A method for preparing a clay nanotube@ZIF-8-based adsorbent by a microwave-assisted method, the clay nanotube@ZIF-8-based adsorbent and application thereof

Abstract

This invention discloses a microwave-assisted method for preparing clay nanotubes@ZIF-8 based adsorbents, the clay nanotubes@ZIF-8 based adsorbents, and their applications. First, clay nanotubes are activated with hydrochloric acid and modified with polydopamine (PDA) to enhance the active sites and interfacial binding force of the carrier. Then, ZIF-8 is synthesized in situ with microwave assistance, reducing the reaction cycle from over 24 hours to 20 minutes, increasing efficiency by 90%, significantly reducing energy consumption, and inhibiting particle agglomeration. Finally, ethylenediamine (EDA) amino modification optimizes the pore structure and adsorption sites, preventing pore blockage. The resulting material has a microporous-mesoporous hierarchical pore structure, high specific surface area, good mass transfer performance, and combines the physical sieving and amino chemical adsorption functions of ZIF-8, exhibiting excellent thermal stability and cycling performance. This method uses inexpensive raw materials, is simple in process, and has strong versatility, making it suitable for industrial production and meeting the CO2 capture requirements of flue gas from coal-fired power plants.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and relates to adsorbents for CO2 capture and their preparation methods. Specifically, it relates to a method for preparing clay nanotube@ZIF-8 based adsorbents by microwave-assisted method, the clay nanotube@ZIF-8 based adsorbents and their applications. Background Technology

[0002] Against the backdrop of my country's "dual carbon" (carbon and carbon emissions), controlling CO2 emissions from fossil fuel utilization has become a core task for the green and low-carbon transformation of the industrial sector. As one of the core sources of concentrated CO2 emissions in my country, flue gas from coal-fired power plants is a key technological support for achieving carbon reduction targets, as the development of efficient, low-cost, and easily scalable CO2 capture technologies is crucial. Among numerous CO2 capture technologies, Pressure Swing Adsorption (PSA) technology, with its advantages of simple operation, low energy consumption, no secondary pollution, and excellent cycle stability, has become one of the mainstream technologies in flue gas CO2 capture. The core of its application performance depends on the development and optimization of high-performance CO2 adsorbent materials.

[0003] Zeolite imidazole ester frameworks (ZIFs), as a typical class of metal-organic frameworks (MOFs), have attracted much attention in the field of gas adsorption and separation due to their combination of the high stability of inorganic molecular sieves and the structural designability of MOFs. Among them, ZIF-8, with its regular and tunable microporous structure, excellent hydrothermal stability, and chemical resistance, shows great application potential in the adsorption and separation of CO2 in flue gas. However, pure-phase ZIF-8 still faces inherent bottlenecks in industrial applications: on the one hand, ZIF-8 nanoparticles have high surface energy, making them prone to aggregation during preparation and application, resulting in the burial of a large number of adsorption active sites, a significant decrease in specific surface area and active site utilization, and a direct result in a significant decline in adsorption performance; on the other hand, the high cost of pure-phase ZIF-8 raw materials limits its large-scale industrial promotion.

[0004] To address these challenges, current research often employs natural clay nanotubes as a carrier to load ZIF-8 and prepare composite materials. Natural clay offers advantages such as wide availability, low cost, and good mechanical stability. Using it as a carrier for ZIF-8 can effectively inhibit the aggregation of ZIF-8 nanoparticles, improve the exposure and utilization efficiency of active sites, and significantly reduce the raw material cost of the adsorbent. Furthermore, the mesoporous structure of clay itself can form a hierarchical pore system with the microporous structure of ZIF-8, reducing gas mass transfer resistance. However, current preparations of clay@ZIF-8 composite materials largely rely on traditional hydrothermal / solvothermal methods. These methods have a synthesis cycle of 24–72 hours, resulting in extremely low production efficiency, high energy consumption, and poor batch stability, making it difficult to meet the demands of large-scale production. In addition, the insufficient number of chemisorption sites in clay@ZIF-8 composite materials means that the CO2 adsorption capacity and separation coefficient of the composite material still have significant room for improvement, making it difficult to meet the large-scale industrial application requirements for CO2 capture in flue gas from coal-fired power plants. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention aims to provide a microwave-assisted method for preparing clay nanotube@ZIF-8 based adsorbents, the clay nanotube@ZIF-8 based adsorbents, and their applications. Microwave-assisted synthesis significantly shortens the ZIF-8 preparation cycle. Combined with polydopamine (PDA) pretreatment, the dispersibility and interfacial bonding of ZIF-8 on the support surface are improved. Simultaneously, EDA modification is used to construct amino sites, resulting in a composite material with a well-developed microporous-mesoporous hierarchical pore structure, high CO2 adsorption capacity, excellent CO2 / N2 selectivity, and good cycling stability. This method is universally applicable to various clay nanotube supports, uses inexpensive and readily available raw materials, and offers strong process controllability, making it suitable for industrial production.

[0006] This invention is achieved through the following technical solution: A method for preparing clay nanotube@ZIF-8 based adsorbents using a microwave-assisted method includes the following steps: Step 1: After pretreating the clay nanotube carrier, disperse it in deionized water to obtain a clay nanotube suspension. Add 15-25% of dopamine hydrochloride by mass of clay nanotubes to the suspension, stir evenly, adjust the pH of the system to 8.0-9.0, and continue stirring for 20-40 min to complete the in-situ polymerization reaction of dopamine. After centrifugation, washing and drying, the product is obtained as a PDA-modified clay nanotube carrier. Step 2: Disperse the PDA-modified clay nanotube carrier obtained in Step 1 in methanol at a material-to-liquid ratio of 1 g:(80~120) mL. After ultrasonic treatment, add zinc source solution and imidazole ligand solution sequentially according to the mass ratio of PDA-modified clay nanotube carrier, zinc nitrate hexahydrate, and 2-methylimidazole of 1:(0.1~0.15):(0.3~0.35). After mixing evenly, transfer to a microwave reactor for microwave-assisted in-situ synthesis reaction. The microwave power is 200~600 W, the reaction temperature is 40~80 ℃, and the reaction time is 15~25 min. After the reaction is completed, the product is washed and dried to obtain clay nanotube@ZIF-8 composite material. Step 3: The clay nanotubes@ZIF-8 composite material obtained in Step 2 is added to an ethylenediamine methanol solution with a concentration of 30-40 wt.% at a material-to-liquid ratio of 0.25 g:(40-60) mL. The mixture is stirred at 70-90 °C for 1-2 h to carry out amino functionalization modification. After the modification is completed, the mixture is centrifuged, washed, and dried to obtain the amino-modified clay nanotubes@ZIF-8 based adsorbent.

[0007] The present invention also has the following technical features: Preferably, the clay nanotube carrier mentioned in step one includes any one of halloysite, attapulgite, and sepiolite.

[0008] Preferably, the pretreatment method for the clay nanotube carrier in step one includes mixing clay nanotubes and deionized water at a material-to-liquid ratio of 1 g:(80~120) mL, ultrasonically treating for 0.5~1.5 h, centrifuging to separate the precipitate, adding hydrochloric acid with a concentration of 0.5~1.5 mol / L at a material-to-liquid ratio of 1 g:(40~60) mL for activation at a temperature of 50~70 ℃ for 1.5~2.5 h, and washing with deionized water until neutral after activation.

[0009] Preferably, the ultrasonic treatment time in step two is 5 to 15 minutes.

[0010] Preferably, the centrifugation separation in steps one, two and three is centrifugation at a speed of 4000~6000 r / min for 3~8 min.

[0011] The washing described in steps one, two and three involves washing twice with methanol.

[0012] The washing and drying process described in steps one, two, and three involves placing the item in a drying oven at 50-60°C for 10-14 hours.

[0013] Preferably, the heating time in the microwave-assisted in-situ synthesis reaction in step two is 3-8 min, and the isothermal reaction time is 10-20 min.

[0014] This invention also protects a clay nanotube@ZIF-8 based adsorbent prepared according to the above method and its application in the selective adsorption and separation of CO2 in flue gas from coal-fired power plants.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention uses microwave-assisted synthesis technology to replace the traditional solvothermal method, which significantly shortens the synthesis cycle of ZIF-8 from more than 24 hours to less than 20 minutes, improves the synthesis efficiency by more than 90%, and significantly reduces production energy consumption and time costs. At the same time, the uniform heating characteristic of microwaves can promote the uniform nucleation and directional growth of ZIF-8 crystals on the carrier surface, effectively inhibit particle agglomeration, and greatly improve the utilization rate of active sites. This invention first pre-treats the clay nanotube carrier with hydrochloric acid activation and PDA functionalization. Hydrochloric acid activation can remove impurities from the carrier, expand the porosity, and increase the surface hydroxyl density, providing sufficient active sites for ZIF-8 nucleation. PDA modification can introduce abundant active groups on the carrier surface, significantly enhance the interfacial bonding force between the carrier and ZIF-8 crystals, further improve the dispersibility of ZIF-8, and provide anchoring sites for subsequent amino grafting. This invention utilizes the EDA amino modification process and, by adjusting the loading concentration, avoids the problems of pore blockage and increased mass transfer resistance caused by single high-concentration modification, while realizing the utilization of CO2 chemisorption sites, significantly improving the CO2 adsorption capacity and CO2 / N2 separation selectivity of the composite material. The preparation method of this invention has excellent universality for various clay nanotube carriers such as halloysite, attapulgite, and sepiolite. The raw materials are all inexpensive and readily available natural minerals, resulting in low production costs, simple and controllable processes, no need for complex equipment, and suitability for large-scale industrial production. The composite material prepared by this invention has a microporous-mesoporous hierarchical pore structure, high specific surface area and well-developed pore volume. It also has the physical sieving effect of ZIF-8 and the chemical adsorption effect of amino groups. The CO2 adsorption capacity can reach up to 2.60 mmol / g (25℃, 10 bar), the CO2 / N2 separation coefficient can reach up to 71.6, and the adsorption capacity retention rate is more than 90% after 8 adsorption-desorption cycles. It has excellent thermal stability, cycle stability and adsorption separation performance, which fully meets the practical application requirements of CO2 capture in flue gas of coal-fired power plants. Attached Figure Description

[0016] Figure 1Comparison of CO2 adsorption capacity of amino-modified clay nanotube@ZIF-8 composite materials prepared in Examples 1-3 (25 °C, 10 bar). Figure 2 Comparison of CO2 / N2 separation coefficients for the amino-modified clay nanotube@ZIF-8 composite materials prepared in Examples 1-3; Figure 3 The CO2 adsorption cycle performance of WPHNT@ZIF-8-NH2 prepared in Example 1 is shown in the figure (25 °C, 10 bar, 8 cycles). Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0018] Example 1 This embodiment provides an amino-modified halloysite@ZIF-8 composite material, and its preparation method includes the following steps: Step 1: Pretreatment of Halloysite Support: Weigh 1.0 g of halloysite (HNTs) and mix with 100 mL of deionized water. Soak the mixture using an ultrasonic device at 40 kHz for 1 h. Then, centrifuge the suspension at 5000 r / min for 5 min and discard the supernatant containing impurities. Immerse the moistened precipitate in 50 mL of 1 mol / L HCl solution and stir at 60 ℃ for 2 h to activate it. After the reaction, wash with deionized water until neutral, and uniformly disperse in 100 mL of deionized water. Sonicate for 5 min to obtain a stable suspension. Add 0.2 g of dopamine hydrochloride to the suspension and magnetically stir for 30 min to ensure full adsorption onto the halloysite surface. Then, inject 1 mol / L potassium hydroxide solution to adjust the pH to 8.5 and continue stirring for 30 min to complete the in-situ polymerization of dopamine. After the reaction, wash the product twice with methanol at 5000 r / min for 5 min to remove unreacted monomers and byproducts. Dry in a drying oven at 55 ℃ for 12 hours. After h, polydopamine-modified halloysite carrier PHNT was obtained; Step 2: Microwave-assisted preparation of halloysite@ZIF-8 composite material: 1.0 g of PHNT obtained in Step 1 was dispersed in 100 mL of methanol and sonicated for 10 min. A zinc source solution containing 0.139 g of zinc nitrate hexahydrate and a ligand solution containing 0.318 g of 2-methylimidazole were added sequentially. After thorough mixing, the mixture was transferred to a microwave reactor. The microwave power was set to 400 W, the reaction temperature to 80 ℃, and the total reaction time to 20 min, including 5 min of heating and 15 min of isothermal hold. After the reaction, the product was washed twice by centrifugation at 5000 r / min for 5 min with methanol, and dried at 55 ℃ for 12 h to obtain the halloysite@ZIF-8 composite material WPHNT@ZIF-8. Step 3, Amine Modification: 0.25 g of WPHNT@ZIF-8 obtained in Step 2 was added to 50 mL of 40 wt.% EDA methanol solution and stirred at 80 °C for 2 h. The product was washed twice by centrifugation at 5000 r / min for 5 min with methanol. The final product was vacuum dried at 55 °C for 12 h to obtain the amino-modified halloysite@ZIF-8 composite material WPHNT@ZIF-8-NH2.

[0019] Figure 1 Comparison of CO2 adsorption capacity of amino-modified clay nanotube@ZIF-8 composite materials prepared in Examples 1-3 (25 °C, 10 bar). Figure 2 Comparison of CO2 / N2 separation coefficients for the amino-modified clay nanotube@ZIF-8 composite materials prepared in Examples 1-3; The specific surface area of ​​WPHNT@ZIF-8-NH2 prepared in this embodiment was measured to be 304.12 m². 2 / g, pore volume is 0.13cm 3 / g, with a micropore size of 0.74 nm; under simulated flue gas conditions of 25 ℃ and 10 bar, the CO2 adsorption capacity is 2.28 mmol / g (e.g., Figure 1 As shown), the CO2 / N2 separation coefficient is 69.6 (as shown). Figure 2 (as shown) Figure 3 The image shows the CO2 adsorption cycle performance of WPHNT@ZIF-8-NH2 prepared in Example 1. Figure 3 As shown, after eight CO2 adsorption-desorption cycles, the adsorption capacity of WPHNT@ZIF-8-NH2 material remained stable at 2.06 mmol / g, which is equivalent to 90.3% of the initial capacity, demonstrating good cycling stability.

[0020] Example 2 This embodiment provides an amino-modified halloysite@ZIF-8 composite material, and its preparation method includes the following steps: Step 1: Pretreatment of the attapulgite carrier: Weigh 1.0 g of attapulgite (ATP) and mix with 100 mL of deionized water. Soak the mixture using an ultrasonic device at 40 kHz for 1 h. Then, centrifuge the suspension at 5000 r / min for 5 min and discard the supernatant containing impurities. Immerse the moistened precipitate in 50 mL of 1 mol / L HCl solution and stir at 60 ℃ for 2 h to activate it. After the reaction, wash with deionized water until neutral, and uniformly disperse in 100 mL of deionized water. Sonicate for 5 min to obtain a stable suspension. Add 0.2 g of dopamine hydrochloride to the suspension and magnetically stir for 30 min to ensure full adsorption onto the attapulgite surface. Then, inject 1 mol / L potassium hydroxide solution to adjust the pH to 8.5 and continue stirring for 30 min to complete the in-situ polymerization of dopamine. After the reaction, wash the product twice with methanol at 5000 r / min for 5 min to remove unreacted monomers and byproducts. Dry in a drying oven at 55 ℃ for 12 hours. After h, polydopamine-modified attapulgite carrier PATP was obtained. Step 2: Microwave-assisted preparation of attapulgite@ZIF-8 composite material: 1.0 g of PATP obtained in Step 1 was dispersed in 100 mL of methanol and sonicated for 10 min. A zinc source solution containing 0.139 g of zinc nitrate hexahydrate and a ligand solution containing 0.318 g of 2-methylimidazole were added sequentially. After thorough mixing, the mixture was transferred to a microwave reactor. The microwave power was set to 400 W, the reaction temperature to 80 ℃, and the total reaction time to 20 min, including 5 min of heating and 15 min of isothermal treatment. After the reaction, the product was washed twice by centrifugation at 5000 r / min for 5 min with methanol, and dried at 55 ℃ for 12 h to obtain the attapulgite@ZIF-8 composite material WPATP@ZIF-8. Step 3, Amine Modification: 0.25 g of WPATP@ZIF-8 obtained in Step 2 was added to 50 mL of 40 wt.% EDA methanol solution and stirred at 80 °C for 2 h. The product was washed twice by centrifugation at 5000 r / min for 5 min with methanol. The final product was vacuum dried at 55 °C for 12 h to obtain the amino-modified attapulgite@ZIF-8 composite material WPATP@ZIF-8-NH2.

[0021] The specific surface area of ​​WPATP@ZIF-8-NH2 prepared in this embodiment was measured to be 255.31 m². 2 / g, pore volume is 0.11cm 3 / g, with a micropore size of 0.74 nm; under simulated flue gas conditions of 25 ℃ and 10 bar, the CO2 adsorption capacity is 2.60 mmol / g (e.g. Figure 1 As shown), the CO2 / N2 separation coefficient is 71.6 (as shown). Figure 2 As shown in the figure, it has excellent adsorption and separation performance.

[0022] Example 3 This embodiment provides an amino-modified halloysite@ZIF-8 composite material, and its preparation method includes the following steps: Step 1: Pretreatment of sepiolite carrier: Weigh 1.0 g of sepiolite (SP) and mix with 100 mL of deionized water. Soak the mixture using an ultrasonic device at 40 kHz for 1 h. Then, centrifuge the suspension at 5000 r / min for 5 min and discard the supernatant containing impurities. Immerse the moistened precipitate in 50 mL of 1 mol / L HCl solution and stir at 60 ℃ for 2 h to activate it. After the reaction, wash with deionized water until neutral, and uniformly disperse in 100 mL of deionized water. Sonicate for 5 min to obtain a stable suspension. Add 0.2 g of dopamine hydrochloride to the suspension and stir magnetically for 30 min to ensure full adsorption onto the sepiolite surface. Then, inject 1 mol / L potassium hydroxide solution to adjust the pH to 8.5 and continue stirring for 30 min to complete the in-situ polymerization of dopamine. After the reaction, wash the product twice with methanol by centrifugation at 5000 r / min for 5 min, and dry at 55 ℃ for 12 h to obtain polydopamine-modified sepiolite carrier PSP. Step 2: Microwave-assisted preparation of sepiolite@ZIF-8 composite material: 1.0 g of PSP obtained in Step 1 was dispersed in 100 mL of methanol and sonicated for 10 min. A zinc source solution containing 0.139 g of zinc nitrate hexahydrate and a ligand solution containing 0.318 g of 2-methylimidazole were added sequentially. After thorough mixing, the mixture was transferred to a microwave reactor. The microwave power was set to 400 W, the reaction temperature to 80 ℃, and the total reaction time to 20 min, including 5 min of heating and 15 min of isothermal control. After the reaction, the product was washed twice by centrifugation at 5000 r / min for 5 min and dried at 55 ℃ for 12 h to obtain the sepiolite@ZIF-8 composite material WPSP@ZIF-8. Step 3, Amine Modification: 0.25 g of WPSP@ZIF-8 obtained in Step 2 was added to 50 mL of 40 wt.% EDA methanol solution, stirred at 80 ℃ for 2 h, and centrifuged and washed twice with methanol; in the third step, 50 mL of 55 wt.% EDA methanol solution was added, stirred at 85 ℃ for 1 h, and the product was washed twice with methanol at 5000 r / min for 5 min to remove free amino groups; the final product was vacuum dried at 55 ℃ for 12 h to obtain the amino-modified sepiolite@ZIF-8 composite material WPSP@ZIF-8-NH2.

[0023] The specific surface area of ​​the WPSP@ZIF-8-NH2 prepared in this embodiment was measured to be 174.52 m². 2 / g, pore volume is 0.068cm³ 3 / g, with a micropore size of 0.72 nm; under simulated flue gas conditions of 25 ℃ and 10 bar, the CO2 adsorption capacity is 1.90 mmol / g (e.g., Figure 1 As shown), the CO2 / N2 separation coefficient is 49.0 (as shown). Figure 2 (As shown).

[0024] Example 4 This embodiment provides an amino-modified halloysite@ZIF-8 composite material, and its preparation method includes the following steps: Step 1: Pretreatment of Halloysite Support: Weigh 1.0 g of halloysite (HNTs) and mix with 80 mL of deionized water. Soak the mixture using an ultrasonic device at 40 kHz for 0.5 h. Then, centrifuge the suspension at 4000 r / min for 8 min and discard the supernatant containing impurities. Immerse the moistened precipitate in 40 mL of 0.5 mol / L HCl solution and stir at 50 ℃ for 2.5 h to activate it. After the reaction, wash with deionized water until neutral, and uniformly disperse in 100 mL of deionized water. Sonicate for 5 min to obtain a stable suspension. Add 0.15 g of dopamine hydrochloride to the suspension and magnetically stir for 30 min to ensure full adsorption onto the halloysite surface. Then, inject 1 mol / L potassium hydroxide solution to adjust the pH to 8 and continue stirring for 20 min to complete the in-situ polymerization of dopamine. After the reaction, wash the product twice with methanol at 4000 r / min for 8 min to remove unreacted monomers and byproducts. Dry in a drying oven at 50 ℃ for 14 hours. After h, polydopamine-modified halloysite carrier PHNT was obtained; Step 2: Microwave-assisted preparation of halloysite@ZIF-8 composite material: 1.0 g of PHNT obtained in Step 1 was dispersed in 80 mL of methanol and sonicated for 10 min. A zinc source solution containing 0.1 g of zinc nitrate hexahydrate and a ligand solution containing 0.3 g of 2-methylimidazole were added sequentially. After thorough mixing, the mixture was transferred to a microwave reactor. The microwave power was set to 200 W, the reaction temperature to 40 ℃, and the total reaction time to 25 min, including 8 min of heating and 17 min of isothermal control. After the reaction, the product was washed twice by centrifugation at 4000 r / min for 8 min with methanol and dried at 50 ℃ for 14 h to obtain the halloysite@ZIF-8 composite material WPHNT@ZIF-8. Step 3, Amine Modification: 0.25 g of WPHNT@ZIF-8 obtained in Step 2 was added to 40 mL of 30 wt.% EDA methanol solution and stirred at 70 ℃ for 1.5 h. The product was washed twice by centrifugation at 4000 r / min for 8 min with methanol. The final product was vacuum dried at 50 ℃ for 14 h to obtain the amino-modified halloysite@ZIF-8 composite material WPHNT@ZIF-8-NH2.

[0025] Example 5 This embodiment provides an amino-modified halloysite@ZIF-8 composite material, and its preparation method includes the following steps: Step 1: Pretreatment of Halloysite Support: Weigh 1.0 g of halloysite (HNTs) and mix with 120 mL of deionized water. Soak the mixture using an ultrasonic device at 40 kHz for 1.5 h. Then, centrifuge the suspension at 6000 r / min for 3 min and discard the supernatant containing impurities. Immerse the moistened precipitate in 60 mL of 1.5 mol / L HCl solution and stir at 70 ℃ for 1.5 h to activate it. After the reaction, wash with deionized water until neutral, and uniformly disperse in 100 mL of deionized water. Sonicate for 15 min to obtain a stable suspension. Add 0.25 g of dopamine hydrochloride to the suspension and magnetically stir for 30 min to ensure full adsorption onto the halloysite surface. Then, inject 1 mol / L potassium hydroxide solution to adjust the pH to 9 and continue stirring for 40 min to complete the in-situ polymerization of dopamine. After the reaction, wash the product twice with methanol at 6000 r / min for 3 min to remove unreacted monomers and byproducts. Dry in a drying oven at 60 ℃ for 10 minutes. After h, polydopamine-modified halloysite carrier PHNT was obtained; Step 2: Microwave-assisted preparation of halloysite@ZIF-8 composite material: 1.0 g of PHNT obtained in Step 1 was dispersed in 120 mL of methanol and sonicated for 15 min. A zinc source solution containing 0.15 g of zinc nitrate hexahydrate and a ligand solution containing 0.35 g of 2-methylimidazole were added sequentially. After thorough mixing, the mixture was transferred to a microwave reactor. The microwave power was set to 600 W, the reaction temperature to 60 ℃, and the total reaction time to 15 min, including 3 min of heating and 12 min of isothermal hold. After the reaction, the product was washed twice by centrifugation at 6000 r / min for 3 min with methanol, and dried at 60 ℃ for 10 h to obtain the halloysite@ZIF-8 composite material WPHNT@ZIF-8. Step 3, Amine Modification: 0.25 g of WPHNT@ZIF-8 obtained in Step 2 was added to 60 mL of 35 wt.% EDA methanol solution and stirred at 90 °C for 1 h. The product was washed twice by centrifugation at 6000 r / min for 3 min with methanol. The final product was vacuum dried at 60 °C for 10 h to obtain the amino-modified halloysite@ZIF-8 composite material WPHNT@ZIF-8-NH2.

[0026] This invention innovatively employs microwave-assisted synthesis technology to replace the traditional solvothermal method, significantly shortening the in-situ growth cycle of ZIF-8 from the existing 24-72 hours to less than 20 minutes, and improving the synthesis efficiency by more than 90%. This not only significantly reduces energy consumption and time costs in the production process, but also promotes the uniform nucleation and directional growth of ZIF-8 crystals on the surface of clay nanotube carriers by leveraging the uniform heating characteristics of microwaves. This effectively inhibits the aggregation of ZIF-8 nanoparticles, greatly improves the exposure and utilization efficiency of adsorption active sites, and overcomes the industry pain points of low efficiency, high energy consumption, and poor batch stability of traditional synthesis methods, laying the foundation for the large-scale mass production of adsorbents.

[0027] This invention employs a two-step pretreatment process of "hydrochloric acid activation + PDA functionalization". Compared with existing single activation or no pretreatment schemes, hydrochloric acid activation can effectively remove impurities on the surface of clay nanotube carriers, expand the carrier's pore structure, and increase the surface hydroxyl density, providing sufficient active sites for ZIF-8 crystal nucleation. PDA modification can introduce abundant amino and hydroxyl groups on the carrier surface, which significantly enhances the interfacial bonding force between the clay nanotube carrier and ZIF-8 crystals, avoiding the problem of ZIF-8 detachment during the use of the composite material. On the other hand, it further improves the dispersibility of ZIF-8 on the carrier surface and provides stable anchoring points for subsequent amino functionalization modification, thereby maximizing the synergistic effect between the carrier and ZIF-8.

[0028] This invention utilizes the uniform loading and efficient utilization of amino groups on the adsorbent surface to construct sufficient CO2 chemisorption sites. Combining the physical adsorption sites formed by the mesoporous structure of clay nanotubes and the microporous structure of ZIF-8 with the amino-modified chemisorption sites, the CO2 adsorption capacity, CO2 / N2 selectivity, and cycling stability of the amino-modified clay nanotube@ZIF-8 composite material are synergistically improved.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing clay nanotube@ZIF-8 based adsorbents using a microwave-assisted method, characterized in that, Includes the following steps: Step 1: After pretreating the clay nanotube carrier, disperse it in deionized water to obtain a clay nanotube suspension. Add 15-25% of dopamine hydrochloride by mass of clay nanotubes to the suspension, stir evenly, adjust the pH of the system to 8.0-9.0, and continue stirring for 20-40 min to complete the in-situ polymerization reaction of dopamine. After centrifugation, washing and drying, the product is obtained as a polydopamine-modified clay nanotube carrier. Step 2: Disperse the polydopamine-modified clay nanotube carrier obtained in Step 1 in methanol at a material-to-liquid ratio of 1 g:(80~120) mL. After ultrasonic treatment, add zinc source solution and imidazole ligand solution sequentially according to the mass ratio of PDA-modified clay nanotube carrier, zinc nitrate hexahydrate, and 2-methylimidazole of 1:(0.1~0.15):(0.3~0.35). After mixing evenly, transfer to a microwave reactor for microwave-assisted in-situ synthesis reaction. The microwave power is 200~600 W, the reaction temperature is 40~80℃, and the reaction time is 15~25 min. After the reaction is completed, the product is washed and dried to obtain clay nanotube@ZIF-8 composite material. Step 3: The clay nanotubes@ZIF-8 composite material obtained in Step 2 is added to an ethylenediamine methanol solution with a concentration of 30-40 wt.% at a material-to-liquid ratio of 0.25 g:(40-60) mL. The mixture is stirred at 70-90 °C for 1-2 h to carry out amino functionalization modification. After the modification is completed, the mixture is centrifuged, washed, and dried to obtain the amino-modified clay nanotubes@ZIF-8 based adsorbent.

2. The method for preparing clay nanotube@ZIF-8 based adsorbents using microwave-assisted methods according to claim 1, characterized in that, The clay nanotube carrier mentioned in step one includes any one of halloysite, attapulgite, and sepiolite.

3. The method for preparing clay nanotube@ZIF-8 based adsorbents using microwave-assisted methods according to claim 1, characterized in that, The pretreatment method for the clay nanotube carrier described in step one includes mixing clay nanotubes and deionized water at a material-to-liquid ratio of 1 g:(80~120) mL, ultrasonically treating for 0.5~1.5 h, centrifuging to separate the precipitate, adding hydrochloric acid with a concentration of 0.5~1.5 mol / L at a material-to-liquid ratio of 1 g:(40~60) mL for activation at a temperature of 50~70 ℃ for 1.5~2.5 h, and washing with deionized water until neutral after activation.

4. The method for preparing clay nanotube@ZIF-8 based adsorbents using microwave-assisted methods according to claim 1, characterized in that, The ultrasonic treatment time in step two is 5 to 15 minutes.

5. The method for preparing clay nanotube@ZIF-8 based adsorbents using microwave-assisted method according to claim 1 or 3, characterized in that, The centrifugation separation described in steps one, two and three is centrifugation at a speed of 4000~6000 r / min for 3~8 min.

6. The method for preparing clay nanotube@ZIF-8 based adsorbents by microwave-assisted method according to claim 1, characterized in that, The washing described in steps one, two and three involves washing twice with methanol.

7. The method for preparing clay nanotube@ZIF-8 based adsorbents by microwave-assisted method according to claim 1, characterized in that, The washing and drying process described in steps one, two, and three involves placing the item in a drying oven at 50-70°C for 10-14 hours.

8. The method for preparing clay nanotube@ZIF-8 based adsorbents by microwave-assisted method according to claim 1, characterized in that, In step two, the heating time during the microwave-assisted in-situ synthesis reaction is 3-8 min, and the isothermal reaction time is 10-20 min.

9. A clay nanotube@ZIF-8 based adsorbent prepared by the method according to any one of claims 1 to 8.

10. The application of the clay nanotube@ZIF-8 based adsorbent according to claim 9 in the selective adsorption and separation of CO2 in flue gas from coal-fired power plants.

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