​D4 is only 749.9 m². 2 / g, the carbon dioxide adsorption performance is greatly reduced.

[0103] Comparative Example 5

[0104] The preparation method of Example 1 was followed, except that the volume ratio of the precursor mixture to the mass ratio of the acidified multi-walled carbon nanotubes was 12500:1, and the low-acidified multi-walled carbon nanotube doped adsorbent D5, denoted as Ca-Cu-BTC@0.5CNT, was obtained, with the mass fraction of acidified multi-walled carbon nanotubes being 0.45%.

[0105] Insufficient carbon nanotube content weakened the synergistic effect, reducing the specific surface area of ​​D5 to 1238.2 m². 2 / g, CO2 saturated adsorption capacity decreased to 2.67 mmol / g.

[0106] A comparison of the embodiments and comparative examples shows that the present invention uses Ca 2+ The adsorbent material prepared by binary synergistic modification with acidified carbon nanotubes exhibits optimal carbon dioxide adsorption capacity and cycle stability under ambient temperature and pressure conditions.

[0107] The adsorbent material in Comparative Example 1 was not modified in any way, lacking bimetallic active sites and carbon nanotube mass transfer channels, resulting in the lowest adsorption capacity and severe cycle decay. The adsorbent material in Comparative Example 2 was modified only with calcium ions, without carbon nanotube support framework, and the pores were easily damaged after repeated use, resulting in limited performance improvement. The adsorbent material in Comparative Example 3 had an excessive amount of carbon nanotubes added, which agglomerated and blocked the micropores, reducing the number of effective adsorption sites. The adsorbent material in Comparative Example 4 had excessive calcium ion doping, which directly destroyed the MOF crystal framework structure, and the specific surface area and adsorption capacity decreased significantly simultaneously.

[0108] Figure 3 In the above, Cu-BTC is the adsorbent material prepared in Comparative Example 1, 14% Ca-Cu-BTC is the adsorbent material prepared in Comparative Example 2, Ca-Cu-BTC@1CNT is the adsorbent material prepared in Example 1, and Ca-Cu-BTC@1CNT Cycle is the adsorbent material prepared in Example 1 after 7 cycles.

[0109] Simultaneously, combined with the characterization results of XRD, SEM, XPS, and TGA, the adsorbent material in Example 1 completely retains the Cu-BTC crystal structure, Ca 2+ The carbon nanotubes were successfully embedded into the framework and uniformly attached to the crystal surface. The micropores of the material were concentrated in the range of 0.8~1.2nm, which is suitable for the diffusion of small CO2 molecules. After 7 cycles, the crystal did not collapse significantly, and the thermal decomposition temperature was significantly delayed compared with pure Cu-BTC, indicating stronger thermal stability.

[0110] Figure 4In the image, a and b are scanning electron microscope (SEM) images of the adsorbent material in Comparative Example 1. The images show a typical octahedral crystal structure with a smooth surface and sharp edges, indicating that the experiment successfully synthesized Cu-BTC material with high crystallinity and regular morphology. c and d are SEM images of the adsorbent material in Comparative Example 2. 2+ The ion-doped 14% Ca-Cu-BTC sample still maintained its octahedral main structure, but the crystal surface became rougher with attached microparticles and the edges became blunted. This is consistent with the decrease in crystallinity observed in XRD, indicating that Ca... 2+ The introduction of CNTs affected the crystal growth process to some extent; e and f are scanning electron microscope images of the adsorbent material in Example 1. After further composite CNTs, the octahedral structure of the Ca-Cu-BTC@1CNT sample remained intact, but the crystal surface was covered with a denser layer of flocculent material, indicating that CNTs were successfully loaded onto the MOF crystal surface to form a composite structure; g and h are scanning electron microscope images of the adsorbent material in Example 1 after the cycling experiment. In the sample after the cycling experiment (in which the crystal still maintains the octahedral framework structure, but the surface roughness is significantly reduced due to Ca 2+ The characteristics introduced by doping and CNT composite largely disappeared, indicating that significant desorption of dopant ions from the surface-loaded CNTs occurred during multiple adsorption-desorption processes. Although the surface modification traces disappeared, the main octahedral crystal structure of the material remained intact, without obvious structural collapse, indicating that the MOF framework itself possesses a certain degree of stability.

[0111] Figure 7 In the image, the blue cube represents a Ca-Cu-BTC crystal.

[0112] Figure 7 The diagram above illustrates the synthesis of Ca-Cu-BTC@CNT from Ca-Cu-BTC and carboxylated carbon nanotubes (CNTs): the left side shows the Ca-Cu-BTC crystal framework and its bimetallic coordination unit structure, while the right side shows acidified carbon nanotubes with numerous carboxyl groups (-COOH) modified on their walls. During the in-situ composite process, the carboxyl groups on the carbon nanotube surface act as heterogeneous nucleation sites to capture metal ions, inducing the growth of Ca-Cu-BTC crystals on the outer wall of the carbon nanotubes and in the gaps between the tube bundles. The carbon nanotube framework interpenetrates and encapsulates the MOF crystals, effectively alleviating crystal aggregation and ultimately yielding the Ca-Cu-BTC@CNT composite porous adsorbent material. Since multi-walled carbon nanotubes exhibit a multi-layered, interwoven structure, complete tube bundles can obscure internal active sites, hindering a clear visualization of gas adsorption behavior. Therefore, the diagram below uses a single-layer carbon nanotube as a simplified model to clearly illustrate the interaction process between oxygen-containing functional groups, bimetallic sites, and CO2 molecules.

[0113] like Figure 7The adsorption diagram below visually reveals the multiple synergistic mechanisms by which the Ca-Cu-BTC@CNT composite material adsorbs CO2: The carbon nanotube walls are grafted with a large number of carboxyl (-COOH) polar functional groups. The oxygen atoms in the carboxyl groups possess strong electronegativity and can affinityally adsorb CO2 molecules through intermolecular forces. The Ca-Cu-BTC bimetallic MOF supported on the tube walls, through Ca… 2+ Doping introduces a large number of unsaturated coordination metal sites, enhancing the Lewis acidity of the MOF framework. Additionally, Ca... 2+ By enhancing the acidic sites and regulating the pore structure of the material, the two work synergistically to strengthen CO2 adsorption performance. The blue arrows in the figure illustrate the entire process of CO2 molecules diffusing to the surface of the composite material and being fixed. The carbon nanotube framework not only disperses Ca-Cu-BTC grains and prevents crystal aggregation, but also constructs continuous mass transfer channels, shortening the CO2 diffusion path. Highly efficient CO2 adsorption is achieved through the synergistic effect of surface oxygen-containing functional groups and Ca-Cu-BTC bimetallic active sites.

[0114] In summary, this invention achieves synergistic modification of composite acidified carbon nanotubes through in-situ calcium ion doping, simultaneously optimizing the material's pore structure, increasing multiple CO2 adsorption active sites, and constructing continuous gas mass transfer channels. The preparation process is simple and mild, and the raw materials are readily available. The resulting adsorption material exhibits superior carbon dioxide capture capacity and cycle regeneration durability compared to single-modified or unmodified Cu-BTC, and can be widely applied to various industrial flue gas ambient temperature CO2 capture scenarios.

[0115] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A metal-organic framework CO2 adsorbent material, characterized in that, The material is a Cu-BTC modified material, with Ca doped within the Cu-BTC crystal. 2+ Based on the total mass of the material, Ca 2+ The mass fraction is 8-16%; The material surface is uniformly loaded with acidified multi-walled carbon nanotubes, and the mass fraction of acidified multi-walled carbon nanotubes is 0.5% to 1.5% based on the total mass of the material. The material has a hierarchical porous structure, with micropores of 0.8~1.2 nm accounting for 62~68% of the total porous structure.

2. The metal-organic framework CO2 adsorbent material according to claim 1, characterized in that, The BET specific surface area of ​​the material is 1200~1340 m². 2 / g, pore volume 0.5~0.6 cm³ 3 / g; At 25℃ and an inlet flow rate of 20 mL / min, the CO2 adsorption capacity is 2.96~3.17 mmol / g.

3. The metal-organic framework CO2 adsorbent material according to claim 1, characterized in that, After seven adsorption-desorption cycles, the material retains 70-75% of its initial CO2 adsorption capacity. The thermal decomposition temperature of the material is 300~370℃.

4. A method for preparing the metal-organic framework CO2 adsorbent material according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Immerse multi-walled carbon nanotubes in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid, stir for the first time, wash with deionized water, and dry for the first time to obtain acidified multi-walled carbon nanotubes. S2. Copper nitrate trihydrate, calcium acetate monohydrate and deionized water are mixed to obtain a metal ion solution. 1,3,5-benzenetricarboxylic acid and anhydrous ethanol are mixed to obtain an organic ligand solution. The metal ion solution and the organic ligand solution are mixed, sonicated and stirred for a second time to obtain a precursor mixture. S3. The acidified multi-walled carbon nanotubes obtained in step S1 are mixed with the precursor mixture obtained in step S2, and subjected to hydrothermal reaction, cooling, washing, and second drying to obtain the metal-organic framework CO2 adsorbent material.

5. The method for preparing the metal-organic framework CO2 adsorbent material according to claim 4, characterized in that, In step S1, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:2~4; The mass ratio of the multi-walled carbon nanotubes to the volume ratio of the mixed acid solution is 1:30~50; The conditions for the first stirring include: stirring at 40~60℃ for 20~24h; The deionized water is washed until neutral; The first drying conditions include: vacuum drying at 50~70℃ for 20~24h.

6. The method for preparing the metal-organic framework CO2 adsorbent material according to claim 4, characterized in that, In step S2, the mass ratio of copper nitrate trihydrate, calcium acetate monohydrate, and deionized water is 1:0.08~0.16:22~26; The mass ratio of 1,3,5-benzenetricarboxylic acid to the volume ratio of anhydrous ethanol is 1:46~50; The volume ratio of the metal ion solution to the organic ligand solution is 1:0.9~1.1; The conditions for the ultrasound include: ultrasound time of 25-35 minutes; The conditions for the second stirring include: stirring time of 0.8 to 1.2 hours.

7. The method for preparing the metal-organic framework CO2 adsorbent material according to claim 4, characterized in that, In step S3, the mass ratio of the acidified multi-walled carbon nanotubes to the volume ratio of the precursor mixture is 1:6000~12000.

8. The method for preparing the metal-organic framework CO2 adsorbent material according to claim 4, characterized in that, In step S3, the conditions for the hydrothermal reaction include: reacting at 110~130 ℃ for 14~18 h.

9. The method for preparing the metal-organic framework CO2 adsorbent material according to claim 4, characterized in that, In step S3, the cooling conditions include: natural cooling to 20~30℃; The second drying conditions include: vacuum drying at 90~110℃ for 22~26 hours.

10. The method for preparing the metal-organic framework CO2 adsorbent material according to claim 4, characterized in that, The material is activated before adsorbing CO2, and the activation conditions include: vacuum heating at 90~110℃ for 4~6 hours.

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